77/57
HANDBOOK ON ENGINEERING
PUBLISHERS OF BOOKS F O R^
Coal Age v Electric Railway Journal Electrical World v Engineering News -Record American Machinist v Ingenierfa Internacional Engineering § Mining Journal <*• Po we r Chemical 6 Metallurgical Engineering Electrical Merchandising
HANDBOOK ON
ENGINEERING
THE PRACTICAL CARE AND MANAGEMENT
OF
DYNAMOS, MOTORS, BOILERS, ENGINES, PUMPS, INSPIRATORS AND INJECTORS, REFRIGERATING MACHINERY, HYDRAULIC ELEVATORS, ELEC- TRIC ELEVATORS, AIR COMPRESSORS, ROPE TRANSMISSION AND ALL BRANCHES1 OF STEAM ENGINEERING.
BY
HENRY C. TULLEY, Engineer and Member Board of Engineers, St. Louis.
SIXTH EDITION— SIXTH IMPRESSION Revised and Enlarged
McGRAW-HILL BOOK COMPANY, INC;. 239 WEST 39TH STREET. NEW YORK
LONDON: HILL PUBLISHING CO., LTD. 6 & 8 BOUVERIE ST., B. C.
Entered according to Act of Congress, in the year 1900, by
HENEY C. TULLEY, In the Office of the Librarian of Congress, at Washington.
Copyrighted, 1907.
INTRODUCTION.
The object of the Author in preparing this work has been to present to the practical engineer a book to which he can, with confidence, refer to for information regarding every branch of his profession.
Up to the date of the publication of this book, it was impossi- ble to find a plain and practical treatise on the steam boiler, steam pump, steam engine, and dynamo, and how to care for them; electric and hydraulic elevators, and how to care for them ; and all other work that an engineer is apt to come in contact with in his profession.
An experience of over twenty-five years with all kinds of en- gines and uoilers, pumps, and all other kinds of machinery, ena- bles the Author to fully understand the kind of information most needed by men having charge of steam engines of every descrip- tion, and what they should comprehend and employ.
With this object in view, the Author has carefully made note of his past experience, and has also made note of things that came to his notice while visiting different engine rooms, and accord- ingly, has taken up each subject singly, excluding therefrom, everything not strictly connected with steam engineering.
Particular attention has been given to the latest improvements in all classes of steam engines, with rules and formulas ac- cording to the best modern practice, which, it is hoped, will be of great value to engineers, as nothing of the kind has heretofore been published.
This book also contains ample instructions for setting up, lining, reversing and setting the valves of all classes of engines.
THE AUTHOR.
IV?
on)
CONTENTS.
For Alphabetical Index to Subjects, see page 963.
CHAPTER I.
PAGE
THE ELEMENTARY PRINCIPLES OF ELECTRICAL MA-
CHINERY j
A permanent magnet 1 to 2
Two-bar magnet 3 to 6
A magnet needle 3
Magnetic lines of force 6
Lines of force 6 to 14
Magnetic force 13
To find the lifting capacity of a magnet 13
CHAPTER II.
THE PRINCIPLES OF ELECTROMAGNETIC INDUCTION 14 to 22 The armature cores 23 to 27
CHAPTER III.
TWO-POLE GENERATORS AND MOTORS ........ 27
The simplest type of armature winding 27 to 29
Two-pole generators and motors 27 to 30
The general arrangement of the field and armature in a two-pole
machine 33 to 36
The reason why brushes are set differently on motors than on
dynamos 36 to 37
v
VI CONTENTS.
CHAPTER IV.
PAGE,
MULTIPOLAR MACHINES 38
Multipolar machines 38 to 39
Setting the brushes on a four-pole machine 40
Setting the brushes on an eight-pole machine 41
The lap and wave winding for four-pole machine* . . . . . 42 to 46
CHAPTER V.
SWITCH BOARD, DISTRIBUTING CIRCUITS, AND SWITCH
BOARD INSTRUMENTS 47
Generators of the constant potential type 47 to 48
The switch-board arranged for two generators of the shunt
type 49 to 54
Switch-board for three-wire system 56 to 57
To wire a large building with a lighting and power system . 58 to 60
The ammeter 60
Circuit breakers 62 to 63
The electromotive force in volts, etc 63
CHAPTER VI.
ELECTRIC MOTORS 64
Motors and their connections 64 to 73
The strength of an electric current, etc 73
The watt 73
The ampere 73
Candle power 73
CHAPTER VII.
INSTRUCTIONS FOR INSTALLING AND OPERATING SLOW
AND MODERATE SPEED GENERATORS AND MOTORS . . 74
To remove the armature 74
Assembling the parts 74
Filling the bearings 74
To complete the assembly 74
Starting 74
Care of commutator 75
CONTENTS. yj|
If commutator gives trouble *
General directions for starting dynamos . 7fi
Bringing dynamos to full speed . . . ' 77
Connecting one dynamo with another 78
Switching dynamos into circuit 7g
How dynamos may be connected together
Dynamos in parallel 7g
Directions for running dynamos and motors 80
Precautions in running dynamos . . - 81
Personal safety '. . . , ,81
CHAPTER VIII.
WHY COMMUTATOR BRUSHES SPARK AND WHY THEY DO
NOT SPARK 82 to 84
The way in which the current is shifted, etc 84, 85
Diagram illustrating the same 85
If the commutated coil, etc 86
Even when the machine is properly proportioned, etc 87
Sparking 87 to 91
Noise - 91 to 92
Heating in dynamo or motor 93 to 94
The effect of the displacement of the armature 94 to 98
Table of carrying capacity of wires 99, 101
Insulation resistance 100
Soldering fluid 101
Table showing the size of wire of different metals that will be melted by currents of various strengths . 102
CHAPTER IX.
INSTRUCTIONS FOR INSTALLING AND OPERATING APPA- RATUS FOR ARC LIGHTING.
Brush arc light generator . . . . . 0 . . 10*
Multiple circuit Brush arc generator . . . 0 105
Armature circuits of Brush machine .., 0 .... o ... 106
Diagram of multiple circuits . «. .... 107
Current regulator for Brush arc generator . , . . . . . » . Position of brushes on arc lighting generator ,109
Vlll CONTENTS.
PAGE.
Setting brushes of arc light generator 110
Care of the commutator and brushes Ill
Series system of arc lighting 112
Transformers for series system , 113
General Electric Co.'s transformer 114
Operation of transformer, series system 115
Sizes of General Electric transformers 116
Switchboards for arc lighting apparatus 117
General Electric Co.'s switchboards , ... 118
Switchboard for Westinghouse system 119
Westinghouse transformers, series system 120
Western Electric Co.'s regulator 121
Regulator for constant current series system . . * 122
Adams-Bagnall regulator 123
Fort Wayne Electric Co.'s regulator 124
General arrangement of Fort Wayne circuits 125
Fort Wayne system of arc lighting , 126
Alternating current, constant current circuits 127
General Electric Co.'s enclosed arc lamp 128
Westinghouse lamp 129
Lamp for series alternating current circuits 130
Fort Wayne lamp 131
CHAPTER X.
Western Electric Co.'s lamp 132
Actuating clutches for enclosed lamps 133
Westinghouse, Western Electric and Fort Wayne clutches . . . 134
Carbon holders . 1 35
Enclosed direct current lamps 136
General Electric Go's, lamp 137
Voltage of General Electric Co.'s lamp 138
Westinghouse and Fort Wayne enclosed lamps 139
Fort Wayne lamp for direct current circuits 140
Enclosed lamps for power circuits 141
Construction and operation of enclosed lamps 142
Series arc lamps for power circuits 143
CONTENTS.
Westinghouse direct current enclosed lamp
Cut-out for General Electric lamp ,
Constant potential enclosed lamps
Fort Wayne constant potential lamp ...'.'.'
Westinghouse lamp . . .....
General Electric Co.'s lamp . .
Fort Wayne street lighting system ......
Lamp used with Fort Wayne system , 151
Luminous or flaming arc lamp , . . ..... 152
The Excello lamp • '••...,.,..'."-
Excello lamp for direct current . . . . 154
Life of carbons in the Excello lamp .......
Directions for care of lamps ........... 156
How to trim lamps . ..... ....... 157
Care of dashpot and globes „ ...... . 153
How to install arc lamps , ....... . e 150
CHAPTER Xa.
INCANDESCENT WIRING TABLES ....... 161 to 162
Amperes per motor, table .............. 169,170
Volts lost at different per cent drop .......... 171, 172
Amperes per lamp,table ................ 173
Approximate weight of " O. K." triple braided weatherproof copper
wire ...................... 174
Table showing difference between wire gauges in decimal parts of an
inch ...................... 175
Electric light conductors, table ...... ...... . . 176
CHAPTER XI.
THE STEAM ENGINE ............ .... 177
The selection of an engine ............... 177
The gaia by expansion ......... •• ...... 183
Table of cut-off in parts of the stroke . . ......... 183
The steam engine governor ............ 183 a»d 1J
The fly-wheel .................... 184
Horse power .................... *'
Care and management of a steam engine . „ ........ 185
X CONTENTS.
PAGE.
Lubrication of an engine 186
Selecting an oil for an engine 187
The piston packing 187
Crank-pins , . 188
Connecting rod brasses 189
Knocking in engines 189 to 190
The main bearings '. . . . 190 to 192
Repairs of engines 191
Fitting a slide valve 191
Eccentric straps 192
Heating of journals 193
Automatic engines 194
To find the dead centers . . . . • 195
View of tandem compound engine and its foundation 198
How to line an engine 199 to 203
View of twin tandem compound engine, showing arrangement of piping 200
CHAPTER XIa.
Directions for setting up, adjusting and running the improved Cor- liss steam engine 205
Adjustment of Corliss valve gear with single and double eccentrics. 206
Adjustment with two eccentrics .• 215
The compound engine 222
Horse power of compound engine 232
Condensing engines 232
Condensers 235 to 253
Setting the piston type of valve 261
Setting the cut-off valve . . 266
Flat valve riding cut- off .' ... 268
Starting and running a compound engine 253
. CHAPTER XII.
THE STEAM ENGINE — CONTINUED 274
What is work 274
What is power 274
Horse power, stroke and weights of engine 273,275
General proportions of engine 275
CONTENTS. xj
Rules for weights of fly-wheels ...... AGE*
View of the Russell engine ......
Setting the valves of Russell engines ..... 277
View of the Porter-Allen engine ......
Description of the Porter-Allen engine ...... ' 282-287
Directions for setting the valves, and running the Porter-Allen
................... 271,288
The Porter governor ............ 289
The Armington and Sims engine ...... * 290*
Setting the valve in an Armington and Sims engine . . 290
The Harrisburg engine ......... 291
The care and management of the Harrisburg engine . . 291-296
The Mclntosh and Seymour high speed engine . . 296
How to set the valves of an M. and S. engine ..... 296
The Ideal engine ........... . 298
Instructions for starting and operating Ideal engines .... 298-306
Instructions for indicating Ideal engines .......... 306
The Westinghouse compound engine ........ . 308
Westinghouse compound., diagram of cylinders ........ 309
How to set the valve on a Westinghouse engine ....... 307
Some points on cylinder lubrication ............ 309
Automatic lubricators ........ ...... 310,312
Setting a plain slide valve with link motion ....... 313, 318
Valve setting for engineers ...... ;*> ...... 318,322
View of a slide valve engine showing the point of taking steam . .321 View of a slide valve engine showing the point of cut-off . . . .321
View showing the position of the valve when compression begins ................ . . . 321, 322
CHAPTER XIII.
TAKING CHARGE OF A STEAM POWER PLANT ..... 323
Economy in steam power plants ... ........ 327, 32
Priming in boilers . . . . .............. 3!
Table of properties of saturated steam ........... 31
High pressure steam ............... ; 132, 33
Using steam full stroke .............. 335,337
Xll CONTENTS.
PAGE.
Slide valve engines . 337
Regular expansion engines 338
Automatic cut-off engines 339,340
The Gardner spring governor 341, 344
The Gardner standard governor 342, 344
CHAPTER XIV.
A FEW REMARKS ON THE INDICATOR 345
The use of the indicator in setting valves, etc 346
A card from a throttling engine 347, 349
A card from an automatic cut-off engine 350
Calculating mean effective pressure 351
The theoretical curve 353, 357
A card from a Corliss engine 357
A stroke card 358
A steam chest card 359
Eccentric out of place, cards 360,361
Eccentric cards 361,365
How to take an indicator diagram 365
Cards from " Eclipse " ice machine .. . . . . . . . . . 371,373
A collection of diagrams, which illustrate very nicely the peculiari- ties and difference in the action of throttling and automatic en- gines . 375, 379
CHAPTER XV.
ECONOMY AND OPERATION OF STEAM ENGINES .... 380 The question whether or not more steam is used when an engine is made to run faster without changing either the cut-off or the pres- sure 380
How to increase the power of a Corliss engine . . . . . . 381, 382
How to increase the power of an engine having a throttling governor 383 How to increase the horse power of an engine having a shaft gov- ernor 385
How to line an engine with a shaft placed at a higher or a lower
level . . 385, 387
How to line the engine with a shaft to which it is to be coupled clireel}, .,,....,...<,,,...•... 387
CONTENTS.
PAGE. How to set a slide valve in a hurry ......... 3g8
A few things for an engineer to remember ....
The travel of a slide valve ............ u 39Q
Loss of heat from uncovered steam pipes ...... .391
Rules and problems appertaining to the steam engine . . . 392, 395 To find the water consumption of a steam engine ..... 395 397
Table of sizes of boiler feed pump ............ 397
CHAPTER XVI.
THE STEAM BOILER 398
The force of steam and where it comes from ...... 398, 400
The energy stored in steam boilers 400, 401
Special high pressure boilers 401
Types of boilers 402
Horse power of boilers • . . . 402, 404
The rating of boilers 404
Working capacity of boilers 405, 406
Code of rules for making boiler tests 407,414
Definitions as applied to boilers and boiler material 415
Heat and steam • . . 416,421
Selection of a boiler ....... 422, 425
Boiler trimmings 426, 432
The care and management of a boiler 433, 437
Water for use in boilers 438,448
CHAPTER XVII.
USE AND ABUSE OF THE STEAM BOILER . . . . . 449, 453
Design of steam boilers . *54> 455
Forms of steam boilers . ' . . . • 456
Setting steam boilers 456> 457
Defects in the construction of steam boilers . 457,453
Improvements in steam boilers • *59> 4<
Strength of riveted seams 4(ilJ *(
Maximum pitches for riveted lap joints . . . . • *'
Iron plates and iron rivets, double riveted lap joints 467
XIV CONTENTS.
PAGE.
Zigzag riveting and chain riveting 468, 472
Single riveted lap joints, iron plates 469
Steel plates and steel rivets, S. R. L. J 470
Steel plates and steel rivets, D. R. L. J 471
Strength of stayed flat boiler surfaces » 473
Boiler stays 474, 477
Chart to find steam pipe for heating water 478
Chart to find boiler power to heat water 479-483
Data relating to ventilation 484
Sizes of mains and branches, — table of pipe 485
Pulsation in steam boilers 487, 488
Weight of square and round iron per lineal foot 488
Water columns for boilers 489
Steam gauges 489, 490
Safety valves 491,499
Table of the rise of safety valves 494
Safety valve rules 497
Table of heating surfaces in square feet 501
Centrifugal force . 501
CHAPTER XVIII.
THE WATER TUBE SECTIONAL BOILER 502
The down draft furnace 503, 522
View of boiler setting and furnace common in the East 513
Vertical tubular boilers 514, 521
Proper water column connections 515
Table of pressures allowable in boilers 516
Fire line in boiler settings 520
Proper location of gauge cocks 521
Number of bricks required for boiler setting . . . • 522
Specifications for a sixty-inch 6-inch flue boiler 524
Banking flres 531
Instructions for boiler attendants 532
Rules and problems anent steam boilers . 536
Steam jets for smoke prevention 542
CONTENTS. xv
CHAPTER XIX.
PAGE.
THE STEAM PUMP ^
The Worthmgton compound pump 544
View of steam valves properly set t 545
The Deane steam pump ( ^ 5^6
View of steam valves properly set ( . 547
The Cameron steam pump , ( 543
Explanation of steam end 543
View of steam valves properly set . 543
The Knowles steam pump ...... 550
Explanation of steam valves 550
View of steam valves properly set 552
The Hooker steam pump 553
Operation of the Hooker pump 553
View of steam valves properly set 555
The Blake steam pump 555
Operation of the Blake pump 556
View of steam valves properly set 558
Miscellaneous pump questions and answers 559 and 571
How to set the steam valves of a duplex pump 567
View of steam valves properly set 568
Proper pipe connections 569
View of pipe connections 570
Pumps refusing to lift water 577
Corrosion in water pipes 579
Pumping acids 579
Selecting boiler for a steam pump 580
The Worthington water meter - .581
Table of water pressure due to height 582
Table of decimal equivalents of IGths, 32nds and 64ths of an inch . 583
Capacity of tanks in U. S. gallons 584
Capacity of square cisterns in U. S. gallons . . 585
Weight of water 685
Cost of water 587
Loss by friction of water in pipes a
How water may be wasted **
Ignition points of various substances 68S
XVI CONTENTS.
CHAPTER XX.
PAGE.
THE INJECTOR AND INSPIRATOR 591
First appearance of the injector 592
Range of the inspirator and injector 592
General directions for piping injectors 594
Care and management of injectors 599,602
Directions for connecting and operating the Hancock inspirator . . 597
Water between 32° and 212° Fah 602
Steam pump problems 603
Water pipe problems 608
CHAPTER XXI.
MECHANICAL REFRIGERATION 619
How it is produced 619
Principles of operation 620
Operation of apparatus 620
Function of the pump and condenser 62 1
What does the work 621
Mechanical cold easily regulated 622
Utilizing the cold 622
Brine system 622
Direct expansion system 623
Rating of the machine in tons capacity 623
Difference in the ratings 623
Instructions for operating refrigerating machinery 624
Steam condensers 627
Air in the system « 628
Gases in the plant 628
A few tests for ammonia 631
Testing for water by evaporation 631
Lubrication of refrigerating machinery . 632
Effects of ammonia on pipes . 633
To charge the system with ammonia 634
Process of mechanical refrigeration 635
View of the " Eclipse " compressor 637
How heat is removed 636
Section of De La Vergne compressors 638, 639
Diagram of De La Vergne system 640
CONTENTS. xv jj
PAGE.
General arrangement of refrigerating plant . . „ • 641
De La Vergne ice-making plant . . . .642
Ice-making plant, showing distilling apparatus ...... 643
Electrically-driven ammonia compressor 645
Horizontal-vertical refrigerating machine „ 646
Location of high and low pressure gauges . , 647
CHAPTER XXII.
SOME PRACTICAL QUESTIONS USUALLY ASKED ENGI- NEERS WHEN APPLYING FOR LICENSE . '.
Reasons why pumps do not work
Priming in boilers 648
Foaming in boilers 648
In case of low water in a boiler 649
Best economy in running an engine . 650
What is valve lead 653,666,668
What is meant by expansion of steam 654
Describe the Corliss valve gear 654
What is lap on a valve . . . . 654,666,670*
Taking up lost motion in an engine . 654
Direct and indirect valve motion 668-
To test a piston for leakage of steam . 669
CHAPTER XXIII.
INSTRUCTIONS FOR LINING UP EXTENSION TO LINE SHAFT 672
Simplicity in steam piping 674
Cutting pipe to order 675
Feed water required for small engines 676
Heating feed water 676
Bating boilers by feed water . * .... 676
Weights of feed wa^er and of steam 677
Feed water heaters 678
Table showing the units of heat required to convert one pound of water at the temperature of 32° Fah., into steam at different pres- sures 679
Table showing gain in use of feed water heaters, and percentage of heat required to heat water for different feed and boiling tempera- tures, as compared with a feed and boiling temperature of 212° . 680
XV1H CONTENTS.
-
PAGE.
Pure water 681
The temperature and pressure of saturated steam 684
Something for nothing • . 686
Melting point of metals 687
Chimneys 688 to 694
Weight of steel smoke stacks per linear foot 694
CHAPTER XXIV.
HORSE POWER OF GEARS 695
Table of H. P. of shafts 697
Prime movers 697
Wheel gearing 698
The pitch line of a gear wheel 698
To find the pitch of a wheel . 698
To find the chordal pitch 699 to 703
To find the diameter of a wheel 699 to 703
To find the number of teeth for a wheel 699 to 703
To find the proportional radius of a wheel or pinion 700
To find the diameter of a pinion 700
To find the circumference of a wheel 700
To find the number of revolutions of a wheel or pinion ^ . 700 to 701
Stress on gear teeth 705
A train of wheels and pinions 701
Table of diameters and pitches of wheels 704
Curves of teeth . 705
Construction of gearing 706
Bevel wheels 707
Worm-screw 708
Proportions of teeth of wheels 709
To find the depth of a cast-iron tooth 709
To find the horse-power of a tooth 710
Calculating the speed of gears 710
When time must be regarded 711
Table of weight of a square foot of sheet iron 712
Screw cutting 713
Transmission of power by manila rope 714, 812, 813
Decimal equivalents of one foot by inches 714
Table of transmission of power by wire ropes 715 and 8 14
CONTENTS. x-lx
CHAPTER XXV.
ELECTRIC ELEVATORS The Otis elevator ...
........
Belt driven elevators . ' 'TIC
• • • • « « 1 lo« 7*5
Direct connected elevators .......... 717 730
The motor-starting switch ......... ' 71g
The elevator machine brake ....... ' 72n
The main hand rope ......... . . , ' 721
View of connections of gravity motor controller to elevator .' 722
View of connections of gravity motor controller with separate rope attachment ............... ^ 72g
Direct connected electric elevators ........ t 730
Automatic stops ............. 9 733
View of circuit connections .......... , < 734
The starting resistance ...... ......... 735
The switch lever .................. 736
Cutting out the series field coils ..." .......... 737
The safety brake magnet ................ 739
The proper care of machines ............ 739; 779
How to start the car . ................ 743
The car switch ................... 748
The slack cable switch ................ 749
Electric control for private house elevators ......... 749
View of wiring for private houses ............. 750
The Sprague Electric Co.'s elevators ........... 756
View of operative circuits for Sprague screw elevator ..... 762
The pilot motor ....... ' ............ 763
Care of electric elevators ............... 765
Directions for the care and operation of electric elevators .... 765
CHAPTER XXVI.
ELECTRIC ELEVATORS 769
Drum type, limits for tall buildings 769
Motor and drum speeds 769
Diagram of Frazer duplex type 770
General arrangement and operation of duplex type 771
Duplex elevator motor , • 772
XX CONTENTS.
PAGE.
Running qualities of the duplex type elevator . 773
Objections to the duplex elevat >r 773
Wiring diagram of the Frazer duplex elevator 774
Controller for the duplex motor 775
Frazer limit switch 776
Detail view of Frazer controller 777
The traction type of elevator . . . . , , 778
Diagram of the traction type 779
Considerations concerning traction-type motors 780
Cable-drive elevator machine 781
Counter-balance used with cable-drive type , . 782
Compl te installation of cable-drive elevator , 783
Wiring diagram for traction elevator 784
Controlling device for electric elevator 785
Line wires for traction type 787
Operation of car and limit switches 787
CHAPTER XXVII.
THE DRIVING POWER OF BELTS 788
The average strain or tension at which belting should be run . . . 788
Rules and problems anent belting 788, 797
Notes on belts 790
Transmitting power of belts 795
Table of horse-power of belts 796,799
Directions for adjusting belting 798
Horse power of belting 799
CHAPTER XXVIII.
AIR COMPRESSORS, THERMOMETERS, THE METRIC SYS- TEM, AND ROPE TRANSMISSION 800
Losses in air compressors 800
Capacity of air compressors 800
Contents of a cylinder in cubic feet for each foot in length .... 801
The McKierman air compressor 801
The Bennett automatic air compressor 803
The Ingersoll-Sergeant air compressor 803
The Pohle air lift system 807
CONTENTS. xx j
PAGE.
The metric system 80)
Thermometers t gu
Rope transmission 812
Horse-power transmitted by hemp ropes 813
To test the purity of hemp ropes 814
Wire rope data . 0 • 814
CHAPTER XXIX.
ALTERNATING CURRENT MACHINERY 815
The principles of alternating currents 815
Diagrams representing a generator of either continuous or alter- nating currents 817
Diagrams showing the relations between alternating currents and
e.m.fs 821,824
One reason why alternating currents vary, etc 825
Diagrams showing the way in which sine curves are used, etc. . . 826
Polyphase currents 832
Unbalanced three-phase currents, etc 834
Inductive action in alternating current circuits, etc 834
The angle of lag between the current, etc 837
By the use of condensers, etc 8*°
The general principle of construction of a condenser, etc 841
Mutual induction 84:2
Transformers 8'
The action in a transformer 8
The object in using transformers 8
Alternating current generators 8
Diagram illustrating a simple alternating current generator ... 853
Alternator of the multipolar type 8
How alternating current generators are run ....••••• 8
If an alternator is of the multipolar type 854
A revolving field alternator 857
An inductor alternator
Alternating current generators
Alternators run in parallel
Starting alternators connected in parallel
The way in which synchronizing lamps are connected . . Compensating and compounding alternators
XX11 CONTENTS.
PAGE.
Field magnetizing currents a .. 867
Alternating current motors . . 867
Two-phase revolving field synchronous motor « . 869
Power factor • 870
Induction and other types of motors 871
Principle of the induction motor • 872
Induction motors if very small 877
Three-phase induction motors 877
While induction motors are very satisfactory machines 878
Rotary transformers and rotary converters . . ....... 878
Principle of the rotary transformer 879
Alternating current distributions 882
Starting 886
Parallel running of alternators . 887
Types suitable for parallel operation . . . . • 887
Division of load 887
Compound alternators 887
Belted machines 888
Direct coupled machines 888
Starting 889
Shutting down 890
Care of machines 890
CHAPTER XXXo
TABLES —
Actual ratios of expansion 935
Ammonia gas per ton refrigeration „ . 898
Boiling points of various substances „ . . . . . 907
Capacity of duplex pumps 893
Capacity of low pressure pumps . 984
Capacity of reservoir in gallons 910
Coal burned per square foot of grate 908
Cost of coal per annum 909
Diameters, circumferences and areas of circles , . . 895
Horsepower for one pound m.e.p 924
Horsepower of slide-valve engines 922
CONTENTS. xxjj;
PAGE.
Horsepower per ton of refrigeration 904
Horsepower to compress one cu. ft. ammonia . .
Hyberbolic logarithms ' gg2
Iron and steel hoisting ropes ' 91g
Iron and steel transmission ropes 918
Mean absolute pressures 925
Mean pressure of diagram, ammonia compressor . . 902
Measurements of riveted seams 929-934
Melting points of fusible plugs . t 907
Melting points of various substances t 997
Piston speed in feet per minute . 912
Power gained by adding condenser 923
Properties of ammonia 597
Properties of brine solution 900
Properties of carbonic acid 900
Properties of saturated steam 330, 913
Properties of sulphur dioxide 898
Reaumur, Fah. and Celsius thermometers 903
Ropes for inclined planes 920
Speed and capacity of centrifugal pumps 927
Sizes and dimensions of Corliss engines 926
Sizes of cylinders for compound pumps 923, 927
Specifications for riveted seams 928
Transmission of power by ropes 921
Weight and strength of iron bolts 906
Weight of rivets and bolts 905
Horizontal return tubular boilers 937, 938-939
Table of wages e . 924
Air for Rock drills 934
Areas of segments of circles . . . o . 935
Staying boiler heads 938
Table of Steam Pressure per square inch allowable on lap
welded flues made in sections ' • • 952, 953
Steam Pressure allowable on lap-welded flues 952, 953
CHAPTER XXXI,
HYDRAULIC ELEVATORS 964
Types of elevator machines 954
Horizontal pushing type 955, 957
Actuating lever in the car a a - • - • •• .956
XXIV CONTENTS.
PAGE.
Elevation of horizontal machine 958
Plan of elevator cylinder and sheaves 960
Pilot and main valves 961
Morse and Williams horizontal pushing type 962
Horizontal elevators, pulling type 963
Whittier pulling type 964
Valve of Whittier machine 965
Automatic stop for Whittier machine 967
Otis vertical elevator 968
Otis vertical elevator system 969
The Otis valve 970
Valve construction 971
Otis machine with pilot valve control 972
Method of operating Otis pilot valve 973
Main valve with pilot valve control 974
Details of Otis pilot valves 975
Otis differential and pilot valve 977
Main valve with magnet-operated pilot . » 978
Pipe connections for magnet-operated pilot 979
Otis main valve with magnet control 981
Pipe connections for Otis main valve 982
Private house elevator, push-button control 984
Floor controller for push-button system 985
Wiring diagram for push-button system 987
Double power hydraulic elevators 987
High pressure hydraulic elevators 988
Otis double pressure type 989
High pressure horizontal machine , 991
Hydraulic elevator system with inverted plunger 993
Valves used with inverted plunger type . • . . . 995
Automatic stop valve for plunger type 996
Speed controller for plunger type . . s , ,...*>.. 998
Plunger elevators ».-... 998
Accumulators used with plunger type .....»•••*. 999
Valve for accumulator 1000
Plunger elevator, complete installation s . 1002
Plunger Elevator Co'.s machine 1004
Details of plunger elevators 1006
CONTENTS. xxy
PAGB.
Pilot and automatic stopping valves 1007
Valve for elevator control
Elevator for pilot valve control .............
How to pack vertical cylinder machine . t 10i2
Plunger elevator with hand rope control 1013
Valve for hand rope control .1014
Packing vertical cylinder piston from top 1015
Packing vertical cylinder valves .1016
Packing piston rods 1016
Water for use in hydraulic elevators 1017, 1022
Causes for car settling . . 1019
Elevator enclosures and their care 1019
Standard hoisting rope , 1021
Cables and how to care for them 1021
Leather cup packings for valves 1022
Closing down elevators , 1022
Lubrication for hydraulic elevators • 1023
Useful information 1023
Decimal equivalents of an inch 1021
Water , 1024
Elevator safeties 1025
Otis wedge safety 1026
Safety governor, single acting 1028
Otis roller safety 1029
Governor rope for roller safety 1030
Lifting rope for roller safety 1031
Brake safety for iron guides « 1032
Governor rope for brake safety
Morse and Williams, brake safety 1°35
Pratt brake safety 1036
Otis double acting safety governor . . li
Pipes and Tanks. Contents in cubic feet; in U. S. gallons . . .1039
Friction and lubrication 1(
Uses of friction 1(
Coefficient of friction 1(
Illustrating laws of friction 1(
1044 Laws of friction
Theory of lubrication *'
Petroleum oils -
XXVI CONTENTS.
PAGE The conditions which produce the greatest difference in
ordinary lubrication 104
The best lubricant 104
Cylinder and valve lubrication 104!
Wet steam 105'
Lubrication of refrigerating machinery 105
Different makes of refrigerating machines 1054
HANDBOOK ON ENGINEERING.
CHAPTER I.
THE ELEMENTARY PRINCIPLES OF ELECTRICAL MACHINERY.
The operation of electric generators, or dynamos, as they are ordinarily called, and also that of electric motors, depends upon a simple relation between electricity and magnetism, which will be explained in a simple manner in the following paragraphs.
s
[JT
Fig. 4.
Fig. 1. Fig. 2. Fig. 3.
Forms of magnets.
A permanent magnet, as is well known, is a bar of steel which possesses the power of attracting pieces of iron. These bars may be made straight, as in Fig. 1, or in the form of a U, as in Fig. 2, or in any other shape desired. The strength of a permanent magnet depends upon the kind of steel of which it is made, and
1
2 HANDBOOK ON ENGINEERING.
also upon the temper it is given. Generally speaking, the harder the steel the stronger the magnet. A bar of soft steel, or wrought iron, cannot be made into a permanent magnet of any noticeable strength, but if such a bar is covered with a coil of wire, as shown in Figs. 3 and 4, and a current of electricity is passed through the wire, the bar will be converted into a very strong magnet so long as the current flows. As soon as the electric current stops flowing through the wire, the magnetism of the bar will die out. Magnets of the last-named type are called electro-magnets, as they do not possess magnet properties except when the electric current flows around them. Electro-magnets, when energized by sufficiently strong electric currents, can be far more powerful than the permanent magnets, and on that account they are used in electric generators and motors. In addition to being a stronger magnet, the electro-magnet has the advantage that it can be magnetized and demagnetized almost instantly, by simply cutting off the exciting electric current, and on this account they can be used for parts of electrical machines and apparatus, for which the permanent magnet would be entirely unsuited.
If we test the attractive power of a magnet, we will find that it is greatest at the ends, the force at the middle point being scarcely noticeable. A bar such as Fig. 1 or Fig. 3 might hold a piece of iron weighing several pounds , if presented to either end , while at the middle point, it might not be able to sustain more than an ounce or two. Owing to this fact, the ends are called the poles of the magnet. When a magnet is suspended from its center, like a scale beam, and allowed to swing freely, it will be found that it will come to rest in a north and south position, and no matter how violently it may be moved around, it will always come to a state of rest with the same end pointing towards the north. On this ac- count, the ends are called north and south poles, the north pole being the end that points toward the north.
HANDBOOK ON ENGINEERING. 3
If two bar magnets are suspended side by side with the north end of one at the top and the north end of the other at the bottom, as illustrated in Fig. 5, they will attract each other; but if both magnets have the north end at the top, they will push away, as shown in Fig. 6. It is evident that there is a good reason for this difference in action, and this reason we can obtain by experiment.
a
a
Figs. 5 and 6. Showing effect of changing the poles.
A magnet needle, such as is used in the mariner's compass, is simply a small magnet. If we place a magnet bar, as shown in Fig. 7, and then set near to it, in different positions, a compass containing a very small needle, we will find that in these several positions the direction of the needle will be about as is indicated by the small arrows marked b on the curved lines a a; the arrow pointing towards the north end, or pole of the needle. The reason why the needle will take up these positions is that the north end of the bar attracts the south end of the needle, and pushes away the north end, just as in Figs. 5 and 6, and the south end of the bar acts in the same way ; so that there is a tug of war going on, so to speak, between the attractions and repulsions of
4 HANDBOOK ON ENGINEERING.
the two ends of the bar upon the two ends of the needle, the result being that the position assumed by the needle is the re- sultant of these several forces. When the needle is near the
\
V
Of
y
^pp^''
. Figs. 7 and 8. Illustrating lines of force.
north pole of the bar, its south end is attracted with the greatest force, and when near the south end of the bar, the north end ex- periences the greatest attraction.
If we were to place the exploring needle in all possible posi- tions near the magnet and trace lines parallel with it, in these positions, we would obtain a large number of curves about the shape of those shown in Fig'. 8. As these curves represent the direction into which the magnet needle is turned at the various points in the vicinity of the magnet, they represent the direction in which the combined forces of the two poles act at these two points, hence, these lines are called magnetic lines of force.
HANDBOOK ON ENGINEERING.
When two magnets are suspended as in Fig. 5, the lines of force of both will be in the same direction as is indicated in Fig. 9 by the arrow heads on the curves a a. That this is true can be seen from Fig. 7, in which it will be seen that the arrow heads point toward the south pole and away from the north pole. As the north pole of a magnet has an attraction for the south pole, we can readily see that there is an endwise pull in the lines of force, which tends to make them contract, like rubber bands, hence, we can imagine the lines a a in Fig. 9 to contract and thus draw the two magnet bars together.
The repulsion of the two magnets, when the north poles are at the same end, is illustrated in Fig. 10. Here we see that the lines of force passing on the outside of the bars, as indicated by lines a a, are unobstructed, and can assume their natural posi-
a
s
JV
Figs. 9 and 10. Lines of force in two bar magnets.
tion, but those that pass between the bars, along line c, are pressed out of position. If we assume that the lines of make an effort to retain their position, like so many wir<
6 HANDBOOK ON ENGINEERING.
springs, then we can see that the repulsion is due to the effort that the lines make to assume their natural form in the space between the bars.
Magnetic lines of force have no real existence, they simply in- dicate the direction in which the force acts, but if we keep this fact in mind, it helps us to understand magnetic actions, if we treat the lines of force as if they were something real. This fact will become more evident as we proceed.
Lines of force always pass from the north to the south pole through the space between these poles, and through the magnet itself, they are assumed to pass from the south to the north pole. The form of the lines of force depends upon the relative position of the north and south poles. In Fig. 9 they are curved, as
a
|
<s |
JV |
55== |
S JV |
Fig. 11. Lilies of force between ends of magnets.
the magnets are placed side by side, but if the bars were arranged end to end, as in Fig. 11, the lines of force would be straight, as is shown at a. From the north end of the right side magnet, the lines of force would pass in curved line, as in Fig. 10, to the south pole of the magnet on the left side, thus completing the magnetic chain, or circuit, as it is called.
If we take the two magnet bars of Fig. 1 1 and stand them on end, as in Fig. 12, and suspend a bent wire C in the manner shown, effects can be produced that are interesting and instruct- ive, as they illustrate the principle upon which generators and motors act. The wire C should be journaled at D D, so as to swing with as little friction as possible, and its ends are to be con- nected with a battery J5, by means of fine wires a and b ; a switch being provided at c so as to stop the flow of current when desired.
HANDBOOK ON ENGINEERING. 7
If the switch c is opened, so that no current flows through C, the latter will not be disturbed, and if we give it a swing, it will oscil- late back and forth, like a clock pendulum, and in a few seconds come to rest in the position in which it is shown. If the switch is closed, C will at once swing out of the stream of magnetic lines of force and will remain in that position as long as the current from the battery passes through it. The direction in which C
Fig. 12. Showing the principle of the electric generator
will swing will depend upon the direction of the current through it. If with the wires a and b connected with the battery, in the manner shown, the wire C swings to the right side, then if a is connected with e, and b with d, the direction of swing will reversed ; that is, C will swing toward the left.
From this experiment we see that the magnetic lines of can develop a repulsive force against an electric current, ai the direction of the repulsion depends upon the direct*
8
HANDBOOK ON ENGINEERING.
electric current with respect to the direction of the lines of force. We shall now explain why this repulsion is developed, and this we can illustrate by the following experiments: —
If we arrange three wires as shown in Figs. 13, 14 and 15, so as to run north and south, the upper end being north, and place over these magnet needles D D D, pivoted at e e e, we will find that if there is no current flowing through the wire, the needle will point toward the north, or be parallel with the wire, as is
Fig. 13. Fig. 14. Fig. 15.
Showing effect of current on the needle.
shown in Fig. 14. If the current flows through the wire from
south to north, the north end of the needle will swing to the right, as in Fig. 15, and if the current flows through the wire from north to south, the north end of the needle will swing toward the left, as in Fig. 13. From this we see that an electric current can repel a magnet, and that the direction in which it repels it depends upon the direction of the current.
If we stand the three wires on end, as shown in Figs. 16, 17 and 18, in which A B C represent the wires as seen from above, we will find out more about the relation between electric currents
HANDBOOK ON ENGINEERING. 9
and magnets. If we place four small magnet needles around each one of the wires, as shown at a a a a, we will find that those around the center wire, through which no current flows, will all
a
Fig. 16. Fig. 17. Fig. 18.
Wires surrounded by magnetic lines of force.
point toward the north, as shown, while those around the wire Fig. 16, through which a current flows upward, that is, away from the center of the earth, will point in a direction opposite to that in which the hands of a clock move; and in wire Fig. 18, in which the electric current flows down toward the center of the earth, the north ends of all the needles will point in the direction in which the hands of a clock move, that is, just opposite to those in Fig. 16.
Figs. 19 and 20. Directions of lines of force. From these actions, we infer at once that when an electrio current flows through a wire, the latter becomes surrounded with magnetic lines of force, as is illustrated in Figs. 19 and 20,
10 HANDBOOK ON ENGINEERING.
and that there is a fixed relation between the direction of the current and that of the lines of force. At A, Fig. 19, the direc- tion of the lines of force is shown for a current moving up- ward, and at J5, Fig. 20, the direction of the lines of force is that due to a current moving downward through the wire.
Inasmuch as an electric current flowing through a wire is surrounded by magnetic lines of force, we can say that a com- plete electric current consists of two parts, one the current proper, which traverses the wire, and the other the magnetic casing which envelops the wire. It is the action between the latter part of the current and the lines of force of magnets that develops the current in a generator, or the power in a motor.
With the aid of Figs. 21 and 22, we can now show how the force is developed that thrusts the wire to one side in Fig. 12. The lines of force of the magnet, which constitute what is called the magnetic field, will flow from the north pole at the top to the south pole at the bottom, as is shown in Figs. 21 and 22. If the electric current flows through the wire C from the back toward the front, the lines of force developed around it will have the direction shown in Fig. 21. As lines of force cannot flow in op- posite directions in the same space, the lines of the field will swing over to the left side of the wire, but in doing so they will be stretched out of the straight form, and they will also push the lines surrounding the wire out of their central position. Under these conditions, which are illustrated in Fig. 21, the effort made by the field lines to straighten out, together with the effort made by the wire lines to return to the central position, will develop a thrust between the wire and the field, and thus force the former out toward the right side.
If the direction of the current through the wire is reversed so as to flow from front to back, the direction of the lines of force around the wire will be reversed, and will be as in Fig. 22. Under these conditions, the lines of force of the magnetic field will
HANDBOOK ON ENGINEERING. jj
swing over to the right side of the wire, and thus the thrurt will be in the opposite direction.
Fig. \2 represents the principle of an electric motor in ite sim plest form, and from it we see that the force that causes the armature to rotate is developed by the repulsion between the mag- netism of the field magnet and the magnetism that surrounds the wires wound upon the armature.
V
Figs. 21 and 22. Showing effect of magnetic Aeld.
It is self-evident that if we undertake to force the wire C through the magnetic field in the opposite direction to that in which it swings, we will have to make an effort to do so ; that is, if we try to move the wire from right to left in Fig. 21, or from left to right in Fig. 22, we will have to apply power. Now nature is a strict accountant and does not allow any power to be lost ; therefore, all the energy we expend in moving the wire through the magnetic field must appear in some other form, and the form in which it appears is as an electric current that is generated in
12 HANDBOOK ON ENGINEERING.
the wire. If we were to remove the battery in Fig. 12 and put in its place an instrument to indicate the presence of a current in the wire, we would find that ,>hen we move the latter in the opposite direction to that in which it moves under the influence of the current, we generate a current; that is, we convert the device into a simple electric generator. If in Fig. 21, we move the wire from right to left, the direction of the current generated in the wire will be the same as that of the current which causes the wire to swing in the opposite direction, that is, from back toward the front. As it is a poor rule that does not work both ways, we would naturally infer that if moving the wire from right to left develops a current from back to front, movement in the opposite direction would develop a current from front to back ; and such is actually the case. This fact can be demonstrated by Fig. 12. Suppose that in this figure we hold C stationary in the central position, and then pass a current through from back toward the front ; this current would exert a force to swing C to the right side. If we release the wire, it will swing to the right and as soon as it begins to move, the current will become weaker, show- ing that the movement of the wire developed therein a current in the opposite direction. If we force the wire over to the left side, the current flowing through it will begin to increase as soon as the wire moves.
All the foregoing shows us that when a wire is moved through a magnetic field, a current will be generated in it if it forms part of a closed circuit, and it makes no difference whether there is a current already flowing in the wire or not. When the wire is caused to move through the magnetic field by a current flowing through it from an external source, the current developed in it will be in opposition to that which comes from the external source, and, as a consequence, the movement produces an actual reduc- tion of the strength of current flowing through the wire. The stronger the magnetic field and the greater the velocity of the
HANDBOOK ON ENGINEERING. 13
wire, the stronger the current generated in opposition to the driv- ing current, and, therefore, the weaker the latter. It is on this account that if a motor is allowed to run free, the faster it runs the weaker the current through it becomes, as the actual current in every case can only be the difference between the main driving current and the one developed in the wire, which latter runs in the opposite direction.
Magnetic force is measured in units that are based upon the centimeter gram second system which is too technical to be ex- plained in a few words. Briefly stated a unit of magnetic force will exert a pull of unit mechanical force at a unit distance.
The force of magnets is measured either by the total force of the magnet, or by the force exerted by each unit of cross-section. When the measurement is based upon the total force of the mag- net, the unit is called a Maxwell ; thus we speak of the total flux of a magnet as so many maxwells. When the , measurement is referred to the force per unit of cross-section, it is spoken of as the magnetic density, or density of magnetization, and the unit used is called a Gauss ; thus we speak of a magnet as having a density of so many gausses per square centimeter, or square inch of cross-section. The density of magnetization is deter- mined by a rule given on page 46.
The lifting capacity of a magnet can be determined by the following rule : —
TO FIND THE LIFTING CAPACITY OF A MAGNET IN POUNDS.
Multiply the area of cross-section of the magnet pole in square inches, by the square of the density of magnetization per square inch, and divide this product by 72 millions.
This rule gives the pull for one pole. For horse shoe magnets double the figures. If the object lifted is not in contact with the poles the pull will be less than rule gives.
14 HANDBOOK ON ENGINEERING
CHAPTER II. THE PRINCIPLES OF ELECTROMAGNETIC INDUCTION.
By electromagnetic induction, is meant the induction of electric currents by magnetic action. In the preceding chapter it has been shown that if we move a wire through a magnetic field, an electric current will be generated in it, providing its ends are joined, so as to form a closed circuit. If the ends are not joined, then there will be no current developed, because, an electric current cannot flow except in a closed circuit. When the ends of the wire are not joined, the movement through the field develops simply an electromotive force. Electromotive force is that force which causes an electric current to flow when there is a circuit in which it can flow. Electromotive force is a long-winded name and on that account it is always abbreviated into e.m.f., so that here- after when these letters are used, it will be understood that they stand for electromotive force.
Metals and all other substances that allow electric currents to flow through them are called conductors, while glass, mica, wood, paper and many other similar forms of matter that do not allow currents to flow through them are called insulators. The difference between conductors and insulators is only one of degree, for there is no known substance that is an absolute non^ conductor of electricity ; that is, a perfect insulator ; and there is no substance that does not resist to some extent the passage of a current — that is, there is no such thing as a perfect conductor. Some substances, like damp paper or wood, which stand midway between good conductors and good insulators, can be regarded as Cither one or the other, depending upon the service for which they are used. For currents of very low e.m.f., they would be in-
HANDBOOK ON ENGINEERING. 15
sulators, but for currents of very high e.m.f., they would be conductors.
The current that will flow through any circuit when impelled by an e.m.f., will have a strength that will depend upon the amount of resistance that opposes its flow. As all conducting materials are not of the same degree of conductivity, their relative values are determined by the amount of resistance they interpose to the flow of the current. The resistance of a conductor is measured in units called ohms; the strength of current is measured in units called amperes, and the e.m.f. is measured in units called volts. The relation between these units is such that an e.m.f . of one volt will cause a current of one ampere to flow in a circuit having a resistance of one ohm.
When a wire is moved through a magnetic field, the e.m.f. induced in it will be determined by the strength of the field and the velocity with which the wire moves, and will not be affected in any way by the resistance of the circuit of which the wire forms a part. If the resistance is very great, the strength of current generated will be very low, and if the resistance is very low the current will be strong, but in either case the e.m.f. will be the same.
If movement of the wire in one direction develops an e.m.f. in a given direction through the circuit, then movement of the wire in opposite direction will reverse the direction of the e.m.f. Thus, in Fig. 23, which represents a magnetic field between the poles N $, if wire a is moved 'from right to left, it will have induced in it an e.m.f. that will be from back to front, and if the direction of motion of the wire is reversed, the e.m.f. will also be reversed. This will be true whether the wire is near the N pole or S pole. This being the case, it can be seen that if a represents the end of a wire moving in the direction of arrow d, and b the end of a wire moving in the opposite direction, the e.m.f. 'sin these two wires will be in opposite directions. The
16
HANDBOOK ON ENGINEERING.
direction of the e.m.f . in a will be up from the paper toward the observer, and the direction of the e.m.f. in b will be down through the paper. If these two wires are secured to a shaft placed in the center of the field, then by the continuous rotation
Figs. 23 and 24. Illustrating the principle of the armature.
of the shaft, the two wires can be made to revolve around the circular path shown.
If these two wires are joined at the ends, as shown in Fig. 24, they will form a closed loop, and although the direction of the induced e.m.f. in the two sides will be opposite, when compared to a fixed point in space, they will be in the same direction so far as the loop is concerned ; that is, both e.m.f.'s will develop currents that will flow through the wire in the same direction.
Returning to Fig- 23 it will be noticed that if the wires re- volve around the circular path at a uniform velocity, their move- ment in the direction of line c c will not be uniform, but will be the greatest when the wires are in the position shown, and least, when they cross the line c c. In fact, when the wires cross line c c their motion in the direction of this line will be zero, for this
HANDBOOK ON ENGINEERING. 17
is the point where the direction of movement reverses No* the magnitude of the e.m.f. induced in the wire is proportional' to the veloorty in the direction of the line c c, hence, when the wires are crossing this line, the e.m.f. will be zero, and when they are one-quarter of a turn ahead of the line, the e.ra.f will be the highest.
In Fig. 24 we see that in side «, the direction of the current is toward the front, and in 6 it is the reverse; now, when « moves through half a turn, it will take the place of b, and the direction of the e.m.f. induced in it will be the same as in b in the figure ; that is, it will be the reverse of what it is when pass- ing in front of the pole N. This being the case, it is evident that each time the loop makes a half-revolution, the direction of the current generated in it reverses.
Fig. 25. Arrangement of the collector rings.
As the loop in Fig. 24 is closed, the current generated in it would be of no practical value, but if we cut the wire at one side and connect the ends with rings as shown at a and b in Fig. 25, then by means of collecting brushes c c we can take the cur-
18
HANDBOOK ON ENGINEERING.
rent off through the wires d d. This current, however, would consist of a series of impulses that would flow in opposite direc- tions, each one starting from nothing and increasing to its greatest
Fig. 26. Construction of simple commutator.
strength when the loop reaches the position shown in the figure, and then declining and reaching the zero value when the loop reaches the vertical position. Such a current is called an alter- nating current, because it flows first in one direction and then in the opposite direction. All forms of machines that generate cur- rents by electromagnetic induction, develop alternating currents, but in the class of machines known as direct or continuous current, a rectifying device is used which rectifies the current before it reaches the external circuit. This rectifying device is called a commutator, and is illustrated in its simplest form in Fig 26. In this illustration it will be noticed that the ends of the wire, instead of being attached to two independent rings, placed side by side, are secured to two half-rings, placed opposite each other. The brushes c d, through which the current is taken off, are held stationary ; therefore, as can be readily seen, c will make contact
HANDBOOK ON ENGINEERING. 19
with a during one-half of the revolution, and with b during the other half ; and this will also be the case with brush d. Now, as the half-rings with which the brushes are in contact change at each half revolution, it follows that by properly setting the brushes, they can be made to pass from one-half ring to the other at the very instant when the direction of the current in the loop reverses, so that through each brush there will be a succession of current impulses, but all in the same direction.
The device shown in Fig. 25 is a perfect alternating current generator, and that shown in Fig. 26 is a perfect direct current generator. In both cases, however, the e.m.f. induced is so low as to be of no practical value. To obtain serviceable machines, capable of developing the e.m.f. and current strength required in practice, it is necessary to provide very strong mag- netic fields and to rotate in these a large number of loops of wire. In order that the operation of such machines may be understood, we will first show how the powerful magnetic fields are obtained.
In Fig. 27 two wires are shown as seen from the end, these being marked A and B. The lines of force surrounding them are
m '
*^^4t fa J \ v \^ — 'o-**^~~^' /<
i_ '^'^4-J ' ^ \ \ ^ — "^ ^*~-**"^s /
:^—'*1' i \\ v I X^ /
Figs. 27 and 28. Effects of direction of current in wires.
in directions that correspond to opposite directions of current in the wires. In wire A, the current flows away from the observer. As can be seen, the lines of force of both wires have to crowd into
20 HANDBOOK ON ENGINEERING.
the space between the wires, for on the outside of A the two sets of lines would meet each other head on, and this would also be the case on the right side of wire JB. This crowding of the lines, of force into the space between the wires causes them to distort from their natural position and instead of being central with the wires, are eccentric to them. If we take a long wire through which a current is flowing and bend it into a loop, we will see that if the current flows out through one side, it will return through the other side, so that in the two sides of the loop the current will flow in opposite directions. This being the case, Fig. 27 can be regarded as showing the two sides of such a loop, and from it we find that the effect of such a loop is to concentrate within its interior nearly all the lines of force that surround the wire.
In Fig* 28 the two wires A and B are surrounded with lines of force that correspond to the same direction of current. In this case it will be noticed that in the space between the wires the lines of force flow in opposite directions ; hence, only a few of the lines will follow this path, simply that number surrounding each wire that can traverse the space without encroaching upon the path of the lines belonging to the other wire. If the two wires are very near to each other i practically all the lines of force of both wires will join forces, so to speak, and pass around the two wires. Now, if we wind a wire into a coil of many turns, the direction of the current in the several turns will be the same, so that the lines of force of all the turns will combine into one large stream and circulate around the entire coil side, no matter how many turns of wire it may contain. From this it can be seen that if we have a current of , say, ten amperes, we can make it produce just as powerful magnetic effect as a current of one thousand amperes, by simply increasing the number of turns of wire in the coil. A current of ten amperes passing through a coil of wire containing one hundred turns, will have the same magnet-
HANDBOOK ON ENGINEERING. 21
ism in effect, as a current of one hundred amperes passing through a coil of ten turns, or as a current of one thousand amperes pass- ing through a coil of a single turn.
If we place at the side of a wire through which an electric current is flowing a piece of iron, as is shown in Fig. 29, the effect will be that the lines of force will no longer flow in circular paths, as indicated by the circle a, but will be deflected in the manner illustrated, by the presence of the iron. If, instead of
Figs. 29 and 30. Lines of force through wires and magnets.
the straight iron bar, we substitute a ring of iron, as in Fig. 30, nearly all the lines of force will be concentrated in the metal, and the magnetic field in the space (7, between the ends of the ring, will be vastly greater than at any other point. The explanation of these actions is that all forms of matter oppose .the develop- ment of magnetic force, but some offer greater resistance than others. Iron, steel, nickel, and one or two other metals, offer less resistance to the magnetic lines of force than air, and are said to have a higher magnetic permeability. Nickel is only a slight improvement on air, but steel and iron are far superior, iron being of about two to three times the permeability of hard-
22
HANDBOOK ON ENGINEERING.
ened steel, and about one thousand times the permeability of air, when magnetized to the density ordinarily used in practice. The iron in Figs. 29 and 30, therefore, becomes the path of the lines of force, because it interposes a much lower resistance. Owing to this difference in the resistance of iron and air, it is possible to make an iron magnet core of any desired form, and to con- centrate within it nearly all the lines of force developed by the current flowing through the wire wound upon it. The presence of the iron not only serves to concentrate the magnetism in it, but as it reduces the resistance opposing the development of the magnetism, it enables the field to be made vastly stronger than it could be with air alone, say a thousand times as great.
If we make & magnet in the form of Fig. 31, with a coil of wire around the part jB, practically all the lines of force will flow to
Fig. 31. Principle of construction of bipolar machine.
the poles N $, and will pass through the air space between them. If this air space is nearly filled with a cylindrical mass of iron, A, the strength of the magnet will be increased, for, by doing this,
HANDBOOK ON KNU1NKKR1NU. 23
we replace air which is a poor magnetic conductor, by iron wliieh is a far superior conductor. Electric motors and generators are made with a cylindrical mass of iron at A, which is the armature
Fig. 32. Solid core.
Ring core.
core, and the air space between it and the faces of the poles of the field magnet is made just sufficient to accommodate the wire coils, and by this means the field strength is increased as much as possible.
The armature cores are sometimes made solid, as in Fig. 32, and sometimes as a ring, as in Fig. 33. When they are solid, the lines of force cross through them in straight lines, see Fig. 32 ; and when they are ring form, the lines follow the ring and do not penetrate the interior space.
If the single loop of Fig. 24 is replaced by a coil containing many turns of wire, the e.m.f. induced in it will be increased in proportion with the number of turns of wire in the coil, so that by using such a coil in a field such as shown in Fig. 31, a high e.m.f. can be obtained. This e.m.f., however, would be alter- nating, and if the current were rectified by means of a commu-
24 HANDBOOK ON ENGINEERING.
tator, it would not be of uniform strength, but would fluctuate from a maximum value to zero. Just how the current would fluctuate and how the construction can be changed so as to get rid of the fluctuation, we can explain by presenting a diagram that illustrates the alternating current as it flows in the armature coil, and the rectified current as it leaves the commutator.
In Fig* 34> let the distance / /*,, h i, i w, along the line// represent half -revolutions of the coil, and let distances measured on the vertical line c d represent the strength of current, distances above/ being current flowing in one direction, and distances below /being for current flowing in the opposite direction. Let us con- sider the instant when the coil is passing the point where the e.m.f. induced is zero ; then this instant will be represented by the point /, at the left of the diagram, and the curve a will start from this point ; as at that instant, the current which it represents has no value. As the coil rotates, the current begins to grow, and this fact we indicate by causing curve a to gradually
Figs. 34 and 35. Illustrating flow of alternating current.
rise above the horizontal line. At the quarter turn, the current reaches its greatest strength, thus this forms the highest point of curve a, and is midway between / and h. From this point
HANDBOOK ON ENGINEERING. 25
onward, the current declines and becomes zero, when the rotation of the coil has reached one-half of a revolution, which is repre- sented by the point h. In the next half -revolution, the current
Fig. 86. Two coils on armature. Fig. 37. Four coils on armature.
flows in the reverse direction, but has the same maximum strength and increases and decreases at the same rate; therefore, the curve 6, drawn below the horizontal line, represents the reverse current ; and point i corresponds to one complete revolution, so that beyond i the curves a and b are repeated in systematic order.
Now, if we provide a commutator to rectify this current, all we can accomplish is to turn curve b upside down and transfer it to the upper side of the horizontal line, as in Fig. 35 ; but, as will be seen, all we accomplish by this act is to obtain a current that flows always in the same direction, but at each half-revo- lution it drops down to a zero value.
If we wind two coils upon the armature, placing them at right angles with each other, as is indicated by A and B in Fig. 36, then if the currents of these two coils are rectified, they will bear the relation toward each other shown at the upper line in Fig. 38, the a a curves in solid lines representing the current from the A coil, and the b b curves in broken lines, representing the current from the B coil. As will be seen, when one of these currents is zero, the other is at its greatest value, so that if we run both into
26
HANDBOOK ON ENGINEERING.
the same circuit, the lowest value of the combined current would be equal to the maximum of either one of the single currents, and the maximum value would be equal to the sum of the two currents when the coils are on the eighths of the revolution.
Fig. 38. Showing effect of larger number of coils.
This resulting current is shown on the lower line in Fig. 38 by the curve d d. From this curve we see that the number of fluctuations in the current has been doubled, but the variation in the strength is greatly reduced. If we wound four coils upon the armature, as indicated by A B C Z>, in Fig. 37, the number of undulations in the combined current would be again doubled, but the fluctuation would be very much less. If the number of coils is increased to twenty-five or thirty, the fluctuations in the current become so small as to be hardly worth noticing.
With coils such as shown in Fig. 26, a separate commutator would have to be provided for each coil, and this would render the machine very complicated, if the number of coils were even six or eight ; hence, in actual machines, the winding of the coils is modified so as to be able to use a single commutator for any number of coils. This construction will be explained in the next chapter.
HANDBOOK ON KNOINKKRING.
27
CHAPTER III. TWO POLE GENERATORS AND MOTORS.
The simplest type of armature winding is that used with ring cores, and is illustrated in Fig. 39. As will be seen, it is simply a continuous winding all the way around the circle, the end of the last turn of wire being connected with the beginning of the first turn, so as to form an endless coil. If wires are attached at a and &, and a current is passed through, it will divide into two halves, one part flowing through the wire above a 6, and the other part through the wire below a b. In the upper half of the wire, the direction of the current in the front sides of the turns will be toward the center of the ring, as is indicated by the arrow heads, and in the lower half it will be away from the center. If, in-
Figs. 39 and 40. Windings on ring armatures.
stead of attaching wires at a and b we place stationary springs, so as to press against the wire, then we could revolve the ring, and still the current would enter and leave the wire at the same points. Small armatures are often made in this way, but for regular
28 HANDBOOK ON ENGINEERING.
.
machines it is more desirable to provide a commutator as shown in Fig. 40 at (7, and then the several segments can be connected with the wire at regular intervals. In the figure, the commutator is provided with twelve segments, and these connect with the armature wire at every fourth turn, so that the wire is divided into twelve coils of four turns each.
The only difference between this diagram and a regular gen- erator armature of the ring type, is that it shows the wire coils spread out with a considerable space between them, and only in one layer, while in the actual machine, the wire is wound close together and generally, in several layers; but no matter how many layers there may be, or how many turns in a coil, the principle of winding is the same.
We have shown the ring winding first, because it is so simple that it can be understood with the most superficial explanation. The drum winding, which is used to a much greater extent, is the same in principle as the ring, but owing to the fact that the coils cross each other at the ends, it appears to be decidedly different. By the aid of Figs. 41 to 44, the drum winding can be made per- fectly clear.
Fig, 4J shows a ring armature core with a single coil wound upon it ; and Fig. 42 shows a drum core, with a single coil wound upon it. In the ring, only one side of the coil appears upon the outer surface of the armature, but in the drum, as there is no open space for the coil to thread through, both sides of the coil must be placed upon the outer surface. The side B of the coil may be called the live side, as it is the one from which the ends project, and the lower side c, may be called the dead side. Since only the live side of the coil has ends to be connected, it can be readily seen that if in the drum winding we leave spaces between the live sides for the dead sides, and then connect the ends of the live sides by jumping over the dead side between them, that we will have the same order of connection as in the ring winding.
HANDBOOK ON ENGINEERING.
b
29
Fig. 41. Ring armature core. Fig. 42. Drum armature core.
The dead side of each coil adjoins the live side of a coil that is, in reality, half a circumference away from it; thus, in Fig. 43, the live side of coil a is at the top and the dead side is at the bottom ; while the live side of coil n is at the bottom and the dead side is at the top. The live sides of these two coils are on opposite sides of the armature, so that the coil side to the right of a is simply
Figs. 43 and 44. Windings of drum armature.
30 HANDBOOK ON ENGINEERING.
the dead side of a coil whose live side is on the other side of the armature. In Fig. 44 the two coils a and b are adjoining coils, for the coil side between them is the dead side of coil n,. To con- nect the armature, therefore, we join end 2 of coil a with end 1 of coil Z>, and the end 2 of coil b would jump over a dead sjdeand connect with end 1 of coil c. Coil c, however, would appear to be two coils ahead of £>, just as b appears to be two coils ahead of a.
In winding drum armatures, the coils are generally placed in pairs, as shown in Fig. 43 and also in Fig. 44. The object of this is simply to make the ends of the armature look more even. A drum armature can be wound out of a continuous wire, by simply making a loop to take the place of the ends 1 and 2, and then skipping a space, as shown by coils a and b in Fig. 44. After the armature is half covered, there will be spaces left between the coils, these spaces being of the width of a coil ; we then proceed to fill up the vacant spaces, and when they are all filled, the last coil put in will be the proper position to connect with the first one wound. A little practice with a piece of twine and a wooden cylinder, will enable any one to find out in short order how to wind drum armatures.
The two types of winding just explained, are those used with two pole machines,- motors as well as generators. It may be added that there is no difference, electrically, between a motor and a generator, and any machine can be used for either service. Motors, however, are somewhat modified in design so as to make them more suited to the work they have to perform. The modi- fication consists mainly in protecting the parts liable to be injured by objects falling upon them.
The general arrangement of the field and armature in a two pole machine is shown in Fig. 31. The design can be changed in a vast number of ways, but it will always be two- pole, or bipolar, as it is called, if only two poles are presented to the armature.
HANDBOOK ON ENGINEERING.
31
Generators and motors are arranged so that the current that magnetizes the field may be the whole current that flows in the circuit, or only a part of it. When the whole current passes through the field magnetizing coils, the machine is said to be of the series type ; this name being given because the armature wire and the field coils are connected in series, so that the current first passes through one and then through the other. If the field coils are traversed by only a portion of the current, the machine
Fig. 45. Showing series connection. Fig. 46. Showing shunt connection.
is said to be of the shunt type, owing to the fact that the field is supplied with a current that is shunted from the main circuit. Generators and motors are also arranged so that there are two sets of field coils and one is traversed by the whole current, and the other by a portion thereof. The best way to understand these different types of connection is by means of simple diagrams that show the wire coils of the field and the outline of the arma- ture. Such diagrams are presented in Figs. 45 to 50. Fig. 45
32
HANDBOOK ON ENGINEERING.
represents the series connection, A being the armature, C the commutator, and M the field coil. The direction of the current is indicated by the arrow heads. Fig. 46 is the shunt connection, and the arrow heads show the direction of the currents in the case of a generator. As will be seen, at d the field current branches off from the main line and returns to it at a, after having passed through the field coil. Fig. 47 shows the type in which the field is magnetized by two sets of coils, one being in series with the main circuit and the other in shunt. As will be noticed, all the armature current passing out through wire d, goes through coil F, except the portion that is shunted at c, into the shunt coil M. This type of winding is called compound, being a combination of the series and shunt. When the shunt coil is connected as in
Fig. 47. Field magnetized by two sets of coils.
Fig. 48. Illustrating long shunt.
Fig. 47, it is called a short shunt, and when as in Fig. 48, it is a long shunt. In the first case, the coil M shunts the armature only, and in the second, it shunts the coil F also.
HANDBOOK ON ENGINEERING. 33
Figs* 49 and 50 show the shunt and compound types for motors, and as will be noticed, the only difference between them and the generator diagrams, is that the direction of the current
Fig:. 49. Shunt type of motor.
Compound type of motor.
in the shunt coils is not the same. This difference in direction is due to the fact that in the generator the armature generates the current that passes through coil M; hence, at point d, the cur- rent flows up to the main line and down to the field coil. In the motor, the current comes from an external source through main 7i, and thus passes from a to the armature, and also to the field coil, thus traversing the latter in the opposite direction. In the series coil F, the direction of the current is the same in both machines.
Generators are made so as to keep the strength of the current constant, and allow the voltage to vary as the demands of the service may require ; or they may be wound so as to keep the voltage constant and allow the current strength to vary. Machines
34 HANDBOOK ON ENGINEERING.
of the first class are called constant current, and are used principally for arc lighting. Machines of the second class are called constant potential and are the kind used for incandescent lighting, for electric railways and for the operation of motors of every description. For constant current generators the series winding is used in connection with some kind of regulating device that prevents the current strength from varying more than the small fraction of an ampere. The shunt and compound windings are used for constant potential genera- tors. If the armature wire had no resistance, the shunt winding would enable a generator to maintain a constant voltage at its terminals, no matter how much the strength of the current might vary ; but armatures without resistance cannot be made ; there- fore, a shunt-wound machine will develop a slightly lower voltage with full current than with a weak one, but the difference will not be more than three to five per cent. By the aid of the com- pound winding, the generator can be made so as to develop the same voltage with light or full load, and if desired, the voltage can be made to increase as the current increases. If a com- pound generator is so proportioned that the voltage is the same for weak and strong currents, it is said to be evenly-compounded, and if the voltage increases as the current increases, it is said to be over-compounded. If the voltage is five per cent higher, with full load than with no load, the generator is said to be over-com- pounded five per cent, and if the increase is ten per cent, it is said to be over-compounded ten per cent.
The way in which a compound generator increases the volt- age can be readily understood from an examination of Fig. 47. The current that passes through the shunt coil M, is practically one of the same strength at all times ; therefore, the magnet- izing effect of this coil does not change. Through coil F the whole current passes, hence, the magnetizing effect of this coil increases as the current strength increases. Now the total field
HANDBOOK ON ENGINEERING. 35
magnetism is that due to the combined action of the two coils, so that as the action of F increases, the strength of the field in- creases. If F has only a few turns of wire, it will only help slightly to magnetize the field ; therefore, its increased effect, due to increase in current, will not be very noticeable ; but if F has many turns, it will develop a large proportion of the field magnet- ism, and, under this condition, the change in current strength will make a decided change in the strength of the field, and thus in the voltage, for the voltage is directly proportional to the strength of the field.
In motors, the coil F can be connected so as to act with coil Jf, or against it. If both coils act together, the motor is compound-wound ; and if F acts against M, the motor is differ- entially-wound. A compound- wound motor will slow down more with a heavy load than a simple shunt machine, but it will carry the load with a smaller current, and, on this account, this wind- ing is commonly used for elevator motors. A differential motor will hold up the speed better with a heavy load than a simple shunt machine, but it will take a correspondingly larger current to do the work. The differential winding is not used to any great extent, except in cases where it is desired to obtain as uniform a velocity as possible.
In explaining the principles of armature winding, it was shown that the commutator brushes must make contact with the com- mutator on the sides, that is, that in Fig. 51, they would be placed on the diameter n n. In actual machines, they are either ahead of this line, as in Fig. 52, or back of it, as in Fig. 53. The first position is that of the generator and the second that of the motor. The reason why the brushes have to be set ahead of line n n in a generator, and back of the line in a motor, is that the armature current develops a magnetization of its own, and this reacts upon the magnetism of the field so as to twist the lines of force out of their true path. If we look at Fig. 39, we can see
36 HANDBOOK ON ENGINEERING.
that the direction of the current through the wires is such that the magnetizing effect produced upon the armature core is the same as it would be if the wire were wound in the way indicated by the vertical lines in Fig. 51. Now this current will develop a magnetization in the direction of line nn; that is, at right angles to the field magnetism. These two magnetic forces of the arma- ture and the field, engage in a tug of war, and the result is that the actual magnetization that acts upon the armature wire is the combined effect of the two. ' If the strength of the field magnetism
Fig. 51. Fig. 52. Fig. 53.
Showing proper position of brushes.
is proportional to line c a, and the strength of the armature mag- netization is proportional to line c &, then the actual magnetiza- tion will be equal to line c d, and in the direction d d. In Fig. 52, which represents a generator, if the current in the field coils passes over the front side in the direction of arrow *', and the armature revolves in the direction of arrow cZ, then the armature current will be in the direction of arrow / and the armature mag- netization will be in the direction of arrow h. The field magneti- zation will be from N to $, therefore, the resulting magnetization will be in the direction of line a a. Now the proper position for
HAMDBOOK ON ENGINEERING.
37
the brushes is on a line at right angles to the direction of the field, hence, they mast rest upon line c c. If the machine is a motor, the only change effected will be that the direction of the armature current will be reversed, so that arrow / will point downward instead of upward, and the magnetism of the armature will be directed to the right as shown by arrow c. Under these conditions, the actual direction of the field magnetism will be that of line b &, and upon line e e, at right angles to this the brushes must be set.
WIRING TABLE FOR 110- VOLT, 16 CANDLE POWER LAMPS.
(Size of Wire in B. & S. Gauge.)
|
«w cc o p, 2* ^^ |
DISTANCE IN FEET TO CENTER OF DISTRIBUTION. |
||||||||||||||||
|
20 |
25 |
30 |
35 |
40 |
45 |
50 |
60 |
70 |
80 |
90 |
100 |
120 |
140 |
160 |
180 |
200 |
|
|
2 |
20 |
19 |
19 |
19 |
19 |
19 |
19 |
19 |
18 |
18 |
17 |
16 |
16 |
15 |
15 |
14 |
13 |
|
3 |
19 |
19 |
19 |
19 |
19 |
18 |
18 |
17 |
16 |
16 |
15 |
15 |
14 |
13 |
13 |
12 |
12 |
|
4 |
19 |
19 |
19 |
18 |
18 |
17 |
16 |
16 |
15 |
14 |
14 |
13 |
13 |
12 |
11 |
11 |
10 |
|
5 |
19 |
19 |
18 |
17 |
16 |
16 |
16 |
15 |
14 |
14 |
13 |
13 |
].' 11 |
11 |
10 |
10 |
|
|
6 |
19 |
18 |
17 |
16 |
16 |
15 |
15 |
14 14 |
13 |
13 |
12 |
11 |
11 |
10 |
10 |
9 |
|
|
7 |
18 |
17 |
16 |
16 |
15 |
15 |
14 |
14 |
13 |
12 |
12 |
11 |
11 |
10 |
9 |
9 |
8 |
|
8 |
18 |
17 |
16 |
15 |
15 |
14 |
14 |
13 |
12 |
12 |
11 |
11 |
10 |
9 |
9 |
8 |
8 |
|
9 |
17 |
16 |
15 |
15 |
14 |
14 |
13 |
12 |
12 |
11 |
11 |
10 |
9 |
9 |
8 |
8 |
7 |
|
10 |
17 |
16 |
15 |
14 |
14 |
13 |
13 |
12 |
11 |
11 |
10 |
10 |
9 |
8 |
8 |
7 |
7 |
|
12 |
16 |
15 |
14 |
14 |
13 |
13 |
12 |
11 |
11 |
10 |
10 |
9 |
8 |
8 |
7 |
7 |
6 |
|
14 |
15 |
14 |
13 |
13 |
12 |
12 |
11 |
10 |
10 |
9 |
9 |
8 |
7 |
7 |
6 |
6 |
5 |
|
16 |
15 |
14 |
13 |
12 |
12 |
11 |
11 |
10 |
9 |
9 |
8 |
8 |
7 |
6 |
6 |
5 |
5 |
|
18 |
14 |
13 |
12 |
11 |
11 |
10 |
10 |
9 |
9 |
8 |
8 |
7 |
6 |
6 |
5 |
5 |
4 |
|
20 |
14 |
13 |
12 |
11 |
11 |
10 |
10 |
9 |
8 |
8 |
7 |
7 |
6 |
5 5 |
4 |
4 |
|
|
25 |
13 |
12 |
11 |
10 |
10 |
9 |
9 |
8 |
7 |
7 |
6 |
6 |
5 |
4 |
4 |
3 |
3 |
|
30 |
12 |
11 |
10 |
10 |
c |
8 |
8 |
7 |
6 |
6 |
5 |
5 |
4 |
a |
3 |
3 |
2 |
|
35 |
11 10 |
10 |
9 8 |
8 |
7 |
7 |
6 |
K |
5 |
4 |
4 |
3 |
2 |
2 |
1 |
||
|
40 |
11 |
10 |
c |
8 8 |
7 |
7 |
6 |
5 |
B |
4 |
4 |
3 |
2 |
1 |
1 |
1 |
|
|
45 |
10 |
9 |
8 |
8 7 |
7 |
6 |
5 |
^ |
4 |
4 |
3 |
2 |
2 |
1 |
1 |
0 |
|
|
50 |
9 |
c |
8 |
7 |
7 |
6 |
6 |
5 |
4 |
4 |
3 |
3 |
2 |
1 |
1 |
0 |
0 |
|
60 8 70 7 |
8 7 |
7 7 |
7 6 |
6 5 |
6 5 |
5 4 |
4 4 |
CO CO |
c o 2 |
2 2 |
2 1 |
1 1 |
1 0 |
0 0 |
|||
|
80 |
6l 6 |
6 |
5 |
5 |
4 |
4 |
3 |
2 |
2 |
1 |
1 |
u |
0 |
||||
|
90 |
6 |
6 |
f |
5 |
4 |
4 |
J |
2 |
2 |
1 |
1 |
0 |
0 |
||||
|
100 |
5 |
5 |
5 |
4 |
4 |
3 |
3 |
2 |
1 |
1 |
0 |
0 |
38
HANDBOOK ON ENGINEERING.
CHAPTKJLt IV. MULTIPOLAR MACHINES.
The only difference between a bipolar and multi polar machine is, that the latter has two poles, and the former has two or more pairs of poles. In consequence of this difference in the number
Fig. 54. Showing four-pole machine.
of poles, the armature winding has to be slightly modified, as will be presently explained. Fig. 54 illustrates a four-pole machine
HANDBOOK ON ENGIN BERING.
39
and, as will be noticed, the N and S poles alternate around the circle. This arrangement is followed, no matter what the number of poles may be.
The advantage of the multipolar construction is that it in- creases the capacity of the machine for a given size and weight. Figs. 55 to 57 illustrate the gain effected in weight. The first figure shows a two-pole machine, the second a four-pole and the third an eight-pole, the three being of the same capacity. The poles of the second machine are half as wide as those of the first, as there are twice as many. The other parts are reduced in like proportion. In Fig. 57, the poles are one-quarter as wide as in
Fig. 55. Fig. 56. Fig. 57.
Effect of increasing the Dumber of poles.
Fig. 55, as there are four times as many. On account of the reduction in the width of the poles, the armatures can be increased in diameter as the number of poles is increased, without increas- ing the outside dimensions of the machine, so that in reality, Fig. 56 is somewhat more powerful than Fig. 55, and Fig. 57 is still more powerful.
The fields of multipolar machines are wound the same as those of the bipolar ; that is, as series, shunt or compound. Figs. 58 to 60 show the three types of winding for a four-pole machine and Fig. 61 is a diagram of compound winding for an eight-pole generator. The number of commutator brushes used is equal to the number of poles, although with one type of armature
40
HANDBOOK ON ENGINEERING.
winding, two brushes are sufficient, no matter how many poles the machines may have. In practice, however, even with this winding, the number of brushes is generally made equal to the number of poles.
With a four-pole machine the brushes can be connected in a simple manner, as shown in Figs. 58 to 60, but with a greater number of poles, two rings are generally provided, to which the brushes are connected in the manner shown in Fig. 62.
Figs. 58 and 59. Connection of brushes on four-pole machine.
Looking at Fig. 54, it can be seen that if the current flows up from the paper, under the N poles, it will flow down through the paper, under the S poles ; hence, the armature coils in a four- pole machine must span only one-quarter of the circumference, and not one-half, as in the two-pole armature. For a six-pole armature, the coils must span one-sixth of the circumference, and for an eight-pole, one-eighth, and so on, for any higher number of poles.
There are two types of winding for multipolar armatures, one being called the lap, or parallel winding, and the other the wave
HANDBOOK ON ENGINEERING.
41
42
HANDBOOK ON ENGINEERING.
or series winding. Fig. 62 is a diagrammatic illustration of the lap winding, and Fig. 63 of the wave winding, both for four poles.
Fig. 62. Diagram of lap winding.
The small circles around the outside of the armature represent bars or wires, which are connected with the commutator segments by means of the solid lines, and with each other at the opposite side of the armature, by means of the broken lines.
If we start from coil side, or bar 1 on the left, and follow the connections as guided by the numbers, we will finally reach 32, and thus come back to left side brush a, which is the starting point. As will be seen, bar 1 connects at the back of armature,
HANDBOOK ON ENGINEERING.
43
with bar 2, and then over the front, the connection runs in the backward direction, to bar 3 ; thence, forward again, at the back end, to bar 4, and again backward over the front, to bar 5. The connections, therefore, lap over each other and it is on this account, that it is called a lap winding.
Fig* 63 shows the wave winding, and it will be noticed that if we start from bar 1 at the top, we advance around the right to bar 2, and then we go further ahead to bar 3, and in like manner advance to bar 4, the connections in every case advancing in the
Fig. 63. Diagram of wave win
same direction around the circle. It will be further noticed that the connections run zig-zag from side to side of the armature core
44 HANDBOOK ON ENGINEERING.
as they advance, thus forming a wave-like path for the current, and it is on this account that this style of connection is called wave winding.
With the lap winding, the brushes a a are connected with each other, and so are the b b brushes. In the wave winding, two brushes set one-quarter of the circle from each other, will take the current off properly as indicated by a and b in Fig. 63, but four brushes can also be used.
In Fig* 54, the brushes are shown midway between the poles, while in Figs. 62 and 63, they are opposite the poles. This dif- ference in position is due to the fact that in the last two named figures, the connections between the armature coils and the com- mutator segments do not run in radial lines from either side, but one connection bends backward and the other forward. In actual machines, the connections are run as in these diagrams, and in some cases, one of the sides runs in a radial direction; there- fore, in some generators, the brushes are opposite the poles, and in others they are between them.
Diagrams 62 and 63 show coils of a single turn, but by regard- ing the broken lines as representing the position of the end of the coil at front as well as the back of the armature, and the solid lines as simply the ends of the wire that connect with the com- mutator segments, they become accurate representations of coils of any number of turns.
The coils of multipolar armatures are made on forms, and in the finished state are placed upon the armature core. Some coils are so formed as to bend down over the ends of the armature, and are then given the form at the ends, shown in Fig. 64, so they may fit into each other. In some machines, the coils do not bend down over the ends of the armature, but run out parallel with the shaft. Armatures so wound are sometimes said to have a barrel winding, and the coils, if laid out upon a flat surface, would present the appearance of Fig. 65 ; that is, if they con-
HANDBOOK ON ENGINEERING.
abed
45
Figs. 64 and 65. Armature windings.
tained more than one turn. If of the single-turn type, they would look like Fig. 66, if for a lap winding; and like Fig. 67, if for a wave winding, the ends d d being joined and then con- nected with the commutator segments.
In connecting the field coils of multi polar machines, it is necessary to be careful not to make mistakes, so that some of the
abc
ab c
d ' 'd d
Figs. 66 and 67. Drum and barrel windings
46 HANDBOOK ON ENGINEERING.
coils will act to magnetize the field in the wrong direction. By studying Fig. 27 and the explanation of it, the direction of the magnetic lines of force with respect to the direction of the current through the magnetizing coils, can be clearly understood, and then there will be no difficulty in determining the proper way in which to connect the coil ends, for all we have to do is to make the connections such that if one pole is N the one next to it is S. With two-pole machines, it is also necessary to be careful not to connect the field coils improperly; that is, if there is more than one coil, and in most machines this is the case.
The current that energizes a magnet is called the magnetizing force and is measured in ampere turns. The ampere turns are obtained by multiplying the number of turns of wire in coil, by the amperes of current flowing through it.
All forms of matter resist the development of magnetic force. This resistance is called magnetic reluctance. The reluctance of air is much greater than that of iron or steel, but is constant; that of iron and steel is not. If one thousand ampere turns develop a certain magnetic density in a circuit composed wholly of air, two thousand ampere turns will double this density. In iron and steel it will require much more than double the ampere turns to double the magnetic density.
If in a magnetic circuit ten inches long, 100 ampere turns develop a certain density, it will require 200 ampere turns to develop the same density if the magnetic circuit is double the length.
HANDBOOK ON ENGINEERING. 47
CHAPTER V.
SWITCH-BOARDS, DISTRIBUTING CIRCUITS AND SWITCH- BOARD INSTRUHENTS.
Generators of the constant potential type are made so as to develop a certain voltage at a given velocity, but in some cases it is not practicable to run them at the exact speed for which they are designed ; and in others, it is desired to vary the voltage slightly, hence, all machines are provided with means for chang- ing the e.m.f. slightly. This regulating device is also necessary in cases where the load is for a time light, and for the balance of the time heavy ; for, as we have shown, the voltage will vary to some extent with changes in the strength of the current. If the generator is at some distance from the points where the cur- rent is used, the drop of voltage in the lines will be greater with strong currents ; hence, when the load is heavy, it is necessary to increase the voltage developed by the generator. As it is not advisable to change the speed of the engine, the variation of volt- age is obtained by changing the strength of the current that flows through the shunt field coils, and this is accomplished by providing a resistance that can be cut in or out of the shunt coil circuit, as is illustrated in Fig. 68, in which R represents the resistance, or field regulator, as it is called. When the lever is moved to the extreme left position, all the regulator resistance is cut out of the circuit, and then the voltage of the generator is the highest that can be obtained with the speed at which it is run- ning. When the lever is moved to the extreme right, all the resistance of the regulator is introduced into the shunt coil cir- cuit, and then the voltage is the lowest. By placing the lever in
48
HANDBOOK ON ENGINEERING.
intermediate positions between the extremes right an-d left, differ- ent voltages may be obtained.
To be able to operate a generator furnishing current to a sys- tem of distributing wires, it is necessary to have a number of
a,
d
R
Fig. 08. Resistance regulator for shunt coil.
instruments and other devices, included in the circuit, some of which are absolutely indispensable, and others of which are simply conveniences, and may be looked upon as luxuries. The various devices required are shown in Fig. 69. The generator is shown at M, and at e the field regulator is placed, and it is connected with one of the generator armature terminals and with one end of the shunt coil wires by means of wires cif d. The wires c c run from the generator terminals to the voltmeter F, and thus enable us to see what the voltage is at all times. Wires a and b convey the current to the external circuit, with which they can be connected or disconnected by means of switches ss ss. At A an ammeter is placed which indicates the strength of current in
HANDBOOK ON ENGINEERING.
49
amperes. The ammeter can be placed in either a or 6, as the same strength current flows in both. At// safety fuses are pro- vided, so as to open the circuit in case the current becomes so strong as to be capable of overheating the generator wire. If one of the line wires runs out into the open air, and is carried along on poles, we will have to provide a lightning arrester, as shown at ft, this being connected with the ground as at g. If both lines run into the open air, an arrester must be placed in both ; and if both are confined to the interior of a building, no arresters will be required. From the points m m branch circuits may be run off in as many directions as necessary, and by providing switches s s, these can be connected or disconnected from the main line when desired.
This crude arrangement would enable us to operate the system successfully, but it would not be so convenient as a more methodi-
Fig. 69. Instruments required in the circuit.
cal grouping of the several devices and instruments. It repre- sents the way things were done in the early days of electric light- ing, but at the present time, instead of having the several parts scattered about in a helter-skelter fashion, they are all assembled
4
50
HANDBOOK ON ENGINEERING.
upon a large panel, which is called a switch-board. Fig. 70 give the general arrangement of wiring and location of devices for i simple board arranged for one generator feeding into five externa
\n \P
Fig. 70. General arrangement of switchboard.
HANDBOOK ON ENGINEERING. 51
cated by the lines n _p, //, being safety fuses. The wires i i con- vey the main current from the generator to a circuit breaker Z>, which is simply a switch that is constructed so that it will open automatically when the current becomes too strong. From the circuit breaker, the current passes through wires a and b to the main switch F, and by wire c, it runs from here to the ammeter A and from the latter by wire c? to a rod 1 which is called a bus bar. The upper side of the main switch is connected directly with bus 2. The voltmeter is connected with two busses by the wires e e. The field regulator is located back of the board at J£, and is connected in the shunt coil circuit by means of wires h h. The switch of the regulator E is connected with a hand-wheel on the front of the switch-board, so that the attendant can watch the voltmeter as he turns the wheel and thus see just what affect the movement is producing on the voltage.
In addition to the devices shown in Fig. 70, we can, if desired, provide a recording ammeter, a recording voltmeter and a watt- meter ; the first two would give us a record of the amperes and volts for a certain length of time, generally 24 hours, and the last one would register the amount of electrical energy. We could also provide ammeters for each one of the distributing cir- cuits, so as to know the strength of current in each one.
If we desire to arrange the switch-board for two generators, and these are of the shunt type, we will require no changes in Fig. 70, except to provide another regulator and a main switch and circuit breaker for the additional machine. This arrange- ment of board is suitable for a single compound wound generator", or any number of shunt wound machines, but if we have two or more compound generators, the connections between these and the bus bars will have to be somewhat modified.
The modifications required in a switch-board for two or more compound generators can be made clear by the aid of Figs. 71 and 72, In the first figure, we can see that if the current return-
52
HANDBOOK ON ENGINEERING.
ing from the main line through n divides into wires a and 6, it will remain divided until it passes through the armatures and the F coils of the two machines, and thence through wires e e, it will
Fig. 71. Connections from machines to switchboard.
reunite again in wire p. In Fig. 72, the two parts of the current will flow through wires d d to the single wire e, and then divide into wires//, and thus reach the coils F F, and, finally, through wires h 7i, reach p. In Fig. 71, if the right side armature gen- erates more current than the other one, the F coil of that gener- ator will be traversed by the strongest current, for in each machine the strength of current in the armature and the F coil will be nearly the same. Now, if the right side machine generates the strongest current, it is because its voltage is the highest, but the fact that its F coil will be traversed by the strongest current will make its voltage still higher, thus increasing the difficulty. In Fig. 72, the current flowing through the two F coils will be the same, no matter how much the two armature currents may differ,
HANDBOOK ON ENGINEERING.
53
for these come together in wire e, and passing from this to the two F coils, the current will divide in equal amounts. As can be seen, the effect of adding the wires d d, e and //in Fig. 72 is to equalize the currents that flow through the F coils, and thus pre- vent, as far as possible, the unequal action of the generators.
When two or more compound generators are connected so as to feed into the same general circuit, the connections are made in accordance with Fig. 72. Fig. 73 illustrates a switch- board for two compound generators, and, as will be noticed, the most striking difference between it and Fig. 70, is that there are three bus bars instead of two. One of these busses is called the equalizer, and it takes the place of wires d d e and
Fig. 72. Arrangement of equalizing connections.
//in Fig. 72. The equalizing connections run from generator wires/ to the main switches S, and thence to bus 1. The h wires of the generators run to one side of the circuit breakers D E,
54
HANDBOOK ON ENGINEERING.
and thence to the middle blades of the S switches, and from these to the bus 2. The generator wires run to the outside blades o:
•
ff
Fig. 73. Switchboard for two compound generators.
the circuit breakers, and from these to the ammeters A A, anc thence to bus 3. The voltmeters are connected with wires k am /, and thus indicate the e.m.f.'s of the generators.
HANDBOOK ON ENGINEERING. 55
If another generator were added, it would be connected with the bus bars in the same way.
In starting two or more compound- wound generators, one machine is started first, and then the second is run up to full speed, and its voltage is adjusted by means of the regulator R, so as to be the same as that of the machine that is running. When the voltages of the two machines are equal, the main switch of the second machine is closed so as to connect it with the bus bars. This action will generally make a slight change in the voltage of the second machine, causing it to run up or down a trifle ; and as a result by looking at the ammeters, we will find that it is taking more or less than its share of the load. If such is the case, we manipulate the regulator R, until the loads are properly divided. Whether the voltage of the second machine will rise or fall after it is connected with the bus bars, will depend upon the extent to which it is compounded ; if slightly compounded, the voltage will drop, and if heavily compounded, it will rise.
The switch-boards illustrated are adapted to what is called the two- wire system of distribution, but in cases where it is desired to transmit the current to a considerable distance, without using extra large wire, the three-wire system of distribution is employed. This system is illustrated in Figs. 74 to 76.
Suppose we have two generators as indicated at G O in these diagrams, and let the direction of the current through both be from bottom toward the top ; then it is evident, that if we remove the middle wire 0, the lower machine will deliver current into the upper one, and if each generator develops an e.m.f. of 115 volts, the combined e.m.f. will be 230 volts, and this will be the pressure between the bottom and top wires ; but the voltage between either wire and the center one will only be 115. Suppose we have a number of lamps connected between wire P and the center wire 0, and an equal number of lamps between 0 and N, as \s shown in Fig. 74 ; then it is evident that the same amount
HANDBOOK ON ENGINEERING.
of current will flow through both sets, arid as a consequence, a the current that passes from the upper generator into wire P wi go directly through both sets of lamps to the lower wire N, an thus return to the lower side of the bottom generator. Und<
Arrangements of three- wire system.
these conditions, the lamps will be acted upon by 115 volts eact but the current will be driven through the circuit by a voltage c 230. Now, if the voltage is doubled, four times the number c lamps can be supplied with the same size wires ; hence, the cos of line wire per lamp will be reduced to one-fourth. Suppose that instead of having the lamps equally divided as in Fig. 14
HANDBOOK ON ENGINEERING. 57
they are arranged as in Fig. 75 ; then since the current fed into the system from the upper wire P is only sufficient for five lamps, while there are seven lamps in the lower section, it follows that through wire 0 a current sufficient for two lamps must be sup- plied. The way in which the currents would flow in this case is clearly indicated by the arrows.
In Fig* 74, it will be seen that if we removed the middle wire, the lamps would not be affected, for none of the current comes through it; but in Fig. 75, if we cut the middle wire, two of the lower lamps would be unprovided for. From this it will be seen that the object of the middle wire is simply to provide the extra current required for the side that carries the largest number of lamps. If the lights are so arranged that on both sides of the central wire 0 the number is practically the same at all times, the center wire can be made very small, but such perfect balance cannot be obtained always, and on that accouut, the center, or neutral wire, as it is called, is made of the same size as the others, except in large systems, in which it is sometimes not more than one-third the size.
As motors require large amounts of current, they are nearly always made to operate with a voltage of 230, and are connected with the outside wires of the system, as is shown in Fig. 76, in which a a a a and c c c c indicate lamps connected between the sides and the neutral wire, and ABC are motors connected across the outside lines.
When a switch-board is arranged for two generators connected with a three-wire system, we use three bus bars, just as in Fig. 70, but discard the equalizing connection, and connect the generators with the busses in the same way as they are connected with wires N 0 and P in Figs. 74 to 76. If we have a number of generators feeding into the three- wire system, then we connect each set with an equalizer bus; that is, provide two sets of busses, and the P and N busses of these two sets we connect
58
HANDBOOK ON ENGINEERING.
with a third set in the proper order for the three-wire system, and from the latter busses the external circuits are fed.
If we desire to supply a larger building with a lighting and power system, we can run the wires in almost any way, providing we make connections with the lamps and motors, but if we adopt
Fig. 77. Light and power system for building.
a systematic arrangement it will require less labor to operate the plant, and when anything goes wrong we will be able to locate the difficulty with much less trouble and in less time. The best way to accomplish this is by the use of small switch-boards located at different points in the building, these becoming centers
HANDBOOK ON ENGINEERING. f)9
of distribution, from which all the lamps are supplied. The general arrangement of such a system dan be understood from Fig. 77, in which B represents the main switch-board, located in the engine room, and e e e the several floors upon which the lights are located. From the main switch-board we run up four lines, one to each floor, and locate secondary boards at C C and D DD. We can also run out lines directly from the board to the lamp circuits as at c c c c. From the boards C (7, we run circuits to smaller boards, as shown at J5J, F, A, A, A, and b b b. From each one of these small boards we can run out circuits to the lamps.
These small switch-boards are called panel boards or boxes, and also distribution boards. They are made of all sizes from eight or ten inches square, up to four or five feet, and are arranged to feed into one or two, or fifty or sixty circuits, supplying anywhere from five or six lights up to a thousand or more.
The construction of distribution boards can be understood from Figs. 78 and 79, the first being arranged for the three- wire system, and the second for the two- wire. Fig. 78 is ar- ranged to feed ten circuits, and is provided with one main switch by means of which the entire box can be disconnected from the main line. The distributing circuits are provided with proper safety fuses on the outside wires, so that if anything goes wrong and the current increases to a dangerous point, the circuit will be open. No fuse is placed on the middle wire, as it is not neces- sary, and might result in cutting out both sides of the circuit when only one was disabled.
Fig* 79 is a mor'e complete panel, because each one of the six distribution circuits is provided with a switch, so that it is pos- sible to disconnect any of the circuits without interfering with the others. In some cases a distribution board of this kind is the only thing that will answer the purpose, but in others, the more
60
HANDBOOK ON ENGINEERING.
simple construction of Fig. 78 answers just as well. The fuses in Fig 78 are shown at E F. These fuses are sometimes made so that they can be used as switches ; that is. they can be pulled out
Fig. 78. Board for three-wire system.
Fig. 79. Board for two-wire system.
of place and thus open the circuit, and if one blows out it can be removed and a new fuse be put in, and then it can be replaced, thus placing the disabled circuit in service without interfering with the others.
The ammeters and voltmeters used on switch-boards depend for their operation upon the repulsion between magnetic lines of force. A great many different constructions are used, but most of them operate upon the principles illustrated in Fig. 80 or 81. If a small bar of iron c is placed between the poles of a permanent magnet, as in Fig. 80, it will be held in the horizontal position by the attraction of the magnet. If it is surrounded by a stationary coil of wire &? through which a current of electricity passes, then
HANDBOOK ON ENGINEERING. 61
it will be under the influence of two forces, one the attraction of the poles N S of the magnet, and the other the attraction of the lines of foice developed by the current flowing through coil b. The action of the latter will tend to swing the rod c into the ver- tical position . The force of the magnet will remain constant, but the force of the coil will vary with the strength of the current passing through it ; hence, the stronger the current the more the bar c will be swung around into the vertical position. If we pro- vide a small counter- weight, as shown in the illustration, to resist the action of the coil, we will have a means that will enable us to adjust the movement of the bar, so that it will swing around through a given angle for a given increase in current. If a pointer a is secured to c it will swing over the scale as shown, when c is rotated by the action of the coil.
If coil b is mounted so that it may swing around the center pivot, we can discard bar c, for then as soon as a current traverses &, the lines of force developed around it will be attracted by
Figs. 80 and 81. Principles of ammeter and voltmeter.
those of the permanent magnet, and will exert a twisting force so as to place the axis of the coil parallel with the lines of force passing from N to S. In this case as in the previous case, the
6B HANDBOOK ON ENGINEERING.
effort to twist b around will be proportional to the strength of the current, hence, the stronger the current the greater the swing. Ammeters and voltmeters are made on these principles, and the only difference in the two instruments is in the size of the wire used for the coils.
Figs* 82 and 83 illustrate the principle upon which circuit breakers are made. In Fig. 82, suppose a current flows through magnet 2£, then it will attract the lever A, the latter being made
Figs. 82 and 83. Principles of circuit breakers.
of iron. If the current is weak it may not develop a sufficient attractive force in E to lift the weight D, and in that case A will remain where it is. If, however, the current is increased until E becomes strong enough to lift Z>, then A will move over toward the magnet, and the catch " a " falling behind it, will not allow it to return to its former position until placed there by hand. When A swings over, it carries J5, and thus breaks the connec- tion with C and opens the circuit. Thus it will be seen that by properly adjusting the weight D and the magnet E, we can set the device so as to open the circuit whenever the current reaches a certain strength. This is the principle upon which circuit break-
HANDBOOK ON ENGINEERING. 63
•*rs act, but such a device as Fig. 82 would be of no service for lighting circuits, because the distance by which 0 and B are separated is too small to break the current. By modifying the construction as in Fig. 83, we can obtain a device that will give a wide separation at the breaking point. In this construction , the lever A when drawn towards the magnet, strikes the catch a, so as to release lever .B, and then the weight D throws the latter down to the position shown in broken lines, thus giving a wide separation between F and (7. By moving the weight on the lower arm at A, the device can be adjusted so as to act with different strengths of current.
Circuit breakers as actually constructed, do not have the appearance of this diagram, but they operate on the principle illustrated by it.
The electromotive force in volts developed in the armature of a motor, or generator, can be determined if we know the number of wires upon the outer surface, the number of maxwells of mag- netic flux that pass through the armature, and the revolutions per second. The rule for the calculation is as follows : —
Multiply the number of wires on the outer surface of the arma- ture by the maxwells of magnetic flux and by the revolutions per second, and divide this product by 100,000,000.
This is the rule for two pole armatures. For multipolar arma- tures with series, or wave winding, use same rule making the flux equal to the sum of the fluxes issuing from all the positive poles.
For multipolar armatures with a lap, or parallel winding, use same rule but take the flux issuing from one pole only.
To obtain the pull in pounds of a motor armature at one foot radius use the following rule : —
Multiply the number of wires on the outer surface of armature by the amperes of armature current, and by total number of max- wells of magnetic flux passing through armature, and divide this product by 852,000,000. See pages 13 and 46.
64 HANDBOOK ON ENGINEERING.
'
CHAPTER VI.
ELECTRIC MOTORS.
'
Motors are made so as to run at a constant velocity, or for variable speed. For the latter type of machine, the field coils are wound in series, and for constant speed the shunt winding is used. A motor of either kind cannot be started successfully without placing an external resistance in the armature circuit, because, when the armature is at a standstill, there is nothing but the resistance of the wire to hold the current back, and as a result, if no extra resistance is provided, the first rush of current would be very great. As soon as the armature begins to revolve, an e.m.f . is induced in its wires, and this acts in opposition to the e.m.f. of the line current ; that is, it acts like a back pressure, and holds the current back. On this account, the e.m.f. of a motor is called a counter e.m.f., and it is abbreviated into c. e.m.f.
The way in which the external resistance is connected with a motor is illustrated in Fig. 84, in which M is the motor and R the external resistance. D is a main switch, by means of which the motor is connected with the main line. This switch is closed first, and then switch F is moved to the right until it cov- ers the first contact of the resistance R. The current can then pass directly to the field shunt coils through wire e, and thence by wire a, return to the main line. The armature current, however, has to first pass through the resistance R, before it can reach wire i, and thus the armature. As soon as the armature begins to speed up, the switch F is advanced, step by step, and in a few seconds it is moved to the extreme right position, in which all the resistance R is cut out of the armature circuit. When F reaches this position, the motor should be running at full speed.
HANDBOOK ON ENGINEERING.
65
If the current should stop while the motor is running, the machine would stop, also, and then, if the current were turned on again, the motor would be caught with the armature connected across the line without an external resistance, and as it would be at a standstill, the current would rise to an enormous strength. To prevent this, the switch F is always opened whenever the motor stops. The attendant may forget to do this, however; therefore automatic switches have been devised that will open themselves whenever the current dies out.
Fig. 84. External resistance connected with motor.
A simple switch provided with a resistance so as to be suited to start a motor, is called a motor-starter, and one that in addi- tion is provided with means for automatically flying to the open position whenever the current fails, is called an automatic under- load starter.
If the motor is very much overloaded, its speed will slow down and the current will increase in strength. If the overload is suf- ficient, the current will become so strong as to be able to burn out
66
HANDBOOK ON ENGINEERING.
the armature ; hence, it is desirable to provide a circuit breaker that will open the circuit when the current becomes so strong as to be liable to burn out the machine. Motor-starters are made with a circuit-breaking attachment, and are then called automatic overload motor-starters. A device that combines the under and overload starter, features is called an automatic under and over- load starter, and by some people it is called -a u no voltage " and " overload starter."
When motors were first introduced, a great deal of trouble was experienced with the starters, owing to the fact that they were arranged so that when the motor was stopped, the connection with the field coils was broken. Now, the current flowing through the field coils objects to stop flowing when the connection is broken, and, consequently, it continues to flow between the end of switch F in Fig. 84, and the last of the contacts of R, until the distance is more than the e.m.f. of the current can overcome.
Principle of motor starter.
This action produces serious sparking at the last terminal, and in addition, produces a severe strain upon the insulation of the
HANDBOOK ON ENGINEERING. 07
field coils, because, as the current is headed off in one direction, it tries to find an outlet in another. This action is what is
Fig. 86. Another style of motor starter.
commonly called the "kick of the motor field." All this trouble can be obviated by connecting the starter with the motor in such a way that the field circuit is never opened, as is shown in Fig. 84. As this is quite an important device it is presented in a more simple form in Fig. 85, in which it will be seen that the field coils and armature are permanently connected, so that when switch S opens the circuit, the field current can flow through the armature, until it dies out. All first-class concerns make motor starters with this connection, at the present time. Some of them add the curved contact e. Without this contact, it can be seen that when the switch S is moved to the top position, the
68 HANDBOOK ON ENGINEERING.
resistance R is simply transferred from the armature to the field circuit, and that the current going to the field coils has to pass through this resistance. As this resistance is insignificant in comparison with that of the shunt coils, it makes little difference whether it is left in the field circuit or not, but by the addition of e it can be cut out.
Variable speed motors are always arranged so that the speed may be changed by hand as conditions may require. Trolley-car motors are of this type, and so are the motors used for printing presses, and many other kinds of work. Figs. 86 to 88 show arrangements by means of which the speed may be varied with series wound motors. In Fig. 86, E is the starting box and F is the speed regulator. In the act of starting, the switches are in the position shown. To start, the switch S and E is turned so as to close the circuit with the resistance R all included. S is moved toward the left as the armature speeds up, and reaches the last position when full speed is attained. If the switch of F is now closed, a portion of the current will be diverted from the armature, and thus its rotating force will be reduced, and thereby its speed. This method of speed control is also arranged so that the two switches act together, so as to introduce resistance into the motor circuit, and at the same time divert more or less of the current around the armature. It is not used extensively, as all the current that passes through F is just so much thrown away.
In Fig. 87 the speed is controlled by means of the switch F, which cuts out portions of the field coils and this changes the strength of the field. With this arrangement, if a portion of the field is cut out, the motor will run faster, because the c.e.m.f will be reduced, therefore, the armature current will be increased. To obtain a wide range of regulation, it is necessary to wind a large number of turns of wire on the field, so that with all the wire in service, the speed may be the lowest required.
HANDBOOK ON ENGINEERING.
69
Fig. 88 shows another arrangement that varies the strength of the field by diverting a portion of the current through switch F. It gives as wide a range of regulation as Fig. 87, but is not so economical.
Figs- 86 and 88 cannot be used to regulate the speed of shunt motors, but Fig. 87 can. The first two named figures, if used
Fig. 87. Regulator for shunt motor.
with a shunt motor, would simply afford a third path through which current could pass from one side of line to the other, that is, from the p to the n wires, but this would not materially affect the strength of current that would flow through the armature and field coils. They work with series wound motors, because the current is not shunted from wire p to wire n but simply from one side of the armature, or the field, to the other.
70
HANDBOOK ON ENGINEERING.
Fig* 89 shows an arrangement by means of which a shunt motor can be made for variable speed. In this case, the switch
Fig* 88. Device for varying strength of field.
and resistance E is simply an ordinary starter, and F is a resist- ance that is introduced in the field circuit, so as to vary the strength of the field. With this arrangement the slowest speed is obtained when all the resistance of F is out of the circuit.
The direction in which a motor runs can be reversed by sim- ply reversing" the direction of the current through the armature. Any of the arrangements for varying the speed can be used in connection with reversible motors by arranging the switch so as
HANDBOOK ON ENGINEERING.
71
to reverse the armature connections. Fig. 90 will give a fair idea of the way in which a reversing switch is made. This repre- sents the type of switch used most generally for this purpose, and it is known as the cylinder switch. It is the kind used on trol- ley-cars. The vertical row of circles numbered from one to eleven represents stationary contact pieces, to which the terminals of the motor, the line and the resistance are attached. The shaded parts B B are metal plates that are secured to the surface of a cylinder, that is so located that as it is turned in one direction or the other, these plates slide over the stationary con- tacts. If the cylinder is turned so that the plates on the right side slide over the contacts, the motor will run in one direction, and if the cylinder is turned in the other direction, the motor will be reversed. Suppose the right side plates slide over the con-
Fig. 89. Device for varying speed of shunt motor.
tacts, then the current from^> will pass to contact 2, and thence to wire a, and to the left-side of the field. Through wire d it will return from the field to contact 5, and by means of
T2,
HANDBOOK ON ENGINEERING.
plates N and T, which are connected as shown at JX1, it will reach contact 3 and wire fr, which runs to the lower side of the arma- ture. From the top of the armature, through wire c, the current will return to contact 4 and through plates S and M and the con- nection X will reach contact 6 , which by one of the wires e con-
Fig. 90. Principle of reversing device.
nects with the left-side of the resistance U. From the right-side of this resistance, the current will pass to contact 10, and thus to contact 11, through the cylinder plate, and in that way reach line wire n.
If the cylinder is turned further around, contact 7 will be cov- ered by plate M , and this will cut one section of D. By a further
HANDBOOK ON ENGINEERING. 73
movement, contact 8 will be covered, thus cutting out another section, and by continuing the movement, all of D can be cut out.
If the cylinder is turned so as to slide the left-side plates over the contacts, the change effected will be that contact 5 will be connected with 4 instead of with 3, and contact 6 will be con- nected with 3 instead of 4, thus reversing the direction of the current through the armature.
The strength of an electric current is measured in amperes. The electromotive force that drives an electric current through a circuit is measured in volts. The resistance that a wire or other circuit offers to the passage of an electric current through it is measured in ohms.
The unit of resistance, the ohm, is the resistance of a column of mercury about 40 inches long and about five hundredths of an inch in diameter, or, to be more exact, 106 centimeters long, and one millimeter in diameter.
THE WATT.
The watt is the unit of electric power — the volt-ampere, the power developed, and is equal to TJ^ of one horse power. A con- venient multiple of this is called the Kilowatt, written K. W., and is equal to 1,000 watts.
THE AHPERE.
The ampere is the practical unit of electric current, such a cur- rent [or rate of flow, or transmission of electricity] as would pass, with an electromotive force of one volt, through a circuit whose resistance is equal to one ohm ; a current of such a strength as would deposit from solution .006084 grains of copper per
second.
CANDLE POWER.
The candle power is the unit of light ; and a standard candle is a candle of definite composition which with a given consump- tion in a given time, will produce a light of a fixed and definite brightness. A candle which burns 120 grains of spermaceti wax per hour, or two grains per minute, will give an illumination equal to one standard candle.
74 HANDBOOK ON ENGINEERING.
CHAPTER VII.
INSTRUCTIONS FOR INSTALLING AND OPERATING SLOW AND MODERATE SPEED GENERATORS AND HOTORs!
To remove the armature, take off the brush-holders, brush yoke, pulley and bearing caps and put a sling on the armature, as shown in accompanying illustration. A spreader of suitable length should be used and its location adjusted to prevent the rope from drawing against the flange or end connections.
In assembling, marked parts of the machine should be assem- bled strictly according to the marking. Clean all connection joints carefully before clamping them together. Wipe the shaft- bearing sleeves and oil cellars perfectly clean and free from grit. Place the bearing sleeves and oil rings in position on the shaft and then lower the armature into place, taking care that the oil rings are not jammed or sprung. As soon as the armature is in position, pour a little oil in the bearing sleeves, put the caps on the boxes and screw them down snugly. The top field should next be put on and bolted firmly into position, and a level placed on the shaft to check the leveling of the foundation.
Fill the bearings with the best grade of thin lubricating oil and do not allow it to overflow. Oil throwing is usually due to an excess of oil and can be avoided by care in filling the oil cellars.
To complete the assembly, place the pulley on the shaft, draw up the set screws and put on the brush rigging and connection blocks.
STARTING.
Before putting on the belt, see that all screws and nuts are tight and turn the armature by hand to see that it is free and
HANDBOOK ON ENGINEERING.
75
does not rub or bind at any point. Put on the belt with the machine so placed on the rails as to have the minimum distance between pulley centers. Start the machine up slowly and see that the oil rings in bearings are in motion. As the machine
Fig. 91. Method of raising an armature.
comes up to speed, tighten the belt till it runs smoothly, and run the machine long enough without load to make sure that the bear- ings are in perfect condition. The bearings, when running, should be examined at least once a week.
iCARE OF COMMUTATOR. The commutator brushes and brush-holders should at all times be kept perfectly clean and free from carbon or other dust. Wipe the commutator from time to time with a piece of canvas lightly coated with vaseline. Lubricant of any kind should be applied very sparingly.
76 HANDBOOK ON ENGINEERING.
If a commutator when set up begins to give trouble by rough- ness, with attendant sparking and excessive heating, it is neces- sary to immediately take measures to smooth the surface. Any delay will aggravate the trouble, and eventually cause high tem- peratures, throwing off solder, and possibly displacement of the segments. No. 0 sandpaper, fitted to a segment of wood, with a radius equal to that of the commutator, if applied in time to the surface when running at full speed (and if possible with brushes raised), and kept moving laterally back and forth on the commu- tator, will usually remedy the fault.
DIRECTIONS FOR STARTING DYNAMOS.
General* — Make sure that the machine is clean throughout, especially the commutator, brushes, electrical connections, etc. Remove any metal dust, as it is very likely to make a ground or short circuit.
Examine the entire machine carefully, and see that there are no screws or other parts that are loose or out of place. See that the oil-cups have a sufficient supply of oil, and that the passages for the oil are clean and the feed is at the proper rate. In the case of self -oiling bearings, see that the rings or other means for carrying the oil work freely. See that the belt is in place and has the proper tension. If it is the first time the machine is started, it should be turned a few times by hand, or very slowly, in order to see if the shaft revolves easily and the belt runs in center of pulleys.
The brushes should now be carefully examined and adjusted to make good contact with the commutator and at the proper point, the switches connecting the machine to the circuit being left open. The machine should then be started with care and brought up to full speed, gradually if possible; and in any case
HANDBOOK ON ENGINEERING. 77
the person who starts either a dynamo or a motor should closely watch the machine and everything connected with it, and be ready to throw it out of circuit if it is connected, and shut down and stop it instantly if the least thing seems to be wrong, and should then be sure to find out and correct the trouble before starting again.
STARTING A DYNAMO.
In the case of a dynamo it is usually brought up to speed either by starting up a steam-engine or by connecting the dynamo to a source of power already in motion. The former should, of course, only be attempted by a person competent to manage steam-engines and familiar with the particular type in question. This requires special knowledge acquired by experi- ence, as there are many points to consider and attend to, the neglect of any of which might cause serious trouble. For ex- ample, the presence of water in the cylinder might knock out the cylinder-head ; the failure to set the feed of the oil-cups properly might cause the piston-rod, shaft, or other part, to cut. And other great or small damage might be done by ignorance or care- lessness. The mere mechanical connecting of a dynamo to a source of power is usually not very difficult; nevertheless, it should be done carefully and intelligently, even if it only requires throwing in a friction-clutch or shifting a belt from a loose pul- ley. To put a belt on a pulley in motion is difficult and danger- ous, particularly if the belt is large or the speed is high, and should not be tried except by a person who knows just how to do it. Even if a stick is used for this purpose, it is apt to be caught and thrown around by the machinery, unless it is used in exactly the right way.
It has been customary to bring dynamos to full speed before the brushes are lowered into contact with the commutator ; but
78 HANDBOOK ON ENGINEERING.
this is not necessary, provided the dynamo is not allowed to turn backwards, which sometimes occurs from carelessness in starting, and might injure copper brushes by causing them to catch in the commutator. If the brushes are put in contact before starting, they can be more easily and perfectly adjusted and the e.m.f . will come up slowly, so that any fault or difficulty will develop gradually and can be corrected ; or the machine can be stopped, before any injury is done to it or to the system. In fact, if the machine is working alone on a system, and is absolutely free from any danger of short-circuiting any other machine or storage bat- tery on the same circuit, it may be started while connected to the circuit, but not otherwise. If there are a large number of lamps connected in the circuit, the field magnetism and voltage might not be able to " build up " until the line is disconnected an instant.
If one dynamo is to be connected with another, or to a circuit having other dynamos or a storage battery working upon it, the greatest care should be taken. This coupling together of dynamos can be done perfectly, however, if the correct method is followed, but is likely to cause serious trouble if any mistake is made.
SWITCHING DYNAHOS INTO CIRCUIT.
Two or more machines are often connected to a common cir- cuit. This is especially the case in large buildings where the number of lamps required to be fed varies so much that one dynamo may be sufficient for certain hours, but two, three or more machines may be required at other times. The various ways in which this is done depending upon the character of the machines and of the circuit and the precautions necessary in each case make this a most important and interesting subject, which requires careful consideration.
Dynamos may be connected together either in parallel (mul- tiple arc) or in series.
HANDBOOK ON ENGINEERING. 79
DYNAMOS IN PARALLEL.
In this case the + terminals are connected together or to the same line, and the — terminals are connected together or to the other line. The currents (i. e. amperes) of the machines are thereby added, but the e.m.f . (volts) are not increased. The chief condition for the running of dynamos in parallel is that their voltages shall be equal, but their current capacities may be different. For example : A dynamo producing 10 amperes may be connected to another generating 100 amperes, provided the voltages agree. Parallel working is, therefore, suited to constant potential circuits. A dynamo to be connected in parallel with others or with a storage battery, must first be brought up to its proper speed, e.m.f., and other working conditions, otherwise, it will short-circuit the system, and probably burn out its armature. Its field magnetism must, therefore, be at full strength, owing to the fact that it generates no e.m.f. with no field magnetism. Hence, it is "well to find whether the pole pieces are strongly magnetized by testing them with a piece of iron, and to make sure of the proper working of the machine in all other respects before connecting the armature to the circuit. It is a common accident for the field-circuit to be open at some point, and thus cause very serious results. In fact, a dynamo should not be connected to a circuit in parallel with others until its voltage has been tested and found to be equal to, or slightly (not over 1 or 2 per cent) greater than that of the circuit. If the voltage of the dynamo is less than that of the circuit, the current will flow back into the dynamo and cause it to be run as a motor. The direction of rotation is the same, however, if it is shunt- wound, and no great harm results from a slight difference of potential. But a compound-wound machine requires more careful handling.
80 HANDBOOK ON ENGINEERING.
DIRECTIONS FOR RUNNING DYNAMOS AND MOTORS.
In the case of a machine which has not been run before, or has been changed in any way, it is of course wise to watch it closely at first. It is also well to give the bearings of a new machine plenty of oil at first, but not enough to run on the arma- ture, commutator or any part that would be injured by it, and to run the belt rather slack until the bearings and belt have got- ten into easy working condition. If possible a new machine should be run without load or with a light one for an hour or two, or several hours in the case of a large machine ; and it is always wrong to start a new machine with its full load, or even a large fraction of it.
This is true even if the machine has been fully tested by its manufacturer and is in perfect condition, because there may be some fault in setting it up, or some other circumstance which would cause trouble. All machinery requires some adjust- ment and care for a certain time to get it into smooth working order.
When this condition is reached, the only attention required is to supply oil when needed, keep the machine clean and see that it is not overloaded. A dynamo requires that its voltage or current should be observed and regulated if it varies. The per- son in charge should always be ready and sure to detect the beginning of any trouble, such as sparking, the heating of any part of the machine, noise, abnormally high or low speed, etc. ; before any injury is caused, and to overcome it by following directions given elsewhere. Those directions should be pretty thoroughly committed to mind, in order to facilitate the prompt detection and remedy of any trouble when it suddenly occurs, as is apt to be the case. If possible, the machine should be shut
HANDBOOK ON ENGINEERING.
81
down instantly when any trouble or indication of one appears, in order to avoid injury and give time for examination.
Keep all tools or pieces of iron or steel away from the machine while running, as they might be drawn in by the magnetism, and perhaps get between the armature and pole-pieces and ruin the machine. For this reason, use a zinc, brass or copper oil-can instead of iron or " tin " (tinned iron).
Particular attention and care should be given to the commu- tator and brushes to see that the former keeps perfectly smooth and that the latter are in proper adjustment. (See Sparking).
Never lift a brush while the machine is delivering current, unless there are one or more other brushes on the same side to carry the current, as the spark might make a bad burnt spot on the commutator.
Touch the bearing's and field-coils occasionally to see that they are not hot. To determine whether the armature is running hot, place the hand in the current of air thrown out from it by centrifugal force.
Special care should be observed by any one who runs a dynamo or motor to avoid overloading it, because this is the cause of most of the troubles which occur.
BATTERIES.
|
Name of Cell. |
E.M.F. |
Material in Plates. |
Electrolyte. |
|
|
Bunsen . . |
1.95 |
Zinc. |
Carbon. |
Nitric and Sulphuric Acid. |
|
Grove . |
1.93 |
« |
ft |
a it tt {t |
|
Gravity . . |
LOG |
a |
Copper. |
( Copper Sulphate. \ Zinc " |
|
Leclanche |
1.45 |
<( |
Carbon. |
Sal Ammoniac. |
|
Dry Cell . . |
1.49 |
tt |
f< |
Sal Ammoniac Paste. |
|
EdisonLelande |
0.9 |
u |
CopperOxide |
Caustic Potash. |
|
Lead Storage . |
1.98 |
Lead. |
Lead. |
Sulphuric Acid. |
-32 HANDBOOK ON ENGINEERING.
CHAPTER VIII.
WHY COMMUTATOR BRUSHES SPARK AND WHY THEY DO
NOT SPARK.
A long list of reasons might be given why commutator brushes spark, and why they do not spark, but by such a procedure no light would ,be thrown on the subject, because the reasons would not be understood unless fully explained. It is preferable to explain the subject and let the reader tabulate the reasons after digesting the explanation of the principles involved.
Whenever an electric current is interrupted, a spark is pro- duced and it makes no difference how the current is generated, or what kind of a conductor it is flowing through. To break a current without a spark is not a possibility; hence, if we desire to open a circuit without producing a spark, the only way to accomplish the result is by killing the current before the circuit is opened. The brushes resting on the commutator of a motor or a generator have to transmit to the armature and take away from it the current that is generated, in the case of a generator, or the current that drives the machine in the case of a motor. If the brushes were made so narrow that they could only make contact with one commutator segment at a time, it would be impossible to run the machine without producing very destruc- tive sparks. Commutators, however, are not made in this way. The insulation between the segments is narrow, and the brushes are wide enough to be always in contact with two segments, and part of the time with three. Suppose that the proportions are such that during most of the time the brush only touches two
HANDBOOK ON ENGINEERING. 83
segments, as shown in Fig. 92. With these proportions it will be seen, that so long as there are two segments in contact with each brush, it is a possibility \>r the current to be diverted through one of them only. Suppose that at the instant when the forward segment is passing from under the brush, all the current flows through the rear segment ; then it is quite evident that the first- named segment will break away from contact with the brush with- out making a spark, for there will be no current flowing from it to the brush.
All the foregoing: is self-evident, but it will be suggested that although the brush can break away from the front segment with- out producing a spark, it cannot do the same thing with the rear segment, for all the current is flowing through this one. While it is true that when the forward segment passed from under the brush all the current was flowing through the rear segment, it is not true that the current continues to follow this path. As soon as the front segment passes from under the brush, the rear one becomes the forward segment, and while it is advancing to the point where it must pass from under the brush, the current can be transferred to the next segment back of it which now plays the part of rear segment. Thus we see that to be able to run a machine without producing sparks at the commutator, all we have to do is to provide means whereby the current is transferred from one segment to the one back of it as the commutator revolves, so that when the segments pass from under the brush there is no current flowing through them. This result is accomplished more or less perfectly in all machines, made by responsible firms. There are machines on the market that have been designed by men who are not well enough posted in the principles of electrical science to obtain proper proportions, and these are not propor- tioned so as to shift the current from the forward to the rear segment as fast as the machine revolves ; such machines always produce more or less serious sparking.
84 HANDBOOK ON ENGINEERING.
If a machine is accurately made and the armature coils and commutator segments are properly spaced and sufficient in num- ber, it is possible to get the brushes so there will be little or no spark at a given load ; but if the current strength be increased or reduced, the sparks will appear, and the more the current is changed the larger the sparks will be, the increasing current producing the greatest sparking.
The way in which the current is shifted from the front to the rear segment will be explained in connection with Fig. 92. In this figure, A represents a portion of the core of a ring armature. The shaft upon which it is mounted is shown at D, and P N are the corners of the poles between which it rotates. The small blocks C represent a portion of the commutator segments, which we have placed outside of the armature, so as to make the diagram as simple as possible. For the same reason we have shown the armature coils as made of two turns of wire each. The line F divides the space between the ends of the poles into two equal parts, and the line E divides the armature into two halves on which the directions of the induced currents is opposite. In all the coils to the right of line E the currents are induced in a direction away from the shaft, and in all the coils to the left of line E the currents flow toward the shaft, all of which is clearly indicated by the arrow heads placed upon the lines repre- senting the coils. The outline B represents the end of one of the brushes, and from the direction in which it is inclined it will be understood that the armature revolves in a direction counter to that of the hands of a clock.
When the armature is in the position shown, the current flow- ing in the coils to the right of line E passes to segment &, and thus reaches the brush, while the current flowing in the coils to the left of line E reaches segment a, and through this passes to the brush. As the brush rests upon segments a and b the coil with which they connect is short-circuited, and therefore a
HANDBOOK ON ENGINEERING.
85
current can flow in it in any direction, or there may be no cur- rent. To be able to run without spark, or to obtain perfect commutation, as it is called, the current in this short-circuited coil, when in the position shown, should be zero, or nearly so. This coil, which is short-circuited by the brush, is called the corn- mutated coil, or the coil undergoing commutation. It will be noticed that this commutated coil is in a position just forward of
Fig. 02. Portion of core of ring armature.
the line E ; hence, the action of pole P will be to develop a current in it that will flow in the same direction as the current in the coils ahead of it, that is, in the coils to the left. Now if this current flowed through the brush, it would be in a direction contrary to that of the arrow at a; hence it would act to check the current flowing from the front segment a to the brush, and would divert it through the commutated coil to the rear segment
86 HANDBOOK ON ENGINEERING.
b. If the action of pole P upon the commutated coil is sufficiently vigorous, the current developed in it will be as strong as the cur- rent in the coils ahead of it, by the time the end of the segment is about to break away from the brush ; and this being the case there will be no current from segment a to the brush, and conse- quently, no spark. If the action of pole P is not strong enough, then there will be a small current from segment a to the brush when they separate, and as a result, a small spark. If the action of pole P on the commutated coil is too vigorous, then the current developed in it will be too great, and it will not only divert all the current coming from the forward coils, through the commuta- ted coil to segment &, but in addition will develop a local current that will circulate through the end of the brush, and, therefore, when the separation occurs, there will be a current flowing from the brush to the front segment, and consequently a spark.
If the commutated coil were placed astride of line E, the action of pole P upon it would be no greater than that of pole N, so that no current would be developed in it while undergoing com- mutation. The farther the coil is in advance of line J£, when short- circuited by the brush, the stronger the action of pole P upon it ; therefore, the strength of the current developed in the commutated coil can be increased by moving the brush farther away from pole P. Hence, by trial, a point can be found where the current developed will be just sufficient for the purpose and no more. This is true, supposing the current developed by the armature to remain con- stant, but, if it varies, the current in the commutated coil will be either too great or too small. If, when the brushes are set, the armature is delivering a current of, say, twenty amperes, then the current flowing through the coils to the left of the brush will be ten amperes, and the current in the commutated coil will also be ten amperes. If the armature current increases to forty amperes, the current in the forward coils will be twenty amperes, and as that in: the commutated coils will still be ten amperes, it will have only
HANDBOOK ON ENGINEERING. 87
one-half the strength required for perfect commutation. In prac- tice, however, it is found that if the commutator have a sufficient number of segments, and the proportions of the machine are such that the line E remains practically in the same position for all strengths of armature current, then, if the brushes are set so as to run sparkless with an average load, they will run so nearly spark- less with a heavy or light load as to make it difficult to detect the difference.
Even when a machine is properly proportioned, the brushes may spark badly if they are not set in the proper position and with the proper tension. If the tension is not right, they will spark no matter where they are set. If the tension is too light, they will spark, because they will chatter and thus jump off the surface of the commutator. If the tension is too great, they will spark because they will cut the commutator, and then the latter will act as a file or grindstone and cut away particles from the brushes, and these will conduct the current from segment to seg- ment, as well as from the segment to the brush. Whenever a com- mutator is seen to be covered with fine sparks, some of which run all the way around the circle, it may be depended upon that the surface is rough, due in most cases to too much pressure on the brushes, and the remedy is to smoothitup and reduce the tension and set the brushes where they will run with the smallest spark. When the brushes begin to spark they rarely cure themselves and the longer they are allowed to run with a heavy spark the worse they will get.
Of all the troubles which may occur, sparking is the only one which is very different in the different types of machines. In some its occurrence is practically impossible. In others, it may result from a number of causes. The following cases of sparking apply to nearly all machines, and they cover closed-coil dynamos and motors completely.
Cause J* — Brushes not set at the neutral point.
88 HANDBOOK ON ENGINEERING.
Symptom* — Sparking, varied by shifting the brushes with rocker-arm.
Remedy* — Carefully shift brushes backwards or forwards until sparking is reduced to a minimum.
The usual position for brushes in two-pole machines is opposite the spaces between the pole-pieces.
Cause 2* — Commutator rough, eccentric, or has one or more " high bars " projecting beyond the others, or one or more flat bars, commonly called " flats," or projecting mica, any one of which causes brush to vibrate, or to be actually thrown out of contact with commutator.
Symptom* — Note whether there is a glaze or polish on the commutator, which shows smooth working ; touch revolving com- mutator with tip of finger-nail, and the least roughness is perceptible, or feel of brushes, to see if there is any jar. If the machine runs at high-voltage (over 250), the commutator or brushes should be touched with a small stick or quill to avoid danger of shock. In the case of an eccentric commutator, careful examination shows a rise and fall of the brush when commutator turns slowly, or a chattering of brush when running fast.
Remedy* — Smooth the commutator with a fine file or fine sand- paper, which should be applied by a block of wood which exactly fits the commutator (in latter case, be careful to remove any sand remaining afterward ; and never use emery) . If bearing is loose put in new one. If commutator is very rough or eccentric, it should be taken out and turned off.
Cause 3* — Brushes make poor contact with commutator.
Symptom* — Close examination shows that brushes touch only at one corner, or only in front or behind, or there is dirt on sur- face of contact. Sometimes, owing to the presence of too much oil or from other cause, the brushes and commutator become very dirty and covered with smut. They should then be carefully cleaned by wiping with oily rag or benzine, or by similar means.
HANDBOOK ON ENGINEERING. 89
Occasionally a " glass-hard " carbon brush is met with. It is incapable of wearing to a good seat or contact and will only touch in one or two points, and should be discarded.
Remedy* — File, bend, adjust or clean brushes until they rest evenly on commutator, with considerable surface of contact and with sure but light pressure.
It sometimes happens that the brushes make poor contact, because the brush-holders do not turn or work freely.
Cause 4* — Short-circuited coil in armature or reversed coil.
Symptom* — A motor will draw excessive current, even when running free without load. A dynamo will require considerable power even without any load.
The short-circuited coil is heated much more than the others, and is very apt to be burnt out entirely ; therefore, stop machine immediately. If necessary to run machine to locate the short- circuit, one or two minutes is long enough, but it may be re- peated until the short-circuited coil is found by feeling the arma- ture all over.
An iron screw-driver or other tool held between the field- magnets near the revolving armature vibrates very perceptibly as the short-circuited coil passes. Almost any armature, par- ticularly one with teeth, will cause a slight but rapid vibration of a piece of iron held near it, but a short-circuit produces a much stronger effect only once per revolution.
The current pulsates and torque is unequal at different parts of a revolution, these being particularly noticeable when arma- ture turns rather slowly. If a large portion of the armature is short-circuited, the heating is distributed and harder to locate. In this case a motor runs very slowly, giving little power, but having full-field magnetism.
Remedy* — A short circuit is often caused by a piece of solder or other metal getting between the commutator bars or their con- nections with the armature, and sometimes the insulation between
90 HANDBOOK ON ENGINEERING.
or at the ends of these bars is bridged over by a particle of metal. In any such case the trouble is easily found and corrected. If, however, the short-circuit is in the coil itself, the only real cure is to rewind the coil.
One or more ' ' grounds ' ' in the armature may produce effects similar to those arising from a short circuit.
Cause 5* — Broken circuit in armature.
Symptom* — Commutator flashes violently while running, and commutator-bar nearest the break is badly cut and burnt ; but in this case no particular armature coil will be heated, as in the last case and the flashing will be very much worse, even when turn- ing slowly. This trouble, which might also be confounded with a bad case of " high- bar " or eccentricity in commutator (sparking), is distinguished from it by slowly turning the arma- ture, when violent flashing will continue if circuit is broken, but not with eccentric commutator or even with " high bar."
Remedy* — The trouble is often found where the armature wires connect with the commutator and not in the coil itself, and the break may be repaired or the loose wire may be resoldered or screwed back in place. If the trouble is due to a broken com- mutator connection and it cannot be fixed, then connect the dis- connected bar to the next by solder, or " stagger " the brushes ; that is, put one a little forward and the other back so as to bridge over the break. If the break is in the coil itself, rewinding is generally the only cure.
Cause 6* — Weak field-magnetism.
Symptom* — Any considerable vibration is almost sure to pro- duce sparking, of which it is a common cause. This sparking may be reduced by increasing the pressure of the brushes on the commutator, but the vibration itself should be overcome by the remedies referred to above.
Cause 7* — Chatter of Brushes. The commutator sometimes
HANDBOOK ON ENGINEERING. 91
becomes sticky when carbon brushes are used, causing friction, which throws the brushes into rapid vibration as the commutator revolves, similarly to the action of a violin-bow.
Symptom* — Slight tingling or jarring is felt in brushes.
Remedy* — Clean commutator and oil slightly. This stops it at once.
NOISE.
Cause 8* — Vibration due to armature or pulley being out of balance.
Symptom* — Strong vibration felt when the hand is placed upon the machine while it is running. Vibration changes greatly if speed is changed.
Remedy* — The easiest method of finding in which direction the armature is out of balance is to take it out and rest the shaft on two parallel and horizontal A-shaped metallic tracks suffici- ently far apart to allow the armature to go between them. If the armature is then slowly rolled back and forth, the heavy side will tend to turn downward. The armature and pulley should always be balanced separately. An excess of weight on one side of the pulley and an equal excess of weight on the opposite side of the armature will not produce a balance while running, though it^ does when standing still ; on the contrary, it will give the shaft a strong tendency to "wobble." A perfect balance is only obtained when the weights are directly opposite, i. e., in the same line perpendicular to the shaft.
Cause 9* — Armature strikes or rubs against pole pieces.
Symptom* — Easily detected by placing the ear near the pole- pieces, or by examining armature to see if its surface is abraded at any point, or by examining each part of the space between armature and field, as armature is slowly revolved, to see if any
92 HANDBOOK ON ENGINEERING.
portion of it touches or is so close as to be likely to touch when the machine is running. Or turn armature by hand when no current is on, and note if it sticks at any point.
Remedy. — Bind down any wire, or other part of the armature that may project abnormally, or file out the pole-pieces where the armature strikes, or center the armature so that there is a uni- form clearance between it and the pole-pieces at all points.
Cause JO* — Singing or hissing of brushes. This is usually occasioned by rough or sticky commutator, or by tips of brushes not being smooth, or the layers of a copper brush not being held together and in place. With carbon brushes, hissing will be caused by the use of carbon which is gritty or too hard. Vertical carbon brushes, or brushes inclined against the direction of rotation, are apt to squeak or sing. A new machine will sometimes make noise from rough commutator, no matter how carefully it is turned off, because the difference in hardness between mica and copper causes the cut of the tool to vary, thus forming inequali- ties which are very minute, but enough to make noise. This can be best smoothed by running.
Remedy* — Apply a very little oil or vaseline to the com- mutator with the finger or a rag. Adjust the brushes or smooth the commutator. Carbon brushes are apt to squeak in starting up, or at slow speed. This decreases at full speed, and can usually be reduced by moistening the brush with oil, care being taken not to have a ay drops, or excess of oil. Shortening or lengthening the brushes sometimes stops the noise. Run the machine on open circuit until commutator and brushes are worn smooth.
For alternating current machinery and principles of alternating current see page 815.
HANDBOOK ON ENGINEERING. 93
HEATING IN DYNAHO OR MOTOR.
General Instructions* — The degree of heat that is injurious or objectionable in any part of a dynamo or motor is easily deter- mined by feeling the various parts. If the heat is bearable for a few moments, it is entirely harmless. But if the heat is unbear- able for more than a few seconds, the safe limit of temperature has been passed, except in the case of commutators in which solder is not used ; and it should be reduced in some of the ways that are given above. In testing with the hand, allowance should always be made for the fact that bare metal feels much hotter than cotton, etc. If the heat has become so great as to produce an odor or smoke, the safe limit has been far exceeded and the current should be shut off and the machine stopped immediately, as this indicates a serious trouble, such as a short-circuited coil or a tight bearing. The machine should not again be started until the cause of the trouble has been found and positively overcome. Of course neither water nor ice should ever be used to cool elec- trical machinery, except possibly the bearings of large machines, where it can be applied without danger of wetting the other parts.
Feeling for heat will answer in ordinary cases, but of course, the sensitiveness of the hand differs, and it makes a very great difference whether the surface is a good or bad conductor of heat. The back of the hand is more sensitive and less variable than the palm for this test. But for accurate results a thermometer should be applied and covered with waste or cloth to keep in the heat. In proper working the temperature of no parts of the machine should rise more than 45° C., or 81° F. above the tem- perature of the surrounding air. If the actual temperature of
94 HANDBOOK ON ENGINEERING.
the machine is near the boiling point, 100° C., or 212° F., it is seriously high.
It is very important in all cases of heating to locate correctly the source of heat in the exact part in which it is produced. It ./s a common mistake to suppose that any part of a machine which is found to be hot is the seat of the trouble. A hot bearing may cause the avmature or commutator to heat or vice versa. In every case, all parts of the machine should be felt to find which is the hottest, since heat generated in one part is rapidly diffused throughout the entire machine. It is generally much surer and easier in the end to make observations for heating by starting with the whole machine perfectly cool, which is done by letting it stand for one or more hours or over night, before making the examination. When ready to try it, run it fast for three to five minutes, with the field magnets charged ; then stop, and feel all parts immediately. The heat will be found in the right place, as it will not have had time to diffuse from the heated to the cool parts of the machine. Whereas, after the machine has run some time, any heating effect will spread until all parts are equal in temperature, and it will then be almost impossible to locate the trouble.
Excessive heating of commutator, armature, field magnets, or bearings may occur in any type of dynamo or motor, but it can almost always be avoided by proper care and working conditions.
THE EFFECT OF THE DISPLACEHENT OF THE ARMATURE.
If a machine is old, it is more than likely the shaft will be found out of center, and if this fact is discovered at a time when things are not working as they should, it is taken for granted this is the cause of the trouble. What is true of shafts out of the
HANDBOOK ON ENGINEERING.
95
center is true of several other things that are liable to get out of place. For the present it will be sufficient to investigate just what effect the displacement of the shaft can have.
Fig1* 93 illustrates an armature of a two-pole machine which is out of center in one direction, and Fig. 94 shows another two-pole armature out of center in a direction at right angles to that shown in the first figure. The condition shown in Fig. 93 could be produced by a heavy armature running in rather light bear- ings for several years, and the side displacement of Fig.94could be produced by the tension of an extra tight belt. The mechan-
Figs. 93 and 94. Showing armature out of center.
ical effect of both these conditions would be to increase the pres- sure on the bearings, as the part a of the armature would be drawn toward the poles of the field with greater force than the opposite side. The downward pull, due to the attraction of the magnetism, would be greater in Fig. 9 3 than the side pull in Fig. 9 4 supposing both armatures and fields to be the same in both cases, and the displacement of the shafts equal. This difference is due to the fact that in Fig. 93 the magnetism of both poles is concentrated at the lower corners on account of the shorter air gap ; hence both sides pull much harder on the lower side. In
^(5 HANDBOOK ON ENGINEERING.
Fig. 94 the pull of the N pole is greater than that of the other, simply because in the latter the magnetism is more dispersed, but the difference in the density on the two sides will not be very great. If the bearings of a machine, with the armature dis- placed, as indicated, have shown any signs of cutting, or if they run unusually warm, their condition will be improved by putting in new bearings that will bring the shaft central.
If the armature is of the drum type, the displacement of the shaft will have no effect upon it electrically. This is owing to the fact that all the armature coils are wound from one side of the core to the other, and, therefore, at all times, every coil has one side under the influence of one pole and the other side under the influence of the opposite pole, and if one side is acted upon strongly by one pole, it will be acted upon feebly by the other. If the armature is of the ring type, then the displacement of the shaft will affect it electrically, for in a ring armature, the coils on one side are acted upon by the pole on that side, only, and as the magnetic field from one pole will be stronger than that from the other (that is, considering the action upon equal halves of the armature) , the voltage devel- oped in the coils on one side of the armature will be greater than that developed on the other side.
The effect of the disturbance of the electrical balance will be that the brushes will spark badly, because the voltage of the cur- rent generated on one side of the armature will be greater than that of the current on the other side. Hence, when these two currents meet at the brushes, the strong one will tend to drive the weak one backward. If, while the armature is out of center, we wish to adjust the brushes so as to get rid of the excessive sparking, all we have to do is to set them to the right of the cen- ter line, as in Fig. 94 so that the wire on the left side will cover a greater portion of the circumference than the right.
.
HANDBOOK ON ENGINEERING. 97
In a multipolar machine, the displacement of the armature will have the same effect mechanically as in the two-pole type ; nmltipolar armatures are connected in two different ways, one of which is called the wave or series winding, and the other the lap or parallel winding. In the first named type of winding, the ends of all the coils on the armature are connected with each other and with the commutator segments in such, a manner that there are only two paths through the wire for the current ; there- fore, these two armature currents pass under all the poles and the voltage of each current is the combined effect of all the poles. From this very fact, it can be clearly seen that it makes no difference what the distance between the several poles and arma- ture may be, for if some are nearer than the others, the only effect will be that these poles will not develop their share of the total voltage, but whatever their action may be, it will be the same on the coils in both circuits.
When a multipolar armature is connected so as to form a parallel or lap winding, then the connections between the coil ends, and between these ends and the commutator segments, are such that as many paths are provided for the current as there are poles, and each one of these paths is located under one pole, and as a consequence, the voltage developed in it is proportional to the action of this pole. The diagram Fig. 95 illustrates a six-pole armature with the ends of the field poles, and the arrows a a, b 6, c c, indicate the six separate divisions of the coils in which the branch currents are developed. Now, it can be clearly seen that as the armature is nearer to the lower poles than to any of the others, the action of these will be the strongest. Hence, the cur- rents a a will be stronger than the others and will have a higher voltage.
The two upper currents are weaker than the side ones and
7
98
HANDBOOK ON ENGINEERING.
their voltage is also lower, so that, the current returning to the commutator through the brushes at the upper corners, will not divide equally, but the larger portion will be drawn into the coils on the side ; and as the upper coils will have to fight to hold their own, so to speak, there will be a disturbance of the balance that
Fig. 95* Diagram of six-pole armature.
is re-quired for smooth running. The result will be heavy spark- ing at these brushes. In the great majority of cases, if the brushes of a multipolar machine spark on account of the armature being out of center, the only cure is to reset the bearings, if they are adjustable, and if they are not, to put in new ones.
HANDBOOK ON ENGINEERING.
99
Table of Carrying Capacity of Wires* — Below is a table which must be followed in placing interior conductors, showing the allowable carrying capacity of wires and cables of ninety-eight per cent conductivity, according to the standard adopted by the American Institute of Electrical Engineers.
|
TABLE A. |
TABLE B. |
||
|
Rubber-Covered |
Weatherproof |
||
|
Wires. |
Wires. |
||
|
B. A S. G. |
Amperes. |
Amperes. |
Circular Mile. |
|
18 |
3 |
5 |
1,624 |
|
16 |
6 |
8 |
2,583 |
|
14 |
12 |
16 |
4,107 |
|
12 |
17 |
23 |
6,530 |
|
10 |
24 |
32 |
10,380 |
|
8 |
33 |
46 |
16,510 |
|
6 |
46 |
65 |
26,250 |
|
5 |
54 |
77 |
33,100 |
|
4 |
65 |
92 |
41,740 |
|
3 |
76 |
110 |
52,630 |
|
2 |
90 |
131 |
66,370 |
|
1 |
107 |
156 |
83,690 |
|
0 |
127 |
185 |
105,500 |
|
00 |
150 |
220 |
133,100 |
|
000 |
177 |
262 |
167,800 |
|
0000 |
210 |
312 |
211,600 |
|
Circular MJls |
|||
|
200,000 |
200 |
300 |
|
|
300,000 |
270 |
400 |
|
|
400,000 |
330 |
500 |
|
|
500,000 |
390 |
590 |
|
|
600,000 |
450 |
680 |
|
|
700,000 |
500 |
760 |
|
|
800.000 |
550 |
840 |
|
|
90u,000 |
600 |
920 |
100 HANDBOOK ON ENGINEERING.
|
TABLE A. |
TABLE B. |
|
|
Rubber-Covered |
Weatherproof |
|
|
Wires. |
Wires. |
|
|
Circular Mile. |
Amperes. |
Amperes. |
|
1,000,000 |
650 |
1,000 |
|
1,100,000 |
690 |
1,080 |
|
1,200,000 |
730 |
1,150 |
|
1,300,000 |
770 |
1,220 |
|
1,400,000 |
810 |
1,290 |
|
1,500,000 |
850 |
1,360 |
|
1,600,000 |
890 |
1,430 |
|
1,700,000 |
940 |
1,490 |
|
1,800,000 |
970 |
1,550 |
|
1,900,000 |
1,010 |
17610 |
|
2,000,000 |
1,050 |
1,670 |
The lower limit is specified for rubber-covered wires to pre= vent gradual deterioration of the high insulations by the heat of the wires, but not from fear of igniting the insulation, The question of drop is not taken into consideration in the above tables.
Insulation Resistance* — The wiring in any public building must test free from grounds ; i. e., the complete installation must have an insulation between conductors and between all conduc- tors and the ground (not including attachments, sockets, recep- tacles, etc.) of not less than the following: -
Up to 5 amperes, 4,000,000 Up to 200 amperes, 100,000
" 10 " 2,000,000 " 400 25,000
" 25 " 800,000 " 800 " 25,000
" 50 " 400,000 " 1,600 " 12,500 " 100 " 200,000
All cutouts and safety devices in place in the above. Where lamp sockets, receptacles and electroliers, etc., are con- nected, one-half of the above will be required.
HANDBOOK ON ENGINEERING. 101
Soldering Fluid* — a. The following formula for soldering fluid is suggested : —
Saturated solution of zinc chloride, 5 parts. Alcohol, 4 parts.
Glycerine, 1 part.
Bell or Other Wires* — a. Shall never be run in same duct with lighting or power wires.
Table of Capacity of Wires. —
a~
CO 02
*<*
|
PQ 19 |
1,288 |
0 fc |
Vr— i M QQ |
|
|
18 |
1,624 |
... |
... |
3 |
|
17 |
2,048 |
... |
... |
0.. |
|
16 |
2,583 |
... |
... |
6 |
|
15 |
3,257 |
... |
... |
... |
|
14 |
4,107 |
... |
... |
12 |
|
12 |
6,530 . |
... |
... |
17 |
|
... |
9,016 |
7 |
19 |
21 |
|
.0. |
11,368 |
7 |
18 |
25 |
|
... |
14,336 |
7 |
17 |
30 |
|
0.. |
18,081 |
7 |
16 |
35 |
|
... |
22,799 |
7 |
15 |
40 |
|
... |
30,856 |
19 |
18 |
50 |
|
..0 |
38,912 |
19 |
17 |
60 |
|
..« |
49,077 |
19 |
16 |
70 |
|
..0 |
60,088 |
37 |
18 |
85 |
|
... |
75,776 |
37 |
17 |
100 |
|
..0 |
99,064 |
61 |
18 |
120 |
|
.0. |
124,928 |
61 |
17 |
145 |
|
... |
157,563 |
61 |
16 |
170 |
102
HANDBOOK ON ENGINEERING.
8 8,
198,677 61 15 200
250,527 61 14 235
296,387 91 15 270
373,737 91 14 320
413,639 127 15 340
When greater conducting area than that of B. & S. G. is re- quired, the conductor shall be stranded in a series of 7, 19, 37, 61, 91 or 127 wires, as may be required; the strand consisting of one central wire, the remainder laid around it concentrically, each layer to be twisted in the opposite direction from the pre- ceding.
TABLE SHOWING THE SIZE OF WIRE OF DIFFERENT METALS THAT WILL BE MELTED BY CURRENTS OF VARIOUS STRENGTHS.
|
Strength of Current in Amperes. |
DIAMETER OF WIRE IN THOUSANDTHS OF AN INCH. |
|||||
|
Copper. |
Aluminum. |
Platinum. |
• German Silver. |
Iron. |
Tin. |
|
|
1 |
.002 |
.003 |
.003 |
.003 |
.005 |
.007 |
|
2 |
.003 |
.004 |
.005 |
.005 |
.008 |
.011 |
|
3 |
.004 |
.005 |
.007 |
.007 |
.010 |
.015 |
|
4 |
.005 |
.006 |
.008 |
.008 |
.012 |
.018 |
|
5 |
.006 |
.008 |
.010 |
.010 |
.014 |
.021 |
|
10 |
.009 |
.012 |
.016 |
.016 |
.022 |
.033 |
|
15 |
.013 |
.016 |
.020 |
.020 |
.028 |
.044 |
|
20 |
.015 |
.019 |
.025 |
.025 |
.034 |
.053 |
|
25 |
.018 |
.022 |
.029 |
.029 |
.040 |
.062 |
|
30 |
.020 |
.025 |
.032 |
.032 |
.045 |
.069 |
|
35 |
.022 |
.028 |
.036 |
.036 |
.050 |
.077 |
|
40 |
.025 |
.030 |
.039 |
.039 |
.055 |
.084 |
|
50 |
.027 |
.033 |
.042 |
.042 |
.059 |
.091 |
|
60 |
.029 |
.035 |
.045 |
.045 |
.063 |
.098 |
HANDBOOK ON ENGINEERING. 1Q3
CHAPTER IX.
ARC LIGHTING APPARATUS.
INSTRUCTIONS FOR INSTALLING AND OPERATING APPARA- TUS FOR ARC LIGHTING.
Within the past few years the arc lighting industry has under- gone a decided transformation, new systems of lighting, together with new forms of lamps, generators and accessory apparatus, having practically superceded the older types. In so far as the manufacture of arc lighting apparatus is concerned, the new has entirely replaced the old. The latter, however, is still to be found in operation in many parts of the country, but is rapidly being replaced.
In the early days of the electrical industry, arc lamps were of the type now known as " Open arc, " and were connected in series in circuits that were supplied with current from constant current generators, commonly called u Arc dynamos. " In about the year 1894, what is now known as the " Enclosed arc " lamps came into use. These lamps found favor with incandescent lighting stations, because they could be operated successfully on their circuits, and were economical owing to the fact that the car- bons would last from 100 to 150 hours, which is about twenty times as long as they last in the open arc lamp.
The enclosed lamps did not meet with favor with the regular arc lighting stations because to burn with a strong and steady light, they must be adjusted for a much longer arc, and this means a much higher voltage, consequently a smaller number of lamps on the circuit. It can readily be seen that no matter what the advantages offered by the enclosed lamp might be, they
104 HANDBOOK ON ENGINEERING.
would not impress an arc light station manager favorably when he found that to make them operate well he would have to reduce the number of lamps on a 65 light circuit to 45 or 50. Owing to this fact, the enclosed lamps were confined exclusively to the Ed- ison incandescent light circuits in the beginning of their career. Soon thereafter, however, they began to be used on alternating current incandescent lighting circuits. Next they found their way onto power circuits, and at about the same time " Arc lighting " transformers were devised, by means of which lamps could be run in series, with alternating currents, in precisely the same way as the old open arc lamps were run from arc dynamos. This latter system, using " Arc lighting *' transformers, or regu- lating transformers as they are commonly called, in connection with the enclosed lamps, may truly be said to be the successor of the original arc lighting system.
Many of the old time arc light dynamos that were wound for a current of 6.6 amperes, to operate 1200 candle power lamps are now used to operate enclosed arc lamps of the nominal 2000 candle power, but the number of lamps in the circuit is reduced to about two-thirds. Some of the 10 ampere dynamos have been rewound so as to give a current of 6 amperes, with a correspond- ingly increased voltage, and these also are used to operate en- closed lamps. The manufacture of arc light generators has been abandoned by nearly all the former makers, with the exception of the Brush Company, in so far as we know. As the latter type of arc generator is still made, and as many of these machines are in use, and probably will be for years to come, it is thought advis- able to describe it briefly herein.
The latest type of brush arc generator is shown in Fig. 96. This illustration also shows the way in which the lamp circuits are arranged. As will be noticed there are four independent cir- cuits, that are connected with the upper set of binding posts of the connection board in the upper right hand corner of the figure.
HANDBOOK ON ENGINEERING.
105
The wires coming from the generator are connected with the lower set of binding posts of the connection board. By means of this
Fig. 96. Multiple Circuit Brush Arc Lighting Generator.
arrangement, it is possible, as can be easily seen, to connect any one of the generator circuits, with any one of the lamp circuits. The generator is connected so as to feed current into four circuits, that are connected with each other, but at the same time are in- dependent. The object of dividing the current into four separate circuits is to reduce the voltage on each one, not only to make it safer, but also to reduce the strain on the insulation. The old 65 light brush machines fed current to open arc lamps that required
106 HANDBOOK ON ENGINEERING.
45 volts each, so that the total voltage of the machine was about 3000. The enclosed arc lamps now used require about 80 volts each, so that to operate 65 on one circuit would require an e. m. f. of about 5000 volts, which would bring so great a strain on the insulation as to cause frequent disturbances, not to say anything about the greater danger the men operating the apparatus would be exposed to.
Fig. 97. Diagram Showing Arrangement of Circuits in Brash Multiple Circuit Arc Lighting Generator.
The modern Brush generators of 100 light capacity, develop an e. m. f. of about 8000 volts, but as this is divided among four circuits, the e. m. f. acting on each one is only 2000 volts.
The way in which the Brush generator is wound so as to supply four circuits, is easily explained. Looking at Fig. 96, it will be seen that there are four separate pairs of commutator
HANDBOOK ON ENGINEERING. 107
rings, each one of which is made the same as the single pair used on a single circuit machine. It will also be seen that the arma- ture is wound with a large number of narrow coils, their actual
number being 32. If these coils were numbered 1234, 12
34, — 1 2 3 4, all the way around the circle, then if the connec- tions were traced out, it would be found that all the No. 1 coils are connected with one pair of commutator rings, ail the No. 2 coils with another pair of commutator rings, all the No. 3 coils with the third set of rings, and all the No. 4 coils with the fourth pair of commutator rings. This way of connecting the armature coils with the commutator rings can be more fully understood from the diagram Fig. 97, in which 1, 2, 3, 4, represent the four sets of armature coils, and, A, JB, 0, Z>, represent the four lamp circuits. In looking at this diagram it will be seen that although the lamps are connected in four independent circuits, these cir- cuits are not actually disconnected from each other, but are con- nected through the several sets of armature coils. Thus the A circuit, starts from the end of the No. 1 set of coils, and ends at the entering end of No. 2 set of coils. Passing through this set of coils the current enters the B lamp circuit, and thence passes through the No. 3 armature coils, to the C lamp circuit, and through the No. 4 armature coils to the D lamp circuit and thus to the entering end of the No. 1 coils. The switches a b c d, shown in Fig. 97, are the same as those seen on the switch board mounted on the generator in Fig. 96, and are for the purpose of cutting out any one of the lamp circuits if it is desired.
An arc light generator must be so arranged that it will keep the strength of the current uniform, and vary the voltage in ac- cordance with the number of lamps in operation . The enclosed lamps require a current of about 6 amperes so that the generator must be regulated so as to give this amount of current regard- less of the number of lamps in operation. To accomplish this result a regulator is used, which is secured to the base of the
108
HANDBOOK ON ENGINEERING.
generator directly under the commutator, as clearly shown in Fig. 96. This regulator acts by varying the strength of the cur-
rent that passes through the field coils of the generator, and it regulates the voltage in each one of the four lamp circuits owing to the fact that these circuits are connected with each other
HANDBOOK ON ENGINEERING.
109
through the armature coils. Thus if there were five lamps burn- ing in circuit A and five in circuit (7 while in circuit B the full number of 25 were in operation, then the greater part of the volt- age of coils 2 and 3 would act on the fully loaded circuit U, while the small remaining portions would act on the lightly loaded circuits A and C.
Fig. 99. Diagram Showing Position of Brushes on Brash Generator.
An enlarged view of the regulator is shown in Fig. 98 at A, and the way in which it operates is fully illustrated in the line drawing B. In order that the operation of the regulator may be fully understood it is necessary to say that the field coils of the generator are connected in parallel with a resistance, and that the action of the regulator is to reduce the resistance in the parallel circuit, when the voltage of the generator is to be reduced, and to increase this resistance when the voltage is to be increased. If
110 HANDBOOK ON ENGINEERING.
the resistance in the circuit, that is parallel with the field, is re- duced, more current will pass through it, and, therefore, less cur- rent will pass through the generator field coils hence the voltage will be reduced. Increasing the resistance in the parallel circuit will have the opposite effect. From diagram B, Fig. 98, it will be seen that the regulator is driven from the generator shaft by a belt, which rotates a small oil pump which draws oil from a tank and forces it through a valve T, the ports of which are never completely closed ; so that even when it is in the central position oil can flow through. The valve is controlled by an electro magnet F whose armature U moves lever II. The strength of magnet F varies with the strength of the current gen- erated. A spring G acts to pull lever H in the opposite direc- tion from that in which the magnet acts, hence, the stronger the latter the more the valve is raised, and the weaker it is the more jPis pulled down by G. The tension of G is adjusted by a nut R. This nut is adjusted so that the valve T is held in the cen- tral position when the current is of the proper strength. If the current becomes too strong magnet F pulls down U and raises T thus forcing oil on the upper side of piston S and allowing it to flow out from the under side. This action forces piston X around clockwise. The shaft upon which X is mounted carries at its in- ner end gearing that moves the rheostat lever A so as to reduce the resistance and thus lower the field current, when the genera- tor current drops below the normal, the reverse action takes place, and resistance is cut in by the movement of A in the op- posite direction. When A is rotated the gear Z swings the arm N and thus the position of the commutator brushes is varied with the strength of the field current, so as to automatically keep the spark of the proper length, which should be about J" for light load, to |" for full load.
In order that a Brush generator may run well it is necessary that the brushes be properly set. The brushes should project
HANDBOOK ON ENGINEERING. Ill
from the holder about 5^", and all the sets should be in line. They can be brought into line by setting those at one end first, then rotate the rocker until the end of the brush is on a line with the end of a copper segment, as shown in Fig. 99. Then set the brush at the other end of the commutator so as to come in line with the end of the copper segment, the same as the first one. The other brushes can be brought into line by using a hard wood straight edge. The two sets of brushes must be placed 90 degrees apart, which can be accomplished by setting them to the edges of the copper segments following each other, as is clearly shown in Fig. 99.
The brushes should be set so that they bear on the commuta- tor at the end and for a distance of about J" back. If they are too long they will not bear t-t the end and will thus increase the sparking, and if too short they will drop unto the commutator slots and injure the copper tips.
The commutator should be cleaned off with fine sand paper every day as soon after stopping as possible. To keep the seg- ments all even and true, the sand paper can be placed around a stick planed true and held against the commutator while it is running. It is better to remove the brushes, when polishing the commutator, and make sure that the current is open.
As the current of these machines is of very high voltage, they must be handled with great care, to avoid injury. A rubber mat should be provided for the attendant to stand upon, and no one should ever touch any part of the machine if not standing on rubber, or thoroughly dry wood, known by trial to be a safe in- sulator. Only one hand should be used in handling any part of the machine, unless it is not running. It is a good idea to use rubber gloves when working around these machines.
HANDBOOK ON ENGINEERING.
CHAPTER X.
THE ALTERNATING CURRENT SERIES ARC LIGHTING SYSTEM.
In alternating current arc lighting systems of the series type, a special type of transformer is used, which is commonly called a regulating transformer, or a constant current transformer. The general principles^ and the operation of transformers is fully ex- plained in the section on alternating currents. In this connection it will be sufficient to say that in alternating current systems, the currents sent out from the central station are of a much higher voltage than is required to operate the lamps or other apparatus in which the current is used. This high primary current voltage is used so as to be able to transmit a large amount of energy with wires of small size. At the receiving end of the line the current is passed through transformers that generate secondary currents of whatever voltage may be required. For the operation of in- candescent lamps, motors and other devices, constant potential currents are necessary ; that is, currents that keep the voltage constant but change the strength, or amperes. For series arc lighting it is necessary to have currents that are just the opposite of this ; that is, the amperes remain constant, but the volts in- crease and decrease as the number of lamps increase and de- crease. A transformer acting in its natural way will develop a constant potential secondary current ; therefore, to make it de- velop a constant current with variable potential, it is necessary to resort to mechanical means.
HANDBOOK ON ENGINEERING.
113
The way in which transformers are arranged so as to develop constant currents is very simple as well as effective, it consists
Fig. 100. Constant Current Transformer for General Electric Series Alternating Arc Lighting System.
merely in constructing the transformer so that one of the coils may be moved close up or far away from the other. If the two coils, primary and secondary, are close together, the effect of the primary upon the secondary will be much greater than if they are far apart ; hence, when close together the voltage generated in the secondary will be high, and when far apart the voltage of the secondary will be low. From this it will be seen that to make a transformer so that it will regulate the voltage in proper propor- tion for any number of lamps in the circuit, all that is necessary is that the distance between the coils be varied in a manner to agree with the variation in the number of lamps,
8
114
HANDBOOK ON ENGINEERING.
THE GENERAL ELECTRIC CONSTANT CURRENT TRANSFORMER.
How the proper movement of the transformer coil is accomp-
c.0-^-0-
W
t»iym
• a *oa. £ fe
Q— Q
i i
/^^v /^^
a
-o— o
t
.2 « •J? a §0
3 «
V k»
A*
a
s ^
&> 02
HANDBOOK ON ENGINEERING. 115
lished can be made clear by means of Fig. 100, which shows a General Electric Regulating transformer with the outer casing re- moved. Looking at this illustration it will be seen that there is a rocking lever, which carries at one end a weight, while to the other end the upper coil of the transformer is attached. The ob- ject of the weight is to balance the coil so that a very small up- ward force will move the latter upward. Generally, the lower, stationary coil is the primary, and the upper, movable coil, is the secondary, The currents flowing in these two coils repel each other, in the same way that magnet poles of the same polarity re- pel each other. If the current in the secondary becomes too strong, the repelling force is increased, and the upper coil is raised. The raising of this coil causes the current to reduce, because the further apart the coils are the weaker the inductive action of the primary upon the secondary. If the current in the secondary becomes too weak the upward push will be reduced and the coils will come closer together, and as a result the secondary current will be increased. In either case the change in the position of the secondary coil will have the effect of returning the current in the secondary to the proper strength ; that is, if it is too strong it will be reduced, and if it is too weak it will be in- creased. The counterbalance weight is so proportioned that the excess of weight in the movable coil is just enough to balance the upward push of the current when the latter is of the proper strength. This being the case, it can be seen that if the rocking beam is mounted so as to swing freely, and the transformer is set so that the coil will not rub against the iron core, the apparatus will respond to very small changes in the strength of the current. This apparatus, like a steam engine governor, can be made so as to be sensitive, and if too sensitive, it will have a pumping ac- tion, that is, the rocking beam will acquire a see-saw movement, and the current will increase and decrease in time with the move- ment, thus causing the lamps to bum unsteady The manufac-
116
HANDBOOK ON ENGINEERING.
turers, by actual trial adjust the weight to the point that will give the closest regulation without causing a pumping action.
These regulating transformers are made in many sizes, the General Electric Company make them from 6 to 100 lamp capac- ity. The smaller sizes are constructed so as to be cooled by the currents of air that naturally circulate through them. The larger
A B
Fig. 102. Front and Back Yiews of Switchboard Shown in Diagram Fig. 101,
sizes are provided with a tight casing which is filled with oil, this construction being used so as to cool off the coils more thoroughly than they would be with air. If the transformer is of the air cooled type, a dash pot is generally provided to prevent the movable coil from moving too rapidly when a large number of
HANDBOOK ON ENGINEERING.
117
u 3 H \l $£
i t ? t t « * ,
o -s
II
I!
M
fl
I!
2 * 1=3 1
y^B"
118
HANDBOOK ON ENGINEERING.
lamps are cut in or out of the circuit at a time. The oil cooled transformers do not require a dash pot because the oil retards the movement of the coil.
From Fig. 101, the way in which a regulating transformer, such as shown in Fig. 100, is connected with the primary circuit.
Fig. 104. Front, Back and Side Yiews of Switchboard Shown in Diagram Fig. 108.
and with the lamp circuit, can be easily understood. At G is a wiring diagram showing all the connections, and A and B show in outline, the front and side view of the switchboard. As the explanatory notes on these diagrams are complete, no further ex- planation will be necessary.
HANDBOOK ON ENGINEERING.
119
Fig. 102 gives photographic views of the front and back of the switchboard, respectively.
Fig. 105. Westinghouse Constant Current Transformer for Series Alternating Arc Lighting.
Fig. 106. Front, Back and Side Views of Switchboard used with Westinghouse Series Alternating Arc Lighting System.
120 HANDBOOK ON ENGINEERING.
The diagram (7, Fig. 101, shows the circuit connections for a small size transformer feeding into a single lamp circuit, but large transformers are commonly arranged so as to feed into two lamp circuits. Fig. 103 shows the outline A, of the front, and JB, of the side of a switchboard, for a large transformer feeding into two lamp circuits, and the wiring diagram C. The front, side and back of this switchboard are shown in Fig. 104. THE WESTINQHOUSE CONSTANT CURRENT TRANSFORMER.
Fig. JOS is a photographic view of the regulating transformer made by the Westinghouse Company. There is some difference in the details of construction between this transformer, and the one shown in Fig. 100, but the principle of action is the same. In this design, there are two movable coils instead of one, and the stationary coil is secured between them. The counterbalanc- ing weights are connected with the movable coils through chains that run over large sheaves, each coil being independently coun- terbalanced, as it must be, for in this arrangement, when the upper coil rises, the top one will move down. The two coils, however, can be connected with separate lamp circuits, and then each one will move according to the demands of its circuit, and without reference to the movement of the other.
Fig. 106 is a photographic view of the front and back of the Westinghouse switchboard, used in connection with the regulat- ing transformers. The transformer Fig. 105, is of the oil cooled type, and of 100 lamp capacity. With the air cooled transform- ers this company provide a dash pot that is constructed with a valve that retards the movement of the coils when they come to- gether, more than when they separate, so that the current may not increase in strength too rapidly.
REACTANCE COIL CONSTANT ALTERNATING CURRENT REGULATORS.
The General Electric and the Westinghouse, regulating trans- formers, are transformers arranged so as to generate a secondary
HANDBOOK ON ENGINEERING. 121
current of constant strength and variable voltage, by being so constructed that the distance between the primary and sec- ondary coils may be varied, being increased to lower the voltage and reduced to increase it. There is another way in which a constant secondary current can be obtained, and this consists in using what is commonly called a choke coil or reactance coil, and arranging this so that its choking effect may be varied automati- cally as the voltage required varies. To make clear the action of choking coils it will be necessary to say that when an alternating current passes through a coil of wire, it reacts upon itself, that is, it tends to generate a current flowing in the opposite direction. It cannot generate such a current, but it can develop a back pressure or e. m. f. and this will reduce the flow of current. If the coil of wire is wound upon paper tube, the choking action will be very much less than it will be if a core made of finely lam- inated iron is inserted within the tube. With a little reflection it can be seen that with this difference existing between the effect of a core of iron and no core, the choking action can be varied by providing an iron core that can be drawn in or out of the coil.
THE WESTERN ELECTRIC REGULATOR FOR CONSTANT ALTERNATING CURRENTS.
The Western Electric Company make a regulator for series al- ternating arc lighting that operates on the principle explained in the foregoing. A side view of this regulator is shown in Fig. 107. The wire coil is suspended from one end of a rocking beam which carries at its other end a counter-balancing weight. This coil with the iron core and the side pieces constitutes what is commonly called a solenoid magnet. Such magnets exert a pull upon the iron core when a current passes through the coil, and the magnitude of the pull increases with the strength of the cur- rent. From this it will be seen that when current passes through the coil of Fig. 107, the pull exerted draws it upward, the
122 HANDBOOK ON ENGINEERING.
stronger the current the higher the position to which the coil is drawn. Now the choking action of the coil will increase as the uoil is raised, because more of the iron core will be within it. The choking action reduces the strength of the current ; there- fore, as the coil is raised by the increased pull due to the in- creased current, the choking action is increased, and the increase in current strength is checked. By properly adjusting the
•
Fig. 107. Western Electric Regulator for Constant Current Series Alternating Arc Lighting System.
counterbalancing weight, the apparatus can be made so that a very small increase in current strength will move the coil up to its highest position, and as it only requires a small movement of the coil to effect a considerable change in the strength of the cur- rent, it can be seen that the regulating action can be made very accurate. It is said that these regulators will respond to a vari- ation of one-tenth of an ampere in the current strength, when Carefully adjusted.
HANDBOOK ON ENGINEERING. 123
THE ADAMS-BEGNALL REGULATOR FOR CONSTANT ALTERNATING CURRENTS.
Fig> 108 shows another choke coil regulator made by the Adams-Begnall Electric Company. Comparing this illustration with Fig. 107 it will be seen that while the principle of operation is the same, there is a considerable difference in the design. An important feature about this regulator is the arrangement of the dash pot. It is found in practice that the retarding action of the
Fig. 108. Adams-Begnall Regulator for Constant Current Series Alternating Arc Lighting Systems.
dash pot is not required to correct small changes in the strength of current, because such changes are corrected by a very small movement of the coil, so that in such cases the dash pot is really objectionable. When, however, a large number of lamps are cut in or out of the circuit at one time, there is a tendency to greatly increase or decrease the current, and then the coil must
124 HANDBOOK ON ENGINEERING.
move over a considerable distance to keep the current constant. If the coil moves over a long distance it will acquire a velocity that will carry it beyond the mark, and thus over regulate, unless its motion is retarded; hence, the dash pot is desirable to con- trol the movement of the coil when it has to move over long dis- tances, but not for short distances. In the regulator Fig. 108 this result is accomplished by providing a certain amount of lost motion in the connections between the coil and the dash pot rod, so that the coil has to move through some distance to take up the slack in these connections before the dash pot plunger is moved. This last motion is sufficient to cover the range of reg- ulation over which the best results are obtained when the coil moves freely.
THE FORT WAYNE REGULATOR FOR CONSTANT ALTERNATING CURRENTS.
Fig. J09 is a side view of the regulator made by the Fort Wayne Electric Works. This regulator, like the two last de-
Fig. 109. Fort Wayne Regulator for Constant Current Series Alternating Arc Lighting System.
scribed, is of the choke coil, or reactance coil type. The dis- tinctive feature of this regulator is that the iron core, as well as the wire coil are made movable, and when the latter moves up,
HANDBOOK ON ENGINEERING.
125
the core moves down. The two parts are suspended from the opposite ends of rocking levers, the distances from the point of
|
if 1? |
Ground |
O oo c L_ 1 |
d> 5 o o (0 S L. S |
-o- § $ 00 3 d -<>- |
||
|
AmrneLer |
||||||
|
t |
o 1 |
X "N — |
||||
|
<> 31 i |
Reactance |
|||||
S g
Sfe
*
I
S2
iii
support to the ends being properly proportioned so that the core
126 HANDBOOK ON ENGINEERING.
balances the coil, thus making the former take the place of the counterbalancing weight in Fig. 107 and 108.
With the choke coil, or reactance type of regulator, the arc light circuit can be connected directly with the primary alterna- ting current mains, if the voltage of the latter is high enough. In cases where the primary voltage is too low, an ordinary step up transformer is used to generate a secondary current of the proper voltage.
The following wiring diagrams, which show the way in which the Fort Wayne apparatus is connected in the circuit, will serve to illustrate the general arrangement of all types of react- ance coil regulators, as the difference between them is in the details, and not in the general principle of operation.
Diagram A of Fig. 110 shows the connections between the bus bars of the primary circuit, and the arc lamp circuit for the Fort Wayne system when no step-up transformer is used. This arrangement is possible if the primary voltage is 1100 or 2200. With the former voltage an arc lamp circuit with 12 lamps can be operated, and with the 2200 volts 25 lamps can be used. For a greater number of lamps, a step-up transformer is required. As a rule, it is considered preferable to use a transformer in all cases, whether the primary voltage is high enough or not, as by this arrangement the lamp circuit is completely isolated from the main line.
In this diagram the regulator is shown with the coil and core in the position they assume when the lamp circuit is short cir- cuited, when the circuit is first connected with the main line bus bars, this is not the position of the regulator, in fact the coil is in the bottom or full load position. On this account a special re- actance coil is provided, as shown in the diagram, the office of which is to hold back the current, momentarily, until the regu- lator assumes its proper position. When the starting switch is closed this coil is cut out.
HANDBOOK ON ENGINEERING. 127
Diagram B, Fig. 110, is a more elaborate arrangement which shows the connections when a step-up transformer is used, and in addition includes a watt meter, a potential transformer for the latter, and a current transformer for the ammeter. These two last named transformers are provided simply to obtain currents of the proper voltage and strength for the instruments they actuate.
The operation of starting a Fort Wayne arc lamp circuit is as follows : — Looking at diagram J., Fig 110, the first operation is to close the plug switches that connect with the primary bus bars. This being done the current will flow from the upper bus bar through the regulator, the reactance coil and the lower part of the starting switch, back to the lower bus bar. The current pas- sing through the regulator will at once move it to the no load position, so that if now the starting cwitch is moved to the posi- tion that short circuits the reactance coil, no damage will be done, as the regulator will be in position to check the flow of current. During this time the lamp circuit has been short circuited through the lower connection of the starting switch, but the final movement of this switch opens the lamp circuit. The explanation of diagram jB, Fig0 110, is the same as the foregoing, for as will be seen the introduction of the step-up transformer does not alter the switching arrangements.
ALTERNATING CURRENT ENCLOSED ARC LAMPS FOR CON- STANT CURRENT SERIES CIRCUITS.
Alternating current arc lamps for series circuits are of the differential type. They are manufactured by the large companies and by many small concerns. All of them are practically the same in principle of operation, being provided with a clutch act- ing directly upon the carbon, and mechanism to actuate the clutch.
The lamp of this type made by the General Electric Company
128
HANDBOOK ON ENGINEERING.
is illustrated in Fig. Ill A showing the external appearance, and B the actual mechanism. The way in which the lamp oper- ates can be understood from the diagram (7, which shows the parts in the position they assume when the current is turned off. The switch at the upper right hand corner short circuits the lamp, making a direct connection from one binding post to the other. When this switch is opened, the current first passes through the
Fig. 111. General Electric Enclosed Arc Lamp for Series Alternating Current Circuits.
HANDBOOK ON ENGINEERING. 129
but as the carbons burn away, the increased length of the arc will cause the current through the shunt magnet to increase, thus in- creasing the pull of the latter. As the shunt magnet gradually strengthens, it gradually pulls up its end of A thereby bringing the carbons closer together, and when A has been lowered enough at its left hand end, the clutch strikes the stop and permits the carbon to slip through. If the carbon should fail to feed, or the circuit through the lamp should open through any cause, the shunt magnet will become strong enough to pull up its end of A until the cut out switch is closed.
In this lamp as shown in this diagram, the upper carbon holder slides within a tube and connection between it and the wire lead- ing from the series magnet is made through a flexible cable. The General Electric Company also makes lamps in which the upper carbon holder is attached to a cross-head that slides between two parallel rods, but the method of conveying the current to the upper carbon remains the same, that is, by a flexible cable.
The adjusting weight on A is for the purpose of adjusting the lamp so as to operate with more or less current. If the weight is moved toward the clutch rod end, the arc is short- ened and the voltage lowered. Movement in the opposite di- rection produces the opposite effect. A dash pot, shown at D, is provided to prevent too violent movement of the clutch lever A.
THE WESTINGHOUSE ALTERNATING CURRENT LAMP FOR CONSTANT CURRENT SERIES CIRCUITS.
The external appearance of the Westinghouse enclosed lamp is shown at A in Fig. 112, the mechanism of the constant cur- rent series type is shown at B, and a diagramatic representation of the latter is given in (7. It will be seen from this diagram that this lamp has all the parts shown in Fig. Ill, although they
9
130
HANDBOOK ON ENGINEERING.
differ considerably in form and are not in the same position. The series and shunt magnets act upon the opposite ends of lever A, and an adjusting weight is provided to regulate the length of the arc. The cut-out switch, although differently located, is actuated in the same mariner. The upper carbon holder slides within a tube and connection is made with it through a flexible cable. In the General Electric lamp the tube is slotted, and an ex-
Fig. 112. Westinghouse Enclosed Arc Lamp for Series Alternating Current Circuits.
• tension from the upper carbon holder passes through this slot and
connects with the cable. In the Westinghouse lamp the cable is attached to the top of the carbon holder and runs up within the tube to the upper end where it is secured.
HANDBOOK ON ENGINEERING.
131
THE FORT WAYNE ALTERNATING CURRENT ENCLOSED
LAMPS.
The external appearance of a Fort Wayne "Wood" enclosed arc lamp is shown at A in Fig. 113, and the mechanism of the lamp for series alternating current circuits is shown at B. Al- though there is a considerable difference in the design of the
Type Sa Lamp Form C
B
Figr. 113. Fort Wayne "Wood" Enclosed Arc Lamp for Series Alternating Current Circuits.
mechanism, the principle of operation is the same as in the lamps already described, so that in so far as the electrical connections are concerned it could be represented diagram atically by either of the two diagrams shown in connection with Figs. Ill and 112. ID the design of the mechanism the most important differences are in
132
HANDBOOK ON ENGINEERING.
the arrangement of the magnets, and in the means for conveying current to the upper carbon holder. The magnets instead of be- ing placed side by side at the top of the lamp are set one above the other, and they act upon an armature made in the form of a letter H. There are two series *coils and two shunt coils, the for- mer being at the top and surrounding the upper legs of the arma- ture, while the latter are at the bottom and surround the lower
A B C
Fig. 114. Western Electric Enclosed Arc Lamp for Series Alternating Current Circuits.
legs of the armature. The long coil seen at the left of the lamp is the starting resistance. The connection with the upper carbon holder is made by providing the fatter with contacts made in the form of springs, that rub against the inner surface of the tube within which the holder slides.
The appearance of the Western Electric Company's enclosed arc lamp is shown at A in Fig. 114. The mechanism for the se-
HANDBOOK ON ENGINEERING.
133
ries alternating current type is shown at .Band (7, the first illus- tration being a side view of the mechanism, and the second a front view. This lamp is provided with double coil magnets, and, as will be seen, they pull down on the lever that actuates the clutch rod. The coil located at the top of the lamp, is the start- ing resistance. The tube within which the upper carbon holder slides is of rectangular form and so is the upper end of the car-
B
Fig. 115. Types of Clutches Used in Enclosed Arc Lamps.
bon holder. Connection with the circuit is made through a cop- per ribbon which is bent in zig-zag fashion so as to compress when the carbon holder is pushed up and extend when it drops down as the carbon is consumed.
The construction of enclosed lamps is so simple that there are but few details that require special explanation, since all the working parts are well shown in the illustrations already pre- sented. The clutch is made in every case, so as to grip directly
134 HLNDBOOK ON ENGINEERING.
upon the carbon, instead of upon a carbon rod. as is the case .with open arc lamps. For the latter type of lamp a clutch acting on the carbon directly would not give satisfactory results owing to the fact that the arc is very short, but in the enclosed arc lamps the arc is about three times as long, hence, such accuracy of movement in feeding the carbons down is not required.
Fig* \15 shows three types of clutches, A being the design used by the Western Electric Company, B the design of the Fort Wayne Electric Works, and C the design of the Westinghouse Company.
The Western Electric Clutch is of the type called double clutch, and as can be easily seen consists of two clamping rings, the lower one being held up by the top one. When the carbon feeds down the lower ring strikes the stop and as soon as it set- tles sufficiently to release its hold, the carbon slips through. This shortens the arc and strengthens the shunt magnets so that they draw up their end of the clutch lever and prevent further feeding of the carbon .
The Fort Wayne clutch, shown at B, consists of a sleeve to which a clamping lever is connected. The whole device is held by this lever so that it clamps the carbon until the sleeve has moved so far down as to rest on the stop and permit the lifting end of the lever to drop far enough to release the rod.
The Western Electric and the Fort Wayne clutches are made wholly of metal, and in fact most clutches are so made. The Westinghouse Company, however, use a clutch which is made of a porcelain centre and a metallic supporting band, as is well shown at (7. The porcelain ring is the clutch proper, and the metallic band is provided simply to hold it. This band is made with clinching points on both sides so as to hold the ring firmly. The object of using a porcelain ring is to prevent current from pass- ing through the clutch to the carbon. If the clutch is made of metal there is a remote possibility of current passing through it,
HANBBOOK ON ENGINEERING.
135
and if it should, in sufficient quantity, the carbon might be burned away so as to form a depression into which the clutch could drop and thus prevent the lamp from feeding.
In Fig. \\6, are shown the Fort Wayne upper carbon holder at A, the Western Electric upper carbon holder at B, and at C the square tube within which this holder slides, together with the
B
Fig. 116. Upper Carbon Holders Used with Enclosed Arc Lamps.
copper ribbon that conveys the current from the upper end of the tube to the top of the carbon holder.
As shown in the foregoing, the General Electric and the West- jnghouse lamps are made so as to convey the current to the upper carbon holder through a cable, and this construction is the one most generally used ; the two arrangements of Fig. 116, are, how- ever, worthy of being described as their constructions differ from
136 HANDBOOK ON ENGINEERING.
each other and from general usage. The Fort Wayne carbon holder is provided with collector springs at its upper end, and these rub against the under surface of the tube into which the holder and carbon telescope when the latter is of full length. As these springs slide over the inner surface of the tube they keep it bright j and also maintain their own contact points bright, so that a good electric connection is always insured.
In the Western Electric upper carbon holder, I?, Fig. 116, the upper end is made square, so as to prevent it from turning, while sliding up and down in the tube C. This arrangement is neces- sary because a copper ribbon bent in zig-zag fashion is placed in- side the tube, and one end is secured to the top of the carbon holder, while the other end is fastened to the top of the tube. If the holder could twist around, it would soon get the ribbon in such a shape that it would bind against the sides of the tube and prevent the carbon from moving freely.
DIRECT CURRENT ENCLOSED ARC LAHPS OF THE CONSTANT POTENTIAL TYPE.
Enclosed arc lamps are used extensively at the present time on incandescent lighting, constant potential circuits, direct current and alternating current. These lamps are in great favor for indoor lighting, owing to the fact that they operate with low voltage currents that are not dangerous. All the arc lamp man- ufacturers make lamps of this type.
A general Electric constant potential lamp is shown in Fig. 117 at A. The mechanism is seen at B and a diagram illustrat- ing the principle of operation is given at C. As will be seen from the latter figure, the construction is very simple. There is but one set of magnet coils, and these pull directly upon the clutch rod. The construction is simple because the principle of action makes it possible to use simple construction. In the series lamps described in the foregoing, it is necessary to have magnet coils
HANDBOOK ON ENGINEERING.
137
connected in shunt to the arc as well as coils in series with the arc. This arrangement is required because the current remains practically constant, hence, the pull of the series magnets varies next to nothing ; therefore, these magnet coils alone cannot cause the upper carbon to feed down as the arc lengthens out. The shunt magnet coils, however, become stronger as the arc becomes longer, because the resistance of the latter is increased, hence, as the carbons burn away, the strength of the shunt magnet in-
General Electric Enclosed Arc Lamp for Constant Potential Direct Current Circuits.
creases and lifting its end of the actuating lever, depresses the clutch rod, causing the clutch to strike the stop when the carbons have burned away enough to require feeding. In a constant potential lamp the current weakens as the arc lengthens and thus the pull of the magnet is reduced. As the length of the arc
138
HANDBOOK ON ENGINEERING.
gradually increases, the magnet pull gradually reduces, so that the clutch rod slowly descends until the clutch strikes the stop and permits the carbon to slip through. The long coil seen on
the left side of the diagram is simply a resistance used to balance the portion of the voltage not required for the lamp. These lamps operate with a voltage of about 75 to 80 and as the cur- rent voltage is from 110 to 115, a resistance has to be used to
HANDBOOK ON ENGINEERING. 139
balance <the extra 35 volts0 The illustration B and the diagram C show clearly the upper carbon holder and the way in which it is guided between parallel rods ; the former shows the way in which the magnet armature is connected directly with the clutch. In the diagram G it will be seen that the wire from the P binding post is connected with a ring midway between the ends of the resistance coil. This is a contact ring that is provided so that by sliding it up or down more or less of the resistance can be cut into the circuit. When the ring is in the position that intro- duces the proper amount of resistance, it is made fast so that it may not become displaced thereafter.
THE WESTINGHOUSE CONSTANT POTENTIAL LAHP.
Fig* \ f 8 shows the mechanism of the Westinghouse constant potential lamp at B. In this design the balancing resistance is wound upon a large porcelain spool and occupies the upper part of the lamp casing. The actuating magnet coils are directly below it. The external appearance of the lamp is shown at A in Fig. 118, and a diagrammatic representation of the mechanism and circuit connections is given at C. From this diagram it will be seen that the connections with the circuit are the same as in the General Electric lamp. The portion of the resistance coil that is cut into the circuit is adjusted by means of a sliding contact B which presses against the surface of the resistance wire, the latter being bare. When B has been moved to the proper posi- tion the screw at A is tightened and this holds B in position.
THE FORT WAYNE CONSTANT POTENTIAL LAMP.
Fig. U9 shows the mechanism of the Fort Wayne constant potential lamp at A. The first impression gained from looking at this illustration is that the construction is entirely different in principle from the two lamps of this type already described; such, however, is not the case. The apparent difference is due
140
HANDBOOK ON ENGINEERING.
to the fact that the balancing, or steadying, resistance" as it is also called, is placed in the separate cylindrical part directly above the lamp. In the wiring connections of the lamp there is a difference that is quite noticeable. In the diagram B it will be seen that in addition to the ordinary balancing resistance, shown at the top of the diagram, there are two resistances, one for regulating the strength of the current and the other for ad- justing the voltage. The latter resistance is in reality a part of
steadying resistance
Fig. 119. Fort Wayne Enclosed Arc Lamp for Constant Potential Direct Current Circuits.
the steadying resistance, that portion that has to be cut in or out of the circuit to obtain the proper voltage at the arc. The cur- rent adjusting resistance, however, is an addition, and is for the purpose of adjusting the lamp for different strengths of current. The normal current is 5 amperes, but by means of the current
HANDBOOK ON ENGINEERING.
141
adjusting resistance it may be reduced or increased considerably, one ampere about. The reduced current will give less light and the increased current more light with the same voltage.
DIRECT CURRENT ENCLOSED LAMPS FOR OPERATION ON POWER CIRCUITS, MULTIPLE SERIES SYSTEM.
The lamps described in the preceding section are used on in- candescent Mghting circuits of 110 to 125 volts, and each lamp
A B C
Fig. 120. Fort Wayne Multiple Series System Lamp for Op- eration on Power Circuits Direct Current.
is connected directly across the line, just the same as incan- descent lamps are. Enclosed arc lamps are also used on 220 and 500 volt circuits. With the first named voltage they are con- nected two in "series, and with the second, five in series. Lamps Of this type, which we will describe in this section are called
142 HANDBOOK ON ENGINEERING.
" Multiple series lamps. " The mechanism of these lamps is somewhat different from that of the simple constant potential lamps used on 110 volt incandescent lighting circuits, and in the case of most manufacturers the external appearance is slightly modified. The external appearance of the Fort Wayne lamp of this type is shown at A in Fig. 120. By comparing it with Fig. 119 it will be seen that the resistance drum on top of the lamp proper is considerably longer. A comparison between the me- chanism of the two lamps will at once reveal the fact that in internal construction there is quite a difference. The arrangement and operation of this mechanism can be clearly understood from the diagrammatic representation of it at C in Fig. 120. Looking at this diagram it will be seen that there are two magnets, a series and a shunt. There is also a cut-out and a cut-out resistance, the latter being made equal to the normal resistance of the arc. The cut-out and its resistance are required so that if the lamp is turned out intentionally, or cuts itself out through the failure of the carbons to feed, the other lamps connected in series with it will not be affected. If the resistance were not used, the cur- rent would increase decidedly when one lamp is cut out, even if there are five in series. Cutting out the second light would make a still further increase in the current, and this increase would probably be sufficient to burn out the magnet coils of the three lamps left in the circuit. The steadying resistance shown to the left of the cut-out resistance is for the purpose of balancing the voltage not required for the lamp proper. If five lamps are connected in series on a 500 volt circuit, the voltage correspond- ing to each lamp will be 100, and as the voltage of the arc is about 75, there must be an additional resistance able to balance about 25 volts. Some of this resistance is placed in the voltage adjusting resistance, but the bulk of it is in the top resistance. When the lamp is switched into circuit by turning the switch to the " On " position, as in the diagram, the current from binding
HANDBOOK ON ENGINEERING.
