International Library of Technology
459
Steam Boilers and Equipment
317 ILLUSTRATIONS
By
C. B. LINDSTROM
AND I.C.S. STAFF
Prepared Under Supervision of
A. B. CLEMENS
DIRECTOR, MECHANICAL SCHOOLS
INTERNATIONAL CORRESPONDENCE SCHOOLS
TYPES OF STEAM BOILERS
BOILER MOUNTINGS
BOILER DETAILS
PIPES AND PIPE FITTINGS
BOILER FURNACES, SETTINGS, AND CHIMNEYS
Published by
INTERNATIONAL TEXTBOOK COMPANY
SCRANTON, PA.
1928
! !
Types of Steam Boilers: Copyright, 1925, by INTERNATIONAL TBXTUOOK COMPANY,
Boiler Mountings: Copyright, 1925, by INTERNATIONAL TEXTBOOK COMPANY.
Boiler Details, Parts 1 and 2: Copyright, 1925, by INTERNATIONAL TKXTKOOK COM-
PANY.
Pipes and Pipe Fittings: Copyright, 1925, by INTERNATIONAL TEXTBOOK COMPANY.
Boiler Furnaces, Settings, and Chimneys, Parts 1 and 2: Copyright, 1925, by
INTERNATIONAL TEXTBOOK COMPANY.
Copyright in Great Britain
All rights reserved
Printed in IT. S. A.
PRESS OF
INTERNATIONAL TEXTBOOK COMPANY
SCRANTON, PA,
459
92715
PREFACE
The volumes of the International Library of Technology are
made up of Instruction Papers, or Sections, comprising the
various courses of instruction for students of the International
Correspondence Schools. The original manuscripts are pre-
pared by persons thoroughly qualified both technically and by
experience to write with authority, and in many cases they are
regularly employed elsewhere in practical work as experts.
The manuscripts are then carefully edited to make them suit-
able for correspondence instruction. The Instruction Papers
are written clearly and in the simplest language possible, so as
to make them readily understood by all students. Necessary
technical expressions are clearly explained when introduced.
The great majority of our students wish to prepare them-
selves for advancement in their vocations or to qualify for
more congenial occupations. Usually they are employed and
able to devote only a few hours a day to study. Therefore
every effort must be made to .give them practical and accurate
information in clear and concise form and to make this infor-
mation include all of the essentials but none of ,the non-
essentials. To make the text clear, illustrations are used
freely. These illustrations are especially made by our own
Illustrating Department in order to adapt them fully to the
requirements of 'the text.
In the table of contents that immediately follows are given
the titles of the Sections included in this volume, and under
each title are listed the main topics discussed.
INTERNATIONAL TEXTBOOK COMPANY
B
CONTENTS
NOTK.- This volume is made up of a number of separate parts, or sections,
a t indicated by their titles, and the page numbers of each usually begin with 1. In
thus list of contents the titles of the parts are given in the order in. which they appear
in the book, and under each title is a full synopsis of the subjects treated.
TYPES OF STEAM: BOILERS p ages
Stationary, Marine, and Locomotive 1-86
Terms and Definitions 1-2
Stationary Boilers 2-47
Shell, Flue, Tubular, and Water-Tube Types 2-22
Plain cylindrical, or shell, boiler; Flue boiler; Horizontal
return-tubular boiler; IJniflow return-tubular boiler;
Robb- Mum ford boiler; Clyde, or Dry-back, boiler; Verti-
cal tubular boiler; Manning boiler.
Semi- Portable and Portable Boilers 23-28'
Distinctive features; Locomotive-type boiler; Wet-bottom
firebox type; Pennsylvania boiler.
Horizontal Water-Tube Boilers 29-37
Advantages of water-tube boilers; Babcock and Wilcox
boilers"^ Heine water*tube boiler; Edge Moor water-
tube boiler.
Vertical Water-Tube Boilers 38-47
Bigelow-Hornsby water-tube boiler; Stirling water-tube
boiler; Hazclton water-tube boiler; Wickes water-tube
boiler; Cahall boiler,
Marine Boilers 48-81
Fire-Tube Marine Boilers 48-57
Scotch boilers; Single-ended Scotch boiler; Double-ended
Scotch boiler; Advantages of Scotch boiler.
Gunboat boilers 57-60
Locomotive type for marine purposes; Tubular type.
v
vi CONTENTS
TYPES OF STEAM BOILERS
(Continued) Pages
Water-Tube Marine Boilers ....................... 60-81
Types of water-tube marine boilers; Features of large-
tube and small-tube boilers; Tube arrangements; Belle-
ville water-tube boiler; Babcock and Wilcox marine
boiler; Babcock and Wilcox box-type marine boiler;
Babcock and Wilcox drum-type boiler; Thornycroft
water-tube boiler; Thornycroft-Schulz water-tube boiler;
Modified Thornycroft boiler with superheater; Yarrow
water-tube boiler ; Yarrow water-tube boiler with super-
heater; Normand water-tube boiler; White- Forster
boiler.
Locomotive Boilers ............................... 82-86
Classes of locomotive boilers; Straight-top boiler with
wide firebox; Extended wagon-top boiler with Belpaire
firebox; Conical boiler with Jacobs- Shupert firebox.
BOILER MOUNTINGS
Safety Devices .................................. j.,.3 ^
Safety Valves ................................... }_jg
Forms of Safety Valves . , ......................... 1-12
Purpose of safety valve; Classes of safety valves; Lever
safety valve; Pop safety valves; Pop safety valves for
stationary boilers; Safety valves for marine boilers'
Locomotive-boiler safety valves; Use and care of safety
valves; bafety-valve rules and regulations.
Safety- Valve Calculations ........................ 13-19
Lever safety-valve calculations; Spring safety-valve cal-
culations; Methods of checking safety-valve capacity.
Fusible Plugs ........................... 20-22
P Sc% f fUSiW ? ? lu &'' Inside ' and ou ^<le fusible* plugs;*
Rules for use of fusible plugs; Location of fusible plugs!
Water-Level Indicators ....... 22 29
Pressure Gauges ..... ..........................
' St S ga p UgC - ; Ste 1 ? m :^ a uge siphons ; Testing stUm satwres '
Rules for installation and use of steam gauges
Superheaters ......
