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Full text of "Audels engineers and mechanics guide ... a progressive illustrated series with questions--answers--calculations, covering modern engineering practice"

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AUDELS 

ENGINEERS 

ANO 

MECHANICS 
GUIDE 1 

/\ PR06RESSIVF. ILLUSTRATED SERIES 
WITH QUESTIONS-ANSWERS 
CALCULATIONS 

covEaiNG 

MODERN 
ENGINEERING PRACTICE 

SPECIALLY PREPARED FOR ALL ENGINEERS 
ALL MECHANICS AND ALL ELECTRICIANS. 
A PRACTICAL COURSE OF STUDY AND 
REFERENCE FOR ALL STUDENTS AND 
WORKERS IN EVERY BRANCH OF THE 
ENGINEERING PROFESSION 
BY 

FRANK D. GRAHAM, BS.,M.S.,M.E. 

GRADUATE PRINCETON UNIVERSITY 
AND STEVENS INSTITUTE-LICENSED 
STATIONARY AND MARINE ENGINEER 



THEO. AUDEL 8c CO. . pubushers 
72 FIFTH AVE. NEW YORK u.s.a. 



COPYRIGHTED, 1921, 

BY 

THEO. AUDEL & CO., 
New York 



■tted in the United States 



NOTE 



In planning this helpful series of Educators, it has been the 
aim of the author and publishers to present step by step a 
logical plan of study in General Engineering Practice, taking 
the middle ground in making the information readily available and 
showing by text, illustration, question and answer, and calcula- 
tion, the theories, fundamentals and modern applications, includ- 
ing construction in an interesting and easily understandable 
form. 

Where the question and answer form is used, the plan has 
been to give shorty simple and direct answers, limited to one 
paragraph, thus simplifying the more complex matter. 

In order to have ajiequate space for the presentation of the 
important matter and not to divert the attention of the reader, 
descriptions of machines have been excluded from the main 
text, being printed in smaller type under the illustrations. 

Leonardo Da Vinci once said: 

"Those who give themselves to ready and rapid practice 
before they have learned the theor}^, resemble sailors who go 
to sea in a vessel without a rudder" 

—in other words, **a little knowledge is a dangerous thing.'** 
Accordingly the author has endeavored to give as much infor- 
ination as possible in the space allotted to each subject. 

The author is indebted to the various manufacturers for 
their co-operation in furnishing cuts and information relat- 
ing to their products. 

These books will speak for themselves and will find their 
place in the great field of Engineering. 



CONTENTS OF GUIDE No. 1 



Contents of Guide No. 1 

CHAPTER PAGES \ 

1. Basic Principles 1 to 46 ] 

Water — heat — work — Joule^s experiment — energy — pressure — the bar- - 
ometer — temperature scales — steam — what an engineer should know 
about steam — From Ice to Steam — condensation— STEAM TABLES, i 

2. The Steam Engine 47 to 102 | 

How an engine works — expansion of steam — Boyle's law — saving by '] 
expansion — cut off — initial, terminal and mean elective pressures — ! 
hypobolic logarithms — diagram factor — horse power — size of cylinder j 
(calculations). . ' . i 

3. Steam Engine Parts 103 to 178 

Cylinder — stuffing box — piston — piston rod — cross head and guides — 
Scotch yoke — connecting rod — crank shaft — main bearings — fly wheel 
—belts. 

4. Tlie Slide Valve .., 179 to 224 I 

Requirements — valve — seat — steam and exhaust edges — port — passage j 
— wire drawing — lap — neutral and line and line positions — lead — pre- | 
admission — admission — cut off — pre-release — release — compression — .■ 
port opening — travel (throw) — ^linear advance — how to design a slide I 
valve for a 7 X 7 engine applying the Bilgram diagram — defects of j 
the slide valve. i 

i 

5. The Valve Gear 225 to 242 1 

i 

Yoke — stem^-guide — rocker levers — eccentric rod — eccentric and strap : 
— throw — angular advance — objections to eccentrics . \ 



CONTENTS OF GUIDE No. 1 



6. Variable Cut Off 243 to 290 

Principles of variable cut off — shifting, swinging and offset swinging 
eccentrics — independent cut o/f— defects of slide valve at early cut 
off — Gonzenback valve — riding cut off, with: 1, variable angular 
^K advance; 2, variable lap; 3, variable travel. 

7' Modified Slide Valves, . , 291 to 308 

Balanced slide valves — piston valves — outside and inside admission — 
double admission — double ports — compound engine valves — adjustable 
valve — pressure plate valves — quadruple admission and double exhaust 
— ball valve. 

8. Reversing Valve Gears; Loose Ec- 
centrics e . . . . 309 to 316 

Principle of loose eccentric — spiral slot marine type: 1, on main shaft; 
2, on valve shaft — loose eccentric control methods — various drives for 
loose eccentrics — Rabbe triple expansion marine engine illustrating 
adaptation of loose eccentrics to marine practice. 

9. Reversing Valve Gears; Link Mo- 
tions 317 to 338 

Williams link — so called Stephenson or shifting link — single and double 
reach rods — end and center suspension — offset link — open and crossed 
rods — adjustable cut off with shifting link — forms of link — steam dis- 
tribution with link — slip — Gooch link — stationary — Allen and Fink 
links. 

10. Reversing Valve Gears; Radial Valve 
Motions 339 to 362 

Principles — Hackworth gear: 1, inside connected; 2, outside connected 
types — Marshall gear — Bremme gear — ^Joy gear— Joy and Bremme gear 
compared — ^Walschaerts gear. 

11. Governors 363 to 402 

Classes of governor — centrifugal, pendulum and loaded pendulum 



CONTENTS OF GUIDE No. 1 



Governors — Continued 

governors — sensitiveness — stability — isochronism — hunting — iner- 
tia governors — spring governors — regulating mechanism — throttling and 
cut off governors — regulation — shaft governors — auxiliary devices — ^vari- 
able speed governors— GOVERNOR TROUBLES. 

12. Pump Valve Gears ^. . . 403 to 432 

Principles — main valve — auxiliary piston — auxiliary valve — separate 
auxiliary valve — auxiliary valve and. auxiliary piston combined — duplex 
valve gear — method of locating cross head centers — duplex valve setting; 
short rules. 

13. Valve Setting 433 to 462 

How to set the slide valve: \, finding dead center; 2, adjusting valve 
stem, Z, finding angular advance Xgeneial, and on large engines) — settmg 
slide valve: 1, without removing chest cover; 2, without finding dead 
centers; 3, with inside admission; 4, emergency rule — taking laths — 
setting riding cut off gear: 1, movable eccentric; 2, fixed 'eccentric — setting 
link motion — ^valve setting with indicator. 



BASIC PRINCIPLES 



CHAPTER 1 
BASIC PRINCIPLES 



"'he Medium. — In the operation of a steam engine, steam 
is the medium or working substance by which some of the heat 
energy, liberated from the fuel by combustiony is transmitted to the 
engine, and partly converted by the latter into mechanical work. 
The behavior of this medium under various conditions should 
therefore be thoroughly understood by the engineer. Accord- 
ingly, water, from which it is formed by the application of heat, 
should be first considered. 

Water. — This remarkable substance is a compound of hydrogen 
and oxygen in the proportion of 2 parts by weight of hydrogen to 
16 parts by weight of oxygen: 

Since the atom of oxygen is believed to weigh 16 times as much as the 
atom of hydrogen, the molecule of water is said to contain 2 atoms of 
hydrogen and 1 atom of oxygen, being represented by the formula H2O. 

Under the influence of temperature and pressure this substance H2O 
may exist as 

1. A soHd; 

2. A liquid, or 

3. A gas. 

As a solid it is called ice*\ as a liquid, water, and as a gas, steam. 



*NOTE. — One cu. ft. of ice at 32" Fahr., weighs 57.5 lbs.; one lb. of ice at 32* F. has a 
volume of .0174 cu. ft., or 30.067 cu. ins. The relative volume of ice to water at 32** F., is 
1.0855, the expansion in passing into the solid state being 8.55%. Specific gravity of ice =.922, 
water at 62° F. being \.— Clark. 



BASIC PRINCIPLES 



Oues. What is the most remarkable characteristic 
of water? 

Ans. Water at its maximum density (39.1 degrees F.) will 
expand as heat is added, and it will also expand slightly as the 
temperature falls from this point, as illustrated in figs. 1 to 3. 

Ques. What is the freezing and boiling points of water 
at atmospheric pressure at the sea level? 




MAXIMUM 
DENSITY 

Figs. 1 to 3. — The most remarkable characteristic of water: expansion below and above its 
temperature or "point of maximum density" 39.1°Fahr. Imagine one pound of water at 39.1" F. 
placed in a cylinder having a cross sectional area of 1 sq. in. as in fig. 1. The water having a 
volume of 27.68 cu. ins., will fill the cylinder to a height of 27.68 ins. If the liquid be cooled 
it will expand, and at say the freezing point 32° F., will rise in the tube to a height of 27.7 ins., 
as in fig. 2, before freezing. Again, if the liquid in fig. 1 be heated, it will also expand and 
rise in the tube, and at say the boiling point (for atmospheric pressure 212° F.), will occupy 
the tube to a height of 28.88 cu. ins, as in fig. 3. 



Ans. It will freeze at 32° Fahr., and boil at 212°, when the 
barometer reads 29.921 inches.* 

Oues. Is the boiling point the same in all places? 

Ans. No. 

The boiling point of water will lower as the altitude increases ; at an alti- 
tude of 5,ooo feet, water will boil at a temperature of 202° Fahr. 



*NOTE — 29.921 inches of mercury = standard atmosphere= 14. ( 
Marks and Davis. 



> lbs. per sq. inch. — 



BASIC PRINCIPLES 



Oues. How does pressure affect the boiling point of 
water? \ 

Ans. An increase of pressure will elevate the boiling point. ■] 




Fig. 4. — The syphon. Let A B C, be a bent syphon, or tube, of which the leg A B, is plunged 
into a vessel D E, containing water. If the surface of the water be F G, the leg of the syphon, 
A B, will be filled w:ith water as high as the surface, that is, up to H, the portion H B C, 
remaining full of air. If, then the air be drawn off by suction through the aperture C, the 
liquid also will follow. And if the aperture C, be level with the surface of the water, the 
syphon, though full, will not discharge the water, but will remain full: so that, although it 
is contrary to nature for water to rise, it has risen so as to fill the tube ABC, and the water 
will remain in equilibrium, like the beams of a balance, the portion H B, being raised on high, 
and the portion B C, suspended. But if the outer mouth of the' syphon be lower than the 
surface F G, as at K, the water flows out, for the liquid in K B, being heavier, overpowers 
and draws toward it the liquid B H. The discharge, however, continues only until the 
surface of the water is on a level with the mouth K, when, for the same reason as before, 
the efflux ceases. But if the outer mouth of the tube be lower than K, as at L, the discharge 
continues until the surface of the water reaches the mouth A. 



Oues. What is the weight of a cubic foot of water at \ 
maximum density? 

Ans. It is generally taken at the figure given by Rankine, i 

62.425 lbs.* \ 



*NOTE. — Some authorities give as low as 62.379. The figure 62.5 commonly given is 
approximate. The highest authoritative figure is 62.428. At 62° Fahr., the figures range 
from 62.291 to 62.36. The figure 62.355 is generally accepted as the most accurate, though for 
ordinary calculations, the figure 62.4 is generally taken, this corresponding to the weight at 
53* F. 



BASIC PRINCIPLES 



Oues. What is the weight of one U. S. gallon of water? 

Ans. One U. S. gallon (231 cu. ins.) of water weighs S}^ 



lbs. 



The figure 8 H is correct when the water is at a temperature of 65° Fahr* 




Fig. 5. — Hydraulic principles; 2. Pressure exerted anywhere upon a mass of liquid is trans^ 
mitied undiminished in all directions, and acts with the same force on all equal surfaces^ and 
in a direction at right angles to those surfaces. CD, above is a vessel composed of two cylin- 
drical parts of unequal diameters, and filled with water to a. The bottom of the vessel 
CD, supports the same pressure as if its diameter were everywhere the same as that of its 
lower part; and it would at first sight seem that the scale MN, of the balance in which the 
vessel CD, is placed, ought to shqw the same weight as if there had been placed in it a cylin- 
drical vessel having the same weight of water, and having the diameter of the part D. But 
the pressure exerted on the bottom of the vessel is not all transmitted to the scale MN: 
for the upward pressure upon the surface n o, of the vessel is precisely equal to the weight 
of the extra quantity of water which a cylindrical vessel would contain, and balances an 
equal portion of the downward pressure on m. Consequently the pressure on the plate MN, 
is simply equal to the weight of the vessel CD, and of the water which it contains. 



Oues. How does the pressure of water due to its weighty 
vary? 

Ans. It varies with the head, and is equal to .43302 lbs. 
per sq. in. for every foot of (static) head. 



NOTE. — Compressibility of water. — Water is very slightly compressible. Its compres- 
sibility is from .00004 to .000051 for one atmosphere, decreasing with increase of temperatuie. 
For each foot of pressure, distilled water will.be diminished in volume .0000015 to .000001.3. 
Water is so incompressible that even at a depth of a mile a cubic foot of water will weigh only 
about ^2 !!>• more than at the surface. — Kent. 




BASIC PRINCIPLES 



' Heat. — By definition heat is a form of energy known by its 

effects. 

These effects are indicated through the touch and feeHng, as well as by 
the expansion, fusion, combustion or evaporation of the matter upon which 
it acts. 

Oues. What is temperature? 

Ans. That which indicates how hot or cold a substance is; 
a measure of sensible heat. 




Fig. 6.— Method of judging the heat of a soldering bit or so called "iron," illustrating se/isibfe i 
heat. 

Ones. What is sensible heat? 

Ans. That heat which produces a rise of temperature as dis- ] 
tinguished from latent heat. \ 

Oues. What is latent heat? ] 

Ans. The quantity of heat required to change the state or 
condition under which a substance exists without changing its 
temperature. ] 



BASIC PRINCIPLES 



Thus a definite quantity of heat must be transferred to ice at 32° to- 
change it into water at the same temperature. 



Oues. What is specific heat? 

Ans. The ratio of. the quantity of heat required to raise the 
temperature of a given weight of any substance one degree to 
the quantity of heat required to raise the temperature of the 
same weight of water from 62° to 63° Fahr. 




Figs. 7 to 9. — ^Three ways in which heat is transferred; fig. 7, by radiation; fig. 8, by conduction; 
fig. 9, by convection. In fig. 7, the water in the beaker is heated by heat rays which radiate 
in straight lines in all directions from the flame. In ng. 8, the flame will not pass through . 
the wire gauze, because the latter conducts the heat away from the flame so rapidly that 
the gas on the other side is not raised to the temperature of ignition. In fig. 9, the water 
nearest the flame becomes heated and expanded. It is then rendered less dense than the 
surrounding water, and hence rises to the top while the colder and therefore denser water 
from the sides flows to the bottom thus transferring heat by convection currents. 

Owes. Explain the term "transfer of heat." 

Ans. When bodies of unequal temperatures are placed near 
each other, heat leaves the hot body and is absorbed by the colder 
body until the temperature of each is equal. 

The rate by which the heat is absorbed by the colder body is proportional 
to the difference of temperature between the two bodies. The greater the 
difference of temperature, the greater the rate of flow of the heat. 



BASIC PRINCIPLES 



Oues. How does a transfer of heat take place? 

Ans. By radiation, conduction or convection. 

Thus, in a boiler, heat is given off from the furnace fire in rays which 
radiate in straight Hnes in all directions being transferred to the crown and 
sides of the furnace by radiation; it passes through the plates by con- 
duction, and is transferred to the water by convection, that is, by currents. 




Fig. 10. — Diagram showing principle and construction of the- Whitney hot wire instruments 
illustrating expansion by the action of heat. The action of instruments of this type 
depends on the heating of a wire by the passage of a current causing the wire to lengthen. 
This elongation is magnified by suitable mechanism and transmitted to the pointer of the 
instrument. 



Oues. What is an important effect of heat? 

Ans. Bodies expand by the action of heat. For instance, 
boiler plates are riveted with red hot rivets in an expanded 
state; on cooling the rivets contract and draw the plates to- 
gether with great force making a tight joint. 

An exception to the rule, it should be noted, is water, which contracts 
as it is heated from the freezing point 32° Fahr., to the point of maximum 
density 39.1°; at other temperatures it expands. 



8 



BASIC PRINCIPLES 



Heat and Work. — Heat develops mechanical force, and 
motion, hence it is convertible into mechanical work, 

Oues. How can heat be measured ? 

Ans. By a standard unit called the British unit of heat, 
or British thermal unit (B.',u,), 

Ques. What is the British thermal unit? 

Ans. The heat required to raise one pound of water from 
62° to 63° Fahr. (Peabody). 



I LB. OF WATER 
AT 32 • FAHR 





I LB. OF WATER 
AT 212' FAHR. 



Figs. 11 and 12. — Experiment illustrating the British thermal unit. Place one pound of water 
at 32° Fahr. into a beaker over a Bunsen burner as in fig. 11 assuming no loss of heat from 
the water. It will, according to the definition, require 180 heat units to heat the water from 
32° to 212° Fahr. Now, if the transfer of heat take place at a uniform rate and it require, 
say five minutes to heat the water to 212°, then one heat unit will be transferred to the 
water in (5 X60) -t-180 =2 seconds. 

Ques. What is the mean British thermal unit? 

Ans. ^ 180 part of the heat required to raise the temperature of 
one pound of water from 32° to 212° Fahr.^ f 



*NOTE. — The old definition of the heat-unit (Rankine), viz., the quantity of heat re- 
quired to raise the temperature of 1 lb. of water 1° Fahr., at or near its temperature of maximum 
density (39.1° F.) was the standard till 1909. 

tNOTE. — By Peabody's definition, the heat required to raise 1 lb. of water from 32° to 
212° is 180.3 instead of 180 units, and the latent heat at 212° is 969.7 instead of 970.4. 



BASIC PRINCIPLES 



It should be noted that this is the definition adopted in this work for the 
British thermal unit (B. t. u.), corresponding to the unit used in the Marks 
and Davis steam tables, which is now the recognized standard. 

Owes. What is work? 

Ans. The overcoming of resistance through a certain distance 
by the expenditure of energy. ^ ' , 

Oues. How can work be measured? 

Ans. By a standard unit called the foot pound. 



■^^m 




Fig. 13. — Experiment showing relation between heat and work. Take a brass tube A B, at- 
tached to a spindle geared to rotate rapidly and partly fill the tube with water and insert a 
cork. Apply a friction clamp D, and rapidly rotate the tube by turning the wheel C. The 
energy expended in overcoming the friction due to the clamp and rotating the tube causes 
the water to heat and finally boil; if continued long enough, the pressure generated will expel 
the cork. During the operation work has been transformed into heat. 



Oues. What is a foot pound? 

Ans. It is the amount of work done in raising one pound one 
foot, or in overcoming a pressure of one pound through a distance 
of one foot. 

Thus, if a 5 pound weight be raised 10 feet, the work done is 5X10 = 50 
foot pounds. 



12 BASIC PRINCIPLES 



A body may possess energy whether it do any work or not, but no work 
is ever done except by the. expenditure of energy. There are two kinds of 
energy : 

1. Potential energy; 

2. Kinetic energy. 

Potential energy is energy due to position, as represented, for instance, 
by a body of water stored in an elevated reservoir, capable of doing work 
by means of a water wheel. 

Kinetic energy is energy due to momentum, that is to say, the energy of 
a moving body. 

Conservation of Energy. — The doctrine of physics, that 
energy can be transmitted from one body to another or trans- 
formed in its manifestations, but may neither he created nor 
destroyed. 

Energy may be dissipated, that is, converted into a form from which it 
cannot be recovered, as is the case with the great percentage of heat 
escaping with the exhaust of a locomotive, or the condensing water of a 
steamship, but the total amount of energy in the universe, it is argued, 
remains constant and invariable. 

Thus, in Joule's experiment, fig. 14, the potential energy of the weights 
is not lost, but is transformed into heat, which is one form of energy. 
The apparatus possesses the same amount of energy at the end as at the 
beginning of the experiment, but the distribution of the energy has been 
changed, that is the potential energy given up by the weight has been 
transformed into heat, raising the temperature of the water. 

Power. — By definition, power is the rate at which work is 
done; in other words, it is work divided by the time in which 
it is done. 

The unit of power in general use is the horse power "^ which 
is defined as 33,000 joot pounds per minute. 

That is, one horse power* is required to raise a weight of 

33,000 pounds 1 foot in one minute 

3,300 pounds 10 feet in one minute 

33 pounds 1,000 feet in one minute 

3.3 pounds 10,000 feet in one minute 

1 pound 33,000 feet in one minute 

etc. 



*NOTE. — The term "horse power" ._ ^ „ 

power of a strong London draught horse to do work during a short interval, and used it as a 
power rating for his engine* 




BASIC PRINCIPLES 



13 



60ILIN6 INCHES 

POINT OF 

DE6.FAHR. MERCURY 




Pressure. — According to 
Rankine, the term pressure, in 
the popular sense, which is also 
the sense generally employed in 
applied mechanics, is used to 
denote a force, of the nature of a 
thrust, distributed over a surface; 
in other words, the kind of 
force with which a body tends 
to expand, or resists an effort to 
compress it. 

In the definition it should be care- 
fully noted that the pressure is con- 
sidered as distributed over a surface. 

The pressure distributed over a 
surface is usually stated in terms of 
the pressure distributed over a unit 
area of the surface, as pounds per 
square inch, meaning that a press- 
ure of a given number of pounds is 
distributed over each square inch of 
surface. This should be very clearly 
understood by the engineer, as fur- 
ther explained in figs. 18 and 19. 



Fig. 17. — Mercurial barometer, illustrating 
the boiling point for various pressures. 



NOTE. — Boiling point of various sub- 
stances at atmospheric pressure (14.7 lbs.): 

Ether, sulphide 100° P^'ahr. 

Carbon bisulphide US'' " 

Chloroform 140" " 

Bromine 145° " 

Wood spirit 150° " 

Alcohol 173° " 

Benzine 176° « 

Water 212° ^ 

Average sea water 213.2° 

Saturated brine 226° " 

Nitric acid 248° " 

Oil of turpentine 315* ' " 

Aniline 363° 

Naphthaline 428° ^ 

Phosphorus ^^o « 

Sulphuric acid ^^^^ 

Linseed oil ^^^o « 

Mercury 676° 

Sulphur • 800° 



10 



BASIC PRINCIPLES 



Ones. What is the relation between the unit of heat 
and the unit of work? 

Ans. It was shown by experiments made by Joule (1843-50) 
that 1 unit of heat = 772 units of work. This is known as the 
* 'mechanical equivalent of heat" or Joule* s equivalent. ' 

More recent experiments by Prof. Rowland (1880) and others give 
higher figures; 778 is generally accepted, but 777.5 is probably more nearly 
correct, the value 777.52 being used by Marks and Davis in their steam tables. 

The value 778 is sufficiently accurate for ordinary calculations. 




Fig. 14. — The mechanical equivalent of heat. In 1843, Dr. Joule of Manchester, England , 
performed his classic experiment, which revealed to the world the mechanical equivalent 
of heat. As shown in the figure, a paddle was made to revolve with as little friction as possible 
in a vessel containing a pound of water whose temperature was known. The paddle was 
actuated by a known weight falling through a known distance. A pound falling through a 
distance of one foot represents afoot Pound of work. At the beginning of the experiment a 
thermometer was placed in the water, and the temperature noted. The paddle was made 
to revolve by the falling weight. When 772 foot pounds of energy had been expended on 
the pound of water, the temperature of the latter had risen one degree, and the relationship 
between heat and mechanical work was found; the value 772 foot pounds is known as Joule's 
equivalent. More recent experiments give higher figures, the value 778, is now generally ; 
used but according to Kent 777.62 is probably more nearly correct. Marks and Davis in 
their steam tables have used the figure 777.52. 

Joule's Experiment. — In fig. 14, a weight W is attached to 
a cord which passes over a pulley R, and is wound around a 
revolving drum B. Attached to the drum is a spindle having 
fastened at its lower end vanes or paddles P P made of thin 



BASIC PRINCIPLES 



11 



pieces of sheet metal. These paddles are immersed in a vessel 
V, containing a definite quantity of water. 

In operation, as the weight W, falls, the paddles rotate in the water, the 
water itself being kept from rotating by fixed pieces not shown. It was 
discovered that the work done by the weight in descending, was not 
lost but appeared as heat in the water, the agitation of the paddles having 
increased the temperature of the water by an amount which can be meas- 
ured by a thermometer. 



ELEVATED 
TANK 




y 



BHiBBBiiBBaaBEl, 

i.||.i lull kIi.IiiIiii .iI- I.. ,:i'llii|,illl.:,l|i"|M 



TiC^=^ 



ES- 



^ 



35 



DVNAMO STORAGE BATTERY 

Figs. 15 and 16. — Potential, and kinetic energy. In fig. 15, the water stored in the elevated tank 
possesses energy by virtue of its position; being higher than the water wheel, the water 
will flow by gravity through the pipe and do work on the wheel. Thus, the potential energy 
of the water at rest in the tank, is, when it flows through the pipe converted into kinetic 
energy which is spent on the wheel. Fig 16 represents a railway car with axle lighting system. 
If the car be set in motion and then no further power be applied its momentum or kinetic 
energy will drive. the dynamo which in turn will charge the storage battery, and acting like 
a brake will gradually bring the car to rest. During this operation, the kinetic energy, 
originally possessed by the moving car, is absorbed by the dynamo (neglecting friction) 
and delivered to the battery as electrical energy which may be used in lighting the car. 

By numerous experiments, Joule determined with the utmost care that 
one pound of water was increased in temperature one degree by the work 
done on it during the descent of 772 pounds through one foot. 

This value, as before mentioned, is too small for ordinary calculation, 
the value 778, the generally accepted standard, should be used; the value 
777.52 is probably more nearly correct. 



Energy. — By definition, energy is stored work, that is, the 
ability to do work, or in other words, to move against resistance. 



12 BASIC PRINCIPLES 



A body may possess energy whether it do any work or not, but no work 
is ever done except by the. expenditure of energy. There are two kinds of 
energy : 

1. Potential energy; 

2. Kinetic energy. 

Potential energy is energy due to position, as represented, for instance, 
by a body of water stored in an elevated reservoir, capable of doing work 
by means of a water wheel. 

Kinetic energy is energy due to momentum, that is to say, the energy of 
a moving body. 

Conservation of Energy. — The doctrine of physics, that 
energy can be transmitted from one body to another or trans- 
formed in its manifestations, but may neither he created nor 
destroyed. 

Energy may be dissipated, that is, converted into a form from which it 
cannot be recovered, as is the case with the great percentage of heat 
escaping with the exhaust of a locomotive, or the condensing water of a 
steamship, but the total amount of energy in the universe^ it is argued, 
remains constant and invariable. 

Thus, in Joule's experiment, fig. 14, the potential energy of the weights 
is not lost, but is transformed into heat, which is one form of energy. 
The apparatus possesses the same amount of energy at the end as at the 
beginning of the experiment, but the distribution of the energy has been 
changed, that is the potential energy given up by the weight has been 
transformed into heat, raising the temperature of the water. 

Power. — By definition, power is the rate at which work is 
done; in other words, it is work divided by the time in which 
it is done. 

The unit of power in general use is the horse power "^ which 
is defined as 33,000 foot pounds per minute. 

That is, one horse power* is required to raise a weight of 

33,000 pounds 1 foot in one minute 

3,300 pounds 10 feet in one minute 

33 pounds 1,000 feet in one minute 

3.3 pounds 10,000 feet in one minute 

1 pound 33,000 feet in one minute 

etc. 



*NOTE. — The term "horse power" is due to James Watt, who figured it to represent the 
power of a strong London draught horse to do work during a short interval, and used it as a 
power rating for his engine* 



BASIC PRINCIPLES 



13 



601HN6 INCHES 



POINT OF 
16.FAHR. MERCURY 




31 


2ia 


29.921 - 


209.55 


2850 - 


205.87 


26.47 - 


201.96 


24.43 - 


197.75 


22.40- 


195.22 


20.56- 


188.27 


18.32- 


182.86 


16.29- 


176.85 


14.25 - 


170.06 


12.22 - 



162.28 10.18 



ABSOLUTE 
PRESSURE 
LBS.PERSO.IN. 

-15.226 

-14.696 

-14 

13 

-12 



- II 



10 



- 9 



o 



o 




Pressure. — According to 
Rankine, the term pressure^ in 
the popular sense, which is also 
the sense generally employed in 
applied mechanics, is used to 
denote a force, of the nature of a 
thrust, distributed over a surface; 
in other words, the kind of 
force with which a body tends 
to expand, or resists an effort to 
compress it. 

In the definition it should be care- 
fully noted that the pressure is con- 
sidered as distributed over a surface. 

The pressure distributed over a 
surface is usually stated in terms of 
the pressure distributed over a unit 
area of the surface, as pounds per 
square inch, meaning that a press- 
ure of a given number of pounds is 
distributed over each square inch of 
surface. This should be very clearly 
understood by the engineer, as fur- 
ther explained in figs. 18 and 19. 



32 




Fig. 17. — Mercurial barometer, iMustrating 
the boiling point for various pressures. 



NOTE. — Boiling point of various sub- 
stances at atmospheric pressure (14.7 lbs.): 

Ether, sulphide 100° Fahr. 

Carbon bisulphide 118° " 

Chloroform 140° " 

Bromine 145° " 

Wood spirit 150° " 

Alcohol 173° '^ 

Benzine 176° " 

Water 212° ^ 

Average sea water 213.2° 

Saturated brine 226° 

Nitric acid " 248° ^ 

Oil of turpentine 315* 

Aniline 363° "" 

Naphthaline 428° ** 

Phosphorus 554° " 

Sulphuric acid 590° " 

Linseed oil 597° |^ 

Mercury 676° " 

Sulphur 800° " 



16 



BASIC PRINCIPLES 



Pressure Scales. — The term vacuum is a much abused word; 

strictly speaking it is defined as a space devoid of matter. This 
is equivalent to saying a space in which the pressure is zero. 




Figs. 21 and 22. Bent tube and diaphragm of corrugated metal as used in two types of 
steam gauge. In the one class, the pressure of the steam acts upon diaphragms or plates 
of some^ kind, shown in fig. 21, which represents a section of a pair of metal plates, A A, 
of this kind. These are made with circular corrugations, a^ shown in section and also by the 
shading. The steam enters by the pipe c, and fills the chamber between the metal plates 
or diaphragms. The corrugations of the latter give them sufficient elasticity, so that when 
the pressure is exerted between them they will be pressed apart by the steam. If they were 
flat, it is plain that they would not yield, or only to a very slight degree, to the pressure of 
the steam. In the other class of gauge, the steam acts upon a bent metal tube of a flattened 
or_ elliptical section, such as shown in fig. 22. The pressure has a tendency to straighten 
this tube, and this straightening tendency is directly proportioned to the pressure; the free 
end of this tube is connected through suitable gearing to the pointer or hand. 



The word vacuum has come, by ill usage to mean any space in 
which the pressure is less than that of the atmosphere, and ac- 
cordingly, it is necessary to accept the latter definition. 




BASIC PRINCIPLES 



17 



This gives rise to two scales of pressure: 



1. Gauge pressure; 

2. Absolute pressure. 




Fig. 23. — Elementary boiler 
or closed vessel illustrating 
the difiference between 
gauge, and absolute pres- 
sure. 



When the hand of a steam gauge 
is at zero, the pressure actually 
existing is 14.73 lbs. (referred to a 
30 inch barometer) or that of the 
atmosphere. The scale in the gauge 
is not marked at this point 14.73 lbs. 
but zero because m the steam boiler 
as well as any other vessel under 
pressure, the important measure- 
ment is the difference of pressure 
between the inside and outside. 
This difference of pressure or eff ec - 
tive pressure for doing work is called 
the "gauge pressure" because it is 
measured by the gauge on the boiler. 
The second pressure scale is known 
as absolute pressure, because it gives 
the actual pressure above zero. In all 
calculations relative to the expansion 
of steam the absolute pressure scale 
must be used. 



Oues, How is gauge pres- 
sure expressed as absolute 



pressure r 



Ans. By adding 14.73, or for ordinary calculations, 14.7 lbs. ' 

Thus 80 lbs. gauge pressure = 80 + 14.7 =94.7 lbs. absolute pressure. 



Oues. How is absolute pressure expressed as gauge 
pressure. 

Ans. By subtracting 14.7. 



18 



BASIC PRINCIPLES 



INCHES 

OF 
MERCURY 
31- 

Z9SZ\* 
f 29 
28 
27- 
26- 
25 
24 
23 H 
22 
21 - 
20 
19- 
18 
17 
16- 
15 
14 
13 
12 
I I 
10 
9 
8 
7 
6 
5 



ABSOLUTE 
PRESSURE 
PER.SQ.IN. 

-15.226 

-^14.696 

•14 

13 

-12 

-II 

10 

9 

8 

7 

(o 

5 

4 

3 




Fig. 24. — Mercurial barom- 
eter illustrating the relation 
between "inches of mercury" 
and absolute pressure in 
lbs. per sq. in. 



Thus 90 lbs. absolute pressure = 90 — 14.7 
= 75.3 lbs. gauge pressure. 



Oues. How are pressures below 
that of the atmosphere usually 
expressed ? 

Ans. As pounds per square inch in 
making calculations, or the equivalent 
in ''inches of mercury" in practice. 

Thus, in the engine room, the expression 
"28 inch vacuum" would signify an absolute 
pressure in the condenser of .946 lb. per sq. in. 
absolute, that is to say, the mercury in a 
mercury column connected to a condenser 
having a 28 inch vacuum, would rise to a 
height of 28 inches, representing the difference 
between the pressure of the atmosphere and 
the pressure in the condenser, or 

14.73— .946 = 13.784 lbs. 
referred to a 30 inch barometer. 

Oues. What is the meaning of 
the term "referred to a 30 inch 
barometer?" 

Ans. It means that the variable 
pressure of the atmosphere is in value 
such that it will cause the mercury in 
the barometer to rise 30 inches. 

Oues. How is the pressure in 
pounds per square inch obtained 
from the barometer reading? 

Ans. Barometer reading in inches X 
.49 116 = pressure per sq . inch. 



BASIC PRINCIPLES 



19 



Thus, a 30 inch barometer reading signifies a pressure of 

.491 16 X30 = 14.74 lbs. per sq. in. 
The following table gives the pressure of the atmosphere in pounds per 
square inch for various readings of the barometer. 

Pressure of the atmosphere per square inch for various readings of 

the barometer: 

Rule. — Barometer in inches of mercury XA9116= lbs, per sq. i?i. 



Barometer 


Pressure 


Barometer 


Pressure 


(ins. of mercury) 


per sq. ins., lbs. 


(ins. of mercury) 


per sq. ins., lbs. 


28.00 


13.75 


29.921 


14.696 


28.25 


13.88 


30.00 


14.74 


28.50 


14.00 


30.25 


14.86 


28.75 


14.12 


30.50 


14.98 


29.00 


14.24 


30.75 


15.10 


29.25 


14.37 


31.00 


15.23 


29.50 


14.49 






29.75 


14.61 







The above table is based on the standard atmosphere, which by defin- 
ition =29.921 ins. of mercury = 14.696 lbs. per sq. in., that is 1 in. of 
mercury = 14.696-^29.921 = .49116 lbs. per ^q. in. 

Temperature Scales. — Temperature is a measure of sensible 
heat, that is, the temperature of a substance indicates how hot 
or cold it is. 



The instrument for measuring temperature is the well known ther- 
mometer. Briefly, it consists of a hollow stem of tube of glass with an 
enlargement or bulb at the foot filled with mercury which expands into 
the tube. ^ The stem being uniform in bore, and the apparent expansion of 
mercury in the tube being equal for equal increments of temperature, it 
follows that if the scale be graduated with equal intervals, these will indicate 
equal increments or "degrees" of temperature. 

There are three kinds of thermometer scales in general use: 

1. Fahrenheit; 

2. Centigrade; 
S. Reaumur. . 



20 



BASIC PRINCIPLES 



The relation between these scales is shown in figs. 25 to 27. 3 

The Fahrenheit scale is generally used in English speaking countries, : 
the freezing point is 32°, and boiling point, 212°. ^ 

The Centigrade scale is used in France. The freezing point is 0°, and " 
boiling point, 100°. j 

The Reaumur scale is used in Russia, Sweden, Turkey and Egypt. \ 
The freezing point is zero and boiling point 80°. ■ ; 

Fahrenheit is converted into Reaumur by deducting 32° and taking ; 
four-ninths of the remainder, and Reaumur into Fahrenheit by multi- : 
plying by nine-fourths, and adding 32° to the product. \ 



100 



75 

50 

25 




212 



167 
122 

77 

32 



80 



BOILING POINT 
~ OF WATER 



60 



40 



20 




FREEZING POINT 
OF WATER 



Figs. 25 to 27. — Various thermometer scales. Fig 25, Centigrade; fig. 26, Fahrenheit; fig. 
27, Reaumur. From the figure the scales may be clearly compared, and degr'^es converted 
from one scale to another without calculation. 



Centigrade temperatures are converted into Fahrenheit temperatures 
by multiplying the former by 9, dividing by 5, and adding 32° to the 
quotient; and conversely, Fahrenheit temperatures are converted into 
Centigrade by deducting 32° and taking 5-9ths of the remainder. 

R.eaumur degrees are multiplied by five-fourths to convert them into the 
equivalent Centigrade degrees; conversely, four-fifths of the number of 
Centigrade degrees give their equivalent in Reaumur degrees. 



I 



BASIC PRINCIPLES 



21 



Steam. — It has been stated that steam is the medium or 

working substance by which some of the heat energy, liberated 
from the fuel by combustion is transmitted to the engine and 
J}artly converted into mechanical work, 
' rv 

Owing to the peculiarities of steam, 

it is important that engine operators 

should know its exact nature 

^ ""^^--^.^^^ or behavior under different 

vD ^ " ^"^^"-^ conditions. 



AB5. 675" 493^^59.6^ Q^ 

Fig. 28. — -Graphical method of determining the absolute zero. It is found by experiment that 
when air is heated, or cooled under constant pressure, its volume increases or decreases in 
such a way that if the volume of the gas at freezing point of water be 1 cu. ft., then its volume 
when heated to the boiling point of water, will have expanded to 1.3654 cu. ft. Or, inversely, 
if the volume remain c'onstant, and the pressure exerted by the gas at freezing point = 1 
atmosphere, then the pressure at boiling point of water = 1.3654 atmospheres. These results 
may be set out in the form of a diagram, as here shown. In construction, draw a vertical 
line to represent temperatures to any scale, and mark on it points representing the freezing 
point and boiling point of water, marked 32° and 212° respectively. From 32° set out, at 
right angles to the line of temperature, a line of pressure AB = 1 atmosphere to any scale, 
and at 212° a line CD = 1.3654 atmospheres to the same scale. Join the extremities DB, 
of these lines to intersect the line of temperatures. It is assumed by physicists that, since 
the pressures vary regularly per degree of change of temperature between certain limits 
within the range of experiment, they vary also at the same rate beyond that range, and, 
therefore, that the point of intersection of the straight line DB, produced gives the point at 
which the pressure is reduced to zero, this point being known as the absolute zero. 



NOTE. — Absolute temperature. — This is defined as the actual temperature of anything 
reckoned from absolute zero. It is taken as the teniperature indicated by the thermometer or 
similar instrument, to which is added 273.1° centigrade or 459,6° Fahrenheit, the difference 
between absolute zero and the zeros of the respective thermo metric scales, which are arbi- 
trarily fixed. 

NOTE. — Absolute zero. — In physics, temperature or the heat which it represents is 
regarded as a manifestation of rnolecular activity in any substance, the higher the tempera- 
ture, the greater the motion or vibration among the molecules of which every solid, liquid or 
gaseous body is composed. Experiments have demonstrated that a gas expands when at the 

freezing point and under constant pressure about -„. of its volume for each increase of 1" 

Fahr. in pressure. This tends to show, that at some point about 491.6° — 32° or 459.6° below 
zero or Fahrenheit's scale, tfee volume of the gas would have become zero or it would have lost 
all the molecular vibration which manifests itself as heat. The temperature of this absolute 
zero point, from which all temperatures of gases are reckoned, is estimated at — 273.1° C. or 
-7-459.6° F. The lowest temperatures yet obtained by anyone are those at which hydrogen 
liquifies, — 423° F., and its freezing point, 430.6° F. 



22 



BASIC PRINCIPLES 



Oues. What is steam? 

Ans. Steam is the vapor of water. 

It is a colorless, expansive, invisible fluid. The white cloud seen issuing 
from an exhaust pipe, and usually called steam, is not steam but in reality 
a fog of minute liquid particles produced by condensation. 




X 



Fig. 29. — The various states of steam as exemplified in the operation of a safety valve. By 
closely observing a safety valve when blowing off, as for instance the safety valve on a loco- 
motive, or better the safety valve on a marine boiler, furnishing superheated steam, very 
interesting phenomena can be observed. At A, very close, the escaping gas is entirely 
invisible being at this point superheated. At B, the outline of the ascending column is seen, 
the interior being invisible and gradually becoming "foggy" and as the vapor ascends 
from B to D, denoting the gradual reduction in temperature, the steam becoming saturated 
and superheated or wet, reaching the white state at D, where it is popularly and erroneously 
known as "steam." Steam is invisible. The reason the so called wet steam can be seen is 
because wet steam is a mechanical mixture made up of saturated steam which is invisible, 
and which holds in suspension a multiplicity of fine water globules formed by condensation; 
it is the collection of water globules or condensate that is visible. 

Oues. How is steam classified according to its quality? 

Ans. As wet, dry^ saturated, superheated, or gaseous. 



BASIC PRINCIPLES 



23 




Fig. 30.* — The phenomena of vaporization. When heat is applied to water in a vessel as 
shown, it is conducted through the heating surface to the lower state which gradually be- 
comes heated to the boiling point. This is followed by the formation of globules of steam 
on the heating surface indicatmg that particles of the water have received a supply of heat 
equal to the sensible and latent heat of steam at the pressure existing at the bottom of the 
vessel, thus a change cf slate has taken place, and this may be called initial vaporization 
as distinguished from vaporization or the completion of the process. As more heat is added, 
more of the water adjacent to the globules is converted into steam which causes the globules 
to increase in size until their buoyancy becomes sufhcient to overcome the tension with the 
heating surface and imtial disengagement takes place. Following the course of a globule dis- 
engaging from the central and hottest portion of the heating surface, it rapidly rises to the 
surface, and expands as it rises because the pressure gradually decreases due to diminishing 
head of water. On reaching the disengaging surface, a bubble is formed which at once bursts 
as the water closes in behind the steam contained in the bubble, thus completing the process 
of vaporization of the original particles of water; that is to say, a change of state has taken 
place and the steam has been disengaged from the water. 

NOTE. — It should be noted in the above illustration that all of the steam globules formed 
on the heating surface do not reach the surface, as for instance, the globule A, found near the 
side of the vessel will, as it rises, take same course as Al, A2, A3, expanding as it rises. After 
passing the portion A3, it may be deflected over toward the side of the vessel into relatively 
■ cold water as indicated by the arrow, giving up its heat to the cold water, resulting in conden- 
sation and the gradual collapse of the globule as indicated. It should be noted further that 
the pressure at the bottom of the vessel or heating surface being greater than the pressure at 
the disengaging surface, the temperature at which initial vaporization takes place is greater 
than that of vaporization proper. 



24 



BASIC PRINCIPLES 



Wet steam contains intermingled moisture, mist or spray, and has th^ 
same temperature as dry saturated steam of the same pressure. \ 

Dry steam contains no moisture; it may be either saturated or super-^ 
heated. * r. 

Saturated steam is steam of a temperature due to its pressure. I 

^Superheated steam is steam having a temperature above that due to itsj 



pressure. 




|SJ STATE 



"i \ (ICE) 



VSOLID 

J 



-l. 



fusion; 



^IST CHANGE. 
, OF STATE. 



'''U 

~'^^-'^'. 






' ' i^ 



;^4^n'3'??5JArE 

GAS 

(STLAM) 





2':'? STATE 

VAPORIZATION — 



f-LIQUID 

(WATER) 




Fig. 31. — The three states: Solid, liquid and gas. The cake of ice represents a substance in ' 
the solid state. If the temperature of the surrounding air be above the freezing point' 
(32® Fahr.) the ice will gradually melt, that is to say, change its state from solid to liquid] 
this process being known as fusion. If sufficient heat be transferred to the liquid, it will: 
boil, that is to say, change Us state /row liquid to gas, this process being known as vapori- ; 
zation.^ Very interesting phenomena take place during these changes, which are ex- ^ 
plained in the accompanying text. J 



Oues. Under what conditions does steam exist? 

Ans. When there is the proper relation between the! 



*NOTE. — ^A term sometimes, though ill advisedly, used for highly superheated steam is^ 
gaseous steam or steam gas. The saving in the water consumption of a steam engine due to \ 
superheating the steam is a little over one per cent for each ten degrees of superheat. i 



BASIC PRINCIPLES 



25 



temperature of the water and the external pressure. For 
instance, for a given temperature of the water there is a certain 
external pressure above which steam will not form, 

Oues. How is steam produced? 

Ans. By heating water until it reaches the boiling point. 




Fig, 32. — The fusion of ice, illustrating the work done when the pound of ice at 32** Fahr. 
is melted or converted into water at the same temperature. The latent heat of fusion being 
143.57 heat units, and since one heat unit is equivalent to 778 ft. lbs. the work done during 
the fusion of one pound of ice is 778X143.57=111,698 ft. lbs. This is approximately 
equivalent to the work done when a hoisting engine hoists 2,000 lbs. a distance of 55.8 ft. 
as shown in the illustration. 



What an Engineer should know about Steam. — As has 

been stated, the medium which transmits heat energy to the 
engine to be transformed into mechanical work is a very re- 
markable substance; it disobeys the general law of expansion 
by heating, and, can exist in three different states, that is, as 

1. A solid (ice); 
^ 2. A liquid (water), or 

3. A gas (steam). 



26 



BASIC PRINCIPLES 



THE HEAT AND WORK REQUIRED 

TO MAKE STEAM 
Stage 1 Stage 2 Stage 3 Stage 4 





^-■ 
















Ui 








2 






X 

5 


o 






h 


o 














f. 


3 

o 


2 










2 


o 


or 


= 






c 




O 






o 










Q 


z 


o 




z 


z> 




r- 


3 


t- 






a 


< 


















> 


> 










z 






-1 


o 




o 


o 




lO 




> 


lnTF 


llli 


/ 


\ 


m- 


^li 




















5f age 5 



S cr «n 
o. «o -I 



EI 




s 



i 



5 ? a 



< 


Stag 


e(? 




I 


llllhlllll 




F'-'.; >:. "I 








> 

CO 


-v-:;.?£ 










o 


.■ -oi 










Ul 


■■■■■■■ -^^ 










a. \- 


< 










-^ 


■;■■"■/ -2 










o I* 


-.■ < 






H 


O o 








± 


J ^ 


w 




H UI 

1^2 








Si 




be 






r cv»: 






'^ z 


o 


■t- 




ifio 


tj Uj 


■■. • •: ■< 




T 


? 5 


... [2 






S2 


t> 3 








Q_: 














o o 












> > 

N 


i:! 












---1 











\^ 




tTN 


* 


T 


'""""^ 






t- 



Figs. 33 to 38. — From ice to 8tearn> illustrating the six stages in the making of steam trom ^ 
ice at 32° Fahr. i 



BASIC PRINCIPLES 



27 



depending upon conditions of pressure and temperature. These 
changes are shown in the accompanying series of diagrams, 
(figs. 33 to 38), which represent the several stages in transforming 
a pound of ice at 32° Fahr. into saturated steam at 212°, the 
temperature corresponding to atmospheric pressure. The 
engineer should make a careful study of these diagrams and the 
matter following to properly understand the nature of the medium 
he has to deal with in the operation of an engine. 



NJON-CONDUCTING VESSEL 



3 LBS OF WATER 



I LB. OF ICE 

AT 32" FAHR 

/ 





2 LBS. OF WATER 

AT 88° 

Figs. 39 to 41. — Experiment illustrating the latent heat of fusion. It requires *144 heat units 
to "melt" a pound of ice at 32° Fahr., that is, to convert it into water of the sarne temperature. 
Accordingly, if a pound of ice (fig. 39) be placed in a non-conducting vessel with two pounds 
of v/ater at 88" Fahr., it will be found that when all of the ice has been melted by the 
transfer of heat from the water to the ice the temperature of the mixture (fig. 41) of melted 
ice and the water will be the same as the original temperature of the ice, 32°. The reason for 
this is because the total heat above 32° in the water at 88° was the same as the latent 
heat of the ice, or 144 heat units, that is to say, the total heat above 32° in the water was 
(88 X 2) — 32 = 144 heat units. It should be understood that the term non-con- 
ducting vessel implies one in which allows no heat to pass through its sides. Such a vessel 
is not possible to construct, but by covering an ordinary vessel all over with a thick layer of 
asbestos very little heat will be lost. 



It will be noted from the diagrams that the stages into which 
the process of transforming ice into steam by heating are 

1. Fusion of the ice (at 32° F.); 

2. Contraction of the water (between 32° and 39.1°); 

3. Expansion of the water (between 39.1° and 212°); 

*N0TE. — According to the U. S. Bureau of Standards, 1915, the latent heat of fusion of 
ice is 143.57 B. t. u., however for ordinary calculations the value 144 is conveniently used. 



28 



BASIC PRINCIPLES 



4. Vaporization, or formation of steam at 212°. i 

During the process two changes of state have occurred: ' 

1. Solid to liquid (ice to water) at freezing point 32° Fahr. ;, 

2. Liquid to gas (water to steam) at boiling point 212° Fahr.^n 

To effect these two changes of state, a considerable amount of work is* 
done, especially in the case of the second change from liquid to gas, thev 
amounts required being i 




Figs. 42 to 44, — The bursting of pipes during freezing weather, illustrating the effect of pressure j 
upon the freezing point. In draining pipes exposed to prevent freezing, care should be taken ; 
to remove all the water out of any water pockets that may exist, such as shown in fig. 42. \ 
The bursting of a pipe due to water in a pocket is illustrated in figs. 43 and 44, whicTi show < 
fig. 42 in section. Assuming the pocket to be full of water in freezing weather, it sometimes \ 
happens that the water at A and B, will freeze before it does at C, thus forming two slugs of ] 
ice enclosing the water C. When C, freezes, there being no room for expansion, the pipe 
bursts as indicated at D. The popular impression that pipes will burst at or very little 
below 32° Fahr., is erroneous. In fact the enormous pressure required to burst so called ; 
wrought iron pipe is not generally known, nor the effect of the pressure on the freezing point, j 
For instance, the average bursting pressure of one-half inch standard pipe is 14,000 lbs., or \ 
911.5 atmospheres; per sq. in. and since the freezing point is lowered .0133° Fahr. for each > 
additional atmosphere, the freezing point required to burst one-half inch pipe is 32 — (911.5 X , 
.0133) =20'" Fahr.; that is to say, it would require a temperature of 20° to burst a one-half i 
inch pipe of average strength by freezing. ' 



1. To melt the ice 143.57 B. t. u. 

2. To change the water at 212° Fahr. into steam of the 

same temperature 970.4 B. t. u. 



BASIC PRINCIPLES 



29 



It will be noted from these two items that it takes over five times as 
much heat to evaporate water at 212° Fahr. into steam of the same tem- 
perature, as it does to heat the water from the freezing point to the boiling 
point. That is to raise the temperature of the water from the freezing 
point to the boiling point requires 212 — 32 = 180 B. t. u., and from item 2, 
which represents the latent heat of steam, 970.4 B. t. u. are required to evap- 
orate the water at 212° into steam of the same temperature. From which 

>0 / — A ^ 





Figs. 45 to 47. — Experiment illustrating the latent heat of steam or the considerable amount 
of heat which must be added to water at the boiling point to convert it into steam at the same 
temperature. In fig. 45, suppose the glass vessel to contain one pound of water at 32° Fahr., 
and heat be transferred to it, as indicated by the bunsen burner, at such rate that its 
temperature is raised to the boiling point 212° in five minutes. In this time the water has 
received 212 — 32 = 180 heat units. Now, if the heat supply be continued at the same rate, 
it will require (since the latent heat of steam at atmospheric pressure is 970.4 heat units) 
970.4 -J- 180 =5.39 times as long, or 5.39 X5 =26.95 minutes to convert the pound of water at 
212° (fig. 46) into steam at the same temperature as indicated by the empty beaker in fig. 
47. That is to say, it takes over five times as much heat to convert water at 212° into steam 
at the same temperature as it does to raise the same amount of water from the freezing point 
32° to 212°. This experiment can be easily performed with water at ordinary temperature 
say 60°. In this case, if it take five minutes to raise its temperature to 212°, it would require 
970.4^(212 — 60) =6.38 times as long or 6.38X5=31.9 minutes to evaporate the water 
at 212°.^ It is thus seen that the latent heat is the big item in steam making. In the well 
known "naphtha launch" and "alco-vapor launch," naphtha, and alcohol were used respectively 
in the boilers in the place of water because of the excessive latent heat of the latter. This 
with a given heating surface or weight (an important factor in marine construction) more 
power could be developed with the above mentioned liquids than with water, because of 
their relative low latent heat of evaporation. For instance, for alcohol the latent heat is 
364.3 heat units or only a little over one- third of that of water. Operators of alco-vapor 
launches who have tried using water in the boiler can appreciate the considerable difference 
in the results obtained. From experiments made by the Gas Engine and Power Co., builders 
of the naphtha launches, it was claimed that the power obtained on the brake was in the ratio 
of about 5 to 9 for steam and naphtha, that is, the same quantity of heat was turned into 
nearly twice as much work by the expansion of naphtha vapor as by the expansion of steam 
under the same conditions. Some of the results obtained during the tests were: 1, with 
steam, mean pressure 37.99 lbs., r.p.m., 312.6; 2, with naphtha, mean pressure 55.8, 
r.p.m.. 552.2. 



30 



BASIC PRINCIPLES 



it requires 970.4 -^ 180 = 5.39 times as much heat to evaporate the water 
as it does to heat the water between the Hmits given. This relation can be 
approximately determined by the interesting experiment shown in figs. 45 
to 47. The heat which must be supplied during the process of evaporation 
has been expended in two ways. 

1 . In overcoming the molecular resistance of the medium H2O in changing 
its state from a liquid to a gas; 

2. In making room for itself against the pressure of the atmosphere, that 
is, doing external work. These two amounts of heat are called respectively 

1. The internal latent heat; 

2. The external latent heaty 
^n both making up the latent heat of steam. 




Fig. 48. — ^The work done in the formation of steam from water at 32° P'ahr. , In converting 
one pound of water at 32° into steam at 212°, 180 heat units are required to raise the tem- 
perature of the water to 212°; 897.51 heat units are absorbed by the water at 212° before 
a change of state takes place, and 72.89 heat units are required for the work to be done on 
the atmosphere to make room for the steam. These three items are known respectively as : 

1, the sensible heat; 2, the internal latent heat, and 3, the external latent heat. The 
mechanical equivalent of one heat unit being 777.52 ft. lbs., the respective amounts of work 
corresponding to the sensible, internal, and external latent heats are 139,954 ft. lbs., . 
097,832 ft. lbs., and 56,674 ft. lbs. To grasp the significance of this, consider a locomotive 
boiler weighing, say 50,000 lbs. being lifted by a crane. The work done in lifting the boiler 
is equal to its weight in pounds multiplied by the distance raised in feet. Accordingly, for 
item 1, the work done is equivalent to raising the boiler 139,954 4-50,000 =2.8 ft.; for item 

2, equivalent to 697,832-7-50,000 = 13.96 ft., and for item 3, equivalent to 56,674-5-50,000 = 
1.13 ft. Also the total work done in changing a pound of water at 32° into steam at 212°, 
or the sum of the three items is equivalent to raising the boiler 2. 8 -f 1 3. 96 -f 1.03 =17.89 ft. 



BASIC PRINCIPLES 31 



The author does not agree with the generally accepted calculation for 
the external latent heat, or external work of vaporization and holds that 
it is wrong in principle. The common method of calculating this work is 
based on the assumption that the amount of atmosphere displaced per 
pound of steam, is equal to the volume of one pound of saturated steam 
at the pressure under which it is formed; it is just this point wherein the 
error lies, as will now be shown. The volume of one pound of water at 
212° atmospheric pressure, is 28.88 cu. ins. Now, if this water be placed 
in a long cylinder, having a cross sectional area of 144 sq. ins. it will occupy 
a depth of .0167 ft. 

If a piston (assumed to have no weight and to move without friction) be 
placed on top of the water as in stage 4 (fig. 36), and heat applied, vapor- 
ization will begin, and when all the water has been changed into saturated 
steam, the volume has increased to 26.79 cu. ft., as in stage 6, (fig. 38), that 
is, the volume of one pound of saturated steam at atmospheric pressure is 
26.79 cu. ft. 

Since the area of the piston is 1 sq. ft., the linear distance from the 
bottom of the cylinder to the piston is 26.79 ft., but the piston has not 
moved this distance. The initial position of the piston being .0167 ft. 
above the bottom of the cylinder, its actual movement is 
26.79 — .0167=26.7733 ft. 

Accordingly, the work done by the steam in moving the piston against 
the pressure of the atmosphere to make room for itself or 

external work — area piston X pressure of atmosphere X movement of piston 
= 144 sq. ins. X 14.7 lbs. per sq. ins. X 26.7733 ft. 

= 56,673.72 ft. lbs. 
The erroneous method of making this calculation is to consider the 
movement of the piston equal to the distance between the bottom of the 
cylinder and the piston, or 26.79 ft., which would give for the external 
Work 

144X14.7X26.79 =56,709.07 ft. lbs. 

being in excess of the true amount by 

56,709.07 — 56,673.72 = 35.35 ft. lbs. 
or 

.0167 ft. X 144 sq. ins. X 14.7 = 35.35 ft. lbs. 

Motion is purely a relative matter, and accordingly something must 
be regarded as being stationary as a basis for defining motion; hence the 
question : 

75 the movement of the piston in stage 6 (fig. 38) to he referred to a station- 
ary water level or to a receding water level? 

The author holds that the movement of the piston referred to a stationary 
water level gives the true displacement of the air and is accordingly the 
proper basis for calculating the external work. It must be evident that 
since the water already existed at the beginning of vaporization, the 
atmosphere was already displaced to the extent of the volume occupied 



32 



BASIC PRINCIPLES 



S Of: 






g §• c 



S« c Q °* 



Co 



«5, 



^"F 



^ 15! 



■ (^ X 



is ^S. 



12 t -5 § -^ 



1 ?s 



CO (N«^ 









e 

tg 



^ 



BASIC PRINCIPLES 



33 



by the water, and therefore this displacement must not be considered as 
contributing to the external work done by the steam during its formation. 
The amount of error (35.35 ft. lbs.) of the common calculation, though very 
small, is an appreciable amount; its equivalent in heat units is 

35.35 -^ 777.52 = .0455 B. t. u. 



The thermal equivalent of the external work is 

56,673.72-^777.52=72.89 B. t. u. 



GAUGE 
PRESSURE 




Condensation of 
Steam, —r When the 
temperature of steam 
becomes less than that 
corresponding to its 
pressure y condensa- 
tion takes place, that 
is, it ceases to exist as 
steam and becomes 
water. 



Fig. 49. — The generation of steam at pressures above the atmosphere. If a ring B, be riveted 
in a cyUnder to limit the movement of a piston resting, at the beginning of the experiment, on 
top of a small quantity of water (as indicated by dotted lines A, and heat be applied, the 
piston (assumed to have no weight) will rise as steam is formed at atmospheric pressure until 
it comes in contact with the ring B, Additional heat will cause the pressure of the steam 
to increase in a definite rate corresponding to the temperature until all the water is evaporated, 
the cylinder being now filled with saturated steam. The pressure of this saturated steam will 
depend on the relation between its volume and the volume of the water from which it was 
generated. If more heat be now added, the temperature of the steam will increase above 
that due to its pressure, and the steam becomes superheated. Removing the heat supply, 
the temperature of the gas will gradually diminish, and it loses its superheat and returns to 
the saturated condition, at which point condensation begins, the pressure and temperature 
during these changes gradually falling. Condensation continuing until all the steam has 
condensed, the piston returning to its initial position A. If* during the cooling process, the 
piston be fastened at the ring B, the pressure of the steam will become less than the atmos- 
pheric pressure outside when the temperature falls below 212* Fahr., forming a so called 
vacuum. The degree of vaauum now increases, or in other words, the pressure under the 
cylinder or absolute pressure becomes less and less until, when all the steam is condensed, 
it becomes approximately zero, or 14.72 lbs. lower than the pressure of the atmosphere or 
gauge pressure, (assuming the barometer reads 30 inches). The pressure remains a little 
above zero because of the small percentage of air originally contained in the water, which 
does not recombine with it when the steam condenses, that is, a perfect vacuum is not formed 
because of this air, necessitating, in the case of condensing engines, an air or so called vacuum 
pump. 



34 



BASIC PRINCIPLES 



Thus in fig. 50, if cold water be poured on the inverted flask, containing 
steam and water, the steam will be cooled below its temperature correspond- 
ing to its pressure (as given in the steam table) and some of it will condense. 
This will cause a reduction of pressure because the volume of steam is 
greatly diminished after condensation.* On account of the reduction in 
pressure, the water will again boil vigorously until enough steam has been 
formed to increase the pressure to correspond with the boiling point. 



COOLING 
WATER 




VACUUM &>\U6E: 



Fig. 50. — Lowering the boiling point by diminishing the pressure. Fill a round bottomed flask 
with water and boil. After it has boiled some time, until the air has been drawn out of the 
flask by the steam, insert a rubber stopper, having fitted to it a connection leading to a 
vacuum gauge and invert the flask as shown. The vacuum gauge will now read zero. Now, 
ii some cold water be poured over the flask, the temperature will fall rapidly and some of the 
steam will condense, thus lowering the pressure within the flask, that is, the vacuum gauge 
will read 5 or 10 inches indicating a vacuum. The reduced pressure disturbs the equilibrium 
between pressure and temperature and the water will boil until equilibrium is again restored. 
The operation may be repeated several times without reheating, the pressure gradually 
falling each time. At the city of Quito, Ecuador, water boils at 194° Fahr., and on the top 
of Mt. Blanc at 183°. Again, in a steam boiler in which the pressure is 200 lbs., the boiling 
point is 387.7°. 



*NOTE.— It should be remembered that 1 cu. ft. of steam at atmospheric pressure is 
reduced in volume after condensation to approximately 1 cu. in. 



BASIC PRINCIPLES 35 

A second application of cold water will again cause the water to boil, 
pthe result being the same so long as the water in the flask is at a higher 
temperature than the water applied outside. 

The greater the difference in temperature, the more vigorous will the 
water boil. This illustrates an important effect in the behavior of steam 
in a steam engine, namely, re-evaporation which will be later explained. 

Ones. If a closed flask containing steam and water be 
allowed to stand for a length of time, what happens? 

Ans. The atmosphere being at a lower temperature than 
that inside the flask, will abstract heat from the steam and water, 
but the heat will leave the steam quicker than the water. The result 
is a continuous condensation of the steam and re-evaporation 
of the water, during which process the temperature of the whole 
mass and the boiling point is gradually lowered until the tem- 
perature inside of the flask is the same as that outside. This 
process is accompanied by a gradual decrease in pressure. 

Oues. Why does the pressure fall? 

Ans. Because the temperature falls. 

There is a fixed pressure for each degree of temperature of the water 
as tabulated in the steam tables. 

Oues. Can this pressure be reduced to zero by reducing 
the temperature of the water? 

Ans. It could, if the mass could be cooled to 459.4° below 
zero Fahr.*, but at ordinary temperatures the pressure could 
not be reduced to zero. Water contains a small amount of air 
which it gives up when evaporated; this of itself would prevent 
the pressure falling to zero, if all the steam were condensed. 
If the contents of the flask be cooled to 80° there would be 
inside the flask a pressure of one-half pound per square inch, 

*NOTE. — 459.6° below zero Fahr., as previously explained, is a point called the absolute 
zero. A perfect gas contracts in volume a definite amount for each degree in temperature it 
is cooled. The absolute zero then is the point to which a perfect gas must be cooled to reduce 
its volume to nothing. 



36 



BASIC PRINCIPLES 



if the water be cooled to 32°, the pressure would be .089 pounds, j 
There is then always some pressure inside the flask, the intensity ; 
of which depends upon the temperature of the water. j 

Oues. How was this principle first made use of? 

Ans. The early engineers discovered that by condensation; 
the pressure of the atmosphere is made available for doing work. ; 

Fig. 51. — Newcomen's atmospheric 
engine. The parts are: A, 

furnace; B, boiler; C, valve; D, ' 
cylinder; E, piston; F, piston rod; ' 
G, walking beam; H, pump rod; 
J, pump cylinder; K, pump; 
barrel; L, injection water pump; : 
M, injection water pipe; N, ' 
injection valve; O, water supply 
cock to seal piston; P, air check 
or snifting valve; Q, injection 
water discharge pipe; R, hot 
well. In Newcomen's engine, the '• 
piston was attached by rod and i 
chain to one end of the walking- ' 
beam, and the pump rod to the 1 
other end. The pump rod was \ 
heavy enough to sink it in the j 
barrel and raise the steam piston, ] 
or else a weight was added. The I 
periphery of the piston was | 
covered with leather and kept i 
air tight by water above it, ad- ' 
mitted through cock O. The ! 
cylinder D, was placed above the ! 
boiler B, and steam was admitted [ 
to it through the cock C, which ' 
was tended by hand, the strokes i 
being slow. At starting, the air from the cylinder, displaced by the steam, passed out through ■ 
the pipe which proceeds from the bottom of the cylinder, and issued at the valve P, which | 
opened upwardly. This is the blow valve or snifting valve of the engine. The cock C, being then 
closed, shuts off the steam, and the cock N, being opened, allows injection water to enter the ' 
cylinder from injection pump K, through pipe M. The water, being condensed into about | 
Vi728 of its bulk, formed a nearly perfect vacuum, and the atmospheric pressure of 14.7 i 
pounds to the square inch bearing upon the piston depressed the latter, and consequently j 
raised the pump rod, the weight (if there be any), and the load of water. The downward ■ 
stroke only of the piston was used effectively. The water of injection and condensation i 
passed by the pipe Q, leading from the bottom of the cylinder to the hot well R, issuing through ) 
a check valve, and was used to feed the boiler. It wiK be observed that the piston and \ 
pump rod are merely suspended by chains; the action of each is to pull, not push, and a ' 
stiff connection was not necessary. At first Newcomen adopted Savery's plan of external I 
condensation, but a faulty cylinder having admitted water internally, the condensation i 
was more rapid with increased effect from the engine. i 




NOTE. — The taps which answered as valves in the Newcomen engine required the most 
unremitting attention of the person in charge, to introduce steam into the cylinder to lift the 
piston, or the shower of cold wa.ter which was to condense the steam and cause the depression 
of the piston by the atmospheric pressure above it. A. Cornish boy, named Potter, in order 
to have some time for play conceived and put in execution the idea of connecting the beam to 
the handle of the taps, so as to work them automatically. ^ Hence the valve motion. For the 
first time, the engine worked by itself. With the exception of Smeaton's improvements in 
details, the Newcornen engine remained in the state to which its inventor had brought it, from 
1710 to 1764, about which time Watt appeared. 




BASIC PRINCIPLES 



37 



Ones. What is the chief objection to this engine? \ 

Ans. It was discovered by James Watt in 1763 that there | 

was a large waste of steam in the cylinder owing to condensation \ 

of the steam through contact with the cold wet cylinder walls. | 

Ones. How did Watt overcome this defect? 



CIRCULATING 
WATER 



-^"4 5TE.A»^ 




WE.LL 



Fig. 52. — The condensation of steam. If water be boiled in a flask A, and the steam thus 
produced led off through pipe C, having a coiled section surrounded by cold water, it will 
here be cooled below the boiling point and will therefore condense, the condensate passing 
out into the receptacle B, as water. The cooling or "circulating" water enters the condenser 
at the lowest point D, and leaving at the highest point E. 



Ans. He invented a separate chamber in which the con- 
densation took place. The steam was passed from the cylinder 
into this chamber, called the condenser where it was condensed 
by contact with cold water without the need of cooling the 
cylinder itself. 



38 BASIC PRINCIPLES 



The elementary condenser shown in fig. 52 illustrates the method of 
condensing steam after it leaves the engine cylinder by bringing it in 
contact with a cold metallic surface. Such method is called surface con- 
densation, and the apparatus, a surface condenser. 

In the figure, the flask A, placed over a Bunsen burner, is fitted with a 
rubber cork and tube C, part of which is coiled and surrounded by flowing 
cold water. A glass vessel or beaker B, is placed under the end of the coil 
as shown. 

When water is boiled in A, the steam thus formed will pass off through C, 
and in traversing the coiled part it is cooled below the temperature cor- 
responding to its pressure and condenses. The water thus formed or con- 
densate passes in drops from the end of the tube C, into the vessel B. When 
all the water has been evaporated from A, it will be found that the same 
weight of water originally placed in A, has been deposited in B. 

The condensation of steam may also be illustrated by fig. 49, assuming 
the supply of heat to be removed. 

If the piston be pushed downward, the tendency will be to increase both 
the pressure and temperature of the steam. However, if there be any 
increase in the temperature of the steam it is immediately cooled by the 
water which causes condensation and keeps the pressure constant. In 
fact all the steam could be condensed by pushing the piston downward 
until it rested on the surface of the water. 

If the piston be now returned to its original position, steam will im- 
mediately form and fill the space, the pressure remaining constant. The 
reason for this is that unless the empty space formed by the receding piston 
be immediately filled, the pressure will fall, thus exposing the water which 
is at 212° to a pressure lower than the boiling point. Under these con- 
ditions the water boils until the empty space is filled with steam of a 
density corresponding to the boiHng point, thus preserving a constant 
pressure. 

How to Use the Steam Table. — The various properties of 
saturated steam are usually presented in tabulated form for 
convenience in making calculations. The values of the properties 
of steam here given are condensed from Marks and Davis steam 
tables which are now (1917) generally accepted as the standard, 
and are the most accurate that have yet been published. 

In the first column is given the gauge pressure, and in the second, the 
absolute pressure. The second column, then, is made up by adding 14.7 
lbs. to the pressures given in the first column. Before using a steam table, 
the difference between gauge and absolute pressure should be thoroughly 
understood. 



BASIC PRINCIPLES 39 



The third column gives the temperature in degrees Fahrenheit, beginning 
with the freezing point 32°, which for convenience is taken as the temperature 
of no heat. 

Column four gives the total heat above 32° in each pound of water at 
the different pressures ; similarly in column five is given the total heat above 
32° for each pound weight of steam. 

The latent heat in the next column is clearly the difference between 
the heat in the steam and the heat in the water, or column 5-^column 4. 

The relative volume of the steam is given in column seven ; for instance, 
one cubic foot of water at 212° will occupy 26.79 cu. ft. when evaporated 
into steam at the same temperature. 

Column eight gives the weight per cu. ft., and the last two columns the 
entropy values. 

The following examples illustrate how to use the steam table: 

Example. — How many heat units are saved in heating 25 lbs. of feed 
water from 90 to 202°? 

In column 4, total heat in the water at 201.96° = 169.9 
In column 4, total heat in the water at 90° = 58.0 
Heat units saved per lb. of feed water =111.9 

Total heat units saved = 111.9X25 =2,797.5 

Example. — What is the weight of 20 cu. ft. of steam at 150 lbs. absolute 
pressure? 

The weight of 1 cu. ft. steam at 150 lbs. abs. is given in column 9 at 
.332 1b. Twenty cu. ft. then will weigh: .332X20 = 6.64 lbs. 

Example. — How much more heat is required to generate 26 lbs. of steam 
at 150 lbs. abs., than at 90 lbs. abs. 

In column 5 total heat in steam at 150 lbs. abs. =1,193.4 
In column 5 total heat in steam at 90 lbs. abs. = 1,184.4 
Excess heat required per pound (weight) = ,9 B. t. u. 

Total for 26 lbs. =9X26=23.4 B. t. u. 

Example. — How much heat is absorbed by the cooling water, if a con- 
densing engine exhaust 17 lbs. of steam per hour at a terminal pressure 
of 18 lbs. absolute into a 28 inch vacuum. 

In column 5, total heat in the steam at 18 lbs. abs. = 1,154.20 
In column 4, total heat in the water with 28" vacuum = 67.97 
Heat to be absorbed per lb. of steam . ....... =1,086.23 

Total heat absorbed by the cooling water per hour 



1,086.23X17 = 18,465.9 B. t. u. 



40 



BASIC PRINCIPLES 



Properties of Saturated Steam 

Condensed from Marks and Davis' Steam Tables and Diagrams, 1909, 
permission of the publishers, Longmans, Green & Co. 



*o 


< 


as a 


Total Heat 
above 32° F 


"1 

IT 
3« 


.9 
^ 1 

> 


if 

Sea 


O 
|l 


i 




11 


If 


> 
1^ 


29.74 


0.0886 


32 


0.00 


1073.4 


1073.4 


3294 


0.000304 


0.0000 


2.1832 


29.67 


0.1217 


40 


8.05 


1076.9 


1068.9 


2438 


0.000410 


0.0162 


2.1394 


29.56 


0.1780 


50 


18.08 


1081.4 


1063.3 


1702 


0.000587 


0.0361 


2.0865 


29.40 


0.2562 


60 


28.08 


1085.9 


1057.8 


1208 


0.000828 


0.0555 


2.0358 


29.18 


0.3626 


70 


38.06 


1090.3 


1052.3 


871 


0.001148 


0.0745 


1.9868 


28.89 


0.505 


80 


48.03 


1094.8 


1046.7 


636.8 


0.001570 


0.0932 


1.9398 


28.50 


0.696 


90 


58.00 


1099.2 


1041.2 


469.3 


0.002131 


0.1114 


1.8944 


28.00 


0.946 


100 


67.97 


1103.6 


1035.6 


350.8 


0.002851 


0.1295 


1.8505 


27.88 


1 


101.83 


69.8 


1104.4 


1034.6 


333.0 


0.00300 


0.1327 


1.8427 


25.85 


2 


126.15 


94.0 


1115.0 


1021.0 


173.5 


0.00576 


0.1749 


1.7431 


23.81 


3 


141.52 


109.4 


1121.6 


1012.3 


118.5 


0.00845 


0.2008 


1.6840. 


21.78 


4 


153.01 


120.9 


1126.5 


1005.7 


90.5 


0.01107 


0.2198 


1.6416 


19.74 


5 


162.28 


130.1 


1130.5 


1000.3 


73.33 


0.01364 


0.2348 


1.6084 


17.70 


6 


170.06 


137.9 


1133.7 


995.8 


61.89 


0.01616 


0.2471 


1.5814 


15.67 


7 


176.85 


144.7 


1136.5 


991.8 


53.56 


0.01867 


0.2579 


1.5582 


13.63 


8 


182.86 


150.8 


1139.0 


988.2 


47.27 


0.02115 


0.2673 


1.5380 


11.60 


9 


188.27 


156.2 


1141.1 


985.0 


42.36 


0.02361 


0.2756 


1.5202 


9.56 


10 


193.22 


161.1 


1143.1 


982.0 


38.38 


0.02606 


0.2832 


1.5042 


7.52 


11 


197.75 


165.7 


1144.9 


979.2 


35.10 


0.02849 


0.2902 


1.4895 


5.49 


12 


201.96 


169.9 


1146.5 


976.6 


32.36 


0.03090 


0.2967 


1.4760 


3.45 


13 


205.87 


173.8 


1148.0 


974.2 


30.03 


0.03330 


0.3025 


1.4639 


1.42 

lbs. 

gauge 


14 


209.55 


177.5 


1149.4 


971.9 


28.02 


0.03569 


0:3081 


1.4523 


14.70 


212 


180.0 


1150.4 


970.4 


26.79 


0.03732 


0.3118 


1.4447 


0.3 


15 


213.0 


181.0 


1150.7 


969.7 


26.27 


0.03806 


0.3133 


1.4416 


1.3 


16 


216.3 


184.4 


1152.0 


967.6 


24.79 


0.04042 


0.3183 


1.4311 


2.3 


17 


219.4 


187.5 


1153.1 


965.6 


23.38 


0.04277 


0.3229 


1.4215 


3.3 


18 


222.4 


190.5 


1154.2 


963.7 


22.16 


0.04512 


0.3273 


1.4127 


4.3 


19 


225.2 


193.4 


1155.2 


961.8 


21.07 


0.04746 


0.3315 


1.4045 


5.3 


20 


228.0 


196.1 


1156.2 


960.0 


20.08 


0.04980 


0.3355 


1.3965 


6.3 


21 


230.6 


198.8 


1157.1 


958.3 


19.18 


0.05213 


0.3393 


1.3887 


7.3 


22 


233.1 


201.3 


1158.0 


956.7 


18.37 


0.05445 


0.3430 


1.3811 


8.3 


23 


235.5 


203.8 


1158.8 


955.1 


17.62 


0.05676 


0.3465 


1.3739 


9.3 


24 


237.8 


206.1 


1159.6 


953.5 


16.93 


0.05907 


0.3499 


1.3670 


10.3 


25 


240.1 


208.4 


1160.4 


952.0 


16.30 


0.0614 


0.3532 


1.3604 


11.3 


26 


242.2 


210.6 


1161.2 


950.6 


15.72 


0.0636 


0.3564 


1.3542 


12.3 


27 


244.4 


212.7 


1161.9 


949.2 


15.18 


0.0659 


0.3594 


1.3483 




BASIC PRINCIPLES 



41 



Properties of Saturated Steam — Continued 



i 




g_d 




iSg- 


©.-fe 


si 


1^ 


< ■ 


H 



Total Heat 
above 32° F 






II -s 



^ 



E -a 



T-l-O 






28 


246.4 


29 


248.4 


30 


250.3 


31 


252.2 


32 


254.1 


33 


255.8 


34 


257.6 


35 


259.3 


36 


261.0 


37 


262.6 


38 


264.2 


39 


265.8 


40 


267.3 


41 


268.7 


42 


270.2 


43 


271.7 


44 


273.1 


45 


274.5 


46 


275.8 


47 


277.2 


48 


278.5 


49 


279.8 


50 


281.0 


51 


282.3 


52 


283.5 


53 


284.7 


54 


285.9 


55 


287.1 


56 


288.2 


57 


289.4 


58 


290.5 


59 


291.6 


60 


292.7 


61 


293.8 


62 


294.9 


63 


295.9 


64 


297.0 


65 


298.0 


66 


299.0 


67 


300.0 



214.8 
216.8 
218.8 
220.7 
222.6 
224.4 
226.2 
227.9 
229.6 
231.3 
232.9 
234.5 
236.1 
237.6 
239.1 
240.5 
242.0 
243.4 
244.8 
246.1 
247.5 
248.8 
250.1 
251.4 
252.6 
253.9 
255.1 
256.3 
257.5 
258.7 
259.8 
261.0 
262.1 
263.2 
264.3 
265.4 
266.4 
267.5 
268.5 
269.6 



1162.6 
1163.2 
1163.9 
1164.0 
1165.1 
1165.7 
1166.3 
1166.8 
1167.3 
1167.8 
1168.4 
1168.9 
1169.4 
1169.8 
1170.3 
1170.7 
1171.2 
1171.6 
1172.0 
1172.4 
1172.8 
1173.2 
1173.6 
1174.0 
1174.3 
1174.7 
1175.0 
1175.4 
1175.7 
1176.0 
1176.4 
1176.7 
1177.0 
1177.3 
1177.6 
1177.9 
1178.2 
1178.5 
1178.8 
1179.0 



947.8 
946.4 
945.1 
943.8 
942.5 
941.3 
940.1 
938.9 
937.7 
936.6 



935 

934 

933 

932 

931 

930 

929 

928 

927.2 

926.3 

925.3 

924.4 

923.5 

922.6 

921.7 

920.8 

919.9 

919.0 

918.2 

917.4 

916.5 

915.7 

914.9 

914.1 

913.3 

912.5 

911.8 

911.0 

910.2 

909.5 



14.67 

14.19 

13.74 

13.32 

12.93 

12.57 

12.22 

11.89 

11.58 

11.29 

11.01 

10.74 

10.49 

10.25 

10.02 

9.80 

9.59 

9.39 

9.20 

9.02 

8.84 

8.67 

8.51 

8.35 

8.20 

8.05 

7.91 

7.78 

7.65 

7.52 

7.40 

7.28 

7.17 

7.06 

6.95 

6.85 

6.75 

6.65 

6.56 

6.47 



0.0682 
0.0705 
0.0728 
0.0751 
0.0773 
0.0795 
0.0818 
0.0841 
0.0863 
0.0886 
0.0908 
0.0931 
0.0953 
0.0976 
0.0998 
0.1020 
0.1043 
0.1065 
0.1087 
0.1109 
0.1131 
0.1153 
0.1175 
0.1197 
0.1219 
0.1241 
0.1263 
0.1285 
0.1307 
0.1329 
0.1350 
0.1372 
0.1394 
0.1416 
0.1438 
0.1460 
0.1482 
0.1503 
0.1525 
0.1547 



0.3623 
0.3652 
0.3680 
0.3707 
0.3733 
0.3759 
0.3784 
0.3808 
0.3832 
0.3855 
0.3877 
0.3899 
0.3920 
0.3941 
0.3962 
0.3982 
0.4002 
0.4021 
0.4040 
0.4059 
0.4077 
0.4095 
0.4113 
0.4130 
0.4147 
0.4164 
0.4180 
0.4196 
0.4212 
0.4227 
0.4242 
0.4257 
0.4272 
0.4287 
0.4302 
0.4316 
0.4330 
0.4344 
0.4358 
0.4371 



^ASIC PRINCIPLES 





Properties of 


Saturated Steam — Continued 






^.2 




Total Heat 
above 32° F 


«l 

IS 

1^ 


.2 

£8 


S 


^ 


1 


is 


< 




1 -2 

ri 


1 •§ 
S 1 


4 

> 


fa- 

r 


o 

II 


|1 


53.3 


68 


301.0 


270.6 


1179.3 


908.7 


6.38 


0.1569 


0.4385 


1.1946 


54.3 


69 


302.0 


271.6 


1179.6 


908.0 


6.29 


0.1590 


0.4398 


1.1921 


55.3 


70 


302.9 


272.6 


1179.8 


907.2 


6.20 


0.1612 


0.4411 


1.1896 


56.3 


71 


303.9 


273.6 


1180.1 


906.5 


6.12 


0.1634 


0.4424 


1.1872 


57.3 


72 


304.8 


274.5 


1180.4 


905.8 


6.04 


0.1656 


0.4437 


1.1848 


58.3 


73 


305.8 


275.5 


1180.6 


905.1 


5.96 


0.1678 


0.4449 


1.1825 


59.3 . 