143
post P passes to the switch, thence to the upper carbon, through the arc to the lower carbon, and then through the series magnet coil and the steadying resistance to the N binding post. The current for the shunt magnet coil starts from the left side
switch contact, and passing through the shunt coil connects with the wire running from the upper end of the series coil to the righ. side of the resistance. The circle that repre-
144 HANDBOOK ON ENGINEERING.
sents the cut-out contact is connected with the right side of the cut-out resistance, so that when the cut-out acts, post P is con- nected directly with post JV through the cut-out and steadying resistances.
The mechanism of the Westingnouse multiple series lamp is shown at A, in Fig. 121, a diagrammatic representation of the same is given at B, and the lamp complete is shown at C. As will be seen there are two magnets, a series and a shunt, just as in the Fort Wayne lamp. The voltage and current adjusting re- sistances are not used, but in their stead a weight is placed upon the clutch actuating lever, and the necessary adjustment is ob- tained by setting this weight in the proper position. In each lamp there is placed a cut-out resistance, that is equal to the re- sistance of the arc when burning normally. This resistance is shown at the lower portion of the diagram. The way in which the cut-out acts is so clearly shown as to require no explanation. The resistance to balance the excess of voltage is located in the drum above the lamp, but in many cases the drum is not used, and the resistance is placed in a separate casing adapted to be fastened to the wall.
The General Electric Company make a lamp for multiple series operation that is practically the same as their 110 volt constant potential lamp. The only difference between it and the latter is that it is provided with an adjusting weight by means of which the several lamps in a series are made to move the clutch lever alike for the same strength of current. This adjusting weight is carried on a bell crank pivoted on the under side of the cap of the lamp, as is clearly shown at J3, in Fig. 122. The other end of the bell crank is connected with the magnet armature through a link. By properly setting the weight on the lever in the several lamps, all will work the same, the magnet of each one holding its armature in the same position for the same current strength. By
HANDBOOK ON ENGINEERING.
145
means of this simple mechanical device the shunt magnet is dis* pensed with, and the mechanism is correspondingly simplified.
In most cases this lamp is not provided with a cut-out, so that if a lamp fails to operate it will go out and so will the other lamps in the series with it. The operation of the lamp is considered to be so reliable that unless it is an unusual case no cut-out is provided. When a cut-out is installed it is placed in a separate casing and
A B C
Fig. 122. General Electric Multiple Series Arc Lamp for Power Circuits Direct Current.
is suspended above the lamp as shown in A, Fig. 122. This cut- out is so arranged that if a lamp goes out it can be removed to be readjusted without interfering with the operation of the other lamps in the series. The wiring diagram for this cut-out is shown at 0, and as will be seen it consists of the cut-out resistance and a magnet directly under it. The coil of this magnet is connected in series with the lamp so that it will hold the switch under it
10
146 HAr^rfOOK ON ENGINEERING.
open as long as current flows through the lamp, but it current fails to pass through the lamp the switch will close and the cur- rent will pass through the cut-out resistance, and, as can be seen, the lamp can then be disconnected without opening the circuit.
ENCLOSED ARC LAMPS FOR CONSTANT POTENTIAL ALTERNATING CURRENT CIRCUITS.
The only difference between constant potential arc lamps for alternating and for direct currents is that in the latter a balan- cing or steading resistance is used to balance the voltage not util- ized in the lamp, while in the former a choke coil is employed to perform the same office. A choke coil cannot be used in the di- rect current lamps, because it will not have any choking effect when traversed by a direct current. For information on this point see the section on alternating currents.
A resistance coil placed in the circuit absorbs energy in pro- portion to the voltage it balances, so that in a direct current lamp on a 110 volt circuit, if the resistance balances 35 volts, and the arc 75, then the energ}7 made useful in the lamp will be to the en- ergy lost in the resistance as 75 is to 35. A choke coil does not absorb energy in proportion to the voltage it balances, or any- thing like this amount. A choke coil sets up a back pressure, but the actual amount of energy it absorbs is only that neces- sary to pass the current through the wire, and this is generally only a small percentage of the portion of the voltage balanced. Owing to this fact alternating current lamps on constant potential circuits are far more efficient in so far as the use of the electrical energy is concerned, than direct current lamps ; for while the lat- ter lose 25 to 30 per cent of the energy, the former only lose two or three per cent. Direct current lamps, however, give more light for the same amount of electrical energy, so that the practi- cal result is about the same for both types.
HANDBOOK ON ENGINEERING.
147
The mechanism of a Fort Wayne alternating current constant potential lamp is shown at A in Fig. 123, and a diagrammatic rep- resentation of the same is given at B. Comparing this latter il- lustration with the diagram of Fig. 119, it will be seen that they look very much alike, in fact the only difference is that the steadying resistance of the latter is replaced by a reactance, choke coil. In other respects the two lamps are the same. In
A
B
Fig. 123. Fort Wayne Arc Lamp for Constant Potential
Alternating Current Circuits.
the direct current lamp, means .are provided for cutting in more or less of a voltage regulating resistance, which as already stated is really a part of the steadying resistance ; in the alternating current lamp, the reactance coil is made with a number of con-
148
HANDBOOK ON ENGINEERING.
nections to different parts of its convolutions, so that more or less of it may be cut into the circuit.
In the construction of the magnet cores of the alternating and the direct current lamps there is a decided difference. The direct current lamps are made with solid iron cores, but the magnets of the alternating current lamps have laminated cores, made of very thin sheet iron or soft steel. This difference is necessary owing
A B
Fig. 124. Westinghonse Lamp for Constant Potential Alternating Current Circuits.
to the fact that in a solid core the alternating current would in- duce an electric current that would soon make the metal very hot and the strength of the magnet w»ould be practically nothing.
The mechanism of the Westinghouse constant potential lamp for alternating currents is shown at A in Fig. 124. A diagram of the same is ahown at B. Comparing Figs. 118 and 124 it
HANDBOOK ON ENGINEERING.
149
will be seen that the resistance coil of the former is replaced by a reactance coil. The direct current lamp, Fig. 118, has two mag- net coils to pull down the clutch actuating lever, while the alter- nating current lamp, Fig. 124, has only one coil, but both lamps operate in the same way. By comparing the diagrams of the two lamps their similarity is seen at once.
The mechanism, the external appearance, and the diagram of
Fig. 125. General Electric Lamp for Constant Potential Alternating Current Circuits.
connections of the General Electric constant potential lamp are given in Fig. 125. The principle of operation of this lamp is the same as that of the other two explained in the foregoing. The diagram shows very clearly how the magnet pulls directly upon the clutch connecting link.
150
HANDBOOK ON ENGINEERING.
THE FORT WAYNE HULTIPLE ALTERNATING CURRENT STREET ARC LIGHTING SYSTEM.
The Fort Wayne Company make an alternating current street lighting system of the constant potential type that is intended for small towns or for places where there are several centres in which
Fort Wayne System.
General Plan of Multiple Alternating Current Street Arc Lighting System. Fig. 126.
numerous lights are used, these centres being some distance from each other and from the central station. The general principle of the system is to generate an alternating current of high voltage
HANDBOOK ON ENGINEERING.
151
at a central station, and to convey this to the centres of distribu- tion where it is utilized in arc lamps through individual trans- formers which develop secondary currents of the voltage and amperage required for the lamps. The system is designed so as to be used for incandescent lighting as well as arc.
Fig. 127. Fort Wayne Enclosed Are Lamp Used with System Illustrated in Diagram Fig. 126.
The diagram Fig. 126, shows the general arrangement of the system. The alternator and switchboard shown are supposed to be located at the central station, probably several miles distant. The wires coming from the alternator are connected with lower terminals of the two pole switch and also the arc circuit switch. From the upper terminals of the two pole switch the connections
152 HANDBOOK ON ENGINEERING.
run out to the transmission lines, the ammeter being connected in one of these connections. At the centres of distribution these line wires are connected with the primary coils of step-down transformers that furnish current for incandescent lighting. From the upper terminal of the arc circuit switch a connection runs out to a third transmission line which also goes to the cen- tres of distribution. At these centres, the primary coils of small transformers, each one of sufficient capacity to operate one arc lamp, are connected with the arc transmission main, and one of the incandescent mains, as clearly shown in the diagram. These small transformers are proportioned so that they give a secondary current of about 6 amperes and 77 volts, or just sufficient to op- erate a lamp. The transformers which are shown directly above the lamp in the diagram, are placed in any convenient position, generally at the top of the arc light pole.
As the transformer furnishes a current of the proper voltage for the lamp no reactance coil is required in the latter, and as a consequence the construction is considerably simplified, as can be seen from Fig. 127 which shows the lamp mechanism at A and the diagram of connections at B.
LUMINOUS OR FLAMING ARC LAHPS.
Open arc lamps frequently give a poor light owing to the fact that the carbons are of inferior quality, and as a result are va- porized by the heat of the arc. This vapor burns and produces a reddish or purple flame that not only changes the color of the light, but reduces its brilliancy. By experimenting with carbons of different composition it has been found that the flame pro- duced can be varied in color, and at the same time can be intens- ified so that it will give a strong light. Thus that which was originally an objectionable feature of arc lamps has been made use of in developing a new type of lamp in which the flaming ac-
HANDBOOK ON ENGINEERING.
153
tion is increased, and the brilliancy of the flame is depended upon to give the color of light desired, and also the intensity. Lamps that operate on this principle are called Flaming arc lamps and also Luminous arc lamps. At the present time they are used quite extensively in Europe, and are rapidly gaining headway in this country, owing to the fact that they give more
ABC Fig. 128. Excello Luminous Arc Lamp.
A. —Diagram of Mechanism and Circuit Connections for Direct Current Lamp. C.— Diagram of Mechanism and Circuit Connections for Alternating Current Lamp.
light for the same amount of current energy and the light is of a very fine color, being nearly white.
THE EXCELLO LUMINOUS ARC LAMP.
In Fig* 128, the Excello Luminous Arc Lamp is shown, the
154 HANDBOOK ON ENGINEERING.
diagram A being that of the direct current lamp, and C that of the alternating current lamp. As will be seen, in both diagrams, the carbon rods are set at an incline toward each other, and are held up by chains that pass around a drum. The weight of the carbon rods furnishes the force required to rotate the drum, and clock work controls the velocity of rotation when the catch /is drawn out of the way.
In the direct current lamp, diagram A, there is a series mag- net at the side of the drum, which depresses rod b when the cur- rent is turned on, and through the links at the bottom separates the carbons. The shunt magnet n then becomes strong enough to draw e around and lift b and cause the slider d to bring the carbons together to strike the arc. As the carbons burn away e rotates further owing to the fact that the shunt magnet n becomes stronger. When e moves far enough /is pulled out of the way and then the clock work begins to rotate and the chains on the drum unwind thus permitting the carbons to feed down. When the carbons are fully consumed, a small detent on the chain stops the further feeding and then when the arc becomes sufficiently long the current breaks and the lamp goes out.
The diagram C shows the alternating current lamp. In this lamp there is a small disc that is rotated in one direction by the action of the series magnet H and in the opposite direction by the shunt magnet N. When the current is turned on the series magnet H rotates the disc in a direction that lifts and separates the carbons. As the carbons separate, the force of the shunt magnet increases and gradually counteracts the force of H so that when the arc is of the proper length, the disc stops turning. As the carbons burn away the shunt magnet becomes stronger and then by overpowering H causes the disc to rotate in the opposite direction thus causing the carbons to feed down.
These lamps are made so as to run with currents of 6.8, 10
HANDBOOK ON ENGINEERING.
155
and 12 amperes, and are burned two in series on 115 volt circuits, or four in series on 230 volts. For the same amount of electri- cal energy they give more light than regular enclosed arc lamps. The carbons last about 18 hours. The light is clear white, but for advertising purposes it can be made of different colors by changing the composition of the carbons. Just above the arc is
A B
Fig. 129. General Electric Luminous Arc Lamp.
placed a small porcelain reflector i which acts as a protector of the parts above the flame and also as a reflector.
Fig* J29 shows a flaming arc lamp made by the General Electric Company. At A is seen the external appearance of the lamp while B shows the mechanism. In this lamp the lower carbon is
156 HANDBOOK ON ENGINEERING.
a composition contained in an iron tube and is fed upward by the magnets above the arc through the side connection as. shown in B. The main frame of the lamp consists of a central tube of good size that serves as a chimney to carry off the fumes from the arc. The lower carbon burns for about 150 hours. In place of an upper carbon, a copper disc is used and this is of such size that it remains comparatively cool so that its life is about 2000 hours. The arc remains in the same position all the time so that a reflector made of enameled iron can be secured stationary just above the arc.
This lamp is made for direct currents to operate in series and consumes a current of four amperes at an e. m. f . of about 75 volts. Its light giving efficiency is said to be very high.
GENERAL DIRECTIONS FOR THE CARE AND OPERATION OF ENCLOSED ARC LAMPS OF ALL TYPES.
It is not practicable to give in this book detailed directions for the operation and care of each and every make of enclosed arc lamp on the market, as there are so many of them that such di- rections would fill a volume by themselves. In what follows di- rections are given that apply to all types of lamps, but any one desiring minute directions relative to any particular lamp can easily obtain them by applying to the manufacturers who publish instruction books that contain all this information.
Carbons: For alternating, as well as direct current lamps, only the highest grade of carbons should be used, as they not only give a better and more steady light, but they last much longer.
For direct current lamps only solid carbons should be used.
For alternating current lamps one of the carbons should be solid and the other cored.
No carbons should be used that are not perfectly straight, round and smooth, if they are not smooth rub them with a piece of sand paper to take off the blisters and lumps.
HANDBOOK ON ENGINEERING. 157
It is necessary that the carbons be very nearly the proper di- ameter to enable the lamp to feed properly. The manufacturers furnish a gauge provided with two holes, and all carbons that pass through the smaller hole as well as those that will not pass through the larger hole are to be rejected as too large and too small to be used. The maximum variation from the standard di- ameter is not quite one hundredth of an inch either under or over size.
In direct current lamps, if the upper carbon is 12" long, the lower one should be 5J" and in almost every case the stump left in the upper holder when the carbons have burned out is used for the lower carbon in the next trimming, as it is of ample length for the purpose.
For alternating current lamps the upper carbon 12" and the lower one 7". Most of the carbons used are ^" diameter, but T7^" and |" are also used in direct current lamps. Some lamps are also made so as to use 9" carbons in the upper holder.
If the lamps are in good order, with tight fitting globes, and the carbons are first class, they should burn for about 150 hours before requiring retrimming, that is for 12" upper carbon, J" di- ameter. This is the life for direct current ; for alternating cur- rent lamps the life is about 100 hours.
How to trim lamps : In trimming or renewing the carbons in a lamp care should be taken that the upper carbon is pushed up as far as it will go, so as to make a good contact with the holder. So as to facilitate this operation it is best to use carbons with a tapering end.
Be sure that the carbon slides freely through the clutch and the metal cap of the enclosing globe.
Remove the dust from around the gas check and see that the mechanism all works freely, if this is not done, the lamp will not burn well, and will probably lengthen the arc and thus shorten the life of the carbons.
158 HANDBOOK ON ENGINEERING.
Never put oil in the dash pot, it is made to work dry.
To secure a good light the inner enclosing globe should be cleaned every time new carbons are put in, so as to remove the coating deposited by the gas from the arc. In large stations it is the custom, generally, to provide duplicate lower carbon holders, and these are trimmed and secured to the globe and are then placed in baskets provided with partitions to receive them. They are carried by the trimmers in a wagon and then in trim- ming the lamps the old globe with the lower carbon holder is re- placed by the new one. This saves the trouble of cleaning the globe and inserting the lower carbon at the lamp.
In order that the life of the carbons may be long it is necessary that the enclosing globe be fitted perfectly tight, if air can get in the carbons will soon burn out. Owing to this fact the edge of the globes should be well examined every time the lamp is trimmed to make sure that there are no pieces nicked out, and care should be taken to see that the globes come down properly to their seats, and make a tight joint. Never try to burn an en- closed arc lamp with the enclosing globe removed. Keep all the electrical contacts tight.
Be sure that the dash pots always work freely.
Make sure that the upper carbon does not bind.
Lamps should be suspended from a strong support.
The clutch should work smoothly and reliably.
Use no crooked, rough, dirty or inferior carbons.
Always have top carbon positive. If you do not know whether it is positive or not, light the lamp for a few minutes, then put it out and the top carbon will remain hot longer than the lower one, if it is positive.
Do not use any inner globes that are cracked, nicked or do not fit tightly against their seats.
Use no oil on any part of the lamp where it can possibly get on the carbons, as this will cause flickering and flaming.
HANDBOOK ON ENGINEERING. 159
Keep under side of gas cap clean and bright by wiping at each trimming. The bright metal attracts the gases and prevents them from depositing on the globe.
Remove the casing that encloses the mechanism occasionally and inspect the parts carefully for possible faults.
Keep the space between carbon bushings in the gas cap clean and free from dust.
Renew the bushings whenever they show much wear, as increase in the diameter of the hole permits more air to enter the globe around the carbon and this shortens the life of the carbons.
Be sure to wipe inner globes clean at each trimming so as to prevent deposits from forming. Should deposits form that can- not be wiped off, they can be removed with a weak solution of muriatic acid.
Never run alternating current lamps on the wrong frequency. Many alternating lamps are made to run on different frequencies by slightly changing the connections. For information as to how to make these changes see instruction books of the makers of the lamp.
Installing lamps : Lamps should not only be installed in places where they will destribute light over the greatest possible area, but also where they are easily accessible when it is desired to trim or inspect them.
Outdoor lamps should be suspended from 25 to . 30 feet from the ground, to give the best service, and in positions where their light will be obstructed as little as possible. The distance be- tween lamps should not be more that about 300 feet to obtain satisfactory illumination. The globes used for outdoor lighting should be clear, for the inner as well as the outer globe.
For indoor lighting the inner globe should be ground glass or opal, the outer one clear glass. For outdoor lighting metal re- flectors are commonly used, but no reflector is used with indoor lamps.
HANDBOOK ON ENGINEERING,
CHAPTER Xa.
Incandescent Wiring Table.
Table on two following pages is arranged to enable wiremen to select the right sizes of wire for service connections and inside work. The figures at the top indicate distance in feet to center of distribution, in reality half the length of the circuit ; the four columns at the left showing the number of 16-candle power lamps at various voltages; the other, figures showing the sizes of wire, Brown & Sharpe gauge, to be used for distributing the number of lamps stated at the distances indicated and with the loss of 1 volt.
For example: To distribute 30 lamps of 110 volts at a dis- tance of 80 feet with a loss of 1 volt. In colamn of 110-volt lamps find the number 30, then follow the same line of figures to the right until the column headed 80 is reached, and it appears that No. 6 wire must be used.
The same table may be used for other losses than 1 volt by dividing the given number of lamps by the number of volts to be lost, then with this product proceed as before in the table.
For example : To distribute 30 lamps of 110 volts at a distance of 80 feet with a loss of 2 volts, divide 30 by 2 which gives 15, then find 15 in the column headed 110 volts and follow the same line of figures to the right until column headed 80 is reached, and it is found that No. 8 wire must be used.
No wire smaller than No. 14 is shown in the table as the Na- tional Board of Fire Underwriters prohibits the use of a smaller size. Odd sizes smaller than No. 5 are not commercial and are therefore omitted.
HANDBOOK ON ENGINEERING.
Incandescent Wiring: Table.
Sixteen Candle Power Lamps. Lo«s One Volt
TABLE No. 1. Sizes of Wire are by B. & S. Gauge.
161
|
52 Volt 3i |
110 Volt 34 |
220 Volt 4 |
550 Volt 4 |
Distance in feet to center of Distribution. |
|||||
|
Watt |
Watt |
Watt |
Watt |
||||||
|
Lamps |
Lamps |
Lamps |
Lamps |
1 |
|||||
|
20' |
25' |
30' |
35* |
40' |
45' |
||||
|
1 |
2 |
3 |
9 |
14 |
14 |
14 |
14 |
14 |
14 |
|
2 |
4 |
7 |
18 |
14 |
14 |
14 |
14 |
14 |
14 |
|
3 |
6 |
11 |
28 |
14 |
14 |
14 |
14 |
14 |
14 |
|
4 |
8 |
15 |
37 |
14 |
14 |
14 |
14 |
14 |
14 |
|
5 |
Iff |
18 |
46 |
14 |
14 |
14 |
14 |
12 |
12 |
|
6 |
12 |
23 |
56 |
14 |
14 |
14 |
12 |
12 |
12 |
|
7 |
15 |
26 |
65 |
14 |
14 |
12 |
12 |
12 |
10 |
|
8 |
17 |
30 |
74 |
14 |
12 |
12 |
12 |
10 |
10 |
|
9 |
19 |
33 |
83 |
14 |
12 |
12 |
10 |
10 |
10 |
|
10 |
21 |
37 |
93 |
12 |
12 |
12 |
10 |
10 |
10 |
|
12 |
25 |
44 |
111 |
12 |
10 |
10 |
10 |
8 |
8 |
|
14 |
30 |
52 |
130 |
12 |
10 |
10 |
8 |
8 |
8 |
|
16 |
34 |
59 |
148 |
10 |
10 |
8 |
8 |
8 |
8 |
|
18 |
38 |
66 |
107 |
10 |
8 |
8 |
8 |
8 |
6 |
|
20 |
42 |
74 |
185 |
10 |
8 |
8 |
8 |
6 |
6 |
|
25 |
63 |
92 |
232 |
8 |
8 |
6 |
6 |
6 |
6 |
|
80 |
63 |
111 |
278 |
8 |
6 |
6 |
6 |
5 |
5 |
|
$5 |
74 |
130 |
324 |
6 |
6 |
6 |
5 |
5 I |
4 |
|
40 |
85 |
148 |
371 |
6 |
6 |
6 |
5 |
4 |
4 |
|
45 |
95 |
166 |
428 |
5 |
5 |
5 |
4 |
4 |
3 |
|
60 |
106 |
185 |
464 |
5 |
5 |
4 |
4 |
3 |
3 |
|
55 |
116 |
203 |
510 |
4 |
4 |
4 |
3 |
3 |
2 |
|
€0 |
127 |
222 |
557 |
4 |
4 |
4 |
3 |
2 |
2 |
|
65 |
138 |
240 |
603 |
3 |
3 |
3 |
3 |
2 |
2 |
|
70 |
148 |
260 |
650 |
3 |
3 |
3 |
2 |
2 |
1 |
|
75 |
159 |
277 |
696 |
2 |
2 |
2 |
2 |
1 |
1 |
|
80 |
170 |
296 |
742 |
2 |
2 |
2 |
2 |
1 |
1 |
|
90 |
191 |
333 |
835 |
1 |
1 |
1 |
1 |
1 |
0 |
|
100 212 il |
370 |
92$ |
1 |
1 |
1 |
1 |
0 |
0 |
Iff2 HANDBOOK ON ENGINEERING
Incandescent Wiring, Table.
Sixteen Candle Power Lamps, Loss, One Volt. TABLE No. la. Sizes of Wire are by B. & S. Gauge.
DISTANCE IN FKET TO CENTER OP DISTRIBUTION.
|
60' |
60' |
70' |
80' |
HO' |
100' |
120' |
140' |
IbO' |
180' |
200' |
|
14 |
14 |
14 |
14 |
14 |
14 |
14 |
14 |
14 |
14 |
12 |
|
14 |
14 |
14 |
14 |
14 |
12 |
12 |
12 |
10 |
10 |
10 |
|
14 |
14 |
12 |
12 |
12 |
10 |
10 |
10 |
8 |
8 |
8 |
|
12 |
12 |
12 |
10 |
10 |
10 |
8 |
8 |
8 |
8 |
6 |
|
12 |
10 |
10 |
10 |
10 |
8 |
8 |
8 |
6 |
6 |
6 |
|
10 |
10 |
10 |
8 |
8 |
8 |
8 |
6 |
6 |
6 |
6 |
|
10 |
10 |
8 |
8 |
8 |
8 |
G |
G |
G |
5 |
5> |
|
10 |
8 |
8 |
8 |
8 |
G |
G |
6 |
5 |
5 |
4 |
|
10 |
8 |
8 |
8 |
6 |
G |
6 |
5 |
5 |
4 |
4 |
|
8 |
8 |
8 |
G |
G |
G |
5 |
5 |
4 |
4 |
a |
|
8 |
8 |
6 |
G |
6 |
5 |
5 |
4 |
3 |
3 |
2 |
|
8 |
C |
6 |
G |
5 |
5 |
4 |
3 |
3 |
2 |
2 |
|
6 |
C |
6 |
5 |
5 |
4 |
3 |
3 |
2 |
2 |
1 |
|
0 |
G |
5 |
5 |
4 |
4 |
a |
2 |
2 |
1 |
1 |
|
6 |
5 |
5 |
4 |
4 |
3 |
2 |
2 |
1 |
1 |
0 |
|
5 |
5 |
4 |
3 |
3 |
2 |
1 |
1 |
0 |
0 |
OOi |
|
5 |
4 |
3 |
2 |
2 |
1 |
1 |
0 |
0 |
00 |
00 |
|
4 |
3 |
o |
2 |
1 |
1 |
0 |
00 |
00 |
000 |
000 |
|
3 |
2 |
2 |
1 |
1 |
0 |
00 |
00 |
000 |
000 |
0000 |
|
3 |
2 |
1 |
1 |
0 |
0 |
00 |
000 |
000 |
0000 |
0000 |
|
2 |
1 |
1 |
0 |
0 |
00 |
000 |
000 |
0000 |
0000 |
|
|
1 |
||||||||||
|
* |
1 |
0 |
0 |
00 |
00 |
000 |
0000 |
0000 |
||
|
\ |
1 |
0 |
00 |
00 |
000 |
000 |
0000 |
0000 |
||
|
I |
0 |
0 |
00 |
00 |
000 |
0000 |
0000 |
|||
|
1 |
0 |
00 |
00 |
000 |
000 |
0000 |
||||
|
0 |
0 |
00 |
OOQ |
000 |
0000 |
(0000 |
! . |
|||
|
0 |
00 |
00 |
000 |
000 |
0000 |
|||||
|
0 |
00 |
000 |
000 |
0000 |
0000 |
|||||
|
00 |
000 |
000 |
0000 |
0000 |
163
Feet x 2 x 10,70.
TABLE No. 2.
|
Feet to end of Circuit. |
Ft. x2x!0.70. |
Feet to end of Circuit. |
Ft.x2xlO.70. |
Feet to end of Circuit. |
Ft. x2x 10.70. |
|
5 |
107 |
185 |
3,969 |
365 |
7,8.11 |
|
10 |
214 |
190 |
4,066 |
370 |
7,918 |
|
15 |
321 |
195 |
4,173 |
375 |
8,025 |
|
20 |
428 |
200 |
4,280 |
380 |
8,132 |
|
25 |
535 |
205 |
4,387 |
385 |
8,239 |
|
30 |
642 |
210 |
4,494 |
390 |
8,346 |
|
35 |
749 |
215 |
4,601 : |
395 |
8,453 |
|
40 |
856 |
220 |
4,708 |
400 |
8,560 |
|
45 |
963 |
225 |
4,815 |
405 |
8,667 |
|
50 |
,070 |
230 |
4,922 |
410 |
8,774 |
|
55 |
,177 |
235* |
5,029 |
415 |
8,381 |
|
60 |
,284 |
240 |
5,136 |
420 |
8,988 |
|
65 |
,391 |
245 |
6,243 |
425 |
9,095 |
|
70. |
.498 |
250 |
6,350 |
430 |
9,202 |
|
75 |
,605 |
255 |
5,457 |
435 |
9,309 |
|
80 |
J12 |
260 |
5,564 |
440 |
9,416 |
|
85 |
,819 |
265 |
6,671 |
44$ |
9,523 |
|
90 |
,926 |
270 |
5,778 |
450 |
9,630 |
|
95 |
2,033 |
215 |
6,885 . |
455 |
9,737 |
|
100 |
2,140 |
280 |
5,992 |
460 |
9,844 |
|
105 |
2,247 |
285 |
6,099 |
465 |
9,951' |
|
110 |
2,354 |
290 |
6,206 |
470 |
10,058 |
|
115 ' |
2,461 |
295 |
6,313 |
475 |
10,165 |
|
120 |
2,568 |
300 |
6,420 |
480 |
10,272 |
|
125 |
2,675 |
305 |
6,527 |
485 |
10,379 |
|
130 |
§,782 |
310 |
6,634 |
490 |
10,486 |
|
135 |
2,889 |
315 |
6,741 i |
495 |
10,693 |
|
140 |
2,996 |
320 |
6,848 |
600 |
10,700 |
|
145 |
3,103 |
325 |
6,955 |
510 |
10,914. |
|
150 |
3,210 |
330 |
7,06fc |
520 |
11,128. |
|
155 |
3,317 |
335. |
7,169 |
530 |
11,342 |
|
160 |
3,424 |
340 |
7,276 |
640 |
11,555 |
|
165 |
3,531 |
345 |
7,383 |
550 |
11.770 |
|
170 |
'3,638 |
350 |
7,490 |
560 |
11,984 |
|
175 |
8,745 |
355 |
7,«97 |
570 |
12,198 |
|
180 |
3,852 |
360 |
7,704 |
580 |
12,412 |
HANDBOOK ON ENGINEERING. Feet x 2 x 10.70.
TABLE No. 2.
|
Feet to end of Circuit. |
Ft. x2x!0.70. |
Feet to end of Circuit. |
Ft.x2xlO.70 |
Feet to end of Circuit. |
Ft. X2X10.7Q |
|
690 |
12,626 |
970 |
20,753 |
1,350 |
28,890 |
|
600 |
12,840 |
980 |
20,972 |
1,360 |
29,104 |
|
610 |
13,054 |
900 |
21,186 |
1,370 |
29,318 |
|
620 |
13,268 |
1,000 |
21,400 |
1,380 |
29,535? |
|
630 |
13,482 |
1,010 |
21,614 |
1,390 |
29,746 |
|
640 |
13,^696 |
1,020 |
21 j #28 |
1,400 |
29,960 |
|
650 |
13,910 |
1,030 |
22,042 |
1,410 |
30,174 |
|
660 |
14,124 |
1,040 |
22,256 |
1,420 |
30,388 |
|
670 |
14,338 |
1,050 |
22,470 |
1,430 |
30,602 |
|
680 |
14,552 |
1,060 |
1; 22,684 |
1,440 |
30,810 |
|
6'JO |
14,766 |
1,070 |
22,898 |
1,450 |
31,030 |
|
700 |
14,980 |
1,080 |
23,112 |
1,460 |
31,244' |
|
710 |
15,194 |
1,090 |
23,326 |
1,470 |
31,458' |
|
1720 |
15,408 |
1,100 |
23,540 |
1,480 |
31,672 |
|
730 i |
J5,622 |
1,110 |
i! 23,764 |
1,490 |
31,886 |
|
1740 |
'15,836 |
1,120 |
23,968 |
1,500 |
32,100 |
|
750 |
16,050 |
1,130 |
24,182 |
1,510 |
32,314 |
|
760 i |
56,264 |
1,140 |
24,396 |
1,520 |
32,528 |
|
770 ..; |
16,47® |
1,150 |
24,610 |
1,530 |
82,742 |
|
780 |
16,692 |
1,160 |
24,824 |
1,540 |
82,956 |
|
790 |
16,906 |
1,170 |
25,038 |
1,550 |
33,170 |
|
800 |
f7,120 |
1,180 |
25,252 |
1,560 |
33,384 |
|
810 |
17,334 |
1,190 |
25,466 |
1,570 |
33,598 |
|
820 |
17,548 |
1,200 |
25,680 |
1,580 |
33,812 |
|
830- |
17,762 |
1,210 |
25,894 |
1,590 |
84,026 |
|
840 |
17,976 |
1,220 |
26,108 |
1,600 |
34,240 |
|
850 |
18,190 |
1,230 |
26,322 |
1,610 |
34,454 |
|
860 |
18,404 |
1,240 |
26,536 |
1,620 |
34,668 |
|
870 |
18,618 |
1,250 |
26,750 |
1,630 |
34,882 |
|
880 |
18,832 |
1,260 |
26,964 |
1,640 |
35,096 |
|
890 |
19,046 |
1,270 |
27,178 |
1,650 |
35,310 |
|
900 |
19,260 |
1,280 |
27,392 |
1,660 |
35,524 |
|
910 |
19,474 |
1,290 |
27,606 |
1,670 |
35,738 |
|
920 |
19,688 |
1,300 |
27,820 |
1,680 |
35,952 |
|
930 |
19,902 |
1,310 |
28,034 |
1,690 |
36,166 |
|
940 |
20,116 |
1,320 |
28,248 |
1,700 |
36,380 |
|
950 |
20,330 |
1,330 |
28,462 |
1,710 |
86,594 |
|
960 |
20,544 |
1,340 |
28,676 |
1,720 |
36,808 |
HANDBOOK ON ENGINEERING,
163
Feetx 2x10.70.
No. 2.
|
Feet |
Feet |
Feet |
|||
|
to end of |
Ft.x2xlO.70. |
to end of |
Ft.x2xlO.70. |
to end of |
Ft.x2xlO,70. |
|
Circuit. |
Circuit. |
Circuit. |
|||
|
1,730 |
37,022 |
2,450 |
52,430 |
4,250 |
90,950 |
|
,740 |
37,236 |
2,500 |
53,500 |
4,300 |
92,020 |
|
,750 |
37,450 |
2,550 |
54,570 |
4350 |
93090 |
|
,760 |
37,664 |
2,600 |
55,640 |
4,400 |
94,160 |
|
,770 |
37,878 |
2,650 |
56,710 |
4,450 |
95,230 |
|
,780 |
38,092 |
2,700 |
67,780 |
4,500 |
96300 |
|
J90 |
38,306 |
2,750 |
58,850 |
4,550 |
97,370 |
|
,800 |
38,520 |
2,800 |
59,920 |
4,600 |
98,440 |
|
,810 |
38,734 |
2,850 |
60,990 |
4,650 |
99,510 |
|
,820 |
38,948 |
2,900 |
62,060 |
4,700 |
100,580 |
|
,830 |
39,162 |
2,950 |
63,130 |
4,750 |
101,650 |
|
,840 |
39,376 |
3,000 |
64,200 |
4,800 |
102,720 |
|
,850 |
39,590 |
3,050 |
65,270 |
4,850 |
103,790 |
|
,860 |
39,804 |
3,100 |
66,340 |
4,900 |
104,860 |
|
,870 |
40,018 |
3,150 |
67,410 |
4,950 |
105,930 |
|
,880 |
40,232 |
3,200 |
68,480 |
6,000 |
107,000 |
|
,890 |
40,446 |
3,250 |
69,550 |
6,050 |
108,070 |
|
,900 |
40,660 |
3,300 |
70,620 |
6,100 |
109,140 |
|
,910 |
40,874 |
3,350 |
71,690 |
5,150 |
110,210 |
|
,920 |
41,088 |
3,400 |
72,760 |
5,200 |
111,280 |
|
,930 |
41,302 |
3,450 |
73,830 |
5,250 |
112,350 |
|
,940 |
41,516 |
3,500 |
74,900 |
6,300 |
113,420 |
|
,950 |
41,730 |
3,550 |
75,970 |
5,350 |
114,400 |
|
1,960 |
41,944 |
3,600 |
77,040 |
5,400 |
115,560 |
|
1,970 |
42,158 |
3,650 |
78,110 |
5,450 |
116,63Q |
|
1,980 |
42,372 |
3,700 |
79,180 |
6,500 |
117,700 |
|
1,-990 |
42,586 |
3,750 |
80,250 |
5,550 |
118,770 |
|
2,000 |
42,800 |
3,800 |
81,320 |
5,600 |
119,840 |
|
2,050 |
43,870 |
3,850 |
82,390 |
6,650 |
120,910 |
|
2,100 |
44,940 |
3,900 |
83,460 |
5,700 |
121,980 |
|
2,150 |
46,010 |
3,950 |
84,530 |
6 750 |
123,050 |
|
2,200 |
47,080 |
4',000 |
85,600 |
5,800 |
124,120 |
|
2,250 |
48,150 |
4,050 |
86,670 |
5,8*0 |
125,190 |
|
2,300 |
49,220 |
4,100 |
87,740 |
5,900 |
126,260 |
|
2,350 |
50,290 |
4,150 |
88,810 |
6,950 |
127,330 |
|
2,400 |
51,360 |
4,200 |
89,880 |
6,000 |
128,400 |
166
TAB»-B No. 2.
HANDBOOK OK ENGINEERING*
Feet x2x 10.70.
|
Miles. |
Ft.x2xlO.70 |
Miles. |
Ft.x2xlO.70 |
Miles. |
Ft.x2xlO.70 |
|
ft |
564,960 |
4 |
451,968 |
74 |
847,440 |
|
1 |
112,992 |
4* |
508,464 |
8 |
903,936 |
|
14 |
169,488 |
5 i |
664.960 |
64 |
960.432 |
|
2 j |
225,984 |
54 |
621,456 |
9 |
1,016,928 |
|
24 |
282,480 |
6 |
677,952 |
94 |
1,073,424 |
|
8 |
838,976 |
6J |
734.448 |
10 |
1,129,920 |
|
•i |
895,472 |
7 |
790,944 |
(A) (B) (C)
Feet x 2 x 10.7 x Amperes
^Volts lost Feetx 2x 10.7 x Amperes
Circular mils. Circular mils x volts lost
= Circular mi}s.
= Volts lost.
= Amperes.
Feetx 2x10. 7
In calculating the sizes of wire as shown in the Incandescent Wiring Table a formula (A) has been used in wliich there is a Constant 10.7, the number of circular mils in a copper wire which would have a resistance of one ohm for one foot of length. One ampere through one ohm resistance loses one volt* To determine the size of wire necessary for carrying a given current a given distance in feet, multiply the number of feet by 2 to obtain the actual length of circuit, multiply this product by the constant 10.7 and it will give the circular mils necessary for one ohm re- sistance, multiply this by the amperes and it gives the circular mils necessary for the loss of one volt. Divide this- last result; by the volts lost and it gives the circular mils necessary. Hence the formula "A."
By simply transposing the terms we obtain formula " B," which can be used to determine the volts lost in a given length of wire Of certain size carrying a certain, number of amperes.
HANDBOOK ON ENGINEERING. 167
Again, by another change in the terms, we obtain formula " C," which shows the number of amperes which a wire of given size and length will carry at a given number of volts lost.
Table No. 2 has been arranged for the purpose of saving time in the use of these formulas. It shows the result of Feet x 2 x 10.7 for various distances over which it may be desired to trans- mit current.
A few examples will assist in showing the use of the formulas and tables.
Suppose we wish to distribute 300 16 c. p. 3.5 watt lamps of 110 volts at a distance of 490 feet with a loss of 10 per cent. Using formula A,
490 feet x 2 x 10.7 (find it in table No. 2) = 10486. 300 lamps of 110 volts = 152.7 amperes. (See table No. 3 for amperes per lamp, and multiply by 300) 10 per cent loss on 110 volt system = 12.22 volts. (See
table No. 4.) 10486 x 152.7 amperes = 1601212 circ. mils, -v-12.22 volts
lost= 131032 circ. mils.
In our table it shows the size of wire for this number of circ. mils, to be 00.
To check this and determine exactly the volts lost in this cir- cuit by using No. 00 wire use formula B, as follows :
10,486 x 152.7amperes= 1601212 —- 133079 circ. mils. = 12.03 volts lost.
Suppose it is desired to distribute 1,000 lamps at a distance of 1950 feet by 3-wire system, viz., 220 volts, with a loss of 10 per cent.
Using formula A,
1950 feet x 2 x 10.7 (see table) == 41730. 1000 lamps on 220 volt system =291 amperes. (See table No. 5 for amperes per lamp, and multiply by 1000.)
168 HANDBOOK ON ENGINEERING.
10 per cent on 220 volt system = 24.44 volts lost. (See
table No. 4.) 41730 x 291 amperes = 12143430 -;- 24.44 volts lost
= 496867 circ. mils. 500000 circ. mils., the nearest commercial size, should be
used. Check this as before by formula B.
41730 x 291 amperes == 12 143430 -=- 500000 circ. mils.
= 24.29 volts lost.
Suppose we wish to deliver 100 h. p. to a 500 volt motor, at a distance of 4850 feet with 10 per cent loss : Again using formula A,
4850 feet x 2 x 10.7 = 103790.
100 h. p. at 500 volts = 160 amperes. (See table No. 3.)
10 per cent loss on 500 volts system =55. 5 volts. (See
table No. 4.)
103790 x 160 amperes = 16606400 -f- 55.5 volts = 299215 circ. mils.
30000 circ. mils, cable should be used. Check this as before by formula B.
103790 x 160 amperes = 16606400 -f- 300000 circ. mils.
= 55.35 volts lost.
To ascertain how many amperes could be carried to a distance of 4850 feet with 500 volts with ten per cent loss, use formula C : 4850 feet x 2 x 10.7 = 103790. 10 per cent loss on 500 volts system = 55.5 volts. 300000 circ. mils, x 55.5 volts lost-;- 103790 = 160.42 am- peres, which as will appear by reference to table No. 3, will permit the use of 100 h. p. motor.
HANDBOOK ON ENGINEERING.
169
TABLE No. 3.
Amperes per Motor.
|
H. P. |
Per Cent Efficiency |
Watts. |
VOLTS. |
||
|
110 |
115 |
120 |
|||
|
i |
65 |
860 |
7.82 |
7.48 |
7.17 |
|
i |
65 |
1148 |
10.4 |
9.98 |
9.57 |
|
2 |
66 |
2295 |
20.8 |
20.0 |
19.1 |
|
2h |
75 |
2487 |
22.6 |
21.6 |
20.7 |
|
H |
75 |
3480 |
31.6 |
30.3 |
29.0 |
|
5 |
80 |
4662 |
42.4 |
40.5 |
38.8 |
|
74 |
80 |
6994 |
63.6 |
60.8 |
68.3 |
|
10 |
85 |
8776 |
79.8 |
76.3 |
73.1 |
|
15 |
85 |
13166 |
120. |
114. |
110. |
|
20 |
90 |
16578 |
151. |
144. |
138. |
|
25 |
90 |
20722 |
188. |
180. |
173. |
|
80 |
90 |
24867 |
226. |
216. |
207. |
|
40 |
90 |
33155 |
301. |
288. |
276. |
|
50 |
90 |
41444 |
377. |
360. |
345. |
|
70 |
90 |
68022 |
628. |
605. |
484. |
|
90 |
90 |
74600 |
678. |
649. |
622. |
|
100 |
93 |
80215 |
729. |
697. |
668. |
|
125 |
93 |
100269 |
912. |
872. |
836. |
|
150 |
93 |
120323 |
1094. |
1046. - |
1003. |
The above table Js arranged to show the amperes per motor at dif * ierent voltages lor several sizes of motors at efficiencies obtained in ordinary practice.
170
HANDBOOK ON ENOINEERING.
TABLE Ko.8.
Amperes per Motor.
VOLTS,
|
125 |
220 |
250 |
500 |
525 |
550 |
|
6.88 |
8.91 |
3.44 |
1.72 |
1.64 |
1.56 |
|
9.18 |
5.22 |
4.59 |
2.30 |
2.19 |
2.09 |
|
18.4 |
10.4 |
9.18 |
4.59 |
4.37 |
4.17 |
|
19.9 |
11.8 |
9.95 |
^197 |
4.74 |
4.52 |
|
27.8 |
15.8 |
13.9 |
v6.96 |
6.63 |
6.33 |
|
87.3 |
21.2 |
18.6 |
9.32 |
8.88 |
8.48 |
|
66.0 |
31.8 |
28.0 |
14.0 |
13.3 |
12.7 |
|
70.2 |
39.9 |
85.1 |
17.6 |
16.7 |
16,0 |
|
105. |
59.8 |
52.6 |
26.3 |
25.1 |
23.9 |
|
188. |
75-4 |
66.3 |
33.2 |
31.6 |
SO.l |
|
166. |
94.2 |
82.9 |
41.4 |
39.5 |
37. 7 |
|
199. |
113* |
99.4 |
49.7 |
47.4 |
45.2 |
|
265. |
151. |
1,33. |
66.3 |
63.2 |
60. a |
|
382. |
188. |
166. |
82.9 |
79.0 |
75.4 |
|
464. |
264. |
232. |
116. |
111. |
106. |
|
597. |
339. |
298. |
149. |
142. |
136. |
|
642. |
365. |
321. |
160. |
153. |
146. |
|
802, |
456. |
401. |
200. |
191. |
182. |
|
963, |
547, |
481. |
241. |
229. |
219. |
The above table is arranged to show the amperes per motor at different voltages for Several 01338 of motors at efficiencies QbtainecMn
HANDBOOK ON ENGINEERING.
171
Volts- Lost at Different Per Cent Drop*
Voltage at Lamp or Distribution Point, Top Row. TABLE No. 4.
|
VOLTS |
52 |
75 |
ICO |
110 |
220 |
400 |
|
\% |
.261 |
.376 |
.502 |
.552 |
1.10 |
2.01 |
|
\% |
.525 |
.757 |
1.01 |
1.11 |
2.22 |
4.04 |
|
\Vh |
.787 |
1.14 |
1,52 |
1.67 |
3.35 |
6.09 |
|
2% |
1.06 |
1.53 |
2.04 |
2.24 |
4.48 |
8.10 |
|
2*% |
1.33 |
1.92 |
2.56 |
2.82 |
5.64 |
10.25 |
|
3% |
1.61 |
2.31 |
3.09 |
3.40 |
6.80 |
12.37 |
|
4% |
2.16 |
3.12 |
4.16 |
4.58 |
9.16 |
16.06 |
|
b% |
2.73 |
3.94 |
5.26 |
5.78 |
11.57 |
21.05 |
|
f>%' |
3.31 |
4.78 |
6.38 |
7.02 |
14.04 |
25.53 |
|
1% |
3.91 |
5.C4 |
7.52 |
8.27 |
16.55 |
30.10 |
|
•*% |
4.52 |
6o52 |
8.69 |
9.56 |
19.13 |
34.78 |
|
9% |
5.14 |
7.41 |
9.89 |
10.87 |
21.75 |
39.56 |
|
10% |
5.77 |
8.33 |
11.11 |
12.22 |
24.44 |
44.44 |
|
12% |
7.09 |
10.22 |
13.63 |
14.99 |
29.99 |
54.54 |
|
13% |
7.76 |
11.10 |
14.04 |
16.43 |
32.87 |
59.76 |
|
14% |
8.46 |
12.20 |
16.27 |
17.90 |
35.81 |
65.1 |
|
15% |
9.17 |
13.23 |
17.64 |
19.41 |
38.82 |
70.5 |
|
20% |
13. |
18.75 |
25. |
27.50 |
55. |
100, |
|
25% |
17.33 |
25. |
33.33 |
36.66 |
73.33 |
133. |
The above table shows the loss In voltage between dynamos and distribution point at different per cents and for various voltages.
172
HANDBOOK ON ENGINEERING.
Yolts Lost at Different Per Cent Drop.
Voltage at Lamp or Distribution Point. Top Row. TABLE No. 4.
|
500 |
600 |
800 |
1000 |
1200 |
2000 |
|
2.51 |
3 01 |
402 |
5 02 |
C.03 |
10.05 |
|
6 06 |
6.66 |
8.08 |
10.10 |
12.12 |
20.2 |
|
7.61 |
9.13 |
12.1 |
152 |
18.2 |
30.4 |
|
10 2 |
12.2 |
, 16 3 |
204 |
24.4 |
40.8 |
|
12 8 |
15 3 |
20.5 |
25.6 |
30.7 |
51.2 |
|
15.4 |
18.5 |
24.7 |
30.9 |
37.1 |
61.8 |
|
20.8 |
24.9 |
33.3 |
41.6 |
49 9 |
83.3 |
|
26.3 |
31.5 |
42.1 |
52.6 |
63.1 |
105. |
|
81.9 |
38.2 |
51. |
63.8 |
76. 5 |
127. |
|
37.6 |
45.1 |
60.2 |
752 |
90.3 |
150. |
|
43.4 |
62.1 |
69.5 |
86.9 |
104. |
173. |
|
49.4 |
59.3 |
79.1 |
98.9 |
118. |
197. |
|
555 |
66.6 |
88 8 |
111. |
133. |
222. |
|
61.7 |
71.1 |
98 8 |
123. |
148. |
247. |
|
68.1 |
81.8 |
109. |
136. |
163. |
272. |
|
74 7 |
89.6 |
119. |
149. |
179. |
298. |
|
81.3 |
97.6 |
130. |
162. |
195. |
325. |
|
88.2 |
105. |
141. |
176. |
211. |
352, |
|
125. |
150. |
200. |
250. |
300. |
400. |
|
166. |
200. |
266. |
333. |
400. |
666. |
,By adding the volts given in the table to the voltage at motor or lamp the result shows the voltage necessary at dynamo for voltage required at point of distribution,
HANDBOOK ON ENGINEERING.
173
S
fferent
05
£
o
<2
d d
c3
a
03 bC5
J*|
D, O .r
S " 5 •S 53 a
S &!§ Ml
2 .2 * S.5 *
S o
o g
o O
ad o •2 <~
73 g
03
b ^
s*~< o
o ^
co" ^
5 a
C/)
o
fc ^
^ <D
I ^
a S
:3 -2
CO CJ ^. „
S w CL -r d«
S 5
O IS./
bC ^ £
i « g
h co ^
20^0
CO p ^
'^ <D CO
^ *0 £
,Q « O
g
•I! i
co ^5
£ 8
a
^ 73
03 d II
I c;
bf)
^ § bD "2 'S a S
.2 § § a. 2
^ o -v>
,2 t- O3 S-H 2
Q L*- O O o3
Sir 11
X3 Q^ ^3 ^3
H -^ bo H
J3 — O1 c3 O ^3 O k cn
— o d
o* O
\J (— I
|
>> . rv* «? |
0 • oh» . co IT |
0 •^ |
co t» t« eo o eo IO<0 O 4O <0 «H . 00 ^ ^H r- (M |
|
«P aS |
o • s> |
O "* |
oo co ££> *o »o'co - lO l^. — -«t< b- CC O O r-H i-4 i-i IM |
|
s^ 02 |
§> iO ^ |
0 • •^ |
-* O 00 O <M CO co ao <M co as »o o o «-« r" *-" M , |
|
o • s>- |
o T*« |
»C CM •— eo CD /N ^ QO as o co oo r-i •-« W CO T »O |
|
|
CO 3 |
»O CO |
»O OO Ci Cff *•*• OO >0 — 0 CC CC — <N CO «O CO t>- O ' I-I |
|
|
0 |
CO |
»O «N — T»- CO CM (M OO lO CO b- O CM M ^f »O ^ OS |
|
|
1 |
w» |
Oi !-*• 00 co ao t>» CO CO CO t>- O b~ CM CO UJ ••£• OO O |
|
|
CO |
•^ |
||
|
2 |
CO |
QO 00 1-- CO IO TH CO O5 t» O5 -H »O (M <M ^ O !>. OS |
|
|
3 |
»0 |
O O 0 00 0 CO »O CO O •*»• (M C<l CO »O t>- OO ^-« |
|
|
O > |
CO |
*-' |
|
|
0 O |
2 |
00 O CO O **• -M ** -H a> TVJ -*• as CNJ co *«• co t>- as |
|
|
0 <* |
«3 as — • oo co — • ^- CO CO CO Tf CO CO l>- (N «5 00 -<f * t-< r-i — (N |
||
|
*J 1 |
»0 CO |
00 CO b- CO «O •* co r>. t- •*»•—» »o »O CO O CO CO -< , * |_4 >-H r-4 CO |
|
|
•; (_4 |
!>. CO -* S<l — OO i>» OS 10 as co o i** »o as — i "* as |
||
|
CO |
^ f-4 •-• |
||
|
I •*** O <SO O (M CO CO 00 (M CO OS 0 |
|||
|
"* |
*--«~.^j |
||
|
CO O CM O 00 T* «3 t>- i-< •**> fO <>J |
|||
|
0 |
CO |
-- t-i «' oa |
|
|
»o |
r-« |
'O O <>J O 00 -rf Oi !M 05 •* 00 00 rf co as IM -^ as |
|
|
co |
^r-^, |
||
|
<r. *j |
£ |
PH P^ PU Ok CU (Li |
|
|
81 ^ |
o L 0) a |
OOOOOO ! 00 O CO O •* CVJ ^_ — c^i jvj co |
174
HANDBOOK ON ENGINEERING.
APPROXIMATE WEIGHT AND MEASUREMENT Of "0. K." TRIPLE 5RAIDED TABLE No. 6 WEATHERPROOF COPPER WIRE.
|
B. & S. Gauge No. |
Feet Per Pound |
Pounds Per 1000 Ft. |
Pounds Per Mile |
|
0000 |
1.30 |
767 |
4050 |
|
000 |
1.59 |
629 |
3320 |
|
00 |
2.02 |
495 |
2610 |
|
0 |
2.45 |
407 |
2150 |
|
1 |
3.22 |
310 |
1640 |
|
2 |
4.00 |
250 |
1320 |
|
3 |
5.03 |
199 |
1050 |
|
4 |
6.10 |
164 |
865 |
|
5 |
7.43 |
135 |
710 |
|
6 |
9.00 |
in |
587 |
|
8 |
13.54 |
74 |
390 |
|
10 |
18.85 |
53 |
280 |
|
12 |
28.54 |
35 |
185 |
|
14 |
40.61 |
25 |
130 |
|
16 |
60.00 |
17 |
88 |
|
18 |
75.43 |
13 |
70 |
TABLE OF MAGNETIZING FORCE IN AMPERE TURNS REQUIRED PER INCH OF LENGTH OP MAGNETIC CIRCUIT.
|
Magnetic Den- sity per Square inch in Gausses. |
MAGNETIZING FORCE IN AMPERE TURNS |
|||
|
Air. |
Cast Iron. |
Steel. |
Wrought Iron. |
|
|
5,000 |
1,567 |
3.80 |
2.85 |
1.50 |
|
10,000 |
3,134 |
5.35 |
4.25 |
2.40 |
|
15,000 |
4,701 |
6.80 |
5.35 |
3.20 |
|
20,000 |
6,268 |
8.00 |
6.30 |
3.90 |
|
25,000 |
7,835 |
10.30 |
7.50 |
4.60 |
|
30,000 |
9,402 |
16.20 |
8.80 |
5.30 |
|
35,000 |
10,969 |
28.70 |
10.20 |
5.90 |
|
40,000 |
12,536 |
49.00 |
11.70 |
6.50 |
|
45,000 |
14,103 |
80.00 |
13.40 |
7.10 |
|
50,000 |
15,670 |
160.00 |
15.40 |
8.20 |
|
55,000 |
17,237 |
240.00 |
17.80 |
9.50 |
|
60,000 |
18,804 |
350.00 |
20.70 |
11.00 |
|
65,000 |
20,371 |
490.00 |
24.10 |
13.50 |
|
70,000 |
21,938 |
650.00 |
28.00 |
17.00 |
|
75,000 |
23,505 |
|
34.00 |
21.80 |
|
80,000 |
25,072 |
|
42.00 |
27.50 |
HANDBOOK ON ENGINEERING.
Table Showing Difference Between Wire Ganges in Decimal Parts TABLE No. 1 of an Inch.
|
2 *l *3 6« K |
American or Brown & 8harpe. |
Birmingham or Stubs'. |
WnshburnA Moen Manufacturing Co., Worcester, Mass. |
Trenton Iron Co., Trenton. N. J. |
Mew British. 1 |
la 52 3* fia 22 o« |
No. of Wire. 41 |
|
000000 |
.46 |
000000 |
|||||
|
00000 |
.43 |
.46 |
00000 |
||||
|
0000 |
.46 |
.454 |
.393 |
.4 |
.4 |
0000 |
|
|
000 |
.40964 |
.425 |
.362 |
.36 |
.372 |
000 |
|
|
00 |
.3648 |
.38 |
.331 |
.33 |
.348 |
00 |
|
|
o |
.32495 |
.34 |
.307 |
.305 |
.324 |
0 |
|
|
1 |
.2893 |
.3 |
.283 |
.285 |
.3 |
I |
|
|
2 |
.25763 |
.284 |
.263 |
.265 |
.276 |
2 |
|
|
8 |
22942 |
.259 |
.244 |
.245 |
.252 |
3 |
|
|
.20431 |
.238 |
.225 |
.225 |
.232 |
4 |
||
|
5 |
.18194 |
.22 |
.207 |
.205 |
.212 |
5 |
|
|
6 |
.16202 |
.203 |
.192 |
.19 |
.192 |
6 |
|
|
7 |
.14428 |
.18 |
.177 |
.175 |
.176 |
1 |
|
|
8 |
.12849 |
.165 |
.162 |
.16 |
.16 |
8 |
|
|
9 |
.11443 |
.148 |
.148 |
.145 |
.144 |
9 |
|
|
10 |
.10189 |
.134 |
.135 |
.13 |
.128 |
10 |
|
|
11 |
.090742 |
.12 |
.12 |
.1175 |
.116 |
11 |
|
|
12 |
.080808 |
.109 |
.105 |
.105 |
.104 |
12 |
|
|
13 |
'.071961 |
.095 |
092 |
.0925 |
.092 |
13 |
|
|
14 15 16 17 18 19 20 21 22 .23 24 25 26 27 28 29 30 31 •32 83 84 36 •86 37 |
.064084 .057068 .05082 .045257 .040303 .03589 .031961 .028462 .025347 .022571 .0201 .0179 .01594 ,014195 .012641 .011267 ,010025 .008928 .00795 .00708 .006304 .005614 .005 .004453 |
.083 .072 .065 .058 .049 .042 .035 .032 .028 .025 .022 .02 .018 .016 .014 .013 .012 .01 .009 .008 •007 .005 .004 |
.08 .072 .063 .054 .047 .041 ,035 .032 .028 .025 .023 .02 .018 .017 .016 .015 .014 ,0135 .013 .011 .01 .0095 009 .0085 |
.08 .07 .061 .0525 .045 .039 .034 .03 .27 .024 .0215 .019 .018 .017 .016 .015 .014 .013 .012 .011 .01- .009 .008 .00125 |
.08 .072 .064 .056 ,048 .04 .036 .032 .028 .024 .022 .02 .018 .0164 .0148 .0136 .0124 .0116 .0108 .01 .0092 .0084 .0076 .0068 |
083 ,072 .065 .058 .049 .04 .035 0315 .0295 .027 .025 .023 .0205 .01875 .0165 .0155 .01375 .01225 .01125 .01025 .0095 ,009 .0075 t .0965 |
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 |
|
38 |
.003965 |
,XX)8 |
.0065 |
.006 |
.00575 |
38 |
|
|
89 40 |
.003531 .003144 |
• ; |
.0075 .007 |
.00575 .005 j |
.0052 .0048 |
.005 .0045 |
39 46 |
170
HANDBOOK ON ENGINEERING.
Weather- proof in- sulation.
•pnnoj
J9d 5^0 J
•pnnoj
s s
Is
tp to ci
* O V-< -«• -H C* C7» O^T. O^UJ CCS
Weather- proof In- sulation.
Jddepunoj
8§§
r«r-O5 c-ir-M o to co
•^90 J 000* I
JOd
00 t
10
to <M o OP o — co i
igh
5
a o
I
JOdspunoj
si^s s«s
OO — « CO *•
5«ort> oo
laotf 000^ ^od.epunoj
CO-*O5 ^OD T CO O O O 00 «
00 00
Safe Cing Capacity in Amperes.
arryi acit
II
CO -oa
ss
?S §ScS Sg^
§00 o o o-^ coco
O -O » O -O
O« «C?« • r-i -r-l
co»n c
5 ft O5 oo — »
; cc r^» o — flo 5^-« coyso
SO t"» CO C^ v OOCO iO^Cl
D — to eoooo
3 «* ia i e* o poo
•i oi e? >* co -^ «* «
»ooo 0:005
OOO Cl^Oi
I
fc^OS
Diam
-*OCO -^ TO •* 1^31-^
OOOCO O-*-* CMC/OOI
CO ^ CM C4 CO O 00 r-t CO
rH O O) 00 r- CD »0 O "*
Is
O^O OO^ C«—H-^
oSoo osccco -^coo:
^*« — o o —
?3 SS
2
tt
1
I g- Q-5
HANDBOOK ON ENGINEERING. 177
THE STEAM ENGINE.
CHAPTER XI. THE SELECTION OF AN ENGINE.
There are so many conflicting statements in regard to the merits and demerits of the several engines placed in the market that one is often confused in judgment, and scarcely knows how to proceed in the matter of selection.
It is easy to advise that " When you are ready to buy, select the best engine, for in the long run the best is the cheapest." No one would pretend to deny this as a general rule, yet there are circumstances which so materially modify this rule that it would seem to a casual observer to be entirely set aside. There are localities in which the price of fuel is so low that it scarcely war- rants the doubling of the price on an engine to save it ; and in such localities the owners usually want an engine of the very simplest construction ; hence, they almost invariably select an ordinary slide valve engine with a throttling governor. This selection is made for several reasons, among which are low first cost, simple in detail, remoteness from the manufacturer or from repair shops.
For small powers in which it is desirable that the investment be as low as consistent with commercial success, the engine selected should be fitted with a common slide valve ; this will in general apply to all engines having cylinders eight inches or less in diameter.
If upon a thorough canvass of the situation, it then be thought advisable to employ an automatic cut-off engine, the next ques- tion would probably be whether it shall be fitted with a positive or some one of the various "drop" movements now in the market.
12
178 HANDBOOK ON ENGINEERING.
For the smaller sizes, say 8 to 24 inches diameter of cylinder it will perhaps be found more desirable to use an automatic slide cut-off, of which there are now several varieties offered through the trade. This style of engine has the advantage of being low- priced, efficient and economical.
Small engines are usually required to run at pretty high speed ; there is a very decided advantage in this on the score of economy, as a small engine running at a high speed will be quite as efficient as a large engine running at a slow speed, with the further advantage that the former will not cost in original outlay more than about two-thirds of the latter, while the cost of operat- ing will be no greater per indicated horse-power.
The slide valve is still used to the almost total exclusion of all other kinds in locomotives. It is doubtful whether a better valve for that particular use can be devised. It is simple, efficient', and readily obeys the action of the link when controlled or adjusted by the engineer. For portable engines and the smaller stationary engines it leaves little to be desired in point of simplicity.
One objection to a slide valve is that it cannot readily be made to cut off steam at, say, half -stroke or less, without interfering with the exhaust. In ordinary practice f to f seems to be where most slide valves cut off as a minimum, perhaps | would repre- sent nearer the actual average conditions.
It can easily be shown that this is very wasteful of steam, and consequently not economical in fuel ; but as there are cases in which the loss in fuel is fully gained by other advantages, the ordinary slide valve will, in all probability, continue to be used.
High speed engines* — The general tendency seems now to be in the direction of a horizontal engine with a stroke of medium length having a rapid piston speed and a rapid rotation of crank shaft, rather than a longer stroke with a less rate of revolution. This rapid movement of piston and crank shaft permits the use of
HANDBOOK ON ENGINEERING. 179
small fly-wheels and driving pulleys, and thus very materially reduces the cost of an engine for a given power.
To illustrate this, it may be said that a 16 x 48 inch engine using steam at 80 Ibs. pressure and cutting off J stroke, running at the rate of 60 revolutions per minute, may be replaced by an engine having a 13 x 24 inch cylinder, running at the rate of 200 revs, per minute, the pressure of steam and point of cut- ting off remaining the same, both engines being non-condensing and representing the best examples of their kind. The differ- ence between 60 and 200 revolutions per minute in millwright work is very great, but there is a constantly growing demand for an engine which shall meet such a requirement whenever it shall present itself ; by this it is not to be understood an engine which shall be used at either speed indiscriminately, but rather a type of engine which shall be economical in fuel, and shall be of a kind by which the rate of revolution may be such as to suit the millwright's work without loss of economy in working, and with- out excessive outlay for the engine itself in proportion to power developed.
Slow speed engines are designed and built from a standpoint entirely different from that of high speed engines ; in the former case the reciprocating parts are made as light as possible, con- sistent with safety. The fly-wheel is large in diameter and made with a very heavy rim, especially is this the case with auto- matic cut-off engines of long stroke and slow revolution of crank shaft.
In High speed engines the reciprocating parts are often of great weight, in order to insure the utmost smoothness of running. The piston and cross-head are made of unusual weight that at the bginning of the stroke they may require a large part of the steam pressure to set them in motion ; this absorbing of power at the beginning of the stroke is for the purpose of temporarily storing it up in the reciprocating parts that it may be given off at the
180 HANDBOOK ON ENGINEERING.
later portions of the stroke, by imparting their momentum to the crank ; thus at the beginning of the stroke, these reciprocating parts act as a temporary resistance, but once in motion they tend by their inertia to equalize the pressure on the crank pin, and so produce not only smooth running, but a very uniform motion.
Results to be obtained in practice* — The best automatic non- condensing engines furnish an indicated horse-power for about three pounds of good coal, depending somewhat upon the fitness of the engine for the work and the quality of the coal. With a condenser attached, a consumption as low as two pounds has been reported, but this is an exceptional result, 2J pounds may be quoted as good practice. The larger the engine the better the showing, as compared with smaller engines.
For ordinary slide valve engines, the coal burned per indicated horse-power will vary from 9 to 12 Ibs., for the sake of illustra- tion, we will say 10 Ibs., and that the engine is of such size as would require for a year's run $3,000 worth of coal; now an ordinary adjustable cut-off engine with throttling governor, ought to save at least half that amount of coal, or say $1,500 per year ; if the best automatic engine were employed using 2 J Ibs. of coal per horse-power, a further saving of $750 per year could be effected, or between the two extremes $2,250 per year in saving of coal, without interfering in anyway with the power, with the exception perhaps, that the automatic engine will furnish a better power than the former engine. It is easy to see that it is true economy to buy the best engine and pay the extra cost of con- struction, if the saving of fuel is an element entering into the question of selection.
The cost of an engine for any particular service is always to be taken into consideration, for it is possible to contract for a certain saving of coal at too high a price, not simply when paid out as the original purchase money, but with this economy of fuel, the purchaser may have many vexatious and damaging
HANDBOOK ON ENGINEERING. 181
delays caused by the breaking of the automatic mechanism of the engine. All such delays, which would not have occurred to an ordinary or simpler engine, are to be charged against any saving credited to the engine, which failed in producing a regular and constant power. Take a flouring mill for example, producing 400 barrels per day ; it is easy to see how a single day's stoppage would interfere with the trade and shipment by the proprietors, yet it would require a very small break in an engine that would require less than a day for repairs.
This does not argue against high grade engines, but the pur- chaser should be certain that the engine when once on its founda- tions shall be as free from dangers of this kind as any other engine of similar economy.
There are engines, which, from their peculiar construction appear to be very complex, and this objection is often urged against them, while the fact is the complexity is apparent rather than real. Take the Corliss engine, for example ; it is doubtful whether there is another automatic cut-off engine in successful use in this or any other country which has cost less for repairs during the last ten or twenty years. It is true it contains a great many separate pieces in the valve mechanism, but the pieces themselves are simple, durable, easily accessible and always in sight. These several parts are not liable to excessive wear, but such as there is can be readily adjusted.
The engines to be preferred are those in which the valve adjusting mechanism is outside of the steam chest and which is in plain sight at all times when the engine is in motion.
Location of engine* — This will depend upon circumstances, but it is far from true economy to place an engine in a dark cellar, or in some inconvenient place above ground. The engine as the prime mover, should have all the care and attention which may be needed to insure regular and efficient working.
Machinery in the dark is almost sure to be neglected. If the
182 HANDBOOK ON ENGINEERING.
design of the building, or the nature of the business, is such that the engine must be located underground, there should be some provision for letting in the daylight ; the extra expense incurred will soon be saved by the order, cleanliness and fewer repairs required.
The engine should always be close to, but not in the boiler room. Many a high-priced engine has had its days of usefulness shortened by the abrasive action of fine ashes and coal dust coming in contact with the wearing surface. There should always be a wall or tight partition between the engine and fire room.
The foundations for an engine should be large and deep. Too many manufacturers in marking dimensions of foundation drawings for engines, make them altogether too shallow. The stability of an engine depends more on the depth than on the breadth of the foundations. Stone should be used for founda- tions rather than brick, but if the latter must be used they should be hard burned and laid in a good cement rather than a lime mortar. If the bottom of the pit dug for the engine foundation be wet, or the soil uncertain in its stability, it is a good plan to make a solid concrete block about a foot and a half thick, on which the foundation may be continued to the top. If such a concrete block be made with the right kind of cement it will be almost as hard and solid as a whole stone.
The most economical engine is the one in which high pressure steam can be used during such portion of the stroke as may be necessary, then qickly cut off by a valve, which shall not inter- fere with the exhaust at the opposite end of the cylinder, and allow the steam to expand in the cylinder to a pressure, which shall not fall below that necessary to overcome the back pressure on the piston. In general, the most successful cut-off engines use the boiler pressure for a distance of one-fifth to three-eighths of the stroke from the beginning; at this point the steam is cut off and allowed to expand throughout the balance of the stroke.
HANDBOOK ON ENGINEERING
183
The gain by expansion consists in the admission of steam at a pressure much above the average required to do the work, and allowing it to follow but a small portion of the stroke, then ex- panding to a lower than the average pressure at the end of the stroke. The mean effective pressure on the piston is that by which the power of the engine is measured, hence, it follows that the higher economy is to be reached, other things[being equal, where the mean effective pressure on the piston is highest when com- pared with the terminal pressure, or the pressure at the end of the stroke. In order to get this, a high initial pressure is used ; the steam follows as short a distance as possible to keep the motion regular under a load, and then expanding down to as near tho atmospheric pressure as possible.
The following table exhibits at a glance the performance of a non-condensing engine cutting off at different portions of the stroke. The initial pressure of steam being in each case eighty pounds per square inch.
CUT-OFF IN PARTS OF THE STROKE.
|
1 10 |
2 10 |
3 10 |
4 To |
5 To |
|
|
Mean effective pressure . |
18 |
35 |
48 |
.57 |
65 |
|
Terminal pressure . . . |
11 |
20 |
30 |
39 |
48 |
|
Pounds water per h'r per H. P |
27 |
24 |
25 |
27 |
28 |
Fractions are omitted in the above table and the nearest whole number given.
Governor- — Any automatic device by which the speed of an engine is controlled may properly be called a governor. There
184 HANDBOOK ON ENGINEERING.
are now two distinct methods by which the steam supplied to an engine is thus brought under control. The first is usually applied to side valve engines having a fixed cut-off, and consists in the adjustment of a valve by which the pressure of steam in the cylinder is increased or diminished in order to maintain a con- stant rate of revolution with a variable load. The second device consists in a mechanism by which the whole boiler pressure is admitted to the cylinder, which is allowed to follow the piston to such portion of the stroke as will maintain a regular rate of revo- lution ; the steam is then suddenly cut off at each half revolution of the engine, thus furnishing a greater or less volume of steam at a constant pressure. Neither of these two varieties of governors will act until a change in the rate of revolution of the engine occurs, and this change will either admit more or less steam as it is slower or faster than that for which the governor is adjusted. The commonest form of a governor consists of a vertical shaft to which are hinged two arms containing at their lower ends a ball of cast iron ; as the shaft revolves the balls are carried outward by the action of what is commonly called centrifugal force ; the greater the rate of revolution the farther will the balls be carried outward ; advantage is taken of this property to regulate the ad- mission of steam to the engine. The action of the balls and that of the valve include two distinct principles and should be consid- ered separately ; an excellent valve may be manipulated by an indifferent governor and so produce unsatisfactory results ; on the other hand, the governor mechanism may be satisfactory in its operation, but being connected with a valve not properly balanced , is likely to cause a variable rate of revolution in the engine.
Fly- wheel* — The object in attaching a fly-wheel to an engine is to act as a moderator of speed. The action of the steam in the cylinder is variable throughout the stroke, against which the rev- olution of a heavy wheel acts as a constant resistance and limits the variations in speed by absorbing the surplus power of the first
HANDBOOK ON ENGINEERING. 185
portion of the stroke, and giving it out during the latter portion. The fly-wheel is simply a reservoir of power, it neither creates nor destroys it, and the only reason why it is attached to an engine is to simply regulate the speed between certain permitted variations, which are necessary to cause the governor to act, and to equalize the rate of revolution for all portions of the stroke, thus con vert- ing a variable reciprocating motion into a constant rotary one. It is considered good practice to make the diameter of the fly-wheel four times the length of the stroke for ordinary engines, in which the stroke is equal to twice the diameter of the cylinder. This may be taken as a fair proportion in engine building, and furnishes a wheel sufficiently large to equalize the strain and reduce any variation in speed to within very narrow limits, if the engine is supplied with a proper governor. The greater the number of revolutions at which the engine runs, the smaller in diameter may be the fly-wheel, and it may also be largely reduced in weight for engines developing the same power.
Horse-power- — By this term is meant 33,000 pounds raised one foot high in one minute. The horse-power of an engine may be found by multiplying the area of the p.iston in square inches by the mean effective pressure: this will give the total pressure on the piston ; multiply this total pressure by the length of the stroke of the piston in feet ; this will give the work done in one stroke of the piston ; multiply this product by the number of strokes the piston makes per minute, which will give the total work done by the steam in one minute ; to get the horse-power, divide this last product by 33,000. From this deduct, say, 20 per cent, for various losses, such as friction, con- densation, leakage, etc.
CARE AND MANAGEMENT OF A STEAfl ENGINE
It is to be supposed to begin with that the engine is correctly designed and well made, and that, after a suitable selection of an
186 HANDBOOK ON ENGINEERING.
engine for the work to be done, nothing now remains except proper care and management.
Lubrication* — The first and all-important thing in regard to keeping an engine in good working order is to see that it is properly lubricated. This does not imply, neither is it intended to encourage, the use of oil to excess ; all that is needed is simply a film of oil between the wearing surfaces. It is marvelous hew small a quantity of oil is required when of good quality and con- tinuously applied. There are several self-feeding lubricators in the market which have been tested for years and area pronounced success; these include crank-pin oilers, in which the oscillatory motion of the oil makes a very efficient self -feeding device, the flow being regulated by means of an adjustable opening to the crank-pin, or in the adjustment of a valve by which its lift is reg- ulated by each throw of the crank ; and in others by a continual flow through a suitable tube containing a wick or other porous substance. For stationary engines, it is desirable that the main body of the oiler be made of glass that the flow of oil may be closely watched and adjusted accordingly. For the reciprocating and rotary parts of the engine, a modification of the above men- tioned oilers may be used. They are of various patterns and devices and many of them very good. It is also a good plan to have some device by which the cross-head at each end of each stroke will take up and carry with it a certain amount of oil ; for the lower half of the slide this is not difficult to arrange ; for the upper side an automatic feeder placed in the middle of the slides will provide ample lubrication.
For oiling the main bearing there should be two separate devices, one an automatic glass oiler; and in addition, a large tallow cup attached to the cap of the bearing. This cup should be filled with tallow mixed with powdered plumbago ; the open- ings from the bottom of the cup to the shaft should be not less than quarter inch for small engines, and three-eighths to half -inch
HANDBOOK ON ENGINEERING. 187
for larger ones ; so long as the main bearing runs cool the tallow will remain in the cup unmelted ; but if heating begins, the tallow will melt and run down on the surface of the revolving shaft, and thus provide an efficient remedy when needed. For oiling the valves and piston, a self -feeding lubricator should be attached to the steam pipe ; this by a continuous flow of oil will be found not only satisfactory in its practical working, but economical in the use of oil.
In selecting an oil for an engine, it is in general better to use a mineral rather than animal oil, especially for use in the valve chest and cylinder. The objection to an animal oil, and espe- cially to tallow or suet, is that it decomposes by the action of heat, often coating the surface of the steam chest, the piston ends and the cylinder heads with a deposit of hard fatty matter ; or forms into small balls not unlike shoemakers' wax. There is no such decomposition and formation in connection with mineral oils, which may now be had of uniform quality and consistency, and at much lower prices than animal oils.
The slide valve should be kept properly set and should be examined occasionally to see that the face and seat are in good condition. So long as this is the case, the valve mechanism and the valve itself must be let alone nnd not tampered with,
The piston packing1 will need looking after occasionally to see that it does not gum up and stick fast, which it is very likely to do when the cylinder is lubricated with tallow or animal oil.
The rings should fit the cylinder snugly and should be under as little tension as possible and insure perfect contact. If the rings are set out too tight they are liable to scratch or cut the cylinder ; if too loose, the steam will blow through from one end of the cylinder, past the piston and into the other. In adjusting the springs in the piston, care must be exercised that the adjust- ments are such as will keep the piston rod exactly central, to prevent springing the rod, or causing excessive wear on the stuf-
188 HANDBOOK ON ENGINEERING.
fing-box. There are several packings, which do not require this adjustment, the rings being narrow, and either expanding by their own tension or by means of springs underneath. The only thing to be done with such a packing is to keep it clean, and when lubricated with a mineral oil this is not a difficult matter. If it groans, take rings out and file sharp edges off.
The stuffing-boxes whether for the piston or valve-stem need to be looked after carefully, and to prevent leaking, will require tightening from time to time. There are several kinds of ready- made packings in the market, containing rubber, canvas, hemp, soapstone, asbestos and other substances which form the basis of a good durable packing. These can be had in sizes suitable for all ordinary purposes, and their use is recommended. In the absence of any of these, a packing made of clean manilla or hemp fiber will serve a useful purpose. Formerly it was the only sub- stance used, but is being gradually superseded by the other kinds mentioned above. In packing the small and delicate parts, such as a governor stem, a good packing is made by pleating together three or more strands of cotton candle-wick. This is soft, pliable, free from anything like grit, and will not get hard until soaked with grease and baked into a brittle fiberless substance not easily described.
Crank-pins* — There are few things more troublesome to an engineer than a hot crank-pin, and it is sometimes very difficult to get at the real reason why it heats. Among the principal rea- sons for heating are: the main shaft is not " square " with the engine, or, that the pin is not properly fitted to the crank ; or, perhaps, it is too small in diameter — defects which are to be remedied as soon as practicable. Heating is often caused by the boxes being keyed too tightly, or by insufficient lubrication. There are now several good self -feeding lubricators in the market which will supply the oil to a crank-pin continuously ; these are recommended rather than the old style of oil cup, which was
HANDBOOK ON ENGINEERING. 189
not only uncertain, but doubtful in its action. Many trouble- some crank-pins have been cured of heating by this simple matter of constant lubrication. When the crank-pin is rather small for the engine and the load variable, there is a possibility of having a hot pin at any time ; it is advisable to have ready some simple and effective expedient to be applied when it does occur ; for this there is perhaps nothing better and safer than a mixture of good lard oil and sulphur.
Connecting tod brasses* — In quick running engines the brasses should be fitted metal to metal ; or if this is not desir- able, several strips of tin or sheet brass should be inserted be- tween them and keyed up tight. This gives a rigidity to a joint which is difficult to secure when the brasses have a certain amount of play in the strap. It is a common practice to bore the brasses slightly larger than the pin, so that when fitted to it the hole shall be slightly oval, and thus permit a freer lubrica- tion than is secured by a close fit around the whole circum- ference.
Knocking* — There are several causes which, combined or singly, tend to produce knocking in steam engines. In most cases the difficulty will be found to be in the connecting rod brasses ; but whether in the crank-pin end or at the cross-head is not easily determined in all cases. A very slight motion will often produce a very disagreeable noise ; the remedy is, in most cases, very simple, and consists in simply tightening the brasses by means of the key or other device that may have been pro- vided for their adjustment. In adjusting a key it is the common practice to drive it down as far as it will go, marking with a knife blade the upper edge of the strap, then drive the key back until it is loose ; after which drive it down again, until the line scratched on the key is within J or J inch of the top of the strap. The size of the strap joint and the judgment of the per- son in charge must decide the best distance. This may be done
190 HANDBOOK ON ENGINEERING.
at both ends of the connecting rod. On starting the engine, the cross-head and crank-pin mast be carefully watched, and upon the slightest indication of heating, the engine should be stopped and the key driven back a little farther. A slight warmth is not particularly objectionable, and will, as a general thing, correct itself after a short run. Knocking is sometimes occasioned by a misfit, either in the piston, or crosss-head and the piston-rod. These connections should be carefully examined, and under no circumstances should lost motion be permitted at either end of the piston rod.
If the means of securing are such that the person in charge can properly fasten the piston to the rod, he should see that it is kept tight ; if not, then it should be sent to the repair shop at once, as there is no telling when an accident is likely to overtake an engine with a loose piston.
The connection between the piston-rod and cross-head is usu- ally fitted with a key and furnishes a ready means of tightening the joint, if proper allowance has been made for the draft of the key. In case there has not, the piston-rod and cross-head should be filed out so that the draft of the key will insure a good tight joint when driven down.
The main bearing should be examined and if there should be too much lateral movement of the shaft, the side boxes might then be adjusted until the shaft turns freely, but has no motion other than a rotary one. The cap to the main bearing should also be carefully examined, as it may need screwing down and thus prevent an upward movement of the shaft at each stroke ; this applies more particularly to quick running engines.
Engines which have been in use for some time are likely to have a knock caused by the piston striking the head. This is brought about by having a very small clearance in the cylinder and in not providing, by suitable liners, for the wear of the connecting rod brasses. In case of this kind, liners should be inserted behind
HANDBOOK ON ENGINEERING. 191
the brasses in the connecting rod, or new brasses put in, which will restore the piston to its original position.
Knocking may be caused by defects in the construction of the engine ; such, for example, as not being in line, the crank-pin not at right angles to the crank, the shaft may be out of line, etc.
Whenever the cause is one in which it can be shown that it is a constructive defect, there is but one remedy, and that is the re- placing of that part, or the assembling of the whole until perfect truth is had in alignment of all the parts. This will require the services of an experienced engineer but all improperly fitting pieces should be replaced by new ones as a safeguard against accident, which is likely sooner or later to overtake badly fitting pieces.
If the boiler is furnishing wet steam, or priming, so as to force water into the steam pipe, it will collect in the cylinder and will not only cause knocking, but on account of its being practically incompressible there is danger of knocking out a cylinder head, bending the piston-rod, or doing other damage to the engine. The cylinder cocks should be opened to drain any collected water away from the cylinder.
Repairs* — Whenever it is necessary to make repairs the work should be done at once ; oftentimes a single day's delay will in- crease the extent and cost fourfold. If an engine is properly designed and built, the repairs required ought to b.e very trivial for the first few years it is run, if it has had proper care. It may be said in reply to this "true, but accidents will happen in spite of every care and precaution." That accidents do occur is true enough ; that they occur in spite of every care and precaution is not true. In almost every case, accidents may be traced directly back to either a want of care, negligence, or to a mistake.
Fitting slide-valves* — The practice of fitting a slide-valve to its seat by grinding both together with oil and emery, is wrong and should never be resorted to. The proper way to fit the sur-
192 HANDBOOK ON ENGINEERING.
faces is by scraping ; this insures a more accurate bearing to begin with, and will also be entirely free from the fine grains of emery which find their way and become imbedded in the pores of the casting, and are thus liable to cut the valve face and destroy its accuracy. The scraping of the valve and seat has a beneficial effect by causing the removal of the fine particles of iron, which are loosened by the action of the cutting tool in the planing machine, and which ought to be fully removed before the engine leaves the manufacturers' hands. Aside from this, it is doubtful whether the scraping amounts to anything practically, for the reason that the cylinder and valve are fitted cold, and their relative positions are distorted by the action of the heat of the steam, once the engine is in use. The scraping, which simply renders the valve face and seat smooth and hard, is all that is sufficient to begin with, and may be re-scraped after the valve has been in use a few days, should it be found necessary, which will not often be the case in small and ordinary sized engines.
Eccentric straps are likely to need repairs as soon as any- thing about an engine. They should be carefully watched at all times. If they are likely to run hot, it is also probable there is more or less abrasion or cutting going on, and if prompt measures are not taken to arrest it, they are likely to cut fast to the eccentric, and a breakage is sure to occur.
When the straps begin to heat, the bolts should be slackened a little, and at night, or perhaps at noon, the straps should be taken off and all cuttings carefully removed with a scraper (not with a file) ; the rough surfaces on the eccentric should be removed in the same manner.
The straps should be run loose for a few days, gradually tightening as a good wearing surface is obtained.
The main bearing, if neglected, is a very troublesome journal to keep in order. The repairs generally needed are those which
HANDBOOK ON ENGINEERING. 193
attend overheating and cutting. The shaft, whenever possible, should be lifted out of the bearing, and both the shaft, bottom of main bearing and side boxes, carefully scraped and made perfectly smooth. It sometimes occurs that small beads of metal project above the surface of the shaft which are often so hard that neither a scraper nor file will remove them ; chipping is then resorted to and the fitting completed with a file and fine emery cloth.
Heating* of journals. — A very common cause for the heating of journals having brasses and boxes composed of two halves, is that both halves alter their shape from causes attending their wear. Thus, most engineers will have noticed that, although there is no wear between the sides of a brass and the jaws of a box, yet in time the brass becomes a loose fit in the box. Now, since the sides of the brass have, when fitted, no movement in the box, it is evident that this cannot have proceeded from wear be- tween those surfaces, and it remains t) find what causes this looseness. Most engineers will also have observed that though the bottom or bedding surfaces of a brass and of the. box may have been carefully filed to fit each other when new, yet if in the course of time the brasses be taken out and examined, and more especially the bottom brass that receives the weight, the file marks will become effaced on all parts where the surfaces have bedded together well, the surface having a dull bronze and condensed appearance. This is caused by the vibrations under pressure hav- ing condensed the metal. Now, this condensation of the metal moves or stretches it, and causes the sides of the brass to move away from the sides of the box, and, consequently, to close upon the journal, creating excessive friction that may often, and very often does, cause heating. It is for this reason that on such brasses the sides of the brass boxes are by a majority of engi- neers, eased away at and near the joint, and it follows from this cause the same easing away is a remedy.
Governor* — It not infrequently occurs that after an ordinary
194 HANDBOOK ON ENGINEERING.
throttling engine has been used a few years, the speed becomes variable to such a degree that it interferes with the proper run- ning of the machinery. This occurrence can generally be traced directly to the governor. When it does occur, the governor should be taken apart and thoroughly examined ; if the needed repairs are such as can be easily made in an ordinary repair shop, they should be made at once ; if not, a new governor should be purchased. The price of governors is now so low that it is better and more economical to buy a new one than loose the time and pay the bills for repairing an old one.
AUTOMATIC ENGINES.
In the care and management of this class of engines, it is diffi- cult to say jnst what particular attention they need, owing to the variety of styles and the peculiarities of each. As a rule, how- ever, they require first, to be kept well oiled ; second, to be kept clean ; third, to be kept well packed ; and fourth, to be left alone nights and Sundays. There is little doubt that there has been more direct loss rasulting from a ceaseless tinkering with an engine than results from legitimate wear and tear to which the engine is subjected. It is not to be inferred from the preceding remark that builders of this class of engines are infallible ; it might be difficult to prove any such assertion in case it was made ; but it may be said with truth, that the engines of this class now .in the market are carefully designed, well proportioned, of good materials and workmanship, and as examples of mechanism are entitled to take very high rank. Engineers know of several engines of this class which have not cost their owners for repairs so much as five dollars in five years' constant use. It is essential to the economical working of these engines that the cut-off mechanism be in good order and properly adjusted. Whenever the valves need resetting, the final adjustment should be made
HANDBOOK ON ENGINEERING. 195
with a load on the engine and with the indicator attached to the cylinder, the valves being set by the card rather than by the eye. No general rule can be given for setting the valves, as the prac- tice varies with the size and speed of the engine ; nor is any rule needed, for the indicator will furnish all the data required. The adjustments may then be made so as to secure prompt admission, sharp cut-off, prompt release, and the proper compression.
TO FIND THE DEAD CENTERS.
When setting the valve of an engine by measuring the lead, as is the usual method, it is necessary that the crank be accurately placed on the dead centers at each end of the stroke. Sometimes an engineer, when adjusting the valves of his engine, will attempt to place the crank on the dead center by watching for the point at which the travel of the cross-head stops, or by the appearance of the connecting-rod as related to the crank. These methods are totally unreliable for obtaining accurate results, especially the first one mentioned. The travel of the cross-head and the piston near the point of reversal of motion is very slow when compared with the valve. The velocity of travel of the valve is at nearly its maximum amount when the crank is on the dead center, and a slight error in finding the dead center point makes a very appre- ciable error in the position of the valve, with a subsequent error in its proper setting.
There are several methods for finding the dead center. The method that can be recommended and the one that should always be used when the dead center of an engine is to be fonnd is that familiarly known as " tramming." The dead centers when found by this method, are geometrically accurate, no matter if the engine is out of level or if the shaft is above or below the axis of the cylinder. Some simple tools are required which are generally available, with the exception of the trams, which may be readily
196
HANDBOOK ON ENGINEERING.
made for the purpose. Two trams are required, one of which should be 6" or 7" long and the other about 24" or 30", as the condition may require. The smaller tram may be made of i steel wire with the points turned over at right angles to the body, so as to project about 1". The points should be sharpened so that a hair line may be drawn by them. The larger tram should be made from rod of at least f " diameter and the points made in the same way as for the smaller tram. Oftentimes, the long tram
Fig. 130. Finding the dead center.
is made with one leg longer than the other, on account of being handier to reach some stationary part, but this is a minor point, which has nothing to do with the principle to be described. The other tools required are a light hammer, a prick-punch a pair of 10" or 12" wing dividers and a hermaphrodite caliper, or a scrib- ing block. A piece of chalk will also be found convenient to facilitate scribing lines on the metal parts with the trams or dividers. Fig. 130 shows the use of the trams.
Having the necessary tools, we are ready to begin operations, — and may start at either end of the stroke, as circumstances may favor. The fly-wheel is turned so that the crank stands at about the angle shown in the accompanying illustration, which
HANDBOOK ON ENGINEERING. 197
may, however, be approximated as the operator may desire. The effort made, being to give sweep enough to the cross-head to allow accurate measurements and still not have such an excessive arc on the fly-wheel as to make its bisection difficult.
A prick mark is made on the guides, or some convenient sta- tionary point, as at .B, and an arc struck on the cross-head with the small tram. At the same time, an arc is scribed on the rim of the fly-wheel at 6r, using some convenient point for the lower point of the tram as at 7T, The fly-wheel is now turned until the crank passes the center and the cross-head travels back until the scribed line will coincide exactly with the point of the tram when held in the same position as in the first case. When this point has been reached, the wheel is stopped and a second arc is scribed on the fly-wheel rim at F with the tram J. The herma- phrodite caliper, or the scribing block, is now used to scribe a concentric line D E on the fly-wheel rim and the arc C F is bisected with the dividers. When the center H has been accu- ately located, it should be carefully prick-marked. The scribing of the concentric line D E is a refinement that is not strictly necessary if care be taken to locate the points of the dividers at the same distance from the outer periphery of the wheel in each instance when finding the center H. The marks left by the lathe tool will sometimes be plain enough for a guide. When the center H has been found, the fly-wheel is turned so that the point of the tram will fall into the prick-mark H when its lower end is in the stationary point K. When this condition is effected, the crank is exactly on the dead center and the position of the valve may be taken with confidence that its location at the dead center point is accurately found. The same procedure is followed to place the crank on the dead center at the opposite end of the stroke.
The cut on page 198 is an elevation of Tandem Compound Engine, showing engine erected on brick foundation. It also shows a line through cylinders ; also a line over the shaft.
198
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 199
These lines are used in the erection of a new engine, or to line up an old one, or with an engine that is out of line. The cut also shows how the foundation is made ; also how the anchor bolt is fastened.
The cut on page 200 shows how to pipe a Twin Tandem Compound Condensing Engine. The plan shows two receivers, iieaters, relief valves, gate valves, etc., and is so arranged that either side can be run independently of the other. It also shows how to line a pair of these engines by following the lines and noting the distance between each line. An engineer would have no trouble in lining up a pair of these engines.
HOW TO LINE AN ENGINE.
The method followed when lining different types of engines, such as vertical, horizontal, portable etc. is as follows: —
The method followed in lining any piston engine is essentially the same in all cases, as far as determining when adjustments are needed. The method of making the adjustments after the char- acter and amount of them is determined, depends entirely on the construction of the engine, and will necessarily have to be deter- mined in each individual case, Lining an engine consists of ad- justing the guides so they shall be parallel to the bore of the cylinder, and in such a position that the center of the piston socket of the cross-head shall coincide with the axis of the cylin- der. Under these conditions only, can the piston and cross-head travel through the stroke freely, and without distorting any of the parts. After this adjustment has been made, the truth of the right-angle position of the shaft must be determined as being "out of square;" this will make an engine run badly, and is often the unsuspected cause of much trouble to engineers. We will assume that we have an engine with four-bar or locomotive guides, and that the connecting rod, cross-head, back cylinder
200
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING.
201
head and piston have been removed. If the engine is of the horizontal type the first step will properly be to ascertain if the engine is level on the foundation, and if not, proceed to make it so. After having leveled the engine, stretch a smooth linen line, as shown in Fig. 133, through the bore of the cylinder and the stuffing-box, to a point beyond the shaft, where it should be attached to an iron rod driven into the floor. The other end is fastened to a cross-bar bolted across the face of the cylinder to
Fig. 183. Lining up an engine.
two of the studs, as shown in Fig. 133, or the bar may preferably be somewhat longer than one-half of the diameter of the cylinder, and with a saw cut for a short distance lengthwise at the inner end. In this case, it is held by only one of the cylinder studs and can be somewhat more easily adjusted. The line or cord is adjusted to approximately the proper position, and is drawn taut and fastened through the cross-bar by being tied to a short stick that is too long to pass through the hole. In this position it is held by the friction, and can be readily adjusted to the required position. An assistant is required to move the line in the direc- tions indicated, as the work proceeds, and then we are ready to center it in the cylinder. The only tool required for this purpose is a light pine stick of slightly less length than the radius of the
202 HANDBOOK ON ENGINEERING.
bore, and it should have an ordinary pin pushed into the head for a ' 'feeler." Now adjust the line in the cylinder so that the head of the pin will just tick the line from four points of the counter- bore, which is always the part of the cylinder to work from, as it is not affected by the wear. The line should then be adjusted to the center of the other end of the cylinder, but not from the stuffing-box, as this is likely to be out of center somewhat. Make the adjustment at this end from the counterbore, if pos- sible, the same as in the first instance, and then it will be neces- sary to try the position of the line in the back end of the cylinder as the changes made at the other end will affect it slightly. After the line is truly centered, we are ready to adjust the guides. With some types of cross-heads, it is possible to use the cross- head for determining the proper location of the guides, but with the ordinary form, such as shown in Fig. 133, this cannot be done but we will need a tool similar to that shown in sketch, which consists simply of a piece of flat iron long enough to reach across the guides, and having a hole drilled and tapped in the center for the thumb-screw. This thumb-screw is adjusted so that its point is the same distance from the lower side of the bar, as the lower face of the wings of the cross-head are from the center of the piston socket. To find this distance, lay a straight edge across the end of the cross-head and draw the line A B, and then, hav- ing found the center of the hole, the measurement may be accur- ately taken. The lower guides are now adjusted by the tool, so that the point of the screw will tick the line throughout the length, and then the top guides are put in position with the cross- head in place and adjusted for a proper working fit.
Before removing the line from the cylinder, however, the shaft should be tested for the truth of its right-angle position, which may be done by calipering between the crank disc and the line at the points H and J. If the distances are equal, the shaft is square with the bore of the cylinder, providing, of course, that
HANDBOOK ON ENGINEERING. 203
the disc is faced true with the shaft. If there is any doubt as to its accuracy, turn the shaft as nearly half way around as the crank-pin will admit without disturbing the line. Then caliper the distance of a point on the disc that will not be far removed from the first position, thus reducing the chance for error. If the shaft shows 4 ' out ' ' move the outward bearing until the meas- urements show equal in both positions. The horizontal truth of the shaft can be found by laying a level on it and if " out," raise or lower the out-board bearing until the level shows fair. Work of this kind requires skill and patience and belongs prop- erly to the sphere of the chief engineer. It requires a delicacy of touch and an appreciation of what is meant by close measurement that can come only through experience. In centering the line, one should be able to detect when it is as little as T^TF of an inch out of center. A piece of ordinary tissue paper is about .00125 inch thick. A man should be able, therefore, to adjust a line so accurately that if the " feeler," with one or more pieces of the paper under it, just clips the line, it will miss the line when one thickness is removed. While it may not always be necessary to work as closely as this, a person cannot expect to line up engines successfully until he has a full knowledge of what this degree of accuracy means.
Engine Formulas.
Diam. cyl. for given H.P. = -,/ __ 33000 XH.P. ^
v Piston speed XM.E.P. '
Stroke in feet = P^ton speed in feet per min.
Revs. X 2
Piston speed in feet per min. Keys, per min. = Length of stroke in feet X 2
83000 XH.P. _ Piston speed = Areft Qf p.gton in gq inches x M E p>
33000 XH.P. Area of piston in sq. ins. = M.E.P.X piston speed
33000 X H. P. M.E.P. required = Area of ristOnX Piston speed
204
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 205
CHAPTER XIa.
DIRECTIONS FOR SETTING UP ADJUSTING AND RUNNING THE CORLISS STEAM ENGINE.
Location of foundation* — The foundation must be at right angles with main line shaft. If main line shaft is not already in position, then foundation must be set by two points, located and connected with a line parallel with the buildings, and at right angles to an imaginary line through center of cylinder.
Foundation plans should show all center lines. If a templet is furnished to locate the foundation accurately for the mason, the center line of engine cylinder and guides and right angle for crank center are drawn thereon.
Cap Stones* — Examine carefully the lap faces of cap stpnes and, if necessary, have them trimmed off by cutter or mason, so that each is true and level, and in exactly the plane shown in foundation plan.
Cylinders and frame* — Put engine cylinder and frame in position and bolt them together.
Lining; off crank shaft and out-end bearing. — Stretch a line at right angles to main center line, through main bearing to represent center line of crank shaft. See that this line is exactly in the center and level. By this line place out-end bearing square and true. Put crank shaft in its bearings after bottom box has been placed in main bearings. Insert quarter boxes and adjust- ing wedges into main bearing and put cap on.
To ascertain that shaft is at exact right angles to main center line, turn engine shaft until the crank pin comes nearly to the
206 HANDBOOK ON ENGINEERING.
main center line, then with a pair of calipers, or rule, measure from shoulder of crank-pin to line, and after noting this distance, turn the crank back towards opposite center until pin is in same relative position to line, and measure again. If both measurements do not correspond, out-end bearing must be moved either way as required, until measurements show equal. Then take up slack around shaft in main bearing, being careful not to force the adjusting wedge too tight.
Fly-wheels* — The fly-wheel is next placed on shaft and firmly keyed in position.
Placing1 valve gear* — Steam and exhaust valve covers or bon- nets on valve gear side are next bolted to place, taking care that no dirt or foreign substance gets between the surface underneath the covers.
Valve stems are inserted from opposite or front of cylinder and the valves put in after them, the T head of valve stem entering slot in valve. Couple up all valve gear parts, i. e., disc plate valve-steam cranks, valve-connecting rods, dash-pots and dash-pot rods, vajye-rod rocker, eccentric and straps on crank-shaft, first and second eccentric rods. The dash-pots should be thoroughly cleaned and oiled before putting in place.
ADJUSTMENT OF CORLISS VALVE GEAR WITH SINGLE AND DOUBLE ECCENTRICS.
A brief description of the essential parts of the Corliss engine valve gear will assist in obtaining a clear conception of the subject.
When a single eccentric drives both steam and exhaust valves the range of cut-off is limited to about half the piston stroke. This Tvill become obvious by considering the following necessary conditions ; —
HANDBOOK OF ENGINEERING
207
After the eccentric has reached the extreme of its throw as shown in Fig. 135 in either direction all valve gear motions are reversed.
Fig. 135. Showing eccentric in extreme position.
The steam valve must be released before the eccentric motion is reversed, for if the hook does not strike the knock-off cam during its forward motion, it cannot strike it during its return motion.
The maximum exhaust opening, or the middle of the exhaust period, must occur when the eccentric is at the extreme of its throw as in Fig. 135.
Now, in order to release the expanded steam in the cylinder before the commencement of the return stroke and to secure the exhaust closure a little before the end of the return stroke, the middle of the exhaust period or the extreme of the eccentric throw must evidently occur before the middle of the return stroke, and, therefore, the extreme throw of the eccentric in the opposite direction must occur before the middle of the forward stroke, and the valve must be released before this point is reached if released at all.
It will be understood from the foregoing that late release and late exhaust closures are conditions imposed by the single eccentric valve gear, and these conditions agree very well with moderate rotative speed ; but at higher speed earlier release and
208 HANDBOOK ON ENGINEERING.
more compression may be required. This may be effected by moving the eccentric forward on the shaft, but the reversing of the steam valve motion would then occur at an earlier stage of the forward stroke and the range of cut-off would be correspond- ingly shortened. Earlier exhaust closure could be had by giving the exhaust valve more lap, but this would involve a later release of the expanded steam at the end of the stroke. On the other hand, shortening the exhaust lap would give earlier release but insufficient or no compression.
In Figs* 136 and 137 similar capital letters of reference indicate the same parts of the mechanism.
Fig. 136 shows all the essential parts of the valve gear. The steam valves work in the chambers S 8 and the exhaust valves work in the chambers E E. The double-armed levers D D work loosely on the hubs of the steam bonnets ; they are con- nected to the wrist-plate B by thr rods K K, the levers M M are keyed to the valve stems J J, and are also connected by the rods 0 0 to the dash-pots P P. The double-armed levers D carry at their outer ends what are called steam hooks FF, these being pro- vided with hardened steel catch plates, which engage with arms M M, making the arm M and the hook F work in unison until steam is to be cut off. At this point another set of levers or cams G 6r, which are connected by the cam rods II H, to the governor? come into play, causing the catch plates on the hooks F to release the arms M M, the outer ends of which are then pulled downwards by the dash-pot plunger, causing the steam valves to rotate on their axis and thus cut off steam. These are the essential fea- tures of the Corliss gear.
The exhaust valve arms N are connected to the wrist-plate by the rods L Z/, and it is seen that all the valves receive their motion from the wrist- plate B; the latter receives its motion from the hook-rod A; this rod is generally attached to a rocker arm not shown; to this arm the eccentric rod is
HANDBOOK ON ENGINEERING.
210
HANDBOOK ON ENGINEERING,
also attached. The rocker arm is usually placed about mid- way between the wrist-plate and eccentric, and in the center of its travel stands in a vertical position.
The setting of the valves is not a difficult matter, when, on the wrist-plate, its support, valves and cylinder, the customary marks have been placed for finding the relative positions of wrist-plate and valves.
0 c
•- H
>t
'
Q-
f*l- t Af
j^ ft. ^
Fig. 187. Diagram of Corliss gear and valves.
Now, referring to Fig. 137, when the back bonnets of the valve chambers have been taken off, there will generally be found a mark or line, r, on the end of each steam valve s s, coinciding with the working or opening edge of each valve ; another line, £, will be found on each face of the steam valve chamber coinciding with the working edge of the steam port. The exhaust valves and their chambers are marked in a similar way, i. e., the line u on the end of each exhaust valve coincides with the working edge of the valve, and the line #, on the face of ^ach exhaust valve
HANDBOOK ON ENGINEERING. 211
chamber, coincides with the working edge of the exhaust port. On the hub of the wrist-plate will be found three lines n, c, w, placed in such a way that when the line c coincides with the line b on wrist -plate, the wrist plate will stand exactly in the center of its motion, and when the line b coincides with either of the lines TI, ft, the wrist -plate will be at one of the extreme ends v or w of its travel.
In setting the valves, the first step will be to set the wrist- plate in its central position, so that the lines b and c will coin- cide, and fasten the wrist-plate in this position by placing a piece of paper between it and the washer R on its supporting pin. Now set the steam valves so that they will have a slight amount of lap, that is to say, the lines r, r, must have moved a little beyond the lines £, t. The amount of this lap depends much on individual preference and experience ; it ranges from ^ to J for small engines, and from J to | inch for compara- tively large engines. This lap is obtained by lengthening or shortening the rods K K\>y means of the adjusting nuts.
Now place the exhaust valves e, e, by lengthening or shorten- ing the rods L L by means of the adjusting nuts, in a position so that the working edges will just open the exhaust ports, or, in other words, place the lines u and x in line with each other as indicated in illustration.
The next step will be to adjust the rocker arm. . Set this arm in a vertical position by means of a plumb line, and connect the eccentric rod to it ; then turn the eccentric around on the shaft, and see that the extreme points of travel are at equal distances from the plumb line. To secure this a little adjustment in the stub end of the eccentric rod may be necessary. Now connect the hook rod A to the wrist-plate. The paper between the wrist- plate and the washer on the supporting pin should now be taken out, so that the wrist-plate,which is connected to the valves, can be swung on its pin. Now turn the eccentric around on the shaft
212 HANDBOOK ON ENGINEERING.
in order to determine the extreme points of travel of the wrist- plate. If all parts have been correctly adjusted, the line b will coincide with the lines w-, n, at the extreme points of travel ; if this is not the case, the hook rod will have to be adjusted at its stub end so as to obtain the desired equalized motion of the wrist-plate.
The next step will be to set the valves correctly with reference to the position of the crank ; to do this the length of the rods K, K, L, and L must not be changed, but the following mode of procedure should be followed : Place the crank on one of its dead centers (see page 195) and turn the eccentric loosely on the shaft in the direction in which the engine is to run, until the steam valve nearest to the piston shows an opening or lead of -J^- to -fa inch. After the proper lead has been given to this valve, secure the eccentric, and turn the shaft with eccentric in the same direc- tion in which the engine is to run until the crank is on the oppo- site dead center, and notice if the opening or lead at this end of the cylinder is the same as on the other steam valve ; if not, shorten or lengthen slightly, as may appear necessary, the con- nection between the wrist-plate and eccentric. Of course much adjustment in the length of these connections is not admissible without resetting the valves with reference to the wrist-plate. The compression on an engine is a very important factor, upon which cool and quiet running depends. With exhaust valves line and line about 5 per cent compression is secured, which is equal to If for 36" stroke and 2" for 42" stroke. In case more compression is desired, the exhaust valves must be given a little lap.
To set the exhaust valves for a given compression, say, 2 inches, first measure off 2 inches from the ends of the cross- head travel as shown in Fig. 138 (not from the ends of the guide). Then turn the crank in the direction it is to run until the end of the crosshead reaches the line on the guide. Adjust the exhaust valve corresponding to this end of the stroke so that it just closes
HANDBOOK ON ENGINEERING.
213
the port. Turn the crank over the center and back on the return stroke until the opposite end of the cross-head reaches the line on the opposite end (to the first mark) of the guide. Then adjust the exhaust valve corresponding to this end of the stroke so that it just closes the port. Both exhaust valves will then close the ports when the piston reaches a point 2 inches from the working end of the guide and the engine will then have exactly 2 inches
Fig. 138. Laying out compression marks on guide.
compression. If this is found to be too much or too little, as determined by the running qualities of the engine, it may be varied either way by adjusting the length of the rods L and L, being careful to turn each nut exactly the same amount.
The only thing which remains now to be done is to adjust the cam rods H, H, to produce an equal cut-off at each end of the cylinder. On the column of most Corliss engine governors will be found a stop device, sometimes in the form of a loose pin, some form of cam motion or movable collar. This device is for the purpose of preventing the governor from reaching its lowest position, for when it reaches the latter position the valves should not hook on. Should the governor belt break or become ineffect-
214 HANDBOOK ON ENGINEERING.
ive, the governor will stop and reach its lowest position on the column, thereby bringing the safety cam Y in underneath the inner member of the hook F which prevents the latter from engaging arm Jf, and as the valves cannot hook on when it is in this position the admission of steam to the cylinder is entirely shut off and the engine will come to a standstill.
It will be apparent that the stop on the governor column should be removed or otherwise rendered inoperative as soon as the engine has attained full speed, and should again be placed in active position when stopping the engine in the usual way. As the stop just mentioned determines the lowest position of the governor at which the valves should hook up, it should be kept in place while the foregoing adjustments are being made.
Next, unhook the reach rod from the wrist-plate and by means of the starting bar move the wrist-plate over until the lines b and n are nearly opposite each other. The head end valve should now have opened the port to nearly the limit, which may be ascertained by the marks on the ends of the valve. Now, adjust the governor rod H so that the projection or cam on the disk G operated by the governor will come in contact with the inner member of the steam hook F, so that the valve will be tripped or released when the marks b and n are exactly in line. As all governors do not move an equal amount to produce a given change in the point of cut-off, it will be safer to hook the reach rod on the wrist-plate and have the engine turned in the direction in which it is to run, until the head end valve is released, than to adjust the cut-off with the use of the starting bar only. To prove the correctness of the cut-off adjustment, raise the gover- nor balls to a position where they probably would be when at work and block them there ; then, with the connections made between the eccentric and the wrist-plate, turn the engine shaft slowly in the direction in which it is to run, and when the valve is released, measure upon the slide the distance which
HANDBOOK ON ENGINEERING.
215
the crosshead has moved from its extreme position. Continue to turn the shaft in the same direction, and, when the other valve is released, measure the distance through which the crosshead has moved from its extreme position, and if the cut-off is equalized, these two distances will be equal to each other. If they are not, adjust the length of the cam rods until the points of cut-off are equal distances from the beginning of the stroke. Replace the back bonnets and see that all connections have been properly made, which will complete the setting of the valves.
Fig. 139. Diagram of doable eccentric gear.
ADJUSTMENT WITH TWO ECCENTRICS.
In order to obtain a greater range of cut-off in Corliss engines a separate steam and exhaust eccentric is used. With two eccen- trics the admission and exhaust valves can be adjusted independ- ently, and steam may be cut off anywhere, nearly to the end of the stroke.
The work of setting the valves of a Corliss engine having two
216
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 217
eccentrics is not particularly complicated as many engineers seem to think. After inspecting the type of releasing gear employed and knowing in which direction the engine is to run, finding the direction in which to turn the eccentric becomes a very simple matter. When setting the steam valves we have one eccentric to turn as in the case of the single eccentric engine, and when set- ting the exhaust valves another eccentric must be turned, but this does not add complication to the work, although it requires a little more time. The work of centralizing the positions of the various parts, equalizing the movements and setting and adjust- ing the valve gear is practically the same as with the single eccen- tric engine. Set the wrist-plate central as shown in Fig. 139, and adjust the valve rods ; but in this case the steam valves are set with negative lap, which is usually a little less than half the port opening. The first step is to set the exhaust eccentric (as it is generally placed next to the bearing). To do this turn the engine until the piston is in the position shown in Fig. 140, so as to obtain a compression of about 5 per cent of the stroke. Then turn the exhaust eccentric loosely on the shaft in the direction the engine is to run, until the exhaust valves are line and line. Then secure the eccentric and turn the engine on the other end in the same position to prove the correctness of the other exhaust valve.
The next step is to set the steam eccentric ; place the crank on either one of its dead centers, then turn the steam eccentric loosely on the shaft until the steam valve on the same end the piston is, has the required opening or lead, which varies from -fa"
to Ty.
These directions apply to engines in which the reach rod from the eccentric is connected to the wrist-plate above the center pin R, Fig. No. 136. When the reach rod is connected to wrist- plate below the pin jR, the eccentric should be turned the opposite direction to that in which the engine is to run.
218
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING.
219
The arrangement of the steam rods in Fig. 136 is in every re- spect satisfactory in connection with a single eccentric valve gear, for in that case a slow initial valve motion is imperative, and it is obtained by the lateral movement of the radius rod. But with two eccentrics quicker initial motion is feasible and desirable, and it is obtained by reversing the valve motion as in Fig. 139. Sepa- rate eccentrics require separate wrist-plates, which are usually placed on the same pin.
Fig. 142. Diagram showing steam distribution.
Figs* 141 and 142 show how the eccentrics may be placed on the shaft. The steam eccentric is at point 4, Fig. 141, the exhaust eccentric is at point 1, Fig. 142, and the crank is at its dead center at C. Individual eccentric circles are shown for the sake of clear- ness. An imaginary motion of the eccentric will point out the various events. Referring to Fig. 141, near point 2, at the end of
220
HANDBOOK ON ENGINEERING.
the throw, the hook connects with the steam valve ; at point 3 the steam edges are at the point of separating and the eccen- tric motion 2-3 determines the initial valve motion. When the eccentric is at point 4 the crank is at its dead center as shown. At point 5 the steam wrist-plate is in its central position and in that position the valve does not cover the port, as with the single eccentric gear, but the port is open to a certain extent, determined by the eccentric motion 3-5. Point 7 marks the end
Fig. 148. Diagram showing steam distribution.
of the throw, and the corresponding position of the crank is at C1 at about three-quarters of the piston stroke, and the limit of cut- off is a little later. If the hook does not strike the knock- off cam the valve will remain open until closed by the return stroke of the eccentric at point 9, near the middle of the return piston stroke. The exhaust action is discernible, Fig. 141.
HANDBOOK ON ENGINEERING.
221
It is similar to the single eccentric action, but with this differ- ence, that the release at point 5 occurs at about 95 per cent of the stroke, and the exhaust is also cut off at about 95 per cent of the return stroke at point 8.
The motion of the exhaust valve after it has closed the port is determined by the eccentric motion 8-2-5, and full period of exhaust opening is obtained by the eccentric motion 5-7-8. In case the exhaust valve motion is designed and set with lap, Fig. 143 shows the effect lap has on the exhaust valves. The lap when wrist-plate is central is determined by motion A-B. It will be
Fig. 144. Relative position of valves and crank pin.
noticed that the compression begins at A at about 90 per cent of the stroke, and the release at E occurs at 98 per cent of the return stroke and the exhaust opening E, (7, A, is shortened. Where lap is used on the exhaust valve it has the effect of making earlier compression and later release. A valve gear designed to be operated by a single eccentric cannot very well be made to cut off much later than at half stroke, even when a separate exhaust eccentric is added. For the slow initial valve motion requires at least half the throw of the eccentric, and the other half is not sufficient for a late cut-off, and it will readily be seen from an in- spection of Figs. 137 and 139, that a quicker initial valve motion in
222 HANDBOOK ON ENGINEERING.
.
Fig. 137 would involve radical changes in the valve gear. However, the range of cut-off may be extended by moving the eccentric back, sacrificing the lead, and to this there is no objections when it does not involve later release. The advantage gained by a second eccentric would consist in more compression and earlier release. After setting the valves and making the final adjustment, if it is convenient an indicator should be applied to the engine when at work to verify the adjustment of the valves for the best possible conditions for economical operation.
Fig. 143 indicates position of eccentric at f cut-off, which can be extended some by giving the steam valves a little more nega- tive lap, but as this shortens the amount of lap when closed, it may cause leakage in the steam valves. '
COMPOUND ENGINE.
The compound engine is practically two single engines con- nected together and so arranged that the exhaust steam from one engine passes into and becomes the c ' live " steam for the other, in other words the first, or high pressure cylinder receives its supply of steam from the boiler and the second or low pressure cylinder receives its supply from the high pressure cylinder. The object of the compound engine is to enable the steam to expand to the lowest possible pressure with the least loss by condensation. When steam expands its temperature decreases, so that by the time the piston reaches the end of the stroke the temperature of the steam and consequently the tem- perature of the cylinder walls is considerably below the temper- ature of the incoming steam. The fresh steam of high tempera- ture coming from the boiler comes in contact with the walls of the cylinder which have been cooled to the temperature of the exhaust steam, and the result is a considerable portion of the fresh steam is condensed, the latent heat serving to reheat the
HANDBOOK ON ENGINEERING.
223
224 HANDBOOK ON ENGINEERING.
cylinder walls. It will be understood that were it possible to keep the cylinder at a higher temperature, less steam would be condensed in warming it at each stroke and consequently more steam would be available for useful work. In the compound engine the steam is expanded partly in one cylinder and partly in the other so that the difference between the temperatures of the incoming and exhaust steam in each cylinder is greatly reduced. By this means steam may be expanded from a given initial pres- sure to a given final pressure with a loss of nearly twenty-five per cent less than would be incurred were the same expansion to take place in a single cylinder. It is due principally to avoiding the loss by cylinder condensation that the compound engine, considered as a type of engine, can perform nearly twenty-five per cent more work with the same weight of steam than can be obtained when the steam is expanded in one cylinder only.
In order to utilize the low pressure steam escaping from the high pressure cylinder it is necessary to provide a larger area of piston so that the low pressure steam acting on a large sur- face will do as much work as the high pressure steam acting on a smaller area. It is for this reason that the low pressure cylinder of compound engines is always made larger than the high pressure cylinder. The required size of low pressure cylinder for a given size of high pressure, depends upon the number of times the steam is to be expanded, the initial steam pressure and the nature of the work the engine is intended for. For steady loads the difference in the size of the two cylinders may be greater than where the load is constantly changing between wide limits as nearly always occurs in street railway service.
Compound engines, as this term is generally employed, are built of two types, the tandem compound, Fig. 145, and the cross compound, Fig. 146. In the tandem compound the work of both pistons is transmitted to the crank through one piston rod, cross- head and connecting rod, while in the cross compound there are
HANDBOOK ON ENGINEERING.
225
226 HANDBOOK ON ENGINEERING.
two complete engines placed side by side, the cranks of which are generally set 90 degrees apart. It will be seen that in the tandem compound engine it makes but little difference from the mechanical standpoint whether the work is divided evenly between the two c}7linders or not because both pistons move in unison and drive the same crank. In the cross compound engine it is necessary, in order to secure a uniform turning effort at the shaft, to have the work divided as nearly equally between the two cylinders as the conditions will permit. In the tandem com- pound engine the principal consideration is the proper working of the steam, and the sizes of the cylinders are determined by the number of expansions to be effected in both cylinders, or the total number of expansions, as it is called, and the initial pressure. As the equal division of the work between the two cylinders in compound engines is essential, the ratio of the cylin- ders is generally for noncondensing 2i to 1 for 100 Ibs., 2J to 1 for 125 Ibs., and 3 to 1 for 150 Ibs. initial pressure, and for con- densing 3 to 1 for 100 Ibs., 3J to 1 for 125 Ibs., and 4 to 1 for 150 Ibs., initial pressure.
The number of expansions required in a compound engine is represented by the quotient of the absolute initial pressure divided by the absolute terminal pressure. If steam is to be used at 105 pounds gauge pressure and is to be expanded down to 10 pounds
105 + 15 absolute in the low pressure cylinder, there will be r^ = 12
HANDBOOK ON ENGINEERING. 227
3.2, equals ratio of cylinders. Care should be taken in non- condensing engines so that the ratio of the low pressure cylinder is not too large, as in such cases the steam in low pressure cylin- der would expand to less than the atmospheric pressure, and thus make loops on indicator card which would incur a serious loss.
The calculation of the diameters of cylinders for a compound condensing engine when the data are given, follows. Take an engine that is to develop 500 horse power with an initial pressure of 105 pounds gauge, or 120 pounds absolute, the steam to be expanded to a terminal pressure of 6 pounds absolute. The total expansion of steam in both cylinders is 120 -r- 6 =20.
Expansion in each cylinder = ^/ 20 =4.47.
Point of cut-off in each cylinder, per cent of stroke = =
22.3 per cent, 1 + hyp. log. of expansion in each cylinder = 1 + hyp. log. 4.47 = 2.497.
Terminal and back pressure in high pressure cylinder, and the
120 initial pressure in the low = j^: = 26.8 pounds.
Mean effective pressure in h. p. cyl. =26.8 X2.497 — 26.8 = 40.11 pounds.
Mean effective pressure in 1. p. cyl. (assuming 3 Ibs. back press.) = 6 X 2.497 — 3 = 11.98 pounds.
If half the work is to be done in each cylinder, which is de- sirable in cross compound engines, each cylinder must do 250 horse power of work. Assuming the piston speed to be 600 feet per minute, the area of the low pressure cylinder is
33000 XH.P. 33,000 X 250
Piston speed X effective press. == 600 X H-98 = L47* 7 SqU8 inches =38 ins. diameter.
33,000 X 250 Area of high pressure cylinder by same rule is : — I
OUU /\ 4U.XJ.
= 342.3 square inches = 21 inches diameter.
228
HANDBOOK ON ENGINEERING.
Ratio of cyl. =
40.11 11.98
= 3.3 to one.
The clearance and the areas of the piston rods have not been taken account of by separate processes in the foregoing calcu- lations. These should always be included when making calcu- lations involving the pressure and expansion of steam in engine cylinders. The method of finding the number of expansions taking place in a compound engine may be readily understood by referring to the diagram, Fig. 147. The shaded area in the
Fig. 147. Relative volume of high and low pressure cylinders.
smaller cylinder represents the initial volume of steam in the high pressure cylinder, that is to say, this represents the volume of steam taken from the boiler for one stroke, or during one-half revolution. The point of cut-off is at one-third stroke and the area of the low pressure cylinder is three times that of the high pressure cylinder. It will be seen that when the low pressure piston moves to one-third stroke the volume of the cylinder F behind the piston is equal to the volume of the entire high pres- sure cylinder. This shows that the capacity or contents of the low pressure cylinder is three times that of the high so that for every
HANDBOOK ON ENGINEERING.
229
volume of steam and therefore for every expansion taking place in the high pressure cylinder there will be three volumes, and three expansions taking place in the low pressure cylinder. This shows why the total number of expansions in a compound engine is the number in the high pressure cylinder multiplied by the number in the low pressure cylinder. In the diagram, Fig. 147, when the small piston reaches the end of the stroke the steam will have expanded three times, that is, it will occupy three times the space it did at the point of cut-off. Now when the large piston reaches the end of the stroke each of the three volumes a, a and a, Fig. 148, will have been expanded three more times and the total will be 3 X 3 = 9 expansions, that is, the original volume a, Fig. 147, will then occupy nine times the space it did when
0
Fig. 148. Showing number of expansions in both cylinders.
first let into the high pressure cylinder. To find the number of expansions in a compound engine multiply the number of expan- sions in the high pressure cylinder by the number in the low, or multiply the number of expansions in the high pressure cylinder by the ratio of cylinder areas ; the product will be the number required.
Again referring to Fig. 148, it will be seen that the low pressure cylinder must receive a high-pressure cylinderf ul of steam at each
230 HANDBOOK ON ENGINEERING.
stroke otherwise the pressure in the receiver and the back pressure on the high pressure piston will rise too high and a loss of power will result, or if the pressure be too low in the larger cylinder the small piston will drive the larger one which will again result in loss of power. It has been shown that the volume of both cylinders vary in proportion to the areas, that is, if the areas are as 1 to 3 then when both pistons have reached, say, one-third stroke the volume of one will be 3 times the volume of the other, and when the larger piston in this case travels one-third of the stroke- the capacity of the low pressure cylinder behind the piston will then be equal to the whole of the smaller cylinder and will be capable of containing all the steam used during a full stroke of the smaller piston, or a high-pressure cylinderful of steam. This steam then expands during the remaining two-thirds of the stroke. Now it will be readily understood that if a cut-off valve were pro-
~ Vacuum
Figs* 149 and 150. Diagram from h. p. and 1. p. cylinders.
vided on the low pressure cylinder and is set to cut off at less than one-third stroke (with a ratio of cylinder areas 1 to 3) the low pressure cylinder will not take a high pressure cylinderful of steam when steam is cut off, and the pressure in the receiver must necessarily rise. Reducing the volume of steam entering the low pressure cylinder apparently tends to lessen the work done by the larger piston and consequently more work must apparently be
HANDBOOK ON ENGINEERING. 231
done by the high pressure piston. This in turn causes a later cut-off in the small cylinder as shown in Fig. 149, dotted lines, which serves to neutralize the effect of the higher back pressure so that while the cut-off has been made later, the mean effective pressure remains practically the same. The higher back pressure on the small piston means a higher initial pressure in the low pressure cylinder, see Fig. 150 dotted lines, which causes more power to be developed in the latter cylinder. Thus it is seen that, within certain limits, shortening the cut-off in the low pres- sure cylinder puts more of the load upon the low pressure piston.
On the other hand when the low pressure piston is doing more work than the high pressure, the cut-off in the low pressure cylinder maybe lengthened. This permits the low pressure cylinder taking more steam and consequently the receiver pressure and the back pressure on the high pressure piston are reduced and the work done by the high pressure piston is thus increased. By manipulating the cut-off on the low pressure cylinder the load on the two pistons may be equalized or very nearly so except when the engine is considerably underloaded or overloaded. The range of maximum economy is not as great with the compound as with the simple engine, that is to say, the loads :$aay be varied more widely from the point where the best economy is obtained, in the simple engine than in the compound which is due to the large difference in cylinder areas in the latter engine. At very early cut-off both the high pressure and the low pressure cylinders work the steam very similarly to the simple engine and as the loss by cylinder condensation increases with an increase in the range of temperatures it follows that an underloaded compound engine is but little if any more economical than a simple engine working with a similar initial point of cut-off.
In compound automatic cut-off engines the point of cut-off will be nominally the same in both cylinders, we say nominally (in name only) because the initial pressure and the extent of the
232 HANDBOOK ON ENGINEERING.
vacuum have some influence upon the receiver pressure and the mean effective pressure in the low pressure cylinder. In most compound engines in which the cut-off mechanism of both cylin- ders are operated by a single governor, provision is made for adjusting the cut-off of the low pressure cylinder relative to that in the high, so that while the nominal cut-off may be, say, one- fourth stroke, the actual points of cut-off maybe one-fourth in the high pressure and T5^ in the low pressure cylinder, the governor, however, varying both points of cut-off as the load changes.
HORSE POWER OF COMPOUND ENGINE.
Little can be done in finding the horse power of compound en- gines without the indicator because of the uncertainty of the points of cut-off and consequently of the back pressure and mean effec- tive pressures. The mean effective pressure in each cylinder may be computed by using assumed data, by the same rules given for simple engines, but it will readily be understood that assumed data furnishes assumed results only. Knowing the mean effective pressure areas and speed of the pistons the horse power of a compound engine is found as follows: Multiply the area of the high pressure piston by its mean effective pressure and divide by the area of the low pressure piston, then add this quotient to the mean effective pressure in the low pressure cylinder.* Call this answer 1. Multiply the area of the low pressure piston by the piston speed in feet per minute and by answer 1, and divide the last product by .33, 000; the quotient will be the indicated horse power.
CONDENSING ENGINES.
It has been explained that the atmosphere exerts a pressure of about 15 Ibs. per square inch on all surfaces with which it
* This quantity is to be taken as the M. E. P. when finding steam con- sumption of compound engine.
HANDBOOK ON ENGINEERING. 233
is in contact. The atmosphere is in contact with one side of an engine piston when the exhaust is open, and, consequently, the steam in pushing the piston forward, has to overcome this atmospheric pressure of 15 Ibs. per square inch. The useful pressure of steam is, therefore, whatever pressure there is above the pressure of the atmosphere, and this is the pressure that the steam gauge shows. When the gauge says 60 Ibs. we really have 75 Ibs., but 15 Ibs. of it does not count, because it is balanced by the atmospheric pressure on the other side of the piston. If we had sixty-pound steam pressing on the pis- ton and could get rid of the atmospheric pressure on the side of the piston, the steam would exert a force of 75 Ibs. per square inch, a very respectable gain, indeed. We might remove the air pressure by pumping it out, but the amount of power required in doing the pumping would be equal precisely to all gain hoped for, plus the friction of the pump; therefore, there would be an actual loss in the operation. But there is another way of remov- ing the air pressure. It has been explained that a cubic inch of water vaporizes and expands into a cubic foot of steam at -atmos- pheric pressure. If, after getting this cubic foot of steam, we take the heat out of it, we again turn it into the cubic inch of water. Assume the engine cylinder to hold just a cubic foot of steam, and assume that the stroke is complete and ready for the exhaust valve to open and permit this foot of steam to escape, and assume that this cubic foot of steam has expanded down to atmospheric pressure, that is, 15 Ibs., absolute pressure. Now, instead of opening the cylinder to the atmosphere, we dose the cylinder with cold water. The heat leaves the steam and goes into the water and the steam turns to water, leaving in the cylinder the condensed steam in the form of a cubic inch of water. The steam formerly filled the cylinder, and now it fills but a cubic inch of it, consequently, we have produced in the cylinder a vacuum, which has the effect of adding about 15 Ibs.
234 HANDBOOK ON ENGINEERING.
per square inch, to the force of the steam on the other side of the piston, by virtue of removing that much resistance to its forward motion. The heat,which was in the steam, has gone into the con- densing water, except the trifle that remains in the cubic inch of condensed steam. We must get this condensed steam out of the cylinder, and it will be an advantage to pump it back into the boiler, for it is pure and it is hot.
This is the general principle of the condensing engine. It gives us the grand advantage of a heavy increase in the useful pressure acting to push the piston forward ; it gives us pure water for use in the boiler, and it saves in the feed- water the heat that would otherwise go out of the exhaust pipe. But it is not practicable to condense the steam in the cylinder by dosing the cylinder with cold water. In practice, the steam is allowed to go into a separate condensing vessel, called the condenser. The condenser is precisely the opposite of the boiler. The boiler is the machine for putting heat into the steam to vaporize it, and the condenser is the machine for taking heat out of the steam and turning it into water again. In the condensing engine, one of these machines is pushing on the piston and the other machine is pulling on the piston. The gain by condensing is so great that it is a profitable piece of business to apply a condenser to any large non-condensing engine. The condenser requires a pump to withdraw the water of condensation, and this pump must be in reality an air-pump. In practice, they employ an air-pump and condenser combined in one structure, separate from the engine, and driven either by rod connection from the engine, or by a belt from the engine, or by an independent steam device. The arrange- ment will depend much upon the situation. The belt-driven pump permits of the condenser being set in any convenient position independent of the engine.
HANDBOOK ON ENGINEERING. 235
CONDENSERS.
When steam expands in the cylinder of a steam engine, its pressure gradually reduces and ultimately becomes so small that it cannot profitably be used for driving the piston. At this stage, a time has arrived when the attenuated vapor should be disposed of by some method, so as not to exert any back pressure or resistance to the return of the piston. If there were no atmos- pheric pressure, exhausting into the open air would effect the desired object. But, as there is in reality a pressure of about 14.7 pounds per square inch, due to the weight of the super- incumbent atmosphere, it follows that steam in a non-condensing engine cannot economically be expanded below this pressure, and must eventually be exhausted against the atmosphere, which exerts a back pressure to that extent.
It is evident that if this back pressure be removed, the engine will not only be aided by the exhausting side of the. piston being relieved of a resistance of 14.7 pounds per square inch, but moreover, as the exhaust or release of the steam from the engine cylinder will be against no pressure, the steam can be expanded in the cylinder quite, or nearly, to absolute 0 of pressure, and thus its full expansive power can be obtained.
Contact, in a closed vessel, with a spray of cold water, or with one side of a series of tubes, on the other side of which cold water is circulating, deprives the steam of nearly all its latent heat, and condenses it. In either case the act of condensation is
236 HANDBOOK ON ENGINEERING.
almost instantaneous. A change of state occurs and the vapor steam is reduced to water. As this water of condensation only occupies about one sixteen-hundredths of the space filled by the steam from which it is formed, it follows that the remainder of the space is void or vacant, and no pressure exists. Now, the expanded steam from the engine is conducted into this empty or vacuous space, and, as it meets with no resistance, the very limit of its usefulness is reached.
The vessel in which this condensation of steam takes place is the condensing chamber. The cold water that produces the con- densation is the injection water ; and the heated water, on leaving the condenser, is the discharge water. To make the action of the condensing apparatus continuous, the flow of the injection water and the removal of the discharge water, including the water from the liquefaction of the steam, must likewise be continuous.
The vacuum in the condenser is not quite perfect, because the cold injection water is heated by the steam and emits a vapor of a tension due to the temperature. When the temperature is 110 degrees Fahr. , the tension or pressure of the vapor will be represented by about 4" of mercury ; that is, when the mercury in the ordinary barometer stands at 30", a barometer with the space above the mercury communicating with the condenser, will stand at about 26". The imperfection of vacuum is not wholly traceable to the vapor in the condenser, but also to the presence of air, a small quantity of which enters with the injection water and with the steam ; the larger part, however, comes through air leaks and faultly connections and badly packed stuffing boxes. The air would gradualty accumulate until it destroyed the vacuum, if provision were not made to constantly withdraw it, together with the heated water by means of a pump.
The amount of water required to thoroughly condense the steam from an engine is dependent upon two conditions : the total beat and volume of the steam, and the temperature of the injection
HANDBOOK ON ENGINEERING.
237
water. The former represents the work to be done, and the latter the value of the water by whose cooling agency the work of con- densation of the steam is to be accomplished. Generally stated, with 26" vacuum, the injection water at ordinary temperature, not exceeding 70° Fahr., from 20 to 30 times the quantity of water evaporated in the boilers will be required for the complete liquefaction of the exhaust steam. The efficiency of the injection water decreases very rapidly as its temperature increases, and at 80° and 90° Fahr. , very much larger quantities are to be employed. Under the conditions of common temperature of water and a vacuum of 26" of mercury, the injection water necessary per H. P. developed by the engine, will be from 1J gallons per minute when the steam admission is for one-fourth of the stroke, up to two gallons per minute, when the steam is carried three-fourths of the stroke of the engine.
WEIGHT OF WATER REQUIRED TO CONDENSE 1 POUND OF
STEAM.
|
Temp, of Hot Well. |
Back Press, in Cylinder. Lbs. |
Temperature of Injection Water, Degs. F. |
|||||
|
40 |
50 |
60 |
70 |
80 |
90 |
||
|
100 |
.94 |
17.8 |
21.4 |
26.8 |
35.7 |
53.5 |
107. |
|
110 |
1.27 |
15.1 |
17.7 |
21.2 |
26.5 |
35.3 |
53. |
|
120 |
1.68 |
13.1 |
15. |
17.5 |
21. |
26.3 |
35. |
|
130 |
2.21 |
11.6 |
13. |
14.9 |
17.3 |
20.8 |
26. |
|
140 |
2.88 |
10.3 |
11.4 |
12.9 |
14.7 |
17,2 |
20.6 |
For other temperatures use the following formulas: —
JET CONDENSER. SURFACE CONDENSER.
Weight of water per Weight of water per
Ib. steam condensed =
1170
Ib. steam condensed =
H + 32 — Ti
_ , . ti _ ^
In which T = temperature of hot well, t = temperature of the injec- tion water, TI = temp. of condensed steam, ti = temp of circulating water leaving, and t2, the temp, of the circulating water entering the condenser, H = total heat in steam above 32° F.
238
HANDBOOK ON ENGINEERING.
CHANGING FROM NONCONDENSING TO CONDENSING.
When it becomes necessary or desirable to change a simple noncondensing engine to a simple condensing engine, or to change a compound noncondensing to a compound condensing engine, a slight change in the adjustment of the exhaust valves of the simple engine and of the exhaust valves on the low pressure cyl- inder of the compound will in nearly all cases be found necessary in order to preserve the running qualities of the engine. The cause for this change may be explained as follows : In the first place it should be borne in mind that the pressure of steam varies inversely (oppositely) as the volume, and that when considering the volume and pressure of steam, all pressures are taken or measured above a perfect vacuum or above zero, in other words, only absolute pressures are to be considered. If 10 cubic feet of steam at zero gauge pressure, or at atmospheric pressure, which is 15 pounds absolute, be compressed into a space containing 5
2/a,cutttn Line..
Fig. 151. Showing point of exhaust closure non-condensing.
cubic feet, the pressure of the steam will be raised to 30 pounds absolute, or 30 — 15 = 15 pounds by the gauge. Thus reducing toe volume one-half serves to double the pressure. It will be
HANDBOOK ON ENGINEERING. 239
understood that this rule works both ways, namely, if the volume be doubled the pressure will be reduced one-half. Applying this principle to an engine, suppose the pressure during the return stroke in Figure 151 is 18 pounds absolute, and that the exhaust valve closes when the piston reaches the point A. The volume of steam entrapped in the cylinder at this point in the stroke is taken as the original volume. When the piston moves to the point B, the volume will have been reduced one-half, and consequently the pressure will have been doubled and will have risen to 36 pounds. When the piston reaches the point (7, the volume will be but one- fourth of the original volume, and consequently the pressure will be four times the pressure of the original volume, or 18x4 = 72 pounds absolute, or 72 — 15—57 pounds by the gauge. As the space x represents the clearance, the steam cannot be further compressed so that the pressure of compression in this case is 72 pounds absolute, or 57 pounds gauge pressure. Suppose that the engine runs perfectly smooth and noiselessly with that amount of compression. If the compression be increased or decreased the engine will be apt to pound and possibly to run warm. Now suppose the engine be changed to condensing and that the back pressure be reduced to 4 pounds absolute. If the adjustment of the exhaust valves be not changed compression will begin at the same point in the return stroke. Referring to Figure 152, it will be seen by the full lines that the pressure of the original volume is now 4 pounds absolute. When the piston reaches the point the volume will be one-half of the original volume and conse- quently the pressure will be doubled, and will now be 8 pounds absolute. When the piston reaches the point (7, the volume of steam will be reduced to one-fourth the original volume, and the pressure will be four times the pressure of the original volume, or 16 pounds absolute, which is 1 pound by the gauge. It will thus be seen that if the engine requires 57 pounds compression in order to run smoothly it cannot be expected to run smoothly with
240
HANDBOOK ON "ENGINEERING.
only 1 pound compression by the gauge. In order to obtain the same pressure at the end of compression with steam of lower pres- sure the exhaust valve must close the port earlier in the return stroke. With the Corliss engine this may be accomplished by adjusting the radial rods connecting the exhaust valves with the wrist plate and in slide valve engines by adding exhaust or inside lap to the valve. To find the number of times the volume of the clearance x must be increased in order to lower the pressure from 72 pounds to 4 pounds absolute, divide the pressure of compres-
C 3 A l/a*,u,K,tn Line
Fig. 152. Showing point of exhaust closure condensing.
sion by the back pressure thus 72 -~ 4 = 18 times. Now, by simply reversing this rule it will be seen that, in order that steam of 4 pounds may be compressed to a pressure of 72 pounds the volume must be reduced to fa of the original volume, therefore the origi- nal volume a must be equal to 18 times the volume of the clearance space x as shown by the dotted lines in Figure 152. Now, when the exhaust valve closes at a, Figure 152, the pressure is 4 pounds ; at b the volume is but one-half, and the pressure 8 pounds ; at c the volume is one-fourth and the pressure 16 pounds ; at d the volume is -j^ °f the original volume a, and the pressure is 18x4 =^72 pounds, which is the pressure required for smooth
HANDBOOK ON ENGINEERING. 241
running. It will thus be seen that the same pressures are required whether running noncondensing or condensing, and that in order to get the same pressure of compression when running condens- ing as when running noncondensing, the exhaust valve must close earlier in the return stroke.
It will also be understood that when changing from condens- ing to noncondensing the order of things must be reversed, viz., the exhaust valve must close the port later in the return stroke because the higher the back pressure, the greater will be the pressure of compression. This explains why a condensing engine pounds and heats when the vacuum becomes impaired or is lost altogether. In this case the back pressure rises from that obtained when running condensing to the pressure obtained non- condensing and consequently the compression is much too high for smooth running. On the other hand when changing from noncondensing to condensing the back pressure is so low that scarcely any compression can be obtained, and if the engine requires considerable compression it is apt to pound and heat when the change is made provided the exhaust valves are not readjusted.
It frequently happens that the change from noncondensing to condensing is made at the end of the week, and in this case it is desirable to adjust the valves on Sunday to their approximate position by means of the marks on the valves, so as to avoid, as far as possible, any trouble when starting up on Monday morn- ing. Under these circumstances it is desirable to estimate the extent of the change necessary in the adjustment of the valves. Multiply the length of the stroke in inches by the percentage of clearance and by one-fourth the absolute pressure of compression when running noncondensing ; this product is the approximate point of exhaust closure when running condensing. Then lay off this distance, beginning at the ends of the guides. When the crosshead is within this distance of the end of
16
242 HANDBOOK ON ENGINEERING.
the return stroke, the exhaust valve should have just closed the port. For illustration, suppose an 18x42 Corliss engine is to be changed from noncondensing to condensing. The clearance is 3 per cent and the pressure of compression is 44 pounds absolute. The clearance is equal to 42x.03 = 1.26 inches of the stroke, and one-fourth of the pressure of compression when running noncondensing is 44 -v- 4 = 11 pounds, so that the distance to be laid off on the guides is 1.26x11 = 13.86 or 13| inches, that is, when the back pressure is reduced to 4 pounds absolute by the condenser, the exhaust valve should close when the piston reaches a point 13 £ inches from the ends of the return stroke in order to obtain approximately the same compression as when running noncondensing.
It will be understood that this is merely a method of approxi- mating the pressure and should not be relied upon except for making temporary adjustments.
The only reliable method of setting the exhaust valves when making changes of this kind is by means of the indicator be- cause the pressures vary from several causes the effect of which cannot be calculated with a sufficient degree of accuracy for this purpose. This is true of both the simple and compound engines, the same method being used with the low pressure cylinder of the compound as with the simple or single cylinder engine.
TYPES OF CONDENSER.
Condensers may be divided into three general types or classes known as the surface, the jet and the siphon condensers. The latter type is sometimes referred to as the barometric condenser. The surface and jet condensers require an air pump and these two types are either direct driven or independent. The direct driven condenser is now little used for stationary work, being confined almost entirely to marine engines, and even there the independent
HANDBOOK ON ENGINEERING. 243
condenser is being very extensively used. The direct connected condenser is driven either by a belt or a direct connection to the crosshead of the main engine. The working vacuum is not obtain- able in the direct connected condenser until after the engine is started and has made several revolutions. The disadvantage of the direct connected condenser is that the speed is always proportional to the speed of the engine so that the vacuum can only be regulated by changing the supply of injection or circulating water as the case may be. The independent condensers are driven by a steam cylinder forming a part of the condenser apparatus so that the vacuum can be maintained by regulating the supply of condensing water, and also by changing the speed of the air pump irrespec- tive of the speed of the engine. The greater flexibility of the independent condenser enables it to maintain the working vacuum under widely changing loads and speeds. The cost of operating the latter type of condenser is greater than of the direct driven types because the power required for direct driving is obtained at the same cost per horsepower as that delivered by the engine, while the cost of operating the independent condenser is practi- cally the same as that of an ordinary steam pump. This apparent loss can be largely avoided by utilizing the exhaust steam from the condenser for heating the feed water.
The following illustrations represent the three principal con- structions of condenser to be found in the average stationary practice.
A sectional view of the surface condenser with air and circu- lating pumps attached is shown in Fig. 153. It consists of a shell, usually of cast iron, containing a large number of small brass or copper tubes through which the condensing, or circulat- ing water as it is called, is pumped by the circulating pump. The water enters the chamber at one end of the condensing chamber and flows through one bank of tubes into a chamber at the opposite end and thence back again and out at the top into
244
HANDBOOK ON ENGINEERING.
the discharge pipe. The steam enters the condensing chamber at the top where the current is divided by a baffle plate, which sends the steam in both directions and distributes it more evenly over the cool tubes, the steam being condensed by coming in contact with the tubes, the temperature of which is the same as that of the circulating water flowing through them. The con- densed steam collects in the bottom of the condensing chamber and flows into the suction pipe of the air pump, which also removes the air and aids in maintaining the vacuum. The steam cylinder
Fig. 158. Diagram of Surface Condenser.
is placed between the air and circulating pumps, the pistons being connected to the same piston rod.
Surface condensers embody two constructions or arrangements of tubes. In one the tubes are connected to tube plates, the arrangement being similar in every way to the return tubular boiler. The other construction is known as the double tube con- denser in which two sets of tubes are employed, one within the other as shown in Fig. 153. The circulating water flows through
HANDBOOK ON ENGINEERING. 245
the inner tubes and returns through the outer or larger ones. This construction has the advantage in that the outer tubes are kept at practically the same temperature throughout their length, thus increasing the efficiency of the tube surface. Water will absorb heat more rapidly when flowing at a high velocity than at a low velocity, consequently the double tube condenser can be made smaller for a given capacity than the single tube type. The air pump discharges into the hot well, and as the circulating water does not come in contact with the steam, either before or after it is condensed, the water in the hot well is always pure, or nearly so, and suitable for use in the boilers. When the surface condenser is employed the steam passes from the low pressure cylinder into the hot well and consequently some provision should be made for removing the oil from the exhaust steam. Greasy condenser tubes are not as efficient as clean ones and for this reason it is advisable to place the oil extractor between the low pressure cylinder and the condenser. Any oil that may pass through the extractor and into the hot well may be avoided by taking the supply to the boiler feed pump at a point below the surface of the water in the hot well.
The surface condenser is particularly valuable where the water is unfit for use in the boilers and for this reason it is used more largely for marine than for stationary work.
The surface condenser furnishes the more reliable means of measuring the steam consumption of engines and pumps because the discharge of the air pump in a given time represents exactly the quantity of water required by the engine in the same length of time.
Fig. 154 is a sectional view of the independent jet condenser. The external appearance, and sometimes the minor details of con- struction, will vary slightly in this style of condenser but it is fortunate for engineers that the principles involved and the practical operation of jet condensers are precisely the same in all.
246
HANDBOOK ON ENGINEERING.
The steam and water cylinders and valves of the jet condenser are identical to similar parts of the ordinary direct acting pump, in fact, the jet condenser is a direct acting pump with a simple condensing chamber connected to the pump suction. The con- densing chamber resembles an air chamber in form, except that it
Fig. 154. Independent Jet Condenser.
is larger, and it is provided with an inlet for the exhaust steam and an outlet for the injection or condensing water. The inlet for the water is carried down to the spherical part of the condens- ing chamber and terminates in a cone-shaped spraying device, which throws the water out in an umbrella-shaped film against the sides of the chamber. The exhaust steam enters above the
HANDBOOK ON ENGINEERING. 247
,
spray and cannot reach the pump below without passing into the spray of cold water, which condenses it. The mixture of con- densed steam and injection water is then drawn into the pump and is finally discharged into the hot well. The admixture of the condensed- steam with the injection water improves the quality of the water in the hot well, provided means are employed for removing the oil from the exhaust steam, thus rendering the water better fitted for use in the boilers. The injection water is regulated by means of a hand wheel at the top of the condensing chamber which regulates the position of the cone at the end of the water inlet.
When engines are lightly loaded, or liable to be for any length of time, it is especially desirable to provide a safety device which
Tig. 155. Device for Breaking the Vacuum.
will break the vacuum when the water rises to a certain height in the condensing chamber. If this is not done injury to the engine is liable to occur at any time because should the speed of the pump slacken, thus permitting water to accumulate in the con- densing chamber, the vacuum will be impaired and the low
•
248
HANDBOOK ON ENGINEERING.
pressure cylinder will then act as an air pump, owing to the small amount of steam admitted and the low pressure due to expansion, and will thus draw the water into the cylinder probably wrecking the cylinder completely. A simple safety device adapted to pre- vent injury to the engine as the result of flooding the condenser is illustrated in Fig. 155. It consists of a simple float con-
Fig. 156. Method of connecting up a Jet Condenser.
nected to an air valve at the side of the condensing chamber so that when the water level rises high enough to raise the float, air is admitted and the vacuum immediately destroyed. The ex- haust steam from the engine then flows out through the atmos- pheric relief valve into the atmosphere, and the engine is con-
HANDBOOK ON ENGINEERING. 249
verted into a noncondensing engine automatically and without stopping.
Jet condensers will raise water for condensing purposes from 16 to 20 feet although it is desirable to keep the lift as low as pos- sible because the higher the lift, the more it costs to operate the condenser and consequently the net saving by running condensing is correspondingly less.
The jet condenser requires precisely the same care as the direct acting pump except that greater pains must be taken to prevent the leakage of air and water. An engineer who can keep a direct acting pump in first-class running order need have little trouble in caring for a condenser whether it be large or small.
Fig. 156 illustrates the method of connecting the jet condenser with the engine. When the exhaust steam from the condenser cannot be profitably used for heating the feed water it can be turned into the engine exhaust pipe, or into the condensing chamber direct, and the condenser thus be made to run condens- ing also.
The siphon condenser is illustrated in Fig. 157, and is the simplest form of condenser in use at the present time. The exhaust steam enters the somewhat contracted condensing cham- ber through the cone-shaped nozzle, while the condensing water enters at the side and surrounds the cone, the water issuing into the chamber below through the annular orifice formed between the cone and the walls of the condensing chamber. The water issues at rather high velocity and expels the air from the exhaust pipe. The steam upon leaving the cone-shaped nozzle flows into an inverted cone, formed by the film of water issuing from the annular orifice which condenses the steam. The condensed steam and injection water flow at rather high velocity down through the contracted neck, where the stream is solidified, into the tail pipe, thence into the hot well. The neck of the condensing chamber is contracted, thus forming a combining tube, for the purpose, of
250
HANDBOOK ON ENGINEERING.
giving the water sufficient velocity to maintain a siphon-like action that draws the steam from the exhaust pipe and causes a vacuum to exist in it. This style of condenser should be placed 34 feet above the level of the water in the hot well. An atmos- pheric discharge or relief valve is placed at the top which opens automatically when the vacuum is destroyed thus permit- ting the exhaust steam to flow into the atmosphere. The siphon
Fig. 157. Siphon Condenser.
condenser will raise the condensing water to a height of from 15 to 18 feet so that when the water supply is located within that distance of the top of the condenser no pump is required, the condenser continuing to siphon over the water as long as steam is condensed. When the condenser is operated without a pump a starting pipe will be necessary ; this pipe connecting the water supply with the tail pipe as shown in Fig. 158. When starting the condenser, the valve in the starting pipe is opened, and the
HANDBOOK ON ENGINEERING.
251
water flowing through this and down the tail pipe will gradually exhaust the air from the upper part of the tail pipe until sufficient vacuum is formed to draw the water up to the condenser and start the water flowing through it. When this is done the valve in the starting pipe is closed, and the engine started.
Fig. 158. Siphon Condenser and Starting Talve.
Fig. 159 shows the method of connecting a siphon condenser with the engine. In this illustration the condensing water is supplied by a pump.
It frequently becomes necessary to destroy the vacuum and to stop the engine on short notice, and for this reason it is desirable to have some means of opening the atmospheric relief valve at the top of the condenser. This is especially desirable when the con- denser is arranged to siphon the water because any failure of the condenser with a light load on the engine would result in water being drawn into the low pressure cylinder and probably wrecking it. An arrangement for thus breaking the vacuum is shown in Fig. 159.
The water in the hot well consists of a mixture of condensing
252
HANDBOOK ON ENGINEERING.
water and condensed steam so that if the water is to be used in the boilers means should be provided for removing the oil from the exhaust steam, and the supply to the boiler feed pump
Fig. 159. Siphon Condenser connected to Engine and Pump.
should be taken at a point considerably below the water level in the hot well.
The siphon condenser, when properly proportioned and con- nected up maintains a good vacuum and possesses the advantage
HANDBOOK ON ENGINEERING. 253
that it contains no moving parts and nothing to get out of order, while it is adapted to engines of all sizes, and under all condi- tions which will permit it to be elevated to a height of 34 feet above the level of the water in the hot well.
The quantity of condensing water required by the siphon con- denser is the same as for the jet condenser and may be found by means of the formulas on page 237.
STARTING AND RUNNING A COMPOUND CONDENSING ENGINE.
The principal aim of the engineer in charge of a plant is to keep his engine running, and to run safely, and when running condensing the object also is to maintain the vacuum. The vacuum is formed by removing the air from the exhaust pipe and its immediate connections, including the condenser. Therefore when air leaks in or is admitted through a valve either intentionally or otherwise the vacuum will at once be destroyed. It will be understood from this that all air leaks should be carefully stopped. The principal points to receive attention when testing for air leaks are, the stuffing boxes on both the engine and the condenser, and also on the valves in pipes leading to and from the condenser. A condensing engine and its condenser should be provided with a solid foundation and be securely bolted to it. Vibration in the piping is a common cause of leaky joints, and air leaks will affect the vacuum very seriously. It is a good plan to test the exhaust and condenser piping occasionally while the engine is running. A lighted candle held close to the joints will serve to locate aleak, which should be marked with a piece of chalk so as to be readily found when an opportunity occurs to make repairs.
The vacuum may be reduced and even destroyed by too much water as well as by too little. When too little water is admitted all the steam is not condensed, and the accumulation of uncon-
254 HANDBOOK ON ENGINEERING.
densed steam raises the pressure in the condenser until finally the back pressure valve opens and the engine exhausts into the atmos- phere and, of course, becomes a noncondensing engine. When too much water is admitted the air pump becomes flooded, the volume of the condenser is decreased, .the injection interfered with, and air gradually accumulates, causing the vacuum to become less, sometimes rapidly and at others quite gradually depending on the excess of water.
The condenser should be run at as low a speed as possible and be able to discharge the necessary quantity of water, and to main- tain the required vacuum. When air leaks occur the speed of the condenser must be increased with the same load on the engine and with other conditions the same, so that when it becomes nec- essary to gradually increase the speed it indicates that leakage is occurring either at some point in the exhaust piping, in the in- jection pipe leading to the condenser or in the valves or piston in the condenser itself. It is not profitable to allow the packing in the stuffing boxes on the engine and condenser, and on the valves in the piping, to remain as long as it will apparently work air tight because when old packing begins to give out it generally becomes useless in a very short time, and, furthermore, it seldom admits of any adjustment with beneficial results. It is better to renew the packing at shorter intervals and know that when a gland is tightened the leakage will be stopped.
Generally speaking the higher the vacuum the better, but this is not always true. When engines are very lightly loaded and have but little resistance above that due to friction, it is sometimes better economy to reduce the vacuum, thus slightly increasing the period of admission, because the engine uses steam expansively and the condenser does not, so that a part of the steam required by the condenser can be used to better advantage in the engine cylinder. It sometimes occurs that the boilers are too small, and where an exhaust steam feed water heater is placed in the
•
HANDBOOK ON ENGINEERING. 255
low pressure exhaust pipe it will frequently be found more eco- nomical to reduce the vacuum and thus send the feed water to the boilers at a higher temperature. The regulation of the vacuum under ordinary conditions should be governed by the position of the governor as well as by the vacuum gauge, the object being to maintain a vacuum that will keep the governor at the highest position. Under certain conditions of load the cut-off will be found to be shorter with 26 inches than with 27 or 28 inches vacuum. The receiver pressure also has something to do with the position of the governor. The receiver is usually a plain metal cylinder placed beneath the engine room floor, and to which the exhaust pipe from the high pressure cylinder and the steam pipe to the low pressure cylinder are connected. The high pressure cylinder exhausts into the receiver and the low pressure cylinder takes its steam from the receiver. It will be understood from this that the receiver virtually serves as the boiler for the low pressure cylinder. The pressure in the receiver is generally a little lower than the terminal pressure in the high pressure cylin- der, while the receiver pressure and the initial pressure in the low pressure cylinder are practically the same.
What is known as a reheater, which is sometimes used in con- nection with compound engines, is merely a coil of steam pipe placed in the receiver, steam of higher temperature than that of the exhaust from the high pressure cylinder being admitted to the coil which heats the steam in the receiver to a temperature higher than that due to the pressure, thus serving to reduce the loss due to condensation in the low pressure cylinder, and incidentally improving the economy of the engine as a whole. Changing the receiver pressure will oftentimes alter the position of the governor by improving the distribution of the load between the high and low pressure cylinders. It should be remembered in this con- nection that lengthening the point of cut-off in the low pressure cylinder reduces the receiver pressure and consequently tends to
256 HANDBOOK ON ENGINEERING.
throw more of the load on the high pressure cylinder, while short- ening the cut-off in the low pressure cylinder tends to throw more of the load on to the low pressure cylinder. The receiver pressure is governed by two things, viz., the amount of steam put into it, and the amount of steam drawn out of it. If the low pressure cylinder draws more out of it than the higher pressure cylinder puts into it, the pressure must fall because the volume is thus in- creased. Engine cylinders are generally so proportioned that the receiver pressure will be from 4 to 6 pounds lower than the ter- minal pressure in the high pressure cylinder when the engine has a fair load. When an engineer knows what the terminal pressure in the high pressure cylinder is it is not difficult to set the cut-offs to produce the desired results. When the high pressure exhaust valves pound and lift from the seats it may be safely assumed that the receiver pressure is higher than need be, and it will generally be found practicable to lessen the pressure, which may be done by lengthening the period of admission in the low pressure cylin- der, being careful to note exactly the extent of the adjustment because there is the possibility of other things causing the valves to pound, and in that case the cut-off should be shortened again exactly the same amount to which it had been lengthened.
For usual ratios of cylinder volumes, viz., from 3 to 1 or 4 to 1, and under average conditions of load on condensing engines, a boiler pressure of 80 or 90 pounds will produce a receiver pres- sure of about 5 pounds ; 100 pounds will produce from 7 to 10 pounds; 125 pounds from 12 to 15, and 150 pounds from 18 to 20 pounds. The receiver pressure frequently rises from 1 to 3 pounds with changes of load.
The best results are generally obtained when the load is equally divided between the high and low pressure cylinders. The gov- ernor should thus remain at the highest obtainable point with any given load and with a moderately high vacuum, say 26 or 26 £ inches. The extent of changes to produce these results cannot
HANDBOOK ON ENGINEERING. 257
be foretold, but must be ascertained by experiment in each case.
When about to start a compound condensing engine the first thing to be done is to see that all the water is drained out of the piping. If the engine is a Corliss or other four-valve engine the high* pressure cylinder will readily get rid of the water, but this water drains into the receiver, and if not removed will enter the low pressure cylinder when the engine is started, and probably wreck it. If there is a separator it should be carefully drained.
Then the pipe above the engine throttle, then the cylinder and lastly the receiver. If these parts are thoroughly drained before starting, what little water may enter the low pressure cylinder, due to condensation in the high pressure cylinder and receiver, will cause no trouble or damage provided the engine is started slowly so as to give the water time to pass out through the exhaust ports. The steam line to the condenser should also be drained down to the condenser throttle so that when it is time to start the condenser it can be done without delay.
About 20 minutes before time for starting the plant begin to warm the cylinders. Place the wrist plates at their central posi- tion. Open the throttle a little and also the live steam valve to the receiver. Allow the receiver drain to remain open a little until after starting. Then open the oil cups and the cylinder lubricators and see that they are feeding the proper quantity of oil.
If it is not desirable for any reason to start the engine in advance of the other machinery, the wrist plates can be worked back and forth a few times by hand, after which the throttle and receiver valve should be closed, leaving the wrist plates in the central position. A little practice will indicate how wide the throttle can be opened and how high the receiver pressure may be allowed to rise without moving the engine when working the wrist plates. After warming the cylinders, the condenser may be
17
258 HANDBOOK ON ENGINEERING.
started. If the air pump is in proper running order the vacuum gauge will soon indicate the vacuum, which ought to be increased to about 25 inches. If the exhaust from the steam cylinder of the condenser is run into the condensing chamber, the injection water should be turned on after the air pump has made three or four strokes, otherwise the injection water may be turned on immediately upon starting the engine, or before if desired. When the run- ning position of the injection valve is not known it may be tried at from one-half to two-thirds open. When the air pump is running properly inspect the overflow to see that the water is discharged properly and freely. Considerable water will be discharged from the condenser if the injection valve is open and the condenser is working properly.
Returning to the engine, hook in the low pressure reach rod and then the high pressure. Then open the throttle a little and start the engine slowly so that any slight condensation which may have accumulated can be worked out more slowly. After the engine has made one or two revolutions attention should be paid to the vacuum gauge to see that the condenser is getting the proper amount of water. It is probable the injection valve will have to be opened wider. The engine should be worked up to speed gradually so that proper attention can be given to the regulation of the injection water as the steam flowing into the condenser gradually increases.
When the engine is up to speed and before the load is thrown on it is a good plan to go to the end of the condenser discharge pipe and find out how hot the water is. This may be done with the hand. The water should be decidedly cooler than the hand, but if not, more injection water must enter the condenser. When the load is thrown on, it is a safe plan to again test the dis- charge water and if the condenser is working properly it will now be perceptibly warmer than the hand. It may be about as warm as a person would ordinarily heat water for washing the hands.
HANDBOOK ON ENGINEERING. 259
When the discharge becomes' so hot as to be unbearable to the bandit is a sign of impending danger, viz., that of losing the vacuum.
It is a good plan to have a small auxiliary injection pipe con- nected to the city mains or to the delivery pipe of any cold water pump, which can be used to supplement the main injection in emergencies of this kind. When a jet condenser lifts its own water, it must lose the suction, as it is called, whenever it loses the vacuum, so that without the aid of the auxiliary injection pipe it can seldom regain the vacuum without allowing the engine to exhaust into the atmosphere until the condenser can be cooled. When xhe load suddenly increases and the discharge becomes too hot, the normal temperature can generally be quickly restored by opening the auxiliary injection valve. The auxiliary injection is generally provided on condensers. It may enter anywhere in the exhaust pipe. An auxiliary injection can be made of a piece of 1£ or 2-inch pipe about 3 feet long, per- forated with small holes so as to make a sprayer head, the sprayer head being connected with the same sized pipe from the city main or pump. The auxiliary injection is in every sense an emergency apparatus and should be carefully watched while in operation, and shut off as soon as the need of it ceases because it is not automatic and if allowed to run unnoticed there is danger of flooding the condenser and exhaust pipe and of working water back to the engine. When the load on the engine is fairly steady, or when the load fluctuates uniformly between certain limits the condensing apparatus will require very little attention. The same precautions should be taken with a condenser that raises its own water as with a boiler feed pump, viz., to see that nothing inter- feres with its continued operation, that the suction pipe is properly protected so that no obstruction may enter and that the discharge is always free.
It is sometimes necessary to change from noncondensing to condensing without stopping the engine. In this case the gate
260 HANDBOOK ON ENGINEERING.
valve in the exhaust pipe leading to the condenser will be found closed because this valve should always be closed when the con- denser is not in use, otherwise the steam would be apt to injure the valves in the condenser. The air pump is first started and the injection valve opened in the same manner as when about to start the engine, and is opened to the running position with a load. When the condenser is working properly an assistant should be stationed at the back pressure valve ready to close it when signaled by the engineer. The gate valve in the exhaust pipe is then partly opened, the engineer watching the vacuum gauge to note the point at which the vacuum begins to drop. At that moment he signals the assistant, who then closes the back pressure valve. The gate valve is then opened wide. When opening the gate valve, and before the back pressure valve is closed, care must be taken not to continue to open the valve after the vacuum begins to fall, otherwise the vacuum will be quickly lost entirely.
When changing from condensing to noncondensing all that is necessary is to close the gate valve in the exhaust pipe and stop the condenser. As soon as the pressure in the exhaust pipe equals that of the atmosphere, the back pressure valve opens automatically.
The surface condenser is worked in the same manner as the jet condenser, which has just been described. There is an extra pump, which must keep the circulating water flowing through the condenser tubes ; that much work being taken off the air pump. The air pump has air and some water to handle in the same manner as though it pumped the cooling water. Both these pumps, together with the pump of the jet condenser, require the same care and attention that the boiler feed pump does or any pump that lifts water by suction.
When stopping a condensing engine, stop the engine first, then the condenser, then shut off the oil cups and lubricators and lastly open the drips.
HANDBOOK ON ENGINEERING.
261
SETTING THE PISTON TYPE OF VALVE.
The simple piston valve admitting steam between the pistons is, in operation, the reverse of the plain D slide valve, which ad- mits steam at the outer edges, or ends of the valve. To make this still clearer it may be said that were the live steam to enter through the exhaust cavity of the D slide valve its operation and the position of the eccentric relative to the crank would be iden-
WMMWr/////J^<.
Fig. 160. Similarity between the slide and piston valves.
tical to the piston valve. Fig. 160 illustrates the similarity of action and eccentric positions were these conditions to obtain.
In these types of valve, as ordinarily employed, the steam is admitted at the ends of the slide valve, and between the pistons or at the middle of the piston valve. The change from the end to the middle of the valve necessitates a change in the position of the eccentric relative to the crank in order to have the direc- tion of rotation remain the same. The positions of the eccentric when driving the simple D valve, and the piston valve, are indi-
262
HANDBOOK ON ENGINEERING.
cated in Fig. 161. It will be noticed that the crank revolves in the same direction in both cases, and that when the crank leaves the dead center, moving in the direction of the arrow, the same port, viz., the one at the head end of the cylinder, will be opened at the same time and to the same extent. This proves the positions as( shown to be correct and illustrates why the eccentric must be moved in the same direction the engine is to run with the D valve, and in the opposite direction with the piston valve, in order to secure the same direction of rotation in the engine.
f
Fig* 161* • Valves opening: the ports for admission.
When setting valves it is a good plan to obtain as much uni- formity of methods as possible, because of the liability to con- fusion when methods involving different movements of the eccentric are employed. In all the directions that follow it is assumed that the crank is placed on the dead center (sae page 195) nearest the cylinder so that when setting the different styles of valves, the same steam port will always be opened first, namely, the one at the head end of the cylinder. The engine, it will be
HANDBOOK ON ENGINEERING.
263
seen, 'is thus treated as though it contained but one steam port, which greatly simplifies matters.
In order to show that each particular form of valve of the same type does not require different methods for its proper adjustment, both the simple piston valve and the main valve of the round riding cut-off are illustrated together, the same directions applying to both.
Where marks appear upon the valve stem, or seat, it becomes an easy matter to set a valve quickly and correctly but when these do not appear a different method must be pursued for obtaining them. First remove the chest covers at both ends of the chest
Fig. 162. Templates used in setting piston valves.
and also the valve (both styles) from the chest and lay it upon a clean place on the floor, or bench. Procure a piece of sheet steel about T\ inch thick and file it to the form shown in Fig. 162. Make the length of the gauge thus formed equal to the thickness of the piston on the valve plus the lead, which may betaken as ^ inch. Replace the valve in the chest and connect it to the valve stem. Turn the eccentric from one extreme position to the other and see that the valve opens the ports an equal amount. It is not necessary that the ports be opened exactly wide, the object being to secure exactly the same opening at each end of the valve. If the head end port is opened farther than the other, the eccentric
264 HANDBOOK ON ENGINEERING.
rod should be lengthened an amount equal to one-half the differ- ence, and should the port at the crank end be opened farthest, the eccentric rod should be shortened a like amount.
Turn the eccentric to the extreme position farthest from the cylinder. Then place the small end of the gauge against the inner edge of the port, and with a scriber make a fine line (a) on the seat as shown in Fig. 163. Remove the gauge, and turn the eccen- tric in the same direction the engine is to run until the end of the valve reaches the fine line on the seat. Secure the eccentric to the shaft, being careful not to move the eccentric in either direc- tion. Now turn the crank in the direction it is to run until the eccentric reaches the extreme position nearest the cylinder. The gauge is now placed against the edge of the opposite port and a
Fig. 163. Showing the use of the template.
fine line drawn on the seat, at the end of the gauge, in the same manner as shown in Fig. 163. Turn the crank to the dead center farthest from the cylinder when the end of the valve should have just reached the line on the seat. If it does not, the crank should be turned sufficiently to enable the distance between the valve and the mark, being measured. The eccentric rod is then to be adjusted so as to move the valve a distance equal to one- half of what the valve lacks of exactly reaching the line on the seat. The valve will then open both ports to the extent of the
16
HANDBOOK ON ENGINEERING. 265
lead when the crank occupies the exact dead centers. It is very desirable to have a method of setting the valve without removing the chest covers. By the aid of simple gauges this can be readily accomplished. Take a piece of steel wire and sharpen the ends and bend into the form shown in Fig. 164. With a prick punch make a mark (&) on the guide block, place one end of gauge in this mark and make another mark (c) where the opposite end of the gauge touches the valve stem. This gauge enables the valve stem being disconnected from the valve stem guide block, and the chest cover put on, and the stem afterward con- nected up again in exactly the same position (see page 243). Having made this second gauge, place the crank on the exact dead center nearest the cylinder. Then make a prick punch mark (d) on the stuffing-box, place one end of the gauge in this mark and then make a second mark (e) where the other end of the gauge touches the valve stem. It will readily be seen that when testing the setting of the valve all that is necessary is to place the crank on the dead center nearest the cylinder, then place the gauge in the mark (d) on the stuffing-box, and have the eccentric moved until the punch mark (e) on the valve stem falls under the point of the gauge. The valve will then have opened the port to the extent of the lead, because it was in this position when the gauge and the marks were first made. If the punch marks are nicely made and not too large the extent of the lead opening may be measured at both ports, by turning the crank to the opposite dead center and making a second punch mark (/) on the valve stem by means of the gauge. These two guages should be carefully preserved from injury and from being mislaid so that in case of emergency, such as the slipping of an eccentric, the latter can be returned to its correct position without unnecessary loss of time.
266
HANDBOOK ON ENGINEERING.
SETTING THE CUT=OFF VALVE.
The following directions are applicable to both the flat slide and the round types of slide valves.
The point of latest cut-off is seldom known exactly by the average engineer because of its unimportance while the engine is in running order, and as this point varies with different engines it is advisable to discard it as an element in valve setting. First place the main valve in its position of mid -travel, that is, place it centrally over the ports. This may be accomplished by finding the center between the punch marks (/) and (e) on the valve stem, bringing the center mark g under the point of the gauge in the manner shownin Fig. 164. The travel of thecut-off valve must first be equalized which is accomplished by turning the cut-off
Fig. 164. Trams for setting the cut-off valve.
eccentric to its extreme positions and noting the travel of the cut-off valve over the ports of the main valve. The cut-off eccen- tric rod should be lengthened or shortened so that the cut-off valve will travel evenly over the ports in the main valve. This, of course, is obtained by measuring the distance from the edge of the ports in the main valve to the ends of the cut-off valve when the latter occupies its extreme positions.
First, assume the engine to have a fixed, or a hand-adjusted cut-off, and that the cut-off valve is to be set to cut off steam at
HANDBOOK ON ENGINEERING.
267
one-half stroke. Place the crank on the dead center (see page 195) and the full part of the cut-off eccentric the same. Then measure off one-half the length of the stroke from the end of the cross-head as in Fig. 165 and make a light line/ on the guide. Turn the engine in the direction it is to run until the end of cross-head
Fig. 165. Method of equalizing the cut-off.
reaches the line / on the guide. The piston will now have com- pleted one-half its stroke. Turn the cut-off eccentric in the direction the engine is to run until the cut-off valve opens the port in the main valve wide and just closes the port again in the main valve.
Secure the cut-off eccentric to the shaft at this point. Turn the crank over to the opposite dead center and far enough beyond the center so that the same end of the crosshead will have again reached the line (/) on the guide as in Fig. 165. The piston will now have completed one-half of the return stroke and the cut-off valve should have just closed the port in the main valve. If the cut-off valve has moved too far, or notfar enough, measure the amount it lacks of just closing the port and then adjust the cut-off eccentric rod an amount equal to one-half the amount of
268 HANDBOOK ON ENGINEERING.
the discrepancy. The cut-off valve will then close the port in the main valve at exactly the same point in both forward and return strokes.
When an automatic cut-off engine, in which the cut-off eccentric is operated by a shaft governor, first block out the weights to their extreme position or against the stops, the travel of the cut-off valve having been previously equalized in the manner explained above. Then turn the crank to the dead center, preferably the one nearest the cylinder, and turn the full part of the cut-off eccentric to the same position as a starting point. Then turn the eccentric in the direction the engine is to run until the cut-off valve opens the port in the main valve to the extent of the lead or from ^ to -^ inch. Secure the governor wheel to the shaft at this point. Turn the crank to the opposite dead center and see that the cut-off valve has opened the port in the main valve to the same extent , If it hac not done so, adjust the length of the eccentric rod an amount equal to one-half the differ- ence between the two lead openings. Take out the blocks and the work will be completed. It will readily be understood that, were the speed of the engine to reach a point, where the governor weights strike the stops, the cut-off valve will admit only steam enough to fill the clearance, which should always be done, because while it does not tend to accelerate the speed it does prevent forming a vacuum in the cylinder, and from drawing in whatever may happen to be in the vicinity of the end of the exhaust pipe. The point of latest cut-off will then take care of itself and will occur at that point for which the valve and gear were designed.
FLAT VALVE RIDING CUT-OFF.
In medium and slow speed engines it is very desirable to have a uniform point of release and constant compression. If the engine is of the automatic cut-off variety the point of cut-off will
HANDBOOK ON ENGINEERING. 269
necessarily change with each change of load, and if the steam is released, and the point of compression determined by the valve effecting the cut-off, it is plain that as the cut-off varies, the point of exhaust and of compression must also vary proportionately. In order to secure a uniform amount of lead, a constant point of release and of compression, it is necessary that the valve deter- mining these points be given a constant travel. Then in order to produce a variable cut-off a separate cut-off valve must be pro- vided. This is the object of the riding cut-off. The main valve determines the lead, point of release and point of exhaust closure and as the travel of the main valve relative to the crank is un- changeable these functions always remain the same. The duty of the cut-off valve is simply to close the ports in the main valve, and it determines the point of cut-off only. It will be seen, there- fore, that with this arrangement of valves, constant lead, exhaust
Fig. 166. Riding cut-off — Showing yalyes and eccentrics.
opening and constant compression are secured while the point of cut-off is constantly changing with the load. Keeping these fun- damental facts in mind, it is readily seen that the main valve of the riding cut-off is, in operation, exactly the same as the ordi- nary D slide valve having a fixed travel. In the riding cut-off the travel of the cut-off valve is fixed, so far as length of stroke is concerned, but the times of closing the ports in the main valve are variable and are determined either by hand adjustment or by the governor, depending upon whether the engine is a throttling or an automatic cut-off engine. The points of cut-off are changed by rolling the cut-off eccentric around on the shaft.
270
HANDBOOK ON ENGINEERING.
The farther the cut-off eccentric is set in advance of the crank the earlier in the stroke will steam be cut off, and, the nearer together the two eccentrics are set, the later will the cut-off occur. The main valve is generally designed to cut off steam at f or J stroke, so that if the cut- off valve and main valve move together the point of cut-off will be determined by the main valve and will occur at f or | stroke. Now if the cut-off eccentric (c) be set ahead of the main eccentric (m) as in Fig. 166, it will reach the end of its stroke and start back again before the main eccentric has com- pleted the stroke, thus the cut-off valve moves in one direction and the main valve in the opposite direction and that point in the piston stroke at which the centers of the two valves meet will be the point of cut-off. If the cut-off eccentric be set nearly oppo- site the main eccentric it is evident that when the main valve reaches one-half of the outward stroke the cut-off valve will have reached nearly one-half of the return stroke and the cut-off will occur at about this point in the piston stroke, which will be approximately one-fourth stroke.
Fig. 167. Setting yalyes of the riding cut-off.
When setting the valves, first equalize the port opening of the main valve. This is accomplished by turning the main eccentric from one extreme position to the other seeing that both ports in the valve seat leading into the cylinder are opened exactly the same amount. It is not necessary that these ports be opened exactly wide ; the object is to see that both ports are opened to the same extent when the eccentric is in its extreme positions.
HANDBOOK ON ENGINEERING. 271
Having equalized the travel of the main valve place the crank on the dead-center, see page 195, and turn the full side of the main eccentric to a corresponding position. Then turn the eccentric in the direction the engine is to run until the port in the main valve, corresponding to the position of the crank or piston, opens the port leading into the cylinder to the amount of the lead, which may be taken as ^ inch. Now, before moving the engine make a gauge of the form shown in Fig. 167. Put a punch mark on the stuffing-box, and, placing one end of the gauge in this mark, draw a fine line on the valve stem at the opposite point of the gauge. Turn the crank to the opposite dead-center and note the amount of lead opening. If it is not the same as first obtained adjust the eccentric rod to the extent of one-half the difference. Then place the gauge in the punch mark on the stuffing-box and draw a fine line at the opposite point of the gauge.
Turn the crank back again to its first position and note the lead. If it is found to be equal at both ends, apply the gauge again and this time make a light punch mark at the outer point of the gauge. Then put a similar punch mark on the fine line representing the lead at the opposite end of the valve travel. By means of these marks it will be possible to set the main valve correctly without removing the steam chest cover. Now divide the distance between the two punch marks and put a third punch mark at the middle. Turn the crank around in the direction the engine is to run until the middle punch mark falls under the outer point of the gauge. The main valve will now be at the middle of its travel. The travel of the cut-off valve must now be equalized so that the latter valve will travel equal distances be- yond the ports in the main valve. This is accomplished in pre- cisely the same manner as with the main valve. Having equalized the travel of the cut-off valve, turn the crank in the direction the engine is to run until the cross-head reaches the point in the stroke at which the cut-off is to occur, which is to be de-
272 HANDBOOK ON ENGINEERING.
signated by a line drawn on the guide. Now turn the cut-off eccentric in the same direction until it reaches its extreme position. Continue to move the eccentric until the cut-off valve just closes the port in the main valve. Secure the cut-off eccentric to the shaft at this point. Then turn the crank around until the cut- off takes place on the return stroke and see if it corresponds to the point on the previous stroke. If not, adjust the length of the cut-off eccentric rod an amount equal to one-half the differ- ence.
It is important to be able to set the cut-off valve also without taking off the steam chest cover. One punch mark only is re- quired for this. Place the main valve in its position of mid- travel by means of the gauge. Then put a punch mark on the stuffing-box of the cut-off valve stem and, placing the gauge in this mark, put another at the opposite end of the gauge on the cut-off valve stem. See Fig. 167.
This method furnishes a simple and quick means of setting both the main and cut-off valves when an eccentric slips. All that is necessary is to place the crank on the dead-center and bring the proper punch mark under the point of the gauge. Then bring the main valve to its position of mid-travel and with the gauge bring the cut-off valve to its proper position.
The foregoing directions for setting the cut-off eccentric apply to the hand-adjusted gear only. When the cut-off eccentric is operated by the governor, the travel is equalized in precisely the same manner as when hand-adjusted. After equalizing the travel of the cut-off valve, place the crank on the dead-center. The main valve, which is invariably set first, will now open the port, corresponding to the position of the piston to the extent of the lead. Next block out the governor weights against the stops. Turn the full side of the cut-off eccentric to correspond to that of the crank as a starting-point. Then turn the cut-off eccentric (governor wheel), around on the shaft in the direction the engine
HANDBOOK ON ENGINEERING. 273
is to run until the port in the main valve is opened to the extent of the lead. Secure the governor wheel to the shaft. Turn the crank to the opposite dead-center and see that the cut-off valve opens the port in the main valve to the same extent. If the difference is slight it may be equalized by adjusting the length of the cut-off eccentric rod an amount equal to one-half the differ- ence of the lead openings. Should the difference be great, say, one-half inch, that is, should the cut-off valve lack one-half inch of opening the port in the main valve, it indicates that the cut-off valve is too long, which is apt to be the case where two cut-off valves are employed on the same stem. The valve may be shortened by moving the two parts closer together, moving each part one-fourth of the amount the cut-off valve lacked of opening the port in the main valve. Then begin over again to set the cut-off eccentric and if the adjustments have been carefully made it will open the ports correctly at both ends of the main valve. After fastening the main eccentric and the governor wheel securely to the shaft remove the blocks from the governor weights and the job will be finished.
When the valve gear contains a rocker-shaft of the construc- tion shown on page 322, the eccentric must be turned in the opposite direction to that in which the engine is to run, until the main valve opens the port leading into the cylinder, to the extent of the lead.
To Find Arerage Length of Stroke of Piston.
Revs, per Mln.
25 to 90 Dlam. of cyl. X 2.5 = Length of stroke In inches.
90 " 176 " " x 2 = "
175 " 300 " "X 1.33= " " "
Single Acting, " " x 1 = "
Weight of Engines per Cubic Foot Cyl. Volume.
Girder Frame. Box Frame.
Lowspeed 4800Lbs. 4400 Lbs.
Highspeed 6000 " 4800 *«
Cross compound non -condensing 8600 "
Cross compound condensing 9300 |
Tandem compound condensing 8650
Tandem compound non-condensing °°7d
274 HANDBOOK ON ENGINEERING.
CHAPTER XII. THE STEAM ENGINE. — CONTINUED.
Work consists of the sustained exertion of force through space. The unit of work, the foot-pound, is a force' of one pound exerted through one foot space. The work done in lifting one pound ten feet, or ten pounds one foot, is ten foot-pounds.
Power is the rate of work, or the number of foot-pounds ex- erted in a unit of time. The unit of power is the horse-power, and equals 33,000 foot-pounds exerted in a minute, or 550 foot- pounds exerted in a second, or 1,980,000 foot-pounds exerted in an hour. An engine developing fifty horse-power, exerts 27,500 foot-pounds per second, 1,650,000 foot-pounds in a minute. It could raise (friction neglected) 41,250 pounds forty feet in one minute.
A belt running over a .pulley at 4,000 feet per minute, pulling with a force of 240 pounds (fair load for a 4-inch belt) will transmit
240x4.000
— OQ QQQ — equal thirty horse-power (nearly).
If moving at 1,100 feet pe'r minute, the result would be
240x1,100
• — QQ QQQ — *equa~l eight horse-power.
A gear-wheel, the cogs of which transmit a pressure of 1,800 pounds (fair load for 1J" pitch 6" face) to the cogs of its mate, the periphery velocity of the wheels being ten feet per second, transmits
1,800x10
equal thirty-three horse-power nearly.
HANDBOOK ON ENGINEERING. 275
If speed was 360 feet per minute, it would transmit
1,800x360
— QQ QQQ — equal twenty horse-power nearly.
The horse-power developed by a steam engine consists of two primary factors, Piston Speed and Total Average Pressure of steam upon the piston.
Piston speed depends upon the stroke of engine and the num- ber of revolutions per minute. An engine with stroke of twelve inches, making 300 revolutions per minute, has a piston speed of
2 x 12 x 300
— r-^-; equal 600 feet per minute.
La
Piston speed of an engine with 24" stroke at 150 revolutions per minute :
2x24x150
T^- equal 600 feet per minute.
L4
Total average pressure depends on area of piston and mean effective pressure per square inch exerted on piston throughout stroke. The mean effective pressure (M. E. P.) in any case can only be accurately obtained by means of the steam engine indi- cator, and depends upon the load engine is carrying.
GENERAL PROPORTIONS.
Diameter of steam pipes :
Slide-valve engine, J diameter of piston. Automatic high-speed engines, | diameter of piston. Corliss engine, T3^ diameter of piston.
Diameter of exhaust pipes :
Slide-valve engine, | diameter of piston. Automatic high-speed engine, f diameter of piston. Corliss engine, f to f diameter of piston.
276 HANDBOOK ON ENGINEERING.
Displacement of piston
Clearance spaces : in °ne stroke.
Slide-valve engine 0.06 to 0.08
Automatic high-speed engine, single valve . 0.08 to 0.15
Automatic high-speed engine, double valve . 0.03 to 0.05 Automatic cut-off engine, Corliss type, long
stroke 0.02 to 0.04
Weights of engines per rated horse-power :
Slide-valve engine 125 to 135 Ibs.
Automatic high-speed engine 90 to 120 Ibs.
Corliss engine 220 to 250 Ibs.
Fly-wheels, weight per rated horse-power :
Slide-valve engine 33 Ibs.
Automatic high-speed engine 25 to 33 Ibs.
(According to size and speed.) Corliss engine 80 to 120 Ibs.
(According to size and speed.)
RULES FOR FLY-WHEEL WEIGHTS, SINGLE CYLINDER ENGINES.
Let d = diameter of cylinder in inches. S = stroke of piston. D = diameter of fly-wheel in feet. R = revolutions per minute. W = weight of fly-wheel in pounds.
d2 S For slide-valve engines, ordinary duty . W= 350,000 jyTlp
d* S For slide-valve engines, electric lighting. W= 700,000 ^ ^
d? S For automatic high-speed engines . . W= 1,000,000 ™ j*
HANDBOOK ON ENGINEERING.
For Corliss engines, ordinary duty . . W= 700,000
277 d* S
U* IP
d* 8
For Corliss engines, electric lighting . W = 1,000,000 -™ —
Fig. 168. The Russell engine.
-
SETTING THE VALVE ON A RUSSELL ENGINE, SINGLE VALVE TYPE. THE SAHE PRINCIPLE LAID DOWN IN THE SET- TING OF THE COHMON SLIDE VALVE MUST BE ADHERED TO.
The style of valve is shown in cut, Fig. 169. It is, to some extent, a moving steam chest with the steam all within itself , admitting only enough steam into the chest to keep the valve to its seat, against the maximum tendency to leave it. This pres- sure in the chest is found with the valve as at present propor- tioned, to be about 45 per cent of that contained within the valve. The cut shows the valve and section of cylinder so plainly as to render any detailed explanation of same almost unnecessary.
278
HANDBOOK ON ENGINEERING.
The eccentric operating the valve is under control of the gover- nor, as shown in cut Fig. 170, which regulates the speed of the engine by sliding the eccentric across the shaft, either forward or backward, as the weights change their position, thereby cutting the steam off earlier or later in the stroke, as the governor, or more properly, the weights adjust themselves to the load.
When the eccentric is moved across the shaft in a direction that reduces its 'eccentricity, the steam is cut off earlier in the
Fig. 169. Sectional view of Russell steam valve.
stroke; when the eccentric is moved in the opposite direction, the steam is cut off later in the stroke. The extreme range of this cut-off is from 0 to | of the engine's stroke, and this whole range of adjustment is under complete control of the governor.
To preserve & certain determined speed with the smallest pos- sible variation, as changes occur in the load or pressure, is the function of the governor. The cut-off must always be propor- tioned to the load. When the engine is running empty, the steam is cut off at the beginning of the stroke and the governor weights are at their extreme outer position. With a heavy load, steam follows farther and the weights are nearer their inner position . Be-
16
HANDBOOK ON ENGINEERING.
279
tween these two limits, any number of positions of the weights, and corresponding angular positions of the eccentric, may be had ; and
Fig. 170. The Russell shaft governor.
as the steam is thus adapted to the load in each position, it follows that a slight increase or decrease in speed must make a change in the cut-off and bring the engine again to standard speed.