*" '- "
CONTENTS vii
BOILER DETAILS, PART 1 p affcs
Fire-Tube and Water-Tube Boiler Details 1-49
Riveted Joints 1-25
Rivets and Riveting .' 1-3
Forms of Riveted Joints 4- 9
Terms used in riveted work ; Double- and triple-riveted lap
joints; Single-riveted single-strap butt joint; Double-
strap butt joint; Butt joints with straps of equal widths.
Arrangements of Riveted Joints 10-18
Location of longitudinal seams in shell boilers; Location
of longitudinal joints in internally fired furnaces; Con-
necting longitudinal lap joints at girth seam; Connecting
single-strap butt joint and girth seam; Longitudinal seam
at smokebox of locomotive boiler; Connecting double-
strap butt joint and girth seam; Seam connections of
shells of locomotive boilers; Arrangement of smokebox
joints ; Methods of making angular connections.
Arrangement of Firebox Joints 19-25
Fire-door and mud-ring connections; Connecting sheets to
mud-rings; Kire-eracks in joints.
Heads of Boilers and Drums 26-29
Flat heads; Bumped heads.
Domes and Drums 30-39
Steam domes; Steam drum; Mud-drums and blow-outs.
Openings in Boilers 40-49
Steam, water, and washout openings; Manholes; Water
and stcampipe openings.
PART 2
Staying 1-20
Types of Stays and Braces 1-20
Purpose and Classification 1-2
Types of Direct Stays t 2-7
Solid screw staybolt; Screw staybolt with telltale hole;
, Screw staybolts with nuts; Through stays; Flexible
staybolts ; Stay-tubes.
Diagonal Stays 8-13
Radial stays; Flexible radial crown stays; Gusset stays;
Diagonal stays.
Girder Stays , 14-17
Girder stays in Scotch boilers; Locomotive-boiler crown
bars.
.viii CONTENTS
BOILER DETAILS, PART 2 (Continued) Pages
Miscellaneous Braces 17-20
Throat braces ; Steel angle stays.
Tubes, Flues, and Furnaces 21 -3( >
Boiler Tubes and Flues 21-27
Boiler Tubes 21-26
Purpose of boiler tubes; Manufacture of boiler tubes;
Sizes and gauges of boiler tubes; Upset tubes; Installa-
tion of boiler tubes.
Boiler Flues 27
Furnace Flues and Combustion Chambers 28-36
Cylindrical furnace flues ; Corrugated furnaces ; Combustion
chambers.
PIPES AND PIPE FITTINGS
Pipes 1-29
Wrought Pipe 1- g
Wrought-iron and mild-steel pipe; Commercial grades of
wrought pipe; Galvanized pipe; Spiral jointed pipe,
Pipe Fittings K-2 ( )
Materials for fittings; Pipe couplings; Pipe unions; Mange
unions; Pipe flanges; Types of pipe flanges; Gaskets for
flanges; Types of pipe joints; Expansion and contraction
of pipes; Expansion joints; Pipe bends; Pipe coverings;
Pipe supports; Flanged fittings.
Valves and Cocks 30-40
Globe valves; Angle valve; Gate valves; Automatic stop-
valve; Check-valves; Blow-off valves and cocks; Pres-
sure-reducing valves.
Steam-Piping Accessories 41-44
Separators; Classes of steam separators; Centrifugal
separator; Baffle-plate separator; Drip pockets; Exhaust
heads.
Steam Traps 45-50
Purpose of steam trap; Classes of steam traps; Bucket
trap; bteam-trap connections; Tilting trap; Float trap*
Ihermostatic trap; Suggestions for trap installations.
Design and Arrangement of Piping 50-61
Principles of Design t 50-52
General requirements; Drainage; Water hammer; Con-
densation and friction.
CONTENTS ix
PIPES AND PIPE FITTINGS
( Continued ) Pages
Arrangement of Piping 53-59
General requirements ; Connecting main steam pipe to
boiler; Steam piping for small plant.
Single- Pipe and Double-Pipe Systems 59-61
Pipe Calculations 62-67
Steam-Pipe Sizes 62-65
Flow of steam in pipes ; Velocity of steam in pipes ; Supply
pipes for steam engines ; Sizes of main steam pipes ;
Friction of valves and fittings.
Flow of Water in Pipes 66-67
Finding size of pipe; Velocity of flow.
BOILER FURNACES, SETTINGS, AND CHIMNEYS
PART 1
Furnaces and Steam Boilers 1-60
Furnace Design and Construction 1-18
Conditions Affecting Furnace Design 1-5
Furnace volume; Furnace temperature; Effect of compo-
sition of coal on furnace volume; Firebrick arches and
walls ; Distance between boiler and grate.
Furnace and Ash-Pit Details 6-12
Furnace mouth; Bridge wall; Rear arch; Ash pits.
Special Types of Furnaces 13-18
Dutch oven; Hawlcy down-draft furnace; Burke furnace;
Dorrance furnace ; Wooley furnace.
Grates 19-26
Stationary Grates 19-23
Grate characteristics ; Common form of fixed grate ; Saw-
dust grate ; Special forms of grate bars ; Adapting grate
to fuel ; Installing 1 stationary grate bars ; Disadvantages
of stationary grates; Grates for vertical boilers.
Shaking Grates 24-26
Settings for Steam Boilers 27-60
General Features 27-28
Foundations and walls; Firebrick,
Settings of Return-Tubular Boilers 29-35
Details of Brickwork 29-32
Forms of wall construction; General arrangement of
boiler.
x CONTENTS
BOILER FURNACES, SETTINGS, AND CHIMNEYS
PART I (Continued) Page*
Supports for Return-Tubular Boilers ................ 32-36
Columns; Cross-beams.
Settings of Water-Tube Boilers .................... 36
Methods of supporting boilers ; Baffles.
Mechanical Stokers .............................. 37-60
Development and Classification . . .................. 37-39
Development of mechanical stoker; Advantages and disad-
vantages of stokers; Economic considerations; Classifi-
cation of stokers; Finding size of stoker.
Overfeed Stokers ................................ 40 47
General construction of overfeed stoker; Roney stoker;
Wilkinson stoker; Murphy automatic furnace.
Underfeed Stokers ............................... 4g, ..... cy
Characteristics of underfeed stokers; Jones' underfeed
stoker; Cleaning Jones stoker; American stoker.