74 


306.7 


276.5 


1180.9 


904.4 


5.89 


0.1699 


0.4462 


1.1801 


60.3 


75 


307.6 


277.4 


1181.1 


903.7 


5.81 


0.1721 


0.4474 


1.1778 


61.3 


76 


308.5 


278.3 


1181.4 


903.0 


5.74 


0.1743 


0.4487 


1.1755 


62.3 


77 


309.4 


279.3 


1181.6 


902.3 


5.67 


0.1764 


0.4499 


1.1732 


63.3 


78 


310.3 


280.2 


1181.8 


901.7 


5.60 


0.1786 


0.4511 


1.1710 


64.3 


79 


311.2 


281.1 


1182.1 


901.0 


5.54 


0.1808 


0.4523 


1.1687 


65.3 


80 


312.0 


282.0 


1182.3 


900.3 


5.47 


0.1829 


0.4535 


1.1665 


66.3 


81 


312.9 


282.9 


1182.5 


899.7 


5.41 


0.1851 


0.4546 


1.1644 


67.3 


82 


313.8 


283.8 


1182.8 


899.0 


5.34 


0.1873 


0.4557 


1.1623 


68.3 


83 


314.6 


284.6 


1183.0 


898.4 


5.28 


0.1894 


0.4568 


1.1602 


69.3 


84 


315.4 


285.5 


1183.2 


897.7 


5.22 


0.1915 


0.4579 


1.1581 


70.3 


85 


316.3 


286.3 


1183.4 


897.1 


5.16 


0.1937 


0.4590 


1.1561 


71.3 


86 


317.1 


287.2 


1183.6 


896.4 


5.10 


0.1959 


0.4601 


1.1540 


72.3 


87 


317.9 


288.0 


1183.8 


895.8 


5.05 


0.1980 


0.4612 


1.1520 


73.3 


88 


318.7 


288.9 


1184.0 


895.2 


5.00 


0.2001 


0.4623 


1.1500 


74.3 


89 


319.5 


289.7 


1184.2 


894.6 


4.94 


0.2023 


0.4633 


1.1481 


75.3 


90 


320.3 


290.5 


1184.4 


893.9 


4.89 


0.2044 


0.4644 


1.1461 


76.3 


91 


321.1 


291.3 


1184.6 


893.3 


4.84 


0.2065 


0.4654 


1.1442 


77.3 


92 


321.8 


292.1 


1184.8 


892.7 


4.79 


0.2087 


0.4664 


1.1423 


78.3 


93 


322.6 


292.9 


1185.0 


892.1 


4.74 


0.2109 


0.4674 


1.1404 


79.3 


94 


323.4 


293.7 


1185.2 


891.5 


4.69 


0.2130 


0.4684 


1.1385 


80.3 


95 


324.1 


294.5 


1185.4 


890.9 


4.65 


0.2151 


0.4694 


1.1367 


81.3 


96 


324.9 


295.3 


1185.6 


890.3 


4.60 


0.2172 


0.4704 


1.1348 


82.3 


97 


325.6 


296.1 


1185.8 


889.7 


4.56 


0.2193 


0.4714 


1.1330 


83.3 


98 


326.4 


296.8 


1186.0 


889.2 


4.51 


0.2215 


0.4724 


1.1312 


84.3 


99 


327.1 


297.6 


1186.2 


888.6 


4.47 


0.2237 


0.4733 


1.1295 


85.3 


100 


327.8 


298.3 


1186.3 


888.0 


4.429 


0.2258 


0.4743 


1.1277 


87.3 


102 


329.3 


299.8 


1186.7 


886.9 


4.347 


0.2300 


0.4762 


1.1242 


89.3 


104 


330.7 


301.3 


1187.0 


885.8 


4.268 


0.2343 


0.4780 


1.1208 


91.3 


106 


332.0 


302.7 


1187.4 


884.7 


4.192 


0.2336 


0.4798 


1.1174 


93.3 


108 


333.4 


304.1 


1187.7 


883.6 


4.118 


0.2429 


0.4816 


1.1141 


95.3 


110 


334.8 


305.5 


1188.0 


882.5 


4.047 


0.2472 


0.4834 


1.1108 


97.3 


112 


336.1 


306.9 


1188.4 


881.4 


3.978 


0.2514 


0.4852 


1.1076 


99.3 


114 


337.4 


308.3 


1188.7 


880.4 


3.912 


0.2556 


0.4869 


1.1045 



BASIC PRINCIPLES 



Properties of Saturated Steam — Continued 





si 


if 
II 

1- 


Total Heat 
above 32 °F 




^1 
1 

> 


. 

if 


2 

II 


5 


If 
11 


1 ^ 


1 ^ 

5 i 


•s 

1^ 


101.3 


116 


338.7 


309.6 


1189.0 


879.3 


3.848 


0.2599 


0.4886 


1.1014 


103.3 


118 


340.0 


311.0 


1189.3 


878.3 


3.786 


0.2641 


0.4903 


1.0984 


105.3 


120 


341.3 


312.3 


1189.6 


877.2 


3.726 


0.2683 


0.4919 


1.0954 


107.3 


122 


342.5 


313.6 


1189.8 


876.2 


3.668 


0.2726 


0.4935 


1.0924 


109.3 


124 


343.8 


314.9 


1190.1 


875.2 


3.611 


0.2769 


0.4951 


1.0895 


111.3 


126 


345.0 


316.2 


1190.4 


874.2 


3.556 


0.2812 


0.4967 


1.0865 


113.3 


128 


346.2 


317.4 


1190.7 


873.3 


3.504 


0.2854 


0.4982 


1.0837 


115.3 


130 


347.4 


318.6 


1191.0 


872.3 


3.452 


0.2897 


0.4998 


1.0809 


117.3 


132 


348.5 


319.9 


1191.2 


871.3 


3.402 


0.2939 


0.5013 


1.0782 


119.3 


134 


349.7 


321.1 


1191.3 


870.4 


3.354 


0.2981 


0.5028 


1.0755 


121.3 


136 


350.8 


322.3 


1191.7 


869.4 


3.308 


0.3023 


0.5043 


1.0728 


123.3 


138 


352.0 


323.4 


1192.6 


868.5 


3.263 


0.3065 


0.5057 


1.0702 


125:3 


140 


353.1 


324.6 


1192.2 


867.6 


3.219 


0.3107 


0.5072 


1.0675 


127.3 


142 


354.2 


325.8 


1192.5 


866.7 


3.175 


o.3r>o 


0.5086 


1.0649 


129.3 


144 


355.3 


326 9 


1192.7 


865.8 


3.133 


0.3192 


0.5100 


1.0624 


131.3 


146 


356.3 


328.0 


1192.9 


864.9 


3.092 


0.3234 


0.5114 


1.0599 


133.3 


148 


357.4 


329.1 


1193.2 


864.0 


3.052 


0.3276 


0.5128 


1.0574 


135.3 


150 


358.5 


330.2 


1193.4 


863.2 


3.012 


0.3320 


0.5142 


1.0550 


137.3 


152 


359.5 


331.4 


1193.6 


862.3 


2.974 


0.3362 


0.5155 


1.0525 


139.3 


154 


360.5 


332.4 


1193.8 


861.4 


2.938 


0.3404 


0.5169 


1.0501 


141.3 


156 


361.6 


333.5 


1194.1 


860.6 


2.902 


0.3446 


0.5182 


1.0477 • 


143.3 


158 


362.6 


334.6 


1194.3 


859.7 


2.868 


0.3488 


0.5195 


1.0454 


145.3 


160 


363.6 


335.6 


1194.5 


858.8 


2.834 


0.3529 


0.5208 


1.0431 


147.3 


162 


364.6 


336.7 


1194.7 


858.0 


2.801 


0.3570 


0.5220 


1.0409 


149.3 


164 


365.6 


337.7 


1194.9 


857.2 


2.769 


0.3612 


0.5233 


1.0387 


151.3 


166 


366.5 


338.7 


1195.1 


856.4 


2.737 


0.3654 


0.5245 


1.0365 


153.3 


168 


367.5 


339.7 


1195.3 


855.5 


2.706 


0.3696 


0.5257 


1.0343 


155.3 


170 


368.5 


340.7 


1195.4 


854.7 


2.675 


0.3738 


0.5269 


1.0321 


157.3 


172 


369.4 


341.7 


1195.6 


853.9 


2.645 


0.3780 


0.5281 


1.0300 


159.3 


174 


370.4 


342.7 


1195.8 


853.1 


2.616 


0.3822 


0.5293 


1.0278 


161.3 


176 


371.3 


343.7 


1196.0 


852.3 


2.588 


0.3864 


0.5305 


1.0257 


163.3 


178 


372.2 


344.7 


1196.2 


851.5 


2.560 


0.3906 


0.5317 


1.0235 


165.3 


180 


373.1 


345.6 


1196.4 


850.8 


2.533 


0.3948 


0.5328 


1.0215 


167.3 


182 


374.0 


346.6 


1196.6 


850.0 


2.507 


0.3989 


0.5339 


1.0195 


169.3 


184 


374.9 


347.6 


1196.8 


849.2 


2.481 


0.4031 


0.5351 


1.0174 


171.3 


186 


375.8 


348.5 


1196.9 


848.4 


2.455 


0.4073 


0.5362 


1:0154 


173.3 


188 


376.7 


349.4 


1197.1 


847.7 


2.430 


0.4115 


0.5373 


1.0134 


175.3 


190 


377.6 


350.4 


1197.3 


846.9 


2.406 


0.4157 


0.5384 


1.0114 


177.3 


192 


378.5 


351.3 


1197.4 


846.1 


2.381 


0.4199 


0.5395 


1.0095 


179.3 


194 


379.3 


352.2 


1197.6 


845.4 


2.358 


0.4241 


0.5405 


1.0076 



44 



BASIC PRINCIPLES 







Properties of Saturated Steam — 


Continued 




cT 




Total Heat 




a 


^ 








fc- 




above 32° F 


III 




f^ 




k 




< 


is 






r 


^1 


6 

r 


1 


cS 


1^ 


1 i 
>5 W 


In the Steam 

H 
Heat-Units. 


o 

u 

a *-• 


181.3 


196 


380.2 


353.1 


1197.8 


844.7 


2.335 


0.4283 


0.5416 


1.0056 


183.3 


198 


381.0 


354.0 


1197.9 


843.9 


2.312 


0.4325 


0.5426 


1.0038 


185.3 


200 


381.9 


354.9 


1198.1 


843.2 


2.290 


0.437 


0.5437 


1.0019 


190.3 


205 


384.0 


357.1 


1198.5 


841.4 


2.237 


0.447 


0.5463 


0.9973 


195.3 


210 


386.0 


359.2 


1198.8 


839.6 


2.187 


0.457 


0.5488 


0.9928 


200.3 


215 


388.0 


361.4 


1199.2 


837.9 


2.138 


0.468 


0.5513 


0.9885 


205.3 


220 


389.9 


363.4 


1199.6 


836.2 


2.091 


0.478 


0.5538 


0.9841 


210.3 


225 


391.9 


365.5 


1199.9 


834.4 


2.046 


0.489 


0.5562 


0.9799 


215.3 


230 


393.8 


367.5 


1200.2 


832.8 


2.004 


0.499 


0.5586 


0.9758 


220.3 


235 


395.6 


369.4 


1200.6 


831.1 


1.964 


0.509 


0.5610 


0.9717 


225.3 


240 


397.4 


371.4 


1200.9 


829.5 


1.924 


0.520 


0.5633 


0.9676 


230.3 


245 


399.3 


373.3 


1201.2 


827.9 


1.887 


0.530 


0.5655 


0.9638 


235.3 


250 


401.1 


375.2 


1201.5 


826.3 


1.850 


0.541 


0.5676 


0.960O 


245.3 


260 


404.5 


378.9 


1202.1 


823.1 


1.782 


0.561 


0.5719 


0.9525 


255.3 


270 


407.9 


382.5 


1202.6 


820.1 


1.718 


0.582 


0.5760 


0.9454 


265.3 


280 


411.2 


386.0 


1203.1 


817.1 


1.658 


0.603 


0.5800 


0.9385 


275.3 


290 


414.4 


389.4 


1203.6 


814.2 


1.602 


0.624 


0.5840 


0.9316 


285.3 


300 


417.5 


392.7 


1204.1 


811.3 


1.551 


0.645 


0.5878 


0.9251 


295.3 


310 


420.5 


395.9 


1204.5 


808.5 


1.502 


0.666 


0.5915 


0.9187 


305.3 


320 


423.4 


399.1 


1204.9 


805.8 


1.4.56 


0.687 


9.5951 


0.9125 


315.3 


330 


426.3 


402.2 


1205.3 


803.1 


1.413 


0.708 


0.5986 


0.9065 


325.3 


340 


429.1 


405.3 


1205.7 


800.4 


1.372 


0.729 


0.6020 


0.9006 


335.3 


350 


431.9 


408.2 


1206.1 


797.8 


1.334 


0.750 


0.6053 


0.8949 


345.3 


360 


434.6 


411.2 


1206.4 


795.3 


1.298 


0.770 


0.6085 


0.8894 


355.3 


370 


437.2 


414.0 


1206.8 


792.8 


1.264 


0.791 


0.6116 


0.8840 


365.3 


380 


439.8 


416.8 


1207.1 


790.3 


1.231 


0.812 


0.6147 


0.8788 


375.3 


390 


442.3 


'419.5 


1207.4 


787.9 


1.200 


0.833 


0.6178 


0.8737 


385.3 


400 


444.8 


422 


1208 


786 


1.17 


0.86 


0.621 


0.868 


435.3 


450 


456.5 


435 


1209 


774 


1.04 


0.96 


0.635 


0.844 


485.3 


500 


467.3 


448 


1210 


762 


0.93 


1.08 


0.648 


0.822 


535.3 


550 


477.3 


459 


1210 


751 


0.83 


1.20 


0.659 


0.801 


585.3 


600 


486.6 


469 


1210 


741 


0.76 


1.32 


0.670 


0.783 


Source 


684 


500 


484 


1209 


725 


0.66 


1.52 


0.686 


0.755 




1062 


550 


542 


1200 


658 


0.42 


2.36 


0.743 


0.650 




1574 


600 


604 


1176 


572 


0.27 


3.75 


0.799 


0.540 




2265 


650 






441 


0.16 


6.2 




0.396 




2974 
3075 


689 
700 








0.05 








* 












* 


4.300.2 


752 


^FromG. 


A. Goodenough's ta 


bles 1915. 






t 


5017.1 


779 


|-Calculat( 


id by J. McFarlane 


Gray—/ 


Voc. In^i. 


M.E., July, 1889. 


t 


5659.9 ! 


810.6 













BASIC PRINCIPLES 



45 



Properties of Superheated Steam 

(Condensed from Marks and Davis' Steam Tables and Diagrams.) 

V = specific volume in cu. ft. per lb., h = total heat, from water at 32° F. in 

B. t. u. per lb., n = entropy, from water at 32°. 



Press. 




Degrees of Superheat. 


Abs. 


Temp. 




Lbs. 


Sat. 






















per 
Sq. In. 


Steam. 





50 


100 


loO 


200 


250 


300 


400 


500 


GOO 


20 


228.0 


V 20.08 


21.69 


23.25 


24.80 


26.33 


27.85 


29.37 


32.39 


35.40 


38.40 






h 1156.2 


1179.9 


1203.5 


1227.1 


1250.6 


1274.1 


1297.6 


1344.8 


1392.2 


1440.0 






n 1.7320 


1.7652 


1.7961 


1.8251 


1.8524 


1.8781 


1.9026 


1.9479 


1.9893 


2.0275 


40 


267.3 


V 10.49 


11.33 


12.13 


12.93 


13.70 


14.48 


15.25 


16.78 


18.30 


19.80 






h 1169.4 


1194.0 


1218.4 


1242.4 


1266.4 


1290.3 


1314.1 


1361.6 


1409.3 


1457.4 






n 1.6761 


1.7089 


1.7392 


1.7674 


1.7940 


1.8189 


1.8427 


1.8867 


1.9271 


1.9646 


60 


292.7 


v7.17 


7.75 


8.30 


8.84 


9.36 


9.89 


10.41 


11.43 


12.45 


13.46 






h 1177.0 


1202.6 


1227.6 


1252.1 


1276.4 


1300.4 


1324.3 


1372.2 


1420.0 


1468.2 






n 1.6432 


1.6761 


1.7062 


1.7342 


1.7603 


1.7849 


1.8081 


1.8511 


1.8908 


1.9279 


80 


312.0 


v5.47 


5.92 


6.34 


6.75 


7.17 


7.56 


7.95 


8.72 


9.49 


10.24 






h 1182.3 


1208.8 


1234.3 


1259.0 


1283.6 


1307.8 


1331.9 


1379.8 


1427.9 


1476.2 






n 1.6200 


1.6532 


1.6833 


1.7110 


1.7368 


1.7612 


1.7840 


1.8265 


1.8658 


1.9025 


100 


327.8 


V4.43 


4.79 


5.14 


5.47 


5.80 


6.12 


6.44 


7.07 


7.69 


8.31 






h 1186.3 


1213.8 


1239.7 


1264.7 


1289.4 


1313.6 


1337.8 


1385.9 


1434.1 


1482.5 






n 1.6020 


1.6358 


1.6658 


1.6933 


1.7188 


1.7428 


1.7656 


1.8079 


1.8468 


188.29 


120 


341.3 


V3.73 


4.04 


4.33 


4.62 


4.89 


5.17 


5.44 


5.96 


6.48 


6.99 






h 1189.6 


1217.9 


1244.1 


1269.3 


1294.1 


1318.4 


1342.7 


1391.0 


1439.4 


1487.8. 






n 1.5873 


1.6216 


1.6517 


1.6789 


1.7041 


1.7280 


1.7505 


1.7924 


1.8311 


1.8669 


140 


353.1 


V3.22 


3.49 


3.75 


4.00 


4.24 


4.48 


4.71 


5.16 


5.61 


6.06 






h 1192.2 


1221.4 


1248.0 


1273.3 


1298.2 


1322.6 


1346.9 


1395.4 


1443.8 


1492.4 






n 1.5747 


1.6096 


1.6395 


1.6666 


1.6916 


1.7152 


1.7376 


1.7792 


1.8177 


1.8533 


160 


363.6 


V2.83 


3.07 


3.30 


3.53 


3.74 


3.95 


4.15 


4.56 


4.95 


5.34 






h 1194.5 


1224.5 


1251.3 


1276.8 


1301.7 


1326.2 


1350.6 


1399.3 


1447.9 


1496.6 






n 1.5639 


1.5993 


1.6292 


1.6561 


1.6810 


1.7043 


1.7266 


1.7680 


1.8063 


1 .8418 


180 


373.1 


V2.53 


2.75 


2.96 


3.16 


3.35 


3.54 


3.72 


4.09 


4.44 


4.78 






h 1196.4 


1227.2 


1254.3 


1279.9 


1304. § 


1329.5 


1353.9 


1402.7 


1451.4 


1500.3 






n 1.5543 


1.5904 


1.6201 


1.6468 


1.6716 


1.6948 


1.7169 


1.7581 


1.7962 


1.8316 


200 


381.9 


V2.29 


2.49 


2.68 


2.86 


3.04 


3.21 


3.38 


3.71 


4.03 


4.34 






h 1198.1 


1229.8 


1257.1 


1282.6 


1307.7 


1332.4 


1357.0 


1405.9 


1454.7 


1503.7 






n 1.5456 


1.5823 


1.6120 


1.6385 


1.6632 


1.6862 


1.7082 


1.7493 


1.7872 


1.8225 


220 


389.9 


V2.09 


2.28 


2.45 


2.62 


2.78 


2.94 


3.10 


3.40 


3.69 


3.98 






h 1199.6 


1232.2 


1259.6 


1285.2 


1310.3 


1335.1 


1359.8 


1408.8 


1457.7 


1506.8 






n 1.5379 


1.5753 


1.6049 


1.6312 


1.6558 


1.6787 


1.7005 


1.7415 


1.7792 


1.8145 


240 


397.4 


vl.92 


2.09 


2.26 


2.42 


2.57 


2.71 


2.85 


3.13 


3.40 


3.67 






h 1200.9 


1234.3 


1261.9 


1287.6 


1312.8 


1337.6 


1362.3 


1411.5 


1460.5 


1509.8 






n 1.5309 


1.5690 


1.5985 


1.6246 


1.6492 


1.6720 


1.6937 


1.7344 


1.7721 


1.8072 


260 


404.5 


V 1.78 


1.94 


2.10 


2.24 


2.39 


2.52 


2.65 


2.91 


3.16 


3.41 






h 1202.1 


1236.4 


1264.1 


1289.9 


1315.1 


1340.0 


1364.7 


1414.0 


1463.2 


1512.5 






n 1.5244 


1.5631 


1.5926 


1.6186 


1.6430 


1.6658 


1.6874 


1.7280 


1.7655 


1.8005 



46 



BASIC PRINCIPLES 







Properties of Superheated Steam- 


—Continued 






Press. 
Abs. 


Temp. 

Sat. 
Steam. 


Degrees of Superheat. 


Lbs. 

per 

Sq. In. 





50 


100 


150 


200 


250 


300 


400 


500 


600 


280 


411.2 


V 1.66 


1.81 


1.95 


2.09 


2.22 


2.35 


2.48 


2.72 


2.95 


3.19 






h 1203.1 


1238.4 


1266.2 


1291.9 


1317.2 


1342.2 


1367.0 


1416.4 


1465.7 


1515.1 






n 1.5185 


1.5580 


1.5873 


1.6133 


1.6375 


1.6603 


1.6818 


1.7223 


1.7597 


1.7945 


300 


417.5 


V 1.55 


1.69 


1.83 


1.96 


2.09 


2.21 


2.33 


2.55 


2.77 


2.99 






h 1204.1 


1240.3 


1268.2 


1294.0 


1319.3 


1344.3 


1369.2 


1418.6 


1468.0 


1517.6 






n 1.5129 


1.5530 


1.5824 


1.6082 


1.6323 


1.6550 


1.6765 


1.7168 


1.7541 


1.7889 


350 


431.9 


V 1.33 


1.46 


1.58 


1.70 


1.81 


1.92 


2.02 


2.22 


2.41 


2.60 






h 1206.1 


1244.6 


1272.7 


1298.7 


1324.1 


1349.3 


1374.3 


1424.0 


1473.7 


1523.5 






n 1.5002 


1.5423 


1.5715 


1.5971 


1.6210 


1.6436 


1.6650 


1.7052 


1.7422 


1.7767 


400 


444.8 


V 1.17 


1.28 


1.40 


1.50 


1.60 


1.70 


1.79 


1.97 


2.14 


2.30 






h 1207.7 


1248.6 


1276.9 


1303.0 


1328.6 


1353.9 


1379.1 


1429.0 


147».9 


1528.9 






n 1.4894 


1.5336 


1.5625 


1.5880 


1.6117 


1.6342 


1.6554 


1.6955 


1.7323 


1.7666 


450 


456.5 


V 1.04 


1.14 


1.25 


1.35 


1.44 


1.53 


1.61 


1.77 


1.93 


2.07 






h 1209 


1252 


1281 


1307 


1333 


1358 


1383 


1434 


1484 


1534.0 






n 1.479 


1.526 


1.554 


1.580 


1.603 


1.626 


1.647 


1.687 


1.723 


1.758 


500 


467.3 


vO.93 


1.03 


1.13 


1.22 


1.31 


1.39 


1.47 


1.62 


1.76 


1.89 






h 1210 


1256 


1285 


1311 


1337 


1362 


1388 


1438 


1489 


1539 






n 1.470 


1.519 


1.548 


1.573 


1.597 


1.619 


1.640 


1.679 


1.715 


1.750 



Volume of Superheated Steam — Linde's equation (1905), 
(150,300,000 



:^:;=0.5962T-/)(1 +0.0014/)) 



"ps 



-0.0833) 



in which p, is in lb. per sq. in., v, is in cu. ft. and T, is the absolute temperature on the Fahren- 
heit scale, has been used in the computation of Marks & Davis' steam tables. 

Specific heat of superheated steam. — Mean specific heats from the temperature of sat- 
uration to various temperatures at several pressures — Knoblauch and Jakob (from Peabody's 
Tables) . 



Lb. per sq. in. 


14.2 


28.4 


56.9 


85.3 


113.3 


142.2 


170.6 


199.1 


227.5 


256.0 


284.4 


Temp. sat. °F. 


210 


248 


289 


316 


336 


350 


368 


381 


392 


403 


412 


°F. 


°C. 
























212 


100 


0.463 






















302 


150 


.462 


0.478 


0.515 


















392 


200 


.462 


.475 


.502 


0.530 


0.560 


0.597 


0.635 


0.677 








482 


250 


.463 


.474 


.495 


.514 


.532 


.552 


.570 


.588 


0.609 


0.635 


0.664 


572 


300 


.464 


.475 


.492 


.505 


.517 


.530 


.541 


.550 


.561 


.572 


.585 


662 


350 


.468 


.477 


.492 


.503 


.512 


.522 


.529 


.536 


.543 


.550 


.557 


752 


400 


.473 


.481 


.494 


.504 


.512 


.520 


.526 


.531 


.537 


.542 


.547 



THE STEAM ENGINE 47 



CHAPTER 2 

THE STEAM ENGINE 



Oues. What is a steam engine? 

Ans. A machine for converting heat into mechanical power. 

Oues. Into what three classes are engines divided with 
respect to service? 

Ans. Stationary, marine and locomotive. 

Oues. Into what two classes are engines divided with 
respect to their mode of operation? 

Ans. Non-condensing and condensing. 

Oues. What is a non-condensing engine? 

Ans. A non-condensing engine (sometimes called a simple, 
or high pressure engine) is one that exhausts against the pressure 
of the atmosphere. 

Oues. What is a condensing engine? 

Ans. A condensing engine is one that exhausts into a condenser 
or device which condenses the exhaust steam, and in which, by 
means of an air pump, a partial vacuum is maintained, thus 
reducing the back pressure. 



48 



THE STEAM ENGINE 




THE STEAM ENGINE 49 

How an Engine Works. — In a steam engine, heat accom- 
plishes work only by being *'let down" from a higher to a lower 
temperature ; in the process some of the heat is converted into 
useful work. The mechanism by which this is accomplished is 
not so complicated as would at first seem, and its operation is 
easily understood. 

Fig. 54 is a sectional plan view of a simple form of steam engine. 
C, is a cylinder into which steam is admitted alternately by the 
valve V, through the steam passages S, S'. This causes a steam 
tight piston P, to move back and forth in the C3dinder. 

The pressure of the steam on the piston is transmitted through 
a piston rod to a connecting rod CR, which causes the crank K, 
to revolve; thus, the reciprocating motion of the piston is trans- 
formed into rotary motion of the crank.* 

In the revolution of the crank, the connecting rod will make various 
angles with the piston rod, hence, to allow for this, a cross head H, is placed 
at the point where the two rods meet, thus forming a hinged joint. The 
cross head is provided with guides to prevent the piston rod being broken 
or bent by the oblique thrusts and pulls which it imparts to the crank by 
means of the connecting rod. The crank is keyed or forged to a shaft Z, 
upon which is fastened a fly wheel. 

In the operation of the engine, it is evident that while steam is being 
admitted at one end of the cyhnder, the supply already in the cylinder 
from the previous stroke, must be exhausted from the other end. This is 
accomplished by means of a slide valve V. 

The two steam passages S, S', connect the ends of the cylinder with a 
box-like projection M, called the steam chest. These passages terminate in a 
smooth flat surface V S, known as the valve seat, and upon which the valve 
moves ; the ends of the passages terminating at the valve seat being called 
the ports. Careful distinction should be made between the terms passages 
and ports. 

The two ports just mentioned are called the steam ports, to distinguish 
them from a third and larger port located midway between them and 



*N0TE, — When James Watt produced his "rotative engine*" in 1780 he was unable to 
use the crank because it had already been patented by Matthew Wasborough. Watt was 
not discouraged and within one year had himself patented five other devices for obtaining 
rotary motion from a piston rod. 



50 



STEAM ENGINE PARTS 




THE STEAM ENGINE , 51 



called the exhaust port, through which steam passes from the cylinder to 
the exhaust pipe. The transverse form of these passages is long and narrow, 
so that steam may be quickly admitted and exhausted from the engine 
with only a slight valve movement. 

The valve itself, is a rectangular iron box, having a cavity, similar in 
form to the letter D. The size of the valve is so proportioned that in 
moving back and forth over the valve seat it will alternately cover and 
uncover the two steam ports, allowing steam to flow alternately into the 
cylinder ends from the steam chest. 

The exhaust cavity EC. connects either steam port to the exhaust port, 
so that while steam is being admitted to one end of the cylinder it is ex- 
hausted from the other end. 

The mechanism which imparts the to and fro motion to the valve is 
called the valve gear, and is quite similar to the connections between the 
piston and crank. 

Instead of a crank, there is usually an eccentric to impart motion to the 
valve. This consists of a disc bored out of the center and fastened by a 
key, or set screw to the shaft. Around the eccentric is a grooved ring called 
the eccentric strap. Motion is transmitted from the eccentric to the valve by 
means of an eccentric rod and valve stem as shown, a valve stem guide 
being provided to prevent the valve stem springing out of position on 
account of the side thrust of the eccentric rod. By turning the eccentric 
on the shaft, the relation between the valve movement and piston move- 
ment may be changed, hence, the eccentric may be adjusted so as to give 
the proper distribution of steam to and from the cylinder. 

In the figure, the piston is shown at the end of the cylinder or just be- 
ginning the stroke. In this position, the piston rod and eccentric rod 
are in a straight line, so that no matter how much steam pressure there 
may be on the piston it will not cause the crank to rotate. This happens 
when the piston is at either end of the cylinder, the corresponding positions 
of the crank pin being called dead centers. 

To prevent the engine stopping on a dead center, a fly wheel having a 
heavy rim is provided, which by its momentum keeps the engine in motion 
in passing these centers. 

Owes. Describe the operation of the engine. 

Ans. As shown in fig. 54, the piston is at the beginning of the 
stroke and the valve has just begun to open the steam port, 
admitting steam to the cylinder. As the piston moves, the valve 
opens the port to its full extent and closes it before the stroke is 
completed, thus "cutting off'* the supply of steam. During 
these ''events" of the power stroke the exhaust cavity of the 



52 . 



THE STEAM ENGINE 




Figs. 55 to 61. — Diagrams showing 
several positions of the piston, valve, 
crank and eccentric during one 
stroke. The diagrams show the 
relative movements of the parts, the 
crank and eccentric positions being 
shown at the right. 



valve connects the other steam port 
with the exhaust port E allowing 
the steam which was admitted 
during the previous stroke to ex- 
haust into the atmosphere, or con- 
denser, according to whether the 
engine be run non-condensing or 
condensing. 



Since the supply of steam is cut off 
by the valve before the piston completes 
the stroke, the steam in the cylinder 
expands from the point of cut off until 
the piston has almost completed the 
stroke. It is released at this point by 
the valve connecting the proper steam 
port with the exhaust port E. 

The movement of the valve, eccentric 
and piston during one revolution of the 
crank may be more easily understood by 
the aid of a series of diagrams, figs. 55 to 
61. The crank and eccentric positions 
corresponding to the several piston and 
valve positions, are shown at the right. 

In each figure the center of the crank 
pin, center of the shaft and the eccen- 
tric are shown at the right. 

In fig. 55 the piston is at the beginning 
of the stroke; the valve has just begun 
to open the steam port to the left for 
the admission of steam, w^hile the steam 
port to the right is iuWy open for ex- 
haust. To bring the valve in this . 
position, the eccentric has been set in 
advance of the crank as indicated. The 
reason for this will be explained later. 

In fig. 56, the piston has advanced to 
the right about Vio of the stroke and 
the valve has moved so that the port 
at the left is nearly wide open for the 



THE STEAM ENGINE 53 



admission of steam. Up to this point the piston and valve have been 
moving in the same direction. 

The valve now begins its return stroke and when the piston has moved 
about Vio of its stroke, the valve has just closed the port at the left, thus 
cutting off the steam supply as shown in fig. 57.' The steam now expands 
as the piston continues to move, but during this interval the port to the 
right is gradually being closed to the exhaust. 

When the piston has moved about Vio of its stroke, this port is closed 
and the steam remaining in the cylinder at that end is compressed which 
helps to bring the piston to rest without jar as it reaches the end of the 
stroke. 

The velocity of the piston is greatly reduced as it nears the end of the 
stroke while the movement of the valve is increased. 

In fig. 59 when the piston has moved only slightly from its position in the 
preceding figure, the valve is at the point of opening the port at the left 
to release the stearii for exhaust. 

In the next two figures the piston completes its stroke, while the port 
at the left is being very rapidly opened to exhaust. 

Fig. 61 shows the pistpn at the end of the stroke and the valve just be- 
ginning to admit steam to the port at the right for the return stroke, 
completing one stroke, the same cycle of events being repeated for the 
return stroke. 

The Expansion of Steam. — In the operation of a steam 
engine, steam, as just explained, is admitted and exhausted 
alternately at the ends of a cylinder within which, is a piston. 
The force exerted by the steam causes the piston to move to and 
fro which by suitable connections is made to do useful work. 
The distance the piston moves in either direction is called the 
stroke. 

*When engines are required to exert their full power for a short period 
as happens, for instance, when a locomotive is pulling a heavy train up an 
incline, steam is admitted to the cylinder at full pressure through the greater 



*NOTE. — Steam was first used expansively in an engine by Watt who in making appli- 
cation for a patent said, "My improvement in steam engines consists in admitting steam into 
the cyhnder, or steam vessels of the engine only during some part or portion of the descent 
or ascent of the piston of said cylinder, and using the elastic forces, wherewith the said steam 
expands itself in proceeding to occupy larger spaces as the acting powers on the piston through 
the other parts or portions of the length of the stroke of said piston." All engines now operate 
^tt this principle except where extraordinary conditions prevail. 



54 



THE STEAM ENGINE 



part of each stroke, without regard to economy in its use. However, this 
is not the way the medium is ordinarily used in an engine, for although an 
extra amount of work is done, it is at the expense of an excessive proportion 
of steam and fuel compared with the gain in work. 



Boyle's Law. — The behavior of a gas in expanding has been 
stated by Boyle as follows: Tlie pressure of a perfect gas at 
constant temperature varies inversely as its volume."^ 



CENTER CRANK 




>WIN&ING 
ECCElNTRiC 



SHAFT 
GOVERNOR 



Fig. 62. — The Atlas medium speed center crank engine with automatic cut off. This engine 
adjusts its power output to meet fluctuations in the load by the automatic action of the 
shaft governor which varies the point of cut off. Steam is expanded to a higher degree 
than with a throttUng engine resulting in superior economy. 



*N0TE. — The student should distinguish between isothermal and adiabatic expansion. 
Isothermal expansion means expansion at constant temperature; adiabatic expansion denotes 
expansion 'Z£;t7^0M/ receiving or giving up heal. It should be noted that the expansion of steam 
in an engine cylinder is neither isothermal nor adiabatic. According to Rankin, when steam 
expands in a closed cylinder, as in an engine, the approximate law of the expansion is 

P«<; V~^°/9. orPV*-"^=a constant. The curve constructed from this formula is called the 
adiabatic curve. The author does not believe the expansion of steam even approximately 
follows the adiabatic curve, and may be said to depart considerably therefrom, especially 
with very early cut off where the effects of condensation and re-evaporation are marked. Pea- 
body says: "It is probable that this equation (Rankin's equation above mentioned) was 
obtained by comparing the expansion lines on a large number of indicator diagrams." He 
states also that "there does not appear to be any good reason for using an exponential equation 
in this connection." Also that "the action of a lagged steam engine cylinder is far from being 
adiabatic." For general calculation steam may be taken as expanding in the cylinder according 
to Boyle's law, above given. 



THE STEAM ENGINE 



55 



This law may be illustrated by the following experiment: In fig. 63 is 
shown a cylinder, having a piston sliding air tight in its length. If air be 
compressed in front of the piston as it is forced from one end toward the 
other, the pressure exerted by the air will increase in ratio as the volume 
is diminished. This fact may be shown by inserting in the wall of the 
cylinder at different points a number of tubes, each provided with an air 
tight piston upon which bears a spiral spring holding it, as at A, when the 
pressure on the piston is the same on both sides. 




Fig. 63. — Experiment illustrating Boyle's law. This law was discovered by the Hon. Robert 
Boyle, in 1660, and in 1661 he presented to the Royal Society his work, "Touching the Spring 
of Air and its Effects." With respect to the experiment on air he says: " 'Tis evident 
that as common air when reduced to half its natural extent obtained a spring about twice 
as forcible as it had before, so the air, being thus compressed; being further crowded into 
half this narrow space, obtained a spring as strong again as that it last had, and conse- 
quently four times as strong as that of common air." Boyle does not appear to have con- 
sidered his law to possess the wide application afterwards credited to it. He believed that 
for pressure above four atmospheres, the compression of air was less than the amount 
correspondmg to the law. 

The area of each small piston is assumed to be one square inch, and the 
spring of such a tension that it will move upward through one of the spaces, 
between the horizontal lines on the diagram with each ten pounds of added 
•ressure. in the large cylinder. 



m 



56 



THE STEAM ENGINE 



Now when the piston moves in the cylinder, the pressure will gradually \ 
rise due to the compression of the air and the small pistons will rise against I 
the tension of the springs to increasing heights. % 

As the piston moves from the end of the cylinder to the following points: \ 
initial position, 3^ stroke M stroke Y^ stroke j 

the positions of the small pistons as shown in the figure will indicate the ; 
following pressures: 

14.7 lbs. 29.4 lbs. 58.8 lbs. 117.6 lbs. j 




Fig. 64. — To describe the hyperbolic curve for compression. Draw the zero or vacuum line \ 
A B, (any convenient Scale) = length of stroke or volume displaced by the piston, and extend - 
it to C, making A C, of length = clearance, that is, if the clearance volume be say, 8 per cent "' 
of piston displacement then length of A C =8% of A B, or .08 X A B. If the engine be running ; 
non-condensing and exhausting at say 2 lbs. gauge pressure, that is 14.7+2=16.7 lbs. ; 
absolute, this would be represented by a horizontal line at a height above A B, corresponding ; 
to 16.7 lbs., on the scale of pressures, as the dotted line beginning at B'. Suppose the exhaust , 
valve to close when the piston has reached the point D, corresponding to D' in the diagram, 
then C D, represents the volume to be compressed. By Boyle's law, the pressure is inversely ■ 
proportional to the volume, hence, when the piston has moved to E, reducing the volume, i 
one-half, the pressure will be doubled and equal to 16.7 X2 =33.4 lbs. Measuring up from E i 
alength corresponding to 33.4 lbs. gives E', a point on the curve. Similarly, when the ^ 
piston moves to A, compressing to one-quarter the original volume C D, the pressure rises \ 
to 16.7 X4 =66.8 lbs., giving the point A', on the curve. The curve may be described through i 
the points D', E', A', just obtained, or if greater accuracy be desired more points may be \ 
obtained, thus, by Boyle's law, pressure Xvolume = constant, from which, pressure = ' 
• constant -^volume. If C D =say, 3 ins., then the constant =3 X16. 7 =50.1, hence, when the ^ 
piston has moved to any point as F, reducing the volume to 2, then pressure for position F, = '^ 
50.1 y2 =25.05 lbs. abs. Similarly, other points may be obtained, but it should be noted : 
that it is a waste of time to obtain more than say 4 points. i 



THE STEAM ENGINE 



57 



thus showing that if the volume be diminished by half, the pressure is 
doubled. If a curve be drawn so as to pass through the center of each 
of the small pistons, it will show the pressure corresponding to every posi- 
tion of the large piston. 

To apply this to the conditions of operation in a steam engine, it may 
be assumed that the piston has moved from the left end of the cylinder to 
a point C, or 3^ stroke, and during this time, steam is admitted at a 
constant pressure of 58.8 lbs. and then the supply cut off. 

If the piston now move to B, the steam w^ll expand to double its volume 
and its pressure will be reduced to half, or 29.4 lbs. 



THROTTLE 
VALVE. 




SELF 
CONTAmEO 
OUTER BEARING 



OVERHUNG TYPE CYLINDER 



SIDE CRANK 



Fig. 65. — The Houston, Stanwood, and Gamble, side crank self-contained, throttling engine. 
The steam supply is "throttled" or varied automatically by the governor to meet load changes, 
the point of cut off being the same for all loads. This type of engine is cheaper than an 
automatic cut off engine but is not as economical in the use of steam. 

Again, if the piston move to the end of the stroke (to A) the volume thus 
obtained would be four times the original volume, and the pressure one- 
fourth the original pressure, or 14.7 lbs. 

The curve shows the expansion of the steam for any position of the 
piston during the expansion and is, therefore, called the curve of expansion.* 



Oues. What curve is taken ordinarily to represent 
tthe expansion of steam in an engine? 



58 



THE STEAM ENGINE 



Ans. The equilateral or rectangular hyperbola referred to 

its asymptotes.* 

The Saving due to Expansion. — The advantage of using 

C A' D' steam expansively may be clearly 

shown by a diagram as in 

fig. 71, which represents the 

work done by an engine during 




C A 1 


D 


M E 


B 






S 






^ 







Fig. 66. — To describe the hyberbolic curve for expansion, 1st method: This is practically 
the reverse of the process described in fig. 64. As before, draw the zero line A B = stroke and 
volume displaced by the piston. When clearance is to be considered extend it to C, making 
A C =clearance, as explained in fig. 64. At D, piston position at cut off, measure vertically 
a distance = pressure at cut off giving the point D', then C D', represents the volume of 
steam admitted considering clearance, and A' D', the volume admitted not considering 
clearance. Applying Boyle's law, 1, considering clearance, when the initial volume 
C D, is doubled by expansion to point E, pressure is reduced to J^, that is E E' =3^ D D'. 
Similarly G G' =3^ E E', or 34 D D', giving the points D',E',G', through which the curve 
passes. 2^ If clearance be not con^/J^r^c?, as is often the case, the initial volume is taken as 
A D.^ Again applying Boyle's law, points D' M' N' are obtained giving the lower curve. 
Considering a theoretical diagram the error introduced by not considering clearance is here 
indicated by the shaded area D' E' B' N' M' D', however, such error is usually allowed for 
in fixing the value of the diagram factor as explained in the accompanying text. 

^NOTE. — The hyperbolic curve is of such importance that it should be thoroughly under- 
stood. The following definitions, accordingly, should be carefully noted: Hyperbola. — A 
plane curve such that the difference of the distances from any point on it to two fixed points, called 
the foci, is equal to a given distance. The line passing through the foci and terminating at the 
two branches of the curve is the transverse axis, and a line perpendicular to this axis drawn half 
way between the foci is the conjugate axis. An asymptote of a hyperbola is a right line which 
an infinite branch of the curve continually approaches but does not reach, in other words, a tangent 
to the curve at infinity. The equilateral hyperbola. — A hyperbola whose asymptotes are per- 
pendicular to each other. This is the form of hyperbola which represents the law of expansion 
of steam, or Boyle's law. In this hyperbola, the product of the abscissa and ordinate at any 
point is equal to the product of abscissa and ordinate of any other point, that is, if p, be the 
ordinate at any point and v, its abscissa and p' and v', are the ordinate and abscissa at any 
other point, then pv=p'v', or p v=a. constant. See Boyle's law, page 54. Abscissae and 



THE STEAM ENGINE 



59 



one stroke. As in the preceding figure the vertical distances 
represent pressures and horizontal distances, piston positions. 

In the figure, F D, is the length of the stroke; the line being placed at such 
a height above a horizontal hne of no pressure, that any point on it is at 
atmospheric pressure. This line, therefore, is called the atmospheric lire 
in distinction from the line of no pressure, or vacuum line. 

The distance between these lines depends on the scale used in measuring 
pressures, thus, if Vio inch of vertical distance be taken to represent one 
pound pressure, the distance between the lines will be .1 X 14.7 = 1.47 inch. 

C' A' D' I 2 

- -r 





100 




90 


u 

-J 

< 
o 


80 
70 


60 




50 


\n 
if) 

UJ 

or 
a 


40 
30 
20 



ia.7 

10 




Fig. 67. — To describe the hyperbolic curve for expansion, 2nd method: Draw the zero 
line A B =stroke, and extend it to C, making A C=clearance. Take the distance C C — 
admission pressure, and at the point of cut off D, erect the perpendicular D D', giving the 
admission line A' D'. Extend C D'. and lay off any number of points 1, 2, 3, etc. From C, 
draw radial lines, Cl, C2, C3, etc. Draw horizontal lines through 1', 2', 3', etc., and vertical 
lines through 1, 2, 3, etc. Their intersections 1", 2", 3", are points on the hyperbolic curve. 

*NOTE.— Con^mwcJ. 
ordinates. — If X and Y, be two intersecting axes, X, being the axis of abscissae, and, Y, the 
axis of ordinates, then, the distance of any point P, from the Y axis, measured parallel to the axis 
of X', is called the abscissa of the point; also, the distance from the X axis, measured parallel 
to the Y axis is called the ordinate. The abscissa and ordinate taken together are called the 
co-ordinates of the point P. 



60 



THE STEAM ENGINE 



CONJUGATE 
HYPERBOLA 



ASYMPTOTE 



TRANSVERSE 
AX15 




Y- ASYMPTOTE. 
OR AXIS 
OF PRESSURE 



'BRANCH OF 

iHYPERBOLA USED 
REPRESENT 
EXPANSION AND 
COMPRtSSlONOF 
STEAM 




ASYMPTOTE 



Figs. 68 and 69. — ^Appearance of equilateral hyperbola 1, as referred to its rectangular axes, 
fig. 68, and 2, as referred to its rectangular asymptotes, fig. 69, one branch of the hyperbola 
in this position being used to represent the expansive action of steam. Comparing the two 
figures it will be noted that fig. 69 is the same as fig. 68, rotated through 45 degrees, the general 
method of constructing the hyperbole in fig. 69, is shown in fig. 70, and other methods in the 
accompanying diagrams. 




Fig. 70. — To describe an equilateral or rectangular hyperbola referred to its rectangular v 
asymptotes. General method: Draw the axis of volumes, or horizontal asymptote X X', | 
and the axis of pressures, or vertical asymptote Y Y', cutting X X', at O, or hyperbolic center, j 
Through O, draw M S, at 45° to X X'. Take any point on M S, as B, and with radius O B, j 
describe a circle, cutting M S, in B and A, giving A B, the transverse axis. At B, erect a t 
perpendicular cutting Y Y', at D, giving O D, the directrix. With O D, as radius describe ;• 
a circle cutting M S, at F and F'; these points are the foci of the hyperbola. On M S, take i 
any number of points 1, 2, 3, etc., and from F, and F' as centers, with Al, Bl, A2, B2, etc., : 
as radii, describe arcs cutting each other in 1', 2', 3', etc., and V\ 2", 3", etc., through which \ 
points the branch H B G, of the hyperbola is described. Similarly, the other branch H A G, j 



THE STEAM ENGINE 



61 



If steam be admitted at say, 100 lbs. per square inch absolute pressure 
when the piston is at F, and the supply continued at constant pressure 




f»CALE or VOLUME 

Fig. 71. — Theoretical card or diagram showing the theoretical advantage of using steam 
expansively. 



Fig, 70. — Continued. 

and conjugate hyperbola shown in dotted lines may be described, but for the purpose in view, 
only one branch H B 6 need be described. It is a property of the hyperbola referred to its 
rectangular asymptotes, as above, that if one asymptote as X X', be taken as an axis of 
volumes and the other an axis of pressures measured from the intersection O, then for any 
point on the curve as B, the product of its distance from Y Y', multiplied by its distance from 
X X', = constant, that is B VXB P=constant, or pressure X volume = constant which is in 
accordance with Boyle's law. 



62 



THE STEAM ENGINE 



for one-quarter oi the stroke, namely, till the piston reaches E, as shown, 
this may be represented in the diagram by the horizontal line AB, drawn 
at a height corresponding to 100 lbs. pressure. 

Now, if the steam be released, the pressure will fall to that of the atmos- 
phere as indicated by the line BE, and the work done for each square inch 
of piston area, will be equal to the area of the shaded rectangle ABEF, or 
M, because 

{load) {distance moved) {area) 

work done = AF X FE =ABFE 

If, instead of exhausting the steam when the piston has made only 
one-quarter stroke, the supply previously admitted be retained in the 
cylinder without any additional supply, and be allow^ed to expand, the 



^THEORETICAL DIAGRAM 

^ACTUAL DIAGRAM 

■ LOSSES 




Fig. 72. — Comparison of theoretical and actual diagrams illustrated by solid black section losses ] 

in the actual engine which reduce the theoretical gain due to expansion. \ 

curve of expansion BC will represent the gradual fall of pressure during \ 

the expansion. { 

At the end of the stroke, the absolute pressure C, due to the expansion | 

is called the terminal pressure. At this point, the steam is released and its j 

pressure falls to that of the atmosphere and then it is exhausted as in- . I 

dicated by the line CD. \ 

The gain due to expanding the steam will be clearly seen by noting the 

size of the four sided figure BCDE, or S, as compared with the shaded ' 
figure M. This area S, represents the work done by the steam in expanding 

just as the shaded area M, represents the work of the steam during admission, \ 

the exact amount of gain being determined by measuring the areas of M j 

and S, and dividing the combined area of the two by the area of M, that is, ' 

.M+S 



gain by expansion = - 



M 



The method of measuring these areas will be explained later. 



THE STEAM ENGINE 



63 





r 


ii: 




\ 


§1 






. c 






SI 






. o 


/ 




bo 






^\^ 


/ 




..o 


^ / 




.So 
be . 


o / 




»- ' / 




S5c 


3 / 




■i|l 


O / 




h. / 




J-, o-w 


^^^ 




0! Y"^ 

egg 










»^ o rt 






^.og 






-d^:^ 






■ m 


G 3 




C8 •- o 






S r- 


P 






/ 




G O 








/ 




O § a; 


/ 

/ 




o.H s 




w O 
w c o 


^ / 




o / 




»- / 




x ' s 


o / 






^ y 




^^^ 

i?.ii 
















°^s 






^r.s 


O rt ^ 


-. y c2 


u- 


Ml 


■u. / 




|§-i 


O / 




^ / 




^^g 


3 / 




M_^-d 


O / 






V 




w 0) *- 






























c'b -S 






cc rt w 






m 






Q^-^ 






l^"-3 






O o o 






-tJ "^ o 






^:S^ 


— 1 




: ,:,.., J 1 1 111 1 





To illustrate the great waste which re- 
sults in admitting steam to the cylinder 
the full length of stroke, as in the case of 
the ordinary steam pump, it may be 
assumed that instead of cutting off the 
supply at B, it be continued at the same 
pressure to the end of the stroke as rep- 
resented by the dotted line BG. 

If now the steam be released, its pressure" 
will fall to that of the atmosphere as in- 
dicated by the line GD, and the work done 
during the stroke will be represented by 
the area of the rectangle AGDF. 

The increase in power secured by ad- 
mitting steam for full stroke instead of 
cutting off at one-quarter stroke and ex- 
panding, is indicated by the area of the 
three sided figure BGC. To obtain this 
increase in power, it should be noted, 
requires four times the amount of steam 
as when cutting off at one-quarter stroke 
and expanding. 

By comparing the areas of the figure, it 
will be seen that in admitting steam for 
full stroke, the steam consumption is ex- 
cessive, and all out of proportion to the 
gain in power. 



Cut Oil. — When steam is used 
expansively in a cylinder, it is ad- 
mitted during a portion of the stroke 
at a constant pressure, and then the 
supply suddenly discontinued. That 
point of the stroke in which this 
occurs is called the cut off* and is 
usually expressed as a fraction of the 
stroke, thus J^, H, etc. 



s s § ^ ^^2o [3^ a 
3jLmosQV9gi ^ 



*NOTE. — This is the apparent cut off as dis- 
tinguished from the real cut off. later explained. 



64 



THE STEAM ENGINE 



Number of Expansions. — The degree in which steam isi 
expanded is expressed in terms of the original volume, thus, fourj 
expansions mean that steam has been expanded to a vohime| 
four times as large as its original volume. The number of! 
expansions is determined by the cut off. ; 

Rule 1. Number of expansions equal one divided by the cut off, * 



lUT OFF 




Fig. 76. — Diagram illustrating initial -pressure. This is the pressure in the cylinder at the he- ] 
ginning of the stroke and on the theoretical diagram is assumed to remain constant up to the- ' 
point of cut off. Some initial pressures: Atmospheric engines, lbs. gauge; low pressure \ 
engines, 20 lbs.; early walking beam marine engines, 25 lbs.; later types 50 to 75 lbs.; j 
stationary engines, 50 to 250 lbs.; marine screw engines, 80 to 250; locomotives, 150 to 275: , 
locomobiles and special engines, 250 to 500 lbs. i 

Thus, if steam be cut off at one-quarter stroke, . \ 

4 I 

number of expansions = 1 ^ J^ = 1 X-j-- =4. I 

Rule 2. — Number of expansions equal absolute pressure at cut \ 
off divided by terminal pressure. 

Thus if steam be expanded from 100 lbs. absolute cut off pressure to 20 1 
lbs. absolute terminal pressure, number of expansion = 100 -^ 20 = 5. j 



THE STEAM ENGINE 



65 



Initial Pressure. — This is the pressure at which steam is ad- 
mitted to the cylinder, and should not be confused with the boiler 
pressure.* It is theoretically the same as the cut off pressure, 
but in practice may be quite different. 
C A' D' 



TERMINAL PRESSURE 




LOSS DUE TO 
PRE- RELEASE 



Fig. 77. — Diagram illustrating terminal pressure. The valve g'^ar of a steam engine is so 
constructed that exhaust begins before the piston has completed the stroke, that is, the 
steam is pre-r pleased when the piston is near the end of the stroke, so that (especially in the 
case of high speed engines) the pressure of the steam in the cylinder will be reduced as near 
as possible to the exhaust pressure at the beginning of the exhaust stroke. Theoretical 
calculations, however, are simplified by assuming that exhaust does not begin till the end 
of the stroke. Accordingly the pressure at that point due to expansion, called terminal pressure, 
may be defined as the imaginary pressure that would exist in the cylinder at the end of the 
stroke if the steam were expanded to this point instead of being pre-released. Some terminal 
pressures: Single cylinder non-condensing 25 to 20 lbs. abs., condensing 20 to 12; multi- 
cylinder condensing 12 to 5 lbs. abs. 



*NOTE. — In practice the initial pressure is always less than the boiler pressure because 
of the resistance offered to the flow of steam through the steam pipe, engine ports and passages, 
especially where the engine is at some distance from the boiler and the steam line contains 
numerous elbows: these conditions and condensation all contribute to cause drop in pressure 
between boiler and engine. In ordinary plants this drop is usually two or more pounds. It 
should be noted in applying Boyle's law that absolute pressures should be used. Thus, 90 \h. 
gauge boiler pressurie with 2 lb. drop would give 90+14.7 — 2 = 102.7 lbs. absolute initial 
pressure. 



66 



THE STEAM ENGINE 



Ones. In theoretical calculations what assumption 
is made in regard to the initial pressure? 

Ans. It is assumed to remain constant during admission, 
that is to the point of cut off. 



-|OOX«O=I,00O EXPANSION CONSTANT 
1,000 -i- 15 = bbV5 LB5. 
1,000-^20-50 LBS. 

1,009- aS^^OLBS. 

1,000- 30 = 33 J^ LBS 




10 15 20 

VOLUME SCALE 

Fig. 78. — Diagram illustrating the expansion constant and its use. According to Boyle's 
law, pressure Xvohcme = constant. If, as indicated in the diagram, steam be admitted to 
a cylinder during 10 inches of the stroke and expanded to 30 inches, the expansion constant = 
100 X 10 = 1,000, from which the pressure at any other point =constant -^volume, that is, when 
the piston is at 

15 ins. 20 ins. 25 ins. 30 ins. 

of the stroke, the expansion constant -^volume is 

1,000^15 1,000-^20 1,000-^25 1,000-7-30 

which is equal to 

m% lbs. 50 lbs. 40 lbs. 33i^ lbs. 

Similarly volume = constant -^pressure, that is, when the pressure due to the expansion is 

662^ lbs. 50 lbs. 40 lbs. 33^ lbs. 

the expansion constant -^pressure is 

1,000^66^ 1,000-^50 1,000^40 1,000 -^33K 

which is equal to 

15 ins. 20 ins. 25 ins. 30 ins. 



Terminal Pressure. — If steam he expanded to the end of the 
stroke, the pressure at that point is called the terminal pressure. 
It is determined from the initial pressure and the number of 
expansions. 



THE STEAM ENGINE 



67 



Rule. The terminal pressure equals the initial pressure divided 
by the number of expansions. 

Thus, if the initial pressure be 100 lbs. absolute, and the number of 
expansions 4, 

terminal pressure = 100 -^ 4 =25 lbs. absolute. 

Example. — If the initial pressure be 100 lbs. gauge, and the number of 
expansions be 4, what is the terminal gauge pressure? 
100 lbs. gauge = 100 + 14.7 = 114.7 lbs. absolute. 
iiA 7^A I =28.69 lbs. absolute, or 
J14./ .4 (=.28.69-14.7=13.99 gauge. 




Fig. 79. — Diagram illustrating effect of expanding to a terminal pressure less than the exhaust 
pressure. In the above card, representing non-condensing operation, steam is expanded 
to A, below the exhaust line, giving the negative area S, which must be subtracted from M, 
to obtain the effective work area. 



Expansion Constant. — To determine the pressure at any 
point of the stroke, use is made of a constant found by multi- 
plying the volume of steam at cut off by the initial pressure. 

For instance, if steam at 80 lbs. absolute pressure be cut off when the 
piston has moved 10 inches of the stroke, then 

volume X pressure = constant 
substituting the above values 
^ 10 X 80 = 800 



68 



THE STEAM ENGINE 



Rule. The pressure at any point of the stroke equals the ex- 
pansion constant divided by the volume at that point. 

Thus, when the piston has passed through 20 inches of the stroke 
the pressure at that point is 

800 -^ 20 = 40 lbs. absohite. 

Rule. The volume corresponding to any pressure is equal to 
the expansion constant divided by the pressure at that point. 

Thus when the pressure has decreased to 40 lbs. absolute, the volume 
corresponding as measured by the piston movement is 

800-1-40 = 20 inches 

A A 





Figs. 80 and 81. — Theoretical cards illustrating mean forward pressure and back pressure. 

The two cards are the same as the card in fig. 78. If in fig. 78 an ordinate be drawn through 
the middle of each of the areas CDC D', D' H F D, etc., they will appear in fig. 80 as the 
dotted vertical lines A B, C D, E F, etc. The mean forward pressure represented by the 
area of M -i-its length L L' X the pressure scale, is equal to the average of the ordinates, 
that is, their sum divided by the number, and multiplied by the pressure scale, or 

(AB-hCD+EF+GH+IJ)^ , o- -i i • ^ oi *i. ,. , 

•^^ ^ — — Xpressure scale. Similarly in fig. 81, the back pressure. 



= area S -v- its length L L' X pressure scale 



A' B + C D + E' F+G' H+V J 



X pressure 



scale, or since in this case all are of the same length, back pressure = 
sure scale. 



height of S X pres- 



Mean Effective Pressure. — In the diagrams, figs. 82 and 
83, the effective pressure which tends to move the piston is 
clearly the difference between the steam pressure acting on one 
face of the piston and the atmospheric pressure acting on the 
other face in the opposite direction. 

The steam pressure acting in the direction in which the piston moves is 
called the forward pressure, and any pressure as that of the atmosphere 



THE STEAM ENGINE 



69 



acting on the opposite face, and opposing the movement of the piston is 
called the hack pressure. 

If steam be expanded as in the diagram, its pressure will vary, hence it 
is necessary to find an average or mean pressure which shall be the equivalent 
vine: forward pressure. 



of this varying forward pressure. 



The mean elective pressure is equal to the difference between 
the mean forward pressure and the mean hack pressure. That is, 
the mean effective pressure, or 

M.E. P. = mean forward pressure — mean hack pressure. "^ 




Figs. 82 and 83. — Theoretical cards illustrating mean effective pressure: fig. 82, constant 
back pressure; fig. 83, variable back pressure. Since the back pressure directly opposes 
the forward pressure, evidently the net or actual pressure tending to move a piston, or 
mean effective pressure is the difference between these two pressures, that is, Af . E. P. =mean 
forward pressure — back pressure. In fig. 80 the mean forward pressure is figured from the 
area M, and in fig. 81, the back pressure from the area S, hence, the mean effective pressure 
must depend on the difference of these two areas, that is M — S, or M' as shown in fig. 82, 
when the back pressure is constant. Where compression is taken into account, as in fig, 83, 
evidently M. E. P. =mean forward Pressure — mean back pressure, but in the figure, the 
mean back pressure is figured from area S+area S', hence, in this case M. E. P. depends on 
the difference between area M in fig. 80 and areas S+S' in fig. 83, and giving the area M" 
where average ordinate XPressure scale=M. E. P, 



If the distance of all points on the expansion line from the vacuum line 
be measured, and the sum of these distances be divided by their number, 
the quotient will equal the mean forward pressure; from which is deducted 
the back pressure, both in pounds absolute, and the result will be the mean 
effective pressure. 



*NOTE. — In the theoretical card, fig. 82, the back pressure S, is constant, but in practice 
it varies, hence in the actual card, the mean effective pressure =mean forward pressure — mean 
back pressure. It should be noted that in a theoretical card, taking into account compression, 
the mean back pressure must be subtracted from the mean forward pressure to obtain the 
M. E. P. 



70 



THE STEAM ENGINE 



Hyperboiic Logarithms. — In the diagram, fig. 84, the exact 
value of the area S, may be readily obtained by referring to a 
table of hyperbolic logarithms; for, since the cvirve of expansion 
is an hyperbola, the hyperbolic logarithm of the number of 
expansions expresses the relation between the area S, during 
expansion and the area M during admission. That is, if 
admission area M = unity 
A_ B 




M+S «l+ HYPERBOLIC LOGARITHM 



Fig. 84.— Reproduction in part of fig. 71, showing the application of the hyperboHc logarithm 
in finding the mean effective pressure. 



and 



expansion area S = hyperbolic logarithm 
total area M.-\-S = l-\- hyperbolic logarithm 



Thus, if steam be cut off at one-quarter stroke, it is expanded to 4 times 
its original volume; then if the area during admission = 1, the area during 
expansion = the hyperbolic logarithm of 4. 

Now, turning to the table of hyperbolic logarithms on page 71, the 
hyp. log. of 4 is 1.3863. This is the theoretical gain by expansion, that is, 
if 1 represent the work M, done before expansion, the work S, done during 
expansion is 1.3863 times greater than the work M, done before expansion. 



THE STEAM ENGINE 



71 



The total work done during the stroke is equal to 

M+S = l+%^ log. 4 = 1+1.3863=2.3863 
Hence, over twice the work is done by admitting steam one-quarter 







Table of Hyperbolic Logarithms 






No. 


Hyp. log. 


No. 


Hyp. log. 


No. 


Hyp. log. 


No. 


Hyp. log. 


1.1 


0.0953 


4.5 


1.5041 


7.9 


2.0669 


19.0 


2.9444 


1.2 


0.1823 


4.6 


1.5261 


8.0 


2.0794 


20.0 


2.9957 • 


1.3 


0.2624 


4.7 


1.5476 


8.1 


2.0919 


21.0 


3.0445 


1.4 


0.3365 


4.8 


1.5686 


8.2 


2.1041 


22.0 


3.0910 


1.5 


0.4055 


4.9 


1.5892 


8.3 


2.1163 


23.0 


3.1355 


1.6 


0.4700 


5.0 


1.6094 


8.4 


2.1282 


24.0 


3.1781 


1.7 


0.5306 


5.1 


1.6292 


8.5 


2.1401 


25.0 


3.2189 


1.8 


0.5878 


5.2 


1.6487 


8.6 


2.1518 


26.0 


3.2581 


1.9 


0.6419 


5.3 


1.6677 


8.7 


2.1633 


27.0 


3.2958 


2.0 


0.6931 


5.4 


1.6864 


8.8 


2.1748 


28.0 


3.3322 


2.1 


0.7419 


5.5 


1.7047 


8.9 


2.1861 


29.0 


3.3673 


2.2 


0.7885 


5.6 


1.7228 


9.0 


2.1972 


30.0 


3.4012 


2.3 


0.8329 


5.7 


1.7405 


9.1 


2.2083 


31.0 


3.4340 


2.4 


0.8755 


5.8 


1.7579 


9.2 


2.2192 


32.0 


3.4657 


2.5 


0.9163 


5.9 


1.7750 


9.3 


2.2300 


33.0 


3.4965 


2.6 


0.9555 


6.0 


1.7918 


9.4 


2.2407 


34.0 


3.5263 


2.7 


0.9933 


6.1 


.1.8083 


9.5 


2.2513 


35.0 


3.5553 


2.8 


1.0296 


6.2 


1.8245 


9.6 


2.2618 


36.0 


3.5835 


2.9 


1.0647 


6.3 


1.8405 


9.7 


2.2721 


37.0 


3.6109 


3.0 


1.0986 


6.4 


1.8563 


9.8 


2.2824 


38.0 


3.6376 


3.1 


1.1312 


6.5 


1.8718 


9.9 


2.2925 


39.0 


3.6636 


3.2 


1.1632 


6.6 


1.8871 


10.0 


2.3026 


40.0 


3.6889 


3.3 


1.1939 


6.7 


1.9021 


10.5 


2.3513 


41.0 


3.7136 


3.4 


1.2238 


6.8 


1.9169 


11.0 


2.3979 


42.0 


3.7377 ' 


3.5 


1.2528 


6.9 


1.9315 


11.5 


2.4430 


43.0 


3.7612 


3.6 


1.2809 


7.0 


1.9459 


12.0 


2.4849 


44.0 


3.7842 


3.7 


1.3083 


7.1 


1.9601 


12.5 


2.5262 


45.0 


3.8067 


3.8 


1.3350 


7.2 


1.9741 


13.0 


2.5649 


46.0 


3.8286 


3.9 


1.3610 


7.3 


1.9879 


13.5 


2.6027 


47.0 


3.8501 : 


4.0 


1.3863 


7.4 


2.0015 


14.0 


2.6391 


48.0 


3.8712 , 


4.1 


1.4110 


7.5 


2.0149 


15.0 


2.7081 


49.0 


3.8918 


4.2 


1.4351 


7.6 


2.0281 


16.0 


2.7726 


50.0 


3.9120 


4.3 


1.4586 


7.7 


2.0412 


17.0 


2.8332 






4.4 


1.4816 


7.8 


2.0541 


18.0 


2.8904 




' 



NOTE. — Hyperbolic or Naperian logarithms are common logarithms multiplied by 
2.3025851. 



72 THE STEAM ENGINE 



stroke and expanding four times than by admitting steam one-quarter 
stroke and exhausting at that point into the atmosphere. 

If the distance F E be called 1, then 4 expansions F D =4. Now, if the 
total area M+S, be divided by F D, or 4, it will give the height of a rectangle 
whose area = M-|-S, and the height of this rectangle will represent the mean 
effective pressure, hence: 

Rule. — To find the mean effective pressure, multiply the initial 
pressure in lbs. absolute hy 1+hyp. log. of the number of ex- 
pansions, and divide by the number of expansions. From the 
quotient, subtract the absolute back pressure. 

In the form of an equation the mean effective pressure or 

- -. ^ ^ initial pressure abs .XI -\- hyp . log .no. of expansions , , 

M.E.P.= ^ 1 j-^ — ^: -^ — ^ back pressure abs, 

number of expansions 

or, expressed in the usual symbols 



It should be remembered that the initial pressure P, and 
back pressure B. P., are taken in lbs. absolute. 

Example, — What is the mean effective pressure, with 80 lbs. initial 
gauge pressure, one- third cut off, 16 lbs. absolute back pressure? 

Initial pressure absolute = 80 + 14.7 = 94.7 lbs. 

Number of expansions = 1 -i- Va = 1 X^A =3. 

Hyp. log. of 3 (from table page 71) =1.0986. 

1+hyp. log 3 = 1+1.0986=2.0986. 

TVT « ^' 94.7X2.0986 _ .^ o iu 
Mean effective pressure = 16 = o0.2 lbs. 



Oues. In the operation of an engine is there as much 
advantage from working steam expansively as the above 
calculations indicate? 



THE STEAM ENGINE 



73 



Ans. No; it is not possible in steam engines to convert all the 
energy of the steam into useful work. There are various losses 
due to leakage, radiation, condensation and other causes, all of 
which tend to make the actual mean effective pressure obtained in 
an engine less than that calculated, as shown in fig. 85, 



Table for Finding Mean Pressure 



Number 

of 

expansions 


1 +hyp. log. r 
r 


Number 

of 
expansions 


1 +hyp. log. r 

r 


1.0 
1.5 
2.0 
2.5 
3.0 
3.5 
4.0 
4.5 
5.0 
5.5 
6.0 
7.0 
8.0 
9.0 
10.0 


1.00 

0.937 

0.847 

0.766 

0.700 

0.644 • 

0.597 

0.556 

0.522 

0.492 

0.465 

0.421 

0.385 

0.355 

0.330 


11.0 
12.0 
13.0 
14.0 
15.0 
16.0 
17.0 
18.0 
19.0 
20.0 
21.0 
22.0 
23.0 
24.0 
25.0 


0.309 
0.290 
0.274 
0.260 
0.247 
0.236 
0.226 
0.216 
0.208 
0.200 
0.192 
0.186 
0.180 
0.174 
0.169 



How to Use the Table. — The mean pressure is obtained for 
any number of expansions by multiplying the initial pressure 
absolute by the factor given. 

Example. — What is the mean pressure of steam for 100 lbs. initial gauge 
pressure, and one-quarter cut off? 

100 lbs. gauge pressure = 100+14.7 = 114.7 lbs. absolute pressure; 
J^cut-off = 1 -7- 3^ = 4 expansions. ♦ 

In the table the factor for four expansions is .597, from which the mean 
pressure is 

1 14.7 X. 597 = 68.5 lbs. 

To find the mean effective pressure, the absolute back pressure is subtracted 
from the mean forward pressure just obtained. 



74 



THE STEAM ENGINE 



Thus in the example just given, if the engine be running non-condensing, 
and exhausting against a back pressure of 2 lbs. gauge, then the absolute 
back pressure = 24-14.7 = 16.7 and the mean effective pressure = 68.5 — 16.7 
= 51.8 lbs. 

Again, if the engine be running condensing with a 28 inch vacuum, the 
absolute pressure corresponding to this vacuum is, from the steam table 
on page 40, .946 lbs. absolute, and the mean effective pressure is 
68.5 — .946 =67.55 lbs. 



Diagram Factor. — From the answer to the last question, 
(page 73), it is seen that no such results are obtained in the 

PRE-ADM15SI0N LOSS 

-LOSS BETWEEN BOILER AND ENGINE 
ADMISSION LOSS 

LOSS DUE TO DROP AT CUT OFF 
-AND CONDENSATION 

RE-EVAPORATION GAIN 

PRE-RELEASE 
LOSS 



INITIAL 

EXHAUST 

LOSS 




, COMPRESSION 
LOSS 




EXHAUST LOSS 



ATMOSPHERIC LINE 
ZERO LINE 



Fig. 85. — Comparison of theoretical and actual cards showing the various losses which tend 
to reduce the area of the actual card, making it in some cases considerably less than that of 
the theoretical card. In the figure, A B C D E A, is the theoretical card and A' B' C D' E' F A', 
the actual card. In practice, an initial loss occurs in getting the steam from the boiler to the 
engine making the beginning of the actual card at A' instead of A. During admission, the 
pressure drops because of friction through ports and passages, becoming very pronounced 
at cut oflF by "wire drawing." During expansion, the curve at first is below the theoretical 
because of loss of pressure at cut off, later condensation, and re-evaporation causes it to 
rise slightly above before pre-release. During pre-release the pressure drops very quickly, 
but does not reach exhaust pressure until the piston has begun the exhaust stroke. During 
exhaust, the pressure is always greater in the cylinder than the external back pressure of 
the atmosphere or condenser. During compression, sometimes considerable area of card is 
lost. During pre-admission the steam is retarded in rising to admission pressure because 
of wire drawing, this loss during this period is very small, and in some cases not noticeable 
especially if there h% liberal lead because the piston is practically stationary. 

actual engine, as in theoretical calculations. The diagram, fig. 84 
is known as a theoretical (indicator) card and represents a perfect 
performance, assuming hyperbolic expansion, that is, if the valves 



THE STEAM ENGINE 



75 






U- 




oo 


Q 




1 








U-. . 


w 








OUJ 


--> 


/w^ 








> 




II, Jn^ 








i-q: 


\ jW 








=33 


nriJL 


'w^ 








^o 


<*.^ 


<^ 








-J 

< 

ID 




f 








H^ 


^y^ 










^V A 


«$y 










y 


V 








GO 


^ 


LJ 
O 

-J 




i 


U 


< 




y 


^^^ 


w^. 


LU 




/ 





§•'2 ^.S a;< >,'^ S-S II 









<.5 






1:0 o 



; ^^JH.^ rt ^ g ^j 






g tnW 0^ " Vh (U .4)7 

S S<: g j:^^ y^ g-^ -I- 



^^«a)bc<u'ort;r5 rll 

^S:e-o3'S'5-ii s 

.0-2 .§0.0^ 



C <U (U o » 



op§rt"gi;<<a55^g 



00 






could open and close 
instantly, avoiding 
**wire drawing" or 
loss of pressure while 
not fully open or 
closed. 

If there were no con- 
densation, or any other 
condition causing a loss 
of pressure, the diagram, 
fig. 84, would represent 
the performance of an 
engine working under 
such conditions. 

In practice, as be- 
fore stated no suck 
results are possible, a 
diagram of less area 
(which means less 
work) being obtain- 
ed. This diagram is 
obtained by means of 
an indicator and is 
called the actual or 
indicator diagram to 
distinguish it from 
the theoretical dia- 
gram which is con- 
structed from the 
calculated perform- 
ance. The relative 
value of these dia- 
grams is expressed 
bv a coefficient 



76 



THE STEAM ENGINE 



called the diagram factor, which may be defined as the ratio 
of the actual card area to the theoretical card area, that is 
,. i. . ci'^^CL of actual card 

diagram factor = --^- 7—, r 

area of theoretical card 

Remembering that the work represented by the actual card, that is, 
its area, is always less than the area of the theoretical card, it must be 
evident that if an engine cylinder be proportioned for a certain horse power, 
based on mean effective pressure of the theoretical card, it will, when built 
and tested, develop less power because of the various conditions before 
mentioned which tend to reduce this pressure, or theoretical mean effective 




Fig. 88. — Theoretical and "expected" cards of Corliss engine operating under conditions given 
in example on page 97. After drawing the theoretical card A B C D E, to correspond with 
the given operating condition, the designer inscribes or sketches within the expected card 
making such allowance for the various losses as his experience and judgment dictates. 
The M. E. P. can be obtained, 1, by finding the diagram factor and multiplying it by the 
theoretical M. E. P., or 2, by finding the expected M. E. P. direct from the expected card. 
Clearly, the first method would be a waste of time, unless, the designer desire to check the 
accuracy of his judgment by comparing the diagram factor, with diagram factors of other 
similar engines already built and operating under similar conditions. 

pressure as it is called. Accordingly, since the power developed by an engine 
at any given speed is directly proportional to the mean effective pressure 
actually obtained in operation, the designer, after constructing a theo- 
retical card for the working conditions of initial pressure, cut off, etc., 
desired, and finding the theoretical mean effective pressure from this card, 
multiplies this by the diagram factor corresponding to the type of engine 
being designed. The value thus obtained is called the expected mean 
effective pressure^ because the diagram factor, being obtained by comparing 
the indicator card of a large number of engines of a similar type working 
under similar conditions with the theoretical card, and therefore repre- 
senting the allowance which must be made for the various conditions 



THE STEAM ENGINE 



77 



tending to reduce the theoretical mean effective pressure, gives, as near 
as can be calculated, the actual or "expected" mean effective pressure, 
when multiplied by the theoretical mean effective pressure. 

Example* — The theoretical mean effective pressure of a given theo- 
retical card is 40 lbs. What mean effective pressure must be used in de- 
signing an engine to develop a given horse power from the theoretical card 
if the diagram factor be .85? The mean effective pressure to be used in 
obtaining the cylinder dimensions, or 

expected M. E. P. = 40 X .85 = 34 lbs. 

It should be noted that if the diagram factor were disregarded and 
40 lbs. taken as the M. E. P., then the actual engine, if calculated for, 
say, 100 horse power at 300 revolutions per minute, would develop ap- 
proximately only 

34 

100 X 27^ = 85 horse power 

being 100 — 85 = 15 horse power short of the calculated power. 

If the theoretical mean pressure be calculated, and the necessary cor- 
rections made for clearance and compression, according to Sea ton the 
expected mean effective pressure may be found by multiplying the results 
by the factor in the first column of the following table : 

Diagram Factors 



Particulars of Engine 

Expansive engine, special valve gear, or with a 

separate cut off valve, cylinders jacketed 

Expansive engine having large ports, etc., and good 

ordinary valves, cylinders jacketed 

Expansive engines with the ordinary valves and gear 

as in general practice and unjacketed 

Compound engines, with expansion valve to H. P. 

cylinder; cylinders jacketed, and with large 

ports, etc 

Compound engines, with ordinary slide valves, 

cylinders jacketed, and good ports, etc 

Compound engines as in general practice in the 

merchant service, with early cut off in both cylinders 

without jackets and expansion valves 

Triple expansion engines, with ordinary slide valves, 

good ports, unjacketed, moderate piston speed. . . . 
•Fast running engines of the type and design usually 

fitted in war ships 



Diagram Factor 



.94 

.9 to .92 

.8 to .85 

.9 to .92 

.8 to .85 

.7 to .8 
.65 to .7 
.6 to .7 



.9 

.86 to .88 

.77 to .82 

.86 to .88 

.77 to .82 

.67 to .77 
.62 to .67 
.58 to .67 



78 THE STEAM ENGINE 



If no correction be made for the effects of clearance and compression, 
and the engine is in accordance with general modern practice, the clearance 
and compression being proportionate, then the theoretical effective mean 
pressure may be found by multiplying the results in the last column by .96, 
giving the values in the second column 

Horse Power. — This unit, as before stated was introduced 
by James Watt to measure the power of his steam engines and 
which he considered as being the power of a strong London 
draught horse to do work for a short time. This he estimated 
to be equal to 33,000 foot pounds per minute.* One horse 
power then, or 

one H, P. =33 fiOO ft. lbs. per minute 
which is the accepted standard. 

According to definitions, and the manner in which it is determined, 
horse power may be classed as 

1. Nominal (N. H. P.); 

2. Theoretical (T. H. P.); 

3. Indicated (I. H. P.); 

4. Brake (B.H. P.); 

5. S. A. E.; 

6. Electrical (E. H. P.); etc. 

Nominal Horse Power. — In the early days Watt, according to Seaton, 
found that the mean pressure usually obtained in the cylinders of his engines 
was 7 lbs. per sq. ins. He had also found the proper piston speed at 128 X 
-v^stroke per minute, and his engines were arranged to work at this speed, 
so that he estimated the power which would be developed when at work to be 

tN. H. P. = A X 7 X 128 X v's' 



*NOTE. — ^James Watt was early asked by would be purchasers as to how many horses 
his engines would replace. To obtain data as to actual performance in continuous work, he 
experimented with powerful brewery horses, and found that one traveling at 2^ m.iles per hour, 
or 220 feet per minute, and harnessed to a rope leadmg over a pulley and down a vertical shaft, 
could haul up a weight averaging 100 lbs., equaling 22,000 foot pounds per minute. To give 
good measure. Watt increased the measurement by 50 per cent., thus getting the familiar unit 
of 33,000 foot pounds per minute. 

tNOTE. — The power calculated by the formula above was called "nominal," because 
the engine was described as of that power, and in practice that power was actually obtained. 
However, when the boiler could be constructed so as to supply steam above atmospheric 
pressure, and the engine was run with more strokes per minute than before, the power developed 
exceeded the nominal power, thus causing the nominal horse power rating to be discontinued. 