280 HANDBOOK ON ENGINEERING.
In setting the valves it is necessary to mark the ports in the valve face at the outer edge of the steam chest, and also to mark on the back of the valve the ports in its face, so that it may be adjusted after being placed in the chest, in which position it pre- sents a blank surface that, without these marks, would afford no means for knowing its position.
In placing the valve in the chest, see that it fits perfectly against the seat and that the bottom bearing, on which the valve rides, is at right angles to the valve seat, and in such a condition that the valve will not be tipped away from its seat, but rather against it. This latter condition will be insured by easing off the bottom strip at the inner corner, so that the valve would bear hardest at the outer edge. The hinge nut, into which the valve stem is screwed, as well as its trunnion bearings, should fit so that the valve lays closely to its seat, rather than be held away from it.
Having extended the marks of the ports as well in the valve seats as in the valve itself, to the outside, it now becomes neces- sary to get the center of the travel of the eccentric and connect the valve and rody so that the valve will travel equally on either side of this center. The throw of the eccentric leads the crank in the direction the engine runs, and with the eccentric properly located, as it cannot help being, because .it is attached to the governor and the governor is keyed to the shaft, the lead will remain the same with the governor weights in their outer as well as in their inner positions.
These valves are usually marked with the engine on the center at either end, marks corresponding with the admission edges of valve and seat. The hinge nut connection makes it convenient to examine these valves without disconnecting or disturbing any adjustments made. The valve rod has right and left-hand threads for adjustment, and final adjustment can be made without taking off the steam chest cover.
17
HANDBOOK ON ENGINEERING.
281
1
a
282
HANDBOOK ON ENGINEERING.
Fig. 172. Governor connections — Porter- Allen engine.
THE ADJUSTABLE PRESSURE PLATES.
Description of these plates* — The construction of these pres- Mire plates and the method of ad justing them are fully represented jathe sections of the cylinder, Figs. 173 and 174.
On the lowei4 side of the horizontal section Fig. 173, both admission valves are shown, working between their opposite parallel seats, one of which is formed on the cylinder, and the other on the pressure plates, the latter having cavities opposite the ports.
The valve at the farther end of the cylinder is at the extremity of its lap, while the one at the crank end has com- menced to open the four passages for admission of the steam.
HANDBOOK ON ENGINEERING.
283
The vertical cross-section, Fig. 174, passes through the middle of one pressure plate and shows its form and the means employed for its adjustment. It is made hollow and most of
Fig. 173. Cylinder and yalves — Porter- Allen engine.
the steam supplied to two of the openings passes through it. It is arched to resist the pressure of the steam without deflec- tion. It rests on two inclined supports, one above and the other below the valve. These inclines are steep, so that the plate will be sure to move freely down them under the steam pressure, and also that it may be closed up to the valve with only a small vertical movement. It is prevented from moving down these inclines by a screw, passing through the bottom of the chest, the point of which, as also the plug against which it bears, is of hardened steel.
The pressure plate is held in its correct position by projections in the che^t, on one side, and tongues projecting from the cover on the other, which bear against it near each end, as shown.
284
HANDBOOK ON ENGINEERING.
Between these guides, it is capable of motion up and down its inclined supports, and also directly back and forth between the valve and the cover.
The pressure of steam is always on this plate, and tends to force it down the incline to rest on the valve. By means of the screw it is forced against the steam pressure, up the in- clines and away from the valve. This adjustment is capable of great precision, so that the valve works with entire freedom between its opposite seats, and still is steam-tight.
How these plates act as relief valves* — Whenever the pres- sure in the cylinder exceeds that in the chest, the admission
Fig. 1&4. Cross-section of cylinder and valves.
pressure plate is instantly moved back to contact with the cover, thus affording an ample passage for the discharge of water before it can exert a dangerous strain. This plate is superior
HANDBOOK ON ENGINEERING.
285
in this action to any of the ordinary forms of relief valve, both in the area opened, and also in being self -adjusted to the pressure, and opening fully the instant that is exceeded.
How to keep the admission valves tight* — These valves, though moving in complete equilibrium, are liable to slight wear.
Fig. 175. Section of Porter-Allen steam valve.
This should be taken up as it appears, by letting down the pressure plates. The construction of these plates and the method of adjusting them, are shown in the accompanying sections, made through the steam chest at one end of the cylinder. Of these, the drawings are horizontal sections, showing the four-openings of
286
HANDBOOK ON ENGINEERING.
the valve — first, when commencing to open, with arrows indicating the course of the steam ; and, second, at the extreme point of its lap; while Figs. 176 and 177 are vertical sections, showing the
Fig. 176. Cross-section of pressure plate.
pressure plate — first, when by turning the bolt d forward it is forced up the inclines and away from the valve, producing a leak ; and second, when it is let down to its proper working position. A is the port, B the valve, and C the pressure plate. The latter
Fig. 177. Porter- Allen valve and pressure plate, is made with a trussed-back and so cannot be deflected by the steam pressure. Through the passage thus formed, the steam reaches two of the openings.
HANDBOOK ON ENGINEERING. 287
The pressure plate rests on two inclined supports, c, c, and the pressure of the steam forces it down these inclines as far as the bolt d underneath will allow. This bolt holds the plate just off from the valve, so that the latter moves freely, and is still steam tight. Whenever leakage appears, a minute turning of this bolt backwards lets the pressure plate down and closes it.
Provision is made for readily detecting the least leakage, as follows : When the engine is warmed up in its normal working condition, open the indicator cocks, or in the absence of these, remove the plugs from the top of the cylinder, unhook the link rod, and set the valves by the starting bar so that both ports are covered, and turn on the steam. If the valve leaks at the end of the cylinder, which is not then open to the atmosphere or the condenser, the steam will blow out at the opening provided, having no other outlet. Then let down its pressure plate by backing the bolt very carefully till the leak disappears. The valve should still move freely when the leak has disappeared, and the pressure plate must not be let down any closer than is necessary for this purpose.
Leakage at the opposite end of the cylinder will not generally be seen, the steam escaping freely by the open exhaust. To test its valve in the same manner, the engine must be turned on to the opposite stroke. These examinations should be made from time to time.
In the small engines, which have no starting bar, the valve rod can be disconnected and moved by hand to test this point.
An engine should never be started till it is warmed up. The valves warm quicker than the supports on which the pressure plates rest, and are tight between their seats by expansion, until the temperatures have become nearly equalized. Provision for detecting and stopping any leak of steam is the crowning excellence of this valve.
288 HANDBOOK ON ENGINEERING.
DIRECTIONS FOR SETTING THE VALVES OF THE PORTER- ALLEN ENGINE.
To set the admission valves* — Place the engine on one of its dead centers as explained on page 195. Then raise the governor, bringing the center of the block between the centers of the trunnions of the link.
"With the governor remaining up, set the valve that is about to open, giving to it a lead of from Ty to T3¥" , according to the size of the engine. High speed requires considerable lead. Repeat this for the other valve on the opposite center.
On letting the governor down, the crank remaining on the dead center, it will be seen that the valve is moved a short dis- tance. This motion of the valve, produced by moving the block from the trunnions to the extremity of the link while the crank stands on the center, is the same in amount on either center and takes place in the same direction ; namely, towards the crank. Its effect is, therefore, to cover the port nearest the crank and to enlarge the opening of the port farthest from it ; so that the lead, which is equal at the earliest point of cut off, is at the crank end of the cylinder gradually diminished, and at the back end increased in the same degree as the steam follows farther.
The effect of this is to equalize the opening and cut-off move- ments, so that, on setting the governor at any elevation whatever and turning the engine over, the openings made and the points of cut-off will be found to be identical on the opposite strokes, from the commencement up to the maximum admission. This differ- ence in the lead is also singularly adapted to the difference in the piston velocity at the two ends of the cylinder.
In case the indicator shows that the lead of either admission valve requires to be changed, this is done without opening the chest, by lengthening or shortening the stem at the socket of
HANDBOOK ON ENGINEERING.
its guide, bearing in mind that each valve moves towards the middle of the cylinder to open its port.
To set the exhaust valves* — These have an invariable motion, and are admirably adapted to their purpose. They are set so as to open before the end of the stroke enough to give ample lead, and close again when the piston is on the return stroke, early enough to effect the required compression.
All the valves are held between pairs of brass nuts, of which the inner one is flanged. These nuts must be securely locked, and should be so set upon the valve that it is free to adjust itself between the nuts while yet sufficiently tight that no ' ' lost motion ' ' exists. To avoid the consequences of a mistake, care should be taken, before closing the valve chests, to turn the engine slowly through an entire revolution, while the movements of the valves are carefully watched, so as to insure that they have not been so set as to bring the valves or their nuts into contact with the ends of the chest at the extremes of their movements.
The governor* — The Porter governor, original in its type, stands unexcelled as adapted to stationary engines, requiring close regulation. The active parts are very light, the power being derived from a high rotative speed, causing a sensitiveness in its movements that will arrest fluctuations and produce uniformity in the running of the engine. It has been so perfected that at the present day it is easily adapted to the requirements of any class of work necessitating a governor, and is especially desirable for an engine where a steady speed is necessary.
The speed of this governor being constant, makes it equally efficient upon an engine running either at a high or low number of revolutions. That is to say, the speed of engine can be altered from time to time by changing the governor pulley, the governor itself continuing to run at the same speed and under the same strains, and being stationary, it is always open to observa- tiop-
290
HANDBOOK ON ENGINEERING.
The Ar mmgton and Sims engine, as is well known, is of the high speed type, and in its earlier form was designed with double eccentrics, one inside of the other. These eccentrics are operated by the shaft governor, and the compound motion produced by the movements of the two eccentrics is such that the valve has equal lead for all points of cut-off.
Fig. 178. Yalye gear of the Armington & Sims automatic engine.
The method of setting the valve is very simple, for all engines of this make are sent out with the valve stem and slide marked at points C and B in the sketch, and these points should be set just three inches apart. The following are the directions which the builders supply : —
" If the distance between B and C is just three inches you will know that the valve is all right. If, however, you wish to put in a new valve and adjust, then remove the steam-chest cover and place the engine on the center as follows: Place line marked A, which is on the crank pin side, with line on opposite side of rim marked F (not shown in drawing), level with engine; now take out, or loosen up the springs and block the weights out so that the distance betweendweights and pin at D E will be | of an inch ; adjust the valve-stem at the guide so that by turning the engine over
HANDBOOK ON ENGINEERING.
291
from one center to the other the lead will be the same at both ports ; then make a new mark distinctly on the valve-rod, so that the distance B C will be the standard three inches. See Fig. 178. u It is not possible to reverse the direction of running without sending to the factory for new parts. The governor is not con- structed so that one set of parts can be used for running both ways."
THE CARE AND MANAGEMENT OF HARRISBURQ ENGINES.
It is essential to the successful operation of any high-class and expensive machinery, that the person in charge be gifted with a fair degree of intelligence and alertness, and while it is not attempted to formulate new rules as a guide to the person in
Fig, 179. Sectional elevation of Harrisburg standard four-valve tandem compound engine.
charge of an engine, the fact must not be overlooked that a great deal depends upon the skill and judgment of the operator himself, and that it is manifestly impossible to give rules other than of a general character and which may frequently have to be modified to suit the different conditions that may arise. However, the
292 HANDBOOK ON ENGINEERING.
following are some suggestions for the convenience of operating engineers : —
When engines of these styles have been properly erected, the steam, exhaust and drain connections completed, and the piston and valve rods packed, the operator should be careful to see that all parts are in proper position and firmly secured.
The bed should be thoroughly cleansed inside and a good quality of machine oil poured into the reservoir beneath the crank, until it is just in contact with the crank disc.
A mineral oil only should be used, and of medium viscosity. Fill the eccentric lubricating cup and flush the main bearings with the oil.
The cylinder lubricator should be filled with a first-class qual- ity of cylinder oil, of heavy body.
The best oils obtainable are the most economical, without question.
Careful preparations before starting engine* — The cylinder and steam chest drain valve should now be opened, and the throttle valve carefully started just enough to allow a small quan- tity of steam to flow through the cylinder and out through the drain pipes, but not enough to actually start the engine in motion.
After the cylinder and valves have been thoroughly heated and any water standing in the steam pipes thus blown off, start the oil flowing in the cylinder lubricator cup. A general survey of the engine should now be taken and if everything is found to be in proper condition, carefully open the throttle valve and bring the engine gradually up to speed, when it should be noted that the governor is controlling the machine. Examine the bearings and eccentric to see if the oil is flowing properly, and make sure that every part is operating smoothly, after which the drain valves may be closed.
Adjustments for wear* — When the engine has been in opera-
HANDBOOK ON ENGINEERING. 293
tion long enough to necessitate the adjustment of the working parts, care should be used to avoid adjusting them so close as to cause heating, and the following general rules should be observed : —
The caps on the main bearings should always have sufficient liners underneath to enable the nuts on the bearing studs to draw the cap down solidly upon them and not pinch the shaft, which should be free to revolve in its bearings without unnecessary play.
Adjustment of crank-end connecting rod* — In adjusting the connecting rod box at the crank pin end the same general rules should be observed regarding the liners under the cap, the large nuts drawn solidly upon it, the small nuts firmly jammed, and the cotter pins placed in position.
The adjustment of the box should then be tested with a lever about 12 inches in length, the adjustment being so made that with a lever of this length the operator can easily move the end of the connecting rod sufficiently to take up the side play between the flanges on the crank pin and the ends of the box. The adjustment should never be made so close that this side movement cannot be observed.
Adjustment of cross-head pin box* — The adjustment of the connecting rod box at the cross-head pin end should be made by removing the name plate from the engine frame and placing the crank on the center nearest the cylinder, then with the wrench provided for that purpose, slack off both wedge screws at the upper and lower sides of the connecting rod, and draw the wedge up until it is solid against the box, then slack off that screw about a sixth of a turn and draw up the other so as to firmly lock the wedge; this method prevents the box from pinching the cross-head pin.
The " flats " on the cross-head pin should always be at the top and bottom to avoid wearing a shoulder, and the nut on the end should be drawn up firmly, but not so much as to spring the
294 HANDBOOK ON ENGINEERING.
bosses of the cross-head together, nor yet enough to make the box tight on the ends.
Proper adjustment of cross-head in the guides is made by liners of paper or tin, placed between the bronze shoes and the body of the cross-head.
Adjustment of cross-head shoes* — In order to do this it is necessary to remove the pin and the end of the connecting rod from the cross-head, and with a wooden lever placed in the pin hole turn the cross-head until the shoes are out of the guides, then remove the shoes and place the liners beneath them. Care should be used that the cross-head does not fit the guides too closely, and that it can be moved freely with a short lever from one end of the guides to the other, while disconnected from the connecting rod.
The cross-head should never be run very close and should always be free enough to allow long and continuous runs without causing the top of the bed over the guides to feel uncomfortably warm to the touch.
Attachment of cross-head to piston rod* — When making any adjustments of the cross-head, it is well for the operator to assure himself that the lock nut, which prevents the piston rod from turning in the boss at the end of the cross-head, is securely in place. All but the largest Harrisburg engines are tested under steam before leaving the works, and the valves set with the indicator.
The distance from the cylinder head end of the valve, when the crank is on the center nearest the cylinder, is marked on the end of the cylinder directly underneath the steam chest cover. If from any cause the valve should become deranged, place the crank on the center described and with a scale or rule, see that the valve position corresponds to the dimension marked on the end of the cylinder ; and if out of position, it can easily be re- adjusted by means of t^he device provided for that purpose, at the outer end of the valve stem.
HANDBOOK ON ENGINEERING. 295
On the Harrisburg Ideal engines, where the ball joint con- nection is used between the valve stem and the eccentric rod, the wear is followed up by filing the end of the bronze connection that the cap is screwed against, which holds the ball in place. And on the Harrisburg Standard engines, where the ram box connection is used, the adjustment is made by filing the half of the bronze box, which is attached to the end of the eccentric rod that connects with the ram.
Adjustment of eccentric strap* — The eccentric strap adjust ment is made by liners placed between the halves of the strap and double nutted bolts. When adjustment is necessary, the other end of the eccentric rod should be disconnected and after drawing up the strap bolts it should be tested by giving the strap a half revolution about the eccentric. If it is found that the friction between the strap and eccentric is sufficient to support the weight of the rod, the bolts should be loosened until the strap moves freely without lost motion. The double nuts should then be locked and the cotter-pins replaced in the ends of the bolts.
How to alter engine speed* — The governor used on all Har- risburg engines is the centrally balanced centrifugal inertia type. A few words of explanation may be of service to operating engineers.
The weight arms are constructed with differential weight pockets, to allow of a considerable range of speed adjustment without altering the tension of the springs. If an increase in speed is desired, remove weights of an equal thickness from the weight pockets of the levers, and add weights of an equal thick- ness to obtain a decrease in speed. If an increased speed causes the governor to " race " or " weave," move the clamp in the -slot, to which the outer end of the spring is attached, farther from the small end of the weight lever. If this does not entirely correct this sensitive condition, screw the plug into the spring until the racing ceases. If the decrease of speed so obtained renders the governor too sluggish in action, move the clamp in the
296 HANDBOOK ON ENGINEERING.
slot in the opposite direction. If this does not improve the regu- lation, and the speed is lower than desired, add weights of an even thickness, increasing the spring tension until the proper speed is obtained. The main lever bearings, which are equipped with anti-friction steel rollers, should be oiled about once a week, and taken out and cleaned about once a month ; the other joints fitted with compression grease cups, should be treated in the same manner. About once a month, also, the springs should be dis- connected and the governor and valve gear tested by hand, to make sure all joints are working freely.
The foregoing will apply also to the Harrisburg Standard and Ideal compound engines, and, in general, to the Harrisburg self- oiling four- valve engines. Adjustment for wear in the valve gear connection of the latter type of engines is obtained by filing the halves of the bronze boxes on the ends of the rods connecting the valves with the wrist- plates and rocker arms, and on the wrist-plate and rocker arm pins, by means of bronze shoes let into the sides of the bearings, the wear being followed up by the screws provided with lock-nuts, and all bearings lubricated by means of compression grease cups. The Harrisburg Corliss en- gines,of the larger sizes, are provided with quarter-boxes in the main bearings with wedge and screw adjustment, and are built self- oiling or otherwise, according to size. The lubrication of the prin- cipal bearings is accomplished by means of oil cups, and the valve- gear connections by means of conveniently arranged grease cups*
McINTOSH AND SEYHOUR HIGH SPEED ENGINE.
How to set the valve* — When the engine is sent out from the shop, the valves are set and trammed with three -inch tram from the valve rod to the valve rod slide at 0 D, and from the eccentric rod to the eccentric rod head at E F, on the valve slide end, and a tram is furnished with the engine, or a new tram can be made with exactly three inches distance between the points , which will suffice.
HANDBOOK ON ENGINEERING.
297
In case the tram marks become lost, or, owing to wear of the valve gear, the length of connection is altered, the proper procedure is to put the engine on one center, and then on the
Fig. ISO. A sectional cut of Mclntosh and Seymour high-speed engine, showing valve and governor.
other, and observe the leads which occur when the governor is in the normal position of rest. See Fig. 180. The lead on the crank end should be three times as much as the lead on the head end, if the connection between the valve and eccentric is of proper length.
When the valve is set this way, the cut-off on the two ends of the cylinder will be approximately equal at one-quarter cut-off on the smaller size engines having inside governors. ;
Preliminary to adjusting connections between the valve and eccentric, care should be taken that the mark on eccentric G H, corresponds to the mark on the pendulum.
In examining the steam leads, as described above, it should be noted that the surface B on the valve has nothing to do with the steam distribution, but it is merely to give ample wearing sur- face, and that the steam is admitted to the cylinder through the port which is between B and the steam edge,which is at A* and the lead should be measured between this steam edge and the
298 HANDBOOK ON ENGINEERING.
edge of the port leading to the cylinder. On engines of larger size having outside governors, a similar method should be em- ployed in setting the valves, except that the trams are four inches from point to point, and should be used between the valve rod slide and valve rod, and the eccentric rod and the eccentric
rod head at governor end, instead of slide end, as above.
.
INSTRUCTIONS FOR STARTING AND OPERATING IDEAL
ENGINES.
Before starting engine* — Open cylinder cocks and throttle valves sufficiently to warm the cylinder and valve. Place sufficient oil in the basin under the crank so it will stand one inch above the bottom of crank discs. When receiving a new "engine from the shops with visible stuffing-box and water drain, before tilling the crank case with oil, previous to starting, pour water in opening
Fig. 181. The Ideal high speed engine.
in frame into pocket under piston rod stuffing-box, until water overflows through trap connected therewith attached to outside of frame. Fill cylinder lubricator and start it to feeding. Fill oil
HANDBOOK ON ENGINEERING.
299
pump, and pour engine oil into pocket on main bearings. Fill eccentric oiler and start it feeding. After the steam chest and cylinder are warm, turn the engine over by hand to see that all is free and right to start.
Open the throttle valve gradually, start engine slowly. After the engine is up to speed, pump five or six strokes of oil into cylinder with oil pump. The oil should flow in streams through both pipes on the crank cover into the pockets of the main shaft bearings.
This oil passes from the main bearings through the crank pin and is distributed over cross-head pin and slides. Occasionally clean out the oil passages in crank pin.
Supply , as needed, a little fresh oil to the basin, and if the oil in the engine bed becomes thick, gritty or dirty, so as not to flow freely through oil passages, draw it off and replace with fresh oil. Filter the old oil and use it over continuously. Use a pure mineral oil that will not thicken by the churning it receives.
Serious damage and cutting of the cylinder and valve will result from allowing the lubricator to cease feeding, even for a few minutes. If the engine is a new one from the shops, feed plenty of oil through the lubricator and oil pump for the first few weeks after starting. Use one drop of oil per minute for each ten horse-power, or ten drops per minute for 100 horse-power engine, for the first thirty days ; after which, one-half this amount will be sufficient, if the oil is of good quality. If the boiler is priming or foaming, use double the quantity of oil to protect the cylinder and piston from cutting. A little graphite fed into cylinder is very beneficial.
The governor* — Fill the cups on governor bearing with grease and give the cap J turn every day. Screw the cap to the stuffing- box on dash-pot loosely, only using the hand to turn the cap. The governor should be taken apart every two or three months and bearings cleaned with coal oil to remove gum. If governor
300 HANDBOOK ON ENGINEERING.
has a dash-pot, it should be refilled with glycerine once or twice a year. Oil may be used in the dash-pot in place of glycerine, unless the engine is in a cold room where the oil is liable to congeal. To refill dash-pot, unscrew cover on end.
In taking the governor apart, allow the sliding block, which holds the end of the governor spring,to remain with its outer edge on a line with a mark across the face of the slide, and in re- adjusting the spring, place the same tension on it as .before, which can be ascertained by measuring the length of the thread through the nuts before slacking up the spring. If trouble is had with springs breaking it is because of their being worked under too much tension. The speed of the governor is changed by moving the weight on the lever.
To increase the speed of the engine, move the weight on the governor lever near to the fulcrum pin. To reduce the speed, move the weight out toward the end of the lever. Tightening the spring will also increase the speed, but will cause the engine to " race," unless at the same time the block,which holds the end of the spring, is moved toward the center of the wheel. The proper way to change the speed is by moving the weight, allowing the spring to remain in its marked position.
Moving the block, which holds the spring, towards the rim of the wheel, will make the governor more sensitive and regulate more closely ; but if moved too far, this will cause the governor to " race." Moving the block towards the hub of the wheel has a tendency to stop the u racing," but if moved too far the speed of the engine will be reduced with the increased load. If any of the bearings of the governor bind, or require oiling or cleaning, the governor will " race." These bearings should be kept clean and in good condition and the stuffing-box to the dash pot must not be screwed up tight, as that will cause the governor to " race ' ' when set for close regulation.
The face of the slide is marked with a line where the outer
HANDBOOK ON ENGINEERING.
edge of block which holds the spring should be. Figures stamped on the face of the slide, give length of end of eye-bolt extending through nuts. This gives the right tension to the spring. Tightening the spring will give closer regulation, but will cause the governor to " race " if the spring is too tight. " Racing " caused by over-tension of spring, can be stopped by moving block nearer to center of wheel.
To set valve* — When necessary to ascertain if the steam valve is properly set, proceed as follows : Take off the cover or elbow on outer end of steam chest, so access can be had to end of valve. Turn the engine over until the valve has traveled as far as it will go towards end of steam chest. Then measure from the end of steam chest to the end of the valve, and this distance should be represented by the figures in inches and fractions on end of steam chest. If measurements do not agree, set valve by screwing the valve stem at the ball joint.
Square* braided flax packing is the best kind for piston rod and valve stem. Don't screw the glands up tight ; allow them to leak a little. The valve stem has only exhaust steam — don't pack it tight. Screw it up by hand only. Screwing the piston rod gland up tight may cause the piston to thump or pound the cylinder, and heat and cut the piston rod.
Safety caps* — The safety caps attached to drip valve under the cylinder are intended to break, in order to save damage to the engine if water enters cylinder. They will protect the engine from breaking if the amount of water is not too large to pass through the valves and pipes. If they break, they have accom- plished their purpose and new ones should be attached.
Eccentric* — Take up lost motion by reducing the brass liners between the lugs on eccentric strap, and unscrew and dis- connect the ball joint on the eccentric rod to see that the eccen- tric strap will turn freely on the eccentric. If a close fit it will heat, cut, seize and break the eccentric rod or valve stem. Allow
302 HANDBOOK ON ENGINEERING.
the eccentric strap to run loose ; no harm if it knocks a little. It will not wear out of round on account of running loose ; it is dangerous to run with the strap snug.
Ball joint* — Take up lost motion in the ball joint, on the valve stem, by unscrewing the joint at eccentric rod and turning or filing off the face of the brass part attached to the valve stem, so as to allow the male part to screw in a greater distance.
Connecting rod* — Take up the lost motion on the crank pin bearing b}^ removing the cap and taking out two of the steel liners ; take one from each side, put the cap back and set the nuts up snug. Disconnect the cross-head end of the rod by re- moving cross-head pin, and try lifting the rod up and down to see that it does not pinch the crank pin. If it pinches the pin when the bolts are drawn up snug, place the liners back or substitute thinner ones. Always screw the cap back solid on the liners, and keep in sufficient liners so the cap will not pinch the pin when the bolts are screwed down snug. NEVER RUN THE ENGINE WITHOUT
HAVING THE CAP SCREWED UP SOLID AGAINST THE ROD, with
liners between if needed, to make the proper fit. When liners are removed be sure to take out an equal amount from each side, because taking out more on one side only is liable to throw the cap at an angle in tightening up the bolts, which, in time, will cause the bolt to break and is liable to wreck the engine.
The brass in the cross-head end of the connecting rod is set up 3y a wedge. This wedge is drawn down by the steel bolt until the brass is forced solid against the shoulders in the end of the connecting rod, which prevents any movement of the brass. The upper bolt is used to lock the wedge in position ; also in withdrawing the wedge when the brass is to be removed.
To take up lost motion in the cross-head end of the connecting rod, remove the brass and file an equal amount, even and square, from each edge of the brass, so as to allow the brass part to come up to the pin. When filing the brass, try the pin in the rod
HANDBOOK ON ENGINEERING.
and do not file enough to allow the brass to pinch the pin when the wedge is screwed down solid. If, by mistake, too much is filed off, put in a sheet of copper or sheet brass liner, so the wedge may be drawn snug without pinching the pin.
Cross-head* — For adjusting the lower cross-head slide, take out the cross-pin, turn cross-head J round with the lower brass slipper opposite opening in engine frame ; loosen nuts and insert paper or thin metal strips between cross-head and slipper. The top slide will never require adjustment. The lower slide should run five years before requiring lining or adjustment. Turn the cross-head pin J way around every three months. This will prevent it wearing out of round.
Main bearings* — To take up lost motion in the main shaft bearings, remove the cap and file, scrape or plane an equal amount from each of the babbitt metal liners or strips, which are in the main bearings under the inside edge of the cap. Remove the metal evenly, so the liners will remain of equal thickness at each end. Do not remove enough from the liners to allow the cap to pinch the shaft when the nuts are screwed down snug. If, by mistake, too much metal is removed, put in paper strips on top of the liners so the cap can be screwed down solid without pinching the shaft. Ascertain when the cap pinches the shaft by turn- ing the engine over by hand ; it will not turn freely when the cap is too tight. With proper care the main bearings will run two years before requiring adjustment. NONE OF THE BEARINGS OF
THE ENGINE SHOULD BE SO TIGHT AS TO PREVENT TURNING THE
ENGINE FREELY OVER BY HAND. Always test the engine in this manner after adjusting bearings.
If a bearing heats* stop the engine immediately, take out shaft or box, clean out the cuttings, scrape smooth, clean out oil pass- ages and run bearings loose.
Heating or cutting will never occur if liners are put in so caps cannot be set up to pinch the bearings and they receive proper
304 HANDBOOK ON ENGINEERING.
lubrication with oil free from grit or dirt. After adjusting any of the bearings, run the engine for a few minutes ; then stop the engine and feel the bearings which have been adjusted to see if they are running cool. This precaution may obviate having to shut down the engine while performing regular duty.
Do not allow the engine to run with bearings so loose as to thump or pound, as this will cause the bearings to wear out of round. If the shaft or wheels run out of true or wabble, it is because the main bearings are loose and should be taken up. The engine will run smooth and noiseless if bearings are properly adjusted.
THE STEAfl CHEST.
Fig. J82 shows a section through cylinder and valve. The steam chest is bored out and fitted with a pair of cylinders or bushings,
182. Cylinder and valve — Ideal engine.
which have supporting bars across the ports, to prevent any pos- sibility of the valve catching upon the ports.
The valve is of the hollow piston type — a hollow tube with a piston at each end. The live steam is entirely upon the outside
19
HANDBOOK ON ENGINEERING.
305
of this piston, pressing equally on each end ; the exhaust steam is entirely on the inside of the piston, so the valve is perfectly bal-
Fig. 188. Tandem compound Ideal engine.
anced and can easily be moved by hand when under full boiler pressure.
Fig. \ 84 is a cross-section of cylinder and valve of the Tandem Compound engine. The cylinders of the Ideal Compound engine inFig. 184, the stuffing-box between the two cylinders, is dispensed with entirely. It is replaced by a long sleeve of anti-friction metal. This sleeve is light and free to adjust itself central with the rod. Grooves are turned on the inner surface, so as to form a water packing.
Both valves of engine are controlled by the same governor on the same stem, moving together and varying in stroke as the load and steam pressure vary. This gives the advantage of automatic cut-off in both cylinders and dispenses with the complication of double eccentrics, rock arms, slides and stuffing-boxes.
306
HANDBOOK ON ENGINEERING.
and keep clearance spaces at minimum, which thus gives a quick and wide opening at the beginning of the stroke, in order to reduce the pressure on exhaust end of high-pressure piston.
Fig. 184. Section of cylinders of Ideal compound engine.
The cover of this valve is held in place by springs and will lift and prevent excessive pressure in the cylinder from water or other causes.
FOR INDICATING IDEAL ENGINES.
The illustration, Fig. 185, shows the reducing motion attached to engine ready for taking indicator cards.
To apply the Ideal indicator rig: Screw slotted stud in cross-head pin, first removing the cap screw. Set the slot per- pendicular to line of motion of cross-head. Set cross-head exactly in center of its travel. Fasten on top of bed where oil funnel is placed, first removing the oil funnel.
Lever should be adjusted so it will travel in slot without strik-
HANDBOOK ON ENGINEERING.
307
ing bottom, or passing out at top. Make sure that lever wiE travel freely in slot without binding. Select a hole on string carrier that will give the necessary motion to indicator drum.
Fig. 185. Method of attaching indicator to Ideal engine.
With string attached from indicator through hole, so adjust this carrier that lines drawn on polished surface shall come exactly parallel with string. Make all adjustments while cross-head is in center of its travel.
HOW TO SET THE VALVE ON A WESTINGHOUSE COMPOUND
ENGINE.
The only exact and final setting of the valve is by means of the indicator. As the valves are permanently set and all adjust- ments made before the engine is shipped, it is not supposed that
308
HANDBOOK ON ENGINEERING.
1;he engineer will have occasion to reset them. 'Should the neces- sity for setting the valves arise, however, the following method will be sufficiently accurate : Break joints and take off the throttle- valve. The steam ports in the bushing will then be seen through the steam connection S. (This opening is on the side in fact, but is here shown on the top for convenience.) Bring the high- pressure piston exactly to the top of its stroke by turning the shaft in the direction the engine runs. This may be ascertained
Fig. 186. Westinghonse compoun _
by either taking off the water relief valve and measuring through
its port, or more conveniently, by bringing the middle of the key- way in the shaft exactly over the center of the shaft. The key- ways are planed exactly with the cranks, so that the position of the key way is the position of the high-pressure piston. With this piston at the top of its stroke, the valve edge a a, should show about T^ of an inch port or lead, and be moving towards the right when standing behind the engine. If out, it may be brought to position by screwing the valve-stem into or out of the
:
HANDBOOK ON ENGINEERING.
309
valve, which is tapped to receive it. Be sure and set the jam nut solid when through.
Fig. 187. Cylinders of Westingliouse compound. SOME POINTS ON CYLINDER LUBRICATION.
In the first place, use the best automatic feed cup that can be secured. Don't be satisfied with the old-fashioned direct feed, or a cheap automatic. A good cup will save many a hun- dred per cent on its cost in a year. Don't get the kind which, on account of its peculiarity of feed, is adapted for a light oil only ; it will then be shut out from using a dark oil, which may be far more serviceable and economical in every respect. Get a cup where the drop of oil cuts off square and passes either down or up through a glass tube into the steam pipe. This kind will feed oil perfectly ; it is well to use this kind.
Take good care of the cup. Don't let it leak around the glass tubes or other joints, for if it does the water will escape as it condenses, and the oil will clog up the escape pipe and stop feeding. Use in it only the best grades of cylinder oil, made by large manufacturers of established reputation. Don't run in the cylinders any kind of poor stuff that may be offered, because it is cheap ; it is a dangerous experiment. Feed a good
310 HANDBOOK ON ENGINEERING.
oil sparingly — don't drench the cylinder. Too much oil is a» bad as water in the cylinder. Engineers have been known to run a couple of quarts per day of cheap oil into an ordinary sized cylinder, and thought they were doing just right ; this is positive abuse of an engine. In almost all cases where too much oil is fed, — cut it down. Two to four drops per minute on engines from 50 to 150 H. P. are all that is necessary, if the oil is good. Just enough to do the work and no more, will afford best results. As long as the valve stem does not cause trouble, rest assured the valves are working smoothly.
AUTOMATIC LUBRICATORS.
An automatic sight feed lubricator should be furnished with every engine which enables the engineer to see the oil as it is fed drop by drop to the engine. The construction of these lubricators is such that the steam entering a chamber is condensed and this water of condensation finds its way into another com- partment of the lubricator, wherein is contained the oil to be fed to the engine. The drop of water, by reason of its greater spe- cific gravity, seeks the bottom of this oil compartment and forces out an equivalent bulk of oil into the steam pipe, whence it is carried by the current of steam into the cylinders and is distrib- uted upon the wearing surfaces intended to be lubricated. This method insures regularity and economy.
There are numerous automatic lubricators made by various manufacturers throughout the country, many of which will per- form their functions successfully. The illustrations on the opposite page represent what may be called the standard type of hydrostatic lubricator employed for lubricating the valves and pistons of steam engines.
This is the up-feed cup, showing an external view and sec- tional view of the same. Attachment is made to the steam-pipes
HANDBOOK ON ENGINEERING.
311
at the points F and K. In operation, the condensing chamber F provides for the condensation of steam, which enters at the pipe F. This water of condensation passes down through the valve D and through the tube P shown in the section and discharges into the bottom of the oil vessel A. This vessel is filled with oil when the cup is started, the height of oil being shown in the index glass J.
Figs. 188 and 189. Sight feed cylinder lubricator.
The operation is as follows : The valve N being opened, the valve D is opened and the drop of water is allowed to pass from the condensing chamber F downward through the water tube and into the bottom of the oil chamber -4, where it displaces a drop of oil of equal bulk on account of its greater gravity, and this drop of oil is forced out past the valve E, making its appearance in the feed glass H, as it starts on its way to the steam-pipe. It is carried by the current of steam to the engine and lubricates the valve and the pistons. When the oil cup is empty, the valve D
312
HANDBOOK ON ENGINEERING.
is closed and the drain valve G is opened, which will allow the water in the oil chamber to be blown out preparatory to the re- filling at the plug C. By opening the valves G and Z>, steam will be blown through the sight glass J, thereby clearing the same from any clogging up of the oil, which would disfigure it. The amount of oil to be fed by the lubricator will be regulated by the valve 7), controlling the amount of water admitted, and the valve E controlling the discharge of the oil into the sight glass. The valve N is to be left wide open in operation and its object is to provide jfor the accidental breaking of the glass H.
Fig. 190. Proper method of attaching cup to prevent the oil from dropping into the well, and not going into the cylinder.
These cups should be attached to the steam pipe, in strict ac- cordance with the instructions contained in the box in which the lubricator is packed. The greatest enemy to proper performance is leakiness ; all joints must be absolutely tight, otherwise the
HANDBOOK ON ENGINEERING. 313
water of condensation, instead of performing its duty of displac- ing the oil, will ooze out at the leaks and the cup will refuse to work. In most cases, provision is made for a column of water which may stand 12" or more in height and enable the cup to work more positively, by giving it a greater pressure in the dis- placement chamber, due to the height of the column. A suitable oil is essential to the proper working of such a lubricator, as well as to the proper lubricating of a steam engine. An improper oil will not feed through the cup as it should, on account of its dis- position to disintegrate and go off in bubbles, when exposed to the heat of the steam.
SETTING A PLAIN SLIDE VALVE WITH LINK NOTION.
The setting of a slide valve operated by a link motion does not differ materially in principle from the method pursued when setting the ordinary slide valve driven by one eccentric. A link motion may be considered as a means of driving a valve by two independent .eccentrics, either of which controls the functions of the valve wholly or in part, according to the position of the link. Thus when the link is in either extreme position, the eccentric driving that end of the link in line with the link-block pin may be considered as being entirely in control of the valve action, and, vice versa, when the link occupies the other extreme position of its throw, as actuated by the reverse lever, the other eccentric becomes possessed of the controlling function. Practically, however, the operation of the link motion is very complicated and the movement of one eccentric materially modifies the action of the other. Since the interfering action is least at the extreme positions of the link and greatest in mid-gear, the plan is followed of setting the valve with the link in full gear both forward and backward motion, and, as before stated, the procedure is on the theory of independent action of the eccentrics.
314
HANDBOOK ON ENGINEERING.
In the accompanying diagram, a link motion is shown driving a plain slide valve without the intervention of a rocker. Each eccentric is set with reference to the crank pin, the same as it would be with a simple slide-valve engine. The eccentric A is set on the shaft with the same angular advance, QMO, as would be required for an ordinary engine to run in the direction indi- cated by the arrow. Now, since the crank pin is at (7, if it were necessary to reverse the simple engine with one eccentric, it would be necessary to change the position of the eccentric so that instead of being ahead of the bottom quarter line QJf, it would be ahead
Fig. 191. Diagram of link reversing gear.
of the top quarter line PM by an amount of angular advance made necessary by the lap and lead of the valve. Therefore, the eccen- tric would come in the position of the eccentric A1, or with its center line coinciding with MN^ giving it the angular advance PMN. Now it should be clear that if an engine is to be equipped with two eccentrics, so that it may run with equal facility in either direction, they will occupy the positions A and A1. We will suppose that an engine having a link motion is to be over- hauled and the valve motion to be properly set. This will mean that the eccentrics will be properly located for the correct angular advance, and that the eccentric rods will be adjusted to the right length. When these conditions are obtained, the valve should
HANDBOOK ON ENGINEERING. 315
perform its functions properly in both forward and backward motions, and also when the link is " hooked up."
Before starting to set the valve, it is best to take a general survey of the valve motion parts and see if the eccentrics are somewhere near the proper location on the shaft relative to the crank-pin. If they are obviously much out of position, they should be shifted and adjusted as near the correct position as possible by the eye ; doing this at the beginning will often save confusion and much time. The dead centers will be found by the method given on page 195. The operation should be carefully performed, as upon it depends the success of the work. After having found the dead centers and having them marked so that no mistake will occur when " catching " them with the tram, the valve positions may be taken for the four positions , that is, front and back centers -in forward motion, and the front and back centers in backward motion. Put the reverse lever in full gear in one motion or the other, whichever is most convenient, and turn the fly-wheel in the direction the engine would run for the given reverse lever position. Suppose the link stands in the position shown in the diagram, the fly-wheel should be turned in the direc- tion indicated by the arrow until the dead center is reached, which is known when the tram drops into the prick mark. The position of the valve is then noted and a measurement taken. If the valve shows the steam port open, measure the distance with a steel scale, or it may be done by sharpening a stick wedge-shaped and shoving it into the opening. By noting the depth to which it goes at the valve face the opening can be readily measured on the removal of the wedge. We will suppose the distance is found to be 4". The measurement should be set on a sheet of paper
o
laid out as follows : —
FORWARD MOTION. BACKWARD MOTION.
Front center, Front center,
Back centero Back center, f" lead.
316 HANDBOOK ON ENGINEERING.
It will be seen that the valve opening is set down as being |" lead, and as being on the back center in the backward motion. After having verified the measurement taken, the engine can be " turned over " in the same direction as before until the opposite dead center is caught by the tram. It may be found that the valve does not show open in this position but covers the steam port. To find the position of the valve edge relative to the steam port, scribe a line in the valve seat face along the edge of the valve and then turn the fly-wheel until the valve uncovers the steam port. The distance the valve laps over when the crank is on this dead center can then be readily measured. Suppose the distance is found to be ^". It is set down on the log as follows : —
FORWARD MOTION. BACKWARD MOTION.
Front center. Front center, J" blind.
Back center. Back center, f " lead,
The valve position is put down as being £" blind, which is the same as saying that it has i" negative lead, and is fully as com- prehensive as the latter term. The reverse lever should now be thrown into the opposite gear and the measurements taken for both front and back centers the same as has been described for the backward motion. It may now be supposed that when all the measurements have been taken the log reads as follows : —
FORWARD MOTION. BACKWARD MOTION.
Front center, J" blind. Front center, |" blind.
Back center, T5F" lead. Back center, f " lead.
When in forward motion, the valve is open Ty on the back center and lacks J" of being open when the crank is on the front center. The total lead due to the angular position of the eccentric is ^" minus J" = Ty. One-half the total lead should be given to each edge of the valve so that it will be necessary to lengthen the eccentric rod Bl, ^" + i" = -£s" to get the valve
HANDBOOK ON ENGINEERING. 317
fnto its proper position. A little reflection will show the reason for lengthening the eccentric rod J51. In speaking of the front and back centers, they are taken to coincide with the crank and head ends of the cylinder. When the piston is at the crank end of the cylinder, the crank is on the front center. By referring to the log it will be seen that to adjust the backward eccentric rod B, it will also be necessary to lengthen it. The valve is |" blind on the front center and has |<* lead on the back center. The total lead is, therefore, f" minus £"= J". One-half J"=J", which being added to the amount the valve is lapped on the front center, makes J", or the amount the eccentric rod B will have to be lengthened to make the valve open equally at each end of the piston stroke. The opening the valve has when the crank is on the centers is called the lead and in the case of the backward motion, it is found that after the eccentric rod is lengthened, the lead is |", which -is too much for most cases and in this one we can assume that -fa" would be about right.
Before explaining the adjustment of the eccentric for the cor- rect angular advance, it will be in order to call attention to the necessity of making the adjustment for the eccentric rod lengths first. The eccentric rods are lengthened or shortened, as the case may require, by inserting or removing liners between the eccentric rods and straps at E. Other forms of construction provide different means for adjustment, but the principle is the same in each. It will be noted that the correct length for the two motions is obtained by adjusting the eccentric rod corre- sponding to that motion. Any attempt to correct an irregularity by changing the length of the valve rod F will result erroneously, unless both eccentric rods require the same amount of movement and in the same direction. After having adjusted the eccentric rods to the correct lengths, the angular advance of the eccentric A can be changed. Place the crank on a dead center and have the reverse lever thrown in the backward motion and then
318 HANDBOOK ON ENGINEERING.
loosen the set screws that hold the eccentric to the shaft and tarn it towards the crank until the valve shows open J^" , and then tighten the set screws on the shaft. After all the adjustments have been effected, it is always advisable to turn the engine over again and catch all the dead centers, so that the correctness of the adjustments can be verified. After taking the new log, it will usually be found that some slight irregularities have been introduced, especially if any of the adjustments have been consid- erable, as the changes made for one motion will affect the other slightly.
The link motion shown in the cut is so connected that the lead increases as the link is shifted towards the center. If the eccen- tric rods be oppositely connected to the link, the engine will run in an opposite direction for a given reverse lever position and the lead will decrease as the lever is shifted towards the center. The link motion for hoisting engines is quite commonly connected in this manner, for the reason that the engine will stop when the lever is put on the center, which is not the case when connected as shown. Of course, in such a case, the admission and cut-off take place at the same position in the stroke and the compression is high, but with a light load the engine will run on the center, which is considered objectionable in the case of the hoisting engine.
VALVE-SETTING FOR ENGINEERS.
Plain slide- valve* — The plain slide-valve, while the simplest valve made, is perplexing to one who has not made a study of it. Unless one understands the principles of the valve and its connections, he will probably meet with trouble when he attempts to set it. We will first place the engine (see p. 195) on the dead center, and will simply explain the other steps that have to be taken. In the first place, it should be understood what result is obtained by adjusting the position of the eccentric
HANDBOOK ON ENGINEERING. 319
and the length of the valve stem. The position of the eccentric, when the valve is set, depends upon which way the engine is to run and whether the valve is connected directly to the eccentric or whether it receives its motion through a rocker which reverses the motion of the eccentric. When the valve is direct connected, the eccentric will be ahead of the crank by an amount equal to 90°, plus a small angle called the angular advance. When a reversing rocker is used, the eccentric will be diametrically opposite this position, or it will have to be moved around 180° and will follow instead of lead the crank. Shifting the eccentric ahead has the effect of making all the events of the stroke come earlier, and moving it backwards has the effect of retarding all the events. Lengthening or shortening the valve stem cannot hasten or retard the action of the valve, and its only effect is to make the lead or cut-off, as the case. may be, greater on one end than on the other. The general practice is to set a slide-valve so that it will have equal lead. The lead is the amount that the valve is open when the engine is on tfre center. To set the valve, therefore, put the engine on the center, remove the steam-chest cover so as to bring the valve into view, and adjust the eccentric to about the right position to make the engine turn in the direction desired. Now make the length of the valve-spindle such that the valve will have the requisite amount of lead, say T^ of an inch, the amount, however, depending upon the size and speed of the engine. Turn the engine over to the other center and measure the lead at the end. If the lead does not measure the same as before, correct half the difference by changing the length of the valve-stem, and half by shifting the eccentric. Suppose, for example, that the lead proved to be too great on the head end by half an inch. Lengthening the valve-stem by half of this, or £ inch, would still leave the lead i inch too much on the crank end. That is to say, the valve would then open too soon at both head and crank ends, and to correct this, the eccentric would
320 HANDBOOK ON ENGINEERING.
.
have to be moved back far enough to take up the other quarter- inch. Sometimes it is not convenient to turn the engine over by hand, in which case the valve may be set for equal lead as fol- lows: To obtain the correct length of the valve-stem, loosen the eccentric and turn it into each extreme position, measuring the total amount that the valve is open to the steam ports in each case. Make the port opening equal for each end by changing the length of the valve-stem. This process will make the valve- stem length as it should be. Now put the engine on a center and move the eccentric around until the valve has the correct lead and fasten the eccentric in that position. This will determine the angular advance of the eccentric.
The plain slide valve* — The function of the slide-valve is to admit steam to the piston at such times when its force can be usefully expended in propelling it, and to release it when its pres- sure in the cylinder is no longer required. Notwithstanding its extreme simplicity as a piece of mechanism, no part of the engine is more puzzling to the average engineer when the problem to be solved is to determine beforehand the results which will be pro- duced by a given construction and adjustment, or the proportions and adjustment required to produce given results. All who have had any experience in constructing and setting slide-valves are aware, in a general way, that the events of the stroke cannot be independently adjusted; for instance, a cut-off earlier than about -| of the stroke.
To set a slide valve* — The valve should be set in such a man- ner that when the engine is on the dead center, the part admitting the steam to the cylinder is open a small amountas shown in Fig. 1 85 , which is called lead. The object of lead is to enable the steam to act as a cushion against the piston before it arrives at the end of the stroke, to cause it to reverse its motion easily, and also to supply steam of full pressure to the piston the instant it has passed dead center. The lead required varies in different engines from
HANDBOOK ON ENGINEERING
321
to ^ without regard to size or kind. Fig. 192 also shows the position of eccentric, which should always be set ahead of the
Fig. 192. At point of taking steam
crank at an angle of 90°, plus another angle, called the " angular advance." When the valve is to have lead the angular advance must be a little greater than when no lead is desired.
193. At point of cut-off. Fig. J93 shows the position of eccentric at point of cut-off ; also position of piston.
Fig. 194. Position when compression begins. Fig. J94 shows position of valve when compression begins. It also shows position of eccentric, The compression at the left
21
322
HANDBOOK ON ENGINEERING.
end, towards which the piston is moving, has just commenced, and the exhaust is about to take place from the other end.
Fig. 195. At point of taking steam.
Fig* J95 shows the position of eccentric and valve in an engine with a rocker-arm.
fig. 106. At point of cut-off.
Fig- J96 shows the position of valve and eccentric nt point of cut-off.
Fig. 197. Showing point of compression.
HANDBOOK ON ENGINEERING, 323
CHAPTER XIII.
TAKING CHARGE OF A STEAH POWER PLANT.
It is frequently the case that an engineer, on assuming charge of a steam power plant, proceeds as though he were thoroughly familiar with the condition of the engine, boiler and entire sur- roundings. He plunges headlong into his duties, without first taking his bearings. A skillful physician on taking a case, would not proceed in this manner ; neither would a lawyer. The physi- cian would feel the patient's pulse, look at his tongue, take his temperature, observe his color and ask a number of questions, all for the purpose of enabling him to make a correct diagnosis of the patient's ailment. The first duty of an engineer, when he takes charge of a plant, is to ascertain the arrangement and con- dition of the plant. Since the boiler is the most important mem- ber of the plant, it should be the first to engross his attention, and it, together with its connections, should be examined as closely as time and surrounding conditions will permit. He should look the boiler all over, internally and externally, if possible, in search of
324 HANDBOOK ON ENGINEERING
mud, scale, grooving, pitting and defective braces. The furnace should be examined next, in view of burnt-out brickwork, grate bars and door linings. It may be that the furnace has distorted or cramped proportions, or it may be too large. The bridge-wall may be so constructed as to huddle the flames in one spot on the fire sheets of the boiler ; or it may be of such shape and in such condition as to cause the ignited gases to become dissipated in the combustion chamber. Even the combustion chamber itself may require the service of a bricklayer. He should next examine the safety valve and see that it is of ample capacity to relieve the boiler of surplus steam, and that it is in thorough working order. The first duty of an engineer when entering his plant at any time, is to ascertain how the water in the boiler stands, or, in other words, just how much water the boiler contains. He should open the gauge cocks first and note what comes from each in turn ; then open the cocks or valves connecting the glass gauge and note the water line there shown. He should also blow the water column out, in case any sediment may have choked any of the passages, which would be liable to give a false impression as to the actual quantity of water contained in the boiler. Should the water be found at tho correct height, he may now proceed to get up steam ; open the damper, pull down the banked fire and spread it evenly over the grate, adding a quantity of green fuel. Allow the steam to rise slowly ; do not force it. This applies especially to raising steam in a boiler which has been cold, as the expansion of the parts of the boiler due to the heat should take place slowly and evenly; otherwise, the life of the boiler will be shortened. While waiting for the steam to come up to the desired point, the engineer should now get his engine ready for the day's run. Fill all the oil cups and cylinder lubricator, so as to be ready to operate as the engine starts. With a hand oil squirt can, go around all the small brasses, connections, etc., and, in a word, well lubricate all the parts where friction takes place. If
HANDBOOK ON ENGINEERING.
he uses an oil pump for the cylinder and valves, it would be well to inject a small quantity of cylinder oil before the engine is started, while the stop-valve is open, during the time the engine is being " warmed up." After the engine cylinder is warmed through, the fire should again be looked at, and dealt with according to the indications. Of course, the water gauge glass must be looked at frequently, not only while raising steam in the morning, but at all times while the boiler is in operation.
Everything being in readiness, the engine is started slowly at first, the speed being gradually increased until the limit is reached. The day's run is now fairly commenced. A boiler should be blown down one gauge every morning before starting the day's run to get rid of 'the mud, scale or anything that is held in mechanical suspension in the water. Before starting in the morning and at noon is the best time to do this, as the sediment has settled to the bottom during the night, after the circulation of the water has stopped. When blowing a boiler down, always remember to open the blow- valve slowly — be careful not to blow too long, and then to close the valve slowly.
An engineer or attendant cannot be too careful in handling the many appliances with which a steam plant is equipped. The principal things to which an engineer should give his attention during the operation of his boiler day by day are, as follows: The maintenance of the water at the proper level, as near as pos- sible, and avoiding fluctuations in the pressure of steam. See that the firing is done correctly and economically so as to obtain from every pound of coal all that is possible under the con- ditions existing. The raising of the safety valve from its seat, at least once daily ; the blowing out of the water column twice daily, or oftener, if the water used is very dirty ; the frequent opening of the water gauge cocks, or try cocks, as they are sometimes called, and not depending entirely on the gauge glass for the correct height of water ; the blowing down of the boiler
326 HANDBOOK ON ENGINEERING.
one gauge every day ; the keeping of all valves, cocks, fittings, steam and water-tight, clean and in good working order.
When shutting down the plant for the night, the fires should be cleaned out and the live coals shoved back on the grates and banked ; that is, green coal should be thrown upon them, suffi- ciently thick to cover all the glowing fuel. Pump in the water until it reaches the top of the glass gauge. This should be done to insure a sufficient quantity from which to blow down in the morn- ing, and also to allow for any small leaks. Then close the cocks or valves connecting the glass gauge. Should this glass break dur- ing the night and the valves be left open, there would not be much water to start with in the morning. Leave the damper open a little, just sufficient to allow the gases which will rise from the banked fires to escape up the chimney. Finally, make sure that all the valves about the plant which should be closed, are closed ; and all those which should be left open, are open. Of course, the foregoing is applicable to a plant where there is no night engineer. But in any case, no matter how many assistants an engineer may have under his control, he should be familiar with all details of the plant under his charge.
One of the most important points in connection with the opera- tion of a steam boiler, is the preventing of corrosion, both internally and externally. One of the best aids to secure the well working and longevity of the steam boiler, or, in fact, the whole plant, is by being regular and punctual in a certain course of treatment, which has been proven to be effectual and beneficial in its results. All conditions do not require the same methods of treatment; therefore, it is absolutely necessary that the engineer in charge familiarize himself with all the conditions under which his plant is running, for then, and then only, can he intelligently prescribe and act accordingly. Above all, let him remember the adage, " Eternal vigilance is the price of safety," especially where a steam boiler is concerned.
HANDBOOK ON ENGINEERING. 327
ECONOMY IN STEAM PLANTS.
In these days of close figuring upon expense in office buildings and manufacturing plants, what may at first appear insignificant items may actually make all the difference between a good margin of profit and an actual loss.
The fuel expense is one of the largest in the operation of the majority of plants, and any reduction which can be made in the amount of fuel used, while maintaining the same amount of power, is considered a direct gain. The evaporation of more than nine pounds of water per pound of coal, is looked upon with suspicion by many, as it is not thought possible to obtain more than this amount in even the best designed and well regulated furnaces and boilers, especially when the firing is done by hand. The actual value of the fuel depends upon the way in which it is used, fully as much as on any other factor. The heat unit in the coal should be as much as possible utilized, as in one pound of good steam coal there is about 14,000 B. T. U., and about 10,000 of this amount can be utilized, so that 4,000 heat units are lost. The mixture of gases in a furnace depends upon the amount of air used. One pound of coal requires, theoretically, about twelve pounds of air to bum completely. But, in practice, about twice this amount is required in the present boiler furnace. To have good combustion coal requires a good draft. The gases are con- sumed near the fire, and the waste gases carry the heat to the boiler on their way to the stack. The boiler ought to have suffi- cient heating surface, or the hot wasted gases ought to travel a sufficient distance to be cooled down to about 350 degrees Fah- renheit ; which temperature is found high enough to produce a good draft in a stack of, at least, 100 feet high.
How a bad draft will unnecessarily increase the coal bill, is this: That of all the fuel burnt to perform certain work, a cer- tain proportion is consumed to keep the heat of the furnace up
328 HANDBOOK ON ENGINEERING.
to say, 212 degrees Fahr., without making any steam whatever which is available for work. This quantity varies from 20 to 30 percent, according to conditions, which are affected by various causes, such as leakages of steam, air, or water. Now, the only available power for work which we get from our fuel is the margin between this, say thirty per cent required for the said purpose, and what we generate above that. An engineer should notice the general condition of his boiler or boilers, and the equipments of same ; he should examine the boiJer both inside and outside, ascertain the dimension of grates, heating surfaces, and all im- portant parts. The area of heating surfaces is to be computed from the outside diameter of water-tubes, and the inside diameter of fire-tubes. All the surfaces below the main water level which have water on one side and products of combustion on the other, are to be considered as water-heating surfaces. If he finds that the boiler does not come up to what he thinks it should, he should put the boiler and all its appurtenances in first-class condition. Clean the heating surfaces inside and outside of boiler, remove all scale from flues and inside of boiler ; remove all soot from inside of flues, all ashes from the flame-bed or com- bustion chamber, and all ashes from smoke connections. Close all air leaks in the masonry and poorly fitted cleaning door. See that the damper in britching or smoking-flue will open wide and close tight. Test for air leaks through the crevices, by passing the flame of a candle over cracks in the brick work. A good, attentive fireman, who understands his business and will keep his bars properly covered without choking his fires, is really worth double the wages of an ignorant or inattentive one, as his coal bills would certainly prove. All an engineer can do is to keep the steam piston and valve or valves tight. Also the drains from his engine, and all drains on steam traps in the plant tight ; also, his engine cleaned and well-oiled, and not keyed up too tight. If in a heating plant, he should see that the back pressure valve is
HANDBOOK ON ENGINEERING.
329
at all times tight, as it does not take much of a le.ak to show a difference in his coal bill at the end of a month. He should keep all valves in the pumps in his plant tight, and see that the pump piston is packed, but not too tight. After a pump is packed, he should be able to move it back and forth by hand ; if the pump valves leak he can take them out and smooth them up with sand- paper. He should see that the feed-water to the boiler is at least 208 degrees Fahrenheit ; if it is under 204 degrees, his heater is not right, as the poorest heater will heat the feed- water to 204 ; it would be well to overhaul the heater — it may be full of scale ; or, if an open heater, the spray may be off. In most first-class plants, the feed-water is 212 Fahrenheit.
PRIMING.
The term priming is understood by engineers to mean the passage of water from the boiler to the steam cylinder, in the shape of spray, instead of vapor. It may go on unseen, but it is generally made manifest by the white appearance of the steam as it issues from the exhaust-pipe as moist steam, which has a white appearance and descends in the shape of mist, while dry steam has a bluish color and floats away in the atmosphere. Priming also makes itself known by a clicking in the cylinder, which is caused by the piston striking the water against the cylinder head at each end of the stroke. Priming is generally induced by a want of sufficient steam-room in the boiler, the water being car- ried too high, or the steam-pipe being too small for the cylinder, which would cause the steam in the boiler to rush out so rapidly that, every time the valve opened, it would induce a disturbance and cause the water to rush over into the cylinder with the steam.
HANDBOOK ON ENGINEERING.
TABLE OF PROPERTIES OF SATURATED STEAM.
|
8 |
2 . |
,3 |
2 |
8 5 |
d |
«J |
rt |
§ |
|
Pressure in pounds per square inct above vacu |
Temperatu in degrees Fahrenheit |
Total heat in heat uni from water at 32°. |
Heat in liqi from 32° in units. |
Heat of vap Ization or latent heat heat units. |
s?5 tm ££§§, |
Volume of one pound .in cubic fee |
Factor of equivalent evaporatioi at 212°. |
Total press above vacuum. |
|
1 |
101.99 |
1113.1 |
70.0 |
1043.0 |
0 00299 |
334 5 |
.9661 |
1 |
|
2 |
126.27 |
1120 5 |
94 4 |
10-26.1 |
0.00576 |
17* 6 |
.97*8 |
2 |
|
3 |
141.62 |
1125.1 |
109.8 |
1015 3 |
0 0<>844 |
118 5 |
.9786 |
3 |
|
4 |
153 09 |
1128.6 |
121 4 |
1007 2 |
0 01107 |
90 33 |
.98-22 |
4 |
|
5 |
162.34 |
1131 5 |
130 7 |
1000 8 |
0 01366 |
73 21 |
.9852 |
5 |
|
6 |
170.14 |
1133.8 |
138 6 |
995.2 |
0 01622 |
61 65 |
.9876 |
6 |
|
7 |
176 90 |
11*5 9 |
145.4 |
990.5 |
0 01874 |
53 39 |
.9897 |
7 |
|
8 |
182 92 |
1137 7 |
151.5 |
986 2 |
0.02125 |
47.06 |
.9916 |
8 |
|
9 |
188.33 |
1139 4 |
256 9 |
982 5 |
0.02374 |
42 12 |
.9934 |
9 |
|
10 |
193.25 |
1140 9 |
161 9 |
979 0 |
0 02621 |
38 15 |
.9949 |
10 |
|
15 |
213 03 |
1146.9 |
181 8 |
965 1 |
0.03826 |
26 14 |
1.000* |
15 |
|
20 |
227 95 |
1151.5 |
196.9 |
954 6 |
0.05023 |
19 91 |
1.0051 |
20 |
|
25 |
240.04 |
1155.1 |
209 1 |
946.0 |
0 06199 |
16.13 |
1 0099 |
25 |
|
30 |
250 27 |
1158.3 |
219 4 |
938 9 |
0 07360 |
13 59 |
1.0129 |
30 |
|
35 |
259.19 |
1161.0 |
228.4 |
932.6 |
0 08608 |
11 75 |
1.0157 |
35 |
|
40 |
267.13 |
1168 4 |
236 4 |
927.0 |
0.09644 |
10.37 |
1.0182 |
40 |
|
45 |
274.29 |
1165.6 |
243.6 |
92-2.0 |
0 1077 |
9.285 |
1.0205 |
45 |
|
50 |
280.85 |
1167 6 |
250.2 |
917 4 |
0 1188 |
8.418 |
1.0225 |
60 |
|
55 |
286 89 |
1169 4 |
256.3 |
913 1 |
0.1299 |
7 698 |
1 0245 |
55 |
|
60 |
292.51 |
1171.2 |
261 9 |
909 3 |
0 1409 |
7-097 |
1.0263 |
60 |
|
65 |
297 77 |
1172.7 |
267.2 |
905.5 |
0 1519 |
6 58* |
1.0-280 |
65 |
|
70 |
302 71 |
1174.3 |
272.2 |
902 1 |
0 1628 |
6 143 |
1.0295 |
70 |
|
75 |
307 38 |
1175.7 |
276.9 |
898 8 |
0.17*6 |
5 760 |
1 0309 |
75 |
|
80 |
311 80 |
1177.0 |
281.4 |
895 6 |
0.1843 |
5 4;i6 |
1.0323 |
80 |
|
85 |
316.02 |
1178 3 |
285.8 |
892 5 |
0.1951 |
5 126 |
1 0337 |
85 |
|
90 |
3-20.04 |
1179 6 |
290 0 |
889 6 |
0.2068 |
4 859 |
1.0350 |
90 |
|
95 |
323.89 |
1180 7 |
294.0 |
886 7 |
0 2165 |
4.619 |
1.0362 |
95 |
|
100 |
327 58 |
1181 9 |
297.9 |
884 0 |
0.2271 |
4.403 |
1.0374 |
100 |
|
105 |
331 13 |
1182.9 |
301 6 |
881 3 |
0 2378 |
4.205 |
1.0385 |
105 |
|
110 |
334 56 |
1184 0 |
305 2 |
878 8 |
0 2484 |
4 026 |
1 0396 |
110 |
|
115 |
337.86 |
1185 0 |
308.7 |
876 3 |
0.2589 |
3 862 |
1.0406 |
115 |
|
!20 |
341.05 |
1186.0 |
312.0 |
874.0 |
0.2695 |
3.711 |
1 0416 |
120 |
|
125 |
344 13 |
1186 9 |
315.2 |
b71 7 |
0.2800 |
3 571 |
1.0426 |
125 |
|
130 |
347.12 |
1187 8 |
318.4 |
869 4 |
0.2904 |
3 444 |
1.0435 |
130 |
|
140 |
352.85 |
1189.6 |
324.4 |
866 1 |
0 3113 |
3 212 |
1 045* |
140 |
|
150 |
358.26 |
1191 2 |
830.0 |
861 2 |
0 3321 |
3 Oil |
1.0470 |
lf.0 |
|
}£Q |
363 40 |
1192.8 |
335.4 |
857-4 |
0 3530 |
2 833 |
1.0486 |
160 |
|
170 |
368 29 |
1194.3 |
340.5 |
853 8 |
0.3737 |
2.676 |
1 0502 |
170 |
|
180 |
372.97 |
1195 7 |
345.4 |
850.3 |
0.3945 |
2.635 |
1.0517 |
180 |
|
190 |
377.44 |
1197 1 |
350.1 |
847 0 |
0.4153 |
2.408 |
1 0631 |
190 |
|
200 |
381.73 |
1198 4 |
354.6 |
84* 8 |
0.4359 |
2.294 |
1 0545 |
200 |
|
225 |
891 79 |
1201 4 |
365.1 |
8*6.3 |
0 4876 |
2.051 |
1 0576 |
2-25 |
|
250 |
400.99 |
1204.2 |
374.7 |
829.5 |
0.5393 |
1.854 |
1.0605 |
250 |
|
275 |
409 50 |
1206.8 |
383.6 |
823 2 |
0.5913 |
1 691 |
1 06*2 |
275 |
|
300 |
417.42 |
1209.3 |
391 9 |
817 4 |
0.644 |
1 553 |
1 0657 |
3<0 |
|
325 |
424.82 |
1211.5 |
399.6 |
811 9 |
0.696 |
1 437 |
1.0680 |
3-25 |
|
360 |
4*1 90 |
1213.7 |
406.9 |
806.8 |
0.748 |
1.337 |
1 0703 |
350 |
|
375 |
438 40 |
1215.7 |
414 2 |
801 5 |
0 800 |
1 250 |
1.0724 |
375 |
|
400 |
445.15 |
1217.7 |
421.4 |
796 3 |
0.853 |
1.172 |
1 0745 |
400 |
|
500 |
466.57 |
1224.2 |
444.3 |
779.9 |
1.065 |
.939 |
1.0812 |
600 |
HANDBOOK ON ENGINEERING. 331
The gauge pressure is about 15 pounds (14.7) less than the total pressure, so that in using this table, 15 must be added to the pressure as given by the steam gauge. To ascertain the equivalent evaporation at any pressure, multiply the given evap- oration by the factor of its pressure, and divide the product by the factor of the desired pressure. Each degree of difference in temperature of. feed-water makes a difference of .00104 in the amount of evaporation. Hence, to ascertain the equivalent evaporation from any other temperature of feed than 212°, add to the factor given as many -times .00104 as the temperature of feed-water is degrees below 212°. For other pressures than those given in the table, it will be practically correct to take the pro- portion of the difference between the nearest pressures given in the table. Example : If a boiler evaporates 3000 Ibs. of water per hour from feed- water at 200 degs. Fah. into steam at 100 Ibs. per sqr. in. by the gauge, what is the equivalent evaporation " from and at"212°? Ans. 3159.24 Ibs.
Operation : Temperature of feed-water = 200 degs.
Then, 212 — 200 = 12 —difference in temperature.
Then, 15 added to the gauge pressure = 115.
Looking in the above table we find the factor 1.0406.
Then, .00104 X 12 =.01248.
And, 1.0406
.01248 1.05308
Then, 3000 X 1.05308 = 3159.24 Ibs. the equivalent evapo- ration.
The H. P. of this boiler would be 91.57.
332 HANDBOOK ON ENGINEERING.
HIGH PRESSURE STEAM.
It is generally believed that high-pressure steam is cheaper to use and costs but little more to generate than low pressure steam. A study of a table of the properties of saturated steam, to be found on another page in this book, will show why high-pressure steam is economical to generate, and a few calculations will prove instructive by showing what may be excepted from its use. To generate one pound of steam at 25 Ibs. pressure, absolute, requires an expenditure of 1,155 thermal units, and to generate steam at 200 Ibs. pressure, absolute, requires 1,198 thermal units, or an increase of only 43 thermal units for an increase of 175 Ibs. pressure. Further investigation shows that the temperature of steam at 25 Ibs. pressure is 240° and at 200 Ibs. pressure, 382°, the difference, 142, being the number of degrees that the tem- perature of steam is raised with an expenditure of 43 thermal units. To put it in another way, the temperature of the steam has been raised nearly 60 per cent, with an increase of less than 4 per cent in the number of thermal units. It is con- venient to consider that the generation of steam takes place by two different steps, one of which is raising the water from 32° to the temperature corresponding to the pressure of the steam, and the other is giving off the steam at this pressure, which process absorbs a quantity of heat that becomes latent or non-sensible. At 25 Ibs. pressure, the sensible heat required to raise one Ib. of water from 32° to 240° is 209 units, and to raise it from 32° to 382 degrees, the temperature of steam at 200 Ibs. pressure requires 355 thermal units. The increase in the sensible heat of the water, there- fore, is 355 minus 209 = 146 units, or about the same as the tem- perature increase for these two pressures, which is 142°. It is thus clear that the total increase in the number of heat units in steam raised from 25 Ibs. to 200 Ibs. pressure is small (43° as found
HANDBOOK ON ENGINEERING.
above) because the laten heat absorbed in the formation of the steam decreases as the pressure increases. It requires less heat to generaU steam froir water raised to 382° at 200 Ibs. pressure, than from water previously raised to 240° at 25 Ibs. pressure. To generate higher pressure steam, therefore, we must first apply enough heat to bring the water to a temperature corresponding to the higher pressure. This heat will be nearly proportionate to the increase in temperature. Then enough heat must be applied to the water to generate the steam, the amount of heat required for this purpose decreasing as the pressure increases. The combined result of these two processes is that it takes only a very small increase in the total heat to pro- duce the higher pressure steam. The idea may be suggested that if this higher pressure is obtained at the cost of so small an expen- diture of heat, it would not be reasonable to expect a large gain in economy from it, since it is not possible for the steam to do a greater amount of work than the equivalent of the heat which it contains. This would be true were it not for the fact that the larger part of the heat in the steam is rejected during the ex- haust. To illustrate, suppose an engine to exhaust at atmos- pheric pressure, or, at about 15 Ibs., absolute, and that the steam is saturated. As may be determined from the steam tables, there would be ejected 1,147 heat units per pound of steam^ or 51 heat units less than were found to be in a pound of steam at 200 Ibs. pressure. That is to say, under the above assumption, there are available only 51 heat units per pound of steam to do the work in the engine cylinder when the steam pressure is 200 Ibs. But we also found that the increase in the heat units in raising the steam pressure from 25 to 200 Ibs. was 43, and hence the increase in proportion to the number available is large, although the increase in proportion to the total number required
334 HANDBOOK ON ENGINEERING.
to generate the steam is small. This shows why high-pressure steam is economical to generate and profitable to use. It should be stated that the only way in which the full benefit can be de- rived from high pressure-steam is by using the steam expansively, keeping the terminal pressure at release as low as possible. We will not take the space to give the calculations to prove this, but will compare a few results of calculations. Suppose steam to be used in a theoretically perfect engine at the pressure of 25 Ibs., 50 Ibs., 100 Ibs. and 200 Ibs. We will assume that in each case the cut-off is at one-third stroke, giving three expansions and a terminal pressure of one-third the initial pres- sure. The steam consumptions will then be, respectively, about 16J, 16, 15 J, and 14 Ibs. per horse-power, showing that gain from the increase in pressure is very slight. On the other hand, suppose the expansions to be carried to the atmospheric pressure in each case. The consumptions will then be about 27, 15, 11 and 8 Ibs. respectively, showing a marked decrease.
Still another point should be mentioned in relation to the relative gain that is to be expected with the increase in pressure. Comparing the last figure, it will be observed that the decrease in consumption when the pressure increased from 25 to 50 Ibs- was 27 minus 15 = 12 Ibs., or 44 per cent. Again, when the pressure doubled from 50 to 100 Ibs., the consumption decreased only 4 Ibs., or 27 per cent; and when the pressure was again doubled to 200 Ibs., the consumption only decreased 3 Ibs., or about 27 per cent. It is evident from this that the saving from an increase in steam pressure grows less as the pressure increases, and this is found to be the case in actual practice. There is another reason for this, also, coming from the losses incident to cylinder condensation and re-evaporation, which is more marked where there is a wide range in pressures than where the pressures are more uniform throughout the stroke. It is found that where the steam pressure is much above 100 Ibs. gauge pres-
HANDBOOK ON ENGINEERING. 335
sure, no gain will result from a further increase in pressure with- out compounding, the advantage of the compound engine being that the extremes of temperature in the cylinders are not so great as with a simple engine.
USING STEAfl FULL STROKE.
The steam engine is nothing in the world but an enlargement upon the end of the steam pipe, containing a piston against which the steam in the boiler may press. The piston moves a certain distance, and then the steam is allowed to press upon its other side, while the steam on the first side is allowed to flow into the atmosphere and go to waste. The slide-valve is the device or- dinarily employed to admit the steam, alternately, to opposite sides of the piston, and to permit the free outflow of steam from the reverse side of the piston. As the steam presses upon the pis ton, the piston moves forward with a force equal to the pressure of steam per square inch, multiplied by the number of square inches of piston surface. Steam occupies the entire space from the sur- face of the water in the boiler, to the piston of the engine. The steam space, therefore, includes the steam space of the boiler, the steam pipe, the steam chest, and the cylinder space upon one side of the piston. As the piston moves, the entire steam space be- comes a little larger, by reason of the cylinder space becoming longer. Thus it will be seen that all of the steam in the boiler and pipe and engine, would expand a trifle and the pressure become somewhat reduced, were it not for the fact that new steam is made by the fire as fast as the piston moves forward. By this means the steam is maintained at about uniform pressure. It will be seen that the pressure is produced upon the piston by the generation of new steam from the water, that is, the fire causes the water to generate a quantity of steam, and this quantity of steam forces its way into the other steam, exerting a force upon the whole body of steam and pushing the piston ahead.
336 HANDBOOK ON ENGINEERING.
If an engine piston has a surface of 100 square inches and a stroke of ten inches, it follows that the piston will yield a thousand cubic inches additional steam space by its movement during one stroke, and consequently, the fire will be called upon to produce 1,000 cubic inches of new steam for each single stroke of the engine. If the pressure of the steam be eighty pounds to the square inch, the engine piston will move with the force of 8,000 pounds. When the engine has completed one stroke, we find an amount of power exerted equal to 8,000 pounds moved ten inches, and we then open the exhaust valve and empty into the atmosphere 1,000 cubic inches of eighty-pound steam. We keep on doing this for each stroke. Now our attention is par- ticularly called to the fact that when we empty the steam out of the cylinder, it is just as good as when it went into the cylinder ; that is, it was 1,000 cubic inches of steam at a pressure of eighty pounds to the square inch, and when it goes into the atmosphere it will expand into over 6,000 cubic inches, at fifteen pounds pressure to the square inch, or the same pressure as the atmos- phere. This 1,000 cubic inches of steam which we dumped out of the cylinder, is precisely the same quality of steam as the steam which we have penned up in the boiler ; and which we have to be making new all the time in order to keep the engine run- ning. Such is the operation of the steam engine which receives its steam the full length of the stroke ; and such an engine may be described briefly, as a very wasteful machine, which throws away steam as good as it receives it, and which requires the gen- eration of a cylinder full of full pressure steam for each stroke. It should be readily understood that when the piston has com- pleted its stroke, and just before the exhaust valve is opened to allow the steam to escape, the cylinder contains 1,000 cnbic inches of steam at eighty pounds pressure, which it is capable of expanding into many thousand cubic inches at constantly de- creasing pressure. The first step in the improvement of such an
HANDBOOK ON ENGINEERING. 337
engine would be to so arrange things as to get some benefit from this enormous power of expansion. The full stroke engine does not get one-half of the power before it throws the steam away. The engine which we would have referred to would yield a power of 8,000 pounds moved ten inches at each single stroke ; 33,000 pounds moved one foot in one minute is a horse-power ; 66,000 pounds moved half a foot would be the same. An engine using steam full stroke is such an extravagant contrivance that we, now- adays, seldom find them in use. There are certain classes of engines built, fitted with link motions for driving the valve, and they are arranged so as to carry their steam full stroke, but pro- vision is also, made for quickly hooking up the link and suppress- ing the full-stroke feature.
SLIDE VALVE ENGINES.
If we have an engine arranged to receive its steam full stroke and to dump the steam out into the air in as good condition as it was received, and we wish to get some of the benefits of the expansive power of the steam, there is a simple way of doing it and without any great change in the engine, and that is, to lengthen out the slide valve so that after the cylinder is half full of steam, the valve will shut and let no more steam enter. Dur- ing the balance of the stroke, the entire power comes from the gradual expansion of the steam shut up in the cylinder, and it will be readily seen that whatever power we succeed in getting out of the expansion of the steam, is pure gain. The lower the pres- sure of the steam is when it is exhausted into the air, the more it has expanded, the more power we have gotten out of it, and the more we have gained. It may be said in a few words, that all slide-valve engines are now arranged to work their steam expans- ively. But it is, unfortunately, found that the slide-valve pos- sesses a peculiar defect, which prevents the system being carried very far. We can lengthen out a slide-valve so as to cut the
338 HANDBOOK ON ENGINEERING.
steam off at nay desired point of the stroke, and we must then increase the throw of the eccentric in order to properly operate the long valve. But the minute we do this we find that we have interfered, to a certain extent, with the proper operation of the exhaust. No matter what we do about the admission of steam or about cutting off before the end of the stroke, we must arrange our exhaust to take place at a certain point at the end of the stroke. It is found in practical operations that this necessary quality of the slide-valve prevents our arranging it to cut off the steam properly at an earlier point than about five-eighths or three- quarter stroke. The consequence is, that an engine with two feet stroke will receive steam 18 inches, then have 6 in. of expansion. It may be fairly said, in a general way, that about all the slide- valve engines now manufactured, cut off the steam at about five- eighths or three-quarters stroke ;and it may be further said that this is about all we can get out of a slide-valve engine. Even the trifling expansion got from such engines as this, represents an immense amount of money in the course of a year in large establishments, but it is not good enough for anyone who seeks even a decent investiment of money, in power-getting appliances.
REGULAR EXPANSION ENGINES.
A liberal expansion of steam being desirable and the slide- valve proving totally incapable of providing for such expansion, the first step in the desired direction is to totally discard the slide valve. The Corliss valve is a cylindrical piece, oscillating in a cylindrical hole. The valve does not fill this hole, but seats against one side only. Hence the fitting qualities are about the same as with the slide-valve and, in fact, the principle is about the same, the Corliss representing a portion of the slide-valve, rolled into the form of a cylinder and operating in a concave seat. We must not only discard the slide-valve arrangement, but in the valve arrangement which we select, we must secure an abso-
HANDBOOK ON ENGINEERING. 339
lute independence between the steam admission part of the sys- tem and the exhaust part. The slide-valve is one chunk of cast iron, letting in and cutting off steam at its outside edges, and opening and closing the exhaust by its inside edges. When one of these valve edges moves, everything else has to move. There is, consequently, no independence of action. In the Corliss engine there are parts to let steam into the cylinder and to quit letting it in at the proper time, and there are valves to let it out at the proper time, and they are perfectly independent of each other in all of their movements. The consequence of this arrangement is, that the steam valve may open, steam flow into the cylinder, the valve suddenly shut and chop the steam off short, the piston move forward in its stroke by the expansion of the confined steam, and finally, be let out by the opening of the exhaust valve, which has all the time stood ready for the dis- charge. Here we have a regular expansion engine. We can cut the steam off as early in the stroke as we desire, and hence, have any degree of expansion we desire. And we can do this without interfering with the exhaust valves. It is found, in practice, that an engine cutting off at about one-fifth of its stroke and expanding the other four fifths, will yield the fairest practical economy.
AUTOMATIC CUT=OFF ENGINES.
In order that those not posted may understand what is meant by the term " Automatic Cut-off Engines," we will have to go back a step. Take, for instance, a full-stroke engine. It ought to be well understood how the ordinary governor does its work. Sup- pose, for instance, that there is no governor, and that we regulate the speed of the engine by having a man stand at the throttle-valve all the time. If the engine runs too fast, he shuts the throttle- valve a little. This makes the steam pipe so small that the steam cannot flow fast enough to keep the pressure up, and consequently
340 HANDBOOK ON ENGINEERING.
the speed goes down. If the engine runs too slow, he opens the throttle- valve and lets the steam flow free, so as to maintain higher pressure. Thus it will be seen that the man at the throttle regulates the engine by altering the pressure with which the steam acts upon the engine. An ordinary engine governor is simply a man at the throttle. When the engine runs too fast the balls fly out, the governor valve shuts a little and the pressure of steam entering the engine is reduced, and so on through all the changes continually taking place. All steam engines, in which the regulation of steam is effected by means of a governor operat- ing upon a throttle, are called throttling engines. They operate by reducing the pressure of the steam admitted to the engine, and thereby taking so much of the vitality out of the steam. It is entirely the wrong way to do it. After once spending our money to get up pressure in the boiler, we should make the greatest possible use of that pressure, so long as we are taking the steam from the boiler. It is, therefore, desirable that the full boiler pressure should be admitted to our cylinder; and the question arises as to how we shall be able to regulate the speed if we do not tinker with this pressure. The automatic engine regulates the speed by the simple act of altering the point of cut-off. If the engine is cutting off at one-fifth stroke, we get a power equal to the incoming force of steam for one-fifth of the stroke, and the expansion of the steam for the other four-fifths of the stroke. If the engine runs too slow we cut the steam off a little later and thereby increase the average pressure during the expansion. The automatic engine, then, is an engine, which cuts off the steam at an earlier point in the stroke, if the engine runs too fast, and cuts it off at a later point if it runs too slow. It is the duty of the governor to say just when the steam valve should close and not let any more steam into the cylinder. In the Cor- liss engine the steam valves open wide at the beginning of the stroke and let full boiler pressure smack in against the piston.
HANDBOOK ON ENGINEERING. Ml
After the piston has advanced to, say one-fifth of its stroke, the valve shuts up as quick as a flash and the expansion begins. If the engine starts too slow, the governor will hold the steam valve open a trifle longer, but will not interfere with its full opening at the beginning of the stroke, or with its flash-like closing when the cut-off is to take place. During all these operations of the governor and the admission valves, the exhaust valves are let entirely alone, and they continue their work unchanged. It will thus be seen that the expansion engine makes provision for the utmost economy in the use of steam, and with the automatic fea- ture added to it, provides that this economy shall not be sacrificed for the purpose of regulating the speed.
THE GARDNER SPRING GOVERNORS.
Construction* — Two balls are rigidly connected to the upper ends of two flat, tapering, steel springs — the lower ends of the springs being secured to a revolving sleeve ,which receives rotation through mitre gears ; links connect the balls to an upper revolv- ing sleeve, which is free to move perpendicularly.
The valve stem passes up through a hollow standard upon which the sleeves revolve, and is furnished with a suitable bearing in the upper sleeve ; the closing movement of the valve is upward, and is obtained in the following manner : The balls at the free ends of the springs furnish the centrifugal force and the springs are the main centripetal agency (gravity is not employed). As the balls fly outward, under the centrifugal influence, they move in a curved horizontal path which may be described as an arc, modified by a radius of changing length — the radius being represented by the length and position of the springs ; the links represent a radius of lesser length, while the sleeve to which the lower ends of the links are pivoted, being free to rise and fall, nullifies the effect of the links in determining the arc in which the balls travel. As the
342
HANDBOOK ON ENGINEERING.
balls move outward in their peculiar path, the sleeve is drawn up- ward by the links, and, as the balls move inward, the sleeve is pushed downward. The change of speed is obtained by increas-
Fig. 108. The Gardner standard governor — class automatic safety stop and speeder.
"A" with
ing or decreasing the centripetal resistance > and accomplished by the action of a spiral spring pivoted against the lever, and by means of a shaft and arm against the valve-stem in the direction to open the valve ; a thumb-screw is used to adjust the compres-
HANDBOOK ON ENGINEERING.
sion. A convenient sawyer's lever is attached to the shaft and a reliable automatic safety stop is furnished when desired.
Fig> f 98 on the preceding page represents the Gardner Standard Governor, Class "A."
This is a gravity governor, having an automatic safety stop and speeder. It is made in sizes from 1 £ inches to 16 in., and is especially adapted to the larger type of stationary engines. In action, the centrifugal force of the pendulous balls is opposed by the resistance of a weighted lever, the speed being varied by the position of the weight. The automatic safety stop is very simple in construction and reliable in action. It is accomplished by allowing a slight oscillation of the shaft bearing, which is sup- ported between centers and held in position by the pull of the belt ; a projection at the lower part of the shaft bearing supports the fulcrum of the speed lever. If the belt breaks or sups off the pulley, the support of the fulcrum is forced back, so as to allow the fulcrum to drop and instantly close the valve. The valve is not affected by steam current and both valve and seats are made of special composition, that effectually resists wear and the cutting action of the steam. The governor is made for all pressures, all parts being made by the duplicate system, with special machinery.
Fig, 199 on the following page represents Class "B" gov- ernor— a combination of the gravity and spring designs.
They are made in sizes from f to 10 inches inclusive, and are adapted to all styles of engines. They are provided with speeder and sawyer's lever, but are not automatic. In the Class " B " governor the centrifugal force of the pendulous balls operates against the resistance of a coiled steel spring, inclosed within a case and pivoted on the speed lever by means of a screw ; the amount of compression of the spring can be changed so as to give a wide range of speed. A continuation of the speed lever makes a convenient sawyer's hand lever, which controls the valve by
344 HANDBOOK ON ENGINEERING.
means of a cord. Sizes £ to 1J in., inclusive, have an adjustable frame, which can be set at any desired angle in relation to the
Fig. 199. The Gardner standard governor— Class "B."
valve chamber. The valve and chamber are the same as used on Class " A " governor, and they are made with the same care and style of workmanship.
HANDBOOK ON ENGINEERING.
345
CHAPTER XIV. A FEW REHARKS ON THE INDICATOR.
The steam-engine indicator is an instrument designed to show the steam pressure in the cylinder at all points in the stroke. It consists primarily, of a piston of known area capable of moving in a cylinder and resisted by a coil spring of known strength. To this piston is attached, by means of suitable piston rod and levers, a pencil capable of tracing a line corresponding to the motion of the indicator piston. This line is traced on a paper slip attached to the drum of the indicator, which drum is con- nected to some moving part of the engine in such a way as to have a back and forward movement, coincident with the steam piston of the engine.
Fig. 200. Exterior and interior of indicator.
By referring to the above sectional view of an indicator, which is generally recognized as the best type, the construction will be readily understood.
346 HANDBOOK ON ENGINEERING.
THE USE OF THE STEAH EiNQINE INDICATOR IN SETTING VALVES AND THE INVESTIGATION OF SOME OF THE DE- FECTS BROUGHT OUT BY THE INDICATOR CARDS.
The steam-engine indicator has come into such general use that to-day there are but few men running engines who are not familiar with its construction and manner of attachment to en- gines, and the method of calculating horse power from cards. The indicator is attached to pipes tapped into the cylinder heads, or into the barrel of the cylinder opposite the counterbore, beyond the travel of the piston rings. The indicator consists of a cylin- der with piston and compression spring and a drum attached to a coiled spring, used for returning the same. The pressure of steam on the piston of the indicator compresses the spring above it. The motion of the piston is carried by a piston-rod to a pencil motion, which multiplies the motion of the spring some five or six times. The springs are marked 20, 40, 80, etc. This meaning that 80 Ibs. pressure per square inch on the indicator piston (or whatever the spring may be marked) will cause the pencil at the end of the pencil-arm to move an inch. The pencil marks on paper, which is fastened on a drum. This drum is moved by the cross-head of the engine, through some form of reducing motion, such as pantograph, lazy-tongs, brumbo pulley, etc. To obtain the horse power, we first need the mean pressure equiva- lent to the variable pressure on the card. This is most easily found by dividing the area of the card by the length, giving the height of a rectangular card of equivalent area, and then multi- plying this height by the scale of the spring. The mean effective pressure per square inch on the piston, times the area of the pis- ton in square inches, times the speed of the piston in feet per minute, divided by 33,000, gives the horse power. If there is a loop at either end of the card, the area of this loop is to be sub- tracted from the larger area before finding the mean height of
HANDBOOK ON ENGINEERING.
347
the card, since such a loop represents work opposed to the work- ing side of the piston. In getting areas by means of a planimeter, no attention need be given to the loops. By following the lines in order, as drawn by the indicator pencil, the loops will be sub- tracted from the main card, for if the main body of the card is traced in a right-handed rotation, the loops will be traced in a left-handed rotation.
DIAGRAM ANALYSIS.
Figs* 20 J and 202 are from throttling engines ; the former repre- senting good performances for that class of engine, and the latter,
Fig. 201. Diagram from a throttling engine.
in some respects, which the engineer will readily recognize, bad performances*
348 HANDBOOK ON ENGINEERING.
.
Figs. 203, 204, and 205, are from automatic8 ; Fig. 203 repre- senting what is now considered rather too light a load for best practical economy ; Fig. 204 about the best load, and Fig. 205 is from a condensing engine.
Line A B is the induction line, and B C the steam line ; both together representing the whole time of admission.
(7 is about the point of cut-off, as nearly as can de determined by inspection. It is mostly anticipated by a partial fall of pres- sure due to the progressive closure of the valve.
The usual method is, to locate it about where the line changes its direction of curvature.
C D is the expansion curve. D is the point of exhaust.
D E is the exhaust line, which begins near the end of the stroke and terminates at the end of the stroke, or, at latest, before the piston has moved any considerable distance on its return stroke.
The principal defect of Fig.202 is, that this line occupies nearly all the return stroke. E Fis the back pressure line, which, in non-condensing engines, should be coincident with, or but little above, atmospheric pressure. In Fig. 205 it is below the atmos- pheric line to the extent of the vacuum obtained in the cylinder. Some authorities would call it the vacuum line in Fig. 205 but that name properly belongs to a line representing a perfect vacuum.
jFMsthe point of exhaust closure (slightly anticipated by rise of pressure) and F A the compression curve, which, joining the admission line at A, completes the diagram proper, forming a closed figure.
G G is the atmospheric line traced when the piston of the indi- cator is subject to atmospheric pressure, above and below alike. Some pull the cord by hand when tracing it, to make it longer than the diagram. H H is the vacuum line, which, when re- quired, is located by measurement such a distance below the atmospheric line as to represent the atmospheric pressure at the time and place as nearly as can be ascertained. The mean
HANDBOOK ON ENGINEERING. 349
atmospheric pressure at the sea level is 14.7 pounds. For higher altitudes, the corresponding mean pressure may be found by multiplying the altitude by .00053, and subtracting the product from 14.7. When a barometer can be consulted, its reading in inches multiplied by .49 will give the pressure in pounds.
FIfr. 202. Diagram from a throttling engine.
1 is the clearance line* representing by its distance from the nearest point of the end of the diagram at the admission end, as compared with the whole length, the whole volume of clearance known to be present. Its use is mainly to assist in constructing ft theoretical expansion curve by which to test the accuracy of the Actual one.
Calculating mean effective pressure* — Since the simplification' «ad popularization of the planimeter, no engineer who has occa*
350
HANDBOOK ON ENGINEERING.
sion to compute the " indicated horse-power " (IHP) of engines should be without one; for, if properly handled, the results
Fig. 203. Diagram from an automatic cut-off engine*
obtained by them are more accurate and more quickly obtained than by any other process. The diagram is pinned to a smooth board covered with a sheet of smooth paper, the pivot of the leg pressed into the board at a point which will allow the tracing point to be moved around the outline of the diagram without forming unnecessarily extreme angles between the two legs, and a slight indentation made in the line at some point convenient for begin- ning and ending ; for it is vitally important that the beginning and ending shall be at exactly the same point. The reading of the wheel is taken, or it is placed at zero, and the tracing point is
HANDBOOK OF ENGINEERING.
351
passed carefully around the diagram, following the lines as closely as possible, moving right-handed, like the hands of a watch. The reading obtained (by finding the difference between the two, if the wheel has not been placed at zero) is the area of the diagram in square inches, which, multiplied by the scale of the diagram, and divided by its length in inches, gives the mean effective pressure.
The process of finding the mean effective pressure by ordinates* — Divide the diagram into 10 equal parts as shown by the full lines in Fig. 204 : when performing this work a frequent mistake is made, viz.,
Fig* 204. Erecting the or di nates.
making all the spaces equal. The end ones should be half the width of the others, since the ordinates stand for the centers of
352
HANDBOOK ON ENGINEERING.
equal spaces. Ten is the most convenient and usual number of ordinates, though more would give more accurate results. The aggregate length of all the ordinates (most conveniently measured consecutively on a strip of paper) divided by their number, and multiplied by the scale of diagram, will give the mean effective
Fig. 205. Diagram from a condensing engine.
pressure. A quick way of making a close approximation to the mean effective pressure of a diagram is, to draw line a 6, Fig. 206, touching at a, and so that space d will equal in area spaces c and e, taken together, as nearly as can be estimated by the eye. Then a measure,/, taken at the middle, will be the mean effective pressure. With a little practice, verifying the results with the planimeter, the ability can soon be acquired to make estimates in
HANDBOOK ON ENGINEERING.
353
this way with only a fraction of a pound of error with diagrams representing some degree of load. With very high initial pres- sure and early cut-off, it is not so available.
a
Fig. 206. Mer nod of estimating the mean pressure.
The indicated horse-power. — IHP is found by multiplying together the area of the piston (minus half the area of the piston- rod section, when great accuracy is desired), the mean effective pressure and the travel of the piston in feet per minute, and dividing the product by 33,000. It is sometimes convenient to know the HP constant of an engine, which is the HP for one revolution at one pound mean effective pressure. This multiplied by the mean effective pressure, and by the number of revolutions per minute, gives the IHP.
THEORETICAL CURVE.
Testing expansion curves. — It is customary to assume that steam, in expanding, is governed by what is known as Mariotte's law, according to which its volume and pressure are inversely pro-
23
354
HANDBOOK ON ENGINEERING.
portional to each other. Thus, if a cubic foot of steam at, say, 100 pounds pressure be expanded to 2 cubic feet, its pressure will fall to 50 pounds, and proportionately for all other degrees of expansion. The pressures named are lt total pressures ; " that is, they are reckoned from a perfect vacuum. A theoretic ex- pansion curve which will conform to the above theory may be
\
\,
\
s.
10
Fig. 207. Locating the trne expansion curve.
traced by the following method : Referring to Fig. 207, having drawn the clearance and vacuum lines as before explained, draw any convenient number of vertical lines, 1, 2, 3, 4, 5, etc., at equal distances apart, beginning with the clearance line and num- ber them as shown. Decide at what point in the expansion curve
HANDBOOK ON ENGINEERING.
of the diagram we desire the theoretic curve to coincide with it. Suppose we choose line 10, on which we find the indicated pres- sure to be 25 pounds. Multiply this pressure by the number of the line (10) and divide the product (250) by the numbers of each of the other lines in succession. The quotients will be the pressures to be set off in the lines. Thus, 250 divided by 9 gives 27.7, the pressure on line 9 ; and so for all the others. The same curve may also be traced by several geometric methods, one of which is as follows, referring to Fig. 208 : —
E
H
Fig. 208. Drawing the hyperbolic curve.
Having drawn the clearance and vacuum lines as before, select the desired point of coincidence, as a, from which draw the perpendicular a A. Draw A B at any convenient height above or near the top of the diagram, and parallel to the vacuum line D C. From A draw A C and from a draw a b parallel to D (7, and from
356 HANDBOOK ON ENGINEERING.
its intersection with A B, erect the perpendicular b c, locating the theoretical point of cut-off on A B. From any convenient num- ber of points in A B (which may be located without measurement) as E, F, 6r, H, draw lines to (7, and also drop perpendiculars E e, Ff, Gg, Hli, etc. From the intersection of E 0 with b c, draw a horizontal to e, and the same for each of the other lines F <7, G (7, H C; establishing points e,/, #, ft, in the desired curve. Any desired number of points may be found in the same way. But this curve does not correctly represent the expansion of steam. It would do so if the steam during expansion remained or was maintained at a uniform temperature ; hence, it is called the isothermal curve, or curve of same temperature. But, in fact, steam and all other elastic fluids fall in temperature during expan- sion, and rise during compression ; and this change of temperature augments the change of pressure slightly ; so that if, as before assumed, a cubic foot of steam at 100 pounds total pressure be expanded to two cubic feet, the temperature will fall from nearly 328° to about 278°, and the pressure instead of falling to fifty pounds, will fall a trifle below 48 pounds. A curve in which the pressure due to the combined effects of volume and resulting temperature is represented, is called the adiabatic curve, or curve of no transmission ; since, if no heat is transmitted to or from the fluid during change of volume, its sensible temperature will change according to a fixed ratio, which will be the same for the same fluid in all cases. It is not necessary to give any of the usual methods of tracing the adiabatic curve, since the isothermal curve is the one generally used for that purpose. And while it is incorrect in that it does not show enough change of pressure for a given change of volume, the great majority of actual diagrams are still more incorrect in the same direction ; so that when a diagram conforms to it as closely as the one used in these illustrations, it is considered a remarkably good one. A sufficiently close approximation to the adiabatic curve to enable the non-profes-
HANDBOOK ON ENGINEERING. 357
sional engineer to form an idea of the difference between the two, may be produced by the following process: Taking a similar diagram to those used for the foregoing illustrations, we fix on a point A near the terminal, where the total pressure is 25 pounds. As before, this point is chosen in order that the two curves may coincide at that point. Any other point might have been chosen for the point of coincidence ; but a point in that vicinity is generally chosen so that the result will show the amount of power that should be obtained from the existing terminal. This point is 3.3 inches from the clearance line, and the volume of 25 pounds is 996 ; that is, steam at that pressure has 996 times the bulk of water. Now, if we divide the distance of A from the clearance line by 996, and multiply the quotient by each of the volumes of the other pressures indicated by similar lines, the products will be the respective lengths of the lines measured from the clearance line, the desired curve passing through their other ends. Thus, the quotient of the first, or 25-pound pressure line divided by 996 is .003313; this multiplied by 726, the volume of 25-pound pressure, gives 2.4, the length of the 25-pound pressure line ; and so on for all the rest.
Fig* 209 shows a card taken from a Corliss engine, running at a speed of about ninety revolutions per minute. On account of the slow speed and the quick admission obtained by this form of valve gear, but lit- tle compression is needed. For high speed engines, there is much more com- pression. At high speeds,
the expansion line of the _, .... ._ . . 7: — r.
Fig. 209. Diagram from Corliss
indicator card, instead of engine.
being a smooth curve like that shown in Fig. 209 , is of ten a wavy
line, due to oscillations of the spring in the indicator.
358 HANDBOOK ON ENGINEERING.
Fig. 2 JO represents what is called a stroke card. The indicator
shows us the pressure on one side of the piston for a revolution. When we calculate the horse-power from a card, we are as- suming that the back pres- sure and compression line on the other side of
" "- the piston are the same as
Fig. 210. Showing a stroke card. shown on the card. This
may or may not be the case. In calculating the total horse-power for the two ends of the cylinder, any error from this cause affect- ing the calculation for one end of the cylinder, will be nearly balanced by an opposite error in the calculations for the other end, so that the final result is practically correct. If it were not for the piston-rod making the area of one side of the piston smaller than on the other, there would be absolutely no error arising from this. The stroke card shows the pressure on opposite sides of the piston at all points of the stroke. The difference between the lines at any point is the effective push per square inch. This card is constructed by using the steam and expan- sion lines of the card from one end, and the back pressure and compression lines for the same stroke, from the card taken on the other end. In constructing diagrams for very accurate work, the ratio of the areas of the two sides of the piston have to be considered ; the pressure above the atmosphere for one side being multiplied by this ratio. It will be seen that up to the point of cut-off, the difference of pressure, or effective pres- sure, is nearly constant ; this difference grows less, due to the drop along the expansion curve, till at the point where the two lines cross, the pressure on the two sides balances. Be- yond this point, the pressure exerted to hold the piston back
HANDBOOK ON ENGINEERING.
359
Is greater than that exerted to push it ahead. The energy stored in the fly-wheel during the first part of the stroke is given out here near the end of the stroke to help the engine over the dead point.
STEAfl CHEST CARDS.
By attaching one indicator to the steam chest of an engine, and another to one end of the cylinder, it can be seen whether the pipes and ports are of sufficient size. A sloping steam line on an indicator card may be due to too small a steam pipe, or too small steam ports', or to both of these combined. This does not apply, of course, to engines using throttling governors.
Fig»2n shows the effect of too small steam pipe. When steam is admitted
Fig. 211. Steam chest card on forward stroke.
to the cylinder, there is a
drop in pressure in the
chest. This drop becomes greater in amount as the speed of the
piston increases. At cut- off, the flow of steam into the cylinder stops, then the pressure in the chest reaches boiler pressure. If there is no great drop in the line on the steam chest card, and a consid- erable drop in the steam
Fig. 212. Steam chest card on forward stroke.
too small.
line of the card, it would mean that the ports are Such a case is shown by Fig. 212.
360
HANDBOOK ON ENGINEERING.
Fig. 213. Steam chest card on forward stroke.
If there is a drop in the chest line up to cut- off, and a still greater drop in the steam line of the card, it would indicate that both the steam ports and the steam pipe were too small. Fig. 213 shows such a case.
ECCENTRIC OUT OF PLACE.
Fi g*s* 214 to 2 \1 inclusive, show cards taken from a Corliss en- gine having the eccentric out of adjustment. Similar cards would be obtained from any en- gine having all the valves moved by one eccentric. The plain slide valve and the locomotive, especially in full gear, would give similar cards for the same derangements of eccen- tric.
Fig. 2*4 was taken with Figg. 214 and 21g. Effects o( the eccentric a trifle less Of eccentric.
than 90° ahead of the crank, or about 20° behind where it belongs on this particular engine.
Fig*2J5 shows the eccentric moved too far ahead of the crank.
By comparison with Fig. 209, it will be seen that moving the eccentric back makes all the events of the stroke, such as admis- sion, release and compression and cut-off, in the case of engines without automatic cut-off governor, come later ; while moving the eccentric ahead brings these events earlier.
HANDBOOK ON ENGINEERING.
361
Figs. 2J6 and 217 are similar to Figs. 214 and 215, the only dif- ference being that eccentric is moved a greater distance out of plane.
In Fig. 2 \6 the admission is very late. Release does not occur until after the piston has started on the return stroke, the steam, until released, being com- pressed back along the ex- pansion curve. This com-
pression is always a trifle ^ 216 „„ M7>._ Eccentric below the expansion line, diagrams.
due to the fact that some of the steam has condensed in the interval between the end of the stroke and the release.
Figf. 2J7 shows too much compression and too early a release. Steam is compressed above boiler pressure in the cylinder, when the valve lifts and the steam escapes into the chest.
Cards like Figs. 214 and 215 are very common.
ECCENTRIC DIAGRAMS.
As small distances near the ends of the indicator cards repre- sent a large angular motion of the crank, the events occurring at the ends of the card are so squeezed together that it is hard to tell from the card just what any peculiarity in the lines may be due to. The eccentric rod working the valves of the engine will be moving at its greatest speed when the crank is near the centers and the piston near the ends of the stroke ; since the eccentric is about 90° ahead of the crank. If the motion of the indicator drum is taken from the eccentric rod instead of the cross-head, the card will be changed in shape, compression and release coming near the middle of the card ; these are spread out over consider- able length, the cut-off, expansion and backpressure lines coming near the ends of the card.
362
HANDBOOK ON ENGINEERING.
Figf*2J8 gives a steam card drawn, assuming that the expansion and compression lines are hyperbolic. The eccentric card for this
has been plotted, and cor- responding points marked with the same letters. The
F F
Fig. 218. Combined diagram. Fig. 219. Ordinary diagram.
compression curve, extending from F to A, is a double curve. Admission occurs at A, cut-off at B, release at (7, and compres- sion at F.
Figs* 2 19 and 220 show cards taken from an engine having tight valves and a tight piston. Corresponding points on the two cards
are lettered the same. For a cut-off later than half stroke, the steam line on the eccen- tric card doubles on itself, as shown in Figs. 220 and 222.
The peculiar bend shown by the dotted lines on com-
Fig. 220. Eccentric diagram.
pression curve of the steam card, Fig. 218, is developed on the eccentric card into a well marked flat place. Evidently this rep- resents a loss of pressure at this point, which may be attributed to one or more of three causes : pig. 221. Eccentric diagram. first, leakage by the piston ; second, leakage by the exhaust valves ; third, a rapid condensa-
HANDBOOK ON ENGINEERING. 363
tion of steam. If by leakage, it is probable that there is steam blowing by all through the stroke. Near the end of the stroke the pis- ton is moving at so slow a rate that the leakage overbalances the com- pression. It frequently happens that the pressure drops off at the
end of compression, making the Fig. 222, Eccentric diagram. upper end of the compression line
resemble an inverted letter U. If the leakage is by the piston, it will appear or may be made to appear near release, as will be explained later. The effect of compressing steam is to dry it, or, if dry already, to superheat it. While it may be possible in some cases for some of the drop here to be due to condensation, in the majority of cases leakage is the trouble.
Fig. 223 shows the effect of a bad leakage by the piston. This leakage is made evident by the appearance of the upper end of
the compression curve and by the increase in pressure along the expan- sion line just before re- lease. By referring to the stroke card, it will be seen that near this point
Fig. 223. Effects of leakage. *he pressures on the oppo-
site side of the piston are the greater, so that the leakage is now into the side on which the card is being taken. Unless compression on one side conies earlier than release on the other side, this method would fail. In most engines the valves are set so that compression does come earlier, and all four valve engines can be easily set so as to delay release on one end, and to hasten compression on the other end. In the case of a Corliss engine, this means simply
364
HANDBOOK ON ENGINEERING*
the changing the length of the rods leading from the wrist-plate to the valve arm. This change can be made with the engine run- ning. It is possible that a card like Fig. 223 might be obtained from a four-valve engine having a leaky steam valve on one end and a leaky exhaust valve on the other end.
Fig* 224 represents the head end and the crank end cards taken from a plain slide valve engine. The valve has equal steam lap and equal exhaust lap. The only trouble in this case
Fig. 224. Effects of changing length of ralye stem.
is that the valve spindle is too short. Shortening the valve spin- dle decreases the outside lap of the valve and increases the inside lap for the head end side, and increases the outside lap and de- creases the inside lap for the crank end side. As will be seen by the cards, the head end has the cut-off lengthened, the release delayed, and the compression hastened; the crank-end has the cut-off shortened, the release hastened, and the compression de- layed. If the valve spindle were too long the cards shown would be interchanged, the crank end card being the one marked head end.
THE STEAM ENGINE INDICATOR.
Benefits derived and information ascertained from its use* — The benefits derived, and the information ascertained from the use of the steam-engine indicator are varied and important.
HANDBOOK ON ENGINEERING. 365
The office of the indicator is to furnish a diagram of the action of the steam in the cylinder of an engine during one or more revolutions of the crank, from which is deduced the follow- ing data : Initial pressure in cylinder ; piston stroke to cut-off ; reduction of pressure from commencement of piston stroke to cut- off ; piston stroke to release ; terminal pressure ; gain in econ- omy due expansion ; counter pressure, if engine is worked non-condensing ; vacuum as realized in the cylinder, if engine is worked condensing ; piston stroke to exhaust closure, usually reckoned from zero point of stroke ; value of cushion ; effect of lead and mean effective pressure on the piston during complete stroke. The indicator diagram, when taken in connection with the mean area and stroke of piston and revolution of crank for a given length of time, enables us to ascertain the power de- veloped by engine ; and when taken in connection with the mean area of piston, piston speed and ratio of cylinder clearance, enables us to ascertain the steam accounted for by the indicator.
The mean power developed by engine compared with the steam delivered by boilers, furnishes cost of power in steam, and when compared with the coal, furnishes cost of the power in fuel.
The diagram also enables us to determine with precision the size of steam and exhaust ports necessary, under given conditions, to equalize the valve functions ; to measure the loss of pressure between boiler and engine ; to measure the loss of vacuum be- tween condenser and cylinder ; to determine leaks into and out of the cylinder ; to determine relative effects of jacketed and un jacketed cylinders ; and to determine effects of expansion in one cylinder, and in two or more cylinders.
TO TAKE A DIAGRAM.
Connecting cord* — The indicator should be connected to the engine cross-head by as short a length of cord as possible. Cord
366 HANDBOOK ON ENGINEERING.
having very little stretch, such as accompanies the instrument, should be used ; and in cases of very long lengths, wire should be used. The short piece of cord connected with the indicator is furnished with a hook ; and at the end of the cord, connected with the engine, a running loop can be made by means of the small plate sent with each instrument ; by which the cord can be adjusted to the proper length, and lengthened or shortened as required.
Selecting a spring* — It is not advisable to use too light a spring for the pressure. Two inches are sufficient for the height of diagram, and the instrument will be less liable to damage if the proper spring is used. The gauge pressure divided by 2 will give the scale of spring to give a diagram two inches high at that pressure.
To attach a card* — This may be done in a variety of ways, either by passing the ends of it under the spring clips, or by folding one end under the left clip, and bringing the other end around under the right; but, whatever method is applied, care should be taken to have the card rest smoothly and evenly on the paper drum. Now attach the cord from the reducing motion to the engine ; but be certain the cord is of the proper length, so as to prevent paper drum from striking the inner stop in drum movement on either end of the stroke.
Tension of drum spring* — The tension of the drum spring should be adjusted according to the speed of the engine ; in- creasing for quick running, and loosening for slower speeds.
The steam should not be allowed into the indicator until it has first been allowed to escape through the relief on side of cock, to see if is clean and dry. If clean and dry, allow it into the indi- cator, and allow piston to play up and down freely.
After taking diagram, turn the handle of cock to a horizontal position, so as to shut off steam from piston, and apply pencil to the paper to take the atmospheric line.
HANDBOOK ON ENGINEERING. 367
In applying pencil to the card, always use the horn-handle screw, to regulate pressure of pencil upon paper to produce as fine a line as possible. After the atmospheric line is taken, turn on steam, and press the pencil against card during one revolution.
When the load is varying, and the average horse-power re- quired, it is better to allow the pencil to remain during a number of revolutions, and to take the mean effective pressure from the average of the several diagrams.
Fig. 225* Diagram from a Russell engine.
Fig. 225 was taken from a Russell engine 13" x 20", running 205 revolutions per minute, boiler pressure 98 Ibs., scale of spring 60 Ibs. Duty, electric lighting.
After sufficient number of diagrams have been taken, remove the piston, spring, etc., from the indicator, while it is still upon the cylinder ; allow the steam to blow for a moment through the indicator cylinder ; and then turn attention to the piston, spring, and all movable parts, which may be thoroughly wiped, oiled and cleaned. Particular attention should be paid to the springs, as their accuracy will be impaired if they are allowed to rust ; and great care should be exercised that no grit or substance be intro- duced to cut the cylinder, or scratch the piston. Be careful
368
HANDBOOK ON ENGINEERING.
always not to bend the steel bars or rods. The heat of the steam blown through the cylinder of the indicator will be found to have dried it perfectly, and the instrument may be put together with the assurance that it is all ready for use when required. It is a saving of time to keep indicator in order. Any engineer can easily perform the operation without further instruction.
Fig. 226. Another diagram from Russell engine. Fig. 226 was taken from a Russell engine 16" x 24", running 157 revolutions per minute, boiler pressure 70 Ibs., scale of spring 40 Ibs. Duty, flouring mill.
Fig. 227. Friction load. Fig. 228. Fail load.
HARRISBURG IDEAL SIMPLE SINGLE VALVE ENGINE.
HANDBOOK ON ENGINEERING.
369
Fig. 229. Graduated load. Fig. 230. Extreme load variation. HARRISBURG IDEAL SIMPLE SINGLE VALVE ENGINES
Fig. 231. High pressure Fig. 232. Low pressure
diagrams. diagrams.
HARRISBURG IDEAL COMPOUND SINGLE VALVE ENGINE.
Fig. 233. Friction diagrams. Fig. 234. Full load diagrams.
HARRISBURG STANDARD SIMPLE SINGLE VALVE ENGINE.
370
HANDBOOK ON ENGINEERING.
Fig. 236. Friction load. Fig. 236. Full load.
HARRJSBURG STANDARD SIMPLE FOUR-VALVE ENGINE.
Fig. 237. High pressure diagrams.
Fig. 238. Low pressure diagrams.
HARRISBUKG STANDARD COMPOUND FOUR-VALVE ENGINE.
The indicator diagrams from Fig. 227 to 238 were taken from the Harrisburg Ideal and Standard engines. An engineer will see from these cards the kind of card he should get from a high speed engine of this class.
Fig* 239 is from a Frick Corliss engine, driving a Frick com- pressor : —
Steam Cylinder 19"x28".
Steam . .. 95 Ibs.
Revs. . ... . . . • . . • 58
Cond. Press. . . . . . . . . 164 Ibs.
Back Press. 27 Ibs.
HANDBOOK ON ENGINEERING.
371
Engine, 19" x 28". Steam, 95 Ibs. Revs. 58 Ibs. Cond. Press.. 164 Ibs. Back Press.. 27 Ibs:
Fig. 239. Diagram from 19" x 28" Eclipse Corliss.
INDICATOR DIAGRAMS FRONT 50-TON "ECLIPSE" MACHINE.
JR. Hand Ptimp* 12*" x 28". Scale. 120 //*.
Fig. 240. Diagram from right hand Eclipse pump.
Fig, 240 is R. Hand Pump, 12£" x 26", Scale, 120 Ibs,
372
HANDBOOK ON ENGINEERING.
\
L.- Hand Picmp.
12J" x 28". Scale, J20M*.
Fig. 241. Diagram from left hand Eclipse pump. Fig* 241 is L. Hand Pump. 27|" x 28". Scale, 120 Ibs
Engine, 80" x 36" Steam, 75 /fo. Revs. 44
Conrf. /VMS., 162 Back Press.,
Fig. 242. Diagram from 30" x 36" Eclipse machine.
Figs* 242 to 244, are diagrams from a 100-ton " Eclipse " machine.
HANDBOOK ON ENGINEERING. 373
INDICATOR DIAGRAMS FROM 100-TON "ECLIPSE" MACHINE.
Fig. 243. Diagram from right hand pump.
Fig. 244. Diagram from left hand pump.
374
HANDBOOK ON ENGINEERING.
Fig. 245. Diagrams from a Ball engine.
HANDBOOK ON ENGINEERING.
It will be interesting to note that when the eccentric is simply moved forward or backward around the shaft by the action of the governor, all the events of the stroke — admission, release, cut-off and compression : — will be hastened or retarded together ; but if the eccentric be so designed that the governor will shift it across the shaft instead of around it, the admission and release will be effected differently, and in the opposite direction from the cut-off and compression. If, for example, the cut-off is made to occur earlier in the stroke, the compression will occur earlier /also, but the admission and release will occur later instead of earlier. By combining the two movements of the eccentric and having the governor move it partly around and partly across the shaft, it is possible to keep the admission and release nearly constant, while the cut-off and compression vary. This result is attained to a certain extent in the best single-valve engines. Besides ttiese two types, there are numerous other styles of engines in wliich the point of cut-off is varied automatically. Instead of a shaft gov- ernor with a shifting eccentric, a weighted pendulum governor is sometimes employed to operate the link, or radius rod of some one of the various link motions. Sometimes there are separate admission and exhaust valves, the former being under the con- trol of a shaft governor, and the latter operated by a fixed eccen- tric, so that the points of admission and cut-off only are varied, while the points of release and compression, which depend upon the exfiaust valve, remain fixed. There are a great many modifi- cations of the Corliss engine, as originally constructed by Geo. H. Corliss, and there are many engines which, while not re- sembling the Corliss engine, have some arrangement whereby the cut-off valves are tripped.
On pages 374 and 376 is a collection of diagrams, which illustrate very nicely the peculiarities and difference in the action of throttling and automatic engines. The four diagrams on page 374 were taken from a Ball automatic, in an electric light
376
HANDBOOK ON ENGINEERING.
Fig. 246. Diagrams from a Dickson throttling engine.
HANDBOOK ON ENGINEERING. 377
station. The first diagram was taken late in the afternoon when the engine was started and before any load was thrown on to the machine, and the three succeeding cards were taken at intervals later in the evening as the number of lights increased and the load became heavier. Two or three important points are to be noticed in connection with these diagrams. First, the initial pressure of the steam at the point of admission is very nearly the same in all four cards, the slight variations being due chiefly to a variation in the boiler pressure. Second, the length of the cut-off increases with the load. The compression also becomes later as the cut-off lengthens, and while there is also a change in the points of admission and release, it is not as marked as the changes in cut- off and compression, for reasons that have already been explained.
Taking the cards on page 376, we have four excellent examples of the action of a throttling engine. These cards are from a Dickson engine, taken at the same station and under the same conditions as the Ball engine cards, with the exception that in this case both head and crank-end diagrams were taken on the same cards, while only the head end diagrams from the Ball engine are shown. The two sets of diagrams are well adapted for comparison, because both engines are of the single-valve typej with the valve moved by one eccentric.
The points to be noted are, first, that the points of cut-off are the same, namely at about J stroke, in all the throttling cards, and second, that the power of the engine is increased by the action of the governor in opening a throttle valve wider, allowing steam to enter the cylinder at higher pressure.
It was stated at the outset that automatic regulation is the most approved method for regulating the speed of steam engines at the present time. It is generally believed and it is probably true, that automatic engines give better economy than throttling engines and that they regulate a little more closely. It will readily be seen that when the governor of the automatic engine
378 HANDBOOK ON ENGINEERING.
changes position, it measures out just the quantity of steam that will be required to keep the engine within the speed limits during the following stroke. The effect of this regulation, moreover, is felt at one point in the stroke only — the point of cut-off — so that any change in the governor up to the time when the piston nears the point of cut-off will produce an immediate change in the quantity of steam admitted. In the throttling engine, on the other hand, the regulation is effected during the whole stroke up to the point of cut-off, and the full effect of any change of the gov- ernor cannot be felt until the next stroke. With regard to the relative economy of the two types, it should be kept in mind that the throttling engine is generally of cheap construction, has large clearance, a single, unbalanced slide-valve that does duty for both entering and exhaust steam and aside from the throttling feature, is inferior to the average automatic engine. It is reasonable to suppose, therefore, that at least a part of the large steam con- sumption generally attributed to the throttling engine is due to its inferior design and construction and not to its method of governing.
For example, take the case of the Ball and the Dickson engines, from which cards are shown. They both have a single slide- valve, but the former runs at higher speed than the latter and its valve is balanced, so that for these reasons it would be expected to be a little more economical. We should not expect, however, that a test would show any decided superiority that could be attributed to the method of governing. If we were to compare the average throttling engine with the most approved type of automatic engine, like the Corliss, we should find that the effi- ciency of the latter was much higher. The gain, however, would be due to a large extent to the small clearance spaces, separate steam and exhaust valves, and other important features of the Corliss engine, rather than to its automatic cut-off. It is not the purpose to discuss here why these features give improved
HANDBOOK ON ENGINEERING. 379
economy over the single valve, but simply call attention to the fact that they exert an important influence. The exact influence, which the throttling or automatic features exert apart from the general constructive features of the engine is hard to determine. It is known that high-pressure steam is more economical to use than low pressure steam and the automatic engine, which pre- serves nearly the boiler pressure up to the point of cut-off, gains on this account. On the other hand, it is known that the most economical point of cut-off for a non-condensing engine is about one-third stroke, and when it becomes very much less than this there is a serious drop in the economy. A very short cut-off with high-pressure steam produces so great a variation in the temperature during one stroke of the piston that the cylinder condensation becomes excessive. For very light loads, therefore, it would be better to throttle the steam than to shorten the cut-off. It is necessary for all engines to have a reserve of power and hence the cut-off of throttling engines must come late in the stroke. If it were early in the stroke, there would not be enough reserve power with the reduction in the pressure of the steam that is necessary with this type. The late cut-off produces poor economy when the load is heavy, because there will then be a high terminal pressure, and a large amount of heat, corresponding to this pressure, will be thrown away. A throttling engine there- fore, may be expected to do better at light loads than at heavy ones, and in fact, may do a little better at light loads than the automatic engine. If a throttling engine could be run so as not to vary much from its most economical load, and could be de- signed to have the good features of the best automatic engines, with the cut-off at an earlier period in the stroke, it would prob- ably be nearly or quite as well as the automatic engine. Under the conditions that they have to run, however, the automatic engine will keep the lead, although, as explained above, its superiority is not due entirely to the automatic feature.
380 HANDBOOK OF ENGINEERING.
CHAPTER XV. ECONOMY AND OPERATION OF ENGINES.
Engineers over the country have been discussing whether or not more steam is used when an engine is made to run faster without changing either the cut-off or the back pressure. Some, strange as it may seem, have actually held to the opinion that, since the cut- off is not changed, no more steam is used, and hence, if it were possible to make an engine run faster without changing the cut-off, it would be doing more work than before without any increase in the consumption of steam. Of course, this is wrong. The speed of an engine, almost any engine, may easily be increased without changing the cut-off, and when this is done, the engine will do more work and will use more steam. It is utterly impossible to get something for nothing out of a steam-engine, or out of any engine or appliance. The only way in which a steam-engine can be made to do more work without using more steam is to increase its efficiency. And when everything else is kept the same and the speed only of an engine increased, the efficiency is very slightly increased. The condensation is decreased with an increase of speed, but the decrease would be so slight for most cases that it would hardly be worth considering. When an engine is cutting off at a certain part of the stroke, it uses at every stroke a cer- tain weight of steam which depends upon the initial pressure of the steam, clearance volume of the engine and the point of cut- off. If the engine makes 400 strokes per minute (200 revolu- tions, if a double acting engine) the weight of steam used will be
HANDBOOK ON ENGINEERING.
400 times the weight used in one stroke ; but if the engine be made to make 500 strokes per minute, the weight of steam used per minute will be, neglecting the small difference in condensa- tion, 500 times the weight used in one stroke.
HOW TO INCREASE THE SPEED, OR INCREASE THE POWER OF A CORLISS ENGINE.
There are three ways in which this can be done. Take, for example, a 24" x 48" simple Corliss engine making 70 revolu- tions per minute, the boiler gauge pressure 80 Ibs. per square inch, one-quarter cut-off, or cut-off 12 inches from the beginning of the stroke ; the mean effective pressure, say about 42 Ibs. per sq. in., the governor pulley on the main shaft 10 inches in diam- eter, the pulley on the governor shaft 7 in. in diameter, and the friction of engine, cylinder clearance, condensation, etc., left entirely out of the question. It is desired to increase the speed of this engine to 80 revolutions per minute, and in this manner increase its horse-power.
First method* — Regardless of piston rod, the area of the pis- ton is 452.4 square inches, nearly. The piston speed of this engine is 560 feet per minute, and its horse-power 322, nearly.
452.4x42x560
Thus: Qo/wm ~ =322. So that the horse-power of this
ooUUU
engine at 70 revolutions per minute is 322, nearly, and this is what the manufacturer's catalogue gives. Now, in order to get 80 revolutions per minute, take the 7-inch pulley off the governor shaft, and put in its place an 8-inch pulley. Thus : 70 : 80 : : 7:8. Then, the governor balls will revolve in the same relative • plane that they did before, and the cut-off will remain the same ; that is, at one-quarter, or 12 in. of the stroke. Thus, 7: 10:: 70 : 100. And 8 : 10 : : 80 : 100. So the governor balls make 100 revolutions per minute, both before and after making the change.
382 HANDBOOK ON ENGINEERING.
Now, with the engine speeded up to 80 revolutions per minute, we get 46 more horse-power. Thus: Piston speed equals 640
452.4x42x640 feet per minute. Then, — SSOCK) - = ^^ horse-power,
nearly. And 368 minus 322 =46. Now, it would appear that we are getting 46 horse-power more for nothing, but such is not
452.4x12x2x70 the case. For, - VIZR -- =439.8 + , or nearly 440
cubic ft. of steam per minute, at 80 Ibs. boiler pressure, are
452.4x12x2x80 required to develop 322 horse-power. And,
= 502.6+ or nearly 503 cubic ft. of steam per minute, at 80 Ibs. boiler pressure, are required to develop 368 horse-power. Then, 503 minus 440 = 63 cubic feet more of steam at 80 Ibs. boiler pressure, which means more water evaporated per minute and more coal burned per hour.
Second method* — Retain the same engine speed and the same cut-off, but increase the boiler pressure from 80 to 90 Ibs. Then 80: 90: : 42 : 47 + , call it 48 Ibs. mean effective pressure.
452.4x48x560 Then, - SSOOQ - == ^^ horse-power, nearly, the same as
before, and as given in the manufacturer's catalogue. We are now using 440 cubic feet of steam per minute at 90 Ibs. pressure, with an increase of 6 Ibs. M. E. P. ; consequently, more coal per hour must be burned.
Third method* — Retain the same boiler pressure, that is 80 Ibs., and weight the governor so as to make the balls revolve in a lower plane in order to give a later cut-off. Thus, 322 : 368 :: J:f. That is, the cut-off must take place at about % of the stroke instead of at J. Then, J:f::42:48. That is the M. E. P. will be 48 Ibs. per square inch with a cut-off at % of the
452.4x48x560 stroke. Then, - 33000 - == ^68 horse-power, the same as
HANDBOOK ON ENGINEERING. 383
before. But, % of 48 = 13f , or 13.71 inches nearly, so that, instead of cutting off at 12 inches with 80 Ibs. boiler pressure, we are cutting off at 13.71 inches and using 63 cubic feet more
452.4 x 13. 71x 2x70
steam per minute. Thus, = 503, nearly.
1728
And, 503 minus 440=63, that is, we must use 63 cubic feet more of steam per minute at 80 Ibs. boiler pressure, in order to get 46 more horse-power, which means the evaporation of more water per minute, and the burning of more coal per hour.
HOW TO INCREASE THE HORSE-POWER OF AN ENGINE HAVING A THROTTLING GOVERNOR.
There are three ways in which this can be done, also. We will take, for example, a plain slide-valve engine 10 x 16 inches, making 150 re volutions per minute, with T9^ cut-off, and M. E. P. say 31£ Ibs. per square inch, with a boiler pressure of 60 Ibs. by gauge. The governor pulley on the main shaft 6 inches in diameter, and the pulley on the governor shaft 4 inches in diameter. The horse-power of this engine is about 30.
Thus, 16x2 = 2f ft., and 150 x 2| = 400 ft., the piston speed. \a
10 x 10 x. 7854x31.5x400 = horse_power, nearly.
33000
It is now desired to run the engine at 180 revolutions per minute in order to develop 6 horse-power more. In order to obtain these results, the governor pulley must be enlarged, so as to make the governor balls revolve in the same plane at 180 revo- lutions per minute, that they now do at 150 revolutions. Thus, 4:6:: 150: 225, that is, the governor balls are now making 225 revolutions per minute. And 150 : 180 : : 4 : 4.8. Con- sequently, the governor pulley must be increased to 4.8 inches in
384 HANDBOOK ON ENGINEERING.
diameter. Then, 4.8 : 6 : : 180 : 225, that is, the governor balls, after the change, making the same number of revolutions as before. At 18J3 revolutions per minute, the piston speed is 480
feet per minute. Thus, = 21. And, 180 x 2| = 480.
12
Then, 78>54^3Q1^x480^ 36 horse-power, nearly. It might
seem from the above that we are getting 6 horse-power more for nothing ; but such is not the case. For, cutting off at T9F is equivalent to cutting off at 9 inches of the stroke.
™ 78.54x9x2x150
Then, _ _ _ = 123 cubic ft., nearly.
1728
78.54x9x2x180
— — 147 cubic feet, nearly. And,
1728
147 minus 123 — 24. So that for 6 horse-power more, we are using 24 cubic feet more of steam per minute, at 31.5 Ibs. M. E. P. , which means more water evaporated per minute and more coal burned per hour.
If the boiler pressure may be safely increased, we can get 6 horse-power more out of the engine without increasing its speed, by running the boiler pressure up to 75 Ibs. by gauge. Thus 75 Ibs. boiler pressure would give about 37.8 Ibs. M. E. P. with T9^
cut-off. Then, ^8. 54 x 37.8 x 400 = 36 horse_power nearly.
33000
In this case no change should be made in the governor, nor in the speed of the engine. We can also get 6 horse-power more out of this engine by cutting off later, say at |, in order to get 37.8 Ibs. M. E. P. But a later cut-off is not desirable, because it is not economical of steam, and besides, it would require a new valve, new eccentric, or a change in the length of a rocker arm, if not a change of the valve-seat, because the travel of the valve would have to be increased.
HANDBOOK ON ENGINEERING. 385
HOW TO INCREASE THE HORSE-POWER OF AN ENGINE HAVING A SHAFT GOVERNOR.
Suppose it is desired to increase the speed of the engine from 250 to 275 revolutions per minute, cutting off at i stroke. In this case the governor springs should be so adjusted that the throw of the eccentric will be the same at 275 revolutions that it was at 250 revolutions. This will require an increased consumption of steam per minute at the same initial cylinder pressure as before making the change, consequently more fuel will be required. If the speed of the engine is not to be changed, an increase of the horse-power may be obtained by increasing the initial cylinder pressure, if the condition of the boiler will so permit. Or, the initial cylinder pressure may remain unchanged and the governor springs and levers so adjusted as to give a later cut-off, say at |^ or T7^ of the stroke, or whatever may be required to offset the increased per- manent load, the speed of the engine remaining unchanged. Any one of the changes above described would necessitate an increased consumption of fuel.
HOW TO LINE THE ENGINE WITH A SHAFT PLACED AT A HIGHER OR A LOWER LEVEL.
We will suppose the latter shaft not yet in place, but to be represented by a line tightly drawn. From two points as far apart as practicable, drop plumb lines nearly, but not quite, touching this line. Then by these strain another line parallel with the first, and at the same level as the center line of the engine, and at right angles with this stretch another represent- ing this center line, and extend both each way to permanent walls on which their terminations, when finally located, should be care- fully marked, so they can at any time be reset. The problem is to get the latter line exactly at right angles with the former. Everything depends upon the accuracy with which this right
25
386
HANDBOOK ON ENGINEERING.
angle is determined. It is done by the method of right-angle triangles. There are two ways of applying this method. In the first, one end of a measuring line is attached to some point of line No. 1, and its other end is taken successively to points on line No. 2 on opposite sides of the intersection, as illustrated in the following figure, in which A B is a portion of line No. 1, and C D of line No. 2, the direction of which is to be determined,, B F and B G are the same measuring line fixed at B, and applied to the line C D successively at the points F and G. The dis-
Fig. 247. Lining engine with line shafting.
tances B F and B G being, therefore, the same, when E F is equal to E G, the lines A B and C D are at right angles with each other. In the second, application is made of the law that the square of the hypothenuse of a right-angle triangle is equal to the sum of the squares of the other two sides. Thus 32 -j- 42 = 52. So if the above figure E B = 4, E F=3, and B F=6, the angle at E is a right-angle. Any unit of measure may be used, a foot is generally the convenient one ; so any multiple of these numbers may be taken; as, for example, 6, 8 and 10. Respecting the comparative advantages of these two ways, the situation will of ten determine which is to be preferred. In the former, the diagonal
HANDBOOK ON ENGINEERING. 387
being the same line, fixed at B and brought successively to the points F and 6?, its length is immaterial, though generally the longer the better ; and the only point to be determined is the equality of E F and E G, which may be compared with each other by marks on a rod. In the latter, the proportionate lengths, 3, 4 and 5, or their multiples, must be exactly measured. It is better adapted to places where a floor is laid and the meas- urements can be transferred by trammels. The result should be verified by repeating the operation on the opposite side of the intersection at E, and when so verified we have, in fact, the first process, without the additional and unnecessary trouble of deter- mining the relative lengths of the lines. Care should be taken when a measuring line is used, to avoid errors from its elasticity „ On this account, a rod is often employed. Points on the lines are best marked by tying on a white thread.
HOW TO LINE THE ENGINE WITH A SHAFT TO WHICH IT IS TO BE COUPLED DIRECT.
In this case, it is supposed that the engine bed and the bear- ings for the shaft are already approximately in position. They are leveled by a parallel straight edge and a spirit level. To line them horizontally, a line must be run through the whole series of bearings and continued to a permanent wall at each end, and its terminating points, when determined, carefully marked, as already directed. A piece of wood is tightly set in each end of each bearing and the surfaces of these are painted white or chalked. Then the middle of each piece being found by the compasses, two fine lines are drawn across it, equally distant from the middle, and having between them a space a little wider than the thickness of the line. The line being tightened, nearly touching the blocks, or, if long, having its sag supported by them, the two marks on each block must be seen, one on each side of the line, with the line of white between.
388 HANDBOOK ON ENGINEERING.
HOW TO SET A SLIDE VALVE IN A HURRY.
Open the cylinder cocks; then open the throttle slightly, so as to admit a small amount of steam to the steam-chest. Roll the eccentric forward in the direction the engine runs, until steam escapes from the cylinder cock at the end where the valve should begin to open. Now screw the eccentric fast to the shaft. Roll the crank to the next center and ascertain if steam escapes at the same point, at the opposite end of the cylinder. If so, ring the bell and go ahead. The valve gear can be run until an oppor- tunity occurs to remove cover from steam-chest and examine the valve.
DO YOU DO THESE THINGS?
A writer in a magazine asks and answers the following pertinent questions : —
Do you take a squirt-can in one hand and project a stream of oil as far as you can throw it, in order to save going to the oil hole itself ?
If you do, don't do it any more ; willful waste is downright robbery.
Do you use an oil can at all for oiling, except on emergency, or for the moment ?
If you do, don't do it any more, for much better lubrication can be had by automatic apparatus.
Do you keep an old tin coffee-pot full of suet on the steam- chest, and every time you have nothing else to do, pour a dipper- f ul into the steam-chest ?
If you do, stop it and get a sight-feed cup, which will save you the labor of slushing the cylinder and save the cylinder and valve-seats, the piston and follower, and all other places touched by the grease.
HANDBOOK ON ENGINEERING. 389
Do you feed the boiler until the water is out of sight in the glass, then shut off the feed, put in a big fire and sit down in a dark corner with a four-horse brier pipe and smoke, until you happen to think that maybe- the water is low?
If you do these things you should notify the coroner that some day his services will be needed, but it is better to cease the prac- tice mentioned before the coroner comes.
Do you stop leaks about the boiler as fast as they occur, or do you wait until the places sound like a snake's den before you stir?
If you do, you waste heat, which is the same word as money, only differently spelled. Every jet of hot water leaking from a steam boiler is just so much money thrown away, and if it was your money you would be bankrupt in a short time, in some boiler rooms.
Do you take a screw wrench and yank away at a bolt or nut under steam pressure?
If you do, there will come a time, sooner or later, when you will do so once too often, and either kill yourself or some one else. Bolts and nuts are liable to strip or break if tampered with under pressure, and they never tell any one beforehand when they are going to do it.
Do you attempt to stop pounding in the engine by laying for the crank-pin as it comes round, and trying to hit the key once in a while ?
If you do, ask the strap and neck of the connecting-rod how he likes it, when you don't hit the key and do hit the oil cup?
Do you pack the piston by taking it out of the cylinder, lay- ing it on the floor, setting out the rings, and then when the piston will not go into the cylinder, try to batter it in with a four-foot stick of cord wood?
If you do, you should reform, and pack the piston in the cylinder where it belongs, being sure to get it central by meas- uring from the lathe center in the end of the piston rod.
390
HANDBOOK ON ENGINEERING.
Do you put a new turn of packing on top of the old, hard- burned stuff when the piston rod leaks steam ?
If you do, you will have a scored piston rod and broken gland bolts some day. Packing under heat and pressure gets so hard that it cuts like a file when left in the stuffing-box, and as one begins to leak all the old stuff should be pulled out and new put in its place.
THE TRAVEL OF A SLIDE VALVE.
Figs. 248 and 249. The throw of the eccentric.
The travel of a slide valve is found as follows : The maximum port opening at the head end, plus the maximum port opening at the crank end, plus the lap at the head end, plus the lap at the crank end. Therefore, If" + If" + f" + f"=4J", the re- quired travel of valve. Incidentally, it may be well to mention that the travel of a valve may also be obtained from the eccentric, by subtracting the thin part of the eccentric from the thick part as per Fig. 248, or again, by taking twice the distance between the center of rotation and center of the eccentric. This distance on the eccentric is the end valve travel, and is termed the c G throw ' ' of the eccentric. In the above question, the travel may also be
HANDBOOK ON ENGINEERING.
391
found by the aid of the diagram, Fig. 249, which is explained as follows: From the center^., with a radius of £ inch (lap), describe a circle BCD. From any point in the circumference, say B, lay off the distance B E equal to the maximum port open- ing, If" ; from the center A, with a radius A E, describe the circle E F G; the diameter of the circle E F G is equal to the travel of the valve, which is 4J". Let the reader try this with another set of figures, to prove the correctness of the diagram.
LOSS OF HEAT FROM UNCOVERED STEAM PIPES.
The following table shows the loss of heat through naked sfceam pipes, wrought iron, of standard sizes. The best covering for a steam pipe is hair felt from one to two inches thick, depending on the diameter of the pipe, say one inch thick for pipe from 1 to 4 inches in diameter, and two inches or more for larger pipes. Such covering will save at least 96 per cent. Cheaper coverings will save from 75 to 90 per cent. The chief value of the table is as an aid in estimating the saving that can be made by covering the pipe. The money loss by naked pipe being known, the sav- ing can be estimated and the cost of the covering will decide its value as an investment.
TABLE OF MONEY LOSS FROM 100 FEET OF NAKED STEAM PIPE, FOB ONE YEAR OF 3000 WORKING HOURS. .
|
•335. |
STEAM PRESSURES. |
|||||
|
||t| |
50 |
60 |
70 |
80 |
90 |
100 |
|
fc-oo.2 |
Ibs. |
Ibs. |
Ibs. |
Ibs. |
Ibs. |
Ibs. |
|
1 |
$13.15 |
$13.70 |
$14.20 |
$14.66 |
$15.08 |
$15.47 |
|
H |
16.58 |
17.29 |
, 17.92 |
18.49 |
19.02 |
19.51 |
|
\L |
18.98 |
19.78 |
20.51 |
21.17 |
21.77 |
22.33 |
|
2 |
23.72 |
24.73 |
25.63 |
26.45 |
27.21 |
27.91 |
|
2£ |
28.72 |
29.94 |
31.03 |
32.03 |
32.94 |
33.79 |
|
3 |
34.97 |
36.45 |
37.78 |
38.99 |
40.10 |
41.14 |
|
4 |
44.93 |
46.86 |
48.57 |
50.13 |
51.56 |
52.89 |
|
5 |
55.57 |
57.92 |
60.04 |
61.96 |
63.73 |
65.38 |
|
6 |
66.27 |
69.08 |
71.60 |
73.89 |
76.01 |
77.96 |
392 HANDBOOK ON ENGINEERING.
RULES AND PROBLEMS APPERTAINING TO THE STEAM
ENGINE.
To find the H. P. of a simple non-condensing engine : —
Rule* — Multiply the net area of the piston in square inches, by the mean effective pressure in pounds per square inch, and by the velocity of the piston in feet per minute, and divide the last product by 33,000. The quotient will be the gross H. P. Sub- tract from this from ten to twenty per cent for friction in the engine itself, and the remainder will be the delivered H. P.
Example* — The area of the piston is 500 sqr. ins. Half the area of the piston-rod is 5 sqr. ins. The M. E. P. is 50 Ibs. per sqr. in. The stroke is 3 feet, and the revolutions per minute 125. The friction is 10 per cent. What is the delivered H. P. of the engine? Ans. 506.25 H. P.
Operation* — 3 ft. X 2 = 6 ft. twice the stroke.
Then, 500 — 5 = 495 sqr0 ins. net area of piston.
And, 125 X 6 = 750 ft. the piston speed per minute.
And, =^562.5.
33,000
Then, 562.5 X -90 = 506.25. The delivered H. P.
For a condensing engine : — Add the vacuum to the M. E. P. and proceed as above.
The M. E. P. is the average pressure in the cylinder, less the back pressure.
To find the H. P. of a compound noncondensing engine : —
The usual method of calculating the H. P. of a multiple cyl- inder engine is to assume that all the work is done in the low pressure cylinder alone, and that such a M. E. P. is obtained in that cylinder as will give the same H. P. as is given by the whole engine.
Rule* — Find the ratio of areas of the high and low pressure cylinders, — when of the same stroke, as they usually are, — and
HANDBOOK ON ENGINEERING. 393
multiply it by the number of expansions in the high pressure cylinder, for the total number of expansions in both cylinders. Find the hyperbolic logarithm corresponding to this result and add 1 to it, and divide the sum by the total number of expan- sions. Multiply this result by the absolute steam pressure, and subtract the back pressure. Subtract again the loss in pressure between cylinders, and the remainder will be the M. E. P. Then multiply the net area of the low pressure cylinder by this M. E. P. and by the piston speed in feet per minute and divide by 33,000. Deduct the friction in the engine itself and the remainder will be the delivered H. P.
Example* — Given a tandem compound engine with cylinders 20" and 32" diameter, and 4 feet stroke, making 75 revolutions per minute, boiler gauge pressure 125 Ibs. per sqr. in., J cut-off in high pressure cylinder, back pressure 15J Ibs. per sqr. in., drop in pressure between cylinders 15 per cent, and friction in engine 10 per cent. What is the H. P. delivered of this engine? Ans. 338.4 H. P.
Operation* — Neglecting the areas of the piston rods, we have : —
20 X 20 X .7854 — 314.16 sqr. ins. area of high pressure cylinder.
And, 32 X 32 x .7854 = 804,2 sqr. ins. area of low pressure cylinder.
Then, 804.2 -f- 314.16 =2.56 = the ratio between cylinders.
And, 2.56 X 4 = 10.24 = the total number of expansions. The hyperbolic logarithm of 10.24 = 2.328. (Seetableonp. 892.)
And, 1 + 2.328 = 3.328.
Then, 3.328 ~ 10.24 = .325.
Also, 125 + 15 = 140 Ibs., the absolute pressure.
And, .325 X 140 =45.5 Ibs., forward pressure.
And, 45.5 — 15.25 = 30.25 Ibs., the M. E. P.
.
394 HANDBOOK ON ENGINEERING.
And, 30.25 X .85^25.7 Ibs. =the M. E. P. less the 44 drop."
Then, 804.2 X25.7X8X75_ p>
33,000
And, 376 X .90 = 338.4 H. P. delivered.
For a compound condensing engine, proceed as above, except that the condenser pressure, due to impaired vacuum, only should be subtracted from the forward pressure.
To find the linear expansion of a wrought-iron pipe or bar : —
Rule, — Multiply the length of the pipe or bar in indies by the increase in temperature, and by the constant number .0007, and divide the last product by 100.
Example* — Given a 6-inch wrought-iron pipe 75 feet long. Steam pressure 150 Ibs. by gauge. Temperature of pipe when put up 60 degs. Fah. What is its linear expansion? Ans. 2 ins. nearly.
Operation* — The diameter of the pipe is immaterial.
Then, 150 Ibs. pressure = 366 degs.
And, 366 — 60 •= 306 degs.
Also, 75 X 12 = 900 inches length of pipe.
Then, ' ^1.9278 inch.
For copper, use the constant number .0009 ; for brass, use .00107 ; for fire-brick, use .0003, and proceed as above.
To find the proper diameter of steam pipe for an engine : —
The velocity of steam flowing to an engine should not exceed 6,000 feet per minute.
Rule. — Multiply the area of the~piston in square inches by the piston speed in feet per minute, and divide by 6,000 ; and divide again by .7854, and extract the square root for the diameter of the pipe and take the nearest commercial size.
Example* — Given a 20" X 48" Corliss engine making 72 revo- lutions per minute. What should be the diameter of its steam pipe? Ans. 6 inches.
HANDBOOK ON ENGINEERING. 395
Operation.— 20 X 20 X .7854 =314.16 sqr. ins. And, 48" X 2 X 72 =576 ft. the piston speed.
And> 314.16 X 576 =30>15> 6,000
Then, . 1^. = 6.1". Take 6" pipe.
To find the water consumption of a steam engine: — The most reliable method for determining this, is to make an evaporation test, that is, to measure the water fed to the boiler in a given time and delivered to the engine in the form of steam. But as this method entails considerable trouble and expense, it is frequently figured from indicator diagrams. This plan, however, does not insure correct results, because the amount of water ac- counted for by the indicator is considerably less than it should be owing to cylinder condensation and leakage, so that it might be possible that only 80 per cent of the water passing through the cylinder would be accounted for by the indicator. But the cal- culation, used in connection with an evaporation test, will reveal the extent of the losses caused by cylinder condensation and leakage, by deducting the amount of water found by computation from the amount of water fed to the boiler while making an evaporation test.
Rule* 4- Divide the constant number 859,375 by the M. E. P. of any indicator card, and divide this quotient by the volume of its total terminal pressure, the result will be the theoretical con- sumption in pounds of water per horse power per hour. The constant number 859,375 is found as follows: — Compute the size of an engine that will give just one horse- power at one pound M. E. P. per square inch, thus: Area of piston equals 412.5 sqr. inches. Stroke equals 4 feet, and revolutions per minute equal 10.
396
HANDBOOK ON ENGINEERING.
Then, the piston speed is (4 x 2 X 10) 80 feet per minute. A * 412.5X1X80
33,000
To find how much water it would take to run this engine one hour, allowing 62 1 Ibs. to the cubic foot of water, proceed as follows : —
Twice the stroke equals 96 inches. 412.5 X 96
Then _nzir_l_l_LI- equals 22.91666 cubic feet for one revo- 1728
lution.
And, 22.91666 X 10 equals 229.1666 cubic feet for 10 revolu- tions, or for one minute.
Then, 229,1666 X 60 X 62 £ equals 859,375 Ibs. of water used per hour.
SCALE 40
M. E. P. 37. 6 LBS.
Fig. 250. Finding steam consumption from the diagram.
Fig. 250 is not an actual indicator card, but answers to illustrate the rule.
A A is the atmospheric line, and from A to A is the whole stroke.
VV is the vacuum line.
Points (a) and (b ) are equally distant from the vacuum line. The point (a) is taken at or very near the point of release.
HANDBOOK ON ENGINEERING.
397
Example. — From the indicator card Fig. 250 compute the water consumption, the M. E. P. being 37.6 Ibs. per square inch, the scale of spring used in the indicator being 40, the distance from point (a) to point (6) being 3.03 inches, the stroke AA being 3.45 inches, and the pressure at point (a) being 25 Ibs. per sqr. inch absolute. Ans. 20.14 Ibs.
Operation*— 859,375 ~ 37.6 = 22,855.7.
Now, the absolute pressure at point (a) is 25 Ibs., and steam tables give 996 as the volume of steam at this pressure, that is, steam at this pressure has 996 times the bulk of the water from which it was generated.
Then, 22,855.7 -f- 996 = 22.94 Ibs. of water. But as the period of consumption is represented by (&) (a), AA being the whole stroke, the following correction is required: The distance from point (a) to point (6) is 3.03 ins. Then, 22.94 X 3.03 = 69.5080. And the whole stroke or length of line AA is 3.45 ins.
Then, 69.5080-^-3.45 =20.14 Ibs. of water per indicated horse power per hour.
Boiler Feed or Pressure Pumps.
SIZES AND CAPACITIES.
tl
1
I.
CJ
IJ
O
Capacity per minute at ordinary speed.
!»
¥
5
r I*
10 12 14
16
18
20
14
i*
I ft
J*
5
6
7
8 10 12 14
.031
.05
.07
.11
.25
.35
1.02 1.47 2.00 2.61 5.44 11.75 16.00
150 Strokes. 34 gals. 150 " 4iJ£ •' 74 " 104 "
]?* "
42
49
69
85 102 147 200 261 408 588 800
150 150. 150 125 125 125 100 100 100 100 100 100 75 50 50
10
17x.5 18x 5 26x 6 28x7 31 x 8 44x13 45x14 45x14 55x16 55x16 67x19 67x19 67x20 67x20 80x22 110x27 111x29
25
40 60 .90 130 160 200 250 300 400 600
398 HANDBOOK ON ENGINEERING.
CHAPTER XVI.
THE STEAM BOILER. THE FORCE OF STEAM AND WHERE IT GOMES FROfl.
If water be heated it will expand somewhat, and will finally burst forth into vapor. The vapor will expand enormously, and naturally occupy more space than the water from which it is formed. A cubic inch of water will make a cubic foot of steam ; that is, the water has been expanded by heat to seventeen hundred times its original bulk. The steam is very elastic ; the water was not. When we say that a cubic inch of water will form a cubic foot of steam, we mean that it will do so when the steam is allowed to rise naturally from the water without any confinement. If the steam is confined, as it would be in a boiler, it could not expand, and consequently would not. If the steam is allowed to rise into the atmosphere from an open vessel, the pressure of the steam would be precisely the same as the pressure of the atmosphere, that pressure being about fifteen pounds to the square inch. An ordinary steam gauge only takes notice of the pressure above the atmospheric pressure. When the hand of the steam gauge stands at zero, it indicates that there is no pressure above the ordinary pressure of the atmosphere. An ordinary steam gauge not connected with anything has the atmosphere acting upon it in both directions, the same as the atmosphere acts upon everything when it can reach both sides. If the air be pumped out of the steam gauge, the atmosphere will then act upon one side, and the hand will move backward until it stands at fifteen points less than zero. In this condition the steam gauge indicates the absolute zero of pressure. If now the air be allowed to re-enter where it was
pumped out, it will begin to exert its pressure upon the jsteara
: . ! -
HANDBOOK ON ENGINEERING. 399
gauge, and the hand will move forward ; when the full air pressure is on, the gauge hand will stand at its usual zero. To gx> into this matter in order that it may be understood that the real pressure of steam is always fifteen pounds greater than ordinary steam gauges indicate. In all of the finer cal- culations relating to the action of steam, its total pressure must be known, and this total pressure is to be counted from the absolute zero. The real pressure of steam is always the steam gauge pressure, plus fifteen pounds. When a steam gauge shows fifty pounds, the steam really has a pressure of sixty-five pounds. The fifteen pounds of this pressure is nullified by the atmospheric pressure, and the steam gauge shows us our useful pressure. As before stated, a cubic inch of water will make a cubic foot of steam at atmospheric pressure ; that is, fifteen pounds to the square inch, abolute pressure, or zero by the steam gauge. If this cubic inch of water was made into steam in a boiler holding just a cubic foot, the steam gauge would show zero. If the boiler was only large enough to hold half a cubic foot, the steam would all be in the boiler, and being con lined in half its natural space, it would have double pressure. It would have an absolute pres- sure of thirty pounds to the square inch, and the steam gauge would indicate fifteen pounds. If this steam was then allowed to pass into a chamber holding a cubic foot, the steam would expand until it filled the chamber, and its pressure would go down again to fifteen pounds absolute. In short, the pressure is in reverse proportion to the amount of space it occupies. The pressure of steam may be doubled by compressing the steam into one-half its former volume, and so on. After water is turned into steam, the steam may be made hotter, but it is not very much expanded. The pressure of steam is increased by forcing more steam into the space occupied. If a boiler contains steam at 50 Ibs. pressure, we may increase the pressure by adding more steam, and thus compressing all the
400 HANDBOOK ON ENGINEERING.
steam that the boiler contains. In the ordinary operation of a steam boiler, the fire turns the water into steam and the more steam there is made and confined, the greater the pressure will be. If the steam is constantly flowing out of the boiler into an engine, the pressure in the boiler must be kept up by continually making new steam to take the place of that drawn off. If we make steam as fast as it is drawn off, and no faster, the pressure will remain the same. If we make steam faster than the engine draws it off, the pressure will rise, and if it is drawn off faster than we make it, the pressure will go down.
The pressure of the steam is due to its desire to expand into a larger body, and it acts outwardly in every direction against everything upon which it presses. If we crowd 600 cu. ft. of steam in a boiler, which will only hold 100 cu. ft., the steam will be held compressed into one-sixth its natural bulk, and will thus have a pressure of 90 Ibs., and the steam gauge will show 75 Ibs. If a hole 1 in. square be cut in the boiler, and a weight of 75 Ibs. be laid over the hole, the steam will just lift the weight. If the atmospheric pressure could be removed from one sq. in. of the top of the weight, the steam would then be capable of lifting a 90 Ib. weight. The force which this steam will exert to lift a weight, or any similar thing against which it acts, will equal the pressure per square inch multiplied by the number of square inches which the steam acts upon. It will thus be readily under- stood that if we lead a pipe from the boiler and fit a piston in the pipe, the steam will tend to force this piston out of the pipe.
THE ENERGY STORED IN STEAM BOILERS.
A steam boiler is not only an apparatus by means of which the potential energy of chemical affinity is rendered actual and avail- able, but it is also a storage reservoir, or a magazine, in which a quantity of such energy is temporarily held ; and this quantity,
HANDBOOK ON ENGINEERING. 401
always enormous, is directly proportional to the weight of water and of steam which the boiler at the time contains. The energy of gunpowder is somewhat variable, but a cubic foot of heated water under a pressure of 60 or 70 Ibs. per square inch, has about the same energy as one pound of gunpowder ; at a low red heat, it has about forty times this amount of energy.
The letters B. T. U. are the initial letters of the words British Thermal Unit, and are used as abbreviations of those words. The British Thermal Unit is the unit of heat used in this country and England, and may be said to be the amount of heat required to raise the temperature of one pound of pure water from 39 to 40 degrees Fahr. It is often necessary to distinguish between B. T. U. used in this country and the French thermal unit used in France and most of the countries of Europe. The French ther- mal unit is called the calorie, and is the heat required to raise the temperature of one kilogram of water one degree centigrade.
Safety at high pressure depends entirely upon the design, material, and workmanship, and it is a question that may be re- garded as settled long since, that a steam boiler properly con- structed and designed for a working pressure of 150 pounds is as safe as a properly constructed boiler designed for eighty pounds, with the chances in favor of the high pressure, for the reason that less care is taken in selecting boilers for the ordinary pressure, as anything in the shape of a boiler is regarded, fry careless people, as good enough for the lower pressures, with which they have become so familiar as to become almost too careless.
SPECIAL HIGH PRESSURE BOILERS.
The extending use of compound steam engines, which make necessary the employment of high steam pressures, calls for steam boilers specially designed to successfully operate under working pressures ranging from 100 to 160 pounds. These boilers must be safe and economical and of such construction as to afford
26
402 HANDBOOK ON ENGINEERING.
access for examination and repair, moderate in first cost and maintenance and of simplest possible form. Fortunately, the controlling conditions are not difficult to meet, and there are sev- eral well-tried and approved types Of steam boilers from which to make a selection, choice being governed by the space at dis- posal, arrangement of plant, kind of fuel and other circum- stances.
TYPES OF BOILERS.
Four types that are very succesfully used, and they represent good practice for high pressure w^>rk, being respectively the Hori- zontal Tubular, and Vertical Fixe Box Tubular Boilers. The Fire Box Locomotive Tubular Boiler may safely be added to this list and gives most excellent results.
THE WATER TUBE BOILER.
Steam boilers must be designed with reference to the pres- sure of steam to be carried, and when so designed and constructed are quite as safe at one pressure as another, preference being given to the type that is simplest in form and the least liable to destruction, not so much jj reason of the pressure carried as by failure to provide for the strains of expansion and contraction within itself.
HORSE POWER OF BOILERS.
In determining the proper size or evaporating capacity of a boiler to supply steam for a given purpose, it is necessary to con- sider the number of pounds of dry steam actually required per hour at the stated pressure. The standard horse power rating for any steam boiler is 34^ pounds of water evaporated (made into steam) from feed water at 212°, per hour. The total pounds steam required for any purpose per hour on this basis divided by 34J will give the standard boiler horse power required. Manu-
HANDBOOK ON ENGINEERING. 403
facturers of steam boilers sometimes rate the horse power of their boilers by so many square feet of heating surface per horse power ; 8 to 15 sq. ft. of heating surface, they figure, equals one horse power. This rating does not represent the actual capacity of the steam boiler, the only safe guide being the evaporative perform- ance in pounds of steam from water at 212° to steam at 212°. Some boilers will evaporate this with 8 sq. ft., some requiring from 15 to 18 sq. ft., hence, the absurdity of rating horse power of boilers of unlike construction by the square feet of heating surface. But as the practice is an old one in the case of the well-known tubular boiler, so deservedly popular and used more than any other kind, good practice is to allow approximately as follows: —
Allow for each Horse Power- Steam for Heating, etc. .... 15 sq. ft. heating surface. For Plain Throttle Engine, ... 15 " " " For Simple Corliss Engine ... 12 " " " For Compound Corliss Condensing . 10 " " "
Hence, a boiler for heating purposes or furnishing steam for —
Plain Slide engine with 1,500 sq. ft. surface, equals . 100 H. P. For Simple Corliss Engine, same boiler " . 125 H. f.
For Compound Condensing Engine " . . 150 H. P.
The best method is to compare boilers by their evaporative efficiency and not by heating surface.
The following is an approximate consumption of steam per indicated horse power per hour for engine : —
Plain Slide Engine . 60 to 70 pounds.
High Speed Automatic Engine . . . . . 30 to 50 . "
Simple Corliss Engine' 25 to 35 "
Compound Corliss Engine . . . . . . 15 to 20 "
Triple Expansion Engine . . . ... . 13 to 17 <;
404 HANDBOOK ON ENGINEERING.
depending upon the horse power, steam pressure, condition of engine, load, etc.
Each pound of first-class steam coal consumed under a well- proportioned steam boiler, well managed, should evaporate 10 pounds of water at 212° into dry steam at 212°. The average boiler throughout the country, with ordinary fuel and manage- ment, ranges from 5 to 8 pounds steam per pound of coal, and it would scarcely be safe to make fuel guarantees per horse power of engine without a counter guarantee on the part of the pur- chaser, when his old boiler is used, that the fuel economy is based on an evaporative efficiency of a given weight of water evaporated per pound of coal per hour in his boiler. The usual practice is to ignore the boiler altogether and guarantee pounds of steam per indicated horse power per hour used by the engine. This affords an exact method and is not hampered by unknown con- ditions, and places all tests on an equal or comparative basis.
THE RATING OF BOILERS.
It is considered usually advisable to assume a set of practically attainable conditions in average good practice, and to take the power so obtainable as the measure of the power of the boiler in commercial and engineering transactions. The unit generally assumed has been usually the weight of steam demanded per horse power per hour by a fairly good steam engine. In the time of Watt, one cubic foot of water per hour was thought fair ; at the middle of the last century, ten pounds of coal was a usual figure, and five pounds, commonly equivalent to about 40 Ibs. of feed water evaporated, was allowed the best engines. After the introduction of the modern forms of engine, this last figure was reduced 25 per cent, and the most recent improvements have still further lessened the consumption of fuel and of steam. By general consent the unit has now become thirty pounds of dry steam per
HANDBOOK ON ENGINEERING. 405
horse power per hour, which represents the performance of non- condensing engines. Large engines, with condensers and com- pound cylinders, will do still better. A committee of the American Society of Mechanical Engineers recommended thirty pounds as the unit of boiler power, and this is now generally accepted. They advised that the commercial horse-power be taken as an evaporation of 30 Ibs. of water per hour from a feed water temperature of 100° Fahr. into steam at 70 Ibs. gauge pres- sure, which may be considered equal to 34 £ Ibs. of water evapo- ration, that is, 34 J Ibs. of water evaporated from a feed water temperature of 212° Fahr. into steam at the same temperature. This standard is equal to 33,305 British thermal units per hour. A boiler rated at any stated power should be capable of developing that power with easy firing, moderate draught and ordinary fuel, while exhibiting good economy, and at least one-third more than its rated power to meet emergencies.
WORKING CAPACITY OF BOILERS.
The capacity or horse-power of a boiler, as rated for purposes of the trade, is commonly based upon the extent of heating surface which it contains. The ordinary rating was for a long time 15 sq. ft. of surface per horse-power. At the present time most of the stationary boilers are sold on the basis of from 10 to 12 sq. ft. per horse-power, the power referred to being the unit of 30 Ibs. evaporation per .hour. This method of rating is arbi- trary, inasmuch as it is independent of any condition pertaining to the practical work of the boiler. The fact that 10 or 12 sq. ft. of surface is sold for one horse-power is no guarantee that this extent of surface will have a capacity of one horse-power when the boiler is installed and set to work. The boiler in service and the boiler in the shop are two entirely different things, and where one passes to the other, the trade rating disappears. New
406 HANDBOOK ON ENGINEERING.
conditions, such as draft, grate surface, kind of fuel and man- agement, then take effect, and these have a controlling influence upon the working capacity. The working power may be found to be much less than the arbitrary rate, or it may be a much larger quantity ; all depending upon the surrounding conditions, attention is had to this subject, because it is important in some cases to have a clearer understanding as to what is the working capacity of a boiler. Suppose a boiler manufacturer enters into an agreement to install a boiler, which will have a capacity of 100 horse-power. Suppose that on account of poor draft, low grade of fuel, or unfavorable surroundings, all of which are known beforehand, the boiler develops the power named only with the most careful handling. Is the working capacity, under the cir- i cumstances, 100 horse-power? Assuredly not, for the purchaser could not depend upon it in ordinary running for that amount of power. Yet the builder may claim that he has fulfilled his contract.
The former boiler test committee of the American Society of Mechanical Engineers established a working rate for boiler capac- ity which meets such cases in a definite and satisfactory manner. They realized that for the purpose of good work, a boiler should be capable of developing its capacity with a moderate draft and easy firing; and that it should be capable of doing one-third more in cases of emergency. In other words, a boiler which is sold for 100 horse-power should develop 133^ horse-power under con- ditions giving a maximum capacity. .In the instance cited above, the boiler should have been capable of giving 100 horse-power with such ease that there would be a reserve of 33| horse-power available when urged to this extra power. According to this rule, the capacity of a boiler in a working plant would be found by determining how much water it can evaporate under conditions which will give its maximum capacity ; that is, with w^de open damper, with the maximum draft available arid with the best con-
HANDBOOK ON ENGINEERING. 407
ditions as to the handling of the fire, and in this way ascertain the maximum power available under these circumstances. Hav- ing found this maximum quantity, the working capacity or the rated power would be determined by deducting from the maxi- mum 25 per cent. This rule, it will be seen, does not take into account the extent of the heating surface or the trade rating, but it deals solely with the capabilities of the boiler under the con- ditions which pertain to its work.
CODE OF RULES FOR BOILER TESTS.
Starting and stopping a test* — A test should last at least ten hours of continuous running, and twenty-four hours whenever practicable. The conditions of the boiler and furnace in all respects should be, as nearly as possible, the same at the end as at the beginning of the test. The steam pressure should be the same ; the water level the same ; the fire upon the grates should be the same in quantity and condition ; and the walls, flues, etc., should be of the same temperature. To secure as near an approximation to exact conformity as possible in conditions of the fire and in the temperature of the walls and flues, the follow- ing method of starting and stopping a test should be adopted : —
Standard method* — Steam being raised to the working pres- sure, remove rapidly all the fire from the grate, close the damper, clean the ash-pit, and, as quickly as possible, start a new fire with weighed wood and coal, noting the time of starting the test and the height of the water level while the water is in a quiescent state, just before lighting the fire. At the end of the test, re- move the whole fire, clean the grates and ash-pit, and note the water-level when the water is in a quiescent state ; record the time of hauling the fire as the end of the test. The water-level should be as nearly as possible the same as at the beginning of the test. If it is not the same, a correction should be made by computa-
408 HANDBOOK ON ENGINEERING.
tion, and not by operating pump after test is completed. It will generally be necessary to regulate the discharge of steam from the boiler tested by means of the stop-valve for a time while fires are being hauled at the beginning and at the end of the test, in order to keep the steam pressure in the boiler at those times up to the average during the test.
Alternate method* — Instead of the standard method above described, the following may be employed where local conditions render it necessary : At the regular time for slicing and cleaning fires have them burned rather low, as is usual before cleaning, and then thoroughly cleaned ; note the amount of coal left on the grate as nearly as it can be estimated ; note the pressure of steam and the height of the water-level — which should be at the medium height to be carried throughout the test — at the same time ; and note this time as the time for starting the test. Fresh coal which has been weighed, should now be fired. The ash-pits should be thoroughly cleaned at once before starting. Before the end of the test the fires should be burned low, just as before the start, and the fires cleaned in such a manner as to leave the same amount of fire, and in the same condition, on the grates as on the start. The water-level and steam pressure should be brought to the same point as at the start, and the time of the ending of the test should be noted just before fresh coal is fired.
DURING THE TEST.
Keep the conditions uniform, — The boiler should be run con- tinuously without stopping for meal times, or for rise or fall of pressure of steam due to change of demand for steam. The draught being adjusted to the rate of evaporation or combustion desired before the test is begun, it should be retained constant during the test by means of the damper. If the boiler is not con- nected to the same steam pipe with other boilers, an extra outlet
HANDBOOK ON ENGINEERING. 409
for steam with valve in same should be provided, so that in case the pressure should rise to that at which the safety valve is set, it may be reduced to the desired point by opening the extra outlet, without checking the fire. If the boiler is connected to a main steam pipe with other boilers, the safety valve on the boiler being tested should be set a few pounds higher than those of the other boilers, so that in case of a rise in the pressure the other boilers may blow off, and the pressure be reduced by closing their dam- pers, allowing the damper of the boiler being tested to remain open, and firing as usual. All the conditions should be kept ai nearly uniform as possible, such as force of draught, pressure of steam and height of water. The time of cleaning the fires will depend upon the character of the fuel, the rapidity of combustion and the kind of grates. When very good coal is used and the combustion not too rapid, a ten-hour test may be run without any cleaning of the grates, other than just before the beginning and just before the end of the test. But in case the grates have to be cleaned during the test, the intervals between one cleaning and another should be uniform.
Keeping the records* — The coal should be weighed and delivered to the firemen in equal portions, each sufficient for about one hour's run, and a fresh portion should not be delivered until the previous one has all been fired. The time required to con- sume each portion should be noted , the time being recorded at the instant of firing the first of each new portion. It is desirable that at the same time the amount of water fed into the boiler should be accurately noted and recorded, including the height of the water in the boiler, and the average pressure of steam and tem- perature of feed during the time. By thus recording the amount of water evaporated by successive portions of coal, the record of the test may be divided into several divisions, if desired at the end of the test, to discover the degree of uniformity of com- bustion, evaporation and economy at different stages of the test.
410 HANDBOOK ON ENGINEERING.
.
PRIMING TESTS.
In alt tests in which accuracy of results is important, calori- meter tests should be made of the percentage of moisture in the steam, or of the degree of superheating. At least ten such tests should be made during the trial of the boiler, or so many as to reduce the probable average error to less than one per cent, and the final records of the boiler tests corrected according to the average results of the calorimeter tests. On account of the difficulty of securing accuracy in these tests, the greatest care should be taken in the measurements of weights and temperatures. The thermometers should be accurate to within a tenth of one degree, and the scales on which the water is weighed to within one-hundredth of a pound.
ANALYSES OF GASES.
•
Measurement of air supply, etc* — In tests for purposes of scientific research, in which the determination of all the variables entering into the test is desired, certain observations should be made which are in general not necessary in tests for commercial purposes. These are the measurements of the air supply, the determination of its contained moisture, the measurement and analysis of the flue gases, the determination of the amount of heat lost by radiation, of the amount of infiltration of air through the setting, the direct determination by calorimeter experiments of the absolute heating value of the fuel, and (by condensation of all the steam made by the boiler) of the total heat imparted to the water.
The analysis of the flue gases is an especially valuable method of determining the relative value of different methods of firing, or of different kinds of furnaces. In making these analyses, great care should be taken to procure average samples
HANDBOOK ON ENGINEERING.
411-
since the composition is apt to vary at different points of the flue, and the analyses should be intrusted only to a thoroughly com- petent chemist, who is provided with complete and accurate apparatus. As the determination of the other variables men- tioned above are not likely to be undertaken except by engineers of high scientific attainments, and as apparatus for making them is likely to be improved in the course of scientific research, it is not deemed advisable to include in this code any specific direc- tions for making them.
RECORD OF THE TEST.
A " log " of the test should be kept on properly prepared blanks, containing headings as follows : —
|
PRESSURES. |
TEMPERATURES. |
FUEL. |
FEED WATER. |
||||||||||
|
8c |
« |
. |
£ |
||||||||||
|
bJD |
|||||||||||||
|
oj |
id |
ed |
2 |
<u |
p |
||||||||
|
bJD |
cS |
P |
o |
||||||||||
|
TIME. |
Barome |
1 1 |
W) <M |
Externa |
Boiler r |
. V P E |
Feed w£ |
Steam. |
i S |
Pounds |
1 H |
b ' 0 s |
|
REPORTING THE TRIAL.
The final results should be recorded upon a properly prepared blank, and should include as many of the following items as are adapted for the specific -object for which the trial is made. The items marked with a * may be omitted for ordinary trials, but are desirable for comparison with similar data from other sources.
412 HANDBOOK ON ENGINEERING.
Resources of the trials of a
Boiler at
To determine
1. Date of trial . . .
2. Duration of trial .
DIMENSIONS AND PROPORTIONS.
3. Grate-surface wide long area
4. Water-heating surface
5. Superheating surface
6. Ratio of water-heating surface to gr^te-
surface
AVERAGE PRESSURES.
7. Steam pressure in boiler, by gauge . . Ibs.
*8. Absolute steam pressure Ibs.
*9. Atmospheric pressure, per barometer . in.
10. Force of draught in inches of water . in.
AVERAGE TEMPERATURES.
*11. Of external air deg.
*15. Of fire-room deg.
*13. Of steam deg.
14. Of escaping gases deg.
15. Of feed-water deg.
FUEL.
16. Total amount of coal consumed . . . Ibs.
17. Moisture in coal per cent.
18. Dry coal consumed Ibs.
19. Total refuse, dry pounds equals . . . per cent.
20. Total combustible (dry weight of coal,
item 18, less refuse, item 19) . . . Ibs.
*21. Dry coal consumed per hour . . . Ibs.
*22. Combustible consumed per hour . . . Ibs.
HANDBOOK ON ENGINEERING. 413
RESULTS OF CALORIMETRIC TESTS.
23. Quality of steam, dry steam being taken
as unity
24. Percentage of moisture in steam . . 0 per cent.
25. Number of degrees superheated ... deg.
WATER.
26. Total weight of water pumped into boiler
and apparently evaporated .... Ibs.
27. Water actually evaporated, corrected for
quality of steam Ibs.
28. P^quivalent water evaporated into dry
steam from and at 212° F Ibs.
*29. Equivalent total heat derived from fuel
in B. T. U B. T. U.
*30. Equivalent water evaporated in dry
steam from 212° F. per hour . . . Ibs.
ECONOMIC EVAPORATION.
31. Water actually evaporated per pound of
dry coal, from actual pressure and
temperature . • Ibs.
32. Equivalent water evaporated per pound
of dry coal, from 212° F Ibs.
33. Equivalent water evaporated per pound
of combustible from and at 212° F. . Ibs.
COMMERCIAL EVAPORATION.
34. Equivalent water evaporated per pound
of dry coal with one-sixth refuse, at 70 Ibs. gauge pressure, from temperature of 100° F., equals item tests 33 X. 0.7249 pounds Ibs.
f Corrected for inequality of water level and of steam pressure at beginning and end of test.
414
HANDBOOK ON ENGINEERING.
* KATE OF COMBUSTION.
35. Dry coal actually burned per sq. foot of grate-surface per hour . . . .
Per sq. ft. of grate Consumption of dry surface coal per hour. Coal assumed with one- sixth refuse.
*36. *37. *38.
Per sq. ft. of water heating surface .
Per sq. foot of least area for draught.
RATE OF EVAPORATION.
39. Water evaporated from and at 212° F. per square foot of heading surface per hour.
Per sq. ft. of grate Water evaporated per
hour from temperature of 100° F. into steam of 70 Ibs. gauge pres- sure.
*40. *41. *42.
surface .
Per sq. ft. of heat- ing surface .
Per sq. ft. of least area for draught.
COMMERCIAL HORSE POWER.
43. On basis of 30 Ibs. of water per hour
evaporated from temperature of 100° F. into steam of 70 Ibs. gauge pressure (34£ Ibs. from and at 212°) ...
44. Horse-power, builders' rating at
sq. ft. per horse-power . . . , .
45. Per cent developed above or below rating
IDS.
ibs.
Ibs. Ibs.
Ibs.
Ibs.
H. P.
per cent.
* NOTE. Items 20, 22, 33, 34, 36, 37, 38 are of little practical value. For if the result proves to be less satisfactory than expected on the actual coal, it is easy for an expert fireman to decrease No. 20 by simply taking out some partly consumed coal in cleaning fires, and thus make a fine showing on that simply ideal or theoretical unit, the u pound com- bustible." The question at issue is always what can be done with an actual coal, not the " assumed coal " of items 34, 36, 37 and 38.
HANDBOOK ON ENGINEERING. 415
DEFINITIONS AS APPLIED TO BOILERS AND BOILER flATERIALS.
Cohesion is that quality of the particles of a, body which causes them to adhere to each other, and to resist being torn apart.
Curvilinear seams* — The curvilinear seams of a boiler are those around the circumference.
Elasticity is that quality which enables a body to return to its original form after having been distorted, or stretched by jsome external force.
Internal radius* — The internal radius is one-half of the diam- eter, less the thickness of the iron. To find the internal radius of a boiler, take one-half of the external diameter and substract the thickness of the iron.
Limit of elasticity* — The extent to which any material may be stretched without receiving a permanent " set."
Longitudinal seams* — The seams which are parallel to the length of a boiler are called the longitudinal seams.
Strength is the resistance which a body opposes to a disinte- gration or separation of its parts.
Tensile strength is the absolute resistance which a body makes to being torn apart by two forces acting in opposite direc- tions.
Crushing strength is the resistance which a body opposes to being battered or flattened down by any weight placed upon it.
Transverse strength is the resistance to bending or flexure, as it is called.
Torsional strength is the resistance which a body offers to any external force which attempts to twist it round.
Detrusive strength is the resistance which a body offers to being clipped or shorn into two parts by such instruments as shears or scissors.
Resilience or toughness is another form of the quality of
416 HANDBOOK ON ENGINEERING.
strength ; it indicates that a body will manifest a certain degree of flexibility before it can be broken ; hence, that body which bends or yields most at the time of fracture is the toughest.
"Working strength* — The term " working strength " implies a certain reduction made in the estimate of the strength of ma- terials, so that when the instrument or machine is put to use, it may be capable of resisting a greater strain than it is expected on the average to sustain.
Safe working pressure, or safe load* — The safe working pres- sure of steam-boilers is generally taken as £ of the bursting pres- sure, whatever that may be.
Strain in the direction of the grain, means strain in the direc- tion in which the iron has been rolled ; and in the process of man- ufacturing boiler-plates, the direction in which the fibres of the iron are stretched as it passes between the rolls.
Stress* — By the term " stress " is meant the force which acts directly upon the particles of any material to separate them.
HEAT AND STEAM.
The steam engine is a machine for the conversion of heat into power in motion. The heat is generated by the combustion of fuel ; the transmission is accomplished through the agency of steam ; the power is made available and brought under control by means of the engine.
The effect of heat upon water is to vaporize it, if there be inten- sity enough, the heat will, under proper conditions, cause water to boil ; the vapor produced by boiling is called steam, and steam under pressure is a product which is the end and aim of that por- tion of that steam engine known as the boiler and furnace. The steam engine then is to be considered as a form of the heat engine ; of which the furnace, boiler, and the engine itself are to be regarded as separate portions of the same mechanism.
HANDBOOK ON ENGINEERING. 417
The conditions demanded .upon economic grounds to secure the highest efficiency in the steam engine are : —
1. A proper construction of the furnace so as to secure the perfect combustion of fuel.
2. The heat generated in the furnace must be transferred to the water in the boiler without loss.
3. The circulation in the boiler must be so complete that the heat from the furnace may be quickly and thoroughly diffused throughout the whole body of water.
4. The construction of an engine that will use the steam with- out loss of heat, except so much as may be necessary to perform work required of the engine.
5. The recovery of heat from exhaust steam.
6. The absence of friction and back pressure in the working of the engine.
It is superfluous to say that these conditions are not fulfilled in any engine of the present day. At best the combustion of fuel is only approximately perfect, the losses being due to several causes, among which are, - unburned fuel falling through the spaces in the grates and mingling with the ashes. This, with .some kinds of coal, and improper firing, amounts to a large > Tcentage of the furnace waste. It is not possible with any present method of setting boilers to transfer all the heat of the furnace to the water in the boiler ; nor can there be, for the reason that the temperature of the escaping gases must not be lower than that of the steam in the boilers, or direct loss will result in the radiation of heat from the tubes or flues in the boiler, by MIS reheating the gases to the steam temperature. If the steam pressure is 80 Ibs. per square inch above the atmosphere, the cor- responding temperature due to this pressure is 324° Fahr. The temperature of the escaping gases ought not, therefore, to be less than 350° Fahr., where they leave the boiler flues or tubes to pass off into the chimney. If the temperature of the furnace be taken
27
HANDBOOK ON ENGINEERING.
.
at 2,000° Fahr., and the escaping gases at 400° Fahr., it will be seen that one-fifth of the heat generated in the furnace is passing off without performing work. This is a very great loss, and these figures understate, rather than correctly give, the loss from this one source. Efforts have been made to utilize the tempera- ture of these waste gases by making them heat feed -water by means of coils, or by that particular disposition of pipes and connection known as an economizer. Others have turned it into account by making it heat the air supplied the fuel on the grates. Any heat so reclaimed is money saved, provided it does not cost more to get it than it is worth in coal to generate a similar quan- tity of heat. It is doubtful whether the loss in this particular direction can be brought below 20 per cent of the fuel burned, at least, by any method of saving now known.
The loss by bad firing and by a bad construction of furnace is often a large one. It has been demonstrated experimentally that 20 to 30 per cent of fuel can be saved by a proper construc- tion and operation of the furnace. The direct causes of loss are, too low temperature of furnace for properly burning fuels, espe- cially such as are rich in hydro-carbon gases ; or, by the admis- sion of too much cold air over or back of the fire ; or, by the admission of too little air under the fire so that carbonic oxide gas is generated instead of carbonic acid gas, the former being a product of incomplete, the latter the product of complete combustion. The relative heating powers of fuel burned, resulting in the production of either of these two gases being as follows : -
Heat Units.
1 pound of carbon burned to carbonic acid gas . . 14,500 1 pound of carbon burned to carbonic oxide . . . 4,500
Units of heat lost by burning to carbonic oxide . ^10,000 It will be seen that here is an enormous source of loss, and all that is required to prevent it is a proper construction of furnace.
HANDBOOK ON ENGINEERING. 419
Smoke is a nuisance which ought to be prohibited by stringent legislation. There is no good reason for its polluting presence in the atmosphere, defiling everything with which it comes in con- tact. Smoke regarded as a source of direct loss is greatly over- estimated ; the fact is, the actual amount of coal lost to produce smoke is very trifling. The presence of smoke indicates a low temperature of furnace or combustion chamber ; if the temper- ature were sufficiently high and the furnace properly constructed, smoke could not be generated. The prevention of smoke is easily accomplished, and with it a more economical combustion of hydro-carbon fuels.
Radiation* — A considerable loss of heat occurs by radiation from the furnace walls ; this may be prevented in part by making the walls hollow, with an air space between. If a force blast is used the air may be admitted at the back end of the boiler setting and by passing through between the walls will become heated, and if conveyed into the ash pit at a high temperature will greatly assist combustion and thus tend to a higher economy.
Air required* — In regard to the quantity of air required, it will vary somewhat with the fuel used, but in general, 12 pounds of air are sufficient to completely burn one pound of coal ; prac- tically, however, 15 to 25 pounds are furnished, being largely in excess of that which the fire can use, and must pass off with the gases as a waste product. This surplus air enters cold and leaves the furnace heated to the same temperature as that of the legitimate and proper products of combustion, and thus directly operates to the lowering of the furnace temperature.
Measurement of heat* — A heat unit is that quantity of heat necessary to raise the temperature of one pound of water one degree, from 39° to 40° Fahr., this being the temperature of the greatest density of water. A thermal unit, a heat unit, or unit of heat, all mean the same thing. Experiments have been made to determine the mechanical equivalent of a heat unit, and it is
420 HANDBOOK ON ENGINEERING.
found to be equal to 778 pounds raised one foot high. This is sometimes called "Joule's equivalent," after Dr. Joule, of England ; it is also known as the dynamic value of a heat unit. Knowing" the number of heat units in a pound of coal enables us to calculate the amount of work it should perform. Let us suppose a pound of coal to be burned to carbonic acid gas, and to develop during its combustion 14,000 heat units, then: 14,000x778 equals 10,892,000 foot pounds.
That is to say, if one pound of coal were burned under the above conditions it would have a capacity for doing work repre- sented by the lifting of ten millions of pounds one foot high against the action of gravity. Suppose this to be done in one hour, then we should expect to get from one pound of coal an equivalent of 5.45 H. P. It is well known that only a very small fraction of such equivalent is secured in the very best modern practice. The question is, where does this heat go, and why is it so small a portion of it is actually utilized ? The losses may be accounted for in several ways, and, perhaps, as follows : —
The heat wasted in the chimney .... 25 per cent.
Through bad firing 10 "
Heat accounted for by the engine (not indicated) 10 " Heat by exhaust steam 55 "
100 per cent.
This is about 2 pounds of coal per hour per indicated horse power, which is regarded as a very high attainment, and is seldom reached in ordinary cut-off engines. It requires good coal, good firing, and an economical engine to get an indicated horse power from two pounds of coal burned per hour. As coal varies in quality it is a better plan to deduct the ashes and other incombustible matter, and take the net combustible as a basis of comparison. The best coal when properly burned
HANDBOOK ON ENGINEERING. 421
is capable of evaporating 12 pounds of water from and at a temperature of 212° Fahr. The common evaporation is about half that amount, and with the best improved furnaces and care- ful management, it is seldom that 10 pounds of water is exceeded, and is to be regarded as a high rate of evaporation. In experi- mental tests, 12 pounds have been reported, but it is doubtful whether there is any steam boiler and furnace which is con- stantly yielding any such results.
Circulation of water in a boiler is a very important feature to secure the highest evaporative results. Other things being equal, the boiler which affords the best circulation of water will be found to be the most economical in service. Circulation is greatly hin- dered in some boilers by having too many tubes ; in others, by introducing in the water space of the boiler too many stays and making the water spaces too narrow. To secure the highest economy there must be thorough circulation from below upwards, in the boiler. There is no doubt that a great deal of heat is lost because the construction is such as to hinder a free flow of water around the tubes and sides of the boiler.
The construction of an engine that will use steam without loss of heat, except so much as may be necessary to perform work required of it, is a physical impossibility. Among the sources of loss in an engine are : radiation, condensation of steam in un- jacketed cylinders, and the enormous loss of heat occasioned by exhausting the steam into the atmosphere.
Radiation is usually classed among the minor losses in a steam engine. There is a considerable loss of heat caused by radiation from steam boilers and pipes exposed to the atmosphere, and not protected by a suitable covering. Much of this heat may be saved by employing a non-conducting material as a covering, which, though not preventing all radiation, will save enough heat to make its application economical. It is well known that some bodies conduct and radiate heat less rapidly than others, but it
422 HANDBOOK ON ENGINEERING.
must not be understood that the absolute value of such a cover- ing is inversely proportioned to the conducting power of the material employed, because, in its application, the outer surface is enlarged and the radiation will be going on less actively at any given point, but the enlarged surface exposed reduces somewhat the apparent gain.
SELECTION OF A BOILER.
The selection of a boiler for a particular service will naturally suggest the following questions : —
1 . What kind of a boiler shall it be ?
2. Of what material shall it be made?
3. What size shall it be in order to furnish a certain power? In reply to the first question, it is to be expected there will be
wide differences of opinion, varying with the locality, usage, and service for which it is intended. One of the first things to be taken into account in the selection of a boiler is the quality of water to be used in it for generating steam. If the water is pure, then it makes little difference what kind of boiler be selected, so far as incrustation affects selection. If the water is hard and will deposit scale upon evaporation, then a boiler should be selected which will admit of thorough inspection and removal of any deposit formed within it.
For hard water, the ordinary flue boiler will be found a good one, as it is favorable to a thorough circulation of water, and permits easy access to all parts of it for examination and clean- ing. It does not, however, present the extent of heating surface for a given space that tubular boilers offer ; but with hard water the boiler is quite as economical if kept in good condition.
The difficulty with tubular boilers when used in connection with hard water is that the tubes will in a short time become coated with scale ; this prevents the transmission of heat, not only, but impairs the circulation of the water around them.
HANDBOOK ON ENGINEERING. 423
Both of these are opposed to economy in the fact that it requires more coal to generate a given weight of steam in the first case ; and second, by reason of deficient circulation the plates over the fire are likely to become overheated and burnt and so become dangerous ; thus directly contributing to accident or disaster.
The matter of circulation in boilers is one which should have careful attention in making a selection. There is little trouble in this regard with any of the ordinary types of boilers so long as they are clean and new, and properly proportioned. Nor is there likely to be any difficulty thereafter if the water is soft and clean. Circulation is often seriously impaired by putting in too many tubes in a boiler, the effect of which is to so fill up the space that the heated particles of water forcing their way upwards from below meet with so much resistance that they can hardly over- come it, and the result is that a boiler does not furnish from one- fourth to one-half as much steam for a given weight of fuel as it should, from this very cause.
Boilers intended for use in distant localities where the facilities for repairs are meager or entirely wanting, and fuel low priced, should be of the simplest description. Cylinder boilers or two- flue boilers will perhaps be found most suitable. These are largely used by coal miners, blast furnaces, saw mills, and other branches of industry, which must, of necessity, be removed from the larger towns and engineering work shops.