Chain-Grate Stokers ............................. 53-57
Principle of construction; Green chain-grate stoker' Plav-
ford chain grate. '
Stokers for Small Power Plants ......... . .......... 58-60
Coal-throwing devices; Hand-fired stokers.
PART 2
Boiler Settings .................... ____ - - -
Settings for Burning Oil and Powdered Coal ____ .'.*." ." ' i_p
Oil-Burning Furnaces ................. ....... j'""
" ''
W r, requirements for oil bum-
boiler OH f S r d burning; ^ furnace ^ Scotch
boner, Uii furnace for locomotive boiler- Adaotimr
coal-burning furnaces for oil burning. ' A aptmg
Equipment for Burning Powdered Coal 9 12
*^&titeSf~Z~>
Reclaiming Waste Heat.... * - 7
waste gases from '" *
Chimneys and Draft .........
Handling Flue Gases. ... ...................... JJ":?
....................... 17-34
CONTENTS xi
MOILER FURNACES, SETTINGS, AND CHIMNEYS
PART 2 (Continued) Pages
Hreechings 17-20
Forms of breedings; Breeching design.
Types of Chimneys 21-28
Details of construction; Brick chimney; Reinforced-con-
crete chimney; Steel chimney; Guyed steel stacks.
Proportions of Chimneys 29-34
Requirements of ^ chimney; Height of chimney; Area of
chimney; Maximum combustion rate.
Draft 35-52
Methods of Producing Draft 35-37
Natural draft; Measurement of draft pressure; Mechanical
draft; Advantages and disadvantages of mechanical
draft.
Equipment for Mechanical Draft 38-42
Fans and steam jets; Typical forced-draft installations;
Ash pit fixtures for forced-draft installations; Horse-
power required for producing forced draft; Turbine
blower; Induced-draft apparatus.
Draft Control 42-48
Balanced draft; Automatic damper regulators; Hand-
operated draft regulator.
Other Draft-Producing Devices 49-52
Steam jets; Argand blower; Induced draft by steam jet.
TYPES OF STEAM BOILERS
STATIONARY, MARINE, AND LOCOMOTITE
TERMS AND DEFINITIONS
1. Introduction. A steam boiler is a closed vessel that,
when partly filled with water and heated, is used for the purpose
of generating steam. The steam may be used for power, heat-
ing, or other purposes. The generation of steam for the devel-
opment of power subjects the boiler to the most severe strains
and requires the greatest refinement of design. The descrip-
tions that follow are devoted to boilers representing the various
types in general use,
2. The steam boiler, when in use, is partly filled with
water, the space within it being thus divided into two parts,
known as the steam space and the water space. The water-
line is an imaginary line indicating the level to which the boiler
should be kept filled when in service, in order that steam may
be generated to best advantage. The steam space is the space
in the boiler above the water-line. The heating surface of a
boiler is that part of its surface exposed to the fire, and to the
hot gases from the fire as they pass from the furnace to the
chimney. The furnace is the part of a boiler installation in
which the fuel is burned. The fittings of a steam boiler con-
sist of such attachments as a steam gauge, water column, and
safety valve. The steam gauge indicates the steam pressure
in the boiler. The water column is a device composed of a
glass tube called a water glass, and three gauge-cocks, called
try cocks, that are used to determine the height of the water
level. The safety valve is attached to the steam space of the
2 TYPES OF STEAM BOILERS
boiler; it automatically relieves the steam pressure when the
pressure rises above that for which the valve is set.
3. Classification of Steam Boilers. Steam boilers may be
classified according to their form, construction, and use. Thus,
according to their form, boilers are horizontal or 'vertical; accord-
ing to their construction, they are shell, flue, sectional, fire-tub c,
or water-tube boilers; according to the different conditions under
which they are used, they are designated as stationary, locwtw-
J twe, or marine boilers.
* A shell, or cylindrical, boiler is one consisting of a pkin
i " cylinder closed at both ends. A sectional boiler is one made up
1 of a number of cast-iron sections that are assembled and bolted
I together. This type of boiler is chiefly employed for low-prcs-
; sure heating purposes. A flue boiler is made up of a cylindrical
| shell having one or more large flues, or pipes, 6 inches or more
i t in diameter, surrounded by water and so arranged that the
hot gases must pass through the flues. A fire-tube boiler restm-
| bles a flue boiler in principle, but in it a large number of tubes
! take the place of the flues. The tubes are generally Si inches
i or less in diameter. The hot gases pass through these tubes
just as they pass through the larger flues of a flue boiler. A
water-tube boiler consists of a number of tubes connected to
i drums and so arranged that water circulates within them while
the heating is done by the hot gases surrounding them. The
main features of different types of boilers are frequently com-
bined, giving rise to a large number of special forms.
STATIONARY BOILERS
FLUE, TUBULAR, AND WATOB-TOBK VYPBf
I 4. Plain Cylindrical, or Shell, Boiler.-The plain cylin-
drical, or shell, boiler is now rarely used; but because it is of
simple construction, it will be described, to bring out certain
general features that are common to many boilers, It is not
economical on account of its small heating surface. Its advan-
TYPES OF STEAM BOILERS
tages are : Simplicity
of construction, low
first cost, and the ease
with which it may be
cleaned and repaired.
Its disadvantages are:
Low efficiency, which
causes waste of fuel,
especially if the boiler
is pushed beyond easy
steaming capacity;
large space occupied;
its length, which
makes it difficult to
support without crea-
ting excessive and
dangerous strains in
the sheets and riveted
joints, or seams, due
to the weight of the
boiler and water and
the pressure of steam,
and to unequal expan-
sion and contraction.
These strains change
in amount, from ten-
sion to compression
and vice versa, and
may become very dan-
gerous, resulting pos-
sibly in a rupture of
the boiler.
5. A plain cylin-
drical boiler, Figs. 1
and 2, consists essen-
tially of a long cylin-
der, or shell, made of
I L T 4592
4 TYPES OF STEAM BOILERS
iron or steel plates riveted together, the girth seams having a
single raw of rivets and the longitudinal seams a double row of
rivets. The shells of boilers of this type are usually from 30
inches to 40 inches in diameter, and from 20 feet to 40 feet in
length, although in some cases the length ha been made as
great as 70 feet. The heads, or ends, of the cylinder are either
hemispherical or flat. The former are more generally used, as
they are stronger than flat heads and require no bracing. The
manner of suspending the shell is clearly shown. The boiler is
supported and enclosed by side walls of brick, known as the
boiler setting. The channel beams a are laid across the brick
side walls, and the boiler is suspended from the beams by means
of the hooks b and eyes c, the latter being riveted to the shell
6. The side walls are supported and prevented from buck-
ling by the binders, or buckstaves, d f Fig. 2, bolted together at
the top and at the bottom. The buckstaves are cast-iron bars
of T section. The eyes c are placed about one-fourth of the
length of the shell from each end. This method of suspension
allows the shell to expand and contract freely when heated or
cooled.