THE STEAM ENGINE 79 



in which A = area of piston in sq. ins. ; S = number of strokes per minute. \ 

The term nominal horse power is now obsolete and is only of historical \ 

interest. : 

Indicated horse power. — This is the actual power developed by an engine 

as calculated from the indicator card. It should be understood that it repre- ! 
sents the power developed at the instant the card was taken, and not 

necessarily at any other instant*. It should be carefully noted that the ; 

indicated horse power of an engine does not represent the power delivered, ] 
being in excess of the power delivered by an amount equal to the power 

lost by friction in the engine. j 

Brake Horse Power, — By definition, the actual power delivered by an \ 

engine as determined by a brake test. This is sometimes called the delivered \ 

horse power , and is always less than the indicated horse power by an amount i 

equal to the power absorbed by friction in thfe engine. f \ 

S, A, E, Horse Power, — -In order to reduce all automobile engines to a , 

common basis of rating for determining the class of license required, the j 

commissioners of motor vehicles have adopted a rule known as the S. A. E. '< 
horse power formula, and which assumes that all gas engines will deliver 

or should deliver their rated power at a piston speed of 1,000 feet per minute, ] 

mean effective pressure of 90 lbs. per sq. ins., and mechanical efficiency \ 
of 75 per cent. It should be understood that a formula based on such data 

is worthless for obtaining the actual horse power of an engine and should : 
only be used for the purpose for which it is intended. 

Electrical Horse Power, — It is desirable to establish the relation be- 
tween watts and foot pounds in order to determine the capacity of an electric ; 
generator or motor in terms of horse power. \ 

One watt is equivalent to one joule per second or 60 joules per minute. \ 

One joule in turn, is equivalent to .7374 ft. lbs., hence 60 joules equal: ' 

60 X .7374 = 44.244 ft. lbs. i 



*XOTE. — It should be understood that in operation the power developed is continually 
varying, and, very- strictly speaking, may be said never to be the same during any appreciable 
interval of time. 

tXOTE. — The ratio between the indicated and brake horse power of an engine, that is 
brake horse power -^ indicated horse power represents the mechanical efficiency of the engine; 
this should not be confused with the thermal efficiency, or heat units converted into useful 
-work -T- heat units supplied to the engine. 



80 



THE STEAM ENGINE 



Since one horse power = 33,000 ft. lbs. per minute, the electrical equiv- 
alent of one horse power is 

33,000 -^ 44.244 = 746 watts. 
or, 



746 
1,000 



= .746 kilowatts (K. W.) 



Again, one kilowatt or 1,000 watts is equivalent to 
1,000 -^ 746 = 1.34 horse power. 




Fig. 89. — Diagram illustrating why the decimal .7854 is used to find the area of a circle. If 
the square be divided into 10,000 parts or small squares, a circle having a diameter D, equal 
to a side of the large square will contain 7854 small squares, hence, if the area of the large 
square be 1 sq. in., then the area of the circle will be 7854^10,000 or .7854 sq. ins., that is, 
area of the circle =.7854 XD2 =.7854 XD XD =.7854 XI XI =^.7854 sq. ins. 



How to Calculate Horse Power. — There are various formulas 
for calculating the power of engines, and the student should 
endeavor to understand the principles upon which they are 
based rather than simply committing them to memory. Before 
taking up these formulae a few preliminary considerations are 
necessary. 



Oues. Why is the decimal .7854 used to ascertain the 
area of a circle or piston? 



THE STEAM ENGINE 81 ? 



Ans. Because it represents the relation between a circle 
and circumscribed square. 

This relation is clearly shown in fig. 89. 

Oues. What is understood by the term piston speed? 

Ans. It is the total distance traveled by the piston of an 
engine in one minute — not the actual velocity at any given 
instant of time. 

Ones. How is the piston speed obtained? 

Ans. RULE: Multiply twice the number of revolutions per 
minute by the stroke of the engine in inches and divide the 
product by 12 to reduce to feet. 

Thus, an engine having a stroke of 6 inches and running 500 revolutions 
per minute is said to have a piston speed of 

.2X6X500. 



12 



= 500 feet per minute. 



Oues. What is the usual method of calculating the 
horse power of an engine? 

Ans* RULE: Multiply the mean effective pressure i^i lbs. per 
square inch by the area of piston in square inches and multiply the 
product by the length of stroke in feet, and by the number of strokes 
per minute {twice the number of revolutions) ; divide this last product 
by 33,000 and the answer will be the horse power for a double 
acting engine. 

This method which is very generally used is expressed as a formula as 
follows : 

jj p _ 2XPXLXAXN _ 2(.7854D2)PLN .^. 

33,000 ~ 33,000 



NOTE. — Horse power expressed in thermal units. — Since 1 B. t. u. is equivalent to 
777.52 ft. lbs. (Marks and Davis), and one horse power = 33,000 ft. lbs. per minute, then 
one horse power = 33,000 -r- 777.52 = 42.44 B. t. u. per minute. 



82 THE STEAM ENGINE 



in which 

P=mean effective pressure in lbs. per sq. ins.; 

L = length of stroke in feet; 

A = area of piston in sq. ins. = . 7854 X diameter of piston squared; 

N = number of revolutions per minute ; 

D = diameter of piston. 

It should be noted that the numerator represents the total ft. lbs. done 
by the engine in one minute; the figure 2 is introduced because in the double 
acting engine there are two power strokes each revolution. The denomi- 
nator or 33,000 is the foot pounds per one minute for one horse power. 

Example. — What is the horse power of a 5X6 engine running at 500 
revolutions per minute and 50 lbs. mean effective pressure? 

Substituting these values in the formula, and remembering that the 
area A of the piston = . 7854 X its diameter squared, 

2X (.7854X52) X50Xr2X500 

H. P. = : = 14.87 

33,000 

Oues. What is the objection to the formula just 
given? 

Ans. It involves a considerable waste of time in making the 
calculation. 

Since the stroke of an engine is usually given in inches instead of feet, 
and the revolutions per minute instead of the piston speed, the formula 
just given evidently involves extra calculations for these items as well as 
the extra multiplication and division introduced because of the constants. 
Its use therefore is about as laborious as multiplying and dividing fractions 
without reducing them to their lowest terms. 

The author strongly recommends that the formula just given be not used 
in the form given but reduced to its lowest terms as follows : 

2PLAN 2XPX i^X.7854XD2xN .1309XPLD2N 

H. P.= = L2 ^ . 

33,000 33,000 33.000 

= .00000396 7 PLD2N 

Using the constant .000004 instead of .000003966 v^hich is 
near enough for ordinary calculations, and changing the order 
of the factors, the formula becomes 

H. P. =. 000004 D^LNP . . . (2) 



THE STEAM ENGINE 



83 



Example, — What is the horse power of the engine in the previous 
example (running under the same conditions), as calculated by formula (2)? 
Substituting the given value in (2) 

H. P. =.000004X52X6X500X50 = 15 

Comparing the two formulae, 15 h. p. is here obtained instead of 14.87, 
the error introduced by using the constant .000004 instead of .000003966, 
being only 

86 
15 — 14.8/ =.13 horse power or tTvt: of 1% 

This short formula (2) is very valuable to those who have frequent 
occasions to calculate horse power. The power of any engine on a basis of 
of 500 revolutions and 50 lbs. mean effective pressure can be very quickl}^ 




Fig. 90. — View of Buffalo small vertical piston valve stationary engine. The main bearings 
are ring oiling and receive their supply of lubrication from the bed by the rotation of the 
crank disk; they are carried on a heavy plate bolted to the frame. Removable heads sur- 
mounting them shut out all ^he dust and grit and allow of ready access for adjustment. A 
false head forms a chamber to prevent condensation getting into the engine bed. This is a 
so called "square" engine, that is the stroke is the same length as the piston diameter. The 
5 X ■> size at 475 r. p. m. is rated at 12 horse power, and the 6 X 6 at 450 r. p. m., 18 horse 
power. Compare these ratings with the 5X6 engine given in the example on page 82. 



84 THE STEAM ENGINE 

found with this formula and* the method of using it, as given below, will 
firmly fix it in mind, though as before stated, the author does not recommend 
memorizing formulae but instead, the acquirement of a knowledge of 
principles upon which they depend. 

Now, for a quick calculation of the horse power of the engine in the 
previous example, 

1. Write down the cylinder dimensions, squaring the diameter 

(52X6) 

2. Disregard the decimal point and write 4 instead of .000004 

4 X (52X6) 

3. Insert the revolutions per minute and the mean effective pressure 

4X(52X6)X500X50 

The product of these factors is the horse power when the decimal point is inserted 
in the right place. 

4. Since the product of the first and last two factors is 100,000, dis- 
regarding the ciphers, only the factors inside the parenthesis need be con- 
sidered to obtain the horse power, thus 

52X6 = 5X5X6 = 150 (3) 

It remains only to insert the decimal point, which is determined from the 
sense of proportion , that is, any one familiar with engines would know that 
a 0X6 engine running at 500 R. P. M. and 50 lbs. mean effective pressure 
does not develop 150 h. p. as written in equation (3); neither does it 
develop only 1.5 h. p.; it must then develop 15 h. p. 

From the foregoing it must be evident that to obtain the 
horse power of any engine running at 500 revolutions per minute 
and 50 lbs. mean effective pressure it is only necessary to consider 
the dimensions of the cylinder and to point off one place, or 
multiply by .1 as expressed in the following formula, 

H. P. = .l X diameter piston 2 x stroke . . (4) 
diameter and stroke being taken in inches. Expressed as .a 
rule the formula becomes: 

Rule. — For 500 revohitions per minute, and 50 Ihs. per sq, in, 
M. E. P.y square the diameter and multiply by the stroke, both in 
inches; multiply the product by .1, that is, point off one place. 

Ones. How is the horse power obtained by (4) for 
other than 500 R. P. M. and 50 lbs. M. E. P.? 



THE STEAM ENGINE 



Ans. By multiplying the result obtained in (4) by the ratio 
between the given R. P. M. and 500, and the given M. E. P. 
and 50. 



Expressed as a formula (4) becomes 
H. P. = (h.p. at 500 r. p. m. and 50 lbs. m. e. p.) X?^-^^ X^i^^ . (5) 



500 



50 




Return SfroAe 



Fig. 91. — Working principles of the indicator. In the figure, A, is a small cylinder screwed into 
the engine cylinder and opening into the clearance space B. C, is a piston working within A, 
against the pressure of the steam in B, by means of the tension of the spring D. E, is a 
horizontal arm attached to the rod of the piston C, and carrying on its outer end a pencil 
point F. G, is a carrier bar upon which a board H, carrying a sheet of paper is moved back 
and forth in a direction opposite to that of the piston of the engine, by means of the spring 
L, and the lever M, the upper end of the latter being attached by a cord to the movable 
board and the lower end to some part of the piston rod such as the crosshead N. In oper- 
ation, assume the piston K, to be at its inner dead center o, and the clearance space B, to be 
empty. The piston C, will be down, and pencil point at F. Now, if steam be admitted to B, 
the increasing pressure will drive the piston C, upward, carrying the pencil vertically from 
F, to r, until the pressure in the clearance space is sufficient to move the piston. If this pressure 
be kept constant while the piston travels from o, to p, and moves the board H, through a 
corresponding distance from o', to p', the pencil will trace the line r x. But ordinarily, the 
pressure is not kept constant, the supply of steam being stopped when the piston has 
traveled some part of its forward stroke. Assume that the supply of steam be stopped when 
the piston has traveled a distance equal to one-quarter the length of its full stroke, or to c. 
The movement of the piston from o, to z will carry the board from o', to z', and as the pressure 
is kept constant up to this point, the pencil will trace a horizontal line from r, to s, the cut off 
point. The continued advance of the piston will move the board towards p\ and as it will 
also increase the volume of the steam, the pressure in the engine cylinder will fall, thus 
relieving the compression on the spring D, and alio wing the piston C, to descend. As the result 
of these operations and movements, the indicator pencil will trace the line 5 /, the point t 
coinciding with the point F, on the diagram when the piston is at its outer dead center p, 
and the board at the limit of its backward movement p'. Driven by the stored up energy 
in the fly wheel, the engine piston will travel from p, to o, on its return stroke, pulling the 



86 THE STEAM ENGINE 



Example,— K 5X6 engine at 500 R. P. M. and 50 lbs. M. E. P. develops 
15 horse power. What will be the power at 

1. 250 R. P. M. and 50 M. E. P.? 

2. 500 R. P. M. and 40 M. E. P.? 

3. 400 R. P. M. and 60 M. E. P.? 

The factor in the parenthesis of formula (5) being given in the example 
as 15, the powers developed corresponding to the above running conditions 
are 

1.H.P.^15X||X^J = 7^. 

2. H. P. = 15x55?X- = ^ = 12. 

500 50 5 

3. H.P. = 15x|^X^ = ^><i><-^ = 14.4, 

500 50 5 

This method is useful for mental calculation. 

Expressed as rules, the two principles upon which the above calculations 
are based are : 

Rule. — At constant speed, the horse power of an engine varies directly as 
the mean effective pressure. 

Rule. — At constant mean effective pressure, the horse power of an engine 
varies directly as the speed. 

Oues. Give a very short rule for finding the horse power 
of a single cylinder engine. 

Ans. Square the piston diameter and divide by 2. 



Fig. 91. — Continued. 

board from p' to q', and as no pressure exists in the cylinder, the indicator piston will remain 
down, and the indicator pencil will trace the line t F, and thus complete the diagram, 
the area of which graphically represents the work done by the engine per rev. It should 
be noted that for simplicity, pre-release and excess back pressure are not considered, 
steam being assumed to expand to the pressure of exhaust at t. In actual indicators, 
the pencil arm E, referred to, instead of being attached in a fixed horizontal position to the 
upper end of the rod of the indicator piston is replaced by a system of levers which multiplies 
the motion of the piston, thus permitting the use of indicator cylinders whose pistons have 
a smaller range of motion. Also, the movable board H, is replaced by a rotatable drum 
which carries the paper. A spiral spring in the interior of the drum rotates it in a direction 
opposite to that of the forward stroke of the engine piston , the spring being put into a state 
of tension, when the drum is rotated in the opposite direction, by means of a cord attached 
to the engine piston, during the return stroke of the latter. These substitutions allow very 
compact and efficient mechanical arrangements. 



THE STEAM ENGINE 



This is correct whenever the product of mean effective pressure and piston 
speed = 21,000, as in the following combinations: 



Mean effective pressure 


30 


35 


38.2 

(Approx.) 


42 






Piston speed 


700 


600 


550 


500 




I i I I 

I I I I 



I I i M I I 

/I /I -1 /I /I /I /\ // ;"■ 

H./ / I i ! i 



•^•^. 



/ 



Fig. 92. — Indicator card showing method of finding M. E. P. by summation of ordinates. 

First two Hnes are drawn perpendicular to the atmospheric line and touching the cards at 
the ends as shown. On a slanting line starting at the intersection A, of the atmospheric line 
and the vertical line, a scale is constructed that helps to find the desired ten subdivisions 
on the length of the diagram, and on which the mean height of each tenth is to be measured. 
The scale on the slanting line, starting from the point of intersection A, may be made by 
setting off, first ]4 inch, then, nine 3^ inch spaces, and, finally, again ^ inch, thus making 
the whole scale five inches long. The end point, B, of this scale is connected by a straight 
line with the intersection C, of the atmospheric line, and the second vertical line, and lines 
parallel to B C, are drawn through all the other ten points of the scale, to intersect 
with the atmospheric line. After drawing vertical lines through all these intersecting points, 
the ten mean ordinates, or pressures, can be measured, each individually, or in a convenient 
way, as a sum total, by taking off all the ordinate continuously upon a strip of paper. 
If this sum total be divided by ten, the mean ordinates for the whole diagram is found. To 
find the M. E. P., muUipLy the mean ordinate by the scale of spring. 

Horse Power Constant. — If it be desired to make a number 
of horse power calculations of a given engine under different 
nditions of speed and mean effective pressure to show its 



THE STEAM ENGINE 



power range, it must be evident, that it would be a waste of time 
to multiply the constants such as piston diameter, stroke, 
.000004, etc., for each calculation. Accordingly, if all these 
constants be multiplied, a value is obtained which is called the 
horse power constant, and to obtain the horse power in each 
case, it is only necessary to multiply the horse power constant 
by the variable quantity or quantities. 

Example. — What is the horse power constant of a 5X6 engine using the 
formula H. P. =.000004 D^ L N P. Here .000004; D, diameter = 5, and L, 
stroke = 6 do not vary, while N and P are variables hence 

horse power constant = .000004 XS^XG = .0006 
from which the horse power of this engine at say 500 R. P. M. and 50 ibs. 



M. E. P. is 



.0006X500X50 = 15 



The horse power constant as just found is useful where both N and P, 
the revolutions and mean effective pressure are considered as "variables." 
However, in making a ''horse power table" for a given engine several sets 
of calculations are made for a constant value of N or P. That is regarding 
N as constant, the horse power constant would be 

.000004 D2 L P (1) 

or, regarding P as constant, the horse power constant becomes 

.000004 D2 L N (2) 

The following examples show the application. 

Example. — Calculate the horse power of a 5X6 engine at 30 lbs. mean 
effective pressure for speeds of 100, 200, 300, 400, and 500 revolutions per 
minute. 

In this case the horse power constant is as expressed in (1) and its value is 
.000004X5^X6X30 = .018 
from which: for 100 r. p. m., h. p. =.018X100 = 1.8; for 200 r. p. m., h. p. = 
.018X200 = 3.6; for 300 r. p. m., h. p. =.018X300 = 5.4; for 400 r. p. m., 
h. p. = .018X400 = 7.2; for 500 r. p. m, h. p. = .018X500 = 9. 

Example. — Calculate the horse power of the engine in the preceding 
example at 500 revolutions per minute for mean effective pressures of 40, 
50 and 60 lbs. per sq. in. 

Here, the horse power constant is as expressed in (2), and its value is 
.000004X52X6X500 = .3 
from which: for 40 m. e. p., h. p. =.3X40 = 12; for 50 m. e. p., h. p. = 
.3X50 = 15; for 60 m. e. p., h. p. =.3X60 = 18. The results obtained are 
tabulated as follows: 



THE STEAM ENGINE 



Table of Horse Power Constants 

For formula H.P. =.000004D^LNP; con«f an* =.000004D^LP 



Size of 
cylinder 
(inches) 






Mean effective 


pressure 






25 


30 


35 


40 


oU 


OU V,) 


IX 1 


.0001 


.00012 


. 00014 


. 00016 


.0002 


. 00024 


.0003 


2X 2}4 


.001 


.0012 


.0014 


.0016 


.002 


.0024 


.003 


3X 3 


.0027 


. 00324 


. 00378 


. 00432 


.0054 


.00648 


.0081 


3X 4 


.0036 


. 00432 


. 00504 


. 00576 


.0072 


. 00864 


.0108 


4X 4 


.0064 


. 00768 


.00896 


.01024 


.0128 


.01536 


.0192 


oX 5 


.0125 


.015 


.0175 


.02 


.025 


.03 


.0375 


5X 6 


.015 


.018 


.021 


.024 


.03 


.036 


.045 


6X 6 


.0216 


. 02592 


.0324 


. 03456 


.0432 


.05184 


.0648 


7X 7 


.0343 


.04116 


. 04802 


. 05488 


.0686 


. 08232 


.1029 


7X 9 


.0441 


. 05292 


.06174 


. 07056 


.0882 


. 10584 


.1323 


8X 8 


.0512 


.06144 


.07168 


.08192 


.1024 


. 1628S 


.1536 


8X 10 


.064 


.0768 


.0896 


.1024 


.128 


.1536 


.192 


9X9 


.0729 


. 08748 


. 10206 


. 13464 


.1458 


• . 17496 


.2187 


9 X 12 


.0972 


.1164 


. 13608 


. 15542 


.1844 


.2328 


.2916 


10 X 12 


.12 


.144 


.168 


.192 


.24 


.288 


.36 


11 X 14 


.1694 


. 20328 


.23716 


. 27104 


.3388 


. 40656 


.5082 


12 X 12 


.1728 


. 20736 


.24182 


. 27648 


.3456 


.41472 


.5184 


13 X 13 


.2197 


. 26364 


. 30758 


.35152 


. 52728 


. 92728 


. 6.591 


14 X 14 


.2744 


. 32828 


.38316 


. 43804 


.5488 


. 65656 


.8232 


15 X 15 


. 3375 


.405 


.4725 


.54 


.675 


.81 


1.0125 


16 X 16 


.4096 


. 49052 


. 57344 


. 65536 


.8192 


. 98104 


1.2288 


18 X 18 


.5832 


. 69984 


.81648 


.93312 


1.16640 


1.39968 


1.7496 


20 X 24 


.96 


1.152 


1.344 


1.536 


1.92 


2.304 


2.88 


22X26 


1.2584 


1.51008 


1.66176 


2.01344 


2.5168 


3.02016 


3.7752 


24 X 30 


1.728 


2.0736 


2.4192 


2. 7648 


3.456 


4. 1472 


5.184 


Cor Hi 8 iizes 
















10X24 


.24 


.288 


.336 


.384 


.48 


.576 


.72 


12X24 


.3456 


.41472 


. 48384 


. 55296 


.6912 


. 82944 


1.0368 


12X30 


.432 


.5184 


.6048 


.6912 


.864 


1.0368 


1.296 


14 X 30 


.588 


.7056 


.8232 


.9408 


1.176 


1.4112 


1.764 


14X36 


.7056 


. 84672 


. 98784 


1.12896 


1.4112 


1.69344 


2.1168 


16 X 30 


.768 


.9216 


1.0752 


1.2288 


1.536 


1.8432 


2.304 


16X36 


.9216 


1.10592 


1.29024 


1.47456 


1.8432 


2.21184 


2.7648 


16X42 


1.0752 


1.29024 


1.50528 


1.70232 


2.1504 


2.58048 


3. 2256 


18X36 


1.1663 


1.39936 


1.73282 


1.86608 


3.33261 


2.79872 


3.49892 


18X42 


1.3608 


1.63296 


1.90512 


2. 17728 


2.7216 


3. 26592 


4.0818 


20X36 


1.44 


'1.728 


2.016 


2.304 


2.88 


3.456 


4.32 


20X42 


1.68 


2.016 


2.352 


2.688 


3.36 


4.032 


5.04 


20X48 


1.92 


2.304 


2.688 


3.072 


3.84 


4.608 


5.76 


22 X 42 


2. 0328 


2. 43936 


2. 84592 


3.25248 


4.0656 


4. 87872 


6.0984 


22X48 


2.3232 


2. 78784 


3. 25048 


3.71712 


4.6464 


5. 57568 


6.9696 


22X54 


2.6136 


3. 13632 


3.65904 


4.18176 


5. 2272 


6. 27204 


7. 8408 


24X42 


2.41919 


2.90303 


3.38687 


3.8707 


4.83838 


5. 80606 


7.25757 


24X48 


2.7648 


3.31776 


3.78072 


4.42368 


5.5296 


6. 63552 


8. 2944 


24 X 54 


3. 1104 


3.73248 


4. 35456 


4.97664 


6. 2208 


7.46496 


9.3312 


26X48 


3.24471 


3.89365 


4.54259 


5. 19153 


6.48942 


7.78731 


9.73413 


26 X 54 


3. 6504 


4.38048 


5.11056 


5. 84064 


7.3008 


8. 76096 


10.9512 


26X60 


4.056 


4.8672 


5.6784 


6. 4896 


8.112 


9.7344 


12. 168 


28 X 48 


3. 7632 


4.50584 


5.26848 


6.02112 


7.5264 


9.01168 


11.2896 


28X54 


4.2336 


5.08032 


5.92704 


6.77376 


8. 4672 


10. 16064 


12.7008 


28X60 


4.704 


5. 6448 


6. 5856 


7. 5264 


9.408 


11.2896 


14.112 


30X48 


4.32 


5.184 


6.048 


6.912 . 


8.64 


10. 368 


12.96 


30 X 54 


4.86 


5.832 


6.804 


7.776 


9.72 


11.696 


14.58 


30 X 60 


5.4 


6.48 


7.56 


8.64 


10.8 


12.96 


16.2 


32X48 


4.9152 


5. 89824 


6. 88128 


7.86432 


9.8304 


11.79648 


14.7456 


32X54 


5.5296 


6. 63552 


7.74144 


8.84736 


11.0592 


13.^7104 


16. 5888 


32X60 


6.144 


7.33728 


8.56026 


9.78304 


12. 288 


14.67556 


18.432 


34X54 


6. 24241 


7.49089 


8. 73937 


9.98785 


12.48482 


14.98178 


18.72723 


34X60 


6.935 


8.3132 


9.7104 


11.0976 


13. 87 


16. 6264 


20. 805 



90 



THE STEAM ENGINE 



Horse Power Table 


M. E. P. 


Revolutions per minute 














100 


200 


300 


400 


500 


30 


1.8 


3.6 


4.6 


7.2 


9 


40 


2.4 


4.8 


7.2 


9.6 


12 


50 


3 


6 


9 


12 


15 


60 


3.6 


7.2 


10.8 


14.4 


18 



The values in heavy figures are those obtained in the two examples, 
the other values are obtained by similar calculations, or by a shorter 
process by applying the rule for variable speed as given on page 86. 
Thus, having found the value 2.4 h. p. for 100 r p. m. and 40 lbs. m. e. p., 
the other values for 40 lbs. m. e. p. would 'be, applying the rule, 2.4X2 = 
4.8 h. p. for 200 r. p. m.; 2.4X3=7.2 h. p. for 300 r. p. m., etc. 

Oues. For great accuracy, what should be considered 
in addition to the factors included in the horse power 
formulae already given? 

Ans. The cross sectional area of the piston rod. 

Oues. Why? 

Ans. Because it reduces by a small amount the power in- 
dicated by the formulae. 

Effect of the Piston Rod oh the Power. — It must be evident 
since the piston rod passes through the stuffing box in the 
cylinder head, that the area of the piston tipon which steam acts 
at this end is reduced by an amount equal to the cross sectional 
area of the rod, whereas, on the other side of the piston steam 
acts on its entire area. Accordingly the power developed at the 
* 'crank end" will be less than at the ''head end."* 

Since this reduction of power is so small and the range of power 
of a steam engine so great, this ordinarily need not be 



*NOTE. — The terms crank end and liead end, mean respectively the end nearest or farthest 
from the crank or shaft. 



THE STEAM ENGINE 



91 



considered, and in most cases the extra calculation is a waste of 
time, however, it is important that the principle involved he 
understood. 




Fig. 93. — Sectional diagram of the indicator. A, is the swinging bar; B, the pencil bar; C, the 
indicator frame; D, cylinder containing tension spring; E, coiled spring on drum roller; F, 
revolving cylinder or drum; G, drum pin; H and Z, thumb screws holding drum; 1, nut to 
connect indicator to pipe; K, lever for screwing up I; M, connection between the spring 
cylinder and pipe; P, piston rod; R, joint; S, pin; T, post for guide of pencil bar; V, guide 
pulley for cord from reducing lever; W, swivel sleeve for cord; X, swivel pin; Y, support for 
swivel pin. 



92 



THE STEAM ENGINE 



To simplify the calculation, the average effect is considered, 
that is, half the piston rod area is regarded as being removed 
from each face of the piston, instead of the full area from one 
face only. The following example will illustrate the methods 
of calculation. 

Example* — A 5X6 engine running at 50 lbs. m. e. p., and 500 r. p. m. 
develops 15 horse power, neglecting the effect of the piston rod. What 
power is developed, considering a piston rod 1 inch in diameter? 




Fig. 94. — One form of reducing lever for an indicator attachment. A, is attachment of the cord ; 
B, end of cord; C, pivot of reducing lever; D, swinging joint of reducing lever; E, point of 
attachment to cross- head for the link joining reducing lever at D. The indicator is shown at 
top of cylinder, connected by a three-way cock to pipes from both ends of cylinder. 

1st Solution, 

From table, or by calculation, area 5" piston = 19.635; area cross section 1" 
piston rod = .7854; 3^ piston rod area = . 7854 -r- 2 = .3927 sq. ins. 1 % of 
piston area = 19. 635 X. 01 =.197, hence j^ piston rod area = .3927 -i- 
.197 = .0199, that is 1 .99% of piston area. Accordingly the power is reduced 
1.99%, or 15 X. 0199 = .299 horse power, from which the actual power 
of the engine is 15 — .299 = 14.7 horse power. 

2d Solution. 

Area 5'' piston = i/4V D2 = .7854X52 = .7854X5X5 = 19.635 
Similarly, or from table, 3^ area of 1'' piston rod = .3927. 

Effective piston area = 19.635 — .3927 = 19.2423, say 19.24 sq. ins. 

Now, a rea of piston = .7854D2, f rom which D2 = area of pisto n -t-. 7854, 
or D= Varea of piston X .7854= Vi9;24T?7854= V24.497=4.95 



sq. 



THE STEAM ENGINE 



93 



Substituting, this value of D, and the stroke in formula (4) (page 84) for 
horse power of an engine running at 50 lbs. m. e. p. and 500 r. p. m., 

H.P. = . 1X4.952X6 = 14.7 

Brake Horse Power. — This is the useful horse power de- 
livered by an engine as ascertained by the application of a brake 
or absorption dynamometer. The excess of the indicated 
horse power over that required by the brake, represents the power 
required to move the engine in overcoming its friction. 




Fig. 95. — Prony brake. It consists of a friction band which may be placed around the fly 
wheel or the crank shaft, and attached to a lever bearing upon the platform of a weighing 
scale, as shown. A brake used for testing purposes should be self-adjusting to a certain 
extent, so as to maintain, automatically, a constant resistance at the rim of the wheel. For 
comparatively small engines, various forms of rope brake, satisfy this requirement very well. 
In such cases, a weight is hung to one end of the rope and a spring scale to the other end. 
I The wheel should be provided with interior flanges, holding water for keeping the rim cool. 
For very high speeds, some form of water friction brake should be employed, as they have 
the advantage of being self-cooling. 



The power of small engines running at very high speeds, is 
best obtained by a brake test, since indicator cards become 
disturbed under such conditions, thereby introducing errors. 
The form of absorption dynamometer generally used' for ob- 
taining brake horse power is called the Prony brake (named 
after its inventor). Its construction is shown in fig. 95. 



94 ' THE STEAM ENGINE 

Formula for Brake Horse Power. — The net work of the 
engine or horse power delivered at the shaft is determined as 
follows : 

Let W = power absorbed per minute; 

P = unbalanced pressure or weight in pounds, acting on the lever arm 
at a distance L; 

L= length of lever arm in feet from center of shaft; 

N = number of revolutions per minute; 

V = velocity of a point in feet per minute at distance L, if arm were allowed 
to rotate at the speed of the shaft = 2 tt L N 

P \' 

Since brake horse power = 

^ 33,000 

substituting for V, 

B.H. P. (brake horse power) = 2 tt L N P ^^ 

33,000 
It should be noted that if L=33-^2 tt the equation becomes 

B. H. P. = -^^X — X N P = ii^ (2) 

33,000 27r 1,000 

Accordingly, in order to use the simplified formula (2) the arm L is 
made 33-j-27r or 5.285 feet, very approximately 5 ft. 3]Y6 inches. 

Oues. What important precaution should be taken in 
making a brake test? 

Ans. The lever arm L, should be horizontal when a weight 
is used so that the force due to gravity will act at right angles 
to the arm. 

4 

If the arm he in any other position, the effect will he the same as shortening 
the arm and will introduce an error in the calculation. 

Size of Cylinder.— Having learned the principles and methods 
of calculating the horse power of an engine, as given in the 
preceding pages, the student should now consider how to cal- 
culate the diameter and stroke of an engine to develop a given 
horse power. 



THE STEAM ENGINE 



95 



It must be evident that for, say, a given speed, a great many 
cylinder sizes could be used, each giving the same power, that 
is, a long stroke with small piston, or a large piston with small 
stroke could be used, the best proportion between the stroke 
and diameter being determined by the type of engine, service 
for which it is intended, etc., and a knowledge of best practice 
on the part of the designer. 




Figs. 96 and 97. — Side and end view of rope brake. This type of brake is easily constructed of 
material at hand and being self-adjusting needs no accurate fatting.^ For large powers the 
number of ropes may be increased. It is considered a most convenient and reliable brake. 
In the figure the spring balance, B, is shown in a horizontal position. This is not necessary; 
if convenient the vertical position may be used. The ropes are held to the pulley or fly_ wheel 
face by blocks of wood, O. The weight at W, may be replaced by a spring balance if desirable. 
To calculate the brake horse power, subtract the pull registered by the spring balance, B, 
from the weight W. The lever arm is the radius of the pulley plus one-half the diameter of the 
rope. The formula is, 

*B. H. P. = 27rR N (W — B) 
33,000 
= .0001904 RxN (W — B) 

In the formula R =radius from center of shaft to center of rope; N =revoluiions per 
minute; W=weight; B =spring balance. 



For a given piston speed evidently a short stroke engine will 
make a larger number of revolutions per minute than one with 

*NOTE. — If B be greater than W, the engine is running in the opposite direction; in this 
case use the formula B. H. P. = .0001904 R N (B — W). 



96 



THE STEAM ENGINE 




a long stroke. Thus, for 
say, 800 ft. of piston 
speed, an engine with 1 
ft. stroke will make 800 
-^ (2 XI) = 400 r.p.m., 
whereas, for 2 ft. stroke 
only 800 -^ (2X2) = 200 
r.p.m. will be required. 

Oues. What is the 
meaning of the term 
high speed engine? 

Ans. It means that 
the number of revolu- 
tions per minute or 
rotary speed is high, for 
the particular type of 
engine in question. This 
term should not be con- 
fused with high piston 
speed, as it does not re- 
late to the piston speed. 

Fig. 98. — Troy high speed vertical 
automatic center crank engine 
with self-oiling system. Made in 
sizes ranging from 3^^ X4 to 
12X12; revolutions: highest 600 
to 350, standard 400 to 300; low- 
est, 400 to 275. The oiling system 
consists of a reservoir in base for 
oil, a pump driven from the eccen- 
tric rod, and pipe connections to 
all the bearings. In operation 
the oil is drawn from the supply in the engine base, through a strainer funnel and suction 
pipe to the pump and check valve, then driven through the sight feed, where its movement 
can be noted, to the distributing head and thence through the supply pipes to the bearings, 
keeping them flooded; and, overflowing, finds it way back to the reservoir for repeated use. 
Any water of condensation entering the reservoir is automatically carried away, leaving the 
oil. No water can enter the suction pipe if the designated amount of oil be placed in the 
engine. A special packing is used in the piston rod stuffing box and practically eliminates 
the passage of water. 




THE STEAM ENGINE 97 



The first step in calculating the cylinder dimension is to 
arrange the horse power formula in the proper form for obtaining 
the value of the unknown quantity. 

Thus, starting with the formula 

H. P. = .000004 D'L N P . (1) 

the quantities to be found are D, the diameter of cylinder or 
piston, and L, the length of stroke. Accordingly, solving for 
these quantities 



^2 H. P. ^ I H. P. ' 

D = ^ or D = \ . . (2) 

.000004 L N P ' .000004 L N P 



L= ^ (3) 

.000004 D' N P 



For those who do not understand the solution of equations, 
(2) and (3) are easily obtained from (1) as follows: 

Rule. — On one side the equality sign write down the unknown 
quantity; on the other side, 1, the horse power as numerator, and 2, 
the remaining J actors as denominator. 

Of course, when D is the unknown, since it is squared in the formula, the 
square root must be taken as in (2). 

Example. — Find the size of cylinder of a Corliss engine 
to develop 85 horse power when running under the following 
conditions: Initial pressure, 80 lbs.; J4 cut off; mean back 
pressure, 2 lbs. (non-condensing) diagram factor .9; piston speed 
600 ft. per minute. 

The solution consists of three steps, viz.: finding, 1, the mean 
effective pressure; 2, the stroke, and 3, the diameter of cylinder. 



98 THE STEAM ENGINE 

CASE 1. DIAGRAM FACTOR GIVEN 
1. Mean effective pressure. 

1. Find total number of expansions (neglecting clear ance).t 
Rule. — One divided by the reciprocal* of the cut off. 

1-^1 = 1X4=4 

>i 

2. Find mean forward pressure. 

Rule. — Multiply initial pressure by l-\-hyp. log. of expansions, and 
divide by number of expansions. 

From table page 71, hyp. log. of 4 = 1.3863. 

1+hyp. log. 4 = 1+1.3863=2.3863 

initial pressure absolute = 80 + 14.7 =94.7 

r -, . 94.7X2.3863 kck :^ ^u 
mean forward pressure = =56.5 lbs. per sq. m. 



3. Find mean effective pressure. 

Rule. — Subtract mean back pressure absolute from mean forward pressure, 
and multiply the difference by the diagram factor. 

2 lbs. mean back (gauge) pressure = 2 + 14.7 = 16.7 lbs. absolute 

(56.5 — 16.7) X.9 =35.8 lbs. per sq. in. 

2. Choice of Stroke. 

The length of stroke must be such as will give a desirable number of 
revolutions, and bear a proper relation to the cylinder diameter. The 
Corliss engine is a slow speed or long stroke type, usual ratio of stroke to 
diameter being about 2 : 1 or more, hence of the several lengths of stroke 
that could be used, one should be selected that will come within the ratio 
limits and also give the proper speed in developing the rated power. 
Ordinarily the revolutions may be from 100 to 125, and with valve gears 



fNOTE. — It should be understood that in the example the expression one-quarter cut off 
relates to the point of stroke at which steam is cut off by the valve gear; it does not represent 
the real cut off, with respect to the expansion of steam, because clearance must be considered, 
and on this account is, strictly speaking, called the apparent cut off, which will be explained 
in the chapter on valve gears. The econornical range of horse power being considerable, cor- 
rection for the apparent cut off need not ordinarily be made. 

*NOTE. — The reciprocal of the cut off means one divided by the cut off. 



THE STEAM ENGINE 



99 ^ 




especially designed for high speed, 
150 r. p. m., or higher. The revo- 
lutions or 

R. P. M. = piston speed H-2 
X stroke (in feet) 

thus, for say, 24" stroke and given 
piston speed of 600 feet 

R. P. M.=600-^2X^ = 150 

Similarly, the following table 
is obtained: 

R. P. M. for 600 ft. piston speed 



Stroke 


24 


30 


36 


R. P. M. 


150 


120 


100 



3. Diameter of cylinder. 

The m. e. p. obtained in 1, is 
35.^ lbs. per sq. ins.; now in- 
specting the table in 2, a trial 
may be made with the 36" stroke 
which gives 100 r. p. m. Sub- 
stituting the values in formula 
(2) page 97, 



o=v: 



85 



Q00004X 36X100X35. 8 
= 12.8 (a) 



For the given power, this di- 
ameter of cylinder may be used 
with any stroke in the table in 
2 at the revolutions given, that is 
the cylinder dimension may be 

12.8X36 for 100 r. p.m. 
12.8X30 for 120 r. p.m. 
12.8 X 24 for 150 r. p.m. 



100 THE STEAM ENGINE 



calling the diameter 13 ins., in each case, the stroke diameter ratios are 
2.77, 2.3, and 1.87 respectively, the first two being within limits and the 
■ last two small. 

In the case of a growing plant where more power will be soon required 
the 13 X36 would be desirable, as the r. p. m. could be increased considerably 
to increase the power. Ordinarily, the 13X30 would be desirable, as it 
would cost less, and would run at a more desirable r. p. m. 



CASE 2. DIAGRAM FACTOR NOT GIVEN 

A graphical solution of the example just given consists in 
drawing the theoretical card corresponding to the given values 
of initial pressure, cut off, etc., and inscribing in this diagram 
a card drawn to represent the "expected" performance of the 
actual engine. This card is drawn after considering a large 
number of actual cards of similar engines operating under similar 
conditions. Accordingly, the more experienced the designer, 
the nearer can he come to drawing a card that will represent 
the actual performance of the engine. 

The steps in this graphical method are: 1, drawing the theo- 
retical card; 2, drawinjg the expected card; 3, finding the ex- 
pected m. e. p. ; 4, finding the cylinder dimensions. 

1. The theoretical card. 

In fig. 100, draw the vacuum line, or line of no pressure OV. Using a 
scale of 1"=40 lbs., draw the atmospheric line E D, a distance above 
corresponding to 14.7 lbs. and parallel to O V. At a height corresponding 
to 94.7 lbs. abs. draw the admission line A B, in length = ^ of E D; extend 
A B, by dotted line to 3 and at points 1, 2, 3, drop perpendiculars. From O, 
draw radial lines 01, 02, 03, cutting the perpendicular from B, at 1', 2', 3' 
respectively; the intersection of horizontal lines from these points with 
the perpendiculars, give points 1", 2", C, on the expansion curve, thus 
completing the theoretical card A B C D E, corresponding to the given data. 

2. The expected card. 

At this point all depends on the experience and judgment of the designer 
who sketches within the theoretical card, fig. 100, a card which he thinks 
will represent the actual performance of the engine. He proceeds about 
as follows: The initial pressure being given instead of boiler pressure, 



THE STEAM ENGINE 



101 



no allowance is made for drop between boiler and engine, hence the 
expected admission line begins from A, and proceeds toward B, first hori- 
zontally, and then begins to slope downward (though very slightly) because 
of pressure drop due to initial condensation due to the low temperature of 
the cylinder walls; approaching cut off at 6, the admission becomes curved 
because of drop due co "wire drawing", as the valve closes.* 

The expected expfansion line then begins at 6, at a lower pressure than B. 
Because of this condition and the fact that condensation continues, part 
of the stroke, say to c, a point at which the temperature of the steam and 
cylinder walls are considered the same. 



94.7 
90 




Fig. 100. — The expected diagram. Having drawn the theoretical card A B C D E, success in 
obtaining the proper diagram factor depends upon the experience and judgment of the 
designer which guides him in sketching in the expected diagram a b c d e f g, which he 
"expects" will represent the actual performance of the engine when built and operating 
under the specified conditions. 

Expansion beyond c, will evidently take place at temperature lower 
than that of the cylinder walls, which is regarded as practically constant. 
Accordingly re-evaporation of some of the steam previously condensed 
will take place causing the expected curve to approach and rise above the 
theoretical curve between c and d. 

At d, pre-release occurs, the gradual opening of the exhaust valve causes 
a pressure drop, represented by the rounded end or toe d e. Release is 
taken at 2 lbs., and represented by a Hne extending from e, to some point 



NOTE. — In the Corliss engine this loss is reduced to a minimum owing to the very quick 
movement of the valve, but the act of cutting off steam in any valve gear is far from being 
instantaneous. 



102 THE STEAM ENGINE 



/, selected by the designer at which the exhaust valve closes, that is, at 
which compression begins. 

The compression curve extending from/, to g, may be sketched in by eye, 
or if greater accuracy be desired, by constructing a hyperbolic curve, 
based on the clearance. The latter in the Corliss engine may be taken at 
21/2 to 3% of the piston displacement. 

3. The expected M. E. P. 

This is determined from the area of che expected card, fig. 100, by means 
of the following formula: 

expected m. e. p. = ^^^^ ^^ ^^^^ Xpressure scale (1) 

length of card 

The area is best obtained by use of a planimeter, or approximately by 
ordinates (explained in figure 81). In this case the area is by planimeter; 
length of card 4 ins., and pressure scale 40.. Substituting these values in (1) - 

expected m. e. p. =^i^-^X40=34.2 lbs. per sq. ins. 
4 

4. Cylinder dimensions. 

In Case I, a 36'' stroke was selected for future excess power demands, 
and a 30" stroke where such provision was not made. Substituting the value 
34.2 lbs. per sq. ins. expected m. e. p. in the formula for the 36 ins. stroke 



.=V 



85 

000004X36X100X34.2"-^^'-^ ^^^- ^^^ ^^ ^^^• 



As in Case I, the cylinder dimensions could be either 13X36, or 13X30 
according to conditions and judgment of the designer. 



STEAM ENGINE PARTS 103 



CHAPTER 3 
STEAM ENGINE PARTS 



The numerous parts of which an engine is composed may be 
divided into three classes with respect to operation, as 

1. Stationary; 

2. Revolving; 

3. Reciprocating. 

The stationary parts are the cyhnder, frame and bed plate; the revolving 
parts, the shaft, eccentric; the reciprocating parts, the piston, piston rod, 
crosshead, connecting rod, valve, and valve gear. Of these various parts 
■ the greatest proportion are reciprocating, and these, especially in the case 
of high speed engines, must be of* minimum weight consistent with proper 
strength to avoid undue vibration, thus, the skill of the designer is shown 
by his treatment of these parts. 

The Cylinder. — This consists of a cylindrical chamber, 
as shown in figs. 101, and 102, bored true, and in which is 
fitted a steam tight piston, free to move from one end to the 
other. 

The distance in which the piston, during its stroke, is in 
contact with the cylinder is called the bore. To prevent a 
"shoulder" being formed at either end by the action of the piston, 
the diameter at these points is enlarged so that the 'piston 
slightly over travels the bore. The enlarged sections are known 
as the counter-bore. 

The cylinder is closed by two covers called cylinder heads. These are 
secured to the flanged ends or jaces by bolts. All bearing surfaces are 
finished smooth and true and a steam tight joint is made at each face by 



104 



STEAM ENGINE PARTS 




STEAM ENGINE PARTS 



105 




I 



106 STEAM ENGINE PARTS 



inserting a gasket, that is, a thin sheet of packing cut to size, and then bolting 
the parts firmly together. 

The distance between the faces of the cylinder is such that the piston 
does not touch either head when at the end of the stroke. A small space 
is always left between to prevent contact. This volume plus the volume 
of the steam passage betv/een the cylinder and the valve seat is called the 
clearance, and is expressed as a percentage of the volume displaced by the 
piston in one stroke. 

The term clearance is also used to denote the distance between the 
cylinder head and the piston when the latter is at either end of the stroke, 
being called the linear clearance. 

A hole is bored through one head for the piston rod, a steam tight joint 
being made by means of a stuffing box. This consists of a cylindrical 
chamber, of somewhat larger diameter than the rod. The annular space thus 
left around the rod is filled with fibrous, or metallic packing which is com- 
pressed so as to form a tight joint by a hollow sleeve called a gland. The 
latter is forced into the stuffing box to bring the necessary pressure on the 
packing by adjusting the two bolts. In some cases a screw stuffing box is 
provided, similar to the one shown for the valve stem; this is a lighter 
construction but is liable to come unscrewed unless locked. 

The cylinder has a projection on one side called the steam chest in which 
is the valve. The steam chest is closed by a plate known as the valve or steam 
chest cover; this is fastened to the steam chest by bolts, a gasket being 
placed between the bearing surfaces to make a tight joint. 

In operation, steam passes from the steam chest to the cylinder ends 
through the steam passages, between which is the exhaust passage. 

At the beginning of these passages is a smooth flat surface on which the 
valve moves and which is called the valve seat. 

The two openings in the valve seat to steam passages are called the steam 
ports, and the opening to exhaust passage the exhaust port. Careful dis- 
tinction should be made between the terms passages and ports. 

The valve as shown overtravels the length of the seat to prevent the 
formation of a shoulder by wear, and also, in the case of unbalanced valves 
to reduce the load on the valve pressing it against its seat due to the steam 
pressure, as when the steam edge of the valve overtravels the seat limit, the 
pressure on that portion of the valve not in contact with the seat is neutral- 
ized. Motion is transmitted to the valve by the valve stem. A stuffing box 
is provided to make a steam tight joint at the point where the valve stem 
passes out of the steam chest. 

Loss of heat by radiation is partially prevented by covering the cylinder 
with asbestos or other insulating material. For external appearance and 
to protect the insulating material, it is covered with a wooden or metallic 
lagging. 

An interior view of a steam chest is shown in fig. 102. The valve being 
removed, the valve seat is exposed showing the steam and exhaust ports. 



At the side of the cyHnder is a projecting flanged pipe which forms the 
outlet from the exhaust passage. 

The depression at the farther end should be noted; this terminates the 
valve seat and allows the valve to overtravel for reasons already explained. 

There is a slight projection on the two side walls of the steam chest which 
is planed smooth to serve as a guide for the valve in its direction of travel. 
It also permits the valve being made narrower than the steam chest so that 
it may be easily inserted. These projections are sometimes omitted. 



Fig. 103. — Harris-Corliss cylinder with steam jacket. The section in black is the liner or 
working barrel, around which live steam circulates. The object of a jacket is to reduce 
condensation withm the barrel or cylinder proper. 

Jacketed Cylinders. — Sometimes a liner or working barrel 
of somewhat smaller diameter is fitted to a cylinder as shown 
in fig. 103, leaving an annular space all around through which 
live steam circulates. The object of this is to supply heat to the 
walls of the barrel, to make up for that abstracted during expansion 
and exhaust, so that at admission, the walls will be as hot as 
possible, thus preventing condensation or reducing it to a 
minimum. 



108 STEAM ENGINE PARTS 

In general, the greater the number of expansion, the greater the 
reduction of feed water consumption due to the use of a jacket."^ 

Prof. Schrooter from his work on the triple expansion engines at Augs- 
burg, and from the results of his tests of the jacket efficiency on a small 
engine of the Sulzer type in his own laboratory concludes as follows: 
1. The value of the jacket may vary within very wide limits, or even 
become negative; 2, the shorter the cut off, the greater the gain by the use 
of a jacket; 3, the use of higher pressure in the jacket than in the cylinder 
produces an advantage ; 4, the high pressure cylinder may be left un jacketed 
without great loss, but the other should always be jacketed. 

■ The usual method of fitting liners or working barrels to cylinders to form 
steam jackets are shown in figs. 104 to 106. The construction is such that 
the liner is free to expand or contract independently of the cylinder casting, 
a steam tight joint being made between the two by means of an ordinary 
stuffing box packed with fibrous packing. 

For equal conditions, the gain by jacketing is greater for small cylinders 
than for large, because in small cylinders the cylinder surface per unit 



*NOTE. — ^A test of the Laketon triple expansion pumping engine showed a gain of 
8.3 per cent by the use of the jackets, but Prof. Denton points out that all but 1.9 per cent of the 
gain was ascribable to the greater range of expansion used with the jackets (Trans. A. S. M. E., 
XIV, 1412). 

NOTE. — The value of the steam jacket may be judged from the experiments of Bryan 
Donkin made at Bermondsly on a single vertical experimental engine. The details of the 
engine are: Size 6X8; Meyer valve gear; barrel and heads jacketed, also valve chest cover, 
steam is supplied to each of the four jackets direct from the boiler by a separate pipe. By 
special arrangement the water from the cylinder body jacket was divided into two portions 
and the weight of them given separately. The first portion consisted of the steam condensed 
on the inner vertical surface of the jacket due to the heat passing through the walls into the 
cylinder; the other portion that condensed on the outer vertical surface of the jacket due to 
heat uselessly radiated outwards owing to_ imperfect external covering. Observations were 
taken with small thermometers inserted in one-eighth inch holes, drilled into the metal 
walls and filled with mercury. In all experiments the feed water always included the whole 
of the jacket water. 

Mr. Donkin found that with about 50 lbs. boiler pressure, running condensing, the 
saving due to the jacket was: 40.4% at 6.8 expansions; 40.1% at 6 expan.; 38.5% at 4.8 
expan.; 31.1% at 3.7 expan.; 23.1% at 1.8 expansions. In Mr. Donkin's experiments, the 
temperature of the cylinder itself was observed at various points between the inner and outer 
surface by means of thermometer inserted in small holes drilled in the metal. When the 
jackets were in use the mean temperature of the metal was almost equal to that of the 
steam on admission; when the jackets were not in use it was some 50° lower. The temperature 
as shown by the thermometer was nearly uniform from inside to outside; for the periodic 
chilling of the innermost layer of metal by re- evaporation of condensed steam was too super- 
ficial to be at all fully exhibited in this way. From the experiments it may be inferred that the 
smaller the cylinder, the greater is the percentage of gain from the use of a steam jacket 
arising doubtless from the fact that a small cylinder gives a larger jacket surface for a given 
weight of steam passing through it, than a larger cylinder does. i2nd report of research 
committee on the value of the steam jacket.) 

Other engines experimented upon were: Compound jet condensing beam pumping 
engine; triple expansion pumping engine; compound mill engine. For full particulars of 
Donkin's experiments see Pro, Inst. Mech. Eng. 1892, page 464. 



STEAM ENGINE PARTS 



109 



weight of steam passing through the engine is greater than in large cylinders. 
In some cases the jacket is so constructed that steam supply for the engine 
is used for the jacket, passing through the jacket on its way to the engine. 

Stuffing Boxes. — By definition, a stuffing box is a device 
affording passage and lengthwise or rotary motion of a piece, as 





FLANGF. 





W^\^ 



Figs. 104 to 106. — ^Various methods of fitting liners to cylinders. Fig. 104 is a form of liner 
having a flange at the bottom end secured to the cylinder by sunk head bolts. At the other end 
a steam tight joint is secured by a stuffing box with packing ring. Fig. 105 shows a liner with 
recessed joint at one end and at the other a plain contact joint reinforced by caulking a soft 
copper ring into a dovetailed groove. The figure shows a method of draining condensate 
from the top head by the pipe siphon. Fig. 106 shows a method of bolting the liner fast 
at the top with bolts spaced as far around the cylinder as the ports will admit. Although this 
method has been employed on U. S. Cruisers, the author does not consider it good practice. 
In fitting, the liner is forced into place but because of the danger of bringing too much strain 
upon the cyhnder, the fit cannot be made tight enough to eliminate leakage, hence the 
necessity for stuffing boxes. The flanged joints at the bottom may be made tight with a 
gasket but usually a heavy coat of red lead or mastic cement is sufficient. 

of a piston rod or shaft, while maintaining a fluid tight joint about 
the moving part. 

In construction, there is an annular space around the moving part, 
closed by an adjustable flanged bushing or gland so that when the annular 



110 



STEAM ENGINE PARTS 



14. 

(IRIU&TAPrORH'>><l*l 
AT'B'FOROILCUP 




. DPtuaTAproB 

IfWASTC-PIPCAT'A* 



CROSSHCAD END 

Fig. 107. — Duplex block metallic packing (U. S. Metallic Packing Co.), for stationary and 
marine engine piston rods and valve stems. This packing is in two independent sections, 
separated by the dividing piece 10, the upper section consisting of white metal rings 13, wnth 
vibrating cup, follower, etc., being in the stuffing box, and the lower section consisting of 
blocks 4, with horn rings, sliding plate, ball joint, etc., being contained in the gland 1. The 
upper or inner set of packings consists of three babbitt metal rings 13, each in three parts, 
contained in the vibrating cup 12. There is a ground joint between the flat face of the 
vibrating cup 12, and the dividing piece 10. Above the babbitt metal rings 13, come the follower 
14, and the upper spring bushing 15, in pockets in which are contained the upper follower 
springs 16, and then in the bottom of the stuffing box the preventer 17, varying in length 
according to the depth of the box. As the dividing piece 10, is bolted to the face of the stuf- 
fing box independently of the gland 1, which contains the lower or outer set of packing, 
the blocks in the lower set may be renewed or any other necessary work done to same with- 

f out taking down the upper set of packing or in any way disturbing it. The lower or outer 
section of the packing consists of eight blocks 4, babbitt lined, which are held in rings 5, 
having horns holding springs 6. The packing blocks are put together in sections four blocks 
to a section. Each section is composed of two working blocks and two guide blocks. The 

k joints between the blocks in each section are at right angles to each other, thus "breaking 
joint." Small follower springs 9, in pockets are also used'behind the follower plate 7. The 
combination of the sliding plates and ball ring 2, having ground surfaces, allows for the move- 
ment of rods out of line. The spring pressure is so regulated as to merely hold the parts in 

• place when the engine is running without steam. A hole is drilled in the gland at A for a 
nipple and .globe valve so that condensation can be drained off. The parts are: 1, gland; 
2, ball ring; 3, sliding plate; 4, blocks; 5, horn rings; 6, horn ring springs; 7, follower 
plate: 8, spring bushing; 9, follower springs; 10, dividing piece; 11, swab-holder plate; 

' 12, vibrating cup; 13, babbitt rings; 14, follower; 15, upper spring bushing; 16, upper 
follower springs; 17, preventer. 



STEAM E^^GINE PARTS 



111 



space is filled with fibrous packing the proper pressure may be applied to 
same to secure a tight joint. 





Figs. 108 and 109. — Stuffing box which forms a steam tight joint for the piston or valve stem. 
By means of the adjustable sleeve, the proper pressure Is brought to bear on the packing 
to prevent leakage of the steam. 




Figs. 110 to 115. — Various types of stuffing box Fig 1 10 shows a piain box with ■jtud adjust- 
ment; fig. 113, plam box with screw adjustment. Figs. Ill and 114 show the long sleeve type 
of box, these being identical except that m fig. 1 1 4 the sleeve ha.^ spaced grooves, as an extra 
provision against leakage In construction the sleeve is an accurate sliding fit with the rod and 
is secured by the flange which is Held in a stuffing box, the latter not only serving to prevent 
leakage around the outside of the sleeve but to allow lateral movement ot the sleeve to 
accommodate it to any irregularity in the movement of the rod. Figs, 1 1 2 and 1 15 show two 
types of metallic packing of the ring iorm. The rings have parallel faces and are held be- 
tween the collars of a cast iron casing and the segments are pressed in\ward upon the rod 
by circumferential springs. In fig. 1 12, each ring is oivided radially into three segments, and 
the two rings in one compartment break joint, oeing kept in place by little dowels which 
projec . into the gap in the elastic confining ring. The casing is divided lengthwise in halves. 



112 STEAM ENGINE PARTS 

In some cases the end surfaces of the annular chamber containing the 
packing are flat but usually are slightly conical to force the packing against 
the rod. The accompanying cuts show various types of stuffing box, and 
forms of packing used in same. 

In design, the length and diameter of the stuffiing box depends on the 
material used and the working pressure. In the case of horizontal cylinders 
when the stuffing box becomes also a bearing, it may be made longer. 
For the valve stem, the box is proportionately deeper than for the piston rod. 

In general, the stuffiing box may be from 2 to 3 times the diameter of the 
rod, and its diameter from 1 ^ to 1^4 times diameter of rod. 

In some cases packing under pressure is dispensed with and a long plain 
sleeve depended on for a tight joint, the long close sliding fit between the 
rod and sleeve preventing leakage. The plain sleeve may be modified with 
several grooves spaced along its length to arrest the motion of any steam 
tending to leak through. 

The Piston. — A piston may be described as a device for 
receiving the pressure of, or operating upon, a liquid or gas in a 
cylinder or other enclosing vessel, 

Pistofis may be classified: 

1. With respect to shape, as 

a. Cylindrical {|°J^,^. " 

h. Conical; 

c. Rectangular. 

2. With respect to motion, as 

a. Reciprocating; 
h. Oscillating; 
c. Rotating. 

3. With respect to the action of the steam as 

a. Single acting ; 
h. Double acting. 

The cylindrical reciprocating piston is the most usual form and consists 
essentially of a disc attached to a rod and having rings which press against 
the cylinder walls to secure a steam tight joint. 

For high speed engines, especially those of the marine type, where the 
center of gravity of the engine must be a minimum, the piston is usually 



STEAM ENGINE PARTS 



113 





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LU 



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a: 

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zo 








II 


iiL 




iiU 


mm 




It 




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1 


w 




'ff 


iin 



if 



114 



STEAM ENGINE PARTS 




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O 

X 

in 



tH W^ rt g u, ^ 
^^ (U > 0+3 CO 

£5 73 :3 o S3^ o 



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shaped like a cone, as this gives 
minimum weight, thus reduc- 
ing vibration; its shape per- 
mits shortening the height of 
the engine because the stuffing 
box projects very Httle if any 
beyond the cyHnder head. 

A rectangular reciprocating 
piston consists of a square 
plate arranged to move to and 
fro in a rectangular box the 
steam pressure being received 
on the ends. 

iVn oscillating piston is 
virtually the same as a re- 
ciprocating piston, but be- 
cause of the lateral stresses, 
it is designed preferably with 
a wider rim giving more bear- 
ing surface to reduce wear. 




Fig. 125. — Early junk packing. This 
packing could neither be examined 
nor renewed without removing the pis- 
ton from the cylinder. To Remedy 
this, the groove was made v/ithout 
a flange at the end farthest from the 
crank, and a false flange called a junk 
ring was bolted to the piston to retain 
the junk in place and admit of its 
being removed without taking out 
the piston. The term "junk ring" 
is still in use although junk is no 
longer used to pack pistons; a better 
term is follower ring. 

Rotary engines have a rec- 
tangular rotating pistoix or 
rectangular plate oscillating 
in a sector cylinder and 
attached to a rack shaft or an 
eccentric or toothed cam. 

The distinguishing feature 
of the various type of piston 
are shown in the accompany- 
ing cuts. 



STEAM ENGINE PARTS 



115 



The three essential requirements of a piston are: 

1. Strength to withstand the pressure of the steam. 

2. A steam tight joint between its circumference and the 
' cylinder walls ; 

3. Ability to move with very little friction. 

SNAP RriSfGS 




y///////////////^ A 



^///////////////////. 



y//////////////// /A 




Fig. 12G. — "Snap" piston rings. First used by Ramsbottom, an English engineer, and some- 
times called "Ramsbottom 's rings." They are turned somewhat larger in external diameter 
than the bore of the cylinder, and after being cut across so that they may be compressed 
to fit the cylinder bore, are fitted into recesses turned in the piston face. 



According to Seaton, in the early days, owing to imperfect tools, cylinders 
were not bored true nor were the sides very smooth. Since the steam 
pressures at that time were quite low, pistons could be made steam tight 
by coiling rope or junk soaked in melted tallow in a groove on the rim of the 
piston as shown in fig. 125. 



SNAP RINGS 





EXTENDED FOLLOWER 



Fig. 127. — Snap rings fitted to extended follower, 
taking out the piston. 



This permits removal of rings without 



The gradual increase in steam pressures soon caused the junk packing 
to give way to something more substantial. 

Ramsbottom was the first to introduce metallic rings for piston packing. 
These rings, of small rectangular cross section, are turned somewhat larger 
in external diameter than the cylinder bore, and after being cut across, 



116 



STEAM ENGINE PARTS 



enough metal is filed off at the cut so as to compress them to fit the cylinder 
with the proper tension. The piston is turned to an easy fit and the rings 
fitted into recesses turned in its edge. 



BULL RING 




FOLLOWER RING 

rr:\ f. 




PACKING RINGS 



Fig, 128. — Snap rings fitted to hull ring. This is a modified form of the junk ring, the projecting 
spigot which carries the snap rings is cast separate as shown. The bull ring is held in place 
by a follower plate. 




m 



Figs. 129 and 130. — Mode of turning snap rings to secure uniform pressure along the circumfer- 
ence. The ring is cut at the thinnest section. 



vm [ 



I 



Figs. 131 to 133. — Different methods of cutting snap rings. 



STEAM ENGINE PARTS 



\Vi 



These rings are usually called snap rings, since in putting them on the 
piston they "snap together" when they fall into the recesses. 

In fig. 126 is shown a piston fitted with two snap rings ; when placed so the 
joints are not in Hne, the piston is practically steam tight. This is a de- 
sirable arrangement for small, quick running engines, but for large engines 
it has the objection that the rings cannot be removed without taking out 
the piston. This is overcome by fitting an extended follower consisting of 
a ring having cast with it a cylindrical extension, which goes down into a 
recess, and which is bolted to the outside face of the piston, snap rings being 
fitted into recesses turned on the outer circumference of the spigot as shown 



FOLLOWER PLATE 




SPRINGS 



TONGUE PIECE 



Figs. 134 and 135. — Box piston. To reduce weight, large pistons are usually cast hollow with 
radial ribs. A single packing ring is shown pressed against the cylinder bore by the springs S. 
The ring joint is closed by a tongue piece T. 

in fig. 127. By removing the bolts, the extended follower which carries the 
snap rings may be easily removed from the cylinder. 

A modification of this arrangement consists of casting the extension 
separate. It is then called a hull ring and as shown in fig. 128 is held in place, 
together with the packing rings, by another ring called the follower ring. 

Snap rings are usually made of tough, close grained cast iron, and turned 
eccentric as shown in fig. 129, being cut at the thinnest part. The object of 



118 



STEAM ENGINE PARTS 



PACKING RIMG F^^^. 




Figs. 136 to 140.— Murray- 
Corliss hollow piston 
without follower. 



Figs. 141 to 144.-— 

Murray^ Corliss 
built up piston. 
The packing ring 
i s carried on a 3 unk 
ring, and retained 
in place by a fol- 
lower and follower 
plate. By un- 
" screwing thebolts, 
all these parts are 
easily taken out 
without removing 
the piston from 
the cylinder. 




STEAM ENGINE PARTS 



119 



this is to cause the ring to press against the cylinder bore with uniform 
pressure at all points on the circumference. 

The several ways of cutting snap rings are shown in figs. 131 to 133. Re- 
cesses for snap rings are turned deeper than the thickness of the rings to 
allow a transverse movement independent of the piston body, thus pro- 
viding for lack of alignment between the piston and the cylinder. 

In large cylinders, the necessary pressure of the ring against the cylinder is 
se<;;ured by means of a series of springs as shown in figs. 134 and 135. In this 
construction the packing ring usually consists of one large ring pressed 
outwards against the cylinder by springs, and retained in place by a follower 
plate. 




Fig. 145. — Box piston with wrought iron stay bolts instead of radial ribs, a lighter form of 
piston than that shown in figs. 134 and 135. 




Fig, 146, — Cone piston as used on high speed marine engines. By making the piston in the 
form of a cone great strength is secured, *thus reducmg the weight. 

For horizontal cylinders, the bottom spring is removed and a cast iron 
block put in its place, which takes the weight of the piston. 



In construction, the body of a piston is either made: 

1. SoHd; 

2. Hollow, or, 



120 



STEAM ENGINE PARTS 



3. Built up. 

For small engines, the solid type of piston is used, being simply a flat 
cast iron disc of sufficient thickness to receive the snap rings. 




Fig. 147. — Cone piston of forged steel; very light construction and a desirable form for boats 
of high speed. 



. PACKING 
RINGS 




HUB 

ADJU5TIN6 
" SCREW 

^FOLLOWER 
^ RING 
OUTER RING 

BULL RING 



PACKING RINGS 



Figs. 148 and 149. — Built up piston consisting of spider and bull ring with its packing rings, 
and follower ring. 



STEAM ENGINE PARTS 



121 



In the larger sizes, the piston is made hollow with strengthening ribs 
for reinforced by stay bolts to reduce the weight, as shown in figs. 134 and 135; 
this is called a box piston. Sometimes, instead of cast ribs, this form of 
piston is reinforced by wrought iron or steel stay bolts to further reduce 
the weight, as shown in fig. 145. 




Figs. 150 to 152. — Brownell piston, rings, and piston rod. The piston is of the solid type, 
cored and provided with two spring packing rings cut in such a manner that they make 
a steam tight joint. The piston is pressed on the rod by hydraulic pressure, and held in 
place by a nut. 

Where great strength and light weight are required, as in the case of 
high speed marine engines, pistons are made cone shaped, fig. 146, and for 
extreme light weight they are constructed of cast or forged steel, fig. 147, 
with one or more packing ringc; 




Figs. 153 to 156. — Chandler and Taylor piston nngs, piston rod crosshead and wrist pin. 
The piston is of the hollow cast iron type fitted with two snap rings. The piston rod is made 
of hammered crucible steel. It is fitted into the piston head on a taper, and is locked with a 
heavy nut. The piston rod is screwed into the crosshead. and is locked in position by a nut 
jammed tight against the boss on the crosshead. 

The built-up type of piston is shown in figs. 148 and 149. It consists of: 
1, a spider composed of several radial ribs, and a face cast with a central hub, 
and an outer ring; 2, a bull ring fitting over the outer ring and carrying 
the packing rings, and 3, a large follower ring enclosing the interior space 
of the piston and fastened to the spider by a number of bolts. The bull 
ring may be adjusted for proper alignment between the piston and the 
cylinder by means of the set screws. 



122 



STEAM ENGINE PARTS 



The Piston Rod. — The load due to the steam pressure acting 
on the piston is transmitted by the piston rod out through the 
stuffing box to the crosshead and connecting rod. The alternate 
stresses of compression and tension which come upon the rod 
in rapid succession, severely test the material of which it is made, 
and since it is desirable that the rod be of small cross section, 
it is usually made of the best steel. 

The piston rod has a uniform cylindrical shape except at the 
ends where it is joined to piston and crosshead. The rod should 




Figs. 157 to 159. — Different methods of fastening the piston rod to the piston. Fig. 157, shrink 
fit with shoulder, end riveted; fig. 158,.tapered joint secured by riveting; fig. 159 tapered joint 
with shoulder to prevent seizing, secured by a nut. 



fit steam tight into the piston and be firmly secured to the latter 
so as to hold it rigid against shocks. 

There are numerous ways in which the rod is fastened to the 
piston. 

A simple method consists in reducing the diameter of the rod at the end, 
leaving a shoulder and making a shrink fit between the rod and piston; 
the rod is then riveted to the piston as shown in fig. 157. While this makes 
a cheap and firm joint, it is objectionable in that the rod cannot be readily 
removed. 

To overcome this it is usual to make the end tapered or conical, as 
shown in fig. 158. If the taper be very slight the rod can be easily made a 
tight fit, but unless formed with a shoulder at the end of the taper, it will 
in time become so tightly held by the piston as to withstand all attempts at 
withdrawal, and there would be danger of splitting the piston by the 
wedging action. 



STEAM ENGINE PARTS 



123 



In fig. 159 is shown a rod. having a tapered end with a shoulder and secured 
to the piston by a nut. With the proper taper, this rod may be easily 
removed. 

Piston rods are sometimes fastened to large built up pistons by means of 
a key, as shown in figs. 160 and 161. 

The most usual method of securing the rod to the crosshead 
is a threaded joint and lock nut as shown in fig. 165. This has 
the advantage of permitting adjustment of the rod length so that 




Figs. 160 and 161. — Large built up piston secufed to the piston rod by means of a key. 



the clearance spaces at the cylinder ends may be equalized with 
certainty. 

The manner in which the rod is fitted to the crosshead de- 
pends somewhat on the type of the latter. 

A form commonly used for marine engines is shown in figs. 162 to 164, 
consisting simply of a shoulder, taper, and a nut for holding the rod in 
position. 

Aiother form used extensively in marine and other types of engines, 
consists in forging the body of the crosshead in one piece with the rod as 
shown in figs. 166 and 167. This construction has the serious objections, 



124 



STEAM ENGINE PARTS 



PISTON 
' ROD 




-TAPER 



double: 
WRIST Pin 




TOT'; 



,5TERN GIB 
AHEAD GiB 



Figs. 162 to 164. — Marine type of piston rod connection with crosshead, having a tapered 
joint secured by a nut. With this construction the height of the engine is reduced, lowering 
its center of gravity — a desirable feature for marine service. 




Fig. 165. — Usual method of securing the piston rod to the crosshead by a threaded joint wi^ii 
lock nut. 



STEAM ENGINE PARTS 



125 



however, that if anything happen to the rod, repairs are not so easily nor 
quickly made as when the rod is a separate part, and the rod cannot be 
removed without disconnecting it from the piston. 

On locomotives the piston rod is usually secured to the crosshead by means 
of a key, figs. 160 and 161, the end of the rod fitting into a tapered hole 
in the crosshead. 

When the engines are run intermittently and are * idle for 
long periods, special care should be taken to protect the piston 



FORGED 
ROD END 





llll lliliMIIMM^Illl 



Ix 



Figs. 166 and 167. — Piston rod and crosshead forged in one piece; an objectionable though 
common construction. 



rod from corrosion and pitting. If a rod become pitted, it will» 
be difficult to keep the stuffing box tight. "When an engine is 
to remain idle for a length of time, the packing should be removed 
and the rod well oiled. 

To prevent corrosion, rods are sometimes, made of phosphor 
bronze which has about the same strength as steel, and although 
more expensive is well worth the additional cost for engines which 
are to be run only occasionally. 



126 



STEAM ENGINE PARTS 



iTJ W jrt W ^ 

"^ U3 ►;> V* "^ C 







STEAM ENGINE PARTS 



127 



The Cross Head and Guides.— 

A cross head is simply a ''sliding 
hinge'' which joins the piston rod to 
the connecting rod. By means of 
guides, it prevents the bending of 
the former which otherwise would 
occur on account of the side thrusts 
of the connecting rod. 

The design of the cross head 
varies more than any other detail 
of an engine. 

It consists essentially of a body, fig. 

230, having two jaws B and C, between 

which the connecting rod is pivoted by 

the wrist pin W, fig. 231. This pin 

is inserted in holes bored in the crosshead body, and held firmly in place 

by a nut Z. At either side of the wrist pin are iDcaring surfaces M and S, 




Fig. 229. — ^A large cross head. 




Figs. 230 and 231.-^Cross head and wrist pin. The wrist pin W, is inserted in boles bored through 
the jaws B and C, c»nd the pin is secured by the nut Z. M and S, are the gibs, which bear on 
the guides, and N, the neck to which the piston rod is fastened. 



128 



STEAM ENGINE PARTS 



called gibs*. These run in suitable guides which take the side thrusts of 
the connecting rod. The two jaws come together in a neck N to which is 
attached the piston rod. 




Fig. 232. — ^Wrist pin with tapered ends. The pin is drawn into very firm contact with the 
cross head by the nut on the end. 




Fig. 233. — Wrist pin with cylindrical and tapered ends. A satisfactory method of attachment 
not requiring such precision in machining as when both ends are tapered. 



The usual form of wrist pin is shown in fig. 232. That part in 
contact with the cross head body is usually a tapered surface 
which can be drawn into very firm contact by the nut on the end. 



*NOTE, — ^The cross head gibs are sometimes called shoes or slippers. 



STEAM ENGINE PARTS 



129 



On loosening the nut, the pin is easily withdrawn. A key is 
usually inserted in the pin to prevent any turning. 




Fig. 234. — ^Wrist pin with tapered and threaded ends. This construction has the objection 
that the threads are liable to injury on account of the alternate transverse thrust to which 
they are subjected. 




Fig. 235. — Expanding wrist pin. The ends are split and cylindrical, fitting accurately the 
holes in the crosshead jaws. An inner or expanding plug having tapered ends is drawn into 
the hollow wrist pin, thus expanding the ends, and firmly retaining the pin in position, an 
objectionable construction. 



On some crossheads only one end of the wrist pin is tapered while the 
other is cylindrical as shown in fig. 233. 

Another form of wrist pin is tapered at one end and threaded at the 



130 



STEAM ENGINE PARTS 



other, as shown in fig. 234, a lock nut being provided to retain the pin in 
position. 





Figs. 236 and 237. — ^Approved method of fastening wrist pin where only one side of the cross 
head is accessible. The pin which is tapered at both ends is held in place by bolts which 
pass through the flange. 




Pigs. 238 and 239. — Cross head with compression wrist pin. The cross head iaws A . B. are spht. 
and may be drawn together by the bolts M, S, which project slightly within the holes. These 
bolts register with notches N, N' cut in the wrist pin. When the pin is m position the jaws 
are drawn together by bolts, tightly gripping the pm. 



STEAM ENGINE PARTS 



131 




Some forms of wrist pin have no 
taper at the ends. In this class 
belongs the expanding pin as shown 
in fig. 235. The wrist pin is bored, 
and the bore tapered and split at 
each end where.it rests m the cross- 
head. To the taper in the pin is 
fitted a steel plug. In attaching the 
pin to the crosshead, the tapered 
plug, by means of a finely threaded 
end and nut, is drawn in, expanding 
the ends of the wrist pin against the 
sides of the crosshead This type of 
pin is used to advantage when only 
one side on the crosshead is acces- 
sible. However, the author's ex- 
perience with this pin is that unless 
it be a very close fit with the cross- 
head it will work loose after being 
expanded by the plug, hence, it is 
not to be recommended. 

A better method of fastening the 
wrist pin where only one side of the 
crosshead is accessible is shown in 
figs. 236 and 237. 

A form of wrist pin known as the 
compression type is shown in figs. 2 JS 
and 239; the ends of the pin are 
without taper. The pin which 
accurately fits the holes in the cross- 
head jaws is notched at each end to 
conform to the bolts which project 
within each hole. Each jaw is split 
as shown, hence, w^hen the pin is in 
position the bolts are tightened 
which causes the jaws to firmly grip 
the pin. Several notches are pro- 
vided at the ends of the pin so its 
position may be changed from time 
to time to prevent the pin becoming 
flattened on account of wear. 

The gibs of a crosshead may 
number one, two or four, but 
liberal bearing surfaces are pro- 
vided on account of the velocity 
with which they move. 



132 



STEAM ENGINE PARTS 



When a horizontal engine runs over, all the pressure and wear 
comes upon the lower slipper, as in fig. 240; if the engine run 
under, all the pressure and wear comes upon the upper slipper, 
as in fisf. 241. 




Fig. 242. — Cross head of the Reeves engine. A single bar machined on all four sides serves as 
the guides. This type is frequently used on marine engines. 

Since lubricants flow over the lower guide more easily than the upper, 
and since it is easier to resist the strain on the lower guide, as it usually 
rests on the bed plate, it is customary to cause horizontal engines to run 
over rather than under. 




Tics. 2-13 and 244. — Twin City Corliss cross head. Cylindrical gibs with cross wedge adjustment. 



The greatest pressure upon a guide occurs when the piston is 
near the middle of its stroke which gradually diminishes in intensity 
to zero at the end of the stroke. 

The pressure on the guide being, therefore, very small near the ends of the 



STEAM ENGINE PARTS 



133 



stroke it is not necessary that the entire surface of the gib be in contact 
■ witb the guide at these points. * Hence, the guides may be shortened without 
harm and the gib be allowed to overtravel to quite an extent as shown in fig. 
245. This is done to advantage in engines of very light weight or where parts 
may be made more accessible. In any case, the gib should overtravel the 
guide to prevent wearing a shoulder at the stroke ends, f 



The guides may he one, two or four in number. In marine 
engines quite frequently only one is used. 




Fig. 245. — -Detail of marine crosshead and guides illustrating overtravel. The gibs may pro- 
ject considerably beyond the end of the guide at the stroke ends, because the thrust on the 
guide diminishes to zero at the dead centers. The gibs should overtravel because a full 
length guide is unnecessary, and the parts are usually made more accessible by the shortened 
guides. 

In this case there are two constructions: 1. In which the guide is sur- 
rounded by the crosshead as shown in fig. 242 ; 2. In which the crosshead 
projection containing the rubbing surfaces is partially surrounded by the 
guide as shov/n in figs. 246 and 247. 



*NOTE. — The side thrust on the guide at any point of the stroke is obtained from the 
formula: side thrust = total load on the piston multiplied by the tangent of the angle which 
the connecting rod makes with the line of the piston rod =p tan0. When the connecting rod 
is 2^ times the length of the stroke (the usual proportion), the maximum angle of the con- 
necting rod with the line of piston is 11° 33' and the tangent of this angle is .204 or 
approximately .2, hence, the greatest side thrust on the guide is .2 or 20 per cent, of the 
maximum load on the piston. For a 2:1 connecting rod, tan =.258; for 3:1 rod, tan » =.169, 

tNOTE. — The pressure between the crosshead slipper and the guide should not exceed 
100 pounds per square inch of slipper surface. On many engines it is much less. In loco- 
motives the pressure ranges between 40 and 50 poimds on accotmt of dirt, cinders, etc. 



134 



STEAM ENGINE PARTS 



This type is in fact two guides in one, and is peculiarly suited to marine 
engines since the area of the backing guides B, B', need not be as great as 
that of the forward guide A. As a marine engine is run in the forward 
direction most of the time the backing guide may be of small area without 
harm, thus saving in weight and making the parts more accessible. 

Cross heads for marine engines are sometimes made without a 

wrist pin and carry instead, the 
wrist pin bearing, the pin in the 
construction forming a part of the 
connecting rod. 





Fig. 248. — Cross head of the Brown engine. It is of 
heavy design, with large wearing surfaces. The 
cross head pin is placed in the center of cross head 
so that there is no tendency towards a rocking 
motion. The gibs, which are Babbitt lined, are 
keyed up by a wedge and screw from the face of 
crosshead. This construction allows the removal 
of the gibs without taking the cross head from the 
guides. In adjusting the cross head, loosen check 
nut C, and turn screw B, to the left to drive wedge 
E, in and force the gibs D, out to the right to 
bring the gibs in. Thrust collar A, is pinned to 
adjusting screw B. 

Figs. 246 and 247. — Marine type of cross head 
and guides. The backing guides B, B', present 
less area than the forward guide A, a condition 
well adapted to marine service because the 
allowable thrust on the guide is greater in backing than when going ahead, since the engine 
runs only for short periods when reversed. More liberal surface should be allowed for the 
surfaces B, B. in the case of ferry boat engines, because tliis type of vessel runs equal periods 
in both directions. 




STEAM ENGINE PARTS 



135 



A marine crosshead of this type is shown in figs. 166 and 167. This is 
formed on the end of the connecting rod and is objectional in some respects 
as previously mentioned. 

Stationary engines sometimes have crossheads designed for 
four guides, as shown in figs. 249 and 250, which is a view of 
the Porter-Allen crosshead and wrist pin. 




CLJJ 



Figs. 249 and 250. — Cross head and wrist pin of the Porter-Allen engine. This type which has 
four guides is used extensively on engines having Tangye frames. The wrist pin has tapered 
ends. 