In selecting a boiler for a mill of any kind where they burn shavings or offal, or any other place in which the fuel is of a similar description and the firing irregular, there should be large water capacity in the boiler that it may act as a reser- voir of power in much the same way that a fly wheel acts as a regulator for a steam engine. It is a common notion among wood workers that firing with shavings or light fuel is " easy on the boiler." There is abundant reason to doubt this. The suddenness and rapidity with which an intense fire is kin-
424 HANDBOOK ON ENGINEERING.
died in the furnace, filling all the furnace space and the tubes with flame, and with an intense heat which envelops all within the limits of draft opening, continuing thus for a few minutes only, and as suddenly going out, can hardly be regarded as the ideal furnace. Yet there are thousands of just such furnaces at work, and it is altogether probable that little or no change will be made in them by this class of manufacturers, at least in the near future. In regard to the selection of a boiler for this service, we are brought back again to the question of hard or soft water. The decision should be largely influenced by this, but whatever type of a boiler is selected there should be a surplus of boiler power of at least 20 per cent, that is, if a 50 horse-power boiler is needed to do the Work, put in one of 60 horse-power ; this will prevent the fluctua- tions of speed in the engine which are sure to follow a reduction of boiler pressure.
This increase in boiler power ought not to be simply that of tube surface, but should also include extra water space. The reserve power of a boiler is in the water heated up to a temperature corresponding to the steam pressure ; when this pressure is lowered, the water then gives off steam corresponding to the lower pressure ; the more water the more steam ; and in this way the water in the boiler stores up heat when overtired , to give it off again when the fire is low, and so acts a regulator of pressure, a thing that extra tube surface cannot do. This kind of firing is apt to induce priming, and for this reason a boiler should be selected having a large water surface. Horizontal boilers are, in general, to be preferred over vertical ones for mills, because of the larger water surface exposed in proportion to the heating surface. If a tubular boiler is selected, the water line above the tubes should be not higher than two-thirds the diameter of the boiler measured from the bottom, and the boiler should be made having the upper edge of the top row of tubes at least three inches below this ; there should also be a clear space up through the center of
HANDBOOK ON ENGINEERING.
the boiler of sufficient width to insure a perfect circulation of water.
Horizontal tubular boilers are to be recommended when pure soft water is used. They combine at once the qualities of great strength without excessive bracing, large heating surface, high evaporative capacity without liability to priming, and are conve- nient of access for external and internal examination when set in the furnace.
Firebox boilers, or locomotive boilers, as they are commonly called, are best adapted for small powers and with a fuel which deposits but little soot in the tubes. This kind of boiler is sup- plied with portable or agricultural engines and is very well adapted for that particular service. In canvassing the desirability of this kind of a boiler for stationary use, we must again refer to the kind of water to be used in it. If the water is soft and clean there is then no particular objection to a boiler of this construc- tion being used for small powers ; if the water is hard and will form scale, it ought not to be chosen, but a flue boiler selected instead.
Vertical boilers are used in great numbers for small engines, heating, etc. They have the merit of being compact and low priced. A common defect in the construction of this kind of boiler is that too many tubes are put in the head in the fire box, thereby preventing a proper circulation of water between them. This defect in construction induces priming, with all its attendant annoyances and dangers. This style of boiler is not suited to hard water, but pure soft water only. These boilers should be provided with hand holes above the crown sheet and around the bottom of the water legs ; at least three at each place mentioned. In regard to the material of which a boiler shall be made there is but the simple choice between iron and steel.
Steel for boilers should not be of too high tensile strength ; 55,000 to 60,000 pounds tensile strength per square inch makes
426 HANDBOOK ON ENGINEERING.
the best boilers. If the steel is of too high a grade it will take a temper, and, therefore, is utterly unfit for use in steam boilers ; if the steel is of too low tensile strength it is apt to be loose or spongy. Among the advantages steel possesses over iron may be mentioned the circumstance that it is a practically homogeneous material when properly made and rolled, consequently, it is nearly as strong in one direction as it is in another. In this respect, steel is superior to iron plate of equal thickness, because the latter is made up of several pieces of iron welded together and in rolling into the plate it becomes fibrous, and thus of unequal strength, being greatest in the direction of the fiber, and least, when tested across it.
BOILER TRIMMINGS.
HANDBOOK ON ENGINEERING. 427
lever and weight, or whether it be fitted with a spring. The former is the usual manner of loading a safety valve and has but few objections. For portable engines and locomotives safety valves are loaded with springs, which by suitable adjustment may be made to blow off at any desired pressure.
The following rule is that enforced by the U. S. Government in fixing the area of safety valves for ocean and river service, when the ordinary lever and weight safety valve is employed : —
Rule* — When the common safety valve is employed it shall have an area of not less than one square inch for each two square feet of grate surface.
Another rule is to multiply the pounds of coal burned per hour by 4 ; this product is to be divided by the steam pressure, to which a constant number 10 is added.
EXAMPLE : What would be the proper area for a safety valve for a boiler having a grate surface 5 feet square and burning 12 pounds of coal per hour per square foot of grate ; the steam pressure being 75 pounds per square inch ?
5x5 equal 25 square feet of grate.
25 x 12 equal 300 Ibs. of coal per hour.
300x4 equal 1200.
75 plus 10 equal 85 equal steam pressure with 10 added, then 1200 ~- 85 equal 14.11 inches area, or 4J inches diameter.
A feed pipe should be at least twice the area over that which is regarded as simply necessary to supply the boiler with water, as sediment or scale is likely to form in it, which will materially re- duce its area. In localities where the water is hard the feed pipes should be disconnected near the boiler and examined occa- sionally to ascertain whether or not scale is forming in them.
In general, the sizes of feed pipes leading from the pump to the boiler are fixed by the size of tap used by the maker of the pump. It is not well to reduce the diameter of the pipe and the size should be the same throughout. Care should be
428 HANDBOOK ON ENGINEERING.
cised in putting pipes in place that no strain be brought upon them by imperfect fitting, as it is certain to lead to leaky joints at some time or other. It is also desirable that the pipes be as short and straight as possible. Feed pipes should never be placed under ground if it is possible to make any different disposition of them. In locating pipes it is desirable to arrange for the expansion of the boiler, as well as for that of the pipes themselves. In select- ing a pump it should have a much larger capacity than that needed to supply the boiler, as there are many things which affect the working of a pump, such as a defective suction pipe, leaky valves, etc. It is the practice of most manufacturers to give the capacity of their pumps in gallons of water delivered per minute, from which it is easy to select a suitable size ; but the speed given in the tables at which the pump is to run is generally faster than that which it is desirable to run them. As a general thing, and without referring to any particular maker or design, it is a good plan to select a pump having four times the capacity actually needed for the boiler ; then the speed may be reduced to half that given in the table, and will require less repairs, and will be a more satisfactory purchase in the long run.
In selecting an injector or inspirator, the size should not greatly exceed that actually required to supply the boiler. In making the steam connections the pipes should start from the steam space of the boiler and should not be branches merely from the other steam pipes ; neither should the diameters of the pipes be less than that which the instrument calls for. The pipes should be as short and straight as practicable ; abrupt bends should always be avoided in the suction pipes. If the water is taken from a place in which there are floating particles of wood, leaves, etc., a strainer should be used; a large sheet metal box with perforated sides, makes a good strainer ; the openings ought not too greatly exceed an eighth of an inch in diameter, and should be several times the area of the suction pipe.
HANDBOOK ON ENGINEERING. 429
A check valve should be fitted with a valve between it and the boiler, so that in the event of its not working satisfactorily it may be taken apart, cleaned and replaced without stopping for exami- nation or repairs.
The blow-off pipe should be so arranged that it will entirely drain the boiler of water ; it is also a good plan to set a boiler with a slight inclination toward the blow-off pipe that it may be thoroughly drained ; an inclination of two inches in twenty feet works well in practice. The blow-off pipe is usually fitted at the back end of the boiler.
The steam pipe may be connected at any convenient point on the top of the boiler. If the boiler is to furnish steam for an engine only, the common practice is to make the diameter of the pipe one-fourth that of the cylinder. The steam pipe should be as short and straight as possible. If bends are to be introduced in steam pipes it is better to have a long curved bend than the abrupt right-angle fitting usually employed for the purpose. It is also a good plan to provide a stop-valve next to the boiler to shut off the steam and prevent it condensing in the steam pipe at night, or other long stoppages.
The gauge cocks should not be less than three in number, and may be of any of the various kinds now in the market. For stationary boilers, the Mississippi gauge cock is, perhaps, as good as any. For portable engines a compression gauge-cock is, perhaps, the best. The lower gauge-cock should be at least 2" above the tubes or crown sheet, the middle 2" above the first ordinary water line, the upper 2" to 3" above the second, de- pending on the size of the boiler.
A glass water gauge should be provided for each boiler and should be so located that the water level in the boiler when at the lower end of glass shall be one inch above the top of flue. When glass gauges are so fitted the fireman can always tell at a glance just how much water he has above the flues or crown sheet ; it
430 HANDBOOK ON ENGINEERING.
also permits the easy test of accuracy by trying the gauge-cocks with the water at a certain known level. Too much dependence must not be placed on the glass water-gauge alone, but should be used in connection with the gauge-cocks.
A steam gauge is a very important appendage to a steam boiler, and should be chosen with special reference to accuracy and durability. The ordinary gauges now in the market are the bent tube and the diaphragm gauges. It matters little which of the two kinds is selected, provided it is a good and first-class gauge. A steam gauge should be compared with a standard test gauge at least once a year, to see that it is correct. The importance of this will be fully apparent when it is known that it furnishes the only means by which the fireman is to judge of the steam pressure in the boiler. A siphon should be attached to every gauge, and provision should also be made for draining the gauge or siphon, to prevent freezing when steam is off the boiler. Neglect of this may endanger the accurate reading of the steam gauge and render it useless.
Steam dome* — This is a reservoir for steam riveted to the upper portion of the shell and communicated by a central opening with the steam space in the boiler. When this reservoir forms a separate fixture and is attached to the boiler by cast or wrought iron nozzles, it is then called a steam drum. The latter answers all the purposes for stationary boilers that the former does, and is to be preferred because of the smaller openings in the shell of the boiler. A considerable number of boiler explosions have been traced directly to the weakness of the shell, caused by the large opening in and imperfect staying of the shell underneath the dome. When a dome is employed and has a large hole under- neath, the strength of the shell is impaired in two ways: 1. By reducing the longitudinal sectional area of shell through the cen- ter of opening cut for it, which weakness cannot wholly be made good by a strengthening ring around the opening. 2. By causing
HANDBOOK ON ENGINEERING. 431
a tension equal to that on the crown area of steam dome, upon the annular part of the shell covered by the flange of the dome. The weakest part of the boiler shell will be where the distance from rivet hole at the base of the dome to edge of plate is least. It is difficult, owing to the complex nature of the strains, to form a rule whereby to determine how much the strength of the shell is impaired by using a dome ; but it is quite apparent from gen- eral experience that they are in many cases a source of weakness, and the larger the dome connection with the shell, the greater the liability to rupture. This tendency to rupture is due to the fact that the dome, with its connecting flange, is practically inelastic ; that portion of the shell of the boiler covered by the dome is, as soon as the pressure is introduced on both sides of the plate, simply a curved brace. The pressure of the steam in the boiler has a tendency to straighten the shell under the dome and thus brings about a series of complex strains, which are not easily rem- edied by any system of bracing, so that on the whole it is prefer- able to use a small connecting nozzle with a drum above it, rather than to rivet a large dome directly to the shell.
Dry pipe* — This is a pipe having numerous small perforations on its upper side, and inserted in the upper part of the steam space of the boiler. This pipe does not dry the steam, but acts mechanically by separating the steam from the water when the latter is in a violent state of agitation, and is liable to be carried in bulk toward or into the steam pipe. The object of these numer- ous small holes in the pipe is that a small quantity of steam may be taken from a large number of openings at one time, and thus carried over a larger extent of surface than that afforded by a single opening, and by this single device checking the tendency to priming.
Steam boiler furnaces are receiving more attention now than perhaps ever before. The question of economy of fuel is being closely studied, and there is now an effort to save much of the
432 HANDBOOK ON ENGINEERING.
heat, which had formerly been allowed to go to waste. The main thing in furnace construction is to get perfect combustion. With- out this there must be of necessity a great loss constantly going on. There are some losses which it is difficult to prevent, for example — the loss by the admission of too much air in the ash pit ; the loss by incomplete combustion ; the loss occasioned by the heated gases escaping up the chimney ; the loss by radia- tion ; but, chief among these, is that of incomplete combustion. To burn a pound of coal requires about twenty-four pounds of air, or, say 300 cubic feet. Most boiler settings permit from 200 to 300 feet to pass through the fire. It is needless to point out the great source of loss arising from this one cause alone. This may be prevented in a measure by having a suitable damper in the chimney, and regulating the flow of escaping gases by it, instead of the ash pit doors. If the furnace is so constructed that the fuel is imperfectly burned, so that carbonic oxide instead of car- bonic acid gas is formed, the loss is very great. This results often from too little air supply and too low temperature in the furnace. The furnace doors should be provided with an opening leading into the space between the door proper and the liner ; this opening ought to have a sliding or revolving register by which the admission of air may be controlled. By this means, the quantity of air admitted above the fire may be adjusted to its needs by a little attention on the part of the fireman. The liner to the furnace door should have a number of small holes in it, rather than a solid plate, with a space around the edges. Great care should be exercised in the construction of furnace walls, that the materials and workmanship be good throughout. The entire structure should be brick. The outer walls may be of good hard red brick, but the interior walls, around the furnace and bridge wall, should be of fire brick. The best quality of fire brick for withstanding an intense heat are very, very strong and tenacious ; the structure is open and they are free from black
HANDBOOK ON ENGINEERING. 433
spots, due to sulphuret of iron in the clay ; if well burned they will not be very light colored on the outside, and will have a clear ring when struck.
Fire brick should be dipped in a thin mortar made of fire clay, rather than in a lime and sand mortar, such as is used in ordinary red brickwork. In laying up these portions of a boiler furnace requiring fire brick, provision should be made in the original wall for replacing the fire brick and without disturbing the outer brickwork.
CARE AND MANAGEMENT OF A BOILER.
It is not enough that a boiler be of approved design, made of the best materials, and put together in the best manner ; that it have the best furnace and the most approved feed and safety apparatus. These are all desirable, and are to be commended, but cleanliness and careful management are quite essential to get- ting high results, and are also conducive to long use in service.
Pumps* — Special attention should be given at all times to the feed and safety apparatus ; the pumps should be in good working order ; it is preferable that they be independent steam pumps rather than pumps driven by the engine, or by a belt ; they should be kept well packed and the valves in good condition.
Firing* — Kindle a fire and raise steam slowly ; never force a fire so long as the water in the boiler is below the boiling point. The fire should be of an even height, and of such a thickness as will be found best for the particular fuel to be burned, but should be no thicker than actually necessary. In regard to the size of coal used, that will depend upon circumstances. If anthracite coal is used, it should not, for stationary boilers, be larger than ordinary stove coal. For bituminous coal, which is always shipped in lumps as large as can be conveniently handled, the size will vary somewhat in breaking, but it may in general be used in larger lumps than anthracite. If the coal is likely to cake in burn-
28
434 HANDBOOK ON ENGINEERING.
ing, the fire should be broken up quite frequently with a slice bar, or it will fuse into a large mass in the center of the furnace and lower the rate of combustion. If the coal is likely to form a con- siderable quantity of clinker, or enough to become troublesome, it may be advantageous to increase the grate area and thus lower the rate of combustion per square foot of grate, and have a fire of less intensity. The fire should be kept free from ashes, and the ash pit should be kept clean. Whenever the fire door of a steam boiler furnace is opened, the damper should be closed to prevent the sudden reduction of temperature underneath, which is likely to injure the boiler by contraction, and thus render it likely to spring a leak around the riveted joints. Some firemen are very careless in this respect, and there is little doubt that many a dis- agreeable job of repairing a leaky seam might be prevented by this simple precaution.
Gauge cocks should be used constantly to keep them free from any accumulation of sediment. It is a very common practice to rely wholly on the indications of the glass water gauge for the water level in the boiler. This is all wrong and should be dis- continued, if once begun. The glass water gauge serves a very useful purpose, but it should not be wholly relied on in practice. In using the ordinary gauge cocks, the ear more than the eye, detects the water level, and thus acts as a check on the indications given by the glass gauge.
Water gauges should be tested several times during the day to see that they are clear, and to keep them free from any sediment likely to form around the lower opening to the water in the boiler. If this is not attended to, the water gauge is likely to indicate a wrong water level and a serious accident may be the result.
Steam or pressure gauges are likely to become set after long use and should be tested at least once, or better still, twice a year by a standard gauge known to be correct. They should also be
HANDBOOK ON ENGINEERING. 435
tested every few days if the boilers are constantly under steam by turning off the steam and allowing the pointer to run back to zero. If there are two or more boilers set together in one battery, and each boiler has its own steam gauge, and which will, starting from the zero point, indicate the same pressure on all the gauges, they may be assumed to be correct.
Blow-off cocks or valves should be examined frequently and should never be allowed to leak. In general a cock is to be pre- ferred to a valve, but both is safer than one ; if the latter is selected it should be some one of the various u straight- way valves," of which there are now several in the market. If the cock is a large one, and especially if it has either a cast iron shell or plug, it should be taken apart after each cleaning out of the boilers, examined, greased with tallow and returned.
Blowing out* — This should be done at least once a day, except in the very rare instances in which water is used that will not form a scale. The water should not be let out of a boiler or boilers until the furnace is quite cold , as the heat retained in the walls is likely to injure an empty boiler directly by overheating the plates, and indirectly by hardening the scale within the boiler. Bad effects are likely to follow when a boiler is emptied of its water before the side walls have become cool ; but greater injury is likely to result when cold water is pumped into an empty boiler heated in this manner. The unequal contraction of the boiler is likely to produce leaky seams in the shell and to loosen the tubes and stays. It is a better plan to allow the boiler to remain empty until it is quite cold, or sufficiently reduced in tem- perature to permit its being filled without injury. Many boilers of good material and workmanship have been ruined by the neglect of this simple precaution.
Fusible plugs should be carefully examined every six months, as scale is likely to form over the portion projecting into the water space. It is only a question of time when this scale
436 HANDBOOK ON ENGINEERING.
would form over the end of the plug, and thick enough to with- stand the pressure of steam and thus fail in the accomplishment of the very object for which it was introduced. This applies espe- cially to the fusible plugs inserted in the crown sheets of portable engine boilers.
Cleaning tubes* — This should be done every day if bitumin- ous coal is used. A portable steam jet will be found an extremely useful contrivance which will keep them reasonably clean by blow- ing out the loose soot and ashes deposited in the tubes. Every two or three days, or at least once a week, a tube scraper or stiff brush should be used to take out all the ashes or soot adhering to the tubes and which cannot be blown out with the jet. Flues may be cleaned the same way but will not require to be done so frequently.
Low water* — If from any cause the water gets low in the boiler, bank the fire with ashes or with fresh coal as quickly as possible, shut the damper and ash pit doors and leave the fire doors wide open ; do not disturb the running of the engine but allow it to use all the steam the boiler is making; do not under any circumstances attempt to force water in the boiler. After the steam is all used and the boiler cooled sufficiently to be safe, then the water may be admitted and brought up to the reg- ular working height ; the damper opened and the fires allowed to burn and steam raised as usual; provided, no injury has been done the boiler by overheating.
Foaming and priming are always troublesome and often danger- ous. Some boilers prime almost constantly, because of their bad proportion, and will require the constant care of the person in charge, especially at such times as the engine may be using the steam up to the full capacity of the boiler. In a case of this kind, an increase in pressure will often check, but will not entirely prevent it ; nothing short of an increase of water surface, or a better circulation of water, or a larger steam room will afford a
HANDBOOK ON ENGINEERING. 437
complete remedy. If the foaming or priming is due to a sudden liberation of steam, or on account of impure feed water it may be checked by closing the throttle valve to the engine and opening the fire door for a few minutes. The surface blow may be used with advantage at this time, by blowing off the impurities collected on the surface of the water. The feed pump may be used if necessary, but care should be exercised that too much cold water be not forced into the boiler, and thus lose time by having to wait for the accumulation of the regular steam pressure required for the engine. The dangers attending foaming or priming are : the laying bare of heating surfaces in the boiler, and of breaking down the engine by working water into the cylinder. The com~ monest damage to the engine being either the breaking of a cylin- der head, or the cross-head, or the breaking of the piston. Wbeu boilers are new and set to work for the first time priming is a very frequent occurrence ; in fact, it may be said that for the first few days there is always more or less of it. All that is needed during this time is a little care on the part of the attendant to see that the water is kept up to the required level in the boiler ; it is also recommended that the throttle valve to the engine be partially closed to prevent any very great variation of pressure in the boiler, and thus prevent water passing over with the steam in such quantities as to become dangerous. If a boiler continues to prime* after it has had a weeR's work and then thoroughly cleaned, the causes are to be attributed to other than the grease and dirt in it, which are inseparable from the manufacture. As already said, priming may be caused by a sudden reduction of pressure ; that is, a boiler may be working smoothly and well with, say, 80 pounds pressure ; if an increase of load be suddenly applied to an engine so as to reduce the pressure to 70 or 60 pounds, this sudden reduction of pressure will almost always cause priming ; the less the steam space in the boiler, the greater the tendency to prime, and the greater the
438 HANDBOOK ON ENGINEERING.
difficulty in checking it. The only permanent cure for this is more boiler power ; as a temporary expedient, the engine should be throttled sufficiently to make the drain upon the boiler con- stant instead of intermittent. If the duty required of an engine is irregular, the steam pressure should be carried higher ; in any case similar to the above, it is recommended that the pressure be increased to 90 or 100 pounds and the throttling to begin with the increased drain upon the boiler. But this is at best a mere makeshift, and a larger boiler power becomes imperative both on the score of economy and safety.
WATER FOR USE IN BOILERS.
Water is never pure, except when made so in a laboratory or by distillation ; the impurities may be divided into four classes : 1. Mechanical impurities. 2. Gaseous impurities. 3. Dissolved mineral impurities. 4. Organic impurities.
(a) Mechanical impurities may be both mineral and organic. The commonest suspended impurity in water is mud or sand ; these may be removed by filtration or by allowing the water to stand long enough to let them settle to the bottom of the tank or cistern and then carefully drawing the water from the top, and without disturbing the bottom.
(b) Gaseous impurities in water vary somewhat according to the localities from which they are obtained. The commonest gases found in the water are an excess of oxygen, nitrogen and carbonic acid. These have no effect on water intended for steam boilers.
(c) Dissolved mineral impurities in water are of the most varied description, and are almost always found in it. Among these are found salts of iron, sulphate and carbonates of lime ; sulphate and carbonates of magnesia ; salt and alkalies, such as soda, potash, etc. ; acids, such as sulphuric, phosphoric, and others. All of these are more or less injurious to steam boilers. The most objectionable are the salts of lime and magnesia, which impart to water that property known as hardness. When such
HANDBOOK ON ENGINEERING. 439
water is used in a steam boiler a scale will gradually form, which will, in a short time, become very troublesome.
(d) Organic impurities are present, to a certain extent, in most waters. They are sometimes present in the water in suffi- cient quantities to give it a very decided color and taste.
The presence of organic matter in water is often dangerous to health, and may be a means of spreading contagious diseases, but has little or no bad effect in any water used for steam boilers. In general, water is regarded by engineers as being either soft, hard or salt.
Ebullition is the motion produced in a liquid by its rapid conversion into vapor. When heat is applied to the bottom of a boiler, the particles of water in contact with the plates become heated and immediately expand, and becoming specifically lighter, pass upwards through the colder body of water above ; the heat of the furnace is in this way diffused throughout the whole body of water in the boiler by a translation of the particles of water from below upwards, and from top to bottom in regular succession. After a time this liquid mass becomes heated to a degree in which there is a violent agitation of the whole body of water, steam is given off and it is said to boil. The temperature at the boiling point of water, at ordinary atmospheric pressure, is 212° Fahr., and increases as the pressure of steam above it increases.
Distilled water for boilers is not to be recommended without some reservation. Chemically pure water, and especially water which has been redistilled several times, has a corrosive action on iron which is often very troublesome. The effect on steel plates by the use of water several times redistilled, such, for example, as that supplied for heating buildings, is well known ; information is yet wanting which shall point with certainty to the exact change which the water undergoes and explain why its action on or affinity for steel is so greatly intensified. It has been suggested as a means of neutralizing this corrosive action of the water, to
440 HANDBOOK ON ENGINEERING.
introduce with the feed other water, which shall have the prop- erty of forming a scale and continuing it long enough and at such intervals as will permit the formation of a thin scale in the interior of the boiler. However objectionable this may seem at first sight, it is at present the best practical solution of the difficulty.
Scale is a bad conductor of heat and is opposed to economical evaporation. It is estimated that a thickness of half an inch of hard scale firmly attached to a boiler plate will require a temper- ature of about 700° Fahr. in the boiler plate in order to raise and maintain an ordinary steam pressure of 75 pounds. The mis- chievous effects of accumulated scale in the boiler, especially in the plates immediately over the fire, are : (1) preventing the water from coming in contact with the plates, and thus directly con- tributing to the overheating of the latter; and (2) by causing a change of structure in the plates and the consequent weakening brought about by this continual overheating, which would, in a short time, render an iron or a steel plate wholly unfit for use in a steam boiler. The two principal ingredients in boiler scale are lime and magnesia. The lime, when in combination with carbonic acid, forms carbonate of lime ; when in combination with sulphuric acid, it then becomes sulphate of lime. This is also true of magnesia.
Carbonate of lime will form in the boiler as a loose powder, which is held mechanically in suspenion ; while in this stage it may be blown out of the boiler without injury to it ; but it is seldom that a pure carbonate is formed in the boiler as there are other impurities in the water with which it combines to form a hard scale. This is especially true in such waters as also contain sulphate of lime in solution. This fine powder (carbonate of lime), will form a hard scale should any adhere to the sides or bottom of a boiler ; in any case where the boiler is blown out dry while the furnace walls are still hot; and this, in itself, forms an excellent reason why boilers should stand until the furnace walls
HANDBOOK ON ENGINEERING. 441
are cold before blowing out. When emptied, nearly or all of this slushy deposit may be washed out of the boiler by means of a hose.
Sulphate of lime is not so easily got rid of, as it is heavier than carbonate of lime and adheres to the plates while the boiler is at work. It is the most troublesome scale steam engineers have to deal with ; it is very difficult to remove and by successive layers becomes dangerous, on account of the thickness to which it eventually accumulates.
The carbonates of lime and magnesia may be largely arrested by passing the feed water through a suitable heater and lime extractor. It must be apparent to every one that any device which will accomplish this is a very desirable attachment to a steam boiler. As it is not possible to eliminate all the foreign matter in the water from it, recourse is often had to the use of solvents and chemical agencies for the prevention of scale. Some of these are very simple and within easy reach ; others are sur- rounded by an atmosphere of uncertainty and the real nature of the compound is hidden under a meaningless trade-mark. For carbonate of lime, potato has been found to be very service- able in preventing the formation of scale ; its action appears to be that of surrounding the particles of lime with a coating of starch and gelatine, and thus preventing the cohesion of these particles to form a mass. Various astringents have been used for this purpose, such as extracts of oak and hemlock bark, nutgalls, catechu, etc., with varying success.
Carbonate of soda has been used and with very great success in some localities, not only in preventing, but in actually removing scale already formed. It acts on carbonate of lime, not only, but on the sulphate also. It is clean, free from grit, and is quite unobjectionable in the boiler ; one or more pounds per day, de- pending on the size of the boiler, may be admitted through the pump with the feed water ; or admitted in the morning before
442 HANDBOOK ON ENGINEERING.
firing up, by simply mixing with water and pouring into the boiler through the safety valve or other opening.
Tannate of soda has been similarly employed and is an excel- lent scale preventive. It will also act as a solvent for scale already formed in the boiler, acting on sulphate as well as carbon- ate of lime.
Crude petroleum has been found very beneficial in removing the hard scale composed principally of sulphate of lime.
Zinc in steam boilers* — The employment of zinc in steam boilers, like that of soda, has been adopted for two distinct objects: (1) to prevent corrosion, and (2) to prevent and remove incrustation. To attain the first object, it has been used chiefly in marine boilers, and for the second, chiefly in boilers fed with fresh water. In order that the application of zinc in marine boilers may be effective, it is necessary that the metallic contact should be insured. If galvanic action alone is relied upon for the protection of the plates and tabes, it will doubtless be diminished materially by the coating of oxide that exists between all joints of plates, whether lapped or butted, and also between the rivets and the plates. Assuming the preservative action of zinc to be proved when properly applied, we have now two systems for preventing the internal decay of marine boilers, viz. : allowing the plates and tubes to become coated with scale, and employing zinc. It remains to decide which of these two systems is the best with respect to economy and practicability.
We come now to consider the use of zinc for preventing arid removing incrustation.
At one time it was considered that the action of zinc in pre- venting incrustation was physical or mechanical. The particles of zinc, as it wasted away, were supposed to become mixed amongst the solid matter precipitated from the water, in such a manner as to prevent it adhering together, so as to form a hard scale ; or the particles of zinc were supposed to become deposited
HANDBOOK ON ENGINEERING. 443
upon the plates, and so prevent the scale from adhering to them. Then it was suggested that the zinc acted chemically, and now, it is the generally received opinion that its action is galvanic in preventing incrustation as well as in preventing corrosion. When the water contains an excess of sulphates or chlorides over the carbonates, the acid of the former will form soluble salts with the oxide of zinc, the surface of the zinc will be kept clean, and the galvanic current, to which the efficiency of the zinc is due, will be maintained. On the other hand, should there be a preponderat- ing amount of carbonates, the zinc will be covered first with oxide, then with carbonates and its useful action arrested and stopped. It is quite as important that the zinc should be in metallic con- tact with the plates when used to prevent incrustation, as when employed to prevent corrosion. The application of zinc for the former purpose should never be attempted without first having the water analyzed in order to ascertain whether it is likely to be effective. The use of zinc in externally fired boilers should be attempted with great caution, as when efficacious in preventing the formation of a hard scale, it is liable to produce a heavy sludge that may settle over the furnace plates and lead to over- heating. On the whole we cannot but regard the evidence as to the effect of zinc upon incrustation as being very conflicting.
Leaks should be stopped as soon as possible after their dis- covery ; the kind of leak will indicate the treatment necessary. If it occurs around the ends of the tubes, it may be stopped by expanding the tubes anew ; if in a riveted joint, it should be care- fully examined, especially along the line of the rivets and care should be exercised in determining whether there is a crack extending from rivet to rivet along the line of the holes ; should this prove to be the case, the boiler is then in an extremely dangerous condition and under no circumstances should it be again fired up until suitable repairs have been made which will insure its 'safety.
444 HANDBOOK ON ENGINEERING.
Blisters occur in plates which are made up of several thick- nesses of iron and which from some cause were not thoroughly welded before the final rolling into plates. When such a plate comes in contact with the heat of the furnace the thinnest portion of the defective plate 4t buckles " and forms what is called a blister. As soon as discovered, there should be thorough exami- nation of the plate and if repairs are needed there should be as little delay as possible in making them. If the blister be very thin and altogether on the surface it may be chipped and dressed around the edges ; if the thickness is equal or exceeds Ty the blister should be cut off and patched, or a new plate put in.
Patching boilers* — When a boiler requires patching it is bet- ter to cut out the defective sheets and rivet in a new one ; or if this cannot be done, a new piece large enough to cover the defect in the old sheet may be riveted over the hole from which the defective portion has been cut. If this occurs in any portion of the boilei subject to the action of fire, the lap should be the same as the edges of the boiler seams, and should be carefully calked around the edges after the riveting. Whenever the blisters occur in a plate, patching is a comparatively simple thing as against the repairs of a plate worn by corrosion. In the latter case, the defective portions of the plate should be entirely removed and the openings should show sound metal all around and of full thick- ness. If this cannot be obtained within a reasonable sized open- ing then the whole plate should be removed.
It often occurs that a minor defect is found in a plate and at a time when it is not convenient to stop for repairs ; in such an event a " soft" patch is often applied. This consists of a piece of wrought iron carefully fitted to that portion of the boiler plate needing repairs ; holes are fitted in both plates and patch, and " patch bolts " provided for them. A thick putty consisting of white and red lead with iron borings or filings in them placed evenly over the inner surface of the patch, which is then tightly
HANDBOOK ON ENGINEERING. 445
bolted to the boiler plate. This is best but a temporary make- shift and ought never to be regarded as a permanent repair. A mistake is often made of making a patch of thicker metal than that of the shell of the boiler needing it. A moment's reflection ought to show the absurdity of putting on a T5F or f patch on an old J inch boiler shell ; yet it is not so rare as one would imagine. A piece of new iron T3^" thick will, in most cases, be found to be stronger than that portion of a J" old plate needing repairs.
Inspection* — A careful external and internal examination of a boiler is to be commended for many reasons. This should be as frequent as possible and thoroughly done ; it should include the boiler not only, but all the attachments which affect its working or pressure. Particular attention should be paid to the examina- tion of all braces and stays, safety valve, pressure gauges, water gauges, feed and blow-off apparatus, etc. ; these latter refer more particularly to constructive details necessary to proper manage- ment and safety. The inspection would obviously be incomplete, did it not include an examination into the causes of " wear and tear," and determine the extent to which it had progressed. Among the several causes which directly tend to rendering a boiler unsafe, may be mentioned the dangerous results occasioned by the overheating of plates, thus changing the structure of the iron from fine granular, or fibrous, to coarse crystalline. This may easily be detected by examination, and will in general be found to occur in such cases where the boilers are too small for the work, are fired too hard, or have a considerable accumulation of scale or sediment in contact with the plates. Blistered plates are almost instantly detected at sight, so also is corrosion, from whatever cause it may have proceeded.
Corrosion of boiler plates* — Iron will corrode rapidly when subjected to the intermittent action of moisture and dryness. Land boilers are less subject to corrosion than marine boilers. The corrosion of a boiler may be either external or internal. Ex-
446 HANDBOOK ON ENGINEERING.
ternal corrosion may, in general, be easily prevented by carefully caulking all leaks in the boiler ; by preventing the dropping of water on the plates, such, for example, as from a leaky joint in the steam pipe or from the safety valve. A leaky roof, by allow- ing a continual or occasional dropping of water on the top of a boiler, especially if the boiler is not in constant use, would pro- mote external corrosion. Sometimes external corrosion is caused by the use of coal having sulphur in it, and acts in this way : The sulphur passes off from the fire as sulphurous oxide, which often attaches to the sides of a boiler ; so long as this is dry no especial mischief is done ; but if it comes in contact with a wet plate the sulphurous oxide is converted into sulphuric acid over so much of the surface as the moisture extends ; this acid attacks, and will, in time, entirely destroy the boiler plate. Internal corrosion is not so easily accounted for and is very difficult to correct, especially when it occurs above the water line. It is generally believed to be due to the action of acids in the feed water. Marine boilers are especially subject to internal corrosion when used in connection with surface condensers. A few years ago it was generally supposed to be due to galvanic action but that idea is now almost entirely given up. From the fact that boilers using distilled water fed into them from surface condensers are more liable to internal corrosion than other boilers, has led to the theory that it is the pure water that does the mischief, and that a water containing in slight degree a scale-forming salt, is to be preferred to water which is absolutely pure. Whatever maybe the truth or falsity of this theory, it is a well established fact that distilled water has a most pernicious action on various metals, especially on steel, lead and iron. This action is attributed to its peculiar property, as compared with ordinary water, of dissolving free carbonic acid. One of the worst features in connection with internal corrosion is that its progress cannot be easily traced on account of the boiler being closed while at work. As it does not
HANDBOOK ON ENGINEERING. 447
usually extend over any very great extent of surface, the ordinary hydraulic test fails to reveal the locality of corroded spots ; the hammer test, on the contrary, rarely fails to locate them, if the plates are much thinned by its action.
Testing boilers* — It is the general practice to apply the hydraulic test to all new steam boilers at the place of manufacture, and before shipment. The pressure employed in the test is from one and a half to twice the intended working steam pressure. This test is only valuable in bringing to notice defects which would escape ordinary inspection. It is not to be assumed that it in any way assures good workmanship, or material, or good design, or proper proportions ; it simply shows that the boiler being tested is able to withstand this pressure without leak- ing at the joints, or distorting the shell to an injurious degree. Bad workmanship may often be detected at a glance by an expe- rienced person. The material must be judged by the tensile strength and ductility of the sample tested. The design and pro- portions are to be judged on constructive grounds, and have little or nothing in common with the hydraulic test. The great majority of buyers of steam boilers have but little knowledge on the sub- ject of tests, and too often conclude that if they have a certified copy of a record showing that a particular boiler withstood a test of say, 150 Ibs., it is a good and safe boiler at 75 to 100 Ibs. steam pressure. If the boiler is a new one and by a reputable maker, that may be true ; if it has been used and put upon the market as a second-hand boiler, it may be anything but safe at half the pressure named. By the hydraulic test, the braces in a boiler may be broken, joints strained so as to make them leak, bolts or pins may be sheared off, or so distorted as to be of little or no service in resisting steam when pressure is on.
Hammer test* — The practice of inspecting boilers by sounding with a hammer is, in many respects, to be commended. It requires some practical experience in order to detect blisters and
448
HANDBOOK ON ENGINEERING.
tlie wasting of plates, by sound alone. The hammer test is especially applicable to the thorough inspection of old boilers. It frequently happens in making a test that a blow of the hand hammer will either distort it, or be driven entirely through the plate ; and it is just here that the superiority of this method of testing over, or in connection with the hydraulic test, becomes fully apparent. The location of stays, joints and boiler fittings all modify and are apt to mislead the inspector if he depends upon sound alone. There is a certain spring of the hammer and a clear ring indicative of sound plates, which are wanting in plates much corroded or blistered. The presence of scale on the inside of the boiler has a modifying action on the sound of the plate. When a supposed defect is discovered, a hole should be drilled through the sheet by which its thickness may be determined, as well as its condition.
In order to thoroughly inspect a boiler, the inspector should crawl into the boiler (when it is possible to do so) and he should look for pitting and grooving of plates, test all braces, and examine all inlets and outlets.
TOTAL STORED ENERGY OP STEAM BOILERS.
|
Grate Surface. |
Heating Surface. |
Steam Pressure. |
Rated |
Energy in Foot Pounds Stored in the |
||
|
feq. Ft. |
Sq. Ft. |
Lbd. |
H. P. |
Water. |
Steam. |
Total. |
|
15 |
120 |
100 |
10 |
46605200 |
676698 |
47281898 |
|
15 |
875 |
125 |
425 |
64253160 |
1302431 |
65556691 |
|
20 |
400 |
150 |
35 |
80572050 |
2377357 |
8294 9407 |
|
20 |
1200 |
125 |
600 |
64452270 |
1766447 |
66218718 |
|
22 |
1070 |
125 |
525 |
52561075 |
1483896 |
54044971 |
|
30 |
852 |
75 |
60 |
60008790 1022731 |
51031521 |
|
|
30 |
1350 |
125 |
650 |
69148790 21358U2 |
71284692 |
|
|
32 |
768 |
75 |
300 |
71272370 1462430 |
72734800 |
|
|
36 |
730 |
30 |
60 |
57570750 |
709310 |
58260060 |
|
50 |
1119 |
75 |
350 |
107408340 2316392 |
109724732 |
|
|
70 |
2806 |
100 |
250 |
172455270 |
2108110 |
1745633feO |
|
72 |
1755 |
30 |
180 |
102628410 |
1643854 |
104272264 |
|
72 |
2324 |
bO |
200 |
90531490 |
1570517 |
92101987 |
|
100 |
3000 |
100 |
250 |
227366000 |
3513830 |
230879830 |
HANDBOOK ON ENGINEERING. 449
CHAPTER XVII. USE AND ABUSE OF THE STEAM-BOILER.
Steam-boilers* — A steam-boiler may be defined as a close vessel, in which steam is generated. It may assume an endless variety of forms, and can be constructed of various materials. Since the introduction of steam as a motive power a great variety of boilers have been designed, tried and abandoned; while many others, having little or no merit as steam generators, also have their advocates and are still continued in use. Under such cir- cumstances, it is not surprising that quite a variety of opinions are held on the subject. This difference of opinion relates not only to the form of boiler best adapted to supply the greatest quantity of steam with the least expenditure of fuel, but also to the dimensions or capacity suitable for an engine of a given num- ber of horse-power ; and while great improvements have been made in the manufacture of boiler materials within the past fifteen years, yet the number of inferior steam-boilers seem to increase rather than diminish. It would be difficult to assign any reasonable cause for this, except that, of late years, nearly the whole attention of instructors and mechanical engineers has been directed to the improvement and perfection of the steam-engine, and practical engineers, following the example set by the leaders, devote their energies to the same object. This is to be regretted, as the construction and application of the steam-boiler, like the steam-engine, is deserving of the most thorough and scien- tific study, as on the basis of its employment rest some of the most important interests of civilization. Until quite recently, the idea was very generally entertained that the purely mechanical skill required to enable a person to join
450 HANDBOOK ON ENGINEERING.
-
together pieces of metal, and thereby form a steam-tight and water-tight vessel of given dimensions, to be used for the gen- eration of steam to work an engine, was all that was needed ; experience has shown, however, that this is but a small portion of the knowledge that should be possessed by persons who turn their attention to the design and construction of steam-boilers, as the knowledge wanted for this end is of a scientific as well as of a mechanical nature. As the boiler is the source of power and the place where the power to be applied is first generated, and alsc the source from which the most dangerous consequences may arise from neglect or ignorance, it should attract the special attention of the designing and mechanical engineer, as it is well known that from the hour it is set to work, it is acted upon by destroy- ing forces, more or less uncontrollable in their work of destruc- tion. These forces may be distinguished as chemical and mechanical. In most cases they operate independently, though they are frequently found acting conjointly in bringing about the destruction of the boiler, which will be more or less rapid accord- ing to circumstances of design, construction, quality of material, management, etc. The causes which most affect the integrity of boilers and limit their usefulness are either inherent in the mate- rial, or due to a want of skill in their construction and manage- ment ; they may be enumerated as follows : —
First, inferior material ; second, slag, sand or cinders being rolled into the iron ; third, want of lamination in the sheets ; fourth, the overstretching of the fiber of the plate on one side and puckering on the other in the process of rolling, to form the circle for the shell of a boiler ; fifth, injuries done the plate in the pro- cess of punching ; sixth, damage induced by the use of the drift- pin ; seventh, carelessness in rolling the sheets to form the shell, as a result of which the seams, instead of fitting each other exactly, have in many instances to be drawn together by bolts, which aggravates the evils of expansion and contraction when the
HANDBOOK ON ENGINEERING. 451
boiler is in use ; eighth, injury done the plates by a want of skill in the use of the hammer in the process of hand-riveting ; ninth, damage done in the process of calking.
Other causes of deterioration are unequal expansion and con- traction, resulting from a want of skill in setting ; grooving in the vicinity of the seams ; internal and external corrosion ; blowing out the boiler when under a high pressure and filling it again with cold water when hot ; allowing the fire to burn too rapidly after starting, when the boiler is cold ; ignorance of the use of the pick in the process of scaling and cleaning ; incapacity of the safety- valve ; excessive firing ; urging or taxing the boiler beyond its safe and easy working capacity; allowing the water to become low, and thus causing undue expansion ; deposits of scale accum- ulating on the parts exposed to the direct action of the fire, thereby burning or crystallizing the sheets or shell ; wasting of the material by leakage and corrosion ; bad design and construction of the different parts ; inferior workmanship and ignorance in the care and management. All these tend with unerring certainty to limit the age and safety of steam boilers. On account of want of skill on the part of the designer and avarice on the part of the manufacturer, or perhaps both reasons, boilers are sometimes so constructed as to bring a riveted seam directly over the fire, the result of which is that in consequence of one lap covering the other, the water is prevented from getting to the one nearest the fire, for which reason the lap nearest the fire becomes hotter and expands to a much greater extent than any other part of the plate ; and its constant unequal expansion and contraction, as the boiler becomes alternately hot and cold, inevitably results in a crack. Such blunders are aggravated by the scale and sediment being retained on the inside, between the heads of the rivets, which should be properly removed in cleaning.
The tendency of manufacturers to work boilers beyond their capacity, especially when business is driving, is too great in this
452 HANDBOOK ON ENGINEERING.
country ; and no doubt many boiler explosions may be attributed to this cause. Boilers are bought, adapted to the wants of the manufactory at the time, but, as business increases, machinery is added to supply the demand for goods, until the engine is overtasked, the boiler strained and rendered positively danger- ous. Then again, it not unfrequently occurs that engines in manufactories are taken out and replaced by those of increased power, while the boilers used with the old engine are retained in place, with more or less cleaning and patching, as the case may require. Now, it is evident to any practical mind that boilers constructed for a twenty horse power engine are ill adapted to an engine of forty horse power, more especially if those boilers have been used for a number of years. In order to supply sufficient steam for the new engine, with a cylinder of increased capacity, the boiler must be worked beyond its safe working pressure, consequently excessive heating and pressure greatly weaken it and endanger the lives of those employed in the vicinity. The danger and impracticability of using boilers with too limited steam room may be explained thus : Suppose the entire steam room in a boiler to be six cubic feet, and the contents of the cylinder which it supplies to be two cubic feet ; then at each stroke of the piston one-third of all the steam in the boilers is discharged, and consequently, one-third of the pressure on the surface of the water before that stroke is relieved ; hence, it will be seen that excessive fires must be kept up in order to generate steam of sufficiently high temperature and pressure to supply the demand. The result is that the boilers are strained and burned. Such economy in boiler power is exceedingly expensive in fuel, to say nothing of the danger. Excessive firing distorts the fire- sheets, causing leakage, undue and unequal expansion and con- traction, fractures, and the consequent evils arising from external corrosion. Excessive pressure arises generally from a desire on the part of the steam-user to make a boiler do double the work for
HANDBOOK ON ENGINEERING. 453
which it was originally intended. A boiler that is constructed to work safely at from fifty to sixty pounds was never intended to run at eighty and ninety pounds ; more especially if it had been in use for several years. Boilers deteriorated by age should have their pressure decreased, rather than increased.
One of the first things that should be done in manufacturing establishments would be to provide sufficient boiler power and, in order to do this, the work to be done ought to be accurately cal- culated and the engine and boilers adapted to the results of this calculation. Steam users themselves are frequently to blame for the annoyances and dangers arising from unsafe boilers and those of insufficient capacity. From motives of false economy they are too easily swayed in favor of the cheaper article, simply because it is cheap, when they should consider they are purchasing an article which, of almost all others, should be made in the most thorough manner and of the best material. In view of the fearful explosions that occur from time to time, every steam user should secure for his use the best and safest. The object of a few dollars as between the work of a good, responsible maker and that of an irresponsible one, should not for one moment be entertained.
It is very bad policy for steam-users to advertise for estimates for steam-boilers, or to inform all the boilermakers in the town or city that a boiler or boilers to supply steam for an engine of a certain size is needed, because in this way steam-users frequently find themselves in the hands of needy persons, who, in their anxiety to get an order, will sometimes ask less for a boiler than they can actually make it for ; consequently, they have to cheat in the material, in the workmanship, in the heating surface and in the fittings. As a result, the boiler is not only a continual source of annoyance, but, in many instances, an actual source of danger. The most prudent course, and in fact the only one that may be expected to give satisfaction, is to contract with some responsible
434 HANDBOOK ON ENGINEERING.
manufacturer that has an established reputation for honesty, capability and fair dealing, and who will not allow himself to be brought in competition with irresponsible parties for the purpose of selling a boiler. There are thousands of boilers designed, con- structed and set up in such a manner as to render it utterly impossible to examine, clean or repair them. Generally, in such cases, in consequence of imperfect circulation, the water is expelled from the surface of the iron at the points where the extreme heat from the furnace impinges, and, as a result, the plates become overheated and bulge outward, which aggravates the evil, as the hollow formed by the bulge becomes a receptacle for scale and sediment. By continued overheating, the parts become crystallized and either crack or blister ; this, if not attended to and remedied, will eventually end in the destruction of the boiler. Many boilers, to all appearance well made and of good material, give considerable trouble by leakage and fracture, owing to the severe strains of unequal expansion and contraction induced by the rigid construction, the result of a want of skill in
the original design.
•
DESIGN OF STEAM-BOILERS.
It has become a general assertion on the part of writers on the steam-boiler that the most important object to be attained in its design and arrangement is thorough combustion of the fuel. This is only partially true as there are other conditions equally important, among which are strength, durability, safety, economy and adaptability to the particular circumstances under which it is to be used. However complete the combustion may be, unless its products can be easily and rapidly transferred to the water, and unless the means of escape of the steam from the surfaces on which it is generated is easy and direct, the boiler will fail to produce satisfactory results, either in point of durability or economy of fuel.
HANDBOOK ON ENGINEERING. 455
Strength means the power to sustain the internal pressure to which the boiler may be subjected in ordinary use, and under careful and intelligent management. To secure durability, the material must be capable of resisting the chemical action of the minerals contained in the water, and the boiler ought to be designed so as to procure the least strain under the highest state of expansion to which it may be subjected — be so constructed that all the parts will be subjected to an equal expansion, con- traction, push, pull and strain, and be intelligently and thoroughly cared for after being put in use. These objects, however, can only be obtained by the aid of a knowledge of the principles of mechanics, the strength and resistance of materials, the laws of expansion and contraction, the action of heat on bodies, etc. The economy of a steam boiler is influenced by the following con- ditions: cost and quantity of the material, design, character of the workmanship employed in its construction, space occupied, capa- bility of the material to resist the chemical action of the ingredi- ents contained in the water, the facilities it affords for the transmission of the heat from the furnace to the water, etc. The safety of any structure depends on the designer's knowledge of the principles of mechanics, the resistance of materials and the action of bodies as influenced by the elements to which they are exposed ; and -in the case of steam boilers, the safety depends on the judgment of the designer, the quality of the material, the character of the workmanship and the skill employed in the man- agement. Safety is said to be incompatible with economy, but this is undoubtedly a mistake, as an intelligent economy includes permanence and seeks durability. Adaptability to the peculiar purposes for which they are to be used is one of the first objects to be sought for in the design and construction of any class of machines, vessels or instruments, and it is undoubtedly this that gave rise to the great variety of designs, forms and modifications of steam boilers in use at the present day, which are, with very
456 HANDBOOK ON ENGINEERING.
few exceptions, the result of thought, study, investigation and experiment.
FORMS OF STEAfl-BOILERS.
According to the well-known law of hydrostatics, the pressure of steam in a close cylindrical vessel is exerted equally in all directions. In acting against the circumference of a cylinder, the pressure must, therefore, be regarded as radiating from the axis, and exerting a uniform tensional strain throughout the inclosing material.
Familiarity with steam machinery, more especially with boil- ers, is apt to beget a confidence in the ignorant which is not founded on a knowledge of the dangers by which they are contin- ually surrounded ; while contact with steam, and a thoroughly elementary knowledge of its constituents, theory and action, only incline the intelligent engineer and fireman to be more cautious and energetic in the discharge of their duties. Many regard steam as an incomprehensible mystery ; and although they may employ it as a power to accomplish work, know little of its character or capabilities. Steam may be managed by common sense rules as well as any other power ; but if the laws which regulate its use are violated, it reports itself, and often in louder tones than is pleasant. If steam-boilers in general were better cared for than they are, their working age might be greatly in- creased. Deposits of incrustation, small leaks and slight cor- rosion, are too often neglected as matters of little consequence, but they are the forerunners of expensive repairs, delay and disaster.
SETTING STEAM-BOILERS.
While engineers differ very much in opinion respecting the best manner of setting boilers, they all readily allow that the results obtained, as regards economy of fuel and the generation of steam,
HANDBOOK QN ENGINEERING. 457
depend in a great measure on the arrangement of the setting. Particularly is this the case with horizontal tubular boilers, and there have been numerous plans introduced to obtain a maximum of steam with a minimum of fuel. Some of the most practical designs and best laid plans are frequently rendered useless for want of knowledge on the part of those whose duty it is to exe- cute or carry them out. This has perhaps been more frequently the case as regards the setting of steam boilers than any other class of machines, as it is customary for owners of steam boilers to depend too much on the knowledge of masons and bricklayers ; consequently, a great many blunders have been made which necessitated changes in the size of gratebars, alteration of brick- work, alteration of flues, chimney, etc., with a list of other annoy- ances, such as insufficiency of steam, poor draught, or something else. In setting or putting in boilers, all the surface possible should be exposed to the action of the heat of the fire, not only that the heat may be thus completely absorbed, but that a more equal ex- pansion and contraction of the structure may be obtained. Long boilers are often hung by means of loops riveted to the top of them and connected to crossbeams and arches resting on masonry above them, by means of hangers. This is a very .mischievous arrangement, unless turn-buckles, or some other contrivance, are used to maintain a regular strain on all the hangers, as long boil- ers exposed to excessive heat are apt to lengthen on the lower side and relieve the end hangers of any weight; consequently, the whole strain is transmitted to the central hanger, which has a tendency to draw the boiler out of shape — in many instances inducing excessive leakage, rupture, and, eventually, explosion.
DEFECTS IN THE CONSTRUCTION OF STEAM-BOILERS.
The following cuts illustrate some of the mechanical defects that impair the strength and limit the safety and durability of
458
HANDBOOK ON ENGINEERING.
steam boilers. All punched holes are conical, and unless the sheets are reversed after being punched, so as to bring the small sides of the holes together, it will be impossible to fill them with the rivets. Fig. 251 shows the position of the rivet in the hole without the sheets being reversed ; and it will be observed that, as very little of the rivet bears against the material, the ex- pansion and contraction of the boiler have a tendency to work it loose. It is apparent that such a seam would not possess over one-third the strength that it would if the holes in the sheets
Fig. 251.
Fig. 252.
258.
Fig. 254.
Fig. 255.
Fig. 256.
Showing positions of rivet in rivet hole.
were reversed and thoroughly filled with the rivet, as shown in Fig. 252. Fig. 253 represents what is known in boilermaking as a blind hole, which means that the holes do not come opposite each other when the seams are placed together for the purpose of riveting. Fig. 254 shows the position of the rivet in the blind hole after being driven. It will be observed that the heads of the rivet, in consequence of its oblique position in the hole, bear only on one side, and that even the bearing is very limited, and through the expansion and contraction of the boiler, is liable to
HANDBOOK ON ENGINEERING. 459
work loose and become leaky. Such a seam would be actually weaker than that presented in Fig. 251. Fig. 255 shows the metal distressed and puckered on each side of the blind hole in the sheets, which is the result of efforts on the part of the boiler- maker, by the use of the drift-pin, to make the holes correspond for the purpose of inserting the rivet. Fig. 256 shows the metal broken through by the same means. Now, it will be observed that nearly all the above defects are the result of ignorance and carelessness, showing a want of skill in laying out the work, as well as a want of proper appliances for that purpose. The evils arising from such defects are greatly aggravated by the fact that they are all concealed, frequently defying the closest scrutiny, and are only revealed by those forces which unceasingly act on boilers when in use. Such pernicious mechanical blunders ought to be condemned, as they are always the forerunners of destruction and death. There can be no reason why boilers should not be constructed with the same degree of 'accuracy, judgment and skill as is considered so essential for all other classes of machinery.
IMPROVEMENTS IN STEAM BOILERS.
Until quite recently the steam boiler has undergone very little improvement. This arose, perhaps, from the fact that men of intelligence and mechanical genius directed their thoughts and labors to something more inviting and less laborious than the construction of steam boilers. Consequently, that branch of mechanics was left almost entirely to a class of men that had not the genius to rise in their profession or improve much in anything they attempted. As a result ignorance, stupidity and a kind of brute force were the predominant requirements in the construc- tion of the steam boiler ; but within the past few years this state of things has been changed, as some very important improvements have been made, not only in the manufacture of the material of which boilers are made, but also in the mode of constructing
460 HANDBOOK ON ENGINEERING.
them. The imposing, powerful and accurate- boiler machinery in use at the present time is an evidence that the attention of emi- nent mechanics and manufacturers is directed to the steam boiler, and that in the future its improvement will keep pace with that of the steam engine.
Boiler plate is now rolled of sufficient dimensions to form the rings for boilers of any diameter with only one seam, obviating the necessity of bringing riveted seams in contact with the fire; as was usually the case in former times. In the manner of laying off the holes for the rivets, accurate steel gauges have taken the place of the old-fashioned wooden templet, thereby removing the evils induced by blind holes, and obviating the necessity of using the drift-pin. So, also, in the method of bending the sheets to form the requisite circle — with a better class of machinery, the work is now mo re accurately performed. The old process of chip- ping is, in nearly all the large boilershops, superseded by planing the bevels on the edge of the sheet, preparatory to calking. Recent improvements in u calking " have resulted in perfect immunity from the injuries formerly inflicted on boilers in that process. In most establishments of any repute in this country, riveting is done by machinery, which is (as is well known to all intelligent mechanics) very much superior to hand riveting. It is only small shops that enter into rivalry to secure orders and build cheap boilers, using poor material and an inferior quality of mechanical skill, that use the same old crude appliances — in many cases the merest makeshifts — that were in use a quarter of a century ago, and constructed without regard to any of the rules of design that are considered so essential in appliances for the construction of all other classes of machinery. Every engineer should inform himself on the subject of the safe working pressure of boilers, and when he finds the limit of safety has been reached, he should promptly inform his employer and use his influence to have the boiler worked within the bounds of safety.
HANDBOOK ON ENGINEERING. 461
To find the heating surface of a water tube boiler : —
Rule* — Add the combined outside area of the tubes in square feet to one-half the area of the shell of the steam drum in square feet and the sum will give the total heating surf ace 0
Example f* — What is the heating surface of a water tube boiler having fifty tubes, each three inches outside diameter and fifteen feet long, and the steam drum thirty-two inches in diameter and fifteen feet long ?
Operation* — 3 X 3.1416 equals 9.4248 inches, the circumfer- ence of one tube. 15 X 12 equals 180 inches the length of one
9.4248 X 180 tube. • JIT" " e(luals 11-781 square feet in one tube, and
11.781 X 50 equals 589.05 square feet of heating surface in fifty
32 X 3.1416
tubes. Then, ^ equals 8.3776 linear feet the circum- ference of the steam drum and 8.3776 X 15 equals 125.664 square
125.664 feet of heating surface in steam drum, and 5 equals 62.832
square feet, half the heating surface of steam drum.
Then, 589.05 plus 62.832 equals 651.882 square feet, the total heating surface. Answer.
STRENGTH OF RIVETED SEAflS.
The strength of a riveted seam depends very much upon the arrangement and proportion of the rivets ; but with the best design and construction, the seams are always weaker than the solid plate, as it is always necessary to cut away a part of the plate for the rivet holes, which weakens the plate in three ways: 1st, by lessening the amount of material to resist the strains ; 2d, by weakening that left between the holes ; 3d, by disturbing the uniformity of the distribution of the strains.
462 HANDBOOK ON ENGINEERING.
COMPARATIVE STRENGTH OF SINGLE AND DOUBLE RIVETED SEAMS.
On comparing the strength of plates with riveted joints, it will be necessary to examine the sectional areas taken in a line through the rivet holes, with the section of the plates themselves. It is obvious that in perforating a line of .holes along the edge of a plate, we must reduce its strength. It is also clear that the plate so perforated will be to the plate itself nearly as the areas of their respective sections, with a small deduction for the irregularities of the pressure of the rivets upon the plate ; or, in other words, the joint will be reduced in strength somewhat more than in the ratio of its section through that line to the solid section of the plate. It is also evident that the rivets cannot add to the strength of the plates, their object being to keep the two surfaces of the lap in contact. When this great deterioration of strength at the joint is taken into account, it cannot but be of the greatest importance that in structures subject to such violent strains as boilers, the strongest method of riveting should be adopted. To ascertain this, a long series of experiments was undertaken by Mr0 Fairbairn. There are two kinds of lap joints, single and double riveted. In the early days of steam-boiler construction, the former were almost universally employed ; but the greater strength of the latter has since led to their general adoption for all boilers intended to sustain a high steam pressure. A riveted joint generally gives way either by shearing off the rivets in the middle of their length, or by tearing through one of the plates in the line of the rivets.
In a perfect joint, the rivets should be on the point of shearing just as the plates were about to tear ; but, in practice, the rivets are usually made slightly too strong. Hence, it is an established rule to employ a certain number of rivets per linear foot, which for ordinary diameters and average thickness of plate, are about
HANDBOOK ON ENGINEERING. 463
six per foot or two inches from center to center ; for larger diameters and heavier iron, the distance between the centers is generally increased to, say 2 j- or 2i inches : but in such cases it is also necessary to increase the diameter of the rivet, for while |, or even J inch rivets will answer for small diameters and light plate, with large diameters and heavy plate, experi- ence has shown it to be necessary to use f to J rivets. If these are placed in a single row, the rivet holes so nearly approach each other that the strength of the plates is much reduced ; but if they are arranged in two lines, a greater number may be used, more space left between the holes and greater strength aud stiffness imparted to the plates at the joint. Taking the value of the plate before being punched, at 100, by punching the plate it loses 44 per cent of its strength ; and, as a result, single-riveted seams are equal to 56 per cent, and double- riveted seams to 70 per cent of the original strength of the plate. It has been shown by very extensive experiments at the Brooklyn Navy Yard, and also at the Stevens Institute of Technology, Hoboken, N. J., that double-riveted seams are from 16 to 20 per cent stronger than single-riveted seams — the material and work- manship being the same in both cases :
Taking the strength of the plate at " . 100
The strength of the double-riveted joint would then be . . 70 The strength of the single-riveted would be 56
To find the thickness of plates for the shell of a cylindrical boiler for a required safe working pressure in pounds per square inch : —
Rule* — Multiply the required pressure per square inch by the radius of the shell in inches, and by the constant number 6 for single riveted side seams, and divide the last product by the tensile strength of the plates. For double riveted side seams use the constant number 5 instead of 6.
Example J* — What should be the thickness of plates for a boiler 60 inches in diameter, with single riveted side seams, for a work-
464
HANDBOOK ON ENGINEERING.
ing pressure of 125 pounds per square inch, the tensile strength of the plates being 60,000 pounds per square inch?
125 X 30 X 6 Operation* — -- 6Q QQQ -- equals .375 or 3/8 in. Answer.
Example 2* — What should be the thickness of plates for a boiler 60 inches diameter, with double riveted side seams, for a working pressure of 150 pounds per square inch, the tensile strength of plates being 60,000 pounds per square inch. 150 X 30 X 5
Operation* — -- 60~000 - e(luals -375 or 3/8 in. Answer.
The following formulas* equivalent to those of the British Board of Trade, are given for the determination of the pitch, distance between rows of rivets, diagonal pitch, maximum pitch, and distance from centers of rivets to edge of lap of single and double riveted lap joints, for both iron and steel boilers: —
Let p = greatest pitch of rivets, in inches ; n = number of rivets, in one pitch ; jpd = diagonal pitch, in inches ; d = diameter of rivets, in inches ; T = thickness of plate, in inches; V= distance between rows of rivets, in inches ; E = distance from edge of plate to center of rivet, in inches.
TO DETERMINE THE PITCH.
•
Iron plates and iron rivets —
^X.7854Xtt f P=- —%,— - + ef .
Example : First, for single-riveted joint — Given, thickness of plate (T)=£ inch, diameter of rivet (d) = £ inch. In this case, n = I. Required, the pitch. Substituting in formula, and performing operation indicated.
Piteh = + f = 2.077 inches.
HANDBOOK ON ENGINEERING. 465
For double-riveted joint —
Given, t = £ inch, and d = $% inch. In this case, n = 2. Then —
Pitch = (il)'X.7854X2 , _ 2>886 ^
^
For steel plates and steel rivets : —
28 X «P X » , .
P~- 28 XT + d"
Example, for single-riveted joint : Given, thickness of plate = \ inch, diameter of rivet — -^f inch. In this case, n = l. Then —
Example, for double-riveted joint : Given, thickness of plate — inch, diameter of rivet — J inch, n = 2. Then —
2 + = 2.85 inches.
FOR DISTANCE FROM CENTER OF RIVET TO EDGE OF LAP.
v 3X<* E= ~^
Example : Given, diameter of rivet (d) =| inch ; required, the distance from center of rivet to edge of plate.
E = ^^= 1.312 inches, 2
for single or double riveted lap joint.
FOR DISTANCE BETWEEN ROWS OF RIVETS.
The distance between lines of centers of rows of rivets for double, chain-riveted joints (F) should not be less than twice the diameter of rivet, but it is more desirable that V should not be
i 4* M •+ * less than — - — •
466 HANDBOOK ON ENGINEERING .
Example under latter formula: Given, diameter of rivet — | inch, then —
F^(4X|) + 1 = 2.25 inches. For ordinary, double, zigzag -riveted joints,
V=^
10
Example : Given, pitch = 2.85 inches, and diameter of rivet = J inch, then —
V (11 X 2.85 +4 X|) (2.85 +4 X |) ''
— — - = 1.
.„. . , 487 inches.
DIAGONAL PITCH.
For double, zigzag-riveted lap joint. Iron and steel.
Example: Given, pitch = 2. 85 inches, and eZ — J inch, then —
j
MAXIMUM PITCHES FOR RIVETED LAP JOINTS.
For single-riveted lap joints, maximum pitch =(1.31 X
For double-riveted lap joints, maximum pitch =(2.62 X T) -f If.
Example: Given a thickness of plate = % inch, required, the maximum pitch allowable.
For single-riveted lap joint, maximum pitch = (1.31 X i) + If = 2.28 inches.
For double-riveted lap joint, maximum pitch = (2.62 X i) + If = 2. 935 inches.
The following tables, taken from the handbook of Thomas W. Traill, entitled "Boilers, Marine and Land, their Construction
HANDBOOK ON ENGINEERING.
467
and Strength," may be taken for use in single and double riveted joints, as approximating the formulas of the British Board of Trade for such joints : —
IRON PLATES AND IRON RIVETS.
DOUBLK-RIVKTED LAP JOINTS.
|
Thickness of plates. |
Diameter of rivets. |
Pitch of rivets. |
Center of rivets to edge of plates. |
Distance between rows of rivets. |
|
|
Zigzag riveting. |
Chain riveting. |
||||
|
T |
d |
P |
E |
V |
V |
|
A |
1 |
2.272 |
.937 |
1.145 |
1.750 |
|
32 |
tt |
2.386 |
.984 |
1.202 |
1.812 |
|
f |
n |
2.500 |
1.031 |
. .260 |
1.875 |
|
it |
.23 i2 |
2.613 |
1.078 |
.317 |
1.937 |
|
Jv |
2.727 |
1.125 |
.374 |
2.000 |
|
|
1 |
i| |
2.826 |
.171 |
.426 |
2.062 |
|
jj- |
2.886 |
.218 |
.465 |
2.125 |
|
|
H |
J |
2.948 |
.265 |
.504 |
2.187 |
|
ft |
3.013 |
.312 |
.544 |
2.250 |
|
|
if |
Sf |
3.079 |
.359 |
.585 |
2.312 |
|
1 |
3.146 |
.406 |
.626 |
2.375 |
|
|
ft |
3.216 |
.453 |
.667' |
2.437 |
|
|
1 3.284 |
.500 |
.709 |
2.500 |
||
|
fl |
1A 3.355 |
.546 |
.751 |
2.562 |
|
|
1 |
1A 3.426 |
.593 |
.794 |
2.625 |
|
|
if |
1A 3.498 |
.640 |
.836 |
2.687 |
|
|
1$ |
H 3.571 |
.687 |
1.879 |
2.750 |
|
|
fj |
1A 3.645 |
.734 |
1.923 |
2.812 |
|
|
{ |
1A 3.718 |
.781 |
1.966 |
2.875 |
|
|
H |
iA 3.793 |
.828 |
2.009 |
2.937 |
|
|
II |
U 3.867 |
.875 |
2.053 |
3.000 |
|
|
ft |
1A 3.942 |
.921 |
2.096 |
3.062 |
|
|
i |
1A |
4.018 |
1.968 |
2.140 |
3*125 |
On the following page, Fig. 257 shows a zigzag, and Fig. 258 a chain riveted joint.
468
HANDBOOK ON ENGINEERING.
|
[ |
I |
- -f — t-4. -.- — I — - ...
I I
6 -<±>-- ) O 4
Fig. 257. Zigzag rireted joint.
o -e-
Fig. 258. Chain riveted joint.
HANDBOOK ON ENGINEERING.
IRON PLATES AND IRON RIVETS. SINGLE-KIVETED LAP JOINTS,
469
CD
__*—
|
Thickness of plates. |
Diameter of rivets. |
Pitch of rivets. |
Center of rivets to edge of plates. |
|
|
T |
d |
.P |
E |
|
|
«' |
r |
.524 |
.937 |
|
|
T |
\ |
.600 .676 .753 |
.984 .031 .078 |
|
|
| |
.829 |
.125 |
||
|
• |
I |
!4 |
.905 |
•171 |
|
• |
v |
1 |
1.981 |
.218 |
|
- |
i |
"L |
2.036 |
.265 |
|
. |
2.077 |
.312 |
||
|
** |
\\ |
2.120 |
.359 |
|
|
*g |
ft |
2.164 |
.406 |
|
|
I |
If |
2.210 |
.453 |
|
|
2.256 |
.500 |
|||
|
I |
1 |
iA- 2 A |
2.304 2.352 2.400 |
.546 .593 .640 |
|
] |
I |
2.450 |
.687 |
|
|
; |
1 |
A |
2.500 |
.734 |
|
', |
1 |
2.550 |
.781 |
|
|
. |
| |
2.601 |
.828 |
|
|
' |
2.652 |
1.875 |
||
|
1 |
s |
2.703 2.755 |
1.921 1.968 |
470 HANDBOOK ON ENGINEERING.
STEEL PLATE AND STEEL RjVETS.
SINGLE-RIVETED LAP JOINTS.
. — t ------ , ---
\
O
ET
•
•?(""•
\E
|
Thickness of plates. |
Diameter of rivets. |
Pitch of rivets. |
Center of rivets to edge of plates. |
|
|
r |
<* |
P |
E |
|
|
1 |
Ll |
1.562 |
.031 |
|
|
A |
i |
i |
1.633 |
.078 |
|
A |
! |
1.704 |
.125 |
|
|
H |
i 1.775 |
.171 |
||
|
I |
^ |
| |
1.846 |
.218 |
|
¥ |
^ |
J- |
1.917 |
.265 |
|
j |
1.988 |
.312 |
||
|
if |
-. |
| |
2.036 |
.359 |
|
| |
-| |
2.071 |
.406 |
|
|
iJ |
i |
i |
2.108 |
.453 |
|
iff |
f |
2.146 |
.500 |
|
|
II |
1-3 |
L2 |
2.186 |
.546 |
|
I* |
2.227 |
.593 |
||
|
21 |
J |
S |
2.269 |
.640 |
|
Ll |
1 |
2.312 |
.687 |
|
|
32 |
A |
2.356 |
.734 |
|
|
| |
j |
s |
2.400 |
.781 |
|
32 |
! |
5 |
2.445 |
.828 |
|
1$ |
S |
2.500 |
.875 |
|
|
32 |
12 |
a2 |
2.562 |
.921 |
|
| |
1, |
4 |
2.623 |
.968 |
|
II |
ij |
2.687 |
2.015 |
|
|
a |
Q |
2.750 |
2.062 |
HANDBOOK .ON ENGINEERING.
471
STEEL PLATE AND STEEL RIVETS.
DOUBLE -RIVETED LAP JOINTS.
|
Distance between rows |
|||||
|
Center of |
of rivets. |
||||
|
Thickness |
Diameter |
Pitch of |
rivets to |
||
|
of plates. |
of rivets. |
rivets. |
edge of |
||
|
plates. |
Zigzag |
Chain |
|||
|
riveting. |
riveting. |
||||
|
T |
d |
P |
E |
'V |
V |
|
A |
H |
2.291 |
1.031 |
1.187 |
1.875 |
|
H |
1 1 |
2.395 |
.078 |
1.240 |
1.937 |
|
I |
i |
2.500 |
.125 |
1.295 |
2.000 |
|
ii |
II |
2.604 |
.171 |
1.349 |
2.062 |
|
A |
fl |
2.708 |
.218 |
1.403 |
2.125 |
|
15. 3 2 |
• 32" |
2.803 |
265 |
1.453 |
2.187 |
|
£ |
2 850 |
.312 |
1.487 |
2.250 |
|
|
32f |
2.900 |
.359 |
1.522 |
2.312 |
|
|
¥ |
if |
2.953 |
.406 |
1.558 |
2.375 |
|
t| |
32 |
3.008 |
.453 |
1.595 |
2.437 |
|
1 |
1 |
3.064 |
.500 |
1.631 |
2.500 |
|
i |
fA |
3.122 3.181 |
.546 .593 |
1.669 1.707 |
2.562 2.625 |
|
23 32 |
h4 |
3.241 |
1.640 |
1.745 |
2.687 |
|
if |
3.302 |
1.684 |
1.784 |
2.750 |
|
|
If |
3.364 |
1.734 |
1.823 |
2.812 |
|
|
If |
i-ig. |
3.427 |
1.781 |
1.863 |
2.375 |
|
|1 |
i _ i . |
3490 |
1.828 |
1.902T |
2.937 |
|
£- |
3.554 |
1.875 |
1.942 |
3.000 |
|
|
fl |
r |
3.618 |
1.921 |
1.981 |
3.062 |
|
le |
i-^ |
3.683 |
1.968 |
2.021 |
3.125 |
|
tl |
lit |
3.748 |
2.015 |
2.061 |
3.187 |
|
1 |
11 |
3.814 |
2.062 |
2.102 |
3.250 |
|
I |
On the following page Fig. 259 shows a zigzag riveted joint and Fig. 260 a chain riveted joint with steel plate and steel rivets.
472
HANDBOOK ON ENGINEERING.
;i*~- ?.
6
.•-i — I
O
E
Fig. 259. Zigzag riveted joint.
-+- I I
O -0-
E
*
r
Fig. 260. Chain riveted joint.
HANDBOOK ON ENGINEERING. 473
STRENGTH OF STAYED AND FLAT BOILER SURFACES.
The sheets that form the sides of fire-boxes are necessarily exposed to a vast pressure, therefore, some expedient has to be devised to prevent the metal at these parts from bulging out. Stay-bolts are generally placed at a distance of 4£ inches from center to center, all over the surface of fire-boxes, and thus the expansion or bulging of one side is prevented by the stiffness or rigidity of the other. Now, in an arrangement of this kind, it becomes necessary to pay considerable attention to the tensile strength of the stay-bolts employed for the above purpose, since the ultimate strength of this part of the boiler is now transferred to them, it being impossible that the boiler plates should give way unless the stay-bolts break in the first instance. Accordingly, the experiments that have been made by way of test of the strength of stay-bolts, possess the greatest interest for the practi- cal engineer. Mr. Fairburn's experiments are particularly val- uable. He constructed two flat boxes, 22 inches square. The top and bottom plates of one were formed of £ inch copper, and of the other, f inch iron. There was a 2£ inch water-space to each, with ^| inch iron-stays screwed into the plates and riveted on the ends. In the first box the stays were placed five inches from center to center, and the two boxes tested by hydraulic pressure. In the copper box, the sides commenced to bulge at 450 Ibs. pressure to the sq. in. ; and at 815 Ibs. pressure to the sq. in. the box burst, by drawing the head of one of the stays through the copper plate. In the second box, the stays were placed at 4-inch centers; the bulging commenced at 515 Ibs. pressure to the sq. in. The pressure was continually augmented up to 1,600 Ibs. The bulging between the rivets at that pressure was one- third of an inch ; but still no part of the iron gave way. At 1,625 Ibs. pressure the box burst, and in precisely the same way as in the first experiment — one of the stays drawing through the
474 HANDBOOK ON ENGINEERING.
iron plate and stripping the thread in plate. These experiments prove a number of facts of great value and importance to the engineer. In the first place, they show that with regard to iron stay-bolts, their tensile strength is at least equal to the grip of the plate.
The grip of the copper bolt is evidently less. As each stay, in the first case, bore the pressure on an area of 5 x 5 — 25 square inches, and in the second on an area 4x4 i= 16 sq. inches, the total strains borne by each stay were, for the first, 815 x25 = 20,375 pounds on each stay; and for the second, 1,625 x 16 = 26,000 Ibs. on each stay. These strains were less, however, than the tensile strength of the stays, which would be about 28,000 Ibs. The properly stayed surfaces are the strongest part of boil- ers, when kept in good repair.
BOILER STAYS.
Advantage is usually taken of the self-supporting property of the cylinder and sphere, which enables them, in most cases, to be made sufficiently strong without the aid of stays or other support. But the absence of this self-sustaining property in flat surfaces necessitates their being strengthened by stays or other means. Even where a flat or slightly dished surface possesses sufficient strength to resist the actual pressure to which it is subjected, it is yet necessary to apply stays to provide against undue deflection or distortion, which is liable to take place to an inconvenient de- gree, or to result in grooving, long before the strength of plates or their attachments is seriously taxed. Boiler stays, in any case, are but substitutes for real strength of construction. They would be of no service applied to a sphere subject to internal pressure ; and the power of resistance would be exactly that of the metal to sustain the strain exerted upon all its parts alike. The manner in which stays are frequently employed renders them a source of weakness rather than an element of strength. When
HANDBOOK ON ENGINEERING.
475
the strain is direct the power of resistance of the stay is equal to the weight it would sustain without tearing it asunder ; but when the position of the stay is oblique to the point of resistance, any calculation of their theoretic strength or value is attended with certain difficulties. All boilers should be sufficiently stayed to insure safety, and the material of which they are made, their shape, strength, number, location and mode of attachment to the boiler, should all be duly and intelligently considered. Boiler stays should never be subjected to a strain of more than one- eighth of their breaking strength. The strength of boiler stays may be calculated by multiplying the area in inches between the stays by the pressure in pounds per square inch.
Rule for finding the strain allowed on a diagonal boiler head brace or stay ; also rule for finding the number of stays required for a certain size crown sheet.
Iron stays should not be subjected to a greater stress than from 7,000 to 9,000 pounds per square inch of section, and if they are located obliquely, the diameter will need to be increased an amount that depends on the angle of the stay to the shell. Find the area in square inches to be supported by the stay, and multiply it by the pressure per square inch, multiply. the product by the length of the diagonal stay, and divide the result by the perpendicular length from the flat surface to the end of the stay. The quotient will be the stress on the stay, and to obtain the diameter, divide the stress by the allowable stress per square inch
of section, and the quotient mmmm * by .7854. The square root of
the last quotient will be the
diameter of the stay.
Thus, in the accompanying
diagram, we wish to find the
Fis. 261. Diagonal boiler stay, diameter of the diagonal stay A, which supports an area 6" x 8" or 48 square inches. The
476 HANDBOOK ON ENGINEERING.
length of the stay is 25", and the perpendicular distance be- tween the stayed surface and the end of the stay is 24.148". The boiler pressure is 100 pounds gauge, so that the pressure on the surface supported will be 48 x 100 or 4,800 pounds. We multiply 4,800 by 25 and divide the product by 24.148", which gives 4,970, nearly. The quotient of 4,970, divided by 7,000 equals .71; .71, divided by .7854 equals .9039, and the square root of this is .95 or .95", the diameter of a stay that will support 48 square inches in the position shown. A convenient formula for finding the diameter of oblique stays
D equals
cosB
D equals diameter of the stay.
A " area in square inches to be supported.
P " pressure per square inch.
L " safe load per square inch of stay section.
B " angle between the shell and the stay.
Using the preceding problem as an example and referring to the same diagram, we have angle B equal to 15°, and all the other dimensions as previously given. Therefore,
T. , Q J48 X 100
D equals 1.13A — ° \ 7C
7000 X .96593
The diameter of the stay, when the above is simplified, is .9526", or practically 1". A rule for finding the pitch of stays for any flat surface is given below.
J. A safe formula for the strength of stayed flat surfaces is that given by Unwin's Machine Design. When the spacing of the stays is desired, assuming that it is the same in each direc- tion, we have,
a equals 3 t
N/Z \2 p
HANDBOOK. ON ENGINEERING. 477
where a equals spacing of stays or rivets in inches,/ equals safe working strength of the plate, t equals thickness of plate, and p equals boiler pressure. Expressed as a rule, this reads : Divide the safe strength of the plate by twice the pressure ; extract the square root of the quotient and multiply the final result by three times the thickness of the plate. The result will be the spacing of the stays in inches. For example, boiler pressure 100 pounds, plate 1/2 inch thick, safe strength of plate, 10,000 pounds per square inch ; 2j9 equals 2 x 100 equals 200 ; f/2p equals 10000/200 equals 50; V^O equals 7.07; 3£ equals 3/2 equals 1-1/2 equals 1.5; 7.07x1.5 equals 10.6 for the spacing. In making such a calculation care must be exercised not to assume too high values for the strength of the plate. It is not safe to count on more than 60,000 pounds for the strength of steel plates and 40,000 for iron. The working strength must be taken not higher than 1/6 of this, or 10,000 for steel and 6,666 for iron, and lower values still would be better, say 9,000 for steel and 6,000 for iron.
2* The safe pressure for a boiler to carry, so far as the flat, stayed surfaces are concerned, may be found from the above formula by transposing it a little, as follows: —
9 Z2/ p equals ~^T
Now, applying this to the above example, we have p equals 9 x.52 x 10000 9 x .25 x 10000
2x110.25 2x110.25
22500
duction equals ^^-^ equals 102, or substantially the pressure £i ZO»oO
assumed in the first example.
RIVETED AND LAP-WELDED FLUES.
The following table shall include all riveted and lap-welded flues exceeding 6 inches in diameter and not exceeding 40 inches in diameter not otherwise provided by law, as required by U. S. Gov.
478
HANDBOOK ON ENGINEERING.
CHART TO FIND STEAM PIPE NEEDED FOR HEATING WATER IN TANKS
From careful experiments it is found that one square foot of pipe, filled with steam and immersed in water, will condense 0.155 Ibs. of steam per hour for each Faht. degree of difference between the temperature of the steam and the mean temperature of the water. The Ideal Fitter.
Steam condensed per square root 01 pipe per hour in Lbs.
^ « N co co •* o to' to' t^ oo » o o -' e; n m •* o to £* £ oo » c o -j g
II
I
Chart <fc A M
Example. — It is required to condense 500 Ibs. of steam per hour in a pipe coil immersed in the water of a storage tank.
Temperature of steam in the pipe 220
Initial temperature of the water 40
Terminal temperature of the water 160
Mean temperature of the water * 100
Temp, difference between steam and water . . . 120
HANDBOOK ON ENGINEERING. 479
CHART TO FIND STEAM PIPE NEEDED FOR HEATING WATER IN TANKS. — Continued
How many square feet of pipe must the coil contain?
Referring to Chart A, find the horizontal line marked 120 degrees temperature difference, which intersects the diagonal line at the vertical line reading 18.60 Ibs. (the quantity of steam one sq. ft. will condense in one hour), and as 500 Ibs. is to be condensed divide 500 by 18.60, which gives 27 sq. ft. of pipe. To condense 500 Ibs. in two hours will require half of 27, or 13.5 sq. ft.
These experiments were made with 1| inch black iron pipe. Galvanized iron pipe would doubtless be better, as it would not corrode so quickly. Brass pipe would be the best to use, not so much for its higher conductivity as for its resistance to the action of impure water.
I CHART TO FIND BOILER POWER REQUIRED TO HEAT SWIMMING POOLS
In heating large bodies of water, large boilers are employed, and when anthracite coal is burned in them, there will be avail- able, from each pound of coal burned, 8333 B. T. U. or 8.6 Ibs. water will be evaporated, and on this basis the chart is con- structed.
One square foot of grate will burn 8 Ibs. anthracite coal per hour, whieh is the index for finding the size boiler required for a given quantity of work.
The horizontal lines on Chart " B " represent water in U. S. gallons, which may be increased by any suitable multiplier, pro- viding the coal and steam required are increased in like propor- tion.
The figures at the bottom of vertical lines show the eoal re- quired, each line representing 10 Ibs., and those at the top the
480
HANDBOOK ON ENGINEERING.
steam generated by the combustion of the quantity of coal on the same vertical line — each line representing 86 Ibs. of steam.
The diagonal lines represent the rise, or increase, in tempera- ture of the water per hour in Faht. degrees.
Water in U. S. gallons
iiiiiiiili.
|
!(__ I ip (X ----- |
\2&) ' * :j; = f|||l:: N$ |
|
2 * " 5" 160 — j>:: — zifl;:: |
7c:-_ <: _,i_^^^7 7^/2 l:::i^j^z:i^^! 1290 |
|
t* \\\\\\\ ;Ei::;;!f:;z5 |
/f;::/::/^"^;:::;;:::: 1720 |
|
,^ ^: ^i_ ^ |
ji_^2.IJ_l2l^i *rJ |
|
W ::-l::::-2f:-zf:2f O OKn " ' ~ |
7_::z :_z!:zzL_ _: 2150 » |
|
?. 250 •?; / I / 7 |
"•z.iz-;-?::: a. |
|
HI - , '- _x S - f7 . 77 - |
;:::z:: :::::::::::::::: s. |
|
w > 300 -?--.p-^---^-_7 7 |
i:^:^?::::::::::::::::2580^ |
|
o^ S- — ?<: ' — -^--r ^- |
/--/~^i±. 3010 | |
|
o S350::::-:::^::;:::::-:::z |
|
|
3 o 400^-"-"---?- /----/--^ |
i^:::::::::::::::::::::3440* |
|
0 E. --^ — 7--- ---Z.___z_. z!^ |
78L"" § |
|
J S «of--7--: |
|! --3870g« |
|
L . _ D CO |
|
|
g" S 5002:::_: :2.::::z:::::::^: |
:_::":: :__::__:::_::>::: 4300 S. |
|
S 5' 7 ;z---z~/z^~~~ |
:::::::::::::::::::::::::473o3 |
|
^ • :i::::::i::::S--Oi:::::: |
|
|
^ flo° _/ — z::2ij! |
5160g |
|
650 ^ 2_ tfi*" ~ I |
__. ._ _:_:_--__:: 5580 ss |
|
g ./ ?::!j^ QB --7--1-7 |
-. :::::::::::::::::::::::. I6020S . |
|
860-:^:-::=:::::=::::::::::: |
6880 |
Chart
HANDBOOK ON ENGINEERING. 481
CHART TO FIND BOILER POWER REQUIRED TO HEAT SWinniNd POOLS — Continued
Example 1 . — What size boiler is required to warm the water n a swimming pool, containing 130,000 gallons, from 40° to 80Q n 24 hours.
By reference to Chart B it is found that the horizontal line narked 1000 gallons intersects the 40 degree diagonal line at ;he 40 Ib. vertical line, showing that 40 Ibs. of coal are required ;o add 40 degrees to 1000 gallons of water. Then 100,000 gal- ons will require 100 times as much coal, or 4000 Ibs. In the jame manner 3000 gallons require 120 Ibs., and 30,000 gallons will require ten times 120, or 1200 Ibs., making a total )f 5,200 Ibs. of coal which must be burned to add 40 degrees to L30,000 gallons of water.
Having 24 hours in which to heat the pool, divide 5200 Ibs, >y 24, and it is found that 216 pounds of coal must be burned )er hour for 24 hours. Now as 8 Ibs. of coal is burned per iour on one sq. ft. of grate, divide 216 by 8, which shows that )oilers containing 27 sq. ft. of grate must be provided. Each 'rate section of the usual 36 inch Sectional Boiler contains 2 jq. ft. of grate and cast iron Sectional Boilers have one less 'rate section than the total number of sections in the boiler. Co obtain the 27 sq. ft. of grate, select two which will have 14 sq. ft. in each.
HEATING POOLS BY STEAM COILS.
Example 2 — If the pool is to be heated by steam coils and ;he temperature of the steam is 215°, find the mean temperature )f the water is 40 + 80 ^- 2 = 60° and 215 — 60 = 155 legrees temperature difference between steam and water.
Turn to Chart A, which shows that with this temperature
482 HANDBOOK ON ENGINEERING.
difference 1 sq. ft. of pipe will condense 24 Ibs. of steam per hour, and as 216 Ibs. of coal must be burned per hour, find by interpolation in Chart B tha'o 216 Ibs. of coal will evaporate 1857 Ibs. steam, which divide by 24 and find shall require in round figures 78 sq. ft. of condensing pipe in the pool. The boilers will be the same size as for water.
78 sq. ft. is equal to 180 linear feet of 1£ in. pipe, 156 ft. 1£ in., or 125 ft. of 2 in. If but 12 hours can be allowed to do the work, double the hourly consumption of coal and steam and furnish boilers of double the capacity required for 24 hours' time.
CHART TO FIND BOILER POWER REQUIRED TO HEAT SWIMMING POOLS — Continued.
As there will now be twice as much steam to condense in an hour, double the quantity of condensing coil.
There is, however, another factor which must not be overlooked.
In large bodies of water, warmed in the manner just described, there will be a zone, of which the condensing pipe is the center, where the mean temperature of the water will be much higher than figured in the foregoing, unless artificial means are em- ployed to agitate the water and keep it all at an even tempera- ture. It will, therefore, be good practice to add at least 50 per cent to the condensing coil when used in large bodies of still water.
CHART TO FIND TANK HEATER CAPACITY FOR RAISING WATER IN TANKS TO A SPECIFIC TEMPERATURE.
Power in small tank heaters, 7000 B. T. U. per pound coal:
Size round grate in tank heaters 10" 12" 15" 18" 21" 24" 27" 30"
Average hard coal capacity, Ibs. 25 40 75 120180225 300 370
Average h'd coal available, Ibs. 20 32 60 96 145 180 240 300
Max coal consump'n per hr., Ibs. 4.4 6.310 14 16.325 32 40
(8 Ibs. persq. ft. grate per hr.)
Duration of fire, hrs. in decimals, 4.5 5.1 6. 6.8 6.9 7.2 7.5 7.5.
Example: What size tank heater running at maximum ca- pacity will add 140 degrees to 120 gallons of water in one hour? By referring to Chart " C" we find the 120 gallon horizontal
"
HANDBOOK ON ENGINEERING.
483
line intersects the 140 degrees temperature line at the 20 pound vertical coal line, and a reference to data at bottom of Chart " C " shows that a heater with 24-inch grate will burn 25 pounds coal per hour running at maximum capacity, which would be the correct size to select.
The figures on Chart " C " are based on the work being ac- complished in one hour, and in the above example 20 pounds of coal must be burned in one hour to produce the required energy, but it is obvious that 20 pounds of fuel must be used whether the work is done in one or ten hours. If the time is two hours, select a heater that will burn 10 pounds per hour, or a 15-inch grate. The 10-inch grate will do the work in 4* hours; the 12 inch grate in 4 hours.
POUNDS or ANTHBACrrt COAL RtQumco pen noun
POUNDS Of AyHMOTC tjOM, REQUIUCO Ptff MOU« .
Chart "C."
CHART TO FIND TANK HEATER CAPACITY FOR RAISING WATER IN TANKS TO A SPECIFIC TEflPERATURE.
484 HANDBOOK ON ENGINEERING.
The vertical lines represent coal in pounds. The horizontal lines represent water in gallons. The diagonal lines represent temperatures.
DATA RELATING TO VENTILATION.
Loss of heat caused by —
First. B. T. U. necessary to warm air.
Second. B. T. U. absorbed by walls.
Third. B. T. U. absorbed by ceiling.
Fourth. B. T. U. absorbed by floor.
Fifth. B. T. U. absorbed by windows.
Sources of heat in rooms (Schuman, authority) : —
First. B. T. U. generated by occupants.
Second. B. T. U. generated by gas, lamps or candles.
Third. B. T. U. generated by heating apparatus.
An adult requires each hour for respiration and transpiration 215 cubic feet or 215x.077 = 165 pounds, and generates 290 B. T. U. of which 99 units are in form of vapor and 191 units radiate to surrounding objects.
APPROXIflATE.
An adult vitiates per hour 2.15 cu. ft. air.
Each cubic ft. gas burned requires 8.5 cu. ft. air.
Each Ib. oil burned requires 150 cu. ft. air.
Each Ib. candles burned requires 160 cu. ft. air.
B. T. U. generated by an adult per hour, 191.
B. T. U. generated by burning l.cu. ft. gas, 600.
B. T. U. generated by burning 1 Ib. oil or candles, 15,000 to
18,000.
Average gas burner consumes approximately 4 cu. ft. gas per hour, which equals 2400 B. T. U. per hour. Each flame from oil lamp 430 to 515 B. T. U. per hour. Each candle 454 to 545 B. T. U. per hour.
NOTE. — Above information is quoted from standard authorities. Not guaranteed.
HANDBOOK -ON ENGINEERING.
485
Table of Mains and Branches
Main
1 in. will supply 2 IJin.
14 in.
2 in. 24 in.
3 in. 3£ in.
'4 in. 44 in.
5 in.
6 in.
7 in.
8 in.
Branch
|
fl |
|||||||||||
|
a |
|||||||||||
|
2 |
|||||||||||
|
2 1 2 1 1 1 2 1 2 |
24 24 34 34 4 4 6 6 |
in. in. in. in. in. in. in. in. in. |
and and or and and and and and and |
1 1 1 1 1 1 1 1 1 |
1; 2 3 2 3 3 3 4 5 |
H i in £i in in in in in |
Q. n. y •) 'j •3 ') •1 |
, or 1 , or 2 and 1 , or 2 or 1 cr 1 or 4 or 3 or 5 |
2 2 2 3 4 3 4 4 |
in. in. in. in. in. in. in. in. |
and 1 and 1 or 3 and 4 and 1 and 1 or 10 and 1 and 2 |
|in.
1 in. llin. 14 in. IJin. 14 in.
2 in. 2 in. 2£ in. 2£ in. 2 in. 2 in. 2 in.
Capacities of Wrought Iron Pipe
|
Inside diameter Inches |
1 |
U |
14 |
2 |
24 |
3 |
34 |
4 |
5 |
6 |
|
Length of Pipe ^ |
||||||||||
|
per square foot of > |
2.9 |
2.3 |
2.0 |
1.6 |
1.32 |
1.09 |
0.95 |
0.84 |
0.68 |
0.57 |
|
external surface J |
||||||||||
|
Square feet; surface \ per 1 lineal foot J |
0.34 |
0.43 |
0.50 |
0.62 |
0.75 |
0.92 |
1.05 |
1.18 |
Ml |
1.74 |
Expansion of Wrought Iron Pipe
|
Temperature of the Air when Pipe is fitted |
Length of Pipe when fitted |
Length of Pipe when heated to |
|||
|
215° |
265° |
297° |
338° |
||
|
Zero |
100 feet |
Ft. In. 100 1.72 |
Ft. In. 100 2.12 |
Ft. In. 100 2.31 |
Ft. In. 100 2.70 |
|
32° |
100 " |
100 1.47 |
100 1.78 |
100 2.12 |
100 2.45 |
|
64° |
100 " |
100 1.21 |
100 1.61 |
100 1.87 |
100 2.19 |
486
HANDBOOK ON ENGINEERING.
firmly riveted , with good and substantial rivets, through the hubs of such flanges ; and no such hubs shall project from such flanges less than 2 inches in any case.
Steam pipes of iron or steel, when lap- welded by hand or machine, with their flanges welded on, shall be tested to a hydro- static pressure of at least double the working pressure of the steam to be carried and properly annealed after all the work requiring fire is finished. When an affidavit of the manufacturer is furnished that such test has been made and annealed, they may be used for power purposes.
WROUGHT IRON WELDED PIPE.
DIMENSIONS, WEIGHTS, ETC., OF STANDARD SIZES FOR STEAM, GAS, WATER, OIL, ETC.
1 inch and below are butt- welded, and tested to 300 pounds per square inch hydraulic pressure.
1J inch and above are lap-welded, and tested to 500 pounds per square inch hydraulic pressure.
|
i 5 |
utside Di- ameter. |
xternal Cir- jumference. |
o c3 *""£ |
li I* |
xternal Area. |
Bngth of Pipe con- taining one cubic foot. 1 |
reight per :t. of length. |
o.of threads! 1 per inch of screw. |
intents in *Gallons per foot. |
"eight of Water per foot of Length. |
|
O |
0 |
H |
h-3 |
H |
3 |
j£- |
K |
O |
& |
|
|
Inch. |
Inches. |
Inches. |
Feet. |
Inches. |
Inches. |
Feet. |
Lbs. |
Lbs. |
||
|
§ |
40 |
1.272 |
9 44 |
.012 |
.129 |
2500. |
.24 |
27 |
.0006 |
.005 |
|
I |
.54 |
1.696 |
7.075 |
049 |
229 |
1385. |
.42 |
18 |
.0026 |
.021 |
|
.67 |
2 . 121 |
5.657 |
.110 |
.358 |
751.5 |
.56 |
18 |
.0057 |
.047 |
|
|
I |
.84 |
2.652 |
4 502 |
.196 |
.554 |
472.4 |
.84 |
14 |
.0102 |
.085 |
|
1.05 |
3 299 |
3.637 |
.441 |
.866 |
270. |
1.12 |
14 |
.0230 |
.190 |
|
|
I1 |
1 31 |
4.134 |
2.903 |
.785 |
1.357 |
166.9 |
1.67 |
iii |
.0408 |
.349 |
|
}j |
1 66 |
5.215 |
2.301 |
1 227 |
2.164 |
96.25 |
2.25 |
.0638 |
.527 |
|
|
1.9 |
5.969 |
2.01 |
1.767 |
2.835 |
70.65 |
2.69 |
jj i |
.0918 |
.760 |
|
|
2 |
2.37 |
7.461 |
1.611 |
3.141 |
4.430 |
42.36 |
3.66 |
iis |
.1632 |
1.356 |
|
2» |
2.87 |
9.032 |
1.328 |
4 908 |
6.491 |
30.11 |
5.77 |
8 |
.2550 |
2.116 |
|
3 |
3 5 |
10.996 |
1 091 |
7.068 |
9.621 |
19.49 |
7.54 |
8 |
.3673 |
3.049 |
|
34 |
4. |
12.566 |
.955 |
9.621 |
12.566 |
14.56 |
9.05 |
8 |
.4998 |
4.155 |
|
4 |
4.5 |
14.137 |
.849 |
12.566 |
15.904 |
11.31 |
10.72 |
8 |
.6528 |
5.405 |
|
5. |
15.708 |
.765 |
15.904 |
19.635 |
9.03 |
12.49 |
8 |
.8263 |
6.851 |
|
|
5 |
5 56 |
17.475 |
.629 |
19.635 |
24.299 |
7.20 |
14.56 |
8 |
1.020 |
8.500 |
|
6 |
6.62 |
20.813 |
.577 |
28.274 |
34.471 |
4.98 |
18.76 |
8 |
1.469 |
12.312 |
|
7 |
7.62 |
23 954 |
.505 |
38.484 |
45.663 |
3.72 |
23.41 |
8 |
1.999 |
16.662 |
|
8 |
8.62 |
27.096 |
.444 |
50.265 |
58.426 |
2.88 |
28.34 |
8 |
2.611 |
21.750 |
|
9 |
9 68 |
30.433 |
.394 |
63.617 |
73.715 |
2,26 |
34.67 |
8 |
3.300 |
27.500 |
|
10 |
10.75 |
33.772 |
.355 |
78.540 |
90.792 |
1.80 |
40.64 |
8 |
4.081 |
34.000 |
HANDBOOK ON ENGINEERING.
487
PULSATION IN STEAfl-BOILERS.
Pulsation in steam-boilers, though not discernible to the eye, as in animated nature, goes on intermittently in some boilers whenever they are in use. It is induced by weakness and want of capacity in the boiler to supply the necessary quantity of steam, and sometimes is caused by the boiler being badly de- signed, thereby admitting of a great disproportion between the heating-surface and steam-room. Boilers are frequently found in factories that were originally not more than of sufficient capacity to furnish the necessary quantity of steam, but, as business increased, it became necessary to increase the pressure and also the speed of the engine ; or, perhaps to replace it with a larger one, which has to be supplied with steam from the same boiler. The result is, each time the valve opens to admit steam to the cylinder, about one-third of the whole quantity in the boiler is admitted, thus lowering the pressure ; the next instant, under the influence of hard firing, or, perhaps, a forced draught, the steam is brought to the former pressure, and so on ; this lessening and increasing the pressure continues while the engine is in motion, which has an effect on the boiler similar to the breathing of an animal.
The strains induced By this pulsation are transmitted to the weakest places, viz., the line of the rivet holes, and that marked
by the tool in the process of calking ; the result is, the plate is broken in two, as shown in the above cut. The manner in which the break takes place may be illustrated by filing a small nick, or drilling a small hole, in a piece of hoop or band- iron, and then bending back Fig. 262. Cracked plate.
488
HANDBOOK ON ENGINEERING.
and forth, when it will be discovered that the material will break just at that point, however slight the nick or small the hole may be. Pulsation is frequently very severe in the boilers of tug- boats when commencing to start a heavy tow, and also in loco- motives when starting long trains. Some frightful explosions of the boilers of tug-boats and locomotives have occurred under such circumstances. Pulsation, if permitted to continue, is sure to effect the destruction of the boiler. It is always made mani- fest by the vibrations of the pointers on steam gauges, or an unsteadiness in the mercury column. It may be remedied, to a certain extent, by adding a larger steam dome, but this has a tendency to weaken the boiler and render it more unsafe. The only sure preventive of such a silent and destructive agent is to have the boiler of sufficient capacity in the first place.
WEIGHT OF SQUARE AND ROUND IRON PER LINEAR FOOT.
|
SIDE OR DIAM. |
Weight, Square. |
Weight, Round. |
SIDE OR DIAM. |
Weight, Square. |
Weight. Round. |
SIDE OR DIAM. |
Weight, Square. |
Weight, Round. |
|
iV |
.013 |
.01 |
2 |
13.52 |
10.616 |
5 |
84.48 |
66.35 |
|
? |
.053 |
.041 |
i |
15.263 |
11.988 |
* |
93.168 |
73.172 |
|
iV |
.118 |
.093 |
17.112 |
13.44 |
I |
102.24 |
80.304 |
|
|
1 |
.211 |
,165 |
i |
19.066 |
14.975 |
1 |
111.756 |
87.776 |
|
.475 |
.373 |
I |
21.12 |
16.588 |
||||
|
I |
.845 |
.663 |
i |
23.292 |
18.293 |
6 |
121.664 |
95.552 |
|
1.32 |
1.043 |
i |
25.56 |
20.076 |
\ |
132.04 |
103.704 |
|
|
1 |
1.901 |
1.493 |
i |
27.939 |
21.944 |
i |
142.816 |
112.16 |
|
I |
2.588 |
2.032 |
154.012 |
120.96 |
||||
|
3 |
30.416 |
23.888 |
||||||
|
i |
3.38 |
2.654 |
i |
35.704 |
28.04 |
7 |
165.632 |
130.048 |
|
I |
4.278 |
3.359 |
* |
41.408 |
32.515 |
\ |
177.672 |
139.544 |
|
5.28 |
4.147 |
47.534 |
37.332 |
i |
190.136 |
149.328 |
||
|
1 |
6.39 |
5.019 |
203.024 |
159.456 |
||||
|
£ |
7.604 |
5.972 |
4 |
54.084 |
42.464 |
|||
|
$ |
8.926 |
7.01 |
i? |
61.055 |
47.952 |
8 |
216.336 |
169.856 |
|
1 |
10.352 |
8.128 |
h |
68.448 |
53.76 |
|||
|
1 |
11.883 |
9333 |
\ |
76.264 |
59.9 |
9 |
273.792 |
215.04 |
HANDBOOK ON ENGINEERING. 489
WATER COLUHNS.
Every boiler should be equipped with a safety water column. Next to keeping the steam pressure within the limits of safety, the most important point to be observed in operating steam boilers is the maintenance of the proper water level. If the water level is too low, there is danger of burning the tubes and plates and? perhaps, of wrecking the boiler ; if it is too high, water is liable to be carried along with the steam and cause damage in the engine, while a constant variation in the water level produces a waste of fuel and unsteady pressure, and impairs the life of the boiler. Safety water columns have been devised for the purpose of insuring owners of steam boilers against accidents of this kind. They are so ar- ranged that any variation in the water level beyond reasonable lim- its will be loudly proclaimed by means of a suitable steam whistle.
STEAM-GAUGES.
The object of the steam-gauge is to indicate the steam pressure in the boiler, in order that it may not be increased far above that at which the boiler was originally considered safe ; and it is as a provision against this contingency that a really good gauge is a necessity where steam is employed, for no guide at all is vastly better than a false one. The most essential requisites of a good steam-gauge are, that it be accurately graduated, and that the material and workmanship be such that no sensible deterioration may take place in the course of its ordinary use. The pecuniary loss arising from any considerable fluctuation of the pressure of steam has never been properly considered by the proprietors of engines. If steam be carried too high, the surplus will escape through the safety-valve, and all the fuel consumed to produce such excess is so much dead loss. On the other hand, if there be at any time too little steam, the engine will run too slow, and every lathe, loom, or other machine driven by it, will lose its speed and, of course, its effective power in the same pro-
490 HANDBOOK ON ENGINEERING.
portion. A loss of one revolution in ten at once reduces the pro- ductive power of every machine driven by the engine ten per cent, and loses to the proprietor ten per cent of the time of every workman employed to manage such machine. In short, the loss of one revolution in ten diminishes the productive capacity of the whole concern ten per cent, so long as such reduced rate con- tinues ; while the expenses of conducting the shop (rent, wages, insurance, etc.) all run on as if everything was in full motion. A variation to this amount is a matter of frequent occurrence, and is, indeed, unavoidable, unless the engineer is afforded facilities to prevent it. A very little reflection will satisfy any one that it must be a very small concern, indeed, in which a half- hour's continuance of it would not produce a result more than enough to defray the cost of a very expensive instrument to pre- vent it. If the engineer, to avoid this loss, keeps a surplus of steam constantly on hand, he is constantly wasting the steam, and consequently, fuel, thus incurring another loss, which though less alarming than the first will yet be serious and render any instrument most desirable which can prevent it. It is, there- fore, of great importance to the proprietors of engines to have an instrument which can constantly indicate the pressure in the steam boilers with accuracy. This would enable the engineer to keep his steam at a constant pressure, thus avoiding waste of fuel on the one hand, and the still more serious loss of the productive power of the shop on the other. An instrument, therefore, con- stantly indicating the pressure of steam, reliable in its character, and, with ordinary care, not subject to derangement, is evidently a desideratum both to the engineer and proprietor. The impor- tance of such an instrument, as a preventive of explosion, and of the frightful consequences to life and limb and ruinous pecuniary results of such disaster, is obvious on the slightest consideration ; but the value of the instrument, in the economical results of its daily use is by no means properly appreciated.
HANDBOOK ON ENGINEERING. 491
SAFETY-VALVES.
The form and construction of this indispensable adjunct to the steam boiler are of the highest importance, not only for the pres- ervation of life and property, which would, in the absence of that means of " safety" be constantly jeopardized, but also to secure the durability of the steam boiler itself. And yet, judging from the manner in which many things called safety-valves have been constructed of late years, it would appear that the true principle by which safety is sought to be secured by this most valuable ad- junct is either not well understood, or is disregarded by many engineers and boiler makers.
Boiler explosions have in many cases occurred when, to all appearances, the safety-valves attached have been in good work- ing order ; and coroners' juries have not unfrequently been puzzled, and sometimes guided to erroneous verdicts by scientific evidence adduced before them, tending to show that nothing was wrong with the safety-valves, and that the devastating catastro- phies could not have resulted from overpressure, because in such case the safety-valve would have prevented them. It is supposed that a gradually increasing pressure can never take place if the safety-valve is rightly proportioned and in good working order. Upon this assumption, universally acquiesced in, when there is no accountable cause, explosions are attributed to the u sticking " of the valves, or to "bent" valve-stems, or inoperative valve- springs. As the safety-valve is the sole reliance, in case of neg- lect or inattention on the part of the engineer or fireman, it is important to examine its mode of working closely. Safety-valves are usually provided with a spindle or guide-pin, attached to the under side, and passing through a cross-bar within the boiler, directly under the seating of the valve, which may be seen in
Figr, 263. Lever and weight safety-valve,
corresponding to the pressure required in the boiler. Another difficulty is that the safety-valve levers sometimes get bent, and the weight, consequently hangs on one side of the true center ; this, it will be seen, causes the valve to rest more heavily on one side than on the other, and the greater the added weight the greater the difficulty. The seats of safety-valves should be examined frequently to see that no corrosion has commenced ; as valves, especially if leaky, become corroded and often stick fast, so that no little force is required to raise them. If, when a safety-valve is properly weighted, it should be found leaking, do not put on extra weights, but immediately make an examination, and in all probability the seat or guide-pin will be found cor- roded, or there will be foreign matter between the valve and its
HANDBOOK ON ENGINEERING. 493
seat. By taking the lever in the hand and raising it from its seat a few times, any substance that may have kept it from its seat will be dislodged ; or it may turn out on examination that the lever had deviated from some cause from a true center. Such difficulties can be easily righted, but extra weight should never be added, as it only aggrevates the trouble instead of remedying it. When the weight of the safety-valve is set on the lever at safe working pressure, or at the distance from the fulcrum necessary to maintain the pressure required to work the engine, any extra length of lever should then be cut off as a precaution, to prevenf the moving out of the weight on the lever, for the purpose of increasing the pressure, as, while the lever remains sufficiently long, the weight can be increased to a dangerous extent without attracting any attention ; while if the lever is cut off at the point at which the safe working pressure is designated, any extra increase of pressure can only be accomplished by add- ing more weight to the lever, which is tolerably sure to attract the attention of some one interested in the preservation of the lives and property of persons in the immediate vicinity.
The bolts that form the connection between the lever, fulcrum and valve-stem should be made of brass, in order to prevent the possibility of corrosion, "sticking " or becoming magnetized, as it is termed ; and for the same reason, the valve and seat should be made of two different metals. When safety-valves become leaky they should be taken out and reground on their seats, for which purpose pulverized glass, flour of emery, or the fine grit or mud from grinding stone troughs are the most suitable material ; but whether they leak or not, they should be taken apart at least once a year and all the working parts cleaned, oiled and read- justed. The safety-valve is designed on the assumption that it will rise from its seat under the statical pressure in the boiler when this pressure exceeds the exterior pressure on the valve, and that it Will remain off its seat sufficiently far to permit all the
494 HANDBOOK ON ENGINEERING.
steam which the boiler can produce to escape around the edges of the valve. The problem then to be solved is : What amount of opening is necessary for the free escape of the steam from the boiler under a given pressure? The area of a safety-valve is generally determined from formulae based on the velocity of the flow of steam under differet pressures, or upon the results of experiments made to ascertain the area necessary for the escape of all the steam a boiler could produce under a given pressure. But as the fact is now generally recognized by engineers that valves do not rise appreciably from their seats under varying pressures, it is of importance that in practice the outlets round their edges should be greater than those based on theoretical considerations. The next point to be considered is how high any safety valve will rise under the influeuce of a given pressure! This question cannot be determined theoretically, but has been settled conclusively by Burg, of Vienna, who made careful experiments to determine the actual rise of safety-valves above their seats. His experiments show that the rise of the valve diminishes rapidly as the pressure increases.
'
TABLE SHOWING THE RISE OF SAFETY-VALVES, IN PARTS OF AN INCH, AT DIFFERENT PRESSURES.
Lbs, Lbs. Lbs. Lbs. Lbs. Lbs. Lbs. Lbs. Lbs.
12 20 35 45 50 60 70 80 90 -ffV sV iV li? ifa yis
4*8 A -
Taking ordinary safety-valves, the average rise for pressures from 10 to 40 pounds is about ^ of an inch from 40 to 70 pounds about ¥L, and from 70 to 90 pounds about ^^ of an inch. The following table gives the re'sult of a series of experi- ments made at the Novelty Iron Works, New York, for the pur- pose of determining the exact area of opening necessary for
HANDBOOK ON ENGINEERING.
495
safety-valves for each square foot of heating surface, at different boiler pressures.
TABLE.
|
Vi « |
fl*bC |
^ <D |
342 be |
^ 0? |
p3 43 be |
|
HH O S? |
cS vg |
S O aj |
"" ^.g |
rs o <£ |
§P |
|
§«| |
OX> t, |
o * « |
o&% MCS ^ |
•g |
|
|
^ • |
^a |
« . ® |
|||
|
d * £" |
•g tiH |
rt OD P. |
'C oW |
a«>1< |
?gw |
|
5-g S |
O «M <M |
•S^S w |
O ** «M |
5-og |
|
|
fl S o> 3 £ |
"-• d ^® |
o p | |
^ .OgJ |
.gi |
*- "° ® |
|
S PH^ |
°MS«2 |
pft* |
0|H£*«2 |
sa^ |
®^faj |
|
W) ® |
g££g |
t« V |
ea -t-Li |
tn C |
eg • • ^ |
|
£.5 "5 |
2-S5 |
^000200 |
2-S5 |
£(/3{fiOT |
|
|
s |
^ |
fi; |
^ |
PH |
^ |
|
0.25 |
.022795 |
10 |
.005698 |
70 |
.001015 |
|
0.5 |
.021164 |
20 |
.003221 |
80 |
.000892 |
|
1 |
.018515 |
30 |
.002244 |
90 |
.000796 |
|
2 |
.014814 |
40 |
.001 ; 23 |
100 |
.000719 |
|
3 |
.012345 |
50 |
.001398 |
150 |
.000481 |
|
4 |
.010582 |
60 |
.001176 |
200 |
.000364 |
|
5 |
.009259 |
TABLE OF COMPARISON BETWEEN EXPERIMENTAL RESULTS AND THEORETICAL FORMULAE.
Boiler Pressure, 45 pounds.
Boiler Pressure, 75 pounds.
|
Heating Surface. |
Area of open- ing found by experiment. |
Area of open- ing according to formulae. |
Heating Surface. |
Area of open- ing fonnd by experiment.. |
Area of open- ing according to formulae. |
|
Sq. Ft. |
Sq. Ins. |
Sq. Ins. |
Sq. Ft. |
Sq. Ins. |
Sq. Ins. |
|
100 |
. .089 |
.09 |
100 |
.12 |
.12 |
|
200 |
.180 |
.19 |
200 |
.24 |
.24 |
|
500 |
.45 |
.48 |
500 |
.59 |
.59 |
|
1000 |
.89 |
.94 |
1000 |
1.20 |
1.18 |
|
2000 |
1.78 |
1.90 |
2000 |
2.40 |
2.37 |
|
5000 |
4.46 |
4.75 |
5000 |
6.00 |
6.95 |
496 HANDBOOK ON ENGINEERING.
Now, if we compare the area of openings, according to these experiments, with Zeuner's formula which is entirely theoretical, it will be observed that the results from the two sources are almost identical, or so nearly so as not to make any material difference. In the absence of any generally recognized rule, it is customary for engineers and boiler-makers to proportion safety- valves according to the heating surface, grate surface, or horse- power of the boiler. While one allows one inch of area of safety-valve to 66 square} feet of heating surface, another gives one-inch area of safety-valve to every four-horse power ; while a third proportion's his by the grate surface — it being the custom in such cases to allow one inch of safety-valves to 2 square feet of grate surface. This latter proportion has been proved by long experience and a great number of accurate experiments to, be capable of admitting of a free escape of steam without allowing any material increase of the pressure beyond that for which the valve is loaded, even when the fuel is of the best quality, and the consumption as high as 24 pounds of coal per hour per square foot of grate surface, providing of course that all the parts are in good working order. It is obvious, however, that no valve can act without a slight increase of pressure, as, in order to lift at all, the internal pressure must exceed the pressure due to the load.
The lift of safety-valves, like all other puppet valves, de- creases as the pressure increases, but this seeming irregularity is but what might be required of an orifice to satisfy conditions in the flow of fluids, and may be explained as follows : A cubic foot of water generated into steam at one-pound pressure per square inch above the atmosphere, will have a volume of about 1,600 cubic feet. Steam at this pressure will flow into the atmosphere with a velocity of 482 feet per second. Now suppose the steam was generated in five minutes, or in 300 seconds, and the area of an orifice to permit its escape as fast it is generated be re-
HANDBOOK ON ENGINEERING. 497
quired, 1600 x 144 -*- (482 x 300) will give the area of the orifice, 1| square inches. If the same quantity of water be generated into steam at a pressure of 50 pounds above the atmosphere, it will possess a volume of 440 cubic feet and will flow into the atmos- phere with a velocity of 1791 feet per second. The area of an orifice, to allow this steam to escape in the same time as in the first case, may be found as follows: 440 x 144 -r- (1791 x 300), the result will be ^ square inches, or nearly £ of a square inch, the area required. It is evident from this that a much less lift of the same valve will suffice to discharge the same weight of steam under a high pressure than under a low one, because the steam under a high pressure not only possesses a reduced volume, but a greatly increased velocity ; it is also obvious from these consider- ations, that a safety-valve, to discharge steam as fast as the boiler can generate it, should be pioportioned for the lowest pressure.
RULES.
Rule, — For finding the weight necessary to put on a safety- valve lever when the area of valve, pressure, etc., are known: Multiply the area of valve by the pressure in pounds per square inch ; multiply this product by the distance of the valve from the fulcrum ; multiply the weight of the lever by one-half its length (or its center of gravity) ; then multiply the weight of valve and stem by their distance from the fulcrum ; add these last two prod- ucts together, subtract their sum from the first product, and divide the remainder by the length of the lever ; the quotient will be the weight required.
EXAMPLE.
Area of valve, 12 in 65 13 8
Pressure, 65 Ibs. 12 16 4
Fulcrum, 4 in. . 780 208 62
82
498 HANDBOOK ON ENGINEERING.
Length of lever, 32 in 4 13
Weight of lever, 13 Ibs
Weight of valve and stem, 8 Ibs. . . . . 3120 208
240 32
32)2880 240 90 Ibs.
Rule for finding the pressure per square inch when the area of ralve, weight of ball, etc., are known: Multiply the weight of ball by length of lever, and multiply the weight of lever by one-half its length (or its center of gravity) ; then multiply the weight of valve and stem by their distance from the fulcrum. Add these three products together. This sum, divided by the product of the area of valve, and its distance from the fulcrum, will give the pressure in pounds per square inch.
EXAMPLE.
Area of valve, 7 in 50 12 6
Fulcrum, 3 in 30 15 3
Length of lever, 30 in 1500 180 18
Weight of lever, 12 Ibs 180
Weight of ball, 50 Ibs 18 7
Weight of valve and stem, 6 Ibs
21)1698 3
80.85 Ibs. 21
Rule for finding the pressure at which a safety-valve is weighted when the length of the lever, weight of ball, etc., are known : Multiply the length of lever in inches by the weight of ball in pounds ; then multiply the area of valve by its distance
HANDBOOK ON ENGINEERING. 499
from the fulcrum ; divide the former product by the latter ; the quotient will be the pressure in pounds per square inch.
EXAMPLE.
Length of lever, 24 in 52 7
Weight of ball, 52 Ibs 24 3
Fulcrum, 3 in. . . 208 21
Area of valve, 7 in 104
21)1248
59. 42 Ibs.
The above rule, though very simple, cannot be said to be exactly correct, as it does not take into account the weight of the lever, valve and stem.
Rule for finding center of gravity of taper levers for safety- valves : Divide the length of lever by two (2) ; then divide the length of lever by six (6), and multiply the latter quotient by width of large end of lever less the width of small end, divided by width of large end of lever plus the width of small end. Subtract this product from the first quotient, and the remainder will be the distance in inches of the center of gravity from large end jf lever.
EXAMPLE.
Length of lever 36 in.
Width of lever at large end 3 c
Width of lever at small end 2 '
36 divided by 2 = 18 minus 1,2 = 36.8 in. 36 divided by 6 = 6X1=6 divided by 5 = 1.2.
Center of gravity from large end, 16.8 in.
The safety-valve has not received that attention from engi- neers and inventors which its importance as a means of safety
500 HANDBOOK ON ENGINEERING.
so imperatively deserves. In the construction of most other kinds of machinery, continual efforts have been made to secure and insure accuracy ; while in the case of the safety-valve, very little improvement has been made either in design or fitting. It is difficult to see why this should be so, when it is known that deviations from exactness, though trifling in themselves, when multiplied, not only affect the free action and reliability of machines, but frequently result in serious injury, more partic- ularly in the case of safety-valves.
Safety-valves should never be made with rigid stems, as, in consequence of the frequent inaccuracy of the other parts, the valve is prevented from seating, thereby causing leakage ; as a remedy for which, through ignorance or want of skill, more weight is added on the lever, which has a tendency to bend the stem, thus rendering the valve a source of danger instead of a means of safety. The stem should, in all cases, be fitted to the valve with a ball and socket joint, or a tapering stem in a straight hole, which will admit of sufficient vibration to accommodate the valve to its seat. It is also advisable that the seats of safety-valves, or the parts that bear, should be as narrow as circumstances will permit, as the narrower the seat the less liable the valve is to leak, and the easier it is to repair when it becomes leaky.
All compound or complicated safety-valves should be avoided, as a safety-valve is, in a certain sense, like a clock — any complication of its parts has a tendency to affect its reliability and impair its accuracy.
It has been too much the custom heretofore for owners of steam boilers to disregard the advice and suggestions of their own en- gineers and firemen, even though men of intelligence and experi- ence, and to be governed entirely by the advice of self-styled experts and visionary theorists.
HANDBOOK ON ENGINEERING.
501
TABLE OF HEATING SURFACE IX SQUARE FEET IN HORI- ZONTAL TUBULAR BOILERS.
|
Diam. of Boiler in inches |
24 |
30 |
32 |
34 |
36 |
38 |
40 |
*2 |
44 |
48 |
|
f Heating surface of shell per foot of length. |
4.19 |
5.24 |
5.57 |
5.93 |
6.28 |
6.63 |
6.98 |
7.73 |
7.68 |
8.38 |
|
Diameter of Tube or Flue in inches. |
2 |
24 |
3 |
34 |
4 |
44 |
5 |
6 |
7 |
8 |
|
Whole External Heating surface per foot length. |
.524 |
.655 |
.785 |
.916 |
1.05 |
1.18 |
1.31 |
1.57 |
1.83 |
2.09 |
|
60 |
52 |
54 |
56 |
58 |
60 |
62 |
64 |
66 |
68 |
70 |
72 |
|
8.73 |
9.08 |
9.42 |
9.77 |
10.12 |
10.47 |
10.82 |
11.17 |
11.52 |
11.87 |
12.22 |
12.57 |
|
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
|
2.36 |
2.62 |
2.88 |
3.14 |
3.40 |
3.66 |
3.93 |
4.19 |
4.45 |
4.71 |
4.96 |
5.24 |
CENTRIFUGAL FORCE.
The centrifugal force of a body depends upon its weight Win pounds ; distance R in feet it is from the center of rotation, and the number of revolutions N it makes about that center each
WEN* minute and equals — 9933 — *
Multiply the weight in pounds by radius in feet, by square of number of revolutions, and divide by 2933 = centrifugal force in pounds.
502 HANDBOOK ON ENGINEERING.
CHAPTER XVIII. THE WATER TUBE BOILER.
The water tube boiler has been a growth of many years and of many different minds. There are some two and a half million horse-power in daily service in the United States alone, and the number is rapidly increasing. Large orders for this type of boiler have often been repeated, adding proof that its principles are correct and appreciated by those having them in use and in charge. This being the case, purchasers should note well the points of difference in the various water tube boilers claiming their attention, and particularly see that the claims made for them are embodied in their actual construction. The general principles of construction and operation of this class of steam boilers are now well known to engineers and steam users. In selecting a water tube boiler there are several vital points to be considered : —
1st. Straight and smooth passages through the headers of ample area, insuring rapid and uninterrupted circulation of the water.
2d. The baffling of the gases (without throttling or impeding the circulation of the water) in such a way that they are com- pelled to pass over every portion of the heating surface.
3d. Sufficient liberating surface in the steam drums to insure dry steam, with large body of water in reserve to draw from.
4th. A steam reservoir or steam drum.
5th. Simplicity in construction ; accessibility for cleaning and inspection.
6th. A header, which in its design provides for the unequal expansion and contraction.
HANDBOOK ON ENGINEERING.
503
Fig. 264. O'Brien horizontal safety water tube boiler.
Manufactured by the John O'Brien Boiler Works Company,
of St. Louis, U. 8. A. This type of water tube boiler when provided with a cross-drum
to reduce the head room required is adapted to, and is oftentimes used in heating plants.
Down draft furnace* — A great many of these boilers are fit- ted with the down draft furnaces, and the above illustration shows the style of same, together with the manner in which they are connected.
A full and complete description of these furnaces is given on page 522.
Description* — In construction, this type of boiler consists
504 HANDBOOK ON ENGINEERING.
simply of a front and rear water leg or header, made approx- imately rectangular in shape, overhead combination steam and water drum or drums and with circulating water tubes, as shown in cut, which extend between and connect both front and rear headers, being thoroughly expanded into the tube sheets. The tubes are inclined on a pitch of one inch to the foot and the rear header being longer than the front one, the overhead drum connecting both headers lies perfectly level when the boiler is set in position. The connection of the headers with the combined steam and water drum is made in such a manner as to give prac- tically the same area as the total area of the tubes, so there is no' contraction of area in the course of circulation ; and extending between and connecting the inside faces of the water legs, which form end connections between these tubes and the com- bined steam and water drums or shells, placed above and parallel with them, also a steam drum above these, assures absolutely dry steam and a large steam space, also a large water space. The water legs are made larger at the top, about 11 inches wide, and at the bottom about 7 inches wide, which is a great advantage, allowing the globules of steam to pass quickly up the water legs to the steam and water drums. The water, as it sweeps along the drums, frees itself of steam ; then it goes down the back connec- tion until it meets the inclined tubes, meeting on its passage a gradually increasing temperature, till the furnace is again reached, where the steam formed on the way is directly carried up in the drum as before. The tubes extend between and connect both the front and rear headers and are thoroughly expanded into the tube sheets. Opposite the end of each tube there is an oval hand-hole slightly larger than the tube proper through which it can be withdrawn. It will be noted that the throat of each water leg is 1^ times the total tube area. The rapid and unimpeded circulation tends to keep the inside surface clean and floats the scale-making sediment along until it reaches the back
HANDBOOK ON ENGINEERING.
505
water leg, where it is carried down and settles in the bottom of leg, where it is blown off at regular intervals.
Fte. 265. Formation of front water leg in O'Brien boiler. Steadiness of wate* level — The large area of surface at watei line and the ample passages for circulation, secure a steadiness
506 HANDBOOK ON ENGINEERING.
of water level peculiar to this type. This is a most im- portant point in boiler construction and should always be consid- ered when comparing boilers. The water legs are stayed by hol- low stay-bolts of hydraulic tubing of large diameter, so placed that two stays support each tube and hand-hole and are subjected to only very slight strain. Being made of heavy material, they form the strongest parts of the boiler and its natural supports. The water legs are joined to the shell by flanged and riveted joints and the drum is cut away at these two points to make connection with in- side of water leg, the opening thus made being strengthened by special stays, so as to preserve the original strength. The shells are cylinders with heads dished to form part of a true sphere. The sphere is everywhere as strong as the circular seam of the cylinder, which is well known to be twice as strong as the side seam ; therefore, the heads require no stays. Both the cylinder and the spherical heads are, therefore, free to follow their natural lines of expansion when put under pressure.
The illustration on page 505 plainly shows the formation of the front water leg or header in this type of water tube boiler.
It will be seen that the hand plates are all oval in shape, a] low- ing each one to be removed from its respective hole ; also, the manner of bracing with hollow stay-bolts is shown.
Note that the feed pipes for supplying boiler run back to rear water leg and discharge therein.
Walling' in* — In setting the boiler, its front water leg is placed firmly on a set of strong, cast-iron columns bolted and braced to- gether by the door frames and dead-plates and forming the fire front. This is the fixed end. The rear water legs rest on rollers which are free to move on cast-iron plates firmly set in the ma- sonry of the low and solid rear wall. Thus the boiler and its walls are each free to move separately during expansion or contraction, without loosening any joints in the masonry.
On the lower, and between the upper tubes, are placed light
HANDBOOK ON ENGINEERING. 507
fire-brick tiles. The lower tier extends from the front water leg to within a few feet of the rear one, leaving there an upward pass- age across the rear ends of the tubes for the flame. The upper tier closes into the rear water leg and extends forward to within a few feet of the front one, thus leaving an opening for the gases in front. The side tiles extend from side walls to tile bars and close up to the front water leg and front wall, and leave open the final uptake for the waste gases.
The gases being thoroughly mingled in their passage between the staggered tubes, the combustion is more complete, and the gases impinging against the heating surface perpendicularly, in- stead of gliding along the same longitudinally, the absorption of the gas is more thorough. The draft area, being much larger than in fire tube boilers, gives ample time for the absorption of the heat of the gases before their exit to the chimney.
DESCRIPTION OF THE HEINE SAFETY BOILER.
The boiler is composed of lap- welded wrought-iron tubes ex- tending between and connecting the inside faces of two " water legs," which form the end connections between these tubes and a combined .steam and water drum or " shell " placed above and parallel with them. Boilers over 200 horse-power have two such shells. These end chambers are of approximately rectangular shape, drawn in at top to fit the curvature of the shells. Each is composed of a head plate and a tube sheet flanged all around and joined at bottom and sides by a butt strap of same material, strongly riveted to both. The water legs are further stayed by hollow stay-bolts of hydraulic tubing of large diameter, so placed that two stays support each tube and hand-hole and are subjected to only very slight strain. Being made of heavy metal, they form the strongest parts of the boiler and its natural supports. The
508 HANDBOOK ON ENGINEERING.
water le-s are joined to the shell by flanged and riveted joints, the drum i cut away at these two points to make connects
with inside of water leg, the opening thus made being strength- ened by bridges and special stays so as to preserve 1
strength.
48
HANDBOOK ON ENGINEERING. 509
The shells are cylinders with heads dished to form parts of a true sphere. The sphere is everywhere as strong as the circle seam of the cylinder, which is well known to be twice as strong as its side seam. Therefore, these heads require no stays. Both the cylinder and its spherical heads are, therefore, free to follow their natural lines of expansion when put under pressure. Where flat heads have to be braced to the sides of the shell, both suffer local distortions where the feet of the braces are riveted to them, making the calculations of their strength fallacious. This they avoid entirely by their dished heads. To the bottom of the front head a flange is riveted, into which the feed-pipe is screwed. This pipe is shown in the cut with angle valve and check valve attached. On top of shell, near the front end, is riveted a steam nozzle or saddle, to which is bolted a tee. This tee carries the steam valve on its branch, which is made to look either to front, rear, right or left ; on its top the safety valve is placed. The saddle has an area equal to that of stop valve and safety valve combined. The rear head carries a blow-off flange of about same size as the feed flange, and a manhead curved to fit the head, the manhole supported by a strengthening ring outside. On each side of the shell a square bar, the tile-bar, rests loosely in flat hooks riveted to the shell.. This bar supports the side tiles, whose other ends rest on the side walls, thus closing the furnace or flue on top. The top of the tile-bar is two inches below low water line. The bars rise from front to rear at the rate of one inch in twelve. When the boiler is set, they must be exactly level, the whole boiler being then on an incline, i. e., with a fall of one inch in twelve from front to rear. It will be noted that this makes the height of the steam space in front about two-thirds the diam- eter of the shell, while at the rear the water occupies two-thirds of the shell, the whole contents of the drum being equally divided between steam and water. The importance of this will be ex- plained hereafter.
510
HANDBOOK ON ENGINEERING.
The tubes extend through the tube sheets, into which they are expanded with roller expanders ; opposite the end of each and in the head plates, is placed a hand-hole of slightly larger diam-
.
Fig. 267. Details of construction — Heine boiler.
eter than the tube, and through which it can be withdrawn. These hand-holes are closed by small cast-iron hand-hole plates, , by an ingenious device for locking, can be removed in a
HANDBOOK .ON ENGINEERING. 511
few seconds to inspect or clean a tube. The accompanying cut shows these hand-hole plates marked H. In the upper corner one is shown in detail, H2 being the top view, H* the side view of the plate itself, the shoulder showing the place for the gasket. Hl is the yoke or crab placed outside to support the bolt and nut. Inside of the shell is located the mud drum D, placed well below the water line, usually parallel to and 3 inches above the bottom of the shell. It is thus completely immersed in the hot- test water in the boiler. It is of oval section, slightly smaller than the manhole, made of strong sheet-iron with cast-iron heads. It is entirely inclosed except about 18 inches of its upper portion at the forward end, which is cut away nearly parallel to the water line. Its action will be explained below. The feed- pipe F enters it through a loose joint in front ; the blow-off pipe N is screwed tightly into its rear-head, and passes by a steam- tight joint through the rear-head of the shell. Just under the steam nozzle is placed a dry pan or dry pipe A. A deflection plate L extends from the front head of the shell, inclined up- wards, to some distance beyond the mouth or throat of the front water leg. It will be noted that the throat of each water leg is large enough to be the practical equivalent of the total tube area, and that just where it joins the shell it increases gradually in width by double the radius of the flange.
Erection and walling in* — In setting the boiler, its front water leg is placed firmly on a set of strong cast-iron columns, bolted and braced together by the door frames, deadplate, etc., and forming the fire front. This is the fixed end. The rear water leg rests on rollers, which are free to move on cast-iron plates firmly set in the masonry of the low and solid rear wall. Wherever the brickwork closes in to the boiler, broad joints are left which are filled in with tow or waste saturated with fireclay, or other refractory but pliable material. Thus the boiler and its walls are each free to move separately during expansion or con-
512 HANDBOOK ON ENGINEERING.
traction without loosening any joints in the masonry. On the lower, and between the upper tubes, are placed light firebrick tiles. The lower tier extends from the front water leg to within a few feet of the rear one, leaving there an upward passage across the rear ends of the tubes for the flame, etc. The upper tier closes in to the rear water leg and extends forward to within a few feet of the front one, thus leaving the opening for the gases in front. The side tiles extend from side walls to tile bars and close up to the front water leg and front wall, and leave open the final uptake for the waste gases over the back part of the shell, which is here covered above water line with a rowlock of firebrick rest- ing on the tile bars. The rear wall of the setting and one paral- lel to it arched over the shell a few feet forward, form the uptakes. On these and the rear portion of the side walls is placed a light sheet-iron hood, from which the breeching leads to the chimney. When an iron stack is used, this hood is stiffened by L and T irons so that it becomes a truss carrying the weight of such stack and distributing it to the side walls.
Heine boiler and its operation* — The boiler being filled to middle water line, the fire is started on the grate. The flame and gases pass over the bridge wall and under the lower tier of tiling, finding in the ample combustion chamber space, temperature and air supply for complete combustion, before bringing the heat in contact with the main body of the tubes. Then, when at its best, it rises through the spaces be- tween the rear ends of the tubes, between rear water leg and back end of the tiling, and is allowed to expand itself on the entire tube heading surface without meeting any obstruction. Ample space makes leisurely progress for the flames, which meet in turn all the tubes, lap round them, and finally reach the second uptake at the forward end of the top tier of tiling, with their temperature reduced to less than 900° Fahrenheit. This has been measured here, while wrought iron would melt just above the lower.tubes at
HANDBOOK ON ENGINEERING.
513
rear end. showing a reduction of temperature of over 1,800° Fahr. between the two points. As the space is studded with water tubes, swept clean by a positive and rapid circulation, the absorp- tion of this great amount of heat is explained. The gases next travel under the bottom and sides of shell and reach the uptake at just the proper temperature to produce the draft required. This varies, of course, according to chimney, fuel required, etc. With boilers running at their rated capacity, 450° Fahrenheit are
Fig. 2<»8. A furnace that is used in the Eust.
seldom exceeded. Meanwhile, as soon as the heat strikes the tubes, the circulation of the water begins. The water nearest the surface of the tubes becoming warmer, rises, and as the tubes are higher in front, this water flows towards the front water leg where it rises into the shell, while colder water from the shell falls down the rear water leg to replace that flowing forward and upward through the tubes. This circulation, at first slow, in-
33
514
HANDBOOK ON ENGINEERING.
creases in speed as soon as steam begins to form. Then the speed with which the mingled current of steam and water rises in the forward water leg will depend on the difference in weight of this mixture, and the solid and slightly colder water falling down the rear water leg. The cause of its motion is exactly the same as that which produces draft in a chimney.
Fig. 269. Plain vertical tubular boiler.
This cut shows the place for gauge cocks and water glass in an
upright boiler.
HANDBOOK ON ENGINEERING.
515
cf)d)6ocMooooo ooooo boooo ooooo ooooo ooooo ooooo oooo oooo
O wr^fk O
Fig. 270. Showing the water-column in its proper place.
516
HANDBOOK ON ENGINEERING.
9
a
* « &
$
|
efl
'i
® g
P
i
I
e
£
fc
0
»
*
I?"
Z->OQ I
fl *3o
««0.
oj
juao aad
jo
<M CC GO O CO "•# 00 CO O JO CC OS «-* CQ QO in CO 00 C5 CO — J ffi •** 1C O t- CS 00 Ci «)
S!^J5SJ5rtSS?5i:viS^rt^iSto^Scl'~10^HS
i-
sOt— i(M
J'^'M^H QOT^OeOt-— tO'-HCO'^CO-H
J Oi i-H CO TJJ ?C i-l O <>4 O5 -* CO Oi SO •*# OS
'
O'^rHOOCDrHCNT»«r-l— S 0^1 •* iO i-l OS CV C^ •«* 00
*-« »OCO»0«OI-
CO IO A O^ -^ (
OiO^c^cM-*iocot-c
CN COCOeOCO COO'— lOiGOaOWt-iOCDO i—(»
i^ « oo rt 55 oo c* o op 51 o OD t— so §5 •*« 55 e* IH cot
1
HANDBOOK ON ENGINEERING.
517
ineoMOSc^OS coiot— -<*so»«oo(Mc^(Ms<iO5«ou3frii-H®eo»oooi?D?nocoooc;k««*— ^OOWM
SOCOe^OSCOOSeO«OCOO^iaaOOSt~<0~«50Si^<N»0«000<NOT^rt»
OT* CO^ OS CO OS OS* CO.ro OS IO ;* 00 OS «*» OQ ^ t^ OS C» 30 «O O Q CO 00 ©
t^OiO^?O^^CC^O^QOJ»^^W^(NCO»r30l^C^OC^OC^CC^iOO(>DO5O^Oi
o I-H 35 co •— « co oo Q^I oo r^ ^-oicsi— i-^«oo(M-^<'
OiHlO«lO
"
2
3Seo
Cr^QOOiOC-^
eo Cfl-*^ cocnosoo^Tji^ira^r-'* •* 1-1 » <M-^ co«o •^•^o
i-J ^OOiOt-iCiOOS^KMkO-^MQOr-l^ OiOQOO lijCCeOOr-HOeOt-O
S CM O5 C*« -^<r— OO'JiaiCOCDCOtO O r-. "* I 10 O t- & Z-( ^ 00 rH CO 00 »
'
Of>lt-«^<C^O5»O^-< •«* OO COO-**r-» C CO lO S U3 -^ "* «O C1 00 •* M r- CO O «O (
5COOT^'^O5OSr4o^
'
O'*^-O5 CO"* -<*OC^ COO
SoSS^^
i^'*or--oo
lOO
sft
518
HANDBOOK ON ENGINEERING.
0) 61 ?
*" PrH
-juao jod
- Q t*5
sae
•ainesaij
uoo J8d
•oinseaij;
OCOQOI— -
eorjiot-t
sil
, .6.
55,000 stre 1-6, 9
I
•aineeajj
eo os to os S 2B ® 35 c
•juao iad
•ainssaij
jo
•sained
0
*H «J
38
a
8
HANDBOOK ON ENGINEERING.
519
5«c**»*«o$3»a}io2|3$5w
JSSSSSS ?qSo1igSSSSSS§88§SISS8S§S8a3«9.9S9S«9^
|$S,~3S5»@S$
3r»3ooOO5OJ-^»OOCDc6l7«l^aOQOO5'*'*OOO«Ot-t»QOO3
So3£SS££ 58.'
5C
51
^
J3_
">^$04O
520
HANDBOOK ON ENGINEERING.
ooooo ooooo
OOOQQJDOOOO
ooooo ooooo
oooo oooo
O wrrfk O
Fig. 271. Showing the proper place for closing in the boiler on
the side — also the space between side of boiler and
side walls.
HANDBOOK ON ENGINEERING.
521
Fig. 272. Showing the proper place for grange-cocks in a sub- merged tube boiler.
522
HANDBOOK ON ENGINEERING.
THE AMOUNT OF MATERIAL REQUIRED TO BRICK UP BOILERS OF DIFFERENT SIZE.
|
• Htt • |
M *5 *"• |
||||||
|
GO . GO OQ |
r^ |
o t>> o |
f |
O (jj <4~l . ^ * |
|||
|
*M • |
<x> ~i |
0 |
|||||
|
o gj |
, fl^ |
T3 |
;5 o -S 2 |
on |
—> -^ |
73 ^ |
"S £H § 'cS |
|
I? CftPQ |
1^ rC «4H H <=> |
pq •d S |
a; a> ^ ^2 |
S |
HH ai o |
IS |
a» o o S *2 'as u a - |
|
72"x22' |
18' |
10^500 |
2,500 |
18 bu. |
88 |
8 |
9 bbl. |
|
72"x20' |
18' |
10,000 |
2,300 |
18 bu. |
80 |
8 |
8 bbl. |
|
72"xl8' |
18' |
9,500 |
2,200 |
17 bu. |
72 |
7 |
8 bbl. |
|
60"x20' |
18' |
9;500 |
2,200 |
17 bu. |
80 |
7 |
8 bbl. |
|
60"xl8' |
18' |
9,000 |
2,000 |
16 bu. |
72 |
7 |
8 bbl. |
|
54"x20' |
18' |
8,700 |
1,900 |
15 bu. |
80 |
6 |
8 bbl. |
|
54"xl8' |
18' |
. 8,000 |
1,800 |
15 bu. |
72 |
6 |
8 bbl. |
|
54"xl6' |
18' |
7,500 |
,700 |
14 bu. |
64 |
6 |
7 bbl. |
|
48"xl8' |
18' |
7,500 |
,600 |
14 bu. |
72 |
6 |
7 bbl. |
|
48"xl6' |
18' |
7,200 |
,500 |
14 bu. |
64 |
5 |
• 7 bbl. |
|
42"xl8' |
18' |
7,000 |
,400 |
12 bu. |
72 |
5 |
7 bbl. |
|
42"xl6' |
18' |
6,500 |
,300 |
12 bu. |
64 |
4 |
7 bbl. |
If 13" wall i less on Red Brick.
THE DOWN DRAUGHT FURNACE.
The down draught furnace is known as being one of the best smoke preventing furnaces in the market, while at the same time the cheapest kind of coal can be used.
The down draught furnace makes a -good smoke record, even with overworked boilers, doing variable work, and with a marked economy in fuel. All experience with the down draught furnace, seems to indicate that smoke from boiler furnaces can now be abated by practical means, without hardship, no matter what the type of boiler.
Directions for firing the down draught furnace* — When firing the furnace, throw the coal evenly over the entire grate surface, from 6 to 8 inches in depth, a little heaviest at the rear end of the furnace. Do not put in too much coal — burn more air and economize fuel if possible, and
HANDBOOK ON ENGINEERING.
523
do not pile up the coal in front near the door. Never fire any fresh coal on the lower grates ; let in air below the lower grates. When poking the fire, run the slice-bar down between the water grates and back the full length of the grates ; then rafse the slice- bar and gently shake the coal, and then pull it out without stir- ring up the fire. Never turn the fire over so that black coal gets down upon the water grates, unless there is a large clinker to re- move. Never give the top grates a general cleaning, so as to leave a portion of the grates uncovered and the remainder with a hot lire on them, as this causes an uneven expansion in the differ- ent tubes forming the water grates, and is liable either to bend the tubes or strip off the threads where they enter the drums. When the top fire becomes clogged with clinkers so that it is hard
r
Fig. 273. Down draught furnace.
to keep up steam, run in the slice-bar and raise the clinkers to the top of the fire ; remove the large clinkers, leave the small ones alone, and put on afresh fire. The lower grates must have proper
524
HANDBOOK ON ENGINEERING.
attention. The coals must be raked over evenly and all holes filled up, particular care being taken that the grates are perfectly covered all over. If considerable coals have accumulated on the
••jjfJL 7-i~- -litr-i
. . yO-l" J
Fig. 274. Yiew of the down draught furnace.
lower grates and the air spaces are closed with ashes or clinkers, the slice-bar must be used and the clinkers raised up and turned over and the larger ones removed. It is best to remove the clink- ers every two or three hours, leaving the coals to burn up.
SPECIFICATIONS FOR ONE SIXTY-INCH HORIZONTAL SIX- INCH FLUE BOILER.
General directions* — There will be one boiler 20 feet long from out to out of heads and 60 inches inside diameter.
Material, quality, thickness, etc* — Material in shell of the above named boiler to be made of homogeneous flange steel T5F" thick, having a tensile strength of not less than 60,000 Ibs. to
HANDBOOK ON ENGINEERING.
525
526 HANDBOOK ON ENGINEERING.
the square inch of section, with not less than 56 per cent ductil- ity, as indicated by contraction of area at point of fracture under test, or by an elongation of 25 per cent in length of 8 inches. Heads must be ^" thick and of the same quality of steel as that in the shell. All plates and heads must be plainly stamped with the maker's name, and tensile strength.
Tubes, size, number and arrangement* — The boiler must contain 18-6" lap- welded flues, riveted to the heads with ten £" rivets in each head ; said flues must be made of charcoal iron of the best American make, standard thickness, equal to the National Tube Works Company's make. All flues must have at least 3 inch clear space between them, and not less than 3 inches between flues and shell. All flanging of heads must be free from flaws or cracks of any description, and properly annealed in an annealing oven before riveting to the boiler. If 4-inch flues are wanted in place of 6 -inch, the boiler must have 44 best lap- welded tubes, 4" in diameter and 20 feet long, set in vertical and horizontal rows, with a clear space between them, vertically and horizontally of !£", except the central vertical space, which is to be 4 inches. Holes for tubes to be neatly chamfered off on the outside. Tubes to be set with a Dudgeon expander, and beaded down at each end.
Riveting* — The longitudinal • seams of the boiler must be above the fire line, and have a TRIPLE row of rivets ; all rivets to be |" in diameter ; and all rivets to be of sufficient length to form upheads equal in size to the pressed heads of same. The rivets in the longitudinal seams must be spaced 3J" apart from center to center, and the rows of same to be pitched 2T3^" apart from center to center, so as to give an efficiency of the joint of TYo- per cent of the solid plate. Transverse seams to be single riveted with same size rivets as those in the longitudinal seams pitched 2" apart from center to center. Care must be taken in punching and drilling holes that they may come fair in
HANDBOOK ON ENGINEERING. 527
construction; the use of adrift-pin to bring blind, or partially blind holes in line will be sufficient cause for the rejection of the boiler.
Calking* — The edges of the plates to be planed and beveled before making up the boilers, and the calking to be done with round nose tools, pneumatically driven ; no split or wedge calk- ing will be allowed.
Bracing* — There must be 22 braces in the boiler, one inch area at least, be nine above the flues on the front head and nine similar ones on the back head, none of which shall be less than 3' 6" long, made of good refined iron and securely riveted to the heads ; the other end to be extended to the shell of boiler and riveted thereto with two £'' rivets. Care must be exercised in the setting of them, so they may bear uniform tension. There must be two braces below flues, one on each side of manhead, and riveted to the heads with two X" rivets. The back end of brace to be ex-
o
tended backward to side of shell and riveted thereto by means of two J" rivets ; and two braces in back end above flues, one on each side and riveted the same as the other two below flues.
Manholes* — The boiler to have two manholes of the Hercules or Eclipse pattern, same to be of size 10" x 15", one located in front head, beneath the flues, and the other in rear head above the flues, and each to be provided with a lead gasket, grooved lid, two yokes and two bolts. The proportion of the whole to be such as will leave it as strong as any other portion of the head of like area.
Steam drum* — The boiler must be provided with one steam drum 30" in diameter by 5' in length, shell plates of which are to be Ty thick and heads |" thick, of the same quality of material as that in the boiler. The heads must be bumped to a radius so as to give as near as practicable equal strength as to that in the shell without bracing. The longitudinal seams of the drum are
528 HANDBOOK ON ENGINEERING.
to be double riveted with -J--J-" diameter rivets, pitched 2J" apart from center to center, so as to give an efficiency of the joint of 74 per cent of the solid plate.
Manhole in drum* — The drum must be provided with Her- cules or Eclipse patented manhole, same to be of size 10"xl5", located in the center of one head, and to be provided with a grooved lid, lead gasket, two jokes and two bolts. The propor- tion of the whole to be such as will leave it as strong as any other portion of the head of like area.
To attach to boilers. — The steam drum must be attached to the boiler by means of two flange steel connecting legs, 8" in diameter by 12" in length, and securely riveted to boiler and steam drum shell.
Mud drum* — Boiler must be provided with one mud drum 24" in diameter and of sufficient length so that each end may come flush with the outside of the boiler walls on each side ; the quality and thickness of steel to be the same as that specified for the steam drum, and all seams to be single riveted ; said mud drum to be provided with one Hercules or Eclipse patent manhole in one end, and to be of size 9" x 14", supplied with a grooved lid, lead gasket, two yokes and two bolts.
To attach to boiler* — The mud drum is to be attached to boiler by means of 8" diameter steel connecting leg, about 16" in length, properly riveted to boiler and mud drum shells.
Flanges* — The boiler to have one 8" wrought steel flange riv- eted on top of steam drum ; one wrought steel flange 4" in diam- eter, about 5 feet from front end of boiler for safety valve one 2" wrought steel flange on after end of boiler over the center of mud leg for supply pipe — all flanges to be threaded ; 2" hole in mud drum for blow-off ; also 2 1J" holes, one on top of boiler and one on end near bottom of boiler for water column.
Fusible plugs* — To have two fusible plugs ; one inserted in shell from inside on second sheet, or about 5' from forward end, 1
HANDBOOK ON ENGINEERING. 529
inch above flues ; one plug inserted in top of flue, not more than three feet from after end.
Trimmings* — Furnish one 4" spring or dead weight safety valve, 4" diameter ; one water combination column ; provide same with two 1 J" valves for the steam and water connections between the boiler and column, and one %" valve for blow-pipe ; said blow- pipe to be connected with ashpit ; said combination barrel to be 4'' diameter, IS'1 long, and made of cast-iron. Also, furnish one water gauge having a f'x 15" Scotch glass tube, bodies polished with wood wheels and guards, rods, bodies threaded f " ; three gauge cocks |" register pattern, polished brass bodies ; one steam gauge with 10" dial; one 2" brass feed valve with 2" check valve ; one 2" gate valve for blow-off from mud drum ; also one asbestos packed stop-cock for same, so as to insure against the possibilities of a leak through the blow-pipe. Water column to have crosses in place of ells. Crosses to have brass plugs.
Castings, gr ates, doors, etc* — The boiler must be provided with a heavy three-quarter fire front of neat design, having double firing and ashpit doors, anchor bolts for anchoring fire cronts in place, heavy deadplates, a full set of fire liners 9" deep for sup- porting firebrick on end, front and rear bearing bars ; a full set of ordinary grate bars 4 ft. long, soot door and frame for cleaning out rear ashpit ; a full set of skeleton arch plates ; 12 heavy buck staves 9i' long, provided with tie rods, nuts and washers, heavy back stand with plate and expansion rollers ; also furnish wrought plates to cover mud drum.
Fire tools* — Furnish in addition to above two sets of fire tools consisting of two pokers, two hoes, two slice-bars, two claws, and one six-inch flue brush with |" pipe for handle.
Breeching* — Boiler must have a breeching fitted to front head and fastened thereto by means of bolts, stays and suitable pieces of angle iron, bent to conform to circle of boiler. The underside of breeching is to run across the head between the lower flues and
34
530 HANDBOOK ON ENGINEERING.
the manhole, leaving the manhole freely exposed ; the sides of breeching are to be made of T3¥" steel, the front and doors of |" steel ; said doors to be hung by means of strap hinges, provided with suitable fastenings so as to give free access to all flues when open.
Uptake and damper* — An uptake having an area of 1221 square inches must be fitted to top of breeching. Said uptake must be of convenient form for attaching to a stack 40" in diam- eter and provided with a close-fitting damper having a steel hand attachment, so that same may be operated conveniently from the boiler room floor.
Smoke stack* — There is to be provided for the above boiler one smoke stack 40" in diameter by 90 feet in height, half of which is to be made of No. 8, and the other half of No. 10 best black sheet steel throughout, and supplied with two sets of four guy rods, each consisting of f " galvanized wire cable guy strand with turn-buckles for same.
In general* — The above-mentioned boiler must be made of strictly first-class material and workmanship throughout, and sub- jected to a hydrostatic pressure of 150 pounds to the square inch before leaving the works of the manufacture.
Painting boiler breeching* — Smoke stack and boiler front, steam and mud drum, and all trimmings, to have two good coats of coal tar.
Masonry* — Boiler to be set in good substantial masonry, of hard burned brick and good mortar, made of clean, sharp sand and fresh burned lime. Walls to be 18" thick0 The outside walls to be laid up of selected hard burned brick, with close joints struck smooth and rubbed down. The sides, end and bridge walls, and boiler front, to have a foundation of 24" wide and 12' deep, laid in Portland cement. The ash pit to be paved with hard burned brick set on edge firmly, imbedded in Portland cement. For a distance of seven feet in front of the boiler and
HANDBOOK ON ENGINEERING. 531
continuing across entire width of front of boiler setting to be paved with hard burned brick set on edge, firmly imbedded in sand. The walls to be carried up to the full height and a row- lock course of brick 4" thipk to be carried over top of boiler from side wall to side wall, extending the whole length of boiler, and the entire arch to be plastered over on the outside with mortar. The bridge walls to be 24", carried up to within 6"* of under side of boiler. The top of bridge wall to be of fire brick and made in the form of an inverted arch, conforming to the shell of the boiler. The space under boiler and back of bridge wall to the back end of boiler, to be filled in with earth or sand and the top paved with brick, and tapering from bridge wall back to back end to 12"* at back end, and in a similar form and shape, that is, inverted arch. The uptake for returning the smoke and heat at back end of boiler, to be arched over from rear wall against the back head of boiler 2" above the tubes, the arch being made of arch fire brick, and backed up with red brick. Furnace to be lined throughout with first quality fire brick, dipped in fire clay with close joints and fire brick rubbed to place, from a point 2" below grates, to where it safes in against boiler, and to be continued fire brick as far back as the rear end of setting and across rear end of same ; it being the intent that all interior surfaces of the setting with which the heat comes in contact, shall be faced with fire brick. Every sixth course to be a header course.
Smoke connections* — The connection from boiler to chimney to be made of No. 12 black iron, with cleaning door and damper in same.
BANKING FIRES.
Different engineers pursue different methods in banking fires.
One method is to push the fire back one-third towards the bridge
wall, and clean off the grate in front. Then shovel in from 150
to 300 Ibs. of fine coal on top of the fire, closing ash-pit doors
* These distances should be doubled for bituminous coal.
532 HANDBOOK ON ENGINEERING.
and leaving furnace doors open, with damper open enough to let the gases escape. Others bank after this fashion but close all doors and air holes, leaving the damper partially open. Another method is to level the fire all over the, grate, and shovel in from 150 to 500 Ibs. of fine coal, — depending on the size of the grate, — and then cover the whole surface with wet ashes to a good depth, so that no fire nor flame can be seen, then close the ash-pit doors, leaving the furnace doors ajar, and leave the damper partially open so that the gases may escape. In the morning, rake out the ashes, clean the fire, and throw in fresh coal.
INSTRUCTIONS FOR BOILER ATTENDANTS.
The following instructions apply more particularly to horizontal return tubular boilers, although in a general way they are appli- cable to all types of boilers.
Never start a fire under a boiler until you are positively certain that there is sufficient water in the boiler, — at least two gauges of water. Do not trust to the water gauge alone, but try the gauge cocks also, and try them at intervals during the day, be- cause the water gauge pipe connections may be choked and cause a false water level.
Before starting a fire be sure that the blow-off cock is closed and not leaking.
Before it is time to start the engine, pump up three gauges of water, and blow off one gauge, in order to get rid of mud and other sediment. If the boiler b.as a surface blow-off, — commonly called a ct skimmer," — blow off the scum before stopping the engine for the day.
When the day's work is done, leave three gauges of water in the boiler, to allow for leakage and evaporation during the night.
Never raise steam hurriedly. Sudden changes of temperature may produce fractures, or start leaks.
HANDBOOK ON ENGINEERING. 533
la starting a fire in a furnace, a good plan is to cover the grate with a thin layer of coal and to place the shavings and wood on the coal and then light the shavings.
The advantage of placing a covering of coal on the grate before the wood and shavings, is that it is a saving of fuel, as the heat that would be transmitted to the bars is absorbed by the coal, and the bars are also protected from the extreme heat of the fresh fire.
Lift the safety-valve, — if of the lever pattern, — every morn- ing while raising steam, and satisfy yourself that it is in good working order, and that the ball is set at the proper point on the lever. The most disastrous explosions have occurred with boilers whose safety-valves had been stuck down or overloaded.
Keep the boiler shell free of soot. Soot is a very good non- conductor of heat, and considered worse than scale inside of a boiler.
Keep your boiler tubes free from soot and dust. Choked tubes impair the draft. The tubes should be cleaned twice a week, or oftener.
Soot collects also in a stack or chimney and in the connection between the breeching and stack, and interferes with the draft,
Open your boiler every two weeks, or, as often as necessary,— depending on the kind of feed-water used, — and clean out the mud and scale. At the same time examine all of the stays, and see that they are taut and in good order. Also, look for pitting around the mud-drum connection, and for grooving in the side seams. Examine all outlets and pipe connections, and look for indications of " bagging " in the furnace sheets.
Clean off the fusible plugs both inside and outside of the boiler. A fusible plug covered with soot on the fire side, and with scale on the water side, is no longer a u safety plug." Renew the filling in safety plugs, at least once a year. They are filled with pure Banca tin.
534 HANDBOOK ON ENGINEERING.
Be perfectly satisfied that your boiler is in good condition internally before you close it up.
Just as soon as you have fastened the man-head in its place > turn on the feed-water until you get at least three gauges of water. Fires have been built under empty boilers, and will be again, if you forget to turn on the feed water after cleaning out.
Do not empty a boiler while it is under steam pressure, but allow it to get cold before letting the water run out.
If you are in a great hurry and can't wait for the boiler to cool down, nor for the brickwork or anything else to cool down, draw the fire and open the furnace and ash-pit doors, then turn on the feed water, and from time to time blow out, until the steam gauge shows no pressure ; then shut .off the feed-water, raise the safety valve, open the blow-off cock, then open up the boiler.
Before opening a man -hole, lift the safety-valve, so as to be sure that there is neither pressure nor vacuum in the boiler.
Look well after the brick -work surrounding your boiler, and stop all cracks in the walls with mortar or cement, as soon as discovered. They impede the draft, and cool the plates of the boiler, causing a waste of fuel.
See that the bridge wall is in perfect condition, because a gap in the bridge wall might cause a " bag " in the boiler by concen- trating the flames on one spot.
Never allow any bare places on the grate, nor any accumulation of ashes, or dead coal in the corners of the furnace, as such places admit great quantities of cold air into the furnace, and render the combustion very imperfect.
In firing with anthracite coal, do not poke and stir up the fire, as with soft coal, but let it alone.
In firing soft slack coal, fire very lightly but frequently, carry- ing a thin fire.
In firing with soft lump coal, carry a thick fire, say from six to eight inches deep, according to the size of the furnace.
HANDBOOK ON ENGINEERING. 535
In firing up, you may spread the fresh coal evenly all over the grate, or, you may push the live coals back towards the bridge- wall, leaving a thin bed of live coals near the furnace doors, and spreading the fresh coal on top of it. This is called carrying a coking fire. Some prefer the one and some the other method of firing.
In case you should find the water in the boiler out of sight, and a heavy fire in the furnace, don't get rattled, and don't lose your head. Open the furnace doors, and close the ash-pit doors, and cover the fire with wet ashes, or damp clay, completely smothering it. Let everything else alone, including the safety valve and the engine. Now wait until the boiler cools down and the gauge shows no pressure, then turn on the feed-water.
On the other hand, if there is but very little fire in the furnace, you may draw the fire, instead of covering it with ashes or clay.
If your boiler foams badly and you are uncertain as to the water level, stop the engine, and the true water level will show itself at once.
If your boiler primes and water is carried over to the engine, it shows that there is want of sufficient steam room in the boiler. Either put a dry-pipe in the boiler, or, increase the steam pressure if the boiler will safely stand it.
Never attempt to calk a leaky seam in a boiler under steam pressure, because the jar caused by the hammer blows might cause a rupture of the seam. Better to be on the safe side always when repairs are required in a steam boiler, and wait until the boiler is cold. The above applies to steam pipes and valve casings, also.
Never open any steam valves suddenly, nor close them sud- denly either, because it is highly dangerous to do so, particularly if there is considerable water in the pipes. The effect is the same as water hammer in water pipes.
Smoke is caused by too little air supply, or by the flames being
536 HANDBOOK ON ENGINEERING.
prematurely cooled. Therefore, after firing up with fresh coal, it might be necessary to leave the furnace doors ajar in order to supply sufficient air above the fuel.
Remember that it takes nearly 24 cubic feet of air for the proper combustion of one pound of soft coal. Hard coal does not require so much.
Each and every boiler in a battery should have its own inde- pendent safety-valve and steam gauge.
If you are obliged to force your fire, watch your furnace sheets for indications of " bagging," if the water space below the lowest row of tubes is cramped. Water-tube boilers are less liable to suffer from the effects of forced fires than shell boilers.
With an intensely hot fire under a shell boiler, the furnace sheets are liable to bag, unless there is ample water space be* tween the shell of the boiler and the bottom row of tubes.
The use of mineral oil to remove or prevent boiler scale, is not to be recommended.
Have your feed water analyzed, and use a scale preventer adapted to its requirements.
By all means endeavor to secure a steady furnace temperature, and a steady steam pressure, for herein lies much economy of fuel. Fluctuations are wasteful.
Put a damper in your chimney and adjust it to the needs of your furnace. Try to prevail on your employer to put in a shak- ing grate. It will enable you to carry a steady furnace temper- ature, and also enable you to keep the air spaces in your grate free and open without breaking up your fire.
RULES AND PROBLEMS RELATING TO STEAM BOILERS.
To find the safe working pressure : —
U* S* Rule. — Multiply one-sixth (|) of the lowest tensile strength found, stamped on any plate in the cylindrical shell,
HANDBOOK ON ENGINEERING. 537
by the thickness — expressed in inches or parts of an inch — of the thinnest plate in the same cylindrical shell, and divide by the radius or half diameter — also expressed in inches — and the result will be the pressure allowable per square inch of surface for single riveting ; to which add 20 per cent for double riveting, when all the holes have been " fairly drilled " and no part of such hole has been punched.
A* S. of M* E* Rule* — First, find the tensile strength of the solid plate between the centers of two adjacent rivet holes. Call this factor A. •
Next, find the tensile strength of the solid plate between the centers of two adjacent rivet holes, less the diameter of one rivet hole. Call this factor B.
Next, find the shearing strength of the rivets. Call this factor C.
Now divide whichever is the smaller factor B or C by J., and the quotient will give the strength of the joint as compared with the solid plate — expressed as a percentage. Then multiply the tensile strength of the plates by the thickness of plates — in frac- tional parts of an inch — and multiply this product by the per- centage as found above, and divide this last product by the radius of the shell in inches, and the quotient will be the bursting pressure.
Divide this quotient by the factor of safety and the result will give the safe working pressure.
Example* — What is the safe working pressure for a steel boiler 60 inches in diameter, with side seams double riveted, tensile strength of plates 60,000 Ibs. per sqr. in., thickness of plate | inch. Diameter of rivet holes £f inch, pitch of rivets 3J inches, shearing strength of rivets 38,000 Ibs. per sqr. in., and factor of safety 5 ?
Ans. By U. S. rule, 150 Ibs. per sqr. in. By A. S. of M. E. rule, 106J Ibs. per. sqr. in.
538 HANDBOOK ON ENGINEERING.
Operation by U. S. rule : —
60,000
— ^ — = 10,000. And, 10,000 X f = 37,500.
3750 And, -3Q-= 125. And, 125 X. 20 =25.
Then, 125+25 = 150,
Operation by A. S._of M. E. rule: — f" = .3 75".
I*" = . 9375".
Then, 60,000 X 3J X .375 = 73,125 Ibs., the strength of the solid plate between the centers of two adjacent rivet holes. Call this factor A. Also, 3J- = 3.25.
Then, 3.25 — .9375 = 2.3125.
And, 60,000 X 2.3125 X .375 = 52,031.25 Ibs. the strength of the plate between two adjacent rivet holes. Call this factor B.
Then, .9375 X -9375 X .7854 = .69029 of a square inch, the area of one rivet hole. There are two rows of rivets.
Then, .69029 X 2 = 1.38058 sqr. ins. the area of two rivet holes combined.
Then, 38,000 X 1.38058 =52,462.04 Ibs., the resistance of rivets to shearing. Call this C. Now since B is less than (7, divide 52,031.25 by 73,125 and get as a quotient .71 +, thus showing the strength of the joint to be more than 71 per cent of the strength of the solid plates.
Then, 60,000 X^875 X .71 = ^5 ^ per sqr< .^ ^ bursting pressure.
And, L- = 106.5 Ibs. per sqr. in., the safe working
5
pressure.
HANDBOOK ON ENGINEERING. 539
To find the horse power of a horizontal return tubular boiler, from its heating surface : —
Rule* — Find the heating surface in square feet, of the shell of the boiler, measuring from one fire line to the other. Next find the internal heating surface of all the tubes in square feet. Add the two results together and divide their sum by 12, and the quotient will be the H. P. approximately. The heads are omitted.
Example* — What is the H. P. of a horizontal return tubular boiler 60 inches in diameter and 20 feet long, with 44 four-inch tubes each 20 feet long, the distance from fire line to fire line being 9 feet? Ans. 86.65 H. P.
Operation* — The internal diameter of a 4-inch tube is 3.732 inches.
Then, 20 X 9 — 180 square feet of heating surface in the shell.
3.732 X3-!41^ .9770376 ft., the circumference of
12
one tube in feet.
And, .9770376 X 20 X 44 = 859.793 + sqr. ft., the total heating surface of the tubes.
Then, 180+859-793 = 86.65 nearly. 12
To find the factor of evaporation : —
Rule. — From the total number of heat units in one pound of steam at the given pressure, subtract the number of heat units in one pound of the feed water at its given temperature, and divide the remainder by 965.7, which is a constant.
Example*— A boiler evaporates 6,000 Ibs. of water per hour from feed water at 210 degrees into steam at 125 Ibs. gauge pres-
540 HANDBOOK ON ENGINEERING
sure, what is the equivalent evaporation " from and at," 212°? What is the H. P. of the boiler?
Ans. Equiv. evap. 6276 Ibs. H. P. 182, nearly.
Operation* — The total number of heat units in steam at 125 Ibs. per sqr. in. gauge pressue is 1221.5351.
The number of heat units in feed-water at 210 degrees equals 210.874. The latent heat of steam at atmospheric pres- sure, equals 965.7.
Then, 1221.5351 — 210.874 = 1010.6611.
And, - — '- — — = 1.046, the factor of evaporation. 965.7
And, 6000 X 1-046 = 6276 the equivalent evaporation.
Then, = 181.9 H. P.
34.5
To find how many pounds of steam at a given absolute pressure will flow through an orifice of one square inch area in one sec- one? : —
Rule* — Divide the absolute pressure by the constant number 70.
Example* — How many pounds of steam at 85 Ibs. per sqr. in. gauge pressure, will flow through an orifice one inch in diameter, in one second? Ans. 1.122 Ibs.
Operation* — A hole 1 inch in diameter has an area of .7854 of a sqr. inch.
And 85 + 15 = 100 Ibs. absolute.
Then, 122
The weight of a cubic foot of steam at 100 Ibs. per sqr. in.
1 122 absolute pressure is .2307 of a pound. Then, ' Q?i = 4.86 -{-
cubic feet.
HANDBOOK ON ENGINEERING. 541
To find the width of a reinforcing ring for a round hole in a flat surface, when the ring must contain as many square inches as were cut out of the plate, and when the ring and the plate are of the same thickness : —
Rule* — Find the area of the hole in square inches and multi- ply it by 2. Divide this product by .7854 and extract the square root of the quotient for the diameter of the ring over all. Sub- tract the diameter of the hole from the diameter over all, and divide the remainder by 2 for the width of the ring.
Example* — What should be the width of a reinforcing ring for a hole 10 inches in diameter, the metal cut out, and the metal in the ring being | in. thick? Ans. 2T^ inches.
Operation* — 10 X 10 X .7854 = 78.54 sqr. ins. area of hole.
And, 78.54 X 2 •= 157.08 sqr. ins. in both hole and ring. 157.08
And' T7854":
And,
And, 14.142 — 10 z= 4.142.
• 4.142 Then, — ~ — — 2.071" or practically 2^".
To find the width of a reinforcing ring for an elliptical manhole in a flat surface, when the ring must contain as many square inches as are contained in the hole, and the metal cut out and metal in the ring are of the same thickness : —
Rule* — Square the short diameter of the hole and add to it six times the short diameter multipled by the long diameter, and to this product add the square of the long diameter, and extract the square root of the sum. From this root subtract the sum of the short diameter added to the long diameter, and divide the re- mainder by 4 for the width of the ring.
Example* — What should be the width of a reinforcing ring for a manhole 11" X 15"? Ans. 2J£ inches.
542 HANDBOOK ON ENGINEERING.
Operation.— 11" X 11" = 121.
And, 11 X 15 X6=990.
And, 15 X 15 = 225.
Then, 121 + 990 + 225 = 1336.
And, V 1336 = 36.551.'
And, 11 + 15 = 26.
Then, 36.551 — 26 = 10.551.
10.551
And, — j — = 2.637 + ins. the width of the ring, or, prac- tically 2J£ ins.
Then, 2.637X2 = 5.274".
And, 11 + 5.274 = 16.274" short diameter of ring over all.
And, 15 + 5.274 = 20.274" long diameter over all.
Proof: 20.274 X 16.274 X .7854= 259.13 + square inches area of hole and ring.
And, 15 X 11 X -7854 = 129.59 + sqr. ins. area of hole alone.
Then, 259.13—129.59 = 129.54.
THE AHOUNT OF STEAM USED WITH VALVE OPEN WIDE, WITH STEAfl JETS AS A SMOKE PREVENTIVE.
STEAM JETS.
Given two boilers with separate furnaces, having 4 steam jets in each furnace, and each jet T^- inch in diameter, the steam pres- sure being 100 Ibs. per sqr. inch by the gauge. How many pounds of steam at this pressure will flow through the 8 nozzles in 12 hours? Answer. 1739 Ibs. nearly.
Operation : TV" = .0625 ".
Then, .0625 X -0625 X .7854 = .003067968750 sqr. inch, area of 1 jet.
HANDBOOK ON ENGINEERING. 543
And, .003067968750 X 8 = .02454375 sqr. inch, the com- bined area of 8 jets.
Also, 100 + 15 = 115 Ibs. per sqr. inch, the absolute steam pressure,
115 And, _ — = 1.64 Ibs. of steam per second that will flow
through an orifice of 1 square inch area.
Then, 1.64 X .02454375 = .04025175 Ibs. of steam per second flowing through the 8 jets.
Again: There are 43,200 seconds in 12 hours. Thus: 12X60X60 = 43,200.
Then, .04025175 X 43,200 = 1738.8756 Ibs. of steam will flow through 8 jets in 12 hours' time.
Taking a high speed automatic cut-off engine using 20 Ibs. of steam per H. P. per hour, the 8 steam jets would waste enough steam in 12 hours to run —
A 10 H. P. engine for 8£ hours. A 20 " " " 4£ " A 40 " " " 2J • An 80 " " " 1^ «
Thus 10 X 20 = 200. And, — _ = 8i nearly.
9OO
20 X 20 = 400.
And, = 4i nearly.
80 X 20 = 1600.
And, — f — = lA nearly. 1 1600 J
544
HANDBOOK ON
CHAPTER XIX
THE STEAM PUMP,
Fig. 276. The Worthington compound pump.
THE WORTHINQTON COMPOUND PUMP.
In the arrangement of steam cylinders here employed, the steam is used expansively, which cannot be done in the ordinary form. Having exerted its force through one stroke upon the smaller steam piston, it expands upon the larger during the return stroke, and operates to drive the piston in the other direction. This is, in effect, the same thing as using a cut-off on a crank engine, only with the great advantage of uniform and steady action upon the water.
HANDBOOK ON ENGINEERING.
645
Compound cylinders are recommended in any service where the saving of fuel is an important consideration. In such cases, their greater first cost is fully justified, as they require 30 to 33 per cent less coal than any high-pressure form on the same work,
Fig. 277. Showing a sectional view of the Wortliington compound pump.
This cut shows the steam valves properly set.
On the larger sizes, a condensing apparatus is often added, thus securing the highest economical results.
Any of the ordinary forms of steam pumps can be fitted with compound cylinders.
It should be remembered that, as the compounds use less steam their boilers may be reduced materially in size and cost, compared with those required by the high-pressure form. This principle of expansion without condensation cannot be used with advantage where the steam pressure is below 75 Ibs.
35
546
HANDBOOK ON ENGINEERING.
Fig. 278. The Deane direct acting pump.
Fig. 279. Sectional view of the Deane pamp. DEANE DIRECT ACTING STEAM PUMP.
The operation of the steam valves* — In the Deane steam pump a rotary motion is not developed by means of which an
HANDBOOK ON ENGINEERING.
547
eccentric can be made to operate the valve. It is, therefore, necessary to reverse the piston by an impulse derived from itself at the end of each stroke. This cannot be effected in an ordinary single-valve engine, as the valve would be moved only to the cen- ter of its motion, and then the whole machine would stop. To overcome this difficulty, a small steam piston is provided to move the main valve of the engine. In the Deane steam pump, the lever 90, which is carried by the piston rod, comes in contact
Fig. 280. Showing the valves properly set.
with the tappet when near the end of its motion, and by means of the valve-rod 24, moves the small slide-valve which operates the supplemental piston 9. The supplemental piston, carrying with it the main valve, is thus driven over by steam and the engine reversed. If, however, the supplemental piston fails accidentally to be moved, or to be moved with sufficient prompt- ness by steam, the lug on the valve-rod engages with it and compels its motion by power derived from the main engine.
548
HANDBOOK ON ENGINEERINGS
Fig. 281. Sectional view of the Cameron pump.
The above is a sectional view of the steam end of a Cameron pump.
Explanation : A is the steam cylinder ; (7, the piston ; Z>, the piston rod ; L, the steam chest; F^ the chest piston or plunger, the right-hand end of which is shown in section ; 6r, the slide valve ; H, a starting bar connected with a handle on the outside ; II are reversing valves ; KK&YQ the bonnets over reversing valve chambers ; and E E are exhaust ports leading from the ends of steam chest direct to the main exhaust, and closed by the revers- ing valve //; Nis the body piece connecting the steam and water cylinder.
HANDBOOK ON ENGINEERING. 549
Operation of the Cameron pump : Steam is admitted to the steam chest, and through small holes in the ends of the plunger ; F fills the spaces at the ends and the ports E E as far as the reversing valves II; with the plunger F and slide valve G in position to the right (as shown in cut), steam would be admitted to the right-hand end of the steam cylinder A, and the piston C would be moved to the left. When it reaches the reversing valve / it opens it and exhausts the space at the left-hand end of the plunger .F, through the passage E; the expansion of steam at the right-hand end changes the position of the plunger F, and with it the slide valve 6r, and the motion of the piston C is instantly reversed. The operation repeated makes the motion continuous. In its movements, the plunger F acts as a slide valve to shut off the ports E E, and is cushioned on the confined steam between the ports and steam chest cover. The reversing valves I I are closed immediately the piston C leaves them , by pressure of steam on their outer ends, conveyed direct from the steam chest.
Operation* — Supposing the steam piston C moving from right to left: When it reaches the reversing valve / it opens it and exhausts the space on the left-hand end of the plunger F, through the passage E, which leads to the exhaust pipe ; the greater pres- sure inside of the steam chest changes the position of the plunger F and slide valve 6r, and the motion of the piston C is instantly reversed. The same operation repeated at each stroke makes the motion continuous. The reversing valves //are closed by a pres- sure of steam on their large ends, conveyed by an unseen passage direct from the steam chest. When a pump is first connected, remove the bonnets K K and valves 1 1 and blow steam through to remove any dirt, oil or gum that may be lodged in the steam ports. Take valve F, valve G and //out and wipe off with clean waste, and then oil and put back. Then see that the pack- ing is not too tight. When a Cameron pump has been run a long time, the plunger F becomes worn and leaks enough steam to
550
HANDBOOK ON ENGINEERING.
cause the valve F to become balanced. The effect of this is, the pump will remain on the end ; to- overcome this, take out plunger F, or piston, as it is called by some, and drill the little hole that you will find in the ends of same a little larger, say about one- fourth larger ; that will increase the pressure on both ends of plunger F; as soon as the piston comes in contact with valve 7 the steam is exhausted to exhaust pipe.
Fig. 282. Sectional view of the Knowles pump. THE KNOWLES DIRECT ACTING STEAH PUMP.
Explanation of steam valves, etc* — The Knowles, in fact, all first-class direct acting steam pumps, are absolutely free from what is termed a " dead center," when in first-class order.
This feature in the Knowles pump is secured by a very simple and ingenious mechanical arrangement, i. e., by the use of an auxiliary piston, which works in the steam chest and drives the main valve. This auxiliary or tc chest piston," as it is called, is driven backward and forward by the pressure of steam, carrying
HANDBOOK ON ENGINEERING.
551
with it the main valve, which valve, in turn, gives steam to the main steam piston that operates the pump. This main valve is a plain slide valve of the B form, working on a flat seat. The chest piston is slightly rotated by the valve motion ; this rotative move- ment places the small steam ports, I), E, F (which are located in
Fig. 283. The Kuowles direct acting steam pump.
the under side of the said chest pision) , in proper contact with corresponding ports A B cut in the steam chest No. 31. The steam entering through the port at one end and filling the space between the chest piston and the head, drives the said piston to the end of its stroke and, as before mentioned, carries the main slide valve with it. When the chest piston has traveled a certain distance, a port on the opposite end is uncovered and steam there enters, stopping its further travel by giving it the necessary
552
HANDBOOK ON ENGINEERING.
cushion. In other words, when the rotative motion is given to the auxiliary or valve -driving piston by the mechanism outside, it opens the port to steam admission on one end, and at the same time opens the port on the other end to the exhaust.
Fig. 284. Showing the valves properly set.
Operation of the Knowles pump is as follows : The piston rod, \vith the tappet arm, moves backward and forward from the impulse given by the steam piston. At the lower part of this tappet arm is attached a stud or bolt, on which there is a friction roller. This roller coming in contact with the " rocker bar" at the end of each stroke, operates the latter. The motion given the 44 rocker bar " is transmitted to the valve rod by means of the connection between, causing the valve rod to partially rotate. This action, as mentioned above, operates the chest piston, which carries with it the main slide valve, the said valve giving steam to the main piston. The operation of the pump is complete and
HANDBOOK ON ENGINEERING. 553
continuous. The upper end of the tappet arm does not come in contact with the tappets on the valve rod, unless the steam pres- sure from any cause, should fail to move the chest piston, in which case the tappet arm moves it mechanically.
ADJUSTMENT OF THE KNOWLES PUMP.
1. Should the pump run longer stroke one way than the other, simply lengthen or shorten the rocker connection (part 25) so that rocker bar (part 23) will touch rocker roller (20) equally distant from center (22).
2. Should a pump hesitate in making its return stroke, it is be- cause rocker roller (20) is too low and does not come in contact with the rocker bar (23) soon enough. To raise it, take out rocker roller stud (20 A), give the set screw in this stud a suffi- cient downward turn, and the stud with its roller may at once be raised to proper height.
3. Should valve rod (17) ever have a tendency to tremble, slightly tighten up the valve rod stuffing box nut (28) . When the valve motion is properly adjusted, tappet tip (1 6) should not quite touch collar (15) and clamp (27). Rocker roller (20), coming in contact with rocker bar (23) will reverse the stroke.
Operation and construction of the
HOOKER DIRECT ACTING STEAM=PUMP.
The parts being in position, as shown, the steam on being ad- mitted to the center of the valve chamber, brings its pressure to bear on the main and supplemental flat slide valve 4 and 7, and also within the recess in the center of the supplemental piston 6. The recess incloses the main valve 4, so that this valve will move with the supplemental piston whenever the steam is supplied to
554
HANDBOOK ON ENGINEERING.
and exhausted from each end of this piston. The live steam passes through the left-hand ports A l Bl, driving the main piston 2 to the right, and the exhaust passes out through the right-hand ports A and C under the cavity in the main valve 4 to the atmos- phere. As the main piston nears the right hand port, the valve lever 15, which is attached to the piston rod 3, brings the dog 17, in plate 16, in contact with the valve arm 15, and moves the sup- plemental valve 7 to the right, thus supplying live steam to the
Fig. 285. Plan and sectional views of Hooker pnmp.
right of the supplemental piston 6', and exhausting from the left through the ports e e. As the supplemental piston incloses the main valve, this valve is carried with it to the left. Steam now enters the right-hand ports A B and is exhausted from the left- hand main port A. The engine commences its return stroke and the operation just described becomes continuous. As the main piston (2) closes the main port (A) to the right, it is arrested on compressed exhaust steam. The main valve 4 having closed the auxiliary ports (_B) leading to that end of the main cylinder, the
HANDBOOK ON ENGINEERING.
555
Fig. 286. Showing the steam valves properly set.
etearn being supplied through both the main and auxiliary ports, but released through the main ports only.
BLAKE STEAM PUHP.
Description of the Blake steam pump. — The Blake steam pump is absolutely positive in its action ; that is to say, the operation at the slowest speed under any pressure, is perfectly continuous, and the pump is never liable to stop as the main valve passes its center, if the pump is in good order. An ingenious and simple arrangement is used in the Blake pump to overcome the '•' dead center," as will be seen from the engraving, Fig. 288.
Operation of the Blake steam pump. —The main or pump driving piston A could not be made to work slowly were the valve to derive its movement soJely from this piston ; for
556
HANDBOOK ON ENGINEERING.
when this valve had reached the center of its stroke, in which position the ports leading to the main cylinder would be closed,
Fig. 287. The Blake steam pump.
no steam could enter the cylinder to act on said piston, con- sequently, the latter would come to rest, since its momentum would be insufficient to keep it in motion, and the main valve would remain in its central position or tc dead cen- ter." To shift this valve from its central position and admit steam in front of the main piston (whereby the motion of the piston is reversed and its action continued), some agent independent of the main piston must be used. In the Blake pump, this independent agent is the supplemental or valve-driving piston B. The main valve, which controls the admission of steam to. and the escape of steam from, the main cylinder, is divided into two parts, one of which, (7, slides upon a seat on the main cylinder, and, at the same time, affords a seat for the other part,
HANDBOOK ON ENGINEERING .
557
Z>, which slides upon the upper face of C. As shown in the en- graving, D is at the left-hand end of its stroke, and C at the opposite, or right-hand end of its stroke. Steam from the steam- chest J is, therefore, entering the right-hand end of the main cylinder through the ports E and H, and the exhaust is escap- ing through the ports Hl and H71, K and M, which causes the
Fig. 288. Sectional views of steam cylinder, valves, etc., of the Blake steam pump.
main piston A to move from right to left. When this piston has nearly reached the left-hand end of its cylinder the valve motion
558
HANDBOOK ON ENGINEERING.
(not shown) moves the valve-rod P, and this causes (7, together with its supplemental valve R and S Sl (which form, with (7, one casting) to be moved from right to left. This movement causes steam to be admitted to the left-hand end of the supplemental cylinder, whereby its piston B will be forced toward the right, carrying D with it to the opposite or right-hand end of its stroke ; for the movement of S closes N (the steam port leading to the
Fig. 289. Showing the valves properly set,
right-hand end), and the movement of S1 opens N1 (the port leading to the opposite, or left-hand end). At the same time the movement of 0 opens the right-hand end of the cylinder to the exhaust through the exhaust ports X and Z. The ports C and D now have positions opposite to those shown in the engrav- ings, and steam is, therefore, entering the main cylinder through the ports El and Hl, and escaping through the ports H, E, K and Jf, which will cause the main piston A to move in the op-
HANDBOOK ON ENGINEERING. 559
posite direction, or from left to right, and operations similar to those already described will follow, when the piston approachee the right-hand end of its cylinder. By this simple arrangement the pump is rendered positive in its action ; that is, it will in- stantly start and continue working the moment steam is admitted to the steam chest. The main piston A cannot strike the head of the cylinder, for the main valve has a lead ; or, in other words, steam is always admitted in front of said piston just before it reaches either end of its cylinder, even should the supplemental piston B be tardy in its action and remain with D at that end, toward which the piston A is moving ; for C would be moved far enough to open the steam port leading to the main cylinder, since the possible travel of C is greater than that of D. The supple- mental piston B cannot strike the heads of its cylinders, for in its alternate passage beyond the exhaust ports X and X, it cushions on the vapor intrapped in the ends of this cylinder.
MISCELLANEOUS PUHP QUESTIONS.
Q. What is a pump? A. It is hard to get a definition that will cover the whole ground. A pump may be said to be a mechanical contrivance for raising or transferring fluids ; and as a general thing consists of a moving piece working in a cylinder or other cavity ; the device having valves for admitting or retaining the fluids.
Q. What two classes of operations are included in the term "raising" fluids? A. They may be raised by drafting or suc- tion, from their level to that of the pump ; they may be raised from the level of the pump to a higher level.
Q. Do pumps always "raise" by either method, from one level to a higher one, the liquid which they transfer? A. No ; in many cases the liquid flows by gravity to the pump ; and in some it is delivered at a lower level than that at which it is received.
560 HANDBOOK ON ENGINEERING 0
Q. Where a pump is not used for raising a liquid to a higher level, for what is it generally used ? A. To increase or decrease its pressure.
Q. What classes of Liquids are handled by pumps ? A. Air, ammonia, lighting gas, oxygen, etc.
Q. Name some liquids which are handled by pumps? A. Water, brine, beer, tan liquor, molasses, acids and oils.
Q. Where it is not specified whether a pump is for gas or for liquid, which is generally understood? A. Liquid.
Q. What gas is most frequently pumped? A. Air.
Q. What liquid is generally understood if none other is speci- fied for a pump? A. Water.
Q. Can pumps handle hot and cold liquids? A. Yes; though cold are easier handled than hot.
Q. What is the difference between a fluid and a liquid? A. Every liquid is a fluid ; every fluid is not a liquid. Air is a fluid ; water is both a fluid and a liquid. Every liquid can be poured from one vessel to another.