TYPES' OF STEAM BOILERS 5
The rear wall is built around the rear end of the shell, as
shown in Fig. 1, and continued back to form the chamber e,
into which opens the chimney or stack /. The boiler front,
shown in Fig. 2, is of cast iron. Fig. 1 shows the front in sec-
tion. The front end of the shell is partly surrounded by the
firebrick g, but the weight of the shell comes on the hooks b,
the rear wall and the firebrick g simply keeping the shell in posi-
tion. The furnace h, Fig. 2, is placed under the front end of
the boiler shell. The fuel is thi*own in through the furnace
door i and burns on the grate /, the ashes falling through the
grate into the ash-pit k. To insure a supply of air sufficient for
a more rapid combustion of the fuel than obtains under natural
dnaft, the furnace is sometimes provided with a blower /, con-
sisting of a cylinder leading into the ash-pit k, into which is led
a jet of steam through the pipe m. The steam rushes into the
ash-pit with great velocity and carries a quantity of air with it,
The pressure of the air in the ash-pit is thus increased, more air
is forced through the fire, and the combustion of the fuel is
more rapid and complete. It is more usual, however, to use a
fan blower instead of a direct steam jet for supplying addi-
tional air,
7. Behind the furnace, as shown in Fig. 1, is built the brick
bridge wall n, which serves to keep the hot gases in close con-
tact with the under side of the boiler shell As boilers of this
type are generally quite long, a second bridge wall n' is usually
added. The gases arising from the combustion of the fuel flow
over the bridge walls n and n' into the chamber e, and escape
through the chimney /. The flow of the gases is regulated by
the damper o placed in the chimney. The space p between the
bridge walls is filled with ashes or some other good non-conductor
of heat. The cloor q in the boiler front gives access to the ash-
pit for the removal of the ashes. The tops of the bridge walls,
the inner surfaces of the side and rear walls, and, in general, all
portions of the brickwork exposed to the direct contact of the
hot gases, as shown by the dark section lining, are made of a
special kind of refractory brick that withstands a very high
temperature.
TYPES OF STEAM BOILERS
The brickwork cov-
ers the upper portion
of the boiler shell in
such a manner us to
prevent the hot Arises
from coming into con-
tact with the shell
above the water-line r,
Fig. 2. The top of
the shell is covered by
brickwork or s o in e
other non-conducting
material to prevent
radiat i o n of heat,
Water is forced into
the boiler through the
feedpipe s, Pig. 1,
from a pump or an
> injector. When in op-
eration the wa t c r
stands at about the
level r, the space above
being occupied by the
steam.
8. The safety
valve is shown at t,
Pig, 1. It opens auto-
matically when the
pressure , reaches the
point for which the
valve is set, and al-
lows enough steam to
escape so- that the
pressure will not rise
above the desired
point. Steam is taken
from the boiler
TYPES OF STEAM BOILERS 7
through the steam pipe u. The steam gauge v indicates the
pressure of the steam in the boiler; it is attached to a pipe
that passes through the front head into the steam space.
The gauge-cocks w, w f , and w", Fig, 2, placed in the front
head of the shell, are used to determine the water-level. If
any one of the cocks is opened and water escapes, it is evi-
dent that the water-line is above that cock, while if steam
escapes, the level must be below it. The manhole % is a hole
in the front head through which a man may enter and inspect
or clean the boiler ; it is closed by a plate and yoke. To permit
FIG. 4
the boiler to be emptied, it is provided with a blow-off pipe y f
Fig. 1, through which the water and sediment may be dis-
charged.
9. Flue Boiler. The flue boiler differs from the plain cylin-
drical boiler in having one or more large flues running length-
wise through the shell, below the water-line. Such a boiler
is shown in elevation and section in Figs. 3 and 4. The ends
of the flues a are fixed in the front and rear heads of the shell.
The front end of the shell is prolonged beyond the head, form-
ing the smokebox b f which opens into the smokestack c. "The
8 TYPES OF STEAM BOILERS
front of the smokebox is provided with a door d. The boiler
shell is also provided with the dome e, which forms a chamber
where steam may collect and free itself from its entrained
water before passing to the engine. The manner of support-
ing the shell and the construction of the furnace and bridge
walls are the same as for the plain cylindrical boiler. The hot
gases, however, pass over the bridge walls to the chamber /,
and then back through the flues a into the smokebox b and
out of the stack c. It is plain that the heating surface is
greater than that of the plain cylindrical boiler by the cylin-
drical surfaces of the flues a.
The boiler has a cast-iron front, to which the furnace door
and ash-pit doors are attached. The safety valve g is attached
to the top of the dome. The steam pipe h leads from the dome
to the engine. The steam gauge i and gauge-cocks are placed
on a column / that communicates with the interior of the shell
through the pipes k and /, the former entering the steam space
and the latter the water space. The manhole m is placed on
top of the shell instead of in the head. The feedpipe is shown
at n } and the blow-off pipe at o, both passing through the rear
wall. Access is given to the rear end of the shell and to the
pipes and o through the door p. This form of boiler may
be provided with a blower, as shown at q. The setting is built
and supported in about the same manner as that shown in Fig. 1.
The cast-iron flue plate r rests on the side and rear walls and
supports the brickwork above it.
10- Horizontal Return-Tubular Boiler. The return-tubu-
lar boiler is so largely used in the United States that it is
regarded as the standard American fire-tube boiler. When
properly constructed and operated it is very efficient. It is a
modification of the flue boiler, the flues being replaced by
tubes that are smaller and more numerous than the flue^
usually ranging in size from 2\ to 4 inches in diameter. The
greater part of the heating surface is provided by the tubes
Less space is required for the installation of this type, as com-
pared with the shell boiler or the flue boiler of equal steam-
generating capacity.