Figs. 251 and 252. — Murray-Corliss crosshead, having cylindrical gibs with wedge adjustment. 
Besides the adjusting bolts with lock nuts, two other bolts are provided to prevent the 
possibility of their becoming loose. 



136 



STEAM ENGINE PARTS 



Locomotive cross heads are made for one, two and four guides 
as shown in figs. 253, 254, and 255, 256. 

Y 




Fig. 253. — Locomotive cross head with single guide. On locomotives the piston rod is usually 
attached to the cross head by means of a key K. h, h' , are the gibs, and A, the guide whose 
outer end is bolted to a transverse piece or yoke Y. 




Figs. 255 and 256. — Locomotive cross head with four guides. The end view at the left shows 
more clearly the location of the guides, and the form of the yoke which supports their outer 
I ends. 



STEAM ENGINE PARTS 



137 



^P In general the rubbing surfaces of the gib and guide may be 
either plane, inclined or cylindrical.* 

The gibs are usually made of some other metal because there is less fric- 
tion between rubbing surfaces of dissimilar metals than when made of 
the same metal. Brass, white metal and other alloys are used for gibs. 
They are usually of brass with babbet, or white metal inserted into grooves 
or circular holes. 

On account of the ease of alignment the cylindrical or turned gib is 
generally used. 




Figs. 257 and 258.— Fishkill-Corliss crosshead. The cylindrical gibs are adjustable by means of 
transverse eccentric keys as shown in the sectional end view. A key is used to secure the 
piston rod. 



To allow for wear between the rubbing surfaces, gibs are made 
adjustable. There are various methods of adjustment, the 
simplest of which is the insertion of paper liners between the 
gib and crosshead body. 

Another mode of adjustment is by means of inclined surfaces, moved by 
bolts, or eccentric keys. 



♦NOTE. — Cast iron, hard and close grained is considered the best material for guides. Its 
surface after a few hours' work becomes exceedingly hard and highly polished and offers very 
little resistance to the gib. So long as this hard skin remains intact, no trouble will be experienced, 
but if abrasion take place from heating or other cause, it rarely works well afterwards and 
should at once be planed afresh. 



138 



STEAM ENGINE PARTS 




Figs. 2.'9 and 260. — Fulton-Corliss cross head._ The gits wS, S, have cylindrical faces, and are 
fitted .to the inclined surfaces M, M', being adjustable by the nuts B, C, and B', C, on studs 
A, A'. 



Fig. 261 .— Reeves-Cubberley cross 
head for vertical engine show- 
ing sectional view of wrist pin 
and bearing with oiling device. 
In the cup there is a partition 
A, as shown, oil from the vertical 
pipe fills the oil cup on both 
sides of the partition A. One 
side of the partition connects 
with channel E, through which 
the top half of the cross head pin 
D, and connecting rod box B, is 
lulDricated. When pressure is 
relieved between surface of pin 
D, and rod bearing B, oil on in- 
side of the partition in cup 
flushes this space with oil; with- 
out this partition A, in the cup, 
oil would settle to the bottom 
of cup and the top surface of 
the pin would not get oil as it 
now does. Of course, the bot- 
tom side of cross head pin and 
bearing C,is oiled through chan- 
nel F, in the manner described 
above. 





STEAM ENGINE PARTS 



139 



There are numerous modifications of this mode of adjustment 
as shown in the accompanying cuts. 




Fig. 262. — Cross head of Ames single valve engine. It is of semi-box section and fitted both on 
top and bottom with removable shoes spotted with babbitt forming about 40% of the wearing 
surface. The tapered pin is held in position by four tap bolts passing through the head of 
the pin. By removing these four bolts and replacing in tapped holes provided in the flange, the 
pin may easily be drawn from the cross head without the use of a sledge, making it possible 
to remove and replace the pin from the front side of the engine. The pin may be turned 
90° when worn to provide new wearing surfaces. 




Fig. 263. — Clyde hoisting engine cross head and guide. The cross head is of the single bar 
locomotive type and is fitted with bronze gibs. In reversing engines^he cross heads are 
furnished with bronze gibs for both top and bottom sides of guide bar. The bar, as shown, is 
recessed at each end to permit over-travel of the gib, thus preventing the wearing of shoulders. 
These recesses also retain the oil. 



140 



STEAM ENGINE PARTS 



The first named method of adjustment by inclined surfaces is shown in 
figs. 259 and 260. The gibs S, S', rest on inclined surfaces M, M', of the 
cross head, and by moving them to the left they will be spread further 
apart. By this means wear may be taken up between the rubbing surfaces. 
A stud A, attached to either side of the cross head, passes through a projection 
on each gib. The gibs are retained in any position by means of these studs 
and the nuts B, C, and B', C 




Figs. 264 and 265. — Harris-Corliss cross head. The gibs have V shaped faces with wedge ad- 
justment. A movable, concealed wedge operated by the through bolt, permits the adjust' 
ment of the gibs without any lengthwise movement of the latter. 





Figs. 266 and 267. — Split type of cross head, and wrist pin. The neck is threaded to 
receive the piston rod. Instead of the usual lock nut, the neck is spht, and the two halves 
made to grip the rod by means of cross bolts as shown. This type of joint is satisfactorv 
when the machining is carefully done; a loose fit will cause trouble. 



STEAM ENGINE PARTS 



141 



To make the adjustment, nut B, is first loosened and then nut C, tight- 
ened until the gib is in the desired position, nut B, is then tightened which 
locks the gib in place. 

There are numerous modifications of this mode of adjustment 
as shown in the accompanying cuts. 

The cross head shown in figs. 264 and 265 has the rubbing surfaces inclined 
and the adjustment for wear is made by concealed wedges operated by 
fore and aft adjusting bolts. 

Adjustment by means of eccentric keys is shown in figs. 257 and 258. The 
gibs are fitted with four tapered keys which work crosswise; the con- 
struction is plainly shown in the two views. 

Cross heads are attached to piston rods by screwed joints, or 
by means of keys. 




Figs. 268 and 269. — Eclipse Corliss connecting rod. The type generally used on slow and 
medium speed engines. The rod of circular section tapers from the middle to the forged ends 
which contain the crank and wrist pin brasses. As constructed, one adjustment lengthens 
the rod, while the other shortens it, the combined effect is to keep the length the same. 



In the first method, either a lock nut is provided to prevent the rod 
turning, or else the neck of the cross head is split forming a split bushing 
as shown in fig. 266. The rod, after it is screwed into the bushing, 
is clamped by two bolts with lock nuts. The principle here employed being 
the same as with the wrist pin in fig. 239. In either case, first class machine 
work is necessary as more or less trouble is experienced with a loose fit. 

The Connecting Rod. — The to and fro or reciprocating 
motion of the piston is converted into a rotary motion by the 
connecting rod, which joins the crosshead to the crank. The 
connection is made by the wrist and crank pins, for which there 
are suitable bearings at the ends of the rod. 

The length of the connecting rod, measured between the 



142 



STEAM ENGINE PARTS 



centers of the wrist and crank pins, is usually two to two and a 
half times the length of the stroke; the latter proportion, says 
Thurston, giving a long and easy working rod, and the former 
a rather short, but yet a manageable one. 

The rod must be strong enough to resist not only the alternate 
stresses of tension and compression, but also the bending stresses 
due to its oscillation. 




^ 



/r-T~^ 



1^ 1^^ '- 



^ 



^ 




Figs. 270 and 271. — Ball and Wood connecting rod. This is the form of rod used on high speed 
engines. The rectangular cross section, and the pronounced sidewise taper is the best shape 
to resist the severe bending strains due to high rotative speed. 



For engines of slow and medium rotative speed, the rod is usually of 
circular cross section, tapered from the center to both ends as shown in 
figs. 268 and 269. 

In high speed engines, the rod is made of rectangular section as shown 
in figs. 270 and 271, which is a better shape to resist the bending strains. 

Most connecting rods are made of steel while the bearings or 
brasses are of brass lined usually with Babbitt metal. The rod 
ends are solid or built up. 

There are various arrangements for adjusting the brasses to 
take up wear, such as: 



STEAM ENGINE PARTS 



143 



1. Blocks; 

2. Bolts; 

3. Gibs and cotters. 

Figs. 272 and 273 show a solid end with block adjustment. A rectangular 
slot is cut in the enlarged section in which is inserted the brasses A and B, 
having suitable flanges C and D, to retain them in the slot. A wedge shaped 
block E is fitted to the slide upon B, thus bringing A and B closer together 
and reducing the size of the bearing. Two bolts, F and G, are threaded in 
the ends of the block to secure it in position. 

To adjust the bearing, F is first loosened and then G tightened to the 
desired amount. The block is then locked in place by tightening F. 




v-^ 


-'11^ 


"T^ 1 








i i^ 


f^=^ 


_>--^ 


-^11 .- 


i=^ 





Figs. 272 and 273. — Solid end with block adjustment; used extensively on Corliss connecting 
rods for both the wrist pin and crank pin. The parts are: A, B, brasses, A being provided 
with flanges C, D; E, adjusting block or wedge; F, G, adjustment bolts which retain the 
block in the desired position. 



On marine engines the adjustment is usually made by means of bolts 
especially at the crank end, as shown in figs. 274 and 275, on account of the 
ease with which it is disconnected from the crank. The rod ends in a T sec- 
tion A, upon which is placed the brasses B and C and an iron or steel cap D. 
Two bolts E and P pass through these several members, securing them 
firmly together. A set screw G locks the bolt nuts. 

Sometimes the set screw is omitted and the two nuts provided for each 



144 



STEAM ENGINE PARTS 



bolt which serves the same purpose. Liners H, are inserted between the 
brasses to prevent them seizing the pin when the bolts are tightened. 

To adjust this bearing the bolts are first loosened and then one or more 
liners removed or replaced as the case may be, the bolts tightened, and 
the nuts locked by the set screws. 





() r 


i\ 




1 ■ ML 

! 4^' 




a 




i ' 


1/ 




Figs. 274 and 275. — Marine connecting rod with forked end and double bearing for the wrist 
pin. To the T end A, is attached the brasses B, C, and cap D, by the bolts E and F. 



On large bearings, as shown in fig. 276, the brasses are hollowed out at 
A, and B, to save metal, some provision being made so that the bolts will 
not turn with the nuts. * 




Fig. 276.— The Phoenix connecting rod. The crank pin end is of the marine type while the 
wrist pin end is solid with block adjustment. The illustration shows the arrangement of 
oil grooves, and the recesses in the brasses to retain the Babbitt lining in place. 

*NOTE. — The bolts are usually turned with part of their length reduced to the diameter 
of the bottom of the thread. This makes the bolt more elastic without reducing its strength. 



STEAM ENGINE PARTS 



145 



The wrist pin end of a marine rod is made in several ways. 
It may be : 

1. A solid end with block adjustment as shown in fig. 276; 




"Fig. 277. — Marine connecting rod with forked wrist pin end; the two branches carry the wrist 
pin. 

2. A. forked end having two arms 
to which is attached the wrist pin 
{^g^ 277);. 

3. A forked end carrying two 
wrist pin bearings, as shown in 
figs. 274 and 275. 

In the second mentioned construction 
it should be noted that the wrist pin 
is made fast to the rod instead of to the 
crosshead. This requires that the cross- 
head contain the bearing. 

Many marine engines of the smaller 
sizes have this type of rod end. Figs. 
279 to 281 show the style crosshead 
used with rod in position. 

In figs. 282 and 283 is shown a built up 
rod end with gib and cotter adjustment.* 
The rod end A which is of enlarged rec- 
tangular cross section and the brasses 



Fig. 278. — Marine connecting rod with forked wrist pin end, containing a double bearing for 
the wrist pin. The advantage of this form of rod is that the height of the cyUnders may- 
be less than with other types; it is difficult, however, to make uniform adjustment of the 
two bearings. 




^OT'S.— Continued. 

hence, it is better able to resist the severe shocks that come upon it. To provide for uneven 
adjustments each bolt is made large enough to carry two-thirds of the load and so pro- 
portioned that the stress on it does not exceed 5,000 pounds per square inch at the smallest 
cross section. Since in adjusting the bolts more pressure is liable to be brought on one than 
the other, two-thirds of the load should be considered as being carried by one bolt in determining^ 
its size. 



146 



STEAM ENGINE PARTS 



lii Ol 




Figs. 279 to 281. — Detail of connecting rod with wrist pin in forked end and cross head contain- 
ing wrist pin bearing. 




?IGS. 282 and 283. — Built up connecting rod with gib and cotter adjustment. The parts are: 
A, stub end of rod; B and C, brasses; D, strap; E and F, cotters; G, gib; H, set screw. 



STEAM ENGINE PARTS 



147 



B and C are held together by a strap D, two cotters E and P and the gib G. * 
The latter is a wedge shaped key, which on being driven in, forces the 
strap to the right, thus bringing the brasses closer together. The gib is 
retained in the desired position by the set screw H. . 

Sometimes the cotters E and P are omitted and the strap fastened to 
the rod, as shown in figs. 284 and 285, by the bolts A and B. The brasses 
are adjusted by the gib G which has a threaded end and nut C. At E is 
shown a wiper oil cup. 




U-UlLULGj 




Figs. 284 and 285. — Built up connecting rod cotters. The cross bolts A and B secure the strap 
to the stub end of the rod. The gib G is adjusted at the stud end C. A wiper oil cup for a 
horizontal rod is shown at E . 



Two other methods of gib adjustment are shown m figs. 286 and 287. 
In each case the gib is attached to a bolt; in fig. 286 the bolt forms a part 
of the cotter, and in fig. 287 the cotter is omitted, the bolt being threaded 
into the rod end. 



*NOTE. — The thickness of the gib or key is usually one-fourth of the width of the strap, 
and the breadth parallel to the strap should be such that the cross section will hav^e a shearing 
strength equal to the tensile strength of the section of the strap. The taper of the gib is gen- 
erally about five-eighths inch to the foot. 



148 



STEAM ENGINE PARTS 



If, 9,s a result of adjusting the brasses of a connecting rod, its 
length be changed, the clearance at the two ends of the cylinder 
will be altered. 




Figs. 286 and 287. — Two methods of gib adjustment, 
forms part of the cotter; fig. 287, cotter omitted. 



Fig. 286. — Gib attached to bolt which 



To prevent this, the rod is sometimes constructed in such a way that 
tightening up the brasses at one end lengthens the rod, and tightening at 
the other end shortens it as shown in fig. 288, where taking up wear at 
the crank pin end pushes the outer brass in and shortens the rod, while a 

rm 




Fig. 288. — Twin City CorHss connecting rod with soHd ends and block adjustment. The 
blocks or adjusting wedges are on the same side of the pins, thus tending to maintain a 
constant length of rod. 

similar adjustment at the wrist pin end moves the inner brass outward 
and lengthens the rod. Thus, the effect of the two adjustments tends to 
keep the rod length the same. 



A modification of the solid end rod is shown in fig. 287, which 



STEAM ENGINE PARTS 



149 



is a desirable rod for a large engine; it is known as the "hatchet 
end" type. 

By this arrangement, when the bolt is removed from its position it allows 
a side of the strap to be taken out, so that the rod can be easily lifted off 




Fig. 289. — The "hatchet" end type of connecting rod as used on the Harris-Corliss engine. 
A desirable form for large engines, permitting easy removal of the brasses. 

the pin. The adjustment of the brasses is made by means of concealed 
blocks, set up by adjusting bolts. 

On some rods the end is made removable instead of the side. A rod of 
this kind is shown in fig. 290. The block A at the end is dovetailed to fit 




Pig. 290.-; — Connecting rod of the Ames engine. The extreme end is a separate piece removable 
by taking out the end bolts. The brasses are then easily accessible. The rod is provided 
with block adjustment. 

the ends of the fork and is held in place by a large bolt as shown. By re- 
moving the bolt and block, the bearing may be taken out from the rod 
for inspection without disturbing the adjustment. 



In single acting engines it is not' considered necessary by some 
to use refined methods of taking up wear. 



150 



STEAM ENGINE PARTS 



Fig. 291 shows the connecting rod used on the larger sizes of Westing- 
house vertical single acting engine, no special provision being made for ad- 
justment. 




Fig. 291. — The Westinghouse connecting rod for high speed, short stroke engines. On account 
of the large cyhnder diameter in proportion to the stroke, the bearings are of unusual size 
for the length of rod. 

The strap is held rigid in place by two tap bolts passing through the rod 
end and threaded into one side of the strap. The bronze bearings are lined 
with Babbitt metal and are kept in place sidewise by flanges which embrace 
the sides of the strap and rod. 

When lost motion becomes unusually large it may be taken up by in- 
serting between the stub end of the rod and the bronze, one or more pieces 
of thin sheet steel known as shims or liners. 




Fig. 292 illustrates the general proportion of a 
rod suitable for a short stroke high speed engine. 

The rod ends are very large in proportion to the 
length of the rod. This results from the large cylinder 
diameter as frequently in engines of this class, the 
diameter is greater than the length of the cylinder, 
and the length of the rod with respect to the stroke is 
usually less than for ordinary service. 

Ques. What is a * 'gudgeon"? 

Ans. A gudgeon is an obsolete name for a 
wrist pin. 



Fig. 292. — Sturtevant connecting rod for vertical singie engine. The rod is an open hearth 
steel forging. The marine type crank pirt box is of babbitted malleable iron or semi-steel, 
dependent on size. The wrist pin box is also of the marine type, except in the larger sizes, 
which are of the solid end type with wedge adjvstment. 



STEAM ENGINE PARTS 



151 



Oues. Is the full force exerted on the piston trans- 
mitted to the crank? 

Ans. Only at the dead centers. At any other point of the 
stroke, part of the force is transmitted as a side thrust to the 
guides. 

Oues. When a force is thus divided into two or more 
forces acting in different directions what are they called ? 




Fig. 293. — Parallelogram of forces showing the two component forces at the crosshead due to 
the thrust of the piston. By means of this diagram the pressure on the guides and on the 
crank pin can be obtained. 



Ans. Components. The original force is called the resultant 
because it is the equivalent of the several component forces. 

Oues. How may component forces such as those pro- 
duced by the action of a connecting rod be measured ? 

Ans. By drawing a parallelogram of forces as in fig. 293. 

In the skeleton diagram of the moving parts of an engine, the line of the 
piston is extended, and with any suitable scale the distance A B marked 
off so that it will represent the total load on the piston. 

For instance, if the total load on the piston be 500 pounds, and the scale 
taken be 100 pounds to the inch, then A B will be five inches. 

At A, the center of the wrist pin, the force transmitted to the piston rod^ 
by the piston will split up into two component forces, one acting in the 
direction of the connecting rod and the other acting perpendicular to the 



152 STEAM ENGINE PARTS 



guide. The intensity of these forces is found by drawing Hnes through B, 
parallel to the directions in which they act, giving the points C and D. By 
measuring A C and A D, with the same scale as was used in laying off A B, 
-and multiplying by the pounds per inch the intensity of the forces is 
obtained. 

The thrust on the guide, when the connecting rod is at its maximum angle 
with the axis of the piston rod, may also be found by the formula: 

Thrust =^ tan ^ 
in which 

p = total load on the piston, 
B = maximum angle of connecting rod 
The angle 0, is the angle whose sine = 3^ stroke of piston -i- length of 
connecting rod. Its values for rods of different lengths are: 

Ratio of length of connecting rod to stroke 2 23^2 3 

Maximum angle of the connecting rod 14° 29' 11° 33' 9° 36' 
Tan e .258 .204 .169 

Example. — If the total load on the piston be 5,000 lbs., and the length 
of the rod be 2H times the stroke, then the maximum thrust on the guide is: 
5,000 X.204 = 1,020 lbs. 

Oues. How does the thrust of the connecting rod act 
on the crank pin? 

Ans. It is split up into two component forces. One acts in 
the direction of a tangent"^ to the circle described by the crank 
pin which causes the crank to turn, and the other acts in the 
direction of the axis of the crank arm which causes the shaft 
to press against its bearing. 

Thus, in fig. 294, the thrust of the connecting rod is split up at A, into two 
component forces, one acting in the direction of the tangent A M, and one 
in the direction of the axis A O. By laying off A B, equ-al to the thrust of 
the connecting rod, and completing the parallelogram of forces, the points 
C and D, are obtained giving the lines A C and A D, whose lengths repre- 
sent the intensity of these forces. 

Oues. What is the component A C, called? 

• Ans. The tangential, or turning force. 



*N0TE. — A tangent to a circle is a straight line drawn through a point on its circum- 
ference and perpendicular to a line joining this point at the center. . 



STEAM ENGINE PARTS 153 

Oues. What is the nature of this turning force? 

Ans. It is always less than the force acting on the piston. 
It increases from zero at the dead center to a maximum near 
the center of the stroke and then diminishes to zero at the end 
of the stroke. 

Oues. Since the turning force is always less than the 
force acting on the piston, is there not a considerable loss 
of power caused by this peculiar action of the connecting 
rod? 



Pl5T0^4 



CROSS 

PISTON ROD HI 




Fig. 294. — Parallelogram of forces showing the two component forces at the crank pin. By- 
means of this diagram the tangential force or "turning effect" can be obtained for any- 
crank position. 

Ans. No. Neglecting friction, the same amount of work 
that is done on the piston is delivered to the crank pin by the 
connecting rod in turning the shaft. 

Oues. Why is there no loss of power? 

Ans. Because during each stroke, the crank pin travels a 
greater distance than the piston. Hence, the smaller turning 
force by acting through a longer distance, does the same amount 
of work as the larger force on the piston acting through the 
shorter distance. 

Work is the product of two factors: force and distance through which 
the force acts. These two factors are inversely proportional for a given 



154 



STEAM ENGINE PARTS 



amount of work; that is, if one factor be increased, the other is diminished 
a Hke amount. For instance, to raise one pound ten feet requires the same 
amount of v/crk as is required to raise ten pounds one foot, or two pounds 
five feet. 

Now, in a steam engine, while the crank pin is revolving at a constant 
tangential speed*, the speed of the piston is ever varying. 

Oues. What is the nature of the motion of the piston? 

Ans. It starts from rest at the beginning of the stroke, 
increasing to a maximum near the middle, then diminishes until 
it again comes to rest at the end of the stroke. 




-M 

FORWARD 



3^V R' 



Fig. 295. — Diagram showing the effect of the angularity of the connecting rod. For equal 
crank pin movement from each end of the stroke, the angularity of the rod causes the piston 
to travel further on the forward stroke, than on the return stroke. 

The conditions which prevail at the piston and crank pin clearly illus- 
trate the inverse relations which exist between the factors /orce and distance 
for a given amount of work as can be shown by a series of diagrams. 



Owes. What effect does the connecting rod have on the 
movement of the piston? 

Ans. Starting at the beginning of the forward stroke, the 
inclination or angularity^ of the rod with respect to the cylinder 
axis, causes the piston to move somewhat more than half its 



*NOTE. — The tangential speed of a point revolving in a circle is its equivalent speed if 
it were moving in a straight line. Thus, the speed of a belt as it leaves a pulley is the tan- 
gential speed of a point on the face of the pulley. 

fNOTE.^ — The "angularity" of the connecting rod is sometimes called the obliquity. 



STEAM ENGINE PARTS i 155 

stroke while the crank is moving the first quarter of its revolution, 
somewhat less than half stroke during the second and third 
quarters, and again somewhat more than half stroke during the 
fourth or last quarter of the revolution. 

In fig. 295 is shown the effect of the angularity of the rod in distorting 
the movement of the piston. In the diagram the piston is not shown 
since its position with respect to the stroke corresponds exactly to that of 
the wrist pin C. 

The connecting rod is shown in two positions, C R and C R', such that 
the crank pin has traveled equal distances A R and B R' from the dead 
centers. The piston positions are indicated by C and C\ the piston having 
traveled on the forward stroke the distance M and on the return stroke the 
distance S. For equal crank pin travel from each end of the stroke, it is 
thus seen that the piston travels further on the forward stroke than on 
the return stroke 

Were it not for the angularity of the rod, the piston would travel the 
equal distance M' and S'. The connecting rod then increases the piston 
travel by a distance N C on the forward stroke and diminishes it by a dis- 
tance N' C on the return stroke. 

Oues. On what does the amount of this distortion of 
the pistdh movement depend? 

Ans. On the length of the connecting rod. 

The shorter the rod the greater the distortion. 

Oues. What important effect has the angularity of the 
rod on the steam distribution to the cylinder? 

Ans. It causes cut off to occur too late on the forward stroke, 
and too soon on the return stroke. 

Ques. What is a ''Scotch yoke?" 

Ans. A device sometimes used instead of a connecting rod. 

It consists of a metal frame similar to a Stevenson link but with straight 
sides as shown in fig. 298. To the center of one side is attached the piston 
rod. A continuation of the rod from the other side passes through a bearing 
which prevents any side movement of the yoke. The crank pin passes 
through a block which slides to and fro in the yoke. 



156 



STEAM ENGINE PARTS 



Oues. What are the advantages of a Scotch yoke? 

Ans. There is no distortion in the piston movement and the 
crank shaft may be placed nearer the cyHnder than with a 
connecting rod. . 

Oues. Why then has it been displaced by the con- 
necting rod ? 

Ans. Because the good features of a Scotch yoke are more 
than offset by the friction and wear of the block and by the 
extended piston rod and outer bearing. 



SCOTCH YOKE 




Fig. 296. — The "Scotch yoke." Used to some extent on early engines. Its advantages are 
overbalanced by several objections, such as friction and wear of block, extended piston rod, 
outer bearing, etc. 

The Crank Shaft. — The to and fro, or reciprocating motion 
of the piston is converted into rotary motion by the crank shaft 
which consists of: 

1. The shaft; 

2. The crank arm; 

3. The crank pin. 

In construction, the crank shaft is either built up from separate 
parts or made from a solid forging. 

According to the type of engine, it may be classified as: 



STEAM ENGINE PARTS 



157 



1. Overhung crank; • 

2. Center crank; 

3. One, two or more throw according to the number of 
cylinders. 




KETVWAVlBEAieiNG | 

I \ 



KCYWAV 



I I 

I BC./\f?ING| 

I i 

Fig. 297.; — Usual form of shaft for a stationary engine. The crank arm is fitted to the end A, 
which is turned to slightly reduced diameter. The keyway in the central portion is for the 
fly wheel. 



In the built up type as generally used on stationary engines, 
the shaft itself consists of a cylindrical piece of suitable length 
as shown in fig. 297. 

A portion of the shaft, A, upon which the crank is fastened is sometimes . 
turned to slightly smaller diameter, thus forming a shoulder against which 
. the crank is driven when being fitted. The length B is made such that there 
is sufficient room for the bearings, valve gear and fly wheel. Two keyways 
are provided, as shown in the figure, so that the crank and the fly wheel 
may be keyed to the shaft and thus prevented turning on the latter. 




ri_V WHEEL. 



I BEWRINq 



Fig. 298.— Approved form for a long shaft carrying a heavy fly wheel. The enlarged central 
portion gives stiffness to prevent springing. 



On an engine having a heavy fly wheel and long shaft, it is 
usual to make part of the shaft tapered as shown in fig. 298. 
This gives great strength to resist bending stresses. 



158 



STEAM ENGINE PARTS 



In some cases, instead of reducing the shaft diameter for the crank as 
in fig. 297, a shoulder is formed by a projection or flange as shown in 
fig. 299. 

The crank consists of an arm with a boss at each end, one to take the 
main shaft and the other the crank pin. The arm is made soHd, or of webbed 
cross section as shown in figs. 300 and 301. 




Fig. 299. — Crank end of shaft with flange instead of shoulder, 
diameter of the shaft is not reduced at the crank end. 



With this construction the 



The crank is secured firmly on the shaft by making it a drive or shrink 
fit and further secured by a key. * 

The shrinking is done by boring out the hole a shade smaller than the 
shaft, then heating the crank around the hole, thus causing the material 
to expand and the hole to become larger. The crank is then placed on the 
shaft, and on cooling it contracts and grips the shaft with great firmness. 




Figs. 300 and 301. — Webbed crank arm. The crank is usually fastened to the shaft with a 
drive, or shrink fit, and further secured by a key. The parts shown are: A, shaft; B, 
webbed crank arm; C, crank pin; D, boss at shaft end; D', boss at pin end; E key. 



The crank pin is usually forced in place by hydraulic pressure, or fitted 
by shrinkage and the end riveted as at D' in fig. 300; as a rule no key is 
provided. 

The proportions between the diameter and length of the crank pin vary. 



*NOTE. — The standard proportions for a key are: width =>^ of the shaft diameter, 
thickness = }i of the shaft diameter. 



STEAM ENGINE PARTS 



159 



On slow running engines long pins may be used to advantage, but high 
speed engines require short pins in order to bring the pin closer to the 
main bearing and thus reduce the bending stresses set up by the inertia 
of the connecting rod. It should be noted that for a crank pin of given 
bearing area,* the longer the pin, the cooler will it run. This is because the 
smaller the diameter, the slower the speed of rubbing. 

The way in which cranks are shrunk on to crank pins and 
crank shafts is often objectionable and responsible for many 
subsequent failures, both of shaft and crank pin. 




Pigs. 302 and 303.— Two forms of crank pin. The first is objectionable in that the sharp 
edge of the hole in the crank arm may cut into the pin and start a crack. This danger is 
avoided by the construction shown in fig. 303. 



Where a shoulder is provided as shown in fig. 302, the result is that 
when the crank is shrunk into position on the pin or shaft, as the case may 
be, the sharp edge of the hole in the crank cuts into the material with a 
shearing action and starts a crack which afterwards, under the influence 
of alternating stresses, develops into a fracture, and frequently, as ex- 
perience has shown, leads to a serious breakdown. To avoid this, the 
crank and shaft may be constructed as shown in fig. 303, the part which is 
shrunk on the crank being of slightly larger diameter and of a length 
exactly equal to the thickness of the crank, so that the shrinkage of the 



*NOTE. — The size of the crank pin should be such that the pressure per square inch of 
projected bearing area (that is, the diameter multiplied by the length) should not exceed 
300 to 400 pounds for stationary engines, 400 to 500 pounds for marine engines and 800 to 900 
pounds for paddle wheel engines. 



160 



STEAM ENGINE PARTS 



crank has no tendency to cut into the material and so start an incipient 
fracture. 

The radius of the crank arm is measured from the center of 
the shaft to the center of the crank pin. The throw of the crank 
is equal to the diameter of the crank pin path, that is, the stroke 
of the piston. 




Pig. 304, — Built up crank shaft of the Rollins engine. The crank pin is carried by a disc which 
is counter-balanced. Hydraulic pressure is used to force the pin and shaft in place. 

Built up crank shafts are sometimes constructed with a cast 
iron disc instead of a crank arm as shown in fig. 304. 

The portion of the disc opposite the pin is usually made thicker than 
the other part, the extra weight being used as a balance to the weights of 
the reciprocating parts and known as a counter-weight. In high speed engines 
this is desirable to reduce vibration. The disc is attached to the shaft by 
the methods just described. 



The center crank shaft is usually composed of two lengths 



STEAM ENGINE PARTS 



161 



of shaft, each provided with a disc or arm and having one crank 
pin joining the two, as shown in fig. 305. 

This is the construction usually found in stationary engines. 

In the higher class of engine construction, the crank shaft is made from 
a solid forging for the small and medium sizes, the rough forging as de- 
livered from the forge hammer has the form as shown in fig. 306. The crank 
is first slotted out (fig. 307), then turned in the lathe and finished as shown 
in fig. 308. When counter-weights are provided, they are usually made 
separate and clamped to the crank arms. 





c 






c 




\r^t^'s\ 




p 









Fig. 305. — Built up crank shaft, consisting of two shaft lengths S, S'; two cranks C, C, and a. 
crank pin P. In the built up crank shaft the pieces are usually fitted together by shrinking 
and keying. 




Pigs. 303 to 308. — Construction of a forged center crank shaft. Fig. 306 shows the rotifli 
forging. It is first placed in a slotting machine which removes the metal between the crank 
arras, as in fig. 307, and then turned in a lathe and finished as shown in fig. 308. 



162 



STEAM ENGINE PARTS 



Fig. 309 shows a forged crank shaft with counter-weights attached 
by transverse bolts. There are various methods of attaching these weights. 

In figs. 310 and 312, the discs have V shaped grooves in the side 




Fig. 309. — Crank shaft of the Erieco engine having counterweights attached by transverse 
bolts. 




Figs. 310 and 312. — Crank shaft of the Watertown engine. The counter balance discs are 
fitted to V shaped grooves. 




Fig. 313. — Crank shaft assembly of Watertown engine, shown disassembled in figs. 310 to 312. 



STEAM ENGINE PARTS 



163 




164 



STEAM ENGINE PARTS 



Figs. 314 and 315 show a two throw crank shaft for a compound engine, 
and figs. 316 and 317 a three throw for a triple expansion engine. The 
former has its cranks set at 90^ and the latter at 120°. The order of the 
crank positions is called the sequence of cranks. 



Crank shafts for marine engines, when about 10 inches 
diameter are generally -made in duplicate halves, so that in case 






Fig. 318. — Duplicate section for large multi-cylinder crank shaft. 




Fig. 319.— Taper flange bolts for connecting sections of large built up crank shafts. The 
absence ot a hexagonal head improves the appearance of the joint. 

of damage to a part only half the shaft is condemned, and a 
spare half shaft can be carried on foreign voyages. 

By this plan there is less labor replacing the damaged half than if the 
whole shaft be moved. 



STEAM ENGINE PARTS 165 



• Flange couplings are usually provided at both ends, so as to be reversible 
in case of a flaw showing near the after end. Crank arms are forged with 
the shaft ends, or shrunk on and keyed. The pins are usually shrunk into 
eyes in the arms. 

Large crank shafts are usually built up from duplicate sections, there 
being a section for each crank These have flange connections as shown in 
fig. 318. The several sections being connected by ordinary bolts or taper 
bolts as shown in fig 319. The latter type of bolt requires no head, thus 
giving the flange connections a less clumsy appearance. 



The Main Bearings. — These are the bearings in which the 
crank shaft turns as distinguished from other bearings of the 
engine. The object of the main bearings is to support the 
weight of the shaft and fly wheel, and to hold the former in 
place at right angles to the axis of the cylinder, also to receive 
the pressure due to that portion or component of the thrust 
in the connecting rod which is not spent in turning the crank.* 

The three requirements of a bearing are: 

1. That it be of such size that the pressure of the shaft on 
each square inch of the bearing will be sufficiently low to prevent 
heating ; 

2. That there be means of conveying oil to tHe rubbing sur- 
faces; 

3. Provision for adjusting the bearing to take up wear. 

A simple bearing consists of a box, cap, two brasses, liners 
and bolts to hold the parts together. This kind of bearing is 
used on vertical engines as shown in fig. 320. 

The upper bearing surface or brass B is let into lower brass B', B being 
fitted into a cap C. Both brasses are kept from turning by dowel pins D 
and D'. The brasses are cut away at L and L' and the space filled with 
thin strips of sheet metal or liners; these, together, with the brasses are 
held firmly in place by the bolts M and M'. 



*NOTE. — This force was explained in the section on connecting rods. 



166 



STEAM ENGINE PARTS 



A small hols O, is drilled through the cap and upper brass to convey oil 
from the lubricating device to the bearing and shaft. 

Adjustment for wear is made by taking off the upper bearing and re- 
moving one or more liners from each side. The cap is then replaced and 



/^ v^ "v^ s 




I'iG. 320.— ;-Main bearing for a vertical engine; adjustable by means of the bolts and liners 
on the sides. 




Fig. 321. — Main bearing with liner adjustment for a horizontal engine. The brasses ar3 
divided obliquely so that the resultant thrust of ^he shaft will come centrally, and not 
at the joints. 



STEAM ENGINE PARTS 



167 



the parts again firmly bolted together. Some of the liners are very thin 
so that adjustment may be made with precision. 

This form of bearing is sometimes used on horizontal engines, in which 
case the brasses are divided obliquely instead of horizontally, so that the 
resultant thrust of the shaft will press against the brasses centrally and 
not in the direction of the liners. This construction is shown in fig. 321. 

The type of bearing just described is called a two piece hearing 



ENGINE FRAME 
6 




Fig. 322. — ^A "four piece" main bearing, as generally used on Corliss and other horizontal 
engines. There are two side brasses A and B, an upper brass C, and a lower brass D. Owing 
to the great weight of the wheel, little or no pressure comes on the upper brass C. The 
greatest wear comes on the side brasses, which are adjusted by means of the wedges E', 
and F. 



in distinction from the more complicated form, or four piece 
hearing as generally used on horizontal engines. 

In this bearing the brasses are divided into four parts, because, on medium 
and low (rotative) speed horizontal engines, having large and heavy fly 
wheels, the resulting pressure of the shaft on the bearing is practically in 
a horizontal direction. Hence, in order to have this pressure come centrally 
on a brass instead of at the junction of two brasses, they are arranged as 
shown in fig. 322. 



168 



STEAM ENGINE PARTS 



A and B, are two side brasses, and C and D, upper and lower brasses. 
C and D, are made long enough so that at their extremities, they rest upon 
A and B ; hence, by means of the two adjustable bolts 1 and 2, the four 
brasses are prevented moving in a vertical direction, the cap being secured 
by the bolts 5 and 6. The side brasses A and B, have their outer sides 
inclined which abut against the adjustable wedges E and F. 

To take up wear, the side brasses are forced nearer together by adjusting 
the bolts 3 and 4, which are attached to the wedges E and F. The upper 
brass C, may be adjusted by filing off sufficient metal at the lower extremities, 
and tightening bolts 1 and 2. 



SCREW 
ADJUSTMEWT 



ENGINE 
FRAME 




Fig. 323. — Main bearing of the Skinner engine having screw adjustment, of the outer brass. 



Sometimes liners are inserted between the upper and side brasses, forming 
an easy mode of adjustment. 

The lower brass D, is raised for wear by inserting liners between it and 
the bearing box. In some designs wedge adjustment is provided for the 
lower brass. 

The side brasses are sometimes fitted with screw adjustment in place of 
wedges. On some engines, as shown in fig. 323, only one outer side brass A, 
is adjustable. In this construction, the adjustment always being made on 
one side changes the position of the shaft which makes the cylinder clear- 
ance unequal, unless liners be inserted between box and opposite brass. 



STEAM ENGINE PARTS 



169 




Figs. 324 and 325. — Detail of locomotive driving journal box and assembly in frame. In fig. 
324, A, is the box proper which carries part of the weight of the engine, C, being the bearing. 
Underneath a receptacle B.is filled with cotton waste which is saturated with oil for lubri- 
cation. B, is held in position by two pins P P', as in fig. 325. Th.e box is arranged so as to slide 
up and down in the jaws of the frame. A spring S, is then placed over the box and above the 
frame as shown, resting on a W, shaped saddle G, which bears on the top of the box. The frame 
is suspended to the end of the spring by rods or bars R R', called spring hangers. Since the 
boiler and most of the other parts are fastened to the frames, their weight is suspended on 
the ends of the springs, which cushion the weight they bear. 



170 



STEAM ENGINE PARTS 



Figs. 324 and 325 show detail of locomotive journal box and 
assembly in frame. 

On stationary engines, not self-contained, the second bearing 
for the shaft is called the outboard hearing, and as the stresses 




Fig. 326. — Outboard bearing and pillow block of the Murray- Corliss engine. By means of the 
wedge, bolts, and set screws as shown, the position of the bearing may be adj-usted either 
vertically or horizontally. All engines that are not self-contained should have this type of 
outboard bearing to secure precision in alignment. 




GAUG 



OILING 
RINGS 



DRAIN 




Figs. 327 and 328. — Self -oiling bearing. The oiling rings which dip into the oil reservoir be- 
neath the bearing, in turning with the shaft, carries oil up to the bearing. A glass gauge at 
the left indicates the height of the oil in the reservoir. 



STEAM ENGINE PARTS 



171 



here are less severe, simpler means of adjustment for the brasses 
are provided. 

• Other important adjustments are here necessary. In erecting the engine, 
it would be difficult to get the bearing in line if it were attached direct to 
the foundation, hence provision is made whereby the bearing may be moved 
both up and down, and sidewise. The bearing together with this means of 
adjustment is called a pillow block, the usual construction being shown in 
fig. 326. A wedge A, is inserted between the base B, of the bearing and the 
base plate C. By turning the screws D, and E, the wedge is moved alcn^ 
the inclined surface F which raises or lowers the bearing. 

A sidewise adjustment is made by means of the screws F and C. 




Figs. 329 and 330. — Detail of main bearing of a marine engine showing method of fastening 
the bearing bolts on large engines. 

In making these adjustments the holding down bolts 1, 2, 3, 4 are first 
loosened and then tightened after making the adjustment. Two large 
anchor bolts M, S, secure the pillow block to the foundation. 

A projecting rim R extends around the base plate which retains the 
waste oil from the bearing. Usually a pipe is attached to the base plate 
to allow the oil to drain a vessel. 

The Fly Wheel. — In order to keep the reciprocating parts 
of a steam engine in motion at the dead centers, a large heavy 
wheel is attached to the shaft which by its momentum^ acts as 
a reservoir of energy. 

*NOTE. — Momentum is the power of overcoming resistance possessed by a body by reason 
of its motion and weight. It is that which makes a moving body hard to stop. 



172 



STEAM ENGINE PARTS 



In other words, the excess power produced by the engine in 
the early part of the stroke is stored up in the fly wheel, and 
given out by it in the latter part where little or no power is 
developed on account of the expansion of the steam and the 
engine passing the dead center. 

The fly wheel, therefore, on account of its inertiaf, tends to 
keep the speed constant in spite of the variable turning effect 
produced during the stroke. 




Figs. 331 and 332. — Southern pillow block and pedestal. The pillow block has both vertical 
and horizontal adjustments, whereby the engine shaft may be readily adjusted without 
jacking up shaft. The construction is such that the pillow block may be removed from sole 
plate without disconnecting the latter from foundation. The journal is lined with Babbitt 
metal. The pedestal bearing was designed to meet the demand for an outer bearing that would 
add to the appearance of engine and engine room, and avoid the necessity of extending 
♦ masonry of outer pier through floor of engine room, which is always more or less objectionable. 
The base has large bearing surface, and rests in same plane as engine. Wear is taken up by 
means of adjusting screws and quarter boxes; the upper and lower bearings adjust them- 
selves automatically to the shaft. Pedestal has oil catch basins, and approved method of 
lubrication. 



tNOTE. — Inertia is that property of a body on account of which it tends to continue 
in the state of rest or motion in which it may be placed, until acted upon by some force. 

NOTE. — The moment of inertia of the weight of a body with respect to an axis is the 
algebraic sum of the products of the weight of each elementary particle by the square of its distance 
from the axis. The moment of inertia varies in the same body, according to the position of 
the axis. It is the least possible when the axis passes through the center of gravity. To Mnd 
the moment of inertia in a body, referred to a given axis, divide the body into small parts 
of regular figure. Multiply the weight of each part by the square of the distance of its center of 
gravity from the axis. The sum of the product is the moment of inertia. 



|Hp In the ca^ 



STEAM ENGINE PARTS 



173 



k In the case of a single crank engine the variation of the turning 
"effect is large, while with triple expansion engines having three 
cranks at 120°, the variation is reduced considerably. It is 
clear, therefore, that a large and heavy fly wheel is more nec- 
essary for a single crank engine than for one of the same power 
with three cranks. 

The four cycle gas engine is an example of extreme fly wheel require- 
ments. Here there is only one impulse or power stroke in two revolutions; 
hence, the fly wheel must receive, during the power stroke, enough energy 




Fig. 333.— Various types of Vilter fly wheels. 



to keep the engine moving at approximately uniform speed during the 
three non-power strokes against the back pressure of exhaust, suction and 
compression. The large fly wheels fitted to gas engines clearly indicate 
the variable and intermittent nature of the turning effect.* 

On small engines, power is usually transmitted direct from 
the fly wheel, there being no separate pulley for the belt. 

The diameter of the fly wheel is governed by conditions of 



*NOTE. — So far as turning effect, that is, the number of impulses per revolution, is 
concerned, one double acting steam cylinder is equivalent to two gas engine cylinders of the 
two cycle type, or four, of the four cycle type. 



174 



STEAM ENGINE PARTS 



service, and limited by the tangential velocity, that is, by the 
speed at the rim, or its equivalent, the belt speed. 

Owing to the centrifugal force"^ which increases with the speed 
and which tends to burst the wheel, it is not advisable to run 
fly wheels at a rim speed higher than 6,000 feet per minute, or 
roughly, a mile a minute, f 




Figs. 334 and 335. — Harris- Corliss ordinary split belt wheel. Wheels of 9 feet and less 
diameter are made whole, and those from 10 ft. to 17 ft., are made in halves fastened by- 
turned bolts driven into reamed holes. Each half is provided with four oval arms, a center 
rib, increasing in depth toward the arm, and a return flange follows the outer edge of the 
wheel on both sides. All wheels above 14 ft. diameter, made in halves, have the rim joints 
made through the central arms, instead of between arms. 



Example, — How large a fly wheel could be safely used on an engine 
making 200 revolutions per minute? 



*NOTE. — This is the force which acts on a body revolving in a circular path, tending to 
force it farther from the center of the circle, because all moving bodies move in straight lines 
when not acted upon by external forces. 

fNOTE. — For any given material, as cast iron, the strength to resist centrifugal force 
depends only on the velocity of the rim, and not upon its bulk or weight. Chas. T. Porter 
states that no case of the bursting of a fly wheel with a solid rim in a high speed engine is known. 
He attributes the bursting of wheels built in segments to insufficient strength of the flanges 
and bolts by which the segments are held together. 



STEAM ENGINE PARTS' 



175 



Taking 6,000 feet per minute as the limit of rim speed, the distance 
traveled per revolution by a point on the rim, or the circumference of the 
wheel is : 

6,0004-200 = 30 feet, 
.from which, the diameter corresponding is: 

30-f-7r*=9.5 feet (approximately). 

It is important that an engineer should be able to determine 
the size of belt required to transmit a given horse power. There 




Figs. 336 and 337. — Harris-Corliss segmental belt wheel as used on large engines. Wheels 
18 feet and upward in diameter are constructed in segments, having 8, 10 or 12 segments 
in each wheel, and the same number of arms. The latter are of oval hollow construction, 
as shown in the section A A, this being the form which gives maximum strength. The flanges 
are planed to a fit. The arms are bolted to the rim segments and are held at the shaft be- 
tween the hub flanges. 



are any number of rules for belt sizes,' and the results obtained 
by their application are quite varied. The following rule which 
is easily remembered, will be found suitable for all ordinary cases; 



*NOTE. — TT (pronounced pi) is a greek letter used to denote the ratio between the diameter 
and circumference of a circle. Its value is 3.1416 (nearly); that is, the circumference of a 
circle is equal to 3.1416 multiplied by the diameter. 



176 



STEAM ENGINE PARTS 



it gives a belt width amply large to deliver the power without 
undue strain or wear. 



Rule. — A single belt one inch wide, traveling 1,000 feet per 
minute will transmit one indicated horse power. "^ A double belt 
will transmit twice this amount. 

Example. — What size double belt would be required for a 11" X 24" 
Corliss Engine with an 8 foot fband fly wheel, running at 110 revolutions 
per minute and developing 60 indicated horse power? 




Figs. 338 and 339.— Large fly wheel for Corliss engine. In this wheel, which is 28 ft. in diameter, 
the rim is made in segments and joined by heavy I links. The hub is in halves, and between 
the flanges of these halves, the inner ends of the arms are bolted. The unit division of the 
body of the wheel is one arm with its segment. The rim center is reinforced by side plates 
of cast steel, each of which covers the angle of two arm spaces, and they break joint on the 
two sides so that there is nowhere more than one link joint at any cross section of the rim. 
The whole rim is strongly fastened together by stout pins, which are forced into reamed 
holes by hydraulic pressure, then riveted cold. 



*NOTE. — This corresponds to a working strain of 33 pounds per inch of width. Some 
authorities give for single belts in good condition a working tension of 45 pounds per inch of 
width, and 64 pounds for a double belt. 

fNOTE. — The term "band fly wheel" means that the wheel has a wide rim for the belt 
so that no pulley is required. When a pulley is used, the rim is made narrow and thick so 
that the wheel will not take up much room in the direction of the shaft. 



STEAM ENGINE PARTS 



177 



Fig. 340. — Providence bal- 
ance fly wheel made in 
halves, principally used 
on engines directly con- 
nected to electric genera- 
tors, to a line of shafting, 
or in any service where 
belts or ropes are not used 
to transmit the power 
from the engine. 




Fig. 341.~Providence pul- 

. ley wheel made in halves. 

The rim joint is made at 

a point midway between 

the arms as shown. 



L78 



STEAM ENGINE PARTS 



The rim speed per minute of the fly wheel is : 

Diameter X tt X rev. per min. \ _ / f t. per min. 
8 X3.1416X 110 / ~ \ 2,765 feet. 

Since a single belt, traveling at 1,000 feet per minute, transmits one horse 
power per inch of width it will when run 2,765 feet per minute transmit: 

2,765^1,000 = 2.765 horse power. 




Figs. 342. — Turning a large Vilter rope wheel 



A double belt will transmit twice this amount or 

2.765X2=5.53 horse power. 

Hence, the width of a double belt for 60 horse power is 

60 -f-5.53 = 11 inches. 

The fly wheel rim should be somewhat wider than the belt, so as to lea^ 
a margin of 34 to 3^ inch on each side. This prevents the belt over running 
the rim by any sidewise movement due to uneven working. 




THE SLIDE VALVE 179 



CHAPTER 4 
THE SLIDE VALVE 



Oues. What is a slide valve?* 

Ans. A slide valve is a long rectangular boxlike casting 
designed to secure the proper distribution of steam to and from 
the cylinder. 

Its general form is shown in fig. 343. Here a portion of the valve is 
cut away exposing to view the exhaust edge of the valve, the exhaust port, 
bridges, and one of the steam ports. 

Oues. What other name is given to the slide valve? 

Ans. It is sometimes called the simple D valve], on account 
of its resemblance to the capital letter D turned with the fiat 
side down, and having that side practically all removed, as shown 
in the black cutaway section in fig. 343. 

Oues. What are the requirements of a slide valve with 
respect to the distribution of the steam? 

Ans. Considering first only one end of the cylinder, it must: 
1, admit steam to the cylinder just before the beginning of the 



*NOTE. — In its broad sense the term "slide valve" includes all sliding valves, as dis- 
tinguished from rotary valves. 

fNOTE. — The slide valve in its crude form was invented by Matthew Murray of Leeds, 
England, toward the end of the eighteenth century. It was improved upon by James Watt, 
but the simple D slide valve in use today, is credited to Murdock, an assistant of Watt. It 
came into general use with the introduction of the locomotive, although Oliver Eames, of 
Philadelphia, appears to have realized its value, in fact, for years before the advent of the 
locomotive he applied it to engines of his own make. 



180 



THE SLIDE VALVE 




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THE SLIDE VALVE 



181 




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182 



THE SLIDE VALVE 



As shown in fig. 344, the seat extends from A to H. B, C, and F, G, are 
the steam ports, and D, E, the exhaust port. The steam ports are separated 
from the exhaust port by two walls C, D, and E, F, called bridges. 

In some engines there are finished vertical guide surfaces along the 
two sides of the seat to prevent any side motion of the valve. The port 
edges are terminated by small fillets as at M and S, so that they may be 
properly machined. 

Oues. What is the steam edge of a valve? 

- STEAM EDGES OF VALVE - 
EXHAUST EDGES OF VALVE 




-EXHAUST EDGES OF STEAM PORTS- 
5TEAM EDGES OF 5TtAM PORTS- 

Fig. 345. — Sectional view of valve on seat illustrating the term steam edge, exhaust edge of 
both valve and seat. 

Ans. The edge which opens or closes the port admitting 
and cutting off the steam supply to the cylinder. 

Oues. What is the exhaust edge of a valve? 

Ans. The edge which opens or closes the port for release or 
compression. 

Owes. What is the difference between a port and a 
passage? 

Ans.- A port is the entrance at the valve seat to 1, either 
steam passage leading to the cylinder, or 2, the exhaust passage 
leading to the exhaust pipe. 



THE SLIDE VALVE 



183 







Owes. What governs 
the length (A H, fig. 344) 
of the valve seat? 

Ans. It should be less 
than the length of the 
valve plus its travel so that 
the valve will over travel to 
avoid wearing shoulders in 
the seat. ^i^Mk^-^' ' 



In the case of unbalanced 
valves the valve seat should 
be as short as possible to 
reduce the unbalancing by 
over travel as shown in fig. 
347. 



Oues. Why is the 
length of the ports 
made much greater 
than the width? 

Ans. To secure the re- 
quired amount of port 
opening with very little 
valve movement, and that 
the ports may be quickl3^ 
opened and closed to re- 
duce wire drawing. 

Ones. What is wire 
drawing? 

Ans. The effect pro- 
duced by steam flowing 



184 



THE SLIDE VALVE 




through a constricted 
passage, which results 
in a fall of pressure with 
its attendant loss in 
engine operation. 

Ones. What gov- 
erns the length of the 
ports ? 

Ans. The diameter 
of the cylinder; they 
are usually made about 
.8 of this diameter. 

Ones. What gov- 
erns the width of the 
ports? 

Ans. For a given 
port length, the width 
depends on the amount 
of area required for th^ 
proper flow of the steam. 

Oues. Why is the 
exhaust port made 
wider than the steam 
ports? 

Ans. Because the valve, on account of the extent of its 
movement, partly covers this port during exhaust. 

In fig. 346, the valve is shown at the extreme point of its travel, in which 
position the exhaust port H H' is covered by the valve a distance H C, 
leaving only the opening C H', through which exhaust steam may escape. 



Figs. 348 and 349. — Two views of Brownell high 
speed engine cylinder, showing valve seat and 
entrance of one of the steam passages at the end 
of the cylinder; also arrangement of the studs, 
and exhaust outlet. 



THE SLIDE VALVE 185 



In a well designed valve this opening should not be less than the width F G, 
of the steam port. When the exhaust opening H'C, is less than the width 
of the steam port, the exhaust is said to be choked by the valve. 



Oues. How is the size of the steam port obtained? 

Ans. From the area and speed of the piston, and an assigned 
velocity of 6,000 feet per minute.* 

Owes. What names are given to the principal parts 
of a slide valve? 




Figs. 350 to 353. — Brownell balanced slide valve and pressure plate for the cylinder shown in 
figs. 348 and 349. The valve is a single casting working between its seat and the pressure 
plate. It is double ported and is provided with means for relief from water. 



Ans. The edge at either end of the valve is called the steam 
edge as shown in fig. 345, because this edge controls the 
admission of steam to the cylinder, and for a similar reason 
each inner edge is called the exhaust edge.f 



*NOTE. — In engines having separate exhaust ports, the steam ports are proportioned 
for a velocity of 8,000 feet per minute, but when the sarne port is used for both admission 
and exhaust, the port must evidently be proportioned with respect to the exhaust, that is 
the steam should be exhausted at less velocity than the velocity of admission. In the exhaust 
pipe the velocity should be still less thah in the steam passage — usually 4,000 feet per minute. 

f NOTE. — These terms should be remembered as well as the similar names given to the 
edges of the steam ports as shown in fig. 345. 



186 



THE SLIDE VALVE 



The area of the steam port is found as follows : 

area piston in sq. ins. X piston speed in ft. 



Area steam port 



6,000 



Owes. What important defect is there in the operation 
of the ordinary slide valve? 

Ans. The excessive pressure caused by the steam pressing 
the valve against its seat causing considerable friction and 
wear. * 




-FACE 



FACE- 



Fig. 354. — Sectional view of slide valve showing the principal parts. It is important to 
remember the names given in the figure. 

Example. — What will be the force required to move a 9 X 18 slide valve, 
if there be on it an unbalanced steam pressure of 140 pounds per square 
inch, and the resistance due to friction be .02 of the total load on the valve? 



*NOTE. — A slide valve whose outside dimensions are, say, 9X18 inches has an area of 
162 square inches. If a boiler pressure of 140 pounds per square inch be exerted on this area, 
then the total pressure on the area is 162X140=22,680 pounds. The actual pressure which 
tends to force the valve against its seat is variable, as during some portions of the stroke the 
steam in the ports under the valve exerts an upward pressure, which opposes that on top. 
The pressure on top is also influenced by the fit of the valve. If it be not steam tight, more 
or less steam will get between the valve and its seat, and thus act against the pressure on top, 
whereas if the valve be steam tight, no such action will occur. In any event the pressure on 
top of an unbalanced valve is very considerable. 



THE SLIDE VALVE 



187 



Area of valve =9X18 = 162 sq. ins. 
Total load on valve due to steam pressure : 
= 162X140 = 22,680 
Force required to move the valve: 

= 22,680 X. 02 = 453.6 pounds 




Fig. 355. — Cylinder of Houston, Stanwood and Gamble automatic engine with valve chest 
cover removed showing balanced slide valve. Fig. 356 shows a sectional view of this valve. 

Qvies. What provision is sometimes made for relieving 
the pressure on the slide valve? 

Ans. Various devices have been used to exclude sfeam from 
the top of the valve, so that the pressure cannot be exerted 
in a direction which would press the valve against its seat.* The 
valve is then said to be balanced. 



•NOTE. — Experiments with small engines show that from one to two per cent of the 
whole power of the engine is absorbed in moving the slide valve when unbalanced. 



188 



THE SLIDE VALVE 



Lap 



Oues. What is the lap of a valve? 

Ans. It is that portion of the valve face which overlaps the 
steam ports when the valve is in its central position. 




ENI.ARai» 



Fig. 356. — Sectional view of Houston Stanwood and Gamble balanced slide valve. It is held 
against the seat by steam pressure on a small area of the back of the valve and by this 
means is made nearly steam tight. Also, the valve by this means is made to automatically 
follow up its wear, so that the steam consumption will be lower after the engine has been 
in use for a time, rather than higher. 

In fig. 357 AB, is the outside or steam lap, and CD, the inside or 
exhaust lap. f 

^^ EXHAUST ^ 




Fig. 357. — The plain D slide valve showing "lap." A B is the outside or steam lap; C D , the 
inside or exhaust lap. The figure also illustrates the neutral position of the valve. 



fNOTE. — Since, in some types or engine, steam is admitted at the inside edges of the 
ports and exhausted at the outside edges, the terms steam lap and exhaust lap are therefore 
sometimes used to avoid confusion. 



THE SLIDE VALVE 



189 



Oues. What is usually understood by the term lap? 

Ans. The outside or steam lap. 

Oiies. What is the effect of lap? 

Ans. It causes the valve to shut off the supply of live steam 
to the cylinder before the end of the stroke, the greater the 
amount of lap the sooner does this occur. 

Ques. What is the effect of inside lap? 

M 

I 
NEUTRAL POSITION OF VALVE 




NEGATIVE INSIUE LAP 



POSITIVE INSIDE LAP 



Fig. 358. — Illustrating negative and positive inside lap. A valve'is sometimes given negative 
inside lap at one end to equalize release and compression; the irregularity being due to the 
angularity of the connecting rod. 



Ans. It causes the valve to open later for exhaust and close 
sooner, thus shutting in a larger portion of the exhaust steam. 

Oues. What is the neutral position of a valve? 

Ans. Its central position, or the mid-point of its travel as 
shown in fig. 358, overlapping, equally the steam ports. In 
this position a line drawn through the center of the valve will 



190 



THE SLIDE VALVE 



coincide with a line drawn through the center of the exhaust 
port, when the exhaust lap is the same at each end.* 

Oues. What is negative inside lap? 

Ans. The space (as A B, fig. 358) sometimes left at one end 
of the valve between its exhaust edge, and the exhaust edge 
of the steam port when the valve is in its neutral position. 

It is sometimes, though ill advisedly, called inside clearance. The differ- 
ence between negative and positive \ inside lap is indicated in the figuie. 




Fig. 359. — Illustrating "line and line" position. 



Oues. Why is a valve sometimes given negative inside 
lap at one end? 

Ans. To equalize certain irregularities of exhaust due to the 
angularity X of the connecting rod. 



*NOTE. — These center lines are convenient in locating the valve for different positions. 

tNOTE. — The term inside lap unqualified always means positive inside lap. 

JNOTE. — The term angularity and its effect on the action of the valve gear is later fully 
explained. 



THE SLIDE VALVE 



191 



f 



Oues. What is the effect of negative inside lap? 

Ans. It causes the valve to open sooner and close later to 
;haust. 

That is, pre-release begins earlier, and compression later. 



Oues. What is *'line and line" position? 

Ans. When one edge of the valve is in the same line or 
plane with the corresponding edge of the port as in fig. 359. 

i extra wearing surface 

I ^wAO^s^^-^vO^ outside admission 




Fig. 360. — Sectional view of Phoenix cylinder showing double disc piston valve. The valve 
admits steam from the ends, the valve casing being surrounded by live steam. The two inner 
discs provide extra wearing surface. 



Here the steam edge of the valve is in line with the steam edge of the 
port, and valve is at the point of opening the port. 

Lead 

Oues. What is lead ? 

Ans. The amount by which the port is open for the adraission 



192 



THE SLIDE VALVE 



of steam when the piston is at the beginning of the stroke.'" 

For instance, in fig. 361, the port is open a distance A A', which is the 
lead. This is outside lead as distinguished from inside lead. It is ^ also 
called positive lead to distinguish it from negative lead. 



Oues. What is negative lead? 

Ans. The amount by which the steam port is closed to 
admission when the piston is at the beginning of the stroke. 




Fig. 361. — Valve in lead position 
beginning of the stroke. 



This is the position of the valve when the piston is at 1 



Owes. What is the object of lead? 

Ans. Lead is given to a valve in order to admit live steam 
to the cylinder before the beginning of the stroke so that the 
pressure of the compressed exhaust steam in the clearance 



*NOTE. — Lead varies with the size and type of engine usually from zero to about % 
of an inch. Small or medium sized slow speed engines may have from V64 to Vis, medium 
speed engines a greater amount, and in the case of high speed engines still more unless there be 
considerable compression. Vertical engines usually have more lead at the lower cylinder end 
than at the upper, in order to assist the compression in resisting the excess momentum at 
the lower end due to the weight of the moving parts acting in that direction. In general, the 
greater the compression, the less the amount of lead required. The principal object of lead 
is to secure full steam pressure in the cylinder at the beginning of the stroke, rather than to 
resist the momentum of the moving parts, although in high speed engines where the com- 
pression is not sufficient to bring the moving parts to a state of rest, an extra amount of lead 
's necessary on this account. 



THE SLIDE VALVE 



193 



space will be increased to boiler pressure at the beginning of 
the stroke. This enables the piston to begin its stroke with 
the maximum pressure. 

Oi^es. What is the object of negative lead? 

Ans. On some types of valve gear, as the link motion, the 
lead increases with the degree of expansion. Hence, in full 
gear, that is, for the maximum cut off, a negative lead is given 
to prevent excessive positive lead when cutting off very early. 




Fig. 362. — ^Valve in negative lead position. Negative lead is sometimes given with link motion 
full gear to prevent excessive lead when cutting off short, as on locomotives. 

With negative lead, the valve does not open for the admission of steam 
until after the beginning of the stroke. 



Owes. What is inside or exhaust lead? 

Ans. It is the amount by which the steam port is opened to 
exhaust when the piston is at the beginning of the stroke. 

Oues. What is constant lead? 

Ans. Lead which does not change for different degrees of 
expansion. 



NOTE, — Negative lead is sometimes given to the valves of express locomotives when 
fitted with link motion valve gear. Since the action of the link increases the lead for an early 
cut off (the cut off used except at starting) negative lead is given for full cear so that the lead 
will not be excessive at early cut off. 



194 



THE SLIDE VALVE 




Owes. What is 
variable lead ? 

Ans. Lead which 
changes with the 
degree of expan- 
sion. 

Oues. What is 
equal lead ? 

Ans. Lead which 
is the same at each 
end of the cyHnder. 



Figs. 363 and 364.- 



■Valve in lead position illustrating variable MTG'CLdtTtlSSlOTX 
lead; thus lead M, with gear in late cut off position is less than 
lead S, for early cut off. A peculiarity of the link motion gear is 

this variable lead. With the link motion in shortening the cut OueS ^^hat IS 

off by "hooking up"; open rods give increasing lead, while ^ • t «. o 

crossed rods give decreasing lead. Dre-adHlissiOIl ^ 

Ans. The flow of 
live steam into 
the cyHnder hejore 
the beginning of 
the stroke. 

Oues. On what 
does pre-admis- 
sion depend? 

Ans. On the 
amount of lead. 

That is, the great- 
er the lead, the soon- 
er does the valve 

„ , „^^ xr . . open to admit steam 

Figs. 365 and 366. — Valve in lead positions illustrating equal K^fr^r^ +Vi^ Kom'r.r.in -r 

lead, that is, lead M at one end of the cylinder is the same as Deiore tne Oeginnmg 

lead S at the other end. of the stroke. 




I 



THE SLIDE VALVE 



195 



Ques. What is the object of pre-admission? 

Ans Principally to secure the full steam pressure at the 
beginning of the stroke, and in addition, in some cases, to assist 
the compression in bringing the moving parts to a state of rest. 

Ques. What objection is there to pre-admission? 

Ans. It increases the period during which live steam, at a 
high temperature, is exposed to the comparatively cool cylinder 
walls, thus tending to increase initial condensation. 




Fig. 367. — Valve fully opened for admission; this comes when the piston is about half way 
between the beginning of the stroke and cut off position. Usually the port is only partially 
opened, as here shown, because the speed of the steam through the port during admission 
should be greater than during exhaust. 

NOTE. — In the design of a steam engine it is important to give the proper amount of 
port opening, for if it be too small, the velocity of the entering steam is unduly increased, re- 
sulting in a loss of pressure commonly known as wire drawing. On fixed cut o/f engines, the 
port opening may be less than the port because the latter is proportioned to give the proper 
velocity of the exhaust steam. With variable cut off gears, whose action reduces the port 
opening in shortening the cut off, as for instance the link motion, it is usual to provide excess 
port opening at full gear in order to obtain adequate admission when linked up. For instance 
on locomotives which operate normally at short cut off, the port opening in full gear is con- 
siderable, even exceeding the width of the port as in fig. 375. 

NOTE. — Engines are commonly designed with ports and passages proportioned for a 
nominal steam speed of 6,000 to 8,000 feet per minute when cutting off at about 60% of the 
stroke, using, instead of the maximum velocity, the average velocity, that is 

area piston X piston speed 
area ■t>ort = 

the port and piston areas being taken in sq. ins., and the piston speed in feet per minute. 

NOTE. — It must be obvious that in determining the port opening, the cut off should be 
taken into consideration, since the movement of the piston is not uniform but starts from zero 
at the beginning of the stroke and gradually accelerates to maximum velocity near mid stroke, 
then decreases to zero at the end of the stroke. Prof. Fessenden in his excellent book on valve 
gears has given an elaborate treatment of this subject which should interest those engaged in 
engine design. . 



196 



THE SLIDE VALVE 



Oues. What is meant by initial condensation? 

Ans. The condensation of live steam in the cyHnder which 
takes place during the periods of pre-admission and admission. 

Admission 

Ques. What is admission? 



Kl-^-W 



LEARANCL 



STROKE 



I 



! I 



t-ZZl 



[-^-APPARENT CUT OFF— >{ 

h — — c 



- REAL CUT OFF- 



•l+C 



SCALE 




1 \ Z 3 4 

Fig. 368. — The apparent and real cut off. The effect of cylinder clearance is to make the 
number of expansions less than would correspond to the apparent cut off, that is, the cut 
off of the valve gear. Thus, .if the valve gear cut off at one-half stroke, there would be 
without clearance, two expansions. With, say 10 per cent clearance, the expansions would 
be reduced to 1 -^(.l-^-.5) =1.66. The real cut off would then be 1^1.66 = . 6 stroke. 
In the figure the clearance volume I includes besides the volume between the piston at end 
of stroke and cylinder head, the volume of the steam passage (not shown) up to the steam port. 



Ans. The flow of live steam'^ into the cylinder from the 
beginning of the stroke to the point of cut off. 



*N0TE. — Live steam is steam taken direct from the boiler, and which has not been 
expanded in the cylinder, as distinguished from steam which has been admitted to the cylinder 
and expanded in doing work on the piston. 




THE SLIDE VALVE 



197 



Cut off 

Owes. What is cut oflf? 

Ans. It is the closure of the 
steam port to the admission of 
steam. 



Ones, 
pressed ? 



How is it usually ex- 



Ans. As a fraction of the stroke, 
as one-half, five-eighths, or three- 
fourths cut off. 

Oues. What is cut off thus 
expressed called? 

Ans. The apparent cut off. 

Oues. Why? 

Ans. Because it does not rep- 
resent the actual point at which 
cut off takes place when clearance 
is considered. 



As distinguished from the apparent 
cut off, the term actual or real cut off is 
used to indicate the point at which the 
steam port is closed, taking clearance 
into account. 



Oues. 
off? 



What is the real cut 



198 



THE SLIDE VALVE 



Ans. The sum of the apparent cut off plus the percentage of 
clearance. 

For instance, if the apparent cut off be one-half, or 50 per cent and the 
clearance be 10 per cent, then the real cut off is 10+50 = 60 per cent of the 
stroke. 

In fig. 368, let the volume /, at the end of the cylinder represent the 
clearance in proportion to the volume displaced by the piston during the 
stroke L. This clearance* volume includes all the space between the 
piston when it is at the beginning of the stroke and the face of the valve* 
plus the volume of the steam passage up to the steam port. 




pre-release: 



Fig. 371. — Position of valve at beginning of pre-release. This occurs just before the piston 
reaches the end of the stroke so as to rid the cyHnder of most of the steam before the be- 
ginning of the return stroke, and thus reduce the back pressure of exhaust as much as possible. 

It is evident from the figure that the distance the piston has moved from 
the beginning of the stroke does not represent the real cut off, and that 
the latter is made up of the volume displaced by the piston plus the clearance 
volume, or /+C. Thus in the figure if cut off occur when the piston is at 
5, as shown, the apparent cut off C, is five-tenths or one-half stroke. The 
actual cut off /+C, is six-tenths stroke. 



Pre-release 



Oues. What is pre-release? 



*NOTE. — The term clearance is sometimes used to denote the linear distance between 
the piston and the cylinder head when the piston is at the beginning of the stroke. 



THE SLIDE VALVE 




199 



Ans. The opening of 
the steam port to ex- 
haust before the piston 
has completed its stroke, 
as shown in fig. 371. 

If the steam were con- 
fined in the cylinder until 
the piston had reached the 
end of its stroke, there 
would not be time for it 
to escape without creating 
considerable backpressure. 

Oues. On what 
does pre-release de- 
pend? 

Ans. Primarily upon 
the amount of exhaust 
lap, and in design, upon 
the conditions of oper- 
ation. 

The proper amount of 
pre-release depends on the 
piston speed, and the 
quantity of steam to be 
discharged. Usually the 
valve is so proportioned 
that pre-release begins 
about 90 per cent, of the 
stroke. 

Release 

Oues. What is re- 
lease? 

Ans. The exhaust of 
steam from the beginning 
of the return stroke to 
the point of compression. 



200 



THE SLIDE VALVE 



In fig. 372, the valve is shown open to exhaust to its full extent which 
occurs during this period, and at this instant allows the steam in front 
of the fast advancing piston to escape from the cylinder with the least 
possible back pressure. 



Ques. What happens during pre-release and release? 

Ans. During pre-release the greater part of the expanded 
steam is exhausted, the pressure rapidly falling because of the 
glow movement of the piston at this part of the stroke; during 




COMPRESSION 



Pig. 373. — Position of the valve at the beginning of compression. This occurs usually when 
the piston has travelled about three-quarters of the return stroke, more or less depending 

■ upon the type of engine and working conditions. The object of compression is to introduce 
a spring like back pressure to absorb or "cushion" the momentum of the reciprocating parts 
and bring them to a state of rest at the end of the stroke; also to increase the efficiency by 
saving some of the exhaust steam. Note that the valve is in the same position as at pre- 
release (fig. 371) but is moving in the opposite direction. 



NOTE. — Inside Lead: "Experiments show that the earlier opening of the exhaust ports 
is especially of advantage, and in the best engines the lead of the valve upon the side of the ex- 
haust or the inside lead is Vas to i/is. i- ^-t the slide valve at the lowest or highest portion 
of the piston has made an opening whose height is V25 to Vis of the whole throw of the slide 
valve. The outside lead of the slide valve or the lead on the steam side on the other hand, 
is much smaller, and is often only 1/100 of the whole throw of the valve. The outside lead 
of the slide valve or the lead on the steam side on the other hand, is much smaller, and is often 
only 1/100 of the whole throw of the valve — Weishach (vol. ii, p. 296). 

NOTE. — Equalized Pre-Release and Compression. These events occur at the same 
time when the valve has no inside lap and the correction of one will likewise correct the other. 
It is desired to cause both these events to occur earlier in the forward stroke and later in the 
return stroke. To accomplish this, it is necessary to give an appropriate positive inside lap 
to the end of the valve nearest the crank shaft, and an equal negative, inside lap to the other 
€nd. The laps are easily determined by means of the Bilgram diagram. This diagram is 
explained at length in this Chapter, and should be thoroughly understood by those interested 
in valve gears. 



THE SLIDE VALVE ■ 201 



release the exhaust pressure is always a little higher than the 
external pressure (that is, higher than the pressure of the atmos- 
phere, or condenser as the case may be) on account of the 
rapidly advancing piston forcing the steam through the re- 
stricted passage, port and exhaust pipe at great velocity. This 
pressure is called the back pressure of exhaust^ or simply back 
pressure. 

Compression 

Ques. What is compression? 

Ans. The closure of the steam port to exhaust before the 
piston has reached the end of its stroke, thus shutting in a 
portion of the exhaust steam, and by the forward movement of 
the piston, compressing it until pre-admission begins. 

Ques. What is the effect of compression? 

Ans. The rapidly increasing back pressure due to com- 
pression acts as a spring to cushion the momentum of the moving 
parts, and brings them to a state of rest at the end of the stroke.* 

Ques. On what does compression depend? 

Ans. On the exhaust lap and angular advance; the greater 
the lap or angular advance the sooner compression begins. 

Ques. Should compression begin at the same point 
in a condensing engine as in a non-condensing engine? 

Ans. No. 

Ques. Why? 

Ans. Compression should begin earlier in a condensing engine 
than in a so called high pressure or non-condensing engine in 
order to get an equal amount of cushioning. 



•NOTE. — The effect of compression is sometimes called cushioning. 



202 



THE SLIDE VALVE 



The compression curve of a condensing engine, because exhaust takes 
place at a lower pressure, does not rise so rapidly as when running non- 
condensing, hence, for equal cushioning, compression must begin sooner 
than in a non-condensing engine. 

Oues. Does compression result in a loss of energy? 

Ans. No, because the power required to compress the 
confined steam is again given out by its expansion behind the 
piston on the next stroke. In fact, there is a "direct saving, 







LAP- 



-PORT OPENING 



Fig. 374.— Illustrating port opening and half travel of the valve. The valve is shown in dotted 
section in its neutral position, and in full section in its extreme position. Half travel is equal 
to the lap plus the port opening; the latter being the distance the steam edge of the valve 
moves past the steam edge of the port during admission. This represents the movement 
of the valve on either side of its central or neutral position 2ind.=lap-\-port opening =A'F 
+ F A'. As drawn, the port opening is greater than the port by the amount G A'. 

as the compressed steam is utilized to help fill the clearance 
space instead of filling it entirely with live steam. 



Port Opening 

Oues. What is port opening? 

Ans. The extent to which the steam port is opened when 
the valve is at the end of its to and fro movement as F A', 
fig. 374. 



THE SLIDE VALVE 



203 



Oues. What is the relation between the port opening 
and the width of the port? 

Ans. It may be either greater or less than the width of the 
port, as shown in figs. 375 and 376. 

HALF TRAVEL (MAXIMUM ECCENTRICITY) 



PORT OPENING 

A 




HALF TRAVEL (MINIMUM ECCENTRICITY) 



PORT OPENING 




Figs. 375 and 376. — Valve. in extreme position 
showing: 1, port opening greater than the 
^DADT port, and 2, port opening less than the port. 

KU rs I With plain gear in which the expansion is not 

variable, the valve is designed for a port opening less than the port, because for admission 
less port area is required than for exhaust, the steam being admitted in good practice, at a 
velocity of 8,000 ft. per minute and exhausted at 6,000 ft. per minute. With variable 
expansion gears, which vary the expansion, as later explained by the method of combined 
variable throw and variable angular advance, the' travel of the valve is considerably reduced 
for early cut off, hence, the port opening is made more than sufficient at late cut off as in 
fig. 375, in order that the reduced opening for early cut off as in fig. 376 will not be too small. 



204 



THE SLIDE VALVE 




In the case of a 
throttling engine 
where the travel of 
the valve does not 
change, the port 
opening may be less 
than the width of 
the port, as in fig. 
376, because ad- 
mission does not re- 
quire as much port 
opening as exhaust. 
"W ith automatic cut 
off engines, when 
the cut off is short- 
ened by the method 
of combined variable 
angular advance and 
variable throw, evi- 
dently there must 
be an excess of port 
opening (as in fig. 
375) for a late cut 
off, otherwise at 
early cut off it 
would be insuffi- 
cient for admission, 
on account of the 
considerable de- 
crease in valve 
travel. 

Oues. What 
is the com- 
parison be- 
tween large 
and small port 
opening? 

Ans. A large 
port opening 
permits very 
early cut off 
without choking 
the admission. 



THE SLIDE VALVE 205 



On account of the greater velocity of the valve, the events of the 
• stroke such as cut off release, etc., are more sharply defined; in 
other words, there is less wire drawing. These features are 
offset somewhat by the increased wear of the valve and larger 
valve gear necessary to secure the increased valve travel. 



Travel 

Oues. What is the travel* of a valve? 

Ans. The extent of its to and fro movement as shown in 
fig. 377. 

Here the valve is shown in full lines at one end of its travel, and in dotted 
lines at the other end, the travel being the distance M" M'. 

Oues. How is the travel obtained? 

Ans. From the lap and the port opening. 

Travel of valve = twice the lap -{-twice the port opening. 

In fig. 374, the valve is shown in dotted lines in its neutral position M 
and in full lines at one end of its travel M'. 

It is evident from the figure that the valve has moved a distance to the 
right equal to the lap A F, plus the port opening F A'. 

Now to admit steam to the other end of the cylinder through the port 
F' G', the valve must move an equal distance to the left of its neutral 
position M, that is a distance equal to M M" in fig. 377. Hence, the travel 
equals twice the lap plus twice the port opening. The full travel M" M' is 
shown in fig. 377. 

Oues. What is over travelf? 



*NOTE. — In the year 1836, the word travel was used in a different sense from the present 
meaning. According to Wansbrough, in order to keep the steam on the piston as long as 
possible, the valve moved nearly one-half inch beyond the port at each end or "over opened" — 
this distance or movement beyond the port was called the travel. 

tNOTE. — The term over travel is used by some writers to denote the distance the steam 
edge of the valve moves beyond the exhaust edge of the steam port in opening it. The author 
prefers to define it with respect to the seat limit. 



206 



THE SLIDE VALVE 



Ans. The extent to which the steam edge of the valve moves 
beyond the seat Hmit, as A E or E' D, fig. 377. 

Oues. What is the object of over travel? 

Ans. To preserve uniform wear of the seat, and reduce 
the unbalanced load on the valve. 



UNEAR ADVANCE 




LAP 



-LEAD 



Fig. 378. — Showing valve in its position of linear advance. When the piston is at the 
beginning of the stroke, the yalve must be at a distance from its neutral position equal 
to the lap plus the lead. The valve is shown in solid black in its linear advance position, and 
in dotted section in its neutral position. 



Linear Advance 

Oues. What is the linear advance of a valve? 

Ans. It is the distance the valve has moved from its neutral 
position, when the piston is at the beginning of the stroke. 

Owes. Upon what does linear advance depend ? * 



*NOTE. — It should be remembered that the word lap unqualified always means outside or 
steam lap. The same is true of lead. 




THE SLIDE VALVE 



207 



O o 



o. a 



si 






93 S B 



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Ans. On the amount of lap 
and lead. 

Thus in fig. 378, the valve has 
moved from its neutral position a 
distance MM', equal to its linear 
advance. The valve in its neutral 
position is shown in dotted lines 
and in its linear advance position 
in full section. 

From the figure it is clear that: 
linear advance = lap* -\-lead. 



Early Cutoff 

Oues. How may the cut 
off be varied? 

Ans. By changing both the 
angular advance and throw of the 
eccentric; the greater the angular 
advance and shorter the throw^ 
the earlier the cut off. 

In order not to unduly affect the 
other events of the stroke, the valve 
gear, as will be later explained, is 
arranged to increase the angular ad- 
vance simultaneously as the throw is 
reduced, this being called the method 
of combined variable angular advance 
and variable throw. 

Oues. What objection is 
there to shortening the cut 
off by the above method? 



•NOTE.— See note on page 206. 



208 



THE SLIDE VALVE 



Ans. The shorter the travel, the less the port opening, hence 
for very early cut off there is insufficient port opening for 
admission, moreover, pre-release begins earlier and compression 
later. 

Oues. How may the first objection be overcome? 




Fig. 379. — The Allen valve. The supplementary passage is for double admission which is 
desirable on locomotives fitted with link motion as they are usually run with short cut ofis, 
-.jid the action of the link under these conditions gives very little port opening. 




Fig. 380. — The Allen valve in lead position showing double admission. It should be noted 
that the second admission through the supplementary port, depends on the length of the 
seat which forms the lap. 