SUCTION.
Q. What causes the water to rise in a pump by so-called suction? A. The unbalanced pressure of the air upon the surface of the liquid below the pump, forces the water up into the suction pipe when the piston is withdrawn from the liquid.
Q. How much is the pressure of the atmosphere? A. At the sea level about 14.71bs. per square inch, or 2116.8 Ibs. per square foot.
Q. In what direction is this pressure exerted? A. In every direction equally.
Q. What tends to prevent the water from being lifted? A. The force of gravity, which is the result of the attraction of the earth.
HANDBOOK ON ENGINEERING. 56'1
Q. In what direction does the force of gravity act? A. In radial lines towards the center of the earth.
Q. With what force does this gravity act? A. That- depends upon the substance upon which it is acting.
Q. Why do you refer to the level of the sea in speaking of the pressure of the air and the weight of water? A. Because the air pressure becomes less as, in rising above the sea level, we recede from the center of the earth, and the weight of a given quantity of water or any other substance becomes less than it is at the level of the sea, as we approach to or recede from the center of the earth.
Q. How is it that the weight of any substance becomes less if you go either above or below the sea level? A. The farther you go from the earth, the less its attraction and the less a given body will weigh upon a spring balance. The farther down into the earth you go, the nearer you get to the center of the earth, at which, there being attraction upon all sides, any body would weigh nothing. Going from the surface of the earth towards its center, then, a body weighs less and less upon a spring balance.
Q. Why do you specify a spring balance? A. Because in weighing by counterpoise, both the body to be weighed and the counterpoise by which it is weighed, would change their weights in the same proportion, as the position with regard to the center of the earth was changed.
Q. What are the causes which principally prevent pumps from lifting up to the normal maximum? A. Friction ; leakage of air into the suction, chokes in the suction pipe.
Q. Can a liquid be " drafted" without the expenditure of work ? A. No ; in drafting a liquid to the full height to which it can be drafted, at least as much power must be expended as would lift the same weight of liquid that height by any mechan- ical means ; only the amounts of friction being different.
Q. Then what advantage is there in having a pump draft its
36
562 HANDBOOK ON ENGINEERING.
water to the full possible height, over having it force the watei the full height? A. Convenience in having the pump higher up.
Q. Can a pump throw water higher or farther, with a given expenditure of power, where it flows in, than where it must draft its water? A. Yes; on the same principle that it can throw farther or force harder when the water is forced to its suction side than where it merely flows in.
Q. What is the use of the suction chamber? A. To enable the pump barrel to fill where the speed is high ; to prevent pounding, when the pump reverses.
Q. Upon what does the lifting capacity of a pump depend? A. When the pump is in good order its lifting capacity depends mainly upon the proportion of clearance in the cylinder and valve chamber to the displacement of the piston and plunger.
Q. Which will lift farther, an ordinary piston pattern pump or a plunger pump? And why? A. Other things being as nearly equal as they can be made between these two pumps, the piston pump will lift the farther of the two, because the plunger pump has the most clearance.
Q. What is the advantage of the suction chamber? A. To assist the pump in drafting, especially at high speed.
Q. What is the advantage of the air chamber? A. To make the stream steady.
Q. What difficulty is sometimes met with in using an air chamber? A. Where the pressure is very great sometimes the air is absorbed by the water, and thus the cushion is detroyed.
FORCING.
Q. What will be the volume of the air in the air chamber of a force pump, when the pump is forcing against a head of 67.6 feet? A. It will be reduced to half its ordinary volume, because it will be at the pressure of two atmospheres.
HANDBOOK ON ENGINEERING.
563
Fig. 290. Pump cylinder fitted with liner.
The above cut shows a pump with a removable cylinder or liner, and is packed with fibrous packing set out by adjustable set screws and nuts. This style of a pump is the best for small water-works or elevators, or where a pump is used where the water is muddy or sandy.
To find the horse power necessary to elevate water to a given height: Multiply the total weight of the water in pounds by the height in feet and divide the product by 33,000 (an allow- ance of 25 per cent should be added for water friction, and a further allowance of 25 per cent for loss in steam cylinder.)
The heights to which pumps will force water when running at
564 HANDBOOK ON ENGINEERING.
100 feet piston speed per minute, and the suction and discharge pipes being of moderate length, will be found by dividing the area of the steam piston by the area of the water piston, and multi- plying the quotient by the steam pressure. Deduct 40 per cent for friction and divide the remainder by .434.
Example* — To what height will an 8-inch steam piston, with a 5-inch water piston, force water, the steam pressure being 80 Ibs. by gauge? Ans. 283 ft. nearly.
Operation* — Area of steam piston = 50. 26 sq0 ins. " " water " =19.63 " "
Then, ^^ = 2.56. And 2.56 X 80 = 204.80 Ibs. 19.63
Then, 204.80 less 40% = 122.88 Ibs. And, 122f8 = 283 + feet.
An allowance must be made where long pipes are used.
The normal speed of pumps is taken at 100 piston feet per Jninute, which speed can be considerably increased if desired.
For feeding* boilers, a speed of 25 to 50 lineal feet per minute is most desirable.
A gallon of water, U. S. Standard, weighs 8^ Ibs. and contains 231 cubic inches.
A cubic foot of water weighs 62.425 Ibs. and contains 1,728 cubic inches, or 7J gallons.
Doubling the diameter of a pipe increases its capacity four times.
Friction of liquids in pipes increases as the square of the velocity.
To find the area of a piston, square the diameter and multiply by ,7854.
HANDBOOK ON ENGINEERING. 565
Boilers require, for each nominal horse-power, about one cubic foot of feed water per hour.
In calculating* horse power of tubular or flue boilers, consider 15 square feet of heating surface equivalent to one nominal horse- power.
To find the pressure in pounds per square inch of a column of water, multiply the height of a column in feet by .434. Approximately, we say that every foot of elevation is equal to one-half Ib. pressure per square inch ; this allows for ordinary friction.
The area of the steam piston, multiplied by the steam pressure, gives the total amount of pressure that can be exerted. The area of the water piston, multiplied by the pressure of water per square inch, gives the resistance. A margin must be made between the power and the resistance to move the pistons at the required speed — say from 20 to 40 per cent, according to speed and other conditions.
To find the capacity of a cylinder in gallons : Multiplying the area in inches by the length of stroke in inches will give the total number of cubic inches ; divide this amount by 231 (which is the cubical contents of a gallon of water) and quotient is the capacity in gallons.
To find quantity of water elevated in one minute running at 100 feet of piston speed per minute : Square the diameter of water cylinder in inches and multiply by 4.
Example: Capacity of a five-inch cylinder is desired. The square of the diameter (5 inches) is 25, which, multiplied by 4, gives 100, which is gallons per minute, approximately.
Q. What is the reason that a steam pump of the horizontal double acting type should throw an intermitting stream under pressure, like the stream from milking .a cow, only not quite so bad as that? Have tried valves of different sizes, with different amount of rise, springs or valves of different tension, different
066 HANDBOOK ON ENGINEERING.
. kinds of packing in water piston, and different sized water ports
or passages, without any apparent difference. A. Steam pumps of the horizontal double-acting type are not alone in throwing an Intermitting stream. The same thing shows up in vertical single- acting pumps ; but all horizontal double-acting pumps do not so behave. The steam fire engine shows that no type of pump is exempt from ;t squirting."
Q. How may this squirting be lessened? A. By increasing the suction valve area ; by giving more suction chamber and more air chamber. *********
Q. What is a sinking pump ? A. One which can be raised and lowered conveniently, for pumping out drowned mines, etc.
Q , Into what main general classes may reciprocating cylinder pnmps be divided? A. Into single acting and double acting.
Q. What is a single acting reciprocating pump ? A. One in which each reciprocation or single stroke in one direction causes one influx of fluid, and each reciprocation or single stroke in the opposite direction causes one discharge of fluid. In other words, the pump, as regards its action, is single ended.
Q. What is a double acting reciprocating pump ? A. One in which each end acts alternately for suction and discharge. Re- ciprocation of the piston in one direction causes an influx of fluid into one end of the pump from the source, and a discharge of fluid at the opposite end ; on the return stroke the former suction end becomes the discharge end. In other words, the pump is double ended in its action ; or is " double-acting."
Q. What is the special advantage of having double-acting pump cylinders? A. The column of water is kept in motion more constantly, and hence there is less jar ; smaller pipes may
be u«ed.
***********
Q. How may those pumps which are driven by steam against a
HANDBOOK ON ENGINEERING. 567
steam piston be divided? A. Into those which have a fly wheel and those which have no fly wheel.
Q. Into what classes may those pumps which are driven by steam, without a flywheel, be divided? A. Into direct acting and duplex.
Q. What is the advantage of a fly wheel steam pump? A. Steadiness of action ; the capability of using the steam expan- sively.
Q. What are the disadvantages of fly wheel pumps? A. Great weight ; inability to run them very slowly without gearing down from the fly wheel shaft, as the wheel must run comparatively rapidly.
Q. What is a direct-acting steam pump? A. One in which there is no rotary motion, the piston being reversed by an impulse derived from itself at or near the end of each stroke. There is but one steam cylinder for one water cylinder ; the valve motion of the steam cylinder being controlled by the action of the steam in that cylinder.
HOW TO SET THE STEAfl VALVES ON A DUPLEX PUMP.
The steam valves on duplex pumps generally have no outside lap, consequently, in their central position, they just cover the steam ports leading to the opposite ends of cylinder.
By lost motion is meant, the distance a valve-rod travels before moving the valve; if the steam-chest cover is off the amount of lost motion is shown by the distance the valve can be moved back and forth before coming in contact with the valve- rod nut. The object of lost motion is to allow one pump to almost complete its stroke before moving the valve of its fellow engine. As the steam piston is nearing the end of its stroke, it moves the valve of its fellow engine, admitting steam and start- ing its fellow engine as it lays down its own work ; in other words,
568
HANDBOOK ON ENGINEERING.
the other picks it up. The amount of lost motion required is enough to allow each piston to complete its stroke ; in other words, if there was no lost motion, as the pistons would pass the center of their travel, they would move the valve of theii fellow engine, and the result would be a very short stroke.
Fig. 291. Showing the steam valves properly set.
To set the steam valves, move the steam piston towards the steam cylinder head until it comes in contact with the head ; mark with a scribe on the piston-rod at the face of the stuffing-box follower on steam end ; then move the piston to its contact stroke on the opposite end and make another mark on the piston-rod, exactly half way between the face of the stuffing-box follower on the steam end, and the first mark. Then move the piston back until the middle mark is at the face of piston-rod stuffing-box follower on the pump end. This operation brings the piston exactly in the middle of the stroke. Then take off the steam
HANDBOOK ON ENGINEERING. 569
chest cover, place the slide-valve in the center, exactly over the steam ports. Place the slide-valve nut in exact center between the jaws of the slide-valve, screw the valve-rod through the nut until the eye on the valve-rod head comes in line with the eye of the valve-rod link ; slip the valve-rod head pin through head and the valve is set. Repeat the same operation on the other side of the pump. Where a pump is fitted with four hexagon valve-rod nuts, two either end of the slide-valve, instead of one nut in the center of the valve, set and lock these hexagon nuts at equal dis- tances from the outer end of the slide-valve jaws, allowing a little lost motion, varying from J" on high-pressure pumps, to, say, i" on low service pumps, on each side of valve ; if the steam piston hits the head, take up some of the lost motion ; if the steam piston should not make a full stroke, give more lost motion.
PROPER MANNER OF ARRANGING PIPE CONNECTIONS.
For trie purpose of showing good arrangement, the following cut is presented, Fig. 292.
On long lifts it is necessary to provide the suction pipe S with a foot-valve F. By the use of a foot-valve, the pipe and cylinders are constantly kept charged with water, allowing the pump to start without having to free itself and the suction pipe of air. In case of a long lift, the vacuum chamber V is also essential. This may be readily constructed by using a tee in place of the elbow E, extending the suction pipe and placing a cap upon the top. In order to keep the water back when the pump is being examined or repaired, a gate valve should be placed in the delivery pipe. It sometimes happens that, either purposely or through a leak in the foot-valve, the suction chamber becomes empty. For the purpose of charging the suction pipe and cylin- der a " charging pipe " P is placed outside the check valve, connecting the delivery pipe D with the suction. In order that
570
HANDBOOK ON ENGINEERING.
the pump, in starting, may free itself of air, a check valve Cand a " starting pipe" A should be provided. This pipe may be
Fig. 292. Proper arrangement of pipe connections.
led to any convenient place of discharge. After the pump has started, the valve in the starting pipe should be closed gradually. Faulty connections are generally the cause of the improper action
HANDBOOK ON ENGINEERING. 571
of a pump. Great care should, therefore, be taken to have everything right before starting. A very small leak in the suc- tion will cause a pump to work badly.
Q. What is the peculiarity of the duplex type? A. There are two steam cylinders and two water cylinders ; the piston of one of these cylinders works the valve of the other cylinder, and vice versa. Neither half can work alone. This name is entirely arbitrary.
Q. What would you call a pumping machine in which there are two steam cylinders, each operating a water cylinder in line with it ; each half being a perfect pumping machine independent of the other side? A. A " double " pump.
Q. Can a direct acting steam pump use steam expansively? A. Not to any extent ; in fact, there would be danger of sticking upon the centers in most cases, if there was lap and expansion.
Q. What is the reason that a single cylinder engine cannot well reverse itself without a fly wheel, by means of the ordinary single D valve? A. Because when the valve was at mid-travel, both ports of the valve seat would be closed by the valva faces, and neither exhaust nor admission take place.
Q. What means are employed in a direct acting steam pump to move the valve ? A. A small supplementary piston is used ; this supplementary piston being actuated by the main piston in any one of several different ways.
Q. What are the principal ways of working the supplementary piston from the main piston? A. (1) The main piston strikes the tappet of a small valve, which opens an exhaust passage in one end of the cylinder, containing a supplementary piston, and having live steam pressing upon both ends of the supplementary piston ; (2) by the main piston striking a rod passing through the cylinder head, and moving a lever, which controls the motion of the part of the main valve to which is attached the valves which moves the supplementary piston ; (3) the main piston rod carries a tappet arm, which twists the stem of the supplementary piston,
572 HANDBOOK ON ENGINEERING.
thus uncovering ports which cause its motion ; (4) a projection upon the main piston rod engages the stem and operates the valve which moves the supplementary piston, but if that valve should not, by means of its steam passages, cause quick enough or sure enough motion of the supplementary piston, a lug upon this stem moves the supplementary piston.
Q. In the first of these four classes, what is the principal element in the valve motion? A. A difference in area between the eduction port of the supplemental piston and its induction port
Q. What is the principal feature in the second class? A. A regular slide valve letting steam upon alternate ends of the sup- plemental piston.
Q. In the third class, what is the main feature? A. A twist- ing motion in the supplemental piston.
Q. In the fourth class, what is the principal feature? A. Movement of the supplemental piston by steam controlled by a slide valve, and by the mechanical action of the slide valve itself if its steam distribution is defective.
Q. What are the objections to most pumps of the direct actiig type? A. The unbalanced condition of the auxiliary pistons in the exhaust side, causing a loss of steam when the parts are worn, the choking up of the small ports for the auxiliary pistons, by the gumming and caking of the oil therein.
Q. Can the ordinary direct acting steam pump use steam expansively? A. No.
Q. How may this be done? A. Ity compounding.
Q. What is to be taken into consideration in the use of com- pound steam pumps? A. That they are designed for a certain range of pressure — say from 80 to 120 pounds boiler pressure, and will do their best work between these pressures.
Q. Have all direct acting steam pumps intermittent valve motion ? A. No ; there are some which have continuous valve motion.
HANDBOOK ON ENGINEERING. 573
Q. In most direct-acting steam pumps, are the auxiliary piston heads made together or in separate pieces ? A. Together.
Q. They are in contact with the steam in the chest? A. Yes.
Q. What should be said about the location of a pump? A. It should be as near the source of supply as is convenient.
Q. What may be said about convenience in repairs? A. The pump should have room left upon all sides ; and upon both ends equal to its length, for the removal of the piston rods in case of repairs.
Q. If the floor is not strong enough, how may a good founda- tion be made ? A. By digging two or three feet into the ground and building up the proper height with stone or brick laid in strong cement, with a cap stone.
Q. What may be said about suction pipes? A. They must be as large as possible ; the longer they are the greater in diameter they should be ; they should be as straight as possible, and as free from bends and valves ; they must be air-tight ; they must not bo allowed to get obstructed by foreign substances.
Q. W hat may be said about the area of strainer holes? A. They should have an aggregate area about five times that of the suction pipe.
Q. Where are foot valves necessary ? A. Upon long suctions or high lifts.
Q. Should two pumps take their suction from one pipe ? A. It should be avoided, unless the pipe is very large ; and in case both suctions should be arranged so that one of the pumps should not have to draft at right-angles to the flow of water going to the other pump.
Q. What arrangement should be made where it is necessary to have two pumps draft from one suction? A. There should be a Y connection.
Q. What is a good way to reduce the friction in suction pipes where there are many bends ? A. To use bends of wrought-
574 HANDBOOK ON ENGINEERING.
iron pipe of as long a radius as possible, instead of oast-iron elbows.
Q. What may be said about the lower end of the suction pipe? A. It should generally have a strainer ; and if the lift is over 12 to 15 feet, should have a foot valve.
Q. What is a good thing to do with the discharge pipe near the pump? A. To put a valve in it near the pump, to keep the water in the pipe when the water end is to be opened for inspection or repairs.
Q. What provision should be made for priming the pump? A. There should be a pipe with a stop valve in it connected from the discharge pipe beyond this check valve, or from some other source of supply, to the suction pipe, for the purpose of priming the pump.
Q. When the pump is in position for piping, what care should be taken? A. That the pipes are of proper length, so as not to bring any undue strain upon them in connecting them to the pump as in that case they will be liable to give trouble by breaking or working the joints loose and leaking.
Q. Does any pipe have an effective diameter as great as its nominal diameter? A. No; because the sides retard the flow of the liquid ; there is a neutral film of liquid which practically does not move.
Q. Upon what does the thickness of this film of liquid depend? A. Upon the viscosity (commonly miscalled the " thickness ") of the liquid ; upon the roughness, material and diameter of the pipe ; the pressure, etc.
Q. When long lines of pipe are used, should the diameter of the pipe be the same all the way along, or should there by sections be decreasing diameter, as the distance from the pump increases ? A. Most emphatically, the pipe diameter should remain constant clear out to the end.
HANDBOOK .ON ENGINEERING. 575
TAKING CARE OF A PUMP.
Q. What can be said about taking care of a pump? A. In places where an inferior grade of labor is employed, oil and dirt are sometimes found covering the steam chest and pump to the depth of an inch in thickness ; stuffing boxes are allowed to go leaky and get loose ; the valve motion is never looked after ; lost motion is never taken up, and the pump will be let run in a slip- shod way for months, until some accident occurs. This will sometimes exist in places where the engine is well taken care of.
Q. Should not as good care be taken of a steam pump as of an engine? A. Yes. It is a steam engine, and the fact that it has generally but little adjustability, should not render it liable to lack of care.
Q. What is a very common thing for pump runners to do when anything happens ? A. To condemn the pump at once without finding out the cause of the trouble.
Q. What is one reason of this? A. The man who understands an ordinary engine, will often become quite perplexed when he examines the steam end of a direct acting steam pump, because he does not comprehend the principal feature of its construc- tion— that all direct acting steam pumps which have no fly wheels and cranks, must generally have an auxiliary piston in order to carry them over the " dead center." A direct acting steam pump is really a double engine ; a plain, flat slide valve admitting steam to a small piston, which in turn operates the main valve, which gives steam by the usual arrangement to the main piston.
Q. What would save firemen and engineers much trouble with steam pumps? A. If they would take the trouble to examine their pumps carefully, and find out the way their valves were arranged and actuated.
Q. Upon what does the successful performance of a pump
576 HANDBOOK ON ENGINEERING.
depend, in great measure? A. Upon its proper selection from among the many patterns differing from each other in size, pro- portion and general arrangement.
Q. What may be said about the selection of pumps? A. Pumps are often selected improperly for their work. As an illus- tration, a man who wishes to use a circulating pump for a surface condenser, where the water pressure upon the pump cylinder will never exceed 5 to 10 pounds, will buy a pump intended for boiler feed work, and having its steam cylinder about three times the area of its pump cylinder.
Q. What will be the result in such a case? A. There will be little or no pressure in the steam cylinder when working on the condenser ; and while there is pressure sufficient to move the main piston, there is not enough to operate the auxiliary piston with positiveness.
Q. In ordering a pump, or in asking estimates, what informa- tion should be given? A. In ordering a pump, it is to the inter- est of the purchaser to fully inform the maker or seller on the following questions : 1st. For what purpose is the pump to be used? What is the average steam pressure? 2d. What is the liquid to be pumped ; and is it hot or cold, clear or gritty, fresh, salt, alkaline or acidulous? 3d. What is the maximum quantity to be pumped per minute or hour? 4th. To what height is the liquid to be lifted by suction, and what is the length of the suction pipe, and the number of elbows or bends? 5th. To what height is the liquid to be pumped, and what is the length of discharge pipe?
Q. How can an engineer familiarize himself with the direction of the auxiliary steam and exhaust passages: A. By means of a piece of wire.
Q. What is the special thing to look after in duplex pumps? A. That all packings are adjusted uniformly on both sides.
Q. What would be the result of having the packings different
HANDBOOK ON ENGINEERING. 577
upon the two sides of a duplex pump? A. The machinery would run unsteadily.
Q. If a pump works badly, what should be about the first thing to look at? A. The connections.
Q. When a pump is first connected, what should be done? A. It should be blown through to remove dirt ; if it be of the class which will permit of removing the bonnets and blowing through, that should be done.
Q. What pump piston speed is recommended for continuous boiler feeding service? A. About 50 feet per minute.
Q. What may be said about the care and use of steam pumps of all kinds? A. It is important that the pump be properly and thoroughly lubricated ; that all stuffing-box, piston and plunger packings be nicely adjusted ; not so tight as to cause undue fric- tion ; nor so slack as to leak badly.
Q. In which end of a steam pumping machine is there most likely to be trouble? A. In the water end.
Q. If a pump slams and hammers in its water end, is it neces- sarily defective in its water cylinder? A. No; it may be that there is no suction chamber, or not enough ; or sometimes it slams because the suction pipe is not large enough.
Q. What are very common defects in cheap grades of pumps? A. Too little valve area in the pump end ; too great lift for the valves.
Q. What are the principal causes of pumps refusing to lift water from the source of supply? A. Among these may be mentioned leaky suction pipes, worn out pistons, plungers, pack- ings or water valves ; rotten gaskets on joints in piping or pump ; and sometimes a failure to properly prime the pump as well as the suction pipe.
Q. What is one great cause of a pump refusing to lift water when first started? A. It often happens that a pump refuses to lift water while the full pressure against which it is expected to
37
578 HANDBOOK ON ENGINEERING.
work is resting upon the discharge valves, for the reason that the air within the pump chamber is not dislodged, but only compressed, by the motion of the plunger. It is well, therefore, to arrange for running without pressure until the air is expelled and water follows ; this is done by placing a valve* in the delivery pipe and providing a waste delivery, to be closed after the pump has caught water.
Q. Sometimes when starting, the water may not come for a long time ; what is the best thing to do in this case? A. First, open the little air cock, which is generally located in the top of the pump, between the discharge valves and the air chamber, to let off any accumulation of air, which may there be confined under pressure. Very often, by relieving the pump of this air pressure, it will pick up its water by suction and operate promptly.
Q. What precaution must be taken in priming the pump? A. The air cock, which should be provided at the top of the pump, should be opened to allow the escape of the air from the suction pipe and from the pump, and then the valve in the priming pipe should be opened. The pump should then be started slowly, as it aids in more completely filling the pump cylinders, which otherwise, might not occur and the pump might fail to lift water.
Q. Is there any advantage in having air in the suction? A. Sometimes a small amount of air let into the suction will cause less jarring when the duty is very heavy.
Q. What may be said about pumping hot water? A. Where the hot water is very hot, it should gravitate to the pump, instead of an attempt being made to draft it.
Q. In the plunger pumps, 'what is about the only wearing part of the water end? A. The packing of the plunger stuffing-boxes.
Q. How can a pump be prevented from freezing? A. By having draining cocks and opening them when the pump is idle.
HANDBOOK ON ENGINEERING. 579
Q. What may be said about leather piston packing for water cylinders? A. For cold water, or sandy, gritty water, the leather packing has many points to commend it ; it makes a tight piston, and one that is the least destructive to pump cylinders.
Q. What is the best way to handle the square packing mostly employed, which is composed of alternate layers of cotton and rubber? A. Cut the lengths a trifle short, then there will be room for the packing to swell and not cause too much friction. We have known pistons where this precaution has not been taken to be fastened so securely in the cylinder by the swelling of the dry packing, that full steam pressure could not move tliem.
Q. What is the remedy in such a case? A. Remove the follower, take out the different layers of packing and shorten their lengths.
Q. What is the reason that some soft waters corrode pipes so often? A. Because they contain a large proportion of oxygen.
Q. Will a pump with a 6" water cylinder and a 6" steam cylin- der force water into a boiler, the discharge from water cylinder being 4" diameter; boiler pressure, 80 Ibs.? A. A pump with a 6" water cylinder and 6" steam cylinder will not force water into the boiler which supplies it, no matter what the steam pressure, nor what the size of discharge pipe. It will not move. The pressures would be equalized and there would be nothing to over- come friction of steam and water in pipes, and cylinder. The foregoing case supposes that the water is to be lifted to the pump ; or at least that there shall be no head ; also, that there shall be no fall from pump to boiler. If there were sufficient head or fall to overcome all the various frictions, and no lift, the pump would apparently work ; but really, the water piston would be dragging the steam piston along.
Q. How may acids be pumped? A. By what is known as blowing up ; that is, by employing a pump to put pressure upon
580 HANDBOOK ON ENGINEERING.
the acid in a closed vessel, thereby forcing it through a pipe placed in the bottom of the vessel.
Q. In case any wearing part of a pump gets to cutting, what should be done? A. If it is not practicable to stop the pump nor to reduce its speed, the part which is getting damaged should be given very liberal oiling.
Q. What is the best oil for this purpose? A. That depends on the nature of the cutting surfaces, and on the pressure therein ; the mineral oils are generally more cooling than others, although they have less body to resist squeezing.
% CALCULATING THE BOILER FOR A STEAM PUMP.
The amount of work which a bgiler has to do is very easy of determination. Given the largest number of gallons which a pump will be required to pump per minute, and the height in feet from the surface of the well from which the water is drawn, to the point'of discharge, you can easily tell by multiplying by 8| — the weight in pounds of one gallon — the number of foot pounds of power consumed per minute in lifting the water, adding a cer- tain percentage for friction of the machine and of water in the pipe, we have the total number of foot pounds consumed per minute, and this divided by 33,000 will be the horse power consumed.
The allowance for friction will vary with the style, size and condition of the pump, the size of the pipe, and, above all, the manner in which the pipe is connected up, the number of right angle turns, etc.
This may be arrived at in another way. A column of water 2.3 feet in height exerts a pressure of one pound. Allowing the .3 for friction, we can, by dividing the total left in feet by two, get at the pressure per square inch, which is being exerted against the water piston or plunger, and multiplying by the number of
HANDBOOK ON ENGINEERING. 581
square inches in that piston gives the total pressure against which the pump is working. This multiplied by the piston speed in feet minutes, and divided by 33,000, will give the lift in horse power. In this case, as in the other, the lift must be calculated from the surface of the supply, and not from the pump, when the pump is lifting its supply. If the water flows to the pump it must be calculated from the height of the water cylinder. An allowance of, say, 25 per cent, -should be made above the horse power thus shown, in order to provide for contingencies, and to be on the safe side.
In selecting a boiler to do this work, it must be borne in mind that a boiler which is sold for a certain horse power, is supposed to be able to furnish that power in connection with a good steam engine , and they are not apt to be overrated . Now , the steam pump as usually built, does not approach in economy the ordinary steam engine, and, therefore, a boiler which will develop, twenty-five horse power in connection with a good engine would be too small for a pump which was required to do the same amount of work. The evaporation of 30 pounds of water per hour from feed at 100 degrees Fahr. into steam of 70 Ibs. pressure, has been adopted by several authorities as a horse power. Any good automatic cut-off will run on this amount of water, and if an estimate can be made of the comparative performance of the pump under consideration, a close approximation to the desired size of boiler can be made.
THE WORTHINGTON WATER METER.
The counter registers cubic feet ; one foot being 7T%8^ gallons, United States standard. It is read in the same way as registers of gas meters. The following example and directions may be of use to those unacquainted with the method: If a pointer is between two figures, the smaller one must invariably be taken. Suppose the pointers of the dials to stand as in the engraving.
582
HANDBOOK ON ENGINEERING.
The reading is 6,874 cubic feet. From the dial marked ten wa get the figure 4 ; from the next, marked hundred, the figure 7 ; from the next, marked thousand, the figure 8 ; from the next,
Fig. 293. Worthington water meter, marked ten thousand, the figure 6. The next pointer being between ten and 1, indicates nothing. By subtracting the read* ing taken at one time, from that taken at the next, the consump- tion of water for the intermediate time is obtained.
TABLE OF PRESSURE DUE TO HEIGHT.
s
H
li
ft .
a*
W> W
-3 x
5j
Si
P .
«> ,d
s . II
ft .
0.43 2.16 4.33
6.49 8.66 10.82
12.99 15.16 17.32
19.49 21.65 23.82
25.99 28 15 30.32
32.48 34 65 36.82
38.98 41.15 43 31
HANDBOOK ON ENGINEERING.
583
TABLE OF DECIMAL EQUIVALENTS OF Sths, 16ths, 32ds AND 64ths OF AN INCH.
|
Sths. |
32ds. |
64ths. |
64ths. |
|
i = .125 |
SV = .03125 |
/4- = .015625 |
f| = .546875 |
|
I = .25 |
-3% = .09375 |
^ = .046875 |
i = .578125 |
|
| = .375 |
-359- == .15625 |
•ft = .078125 |
-J = .609375 |
|
i = .50 |
3£ _ .21875 |
•h = .109375 |
jfi = .640625 |
|
| = .625 |
^ = .28125 |
•fy = .140625 |
|| = .671875 |
|
I = .75 |
Ji = .34375 |
iri = .171875 |
|| = .703125 |
|
1 = .875 |
$ = .40025 |
ir| = .203125 |
jj = .734375 |
|
Jf = .46875 |
ir| = .234375 |
|| = .765625 |
|
|
LJ = .53125 |
irj = .265625 |
i = .796875 |
|
|
leths. |
if = 059375 |
irf •== .296875 |
f = .828125 |
|
|^ = .65625 |
Ji = .328125 |
| = .859375 |
|
|
A- = .0625 |
f| = .71875 |
I = .359375 |
f} = .890625 |
|
A = 1875 |
|4 = .78125 |
Jf = .390625 |
^ = .921875 |
|
-,V = .3125 |
f| = .84375 |
|f == .421875 |
i = .953125 |
|
f6- = .4375 |
|f = .90625 |
§} == .453125 |
|| = .984375 |
|
A = .5025 |
|i = .96875 |
J = .484375 |
|
|
H = .6875 |
|3 _- .515625 |
||
|
|| = .8125 |
|||
|
[f = .9375 |
LATENT HEAT OF LIQUIDS, UNDER A PRESSURE OF 30 INCHES OF MERCURY.
(TREATISE ON HEAT, BY THOMAS BOX.)
|
Latent Heat in Units. |
Increase of Tempe- rature of Liquid, if Heat had not become Latent. |
||
|
Water |
966 |
966° |
Hegnault. |
|
Alcohol |
457 |
735° |
Ure. |
|
Ether |
313 |
473° |
a |
|
Oil of Turpentine |
184 |
390° |
tt |
|
184 |
443° |
1C |
|
The boiling point of different liquids varies; and the boiling point of a liquid varies with the pressure
584
HANDBOOK ON ENGINEERING.
O 00 00 b-
r-^ CO
O
00 iQ Oi 00
• . 02
* 00 P
S ajD
2§*
•w^ O -~
5 jj|
a 5 S rv
HANDBOOK ON ENGINEERING. 585
CAPACITY OF SQUARE CISTERNS IN U. S. GALS.
|
5X5 |
5X6 |
5X7 |
5X8 |
5X9 |
5X10 |
6X6 |
6X7 |
6X8 |
6X9 |
6X10 |
|
|
5 ft.. |
935 |
1122 |
1309 |
1496 |
1683 |
1870 |
1346 |
1571 |
1795 2020 |
2244 |
|
|
54 ft.. |
1028 |
1234 |
1440 |
1645 |
1851 |
2057 |
1481 |
1728 |
1975 |
2221 |
2469 |
|
6 ft.. |
1122 |
1346 |
1571 |
1795 |
2019 |
2244 |
1615 |
1885 |
2154 |
2423 |
2693 |
|
64ft.- |
1215 |
1459 |
1702 |
1945 |
2188 |
2431 |
1750 |
2042 |
2334 |
2625 |
2917 |
|
7 ft.. |
1309 |
1571 |
1833 |
2094 |
2356 |
2618 |
1884 |
2199 |
2513 |
2827 |
3142 |
|
74ft.. |
1403 |
1683 |
1963 |
2244 |
2524 |
2800 |
2019 |
2356 |
2693 |
3029 |
3366 |
|
8 ft.. |
1496 |
1795 |
2094 |
2393 |
2693 |
2992 |
2154 |
2513 |
2872 |
3231 |
3592 |
|
84ft.. |
1589 |
1907 |
2225 |
2543 |
2861 |
3179 |
2288 |
2670 |
3052 |
3433 |
3816 |
|
9 ft.. |
1683 |
2020 |
2356 |
2693 |
3029 |
3366 |
2423 |
2827 |
3231 |
3635 |
4041 |
|
94ft.. |
1776 |
2132 |
2487 |
2842 |
3197 |
3553 |
2558 |
2984 |
3412 |
3837 |
4265 |
|
10 ft.. |
1870 |
2244 |
2618 |
2992 |
3366 |
3470 |
2692 |
3142 |
3591 |
4039 |
4489 |
|
6X11 |
6X12 |
7X7 |
,7X8 |
7X9 |
7X10 |
7XH |
7X12 |
8X8 |
8X9 |
||
|
5 ft.. |
2468 |
2693 |
1832 2094 |
2356 |
2618 |
2880 |
3142 |
2394 |
2693 |
||
|
54 ft. . |
2715 |
2962 |
2016 |
2304 |
2592 |
2880 |
3168 |
3456 |
2633 |
2962 |
|
|
6 ft.. |
2962 |
3231 |
2199 |
2513 |
2827 |
3142 |
3456 |
3770 |
2872 |
3231 |
|
|
64ft.. |
3209 |
3500 |
2382 |
2722 |
3063 |
3403 |
3744 |
4084 |
3112 |
3500 |
|
|
7 ft.. |
3455 |
3770 |
2565 |
2932 |
3298 |
3665 |
4032 |
4398 |
3351 |
3770 |
|
|
74ft.. |
3702 |
4039 |
2748 |
3141 |
3534 |
3927 |
4320 |
4712 |
3590 |
4039 |
|
|
8 ft.. |
3949 |
4308 |
2932 |
3351 |
3770 |
4189 |
4608 |
5026 |
3830 |
4308 |
|
|
84ft.. |
4196 |
4577 |
3115 |
3560 |
4005 |
4451 |
4896 |
5340 |
4069 |
4578 |
|
|
9 ft.. |
4443 |
4847 |
3298 |
3769 |
4341 |
4712 |
5184 |
5655 |
4308 |
4847 |
|
|
94ft.. |
4689 |
5116 |
3481 |
3979 |
4576 |
4974 |
5472 |
5969 |
4548 |
5116 |
|
|
10 ft.. |
4936 |
5386 |
3664 |
4188 |
4712 |
5236 |
5760 |
6283 |
4788 |
5386 |
WEIGHT OF WATER.
1 cubic inch 03617 pound.
12 cubic inches 434 pound.
1 cubic foot (salt) 64.3 pounds.
1 cubic foot (fresh) 62.425 pounds.
1 cubic foot 7.48 U. S. Gallons.
NOTE. — The center of pressure of a body of water is at two-thirds the depth from the surface.
To find the pressure in pounds per square inch of a column of water, multiply the height of the column in feet by .434. Every foot elevation is called (approximately) equal to one-half pound pressure per square inch.
586
HANDBOOK ON ENGINEERING.
SHOWING U. S. GALLONS IN GIVEN CUBIC FEET.
NUMBER OF
|
Cubic Feet. |
Gallons. |
Cubic Feet. |
Gallons. |
Cubic Feet. |
Gallons. |
|
0.1 |
0.75 |
50 |
374.0 |
9,000 |
67,324.6 |
|
0.2 |
1.50 |
60 |
448.8 |
10,000 |
74,805.2 |
|
0.3 |
2.24 |
70 |
523.6 |
20,000 |
149,610.4 |
|
0.4 |
2.99 |
80 |
598.4 |
30,000 |
224,415.6 |
|
0.5 |
3.74 |
90 |
673.2 |
40,000 |
299,220.7 |
|
0.6 |
4.49 |
100 |
748.0 |
50,000 |
374,025.9 |
|
0.7 |
5.24 |
200 |
1,496.1 |
60,000 |
448,831.1 |
|
0.8 |
5.98 |
300 |
2,244.1 |
70,000 |
523,636.3 |
|
0.9 |
6.73 |
400 |
2,992.2 |
80,000 |
598,441,5 |
|
1 |
7.48 |
500 |
3,740.2 |
90,000 |
673,246.7 |
|
2 |
14.9 |
600 |
4,488.3 |
100,000 |
748,051.9 |
|
3 |
22.4 |
700 |
5,236.3 |
200,000 |
1,496,103.8 |
|
4 |
29.9 |
800 |
5,984.4 |
300,000 |
2,244,155.7 |
|
5 |
37.4 |
900 |
6,732.4 |
400,000 |
2,992,207.6 |
|
6 |
44.9 |
1,000 |
7,480.0 |
500,000 |
3,740,259.5 |
|
7: |
52.4 |
2,000 |
14,961.0 |
600,000 |
4,488,311.4 |
|
8 |
59.8 |
3,000 |
22,441.5 |
700,000 |
5,236,363.3 |
|
9 |
67.3 |
4,000 |
29,922.0 |
800,000 |
5,984,415.2 |
|
10 |
74.8 |
5,000 |
37,402.6 |
900,000 |
6,732,467.1 |
|
20 |
149.6 |
6,000 |
44,883.1 |
1,000,000 |
7,480,519.0 |
|
30 |
224.4 |
7,000 |
52,363.6 |
||
|
40 |
299.2 |
8,000 |
59,844.1 |
From the above any cubic feet reading can readily be converted into U. S. gallons, as follows:
How many gallons are represented by 53,928 cubic feet? 50,000 cubic feet = 374,025.9 gallons. 3,000 « " = 22,441.5 " 900 " " = 6,732.4 " 20 <f " =. 149.6 " 8 " " = 59.8 "
53,928 cubic feet =* 403,409.2 gallons
HANDBOOK ON ENGINEERING.
587
SHOWING COST OF WATER AT STATED RATES PER 1000 GALLONS.
|
Number of Cubic Feet. |
COST PER 1000 GALLONS. |
|||||||
|
5 Cents. |
6 Cents. |
8 Cents. |
10 Cents. |
15 Cents. |
20 Cents. |
25 Cents. |
30 Cents. |
|
|
20 |
$0 007 |
$0.009 |
$0.012 |
$0-015 |
$0.021 |
$0.030 |
$0.037 |
$0.045 |
|
40 |
0.015 |
0.018 |
0.024 |
0.030 |
0.045 |
0 060 0.075 |
0.090 |
|
|
60 |
0.022 |
0.027 |
0.036 |
0.045 |
0.066 |
0.090 |
0.112 |
0.135 |
|
80 |
0.030 |
0.036 |
0.048 |
0.060 |
0.090 |
0 120 |
0.150 |
0.180 |
|
100 |
0.037 |
0.049 |
0.060 |
0.075 |
0.111 |
0.150 |
0.187 |
0.224 |
|
200 |
0.075 |
0.090 |
O.f20 |
0.150 |
0.225 |
0.299 |
0.374 |
0.449 |
|
300 |
0.112 |
0.135 |
0.180 |
0.224 |
0.336 |
0.449 |
0.561 |
0.673 |
|
400 |
0.150 |
0.180 |
0.239 |
0.299 |
0.450 |
0.598 |
0-748 |
0.898 |
|
500 |
0.188 |
0.224 |
0.299 |
0.374 |
0.564 |
0.748 |
0.935 |
1.122 |
|
600 |
0.224 |
0.269 |
0.359 |
0.449 |
0.448 |
0.898 |
1.122 |
1.346 |
|
700 |
0.262 |
0.314 |
0.419 |
0.524 |
0-786 |
1.047 |
1.309 1-571 |
|
|
800 |
0.299 |
0.350 |
0.479 |
0.598 |
0-897 |
1.197 |
1.496 1-795 |
|
|
900 |
0.337 |
0.404 |
0.539 |
0.673 |
1.011 |
1 346 |
1.683 2.020 |
|
|
1,000 |
0-374 |
0.449 |
0.598 |
0.748 |
1.122 |
1 496 |
1.870 |
2.244 |
|
2,000 |
0.748 |
0.898 |
1.197 |
1.498 |
2.244 |
2.992 |
3.740 |
4-488 |
|
3,000 |
1.122 |
1.346 |
1-795 |
2-244 |
3.366 |
4.488 |
5.610 |
6*732 |
|
4,000 |
1.496 |
1.795 |
2-393 |
2.992 |
4.488 |
5.984 |
7.480 |
8.976 |
|
5,000 |
1.870 |
2.244 |
2-992 |
3-740 |
5.610 |
7.480 |
9.350 |
11.220 |
|
6,000 |
2.244 |
2.692 |
3.590 |
4.488 |
6.732 |
8.976 |
11.220 |
13.464 |
|
7,000 |
2.618 |
3-141 |
4.189 |
5.236 |
7.854 |
10.472 |
13.090 |
15.708 |
|
8,000 |
2.992 |
3.590 |
4-787 |
5-984 |
8.976 |
11.968 |
14.961 |
17.953 |
|
9,000 |
3.366 |
4.039 |
5.385 |
6.732 |
10.098 |
13.464 |
16-831 |
20.197 |
|
10,000 |
3.74 |
4.488 |
5-984 |
7-480 |
11.122 |
14.961 |
• 18.701 |
22.441 |
|
20,000 |
7.48 |
8.976 |
11.96& |
14.961 |
22.443 |
29.992 |
37-402 |
44.882 |
|
30,000 |
11.22 |
13.46 |
17.95 |
22-44 |
33.664 |
44.88 |
56.10 |
67.32 |
|
40,000 |
14.96 |
17.95 |
23-94 |
29.92 |
44.885 |
59.84 |
74-10 |
89.77 |
|
50,000 |
18.70 |
22.44 |
29.92 |
37.40 |
56.103 |
74.80 |
93-50 |
112.20 |
|
60,000 |
22.44 |
26.92 |
35.90 |
44.88 |
67.323 |
89.76 |
112.20 |
134.64 |
|
70,000 |
26.18 |
31-41 |
41.89 |
52.36 |
78.543 |
104.72 |
130.90 |
157-08 |
|
80,000 |
29.92 |
35.90 |
47-87 |
59.84 |
89.766 |
119.68 |
149.61 |
179.53 |
|
90,000 |
33-. 66 |
40.39 |
53.85 |
67.32 |
100. 98b |
134 64 |
168-31 |
201.97 |
|
100,000 |
37.40 |
44.88 |
59.84 |
74.80 |
111.22 |
149.61 |
187-01 |
224.41 |
|
200,000 |
74.81 |
89.76 |
119.68 |
149.61 |
224.43 |
299 22 |
374.02 |
448-82 |
|
300,^00 |
112.20 |
134.64 |
179.53 |
224.41 |
336.64 |
448.83 |
561.03 |
673.24 |
|
400,000 |
149-61 |
179.53 |
239.37 |
299.22 |
448-85 |
598 44 |
748.05 |
897-66 |
|
500,000 |
187.01 |
224.41 |
299.22 |
374.02 |
561.03 |
748.05 |
935.06 |
1122.07 |
|
600,000 |
224.41 |
269.29 |
359.06 |
448 83 |
673-23 |
897.66 |
1122.07 |
1346.49 |
|
700,000 |
261.81 |
314.18 |
418.90 |
523.63 |
785-43 |
1047.27 |
1309.08 |
1570.88 |
|
800,000 |
299 22 |
359.06 |
478.75 |
598.44 |
897-66 |
1196 88 |
1496.10 |
1795.32 |
|
900,000 |
336.62 |
403.94 |
538.59 |
673.24 |
1009- 86 |
1346.49 |
1683.11 |
2019.73 |
|
1,000,000 |
374.02 |
448.83 |
598.44 |
748.05 |
1122,06 |
1498.10 |
1870.12 |
2244.15 |
HANDBOOK ON ENGINEERING.
OOOOOO
i-t
OOOOOO
CO tO CO Oi
oood
o •o'ooo'ooo'o'oor-i
•OOOOOOOOOOOt-i
•O i—1 -r-ieieOUtCOaOOicNOO • O O* O O O* C O o' O <N CO
.
^'Q
ft C'l CO O •**< CO r-l ^H CN 01 O
WCOOOOQO
J9d
HANDBOOK ON ENGINEERING.
589
SHOWING HOW WATER MAY BE WASTED.
GALLONS DISCHARGED PER HOUR THROUGH VARIOUS SIZED ORIFICES UNDER STATED PRESSURES.
|
= |
-M |
Diameters of Orifices in Inches and Fractions of an Inch. |
|||||||||
|
"S S |
3 S <D |
||||||||||
|
HH |
£| | |
i |
1 |
i |
1 |
1 |
1 |
l£ |
11 |
H |
2 |
|
m |
inch |
inch |
inch |
inch |
inch |
inch |
inch |
inch |
inch |
inch |
|
|
Cu GO |
|||||||||||
|
20 |
8.66 |
300 |
720 |
1260 |
1920 |
2760 |
4920 |
7380 |
11100 |
15120 |
19740 |
|
40 |
17.32 |
450 |
960 |
1800 |
2760 |
3960 |
6720 |
10920 |
15720 |
21360 |
27960 |
|
60 |
25.99 |
540 |
1200 |
2160 |
3480 |
4800 |
8580 |
13380 |
19200 |
26220 |
34260 |
|
80 |
34.65 |
620 |
1380 |
2460 |
3840 |
5580 |
9840 |
15480 |
22260 |
30300 |
39540 |
|
100 |
43.31 |
690 |
1560 |
2760 |
4320 |
6240 |
11040 |
17280 |
24900 |
33900 |
44280 |
|
120 |
51.98 |
780 |
1780 |
3000 |
4740 |
6840 |
12120 |
18960 |
27240 |
37440 |
48480 |
|
140 |
60.64 |
816 |
1860 |
3300 |
5100 |
7320 |
13020 |
20160 |
29460 |
39080 |
52320 |
|
150 |
64.97 |
840 |
1920 |
3420 |
5280 |
7620 |
13560 |
21180 |
30480 |
41460 |
54120 |
|
175 |
75.80 |
900 |
2040 |
3660 |
5700 |
8220 |
14640 |
22800 |
32880 |
44940 |
58560 |
|
2CO |
86.63 |
960 |
2220 |
3900 |
6120 |
8760 |
15600 |
25020 |
35880 |
47880 |
62580 |
|
235 |
101.79 |
1080 |
2460 |
4320 |
8280 |
11160 |
17100 |
26760 |
38520 |
52260 |
68460 |
The pressure or head of water is taken at the orifice, no allowance being made for friction in the pipe. In practical calculations to deter- mine the height which water can be thrown, the head consumed by the friction of the water in flowing from the source to the orifice must be considered.
IGNITION POINTS OF VARIOUS SUBSTANCES.
Phosphorus ignites at . , .... 150° Fahr.
Sulphur " " . . . . 500° «
Wood " " . . . . . . . . = c . . . 800° "
Coal . " " . . . .......... 1000° "
Lignite, in the form of dust, ignites at . . , . . c . . 150° "
CaimelCoal, " "" " . . ...... 200° "
Coking Coal, " " " . . . . . . . . 250° "
Anthracite, " « " " 300° "
590 HANDBOOK ON ENGINEERING.
CHAPTER XX, THE INJECTOR AND INSPIRATOR.
The energy of motion of a body is well known to be the prod- act of its mass by the half square of its velocity ; hence, it is possible to communicate to a body of little weight a large amount of energy by moving it fast enough, and in fact, the energy of motion would only be limited by the speed which can be given the body. In this way a small weight of steam flowing from an orifice into a properly shaped jet of water is condensed, while the velocity of the steam is greater than if flowing into air ; the energy thus communicated is made sufficiently great by increasing the weight of steam, which can be done by increasing the area of the steam way, until we find such jet pumps adapted to many purposes. There are, however, two which are of interest to us in this connection, the well-known injector and inspirator, with the large number of lifting and non-lifting varieties, all differing in details as to form of nozzles, area of passages, distances between nozzles, and that class of instruments in which, after a certain energy and velocity have been reached, the operation is rep'eated. These might be called " consecutive " instruments. The illustrations in this book show some of the simplest and adjustable kinds. Within a few years the principle of increase of energy by increase of mass or velocity has been applied by in- creasing the mass of steam used until we find that not only can a few pounds weight of steam put into a boiler, a good many more pounds of water at a much higher temperature than it had, but that in a non-condensing engine it is possible, by using the ex- haust in part, to put into the boiler at a much higher pressure
HANDBOOK ON ENGINEERING. 591
and temperature, a weight of water, which is still greater than that of the steam moving it.
When the injector first made its appearance it was, by many, considered as almost a paradox, especially by those who looked at the question as one of hydrostatics only. That steam from a boiler could put water back into it at the same pressure, and over- come the friction of the passages without the aid that a steam pump had of a difference of piston areas, was to them a puzzle , The use of exhaust steam at atmospheric pressure for the purpose of putting water into a boiler at a pressure of 150 Ibs. per square inch, would be to such minds utterly incomprehensible. The use of an injector and inspirator, has this to recommend them, that the feed-water cannot be introduced into the boiler cold or nearly so> but must be warmed by contact with the steam, and the value of this has been already shown. In small boilers where no heater is used, an exhaust injector is better than a pump, and so is an ordinary injector ; but the former includes in itself an exhaust heater, saving a portion of heat from the exhaust, besides taking the power as heat also ; while, with the common injector, the heat for power and raising temperature are both derived from the live steam in the boiler. The latter portion of heat is, of course, directly returned to the boiler without loss, but that for power is necessarily expended. As to the amount of power used by pump and injector compared with each other, it would seem that the pump is most efficient. There have been many comparative trials of pump and injector, but the results have usually been unsatis- factory from contained discrepancies.
Injectors are of the automatic type, so named on account of their ability to restart when for any reason the supply of either water or steam is momentarily interrupted. This is one of the simplest of its type, all parts being accessible by the simple use of a mon- key wrench. Taking off the bottom plug, the lower interior jet
592 HANDBOOK ON ENGINEERING.
follows it out, as does also the upper or steam jet, by removing the coupling nut. On this account and for other reasons auto- matic Injectors have become very popular, as the engineer is enabled to make his own repairs where parts are interchangeable as in this Injector. In installing an Injector, great care must be exercised in getting tight pipe connections, especially in the suction or water supply pipe, as the least particle of air admitted to this pipe will ruin the vacuum, hence the starting or working of the machine. Before connecting an Injector, from the fact that there is a chance of iron scale or other refuse being in the steam pipe, it should be blown out thoroughly before the Injector is connected, otherwise whatever is in this pipe will be blown into the Injector at the first opening of the steam valve and the jets entirely clogged. It takes but the smallest particle of refuse of any kind lodged in the delivery tube to destroy the working of an Injector. Many engineers wonder why after an Injector has been in use for only a short time it will not work as when first put on. They do not seem to realize that in most all water there is a great deal of solid matter, all of which is deposited by the action of the steam on the interior and the jets of the Injector. This sediment increases very rapidly, and very soon all tapers and horizontal drill holes have become contracted and the range of the Injector destroyed. A solution of ten parts of muriatic acid to one part of water will cut away almost all the sediment so lodged on the jets, and by disconnecting the Injector and immersing the same in the above solution over night this sedi- ment is almost sure to be dissolved.
RANGE OF THE INSPIRATOR AND INJECTOR.
The Steam pressure at which an injector will start and the highest steam pressure at which it will work constitute what is termed the "range" of an injector, and the inspirator varies with the vertical lift and the temperature of the feed water.
HANDBOOK ON ENGINEERING.
593
It must also be borne in mind that the same style of construc- tion in an injector and inspirator, while it confines them to about a specific range between its lowest starting and highest working points, permits of variation as to what the lowest starting point shall be. A style of construction, which gives a range (on say a 2-foot lift) of 25 Ibs. to 155 Ibs. would permit of a range of 35 Ibs. to 165 Ibs. (in fact, to a little higher than 165 Ibs.). Different manu- facturers, therefore, vary as to the starting point in their stand- ard machines — aiming to cover the range which they deem most desirable. Nearly all have adopted about 25 Ibs. on a 2-foot lift, as lowest starting point.
Fig. 294. The World injector.
POSITIVE OR DOUBLE TUBE INJECTORS.
As before stated, this class of injector is provided with two sets f tubes or jets, one set adapted to lift the water and deliver it to
88
594 HANDBOOK ON ENGINEERING.
the second set, which forces the water into the boiler. By this arrangement, it is apparent that inasmuch as the lifting jets supply a proportionate amount of water with varying steam pres- sures, a wider range is obtainable than with an automatic in- jector. In the following cases, it is better to use the double tube injectors : —
1. Where the feed water is of too high a temperature to be handled by the automatic injectors.
2. When a great range of steam variation is accompanied by the condition of a long lift.
The World injector is one of the simplest boiler feeders of the double tube type of injectors. It is entirely self contained. It is supplied even with its own check valve and operated entirely by a single lever, a quarter of a turn of which starts the lifting, after which the completion of the single revolution sets the injector
working to boiler.
• .
GENERAL SUGGESTIONS FOR PIPING-UP INJECTORS AND INSPIRATORS AND SUGGESTIONS THAT SHOULD BE CAREFULLY FOLLOWED WHEN MAKING PIPE CONNEC- TIONS.
Steam* — Connect steam pipe with highest parts of boiler and never connect with a steam pipe used for any other purpose. We would recommend a globe valve being placed in the steam pipe
next to boiler which can be closed in case it is desired to take off
.
the injector. At all other times it can be left open. When the steam connection is made, be sure and take off the injector before the steam is turned on the machine. Then blow out the steam pipe with at least forty pounds steam, which will remove all dirt and scale.
Suction* — This pipe must be tight, and if there is a valve in it the stem must be well packed.
To test the suction pipes for leaks, plug up the end of the pipe
HANDBOOK ON ENGINEERING.
595
and then screw on a common iron cap on the overflow ; or if that is not at hand, unscrew cap X, and place a piece of wood on top of valve ; replace the cap and the wood will hold the valve from rising ; then turn on the steam, which will locate all leaks.
Fig. 295. Complete piping for injector.
All pipes, whether steam, suction or delivery, must be of the same or greater size than the corresponding branch of each injec- tor. Have all piping as short and as straight as possible, and especially avoid short turns.
596 HANDBOOK ON ENGINEERING.
If any old pipe is used, see that it is not partially filled or stopped up with rust.
If the injector or inspirator has to lift the water very high ot draw it very far, have the suction pipe a size or two larger than called for by the suction branch of the injector or inspirator.
Have the water supply (suction) pipe independent of any other connection. The suction pipe must be absolutely air tight ; the slightest leak, in most cases, will prevent the injector or inspirator from forcing water into the boiler.
Always place a globe valve in the suction pipe as close to the injector as possible, and place it so that it will shut down against the water side and see that the stem is packed tight.
When using the injector or inspirator as NON-LIFTING, put two globe valves in the suction, one close to the injector, the other as far from it as you can conveniently, keeping the one farthest from the injector or inspirator tolerably close throttled. This will repay anyone for their trouble. The check valve may be next to boiler with a valve between it and boiler, the farther from injector the better. If the injector forces through a heater, place check valve between injector and heater. Also place a valve between heater and check valve so the latter can be taken out if necessary.
Size of pipes* — If injector or inspirator has over 10 feet lift, or a long draw, use suction pipe from strainer to valve a size larger than the connection on injector, reducing when it reaches the valve.
In all other cases, use for all pipes same size as injector connection.
Blow-off* — Always blow out steam thoroughly BEFORE CON- NECTING INJECTOR, so as to remove any dirt, rust or scale that may be in the pipes.
Caution* — The suction pipe must be ABSOLUTELY TIGHT throughout. To make sure that it is so, test the suction as directed.
HANDBOOK ON ENGINEERING. 597
DIRECTIONS FOR CONNECTING AND OPERATING THE HANCOCK INSPIRATOR.
44 Stationary " pattern* — Connect as shown by cut Fig. 296, showing exterior and section. For full instructions, see page 598.
For a lift of 5 ft., 15 Ibs. steam pressure is required.
*» " 10 " 20 " <4 " u
*' « 15 u 25 4k " u 4t
u ** 20 u 35 " u u "
u " 25 u 45 " u u u
Operation* — Open overflow valves Nos. 1 and 3 ; close forcer steam valve No. 2 and open the starting valve in the steam pipe. When the water appears at the overflow, close No. 1 valve ; open No. 2 valve one-quarter turn and close No. 3 valve. The inspir- ator will then be in operation.
NOTE. — No. 2 valve should be closed with care to avoid damag- ing the valve seat. When the inspirator is not in operation, both overflow valves Nos. 1 and 3 should be open to allow the water to drain from it. No adjustment of either steam or water supply is necessary for varying steam pressures, but both the temperature and quantity of the delivery water can be varied by increasing or reducing the water supply. The best results will be obtained from a little experience in regulating the steam and water supply. If the suction pipe is filled with hot water, either cool off both it and the inspirator with cold water, or pump out the hot water by opening and closing the starting valve suddenly. To locate a leak in the suction pipe, plug the end, fill it with water, close No. 3 valve and turn on full steam pressure. Examine the suction pipe and the water will indicate the leak. If the inspirator does not lift the water properly, see if there is a leak in the suction pipe. Note if the steam pressure corresponds to the lift as above speci- fied, and if the sizes of pipe used are equal in size to inspirator connections. If the inspirator will lift the water, but will not de- liver it to the boiler, see if the check valve in the delivery pipe is
598
HANDBOOK ON ENGINEERING.
in working order and does not u stick." Air from a leak in the suction connections, will prevent the inspirator from delivering the water to the boiler, even more than it will in lifting it only. If No. 1 valve is damaged, or leaks, the inspirator will not work properly. No. 1 valve can be easily removed and ground.
STtAM
Feed to Boiler.
Suction.
Overflow.
ISP
3 Fig. 296. Hancock inspirator.
To remove scale and deposits from inspirator jets or parts, disconnect the inspirator and plug both the suction and delivery outlets with corks. Open No. 2 valve and fill the inspirator with a solution of one part muriatic acid and ten parts water0 Allow this solution to remain in the inspirator over night, then wash it thoroughly in clear water.
NOTE. — It is not generally necessary to return an inspirator for repairs. The repair parts required can be ordered and the inspirator readily put in order.
.HANDBOOK ON ENGINEERING. 599
TO DISCOVER CAUSE OF DIFFICULTIES.
WHEN INJECTOR FAILS TO GET THE WATER.
1. The supply may be cut off by : (a) Absence of water at the source, (b) Strainer clogged up. (c) The suction pipe, hose or valve stopped up ; or if a hose is used, its lining may be loose (a frequent cause of trouble).
2. A large leak in the suction (note that a small leak will pre- vent injector from working, but not from getting the water).
3. Suction pipe or water very hot. Open drip-cock, turn steam on slowly, then shut it off quickly. This will cause the cool air to rush into the suction pipe and cool it off. Repeat if necessary.
4. Lack of steam pressure for the lift ; or, in some instances, too much steam pressure. If the steam pressure is very high, the injector will get the water more readily if the steam is turned on slowly and the drip-cock left open until the water is got.
IF THE INJECTOR GETS THE WATER BUT DOES NOT FORCE IT TO
THE BOILER.
1. No globe valve on the suction with which to regulate the water, or else the supply water not properly regulated.
2. Dirt in delivery tube.
3. Faulty check valve.
4. Obstruction between inj.ector and check valve, or between check valve and boiler.
5. Small leak in suction pipe admitting air to the injector along with the supply water. It is ten to one this is the cause of the difficulty every time.
6. Be sure and understand the directions for starting before condemning the injector.
600 HANDBOOK ON ENGINEERING.
U. S. INJECTOR.
IF THE INJECTOR STARTS BUT "BREAKS."
1. Supply water not properly regulated. If too much water, the waste or overflow will be cool ; if too little, the water will be very hot.
2. Leaky supply pipe admitting air to the injector. It is ten to one this is the cause of difficulty. The suction must be air tight ; test as directed.
Fig. 297. Showing the U. S. injector and pipe connections. 8. Dirt or other obstruction, such as lime, etc., in delivery tubet 4. Connecting steam pipe to pipe conducting steam to other points besides the injector, er not having suction pipe independent.
HANDBOOK ON ENGINEERING.
601
5. Sometimes a globe valve is used on the suction connection that has a loose disc, and after starting the disc is drawn down^ thus partially closing the valve; it is, of course, equivalent to giving the injector too little water. To remedy this, take the globe valve off and reverse it end for end.
To clean* — To clean injector, unscrew plug 0, and the re- movable jet inside resting in it will follow the plug out. . Turn on steam (not less than forty pounds) and all dirt will be blown out. Examine all passages and drill hole's and see that no dirt or scale has lodged in them. Replace jet by setting it in the plug (which acts as a guide) and screw into place tightly. Be careful not to bruise any jets, and use no wrenches on body of injector.
SIZES AND CAPACITIES OF U. S. INJECTOR.
|
SIZE. |
ALL PIPE CONNECTIONS. |
CAPACITY GALLONS PER HOUR. |
HORSE POWER. |
|||
|
MAX. |
MIN. |
|||||
|
oo ... |
lj 1 1 1J If l| H 2 2 2 2} 2j |
n. |
36 65 90 125 170 250 340 475 575 750 9'20 1350 1750 2275 2820 3400 3650 4000 |
15 28 40 60 75 125 ' 140 250 300 ' 350 450 675 850 1000 1300 1700 1800 1950 |
1 t 3 6 8 15 20 30 40 60 70 85 120 165 230 295 375 460 500 |
0 4 8 10 15 20 30 40 60 70 95 120 165 230 295 375 460 500 600 |
|
o |
||||||
|
i |
||||||
|
2 |
||||||
|
3 |
||||||
|
4 .. |
||||||
|
5 |
||||||
|
6 .. |
||||||
|
7 |
||||||
|
8 .. |
||||||
|
9 |
||||||
|
10... |
||||||
|
11 |
||||||
|
12 |
||||||
|
13 . |
||||||
|
14 |
||||||
|
15 .. |
||||||
|
16 |
To test for leaks. — Plug up end of water supply pipe, then fit a piece of wood into cap Z, so that when screwed down it will hold check valve in place, then turn on steam and it will locate leak. Do not fail to do this in case of any trouble.
TO START AND STOP INJECTOR.
To start* — Open full the globe valve in water supply first, and then globe valve in steam pipe wide open. If water issues from overflow, throttle the valve // until discharge stops. Reg-
602
HANDBOOK ON ENGINEERING.
ulate injector with water supply valve, not by steam valve. When water supply is above the injector, in starting open steam valve first.
To stop* — Close the steam valve. The water valve H need not be closed unless the injector is used as a non-lifter, or lift is considerable.
PRICE LIST, CAPACITY, HORSE POWER, ETC. OF PENBERTHY
INJECTOR.
|
Size. |
Price. |
Pipe Connections. |
Capacity per Hour. 1 to 4 ft lift, 50 to 75 Ibs. Pressure. |
Horse Power. |
||||||
|
GO. A |
$16 00 18 00 |
Steam. Suet 2* 2 2 2 |
ion. De 1 1< 1 2 2 |
iv | i( ; . |
cry, D. |
Maximt 80 g 120 165 250 340 475 575 750 920 1300 1740 2270 2820 |
m. al. |
Minlmu 55 g 70 90 135 165 300 350 4 0 500 700 900 1100 1400 |
m. al. |
4 to 8 8 to 10 10 to 15 15 to 25 25 to 35 35 to 50 50 to 60 60 to 95 95 to 162 120 to 150 165 to 230 230 to 2:>() 290 to 365 |
|
A A B |
20 00 25 00 |
|||||||||
|
BB C .. CC. D... E . EK F . FF. |
30 00 40 00 45 00 55 00 60 00 75 00 90 00 110 00 125 00 |
HANDBOOK ON ENGINEERING. 603
To find the number of gallons of water delivered by a steam pump in one minute, when the diameter and stroke of water piston, and the number of strokes per minute are given : —
Rule* — Square the diameter of water piston and multiply the result by .7854. Multiply this product by the stroke of the water piston in inches ; and multiply this product by the number of strokes per minute, and divide the result by 231.
Example* — How many gallons of water per minute will a steam pump deliver, whose water cylinder is 6 inches in diameter and 12 inches stroke, making 60 strokes per minute?
Ans. 88.128 galls.
Operation : 6 X 6 X .7854 28.2744.
28.2744 X 12 X 60 And, ~iar~ - = 88-128-
To find the relative proportion between the steam and water pistons.
Rule* — Multiply the area of the pump piston by the resistance of the water in pounds per square inch ; and divide the product by the pressure of steam in pounds per square inch. The quotient will give the area of steam piston in square inches to balance the resistance. To this quotient add from 30 to 100 per cent of it- self,— depending on the speed of the pump, — and divide the sum by .7854, and extract the square root of the quotient for the diameter of the steam piston.
Example* — What should be the diameter of the steam piston to force water against a pressure of 125 pounds per square inch, the diameter of water piston being 6 ins. and the steam pressure 60 Ibs. per square inch? Ans. 10 J inches.
Operation: 6 X6 X .7854 = 28.2744 sqr. ins.
And, 28.2744 X 125 ^= 3534.3 pounds the total resistance.
3534.3 Then, ~~ — = 58.9 square inches the area of steam piston.
004 HANDBOOK ON ENGINEERING.
We will add 50 per cent for friction in pump and in delivery pipe, and for a moderate speed of pump. Then, 58.9 X .50 = 29.45. And, 58.9 + 29.45=88.35.
88.35 And, -TT = 112.49 sqr iris.
Then, y 112.49 = 10.6 ins. the diameter of the steam piston.
To find the pressure against which a pump can deliver water, when the diameter of steam piston, pressure of steam in pounds per square inch, and diameter of water piston are given : —
Rule* — Multiply the area of steam piston by the pressure of steam in pounds per square inch, and divide the product by the area of the pump piston, and deduct from 30 to 50 per cent for friction in the delivery pipe and in the pump itself.
Example* — The area of the steam piston is 112 square inches, and the area of water piston is 28 square inches, and the steam pressure is 60 Ibs. per square inch, against what pressure can the pump deliver water, the resistance from friction being 48 per cent?
Ans. 125 Ibs. per sqr. in., nearly.
112X60 Operation: — 28 — ~ 24:0*
And, 240 X -48 = 115.20. Then, 240 — 115.20 = 124.8.
To find the steam pressure required when the diameter of the steam piston, the diameter of the water piston, and the resistance against the pump in pounds per square inch are given : —
Rule, — Multiply the area of water piston by the resistance on the pump in pounds per square inch, and divide the product by the area of the steam piston.
HANDBOOK ON ENGINEERING. 605
Example* — The resistance against the pump, including fric- tion, is 240 pounds per square inch. The area of steam piston is 112 square inches, and the area of water piston is 28 square inches. What pressure of steam is required to operate the pump ?
Ans. 60 Ibs. per sqr. in.
- 240 X 28
Operation: — — — =60.
Now anything over 60 Ibs. will operate the pump, and the faster it is run the higher must be the pressure above 60 pounds.
To find the diameter of water piston when the diameter of steam piston, the steam pressure in pounds per square inch, and the resistance against the pump piston in pounds per square inch are given : —
Rule* — Multiply the area of steam piston in square inches by the steam pressure in pounds per square inch, and divide the product by the resistance in pounds per square inch on the water piston.
Example* — The resistance against the pump, including fric- tion, is 240 pounds per square inch ; the area of steam piston is 112 square inches, the steam pressure is 60 pounds per square inch, what should be the diameter of water piston?
Ans. 6 inches.
Operation j 112X6-° = 35.65 sqr. ins. Call it 36 sqr. ins.
Then, ^W = 6.
To find the horse power required in a steam pump to feed a boiler with a given number of pounds of water per hour against a given pressure of steam : —
Rule* — Multiply the velocity of flow of water in feet per min- ute by the total pressure against which the water is pumped in pounds per square incL, and divide the product by 33,000, and the quotient will be the horse power.
606 HANDBOOK ON ENGINEERING.
Example* — What horse power is required to feed a boiler with 600 gallons of water per hour against a total resistance of 112 IbSo per square inch, including the friction in the delivery pipe, lift of water in suction pipe, weight of check valve, and friction in the pump itself? Ans. 1 H. P» nearly.
Operation: 600 X 231 = 138,600 cubic inches of water per hour.
138,600 And, — TiTj — = 2310 cubic inches of water per minute.
2310 And, —rg— =192.5 feet per minute > the velocity of the
water o
The total resistance is 112 Ibs. per sqr. in0 Then, 192.5 X 112 = 21560 foot pounds.
21560 And' 3^000 = -6"H.P.
Now add say 50 per cent and we have .653 X .50 =.3265. And, .653 + .3265 = .9795.
This pump will feed a boiler as shown above, or it will deliver
600 gallons of water per hour under a head of 258 feet. & ^
112 Thus,
To find the horse power of boiler required to furnish steam for a pump running at its fullest capacity.
Rule* — Multiply the number of gallons of water delivered by the pump in one minute by 8£. Multiply this product by the total height in feet to which the water is to be lifted, measuring vertically from the source of supply to the point of delivery, and divide the result by 33,000. Add from 50 to 75 per cent to the quotient for loss from friction of water in the pipe, friction in the pump, waste of steam in the cylinder, and other contingencies, and the result will give the horse power of boiler required.
HANDBOOK ON ENGINEERING. 607
Example* — What horse power of boiler is required to run a steam pump lifting 800 gallons of water per minute to a height of 163 ft. from the source of supply? Ans. 50 H. P., nearly.
Operation : 800 X 8£ = 6667 Ibs. of water.
And, 6667 X 163 = 1,086,721 footpounds. 1,086,721
And' -337000- =33H'P-' near1^'
Then, 33 X .50 = 16.50.
And, 33 + 16.5 = 49.5.
To find the diameter of discharge nozzle for a steam pump, when the diameter and stroke of the water piston and the number of strokes per minute are given, and the maximum flow of water in feet per minute is given : —
Rule. — Find the cubic contents of the water cylinder for one stroke in cubic feet, and multiply it by the number of strokes per minute. Multiply this product by 144 and divide the result by the velocity of the water in feet per minute, and the quotient will be the area of pump nozzle in square inches.
Example* — The diameter of water cylinder is 10 inches, and the stroke of piston is 12 inches, and the speed is 50 strokes per minute. The velocity of water required is 500 feet per minute, what should be the diameter of pump discharge nozzle?
Ans. 3J ins., nearly.
Operation: 10 X 10 X .7854 = 78.54 sqr. ins. area of piston.
And, 78.54 X 12 = 942.48 cubic inches in the cylinder for one stroke.
And, ' = .5454 of a cubic foot for one stroke.
And, .5454 X 50 = 27.27 cubic feet for 50 strokes per minnte.
27 27 X 144 Then, - ""XnrT ~~ == 7-853? s(lr' ins' tlie area of tlie
\1^1 = 3. \.7854
And, = 3.1 ins. the diameter.
608 HANDBOOK ON ENGINEERING.
Xo find the approximate size of suction pipe when its length does not exceed 25 ft. and when there are not more than two elbows in the same : —
Rule* — Square the diameter of water cylinder in inches and multiply it by the speed of the piston feet in per minute ; divide this product by 200, and divide this quotient by .7854 and extract the square root, and the result will be the diameter of suction pipe, except for very small pipes when it should be made larger than the size given by the rule, in order to lessen the friction of the moving water.
Example* — The diameter of water cylinder is 6 ins., the stroke of piston is 12 ins., and the number of strokes per miuuteis 60, what should be the diameter of suction pipe? Ans. 4 ina»
And, i|i= ,3.75.
Then, «J13.75 = 3.7 ins. There is no pipe of this size made, BO take 4-inch pipe.
To find the velocity in feet per minute necessary to discharge a given number of gallons of water per minute through a straight smooth iron pipe of a given diameter, regardless of friction : —
Rule* — Reduce the gallons to cubic feet and multiply by 144, and divide the product by the area of the pipe in square inches.
Example* — What should be the velocity of the water to dis- charge 100 gallons of water per minute through a 4-inch pipe?
Ans. 149 ft. per minute.
Operation j — -£- — =13 cubic feet.
And, 13 X 144 — 1872 cubic inches placed in a continuous line.
Then, 4 X 4 X -7854 = 12.5664 square inches, the area of pipe.
And, _==
12.5664
HANDBOOK ON ENGINEERING. 609
To find the velocity in feet per minute of water flowing through a pipe of given diameter, when the diameter of water cylinder and speed of piston in feet per minute are given : —
Rule* — Multiply the area of water cylinder in square inches by the piston speed in feet per minute, and divide the product by the area of the pipe in square inches.
Example* — The diameter of water cylinder is 8 ins., and the piston speed is 100 ft. per minute, and the diameter of discharge pipe is 4 ins., what is the velocity of the water in the discharge pipe? Ans. 400 ft. per minute.
Operations 8 X 8 X .7854 = 50.26 sqr. ins. area of the water piston.
And, 50.26 X 100 = 5026.
The area of the pipe is 12.56 sqr. ins.
Then, =-. 400.
' 12.56
To find the number of gallons of water discharged per minute through a circular orifice under a given head : —
Rule*— Find the velocity of discharge in feet per second and multiply it by 60, then multiply this product by the area of the orifice in square feet, and multiply this last product .by 7.48, and the result will be the gallons discharged per minute.
Example. — How many gallons of water will be discharged per minute through an orifice 4 inches in diameter under a head of 81 feet? Ans. 2829.7 galls.
Operation: «J81 = 9. And, 9 X 8.025 = 72.225 feet per second, the velocity of discharge. The factor 8.025 is a con- stant for any head, and is found thusly: —
v'2 X32.2 =8.025.
Or, the velocity of discharge may be found in this manner ; — y2 X 82.2 X 81 = 72.22 feet per second, that is, the veloc- ity in feet per second equals the square root of the acceleration
39
610 HANDBOOK ON ENGINEERING.
due to gravity multiplied into the head in feet. Continuing the operation, we have : —
72.225 X 60 = 4333.5 feet per minute.
And, 4 X 4 X -7854 = 12.5664 sqr. ins. area of orifice.
And, — = .0873 of a square foot, the area of orifice.
144
also.
Then, 4333.5 X -0873 = 378.3 cubic feet.
And, 378.3 X 7.48 = 2829.7 galls.
NOTE. — With a ring orifice only 64 per cent of the above amount of water would be discharged, and with a funnel-shaped orifice only 82 per cent.
To find the number of gallons of water discharged per minute under a given pressure in pounds per square inch : —
Rule* — Divide the given pressure in pounds per square inch by .433 in order to get the head in feet, and then proceed accord- ing to the foregoing rule.
Example* — • How many gallons of water will be discharged per minute through an orifice one square inch in area, under a pres- sure of 35.073 Ibs. per square inch? Ans. 81 galls, per minute.
35.073 Operation: 4oo —81 ft., head equivalent to the given
pressure.
And, >/2 X 32.2 X81 = 72.225 ft. per second the velocity. And, 72.225 X 60 = 4333.5.
Also, rrr = .00694 of a square foot, equals the area of the
orifice.
And, 4332.5 X .00694 =.30.07449. And, 30.07449 X 7.48 = 224.9 galls. Then, deducting 64 per cent, we have: — 224.9 X .64= 143.9. And, 224.9 — 143.9 =81.
HANDBOOK ON ENGINEERING. 611
To find the area of orifice in square ins. necessary to discharge a given number of gallons of water per minute under a given head in feet : —
Rule* — Divide the number of gallons by the constant number 15.729 multiplied into the square root of the head, and the result; will be the area of orifice in square inches.
Example* — What must be the area of orifice to discharge 1778.5 gallons of water per minute under a head of 81 feet?
Ans. 12.56 sqr. ins.
Operation: >/8T = 9.
And, 9 X 15. 729 = 141.6.
1778.5 Then, — — =12,56.
To find how many gallons of water will flow through a straight smooth iron pipe in one minute under a given pressure in pounds per square inch, or head in feet : —
Rule* — Multiply the inside diameter of the pipe in feet by the head in feet, and divide the product by the length of pipe in feet. Extract the square root of the quotient and multiply it by 48, and the product will be the velocity of flow in feet per second. Multiply this result by 12 to reduce it to inches, and by 60 for the flow per minute, and multiply again by the area of the pipe in square inches, and divide by 231 for the gallons discharged per minute.
Example* — How many gallons of water will be discharged per minute through a 4-inch pipe 2000 feet long, under a head of 92 feet? Ans. 230 galls, per minute,
Operation : 4 ins. = .33 of a foot.
And, 92 X .33 = 30.36.
30.36 And' 2000"
12 HANDBOOK ON ENGINEERING .
And, V^l5 =.1225.
Then. .1225 X 48 X 12 = 70.56 ins. per second.
And, 70.56 X 60 =4233.60 ins. per minute.
Then, 4 X 4 X .7854 = 12.56 sqr. ins. the area of the pipe.
And, 4233.60 X 12.56 =53174.016 cubic ins.
53174.016 Then, — -- = 230.2.
Example. — Assume two wells A and B with their mouths on a level. Well A is 26 ft. deep, and well B is 40 ft. deep. Well A is fed by natural springs and has a depth of water of 5 feet. The distance between the wells is 600 feet. How many gallons of water will a 1 inch pipe, laid perfectly straight and level, syphon over in one minute providing well B is always pumped dry, and that the pipe extends into well A 26 feet, and into well B 38 feet, using bends instead of elbows?
Ans. 4 galls, per minute.
Operation. — The head equals 38 feet. The diameter of the pipe equals .0833 foot. Then, 600 + 38 + 26 = 664 ft. total length of pipe. And, 38 X -0833 = 3.1654.
3.1654 And,
And, V .0047 = .068.
Then, .068 X 48 = 3.264 ft. velocity per second. And, 3.264 X 60 = 195.840 ft. velocity per miD. The area of pipe equals .7854 sqr. inch. Then, 195.840 X .7854 = 153.8127. And, 153.8127X7.48 = 1150.52.
1150.52 And, — ^-JT — = 8 nearly, gallons.
HANDBOOK .ON ENGINEERING. 613
Deducting 50 per cent on account of 2 bends and friction, we have 4 gallons per minute syphoned over.
To find the head in feet due to friction in a pipe running full : -
Rule* — Multiply the length of the pipe in feet by the square of the number of gallons per minute, and divide the product by 1,000 times the 5th power of the diameter of the pipe in inches. The quotient less 10 per cent is the head in feet necessary to over- come the friction.
NOTE. — The head is the vertical distance from the surface of the water in the tank or reservoir, to the center of gravity of the lower end of the pipe, when the discharge is into the air, or, to the level surface of the lower reservoir when the discharge is under the water.
Example* — A 2-inch pipe 100 feet long and running full, discharges 50 gallons of water per minute, what is the head in feet due to friction? Ans. 7.029 feet.
Operation : 2 X 2 X 2 X 2 X 2 = 32 = the 5th power of the diameter of the pipe.
And, 50 X 50 = 2500. And, 2500 X 100 = 250,000. Also, 32 X 1,000 = 32,000.
Then> iw = 7'81-
And, 7.81 less 10 percent of itself equals 7.029. The resistance to the flow of water in pounds per square inch> due to friction, is found by dividing the friction head by 2.3.
7.029 Thus, ^-^g- = 3.051bs.
To find the size of pump required to feed a boiler of a given capacity : —
614 HANDBOOK ON ENGINEERING.
Rule* — Multiply the number of pounds of water evaporated per pound of coal by the number of pounds of coal burned per sqr. foot of grate surface per hour, and multiply this product by the number of square feet of grate surface in the boiler furnace. This will give the number of pounds of water evaporated by the boiler in one hour. Divide this by 60 to find the evaporation per minute, and divide again by 8| in order to get the evaporation in gallons per minute ; add from 10 to 15 per cent to the last result for leakage and other contingencies, and select a pump that will deliver the gross number of gallons of water per minute at any speed that may be desired, usually taken, however, at fifty feet per minute.
Example* — What should be the dimensions of the water end of a steam pump, and what should be the speed of piston to sup- ply a boiler having a grate surface of 20 square feet, and burning 15 pounds of coal per square foot of grate, and evaporating 9 pounds of water per pound of coal per hour?
Operation: 20 X 15 X 9 =2700 pounds of water evapo- rated per hour.
2700
And, = 45 Ibs. of water evaporated per minute.
60
And, -— = 5.4 galls, per minute.
Then, 5.4 plus 10 per cent of itself, equals 6 galls, nearly per per minute.
Referring to a pump maker's catalogue we find that a single pump 3£" X 2J" X 5", making 90 strokes per minute, will do the work, or, a duplex pump 3" X 2" X 3", making 100 strokes per minute will do the work equally as well. Again, adding 10 per cent to the pounds of water evaporated per minute we have, 45 + 4.5 =49.5 pounds. And, 49.5 X 27.71 = 1371.64 cubic inches displacement in the water cylinder per minute, and at 90 strokes per minute we have 15.24 cubic inches displacement per stroke.
HANDBOOK .Off ENGINEERING. 615
Thus, 1371*64 = 15.24, which is all that is required for our
yo
boiler.
Now, taking the above single pump we have: 2.25 X 2.25 X .7854 X 5 = 19.8 cubic inches displacement per stroke. And, taking the duplex pump we have: 2 X 2 X .7854 X 3 X 2 = 18.8 cubic ins. displacement for each double stroke of the piston, or, plunger, showing that either pump is of ample capacity to feed the boiler at a fair piston speed.
To find the duty of a pumping engine when the number of pounds of coal burned, the number of gallons of water pumped, the pressure in pounds per square inch against which the pump piston works, and the height of suction are given : —
Rule* — Find the head in feet against which the pump works, by multiplying the pressure by 2.3, add the suction in feet to this head in order to get the total head. Multiply the gallons of water by 8J to get the pounds of water deliv- ered. Then multiply the total number of pounds of water by the head in feet, and divide the product by the number of pounds of coal divided by 100, and the result will give the duty in foot pounds. The duty of a pumping engine is the number of pounds of water raised one foot high for each 100 pounds of coal burned.
Example* — What is the duty of an engine pumping 2,890,000 gallons of water in 12 hours against a pressure of 30 pounds per sqr. inch, the suction being 12 feet, and coal burned 24,470 pounds? Ans. 8,070,426 foot pounds.
Operation: 30 X 2.3 = 70 nearly the head in feet.
And, 2,890,000 X 8£ == 24,083,333 pounds of water.
Also, 70 + 12 = 82 ft. total lift of water.
And, 24,083,333 X 82 = 1,974,833,306 Ibs. of water lifted one foot high in 12 hours.
Then, ^=,244.7.
616 HANDBOOK ON ENGINEERING.
And) 1,974888806 = 8>070>426.
To find the horse power of a pumping engine : —
Rule* — Divide the number of pounds of water raised one foot high in one minute by 33,000.
Example* — What is the H. P. of the pumping engine given in the above example? Ans. 83.11 H. P.
Operation: 12 X 60 = 720 minutes.
And, 1'974'833'8Q6 == 2,742,824 Ibs. of water raised one foot
7 &0
high in one minute 0
Then, ''^ 83.11. 33,000
To find the capacity of a pump to feed a boiler it is necessary to know how much water the boiler is capable of evaporating per minute or per hour. Each horse power of boiler capacity corre- sponds to an evaporation of thirty pounds of water per hour. It is good practice to operate a pump slowly and continuously, and for this reason the pump running at its normal speed should be capable of supplying about twice as much water as the boiler evaporates under usual conditions.
To find the diameter of water cylinder to deliver a certain num- ber of gallons of water per minute, when the stroke of the piston and the number of strokes per minute are given : —
Rule* — Multiply the number of gallons by 231, and divide the product by the stroke of the piston, and divide this quotient by the number of strokes per minute, and divide this last quotient by .7854, then extract the square root of the result for the diameter of the water piston.
Example* — A battery of boilers evaporate 100,000 pounds of water in one hour, what should be the diameter of water cylinder to supply this battery, the stroke of piston being 12 inches and making 100 strokes per minute? Ans. 7 inches.
HANDBOOK ON ENGINEERING. 617
100,000 Operation: ^Q — -=1666| pounds of water evaporated in
one minute.
L666| And, ' Qt ' = 200 galls, evaporated in one minute. Then
following the above rule we have : — 200X231 = 46200.
46200 And, -jg— ^3850.
3850 And, -J0JJ- ^38.5.
38.5 And' 77854 ==49-
Then, j/49 = 7" the required diameter.
To determine the H. P. of boiler a steam pump of given dimensions will supply when the number of strokes per minute are given : —
Rule* — Multiply the area of the piston is square inches by the stroke of piston in inches, and this product divided by 231 will give the gallons per stroke. Multiply this quotient by the num- ber of strokes per minute for the number of gallons per minute, and by 60 for the number of gallons per hour. Multiply this product by 8^ to find the number of pounds of water per hour deliA'ered by the pump, and divide this product by 30 for the H. P. of boiler the pump will supply. This rule is based upon the assumption that the full capacity of the water cylinder is deliv- ered at each stroke, no allowance being made for slippage, leak- age, or short strokes.
Example* — • The water piston of a steam pump is 6 inches in diameter and has a stroke of 12 inches, making 100 strokes per Vfeinute, what H. P. of boiler will the pump supply?
Ans. 2448 H. P.
618 HANDBOOK ON ENGINEERING .
Operation: 6 X 6 X .7854 =28.2744 sqr. ins. area of piston .
And, 28.2744 X 12 = 339.2928 cubic inches for one stroke.
339 2928
And, — i - — 1.4688 galls, per stroke. Z6 1
And, 1.4688 X 100 = 146.88 galls, per minute.
And, 146.88 X 60 = 8812.8 galls, per hour.
And, 8812.8 X 8£ = 73,440 pounds of water per hour.
73440
Then, Qn = 2448 H. P. of boilers. oU
Watt allowed one cubic foot (62£ Ibs.) of water per H. P. per hour. Then taking this allowance instead of 30 as above, we
73440
would have, go - =1175 H. P. of boilers which the above pump b J.O
would be suitable for, and which could be run very slowly, thus prolonging the life of the pump.
Even though a suction pipe should be perfectly air tight, a perfect vacuum cannot be formed in it, because water contains air, and even the coldest water gives off some vapor tending to impair the vacuum. Twenty-eight feet is a very good lift for a pump taking its water by suction.
Pnmp Formulas.
Gals, per Min. = .0034 X Diameter2 X Stroke in ins. X No. of
Strokes. Sq. of Diam. = Gals, per Min. -fr (.0034 X Stroke in ins. X
No. of Strokes).
Square of Diameter X 34 Length of Stroke = Gals, per Min. - No. of Stroke8
Square of Diameter X 34 No. of Strokes = Gals, per Min. - - Length of Stroke
HANDBOOK ON ENGINEERING.
619
CHAPTER XXI. MECHANICAL REFRIGERATION.
About the first thing asked by persons who are becoming interested in the subject of refrigerating and ice-making is, " Tell me how the thing is done ? "
Mechanical refrigeration, primarily, is produced by the evapo- ration of a volatile liquid which will boil at low temperature, and by means of a special apparatus the temperature and desired amount of refrigeration is placed under control of the operator.
Simplest Apparatus
Brine Tank or Concealer A.
Fig. 298. Elememtal refrigerating apparatus.
The simplest form of refrigerating mechanical apparatus consists of three principal parts: A, an u evaporator," or, as sometimes called, a " congealer," in which the volatile liquid is vaporized; -B, a combined suction and compressor pump, which
620
HANDBOOK ON ENGINEERING.
sucks, or properly speaking, " aspirates " the gas discharged by the compressor pumps, and under the combined action of the pump pressure and cold condenser, the vapor is here reconverted into a liquid, to be again used with congealer. We now see the function of the compressor pumps and condensers.
PRINCIPLES OF OPERATION.
The action of all refrigerating machines depends upon well- defined natural laws that govern in all cases, no matter what type of apparatus or machine is used, the principle being the same in all ; while processes may slightly vary, the properties of the par- ticular agent and manner of its use affecting, of course, the efficiency or economic results obtained.
Watef Suppl/
j^CondenserO
B B U H B y U B
— ^^^JSy EXPANSIONS
i Brine Tank or Congealer A.
Compression
Refrigerating
Apparatus
Three Parts
Fig. 299. Outline drawing of mechanical compression system.
OPERATION OF APPARATUS.
I
See Fig* 299* The apparatus being charged with a sufficient quantity of pure ammonia liquid, which we will, for simplicity, assume to be stored in the lower part of the condenser 0, a small cock or expansion valve controlling a pipe leading to the congealer
HANDBOOK ON ENGINEERING. 621
or brine tank A, is slightly opened, thus allowing the liquid to pass in the same office as a tube or flue in steam boiler and having precisely the same function, it may be called heating or steam making service. The amount of water capable of being boiled into steam in a boiler depends upon the square feet of heating surface, temperature of fire and pressure of steam ; and the same is true of the capacity of heating surface pre- . sented by the coils in the evaporator. The heat is transmitted through the coils from surrounding substance to the ammonia liquid, which is boiled into a vapor the same as water is boiled into steam in a steam boiler ; as previously explained, the heat thus becomes cooler ; the amount taken up and made negative being in proportion to the pounds of liquid ammonia evaporated.
FUNCTION OF THE PUMP AND CONDENSER.
The office of the compressor, pump and condenser is to re- convert the gas after evaporation into a liquid, and make the original charge of ammonia available for use in the same appa- ratus, over and over again. It will appear to the reader, after having carefully followed the text, that the pump and condenser might be dispensed with, but these conditions may only be eco- nomically realized when the at present expensive ammonia liquid can be obtained in great quantities and at less cost than the process of reconverting the vapor into a liquid by compression machinery and condenser on the spot.
WHAT DOES THE WORK?
The real index of the amount of cooling work possible is the number of pounds of ammonia evaporated between the observed range of temperature. To make the above clear, we will add that each pound of ammonia during evaporation is capable of Storing up a certain quantity of heat, and that the simplest forms
622 HANDBOOK ON ENGINEERING.
of refrigerating apparatus might consist, as shown by engraving, of two parts, to wit : A congealer and a tank of ammonia. In this apparatus the ammonia is allowed to escape from the tank into the congealer as fast as the coils therein are capable of evapo- rating the liquid into a gas. When completely evaporated the resulting vapor is allowed to escape into the atmosphere, which means it is wasted, the supply being maintained by furnishing fresh tanks of ammonia as fast as contents are exhausted. This process, while simple, would be tremendously expensive, costing at the rate of about $200 per ton, refrigerating or ice-melting capacity. To recover this gas and reconvert to a liquid on the spot in a comparatively inexpensive manner, is the object to be obtained.
MECHANICAL COLD EASILY REGULATED.
This being under the control of the cock or valve leading from the condenser called an expansion valve. As the gas begins to form in the evaporator, the compressor pump B is set in motion at such a speed as to carry away the gas as fast as formed, which is discharged into the condenser under such pressure as will bring about a condensation and restore the gas to the liquid state ; the operation being continuous so long as the machinery is kept in motion.
UTILIZING THE COLD.
To utilize the cold thus produced for refrigerating, two meth- ods are in use, the first of which is called the brine system ; the second is known to the trade as the direct expansion system, both of which systems will be explained at some length.
BRINE SYSTEM.
In this method, the ammonia evaporating coils are placed in a tank, which is filled with strong brine made of salt, which is well known not to freeze at temperature as low as zero. This is the brine
HANDBOOK. ON ENGINEERING. 623
tank or congealer A. The evaporating or expansion of the ammo- nia in these coils robs the brine of heat, as heretofore explained, the process of storing cold in the brine going on continuously and being regulated, as required, at the gas expansion valve. To practically apply the cold thus manufactured, the chilled brine or non-freezing liquid is circulated by means of a pump through coils of pipe which are placed on the ceilings or sides of the apart- ments to be refrigerated, the process being analogous to heating rooms by steam.
THE BRINE COOLS THE ROOMS.
The cold brine in its circuit along the pipes becomes warmer by reason of taking up the heat of the rooms, and is finally returned to the brine tank, where it is again cooled by the ammo- nia coils, the operation, of course, being a continuous one.
DIRECT EXPANSION SYSTEM.
By this method, the expansion or evaporating coils are not put in brine tanks, but are placed in the room to be refrigerated, and the ammonia is evaporated in the coils by coming in direct con- tact with the air in the room to be refrigerated, no evaporating tank being used.
RATING OF THE MACHINE IN TONS CAPACITY.
For the information of the unskilled reader, we will state that machines are susceptible of two ratings; that is, either their capacity is given in tons of ice they will produce in one day (24 hours), called ice-making capacity ; or they are rated equal to the cooling work done by one ton of ice-making per day (24 hours), called refrigerating capacity.
DIFFERENCE IN THESE RATINGS
Ordinarily the ice-making capacity is taken at about one-half of the refrigerating capacity, but this is only approximate,
624 HANDBOOK ON ENOINKKR1NG.
INSTRUCTIONS FOR OPERATING REFRIGERATING AND ICE- MAKING HACHINERY.
First, a competent engineer should be placed in charge of the plant, and he should be held responsible for the performance of the plant.
He should have charge of all help in the engine room, tank- room, and all men who work around the plant.
He should acquaint himself with all pipe and valves about the plant, so that in case of trouble, he will know what to do.
Valves should be provided in suitable places, so that if it be- comes necessary, he can transfer the ammonia from one part of the plant to another ; before attempting to transfer the ammonia, the engineer in charge should carefully see that he fully under- stands where the ammonia is to be put, and that there is suffi- cient space to contain same. In making transfers, always run the machine very carefully.
When starting the engine, start slowly, and before the pumps show a vacuum in the coils, open the regulating valve slightly, and then speed up the engine gradually.
The back pressure should be kept at about 15 pounds above zero, depending on the frost shown on suction pipe. When the machine is run to its full capacity, it should show frost on the suction pipe just above the brine tank ; in some machines, it is necessary to freeze back to machine, as the frost takes up the heat of compression and takes the place of the water jacket.
In general, the engineer in starting the machine, will first see that the discharge valves are open, then start the machine slowly, and open the suction valves slowly. When the machine is fully up to speed, watch the gauges and note the pressure. The con- denser pressure should be somewhere between 150 and 180 Ibs.
HANDBOOK -ON ENGINEERING. 625
depending upon the temperature of the water and atmosphere. The suction or back pressure should be about 20 pounds, unless the temperature of the brine in the tanks is below 18 degrees ; if it is, the low pressure should be reduced in proportion ; the frost on the suction pipe will determine the back pressure to be carried. It is advisable to use as high a back pressure as possible without frosting back.
Regulate the low pressure by means of the feed valves. The pressure should rise slowly ; watch carefully to see that the feed valves work regularly so that each valve may supply the proper amount of ammonia to the coils .
The frosting of the valves will indicate how they are working, and a little practice will enable the engineer to judge of this.
When the ammonia disappears from the liquid receiver, it is possible that too much feed has been given the coils, and that they are flooded ; it is well to shut off the main liquid valve to the tanks and pump them out until the back pressure falls to about five pounds ; the valve can then be opened and the regular operation resumed.
This pumping down is for the purpose of getting the ammonia all out of the tank coils, where it will sometimes lie; when this is the case, the suction line to the machine will be frosted, even when the tanks are not below temperature of 18 degrees ; when the tanks are below 18 degrees, frost will generally appear in the suction line to the machine.
In case of a leak in the pipe, the connections are made to the pumps so that the large valves on the suction and discharge pipes may be closed, and the small by-pass valves opened and by running the machine slowly, the discharge pipe system can be pumped into the suction and brine tanks. In case of a leak in the suction side, it is only necessary to shut off the liquid valve and pump all of the ammonia up into the condenser and keep it there by shutting the valve.
When shutting down a machine, close the liquid valve on the
626 HANDBOOK ON ENGINEERING.
brine tank, and run the machine until the pressure is brought down to zero on the gauge. Do not create a vacuum, because air is liable to leak into the pumps through the stuffing boxes.
It is well to watch the compressor carefully for leaks ; a leak into the cylinder either through leaky discharge valves, the gaskets or the cylinder head gasket between the cylinder and the discharge port, will materially reduce the compressor capacity. It will not take long for a compressor to waste a ton of coal.
If the engineer in charge of a compressor has a chance, he should take off the cylinder head and examine the cylinder gasket. If it looks bad, replace it with a new one; rub the valves to their seats with flour of emery and oil, and see that they have a good bearing ; also examine the valve cage gaskets.
A good test for a compressor, to see whether all connections are tight about the compressor, is to connect a pressure gauge to the indicator connection ; compress the gas in the cylinder so as to have a high pressure. Note the pressure on the gauge. If it does not decrease, the compressor and connections are tight. . If it decreases rapidly, either the valves need regrinding, or the piston needs new rings, or the cylinder should be rebored, or all these troubles may exist at the same time.
All pipe and fittings between the machine and condenser, should be looked after as all flanges are provided with lead gaskets, and these flanges should be examined occasionally, and when the plant is shut down and allowed to cool, the flanges should be tightened up.
The pipes of the condensers should be kept as clean as possible, so that the water will flow evenly over all pipes alike, in order to extract as much heat as possible from the ammonia.
The colder the ammonia can be kept in the condenser, the
HANDBOOK ON ENGINEERING. 627
more work it will do in the tanks ; on this account, well water 18 to be preferred.
The oil trap on the line from the machine to the condenser, should be examined once every ten days and the oil drawn off.
If the system gets clogged with oil, and where there is more than one tank, pump the brine into the other tanks and when the brine is all out of the tank, disconnect the coil at top and bottom, con- nect steam, attach a gauge, and then drive a pine plug in bottom of coil and put about 30 pounds of steam on coil for ten or twenty minutes ; on the bottom of the return header is a purge cock that must be opened frequently, while the steam is on coil. Then knock plug out of coil at bottom, and let the steam come through coil for a short time, and then disconnect the steam and connect the air pump to the coil and put on thirty pounds air pressure for ten minutes ; all coils must be treated in the same way.
If there is only one tank, the coils must be taken out of tank and blown out, or the brine pumped into the cans. At the same time, the expansion valves must be overhauled. After all coils and headers are connected the whole should be tested for leaks, first, under air pressure, and second, with ammonia and a sulphur stick while the tank is empty.
The sulphur sticks are prepared by dipping a stick of wood into melted sulphur. The sticks are then burned close to where leaks are suspected. Any leak is at once indicated by a white
smoke. •
STEAH CONDENSERS.
Steam and ammonia condensers should be kept clean and free from all scale, and should be supplied with sufficient water to condense the steam and ammonia.
628 HANDBOOK ON ENGINEERING.
THE REBOILERS.
The reboilers are for the purpose of removing any air or gases which may be in the steam. The water in the reboilers should at all times be kept boiling, for if it is not, the ice will be white. The regulating valves on the reboilers should be exam- ined often, to see that they are not sticking. A steam connection should be provided in the flat coolers, so that after shutting off the water, which flows over the cooler, and the water from the reboilers, steam may be blown through it from the top downward and out at the bottom of the coil ; this should be done frequently, land it will be found to save the filters.
The oil separator should be examined at least once a year and cleaned. The object of this separator is to remove the oil from the steam, and, if working properly, there should be a small stream of water and oil flowing from the drain.
AIR IN THE SYSTEM.
When air or permanent gases are in the system, it will be manifested by unusually high condenser pressure, and the effi- ciency of the machine will be reduced. To remove the air, attach a bent piece of one-fourth inch pipe to the small valve placed on the top of the condenser ; place the other end of the pipe in a bucket of water ; open the valve slightly, and if air is present, it will bubble up through the water, while the ammonia will produce a crackling noise, the same as when steam is turned into water,
GASES IN THE PLANT.
Accumulation of gases in a plant sometimes consists of atmos- pheric air, but sometimes also of hydrogen and nitrogen, due to the decomposition of ammonia.
HANDBOOK -ON ENGINEERING. 629
The best way to remove these gases from the system, is by drawing them off at the top of the ammonia condenser coils, where a small valve will be found on top of each coil where a small pipe may be attached to the small valves ; put the other end in a bucket of water. If, on opening the valve, bubbles are seen to escape through the water, the valve should be kept open as long as such bubbles appear ; when a crackling noise is heard in the water, close the valve.
Every engineer should keep himself posted as to the exact clearance existing between the piston and the head or heads of the compressor. A convenient way to ascertain this, is to remove one of the valves from the compressor head and insert a piece of soft lead rolled in the shape of a wire through the valve chamber into the cylinder and pinch the machine over until the piston of the compressor squeezes the lead against the head. When the lead is withdrawn, the exact clearance will be shown.
If the valves pound, it may be that the valves have too much lift. Try a stiffer spring. A spring that is too stiff will also cause valves to pound.
Never create a vacuum in an ammonia system, unless it is absolutely necessary to repair a leak or for similar purposes ; it will have a tendency to admit air into the system ; the air must be kept out ; pump to zero on the gauge, but no lower.
Never put any ammonia in a plant until it has been tested ; this can be done by drawing a sample out of the drum and seeing that it will all evaporate and leave no residue.
Keep a record of the temperatures of brine and condensing water, and evaporating and condensing pressures.
It is a good plan to have a duplicate set of valves on hand, all ready to replace any leaky valve.
A leaky suction valve is sometimes the cause of considerable loss in capacity. It can be located by heat on the suction con- nection or by the hiss that is ever present when a valve leaks, or by the appearance of the valve.
630 HANDBOOK ON ENGINEERING.
Test the oil that is being used in the compressors by subject- ing a sample to low temperature — get a bottle of the oil and cover with fine ice and salt ; the result will demonstrate whether it will stand a low temperature or not. If the oil gets thick and gummy, and a separation occurs, leaving a thin transparent, watery liquid, in which the heavy part of the oil settles, and which gives off an odor like benzine. Reject the oil, as it will produce gases in the system, and give trouble.
Oil may be tested with ammonia gas ; animal fat will saponify when subjected to alkali tests.
In ice plants, the engineer should see that the ice is always pulled regularly. The distilled water is supplied regularly and it should be used in the same way ; pull but one can and refill before pulling the next.
Keep the brine in the tanks over the top pipe ; at the end of the season, when the plant is shut down, leave the cans in the brine for if the cans are taken out, the brine will be lowered and where the pipes are exposed, they will rust very fast ; keep the tank covers clean. The strength of the brine should be about 80 on a saltometer.
If ice forms on the coils, the brine is weak, and the brine must be strong enough so it will not freeze.
In making repairs to coils, while immersed in brine the work- men should besmear their arms and hands with cylinder oil, or lard or tallow, as that will enable them to keep them in the brine longer.
In case the temperature of the brine rises above 30 de- grees, do not attempt to reduce the temperature without first examining the cans to see whether the ice has thawed loose from them; in case it has thawed, pull all ice and refill the cans before reducing temperature ; if this is not done, the freezing of the water around the ice in the cans will burst them.
HANDBOOK ON ENGINEERING. 631
TESTING FOR WATER BY EVAPORATION.
As shown by the engraving, screw into the ammonia flask a piece of bent one-quarter inch pipe, which will allow a small bot- tle to be placed so as to receive the discharge irom it. This test bottle should be of thin glass with wide neck, so that quarter-inch pipe can pass readily into it, and of about 12 cubic inches capac- ity. Put the wrench on the valve and tap it gently with a ham- mer. Fill the bottle about one-third full and throw sample out in order to purge valve, pipe and bottle. Quickly wipe off mois- ture that has accumulated on the pipe, replace the bottle and open
Fig. 300. Showing connections to flask.
valve gently, filling the bottle about half full. This last operation should not occupy more than one minute. Remove the bottle at once and insert in its neck a stopper with a vent hole for the escape of the gas. A rubber stopper with a glass tube in it is the best, but a rough wooden stopper, loosely put in, will answer the purpose. Procure a piece of solid iron that should weigh not less than eight or ten pounds, pour a little water on this and place the bottle on the wet place. The ammonia will at once begin to boil, and in warm weather will soon evaporate. If any residuum, pour it out gently, counting the drops carefully. Eighteen drops are about equal to one-tenth of an ounce, and if the sample taken
632
HANDBOOK OX ENGINEERING.
amounts to, say, 6 cubic inches, we can readily approximate the percentage of the liquid remaining.
Fig. 301. Sectional view of 10-ton refrigerating machine.
LUBRICATION OF REFRIGERATING MACHINERY.
It is well to speak of this, for the reason that it is an important subject ; and some users of machinery think that a cheap, low
HANDBOOK ON ENGINEERING. 633
grade of oil is really the cheapest. To disabuse their minds of this idea and suggest the necessity of high grade oils, both on the score of economy and to keep the machinery at all times in efficient running order, we suggest the following: First-class refrigerating machinery calls for the use of at least three different kinds of oil, Nos. 1, 2 and 3, each of high grade : —
No* J* For use in the steam cylinder, and is known in the trade as cylinder oil. This ranges in price from 50c, to $1 per gallon. Good cylinder oil should be free from grit, not gum up the valves and cylinder, should not evaporate quickly on being subjected to heat of the steam, and when cylinder head is removed, a good test is to notice the appearance of the wearing surfaces ; they should be well coated with lubricant which, upon application of clean waste, will not show a gummy deposit or blacken. Use this oil in a sight feed lubricator with regular feed, drop by drop.
No* 2* For use of all bearing and wearing surfaces of machine proper — an oil that will not gum, not too limpid, with good body, free from grit or acid and of good wearing quality, flowing freely from the oil cups at a fine adjustment without clogging, and a heavier grade should be used for lubricating the larger bearings.
No* 3* For use in compressor pumps. This oil should be what is called a cold test, or zero oil, of best quality.
Best paraffine oil is sometimes used ; as also a clear West Vir- ginia crude oil. This oil, when subjected to a low temperature, should not freeze.
EFFECTS OF AMMONIA ON PIPES.
Ammonia has no chemical effect upon iron ; a tank, pipe or stop-cock may be in constant contact with ammonia for an in- definite time and no action will be apparent. The only protec- tion, therefore, that ammonia-expanding pipes require is from corrosion on the outer surface. As long as the pipes are covered
634 HANDBOOK ON ENGINEERING.
with snow or ice, corrosion does not occur ; the coating of ice thoroughly protects them from the oxidizing effect of the atmos- phere ; but alternate freezing and thawing requires protected sur- faces, which are best obtained by applying a coat of paint every season.
Expansion coils having to withstand but a maximum working pressure of thirty pounds per square inch, are constructed with such absolute security, in whole and in detail, as to make them one of the most perfect pipe constructions on a large scale ever applied in practice.
Fig. 302. Position of tank to be emptied.
TO CHARGE THE SYSTEM WITH AMMONIA.
Position of the tank should be as shown, the outlet valve pointing upwards and the other end of the tank raised 12" to 15". The connection between the outlet valve of the tank and the inlet cock of the system should be a |" pipe. In charging, open valve of the tank cautiously to test connection ; if this is tight, open valve fully ; start machine and run slowly till tank is empty. The tank is nearly empty when frost begins to appear on it ; run the machine till suction gauge reaches atmospheric pressure. If it holds at this pressure when machine is stopped, the tank is empty ; if not, start up again. In disconnecting, close the valve on the tank first, the inlet cock of the system. Weigh tank
HANDBOOK (ON ENGINEERING. 635
before and after emptying ; each standard tank contains from 100 to 110 pounds of ammonia.
PROCESS OF MECHANICAL REFRIGERATION.
The process of mechanical refrigeration is simply that of removing heat, and mechanism is necessary, because the rooms and articles from which the heat is to be removed are already as cold, or colder than their surroundings, and consequently, the natural tendency is for the heat to flow into them instead of out of them. The fact that a body is already cold does not prevent the removal of more heat from it and making it still colder. The term cold describes a sensation and not a physical property of matter ; the coldest bodies we commonly meet with are still possessed of a large quantity of heat, part of which, at least, can be abstracted by suitable means. The only means by which heat can be removed from a body is to bring in contact with it a body colder than itself. This is the function that ammonia performs in mechanical refrigeration. It is so manipulated as to become colder than the body we wish to cool. The heat thus abstracted by it is got rid of by such further manipulation that (while still retaining the heat it has absorbed) it will be hotter than ordi- nary cold water, and therefore, part with its heat to it. Ammonia thus acts like a sponge. It sops up the heat in one place and parts with it in another, the same ammonia constantly going backward and forward to fetch and discharge more heat. The complete cycle of operation comprises three parts : —
1st. A compression side, in which the gas is compressed.
2d. A condensing side, generally consisting of coils of pipe, in which the compressed gas circulates, parts with its heat and liquefies.
3d. An expansion side, consisting also of coils of pipe, in which the liquefied gas re-expands into a gas, absorbs heat, and performs the refrigerating work.
()36 HANDBOOK ON ENGINEERING.
In order to render the operating continuous, these three sides or parts are connected together, the gas passing through them in the order named. The liquefied gas is allowed to flow into the expansion or evaporating coils, where it vaporizes and expands under a pressure varying from 10 to 30 pounds above that of the atmosphere, when ammonia is the agent in use. The gas then passes into the compressor, is compressed and forced into the condensers, where a pressure from 125 to 175 pounds per square inch usually exists ; here liquefaction takes place and the re- sulting liquefied gas is allowed to flow to a stop-cock having a minute opening, which separates the compression from the expan- sion side of the plant. The expansion side consists of coils of pipe similar to those of the condensing side, but used for the reverse operation, which is the absorption of heat by the vapor- ization of liquefied gas instead of the expulsion of heat from it, as in the former operation. Heat is conducted through the ex- pansion or cooling coils to, and is absorbed by, the vaporizing and expanding liquefied gas within such coils, for the reason that they are connected to the suction or low pressure side of the apparatus from which the compressors are continually drawing the gas and thereby reducing the pressure in said coils, as already stated, to a pressure of 10 to 30 pounds above the atmosphere; it being kept in mind that liquefied ammonia in again assuming a gaseous condition, has the power or capacity of reabsorbing, upon its expansion, a large quantity of heat. The liquefied gas entering these coils through the minute openings of the stop-cock, above referred to, is relieved of a pressure of 125 to 175 pounds, the amount requisite to maintain it in a liquid condition, when it begins to boil, and in so doing passes into the gaseous state. To do this it must have heat, which can be supplied only from the substance surrounding the pipes, such as air, brine, wort, etc. As a natural result the surrounding substances are reduced in temperature, or cooled.
HANDBOOK ON ENGINEERING.
637
PURGING VALVE
IDICATOR VALVE
Sectional yiew of « Eclipse" Compressor.
638
HANDBOOK ON ENGINEERING.
304. Section of De La Vergne Donble-Acting Vertical Ammonia Compressor.
HANDBOOK ON ENGINEERING.
639
640
HANDBOOK ON ENGINEERING.
THE DE LA VERQNE SYSTEM.
The diagram on page 640 is seen to be extremely simple in conception. Ammonia gas is received by the compressor ^ from which it is discharged into the pressure tank B. The gas continues into the condenser, where it is liquified and collects in the liquid storage tank D. The liquid ammonia is taken off from the bottom of the second tank and passes through the expansion cock E into the expansion or refrigerating coil, where it boils into vapor. This is drawn off into the compressor to pass around again in the order above described. Before entering the com- pressor the gas passes through the scale separator or trap shown near the gauge plate where any scale or foreign matter is re- moved from the ammonia.
Fig. 306. A Diagram of the De La Vergne System.
HANDBOOK ON ENGINEERING.
64!
642 HANDBOOK ON ENGINEERING.
On page 641 is shown in diagram the general arrangement of a standard De La Vergne Refrigerating System with horizontal machine. The hot gas discharged by the compressor passes first to the pressure tank from whence it passes up the riser marked hot gas line, through a check valve and down a header through two inch pipes and soft seated globe valves of the same size to the individual stands of atmospheric condensers at the bot- tom, and as the liquid forms, it is drawn off at different levels through the several small pipes shown in the illustration, and passes into the liquid header from where it goes to the liquid tank. The outlet from the liquid header rises a few inches to form a gooseneck, which maintains a liquid seal on the condenser and prevent gas from the pressure tank from getting into the liquid line leading to the expansion coils. The liquid line from the con- denser is provided, just before it reaches the liquid tank, with a pocket into which any scale or foreign matter is precipitated.
DE LA VERGNE CAN ICE MAKING PLANT.
In the distilling apparatus for can ice plants, illustrated on page 643 , the exhaust steam from the engine which drives the compressor is passed first through a grease separator A, in which the exhaust steam impinging on the water in the bottom of the shell and the baffle plate between the inlet and the outlet, pre- cipitates and entrained oil. From the grease separator the steam passes the usual boiler feed water heater J5, and is finally con- densed in the surface steam condenser (7, the condensation from which together with that from the feed water heater passes to the combined skimmer and reboiler D.
In the reboiler the ebullition is effected in a central tank, con centric to which is a second or outer tank, the space between the two being utilized as a skimming tank. The overflowing wate in the jacket of the skimming tank prevents radiation of hea from the reboiling tank proper, and there being no ebullition in
HANDBOOK ON ENGINEERING.
643
644 HANDBOOK ON ENGINEERING.
this outer tank to disturb the surface of the water, skimming is effected with a minimum loss of sweet water.
From the reboiler the water passes to the hot water storage tank, E.
In order to keep the remaining parts of the distilled water sys- tem filled at all times and thereby prevent any re-absorption of air which might otherwise take place, a regulating mechanism is employed which in case of low water in the hot water storage tank, closes the valve through which the water passes into the hose of the can filler.
Ordinarily the hot, reboiled, distilled water from tank E, passes through the condensed water cooling coil F, over which is showered cold water from the main supply line. The hot dis- tilled water enters this cooler from below, and leaving the top of the water-cooling coil, it then again passes downward and through the deodorizer H. This device consists of a cylindrical shell of am- ple dimensions filled with charcoal. The water is introduced through a strainer under a false bottom so perforated as to give the upward flow of water an even distribution over the entire cross section of the filter bed. At the top the water passes a second strainer from which it flows to the can filler.
The liquid ammonia leaves the liquid tank at the bottom through the main liquid line, a branch from which after passing through a strainer is connected with the main suction line just above the compressor cylinder, and supplies liquid for regulating compressor temperatures while starting up, pumping out, etc.
Just outside the main liquid valve a small connection is made into the main liquid line to which ammonia drums may be con- nected for charging the system. Beyond this connection the main line passes to the cold storage rooms and branches out to the individual expansion valves on the various cooling coils.
The ammonia gas returning from each coil passes through a two inch soft metal seated globe valve, which together with the
HANDBOOK ON ENGINEERING.
645
0,
o
be
£
646
HANDBOOK ON ENGINEERING.
expansion valve allows the individual coils to be pumped out, shut off and disconnected.
The main suction line is provided with a scale separator or trap which prevents any scale or other foreign substances from entering and damaging the compressor and valves.
The compressor is lubricated by means of a small oil pump shown attached to the right hand side of the machine. The oil from this pump is forced through a three-way cock, through the
Fig. 310* Twin cylinder compressor, witn
steam cylinders
piston rod stuffing box lantern and into the oil pot situated just above the stuffing box. The second line leading from the three-way cock connects with the pressure tank and through this line the oil carried over with the ammonia gas may be blown back through a strainer into the lubricating system.
The system is arranged with by-passes so that the ammonia from any part of the whole of the high pressure side can be pumped out and discharged into the low pressure side.
HANDBOOK ON ENGINEERING. 647
Through the connection between the suction and equalizing lines (shown just above the gauge board in the cut), any one stand of the condensers can be pumped out singly.
Both the liquid and pressure tanks are provided with gauge glasses so that the height of tlie oil or liquid ammonia can be readily observed at any time.
The condensers are provided with a purging and equalizing header running the entire width of the battery of condensers con- nected with each stand through a half-inch soft metal seated valve. The impure gases collecting at the top of the condensers may be purged from the header through the blow-off valve.
Any ammonia gas entering the oil pot from the stuffing box lanterns or from the oil blown back from the back pressure tank passes up through the equalizer from the oil pot and enters the main suction from the top. A continuation of this furnishes the low pressure gauge connection, while the high pressure gauge is connected to the pressure tank.
648 HANDBOOK ON ENGINEERING.
CHAPTER XXII.
SOflE PRACTICAL QUESTIONS USUALLY ASKED OF EN- GINEERS WHEN APPLYING FOR LICENSE.
Q. If you were called on to take charge of a plant, what would be your first duty? A. To ascertain the exact condition of the boiler and all its attachments (safety-valve, steam-gauge, pump, injector) and engine.
Q. How often would you blow off and clean your boilers if you had ordinary water to use? A. Twice a month.
Q. What steam pressure will be allowed on a boiler 50" diam- eter, f" thick, 60,000 T. S. £ of tensile strength factor of safety? A. One-sixth of tensile strength of plate, multiplied by thick- ness of plate, divided by one-half of the diameter of boiler, gives safe working pressure.
Q. How much heating surface is allowed per horse-power by builders of boilers ? A. 12 to 15 feet for tubular and flue boilers.
Q. How do you estimate the strength of a boiler? A. By its diameter and thickness of metal.
Q. Which is the best, single or double riveting? A. Double riveting is from 16 to 20 per cent stronger than single.
Q. How much grate surface do boiler-makers allow per horse- power? A. About f of a square foot.
Q. Of what use is a mud drum on a boiler, if any? A. For collecting all the sediment of a boiler.
Q. How often should it be blown out? A. Three or four times a day, in the morning before starting, and at noon.
Q. Of what use is a steam dome on a boiler? A. For storage of dry steam.
HANDBOOK ON ENGINEERING. 649
Q. What would you do if you should find your water gone from sight very suddenly? A. If a light fire draw and cool off as quickly as possible ; if a heavy fire cover with wet ashes or slack coal. Never open or close any outlets of steam when your water is out of sight.
Q. What precautions should you take to blow down a part of the water in your boiler while running with a good fire? A. Never leave the blow-off valve, and watch the water level.
Q, How much water would you blow off at once while running ? A. Never blow off more than one gauge of water at a time while running.
Q. What precautions should the engineer take when necessary to stop with heavy fires? A. Close dampers, put on injector or pump, and if a bleeder is attached, use it.
Q. What is an engineer's first duty on entering a boiler-room? A. To ascertain the true water level, and look at steam gauge.
Q. When should a boiler be blown out? A. After it is cooled off — never while it is hot.
Q. When laying up a boiler what should be done? A. Clean thoroughly inside and out ; remove all ' 4 Rust ' ' and paint rust places with red lead ; examine all stays and braces to see if any are loose or badly worn.
Q. Of what use is the indicator? A. The indicator is used to determine the power developed by an engine, to serve as a guide in setting valves and showing the action of steam in the cylinder.
Q. How would you increase the power of an engine? A. To increase the power of an engine, increase the speed, or get higher pressure of steam ; or use less expansion.
Q. How do you find the horse-power of an engine? area of piston X M.E.P. X piston speed. 33,000.
Q. Which has the most friction, a perfectly fitted, or an im- perfectly fitted valve or bearing? A. An imperfect one.
650 HANDBOOK ON ENGINEERING .
Q. How hot can you get water under atmospheric pressure with exhaust steam? A. 212°.
Q. Does pressure have any influence on the boiling point? A. Yes.
Q. Which do you think is the best economy, to run with your throttle wide open or partly shut? A. Always have the throttle wide open on a governor engine.
Q. At what temperature has iron the greatest tensile strength? A. About 600°.
Q. About how many pounds of water are required to yield one horse-power with our best engines? A. From 15 to 30.
Q. What is meant by atmospheric pressure? A. The weight of the atmosphere.
Q. What is the weight of atmosphere at sea level? A. 14.7 pounds per square inch.
Q. What is the coal consumption per hour per indicated horse- power? A. Varies from 1| to 7 Ibs.
Q. What is the consumption of coal per hour on a square foot of grate surface? A. From 10 to 12 Ibs.
Q. What is the water consumption in pounds per hour per indicated horse-power? A. From 15 to 45 Ibs.
Q. How many pounds of water can be evaporated with one pound of best soft coal? A. From 7 to 10 Ibs.
Q. How much steam will one cubic inch of water evaporate under atmospheric pressure? A. One cubic foot of stearo ( approximately) .
Q. What is the weight of a cubic foot of fresh water? A. 62.425 Ibs.
Q. What is the weight of a cubic foot of wrought iron? A. 480 Ibs.
Q. What is the last thing to do at night before leaving the plant? A. Look around for greasy waste, hot coals, matches, 01 anything which could fire the building.
HANDBOOK ON ENGINEERING. 651
Q. What is the weight of a square foot of one-half inch boiler plate? A. 20 Ibs.
Q. How much wood equals one ton of soft coal for steam pur- poses? A. About 4,000 Ibs. of wood.
Q. What is the source of all power in the steam engine? A. The heat stored up in the coal.
Q. How is the heat liberated from the coal ? A. By burning it — that is, by combustion.
Q. Of what does coal consist? A. Carbon, hydrogen, nitro- gen, sulphur, oxygen and ash.
Q. What are the relative proportions of these that enter into coal? A. There are different proportions in different specimens of coal, but the following shows the average per cent : Carbon, 80 ; hydrogen, 5 ; nitrogen, 1 ; sulphur, 2 ; oxygen, 7 ; ash, 5.
Q. What must be mixed with coal before it will burn? A. Air.
Q. Of what is air composed? A. It is composed of nitrogen and oxygen in the proportion of 77 per cent nitrogen to 23 of oxygen.
Q. What parts of the air mix with what parts of coal? A. The oxygen of the air mixes with the carbon and hydrogen of the coal.
Q. How much air must mix with coal? A. 300 cubic feet of air for every pound of coal.
Q. How many pounds of air are required to burn one pound of carbon? A. From 20 to 24, generally taken at 24.
Q. How many pounds of air to burn one pound of hydrogen? A. Thirty-six.
Q. Is hydrogen hotter than carbon? A. Yes, 41 times hotter.
Q. What part of the coal gives out the most heat? A. The hydrogen does part for part, but as there is so much more of carbon than hydrogen in the coal, we get the greatest amount of heat from the carbon.
652 HANDBOOK ON ENGINEERING.
Q. In how many different ways is heat transmitted? A, Three, by radiation, by conduction and convection.
Q. If the fire consisted of glowing fuel, show how the heat enters the water and forms steam ? A. The heat from the glow- ing fuel passes by radiation through the air space above the fuel to the furnace crown ; there it passes through the iron of the crown by conduction ; there, it warms the water resting on the crown, which then rises and parts with its heat to the colder water by conduction till the whole mass of water is heated ; then the heated water rises to the surface and parts with its steam, so a constant circulation is maintained by convection,
Q. Of what does water consist? A. Oxygen and hydrogen.
Q. In what proportion? A. Eight of oxygen to one of hydrogen, by weight.
Q. What are the different kinds of heat? A. Latent heat, sensible heat and sometimes, total heat.
Q. What is meant by latent heat? A. Heat that does not affect the thermometer and which expends itself in changing the nature of a body, such as turning ice into water or water into steam.
Q. Under what circumstances do bodies get latent heat? A. When they are passing from a solid state to a liquid state, or from a liquid to a gaseous state.
Q. How can latent heat be recovered? A. By bringing the body back from a state of gas to a liquid, or from that of a liquid to that of a solid.
Q. What is meant by a thermal unit? A. The heat necessary to raise one pound of water, at any temperature — one degree Fan.
Q. If the power is in coal, why should we use steam? A. Be- cause, steam has some properties which make it an invaluable agent for applying the energy of the heat to the engine.
Q. What is steam ? A. It is an invisible vapor generated from water by the application of heat.
Q. What are the properties which make it so valuable to us ?
HANDBOOK ON ENGINEERING. 653
A. 1. The ease with which we can condense it. 2. Its great expansive power. 3. The small space it occupies when con- densed.
Q. Why do you condense the steam? A. To form a vacuum and so destroy the back pressure that would otherwise be on the piston, and thus get more useful work out of the steam.
Q. What is vacuum? A. A space void of air.
Q. How do you maintain a vacuum? A. By the steam used being constantly condensed by the cold water or cold tubes, and the air pump constantly clearing the condenser of air.
Q. Why does condensing the used steam form a vacuum? A. Because a cubic foot of steam at atmospheric pressure shrinks into about a cubic inch of water.
Q. What do you understand by the term horse-power? A. A horse-power is equivalent to raising 33,000 Ibs. one foot per min- ute, or 550 Ibs. raised one foot per second.
Q. What do you understand by lead on an engine's valve? A. Lead on a valve is the admission of steam into the cylinder be- fore the piston starts its stroke.
Q. What is the clearance of a cylinder as the term is applied at the present timer A. Clearance is the space between the cylinder head and the piston head, with ports included.
Q. What are considered the greatest improvements on the stationary engine in the last forty years? Ac The governor, the Corliss valve gear, and the triple expansion engine.
Q. What is meant by triple expansion engine ? A. A triple expansion engine has three cylinders, using the steam expansively in each one.
Q. Is there any danger of a well-fitted and tightly-keyed fly- wheel coming loose? A. Yes ; water in the cylinder by produc- ing a heavy jar would tend to loosen a fly-wheel and frequently reversing an engine under a load arid high speed, would tend to produce the same effect.
654 HANDBOOK ON ENGINEERING.
Q. What is a condenser as applied to an engine ? A. The con- denser is a receptacle into which the exhaust steam enters and is there condensed.
Q. What are the principles which distinguish a high-pressure from a low-pressure engine? A. Where no condenser is used and the exhaust steam is open to the atmosphere it is high pressure.
Q. About how much gain is there by using the condenser? A. 17 to 25 per cent, where cost of water is not figured.
Q. What do you understand by the use of steam expansively? A. Where steam admitted at a certain pressure is cut off and allowed to expand to a lower pressure.
Q. How many inches of vacuum give the best results in a con- densing engine? A. Usually considered 25".
Q. What is meant by a horizontal tandem engine? A. One cylinder being behind the other, with two pistons on same rod.
Q. What is a Corliss valve gear ? A. (Describe the half moon, or crab-claw gear, or oval-arm gear with dash pots.)
Q. From what cause do belts have the power to drive shafting? A. By friction or adhesion.
Q. What do you understand by lap? A. Outside lap is that portion of valve which extends beyond the ports when valve is placed on the center of travel ; and inside lap is that portion of valves which projects -over the ports on the inside or towards the middle of valve.
Q. What is the use of inside lap? A. To give the engine compression.
Q. Where is the dead center of an engine? A. The point where the crank and the piston rod are in the same right line.
Q. In what position would you place an engine to take up any lost motion of the reciprocating parts ? A. Place the engine in the position where the least wear takes place on the journals. That is, in taking up the wear of crank-pin brasses, place the engine on either dead center, as when running, there is little wear
HANDBOOK ON ENGINEERING. 655
upon the crank-pin at these points. If taking up the cross-head pin brasses — without disconnecting and swinging the rod — place the engine at half stroke, which is the extreme point of swing of the rod, there being the least wear on the brasses and cross-head pin in this position.
Q. What benefits are derived from using fly-wheels on steam engines ? A. The energy developed in the cylinder while the steam is doing its work, is stored up in the fly-wheel, and given out by it while there is no work being done in the cylinder — that is, when the engine is passing the dead centers. This tends to keep the speed of the engine shaft steady.
Q. Name several kinds of reducing motions, as used in indi- cator practice? A. The pantograph, the pendulum, the brumbo pulley, the reducing wheel.
Q. How can an engineer tell from an indicator diagram whether the piston or valves are leaking? A. Leaky steam valves will cause the expansion curve to become convex ; that is, it will not follow hyperbolic expansion, and will also show increased back pressure. But if the exhaust valves leak also, one may offset the other, and the indicator diagram would show no leak. A leaky piston can be detected by a rapid falling in the pressure on the expansion curve immediately after the point of cut-off. It will also show increased back pressure. A falling in pressure in the upper portion of the compression curve shows a leak in the exhaust valve.
Q. What would be the best method of treating a badly scaled boiler, that was to be cleaned by a liberal use of compound? A. First, open the boiler up and note where the loose scale, if any, has lodged. Wash out thoroughly and put in the required amount of compound. While the boiler is in service, open the blow-off valve for a few seconds, two or three times a day, to be assured that it does not become stopped up with scale. After running the boiler for a week, shut it down, and when the
HANDBOOK ON ENGINEERING .
pressure is down and the boiler cooled off, run the water out and take off the hand-hole plates. Note what affect the compound has had on the scale, and where the disengaged scale has lodged. Wash out thoroughly and use judgment as to whether it is advis- able to use a less or greater quantity of compound, or to add a small quantity daily. Continue the washing out at short intervals, as many boilers have been buined by large quan- tities of scale dropping on the fire sheets and not being removed.
Q. What is an engineer's first duty upon taking charge of a steam plant? A. The first duty of an engineer assuming charge of a steam plant is to familiarize himself with his surroundings, ascertain the duty required of each and every piece of machinery contained therein, and in just what condition each one is. Let us discuss it at length, assuming that when just engaged he is informed as to the nature of the work required of the plant in question, namely: Whether it is a heating plant, electric lighting, hydraulic or electric elevator, power station, or any other kind of the various steam plants in existence. Of course, a great deal depends upon the size and kind of plant under con- sideration and the number of men employed, hours in operation, and some other things in general which most engineers know of. He should first see just what his plant contains "from cellar to garret," so to speak ; whether all that is contained has to run continually, or almost so, and what can be depended on in case anything should suddenly become deranged or give out entirely. Next, he should ascertain the general condition of everything, going over each portion in turn, as time and opportunity permit, and conclude from what he has seen how much longer it may be run safely and economically. It will be remembered that a piece of machinery may be run safely and yet not with economy. So, if he should wait for the safety limit to be reached, without taking other things into consideration, he might wait
HANDBOOK ON ENGINEERING. 657
a long time and in so doing waste many dollars of his employer's money before it was thought necessary to reno- vate, repair or renew. In going over everything, examining each part critically, it would be well to make copious notes, and, sketches might be added, to which the engineer can again refer. It sometimes happens that engineers, in making an examination of machinery, do not take dimensions or make sketches of certain parts, which have to be repaired, or perhaps renewed, thinking that the next time the apparatus is looked at will do for that. Now, it sometimes happens that the " next time " is the time when some accident occurs, finding him unprepared, causing con- fusion, in the midst of which the making of sketches and taking of dimensions cannot be thought of. All such should be done at the first opportunity, and spare parts of the different machinery should be kept on hand, especially in the case of a plant which has only the machinery which is constantly in use. Another point of importance to which an engineer should give attention, is to ascertain the quantity and kind of supplies which are on hand, that he may know when to make requisition for more, and so not run short, as he otherwise might do. It is also important to see what tools the plant contains and upon what he can depend in case of the break -down of any part of the machinery. Of course all the above cannot be done in one day, but no time should be lost in doing all these things as early as possible, for the sooner he gets all the particulars and details of his plant at his "fingers' ends," the lighter will be his own labors, and the more free will his mind be to think and act intelligently for the emergencies of the future. Therefore, by performing this first duty as early and thoroughly as possible, the succeeding ones will be comparatively easy to handle and perform, for the reason that he will be prepared for them.
Q. Define and explain the difference between sensible and latent heat? A. The difference between sensible and latent heat
42
658 HANDBOOK ON ENGINEERING.
is explained thus : Sensible heat may be measured with a ther- mometer, that is, it affects the mercury in a thermometer, caus- ing it to rise in the stem so that the degree of heat may be measured on the graduated scale affixed. Latent heat does not affect the thermometer. Bodies get latent heat when they are passing from a solid state to a liquid state, and also when passing from a liquid to a gaseous state ; and moreover, this latent heat can be recovered bj bringing a body back from a gaseous to a liquid state, and from liquid to solid. Water is most com- monly seen under the three forms of matter just mentioned, namely, solid, ice ; liquid, water ; gaseous, steam. The following method has -been used to explain how latent heat exists : A quantity of powdered ice is placed in a vessel and brought into a very warm room. As long as it remains as ice, it may be any degree of heat below 32° Fahr., but the instant it begins to melt, owing to the heat of the room, a thermometer placed in it will record 32° Fahr. The thermometer will continue at 32° as long as there is any ice in the vessel, but just as soon as the last piece of ice has melted it will begin to rise, and continue to do so until the water boils, when it will stand at 212° ; but although the water goes on receiving heat after this, the instrument will stand at 212° until all the water has boiled away. Now, a great amount of heat must have entered the water since the ice began to melt, but it has no effect on the thermometer, which continues at 32°, as noted above ; the heat that has so entered is called ' ' the latent heat of water." The heat that has entered the water from boiling till it all becomes steam is called the " latent heat of steam." The latent heat of water has been found to be 143° Fahr. and the latent heat of steam, at the pressure of the atmosphere, is 966°. This is the way the above was determined: A quantity of water at a temperature of 32° Fahr. is made to boil, and the time taken to do so noted ; in this case, it took one hour. The water must be kept boiling until it has all evaporated.
HANDBOOK ON ENGINEERING. 659
and the time noted from boiling till evaporation, which in this case will be 5^ hours. Therefore,
Temperature of boiling point, ' . . 212°
Temperature of water at first, 32°
Heat that has entered the water in one hour, . . „ . 180° Number of hours boiling, e . . 51
900 60
Heat that has entered during the 5i hours, . 9 . . 960°
From this we see that the heat necessary to form steam, instead of being only 212°, must be 966° + 212° = 1178°, or 5£ times as great. Therefore, if it were not for latent heat, we would require to burn 5J times the amount of coal that we now do to generate steam. The sensible and latent heats alter with the pressure, but as the sensible increases the latent decreases, and, roughly speaking, the total heat, or the sum of the two, is the same. In connection with the foregoing questions, we would recommend the reader to spend a little time in looking over the " steam tables," and make comparisons between the different quantities noted therein. By so doing he will get an exact knowledge of the prop- erties of saturated steam.
Q. Explain the term tc clearance/' as used in connection with an engine cylinder ? A. There are two kinds of clearance, cylinder clearance and piston clearance . Cylinder clearance means the space or volume, which exists between the piston and the valve, when the piston is exactly at the beginning of the stroke and the crank is on the dead center. This volume can be found by taking care- ful and exact measurements and making calculations from them, but a more correct way is to fill the space with water, noting the quantity used, and so make calculations to find the cubic con-
660 HANDBOOK ON ENGINEERING.
tents. The cubic contents of the clearance space is a certain per- centage of the total volume of the cylinder itself and such clear- ance is expressed as so much per cent. This clearance causes a small loss of steam each stroke, owing to the difference between the initial and compressive pressure. Piston clearance is the space between the piston and cylinder head when the crank is on the dead center. This clearance is necessary to prevent the cylinder head being knocked out, in case of an unusual quantity of water gaining entrance to the cylinder while the engine is running at its usual speed ; and also to admit of the crank-pin and wrist-pin brasses being keyed up at certain intervals. The way to find the piston clearance of an engine is as follows : First, disconnect the wrist-pin end of the connecting rod from the cross-head, and with a bar push back the cross-head until the piston strikes the cylinder head ; then make a mark with a scriber or sharp chisel, on both the sides of the cross-head and on the guide in which the cross-head runs ; these marks must be exactly in line with each other while the piston is in the above stated position. Next, move the piston to the other end of the cylinder till it strikes the head, and make a mark on the guide similar to that on the other end, using the same mark which was made on the cross-head. The new mark must also be in line with this, as at the first mentioned end. We now have a mark at each end of the guide, which represents the place at which the piston strikes the cylinder head, when they alternately coincide with the mark on the cross-head itself. Now, connect the rod to the cross-head again and place the engine or crank on the center. Next, produce or extend the mark on the cross-head to the guide, this time using a pencil instead of a chisel and scriber. The distance between the new pencil mark and the first mark made on the guide is the amount of piston clearance which exists at that end of the cylinder. Repeat the operation on the other end and we will obtain the clearance existing there. If these clear-
HANDBOOK ON ENGINEERING. 661
ances are not equal, as indicated by the marks, make them so by the means provided for in the design of the piston rod and crosshead. After the clearance has been equalized, the pencil marks may be obliterated and marks similar to the first ones may be cut in, thus leaving a permanent mark, which can be seen while the engine is running, and from which can be determined whether the clearance is lessening, and at which end.
Q. What is the pressure of the atmosphere at the sea level, and how determined? A. The pressure of the atmosphere is generally spoken of as 15 Ibs. per square inch, but as the pressure of the atmosphere is constantly varying at any one spot, corrections have to be made according to the reading of a barometer. Generally speaking, 15 is as nearly correct as engineers require it. The pressure of the atmosphere can be ascertained by the following experiment: Take a glass tube about 33 inches long, having a bore equal to a square inch in section. Let one end of the tube be closed in or capped, so that it can contain a fluid. Then fill it with pure mercury, carefully expelling any air bub- bles. When it is full, cover the open end of the tube with a piece of glass and invert the whole tube. Place the open end into a cup of mercury, the surface of which is subject to the pressure of the air, and then withdraw the piece of glass. The mercury in the tube will drop about three inches and then stop. When it has ceased to fall, again cover the end of the tube with the glass. Lift the tube out of the cup and remove the glass so that the mercury may run out into a scale-pan provided for that purpose. Upon actually weighing the mercury lately contained in the tube, it will be found to weigh 14.7 Ibs. The mercury will stop falling in the tube at 30 inches, or at the sea level. Hence, we know that the atmosphere balances, or exerts a pressure of 14. Tibs, per square inch at the sea level.
Q. Upon what does the efficiency of a surface condenser de* pend? A. The efficiency of a surface condenser depends upon:
662 HANDBOOK ON ENGINEERING.
1st, the proper amount of cooling surface ; 2d, the rapidity with which the water is made to circulate through the tubes ; 3d, the water being made to flow in an opposite direction to the steam. The temperature of the circulating water also has a bearing on the question, as it is obvious that the colder the water the more effective it will be in condensing the steam.
Q. A feed pump has a steam cylinder of 6 inches in diameter, and water cylinder of 4 inches diameter ; assuming the steam pressure carried to be 80 Ibs. per square inch throughout the stroke, what will be the balancing pressure per square inch against the water piston, friction being entirely neglected, and gauge pressure being used? A. In this question, we first find the area, the number of square inches contained in the steam piston. Thus : The diameter = 6 in. and 62 x .7854 = the area. Worked out it appears thus: 62 means that 6 is to be squared, or multiplied by itself, or 6 x 6 = 36 square inches, and 36 square inches multiplied by the constant .7854 = 28.27 square inches area contained in the steam piston. Since the pressure is stated to be 80 Ibs. per square inch, then 28.2 7 x 80 = total pressure on the piston in pounds, or 2261.60 Ibs. Now, we will find the area of the water piston, which is 4 inches in diameter, 42 x .7854 = 12.5664 square inches contained in the water piston. Therefore, the water piston, with an area of 12.56 sq. in., has to have a resistance against which it will act of 2261.60 Ibs., in order to balance the pressure against the steam piston. Hence, the pressure per square inch can be found by dividing 2261.60, or 2261.60 divided by 12.56 == 180 Ibs. per square inch, the balancing pressure on the 4-inch water piston.
Q. State what you consider a good standard of strength for steel boiler plate? A. The American Boiler Makers' standard, as used, is as follows : Tensile strength, from 55,000 to 60,000 Ibs. per square inch section ; elongation in 8 inches, 20 per cent for plates | inch thick and under; 22 per cent for plates f to |
HANDBOOK ON ENGINEERING. 663
inches ; 25 per cent for plates J inch and under ; the specimen test piece must bend back on itself when cold, without showing signs of fracture ; for plates over | inch thick, specimens must withstand bending 180° (or half way) round a mandrel 1J times the thickness of the plate. The chemical requirements are as follows: Phosphorus, not over .04 per cent; sulphur, not over .03 per cent.
Q. What is meant by the heating surface of a boiler? A. The heating surface of a boiler is that surface of plates or tubes on one side of which is water, and on the other, hot gases. It has been decided that the surface next the water shall be reckoned, the value to be given in square feet. In a fire tube, or tubular boiler, it will include the under side of the shell from fire-line to fire-line (usually about one-half of it), the tubes and such part of the back-tube sheet as is below the back arch and not taken up by the tube ends. For a water-tube boiler, the heating sur- face will include the tubes, such part of the headers as are in contact with the hot gases, and the lower part (about one-* half) of the steam drum. In calculating the heating surface, none should be taken which has steam on one side and hot gases on the other, as such parts tend to superheat the steam, and are known as superheating surfaces.
Q. What is a boiler horse-power? A. A boiler horse-power has been recently defined as the evaporation of 34J pounds of water per hour from a feed water temperature of 212° Fahr. into steam at a temperature of 212° Fahr., and at a pressure of one atmosphere. Under these conditions each pound of water evaporated will take up 966 heat units, and the 34| Ibs. will take 34J x 966 — 33,327 heat units per hour. Hence, to find the horse-power of a boiler, it is necessary to find the heat units delivered per hour to the water and divide that number by 33,327.
Q. What will be the heating surface of a fire-tube boiler 6 feet in diameter, having 150 tubes 3 inches in diameter and 15
664 HANDBOOK ON ENGINEERING.
feet long? A. Each tube will have a heating surface equal to its outside area, since the water is on the outside of the tubes. The area of a cylinder 3 in. in diameter and 15 ft. long will be the circumference times the length ; 3 in. = 1 ft. and the circumfer- ence = 3.1416 x£ = .7854 ft.; this, times the length 15 ft. — 11.78 sq. ft. for one tube ; for 150 tubes, it will be 150 times that = 1767 sq. ft. The lower half of the shell is usually con- sidered as heating surface. The circumference of a circle 6 ft. in diameter is 6x3.1416 = 18.85 ft. and the area of the shell = 18.85x15 = 282. 75 sq. ft. Half this will be 141.37 sq. ft. For the back end or tube plate, the total area will be the diameter squared times .7854 = 62 x .7854 sa 28.27 sq. ft. ; -f of this will be below the arch, and f of 28.27 = 18.85 sq. ft. From this must be subtracted the area of the ends of the tubes. The end area of one tube is Q)2 x .7854 = .049 sq. ft., and for 150 tubes it is 150 times that, or 7.35 sq. ft. The heating surface of the tube plate will then be 18.85 minus 7.35 = 11.5 sq. ft. The 'front tube plate is not considered, because the gases are cooled too much to be effective by the time they have passed through the tubes. The total heating surface is 1767 + 141.37 + 11.5 = 1919.87 sq. ft.
Q. On what does the efficiency of a boiler depend? A. The efficiency of any piece of machinery is the ratio of the energy made useful to that furnished. The object of the boiler is to make steam ; hence, the enegy used is that which has gone into the steam. The proportion of the heat generated in the furnace which is transferred to the steam, will depend on the thickness of the plates of the boiler, on their condition as to cleanliness, on the amount of time during which the gases are in contact with the plates in their passage from furnace to chimney, on the completeness with which all parts of the gases are brought in contact with the plates, and on the temperature of the hot gases. Evidently, heat will pass through a thin plate more readily than through a thick one, and more
HANDBOOK ON ENGINEERING. 665
readily through a clean plate than through one on which a non- conducting coating of soot or scale has formed ; the more time available for the transfer of heat, the greater will be the amount transferred ; the more complete the contact between plates and gases, the more opportunity will there be for the transfer of heat, and the higher the temperature of the gases, the more rapidly will the heat be transferred. To have a boiler efficient, it is necessary to have plenty of heating surface, so that the hot gases will have time for contact, to keep the plates clean, to have good circulation of the gases, and to keep their temperature high by preventing radiation and allowing as little air to enter the furnace as is needed for good combustion. The efficiency of the furnace, that is, the ratio of the heat generated in the furnace to that con- tained in the coal, is a separate matter, though often the two are lumped together. It depends on the adaptation of the furnace to the kind and size of coal used, on the size of the combustion chamber and on the proper firing of the coal.
Q. On what its satisfactory working? A. In order to work satisfactorily, a boiler must not only be efficient, but must make steam rapidly, must make dry steam, must be easily fired and cleaned, and must be capable of standing a considerable amount of forcing without serious priming. To get rapid steam making, it is necessary to have good circulation of the water in the boiler ; to get dry steam, plenty of steam space is needed, so that the steam may circulate slowly and allow the water to drop out of it ; easy firing means a low fire door of good size, and a rather short grate ; easy cleaning means accessible parts, good sized man-holes, good sized and well placed hand-holes, a large blow- off and a short boiler ; the prevention of priming when carrying an overload is a difficult matter ; the tendency to such an occur- rence depends largely on the feed-water used ; plenty of steam space and good circulation are helpful, but some waters will foam in spite of all precautions.
666 HANDBOOK ON ENGINEERING.
Q. Suppose a slide valve cutting off at £ stroke, and a | cut- off is desired, how would you proceed? A. Put on a new valve with more outside lap. This would require a greater travel of the valve, and therefore would increase the throw of the eccentric, also.
Q. Which requires the greater outside lap, cutting off at T9^ oi the stroke, or cutting off at |? A. Cutting off at T9¥. The earlier the cut-off, the greater should be the outside lap.
Q. Are all plain slide valves made alike, as regards the exhaust cavity of the valve? A. No ; sometimes they are made '•' line and line " inside, that is, the width of the exhaust cavity is equal to the distance between the inner edges of the two steam ports ; and again, the width of the exhaust cavity is made greater or less than this distance, according as an earlier or later release is desired.
Q. What is the effect of giving inside lap to a slide valve? A. It delays the release and increases the compression.
Q. What is the effect of giving inside lead to a slide valve? A. It gives an early release and decreases the compression.
Q. Suppose a simple slide valve engine with a fly-ball governor, and the governor belt should break or slip off, what would happen? A. If it were a plain governor the engine would race ; but if a governor with an automatic stop, the engine would slow down and stop.
Q. What two forces are opposed to each other in a case of fly- ball governor? A. Centrifugal force, tending to throw the balls away from the governor staff, and the force of gravity, tending to draw the balls to the staff.
Q. What other name is given to a fly-ball governor? A. It is also called a throttling governor, because the steam in passing through the governor valve is throttled, choked, or wire- drawn.
Q. Are all fly-ball governors throttling governors? A. No; the governor of a Porter-Allen engine and those of all Corliss
HANDBOOK ON ENGINEERING. 667
engines, while of the fly-ball type, are not throttling governors, because the steam does not pass through them.
Q. If the governor shaft of a fly-ball governor on a plain slide- valve engine should break, could the engine be run? A. Yes; by regulating the speed of the engine by hand at the throttle- valve.
Q. Describe an automatic cut-off engine? A. In this class of engines, as the load on the engine becomes greater or less, the steam entering the cylinder is cut off later or earlier, and it is done through a fly-ball governor in the case of a Corliss engine, or through a shaft-governor or regulator in the case of a high- speed engine.
Q. In an automatic cut-off high-speed engine with shaft-gov- ernor, is the eccentric fastened to the shaft? A. It is not. It is so arranged as to move freely across the shaft, in order to per- mit the center of the eccentric to approach or to recede from the center of the shaft, according as the load on the engine decreases or is increased. And herein lies the chief difference between a plain slide-valve and an automatic cut-off slide-valve engine.
Q. If the connecting rod of an engine had box liners at both ends and in taking it down the liners were all mixed up, how could the length of the rod from center to center of boxes be found? A. Put the cross-head in the middle of its stroke — after finding the piston striking points — and then measure from the center of the cross-head wrist to the center of the main shaft. If the piston clearance at both ends of the cylinder is known, the piston may be pushed to the crank end of the cylinder until it touches the head, and the distance from the center of the cross- head wrist to the center of the main shaft found, to which should be added the length or throw of the crank, and also the piston clearance at the crank end of the cylinder.
Q. But suppose it were more convenient to push the piston to the head end of the cylinder, what then? A. Find the distance
668 HANDBOOK ON ENGINEERING.
from the center of cross-head wrist to center of main shaft and deduct the throw of the crank, and also the clearance.
Q. How is the length of the valve stem and of the eccentric rod found for a plain slide valve engine having a rock shaft? A. If the motion of the slide valve is parallel with the motion of the piston, the length of the valve stem may be found by measuring in a horizontal line from the center of the valve seat to the center of the rock shaft ; and for the eccentric rod by measuring from the center of the rock shaft, horizontally, to the center of the main shaft, which would include one-half the yoke.
Q. What is a direct, and also an indirect valve motion? A. When there is no rock shaft between the eccentric and the valve to compound the motion, it is called " direct/' and when a rock shaft intervenes, it is called an tc indirect " valve motion.
Q. Is the valve motion of a Corliss engine direct or indirect? A. It is direct.
Q. How so ; it has a rock shaft between the eccentric and the wrist plate? A. Even so, it is a direct valve motion; because all connections to the rock-shaft arm are above the center of the shaft, consequently, the motion is simple and not compound.
Q. When is an engine said to " run under," and when to " run over? " A. When the crank pin is above the center of the main shaft and the pin moves towards the cylinder, the engine is said to " run under ; " and when it moves away from the cylinder, the engine is said to " run over."
Q. What is meant by lead of valve, and what is it for? A. Lead is the amount that the port is open to steam when the crank is on its center. It is given in order to allow the full pressure of steam to come on the piston at the beginning of the stroke, and to provide a cushion for the piston.
Q. Could not cushion for the piston be obtained in some other manner? A. Yes, by producing compression by an early closing of the exhaust.
HANDBOOK ON ENGINEERING. 669
Q. Suppose a slide valve had f " lap and no lead, and it was desired to give it -+-' lead, how should it be done? A. By mov- ing the eccentric.
Q. Why could it not be done by altering the length of the eccentric rod ? A. Because the eccentric rod does not establish the amount of lead ; it simply equalizes the lead given by moving eccentric.
Q. How would you test the piston of a steam engine to see whether it was steam-tight or not? A. Put the crank on the outboard center ; remove the cylinder head on the head end ; block the cross-head and admit steam to the crank-end of cylinder and note the effect. The fly-wheel, or the cross-head may be securely blocked and the piston tested in this manner at different points in the stroke.
Q . W hy are two eccentrics and two wrist plates put on some Corliss engines ? A. One eccentric is for the induction valves to lengthen the range of the cut-off ; the other for the exhaust valves to admit of early release, without excessive compression. With a Corliss engine having but one eccentric, the limit of cut-off is at less than one-half stroke, but with two eccentrics the cut-off may be still later in the stroke," and still release the steam at the proper time.
Q. What is meant by a ic blocked up " governor en a Corliss engine? A. When the safety stop is "in, "the governor is said to be blocked up.
Q. With a blocked up governor, suppose the main driving belt should break, what would be the result? A. The engine would race and would, perhaps, be wrecked.
Q. What is meant by the fire line of a horizontal cylindrical boiler ? A. It is the height to which the shell is exposed to the action of the flames.
Q. How high should the fire line be run? A. It maybe run as high as the lower gauge cock water level, although it is frequently run no higher than the top row of flues.
670 HANDBOOK ON ENGINEERING.
Q. What causes a chimney or smoke-stack to draw? A. The difference in the temperature of the air inside the chimney and that outside. The air inside expands and exerts less pressure than the outside air, which rushes in to equalize the pressure.
Q. What does the amount of grate surface determine? A. It determines the amount of coal that can be burned per hour, and consequently, the amount of steam that can be generated.
Q. What is the object in giving a slide valve outside lap? A. To save steam by cutting off the flow of steam into the cylinder before the piston reaches the end of its stroke. For example: With 24 in. stroke of piston and | cut-off, the flow of steam to the piston is cut off when the piston has moved 15 inches and it is driven the remaining 9 inches by the expansive force of the steam.
Q. What amount of refrigerating water is required for a con- denser? A. For a surface condenser about 50 times, and for a jet condenser 30 times the amount of water evaporated in the boiler ; more or less than these quantities being required accord- ing to the temperature of the exhaust steam.
Q. Suppose your condenser was out of order and undergoing repairs, could you run the engine? A. Yes; by attaching an exhaust pipe to the engine and exhausting into the atmosphere.
Q. With a lever safety valve, should the end of the valve stem upon which the lever rests, be square or concave? A. Neither one; it should be pointed, so that the lever will always bear directly on a line with the center of the valve stem.
Q. What is the proper proportion of a safety valve lever? A. About 7 to 1 ; that is, if the distance from the center of the valve to the fulcrum is 1 inch, the distance from the center of the valve to the end of the long arm of the lever should be about 7 inches.
Q. How should the grates be set in a boiler furnace? A. They should be set level, because this plan will enable the fire-
HANDBOOK ON ENGINEERING.
man to more easily carry a bed of fuel of uniform depth ; besides, it is less laborious to clean the fire than when the grates are lower at the bridge wall.
Q. What is momentum? A. It is the product of the mass or bulk of a moving body, taken in pounds or tons, multiplied by the velocity of the moving mass, generally taken in feet per second.
Q. Will an injector work at the same steam pressure wnen it lifts the water as when the water flows to it under pressure ? A. No ; when the water flows to an injector under pressure it will work down to the lowest steam pressures, but when lifting the water it requires a steam pressure of ten pounds or over to work the injector.
Q. What is the greatest height to which an injector will lift water? A. That depends upon the starting steam pressure. There are injectors that will lift water two feet with 10 Ibs. steam pressure, five feet with 30 Ibs., and from 12 to 25 feet with 60 Ibs. and over.
Q. If the pulley on the main shaft of an engine driving a fly- ball governor be reduced in diameter, what affect will it have on the speed of the engine? A. The speed of the engine will be increased.
Q. Which is the greater, the bursting or the collapsing pressure of a boiler tube? A. A boiler tube will collapse under less pres- sure than would be required to burst it.
Q. Should a horizontal externally fired boiler be set level or with a pitch? A. It is customary to set such a boiler one inch lower at the end to which the blow-off pipe is attached, in order to drain the boiler readily.
Q. In a slide valve engine with a connecting rod, will the valve cut off the same at both ends of the stroke if it has equal lap and lead? A. No ; owing to the angularity of the connecting rod.
Q. Is it proper to close the damper with a banked fire? A. The damper should never be closed tightly while there is fire.
672
HANDBOOK ON ENGINEERING.
CHAPTER XXIII. INSTRUCTIONS FOR LINING UP EXTENSION TO LINE SHAFT.
The erection of a line shaft, or an extension to one, is a job that should have the services of a competent millwright or machinist, as it is one calling for experience and considerable skill.
The following drawing will serve to illustrate the operation. A linen line or fine wire should be stretched beneath the shaft and parallel to it, and extending beyond the termination of the extension.
4JL,
L1NE
VA
Fig. 311. Method of lining up shafting.
To set the line parallel to the main line shaft, hang the plumb- bobs A A over the shaft, as shown in the sketch, and then adjust the line until it just touches the lines supporting the bobs, with- out disturbing their position. If the plumb-bobs give trouble by swaying, set pails of water so that the bobs will be immersed ; this will stop the swaying without destroying their truth. The plumb-bobs may just as well be old nuts or similar pieces of iron,
HANDBOOK ON ENGINEERING. 673
A
as the regulation type, since the result will be exactly the same. After getting the line adjusted to the desired position, suspend the plumb-bobs A A along the direction of the extension, so that their supporting cords will just touch the line without disturbing it. The new section of the shaft is now brought in position sideways until it also touches the cords of the plumb-bobs ^4 A , which, of course, locates it parallel with the main shaft in a horizontal plane. To get it to the right height, enter the shaft coupling of the new part into coupling of the main shaft, and then adjust until the shaft shows level when tested with an accurate spirit level. A level suitable for this work should be of iron and planed on the under side with a V-groove, which will always locate it parallel with the shaft when testing it. Before leveling the new part of the shaft, it will be necessary to try the shaft already in position, as it may not be level. If found " out " it should be leveled, but sometimes this will not be possible or feasible, in which case it will be necessary to set the new part at the same inclination. To do this, test the main shaft and find how much it is out, and adjust the level by strips of paper until it shows " fair." The paper should be secured to the level by glue or other means and used on the new shaft in that condition, always keeping the level with the " packed" end pointing in the same direction. After getting the new part in position, it is well to test it before con- necting it to the main part ; that is, it should be turned by hand to determine if the frictional resistance is excessive or not. After connecting with the main part, it is not a bad idea to test it again by hand, if possible. With a long shaft it may be necessary to disconnect the farther sections and remove the belts from the connected machines. In this way a fair idea of the frictional resistance may be obtained. As before stated, this work requires experience and skill, and should properly be done by one thor- oughly competent for the work ; for, while his services may seem a trifle expensive, it will usually be found to pay better in the
43
674 HANDBOOK ON ENGINEERING.
long run, as the frictional resistance of an improperly lined shaft will quickly consume coal enough to pay the difference.
SIMPLICITY IN STEAM PIPING.
In building steam power plants, and especially in arranging the piping connections for them, simplicity is a characteristic the value of which is often too little appreciated. It should be borne in mind that extra valves and duplicate piping mean a very considerable amount of capital lying at waste to meet a contin- gency, which may, in all probability, never arise, not to speak of the care and attention required to keep piping and valves which are rarely used in shape for service. Another point which ought to be realized in the design of piping, is that every square foot of uncovered surface, as in flanges and the like, causes the loss of about one dollar per year in condensation of steam , and each square foot of uncovered surface represents the loss of nearly one-quarter of this amount. The principle of construction is to design the piping with the utmost simplicity possible ; without any double connections, put it up so that no accidents can happen to it. It is argued that this is impossible, but it is equally impossible to insure absolute immunity against " shut downs," of greater or less duration, by any amount of duplex connections, for even the blowing out of a single gasket can blow down a whole battery of boilers before a 12 -inch valve can be closed and another opened. With the more extensive introduction of high-pressure valves and fittings, it is possible, by proper design, to reduce the liability to accident very nearly to the point of absolute safety, and by the introduction of one or two extra valves, it is generally possible to divide the plant into sections, any one of which can, if occasion demands, be operated independently. No fixed rules can be laid down and the line between absolute sim- plicity and necessary complexity must be drawn separately for each plant with due regard to the work it has to perform , but it
HANDBOOK ON ENGINEERING.
675
should be remembered that the more simple a plant can be made to accomplish the work with absolute reliability, the greater the achievement in economy of first cost, and in availability and economy of operation.
Fig. 312. Diagram showing screwed yalve and fittings.
St^^rW—itt) I &
T
Fig. 313. Diagram showing flanged valye and fittings.
CUTTING PIPE TO ORDER.
In placing orders for pipe, a diagram should be made, accord- ing to above cuts. Great care should be taken in making a diagram for large pipe ; all measurements should be from centers. When flanged fittings are used, state if desired drilled, and if with bolts and gaskets complete. If it is desired that the
67G
HANDBOOK ON ENGINEERING.
fittings be made tight, then mark such pieces at point joint is desired, on diagram.
FEED=WATER REQUIRED BY SHALL ENGINES.
|
Pressure of Steam in Boiler, by Gauge. |
Pounds of Water per Effective Horse -power per Hour. |
Pressure of Steam in Boiler, by Gauge. |
Pounds ot Water per Effective Horse- power per Hour. |
|
10 |
118 |
60 |
75 |
|
15 |
111 |
70 |
71 |
|
20 |
105 |
80 |
68 |
|
25 |
100 |
90 |
65 |
|
30 |
93 |
100 |
63 |
|
40 |
84 |
120 |
61 |
|
50 |
79 |
160 |
58 |
HEATING FEED-WATER.
Feed-water, as ^ comes from the wells or hydrants j has ordi- narily a temperature of from 35° in winter to from 60 to 70° in summer. Much fuel can be saved by heating this water by the exhaust steam, whose heat would otherwise be wasted. Until quite recently, only non-condensing engines utilized feed -water heaters but lately they have been introduced with success between the cylinder and the air-pump in condensing engines. The saving in fuel due to heating feed-water is given on page 680.
RATING BOILERS BY FEED-WATER.
The rating of boilers has, since the Centennial Exposition in 1876, been generally based on 30 pounds feed-water per hour per horse-power. This is a fair average for good non-condensing engines working under about 70 to 100 ponnds pressure. But different
HANDBOOK ON ENGINEERING.
677
pressures and different rates of expansion change the require- ments for feed-water. The following table gives Prof. R. H. Thurston's estimate of the steam consumption for the best classes of engines in common use when of moderate size and in good order : —
WEIGHTS OF FEED WATER AND OF STEAM.
NON-CONDENSING ENGINES. — R. H T.
|
Steam Pressure. |
Lbs. per H. P. per Hour. — Ratio of Expansion. |
||||||
|
Atmos- phere. |
Lbs. per sq. ID. |
2 |
3 |
4 |
£ |
7 |
10 |
|
3 |
45 |
40 |
39 |
40 |
40 |
42 |
45 |
|
4 |
60 |
35 |
34 |
36 |
36 |
38 |
40 |
|
5 |
75 |
30 |
28 |
27 |
26 |
30 |
32 |
|
6 |
90 |
28 |
27 |
26 |
25 |
27 |
29 |
|
7 |
105 |
26 |
25 |
24 |
23 |
25 |
27 |
|
8 |
120 |
25 |
24 |
23 |
22 |
22 |
21 |
|
10 |
150 |
24 |
23 |
22 |
21 |
20 |
20 |
CONDENSING ENGINES.
|
2 |
30 |
30 |
28 |
28 |
30 |
35 |
40 |
|
3 |
45 |
28 |
27 |
27 |
26 |
28 |
32 |
|
4 |
60 |
27 |
26 |
25 |
24 |
25 |
27 |
|
5 |
75 |
26 |
25 |
25 |
23 |
22 |
24 |
|
6 |
90 |
26 |
24 |
24 |
22 |
21 |
20 |
|
8 |
120 |
25 |
23 |
23 |
22 |
21 |
20 |
|
10 |
150 |
25 |
23 |
22 |
21 |
20 |
19 |
Small engines having greater proportional losses in friction, in leaks, in radiation, etc., and besides receiving generally less care
678 HANDBOOK ON ENGINEERING.
in construction and running than larger ones, require more feed water (or steam) per hour.
FEED WATER HEATERS.
Inattention to the temperature of feed water for boilers is en- tirely too common, as the saving in fuel that may be effected by thoroughly heating the feed water — by means of the exhaust steam in a properly constructed heater — would be immense, as may be seen from the following facts : A pound of feed water en- tering a steam boiler at a temperature of 50° Fahr., and evapo- rating into steam of 60 Ibs. pressure, requires as much heat as would raise 1157 Ibs. of water 1 degree. A pound of feed water raised from 50° Fahr. to 220° Fahr. requires 987 thermal units of heat, which if absorbed from exhaust steam passing through a heater, would be a saving of 15 per cent in fuel. Feed water at a temperature of 200° Fahr., entering a boiler, as compared in point of economy, with feed water at 50°, would effect a saving of over 13 per cent in fuel ; and with a well-constructed heater there ought to be no trouble in raising the feed water to a temperature of 212° Fahr. If we take the normal temperature of the feed water at 60°, the temperature of the heated water at 212° and the boiler pressure at 20 Ibs., the total heat imparted to the steam in one case is 1192.5° minus 60° = 1132. 5°; and in the other case, 1192.5° minus 212° = 980.5°, the difference being 152°, or a saving of 152/1132.5 = 13.4 per cent. Supposing the feed water to enter the boiler at a temperature of 32° Fahr., each pound of water will require about 1200 units of heat to convert it into steam, so that the boiler will evaporate between 6| and 7^ Ibs. of water per pound of coal. The amount of heat required to convert a pound of water into steam varies with the pressure, as will be seen by the following table : —
HANDBOOK ON ENGINEERING.
679
TABLE SHOWING THE UNITS OF HEAT REQUIRED TO CONVERT ONE POUND OF WATER, AT THE TEMPERATURE OF 32° FAHR., INTO STEAM AT DIFFERENT PRESSURES.
|
Pressure of |
Pressure of |
||
|
Steam in Ibs. per |
Units of Heat. |
Steam in Ibs. per |
Units of Heat. |
|
Sq. In. by Gauge. |
Sq. In. by Gauge. |
||
|
1 |
1,148 |
110 |
,187 ' |
|
10 |
1,155 |
120 |
,189 |
|
20 |
1,161 |
130 |
,190 |
|
30 |
,165 |
140 |
,192 |
|
40 |
,169 |
150 |
,193 |
|
50 |
,173 |
160 |
,195 |
|
60 |
,176 |
170 |
,196 |
|
70 |
,178 |
180 |
,198 |
|
80 |
,181 |
190 |
,199 |
|
90 |
1,183 |
200 |
,200 |
|
100 |
1,185 |
If the feed water has any other temperature the heat necessary to convert it into steam can easily be computed. Suppose, for instance, that its temperature is 65°, and that it is to be converted into steam having a pressure of 80 Ibs. per square inch. The difference between 65 and 32 is 33; and subtracting this from 1181 (the number of units of heat required for feed water hav- ing a temperature of 32°), the remainder, 1148, is the number of units for feed water with the given temperature. Yet it must be understood that any design of heater that offers such resistance to the free escape of the exhaust steam as to neutralize the gain that would otherwise be obtained from its use, ought to be avoided, as the loss occasioned by back pressure on the exhaust, in many instances, counteracts the advantages derived from the heating of the feed water.
Feed water heaters are a most important feature of a good steam plant. First, by utilizing the heat of the exhaust steam
680
HANDBOOK ON ENGINEERING.
from the engine or waste gases in chimney, the feed water may be heated to about 210° Fahr., with ease, before entering boilers, by this means saving fuel and increasing capacity of boiler. Second. By heating the water, the boilers are protected from serious and unequal strain, as the difference of temperature be- tween incoming water and outgoing steam may be kept about 1 10° (210° to 320°). Third. Every heater must necessarily be a water purifier, as the mud and lime are eliminated, to some degree at least, before the water reaches the boiler, by heat.
TABLE.
SHOWING GAIN BY USE OF FEED WATER HEATER. PERCENTAGE OF HEAT REQUIRED TO HEAT WATER FOR DIFFERENT FEED AND BOILING TEMPERATURES, AS COMPARED WITH A FEED AND BOILING TEM- PERATURE OF 212°.
|
Boiling •T) • A. |
Initial Temperature of feed water. |
||||||||||
|
IrOint. Fahr. |
32° |
50° |
68° |
86° |
104° |
122° |
140° |
158° |
176° |
194° |
212° |
|
212 |
1.19 |
1.17 |
1.15 |
1.13 |
1.11 |
1.10 |
1.08 |
.06 |
1.04 |
1.02 |
1.00 |
|
230 |
1.20 |
1.18 |
1.16 |
1.14 |
1.12 |
1.10 |
1.08 |
.06 |
.04 |
1.02 |
1.01 |
|
248 |
1.20 |
1.18 |
1.16 |
1.14 |
1.13 |
1.11 |
1.09 |
.07 |
.05 |
1.03 |
1.01 |
|
266 |
1.21 |
1.19 |
1.17 |
1.15 |
1.13 |
1.11 |
1.09 |
.07 |
.06 |
1.04 |
1.02 |
|
284 |
1.21 |
1.20 |
1.18 |
1.16 |
1.14 |
1.12 |
1.10 |
.08 |
.06 |
.04 |
1.02 |
|
302 |
1.22 |
1.20 |
1.18 |
1.16 |
1.14 |
1.12 |
l.ll |
1.09 |
.07 |
.05 |
.03 |
|
320 |
1.22 |
1.21 |
1.19 |
1.17 |
1.15 |
1.13 |
1.11 |
1.09 |
.07 |
.05 |
.03 |
|
338 |
1.23 |
1.21 |
1.19 |
1.17 |
1.15 |
1.14 |
1.12 |
1.10 |
.08 |
.06 |
.04 |
|
356 |
1.23 |
1.22 |
1.20 |
1.18 |
1.16 |
1.14 |
1.12 |
1.10 |
1.08 |
.06 |
.04 |
|
374 |
1.24 |
1.22 |
1.20 |
1.18 |
1.17 |
1.15 |
1.13 |
1.11 |
1.09 |
.07 |
.05 |
|
392 |
1.24 |
1.23 |
1.21 |
1.19 |
1.17 |
1.15 |
1.13 |
1.11 |
1.09 |
1.07 |
.06 |
|
410 |
1.25 |
1.23 |
1.22 |
1.20 |
1.18 |
1.16 |
1.14 |
1.12 |
1.10 |
1.08 |
.06 |
|
428 |
1.25 |
1.24 |
1.22 |
1.20 |
1.18 |
1.16 |
1.14 |
1.12 |
1.11 |
1.09 |
.07 |
There are two distinct types of heaters in which heat is derived from exhaust steam. These are known as closed and open heaters. Each has its advantages and disadvantages. The closed heater is constructed so that the water is forced under pres-
HANDBOOK ON ENGINEERING. 081
sure through tubes or chambers surrounded by the exhaust steam, the heat being transmitted through the walls of the tubes and cham- bers. The open heater is a vessel in which the feed water comes into direct contact with the exhaust steam, by spraying or inter- mingling. The heated water is pumped hot into the boiler. The closed heater has tbe advantage of permitting the water to pass through the pump cold and in that state is easily handled. To pump hot water from an open heater requires special care in piping and packing the feed pump. The closed heater, being a purifier (if any lime is present in water, a portion is bound to be precipitated by heat), should be cleaned, a job about as difficult as cleaning a boiler ; or blown out, which is never a satisfactory method. In the precipitation of lime by heat, carbonic acid gas is set free and chemists say that this gas in a nascent state (just being born) attacks iron and brass. Whatever the cause, experi- ence has demonstrated that ordinary wrought iron, steel and brass, corrode under this action. The open heater, being usually a large chamber, is accessible for cleaning out, and if made with ordinary care will last a long time. A leak in it is not a serious matter, while a leak in the closed heater means a waste of hot water into the exhaust pipe. The open heater has, at times, been the cause of serious mishaps. In it the steam and water mix ; with any stoppage in exit of feed water, there is danger of flooding the cylinder of the steam engine through exhaust pipe, causing a wreck. The more modern forms of these heaters and the experience obtained in their use have reduced this difficulty to a minimum.
WATER.
Pure water at 62° F. weighs 62.355 pounds per cubic foot, or 8i Ibs. per U. S. gallon; 7.48 gallons equal 1 cu. ft. It takes 30 Ibs., or 3.6 gal. for each horse-power per hour. It would be difficult to get at the total daily horse-power of steam used in the
682 HANDBOOK ON ENGINEERING.
U. S., but it reaches into the billions of gallons of feed water per day. The importance of knowing what impurities exist in most feed waters, how these act on a boiler and how they may be re- moved is, therefore, patent to every intelligent engineer. We give therefore, the thoughts of some prominent investigators on the subject.
Prof* Thurston says : —
" Incrustation and sediment are deposited in boilers, the one by the precipitation of mineral or other salts previously held in solution in the feed water, the other by the deposition of mineral insoluble matters, usually earths, carried into it in suspension or mechanical admixture. Occasionably also, vegetable matter of a glutinous nature is held in solution in the feed water, and, pre- cipitated by heat or concentration, covers the heating surfaces with a coating almost impermeable to heat, and hence, liable to cause an overheating that may be very dangerous to the struc- ture. A powdery mineral deposit sometimes met with is equally dangerous, and for the same reason. THE ANIMAL AND VEGE- TABLE OILS AND GREASES CARRIED OVER FROM THE CONDENSER OR FEED WATER HEATER ARE ALSO VERY LIKELY TO CAUSE TROUBLE.
Only mineral oils should be permitted to be thus introduced, and that in minimum quantity. Both the efficiency and safety of the boiler are endangered by any of these deposits.
" The amount of the foreign matter brought into the steam boiler is often enormously great. A boiler of 100 horse-power uses, as an average, probably a ton and a half of water per hour, or not far from 400 tons per month, steaming ten hours per day ; and even with the water as pure as the Croton at New York, receives 90 pounds of mineral matter, and from many spring waters a ton, which must be either blown out or deposited. These impurities are usually either calcium carbon- ate or calcium sulphate, or a mixture ; the first is most com- mon on land, the second at sea. Organic matters often
HANDBOOK ON ENGINEERING. 683
harden these mineral scales and make them more difficult of removal.
"The only positive and certain remedy for incrustation and sediment, once deposited, is periodical removal by mechanical means at sufficiently frequent intervals to insure against injury by too great accumulation. Between times, some good may be done by special expedients suited to the individual case. No one process and no one antidote will suffice for all cases.
" Where carbonate of lime exists, sal-ammoniac may be used as a preventive of incrustation, a double decomposition occur- ring resulting in the production of ammonia carbonate and calcium chloride — both of which are soluble, and the first of which is volatile. The bicarbonate may be in part precipitated before use by heating to the boiling point, and thus breaking up the salt and precipitating the insoluble carbonate. Solutions of caustic lime and metallic zinc act in the same manner. Waters containing tannic acid and the acid juices of oak, sumach, logwood, hemlock, and other woods, are sometimes employed, but are apt to injure the iron of the boiler, as may acetic or other acid contained in the various saccharine matters often introduced into the boiler to prevent scale, and which also make the lime-sulphate scale more troublesome than when clean. Organic matter should never be used.
c c The sulphate scale is sometimes attacked by. the carbonate of soda, the products being a soluble sodium sulphate and a pulver- ulent insoluble calcium carbonate, which settles to the bottom like other sediments and is easily washed off the heating surfaces. Barium chloride acts similarly, producing barium sulphate and calcium chloride. All the alkalies are used at times to reduce incrustations of calcium sulphate, as is pure crude petroleum, the tannate of soda and other chemicals.
" The effect of incrustation and of deposits of various kinds, is to enormously reduce the conducting power of heating surfaces ;
684 HANDBOOK ON ENGINEERING.
so much so, that the power, as well as the economic efficiency of a boiler, may become very greatly reduced below that for which it is rated, and the supply of steam furnished by it may become wholly inadequate to the requirements of the case.
"It is estimated thaty1^ of an inch (0.16 cm.) thickness of hard scale on the heating surface of a boiler will cause a waste of nearly one-eighth of its efficiency, and the waste increases as the square of its thickness. The boilers of steam vessels are peculiarly liable to injury from this cause where using salt water, and the introduction of the surface condenser has been thus brought about as a remedy. Land boilers are subject to incrus- tation by the carbonate and other salts of lime and by the deposit of sand or mud mechanically suspended in the feed water.
THE TEMPERATURE AND PRESSURE OF SATURATED
STEAM.
The accompanying diagram and explanation, taken from the technical publication, The Locomotive, will be found much more convenient for reference than steam tables. The description says that one of the most fundamental and best known facts in steam engineering is that saturated steam has a certain definite tem- perature for each and every definite pressure ; and in all books on steam we find tables of corresponding temperatures and pres- sures, by the use of which we are enabled to find out what the temperature of the steam is when we know what the pres- sure is, and vice versa. For accurate work these tables are all right ; but when (as is usually the case) we do not need to know either the temperature or the pressure with any very great precision, a diagram which presents the facts directly to the eye is much more convenient. Such a diagram is presented herewith. On the left-hand side of each vertical line are marked the pressures, and on the right-hand side of the same lines are marked the corresponding temperatures. The pres-
50—- u* -
— 235'
45
40—1
- — 235* - — -
35——2SO' 55— _
30
—275* —270'
25 — 1
10
Us
HANDBOOK ON ENGINEERING. 100— |
'1*9 H
685
-230*
SO-
^-r260', 70-r
15— — 250 65—
60
^-210'
-220'
740—
— — ^ /25^
-J/5'
-— J/0*
115
110 —
705 —
700 —
/SO —
175—
7^5 —
— J45*
— J40*
155—
Us ~
— 380'
—37S*
-370*
3H, Comparative diagram showing the temperature and pressure «f saturated steam.
686 HANDBOOK ON ENGINEERING.
sures are all gauge pressures, that is, they represent the direct gauge reading or pressure above that of the atmosphere. The temperatures are on the Fahrenheit scale. The diagram is based upon Prof. Cecil H. Peabody's steam tables, it is therefore assumed that the average atmospheric pressure is 14.70 pounds per square inch.
A few examples will make the use of the diagram clear: (1) What is the temperature of saturated steam when it's pressure, above the atmosphere, is 75 pounds per square inch? Ans. We find 75 pounds on the left-hand side of the second vertical line, and looking on the other side of the line we see that the corre- sponding temperature is just a fraction of a degree less than 320 degrees Fahr. (2) What is the temperature of saturated steam when its pressure, above the atmosphere, is 197 Ibs. per square inch? Ans. We find 197 Ibs. on the left-hand side of the last vertical line. It is not marked in figures, but 195 is so marked, and 197 is two divisions higher than 195. Looking opposite to 197 we see that the corresponding temperature is about half way between 386 degrees and 387 degrees. Hence, we conclude that the temperature of saturated steam at the given pressure is about 386^°. (3) When the temperature of saturated steam is 227°, what is its pressure? Ans. We find 227° on the right-hand side of the first line, two divisions above 225° ; and looking opposite to it, we see that the gauge pressure corresponding to this temperature is almost exactly five pounds. (4) When the temperature of saturated steam is 363°, what is its pressure? Ans. We find 363° on the right-hand side of the third vertical line, three divisions above 360°, and looking on the other side of the vertical line, we see that the corresponding gauge pressure is about 144J Ibs. to the square inch.
SOMETHING FOR NOTHING.
In the first place, it should be remembered that in mechanics the measure of work done is the foot pound, a term which defines
'
HANDBOOK ON ENGINEERING.
68?
itself. A foot pound of work is the amount of energy required to lift one pound one foot high. A foot pound, therefore, is the product of force and distance, force being simply a push or a pull. A machine can be made to increase the acting force, as is seen in the case of a crane, where the weight lifted is much greater than the force applied at the handle by the operator. It is also possible to increase the distance moved by some part of a machine, but it must be done by applying a greater force as in the case of a steam engine, where the distance moved by the belt is greater than the space passed over by the piston, but the total pressure of the steam against the piston is greater than the effective pull exerted by the belt.
Melting Points of Metals and Solids.
|
Deg. Fahr. |
Deg. Fahr. |
||||
|
Antimony |
melts at |
.... 951 |
Platinum melts at |
.... 4680 |
|
|
Bismuth |
cc |
.... 476 |
Potassium |
tt |
.... 136 |
|
Brass |
tt |
.... 1900 |
Saltpeter |
te |
.... 600 |
|
Cadmium |
" |
.... 602 |
Steel |
tt |
. 2340 to 2520 |
|
Cast Iron |
ft |
. 1890 to 2160 |
Sulphur |
(t |
.... 225 |
|
Copper |
ft |
.... 1890 |
Silver |
ft |
.... 1250 |
|
Glass |
tt |
.... 2377 |
Tin |
ft |
.... 420 |
|
Gold |
ft |
.... 2250 |
Wrought Iron |
. 2700 to 2880 |
|
|
Lead |
ft |
.... 594 |
Zinc |
ft |
.... 740 |
|
Ice |
tt |
.... 32 |
Aluminum |
ft |
.... 1260 |
In both the crane and the steam engine, however, the applied force multiplied by the distance through which it moves in a given time, must be enough greater than the product of the force at the crane hook or the rim of the fly-wheel, and the distance through
688 HANDBOOK ON ENGINEERING.
which it moves to make up for the loss through friction in the machine itself. The foot pounds of work done by any machine whatever must always be less than the foot pounds put into the machine in the same length of time. A study of this principle and of the methods of applying it, is all that is necessary to enable one to decide upon the soundness of the claims made for any power multiplying device. A British Thermal Unit (B. T. U.) is the amount of heat required to raise the temperature of a pound of water 1° Fahr., and its dynamic value is 778 Ibs. raised to a height of one foot.
CHIMNEYS.
Chimneys are required for two purposes: 1st, to carry off obnoxious gases ; 2d, to produce a draft, and so facilitate com- bustion. The first requires size, the second, height. Each pound of coal burned yields from 13 to 30 pounds of gas, the volume of which varies with the temperature. The weight of gas to be car- ried off by a chimney, in a given time, depends on three things — size of chimney, velocity of flow and density of gas. But as the density decreases directly as the absolute temperature, while the velocity increases with a given height, nearly as the square root of the temperature, it follows that there is a temperature at which the weight of gas delivered is a maximum. This is about 550° above the surrounding air. Temperature, however, makes so little difference that at 550° above the quantity is only 4 per cent greater than at 300°. Therefore, height and area are the only elements necessary to consider in an ordinary chimney. The in- tensity of draft is, however, independent of the size, and depends upon the difference in weight of the outside and inside columns of air, which varies nearly as the product of the height into the difference of temperature. This is usually stated in an equiva- lent column of water, and may vary from 0 to possibly 2 inches. After a height has been reached to produce draft of sufficient
HANDBOOK ON ENGINEERING.
689
Fig. 315. Section and deration cf steel stack.
HANDBOOK ON ENGINEERING.
intensity to burn fine, hard coal, provided the area of the chimney is large enough, there seems no good mechanical reason for add- ing further to the height, whatever the size of the chimney required. Where cost is no consideration, there is no objection to building as high as one pleases ; but for the purely utilitarian purpose of steam making, equally good results might be attained with a shorter chimney at much less cost. The intensity of draft required varies with the kind and condition of the fuel and the thickness of the fires. Wood requires the least, and fine coal or slack the most. To burn anthracite slack to advantage, a draft of 1J inch of water is necessary, which can be attained by a well- proportioned chimney 175 feet high. Generally, a much less height than 100 feet cannot be recommended for a boil!er, as the lower grades of fuel cannot be burned as they should be with a shorter chimney.
The proportioning of chimneys is very largely a matter of expe- rience and judgment. Various rules have been formulated for this purpose, but they all vary more or less. A chimney must have sufficient cross- section to easily carry off the products of combustion, and be high enough to produce sufficient draft for complete and rapid combustion. Where there is a choice between a high narrow stack and a lower wide one, the nature of the fuel should decide the matter ; as a rule, the taller stack is preferable. The amount of fuel to be burnt per square foot of grate per hour has been increasing in modern practice; therefore, the old rules do not fit the case any more. Then again, it makes a difference how many boilers are to run into the same chimney. The heaviest work of the chimney is immediately after firing, since the friction through the fresh coal is greater and the temperature less then than some minutes later. But it would be bad practice to fire all boilers or all doors simultaneously. Hence, the second boiler does not require as much area as the first ; say, 75 per cent will do. After that there comes the additional consideration that as
HANDBOOK ON ENGINEERING,
rlM
691
Fig. 316. Section ami elevation of brick slack.
692
HANDBOOK ON ENGINEERING.
the diameter of the stack increases, the friction in stack and breeching decreases rapidly. Therefore, for the third and each succeeding boiler, 50 per cent of the first area will suffice. But as more are added, the height should be increased, more espe- cially if the horizontal flue from boiler to stack increases in length, as it usually will. A good rule is to make the height 25 times the diameter, with possibly a gradual decrease in the ratio to 20 times the diameter for the larger chimneys. Thus a 4-foot diame- ter would call for 100 feet height, and a 5-foot, for 120 feet, a 6-foot for 140 feet, and a 10-foot for 200 feet height.
TABLE OF SIZES OF CHIMNEYS.
|
«l ja 3 0> i |
Diameter and Nominal Horse Power. |
|||||||||||||
|
20" |
26" |
30" |
34" |
36" |
40" |
44" |
50" |
54" |
58" |
60" |
64" |
72" |
78" |
|
|
70 ft. 80ft. 90ft. 100 ft. 110ft. 120 ft. |
40 50 |
60 75 |
||||||||||||
|
100 120 |
130 150 |
150 175 |
175 200 |
200 225 250 |
||||||||||
|
300 340 360 |
||||||||||||||
|
375 400 425 |
430 455 500 |
500 550 600 |
600 650 700 |
750 825 900 |
930 990 1050 |
|||||||||
|
. |
||||||||||||||
|
I |
IRON CHIMNEY STACKS.
In many places iron stacks are preferred to brick chimneys. Iron chimneys are bolted down to the base so as to require no stays. A good method of securing such bolts to the stack is shown in detail in the figure on page 693. Iron stacks require to be kept well painted to prevent rust, and generally, where not bolted down, as here shown, they need to be braced by rods or wires to surrounding objects. With four such braces attached to an angle iron ring at f the height of stack, and spreading laterally at
HANDBOOK ON ENGINEERING.
693
least an equal distance, each brace should have an area in square inches equal to y^1^ the exposed area of stack (dia. x height) in feet. Stability or power to withstand the overturning force of
Fig. 817. Holding down bolts and lugs.
the highest winds, requires a proportionate relation between the weight, height, breadth of base, and exposed area of the chimney. This relation is expressed in the equation
dh*
ri __ TIT"
0 b T'
in which d equals the average breadth of the shaft ; k =. its height ; b = the breadth of base — all in feet ; W = weight of chimney in Ibs., and C = a coefficient of wind pressure per
694
HANDBOOK ON ENGINEERING.
square foot of area. This varies with the cross-section of tbe chimney, and = 56 for a square, 35 for an octagon and 28 for a round chimney. Thus a square chimney of average breadth of 8 feet, 10 feet wide at base and 100 feet high, would require to weigh 56x8x100x10=448,000 Ibs., to withstand any gale likely to be experienced. Brickwork weighs from 100 to 130 Ibs. per cubic foot; hence, such a chimney must average 13 inches thick to be safe. A round stack could weigh half as much, or have less base.