TYPES OF STEAM BOILERS 9
A horizontal return-tubular boiler and its setting are shown
in perspective in Fig. 5. A part of the setting and the boiler
front a have been broken away in order to show the construc-
tion clearly. The tubes extend the whole length of the shell
and their ends are expanded into holes in the boiler heads and
beaded over; sometimes they are welded to the heads after
being beaded. A smokebox b is formed at the front of the
boiler by brickwork, the arch c separating the smokebox from
the furnace. The connection from the top of the smokebox to
the chimney is generally made by a sheet-iron flue, although
FIG. 5
occasionally a brick flue leading to the chimney is built on top
of the boiler. The boiler is supported on the brick walls of
the boiler setting by the brackets d riveted to the shell, These
brackets usually rest on cast-iron plates let into the brickwork,
rollers being set between the brackets and plates to allow the
Doiler to expand freely. A dome e, which increases the steam
space, may be provided, though it is usually left off and an
nternal dry pipe is used instead. The walls are built and
;upported by buckstaves in practically the same manner as
hose previously described.
10 TYPES OF STEAM BOILERS
11. Firebrick is used for all parts of the wall exposed to
the fire or heated gases. The fittings are not shown in Fig. 5.
The safety valve is placed on top of the dome, and the pres-
sure gauge and gauge-cocks are placed on the front. The
manhole may be either in one of the heads or on top of the
shell, although sometimes manholes are provided in both ends
and in the top of the shell. The feedpipe may enter the front
head, while the blow-off pipe i is placed at the bottom of the
shell, at the rear end. Access is given to the rear end of the
boiler through a clean-out door. The tubes are made accessible
for cleaning out, etc., by large doors, as /, in the boiler front.
The furnace and grates g are placed under the front end of the
boiler. The gases pass over the bridge h, along under the
boiler into the chamber at the rear, then back through the tubes
to the smokebox b, and thence to the chimney.
12. Horizontal return-tubular boilers are installed with
either flush fronts or overhanging fronts. These fronts are
made of cast iron, or of steel plate formed into the shape for
the doors, door frames, and rings that are used for supporting
the smokebox doors. In- the flush front setting, Fig, 5, the
boiler does not extend beyond the boiler front. It is set back
of the cast-iron front a, so that the gases have a large smoke
space b to travel through before entering the stack.
The general arrangement of a return-tubular boiler having
an overhanging front is shown in Fig. 6 (a). In this case the
boiler has a steel smokebox a that extends beyond the steel
front b. In such construction the front tube-sheet is installed
so that the flange of the tube-sheet c extends outwards as
shown in view (b). This drawing further illustrates the rela-
tive arrangement of the tubes d and the diagonal braces * that
support the flat section of the tube plate, above the tubes, com-
monly referred to as the tube-head segment. The stavs w
riveted to the boiler shell and tube head. The nozzle f is
pressed from steel plate, having at the bottom a flange by which
the nozzle may be riveted to the shell plate. The upper end
of the nozzle has a flange to which the safety valve is bolted
To prov.de an entrance to the shell for inspection, for clean-
12
TYPES OF STEAM BOILERS
located a drain, or blow-off, h, that is employed for removing
the water from the boiler periodically and for cleaning pur-
poses. The boiler shown in view (a) is suspended from
I beams i that are supported by cast-iron columns /. Suitable
hanger rods k and hanger straps / are employed in suspending
the boiler. This method of setting a boiler is more flexible
than is obtainable with the use of brackets. The rear end is
FIG. 7
set from 1 inch to 1J inches lower than the front end to facili-
tate draining off the water through the blow-off at the rear.
13. Uniflow Return-Tubular Boiler. The uniflow boiler
is^ a modification of the horizontal return-tubular boiler. In
Fig. 7 is shown a typical installation, with the boiler setting.
The boiler is suspended from I beams a by suitable hangers.
A brick setting b surrounds the boiler and forms the sides of
the furnace. The furnace setting consists also of a bridge
wall c, and an inverted arch d that runs from the bridge wall
TYPES OF STEAM BOILERS
13
to the rear of the boiler. This feature in the arch construc-
tion increases the velocity of the gases and causes them to flow
in contact with the bottom of the shell plate of the boiler. The
extension smokebox e is a steel-plate ring, fastened to the front
head of the boiler by lugs / that are bolted to both the smoke-
box .and the boiler head. This construction permits the
removal of the smokebox, if repairs are required on the boiler
head, or in case some of the tubes must be removed and new
ones installed. To provide means for cleaning, inspecting, and
FIG. 8
repairing the boiler, manholes g are installed above and below
the tubes. A water column h, with gauge-cocks i and a gauge
glass /, is conveniently placed at the front of the boiler, so that
the water level in the boiler can be readily seen.
14. The tubes k, Fig. 7, shown also in the cross-section,
Fig. 8, are arranged in parallel vertical rows, but are staggered in
the horizontal alinement. They are grouped in three divisions,
thus forming an arrangement called tube nests, or tube banks'.
14
TYPES OF STEAM BOILERS
The water is fed into the boiler through the connection /, placed
on the side of the front head above the tubes. The f eedwater
is discharged downwards between the center and outer tube
banks. Circulation of the water and steam is indicated by
the arrows. Steam rises directly from the heating surface to the
steam space and the cooler water flows downwards between the
tubes and replaces the hotter water carried away by the upward
circulation. The boiler derives its name from this provision
for the circulation of the water.
15. Robb-Mumford Boiler. The boilers so far described
have the furnace outside of the boiler itself, and hence are said
FIG. 9
to be externally fired. Many boilers are in use, however, in
which the furnace is inside the boiler; such boilers are referred
to as being internally fired. The Robb-Mumford boiler, shown
in section in Fig. 9, is an example of an internally fired hori-
zontal boiler. It consists of two cylindrical drums a and b con-
nected by the cylindrical nozzles, or necks, c and d, one at each
end. The lower drum a contains a cylindrical furnace * fitted
at one end with a furnace front containing a fire-door and an
ash-pit door, and at the other end with a tube-sheet into which
are expanded the tubes /. The tubes are also expanded into the
TYPES OF STEAM BOILERS IS
rear head of the lower drum a. The lower drum is inclined
about 1 inch per foot, this inclination promoting the circulation
of the water in the boiler, and also facilitating the complete
emptying of the boiler, as the blow-off pipe is attached to the
lower end of the lower drum a. The upper drum b serves as a
steam drum. The gases of combustion pass from the furnace
through the tubes / and return about the lower and upper drums,
passing then to the smoke outlet g at the front of the boiler.