THE SLIDE VALVL 




209 



Ans. By providing 
a supplementary pas- 
sage in the valve for 
the admission of steam, 
as shown in fig. 379, 
which represents the 
Allen valve, used 
principally on loco- 
motives. This passage 
terminates in the lap 
at B F and B' F'. 
The seat limit is such 
that A F, the lap of 
the valve equals B' E', 
which acts as lap for 
the supplementary 
passage. As the valve • 
moves, for instance, to 
the right, A, passes F, 
at the same, time that 
B', passes E', hence, 
steam is admitted 
simultaneously by both 
ends of the valve as 
shown in fig. 380. The 
effect is the same as an 
ordinary valve moving 
at double speed. 
Following the further 
movement of the valve, 
it will be seen that 
the valve continues to 
open the port FG at. 



210 



THE SLIDE VALVE 



double speed until it has reached the position shown in fig. 381. 
Here the total port opening is F A+B C. This opening will 
not be increased by any further movement of the valve in 
traveling to its extreme position as shown in fig. 382, on account 
of the closing of the supplementary port. In this position the 
opening F A (fig. 382) =F.A (fig. 381)+ B G. 




Figs, 384 to 386. — Allen valve with negative lap. When the valve has a large steam lap, it 
is not difficult to keep the opening of supplementary port within this lap, and even to leave 
a small positive inside lap I, fig. 385. but when the main lap s is smaller, or the width h is 
increased, there will be a negative lap to the supplementary port as at /, fig. 386. The 
result is, that during a brief time a passage is opened from one end of the cylinder to the 
other, with some tendency to modify the exhaust operation. Thus in fig. 386 the valve 
is at the distance /' and moving toward the right. Compression has begun in the left end 
of the cylinder, and now steam which has not yet been released in the right end is about 
to flow over and increase the pressure and the amount of the clearance steam in the other 
end. This action will occur while the valve travels through the distance 21, but since it 
moves rapidly near neutral position and the openings involved are small, the effect upon 
the steam distribution will be small. 

If the steam ports be enlarged as shown in fig. 383 they would be com- 
pletely opened when the valve reaches the extreme position. This would, 
however, necessitate a somewhat longer valve. 

How to Design a Slide Valve. — The method of designing a 
valve as here given is so simple that it should present no difficulty, 
and the engineer who learns and understands the method will 
have no trouble in designing and setting a valve. 



THE SLIDE VALVE 211 

r Although the dimensions of a valve may be worked out by 
^mathematics, it is essentially a drawing board problem, and is 
better solved in that way. In solving the problem graphically, 
use is made of a valve diagram for obtaining the lap, angular 
advance, etc. There are a number of these diagrams of which 
Bome writers employ the one devised by Zeuner. The author 
considers the Bilgram by far the best and simplest and it is the 
one here used. The Zeuner diagram is objectionable in that 
it is a **cut and try" method.* 

The following example will serva to illustrate the application 
of the Bilgram diagram. 

Example, — A 7X7 engine is to be run at 450 revolutions per minute. 
What are the principal dimensions of the slide valve and ports for a steam 
velocity of 8,000 feet per minute through the port opening and 6,000 feet 
through the ports? Lead He inch, cut off %, release .9 stroke, length 
of ports .8 the diameter of the cylinder, and length of connecting rod 2}/^ 
times the stroke. 

1, Find area and dimensions of port opening and port. 

area piston m sq. ins. y^piston speed in feet 
area port opening in sq. ins. = 



8,000 
(72 X. 7854) X (450XVi2X2) 



= 2.53 sq. in. 



8,000 

Since the velocity of the steam through the port is reduced to 6,000 feet 
per minute, it is made larger than the port opening in the proportion of 
8,000-7-6,000, or 

8 
area of port= 2,5SX — = 3. 37 sq.m. 
6 



*NOTE. — Mr. Halsey in his admirable book on Slide Valve Gears, says, in criticising the 
Zeuner diagram: "The leading data that are given in designing a valve motion are the point 
of cut off, the port opening, and the lead of the valve (not the lead angle of the crank, as is 
often conveniently assumed). It is the radical defect of the Zeuner diagram that none of these 
dimensions cfen be laid off from known points. The lead must be laid off from an unknown 
point of the center line, and the port opening from an unknown point on an unknown line. 
Finally, through these unknown points and the center of the shaft the valve circle is to be 
drawn from an unknown center and with an unknown radius. Under these circumstances 
the result sought is found only through blind trial." Continuing he says: "With Mr. Bil- 
gram's method all this is changed. The lead is laid off from a fixed Une. the port opening from 
a fixed point, and the cut off position of the crank is located. The lap circle is then drawn 
tangent to these lines, and the problem is solved. Moreover, the awkward conception of the 
backward rotation of the crank is obviated. Finally, these marked advantages are not ac- 
companied by any compensating disadvantages whatever." The author is in accord with the 
above views. 



212 



THE SLIDE VALVE 




The length of the ports is made 
. 8 the cyHnder diameter, or 

Length of ports = 7 X . 8 = 
5.6, say 53^ ins. 

Width of steam ports 

= area -i- length 
or 

3.37-^53ij= .612, say 5^ in. 
Width of port opening = 



^X 



6,000 
8,000 



= 15^ 



!, say yi m. 



2. Find the position of the 
crank for 3/^ cut off. 

In fig. 387 draw a horizontal 
line, and near one end describe a 
circle with any radius as O E. 
Measure off the length of the 
connecting rod A E = 5X0 E, 
and A B =2X0 E. A B, then is 
the length of the stroke. 

Find the position of the cross 
head F, when the piston is at % 
stroke by taking A F = 3^ A B. 
With F, as center and radius 
F D = A E, describe an arc 
cutting the circle in C. This is 
the position of the crank pin 
when the piston is at % stroke. 

3. Find the lap, linear ad^ 
vance and travel of the valve* 

Use is here made of the Bil- 
gram diagram, and the succes- 
sive steps in its application are 
as follows : 

a. A horizontal line K N, is 
drawn, and the crank position 
for % cut off transferred from 
fig. 387 to fig. 388. 

b. Draw a line M S parallel to 
K N at a distance above {1{q in.) 
equal to the lead; M S, then is 
the lead line. 



I 



THE SLIDE VALVE 



213 



c. With a radius O A, equal to the port opening (3/2. in.), describe the 
port opening circle. 

d. Now, find by trial the radius E F, and center E, of a circle that shaU 
be tangent to the lead line M S, the port opening circle, and the cut off 
line O C. The radius BF, of this circle is the outside lap. 

e. Draw E H perpendicular to K N, then the distance E H is the linear 
advance. 

J. Now by the method of fig. 387, find the crank position for release at 
.9 stroke. In fig. 388, draw this crank position O C, and a circle tangent 
to it with center E G The radius E G, of this circle is the inside lap. 



COMPRESSION 




EF= OUTSIDE LAP 
EG=^ INSIDE LAP 
LINEAR ADVANCE 
yie LEAD 

ANGULAR ADVANCE 



Fig. 388. — The Bilgram diagram for finding the lap, angular advance travel, etc., of the slide 
valve. With this diagram, any valve problem may be easily and quickly solved. 

g. A second tangent O C, to this circle gives the crank position for 
compression. 

Measuring the diagram, the dimensions for the valve are 
Outside lap = }/2 in. Linear advance = ^e ^^• 

Inside lap =^2^^- TrcCvel of valve = 2 ins. 



With the dimensions just obtained and the given data, the 
valve and ports may be laid down in the following manner: 



214 



THE SLIDE VALVE 



1, Find length of valve face. 

Length of valve face = outside lap-\-width of steam port-\- 
insidelap = }4-i-^+^2 = '^'H2 

In fig. 389 the steam port and one end of the valve is drawn in neutral 
position giving length of valve face. 

2. Find width of exhaust port. 

This is done as shown in fig. 390. Draw a horizontal line representing 

NEUTRAL POSITION 




Fig. 389. — How to lay out the slide valve. I. With the dimensions obtained by the 
Bilgram diagram the length of the face is determined by sketching one end of the valve 
in its central or neutral position as here shown. 



the valve seat and lay off the steam port FG. = ^ in. Next lay off the 
bridge G H * making it }^ inch wide. 

Draw one end of the valve in its extreme position for admission, 
this position, the distance FA, is equal to the port opening. 



For 



*NOTE. — The width of the bridge depends on the size and thickness of the cylinder 
casting: it should, of course, be amply wide to give a steam tight joint when covered by the 
valve face. 



THE SLIDE VALVE 



215 



As steam is being exhausted from the other end of the cylinder when 
the valve is in this position, it is evident that the exhaust opening B H', 
must equal the width of the steam port so as not to choke the exhaust. 
Hence, lay off B H' = F G, and draw the bridge H' G' = G H. H H' then 
is the required width for the exhaust port. 

2. Locate the seat limit. 

Draw one end of the valve in its extreme position for exhaust as shown 

EXTREME POSITION 



PORT OPENING 




Fig. 390. — How to lay out the slide valve. II. The width of the exhaust port is obtained by 
sketching one end of the valve in extreme position for admission. Evidently H', must be 
so located that B H' =F G, in order not to choke the exhaust. 



in fig. 391. To do this, lay off G B', equal to the exhaust lap and draw the 
dotted line which is the neutral position of the exhaust edge of the valve. 
For the extreme position this edge moves to the left a distance B' B, equal 
to one-half the travel of the valve ( = 1 in., see page 213). 

Valve end is now drawn in its extreme position thus found, and the seat 
limit E, (fig. 391) may be located at any point between A and B, which gives 
sufficient seal E B. to prevent leakage of the steam and a clearance A E, 



216 



THE SLIDE VALVE 



for over travel. In this case the over travel is taken at one-half inch. It 
is recommended for unbalanced valves that the seal E B, be made no more 
than is necessary for a steam tight joint to reduce the unbalancing. 

4, Draw valve seat and valve in neutral position. 

From the dimensions already obtained the valve seat is laid down as 
shown in fig. 392. The two faces of the valve A B and C D, are located 
in neutral position and the remainder of the valve drawn. 

EXTREME POSITION 




•5EAT LIMIT 



Pig. 391. — How to lay out the slide valve. III. The seat limit is obtained by sketching one 
end of the valve in extreme position for exhaust as shown and locating the seat limit E 
between A B, at some point which will give sufficient contact E B, for a tight joint, this 
distance being called the seal. 



The dimension now needed is . the distance B C, between the exhaust 
edges. After measuring this distance it should be checked as follows: 

Distance between exhaust edges = width of exhaust port +2 X width 
of bridge — 2 X exhaust lap. That is 

BC = HH'+2GH — 2 GB 
= 1% +2X3^ — 2% = 2i^2. 



THE SLIDE VALVE 



217 










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218 



THE SLIDE VALVE 



Defects of the Slide Valve 

1. A small increase in the port opening requires a great increase 
in lap and travel. 

A valve hciving the proportions of the one in the foregoing example, 
would be suitable for an engine with a fixed cut off. If it were designed 
for a variable cut off engine, the port opening should at least be equal to 
the width of the port, or somewhat greater to provide for sufficient opening 



^/4 CUT OFF 




I J TRAVEL FOR ^2 IN. \^ 
i I PORT OPENING )\ 



- TRAVEL FOR V^ IN, PORT OPENING — 

Fig. 393. — Defects of the slide valve: A small increase in the port opening requires a large 
increase in the travel, and additional lap. In the diagram increasing the port opening O A, 
to O A', ^ inch, increases the travel K N, to K' N', or l^^inches. 

at early cut off. The effect of this is seen by drawing another diagram 
as in fig. 393, increasing the port opening from one-half to, say, three-fourths 
inch. 

In the diagram, the original proportions are shown in dotted lines from 
which it is seen that for an increase A A', of one-fourth inch of port opening 
the travel K N, is increased to K' N', or lYs inches. 



THE SLIDE VALVE 



219 




In fig. 394 the 
original valve is 
shown in cross sec- 
tion and one having 
the new proportions 
in dotted lines. 
Comparing the two, 
it is seen that the 
exhaust cavity is 
larger. This to- 
gether with the 
additional lap, con- 
siderably increases 
the length of the 
valve, thus exposing 
a larger unbalanced 
area to the action 
of tne steam. 

Quite as objec- 
tionable is the in- 
crease in the travel, 
requiring as it does, 
larger ports for 
moving the valve. 



2. The travel 
is excessive when 
the valve is de- 
signed for an 
early cut of; con- 
siderable lap is 
required. 

The effect of 
shortening the cut 
off from three- 
fourths to, say, one- 
half stroke is shown 
in fig. 395. The 
full lines show the 
proportions for 
three-fourths cut 
off, and the dptted 
lines for one-half 



220 



THE SLIDE VALVE 



cut off. By measuring the diagram it is found that the travel has increased 
from 2 ins. to 3iJ^2 i^s., also the lap has increased from 3^ to IJ^. 

The size of the valve is greatly increased as shown in fig. 177. The three- 
fourths cut off valve is shown in cross section and the one-half cut off valve 
in dotted lines. The valve seat for the latter being shown in dotted cross 
section. 

3. On account of the large proportions and excessive travel 
necessary, the slide valve ^\^^ CUT OFF A ^ CUT OFF 

is considered undesir- 
able for cut offs shorter 
than one-half stroke.'^ 




K- 



TRAVEL FOR ^/4 CUT OFF 



TR/^V&LFOR Va CUT OFF 



Fig. 395. — Defects of slide valve: The traveCis excessive when the valve is designed for an early 
cut off; considerable lap is required. The diagram shows the large increase in travel necessary 
in shortening the cut off from %to Y^ stroke, and also why the slide valve is not suitable for 
cut offs shorter than H stroke. 

In general, to keep the proportions of a valve within limits, for a short 
cut off, the ports must be made as long as possible sc as to reduce the 



*NOTE. — It should be understood that this means the cut off with full travel. Any 
valv^ may be made to cut off shorter by reducing the travel as before explained but this is at 
the expense of reducing the port opening. 



THE SLIDE VALVE 



221 



width and thus secure the proper admission with a minimum of valve 
movement. 

The Allen valve requires only one-half the lap and travel of the 9rdinary' 
valve as shown in the diagram fig. 396*, the diagram for the Allen valve 
being shown in full lines, the other dotted. In figs. 397 and 398 are shown 
the proportions required for the ordinary valve cutting off at three-fourths 
and one-half, and the Allen valve with one-half cut off. M, is the half 



»/^CUT OFF 




TRAVEL ORDINARY VALVE 



Fig. 396. — Comparative diagrams showing travel of AUeii and plain slide valve. The Allen 
valve requires only half the travel and half the lead of the plain slide valve. 



travel required for three-fourths cut off, M', for one-half cutoff, and M", 
for one-half cut off with the Allen valve. The figures are intended to show 
by comparison the undesirable features of the ordinary valve at early cut off. 



*NOTE. — In the diagram the port opening arc A B, is taken with radius one-half smaller 
than A' B', the port opening arc of the ordinary valve because double admission is secured with 
the Allen valve. 



222 



THE SLIDE VALVE 



The full benefit to be derived from the Allen valve may be obtained by 
so modifying the steam ports, as shown in figs. 383 and 398, that the 
supplementary ports are not closed when the valve is in the extreme 
positions. 



SIZE FOR 
5^ CUT OFF 



1 5\ZL FOR 

' '/4 CUT OFF 



//////////■ 













Figs. 397 and 398. — Showing sizes of valve for K and M cut off corresponding to the diagram 
fig. 396. The considerable increase in the length of valve and seat necessary for the shorter 
•cut off as indicated by the dotted lines should be noted. Fig. 398 shows the Allen valve with 
modified steam ports for y^ cut off as compared with the plain slide valve for >^ and % cut off. 

4. For a short cut off, release and compression occur too early. 
This is illustrated in the diagram fig. 399. A, A', and B, B', are the cranir 



THE SLIDE VALVE 



223 



positions of release and compression for three-fourths and one-half cut off 
respectively. Either may be corrected by the addition of positive or nega- 
tive inside lap, but it must be evident that to correct one, will cause the 
other to occur still more prematurely. 



5. For variable expansion, the port opening is inadequate, and 
release and compression occur too early at short cut off. 




COMPRESSION \ 
(•/2CUT OFF) ( BOTH 
/ Too 
^, RELEASE ( 50DN 

^ r (5i CUT off); 

"^B^ COMPRESSION 
i^A CUT OFF) 

RELEASE 

C ^4 CUT off; 



Fig. 399. — Defects of the slide valve: For a short cut off release and compression occur 
too early. The diagram shows the effect on release and compression, of changing the cut off 
from^^to^. Either may be corrected with positive or negative inside lap but the error 
of the other will be correspondingly magiiified. 



As will be explained in detail in a later chapter, the cut off may be varied 
by the method of combined variable angular advance and variable throw , 
as is done mainly on engines having shifting or swinging eccentrics 
known popularly as "automatic cut off engines." 



224 



THE SLIDE VALVE 



Assume latest cut off at J^ stroke and that TT, is greatest travel mechani- 
cally feasible. Draw O C = % cut off and describe travel circle with radius 
O T, and on this circle draw lap circle tangent to O C, and lead line. The 
corresponding port opening A' B', as seen, is considerably in excess of the 
required or normal opening A B. 

Now since the travel is reduced as the cut off is shortened a series of lap 
circles R, R', R", will appear in the diagram on a Hne M S, drawn parallel to 

fCUT OFF FOR NORMAL 
l PORT OPENING 



CUTOFF 



J4 CUT OFF. 




MAXIMUM 
TRAVEL 



MINIMUM 
TRAVEL 



A' 
A 
A" 



b'^ 



.^-^djEXCESS PORT OPtiNING 
P lAT LATE CUT OFF 

^NORMAL PORT OPENING 



^/INADEaUATE PORT OPENING 
VAT EARLY GUT OFF 



Fig. 400. — Defects of the slide valve 5. — For variable expansion the port opening is in- 
adequate, and release and compression occur too early at short cut off. The diagram shows 
the effects of changing the cut off from M to >^ by the method of combined variable angular 
advance and variable travel. Evidently, when variable expansion is thus obtained, the travel 
of the valve should be as great as possible in "full gear," because of the decreasing port 
opening with shortening of the cut off. From the diagram, it is also clear that the shorter 
the full gear cut off, the larger the port opening at earliest cut off. 

the lead line (assuming constant lead). Thus lap circle R', for normal 
port opening, gives a cut off O C\ near one half stroke. 

Ordinarily the most economical cut off is at }4 stroke (non-condensing), the lap circle R", 
in the diagram giving this cut off. The port opening as seen for }4 cut off is reduced to A" 
B", being about one half less than the required amount A B. 

Accordingly the operation of automatic cut off engines at early cut off is characterized 
by a sloping admission line on the indicator card the pressure drop reducing the efficiency. 
Moreover release and compression occur as the cut off is shortened, being entirely too early 
at }4 cut off. In the diagram these events are represented by the crank position O R, O R' 
and O R", corresponding to cut offs O C, O C, and O C* respectively. 



THE VALVE GEAR 225 



CHAPTER 5 
THE VALVE GEAR 



Oues.. What is the valve gear? 

Ans. The mechanism, or combination of parts by which a 
reciprocating, or to and fro motion is imparted to the valve from 
the rotary motion of the shaft. The simplest form of valve 
gear consists of: 

1. Yoke; 

2. Stem; 

3. Guide; 

4. Eccentric rod ; 

5. Eccentric strap; 

6. Eccentric. -.^^^..^'/-^^Ir. -^ 

These parts are shown assembled in fig. 401. 

The Valve Yoke. — The valve is held in position by a yoke 
which consists of a rectangular band (fig. 402) which surrounds 
the upper part of the valve. The latter is indicated by dotted 
lines illustrating the position of the valve with respect to the 
yoke. 

The fit between the yoke and valve is such that the latter is free to move 
up or down and thus adjust itself to the seat. At A, is a slight enlargement 
to receive the valve stem. 

In some cases the yoke is omitted and the stem attached direct 
to the valve as shown in fig. 403. 



226 



THE VALVE GEAR 




The valve is retained in place by 
the nuts A and B, by which the length 
of the stem is adjusted in setting the 
valve. In fig. 402, the adjustment of 
the stem is at A. 



The Valve Stem.— This is 
usually made of steel and serves 
to transmit the motion of the 
eccentric rod to the valve. Fig. 
402 shows the type stem used 
with a yoke, and fig. 403 the 
form used without yoke. From 
figs. 404 to 406 it is seen that a 
valve stem consists essentially of : 

1.' A threaded section A form- 
ing a connection for yoke or 
valve, and providing for adjusting 
the length of the stem in setting 
the valve; 

2. A cylindrical section B, 
which passes out of the steam 
chest through the stuffing box; 

3. An enlarged section C to 
secure sufficient bearing area for 
the guide; 

4. A pin connection D for the 
eccentric rod. 



NOTE. — The valve stem is designed to move 
the valve under the most unfavorable conditions. 
A short rule is: diam. stem =1/3 diam. cylinder 
diam. piston rod. Seaton's formula. 

"^ ~ -^1 , where p = boiler pressure; L and B. 



■f 



length and breadth of (slide) valve; F = 10,000, 
for long iron stem = 12,000 for long steel stem. 



THE VALVE GEAR 



227 



^oy<<z 




Fig. 402. — The valve yoke, or rectangular frame which embraces the box shaped section 
of the valve, and to which the valve stem is attached. The valve is shown in dotted lines to 
indicate the position of the yoke. 




5TEM 



Fig. 403. — Method of connecting the valve stem to the valve without a yoke. The stem 
passes through a circular section cast in the valve, being adjustable by means of the nuts 
A, B, at each end. 



228 



THE VALVE GEAR 




THE VALVE GEAR 



229 




g a 



^^ 



^ / ^^ 



11 



6:2 



In many cases 
the eccentric can- 
not be placed di- 
rectly in line with 
the valve stem on 
account of the 
room required for 
the main bearing. 
To provide for this 
the eccentric rod 
connection is 
placed between 
the valve and the 
guide, and an off- 
set pin is attached 
to the enlarged 
section projecting 
out to the line of 
the eccentric rod 
as shown in fig. 
407. Here, it is 
necessary to make 
the enlarged 
section of the 
valve stem square 
or rectangular, to 
prevent the stem 
turring due to the 
angular thrust of 
the eccentric rod.* 
On account of this 
turning action, it 
is important that 
there he no lost 
motion in the guide 
hearings. 



The Guide.— 

The object of 
the guide is to 



5ET SCREW \ 



6^ 



*N0TE.— In this type 
of valve stem, the square 
section is usually a sepa- 
rate part with a threaded 
joint A, (figs. 402 and 
407), to facilitate con- 
struction and adjustment. 



230 



THE VALVE GEAR 



prevent the previously mentioned turning motion, and any side 
movement of the valve stem which may occur on account of 
the action of the eccentric rod. In fig. 408, the guide consists of 
a U shaped piece attached to the lower end of the steam chest. 
This style is used extensively on marine engines when the 
eccentric is directly under the stem; it is, however, somewhat 
in the way when packing the stuffing box. 



iiiiiiiii liitmi 




Fig. 408. — Detail of marine type of valve stem guide with adjustable brasses. 



The valve stem guide shown in fig. 401 has no means of adjustment for 
wear. A more desirable form is shown in fig. 408 having a box with ad- 
justable brasses; this is the regular marine type as used on large engines. 

On engines having offset eccentrics, there are usually two guides which 
are attached to the engine frame as shown in fig. 407. 

Two projecting arms B, C, are cast to the frame with cross pieces D, E, 
bolted on, and serving as guides. The offset pin F is screwed into the 
square section of the stem and locked by a nut. 

There are numerous forms of guide depending on the design of the 
engine. In fig. 409 is shown the guides of the Brownell engine. Lubricating 
devices are attached to the guides and below is a tray to catch the waste oil. 



THE VALVE GEAR 



231 



Rocker Levers. — Sometimes an offset pin is carried on two 
rocker levers, M, and S, as shown in fig. 410, which illustrates 
the construction used on the American Ball engine. 



OFF SET 



^ALVE STEM END OFF 5ET PIN 




OIL TRAY 



Fig. 409. — ^Valve stem guides, and offset pin of the Brownell engine. The figure shows also 
the oihng devices, and a drain tray for the oil. 



ECCENTRIC ROO 




Fig. 410. — The American-Ball engine. View showing rock shaft C, and rocker levers M, S, 
which carry the offset pin, the latter being attached at D and E. 



232 



THE VALVE GEAR 



The pin is carried by two rocker levers M, and S, keyed to the 
shaft C. There are pivoted joints at D, and E, for the valve stem 
and eccentric rod. 

In operation, the rockers move through a small arc, and a 
slight up and down movement is produced owing to the circular 
path of D. The stem is sufficiently flexible to allow for this, 
hence no special provision is made. This style of offset pin is 
used to advantage on engines having the eccentric rod located 




Fig. 411. — Erie City high speed engine. An indirect rocker fulcrumed at A, is used in place 
of an offset pin. The valve stem is attached at B, and the eccentric rod at C. To allow for 
side motion due to the rocker, a flexible joint is provided at S. 



outside the flywheel where the offset, or distance D E, is con- 
siderable. 

Another type of rocker used on engines of this class consists of a hori- 
zontal lever, pivoted near the center as shown in fig. 411. 

A projection M, bolted to the engine frame carries the lever whose ful- 
crum is at A, connection at B, being made with the valve stem, and at C, 
with the eccentric rod. Since the arm A B, is rather small, the arc 
described by B, will cause more side motion of the stem than is occasioned 
by the movement of D, in fig. 410, hence a flexible joint is provided at S, 
to relieve the stem of undue bending. 



THE VALVE GEAR 



233 



Oues. What is a direct valve gear? 

Ans. One in which the valve stem and eccentric rod move in 
the same direction as shown in fig. 410. 

Oues. What is an indirect valve gear? 

Ans. One in which the valve stem and eccentric rod move 
in opposite directions as shown in fig. 411. 




Fig. 412. — "Vim" horizontal automatic cut off engine with direct valve gear without rocker. 
The eccentric rod, as seen, is offset with pin attached to a wide rectangular valve stem end 
piece workinig in two bearings to prevent lateralor twisting motion. 



The Eccentric Rod. — Motion is transmitted from the 
eccentric to the valve stem or rocker by the eccentric rod.. The 
rod may be either round or of rectangular section. A simple 
form of rod is shown in fig. 413 with the end connections in- 
dicated by dotted lines. In fig. 415 is shown a rectangular rod 
which is secured to the strap by a cross piece A, and stud bolts 
B and C. 



234 



THE VALVE GEAR 



^— 




0- 

<: 






^1 



rt.o 






THE VALVE GEAR 



235 



Where two eccentrics are employed, as with link motion, the pin end is 
offset as shown at D, fig. 414, the offsets of the two rods being on opposite 
sides to permit the link to work centrally. The pin is held by the two 
jaws, E and F. 

On marine beam engines the eccentric rods are of great length and to 
make them rigid each rod is usually built up of flat wrought iron bars in 
shape of a tapering lattice girder. The extreme end is a solid bar, with a 
notch for hooking on to the rocker pin. 

A pin is used in place of an eccentric on many high speed engines where 
the rod is located outside the fly wheel ; the rod being constructed as shown 
in fig. 416. Part of the fly wheel and the rocker are indicated in dotted 
lines to show the position of the rod. 



Fi:x WHEEL 



ROCKER PIN 



ECCENTRIC PIN 




Fig. 416.— Outside eccentric rod of a high speed engine. With rods of this type, an 
eccentric pin is used in place of an eccentric. The other end of the rod is usually attached 
to a direct rocker. This and part of the fly wheel are shown in dotted lines. 



The Eccentric and Strap. — ^An eccentric is the equivalent 
of a crank pin which is so large in diameter that it embraces the 
shaft to which it is attached and dispenses with arms. Its object 
is to change the rotary motion of the shaft into a reciprocating, 
or to and fro motion. This motion is transmitted by the strap 
and eccentric rod to the valve stem and valve. An eccentric 
and strap of simple construction is shown in figs. 417 and 418. 

The eccentric E, is a cast iron disc having a projecting boss or hub H, 
containing a set screw I, to secure it in any position on the shaft. A, is 



236 



THE VALVE GEAR 




the center of the ec- 
centric, and O, the 
center of the shaft. 
The hole for the 
shaft is drilled out 
of center or 
"eccentric" with the 
center of the disc, 
hence the name 
eccentric. 

The distance O A 
between the center 
of the shaft and the 
center of the eccen- 
tric is the eccentricity 
and is equal to one 
hcilf the throw. This 
distance is sometimes 
wrongly called the 
throw. 



Throw 

Oues. What is 
the throw of an 
eccentric? 

Ans. Twice the 
eccentricity or the 
amount of to and 
fro movement 
produced. 

The throw is equal 
to the diameter of 
the circle described 
by the center of the 
eccentric as it re- 
volves around the 
shaft. Thus, in figs. 
417 and 418, when 
the center of the 
eccentric is at A' 
and the end of the 



THE VALVE GEAR 



237 



rod at T', the end of the rod moves from T' to T" as the center of the 
eccentric moves from A' to A". The distance T T' or A' A" is the throw, 
some erroneously call half this distance the throw. 

The eccentric is embraced by a strap usually made in two pieces D, D'. 
These are held together by the bolts M, S, liners being inserted at X and Y 
for adjustment. The circumference of the eccentric is recessed at J and K, 
to register with a groove in the strap; this prevents any side motion of the 
strap. 

The eccentric rod is attached to a projection or neck N, usually by a 
threaded conhection as shown. At W, is an oil well for lubrication. 

The strap is recessed at F and G, to register with a side of each bolt which 
prevents the latter turning when the nuts are tightened. 



ECCENTRICITY, OR 
'A THE THROW. 




CRANK 



Figs 419 and 420. — Comparison of eccentric and crank. An eccentric is equivalent to a small 
crank whose arm O' E' is equal to the distance O E between the center of the shaft, and the 
center of the eccentric. This distance is the eccentricity, or one-tialf the throw. Sometimes 
erroneously called the throw. 

There are numerous forms of eccentric, the one shown in fig. 417 and 418 
serves to illustrate the principles and parts; it is such as would be used 
on a small horizontal engine. 



Angular Advance 



Oues. What is the angular advance of an eccentric? 

Ans. The number of degrees the eccentric must be moved 
forward from a position at right angles to the crank to give 
the valve its linear advance ^ that is, to move it from its neutral 
position to its position when the crank is at the beginning of 
the stroke. 



238 



THE VALVE GEAR 



This is illustrated in figs. 421 and 422. In fig. 421, the crank is on the 
dead center and the valve in its neutral position. The corresponding 
position of the eccentric is shown 90 degrees ahead of the crank. 

When the crank is on the dead center the valve must be in the position 
- shown in fig. 422, a distance M M', to the right equal to the lap plus the lead 
or linear advance. Hence the eccentric must be turned ahead on the shaft 
far enough to move the valve this distance from its neutral position. 

To find the angular advance, MM', is measured off to the right of the 
vertical line and a parallel line drawn. This cuts the path of the eccentric 



NEUTRAL POSITION OF VALVE 




LEAD 



PATH OF ECCENTRIC CENTER 
Figs. 421 and 422. — Illustrating linear, and angular advance. When the crank is on the dead 
center, and the eccentric set 90'-' ahead, the valve should be in its neutral position as shown 
in fig. 421. The valve, however, when the engine is on the dead center, must be at a distance 
(M M', fig. 422) from its neutral position equal to the lap + lead or in its position of 
linear advance. The eccentric then must be turned ahead through an angle A O A', its 
angular advance, sufficient to move the valve to its linear advance position M' . 

center at A', from which it is evident that the eccentric must be turned 
ahead through the arc A A', to move the valve to the position M', A O A' 
being the angle of advance j or angular advance as it is called. 



Oues. What objections are there to eccentrics? 



THE VALVE GEAR 



239 



Ans. The diameter is large in proportion to the throw. On 
account of this large diameter, the velocity of rubbing against 
the strap is considerable as compared with an equivalent crank 
pin. This causes an increase of friction and tendency to heat 
which requires closer attention to be given to lubrication and 
adjustment of the strap. 

Sometimes the eccentrics on small engines have straps with only a single 
adjustment as shown in fig. 423. 

5TRAP ADJUSTMENT 
ONE PIECE 5TRAP 

ECCENTRIC 
ECCENTRIC ROD 




Fig. 423. — Eccentric strap in one piece. A type of strap for use in inaccessible places, as on 
small multi-cylinder marine engines having cast frames and valves on the side. On account 
of the poor fit after adjustment, this type of strap is liable to heat, and should be avoided 
in design wherever possible. 

The strap is one piece and consists of a split ring with projecting lugs for 
the adjusting bolt. Liners may be inserted in the space between the lugs, 
or a set screw provided to hold the bolt in position. 

Eccentrics of this type are regarded by some (including the author) as 
being only a little better than a makeshift because when wear is taken 
up the strap looses its circular form and no longer bears properly on the 
eccentric, making it more liable to heat in operation. 



240 



THE VALVE GEAR 



Large eccentrics are usually made in two unequal parts H and 

H', as shown in fig. 424. 

These are held together by the key bolts M, and S; the keys retain them 
in position and prevent turning when the nuts are tightened. A keyway 
K, is provided to retain the eccentric in position on the shaft and also a set 




Fig. 424. — Eccentric for large engines. Usually made in two unequal parts H, H', and held 
together by the key bolts M, S. The eccentric is retained in position by a key and set screw. 

screw C. The larger part H, of the eccentric is cast with ribs (R, R', R'0> 
which reduces the weight and provides room for the bolts and set screw. 

An eccentric strap having micrometer adjustment as used 
on the Ideal engine is shown in figs. 425 to 428. 



THE VALVE GEAR 



241 



The two halves of the strap are joined at the bottom by a construction 
possessing the elements of a hinge. At the top, the uniting bolt M, passes 
through a sleeve nut S, which is threaded into the base lug L, and fixes the 
distance between the two halves. In adjusting the strap, the nuts M, are 
slacked and the sleeve nut S, turned to regulate the distance between the 
two halves, and the nuts M, again tightened which holds the two halves 
rigidly together. 




HIN&E CONNECTIOH 



Figs. 425 to 428. — Eccentric strap of the Ideal engine, having micrometer adjustment. Thi; 
two halves are joined, at the bottom by a hinge connection, fig. 428, and at the top by a 
uniting bolt M, fig. 426; this passes through a sleeve nut S, which is threaded into the base 
lug and fixes the distance between the two halves. 



NOTE. — There are several kinds of eccentric: 1, the circular, or eccentric properly so 
called, and 2, the various other contrivances bearing the name of eccentrics, but which are 
virtually cams, such as the heart shaped eccentric, the triangular eccentric, eccentrics with 
a uniformly varied motion, etc. 

NOTE. — ^The large amount of friction produced between the eccentric and its strap renders 
the application of the eccentric irnpracticable in cases in which it is required to transmit a 
great force. The same may be said of all contrivances bearing the name of eccentrics; they 
are applicable only when the force to be transmitted is small. 

NOTE. — Because of the relatively high velocity of the rubbing surface as compared with 
an eccentric pin, the latter is the more desirable and is used in best practice where the con- 
struction permits, as for instance, in marine engines having valves on the side operated from a 
valve shaft. 

NOTE. — In marint; practice, eccentric rods are generally made of steel with bushings 
at the top ends, and the eccentric straps are generally constructed of cast steel lined with 
white metal as bearing surfaces, the eccentrics being of cast iron or cast steel, preferably of 
the former metal except in very light construction. 



242 



THE VALVE GEAR 



In fig. 429 is shown the strap and eccentric rod of the Erieco 
engine. The rod is attached to the strap at A, and held by the 
set screw D. 




Fig. 429. — Erieco eccentric strap and rod. The strap is lined with Babbitt metal, and the 
eccentric, being an arc which properly fits the strap, makes a ball and socket joint. This 
arrangement insures cool running even though there be a lateral error in the alignment. 

The length is adjustable by means of the threaded end E, and nut B. 
Adjustment for the bearing is made at C. 



NOTE. — Eccentric Rod — The diameter of the eccentric rod in the body and at the eccen- 
tric end may be calculated in the same way as that of the connecting rod, the length being taken 
from center of strap to center of pin. Diameter at the link end = .8 D + .2 in. This is for 
wrought iron. Eccentric rods are often made of rectangular section. 



VARIABLE CUT OFF 243 



CHAPTER 6 
VARIABLE CUT OFF 



Where economy of steam is desirable, engines are used which 
automatically adjust themselves to any change in the load by 
altering the cut off. These are called automatic cut off engines'^ 
as distinguished from throttling engines, in which the cut off is^ 
fixed and the steam supply varied at the throttle valve. In 
either class the regulation is controlled by an automatic governor. 

There are several methods employed to vary the cut off as by: 

1. Shifting eccentric ; 

2. Swinging eccentric j offset; 

3. Rotating eccentric (independent cut off valve); 

4. Fixed eccentric (adjustable lap cut off valve) ; 

5. So called expansion valve gears. f 

These various methods may be divided into two classes, 
according as the cut off is varied : 



*NOTE. — The term automatic cut off engine is popularly applied to that large class of 
small and medium sized high speed engines having non- releasing valve gear; broadly speaking, 
any type of engine which adjusts itself to changes in load by automatically varying the cut off 
is an automatic cut off engine. 

fNOTE. — The au,thor objects to the term "expansion valve gears," because by usage it 
has come to mean single variable expansion gears as distinguished froni fixed expansion, and 
double gears, all gears being expansion gears except a few, as for instance, pump gears, 
which admit steam for the full length of the stroke 



244 



VARIABLE CUT OFF 







VARIABLE CUT OFF 



245 



1. By single valve gear, or, 

2. By double valve gear. 

When a single valve gear method is employed, the cut off is called 
variable^ as distinguished from the methods using double valve gear, in 
which case the cut off is said to be independent. 

ANGULAR ADVANCE 
.^ LATE CUTOFF^ 




F\GS. 432 to 434. — Diagrams showing why both the throw and angular advance must be 
varied to change the cut off. In the figures let O , be the center of the shaft, and E, the center 
of the eccentric for maximum throw, then NOE, is the angular advance for maximum throw. 
Now, if only the throw be changed as in fig. 433, the center of the eccentric will be at some 
point E' on radius OE; evidently this reduces the linear advance LA, to L'A', thus dis- 
turbing the lead. Hence, when the travel is changed, as by reducing the eccentricity from 
OE to OE', figs. 432 and 433, the angular advance must be increased from NOE, to NOE", 
fig. 434, in amount sufficient to maintain the linear advance constant in order not to alter 
the lead. 

Principles of Variable Cut Off .—The cut off of the ordinary 
slide valve may be altered by changing both the throw and 
angular advance. In making these changes, the shorter the 
travel, the earlier the cut of. This way of changing the cut off 
may be called the method of combined variable travel and variable 
angular advance. There are two methods of moving the eccentric 
to vary both the travel and angular advance: 



246 



VARIABLE CUT OFF 



1. By shifting; 

2. By swinging. 

To distinguish the two constructions, the first is called the shifting 
eccentric, and the second the swinging eccentric, most engines being fitted 
with the latter. 

The Shifting Eccentric. — The principle of a shifting eccentric 
is illustrated in fig. 435. A slot S, is cut in the eccentric at right 



LATE CUT'OFF 
POSITION 




STRAIGHT 5L0T 
CRANK PIN 



POSITION 



Fig. 435.— The shifting eccentric. Two arms A, B, attached to the eccentric, pass through 
the bearings C, D. The eccentric has a slot S to permit linear movement on the shaft. 
By shifting it from E to E', the throw is reduced, and the angular advance increased, the 
combined effect of which produces an earlier cut oflf. There is considerable movement and 
friction in the bearings C, D, as compared with the swinging eccentric. The lead is constant 
(not considering the angularity of the eccentric rod). 

angles to the crank; two arms A, B, project from the eccentric 
to the bearings, C, D, which are attached to the fly wheel, thus 
permitting the eccentric to ''shift" at right angles to the crank. 

For a late cut off (full gear), the position of the eccentric is shown in full 



VARIABLE CUT OFF 



247 



lines with its center at E. In this position O M, is equal to the eccentricity, 
or half the throw, and N O E, the angle of advance. 

The cut off is shortened by reducing the throw and increasing the angular 
adiance. This is done by shifting the eccentric along the slot to some inter- 
mediate position as that shown by the dotted line:: with center at E'. This 
reduces the eccentricity, or half throw from O M, to O M', hence, the travel 
of the valve has been reduced twice the distance MM', and the cut off 
shortened an amount corresponding with the increase (E O E') in the 
angular advance. 




Figs. 436 and 437. — Some examples of shifting eccentrics as used on traction engines, for both 
variable cut 'off and reverse. Fig. 436, Heilman gear. As seen, the shifting eccentric slides 
in V, grooves, being geared to a double bell crank, which is connected by a Imk to a disc and 
collar arranged to slide along the shaft. A second bell crank and rod connects the collar with # 
the control lever. Fig. 437 shows the Russell variable cut off and reverse. As constructed, 
the eccentric is made to shift for change of cut off or reverse by a single bell crank. 



248 



VARIABLE CUT OFF 



Since the center of the eccentric n^oves in a line E E', at right angles 
to the crank, the lead remains constant.* The angular advance increases 
as the cut off is shortened. In moving the eccentric from E to E', the 
angular advance increases from N O E to N O E'. 

Oues. What is the action of a shifting eccentric in 
shortening the cut off? 

Ans. It shortens the cut off by reducing the throw and increas- 
ing the angular advance, sufficiently to maintain a constant linear 
advance, {not considering the eccentricity of the eccentric rod). 




SWING CENTER 

EARLY CUT OFF 

Fig. 438. — The swinging eccentric. The arm A, is pivoted at B, in line with the shaft and crank ■ 
pin. This location of the swing center causes the lead to increase as the cut off is shortened. 
If the swing center be located on the opposite side at B', the lead will decrease as the cut off 
is shortened. 



The Swinging Eccentric. — The chief objection to the shifting 
eccentric is the friction brought on the bearings (C, D, fig. 435) 
which is Hable to interfere with the free movement of the eccen- 
tric, and thus reduce the sensitiveness of the governor, especially 

*N0TE. — The effect of the angularity of the eccentric rod is to diminish the lead as 
^the eccentric moves from E to E', but since the rod is very long in proportion to the throw, 
the lead is only slightly reduced, hence for simplicity the angularity is neglected in the ex- 
planation. 



VARIABLE CUT OFF 



249 



on account of the difficulty of lubricating a bearing rotating 
around a center, accordingly the shifting eccentric is better 
adapted for an adjustable or non-automatic cut off engine.* 

To overcome this defect, the swinging eccentric has been devised by 
means of which the considerable Hnear motion through the bearings 
(C, D, fig. 435) has been reduced to a very small circular motion. 




Fig. 439. — Fly wheel and governor of Buffalo engine illustrating the swinging eccentric. It 
should be noted that in the design here illustrated the swing center is near the radial slot 
instead of at the end of the arm as in fig. 438. 



A swinging eccentric has one arm A, fig. 438, of any convenient length, 
and pivoted at some point as B, on a line joining the shaft and crank pin 
centers. The point B, is called the swing center. A circular slot S, is cut in 
the eccentric, having sides in the form of arcs of circles described with 
B, as center. 



*N0TE. — Owing to the centrifugal force thus set up, the oil will not remain long in the 
bearing but is thrown off at the outer ends. 



250 



VARIABLE cur OFF 



The action is similar to that of the shifting eccentric, that is, the cut off 
is shortened by a reduction of throw and an increase of angular advance. 
This is done by swinging the eccentric about the swing center B, from its 
full gear position E, to some intermediate position E'. Here, the angular 
advance has increased from N O E, to NO E', and the throw reduced by 
twice the distance M'M. 

Oues. What is the action of the swinging eccentric 
in shortening the cut off? 

Ans. It shortens the cut off hy reducing the throw and' increas- 
ing the angular advance in such proportion as to give an increasing 
lead, 

RADIAL SLOT 
LATE CUT OFF 

SWING CENTER 

CRANK PIN 

\ 




EARLY CUT OFF 



Fig. 440. — The offse swinging eccentric. With the swing center located as in the figure, 
the lead is the same for maximum and minimum cut off and greatest in mid position. 

It should be noted in fig. 438, that as the center of the eccentric is moved 
from E to E', to shorten the cut off, the lead is increased an amount equal 
to the distance L*. 

Ques. How would the action of the swinging eccentric 
be modified if the swing center be located on that side of 
the shaft opposite the crank pin? 

Ans. The lead would decrease as the cut off is shortened. 



*NOTE. — Taking into account the angularity of the eccentric rod, the actual increase 
in the lead is slightly less than the distance L. 



VARIABLE CUT OFF 



251 



This is objectionable in that it reduces the port opening as the cut off is 
shortened, thus producing wire drawing which lowers the admission pressure. 



The Ofifset Swinging Eccentric. — On some engines the 
swinging eccentric is located with its swing center offset from the 
line joining the shaft and crank pin centers as shown in fig. 440. 




Fig. 441.— Valve gear of the 
Lentz poppet valve engine, 
illustrating the shifting type 
eccentric. In this eccentnc, 
the shifting slot is cut straight, 
the axis of the slot making 
with the line joins the center 
of the shaft and center of the 
eccentric, an angle equal to 
the angular advance, the 
eccentric axis being in advance of the slot axis. The effect of straight slot eccentric wh«n 
used for variable cut off is to give a constant lead for all degrees of expansion (not con- 
sidering the angularity of the eccentric rod) . 



Ques. What is the object of offsetting the swing center? 

Ans. To compromise between the conditions described in 
the last two examples, that is, instead of an increasing or de- 
creasing lead, by offsetting the swing center the same lead is 
obtained at both maximum and minimum cut off with a somewhat 
larger lead in mid position. 



252 



VARIABLE CUT OFF 



In fig. 440, the swing center B, is offset above the crank axis one-half the 
distance from E, to this axis. This position B, gives the same lead in the 
two extreme positions, and it should be noted that the total increase of 
lead L, is only one-half the increase L, of fig. 438. The two positions illus- 
trated, correspond to those of the two preceding figures showing the same 
angles of advance but less increase of lead. From the figure it is seen 
that if the eccentric be moved to the extreme position E", the lead will 
decrease and become equal to the original amount for the full gear 
position E. 




Pig. 442. — ^Leffel adjustable shifting eccentric. It consists of a hub plate keyed to shaft with 
valve eccentric bolted thereto, in a manner enabling adjustment of the cut off up to three- 
fourth stroke, or reversing motion of engine with same range of cut off. 



Owes. What is the action of the offset swinging eccen- 
tric in shortening the cut off? 

Ans. It shortens the cut of? by reducing the throw and increas- 
ing the angular advance, in such proportion that the lead increases 
for full gear to mid position and then decreases to the original 
amount at minimum cut of, the total increase being less than 
that produced by. the swinging eccentric. 



VARIABLE CUT OFF 



253 



Independent Cut Off. — For maximum economy, a much 
earlier cut off is required than that produced by a sUde valve in 
full gear. For instance, a single cylinder engine to run with the 
least steam consumption per horse power . must cut off from 
one-third to one-fifth when running non-condensing and from 
one-fifth to one-seventh when running condensing, the particular 
point depending upon the pressure and quality of the steam, etc. 



ECCENTRIC 



SWING 
CENTER 



CENTER OF 
SHAFT 




Fig. 443. — ^Wheel end of American Ball automatic cut off engine showing eccentric pin, largely 
used in place of an eccentric. The arms and spring are parts of the governor. 



A considerable range of cut off is required on account of 
variations in power demands. 

The plain slide valve is designed for the latest cut off required 
and with a movable eccentric the valve is made to cut off shorter 



254 



VARIABLE CUT OFF 



INCREASE IN ANGULAR ADVANCE /^^ 



ECCENTRIC AT END OF THROW - 
BEFORE PORT. 15 FULLY OPENED 




i. Slow and insufficient opening of the port for admission 

THROW FOR LATE CUT OFF };rj 
THROW FOR EARLY CUT OFF 




2. Pre-release occurs too early 



LINEAR DISPLACEMENT CAUSING-^ 
PREMATURE COMPRESSION X 




% 



3. Compression begins too early 

Figs. 444 to 446. — Defects of the slide valve at early cut off: 1, fig. 444 , slow and insufficient 
Port opening. Note that the eccentric center E', is at the end of its throw; hence the valve 
movement in opening the port is comparatively slow; 2, fig. 445, pre-release occurs too early. 
This is due to the increased angular advance displacing the valve to the left by the distance 
AB; 3, fig. 446, compression begins too early. Similarly as in 2, the increased angular 
advance displaces the valve to right by the distance A'B', causing the valve to close to 
exhaust too soon. In the figures, E, is the center of the eccentric for full gear or late cut off, 
and E', for early cut off. 



VARIABLE CUT OFF 



255 



as previously explained. This combination has the advantage 
of simplicity but for very early cut offs it possesses certain 
defects which become more pronounced with the shortening 
of the cut off. These defects are, briefly: 

1. Slow and insufficient opening of the port for admission. 




LATE CUT OFF 

[*HNCREA5E IN LEAD (EARLY CUT OFF) 
NORMAL LEAD (lATE CUT OFF) 




CAU5E OF 
.'INCREASE IN LEAD 



EARLY CUT OFF 




SWING CENTER 



Figs. 447 and 448. — Defects of the slide valve at early cut off: 4, lead not constant with swinging 
eccentric. Case I, Swing center between shaft and crank pin. For early cut off, the center 
E, of the eccentric swings through the arc EE', fig. 448, to position E', thus increasing the 
angular advance and reducing the travel, but in so doing, the valve is displaced to the right 
a distance AB, increasing the lead by this amount. 

On account of the reduced travel, the valve moves slower at admission 
and cut off; this causes wire drawing at these points which together with 
insufficient port opening due to the small travel results in a loss of pressure. 



2. Pre-release occurs too soon. 

Since the valve opens to exhaust sooner than is necessary, the full benefit 
which might be derived from expansion of the steam is not realized. 



256 



VARIABLE CUT OFF 



3. Compression begins too early. * 

This produces a resistance in excess of that required to overcome the 
momentum of the reciprocating parts. The slower the engine speed, the 
more pronounced is this effect. 




SWING 

SWING CENTER 



Figs. 449 and 450. — Defects of the slide valve at early cut off; 5, lead not constant with 
swinging eccentric. Case H, swing center and crank pin on opposite sides of shaft. When 
the center of the eccentric swings through the arc EE', fig. 450, to shorten the cut off, the 
valve is displaced to the left a distance AB, thus decreasing the lead -by this amount. 



4. The lead is not constant (^with swinging eccentric). The 
variation of lead is influenced chiefly by the position of the 
swing center, and also by the length of the swing radius. 

The independent cut off is intended to overcome these defects 
and consists of: 



VARIABLE CUT OFF 



257 



1. A main valve which controls the points of admission release 
and compression, and 

2. A cut off valve which controls the cut off. 

There are two eccentrics, one for each valve. The main valve is operated 
by a fixed eccentric, and the cut off valve by a rotating eccentric. With 
this combination, the cut off may be varied without changing the positions 
of release and compression. 

Oues. Where is the cut ofif valve located? 




Fig. 451. — The Gonzenbach independent cut off valve. This is located in a separate steaitt 
chest above the main valve, the latter being an ordinary slide valve which controls the 
steam distribution with the exception of cut off. The range of cut off is limited, and the 
lower steam chest presents a large clearance which is objectionable. Moreover, the main 
valve is inaccessible. 



Ans. It may be, 1, placed in a separate steam chest, or 2, 
arranged to work on the back of the main valve. 

Oues. What is it called when arranged to work on the 
back of the main valve? 

Ans. A riding cut off. 

Oues. Describe the type with separate steam chest* 



258 



VARIABLE CUT OFF 



Ans. The Gonzenbach valve shown in fig. 451 is an example 
of this type. In the figure, the main valve, which is the lower, 
is an ordinary slide valve; the cut off valve which works on a 
ported partition directly above, is of the gridiron type, that is, 
there are a number of steam ports (A, B, C,) in order to secure 
.a quick cut off with moderate travel. 

During admission, steam passes through the ports A, B, C, into the 
lower steam chest and to the cylinder through either one of the cylinder 

-NEGATIVE LAP 




Fig. 452,- 



STEAM PORTS- 

-Gonzenbach cut off valve in neutral position showing negative lap. 



ports which happens to be open. The action of the cut off valve differs 
from the ordinary valve in that while the latter opens and closes the port 
with the same edge, the cut off valve does this with the two edges, that 
is, the port in the valve passes bodily across the port in the seat. 

Oues. How is the cut oflf varied? 



NOTE. — If the travel of the valves on a lodomotive for full gear be 414 to 5 inches, for a 
lead of i^ inch at full gear, and ^e inch at mid-gear, a steam lap of % inch and no exhaust lap 
will secure excellent results; but if the engine were never to run at a speed of over 20 miles 
an hour, an exhaust lap of }4 inch could be used to advantage. Most builders of stationary 
engines give so much exhaust lap that a considerable back pressure is caused, and the 
engines can not be run at high speed, and for two reasons: 1st, that this steam* does not get 
ooit of the cylinder fast enough, and, 2nd, there is not enough cushion to take up the momentum 
of the connections at high speed. An early release and strong cushion are required for high 
speeds. At moderate speed an early release and strong cushion deaden the motion of the 
engine over the centers, and the use of two slide valves, one on top of the other, was suggested 
by Meyer. A false valve seat was suggested by Rankine, with the object of obtaining a quicker 
cot off, the seat being moved by one eccentric while the valve was moved by another. In 
this way the effect of an eccentric w ith greater throw was obtained. The first change suggested 
by Gonzenbach consisted in making the steam chest in two chambers. In the one next the 
cylinder, the ordinary slide was employed while the steam came in through openings from the 
other cham.ber, these openings were covered by a simple slide moved by an eccentric. Thus 
the inlet and exhaust were regulated by the ordinary slide, but the second one cut off the sup- 
fily of steam. As the principal objection to this was the large clearance space left in the main 
steam chest and the consequent waste of steam, the Meyer gear became the favorite. 



VARIABLE CUT OFF 



259 



Ans. By turning the cut off valve eccentric forward or back- 
ward on the shaft as the case may be.* 

Fig. 452 vshows the cut off valve in its neutral position from which it is seen 
that the valve has negative lap. This may equal or exceed the width of 
the ports in the seat; the negative lap being the distance A, measured 
from one edge of the seat port to the opposite edge of the valve port. 



The principles of the Gonzenbach valve are best understood 
by the application of the Bilgram diagram. 




Fig. 453. — Rider variable cut off gear. In this riding cut off gear, the cut off is altered, as in 
the Meyer gear by varying the lap. In construction, the back of the main valve is hol- 
lowed into a part of a cylinder whose axis is the center of the riding valve. The lap edges 
of the riding valve and steam edges of the main valve are tapered in such a manner that by 
rotating the riding valve, its lap is changed. This rotation is accomplished by a spindle 
attached to the governor, gearing into a sector on the valve stem. 

Problem. — In a Gonzenbach valve gear the main valve has }/(q lead; 
J/^ inch port opening, and cuts off at ^/lo stroke; the cut off valve has 
3 ports giving 3^ inch port opening each. Required the negative lap and 
positions of the cut off valve eccentric for the earHest and latest cut off. 



*N0TE. — The effect of this is to change the angular advance which alters the cut off. 
The expansion eccentric, unlike the shifting or swinging eccentric, does not reduce the travel 
in changing the cut off. 



260 



VARIABLE CUT OFF 



In fig. 454 crank position C, for latest cut off, the center Em, of the 
main eccentric, and lap of the main valve are found in the usual way. 

The lead position is now found by drawing the line LL', through O, and 
tangent to the main valve lap circle. 

At the latest cut off (^/lo stroke), the negative lap circle must be 
tangent to the line OC, and also tangent to the lead position OL. 




VAt,\/£S IN LEAD POSITION 



Fig. 454. — Application of the Bilgram diagram to the Gonzenbach independent cut off gear. 
The relative positions of the valves and eccentrics are shown for four crank positions which 
illustrates the operation of the gear. 



Since the cut off valve has three ports, it is equivalent to a single valve 
having three times the port opening and travel. Hence, with radius of IJ^ 
inch equal to three times the port opening of each port of the cut off valve, 
describe the negative lap circle tangent to OC and OL, which gives the 
position Q', of the cut off, valve eccentric for latest cut off. 

Starting at crank position A, and with the cut off eccentric at Q', both 
valves are open to lead; the main valve is at a distance QB, from its neutral 



VARIABLE CUT OFF 261 



position, and the cut off valve at a distance Q'B'. This latter distance 
being less than the negative lap, the cut off ports are open an amount 
B'M equal to. the lead. 

As the crank moves, the cut off ports are further opened, up to position 
C, where they stand wide open as shown, this being the neutral position 
for the cut off valve. 

As the crank advances further, the cut off begins to close the port, not 
by changing its direction as in the case of the slide valve but by continuing 
its movement to the end of its travel. Cut off occurs at crank position C. 

The earliest point of cut off is determined by extending CO, downward 
and finding Q", such as to make the negative lap circle tangent to CO, 
extended, and drawing OC", tangent to the negative lap circle which gives 
the crank position for earliest cut off. After passing this point expansion 
takes place both in the cylinder and the lower steam chest until the main 
valve cuts off at position OC, where it is continued in the cylinder alone 
until pre-release. 

Ques. Mention the defects of the Gonzenbach valve. 

Ans. In shortening the cut off with this valve gear admission 
to the lower steam chest occurs earlier and earlier, hence there is 
a point beyond which the cut off valve would admit steam to the 
lower steam chest before the main valve had closed its port ta . 
admission in the previous stroke, thus admitting steam to the 
cylinder twice during the stroke. 

Thus in fig. 454, if the cut off eccentric be advanced to Q"\ the negative 
lap circle will cut OC, extended, indicating that the cut off valve ports were 
open a distance RS, when the main valve closed on the previous stroke^ 
thus readmitting steam to the cylinder from crank positions Cs, to Cr, 
during the expansion period of the previous stroke. 

This limits the range of cut off, and in order to secure an earlier cut off, it is 
necessary to design the main valve for shorter cut off. The range of cut off 
is therefore limited. Moreover, on account of the large clearance of the 
lower steam chest, the full expansion due to the cut off is not secured, the 
difference between the apparent and real expansion increasing for early 
cut offs. An additional defect is that the main valve is inaccessible. 

The Gonzenbach valve, on account of these objections is not 
extensively used, however, it serves to make cleg,r the general 
principles of independent cut off. 



252 



VARIABLE CUT OFF 



The Riding Cut Off. — The large clearance and inaccessible 
main valve of the Gonzenbach gear are overcome in the riding 
cut off by placing both valves in one steam chest and using the 
back of the main valve as a seat for the cut off valve, that is, 
the cut off valve ''rides" on the main valve, hence the name 
riding cut df. 

NEC. LAP 



STEAM EDGE 



RIDING 



CUT OFF 
STEAM 



PASSAGE 




MAIN VALVE 



Fig. 455. — ^Riding cut off valve with outside cut off edges. In operation the cut off valve 
travels or "rides" on top of main valve, and with fixed lap as above, receives its movement 1, 
from a rotating eccentric, that is, an eccentric loosely journalled on the shaft so that its 
angular advance may be changed to vary the cut off, under control of: 1, a governor, or 2, 
a fixed eccentric with link motion. The riding cutoff valve with outside cut off edges gives 
quickest cut off with early cut offs . 




STEAM 
ETDGE 



Fig. 456. — Riding cut off valve with inside cut off edges. This arrangement having inside cut 
<iff edges gives quickest cut off with late cut offs. 

Fig. 455 shows a simple form of riding cut off. Both valves are shown 
in neutral position, in order to show the positive lap of the main valve, and 
negative lap of the cut off valve. 

The main valve is nothing more than the ordinary slide valve having 
steam passages in the end leading to the back which is machined to form 
the seat for the cut off valve. 

Fig. 456 sho^s a riding cut off valve which cuts off at the inside edges 
of the ports; it necessarily has considerable positive lap. 



VARIABLE CUT OFF 



263 




Methods of Variable Cut 
Off with Riding Valve.— 

Cut off by a riding valve may 
be varied in three ways, 
as by: 

1. Variable angular ad- 

vance; 

2. Variable lap; 

3. Variable travel. 

The first method employs a 
rotating, or loosely journaled 
eccentric for the cut off valve 
whose angular advance is con- 
trolled by a governor. 

The second method has a 
fixed eccentric to operate the cut 
off or "riding" valve, the lap of 
the latter being adjustable by a. 
right and left screw. 

The third method employs a 
link to vary the travel of the 
riding valve. 

For convenience, the eccentric 
which operates the riding valve 
is called the riding eccentric* ; it is 
called by some writers the cut 
off eccentric, and more commonly, 
though ill advisedly, the ex- 
pansion eccentric. 

1. Riding Cut Off; Va« 
riable Angular Advance. — 

The usual range of angular 
advance given to the riding 



,; C a» rt S 
O rt w 1-1 rt 



*NOTE. — The term riding eccentric is 
used for the loosely journaled eccentric 
connected to the riding valve to distinguish 
it from the fixed or main eccentric which, 
operates the main valve. The symbols Br- 
and Em being used to respectively desig- 
nate each. 



264 



VARIABLE CUT OFF 



eccentric is from a little less than 90° up to 180°. The relative 
positions of the two eccentrics are such that the valves move in 
opposite directions at cut off (within limits) for a well designed 
gear. I 

The following example will serve to illustrate the features of 
this gear. 

V 

VS CUTOFF ^^- ~^^ 

V8 CUT OFF 

F 




Pig. 458. — Method of transferring crank positions determined for given cut off. In order not 
to complicate the Bilgram diagram all unnecessary lines should be omitted, hence the crank 
positions for given cut offs are best determined in a separate diagram as in fig. 457 and then 
transferred, as above. In the figure draw a horizontal line, and with radius = D, of fig. 457, 
describe the semi-circle D E F G. With D, as center, and radius = distance D to E, of fig. 457 
describe an arc cutting the semi-circle at E, giving crank position O E, for Vo cut off. A 
similar construction gives O F, crank position for H cut off. After locating O E and O F, the 
semi-circle and radii D E and G F, should be erased leaving only the horizontal line and the 
two cut off positions O E and O F, to be used in the Bilgram diagram fig. 459. 



e:'/5C,o 



F^/fiC.O 




PORT OPENING ARC 



Scale: full size 



Fig. 459.— Bilgram diagram for main valve. Here the lap, angular advance, and travel are 
determined for J^ cut off and ^ port opening as explained in the accompanying text. 



VARIABLE CUT OFF 



265 



Example. — Determine the dimensions of a riding cut off that will meet 
the following requirements: maximum cut off % stroke; lead ^6 in.; 
ports, ^i in. ; port opening not less than 3^ in. for any cut off up to Vs 
stroke. Bridges ^2 in. ; connecting rod ratio 23^ : 1. 

1. Find crank position for Vs and J4 stroke as in fig. 457; 

2, Transfer the crank positions for \^ and ]4 cut off just found to fig. 459, 
as explained in fig. 458; 

Cm Cr 
NEUTRAL T POSITION 




STEAM EDGE 
STEAM PASSAGE 

I' H 




EXTREME 
POSITION 



Scale: half size 

Pigs. 460 and 461. — Detail of main valve and seat. On A B, lay off the steam port C E== 
M in., the port opening C D=^A in., and the bridge E F = H in. Sketch in valve end in 
extreme position. D, will be the steam edge. Lay off D H = ^ in. and draw D D', and 
H H', giving the steam passage through the valve. This is usually made same size as the 
port to reduce friction. I F, the end of the valve is located far enough beyond H H', to give 
a steam tight joint, say }4 in. Locate G, the exhaust edge of the valve, so that D G = lap + 
port =% in. +^ in. The edge G', of the bridge is so located that G G' = C E. The center 
line O O, is now drawn half way between P and G'. Transfer the detail of valve end thus 
found to A' B', showing it in neutral position, and complete the valve and seat as shown. 

3, Find outside lap and travel of main valve for He lead, J/g cut off, and a 
trial port opening of say, ^ in ; 

In fig. 459 draw the lead line Vie in. above, and parallel to the horizontal line. 
With radius O B =^ in. port opening, describe the port opening arc B D. 



NOTE. — In this chapter, O 0,=center line of valve seat; Cm=center line of main valve; 
Cr=center Hne of riding valve; Em=center of main eccentric; Er=center of riding eccentric; 
Ev =center of virtual eccentric. 



266 



VARIABLE CUT OFF 




> «> S^ 1^ «^ 

^•^rc; c ^ <u 
w o o <u.i2'^ 



Describe, with a center Q, 
and radius found by trial the 
lap circle tangent to cut off 
line O F, lead line and port 
opening arc B D. Q L, then 
= outside lap, and O Q=half 
the throw, or eccentricity. 

4. Draw main valve and 
seat as in figs. 460 and 461 ; 

5. Determine from fig. 
459 displacement of main 
valve for crank position O E, 
and draw valve in this 
position as in fig. 462; 

In fig. 459 draw Q M 
perpendicular to O E ex- 
tended which gives the dis- 
placement. 

Fig. 462 shows the valve 
in this position. This is the 
position of the main valve 
when the crank is at V« 
stroke, the point of cut off 
by riding valve. 

The crank and eccentric 
position corresponding to 
that of the main valve are 
shown at the right. 

It will be observed that 
the valve is practically fully 
open and about to change 
its direction of travel. 

If the angular advance 
of the riding eccentric be 
made Q', fig. 459, for Vs cut 
off, such that the riding valve 
will be in the neutral position, 
that is 0', will be on O E, 
the riding valve will be 
traveling at its maximum 
velocity, tending to give a 
sharp cut off which is to be 
desired. 

In fig. 459, the main 
valve for crank position O E 
(Vs cut off j is displaced the 
distance Q M, or its equal 
Q' M'. Now, if the riding 
valve had zero lap, the main 
valve port would still be 
covered by the distance Q' 
M'. Hence, if cut off is to 
occur at O E ( Vs stroke), 
the riding valve must have 
a negative lap equal to Q' M', 



VARIABLE CUT OFF 



267 




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268 



VARIABLE CUT OFF 



6, Determine if the port opening for Vs cut off be not less than the limit 

Fig. 462 shows the positions of the two valves at Vs cut off, their centers being 
displaced a distance Cr Cm^ If the crank be rotated backward, the port will be opened 
by a movement of the rnain valve to the left, and a movement of the cut off valve to the 
right. Hence, for position of 3^ port opening the crank must be rotated backward 
until Cr, reaches the position C'r, with respect to Cm, such that C'r Cm =Cr Cm — 3^ 
in. This position is obtained as in fig. 464, the valves and positions of eccentrics being 
shown in fig. 463. The figure shows that the port opening C D, of the main valve is 
less than C D', of the riding valve by an amount equal to D D''. At no point of admis- 
sion does the port opening become ^" because, as is evident, if the crank be turned 
backward the main valve closes; if forward, it opens, but the riding valve closes, hence, 
the design must be modified to obtain not less than ^" port opening through both 
valves. 




Scale: 
half size 



Fig. 465. — Bilgram diagram for modification of main valve and riding eccentric setting to 
give 3^ in. effective port opening for V5 cut off. The diagram is constructed in the usual 
way giving Q, for the modified main egcentric, and the new lap circle. Through Q.draw Q T, 
parallel with Vs cut off crank position O E Vs C. O. If the original negative lap of the riding 
valve be retained, its travel will remain the same but the angular advance will be slightly 
changed. With radius = the negative lap and center on the smaller travel semi-circle, describe 
an arc tangent to Q T, giving Q', the new position of the riding eccentric. For position 
O E 1/5 C. O., the main valve is displaced a distance Q A, hence the riding valve to cut off at 
this point must be displaced this distance minus its negative lap that is Q A — 0' N, or Q' A'. 



7. Modify design for Y^ in. port opening at Vk cut off; 

This may be done by re-designing the main valve for a larger port opening, say 
11/16, as in figure 465. 



VARIABLE CUT OFF 



269 




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270 



VARIABLE CUT OFF 




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VARIABLE CUT OFF 271 



The diagram, fig. 470, gives the displacement of the valves for the two cut oflFs, 
and figs. 471 and 472, the crank positions for }/^ port opening of the riding valve for the 
]4 and ^ cut off settings of the riding eccentric. 

Figs. 473 and 474 show the positions of the valves corresponding to the 14 and }4 
cut off respectively. 

Fig. 473 indicates that the later. cut offs are "sluggish," the valves traveling in 
the same direction at almost the same speed. From the positions of the eccentrics 
shown at the right, evidently, the main valve is traveling the faster, hence the riding 
valve will reopen the port, but as the main valve cuts off at this point, re-admission will 
not occur. 

Fig. 474 shows a sharper cut off at 3^ stroke. Here both valves are still traveling 
in the same direction, the main valve being almost stationary while the riding valve 
is traveling at about maximum velocity. 



EK2C.O. 

E^/8 CjO. 






Scale: full size 

Fig. 470. — Diagram for % and J^ cut off of the riding valve. Evidently for any cut off, the 
displacement of the riding valve is equal to the displacement of the main valve less the negative 
lap of the riding valve. Hence, describe an arc about Q, equal to the negative lap Q A', and draw 
a tangent parallel to the given cut off position of the crank, cutting the ridmg travel circle. 
Thus, for O E J^ C. O., the main valve is displaced a distance Q A. If the riding valve is 
to cut off at this point it must be displaced from the main valve an amount equal to its neg- 
ative lap, or A', that is, it is displaced a distance A A', on the other side of the neutral axis 
corresponding to O Cr, in fig. 473. The tangent through A', gives Q' , the corresponding position 
of the eccentric. Similarly for J^ cut off, Q B, is the displacement of the main valve, and 
QB — QB', or B B', displacement of riding valve, Q" being the corresponding center of 
the eccentric. Here B B', corresponds to O Cr, and B Q, to O Cm, in fig. 474. 

Fig. 466 shows a still sharper cut off at Vs stroke, the valves in this case moving 
. in opposite directions, the main valve being almost at rest, and the riding valve, at 

maximum velocity. 

Figs. 475 and 476 show position of valves for J^ in. port opening of the riding valve 
for the Vi and }4 cut off settings of the riding eccentric. The port opening of the 
main valve in each case being greater than }4 in. but less for }^ than for y% cut off. 

9. Test for over travel of the riding valve ; 

Figs. 473, 474 and 469 show that the earlier the cut off, the greater the angle be- 
tween the two eccentrics. In other words the shorter the cut off, the greater the travel 
of the riding valve with respect to the main valve regarding the latter as stationary. 



272 



VARIABLE CUT OFF 



Hence, assuming no overtravel of the riding valve with respect to the main valve, at 
latest cut off, it is desirable to know at what cut off overtravel begins, because the 
constant running of the engine with undertravel would cause the riding valve to wear 
a "shoulder" on the main valve, causing leakage and perhaps a knock at short cut off. 
Unless there be overtravel for cut offs near the working cut off (Vs in this case), the 
design should be further modified and the range of overtravel made as great as possible. 



E.it"P.O 



e:% CO. 




Scale: full size 



EVec.o. 




Scale, 



Figs. 471 and 472. — Diagrams for obtaining crank positions corresponding to }4 in. port 
opening of the riding valve for J4 and ^ cut off settings of the riding eccentric respectively. 



Regarding the main valve as stationary, the travel of the riding valve on the main 
valve may be regarded as obtained from an imaginary eccentric of such throw and 
angular advance as to duplicate the movement of the riding valve with respect to the main 
valve as obtained from the two eccentrics; such imaginary eccentric or radius is called 
the virtual eccentric, from which the cut off setting at which overtravel begins is 



VARIABLE CUT OFF 



273 




274 



VARIABLE CUT OFF 




VARIABLE CUT OFF 



275 



easily obtained. For this setting, clearly, the K travel of the riding valve on the main 
valve is equal to negative lap of the riding valve -{-width of the end bridge of the main valve 
as in fig. 477, the two valves being shown in the position at which over travel begins, 
that is "line and line" or "zero" over travel position-in fig. 478. Hence for this setting, 
the two eccentric centers, Q and Q', in the Bilgram diagram will be displaced a distance 
equal to Cf Cm, or A-f B in figs. 477 and 478. Q Q', in fig. 479 then is the radius or 
throw of the virtual eccentric. 

The cut off corresponding to zero over travel is determined as explained under the 
figure, being, as indicated in the diagram, fig. 479, 3^ stroke. This leaves no margin 
for cut off later than the working cut off, and in practice the design should be further 
modified to increase the range of over travel. A remedy would be to increase the throw 
of the riding eccentric. 

10. Locate the seat limit; 

This is done by the same method as explained on page 286, fig. 504, illustrating 
the seat limit for the Meyer main valve. 



WIDTH OF END BRIDGE 
JEGATIVE LAP 



LINE AMD LINE r^ 
OR ^ 



Cm 




Figs. 477 and 478. — Detail of one end of valves showing that the half travel of the riding valve 
on the back of the main valve or virtual half travel for zero over travel is equal to riding 
negative lap -\^ end bridge width. Fig 477, shows both valves in neutral position, and 478, 
valves in position of zero over travel. 

Evidently that portion of the valve which over travels L, is in balance with respect 
, to the steam, hence the shorter the length of the seat the less the load on the valve due 
to the steam pressing it down on the seat. 

Features of Riding Cut Off with Variable Angular Ad- 
vance. — ^A study of the example just given will show certain 
characteristics of the gear which are in brief: 



2. Increasing the angular advance of the riding eccentric shortens the cut ojf. 

2, The cut off is ** sluggish'' for late cut off, increasing in sharpness with 
the degree of expansion. 

3, The effective port opening decreases as the cut off is shortened, 

4, The virtual travel increases as the cut off decreases. 



276 



VARIABLE CUT OFF 



CO. FOR ZERO 
OVERTRAVEL 



Scale: half size 



■x-\ 



^^XijA- 



<\ ^^ 



\ \'^-V'\ \ 




^ ^ 



STROKE 



VIRTUAL ECCENTRICITY 
FOR ZERO OVERTRAVEL 



VIRTUAL HALF TRAVEL =^(QQ' OR ErE^,) 

Cr \ Cm 




END BRIDGE 



Figs. 479 and 480. — ^Application of Bilgram diagram for determining cut off setting of riding valve 
for zero overtravel. The two travel circles of the main and riding eccentrics, and Q, are 
transferred from 465, being here drawn on same scale as the valves. With Q, as center 
and radius equal to A +B, in fig. 477, describe an arc cutting the riding eccentric travel circle 
at Q'. Q Q', then is the virtual eccentric for zero overtravel. Draw crank position O E, per- 
pendicular to Q Q'. Evidently Q and Q', are at their maximum displacement, that is, Q', 
is at half travel with respect to Q, hence O E, is crank position when the valve ends are line 
and line or at zero overtravel, as shown in fig. 480, the distance Cr Cm =Q Q\ being called 
the virtual eccentricity. From fig. 480, for cut off, the riding valve must move to the 
right a distance equal to the width of the end bridge. Hence in fig. 479, on Q Q', lay off Q'B = 
width of end bridge, and with Q, as center and radius Q B, describe an arc. Draw through 
Q', a tangent to this arc Q' T, and O E', parallel to Q' T. O E' then is the crank position for 
cut off corresponding to zero overtravel. Utilizing the main eccentric travel circle as a crank 
circle, in connection with the dotted line construction to the left, the piston position cor- 
responds to O E', is found to be 34 stroke, the design giving overtravel for cut off not later 
than about }4 stroke. 



VARIABLE CUT OFF 



277 



VIRTUAL 
ECCtNTRiC 



VIRTUAL 

ANGULAR 

ADVANCE. 




Figs. 481 to 483. — ^The virtual eccentric. By definition: the virtual eccentric is an imag-> 
inary eccentric of such throw and angular advance that if keyed to the main shaft and con- 
nected with the riding valve, would give it a movement over the main valve (regarded as at rest) 

precisely the same as it has when both valves are moving. Fig. 482 shows both valves in neutral 
position, and in the diagram fig. 481, O E', is the crank position of cut off for zero overtravel. 
With a radius equal to Q Q' (fig. 479 = Cr Cm, fig. 4S0) describe a circle whose center is o. 
The diameter of this circle will be the throw of t\\e virtual eccentric, or virtual throw. For 
cut off at o E\ evidently the riding valve must move to the left a distance equal to the 
negative lap. Hence, lay off o B = negative lap, and project down the dotted line cutting 
the virtual throw circle at Ey Ev then is the center of the virtual eccentric, and its eccen- 
tricity is equal to o Ev, for the setting giving zero overtravel. 



278 



VARIABLE CUT OFF 



Scale: 
half size 



VQ CO. 
SETTING 



Riding Cut Oflf; Variable 
Lap. — This method of riding 
cut off is known as the Meyer 
gear, and is largely used in 
marine engines. The riding 
valve is operated by a fixed 
eccentric, and the cut off 
altered by varying the lap of 
the riding valve. 

The gear consists of a main 
and riding valve, the latter 
divided into two plates or blocks 
connected by a right and left 
handed screw, the screw serving 
as a valve spindle and as a 
means of varying the lap. 

The riding eccentric is fixed 
and usually has a throw 
greater than the main eccen- 
tric. Its angular advance is 
90° for reversing engines, and 
a little less than 90° for 
engines which run in only 
one direction. In this gear, 
as in all riding gears, cut oflE 
takes place when the riding 



Figs. 484 to 487. — Detail of valve ends with 
riding valve at end of virtual travel, 
showing undertravel for Ys and }^ cut 
offs, and overtravel for Vs cut oflf. In fig. 
484 imagine Em as center of main eccen- 
tric, fixed in such position that the main 
valve is in the neutral position, then 
Er, E'r and E'V are centers of virtual eccentric for the riding valve for throws corresponding 
to K, 3^ and V5 cut oflF respectively. As shown, the virtual eccentrics are at one end ot 
the throw displacing the riding valve a distance equal to H the virtual travel. 




VARIABLE CUT OFF 



279 



valve is at a distance from the center of the main valve equal to 
its lap, that is, when the steam edge of the riding valve is line 
and line with the steam edge of the bridge of the main valve. 
The following example will serve to illustrate the features 
of the Meyer gear. 

Example. — Design a Meyer valve gear for an 8 X 10 marine engine 
suitable for the following conditions of operation: Speed 300 R. P. M.; 

E'/eC.O. 

CI' 

E*/6C.O 




-TRAVEL OP MAIN VALVE.- 



-TRAVEL OF RIOINQ VALVE- 



Scale: full size 

Fig. 488.— Bilgram diagram for main valve of Meyer cut off gear, showing method of locating 
the riding eccentric to avoid readmission as at Q'. If Q', be located above Q X, a line drawn 
perpendicular to latest cut off O E J^ C. O., re-admission will not occur. 

lead j/fe; cut off range 3^ to Mi by riding valve, main valve cut off J^; 
connecting rod ratio 2:1. 

2. Find area of steam port; 

For a steam velocity of 6,000 ft. per minute through steam port. 

area piston X piston speed n^ 



area piston = 



6,000 

.7854 X diameter2 = .7854 X64 =50.27 sq. ins. 



280 



VARIABLE CUT OFF 



substituting in (1) 



piston speed =2 X — X300 =500 ft. 



50.27X500 , 
area = — =4.19 sq. ms. 



6,000 



2. Find width of steam port; 

width = area -^ length . 



(2) 




Scale: half size* 



Figs. 489 and 490. — Detail of trial main valve and seat for Meyer cut off. On A B, lay off the 
steam port C E =1^6 in., the port opening C D = width of port +i^ =i?^6 in., and the bridge 
E F =?say % in. Sketch in valve end in extreme position as in fig. 490. D, will be the steam 
edge. Lay off D H =width of poTt=^\^p in., and draw D D' and H H', giving the steam 
passage through the valve. H H' = height of exhaust cavity + thickness of metal over 
cavity = width of port C E +say H in. = 1 X% in. The steam passage through valve is usually 
made same size as steam port so as to reduce friction. I I', the end of the valve is located 
far enough beyond H H', to give a steam tight joint, say 3^ in. Locate G, the exhaust 
edge of the valve, so that D Q=outside lap+port (for zero inside lap) =i5^2+"/i6 = 1*'4' 
The edge G', of the bridge is so located that G G' =C E. The center line O O, is now drawn 
half way between F and G'. The center line Cm. of the valve is now located at a distance 
to the right of O O =one-half travel cf main valve, as measured from the diagram, fig. 488. 
Fig. 489 shows the valve and seat complete with valve in neutral position. The method of 
finding the seat limit is later explained. 



Call length .8 of cylinder diameter =.8X8 =6.4, say, 6.5 ins., then substituting in (2) 

width =4.19 -J- 6.5= .64, say .69 or %. 



VARIABLE CUT OFF 



281 



3, Design main valve \ 

The crank position for J/g cut off and Bilgram diagram are constructed in the usual 
way from the given data as in fig. 488 and the main valve shown in detail in figs. 489 and 
490. The port opening is made a little larger than 'the port {% in.) so that the effective 
port opening at short cut off will not be too small. 

4» Determine travel of riding eccentric; 

Since the engine must reverse, the angular advance of the riding eccentric is made 
90°, hence its center Q', in fig. 488, will be on the vertical line through O. To guard 
against re-admission Q', must be located on or above the line Q X, drawn perpendicular 
to O E, K C. O., the latest cut off. 



E.^eco. 




E'7/BC-O- 



Scale: full size 

Fig, 491. — Diagram showing laps for various cut offs of Meyer cut off gear. 



If Q', be located on Q X (fig. 488) , and the riding valve be given a negative lap equal 
to 0' Q, it will cut off and immediately re-admit at crank position O E (J^ C. O.). 