WEIGHT OF SHEET LAP RIVETED STEEL SMOKE STACKS, PER FOOTo
THICKNESS.
|
DIJL. |
No. 18 |
No. 16 |
No. 14 |
NO. 12 |
No. 10 |
No. 8 |
A" |
aV |
i" |
A" |
A" |
ii" |
i" |
H" |
A" |
W |
V9 |
|
12" |
8 |
10 |
13 |
17 |
21 |
254 |
314 |
37 |
42 |
47 |
524 |
58 |
63 |
68i |
734 |
78} |
84 |
|
14" |
<-»i |
114 |
15J |
20 |
24* |
29} |
36} |
42 |
484 |
544 |
62i |
67 |
734 |
79i |
85 |
91 |
97 |
|
16" |
10* |
13 |
174 |
23 |
28 |
34 |
42 |
49 |
56 |
63 |
70 |
77 |
84 |
91 |
98 |
105 |
112 |
|
18" |
Hi |
14i |
26 |
31| |
47 |
55 |
63 |
71 |
79 |
86 |
94 |
102 |
110 |
118 |
126 |
||
|
20" |
13 |
16 |
22 |
2^} |
35* |
42* |
52 |
60 |
69 |
78 |
86 |
95 |
104 |
113 |
121 |
131 |
138 |
|
22" 24" |
14* 154 |
HI 19* |
24J 264 |
3lf 34i |
38| 42 |
51 |
54 59 |
63| |
73 784 |
82 88 |
91 98 |
99 108 |
108 118 |
118 128 |
127 137 |
137 147 |
146 157 |
|
26" |
16| |
21 |
28} |
37 |
454 |
63 |
734 |
84 |
94 |
105 |
115 |
126 |
137 |
147 |
158 |
168 |
|
|
28" |
18 |
31 |
40 |
49 |
694 |
67 |
78 |
89* |
100 |
111 |
122 |
134 |
145 |
156 |
167 |
179 |
|
|
80" |
244 |
33 |
42} |
52| |
71 |
83 |
95" |
1064 |
118 |
130 |
142 |
154 |
166 |
178 |
190 |
||
|
32" |
35 |
45i |
56 |
68 |
75 |
874 |
1004 |
113 |
125 |
138 |
150 |
163 |
175 |
188 |
201 |
||
|
34" |
28 |
37 |
48; |
594 |
72J |
80 |
93 |
106 |
119 |
132 |
146 |
160 |
173 |
186 |
199 |
212 |
|
|
36" |
39 |
51 |
63 |
76J |
85 |
100 |
114 |
128 |
143 |
158 |
173 |
188 |
202 |
216 |
230 |
||
|
38" |
3lf |
41* |
53| |
664 |
90 |
105 |
120 |
135 |
151 |
166 |
182 |
198 |
213 |
227 |
242 |
||
|
40" |
33| |
43* |
68 |
70 |
85 |
94 |
110 |
126 |
142 |
158 |
174 |
191 |
208 |
224 |
239 |
254 |
|
|
42" |
35 |
45} |
59J |
734 |
89* |
98 |
115 |
132 |
149 |
166 |
183 |
200 |
217 |
234 |
260 |
266 |
|
|
44" |
36} |
48 |
62 |
77 |
934 |
103 |
121 |
138 |
155 |
173 |
191 |
209 |
227 |
245 |
262 |
279 |
|
|
4«" |
65 |
804 |
97} |
107 |
126 |
144 |
162 |
181 |
199 |
218 |
237 |
255 |
273 |
291 |
|||
|
48" |
40 |
524 |
68 |
84 |
102 |
112 |
131 |
150 |
169 |
188 |
208 |
227 |
247 |
266 |
284 |
303 |
|
|
60" 52" 64" |
54} 57 |
71 74 77 |
874 91 944 |
106J 1104 114} |
116 121 124 |
136 142 147 |
156 162 168 |
176 182 189 |
195 203 211 |
216 224 233 |
236 245 254 |
258 266 276 |
277 287 298 |
296 307 319 |
315 328 349 |
||
|
68" |
80 |
98* |
119* |
133 |
158 |
180 |
202 |
225 |
248 |
270 |
294 |
317 |
340 |
363 |
|||
|
58" |
83 |
102 |
123* |
137 |
164 |
186 |
209 |
232 |
256 |
280 |
304 |
327 |
351 |
375 |
|||
|
60" |
86 |
106 |
127* |
142 |
169 |
192 |
215 |
240 |
264 |
289 |
314 |
338 |
362 |
387 |
|||
|
62" |
89 |
110 |
131} |
146 |
174 |
198 |
222 |
247 |
273 |
298 |
324 |
349 |
374 |
400 |
|||
|
6i" |
.... |
92 |
114 |
136 |
151 |
179 |
204 |
229 |
255 |
281 |
307 |
333 |
359 |
885 |
412 |
HANDBOOK ON ENGINEERING. 695
CHAPTER XXIV. HORSE=POWER OF GEARS.
To determine the horse-power, which any gear-wheel will trans- mit, four facts are required to be known : —
1st. The kind of wheel, whether spur, bevel, spur mortise, or bevel mortise. 2d. The pitch. 3d. The face. 4th. The velocity of pitch circle in feet per second.
Generally, the fourth fact is not known. It can be found if the pitch diameter of the wheel in inches and the number of revo- lutions per minute are given, for it can be obtained from them by the following rule : —
Rule, — Given the pitch diameter in inches and the number of revolutions per minute ; to find the velocity of pitch line in feet per second.
First, multiply the pitch diameter (in inches) by the number of revolutions per minute. Second, divide the product thus found by 230. The quotient is the velocity required.
Example. — What is the velocity of the pitch circle of a gear-wheel in feet per second, the pitch diameter = 43 inches, the revolutions per minute =125?
43 x 125 divided by 230 = 23.4 feet per second.
Table A shows the greatest horse-power, which different kinds of gears of 1-inch pitch and 1-inch face will safely transmit at various pitch-line velocities. To find the greatest horse-power which any other pitch and face will safely transmit, the following rule can be used : —
Rule* — Given, the pitch (in inches), face (in inches), velocity of pitch circle (in feet per second), and kind of gear ; to find the greatest horse-power that can be safely transmitted.
First. Find the horse-power in Table A, which the given kind
696
HANDBOOK ON ENGINEERING.
of wheel with 1-inch pitch and 1-inch face will transmit at the given velocity. Second. Multiply the pitch by the face. Third. Multiply the horse-power found by the product of pitch by face. The final product is the horse-power required.
Example. — What is the greatest horse-power that a bevel- wheel, 43" pitch diameter, 2" pitch, 6" face, and 125 revolutions per minute will safely transmit?
From previous example, we have found the pitch-line velocity to be 23.4 feet per second, which is nearest to a velocity of 24 feet per second in Table A.
First, the horse-power which a bevel wheel of 1" pitch and 1' face will transmit is (from table) at this velocity 4.931.
Second, the product of pitch by face is 2x6 = 12.
Third, 12x4.931 —59.17 horse-power. Answer.
Whenever it is desirable to know about the average horse- power that any wheel will transmit, f or | of the results obtained by the rule above should be taken.
TABLE A. — TABLE SHOWING THE HORSE-POWER WHICH DIFFERENT KINDS OF GEAR WHEELS OF ONE INCH PITCH AND ONE INCH FACE WILL TRANSMIT AT VARIOUS VELOCITIES OF PITCH CIRCLE.
|
1 |
2 |
3 |
4 |
5 |
|
Velocity of pitch circle in ft. per sec. |
Spur Wheels. |
Spur Mortise Wheels. |
Bevel Wheels. |
Bevel Mortise Wheels. |
|
2 |
1.338 |
.647 |
.938 |
.647 |
|
3 |
1.756 |
.971 |
1.227 |
.856 |
|
6 |
2.782 |
1.76 |
1.76 |
1 363 |
|
12 |
4.43 |
3.1 |
3.1 |
2.16 |
|
18 |
5.793 |
4.058 |
4.058 |
2.847 |
|
24 |
7.052 |
4.931 |
4.931 |
3.447 |
|
30 |
8.182 |
5.727 |
5.727 |
4.036 |
|
36 |
9.163 |
6.314 |
6.414 |
4.516 |
|
42 |
10.156 |
7.102 |
7.102 |
4963 |
|
48 |
10.683 |
7.680 |
7.680 |
5.411 |
HANDBOOK ON ENGINEERING.
697
NOTE. — When velocities are given, which are between those in table, the horse-power can be found by interpolation.
Thus, the horse-power for spur wheels at 14 feet velocity is found as follows : —
14 minus 12 = ! 18 " 12 = (
5.793 minus 4.43= 1.363.
Then £ of 1.363 == .454 and .454 + 4.43 = 4. 884 horse-power.
TABLE B. — SHAFTING. — HORSE- POWER TRANSMITTED BY VARIOUS SHAFTS, AT 100 REVOLUTIONS PER MINUTE UNDER VARIOUS CON- DITIONS.
|
1 |
2 |
3 |
4 |
1 |
2 |
3 |
4 |
|
Shafts |
Shafts |
||||||
|
Diameter of Shaft. |
Line Shafts. |
Shaft as . a Prime Mover. |
Under Slight Bending |
Diameter of Shaft. |
Line Shafts. |
Shaft as a Prime Mover. |
Under Slight Bending |
|
Strain. |
Strain. |
||||||
|
1H' |
.7 |
.4 |
1.3 |
*w |
40. |
20. |
80 |
|
1.3 |
.7 |
2.6 |
3if" |
49. |
25. |
97- |
|
|
1-Jg.' |
2.4 |
1.2 |
4.7 |
^tV |
70. |
35. |
139. |
|
jll' |
3.8 |
1.9 |
7.6 |
4i|' |
96. |
48. |
192. |
|
itf |
5.8 |
2.9 |
11.5 |
5-V |
126. |
64. |
256. |
|
2iV |
8.3 |
4.2 |
16.6 |
45* |
167. |
84. |
334. |
|
2ft; |
11.5 15.5 |
5.8 7.8 |
23. 31. |
1 |
266. 399. |
133. 200. |
532. 797. |
|
2^' |
20. |
10. |
40. |
8||; |
570. |
285. |
1139. |
|
8iV |
26. |
13. |
51. |
783. |
.392. |
•I 566. |
|
|
3&" |
33. |
17. |
65. |
This table gives the horse-power that various sizes of shafts will safely transmit at 100 revolutions per minute under various conditions.
Prime movers are those shafts in which the variation above and below the average horse-power transmitted is great, also where the transverse strain due to belts or heavy pulleys is large, such as jack-shafts, crank-shafts, etc.
698 HANDBOOK ON ENGINEERING.
WHEEL GEARING.
The pitch line of a wheel is the circle upon which the pitch is measured, and it is the circumference by which the diameter, or the velocity of the wheel, is measured. The pitch is the arc of the circle of the pitch line, and is determined by the num- ber of teeth in the wheel. The true pitch (chordal), or that by which the dimensions of the tooth of a wheel are alone determined, is a straight line drawn from the centers of two contiguous teeth upon the pitch line. The line of centers is the line between the centers of two wheels. The radius of a wheel is the semi-diameter running to the periphery of a tooth. The pitch radius is the semi-diameter running to the pitch line. The length of a tooth is the distance from its base to its ex- tremity. The breadth of a tooth is the length of the face of wheel. The teeth of wheels should be as small and numerous as is consistent with strength. When a pinion is driven by a wheel, the number of teeth in the pinion should not be less than eight. When a wheel is driven by a pinion, the number of teeth in the pinion should not be less than ten. The number of teeth in a wheel should always be prime to the number of the pinion ; that is, the number of teeth in the wheel should not be divisible by the number of teeth in the pinion, without a remainder. This is in order to prevent the same teeth coming together so often as to cause an irregular wear of their faces. An odd tooth introduced into a wheel is termed a hunting-tooth or cog.
TO COMPUTE THE PITCH OF A WHEEL.
Rule* — Divide the circumference at the pitch-line by the num- ber of teeth.
Example. — Awheel 40 in. in diameter, requires 75 teeth; what is its pitch ?
3.1416 x40=
HANDBOOK ON ENGINEERING. 699
TO COMPUTE THE CHORDAL PITCH.
— Divide 180° by tHe number of teeth, ascertain the sin. of the quotient, and multiply it by the diameter of the wheel.
Example. — The number of teeth is 75 and the diameter 40 in. ; what is the true pitch ?
i^_ = 2° 24' and sin. of 2° 24' = .04188, which x 40 = 1.6752 in.
TO COMPUTE THE DIAMETER OF A WHEEL.
Rule* — Multiply the number of teeth by the pitch, and divide the product by 3. 1416.
Example. — The number of teeth in awheel is 75, and the pitch 1.675 in. ; what is the diameter of it? 75x1.675
3.1416
= 40 in.
TO COMPUTE THE NUMBER OF TEETH IN A WHEEL.
Rule* — Divide the circumference by the pitch.
TO COMPUTE THE DIAMETER WHEN THE TRUE PITCH IS GIVEN.
Rule* — Multiply the number of teeth in the wheel by the true pitch, and again by .3184.
Example. — Take the elements of the preceding case. 75 x 1.6752 x .3184 == 40 in.
TO COMPUTE THE NUMBER OF TEETH IN A PINION OR FOLLOWER TO HAVE A GIVEN VELOCITY.
Rule* — Multiply the velocity of the driver by its number of teeth, and divide the product by the velocity of the driven.
Example. — The velocity of a driver is 16 revolutions, the number of its teeth 54, and the velocity of the pinion is 48 ; what is the number of its teeth ?
= 18 teeth. 48
700 HANDBOOK ON ENGINEERING.
2. A wheel having 75 teeth is making 16 revolutions per min- ute. What is the number of teeth required in the pinion to make 24 revolutions in the same time? 16 x 75
24
= 50 teeth.
TO COMPUTE THE PROPORTIONAL RADIUS OF A WHEEL OR PINION.
Rule* — Multiply the length of the line of centers by the num- ber of teeth in the wheel for the wheel, and in the pinion for the pinion, and divide by the number of teeth in both the wheel and the pinion.
TO COMPUTE THE DIAMETER OF A PINION, WHEN THE DIAMETER OF THE WHEEL AND NUMBER OF TEETH IN THE WHEEL AND PINION ARE GIVEN.
Rule* — Multiply the diameter of the wheel by the number of teeth in the pinion, and divide the product by the number of teeth in the wheel.
Example. — The diameter of a wheel is 25 in., the number of its teeth 210, and the number of teeth in the pinion 30 ; what is the diameter of the pinion ?
25x30
210
= 3.57 in.
TO COMPUTE THE CIRCUMFERENCE OF A WHEEL.
Rule* — Multiply the number of teeth by their pitch.
TO COMPUTE THE REVOLUTIONS OF A WHEEL OR PINION.
Rule* — Multiply the diameter or circumference of the wheel or the number of its teeth, as the case may be, by the number of its revolutions, and divide the product by the diameter, circumfer- ence, or number of teeth in the pinion.
Example. — A pinion 10 in. in diameter is driven by a wheel
HANDBOOK ON ENGINEERING. . 701
2 ft. in diameter, making 46 revolutions per minute ; what is the number of revolutions of the pinion ? 2 x 12 x 46
10
= 110.4 revolutions.
TO COMPUTE THE RELATIVE VELOCITY OF A PINION.
Rule* — Divide the diameter, circumference or number of teeth in the driver, as the case may be. by the diameter, etc., of the pinion.
WHEN THERE IS A SERIES OR TRAIN OF WHEELS AND PINIONS.
Rule* — Divide the continued product of the diameter, circum- ference, or number of teeth in the wheels by the continued product of the diameter, etc., of the pinions.
Example. — If a wheel of 32 teeth drive a pinion of 10, upon the axis of which there is one of 30 teeth, driving a pinion of 8? what are the revolutions of the last?
32 30 960
77, x — = -57- =12 revolutions.
1U o oU
Ex. 2. — The diameters of a train of wheels are 6, 9, 9, 10 and 12 in. ; of the pinions, 6, 6, 6, 6, and 6 in. ; and the number of revolutions of the driving shaft or prime mover is 10 ; what are the revolutions of the last pinion ?
6 x 9 x 9 x 10 x 12 x 10 583200
= ==_ 75 revolutions.
6x6x6x6x6 7776
TO COMPUTE THE PROPORTION THAT THE VELOCITIES OF THE WHEELS IN A TRAIN WOULD BEAR TO ONE ANOTHER.
Rule* — Subtract the less velocity from the greater, and divide the remainder by one less than the number of wheels in the train ; the quotient is the number, rising in arithmetical progression from the less to the greater velocity.
702 HANDBOOK ON ENGINEERING.
Example. — What should be the velocities of three wheels to produce 18 revolutions, the driver making 3 ?
18 minus 3 = 15 _ K
— = 7.5 = number to be added to velocity of the 3 minus 1=2
iriver = 7.5 + 3 = 10.5 and 10.5 + 7.5 = 18 revolutions. Hence, 3, 10.5 and 18 are the velocities of the three wheels.
GENERAL ILLUSTRATIONS.
1. A wheel 96 inches in diameter, making 42 revolutions per minute, is to drive a shaft 75 revolutions per minute, what should be the diameter of the pinion ?
96x42
=53.76 m.
75
2. If a pinion is to make 20 revolutions per minute, required the diameter of another to make 58 revolutions in the same time. 58 divided by 20 = 2.9 = the ratio of their diameters. Hence if one to make 20 revolutions is given a diameter of 30 in., the other will be 30 divided by 2.9 = 10.345 in.
3. Required the diameter of a pinion to make 12 J revolutions in the same time as one of 32 in. diameter making 26.
32x26 „ -„ .
66.56 in.
12.5
4. A shaft making 22 revolutions per minute, is to drive another shaft at the rate of 15, the distance between the two shafts upon the line of centers is 45 in. ; what should be the diameter of the wheels ?
Then, 1st, 22 + 15 : 22 : : 45 : 26.75 = inches in the radius of the pinion.
2d. 22 + 15 : 15 : : 45 : 18.24 = inches in the radius of the spur.
5. A driving shaft, making 16 revolutions per minute, is to drive a shaft 81 revolutions per minute, the motion to be com- municated by two geared wheels and two pulleys, with an inter- mediate shaft ; the driving wheel is to contain 54 teeth, and the
HANDBOOK ON ENGINEERING. 703
driving pulley upon the driven shaft is to be 25 in. in diameter ; required the number of teeth in the driven wheel, and the diameter of the driven pulley. Let the driven wheel have a velocity of V 16x81=36 a mean proportional between the extreme veloci- ties 16 and 81.
Then, 1st, 36 : 16 : : 54 : 24 = teeth in the driven wheel.
2d. 81: 36:: 25: 11. 11= inches diameter of the driven pulley.
6. If , as in the preceding case, the whole number of revolutions of the driving shaft, the number of teeth in its wheel and the diameter of the pulley are given, what are the revolutions of the shafts ?
Then, 1st, 18 : 16 : : 54 : 48 = revolutions of the intermediate shaft.
2d. 15 : 48 : : 25 : 80 = revolutions of the driven shaft.
TO COMPUTE THE DIAMETER OF A WHEEL FOR A GIVEN PITCH AND NUMBER OF TEETH.
Rale* — Multiply the diameter in the following table for the number of teeth by the pitch, and the product will give the diam- eter at the pitch circle.
Example. — What is the diameter of a wheel to contain 48 teeth of 2.5 in. pitch?
15.29x2.5 = 38.225 in.
TO COMPUTE THE PITCH OF A WHEEL FOR A GIVEN DIAMETER AND NUMBER OF TEETH.
Rule* — Divide the diameter of the wheel by the diameter in the table for the number of teeth, and the quotient will give the pitch.
Example. — What is the pitch of a wheel when the diameter of it is 50.94 in., and the number of its teeth 80?
50.94
. 9 ,„
25.47 -^ln-
704
HANDBOOK ON ENGINEERING.
PITCH OF WHEELS.
A TABLE WHEREBY TO COMPUTE THE DIAMETER OF A WHEEL FOR A GIVEN PITCH, OR THE PITCH FOR A GIVEN DIAMETER.
From 8 to 192 teeth.
|
S |
03 |
,c |
| |
j |
03 |
^ |
£ |
a |
g |
|
«M 03 |
03 |
•nt; |
03 |
<M 03 |
"03 |
** 03 |
03 |
s- 03 |
"S |
|
•H |
g cs |
0 0) |
I |
0 03 |
I |
0 03 |
g |
003 |
B |
|
z; |
5 |
5z |
5 |
& |
5 |
fc |
S |
& |
5 |
|
8 |
2.61 |
45 |
14.33 |
82 |
26.11 |
119 |
37.88 |
156 |
49.66 |
|
9 |
2.93 |
46 |
14.65 |
83 |
26.43 |
120 |
38.2 |
167 |
49.98 |
|
10 |
3.24 |
47 |
14.97 |
84 |
26.74 |
121 |
38.52 |
158 |
50.3 |
|
11 |
3.55 |
48 |
15.29 |
85 |
27.06 |
122 |
38.84 |
159 |
50-61 |
|
12 |
3.86 |
49 |
16.61 |
86 |
27.38 |
123 |
39.16 |
160 |
50.93 |
|
13 |
4.18 |
50 |
15.93 |
87 |
27.7 |
124 |
39.47 |
161 |
51.25 |
|
14 |
4.49 |
51 |
16.24 |
88 |
28.02 |
125 |
39.79 |
162 |
51.57 |
|
15 |
4.81 |
52 |
16.66 |
89 |
28.33 |
126 |
40.11 |
163 |
51.89 |
|
16 |
5.12 |
53 |
16.88 |
90 |
28.65 |
127 |
40.43 |
164 |
52.21 |
|
17 |
5.44 |
54 |
17.2 |
91 |
28.97 |
128 |
40.75 |
165 |
52.52 |
|
18 |
5.76 |
55 |
17.52 |
92 |
29.29 |
129 |
41.07 |
166 |
52.84 |
|
19 |
6.07 |
56 |
17.8 |
93 |
29.61 |
130 |
41.38 |
167 |
53.16 |
|
20 |
6.39 |
57 |
18.15 |
94 |
29.93 |
131 |
41.7 |
168 |
53.48 |
|
21 |
6.71 |
58 |
18.47 |
95 |
30.24 |
132 |
42.02 |
169 |
53.8 |
|
22 |
7.03 |
59 |
18.79 |
9« |
30.56 |
133 |
42.34 |
170 |
54.12 |
|
23 |
7.34 |
60 |
19.11 |
97 |
30.88 |
134 |
42.66 |
171 |
54.43 |
|
24 |
7.66 |
61 |
19.42 |
98 |
31.2 |
135 |
42.98 |
172 |
54.75 |
|
25 |
7.98 |
62 |
19.74 |
99 |
31.52 |
136 |
43.29 |
173 |
55.07 |
|
26 |
8.3 |
63 |
20.06 |
100 |
31.84 |
137 |
43.61 |
174 |
55.39 |
|
27 |
8.61 |
64 |
20.38 |
101 |
32.15 |
138 |
43.93 |
175 |
55.71 |
|
28 |
8.93 |
65 |
20.7 |
102 |
32.47 |
139 |
44.25 |
176 |
56.02 |
|
29 |
9.25 |
66 |
21.02 |
103 |
32.79 |
140 |
44.57 |
177 |
56.34 |
|
30 |
9.57 |
67 |
21.33 |
104 |
33.11 |
141 |
44.88 |
178 |
56.66 |
|
31 |
9.88 |
68 |
21.65 |
105 |
33.43 |
142 |
45.2 |
179 |
56.98 |
|
32 |
10.2 |
69 |
21.97 |
106 |
33.74 |
143 |
45.52 |
180 |
57.23 |
|
33 |
10.52 |
70 |
22.29 |
107 |
34.06 |
144 |
45.84 |
181 |
57.62 |
|
34 |
10.84 |
71 |
22.61 |
108 |
34.38 |
145 |
46.16 |
182 |
57.93 |
|
35 |
11.16 |
72 |
22.92 |
109 |
34.7 |
146 |
46.48 |
183 |
58.25 |
|
36 |
11.47 |
73 |
23.24 |
110 |
35.02 |
147 |
46.79 |
184 |
58.57 |
|
37 |
11.79 |
74 |
23.56 |
111 |
35.34 |
148 |
47.11 |
185 |
58.89 |
|
38 |
12.11 |
75 |
23.88 |
112 |
35.65 |
149 |
47.43 |
186 |
59.21 |
|
39 |
12.43 |
76 |
24.2 |
113 |
35.97 |
150 |
47.75 |
187 |
59.53 |
|
40 |
12.74 |
77 |
24.52 |
114 |
36.29 |
151 |
48.07 |
188 |
59.84 |
|
41 |
13.06 |
78 |
24.83 |
115 |
36.61 |
152 |
48.39 |
189 |
60.16 |
|
42 |
13.38 |
79 |
25.15 |
116 |
36.93 |
163 |
48.7 |
190 |
60.48 |
|
43 |
13.7 |
80 |
25.47 |
117 |
37.25 |
154 |
49.02 |
191 |
60.81 |
|
44 |
14.02 |
81 |
25.79 |
118 |
37.66 |
155 |
49.34 |
192 |
61.13 |
HANDBOOK ON ENGINEERING. TO COMPUTE THE STRESS THAT MAY BE BORNE BY A TOOTH.
Rule* — Multiply the value' of the material of the tooth to re- sist transverse strain, as estimated for this character of stress, by the breadth and square of its depth, and divide the product by the extreme length of it in the decimal of a foot.
TO COMPUTE THE NUMBER OF TEETH OF A WHEEL FOR A GIVEN DIAMETER AND PITCH.
Rule* — Divide the diameter by the pitch, and opposite to the quotient in the preceding table is given the number of teeth.
TEETH OF WHEELS.
Epicycloidal* — In order that the teeth of the wheels and pin- ions should work evenly and without unnecessary rubbing fric- tion, the face (from pitch line to top) of the outline should be determined by an epicycloidal curve, and the flank (from pitch line to base) by an hypocycloidal. When the generating circle is equal to half the diameter of the pitch circle, the hypocycloid de- scribed by it is a straight diametrical line, and consequently the outline of a flank is a right line and radial to the center of the wheel. If a like generating circle is used to describe face of a tooth of other wheel or pinion respectively, the wheel and pinion will operate evenly.
Involute* — Teeth of two wheels will work truly together when surfaces of their face is an involute ; and that two such wheels should work truly, the circles from which the involute lines for each wheel are generated must be concentric with the wheels, with diameters in the same ratio as those of the wheels.
Curves of teeth* — In the pattern shop, the curves of epicy- cloidal or involute teeth are defined by rolling a template of the generating circle on a template corresponding to the pitch line,
a scriber on the periphery of the template being used to define
45
70b
HANDBOOK ON ENGINEERING.
the curve. Least number of teeth that can be employed in pin- ions having teeth of following classes, are: involute, 25; epicycloidal, 12 ; staves or pins, 6.
CONSTRUCTION OF GEARING.
If the dimensions of two wheels are determined, as well as the size of the teeth and spaces, the wheel is drawn as shown in figure. The star ting- point for the division of the wheels is where the two pitch circles meet in A. It is advisable to determine the exact diameters of the wheels by calculation, if the difference between them is remarkable ; for any division upon two circles of unequal size
by means of a divider, jolg. 313. involute gear teeth. is incorrect, because the latter measures the chord instead of the arc. From the point A we construct the epicycloid (7, by rolling the circle A upon 5, as its base line. That short piece of the epi- cycloid, from the pitch line to the face of the tooth, is the curva- ture for that part of the tooth and the wheel B. This curvature obtained for one side of the tooth, serves for both sides of it, and also for all the teeth in the wheel. The lower part of the tooth, or that inside the pitch -line, is immaterial to the working of the wheel ; this may be a straight line, as shown by the dotted lines which are in the direction of the diameters, or may be a curved line, as is seen in the wheel A. This line must be so formed as not to touch the upper or curved part of the tooth. The root of
\
HANDBOOK ON ENGINEERING.
707
the tooth, or that part of it which is connected with the rim of the wheel, is the weakest part of the tooth, and may be strengthened by filling the angles at the corners. The curvature for the teeth in the wheel A is found in a similar manner to that of B. The pitch circle A serves now as a base line, and the circle B is rolled upon it, to obtain the circle D. This line forms the curvature for the teeth of A, and serves for all the teeth in A — also for both sides of the teeth. In most practical cases the curvature of the teeth is described as a. part of a circle, drawn from the center of the next tooth, or from a point more or less above or below that center, or the radius greater or less in strength than the pitch of the wheel. Such circles are never correct curves, and no rule can be established by which their size and center meets the form of the epicycloid.
BEVEL WHEELS.
If the lines C A and B C represent the prolonged axes, which are to revolve with different or similar velocities, the position and
sizes of the wheels for driving these axes are determined by the dis- tance of the wheels from the point C. The diame- ters of the. wheels are as the angles a and b and inversely as the number of revolutions. These angles are, therefore, to be determined before the
319. Bevel gears. wheels can be drawn.
By measuring the distances from C to the line E, or from C to F, the sizes of the wheels are determined. These lines E, F and D F, are the diameters for the pitch lines ; from them the form
708
HANDBOOK ON ENGINEERING
of the tooth is described on the beveled face of the wheel. If the form of the tooth is described on the largest circle of the wheel, all the lines from this face run to the point (7, so that when the wheel revolves around its axis, all the lines from the teeth concentrate in the point (7, and form a perfect cone. Curvature, thickness, length and spaces are here calculated as on face wheels ; the thickness is measured in the middle of the width of the wheel.
WORM-SCREW.
If a single screw A works in a toothed wheel, each revolution of the screw will turn the wheel one cog ; if the screw is formed of more than one thread, a corresponding number of teeth will be moved by each revolution. With the increase of the number of threads, the side motion of the wheel and screw is accelerated ; and when the threads and num- ber of teeth are equal, an angle of 45° is required for teeth and thread, provided their diameters also are equal. This motion causes
a great deal of friction and ™.
Fig. 320. Worm and worm wheel.
it is only resorted to where no other means can be employed to produce the required motion. In small machinery, the worm is frequently made use of to produce a uniform, uninterrupted motion ; the screw, in such cases, is made of hardened steel and the teeth of the wheel are cut by the screw which is to work in the wheel. If the form of the teeth in the wheel is not curved and its face is concave so as to fit the thread in all points, the screw will touch the teeth but in one point and cause them to be liable to breakage.
HANDBOOK ON ENGINEERING. 709
PROPORTIONS OF TEETH OF WHEELS.
Tooth*— -In computing the dimensions of a tooth, it is to be considered as a beam fixed at one end, the weight suspended from the other, or face of the beam ; and it is essential to con- sider the element of velocity, as its stress in operation, at high velocity with irregular action, is increased thereby. The dimen- sions of a tooth should be much greater than is necessary to resist the direct stress upon it, as but one tooth is proportioned to bear the whole stress upon the wheel, although two or more are actually in contact at all times ; but this requirement is in consequence of the great wear to which a tooth is subjected? the shocks it is liable to from lost motion when so worn as to reduce its depth and uniformity of bearing, and the risk of the breaking of a tooth from a defect. A tooth running at a low velocity may be materially reduced in its dimensions compared with one running at high velocity and with a like stress. The result of operations with toothed wheels, for a long period of time, has determined that a tooth with a pitch of 3 inches and a breadth 7.5 inches will transmit, at a velocity of 6.66 feet per second, the power of 59.16 horses.
TO COMPUTE THE DEPTH OF A CAST-IRON TOOTH.
1. When the stress is given.
Rule* — Extract the square root of the stress, and multiply it by .02.
Example. — The stress to be borne by a tooth is 4886 Ibs. ; what should be its depth?
1/4886 x .02 = Io4 in.
2. When the horse-power is given.
Rule* — Extract the square-root of the quotient of the horse- power divided by the velocity in feet per second, and multiply it by .466.
710 HANDBOOK ON ENGINEERING.
Example. — The horse-power to be transmitted by a tooth is 60, and the velocity of it at its pitch-line is 6.66 feet per second ; what should be the depth of the tooth ?
60 x .466 = 1.398 in.
6.66
TO COMPUTE THE HORSE -POWER OF A TOOTH.
Rule* — Multiply the pressure at the pitch-line by its velocity in feet per minute, and divide the product by 33,000.
CALCULATING SPEED WHEN TIME IS NOT TAKEN INTO ACCOUNT.
Rule* — Divide the greater diameter, or number of teeth, by the lesser diameter or number of teeth, and the quotient is the number of revolutions the lesser will make, for one of the greater.
Example. — How many revolutions will a pinion of 20 teeth make, for 1 of a wheel with 125 ?
125 divided by 20 =±= 6.25 or 6J revolutions.
To find the number of revolutions of the last to one of the first, in a train of wheels and pinions : —
Rule* — Divide the product of all the teeth in the driving by the product of all the teeth in the driven ; and the quotient equals the ratio of velocity required.
Example 1. — Required the ratio of velocity of the last, to 1 of the first, in the following train of wheels and pinions, viz. : pinions driving — the first of which contains 10 teeth, the second 15, and third 18. Wheels driven, first teeth 15, second 25,
10x15x18 and third 32. ^ — ^ — ^-0 — .225 of a revolution the wheel
10 X ^0 X O&
will make to one of the pinion.
Example 2. — A wheel of 42 teeth giving motion to 1 of 12, on which shaft is a pulley of 21 inches diameter, driving 1 of 6 ;
HANDBOOK ON ENGINEERING. 711
required the number of revolutions of the last pulley to 1 of the
42x21 first wheel, j^ g— 12.25 or 12J revolutions.
NOTE. — Where increase or decrease of velocity is required to be communicated by wheel- work, it has been demonstrated that the number of teeth on each pinion should not be less than 1 to 6 of its wheel, unless there be some other important reason for a higher ratio.
WHEN TIME MUST BE REGARDED.
Rule* — Multiply the diameter or number of teeth in the driver by its velocity in any given time, and divide the product by the required velocity of the driven ; the quotient equals the number of teeth or diameter of the driven, to produce the velocity required.
Example 1. — If a wheel containing 84 teeth makes 20 revolu- tions per minute, how many must another contain, to work in contact, and make 60 revolutions in the same timer 80 x 20 divided by 60 =27 teeth.
Example 2. — From a shaft making 45 revolutions per minute and with a pinion 9 inches diameter at the pitch-line, we wish to transmit motion at 15 revolutions per minute ; what, at the pitch-line, must be the diameter of the wheel?
45 x 9 divided by 15 = 27 inches.
Example 3. — Required the diameter of a pulley to make 16 revolutions in the same time as one of 24 inches making 36. 24x36 divided by 16 == 54 inches.
The distance between the centers, and the velocities of two wheels being given, to find their proper diameters : —
Rule* — Divide the greatest velocity by the least ; the quo- tient is the ratio of diameter the wheels must bear to each other. Hence, divide the distance between the centers by the ratio -|- 1 ; the quotient equals the radius of Lhe smellier wheel ; and subtract
712 HANDBOOK ON ENGINEERING.
the radius thus obtained from the distance between the centers ; the remainder equals the radius of the other.
Example. — The distance of two shafts from center to center is 50 in. and the velocity of the one 25 revolutions per minute, the other is to make 80 at the same time ; the proper diameters of the wheels at the pitch line are required.
80 divided by 25=3.2, ratio of velocity, and 50 divided by 3.2+ 1 = 11.9, the radius of the smaller wheel ; then 50 minus 11.9 =38.1, radius of larger ; their diameters are 11.9x2 = 23.8 and 38.1x2 = 76.2 in.
To obtain or diminish an accumulated velocity by means of wheels and pinions, or wheels, pinions and pulleys, it is necessary that a proportional ratio of velocity should exist, and which is thus attained ; multiply the given and required velocities together ; and the square root of the product is the mean or proportionate velocity.
Example. — Let the given velocity of a wheel containing 54 teeth equal 16 revolutions per minute, and the given diameter of an intermediate pulley equal 25 in., to obtain a velocity of 81 revolutions in a machine ; required the number of teeth in the intermediate wheel and diameter of the last pulley.
->/ 81x16 = 36 mean velocity ; 54 x 16 divided by 36 = 24 teeth, and 25x36 divided by 81 = 11.1 in., diameter of pulley.
TABLE OF THE WEIGHT OF A SQUARE FOOT OF SHEET IRON IN POUNDS AVOIRDUPOIS.
No. 1 is T5^ of an inch ; No. 4, J ; No. 11, -|, etc.
No. on wire gauge, 1 2 3 4 5 6 7 8 9 10 11 12 Poundsavoir., 12.512 11 10 9 8 7.5 7 6 5.68 5 4.62
No. on wire gauge, 13 14 15 16 17 18 19 20 21 22
Poundsavoir., 4.31 4 3.95 3 2.5 2.18 1.93 1.62 1.5 1.37
HANDBOOK ON ENGINEERING. 713
SCREW-CUTTING .
In a lathe properly adapted, 'screws to any degree of pitch, or number of threads in a given length, may be cut by means of a leading screw of any given pitch, accompanied with change wheels and pinions ; coarse pitches being effected generally by means of one wheel and one pinion with a carrier, or intermediate wheel, which cause no variation or change of motion to take place ; hence, the following : —
Rule* — Divide the number of threads in a given length of the screw which is to be cut, by the number of threads in the same length of the leading screw attached to the lathe, and the quotient is the ratio that the wheel on the end of the screw must bear to that on the end of the lathe spindle.
Example. — Let it be required to cut a screw with 5 threads in an inch, the leading screw being of J inch pitch, or containing 2 threads in an inch ; what must be the ratio of wheels applied ?
5 divided by 2 = 2.5, the ratio they must bear to each other. Then suppose a pinion of 40 teeth be fixed upon for the spindle ; 40 x 2.5 = 100 teeth for the wheel on the end of the screw.
But screws of a greater degree of fineness than about 8 threads in an inch are more conveniently cut by an additional wheel and pinion, because of the proper degree of velocity being more effectively attained, and these, on account of revolving upon a stud, are commonly designated the stud- wheels, or stud-wheel and pinion ; but the mode of calculation and ratio of screw are the same as in the preceding rule. Hence, all that is further neces- sary is to fix upon any three wheels at pleasure, as those for the spindle and stud-wheels ; then multiply the number of teeth in the spindle-wheel by the ratio of the screw and by the number of teeth in that wheel or pinion, which is in contact with the wheel on the end of the screw ; divide the product by the stud-wheel in contact with the spindle-wheel, and the quotient is the number of teeth required in the wheel on the end of the leading screw.
714
HANDBOOK ON ENGINEERING.
Example. — Suppose a screw is required to be cut containing 25 threads in an inch, and the leading screw, as before, having two threads in an inch, and that a wheel of 60 teeth is fixed upon for the end of the spindle, 20 for the pinion in contact with the screw-wheel, and 100 for that in contact with the wheel on the end of the spindle ; required the number of teeth in the wheel for the end of the leading screw.
25 divided by 2 = 12.5, and 6°X^Q5^20 = 150 teeth.
Or suppose the spindle and screw wheels to be those fixed upon, also any one of the stud-wheels, to find the number of teeth in the other.
150x100 60x12.5x20
= 20 teeth, or - ^^ - — 100 teeth.
60x12.5
150
Transmission of Power by Manilla Rope, power Transmitted.
Horse-
|
Feet per minute .... |
1000 |
1500 |
2000 |
2500 |
3000 |
3500 |
4000 |
4500 |
5000 |
|
Diameter of Rope . | (( U I " • " ! a " " . 14 " " . u <c « . .2 |
11 31 6* 74 10 13 |
21 *i 74 11 15 194 |
34 64 10* 15 20 26 |
44 8 13 18 25 33 |
54 10 15 22 30 39 |
64 11 18 26 35 46 |
7 13 20 30 40 52 |
8 15 23 34 45 59 |
9 16 26 37 50 65 |
Inches Expressed in Decimals of a Foot.
|
1 |
k |
1 |
1 |
2 |
3 |
4 |
5 |
|
.0208 |
.0417 |
.0626 |
.0833 |
.1667 |
.2500 |
.3333 |
.4167 |
|
6 |
7 |
8 |
9 |
10 |
11 |
12 |
|
|
.5000 |
.5833 |
.6667 |
.7610 |
.8333 |
.9167 |
1.000 |
HANDBOOK ON ENGINEERING.
TABLE OF TRANSMISSION OF POWER BY WIRE ROPES.
This table is based upon scientific calculations, careful observations and experience, and can be relied upon when the distance exceeds 100 feet. It is also found by experience that it is best to run the wire rope transmission at the medium number of revolutions indicated in the table, as it makes the best and smoothest running transmission. If more power is needed than is indicated at 80 to 100 revolutions, choose a larger diameter of sheave.
|
1 Diameter of Sheave in ft. |
Number of Revolutions. |
Diameter of Rope. |
Horse - Power. |
Diameter of Sheave in ft. |
Number of Revolutions. |
Diameter of Rope. |
Horse - Power. |
|
3 |
80 |
| |
3 |
7 |
140 |
A |
35 |
|
3 |
100 |
| |
4 |
8 |
80 |
1 |
26 |
|
3 |
120 |
1 |
4 |
8 |
100 |
1 |
32 |
|
3 |
140 |
4£ |
8 |
120 |
1 |
39 |
|
|
4 |
80 |
1 |
4 |
8 |
140 |
1 |
45 |
|
4 |
100 |
1 |
5 |
9 |
80 |
{At |
\ 47 i 48 |
|
4 |
120 |
I |
6 |
9 |
100 |
{At |
1 58 / 60 |
|
4 |
140 |
I |
7 |
9 |
120 |
{At |
\ 69 / 73 |
|
5 |
30 |
A |
9 |
9 |
140 |
{At |
\ 82 / 84 |
|
5 |
100 |
A |
11 |
10 |
80 |
{t H |
1 64 ; es |
|
5 |
120 |
A |
13 |
10 |
100 |
{t H |
\ 80 / 85 |
|
5 |
140 |
A |
15 |
10 |
120 |
'{I H |
1 96 /102 |
|
6 |
80 |
h |
14 |
10 |
140 |
(M* |
\112 hi9 |
|
6 |
100 |
i |
17 |
12 |
80 |
{HI |
Y 93 / 99 |
|
6 |
120 |
i |
20 |
12 |
100 |
{HI |
\116 / 124 |
|
6 |
140 |
* |
23 |
12 |
120 |
{HI |
\140 J 149 |
|
7 |
80 |
A |
20 |
12 |
120 |
i |
173 |
|
7 |
100 |
A |
25 |
14 |
80 |
{"< |
1141 J 148 |
|
7 |
120 |
A |
30 |
14 |
100 |
{"• |
\176 J 185 |
716 HANDBOOK ON ENGINEERING.
CHAPTER XXV. ELECTRIC ELEVATORS.
In factories, warehouses and business buildings, freight, and in some instances passenger elevators, are operated by machines that are arranged to be driven by a belt. Such machines are variously called belted elevators, factory elevators and sometimes warehouse elevators.
In factories where there is a line of shafting kept running continuously, they are driven from it. As a rule the elevator machine is driven from a countershaft which latter is belted to the line shaft. Very often the elevator machine is driven directly from the line shaft. As the line shaft runs always in the same direction, the only way in which the elevator machine can be made to run in both directions is by the use of two belts, one open and the other crossed, or some form of gearing that will accomplish the same result. The common practice is to use double belts. Either one of these belts can be made to drive by using friction clutches, or by having tight and loose pulleys, and a belt shifter. The latter arrangement is the most common.
In buildings where there is no line of shafting, power for oper- ating the elevator machine must be derived from some kind of motor installed expressly for the purpose. Nowadays electric motors are very extensively used for this purpose, and the com- bination of an elevator machine and an electric motor to drive it is very generally called an electric elevator, although in reality it is not such, but simply a belted elevator machine driven by an electric motor. It has become so common, however, to call such com- binations electric elevators, that true electric elevators are generally designated as " direct connected electric elevators."
HANDBOOK ON ENGINEERING. 711
The first impression would be that in the combination of a belted elevator machine, and an electric motor to drive it, as the motor simply furnishes the power to set the machine in motion, there can be nothing about the combination that requires any special elucidation. Such a conclusion, however, would not be correct, for there are several ways in which the combination can be arranged, and in what follows we propose to explain these several combinations, pointing out the important features of each.
The simplest way in which a motor can be installed to drive an elevator, is to arrange it so as to drive the counter shaft con- tinuously, in which case the elevator is stopped and started by throwing the belts on the tight or the loose pulley. Although this is a very simple arrangement, it is not desirable unless the elevator is kept in service all the time. In buildings where the elevator is used only at intervals, a great amount of power is wasted if the shafting is kept running all the time ; hence it is desirable to arrange the motor so that it can be stopped when the elevator is stopped, and started whenever the elevator is to be used.
If the motor is arranged so as to run all the time, it is provided with a simple motor-starting switch, the same as is used for any motor installed to operate machinery of any kind. If the motor is started and stopped whenever the elevator is started and stopped, it is necessary to provide a motor-starter that can be operated from the elevator car. A very common way of arranging a motor to start and stop with the elevator is illustrated in the diagram Fig. 321.
In this diagram the elevator car is shown at (7, with the lifting ropes running over the sheave F at the top of the elevator shaft, and then down and around the drum A of the elevator machine. This drum is driven by means of screw gearing, as a rule, with driving pulleys on the screw shaft as shown at B. The
718
HANDBOOK ON ENGINEERING.
driving motor is shown at Jf, and the counter-shaft to which it is belted is at D. In this arrangement the elevator machine is pro- vided with a tight center pulley and loose pulleys on the two sides. The belts are shown on the loose pulley s? one being open and the
Fig* 321. Belt driven electric elevator.
other being crossed „ The countershaft carries a drum wide enough to allow for the side movement of the belts when one or the other is shifted upon the tight center pulley by the belt shifter $. To operate the elevator car, a hand rope is provided which
HANDBOOK ON ENGINEERING. 719
runs up the elevator shaft at one side of the car from bottom to top of building. This rope is shown in the diagram at J, and runs around two small sheaves a a. The lower one of these sheaves is provided with a crank pin, which moves the connecting rod 6, and thus rocks the lever r, and thereby moves the belt shifter s. To cause the car to ascend the hand rope I is pulled down, and to make the car descend, the hand rope is pulled up. As will be seen from this explanation, the lower sheave a will rotate in one direction when the hand rope is pulled to make the car go up, and in the opposite direction when the rope is pulled to make the car run down. In the diagram, sheave a is shown in the stop posi- tion, therefore when the hand rope is pulled down so as to make the car run up, the sheave will turn in a direction opposite to the movement of the hands of a clock, and thus the belt shifter will be moved to the right, and the open belt will be run onto the tight center pulley. If the hand rope is pulled up sheave a will rotate in the direction of the hands of a clock, and the belt shifter will move toward the left and thus shift the crossed belt onto the tight pulley. The rope p is a stop rope and is connected with the two sides of the hand rope in the manner shown, so that when the car is running in either direction, if p is pulled hard it will bring I to the position shown in the diagram, and thus stop the car. This rope can be dispensed with, but the objection is that in pulling the hand rope I to stop the car it may be pulled too far and then the car will not only be stopped but it will be caused to run in the opposite direction.
The motor starting switch'is shown at E, the line wires being connected with the two top binding posts. The lever c c is in one piece and is independent of lever e, but both swing around the same pivot. At m, a dash pot is provided which acts to prevent the too rapid movement of lever e. As will be noticed, lever c has a projection which holds lever e up. The operation of this motor starter is as follows : When the hand rope I is pulled in
720 HANDBOOK ON ENGINEERING.
either direction, the rope h draws lever c towards the left and causes it to make contact with the switch jaw./. In this way the current from the upper binding post which is connected with j through wire g, passes to lever e, and thus to the starting resist- ance, which is indicated by the dotted lines t, to binding post ft, from where it goes to the motor armature through wire d, and re- turns through the other wire d to the upper binding post at the right side, which is connected with the opposite side of the main line, thus completing the circuit. The field current branches off from the upper end of the starting resistance i and reaches the field coils through wire /, and through the lower wire / reaches the return armature wire d and thus the opposite side of the cir- cuit. When the rope h pulls lever c over toward the left, the lever e does not follow it, as it is held up by the dash pot m. The weight on the end of e gradually overcomes the resistance of the dash pot, and thus causes lever e to move downward slowly. The velocity at which e moves downward is graduated by adjusting the opening in the dash pot through which the oil flows.
From the foregoing it will be seen that the starter E is made so as to accomplish automatically just what a man accomplishes when he moves the lever of an ordinary motor-starter ; that is, it first closes the circuit through the motor, by bringing lever c into contact withj; and then allows lever e to move slowly so as to cut the resistance i out of the armature circuit gradually. When the elevator is stopped, by pulling the hand rope I to the stop position, the rope h slacks up and then the weight on the end of lever c causes it to descend, and thus return lever e to the posi- tion shown in the diagram, and also to break the circuit between c and j.
The elevator machine A is provided with a brake, which is actuated by the belt shifter s, so that when the belts are shifted upon the side pulleys, as shown in the diagram, the brake is put on, and thus the machine is stopped. As soon as the belt shifter
HANDBOOK ON ENGINEERING. 721
is moved to set the car in motion the brake is raised, so as to allow the machine to run free.
This arrangement is used very extensively, although the motor- starting switch is not always made in strict accordance with the one shown at E. In fact, there are a great many different designs on the market, but they all accomplish the same result, although the means employed may be very different.
Although it is very advantageous to have the motor arranged as in Fig. 321, so that it may be stopped and started together with the elevator, there is one objection to it which is sometimes re- garded as serious, and that is, that as it requires a great amount of power to start an elevator from a state of rest, the motor will take a very strong current in the act of starting. To get around this objection, it is a common practice to provide a separate rope for starting the motor, and then when it is desired to use the ele- vator, the motor rope is pulled first, and in half a minute or so, the main hand rope is pulled. In this way the motor gets a start ahead of the elevator., and the headway of the motor armature helps to set the elevator car in motion, so that the current taken by the motor to start the elevator is very much reduced.
When a separate rope is used to start the motor in advance of the elevator, the starter E, or the levers connecting with it, are made so that while the motor can be started independently of the elevator car, when the main hand rope is pulled, to stop the car, it also stops the motor. If this arrangement were not provided, the operator might stop the elevator and forget to stop the motor, in which case the latter would keep on running and waste power.
The main hand rope I is provided with stops at top and bottom of the elevator shaft, so that the car may be stopped auto- matically should the operator forget to pull the hand rope at the proper time.
It is the universal practice with elevator machines of the type shown in Fig. 321 to counterbalance the elevator car, but we have not shown a counterbalance in this diagram as it would only serve
722
HANDBOOK ON ENGINEERING.
to complicate its appearance, and it is not necessary to show it as the electrical features will be the same whether there is a counter- balance or not. This diagram also shows a separate rope h for actuating the starter E, but in actual machines E is generally
CONTROLLER
ELEVATOR
MOTOR
Fig. 322. Connections of gravity motor controller.
rig. ozz. ^oniieciioiis 01 gruviij iiioior coin uiivr. operated from the lower sheave a, which also actuates the belt
shifter.
Fig. 322 is a diagram tnat shows the way in which one of the various motor starters in actual use is connected with the motor
HANDBOOK ON ENGINEERING,
723
and the operating hand rope. In this illustration A is the lower sheave a of Fig. 321, and ^represents the hoisting drum and E the driving pulleys of the elevator machine, G being the lifting ropes from which the car is suspended. The sheave A is rotated
MOTOR.
Fig. 328. Gravity controller with rope attachment, through one quarter of a turn in either direction by the pull on
the hand rope J5, and when so rotated shifts the belt shifter and also lifts the brake from the brake-wheel. At the same time the crank pin C pulls up the connecting rod, and thus the upper end
724 HANDBOOK ON ENGINEERING.
of rod c, which takes the place of lever c in Fig. 321. In this way the switch blades in the lower end of c are raised into con- tact with the clips jf/, which take the place of contact Jin Fig. 321, and thus the circuit is closed. A projection s on c holds the switch e in the upper position, but when c is raised, s goes up with it, and then e is free to descend by the force of gravity acting upon the weight w. The dash pot m is set so as to retard the movement of e as much as may be desired. The outer end of e glides over the contacts i in its downward movement, and thus cuts out of the armature circuit the starting resistance. This resistance is contained in the controller box.
Fig, 323 shows the same type of controller as in Fig. 322, but it is arranged so that the motor may be started ahead of the elevator. The separate motor-starting rope is shown at H. When this rope is pulled, it elongates the spiral spring K which is connected with the stud 6r fixed in the upper end of rod c. The rope H is pulled up enough to stretch K until the lever Z>is lifted, H being attached to its outer end I. When D is lifted sufficiently, its inner end dis- engages the stud G, and allows it to slide upward in the slot shown in dotted lines, in the lower end of the connecting rod. In this way the motor is started ahead of the elevator machine. If now the elevator machine is started, by pulling on the main hand rope FF, the crank pin C' on the hand rope sheave will lift the connecting rod (7, and when it reaches its upper position, the catch-lever D will drop into the position shown in the illustration, and thus lock the stud Gr, so that when the elevator is stopped, the rotation of the hand rope sheave will push rod G downward and thus stop the motor, as well as shift the belts and stop the elevator machine.
In the three illustrations shown the motor is run always in the same direction and the reversing of the direction of rotation of the hoisting drum is effected by the use of double belts and a belt shifter, or friction clutches, which cause one or the other of
HANDBOOK ON ENGINEERING. 725
the belts to do the driving. The way in which machines of this
726 HANDBOOK ON ENGINEERING.
This figure shows the position of the motor, the countershaft and the elevator machine with reference to the elevator shaft. This illustration is so clear that an explanation of it would be superfluous.
In relation to the installation of elevator plants of this type all that need be said is that the motor must be of the shunt type, the same as those used for driving machines of any kind. A series wound motor, such as are used for electric railway cars, must not be used. Shunt wound motors cannot run above a certain speed, unless forced to do so by power applied from an external source, and in such an event they become generators of electricity and thus resist rotation. On this account, when they are used for elevator service, they not only move the elevator car, but when the latter is descending under the influence of a heavy load and tends to run away, the motor, at once begins to act as a gen- erator, and is thus converted into a brake, which holds the car and prevents it from attaining a speed much above the normal ; in fact, the difference between the car velocity when lifting a heavy load, and when running down under the influence of a similar load is hardly enough to be noticed by any one not familiar with the elevator.
The motor in these combinations is to be given the same care as those used for other purposes ; that is, it must be kept clean and the brushes properly set so as to run with as little spark as is possible. The controller switch requires more attention than the motor starters used with stationary motors, for the simple reason that it is used to a much greater extent. Every time the elevator is started or stopped the controller switch is actuated, hence, the switch levers are subjected to a considerable amount of wear, and the contacts are liable to become rough, either by cutting or by being burned on account of making imperfect contact. On this account the contact must be well examined at least once every day, and if burned or rough must be smoothed up. It is also
HANDBOOK ON ENGINEERING.
727
necessary to see that all parts of the controller are properly se- cured, that none of the screws or pins are working out, and that the contacts and switch levers are not out of their normal posi- tion.
Fig. 325. Wiring used with reversible motor.
As electric motors can be run as well in one direction as the other, and as all that is required to make any motor reversible is to provide a reversing switch, it can be seen at once that by mak- ing use of such a switch, the direction of movement of the ele«
728 HANDBOOK ON ENGINEERING.
vator car can be reversed by simply reversing the motor, and thus do away with the complication of a countershaft and tight and loose pulleys. Owing to this fact elevator machines are now made so as to be used with reversing motors. These are usually called single-belt machines. The way in which such machines are connected with the motor and the type of controller required can be understoood from the diagram Fig. 325.
As will be seen, the principal difference in the machine itself is that the tight and loose pulleys are replaced by a single tight pulley, which is only wide enough to carry the driving belt. Usually an extra pulley is provided for the brake, and this brake is mechanically operated in the same manner as upon machines provided with shifting belts. Another modification, which is sometimes used, but is not shown in the diagram, is the arrange- ment of a brake so that same is operated by a magnet instead of by mechanical means. With this arrangement the magnet is arranged so that when the machine is in motion, the current passing through the magnet coil acts to lift the brake, and when the machine stops, the magnet lets go, and the brake goes on. By arranging the brake in this way it becomes perfectly safe ; for if the brake magnet fails to act, the brake will not be raised, and the machine will not move ; that is, failure of the device to work properly will not permit the elevator car to move, thus calling attention to the fact that something is out of order.
The operation of the reversing controller is as follows : the current from the line wires passes along the dotted connections h h to the contacts 1,1, i,i. The upper left hand i contact is con- nected with the lower right hand one, and the upper right hand with the lower left hand. The switch lever c is connected with lever e by means of the two springs r r, so that c may be moved either up or down without carrying e with it. The curved con- tact o is connected with,/, while g is connected with the ends of the start- ing resistance n n by means of the wire / and the two wires s s. The
HANDBOOK ON ENGINEERING. 729
contacts y y are connected to k and the lower left-hand contact i is con- nected to x. If the hand rope I is pulled so as to carry lever c upward, the current from the left side line wire will pass through the upper left side contact i, to o, thence to j and through wire b to the motor arma- ture, returning through the other b wire to gr, then via / and lower s to the lower end of n, over the lever e, to the inner end of lever c which will be in contact with the upper right-hand i contact and finally to the right side line wire. The current for the field magnet coils will be drawn from the upper left side i contact to the adjacent y contact, thence to con- tact k, through the fields and back to x, finally to the left side line wire. As lever c has been moved upward, the upper spring r will be compressed, and the lower one will be stretched, hence a force will be exerted to move e downward over the lower contacts n and thus cut out the starting resistance. As in the case of the con- troller in Fig. 321 the dash pot m by its resistance retards the move- ments of e, so as to cut out the resistance as gradually as may be desired.
In the chapter on stationary motors it is shown that to prevent destructive sparking, when the starting switch is opened, the armature and field coils are connected so as to form a permanently closed loop. This style of connection is used in the non-revers- ing controller of Fig. 321, but it cannot be employed with a re vers- ing controller, because both ends of the armature circuit must be free, so that they may be reversed when the direction of rotation is reversed. As this connection cannot be made, a very common expedient resorted to to prevent serious sparking when the switch is opened is to connect a string of incandescent lamps across the terminals of the field circuit, as is indicated at v v v. These lamps, together with the field coils, form a closed, circuit, so that when the switch is opened, the field can discharge through the lamps, and thus avoid sparking at the controller contacts. The only objection to this arangement is that all the current that passes through the lamps is wasted, but by placing two or three
730 HANDBOOK ON ENGINEERING.
in series the loss is reduced to an insignificant amount. Another way in which the sparking is subdued, but only to a slight ex- tent, is by connecting the brake magnet coil with the binding posts x and fc, which is the simplest and most generally used con- nection. The brake magnet coil together with the field coils form a closed loop when connected with x and ft, but when the main cir- cuit is opened, the currents flowing in the two coils meet each other at x and ~k flowing in opposite directions, hence they both follow along the main circuit and try to jump across the gaps at the switch, and thus produce about as much sparking as if they were connected independently of each other. In tracing out the path of the current when lever c is moved upward, it was shown that the left side line went directly to the upper commutator brush. Now when c is moved downward, this same line wire runs to the lower commutator brush since the connections between the two upper i contacts and the two lower ones are crossed. To reverse the direction of rotation of a motor all that is required is to reverse the direction of the current through the armature, that through the field remaining unchanged, hence it will be seen that by cross- ing the connections between the upper and lower i contacts, the direction of rotation of the motor is reversed when the c lever is moved in opposite directions.
DIRECT CONNECTED ELECTRIC ELEVATORS.
The machines explained in the foregoing pages are simply combinations of an electric motor and a belt driven electric ma- chine, but, as already stated, they are commonly spoken of as 44 electric elevators." In what follows it is proposed to explain the construction and operation of true electric elevators, which are called 44 direct connected machines " to distinguish them from the combinations so far described.
There are many designs of direct connected electric elevators
HANDBOOK ON ENGINEERING.
731
now upon the market, and it would be out of the question to un- dertake to describe all of them in the space that can be devoted to the subject in this book. On that account the discussion will be confined to the designs that are most extensively used. The explanations here given, however, will be sufficient to enable any
Fig. 326. The Otis direct connected elevator.
one to understand the operation of any of the machines not de- scribed because the difference in the principle of operation is only slight.
732 HANDBOOK ON ENGINEERING.
Perhaps the type of direct connected electric elevator that is most extensively used is the Otis drum elevator with hand rope control which is illustrated in Fig. 326. This machine has been upon the market for twelve years or more, and is still one of the standard Otis machines. It is called a hand rope control machine because the starting and stopping is controlled by the movement of a hand rope that passes through the elevator car. In the illustration, the sheave around which the hand rope passes can be seen located on the front end of the drum shaft. In a modification of the design, this sheave is mounted upon a sep- erate shaft but the way in which it acts is the same as in the pres- ent design. When the hand rope is pulled the sheave is rotated and the horizontal bar, running from it to the controller box, which is mounted on top of the motor? shifts the starting switch so as to run the machine in the direction desired. At the same time, the vertical lever ex- tending upward from the side of the brake wheel, lifts the brake and thus frees the motor shaft so that it may revolve unobstructed. The motor carries a worm on the end of the armature shaft which gears into the under side of a worm wheel mounted upon the drum shaft. This worm wheel runs in a casing seen just back of the hand rope sheave wheel. The sheave mounted upon the shaft directly above the drum is for the purpose of guiding the coun- terbalance ropes, which run up from the back of the drum. In some buildings these ropes can be run up straight from the back of the drum, but in most cases they must run up in the elevator shaft in the space between the car and the side of the shaft. As these ropes wind upon the drum from one side to the other, the guiding sheave must move endwise on the shaft, hence it is called a traveling, or vibrating sheave. The levers seen projecting to the right of the machine from a small shaft just above the drum are what is called a slack cable stop, and their office is to stop the machine if the lifting cable becomes slack through the wedg-
HANDBOOK ON ENGINEERING. 733
ing of the car in the elevator, shaft or any other cause. These levers are held in the position shown when the lifting ropes are tight, but drop out of position if the rope slackens up, and in dropping they release a lever, which holds the weight seen under the hand rope sheave. The movement of this lever operates a catch that engages with the hand rope sheave and thus the hori- zontal bar that operates the brake and the controller switch is brought to the stop position and the rotation of the hoisting drum is stopped.
The hand rope has fastened to it at the top and bottom of the elevator shaft stops that are moved by the car when it reaches either end of its travel, and thus the elevator machine is stopped automatically. This arrangement is the same as that used with the belt driven machines already described, but as an additional safety, a stop motion is provided on the machine itself, so that if the stops on the hand rope become displaced, the car will still be stopped automatically at the top and bottom landings. This stop motion is seen on the end of the shaft, just in front of the hand rope sheave, and consists of a nut that travels on the shaft as the latter revolves. At both sides of the screw there are projection cases upon the inclosing frame, which are struck by the traveling nut when it comes near enough to either end. When the nut strikes the projection, the hand rope sheave is revolved with the shaft and thus the machine is stopped. To understand this ac- tion it must be remembered that the hand rope sheave does not revolve except when turned by the pull on the hand rope or by the action of the slack cable stop or the traveling nut.
The controller box on top of the motor contains the starting resistance, the starting and reversing switch, and also a magnet to actuate a switch that gradually cuts out the starting resistance. The way in which the switches act to start and stop the motor can be readily explained by the aid of the diagram Fig. 327.
This shows the circuit connections in the simplest possible
734
HANDBOOK ON ENGINEERING.
form. In this diagram all the wires whose presence would make
t
SArETY MAGNET FOR BRAKE ON MA CHINE
SHUNT FILLD
Fig. 327. Diagram of controller box and wiring.
the drawing confusing have been removed, but the manner in
HANDBOOK ON ENGINEERING. 735
which they are connected will be readily understood from the following explanation : —
The main switch, which connects the motor circuits with the line, is located at the upper left hand corner of the diagram, the main line wires being marked-}- and — . When this switch is closed, the motor circuits are connected with the line, but the motor circuit itself is not closed so long as the switch M remains in the position shown. When this switch is turned about one quarter of a revolution in either direction, one end will ride over the upper contact and the other one over the lower contact. The reversing drum and switch M are mounted on the same spindle and move together. They are located within the con- troller box, on top of the motor, and are moved by the horizontal bar ; see Fig. 326. The shaded portions of the drum, on which the brushes h and i rest are made of insulating material so that when switch M and the reversing drum are in the position shown the motor circuit is open at two points. This is the position of these parts when the machine is stopped.
The starting resistance is shown above the reversing drum, and in the machine it occupies the space at the back of the con- troller box, shown on top of the motor in Fig. 326. The segment R is a series of contacts that are connected with the resist- ance in the resistance box; No. 2 contact being con- nected with point 2 on the resistance and so on for all the other numbers. The switch arm JVis moved over the contacts R by a magnet that is represented by the spiral L. The motor arma- ture and the shunt and series field coils are shown at the bottom of the diagram. The motor is compound wound, it being made so for the purpose of keeping the starting current as low as possi- ble. The path of the current through the wires is as follows : Sup- pose the reversing drum andtheJtf switch are revolved in the direc- tion in which the hands of a clock move, then brushes # and i will rest on one segment, and h and Jc will rest on the other segment.
736 HANDBOOK ON ENGINEERING.
As switch M will now be closed, the current will flow to brush g and through the reversing drum segment to brush i; then it will follow the wire to the right side / of the armature and pass- ing through the latter will reach wire E and thus brush h, from which it will pass to brush Jc. From this brush the current will go to and through magnet L and by wire C ' and switch N will reach contact No. 10. As this contact is connected with point 10 of the resistance the current will reach the latter and will pass through the whole of it, coming out at the opposite end C. This end is connected with contact (7, so that from this segment the current can flow through wire 0 to the end F of the series field coils, and passing through these to end H, will find its way to wire /, and thus return to the opposite side of the main line. From this explanation it will be seen that the current will pass through the motor armature, and then through the whole of the resistance in the resistance box, and then through the series field coils, and finally reach the other side of the main line. From the switch M another current will branch off and run to binding post .D, and thence through the shunt field coil . to binding post .fiT and thus to wire/, and through the latter to the opposite of the main line.
The switch lever N is in some cases arranged so that the mag- net L acts to hold it upon contact 10 and a spring acts to carry it forward toward contact^.; in other cases the magnet is wound with two coils, one of which pulls N in one direction and the other pulls it in the opposite direction, the two coils being so pro- portioned that N moves gradually from contact 10 toward con- tact A. If we take the spring arrangement, then magnet L will pull N back toward contact 10, and the spring will pull it forward. As the starting current is very strong, ^Twill be held on contact 10, but as the current weakens, the spring will begin to overpower the magnet, and N will slide over contact 9 and then 8 and 7 and so on to contact A. As contact 9 is connected with the point 9
HANDBOOK ON ENGINEERING. 737
of the resistance, when JV reaches it, the section of the resistance between points 10 and 9 will be cut out. When N reaches con- tact 7 the resistance between points 10 and 7 will be cut out for the latter point is connected with contact 7. As all the contacts are connected with the corresponding points of the resistance, when N reaches contact (7, all the resistance in the resistance box will be cut out of the circuit. As will be noticed, contact B is connected with the center point G of the series field coil so that when N reaches contact B one-half of the series coils will be cut out in addition to the whole of the resistance box. When N reaches contact^ the current will pass directly to wire/, and thus cut out all the series field coils and then the motor will run as a plain shunt-wound machine, and its speed will be the highest it can attain.
If the reversing drum and switch M are now revolved to the position shown in the diagram, the circuit through the motor will be broken and the machine will come to a state of rest. If the reversing drum and M are now revolved in the opposite direction, that is, contrary to the movement of the hands of a clock, the brushes g and h will rest on one of the revolving drum segments, and i and k on the other segment. If the path of the current is now traced it will be found that it will enter the armature through wire E, and the left side, instead of through wire 7, as in the pre- vious case. It will also be found, however, that 'the current after passing through the armature will reach the series field coils through Fj which is the same path as before, so that the direction of the current has been reversed through the armature only, which is what is required to reverse the direction of rotation of the motor. Whichever way the switch M and the reversing drum are turned, the direction of the currents through the series field coils and the shunt field coil will be the same, and only the arma- ture current will be reversed.
Cutting out the series field coils not only increases the speed
47
738 HANDBOOK ON ENGINEERING.
of the motor, but obviates the danger of the car attaining a dan- gerously high speed if the load is being lowered. A shunt wound motor will run as a motor up to a certain speed, but if the veloc- ity is forced above this point by driving the machine by the ap- plication of external power, then the motor will begin to act as a generator, and as it takes power to run a generator the motor will begin to hold back. Now if an elevator car is running down with a heavy load, the load will draw the car down, and unless a resistance of some kind is interposed, the speed will become preater and greater as the car descends, and by the time it reaches the bottom of the shaft it may be running at a velocity almost equal to that attained by a free fall. The power required to drive the motor when acting as a generator serves to hold the car back, for the current developed increases very rapidly with increase of speed, so that an increase of speed of ten or fifteen per cent above the normal running velocity will be about as much as can be reached even with an extra heavy load.
Although the motor will act as a generator and hold the car so that it cannot attain a dangerous speed when descending under the influence of a heavy load, it will only accomplish this result when the circuit is closed ; for if the circuit is open there will be no power generated ; hence, no power will be absorbed by the motor. As can be readily seen, it is possible for the circuit out- side of the motor to become broken by the melting of a fuse or some other cause, and if this occurs when the car is coming down with a heavy load there might be a serious accident. To obviate such mishaps the main switch is made with a magnet &, which holds the switch closed so long as current passes through it, but allows the switch to swing open if the line current disappears. This switch on this account is called a potential switch, because it is arranged to be actuated by the difference of potential be- tween the two sides of the line. When the line current fails, and the potential switch opens, the blade m comes into contact with w
HANDBOOK ON ENGINEERING. 739
and thus the circuit for the motor armature is closed through the resistance wire s, which is connected with contact 7. This con- nection short circuits the armature through a resistance sufficient to keep it from being burned out, but not enough to prevent the motor from acting as a brake and holding the car down to a safe speed.
The wire c c, which runs from magnet b of the potental switch it will be noticed, connects with a coil marked safety brake mag- net. This magnet acts normally to hold the brake off when the machine is running, but if the current passing through it dies out, then it acts to put the brake on. Now, as has already been ex- plained, when the current is flowing in the main line, there is a current passing through coil b of the potential switch ; hence, there is a current passing through the coil of the safety magnet for the brake ; but if the line current fails the current through the brake magnet will also fail and the brake will go on ; so that the car will be doubly protected, one protection being the short cir- cuiting of the motor circuit through wire s, and the other the ap- plying of the brake by reason of the failure of the current to flow through the safety brake magnet.
As to directions for the proper care of these machines, very little need be said, as they are simple and substantial in con- struction and give very little trouble. The motor proper requires the same attention as is given to any stationary -motor, that is, the commutator and all other parts must be kept as clean as pos- sible and the brushes must be properly set. As to the other parts, all that need be said is that the bearings must be well lubri- cated and free from grit. They must be tight enough to not al- low the parts to play, but at the same time care must be taken that they are not so tight as to heat up or cut. All bolts and nuts must be regularly examined and kept tight, so that they may not work loose or out of place. The most important point to observe, however, is not to undertake under any circumstances
740 HANDBOOK ON ENGINEERING.
to tinker with the sheave wheel and the gears that connect it with the horizontal bar that operates the brake and controller switches. Neither must the brake or the switches be disturbed. All that is to be done to the latter is to keep the contacts bright and clean. If any of these parts, from the sheave wheel to the controller switches, get out of set, so that the machine will not run satisfactorily, do not undertake to readjust them, but send for an expert from the elevator company. If any of these parts are removed or shifted there is danger of their not being put back in their proper position, and if they are misplaced a very serious accident may be the result. If the proper adjustment of these parts is destroyed, the elevator will not stop automatically at the top and bottom landings, but will run too far at one end and stop short of the mark at the other ; hence, the car may either strike violently against the floor or ran at full speed into the overhead beams, and in either case the results might be very serious. Even elevator experts have to go cautiously in adjust- ing the position of the sheave wheel and the parts connected with it.
The fact that those not thoroughly posted in the operation of these elevators should not tamper with the hand rope sheave and its connections, is not at all unfortunate, for it is next to impos- sible for them to get out of place ; but special caution is advised at this point, because there are many men who are apt to take it for granted that if the machine runs poorly from some trifling cause that they have not been able to locate, the trouble must be due to some defect in the adjustment of the several parts of the operating sheave and its connections. They will then proceed to pull the machine apart, and when they put it together again they are very liable to get it connected wrong, and if such should be the case the first trip made by the elevator might end seriously.
Although the machine described in the foregoing works in an entirely satisfactory manner, it has been superseded almost en-
HANDBOOK ON ENGINEERING.
741
tirely in first-class installations of recent date by machines that are controlled by means of a small switch in the car instead of the hand rope. There are several types of such elevators made by the Otis company, one of the latest designs being shown in Fig. 328.
w
Fig. 328. Latest design of direct connected machine.
As will be noticed at once, this machine is different in several respects from" the hand rope control machine shown in Fig. 326 . As the machine is controlled by the movement of a switch in the car, the brake cannot very well be actuated mechanically, hence a magnetic brake is provided, the magnet being seen at the top of -the stand to the right of the motor. The automatic stopping de- vices and the slack cable stop are also arranged so as to act upon
742
HANDBOOK ON ENGINEERING.
switches, which are contained within the casings seen at the front end of the hoisting drum. The controller for this type of machine is not placed on top of the motor, generally, for since it
CAff
Fig. 329. Diagram of wiring connections for controller.
is not connected mechanically with any of the moving parts of the machine, it can be located at any convenient point, and is then connected with the motor armature, field coils and with the brake
HANDBOOK ON ENGINEERING. 743
magnet and automatic stop switches by means of copper wires. The controller used with this type of machine is arranged after the fashion of a switchboard, the switches being located on the front, and the connecting wires, together with the starting resist- ance, being at the back. The switches are actuated by means of electromagnets, and on that account the device is called a magnet controller. The diagram of the wiring connections with this con- troller is more complicated than that for the hand rope controller, but for the purpose of simplifying the drawing as much as pos- sible we have removed all the connections that are not actually necessary for a proper understanding of the general arrangement of the circuits. This simplified diagram is shown in Fig. 329.
The front of the controller is shown in Fig. 330, and the back of same in Fig. 331, the starting resistance being removed in this illustration so as to afford a clear view of the wire connections. The side of the starting resistance can be seen in Fig. 330. In this last named illustration, all the switches are in the position they take when the elevator is stopped. The two large switches on either side at the bottom of the board are the starting switches, one acting to run the car up and the other one to run it down. The two smaller switches occupying the center of the bottom panel of the board and the two switches in the upper corner are for the purpose of accelerating the velocity of the motor when it is started. When the motor starts, there is a resistance in the armature circuit, and the current after passing through the arma- ture is passed through series field coils. After the motor has started, the starting resistance is cut out, and then the series field coils are cut out, so that when the full speed is attained, the motor is a simple shunt- wound machine. In this respect the arrangement of the motor circuits is the same as in the hand rope controller machine.
When it is desired to start the car, a small switch in the latter is moved toward the right or left, according to the direction in
744
HANDBOOK ON ENGINEERING.
which the car is to move. To run the car up, the car switch is turned to the left, and this movement sends a current through the magnet of the lower right side magnet on the controller board.
Fig. 330. Showing front of controller.
This magnet then lifts its plunger and the two discs mounted upon the latter come into contact with the stationary connectors located just above them, and then the current can find its way through
HANDBOOK ON ENGINEERING „
745
the motor circuits in the proper direction to produce the upward motion. The four small switch magnets on the controller board are connected in separate circuits that are in parallel with each
Fig. 881. Back ot controller.
other, and in shunt relation to the armature of the motor. When the motor first starts, the counter electromotive force developed by the armature is not as great as when it is running at full speed,
746 HANDBOOK ON ENGINEERING,,
HANDBOOK ON ENGINEERING. 74?
ping the motor, if the car reaches either end of its travel without being stopped by the operator, or the action of the stop motion switch. This switch is closed under ordinary conditions, so that the current in wire C can flow all the way to the lower contact a of the car switch. If it is desired to run the car down, the car switch is turned to the right, and then wire G is connected with wires D ' and FD. The stop motion switch is normally in the position shown so that the current in wire D ' can pass to D0 and following this wire it will reach contact DO which is under the lower disc of the right side starting switch. Through the disc this contact is connected with the corresponding contact on the other side of the disc, and this latter contact is connected with a wire that carries the current to the magnet of the left side starting switch. Considering now the main current in the + line it can be seen that it can flow down to the line near the bottom of the controller portion of the diagram, and which terminated in the -f- contacts of both the starting switches, but can go no further so long as the discs on the plungers of the magnets are in the lower position. As soon, however, as the current coming from the car switch passes through the magnet of the left side switch, as just explained, the plunger will be lifted, and then the disc will connect the + contact with the S2 contact, and also with a smaller contact B. When this connection is made, the main cur- rent can flow from contact S2 to contact 82 of the right side switch, and thence through the connecting disc to contact I which is connected by wire to binding post I; the latter being con- nected with the right side armature terminal I. After passing through the armature the main current reaches binding post E and through the connecting wire the contact E at the top of the left side starting switch, and as the plunger of this switch is in the raised position, the current can pass to contact R and thus reach the upper end R of the starting resistance in the resistance box.
748 HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 749
Thus it will be seen that the four switches, 1,2, 3 and 4, will act one after the other. This same operation is repeated if the car switch is moved to the right, so as to run the elevator down, the only difference being that the starting switch at the right side of the board will be lifted, but the action of the four smaller switches will be the same.
In addition to the operating circuits described in the foregoing there are wires that connect the slack cable switch with the motor circuits and other connections by means of which the elevator may be run from the controller board whenever desired. These con- nections are not shown in Fig. 329, as they would complicate the drawing, and it is not thought advisable to complicate the explan- ation of the main part of the system for the sake of introducing the minor details.
This type of electric control is used for elevator machines in- stalled in office buildings , and others placed where the car is oper- ated by a regular attendant. For private house elevators and for dumb waiters it is necessary to modify the controlling system so that the car may be operated not only from within, but also from any of the floors of the building. It is further necessary that the circuit connections be such that if the car is operated from any floor, it will run to that floor, whether above or below it, and further, so that if it is being operated by a person within the car it cannot be operated by any one else from any of the landings. It must also be arranged so that if the car is set in motion from any floor it cannot be stopped or interfered with in any way by a person at another floor. For the purpose of safety the system must also be arranged so that the car cannot move away from any floor until the landing door is closed. This feature is necessary to guard against people falling through the open doorway into the elevator shaft. Although it would appear difficult to accomplish all these results without resorting to great complications, as a matter of fact the system used by the Otis company is decidedly
750
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 751
simple. At each floor of the building a push button is placed, and by pressing this for an instant the car is set in motion wher- ever it may be, providing it is not being used by some other per- son, and when it reaches the floor from which it has been operated it will stop automatically. If the elevator is operated from the car, a button is pushed that corresponds to the floor at which it is desired to stop, the car will then begin to move, and when the floor is reached it will stop. If the passenger after stepping out of the car forgets to close the landing door, the elevator cannot be moved away from the landing by the manipulation of any of the push buttons on the various floors or within the car. The way in which all these results are accomplished can be made clear by the aid of Fig. 332, which is a simplified diagram of the wiring.
In this diagram most of the parts are marked with their full name. The floor controller is a drum, which is revolved by the elevator machine, and its office is to shift the connections of the wires 11, 22, 33, 44, from one side of the circuit DU to the other as the car ascends and descends in the elevator shaft. This shifting of these connections is necessary to cause the car to run down if above the landing from which it is operated, and to run up if it is below the landing. The actual position of the floor con- troller with reference to the elevator machine can be seen in Fig. 333 in which the floor controller is located back of the motor and is driven from the drum shaft by means of a chain and sprocket wheel. In the diagram Fig. 332 it will be noticed that the drum surface is divided into two segments and upon one rests the brush of wire D while upon the other rests the brush of wire U. The twelve contacts shown at G form the operating switch. The center row marked m n o p are movable, and the four contacts above them as well as the four below are stationary. The center row of con- tacts m n o p are moved upward by a magnet represented by the coil D and they are moved downward by another magnet repre-
752 HANDBOOK ON ENGINEERING.
sented by the coil V. From this it will be seen that if a current comes from the floor controller through wire D the movable con- tacts of G will be lifted and will connect with the top row, while if the current comes from the floor controller through wire (7, the movable contacts will be depressed and will make connections with the lower row of contacts.
The main switch that connects the motor circuits with the main line is shown at S. As will be noticed, a wire marked d + H runs from the + wire to the right side of the diagram, where the landing and the car push buttons and their connections are shown. This wire runs from top to bottom of the elevator shaft and is con- nected with switches that are closed when the landing doors are closed, and open when the doors are open. These switches are indicated by the four circles marked door contacts, the diagram being for a building four stories high. If the door contacts are closed, the current can pass as far as the wire marked -f- which runs through the flexible cable to the car. In the car there is a switch in this wire and further on a gate contact, which is closed when the car door is closed. If these switches are closed, the current can return from the car through wire A and run as far as the center of the diagram under the main switch S. The floor controller is shown in the position corresponding to the car at the bottom of the shaft. Suppose now that the landing push button I is pressed for a second, then the wires B and I will be connected, and the current in wire A will pass to wire B and through the push button to wire I and thence to wire II. The coil between wire I and wire II is a magnet, and as soon as the current passes through it, it draws the contact to the right and thus provides a path for the current direct from wire A to wire ZZ, so that the push button may be raised without opening the circuit. The current in wire II will pass through the floor controller to wire £7 and thus through magnet U of the operating switch G. This magnet will then draw down the movable contacts m n o p, and the main line
HANDBOOK ON ENGINEERING.
753
current from the -f- wire will pass from contact m to wire m' and through wire m' to point zo, hence through wire wr to the acceler- ating, or starting resistance, and to wire F which leads to tha series field coils. Returning from these coils through wire H to Eaagnet switch 2 and thence wire n' to contact n, and as this con-
Fig?. 333. Direct connected eleyator with floor controller.
tact is pressing against the one directly below it, the current will flow through the connection to wire E and thus to the armature ; returning from the latter through wire I and wire o' to the contact below o and thus to o and through the permanent connection to contact p and to the lower right hand contact, which is connected
48
754 HANDBOOK ON ENGINEERING.
with wire r, which runs to the — side of the main switch. The shunt field current is derived from wire m' and returns to contact p and thus to wire r through wire p* ', as can be clearly traced. The brake magnet current starts from the left side contact of G through wire + B and returns directly to the lower end of wire r.
The magnet switches 1 and 2 act in the same manner as those in diagram Fig. 329, that is, by the increase in the counter electro- motive force of the armature which causes the current that passes through them to increase in strength. When magnet I closes its switch, the current passes from wire w9 to wire F and thus the accelerating resistance is cut out. When magnet 2 closes its switch the current passes from wire m" directly to n' and thus to the armature without going through the series field coils ; thus the latter are cut out.
Returning now to the operation of the floor controller it will be seen that as the current is flowing through wire II the circuit will be broken if the controller is rotated until the gap at the top comes under the brush of wire II. Now the floor controller drum begins to turn as soon as the elevator machine moves, and it is so geared to the elevator drum that when the car comes op- posite the first floor the brush of wire II will be over the upper gap, and then the circuit will be open and the magnet U will be de-energized and allow switch G to move back to the stop position.
If button No. 4 is pressed instead of No. 1 the car will not stop until the gap at the top of the floor controller drum comes under the brush wire 44, for the circuit between this wire and wire U will be closed until that position is reached.
If the car is run up to the fourth floor, as the gap at the top of the floor controller drum will then be under the brush of wire 44, the brushes of wire 11, 22 and 33 will rest upon the same segment as the brush of wire D; therefore, if with the car at the top floor a button is pressed at any one of the lower floors
HANDBOOK ON ENGINEERING. 755
the current will pass from its corresponding wire to wire D and thus through magnet coil D and to wire / and wire r. The cur- rent passing through magnet D will draw the movable contacts of the operating switch 6 upward, and thus set the elevator machine in motion in the opposite direction from that in which it runs , when the IT magnet is energized.
In tracing out the circuits from the floor push buttons as just explained it will be noticed that if any one of them is depressed, the current in wire A will flow through wire B to the button de- pressed, and then enter the wire returning from that button. When the car buttons are depressed the current in wire A will pass to wire C and then through the button in the car to the proper return wire ; that is, to one or the other of the wires 1, 2, 3, 4. After entering one of these four wires the current follows the same path as it does when one of the floor buttons is depressed. The magnet B' in the B wire, and the magnet C' in the C wire, are for the purpose of preventing in- terference between a person operating the elevator from within the car and another one at one of the landings. The B' switch is actuated by a magnet that is wound with two coils that act in opposition to each other. These coils are shown to the left of B' '. When the elevator is operated from one of the floor push buttons the current in wire A passes through both the coils on the magnet of switch Bf and as one coil counteracts the other the switch is left closed and the current passes directly to wire B. If the elevator is operated from within the car the current from wire A in passing to wire C passes through one of the coils of the mag- net that actuates switch B' ', hence this switch is opened and the connection with wire B is broken, so that if now any one of the floor buttons is pressed it will have no effect as the circuit is opened at switch B'. The current flowing through wire C passes through a magnet that acts to close the switch C' and thus allow a portion of the current to pass directly to wire r. This current
756 HANDBOOK ON ENGINEERING.
will continue to flow even after the car has stopped at the landing, providing the door is not opened. As soon as the door in the car, or the landing door, is opened the circuit is broken either in wire Hor in wire A, and then the car cannot be moved until the doors are closed. If it were not for switch (7 it would be possi- ble for a person at one end of the landings to move the car if he pressed the button during the short interval of time between the stopping of the car and the opening of the landing door. The opening of the door would stop the car, but by this time it might be a foot or two away from the floor level. The current that passes from switch C" to wire r is kept down to a small amount by passing it through a high resistance which in the diagram is marked 700 w.
The electrical portion of the Otis electric elevators has been supplied for many years to four or five of the leading companies, which were controlled by the Otis, and during the last two or three years it has been supplied to practically all the prom- inent makers, as these are now part and parcel of this company ; hence the descriptions given in the foregoing are more than likely to cover any case met with in practice, for although there are numerous small manufacturers, the sum total of their elevators in use is comparatively small. The only electric elevators in addition to those described in the foregoing that have come into extensive use are those made by the Sprague Electric Co.
These machines are of two different types, one being the ordi- nary drum design, and the other the screw machine. The drum machine is similar in its main features to the same type of ma- chine of other makers, and it is only in the minor details of con- struction that any radical difference can be noted. In the means employed for controlling the motion of the motor, however, there is a decided difference. In all the Sprague elevators the car is controlled electrically, hand rope control not being used in any
HANDBOOK ON ENGINEERING.
757
3
<yf
8
I
"»
758 HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING.
759
Fig. 335. Elevator controller board.
760 HAND BOOK ON ENGINEERING.
The nut carried by the traveling cross- head is so arranged that when the latter reaches the end of its travels at either end of the screw, the nut is released and then rotates with the screw with- out moving the cross -head. This forms a perfect top and bottom limit stop, for even if the motor continues to run, the car cannot be carried beyond the positions corresponding to the points at which the nut slips around in the cross-head.
The brake for holding the machine is mounted upon the outer end of the armature shaft, ancj. can be seen at Fig. 334 at the ex- treme right hand side. This brake is actuated by a magnet that releases it, and a spring that throws it on. When the current is on, the brake is lifted and when the current is off the brake goes on. In this respect, the action is the same as in all other electric elevators.
The operation of the motor is controlled by a small switch in the car, which is connected with the motor circuits by means of wires contained in a flexible cable, just like the Otis electrically controlled machines. The controller consists of a main switch, which is moved by a small motor called a pilot motor, and a num- ber of smaller magnetic switches whose action will be presently explained. All these parts are mounted upon a switchboard, and present the appearance shown in Fig. 335. The pilot motor and main switch are located at the top of the board, and the magnet switches cover the space below, while the starting and regulating resistance is mounted on the back of the board.
The complete wiring diagrams for these machines is decidedly complicated owing to the fact that there are numerous switches and devices whose office is to afford additional safety, or to ren- der the control more perfect. When all the parts that are not actually necessary to illustrate the system are removed, however, the diagram becomes quite simple and can be readily understood. Such a diagram is shown in Fig. 336. This diagram shows the motor together with the screw and sheaves, the elevator car, the
HANDBOOK ON ENGINEERING. 761
counterbalance, and the operating switches. The wires marked + and — are connected with the main line. The switch in the car is connected with the controller by means of four wires, marked c b d and s. The lower one of these wires, marked s, is connected with the stud around which the car switch swings. When the car switch is moved onto the upper contact, it connects wire s with wire c and then the car runs up. When the car switch is moved down onto the lower contact, wire s is connected with wire d, and then the car runs down. When the car switch is placed in the central position wire s is connected with wire b and then the elevator stops. The two switches marked " up limit," " down limit," are for stopping the car automatically at the top and bot- tom landings. Normally the up limit switch is closed and the down limit switch is open. With these switches in this position, which is the position in which they are shown in the diagram, the current from the + wire can pass through the up limit switch to wire fc, and thence through wire I to the armature of the motor, and then through the field coils, and reach wire m. It cannot go beyond this point until the switch C is moved. This is the main operating switch, which in Fig. 335 is seen at the top of the board, the contacts being arranged in two circles. The pilot motor that rotates the arm of this switch, which is clearly shown in Fig. 335, is represented in this diagram, Fig. 336, at A. As will be seen in this diagram, this motor has a field provided with two magnetizing coils, one for the up motion, and one for the down motion, and in addition it is provided with a brake to stop it quickly and hold it when not in use. The portion of the diagram marked B is the reversing switch.
Let us suppose now that the car switch is moved upward, so as to cause the elevator to ascend, then wire s will be connected with wire c. From the + wire a current will pass through wire a to s and thus to c, and through magnet e of switch ^, thus closing this switch so as to connect wires li and i. The current in wire c will
762
HANDBOOK ON ENGINEERING.
pass to B and through the connecting plate u will reach the end of the up field coil of the pilot motor, and then pass through the armature of this motor, and finally through the magnet that re- leases the brake. The pilot motor will now rotate the reversing switch B so that the contact plates will move toward the left. This movement will bring plate w under the ends of wires s and t, thus permitting a current from s to pass to tf, and as switch g is
Fig. 886. Diagram of elevator controller board.
closed this current will reach wire h and thus the magnet J, thereby lifting the plunger switch that closes the gap between wire q and the — wire. As the arm of the main switch 0 moves with the reversing switch _B, this arm will ride over the contacts on the right side, marked" up res." and thus the current from wire m will be able to reach wire q after passing through the up resistance.
HANDBOOK ON ENGINEERING. 763
If sthe car switch is left on the upper contact, the pilot motor will continue to rotate until the arm of switch C reaches the top of the resistance contacts, marked Full Up. When this point is reached, the contact plate u of the reversing switch B will pass from under wire c and the terminal of the up field of the pilot motor, and then this motor will stop rotating.
If the car switch is not kept on the upper contact very long, the pilot motor can be stopped with the. arm of switch G at some intermediate point on the resistance contacts, thus by the time during which the car switch is kept upon the upper contact, the amount of resistance cut out of the motor circuit can be con- trolled and thereby the speed of the car can be controlled.
In this operation it will be noticed that the motor is connected with the main line and that the current enters through the + wire and passes out through the — wire. If now we turn the car switch downward, the s wire will be connected with the d wire and by following the latter to the reversing switch B it will be seen that through connecting plate v it is connected with wire z which leads to the end of the down field of the pilot motor, thus setting the latter in motion in the opposite direction so as to shift the contact plates of B toward the right, and at the same time rotate the arm of the main switch C to the left, thereby making contact with the contacts of the down resistance. With the arm of G in this position, it will be seen that the current in wire I can flow through the motor armature and field and through wire m to the arm of switch G and through the down resistance to wire n and thus back to wire Z, thereby forming a closed circuit within the motor wires and connections, and disconnected from the main line except on the side of the + wire. The rotation of B causes the connecting plate x to ride upon the terminals of wires s and £, and thus a current is sent through the brake magnet so as to lift the brake, and allow the elevator machine to run. When the pilot motor moves the arm of C so far as to reach the top of the down
764 HANDBOOK ON ENGINEERING.
resistance, the contact plate v of the reversing switch B will pass beyond the terminals of wires d and z, thus breaking the circuit of the pilot motor and bringing the latter to a stop.
When the reversing; switch B is in the stop position, as shown in the diagram, the terminal of wire b does not rest upon a con- necting plate but when the switch is rotated for the up motion, the terminal of b rests on plate v so that if the car switch is turned to the stop position, the current from wire b will pass to wire z and thus reverse the direction of rotation of the pilot motor, and return the switches to the stop position. If the car is running down, when the car switch is turned to the stop position, the current from wire b will pass to wire z and thus reverse the direction of rotation of the pilot motor, and return the switches to the stop position. If the car is running down, when the car switch is turned to the stop posi- tion, the wire b will ride over the plate u and thus the current will pass through the pilot motor through the up field and thus rotate the switches back to the stop position. In each case, as will be noticed, whenever the current flows through wire b it ene gizes coil / and thus opens switch g. When the car is running up the current for the brake magnet passes from wire i through the switch which is energized by the main current flowing in wire q. When the car runs too far down, and closes the down limit switch, the motor circuit becomes closed through wires j), r and &, thus giving another path for the current generated by the motor arma- ture and thereby increasing the resistance to rotation.
The controller for the Sprague drum machines is very similar to the one just described. It is operated by a pilot motor, and in so far as the controller switchboard is concerned looks the same. The only difference is that rendered necessary by the fact that in lowering as well as in raising the load, the motor is connected with the line. This requires a slight change in some of the wire connections.
HANDBOOK ON ENGINEERING. 765
The electrical parts of the Sprague elevators require very little attention other than to keep them clean and all the contacts bright and in proper adjustment, so that when moved a good contact may be made. Of the mechanical portion, the drum machines require about the same attention as other machines of this type. As to the screw machines, the part that requires most attention is the screw and the nut. As can be readily understood, if the nut were solid, the friction against the screw would be very great ; therefore, to reduce this friction, the nut is made so as to carry a large number of friction balls. These run in a groove cut in the side of a thread and roll between the thread and the screw and the thread in the nut. A tube is attached to the nut to provide a path through which the friction balls can pass from the end of the thread to the beginning, thus making an endless path in which they move. As these friction balls are subjected to a heavy pres- sure, there is more or less danger of their giving trouble and on that account the thread on the screw should be carefully examined and kept as clean and free from grit as possible. Under favorable conditions these screws run very well, the wear being trifling, but in some instances they are liable to cut badly, hence they should be closely watched.
DIRECTIONS FOR THE CARE AND OPERATION OF THE ELECTRIC ELEVATOR.
Whenever the attendant wishes to handle the machine to clean, adjust, repair or oil it, he should see that the current is shut off at the switch, and thus prevent all possibility of accident.
Cleaning. — Keep the entire machine clean. Clean the com- mutator and other contacts and brushes carefully with a clean cloth and keep them free from grease and dirt. If the face of the rheostat on which the rheostat arm brushes work becomes burnt, clean with a piece of fine sand-paper (No. 0), or if necessary use
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 767
resistance is cut out of the armature circuit by slightly easing off the weight, which acts in opposition to the core of the small solenoid. This solenoid controls a valve in the dash-pot and thereby regulates its speed in proportion to the current passing. If a governor starter is used and the current is admitted too rapidly, tighten the governor spring on the armature shaft, or close the vent in air dash-pot. If the car refuses to ascend with a heavy load, immediately throw the lever to the center and reduce the load, as in all probability it is greater than the capacity of the elevator. If it refuses to ascend with a light load, throw the lever to the center and have the fusible strip examined. If, in descending, the car should stop, throw the lever to the center and examine safeties, fusible strip and machine, and before starting, be sure that the cables have not jumped from their right grooves. If the car refuses to move in either direction, throw the lever on the center and have the fusible strips examined. Never leave the car with- out throwing the lever to the center. If the car should be stalled between floors, it can be either raised or lowered by raising the brake and running it by turning the brake-wheel by hand. Such a stoppage might be caused by the current being shut off at the station, undue friction in the machine, too heavy a load, fuses burnt out, or a bad contact of the switches, binding posts or elec- trical connections. If the car by any derangement of cables or switch cannot be stopped, let it make its full trip, as the auto- matic stop will take care of it at either end of the travel. The bearings should be examined occasionally to insure no heating and proper lubrication.
General directions* — Have the machine examined occasionally by someone well posted in electric motors and elevators. The attendant should inspect the machine often. All brushes and switches should be sufficiently tight to give a good contact, but no tighter. None of the brushes should spark when in their
768 HANDBOOK ON ENGINEERING.
normal position. When the brushes become burnt dress witn sandpaper or file, or, if necessary, replace with new ones. If brushes spark, dress with sandpaper or file to a good bearing, and, if necessary, set up springs, but do not make the ten- sion such as to interfere with their ready movement. Adjust commutator brushes gradually for least sparking. These should be close to the central position. Contacts and brushes should be kept clean and smooth and lubricated sparingly. While replacing a fusible strip, be sure that main switch is open, and be careful not to touch the other wire with your tool or otherwise, as such contact would be dangerous. Never put in a larger fuse than the one burnt. Inspect the worm and worm-wheel occasion- ally through hand-holes in casing, to see that they are well lubri- cated, and that no grit gets into the oil. They should show no wear. The stuffing-box on the worm shaft should be only tight enough to keep the oil from leaking out of the worm chamber. Be sure that all parts are properly lubricated, and that none of the bearings heat. To make sure that the car and machinery run freely, lift brake lever and then rotate worm shaft by pulling on the brake wheel. The empty car should ascend without any exer- tion. Keep operating cables properly adjusted. Open main switch when the elevator is not in service.
The Lever.
Relative Position of Power, Weight and Fulcrum in : Lever of the first class Power. Fulcrum. Weight.
Lever of the second class Power. Weight. Fulcrum.
Lever of the third class Weight. Power. Fulcrum.
Power X power-arm Power V power-arm
"— = Weight. Weight -- = Weight-arm.
Weight X weight-arm Weight X weight-arm
Power-arm ~ - Power' Power = Powei"arm-
Weight power = ratio of, or proportion of, power-arm to weight-arm.
Power-arm
Weight-arm = ratio of> or Pr°PortiO11 of ; weight to power.
HANDBOOK ON ENGINEERING. 769
CHAPTER XXVI. ELECTRIC ELEVATORS.
Electric elevators of the drum type while very satisfactory for buildings of moderate height, are not well adapted to office build- ings of many floors, where the run is from 200 to 300 feet. The objection to them for such cases is that the drum has to be of such large dimensions that frequently space near the elevator well can- not be had for it. As can be easily seen the drum must be of such diameter and length that all .the rope required to lift the car to the top of the building can be wound upon it. If the diameter of the drum is enlarged so as to provide the requisite surface, there is difficulty in obtaining the desired car speed, because the worm gear has to be increased proportionately with the drum, so that the pressure in the teeth may be not so great as to cause them to cut. If the worm gear is large the motor must make a greater number of revolutions for each turn of the drum, hence, although the car will travel further per turn of drum, the increase in this direction is not as great as the increase in the ratio between the speed of the motor and that of the drum. The motor speed can be reduced considerably by using a worm with double thread, but even then high motor speed is required for high car speed, higher than with elevators running to a moderate height. If the re- quired drum surface is obtained by increasing the length of the drum, then the machine is liable to become so wide that it cannot be placed In the opening at the side of the elevator well provided for it. If there is space enough for the machine, the spread of the ropes when they are unwinding from the sides of the drum may be greater than the width of the elevator well.
770 HANDBOOK ON ENGINEERING,
It was to overcome the above difficulties that the Sprague screw
Fig. S37. Diagram of Frazer Duplex Elevator*
machine was devised, bat this machine has not withstood the test
HANDBOOK ON ENGINEERING. 771
of time and is no longer manufactured. Another machine that overcomes the objections to the drum machine for high buildings is the Frazer Duplex Motor Elevator.
The general arrangement and principle of operation of the Frazer elevator can be made clear by the aid of the diagram Fig. 337. As will be seen in this diagram there are two motors placed one on top of the other. On the ends of the amature shafts are mounted grooved sheaves, and under these sheaves run endless cables in the manner clearly shown. The elevator car is suspended from the frame of one of the traveling sheaves around which the cables pass, and a counter-balance weight is suspended from the frame of the other travelling sheave. The two motors are arranged to rotate in opposite directions, as indicated by the arrows. In the operation of the elevator the motors never re- verse, but always run in the same direction. The motors are of the variable speed type, and the running of the elevator car in either direction is effected simply by changing the velocity of the motors. Looking at the diagram it can be seen that if both motors are running at the same speed, the top one will run the cables out to the right just as fast as the lower one will run them to the left, hence, the travelling sheaves will not move, and the car will stand still. Now suppose the top motor runs faster than the lower one, then the top ropes will run out to the right faster than the lower ones will run out to the left, and as a result the right side travelling sheave will move up, and the other one will move down, thus causing the car to rise, and the counterbalance to descend. If the motor velocities are reversed, that is, the top one reduced to a speed lower than the lower one, then the top one will not run the cables out to the right as fast as the lower one will run them to the left, and as a result the left side travel- ling sheave will rise, thus causing the car to run down and the counterbalance to run up. By varying the speed of the two
772
HANDBOOK ON 'ENGINEERING.
motors any desired velocity of the car can be obtained from zero to the maximum running in either direction.
Fig. 3B7a. Duplex Motor.
The motors used are made so that their speed can be varied from 280 to 520 revolutions per minute, the. average velocity being 400. When both motors are running at 400 the car stands still, and when the top motor runs 280 and the bottom one 520
HANDBOOK ON ENGINEERING. 773
the maximum car speed is obtained with the car on the up trip. The sheaves on the shafts of the. motor armatures are about 19 inches in diameter, so that with the speeds above named, the car travels about 600 feet per minute.
Although the car should stand still when the two motors are running at the same speed, in practice this result cannot be obtained, as slight variations in velocity will occur, and these fluctuations will cause the car to shake. To overcome this trouble a brake is provided to hold the top sheave over which the car lifting ropes pass, as clearly shown in the diagram. Gener- ally the motors are stopped when the elevator is stopped.
This elevator is the most perfect in operation of any electric elevator that has been devised, its velocity can be varied at the will of the car operator from zero to the maximum speed, and it can be stopped and reversed when running at full speed without producing the slightest jolt ; but it possesses undesirable features that tend to offset its fine running qualities. The main objection is that the driving sheaves mounted on the ends of the armature shaft have to be of very small diameter, so as to not impart too high a velocity to the driving ropes. As these sheaves are only 19 inches in diameter, steel ropes cannot be used, in their stead hemp ropes with a steel core are used, and while these may be just as safe as steel cables, they do not inspire the same amount of confidence.
• As there is very little friction about the Frazer elevator, it would naturally be inferred that it will require less current to do the same work, but actual practice seems to show that it ia not any more economical than the drum machine.
The duplex motor of the Frazer elevator is shown in Fig. 337a, and is so simple as to require no explanation, being in fact noth- ing but two motors mounted one on top of the other.
The way in which the Frazer elevator is controlled can be ex- plained in connection with the wiring diagram Fig. 338. The
774
HANDBOOK ON ENGINEERING.
s
I
s
g
ft s-
OJ
2
bo
upper part of the diagram represents the car switch, a photo- graphic view of which is shown in Fig. 338a. The car switch is
HANDBOOK ON ENGINEERING.
775
Fig. 338a. Frazer Car Controller.
provided with resistances that can be connected in parallel with the field coils of either motor, so as to vary the velocity. The parts marked U limit, and D limit are automatic stopping switches that are located in the elevator well near the top and bottom, and in such position that they may be moved by the elevator car when it reaches either end of its travel. These limit switches stop the car gradually by cutting in the resistance in the manner clearly indicated in the diagram. A photographic view of the D limit switch is given in Fig 338b. The U limit switch is substantially the same in construction and appearance. As will be seen the switch lever is actuated by a rod that carries a roller at its end, this roller being placed in a position where it will be struck by an inclined plane attached to the elevator car, so as to gradually
776 HANDBOOK ON ENGINEERING.
cut the resistance into the circuit. The lower part of the dia- gram constitutes the controller and the several switches of which it is composed are assembled on a slate panel in the manner shown in Fig. 338o, which is a photographic view of the con- troller front.
The operation of the controller is as follows : — The potential switch is jlosed by hand, but is arranged like a circuit breaker, so that it will open whenever the potential of the current dies out. To start the motors, the car switch D is closed, and then a cur-
Fig. 338b. Frazer Limit Switch.
rent starting from A will pass through D and thence through the magnet of S and following the path indicated by the arrow heads will reach wire E and thus return to the lower side of the potent- ial switch. As soon as the magnet of S is energized, the contact plates will be raised so as to close the main circuit, and then the current will flow through the starting series field and thence through the armatures of the two motors and back to lower side of potential switch. From the end of the series field a current will branch off through the magnet of AS' and through the magnets
HANDBOOK ON ENGINEERING.
777
of the switches that cut out the series field. The shunt fields of the two motors are connected in series and to the left side contact at top of switch S' and to the lower right side contact of $. To
Fig. 338c. Front of Frazer Controller.
make the car run in either direction it is necessary to change the speed of the motors, and this is done by moving the contact B in the car switch, by means of the operating lever, to one side or the
778 HANDBOOK ON ENGINEERING.
other. Let B be moved to the left, then current coming up from A will pass through B to the lever of the U limit and thence fol- low the arrow heads to point C between the shunt field coils of the two motors. In this way the resistance in the car switch is connected in parallel with the field coil on the right of (7, hence, the field of this motor, will receive less current than, the field of the other motor, and as a result its amature will run faster. If B is moved to the right, then current will flow from point C in the opposite direction, as indicated by the arrows a, and reaching the D limit will pass through the lever and thence through the car switch resistance, through B and thence through wire E will reach points F. In this case all the field current will pass through the right side field but at C it will divide part going through the left side field and the remainder following the path of arrows a to point F. Thus by swinging the lever of the car switch to one side or the other, one or the other of the motors can be made to run faster and the direction of the car can be reversed, while the speed can be varied as may be desired.
THE TRACTION TYPE OF ELECTRIC ELEVATOR.
Another form of electric elevator designed to overcome the disadvantages of drum machines for high runs is what is known as the traction type, and is illustrated diagrammatically in Fig. 339 on the left side. In this construction only one motor is used and on the end of its armature shaft is mounted a sheave much larger than those used on the Frazer machine. The size of the sheave is large enough to permit the use of regular steel wire cables. These cables pass over two travelling sheaves, in the manner clearly shown in the diagram, and the ends are anchored to suit- able supports as shown. The car is suspended from ropes that pass over a sheave at tlie top of the elevator well and run down to the frame of one of the travelling sheaves. The counterbalance is similarly connected with the other sheave frame.
HANDBOOK ON ENGINEERING. 779
From an inspection of the diagram it will be seen that this ma-
MODIFIED FORM'
Fig. 389. Traction Types of Electric Elevator.
chine is geared two to one, that is, the car speed is one-half the
780 HANDBOOK ON ENGINEERING.
velocity of the circumference of the driving sheave on the motor shaft. In the Frazer machine the car is ran in either direction while the motors always run in the same direction, and the car can be stopped without stopping the motors, simply by bringing the two to the same speed. In the traction system this cannot be done, the motor must be stopped to stop the car, and it must be reversed to reverse the direction of the car. For these reasons the control is not so perfect as in the Frazer machine, but the difference is slight in practice, in fact hardly worth noticing ; but as an offset we have the fact that a sheave of standard size can be placed on the motor shaft and, therefore, regular steel ropes can be used instead of hemp ropes with a steel centre.
In looking at the diagram this arrangement of elevator appears to be as simple as anything can be, but the actual apparatus is not as simple as the diagram. The traveling sheaves have to run in guides and these must extend something more than half the height of the elevator well. Such guides are expensive, and in addition take up a considerable amount of space, which in office buildings in large cities is very valuable. Now it can be easily seen that if a motor can be made that will drive an elevator by being geared two to one as in the diagram, it is only necessary to make the motor so as to pull twice as hard and then it can be connected directly with the elevator. To do this the size of the motor must be increased, but as an offset we have the fact that all the expense of the traveling sheaves can be used to cover the additional cost of the motor, and the space occupied by the sheave is saved, which is so much clear gain, in addition to which the greater simplicity must be taken account of. An elevator of this type is shown in the diagram at the right of Fig. 339, and it is known as one to one cable drive elevator.
This elevator which has been developed by the Otis Elevator Company is now being introduced for high speed elevators in large office and other buildings. The principle of operation is
HANDBOOK ON ENGINEERING.
781
the same as that used in cable railroads. The motor carries on the end of the amature shaft a grooved sheave about 36 inches in diameter, and an idle sheave is placed directly above the motor sheave. The lifting ropes pass over the upper sheave once, and under the motor sheave twice. This double wrap around the the driving sheave has been found by many trials to give all the
Fig. 340. Cable Drive Elevator Machine.
adhesion required to lift the heaviest loads the elevator can carry. A side view of the motor is shown in the centre of diagram Fig. 339, from which the relative position of the driving and the idle
782 HANDBOOK ON ENGINEERING.
sheave can be understood. The construction is still better shown in Fig. 340 which is a photographic view of the motor. The brake on the motor is located between the field frame and the bearing at the driving sheave end, and is actuated by powerful springs. A magnet is used to pull the brake off when the motor is running. As soon as the current stops the magnet releases the brake and the springs apply it with all the force necessary to pre- vent the shaft from rotating even with ithe heaviest load in the car. The counterbalance weight used with these elevators weighs as much as the car and one-half the maximum load that it is in- tended to lift, from which it will be seen that the break does not have to be so powerful as might appear at a first glance.
In some cases these elevator machines are placed at the top of the elevator well, and then the idle sheave is placed under the motor, and is secured to overhead framing provided for the the purpose. Such a construction is shown in Fig. 340a which is a perspective view of a complete elevator, broken away at two places so as to shorten the picture.
The elevator machine has no safety appliances attached to it other than the break, as none are required upon it. The auto- matic stops are arranged^in the elevator well mear the top and bot- tom landings, in a manner that will be explained presently. The break on the motor is arranged so that normally it acts with a moderate pressure, but if the occasion requires it the breaking force can be instantly increased by simply moving the operating switch in the car to the central position. The connections of the motor with the controller are such that in stopping the motor is converted into a generator, and thus has to be driven by the force of the descending weight.
As will be seen in Fig. 340a there is a small governor located by the side of the moter, this is the regular Otis safety governor that is arranged so as to stop the car if it attains an excessive velocity from any cause. In this machine this governor has an
HANDBOOK ON ENGINEERING.
783
Fig. 340a.
additional appliance consisting of a switch that acts to stop the
784
HANDBOOK ON ENGINEERING.
motor whenever the governor throws the car safeties into action, thus preventing the lifting ropes from becoming slack.
HANDBOOK ON ENGINEERING.
785
This cable drive elevator is arranged so as to run at different speeds, the result being accomplished by the movement of the arc switch handle to different positions. The change in the velocity of the motor is effected in different ways. In one arrangement
w
CJ
1
•2
s
I
§
if 5
of the controlling devices, the speed variation is obtained by vary- ing the strength of the current passing through the field of the motor; in another it is obtained by introducing resistance in the armature circuit, and by sending more or less current through a
78(5 HANDBOOK ON ENGINEERING.
by pass around the armature. In another arrangement both these methods are combined. The wiring diagram, Fig. 341, illus- trates the latter arrangement. The appearance of the controller to which this diagram corresponds is shown in Fig. 34 la.
In the wiring diagram, Fig. 341, the heavy lines indicate wires through which the strong armature current passes, the fine lines are wires through which the field current, and the switch magnet currents pass. A complete explanation of this diagram would be very lengthy, and to avoid this we have placed arrow heads on all the lines which will greatly facilitate the understanding of the condensed explanation that follows : —
The line wires are connected with the two pole switch at the right of the diagram. From this switch connections run to a potential switch directly to the left. The accelerating magnet cuts out the resistance shown above it, from the armature circuit, when the highest velocity is desired. Directly to the left of the accelerating magnet are shown a number of magnetic switches, that act to cut resistance out of the armature circuit, and to in- crease the resistance in a circuit that shunts the armature, and finally to open this circuit. These switches are operated from the car switch, which is shown at the left side of the diagram. The circle marked A represents the motor armature, and at the bottom of the diagram is shown the shunt field coils. The motor is of the plain shunt type. Following the wire starting from A it will be seen that it passes through the field coils of the motor and ends at B. The circuit from A through the potential switch can be easily traced to (7, and from here the fine wire runs through switch 5, to and through E, and from here to switch 1 and to the lower up contact of the car switch. E is the magnet coil of one of the starting switches E' ', and if the car switch is turned so as to cover the first contact, the current after reaching this, will re- turn through the centre wire from the car and reach the point 0' on the potential switch. The current will then flow through the
HANDBOOK ON ENGINEERING. 787
motor by way of switch E' in the way indicated by the arrow heads. As the car switch is advanced it covers in succession the contacts from which lead wires that pass through the roller switches, 1, 2, 2, 3, 5, and thence to the magnets of the switches that cut the resistances A' into the circuit that shunts the arma- ture, and cut out the resistances directly above, that are in series with the armature. In this way the motor speed is increased. When the accelerating magnet cuts out all its resistance it also closes the circuit of F and then resistance F' is cut into the shunt field circuit, and the motor speed further increased. The roller switches 1, 2, 3, 4, 5, are limit switches to stop the car automatically at the top floor, if the operator fails to turn the car switch to the stop position. Similar limit switches are shown in the wires running from the do.wn side of the car switch. In Fig. 340a two of these switches can be seen at the side of the guide near the bottom of the well. The two roller switches seen at the right of the diagram are final limit switches that are actuated if the car overruns the limits. When one of these switches is moved, the motor is disconnected from the circuit, the brake goes on with full force, the armature generates a strong current and the motor stops at once.
788 HANDBOOK ON ENGINEERING.
CHAPTER XXVII.
THE DRIVING POWER OF BELTS.
The average strain or tension at which belting should be run is claimed to be 55 pounds for every inch in width of a single belt, and the estimated grip is one-half pound for every square inch of contact with pulley, when touching one-half of the circumference of the pulley. For instance a belt running around a 36-inch pul- ley would come in contact with one-half its circumference, or 56£ inches, and allowing a half-pound per inch, would have a grip 28£ pounds for each inch of width of belt.
MECHANICAL PROBLEMS AND RULES.
Problem 1. To find the circumference of a circle or a pulley : —
Solution. Multiply the diameter by 3.1416 ; or, as 7 is to 22 so is the diameter to the circumference.
Problem 2. To compute the diameter of a circle or pulley : —
Solution. Divide the circumference by 3.1416; or multiply the circumference by .3183 ; or as 22 is to 7, so is the circumfer- ence to the diameter, equally applicable to a train of pulleys, the given elements being the diameter and the circumference.
Problem 3. To find the number of revolutions of driven pulley, the revolution of.driver, and diameter of driver and driven being given : —
Solution. Multiply the revolutions of driver by its diameter, and divide the product by the diameter of driven.
HANDBOOK ON ENGINEERING. 789
Problem 4. To compute the diameter of driven pulley for any desired number of revolutions, the size and velocity of driver being known : —
Solution. Multiply the velocity of driver by its diameter and divide the product by the number of revolutions it is desired the driven shall make.
Problem 5. To ascertain diameter of driving pulley : —
Solution. Multiply the diameter of driven by the number of revolutions it is desired it shall make, and divide the product by the number of revolutions of the driver.
6. Rule for finding; length of belt wanted: Add the diame- ters of the two pulleys together, divide the result by two, and multiply the quotient by 3 1/7. Add the product to twice the distance between the centers of the shafts, and we have the length required.
FOR CALCULATING THE NUMBER OF HORSE-POWER WHICH A BELT WILL TRANSMIT, ITS VELOCITY AND THE NUMBER OF SQUARE INCHES IN CONTACT WITH THE PULLEY BEING KNOWN.
Divide the number of square inches of belt in contact with the pulley by two, multiply this quotient by velocity of the belt in feet per minute and divide the product by 33,000 ; the quotient is the number of horse-power.
Example. — A 20-inch belt is being moved with a velocity of 2,000 feet per minute, with six feet of its length in contact with the circumference of a four-foot drum ; desired its horse- power. 20 x 72 equal 1,440, divided by two, equals 720, x 2,000 equal 1,440,000, divided by 33,000 equals 43| horse-power.
Rule for finding width of belt, when speed of belt in feet per minute and horse-power wanted are given : —
For single belts* — Divide the speed of belt by 800. The horse- power wanted divided by this quotient, will give the width of belt required.
790 HANDBOOK ON ENGINEERING.
Example. — Required the width of single belt to transmit 100 horse-power. Engine pulley 72" in diameter. Speed of engine, . 220 revolutions per minute.
800) 4146 (speed of belt per minute).
5.18)100.00 (horse-power wanted). 19" width of belt required.
For doable belts* — Divide the speed of belt in feet per minute by 560. Divide the horse-power wanted by this quotient for the width of belt required.
Example. — Required the width of double belt to transmit 500 horse-power. Engine pulley 72" in diameter. Speed of engine, 220 revolutions per minute.
560)4146 (speed of belt per minute). 7.4)500.00 (horse-power wanted). 67J" width of belt required.
NOTES ON BELTS.
PRINCIPLES GOVERNING BELTS.
Although there is not near as much known in general about the power of transmitting agencies as there should be, still it seems that almost any other method or means is better understood than belts.
One of the chief difficulties in the way of a better knowledge of the belting problem, is the relation that belts and pulleys bear to each other. The general supposition, and one that leads to many errors, is that the larger in diameter a pulley is, the greater its holding capacity — the belt will not slip "so easily, is the belief. But it is merely a belief, and has nothing to sustain it, unless it be faith, and faith without work is an uncertain factor. It is very
HANDBOOK ON ENGINEERING. 791
desirable to impress upon the minds of all interested, the folio wing immutable principles or law : —
1. The adhesion of the belt to the pulley is the same — the arc or number of degrees of contact, aggregate tension or weight being the same — without reference to width of belt or diameter of pulley.
2. A belt will slip just as readily on a pulley four feet in diam- eter, as it will on a pulley two feet in diameter, provided the conditions of the faces of the pulleys, the arc of contact, the ten- sion, and the number of feet the belt travels per minute are the same in both cases.
3. A belt of a given width and making two thousand, or any other given number of feet per minute, will transmit as much power running on pulleys two feet in diameter as it will on pulleys four feet in diameter, provided the arc of contact, tension and conditions of pulley faces all be the same in both cases.
It must be remembered, in reference to the first rule, that when speaking of tensions, that aggregate tension is never meant unless so specified. A belt six inches wide, with the same tension, or as taut as a belt one inch wide, would have six times the aggre- gate tension of the one inch belt. Or it would take six times the force to slip the six inch belt as it would the one inch. It is well to induce readers to become practical students and to be able to learn for themselves. Information obtained in that way is far more valuable, and liable to last much longer.
In order that the reader may more fully understand whether or not a large pulley will hold better than a small one, let him provide a short, stout shaft, say three or four feet long and two inches in diameter. To this shaft firmly fasten a pulley, say 12 in. in diameter, or any other size small pulley that may be convenient. The shaft must then be raised a few feet from the floor and firmly fastened, either in vises, or by some other means, so that it will not turn. It would be better, of course, to have
792 HANDBOOK ON ENGINEERING.
a smooth-faced iron pulley, as such are most generally used. So far as the experiment is concerned, it would make no difference what kind of a pulley was used, provided all the pulleys experi- mented with be of the same kind, and have the same kind of face finish. When the shaft and pulleys are fixed in place, procure a new leather belt and throw it over the pulley. To one end of the belt attach a weight, equal, say, to forty pounds — or heavier, if desired — for each inch in width of belt used ; let the weight rest on the floor. To the other end of the belt attach another weight, and keep adding to it until the belt slips and raises the first weight from the floor. After the experimenter is satisfied with playing with the 12 in. pulley, he can take it off the shaft and put on a 24 in., a 36 in., or any other size he may wish ; or, what is better, he can have all on the shaft at the same time. The belt can then be thrown over the large pulley and the experiment repeated. It will then be found if pulley faces are alike, that the weight which slipped the belt on the small pulley will also slip it on the large one. The method shows the adhesion of a belt with 180 degrees contact, but as the contact varies greatly in practice, it is well enough to understand what may be accomplished with other arcs of contact. But, after all, many are probably at a loss how to account for some obser- vations previously made. They have noticed that when a belt at actual work slipped, an increase in the size (diameter) of the pulleys remedied the difficulty and prevented the slipping.
A belt has been known to refuse to do the work allotted to it, and continue to slip over pulleys two feet in diameter, but from the moment pulleys were changed to three feet in diameter there was no further trouble. These observed facts seem to be at variance with and to contradict the results of the experiments that have been made. All, however, may rest assured that it is only apparent, not real.
The resistance to slippage is simply a unit of useful effect (or
HANDBOOK ON ENGINEERING. 793
that which can be converted into useful effect). The magnitude of the unit is in proportion to the tension of the belt. The sum total of useful effect depends upon the number of times the unit is multiplied. A belt 6 inches wide and having a tension equal to 40 Ibs. per inch in width, and traveling at the rate of 1 foot per minute, will raise a weight of 240 Ibs. 1 foot high per minute. If the speed of the belt be increased to 136.5 feet per minute, it will raise a weight of 33,000 Ibs. per minute, or be transmitting 1 horse-power. The unit of power transmitted by a belt is rather more than its tension, but to take it at its measured tension is at all times safe, and 40 to 45 Ibs. of a continuous working strain is as much, perhaps, as a single belt should be subjected to. A little reflection will now convince the reader that a belt transmits power in proportion to its lineal speed, without reference to the diameter of the pulleys. Having arrived at that conclusion, it is then easy to understand why it is that a belt working over 36-inch pulley will do its work easy, when it refused to do it and slipped on 24-inch pulleys. If the belt traveled 800 feet per minute on the 24-inch pulleys, on the 36-inch it would travel 1,200 feet, thus giving it one-half more transmitting power. If, in the first instance, it was able to transmit but 8 horse-power, in the second instance it will transmit 12 horse-power. All of which is due to the increase in the speed of the belt and not to the increase in the size of the pulleys ; because, as has been shown, the co-efficient of friction, or resistance to slippage, is the same on all pulleys with the same arc of belt contact.
There is no occasion for elaborate and perplexing formulas and intricate rules. They serve no useful purpose, but tend only to mystify and puzzle the brain of all who are not familiar with the higher branches of mathematics, — and it is the fewest number of our every-day practical mechanics who are so familiar. In all, or nearly all treatises on belting, the statement is made that at 600, 800 or 1,000 feet per minute, as the case may be, a belt one
794 HANDBOOK ON ENGINEERING.
inch wide, will transmit one horse-power ; and yet, when we come to apply these rules in practice, no such results can be obtained one time in ten. The rules are just as liable to make the belt travel 400, 1,000 or 1,600 per minute per horse-power as the number of feet they may give as indicating a horse-power.
All .of the following simple calculations are based upon the assumption that a belt traveling 800 feet per minute, and running over pulleys, both of which are the same diameters, will easily transmit one horse-power for each inch in width of belt. A belt under such circumstances would have 180 degrees of contact on both pulleys without the interposition of idlers or tighteners.
The last proposition being accepted as true and the basis cor- rect, the whole matter resolves itself into a very simple problem, so far as a belt with 180 degrees contact is concerned. It is simply this : If a belt traveling 800 feet per minute transmit one horse-power, at 1,600 feet, it will transmit two horse-power ; or if 2,400 feet, three horse-power, and so on. It is no trouble for any one to understand that, if he understands simple multiplica- tion or division.
It is not, however, always the case that both pulleys are the same size, and as soon as the relative sizes of the pulleys change, the transmitting power of the belt changes ; and that is the rea- son why no general rule has ever, or ever will be made for ascer- taining the transmitting capacity of belts under all circumstances. When the pulleys differ in size, the larger of the two is lost sight of — it no longer figures in the calculations — the small pulley, only, must be considered. To get at it, the number of degrees of belt contact on the small pulley must be ascertained as nearly as possible and use for a guide, for getting at the transmitting power, the next established basis given. Of course, the experi- menter can make a rule for every degree of variation, but it would require a great many, and is not necessary. Five divisions are used, as follows: —
HANDBOOK ON ENGINEERING. 795
For 180 degrees useful effect .... 100
For 157| " " " 92
For 135 " " ' " 84
For 112i u 44 fi 76
For 90 " " " 64
The experimenters may find that the figures are under obtained results, which is exactly what they are intended to be, more especially on the 90 degree basis. Always make ample allow- ance.
To ascertain the power a belt will transmit under the first-named conditions : Divide the speed of the belt in feet per minute by 800, multiply by its width in inches and by 100. For the second, divide by 800, multiply by width in inches and by .92. Third place, divide by 800, multiply by width in inches and by .84. Fourth place, divide by 800, multiply by width in inches and by .76. Fifth place, divide by 800, multiply by width in inches and by .64. As an example: What would be the transmitting power of a 16-inch belt traveling 2,500 feet per minute by each of the above rules?
1st: 2,500 divided by 800 equal 3.125 x 16 x 100 equal 50 h. p. 2d: 2,500 " 800 " 3.125 x 16 x .92 equal 46 "
3d: 2,500 " 800 " 3.125 x 16 x .84 equal 42 "
4th: 2,500 " 800 " 3.125 x 16 x .76 equal 38 "
5th: 2,500 " 800 " 3.125 x 16 x .64 equal 32 "
As stated, when the degrees of contact come between the divisions named above, in order to be on the safe side, calculate from the first rule below it, or make it approximate as desired.
If the above rule is studied well and strictly used, there can be no excuse for any mechanic putting in a belt too small for the work it has to do, provided he knows how much there is to do, which he ought, somewhere near at least.
796
HANDBOOK ON ENGINEERING.
HORSE-POWER TRANSMITTED BY LEATHER BELTS.
DRIVING POWER OF SINGLE BELTS.
|
Speed in Feet per Minute. |
Width of Belt in Inches. |
|||||||||
|
2 |
3 |
4 |
5 |
6 |
8 |
10 |
12 |
14 |
||
|
H. P. |
H. P. |
H. P. |
H. P. |
H. P. |
H. P. |
H. P. |
H. P |
H. P. |
||
|
400 |
1 |
Ij |
1 |
2 |
2^ |
3 |
4 |
5 |
6 |
7 |
|
* 600 |
H |
I |
3 |
31 |
41 |
6 |
71 |
9 |
101 |
|
|
800 |
2 |
3 |
4 |
5 |
6 |
8 |
10 |
12 |
14 |
|
|
1,000 |
21 |
31 |
5 |
64 |
71 |
10 |
"I |
15 |
171 |
|
|
1,200 |
3 |
4, |
7 |
71 |
9 |
12 |
15 |
18 |
21 |
|
|
1,500 1,800 |
31 41 |
6 6; |
92 |
92 H4 |
st |
15 18 |
221 |
221- 27 |
261 311 |
|
|
2,000 |
5 |
7- |
10 |
121 |
15 |
20 |
25 |
30 |
35 |
|
|
2,400 |
6 |
9' |
12 |
15 |
18 |
24 |
30 |
36 |
42 |
|
|
2,800 |
7 |
10- |
I |
14 |
171 |
21 |
28 |
35 |
42 |
49 |
|
3,000 |
71 |
11: |
( |
15 |
181 |
221 |
30 |
371 |
45 |
52£ |
|
3,500 |
81 |
13 |
171 |
22 |
26 |
35 |
44 |
52 £ |
61 |
|
|
4,000 |
10 |
15 |
20 |
25 |
30 |
40 |
50 |
60 |
70 |
|
|
4,500 |
114 |
17 |
22J |
28 |
34 |
45 |
57 |
69 |
78 |
|
|
5,000 |
121 |
19 |
26 |
31 |
371 |
50 |
621 |
75 |
87 |
DRIVING POWER OF DOUBLE BELTS.
|
Speed in Feet per Minute. |
Width of Belts in Inches. |
||||||||
|
6 |
8 |
10 |
12 |
14 |
16 |
18 |
20 |
24 |
|
|
H. P. |
H. P. |
H. P. |
H. P |
H. P. |
H. P. |
H. P. |
H. P |
H. P. |
|
|
400 |
44 |
51 |
74 |
84 |
10 |
H4 |
13 |
144 |
174 |
|
600 |
61 |
81 |
11 |
13 |
15 |
174 |
194 |
22 |
26 |
|
800 |
«! |
Hi |
141 |
174 |
204 |
23 |
26 |
29 |
344 |
|
1,000 |
11 |
14J |
184 |
214 |
254 |
29 |
324 |
36 |
434 |
|
1,200 |
13 |
171 |
22 |
26 |
304 |
344 |
39 |
44 |
524 |
|
1,500 |
164 |
211 |
274 |
324 |
38 |
434 |
49 |
544 |
654 |
|
1,800 |
191 |
26 |
321 |
39 |
454 |
52 |
59 |
654 |
784 |
|
2,000 |
2l| |
29 |
361 |
434 |
504 |
58 |
654 |
724 |
87 |
|
2,400 |
26 |
341 |
44 |
524 |
604 |
694 |
784 |
88 |
105 |
|
2,800 |
801 |
401 |
51 |
61 |
71 |
81 |
914 |
102 |
122 |
|
3.000 |
32 L |
431 |
541 |
654 |
76 |
874 |
98 |
108 |
131 |
|
3,500 |
38 |
501 |
634 |
76 |
89 |
101 |
114 |
127 |
153 |
|
4,000 |
43^ |
584 |
721 |
87 |
101 |
116 |
131 |
145 |
174 |
|
4,500 |
49 |
65 |
82 |
98 |
114 |
131 |
147 |
163 |
196 |
|
5,000 |
54£ |
72| |
91 |
109 |
127 |
145 |
163 |
182 |
218 |
HANDBOOK ON ENGINEERING. 797
Example. — Required the width of a single belt, the velocity of which is to be 1,500 feet per minute ; it has to transmit 10 horse- power, the diameter of the smaller drum being four feet with five feet of its circumference in contact with the belt.
33,000 x 10 equal 330,000, divided by 1,500 equal 220, divided by 5 equal 44, divided by 6 equal 1\ inches, the required width of belt.
Directions for calculating the number of horse power which a belt will transmit. Divide the number of square inches of belt in contact with the pulley by two ; multiply this quotient by the velocity of the belt in feet per minute ; again we divide the total by 33,000 and the quotient is the number of horse-power.
Explanations. — The early division by two is to obtain the number of pounds raised one foot high per minute, half a pound being allowed to each square inch of belting in contact with the pulley.
Example. — A six-inch single belt is being moved with a velocity of 1,200 feet per minute, with four feet of its length in contact with a three-foot drum. Required the horse-power.
6x48 equal 288, divided by 2 equal 144 x 1,200 equal 172,- 800, divided by 33,000 equal, say, 5J horse-power.
It is safe to reckon that a double belt will do half as much work again as a single one.
Hints to users of belts. — 1. Horizontal, inclined and long belts give a much better effect than vertical and short belts.
2. Short belts require to be tighter than long ones. A long belt working horizontally increases the grip by its own weight.
3. If there is too great a distance between the pulleys, the weight of the belt will produce a heavy sag, drawing so hard on the shaft as to cause great friction at the bearings ; while, at the same time, the belt will have an unsteady motion, injurious to itself and to the machinery.
4. Care should be taken to let the belts run free and easy, so
798 HANDBOOK ON ENGINEERING.
as to prevent the tearing out of the lace holes at the lap ; it also prevents the rapid wear of the metal bearings.
5. It is asserted that the grain side of a belt put next to the pulley will drive 30 per cent more than the flesh side.
6. To obtain a greater amount of power from the belts the pul- leys may be covered with leather ; this will allow the belts to run very slack and give 25 per cent more durability.
7. Leather belts should be well protected against water, oil and even steam and other moisture.
8. In putting on a belt, be sure that the joints run with the pulleys, and not against them out.
9. In punching a belt for lacing, it is desirable to use an oval punch, the larger diameter of the punch being, parallel with the belt, so as to cut out as little of the effective section of the leather as possible.
10. Begin to lace in the center of the belt and take care to keep the ends exactly in line and to lace both sides with equal tight- ness. The lacing should not be crossed on the side of the belt that runs next the pulley. Thin but strong laces only should be used.
11. It is desirable to locate the shafting and machinery so that belts shall run off from each other in opposite directions, as this arrangement will relieve the bearings from the friction that would result where the belts all pull one way on the shaft.
12. If possible, the machinery should be so planned that the direction of the belt motion shall be from the top of the driving to the top of the driven pulley.
13. Never overload a belt.
14. A careful attention will make a belt last many years which through neglect might not last one.
DIRECTIONS FOR ADSUSTINd BELTING.
In lacing-, cut the ends perfectly square, else the belt will stretch unevenly. Make two rows of holes in each end ; put the
HANDBOOK ON ENGINEERING.
799
ends together and lace with lace leather, as shown in Figs. 342 and 343. For wide belts, in addition, put a thin piece of leather or
Figs 342 and 843. Showing laced joint.
rubber on the back to strengthen the joint, equal in length to the width of the belt, and sew or rivet it to the belt. In putting on belting, it should be stretched as, tight as possible, and with wide belts, this can be done best by the use of belt clamps.
HORSE POWER OF BELTING.
To ascertain horse-power which belts will transmit, multiply width of 'belt ,by diameter of pulley in inches, by revolutions of pulley per minute, by number in table corresponding to the pull the belt can exert per inch of width.
Example. — 10" single horizontal belt, 36" pulley, 200 revolu- tions, pull taken at501bs.
10" x 36" x 200 x 0.0004 = 28.8 horse-power.
The pulls which belts 1" witle will transmit are as follows : —
Constant.
Single horizontal belts (pulley same diameter) 50 Ibs. .0004 Double tfc " ' " ' " " 100 kt .0008
Single vertical " " " " 40 ' .00032
Double " " " " " 60 4 .0005
Single belts (large to very small pulleys) . 10 ' .0001
Double " *« '" " . 15 4 .00012
Quarter twist, single belts . . . 0 . . 25 ' .0002
" " double " • „ 40 ' -00032
800 HANDBOOK ON ENGINEERING.
CHAPTER XXVIII. CAPACITY OF AIR COHPRESSORS.
To ascertain the capacity of an air compressor in cubic feet of free air per minute, the common practice is to multiply the area of the intake cylinder by the feet of piston travel per minute. The free air capacity of the compressor, divided by the number of atmospheres, will give the volume of compressed air per minute. To ascertain the number of atmospheres at any given pressure, add 15 Ibs. to the gauge pressure ; divide this sum by 15 and the result will be the number of atmospheres. The above method of calculation, however, is only theoretical and these results are never obtained in actual practice, even with com- pressors of the very best design working under the most favor- able conditions obtainable. Allowances should be made for losses of various kinds, the principal losses being due to clear- ance spaces, but in machines of poor design and construction other losses occur through imperfect cooling, leakages past the piston and through the discharge valves, insufficient area and improper working of inlet valves, etc. In practice there are com- pressors where losses through imperfections and improper working conditions range from 15 to 25 per cent, while und-er favorable conditions and with the average compressor, the loss averages from 8 to 12 per cent. So that to get sufficiently accurate results in finding capacity of the compressor, subtract 12 per cent from above computation, which gives nearly accurate figures. The following table will be found useful for quickly ascertaining the capacity of an air compressor, also to find the cubical contents of any cylinder, receiver, etc. The first column
HANDBOOK ON ENGINEERING.
801
is the diam. of cylinder in inches. The second shows the contents in cubic feet, for each foot in length.
Contents of a Cylinder in Cubic Feet for Each Foot
in Length.
|
Diam. Inches. |
Cubic Contents. |
Diam. Inches. |
Cubic Contents. |
Diam. Inches. |
Cubic Contents. |
• OQ g CD I A 51 |
Cubic Contents. |
Diam. Inches |
Cubic Contents. |
|
1 |
.0055 |
6 |
.1963 |
11 |
.6600 |
20 |
2.182 |
36 |
7.069 |
|
« |
.0085 |
« |
.2130 |
Hi |
.6903 |
204 |
2.292 |
37 |
7.468 |
|
ij |
.0123 |
6i |
.2305 |
U4 |
.7213 |
21 |
2.405 |
38 |
7.886 |
|
1| |
.0168 |
.61 |
.2485 |
ill |
.7530 |
214 |
2.521 |
39 |
8.296 |
|
2 |
.0218 |
7 |
.2673 |
12 |
.7854 |
22 |
2.640 |
40 |
8.728 |
|
2i |
.0276 |
7* |
.2868 |
12* |
.8523 |
224 |
2.761 |
41 |
9.168 |
|
2* |
.0341 |
74 |
.3068 |
13 |
.9218 |
23 |
2.885 |
42 |
9.620 |
|
2| |
.0413 |
7| |
.3275 |
13J |
.9940 |
234 |
2.885 |
43 |
10.084 |
|
3 |
.0401 |
8 |
.3490 |
14 |
1.069 |
24 |
3.012 |
44 |
10.560 |
|
8* |
.0576 |
8* |
.3713 |
i« |
1.147 |
25 |
3.142 |
45 |
11.044 |
|
3£ |
.0668 |
84 |
.3940 |
15 |
1.227 |
26 |
3.400 |
46 |
11.540 |
|
8} |
.0767 |
8| |
.4175 |
15J |
1.310 |
27 |
3.687 |
47 |
12.048 |
|
4 |
.0873 |
9 |
.4418 |
16 |
.396 |
28 |
3.976 |
48 |
12.566 |
|
« |
.0985 |
9* |
.4668 |
164 |
.485 |
29 |
4.587 |
f |
|
|
*l |
.1105 |
n |
.4923 |
17 |
.576 |
30 |
4.909 |
||
|
4| |
.1231 |
9| |
.5185 |
174 |
.670 |
31 |
5.241 |
||
|
5 |
.1364 |
10 |
.5455 |
18 |
.767 |
32 |
5.585 |
||
|
-5i |
.1503 |
IQi |
.5730 |
184 |
.867 |
33 |
5.940 |
||
|
*S |
.1650 |
10£ |
.6013 |
19 |
.969 |
34 |
6.305 |
||
|
5| |
.1803 |
lOf |
.6303 |
19^ |
2.074 |
35 |
5.681 |
To find the capacity of an air-cylinder, multiply the figures in the second column by the piston travel in feet per minute. This applies to double-acting air cylinders. In the case of single- acting air cylinders, the result should be divided by 2.
•
THE McKIERMAN DRILL COMPANY'S AIR COMPRESSOR.
The air -cylinder and water-jacket are one complete casting. The heads are made with hoods and provision made for cool air
in-take. "
51
802
HANDBOOK ON ENGINEERING.
The atmosphere valves ste bronze, of poppet form. There- fore, there is no vacuum and the cylinder fills absolutely with free air. The valves are closed by mechanical means.
The discharge valves are self-acting, are made of bronze. All of them are free to inspection without removal or disturbance of other parts.
The cooling apparatus, or heat-preventing device, is extremely effective. Water jacket completely surrounds the cylinder, water
Fig. 344. Horizontal single stage compressor.
is forced to wash the walls and is kept in rapid motion from bot- tom to top, from end to end, absorbing heat rapidly. It enters the jacket at bottom, flows from end to end, around partitions, back and forth and up. Follows natural laws in absorbing, retaining and dispelling the heat of air.
Regulation of pressure and speed is entirely automatic. The regulating device is one of those in which the air weighs the steam admitted to tte cylinder. Throttle may be thrown wide open at start, then the regulator takes absolute control, governing the speed from highest to lowest rate, varying the speed for
HANDBOOK ON ENGINEERING.
803
variable amounts of air which may be required and in such man- ner as to keep the pressure constant.
D ui SBCTKM. A<«-CiiiHUi»-ENo ELE.ATIO*.
> SuovfiMi Y*iv«».
Fig. 345. The Bennett automatic air compressor.
Fig. 346. Iiigersoll-Sergeaiit air compressor.
804
HANDBOOK ON ENGINEERING.
INGERSOLL-SERGEANT AIR COMPRESSOR.
This engine, illustrated in Fig. 346, is fitted with Inger- soll-Sergeant air compressor cylinders, and in connection with the Pohle air lift system, has double the supply of water, using only one-half the fuel previously required. The steam cylinders are of the duplex Corliss condensing type and con- nected tandem, and on each side are two Ingersoll-Sergeant air cylinders and two Conover water cylinders. When the engine
Fig. 347. Sectional view of air cylinder with vertical lift valves, class "E" and "F" compressors.
is in operation, the air cylinders raise the water by the Pohle air lift system, from the wells to a tank at the surface, and from there it is taken by the water cylinders and forced to the stand- pipe. The cost of this combination compares favorably with the old plan of using separate compressors and water pumps, each with their own steam cylinders, and the saving in attendance, friction and foundation commends its use. The engines run at a fixed moderate speed and the regulation of the air and water is effected by passing the water from suction to discharge when the tank is too low, and by mechanically unloading the air cylinders
HANDBOOK ON ENGINEERING. 805
with a pressure regulator when the tank is too full. The regula- tion is done mechanically, with floats at the top and bottom of the receiving tank. This combination can also be furnished with straight line compressors ; the advantage of the duplex is that should it be necessary, the one side of the engine can be discon- nected and the other side made to do the work.
As will be seen, the inlet valves, which are on the lower side of the cylinder are offset, thus preventing their being sucked into the cylinder and wrecking the compressor. They are made out of a solid piece of steel and are extremely durable, because they are placed vertically, work in a bath of oil and do not slide on their seats. Both the inlet and discharge valves, being in the cylinder, allow the heads to be thoroughly water- jacketed, and .this is an important feature when it is remembered that the heat of compression is greatest at the end of the stroke. The cylinder is, therefore, completely water- jacketed. The valves are arranged so that the air can be taken from outside of the engine room, which increases the efficiency of the machine 8 to 15 per cent, and are easily accessible.
The two inlet valves are located in the piston, and, with the tube, are carried back and forth with the piston. The valve on that face of the piston which is toward the direction of move- ment is closed, while the one on the other face is open. This is exactly as it should be in order to force out the compressed air from one end of the cylinder while taking in the free air at the other ; when the piston has reached the end of its travel there is, of course, a complete stop while the engine is passing the center, and an immediate start in the other direction. The valve which was open immediately closes „ There is no reason for its remain- ing open any longer, and it closes at exactly the right time, its own weight being all that is necessary to move it. The valve on the other side is left behind by the piston and the free air is admitted to that end of the cylinder for compression on the
806
HANDBOOK ON ENGINEERING.
return stroke. No springs are used, and there is none of the throttling of the incoming air, and none of the clattering or hammering so noticeable with poppet-valves. As there is nothing to make the valve move faster than the piston, it stays behind until the piston stops, leaving the port wide open for the admission
DETAILS OF PISTON INLET AIR CYLINDER.
A.— CircuTatfng Water Jnlet, D.— Oil Hole for Automatic Oil Cup. G.— Piston Inlet Vair B.—Circulating Water Outlet. K— Air In let (through piston in let pipe). H.— Discharge Valve, C.-Wat6r Jacket Drain Pipe. F.— Air Discharge (showi&g flange); }.— Water Jacket.
Fig. 348. Sectional view of Ingersoll-Sargeant single compressor.
of air. It is well known that while the fly-wheel and, of course, the crank, rotate at a uniform speed, the movement of the piston is not uniform, but gradually increases in speed from the start till the crank has reached half -stroke, when it gradually slows up till the crank is on the center, and at this moment of full stop the valve gently slides to its seat.
HANDBOOK ON ENGINEERING.
807
Fig. 349. The Pohle air lift system.
808 HANDBOOK ON ENGINEERING.
The illustrations on page 807 show the method of pumping water by air. A compressor in connection with the air-lift sys- tem pumps the water by direct air pressure. The pump con- sists of a water pipe and an air pipe, the latter discharging the air into the former at its bottom, through a specially designed foot-piece. The natural levity of the air compared with the water, causes it to rise and, in rising, to carry the water with it in the form of successive pistons, following one another. This system of pumping has found a large range of application and is of peculiar service in connection with deep well pumping. For this purpose, the absence of mechanical parts many feet below the surface, offers a commanding advantage. Method No. 1 and No. 2 are almost alike, consisting in placing the air and water pipes alongside of one another in the well, connecting them at the bottom with an end piece. Method No. 3 consists in placing a water discharge pipe into the well ; the air passing down into the well through the annular space between the well casing and the water pipe. Method No. 4 consists in using {he well casing as the water discharge pipe, and simply putting an air pipe down into the well, with a specially designed foot-piece attached at the bottom through which the air escapes.
Air Lift Formulas.
Height of Lift For maximum economy ^ s^mersioiT should eQual °-5
125 X Cu. Ft. Free Air Gallons of water raised per Mm. = -
Cubic feet of free air per Min. = Lift in feet above water level =
Lift in Feet Gals, raised per Min. X Lift
125 125 X Cu. Ft. Free Air
Gals, per Min.
Air press, required to start lift = Submersion + Lift X -*34 4- 5 Ratio of areas of water pipe to air pipe = 6 to 1
HANDBOOK ON ENGINEERING. 809
CHAPTER XXVIII. — CONTINUED. THE METRIC SYSTEM.
It frequently happens that an engineer, in reading books and papers devoted to steam engineering, is confronted with terms taken from the metric system, which he does not understand. We present a few of the metric system terms most commonly used, with their values in feet and inches, also, gallons, quarts, pounds, tons, etc.
A French meter is 39.37079 inches long, or a little less than 39| inches. It is generally taken, — for convenience in fig uring, — at 39.37 inches.
1 decimeter is -^ of a meter, or, 3.937 inches nearly.
1 centimeter is T^ " " " .3937 " "
1 millimeter is ^fa " " " .03937 " "
ALSO.
1 decameter equals 10 meters, or, 32.80 feet nearly. 1 hectometer " 100 " " 328 " " 1 kilometer " 1000 " " 3280 " "
APPLICATION.
1. An engine shaft is 5 meters long, what is its length in feet and inches? Ans. 16 ft. 4£ ins. nearly.
qq 07 \s K
Operation J °"'°'* ° = 16.4 ft. nearly.
MM
2. An engine cylinder is 10.3 decimeters in diameter, ho^i much is this in inches? Ans. 40J ins. nearly
Operation: 3.937 X 10.3 = 40.55 ins. nearly.
810 HANDBOOK ON ENGINEERING.
3. A piston-rod is 8.7 centimeters in diameter, how much is this in inches? Ans. 3| ins. nearly.
Operation : -3937 X 8.7 .= 3.42 ins. nearly.
4. A chimney is 5.1 decameters tall, how much is this in feet and inches? Ans. 167 ft. 3 ins. nearly.
Operation : 32.80 X 5.1 = 167.28 ft.
5. How many miles are there in 30.2 kilometers?
Ans. 18-j?^ miles nearly. Operation : There are 5280 ft. in a mile.
Then, 828° X 80'2 =, 18.7 miles. 5280
6. A valve has 2 millimeters lead, how much is this in frac- tional parts of an inch? Ans. -f-^ in. nearly.
Operation: .03937 X 2 = .07874. And, .07874 X 64 = /¥ nearly.
7. How many square feet in a circle whose diameter is one meter? Ans. 8£ nearly.
n 39,37 X 39.37 X .7854
Operation : — — = 8.45.
144
8. The cylinder clearance is 1.1 cubic decimeter, how many cubic inches in the clearance? Ans. 67 nearly.
Operation: 3.937 X 3.937 X 3.937 X 1.1 = 67.12+
ALSO.
1 gramme equals 15.433 grains, or 1 ounce nearly. 1 kilogramme equals 2.2047 pounds avoirdupois. 1 tonne equals 1.1024 tons of 2000 Ibs.
ALSO. 1 litre equals 1.0566 quarts.
HANDBOOK ON ENGINEERING. 811
CONSEQUENTLY,
1 U. S. gallon equals 3.79 litres nearly. 1 U. S. pint equals .4732 litres nearly.
1. A main shaft weighs 800 kilogrammes, how much is this in avoirdupois pounds? Ans. 1763J Ibs. nearly.
Operation : 2.2047 X 800 = 1763.76.
2. An engine weighs 12 tonnes, how much is this in U. S. tons of 2000 Ibs. each? Ans. 13 J tons nearly.
Operation: 1.1024 X 12 = 13.2288.
3. A tank contains 9000 litres of water, how much is this in U. S. gallons? Ans. 2377.35 galls.
1.0566 X 9000 Operation: T~ — Because 4 quarts equal 1 gallon.
THERMOMETERS.
In the U« S* the Fahrenheit scale is the one in most common use, although in our laboratories and for scientific purposes it is displaced by the Reaumer and Centigrade scales. Fahrenheit's scale marks the boiling point by 212 degrees, and the freezing point by 32 degrees above zero.
The Reaumer scale marks the boiling point by 80 degrees, and the freezing point by zero.
The Centigrade, or Celsius scale, marks the boiling point by 100 degrees, and the freezing point by zero. So that, reckoning from the freezing point of Fahrenheit, 180 degrees Fah. equal 80 degrees Reaumer, and 100 degrees Centigrade. Bearing in mind that Fahrenheit's zero is 32 degrees below the freezing point, one scale may readily be converted into another.
To convert degs. of Reaumer into those of Fah.
Rule* — Multiply by 9, divide by 4, and add 32.
812 HANDBOOK ON ENGINEERING.
Example: 80 degs. Reaumer equals how many degs. Fah?
Ans. 212. Operation: 80 X 9 = 720.
720
And, 1— — 180. Then, 180 + 32 =212. 4
To convert the degs. of Centigrade into those of Fahrenheit. Rule* — Multiply by 9, divide by 5, and add 32. Example: 100 degs. Centigrade equal how many degs. Fah.?
Ans. 212. Operation: 100X9 =
And, 180.
o
Then, 180+32 = 212.
So, also, 3 degs. Centigrade equal 37.2 degs. Fahrenheit.
Thus; 3X9 = 27. And, £i =5.2. Then, 5.2 + 32 =37.2.
ROPE TRANSMISSION.
There are two systems of rope transmission, the English, or multiple-rope system, and the American or continuous wound rope system in which the necessary adhesion of rope to sheave is obtained by a tension carriage. We will treat of the American sys- tem only, as it is almost universally used in this country to the exclusion of the other. One of the most common mistakes is to lead the rope to the tension carriage from the tight or pulling side of the drive, and putting on an abnormal amount of tension weight in a vain endeavor to take out the slack. Under the enor- mous strain of such an arrangement the rope wears out very rap- idly, and more frequently parts at the splice. It is desirable in all cases of rope transmission to so arrange the drive that the slack side of the rope shall be on the upper part of the pulley
HANDBOOK ON ENGINEERING.
813
thus increasing the arc of contact, as the two sides will then approach each other when in motion. The working strain in pounds on a rope should not exceed 200 times the square of the diameter of the rope. The speed of the rope should not exceed 5500 feet per minute, and this speed gives the best results in H. P. The practical limit to the number of ropes for one sheave cannot be definitely named. The only limiting condition is the ability of the tension carriage to keep up the slack and when the number of ropes exceeds the capacity of one carriage, a second may be added and the drive made double. Diameters of sheaves should not be less than 40 diameters of the rope, and 50 to 60 diameters are advisable, being justified by greater length of life of the rope.
HORSE POWER TRANSfllTTED BY ROPES.
The following table gives the horse-power transmitted by a single manila rope when the arc of contact is not less than 165 degrees, and the tension not greater than 200 times the square of the diameter of the rope.
|
Velocity |
Diameter of Rope. |
||||||
|
of Kope in |
|||||||
|
Feet per Minute. |
5Is" |
3/4" |
1" |
ir |
IV |
11" |
2" |
|
1000 |
1.24 |
2.25 |
3.57 |
5.59 |
8.02 |
10.85 |
14.20 |
|
2000 |
2.70 |
3.84 |
6.84 |
10.68 |
15.39 |
20.93 |
27.36 |
|
2500 |
3.30 |
4.71 |
8.38 |
13.10 |
18.86 |
25.66 |
33.54 |
|
3000 |
3.83 |
5.46 |
9.80 |
15.39 |
21.87 |
29.74 |
38.88 |
|
3500 |
4.30 |
6.23 |
11.09 |
17.33 |
24.94 |
34.03 |
44.35 |
|
4000 |
4.74 |
6.83 |
12.15 |
18.98 |
27.33 |
37.17 |
48.59 |
|
4500 |
5.01 |
7.24 |
12.89 |
20.15 |
29.00 |
39.45 |
51.57 |
|
5000 |
5.20 |
7.47 |
13.29 |
20.76 |
29.89 |
40.65 |
53.15 |
|
5500 |
5.29 |
7.60 |
13.53 |
21.14 |
30.43 |
41.39 |
54.11 |
|
6000 |
5.08 |
7.32 |
13.10 |
20.36 |
29.32 |
39.77 |
52.12 |
|
6500 |
4.74 |
6.83 |
12.13 |
19.00 |
27.34 |
37.21 |
48.63 |
|
7000 |
4.12 |
5.93 |
10.54 |
16.47 |
23.72 |
32.26 |
42.18 |
|
7500 |
3.25 |
4.67 |
8.32 |
13.00 |
18.73 |
25.42 |
33.23 |
814
HANDBOOK ON ENGINEERING.
TO TEST THE PURITY OF ROPE.
A simple test for the purity of manila or sisal rope is as fol- lows : —
Take some of the loose fiber and roll it into balls and burn them completely to ashes, and, if the rope is pure manila, the ash will be a dull grayish black. If the rope be made from sisal the ash will be a whitish gray, and if the rope is made from a com- bination of manila and sisal the ash will be of a mixed color.
WIRE ROPE DATA.
HOISTING ROPE.
PATENT FLATTENED STRAND.
1 H
4 l|
2
2*
HERCU- LES.
13.5 22.5 32
40.5
56
67
84 124 168 211 260
CRUCI- BLE.
I!
5-2
24 30
50" 59J 86
121
144
182
9
15
21
29
38
47
56
81
109
140
176
4 6 9 13 17 21 28 40 54 66 75
|
19 WIRE ROUND STRAND. |
||||||
|
03 |
HEKCU- LES. |
CKUCI- | BLE. |
IRON. |
|||
|
w |
•Q |
oo |
||||
|
Dd |
O |
fl |
0 |
fl . |
o |
fl . |
|
0 |
**' |
^£ |
£5 |
o . |
22 |
|
|
£ fl |
||||||
|
M |
»s |
5 go |
AS |
•2 a- |
&•§ |
fl"s |
|
B |
ga SI |
IP |
1" |
IP" 03 * |
IH cu |
IP |
|
1 |
16J "5 |
12.5 20 |
11 14 |
8.8 13 6 |
8 12 |
6 |
|
1 |
30 |
29 |
18 |
19.4 |
16 |
9 |
|
1 |
39 |
36 |
23 |
26 |
20 |
13 |
|
1 |
a |
50 60 |
30 38 |
34 42 |
26 33 |
17 21 |
|
ij |
71 |
77 |
46 |
50 |
40 |
25 |
|
Ji |
103 |
113 |
66 |
72 |
57 |
36 |
|
11 |
147 |
157 |
93 |
96 |
80 |
48 |
|
2 |
172 |
191 |
111 |
124 |
92 |
62 |
|
2* |
218 |
238 1 |
142 |
156 |
117 |
74 |
HANDBOOK ON ENGINEERING. 815
ALTERNATING CURRENT MACHINERY.
CHAPTER XXIX. THE PRINCIPLES OF ALTERNATING CURRENTS.
The actions of alternating currents are not so easily under- stood as those of continuous currents and to most men not familiar with the subject they appear to be a mystery that can only be fathomed by those who are well versed in the higher branches of mathematics. As a matter of fact, when we once get on the right track, alternating current actions present no more difficulty to the man of fair mental ability, who is willing to work to learn, than the more simple continuous current actions. What makes alternating currents difficult to understand is, that in con- sequence of the ever-changing strength of the current, inductive actions are developed that react upon the current itself so that it becomes impossible to determine the magnitude of the current, the e.m.f . or the energy flowing in the circuit by the simple rules used for continuous currents. As the strength of an alternating current is constantly changing the magnitude of the inductive actions is constantly changing, and this fact further increases the difficulty of the subject.
In studying the principles of continuous currents we learn that when a conductor is moved across a magnetic field an e.m.f. is developed in it ; arid thus we understand the operation of a gen- erator, as we know that when the armature revolves, it carries the conductors upon its surface through the magnetic flux that issued from the poles of the field. We further learn that inas-
816 HANDBOOK ON ENGINEERING.
much as the magnitude of the e.m.f . is increased by increasing the strength of the magnetic flux, or the number of conductors on the armature or the velocity of rotation', that one or all these factors must be increased to increase the voltage. Thus we come to consider that to induce a high e.m.f. we must have a strong magnetic field. Now one of the first things that the student of alternating currents finds out is that in an alternating current circuit, the strongest e.m.f. induced by the action of the current itself, comes at the very time when the magnetic field is the weakest, and this appears to him to completely upset all the principles of continuous currents ; but in reality it does not. To be able to get over this stumbling block successfully it is necessary to realize that the magnitude of the e.m.f. induced in a conductor that is moved through a magnetic field is not depend- ent upon the strength of the magnetic field, but upon the rate, or rapidity with which the conductor cuts the magnetic flux. Now it so happens that in a continuous current generator, the rapidity with which the conductors cut the magnetic flux increases with increase in the strength of the magnetic field, or the velocity of rotation, and thus it comes about that in this case, the increase in the induced e.m.f. appears to be due to increase in armature velocity or field strength when in reality it is due to increase in the rate at which the conductors cut through the magnetic flux. The magnetic flux developed by an alternating current alternates precisely as the current does, and, as will be clearly explained presently, this magnetic flux cuts through any conductors in its path, and the rate at which it cuts them is the greatest at the in- stant when the direction of the flux is changing, and this is the instant when the flux is nothing, so that the e.m.f. induced by the magnetic flux developed by an alternating current is the greatest at the very instant when the magnetic field has a zero strength. The foregoing facts can be made more clear by refer- ence to diagrams.
HANDBOOK ON ENGINEERING.
817
Fig-* 350 is a simple diagram that can be taken to represent a gen- erator, either of continuous or alternating currents. The dark circles A A, B B and G G represent the sides of three loops of wire which may be regarded as wound upon the surface of an armature.
Figs. 350 and 851. Principle of electric generator.
The vertical lines represent a magnetic flux passing between the field poles Pand N. If the armature upon which the three loops are mounted is rotated, e.m.fs., will be induced in each one of the loops, but the magnitude of these e.m.fs. will not be the same. If we take the instant when the loops are in the position shown, the e.m.f . in A A will be zero, while that in G G will be the highest and that in B B will be seven-tenths of that in G G. Now all these coils rotate at the same velocity being mounted upon the same armature, and all move through a magnetic field of the same strength, yet, in A A no e.m.f. is developed while in B B the e.m.f. is only seven-tenths of that developed in G (7. The question is, why this difference? The answer is, that while loops A A move just as fast as G G they do not cut the magnetic flux
52
818 HANDBOOK ON ENGINEERING.
because they are moving in a direction parallel with the lines of force, the vertical lines, hence, the rate at which the magnetic flux is cut by them is zero, therefore the e.m.f . developed is zero. In B B the e.m.f. is seven-tenths of that developed in G (7, because the sides of this loop are moving in a direction that is not directly across the magnetic flux, but forms an angle of 45 degrees with it, so that their actual velocity in a direction parallel with A A is seven-tenths of the velocity of G 0 in. this same direction.
From the foregoing it will be seen that when we get down to a close examination of Fig. 350 we find that the magnitude of the e.m.f. developed in the several loops is directly proportional to the rate at which the sides of the loop cut through the magnetic flux.
Let us now consider Fig. 35 1. In this diagram, circle A repre- sents a wire, seen end on, through which an alternating current is flowing. An alternating current is one that flows first in one direction, and then in the opposite direction, and continues changing the direction in which it flows at regular intervals of time. Now it is self-evident that if a current flows through a wire in alternate directions, it must stop flowing in one direction before it can flow in the opposite direction, that is at the instant when the direction of flow is changing, there can be no current. Such being the case, when the current begins to flow in either direction, it must increase in strength gradually up to a certain point, and then begin to decrease, so as to reduce to nothing at the instant when the direction of flow changes. As is explained in the section on continuous currents, when a current of elec- tricity flows through a wire, a magnetic flux is developed around the wire and this can be represented by lines of force drawn in the form of circles, as in Fig. 351. If there is no current flowing through the wire there is no magnetic flux, therefore, if we consider the instant when a current begins to flow, we can imagine
HANDBOOK ON ENGINEERING. . 819
that at this instant the magnetic flux begins to expand outward from the wire, and since the circular lines are drawn to represent this flux we can assume that these expand outward, like the rip- ples on the surface of a pond when a pebble is thrown into the water. So long as the current flowing through the wire increases in strength, just so long will the magnetic circles of force expand, but when the current reaches its greatest strength the circular lines of force will become stationary, and will remain so if the current remains at its maximum strength ; but if the current begins to reduce in strength as soon as it reaches its maximum, then the circular lines of force will begin to contract immediately after they stop expanding, just as a swing will begin to move backward the instant it stops swinging forward.
If the circles B and G in Fig. 351 represent two wires parallel with A, it is evident that the magnetic circles of force when they move outward from A will cut through B and C in one direction, and when they contract back upon A they will cut through these two wires in the opposite direction. When these circular lines of force cut through the wires B G they will induces. m.fs. in the latter, and if these e.m.fs. are positive when the lines of force ex- pand, they will be negative when the lines contract. When the current reaches its maximum strength and the circular lines of force become stationary for an instant, they will not cut the wires B and C and at this instant there will be no e.m.f. induced in these wires. Now the circular lines of force become stationary at the very instant when the current flowing through the wire reaches its greatest strength and is on the point of reducing, so that at this instant the e.m.f. induced in the wires B and C is zero
The highest e.m.f. induced in B and C occurs at the instant when the current flowing through A is changing its direction, or, in other words, at the instant when there is no current. Just before the current reduces to zero, the circular lines of force are contracting upon wire A, and the instant after the cur-
820 HANDBOOK ON ENGINEERING.
rent reduces to zero and changes its direction, tlKse lin?s of force will be expanding so that in the first case the lines of force will sweep over wires B and 0 in a direction toward A, and in the second case they will sweep over these wires in a direction away from A. From this fact it might be inferred that the e.m.f. induced in the two cases would be in opposite direc- tions, but this is not so, owing to the fact that the lines of force change in direction when the current changes, so that if while contracting they are directed clockwise, as soon as they begin to expand they will be directed counter clockwise. As a result of this change in the direction of the lines of force when they change from contracting to expanding, the e.m.fs. induced in B and C are in the same direction before the lines stop contracting and after they begin to expand. The circular lines of force stop con- tracting and begin to expand at the same instant, so that the inductive action developed by the contracting lines is followed up without a break by the expanding lines. In alternating currents such as are actually used in practice, the rate at which the strength of the current changes is the greatest when it is just beginning to grow, and when it is reduced almost to zero, and on this account the highest e.m.f. induced in wires B and G occurs at the instant when the direction of the current is changing, that is, when the current is zero. Alternating currents can be de- veloped in which the rate of change in the current is not the greatest just when they begin to grow and when they are reduced nearly to zero and with such currents the highest e.m.f. induced in wires B and 0 would not come at the instant when the current is zero, but would come at the instants when the change in the current is the most rapid.
In every kind of alternating current, however, the instant when the e.m.f. induced in B and C is zero is the instant when the current reaches the maximum value, and begins to decrease, for this is the only instant when the circular lines of force are
HANDBOOK ON ENGINEERING.
821
immovable ; it being the instant when they are about to change from expanding to contracting, while still flowing in the same direction. When the current becomes zero, the lines of force change from contracting to expanding but at this instant they also change their direction so that the new expanding circular lines of force take up the work if inducing an e.m.f. in the wires B and (7 at the very point where the contracting lines leave off.
The circular lines of force developed by the current flowing in A, cut through this wire as well as through B and (7, hence, they induce an e.m.f. in A; that is an alternating current induces an e.m.f. in its own circuit as well as in adjoining circuits. The action upon adjoining wires is called mutual induction, and that upon its own wire is called self-induction. These e.m.fs. act in a direction opposite to that of the current that induces them.
The relations between alternating currents and e.m.fs. can be shown by means of diagrams, the simplest of which are con*
Fig. 352. Relation between current and electro- motive force*
structed in the manner shown in Fig. 352. In diagrams of this type the line 0 T represents time, thus if a point is assumed to move from 0 in the direction of T at a uniform velocity of say one foot per second, then a length of one inch will represent an interval of time of one-twelfth of a second. Distances measured in the vertical direction, along 0 S represent the magnitude of
822 HANDBOOK ON ENGINEERING.
the current or e.m.f. Positive currents and e.m.f. are indicated above the time line 0 T and negative currents and e.m.fs. below this line. Thus the wave line A A A can represent an alternating current or e.m.f. or an alternating magnetic flax. This curve it will be seen is above 0 T from 0 to 6, and below 0 Tfrom b to d, being again above from d to T. The two sections of the curve from 0 to d constitute one cycle, or two alternations. The portions between the lines 0 a, a 6, b c, c d are called quarter cycles or quarter periods. The time from O to d is called one period, and if this is equal to one-tenth of the distance that represents one second, then there are ten periods to one second. This fact is indicated by saying that the periodicity of the current is ten, or that its frequency is ten. The frequency of alternating currents in common use ranges between 20 and 130.
The curve A A in Fig. 352 represents a current or e.m.f. that increases or decreases at a certain rate, but for a current varying at some other rate it would be necessary to use a curve of differ- ent shape to correctly represent it. Thus if the current does not increase so fast when rising from the zero value, but increases faster when nearing its maximum value we will require a modifica- tion of the curve such as is indicated by B, in which the slope is more gradual on the start, and near the middle becomes more steep. If on the other hand the current increases more rapidly on the start, and less rapidly as it approaches the maximum value, we will have to use a curve something like C which is steeper at the ends and flatter at the middle.
The actual form of curve required to correctly represent an alternating current depends upon the rate at which the current varies, and this rate depends upon the construction of the machine in which it is generated. For the purpose of simplifying calcula- tions it is necessary to assume that the rate of variation of a cur- rent is such that it can be represented in a diagram such as Fig* 352 by some form of curve that can be drawn in accordance with
HANDBOOK ON ENGINEERING.
823
some fixed rule. The curve A A is of circular form, but there are few alternating current generators that develop currents that such a curve can properly represent.
If a current alternates in equal intervals of time, and the rate of variation is the same when it is flowing negatively as when it is flowing positively, then it can be represented by a curve that is of symmetrical construction, such as A A in which the intervals of time 0 &, b d are equal and the curves above the line 0 T are of the same shape as those below it. Such a current is called a symmetrical periodic current, and it is the only kind with which we have to do in practice. It can be readily understood, however, that the current can be far from regular, that is, the time during which it flows positively can be more or less than the time during which it flows negatively, and the rate of variation in the two
0
&
Fig. 353. Irregular periodic curve.
instances can be different. The curves in Figs 353 and 354 illus- trate currents of this kind. In Fig. 353 the positive impulses of the current are longer than the negative, as is shown by the greater length of lines 0 a, b c as compared with a b. It will also be seen that the rate of variation is different as is indicated by the difference in the form of the portions A A and B B of the curve. In Fig. 354 the irregularity is still greater, as all the time intervals Oa, a &, & c, c d, are different, as are also the portions A B C D E of the curve.
824
HANDBOOK ON ENGINEERING.
The alternating currents developed by alternating current generators have such a rate of variation that they can be repre- sented in diagrams by means of what is known as a sine curve.
s
Tig. 354. Showing still greater irregularity.
Tnis curve is not a perfectly true representation of practical alternating currents, but it comes so near to it that calculations I M,sed upon the assumption that the sine curve represents the actual
a a,
ff
\
Fig. 355. Construction of sine curve.
variation, do not depart from the truth by more than two or three per cent, and in some cases less than that. As the sine curve is commonly used to represent alternating currents we will show
HANDBOOK ON ENGINEERING. 825
how it is constructed by the aid of Fig. 355. In this diagram dia- metrical lines a b c are drawn on the circle B, dividing it into any desired number of equal parts. A distance 0 T on the hor- izontal line is divided into an equ^l number of equal parts and perpendicular lines a a are drawn at these divisions. From the points where the lines a b c cut the circle lines are drawn parallel with 0 T as shown at e f g and the points where these cut the corresponding perpendicular lines a a form points of the sine curve A A. The distance O T can be made anything desired without affecting the character of the curve, the only difference being that if it is short the curve will be more pointed than if it is long.
One reason why it is assumed that alternating currents vary in accordance with a sine curve is that if the variation is at this rate the e.m.f . induced by the magnetic flux developed by the current will also vary in accordance with the sine curve, so that the current, the magnetization and the induced e.m.f. can be rep- resented by sine curves, and thus the process of calculating the effect of the induced e.m.f. upon the strength of the current can be greatly simplified.
By looking at Fig. 350 it can be seen at once that if the loop A A is revolved at a uniform velocity, and the magnetic field between the poles P and N is of uniform strength at every point, the e.m.f. induced in A A will vary in strict accordance with the variations of the sine curve A A of Fig. 355, for in the position A A the e.m.f. will be zero, and in position G C it will be the maximum, while in any in- termediate position such as B B it will be equal to the actual velocity of the sides of the loop measured in the direction parallel with AA , and this velocity is equal to the distance of the side of the loop from the horizontal line A A. Now the height of the sine curve A A in Fig. 355 at any point is also equal to the distance from the end of the corresponding line in circle B from the horizontal
826
HANDBOOK ON ENGINEERING.
line, that is, the distrance e e' from the horizontal line to the curve is the same as the distance e e on the circle.
The complete sine curve from 0 to T is traced by following the rotation of the radius of the circle through one complete revolu- tion. On that account this distance 0 T is taken to represent one revolution, and is divided into 360 degrees, the same as the circle. Half the distance, or 0 d, is equal to 180 degrees, and one-quarter the distance is 90. The vertical lines a a in Fig. 355 are 30 degrees apart.
The way in which sine curves are used to represent alternat- ing currents and e.m.fs. is shown in Fig. 356. In this diagram,
a
Fig. 356. Manner of indicating alternating currents.
let the curve A represent an alternating current flowing through a wire. As is fully explained in the foregoing, this current will develop an alternating magnetic flux, and this flux will increase and decrease as the current increases and decreases, that is, it will keep in time with the current, or in step with it, as it is com- monly expressed. Such being the case, the curve A can be used to represent the magnetic flux as well as the current, providing we assume a proper scale for both. Looking at the half circle to the left of the figure, it will be seen that curve A is described by
HANDBOOK ON ENGINEERING. 827
a radius rotating around the middle circle. Remembering what was said in connection with Fig. 351 as to the time relation between the magnetic flux and the e.m.f . induced thereby, we will realize that at the instant 0 when the flux is zero, the induced e.m.f. must be at the maximum value, and it will act in opposition to the e.m.f. that drives the current through the wire, hence, in the diagram, it will have to be drawn below line 0 T. Let the maxi- mum value of this induced e.m.f. be equal to 0 c, then for all other values it will be correctly represented by the sine curve .B, which is traced by the rotation of the radius of the inner circle.
At the instant of time 0, the magnetic flux is zero, hence the radius of the middle circle from which curved is traced must be in the direction of line 0 T. At this same instant the induced e.m.f. is at the maximum value hence the radius that traces curve B must be in the vertical position parallel with O c. From this we see that in relation to time the curves A and B that repre- sent the magnetic flux and the induced e.m.f. are one-quarter of a cycle apart, that is the induced e.m.f. is 90 degrees behind the magnetization, and also 90 degrees behind the current that flows through, the wire.
No kind of electric current, whether continuous or alternating, can flow through a circuit unless there is an e.m.f. to drive it, and this e.m.f. must be sufficient to impel the current against all resistances of any kind that it may encounter. The e.m.f. that impels a current through an alternating current circuit is called the impressed e.m.f. In Fig. 356 it is evident that the impressed e.m.f. must be sufficient not only to overcome the actual resistance that opposes the flow of the current represented by curve -4, but also sufficient to overcome the opposing action of the induced e.m.f. represented by curve B. Now the e.m.f. required to overcome the resistance that opposed the flow of the current can be represented by the curve -4, in precisely the same
828 HANDBOOK ON ENGINEERING.
way as this curve represents the magnetization ; hence, the curve G which represents the impressed e.m.f. must at every point be equal, in height, from the line 0 T, to the sum of the heights of the curves A and B, when these two curves are on opposite sides of 0 T, or to their difference when they are on the same side. At the instant 0 it is clear that as the current is zero, the impressed e.m.f. C must be of the value 0 c' to balance the induced e.m.f. B for if it were not, there would be a current flowing negatively under the influence of e.m.f. B. At any instant between O and d, the impressed e.m.f. C must be equal to the sum A and B, that is, the distance from G to the time line 0 T must be equal to the distance between the curves ^4 B measured on the same vertical line. At the instant d the induced e.m.f. is zero, hence the impressed e.m.f. is equal to the distance of curve A above line 0 T. For any interval of time between d and e, the impressed and the in- duced e.m.fs. are acting together, so that the first named, that is, curve (7, need only be equal to the difference between A and B.
By studying the diagram Fig. 356 it will be seen that the curve (7, which represents the impressed e.m.f., is described by the rotation of the radius of the outer circle at Z), and in order that this e.m.f. may have the value of 0 cf at the instant 0, it is nec- essary for the describing radius at this instant to be in the posi- tion b. From this it will be seen that the impressed e.m.f. is not in time with the current but in advance of it by a time interval that is equal to the angle formed by the radius b with the line 0 T.
If two alternating currents, e.m.f. or magnetic fluxes are in time with each other they are said to be in phase, but if they are not in time they are out of phase. In Fig. 356 the current, the impressed e.m.f. and the induced e.m.f. are out of phase with each other. The impressed e.m.f. leads the current, and the latter leads the induced e.m.f. This relation is also expressed by say
HANDBOOK ON ENGINEERING.
829
ing that the current lags behind the im- pressed e.m.f. and the induced e.m.f. lags behind the current. The current and the impressed e.m.f. can never be out of phase by an angle as great as 90 degrees, but the phase difference can be any angle less than this. The induced e.m.f. is always 90 degrees out of phase with the current. The induced e.m.f. in the circuit in which the current flows is called the self-induction.
The relations between the impressed e.m.f., the current and the self-induc- tion both in magnitude and phase are clearly shown in Fig. 357, which is simply an enlarged view of the left side of Fig. 356. The radius A of the outer circle is the impressed e.m.f. The
radius B of the middle circle is the cur- Fig. 357. Enlarged Yiew
of Fig. 356. rent, and the radius C of the inner
circle is the self-induction. The magnitude of any one of these three quantities at any instant of time is equal to the distance from the end of the line to the horizontal line. The radius B which represents the current is on the horizontal line, hence the current at the instant represented by the diagram is zero. The self-induction C has a value at this instant equal to. the length of the line, that is, it is at the maximum value, and as it is below the horizontal line it is negative. The impressed e.m.f. A, has the value of a a, and being above the horizontal line, it is positive. The phase relation and also the magnitude of these quantities is also shown in Fig. 358, which is constructed from Fig. 357 by remov- ing the self-induction to the position of line a a. From Fig. 358 it
830
HANDBOOK ON ENGINEERING.
CURRENT.
can be seen that if we know two of the quantities we can always determine the other one by sim- ply constructing a right angle triangle.
The self-induction acts to oppose the flow of current, hence it is equivalent to the addition to a certain amount of resistance to the circuit, but as can be seen from the diagrams it cannot be added directly, after the fashion in which numbers are added. To add it properly it must be placed at right angles to the resistance.
If the self-induction is divided by the strength of the current, we get a quantity that can be compared with the resistance, and this quantity is called the
RESISTANCE.
Figs. 858 and 859. Illustrating
resistance, reactance and
impedance.
reactance and is measured in ohms precisely as the resistance is.
The flow of current in a continuous current circuit is opposed by the resistance only, but in an alternating current circuit it is opposed by the resistance and the reactance and the combined effect of these two is called the impedance of the circuit.
The relation between resistance, reactance and impedance is the same as that between impressed e.m.f., current and self- induction, and is shown in Fig. 359.
The reactance multiplied by the current gives the self -induction.
The impedance multiplied by the current gives the impressed e.m.f.
HANDBOOK ON ENGINEERING.
831
The resistance multiplied by the current gives the e.m.f. in phase with the current, which is also called the active e.m.f.
A sine curve diagram, such as is shown in Fig. 356, serves very well to enable the learner to under- stand the relation between the current and e.m.fs. but when this relation has been fully mastered, what is known as a clock dial diagram becomes more convenient, especially if we desire to represent several currents arid their e.m.fs. Fig. 357 is virtually one-half of a clock dial diagram. A regular clock dial diagram to represent a single alternating current is shown in Figs. 360 to 362. The radius A represents the current, and is
Figs. 360, 361 and 362. Clock dial diagrams.
supposed to rotate at a velocity equal to the frequency of the current. The strength of the current for any instant of time is obtained, by measuring the distance from the horizontal line S S to the end of the radius at that particular instant as indicated by line a a in Fig. 361. If A is above the line S S the current is positive, and if it is below S S the current is negative. At the instant when A is in the vertical position, as in Fig. 362, the current is at its maximum value, and when A is horizontal as in Fig. 360 the current is zero. If we -desire to find the relation between the current and impressed e.m.f. or the self-induction, we draw radial lines of the proper length to represent these e.m.fs. and in the proper angular position with reference to the current and then assume them to be locked together when they
832
HANDBOOK ON ENGINEERING.
are rotating so that the distances from the ends of each one to the line JS S at any instant gives the values of the quantities at this instant.
Diagrams of this type are specially valuable for the represen- tation of polyphase currents. Currents of this type are commonly spoken of as a two-phase current, or a three-phase current, or a polyphase current. Now there are no multiplephase currents. What is improperly called a two-phase current is a combination or two simple alternating currents so timed that they are out of phase with each other by one quarter of a period, or revolu- tion. This constitutes a system of two-phase currents. Three simple alternating currents so timed as to be out of phase with each other by one-third of a period, constitute a system of three phase currents. In the first case we have two currents, and in the second we have three currents. These currents in either system are connected so as to act together in the same system of circuits. If the phase relations are not such as given above, they cannot constitute true, two or three-phase systems.
Pigs. 363, 364 and 365. Phase relations for two-phase system.
The phase relations for the two-phase system are shown in Fig. 363 and for the three-phase system in Fig. 366. The two currents A B in Fig. 363 are at right angles with each other, and the three currents in Fig. 366 are 120 degrees apart, or one-third of a period, or cycle. To obtain the values of the two currents in
HANDBOOK ON ENGINEERING.
833
Fig. 363 at any particular instant, they are rotated together as is in- dicated in Figs. 364 and 365. The values will be equal to the lines a a and b b. In the same way the values of the three currents in a three-phase system are obtained for any instant as is illustrated in Figs. 367 and 368.
For the transmission of the currents of a two-phase system, three or four wires can be used. In the three-phase system, if the three currents are equal, three wires are sufficient, but if these currents are not equal a fourth wire is required to carry the surplus
a
Figs. 366, 367 and 368. Phase relations for three-phase system.
current as it may be called. When the three currents of a three, phase system are equal it is called a balance system, but if they are not equal the system is unbalanced. In Figs. 366 to 368 the three currents are drawn of equal length and it will be found that in every position in which the lines can be placed the sum of the two currents on one side of line S S will be just equal to the cur- rent on the other side, so that if the current is flowing away from the generator through one wire, it will divide up and return through the other two, and provide for each wire just the amount of current required. Thus in Fig. 366 the current flowing in A is zero, and the positive current in B is equal to the negative current in (7. In Fig. 367 the two positive currents a a and b b in lines A J5, are just equal to the one negative current in (7, and this is also the case in Fig. 368.
834 HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 835
tive e.m.f . in the circuit and thus retard the current, so that the actual amount of current flowing will be less than it would be in a continuous current circuit acted upon by an impressed e.m.f. of the same magnitude. As will be noticed, the direction of the flux at (7 and D is such that they oppose each other, that is the lines C and D flow through the space between the two sides of the loop A A in opposite directions, and on that account the lines G can only extend to the center of the space, while lines D will occupy the upper half. This being the case it is evident that if the cir- cuit wires are brought closer together as indicated by the lines B JB, the magnitude of the magnetic flux that will surround each wire will be correspondingly reduced as is indicated by the lines a a. The self -inductive e.m.f. developed in the circuit will be propor- tionaHo the magnitude of the flux that surrounds the wire, hence the nearer the two sides are brought to each other the less the self-induction, and if the two wires could be placed side by side the inductive effect would be practically nothing. From this it
'£^xD
•* <MT
m
. ~-, -^
Fig. 369. Inductive action in alternating current circuits.
will be seen that if an alternating current is transmitted to a dis- tance the nearer the line wires to each other the smaller the self- induction developed in them.
In an alternating current circuit the self-induction developed in every portion is not the same, and the total effect is equal to the sum of the several effects. For example in Fig. 370 let A A A represent a circuit that is fed by a generator at G. The self-
836
HANDBOOK ON ENGINEERING.
induction on the line A will be small, specially if the wires are placed near each other. If a number of incandes- cent lamps are connected at C the self-induction of these will be practically nothing. If at B we place some kind of device that is provided with wire in the form of coils, then at this point a large self-induction will be developed, for then the magnetic flux from each turn of wire in the coil will be able to cut
Fig. 370. Illustrating alternating current circuit.
through many other turns, and thus greatly increase the inductive action. To determine the total amount of inductive action in this circuit, so as to ascertain the amount of current that will flow through it, we will have to find the total impedance of the circuit, and this we do by finding the impedance of each part and then adding these impedances, but all this operation is carried out not in the way in which we add figures, but in the manner shown in Fig. 359. The diagram Fig. 371 illustrates the operation. By actual measurement we can find the resistance of the line A in ohms and we can mark it down on the diagram as o a. By calculation, we find the reactance of line A and mark it down as a a', thus we obtain the impedance of oa' of the line. Next, we find the resistance of the lamps 0 which we mark down at a' &, and from b draw b bf equal to the reactance of the lamps, thus obtaining the impedance a' &', of the lamps. We now draw b' c equal to the resistance of B and c c' equal to the reactance of
HANDBOOK ON ENGINEERING. 837
B and thereby obtain the impedance b' c' of B. We now join o
Fig. 371. Determining total inductive action.
with c' and obtain the line G which is the total impedance of the circuit, and line B, which is the total reactance, while line A is the total resistance. A glance at the diagram will show that the total impedance C is less than the sum o a' a' b' and b' c' if these were added in the ordinary way, so that the total impedance of a circuit can be less than the direct sum of the impedances of its several parts.
Fig. 872. Showing e.m.f. and current in phase.
The angle of lag between the current and impressed e.m.f. in an alternating circuit plays a very important part in determin- ing the actual amount of energy that is transmitted. In a continuous current circuit the energy is always equal to the
838
HANDBOOK ON ENGINEERING.
product of the volts by the amperes but in an alternating circuit it may be equal to this product and it may not be as much as one per cent of this product. What proportion of the product of the volts by the amperes will represent the actual energy trans- mitted will depend upon the angle of lag between the current and the impressed e.m,f., the greater this angle the less the en- ergy. The way in which the angle of lag affects the amount of energy flowing in the circuit can be made clear by means of Figs. 372 to 374. In these figures, curve A represents the impressed e.m.f. and curve B is the current, while the shaded curves repre- sent the energy. In Fig. 372 the impressed e.m.f. and the current
Fig. 373. Angle of lag affects energy in circuit.
are shown in phase with each other, and as a result the curves (7, which represent the energy are drawn above line 0 T, thus show- ing that all the energy is positive, and it is equal to the direct product of the volts by the amperes. In Fig. 373 the current and impressed e.m.f. are drawn out of phase 90 degrees. Starting from 0, the e.m.f. is positive while the current is negative, curve B being below line 0 T. This means that the current and e.m.f. act against each other hence the energy represented is negative. After the first quarter of a period, the current becomes positive
HANDBOOK ON ENGINEERING.
839
and then the energy is positive. Thus for the first half period we have two energy curves, D negative, and C positive, both of these are equal and, therefore, just offset each other, so that the net energy flowing in the circuit during this time is zero. As will be seen, during the following half periods, the same operation is re- peated, so that the actual result is that energy is put into the circuit during one quarter period, and during the next quarter it is taken
Fig. 374. Energy in circuit affected by lag.
out, and the actual energy flowing through the circuit is nothing. The action is the same as when a swing is set in motion, during the first half of each swing energy is .accumulated by the descent of the weight, but during the next half it is all absorbed in lifting the same weight, and unless we supply from outside enough en- ergy to overcome the friction the swing will soon come to a standstill. In an alternating current circuit, if the impressed e.m.f. and the current were out of phase 90 degrees no energy would be introduced into the circuit, hence, no current at all could flow, but if the angle is a trifle less than 90, say 89, a suf- ficient amount of energy can be put into the circuit to overcome the resistance loss, and then a strong current will sway back and forth that is not capable of doing any work. A current of this
840 HANDBOOK ON ENGINEERING.
•
kind is called a wattless current as it carries no energy. The rea- son why it carries no energy is that the self-induction very nearly balances the impressed e.m.f. so that the effective e.m.f . is very small, in fact it is just enough to force the current against the resistance of the circuit.
In Fig* 374 the current and impressed e.m.f. are shown out of phase by an angle of 45 degrees, and as will be seen the shaded curves C which represent positive energy, are much larger than those below line 0 T, which represent negative energy. The difference between these two is the actual energy flowing in the circuit. It can be clearly seen that the smaller the angle of lag between the current and impressed e.m.f. the larger the shaded curves above line 0 T and the smaller those below the line ; hence, the greater the energy flowing in the circuit.
By the use of condensers, the effect of self-induction can be counteracted, and in that way the lag of the current can be re- duced and thus the energy in the circuit can be increased. A condenser is a device that is so constructed as to be able to re- ceive a very large electriostatic charge. To explain the nature of electrostatic charges so that they may be understood we may say that bodies arranged so as to hold a charge will carry this charge upon their surface. Thus we can picture to the mind's eye the charge as flowing over the surface until it completely covers it. When a condenser is used in an alternating current circuit, it is charged and discharged each time the current alternates, and the time relation of the charging and discharging currents is such as to be directly opposite to the current that would flow under the effect of the self-induction, or, to put it in another way, the e.m.f of the condenser current is 180 degrees out of phase with the self-induction. Now, by properly proportioning the condenser it can be made to just balance the self-induction, and then we get the relations illustrated in Fig. 3 75 in which curve B represents the self -induction, curve C the condenser e.m.f. which
HANDBOOK OK ENGINEERING.
841
is directly opposite and of equal magnitude. Curve A represents the impressed e.m.f . as well as the current, both being in phase with each other.
The general principle of construction of a condenser is illus- trated in Fig. 376, in which the plates A B represent the condenser,
Fig. 375. Self-induction and condenser e.m.f.
and G the generator that provides the current, the connecting wires being S S. A device of this kind, if placed in a continuous
8
B
Fig. 876. Principle of the condenser.
current circuit, will simply prevent the flow of current ; but when connected in an alternating current circuit, if of the proper pro- portions, will act as if it did not break the circuit. This is because
842
HANDBOOK OK ENGINEERING.
the large surfaces on the plates A B act as reservoirs and accumu- late all the current that flows into them during the short time each impulse lasts. When the current reverses, the charge in the con- denser runs out together with the generator current. We can thus consider that if a positive impulse of the current fills plate A and empties plate B, a negative impulse will reverse the operation.