A steel casing h, containing suitable doors i that give access to
the interior, surrounds both the upper and lower drums.
16. An important factor in the operation of a boiler is the
circulation, or movement of the water. When the water is
heated, it expands, becomes lighter, and rises to the surface. In
the boiler shown in Fig. 9, the heated water strikes the sloping
upper surface of the lower drum a and flows toward and up
through the neck c. When the water begins to boil, the steam
bubbles up through the water, forming a mixture of steam and
water. This condition increases the rapidity with which it rises
through the neck c, and the more rapid the boiling, the more
rapid the circulation becomes. When the mixture reaches the
surface of the water, the steam separates and accumulates in
the drum &, above the water level. As the mixture rises through
the neck c, water takes its place in the lower drum, and the
neck d is provided for this purpose. Therefore, as the water
and steam rise through the neck c, the water descends from
the upper to the lower drum through the neck d, thus complet-
ing the circulation.
17. The blow-off /, Fig. 9, is located at the front of the
boiler, and when the blow-off valve * is opened the water and
steam will be carried through a pipe to the outside of the boiler
room or into a sewer. The purpose of the bottom, blow-off is
to remove mu'd and sediment that collect at the bottom of the
boiler. Feedwater enters through the openings /, and the out-
side water pipe m is led to the discharge end of a feedwater
pump or injector. The water column n and the gauge glass o
are joined to the boiler by the pipes p. The upper pipe enters
the steam space and the lower pipe the water space. This
p
I
i;
16 TYPES OF STEAM BOILERS
arrangement of the devices and piping makes it possible to
determine the height of the water level in the boiler at all times.
The rocking grates r in the boiler furnace are supported at the
rear by an arch s and at the front by an angle-iron support. A
pipe t, called the dry pipe, is connected to the main steam outlet.
It is of cylindrical shape, from 4 to 6 inches in diameter, having
a number of holes along the top, through which steam enters
in its travel to the steam outlet. The purpose of the dry pipe
is to remove water held in suspension in the steam. The cas-
ing that surrounds the boiler is built of steel plate with angle-
iron stiffeners u f and is made in sections that are bolted
together. The inside of the casing and the top of the steam
drum are lined with non-conducting material.
9
18. Clyde, or Dry-Back, Boiler. The Clyde boiler shown
iji m Fig. 10 is entirely self-contained, requiring no brick set-
ting. It was originally designed for marine use, but on account
of the small space it occupies it is used in many stationary
steam plants. This type of boiler has a very large amount of
heating surface in proportion to its grate area. The boiler
consists of a large cylindrical shell a, its ends being closed
with flat heads b. The corrugated furnace c, commonly
referred to as the Morison corrugated furnace, is riveted to
the front and rear heads, which are flanged inwards for this
purpose. Tubes d extend from head to head, thus providing
heating surface and a means for conveying the gases from
the furnace to the uptake or smokestack e that connects with the
chimney /. The smokebox is also commonly called a breech-
ing. The flat heads are stayed by end-to-end stays g called
through stayrods, which prevent bulging of the heads The
remaining parts of the flat heads are supported by the tubes
which are expanded and beaded over, and by the furnace flue'
The furnace is formed within the flue, and comprises the
grate A, the ash-pit i, and the bridge /. The gases of combus-
tion flow to the rear into the combustion chamber k and then
pass through the tubes to the front and into the uptake e
chamber ft, Fig. 10, is formed by a
thin cylindrical shell attached to the rear end of the boiler, and
17
18 TYPES OF STEAM BOILERS
I , is
. lined with firebrick or thick asbestos millboard, which is
light and is not affected by intense heat. The back plate is
removable, giving access to the rear ends of the tubes. A
door I gives access to the combustion chamber for the removal
of ashes and soot and for the purpose of examination and
repair. The feedwater enters the boiler at m and, passing
through the internal perforated feedpipe n, is discharged
downwards alongside the shell in small streams. The various
fittings, such as the steam gauge, water column, and safety
valve, are not shown in the illustration. The water column
and steam gauge would be located conveniently for reading
the steam pressure and for determining the water level. The
safety valve would be bolted to the nozzle o, and the steam
pipe to the nozzle p. The steam is collected by the dry pipe q,
which is effective in removing water mixed with the steam.
The manhole is placed in the shell at r, and hanclholes are
arranged in the front head, at j. The blow-off connection is
placed at t. The boiler is supported by structural members ,
made of angle iron and plate, and so arranged that each one
carries approximately the same weight.
20. Vertical Tubular Boiler. The vertical, or upright,
fire-tube boiler may be considered as a ' modification of the
locomotive type placed on end, and, in common with that
type,' is self-contained. It has the advantage that it requires
less floor space than the horizontal return-tubular type ; and,
being self-contained, the outer shell can be made as heavy as
desired for any working pressure. Vertical boilers are used
to supply steam for hoisting engines, power shovels, and
other installations requiring a small, compact boiler. The
large sizes are employed for power purposes in some of the
large power plants ; but as a rule the vertical boiler is rather
inefficient and hard to keep free from soot. Leakage of upper
tube ends often occur, owing to forcing.
21. A common form of vertical boiler is shown in Fig, 11,
It consists of a vertical shell, at the lower end of which is the
firebox a. The lower rim of the firebox and the lower end of
the shell are separated by a wrought-iron ring 6, commonly
TYPES OF STEAM BOILE.RS
19
called a mud-ring. Both shell and firebox are riveted to the
ring, the rivets extending through both plates and the ring.
For the larger sizes of boiler,
the shell is made up of a num-
ber of cylindrical sections that
are riveted together; or, as in
the illustration, where a large
firebox is required, the lower
section of the boiler shell is
joined to the smaller upper sec-
tion by a taper course c. By
this arrangement a large water
space is obtained at the bottom
of the shell between the tubes
and the shell plate; also, it is
easy to get at the tubes d and
the tube-sheet e, commonly
called crown sheet, for inspec-
tion and cleaning purposes.
Entrance to the boiler is gained
through the manhole /. Hand-
holes g, conveniently arranged
for cleaning purposes, are placed
just above the tube-sheet and
the mud-ring.