If the center of the riding eccentric be located at Q", below Q X, the riding valve 
will cut off and immediately admit again when the crank is at O E', before cut off by the 
main valve, thus disturbing the steam distribution to the cylinder; hence, the im- 
portance of correctly locating t|j^e riding eccentric, in this case giving it sufficient throw, 
the angular advance being fixed. 



5. Find lap for earliest }4> ^"^ off, and for latest cut off; 

Since both eccentrics are fixed Q and Q', in fig. 491 remain the same as in fig. 488. 
In fig. 491, draw crank positions for K and % cut offs, and through O, a line parallel to 
O E K C, O. 

The small lap circle at Q', tangent to the line parallel O E K C. O., gives the posiiive 
lap for % cut off. ¥ot% cut off, the main valve is displaced a distance Q A, on 



282 



VARIABLE CUT OFF 



one side of J4 C. O., and the riding valve, a distance Q' A'. The arc described about Q\ 
and tangent to a line Q T, through Q, parallel to O E J'^ C. O., gives the negative lap 
(Q' A'O for Vs cut off. 

6, Determine width of riding valve blocks', 

The blocks evidently must be wide enough so they will not re-admit steam by the 
back edges when at the end of the virtual travel. 

For shortest cut off the blocks are farthest apart, hence this setting and the 
virtual half travel must be considered in determining the width. Thus at shortest 
cut off, width of blocks =lap -{-width of port -{-virtual half travel -{rseal. 

Thus, fig. 492 shows main valve and one block in neutral position with positive 
lap A B, for shortest cut off. From steam edge of block, lay off to the right the positive 



WIDTH OF PORT 

VIRTUAL HALF TRAVEL 



TOTAL LAP ADJUSTMENT 
POSITIVE LAP 




Fig. 492. — Method of finding width of block of Meyer cut off gear. 

Fig. 493. — Modified main valve for Meyer cut off gear showing new location of the steam 
port H" D" in top of valve to permit lap adjustment of blocks for latest cut off. 



lap A B, and project up to A' B'. From B', lay off the width of port, virtual half travel 
and seal, making the latter say, H inch, giving C, which locates the inner edge of the 
bloclc. • 

7. Modify steam passage of main valve to permit lap adjustment of blocks ; 

In fig. 493 first draw the block of length just found. From the inner end I, of block 
lay off positive lap for H cut off and negative lap for J/^ cut off, as shown, thus locating 
the center line O O, of the riding valve for % cut off setting. 

Draw main valve referred to O O, and locate edges H D, of the steam passage 
through the main valve. The steam passage instead of being straight and terminating • 
at H' D', as in the preliminary design, must be curved outward and terminate at H" D", 
to permit negative lap adjustment for late cut off. The point H", is located at a distance 
from the steam edge L, of the block equal to the positive lap of earliest cut off. 



VARIABLE CUT OFF 



283 



8. Determine characteristics of the gear; 

Construct diagram, fig. 494, showing valve displacements for ^, i^ and 3^ cut 
offs, and diagram, fig. 495, showing valve displacements at middle of admission periods 
for ^, ^ and % cut off. settings. From these diagrams one half section of valves aa-e 
drawn m position corresponding to the cut offs, and mid-admission positions respec- 
tively as in figs. 496 to 498. 

The figures show that the sharpness or rapidity of cut off increases as the cut 
off is shortened, the valves moving in the same direction for ^ and ^ cut off, and ia 
opposite directions for H cut off. 



E % CO 



E '/zC.O. 



E. ^4 CO. 




Scale: half size P^ 

Fig. 494. — ^Valve displacement diagram ior %, }4 and K cut off. 



Cut off 
fositions 




Mid-admission 
positions 



Scale: half size 



Fig. 495. — ^Valve displacement diagram for mid-admission crank positions O E, O F, and O G 
corresponding to ^, J^ and % cut off respectively. 



Figs. 499 to 501 indicate that for mid-admission positions, the effective port opening 
is greater for the ^ cut off setting than for either the ^ or 3^ cut off settings. 

The reason the port is not fully open in fig. 499 is because the port opening of the 
main valve exceeds the width of the port. Henoe in such case the steam passage 



284 



VARIABLE CUT OFF 



V^CUT OFF Cr 




Figs. 496 to 498. — Positions of valves, eccentrics, 
and crank, for %, K and K cut ofE. By noting 
the positions of the eccentrics it is evident that as 
the cut off is shortened it becomes sharper. Figs. 
496 and 497 show valves moving in same direction, 
and fig. 498, valves moving in opposite directions. 



Scale: half size 



VARIABLE CUT OFF 



285 



*4 CO. SETT 




Scale: half size 



Figs. 499 to 501. — Positions of valves, eccentrics and crank for mid-admission corresponding 
to K, H and H cut offs, showing effective port opening at these positions. 



286 



VARIABLE CUT OFF 



through the valve should be widened at A (fig. 499) to A', making A A' = difference 
between the port opening of main valve and width of port in valve. 

It should be noted that the effective port opening in fig. 501 is not the maximum 
for }4 cut off, as by observing the positions of the eccentrics, it will be seen that the 

greatest opening occurs just after the rnid-admission position. The small port opening 
ere obtained at early cut off will indicate the necessity of designing the main valve 
for large port openings where the engine is to be worked_at early cut offs. 

Scale: half size 



'/fe VIRTUAL TRAVEL 

>L-^B 




NEG.LAP 



NE6. LAP. FOR ZERO 
Q OVERTRAVEL £^ 




ZERO.OVERTRAVEL 



VIRTUAL HALF TRAVEL 



Figs. 502 and 503. — Detail of valve end and diagram for finding cut off setting of the blocks 
corresponding to zero overtravel. 

9, Test for overtravel; 

Draw one end of main valve as in fig. 502. Lay off, from end of valve, A B =H 
virtual travel, then C D, is the negative lap setting for, zero overtravel. In the diagram 
fig. 503, describe the negative lap circle with radius Q'A=CD,in fig. 502. Draw 
tangent Q T, and crank position O Eq. parallel to Q T; then O Eq, is cut off settm^ for 
zero overtravel. 



SEAT LIMIT 



HALF TRAVEL 

Cm j_ O 




Fig. 504. — Seat limit for Meyer main valve. 



10, Locate seat limit. 

Draw end of valve in extreme position or at the end of its travel as in fig. 504. 
From the exhaust edge G, of the valve, lay off the seal, G S, say J4 inch, giving the 
point S, which is the seat limit. 



VARIABLE CUT OFF 287 



Features of Riding Cut Off with Variable Lap. 

From the example just given illustrating the design of Meyer 

gear for a marine engine, it will be noted that: 

i. Increasing the lap of the riding valve (that iSj moving the blocks apart) 
shortens the cut off; 

2. The cut off is ''sluggish" for early and late cut offy hut somewhat improved 
for intermediate cut offs; 

3. The effective port opening decreases as the cut off is shortened; 

4. Where very early cut off is desired, the main valve should he designed 
for large port opening, to secure adequate effective port opening at early cut off; 

5. For reversing engines, the angular advance of the riding eccentric should- 
he 90° to secure symmetrical distribution for both forward and reverse motions; 

6. For engines running in only one direction the angular advance of the 
riding eccentric is usually a little less than 90°; 

7. Re-admission is avoided by the proper location of the center Q', of the 
riding eccentric; 

8. The length of main valve may be reduced by shortening the latest cut off 
of riding valve. 

Riding Cut Off; Variable Travel. — This method of variable 
cut off is shown in fig. 505 to 512. For illustration and com- 
parison the main valve of the Meyer gear shown in fig. 489 is used 
with the same travel and angular advance. The maximum throw 
of the liding eccentric is made the same as for the Meyer gear. 
The amount of lap to be given the riding valve will depend on 
the earliest or latest cut off and angular advance of the riding 
eccentric. 

Taking Ql, fig. 505, for latest cut off with angular advance a little less 
than 90°, then if the earliest cut off is to be say, zero, the negative lap 
necessary is equal to the lap plus the lead of the main valve, because a line * 
Q A, through Q, parallel to crank position (E.O.C.O.) is above at a distance 
—lap-\-lead. 

The radius of the negative lap circle thus is equal to lap -{-lead of main 
valve. 

For latest cut off, describe a negative lap circle through Ql, and draw- 
tangent QT. A line Qo E.L.C.O., parallel to OT, gives crank position 
for latest cut off. 



288 



VARIABLE CUT OFF 



E.L.C.O. 



E'/6C.O. 




Scale: half size 



Figs. 505 to 508. — Bilgram diagram for riding cut off with variable travel and positions of valves, 
eccentrics and crank for latest, one-sixth, and zero cut offs. 



VARIABLE CUT OFF 



289 




LATEST 
C.O.SETTING 




Scale: half size 



Figs. 509 to 512. — Bilgram diagram and positions of valves, eccentrics and crank for mid- 
admission corresponding to latest, one-sixth and one-fourth cut offs, showing effective port 
opening. The diagrams show the gradual reduction in port opening as the cut off is short- 
ened, a defect inherent in this type of variable cut off gear. 



290 VARIABLE CUT OFF 



For 3^ cut off, draw QB, parallel to OE J^ C. O., and describe a second 
lap circle tangent to QB, and center on line QoM, giving the eccen- 
tricity Qo Q'^^ for H cut off. 

Figs. 505 to 508 show position of valves, eccentrics and crank for latest, 
3^, and zero cut offs. By observing the position of the eccentrics, the 
quality or sharpness of the cut off may be judged. 

In fig. 509 QoE, QoF and QoG, are mid-admission crank positions cor- 
responding to cut off settings of latest, 3^ and }^ cut offs respectively „ 

The valve positions corresponding to OqE, OqG, and OoF, respectively 
are shown in figs. 510 to 512, from which it will be noted that the effective 
port opening at mid-admission position rapidly decreases as the cut off 
is shortened. 

Features of Riding Cut Off with Variable Travel. — 

A study of figs 505 to 512 indicates the following characteristics 
■of this gear: 

1, Reducing the travel of the riding valve shortens the cut off; 

2, If the range of cut off be up to zero, the negative lap must he equal to lap 
plus lead of the main valve; 

3, For given angular advance and travel of the riding valve, latest cut off 
depends on the lap of the riding valve; 

4, The effective port opening decreases rapidly as the cut off is shortened; 

5, Sharpness of the cut off decreases as the cut off is shortened. 




MODIFIED ^LIDE VALVES 



291 



chaptp:r 7 

MODIFIED SLIDE VALVES 



Balanced Slide Valves. — Since the common D slide valve is 
only adapted to moderate steam pressures, it is necessary where 




Fig. 513. — The Richardson balanced slide valve. Packing strips S. S', are let into the top of th<!i 
valve so as to bear against a plate P, thus excluding steam from the top. A hole O, allpws 
any steam which might leak past the packing to escape into the exhaust cavity V. R is a 
shifting, or relief valve for use on locomotives to admit air into the steam chest, and prevent 
it being drawn in through the exhaust pipes when steam is shut off, and the action of the 
piston creates a partial vacuum in the steam chest. 



high pressures are used, that there be some means of balancing 
to prevent excessive friction and wear. This is done by ex- 
cluding the steam from the top of the valve so that its pressure 
cannot be exerted in a direction to press the valve against its seat. 

Fig. 513 shows one method of accompHshing this. The top of the valve 



292 



MODIFIED SLIDE VALVES 



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MODIFIED SLIDE VALVES 



293 



is provided with packing strips which bear against a plate P, attached to 
the steam chest cover, thus making a steam tight joint. The packing is 
fitted in steam tight grooves, and held in contact with the plate by springs 
underneath. By this means steam is excluded from the space between the 
packing. A hole O, allows any steam which may leak past the packing to 
escape into the exhaust cavity V. 

The several methods used in balancing valves will be illustrated in 
describing the different types. 



Piston Valves. — This type of valve consists of two pistons 




Fig. 516. — Piston valve 
with central passage lead- 
ing to lower port. This 
type of valve is used 
where the steam pipe is 
attached to upper cover 
and is objectionable in 
that the central pipe is 
exposed externally to the 
exhaust steam which 
lowers the temperature of 
the live steam; also the 
steam pipe must be dis- 
connected to remove the 
upper valve cover. 



which cover and uncover the ports in precisely the same manner 
as the laps of the plain slide valve as shown in fig. 514. 

A and A^ are the pistons which are connected by a central 
tube T. The valve works in the short barrels or bushings B, and 
B', which form the seat. 



294 



MODIFIED SLIDE VALVES 



The annular openings O and O', around the ports form the 
steam passages leading to the cylinder C. The valve is made to 
work steam tight by means of the packing rings shown in black. 

The barrels are perforated with numerous openings as S, 
through which the steam passes. The bridges thus formed permit 
the valve to work back and forth across the port without catching 




Fig. 517. — Double admission piston valve. An annular supplementary steam passage A, which 
acts in the same way as the Allen supplementary passage, gives the second admission. The 
valve IS of the inside admission type. , 

or jamming as would otherwise be likely to occur especially on 
account of the tendency of the packing rings to spring out into 
the ports. 

Fig. 517 shows a double admissionf piston valve. The prin- 
ciple is similar to that of the Allen valve. 

An annular supplementary passage is provided which gives a second 
admission. Steam is taken from the inside and exhausted at the ends as 
indicated by the arrows. On account of the surface cut away by the supple- 
mentary port, double admission piston valves are seldom provided with 
packing rings. 



MODIFIED SLIDE VALVES 



295 



The Armington and Sims valve is of the double inside"^ ad- 
mission piston type; instead of the annular passage as in fig. 517- 

Steam passes through a central passkge, being admitted at the inside 
and exhausted at the ends. 

A double ported f piston valve as used on the Ide engine is 
shown in fig. 518. 

This is also of the inside admission type. As shown in the figure, steam 
is admitted from the central cavity to the cylinder through the ports B 




Fig. 518. — The Ide double ported valve giving double admission, but only one opening for 
exhaust. Admission is from the inside, entenng the steam passage through the ports B and 
C ; exhaust passes through the valve to the ends of the cylinder. 

and C, and exhausted at the end through the valve, the course of the steam 
being indicated by the arrows. 



The piston valve is especially adapted to compound engines 
having the pistons working in unison (as on four cylinder loco- 
motives) or having the cranks 180° apart. In either case one 
valve is sufficient for the two cylinders. 



*N0TE. — In multi-cylinder engines using high pressure steam this is an advantage 
since with inside admission for the high pressure cylinder the packing around the valve stem 
is not exposed to the high initial pressure. 

tNOTE. — The difference between a double admission and a double ported valve should 
be clearly understood. A double admission valve gives two openings to steam both of which 
lead the steam to a single steam port in the seat, as shown in fig. 517. A double ported valve 
gives two openings to steam but a separate port is provided for each, as B and C, f:^- '^ !^- 



296 



MODIFIED SLIDE VALVES 



. D E F G F 




Pig. 519. — Detail of Chandler and Taylor balanced piston valve; A, BB, steam inlet ports 
to rings; CCC, steam space; DD, snap rings; E, connecting ring; F, F, wall rings; G, 
wedge ring. 




Fig. 520. — Vauclain piston valve of the Baldwin four cylinder compound locomotive. The 
pistons move in unison, steam being distributed to the cylinders with .a single valve as 
indicated by the arrows. 



MODIFIED SLIDE VALVES 



297 



As applied to locomotives, with pistons working in unison, 
the arrangement of ports, etc., is shown in fig. 520. 

Live steam is admitted to the high pressure cyHnder at the ends, and 
exhausted through an adjacent port in the valve, from -^hich it passes 
through the valve to an admission port at the opposite end for the low 
pressure cylinder. The final exhaust passes only through a central depres- 
sion and passage; the course of the steam through the engine is shown by 
the arrows. 



Fig. 521 illustrates a valve for a compound engine with cranks 
at 180° 



LOW PRESSURE CYLINDER 




HIGH PRESSURE CYLINDER 

Pig. 521. — Piston valve for compound engine distributing the steam to both cylinders. The 
cranks being at 180°, one valve suffices for both cylinders. The arrows indicate the path of 
the steam. 



The central part of the valve or seat is surrounded by steam which is 
admitted through an annular port to the annular valve space, which con- 
nects with the high pressure cylinder as shown. 

The valve has just opened for steam to the upper end of the high pressure 
cylinder, and the exhaust from the lower end is just entering the low pressure 
cylinder, while the low pressure exhaust is escaping from the upper exhaust 
chamber. 

The steam distribution is regulated by five ports: The central port 
admits and cuts off steam to the high pressure cylinder while the exhaust 
from this cylinder passes through its steam ports to the steam ports 
of the low pressure cylinder located at the ends of the seat. The exhaust 
from the low pressure cylinder is controlled by the outer edges of the valve; 
at the upper end the exhaust passes through the valve as indicated by 



298 



MODIFIED SLIDE VALVES 




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;3 







MODIFIED SLIDE VALVES 



299 




Fig. 523. — Sectional view of the Reeves compound engine with cranks at 180°, showing system 
of piston valves. The high pressure valve at the right is only for admission, the other valve 
distributing the steam as exhausted- from the high pressure cylmder to the low pressure 
cylinder. The arrows show the course of the steam in passing through the engine. 




^^^^ $TEAM CHCST 



mm^^m^.^x^v. 



Pig. 524. — ^Reeves double ported adjustable admission piston valves. 



300 



MODIFIED SLIDE VALVES 



Steam is admitted to the high pressure cylinder by a piston valve having 
internal admission and which acts as an admission valve only, being under 
control of the governor. The exhaust from this cylinder, and the compres- 
sion of both cylinders are controlled by the main or central valve which is 
operated by an eccentric with a fixed travel. 

It is obvious that any change in travel or cut off of the admission valve 
will not effect the cut off in the low pressure cylinder, therefore, changes in 
load and consequent cut off does not cause excessive compression as in the 
usual type of compound engines. 




Fig. 525. — Balancing cylinder (B ) , for balancing the weight of large heavy valves. 



On large vertical engines, provision is sometimes made to 
balance the weight of the valve and thus relieve the valve gear 
from considerable friction and wear as shown in fig. 525. 

An extension S of the valve stem is connected to a small piston A which 
works steam tight in a cylinder B. The upper end of the balancing cylinder 
does not admit steam, so that the steam pressure acts upward on the 
lower face of the small piston and balances the weight of the valve. 

The Double Ported Valve.— The difficulty of obtaining suffi- 
cient port opening for high speed engines having cylinders of 



MODIFIED SLIDE VALVES 



301 



large diameter and short stroke is overcome by providing double 
steam ports and constructing the valve to open them in unison 
as shown in fig. 526. It is equivalent to two plain slide valves — 
a long valve V, superposed upon a short one V, each having equal 
steam and exhaust laps. 




Fig. 526. — Double ported slide valve. There are two openings at each end of the cylinder 
(A B and A' B') for admission and exhaust of steam. The valve is equivalent to two plain 
slide valves: a long valve V, superposed upon a short one, and having communicating ex- 
haust passages E and E'. 





EXHAUST^ ^ ' ^^"'^EXHAUSTr, 

Pig. 527. — ^Valve of the Russel engine (Giddings type). Steam enters in the center and ex- 
hausts through the two adjacent cavities. The action of each end of the valve is similar 
to that of the Allen valve; the course of the steam is indicated by the arrows. To prevent 
the live steam lifting the valve from its seat, needle ports fnot shown) are used, one connecting 
the live steam space within the valve to the body of the valve chest, and the second con- 
necting the exhaust with the chest. 

The inner valve V, is similar to a plain slide valve except that there is 
communication between its exhaust space E, and the exhaust space E', of 



302 



MODIFIED SLIDE VALVES 



the outer valve. The two valves form one casting; steam is supplied to 
the inner valve through the passages S and S', which communicate with the 
steam chest at the sides of the valve. Each steam passage to the cylmder 
has two ports A, B, and A', B', and each port is made one-half the width 
necessary for a single port; hence, the travel is only half that required for a 
single ported valve having the same area as the port opening. The valve 
is balanced by means of an equilibrium ring R, fitted to the back of the valve 
as shown. 




Fig. 528.— Pressure plate valve of the Leffel engine. The object of the plate C, is to relieve the 
back of the valve A, from the pressure of the steam, this pressure being carried by the two 
distance pieces H, I, which register with the thickness of the valve. The plate with its de- 
pressions E, F, G, forms a second seat, thus making the valve double ported. The dotted 
lines indicate how the valve and plate are assembled. 

Pressure Plate Valves. — Most automatic cut off engines of 
the high speed type are fitted with valves having two faces, and 
which provide two, three, and in some cases a greater mmiber of 
port openings. 




MODIFIED SLIDE VALVES 



303 



The usual construction is shown in fig. 528. The valve A, 
consists of a long thin rectangular plate which works between 
the valve seat B, and the pressure plate C. This forms, in fact, 
a second seat having depressions E, F, G, corresponding to the 
steam and exhaust ports E', P', G'. By means of the rectangular 
openings in the valve, steam admitted to the ports in the pres- 
sure plate passes to the ports in the seat B. The valve is there- 
fore double ported. 

The pressure of the steam on the back of the plate is carried by two 
projecting strips or distance pieces H, and I, which correspond to the thick- 
ness of the valve, thus relieving the latter from the pressure of the steam. 




Fig. 529. — The Sweet pressure plate valve. C, is the pressure plate which relieves the valve 
of the steam pressure. This is a double ported valve with the second admission entering 
through the passage A, A separate passage B, is used for the second exhaust as seen in ex- 
haust position at the other end of the cylinder. 

By means of two adjusting screws M, and N, the ports in the pressure plate 
are brought opposite those in the seat. 

The action of pressure plate valves is best seen from sectional views 
showing the valve in its lead position as shown in the accompany cuts. 



Fig. 529 illustrates the Sweet valve which embodies all the 
principal features of valves of the pressure plate type. 

It is a double face valve, steam being admitted at the extreme ends of 
the valve, there being two steam edges at each end giving double port 
opening, as shown by the arrows. 

The passage A, conveys steam from the shallow recess in the pressure 
plate to the main port. 



304 



MODIFIED SLIDE VALVES 






Fig. 530. — Sweet valve and valve stem, showing valve assembled in valve chest of Ames engine, 
and parts dissembled. The valve with stem, straps and pressure plate as used on the Ames 
engine. The valve consists of a rectangular casting accurately finished to exact thickness; 
it operates between the seat and pressure plate which is maintained^ at the proper distance 
from the seat by the two strips of iron. The pressure plate is held in position by two fiat 
springs, so arranged that in case the engines receives a charge of water the pressure plate 
is forced from its seat, allowing the water to pass directly to the exhaust pipe. 



MODIFIED SLIDE VALVES 



305 



The chief object of the exhaust passage B, is to secure a quick opening 
and closing of the exhaust, so as to avoid wire drawing. After the exhaust 
is cut off, part of it is compressed and retained in this space before Hve 
steam enters the port. Directly after cut off this steam is allowed to mingle 
with the expanding steam in the cylinder. 

The projections D, D', are for the purpose of protecting the finished 
surfaces of the pressure plate from the cutting action of the exhaust steam. 

In fig. 531 is shown the Woodbury valve which combines the 
steam features of the Sweet, and Allen valves, giving four port 
openings to steam, and two to exhaust. 




Fig. 531. — The Woodbury pressure plate valve. This valve gives quadruple admission, and 
double exhaust. The dotted lines show a supplementary passage connecting E and F; this 
passage acts in the same manner as on the Allen valve. 

The openings A and. B, act in the same way as those of the 
Sweet valve. 

A supplementary passage is provided along each side of the 
valve, and connects the steam passages E and F. 

This passage is shown by the dotted lines and is similar in its action to 
the supplementary passage of the Allen valve. The quadruple admission 
and double exhaust are indicated by the arrows. 

A ledge G, is provided as is done in the Sweet valve to protect the finished 
surface of the pressure plate from the action of the exhaust steam. 



A valve which takes steam at the inside instead of at the ends 



306 



MODIFIED SLIDE VALVES 



is shown in fig. 532, which illustrates the valve, and used on the 
Armstrong engine. 

This valve gives four openings to admission as indicated in the figure. The 
steam pressure tends to lift the plate P, and it is therefore held down on 
its seat by means of the bridle B B. 




Fig. 532. — The Armstrong pressure plate valve. 




S^555^5^^5^ 



^^^^^^^ 



Fig. 533.— The Rice pressure plate valve. Double admission and e.xhaust, the admission being 
from the mside. 

Another valve taking steam from the inside is the Rice valve, 
illustrated in fig. 533. 

As shown, the valve gives two openings to admission and two to exhaust. 
The relief plate consists of a piston aa, fitted to a cy Under hh, which is bolted 



MODIFIED SLIDE VALVES 



307 



to the floor of the steam chest. The piston aa, bears against distance pieces, 
and is held in position by the pressure of the steam. 




Fig. 534. — The Ball valve consisting of two telescopic cylinders A and B, which are pressed 
against the seats by pressure of the steam within. A flexible connection is made with the 
valve stem by the two projecting fingers C and D. 




VALVE 



STEAM PASSAGES 

Figs. 535 and 536. — View of the Ball cylinder and valve, showing ports in the lower seat, and 
the circular exhaust passages. These indirect passages give a rather large clearance; aside 
from this the valve possesses some good features. 



308 MODIFIED SLIDE VALVES 

A modification of the telescopic piston and cylinder of the 
Rice valve is embodied in the design of the Ball valve as illus- 
trated in fig. 534. 

This valve consists of two overlapping cylinders A and B, having parallel 
valve faces at the outer ends. Steam is admitted to the interior of the 
valves which presses each face against its corresponding seat in the steam 
chest. The admission is therefore inside, and exhaust outside from which 
it passes to the exhaust pipe at the bottom as indicated in the figure. The 
only unbalanced area is that portion of the steam ports which is opposite . 
the cylindrical part of the valve during the exhaust period, the valve being 
so proportioned as to leave sufficient unbalanced pressure to secure a close 
contact between the working faces. 

A flexible joint is secured with the valve stem by means of the two fingers 
C, D, which engage in a grove in an end piece attached to the stem. 

The valve seats, ports, and steam passages are more clearly shown in 
fig. 535, and the valve in fig. 536. This valve adjusts itself to wear and has 
favorable conditions for a permanent, steam tight joint between the two 
cylindrical parts; it has the disadvantage, however, of a rather large 
clearance space and indirect steam passages. 



LOOSE ECCENTRICS 309 



CHAPTER 8 
REVERSING VALVE GEARS; LOOSE ECCENTRICS 



There are many conditions of service where it is frequently 
necessary to reverse the motion of the engine, as in the operation 
of locomotives, marine engines, traction engines, etc. Numerous 
valve gears have been designed by which this is quickly and 
easily done, moreover in most cases a considerable range of 
expansion is had by working in the intermediate positions. 

The simplest method of reversing an engine consists in 
rotating the eccentric around the shaft until it has the proper angular 
advance for reverse motion. This operation is shown in figs. 537 
and 538. In both figures the crank is shown in its mid position. 
The corresponding positions of the piston and valve are shown 
directly above. 

In fig. 537, the eccentric is set to run the engine ahead. To reverse the 
engine the valve must be moved an equal distance to the left of its neutral 
position so as to admit steam through the right instead of the left port. 
This is done as shown in fig. 538, the eccentric being rotated through the 
arc E E', making the angular advance A' OE', the same as A O E. This 
gives the valve the same linear advance to the left and opens the right port 
which reverses the motion of the engine.* 

A simple application of this principle is shown in figs. 539 and 540. 

The eccentric E, is loose on the shaft between a fixed collar G, and a 
• hand wheel H. A stud projecting from the eccentric, and passing through 
a curved slot in the wheel, can be clamped b}^ a hand nut F. 



*NOTE. — It should be noted that in the absence of indirect rockers, the eccentric is 
always placed hi advance of the crank, that is, ahead with respect to the direction of motion; 
hence, the direction in which an engine will run is easily determined by noting the eccentric 
position. 



310 



LOOSE ECCENTRICS 



When running forward with the crank at C, the eccentric center is at E, 
and the nut clamped at F. 

To reverse, steam is shut off, and when the engine stops, the nut F, is 
loosened, then moved to B, and clamped. The length and position of the 
slot is such that the angular advance A O E = A' OE', when the hand nut 





Figs. 537 and 538. — Simple method of reversing an engine. By rotating the eccentric on the 
shaft so that it will have a reverse angular advance A' O E' (fig. 538), equal to the forward 
angular advance A O E (fig. 537), the valve will be moved from M to M', and the engine 
will run in the reverse direction. The arrows show the steam distribution. 



F, is at either extremity of the slot. The letters are the same as in figs. 
537 and 538 for comparison. 



The usual method of rotating the eccentric to reverse on 
marine engines is shown in figs. 541 and 542. 



LOOSE ECCENTRICS 



311 



Figs. 541 and 542 show the -construction where the reverse 
gear is attached to the main shaft. In the figures the eccentric 
E, is keyed to a sleeve V, which fits so as to easily revolve on the 
main shaft S ; any movement in the direction of the shaft is pre- 
vented by the bearing B, and collar C. 

COLLAR 

ECCENTRIC V— 1 



HAND WHEEL 




Figs. 539 and 540. — Loose reversing eccentric; an application of the principle illustrated in 
figs. 537 and 538. The eccentric E, is free to turn on the shaft and is held in position by a 
stud and hand nut F. The stud passes through a circular slot in the wheel, so located that 
when the stud is clamped at one or the other end, the eccentric is in correct position for 
forward or reverse motion of the engine. 



A spiral slot M, is cut in the sleeve and hole bored in the 
end of the shaft to H. A straight slot is cut through a portion 
of the bore from H, to the other end of the spiral slot. The rod 
R, works in the bore and has attached to its end cross pins P, P', 
which pass through the shaft and sleeve slots. 



312 



LOOSE ECCENTRICS 




To change the position of 
the eccentric, R, is moved, 
which by the action of 
the pins in traveling the 
length of the slots causes 
the sleeve and eccentric to 
rotate on the shaft, thus 
changing the angular ad- 
vance. 

By giving the spiral slot 
the proper pitch, the eccen- 
tric may be rotated through 
the correct arc when P, is 
moved the length of the 
slot to reverse the motion 
of the engine.* 

This gear as applied to 
engines having valves on 
the side is shown in plan 
in fig. 543 which illustrates 
the construction for a 
compound engine, the 
cylinder outlines being 
shown in dotted lines. 

The eccentrics Eand E', are 
keyed to a valve shaft S', which 
is placed directly under the 
valves and at the sides of the 
main shaft S. 



♦NOTE. — This type of valve gear 
cannot be used to vary the expansion, 
because the travel remains constant, hence 
the lead becomes excessive for intermediate 
positions of the gear. 



LOOSE ECCENTRICS 



313 




314 



LOOSE ECCENTRICS 




Fig. 544. — End view of fig. 543 showing the two gear wheels G, G', which transmit motion 
from the main shafts to the spiral slotted sleeve V, and eccentric shaft S'. R, is the reverse 
rod. 




Fig. 545. — End view of loose eccentric reverse gear with idler between main shaft and valve 
shaft. By using an idler, the diameters of G, and G', may be made quite small, thus reducing 
the tangential velocity of the gear wheels which is desirable. V, is the spiral slotted sleeve; 
S, eccentric shaft, and R, reverse rod. The gear G', is keyed to the sleeve at K. In design, 
the sleeve should be thick enough so that it can be firmly keyed. 



LOOSE ECCENTRICS 



315 



o-^ owe 




Motion is trans- 
mitted from the main 
shaft to the small or 
valve shaft S', by the 
gear wheels G, G'; 
these wheels being of 
the same size, the 
two shafts revolve at 
the same rate, but in 
opposite directions,* 
the valve movement 
then, is indirect, and 
the eccentrics are 
therefore set 180** 
from the usual posi- 
tions. 

The gear wheel G •, 
is keyed to the sleeve 
V, which fits over 
the valve shaft, and 
which has a spiral slot 
M, and a turned pro- 
jection C, at its end. 

This projection or 
collar and the gear 
wheel prevent any 
lengthwise movement 
of the sleeve as it re- 
volves in the bear- 
ing B. 

The valve shaft is 
bored to the point H, 
and has a straight slot 
extending from H, to 
P. 






♦NOTE.— An end view 
of the gears G, G', is shown 
in fig. 544. Sometimes a 
third gear or idler is used 
as in fig. 545. Here the 
motion of the two shafts 
are in the same direction, 
and while there is an extra 
gear, it has the advantage 
of reducing the speed at 
the circumference which 
is favorable to quiet run- 
ning. 



316 



LOOSE ECCENTRICS 




A rod R is inserted in the bore and the cross 
pin P, attached in the same rhanner as in figs. 541 
and 542. 

Reversing is accomplished by sliding R, through 
the bore, which by the action of the slots and pins 
P, P', cause the valve shaft to rotate with respect 
to sleeve V, and thus change the eccentric to the 
position for opposite motion. 




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LINK MOTIONS 



317 



CHAPTER 9 
REVERSING VALVE GEARS, LINK MOTIONS 



The so-called Stephenson* Link Motion. — This, though 
one of the earHest forms of reverse gear is probably used more 
extensively than any other; in the opinion of the author it is as 




Fig. 550.— r/ie Williama Link. The *f olio wing quotation from Burgh's Link Motion and 
Expansion Gears is a full history of the so called Stephenson link motion including conver- 
sation of inventor with the author (Burgh). Howe's invention was suggested by the Wil- 
liams link shown above. "The inventor of the link motion in its simplest original and best 
form is Mr. W. Howe, who introduced it in the month of August in the year 1842. He was 
then a working mechanic in the employment of Messrs. Robt. Stephenson & Co., Engineers, 
Newcastle-on-Tyne. The history of the invention may now be given in Mr. Howe's own 
language, as expressed to the writer. A species of link motion (shown above) was, just 
before this date, suggested by Mr. Williams who was a young gentleman apprentice in the 
works at the time. In the figures. A, indicates the crank shaft B, the proposed link C. is 
the connecting rod, connecting the link to the valve rod D; E, are two eccentrics, and 
F, the block for reversing the motion of the valve and engine. It will be easily seen that 
the suggestion could never have been of the least practical use, because one eccentric bank 
would displace the other when in motion. Several persons employed in the works saw the 
drawing Mr. Williams had made, and amongst them Mr. Howe, but no one brought it into 
a state for practical application until August 1842, when Mr. Howe made a pencil sketch 
and a rough wooden model of his link motion, and both of the originals are now in the 
South Kensington Museum. This model so perfectly indicated what the curved link 
should be, that, acting uj^on the advice of his friend, Mr. Howe showed it to Mr. Hutchin- 
son, then the manager of Stephenson's Works, who at once saw the worth of its application 
practically, not one as a reversing but also as an expansion gear for working the slide valve, 
and he (Hutchinson) sent the model at once to Mr. Robert Stephenson, then in London, 
who also approved of it immediately he saw it. At the time, Mr. Howe was engaged in 
making a working model of a wedge motion for two locomotives, being built, but was directed 
to substitute for this, his link motion. He then made a full size model and proved the 
adaptation of the link motion for any grade of cut off. The dimensions were: outside lap 
one-half; under lap one-sixteenth; port opening 1 in.; throw 3: length of eccentric rods 
five in. 



318 



LINK MOTIONS 



REVERSE LEVrf\ 
FORWARD 

QUADRANT 



STEM 




beautiful a piece of 
mechanism as ever 
was invented. The 
name shifting link 
is sometimes used 
to distinguish . it 
from the stationary 
or Gooch link. 



The Stephenson 
link was originally 
intended for revers- 
ing only, but within 
certain limits it is 
used to advantage 
as a variable cut off 
or so called expan- 
sion gear. This 
feature is made use 
of especially on loco- 
motives, and marine 
engines. 



As shown in fig. 
551, it consists of a 
link L, block M, 



Fig. 551.— The so called 
Stephenson, or shifting 
link. There are two ec- 
centrics E and E', whose 
rods R, and R', are con- 
nected to the Hnk at A, 
and B . When A, is oppo- 
site the block M, as 
shown, the engine runs in 
a forward direction. To 
reverse, lever G, is 
moved to G", which 
brings B, opposite the 
block, thus the motion of 
the reverse eccentric is im- 
parted to the valve stem, 
and the engine reversed. 



LINK MOTIONS 



319 




-/. 



S' 



rm 



9 



T 






Fig. 552. — Plan of shifting link showing double reach rods S and S'. With two rods there is no 
lateral or twisting strain on the stem in reversing; this isa point well worth noting by anyone 
intending to purchase an engine, the ofTset torm of construction being objectionable.^ The 
reach rods are pivoted to the link at C,C', and to the reverse lever G, at D,D'. P is the 
valve stem pin. 

two eccentrics E,E', and eccentric rods R, and 

R', which are pivoted to the link at A and B. 

The valve stem has a forked end, and is 

pivoted to the block by the pin P. Reach rods 

S and S', (one on 
each side of the link) 
connect the latter 
with a notched quad- 
rant H , and latch I ^ 
which retains it in 
any position. 

The link which 
consists of two 
curved bars bolted 
together at the ends, 
freely slides on the 
block when the re- 
verse lever is moved, 
and to a limited ex- 
tent in operation. 

Fig. 553. — Upper end of single cylinder marine engine showing link with adjustable block. 
The link is provided with double reach rods having central connection on each side of the 
link preventing lateral strain. 




320 



LINK MOTIONS 



If the block be at one end of the link, the motion of the ec- 
centric attached to that end of the slot is transmitted to the valve ; 
when the block is at some intermediate position, the valve re- 
ceives the combined motion of the two eccentrics ; if the block be 

at the middle of the slot, or mid- gear, 
position, the valve does not admit 
steam to the cylinder. As shown 
in the figure, the bldck is at that 
end which is attached to the for- 
ward eccentric E, hence the engine 
runs in a forward direction. By 
moving the reverse lever to G", 
the link slides to the right until the 
other end P', which is attached to 
the backward eccentric E', is in 
contact with the block. The valve 
then partakes of the motion of this 
eccentric and the motion of the 
engine is reversed. 

With the reverse lever in any 
intermediate position between full 
gear and mid-gear, the cut off is 
shortened, . because the motion of 
one eccentric tends to counteract 
that of the other ; the combined effect 
is to reduce the travel of the valve. 

Fig. 554. — Small marine engine fitted with an offset shifting link; an objectionable construe- ■ 
tion._ When the link is not central with the axis of the valve stem there is a tendency for 
the link to turn about the valve stem axis every J^me the link is shifted by the reverse lever 
and also during operation a tendency to turn to and fro is caused by the slip of the block. 
The latter effect is augmented by the objectionable location ot the pivot at the center instead 
of at the end of the link inasmuch as the slip is increased when the pivot is at the center. 
This turning tendency is resisted by providing the valve stem with a square end section 
working m a bearing as shown. Evidently any lost motion due to wear will allow the link 
to get out of alignment and sometimes cause it to work roughly or stick in shifting. The only 
advantage due to offsetting the link is that it allows more room for a main bearing. In the 
above example, the square section of the valve stem should be much larger and preferably 
shaped as a flat bar of a width considerably greater than its thickness. The bearing should 
be adjustable for wear. 




LINK MOTIONS 



321 




Figs. 555 to 558. — Movement of the link during one revolution. The figures show the positions 
of the link gear when the crank C is on the dead center, and at H, H and ^ of a revolution. 
The point of suspension being at the center, as on locomotives, the slip is considerable. 



322 



LINK MOTIONS 



Some of the different positions taken by a link for one revolution of the 
crank are shown in figs. 555 to 558, which illustrates a locomotive link 
motion in full gear for four positions of the crank. Fig. 555 shows the gear 
with crank C at the beginning of the stroke; the other figures illustrate 
the position of the link when the crank has made 34, H, and % of a revo- 
lution.* 

Ques. What is the difference between open and crossed 
rods? 

Ans. The eccentric rods are said to be open, if they do not 
cross each other, when the eccentric centers lie between the link 





Figs. 559 and 560. — Diagrams illustrating open, and crossed rods. In shortening the cut off 
by "hooking up," open rods give increasing lead, crossed rods, decreasing lead. When 
it is intended to work the engine linked up, as with a locomotive, it is advisable to have the 
rods open, as a greater range of expansion is obtainable with less reduction of port opening 
than with crossed rods. 



and shaft center as shown in fig. 559. If the reverse condition 
obtain, as in fig. 560, the rods are said to be crossed. 

Ques. What is the effect of open and crossed rods on the 
steam distribution ? 



*N0TE. — In figs. 555 to 558 the reach rod is shown attached to the central portion of the 
link instead of at the end. ^ This construction is for locomotives on account of the position of 
the rocker arm but the action of the link is not so good as when the attachment is at the end 
as in figs. 575 and 576. 



LINK MOTIONS 



323 







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LINK MOTIONS 



The effect of open and crossed rods is shown in figs. 562 to 565. The 
first two figures illustrate why the lead increases with open rods when the 
link is moved from full to mid gear. On account of the inclination of the 
rods, and the position of the eccentric centers both rods tend to push the 




Pigs. 562 and 563. — Diagrams illustrating why open rods give increasing lead. In shifting 
the link trom lull to mid gear, the angularity of the rods is so changed that the valve stem 
pin P, and valve are moved to the left a distance L, thus increasing the lead this amount. 

link and valve to the left at the beginning of the movement. The upper 
rod, after passing the horizontal position, partially counteracts the move- 
ment imparted to the link by the lower eccentric resulting in a gradually 
increasing lead in amount equal to L. The position of the link center for 
full gear (fig. 562) should be noted. 

Figs. 564 and 565 show why crossed rods decrease the lead from full to 



LINK MOTIONS 



325 



mid gear. The combined effect of the angularity of the rods is such that 
in moving the hnk from fitll to mid gear the Hnk and pin P are moved to the 
right a distance L, this decreasing the lead by that amount. • 

In both cases the valve is shown in one of the positions with zero lead, 
that is, in line and line position to clearly illustrate the change in lead. 




Figs. 564 and 565. — Diagrams illustrating why crossed rods give decreasing lead. In shifting 
the link from full to mid gear the angularity of the rods is so changed that the valve stem 
pin P and valve are moved to the right a distance L, decreasing the lead this amount. 

Short rods are used to emphasize the effect of open and crossed rods on the 
lead. 



Oues. When should open and crossed rods be used ? 

Ans. If the link motion is intended to be used as an expansion 



y2Q 



LINK MOTIONS 



gear, on a locomotive, open rods should be used as a greater 
range of expansion may be obtained with less reduction of port 
opening than with crossed rods.* If the link is to be used 
only in full gear, or in connection with an independent cut off, 
crossed rods may be used, and the link made straight. 

Oues. How early may steam be cut off with the 
Stephenson link? 




Fig. 566.— Reeves link motion adjustable cut off for engine driving centrifugal pumps, fans, 
etc. The cut off may be varied while the engine is in motion. The parts are: A, link; B, 
link block; C, D, eccentric rods; E, adjusting block; F, adjusting screw; G, adjusting crank. 



Ans. This depends on the amount of port opening at full 
gear. If, as with locomotives, the port opening at full gear be 
greater than the width of the port, fairly good admission may be 
obtained, cutting off as early as one-quarter stroke. For shorter 
cut off, the admission is poor and one-sixth stroke may be 
taken as the minimum cut off with the ordinary valve. 



*NOTE. — On locomotives it is necessary to give little or no lead, and make the port 
opening greater than the port for full gear in order to prevent excessive lead and too little port 
opening at early cut off. 



LINK MOTIONS 



327 



Ques. What are the diflferent forms of the shifting link ? 

Ans. The slotted link as already described, the open, the 
double bar marine type, and the box link. 

The open link is similar to the ordinary link but differs in that the eccen- 
.tric pins, instead of being attached to one bar, are located as shown in fig. 
567. With this construction, the eccentrics must have a larger throw, since 




M® 




Fig. 567. — The open link; used chiefly on British locomotives where there are no rockers. 
The eccentric rods are pivoted at A and B, and the link suspended from the upper rod pin. 
The fixed point of the reach lods is below the central line of motion. 



pm- 




jrn 



B 



•J 



"^W 




Figs. 568 and 569.— The double bar link as used on marine engines. The eccentric rods are 
pivoted at A, B, and C, D, on the central arc of the link which improves somewhat the steam 
distribution. 



328 



LINK MOTIONS 



the eccentric pins move a greater distance than the maximum travel of the 
valve. The open link is used chiefly on British locomotives where there is 
no rocker, the link being hung from the upper eccentric rod pin with reverse 
shaft below the central line of motion. 

The double bar marine type link is shown in figs. 568 and 569. It con- 
sists of two bars curved to the proper arc and connected at their ends by 
sleeve bolts which retain the bars at the desired distance apart. The 
eccentric rods are attached to two pairs of pins A, B, and C, D, each rod 
end having a double bearing. A third pair of pins E, F, receive the reach 
rods; these pins may be either located at the center as shown, or at the end 




aLOGK HAND WHEEL 

Pig. 570 and 571. — Independent cut' off adjustment for link motion; usually fitted to one or 
more cylinders on multi- cylinder marine engines. This permits regulation of the expansions, 
receiverpressures.etcso as to get a steam distribution best suited to the running conditions. 



as in fig. 575. On marine engines, an independent adjustment for cut' off 
is frequently fitted to the high pressure cylinder valve gear, and sometimes 
to each cylinder. 

With link motion, the independent adjustment as shown in figs. 570and57l 
consists of an arm A, keyed to the reverse shaft, and having at its end, a 
slot within which works a block with screw adjustment. 

The reach rods are attached to pins which project from the block; by 
turning the wheel. W, the block is moved in the slot which changes the 
position of the link and thus alters the cut off. Fig. 572 shows the adjust- 
able cut off arm as fitted on marine engines. 

The box form of link which has the pins in the line of the slot itself is 
shown in fig. 573. Where a short eccentric throw is desired the box link is 



LINK MOTIONS 



329 



used to advantage. It is, however, expensive to make on account of the 
difficult construction. 

Oues Why is a link slot curved ? 

Ans To equalize the lead of the valve for all travels. The 
radius of the link is so proportioned as to make the increase or 
decrease of the lead the same for both strokes of the piston.* 




ADJUSTABLE ARW\ 

Fig. 572. — Independent cut off adjustment for link motion; view showing gear assembled on 
engine. The reach rods are pivoted to a block which works on the. screw S. By turning this 
screw at W, the block is moved in the f^lot and the link shifted, thus changing the cut off. 

ECCE>rTR»C ROD 
PIMS 




^^<'-cr: 







Figs. 573 and 574. — The box link. Used to advantage where a short eccentric throw is desired 
since the valve travel is about the same as the throw. The box link is difficult to construct. 



Oues. What effect has the action of the link on release 
and compression? 

*N0TE. — The radius of the link is a little less than the length of the eccentric rod, or 
about twice the (lap+lead) less than the distance from the center of the link block to the 
center of the eccentric. 



330 



LINK MOTIONS 



Ans. As the cut off is shortened by shifting the position of 
the Hnk, these events occur earlier. 

On locomotives, this peculiarity of the link motion is, within limits, an 
advantage, because when a locomotive is running fast, steam is cut off 
short, and early release and compression is desirable since owing to the 



SLIP WtTH END SUSPENSION 





SLIP WITH CCNTER SUSPENSION 





CENTER SUSPENSION 



Figs. 575 and 578. — Diagrams illustrating the effect of end, and center suspension. When 
possible, the point of suspension should be at the end of the link as shown in fig. 575, because 
the slip is less than with center suspension as in fig. 578. 



LINK MOTIONS 33*^ 



high piston speed-, more time is needed for pre-release, and the increased 
cushioning due to the early compression is absorbed in bringing the re- 
ciprocating parts to rest. The clearance space is thus filled with steam at 
a higher pressure, which reduces the amount of live steam required to 
increase the pressure in the clearance space to that of admission. 

Oues. What is the ''slip?" 

Ans. The sliding of the Hnk on the block which occurs during 
each stroke. 

Oues. Why does the link slip? 

Ans. The center of the block, being pivoted to the valve stem, 
moves in a straight line, while the ends of the reach rods which 
guide the link have a circular movement, hence a side wise 
motion is given to the link, causing it to slip or slide on the block. 

In addition to this, slip is occasioned by what might be called "the 

• angularity of the link," that is, the inclined positions which it takes, cause 

a sliding action as indicated in figs. 575 to 578. It should be noted that 

the end of the link is furtherest from the block when the link is in the nearly 

vertical positions shown at the left of the figures. 

Owes. What is the point of suspension? 

Ans. That point where the reach rods are pivoted to the link. 

Oues. What is the fixed point? 

Ans. The center on the rocker arm at which the reach rods 
are pivoted, and about which the rods swing; the swing center 
of the reach rods. 

Oues. What determines the position of the point of 
suspension? 

Ans. The type of engine, and conditions of operation. 

On locomotives the link is usually suspended near the center, but where 
conditions permit, the point of suspension is best located near the end. 

Figs. 575 to 578 show the two locations of the point of suspension. 
In each figure the link is shown in two corresponding positions from which 



332 



LINK MOTIONS 



is seen the effect which changing the point of suspension has on the sHp. 
As shown in the figure the sHp is less when the hnk is suspended at the end, 
than when suspended at the center. The point of suspension is sometimes 
offset from the Hnk arc, the object being to secure the minimum slip for 
the gear position in which the engine is mostly run. 

Owes. When is the slip greatest and least ? 

Ans. Greatest in full gear, and least in mid gear. 

Owes. What conditions tend to reduce the slip? 

REVERSE ROD 

i 



VALVE STEM 



CENTER 
SUSPENSION 




Fig. 579. — The Gooch stationary link; used chiefly where the valve requires no rocker, as on 
British locomotives. The lead is constant for all cut offs. An abjection to the Gooch link is 
that it requires considerable distance between the shaft and cylinder on account of the long 
radius rod A. 

Ans. Considerable angular advance, short travel, short 
eccentric rods, and a long link. 

Owes. How long should the link be made? 

Ans. It ought to be of such length that its movement in 
reversing is from 23^^ to 3 times the travel of the valve. 



The Stationary Link. Shortly after the appearance of the 



LINK MOTIQNS 



333 



shifting link came the stationary Hnk, also known as the Gooch 
link, named after its inventor Daniel Gooch. It has been used 
extensively on locomotives throughout Great Britain, and the 
continent, but is little used on American locomotives as it is not 
adapted to engines having steam chests on top the cylinders; 
it is especially suited to engines having no rockers. 




-K* 



Fig. 580. — Stationary link motion. Diagram for setting the eccentrics as given by Clark. 
The eccentrics must be so placed as to yield the necessary linear advance of the valve, or the 
double of it between the positions of the link at the two ends of the stroke. Let X X', above 
be the center line, and O , the center of the driving axle. Through O, draw the vertical Y Y', 
and describe the circle A, 43^ ins. in diameter, for the path of the eccentrics. Draw the 
parallels M, N, 12 ins. apart, equally distant from the center line, — the centers of the link 
being 12 ins. apart. On the center O, with the length of the eccentric rod as radius, which 
in this case is assumed for convenience at 27 ins., or six times the throw of the eccentrics, 
cut the line M , at T , and draw TO , set off O R and O S , each equal to the linear advance of the 
valve, — 1-^6 ins. — and draw the perpendiculars RA, SA", to meet the circle. Draw the diam- 
eter A A", then OA and O A",are the positions of the fore eccentric for the lead of the in and out 
strokes respectively. From A and A" as centers, with the length of the rod, cut the line M, at 
B and B", and join AB and A" B". These are the positions of the fore eccentric rod for the 
out and in strokes; and the space BB'', equal to RS, measures twice the linear advance of 
the valve. This construction is empirical, but it is in ordinary cases satisfactory, and the 
points are easily adjusted, if the interval BB'', be not exactly equal to twice the linear ad- 
vance. The position of the back eccentric at A' and A"', is found by drawing parallels to the 
vertical Y Y', through the points A and A". The lower centers of the link, at B' and B"\ are 
found similarly to the centers at B and B''. Draw BCB' and B", C W , for the relative posi- 
tions of the link. From C and C, as centers, with thelength of the sustaining link as radius, 
find the point of intersection F, the position of the fulcrum, over which the hnk will vibrate 
equally on both sides of the vertical FD. The linear advance of the eccentrics, that is, the 
perpendicular distance of their revolving centers from the vertical CD, does not exceed 
seven-eighths inch, which is nevertheless sufficient, aided by the obliquity of the rods, to 
cause an advance of l^e ins. at the link. Applying the samemethod to find the set of the 
eccentrics for the 54 inch rods of the valve motion already illustrated, the advance of the 
eccentrics is exactly 1.075 inches, or over IVfe ins., for I'^g ins. of advance of valve. The 
open forms of link require a like process for the setting of the eccentrics. 



334 



LINK MOTIONS 



The stationary link requires considerable distance between the 
shaft and valve by reason of the long radius rod necessary be- 
tween the link and valve stem. Its feature with respect to the 
steam distribution is that it gives constant lead for all cut offs, 
with either open or crossed rods. 

The concave side of the link is turned toward the valve as shown in fig. 579 
the radius of the link being equal to the length of the radius rod A. To 
reverse the engine, the block M, is moved in the slot by the lever C, and 
reverse arm C, both keyed to the reverse shaft E, the movement being 

REVERSE ROD 




VALVE 



Fig. 581. — The Allen straight slot link; a modification of the Gooch link, and designed to 
secure equal steam distribution at each end of the cylinder. 

transmitted to the radius rod A, through the reverse link L. The link is 
suspended at F, by the reach rod G, which is pivoted at the fixed point H. 
Since the radius of the link is equal to the length of the radius rod A, it is 
evident that the block may be shifted from one end of the slot to the other 
without moving the point S, therefore the lead remains constant for all 
degrees of expansion. 



The Allen Link. — This form of Hnk motion invented by 
Alexander Allen was designed to combine the leading features 
of both the Stephenson, and Gooch links. It is so ■ constructed 



LINK MOTIONS 335 



that the parts are almost balanced, hence on locomotives it does 
not require equalizing springs, or counterweights. 

As shown in fig. 581, it consists of a straight link, with a radius rod A, 
and block M ; both link and rod are moved by a double suspension lever, 
or rocker with arms C, C\ attached to the reverse shaft E. Since the link 
is straight, the center of travel of the block varies, but this is compensated 
for by the effect of changing the slant of the radius rod A. 

The position of the link and radius rod is shifted by means of a third 
arm D, attached to the reverse shaft E. The proper proportioning of the 
two arms C, C is an irnportant point in the design of this link motion. 

Oues. What effect has the Allen link motion on the 
lead? 

Ans. With crossed rods, the lead decreases as the cut off is 
shortened. 

Ones. Is the variation of lead greater with the Allen 
or Stephenson gear? 

Ans. With the Stephenson gear; a well proportioned Allen 
gear, having a long radius rod and short travel, will give prac- 
tically constant lead. 

Ones. What are the advantages of the Allen link? 

Ans. The parts being in balance require no equalizing springs 
^or counterweights ; the slip is small. 

Oues. What disadvantages does the Allen gear possess? 

Ans. It requires considerable distance between the valve 
.and the shaft on account of the radius rod. The lead is constant, 
which is not desirable for locomotives. More parts are required 
than with other types of link. 

The Allen link is specially adapted for use on inside connected loco- 
motives, that is, locomotives having steam chests at tne side of the cylinders 
although a modified form of the Allen gear has been used on American 
locomotives. 



336 



LINK MOTIONS 



The Fink Link, — This is a simple form of link motion and 
is used on the Porter- Allen engine. The lead is constant, and 
its principles of operation are illustrated in fig. 582. 

The link forms a part of the eccentric strap, and is suspended 
at F, the fixed point being below at B. Cut off is varied by shift- 
ing the position of the block M, to which is pivoted the steam 
radius rod D. The figure shows a separate exhaust radius rod D', 



GOVERNOR ROD 
D' 



EXHAUST ROD 




Fig. 582.— The Fink link; a simple form of motion. Its special feature is the long range cut 
off, obtained without disturbing the motion of the exhaust valve. 



which is set permanently in full gear; this rod operates the 
exhaust valves independently of the steam valves. 

Cut off is made automatic by a connection G, to the governor. 
When the Fink link is used as a reversing gear, the point of 
suspension F, is placed at the intersection of the line of centers, 
and a perpendicular to it through the center of the link block 
when in full gear. 



LINK MOTIONS 



337 



The link receives a peculiar motion on account of the horizontal and the 
vertical throws of the eccentric. The horizontal throw alone only moves 
it from one to the other of the lead lines, which motion only draws off the 
lap of the valves. 

The opening movement is produced by the tipping of the link alter- 
nately in the opposite directions beyond the lead lines, these tipping motions 
being given by the vertical throws of the eccentric. 

The upward throw tips the link in the direction from the shaft, and 
opens the port at the further end of the cylinder; and the downward throw 
tips the link towards the shaft, and opens the port at the crank end of the 
cylinder. At the same time its horizontal, throw is drawing the valve back, 
and when, in this return movement, that point in the link at v/hich the block 
stands, crosses the lead line, steam is cut off. 




Figs. 583 and 584.-^Side and end views of the Fink link as constructed for the Porter- Allen 
engine. 



Figs. 583 and 584 show a side and end elevation of the Fink 
link as designed for the Porter-Allen engine. It should be noted 
that the link is suspended from both sides, thus avoiding any 
lateral stresses. The range of cut off is from zero to six-tenths 



338 LINK MOTIONS 



of the stroke. The link is especially suited to a long range cut off 
since the exhaust features are not affected by the degree of 
admission. 

The exhaust valves open and close their ports in such a manner that the 
opening is made while the valve is moving swiftly, and one-half of the 
opening movement has been accomplished when the piston arrives at the 
end of its stroke. 

The valves are so constructed that this portion of the movement opens 
the full area of the port, which does not begin to be contracted again until 
the center line of the link has recrossed the lead lines on its return. The 
speed of the piston is then also diminishing, and the exhaust is not throttled 
at all until the port is just about to be closed. By raising or lowering the 
fixed point B, fig. 582, the equality of lead, and port openings in the two 
strokes is regulated. 

According to the builders of the Porter-Allen engine, this point should 
be so adjusted that the arc of motion at F, shall be tangent to the center 
line of the engine. The motion of F, is distorted on account of the obliquity 
of the line F E. To neutralize this, the makers use a rocker to reverse the 
motion of the valve, and put the center of the eccentric on the crank axis. 

The ratio of F E, to O E, is made the same as the ratio of connecting rod 
to crank so that one error offsets the other, hence the lead and cut off can 
both be equalized. 




RADIAL VALVE MOTIONS 339 



CHAPTER 10 

REVERSING VALVE GEARS; 
RADIAL VALVE MOTIONS 



The object sought in the introduction of the so called radial 
gears is to overcome the defects of the shifting link gear, and in 
some cases to obtain a more accessible gear. 

While the shifting link gives equal lead for various cut offs 
it does not give constant lead, that is, as the cut off is shortened, 
the lead increases or diminishes according as the link is arranged 
with open or crossed rods. Moreover, premature compression 
occurs as the cut off is shortened. These distortions in the 
steam distribution are in many cases undesirable. These de- 
fects, and the desire to avoid a multiplicity of eccentrics on multi- 
cylinder engines, are the chief reasons for the adoption of radial 
gears. 

The better steam distribution secured by radial gears is in some cases 
more or less offset by complicated construction consisting of numerous 
parts and joints subject to wear.* 

General Principle of Radial Gears. — The object sought 
in the invention of radial gears is to obtain from some recipro- 
cating or revolving piece oj the engine, an arrangement of mechanism 



*NOTE. — According to Sothern (Principal, Sothern's Marine Engineering College, 
Glasgow), the general experience of engineers is that the disadvantages of radial gears more 
than balance the advantages, with the result that the ordinary link motion will be found 
fitted in even the most modern and up to date marine engines, as being simpler and more 
reliable. 



340 



RADIAL VALVE MOTIONS 



LAP + PORT 

OPENING 




a point in which shall 
describe an oval curve, 
and by altering the direc- 
tion of the axes of this 
curve, to produce variable 
cut off and reversal. 

Accordingly, a radial 
gear may be defined as 
one in which the motion 
of the valve is taken from 
some point in a vibrating 
rod, one end of which 
moves in a closed curve, 
while a third point on the 
rod moves in a straight 
line or open curve. 

Hackworth Gear. — 

This gear, which was 



HACKWORTH 
GEAR 

Inside connected type 
Forward motion 



ECCENTRIC ROD PIVOT 
ECCENTRIC ROD 
ECCENTRIC 



invented by 
John W. 
H ackworth, 
and patent- 
ed in 1859. 
and 1876, was the 
first radial gear and 
it probably gave 
rise to all modem 
radial gears. 

Fig. 585. — Hackworth in- 
side connected valve gear 
as constructed for a 
marine engine ; view show- 
ing the various parts and 
their names. 



RADIAL VALVE MOTIONS 341 

The principle of the Hackworth gear, as stated by Seaton is 
as follows: ''The motion of a point on a rod, one end of which 
moves in a circle, and the other on a straight line passing through 
the center of that circle, is on an ellipse whose major axis coincides 
with the straight line. If, however, the end of the rod slide on a 
line inclined to this center line, the major axis of the ellipse will 
he inclined y 

There are two types of Hackworth gear which may be clas- 
sified as: 

1. Inside connected; 

2. Outside connected; 

according as the valve rod is connected to the eccentric rod 
between the eccentric and eccentric rod pivot, or beyond the 
eccentric rod pivot. 

Fig. 585 shows the inside connected type as arranged for outside ad- 
mission. Its essential parts are: eccentric, eccentric rod, link, valve rod, 
eccentric rod pivot, link pivot, and valve rod pivot, and means for shifting 
and securing the link in any position within its arc of adjustment. As 
shown, the center of the eccentric is at E, or opposite the crank, corre- 
sponding to 90 degrees angular advance. 

The link consists of a straight slot and guides a reciprocating block 
which is pivoted to the end of the eccentric rod at F. The pivot L, of the 
link is located in the line X X', which passes throllgh the center of the 
shaft perpendicular to the cylinder axis Y Y'. The point of cut off and 
direction of rotation of the engine depend upon the angular position of the 
link witji respect to the axis X X'. 

The location of pivot L, and length E B, of the eccentric rod is such 
that E B =E' L. When these two distances are equal, F, will coincide with 
the center L, of the link when the connecting rod is on either dead center, 
and the slotted link may be turned from full gear forward through its 
horizontal position to full gear reverse without moving the valve. Hence, 
when the lap is the same on both ends of the valve the leads are constant 
for all positions of the link, and consequently for all cut off. 

The valve is set by adjusting the valve stem for equal lead. 

The correct location of the valve rod pivot V, is necessary to secure 
proper steam distribution. V, must be so located that when the engine is 



342 



RADIAL VALVE MOTIONS 



LAP + LEAD 



on the dead center and the link is 
in its horizontal position the distance 
from V to the horizontal axis X X' 
= lap-\-leadf as shown in fig. 586. 

The operation of the gear may 
perhaps be better presented graph- 
ically than by description. Thus, 
figs. 587 to 5iO show the positions 
of the gear in full forward motion 
for the principal events of the stroke, 
viz.: lead, cut off, pre-release, and 
compression, and figs. 591 to 594 
similar positions in full reverse 
motion. 

Figs. 595 to 597 show the gear 
in full forward motion for various 
inclinations of the link giving various 
cuts off. 

In addition to permitting re- 
versal with only one eccentric, 
the chief advantages of this gear 
are its quick motion at the point 
of cut off and the large range 
of cut off possible, wire drawing 
from small opening and slow 
closing of the port, as is the 
case with the shifting link 
motion. 
The chief objec- 
tions to Hack- 
worth's gear are: 
1. The friction and 
wear of the block and 
link especially when 
the link is inclined to 
the XX' axis; 



Fig. 586. — Hackworth gear at dead center p»sition showing that 
the valve rod pivot V, must be so located on the eccentric rod 
that its distance from the horizontal axis X X' = lap -\-lead. This 
must be evident, because the valve as shown in section must have its proper linear advance. 




HACKWORTH GEAR 

Forward motion 
Inside connected type 



PATH OF PIVOT V 
LAP + LEAD 



RADIAL VALVE MOTIONS 



343 



UT OFF 




COMPRESSION 



Figs. 587 to 590. — Hackworth gear at positions of lead, cut off, pre-release, and compression 
for forward full gear motion. 



344 



RADIAL VALVE MOTIONS 



UT OFF 




COMPRESSION 



Pigs. 591 to 594. — Hackworth gear at positions of lead, cut off; pre-release, and compression, 
for reverse full gear motion. 



RADIAL VALVE MOTIONS 



345 





HACKWORTH GEAR 

Various cut offs; forward motion 



Figs. 595 to 597. — Hackworth gear at various 
cut off positions forward motion. 



346 



RADIAL VALVE MOTIONS 





OUTSIDE CONNECTED 



HACKWORTH GEAR 

Inside and outside connected types 
Forward motion 

INSIDE ADMISSION 

LAP + LEAD 



Fig. 598. — ^Hackworth inside connected 
gear as arranged for inside admission 
valve. 



Figs. 599 and 600. — Hackworth out- 
side connected gear; fig. 599, as 
arranged for outside admission valve; 
fig. 600, as arranged for inside ad- 
mission valve. 



OUTSIDE CONNECTED 



RADIAL VALVE MOTIONS 



347 




2. Large eccentric necessary 
when valve rod pivot is located 
between the eccentric and 
eccentric rod pivot; 

3. Considerable traverse 
stress on the eccentric when 
the valve is unbalanced; 

4. Numerous pins, liable to 
derangement. 

In later designs the first objec- 
tion was overcome by using rollers 
instead of a sliding block. The 
gear has worked fairly well, and for 
engines of small power has been 
found a convenient arrangement, 
especially when much variation in 
cut off is required. 

Fig. 598 shows the inside con- 
nected gear arranged for inside 
admission. Here the eccentric is in 
line with the crank, 180° from its 
position for outside admission, that 
is, its angular advance is made — 
90° instead of +90°. Figs. 599 
and 600 show the outside connected 
gear arranged respectively for out- 
side and inside admission. 



HACKWORTH GEAR 

Inside connected type 
Reverse motion 



Pig. 601. — Hackworth inside connected gear as arranged with 
vertical eccentric rod. 



348 



RADIAL VALVE MOTIONS 



LAP + LEAD Since several of the modern 

radial gears are simply modi- 
fications of the Hackworth gear, 
the latter has been presented at 
some length in order to fully 
illustrate underlying principles 
rather than mechanical con- 
struction, as it has largely been 
replaced by the more modem 
forms because of mechanical 
difficulties. 



Gear. — This first 
modification 
of the Hack- 
worth gear, 
due to F. C. 
Marshall, 
was intro- 
du ced to 
overcome the 
chief defect of 
the H ack- 
worth gear, 
that is the 
wear and 
friction of the 
sliding block. 
LAP + lead' 

Fig. 602. — Marshall gear, or first modification of the Hackworth 
gear. 




RADIAL VALVE MOTIONS 



.349 



It is simply the Hackworth gear with a swinging arm substi- 
tuted for the link as shown in figs. 602 and 603, the other parts 
are exactly as Hackworth arranged them. 

Here the eccentric rod pivot F, located at the end of the rod is attached 
to a suspension or radius rod R, the other end of which is pivoted at P, to 
a radius arm R', which turns about L, and whose angular position with 
respect to the central axis y y\ controls the point of cut off and direction 
or rotation. In construction, a geared quadrant is attached to the radius 
arm to provide means for setting the radius arm in any position within 
its arc of adjustment. v 



CENTER OF 
ECCENTRIC 



RADIUS 
ROO^ 




Fig. 603. — Construction detail of Marshall valve gear showing general proportion of parts. 

The pivot L, is located precisely as in the Hackworth gear. 

Since P P, is made equal to P L, the arc described by F, will pass through 
L, for all angular positions of the radius arm, and P, will coincide with L, 
when the engine is on either dead center. Hence, if the laps be the same 
the lead will be constant and equal. 

The motion of the valve is the resultant of the two vertical components 
of motion due to the eccentric and radius arms acting at the ends of the 
eccentric rod. 
. The steam distribution of the Marshall gear is not so good as with the 



350 



RADIAL VALVE MOTIONS 




^ 



a > 

^ 03. 












;3 



RADIAL VALVE MOTIONS 



351 



Si 5h oj ^ 4J <D g 









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352 



RADIAL VALVE MOTIONS 



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RADIAL VALVE MOTIONS 



353 




connected, or pivoted to the end 
instead of the middle of the ec- 
centric rod. 

The gear, as constructed for . a 
marine engine is shown in fig. 610, 
and consists of a single eccentric E, 
which either has to be set directly 
opposite the crank C, or in the same 
direction with the crank, according 
to the design of the valve gear. 

The eccentric operates the eccen- 
tric rod L, which also forms one- 
half of the eccentric strap J, the 
extreme en4 of this lever is attached 
to the valve rod, by means of a 
pivot N, and thus to the valve 
stem. ■ . 

The fulcrum of the eccentric rod 
is at F, about which it is swuug 
vertically by the throw of the 
eccentric, the amount of travel thus 
imparted to the valve being equal to 
the lap and lead for both ports. 

The travel necessary to open the 
port is imparted to the valve through 
port N , by the up and down motion 
of the fulcrum F, due to the horizon- 
tal throw of the eccentric, which 
causes the 
radius rod R, 
pivoted at K, to 
swing, and thus 
raise and lower 
the fulcnim. 



BREMME GEAR 

Forward motion 



ADIUS ARM 

R' 
RADIOS ROD 

OUTSIDE CONNECTED _ 
CCENTRIC ROD PIVOT 



Fig. 610. — Bremme 
gear, or second 
modification of 
the Hackworth 
gear. 



LAP + LEAD 



354 



RADIAL VALVE MOTIONS 



The upper end of the radius rod R, is pivoted to the radius arm R', which 
can be swung about the pin F, by means of the reversing gear, which 
is similar to that shown in fig. 603, the construction being explained in 
the accompanying text. 




BREMME GEAR 

Various cut offs; forward motion 

Pig. 611. — Bremme gear in cut off position for latest cut off; forward gear. 
Fig. 612. — Bremme gear in cut off position for short cut off; forward gear. 

It rnust be understood that when the radius arm R' (sometimes, though 
ill-advisedly called tumbling link*) is at its midway position, no vertical 
motion is given to the fulcrum F, and if it be thrown over into its opposite 

*NOTE. — The author prefers to confine the word link to mean a slotted bar or device 
wherein a block slides as in the shifting or so called Stevens link. 



RADIAL /ALVE MOTIONS 355 

position the motion is reversed to that indicated in the figure. By reducing 
the incHnation of the arm, the cut off is shortened. 

According to the inventor, the angle of the reversing lever (that is, the 
radius arm R', fig. 608) from the central line and known as the "deviation 
line" should never exceed 25° on either side. 

Joy Gear. — This gear invented by David Joy in 1880 is 

perhaps the best known of the radial gears, and avoids altogether 
the use of eccentrics. Its motion is superior to that of the or- 
dinary eccentric in that the parts are opened and closed rapidly 
with slow valve movement during expansion and exhaust. 

The lead is constant, and the cut off nearly equalized for all 
grades of expansion. The compression is less at short cut off 
than with link motion. 

The Joy gear has been extensively used on English locomotives 
and on marine engines. 

The chief objections to the gear are its great number of parts 
and joints which are in the way and subject to wear. In design 
the various pins should be made substantial. 

In the Joy gear motion is obtained from the connecting rod 
and imparted to one end of what corresponds to the eccentric 
rod in the previous gears, the other end of which is connected 
to the valve rod. There are two types of Joy gear, classified 
according as the motion received' from the connecting rod is 
modified by: 

1. A link; 

As in the Hackworth gear, or 

2. Radius rod 

as in the Bremme gear. 

Fig. 613 shows the link type as applied to a marine engine. 

The lever A, (previously mentioned as corresponding to the eccentric 
rod in the radial gears already described, especially the Bremme gear), is 
pivoted at B, to a block arranged to slide in the curved link L, the pivot 
forming the fulcrum of the lever A- 



356 



RADIAL VALVE MOTIONS 



Motion is imparted to the lever A, directly from the connecting rod by 
means of the rod C, one end of which is pivoted to the connecting rod, the 
other end to the rod D. 

The vertical motion of the rod C, moves the valve an amount equal to 
its lap + lead, while the horizontal motion causes the ports to open their 
full opening by moving the fulcrum up and down in the inclined link. 




Fig. 613.— Joy valve gear, link type. In this gear, as can be seen, no eccentric is employed, 
the motion being taken from the connecting rod, thus permitting more liberal main bearings. 



By means of the reversing lever R, the inclination of the link L, can be 
altered, or reversed, to vary the cut off or reverse the engine. 

Fig. 614 shows the radius rod type of Joy gear as applied to a marine 
engine. 



RADIAL VALVE MOTIONS 



357 



Diagram for Setting Out Joy's Valve Gear. — The following 
is the method of design as given by the inventor: 

"On the connecting rod AB, fig. 615, take a point C, so that its total 
vertical vibration DD', is not less than twice the full valve travel, 
perferably a little more. Through DD', draw XX, perpendicular to 




RADIUS 
ROD 



Fig. 614.— Joy valve gear, radius rod type. The substituting of a radius rod in place of the 
link avoids the objectional friction and wear of the latter. 



AB, and at the proper distance from AB, lay down the center line of the 
valve spindle. Mark the extrerne position of the point C, for inner and 
outer dead centers, and choose such a lever CE, whose total angle of vibra- 
tion CEC, does not exceed 90°, and carry the end E, by an anchor link 



358 



RADIAL VALVE MOTIONS 




E F, the mid position of 
which is parallel to the 
connecting rod when 
horizontal. 

''Next, on the center 
line of the valve spindle 
produced, and on each 
side of the vertical X X, 
mark off the points J J', 
each distant from the 
vertical by an amount 
equal to lap and lead. 
From the point J, draw 
a line J H, the center 
line of a link that, by 
virtue of its connection 
to C E, will move the 
point K (the point 
where J H crosses the 
vertical) equally o n 
each side of the central 
point K. The point K, 
is the center of oscil- 
lation of the curved 
guides in which slide the 
blocks carrying the ful- 
crum M, of thelever JH. 
The position of H, is best 
found by a tentative 
process, and to test 
whether the chosen point 
be a correct one, the 
equal vibration required 
is marked off on each side 
of K, and lettered L L. 
The distance LL, is equal 
to the vertical vibration 
of the point C, on the 
connecting rod, that is 
DD'. From D, as center, 
and with C H, as radius, 
mark the point M, on the 
vertical X X, and with 
the same radius, mark 
off N, from D', M and 
N, are the positions of 
H, when the engine is at 



RADIAL VALVE MOTIONS 359 



half stroke, or thereabouts, and these points give the total vertical 
vibration of H. 

"From M, as center, and with HK, as radius, describe an arc cutting 
the vertical XX, and from N, as center and with the same radius describe 
an arc also cutting the vertical XX, then, if the point H, be the correct one, 
the arcs just drawn cut the vertical XX, at L and L. Should the points- 
of intersection fall helow L and L, H is too near E, but if they fall above L 
and L, H is too near C. The exact position of H, is generally found by a 
second trial. The valve rod JG, may be of any convenient length, but 
the center line of the slides must be struck with the same radius. From 
the point K, draw a line KO, parallel to AB, and with center on this, line, 
and with JG, as radius, describe an arc containing K, and cutting the: 
curves LL, struck from K, as center, in PP'. 

"From P, or P', and on each side thereof, mark off on the arcs LL, an 
amount equal to IJ^ times the maximum port opening required, and let 
RR', be the points. With centers on the arc SS, struck from center K,. 
describe arcs passing through K R and K R', these arcs represent the center 
lines of the curved slots for forward and backward gear, and when the: 
latter are in either of these positions the point of cut off is about 75%. 
Should a later cut off be required the slots must be carried still further 
from their vertical position. 

"It is seen in the diagram that the fulcrum K, of the lever JH, coincides 
with the center of oscillation of the curved slots or guides when the crank 
is on either dead center. Evidently when these points coincide, the angle 
of the guide can be altered to any extent without disturbing any other 
part of the mechanism, a state of things which shows that the lead is. 
constant." 

The inventor's pamphlet goes on to say that when the above directions- 
are followed, the leads and cut offs for each end of the cylinder for back- 
ward and forward gear are practically equal. 

The arrangement of the gear just described is the most effective but 
considerable latitude is permissible. For instance the point C, can be 
placed above or below the center line of the connecting rod and the point K, 
can be raised or lowered, so that the line KO, is no longer parallel to AB, 
but it is" not advisable that the line should have a greater inclination to- 
AB, than 4° or thereabouts. 

Again, the anchor link may be dispensed with, the point J, being guided 
in a slide affixed to some convenient part of the engine. For vertical 
engines the same rules apply by placing the diagram vertically and altering, 
relatively the terms vertical and horizontal. 



Joy and Bremnie Gears Compared. — The Joy gear is 
preferred for locomotives, and the Bremme for marine engines. 



360 



RADIAL VALVE MOTIONS 



It is somewhat difficult to arrange the Bremme gear with its eccentric 
rod and reversing arm underneath a locomotive boiler, so as to be compact, 
and to clear the various parts. In marine work, space for this is usually 
abundant. The movement of the parts of the Bremme gear is considerably 
less than the Joy. 



ECCENTRIC 
ROD 



LINK 



VALVE ROD 



VALVE 
5TEM 



^^#»^W 




COMNECTING 
■ ROD 



A GOMBINATJON 
REVERSING LEVER 

SHAFT 



Fig. 616. — Walschaerts valve gear as applied to a locomotive. 



Walschaert Gear. — This type of valve motion is one of the 
most important of the so called radial gears. 

It was invented by Egide Walschaerts* (incorrectly spelled Walschaert, 
Walschart, etc.), of Mechlin, near Brussels, Belgium, and is especially 
adapted to locomotives. 



*^0T^.— Egide Walschaerts died on Xha 18th of February, 1901, at Saint- Gilles, near 
Brussels, at the age of eighty-one years. His mechanism which is so original, has been adopted 
for rnany years in most of the countries of Europe and has been wrongly attributed to Mr. 
Huesinger von Waldegg. He was born Janusry 21, 1820, at Malines, which place became, 
fifteen years later, the central point of the system of Belgian Railways. The line from Brus- 
sels to Malines was opened in 18;:55, and this event decided the career of young Walschaerts. 
Three years later, at the exhibition of products of Malines, there appeared some remarkable 
models executed by him, and described as follows in the catalogue: No. 19. M. E. Wals- 
chaerts, Jr., student of the Municipal College: {a) A stationary steam engine of iron (the main 
piston having the diameter of 4 .5 cm, or 1 .77 in.) (&) A working model of a locomotive in copper 
to the scale of V20 of the railway locomotives, (c) Section of a stationary steam engine. 
{d) Model of a suction pump and a duplex pump, (g) Glass model of an inclined plane. Min- 
ister Rogier was so much struck by it that he had Walschaerts enter the University of Liege, 
but his studies were interrupted by a serious illness, and were never completed. We find 
traces of him at the National Exhibition in Brussels in 1841. The report of the jury men- 
tions with praise a small locomotive constructed entirely by Walschaerts, and a steamboat 
6.50 metres long and 1.75 metres wide, which was capable of carrying sixteen men and travel- 
ing (so the report says) at four leagues an hour on the canal. The boiler of this little boat 
was of a new system invented by the constructor. The jury does not give further details. 
Walschaerts received the silver medal. In 1842 Walschaerts was taken into the shops of the 
State Railway at Malines as a mechanic. Machine tools existed only in the most rudimentary, 
forms, and the store rooms were badly provisioned. The lack of organization in the shops 



RADIAL VALVE MOTIONS 



36t 



The recent development of the locomotive in this eoimtry has presented 
conditions that has caused the extensive use of the Walsbh^erts 'gear in 
place of the shifting link ^ ' - , -/ . . : 

The Walschaerts gear like other radial gears gives a constant lead and 
cannot be adjusted without disturbing the other events. ^ / - 

The layout of this gear is more or less a matter of trial, many minor 




Fig. 617. — Skeleton diagram of Walschaerts valve gear. In operation, the movement given 
to the valve slide A, is the resultant of two components. The first is derived from the eccen- 

■ trie E, through the link L, and varies in amount as B, is moved out from P, and in direction 
relative to the crank as B is above or below P. The second component is derived from the 
cross head through the combination lever C. The resultant effect is equivalent to the motion 
that would be given by a single eccentric shifting along a straight line. 

locations may be varied in design, such as the position of the link pivot^or 
the point where the eccentric rod is pivoted to the link, and in this way 
modifications in the action of the valve may be accomplished. 



l^OT^.— Continued, 
rendered a man of Walschaerts abilities particularly valuable, and at the end of two years 
he was made shop foreman at Brussels. Although he was only twenty-four years of age he 
had already shown the qualities which make an engineer, which should have carried him in 
a few years to be the technical- head of the motive power department. It is humihating to 
be compelled to say that he remained shop foreman throughout his life. The first locomotive 
came from England and had not been in service for more than ten years when Walschaerts 
was made foreman. The railroad was growing rapidly and it was necessary to increase the 
forces and to acquire experience. Walschaerts was not content with the duties incurred in 
these difficult circumstances, but began his career by the invention of his system of valve 
motion. On October 5, 1844, Mr. Fischer, Engineer of the Belgian State Railwa^j-'s, filed 
for Egide Walschaerts an application for a patent relating to a new system of steam 
distribution applicable to stationary steam engines and to locomotives. The Belgian patent 
was issued on November 30, 1844, for a term of fifteen years. The rules of the department did 
not allow a foreman to exploit a Belgian patent for his own profit and this explains probably 
the intervention of Mr. Fischer, who has never claimed the slightest part, material or moral 
of the invention. On October 25th of the same year, Walschaerts took out a patent in France 
for the same invention. There also exists among the documents left by the inventor, a con- 
tract signed at Brussels in 1845 by Demeuldre, from which it appears that he undertook to 
obtain a patent of importation into Prussia for the new valve motion, subject to an assignment 
by Walschaerts of half of the profits to be deducted from the introduction of the new- 
valve motion in this country. It is probable, however, that this contract was never carried 
out. The design attached to the Belgian patent is a primitive arrangement, the link oscil- 
lated on a fixed shaft, in regard to which it was symmetrical, but it had an enlarged 



362 RADIAL VALVE MOTIONS 

In the chapter on locomotives, the Walschaerts gear is de- 
scribed in detail, hence only an outline of its working princi- 
ples need be given here. 