Mutual induction* — In connection with Fig. 351 it was shown that when an alternating current flows through a wire, the alter-
Fig. 377. Illustrating mutual induction.
nating magnetic flux that surrounds the wire, if it cuts through any other wires running parallel with it will induce e.m.fs. in them. The direction and phase of these e.m.fs. will be the same as that of the self-induction in the wire carrying the current. If we have two wires running parallel with each other and alternat- ing currents flow through, then the action of wire No. 1 upon wire No. 2 will be the same as that of No. 2 upon No. 1. This action is called mutual induction, and it is made use of in the
HANDBOOK ON ENGINEERING.
843
construction of an apparatus used for transforming alternating currents which is commonly called a transformer.
By the aid of Fig. 377 the principles of mutual induction can be made quite clear. In this diagram suppose that the circle A rep- resents one wire through which an alternating current is flowing, and circle B represents another wire carrying an alternating cur- rent. If these two wires are some distance apart, it is clear that a considerable portion of the magnetic flux of A will not cut through 5, and in like manner that a considerable portion of the flux of B will not cut though A, as is indicated by
Fig. 378. Inductive effect of wires upon each other.
the dotted circles at a a a. In any case, however, some of the flux of one wire will cut through the other. From this it follows that the effect of the current in each wire upon the other wire will be less than that upon itself, but the closer the wires are to each other the nearer equal the effects will be. When it is desired to avoid the effects of mutual induction as far as possible the wires must be separated to the greatest distance, and when we desire to make the mutual inductive effect the greatest, we must bring the wires as close
844 HANDBOOK ON ENGINEERING.
together as possible. The inductive effect of wires upon each other in some cases produces very objectionable results, for example when telephone wires are run side by side for any distance the inductive action of one wire upon the other serves to render the conversation indistinct. Why this is so it can be appreciated at once from an inspection of Fig. 378, which shows a pole carrying four wires. Telephone currents are not alter- nating but they pulsate and thus produce the same effect as if they were alternating. In Fig. 378 the circles drawn around each one of the wires as will be seen cut through all the other wires. If the two upper wires belong to one circuit and the two lower ones to another, then if one set of wires are crossed at every three or four poles so that the wire running on the right side for a certain distance will then be changed over to the left side, the inductive actions will be counteracted to a very great extent and this method is followed in stringing telephone wires. It is also used in regular alternating current circuits when interference between different circuits is to be avoided.
With regards to the two wires belonging to the same circuit, it is advantageous to string them as close together as possible, for in this case, the effect of mutual induction is to neutralize the effect of self-induction. Referring to Fig. 369 it can be seen at once that if the magnetic flux at 0 develops a self- induction in lower A toward the right, it will develop an induc- tion in upper A also towards the right, but with reference to the wire itself this induction will be just opposite to that in the lower side so that the two will counteract each other. Thus to reduce the reactance of the line, the two sides of the circuit must be placed as near together as is practicable.
Transformers* — A transformer is an apparatus in which the principle of mutual induction is utilized for the purpose of gener- ating a second current by the inductive action of a primary current. Referring to Fig. 377 it can be seen that if wire B is
HANDBOOK ON ENGINEERING.
845
closed upon itself the e.m.f. induced in it by the magnetic flux issuing from A will cause a current to flow and then this current, which is brought into existence by the inductive action of the current in A, will in turn develop a magnetic flux that will react upon wire A in precisely the same manner as if the current were not induced in J5, but it came from an independent source. In a transformer, the wire is wound in the form of compact coils, and one of these coils, which is called the primary, is connected with an alternating current circuit. The current flowing through this coil induces a current in the other coil which is called the second- ary. The general construction of a transformer can be under-
,''~~f~l- ^a
f I s^~ - -Uu V \
I ' r^ N. . \
-H-
m
Fig. 370. Priiiciple of the transformer.
stood from Fig. 379. An iron core G is provided upon which are wound two coils marked A and B. The coil A which is the prim- ary, is connected with an alternating current circuit, and thus the iron coreO is strongly magnetized. The presence of the iron core G serves to greatly increase the magnetic flux but does not in any way interfere with its alternating properties, so that it increases and decreases and changes its direction in precisely the same manner as the flux that surrounds a single wire. The flux de-
846 HANDBOOK ON ENGINEERING.
veloped by A, swells out as indicated by the lines a a a and cuts through the side of the secondary coil B. If the circuit through this coil is close an alternating current will be generated in it, and this current will develop a magnetic flux that will swell out and cut the side of the primary coil A. The e.m.f. induced in A by the flux of B will be in opposition to the self-induction de- veloped by its own flux, hence, if the circuit through B is open, the current flowing through A will be small because the self- induction will counteract the impressed e m.f . so as to leave but a small effective e.m.f. As soon as the circuit through B is closed, the inductive action of this coil upon A will offset to a certain extent the self-induction and thus assist the impressed e.m.f. in forcing more current through A. The more the current through B is increased, the stronger its action upon A and as a result the more the self-induction of A will be neutralized and the stronger the primary current will become. This action, which occurs in a perfectly natural manner, serves to make the trans- former a self -regulating apparatus, so that if a strong current is required in the secondary circuit, a strong current passes through the primary so as to furnish the energy necessary to develop the strong secondary current. If no current is drawn from the secondary, the primary current is reduced to nearly nothing.
To explain fully the action in a transformer would require a rather lengthy discussion of the principles involved, but the action, in a general way, can be made clear without going deeply into the theory. In explaining the phase relation of the current, the self-induction and the impressed e.mafs. in connection with Fig. 357 it was shown that theangle between the self-induction and the current is 90 degrees, and that the angle between the current and the impressed e.m.f. can be anything from zero up to nearly 90 degrees. If the current is passed through transformers or other inductive devices, the current will lag considerably. Suppose it lags 10 degrees, then the total angle between the im-
HANDBOOK ON 'ENGINEERING. 847
pressed e.m.f. and the self-induction will be 100 degrees. Now in a transformer the e.m.f. induced in the secondary coil is in phase with the self-induction in the primary coil, hence, with the above angles it would be 100 degrees behind the impressed e.m.f. in the primary coil. Now if the secondary current lags as much as the primary, it will be 110 degrees behind the primary im- pressed e.m.f. and the magnetic flux developed by this current will induce an e.m.f. in the primary coil 90 degrees behind itself or 200 degrees behind f_ie primary impressed e.m.f. This e.m.f. induced in the primary coil by the action of the sec- ondary current not only counteracts the self-induction in the primary coil, but in addition changes the phase relation between the primary current and its impressed e.m.f., making the angle smaller. This change in the phase relation between the current and impressed e.m.f. results, in turn, in a change of the phase relation of the secondary current, and this change in the phase of the secondary makes a corresponding change in the phase of the primary. If we were to trace up the action back and forth from primary to secondary currents we would finally arrive at the true phase relation of the currents and e.m.fs. in both circuits but this is a complicated and unnecessary process of reasoning. We can easily see that the current induced in the secondary coil will have a certain phase relation with respect to the primary current, and we can further see that the combined magnetizing effect of the two currents, the primary and secondary, is the same as that of a single current having a phase intermediate between the phases of these two. Following this course of reasoning we have only one inductive action to deal with and this is in such a phase relation that as it increases it decreases the self- inductive e.m.f. in the primary and thus permits more current to pass through this coil, and this increase in current in the primary causes a corresponding increase in the secondary current. When the secondary current is very small the self-induction in the
848 HANDBOOK ON ENGINEERING.
primary is very great and as a result the lag of the primary current is increased and its strength is decreased. As the sec- ondary current increases, the self-induction in the primary decreases, and the lag of the primary current reduces while the current strength increases. The strength of the secondary current is varied by varying the resistance in the secondary circuit ; if this resistance is reduced the current is increased.
To make a transformer as perfect as possible it is necessary to place the primary and secondary coils in such a position that the mutual induction between them may be the greatest pos- sible, that is so that all the magnetic flux developed by the primary coil may cut through the secondary and all the flux of the secondary may cut through the primary. If the coils, are arranged as in Fig. 379 it can be seen at once that all the flux of A will not cut through B and in like manner all the flux of B will not cut through A. It is not possible to arrange the coils so that all the flux of one coil will pass through all the turns of wire on the other coil, but this condition can be very nearly realized. If one-half of coil A is wound on each side of the core G and then the B coil is wound in two parts directly over the A coils the chance for the flux of one coil to not pass through the other coil will be greatly reduced.
The flux that does not pass through the opposite coil is called a leakage flux, thus in Fig. 379 the lines a that pass through coil A but not through B constitute the leakage from coil A and in like manner the flux oH coil B that does not pass through A is the leakage of B. The leakage flux represents just so much mag- netism thrown away, hence the effort of the designer is to arrange the coils so as to reduce it to the smallest amount possible. If the two coils were wound together, that is, if we took the wires and wound them side by side forming a single coil, the leakage would be practically nothing, but this construction cannot be used as with it there would be great danger of the insulation between
HANDBOOK ON ENGINEERING.
849
the coils giving away, and this would destroy the transformer. This form of winding can be approximated to by winding each coil in many sections and placing these in sandwich fashion upon
Fig. 380. Position of transformer coils on iron core.
the iron core as is shown in Fig. 380 in which the sections forming one coil are shaded, and those of the other coil are not. This is the construction that is followed generally in large transformers. In the majority of designs, however, the primary and secondary coils are wound one over the other.
Transformers are used for the purpose of changing the voltage of the current. The name transformer is misleading, as it creates the impression that the device transforms the current, when as shown in the foregoing it does nothing of the kind, it simply generates a secondary current, which is in no way connected with the primary. When electric energy is transmitted to a consider- able distance by means of alternating currents, the voltage used is much higher than is required for the operation of lamps or motors, hence, at the receiving end of the line this cur- rent is passed through transformers and secondary currents are generated in these that are of the voltage desired. The voltage
850 HANDBOOK ON ENGINEERING.
of the secondary current is controlled by the number of turns of wire placed upon the secondary coils. Roughly speaking, if the primary coil has ten times as many turns as the secondary the voltage of the secondary current will be one-tenth of that of the primary. If the primary voltage is 2000 and the secondary is 100 the primary coil will have twenty times as many turns of wire as the secondary.
Transformers that deliver a secondary current of lower volt- age than the primary are called lowering transformers, while those that deliver a secondary of higher voltage are called raising transformers. For distributing current to consumers, lowering transformers are used. But in long distance transmission plants, where the current in the transmission line has ane.m.f. of any- where from 10,000 to 30,000 volts, raising transformers are used at the power house, and these take the current from the generators, which may be of 1,000 or 2,000 volts and deliver to the line a secondary current of 10,000 or more volts.
Transformers cannot be used with continuous currents for the simple reason that as these currents do not fluctuate the magnetic flux developed by them remains stationary and, therefore, there is no inductive action.
A medium size transformer is shown in Fig. 381. The com- plete transformer is seen at the right side of the illustration. In the center is shown the lower part of the iron core, with the wire removed from one leg, this wire being shown on the left. The iron plates at the bottom of the figure form the upper part of the iron core.
The iron core of a transformer is built up out of sheet iron. It could not be made a solid mass, for, if it were, secondary cur- rents would be induced in it, and thus the energy in the primary current would be used up in developing useless currents in the iron core. The sheet iron laminations are insulated from each other, so as to prevent the development of currents in the core.
HANDBOOK ON ENGINEERING.
851
As can be seen from the illustration, the wire wound on each leg of the core belongs in part to the primary and in part to the secondary circuit. If the primary wire is proportioned so that it is proper for a 1,000-volt current when the parts on the two legs are connected in series, then it can be made proper for 500 volts
j
Fig. 381. Showing outer coyering of transformer.
by connecting the two parts in parallel. If the secondary coils will develop a voltage of 100 when both parts are connected in series, they will develop 50 volts if both parts are connected in parallel, but in this case the current will be doubled.
The transformer as shown to the right in Fig. 381, is complete, but for the purpose of protecting the wire an outer casing is pro-
852 HANDBOOK ON ENGINEERING.
vided. For high voltage transformers, this casing is made water tight and is filled with oil so as to improve the insulation of the apparatus. Very large transformers are provided with means for cooling them. In some, air is forced through the coils and iron core. In others, coils of pipe are placed within the casing and water circulates through these.
Alternating current generators. In alternating current gen- erators the field is magnetized permanently by means of a con- tinuous current. This current is obtained, generally, from a small continuous current generator that is called an exciter. Some alter- nators, as a rule of small capacity, are provided with a commu- tator to rectify a portion of the current the machine generates so as to provide a continuous current to magnetize the field. An alternating current cannot be used to magnetize the field because the field magnetism must remain unchanged.
Alternators are also arranged so that the field is magnetized by the combined action of the two continuous currents above mentioned, that is, by the current from a separate exciter and the current derived from the armature. Alternators excited in this manner are called compound machines and are the counter- part of the continuous current generator. Alternators that are excited by the current from a separate exciter alone are the coun- terpart of the plain shunt wound continuous current generator.
There are several other ways in which the field can be magnet- ized to make an alternator of the compound type, and the most important of these will be found fully explained under the head- ing of "Compensated Generators."
The object of compound winding in alternators is the same as In continuous current generators, that is, to keep the voltage con- stant and not allow it to drop as the current strength increases. Large alternators used in central stations are always of the com- pound type.
The way in which alternating current generators act can be
HANDBOOK ON ENGINEERING.
853
understood from the diagrams Figs. 382 to 386. In Fig. 382 P and N represent the poles of the field magnet of a two-pole machine. The armature is provided • with a single coil of wire marked a. When this coil is in the position shown, no e.m.f. will be induced in it, but as it begins to rotate from this position an e.m.f. will begin to be induced, and this will increase in mag- nitude until one -quarter of a revolution has been made, when it will be at the maximum value. During the next quarter revolu- tion the e.m.f. will gradually reduce, becoming zero when the half turn is completed. During the next half turn the e.m.f. will again rise to a maximum and fall to zero, but it will be oppositely
Figs. 382, 383 and 384. Generating current in alternator.
directed, so that if during the first half turn the e.m.f. is posi- tive, during the next half it will be negative, and this operation will be repeated for each revolution of the armature. Thus it will be seen that if the armature revolves ten times in a second, the frequency of the current generated will be ten, and in any case the frequency will be equal to the number of revolutions the armature makes in a second. This is true for a two-pole machine, if the generator has four poles the frequency of the current will be equal to twice the number of revolutions per second and for any greater number of poles the frequency will be equal to the number of revolutions of the armature per second multiplied by half the number of poles. Alternating current generators are always made with a large number of poles so that the frequency required may be obtained without running the armature at too great a speed.
854 HANDBOOK ON ENGINEEKING.
The diagram Fig. 382 illustrates a simple alternating current generator, or what is called a single-phase generator. A single- phase machine is one that has one coil on the armature for each pair of poles in the fields and generates one alternating current.
Fig. 383 illustrates diagrammatically a two-phase generator. A two-phase generator is an alternating current generator that gene- rates two alternating currents that are out of phase with each other by one-quarter of a period, that is, by 90 degrees. Such a generator is provided with two coils or sets of coils for each pair of poles and these are placed at right angles to each other in a two-pole machine, and so that the sides of one set come opposite the centers of the other set, in multipolar machines.
In Fig. 383 it will be seen that coil a is in the same position as the coil in Fig. 382, hence no e.m.f. is being induced in it. Coil &, however, is in the position in which the induced e.m.f. is of the maximum value, thus it will be seen that as the armature revolves the e.m.f. in one coil will rise toward the maximum while that in the other coil will be decreasing toward zero.
Fig. 384 illustrates a three-phase generator. A three-phase generator is a machine that generates three alternating currents that are out of phase with each other by an angle of 120 der grees, or one-third of a period. Such a machine has three coils or sets of coils for each pair of field poles.
In Fig. 384 it will be seen that coil a is in the position in which no e.m.f. is generated, and if we assume that the armature is re- volving in the direction of the hands of a clock, then the e.m.f. induced in coil b is very near the maximum value, but is still increasing, and will become the maximum when the coil reaches the horizontal position. In coil c the e.m.f. has passed the maximum and is reducing toward zero, which value it will reach when the coil reaches the vertical position, or the position in which a now is.
If an alternator is of the multipolar type the coils will be dis-
HANDBOOK ON ENGINEERING.
855
posed in the manner shown in Fig. 385. If it is a single-phase machine it will have one set of coils only, those marked A. If it is a two-phase generator it will have two sets of coils, the addi-
Fig. 385. Arrangement of coils in multipolar alternator.
tional set being placed in the position shown in broken lines and marked B. In this construction the machine appears to have as many A coils as there are poles and the same number of B coils, which is in contradiction to the statement made above that a single- phase machine has one coil for each pair of poles. The truth,
Fig. 386. Arrangement of coils in three-phase generator.
however, is that each coil in Fig. 385 is virtually one-half of a coil. Fig. 386 shows the way in which the coils are arranged in a three-phase generator of the multipolar type, the three sets of coils being marked ABC. In monocyclic generators the coils
856
HANDBOOK ON ENGINEERING.
are arranged as in Fig. 385, but they differ from the two-phase winding in that the B coils are one-quarter the size of the A coils. In actual generators the armature coils are seldom given the form shown in these diagrams, but whatever the form may be the prin- ciple of winding is the same.
In an alternator the armature coils forming one set are connected in series with each other, and the entering end of the first coil and the leaving end of the last coil are connected with collector rings mounted upon the armature shaft, and the current is taken from these by means of brushes similar to the commutator brushes of
Fig. 387. Revolving field alternator.
continuous current machines. In monocyclic generators one end of the B set of coils is connected with the middle point of the A set, and the three remaining ends are connected with col- lector rings. This is the arrangement with generators of what is known as the revolving armature type, which is the
HANDBOOK ON ENGINEERING. 857
one illustrated in Fig. 382 to 386. There is another type in which the outer part, which is stationary, is the armature, and the revolving part is the field. Machines of this kind are called re- volving field alternators. The principle of operation is the same in both types, but the revolving field type has the ad vantage that, as the armature is stationary, no collector rings and brushes are required to take off the current. All that is necessary is to pro- vide binding posts to which the ends of the armature coils are con- nected, and from these the external circuit wires are run off.
A revolving field alternator is shown in Fig. 387. In machines of this type, the field magnetizing coils are mounted on the periphery of the revolving part, hence the current that traverses them must pass through collector rings mounted upon the shaft. These rings are clearly shown in the illustration, the collector brushes being held, insulated from each other, by the stand located in front of the rings. Thus it will be seen that this type of machine requires collector rings, just the same as the revolving armature type, but the difference between the two is that in the latter the whole armature current passes through the collector rings, and on that account they must be made very large, while in the revolving field machines they can be made small, as only the field current passes through them, and this is only from one to two per cent of the armature current.
There is still another type of alternating current generator in which the wire on the field as well as the armature is held station- ary. Such machines are called inductor generators. The revolv- ing portion of such generators is simply a mass of iron formed like a very large pinion with correspondingly large teeth. When this part revolves the ends of the teeth sweep over the armature coils, running as close to them as they can without touching. The magnetic flux developed by the field coil issues from the ends of the teeth and cuts through the armature coils thus inducing e.m.fs. in them. It will be seen that the difference between this type of
858
HANDBOOK ON ENGINEERING.
generators and the revolving armature type is that instead of re- volving the armature coils through the stationary field flux, the latter is revolved and the armature coils are held stationary. The
Fig. 888. Inductor alternator.
difference between the inductor generator and the revolving field type is that in the latter the field is magnetized by a number of coils and these are rotated together with the field poles, while in the inductor machine there is a single field magnetizing coil and this remains stationary, the part that revolves being what might be called the poles.
An inductor alternator is shown in Fig. 388. The small machine mounted on the right side of the base is the exciter that
HANDBOOK ON ENGINEERING. 859
furnishes the field magnetizing current. The outer casing of the machine holds a ring built up of sheet iron laminations, which constitutes the armature and supports the armature coils. The large teeth, or polar projections, which are well shown in the illustration, are carried by the revolving part, and when rotating cause the magnetic flux to sweep over the armature coils. The field coil is placed back of these polar projections.
Alternating current generators are run singly, or they may be connected in parallel, but they cannot be run in series. If an attempt is made to run them in series, one of the machines will act as a motor and will be driven by the current generated by the other. When alternators are connected in parallel it is necessary that they run at exactly the same velocity, if they are identical in construction. If the generators are not of the same construe^ tion then their velocities will depend upon the number of poles each one has. Machines of different size and even design, can be connected in parallel, providing the frequency of the currents they generate are the same. To make the frequency the same it is necessary that the velocity of each machine multiplied by the number of poles it has be equal to the same number. Thus if one machine has twice as many poles as the other, it must run at one-half the velocity. The velocity of alternators connected in parallel must be equal, absolutely, and not practically so ; that is, if two machines are alike, and one runs at 1000 revolutions per minute, the other must run at 1000 and it cannot run at 999 or 1001. Since such extreme accuracy in speed is necessary it might be inferred that it is practically impossible to run alter- nators in parallel unless their shafts are coupled together, or they are connected through spur gearing with the same driving shaft. As a matter of fact, however, alternators can be run in parallel even if one is driven by a steam engine and the other by a water wheel, and they may be side by side or several miles apart. The reason why this is the case is that when the machines are in oper-
860 HANDBOOK ON ENGINEERING.
ation, the current holds them in step. If several generators are feeding into the same circuit, and one machine tends to lag behind the others, its current reduces and thus the speed in- creases as less power is required to drive it. If the tendency to lag increases, the machine begins to act as a motor, and is driven by the current from the other machines.
While it is possible to run alternators in parallel under almost any conditions providing they are speeded so as to generate cur- rents of the same frequency and nearly the same voltage, entirely satisfactory results cannot be obtained unless the angular motion is uniform, that is, unless the velocity of rotation is the same at all points of the revolution. If a steam engine has a light fly- wheel the velocity of the shaft will not be the same at all points of the revolution, but will be the slowest when the crank is passing the center, and the fastest when at half stroke. This fact is clearly shown by the irregular motion of the paddle-wheels of river boats driven by a single engine.
If two alternators are driven by two engines whose rotative motion is not uniform and the engines are so timed that one is on the center when the other is at half -stroke, then the action of the two alternators will be irregular, for when one machine is rotating at the highest velocity the other will be ro- tating at the lowest. This uneven action of the alternators may be compared with the work of two horses hitched to a wagon and pulling unevenly. If both horses pull together all the time the whiffle-tree will remain straight and the wagon will be drawn along smoothly ; but as soon as the horses begin to pull unevenly the whiffle-tree will be jerked back and forth and the motion of the wagon will be irregular. In this case the horses soon tire out because they work against each other part of the time. The action between two alternators that do not rotate with uniform velocities is practically the same as that of two horses that do not work together ; the machine that runs ahead not only sends a
HANDBOOK ON ENGINEERING. 861
current into the main circuit, but in addition backs up a cur- rent through the other generator, thus wasting energy by causing a strong current to flow back and forth between the two machines. To overcome this difficulty engines made to drive alternators are provided with extra heavy flywheels, so that the momentum may be sufficient to keep the speed up to the normal point while the crank is passing the center.
With small alternators that have only a few poles and are driven by high-speed engines, the affect of irregular motion is not so great as in large machines having many poles, hence the large slow-speed engines used to drive alternators having a large num- ber of poles, must be provided with excessively large flywheels to run in a satisfactory manner.
The reason why alternators with a large number of poles require greater regularity in motion to give satisfactory results, can be easily understood. Suppose we have a pair of two-pole machines driven by engines whose flywheels are 25 ft. in circumference. Suppose, further, that the irregularity in motion is such that each engine when running at the faster velocity, gets three injches ahead of the other. Then the advance in position will be one per cent, and consequently the currents of the two generators will run ahead and behind each other one per cent at each quarter of a revolution. Now, if these same two engines drive two twenty- pole alternators, then the irregularity in motion will be multiplied ten times, because one-tenth of a revolution will give one cycle of current, and the current of each machine will run ahead and fall behind the other ten per cent, instead of one per cent.
Starting" alternators connected in parallel : — In starting con- tinuous current generators that are connected in parallel all we have to do is to set one machine in operation and then after the second one is running up to full speed, we adjust its field regu- lator until the voltage is the same as that of the first machine, or one or two volts higher. We then throw the switch and connect
862 HANDBOOK ON ENGINEERING.
it with the switchboard. In starting alternators that are con- nected in parallel we have to do more than this, we must not only adjust the second machine so that its voltage is the same as that of the first, but we must bring it up to the proper speed and get its current in phase with that of the first generator before we connect it with the switchboard. To accomplish all this with certainty, devices are used that are called synchronizers, or phase indicators. These devices consist generally of a couple of small transformers one of which is connected with the circuit of each generator. The secondary wires of these transformers are connected with each other and one or two incandescent lamps are connected in this circuit. When the second machine is started up, as its speed is much lower than that of the generator already in operation the frequency of the secondary current of its transformer will be much lower than that of the first machine, and as a result the lamps in the circuit of the two transformers will flicker rapidly. As the second machine builds up its speed the flickering of the lamps will become slower. When the two generators are running at nearly the same speed the flickering will be replaced by rather long periods of darkness and light. During the periods when the lamps are lighted the current generated by one of the transformers is in such a direction as to act in series with the current of the other and thus draw the current through the lamp. When the lamps are dark it is because the currents of the two transformers are in opposition to each other and thus no current passes through the lamps. The second generator is connected with the switch- board during one of the periods of darkness or brightness, de- pending upon the way in which the transformers are connected. The second generator will not be running at exactly the proper speed when it is connected with the switchboard, but as soon as it is connected the currents of the two machines acting upon each other will at once draw the second machine into step with the first one, and they will continue to run in step even if the power
HANDBOOK ON ENGINEERING.
863
driving one of the machines should fail. In the latter case, the first machine would not only furnish current for the main cir- cuit, but would in addition drive the second machine as a motor. The way in which synchronizing lamps are connected in single or polyphase circuits is clearly illustrated in the diagram Fig. 389-
To Bus Bars.
Sy nchr oni zing
"To GeneraCor.
Fig. 389. Showing arrangement of synchronizing lamps.
The three upper lines are connected with the main bus-bars on the switchboard and the lower lines run to the generator that is to be synchronized. The left side of the diagram shows the connec- tions for synchronizing a single-phase generator. In such a case, the middle wire running to the bus-bars and to the generator would not be used. The synchronizing transformers would have their primary coils connected with the side wires in the manner shown by lines //and g g. When the generator current is in synchro- nism with that in the bus-bars, the primary currents in the two synchronizing transformers will flow in the direction of the arrows a a, and the secondary currents will be in the direction of arrows c, that is, in opposition to each other, so that no current will pass through the synchronizing lamps. If the connections of one of
864 HANDBOOK ON ENGINEERING.
the transformers are reversed, either in the primary or secondary, the two secondary currents will flow through the lamps in the same direction as indicated by the arrows d on the right side of the diagram. Thus it will be seen that the synchronizing lamps can be arranged so that they will light up when the generator current is in phase with the bus-bar current, or they may be arranged so as to be dark at this instant. Generally they are arranged so as to be bright when the current is in phase and the switch connect- ing the generator with the switchboard is closed at the instant when the lamps appear to be brighter.
When two and three-phase generators are started up the first time a temporary synchronizing arrangement is connected in the manner shown on the right side of Fig. 389. The synchronizing lamps on the left side will show that the current flowing in the two side wires is in synchronism, but this does not show that the other currents also synchronize. To make sure that the temporary transformer is properly connected the connections e are made first, and if the lamps on both sides of the diagram become dark and bright together, the' connections are correct. The connections are then broken and are transferred to the middle wire ; then when all the currents are synchronized, all the lights will light up together. Generally the internal connections of synchronizing transformers are properly made, and the correct connection of the terminal wires is clearly indicated so that mis- takes in making connections are not very liable.
Compensating and compounding alternators* — Continuous current generators are provided with a compound field winding for the purpose of maintaining the voltage uniform as the arma- ture current increases. Alternating current generators are compounded for the same purpose. If the field of an alternator is excited by a current derived from an exciter the voltage of the machine will drop as the strength of the current generated in the armature increases. A part of the drop is due to the fact
HANDBOOK ON ENGINEERING. 865
that the increased current absorbs more voltage in passing through the armature coils. The balance of the drop is produced by the reaction of the armature current upon the field. As the current of the exciter that magnetizes the field remains constant, the magnetization produced .by it remains constant. The cur- rent flowing in the alternator armature acts to demagnetize the field, and, as its action increases as the strength increases it follows that the stronger the current becomes the weaker the field will be, and, as a result, the lower the voltage of the cur- rent generated in the alternator armature.
If a portion of the current of the alternator armature is recti- fied by being passed through a commutator and is used to assist the exciter current to magnetize the field then the field magnetism will increase as the armature current increases, because the action of the rectified current will increase. Thus by the com- pound action of the exciter current and the rectified armature current, the magnetism of the field of the alternator can be made to increase as the armature current increases, and in this way the voltage is increased so as to compensate for the greater drop of voltage on the armature coils, the result being that the voltage impressed upon the wire remains practically the same for all strengths of current.
The above results can be obtained providing the phase relation between the current and the impressed, or line e.m.f. does not change ; but if the phase relation is continually changing such perfect regulation cannot be realized. The reason why changes in the phase of the current interfere with the regulation is that the same strength of armature current will produce different de- grees of reaction on the field magnetism with different phase relations. .If the lag of the current is increased the reaction upon the field will be increased, and in like manner a decrease in the lag will reduce the reaction upon the field. Several arrangements are used for obtaining field magnetizing currents that will com-
55
866 HANDBOOK ON ENGINEERING.
•
pensate for variations in the lag of the current as well as for va- riations in strength. Alternators provided with such arrange- ments are called " Compensated Generators." The way in which a field magnetizing current is obtained v that will compensate for variations in lag as well as in current strength is by using a por- tion of the armature current to vary the strength of the current generated by an exciter, the exciter being provided with coils through which the current taken from the armature is passed. These coils are so disposed that their governing action upon the exciter is proportional to the lag of the current as well as its strength, hence the current that the exciter sends through the field coils of the alternator is at all times sufficient to compensate for variations in the strength and phase of the armature current.
If an alternator is single-phase, one commutator is sufficient to rectify the portion of the armature current and to magnetize the field. For a two-phase machine, two commutators are required and for a three-phase, three commutators. To obviate using two and three commutators in polyphase generators, trans- formers are employed, two transformers for two-phase and three transformers for three-phase. The recording currents of these transformers are combined into one, and this com- bined current is passed through a single commutator to be recti- fied. In some cases only one of the currents of a two or three- phase generator is rectified, but with most machines, if they are connected in parallel, care must be taken to have the circuits from which the rectified current is taken properly connected with each other ; if not, one armature will short circuit the other. This is due to the fact that when alternators are run in parallel the rectified currents for the field coils are connected with each other through equalizer wires, in a manner similar to that used with continuous current generators.
The ordinary connections for two generator's in parallel are shown in the diagram Fig. 390.
HANDBOOK ON ENGINEERING.
867
As will be seen, the field-magetizing currents derived from the commutators are connected with each other through the equalizer switches, hence, to avoid short circuiting the armature through the equalizer connections, if the commutator rectify one current only,
Commutator
Fig. 890. Connections of composite field alternating generators for running: in parallel.
the two rectified currents must be in phase with each other. The rheostats shown in each field circuit are for the purpose of adjusting the voltage of each generator independently.
The use of transformers to transform the portion of the arma- ture current that is rectified is no objection against polyphase machines, because, even with single phases, the armature voltage is generally so high that a transformer is used so as to obtain a secondary current of low voltage to pass through the field coils.
Alternating current motors* — From the foregoing it can be understood that an alternating current generator can be used as a motor providing it is supplied with the same kind of currents,
868 HANDBOOK ON ENGINEERING.
that is, with a continuous current to magnetize the field, and with an alternating current for the armature. A single-phase alter- nator will run as a motor if connected in a single-phase circuit. Two-phase generators will act as two-phase motors, and three- phase generators will act as three-phase motors. With either one of these three types of machines a continuous current will be required to magnetize the field. Two and three-phase ma- chines can be run with a single alternating current, by connect- ing one of the armature circuits only, or all the circuits may be used if they are connected in parallel.
When an alternator is used as a motor it is called a synchro- nous motor, because it runs in synchronism with the generator that supplies the current. A simple alternator (single-phase ma- chine) becomes a single-phase synchronous motor, and a two or three-phase generator becomes a two or three-phase syn- chronous motor.
A single-phase synchronous motor will not start up of its own accord, but must be set in motion and run up to nearly its full speed before it will begin to act as a motor. If it is started up without a load when it comes rather near to its full speed it will give a sudden jump and swing into step with the current and then continue to run at this velocity. If it is started with a full load it will not fall into step with the current until its speed is very nearly up to the proper point. Synchronous motors are never started under load, they are always started light.
Two and three-phase synchronous motors can be started with- out outside assistance. Synchronous motors are generally pro- vided with a self -starting motor, to set them in motion, or else they are arranged so as to be self -starting by being converted, in the act of starting, into some form of motor that is self- starting.
Fig* 39 \ shows a synchronous motor of large size provided with an induction motor of much smaller capacity to start it.
HANDBOOK ON ENGINEERING.
869
This motor is of .the revolving field type, and, as will be seen, is precisely the same as the same type of generator.
Fiff. 391. 1000 h. p. two-phase revolving field synchronous motor.
Owing to the fact that synchronous motors are not self -starting, they are generally used only where large power is required, unless they happen to be made so as to be self -starting, then they are used in small sizes.
A synchronous motor, when running, will keep in step with the current, no matter how much the load may vary, provided it is not made greater than the capacity of the machine. If the load is made so great that the motor cannot carry it, the armature will be pulled out of step with the current and will imme- diately come to a stop. On this account, motors of the synchronous type are not well adapted to operate cranes or similar machines in which there is a liability of greatly overloading the machine occasionally.
870 HANDBOOK ON ENGINEERING.
The current developed by an alternating current generator will lag behind the impressed e.m.f. as has been fully explained in the foregoing. If this current is passed through a second machine, that acts as a motor, the latter will tend to generate a current that flows in opposition to that of the generator ; hence, in this current the lag will be in the opposite direction of that of the current that drives it. That is when the machine acts as a motor its whole action as a generator is reversed. Owing to this fact, if a synchronous motor is placed at one end of a circuit, and a generator at the other, the motor will act to neutralize the self-induction of the generator, and thus to bring the current in the circuit, and the impressed e.m.f . into phase with each other. Thus, a synchro- nous motor can be made to act in the same way as a condenser, to reduce the lag of the current.
Power factor* — In an alternating current circuit, it is very important to reduce the lag of the current as far as possible because the actual amount of energy carried by the current depends upon the angle of lag, as was fully explained in connection with Figs. 372 to 374. In a continuous current circuit the power is always equal to the product of the volts by the amperes, but in an alternating current circuit this product is not a measure of the power. It is called the apparent power, or the volt-amperes. The actual power is equal to the amperes multi- plied by the e.m.f. in phase with the current, or the active voltage, as it is called. The ratio between the true power and the volt- amperes is called the power factor. The power factor can be obtained by dividing the true power by the volt-amperes, and it may range from 100 per cent when the current and impressed e.m.f. are in phase down to five or ten per cent when the angle of lag is nearly 90 per cent. In actual working circuits the power factor ranges between about 95 and 75 per cent. Any kind of device that has a low reactance, as, for example, incandescent lamps, acts to keep the angle of lag of the current small, and thus
HANDBOOK ON ENGINEERING. 871
the power factor high. Devices having large reactance, such as transformers, and induction motors act to increase the angle of lag of the current, and thus to reduce the power factor. Devices that develop a negative reactance, that is, which cause the current to lead the impressed e.m.f., such as condensers and synchronous motors, can be used in circuits in which transformers and similar devices are operated so as to counteract these and thereby keep up the percentage of the power factor.
Induction and other types of motors* — In addition to the synchronous motors just explained, the only type of machine that requires notice here is the induction motor. This is by far the most extensively used of all alternating current motors, and from the manner in which it acts it has a greater range of adaptability than any other type. It may be well to mention here, however, that a plain motor, such as those used with continuous currents, can be made to operate with alternating currents providing the field cores are made laminated, instead of solid castings. If the field is solid the motor will not run if connected in an alternating current circuit because the large mass of iron constituting the field cannot be magnetized and demagnetized as fast as the current alternates. If we take hold of a freight car and try to shake it we will fail in the effort, simply because the bulk is too great to be set in motion rapidly. If, however, we take hold of the side of a light buggy and shake it we will be able to produce a very vigorous movement, simply because the bulk is light. In the same way, if we attempt to alternate the magnetic polarity of large masses of iron >re fail because the bulk is too great, but if we divide the mass up into many thin sheets we will have no diffi- culty in causing its polarity to change rapidly. Alternating cur- rent motors of this kind which are called commutator motors, have been made, but they are not used or manufactured for com- mercial purposes at the present time, because they are far inferior to other types. They are open to two objections, one of which
872
HANDBOOK ON ENGINEERING.
is that they spark considerably and the other is that they will not give much more than one-third the power that the same machine will develop if supplied with a continuous current. The reason why they give such small power is that on account of the many turns of wire on the field the inductive action is very great, hence the reactance is very high, and as a result the current lags exces- sively so that the power factor is very low, therefore, although the current is strong, the actual energy carried by it is comparatively small. Several other types of alternating current motors have been devised, but they have never got beyond the experimental stage.
Principle of the induction motor- — Induction motors are made for single and polyphase currents. When in operation the
392 and 393. Principle of induction motor.
principle of action is the same in all, but in the act of starting the single-phase machine is different from the others. Single-phase induction motors will not start of their own accord unless provided with special starting arrangements. The most common way of arranging a single-phase induction motor so as to be self-starting is to provide a set of starting coils that virtually convert it into a
HANDBOOK ON ENGINEERING. 873
two-phase machine in the act of starting. When the motor is underway the starting coils are cut out, although in some cases they are left in circuit all the time. The principle of the induc- tion motor can be explained by the aid of the diagrams Figs. 392 to 395. These diagrams illustrate the action in a two-phase machine, which is the one most easily understood. The single-phase induction motor is the most difficult one to ex- plain or to understand, so we will leave it for the last. In an induction motor, the stationary part, which is called the stator, and sometimes the field, is provided with coils that are connected with the operating circuits. The rotating part, which is called the rotor, and sometimes the armature, is provided with coils that are short circuited upon themselves and are not connected with the operating circuits. The principle of operation generally stated is that the currents in the stator develop an in- ductive action upon the coils of the rotor thus developing currents in these, the action being substantially the same as that in a transformer. On that account the stator is also called the primary member, while the rotor or armature is commonly called the secondary member. The primary currents passing through the coils of the stator, develop a magnetic flux and the secondary currents induced in the coils of the rotor also develop a magnetic flux, these two fluxes are at an angle with each other, and, hence, there is a strong attraction exerted between them, the magnetism of the rotor making an effort to place itself parallel with that of the stator. The magnetism of the stator rotates, on account of being developed by alternating currents, and the magnetism of the rotor in trying to place itself parallel with that of the stator also rotates, chasing the latter around the circle but never overtaking it.
In Fig. 392 let A A represent two coils connected in one of the circuits of a two-phase system, and let B B represent two other coils connected in the other circuit of this same system. Suppose
874
HANDBOOK ON ENGINEERING.
we consider the instant of time when the current flowing through the A A coils is at its maximum value, then at this very same instant the current in the B B coils will be zero. The current in the A A coils is then the only magnetizing current acting upon the ring at this instant. Suppose the direction of the current through A A is such as to develop a magnetic flux that will traverse the space in the center of the ring in the direction of arrow C. As the current in the A A coils begins to decrease, that flowing in the B B coils will begin to increase. Let the direction of the current in the B B coils be such as to send a magnetic flux through the center of the ring in the direction of arrow C in Fig. 394. This magnetization will act upon that developed by the current in the A A coils and will have a tendency to twist it around into the direction of arrow C in Fig. 393. When the current in the .4 A coils has reduced and the current in the B B coils has increased until they are both equal, then each one will act with equal force
Figs. 394: and 395. Illustrating operation of induction motor.
to establish a magnetization in its own direction, and the result will be that the actual direction of the magnetic flux will be as indicated by arrow C in Fig. 393. Thus we see that by the decrease in the strength of the current in the A A coils and the
HANDBOOK ON ENGINEERING. 875
increase in the strength of the current in the B B coils until they are both equal, the magnetic flux has been rotated from the position of arrow C in Fig. 392 to its position in Fig. 393. Now as the variation in the currents progresses, and that in A A becomes weaker, while that in B B becomes stronger, the direction of the magnetic flux will be still further rotated so that when the current in B B reaches the maximum value, and that in A A becomes zero, the direction of the flux will be that of arrow C in Fig. 394. As we advance beyond this instant of time, the current in B B will begin to reduce, while that in A A will begin to increase, but its direction will be the opposite of what it was iii Fig. 392, so that when the currents in the two sets of coils become equal again, the direction of the magnetic flux will be that of arrow 0 in Fig. 395. When the current in the A A coils reaches the maximum and that in B B becomes zero, the flux will have rotated through one-half of a revolution and arrow G will be in the vertical position but pointing downward.
If we follow the action of the currents further we will find that as a result of the continuous increasing and decreasing and changing of direction, the magnetic flux indicated by arrow C will continuously rotate keeping time with the frequency of the currents. Now if we suppose that an armature upon which a number of coils are wound in a diametrical position, is placed . within the field ring, and is held stationary, we will see at once that the rotating magnetic flux will cut through its coils and develop e.m.fs. in them. The currents developed in these coils on the stationary armature will be alternating, hence, they will develop a magnetic flux in the armature that will rotate, and keep time with the rotating flux developed by the field coils. Both these fluxes act inductively upon the field and armature coils, their combined effect being equal to that of a single flux located 90 degrees in advance of the e.m.f. induced in the armature coils, hence, somewhat more than 90 degrees ahead of
876 HANDBOOK ON ENGINEERING.
•
the armature current. If we hold the armature by means of a brake, and free this slightly, so that the armature may revolve slowly, it will at once follow around after the rotating field, but as its magnetization is developed by currents that are induced by the action of the field magnetism, it will matter little how fast the armature may revolve, its magnetization will never be able to overtake that of the field.
As can be judged from the foregoing explanation, an induction motor is not a synchronous machine, and its armature can never at- tain a velocity equal to that of the rotating field. If the resistance of the armature coils is made very low, it may reach a velocity very near to that of the rotating flux. The difference between the velocity of the rotating flux and that of the rotating armature is called the slip of the motor.
If the motor is designed for constant speed, the resistance of the armature coils is made very low, and then when the machine is running free, the speed of the armature may run up to 99 or 99£ per cent of the speed of the rotating field, and when the maximum load is put on it may not drop lower than 94 or 95 per cent. If a motor is designed in this way the pull of the armature when it starts up will be small and will gradually increase until the speed is about nine-tenths of the maximum when it will again begin to decrease.
If it is desired to make a motor that will give a strong pull when it starts up, its armature coils must have more resistance, and then it will pull harder on the start, but as fast as the speed builds up the pull will reduce. From this it will be seen that in- duction motors that are made so as to run at nearly a constant speed, say to vary five or six per cent between full load and run- ning free, will not give a strong pull in the act of starting, hence they will have to be started without a load. If a motor is to be made to start under a full load it must be proportioned so that it will not run at a constant speed, but will gradually reduce its velocity as the load is increased.
HANDBOOK ON ENGINEERING. 877
Induction motors, if very small, are started by connecting them directly with the operating circuits, but if they are of any capacity they must be provided with some kind of starting resist- ance so as to keep the starting current down within safe limits. One way of starting is to introduce resistance into the primary circuits, but this results in reducing the strength of the field, and thus the pull of the armature. Another way is to intro- duce resistance into the armature coil circuit. This is the best method, because it enables the motor to start up with a strong pull.
Three-phase induction motors act in precisely the same way as the two-phase, the only difference being that the rotation of the field flux is produced by the increase and decrease in the strength of three currents flowing through three sets of coils equally spaced around the circle instead of by the increase and decrease in two currents flowing in two sets of coils equally spaced around the circle.
In the single-phase induction motor, the magnetic flux developed by the single alternating current traversing a single set of coils on the field combines with the magnetic flux developed by the armature current, to develop a rotating field and this acting upon the armature coils produces rotation in precisely the same way as in the two- phase machine. This is the action that takes place after the armature is set in motion, but if the load is increased and the armature speed is reduced the rotating field begins to become irregular, and by the time the armature velocity is reduced to about one-half, the rotating flux becomes so irregular in its move- ment, that the armature pull begins to reduce very rapidly, and the machine comes to a standstill. Owing to this fact single- phase induction motors cannot be used in cases where it is de- sired to start with a strong pull, or where a wide range of speed variation is desired.
To make a single-phase induction motor self -starting, it is wound
878 HANDBOOK ON ENGINEERING.
with two sets of coils, like the diagrams Figs. 392 to 395, and the current from the single-phase circuit is passed through these two sets of coils in parallel branches, and in one of the branches the reactance is greatly increased, so as to make the current in this branch lag much more than in the other. In this way a phase displacement is obtained between the two currents, and this pro- duces a corresponding displacement in the magnetic fluxes devel- oped by the two sets of coils, so that their combined action develops a rotating field. This field does not rotate at a uniform rate, like the field of a two-phase motor, but it is uniform enough for the purpose of setting the machine in motion. To increase the reactance in the auxiliary starting coils, all that is necessary is to wind them with many turns of fine wire, and this is an arrangement very commonly employed, but, in some cases, sep- arate coils are placed in the auxiliary circuit to obtain the required reactance.
There are other ways in which single-phase induction motors are made self -star ting, but they are not very extensively used.
While induction motors are very satisfactory machines, being adapted to every kind of work, even to the operation of railway cars, they have the objection of being highly inductive devices that act to greatly increase the lag of the current, and thereby to reduce the power factor. On this account they are often used in connection with synchronous motors so that the latter may coun- teract their inductive effect, and thus keep the power factor high.
The small motor shown in Fig. 391, is an induction motor. Induction motors are made in many different designs, and as large as 300 to 400 H. P., but as a rule they are confined to much smaller capacities ; synchronous motors being used for the larger sizes.
Rotary transformers and rotary converters* — A rotary transformer is a machine by means of which a continuous current may be obtained from an alternating current. A rotary con-
HANDBOOK ON ENGINEERING.
879
verier is a machine for accomplishing the same result. The essential difference between the two is that the first is driven by an alternating current and generates a continuous current, while the second changes an alternating into a continuous current. As a result of this difference the rotary transformer can be used to obtain a continuous current of any desired voltage from an alternating current of any given voltage ; but in the rotary con- verter, as the action is to convert the alternating into a con- tinuous current, the voltage relation is fixed so that for a given alternating current voltage we will get a corresponding contin- uous current voltage. Both these machines can be used in the reverse order, that is to transform or convert a continuous into an alternating current.
B
Fig. 396. Principle of the rotary transformer.
Principle of the rotary transformer* — The principle of the rotary transformer is illustrated in Fig. 396. In this diagram A represents a continuous current armature, and B is an alternating current armature. If both these are provided with suitable magnetic fields then if continuous current is passed through A it will become a motor and will drive B and generate therein a single alternating current or a number of them according to the way in which the armature is wound. Thus B may become a single or a polyphase generator. It can further be seen that the
880
HANDBOOK ON ENGINEERING.
voltage of the currents generated by B is in no way connected with the voltage of the current that drives A, and depends wholly upon the way in which B is wound. If B is connected with an alternating current circuit, then it will run as a synchronous motor and drive A and the latter will generate a continuous current. This machine if driven by a continuous current will be self -starting, but if driven by an alternating current it will have to be started. If driven by an alternating current its speed will be controlled by the frequency of the current, but if driven by a continuous current its speed will vary with the magnitude of the load placed upon it.
|
b 0 |
/ |
c |
5 C Ml |
|
|
C |
A |
/ |
y /* |
|
|
u\ |
Us l*> |
Figs. 397 and 398. Principle of the rotary converter.
Figs. 397 and 398 illustrate the principle of operation and the construction of a rotary converter. The armature A is of the continuous current type, having a commutator C. If it is a two- pole machine, then if wires are connected with diametrically opposite segments of the commutator as is indicated in Fig. 398 by the arrows, and these are connected with the collector rings a a, brushes c c placed on these rings, will take of a true alter- nating current if the armature is placed in a suitable field and is driven. While alternating current can be taken from the brashes C c, a continuous current can also be taken from the brushes b &,
HANDBOOK OK ENGINEERING. 881
jyhich bear upon the commutator C. Thus, this machine, if driven, becomes a combination generator which will deliver a continuous and an alternating current at the same time. Machines of this type are constructed and are called double current generators.
If the brushes c c are connected with a single-phase circuit, and the armature is placed in a suitable field, it will rotate and from the b b brushes of the commutator a continuous current can be drawn. If the brushes b b are connected with a continu- ous current circuit, an alternating current will be delivered through the brushes c c.
If four wires are connected with four commutator segments one quarter of the circumference apart, and these are connected with four collector rings, then from these rings two alternating cur- rents 90 degrees out of phase can be obtained. Thus, with four connections with the commutator segments the machine can convert two -phase currents into one continuous current, or one continuous current into two-phase currents, that is into two alter- nating currents 90 degrees out of phase.
If wires are connected with three commutator segments one- third of the circumference apart, and these are connected with three collector rings, then the machine will become a three-phase converter, and if connected with a three-phase system will deliver one continuous current or if connected with a continuous current circuit will deliver the three currents of a three-phase system.
The rotary converter, as will be seen from the foregoing, actually changes a continuous current into one or more alternat- ing currents, or one or more alternating currents into one con- tinuous current, and in every case there is a direct electrical con- nection between the continuous and the alternating current cir- cuits. As this type of machine simply converts the current of one type into current of the other type it is quite evident that there must be a fixed relation between the strength of the alternat-
56
882 HANDBOOK ON ENGINEERING.
ing and continuous currents and also between the voltages. An alternating current if of the sine type, will have an effective value of 70.7 per cent of its maximum value, for the amperes as well as the volts. So that if we have a continuous current of 70.7 amperes and 70.7 volts, we must have an alternating current of 100 amperes maximum value and 100 volts maximum value to be equal to it, and if the energy is also to be equal, the current in the alternating current circuit must be in phase with it e.m.f., that is the power factor must be 100.
In a rotary converter the voltage of the continuous current is equal to the maximum voltage of the alternating current and the strength of the continuous current is equal to one-half the maxi- mum strength of the alternating current. Thus if the maximum voltage of the alternating current is 1,000 volts, the voltage of the continuous current will be 1,000, and if the maximum strength of the alternating current is 100 amperes the strength of the contin- uous current will be 50 amperes. This arises from the fact that the rotary converter does not develop energy, as it drives itself, hence, the energy in the continuous current cannot be more than that in the alternating, in fact it will be a trifle less owing to the energy absorbed in driving the machine. Now if the alternating e.m.f. and current have the maximum values of 1,000 volts and 100 amperes, their effective values will be 707 volts and 70.7 amperes, and the product of these two will be the energy in watts. Thus 707 X 70.7 = 50,000 watts. Now if the voltage of the continuous current is 1,000, its strength must be 50 amperes, less the amount absorbed in overcoming the friction of the machine.
Fig. 399 shows a rotary converter of large size.
Alternating current distributions* — The principal advantage of alternating over continuous currents is that they can be used for transmitting energy to much greater distances, owing to the fact that a high voltage can be used to transmit the main current over the wire, and at the receiving end this current can be passed
HANDBOOK ON ENGINEERING.
883
through transformers, from which secondary currents of low volt- age may be obtained. In a few instances, low voltage alternating
Fig. 399. Rotary converter.
currents are used for distributing current over small areas. The general arrangement of circuits and. apparatus for a three-phase system of this kind is illustrated in the diagram Fig. 400.
B
Fig. 400. General arrangement of three-phase system.
The generator is shown at the extreme left. At A an induction motor is connected with the circuit. At B an " arc " light is corrected in the secondary circuit of a small transformer. At G
884
HANDBOOK ON ENGINEERING.
a number of incandescent lamps are connected. At D the circuit is used to drive a rotary transformer, which develops a continuous current to charge storage batteries at E. The three solid line wires constitute the main circuit and all the apparatus is connected with them. The broken line above these is the neutral wire and is connected with the incandescent lamps only. If the number of these lamps in each circuit is the same, as is shown on the diagram, no current will pass to the neutral wire, but if in one of the circuits there are more lamps t,han in the other, the excess of current will pass to or from the ,ieutral wire. Systems of this type are operated at voltages rang- ing between 200 and 600.
Fig, 401. Arrangement for distances up to four miles.
The diagram, Fig. 401, shows the way in which the circuits are arranged when the distance of transmission is from one to three or four miles. For such cases, the voltage generally used is 2300. The generator at the left develops currents that pass directly to the main line. At A an induction motor is connected directly to the main line. At B transformers are used to develop secondary currents of low voltage to supply the circuit wires C from which the motor D and incandescent lamps E are fed. At F a series transformer is used to develop a secondary current of constant strength to operate the arc lamps G. The difference be- tween a series transformer and the ordinary type is that the former is provided with a mechanical regulator, actuated by the current which maintains the secondary current of constant strength and varies the voltage in accordance with the number of
HANDBOOK ON ENGINEERING.
885
lamps in service. At H another set of transformers are used to develop low voltage secondary currents, which pass through a rotary converter /, and are converted into a continuous current to feed the incandescent lamps at J.
Fig. 402 illustrates the arrangement of circuits and appara- tus for long distance transmissions, which may range all the way from five or six miles up to one hundred or more, the greatest distance covered up to date being 145 miles. To trans- mit current to great distances with a small loss in the trans- mission lines, it is necessary to use very high voltages, ranging from 10,000 to 60,000, and as it is not advisable to construct
Fig. 402. Arrangement for long distances.
generators to develop such high pressures, raising transformers are employed to develop the line current. These transformers are shown in Fig. 402 at A. The generator develops currents at 1,000 volts, and this passing through the primary coils of the trans- formers at A induces secondary currents which may have any voltage desired, say, 20,000. These secondary currents pass to the transmission lines B B, which may extend a distance of ten, twenty or more miles and may deliver all their energy at the end of the line or drop part of it at intermediate points. The trans- formers at C and also those at L develop secondary currents of any lower voltage that may be required ; thus, those at C develop secondary currents for the circuits 7), which may be of, say, 1,000 volts. The motor E is shown connected directly with Z), but
886 HANDBOOK ON ENGINEERING.
motor G and lamps J, K require a still lower voltage, hence the currents in D are passed through a second set of transformers at jP, Hsiud J. The three transformers at L develop secondary cur- rents of sufficiently low voltage to be passed through the rotary converter M , and thus provide a continuous current for the trolley road as shown.
STARTING.
When the armature is turning, see that the oil rings in the bearings are in motion. When the machine is up to speed and all switches are open, lower the brushes on the commutator and col- lector, making sure that each bears evenly and squarely on the surface. Turn the rheostat until all resistance is in, then close the switch in the exciter circuit. Set the exciter brushes properly and adjust the voltage of the exciter to the proper point.
The alternator rheostat may then be turned gradually over until the proper alternating voltage is indicated. The main circuit of the machine may now be closed. The commutator brushes should be adjusted at a non-sparking position. If there is any load the voltage should increase slightly. If it decreases, it shows that the series coils and the separately excited coils are opposing each other, unless this decrease is caused by a drop in speed. If it is found that the coils are opposing each other, unclamp the brush- holder yoke of the alternator and move its commutator brushes backward or forward one and one-half segments in a three-phase machine, and one segment in a two-phase machine. A position giving maximum voltage will be found from which any motion, forward or backward, diminishes the voltage. Having once de- termined the correct setting of the brushes, they may generally remain unchanged, unless the generator is subject to great varia- tion of load when in some machines, slight movements may be found desirable.
HANDBOOK ON ENGINEERING. 887
PARALLEL RUNNING OF ALTERNATORS.
TYPES SUITABLE FOR PARALLEL OPERATION.
If the speeds are exactly adjusted, any two alternators of the same frequency will operate together in parallel. The maximum angular displacement that may take place between two machines in parallel without causing objectionable phase difference decreases with increased number of poles. For this reason high frequen- cies are, generally speaking, less favorable to parallel operation than lower frequencies. Machines of the highest frequencies ordinarily used can, however, be successfully run in parallel if the mechanical arrangements are suitable.
DIVISION OF LOAD.
Machines to operate in parallel must run at such speeds as will give exact equality of frequency. If the prime mover running one machine tends to produce a lower frequency than that run- ning the other, the machines cannot carry equal loads.
When two alternators operate in parallel, each must carry an amount of load proportionate to the power received from its prime mover. If one engine or water-wheel governs in such a manner as to give more power than the other, this machine must carry more load, no matter what the field excitation may be. If under such conditions the field excitations are correct, both machines will de- liver current to the line in approximately the proportions in which they receive power from their prime movers. If the field adjust- ments are incorrect, there will be idle currents between the machines in addition to the currents which go to the line.
COMPOUND ALTERNATORS.
When compound alternators are operated in parallel, equalizer connections should be used so that the rectified alternating
888 HANDBOOK ON ENGINEERING..
current can properly distribute itself into the fields of all the machines. Without equalizers, an unstable condition may exist which will render parallel operation unsatisfactory. This applies particularly in the case of machines driven from the same source of power. The greater the amount of compounding, the greater will be the tendency to instability.
BELTED MACHINES.
If two machines are belted to separate prime movers, their parallel operation is dependent upon the governing of the prime movers. If they are belted to the same source of power, their parallel operation depends upon the proportions of pulleys and belts, and upon the tension and friction of the latter. Under such conditions the pulleys and belts must be adjusted with great nicety, so that both machines will tend, with proper belt tension, to run at exactly the same frequency. Even where pulleys are of exactly the correct dimensions, a slight difference in the thick- ness of belts may cause considerable cross currents or unequal division of load.
DIRECT COUPLED MACHINES.
With such machines, engines must not only be adjusted to run at synchronous speed, but must also be provided with fly- wheels large enough to prevent appreciable variations of fre- quency within each revolution. Inequalities of speed, due to insufficient fly-wheel effect, will cause periodic cross currents between dynamos, or will entirely prevent their operation in parallel. The greater the number of poles in a direct coupled machine, the less the angular speed variation necessary to cause trouble.
High speeds are much more desirable with direct coupled alter- nators than low speeds, and low frequencies present less diffi-
HANDBOOK ON ENGINEERING.
culties than high. The desirabilty of high speeds with direct coupled alternators cannot be too strongly stated. While an increase of fly-wheel effect will equalize the angular irregularities of an engine's motion, it cannot bring about such good results as would be brought about by a similar reduction of angular error effected through an increase of speed. While the large fly- wheel steadies the motion, it may tend to prevent correction of the angular error through the effect of the cross currents. Cross currents, which flow in machines having light fly-wheels may have an effective tendency to hold them together ; while machines with very heavy fly-wheels may tend to act independently of each other as far as angular variations are concerned.
These matters should be carefully considered in installing direct connected alternators. Where engines operate at the same speed and have the same number of cranks, this trouble can sometimes be overcome by synchronizing the engines themselves so that the impulse in both come together. When the fly-wheel effect is insufficient, the frequency will fluctuate and this fluctua- tion may cause serious trouble if synchronous motors or rotary converters are connected to the circuit. When the cranks of two engines coupled to alternators are synchronized, any fluctuation of frequency which is due to lack of fly-wheel effect will still exist, although it may not affect parallel runnkig.
Where alternators have to be operated in parallel by engines to which they are directly coupled, it is generally desirable to use engines having as many cranks as possible, so that the crank efforts will be well distributed throughout the revolution, and
will not tend to produce an irregularity of motion.
'
STARTING.
When a machine driven by a separate engine is thrown in parallel with others which are carrying load, the throttle should be partly closed so that it can just run at synchronous speed with-
890 HANDBOOK ON ENGINEERING.
out carrying load. After it is in step with the other machines, load can gradually be taken on by giving it more steam. If this is carefully done the voltage on the circuit is not disturbed by the addition of the new machine.
When a belted machine is to be thrown into parallel with others driven by the same shaft, its belt tension should first be reduced, which will tend to admit enough slip to bring it into step with the loaded machines. After it is thrown in it will gradually take load as the belt is tightened.
SHUTTING DOWN.
In shutting down machines operating singly, both the gener- ator and exciter field resistance should be cut in by turning the rheostat before the line switch is opened.
When two or more generators are running in parallel on the bus-bars, one may be shut down at any time. The equalizer switch should be opened first, then the load reduced by throttling the engine or by slacking the belt. As soon as the load is prac- tically off, open the main switch.
CAKE OF MACHINES.
With high voltage machines it is absolutely essential that they be kept scrupulously clean. Small particles of copper or carbon dust, may be sufficient to start a disastrous arc.
The commutator collector should receive careful attention and be wiped thoroughly every day.
From time to time the machine should be thoroughly over- hauled and given a coating of air-drying japan after cleaning. Machines of the rotary field type are so constructed that it is a comparatively easy matter to get at every part of the armature coils. In a large station it is recommended that an air compres- sor be installed so that a hose can be led to the machine and the dust thoroughly blown out.
HANDBOOK ON ENGINEERING. 891
It is advisable to have rubber mats in front of high tension switchboards and on the floor at the commutator-collector end of the generator. If it is necessary to adjust the brushes while the machine is in operation, the attendant should stand on the mat and it is also recommended that he wear rubber gloves.
Both commutator and collector rings require a very slight amount of vaseline. In applying it a dry stick with a little chamois leather tied to one end may be used, so that there will be no danger of coming in contact with the brushes.
With the brushes properly set and all screws firmly tightened into place, the generators should require very little attention while running. It is well to note from time to time whether the oil rings are working properly.
Electrical Formulas.
Volts X Volts Watts = Amperes X Volts. Watts = olrnS —
Watts == Amperes X Amperes X Ohms.
Volts Volts — Amperes X Ohms. Amperes = QJ- —
Volts
Ohms:= Amperes Heat Units per Sec* = Amp* X AmP- X OhmsX Sees. X 0.24
Watts Electrical Horsepower = -,„ »
TT "P N.
H. P. lost in conductor = 16.6538 X (initial Volts) X length in miles.
2150 X Watts per lamp Area of cond. in circular mils = x x % Qf drQp X no. of
lamps X dist. to center of distribution in miles, or
. 2150 X dist. to center of distribution X Amperes $Tof Drop X Volts
Distance in miles X Distance in miles Weight of copper = — — XT lx
Volts X volts -5- 100
100 — % of line loss ./ 0/»ft - H. P.del.verec. to motor X -% of „„„ logs
Energy Required to Produce 1 Candle Power.
Watts. Watts. Watts.
Tallow 124 Mineral oils 80 Cannel gas 48
Wax 94 Vegetable oils 57 Incandescent lamp.... 15
Spermaceti 86 Coal gas 68 Arc lamp , 3
892
HANDBOOK ON ENGINEERING.
CHAPTER XXX
A CHAPTER OF TABLES.
TABLE NO. 1.- HYPERBOLIC LOGARITHMS.
|
1 « |
t* 3 |
0 I |
It 3 |
o tf |
I |
0 i |
M o 3 |
£ I |
! |
0 o « |
be 3 |
0 |
ti 5 |
|
1.00 |
.0000 |
2.45 |
.8961 |
3 90 |
1.3610 |
5.35 |
.6771 |
6 80 |
1.9169 |
8.25 |
2.1102 |
9.70 |
2.2721 |
|
1.05 |
.0488 |
2.50 |
.9163 |
3 95 |
1.3737 |
5 40 |
.6864 |
6.85 |
9242 |
8.30 |
2.1163 |
9.75 |
2.2773 |
|
10 |
.0953 |
2 55 |
.9361 |
4 00 |
1.3863 |
5 45 |
.6956 |
6.90 |
.9315 |
8.35 |
2 1223 |
9 80 |
2.2824 |
|
15 |
.1398 |
2 60 |
.9555 |
4 05 |
1 3987 |
5 50 |
.7047 |
6 95 |
.9387 |
8 40 |
2 1282 |
9.85 |
2.2875 |
|
.20 |
.1823 |
2 65 |
.9746 |
4.10 |
1.4110 |
5.55 |
.7138 |
7.00 |
.9459 |
8.45 |
2.1342 |
9.90 |
2 2925 |
|
25 |
.2231 |
2 70 |
• 9933 |
4.15 |
1.4231 |
5.60 |
.7228 |
7.05 |
.9530 |
8.50 |
2.1401 |
9.95 |
2 '2976 |
|
30 |
.2624 |
2.75 |
1.0116 |
4 20 |
1.4351 |
5.65 |
.7317 |
7.10 |
.9601 |
8.55 |
2 1459 |
10.00 |
2.30J6 |
|
.35 |
.3001 |
2.80 |
1.0296 |
4 25 |
.4469 |
5 70 |
.7405 |
7.15 |
.9671 |
8 60 |
2.1518 |
||
|
.40 |
.3365 |
2 85 |
1.0473 |
4.30 |
4586 |
5.75 |
.7402 |
7 20 |
.9741 |
8 65 |
2.1576 |
||
|
.45 |
.3716 |
2 90 |
1 0647 |
4 35 |
4702 |
5.80 |
.7579 |
7 25 |
1.9810 |
8.70 |
2.1633 |
||
|
50 |
.4055 |
2.95 |
1.0818 |
4 40 |
.4816 |
5.85 |
.7664 |
7.30 |
1.9879 |
8.75 |
2.1691 |
||
|
55 |
.4383 |
3.00 |
1.0986 |
4.45 |
4929 |
5 90 |
.7750 |
7.3'. |
1.9947 |
8.80 |
2.1748 |
||
|
60 |
.4700 |
3.05 |
1.1151 |
4 50 |
.5041 |
5 95 |
.7834 |
7 40 |
2.0015 |
8.85 |
2.1804 |
||
|
65 |
.5008 |
3.10 |
1 1314 |
4.55 |
.5151 |
6.00 |
7918 |
7 45 |
2 0082 |
8 90 |
2.1861 |
||
|
70 |
.5306 |
3.15 |
1.1474 |
4.60 |
5261 |
605 |
8001 |
7.50 |
2.0149 |
8.95 |
2.1917 |
||
|
.75 |
.5596 |
3 20 |
1.1632 |
4 65 |
.5369 |
6.10 |
.8083 |
7.55 |
2.0215 |
9.00 |
2.1972 |
||
|
80 |
.5878 |
3 25 |
1.1787 |
4.70 |
.5476 |
6.15 |
.8165 |
7.60 |
2 0281 |
9 05 |
2.2028 |
||
|
.85 |
.6152 |
3.30 |
1.1939 |
4 75 |
.5581 |
6.20 |
.8245 |
7.65 |
2.0347 |
9.10 |
2 2083 |
||
|
1.90 |
.6419 |
3.35 |
1.2090 |
4 80 |
.5686 |
6.25 |
.8326 |
7.70 |
2.0412 |
9.15 |
2.2138 |
||
|
1.95 |
.6678 |
3.40 |
1 2238 |
4.85 |
5790 |
6.30 |
.8405 |
7.75 |
2.0477 |
9.20 |
2 2192 |
||
|
2 00 |
.6931 |
3.45 |
1.2384 |
4 90 |
.5892 |
6.35 |
.8485 |
7.80 |
2.0541 |
9 25 |
2.2246 |
||
|
2 05 |
.7178 |
3 50 |
1.2528 |
4.95 |
.6994 |
6.40 |
.8563 |
7 85 |
2 0605 |
9 30 |
2 2300 |
||
|
2.10 |
.7419 |
3 55 |
1 2669 |
5 00 |
.6094 |
6.45 |
.8641 |
7.90 |
2.0669 |
9.35 |
2.2354 |
||
|
2.15 |
.7655 |
3 60 |
1 2809 |
5.05 |
6194 |
6 50 |
.8718 |
7.95 |
2.0732 |
9 40 |
2.2407 |
||
|
2.20 |
.7885 |
3.65 |
1 2947 |
5.10 |
6292 |
6.55 |
1.8795 |
8.00 |
2.0794 |
9.45 |
2.2460 |
||
|
2.25 |
.8109 |
3.70 |
1 3083 |
5 15 |
.6390 |
6.60 |
1.8871 |
8.05 |
2.0857 |
9 50 |
2.2513 |
||
|
2 30 |
.8329 |
3 75 |
1.3218 |
5 20 |
.6487 |
6 65 |
1 8946 |
8 10 |
2 0919 |
9.55 |
2 2565 |
||
|
2.35 |
.8544 |
3 80 |
1.3350 |
5 25 |
.6582 |
6 70 |
1.9021 |
8 15 |
2.0980 |
9 60 |
2.2618 |
||
|
2.40 |
.8755 |
3.85 |
1.3481 |
5.30 |
6677 |
6 75 |
1.9095 |
8.20 |
2.1041 |
9.65 |
2.2670 |
To find the hyperbolic logarithm of a ratio which is ten times any ratio given in the table, find the ratio in the table which is one-tenth of the giren ratio and add 2.3026 to the corresponding logarithm; the sum will be the required logarithm. Example: What is the hyperbolic logarithm of 155? 155 is ten times 1.55. The logarithm of 1.55 is .4383, and ,4383 + 2.3026 =* 2.7409 which is the hyperbolic logar- ithm of 16.5.
HANDBOOK ON ENGINEERING. TABLE NO. 2.
893
DTJPI/EX STEAM PUMPS.
For Water Pressure Not Exceeding 150 Ibs. Speed from 50 to 100 feet per Minute.
|
i « |
H |
tf JM O |
•s! 6 |
JsU |
!*rf |
|
£ |
£ |
2 |
c 2 ? |
Jc ^ c3 Oa" |
.£ u g>3 a; |
|
£1 |
°2 |
•a |
l|s |
1111*3 |
•S Oi +» o |
|
t.s e^ |
W 3 |
43 i |
l|§ |
SL-S J5 o 6 |
C . 4J» to CO |
|
«u |
ctf PH |
P |
S*fT*!5 |
O C PH fe ^ w |
»j-j f^jQ "Jrt Q |
|
S |
5 |
3 |
S ° |
0< |
0 |
|
3 |
2 |
3 |
.04 |
100 to 250 |
8 to 20 |
|
4% |
2% |
4 |
.10 |
100 to 200 |
20 to 40 |
|
5% |
3% |
5 |
.20 |
100 to 200 |
40 to 80 |
|
6 |
4 |
6 |
.33 |
100 to 150 |
70 to 100 |
|
7% |
4% |
6 |
.42 |
100 to 150 |
85 to 125 |
|
7% |
5 |
6 |
.51 |
100 to 150 |
100 to 150 |
|
7% |
4% |
10 |
.69 |
75 to 125 |
100 to 170 |
|
9 |
10 |
.93 |
75 to 125 |
135 to 230 |
|
|
10 |
6 * |
10 |
1.22 |
75 to 125 |
180 to 300 |
|
10 |
7 |
10 |
1.66 |
75 to 125 |
245 to 410 |
|
12 |
7 |
10 |
1.66 |
75 to 125 |
245 to 410 |
|
14 |
7 |
10 |
1.66 |
75 to 125 |
245 to 410 |
|
12 |
8% |
10 |
2.45 |
75 to 125 |
365 to 610 |
|
14 |
8% |
10 |
2.45, |
75 to 125 |
365 to 610 |
|
16 |
8% |
10 |
2.451 |
75 to 125 |
365 to 610 |
|
18% |
8% |
10 |
2.45 |
75 to 125 |
365 to 610 |
|
20 |
8% |
10 |
2.45 |
75 to 125 |
365 to 610 |
|
12 |
flo |
3.57 |
75 to 125 |
530 to 890 |
|
|
14 |
10%i |
tio |
3.57 |
75 to 125 |
530 to 890 |
|
16 |
10% |
10 |
3.57 |
75 to 125 |
530 to 890 |
|
18% |
10%; |
10 |
3.57 |
75 to 125 |
530 to 890 |
|
20 |
10% |
10 |
3.57 |
75 to 125 |
530 to 890 |
|
14 |
12 |
10 |
4.89 |
75 to 125 |
730 to 1220 |
|
16 |
12 |
10 |
4.89 |
75 to 125 |
730 to 1220 |
|
18% |
12 |
10 |
4.89 |
75 to 125 |
730 to 1220 |
|
20 |
12 |
10 |
4.89 |
75 to 125 |
730 to 1220 |
|
18% |
14 |
10 |
6.66 |
75 to 125 |
990 to 1660 |
|
20 |
14 |
10 |
6.66 |
75 to 125 |
990 to 1660 |
|
17 |
10 |
15 |
5.10 |
50 to 100 |
510 to 1020 |
|
20 |
12 |
15) |
7.34 |
50 to 100 |
730 to 1460 |
|
20 |
fcfc |
15' |
11.47 |
50 to 100 |
1145 to 2290 |
|
25 |
15 |
15! |
11.47 |
50 to 100 |
1145 to 2290 |
894
HANDBOOK ON ENGINEERING.
TABLE NO. 3
Tank or Light Service Pumps.
These pumps are principally used at railroad water stations, gas and oil works, -bleacheries, tanneries, refineries, plantations, distilleries, etc. A variety of valves are used adapted for pumping hot, cold, thick, thin, alka- line or other liquids.
For quarries and clay pits, also for coffer dams, tunnels, foundation pits, ore beds, sewerage and irrigating purposes, these pumps are. especially adapted, having large water passages and valve openings. •
SIZES AND CAPACITIES.
|
c |
' 0) |
m |
I |
||||||
|
I |
1 5.. |
1 I 0> |
1. Sl |
Capacity per minute at ordinary speed. |
H* i •& |
£ fs aj |
i *s» • §3 |
ery pipe, bes. |
Floor Space Required. Inches. |
|
8*0 |
0) O |
X |
o g |
03 o |
ts 13 |
> o |
|||
|
P |
I* |
1 |
3S |
• |
A a |
o a cJ |
is |
||
|
GO |
£ |
03 |
O |
00 |
fir" |
CO |
Q |
||
|
""Ik |
3& |
4 |
.15 |
125 Strokes, .18 gals. |
4. |
* |
14 |
154 |
28 xlO |
|
4 |
4 |
5 |
.27 |
125 33 |
4 |
X |
2 |
14 |
34 xll |
|
5 |
4 |
7 |
.39 |
125 •• 49 |
K |
24 |
2 |
44 x!2 |
|
|
54 |
54 |
7 |
.72 |
125 " 90 |
B |
3 |
24 |
44 xl34 |
|
|
6 |
f>% |
7 |
.72 |
125 " 90 |
i |
3 |
24 |
44 x'134 |
|
|
6 |
6 |
12 |
1.47 |
100 •• 147 |
i |
4 |
4 |
66^x19 ' |
|
|
6 |
7 |
12 |
2.00 |
100 " 200 |
x |
5 |
5 |
662£xl9 |
|
|
74 |
7 |
10 |
1.66 |
100 •• 166 |
54 |
5 |
5 |
56J4xiy |
|
|
74 |
74 |
10 |
1.91 |
100 " 191 |
34 |
5 |
5 |
564x19 |
|
|
8 |
6 |
12 |
1.47 |
100 " 147 |
iff |
4 |
4 |
66^x19 |
|
|
8 |
7 |
12 |
2.00 |
100 •' 200 |
134 |
5 |
5 |
665^x19 |
|
|
8 |
8 |
12 |
2.61 |
100 " 261 |
1J4 |
5 |
5 |
662ix20 |
|
|
8 |
9 |
12 |
3,30 |
100 " 330 |
tM |
6 |
6 |
66^x214 |
|
|
8 |
10 |
12 |
4.08 |
100 »• (408 |
154 |
6 |
6 |
66^x214 |
|
|
10 |
10 |
12 |
4.08 |
100 " 408 |
15< |
14 |
6 |
6 |
66^x214 |
|
10 |
10 |
16 |
5.44 |
75 " 408 |
1J4 |
14 |
6 |
6 |
78^x21>/3 |
|
10 |
12 |
12 |
5.87 |
100 " 587 |
1M |
14 |
8 |
•6 |
66%x23>4 |
|
10 |
12 |
16 |
7.83 |
75 " 587 |
134 |
8 |
6 |
78/8x23'4 |
|
|
12 |
10 |
12 |
4.08 |
100 " 408 |
2 |
gi/ |
6 |
6 |
66^x214 |
|
12 |
10 |
16 |
5.44 |
75 " 408 |
2 |
24 |
6 |
6 |
78^x214 |
|
12 |
12 |
12 |
5.87 |
100. • 587 |
2 |
24 |
8 |
6 |
66^x23^ |
|
12 |
19 |
16 |
7.83 |
75 ' 587 |
2 |
24 |
8 |
6 |
784x23«£ |
|
14 |
12 |
12 |
5.87 |
100 ' 587 |
2 |
24 |
8 |
6 |
(56^x235^ |
|
14 |
12 |
16 |
7.83 |
'75 < 587 |
2 |
24 |
8 |
6 |
784x23^ |
|
14 |
14 |
16 |
10.66 |
75' '• -800 |
2 |
24 |
10 |
8 |
784x27 |
|
14 |
14 |
24 |
16.00 |
£0 *, 800 |
24 |
3 |
10 |
8 |
108 x27 |
|
14 |
16 |
16 |
14.92 |
75. ' 1020 |
24 |
3 |
12 |
10 |
80 x354 |
|
14 |
16 |
24 |
20.88 |
50, ' 1044 |
24 |
3 |
12 |
10 |
108 X35J4 |
|
16 |
14 |
16 |
10.66 |
75 • 800 |
24 |
3 |
10 |
8 |
784x27 |
|
16 |
14 |
24 |
16.00 |
60 ' 800 |
24 |
3 |
10 |
8 |
108 x27 |
|
16 |
16 |
16 |
14.92 |
75 ' 1020 |
24 |
3 |
12 |
10 |
80 x354 |
|
16 |
16 |
24 |
20.88 |
50 " 1044 |
24 |
3 |
12 |
10 |
108 x354 |
|
16 |
18 |
24 |
26.44 |
50 •• 1322 |
24 |
3 |
12 |
10 |
108 x38 |
|
16 |
20 |
24 |
32.64 |
50 " 1632 |
24 |
3 |
14 |
12 |
108 x40 |
|
18 |
16 |
24 |
20.88 |
50 " 1044 |
34 |
4 |
12 |
10 |
110 x354 |
|
18 |
18 |
24 |
26.44 |
50 < 1322 |
34 |
12 |
10 |
110 x38 |
|
|
18 |
20 |
24 |
32.61 |
50 ' 1632 |
34 |
14 |
12 |
110 x40 |
|
|
18 |
22 |
24 |
39.50 |
50 ' 1975 |
34 |
14 |
14 |
110 x42 |
|
|
20 |
18 |
24 |
26.44 |
50 ' 1322 |
34 |
12 |
10 |
118 x38 |
|
|
20 |
20 |
24 |
32.64 |
50 ' 1622 |
34 |
14 |
12 |
118 X40 |
|
|
20 |
22 |
24 |
39.50 |
60 ' 1975 |
34 |
14 |
14 |
118 x42 |
|
|
20 |
24 |
24 |
47.00 |
60 • 2350 • |
q* |
4 |
16 |
16 |
118 £44 |
HANDBOOK ON ENGINEERING.
895
TABLE NO. 4.
DIAMETERS, AREAS AND CIRCUMFERENCES OF CIRCLES.
|
•w |
4 ' d |
|s |
I |
c"3' |
f«5 |
•d |
||
|
§fl |
3X3 |
a>M |
§J3 |
t< |
5« *s |
s§ •o5 |
$ |
|
|
«S |
5* |
<$ |
«s |
.b a |
||||
|
1 |
3.14159 |
'0.78540 |
4 |
12.5664 |
12.566 |
8 |
25.1327 |
50.265 |
|
A |
3.33794 |
0.88064 |
i |
12.7627 |
12.962 |
H |
25 5224 |
51.84.9 |
|
8 |
3.53429 |
0.99402 |
^8 |
12.9591 |
13.364 |
25.9181 |
53.456 |
|
|
1 |
3.73064 3.92699 |
1.1075 1.2272 |
ft |
13.1554 13.3518 |
13.772 14.186 |
$ |
26.3108 26.7035 |
55.088 56.745 |
|
4.12334 |
1.3530 |
A |
13.5481 |
14.607 |
% |
27.0962 |
58.426 |
|
|
rt |
4.31969 |
1.4*49 |
\l |
13.7445 |
15.033 |
% |
27.4889 |
60.133 |
|
/a |
4.51604 |
1.6230 |
13.. 9408 |
15.466 |
% |
27.8816 |
61.862 |
|
|
fc |
4.71239 |
1.7671 |
H |
14.1372 |
15.904 |
9 |
28.2743 |
63.617 |
|
i9<f |
4.90874 |
1.9175 |
14.3335 |
16.349 |
H |
28.6670 |
65.397 |
|
|
£l |
5.10509 |
2.0739 |
/8 |
14.5299 |
KU'OO |
H |
29.0597 |
67.201 |
|
ri |
5.30144 |
2.2365 |
11 |
14.7262 |
17.257 |
96 |
29.4524 |
69.029 |
|
5.49779 |
2.4053 |
% |
14.9226 |
17.721 |
J£ |
29.8451 |
70.882 |
|
|
13 |
5.69414 |
2.5802 |
13 |
15.1189 |
18.190 |
% |
30,2378 |
'72.760 |
|
% |
5.89049 |
2.7612 |
/8 |
15.3153 |
18.665 |
'£ |
30.6305 |
74.662 |
|
h |
6.08684 |
2.9483 |
i1 3 |
15.5116 |
19.147 |
31.0232 |
76.589 |
|
|
2 |
6.28319 |
3.1416 |
r> |
15.7080 |
19.635 |
10 |
31.4159 |
78.540 |
|
>\j |
6.47953 |
3.3410 |
15.9043 |
20.129 |
32.2013 |
82.516 |
||
|
M |
6.67588 |
3.5466 |
/Q |
16.1007 |
20.629 |
l/2 |
32.9867 |
86.690 |
|
6.87223 |
3.7583 |
1\ |
16.2970 |
21.135 |
% - |
33.7721 |
90.763 |
|
|
5* |
7.06858 |
3.9761 |
y± |
16.4934 |
21.4348 |
11 |
34.5575 |
95.033 |
|
5 |
7.26493 |
4.2000 |
8 |
10.0897 |
22.166 |
35.3429 |
99.402 |
|
|
% |
7.46128 |
4.4301 |
% |
10.8861 |
22.691 |
H |
36.1283 |
103.87 |
|
I7* |
7.65763 |
4.6664 |
I7H |
17.0824 |
23.221 |
X |
30.9137 |
108.43 |
|
H |
7.85398 |
4,9087 |
54 |
17.2788 |
23.758 |
12 |
37.6991 |
113.10 |
|
8.05033 |
5.1572 |
*& |
17.4751 |
24.301 |
14 |
38.4845 |
117.86. |
|
|
ft |
8.24668 |
5.4119 |
% |
17.6715 |
24.850 |
r| |
39.2699 |
122.72 |
|
ti |
8.44303 |
5.0727 |
n |
17.8678 |
25,406 |
5^ |
40.0553 |
127.68 |
|
3^ |
8.63938 |
5.9390 |
% |
18.0642 |
25.967 |
13 |
40.840> |
132.73 v |
|
jn |
8.83573 |
6.2126 |
li |
18.2605 |
20.535 |
41.6261 |
137.89 |
|
|
« |
9.03208 |
0.4918 |
% |
18.4569 |
27.109 |
16 |
42.4115 |
143.14 |
|
II |
0.22843 |
6.7771 |
IS |
18.6532 |
27.688 |
k |
43.1969 |
148.49 |
|
3^ |
9.42418 |
7.06S6 |
6 |
18.8496 |
28.274 |
14 |
43.9823 |
153.94 |
|
11.62115) |
7.3662 |
Vs |
19.2423 |
29.465 |
H |
44.767r |
159.48 |
|
|
•8 |
9.81748 |
7.6699 |
14 |
19.6350 |
30.680 |
45.5531 |
165.13 |
|
|
ino |
10.0138 |
7.9798 |
H |
20.0277 |
31.919 |
% |
46.3385 |
170.87 |
|
l'\ |
10.2102 |
8.2958 |
Yz |
20.4204 |
33.183 |
15 |
47.1239 |
176.71, |
|
J5fl |
10.4065 |
8.6179 |
20.8131 |
34.472 |
47.9093 |
182.65. |
||
|
U£ |
10.^029 |
8.9462 |
% |
21.2058 |
35.785 |
Vz |
48.694" |
188.69 |
|
l'7rt |
10.7992 |
9.2800 |
ft |
21.5984 |
37.122 |
% |
49.4801 |
194.83. |
|
i^ |
10.9950 |
9.0211 |
7 |
21.9911 |
38.485 |
16 |
50.2655 |
201.061 |
|
jjjj |
11.1919 |
9.9678 |
22.3838 |
39.871 |
|4 |
51.0509 |
207. 39V |
|
|
11.3S83 |
10.321 |
^ |
22.7765 |
41.282 |
51.8363 |
213.82- |
||
|
io |
1L5846 |
10.080 |
?» |
23.1692 |
42.718 |
% |
52.621" |
220.35 |
|
3a |
11.7810 |
11.045 |
Va |
23.5619 |
44.179 |
17 |
53.4071 |
226.98- |
|
3 |
11.977;.' |
11.418 |
?8 |
23.9546 |
45.664 |
W |
54.192: |
233. 7t |
|
x |
12.1737 |
11.793 |
3/ |
24.3473 |
47.173 |
ll |
54.9779 |
24o 53 |
|
is |
12.3700 |
12.177 |
3 |
24.7400 |
4S.707 |
05.7030 |
247. 4&. |
896
HANDBOOK ON ENGINEERING.
Diameters, Areas and Circumferences of Circles.— Con.
|
Diam. II Inches. |
Circumf. Inches. |
s |
Diam. Inches. |
Circumf. Inches. |
gs |
l| |
Circumf. Inches. |
fi |
|
18 |
56.5487 |
254.47 |
32 |
100.531 |
804.25 |
46 |
144.513 |
1661.0 |
|
54 |
57.3341 |
2t<1.59 |
54 |
101.316 |
816.86 |
H |
145.299 |
1680.0 |
|
58.1195 |
268 80 |
3 |
102.102 |
829.58 |
B |
146.0.S4 |
1698.2 |
|
|
3£ |
68.9049 |
276.12 |
1H2.887 |
842.39 |
146.869 |
716.5 |
||
|
19 |
59.6903 |
283.53 |
33* |
103.673 |
855.30 |
47'4 |
147.65;-. |
734.9 |
|
54 |
60.4757 |
291.04 |
104.458 |
fc'68.31 |
54 |
148.440 |
753.5 |
|
|
H |
61.2611 |
2-J8.65 |
Vi |
105.243 |
881.41 |
149.226 |
772. J |
|
|
62.0465 |
306.35 |
% |
106.029 |
894.62 |
94 |
150.011 |
75>0.8 |
|
|
20 |
62.8319 |
314.16 |
34 |
106.814 |
907.92 |
48 |
150.796 |
1809 6 |
|
54 |
63.6173 |
3^2.06 |
54 |
107.600 |
921.32 |
H |
151.582 |
1828.5 |
|
H |
64.4026 |
330.00 |
H |
108.385 |
934.82 |
152.367 |
1847.5 |
|
|
66.1880 |
338.16 |
109.170 |
•948.42 |
3 |
153. 15H |
1866.5 |
||
|
21 * |
65.9734 |
346.36 |
354 |
109.956 |
962.11 |
49 |
133.938 |
1885.7 |
|
54 |
66.7588 |
354.66 |
54 |
110.741 |
975.91 |
154.723 |
1905.0 |
|
|
V* |
67.5442 |
363.05 |
H |
111. 627 |
989.80 |
y |
155.509 |
1924.2 |
|
68.329H |
371.54 |
112.312 |
1003.8 |
& |
156.294 |
1943.9 |
||
|
224 |
69.1150 |
380.13 |
36 4 |
113.097 |
1017.9 |
50 |
157.080 |
1963.5 |
|
54 |
69.9004 |
388.82 |
54 |
113.883 |
1032.1 |
54 |
157.865 |
1983.2 |
|
H |
70.6858 |
397.61 |
% |
114.668 |
1046.3 |
K |
158.650 |
2003.0 |
|
71 4712 |
406.49 |
115.454 |
J060.7 |
159.436 |
2022.8 |
|||
|
23 |
72.2566 |
415.48 |
37 4 |
116,239 |
1075.2 |
51 4 |
160.221 |
2042.8 |
|
54 |
73 .'0420 |
424.56 |
54 |
117.024 |
1089.8 |
161.007 |
2062.9 |
|
|
y* |
73.8274 |
433.74 |
H |
117.810 |
1104.5 |
H |
161.792 |
2083.1 |
|
% |
74.6128 |
443.01 |
118.596 |
1119.2 |
162.577 |
2103.3 |
||
|
24 |
75.3982 |
452.39 |
384 |
119.381 |
1134.1 |
52/4 |
163.363 |
2123.7 |
|
5-4 |
76.1836 |
461.86 |
H |
120.166 |
1149.1 |
M |
164.148 |
2144.2 |
|
H |
76.9690 |
471.44 |
H |
120.951 |
1164.2 |
H |
164.934 |
2164.8 |
|
* |
77.7544 |
481.11 |
121.737 |
1179.3 |
165.719 |
2185.4 |
||
|
25 |
78.5398 |
490.87 |
39 4 |
122.522 |
1194.6 |
534 |
166.504 |
2206.2 |
|
54 |
79.3252 |
500.74 |
123.308 |
1210.0 |
54 |
167.290 |
2227.0 |
|
|
n |
80.1106 |
510.71 |
Vi |
124.093 |
1225.4 |
168.075 |
2248.0 |
|
|
% |
80.8960 |
520.77 |
94 |
124.878 |
1241.0 |
94 |
168.861 |
2269.1 |
|
20 |
81.6814 |
530.93 |
40 |
125.664 |
1256.6 |
54 |
169.646 |
2290.3 |
|
54 |
82.4668 |
541.19 |
K |
126.449 |
1272.4 |
54 |
170.431 |
2311.5 |
|
K |
83.2522 |
551.55 |
127.235 |
1288.2 |
171.217 |
2332. » |
||
|
84.0376 |
562.00 |
9£ |
128.020 |
1304.2 |
94 |
172.002 |
2354.3 |
|
|
27* |
84.8230 |
572.56 |
41 |
128.805 |
1320.3 |
55^ |
172.788 |
2375.8 |
|
54 |
85.6084 |
583.21 |
54 |
129.591 |
1336.4 |
173.573 |
2397.5 |
|
|
86.3938 |
593.96 |
130.376 |
1352.7 |
y |
174.358 |
2419.2 |
||
|
9s£ |
87,1792 |
604.81 |
94 |
131.161 |
1369.0 |
% |
175.144 |
2441.1 |
|
~H |
87.9646 |
615.75 |
42 |
131.947 |
1385.4 |
56 |
175.929 |
2463.0 |
|
54 |
88.7500 |
626.80 |
54 |
132. 732 |
1402.0 |
176.715 |
2485.0 |
|
|
H |
89.5354 90.3208 |
637,94 649.18 |
y* |
133.518 134,303 |
1418.6 1435.4 |
& |
177.500 178.285 |
2507.2 2529.4 |
|
so'4 . |
91.1062 |
660.52 |
434 |
135,088 |
1452.2 |
57 |
179.071 |
2551.8 |
|
54' |
91.8916 |
671. 9d |
54 |
1469.1 |
179.856 |
2574.2 |
||
|
'/a |
92.67-50 |
683.49 |
Vi |
136 1659 |
1486.2 |
H |
180.642 |
2596.7 |
|
?£ |
93.4624 |
695.13 |
137.445 |
1503.3 |
9i |
181 .427 |
2619.4 |
|
|
BO |
94.2478 |
706.86 |
44* |
138.230 |
1520,5 |
58 |
182.212 |
XJ642.1 |
|
H |
95.0332 |
718.69 |
54 |
139.015 |
1537.9 |
182.998 |
2664.9 |
|
|
H |
95.8186 |
730.62 |
/4 |
139.801 |
1555.3 |
y |
183.783 |
2687.8 |
|
*j |
96.6040 |
742.64 |
a' |
110.586 |
1572.8 |
%t |
184.569 |
2710.9 |
|
81 |
97.3894 |
754.77 |
45' |
141.372 |
1590.4 |
59 |
185.ar>4 |
2734.0 |
|
fe |
98. 1748 |
766. 9j) |
54 |
142.157 |
1608.2 |
186.139 |
2757.2 |
|
|
H |
98.9602 |
779.31 |
H |
142.942 |
1626.0 |
y |
186.925 |
2780.5 |
|
~*» |
99.7456 |
791.73 |
143.728 |
1643.0 |
% |
187.710 |
2803.9 |
HANDBOOK ON ENGINEERING.
897
Diameters, Areas and Circumferences of Circles. — Con.
|
Diam. !| Inches.. |
Circumf. Inches. |
SM % |
Diam. Inches. |
Circumf, Inches. |
f *& |
Diam. Inches. |
Circumf. Inches. |
II |
|
.60 |
188.496 |
2827.4 |
74 |
232.478 |
4300.8 |
88 |
276.460 |
6082.1 |
|
189.281 |
2851.0 |
h |
233.263 |
4329.9 |
k |
277.246 |
6116.7 |
|
|
y* |
190.066 |
2874.8 |
l/2 |
234.049 |
4359.2 |
i? |
278.031 |
6151.4 |
|
% |
190.852 |
2898.6 |
% |
334.834 |
4388.5 |
H |
278.816 |
6186.2 |
|
61 |
191.637 |
2922.5 |
75 |
235.619 |
4417.9 |
,89 |
279.602 |
6221.1 |
|
' J4 |
192.423 |
2946/5 |
& |
236.405 |
4447.4 |
H |
2«0.387 |
6256.1 |
|
5? |
193'. 208 |
2970.6 |
Yz |
237.190 |
4477.0 |
l/2 |
281.173 |
6291.2 |
|
% |
193.993 |
2994.8 |
% |
237.976 |
4506.7 |
u |
281.958 |
6:£H'.4 |
|
62 |
194.779 |
3019.1 |
76 |
^38.761 |
4536.5 |
901/ |
282.743 |
6361.7 |
|
& |
195.564 |
8048.5 |
!/4 |
239.546 |
4566.4 |
283.529 |
6397.1 |
|
|
H |
196.350 |
3068.0 |
tt |
2i0.332 |
4596.3 |
H |
284.314 |
6432.6 |
|
% |
197.135 |
3092.6 |
% |
241.117 |
4626.4 |
' % |
285.100 |
6468.2 |
|
63 |
197.920 |
3117.2 |
77 |
241.903 |
4656.6 |
91 |
285.885 |
6503.9 |
|
1A |
198.706 |
3142.0 |
& |
242.688 |
4086.9 |
H |
286.670 |
6539.7 |
|
4 |
199.491 |
3166.9 |
H |
243.473 |
4717.3 |
M |
287.456 |
6575 5 |
|
% |
200.277 |
3191.9 |
* |
244.259 |
4747.8 |
% |
238.241 |
6611.5 |
|
64 |
201.062 |
3217.0 |
78 |
245.044 |
4778.4 |
$2 |
289.027 |
66-17.6 |
|
H |
201.847 |
3242.2 |
K |
245.830 |
4809.0 |
K |
289.812 |
(5683.8 |
|
H |
202.633 |
3267.5 |
H |
246.615 |
4839.8 |
• l/2 |
390.597 |
6720.1 |
|
% |
203.418 |
3292.8 |
it |
247.400 |
4870.7 |
% |
291.383 |
6756.4 |
|
66 |
204.204 |
3318.3 |
79 |
248.186 |
4901.7 |
88 |
202.168 |
6792.9 |
|
/4 |
204.989 |
3343.9 |
K |
248.971 |
4932.7 |
H |
292.954 |
6829.5 |
|
y$ |
205.774 |
3369.6 |
% |
249.757 |
4963.9 |
'/2 |
293.739 |
6866.1 |
|
% |
206.560 |
3395.3 |
% |
250.542 |
4995.2 |
• % |
294.524 |
6902.9 |
|
66 |
207.345 |
3421.2 |
80 |
251.327 |
5026.5 |
9;4 |
295.310 |
6939.8 |
|
34 |
208.131 |
3447.2 |
k |
252.113 |
5058.0 |
r?H |
296.095 |
6976.7 |
|
H |
208.916 |
3473.2 |
* |
252.898 |
5089.6 |
'/2 |
296.881 |
7013.8 |
|
V |
209.701 |
3199.4 |
% |
253.684 |
5121.2 |
'% |
297.666 |
7051.0 |
|
67 |
210.487 |
3525.7 |
81 |
254.469 |
5153.0 |
95 |
398.451 |
7088.2 |
|
fc |
211.272 |
3552.0 |
y* |
255.254 |
5184.9 |
'H |
399.237 |
7125.6 |
|
l/2 |
-412.058 |
3578.5 |
K |
256.040 |
5216.8 |
' l/2 |
300.022 |
7163.0 |
|
% |
212.843 |
3605.0 |
x |
256.825 |
5248.9 |
^ % |
300.807 |
7200.6 |
|
68 |
213.628 |
3631.7 |
82 |
257.611 |
5281.0 |
96 |
301.593 |
7238.2 |
|
K |
214.414 |
3658.4 |
y\ |
258.396 |
5313.3 |
H |
302.378 |
7276.0 |
|
3 |
215.199 |
3685.3 |
y* |
259.181 |
6345.6 |
3 |
303.164 |
7313.8 |
|
% |
215.984 |
3712.2 |
%• |
359.967 |
5378.1 |
1i |
303.949 |
7351.8 |
|
«9 |
216.770 |
3739.3 |
83 |
260.752 |
5410.6 |
97 |
304.734 |
7389.8 |
|
14 |
217.555 |
3766.4 |
y± |
261.538 |
5443.3 |
M |
305.520 |
742S-.0 |
|
y* |
218.341 |
3793.7 |
1A |
262.323 |
5476.0 |
v H |
306.305 |
7466.2 |
|
u |
219.126 |
3821.0 |
% |
263.108 |
5508.8 |
• % |
307.091 |
7504.5 |
|
70 |
219.911 |
3848.5 |
84 |
263.394 |
5541.8 |
98 |
307.876 |
7543.0 |
|
tt |
220.697 |
3876.0 |
\i |
264.679 |
5574.8 |
H |
308.661 |
7581.5 |
|
l/i |
221.482 |
3903.6 |
H |
265.465 |
5607.9 |
y* |
309.447 |
7620.1 |
|
94" |
222.268 |
3931.4 |
3^ |
266.250 |
5641.2 |
% |
310.232 |
7658.9 |
|
71 |
223.053 |
3959.2 |
55 |
267.035 |
5674.5 |
"i |
311.018 |
7697.7 |
|
H |
223.838 |
3987.1 |
!/i |
267.821 |
5707.9 |
311.803 |
7736.6 |
|
|
3 |
224.624 |
4015.2 |
H |
268.606 |
5741.5 |
H |
312.588 |
7775.6 |
|
% |
225.409 |
4043.3 |
^ |
269.392 |
5775.1 |
% |
313.374 |
7814.8 |
|
72 |
226.195 |
4011.5 |
86 |
270.177 |
5808.8 |
100 |
314.159 |
7854.0 |
|
H |
226.980 |
4099.8 |
H |
270.962 |
5842.6 |
|||
|
Vi |
227.765 |
4128.2 |
% |
271.748 |
5876.5 |
|||
|
% |
228.551 |
4156. 8 |
% |
272.533 |
5910.6 |
|||
|
-73 |
229.336 |
4185.4 |
87 |
273.319 |
5944.7 |
|||
|
230.122 |
4214.1 |
H |
274.104 |
5978.9 |
||||
|
H |
230.907 |
4242.9 |
3 |
274.889 |
6013.2 |
|||
|
3rf |
281.^2 |
4271.8 |
y |
2T6.R75 |
6017.0 |
898
HANDBOOK ON ENGINEERING.
TABLE NO. 5.
CUBIC FEET OF AMMONIA GAS "PER MINUTE TO PRODUCE ONE^TON OF REFRIGERATION PER DAY.
CONDENSER.
|
P |
P |
103 |
"5 |
127 |
139 |
153 |
168 185 |
200 |
218 |
||
|
t ; 65° |
70° |
75° |
80° |
85° |
90°j '95° |
100 |
105° |
||||
|
* |
r A 2O° 7 I o |
5.84 |
5-9 |
5.96 |
6.03 |
6.06 |
6.16 |
6.23 |
6.30 |
6.43 |
|
|
o |
0 |
^o: |
5.35 |
5-4 |
5.46 |
5-52 |
5.58 |
5-64 |
5.70 |
5-77 |
|
|
h |
9 |
— 10 j |
4.66 |
4-73 |
4.76 |
4.81 |
4.86 |
4.91 |
4-97 |
5-°5 |
5-oS |
|
w |
13 |
~" 0 |
4.09 |
4.12 |
4.17 |
4.21 |
4.25 |
4.3° |
4-35 |
4.40 |
4.44 |
|
o |
16 |
° \ |
3.59 |
3-63 |
3-66 |
3-70 |
3-74 |
3.78 |
3.83 |
3.87 |
|
|
2 |
20 |
5 \ |
3-2C |
3.24 |
3-27 |
3.30 |
3-34 |
3.38 |
3-41 |
3.45 |
3-49 |
|
w |
Jo |
10° |
2.87 |
2.9 |
2-93 |
2.96 |
2.99 |
3.02 |
3.06 |
3-°9 |
3.12 |
|
28 |
'5 |
2.59 |
261 |
2.65 |
2.68 |
2.71 |
2-73 |
2.76 |
2.80 |
2.82 |
|
|
!. aj |
20 |
2.31 |
2-34 |
2.36 |
2.38 |
2.41 |
2-44 |
2.46 |
2.49 |
2.51 |
|
|
39 |
25* |
2.06 |
2.08 |
2.10 |
2.12 |
2.» 5 |
2.17 |
2. 2O |
2. -2 2 |
2.24 |
|
|
« |
3° |
1.85 |
1.87 |
1.89 |
I.9I |
1-93 |
1.95 |
1.97 |
2.00 |
2.OI |
|
|
3i> |
1.70 |
1.72 |
1.74 |
1.76 |
1.77 |
1.79 |
1.81 |
1.83 |
1.85 |
TABLE KG. 6.
PROPERTIES OF SULPHUR DIOXIDE.
|
t |
. P |
H |
h |
L |
V |
\\ |
V |
|
. 22 T"1* —4 |
S.S^ 7-23 9.27 |
157.43 158.64 159.84 |
^19-56 —16.30 — »3-°5 |
176.99 •174.95 172.89 |
I3.I7 10.27 8.12 |
.076 .097 .123 |
.4041 .3914 •3791 |
|
5 «4 23 |
11.76 14.74 18.31 |
161.03 162.20 163.66 |
—9.79 -6.53 —3.27 |
170.82 168.73 166.63 |
6.50 5.25 4.29 |
•153 .190 .232 |
•3673 •3559 •3449 |
|
32 4< 5° |
«.53 27.48 33-25 |
164.51 165.65 166.78 |
o.oo 3-27 6.55 |
164.5 r 162.38 160.23 |
3.54 2.93 2.45 |
.282 •340 .406 |
•3344 .3241 .3M2 |
|
59 68 77 |
39 33 47-61 56.39 |
167.90 168.99 170.09 |
9.83 13." 16.39 |
158.07 155-89 153-7° |
2.07 i-75 1.49 |
•483 •570 .669 |
.3046 .2952 .2861 |
|
86 95 104 |
66.36 77.64 90.31 |
171.17 172.54 1 73.30 |
19.69 22.98 26.28 |
15L49 149.26 147.02 |
1.27 1.09 .91 |
.780 .906 1.046 |
.2774 .2689 .2607 |
HANDBOOK ON ENGINEERING.
899
TABLE NO. 7.
PROPERTIES OF AMMONIA.
|
t |
*4 |
A. |
B |
t |
*=4 |
A |
B |
|
—40 |
1.3802 |
.0000 |
.0000 |
60 |
•9959 |
.2136 |
.1707 |
|
— 35 |
1.3569 |
.0118 |
.0115 |
65 |
.9803 |
.2231 |
.1768 |
|
1-3343 |
.0236 |
.0224 |
70 |
.9651 |
.2326 |
.1825 |
|
|
— 25 |
1.3119 |
.0351 |
.0332 |
75 |
.9500 |
.2420 |
.1881 |
|
—20 |
1.2902 |
.0465 |
.0435 |
80 |
•9353 |
•2513 |
•1936 |
|
—15 |
1.2689 |
.0578 |
•0535 |
85 |
.9207 |
.2605 |
.1990 |
|
— 10 |
1.2481 |
.0690 |
.0631 |
90 |
.9065 |
.2696 |
.2042 |
|
— 5 |
1.2276 |
.0800 |
.0726 |
95 |
.8922 |
.2787 |
.2093 |
|
* 0 |
1.2076 |
.0910 |
.0816 |
100 |
.8788 |
.2877 |
.2140 |
|
+5 |
1. 1880 |
.1018 |
.0904 |
105 |
.8650 |
.2966 |
.2186 |
|
10 |
1.1688 |
.1125 |
.0989 |
no |
.8516 |
•3054 |
.2232 |
|
15 |
1.1500 |
.1230 |
.1072 |
115 |
•8385 |
.2276 |
|
|
20- |
1.1315 |
• 1335 |
.1152 |
120 |
.8255 .3228 |
-2319 |
|
|
1.1134 |
.1439 |
,1229 |
125 |
.8129 |
•33i3 |
.2360 |
|
|
30 |
1.0957 |
.1541 |
.1304 |
130 |
.8002 |
.3398 |
.2402 |
|
35 |
1.0783 |
.1643 |
.1376 |
US |
.7878 |
•3483 |
.2441 |
|
40 |
1.0613 |
.1743 |
.1446 |
140 |
•7756 |
•3567 |
.2479- |
|
45 |
1-0445 |
.1843 |
.1514 |
145 |
.7636 |
•3650 |
.2516 |
|
5° |
1.0280 |
.1941 |
.1581 |
150 |
.7518 |
•3732 |
•255* |
|
55 |
1.0118 |
.2039 |
.1645 |
,7402 |
.3814 |
.2586 |
— logeli.
In this table :
AA — A 2 = c loge lj ; where c is the specific heat of liquid ammonia, c is assumed equal to 1; if any other value is taken the numbers in the table must be multiplied by that value..
^-63 = 9s -
Examples of use of table :
(1) Per cent, of liquid in wet compression to prevent superheating = (Bj-B2)/^2.
(2) Superheating above condenser with dry compres-. sion = ,0a,(7Bi7BB;lTB^
(3) Work to compress, i pound of ammonia = 788 (T\ - T2) 9>2 ;— i cubic foot = 788 (T, — T2) <P2 W8.
(4) Mean pressure = «f (T, - T2) <P2 W2.
(5) Equation of adiabatic A9 + «3^2 = Al + »,9r
900
HANDBOOK ON ENGINEERING.
TABLE NO. 8.
PROPERTIES OF CARBONIC ACID.
|
f | |
P |
H |
h L |
v |
w |
0 |
|
|
i |
_ .- |
_ |
|
. |
— , |
. , |
|
|
— 22 |
210 |
98.35 |
—37.80 136.15 |
.4138 |
! 2.321 « |
.3108 |
|
|
— 13 |
249 |
99.14 |
—32.51 |
131.65 |
•3459 |
j 2:759 |
.2945 |
|
— 4 |
292 |
99.88 |
26.91 126.79 |
.2901 |
3-265 |
.2785 |
|
|
1 |
j |
||||||
|
5 ; |
342 100.58 |
^—20.92 |
121.50 |
.2438 |
1 3.853 |
.2613 |
|
|
14 |
396 |
IOI.2I |
— 14.49 I!5-7° |
.2042 |
, 4.535 |
.2441 |
|
|
23 |
457 |
IOI.8I |
—7.56 ' 109.37 |
.1711 |
!' 5.331 I |
.2262 |
|
|
32 |
525 |
102.35 |
o.oo |
102.35 |
.1426 |
•: 6.265 |
*• .2080 |
|
41 |
599 |
IO2.84 |
8.32 |
94-52 |
.1177 |
7-374 |
.1887 |
|
5° |
680 |
103.24 |
17 60 85.64 |
.0960 |
' 8.708 |
•'679, |
|
|
i |
1 |
||||||
|
59 |
768 |
103.59 |
28.22 |
75-37 |
.0763 |
i 10.356 |
.1452 |
|
68 |
864 j 103.84 |
40.86 |
62.98 |
•0577 |
j 12.480 |
||
|
77 |
968 |
10395 |
57.06 46.89 |
.0391 |
:i5475 |
.0873 |
|
|
86 |
1.080 |
10372 |
84.44 ' 19-28 |
.0147 |
21.519 |
.0353 |
|
|
1 i |
TABLE NO. 9.
PROPERTIES OF BRINE SOLUTIO'N. (Common Salt.)
|
1 |
•ifc Wo !- |
i 1. [1 |
i ific Gravity it 60° F. 1 |
:ific heat. |
I . 11 |
i li ^"3, "? e |
1 |
f |
|
I* |
F |
1 * |
I |
I |
So & |
r |
^ |
|
|
o |
0 |
0 |
X. |
i. |
8.35 |
0. |
62.4 |
32. |
|
I |
r-4 |
i |
1.007 |
0.992 |
8-4 |
0.084 |
62.8 |
|
|
5 |
; [20 |
5 |
-037 |
0.96 |
8.65 |
0.432 |
64.7 |
25.4 |
|
10 |
40 |
10 |
.073 |
0.892 |
8-95 |
0.895 |
66.95 |
18.6 |
|
15 |
60 |
15 |
.H5 |
0-855 |
9-3 |
1-395 |
69.57 |
12.2 |
|
20 |
80 |
'9 |
0,829 |
9-6 |
1.92 |
71.76 |
6.86 |
|
|
35 |
IOO |
23 |
.191 |
0.783 |
9-94 |
2.485 |
74,26 |
1.00 |
HANDBOOK ON ENGINEERING.
901
|
00 |
0 »/•> |
t-vO »-• ioO\«^O O Os<^vO ^ VO O* r- T$- o t^c*so r-.oo\o f« \O *^O\>- ^^-VO r-~OO ONQ «- |
|
|
N |
O |
- |
|
|
" |
°g |
Tf-O^N N i-« OsO^"- "- •*? \r> O 10 t^ ^ O *O ON ^ to to *O O^ «O 10000 o •-« M -^-lovo t— ^.oo N c* W- e*> «O «*> «9l **> «O «*> *^ **5 |
|
|
N |
|||
|
. |
st |
0 to |
OO fON O\TJ-IOO\M roto^-io ^•VO M IOCNN ro^MOO M fO rJ-iOt^CO O\- N 'OTfrfioir> C* c» N M P* ^O^OfO^O^O^^^O |
|
kl s |
M |
c\ |
|
|
K 5 |
°0 |
N 1-^vOvO NOO fO»00 *O« TtTfOO - fOtorffOONfOiorj- ro^u-jr^OO OsO.« « M N N |
|
|
§ |
H |
o |
|
|
* g |
CO |
0 tr> |
»OO Tf«^CNOOOO -^-vO r^-NVO ^•^lor^i^r^ioMvooOOO "sf M ro^ftovo r-»OO O\^ONO\O\ NMMMMMMNMNNM |
|
§ |
i? |
OO |
|
|
•^ ^ ^ |
8 |
°o |
00 rfioO M Tj-r>.iooOOO «-• - N >- N • fO N OVO »- fO «O "-< U-) i- N ^"friovovo r^t^r^t^sO MCMMdNNMNNNNM |
|
§ r~. |
M |
00 |
|
|
* kj ^ |
Jt^ |
o |
Nl-vOt^f^Ot^vOOCNOt^ MCNONOOVOCOr^O«OO^lO O O - N ro-'tTl-xoiO'^-'^-rO |
|
s & |
N M |
1^ |
|
|
% % |
lO |
°o |
NO Ot^^vO i^-vOCO M O ONW «oovo -^-o toco ^oo TJ-VOVO O\ONO«NNN.MNM — o Mk'NMNNNMMNMM |
|
^ E> |
M |
t^ |
|
|
§ |
f^ |
ON-t-r--CO «^>vO CNTJ-M t^OO QvO tOO 'sJ-OO ONOOtOONONVO OOOOCNOOOOOOONOOt^ |
|
|
o |
vo |
||
|
0. |
- |
ooooooooooo.o O toO \OO too "^O "^^j10 I I M |
|
|
a, |
^ ^ff-Sg^'S^S^S, . , ._.. .. --J |
a^nssa^a
902
HANDBOOK ON ENGINEERING.
tf
Pk
C
u
*
o
S
rvj p4
3 o • "
1
I
§
1
|
00 M |
0 , to |
0\ 00 ON 00 "t *• O\ O O O 00 NO |
t^ 00 M ON -i ON |
ON «K N ** |
N to |
|
M |
k.H |
O rf OO M to O\ NO NO NO .t» t~- t>» |
N NO 00 00 00 00 |
M ro ON ^* |
3 . |
|
°§ |
Tj* O ^J* M M M to rj» M OO M NO |
O\ ON 00 to to NO |
'oo oo tO ON |
CO |
|
|
• |
00* M to oo ci to »o NO NO NO t>."t>» |
OO M to r> 00 oo |
10 VO CO CO |
00 |
|
|
M |
0 to o |
M NO" NO f> •* t* ••« 00 M to NO NO NO* OO" C* to OO •-" to to NO \o NO r* |
N NO ^* 4 NO* oo* |
00 «•» oo •>• o\ d *^oo |
q 00 |
|
00 NO |
°o |
oo oo d to o NO |
00 CO C? |
Jr,^ |
<g |
|
M |
• ON 1 |
K'&S £#£• |
tfRS |
5S |
S-- |
|
CO m |
0 to |
^5 0^ to ^. 0^ ^. |
-. M Ob |
^Vo |
V> |
|
M |
oo |
to to to to NO NO |
10 «*<• r^ |
OO 00 NO NO |
•4 NO |
|
s |
0 |
Is* •*}• Os O OO OO |
CO to to |
^ ^ |
NO |
|
CO M |
£ |
OO O fO to r-* ON T to »O to to to |
--- |
&3 |
3 |
|
fx N |
o to |
*OJO ,«OR |
t^ ^ Jo |
0* ON |
0 |
|
M |
r*. |
* !? s> s> 3; s |
" KS |
to to |
to |
|
to M M |
o O |
••« oo oo to NO «o |
0 »- 0 |
•3~ |
1 |
|
0 |
o |
-0.0 >0 * ^ |
?.-8<8 |
^-z |
M |
|
M |
NO |
« N *4" IO NO t>» |
oo '• «» «^. |
to to |
0* |
|
c. |
£ |
O 0 CO O 0 O to O ' to O ""> M M M III 1 |
o ' o o 0 to 0 |
0 0 »O O N t^ |
O to to |
|
A |
M M CM |
ft* |
^5 |
•5 |
^ .aunssaud
HANDBOOK ON ENGINEERING.
903
TABLE NO. 12.
Reaumufj Fahrenheit, and Celsius Thermometers Compared.
|
R. |
F. |
C. -Hnn |
|
E-+210-E |
||
|
75-- |
E- 205-E E- 200-E |
--95 |
|
E4- 195-E |
--90 |
|
|
70-- 65-- |
E- 190-E — — j o er |
Q tf |
|
•~ 155 - E- iso-E E- 175-E |
55 --80 |
|
|
60-- |
E- 170- E: E- 165-E |
75 |
|
55-- 50-- 45-- |
E- 160-E E- 155-E :- 150- = |
:-70 |
|
E- 145- E |
R A |
|
|
: 140- _ E- 135-E |
e; K |
|
|
-- 13Q-: |
||
|
40-- 35-- |
E- 125-E - j o A |
:-«» |
|
E- U5-E |
y| •£ |
|
|
E- uo-E |
----- |
|
|
32l |
1-105-1 |
1-40 |
|
R |
R |
C. |
|
+32- - 30-- |
-+104 i — loo-E |
- 35 --30 |
|
25-- |
E— 90~E E— 85-E |
|
|
20-- |
E- so-E |
--25 |
|
15-- |
E— TO -E |
_ OA |
|
E — 65 -E |
||
|
E- eo-E |
-- 15 |
|
|
10-- 5-- |
E— 55-E |
J A |
|
: 50 r — :_ 4Q-E |
-- 5 |
|
|
o-- |
E— 35-E E- 30-E |
-- 0 |
|
-5-- |
E— 25- E E-.20-E |
-— 5 |
|
E— 15-E |
— 10 |
|
|
10-- 15- |
E- IO-E |
— 4R |
|
- :- 0- |
_ |
904
HANDBOOK ON ENGINEERING.
3.
O to
H
PQ
a
•JN3JL
905
HANDBOOK ON ENGINEERING.
TABLE NO. 14.
Weight of Rivets and Round Headed Bolts Without
Per 100.
LENGTH FROM UNDER HEAD. ONE CUBIC FOOT WEIGHING 480 LBS^
|
LENGTH INCHES. |
3/8" DIAM. |
y2" DIAM. |
%" DIAM. |
w DIAM. |
%" DIAM. |
1" DIAM. |
I'/s" DIAM. |
1U" DIAM. |
|
U4 |
5.4 |
12.6 |
21.5 |
28.7 |
43.1 |
65.3 |
91.5 |
123. |
|
1% |
6.2 |
13.9 |
23.7 |
31.8 |
47.3 |
707 |
98.4 |
133. |
|
i% |
6.9 |
15.3 |
25.8 |
34.9 |
51.4 |
76.2 |
105. |
142. |
|
2 |
7.7 |
16.6 |
27.9 |
37.9 |
55.6 |
81.6 |
112. |
150. |
|
2*4 |
8.5 |
18.0 |
30.0 |
41.0 |
59.8 |
87.1 |
119. |
159. |
|
2Y2 |
9.2 |
19.4 |
32.2 |
44.1 |
63.0 |
92.5 |
126. |
167. |
|
23^ |
10.0 |
20.7 |
34.3 |
47.1 |
68.1 |
98.0 |
133. |
176. |
|
3 |
10.8 |
22.1 |
36,4 |
50.2 |
72.3 |
103. |
140. |
184. |
|
3^4 |
11.5 |
23.5 |
38.6 |
53.3 |
76.5 |
109. |
147. |
193. |
|
3V3 |
12.3 |
24.8 |
40.7 |
56.4 |
80.7 |
114. |
154. |
201. |
|
3% |
13.1 |
26.2 |
42.8 |
59.4 |
84.8 |
120. |
161. |
210. |
|
4 |
13.8 |
27.5 |
45.0 |
62.5 |
89.0 |
125. |
167. |
218, |
|
4H |
14.6 |
28.9 |
47.1 |
65.6 |
93.2 |
131. |
174. |
227. |
|
4V2 |
15.4 |
30.3 |
49.2 |
68.6 |
97.4 |
136. |
181. |
236. |
|
43/4 |
16.2 |
31.6 |
51.4 |
71.7 |
102. |
142. |
188. |
244. |
|
5 |
16.9 |
33.0 |
53.5 |
74.8 |
106. |
147. |
195. |
253. |
|
6H |
17.7 |
34.4 |
55.6 |
77.8 |
110. |
153. |
202. |
261. |
|
5V2 |
18.4 |
35.7 |
57.7 |
80.9 |
114.. |
158.- |
209. |
270. |
|
534 |
19.2 |
37.1 |
59.9 |
84.0 |
118. |
163. |
216. |
278. |
|
6 |
20.0 |
38.5 |
62.0 |
87.0 |
122. |
16.9. |
223. |
287. |
|
6V3 |
21.5 |
41.2 |
66.3 |
93.2 |
131. |
180. |
236. |
304. |
|
7 |
23.0 |
43.9 |
70.5 |
99.3 |
139. |
191. |
250. |
321. |
|
7Va |
24.6 |
46.6 |
74.8 |
106. |
147. |
202. |
264. |
338. |
|
8 |
26.1 |
49.4 |
79.0 |
112. |
156. |
213. |
278. |
355, |
|
8Va |
27.6 |
52.1 |
83.3 |
118. |
164. |
223. |
292. |
372. |
|
9 |
29.2 |
54.8 |
87.6 |
124. |
173. |
234. |
306. |
389. |
|
9Va |
30.7 |
57.6 |
9i.8 |
130. |
181. |
245. |
319. |
406; |
|
10 |
32.2 |
60.3 |
96.1 |
136. |
189. |
256. |
333. |
423. |
|
lOVa |
33.8 |
63.0 |
101. |
142. |
198. |
267. |
347. |
440. |
|
11 |
35.3 |
65.7 |
105. |
14S. |
206. |
278. |
361. |
457. |
|
11 Va |
36.8 |
68.5 |
109. |
155.* |
214. |
289. |
375. |
474. |
|
12 |
38.4 |
71.2 |
113. |
161. |
223. |
3QQ. |
388, |
491. |
|
Heads. |
1,8 |
5.7 |
10.9 |
13.4 |
22.2 |
38,0 |
'57.0 |
82;0 |
HANDBOOK ON ENGINEERING.
TABLE NO. 15.
Weight and Strength of Iron Bolts.
|
ENDS ENLARGED OR UPSET. |
ENDS NOT EN- LARGED. |
ENDS ENLARGED OR. UPSET. |
ENDS NOT EN- LARGED. |
||||||
|
8 |
|; |
8 |
*g |
fe |
tfx |
O |
* fc |
||
|
By |
*g |
fc 5 |
P5 . |
g . |
fr « |
oS |
rt |
"g |
|
|
El |
B§ |
'Eg |
i.S |
B H' |
w K |
ng |
5 g |
62 |
gg |
|
JS_ |
°0 |
r |
H 3 * |
£ |
3 S p |
2o |
r |
§a |
i1 |
|
Ine. |
Pounds. |
Tons. 2340 Ibs. |
Ins. |
Lbs. |
Ins. |
Lbs, |
Tons 2240 Ibs. |
Ins. |
Lbs. |
|
V/L |
.0414 |
.245 |
1% |
8.10 |
45.7 |
2.14 |
12«0 |
||
|
& |
.093 |
.553 |
If! |
8.69 |
49.0 |
2.22 |
12.9 |
||
|
I 6 |
.165 |
.983 |
.35 |
.321 |
•*• 1 6 1% |
9.30 |
52.5 |
2.30 |
13.8 |
|
JL |
.258 |
1.53 |
-43 |
.452 |
9.93 |
56.0 |
2.38 |
,14.7 |
|
|
% |
.372 |
2.21 |
.50 |
.654 |
216 |
10.6 |
59.7 |
2.45 |
f!5.7 |
|
ft |
.506 |
3.00 |
.58 |
. .897 |
oys |
12.0 |
63.8 |
2.59 |
17-5 |
|
V* |
.661 |
3,93 |
.66 |
' 1.14 |
2Vi |
13.4 |
71.6 |
2.73 |
19.5 |
|
ft |
.837 |
4.97 |
.73 |
1.41 |
2% |
14.9 |
79.7 |
2.88 |
,21.6 |
|
% |
1.03 |
6.14 |
.80 |
1.67 |
2Vfc |
16.5 |
88.4 |
3.02 |
'23.9 |
|
li |
1.25 |
7.42 |
.88 |
2.03 |
2% |
18.2 |
97.4 |
3.16 |
26.1 |
|
1.49 |
8.83 |
.96 |
2.41 |
2% |
20.0 |
106.9 |
3.30 |
28.5 |
|
|
1* |
1.75 |
10.4 |
1.04 |
2.81 |
21.9 |
116.8 |
3.45 |
31.1 |
|
|
2.03 |
12.0 |
1.12 |
3.26 |
3 |
23.8 |
127.2 |
3.60 |
[33.9 |
|
|
M |
2.33 |
13.8 |
1.20 |
3.77 |
3V4 |
27.9 |
141.0 |
3.86 |
39.1 |
|
i |
2'.65 |
15.7 |
1.27 |
4.27 |
32.4 |
163.6 |
4.12 |
44.4 |
|
|
ift |
2.99 |
16,8 |
1.35 |
4.77 |
3% |
37.2 |
187.7 |
'4.41 |
51.0 |
|
1% |
3.35 |
18.9 |
1.42 |
5.28 |
4 |
42.3 |
213.6 |
4.70 |
57.8 |
|
1ft |
3.73 |
21.1 |
1.49 |
5.81 |
4Vi |
47.8 |
227.0 |
4.98 |
65.2 |
|
1% |
4*13 |
23.3 |
1.55 |
6.39 |
53.6 |
254.5 |
5.25 |
72.9 |
|
|
1ft |
4.56 |
25.7 |
1.64 |
7.04 |
4«I |
59.7 |
283.5 |
5.53 |
'80.5 |
|
1% |
5.00 |
28.2 |
1.72 |
7,74 |
5 |
66.1 |
314.2 |
5.80 |
88.1 |
|
1ft |
~5.47 |
30.8 |
1.80 |
8.48 |
5^4 |
72.9 |
324.7 |
6.08 |
97.0 |
|
5.95 |
33,6 |
1.87 |
9.20 |
51/2 |
80.0 |
356.4 |
6.36 |
106. |
|
|
1ft |
6.46 |
36.4 |
1.94 |
9.88 |
534 |
87.5 |
389.5 |
6.63 |
116. |
|
1% |
6.99 |
394 |
2.00 |
10.6 ' |
6 |
95.2 |
424.1 |
6.90 |
126. |
|
JJi |
,7.53 |
42.5 |
2.07 |
11.3 |
For square Jbarslncrease the breaking strains Vi part.
A long upset rod is no'strpngcr than one not upset, against slowly ap* plied loads or strains.' Therefore in such cases the column of kireate'st diam- eter in the table should be used.
HANDBOOK ON ENGINEERING.
907
TABLE NO. 16.
Boiling: Point* of Various Substances. At Atmospheric Pressure at Sea Level.
|
Substance. |
Degrees Fahr. |
Substance. |
Degrees Fahr. |
|
Alcohol |
173 |
Sulphur |
670 |
|
Ammonia. ... |
28 |
Sulphuric Acid, s. g 1.848 |
590 |
|
Benzine |
176 |
Sulphuric Acid, s. g. 1 3 |
240 |
|
Coal Tar |
325 |
Sulphuric Ether . . ... . |
100 |
|
Linseed Oil |
597 |
315 |
|
|
Mercury |
648 |
Water |
212 |
|
Naptha... |
186 |
Water, Sea |
213.2 |
|
Nitric Acid, s. g. 1.42. . . . |
248 |
Water, Saturated Brine |
226 |
|
Nitric Acid, s. g. 1 5. |
210 |
Wood Spirit |
150 |
|
Petroleum Rectified |
316 |
||
|
TABLE Melting Points of Metals. From D. K. C. |
NO. 17. Melting: Points of Various Solids. From D. K. C. and H. |
||
|
Metal. |
Degrees Fahr. |
Substance. |
Degrees Fahr. |
|
Aluminum |
Full Red Heat. 1150 507 1690 1996 2156 2282 2012 ( 1922 ] to C 2012 .2912 617 —39 1873 ( 2372 < to ( 2552 442 773 |
Carbonic Acid |
-108 2377 32 95 45 112 91 606 120 ( 109 to ( 120 239 92 14 142 154 |
|
Antimony |
Glass |
||
|
Bismuth |
|||
|
Bronze |
Lard |
||
|
Copper |
Nitro-Glycerine |
||
|
Gold, Standard. |
|||
|
Gold, Pure |
Pitch |
||
|
Iron, Cast, Gray |
Saltpetre |
||
|
Iron, Cast, White |
|||
|
Iron, Wrought |
|||
|
Lead |
|||
|
Mercury ... ... |
Tallow |
||
|
Silver . . |
|||
|
Steel |
|||
|
Wax, Bleached |
|||
|
Tin |
|||
|
Zinc |
|||
Melting: Points of Fusible Plugs. From D. K. 0.
|
Softens at |
Melts at |
Softens at |
Melts at |
||
|
2 Tin, 2 Lead |
365 |
372 |
2 Tin, 7 Lead |
377J |
S88 |
|
Tin, 6 Lead |
372 |
383 |
2 Tin, 8 Lead |
3954 |
408 |
908
HANDBOOK ON ENGINEERING.
SJ
Sfc«i=r
§S8§§§!!
Ol T
8^
I!
, § S1
3
q
o
*o^ooc$^coo^icco^ocot~coioio><i<coco'O3o}. •i— (
I
3 O^ O CO IO O O C- CN»J> O t- CO Ci 00 CO CO l> OO i-i O O> CO 00 -^ <
PQ
7;
O O O OO I> O W O CQ CO OO QOCO O t- T-I O O <M O5 O> CO O
_ ocooocooT-*cttpc3cococqcoot>rHioooo«ocoo
o
•
1
O O O O O O O O O 2T) O CO T— < O t* C<l CO Oi O ^ •— < W O5 C
o eo* o o co* n* CQ T-* o" o* oo* r-" t-* co* co* o* »o* o o* -
»0 CO <M* O* 00* t^ CO* »0 »A <•** -* CO* CO CO 00 « O^ C«* C<* 03 09 <N* <M CM
SSISSSSSi
$
HANDBOOK ON ENGINEERING.
909
ieSSS8SS8S8SS88SS8«SS8S8Sg
IOCQ OS
^o5ccoSi2oo0*S^ocosoco
6 3'"
!L
ip
aSS88gSS~S~S"8S sW^l^ 8. S 88888
JO • • •......«.. ...... ^. .....*
"fift j rH O? CO ^ *& ip ?O t* 00 O5 O5 O TH d CO_ CO ^ lO CO_ t^ 00 00 O I
8. S_
*- ^"^<r>-^3^"rH0--— SS^oo^ocoiot^THioc
w-, ^^ >.^ ^ — . , ~ ^- . ^ ^^ ».v ^^ CO U$ ^ tg d 00 tQ rH I> rt< O C w *H rn 0s* CO CQ ^ uj uj CO t* t^ 00 00 Oi O O ^H d d CO Tf* ^
3 essssssssssssssssssssssss" s
iH
•A
8
ri «*«»«««gg!-$gg8g$gg8$sj
III
ft ^* «
iJlO HANDBOOK ON ENGINEERING.
TABLE NO. 20.
Capacity of Reservoirs in Gallons.
NOTE — The columns headed Length and Width denote the length and width in feet; the columns headed Gallons denote the capacity In U. S. gallons for one foot In depth.
|
Length and Width |
Gallons. |
Length aud Width. |
Gallons. |
Length and Width. |
Gallon*. |
Length and Width. |
Gallons, |
|
1x1 2x 1 |
7.481 14.961 |
15 x 7 16 x 7 |
785.455 837.818 |
23x10 24 x 10 |
1720.519 1795.325 |
13x13 14x13 |
1264.208 1361.454 |
|
3X 1 |
22.442 |
17 x 7 |
890.182 |
25x10 |
1870.130 |
15x13 |
1458.701 |
|
2X 2 |
29.922 |
18 x 7 |
942.545 |
26x10 |
1944.935 |
16x13 |
1555.948 |
|
3x 2 |
44.883 |
19 x 7 |
994.909 |
27x10 |
2019.740 |
17x13 |
1653.195 |
|
4x 2 |
59.844 |
20x 7 |
1047.273 |
28x10 |
2094.545 |
18x13 |
1750.442 |
|
6x 2 |
74.805 |
21 X 7 |
1099.636 |
29X10 |
2169.351 |
19x13 |
1847.688 |
|
6x 2 |
89.766 |
8x 8 |
478.753 |
30X10 |
2244.156 |
20x13 |
1944.935 |
|
8x3 |
67.325 |
9X 8 |
538.597 |
11X11 |
905.143 |
21x13 |
2042.182 |
|
4x3 |
89.766 |
10 x 8 |
598.442 |
12X11 |
987.429 |
22x13 |
2139.429 |
|
6x 3 |
112.208 |
11x8 |
658.286 |
13X.11 |
1069.714 . |
23x13 |
2236.675 |
|
6x 3 |
134.649 |
12 x 8 |
718.130 |
14X11 |
1152.000 |
24 x 13 |
2333.922 |
|
7X 3 |
157.091 |
13 x 8 |
777.974 |
15X11 |
1234.286 |
25 x 13 |
2431.169 |
|
8x 3 |
179.532 |
14 X 8 |
837.818 |
16X11 |
1316.571 |
26x13 |
2528.416 |
|
9x 3 |
201.974 |
15 x 8 |
897.662 |
17X11 |
1398.857 |
27x13 |
2625.662 |
|
4X4 |
119.688 |
16 x 8 |
957.507 |
18X11 |
1481.143 |
28 x 13 |
2722.909 |
|
6x 4 |
149.610 |
17 x 8 |
1017.351 |
19x11 |
1563-429 |
29x 13 |
2820.156 |
|
6x 4 |
179.532 |
18 x 8 |
1077.195 |
20X11 |
1645.714 |
30 x 13 |
2917.403 |
|
7x 4 |
209.455 |
19 x 8 |
1137.039 |
21X11 |
1728.000 |
31 x 13 |
3014.649 |
|
8x 4 |
239.377 |
20x 8 |
1196.883 |
22x11 |
1810.286 |
32 x 13 |
3111.896 |
|
fix 4 |
269.299 |
21 x 8 |
1256.727 |
23x11 |
1892.571 |
33 x 13 |
3309.143 |
|
10 x 4 |
299.221 |
22x 8 |
1316.571 |
24x11 |
1974.857 |
34X 13 |
3306.390 |
|
11 X 4 |
329.143 |
23x 8 |
1376.416 |
25X11 |
2057. 143 |
35 x 13 |
3403.636 |
|
12 X 4 |
359.065 |
24X 8 |
1436.260 |
26x11 |
2139.428 |
36 x 13 |
3500.883 |
|
6x 5 |
187.013 |
9x 9 |
605.922 |
27X11 |
2221.714 |
37x13 |
3598:130 |
|
6x 5 |
224.416 |
10 x 9 |
673.247 |
28x11 |
2304.000 |
38x13 |
3695.377 |
|
7x 6 |
261.818 |
11 x 9 |
740.571 |
29x11 |
2386.286 |
39x13 |
3792.623 |
|
8x 5 |
299.221 |
12 x 9 |
807.896 |
30 x 11 |
2468.571 |
14 x 14 |
1466.182 |
|
9x 5 |
336.623 |
13 x 9 |
875.221 |
31x11 |
2550.857 |
15x14 |
1570.909 |
|
10 x 6 |
374.026 |
14" x 9 |
942.545 |
32x11 |
2633.143 |
16x14 |
1675.636 |
|
11 x 5 |
411.429 |
15 x 9 |
1009.870 |
33 x 11 |
2715.429 |
17 x 14 |
1780.363 |
|
12 x 5 |
448.831 |
16 x 9 |
1077.195 |
12x12 |
1077.195 |
18 it 14 |
1885.091 |
|
13 x 6 |
486.234 |
17 x 9 |
1144.519 |
13x12 |
1166.961 |
19x14 |
1989.818 |
|
14 X 5 |
623.636 |
18 x 9 |
1211.844 |
14 x 12 |
1256.727 |
20x 14 |
2094.545 |
|
15 x 5 |
561.039 |
19 x 9 |
1279.169 |
15 x 12 |
1346.493 |
21 XI4 |
2199.263 |
|
ex 6 |
269.299 |
20x 9 |
1346.493 |
16x12 |
1436.260 |
22x14 |
2304.000 |
|
7x 6 |
314.182 |
21 x 9 |
1413.818 |
17x12 |
1526.026 |
23 x 14 |
2408.727 |
|
8x 6 |
359.065 |
22x 9 |
1481.143 |
18x12 |
1615.792 |
24 x 14 |
2513.454 |
|
Ox 6 |
403.948 |
23x 9 |
1548.467 |
19x12 |
1705.558 |
25 x 14 |
2018.182 |
|
10 x 6 |
448.831 |
24 x 9 |
1615.792 |
20 x 12 |
1795.325 |
•26 X 14 |
2722.909 |
|
U x 6 |
•493.714 |
25x 9 |
1683.117 |
21x12 |
1885.091 |
27 x 14 |
2827.636 |
|
12 x 6 |
538.597 |
26 x 9 |
1750.442 |
22 x 12 |
1974.857 |
28x14 |
2932.364 |
|
13 x 6 |
583.480 |
27x 9 |
1817.766 |
23x12 |
2064.623 |
29x14 |
3037.091 |
|
14 x 6 |
628.364 |
10 x 10 |
748.052 |
24x18 |
2154390 |
30X14 |
3141.818 |
|
15 x 6 |
673.247 |
11 x 10 |
822.857 |
25 x 12 |
2244.156 |
31 X14 |
3246.545 |
|
16 x 6 |
718.130 |
12 x 10 |
897.662 |
26x12 |
2333.922 |
32x14 |
3.351.273 |
|
17 x 6 |
763.013 |
13 x 10 |
972.467 |
27 x 12 |
2423.688 |
33x14 |
3456.000 |
|
18 x 6 |
807.896 |
14x10 |
1047.273 |
28 x 12 |
2513.455 |
34x14 |
3560.727 |
|
7x 7 |
366.545 |
15 x 10 |
1122.078 |
29 x 13 |
2603.221 |
35x14 |
3665.454 |
|
8x 7 |
418.909 |
16x10 |
1196.883 |
30 x 12 |
2692.987 |
*36 X 14 |
3770.182 |
|
9x 7 |
471.273 |
17 x 10 |
1271.688 |
31 x 12 |
2782.753 |
37x14 |
3874.U09 |
|
10 x 7 |
523.636 |
18 x 10 |
1346.493 |
33s 12 |
2872.520 |
38.x 14 |
3/79.636 |
|
11 x J |
576.000 |
19 x 10 |
1421.299 |
33 x 13 |
2962.386 |
,'J9 x 14 |
4084.364 |
|
12 x 7 |
628.364 |
20 x 10 |
1496.104 |
34 x 12 |
3052.052 |
40 x 14-x |
4189.091 |
|
13 X 7 |
680.727 |
21 x 10 |
1570.909 |
35x12 |
3141.818 |
41x14 |
4393.818 |
|
14X 7 |
733.091 |
22X10 |
1645.714 |
36 XW |
3231.585 |
42x14 |
4398.545 |
HANDBOOK ON ENGINEERING.
TABLE NO. 21.
Oapaoity of Reservoirs in Gallons. — Continued.
911
|
Length |
Length |
Length |
Length |
||||
|
and |
Gallons. |
and |
Gallons. |
and |
Gallons |
and |
Gallons. |
|
Width |
Width. |
Width. |
Width. |
||||
|
15 x 15 16 x 15 |
1683.117 1795.326 |
28X17 29X17 |
3560.727 3687.896 |
33x80 34 x20 |
4937 143 5086.753 |
52x28 54 x28 |
"ioSi'ese 11310.545 |
|
17 x 15 |
1907.532 |
80X17 |
3815.065 |
35x20 |
5236.364 |
56 x 28 |
11729.454 |
|
18 x 15 |
2019.740 |
81X17 |
3942.234 |
36x20 |
5385.974 |
30 x30 |
6733.467 |
|
10 x 15 |
2131.948 |
82x17 |
4069.403 |
37 x20 |
5535584 |
32x30 |
7181.299 |
|
20X15 |
2244.156 |
33X17 |
4196.571 |
38x20 |
5685 195 |
34 x30 |
7630130 |
|
21 X 15 |
2356.364 |
34 x 17 |
4323.740 |
39x20 |
5834.805 |
36 X30 |
8078.961 |
|
82X-15 |
2468.571 |
18 X 18 |
2423.688 |
40x20 |
5984.416 |
38x30 |
8527.792 |
|
23X15 |
2580.779 |
19X18 |
2558338 |
'23x22 |
3620 571 |
40x30 |
8976.623 |
|
24X15 |
2692.987 |
20X18 |
2692.987 |
24x22 |
3949 714 |
42x30 |
9425.454 |
|
25X15 |
2805.195 |
21X18 |
2827.636 |
26x22 |
4278.857 |
44 x30 |
9874.286 |
|
26X15 |
2917.403 |
22X18 |
. 2962.286 |
28x22 |
4608.000 |
46X30 |
10323.117 |
|
27X15 |
8029.610 |
23X18 |
3096.935 |
30x22 |
4937 143 |
48x30 |
10771.948 |
|
28X15 |
3141.818 |
24X18 |
3231.584 |
32x22 |
5266.286 |
50 x30 |
11220.770 |
|
29X15 |
3254.026 |
25X18 |
3366.234 |
34x22 |
5595.429 |
52x30 |
11669.610 |
|
30X15 |
3366.234 |
26X18 |
3500.883 |
36 x22 |
5924.571 |
54 X30 |
12118.442 . |
|
31 X15 |
3478.442 |
27X18 |
3635.532 |
38x22, |
6258.714 |
56x30 |
125H7.273 « |
|
32X15 |
3590.649 |
28X18 |
3770.183 |
40x22 |
6582.857 |
58x30 |
13016.104 |
|
33 X 15 |
3702.857 |
29X18 |
3904.831 |
43x32 |
6912.000 |
60x30 |
13464. y35 • |
|
34X15 |
3815.065 |
30X18 |
4039.480 |
44x22 |
7241.143 |
32x32 |
7660.052 |
|
35X15 |
3927.273 |
31X18 |
4174.130 |
24x24 |
4308.779 |
34x33 |
8138.805 |
|
86X15 |
4039.480 |
32X.18 |
4308.779 |
26x24 |
4667.844 |
36 x 32 |
n 8617.558 |
|
37X15 |
4151.688 |
33X18 |
4443.429 |
28x24 |
5026.909 |
38x32 |
9098.312. |
|
88X15 |
4263.896 |
34X18 |
4578.078 |
30x34 |
5385.974 |
40 x 32 |
9575.065 |
|
39 X 15 |
4376.104 |
35X18 |
4712.727 |
32x24 |
5745.039 |
42 X 32 |
10053.818 |
|
40X15 |
4488.312 |
36X18 |
4847.377 |
34x24 |
6r04.104 |
44 x33 |
10532.571 |
|
41X15 |
4600.519 |
19 x 19 |
2700.467 |
36x24 |
6463.169 |
46x32 |
11011.325 |
|
43X15 |
4718.727 |
20 X 19 |
2842.597 |
38x24 |
6822.234 |
48 x 32 |
11490.078 |
|
43X15 |
4824.935 |
21 xi9 |
2984.727 |
40x24 |
7181 299 |
50x32 |
11968.831 |
|
44X15 |
4937 143 |
22 x 19 |
3126.857 |
42 x 24 |
7540.364 |
52x33 |
\ 2447. 584 |
|
45X15 |
5049.351 |
. 23 x |9 |
3268.987 |
44x34 |
7899.429 |
54x32 |
12926.338 |
|
16x16 |
1915.013 |
24 X 19 |
3411.117 |
46x24 |
8258.493 |
56 x 32 |
13405.091 |
|
17X16 |
2034.701 |
25 x 19 |
3553.247 |
48 x 24 |
8617.558 |
58x33 |
13883.844 |
|
18X16 |
2154.390 |
26 X 19 |
3695.377 |
26^26 |
5056.831 |
60x32 |
143C2.597 |
|
19x16 |
2274.078 |
27 X 19 |
3837.506 |
28x26 |
5445.818 |
62x32 |
,14841.351 |
|
20x16 |
2393.766 |
28 X 19 |
3979.636 |
30x26 |
5834.805 |
64x34 |
1 15320. 104 |
|
21X16 |
2513.454 |
29X19 |
4121.766 |
32x26 |
6223.792 |
34x34 |
8647.480 |
|
22X16 |
2633.143 |
30X19 |
4263.896 |
34x36 |
6612.779 |
36x34 |
0156.156 |
|
23X16 |
2753.831 |
31 X19 |
4406.026 |
86x26 |
7001.766 |
38x34 |
0664.831 |
|
24X16 |
2872.519 |
32 x 19 |
4548.156 |
38x26 |
7390.753 |
40x34 |
10173.506 |
|
25X16 |
2992.208 |
33X19 |
4690.286 |
40x26 |
7779.740 |
4*x34 |
10682.182 |
|
26X16 |
3111.896 |
34X19 |
4832.416 |
42x26 |
8168.727 |
44x34 |
11190.857 |
|
27 x 16 |
3231 584 |
35X19 |
4974.545 |
44 x26 |
&557.714 |
46x34 |
11699.532 |
|
28X16 |
3351.273 |
36 x 19 |
5116.675 |
46x26 |
8946.701 |
4»x34 |
12208.308 |
|
29 x 16 |
3470.961 |
87 x 19 |
5258.805 |
48x26 |
9835.688 |
50x34 |
12716.883 |
|
80 x 16 |
3590649 |
38 x 19 - |
5400.935 |
50x26 |
9724.675 |
62x34 |
13225.558 |
|
81 X 16 |
3710.338 |
20x20 |
2992.208 |
52x26 |
10113.662 |
54x34 |
13734.231 . |
|
82 x 16 |
3830.026 |
21 x20 |
3141.818 |
28x28 |
5864.727 |
56x34 |
14242.900 |
|
17 x 17 |
2161.870 |
22x20 |
3291.429 |
30x28 |
6283.636 |
58x34 |
14751.584 |
|
18 x 17 |
2289.039 |
23x20 |
3441.039 |
32x28 |
6702.545 |
60x34 |
15260.260 |
|
19 x 17 |
2416.208 |
24x20 |
3590.649 |
34x28 |
7121.454 |
62 x 34 |
15768.935 |
|
20 x 17 |
2543.377 |
25x20 |
3740.260 |
36x28. |
7540.364 |
64x34 |
16377.610 |
|
21 X 17 |
2670.545 |
26x20 |
3889.870 |
38x28 |
7959.273 |
66x34 , |
16786.286 |
|
22 x 17 |
2797.714 |
27 X20 |
4039.480 |
;40x28 |
8378. 182 |
68x34 |
17394.961 |
|
23 x 17 |
2924.883 |
28x20 |
4189.091 , |
142 x 28 |
8797.091 |
36x36 |
9694,753 |
|
24 x 17 |
3052.062 |
29.x 20 |
4338.701 |
f 44 x 28 |
9216.000 |
38 x 36 |
10233.351 |
|
25x 17 |
3179.221 |
80 x20 |
, 4488.312 |
46x28 |
9634.909 |
40x36 |
10771.948 |
|
26 x 17 |
3306.390 |
31 X 20 |
4637.922 |
48x28 |
10053.818 |
43x36 |
11310.545 |
|
27 x 17 |
3433.558 |
82x20 |
4787.532 |
50x38 |
10472.727 |
44x36 |
11849.143 |
|
The United States inspection laws allow 20 per cent more pressure to b<| carried on boilers with double -riveted longitudinal seams, than on single rlveteU ooilera. |
912
HANDBOOK ON ENGINEERING.
w
PQ
p,
GO
O
I
tf
s
CO
o
O
W
tf
"T
rH
T
1 §
~«"
C^CMCM^rO^^^^iOOvOt'-OOOOO^OcMrO^^DCJOOrHcF
^ is" s"
22^
8 SSI
rH CM CMC
338S
oioQioomc in c^- Q CM in jj- c
r-i r-t CM CM CM CM h
§00000000 oo o LO O u) O O u$ O uj ."* lO >
O K5 t>- O JO-^^ OtOOtOOt^-fOCD C — KJ gOtQOOQOOO r^rHi^COCMOOCQtOiOrO'^^riOLOvOOC^-OOC75C"i— iCM^mS
. r-4 1-( rH i— I f-t
J8S
HANDBOOK ON ENGINEERING.
913
TABLE NO. 23.
Properties of Saturated Steam.
|
Pressure per Square Inch. |
Pressure Above Zero. |
Temperature. |
Latent Heat. |
Total Heat Above Lero. |
Weight of One CubicFoot |
|
Inches of Mercury. |
Pounds per Square Inch. |
Fahr. Deg. |
B. T. U. |
Fahr., B. T. U. |
Pounds. |
|
2.04 |
1 |
102 00 |
1042 96 |
1145 05 |
0030 |
|
4 07 |
2 |
126 26 |
1026 01 |
1152 45 |
.0058 |
|
6.11 |
3 |
141.62 |
1015 25 |
1157 13 |
.0085 |
|
8 14 |
4 |
153 07 |
1007 22 |
1160 62 |
0112 |
|
10 18 |
5 |
1K2.23 |
1000 72 |
1163.44 |
0137 |
|
12 22 |
6 |
170 12 |
995.24 |
1165 82 |
.0163 |
|
14 25 |
7 |
176.91 . |
990 47 |
1167 89 |
0189 |
|
16.29 |
8 |
182.91 |
986.24 |
1169.72 |
0214 |
|
18 32 |
9 |
188 31 |
9*2.43 |
1171 37 |
.0239 |
|
20 36 |
10 |
193 24 |
978 95 |
1172 87 |
.0264 |
|
22 39 |
11 |
197 76 |
975 76 |
1174 25 |
0289 |
|
24 43 |
12 |
201.96 |
972.80 |
1175.53 |
.0313 |
|
'26 46 |
13 |
205 88 |
970 02 |
1176 73 |
.0337 |
|
28 51 |
14 |
209 56 |
967.42 |
1177 85 |
0362 |
|
Gauge Press. |
14 7 |
212 00 |
965 7 |
1178.10 |
.0380 |
|
3 |
15 |
213.02 |
964 97 |
1178.91 |
.0387 |
|
1 3 |
16 |
216.29 |
962.65 |
1179.90 |
0413 |
|
2 3 |
17 |
219 41 |
960 45 |
1180 85 |
.0437 |
|
3 3 |
18 |
222 37 |
958 34 |
1181 76 |
.0462 |
|
4.3 |
19 |
225.20 |
956 34 |
1182.61 |
.0487 |
|
6.3 |
20 |
227.91 |
954.41 |
1183 45 |
.0511 |
|
6.3 |
21 |
230 51 |
952 57 |
1184.24 |
.0536 |
|
7 3 |
22 |
233.01 |
950 79 |
1185.00 |
.0561 |
|
83 |
2.5 |
235.43 |
949 07 |
118>.74 |
.0585 |
|
93 |
24 |
237.75 |
947 42 |
1186 45 |
.0610 |
|
10.3 |
25 |
240.00 |
945 82 |
1167.13 |
.0634 |
|
11 3 |
26 |
242.17 |
944.27 |
1187 80 |
.0658 |
|
12 3 |
27 |
244 28 |
942 77 |
1188 44 |
0683 |
|
is. a |
28 |
246 32 |
941 32 |
1189.06 |
0707 |
|
14 3 |
29 |
248.31 |
939 90 |
1189 67 |
0731 |
|
15.3 |
30 |
250 24 |
938 92 |
1190 26 |
.0755 |
|
16 3 |
31 |
252 12 |
937 18 |
1190 83 |
.0779 |
|
17 3 |
32 |
253.95 |
935 88 |
1191 39 |
0803 |
|
18.8 |
38 |
255.73 |
934.60 |
1191 93 |
0827 |
|
19 3 |
34 |
257 47 |
933 36 |
1192 46 |
.0851 |
|
20.3 |
35 |
259.17 |
932 15 |
1192 98 |
.0875 |
|
21 3 |
36 |
260.83 |
930 96 |
1193 49 |
.0899 |
|
22.3 |
87 |
262 . |
929 80 |
1193.98 |
.092- |
|
23 3 |
38 |
264 04 |
928.67 |
1194 47 |
.0946 |
|
24 3 |
89 |
265 59 |
927.56 |
1194.94 |
0970 |
|
25 3 |
40 |
267.12 |
926.47 |
1195.41 |
.0994 |
|
26 1 |
41 |
268.61 |
925.40 |
1195 86 |
.1017 |
|
27 3 |
42 |
270.07 |
924 35 |
1196 31 |
.1041 |
58
914
HANDBOOK ON ENGINEERING.
TABLE NO. 24.
Properties of Saturated Steam— Continued.
|
Gauge Pressure. |
Pressure Above Zero. |
Temperature. |
Latent Heat. |
Total Heat. Above Zero. |
Weight ot one Cubic Foot |
|
Pounds |
Pounds |
||||
|
per Square |
per Square |
Fahr. Deg. |
B. T. U. |
Fahr.,B.T.U. |
Pounds. |
|
Inch. |
Inch. |
||||
|
28.3 |
43 |
271 50 |
923.33 |
1196.74 |
.1064 |
|
29 8 |
44 |
272 91 |
922.32 |
1197.17 |
.1088 |
|
30.3 |
45 |
274.29 |
921 33 |
1197.WO |
.1111 |
|
31 8 |
46 |
275 65 |
920.36 |
1198 01 |
.1184 |
|
32.3 |
47 |
276 98 |
919.40 |
1198.42 |
.1158 |
|
38 3 |
48 |
278 29 |
918 46 |
1198 82 |
.1181 |
|
34.3 |
49 |
279 58 |
917.54 |
1199.21 |
.1^04 |
|
35. 8 |
60 |
280.85 |
916.63 |
1199.60 |
.1227 |
|
36.3 |
61 |
282.09 |
915.73 |
1199 98 |
.1251 |
|
37.8 |
62 |
283 32 |
914.85 |
1200.35 |
. 1274 |
|
38 3 |
53 |
284.53 |
913 98 |
1200 72 |
. 1297 |
|
39 3 |
54 |
285.72 |
913.13 |
1201.08 |
.1320 |
|
40.3 |
65 |
236.89 |
912 29 |
1201 44 |
.1343 |
|
41.3 |
56 |
2S8.05 |
911 46 |
1201.79 |
1366 |
|
42.3 |
57 |
289 11 |
910.64 |
1202.14 |
1388 |
|
43 8 |
68 |
290 31 |
909.83 |
1202.48 |
.1411 |
|
44.3 |
69 |
291 42 |
909.03 |
1202.82 |
1434 |
|
45.3 |
60 |
292 52 |
908.24 |
1203 15 |
.1457 |
|
46.3 |
61 |
293 59 |
907 47 |
1203 48 |
.1479 |
|
47.3 |
62 |
294.66 |
906.70 |
1203.81 |
.1502 |
|
48.8 |
63 |
295.71 |
90.3.94 |
1204.13 |
.1524 |
|
49 8 |
64 |
296.75 |
905.20 |
1204.44 |
.1347 |
|
60.3 |
65 |
297.77 |
904 46 |
1-204.76 |
.1569 |
|
61 3 |
66 |
298.78 |
903.73 |
1205.07 |
.1592 |
|
62 8 |
67 |
299.78 |
903.01 |
12U5 37 |
.1614 |
|
53 3 |
68 |
800 77 |
902.29 |
1205 67 |
.1637 |
|
54.3 |
69 |
301.75 |
901.59 |
1205.97 |
.1659 |
|
55.3 |
70 |
802.71 |
900.89 |
1206.26 |
.1681 |
|
66.3 |
71 |
303.67 |
900 21 |
1206 56 |
.1708 |
|
67.3 |
78 |
304 61 |
899.52 |
1200 84 |
.1725 |
|
68.8 |
73 |
805 55 |
898 85 |
1207.13 |
.1748 |
|
59.8 |
74 |
306.47 |
898 18 |
1207 41 |
.1770 |
|
60.8 |
75 |
307 88 |
897 52 |
1207 69 |
1792 |
|
61 8 |
76 |
308.29 |
896.87 |
1207.96 |
1814 |
|
62.3 |
77 |
309.18 |
896 23 |
1208.24 |
.1836 |
|
68.8 |
78 |
310.^6 |
895 69 |
1208 51 |
.1857 |
|
64.8 |
79 |
310. i,4 |
894.95 |
1208 77 |
.1879 |
|
65 3 |
80 |
314.81 |
894 33 |
1209 04 |
.1901 |
|
66 3 |
81 |
312.67 |
893 70 |
1209 30 |
.1923 |
|
67-8 |
82 |
313 52 |
893 09 |
1209 56 |
.1945 |
|
68 3 |
83 |
314.36 |
892 48 |
1209 82 |
.1967 |
|
69.3 |
84 |
315.19 |
891 88 |
1210.07 |
.1988 |
|
70 3 |
85 |
316 02 |
891 28 |
1210.32 |
.2010 |
|
71.8 |
86 |
316.83 |
890 . 69 |
1210.57 |
.2082 |
|
72.8 |
87 |
317.65 |
890.10 |
1210 82 |
.2053 |
HANDBOOK ON ENGINEERING.
915
TABLE NO. 25.
Properties of Saturated Steam — Continued.
|
Gauge Pressure. |
Pressure Above Zero. |
Temperature |
Latent Heat. |
Total Heat. Above Zero. |
Weight of One CubicFoot. |
|
Pounds |
Pounds |
||||
|
per Square |
per Square |
Fahr. Deg. |
B. T. U. |
Fahr.,B.T.U. |
Pounds. |
|
Inch. |
Inch. |
||||
|
73.8 |
88 |
318 45 |
889.52 |
1211.06 |
.2075 |
|
74 8 |
89 |
319.24 |
888.94 |
1211.81 |
.2097 |
|
75 3 |
90 |
320.03 |
888.37 |
1211.55 |
.2118 |
|
76.3 |
91 |
820.82 |
837 80 |
1211.79 |
.2130 |
|
77.3 |
92 |
321 59 |
887.24 |
1212 02 |
.2160 |
|
78.3 |
93 |
322 36 |
886 68 |
1212.26 |
.2182 |
|
79.8 |
94 |
323 12 |
886.13 |
1212.49 |
.2204 |
|
80 3 |
95 |
323 88 |
885.58 |
1212.73 . |
.2224 |
|
81.3 |
96 |
824 63 |
885.04 |
1212.95 |
.2245 |
|
82.3 |
97 |
325.37 |
884.50 |
1213.18 |
2266 |
|
88 3 |
98 |
326 11 |
883 97 |
1213.40 |
.2288 |
|
84.3 |
99 |
326.84 |
883 44 |
1213 62 |
.2309 |
|
85.8 |
100 |
327 57 |
882.91 |
1213.84 |
.2330 |
|
86.3 |
101 |
328 29 |
882 39 |
1214.06 |
.2301 |
|
87 3 |
102 |
329 00 |
881 87 |
1214.28 |
2371 |
|
88.3 |
103 |
829 71 |
881-35 |
1214.50 |
.2392 |
|
89.8 |
104 |
330.41 |
880 84 |
1214.71 |
.2418 |
|
90 3 |
105 |
331.11 |
880.34 |
1214.92 |
.2434 |
|
91.3 |
106 |
381.80 |
879.84 |
1215.14 |
.2454 |
|
92.8 |
107 |
332 49 |
879 34 |
1215.35 |
.2475 |
|
93.3 |
108 |
333 17 |
878 84 |
1215.56 |
.2496 |
|
94.3 |
109 |
333.86 |
878 35 |
1215.76 |
.2616 |
|
95.8 |
110 |
834.52 |
877 86 |
1215 97 |
.2537 |
|
96.3 |
111 |
335 19 |
877 37 |
1216.17 |
.2558 |
|
97 .3 |
112 |
335 85 |
876.89 |
1216.37 |
.2578 |
|
98 3 |
113 |
336.51 |
876 41 |
1216.57 |
.2599 |
|
99.3 |
114 |
337 16 |
875 94 |
1216.77 |
.2619 |
|
100 3 |
115 |
337.81 |
875.47 |
1216 97 |
.2640 |
|
101.3 |
116 |
838 45 |
875 40 |
1217.17 |
.2661 |
|
102 3 |
117 |
339.10 |
874.53 |
1217.36 |
.2681 |
|
103 3 |
118 |
339 73 |
874.07 |
1217 66 |
.2702 |
|
104 3 |
119 |
340 36 |
873 61 |
1217 75 |
2722 |
|
105 8 |
120 |
340.99 |
873 15 |
1217 94 |
.2742 |
|
106 H |
121 |
311 61 |
872 70 |
1218.13 |
.2762 |
|
107 3 |
122 |
342.23 |
872 25 |
1218.32 |
.2782 |
|
108.8 |
123 |
342 85 |
871 80 |
1218.51 |
.2802 |
|
109 3 |
124 |
343 46 |
871 35 |
1218.69 |
.2822 |
|
110 3 |
125 |
344 07 |
870 91 |
1218.88 |
.2842 |
|
111.3 |
126 |
344 67 |
870 47 |
121906 |
.2862 |
|
112 8 |
127 |
845 27 |
870 03 |
1219.27 |
.2882 |
|
113.3 |
128 |
345 87 |
869.59 |
. 121943 |
.2902 |
|
114.3 |
129 |
346.45 |
869 16 |
1219.61 |
2922 |
|
115.3 |
130 |
347.05 |
868.73 |
1219 79 |
.3942 |
|
116 8 |
131 |
347.64 |
868.30 |
1219.97 |
2961 |
916
HANDBOOK ON ENGINEERING.
TABLE NO. 26.
Properties of Saturated Steam — Continued.
|
Gauge Pressure. |
Pressure Above Zero. |
Temperature. |
Latent Heat. |
Total Heat. Above Zero. |
Weight of One CublcFoot. |
|
Pounds |
Pounds |
||||
|
per Square |
per Square |
Fahr. Deg. |
B. T. U. |
Fahr., B. T. U |
Pounds. |
|
Inch. |
Inch. |
||||
|
117.3 |
13-2 |
348 22 |
867.88 |
1220 15 |
.2981 |
|
118 3 |
133 |
348.80 |
867 46 |
1^0 32 |
.3001 |
|
119.3 |
134 |
349.38 |
867.03 |
It'iU 50 |
.3020 |
|
120 3 |
135 |
349.95 |
866 62 |
U<0 67 |
. 3u»() |
|
121 3 |
136 |
350.52 |
866 20 |
12-/0 85 |
.3u60 |
|
122.3 |
137 |
351.08 |
866 79 |
1221 02 |
3u79 |
|
123 3 |
138 |
351.75 |
865.38 |
1-^1 19 |
3u99 |
|
124.3 |
139 |
352 21 |
864 97 |
12.51 36 |
.31i8 |
|
125.3 " |
ito |
352.76 |
864 56 |
1221 53 |
.3138 |
|
126.3 |
141 |
363.31 |
864.16 |
1221 70 |
.3158 |
|
127 3 |
142 |
358.86 |
863.76 |
12-21 87 |
.3178 |
|
128.3 |
143 |
354.41 |
863.36 |
1222 03 |
.3199 |
|
129.3 |
144 |
354.96 |
86-2.96 |
1222.20 |
3219 |
|
130 3 |
145 |
355 50 |
862 56 |
1222 36 |
.3*39 |
|
131.3 |
146 |
356 03 |
862 17 |
1222.53 |
.3209 |
|
132.3 |
147 |
,85657 |
861.78 |
1*2-2 69 |
.3'/79 |
|
133.3 |
148 |
357.10 |
861 39 |
1222.85 |
3299 |
|
134 3 |
149 |
357 63 |
861 00 |
1223 01 |
.3319 |
|
135.3 |
150 |
358 16 |
860.62 |
1223.18 |
.3340 |
|
136 3 |
151 |
358 68 |
860 23 |
1223 33 |
.3358 |
|
137 3 |
152 |
359 20 |
859.85 |
1223 49 |
.3376 |
|
138 3 |
153 |
359 72 |
859 47 |
1223 65 |
3394 |
|
139.3 |
154 |
360.28 |
859 10 |
12-23 81 |
.3412 |
|
140.8 |
155 |
360.74 |
858.72 |
1223.97 |
.3430 |
|
141.3 |
156 |
361.26 |
858 35 |
1224.12 |
.3448 |
|
142.3 |
157 |
361.76 |
857 98 |
1224 28 |
.3466 |
|
143 3 |
158 |
362.27 |
857.61 |
1224.43 |
.3484 |
|
144 3 |
159 |
362.77 |
857 24 |
1224 58 |
.3502 |
|
145.3 |
160 |
363.27 |
856.87 |
1224.74 |
.3520 |
|
146.3 |
161 |
363 77 |
856 50 |
1224 89 |
.3539 |
|
147.3 |
162 |
364.27 |
856.14 |
1225.04 |
.3558 |
|
148.3 |
163 |
364 76 |
855.78 |
1225.19 |
.3577 |
|
149. 3 |
164 |
365 25 |
855 42 |
1225 34 |
3596 |
|
150.3 |
165 |
365.74 |
855 06 |
1225.49 |
.3614 |
|
151.3 |
166 |
366 23 |
854 70 |
12-25 64 |
.3633 |
|
153.3 |
167 |
366.71 |
854 35 |
1225.78 |
3652 |
|
153 3 |
168 |
367.19 |
853 99 |
1225.93 |
.3671 • |
|
154.3 |
169 |
367 68 |
853.64 |
1226 08 |
.8690 |
|
155.3 |
170 |
368.15 |
853.29 |
1226.22 |
.3709 |
|
156.3 |
171 |
368.63 |
852 94 |
1226.37 |
.3727 |
|
157.3 |
172' |
369.10 |
852 59 |
1226.51 |
.3745 |
|
158.3 |
173 • |
369.57 |
852.25 |
1226 66 |
3763 |
|
159.3 |
174 |
870.04 |
851.90 |
1226 80 |
3781 |
|
160.3 |
175 |
370 51 |
851.56 |
1226.94 |
.3791) |
|
161 3 |
176 |
370.97 |
851 22 |
1227.08 |
.3817 |
HANDBOOK ON ENGINEERING.
917
TABLE NO. 27.
Properties of Saturated Steam — Continued.
|
Gauge Pressure. |
Pressure Above Zero. |
Temperature. |
Latent Heat. |
Total Heat. Above Zero. |
Weight of One Cubic Foot. |
|
Pounds |
Pounds |
||||
|
per Square Inch. |
per Square Inch. |
Fahr. Dcg |
B. T. U. |
Fabr., B. T. U. |
Pounds. |
|
162 3 |
177 |
371.44 |
850.88 |
1227 32 |
.3835 |
|
163 3 |
178 |
371 bO |
850 54 |
1227-37 |
.3853 |
|
164.3 |
179 |
372 36 |
850 20 |
12-27.61 |
.3871 |
|
165.3 |
180 |
372.82 |
849 86 |
1227 65 |
.3889 |
|
166 3 |
181 |
373 27 |
849 53 |
1227 78 |
.3907 |
|
167.3 |
182 |
373 73 |
849 20 |
1227 92 |
.3925 |
|
168.3 |
183 |
374 18 |
848 86 |
1228.06 |
.3944 |
|
169 3 |
184 |
374 63 |
848 53 |
1228 20 |
3962 |
|
170.3 |
185 |
375 08 |
848 20 |
1228.33 |
.3980 |
|
171 3 |
186 |
375.52 |
847.88 |
1228.47 |
.3999 |
|
172 3 |
187 |
375 97 |
847,55 |
1228 61 |
.4017 |
|
173 3 |
188 |
376 .4-1 |
847 22 |
1228 74 |
.4035 |
|
174.3 |
189 |
376.85 |
846 90 |
1228 87 |
.4063 |
|
175.3 |
190 |
377 29 |
846 58 |
1229.01 |
.4072 |
|
176.3 |
191 |
377.72 |
846.23 |
1229.14 |
.4089 |
|
177 3 |
192 |
378 16 |
845.91 |
1229.27 |
.4107 |
|
178.3 |
193 |
378 59 |
845 62 |
1229.41 |
.4125 |
|
179 3 |
194 |
379 02 |
845 30 |
1229.54 |
.4143 |
|
180.3 |
195 |
379 45 |
844.99 |
1229.67 |
.4160 |
|
181.3 |
196 |
379 97 |
844 68 |
1229.80 |
.4178 |
|
182 3 |
197 |
380.30 |
844 36 |
1229.93 |
.4196 |
|
183.3 |
198 |
380 72 |
84* 05 |
1230.06 |
.4214 |
|
184.3 |
199 |
381.15 |
843 74 |
1230 19 |
.4231 |
|
185 3 |
200 |
381.57 |
843 43 |
1230.31 |
.4249 |
|
186.3 |
201 |
381 99 |
84? 12 |
1230 44 |
.4266 |
|
187.3 |
202 |
382.41 |
84° 81 |
1230 67 |
.4283 |
|
188 3 |
203 |
382 82 |
8*? 50 |
1230.70 |
.4300 |
|
189 3 |
204 |
383 24 |
8'? 20 |
1230 82 |
.4318 |
|
190 3 |
205 |
383.65 |
841 89 |
1230 95 |
.4335 |
|
191.3 |
206 |
384.06 |
8*1 59 |
1231 07 |
.4352 |
|
192 3 |
207 |
384.47 |
8' 1.29 |
1231.20 |
.4369 |
|
193 3 |
208 |
384.88 |
840.99 |
1231 32 |
.4386 |
|
194 3 |
209 |
385.28 |
8^0.69 |
1231 45 |
.4403 |
|
195.3 |
210 |
385 67 |
840.39 |
1231 57 |
.4421 |
918
HANDBOOK ON ENGINEERING.
TABLE NO. 28.
|
SWEDES IRON TRANSMIS- |
CRUCIBLE CAST STEEL |
||||||||||||
|
SION OR HAULAGE |
TRANSMISSION OR |
||||||||||||
|
ROPES. |
HAULAGE ROPES. |
||||||||||||
|
7 Wires ta the Strand. Hemp |
7 Wires to the Strand. Hemp |
||||||||||||
|
Centre. |
Centre. |
||||||||||||
|
d |
d® |
bflOQ |
.«, |
d |
bo OD |
• . |
^ |
||||||
|
Diameter in Inches. |
i Price per Foot 1 t Cents. |
Breaking Strai in Tons of 2.0C Pounds. |
Proper Workln Load in Ton of 2,000 Lbs. |
ised for Derricki Ferries, Trang |
Average Weigh per Foot. |
Minimum Size of Drums or Sheaves in Ft |
Diameter in Inches. |
Price per Foot in Cents. |
Breaking Strai in Tons of 2,000 Pounds. |
Proper Workm Load in Tons of 2,000 Pound |
sed for Derrick* jrries, Transmie |
Average Weigh per Foot. |
Minimum Size of Drums or Sheaves in Ft. |
|
9-32 5-16 |
3| |
1.4 17 |
i |
aS "5 "So a, be .; |
.15 |
li J* |
9-32 5-16 |
4^ |
2| 3 |
I |
s£ |
.15 |
3 |
|
!7-16 |
4| 6i |
2 4 3 3 |
i |
£*~y o §«* |
.22 .30 |
2 2| |
7!6 |
if |
5 63 |
1 |
figs |
.22 .30 |
P |
|
9-16 | |
8 10 |
4 2 5.3 6.6 |
1 |
m SSI |
.39 .50 .64 |
| |
9-16 | |
1\ 9 11 |
83 io| 13 |
2 |
|2| |
.39 .50 .64 |
1 |
|
Tl-16 |
12 |
7.9 |
i |
«*gpL, |
.75 |
4 |
11-16 |
13i |
16 |
3 |
SJi ij |
.75 |
6* |
|
If |
14 23 29 86 |
9.3 12. 16. 20. 24. |
! 2-5 ; 1-5 4-5 |
CD 08«_, Hj |
.89 1.20 1.58 2 00 2.45 |
1 |
it |
16 22 28 36 43 |
19 24 32 40 48 |
? 10 |
e Ropes s, Steam L of Powe |
.89 1.20 1.58 2.00 2 45 |
1 |
|
]• |
43 |
29. |
5 4-5 |
J5s |
3 00 |
8 |
if |
51 |
58 |
12 |
y> rtQ |
3.00 |
JIT |
|
H • |
51 |
34. |
7 |
H |
8 55 |
84 |
if |
60 |
68 |
14 |
go-s |
3 55 |
13 |
|
• |
HANDBOOK ON ENGINEERING.
919
TABLE NO. 29.
|
CRUCIBLE CAST STEEL |
SWEDES IRON PLIABLE |
||||||||||||
|
PL LE HOISTING |
HOISTING ROPES. |
||||||||||||
|
ROPES. |
|||||||||||||
|
19 Wires to the Strand. Hemp |
ires to the Strand. Hemp |
||||||||||||
|
Centre. |
Centre. |
||||||||||||
|
a |
|| |
§1 |
beg |
44 bo |
,j |
a |
a |
*1 |
bo O QQ |
1 |
«H |
||
|
I |
I fa |
£c* »* |
o o1 |
§• ^ |
N «* «25 |
.9 |
I |
L| |
03 O1 EH . |
l|* |
Ij |
||
|
(4 ) 0) if i1"1 |
\ Price per | Cents. |
Breaking in Tons < Pounds. |
III |
ll? |
o o g£ |
Minimum of Drumi Sheaves |
Diameter Inches. |
Price per Cents. |
Breaking in Tons < 2,000 Pou |
Diam. of Rope of Strength |
cL^cT £3* |
|| |
Minimum Drums o Sheaves |
|
>16 |
9 3 |
? |
i! |
;i |
. .10 .15 .22 |
u |
5-16 i |
P |
11.20 1.70 2.50 |
9-16 |
1 |
.10 15 .22 |
1 |
|
-16 |
10 |
7 |
li |
1 2-5 |
.30 |
2* |
7-16 |
7* |
3.40 |
1 |
K |
.30 |
•i |
|
t |
11 |
9 |
it |
1 4-5 |
.39 |
8 |
4.40 |
1$ |
1 |
.39 |
ii |
||
|
-16 |
12 |
11 |
i 9-16 |
2 1-5 |
.50 |
2§ |
9-16 |
10 |
5.60 |
1 5-16 |
1 1-10 |
.50 |
2 |
|
14 |
14 |
1| |
24-5 |
.64 |
34 |
12 |
6 80 |
1* |
If |
.64 |
24 |
||
|
18 |
20 |
21 |
4 |
.89 |
4 |
s |
16 |
9.70 |
if |
4 |
.89 |
3 |
|
|
23 |
26 |
2| |
5 1-5 |
1.20 |
4i |
V |
20 |
13. |
2 |
2 3-5 |
1 20 |
3'i |
|
|
30 38 |
34 42 |
3 3| |
6 4-5 8 2-5 |
1 58 2.00 |
i* |
I |
26 38 |
17. 21. |
P |
3 2-5 4 15 |
1.58 2 00 |
*I |
|
|
46 |
52 |
3| |
10 |
2.45 |
61 |
]1 |
40 |
25. |
5 |
2.45 |
|||
|
56 |
63 |
4 |
12 |
3.00 |
7 |
]a |
48 |
31. |
U |
6 1-5 |
3.00 |
6 |
|
|
66 74 93 |
77 86 106 |
1 |
15 17 20 |
3.55 4.15 5.25 |
I |
ii |
57 63 80 |
36. 42. 48. |
4 41 |
7 1-5 8 2-5 9 3-5 |
3.55 4 15 5.25 |
64 |
|
|
111 |
125 |
25 |
6.30 |
12 |
2 |
92 |
62. |
4} |
12 2-5 |
6.30 |
9* |
||
|
I |
142 |
160 |
32 |
8 00 |
13 |
2* |
117 |
78. |
5i |
15 3-5 |
8 00 |
10 |
920
HANDBOOK ON ENGINEERING.
TABLE NO. 30.
|
19 Wires to the Strand. Hemp Centre. |
WIRE ROPE FOR INCLINED PLANES. For the benefit of those desiring to use wire rope on slopes, inclined Planes, etc , a table by which the strain produced by any load may be readily ascertained. This table gives only the strain pro- duced on a rope by a load of one ton of two thousand pounds, an allowance for rolling friction being made. An addi- tional allowance for the weight of the rope will have to be made. Example: For an inclination of 100 feet in 100 feet, corresponding to an angle of 45°, a load of 2,000 pounds will produce a strain on the rope of 1,419 pounds, and for a load of 9,000 pounds the strain on the rope will be |
||||
|
Inches. |
Price per Foot, in Cents. |
Breaking Strain in Tons of 2,000 Pounds. |
Proper Working Load in Tons of 2,000 Lbs. |
Average Weight per Foot. |
Minimum Size of Drums or Sheaves in Ft. |
|
r-16 i-,6 k |
14 15 17 19 22 28 35 45 54 65 80 95 112 136 160 220 |
8 10 13 15 20 30 40 50 63 76 95 115 130 160 220 235 |
2^ P 1 13 16 19 22 25 33 40 |
.22 .30 .39 .50 .64 .89 1.20 1.58 2 00 2 45 3.00 3.55 4.15 5.25 6 30 8.00 |
2 2* P 4 5 6 7 8 9 10 11 12 13 14 15 |
|
>uuu |
|||||
|
Elevation in • 100 Feet. |
bo Boa •CM 3 |
"fl «'g |
evation in DO Feet. |
bo fl - •OM S &CJ- £ |
*g 1*1. S§«2 |
|
7 Wires to the Strand. Hemp Centre. |
31"1 |
||||
|
5 10 1ft 20 25 30 35 40 45 50 65 60 65 70 75 80 85 90 |
11 1-5 144 19 1-5 21 5-6 24i 28 5-6 31 33 1-12 35 37 38f 40i 42 |
112 211 308 404 497 586 673 754 832 905 975 1,040 1,100 1,156 1,210 1,260 1,304 1,347 |
95 100 105 110 115 120 125 130 135 140 145 IftO 155 160 165 170 176 |
455 46* tTf 49 50; 5L 52i 53i 54l- 55i- 56 57; 68 68 4-5 59J 60i |
1,385 1,419 1,457 1,487 1,516 1,544 1,570 1,592 1,614 1,633 1,653 1,671 1,689 1,703 1,717 1,729 1,742 |
|
h6 |
15 18 25 38 42 63 64 76 92 |
11 14 18 28 36 48 60 72 82 100 |
2 !» 6 7 11 18 16 20 |
.39 .60 .64 .89 1.20 1 58 2 00 2 45 3.00 3 55 |
3 4 6 7 8 9 10 11 12 |
A factor of safety of five to seven times should be taken; that is, the working load on the rope should only be one-fifth to one- seventh of its break- ing strength. As a rule, ropes for shafts should have a factor of safety of five, and on inclined planes, where the wear is much greater, the factor of safety should be seven.
HANDBOOK ON ENGINEERING.
921
TABLE NO. 81.
Table of Transmission of Power by Wire Ropes.
This table is based upon scientific calculations, careful observations and expert* ence, and can be relied upon when the distance exceeds 100 feet. We also find by experience that it is best to run the wire rope transmission at the medium number of revolutions indicated in the table, as it makes the best and smoothest running transmission. If more power is needed than is indicated at 80 to 100 revolutions, choose a larger diameter of sheave.
|
Diameter of Sheave in ft. I |
Number of Revolutions. |
Diameter of Rope. |
Horse-Power. |
Diameter of Sheave in Ft. |
Number of Revolutions. |
^ |
Horse- Power. |
||
|
3 |
80 |
i |
8 |
. 7 |
140 |
9-16 |
35 |
||
|
3 |
100 |
3| |
8 |
80 |
i |
26 |
|||
|
3 |
120 |
I |
4 |
8 |
100 |
32 |
|||
|
3 4 |
140 80 |
I |
Ji |
8 8 |
120 140 |
39 45 |
|||
|
4 |
100 |
i |
5 |
9 |
80 |
. |
47 48 |
||
|
4 |
120 |
1 |
6 |
9 |
100 |
9-16| |
58 ' 60 |
||
|
4 |
140 |
1 |
7 |
9 |
120 |
9 16§ |
69 73 |
||
|
5 |
80 |
7-16 |
9 |
9 |
140 |
9 16$ |
82 84 |
||
|
5 |
100 |
7-16 |
11 |
10 |
80 |
g 11 16 |
64 68 |
||
|
5 |
120 |
7-16 |
13 |
10 |
100 |
f 11-16 |
•* |
80 85 |
|
|
5 |
140 |
7 16 |
15 |
10 |
120 |
S 11-16 |
96 102 |
||
|
6 |
80 |
* |
14 |
10 |
140 |
i 11-16 |
i 112 1 119 |
||
|
6 |
100 |
i |
17 |
12 |
80 |
j 11 16} |
93 99 |
||
|
6 |
120 |
i |
20 |
12 |
100 |
11 16| |
! 124 |
||
|
140 |
|||||||||
|
6 |
140 |
} |
23 |
12 |
120 |
11-16J |
149 |
||
|
7 |
80 |
9-16 |
20 |
12 |
140 |
i |
173 |
||
|
141 |
|||||||||
|
7 |
100 |
9-16 |
25 |
14 |
80 |
Hi |
148 |
||
|
176 |
|||||||||
|
7 |
1-20 |
9-16 |
80 |
14 |
100 |
1 1* |
185 |
922
HANDBOOK ON ENGINEERING.
§|ssz
5S8
§ *Sf
JflKSS
8|«
2 S?J«
IJRSa g|n«a
§ [H88
ia&
555
1
Sll
I
S o. p v n S
« S 1-S
tl
a
ts a
22 5 i
ss»l! l°!.1£^
II1
P4CO (,
i5S
at
S-
&&s
HANDBOOK ON ENGINEERING.
923
TABLE NO. 33.
Percentage of Power Gained by Adding a Condenser, the Speed and Point of Cut-Off Remaining the Same.*
VACUUM •== 24.5 INCHES.
|
Per Cent |
Per Cent |
Per Cent |
Per Cent |
||||
|
M. K. P. |
of Power |
M. B. P. |
of Power |
M. E. P. |
of Power |
M. E. P. |
of Power |
|
Gained. |
Gained. |
Gained. |
Gained. |
||||
|
5 |
250 |
17 |
70.5 |
38 |
31,6 |
62 |
19.8 |
|
6 |
200 |
18 |
66.6 |
40 |
30 |
64 |
18.7 |
|
7 |
171.4 |
19 |
63.1 |
42 |
28.5 |
66 |
18.1 |
|
8 |
150 |
20 |
60 |
44 |
27.2 |
68 |
17.6 |
|
9 |
133.3 |
22 |
54.5 |
46 |
26.08 |
70 |
17.1 |
|
10 |
120 |
24 |
50 |
48 |
25 |
72 |
16.6 |
|
11 |
109 |
26 |
46.1 |
50 |
24 |
74 |
16. S |
|
12 |
100 |
28 |
44.3 |
52 |
23.07 |
76 |
15.7 |
|
13 |
92.3 |
30 |
40 |
54 |
22.2 |
78 |
15.9 |
|
14 |
85.7 |
32 |
37.5 |
56 |
21.4 |
80 |
15 |
|
15 |
80 |
34 |
35.2 |
58 |
20.6 |
82 |
14.63 |
|
16 |
76 |
36 |
33.3 |
60 |
20 |
85 |
14.12 |
Calculated gain due to vacuum, friction not considered.
TABLE NO. 34.
glies of Cylinders Usually Furnished for Compound Pumps, and Corresponding Ratios of Expansion.
|
Diameter High Pressure Cylinder. |
Diameter Low Pressure Cylinder. |
Ratio of Expansion. |
|
6 |
10 |
2.78 |
|
7 |
12 |
2.94 |
|
8 |
12 |
2.25 |
|
9 |
14 |
2.42 |
|
10 |
16 |
2.56 |
|
12 |
18 |
2.25 |
|
14 |
20 |
2.04 |
|
16 |
24 |
2.25 |
|
18 |
30 |
2.77 |
924
HANDBOOK ON ENGINEERING.
TABLE NO. 35.
Indicated Horse-power for One Pound of Mean Pressure.
|
Diameter of Cylinder in Inches. |
SPEED ov PISTON IN FEET PER MINUTE. |
|||||||
|
240 |
300 |
350 |
400 |
450 |
500 |
550 |
600 |
|
|
6 |
0-205 |
0-256 |
0-299 |
0-342 |
0-385 |
0-428 |
0-471 |
0-513 |
|
;y |
0-279 |
0-348 |
0-408 |
0-466 |
0-524 |
0-583 |
0641 |
0-699 |
|
8 |
0-365 |
0-456 |
0-532 |
0-608 |
0-685 |
0-761 |
0-837 |
0-912 |
|
9 |
0-462 |
0-577 |
0-674 |
0-770 |
0866 |
0-963 |
1154 |
|
|
10 |
0-571 |
0-714 |
0-833 |
0-952 |
1-071 |
1-190 |
1 \ A)§ |
1-428 |
|
11 |
0-691 |
0-864 |
1*008 |
1-153 |
1-296 |
1-44 |
1-584 |
1-728 |
|
12 |
0-820 |
1-025 |
1-195 |
1-366 |
1-540 |
1-708 |
1-880 |
2-050 |
|
13 |
0-964 |
1-206 |
1-407 |
1-608 |
1-809 |
2-01 |
1-211 |
2-412 |
|
14 |
1-119 |
1-398 |
1-631 |
1-864 |
2-097 |
2-331 |
2-564 |
2-797 |
|
15 |
1-285 |
1-606 |
1-873 |
2131 |
2-409 |
2-677 |
2-945 |
3-212 |
|
16 |
1-461 |
1-827 |
2-131 |
2-436 |
2-741 |
3-045 |
3-349 |
3-654 |
|
17 |
1-643 |
2-054 |
2*396 |
2-739 |
3-081 |
3-424 |
3-V66 |
4-108 |
|
18 |
1-849 |
2-312 |
2-697 |
3-083 |
3-468 |
3-854 |
4-239 |
4-624 |
|
19 |
2-061 |
2-577 |
3-006 |
3-436 |
3-865 |
4-297 |
4-724 |
5-154 |
|
20- |
2-292 |
2-855 |
3-331 |
3-807 |
4-285 |
4-759 |
5-234 |
5-731 |
|
^21 |
2-518 |
3148 |
3-672 |
4-197 |
4-722 |
5-247 |
5-771 |
6-296 |
|
22 |
2-764 |
3-455 |
4-031 |
4-607 |
5-183 |
5-759 |
6-334 |
6-911 |
|
25 |
3-021 |
3-776 |
4-405 |
5-035 |
5-664 |
6-294 |
6-923 |
|
|
24 |
3-289 |
4-111 |
4-797 |
5-482 |
6167 |
6-^3 |
7-538 |
8*223 |
|
25 |
3-569 |
4-461 |
5-105 |
5-948 |
6-692 |
7-436 |
8173 |
8-923 |
|
26 |
3-861 |
4-826 |
5-630 |
6-435 |
7-239 |
8-044 |
8-848 |
9-652 |
|
27 |
4-159 |
5-199 |
6-066 |
6-932 |
7-799 |
8-666 |
9-532 |
10-399 |
|
28 , |
4-477 |
5-596 |
6-529 |
7'462 |
8-395 |
9-328 |
10261 |
11-193 |
|
29 |
4-805 |
6-006 |
7-007 |
8-008 |
9-009* |
10-01 |
11-011 |
12-012 |
|
30 |
5-141 |
6-426 |
7-497 |
8-568 |
9-639 |
10-71 |
11-781 |
12-852 |
|
31 |
5-486 |
6-865 |
8-001 |
9-144 |
10-237 |
11-43 |
12-573 |
13-716 |
|
32 |
5-846 |
7-308 |
8-526. |
9-744 |
10-962 |
12-18 |
13--398 |
14616 |
|
33 |
6-216 |
7-770 |
9-065 |
10-360 |
11-655 |
12-959 |
14.-245 |
15-54 |
|
34 |
6-59 |
8-238 |
9-611 |
10-984 |
12-357 |
13-73 |
15103 |
16;476 |
|
35 |
6-993 |
8-742 |
10-199 |
11-656 |
13-113 |
14-57 |
16-027 |
17-434 |
|
36 |
"7-401 |
9-252 |
10-734 |
12-336 |
13-878 |
15-42 |
16-962. |
18-50} |
|
37 |
7-819 |
9-774 |
11-403 |
13-032 |
14-861 |
16-29 |
17-519 |
19-543 |
|
33 |
8-246 |
1(7-508 |
12-026 |
13-744 |
15-462 |
17'18 |
18-898 |
20-61.6 |
|
39 |
8-618 |
10-86 |
12-67 |
14-48 |
16-29 |
18-1 |
19-91 |
21-61 . |
|
40 |
9-139 |
11-424 |
13-323 |
15-232. |
17-136 |
19-04 |
20-94.4 |
22-843 |
|
41 |
9-604 |
12-006 |
14-007 |
16-008 |
18-009 |
20-00 |
22-011 |
24-012 |
|
42 |
10-065 |
12-594 |
14-693 |
16-792 |
18-901 |
20-99 |
23-089 |
25-188 |
|
43 |
10-56 |
13-20 |
15 :4 |
17-6 |
19-8 |
22-00 |
242 |
26-4 |
|
44 |
11-046 |
13-818 |
16-121 |
18-424 |
20-727 |
23-03 |
25-333 |
27-636 |
|
45 |
11-563 |
14-454 |
16-863 |
19-272 |
21-681 |
24-09 |
26S399 |
28-908 |
|
46 |
12-086 |
15128 |
17«626 |
20-144 |
22-662 |
25-18 |
27-698 |
30<216 |
|
47 |
12-614 |
15-768 |
18-396 |
21024 |
23-652 |
26-28 |
28-908 |
31-536 |
|
48 |
12-816 |
16-446 |
19-187 |
21-928 |
24-669 |
27-41 |
30-151 |
32-152 |
|
49 |
12-933 |
17-142 |
19-999 |
22-856 |
25-713 |
28-57 |
33-427 |
34-2B4 |
|
60 |
14-28 |
17-85 |
20-825 |
23-8 |
26-775 |
29-75 |
32-725 |
35'7 |
NOTE. — Mean effective pressure =^Mean prewure minus the back preasur*
HANDBOOK ON ENGINEERING.