22. The lower outer shell
and the firebox, Fig. 11, are
stayed together -with threaded
stays, called staybolts, which are
screwed into both shell plates, f
so that the ends extend about
f\ inch from the boiler plates.
To increase the holding powers
of the stays, they are headed
at the ends. The boiler shell FlG * u
and the grates h rest on a cast-iron base * that forms the ash-
pit. The vertical tubes extend from the top tube-sheet / to
I L T 4593
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OOOO <3jg>0 OOOO
00
O
20
TYPES OF STEAM BOILERS
the crown sheet of the firebox. The tubes serve as stays to
strengthen the flat surfaces of the tube-sheets, and convey the
gases from the firebox to the chimney or stack connection k.
The tubes pass through the steam space and are, therefore, not
surrounded by water,
as the highest water
level is usually at the
line /. This arrange-
ment is considered a
bad feature, because
the tubes are liable to
become overheated
and collapse, when
the boiler is forced.
On the other hand,
the steam temperature
in the steam space is
increased and drier
steam is obtained, as
the heat from the
tubes slightly super-
heats the steam ; that
is, it heats the steam
to a higher tempera-
ture than that of the
water from which the
steam is formed. The
main steam-pipe con-
nection is made to the
flange m and the safety
valve is bolted by a
suitable fitting to the
flange n. The water
column o, with its
gauge glass and cocks, is connected by the pipes p to the steam
and water spaces of the boiler. A steam gauge q is connected
to the steam space by a drop pipe r so that the gauge is brought
to a suitable position for reading the pressure.
FIG. 12
TYPES OF STEAM BOILERS 21
23. The submerged-head vertical boiler, shown in Fig. 12,
takes its name from the arrangement of the tube-sheet a- and
the tubes b. The tube-sheet a fonns the base of the smoke-
box, and the upper ends of the tubes are expanded into it. By
the use of the conical smokebox the tubes are entirely sur-
rounded by water. Aside from the submerged head and the
construction used in riveting the firebox and the outer shell
together, the boiler is similar to the type shown in Fig. 11. The
firebox d, Fig. 12, is flanged at its base so that the plate forms
a compound curved section c, called an ogee flange. By mak-
ing the flange of this shape, the necessary water space between
the firebox and the outer shell is obtained. This space is
usually referred to as the water leg of the boiler. Boilers
made in this way are generally used for" low working pressures
and for light duty, as for hoisting engines. Vertical boilers
of the form shown in Fig. 11 are employed in power plants, as
such boilers are much larger and can, therefore, produce
greater amounts of steam for power.
24. Manning Boiler. The Manning boiler is used exten-
sively throughout the New England States. In general, it is
a modification of the plain vertical boiler having a tapering
course. The details of its construction are shown in Fig. 13.
The firebox a is a steel cylindrical shell, riveted to the tube-
sheet or crown sheet b at the top, and to the mud-ring c at
the bottom. An outside shell plate d surrounds the firebox
and the two are connected by the staybolts c. To connect the
upper shell / and the lower shell d of the boiler, an ogee flange g
is employed. The advantage of the ogee connection is that it
provides a larger firebox area without a corresponding increase
in the diameter of the shell /, and does not require staying,
being self-supporting on account of the double curvature of
the plate. The tubes are of standard size, 2 inches in diame-
ter, and are installed in lengths up to 20 feet. AH tubes are
held in the tube-sheets by expanding or rolling. The ends of
the tubes extend usually from & to | inch beyond the head.
They are turned clown around the tube holes and beaded ; that
is, the tube ends are turned over to form rounded flares, or
22
TYPES OF STEAM BOILERS
lips, called beads. The beads prevent the tube ends from
burning off and add strength
to the staying qualities of the
tubes.
25. The gases in the Man-
ning boiler, Fig. 13, travel di-
rectly from the firebox through
the tubes to the smoke con-
nection h. The small tubes
break up the products of com-
bustion and give a wider dis-
tribution of the heat and trans-
fer it rapidly to the surround-
ing water. The upper ends of
the tubes are not surrounded
by water, and the heat that is
transmitted through these parts
will superheat the steam. The
steam outlet is at /, and the
safety valve is connected to the
flange k. The water column
and steam gauge are also
shown in their proper posi-
tions on the boiler. The feed-
water connection / is well
above the crown sheet of the
firebox, being so placed that
the colder water does not
strike the heated plates of the
firebox. Handhole open-
ings m are provided in
the shell above the
crown sheet of the fire-
box and just above the
mud-ring. They are
FIG. 13
used when it is necessary to clean out the mud and scale that
collect on the tube-sheet and the mud-ring. The grates n rest
TYPES OF STEAM BOILERS 23
on a support incorporated with the brick foundation that forms
the ash-pit. The vertical type of boiler requires considerable
head room for its installation ; but as compared with other boil-
ers of the same size or capacity it occupies less ground space.
To prevent heat losses by radiation from the outer shell, a cov-
ering of asbestos or magnesia should be applied.
SEMI-PORTABLE AND PORTABLE BOILERS
26. Distinctive Features. It is somewhat difficult to draw
a sharp line of demarcation between stationary, semi-portable,
and portable boilers. Generally speaking, a stationary boiler
is one that is permanently set in brickwork, as, for instance,
the horizontal return-tubular boiler.
A semi-portable boiler is one that is arranged to be shipped
on skids from place to place. It may, of course, be set on a
permanent foundation ; but it is then spoken of as a stationary
boiler of the semi-portable type.
A portable boiler is a boiler mounted on wheels and that can
be hauled by horses or tractors from place to place. Boilers
of this kind are used by building contractors, quarrymen,
threshermen, oil-well operators, etc. They are especially suit-
able to meet conditions requiring a temporary power plant
capable of being moved about at a small expense.
Both semi-portable and portable boilers are generally of the
firebox type, of either the vertical or the modified locomotive
types.
27. Locomotive-Type B o i 1 e r. The internal-firebox
boiler of the locomotive type, shown in Fig. 14, is a modifica-
tion of the larger types used for locomotives in railroad prac-
tice. With the exception of the horizontal return-tubular boiler,
the locomotive-type boiler is used to a larger extent than any
other type of fire-tube boiler. It is employed for tractors, road
rollers, threshing machinery, and power plows, and for station-
ary purposes. The boiler consists of a cylindrical shell a that
is riveted to a steel-plate firebox containing the furnace b. The
firebox, which may be made in various shapes, is composed of a
24
TYPES OF STEAM BOILERS 25
continuous inner sheet c and an outer sheet d, called wrapper
sheets. These sheets are arranged to leave water spaces, or
water legs 2 to 3 inches in width at the sides of the firebox.