The essential features of the gear are shown in fig. 617. 

The motion of the valve is the resultant of two movements, one of which 
is intended to give constant lead, and the other, the required travel of the 
valve. These two movements are due to the cross head and eccentric, 
and are combined and imparted to the valve by the combination lever as 
shown in fig. 616. 

Motion from the cross head is delivered to the lower end of the com- 
bination lever by a stud bar A, fixed to the cross head and rod B, giving 
it a reciprocating motion equal to the length of the stroke. 

The second movement is transmitted from the eccentric through the 
eccentric rod, link pivoted at B, and valve rod (sometimes called radius 
rod), to the combination rod. 

The valve rod is pivoted to the combination rod at a point C, near its 
upper end, so located that the motion received from the cross head will 
reciprocate the valve stem through a space equal to twice the linear ad- 
vance, and thus to place the valve in position with constant lead at the 
beginning of the stroke. 

The link is curved to a radius equal to the length of the valve rod. The 
valve rod has a block pivoted near its end, and arranged to slide in the link 
as shown. 

The cut off is shortened, or motion reversed by shifting the block by 
means of the reverse crank and reach rod which joins this crank to the 
end of the valve rod. 



l^OT'E— Continued. 
opening at the center so that only at the ends was it operated without play by the link blocks 
which was made in the form of a simple pin. There was only' one eccentric, the rod of which 
terminated in a short T, carrying two pins. The reverse shaft operated the eccentric rod and 
maintained it at the desired height. For one direction the lower pin of the T engaged in the 
lower end of the link, and to reverse the engine the rod was raised so that the upper pin engaged 
in the upper end of the link. The angle of oscillation of the link varied with the position 
of the pin in the link, and this oscillation was transmitted by an arm to the combining lever, 
which was also operated by the cross head. The central part of the link could not be used 
for the steam distribution, as it was necessary to enlarge it to allow for the play of the pin 
which was not in operation . It may be asked why the inventor used two separate pins mounted 
on a cross piece on the end of the eccentric rod, instead of a single pin on the center of the 
rod which would have served for both forward and backward motion without requiring the 
center enlargement of the link. It must be borne in mind that the raising or lowering of the 
eccentric rod by the reverse shaft was equivalent to a slight change in the angular advance 
of the eccentric. Consequently with a link of a sufficient length to keep down the effect of 
the angularity it was necessary to reduce as much as possible the movement of the eccentric 
rod. ■ Notwithstanding its differences the mechanism described in the patent of 1844 is in 
principle similar to the valve motion with which every one is to-day familiar and which the 
inventor constructed as early as 1848, as is shown by a drawing taken from the records of the 
Brussels shops, on which appears the inscription "Variable expansion; E. Walschaerts system 
applied to Locomotive No. 98, Brussels, September 2, 1848." 



GOVERNORS 363 



CHAPTER 11 
GOVERNORS 



An important requirement of engine operation for mOst 
conditions of service is the maintenance of ,a practically constant 
speed under variable load. This control is accomplished by an 
automatic device called a governor. With respect to speed 
control, engines may be divided into two general classes, ac- 
cording as they are designed to run at 

1. * Variable speed, or 

2. * Constant speed. 

The speed regulation of the two types is classed respectively as 

1. Hand control; 

2. Automatic. 

Under the first division' are types such as marine, locomotive, and 
hoisting engines, while the second division consists of that lar^e class 
known as stationary engines. 

Classes of Governor. — The varied conditions of service give 
rise to numerous types of governor differing bo'th in principle 
and construction. Accordingly, governors may be classed: 



♦NOTE. — It should be understood that there is a type o. engine called "variable speed 
engine," which works under control of a governor so arranged that the speed may be altered 
as fully explained on page 398. 



364 GOVERNORS 



1. With respect to steam control as 

a. Throttling; 

h. Variable cut off. 

2. With respect to the operating principle, as 



a. Centrifugal I f-J,^^^' 
h. Inertia. 

3. With respect to operation, as 

a. Sensitive; 

b. Isochronous; 

c. Variable speed. 

4. With respect to construction, as 

a. Pendulum {}J,^^^-f^^ 

(shifting eccentric; 
swinging eccentric; 
double eccentric. 

Principle of Centrifugal Governor. — The action of 
governors of the type depends upon the change of centrifugal 
force when the rate of rotation changes. 

In these governors one of two resisting forces is employed 
as that due to gravity, or a spring. Gravity is usually the 
resisting force in pendulum governors, and one or more springs 
in shaft governors. 

In fig. 618 le^ 

h = height of cone of revolution; 

r = radius of rotation of ball; 

W = weight of ball ; 

C = centrifugal force due to speed of rotation 

then 



GOVERNORS 



365 



from which 



W = 



Ch 



C = 



Wr 



Ch_ 



h = 



Wr 



Ques. Upon what does h, or distance of the plane of 
the ball below the point of suspension (popularly expressed 
as ''height of the ball") depend? 

Ans. The distance h varies inversely as the square of the 
speed. 

The weight of the ball and radius of revolution have no effect upon the 
position of the balls. 



POJMT OF^ 
SUSPENSION 





CENTRIFUGAL 
PORCE 



RADIUS OF 
ROTATION 

Fig. 618. — Simple revolving pendulum illustrating the principle of operations of centrifugal 
governors. 

Pendulum Governors.-^In its simplest form the pendulum 
governor consists of two balls suspended upon a vertical shaft 
as in fig. 619. The weight of the balls tends to hold them down, 
and centrifugal force operating against gravity (or a spring) 



366 



GOVERNORS 



tends to raise them (that is, make them fly outward), as ex- 
plained in the preceding sections. 

Theoretically, the action of the balls is independent of their weight 
as the centrifugal force varies in the same proportion as the weight and 
maintains constant the relative effects, so that at constant speed the balls 
will rotate in the same plane, whatever their weight. This is true only 
where the arms are simply hinged at the top without any other connections. 



B-i- 

\ 

A 




Fig. (d19. — Simple pendulum governor actuated by centrifugal force and gravity. In operation, 
assume that at normal speed of the engine, the balls revolve in the plane AA, then let part 
of the load be thrown off and the engine will speed up slightly, or enough to throw the balls 
into some higher plane as BB. This raises the collar on the spindle from C, to D, and by means 
of a lever attachment or equivalent, control the steam supply by throttling or variable cut 
off according as the governor is of the throttling or cut off type. 



In a governor as constructed there are a collar, side rods, etc., 
which, having no rotary motion tending to raise them by cen- 
trifugal force, act as dead weights on the balls and cause them 
to revolve in a lower plane. However, if the balls be made 
heavy in comparison with the weight of the arms and collar, 
this effect becomes small. 



GOVERNORS 



367 




368 GOVERNORS 



The expression for the total centrifugal force horizontally outward is: 

' ..C = 12 W^;2-^gr . . (1) 

in which 

C = total centrifugal force in lbs. ; 
W = weight of both balls in lbs. ; 

z;= tangential velocity of balls in feet per second; 
' g = acceleration due to gravity = 32.16; ; 

' r^radius of rotation of the balls, in inches. 
In the previous section was obtained the expression 

Wr = Ch (2) 

Substituting for C, its value as in (1), 

Wr = 12W v^h^gr (3) 

from which 

h=gr^-^12v^ (4) 

Now the tangential velocity v, of the balls for any rotative speed R, is 

1^ = 2 TT r R^ (12X60) =xrR-T- 360 

and since g = 32. 16, substituting in (4) 

7i = 32.16r2-M2 (7^rR^360)2 = 35,191.7-^R2 (5) 

Example. — In an engine running at 200 r.p.m., the governor is to run 
at half that speed and have a "regulation" within 4 per cent. 

Four per cent regulation means that the maximum speed of the engine 
is to be 

200X1.02=204 r. p. m 

and the minimum speed 

200 X. 98 = 196 r. p. m. 

Then the corresponding maximum and minimum speeds of the governor 
will be half these values or 102 and .98 r. p. m. respectively. Substituting 
these values in (4), for maximum speed 

h = 35,l9l.7^1022 = 3.38 ' 

and for minimum speed 

h = 35,191.7^ 982 = 3.66 

which means that the balls must rise and fall vertically a distance of 

3.66 — 3.38 = .28 inch 

for a total variation of 4 per cent in the speed of the engine, that is for 
4 per cent regulation. The corresponding movement of the collar upon 
the governor shaft will depend upon the lengths of the different arms and 
connecting levers and may be determined graphically. 



GOVERNORS 



sm 



Loaded Pendulum Governors. — In the example given in 
the, preceding section it is evident that there is but little change 
in the height of the governor for even considerable variation 
in speed, and also that for high speeds, the height h of the 
governor becomes so small that the mechanism would be 
difficult to construct. To overcome these defects the governor 
may be loaded, that is, a weight is placed on the collar to assist 
gravity in holding down the balls as in fig. 623. 




LOAD 



COLLAR 



Fig. 623. — Diagram of loaded pendulum governor. In this type a weight (or equivalent) is 
placed on the collar, thus increasing the gravity effect in resisting the centrifugal force. 



The governor equation already found may be stated as 
gravity moment = centrifugal force moment 
or in symbols 

Wr = Ch (6) 

Now if W, be the combined weight of the balls, as before, and W the 
weight of the load placed upon the collar as in fig. 623, then the gravity 



370 



GOVERNORS 



moment is (W+W) r, which substituted for W in equation (6) gives 

(W+WO r = Ch (7> 

Substituting in (7) the value of C, as found in (1) 
(W+W) r = 12 W v'^h^gr 
from which, solving for h 






CO 
UJ 

5 ^ 



o 
o 



v9 
UJ 

X 




(8) 



iO 



12 - 



Fig. 624. — Reasan for loading a governor. If the height h, for a simple pendulum governor be 
calculated for different speeds, it will be found that while the change of height h, for a change 
of speed may be comparatively large when the speed of the governor is low, when the speed 
is increased, the change of height for a change of speed becomes so small as to be of no 
practical value. Thus in the figure from, say 60 to 70 revolutions, the difference in h, is 
large, and say from 110 to 120, it is very small. Hence if a weight or load be added which 
increases the gravity effect, then a large movement of the sleeve may be obtained with a 
high speed of rotation, and at the same time a much more powerful governor is obtained 
than when no central load is used. 



It will be noticed that the second factor of (8) is the same as the value 
ofh,m equation (4), and reduced in (5), hence substituting the value given 
in (5) in equation (8). 

^_W+W' 35,191.7 



w 



R2 




GOVERNORS 371 



from which it appears that the height h,oi a loaded governor is greater than 
an unloaded one to the extent of the factor (W+W)"^ W. 

Assuming the load upon the collar to be 1, then for maximum speed 



/; =i±^x55|^ = 6x3.38 =20.28 

and for minimum speed 

7^=^x55^^ = 6X3.66 = 21.96 

Then the vertical movement of the collar will be 21.96 — 20.28 = 1.68 
in., as compared with .28 in the example of the unloaded governor just given. 

Ones. How is the load proportioned? 

Ans. It is usually made much heavier than the balls. 

Oues. What equivalent is sometimes used in place of 
a weight on loaded governors? 

Ans. Springs. 

These are used especially on throttling governors and are so attached 
that they oppose the centrifugal force obtaining the same effect as a weight. 

Owes. How may a loaded governor be constructed and 
why? 

Ans. It may have comparatively small rotating weights, 
because the centrifugal force increases as the square of the 
number of revolutions and only directly as the weight of the balls. 

Sensitiveness. — A governor is said to be sensitive when a 
small variation of speed causes a considerable movement of the 
regulating mechanism. 

Theoretically, loading a governor has no effect on its sensi- 
tiveness however since, in practice, the friction of the governor 
and regulating mechanism may be considerable, the sensitiveness 
of a loaded governor is actually much greater than that of the 
unloaded type. 



372 



GOVERNORS 




About 2 per cent 
variation of speed of 
the engine may be 
considered as the 
practical limit of vari- 
ation with good gover- 
nors. A less percent- 
age than this reqmres 
an abnormally large 
fly wheel. 

Figs. 625 to 628 
show several types of 
pendulum governors 
arranged in the order 
of their sensitiveness, 
fig. 625 being the least 
sensitive, and fig. 628 
the most sensitive. 

Stability.— A 

governor is said to be 
stable when it main- 
tains a definite position 
of equilibrium at a 
given speed. 

When the reverse 
conditions obtain, it 
is said to be unstable, 
that is, when at a 
given speed it assumes 
indifferently any po- 
sition throughout its 
range of movement. 



GOVERNORS 



373 



Oues. What is the condition for stability? 

Ans. For stability, the centrifugal force must increase more 
rapidly than the radius of rotation of the halls. 

Evidently no governor can maintain a constant speed since it requires 
a change of speed to actuate the regulating mechanism. When the balls 
are in the lowest position the regulating mechanism gives the full steam 
supply for maximum load and when the balls are highest, just enough to 
run the engine against its frictional load. 




Fig. 629. — Early form of parabolic governor, which operates isochronously, that is, the slightest 
variation of speed drives the balls to the end of their travel. This condition is only obtained 
when the balls in rising and falling describe a portion of a parabola, for, in this case the 
height of the cone of revolution is constant for all positions of the arms, and the balls are 
in equilibrium and will remain in any position, so long as the speed remains unchanged. The 
above construction which is said to be the earliest form of parabolic governor known in 
England was introduced in 1851. The balls were suspended by links to rollers, which traveled 
upon arms branching from a vertical spindle, so formed that the centers of the rollers traveled 
in a parabolic curve. An early governor of this type applied to a compound engine was 
rendered useless by its excessive sensitiveness, continually operating the throttle valve. 
The difficulty was overcome by applying an air dash pot. 

If the boiler pressure or the load be changed, a certain amount of dis- 
placement of the balls is necessary to vary the steam supply, and this 
displacement can only be obtained by a change in speed, hence the term 
constant speed is erroneously used as applied to engines where speed is 
controlled by a governor. 



374 



GOVERNORS 



Isochronism. — A governor is said to be isochronous when 
it is in equilibrium at only one speed. 

If, when the balls are displaced, the centrifugal force changes pro- 
portionately to the radius of rotation of the balls, the speed is constant, 
that is, the equilibrium of the governor is neutral, allowing it to revolve in 
equilibrium at only one speed. 

The slightest variation in speed drives the balls to the end of the travel. 
Such a governor is said to be isochronous, and its sensitiveness is theo- 
retically infinitely great. 




APPROXIMATE. 
PARABOLA 



Fig. 630.— Diagram of crossed arm pendulum governor, the approximate equivalent of the 
parabolic type. By producing the two extreme positions of an arm BA and B'A', until 
they intersect at P, and using this as a point of suspension. The curve described by the balls 
during their travel will approximate a parabola and the action of the governor will be 
approximately isochronous. 

Oues. What type of governor is isochronous? 

Ans. The parabolic governor. 

Hunting. — An isochronous governor cannot be used success- 
fully on an engine without being modified so as to obtain a small 
margin of stability to prevent violent changes in the steam 



GOVERNORS 375 



supply, especially if there be much f fictional resistance to be 
overcome by the governor, or where the engine responds slowly 
to the influence of the governor. When a change of speed occurs, 
however quickly the governor acts, the engine's response is 
more or less delayed. 

Jf the regulation be by throttling, the steam chest forms a reservoir to 
draw upon, and if by variable cut off, the opportunity is lost if cut off 
has already occurred, and control cannot begin until the next stroke. A 
sudden decrease of load is accompanied by such increase in speed as to 
cause abnormal governor action giving too little steam for the reduced 
load. Causing a decrease of speed accompanied by excessive increase in 
the steam supply. The governor thus oscillates in its endeavor to find a 
position of equilibrium and such action brought on by over-sensitiveness 
is called hunting. 

Oues. What form of governor is approximately the 
equivalent of a parabolic governor? 

Ans. The pendulum governor with crossed arms as in fig. 630. 

Oues. How is the stability of this governor varied ? 

Ans. Reducing the distance PA, increases the stability; 
increasing P A, gives the reverse effect. If the point P, be too 
far from the spindle, the height of the cone may increase as the 
balls rise and cause unsatisfactory operation. 

Inertia Governors. — The term inertia may be defined as 
that property of a body by virtue of which it tends to continue in a 
state of rest or motion in which it may be placed until acted upon 
by some force. This forms the working principle of inertia 
governors, and in general an inertia governor may be said to 
consist of a heavy body pivoted at its center of gravity and 
connected at a proper point to the regulating mechanism. 

In operation, the heavy body revolving in step with the fly wheel tends 
^K^o revolve at constant speed. Any change of speed of the fly wheel due to 



376 



GOVERNORS 



c3 O Jj be O^T" 

w g^o.S gS.rt o ^^ 




GOVERNORS 377 



variable load produces a change in the position of the heavy body with 
respect to the wheel, thus moving the regulating mechanism. 

The so called inertia governors found on many are, strictly speaking, 
combined centrifugal and inertia governors, as their action depends on 
both forces. According to constructing, one force may be made to either 
oppose or assist the other. 

In fig. 631 a governor disc is pivoted to the fly wheel at P, as shown. If 
the wheel rotate in the direction of the arrow, an increase in speed will 
cause the disc to move outward from the center C, by centrifugal force, 
but if the governor disc be pivoted at the center of the shaft as in fig. 632, 
then the centrifugal force acting radially with respect to the pivot P, will 
have no effect on the disc since the position of the pivot P, coincides with 
the center C, of the fly wheel. 

• If in fig. 632 the speed of the fly wheel increase or decrease, the disc, 
(tending to rotate at constant speed) will respectively lag behind or advance 
beyond the position shown in the figure, that is, it will move with respect 
to the fly wheel in the direction of I, or I', respectively, inertia in this case 
alone being the controlling force, the resisting force being the tension of 
the spring. 

In fig. 632 the force due to inertia is a maximum. This force may be 
made to assist or oppose the centrifugal force according to the location of 
the pivot P. Thus in fig. 633, if the fly wheel be rotating in the direction 
of the arrow, both forces act together and make the governor rapid in its 
movement, while in fig. 634, the forces oppose each other and tend to make 
the governor sluggish. 

Another form is shown in fig. 635, in which the centrifugal force is 
neutralized, the controlling force being due to inertia alone. In the figure 
two discs A and B, connected by an arm are pivoted at the center of gravity 
P, at a distance C P, from the center C, of the fly wheel. 

In operation when the fly wheel revolves disc A, is acted upon by a 
centrifugal force F, and B, by an equal centrifugal force F'. These forces 
acting on opposite sides of the pivot P, and at equal distances neutralize 
each other. 

Now if the fly wheel revolve in the direction of the arrow, and its speed 
be decreased, the inertia of the discs (represented by the forces I' I') will 
cause them to revolve around P, to some position as A' B'. Clearly if the 
speed increase the reverse condition will obtain, that is, the discs will 
revolve around P, to some position as A" B", under the influence of the 
inertia forces V V, 



Spring Governors. — The use of springs for the controlling 
force or to assist gravity is quite common. When springs are 
used the ball aims may be arranged to travel across a vertical 



378 



GOVERNORS 




5, K <U <U <U '^ -^ 






A 


V 


\ 


c 


e. 


^ 


^ 


Ul 


IS 






; » 


J 




^ 


1 








) - 




i/ * 



5 wpq ^ d ^ o 
l.i^.brrt +^ M <u a> 




GOVERNORS 379 



axis, or the governor may be operated in a horizontal position 
and gravity practically eliminated. 

Spring governors can be made practically isochronous if desired, by so 
adjusting the spring that the initial compression in the spring bears the 
same ratio to the total compression that the minimum radius of the balls 
bears to the maximum radius. .a- 

In practice, stability is provided by making the spring a little stronger 
than the above adjustment. 

Fig. 692 illustrates the operation of a spring governor. As shown, the 
balls are attached to bell crank arms, pivoted at P and P', to a frame, 
which revolves around the central upright shaft. The travel of the balls is 
transmitted by the bell cranks to the collar at A A'. An adjustable spring 
presses against the collar and acts as a substitute for gravity. 

In operation as the speed increases the centrifugal force increases and 
the balls move outward. The compression on the spring increases similarly, 
and by suitably adjusting the initial pressure on the spring, the governor 
may be made nearly isochronous, as before mentioned, and rendered very 
sensitive, which is a ch^,racteristic of this class of governor. 

The Regulating Mechanism. — This term is applied to the 
gearing or * 'transmission" which transmits the movement of the 
governor to the control device. 

Figs. 636 to QA2.— Continued. 

(fig. 637), by having more tension on the eccentric arm spring C^, than is maintained on 
the spring attached to the other arm C By this arrangement any amount of friction 
necessary for stability is obtained. The eccentric D, is fastened to one arm A', in its proper 
relation to the suspension and crank pin so that the swinging of the arms move the eccentric 
across the shaft, changing its throw, producing the desired effect of changing the cut off 
of the valve. The sliding block, C-^, to which the arm ends of the springs are attached is 
used to increase the range of the springs. In adjusting, by moving the sliding block along 
the grooves C^, the points of .suspension are changed. By changing the points of suspension 
any desired effect upon the action of the governor is obtained. The inertia arms are pur- 
posely made heavy so as to balance the reciprocating parts of the valve motion. 



NOTE. — Directions for Riblet combined centrifugal and inertia governor. 1. When 
springs are placed in the governor, the suspension points E, of the sliding block must be about 
half way between their minimum and maximum positions. 2. The free arm spring C^, must 
be tightened just enough to hold it in place. 3. The eccentric arm spring CS must be tightened 
so that it is pulled out about ^", or just enough to stop the rattle of the governor. 4. Start 
the engine. 5. If the engine run too fast, put shot in cavity B^ and the same amount in B^. 
6. If the engine run too slow, put shot in cavities B2 and B*. 7. Until the point is reached where 
the required speed is obtained pay no attention to regulation. When the speed is obtained 
apply load to the engine. 8. If the engine run slower as the load is applied, move the springs 
by means of the sliding block toward their maximum position in direction of arm, fig. 642 of 
their points of suspension E; continue this movement until the desired regulation is reached. 
9. If engine run faster as the load is applied, reverse the procedure given in 8. 10. Be sure 
the governor does not stick or bind and that the suspension pins are well lubricated with good 
grease. 



380 



GOVERNORS 




kO D, 



^25 S 



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-oj .-.^ §§^ ft^.S-^^ 
-^ .«^ '^ .;r<N^ W.2 ^ 

^:5i-H w ^ '-'(N ..'" cjj 



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*" _ri >< v-' " 5 o ^ S -r - 









.^.1^^ 






:=3 0) Ck-Z 









ToQ^ '^^< a>''^ «> 



S§.s 






0<pqq3 o M > ^ -" 



^ o o 



GOVERNORS 



381 



According to the nature of the regulations governors are 
classed as 

1. Throttling; 

2. Cut off. 

The throttle valve as introduced by Watt was what is now known as a 
butterfly valve, and consisted of a (^isc turning on a transverse axis across 
the center of the steam pipe. It is now usually a globe, gate, or piston valve. 




Fig. 692. — Elementary diagram showing working principle of spring governors. 

When regulation is effected by varying the cut off, an expansion valve 
or the slide valve or piston type is used, the governor generally acts by 
changing the travel of the valve. In some forms of automatic expansion 
gear, the lap of the valve is altered ; in others, the governor acts by rotating 
the expansion valve eccentric on the shaft and so changing the angular 
advance. These matters are fully explained in the chapters on valve gears. 



Throttling Governors. — If this type of governor had never 
been invented, no doubt some of the world's natural resources 



382 



GOVERNORS 





Fig. 695.— Pickering "ball 
speed ranger," permits 
increasing speed of engine 
50 to 7o per cent from 
normal by turning the 
small hand wheel, which 
can be done_ while the 
engine is running. 



Fig. 693. — Pickering class A throt- 
tling governor fitted with auto- 
matic safety stop, speed regulator 
and sawyer's lever. 





Fig. 694. — Pickering class B 
throttling governor fitted 
with speed regulator and 
sawyer's lever. 



Fig. 696. — Sinker-Davis "Hoosier" throttling governor with wide range speed regulator 
permitting variation of 150 revolutions. Adjustment: Adjust coil springs only to the point 
where the valve works freely and easily. Only sufficient tension is required to balance the 
valve against the steam resistance. The coil springs are not for speed regulation. To change 
the speed: Loosen the lock nuts at the top of the governor above the traveling head, and 
if engine speed is to be increased, run the nuts down until the speed increases to the revolutions 
wanted, then lock them. If the speed is to be decreased, run the nuts up until the speed 
decreases to the revolutions wanted, then lock them. The regular speed of the governor is 
stamped on the traveling head, and a variation of speed not exceeding 75 revolutions, slower 
or faster, can be obtained by changing the nuts as explained above. If more variation be 
required, change the pulley on the main shaft of engine to give required speed on engine and 
on governor. The cam or automatic stop is adjustable for either right or left hand engines. 
The governor should be well oiled before starting, but can be oiled while in motion by oiling 
above the traveling head only; the oil will work down through the governor, and it is not 
necessary to oil at any other point. In packing the stuffing box, be sure to see that the valve 
stem works freely and without tension on the coil springs. 



GOVERNORS 



383 



would be better preserved and the price of fuel not so high. 
However, for some services where waste material is to be dis- 
posed of, and can be used as fuel, a throttling governor may be 
employed. This type of governor may be defined as an auto- 
matic throttle valve which governs by altering the pressure at 
which steam is admitted to the cylinder; that is, the throttle 







Figs. 697 and 698. — ^Waters spring throttling governor. Fig. 697 shows class A, fitted with 
automatic safety stop in which a spring throws the shaft out of gear when the governor belt 
breaks. In erecting, be sure and have the end cap on the bracket stand with the head of 
set screw pointing direct to the pulley on engine shaft. In operation, if the governor belt 
break, the spring throws the shaft out of gear, the top drops and closes the valve. To start 
again, raise the top part, push the gears together and hold it in position while putting on 
the belt. Fig. 698 shows governor fitted with sawyer's lever. 



valve is opened or closed inversely with changes in load, thus 
causing more or less drop in pressure so that the resulting mean 
effective pressure in the cylinder will vary with the load and 
maintain a steady speed. 



384 



GOVERNORS 




Fig. 700.-;—Gardner class B throttling governor 
fitted with speed regulator and Sawyer's lever. 
Class B combines both the spring and gravity 
actions, adapted for all styles of slow and medium- 
speed stationary engines. In operation the 
centrifugal force of the balls operates against the 
resistance of a coiled steel spring enclosed within 
a case and pivoted on the speed lever; by means 
of a screw the amount of compression on 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. By 
attaching a cord to this lever the valve of the 
governor can be controlled at a reasonable dis- 
tance from the governor. Sizes from % inch to 
134 inches, inclusive, have swivel frames which 
can be set at any desired angle in relation to valve 
chambers. The valves and seats of this style are 
the same as used on the Standard Class "A" 
governor. 



Fig. 699. — Gardner class A throt- 
tling governor fitted with auto- 
matic safety stop and speed 
regulator, sizes 13^ to 16 inches 
inclusive. Class A type is of 
the gravity action and is espe- 
cially adapted for the larger 
types of stationary engines. In 
operation the centrifugal force 
of the balls is opposed by the 
resistance of a weighted lever 
and the speed is varied by the ' 
position of the weight on the 
lever. _ The automatic safety 
stop is accomplished by per- 
mitting a slight oscillation of 
the shaft bearing, which is 
supported 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 break 
or slip off the pulley, the support 
of the fulcrum is forced back, 
allowing the fulcrum to drop, 
closing the valve. The valve 
chamber is fitted with valve 
seats made of a composition. 
The valve is of the same ma- 
terial. This style is made for 
both horizontal and vertical 
engines. 
^^..^—^■■^--~. 



GOVERNORS 



385 



Fig. 702 shows the effect of a throttling governor upon the^ 
indicator diagram. 

V/hen working under full load, the diagram has the form shown by the 
full line, but when the load drops, and the engine speeds up slightly, the 
governor acts, partially closes the throttle valve, and the pressure is reduced 




Fig, 701, — Gardner speed and pressure regulator fitted with automatic stop for steam actuated 
compressors. This regulator consists of a class A governor fitted with a brass cylinder con- 
taining a piston upon which the air pressure is exerted. The brass cylinder is connected by 
a pipe with the air receiver set about 25 feet distant from the regulator, so that the latter 
may always be under the direct influence of the air pressure within the receiver. The air ' 
pressure to be maintained is regulated by the position of the weight on the lever. When 
this pressure has been reached it is exerted on the brass piston, pushing it upward and closing 
the governing valve, or keeping it open just wide enough to maintain a constant air pressure. 
On duplex machines, when the desired air pressure has been attained, the regulator will 
bring compressor to a dead stop, starting it up automatically when air pressure falls below 
the required amount. On single compressors it is not desirable to bring the compressor to 
a dead stop, and there is an adjustable device on the regulator which, when set for certain 
pressure, will allow the compressor to just turn over when that pressure has been attained. 
The standard or ball governor acts merely as a speed controller; it has no throttling action 
on the steam until the limit of speed has been reached. By the use of properly proportioned 
pulleys on the governor and compressor, provision can be made for the proper speed limit. 
The ball governor keeps the compressor from exceeding this limit, and it thus serves to pre- 
vent the engine running away in case of sudden loss of air pressure from any cause. 



386 



GOVERNORS 



BOaeR PRESSURE 
A 



CONSTANT CUT OFF 



\}\.L THROTTLE ADMlSSfON 
(heavy- load) 



PARTLY CLOSED THROTTLE ADMISSION 
(light LOADJ 




Pig. 702. — Indicator diagram showing action of throttling governor. 




/ PULLEY BE.LTE:D TO 

PULLEY OKI ENGINE SHAFT 



STEAM FROM 
BOILER 



SUPPLY TO ENGINE 



Fig. 703. — S e c t i o n a 1 
view of throttUng 
governor showing 
general construction. 
The names of the 
parts are: 1, standard; 
2, governor shaft; 3, 
governor balls; 4, arms; 5, stem swivel; 
6, pivots; 7, gears; 8, pulley; 9, oil 
holes; 10, stem; 11, bonnet; 12, stuffing 
box; 13, gland; 14, gland box; 15, valve 
discs; 16, valve seats; 17, stem guard; 
18, throttle valve flange; 19, valve 
chest flange. 



GOVERNORS 



387 



by wire drawing so that the admission and expansion lines take the posi- 
tions shown by the broken lines in the illustration. The resulting drop 
in pressure is always proportional to the reduction in load, so that the 
speed remains constant, or practically constant within certain limits, 
whatever the load upon the engine. 

The general construction of a throttling governor is shown 
in fig. 703. 




Fig. 704.— -Gardner spring throttling governor with speed regulator, sawyer's lever, and 
automatic safety stop. This governor is recommended for traction and high speed stationary 
engines. It is very quick and sensitive in action, and is therefore capable of responding 
promptly to the various changes in load. The balls are rigidly connected to steel springs, 
the lower ends of the springs being secured to a revolving sleeve which receives its rotation 
through mitre gears; links connect the balls to an upper revolving sleeve, which is free to 
move perpendicularly. The balls at the free ends of the springs^ funiish the centripetal 
force, and the springs are the main centripetal agents. No gravity is employed. Sizes, 
3^ to 7 inches. 



The valve 15 is of the balanced or double seat poppet type. 

A different type of valve is shown in fig. 705 which is a sectional view 
of the regulating mechanism of the Waters throttling governor. 



388 



GOVERNORS 



Cut Off Governors. — In this method of regulation, which 
is always used where any regard is had for economy, steam is 
admitted with full throttle opening and the mean effective pressure 
controlled to suit the load by varying the point of cut off. 




PISTON 
VALVE 



VALVE 
SEAT 



STEAM 

FROM BOILER 

Fig. 705. — Regulating 
mechanism of the 
Waters throttling 
governor. In con- 
struction, the valve 
is of the triple ported 
piston type, both 
valve and seat being 
made of composition 
metal. The arrows 
show the paths of the 
steam. Ample ad- 
SUPPLY TO ENGINE mission area is secured 

by the three ports. The four valve seats are all in one casting, which fits the iron body at the 
ends only, providing for expansion and contraction. The valve being of the piston type is 
balanced and the triple ports give the required admission with a correspondingly small travel. 



BOluER PRESSURE 



- EARLY CUT OFF - UGHT UQAO 
-LATE CUT OFF HEAVY LOAD 




Fig. 706. — Indicator diagram illustrating regulation by variable cut off. 



GOVERNORS 



389 



Fig. 706 shows the resulting changes upon the indicator dia- 
gram. Here the initial pressure remains the same, but the area 
of the card, and consequently the amount of work, is reduced 
by shortening the cut off. The original and final areas of the 
diagrams are the same in each case, and the reduction in work 
per stroke is shown by the shaded area. 




ROD 



Pig. 707. — Hartwell spring ball governor with variable cut off regulating mechanism. In 
operation, as the speed increases, the governor raises the position of lever A, and the travel 
of the valve is reduced. This governor is capable of very close regulation, and when the speed 
exceeds a given number of revolutions, the steam supply may be entirely cut off. 



In this class of governor, variable cut off is effected in several 
ways, as by 

1. Variable travel of the valve; 

2. Variable angular advance-; 

3. Combined variable travel and variable angular advance. 

Fig. 707 shows a spring ball governor with regulating mechanism for 



390 



GOVERNORS 




varying the cut off by 
the first method. As 
shown, the regulating 
mechanism regulates 
the travel of a riding 
cut off valve by the 
movement of the lever 
A, in the slotted link B. 

Regulation.— The 

term regulation means 
speed variation, 
usually expressed as a 
percentage of the 
normal speed of an 
engine, running under 
control of a governor. 

Fig. 708. — Nordberg automatic 
cut off governor. This device 
is a combination of trip cut 
off gear and a governor for con- 
trolling the same, designed to 
be attached to the steam pipe 
of slide valve, rocking valve 
and similar engines to regulate 
the speed of the engine. The 
steam is admitted at full boiler 
pressure; is cut off at a point 
corresponding to the demand 
for power, and expanded. In 
construction, the governor 
consists of a double beat 
poppet valve, operated by a 
double trip mechanism. A 
sensitive regulator sets the 
point of cut off, according to 
the demand for steam. The 
range of cut off obtainable is 
from to M or 3^ of stroke. 
An air dash pot causes the 
valve to drop gently on the 
seat. All contact edges about 
the trip gear are made in 
shape of removable hardened 
plates, of best English steel. 
These plates are reversible, 
and all eight edges can be 
used as contact edges. The cut off gear is operated by an independent eccentric furnished with 
the machine; the regulator is driven by a belt. A safety stop is provided which will stop the 
engine in case of any accident to the governor belt, or if the regulator should stick, i He saiety 
stop will keep a uniform tension on the governor belt. Speed of governor up to 2UU r.p.m. 



GOVERNORS 



391 



The conditions of load vary widely in different classes of work. In the 
case of factory or mill engines, the load is practically constant, while wit!?, 
those employed for electric railway work, the load changes constantly as 
the various cars along the line are started and stopped. In the case of 
rolling mill engines, the conditions are even worse, for here the engine may 
be running light, with no load except its own friction, when suddenly the 
rolls are started and the maximum load will be thrown on at once. 

With any governor of whatever type, there must be a certain variation 
in the speed of the engine to operate it. In most well designed engines the 
speed will not vary more than two per cent above or below the mean speed, 
and in many cases even closer regulation is obtainable. 




Figs. 709 and 710. — McEwen right hand engine governor; fig. 363 run over setting; fig. 364, 
run under setting. The wrist pin is shown at 2; there is another hole in the arm directly 
below. 3 is a dash pot, and as centrifugal force interferes with its free operation at high 
speeds the weight 4, is provided to counterbalance it and prevent undue friction. The governor 
arm is pivoted at 5 and rubber buffers are provided at 6 and 7, the ends of travel. Fig. 364 
shows gear reversed. The wrist pin is in the other hole provided for it 



A regulation within 4 per cent means that if the normal speed of the 
engine is 100 r.p.m. at its rated capacity, it should not rise above 102 
r.p.m. when all the load is thrown off, nor drop below 98 r.p.nr. when the 
maximum load for which it is designed is thrown on. 

Oues. What is close regulation? 

Ans. Small speed variation. 

Owes. What is the usual regulation in practice? 

Ans. From 2 to 4 per cent. 



392 



GOVERNORS 



Shaft Governors. — This type of governor is used chiefly in 
that large class of engines popularly known as automatic cut off 
engines. Because of the high rotative speed, a powerful and 
sensitive governor can be provided without undue weight or 
vibration. 

Shaft governors may be classified: 

1. With respect to the controlling force or forces, as 

a. Centrifugal; 

b. Inertia; 




Figs. 711 and 712. — Rites governor as applied to Watertown engine. Fig. 365, governor in 
forward motion; fig. 366 governor reversed. 

c. Combined centrifugal and inertia; 

d. Combined inertia, and neutralized centrifugal. 

2. With respect to the regulating mechanism, as 

1. Variable throw; 

2. Variable angular advance; 

3. Combined variable throw and variable angular advance. 



Many of the so called inertia governors are, in fact, of the 



GOVERNORS 



393 




Figs. 713 and 714. — Harrishurg governor in forward and reversed motion. The eccentric is 
pivoted at 2, and swings across the shaft 3, by action of the weights 4 and 5, which are pivoted 
at 6 and 7, respectively. After reversing governor as in fig. 714, if sluggish, move the ends' 
of the spring toward the rim of wheel; if super-sensitive, move them toward the center. 




Figs. 715 and 716. — Fitchhurg governor in forward and reverse motion. When in the position 
shown the governor is at rest, and the springs draw the heavy weights 2 and 3, inward, thus 
raising the eccentric to its maximum eccentricity. In operation^ centrifugal force throws 
the weights 2 and 3, outward against the force exerted by the springs, reducing the eccen- 
tricity until equilibrium between cut off and load is established. The auxiliary weight 4, 
operates with the main weight 2, as it is pivoted at 6, but the other auxiliary weight 5, 
operates against the main weight 3, as it is pivoted at 7, hence 4 and 5, balance each other, 
but taken together they resist changes in speed, therefore the result is a very steady speed 
under variable load. If in fig. 715, link 8, be disconnected from pin 9, and connected at 10, 
the eccentric will be moved in the opposite direction by centrifugal force. By disconnecting 
link 11, from 12, and connecting it at 13, it also reverses motion because it is pivoted at 7, 
these changes reversing the governor. 



394 



GOVERNORS 




Figs. 717 and 718. — Shaft governors illustrating principles. Fig. 717, centrifugal control, 
variable throw regulation; fig. 718, inertia control, variable angular aidvance regulation. 




Figs. 719 and 720. — Shaft governors illustrating principles. Fig. 719, combined centrffugal 
and inertia control (forces acting together), combined variable throw and variable angular 
advance regulation; fig. 720, combmed centrifugal and inertia control (forces acting in 
opposition), combined variable throw and variable angular advance regulation. 



GOVERNORS 



395 



combined centrifugal and inertia class, these forces acting either 
in unison or in opposition according to construction. 

The principles relating to the controlling forces have been explained 
under inertia governors, and the methods of varying the cut off by altering 
the travel or angular advance, have been treated at length in chapter 6 
on variable cut off. 

Figs. 717 to 720 show four types of shaft governor illustrating the con- 
trolling forces and regulating- mechanism as classified. 

In fig. 717 the action depends on centrifugal force alone. Inertia acts 
along the axis through the pivots P P', and therefore does not tend to rotate 




Figs. 721 and 722. — Shaft governors illustrating principles. Fig. 721, inertia control, variable 
throw and variable angular advance regulation; fig. 722, combined inertia and neutralized 
centrifugal control, variable travel and variable angular advance regulation. 



the ball around the pivot. The regulating mechanism changes the cut off 
by variable throw. 

The governor illustrated in fig. 718, controls the engine speed by inertia 
alone, the two forces acting together; regulation being by variable angular 
advance. 

Figs. 721 and 722 show a regulating mechanism with swinging eccentric 
which regulates by combined variable angular advance and variable throw. 
The control is by combined centrifugal force and inertia, these forces 
acting together in fig. 721, and in opposition in fig. 722. 



396 



GOVERNORS 



Fig. 721 shows a control by inertia alone, the regulation being by variable 
angular advance. 

Fig. 722 is an example of combined inertia and neutralized centrifugal 
control with variable angular advance regulation. 

It should be understood that the series of illustrations, figs. 717 to 722, 
are intended to represent principles rather than construction, and are 
therefore to be regarded as elementary diagrams. 




Figs. 723 and 724. — Mcintosh and Seymour governor in forward and reverse motion. In 
operation, centrifugal force throws the weights 2 and 3, outward giving variable angular 
advance. 




Figs. 725 and 726. — Buckeye governor in forward and reverse motion. Centrifugal control 
and variable angular advance regulation. To reverse, all connections are put in opposite 
places. 



GOVERNORS 



397 



Auxiliary Devices. — Some governors are fitted with dash 
pots or other damping devices to prevent super-sensitiveness. 
All governors should be provided with a safety stop, or device 




Figs. 727 and 728. — Clark combined centrifugal and inertia governor in forward and reverse 
motion. Regulation is by variable angular advance. The centrifugal weights 2 and 3 are 
pivoted at 4 and 5 respectively. Inertia control is secured by the weight 7 pivoted radially 
at 6. 




Figs. 729 and 730. — Russell centrifugal governor in forward and reverse motion. Regulation 
is by variable angular advance. To reverse this engine the main eccentric must be turned, and 
if an offset key be used it must be reversed. The cut off eccentric must be carried around 
on the shaft until it has the same angular position in advance of the crank that it had before. 
It is necessary to reverse the spring connections and weighted arms to accomplish this. The 
eccentrics are made in halves to facilitate their removal. 



398 



GOVERNORS 



which closes the throttle in case the belt or drive gear should 
break. A desirable feature is a speed regulator which permits 
wide adjustment of the speed during operation. 

These devices are illustrated in the various cuts of governors 
as constructed by the various manufacturers. 




Fig. 731. — Variable speed changing cones as applied to the Ball variable speed engine. In 
operation, the speed of the upper cone is constant while that of the lower (together with 
the engine speed), varies as the cone belt is shifted to the right or left by means of the shifter 
operated by the hand wheel. 

Variable Speed Governors. — There are some conditions of 
service, as in paper mills, where it is frequently necessary to 
vary the speed of the engine within a wide range. Engines 
fitted with governors designed especially for speed variations 
are known as variable speed engines, and are intended for all 
classes of manufacturing where the quality, thickness or weight 



GOVERNORS 



399 



uf the raanufactured product is affected by the speed at which 
the machinery runs. The governor is usually of the throttle 
type fitted with a pair of variable speed cones as shown in 
fig. 731, or with friction discs as in fig. 732. 

Since the speed of the governor must always he constant y no matter 
what speed is required of the engine, evidently the speed changing 




Fig. 732.— American Ball variable speed mechanism and automatic stop as applied to paper 
mill engine. At the left in the rear is the speed ^governpr driver through variable speed 
friction discs, and at the right, the automatic engine stop driven directly from the engine. 
The steam valve of the automatic stop remains wide open throughout the whole normal 
range of speeds for which the engine is designed, but in case the speed exceed the prede- 
termined limit, the mechanism is tripped and the weighted lever closes the steam valve. 
At all speeds within range of the variable speed device, the automatic stop has no throttling 
effect and hence cannot affect the speed of the engine. 

part of the mechanism is some form of transmission between the 
engine shaft and the governor by means of which the ratio of 
gearing may be varied, just as, for instance, is done in the 
transmission or gear box of an automobile, only in the case of the 
variable speed governor, there must be possible an infinite 
number of gradations, or speed changes, instead of three or four 
as in the automobile. 



400 GOVERNORS 



Referring to the principle just stated, there is a speed stamped on every 
throttling governor and the valve of the governor will not close until that 
speed is reached. Different sizes and styles of governors are stamped for 
different speeds, but the same principle applies to all. 

To illustrate this, if the governor of an ordinary throttling engine were 
stamped at 200 revolutions, and it was required to run the engine at 100 
revolutions, it would be necessary to put a governor belt pulley on the 
governor shaft one-half the diameter of the governor belt pulley on the 
engine shaft, that is, the diameter of the two pulleys would have to be such 
that, when the engine was running at 100 revolutions the governor would 
be running at 200 revolutions; because, as stated, the governor will not 
regulate the steam supply until it has reached the speed which the manu- 
facturers stamp upon it. 

In showing how this principle is applied with variable speed cones, as 
in fig. 731, it must be remembered that the upper cone of the pair always 
runs at a constant speed because the governor runs at a constant speed; 
the governor shaft and the upper cone being geared together. With this 
in mind, suppose that the short belt connecting the two cones is so placed 
that it is at the big end of the lower cone, and consequently, is at the small 
end of the upper cone. Under these conditions, the engine would run at 
a very slow speed. 

The reverse of this situation would occur when the short belt between 
the cones is shifted to the small end of the lower cone, and consequently 
is at the large end of the upper cone. Under these conditions, the engine 
would run very fast, in order to keep the speed of the governor at the speed 
stamped upon it. 

This belt, which connects the two cones, is held in a frame, and this 
frame is moved from one extreme of the cone to the other, by means of a 
long screw turned at the end by a hand wheel. This hand wheel is shown 
in the figure at the right of the open engine. By turning this wheel, the 
belt is gradually moved along the cones, from one end to the other, and 
this movement causes the engine to run at varying speeds in order that 
the governor may always run at the constant speed stamped on it. 

By means of this device it will be seen that the speed of the engine is 
regulated with the utmost nicety, increasing or decreasing gradually and 
without the slightest shock to the driven machinery, and without shutting 
the engine down. Since the cones are tapered instead of being stepped, 
the number of possible changes between the two extremes is without limit. 

If it be desired to regulate the speed of the engine from some other part 
of the room, the hand wheel, which operates the screw of the regulating 
device, may be replaced by a sprocket wheel and chain. 

Usually a graduated scale and pointer are provided on the speed changing 
device, so that the engine may be set to run at any desired speed, or changed 
from one soeed to another, without using a speedometer. 



GOVERNORS 



401 



Since a variable speed engine usually operates machinery 
worth many times the value of the engine, a secondary speed 
control is provided, which . provides additional means of pre- 
venting damage to the driving machinery in case of accident. 

One type of secondary speed control consists of a quick closing emergency 
stop valve in the steam line, which is automatically closed by a tripping 
device, attached to the rim of the band wheel. This tripping device flies 
out under high speeds and releases a catch which is connected by a rod to 




Pig. 733. — Chandler and Taylor trigger device for secondary speed control. In .operation^ 

when the speed of the engine exceeds a predetermined rate, centrifugal force causes the lever 
A, pivoted at B, to overcome the compression of the spring C, and fly out engaging the 
trip D, pivoted at E, which releases the steam arm F, allowing the weight W to fall and 
close the butterfly valve V. 

the weight lever of the emergency stop valve. When released this weight 
on the lever of the valve swings to its lowest position and shuts off the 
steam. 

A second type of secondary speed control is the shaft governor connected 
to a swinging eccentric and so developed that it will not become operative 
until the speed of the engine arrives at the maximum speed at which it is 
to run. Any effort of the engine to run beyond this maximum speed 
shortens the valve travel and by so doing cuts off the stearn in the steam 
chest. In this device the engine is not brought to a stop as with the trigger 
device. In this second plan the engine operates at its maximimi spee4» 
until it is shut down by hand. 



402 GOVERNORS 



The objection to the trigger device is not in the device itself, but in the 
neglect of it. If the trigger in the wheel be not kept clean and free it is 
apt to gum up and stick, and thus fail to perform its functions, when called 
on to do so. The only objection to the shaft governor device is its increased 
expense. There ai^ no pins to stick in the shaft governor, and the weights 
in the wheels, rotating at the high speeds which they do, have sufficient 
power to take care of any emergency. 

In- the operation of paper machines the shaft governor has still another 
advantage: When the engine speeds up to its maximum speed, the operator 
can tear off the line of paper at a point before it enters the drying rolls, 
and so allow the paper in the dryers to run itself out and clear the machine 
before engine is shut down. 

With the trigger device the engine is shut down at once, leaving all 
the paper in the machine. 

Governor Troubles. — A governor with its delicate control 
and regulating mechanism is a delicate piece of apparatus and 
must be kept in first class condition to secure satisfactory 
working. 

Dry pins often give trouble by introducing excess friction which opposes 
the controlling force. As much alteration should be given to governor 
lubrication as to any other part of the engine. Special attention should be 
given to the lubrication of eccentrics, and the main pin on inertia governors. 

Lost motion in the various joints is not conducive to best operation. 

The engineer should frequently move the governor weight arms by 
hand when the engine is not running; any undue force required in this 
operation on small and medium size engines will indicate that some part 
of the apparatus is not in proper working order. 

Every time the valve stem packing is tightened more resistance is added 
which must be overcome by the controlling force, hence for satisfactory 
governor operation the valve stem packing should be kept in as near one 
adjustment as possible. 

The valve setting or its condition is quite as important as other causes 
of trouble. See if the valve be set properly or if it leak, or the pressure 
plate bind. 

If the normal load be such that the valve does not over travel the seat, 
a shoulder will be worn near the seat limit, hence a slight increase of load 
causing more travel will cause the valve to ride on the shoulder and leak. 
The valve seat should be carefully examined for this defect. 

When springs are too weak to give the required tension, cut off enough 
' turns to produce the proper effect. 



PUMP VALVE GEARS 403 



CHAPTER 12 
PUMP VALVE GEARS 



Principles of Operation.: — Many ingenious valve gears have 
been devised for operating the steam ends of direct acting pumps. 
The need for such special devices is caused by the absence of a 
rotating part which prevents the use of an eccentric. In most 
cases, the necessary movements of the valve gear are obtained 
from two sources : 

1. The movement of the piston or piston rod; 

2. The steam pressure. 

The valve gear when thus operated usually consists of: 

1. A main slide valve which admits and exhausts steam from 
the cylinder; 

2. An auxiliary piston connected to the main valve and moving 
in a cylinder formed in the valve chest ; 

3. An auxiliary valve controlling the steam distribution to 
the auxiliary piston cylinder, and operated with suitable gear 
by the main piston, or piston rod. 

The cycle of operation of a valve gear of this type is as follows : 

As the main piston approaches the end of the stroke, it moves 
the auxiliary valve which causes steam to be admitted to one 
end of the auxiliary piston and exhausted from the other. This 
results in a movement of the auxiliary piston which in turn 



404 



PUMP VALVE GEARS 




W^ 



Figs. 734 and 735. — Valve gear of the Snow pump. The auxiliary valve is a plain flat slide 
operated by a valve stem, the latter being moved back and forth by means of a rocker shaft, 
as shown, the upper end of which alternately comes in contact with the collars on the stem. 
Tlie outer end of the valve stem passes through a sleeve attached to a pin in the upper end 
of the rocker arm, as shown. A knuckle joint near the stuffing box permits the rod to vibrate 
without causing any derangement in the alignment of valve stem through the stuffing boxes. 
On the valve stem at either end of the auxiliary valve is a spring, which tends to keep the 
valve in a central position, so that when the rocker arm engages one of the collars, the valve 
IS drawn against the spring toward that end of the stroke. The result is that the stem and 
valve follow the rocker arm on the return stroke to its mid-position, and are started on the 
latter half of the stroke by the stem, but without shock or lost motion. This, arrangement is 
particularly valuable in the case of condensers, and in pumps where the first part of the stroke 
IS made quickly, and the piston is then suddenly stopped by coming in contact with a solid 
body of water, the latter part of the stroke being made much more slowly. The springs on 
either side of the auxiliary valve take up lost motion and keep the parts in contact, thus 
preventing shocks and unnecessary wear. 

The auxiliary valve controls the admission and exhaust of steam from the steam chest and 
valve piston in the manner common to all slide valve engines. The valve piston is con- 
nected to the main valve, which allows the valve to find its own bearings on the seat and 
not only takes up the wear automatically, but produces even wear. 

To set the auxiliary valve, see that the valve is in its central position when the rocker 
arm is plumb, and that the collars on the valve stem are located at equal distances from 
each end of the sleeve. When the piston moves to one end of the stroke, the auxiliary valve 
will open the small port at the opposite end, provided the collars on the valve stem have been 
properly placed. Setting the collars closer together shortens the stroke of the piston, and 
moving them farther apart lenghens the stroke. The piston should always make a full stroke 
without danger of striking the cylinder heads. 



PUMP VALVE GEARS 



405 







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406 



PUMP VALVE GEARS 




<t 



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an 1 


D 


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Figs. 738 to 742. — ^Valve gear of the Deane pump. The main valve is operated by a valve 
piston without lost motion, as in fig. 738. Steam is admitted alternately to opposite ends of 
the valve piston. The motion of the piston valve is controlled by a secondary valve, which 
admits and exhausts the steam to the valve piston through the small ports at the sides of 

Figs. 736 and 737— Continued. 

tappets, M M, which causes the piston valve to start, after which steam will complete the 
work. When the pump is running, the cross head I, never quite touches the tappets, M 
M, because it engages the tappets L L, admitting steam to the piston valve and shifts it 
before the tappets, M M, are touched. The reason of the double ports in the aijxiliary 
steam ch«st is to have one port D, for steam, and one port N, for the exhaust. Steam 
being imprisoned between these two ports forms a cushion, preventing the piston valve 
striking the heads of the chest. The tappets L L, set closer together or farther 
apart control the stroke of the main piston H. When the pump is running very fast, the 
momentum of the moving parts increases and the tappets will have to be set closer together 
for high speed than for slow. The tappets M M, are adjustable to their right relation with 
the tappets L L. The general design and easy means of adjustment make a reliable single 
cylinder valve motion. 

To set the values. — There are no complicated internal parts requiring adjustment, and 
almost all parts requiring manipulation can be handled while the pump is running. 



PUMP VALVE GEARS 407 



moves the main valve. The steam distribution to the main 
cylinder thus affected, reverses the motion of the main piston, 
and the return stroke takes place, completing the cycle. 

In pumps of different makes, the detail which varies mostly 
is the auxiliary valve and the method by which it is operated. 
With respect to these features the majority of pumps may be 
divided into two classes, as those having: 

1. A separate auxiliary valve; 

2. Auxiliary valve and auxiliary piston combined. 

In pumps of the first mentioned type, the auxiliary valves 
usually have stems or tappets which project into the cylinder at 
the ends and are moved by contact with the raain piston as it 
nears the end of the stroke. 



Figs. 738 to 7 ^^2— Continued, 

the steam chest. The secondary valve derives its motion from the valve stem, tappets, links 
and the piston rod as shown. _ 

In operation, assume the piston moving in the direction of the arrow near the end of the 
stroke ; the tappet block comes in contact with the left hand tappet and throws the secondary 
valve to the left until its edge, A, fig. 741, uncovers the small port, S, figs. 739 and 740, 
admitting steam to the valve piston. The port, E, and chamber, F, in the secondary valve 
5)rovide for the exhaust of steam from the left hand end of valve piston in the same manner 
and at the same time that steam is admitted behind the right hand end. The exhaust ports 
in the chest allow for properly cushioning the valve piston. The small ports on the other 
side of the steam cylinder, figs. 739 and 740, control the motion of the valve in the other 
direction and act in exactly the same manner as those just described. In case the steam 
pressure should fail to start the valve piston in time, a lug. B, fig. 738. whicii forms apart 
of the valve stem, comes in contact with the valve piston and the entire power of the steam 
cylinder starts it. The correct timing of the valve movements is controlled by the position , 
of the tappets. If they be too near together, the valve will be thrown too soon and thus 
the stroke of the pump will be shortened, while on the other hand, if too far apart, the pump 
will complete its stroke without moving the valves. These tappets are set and keved securely 
before leaving the factory The exhaust from the cylinder is cut off when the piston covers 
the inner port, and forms a steam cushion for the piston to prevent it striking the heads. 
To set the valve — Place the steam piston at the end of stroke nearest stuffing box and 
the secondary valve so that it will uncover the steam port, S, figs. 739 and 740. Set the tappet 
next to the steam cylinder on the valve stem against the tappet block and secure it in this 
position. Slide the secondary valve forward until the opposite steam port is uncovered 
and place the steam piston in its extreme outward position, then set the other tappet 
against the tappet block. Now set the valve so that the inside main steam port is open 
and the valve piston in position to engage the main steam valve, put the valve chest on 
the cylinder and secure it in place. The pump will then be ready to start on the admission 
of steam to the steam chest. If when steam is turned on, the pump refuse to start, simply 
move the valve rod by hand to the end of its stroke and the pump will move without 
trouble. In renewing the packing between the steam chest and cylinder, caution should 
be observed to cut out openings for the small ports. 



408 



PUMP VALVE GEARS 



Where the auxiliary valve is combined with auxiliary piston, 
an initial rotary motion is given the latter by the external gear, 
causing it to uncover ports which give the proper steam dis- 
tribution for its linear movement. 

An example of the separate auxiliary valve type is shown in 
fig. 743 which illustrates the steam end of the Cameron pump. 




Fig. 743. — ^Valve gear of the Cameron pump; an example of the separate auxiliary valve class. . 
Its construction and operation is explained in detail in the accompanying text. No valve 
setting is necessary, it being only necessary to keep the valves 1,1, tight by occasional 
grinding. In operation, the piston as it nears the end of each stroke strikes the stem and 
lifts the valve off its seat; this allows the exhaust steam behind the piston valve to escape. 
The live steam pushes the piston towards the exhausted end carrying the main slide valve 
along with it. 



Each auxiliary valve I, has a short stem which projects into 
the cylinder; when the piston C, strikes one of these, the valve 
is driven back, and opens an exhaust passage E, from the 
corresponding end of the auxiliary piston F, which immediately 



PUMP VALVE GEARS 



409 




Figs. 744 to 748. — ^Valve gear of the Knowles pump. The valve piston is driven alternately 
backward and forward by the pressure of steam, carrying with it the main valve, which 
admits steam to the main steam piston that operates the pump. The main valve is a plain 
slide whose section is of B form, working on a flat seat. The valve piston is slightly rotated 
back and forth by the rocker bar H; this rotative movement places the small steam ports 
D, E, F, figs. 746 to 748, which are located in the under side of the valve piston in proper 
position with reference to the corresponding ports A, B, cut in the steam chest. Steam 
enters through the port at one end and fills the space between the valve piston and the head, 
drives the valve piston to the end of its stroke and carries the main slide valve with it. 
When the valve piston has traveled a certain distance, a corresponding port in the opposite 
end is uncovered and steam enters, stopping its progress by giving it the necessary cushion. 
There is no dead center. 

In operation, the piston rod with its tapped arm J, fig. 744, moves backward and for- 
ward with the piston. At the lower part of this tappet arm is attached a stud or bolt K, on 
which is a friction roller I. This friction roller, lowered or raised, adjusts the pump for a 
longer or shorter stroke. This roller coming in contact with the rocker bar at the end of 
each stroke, and this motion is transmitted to the valve stem, causing the valve to roll 
slightly. _ This action opens the ports, admits steam and. moves the valve piston, which 
carries with it the main slide valve which admits steam to the main piston. The upper end 
of the tappet arm does not come in contact with the tappets L, M, on the valve rod, unless 
the steam pressure from any cause should fail to move the valve piston, in which case the 
tappet arm moves it mechanically. 

To set the valve, loosen the set screws in the tappets on the valve stem. Then place the 
piston at mid-stroke, and have the rocker bar H, in a horizontal position, as shown in the 
engraving. The valve piston should then occupy the position shown in fig. 748. The 
valve piston may be rotated slightly in order to obtain this position by adjusting the length 
of connection between the rocker bar H, and the valve stem. Then turn the valve piston 
G, one way or the other to its extreme position, put on the chest cover, and start the pump 
slowly. If the pump make a longer stroke on one end than on the other, lengthen or shorten 
the rocker connection so that the rocker bar H, will touch the rocker roller I, equally distant 
from the center pin J. If the pump hesitate on the return stroke, it is because the rocker 



410 PUMP VALVE GEARS 

is shifted under the action of Hve steam on the opposite side 
of the piston head. 

There is a small hole in each end of the auxiliary piston, 
and when both auxiliary valves are closed, the steam passing 
through these holes leaves the auxiliary piston entirely sur- 
rounded by live steam, and therefore in perfect balance end- 
wise, until the main piston strikes the stem in the opposite 
cylinder head, when the valve moving operations are repeated 
in the opposite direction. 

The space back of the auxiliary valve communicates with 
the steam chest, through a passage shown in dotted lines; the 
valve is therefore closed by steam pressure as soon as the 
piston moves back from the stem. 

It should be noted that the piston closes the exhaust passage before the 
end of the stroke. The confined steam forms a cushion between the piston 
and the cyHnder head, but a Httle passage is cut in the cylinder wall through 
which sufficient stea^n is admitted to start the piston on the return stroke. 

The auxiliary piston which carries the main valve G, shifts the latter in 
the direction the piston travels at the end of the stroke, that is, opposite 
to that of a common slide valve. This valve has, therefore, two cavities, 
each of which alternately puts the cyhnder in communication with the 
steam chest and the central exhaust port. Steam is admitted under the 
outer valve face, as shown in the figure. 

H, is a lever, by means of which the auxiliary piston may be reversed by 
hand when expedient. 

An example of the second mentioned type in which the 
auxiliary valve and auxiliary piston are combined is shown in 
figs. 753 to 755, illustrating the valve gear of the Davidson pump. 



Figs. 744 tp 7 ^S.— Continued. 

roller, I, is too low and does not come in contact with the rocker bar, H, soon enough. To 
raise it, take out the rocker roller stud, K, give the set screw in this stud a sufficient down- 
ward turn, and the stud with its roller may at once be raised to its proper height. If the 
valve rod tremble, slightly tighten the valve rod stuffing box nut. When the valve motion 
is properly adjusted the vertical arm should not quite touch the collar L, and the clamp M. 
Rocker roller I, coming in contact with the rocker bar H, reverses the stroke. 



PUMP VALVE GEARS 



4U 



COMBINED MOVABLE SEAT 
AND AUXILIARY VALVE 




BLAKE SrtMGLE PUMP 

SECTIONAL VIEW 

OF 
STEAM END 




Figs. 749 to 752. — ^Valve gear of the Blake pump. The main valve, is carried by the auxiliary 
piston, and moves on the back of the movable seat (fig. 752), the passages A B C, of which 
serve as steam passages. The lugs G G', control admission of steam to the auxiliary cylinder, 
and the holes H H', control the exhaust from that cylinder. In operation, when the piston 
nearly reaches the left end 'of the cylinder, the movable seat is shifted to the left so that lug 
G, covers the port E, while lug G', uncovers port E', thus admitting steam behind the auxiliary 
piston at the left side. At the same time the exhaust port K, of the auxiliary cylinder is 
opened to the hole S, leading to the exhaust, and forcing the auxiliary piston over to the right, 
uncovering port A, to live steam. Near completion of the stroke the operation is reversed. 
The auxiliary piston is cushioned on steam, because the exhaust port is not out at the end 
of the auxiliary cylinder, and consequently there is steam imprisoned when the piston covers 
the exhaust, as at the left in fig. 751. The main piston is cushioned on live steam, because 
the valve has lead; that is the operation of admitting steam is performed before the piston 
reaches the end of its stroke. It will be seen that if means be provided to shift the movable 
seat from one end of its travel to the other, the rest of the operation is automatic. Fig. 752, 
shows the valve gear provided for this operation. The piston rod is provided with a cross 
head, the latter having a pin as shown. The frame of the pump is built with. an upright 
piece U, to which is pivoted at P, a lever whose lower end is slotted and engages with the 
cross head. The valve rod, which is secured to the movable seat, is provided with two collars 
as shown. These collars are made of split nuts which work on a thread cut on the valve rod 
for a short distance on each side of their ordinary position. Between these two collars is a 
tappet, which is free to slide on the valve rod. The link shown connects the tappet with the 



412 PUMP VALVE GEARS 



The main valve is operated by a positive mechanical connection between 
it and the main piston rod, also by the action of steam on the valve pistons. 
Fig. 753, shows the details of valve gear and steam cylinder. In the fig- 
ures the steam end consists of the cylinder M, valve A, and valve pistons 
B and B. These pistons are connected with sufficient space between them 
for the valve A, covering the steam ports P and Fi, as in fig. 755. 

The valve is operated by the steel cam C, acting on a steel pin D, which 
passes through the valve into the exhaust port N, in which the cam is 
located. In addition to this positive motion, steam is alternately admitted 
to and exhausted from the ends of the valve piston through the ports E 
and El, which moves the pistons B and Bi. 

Assuming the pump to be at rest with the valve A, covering the main 
steam ports F and Fi, in which position the cam C, holds the main valve 
by means of the valve pin D, so that ports E and Ei, admit steam to one 
end of the valve piston at the same time connects the other end with the 
exhaust port. The steam, acting on the valve pistons, moves both, opening 
the main ports F and Fi, admitting steam to one end of the steam cylinder 
and opening the other end to the exhaust. 

If the valve occupy any other position than the one described, the main 
ports, F and Fi, will be opened for the admission and exhaust of steam; 
consequently it is evident that this pump will start from all points of the 
stroke. 

On the admission of steam to the cylinder the main port F, the main 
piston, cam and valve will move in the direction indicated by the arrows. 
The first movement of the cam oscillates the valve, preparatory to bringing 
it into a proper position for the opening of the auxiliary steam ports E, 
to live steam, and E, to exhaust, also to close the valve mechanically just 
before the main piston reaches the end of its stroke. This causes a slight 



Figs. 749 to 752. — Continued. 

lever. When the piston rod moves, the lever rotates about P, carrying the tappet with it; 
and when the tappet strikes either collar it moves the movable seat in the direction in which 
the tappet is moving. By placing the collars so that the tappet strikes them before the 
piston reaches the end of its stroke, the movable seat will be shifted in the required manner. 
To set the valves. — No valve adjustment is required to be made inside the steam chest, 
and the only adjustment which can be performed is that of altering the distance between the 
collars, thus changing the travel of the valve. This is done by loosening the set screws in the 
collars, and rotating the latter until they come to the required point. Changing the distance 
between the collars alters the length of the stroke. This is easily seen, because the action 
of the tappet in striking the collars is what admits and exhausts the steam; and if the 
distance which the tappet has to travel be varied, the time at which the valve is actuated is 
varied, and the stroke varies as well. The adjustment of these collars is very simple, and 
can be performed while the pump is running. In adjusting them it is desirable to make the 
stroke as Jong as possible and secure enough cushioning, for the shorter the stroke the greater 
the amount of the clearance, and the steam required to fill the clearance is wasted on every 
stroke. If the collars on the valve rod be not set at equal distances from the center line of 
the lever when the latter is vertical, the movable seat will be reversed sooner on one stroke 
than on the other, and consequently the piston will travel further in one direction than 
in the other. 



PUMP VALVE GEARS 



413 







Figs. 753 to 755. — Valve gear of the Davidson pump; an example of the combined auxiliary 
valve and auxiliary piston class. To set the valve piston, push the main pistons to the end 
of the stroke until the inner edge of the port and the piston coincide, then loosen the side 
lever, turn the cam C, until the valve piston uncovers the auxiliary steam port E, leading 
to the same end of the steam chest occupied by the main piston. After setting, secure the 
cam and then connect the side lever to the connecting rod. The side lever and cam occupy 
correct relative positions, therefore, the lever should be secured to the cam shaft while in 
this position. The stroke may be regulated by raising or lowering the end of the connecting 
rod in the slotted end of the slide lever. Raising the connecting rod shortens the stroke and 
lowering it lengthens the stroke. When making the foregoing adjustments it is well to have 
the connecting rod at or near the bottom of the slot as shown in the engravings. 



414 



PUMP VALVE GEARS 




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PUMP VALVE GEARS 



415 



The Duplex Pump Valve Gear. If two steam pumps be 
placed side by side, it is found that the main. valve of each may be 
operated directly from the piston rod of the other without the 
aid of any auxiliary pistons or valves as is necessary with single 




Figs. 758 and 7o9. — Plan and elevation of one side of a duplex ptimp showing steam cylinder 
and valve gear. 

pumps. Each piston rod then with suitable connections operates 
the valve of the other pump in such sequence that the strokes 
are alternately made resulting in a discharge, nearer uniform 
than is obtained in a single pump. Figs. 758 and 759 show 
the general arrangement of the valve gear. 



416 



PUMP VALVE GEARS 



The duplex pump has one main valve for each side, there being 
no auxiliary valves. as in single pumps. These main valves, as 
shown in figs. 760 and 761, are* nothing more than ordinary slide 
valves. 

It will be seen from fig. 761 that the valve seat has five ports, giving 
separate steam and exhaust passages and a central exhaust cavity as shown. 

The passages nearest the ends are steam passages while the inner 
passages are for exhaust. These inner passages are covered or closed by the 




H 





Figs. 760 and 761. — Main valve and valve seat of duplex pump; each "side" or pump is fitted 
with a valve and seat as here shown. H and F, are the steam edges of the valve and G and I, 
the exhaust edges. Q and K, are the steam ports and O and R, the exhaust ports; the exhaust 
cavity or outlet is seen at the center of the seat. Fig. 760, shows the lost motion between the 
stem and valve. The amount of lost motion given is such that the inlet ports are not closed 
and the exhaust ports opened too early in order to allow the piston to make a full stroke. 



piston just before the end of the stroke whereby a portion of the exhaust 
steam is compressed and made to act as a cushion between the piston and 
cylinder head, thus preventing the piston striking the cylinder heads when 
operating at high speed; this assists materially in the operation of the 
pump. 

The travel of the valve is such that its exhaust edge never passes by the 
steam edge of the steam port, hence steam can only be exhausted through 
the exhaust port. 



PUMP VALVE GEARS 



417 




In large pumps, a by- 
pass is provided, con- 
necting the steam and 
exhaust ports; the by- 
pass is provided with a 
stop valve by means of 
which the compression 
can be regulated. The 
adjustment of this 
valve depends upon the 
speed of the pump, the 
higher speeds requiring 
more compression. 



The gear by which 
the motion of the piston 
rods is reduced and 
transmitted to the 
valves is fully shown 
in the accompanying 
cuts. From the illus- 
trations it is seen that 
the piston rod of each 
cylinder is provided 
with a cross head which 
connects with a rocker 
arm. This rocker arm 
is attached to a rocker 
shaft, having at the 
other end a short rocker 
arm, which is con- 
nected with the valve 
stem of the other 
cylinder through a con- 
necting link. 

The valve stem is 
not rigidly attached to 
the valve but con- 
siderable lost motion is 
given, as shown in fig. 
762, so that the valve 
is not moved until the 
piston has reached 
nearly half stroke. 



Preliminary to 



418 PUMP VALVE GEARS 

setting the valves of an old pump it should be ascertained if the cross heads 
have shifted on the piston rods. 

Method of Locating Cross Head Centers. — Usually the 
cross heads of duplex pumps are held in position by a pin, 
which is driven through cross head and rod, after the former has 
been adjusted. It is impossible for the cross head to shift its 
position accidentally, unless the pin should drop out, and even 
then, there is a set screw, holding the cross head against slippage 
by ordinary use, and if such a thing should happen, the best 
way to readjust is to find its former position by the pinhole in 
the piston rod- 



Fig. 763. — ^A very small Worthington duplex pump. Its dimensions are as follows : 2 inch dlam. 
steam cylinder; l}/^ inch water cylinder; 2% inch stroke. Its capacity is .004 gallon per 
revolution; rev. per minute, 80j gallons per minute, 3.5. Steam pipe, ^ inch; exhaust pipe, 
yi inch; suction pipe, l_inch; discharge, % inch. Floor space occupied, 1' 9" X 7" wide. 

Sometimes, however, it is necessary to replace the old piston rods by 
' new ones, which may be quite frequently, if the water be bad, and steel rods 
are used. In most cases the engineer will find that the rods can be put 
into their proper places without any trouble, as the builders have always 
exact fitting duplicates in stock, but it is better to be sure of this, by making 
the following test : Mark the extreme position of the cross head on both 
sides of the pump on the frame or on a wood lathe, wedged in between the 
cylinder heads as shown in the figure. 

If a lathe be not used, the positions of the cross heads may be trans- 
ferred to the frame, by using a small set square. 

Next put a mark, on either the frame or the lathe, to correspond with the 
central or mid-stroke position of the cross head. This may be obtained in 
two different ways, both being illustrated in figs. 758 and 759. 

The use of the plumb bob as in fig. 759 should only be used if the pump 



PUMP VALVE GEARS 



419 



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mu 



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be leveled properly, 
while the square may 
be used under any con- 
dition, providing the 
piston rods be not 
worn too badly. 

When dropping the 
plumb bob in line with 
the center of the rock 
shaft as in fig. 759, the 
cross head may be 
moved close to the line, 
and its position be 
transferred to the 
frame as in fig. 758. 

In the other method, 
the square is used 
against the hub of the 
rocker arm, and thus, 
it will be seen by 
examining fig. 759 that 
the heel of the square 
does not indicate the 
center of the rock shaft, 
but is out an amount, 
equal to one-half the 
diameter of the hub of 
the rocker arm, and 
the cross head should 
therefore not be set 
close to the square, 
but a distance, equal 
to the radius of the 
hub, away from it. 
This distance can be 
measured with an in- 
side caliper, or a rule, 
and the position of the 
cross head is then 
transferred to the 
frame as in fig. 758, or 
marked on the lath as 
shown in fig. 764. 

In both of the above 
methods, no marks 
have been made on 



420 



PUMP VALVE GEARS 




Figs. 765 to 770. — ^Valve gear of the Laidlaw-Dunn- Gordon pump. The admission of live 
steam to the cyhnder and of exhaust steam to the atmosphere is controlled by a valve pis- 
ton A, shown in fig. 766. Assume that the piston is in position shown, fig. 769, and, that both the 



PUMP VALVE GEARS 421 



the piston rod, which is always best to avoid, the cross head having served 
for a mark in both cases 

If the pump be small, there is no difficulty to move the pistons for this 
purpose, but on a large pump, the cross head may be unfastened, so as 
to be free to slide on the piston rod. 

The marks A A, representing the extreme positions of the cross head 
have, however, been taken from one end of the cross head, and thus can 
not come equidistant from the mark C, representing the correct central 
position, even if the cross head be set correctly. Thus it will be necessary 
to transfer them toward the opposite end of the cross head, an amount 
equal to one-half the length of the cross head, B B, being the corrected 
marks.. 

If the position of the marks B B, be not equidistant from the center 
mark C, when the cross head is at the extreme ends of the stroke, it should 
be shifted on the piston rod, until in the proper position, the amount it 
is to be shifted will be indicated by the marks B B, fig. 764. 

It will not be necessary to shift the cross head on the rod, if it be out 
only a small amount, as the duplex pump is not such a sensitive machine, 
to require very delicate adjustment, and often it is found, that, if the 



Figs. 765 to 17^.— Continued. 

main and auxiliary valves cover their respective steam ports. By means of a starting bar, 
operating through a stuffing box in the valve chest, the piston valve A, is moved toward the 
head of the steam chest D, thus opening the ports E and L, and admitting live steam 
through L, from the cavities S, of the valve piston to the housing end of the main steam 
cylinder, through the port F fig. 769, forcing the main piston P, toward the opposite end 
of the stroke, or toward the left in the figure. The port E, fig. 453, being open, the exhaust 
steam escapes from front of the main piston through the port F, fig. 769, into the main 
exhaust port G, through the port E. The piston P, travels to its extreme left position and 
the auxiliary slide valve has been drawn to such a position in the direction indicated by the 
arrow in the smaller drawing in fig. 765, as to bring valve piston, A, toward the opposite end; 
the exhaust steam from the steam chest escapes from before it, through the exhaust port K, 
the opening of which into the chest is at such a distance from the head as will permit sufficient 
exhaust steam to remain to afford a cushion to the valve piston. With the auxiliary slide 
valve in position to bring the hole H, over the port J, fig. 770, it is plain that the exhaust 
through the port K, will pass into the main exhaust through the port L. "With the main 
piston at its extreme travel toward the right, the ports E and L, which correspond to F 
and F, respectively in fig. 769, are opened in such a manner as to exhaust steam to the at- 
mosphere from the housing end of the steam cylinder through the port F, and live steam 
from the chest to the head end of the main cylinder, through the port F, thus driving the 
main piston P, toward the housing end of the cylinder, or toward the right. The piston 
and reciprocating parts traveling in this direction move the auxiliary slide valve to its 
maximum point of travel in the opposite direction, thus opening the opposite auxiliary steam 
and exhaust ports and again driving the valve piston toward the head D, of the steam 
chest, whence a new stroke begins. Lost motion in the valve gear is taken up by adjustable 
links, on all sizes above 7 inches diameter by 10 inches stroke and on some smaller sizes. 
Cushioning of the steam pistons in the larger sizes and upwards is accomplished by means 
of suitable valves called cushion valves. In the smaller sizes sufficient cushioning is done 
by exhaust steam passing from the clearance space next the head through a small hole drilled 
into the main steam port. 

To set the valve of this pump it is only necessary to place the piston in its central position 
and adjust the lever so that the valve will occupy its central position. By this proceeding 
the travel of the valve is equalized. 



422 



PUMP VALVE GEARS 



entire mechanism be set correctly, the pump will not work as well under 
steam, as if slightly out of adjustment.* 

If the cross head be out of adjustment it is advisable to test the pump 
under steam, before making alterations. For this purpose the valves 




Figs. 771 to 775. — Valve gear of 
Dean Bros. pump. The auxiliary- 
valve, A, fig. 771, has in its face 
two diagonal exhaust cavities, 
B, Bi. The ports, C Ci, and the ex- 
haust port, D, are placed in a tri- 
angular position with one another, 
the diagonal cavities diverging so 
that the cavity B, when the valve 
is in place, connects the ports Ci 
and D. Cavity Bi, connects the 
ports C and D, when the valve A, 
is at the end of the stroke. The 
three small cuts show relation of 
auxiliary valve to ports. The pis- 
ton starts from left to right when 
the valve A, moves in an opposite 
direction, opens the port C, ad- 
mitting steam to the auxiliary 
cylinder at the moment the main 
piston has reached the end of its 
stroke. The auxiliary piston E, 
is forced to the left, opening the 
main port and admitting steam to 
the main cylinder, reversing the 
movement of the main piston the 
return stroke of the main piston 
reverses the movement of the auxiliary valve, whereby the port C, is closed, at the mo- 
ment the main piston reaches the end of its outer stroke. The port Ci, is opened by the 
valve A, and reverses the valve piston E, opens the main port and reverses the motion of 
the main piston. This port arrangement admits of a short valve with a long travel. The 
stroke of the pump can be regulated by moving the stud up or down in the segmental slot, 



*NOTE. — If a pump work better when slightly out of adjustment it is due to irregularities 
in the steam and exhaust ports, and is liable to give more and earlier compression on one end of 
the cylinder than on the other, and, when running slow, the piston will not travel within the 
same distance from both cylinder heads. 



PUMP VALVE GEARS 423 



should be adjusted to suit the original position of the cross head, and if 
possible, it will be found very useful, to attach a pointer to the crosshead, 
pointing toward that part of the frame, on which the center and extremes 
of the stroke have been marked. 

By running the pump slow, it will be possible to ascertain the ends of the 
working stroke. 

If the extreme positions of the pointer are marked, which can be done best 
by holding a lead pencil against- the pointer, just touching the frame. 
The points, to which the lead pencil is pushed by the pointer on each end 
of the stroke, are the extremes of the stroke, when the pump is running, 
and by comparing these points with the marks previously obtained, indi- 
cating the true ends of the stroke,- the clearance on each end can be ob- 
tained. 

If there be considerable difference in the clearance on both ends, it is 
best to examine the valves, by moving the pistons by hand to the extremes 
of stroke, as found when running, and noting the port opening at both ends, 
for this purpose the valve chest cover has to be removed. 

If there be any difference in port opening at both ends, this may be 
the cause of the unequal clearance, and a preliminary valve adjustment 
should be made, by equalizing the port opening approximately by eye. 

Various types of pumps are provided with different means for such 
adjustments, but the principle remains the same, that is, to either lengthen 
or shorten the valve stems, as occasion demands. 

Most all types of the smaller sizes are provided with the simple adjusting 
device, as indicated in fig. 762 which consists of a square nut, through which 
the valve stem is screwed, and by screwing the stem either in or out, it is 
respectively shortened or lengthened. 

After such a preliminary adjustment has been made, the pump should 



Figs. 771 to lib.— Continued. 

fig. 775, which varies the travel of the auxihary valve and reverses the stroke of the main 
piston as desired. By raising the stud, the pump will make shorter strokes, and by 
lowering it, longer strokes. 