925
i
|
pR |
g |
||
|
Ml |
S |
||
|
-S |
S |
||
|
~ |
« |
||
|
a |
CO |
||
|
M s |
« |
IO |
|
|
OQ H |
« |
Z 2 |
s |
|
h 0 K |
1. |
EXPANS |
« |
|
RACTIO |
*g |
S o |
o m |
|
to fe £ |
.0 |
I |
CO |
|
N o -I? |
^ |
g eo |
|
|
^ |
• |
||
|
« |
„ |
||
|
HIM |
0 00 |
||
|
* |
0 |
||
|
i»d |
II 9JV oins |
nbg 69JJ |
* 00 IO 00 tO 00
i
i 1-
4
1
926
HANDBOOK ON ENGINEERING.
•un*e?s I d
£ J9-JOOTBIQ l£«JO:ow^^^^iO^WOO?OOt-t^t-t-coaocoacoo
£
QQ ~~-puno£ M
I
0 nf a _^^v
H *s;^ eo^^ootrx^cTp^w r^»rft^G^^co^QoT^i^r-r-^co'ocrrf'*rn"co
H °O '-irn*Hi-(rHr-n-(5<tc^c<?i5c<»cowvccoco.-oow*«5
2 ^ ^ ^
h 6
lj;
£
Jl ^
S 2?
oi-^
2
- s
• 4) i^j
O vi ^9
K fi J3
Q 05
PJ 5 Iftl9 ^MNO'Cb-org00^^^1^^
S -
1 g
%
2
04 I
HANDBOOK ON ENGINEERING.
927
51
el
Hi
H
I *«*
- 8
111
2
to
f-H^n^Hr-idcqc^cqc^cococc
CO CO •"
<<?*0*<M<N<M<N<NCOCOCOCO
5 « <N S5 « «
I I
bfi
CO 1
co
ai|f J9d -
uonong
n|j<j jori -
100^ :._ _
jo; pajinboif
J8d
edu uonong
10000000000000
i-rc^rco^H^t^ cT-wTotT
928
HANDBOOK ON ENGINEERING.
o
•199
UJrOO I*" igigg^
9999
> cp cj
left
»b»otb»b
lHOOO
OOt>iO»O
>b»btorb
iiil
it}*&*f<£ aisss
893
ipipipip
»b to to to
QQQ^
rHt-
Cllr-lrHrH
a
86S8
ro?o»OK5
oaoicQC
1-l«
3 Cj5 C5
HANDBOOK ON ENGINEERING.
929
8588&88S88588&88&88&88B88S88S8
88S8S8S888SSSSS8SSS88S88S8S88S
S8S8S8S8S8S8S8S8S8S8S8S8S8S8S8
888885888888888888888888888888
88888888888888888888888S888888
930
HANDBOOK ON ENGINEERING.
^
• 525
w ^
ss -^
H
g
S9VB.I
jo -api
•isn 01 ppv
•Xjuo Jdnog
et o* c*
B ft' * & X 8-.fi &•••« fi. Sri
c* et
2 3
8 S 8 8 & £ S £ £ 8 8 $ 8
,58 S 8 8
838*8
a s s
s si
o" ©~
55 I
3Z «$.
as
8 3 8
»eo co eo eo
CO CO CO b-
,« co -co ^•eo co co
co co co o co
» CO CO CO CO
^?co ^ ^« co co
CO CO CO S>
SCO CO CO CO
) T* •** CD CO
HANDBOOK ON ENGINEERING.
931
0* C* CM
JQ -y
•;aaj ut
.«'8t
3 % S5
goo
is g
-R
o >o 51
o o oi
T-I rH T-I
CO CO «D 'CO CO CO CO CO
;o O) CO
co co ca
CO CO CO .CO CO O»
CO to CO >O
co co co cq co
S S5
8 § S S
932
HANDBOOK ON ENGINEERING.
jo -s
[«!
8 3 & 3 3 8 S £ £ £
5 5 » « S 55 55
55 £ 8
3 3
CO CO CO CO TO
•isri <n PPY
§ §
a»
§ 8
s s
«*
-B »R -B
J» -^
*- »-|rt
t- o> o
CO CO CO CO
«o. CD eo co oo
*s ^
a s s s a
•J9AVOJ 9SJOH
HANDBOOK ON ENGINEERING.
933
|
<e o •• §11 a o « |
u |
ll 1 g a 4» |
FTERS. |
G |
8$g |
|
|
ill c £ 0 |
&M w |
"«• |
§ i s | 5 S X <M 09 S ° <D + ' |
b 0 I |
a |
000 |
|
Q> * fl |
0^ , |
g i2 5 o |
||||
|
<3^ |
0 § « g 5|§ | |
SB .5 |
3S8 |
|||
|
!i| |
^^ |
«o |
||||
|
J^'5 -0 111 S a » 111 O ® -O |
II |
mil |
l|l |5 "0^0 B d •« § o &10 |
a |
HI |
|
|
2g^ ^-8 |
||||||
|
..111 * if II |
Sen V O |f, |
oo «»» •* ^> |
5 |- 3 « * s a 5 •Jil «« •3 | - rt S |
ts fa — |
283 |
|
|
a* :&s If f^ |
«fl QM |
1|1 §* I ^ £ «3 |
SIZES |
fl |
||
|
w S3 2 & • « S s|i |
M |
S5! 2| |
1 |
H* |
||
|
Isl 2 "S |
<2£ S«g »H *J OD 53£ |
sss |
111 11 ?&3 BS fl! « |
3 M i |
ft 2 eo |
SS6 |
|
«3 V o HI 0 o g |
s5 |
«M *• _0 O ^ •§ « a S . |
fl |
|||
|
si |
'» |
"* |
||||
|
rt 2 fc- |
^£N |
§ ^ "3 fi ° |
||||
|
l| « SS| 4* • fl •5^8 |
II |
S!!8li |
^ ^ 3 •& ^ >, 0 <J o f £ o p« o |
«£ |
•°ss |
|
|
.;• s s, |
•1* |
3£2 ^ ^ P. Hd ^ |
. |
|||
|
||| |
bl |
"* S 2 *» o 5 £ o •2 ^ « $ * 0 & f^ |
c» |
r |
||
|
if |
S o 55 |
w-*o«ot-ao |
5'SS 5 H o o »o 30 a 9..fl o < |
jo jac |
^ |
934
HANDBOOK ON ENGINEERING.
TABLE NO. 40. ROCK DRILLS.
Factor lor Deter mi nine: Free Air Per Minute Required for Rock BYills at 30, 7O, 80, 00, 1OO Pounds Pressure, and Altitudes frditu Sea
|
Level to 10,000 Feet Above. |
||||||
|
i |
FACTOR OF MULTIPLICATION. |
|||||
|
ALTITUDE IN |
ATMOSPHERIC |
PRESSURE AT DRILL |
||||
|
FEET ABoVB |
PRESSURE LBS. |
|||||
|
SEA LEVEL. |
FEU SQlt. IN |
|||||
|
60 Ibs. |
70 Ibs. |
80 Ibs. |
90 Ibs. |
100 Ibs. |
||
|
0 |
14.7 |
.00 |
.133 |
2P. |
.40 |
.535 |
|
600 |
14.46 |
.015 |
.15 |
.28 |
.4-25 |
.663 |
|
1,000 |
14.12 |
.03 „ |
.17 |
31 |
43 |
59 |
|
1,500 |
13 92 |
048 |
19 |
.33 |
,48 |
62 |
|
2,000 |
13.61 |
06 |
.21 |
.35 |
.50 |
.645 |
|
3,000 |
13.10 |
10 |
.25 |
.40 |
.55 |
70 |
|
4,000 |
12.61 |
131 |
.287 |
.443 |
60 |
755 |
|
5,000 |
12 15 |
17 |
33 |
4J6 |
:652 |
81 |
|
6,000 |
11 75 |
.20 |
37 |
.537 |
.705 |
1.87 |
|
7,000 |
11 27 |
.24 |
42 |
69 |
.76 |
1.935. |
|
8,000 |
10 85 |
.282 |
1.4H6 |
.<45 |
.825 |
2.00 |
|
9,010 |
10 45 |
1 32 |
1 51 |
1 70 |
1.90 |
2 07 |
|
10,000 |
10.10 |
1 365 |
1 56 |
1.755 |
1.963 |
2.143 . |
TABLE NO. 47.
Oubic Feet of Air Per Minute Required to Operate a Small Number of Rand Drills of Various Sizes at 60 Pounds Air Pressure at Sea Level.
|
No. OK NAME. |
KID. |
No. 1 |
Xo 2 |
No. 3 |
No. 3$ |
No. 4 |
No. 6. |
No. 7 |
|
DIam of Cylinder in Inches. |
JJin. |
2iin |
2|ln. |
3J in. |
3J In. |
3| In. |
4*ln. |
5 In. |
|
Number of Drills. |
||||||||
|
1 |
35 |
53 |
64 |
95 |
103 |
112 |
132 |
164 |
|
2 |
61 |
93 |
112 |
166 |
180 |
196 |
231 |
.270 |
|
3 |
88 |
133 |
160 |
238 |
258 |
280 |
330 |
385 |
Otf ENGINEERING. 93S
TABLE 47.
TABLE OF THE ARRAS OF CIRCULAR SKGMKNTS FOR DIAMETKR = 1.
|
Height |
Area. |
Height. |
Area 1 |
Height | |
Area. |
Height |
Area |
|
.001 |
000 042 |
.064 |
.021 168 |
1-27 |
.Oo7 991 |
.190 |
103 900 |
|
.002 |
.000 119 |
oes |
021 660 |
128 |
058 658 |
.191 |
.104 6f>- |
|
.003 |
.000 219 |
.066 |
022 155 |
129 |
.059 328 |
.192 |
105 472' |
|
.004 |
.000 337 |
.067 |
.022 653 |
.130 |
.059 999 |
.193 |
.10»; 261 |
|
.005 |
.000 471 |
.068 |
.023 155 |
.131 |
.OhO 673 |
.194 |
.107 OM |
|
.006 |
.000 619 |
.069 |
.023 660 |
132 |
.061 349 |
.195 |
.107 843 |
|
.007 |
.000 779 |
.070 |
.024 168 |
.133 |
06-2 027 |
.196 |
.108 636 |
|
.008 |
.000 952 |
.071 |
.024 680 |
134 |
0«2' 707 |
.197 |
.109 4X1 |
|
.009 |
.001 136 |
.072 |
025 1% |
.135 |
063 389 |
.198 |
110 227 |
|
.010 |
.001 329 |
.073 |
.023 714 |
.136 |
064 074 |
.199 |
.111 025 |
|
.011 |
.001 533 |
.074 |
.026 236 |
.137 |
.064 761 |
.200 |
111 824 |
|
.012 |
.001 746 |
.075 |
.026 761 |
138 |
.065 449 |
.201 |
.112 625 |
|
.013 |
.001 969 |
076 |
.027 290 |
.139 |
066 140 |
.202 |
.113 427 |
|
.014 |
.002 199 |
077 |
.027 821 |
.140 |
.066 833 |
.203 |
.114 231 |
|
.016 |
.002 438 |
.078 |
.028 35H |
.141 |
.«67 528 |
.204 |
.115 036 |
|
.016 |
.002 685 |
.079 |
.028 894 |
.142 |
.068 225 |
.205 |
.115 842 |
|
.017 |
.002 940 |
.080 |
.029 436 |
.143 |
068 924 |
.206 |
.116 651 |
|
.018 |
.003 202 |
.081 |
.029 979 |
.144 |
.069 626 |
.207 |
.117 460 |
|
.019 |
.003 472 |
.082 |
.030 526 |
.145 |
.070 329 |
.208 |
.118 271 |
|
.020 |
OOS 749 |
.083 |
.031 077 |
.146 |
.071 034 |
.209 |
.119 084 |
|
.021 |
.004 032 |
.084 |
.031 630 |
.147 |
.071 741 |
.210 |
.119 898 |
|
.022 |
.004 322 |
.086 |
.032 186 |
.148 |
.072 460 |
.211 |
.120 713 |
|
.023 |
.004 619 |
.086 |
.032 746 |
.149 |
.073 162 |
212 |
.121 530 |
|
.024 |
.004 922 |
.087 |
,033 308 |
.150 |
.073 875 |
.213 |
.122 348 |
|
.0-25 |
.005 231 |
.088 |
.033 «73 |
.151 |
.074 590 |
.214 |
.123 167 |
|
.026 |
.005 546 |
.089 |
.034 441 |
.152 |
.075 307 |
.215 |
.123 988 |
|
.027 |
.005 «67 |
.090 |
.035 012 |
.153 |
.076 026 |
.216 |
.124 811 |
|
.028 |
.006 194 |
.091 |
.035 586 |
.154 |
.076 747 |
.217 |
.125 634 |
|
.029 |
.006 527 |
.092 |
.036 162 |
,.155 |
.077 470 |
.218 |
1-26 459 |
|
.030 |
008 866 |
.093 |
.036 742 |
.156 |
.078 194 |
.219 |
.127 286 |
|
.031 |
.007 209 |
.094 |
.037 324 |
.167 |
.078 921 |
.220 |
.128 114 |
|
.032 |
007 559 |
.09-> |
.037 909 |
Jf»8 |
.079 650 |
.221 |
.128 943 |
|
.033 |
.007 913 |
.096 |
.038 497 |
.159 |
.080 380 |
.222 |
.129 773 |
|
.034 |
.008 27.i |
.097 |
.039 087 |
.160 |
.081 112 |
.223 |
.130 605 |
|
.035 |
.008 638 |
.098 |
.039 681 |
.161 |
.081 847 |
.224 |
.131 438 |
|
.036 |
.009 008 |
.099 |
.040 277 |
.162 |
.082 582 |
!225 |
.132 273 |
|
.037 |
.009 383 |
.100 |
040 875 |
.163 |
.083 320 |
.226 |
.133 10(1 |
|
.038 |
009 764 |
.101 |
.041 477 |
164 |
.084 060 |
.227 |
.133 946 |
|
.039 |
.010 148 |
.102 |
.042 081 |
,165 |
.084 801 |
228 |
.134 784 |
|
.040 |
.010 538 |
.103 |
.042 687 |
?166 |
.085 545 |
.229 |
.135 624 |
|
.041 |
.010 932 |
.104 |
.043 296 |
167 |
.086 290 |
.230 |
.136 465 |
|
.042 |
.011 331 |
.105 |
.043 908 |
168 |
.087 037 |
.231 |
.137 »07 |
|
.043 |
.011 734 |
.106 |
.044 523 |
.169 |
.087 785 |
.232 |
.138 151 |
|
.044 |
.012 142 |
.107 |
.045 140 |
.170 |
.088 53IJ |
.233 |
.138 996 |
|
.045 |
012 555 |
.108 |
.045 759 |
.171 |
.089 -288 |
.234 |
.139 842 |
|
.046 |
.012 971 |
.109 |
.046 381 |
.172 |
.090 042 |
.235 |
.140 689 |
|
.047 |
.013 393 |
.110 |
.047 006 |
.173 |
.090 797 |
.236 |
.141 -538 |
|
.048 |
.013 818 |
.111 |
.047 633 |
.174 |
.091 555 |
.237 |
.142 388 |
|
.049 |
.014 248 |
.112 |
.048 262 |
.175 |
.092 314 |
.238 |
.143 239 |
|
.050 |
.014 681 |
.113 |
.048 894 |
176 |
.093 074 |
.239 |
.144 o'.U |
|
.051 |
.015 119 |
.114 |
.049 529 |
.177 |
.093 837 |
.240 |
144 945 |
|
.052 |
.015 561 |
.115 |
.050 165 |
.178 |
.094 601 |
.241 |
.145 800 |
|
.053 |
.016 008 |
.116 |
.050 805 |
.179 |
.095 367 |
..242 |
.146 656 |
|
.054 |
.016 458 |
.117 |
.051 446 |
180 |
.096 135 |
.243 |
.147 513 |
|
.055 |
.016 912 |
.118 |
.052 090 |
.181 |
096 904 ' |
.244 |
.148 371 |
|
.056 |
.017 369 |
.119 |
.062 737 |
.182 |
097 675 |
.245 |
.149 231 |
|
.057 |
.017 831 |
.120 |
.053 385 |
.183 |
.098 447 |
.246 |
.150 091 |
|
.058 |
.018 297 |
.121 |
.054 037 i |
.184 |
.099 221 |
.247 |
.150 95 3 |
|
.059 |
.018 766 |
.122 |
.054 690 |
.1S5 |
.099 997 |
.248 |
.151 816 |
|
.060 |
.019 239 |
.123 |
.055 346 |
.186 |
100 774 |
.249 |
.152 681 |
|
.061 |
.019 716 |
.124 |
.056 004 |
.187 |
.101 553 |
.250 |
.153 546 |
|
.062 |
.020 197 |
.125 |
056 664 |
.188 |
.102 334 |
|
|
|
,063 |
.020 6S1 |
.126 |
.057 327 |
.189 |
.103 116 |
936 SAKdBddS Off ENGINEERING.
TABLE 47. - COM tinned.
TABLE OF THE AREAS OF CIRCULAR SEGMENTS FOft DtAMKffe ft S= I.
|
Height |
Area |
Height |
Area. |
[Height |
Area. |
Height |
Area. |
|
.251 |
.154 413 |
.314 |
.'.Ill 083 |
.377 |
.270 951 |
.440 |
.332 S4* |
|
.262 |
.165 281 |
.315 |
.212 Oil |
.378 |
.271 921 |
.441 |
*333 836 |
|
.953 |
.156 149 |
.316 |
.212 941 |
. .379 |
.272 891 |
.442 |
.334 829 |
|
.254 |
.167 019 |
.317 |
.213 871 |
.380 |
.273 861 |
.443 |
.335 823 |
|
.266 |
.W7 €91 |
.318 |
.214 802 |
.381 |
.274 832 |
.444 |
.336 816 |
|
.266 |
.158 763 |
.319 |
.215 734 |
.382 |
.275 804 |
.445 |
.337 810 |
|
.267 |
.159 636 |
.320 |
.2 IK 666 |
.383 |
.276 776 |
.446 |
.338 809 |
|
.2*8 |
.160 511 |
.321 |
.217 600 |
.384 |
.277 748 |
.447 |
.339 799 |
|
.269 |
.161 386 |
.322 |
.218 534 |
.385 |
.278 721 |
.448 |
.340 793 |
|
.260 |
.162 263 |
.323 |
.219 469 |
.386 |
.279 695 |
.449 |
.341 788 |
|
.261 |
.163 141 |
.324 |
.220 404 |
.3S7 |
.280 669 |
.450 |
.342 783 |
|
//2 |
.164 020 |
.325 |
.221 341 |
.388 |
.281 643 |
.451 |
.343 778 |
|
.263 |
.164 900 |
.326 |
.222 278 |
.389 |
,282 618 |
.452 |
.344 773 |
|
,264 |
.165 781 |
.327 |
.223 216 |
,390 |
.283 593 |
.453 |
.345 768 |
|
.265 |
.166 663 |
.328 |
.224 154 |
' .391 |
284 569 |
.454 |
.346 764 |
|
,.266 |
.167 546 |
.329 |
.225 094 |
.392 |
.285 545 |
.455 |
.347 760 |
|
.267 |
.168 431 |
.330 |
.226 034 |
.893 |
.286 521 |
.456 |
.348 756 |
|
.268 |
.169 316 |
,3ol |
.226 974 |
.394 |
.'267 499 |
.457 |
.349. 752 |
|
.269 |
.170 22 |
.332 |
.227 916 |
.395 |
.288 476 |
.458 |
.360 749 |
|
,270 |
.171 OHO |
.333 |
223 858 |
.396 |
.289 454 |
.459 |
.351 745 |
|
271 |
.171 978 |
.334 |
.229 801 |
.397 |
.290 43-2 |
.460 |
.352 74» |
|
.272 |
.172 868 |
.335 |
.230 745 |
.398 |
.291 411 |
.461 |
.353 739 |
|
.278 |
.1?3 758 |
.336 |
.231 689 |
.399 |
292 390 |
.462 |
.354 736 |
|
,274 |
.174 650 |
.337 |
.232 634 |
.400 |
.293 370 |
.463 |
.355 733 |
|
,275 |
.175 542 |
.338 |
.2*3 580* |
.401 |
.294 350 |
.464 |
.356 730 |
|
.276 |
.176 436 |
.339 |
.234 526 |
.402 |
.295 350 |
.465 |
.357 7-28 |
|
;277 |
.177 330 |
.340 |
.235 473 |
.403 |
.296 311 |
.466 |
.358 725 |
|
.278 |
.178 226 |
.341 |
.236 421 |
.404 |
.297 292 |
.467 |
.3.9 723 |
|
.279 |
.179 122 |
.342 |
.237 369 |
.405 |
.298 274 |
.468 |
.360 721 |
|
,280 |
.180 020 |
.343 |
.238 319 |
.406 |
.299 256 |
.469 |
.361 719 |
|
.281 |
.180 918 |
.344 |
.239 268 |
.407 |
.300 238 |
.470 |
.362 717 |
|
,282 |
.181 818 |
.345 |
.240 219 |
.408 |
.301 221 |
.471 |
.363 715 |
|
.'/83 |
.182 718 |
.346 |
.241 170 |
.409 |
.302 204 |
.472 |
.364 714 |
|
.284 |
.183 619 |
.347 |
.242 122 |
.410 |
.303 187 |
.473 |
.365 712 |
|
w285 |
.184 622 |
.348 |
.243 074 |
.411 |
.304 171 |
.474 |
.366 711 |
|
*286 |
.1*5 426 |
.349 |
.244 027 |
.412 |
.306 156 |
.475 |
.367 710 |
|
,287 |
.186 329 |
'.650 |
.244 980 |
.413 |
.3<>6 140 |
.476 |
.368 708 |
|
.288 |
.187 235 |
.351 |
.245 935 |
.414 |
.307 125 |
.477 |
.369 707 |
|
*289 |
.188 141 |
'.352 |
.246 890 |
.416 |
.308 110 |
.478 |
.370 7ufi |
|
'.290 |
.189 048 |
;353 |
.247 845 |
.416 |
.309 096 |
.479 |
.871 705 |
|
.291 |
.189 956 |
.354 |
.248 801 |
.417 |
.310 082 |
.480 |
.372 704 |
|
.292 |
.190 865 |
.355 |
.249 758 |
.418 |
.311 068 |
.481 |
.373 704 |
|
>293 |
.191 774 |
.356 |
.250 715 |
.419 |
.312 065 |
.482 |
.374 703 |
|
/.294 |
.192 685 |
.357 |
.251 673 |
.420 |
.313 042 |
.483 |
.376 7o2 |
|
',295 |
.193 597 |
.368 |
.252 632 |
.421 |
.314 029 |
.484 |
.376 702 |
|
»296 |
.194 509 |
.359 |
.253 691 |
.422 |
.316 017 |
.485 |
.377 701 |
|
,297 |
.195 423 |
.360 |
.254 551 |
.423 |
.316 OG5 |
.486 |
.378 701 |
|
:298 |
.196 337 |
.361 |
.256 511 |
.424 |
.316 993 |
.487 |
.379 701 |
|
,299 |
.197. 252 |
.362 |
.256 472 |
.425 |
.317 981 |
.488 |
.380 700 |
|
.300 |
.198 168 |
.363 |
.257 433 |
.426 |
.318 970 |
.489 |
.381 700 |
|
301 |
.199 085 |
.364 |
.258 395 |
.427 |
.319 959 |
.490 |
.382 700 |
|
..302 |
.200 003 |
.365 |
.259 358 |
.428 |
.320 949 |
.491 |
.383 700 |
|
^303 |
.200 922 |
.366 |
.260 321 |
.429 |
.321 938 |
.492 |
.384 699 |
|
.304 |
.201 841 |
.367 |
.261 285 |
.430 |
.322 928 |
.493 |
.385 699 |
|
,305 |
.202 762 |
.368 |
.262 249 |
.431 |
.323 919 |
.494 |
.386 699 |
|
.,306 |
.203 683 |
.3«9 |
.263 214 |
.432 |
.324 909 |
.495 |
.387 699 |
|
.307 |
.204 605 |
.370 |
.264 179 |
.433 |
.325 900 |
.496 |
.388 6<)9 |
|
.308 |
.206 528 |
.371 |
.265 145 |
.434 |
.326 891 |
.497 |
.3S9 6«.«9 |
|
.309 |
.206 452 |
.372 |
.266 111 |
.435 |
.327 883 |
.498 |
.390 699 |
|
.810 |
.207 376 |
.373 |
.267 078 |
.436 |
.328 874 |
.499 |
.391 tt'.'9 |
|
.an |
.208 302 |
.374 |
.268 046 |
.437 |
.329 866 |
.600 |
.392 699 |
|
,312 |
.209 228 |
.375 |
.269 014 |
.438 |
.330 868 |
||
|
.313 |
.210 155 |
..376 1 |
.269 982 |
.439 |
.331 851 |
|
HANDBOOK ON ENGINEERING.
937
HARTFORD SPECIFICATIONS;
The following are the specffications, for steel plate, of the Hartford Steam Boiler Inspection and Insurance Co.
OPEN HEARTH FIRE BOX STEEL
To have a tensile strength of. not less than 55,000 lbs.,nor more than 62,000 IDS. per square inch of section, with not less than 56% of ductility as indicated by contraction of area at point of fracture under test and by an elongation of 25£ in a length of 8 inches.
HE ADS- To be made of best Open Hearth Flange Steel, 60,000 T. S. All plates, both of shell and heads, must be plainly stamped with name of maker, brand and tensile strength; brands so located that they may be seen on each plate after bolter is finished. Each shell plate must bear a coupon which shall be sheared off, finished up and tested by the maker of ihe boiler, at his own expense. Each coupon must fill the above requirements as to strength and ductility, and must also stand bending down double when cold, when red hot and after being heated red hot and quenched in cold water, without SILTS of fracture. All plates failing to pass these tests will be rejected. All tests and inspections of material shall be made at the place of manufacture prior, to shipment.
TABLE No. 48.
Showing details of rivet laps for different thicknesses of boiler plate as ad- vocated by the Hartford Steam Boiler Inspection and Insurance Co. for
DOUBLE RIVETED BUTT JOINTS.
2*4X4*
ofi
if
4V» in
il"
9 in
1014 •' 11J4 "
H in
ft::
ir
ill-
IK in2K In . - -
2H' 2M
2^
TABLE No. 48.— Continued. TRIPLE RIVETED BUTT JOINTS.
Thicknes Plate.
iame Riv
Pitch of Riv in inches.
Width o Outside B Strap.
idth of ide Bu Strap.
Thickne Coveri Stra
sg.
Ill &
n
si 53
s~
J°s ^3s
O S3 «>*
C3*3 *
®O <»CC
&D >•
|w
i
y
3|x6| 3ix7
11§ in
ij
p
2il
23
11 in
87.5^
86%
88%
88%
87.59J
87.6^
86.6%
For detailed drawings of above laps, tee pages 946 to 951 inclusive.
938
HANDBOOK ON ENGINEERING.
STAYING BOILER HEADS.
In the return tubular boiler the tubes occupy a considerable portion of the boiler head, usually amounting to about two-thirds of the entire area of the head, as shown by Figure 403. There
•V*
o
_ J
ooooo ooooo ooooo ooooo oooo o
ooooo ooooo ooooo ooooo oooo o
Fig. 403.
Showing No. of stays in a well proportioned boiler of 60 in. in diameter
is very little surface, comparatively speaking, between the tubes for pressure to act upon, and as the tubes serve as stays to a con-
HANDBOOK ON ENGINEERING. 939
siderable extent, it is, therefore unnecessary to introduce stays between them. The remaining flat surface above and below the tubes is exposed to full boiler pressure, and would tend to bulge outward, and thus loosen the tube ends if not properly secured in position. The upper part of the head can be held in position by means of rods connected to both heads, or by means of stays connected to the head and boiler shell. When the area above the tubes is secured by means of rods connected to both heads, the rods are called direct, or through stays, and when the rods run from the head to the shell, they are called diagonal stays.
There is no necessity for using direct or head-to-head stays in the return tubular boiler, because the shell possesses a surplus of strength in the direction of its length, which is sufficient to resist all the pressure that can be brought to bear on the area of the head above and below the tubes. The ability of the shell to aid in strengthening the head can be made use of by putting in the proper number of diagonal stays. The advantages offered by the latter style of stay are that the stays occupy comparatively little space in the steam room of the boiler, thus permitting the interior, both above and below the tubes, to be thoroughly in- spected and cleaned, and the stays being shorter, the effects of expansion are less noticeable upon the boiler heads, and the ten- dency of the sta}Ts to work loose is correspondingly reduced.
When calculating the number of stays required in a boiler head, it is not necessary to include the entire area above the tubes, because it has been found by experiment that the flange of the head imparts sufficient strength to a distance of 3 inches from the flange, and that the tubes tend to stay the head to a distance of 2 inches above the tops of the upper row of tubes. It will be seen, therefore, that the actual area to be stayed ex- tends to within 3 inches of the shell, and to within 2 inches of the top of the tube. The area to be stayed is contained within
940
HANDBOOK ON ENGINEERING.
the dotted lines shown in Fig. 404, and is in the form of a seg- ment of a circle.
In order to find the total pressure or stress on this area it is first necessery to find the area of the segment formed by the dotted lines. It will be seen that the top of this segment is an
i
oooo
Fig. 404.
Showing the area to be stayed.
arc of a circle which is smaller than the boiler head. If we take off 3 inches from the diameter of the head at both top and bot- tom it will give the diameter of the circle of which the segment is
HANDBOOK ON ENGINEERING. 941
a part, and the diameter will be found to be 6 inches less than the diameter of the boiler head. The distance, H, Fig. 404, is called the height of the segment. The area of the segment multiplied by the steam pressure gives the total stress to be re- sisted by the stays, and the total stress divided by the stress which one stay will hold gives the number of stays required .•
To illustrate the method of finding the number of stays re- quired, suppose the stays in a 60-inch and a 72-inch boiler head are to be determined. In a well proportioned boiler head th<* distance from the bottom of the shell to the top of the upper row of tubes is about 60 per cent of the diameter of the head, and 60 per cent of 60 inches is 36 inches, which is the distance, A, Fig. 404. The distaace from the top of the tubes to the top of the boiler head is 60 — 36 = 24 inches. According to the rule previously given we must subtract the width of the space, D, which is three inches, and also the width of the space, E, which is 2 inches thus making the height of the segment equal to 24 — (3+2) = 19 inches, which is the height, H, Fig. 404. Divide the height, H, by the diameter, d, of the circle of which the segment is a part. In the table of areas of segments of circles on page 935, find the quotient in the column headed, Height, and multiply the corresponding decimal in the column headed area, by the square of the diameter of the circle of which the segment is a part ; the product will be the area of the segment included within the dotted lines. Thus, the diam- eter of the circle of which the segment is a part is 60 — 6 = 54 inches, and 19 -f- 54 = .351. In the column headed Height, we find .351 and opposite we find the decimal .2459 which, when multiplied by the square of the diameter of the circle, gives .2459 X (54 X 54) = 717 square inches, the area of the segment. If the boiler pressure is to be 100 pounds on each square inch the total pressure will be 717 X 100 = 71,700 pounds, which is the stress to be borne by all the stays. When stays are not subjected to the action of water they may be
942
HANDBOOK ON ENGINEERING.
allowed a stress of 7,500 pounds per square inch of section, but when subjected to the action of the water in the boiler the stress should not exceed 6,000 pounds.
Now stays in horizontal tubular boilers are generally made of 1 inch round bars and as a bar of this size has an area of .7854 of a square inch each bar or stay will stand a stress of 7,500 X .7854 = 5890 pounds, and the number of stays required is 71,700 ~ 5890 =33 12 stays, as shown in Fig. 403.
J K
Gr
\i
Fig. 405.
Method of connecting a diagonal stay.
The stress on diagonal stays is a little greater than on direct stays running from head to head, so that the area of the 12 stays must be increased in proportion to the increased stress. The minimum length of stay allowable is 3J feet, and the stress on the diagonal stay is as much greater than the stress on the direct stay as the length of the stay FG, Fig. 405, is greater than the distance JK. Suppose the distance, JK, is 45 inches, and the length of the stay, FG, 48 inches, then the stress on the diagonal stay is 48 -=- 45 = lTJo- times the stress on the direct stay and consequently the area of the stay must be 1T^ times the area calculated or .7854 X ITTFTF = -^ °* a S(luare inch, which corresponds to a diameter of l^ inches. Thus the 60-inch boiler requires 12 stays each 1T^ inches in diameter, as shown in Fig. 403.
HANDBOOK ON ENGINEERING. 943
The number of stays required in the 72-inch boiler is found in the same manner. Thus, the diameter of the circle of which the segment to be braced is a part, is 72 — 6 = 66 inches. The dis- tance from the bottom of the shell to the top of the tubes is 60 per cent of 72 inches, or 43 inches, and the distance from the top of the tubes to the top of the shell is 72 —43—29 inches. From this is to be subtracted 3 inches measured from the shell, and 2 inches measured from the tubes, making 5 inches in all, thus leav- ing 29 — 5 — 24 inches, which is the height, H, of the segment represented by the dotted lines. Dividing the height of the seg- ment by the diameter of the circle of which the segment is a part, we have 24-r-66=.363. In the table of areas of segments of circles find .363 in the column headed, Height, and opposite we find the decimal .2574, which, when multiplied by the square of the diameter of the circle of which the segment is a part, gives .2574 X ( 66 X 66 ) = 1121 square inches area of segment. Assume the pressure to be 110 pounds per square inch. The total stress to be borne by all the stays is 1121 X HO = 123,310 pounds. If the stays are to be of 1 inch rods, which is the smallest size used for boilers above 44 inches in diameter, the area of each rod or stay will be .7854 of a square inch, and it will be capable of resisting a stress of 7,500 X .7854 = 5890 pounds.
The number of 1 inch stays required, therefore, is 123,310 -5- 5890=21 stays.
Now, if the distance, J K, Fig. 405, in this case is 48 inches, and the length of the stay 52 inches, the stress on the diagonal stay will be 52 ~- 48 = 1T§ ^ times what it would be on a direct stay, and consequently the area of the stay must be lyf^ times greater, or .7854 X 1.08 = .85 square inch, which corresponds to a diameter of l^ inches, therefore the 72-inch boiler will require 2 1 stays 1-^ inches in diameter.
It sometimes happens that the maximum pressure employed
944
HANDBOOK ON ENGINEERING.
when calculating stays call for a certain number which it is found difficult to properly distribute over the boiler head. In this case the number of stays must be changed, but the combined area of the stays must necessarily remain the same. To illustrate, sup-
oooooo ocoooo oooooo oooooo oooooo ooooo
00
oooooo oooooo oooooo oooooo oooooo ooooo oo
Fig* 406.
No. of stays in a well proportioned boiler of 72 in. in diameter.
pose 21 stays could not be distributed to advantage on the 72-inch head, and it is desired to use, say, 18 stays. Now, the 21 stays have a combined area of .85 X 21 = 17J square inches, and this area divided among 18 stays would give each an area of
HANDBOOK ON ENGINEERING. 945
17| -f- 18 = 1 square inch, which corresponds to a diameter of 1| inches, therefore the 72-inch boiler will require 18 stays 1£ inches in diameter.
The same method is used when finding the number and size of the stays below the tubes. It is seldom practicable, with the usual arrangement of tubes and man -hole, to use more than two stays below the tubes so that the area is made sufficient to enable two stays to carry the stress.
When finding the size and number of screw stays or stay bolts, such are used in the water-legs of locomotive boilers and in the headers of water tube boilers where the bolts are subjected to the action of the water, the maximum stress allowable per square inch of net section, which is the area of the bolt measured at the bottom of the threads, is 6,000 pounds. For instance, what is the diameter, number and stress on the stay bolts required in the water-leg of a locomotive boiler, the flat surface measuring 40 X 54 inches, and the maximum pressure 125 pounds? The total area is found to be 40 X 54 = 2,160 square inches, and the total pressure to be resisted by the stay bolts is 2,160 X 125 = 270,000 pounds, For pressures exceeding 100 pounds per square inch, the pitch of staybolts in stationary boilers should not exceed 4J inches. . The area supported by each bolt is 4J X 4J = 18 square inches and the stress on each bolt is 18 X 125 = 2,250 pounds. The total stress is 270, 000 pounds, consequently 270,000 divided by 2,250 will give the number of bolts which is 270,000 -~ 2,250 = 120. The stress allowed per square inch of net sectional area is 6,000 pounds, and as each bolt must sustain a stress of 2,250 pounds the net area of each bolt is 2,250 -f- 6,000 = .375 or f of a square inch measured at the bottom of the threads, which corresponds to a bolt f inch in diameter measured to outside of threads. This surface, there- fore, requires 120 staybolts -if inch in diameter, spaced 4J inches between centers for a working pressure of 125 pounds.
946
HANDBOOK ON ENGINEERING.
DOUBLE RIVETED LAP AND GIRTH JOINT'S
Longitudinally Riveted.)
This construction is based on a tensile strength of 60,000 Ibs. for plata .and a shearing strength of 38,000 Ibs. for rivets.
LAP JOINT.
GIRTH JOINT.
-23-
• plates, double riveted; holes, %•; rivets, J|". (Efficiency ,
LAP JOINT.
GIRTH JOINT.
plates, double riveted; holes. U',' rivets, fc% (Efficiency, 59
HANDBOOK ON ENGINEERING.
947
Double Riveted Lap and Girth Joints.
LAP JOIKT. GIRTH JOIHT.
-34*
• plate*, doable riveted ; holes, }}• i rivets, £ -. (Efficiency . TO*. )
GIKTH JOINT.
•ai-
' plates, double riveted; hole* I'; rlrets, H*- (Efficiency, TOjt)
OIBTB JOINT.
(I* plat** double rtreted) hol««, 1 A' » rtvet* 1 ' (Efficiency,
948
HANDBOOK
Triple fciveted Lap and Girth Joints.
(Longitudinally Riveted ) This construction is based on a tensile strength of 60.000 Ibs, for plate
ittfra shearing strength of 88,000 Ibs. for rivets.
IiAP JOINT..
GIRTH JOINT.
' plates, triple riveted) holes, }j-i rivets, %•. (Efficiency. 77i.)
LAP JOINT.
k — 3k* —
GIRTH JOINT.
CM
i*o
b* plmtes. triple riveted; holes, % * $ rivets. 14-. (Efficiency, 76*.)
HANDBOOK ON ENGINEERING.
rtAP~ JOINT. GIRTH JOIKT.
K 3*'-
' plates, triple riveted ; holes, {|* ; rivets 2£ '. (Efficiency, 755?.)
LAP JOIKT.
GIRTH JOINT.
1»
«SJ
f
' plates, triple riveted; boles, 18'; rivets, %•» (Efficiency .75*.)
GIRTH JOINT.
I — a*:-
plates, triple riveted ; holes, I • ; rivets, if
949
950
HANDBOOK ON ENGINEERING,
Triple Riveted Butt Joints.
nt for &• plates; holes, &'; rivets, ||». (Efficiency, 88*.)
i
^
0
•^>
f^
ffl
feutt joint for %• plates; holes, y ; rivets, &'. (Efficiency.
Butt joint f or /e • plates; holes, 53 ; • rlvete, %'. (Efficiency, 86*.)
HANDBOOK ON ENGINEERING. TRIPLE RIVETER BUTT JOINTS-CContinued.)
ck.
Butt joint for Vs" plates; holes, 1"; rivets, Jg' (Efficiency, 86.65?.)
i
Butt joint for ft* plates; holes, 1^' ; rivets, 1% (Efficiency, 66£)
Butt Joint tor-K* nl»tew t»J««. I.A' ri»et» f. (Efficiency. 8C*.}
951
952
HANDBOOK ON ENGINEERING.
|
£S8SSgS5&S8gS885Sgi&58Sgg55o |
Thickness of material required. |
||||
|
PPPPPPPPPBPPBPPPPBPBBPP §CiOC5OCiOC5OOOOC5OOOOOOOOOO p'p'p-p-p-p'SrD'erp'P'D'P'P'CrD'P'p'B'D-p'B' ::::;:::.•::::::•.:::::;: . ... Kg |
|||||
|
: : i : ; ; '. '. ' : '. . '. '. ' . : i t w^ o .:::::::::::::::::: £8£g3£| • SH |
Over 6 and not over 7 inches. |
Diameter of flues. |
5*. o >_• P*oo Is |
Least thickness of material allowable. , |
Greatest length of sections allowable, 5 feet. |
|
'• ' S*'® OOCOOOQp' "-* CD 5 « • • • - • 09 • : B>*a 5s |
Over 7 and not over 8 inches. Over 8 and |
||||
|
• • O CO ;C 00 GO -4 • • »^ ft S |
not over 9 inches. |
&*£ Its |
|||
|
i:; i ::::::;:: i »v*g |
Over 9 and not over 10 inches. |
||||
|
^tD^S^ColK • 3 CB ^ |
|||||
|
;;::;;;;;:;;; ; ; s,j |
Over 10 and not over 11 inches. |
is |
Least thickness of material allowable. |
O i (b m 5T B CK5 5 O M> • I o' p OB EL 0* p cr 5* 00 o » |
|
|
•••••••••••••i CS8S33; : 3S| |
|||||
|
::::::: Ilii ' : g*? |
Over 11 and not over 12 inches. |
g-s |
|||
|
O O CD OD •<! ^1 OS CJ? • • fj O ^ :::::::::: : : • • §• |
|||||
|
.:::::::: : : • »« § |
Over 12 and not over 13 inches. |
ik |
|||
|
• • * • • • • '• • occcBcc-^^osolo?" • '• NfD§ |
|||||
|
Sj |
Over 13 and not over H inches. |
ife |
|||
|
::::::: ^^^ :::::. g-c ? |
|||||
|
• a»»d 5 |
Over 14: and not over 15 inches. |
is |
|||
|
• §^Soooo^S§^!aw^ :::::: S»s : : : : : ::::::••§* |
|||||
|
:::::::: g^ 5 |
Over 15 and not over 16 inches. |
is |
|||
|
g3g32g2§;§£g: ::::::: si| |
|||||
|
1: : : ^-^^^H,^^^,-^1 : : : ' : : : : §-| |
Over 16 and not over 17 inches. |
g.w cr^i |
|||
|
-lttf^to32§tC ^{^OT S OB S |
|||||
|
:::::::::: g^? |
Over 17 and not over 18 inches. |
is |
|||
|
: g§^^5g3gS^a§S: ::::::::: 32 1 |
|||||
|
: • : »*d 5 |
Over 18 and not over 19 inches. |
p-b |
|||
|
^^SSS^SSiSg?^: :::::.:::: gs| |
|||||
|
:•:::::::::• • & |
|||||
|
: i : : : i : a^ J |
Over 19 and not over 20 inches. |
is |
|||
|
SSIlSISSSii: ::::::::::: gi| |
HANDBOOK ON ENGINEERING.
953
|
Greatest length of sections allowable, 30 inches. |
J2 3 | *i3 "08 3 53 a •s a J4 £ ^ 00 1 |
*!•§ ' 0 00^3 «•§ ' G |
Diameter of flues. |
•eaqoai ^8 jaAoqoa PUB gg IOAO •89qOUJ 88 18 AO !|OU PUB 28 J9AQ |
sS£:'::'''::': -ococc |
|
1- iiiii ii il iiiihji N ! i i H |SS ::::::::::::::•:::::: :S2^;g gaco ::::::::::.::::::::::: |
|||||
|
SJ| 33 ° c |
•soqouj CS^AO^OU PU« 18 J9AQ |
|SS ::::::::: : ::::::•:::: :^S2SS o p,, .:::::::..::::::::::: oe ..:... |
|||
|
•eaqoui T8 J8AOIJOU PUB 08 J9AQ |
*§ OQ W ^h-OKM^r- S <O 1* -« r- ~H <M <N CN «»«:::::::::.:::::::;:: |
||||
|
S| 05 .C CO y ' fl 8| |
•saqouj 08 J9AO ^ou putt 66 J9AQ |
-§,„:::;::::::::: . • • • S 00 0) U5 QO O CO «O Oi ffl S OJ Vl • • • • r-H ^ <N <N S & S? §»itf::;i:i: ::!::: '.•:>*'r^r-"-"-"-('-''-< |
|||
|
ga<B :::::::::::::•;•; i i |
|||||
|
•soqouj 6S J8A010U pttB $Z J9AQ |
90 20>J-i »-tr-i(MCM51CCCOCO o^g ::..:. |
||||
|
•eaqoui 83 jaAo aou put? 12 aaAQ |
« g OQ OJ • ?C> OS CO CO Oi ffllO QO i-i S « *J ^ -• <N <N (M eo co co •«* gMO;: ••i-(r-(r-«^,rHrtrH^H^: |
||||
|
a, a ::•;::::::::::••: |
|||||
|
S3 C <0,C CO o " fl |
•saqoui is JOAOIOU PUB 9S J8AQ |
|SS ::::::•:::::::: -5S3S;g8$5S3$ §ft« i : i : i : ; ; i ; ; ; i ; • ; |
|||
|
•soqout 9S J9AO 10U pUW Q^ J8AQ •saqoui |
1SS :•:::::::::::: :2,|S§S3^S^!iS^S |
||||
|
«=-:::•::.:::::::: OB |
|||||
|
Si-g a |
QZ J9AO ^OU PUB fj; J8AQ |
§ a> >H • • • <N <M e^ cc co cc .* xH •<* us 1§ • §ftco ::::••••::•::: |
|||
|
"1 |
•saqoui ^ J9AO !JOU pu« 21 J»AO |
«SS :•:::•:::::• :SSS^SS585l-S3B ' : |
|||
|
S^^*' * r-(^Hr^.— Jr-l-^i^r- ii— (rHi-H £.*•» i ; ;;;•:!;•• : : |
|||||
|
Greatest length of sec- tions allowable, 3 ft. |
Least thickness of ma- terial allowable. |
S* fl |
•saqoui g^ J9AO ^OU |
'SaoaJ' <M«oo-*xxM«oocot-o^^ '.!!!!!!!! S g M • «N<MCCCCCC^*'*iOOWX> |
|
|
8| S5S a |
•soqoui ZZ J^AO ^ou PUB IZ J9AQ |
eo • . . § 0) J- 0) 0* 50 CO "* •<* Tt< «0 to (0 «0 |
|||
|
(? ft® : |
|||||
|
•soqoui T£ I9AO !JOU PUB OS ^AO |
"2 a) d CD ^H >ft <3i co r- r-t o os cc r-» a a? »i <>> f0 M 2° •* •* *° o "^ *° ^ |
||||
|
g e.» . • • .....: |
|||||
|
•pajfnbai [VIJ03BUI JO SSOU^Ojqj, |
££ja£*&AjAj&AAjAj:AjaAjA£ja<*jajaja£jaAjaja OOOOOOOOttOOOOOOOO^OOOWOOOO flflflflflflflflflpflflflflflflflflflflflflCflflfl |
||||
|
53?3^^^^S;^^5^^^^^^Jo^^?r«^«*'§5§ |
954 HANDBOOK ON ENGINEERING.
CHAPTER XXXI. HYDRAULIC ELEVATORS.
The purpose of these pages is to furnish such instruction and information as will be of use to engineers in the care of elevator machinery. To accomplish this end, cuts and sectional views of cylinders and valves of the different types of elevator ma- chinery made by the different elevator companies, are herein pro- duced, so as to make the different elevators plain to the engineer. It must be borne in mind that the one point of paramount im- portance for the successful operation of an elevator is proper care and management ; a lack of thorough knowledge of the ma- chine and lack of attention in this respect shortens the life of the machine and often makes extensive repairs necessary.
Hydraulic elevators are designated as horizontal or vertical according to the position in which the lifting cylinder is placed. Horizontal machines are generally placed in buildings where there is ample floor space, while vertical elevators are used in buildings standing on small lots. Vertical elevators are made so as to lift the elevator by means of ropes, and are geared up so that the travel of the piston is considerably less than that of the car, and they are also made so that the piston, or plunger, pushes directly against the bottom of the car and lifts it to the top of the building. This type of elevator, which is now being intro- dued on an extensive scale, is known as the direct plunger, or simply plunger elevator.
Horizontal hydraulic elevators are designated as pushing or pulling machines according to the way in which the power is ap- plied. In pulling machines, the water under pressure is admit-
HANDBOOK ON ENGINEERING.
955
ted between the piston and the front end of the cylinder, and the piston rods pull a set of movable sheaves toward the cylin-
'/* /
/
Fig. 407. Horizontal Hydraulic Elevator. Pushing Type.
956 HANDBOOK ON ENGINEERING.
der, aud thus lift the car. In pushing machines the water is admitted to the back end of the cylinder and the piston rod pushes the movable sheaves away from the cylinder to lift the elevator car.
The general arrangement of a horizontal hydraulic elevator of the pushing type is shown in Fig. 407. This is an Otis machine. The lifting cylinder is at A, B being the piston rod, C the set of movable sheaves and D a set of stationary sheaves. The lifting ropes pass around these two sets of sheaves several times, block and tackle fashion, and then run up and over an overhead sheave E and down to the top of the elevator car. Another set of ropes run up over the sheave F and down to a counterbalance weight G. The number of times that the lifting ropes wind around the sheaves determines the gear of the machine. The gear is always the ratio between the distance traveled by the car and the stroke of the piston. If the car runs ten times the stroke of the piston, the gear is ten to one, and so on for any other ratio. Horizontal machines are geared from six up to 14 to one, the average being about 10 and 12.
The valve for operating the elevator is at jET, and is of the same design as that used by the same makers for their vertical ma. chines and is explained in connection with the latter machines. Another valve is located at / and its office is to stop the elevator automatically at the top and bottom landings, if the operator fails to move the operating lever. This valve is actuated by the chain J which is moved by an arm K attached to the movable sheave frame. This arm strikes stop balls that are secured to J at the proper points to cause the car to stop even with the top and bot- tom landings of the building.
This illustration shows an actuating lever L in the car, which acts through a system of rope connections to move the valve H. This arrangement is used for high speed passenger elevators, but
HANDBOOK ON ENGINEERING.
957
slow speed freight machines are generally arranged so that a hand rope passes through the car and the valve is moved by pulling on this rope. The rope connections between the lever L
Fig. 408. Horizontal Hydraulic Elevator Machine.
and the valve are generally arranged on one of two different sys- tems, which are designated as the running rope and the standing rope. In the former the ends of the ropes are fastened to the ends of a cross-lever located on the back end of the shaft that carries L and therefore run when the car runs. In the standing rope system the ends of the ropes are secured to the top and the bottom of the elevator well and therefore stand still when the car runs. In Fig. 407 it will be seen that there are small sheaves n', ft, at top and bottom of the elevator well, the latter being mounted on the side of a larger sheave over which runs a rope 0. This rope passes around a sheave P located on the valve casing, and by its rotation the valve is actuated in a manner fully explained in connection with vertical elevators. The lever L is connected with the sheaves ri ', ?i, by the ropes m, and by rocking i, to one side or the other, these ropes are drawn up on one side and let out on the other so as to cause one of the n sheaves to rise and the other to fall and thus to rotate the large sheave, am} through rope 0 the valve sheave P.
958
HANDBOOK ON ENGINEERING.
HANBBOOK ON ENGINEERING. 959
Another design of pushing machine is shown in perspective in Fig. 408. This is a Crane machine, and canbe more fully under- stood from Figs. 409-410 the first being a side elevation and the second a plan. Fig. 409 also serves to make clearer the operation of the running rope connection between the car lever and the valve. When the operating valve is moved by means of a car lever, it cannot be moved directly, because the lever swings through a small distance only and on that account the force re- quired to move it would be more than the operator could exert for any considerable length of time. When the valve is operated by a hand rope passing through the car, a small force is required to pull the rope because it is pulled through several feet, which is four or five times the distance through which the lever is moved. To make the lever move freely a small valve is provided, called a pilot valve, and this is what is moved by the car lever. The pi- lot valve permits water to flow in or out of the main valve in such a way as to move it in the desired direction. In Fig. 409 the pilot valve is at M, and the main valve is inside of the chamber L L. The automatic stop valve is within K, and is actuated through rod J by means of the two arm lever H G and the frame F. This frame has attached to it a rod upon which are fastened stops G D and these are struck by an arm E projecting from the movable sheave frame, see Fig. 410. In this way valve Kis moved auto- matically at the top and bottom landings to stop the elevator.
The operation of the main and pilot valves can be understood from Fig. 411 which is a vertical sectional view. The shaft 8 is rotated by the carlever as shown in Fig. 409. If the movement is such as to swing A to the left, the pilot valve at M will be moved in the same direction and water will pass from space B at the large end of the main valve to the discharge pipe C. This will force the valve to the left and thus connect the supply pipe E with the cylinder inlet D through the movement to the left of pis- ton Go The water passing into the cylinder will force the piston
960
HANDBOOK ON ENGINEERING.
m
be
HANDBOOK ON ENGINEERING.
961
out and thus lift the elevator. It will be seen that as soon as the main valve moves to the left, it carries lever / with it, and as this ever swings around J the pilot valve is moved back to the stop position. It can also be seen that the further the pilot valve is moved by the swing of A, the further the main valve must move to swing I far enough to return the pilot to the stop position ; that is, the further the arm is moved, the wider the main valve is opened. Thus the extent to which the main valve is opened is dependent upon the angle through which A swings, and this angle is dependent on the angle through which the car lever L is
M
Fig. 411. Take of Fig. 408 Machine.
moved ; hence, the operator has as perfect control of the move- ment of the main valve as if he moved it by pulling directly upon a hand rope.
Fig* 4f 2 is a photographic view of the Morse & Williams hori- zontal pushing machine. This is what is called a double decked machine and is a construction commonly resorted to when floor space is limited. Each machine operates a different elevator. The valve of this machine is arranged to be operated by a hand rope, the latter being passed around the large sheave wheel A. On the shaft of this wheel is mounted a small pinion that meshes into a rack attached to the end of the valve stem. This construc- tion will be seen illustrated fully and explained in connection with
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING. 963
the vertical elevator machines. The automatic stop valve is op* erated by means of the rope seen at the side of the machine that passes around sheaves J3, (7, the latter acting to close the valve.
HORIZONTAL HYDRAULIC ELEVATORS, PULLING TYPE.
In Fig. 413 is shown a horizontal machine of the pulling type. This is the design made by the Whittier Elevator Company. The stationary set of sheaves is located at the front, and the travel- ling sheaves are between it and the end of the cylinder. The op- erating valve is on top of the cylinder at the front end, the pilot valve being on top of the main valve. The automatic stop valve is just below the main valve and is operated by means of a rope passing over sheaves and provided with stop balls, all of which is clearly shown. The arrangement of the valve and pilot valve can be understood from Figs. 414-415, the first being a plan and the second a vertical section. The pilot valve is moved by lever E which is connected with the actuating ropes A A that run to the car lever. The lever E is pivoted at F so that when it swings in either direction it moves the pilot valve through rod C. The oper- ation of this valve and pilot valve is the same as that of Fig, 411 that is, the movement of the pilot valve to either side of the cen- tral position acts to connect the end Koi the main valve cylinder, either with the pressure pipe P or the exhaust It, thus moving the main valve in one direction or the other. If .ZT is connected with the pressure pipe, the valve is moved to the left and the cylinder is connected with the discharge pipe and the elevator runs down. The movement of the pilot valve in the opposite di- rection will connect K with the discharge and then the main valve will move to the right and the cylinder will be connected with the pressure pipe and the elevater will go up. In either case, the pilot valve is first moved in the same direction in which the main valve is moved immediately after, and the movement of the main
964
HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING.
965
valve acts to return the pilot to the stop position through the lever D and rod C.
The automatic stop valve is shown in Figs. 416-417, the two drawings being taken at right angles to each other. This valve consists of two parts, the valve proper B and a cylindrical car- rier A. The weight shown in Fig. 413 acts to swing A with B into the position shown in Fig. 417, and the automatic stops act to swing these parts so as to cover either one of the ports (7, D. If the car is going up the automatic stop rotates A in a clockwise direction so as to cover port C, and if coming down the rotation
Fig. 414. Valve of Whittle r Machine. Top View.
s opposite, so that A is moved over D. The valve B is held against A by the tension of a spring, and also by the water pres- sure, when the elevator is being stopped ; but when it is started again, by reversing the position of the main valve, the pressure acts to lift B from its seat against A and permit water to leak through slowly and thus allow the car to start up gradually. As soon as the car begins to move, the stop ball is drawn out of the way and the weight acting on A draws it into the position of Fig. 417 so as to open the valve wide and permit the car to attain full speed.
966
HANDBOOK ON ENGINEERING.
VERTICAL HYDRAULIC ELEVATORS.
The construction of a vertical elevator machine, Otis type, can be understood from Fig. 418 which is a vertical elevation of the lifting cylinder and operating valve in section. At A the valve is in the position it takes when the elevator is at rest. At B the position of the valve is that corresponding to the up motion of the car, while at G the position of the valve for the down motion is showno The pipe seen at the side of the cylinder is called a circulating pipe, and its office is to permit the water in the upper end of the cylinder to pass to the lower end, or circulate, while the elevator is running down. As can be clearly seen the easiest
Fig. 415. Talve of Whittier Machine. Side Elevation.
way in which to make a vertical cylinder elevator would be to have the lower end permanently open, and to let water into the upper end to force the piston down and the elevator car up, and to let this water out of the cylinder to permit the piston to run up and the car to run down. A little reflection, however, will show that with this arrangement, simple as it is, the force acting to force the piston down when the latter is at the top of the cylinder would be the pressure of the water only, while when the piston is At the bottom of the cylinder the force would be the pressure plus
HANDBOOK ON ENGINEERING.
967
the weight of water above the cylinder. Now if the cylinder is, say, thirty feet long this water would increase the pressure near- ly 14 pounds, hence, when the car is at the top of the well there would be a greater force than when at the bottom, and the load in all probability would be less. If the circulating pipe is used, the force acting on the piston is the same at every point in the stroke, because the water under the piston is drawn up by the vacuum that tends to form ; therefore, the force of the vacuum act- ing to draw down the piston is just as great as the force due to the weight of the water pressing on top of the piston, and as one
Fig. 416. Fig. 417.
Automatic Stop Valve for Whittier Machine.
increases as fast as the other decreases, the two balance each other at all times and the force acting on the piston remains un- changed.
The valve shown in Fig. 417 is of the kind used with a hand rope passing through the car to operate it. The hand rope is wound around the sheave 13, and when it is pulled it turns the sheave, the direction of rotation of the latter depending on the di- rection in which the rope is moved. The connection of the rope with the hand sheave is made such that if the car is going up the rope must be pulled up to stop, and if coming down the rope
968
HANDBOOK ON ENGINEERING.
SECTION OF ELEVATOR CYLINDER VALVE SHOWING WORK ING 'PARTS]
c
Fig. 418. Otis Vertical Elevator. .
HANDBOOK ON ENGINEERING.
969
must be pulled down to stop. The rotation of the sheave turns the pinion, seen in Fig. 418, and thus through the rack on the valve stem the valve is shifted.
r
Fig. 419. Otis Vertical Elevator System.
With the valve in the position A of Fig. 418 the piston cannot move because the water below it cannot escape. If the valve is raised to the position of JB, the water under the piston can escape
970
HANDBOOK ON ENGINEERING.
to the discharge tank, and then the piston can move down, that is, if it is in any position above the lowest. If the valve is lowered to the position C then the water in the upper end of the cylinder can pass through the valve chamber to the lower end, and the pressure being equalized, the piston will move upward, Fig. 419 is an illustration that serves to show how a complete
Fig. 420. Otis Valye.
vertical elevator system is arranged, although in practice few installations are arranged in this way ; generally the distance be- tween the tanks, and between these and the pump and elevator cylinder, is greater than here shown. In this illustration, the pressure tank is shown directly above the discharge tank, and the steam pump that supplies the water is located at the side of
HANDBOOK ON ENGINEERING. 971
the discharge tank. The pump draws the water from the dis- charge tank and delivers it into the pressure tank. The elevator cylinder draws its supply from the pressure tank and discharges it into the lower tank.
VALVE CONSTRUCTION.
The construction of the valve in Fig. 418 can be understood more fully from Fig. 42 00 It will be seen that the valve pistons are provided with cup packings, the cup in E being set so as to hold pressure acting from below, and F having packings to hold pressure from above. The valve casing opposite F has a brass lining which is perforated with numerous holes about one-quarter of an inch diameter. This construction is used in all hydraulic elevator valves, with the exception of very small pilot valves which are in some cases made solid and ground to a perfect fit. This is done so as to reduce the friction and make them move more freely. The perforated brass lining for the valve chamber is used so as to prevent the cup packing from dropping into the port holes as it passes them. The main pistons of hydraulic lifting cylinders are made so as to be packed with leather cups, also with hemp packing, and in some cases have a combination of cup and hemp packing ; but the latter alone is as good as any- thing, provided it is not pressed up too tight by the follower. Cases have been known where the cylinder has been burst by having the packing pressed up too tight.
The vertical elevator shown in Fig. 418 is provided with a valve that is actuated by the direct pull of a hand rope. This con- struction which was used exclusively in former days, is now em- ployed only for freight elevators, or passenger machines that run at a low speed. For first class service, such as the elevators of modern office buildings, a pilot valve is provided so that the op- erator may be able to control the movement of the car with cer-
972
HANDBOOK ON ENGINEERING.
Fig. 421. Otis Tertical Elevator with Pilot; VaJv« r«nt™i_
HANDBOOK ON ENGINEERING.
973
tainty even at the highest speed. An Otis vertical elevator for first class service, provided with a pilot valve is shown in Fig. 421 This machine is geared four to one. The main valve is similar to
Fig. 422. Otis Vertical Elevator, showing method of operating Pilot Valre.
that of Fig. 418, the only difference being that it has added to its upper end a larger piston, the office of which is to move the valve. In the simple arrangement of Fig. 418 the car is stopped automat-
974
HANDBOOK ON ENGINEERING.
ically at the top and bottom landings by simply placing stop balls on the hand rope is such position that they will be struck by the car at the proper time. This construction cannot be used with the pilot valve system because the operating ropes are held by the lever in the car, and are not free to move. Owing to this fact, a separate automatic stop valve is added and is connected between the main valve and the cylinder, as clearly shown in Fig. 421.
Fig. 423. Otis Vertical Elevator. Main Valve Used with Pilot Valve Control.
This stop valve is operated by means of a cable that passes around a sheave on the valve spindle, and another sheave near the top of the building. On this cable there are stop balls and these are struck by an arm projecting from the traveling sheave frame, the action being the same as in the horizontal machines. The way in which the valve is actuated by the movement of the oar lever is clearly shown in Fig. 421, but the operation of the
HANDBOOK ON ENGINEERING.
975
valves can be made clearer by the aid of Fig. 422. When through the movement of the car lever L, the sheaves P and P* are ro- tated, the pilot valve at h is either raised or depressed. If it is depressed, the pressure pipe is connected with the space T above the large valve piston, through the pipes g and/. The pressure in T forces the valve down so that the water in the upper end of
Fig. 424. Details of Otis Pilot Valve.
the lifting cylinder can circulate through pipe G to the lower end of the cylinder and permit the piston to go up and the car to de- scend. If the pilot valve is raised, the space T is connected with the discharge through pipe/ and/ and the water escapes, and as the pressure above the large valve piston is removed, the valve rises and thus the lower end of the cylinder is connected with the
97() HANDBOOK ON ENGINEERING.
discharge, and the water runs out, while the pressure water passes through port Vio the circulating pipe G and thus to the upper end of the cylinder.
The construction of the main valve can be clearly understood from the drawing Fig. 423 which is a vertical section. As will be seen the only difference between it and the valve Fig. 420 is that it is provided with the additional motor piston G which is in the position occupied by the rack and pinion in the latter drawing, The pilot valve can be understood from Fig. 424 in which the pipe outlets are marked to correspond with Fig. 422.
Additional light can be thrown upon the operation of the pilot and main valves by the aid of Fig. 425 which is a vertical eleva- tion of the valve gear the same as that shown in Fig. 422, but on a larger scale, and divested of the complication due to the pipe connections. The sheave 31 is rotated by the movement of the car lever, and the crank upon shaft 32 moves the lever 17 through the connecting rod 18. As the pilot valve moves easier than the main valve, this movement of 17 shifts the pilot valve, through rod 19. If the pilot valve is depressed, pressure water entering through ports 24 passes out through ports 26 and enters the space at top of main valve chamber, above motor piston 8. The pres- sure forces the main valve down and the upper end 11 of valve 13 uncovers the ports at 12 so that the water in the upper end of the cylinder can pass through the valve to the lower end and the pis- ton can go up, and the car come down. If the pilot valve is raised, ports 26 are connected with the lower end of pilot valve chamber, and the water above piston 8 can escape, so that the main valve may move up and connect ports 12 with the discharge pipe. It will be noticed that for either movement of the pilot valve, the following movement of the main valve acts through lever 17 to return the pilot to the stop position, and the further the latter is moved by the rotation of 31, the further the main valve will have to travel to return the pilot to the stop position ;
HANDBOOK ON ENGINEERING.
977
Fig, 425. Otis Differential and Pilot Valve*
978
HANDBOOK ON ENGINEERING.
thus the extent to which the main valve is moved is in direct pro portion to the extent to which 31 is rotated, and this is in pro portion to the extent to which the car lever is moved.
Fig. 426. Otis Main Valve with Magnetically Operated Pilot Yalre.
Sometimes hydraulic elevators are installed in private houses, or are used to operate dumb waiters, and in either case an opera=
HANDBOOK ON ENGINEERING.
979
tor to run the car is not required. As a rule elevators of this kind are operated by electric machines, but when hydraulic ma- chines are so used, they are arranged in the same way, that is, so that they may be operated by means of push buttons at the several floors and in the car. To make the hydraulic valve gear so as to be electrically operated, all that is necessary is to pro- vide magnets that will move lever 17 in the same way as it is moved by the rotation of sheave 31. A valve gear provided with
SUPPLY
Fig. 427. Pipe Connections for Fig. 426.
such magnets is shown in Fig. 426, in which M M' are electro- magnets, and A A' iron armatures attached to the lever B. If current is turned onto the magnet M , armature A is drawn down and through rod 0 lever D is pushed up carrying the pilot valve with it. If current is turned onto magnet JfcP, armature A' is drawn down and then G pulls D down and with it the pilot valve. The action of the main and pilot valves is the same as in Fig. 425,
980
HANDBOOK ON ENGINEERING.
The pilot valve for this magnet control is made so as to fit tight by grinding, so as to get rid of the friction of the cup packings. The way in which the pilot valve is connected with the main valve chamber, and the supply and discharge pipes is shown in Fig. 427. Two strainers are placed in the supply connection, so that by means of the three-way cocks shown either one may be
Fig. 428. Photographic Yiew of Fig. 427.
disconnected whenever it is desired to clean it. Fig. 428 is a photographic view of this type of magnetic valve gear.
With this arrangement of magnets, the current for operating them is drawn from an incandescent lighting circuit. It is necessary sometimes, however, to arrange the apparatus so that it may be operated by current obtained from primary batteries,
HANDBOOK ON ENGINEERING.
981
a lighting circuit not being available. As the current from primary batteries is weak, and expensive, it becomes necessary to modify the magnetic devices so that they may be actuated with
Fig. 429. Otis Main Valve with Magnet Control Adapted to Operate with Battery Current.
smaller currents. This is accomplished by the arrangement shown in Fig. 429. In this construction, the magnets M M' move
982
HANDBOOK ON ENGINEERING.
a pilot valve B that is much smaller than that used in Fig. 426, and works correspondingly easier. This secondary pilot controls the flow of water into a motor cylinder 7), and the piston in this
3 WAY
&URPLV PIPE
Fig. 480. Pipe Connections for Fig. 429.
cylinder acting through rod E moves the lever P in the same way as it is moved by the magnets in Fig. 426. As valve B is much smaller than the main pilot valve R the power required to move
HANDBOOK ON ENGINEERING.
983
it is much less than that required for the construction of Fig. 426. From Fig. 430, which shows the pipe connections of this double pilot valve construction, the operation of the valves can be more fully understood. The actual appearance of the valve gear is shown in the photographic view Fig. 431.
A complete diagram of a hydraulic elevator arranged for push
Fig. 431. Photographic Yiew of Fig. 430.
button operation is shown in Fig. 432. At C is located a de- vice calld a floor controller, and its office is to change the circuit connections so that by pressing the same button at any floor, the car may be caused to run up, if it is below that floor, or to run down if it is above the floor. A photo- graphic view of the floor controller is shown in Fig. 433.
984
HANDBOOK ON ENGINEERING.
J.
Fig. 432. Otis Private House Elevator, Push Button Control.
HANDBOOK ON ENGINEERING.
985
This floor controller is driven by chain E which is moved by the arm F, of the traveling sheave. The chain rotates a shaft that carries a worm that meshed into gear D and thus rotates C. The controller C has mounted on its surface two metallic strips that are connected with the opposite sides of the circuit. Contact brushes rest on these strips, there being one for each floor. The contact strips are set spirally on the face of the drum of 0, and the drum travels on a thread that is the same pitch as this spiral so that the brushes may always rest on the strips. When the elevator car is below a given floor, the
Fig. 483. Floor Controller for Otis Fash Button System. Fig. 433a.
brush corresponding to that floor rests on one of the metallic strips forming the spiral, but when the car is above this floor the brush rests upon the other strip. In this way the circuit con- nections are changed, so that if the car is above the floor, press- ing the button causes the car to run down, and if it is below the floor, pressing the same button causes it to run up. The way in which all this is accomplished is made clear by the wiring dia- gram, Fig. 434.
Two operating batteries are shown, and either one can be used
986 HANDBOOK ON ENGINEERING.
by turning the switch in the proper direction. If the switch is turned to close the circuit the current will flow into the + wire all the way to the car and back to wire A, and through coils a b to c and to wire B which connects with all the floor and car push but- tons. The coils a b and contacts c represent a magnetic switch with the two coils wound in opposition to each other, so that if current passes through both, contacts c remain closed. If any one of the push buttons is depressed the current will pass through it to the corresponding wire of the set 1, 2, 3, etc., and through the corresponding coil 11, 22, 33, etc., to a corresponding floor controller brush, and then through wire n and the upper magnets back;to the battery. The coils 11, 22, 33, etc., represent mag- netic switches that close the contacts seen to the right of them when a current passes. As soon as the contacts are closed, cur- rent flows through wire m from the junction of coils a b and then the coil b being cut out, the circuit with B is broken at c, so that after this instant, no one can interfere with the movement of the car by pressing another button because there is no current in B. Thus it will be seen that as soon as the car is started from any floor, or from the car itself, all the push buttons are cut out until the trip is completed. The circles seen in the upper part of the + wire represent door switches at the landings, that are open when the door is opened, so that unless the landing door is closed the car cannot move. As soon as the car begins to move, the floor controller begins to rotate, and when the car reaches the floor corresponding to the button pushed, the controller brush through which the current is passing passes onto the break between the segments n' and p' and the circuit through the magnets is broken and the ear stops. If the controller brush connected with the wire through which the current comes is resting onp', insteadof n' the current will flow through the lower valve magnets, and the di rection of the car will be reversed. In Fig. 434 the floor control- ler is shown with the segments eovering less than half a circle, so
HANDBOOK ON ENGINEERING.
987
as to simplify the diagram, but in the actual controller they are arranged in a spiral line as shown in Fig. 433, so as to give more space between the brushes.
Fig. 434. Wiring Diagram for Otis Push Button System. DOUBLE POWER HYDRAULIC ELEVATORS.
Hydraulic elevators of the types so far explained have one de- fect, and that is that it requires just as much power to run the
14
988 HANDBOOK ON ENGINEERING.
car up empty as if fully loaded. This is so from the fact that in either case a cylinder full of water must be used. To obviate this loss of power, the Otis Company make what is called the double power system. The difference between this and the ma- chines so far described is that water at two different pressures is used, the low pressure being about half as much as the high ; gen- erally the low pressure is 100 and the high 180 to 200 pounds. The valves are so arranged that for small loads only low pressure water is used the high pressure being reserved for heavy loads.
The valves of the double pressure system are shown in Fig. 435, and as will be seen are substantially the same as those already shown, the actual difference being that the piston F is added so as to control the flow of high pressure water. The pilot valve is made so that its first movement causes motor piston E to move far enough to let on the low pressure water only. If this is not sufficient to move the car, the operator moves the lever further, and then the pilot valve moves far enough to lift valve F above the lower edge of port i so that high pressure water may flow into the cylinder. In practice it is found that there is an in- jector effect produced which draws low pressure water in together with the high pressure, so that if the load in the car is more than the low pressure can lift, but less than the maximum capacity of the high pressure, then water is drawn from both sources, and the amount drawn from each one is nearly in proportion to the load.
HIGH PRESSURE HYDRAULIC ELEVATORS.
As low pressure elevators take up a considerable room, on ac- count of the large size of the lifting cylinders, the connecting pipes and the tanks, high pressure machines are frequently in- stalled in large office buildings, specially if these occupy small floor space. High pressure machines are made horizontal as well as vertical, but more are made of the latter type. A high
HANDBOOK ON ENGINEERING.
989
Fi?. 435. Otis Double Pressure Eleyator,
990 HANDBOOK ON ENGINEERING.
HANDBOOK ON ENGINEERING.
991
S3
•c
I
$
992 HANDBOOK ON ENGINEERING.
as the pilot valve is operated with low pressure water. The con- struction of the valves is shown in Fig. 438, in which the pilot is on the left, and is moved by the connecting rod E, which in turn is moved by L through rod D. The motor cylinder is in the center, and the main valve on the right. The pilot valve con- trols the flow of water into the motor cylinder, and when the piston Amoves, the piston rod Cr, through the connecting arms J and P, moves the main valve ; and also through lever JT, which swings around the upper end of D, moves the pilot valve back to the stop position. The pilot valve is operated with low pressure water because it would not be practical to use high pressure on account of the smallness of the ports. In fact the first ma- chines of this type were made with high pressure to operate the pilot valves, but they gave a great deal of trouble on account of the wearing out of the ports and valves. The sheave that moves the pilot valve is attached to the disc S, or to the shaft on which this disc is mounted.
In Fig, 437 the automatic stop valve is located near the main valve, at the lower end of the guides for the traveling sheave, and is actuated by levers that extend in the path of the sheave frame, so as to be struck by it at the proper time. The valve is also placed just below the lower end of the lifting cylinder, and is actuated by a chain that passes round a sheave mounted on its spindle and runs by the side of the traveling sheave frame to the lower end where it passes around a carried sheave. In this construction the chain has stop balls placed on it at both ends, and these are struck by a projecting arm on the sheave frame at the proper time to stop the car at the upper and lower floors. The valve used with this arrangement is shown in Figs. 439-440, 441 and 442. The sprocket wheel around which the chain passes is at A, and when the arm on the traveling sheave frame strikes one of the stop balls, A is rotated and with it the valve #, Fig. 4:4:2. The shaft of A carries a pinion that meshes into a gear on
HANDBOOK ON ENGINEERING .
993
Fig* 437t HigU Pressure Hydraulic Elevator System witli Inverted
Plunger,
994 HANDBOOK ON ENGINEERING.
the valve shaft, Fig. 440, so that A turns through several revo- lutions to close the valve G. The wheel C is provided to return the v-'tlve to the central position. A strap, to which a weight is attached, is secured to G and passes between the small wheels D 7), Fig. 440. The weight is heavy enough to rotate C.
The movement of A is geared down so as to produce a slow closing of the stop valve and thus prevent violent stopping of the elevator. The valve G is made so as not to fit perfectly, and is held against the seat in stopping by the pressure of the water, but when the pilot valve is turned to run the car in the opposite direction, the current of water through G changes its direction and the valve is lifted from its seat so that water can leak through fast enough to give the car a smooth start. As soon as the car moves, the arm that struck the stop balls moves out of the way, and then the weight suspended from G rotates the latter and returns the valve to the central position.
Fig. 443 shows two views of a valve not shown in Fig. 437. This valve is simply a speed governor. In high office buildings elevators run at very high speed, 500 to 600 feet per minute, and with such velocities it is possible for a car to run away if the load is light and the operator opens the valve too wide. The object of Fig. 443 is to prevent such run aways by checking the flow of water. In the sectional view of this valve it will be seen that the pipes are connected with the outlets C and D. Now the water to pass from one to the other has to flow through the valve piston B. This piston has small holes E for the water to flow through, and some pressure is lost by the passage of the water through these holes, the amount of pres- sure increasing as the velocity of the water increases. The spring JTact8 to hold piston B in the central position, and is ad- justed so as to hold against the pressure developed by the high- est velocity at which it is desired that the water should flow. If +,m's velocity is exceeded, the pressure due to the loss of head in
HANDBOOK ON ENGINEERING.
995
Fig. 438. YalYesUsedinFir.437.
996
HANDBOOK ON ENGINEERING.
passing through holes E will increase, and then B will be carried to one side of the center and some of the holes in sleeve F will be covered, thus reducing the opening through which the water can pass, and thereby checking the speed of the elevator.
Figs. 444 and 445 are two views of the accumulator. An ac- cumulator is simply a hydraulic cylinder standing upright and provided with a plunger that is loaded with iron weights until the desired pressure of water is obtained. In the illustrations, K
Fig. 439. Fig. 440.
Automatic Stop Valve Used in Fig. 437.
is the cylinder and L the plunger, which is provided with a cross- head at the top, from which depend rods M M that hold the weights A. These weights are made with a hole in the center large enough to clear the cylinder, so that when the water is all out, the weights envelop the cylinder. This construction is used in cases where it is desired to economize head room ; in other cases the weights are set directly on top of the plunger. To prevent pumping enough water into the accumulator to force the plunger out the top. and also to prevent drawing out so
HANDBOOK ON ENGINEERING.
997
much as to empty the cylinder and allow the plunger to strike the bottom, automatic stops are provided to control the pump, and also the flow of water from the accumulator. The rope to which the weight B is attached runs to the valve of the pump, and when the accumulator is full this weight B is lifted by shelf Q and then the pump valve is closed. The flow of water in or out of the accumulator is controlled by valve D. This valve is moved by an arm on the weights A striking the stop balls 2^ on the chain E. When the water is at the low limit, the lower F is struck and this closes valve D so that while water can flow in none can pass out. If the accumulator is full, the upper F is
Fig. 441. Fig. 442.
Automatic Stop Valve Used in Fig. 437.
struck and then D is reversed, so that no more water can be pumped in, but water can flow out freely.
Valve D is shown in Figs. 446 and 447. In the first drawing, the arrows A indicate the course of the water flowing into the ac- cumulator, and the outgoing path is indicated by the dotted ar- rows. The check valve in the outlet passage E opens upward, and check valve in the inlet passage F opens downward. If valve D is in the central position, water can pass through it in either direction, but if rotated in one direction it will stop the flow through E and if rotated in the opposite direction it will stop the flow through F. The passages E and F surround valve D, as
998
HANDBOOK ON ENGINEERING.
seen in Fig. 447 but the ports in the valve D as well as the valve chamber, are so shaped that E &ndF can be connected separately with B but not directly with each other.
Fig. 443. Speed Controller Used in Fig. 437.
PLUNGER ELEVATORS.
In plunger elevators, the lifting cylinder is placed in a hole bored down in the ground directly under the centre of the car.
HANDBOOK ON ENGINEERING
999
The plunger pushes the car to the top of the building; therefore, the plunger and cylinder both have to be made a few feet longer than the height to which the elevator is raised. The cylinder is
Fig. 444. Fiff. 445.
Accumulator Used in Fig. 437.
made of steel pipe, as many lengths as may be necessary bei&g joined together by means of sleeve couplings. The ends of the pipe sections are turned square with the axis of the pipe, and the
1000
HANDBOOK ON ENGINEERING.
threads are cut true so that when the several lengths are joined they may form a straight cylinder. The plunger is also made of lengths of steel pipe which are joined by internal sleeves. These sleeves are made extra long so as to give the plunger just as much strength at the joints as at other points. The pipes form- ing the plunger are turned true and made smooth so as to 'slide through the stuffing box with as little friction as possible, and also so as to make a tight joint at the box. The top of the cyl- inder consists of a casting provided with an outlet for the water
Fig. 446.
Fig. 447.
Valve for Accumulator, Figs. 444 & 445.
pipe to attach to, and a stuffing box at the top ; the latter is in some cases made separate and bolted to the main casting.
The plunger is made from six to seven inches in diameter, and the cylinder is about two inches larger, so that only the top cast-" ing has to be finished to fit the plunger. The lower end of the plunger is finished off with a casting, The hole in the ground is made about 13 inches in diameter, and when the cylinder is in place, the space between it and the sides of the hole is filled with sand.
HANDBOOK ON ENGINEERING. 1001
Plunger elevators have been made for years for short runs, but it is only within the past few years that they have been installed for high buildings and for all classes of service. While there are probably many concerns that make plunger machines for side- walk elevators, and other low runs, there are only two companies that make them for high speed passenger service in high office buildings. These concerns are, The Plunger Elevator Company and The Standard Plunger Elevator Company, both of which have their works in Worcester, Mass.
The general arrangement of the elevator made by the Standard Company is shown in the half tone Fig. 448, and the elevator of the Plunger Company is shown in half tone Fig. 449. From both these illustrations it will be seen that ropes pass from the top of the car over an overhead sheave and down to a counterbalance weight. If the building is high, say from 150 to 300 feet, the plunger will weigh so much that a part of it will have to be counterbalanced, so that the counterbalance weight will be heavier than the car proper, and will actually lift the upper end of the plunger. Owing to this fact, the plunger has to be firmly secured to the bottom of the car so that there may be no dan- ger of its pulling away.
The fact that the counterbalance weight is heavier than the car serves to increase the stiffness of the plunger for the reason that the upper end is subject to a tension, instead of compression, and the tendency to buckle is confined to the lower end. On this account the plungers do not buckle even when 200 to 300 feet long, notwithstanding that the diameter is between six and seven inches. Sometimes when making a quick stop coming down the plunger may spring slightly, but it at once returns to the straight position.
In the Standard Elevator Fig. 448 the main valve is at A, the pilot valve being at the extreme right side end, and is moved by the car lever through the rope connection as clearly shown. The
1002
HANDBOOK ON ENGINEERING*
I
HANDBOOK ON ENGINEERING. 1003
automatic stop valves to stop the car at the top and bottom land- ings are located below the main valve at B, the lower limit valve being at L and the top valve at Lf. These limit valves are act- uated by the ropes E and F. The first being attached to the bottom of the car on the left side. This rope runs over a small sheave and down and around the sheave on the end of the lever L, thence to the top of the elevator well, over a sheave and down to the top of the car where it is fastened on the right side. The other rope starts from the left side of the top of the car, and run- ning over a sheave at the top of the well runs down and around the sheave on the end of L'9 and thence up to the bottom of the car on the right side. Each one of these ropes is given a sharp bend when the elevator reaches its end of the well, and in that way the lever of the corresponding limit valve is raised, and the valve is closed so as to stop the car. The water from the pressure tank enters through pipe S to the main valve chamber, and passing down through the limit valve chamber reaches the cylin- der. In escaping from the cylinder the water passes through the limit valve to the main valve and thence to the discharge pipe D. The operation of the valves will be explained further on.
In Fig. 449 the limit valves are actuated in substantially the same manner as in Fig. 448, but the ropes are stationary, their upper ends being fastened to the framing at the top of the eleva- tor well and the lower ends to the valve levers. In this elevator, the main valve is connected between the cylinder and the limit valves, which is just the opposite of the arrangement in Fig. 448.
The details of construction of the cylinder and plunger of the Standard machine are shown in the line drawings, Figs. 450 and 451, the first being a vertical elevation in section, and the other an outside view taken at right angles to Fig. 450. In the last named drawing, the long sleeve couplings inside of the plunger can be clearly seen, also the construction of the top
36
1004
HANDBOOK ON ENGINEERING.
Fig. 449. Is Plunger Elevator of the Plnnerer Elevator C&.
HANDBOOK ON ENGINEERING. 1005
cylinder casting, with the water pipe opening A. Within the plunger there is a strong steel cable B that is secured to the floor framing of the car, and runs down to the bottom of the plunger where it is firmly secured. This is an extra safeguard to hold the plunger if from any cause it should break away from the un- derside of the car floor. The bottom of the plunger terminates in a brass casting (7, which is made of brass so that that portion of it that does not pass through the stuffing box when the car reaches the top floor, may not become rough by rusting. This casting carries at its lower end three copper wire brushes d which serve to prevent the lower end of the plunger from hitting the sides of the cylinder, and also will permit water to run out of the top of the cylinder if for any reason the car should run above the top limit. This is a safety arrangement provided so that the car cannot run into the overhead beams.
The valves of the Standard Plunger Elevator are shown in Fig. 452. The supply pipe is at £, and the discharge pipe at E. When the car runs up the main valve is moved to the right carry- ing E fast enough to permit water from S to pass S' '. W7hen run- ning up, valve Fisto the left of the position shown, so that from S' the water can pass to D and to the cylinder. In coming down, the main valve is moved to the left far enough for T to connect E with E' and then the water in the cylinder can pass out through D to E' and through the main valve chamber to E.
The pilot valve is located at the right of the main valve, JV being its stem. The lever K is moved by the car lever through the running rope gear as shown in Fig. 448. If K is raised, the rod L lifts the shaft that carries pinion P, and thus the pilot valve is raised, so that the water from the supply pipe /Scan pass through A to the pilot valve chamber and come out through pipe C to pipe P and thence to space M back of the motor piston Q of the main valve. This water will move the main valve to the right and cause the elevator to ascend. At the same time
1006
HANDBOOK ON ENGINEERING.
DETAILS OF PLUNGER ELEVATOR PARTS AND CONNECTION
Fig. 450. For Standard Plunger Elerator. Fig. 45
HANDBOOK ON ENGINEERING.
1007
the movement of rack U will rotate pinion P and cause it to run down on the thread in L and thus lower the pilot valve to the central position. In going down the lever K is depressed and the movement of the pilot valve is in the opposite direction so that pipe P is connected through the lower end of the pilot valve chamber with the pipe leading to the discharge, and in this way end Q of motor cylinder is emptied and the main valve moves to the left. From the foregoing it will be seen that the action of
Fig. 452. Pilot Controlling Valve for Standard Plunger Elevator and Automatic Stopping Yalve for End of Bun.
the pilot and main valves in this construction is substantially the same as in other types of elevators, in fact all hydraulic elevator pilot valve gears act upon the same principle, and only differ in construction. The action of the limit valve is not clearly seen from Fig. 452, because in this drawing the end levers are in an in- rerted position, this being done so as to contract-the drawing by shortening the connections S' E'. If it is kept in mind that the end levers are reversed, as shown in Fig. 448, then it can be seen
1008 HANDBOOK ON ENG1NUE1UNG.
that when W is raised, Yis closed, and that the same is true of Z and F. The valves G G at the inner ends of ]Tand Z are for the purpose of stopping the ports from S' and E' if the ropes that operate the limit valves should break or run off the sheaves. It will be noticed that at the lower end of the shaft of pinion P there are two spiral cams, and a stationary cam is located be- tween them. These cams are for the purpose of preventing a too sudden stop of the car, by an instantaneous closing of the main valve. If the main valve is closed instantly, when the car is running up, the headway will keep the car moving up some distance and as water cannot flow into the cylinder, the plunger will leave the top of the water. The headway of the car will then soon stop and its weight will bring it back and cause the plunger to strike the top of the water in the cylinder, and pro- duce an uncomfortable jolt. If the sudden stop is effected when the car is going down the plunger will buckle to some extent to relieve the jar. The cams below P prevent these sudden stops because L cannot move P vertically any faster than the cams turn around so that even if K is moved ' to the stop position in- stantly, the pilot valve will not move any faster than is per- missible.
The main and pilot valves of the Elevator made by the Plunger Co., Fig. 449 are shown in Fig. 453. The pilot valve is moved by lever H. There are two valves used to perform the pilot work, L the pilot valve proper, and JT, which is called a throttle. If H is lifted, the lever I will swing arouud its upper end and move L to the left. The supply pipe is at E, and is connected with chamber 1 by port 0, and 1 is connected with 2, so that when 1 is moved to the left, water can pass from 1 to 2 thence through 3 to 4 and through pilot valve to passage 6 and to the back end of motor piston- cylinder, and force the main valve to the right, BO that water from E may pass to F and to the lifting cylinder. The movement of the main valve to the right will cause K to
HANDBOOK ON ENOINEERING.
1009
1010 HANDBOOK ON ENGINEERING.
move to the left, and L to the right, thus bringing the pilot valve back to the stop position, just as in all other pilot valve arrange- ments. The movement of K to the left closes the opening be- tween d and / at e so that the only way for water to pass from one space to the other is through the opening opposite the end of screw N. This construction is for the same purpose as the cams on the shaft of pinion P in Fig, 452, that is, to prevent too sudden a stoppage of the elevator. The operation is as follows : Suppose the operator moves the car lever rapidly to the stop posi- tion, then lever H swings down rapidly, and carries the pilot valve with it, but the water in the back of the motor cylinder, to reach the discharge pipe must follow the path indicated by 6 &, c, djf, and g to G. Now as we have shown, the opening be- tween d and / through K has been closed , so that the water has to pass through the hole opposite screw N and by properly ad. justing the position of this screw the passage can be made as small as desired, and the time required for the water to pass can be as much as may be necessary to prevent the main valve from closing too rapidly.
The operation of this valve in going down is the reverse of that above explained. On the down trip the pilot valve water is dis- charged in stopping through spaces 2, 4, and passes through opening opposite screw M , and is adjusted by this screw.
The operation of the limit valves in Fig. 449 can be easily under- stood from the line drawing Fig. 454. The pipes A and B con- necting the limit valves with the pilot valve chamber are for the purpose of giving a direct connection between the supply and discharge and the pilot valve. The main valve shown in Fig. 454 is not a duplicate of that in Fig. 453, the principal difference between them, however, is that in the latter all the connections are made by passages cast in the valve casing, while in the former these connections are made by outside piping.
Fig* 455 shows in outline a simplified form of plunger elevator
HANDBOOK ON ENGINEERING.
ion
Fig. 454. Fine Illustration of the Plunger Elevator Company's Elevator for Pilot Valve Control.
made by the Plunger Co, for freight service. In this arrange- ment the valve is actuated by a hand rope, and, therefore, is of
]012 HANDBOOK ON ENGINEERING.
simple construction, without a pilot valve. The limit valves are also dispensed with as their office is filled by the stop balls attached to the hand rope. The valve used in Fig. 455 is shown in Fig. 456 and is so simple as to require no explanation. It may be well to mention, however, that it shows the exhaust pipe connection on the side of the valve chamber, instead of at the end. This construction is for the purpose of effecting a more perfect balancing of the end thrust by the use of an additional piston C. It can be seen that with the addition of 0 it makes little difference where the discharge tank is placed, either above or below the valve, for if there is any back pressure it will act equally upon B and (7, but if C were removed it would act against B only. When the discharge tank can be placed on a level with the valve, nothing is gained by adding piston C.
HOW TO PACK HYDRAULIC VERTICAL CYLINDER ELEVATORS.
Packing Otis Vertical Piston from bottom* — Remove the top stop-button on hand rope and run the car up until the pis- ton strikes the bottom head in cylinder. Secure the car in this position by passing a strong rope under the girdle or cross- head and over the sheave timbers. When secured, close the gate valve in the supply pipe, open the air cock at the head of the cylinder, and throw the operating valve for the car to go up. Also open the valve in the drain pipe from the side of the cylin- der, and from the lower head of the cylinder, thus allowing the water to drain out of the cylinder. When the cylinder is empty, throw the valve for the car to descend in order to drain the wa- ter from the circulating pipe. In case of tank pressure, where level of water in lower tank is above the bottom of the cylinder, the gate valve in the discharge pipe will have to be closed as soon as the water in the cylinder is on a level with that
HANDBOOK ON ENGINEP:RING.
1013
Fig. 155. Plunger Elevator with Hand Rope Control*
1014
HANDBOOK ON ENGINEERING.
of the tank, allowing the rest to pass through the drain pipe to the sewer. When the water is all drained off, remove the lower head of the cylinder, and the piston will be accessible. Remove the bolts in the piston follower by means of the socket wrench, which is furnished for that purpose. Before removing the piston head, mark its exact position, then there will be no difficulty in replacing it ; also be careful and not let the piston get turned in the cylinder, so as to twist the piston rods. On removing the piston follower, you will find a leather cup turned upwards, with coils of |-inch square duckpacking on the outside. This you will remove and clean out the dirt ; also clean out the holes in the
Fig. 456. Valve for Plunger Elevator with Hand Rope Control.
piston, through which the water acts upon the cups. If the leather cup is in good condition, replace it, and on the outside place three new coils of |-inch square duck packing, being careful that they break joints and also that the thickness of the three coils up and down does not fill the space by J inch, as in such case the water might swell the packing sufficiently to cramp it in this space, thus destroying its power to expand. If too tight, strip off a few thicknesses of canvas. Replace the piston follower and cylinder head, and the cylinder is ready to refill. Close the valves in the drain pipes, leave the air cock open at the head of the cylinder and the operating valve in the position to descend, and open gate valve in the discharge. Slowly open the gate valve
HANDBOOK ON ENGINEERING. 1015
in the supply pipe, allowing the cylinder to fill gradually and the air to escape at the head of the cylinder. When the cylinder is I full of water, leave the air cock open and put the operating valve on the center. The car can then be untied, the stop button can be reset, and the elevator is ready to use. Make a few trips be- fore closing the air valve.
Packing vertical cylinder piston from top* — Run the car to the bottom and close the gate valve in the supply pipe. Open the air cock at the head of the cylinder, and also keep open the valve in the drain pipe from the side of the cylinder long enough to drain the water in the cylinder down to the level of the top of the piston. Now remove the top head of the cylinder, slipping it and the piston rods up out of the way, and fasten there. If the piston is not near enough to the top of the cylinder to be accessible, attach a rope or small tackle to the main cables (not the counter-balance cables) a few feet above the car, and draw them down sufficiently to bring the piston within reach. Remove the bolts in the piston follower by means of the socket wrench furnished for that purpose. Mark the exact position of the piston follower before removing it, so that there will be no difficulty in replacing it. On removing the piston follower you will find a leather cup turned upwards, with coils of |-inch square duck packing on the outside. This you will remove and clean out the dirt ; also clean out the holes in the piston through which the water acts upon the cup. If the leather cup is in good condition, replace it, and on the outside place three new coils of |-inch square duck packing, being careful that they break joints, and also that the thickness of the three coils up and down does not fill ths space by £ inch, as in such case the water might swell the packing sufficiently to cramp it in this space, thus destroying its power to expand. If too tight, strip off a few thicknesses of canvas. Replace the piston follower and let the piston down to its right position. Replace the cylinder
1016 HANDBOOK ON ENGINEERING.
head and gradually open the gate valve in the supply pipe, first being sure that the operating valve is on the down stroke or it is so the car is coming down. As soon as the air has escaped be- fore closing the air cock to make sure the air is all out of the cylinder, make a few trips, and the elevator is ready to run.
Packing the vertical cylinder valves. — To pack the valve, run the car to the bottom and close the gate valve in the supply pipe. Then throw the operating valve for the car to go up, open the air cock at the head of the cylinder and the valve in the drain pipe at the bottom, and the water will drain out of the cylinder. When the cylinder is empty, reverse the valve for the car to run down so as to let the water out of the circulating pipe. In cases of tank pressure, where the level of the water in the lower tank is above the bottom of the cylinder, the gate valve in the discharge pipe will have to be closed as soon as the water in the cylinder is on a level with that in the tank, allowing the rest to pass through the drain pipe to the sewer. As soon as the water has all drained off, take off the valve cap and remove the pinion shaft and sheave, marking the position of the sheave and the relation which the teeth on the pinion bear to the teeth on the rack before removing. You can now take out the valve plunger and put the new cup leather packings on in the same position as you find the old ones. Replace all the parts as first found. Before refilling the cylinder, close the valves in the drain pipes, but leave the air cock at the head of the cylinder open and be careful that the operating valve is in position for the car to go down. Gradually open the gate valve in the supply pipe. When the cylinder has filled with water and the air has escaped, close the air cock and open the gate valve in the discharge pipe.
Packing piston rods* — Close the gate valve in the supply pipe. Remove the followers and glands to the stuffing boxes and clean out the old packing. Repack with about eight turns of
HANDBOOK ON ENGINEERING. 1017
J-inch flax packing to each rod, and replace glands and followers.. Screw down the followers only tight enough to prevent leaking.
If traveling or auxiliary sheave bushing is worn so that sheave binds, or the bushing is nearly worn through, turn it half round, and thus obtain a new bearing. If it has been once turned put in a new bushing. See that the piston rods draw alike. If they do not, it can be discerned by trying to turn the rods with the hand, or by a groaning noise in the cylinder. However, this groaning may also be caused by the packing being worn out, in which case the car would not stand stationary. See that all sup- ports remain secure and in good condition.
WATER FOR USE IN HYDRAULIC ELEVATORS.
In hydraulic elevator service little heed is usually given to the quality of water, with which the system is operated. Much loss of power by friction and many dollars spent annually in repairs can be avoided by a little thought and action on this subject. In order to prove the truth of this statement, one has only to obtain two samples of water, one of soft water and the other of what is commonly known as hard water. For example, take rain water as the first sample and water from the well as the second. Now rub your hands briskly together while holding them im- mersed in one, and then in the other of these samples. You will instantly realize that the quality of water used in elevator service has much to do with the efficiency of the hydraulic ma- chinery. Water from the service pipes of the oity water-works always contains more or less sand and other gritty substances in suspension, and this grit acts much the same 'on the packing and metal parts of the apparatus as does a sand blast. Some engineers, having realized the evil effects of water in the state that is generally used have attempted to remedy the matter by replacing the water which is lost by leakage or evaporation by the
1018 HANDBOOK ON ENGINEERING.
addition of the water which is discharged from the steam traps of the plant; and as this has been distilled, it is almost chemically pure — thus the man who uses distilled water in an elevator sys- tem instead of the water containing grit, is simply getting out of one difficulty into another.
It is a well-known fact in chemistry that pure water is a solvent for every known substance, and will especially attack iron to a large degree. Whenever it is practicable, the water for elevator use should be passed through a filter to remove grit before being allowed to pass into the surge tank. In many cases, however, it would be difficult for the engineer to convince the owner of the advisability of buying and installing a filter for this purpose. A simple and somewhat inexpensive remedy is within reach of all — the plentiful use of soap will obviate many of the evil effects of hardness of the water, will double the life of the packing, will reduce the loss by friction, and will, to a large extent, prevent the chattering of the pistons, making the elevators run much smoother. In laboratory practice, the degree of hardness or softness of water is determined by the amount of pure soap that is necessary to mix with the water to form a lather, or to precip- itate a certain quantity of carbonate of lime and other substances. This same action, on a larger scale, takes place when soap is in- troduced into an elevator tank, and while the oily portion of the soap forms an emulsion with the water, of great lubricating properties, the gritty matter is precipitated and can be gotten rid of through means of a blow-off in the bottom of the tank. The cheapest and most convenient form in which to obtain soap for this purpose, is. the soap powder extensively manufactured by various firms and which can be purchased for about four cents per pound. In a plant of six elevators, with usually a strong capacity of some 8,000 gallons, it is a good practice to use about twenty pounds of this soap each week. The soap should be at first? dissolved in about ten times its weight of boiling water, and
HANDBOOK ON ENGINEERING. 1019
when cold it will form a stiff soft soap. The practice of putting in the refuse oil collected from the drip pans is of little value ; it will not mix with the water, but floats on the surface. It rarely gets low enough to enter the suction pipes of the pumps, and has little or no tendency to precipitate the solid matter that is held in suspension in the water.
If car settles, the most probable cause is that the valve or pis- ton needs repacking. If packing is all right, then the air valve in the piston does not properly seat. If the car springs up and down when stopping, there is air in the cylinder. When there is not much air, it can often be let out by opening the air cock and running a few trips, but when there is considerable air, run the car to near the bottom, placing a block underneath for it to rest upon, then place the valve for the car to descend. While in this position, openthe air cock and allow the air to escape. This may have to be repeated several times before the air is all removed.
Keep the cylinder and connections protected from frost. Where exposed, the easiest way to protect the cylinder is by an air-tight box, open at the bottom, to which point keep a gas jet burning during cold weather. Where there is steam in the build- ing, run a coil near the cylinder. Keep stop buttons on hand cable properly adjusted, so that the car will stop at a few inches beyond either landing, before the piston strikes the head of the cylinder. Regulate the speed desired for the car by adjusting the back stop buttons, so that the valve can only be opened either way sufficiently to give this speed. Occasionally try the governor to see that it works properly. Keep the machinery clean and in good order.
ELEVATOR INCLOSURES AND THEIR CARE.
Elevator inclosures, while intended for protection to passen- gers, are often carelessly neglected and are often a source of
1020 HANDBOOK ON ENGINEERING.
danger, unless looked after and taken care of in a proper manner. It is of the utmost importance that no projection of any kind shall extend into the doorways for clothing of passengers to catch on, thus endangering their lives. The doors should move freely to* insure their action at the touch of the operator. See that all bolts and screws are tight, and replace at once all that fall out, otherwise, the doors and panels may swing into the path of the elevator cage and be torn off, and probably injure some one, thus placing the owner liable to damages. Elevator doors that are automatic in their closing are the best, but all operators should be held strictly responsible for accidents occurring from the carelessness of leaving doors open. All inclosures should be equipped with aprons above the doors to the ceiling and as close to the cage as possible, to prevent passengers from falling out or extending their person through to be caught by ceilings or beams in the elevator shaft. As a rule, proprietors of buildings take a pride in keeping their inclosures and cars in a neat condition, as they are considered an ornament to the building for the purpose for which they are intended, and no expense is spared in the line of art ; so it is recommended that they be kept free from dampness. Dust with a feather duster and use soft rags for cleaning. Never use any gritty substance, soaps or oils. II they become damaged, have the maker repair and relacquer them.
HANDBOOK ON ENGINEERING.
1021
STANDARD HOISTING ROPE WITH 19 WIRES TO THE STRAND.
IRON.
|
0 fc 0) I |
Diameter. |
Circumfer- ence in inches. |
Weight per foot in Ibs. of rope with hemp center. |
Breaking strain in tons of 2000 Ibs. |
f Proper working load in tons of 2000 Ibs. |
Circumfer- ence of new Manilla rope of equal strength. |
Minimum size of drum or sheave in feet. |
|
1 |
24 |
61 |
8.00 |
74 |
15 |
14 |
13 |
|
2 |
2 |
6 |
6.30 |
65 |
13 |
13 |
12 |
|
3 |
11 |
54 |
5.25 |
54 |
11 |
12 |
10 |
|
4 |
II |
5 |
4.10 |
44 |
9 |
11 |
84 |
|
5 |
14 |
41 |
3.65 |
39 |
8 |
10 |
74 |
|
54 |
U |
« |
3.00 |
33 |
64 |
9* |
7 |
|
6 |
14 |
4 |
2.50 |
27 |
54 |
84 |
64 |
|
7 |
H |
34 |
2.00 |
20 |
4 |
74 |
6 |
|
8 |
i |
3* |
1.58 |
16 |
3 |
64 |
5J |
|
9 |
i |
21 |
1.20 |
11-50 |
24 |
54 |
44 |
|
10 |
1 |
24 |
0.88 |
8.64 |
U |
41 |
4 |
|
104 |
i |
2 |
0.66 |
5.13 |
14 |
31 |
34 |
|
10£ |
ft |
If |
0.44 |
4.27 |
1 |
34 |
21 |
|
101 |
4 |
14 |
0-35 |
3.48 |
4 |
3 |
24 |
|
lOa |
ft |
U |
0.29 |
3.00 |
I |
21 |
2 |
|
10i |
14 |
0.26 |
2.50 |
4 |
24 |
14 |
|
|
1 |
Operating Cable or Tiller Rope, 1 in. diam.; | in. diam.; £ in. diam.; | in. diam.
Cables, and how to care for them. — Wire and hemp ropes of same strength are equally pliable. Experience has demonstrated that the wear of wire cables increases with the speed. Hoisting ropes are manufactured with hemp centers to make them more pliable. Durability is thereby increased where short bending occurs. All twisting and kinking of wire rope should be avoided. Wire rope should be run off by rolling a coil over the ground like a wheel. In no case should galvanized rope be used for hoisting purposes. The coating of zinc wears off very quickly
1022 HANDBOOK ON ENGINEERING.
and corrosion proceeds with great rapidity. Hoisting cables should not be spliced under any circumstances. All fastenings at the ends of rope should be made very carefully, using only the best babbitt. All clevises and clips should fit the rope perfectly. Metal fastenings, where babbitt is used, should be warmed before pouring, to prevent chilling. Examine wire ropes frequently for broken wires. Wire hoisting ropes should be con- demned when the wires (not strands) commence cracking. Keep the tension on all cables alike. Adjust with draw-bars and turn- buckles provided.
Leather cup packings for valves* — Leather for cups should be of the best quality, of an even thickness, free from blemish and treated with a water-proof dressing. The cups should be of sufficient stiffness to be self-sustaining when passing over per- forated valve lining. When ordering cups, the pressure of water carried should be specified, aa the stiff cups intended for high- pressure would not set out against the valve lining when low pressure is used.
Water* — Water for use in hydraulic elevators should be per- fectly clear and free from sediment. A strainer should be placed on the supply pipe and water changed every three months, and the system washed and flushed.
Closing down elevators* — If an elevator is to be shut down for an indefinite period, run the car to the bottom and drain off the water from all parts of the machine ; otherwise, a freeze is likely to burst some part of the machinery. If the machine is of the horizontal type, grease the cylinder with a heavy grease ; if vertical, the rods should be greased. Oil cables with raw linseed oil.
HANDBOOK ON ENGINEERING. 1023
LUBRICATION FOR HYDRAULIC ELEVATORS.
The most effectual method of lubricating the internal parts of hydraulic elevator plants where pump and tanks are used, is to carry the exhaust steam drips from the foot of the pump exhaust pipe to the discharge tank, thus saving the distilled water and cylinder oil. This system is invaluable when, water holding in solution minerals is used, as these minerals greatly increase cor- rosion. Horizontal machines operated by city pressure are best lubricated with a heavy grease applied either mechanically or by means of a piece of waste on the end of a pole. The former method serves as a constant lubricator, while in the latter case, greasing is often neglected, and in consequence packing lasts but a short time.
Lubrication of cables* — A good compound for preservation and lubrication of cables is composed of the following : Cylinder oil, graphite, tallow and vegetable tar, heated and thoroughly mixed. Apply with a piece of sheepskin with wool inside. To prevent wire rope from rusting, apply raw linseed oil.
Lubrication of guides* — Steel guides should be greased with good cylinder oil. Grease wood strips with No. 3 Albany grease or lard oil. Clean guides twice a month to prevent gumming.
Lubrication of over head sheave boxes* — In summer use a heavy grease. In winter add cylinder oil as required.
USEFUL INFORMATION.
To find leaks in elevator pressure tanks in which air is con- fined, paint round the rivet heads with a solution of soap and the leak will be found wherever a bubble or suds appear. To ascer- tain the number of gallons in cylinders and round tanks, multi- ply the square of diameters in inches by the height in inches and the product by .0034=gallons. Weight of round wrought
1024
HANDBOOK ON ENGINEERING.
iron : Multiply the diameter by 4, square the product and, divide by 6=the weight in pounds per foot. To find the weight of a casting from the weight of a pine pattern, multiply one pound of pattern by 16.7, for cast-iron, and by 19 for brass. Ordinary gray iron castings = about 4 cubic inches to the pound.
"Water* — A gallon of water (U. S. Standard) contains 231 cu. in. and weighs 8^ Ibs. A cubic foot of water contains 7£ gal. or 1728 cu. in. and weighs 62.425 Ibs. A " Miner's inch " is a measure for the flow of water and is the amount discharged through an opening 1 inch square in a plank 2 in. in thickness, under a head of 6 in. to the upper edge of the opening ; and this is equal to 11.625 U. S. gal. per minute. The height of a column of fresh water, equal to a pressure of 1 Ib. per sq. in., is 2.304 feet. A column of water 1 ft. high exerts a pressure of .433 Ibs. per sq. in. The capacity of a cylinder in gallons is equal to the length in inches multiplied by the area in inches, divided by 231 (the cubical contents of one U. S. gal. in inches). The velocity in feet per minute, necessary to discharge a given volume of water in a given time, is found by multiplying the number of cu. ft. of water by 144 and dividing the product by the area of the pipe in inches.
Decimal Equivalents of an Inch.
|
1-16 |
1-8 |
3-16 |
1-4 |
5-16 |
3-8 |
7-16 |
1-2 |
|
.0625 |
.125 |
.1875 |
.25 |
.3125 |
.375 |
.4375 |
.5 |
|
9-16 |
5-8 |
11-16 |
3-4 |
13-16 |
7-8 |
15-16 |
|
|
.6625 |
.625 |
.6875 |
.75 |
.8125 |
.875 |
.9375 |
HANDBOOK ON ENGINEERING. 1025
ELEVATOR SAFETIES.
All types of elevators in which the car ia lifted by cables are provided with means for arresting the movement of the car if it attains a dangerously high speed through the breaking of the lifting ropes or the disarrangement of any part of the hoisting apparatus. The direct plunger elevators are not provided with safety appliances, it being considered that the plunger on which the car is lifted will prevent the latter from dropping, as it cannot be crushed by the load, nor caused to run down any faster than the water can escape from the cylinder.
In the early days of elevators, when the car speed was low, the safety devices consisted of racks attached to the faces of the guides, and dogs carried by the car, these dogs being held out of action so long as the ropes did not break. With the gradual in- crease in height of buildings, the car speed was increased and then it was realized that the rack and dog devices were not adapt- ed to do the work, as they would stop the car so suddenly as to give the passengers nearly as bad a shaking up as they would re- ceive if the car went to the bottom of the well. For the purpose of producing a more gradual stoppage of the car, wedge safety devices were introduced. . These safeties act by forcing a wedge between the guides on which the car runs and strong iron jaws carried by the car, and as the wedges are tightened slowly, the car can run some distance before it is' stopped, thus producing a gradual stop. The jaws that hold the clamping wedge are fastened to the ends of a massive hard wood plank, and for this reason the apparatus was called a " Safety Plank, " and is known by that name at the present time.
A wedge safety plank, of the type used by the Otis elevator Co. , is shown in Figs. 457, 458, 459, the last two illustrations only show one end of the apparatus. This device is used in connec-
1026
HANDBOOK ON ENGINEERING.
tion with four lifting cables two of which are secured to the ends A B of a rocker (7, 'the other two being similarly connected with
a rocker at the other end. The rocker G has projections that move levers mounted on shaft H, and one of these levers, marked
HANDBOOK ON ENGINEERING. 1027
5, when raised strikes wedge ^and forces it up between the jaw? of the safety plank and the guide M. The end of b is sharp and long enough to reach the guide and cut into it, thus helping to force the wedge up tight enough to hold the car. If one of the lifting cables attached to the ends A B of rocker C should break, that end of C will drop and then shaft H will be rotated so as to swing b upward and force the wedge JVinto action. The rocker C has two projections, one on each side of H so that no matter which way C is tilted, b will be moved upward.
If elevators dropped only when the ropes break, the safety as explained would be sufficient, but as a matter of fact, they can- not very well drop in this way, because all the cables will not break at the same time. In, nearly every case, the elevator does not actually drop, but through some disarrangement of the ma- chinery it attains a dangerously high speed, that is, it runs away. Owing to this fact it is necessary to arrange the safeties so that they will act if the car speed becomes too great, regardless of what the cause may be. This is accomplished by providing a governor, similar to those used on engines, that is driven by the car, and when the speed becomes too great it throws the safety into action. The safety governor of the Otis Co., is shown in Fig. 460. It is driven by a rope that passes over sheave A and runs down in the elevator well to the bottom where it passes under another sheave. This rope is fastened to the end ytoi lever G, Fig. 458, and through lever Jc acts to rotate shaft H. The spring S wound on H is stiff enough to. drive the governor and prevent If from turning, but if the car speed becomes too great, the rod D, Fig. 460, will lift the crank jVand thus throw in a clamp that will hold the rope fast. When this occurs, the downward move- ment of the car will cause lever G to rotate shaft H and thus 6 will force the safety wedge N into position to stop the car.
There are many modifications of the wedge safety, but as they do not work with certainty on iron guides they are now practical-
1028
HANDBOOK ON ENGINEERING.
ly out of date, as wooden guides are not used except in the few cases where they are permitted by the insurance regulations, or where a cheap construction is desired. In large fireproof build- ings they are not allowed.
Tig. 460. Otis Safety Governors Single Acting.
A modification of the wedge safety that was used to some ex- tent a few years ago is shown in Figs. 461 and 462, the first giving the position of the parts when out of action, and the second the position when in action. This is known as the roller safety. The
HANDBOOK ON ENGINEERING.
1029
roller a, when drawn up by the lifting rod, wedges between the iron guide and the jaw of the safety plank and then rolls up
until it binds tight enough to stop the car. The objection to this device is that it grips too soon, in fact it is liable to stop
HANDBOOK ON ENGINEERING.
the; car in two or three inches, so that if the speed is high, the passengers will get a serious shaking up. The lifting rod is operated by a safety governor, the connections with the latter being indicated in Figs. 463 and 464, the first showing the actual
Fig. 403. Governor Rope Connection for Roller Safely.
connection with the governor rope, and the second, the levers, in the top framing of the car, to transmit the movement to the op- posite side so that both rollers may be thrown into action at the
HANDBOOK ON ENGINEERING.
1031
same time. It will be noticed in Fig. 464 that the lifting cables are permanently secured to the car framing, and not to any part of the safety, so that if one or two of them should break, the safety would not go into action. This, however, does not make the device any the less effective, because the car could not drop unless all the ropes broke at the same time, and if this occurred,
|
f^ 1 |
V |
n |
|
|
r- |
|||
|
— r |
-J |
/. |
|
|
i |
|||
|
,'T |
ij, p |
• I ^^ ^ >%^ 222 |
k |
|
a |
j©^D e j^b |
||
|
Iff |
^^& |
||
|
JA |
^1L |
Fit?. 464. Lifting Rope Connections for Roller Safety. '*
the speed would at once increase, and then the safety governor would come into action and throw the rollers up, just the same as if the speed had increased from some other cause. This type of safety is not used now because it stops the car too suddenly. A safety to be satisfactory must be so arranged that it will produce a gradual stop, if it comes into action, This result is
1032
HANDBOOK ON ENGINEERING.
accomplished in the type of safety commonly known as the brake or clamp safety. It consists of strong brake shoes arranged to press against the sides of the guides on which the car runs, with a continuously increasing pressure until the breaking action be- comes sufficient to actually stop the car. It can be easily seen
that with such an arrangement, the effect is to first reduce the car velocity and then gradually bring it to an actual stop, the time, or distance in which the car is stopped depending on the rapidity with which the braking force is increased. Two views of the Otis clamp safety are given in Figs 465 and 466, the first
HANDBOOK ON ENGINEERING. 1033
being a side elevation in section, and the second a plan. The
Fig. 4C7. Governor Rope Connection for Brake Safety*
rope that winds around the actuating drum, Fig. 465, ia attached
1034 HANDBOOK ON ENGINEERING.
to the governor rope, in the way clearly shown in Fig. 467. If the car speed becomes too great, the governor acts, and clarnps the rope, then the drum rope unwinds, and thus rotates the drum, and the latter by turning the right and left hand nuts forces the screws out and thus spreads the toggle links B B Fig. 466, and applies the brakes to the guide. It is evident that the further the car runs after the safety governor has gripped the rope, the further the actuating drum will be rotated, and as a result the more the safety brake jaws will be forced against the guides. By this arrangement the motion of the car is gradually arrested, and the passengers are not seriously jolted. If the load in the car is light, and the guides are not properly lubricated, it is possible for this device to grip suddenly, but it can never act as suddenly as the roller safety.
There are several different designs of these brake safeties, but they are all substantially alike. The Morse and Williams design is shown in Figs. 468 and 469. As will be seen the diff erencebe- tween this and the Otis safety is principally in the details of con- struction of the clamping jaws. In the Otis design a lever C is provided that can be moved by the operator in the car, so as to either put on the brake, or release it after it has caught. In the Morse and Williams design this same result is accomplished through the beveLgears shown, in, Fig. 469, the end M being squared so as to receive a wrench.
Another type of clamp safety is shown in Figsl 470-471-472 This is known ais the " Pratt safety." This device has a strong spring M in addition to the parts used in the two previously ex- plained designs* When the safety is out of action, this spring is held compressed by a catch 'JT, ' as in Fig. 470. When the device goes into action, the first rotation of the drum and its shaft D acts to move ,7 to one side and releasethe catch K thus permit- ting spring M to throw the levers into the position of Fig. 471 and thereby to apply the brake shoes with all the force due to
HANDBOOK ON ENGINEERING,
1035
the tension of the spring. This force is not enough to stop the car suddenly, even if lightly loaded, but it will retard the velocity decidedly. The continued rotation of the drum compresses spring M and thus increases the pressure on the brake shoes until the car comes to rest, and the safety assumes the position shown in Fig. 472.
Fig. 468.
Fig. 469. Morse & Williams Brake Safety
The clamp safety is the only one suitable for electric eleva- tors because it can be easily arranged so as to act on the up as well as the down trip of the car. Electric elevators are almost always arranged so that the counterbalance weighs more than the car. As a rule the counterbalance weighs as much a,s thie car and one half of the maximum load, hence, if the car runs up with*
1036
HANDBOOK ON ENGINEERING.
a light load, and it runs away the counterbalance will run down and send the car up to the top of the building at a high velocity.
jp
Fig. 470. Fiff. 471. Ffe. 472.
Pratt-Brake Safety.
If the car has a full load, then it will weigh more than the coun- terbalance, and as a result will run down to the bottom of the
HANDBOOK ON ENGINEERING. 1037
well at a high velocity. On this account a safety to be of any value on an electric elevator must be able to act for either direc- tion of motion of the car. By looking at Fig. 467 it can be seen that to make the clamp safety act in both directions, all that is necessary is to place another sheave directly under A so as to hold the drum rope in position when the governor rope pulls down as well as when it pulls up. This is the way in which the safety is arranged when used with electric elevators. The safety governor in such cases is made double acting, which is accom- plished by providing rope clamping devices on both sides as shown in Fig. 473, which is the double acting Otis safety governor. This governor will clamp the rope regardless of which direction it is running. The levers shown on the clamping devices of the governor are for the purpose of releasing it after it comes into action.
In addition to the safeties explained in the foregoing, all elevators, hydraulic and electric, are provided with automatic stopping devices that will stop the car automatically at the top and bottom landings, providing they are properly adjusted, and kept in running order, and unless a car attains a very high vel- ocity in running away, these automatic stops will check its speed at the end of its travel. Experience, however, shows that these stops are often allowed to get out of adjustment so that they fail to act properly when called upon. This is also true of the safeties herein explained. If you want to avoid accidents, make sure that the safeties and safety governor, and the automatic stops are properly adjusted, and in perfect working order. Never use a governor or automatic safety rope that looks at all worn, for when called into action it may break, and then an accident will follow.
As can be seen, if the governor rope is not strong, it may snap off when the clamp grips it, and if this occurs, the safety will not act. The ropes used to operate the hydraulic automatic
1038
HANDBOOK ON ENGINEERING.
stops are not so. likely to break because they come into action very often, hence, they are more likely to show when they are
Fig-. 473. Otis Double Acting Safety Governor.
worn out ; but the automatic stops should be kept in perfect adjustment all the time.
As the safeties seldom come into action, they are liable to rust up and stick, unless often examined, oiled up and well cleaned,,
HANDBOOK?
1039
PIPES AOT ITAffKS. CONTENTS^IN CUBIC FEET AND IN UVS. GALLONS,
(FROM TRAUTWINE)
Of 231 cubic inches (or 7.4805 gallons to a cnblc foot); and for one foot of length off the cylinder. For the contents for a greater diameter than any in the table lake. quantity opposite one-half said diameter, and multiply it by 4. Thus, the number .oi cobic feet in one foot length of a pipe 80 inches in diameter is equal t$ 18.728X4=34.912 cubic feet. So also with gallons and areas.
|
8*^ |
For 1 foot in |
For 1 foot in |
o |
For 1 foot in |
|||||||
|
jfl |
>-<M |
length. |
£ j: |
s-r o' ' |
length. |
c |
"£ oj |
length. |
|||
|
:2® |
*? o |
«.£3 |
o |
®J |
-S:- |
0 |
«J |
So |
•i |
||
|
ill |
1 |
2$3 |
Iff |
i! |
ill a •— |
l|l |
Il| |
II |
S3 |
1^1 %- <D"~ |
ggS |
|
S~ , |
51 O |
2 o g |
Ip |
Q |
~ o . j |
lii |
|p |
5 , |
5|: |
«S2 |
!§I |
|
•o |
^73 x. |
o |
j |
°"5 o> |
0 |
.•o |
0*5 \ao |
0 |
|||
|
.0208! 0003 |
.0026 |
.5625| .2485 |
1 859 |
19: |
583 |
1 969 |
14 7* |
||||
|
(5-16 |
.0260! .0005 |
.0040 |
7. |
.58331 .267$ |
1 999 |
i |
625 |
2074 |
35 '5il |
||
|
i |
•03131 .0008 |
.0057 |
i |
.6042' .2868 |
2 144 |
20 |
.666 |
2.182 |
18.32 |
||
|
7-16 |
.0365! 0010 |
.0078 |
1 |
.6250 |
.3068 |
2.295 |
I |
.708 |
3.292 |
17.15 |
|
|
•0417J .0014 |
.0102 |
.6458 |
.3275 |
2 450 |
21 |
750 |
2 405 |
1799. |
|||
|
9-16 |
.0469 .0017 |
.0129 |
8.* |
6667 .3490 |
2 611 |
i |
.792 |
2.521 |
18 Sii. |
||
|
ft |
.0521 |
0021 |
.0159 |
i |
.6875 |
.3713 |
2 777 |
22 |
833 |
2.640 |
19.751 |
|
(11-16 |
.0573 |
.0026 |
;0193 |
j |
.7083 |
.3940 |
2 948 |
i- |
875 |
2.761 |
20.(£ |
|
• 0625 |
.0031 |
.0230 |
.7292 .4175 |
3 125 |
23 |
1.917 |
2 886 |
22.5S\ |
|||
|
113-16 |
.0677 .0031 |
.0270 |
9.* |
.7500 .4418 |
3 305 |
1 |
.958 |
3 012 |
31 5* |
||
|
| |
.0729 .0042 |
0312 |
v i |
.77081 4668 |
3 4i)2 |
24. |
2 000 |
3 142 |
23 50 |
||
|
U5-16 |
.0781 .9048 |
0369 |
i |
.79171 .49-23 |
3 682 |
25v |
2.083 |
3 409 |
25.50) |
||
|
1. |
.0833 |
> -0055 |
.0408 |
i |
.8125 |
.5185 |
3.879 |
26. |
2.166 |
3.687 |
27 58> |
|
i |
.1042 |
i .40085 |
.0638 |
10. |
.8333 |
.5455 |
081 |
27. |
2 250 |
3.976 |
29 7* |
|
1 |
.1250 |
U.0123 |
.0918 |
1 |
8542 |
.5730 |
286 |
28. |
2 333 |
4.276 |
31.99) |
|
i |
.1458 |
I 10168 |
1250 |
x |
.8750 |
.6013 |
.498 |
29. |
2 416 |
4 587 |
31 3* |
|
i2. |
.1667 |
.JD218 |
.1632 |
j |
.8358 |
.6303 |
.714 |
30 |
2.500 |
4.909 |
36. 7fc |
|
i |
.1875 |
.(•276 |
.2066 |
11 . |
.91C7 |
.6600 |
.937 |
31. |
2 583 |
5.241 |
39.2H |
|
(• |
.2083 |
.0341 |
.2650 |
1 |
.9375 |
.6903 |
5.163 |
32. |
2.666 |
5 585 |
41.78» |
|
a |
.2292 |
.0413 |
.3085 |
i |
9583 |
.7213 |
5 395 |
33. |
2.750 |
5940 |
44.41 |
|
13. |
.2500 |
.0491 |
.3673 |
a |
9792 |
.7530 |
5.633 |
31. |
2.833 |
6 306 |
47.171 |
|
.2708 |
.0576 |
.4310 |
12. |
IFoot. |
.7854 |
5 876 |
35. |
2.916 |
6.681 |
49.9$i |
|
|
[I |
.2917 |
.0668 |
.4998 |
1 |
1.012 |
.8523 |
6 375 |
36. |
3 000 |
7 069 |
62 88^ |
|
i |
.3125 |
-.0767 |
.5738 |
13. |
.083 |
.9218 |
6.895 |
37. |
3.083 |
7.468 |
55.86 |
|
If. |
.3333 |
.0873 |
.6528 |
i |
.125 |
.9940 |
7.435 |
38 |
3 166 |
7.876 |
68.91- |
|
i |
.35*2 |
.0985 |
.7370 |
14'i |
.167 |
1 069 |
7.997 |
39. |
3 250 |
8 2% |
6-2.06 |
|
I |
.3750 |
.1105 |
.8263 |
.208 |
1.147 |
8.578 |
40. |
3.333 |
8.728 |
65.29 |
|
|
.3958 |
1231 |
.9205 |
1 15. 5 |
1.250 |
1.227 |
9.180 |
41. |
3.416 |
9.168 |
68.58 |
|
|
15. |
.4167 |
.1364 |
1.020 |
1 . * |
1.292 |
1.310 |
9.801 |
42. |
3.500 |
9.620 |
71.96 |
|
i |
.4375 |
.1503 |
1.124 |
1.333 |
1.396 |
10.44 |
43 |
3.583 |
10 084 |
75.43 |
|
|
! |
.4583 |
1650 |
1.234 |
I i |
1.375 |
1.485 |
11.11 |
44. |
3 666 |
10.560 |
79 00 |
|
.4792 |
. 180^ |
1.H49 |
17'i |
1 417 |
1.576 |
11.79 |
45. |
3.750 |
11.044 |
82 62 |
|
|
*6. |
.5000 |
1963 |
1.469 |
1.458 |
1 670 |
12.50 |
46. |
3.833 |
11.640 |
86.32 |
|
|
l |
.5208 |
!2130 |
1.694 |
18. * |
1.500 |
1.767 |
13.22 |
47. |
3.916 |
12 048 |
90.12 |
|
1 |
.5417 |
.2305 |
1.724 |
1.542 |
.1.867 |
13.97 |
48. |
4.000 |
12.566 |
94.0-2 |
|
|
.-- — ' - |
4 • •'•• ' ~ ^ |
'„.„,., * |
1040 HANDBOOK ON ENGINEERING.
CHAPTER XXXII. FRICTION AND LUBRICATION.
BY WILLIAM M. DAVIS.
Friction has been aptly described as the " Highway robber of mechanical energy," levying tribute on all matter in motion, ex- erting a retarding influence and requiring power to overcome it.
When one realizes that if it were not for the thin film or layer of oil between the surface of the journals and their bearings and the constant supply of oil to maintain this film, the largest loco- motive could not start a heavy train or keep it in motion, or the most powerful marine engine could not drive the ship a mile without heating of the bearings, one readily understands that a knowledge of lubrication and friction and of the laws relating to friction is a very important part of the training of an engineer.
LAWS OF FRICTION.
Friction is defined as the resistance caused by the motion of a body when in contact ivith another body that does not partake of its motion.
There are five commonly accepted and fundamental laws re- lating to the friction of plane surfaces in contact.
First. — Friction will vary in proportion to the pressure on the surfaces. That is, increasing the pressure increases the friction.
Second. — Friction is independent of the areas of the contact surfaces when the pressure and speed remain constant. But distributing the pressure or friction over a larger area renders the liability of heating and abrasion less than if the friction had been concentrated on a smaller area.
Third. — Friction increases with the roughness of the surfaces and decreases *<» the surfaces become smoother.
Fourth. — Friction is greatest at the beginning of motion. In the effort to move a body greater force is required to overcome
HANDBOOK ON ENGINEERING. 1041
the friction at the instant of starting than after motion has com- menced.
Fifth. — Friction is greater between soft bodies than between hard bodies.
These rules hold good within certain limits but will fluctuate under varying conditions of load and lubricant, and condition and composition of the contact surfaces.
Friction is always a resisting and a retarding force, tending to bring everything in motion to a state of rest, and in doing so re- sults in the conversion of energy into heat, it has been calculated that one horse power or 33,000 foot pounds exerted in over-com- ing friction results in the conversion of energy into 43 British Thermal Units of heat.
In the case of machinery in motion the surfaces moving in con- tact have a tendency to adhere to each other ; the minute pro- jections which exist on all surfaces to a greater or less extent (depending upon the hardness and smoothness of the surfaces) have a tendency to cling to each other and in order to operate machinery without undue friction the surfaces must be kept apart, something must be used that will flow or spread out over the surfaces and cover up these projections and prevent the sur- faces from coming in direct contact, for which purpose lubricants of various grades are used.
USES OF FRICTION.
Yet, friction in mechanics has its uses ; it is the friction, or adhesion (as it is sometimes called) of the driving wheels to the rails that enables a locomotive to start and keep in motion a heavy train, it is the friction of the brake shoes on the wheels as applied by the air brakes that stops the train, it is the friction of the belt on the pulley that enables power to be transmitted from one piece of mechanism to another.
Friction as it occurs in mechanics is what is known as friction
1042
HANDBOOK ON ENGINEERING.
of solids and friction of fluids ; friction of solids may be divided into two classes, namely: rolling friction, such as a car wheel rolling on a rail or balls in a ball bearing ; and sliding
friction, such as a cross-head on the guide bars.
CO-EFFICIENT OF FRICTION.
The relation that thepoiver required to move a body bears to the weight or pressure on the body is known as the co-efficient offrictwn, or, to put it in another form, the co-efficient of friction is the ratio between the resistance to motion and the perpendicular pressure, and is determined by dividing the amount of the former by the latter.
One of the simplest methods of demon strati ng graphically the simple laws of friction of plane surfaces and the determination of the co-efficient of friction is by drawing a block of iron or other metal across a table or an iron plate by means of weights sus- pended to a cord which is attached to the block as shown in Figs. 1 and 2.
L*"'
Fig. 1. Illustrating Laws of Friction.
It is noticed that the block is flat on one side, and on the other side are four small projections or legs, each one square inch in area, the size of the block is 12 inches long, 8 inches wide and 2 inches thick, and weighs 50 pounds. If we lay the block with its largest surface down it will have a surface contact with the
HANDBOOK ON ENGINEERING.
1043
table of 96 square inches and placing weights on the cord until the block commences to move we find that it requires a weight of 7 pounds to pull it across the table ; now if the block be turned upside down so that it rests on the four legs it will be found that it requires exactly the same amount of force to move the block that it had before.
As we have found by experiment that to move the weight of 50 pounds required a force or pull of 7 pounds, the co-efficient of friction in this case will be found by dividing the pull by the weight, 7-r-50= .14, or, to put it in another form, it will require .14 of a pound of force to move 1 pound of weight.
Fig. 2. Illustrating Laws of Friction.
The second law states that friction is independent of the areas of the surfaces, it has been found by experiment that it required a pull of 7 pounds to move the block no matter which side it stood on.
Let us prove this.
The block when on its largest side had a surface contact of 8"xl2", or 96 square inches and exerted a pressure due to its weight of 50 Ibs., or .52 of a pound per square inch of area. The co-efficient has been found to be .14, then the pull per square inch of surface would be .52 x. 14 = .0729, which multiplied by the total area, 96 sq. in., will be found to be 6.9888, or practically 7 pounds.
1044 HANDBOOK ON ENGINEERING.
Now, when the block was reversed and stood on the four legs of 1 sq. in. each, the total contact was only 4 sq. inches, but the pressure (50 pounds), remained the same, 50 -i- 4 =12. 5 pounds per square inch, which multiplied by the co-efficient .14 equals 1.75, then again multiplying this result by 4 sq. in, again gives a total of 7 pounds.
Thus it will be seen that the extent of surfaces has no influence on the friction as long as the pressure of weight is constant, but in machine design increasing the area of surface contact allows the total pressure to be distributed over a greater area and re- duces the liability of heating and abrading, or in other words, while the total pressure remains the same the pressure per square inch will be less.
Fig. 3. Laws of Friction.
Another method of determining the co-efficient of friction, or, as it is usually termed, the angle of friction, can be illustrated by means of a weight on an inclined plane.
Place a weight on a board or other plane surface and raise one end slowly as in Fig. 3 until the weight commences to slide ; the angle "a " between the position of the plane surface when the weight commenced to move and the horizontal is the angle of friction, and will vary with the smoothness of the surfaces and the weight or pressure.
The angle of friction indicates the point where the attraction of gravitation just overcomes the friction between the surfaces.
To find the amount of power absorbed by friction multiply the weight by the co-efficient of friction, multiply the result by the velocity in feet per minute and divide that by 33,000.
HANDBOOK ON ENGINEERING. 1045
For instance, a shaft and fly wheel weighs 8,000 pounds, sur- face travel of journals is 300 feet per minute, the co-efficient of friction is taken as being .04.
What would be the horse power required to run the shaft? 8,000 x. 04x300
-=2.&09 H. P. 33,000
While the co-efficient of friction must always be taken into consideration when designing and constructing machinery, it is not always practicable to calculate it with any degree of accuracy, in fact it can only be determined absolutely by experiment.
THEORY OF LUBRICATION.
Lubrication as it is considered in mechanics is the application or introduction of a smooth fluid substance, preferably an oil, between two hard moving surfaces that will keep them from com- ing in direct contact.
Unless the surfaces are kept apart by some medium the asper- ities and irregularities which exist on all surfaces no matter how hard or smooth, will interlock, and the friction caused in tearing them apart and wearing them down will generate heat.
The action of a lubricant is to flow between the close-fitting surfaces, filling up the interstices and covering up the high spots, acting as a cushion and taking up whatever heat may be gener- ated and carrying it off instead of allowing it to be absorbed by the wearing surfaces.
To do this properly, a lubricant should have certain properties, it should be of a fluid nature so that it will flow readily between surfaces that are close-fitting and under heavy pressure. It should possess a certain amount of cohesiveness, or viscosity, as it is usually called.
By cohesiveness is meant the Clinging together of the molecules its own particles.
1046 HANDBOOK ON ENGINEERING.
Oil should have good adhesive properties in order that it will cling well to metallic surfaces.
By adhesion is meant the tendency of a substance to cling to other substances
It should be high in flash test in order that whatever heat it is subjected to will not cause it to give off an inflammable vapor. It should have a cold test of such degree that it will remain fluid at low temperatures.
The above requirements will be found embodied to the greatest degree in the various kinds of vegetable, animal and petroleum oils.
The first oils used in the lubrication of machinery were vegeta- ble oils, such as castor oil, palm oil, and olive oil ; and animal oil such as lard, neats-foot, tallow and sperm oils.
All these oils, while in many respects excellent lubricants are not now used to any extent since the introduction of petroleum or mineral oils, for the following reasons : First. — On account of their higher price as compared with petroleum oils. In recent years the processes of refining petroleum have been brought to such a state of perfection that they have almost entirely driven the animal and vegetable oils from the market as lubricants for machinery. Second. — Being of organic origin they absorb oxygen from the atmosphere, and, in time, become rancid, thick and gummy. These oils are of very poor cold test, congealing at a comparatively high temperature, thus making them inconvenient for use in cold weather.
Petroleum oils have many advantages as lubricants over ani- mal or vegetable oils. First. — Is their cheapness. Second. — • Being of non-organic origin they do not change their condition, do not become rancid, thick or gummy by constant exposure to the air, and have no corrosive action on metals. Third. — By what is known, as fractional distillation they can be separated into a great many different grades, from the lightest spindle oils to
HANDBOOK ON ENGINEERING. 1047
the dense heavy cylinder oils. Fourth. — They are of lower cold test and there is not the liability of spontaneous combustion as with animal oils.
The engineer in charge of a plant will find on the market a wide range of petroleum lubricants to choose from to meet the various conditions which will arise in the proper lubrication of his machinery.
The conditions which produce the greatest differences in ordi- nary lubrication are the nature and quality of the lubricant, the nature and condition of the wearing surfaces, the speed and pressure and the temperature.
Variations of friction of lubricated surfaces occur with every change of condition of either the bearing or journal surfaces, or of the lubricant applied to them.
The ordinary facilities of the engine room do not usually afford means to make elaborate tests of the co-efficient of friction of various oils, nor would such tests be of any practical value to an engineer, as they can only be made with any degree of accuracy on expensive testing machines built expressly for this purpose, which are very little used except in the laboratories of the techni- cal schools and the testing rooms of a few of the large railroad companies and manufacturers of oils.
But an engineer can often make valuable comparative tests of different grades of oil on the ordinary machinery of the engine room ; for instance, a difference between two oils of several de- grees in the temperature of a bearing of an engine or a dynamo may be detected by means of a thermometer placed in the bear- ing, with the bulb resting on the shaft or immersed in the oil chamber.
In tests of this kind care must be taken that the rate of oil feed, the belt tension, the pressure on the bearings and the speed remain constant ; an allowance should also be made for any dif- ference in the temperature of the room during the tests.
1048 HANDBOOK ON ENGINEERING.
Some day, engine builders will equip the main bearings of their engines with thermometers so that the temperature can be noted, the engineer will then be able to see at a glance whether the temperature is above the normal or not, in the same way as he notes the temperature of his feed water by means of a ther- mometer in the boiler feed pipe ; of course, an engine bearing from lack of oil, stoppage of the oil cups or other cause, can be- come overheated to such a degree as to ignite the oil in some particular spot before the rise in temperature would be indicated on a thermometer a few inches away.
But a thermometer in a bearing would indicate from day to day, any difference in the condition of either the lubricant or the bearing — for instance, an engineer on taking up the lost motion of a main bearing notices that the temperature rises 10 to 20 degrees above what it had previously been, this warns him that this bearing must be carefully watched to see that it does not get too hot.
One of the essential points in lubrication is that the lubricant be made to reach every part of the contact surfaces, and in con- nection with lubrication one may assume an oil to have the nature of a mass of globular molecules or atoms, which roll on each other and the wearing surfaces and are carried or flow between the close-fitting surfaces and form an elastic coating to the metal, becoming thinner as the pressure increases or the temperature rises, and thicker as the pressure decreases, or the temperature falls, and absorbing whatever heat may be generated and carrying it off.
The best lubricant for a bearing under normal conditions may not do so well after heating commences, a thick viscous oil which under ordinary conditions on high speed machinery would be comparatively wasteful of power is often an excellent lubricant for a hot bearing, and for the following reason : an engineer on finding a bearing heating up will apply the ordinary oil freely
HANDBOOK ON ENGINEERING. 1049
and at the same time loosen up the bolts so as to allow for in- creased expansion and free flow of oil, if the heating continues, and the engine or machinery must be kept in operation at all haz- ards, he will turn to his cylinder oil, apply it freely, and often with good results. The reason of this is that the cylinder oil, owing to its high fire test, (from 550 to 600), became thin and limpid without burning, and flowed freely between the close- fitting surfaces and kept them apart, and at the same time, ab- sorbed the heat that would otherwise have gone into the metal and carried it away, while the engine oil, being of lower flash test, vaporized, and if the bearing got hot enough, caught fire.
The theory of a heating bearing is as follows : If for any rea- son the oil is prevented from reaching every part of a bearing, the surfaces will come in direct metallic contact, excessive friction is set up and heat is generated ; if the pressure be not great and the bearing area is ample the heat may be absorbed by the metel and radiated out into the air and nothing serious occur. But if the pressure is heavy and the speed high, the heat may be gener- ated faster than the metal can carry it away ; the original dry spot may not have been over J or J of a square inch in area but sufficient heat may have been generated at this point to cause the adjacent oil to evaporate and shrink away, thus increasing the area of dry surface, as the heat increases the metal expands causing the surfaces to fit tighter and thus creating more friction until the temperature reaches such a point that it ignites and burns. As a good engine oil will have a flash test of about 400 degrees the temperature of a metal must rise above that in order to ignite the oil.
CYLINDER AND VALVE LUBRICATION.
In the lubrication of the interior wearing surfaces of the valves and cylinders of steam engines conditions will be met which are
1050 HANDBOOK ON ENGINEERING.
altogether different from those encountered in the lubrication of bearings and journals.
In the latter case, the working and comparing of one oil with another, and the results obtained, can be easily determined by noting the changes of temperature, etc., but in internal lubrica- tion the conditions are altogether different.
In the case of journals and bearings, the oil can be applied directly to the surface to be lubricated ; in cylinder lubrication one must depend upon the flow of steam to convey the oil to the parts of wearing surfaces requiring lubrication.
The points that govern the conditions of interior lubrication are: The conditions of the surfaces, the steam pressure, the amount of moisture in the steam, the piston speed, weight and fit of the moving parts, and the make or type of the engine.
An automatic cut-off engine with balanced or piston valves will usually require less oil. than an engine with a heavy unbalanced valve.
A large cylinder whose piston is supported b}^ a " tail-rod " is more easily lubricated than one whose heavy piston drags back and forth over the bottom of the cylinder.
The dryness of the steam is a very important factor in cylinder lubrication, engines which take their steam supply from foaming or priming boilers, or through long uncovered steam pipes usually require more oil than an engine supplied with dry steam.
Wet steam is the greatest cause for complaint in the lubrica- tion of valves and cylinder surfaces with which an engineer has to contend, but some grades of cylinder oil will give better results in connection with wet steam than others ; they will stick to the moist surfaces better.
An engineer who desires to secure the best results and reduce the friction loss to the minimum must study the various condi- tions which exist in the machinery in his charge ; always bearing in mind that friction costs more than oil, and that a small quan-
HANDBOOK ON ENGINEERING. 1051
tity of good oil properly used will be more economical than any quantity of poor oil.
An oil to be used as a cylinder lubricant in order to give good results must possess certain essential properties.
It must be of high flash test, so that it will not volatilize or vaporize when in contact with the hot steam ; it must have good viscosity or body when in contact with the hot surfaces, and should adhere to, and form a coating of oil so as to prevent wear and reduce as much as possible the friction of the moving parts.
Some of the essentials to be desired in a cylinder lubricant are obtained to the greatest degree in the heavier or more dense and viscid of the petroleum oils, but there is one element in which a pure petroleum oil is usually lacking as a cylinder lubricant and that is its inability to adhere to a wet surface, and for that reason it is necessary that it be combined with some one or more of the various vegetable or animal oils.
There is always a certain amount of moisture present in the valve chambers and cylinders of a steam engine, due partly to condensation of the steam in the pipe on its way from the boilers to the engine and partly to the expansion which takes place in the cylinders.
A petroleum oil, while it may possess the proper viscosity and flash test, will not of -itself mix with or form an emulsion with water and consequently will not stick to the moist surfaces, but will be easily washed out by the action of the steam ; but animal and vegetable oils, while not so viscid 'as the petroleum oil, will combine with it and emulsify freely with water and when com- pounded in the proper proportions with a heavy petroleum pro- duce a cylinder oil that is suitable for interior lubrication.
While the quality of a cylinder oil as shown by the use of testing instruments will give one a general idea of its lubricating value, the engineer who is studying the question cf cylinder lub- rication can determine more accurately its exact value by experi-
1052 HANDBOOK ON ENGINEERING.
meriting on his engines and pumps and under the conditions peculiar to his own plant.
Any engineer in charge of a steam plant knows that nearly every engine will indicate either audibly or otherwise perceptibly, any lack of lubrication.
A Corliss type of engine will usually indicate need of more cylinder oil by a slight groaning of the valves, if not loud enough to be heard, it can be detected by feeling of the valve stem, or by the vibration or trembling of the valve and eccentric rods.
Buckeye, Russell, Porter- Allen and other makes of engines with balanced valves will usually indicate a lack of oil by a rattling noise in the steam chest, rocker-arms and the eccentric and governor connections.
For instance, an engineer has submitted to him for trial three sample lots of cylinder oil, and he wishes to determine which is the most suitable and economical oil for him to use ; he may notice after starting with the first sample that the valves work free and smooth on say, eight (8) drops a minute; he then re- duces the oil feed gradually to four (4) drops, and then notices a slight tremor in the eccentric rods, and later, if a Corliss engine, he may detect a decided groaning sound in one or more of the valves.
If the oil feed is then increased to six (6) or seven (7) drops per minute and the valves begin to work freely again and when the oil feed is reduced to five (5) drops and the valves commence to work hard again, and 'the results are the same after repeated trials, the engineer can determine just how much of this particu- lar brand of oil is required to keep the valves working smoothly and quietly.
The next thing in order is to remove the cylinder head or steam chest cover, or if a Corliss engine, draw out one of the valves and examine the wearing surfaces ; if well lubricated they will present
HANDBOOK ON ENGINEERING. 1053
a dark glossy appearance, and a good coating of oil all over the interior surfaces.
The most reliable test of the condition of the surfaces is to wipe over them with a piece of soft white paper, such as a piece of ordinary newspaper ; if a decided stain of oil is seen on the paper it is an indication of good lubrication. Another method is to wipe over the surface with several thicknesses of tissue paper and note the number of thicknesses that the oil has saturated through.
But if no stain of oil can be seen upon the paper and the sur- faces have a dull appearance, and with traces of metallic wear it is a positive evidence that the oil is not lubricating properly.
Then, if another sample of oil is tried and it is found to require from ten (10) to twelve (12) drops per minute to keep the valves quiet, and the surfaces when examined showed little or no signs of oil, it would prove conclusively that it is a very poor lub- ricant, and would be a most expensive oil no matter how cheap in price per gallon.
But, if after trying the third sample it will be found that the oil feed can be reduced to one (1), two (2), or three (3) drops per minute, or, perhaps one (1) drop every two minutes, and kept at that rate for hours, without showing any evidence of lack of perfect lubrication, and the surfaces after standing cold for several hours still show a good coating of oil and no rust or " raw spots," and these results hold good on all the engines and pumps in the plant, it would prove conclusively that this oil will be the cheapest to use no matter what the price per gallon may be and regardless of all laboratory tests.
LUBRICATION OF REFRIGERATING MACHINERY.
In the operation of refrigerating machinery certain conditions exist which require that the oil used for lubrication shall be of
1054 HANDBOOK ON ENGINEERING.
such a nature that it can be subjected to quite a high temperature and to a very low temperature without congealing.
In the manufacture of artificial ice, or to speak more correctly, in mechanical refrigeration, the anhydrous ammonia gas is com- pressed in the compression cylinders to about 120 to 200 pounds pressure per square inch, according to the class of work done, and the requirements of the plant. It is then allowed to expand down to about 15 pounds in the expansion coils. In some types of machines oil is used to lubricate the ammonia cylinders and pistons and to fill the clearance space and to reduce the heat of compression, for in compressing the ammonia gas to the required pressure its temperature is raised to about 180 to 200 degrees. And the oil for this purpose must have a flash point so high as to not give off any great amount of vapor.
After the ammonia has been compressed to the proper extent it is allowed to flow through the expansion coils and thus pro- duce the refrigerative effect.
All refrigerating plants are provided with a separator in the ammonia discharge pipe which is supposed to, and does to a cer- tain extent, separate the oil and other foreign matter from the ammonia ; but a certain quantity of oil will always go past the separator in the form of vapor and collect in the condensing coils, so that it is very essential that the oil be of such a nature that it will remain in a fluid state when subjected to low temperatures. If the oil be of poor cold test it will congeal and form a coating on the inside of the coils and tend to lower the efficiency of the system and eventually clog up the pipes.
An oil for this work should be of 30 gravity, of about 300 to 325 flash test, and stand a temperature of 5 degrees above zero without congealing.
Different makes of refrigerating machines have different re- quirements as to the use of oil. The De La Vergne machine is what is known as the double-acting type, and oil is used to fill
HANDBOOK ON ENGINEERING. 1055
the clearance space as well as to lubricate the cylinders and pis- tons. On some makes of machines the oil is only used in the space in the stuffing boxes on the piston rods, and none is fed into the compression cylinders ; but no matter how tight the packing is kept some of the oil will work through into the cylin^ ders and pass out with the ammonia gas ; and notwithstanding the fact that the discharge pipes are provided with separators, some of the oil will pass through into the system.
In the lubrication of the steam cylinders of a refrigerating plant, especially where ice is made, certain points must be looked after that are not essential in any other class of engine.
It is customary in the manufacture of ice to condense the ex- haust steam and purify it, and use it to make ice of ; and for this reason the oil used for lubricating the valves and surfaces of the steam cylinders should be of pure petroleum or very nearly so ; and it is well for the engineer in charge of a. refrigerating plant to go on the theory that the less oil used in the cylinders the less there will be to separate from the condensed water. The steam cylinders of refrigerating machines are not as a rule very large, and the piston speed does not as a rule exceed 400 to 600 feet per minute, so that if a first class quality of oil is used very little will be required to give good lubrication.
In the process of making ice the exhaust steam first passes through a separator where the steam is relieved of some of the oil ; from there it passes to a feed water heater, where it im- parts some of its heat to the boiler feed water, then it goes to the condenser and is condensed and the water of condensation is pumped to a re-boiler and skimmer ; and any oil that has not been removed in the preceding processes is taken off, the water passes through the cooling coils and on to the bone dust or charcoal filters, where it is still further cleaned of its impurities, from there it passes to the settling or sweet water tank, as it is
1056 HANDBOOK ON ENGINEERING,
called, and it is finally drawn off through a sponge filter on its way to the freezing cans.
From this it will be seen how important it is that the water be kept as free from oil as possible. If the oil contains any great amount of animal fats in its composition it will form a white milky looking emulsion with the water that will be very difficult to remove.
The presence of a yellow or reddish color in the ice is often attributed to the cylinder oil getting in the ice. This may some- times happen when the oil is used too freely, or the filters are out of order ; but as a general thing the stain is due to the presence of rust in the water. Condensed water has a very active effect on iron when combined with oxygen, and when the plant is shut down and the pipes are empty the action of the air on the moist pipes soon causes them to rust, and when the plant is started again, unless care is taken to prevent it, the rust will be de- posited in the freezing cans.
INDEX.
AIR, composition of, 651. f( compressor, Bennett, auto- matic, 803.
" compressor, capacity of, 800. " compressor, effect of fly wheel,
806.
" compressor, horizontal, 802. " compressor, Ingersoll - Sar- gent, 804. " compressor, McKierman Drill
Co.'s, 801.
" lift, construction of, 808. " " formulas, 808. " " required for combustion,
484.
" volume per pound of coal, 651. Arc lighting apparatus, 103. Atmosphere, pressure of, 560. Atmospheres, number of, to find,
806.
Atmospheric pressure, 233, 661. Auxiliary injection, 259. BANKING fires, 531. Belts, adjusting, 798.
arc of contact, 795, 799. driving power of, 788. effect of size of pulley, 791. effect of speed, 793. grain side of, 768. horizontal, 797. horsepower of, 789, 793, 799. inclined, 797. % lacing, 798. laws relating to, 791. length required, 789. long, effect of, 787. making joints, 799. proper direction to run, 798. pull on, 795.
punching for lacing, 798. resistance to slippage, 792. short, effect of, 797.
Belts, slippage, cause of, 791. " speed of, 793. " testing adhesive qualities,
792.
<e to increase power of, 798. " width of, 789, 797. Bevel wheels, 707. Biowoff cocks, 435. Boiler, area of head to be stayed,
938. " blowing out, frequency of,
435.
" calking leaks, 535. " capacity, to heat water in
tank, 479. " capacity to heat swimming
pool, 479.
" care and management, 433. " cause affecting strength, 450. " cleaning, 533. " compound, how to use, 655. " cooling down and filling,
534.
(l definitions applied to, 415. " efficiency, on what it de- pends, 664.
" foaming and priming, 535. " furnaces, 432. " hammer test for, 447. " heating surface in square
feet, 501. " heating surface required,
327.
" height of fire line, 669. u horsepower, A. S. M. E.
rating, 406.
" horsepower of, 663. " horizontal, how to set, 671. " " specifications,
for, 524-527.
(f importance of circulation, 421, 423.
(1057)
1058
INDEX.
Boiler, inspection of, 328.
" instruction for attendant,
532.
laying up, 649. leaving at night, 650. low water, what to do, 325. materials, definitions, ap- plied to, 415. operating valves on, 535. plain vertical tubular, 514. plate, characteristics of, 662. t( manufacture and use
of, 460. " " strength between rivet
holes, 537. " " strength of solid,
537. " proper point for closing in,
520.
" raising steam in, 324. (e rating by weight of feed
water, 676. " reinforcing ring, size of,
541.
" selection of, 422. " stayed surfaces, strength
of, 473.
" starting and stopping, 532. " staying heads, 938. ie stays, 474. " the Heine safety, 507. " the O'Brien, 503. " to manage with low water,
649.
" trimmings 426. " water tube, sectional, 502. Boilers, blister, cause of, 444.
t( cheap, not economical, 453. " common types of, 402. <f corrosion in, 445. " defects in construction, " 457. " design of, 454. u deterioration, cause of, 451, (f energy stored in, 400, 448. " firebox, when recom- mended, 425. " forms of, 456. " hard patch for, 444.
Boilers, heating surface required, 403.
(e horsepower of, 402.
" what it is, 405.
" improvements in, 459.
te inspection of, 445.
i( material required for set- ting, 522.
" method of comparing, 403.
" patching, 444.
" preventing corrosion, 443. " leaks, 443.
u proportions of joints, 467- 472, 946.
f< pulsation in, 487.
" rating of, 404.
'• riveted seams, strength of; 461.
" rules relating to, 536.
t( safe working pressure, 516- 519.
" settings for, 456.
" single and double riveted seams, 462.
" soft patch, 444.
" special high pressure, 401.
" stayed and flat surfaces, 473.
" steel for use in, 425.
" strength of, on what it de- pends, 455.
" submerged tubes, 521.
" testing of, 447.
te tests, rules for conducting, 407.
" tubular, when recom- mened, 425.
fc use and abuse of, 449»
et use of zinc, 442.
" vertical, when recom- mended, 425.
et working beyond rated capacity, 451.
" working capacity of, 405. British thermal unit, what it is, 401. " " " mech. equiva-
lent, 688.
CARBONATE of lime, 440. Centigrade thermometer, 811.
INDEX.
1059
Centrifugal force, 501.
Changing from non-condensing tc
condensing 238. Chimney, 688.
" cause of draft, 670.
" horsepower of, 692.
te stacks, 692.
Cisterns, capacity of, 585. Cleaning tubes, 436. Clearance, definition of, 653, 659. Coal, composition of, 651. " horsepower for 1 pound, 420. " required to heat water by
steam, 479.
" value of, per pound, 404. Combustion, air required for, 419. Compound engine, 253. Compressing, adjusting valves for,
212. Condenser, 235.
" auxiliary injection, 259.
t( device for breaking
vacuum, 247. " distance will raise
water, 249, 250. " gain by using, 654.
" jet, 246.
" jet, method of connect-
ing, 248.
safety device for, 248. siphon, 249. " and starting
valve, 251.
t( cc method, of con-
necting, 252. " speed of, 254.
starting the, 258. surface, 243. " " efficiency of,
661.
type^ of, 242. " water required for,
237, 258, 670.
Condensing to noncondensing, 238. Connecting rod brasses, 189.
1 " effect on cutoff,
671.
" • " to find length of,
667.
te if
tc
u
Copper staybolt, grip of, 474. Corliss engine, double eccentric,
215. " " long range cutoff,
215.
" " steam distribu-
tion, 219.
" " governor, adjust-
ing, 214. Crankpins, 188. Cutoff, equilizing, 213, 267. Cylinder, capacity in cu. ft., 801.
" lubrication, 309. Dead center, to find, 195. Decimal equivalents of an inch,
1024. Double eccentric valve gear, 215-
222.
Do you do these things, 388. Draft, effect of bad, on economy,
327.
Dynamos and motors, care of, 80. EBULLITION, 439. Eccentric diagrams, 361.
" effect of shifting, 361. " " of moving, 319.
out of place, 360. rod, length of, 668. " " with link motion, 317. straps, 192. throw, 390.
Electrical: —
Alternating and direct currents, 18.
A.C. E.M.F., 821.
" generators, armature circuits,
106.
belted, 888. Brush arc, 104. care of, 890. commutators, 866. compensating and compounding,|864. generators, compound, 887. a compounding, 85?.
" connecting to
switchboard, 862. " direct coupled, 888.
1060
INDEX.
(C
u
Electrical : — •
A. C. generators, division of load,
887.
u exciter, use of, 864. " how run, 859. " inductor, type of,
857.
<» operation, 110. t( " regular speed for,
861.
•« ' regulator, 108.
" " revolving field, 857.
€i u running in parallel,
861, 887. " lt setting brushes,
110.
" " shutting down, 890.
" " starting a, 889.
" " two and three-
phase, 854.
" " voltage of, 106.
Ammeter and voltmeter, construc- tion of, 60.
Ammeter where placed, 50. Ampere, turns required, 46.
" what it is, 73. Angle of lag, 837. Arc lamp, enclosed, A.C., 103. r< " constant current circuits,
127. " " Fort Wayne systems,
126, 150.
" " series system, 112, 118. " " series system, regulat- ors, 120, 124.
" ft series system, switch- boards, 114, 117, 118. " " series systems trans- formers, 113, 120. " " carbons, 156. '• (* carbons, diam., length
and quality, 157. ft " carbons, for D.C. and
A.C., 136.
" " frequency of, 159. " " life of, 157. " " polarity of, 158. Arc lamps, 128, 132, 147, 159. " (t carbon holders, 135.
Electrical: —
Arc lamps, care of gas check, 158. " " clutches, 133, 158. " (- condition of globes, 159. " •' connection to upper
carbon. 135.
" " constant potential, 146e " " current consumption,
154, 156.
" " cut out for, 145. " " dashpot, 158. " " direct current, 136, 145. f< " directions for care, 156. " t( enclosed, 103, 151, 156,
159.
" <e Excello, 153, 155. u " flaming arc type, 152,
156.
" " for power circuits, 141. " " Fort Wayne, 131, 134,
135, 139,142,147,151. " " frequency of alternat- ing, 159.
" " General Electric, 128,
136, 137, 144, 149, 155, 156.
" " how to install, 159. " " how to trim, 157. " " inner globes, 158. " " inspecting mechanism
159.
" " life of carbons, 155. " " multiple series, 141. " " use of oil, 159. a " Western Electric, 132,
134, 135. " " Westinghouse, 129, 134,
139, 144, 148. Arc lighting, A.C.., 104.
s( apparatus, 103. " " constant current
circuits, 127. <f " constant potential,
136, 146.
" " direct current, 136.
" " Fort Wayne street,
150.
te tc power circuits, 141.
te <e series system, 112.
INDEX.
1061
Electrical: —
Arc lighting, coils, connections of.
30. Armature, cores, construction of,
23.
effect of displacement^, flow of current in, 84. method of raising, 75. principle of, 16. pull of, 63. ring, 27.
Balance, effect of distributing, 96. Batteries, 81.
Brushes, connection to, 40. " number of, 39. « position of, 36, 85. Candle power, measurement of, 73, Circuit breakers, principle of, 62. Collector rings, arrangement of,17. Commutator, care of, 76, 88.
lf construction of, 18.
Condenser, use of, 840. Conductors and non-conductors,
14.
Constant current machines, 34. Construction of bipolar machine,
22. Current, how generated, 12.
" measure of strength, 73. Cylinder controller, 72. Direction of rotation, effect of, 15. Distributing boards, 59. circuits, 47.
Distributions, A. C. 882. Drum and barrel windings, 45.
" armature, 29. Dynamos, switching into circuit,
78.
Effect of current on needle, 8. " u direction of current on
conductor, 11, 19. " " number of armature
coils, 25.
" " number of poles, 39. " " turns of wire, 20. Electro-magnetic induction, 14. Electromotive force, how deter- mined, 15. Elevators, 716, 769.
Electrical: —
Elevators, belt driven, 717.
" cable-drive machine,
781.
car switch, 748. " controller for, 728, 775,
777, 785. " diagram of wiring, 774.
784. " diagrams of traction
types, 779. direct, driven, 730. duplex motor, 772. Frazer duplex, 770. " limit of drum type, 769. " limit switch, 776. '• machines, care of, 739-
765. •' machines, Otis .direct
connected, 741.
" machines, types of, 756. if method of controlling,
773.
motor, care of, 726. " plants, installation of,
726.
" traction type, 778. Equalizing connections from gen- erator, 63. Field coils of multipolar machines,
45.
Fluctuation of current, 24. Form of curve, 823. Formulas, 891. Fuses, location of, 60. Generator and motor, installing, 74. " " " running in par- allel, 79, 80.
" Brush arc, 103-110. " compound, connections,
53.
" " operation, 34.
" " wound, start
ing, 55.
" constant potential, 34. " heating in, 93. " multipolar, 38, " noise in, 91. " principle of, 7.
1062
INDEX.
Electrical:—
Generator, series and shunt, 81.
" starting a, 77. Impedance, diagram, 837. Impressed, E. M. F., 838. Inductive action, 834. Instruments required in circuit, 49. Lap winding, 42.
Light and power systems for build- ing, 58.
Lightning arrester, loca ion, 49. Lines of force around conductors, 9.
« « « direction of, 5. Live and dead side of coil, 29. Long shunt, 32. Magnetic field, 10.
tf flux through armature, 63. " force, how measured, 13. Magnetization of field, 32. Magnet, lifting capacity of, 13.
tl needle, 3. Motor, compound, 35.
" current required by, 57.
" effect of overloading, 65.
4< field, regulating strength,69.
11 heating in, 93.
" induction, 871.
" induction, three-phase, 877.
" principle of, 11.
" principle of synchronous, 867.
t( reversing the direction of, 70.
" shunt and compound, 33.
•' shunt, varying speed of, 71.
<e single phase synchronous, 70.
" starting switch, 65.
" to start, 68.
te two and three-phase, 70.
" variable speed, 68. Motors, 64. Mutual induction, 842. Ohm, definition, 73. Panel boards, 59. Permanent magnet, 1. Personal safety, 129. Phase, meaning of, 828. Polyphase, 832.
Electrical: — Power factor, 870. Principles of A. C., 870. Reactance, 830. Resistance of conductor, 15. " regulator, 48. " to magnetic force, 21. Rotary converter, 886. Rotary converter for St. Ry., 885. " transformers and convert- ers, 878. " transformers connection of
brushes, 881. Self-induction, 829. Sine curve, 824.
" " diagram, 831. Soldering fluid, 101. Strength of current, how measured,
15. " " field, effect on speed,
12. Switchboard for three- wire system,
57.
" for two generators, 51.
<e general arrangement,
50.
Switchboards and instruments, 47. Synchronizer or phase indicator,
862.
Synchronizing lamps, 861. Transformers, kinds of, 850.
fC principle of, 844.
fe use of, 849.
Two and three-phase systems, 883 Two and three-wire systems, 56. Two-bar magnets, 3. Voltage, effect on number of lamps,
56.
Watt, what it is, 73. Wave winding, 43. Winding for four-pole machine, 39. " " multipolar armatures,
40.
Why commutators spark, 82. Elevator safeties, 1025.
" <f brake or clamp,,
type, 1031-1034. 4i ee cable connections,
1031.
INDEX.
1063
Elevator safeties, miscellaneous de- vices, 1037. f< ee proper care of,
1037. (C ft requirements of,
1027. " •' roller type, 1028-
1030. " " speed governors
for, 1027.
" {f type used with
electric eleva- tors, 1035-1037. " " wedge type, 1025.
" " wedge type, mod-
ification of, 1027. tf " wedge type, Otis,
1025.
Engine, Armlngton and Sims, 290. u automatic, 376. " care and management, 185. " compound, 222. " " adjusting gov-
ernor, 232, te <c equalizing load,
230.
" " horsepower, 232.
" " mean effective
pressure, 232.
" " points of cutoff,
231. •f u proportion of
cylinders, 227.
" te reheater, 255.
" " starting, 257.
" " starting and
running, 253.
" " total no. of ex-
pansions, 228.
<l " types of, 224.
" condensing, 232. " " advantage of,
234. " connecting piston rod and
crosshead, 190. " Corliss, adjustment of
valves, 206.
41 Corliss, double eccentric, 669.
Engine, effect of cut off and speed,
380.
" formulas, 203. <e foundation, 182. f< high speed, 179. " horsepower, 649. " how to line, 199. " Ideal, 298.
" length of stroke, to find, 273 " location of, 181. " low speed, advantage of.
179. <s performance of non-con-
densing, 183. ** repairs for, 191. u running ^over' and
< under,' 668.
" selecting oil for, 187. " selection of, 177. " sett ug up and running Cor- liss, 205.
" the most economical, 182. " throttling, 376, 379. " to increase horsepower of,
383, 385.
te to increase speed of 381. " to line with direct shaft- ing, 387. " to line with line shafting,
385.
" triple expansion, 653. Engines, automatic, 194.
^ « cutoff, 339.
" clearance spaces, 276.
" gene al proportions, 275.
" regular expansion, 338.
" slide valve, 337.
" steam used by, 403.
•c water required by small,
676.
" weights of, 273 " f< per rated horse-
power, 276. Engineer, the first duty of, 323,
325, 656. Evaporation, factor of, 539.
" highest average, 327.
Exhaust pipes, 275. Expansion curve, locating true, 354.
1064
INDEX.
Expansion gain by, 183, 336.
" to find number, 226. FAHRENHEIT thermometer, 809. Fairburn's experiments, 473. Feed water, gain by heating, 680. " heater open, 681.
" heaters, 678.
Firebrick, 433. Fly-wheel, 184.
weights of, 276. " why used, 655. Foaming and priming, 436. Friction and lubrication, 1040. u coefficient of, 1042. " laws of, 1040. " uses of, 1041. Fuel, utilization of, 327. Furnace boiler, 431, 513, 525. " down draft, 522. " grates, how set, 670. Fusible plug, 533.
" plugs, care of, 435. GEARING, construction of, 706. Governor, 183.
" adjustment for riding
cutoff, 268.
" the Gardner, 341. " throttling, 666.
to block up, 669. Gauge cocks, location and care,
429, 434, 521.
" glass, location and care,
434. " steam, connections and care
430, 434, 489.
HARRIS BURG engine, 291. Heat and steam, 416.
" in water between 32° and 212°, 604.
" latent, 583, 652.
" measurement of, 419.
" mechanical equivalent, 420.
(e of combustion, 418, 484.
" radiation of, 421.
" sensible, definition, 657.
" utilization in boiler, 417. Heater, capacity for heating water,
482. Heating surface, definition, 663.
Heating surface, per horsepower
648. Horsepower, 185, 275.
" definition of, 653.
indicated, 353. <e of gears, 695.
" of shafting, 697.
Hydraulic elevators, 954. Hyd. Elev. accumulators, 996. " " " construc-
tion of, 996.
" te " operation
of, 997.
" " cables, care of, 1021. " " " lubrication,
1023.
" " car, settling of, 1019. " " circulatingpipe, 967. " " closing down, 1022. se " controllers, circuit
connections, 986. " " controllers, eleotric
floor, 985. <e " controllers, operation,
986.
" " Crane, 959. " " cylinder and plunger,
1005. " " double power type,
987.
u enclosures, 1019. " gear of, 956.
" operating, 956. " " guides, lubrication,
1023. (t " hand rope operation,
967. " " high pressure type,
988.
" " horizontal, 954. " " " high pres-
sure, 990. " " leaks, how to find,
1023.
" " lubrication, 102.3. tf u Morse and Williams
design, 961. " " Otis vertical, 966.
"
INDEX.
1065
Hyd. Elev. piston, packing Otis
vertical, 1014. " fe piston, rods, packing,
Otis, 1016. " " plunger, balancing of,
1001. " " " construction,
1000.
" " " Plunger Elev.
Co.'s, 1001.
" " " Standard Plun-
ger Elev. Co.'s, 1001. « type, 998. tf u pulling machines,
horiz., 963. " 'f pushing machines,
horiz., 956.
" se ropes, standard, hoist- ing, 1021. " " sheaves, lubrication,
1023. " " sheaves, traveling,
1007. " " stop balls for hand
rope, 1019.
" " types of, 954. " " valve construction,
971. " " " hand rope type,
1013.
" " " Otis, main, 976.
" <l " pilot, 976, 1005.
" " " " battery
|
type. 981. 1 |
ndic* |
|
control, I |
ndic* |
|
971. |
|
|
floor con- |
< |
|
troller, |
( |
|
push but- |
( |
|
ton, 985. |
t |
|
for verti- |
|
|
cal, 990. |
i |
|
magnet |
t |
|
control, |
|
|
979. |
it |
|
push but- |
|
|
ton con- |
a |
|
trol, 983. |
Hyd. Elev. valve running and standing rope, 957. " " " speed governing,
994. " " " Standard Plunger
Co.'s, 1007.
'•' " a stop for accumu-
lators, 997. " " valves, action of limit,
1007. " " (t automatic stop,
973-1003.
" " t( cup packing
for, 1022. " " " for double
power, 988.
" " " limit, 1012.
" " " main and pilot,
959, 975, 978, 1008, 1010.
" " " plunger type,
limit stop, 1003. " " vertical high pressure,
990.
" " " type, 966.
" " water for, 1017. a K Whittier design, 963. Hyperbolic curve, to draw, 355. IGNITION point of various sub- stances, 589.
Inches in decimals of a foot, 714. Incrustation, 682. Indicating Ideal engines, 306. Indicator, applying pencil to card,
367.
attaching the card, 366. benefit from use of, 364. combined diagram, 362. connecting to cylinder,
346.
construction of, 345. diagram analysis, 347,
377. " ammonia
pump, 373. " Ball engine,
374.
106G
INDEX.
Indicator diagram condensing
engine, 352. Dickson en- gine, 376. Eclipse refrig. mach., 371. " Harrisburg
Ideal, 369. H Harrisburg
Standard, 370. measuring,
346.
" Russell en-
gine, 367. eccentric card,
362. " effect of changing valve
stem, 364.
lf " leakage, 363. of what use, 649. operation of, 346. selecting spring, 366. springs, 346.
" attention re- quired, 366. steam chest cards, 359. stroke cards, 358. " tension of drum spring,
366.
" to take a diagram, 365. Injector, and inspirator, 591.
" capacity, horsepower,
etc., 601.
height of lift, 671. piping an, 594. selection of, 428. starting pressure, 597. the Peuberthy, 600. the World, 593. to discern cause of diffi- culties, 599.
" to test for leaks, 601. Injection, auxiliary, 259. Inspirator, the Hancock, 597.
" to clean, 598. Iron, weight of square and round,
488. JOURNALS, heating of, 193.
1C
it
KNOCKING in engines, 189, 119 LAP, definition of, 654. Lead, adjusting the, 319. " definition of, 653. " inside, 666. " with link motion, 318. Lever, the, 768. Liquids, friction of, 564. Lost motion, taking up, 652. Low water, 436. Lubrication, 186.
adhesion 1046. cohesiveness, 1045. cylinder And valve,
1049. " essent als of cylinder,
1051 " number of drops of
oil, 1052.
" of refrigerating ma-
chinery, 1053.
" petroleum oils, 1046.
(t reliable test, 1053.
" theory of, 1045.
" to detect insufficient,
1052. te wet steam, effect of,
1050.
lubricators, automatic, 310. " sight feed, 312.
MAIN bearing, care of, 190, 192. Mclntosh and Seymour engine,
29o.
Mechanical refrigeration, 619, 635. Melting points of metals, 687. Metric system, 809. Momentum, 671. Mud drum, 648. PETROLEUM in boilers, 442. Pipe, blowoff, 429.
cutting to order, 675. dry, what it is, 431. expansion of wrought iron,
485.
feed, area of, 427. length required to condense
steam, 47£.
Pipes. looa,iiori of steam, 428. " capacities of, 485, 1039.
INDEX.
1067
Pipes, contents in gallons, 1039. " sizes of mai s and branches,
485.
" steam, 785. " " connecting up, 429. Piping, simplicity in steam, 674. Piston, area, to find, 564. " leaking, to tell from dia- gram, 655. " rings, 187. " speed, 275.
" for pumps, 654. " testing for leakage, 669. Pitch for wheels, 704. Pohle, air lift system, 807. Porter- Allen engine, 281, 288. Power, definition of, 274.
if rope transmission of^ 712. Pressure, absolute, 398.
" excessive, effect of, 452. u in receiver, 256. t( mean effective, 349, 351. " test for boilers, 447. tf total average, 275. Priming, effects of, 329. Pump, arranging pipe connections,
569. " Blake, 555.
calculating boiler for, 580.
Cameron, 548.
Deane, direct acting, 546.
duplex, operation of, 569.
formulas, 618.
Hooker, 553.
Knowles, 550.
Lost motion, in, 567.
miscellaneous questions,
550-567, 571-580. <e setting valves on duplex,
567.
" taking care of, 575. " Worthington compound, 544. QUESTIONS asked when applying
for license, 648-671. REAUiMER thermometer, 811. Receiver pressure, 256. Refrigeration, 619-640.
" air in system, 628.
" brine system, 622,
Refrigeration, cold easily regu- lated, 622.
<{ condenser, 626.
" " pressure,
624.
" direct expansion,
623.
lf, effect of ammonia on
pipes, 633.
" expansion coils, 634.
tc function of pump,
621.
tf instructions for oper-
ating plant, 624. leaks in pipes, 625.
" lubrication of ma-
chine, 632.
" oil in the system, 627.
" operation of appar-
atus, 620.
" principles of opera-
ation, 620.
ce process of, 635.
" pump and condenser,
621,636.
" rating of machine,
623.
" reboilers, 628.
" selection of oils, 633.
" shutting down ma-
chine, 625.
te starting machine, 624.
(t steam condensers,
627.
ff suction pressure, 625.
" test for compressor,
626.
" testing for water, 631.
fe to charge system,
634.
" utilizing the cold,
622.
f< valves, location of,
624
" what does the work,
621.
Rocker shaft, influence of, 273, 319. Rope, hoisting, 814. " horsepower transmitted, 813,
1068
INDEX.
Rope, proper diam. of sheaves, 813,
" speed of, 813.
" to test purity of, 814.
" transmission, systems of, 812.
" working strain, 813. Ropes, limit to number, 813.
Rules: —
air cylinder, capacity of, 801. ampere turns required, 46. amperes, to find, 166. area of safety valves, 427. armature pall, 63. belt, length required, 789. " width required, 789. boiler, distance between rows of
rivets, 465.
boiler, maximum pitches of riv- ets, 466. boiler, pitch, diagonal, 464, 456.
" safe working pressure,
477.
centrifugal force, 501. chimney, stability of, 693. chorda! pitch, 699. circle circumference, 788. circular mils, 166. circumference of gear, 700. cylinder, capacity, 565. engine, duty of pumping, 615.
" to increase p >wer, 383.
s( to increase speed, 381. factor of evaporation, 539. gears, depth of tooth, 709.
" distance between centers, 711.
" horsepower of, 695, 710.
" speed of, 7LO.
" velocity of, 695. heating surface in square feet,
539. heating surface of water tube
boilers, 461. horsepower, boiler pump will
supply, 617.
horsepower, of compound en- gine, 392. horsepower of noncondensing
engine, 392.
horsepower of pumping engine,
616.
linear expansion of pipe, 394. magnet, lifting capacity, 13. magnetic flux in maxwells, 63. number of expansions, 226. pinion, diameter of, 700. pulley, diameter of driven, 789. " effect of arc of contact,
791, 795.
" effect of distance be- tween, 797.
" effect of size, 790. " revolution of driver, 788. " speed of driven, 788. " velocity of driver, 788. pump, capacity to feed boiler,
616.
" discharge nozzle, 607. u maximum lift, 618. ' ' pressure can work against,
604.
" size to feed boiler, 613. " suction pipe, size of, 608. " to find diameter of piston,
605. " to find horsepower of
boiler required, 606. " to find horsepower re- quired in a, 605. " to find steam pressure re- quired, 604. proportional radius of gears,
700.
reinforcing ring, width of, 541. relative velocity of pinion, 700. revolutions of wheel or pinion,
700.»
rivets, shearing strength, 537. safe stress for tooth, 705. " working pressure, 536. « " " " A.S.M.E.
rule, 537.
shafting, horsepower of, 697. steam and water pistons, sizes,
603.
gteam pipe size required, 394. " u §ed with steam jets, 542
INDEX.
1069
Rules: —
Steam, weight discharged, 540. strain allowed on stay, 475. strength of boiler joint, 537. strength of diagonal stays, 476.
" of stayed flat surfaces, thickness of plate for shell, 463. train of wheels and pinions, 699. valves, safety, center of gravity
of lever, 499. valves, safety, pressure to raise
weight, 498. valves, safety, U. S. Gov. rule,
427. valves, safety, weight required,
497.
volts lost, to find, 166. water, area for given discharge,
611. " consumption of engine,
395.
" discharge under head, 609. " elevated per minute, 565. " flow in pipe, 611. " gallons delivered per min- ute, 603.
" given press, to find dis- charge, 610. " head, in feet corresp. to
friction, 613. lt horsepower required to
elevate, 563. " pounds per horsepower
for boiler, 618..
" velocity for given dis- charge, 609.
" weight of column, 565. weight of fly-wheels, 276. wheel, diameter of, 699.
t( il for given pitch,
703.
" number of teeth, 697. " pitch of, 698. " proportional velocity of,
701.
wire, size of, 166. Russell engine, setting single valve,
277. SAFETY at high pressure, 401.
Scale, effect of, 440.
" how to remove, 655. Screw-cutting, 713. Shafting, lining up, 672. Sheet iron, weight, 712. Slide valve, changing cutoff, 666.
" " fitting, 191. Smoke, 419. Soda, carbonate, 441. Something for nothing, 688. Staybolt, grip, of copper, 474. Steam coils, 480,481. Steam, consumption in practice,
180. " u of an engine,
834.
" dome, 430.
" effect of compression, 399. " generating, 332. " gage, what it indicates, 399. tf high pressure, 332. " method of condensing, 233. " pipe for heating water, 478. " pipes, loss of heat irom, 391.
" size of, 275. " plants, economy in, 327. " power plant, operating a,
325. " " " taking charge
of, 323.
" pressure of, 400. " properties of saturated, 330. " pump, the, 544. " temperature and pressure,
684.
" used with steam jets, 542. " using full stroke, 335. " velocity in engine, 394. " " of escape, 496.
€( water required to condense,
236. '.' weight condensed in heating
water, 479. " " discharged per second,
540. " where the force comes from,
398.
" why valuable, 652. Steel stacks, weight of, 694.
1070
INDEX.
Stufflngboxes, 188. Sulphate of lime, 441.
Tables: —
actual ratios of expansion, 928. air required for rock drills, 933,
934. ammonia compressor, 902.
" gas for one ton refri- geration, 898. t( horsepower to compress
one cu. ft. 901. " properties of, 899. amperes, per lamp* 173. amperes, per motor, 169, 170. arcs of contact, useful effect,
795. areas of circular segments, 935,
936.
area of safety valve, 495. boiler, energy stored in, 448. boiling points of various sub- stances, 907. brick required for boiler setting,
522. brine solution, properties of,
900.
capacity and horsepower of in- jector, 601.
" of reservoirs in gal-
lons, 910. " of square cistern in
gallons, 585. " of tanks in gallons,
584.
carbonic acid, properties of, 900. carrying capacities of wires, 99-
102.
coal, per sq. ft. of grate, 908. condenser, power gained by ad- ding a, 923. " water required for,
237. contents of cylinder for one foot
length, 801.
te of pipes and tanks, 1039.
Corliss engines, sizes and dimen- sions, 926. cost of coal per annum, 909.
Tables:—
cost of water per 1000 gallons
587. decimal equivalent of an inch,
583. diameters, circumferences, and
areas of circles, 895. dimensions of steam, gas and
water pipe, 486. electric light conductors, 176. feed water required by small
engines, 676.
flues, safe pressure for, 952. fusible plugs, melting points,
907. heating surface in square feet,
501. f( tf per horsepower,
403. heat in water between 32° and
212°, 602. hoisting rope, strength and price,
812,919. horsepower for one pound
M.E.P., 924.
" of slide valve en-
gines, 922.
ft per ton of refrigera-
tion, 904
" " " of belts, 796.
" " « of gear
wheels, 696.
•' " " of manilla,
rope, 712, 813. •' " " of shafting
697. t€ " f( of wire rope
715.
hyperbolic logarithms, 892. ignition points of various sub- stances, 589.
incandescent wiring, 161, 162. latent heat of liquids, 583. loss by friction in water pipes, 588.
INDEX.
1071
Tables:—
Loss, from uncovered pipes, 391. mean absolute pressures, 925. melting points of metals and
solids, 687-907. piston speed ft. per min., 912. pipes and tanks, cap'y, 1039. pitch of wheels, 706, 704. pneumatic tools, 933. pressure in boilers built since
1872, 516-519. " of water due to height,
582. " required to start injector,
597. properties of saturated steam,
330, 913. proportions of boiler joints, 467-
472, 946. ff of parts of engines,
275.
pull of belt one inch wide, 799. pump, boiler feed, 397. pumps, capacity of duplex, 893. " " of low pres-
sure, 894. <f sizes of cylinders for
compound, 923, 927. speed and capacity of
centrifugal, 927. rise of safety valve, 494. riveted seams, measurement of,
944-951. {( specifications for,
937.
ropes for inclined planes, 920. " iron and steel transmis- sion, 918. ft transmission of power, by,
921. •aving by heating feed water,
680. showing how water may be
wasted, 589. sizes of chimneys, 692. Bteam consumption in N C. en- gines, 183.
•ulphur dioxide, properties of, 898.
Tables:—
thermometers, 903. total heat in steam, 677. tubular boilers, 930, 931, 932. U. 8. gallons in given number of
cu. ft., 586. volts, lost for per cent of drop,
171, 172.
wages, table of, 929. weight and strength of iron bolts,
906. weight of engine, 273.
" " rivets and bolts, 905. ' " round iron, per foot, 488. e " steel smoke stacks, 694. < " water, 585. ' per square foot of sheet iron.
712. weights of feed water and of steam,
677. wire gages, difference between,
175.
" u for 110-volt lamps, 37. <f " weight and meas. of
water proof, 174. Tanks, capacity of, 584. Tannate of soda, 442. Teeth of wheels, 705, 709. Theoretical curve, 353. Thermometers, 811. Tubes or flues, materials for, 481. lf " " seamless, 482. " '* " sizes, 482. USEFUL INFORMATION, 1023. VACUUM, effect on economy, 233. " how maintained, 653.
" in condenser, 236. * Valve, check, 429.
" cutoff, setting, 266.
" flat riding cutoff, 268.
" gear, double eccentric, 215,
222. " leaking, how to discover,
655. " motion, direct and indirect,
668.
" plain slide, function of, 320. " piston, riding cutoff, 263. « " type, setting, 261.
1072
INDEX.
Valve, safety, 426, 491, 499. " " area of, 495. (t proportion of lever, 670. " rise of, 494. " setting for engineers, 318. " " plain slide, 318,, 320.
" " riding cutoff with
governor, 272.
" " slide with link-mo-
tion, 313.
" slide, to set in a hurry, 388. " spindle, adjusting length,
319.
'* stem, length of, 668. Ventilation, data relating to, 484. Water, 681, 1024.
" columns, 489, 515.
»< cost of, 587.
" distilled for boilers, 439.
" evaporated per pound of
coal, 650.
tf for use in boilers, 438. (l height of column for given press, 580.
Water, how may be wasted, 589. " kinds of impurities, 438. " loss by friction in pipes,
588. " maximum evaporat on,
421. tf meter^ the Worthington,
681.' " pressure due to height,
582, 585.
te " of column, 565.
" required by boiler, 565. " steam required to heat,
478.
" weight of, 564, 585. Westinghouse compound engine,
307.
Wheel gearing, 698. Wire rope, transmission of
power, 715.
Wood, weight equal to coal, 651. Work, definition of, 274. Worm screw, 708.
THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW
AN INITIAL PINE OF 25 CENTS
WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE.
NOV 2
LIBRARY. BRANCH OF THE COLLEGE OF AGRICULTURE
|
137 |
||
|
Tulley |
TJ151 |
|
|
Handbook |
on |
T8 |
|
engineer!!* |
5* |
1907 |
|
• |
||
|
X" "~ ' |
||
|
• |
||
UNIVERSITY OF CALIFORNIA LIBRARY