To set the valve, turn the steam chest upside down. Put valve stem through the stuffing- 
box and secure in place the clamp for small slide valve. The diameter of valve stem is smaller 
where the clamp is attached. Now screw up the stuffing box nut (having previously removed 
the packing), then move the valve and stem so that the small port at right of valve will be 
open one-sixteenth inch and make a scratch upon the stem close to stuffing box nut. The 
valve should then be moved in the opposite direction to open the other small port one- 
sixteenth inch and make a second scratch upon the valve stem next to stuffing box nut. Pre- 
pare joint, and replace steam chest on cylinder. To square the valve, slacken the screw in 
cross head and move the latter to the end of stroke with edge of cross head flush with the 
end of guide, then set the valve stem so that the first scratch is flush with the face of nut, 
same as when the scratch was made. Tighten screw in set screw under valve rod dog and 
move the cross head to the opposite end of stroke, and note the position of second scratch. 
If it do not come to the position in which it was made, split the difference by slackening the 
set screw under valve rod dog and move the valve rod to equalize the travel of valve. In replacing 
steam chest on cylinder, cover the opening with a thin board, or piece of sheet iron, before 
turning it over to prevent the valve dropping out of place. 



424 



PUMP VALVE GEARS 




^^^^^^^^^^^^^^^ 



fMi 




without jar or noise which is often caused by long travel 
steam chest at B, and fills the space F, between 
auxihary valve chest G, shown in fig. 776. With the 
shown, fig. 777, steam passes into both ports J and 



Figs. 776 to 778.— Valve gear of 
the fiurn/iam pump. Fig. 778 
is a plan of the main cylinder 
valve face, having the same 
arrangement of ports as the 
cylinder shown in fig. 777. A 
longitudinal section of the 
steam cylinder is shown in fig. 
776. Motion is imparted to the 
slotted arm and cam A, by 
means of a cross head and a 
roller on the piston rod. The 
cam work? between and in 
contact with two blocks on the 
valve stem, and by adjusting 
these two blocks the stroke 
may be shortened or lengthened 
as the case may require. The 
valve stem of the auxiliary 
valve H, fig. 777, always moves 
in a direction opposite to that 
of the piston. The action of 
this valve alternately admits 
steam through the double ports 
J J and K K, to each end of 
the valve cylinder, causing the 
valve piston I, to move the 
main slide valve D, which, in 
turn, admits steam to the main 
cylinder through the double 
ports E E and L L. As the 
travel of the cam is only one- 
fifth that of the piston traveU 
the valve moves slowly, and 
and rapid motion. Steam enters the 
the valve piston heads and the 
auxiliary valve, H, in the position 
K, but as the port Ji, is closed 



PUMP VALVE GEARS 425 



again be tried under steam, and the ends of the stroke should again be 
marked. 

Should the marks denoting the clearance of the pistons again fall on the 
same points as before, and a difference in the clearance on both ends of the 
stroke be found, the trouble will be due to the irregular spacing of the 
ports in the cylinder bore, and there will be little chance for improvement, 
and, unless the cross head be found considerably out of adjustment, it 
should not be disturbed, and the final valve adjustment should be made 
to suit the extremes of the stroke while running. 

It, however, rarely occurs that a pump is of such poor workmanship 
as to make proper adjustment impossible. 

The location of the ends of the stroke does not make any difference in 
the manner of adjusting the valve, except, that it must be noted that in 
one case, by the end of the stroke, the extreme positions of the pistons 
when pried over, and in the other case the end positions of the pistons when 
allowed to run, are meant. 

How to Set the Valves of a Duplex Pump. — Place a small 
stick or batten against the end of the valve chest, and mark the 
center of the pin P on the same, as indicated in fig. 762. Then 
move the piston, of the same side, to the other end of the stroke, 
and again mark the position of the pin P, on the same stick, as 
indicated by the dotted lines. The two marks M, and N, thus 
obtained, denote the extreme travel of the pin P. 

It will now be necessary to obtain the marks X and Y on the same stick, 
which indicate the positions of the pin L when the valve has moved from 
one full port opening to the other. * 



Figs. 776 to 778. — Continued. 

by the valve piston I, no steam can enter the valve cylinder through it, but the other port, 
K (extending to the extreme end of the valve cylinder), never being covered by the piston, 
is open, and admits steam into the space M. As this port is quite small the space fills slowly 
and the piston moves gradually until it uncovers the last port Ji, when the full volume of 
steam is admitted, which quickly moves the piston to the opposite end of the valve cylinder. 
During this movement of the valve piston, the large port J, remains open to the exhaust 
until it is covered by the valve piston. When the port J, is covered by the valve as at Ji, 
it has no connection with the exhaust, consequently, there being no outlet for the exhaust 
vapor, it is compressed and forms a cushion for the valve piston, I. The valve piston carries 
with it the main valve D, which admits steam to the main steam cylinder through the 
double ports E, Ei, and L, Li, fig. 776. The same cushioning and slow starting of the piston 
occurs in the main as in the valve cylinder, each having double ports. 

To set the valve. — Set the lever A, plumb and the valve to cover all the ports equally. 



*N0TE. — ^When sliding the valve from one "full port" to the other, care should be taken 
to do this by moving the valve stem, to obtain the full effect of the lost motion between the 
nut and the lugs on the back of the valve as in fig. 760. 



426 



PUMP VALVE GEARS 



Now take a strip of stiff paper, and mark upon it the exact distance 
between the center of the holes in the valve connecting link, as D and E, 
fig. 779. Try the distance between the marks D and E, on the strip of paper, 
against the marks X and M, and Y and N, and if they should coincide as 
in fig. 780, the valve is correctly adjusted, and the links should be put into 
their places, and the valve chest cover replaced. 




^^ 



"TIT 



F 



^_ 



za 



IVI N 



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y 


1 A A 


A 


l\ 


X Y 


M 


N 


i ^i- 1 Nl/ 


\ 1 / 


W 


1 /^ /'/^ 


A 


A1 



X E Y 



M N 



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TT 



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X Y 



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Figs. 779 to 784. — Paper template and batten with center marks as used in adjusting the 
valves of a duplex pump as fully explained in the accompanying text. 



PUMP VALVE GEARS 



427 



If, however, the marks should fall as in fig. 781, or fig. 782, it is evident 
that the valve stem is either too short as in fig. 781, or too long as in fig. 782, 



STEAM CHEST. 




Figs. 785 to 789. — Valve gear of the Warren pump. To set the valve gear: 1, Move piston 
valve A, and steam piston B, until they strike the heads of steam chest«and steam cylinder, 
fig. 785. 2, Place clamp D, so as to allow J^ inch for.Nos. 1, 2, 3, 4; % inch for Nos. 
5, 6. 6^; 1 inch for Nos. 7, 8, 9, 10, U, 12, 13, five port; M inch for Nos. 7, 8, 9, 10, 11, 12, 13, 
three port, between clamp and tappet arm G, fig. 785, also between tip and collar E, fig. 787. 
3, Set clamp D, so that as you roll or turn the valve rod in either direction as far as it will 
go, the clamp will be equally above and below the level. 4, Even up the motion of rocker R, 
by screwing the upper part of rocker connection L, out or in as required. 5, Set the roll K. 
in tappet arm I, up or down, so as to allow ^/fg inch between rocker and roll, when the latter 
is at its extreme of travel. Note the little set screw S, in roll stud T, fig. 789, which is adjustable 
to rest on bottom of tappet arm slot, and prevent the roll stud working down after it has 
been set in its proper position. 6, If, when the pump is run under steam, the tip G, strike 
clamp or collar violently before reversing its motion, the tappet arm roll K, needs to be raised, 
a little at a time, until such action ceases, otherwise the tip is liable to be broken. If, on 
the other hand, the pump run short stroke, drop the roll. The best adjustment is when the 
tip just misses hitting clamp and collar, when the pump is doing its regular work. 



428 



PUMP VALVE GEARS 



and it must be either lengthened an amount equal to the distance E Y, 
fig. 781, or shortened an amount equal to the distance E Y, in fig. 782. 

Figs. 783 and 784, show other positions in which the marks on the stick 
and the strip, of paper may fall. In both cases, the travel of the valve 
between the two inside edges of the steam ports evidently does not coincide 
with the travel of the pin P, fig. 762, indicating that there is either too 
much lost motion between the valve stem and the valve, as in fig. 783, 
or not sufficient, as in fig. 784. Before attempting to alter this, it is advisable 
to remove the valve entirely, and to see whether the distance between the 
steam and exhaust edges of the valve, as F and G, and H and I, fig. 760, 
correspond with the distances between the working edges of the ports 




Fig, 790. — ^Rocker arm and connections as usually designed for large pumps, with lost motion 
adjustment. In this arrangement, the lost motion can be adjusted while the pump is in 
operation. 



K and O, and Q and R, respectively (fig. 761). If these distances agree 
with each other, and the marks representing the valve and pin travel fall as 
in fig. 783, it indicates that the valve has not sufficient motion to fully open 
the ports, hence less lost motion has to be given. Fig. 784 shows the re- 
verse of this condition. 

Should the distance, between the edges F and G, or H and I, be found 
shorter than the distance between their respective port edges, an amount 
equal to one-half the difference between E' E and X Y, fig. 784, the steam 



PUMP VALVE GEARS 



429 



edge of the valve will over travel the inner edge of the steam port, when the 
valve is connected up, but the exhaust port would have just full openings 
indicating that there is some exhaust lap, and if the pump be found to run 
smooth, it is advisable not to tamper with the adjustment of the lost 
motion. 

If it be necessary to increase the lost motion between valve and stem, 
on a pump provided with such an adjustment as in fig. 762, it can be 
done by decreasing the width of the nut, by filing or machining in a shaper. 

To decrease the lost motion, either a new nut must be provided, or sheet 
metal washers of the required thickness may be cut, and placed on the valve 
stem between the nut and the lugs on the back of the valve. 

The method of valve setting just described is only suitable for small 
pumps; the larger ones generally being provided with an adjustment as 





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U M 1 ilili'l 


/ V 


li 

11— 




Ji 




gi 




m\ 


i J 


X 








1 '•^ — 'J" 




L-O— J 


N 


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/ / 


^ 




Fig. 791. — Lost motion arrangement consisting of yoke M, and block S, pivoted at the rocker 
end. In this design the lost motion cannot be changed without altering the length of the 
block S, but the length of the valve stem can be adjusted by means of the sleeve nut N. 



in figs. 760, 761 and 791. The arrangement shown in figs. 760 and 761, 
is very simple, and permits accurate adjustment, but in order to do this, it is 
necessary to remove the valve chest cover. 

The type shown in fig. 791, is mostly used on large and more expensive 
pumps, and permits alterations in the adjustment being made while the 
pump is running. 

In fig. 791, the lost motion can not be altered, without taking off or adding 
to the ends of the block S, but the sleeve nut in the connecting link is a 
good device for altering the length of the valve stem. 

It is seldom the case that the amount of lost motion has to be alter- 
ed, and unless the operator be thoroughly familiar with the details 
and design of the pump, he should not undertake such alterations, as 
the designer knows best what the requirements are. 



430 



PUMP VALVE GEARS 



The above directions can not always be closely followed, as the different 
designs require different treatment, but by thoroughly understanding the 
above, the beginner will be greatly assisted even with the most com- 
plicated construction. 

Short Rules for Setting the Valves of a Duplex Pump. — 

It maybe helpful in acquiring a knowledge of how to set the valves 




Fig. 792. — Sectional view of A merican deep well pumping head showing valve. In the position 
shown the steam is passing through ports 1, 2, 3, 4, and choke valve 5, into the cylinder 7. 
Piston rod 6, is connected to the pumping rods that extend down into the well to the water 
plunger. The number of strokes is regulated by the choke valves 5, 16 and 17. Port 8, is 
opened for the exhaust of steam out through 9. Just before the piston 10, reaches the end 
of its stroke, it closes the exhaust port 8, and forms a cushion. At the same time the valve 
stem 11, is also turned by a roller on the cross head, striking a finger cam on the valve stem. 
The movement changes the position of the auxiliary valve 12. Steam will then flow through 
suitable ports and will move the valve 13, so that port 14, is uncovered, allowing stearn to 
enter the upper end of the cylinder and cause the piston to move in the reverse direction. 
At the same time port 15, is brought into communication with exhaust 9. Choke valve 16, 
controls the exhaust and helps the regulation of the pump. In operating a single acting 
cylinder, where the weight of pump rods is heavier than water, no steam is used on the down 
stroke; then valve 17, is closed and valve 16, shut sufficiently to sustain the weight of the 
pump rods and give the required number of strokes. When the double acting and two stroke 
cylinders are used, valve 17 is opened sufficiently to give a uniformity to up and down strokes. 



PUMP VALVE GEARS 



431 



to consider simply the essential operations without the various 
details or methods of performing them as given in the foregoing 
instructions : They may be briefly expressed in the form of rules 
as follows : 

1. Locate ike steam piston in the center of the cylinder; 




Fig. 793. — ^Valve gear of the McGowan pump. Its main valve is of the B form and is driven 
by a valve piston. Steam enters the central port in valve seat and into the cylinder through 
one of the cavities in the valve and exhausts through the opposite. The two tappet valves 
cover the auxiliary ports, shown by dotted lines, leading to the ends of the steam chest and 
connect with the main exhaust ports. When the piston reaches the end of its stroke it lifts 
one of the tappet levers and with it the corresponding valve is raised from its seat, opening 
the port leading from the end of the steam chest to the main exhaust port. The pressure is 
thus relieved on one end of the valve piston and the steam pressmg on the opposite end 
forces the valve piston to the opposite end of its stroke, thus reversing the distribution of 
steam to the cylinder and starting the piston on its return stroke. The main valve is con- 
nected with the valve piston so that all lost motion is taken up automatically. A rocker 
shaft, extending through the steam chest carries a toe moving in a slot in the top of the valve 
piston, so that the valve can be moved by hand. 

To set the valves. — Simply keep the valves in order. The motion of the piston as it 
nears the end of the stroke opens and closes the valves. 



432 PUMP VALVE GEARS 



This is accomplished by pushing the piston to one end of its stroke 
against the cyhnder head and marking the rod with a scriber at the face 
of the stuffing box, and then bringing the piston in contact with the opposite 
head. 



2. Divide exactly the length of this contact stroke; 



Shove the piston back to this half mark; which brings the piston directly 
in the center of the steam cylinder; 



3. Perform the same operation with the other side; 

A, Place the slide valves in their central position; 

5. Pass each valve stem through the stuffing box and gland; 



The operation of placing the pistons in the center of their cylinders brings 
the levers and rock shafts in a vertical position ; 



6. Screu) the valve stem through the nuts; 



The stem is screwed until the hole in the eye of the valve stemi head comes 
in a line with the hole in the links, connecting the rocker shaft. 



7. Put the pins in their places; 

8. Adjust the nuts on both sides of the lugs. 

Leave about one-eighth to one-fourth inch lost motion on each side. 



VALVE SETTING 



433 



CHAPTER 13 
VALVE SETTING 



How to Set the Slide Valve. — In tlie ordinary valve gear, 
such as the type shown in fig. 794, the eccentric is retained 

in position on the shaft by a set 
screw, and the length of the valve 
stem made adjustable by a thread- 
ed end with jamb nut, or equiva- 
lent. The valve stem may, there- 
fore, be lengthened or shortened, 
and the eccentric placed in any 
angular position. 

On assembling the valve gear it 
is found that the dimensions for the 
valve stem length, and eccentric posi- 
tion are lacking. 

In setting the valve there are 
three distinct operations which are 
to be performed in the order here 
given: 

1 . Locating the engine on the dead 
centers; 

2. Finding the length of the valve 
stem, that is, equalizing the lead; 

"^ witrorTini'^" v^^fve "gtr^ atSe 3. Determining the correct position 

?LTrfV\wTset?fng"'^' '°^ ^^^" of the ecccntric. 




434 VALVE SETTING 



How to Find the Dead Center. — The engine is located on 
the dead center with a tram, such as shown in fig. 795. 

This consists of a piece of one-fourth inch or three-eighth inch tool stee! 
rod, of suitable length corresponding to the size of the engine and having 
a small portion at one end bent to a right angle; each end being ground 
to a fine point and hardened. The tram, in fact, corresponds to the bent 
scriber of a scribing block. 

A permanent center punch mark is made on the engine 
frame to receive the straight end of the tram, and a ring of small 
punch marks made around this permanent mark, to easily 
identify its position for future occasions, especially after painting. 



Fig. 795. — Tram, or instrument used in finding the dead center of an engine. It corresponds 
to the bent scriber of a machinist's scribing block. 

On a vertical engine, the permanent mark may be located on the column 
or bed plate; on a horizontal engine, on the bed plate, in either case the 
punch mark should be made at some convenient place where the other 
end will reach to the crank disc, or fly wheel. 



The dead center may now be located as follows: The engine 
is .turned in the direction in which it is to run until the piston has 
nearly completed the stroke, as shown in fig. 796, crank position 
B. A mark M, to indicate this position, is made across the 
guide and cross head. With the straight end of the tram in 
the permanent punch mark P, as a center, an arc C, is described 
on the side of the fly wheel rim, the surface first being cleaned 
of oil, and rubbed with chalk so the mark is easily seen. The 
engine is now turned past the dead center until the mark on 
the guide again registers with the mark on the cross head cor- 
]"esponding to crank position A. Arc D, is now described with 



VALVE SETTING 



435 



the same center P, and an arc passing through C and D, is 
described from the center of the shaft. That portion of the arc 
included between C and D, is bisected, giving the point E. A 
punch mark is made at this point and the engine turned in the 
direction oj its future rotation until E, registers with the bent 
end of the tram when its other end is in P. In this position the 
engine is on the dead center. The other dead center is found 
in a similar manner. 






Li ) M U 



Fig. 796.-7-Locating the engine on the dead center. In doing this as described in the text, 
the engine should always be turned in the direction in which it is to run so as not to introduce 
any error due to lost motion. The tram marks should be made permanent with a center 
punch. 

The engine should always be turned in one direction in order 
not to introduce any error due to lost motion in the wrist and 
crank pins. It matters not which direction is followed, the 
object being to have the crank pin pressing against the same 
brass for each adjustment. It is usual, however, to turn the 
engine in the direction in which it is to run, presumably because 
this is more easily remembered. 

In case the engine has been moved too far at any time, it is 
not necessary to complete the revolution, but merely to turn it 
back beyond the desired point, and then forward again up to 
that point in the direction of rotation thus taking up the lost 
motion each time in the same direction. 



436 



VALVE SETTING 



Adjusting the Valve Stem. — Having located the dead 
centers, the second step is to equalize the lead, that is, to make it 
the same at each end of the cylinder. First, the eccentric is 
located *'by eye," placing it ahead of its correct position rather 
than behind. 



POSITIVE LEAD 
EASILY MEASURED 



NEGATIVE LEAD 
HARD TO MEASURE 




V/////////77777Z. 



V//////A vzzzz. 







Figs. 797 and 798. — Positive and negative lead. In setting a valve the eccentric is first located 
"by eye." The figures show why it should be placed ahead of its correct position rather 
than behind. 

With the eccentric set ahead, the lead is positive at each end; when 
behind, it will probably be negative at one or both ends, that is, the two 
lead positions of the valve would be about as shown in figs. 797 and 798. 
The reason for setting the eccentric ahead is to avoid negative lead as in 
fig. 798, because it is not easily measured. 

A long wooden wedge should now be provided, tapering from one-half 
inch (more or less depending on the size of the engine) down to "nothing,'* 
and cut into several pieces as shown in figs. 799 to 801. 




Figs. 799 to 801.; — ^Wedges for measuring lead. Prepared from a long piece of wood, tapered 
from one-half inch (more or less depending on the size of the engine) down to "nothing" 
and cut in several pieces. 



With eccentric set well advanced, the engine is placed on the 
dead center, and the amount of lead measured by one of these 
wooden wedges, after which the lead for the other end is found 
in a similar manner. 



VALVE SETTING 



437 




In measuring the leads, a suitable 
wedge is inserted into the ports as far 
as it will go, as shown in figs. 802 and 
803, being careful to keep one side of 
the wedge in contact, that is, parallel 
with the end of the valve, and per- 
pendicular to the seat. For each end, 
a line is scribed across the wedge 
along the steam edge of the port, as 
shown in the figures; these lines (A 
and B, fig. 804) indicate the lead at 
the two ends, being located at points 
on the wedge where the thickness is 
equal to first and second leads. A 
line C, drawn half-way between A 
and B will represent the average^ 
or equalized lead. In taking lead 
measurements with a wedge the same 
side should, of course, always be 
placed next to 'the valve. 



The lead may now be equal- 
ized by adjusting the length of 
the valve stem so that the wedge 
will enter the port up to the line 
of average lead (C, fig. 804). If 
the work has been correctly done, 
the lead will be the same at 
each end. 

Finding the Correct Posi- 
tion of the Eccentric. — Since 
the eccentric was set ''by eye," 
the lead is probably too great, 
or too small as the case may be. 
To correct this, the eccentric is 
turned on the shaft, in the di- 
rection in which the engine is to 
run, until the valve has the 



438 



VALVE SETTING 



desired lead.* The results should be verified by testing the lead 
at the other end, and if both leads be the same, the valve has 
been correctly set.f 

Finding the Correct Position of the Eccentric on Large 
Engines. — To avoid the frequent turning of the engine from 
one dead center to the other, the necessary adjustments may 
be made by equalizing the port opening instead of the lead. 
The eccentric is turned until it gives the maximum port opening, 




Fig. 804.— Equalizing the lead. After obtaining the lead lines A and B, as in figs. 802 and 803, a 
line C, is scribed half way between, which gives the average lead. The valve stem is then 
adjusted so that the wedge will enter the port up to C, thus making the lead the same at 
each end of the cylinder. 



first at one end, and then at the other. These port openings, 
if unequal, are equalized by adjusting the length of the valve 
stem, after which, the engine is placed on the dead center, and 
the eccentric turned until the valve gives the desired lead. 



*NOTE. — The lead given to engines varies considerably from a small negative lead to 
three-eighths inch or more positive lead, depending on the type and size of the engine; its 
amount is decided upon arbitrarily by the designer but may be varied in setting the valve 
simply by changing the angular advance of the eccentric. In general, the amount of lead 
depends on the speed of rotation, and the inertia of the reciprocating parts. 

tNOTE. — In order to clearly fix in mind the general principles involved in setting a slide 
valve, it is recommended that the instructions be read a second time, omitting the minor 
details given in the small type, as these tend to divert the attention from the important 
operations. 



VALVE SETTING 



439 



Setting the Slide Valve Without Removing the Steam 
Chest Cover. — If the set screw of the eccentric should work 
loose during operation, and the eccentric change its position, 
it may be quickly reset without taking off the steam chest cover, 
thus saving valuable time in case of a shut down. 



A permanent punch mark is made on the end of the steam chest as at 
A, fig. 805, for taking measurements on the valve stem with a tram. The 



EXTREME r05ITI0NS 



^J^_^=S^I LEAD POSITIONS 




Figs. 805 and 806. — Method of setting the valve without removing the steam chest coyer, 
when the valve stem does not require adjustment. It consists in equalizing the two positions 
L, L', of the valve when the engine is on the corresponding dead center. 



eccentric is fastened in any position, and the engine turned until the valve 
is at one end of its travel. A tram mark B , is made on the stem to indicate 
this position, and similarly another mark C, to indicate the other end of the 
valve travel. The engine is placed on each dead center and the position 
of the valve located by the tram. This gives the two linear advance 
positions L and L', of the valve, which in case the eccentric has been in- 
correctly set, are at unequal distances L B and L'C, from B and C. 

It remains to adjust the position of the eccentric until L B, is equal to 
L' C, as shown in fig. 806. With this condition fulfilled, the valve is 
correctly set. 



440 



VALVE SETTING 



Setting the Slide Valve Without Finding the Dead 
Centers. — In the case of a very large engine where the operation 
of putting the engine on the dead centers would require one or 
more assistants, the following method will be found useful. 
It consists of: 

1. Equalizing the port opening; 

2. Finding the angular advance. 



TOO SMALL 



CENTER OF 
ECCENTRIC 




Figs. 807 and 808. — Setting the valve without putting engine on the dead center: 1, equalizing 
the port opening. 



Equalizing the Port Opening. — For this purpose a pair 
of inside calipers may be used when the port opening exceeds 
the width of the port, or if less, a wedge should be used. 



VALVE SETTING 



441 



Loosen the eccentric and 
turn it until the valve is at 
one end L, of its travel and 
measure the port opening as 
in fig. 807. Mark this distance 
for reference with aid of a 
scriber as A, in fig. 809. 

Similarly determining the port 
opening at the other end when 
the valve is at that end F, of its \ni 
travel as in fig. 808, and mark it 
as B , in fig. 809. If unequal, set 
calipers for average port opening 
C, in fig. 809. 

Now rotate eccentric until valve 
is at either end of its travel and 
adjust length of valve stem till 
valve gives the average port 
opening according to average 
setting C, of calipers. 



Fig. 809. — Method of 
finding average port 
opening with inside 
calipers and scriber. 
After setting cali- 
pers for port open- 
ing A, fig. 807, draw 
alineasMS.fig. 809 
and place ends of 
caliper legs on this 
line ; mark these 
points aa\ with scri- 
ber as shown. Sim- 
ilarly, set calipers for 
port opening B , fig. 
808, and transfer to 
MS, fig. 809, meas- 
uring from a, and 
obtaining point h. 
Bisect a'b, by de- 
scribing arcs about 
a\ and b, as centers, 
obtaining the point 
c, at foot of a per- 
pendicular through 
the intersection of 
the arcs, ac, or C, 
then is the average 
port opening for 
which the calipers 
*nust be set. The 
wedge method as 
was used for equal- 
izing the lead 
can be used 
\ j^ Q to advantage 
i O when the port 
I opening is 

I less than the 

width of the 
port. 



\>v 



^SETTING 

Compare port open- 
ing at other end and if 
the work has been ac- 
curately done, both port open- 
ings will be the same, that is^ 
the port opening has been 
equalized, as in figs. 810 and 
811. 



Finding the Angular 
Advance . — The several 
operations to be performed 
in finding the angular advance 
and placing tne eccentric in angular advance position are: 



442 



VALVE SETTING 




1. Rotating eccentric till 
valve is in lead position; 

2. Finding angular ad- 
vance ; 

3. Transferring angular 
advance to reference mark 
on shaft; 

4. Rotating eccentric to 
angular advance positi'bn. 

Performing these operations 
in the order given, first rotate 
eccentric until the valve has 
the desired lead and locate 
this position of the eccentric 
by scribing a line M, on the 
eccentric and L, on the shaft 
as in fig. 812. 

Now measure diameter of 
shaft at eccentric with outside 
calipers and set dividers to 
half this length. Wipe all 
grease from the crank and 
chalk same. With one end of 
the dividers in the lathe center 
scribe a circle R, correspond- 
ing to the shaft diameter as 
in fig. 813. 

Next take a small string, or 
preferably strong flax thread 
and make a loop at one end 
and place it around the crank 
pin ; pull very taut, holding it 
so that it intersects the shaft 
lathe center, and scribe the 
point F', where it cuts the 
shaft circle. The thread then 
represents the center line of 
the crank. 

Now by means of a level, 
scribe a horizontal line passing 
through the shaft center and 
cutting the shaft circle at L, 
Evidently the angle LAF, is 
the angular advance^ which can 
be easily transferred to the 
eccentric by a pair of dividers. 



VALVE SETTING 



443 



O O »fc O O J>> ,TM 0) 

<0 O O grd-S O ..S 

:2 o .. « § J ^^-^ 



o-d C ?^ 5i 



cJ s. <-" -* 




444 



VALVE SETTING 



^^z^z^:^^ 




l.l.lfi.l.iJil.i.i.lfi.LiL 



Figs. 815 to 817. — Setting an. inside admission piston valve. The two extreme positions 
are measured as in tig. 815, and the travel equalized by adjusting the valve stem. The 
engine is placed on each dead center, and measurements taken as in figs. 816 and 817. The 
position of the eccentric is then adjusted until E, fig. 816, equals E', fig. 817. If M and S be 
unequal due allowance should be made. 



VALVE SETTING 445 



Set the dividers as in fig. 813 to measure the arc M' S, then place one leg 
of the dividers on M, in fig. 812 and lay off M S, in the direction of rotating. 

Turn the eccentric till its reference mark M, coincides with S, as in fig. 
814 and secure eccentric in this position, when, if all the operations have 
been properly performed the setting will be found correct. 

Setting an Inside Admission Piston Valve. — In this type 
of valve the steam edge of the port being on the inside, the 
valve cannot be set by direct lead measurements as with the 
slide valve; use is therefore made of the exhaust edge of the 
valve as a basis for measurements. The necessary operations 
in setting the valve should present no difficulty if the two 
following principles be understood and remembered: 

1. The two extreme positions of the valve must be equally distant 
on either side of the neutral position. 

2. With equal lead, the linear advance must he the same for each 
end of the cylinder , 

Applying the first principle ^ the valve gear is adjusted so that 
the valve travels an equal distance each side of its neutral 
position. 

To do this, the eccentric is set in any position on the shaft, and the 
engine turned over until the valve has reached one end of its travel as 
position A, fig. 815. The distance E, from the exhaust edge of the valve 
to the end of the cylinder, is measured, and similarly, distance E' when the 
valve is at the other end of its travel, as in position B, shown in dotted 
lines. If the length of the valve stem be not correct, these two distances 
will be unequal. The travel is now equalized by adjusting the length 
of the valve stem until these distances become equal, that is, until E=E'. 

Applying the second principle, the engine is placed on each 
dead center, and the distances of the exhaust edges of the valve 
from the ends of the cylinder measured. 

If the eccentric has not the proper angular advance, these distances 
will be unequal, and it remains to adjust the position of the eccentric until 
they become the same, a? shown in figs, 416 and 417, 



446 



VALVE SETTING 



When E, fig. 816 is equal to E' fig. 817 the linear advance 
is the same for each end of the cylinder, hence the lead has been 
equalized and the valve correctly set. 

Before setting an inside admission valve as just outlined, the location 
of the ports with respect to the cylinder ends should be carefully determined. 
In most cases these are equidistant from the ends, that is, M = S, fig. 818; 
if not, due allowance should be made in setting the valve. 

In locating the ports, the measurements are conveniently made with 
an ordinary rule having a strip of metal soldered on the brass end as 



EXHAUST EDGE 



L 



J3IIEZIJ 




coaziisEi 



Fig. 818. — Method of measuring the location of the ports. ^ A strip of metal is soldered on the 
brass end of the scale as shown, being placed at the side to measure the steam edge M, 
and over the end, for the exhaust edge S. 

shown in fig. 818; in setting the valve, a short steel rule is used. In either 
case a square or straight edge is used in taking the readings to project the 
plane of the cylinder to the rule as shown in the figures. The rule must 
be held plumb with the valve to avoid error. 



Emergency Rule for Setting the Slide Valve. — If the 

eccentric should slip on the shaft, or any other accident throw 
the valve gear out of position, it may be quickly reset as follows: 
The engine is placed on the dead center and the eccentric turned 
a little behind its correct position. 

With the cylinder drain cocks open, a small amount of steam 



VALVE SETTING 



447 



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o 


rCl 


^j 


•4-> 






C/3 
U 


CD 


o 


a 


^ 


9^ 






448 



VALVE SETTING 



Taking Laths from the Valve and Seat. — It is desirable 
to have permanent records of the valve and seat dimensions, 
which are useful in setting the valve. These dimensions are 
transferred directly to laths or battens made of wood, and 
.SCRIBER 




Figs. 820 and 821. — Preparing valve and seat laths. Care should be taken to place the laths 
square with the valve, or seat as indicated by use of the try square. 



planed true and square; they should measure some three inches 
in width by five-eighths inch thick and of convenient length, 
depending on the size of the engine. 

The valve is removed from the engine, and its steam and exhaust edges 
scribed on a lath as shown in fig. 820, care being taken to have the lath 



VALVE SETTING 



449 



at right angles with the edges. Similarly the seat dimensions are trans- 
ferred to a second lath as shown in fig. 821. The spaces on the laths 
representing the ports and exhaust cavity are painted white, and the valve 
faces and bridges black; the seat batten being painted black at the ends 
between the ports and the seat limits. The ends of the battens should be 
marked H and C, denoting ''head end" and "crank end;" the completed 
battens appearing as in figs. 822 and 823. 

5L\DE VALVE 




i^mm 



^SEAT LIMIT ^2. TRAVEL 



Fig. 822 and 823. — Slide valve battens. The ports and exhaust cavity are painted white, 
and the valve faces and bridges black. Lines are drawn corresponding to the half travel, or 
extreme positions, and the ends marked to distinguish head and crank end. 

The batten is specially useful with engines having inside 
admission piston valves as a check on the valve setting. 

The cylinder ends as well as the bushings, or valve seat should be painted 
on the batten as, in setting the valve, measurements are taken from the 
ends;^ the bushings are painted only part way across the. batten to dis- 
tinguish them from the cylinder ends, as shown in fig. 825. The travel 




END OF CYLINDER JliTRAVEL BUSHING 



Pig. 824 and 825. — Inside admission piston valve battens. They are especially useful to check 
^^^.X^^ve setting. The ends of the cylinder should be indicated on the seat battens in 
addition to the bushings. 



of the valve is ascertained and indicated by lines which register as shown 
in the figures; thus the battens may be placed so as to show the extreme 
positions of the valve. 



450 



VALVE SETTING 



Oues. Of what particular use are battens? 

Ans. They are helpful in the absence of an indicator to verify 
the setting of inside admission valves, and more especially to 
check the machine work on the valve and seat; if there be any 
errors in the location of ports, etc., they may be discovered by 
carefully transferring the various measurements of the valve 
and seat to battens for comparison. 



STEAM P/\SSAGES 




Fig. 826. — Showing similarity between the main valve of a riding cut off gear, and the ordinary- 
slide valve. The main valve is simply a plain D valve, having steam passages S, S' at its 
ends, and planed on its back to form a seat for the cut off valve. 

Setting the Riding Cut Off Gear. — There are two types 
of riding cut off gear in general use, the first having a movable 
(rotating) eccentric, and the second a fixed eccentric, but having 
an adjustable cut off valve, known as the Meyer valve. The 
method of setting the valves for each type will now be described: 



1. The Riding Cut Off, Movable Eccentric. 

a. The main valve is set in the same manner as the ordinary 
slide valve. 



VALVE SETTING 



451 




^ To avoid confu- 
sion, it suffices to 
remember that the 
main valve is noth- 
ing more than an 
ordinary D valve 
having steam pass- 
ages at its ends, and 
planed on its back 
to form a seat for 
the cut off valve. 
In setting the valve, 
therefore, the outer 
end walls are to be 
ignored. 

The relation be- 
tween the main 
valve, and an or- 
dinary D valve is 
shown in fig. 826, 
the latter being 
illustrated in solid 
black section; the 
main valve has in 
addition to this, 
the portions shown 
at each end which 
contain the steam 
passages S and S', 



b. The engine is 
now turned in the 
direction in which 
it is to run, until 
this valve is in its 
neutral position. * 



*NOTE.— The reason 
for putting the main valve 
in its neutral position is 
to facilitate this adjust- 
ment, as the necessary 
measurements are more 
conveniently made with 
respect to the main valve 
than to the seat. 



452 



VALVE SETTIN.G 



To locate the neutral position, the engine is turned over until the main 
valve comes in the extreme positions A andB, as shown in fig. 827, and a 
reference mark for each, made on the valve stem with a tram, having one 
end in a convenient fixed center P. The distance A B, is bisected, giving 
the point M, the three points being permanently located with a center 



EXTREME POSITIONS OF CUT OFF VALVE 




Fig 828. — Equalizing the travel of the riding valve. With the main valve in neutral position, 
and cut off eccentric loosened, the distances E and F, are measured for the two extreme 
positions and the valve stem adjusted until these distances become equal. 

punch, and care being taken that the points are in a straight line parallel 
to the stem. 

The valve is now placed in its neutral position, by turning the engine 
in the direction of its rotation until the point M, registers with the end 
of the tram as shown in the figure. 



c. The next step is to equalize the travel of the riding valve, 
that is, to adjust the riding valve stem or eccentric rod to the proper 



FALVE SETTING 



453 



length so that the valve will travel an equal distance each side of 
its neutral position, j 

With the main valve in its neutral position, the movable eccentric is 
loosened on the shaft, and turned in the direction in which the engine is to 
run until the cut off valve is brought into its extreme positions A' and B', 
fig. 828. 

The distance from the steam edge of the riding valve to the end of the 
main valve is measured for the two positions. If the valve stem be too 
long or too short these distances will be unequal; the valve stem or eccentric 
rod, in this case, should be adjusted until these distances E and F, are equal 
as shown in the figure, f Having equalized the travel of the valve, tram 
marks A', B', M', indicating respectively the extreme and neutral positions, 

CUT Orr VALVE CLOSING STEAM 
P/i5SAGE FOR \/Z CUT OFF 




Fig. 829. — Riding valve in cut off position. To locate eccentric for any desired cut off , turn 
engine over till piston is at the desired point of cut off, then turn riding eccentric in the 
direction of motion till riding valve is in cut off position as shown. 

should be made as shown in fig. 827, on the cut off valve stem with the 
tram center at P', using the same tram as was used for the main valve stem. 

d. To complete the setting, it remains only to find the position 
of the movable eccentric which will give the desired cut off. 



tNOTE. — To avoid error, it should be ascertained that the steam ports of the main 
valve are equidistant from the ends; if not, measurements E and F, fig. 828, should be taken 
with respect to the steam edges of the cut off valve, lines being lightly scribed on the back of the 
main valve to indicate the extreme positions. 



454 



VALVE SETTING 



If the valve gear is to cut off at, say one-half stroke, the engine is turned 
in the direction in which it is to run to this point of the stroke, and the 
movable eccentric turned in the same direction until the cut off valve has 
just close 1 the steam passage through the main valve as shown in fig. 413 ; 
the eccentric is now fastened in position. 

e. When the riding cut off valve is operated by an automatic 
governor, as in many stationary engines, this last step is, of course^ 
omitted. 



THREAD^ 

\ 



I 



CUTOFF BLOCKS 
M S 



LEFT 
HREAD 




NEGATIVE LAP 



Fig. 830. — ^The riding cut off with fixed eccentric, showing cut off blocks M, S, screwed together 
when setting the valves. The cut off is latest when the blocks are together, dependingon 
the negative lap. After setting the valves, the blocks should be fully extended for earliest 
cut off to see if there be any reopening after cut off and before the main valve has closed. 

When the engine is provided with a governor, the travel of the cut off 
valve may in some cases be more conveniently equalized, by locating the 
center of the valve seat with a line scribed on the side or flange of the 
steam chest, and equalizing the travel of the cut off valve with respect to 
this line instead of the main valve. By this method it is not necessary to 
retain the main valve in its neutral position while adjusting the cut off 
valve; hence the loose eccentric need not be disconnected from the governor 
in making this adjustment. 



2. The Riding Cut Off: Fixed Eccentric. 

This type of riding cut off is set in much the same way as 
the preceding form. In making the adjustments, the important 



VALVE SETTlNd 455 



principle upon which the gear is based should be understood, 
and kept in mind, viz. : the angular advance being fixed, the cut 
off is varied by changing the lap. The valves are set as follows: 

a. The main valve is set in the same manner as the ordinary 
slide valve. 

b. To set the riding valve, the riding blocks M, S, are first screwed 
closely together as shovun in fig. 830; this being their position for 
latest cut off. 

C. The travel of the riding valve is now equalized by the method 
described on page 452, and the riding eccentric located in the 
position best suited to the conditions under which the engine is 
to be operated. 

For a marine or reversing engine, the riding eccentric is set opposite the 
crank, that i^, at 90 degrees angular cidvance, since the motion of the cut 
off valve is then correct for both forward and reverse motion; in this 
position an equivalent motion of the eccentric may be imparted to the 
valve stem by the cross head through a lever, thus dispensing with the 
eccentric. The angular advance of the riding eccentric on stationary * 
engines is usually a little less than 90 degrees. The effect of reducing the 
angular advance is to require a smaller movement for a given change of 
cutoff. • 

The riding eccentric should be so located that it will give the most rapid 
closure of the steam ports for the cut off mostly used. 

d. The engine is now turned over to see if there be any reopening 
of the riding valve after it has cut off and before the main valve has 
cut off. Similarly it should be observed that there is no reopening 
for earliest cut off. 

e. In case the cut off valve reopen before cut off of the main 
valve, this must be corrected by altering the position of the riding 
eccentric. 

Setting a Link Motion. — Adjustments of the link gear 
should be such that the steam distribution will be favorable to 
smooth running and economy for the particular degree of ex- 
pansion at which the engine is generally run. For instance, 



456 



VALVE SETTING 



engines which work in full gear require a setting different from 
those which cut off short ; the final adjustments therefore should 
be made with respect to obtaining the best results for the gear 
position mostly used. In general, setting a link motion com- 
prises the following operations: 

1. Equalizing the travel; ' 

2. Adjusting the eccentric rods to uniform length; 

3. Finding the correct positions of the eccentrics; 

4. Making final adjustments for best steam distribution in the 
gear position mostly used. 



MUST ETQUAL 



POSITION 




MID-GEAR 



Figs. 831 and 832. — Setting the link motion: 1. Equalizing the travel by adjusting the valve 
stem. The eccentrics must be placed in extreme position and link in mid-gear. 

Equalizing the Travel. — With the engine on the dead 
center, both eccentrics are turned on the shaft to the extreme 
position and the link placed in mid-gear as shown in figs. 831 
and 832. If the length of the valve stem be correct, the valve 
should be in its extreme position, that is, the port opening A/ 
for this dead center should be the same as port opening B, for 
the opposite center. 

In case the port openings be unequal, the travel of the valve must be 
equalized by adjusting the length of the valve stem, or the eccentric rods, 
whichever be the more convenient. 



Adjusting the Eccentric Rods to Uniform Length. — 

Both eccentric rods should be of the same length, and probably 



VALVE SETTING 457 



will be when not made adjustable. If both rods be of the same 
length, the position of the valve is unchanged for either full 
gear position when the engine is on the dead center and the ec- 
centrics are in the extreme position. 

To adjust the eccentric rods to uniform length, the engine is placed on 
the dead center, with the link in full gear and the eccentrics in the extreme 
position as shown in fig. 833. 

The position of the valve or stem is marked in such a way that any 
movement in either direction can be measured. If both rods be of the same 
length, the mark on the valve stem will return to its original position when 




FORWARD FULL GEAR 

Fig. 833. — .Setting the link motion: 2. Adjusting the eccentric rods to uniform length. The link 
is placed in forvyard full gear position. If rods be equal position of valve should be the same 
when link is shifted to reverse full gear. 

the link is shifted to its opposite or reverse full gear position ; if the mark 
be displaced in either direction the reverse rod should be adjusted until 
the line returns to its original position. It is rarely necessary to make 
this adjustment, except when a gear has been completely dismantled. 

Finding the Correct Positions for the Eccentrics. — 

With the engine on either center, the link is placed in the for- 
ward full gear position, and the eccentrics turned from the 
extreme position until they are at right angles with the crank, 
that is, where the angular advance equals zero as shown in 
fig. 834. The forward eccentric is now turned, in the direction 
of forward rotation, until the valve shows the desired lead as 
in fig. 835. 

Similarly, the link is shifted to the reverse full gear position, fig. 836, 
and the reverse eccentric turned, in the direction of reverse rotation, until 



458 



VALVE SETTING 



the proper lead is obtained as shown in fig. 837. Each eccentric is fastened 
after locating its position, and the results tested by trying the leads for the 
opposite centers, which completes the setting for engines operating in full 
gear. 



7ER0 /ANGULAR ADVANCE 



NEUTRAL POSITION 




FORWAf=^D FULL GEAR 

Fig. 835. — Setting the link motion: 3. Locating the eccentrics — first step: Both eccentrics are 
placed at zero angular advance, that is at right angles to the crank, bringing valve into 
neutral position. 

Final Adjustments. — For engines which use the link motion 
as a variable expansion gear, the best results are obtained 
when the valve is set to give the proper lead for the ''running 
cut off." 



LEAD POSITION 



FORWARD EOC. ADVANCED 




FORWARD FULL GEAR 

Fig. 834. — Setting the link motion: 3. Locating the eccentrics — second step: With link in 
forward full gear, the forward eccentric is advanced until valve shows proper lead, bringing 
valve into its forward linear advance position. 

This applies especially to locomotives and engines which usually run 
with a considerable degree of expansion. Since the lead increases from 
full to mid-gear, it is obvious that if it be correct in full gear, it will be too 
great when hooked up for short cut off working. 



The lead may be corrected for the running cut off, by placing 
the link in the running position, and setting back the forward 



VALVE SETTING 



459 



or reverse eccentric, or both, in equal or unequal amounts until 
the desired lead is obtained. 

The particular method of correcting the lead depends on the conditions 
of service. For engines which run mostly in forward gear, as express 
passenger engines, it is of little importance if both eccentrics have the same 



NEUTRAL 
POSITION 




REVERSE FULL GZ^^ 



Fig. 836. — Setting the link motion: 4. Locating the eccentrics — third step: 
to reverse full gear position, bringing valve back to its neutral position. 



The link is shifted 



angular advance, however, for suburban tank locomotives, or those running 
considerable distances in each gear both eccentrics should have the same 
angular advance. 



LEAO POSITtON 




REVERSE ECC- ADVANCED 

Fig. 837.7— Setting the link motion: 4. Locating the eccentrics — fourth step: The reverse 
eccentric is advanced until the valve shows the proper lead; this moves the valve to its 
reverse linear advance position which completes the setting except when final adjustments 
are made to adopt the link motion to special running conditions. 

The following table shows the practice of several railroads 
with respect to the lead. 



NOTE. — When the link block is at one end of the slot, the valve partakes of the motion 
of the eccentric attached to that end of the link. When the block is not at the end of the slot, 
the valve partakes of the combined motion of the two eccentrics, being the equivalent of a 
virtual eccentric of decreased throw and increased angular advance. 

NOTE. — The object in curving a link block is to equalize the lead for all travels of the 
valve. To accomplish this it is necessary to have the radius of curvature of the slot such as 
will make the increase or decrease of the lead the same for both strokes of the piston. 



460 



VALVE SETTING 



Table of Leads for Locomotives 




Forward 
full gear 


Reverse 
full gear 


Lead for 
running 
cut off 


Illinois Central 


+ H2 




+Hi 




Chicago & Northwestern (Allen Valves) . . 


-Vm 




+ H 


New York, Hew Haven & Hartford. . . . 


■ +^^6 


-M 


+M 


Lake Shore & Michigan Southern 


-Vi^ 


-% 


+^/l6 


Chicago Great Western { 


zero 


zero 


8/i6tO% 



*For Mogul freight engines; with this exception the data in the table relates to passenger 

nnfivpf;. 



locomotives. 



The diverse settings given in the table are due chiefly to the peculiarities 
of the several designs; the length of the eccentric rods has a marked 
influence on the methods followed in the different cases. It should be 
noted that the several railroads substantially agree on the amount of lead 
for the running cut off. 



Valve Setting with the Indicator. — ^An important use of 
the indicator is to check the valve setting, for if the adjustments 
be not correct, the errors can be plainly located by taking cards. 
The accompanying cards show the distortions produced by 
various adjustments. 



In setting a valve, changes in the steam distribution can be effected, 
either by shifting the position of the eccentric upon its shaft or by length- 
ening or shortening one or more of the rods connecting the eccentric with 
the valves. The result attained in either case should be clearly under- 
stood, since if it be attempted to make the needed adjustments in the 
wrong place, the engine may be put in worse condition than it was originally. 

Changing the regular position of the eccentric either hastens or retards 
the action of the valves. Moving the eccentric ahead makes all the events 
of the stroke which are dependent upon the eccentric come earlier in the 
stroke, while moving back the eccentric causes all the events to occur 
later in the stroke. 



VALVE SETTING 



461 




Figs. 838 to 848. — Effects of valve adjustments as recorded by indicator diagrams. Card 
No. 1 was taken when the eccentric had the proper angular advance of a little more than 
90 degrees (in the case of a single eccentric Corliss engine) and cut off and compression were 
made as nearly equal as possible. In card No. 2 the angular advance was increased. In 
card No. 3 the angular advance was made still greater. In card No. 4 the eccentric was 
shifted back so that there was no angular advance. Card No. 5 is a crank end card and 
was taken when the eccentric was moved way back and gave a negative angular advance. 
The diagram was traced in the direction indicated by the numbers. Admission occurs at 
1, cut off at 2, release at 3. Card No. 6 is a similar diagram from the head end. In card 
No. 7 the eccentric is moved back and the rods adjusted to give correct steam distribution and 
then under these conditions the eccentric card. No. 8, was taken. In this case the indicator 
derived its motion from the eccentric rod instead of from the cross head and the diagram 
shows the working of the valves of the engine, when the indicator drum is moving at its 
greatest speed; and thus any peculiarities m the action of the valve are magnified. Com- 
pression and release come near the middle of the card and are spread over a considerable 
length. In card No. 9 the head end exhaust rod was lengthened and there is too much 
compression at a. In No. 10 the rod is made still longer. In card No. 11 the head end 
exhaust rod is made too short and there is too little compression at b. 



NOTE. — When setting an eccentric, a rule that can be easily remembered is: Set the 
eccentric far enough ahead of a right angle to the crank to allow for the lap and lead of the valve. 
The mistake of turning the eccentric "just half way around" to reverse the engine should not 
be made. 

NOTE. — An engine properly built, and not run at too high a rotative speed, will run 
smoothly with a moderate amount of compression. To attempt to get smooth running with 
an extra amount of compression or lead means more oil, more coal, and more repairs. 



462 VALVE SETTING 



In the Corliss engine the point of cut off is determined by the governor 
instead of by the eccentric, and so only the points of admission, release 
and compression are affected by shifting the eccentric. In the case of a 
slide valve engine it affects all the events. 

In a slide valve engine an adjustment of the length of the eccentric or 
valve rod simply changes the position of the valve so that it will have more 
lap or lead at one end than before, and less lap or lead, as the case may be, 
at the other end. 

In the Corliss engine an adjustment of the eccentric rod produces the 
same result, increasing or decreasing the lap or lead, as the case may be, 
at one end of the stroke, while it has the opposite effect at the other end. 

The lengths of the eccentric rod or gab rod on a Corliss engine, however, 
should never be changed, unless it is found that the intermediate rocker 
and wrist plate do not travel equally on each side of a vertical center line. 

All the rod adjustment should be made in the radial rods extending from 
the wrist plate to the four valves. Adjusting any of these rods, of course, 
affects only the valve to which each rod is connected and will give greater 
or less lap to that valve, according as it is lengthened or shortened. 

If more lap were given to an exhaust valve in this way, for example, 
the valve would open later and compression would occur earlier, since the 
valve would close earlier. The port opening would also be less. If less 
lap were given to the valve the reverse of these conditions would be true. 



INDEX OF GUIDE No. 1 



READY REFERENCE 

INDEX 



Absissoe, def., 58, 59. 
Absolute, pressure, 17. 

steam engine, 61. 

temperature, def., 21. 

zero, 21, 35. 
Actual cut off, def., 197. 

mean effective pressure, 73. 
Absorption dynamometer, 93. 
Adiabatic expansion, 54. 
Admission, area, formula, 70. 

double, ills., 294. 

inside, ills., 292. 

outside, ills., 292. 

pistcm valve, ills., 292, 299. 

inside, setting, ills., 444-446. 

quadruple, 305. 

slide valve, def., 19G. 
modified, ills., 292. 
open, ills., 195. 
position, ills., 197. 
Advance, angular, 238, 245, 441-445. 

linear, eccentric, ills., 238. 
Allen, link, ills., 334, 335. 

valve, ills., 208, 209. 
principles, 294. 
American Ball, cut off, ills., 253. 

rock shaft, ills., 231. 

variable speed mechanism, ills., 399. 
American pump valve gear, ills., 430. 
Ames, connecting rod, ills., 149. 

cross head, ills., 139. 
Angular advance, eccentric, 237, 238. 

method of, finding, des., ills., 441-445. 

variable cut off, 245. 
Angularity, of connecting rod, effect, des., 

ills., 154. 
Apparent cut off, ills., 196, 197. 
Area, admission, formula, 70. 

circle, formula, 80. 
Armington and Sims valve, 295. 
Asymptotes, ills., 60. 
Atlas steam engine, ills., 54. 
Atomic weight, 1. ^ 

Atmospheric, engine, Ncwcomen's, ills., 36. 

pressure, def., 2, 13, 14. 

barometer readings, 18-20. 
variability, 15. 



Automatic, cut off, engine, def., 243. 

governor, Nordberg, ills., 390. 
throttle valve, def., 383. 
Auxiliary, governor devices, 397. 
piston pump, ills., 413. 
valve pump, ills., 413. 
Axes, rectangular, equilateral parabola, 
ills., 60. 



B 



Back pressure, ills., 68, def., 69. 
Balanced slide valve, 187, 291. 

Richardson, ills., 291. 
Balancing cylinder, steam engine, ills., 300. 
Ball and Wood connecting rod, ills., 142. 
Ball, governor, ills., 389. 

speed ranger, ills., 382. 

valve, ills., 307. 
Band fly wheel, 176. 
Barometer, ills., 13, 15, 18, 19. 
Battens, valve, ills., 426, 449, 450. 
Bearings, 165-17i. 

brasses, 142-144, 146, 230. 

liner adjustment, main, ills., 166. 

locomotive, ills., 169. 

main, 99. 

marine, ills., 171. 

outboard, pillow block, ills., 170. 

requirements, 165. 

self oiling, ills., 170. 

simple, 165. 

two piece, 167. 
Bilgram diagram, 211, 213. 

application, 276. 

main valve, 264, 268, 279. 

mid-admission, 289. 

riding cut off, 288. ^ 
Blake pump, valve gear, ills., 411. 
Boiler, elementary, ills., 17. 

pressure, 65. 
Boiling point, ills., 2, 3, 13, 28, 34. 
Bolt, crank shaft, taper flange, ills., 164. 
Bonnet, valve, ills., 99. 
Box, journal, locomotive, ills., 169. 

link, ills., 329. 

piston, ills., 117, 119. 



II 



INDEX OF GUIDE No. 1 



Boyle's law, ills., 54, 55. 
Brake, horse powers 93, 94. 

prony, ills., 93. 

rope, ills., 95. 
Brasses, 142, 143, 230. 
Bremme gear, des., ills., 352-355. 
British thermal unit, def., 8. 
Brown engine, cross head, ills., 234. 
Brownell steam engine, 121, 184, 185, 231. 
Buckeye, governor, ills., 396. 
Buffalo, pump, valve gear, ills., 405. 

steam engine, ills., 83. 

governor, ills., 249. 
Bull ring, ills., 116. 
Burnham pump, valve gear, ills., 424. 



Calipers, use of, ills., 441. 
Cameron pump, valve gear, ills., 408. 
Card, indicator, see Indicator diagram. 
Center, crank shaft, des., 160. 

dead, steam engine, 151, 435. 
Centigrade scale, ills., 120. 
Centrifugal, control, shaft governors, ills., 
364, 376, 378, 392-397. 

force, des., 174. 
Chandler & Taylor, engine, 121, 206, 404. 
Circle, area, formula, 80. 
Clark governor, ills., 397. 
Clearance, 58, 59, 75, 106. 
Clyde cross head, ills., 39. 
Compound engine. Reeves, section, ills., 299. 
Compression, 201. 

curve, ills., 56. 
Cone, governor. Ball engine, ills., 398. 

piston, ills., 119, 120. 
Condensation of steam, 33, 34, 37, 196. 
Condenser, elementary, parts, 38. 
Condensing steam engine, def., 47. 
Conduction, heat, ills., 6. 
Connecting rod, ills., 141-156. 

action on crank pin, 152. 

Ames, ills., 149. 

angularity, ills., 154, 190. 

Ball and Wood, ills., 142. 

built up, ills., 146, 147. 

composition, 142. 

Eclipse Corliss, ills., 141. 

hatchet end type, des., ills., 149. 

length, 142. 

marine, ills., 144, 145. 

Phoenix, ills., 144. 

Sturtevant, ills., 150. 

Westinghouse, ills., 150. 
Conservation of energy, laws, 12* 
Constant, expansion, diag., 66. 

horse power,^ 87-89. 
Constant lead, slide valve, 193. 
Co-ordinates, def., 59. 
Convection, heat, ills., 6. 
Corliss engine, connecting rod, ills., 143. 

fly wheel, ills., 174, 175. 

gibs, ills., 132. 



Corliss engine, — Continued 
indicator card, 76. 
Murray, parts, ills., 99, 170. 
Cotters, connecting rod, ills., 146, 147. 
Counter-weight, steam engine, use, 160. 
Crank(s), angular position, ills., 263. 
arm, dimension, 158, 160. 
compared with eccentric, ills., 237. 
end, steam engine, def., 90. 
key, ills., 158. 

pin, action on, ills., 151-154, 158, 159. 
position, during one stroke, ills., 52. 
to obtain, diag., 267. 
transferring, 264. 
sequence of, des., 164. 
shaft, 156-164. 
Cross head, pump, 418, 419. 
steam engine, 49, 127. 
Amesy 139. 

attachment methods, 141. 
Brown engine, ills., 134. 
Corliss, Fishkill, ills., 137. 
Fulton, ills., 138. 
Harris, ills., 140. 
Murray, ills., 135. 
hoisting engine, Clyde, ills., 139. 
locomotive, des., ills., 136. 
marine, ills., 134. 
Porter- Allen, ills., 135. 
Reeves, ills., 132. 
split type, ills., 140. 
, stationary engine, 135. 

Crossed rods, link motion, ills., 322, 325. 
Cut off, 63. 

actual, 197. 

affected by angularity of rod, 155. 

apparent, 63, 98, 196. 

crank, 212, 270; 

early, ills., 244. 

defects, ills., 254, 256. 
varied, 207. 
gear, 259, 279, 282. 
Rider, ills., 259. 
riding, ills., 450-454. 
Gonzenbach, 258. 
governors, 388. 

automatic, Nordberg, ills., 390. 
independent, 253. 

link motion, ills., 328, 329. 
parts, 256. 
late, ills., 244. 
marine engine, 328. 
real, 63, 98, 196, 197. 
riding, 257, 262, 278. 

angular advance, 263. 

fixed eccentric, ills., 453, 454. 

inside and outside edges, ills., 262, 

movable eccentric, 450. 

neutral position, ills., 451. 

setting, ills., 450-454. 

sluggish, 271. 

travel, equalizing, ills., 452. 

variable, 262. 

angular advance, 275. 
lap, 287. 
Stephenson link, 326. 



INDEX OF GUIDE No. 1 



III 



Cut off, variable, — Continued 
travel, 290. 
variable, 243-290. 
early, 254-256. 
gear. Rider, ills., 259. 
principles, 245. 
riding, 262, 
shifting, eccentric, ills., 246, 247, 

251, 252. 
swinging eccentric, ills., 248-252. 
offset, 251. 
various, ills., 63. 
Cylinder, steam engine, 103-109. 
balancing, ills., 300. 
calculations, 97. 
dimensions, 94, 99, 102. 
high speed engine, ills., 184. 
insulation, 106. 
jacketted, ills., 107-109. 
operation, 106. 
parts, ills., 104, 105. 
pressure springs, ills., 117, 119. 
size, 94, 99, 102. 



D valve, ills., 179, 188. 

Davidson pump, valve gear, ills., 410, 413. 

Dead center, steam engine, 151. 

locating, ills., 434, 435. 
Deane pump, valve gear, ills., 406, ills., 422. 
Diagram factor, ills., 74-77. 
Diameter cylinder, 99. 

fly wheel, 173. 
Double, admission piston valve, 294, 295. 
ported valve, ills., 295, 299, 300-302. 
Dry steam, def., 24. 
Duplex, metallic packing, ills., 110. 

pump, cross head centers, 418, 419. 
rocker arm, ills., 428. 
valve gear, ills., 415-417. 

setting, 425-432. 
Worthington, small, ills., 418. 
Dynamometer, absorption, 93. 



Early cut off, 207. 
Eccentric, 243, 246, 248, 251. 

angular advance, 237. 

Heilman gear, ills., 247. 

key, ills., 137, 141. 

large, ills., 240. 

linear advance, ills., 238. 

loose, ills., 309-316. 

marine, loose, ills., 312, 313. 

objections, 238. 

offset, swinging, 251. 

valve gear, ills., 229. 

position, during one stroke, ills., 52. 
finding, 437, 438. 

reversing, ills., 309-316. 



Eccentric, — Continued 
riding, 279. 
rod(s), 226, 233-242. 

connections, ills., 234. 
double reach, ills., 319. 
Erieco, des., ills., 242. 
formula, 242. 

high speed engine, ills., 235. 
marine, 235, 241. 
open and crossed, 322-325. 
outside, ills., 235. 
rectangular, ills., 234. 
shifting, ills., 246-248. 
strap, ills., 226, 229, 234, 235, 236, 239, 

241 242. 
swinging, 248-252. 
throw, 236. 
various, 241. 
virtual, 277. 
Eccentricity, slide valve, ills., 203. 
Eclipse Corliss connecting rod, ills., 141. 
Effective pressure, 73. 
Energy, conservation of, 9, 11, 12. 
Engine, see Steam engine. 
Equal lead, slide valve, 194. 
Erieco engine, crank shaft, ills., 162. 
Exhaust, arch, ills., 186. 

cavity, ills., 104, 217, 280, 291. 
edge, ills., 181, 182, 186, 280, 446. 
lap, ills., 180, 188, 301. 
lead, 193. 

lines, long, pipe for, 217. 
opening, ills., 199, 204, 215, 306. 
passage, ills., 104, 181, 182, 294, 295. 
port, ills., 104, 105, 180, 181, 182, 184, 
214, 215. 
Expansion of steam, 53. 
adiabatic, 54. 
constant, 66-67. 
curve, 57, 62. 

hyperbolic, 58, 59. • 
theoretical, 61, 62. 
gain, steam engine, 62. 
isothermal, 54. 
number, 64- 
rules, 64. 
Expansion, valve gears, 243. 

of water, 27. 
Expected, and theo. card, Corliss engine, 76. 

mean effective pressure, 76. 
External latent heat, steam, ills., 30, 31. 



Factor diagram, 74-77. 

Fahrenheit scale, def., ills., 20. 

Fink link, des., ills., 336, 337, 338. 

Fishkill- Corliss engine, cross head, ills., 137. 

Pitchburg governor, ills., 393. 

Fly wheel, steam engine, 48-50, 171-178. 

Buft'alo, 249. 
Follower ring, ills., 116. 
Foot-poimd, def., 9. 



IV 



INDEX OF GUIDE No. 1 



Force, centrifugal, 174, 376. 
formula, 368. 

freezing, water, ills., 28. 

parallelogram, component, 151, 153. 

resultant, ills., 151. 
Forged center crank shaft, ills., 161. 
Formula (ae), centrifugal force, 368. 

circle, area, 80. 

cylinder dimensions, 97, 99, 102. 

fly wheel speed, 178. c 

governor, 369, 370, 371. 

horse power, 78, 81-85, 92, 94, 95. 

pressure, mean effective, 102. 

steam, expansion, 54, 62. 
port area, 183. 
volume of superheated, 46. 

thrust, piston, 152. 

valve stem, Seaton's, 226. 
Forward pressure, ills., 68. 
Freezing point, water, ills., 2, 28. 
Fulton- Corliss cross head, ills., 138. 
Fusion, ills., 27, 28. 



Gallon, water, U. S., weight, 4. 

Gardner governor, ills., 384, 385, 387. 

Gaseous matter, ills., 24. 

Gauge, steam, ills., 16-18. 

Gear, see Valve gear. 

Gib, steam engine, 127, 131, 132, 137, 148. 

Giddings valve, ills., 301. 

Gonzenbach cut off valve, ills., 257-261. 

Gooch link, des., 318. 

Governor (s), steam engine, 363-402. 

auxiliary devices, 397. 

centrifugal, 364, 376, 378, 396, 397. 

classes of, 363. 

close regulation, 391. 

cone, ills., 398. 

cut off, 388, 390. 

hunting, 374. 

inertia, 375, diag., 376. 

isochronous, 374. 

loaded, 369-371. 

parabolic, 373, 374. 

pendulum, 365, 374. 

regulation, 379, 390. 

Riblet, ills., 378. 

Rites, ills., 392. 

Russell, ills., 397. 

sensitiveness, 371. 

shaft, 392-397. 

speed control, 401. 

spring, 377, 381. 

ball, Hartwell, ills., 389. 

stability, 372-375. 

swinging eccentric, 249. 

throttling, ills., 380-387. 

troubles, 402. 

variable speed, 398. 
Gudgeon, def., 150. 
Guide, steam engine, ills., 134-136. 

valve stem, ills., 230, 231. 



H 



Hackworth gear, des., ills., 340-348. 
Harris- Corliss, engine parts, 107, 174, 175. 
Harrisburg governor, ills., 393. 
Hartwell governor, ills., 389. 
Head end, steam engine, def., 90. 
Heat, d^., 5. 

conduction, ills., 6. 

convection, ills., 6. 

latent, def., 5. _ 

mechanical equivalent, ills., 10. 

specific, def., 6. 

measurement, 8. 

radiation, ills., 6. 

sensible, def., 5. 

steam, 30, 31. 

transfer of , 6. 

unit, 8, 10. 
Heilman gear, ills., 247. 
High speed engine, 96. 

parts, 119, 184, 235. 

Erie City, ills., 232. 
Hollow piston, Murray-Corliss, ills., 118. 
Hoosier throttling governor, ills., 382. 
Horizontal engine, automatic cut off, 233. 

parts, ills., 48. 
Horse power, belt, 176. 

brake, 79, 93. 

calculations, 80, 81 

constant, 87-89. 

def., 12, 78. 

electrical, def., 79. 

formulae, 78, 81-85, 92, 94, 95. 

indicated, def., 79. 

nominal, def., 78. 

piston rod, effect, 90. 

S. A, E., def., 79. 

table, 90. 
Hot wire instrument, Whitney, ills., 7. 
Houston Stanwood & Gamble steam engine, 

ills., 57, 126, 187, 188. 
Hydraulics, principles, 3, 4. 
Hydrostatic paradox, ills., 4. 
Hyperbola, def., 58. 
Hyperbolic, curve, 58-60. 

logarithms, 70, 71. 



I 



Ice, fusion, heat energy, 27, 28. 

specific gravity, volume and weight, 1. 

to steam, ills., 24-32. 
Ide double port valve, ills., 295. 
Ideal engine, eccentric strap, des., 240. 
Independent cut off valve gear, 260. 
Inertia, control, ills., 394, 395. 

def., 172,375. 

governor, ills., 375, 376. 
Indicated horse power, 79. 
Indicator, steam engine, ills., 85, 91, 92. 

valve setting with, 460-462. 



INDEX OF GUIDE No, 1 



Indicator diagram, back pressure, 68. 

compression, 56. 

construction, 55, 56, 58, 59, 66, 85, 87. 

Coliss engine, 76. 

cut off, various, 63. 

diagram factor, 75. 

expansion, 58, 59, 61, 66. 

expected card, 101. 

hyperbolic logarithm, 70. 

initial, pressure, 64. 

mean J effective pressure, 69, 70, 87. 
forward pressure, 68. 

steam expansion, advantage, 61, 62. 

summation of ordinates, 87. 

terminal pressure, 65, 67. 

throttling governor action, 386. 

valve adjustments, 461. 

various losses, 74. 
Indirect, rocker, Erie City engine, ills., 232. 

valve gear, 233. 
Initial, condensation, def., 196. 

pressure, steam engine, diag., 64, 65. 
Inside, admission, ills., 292. 

valve setting, des., ills., 444-446. 

cut off edges of valve, ills., 262. 

lap, ills., 189, 198, 200. 

lead, 193. 
Internal latent heat, des., ills., 30, 31. 
Isochronous, governor, 374. 
Isothermal expansion, 54. 



J 



Jacketed cylinders, steam engine, 107, 108. 

Joule's equivalent, 10. 

Journal box, locomotive, ills., 169. 

Joy valve gear, ills., 355-359. 

Judson throttling governor, parts, ills., 380. 

Junk packing, ills., 114. 



K 



Key, crank, proportions, 158. 

cross head, 141. 

piston rod, 123. 
Key way, shaft, ills., 157. 
Kinetic energy, ills., 11, 12. 
Knowles pump, valve gear, ills., 409. 



Laidlaw-Dunn-Gordon pump, valve gear, 420. 
Lap, exhaust, ills., 180, 188. 

formulae, 212. 

inside, ills., 188, 189, 198, 200. 

latest cut off, 281. 

Marshall gear, ills., 350. 

negative, 189, 190, 210, 262, 275, 282. 

outside, ills., 188. 

positive, ills., 189, 190. 

variable, 278. 



Latent heat, 5, 27, 29. 
Lead, 191, 192. 

equal, 194. 

equalizing, ills., 437, 438. 

Hackworth gear, ills., 342, 343, 344, 346. 

inside, 200. 

link motion, effect on, 323-325, 335. 

Marshall gear, 348. 

measurement, 436. 

negative, 192, 193, 436. 

positive, ills., 436. 

variable, 194. 
Leffel engine, valve and valve gear, 252, 302. 
Lentz poppet valve engine, valve gear, 251. 
Lidgerwood hoisting engine, link motion, 323. 
"Line and line" position, ills., 190. 
Linear advance, ills., 206, 212, 238. 
Link motion, 317-338. 

Allen, ills., 334, 335. 

Fink, ills., 336, 337, 338. 

Gooch, des., 318. 

independent cut off, ills., 328, 329. 

length, 332. 

marine engine, ills., 319, 320. 

Reeves, ills., 326. 

rods open and crossed, ills., 322-325. 

setting, ills., 455, 460. 

Stephenson (so called), 317, 318, 326. 

shifting, 318, 319, 327. 

slip, def., 331. 

stationary, 332-334. 

suspension, ills., 330, 331. 

Williams, des., ills., 317. 
Loaded governor, construction, 371. 
Locomotive, cross head, des., ills., 136. 

driving journal box, ills., 169. 

valve, setting, 460. 
gear, 360. 

link, ills., 321, 330. 
Walschaerts, 360. 
Logarithms, hyperbolic, 70, 71. 
Loose eccentric reversing gear, ills., 309-315. 
Lost motion, pump, valve gear, 429. 



McEwen engine governor, ills., 391. 
McGowan pump, valve gear, ills., 431. 
Mcintosh & Seymour governor, ills., 396. 
Main bearings, 165-171. 
Marine engine, bearing, 171. 

connecting rod, ills., 144, 145. 

crank shaft, des., 164. 

cross head, ills., 132. 

eccentric rod, 235. 

piston, ills., 119. 
rod, ills., 124. 

triple expansion, Raabe, ills., 316. 

valve gear, link, 319, 320, 327, 328. 

reversing, loose eccentric, 312, 313. 
Marshall gear, ills., 348-352. 
Mean, effective pressure, 68. 

expected pressure, 76. 
Metallic packmg, ills., 110. 



VIII 



INDEX OF GUIDE No. 1 



Steam engine, — Continued 
Atlas, ills., 54.^ 

atmospheric, Newcomen's, ills., 36. 
automatic, 187, 243. 
back pressure, ills., 68, def., 69. 
"balancing cylinder, ills., 300. 
basic principles, l-;-46. 
bearings, see Bearings, 
belt, power transmitted, rule 176. 
brakeis) , horse power, formula, 94. 

ills., 99, 142, 143, 230. 
Bremme gear, forward motion, 353. 
Buffalo, ills., 83. 
chest, ills., 181. 
calculations, 98, 99, 100, 101. 
classes, 47. 

compound. Reeves, ills., 299. 
compression, ills., 200, 202. 
condensation, initial, 196. 
condensing, 47. 
connecting rody ills., 141-156. 

angularity, 154, 190. 
Corliss, connecting rod, ills., 141. 

fly wheel, ills., 174, 175. 

gibs, ills., 132. 

indicator card, 76. 

Murray, outboard bearing, 170. 

parts of, ills., 99. 
counter- weight, 160. 
crank, see Crank, 
cross head, see Cross head, 
cut off, see Cut off. 
cylinder, see Cylinder, 
dead center, 151, 434, 435. 
diagram, see Indicator diagram. 

factor, ills., 74-77. 
eccentric, see Eccentric, 
efficiency calculations, 55-102. 
exhaust, see Exhaust, 
expansion, see Expansion, 
fly wheel, 48-50, 123, 171-178, 249. 
gauge, ills., 16-18. 
gear, see Valve gears, 
gibs, 127, 137-148. 
governor, see Governor, 
guide, 136, 229. 
gudgeon, 150. 
head end, 90. 
high speed, 96, 184. 
hoisting, 323. 
horizontal, parts, ills., 48. 
horse power, see Horse power. 
Houston, Stanwood & Gamble, ills., 57, 

126, 187. 
indicator card, see Indicator card, 
initial pressure, diag., 64. 
lap, see Lap. 
lead, see Lead. 

Lidgerwood hoisting, ills., 323. 
locomotive cross head, ills., 136. 
marine, guides, ills., 133. 

valve gear, 312, 313, 316, 319, 353. 
mean effective pressure, 68, 72, 73. 
Murray Corliss, parts, ills., 99. 
Newcomen, 37. 
non-condensing, 47. 



Steam engine, — Continued 

operation, 47, 49. 

packing ring, ills., 116. 

parts, 103-178. 

piston, see Piston. 

port, see Port. 

pressure, expected mean effective, 76, 

pressure plate valve, ills., 302-306. 

Prony brake, ills., 93. 

radial gear, ills., 339-352. 

Ramsbottom's rings, ills., 115. 

reciprocating parts, ills., 50. 

regulator, speed, Gardner, ills., 385. 

reversing gear, see Reversing valve gear. 

riding cut off, see Riding cut off. 

rods, open and crossed, ills., 322, 325. 

rope brake, ills., 95. 

rotating parts, ills., 50. 

"rotative," 49. 

running, over and under, 131. 

Scotch yoke, def., 155, 156. 

shaft, see Shaft. 

speed, control, 385, 399, 401. 
regulator, ills., 385, 

stationary, parts, ills., 50. 
shaft, ills., 157. 

steam chest, ills., 181. 

stuffing box, def., 109. 

tangential velocity, 174. 

throttling, 243. 

valve gear, see Valve gear. 

variable cut off, 243-290. 
Stem, valve, see Valve stem. 
Stephenson's link motion, ills., 317-320. 
Strap, eccentric, 226, 229, 234-236, 239-342. 
Stroke, choice of, 98. 
Stuffing box, 109-111. 
Sturtevant connecting rod, ills., 150. 
Superheated steam, 24, 45, 46. 
Sweet pressure plate valve, ills., 303, 304. 
Swing center, offsetting object, 251. 
Swinging eccentric, offset, ills., 250, 251 

variable cut off, principle, 248. 
Syphon, operation, ills., 3. 



Tangent, 152. 
Tangential, speed, 154. 

velocity, 174. ■ 
Taper flange bolt, crank shaft, ills., 164. 
Temperature, def., 5. 

absolute, 21. 

fusion, 27. 

scales, ills., 19, 20. 
Terminal pressure, 62, 65, 66, 67. 
Theoretical, card, steam engine, 61, 62, 74. 

mean, effective pressure, 69, 76. 
forward pressure, 68. 
Thermal unit, British, def., 8. 
Throttle valve, ills., 57, 99, 383. 
Throttling engine, def, 243. 

governors, 381-388. 

Gardner, ills,, 384. 



INDEX OF GUIDE No. 1 



IX 



Throttling engrine, governors, — Continued 

Hoosier, ills., 382. 

Judsen, parts, ills., 380. 

Pickering, ills., 382. 

regulating mechanism, ills., 388. 

Sinker-Davis, ills., 382. 
Throw, eccentric, 236, 245. 
Tram, ills., 434. 
Travel, valve, 204-205. 

. half, ills., 202. 
Triple expansion marine engine, Raabe, 316. 
Troy steam engine, ills., 96. 
Turning, effect, steam engine, 173. 

force, 152, 153. 
Twin City Corliss, parts, 132, 148. 



U 



Unit, heat, 8, 10. 
power, 12. 

thermal, British, def., 8. 
work, 10, 78. 



Valve (s), 51, 179. 

admission^ 195, 196. 

double ported. Reeves, ills., 299. 

maximum, Allen, ills., 209. 

position, ills, 197. 
Allen, ills., 208, 294. 
angular advance, ills., 441-445. 
Armington and Sims, principles, 295. 
auxiliary, pump, ills., 413. 

Houston, Stanwood & Gamble, 188. 

Richardson, ills., 291. 
Ball, ills., 307. 
Bilgram diagram, ills., 213. 
bonnet, ills., 99. 
battens, ills., 448-450. 
Brownell, ills., 185. 
chest, ills., 105. 
constant lead, 193. 
cut off, see Cut off. 
defects, ills., 218-224. 
design, 210-217. 
dimensions, 211-217, 448, 450. 
doublet admission, def., 295. 

ported, ills., 295, 300, 301. 
early cut off, 207. 
edge, steam, ills., 262, 265. 
equal lead, 194. 
exhaust, see Exhaust, 
face, length, 214. 
gear, 225-242. 

Allen, 335. 

Bremme, des.t ills., 352-355. 
marine engine, ills., 353. 
Meyer, ills., 279, 282. 
Rider, ills., 259. 

Gonzenbach, 259. 

Hackworth, ills., 340-348. 



ValveCs), gear, — Continued 

independent cut off, 260. 

indirect, 232, 233. 

Joy, ills., 355-359. 

Lentz, engine, ills., 251. 

link motions, ills., 317-338. 

marine engine, Bremme gear, 353. 
reversing eccentric, 312, 313. 
single cylinder, ills., 319. 
triple expan., Raabe, ills., 316. 

Marshall, 348-353. 

parts, 225. 

poppet valve engine, ills., 251. 

pump, see Pump valve gears. 

reversing, see Reversing valve gears. 
Giddings, ills., 301. 
Gonzenbach, ills., 257-261. 
inside, admission, setting ills., 444-446. 

lap, 189-191. 
lap, see Lap. 
laths, ills , 448-450. 
laying out, ills., 214-217. 
location, ills., 50, 104. 
main, ills., 262, 265, 266, 268, 269,270. 
maximum, eccentricity, ills., 203. 
modified, 291-308. 
over travel, def., 205, 206. 
parts, ills., 180-186. 
passage, supplementary, 209. 
Phoenix, ills., 191. 
piston, 293. 

balanced, ills., 296. 

double, admission, illr., 294. 
ported, ills., 295. 

inside admission,^ setting, 445. 
locomotive, ills., 296. 

Reeves, ills., 298. 

setting, 444, 446. 

Vauclain, ills., 296. 
port, see Port. 
positions, admission, ills., 195-197, 215. 

compression, ills., 200, 201. 

cut off, see Cut off. 

during one stroke, ill ., 52, 53. 

exhaust, 180, 188, 193, 216, 301. 

extreme, 202, 203, 204, 215, 216, 
265, 280. 

late cut off, ills., 289. 

lead, ills., 192-194, 208. 

line and line, ills., 190, 191. 

mid-admission, ills., 289. 

negative, lead, 192, 193. 
positive and negative lead, ills., 436. 
pre-admission, 194, 195. 
pre-release, 198, 200. 
pressure plate, 302-308. 
pump, 403-432. 
release, 199, 200. 
requirements, 179. 
seat, 180-183. 

battens, 448-450. ^ 

dimensions, recording, 448—450. 

formula, 216. _ • 

length, balancing, 183. 

limit, 215. 

neutral position, 216. 



X 



INDEX OF GUIDE No. 1 



Valve(s) , — Continued 

setting, ills., 433-462. 

emergency rules, 446-447. 

pump, 404, 407, 409, 412, 421, 423, 

425 427. 
with indicator, des., ills., 460-462. 
size required, various cut offs, ills., 222. 
steam, edge, ills., 182, 262, 265. 

port, tee Port. 
stem, 104, 105, 226. 

connection, 227, 228, 230, 231, 234. 
templates, ills., 426. 
travel, 180, 202, 204, 205. 
variable lead, 194. 
zero cut off, 288. 
Vaporization, 23, 28. 
Variable cut off, 243-290. 
independent, 253. 
offset swinging eccentric, 251. 
regulating mechanism, 389. 
riding valve, methods, 263. 
shifting eccentric, 246-248. 
swing center, offsetting, 251. 
swinging eccentric, 248-251. 

offset, 251. 
Gonzenbach, 257-262. 
Vauclain piston valve, ills., 296. 
Vilter, rope wheel, ills., 178. 

types, ills., 173. 
Vim direct valve gear, ills., 233. 



W 



Walschaerts gear, ills., 360-362. 

Warren pump, valve gear, setting, ills., 427. 



Water, absolute zero, 35. 

boiling point, 2, 28, 34. 

properties, 1, 2, 3, 4, 12, 27, 28. 

re-evaporation, 35. 

static head, meaning, 4. 

temperature, 12, 27, 28, 34, 35. 

U. S. gallon, weight, 4. 

vaporization, temperature, 28. 
Waters throttling governor, reg. mech., 388. 
Watertown engine, crank shaft, ills., 162. 
Watt, James, engine, 37. 
Wedges, to measure lead, ills., 436. 
Weight, atomic, 1. 

Westinghouse connecting rod, ills., 150. 
Wet steam, def., 24. 
Whitney hot wire instrument, ills., 7. 
Williams link, des., ills., 317. 
Wire drawing, 183. 

Woodbury pressure plate valve, ills., 305. 
Work, units, 8, 9, 10, 25, 78, 153. 
Worthington duplex pump, ills., 418. 
Wrist pin, compression, ills., 130. 

various, 127, 128, 129, 130, 145. 



Yoke, valve gear, 225, 226, 227. 



Y 

525, 22 

Z 



Zero, absolute, def., 21, 35. 
over travel, ills., 276. 



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