The upper plate section e of the outer wrapper sheet is called
the roof, and the top section / of the inside wrapper is known
as the crown sheet. The end section of the outer wrapper is
closed by a flanged head g, called the back head, and the inside
wrapper sheet with a flanged head h, known as the door sheet.
Both of these heads are flanged, as shown at i, to form the door
opening, or door ring. The forward end of the inside wrapper
sheet is closed with a flanged head /, called the firebox tube-
sheet, from which a series of tubes-/? extend to the circular tube-
sheet /. The front of the shell a is extended beyond the tube-
sheet I to form the smokebox m. An opening n is cut in the
smokebox for the stack connection. A flanged sheet o t known
as the throat sheet, is so made that it connects the flat sides of
the outer wrapper sheet of the firebox and the shell a.
28. As the flat sides of the furnace, Fig. 14, are not self-
supporting, they must be braced or stayed. This is done by
staybolts p, which are riveted over at both ends, so as to upset
the stays in the threaded holes and thus produce steam-tight
work. The stays q are known as radial stays, or crown stays,
and support the roof and the crown sheet of the firebox. The
flat surfaces of the back head g above the door ring, and that
above the tubes of the front tube-sheet /, are stayed by diagonal
braces r, called crow-foot braces on account of the shape of
their ends. Circular clean-out openings s are provided above
the mud-ring t and the crown sheet for washing out the boiler.
The mud-ring t closes the water legs at the bottom of the fire-
box, being riveted to both the inner and outer wrapper sheets.
Entrance to the boiler for inspection, repairs, 'and cleaning is
made by removing the manhole cover . A dome v is attached
to the shell a, but in some constructions it is riveted to the roof
sheet. It is preferable, however, from the view-point of stay-
ing the firebox, to have the dome on the shell. The dome head
being flat, is not self-supporting, so it is stayed with crow-foot
braces w that are riveted to the dome head and near the base of
26
TYPES OF STEAM BOILERS
the dome. In some constructions, threaded stayrods are
screwed into the dome head and the shell plate under the dome :
but in such a case the dome opening would not be cut out
entirely as is shown in the illustration. A number of circular
holes would be drilled in the shell plate, to allow free circula-
tion of steam into the dome, but leaving sufficient material
between the holes for installing the screw stays. The feed-
water may be introduced at any convenient place in the boiler
shell below the water-line, usually at the coolest section of the
boiler. This boiler is of the semi-portable type that may be
moved about on skids, and then mounted on a brick founda-
FIG. 15
tion jr. In the operation of stationary boilers, with the excep-
tion of locomotive-type boilers, it is customary to speak of the
end at which the firing is done as the front end. In the case
of locomotive boilers the smokebox end is called the front end,
since it is the forward end of a locomotive.
29. Wet-Bottom Firebox Type. A perspective view of a
semi-portable boiler of the firebox type is shown in Fig. IS.
The bottom of the firebox, instead of opening into an ash-pit,"
is closed by a continuation of the water legs, and hence the fur-
nace is entirely surrounded by water. A boiler thus constructed
is said to be wet-bottomed. In the particular design shown the
27
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oooo
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oooo
oooo
oooo
oooo
_O.QO
e oo
oooo
oooo
oooo
cxo,
28 TYPES OF STEAM BOILERS
fire-door a and ash-pit door b are attached to a cast-iron front c
which, in turn, is bolted to the back head d ; with this construc-
tion the firebox wrapper sheet is riveted directly to flanges
formed on the back head, there being no furnace end or door
sheet. The cylindrical part of the boiler is supported by a cast-
iron cradle e. For convenience of shipment, the boiler is
mounted on skids /, which may also serve as a temporary foun-
dation. Some wet-bottom boilers have an ash-pit door in- the
center of the bottom instead of in the back head.
30. Pennsylvania Boiler. In Fig. 16 is shown a form of
boiler that is a combination of a firebox and a return-tubular
boiler, and which is known as the Pennsylvania boiler. The
firebox, or furnace, has a semicircular crown sheet a, which is
stayed by solid crown bars b having a rectangular cross-section.
The water legs are stayed by screw stays, as in locomotive boil-
ers. The gases of combustion pass through the large, short,
lower tubes c to a combustion chamber forming an extension
of the cylindrical part of the boiler, and then return through
the small, long tubes d to the smokebox e, whence they dis-
charge into the chimney. A bafHe plate / is fitted to the com-
bustion chamber to prevent the hot gases from coming into
contact with the upper part of the tube-sheet, which part is no/
covered by water.
The boiler is self-contained; that is, it requires no elaborate
setting. It has the advantage over the locomotive boiler of
having a much greater depth of water over the crown sheet
and the heated gases have a longer tube travel, thus making it
possible to use a greater amount of the heat from the product*
of combustion. For convenience in shipment, the boiler i<
mounted on skids g, the cylindrical part of the boiler beta* sun*
ported m a cast-iron cradle, h, which is utilized when the boiler
is set permanently on a foundation.
TYPES OF STEAM BOILERS 29
HORIZONTAL WATER-TUBE BO1L.EKS
31. Advantages of Water-Tube Boilers. The boilers pre-
viously described have been of the types in which the water
surrounds the tube or tubes, the flame and hot gases being-
inside the tube. In the water-tube boiler this condition is
reversed ; the water is inside the tubes, which are surrounded
by the fire and hot gases. Water-tube boilers are commonly
known as safety boilers, because an accident to any one tube
or fitting does not necessarily involve the destruction of the
whole boiler. They are extensively used for both land and
marine service. The demand for very high steam pressure has
led to the development of the water-tube boiler.
32. It is maintained that the heating surface in water-tube
boilers is much more effective than an equivalent area of sur-
face in the ordinary tubular boilers. In water-tube boilers, the
direction of the circulation is well defined and there are no
interfering currents. The circulation is rapid and over the
entire boiler, keeping it at a nearly constant temperature and
tending to deposit all the sediment at the lowest point* The
water is divided into small bodies, the boilers steam quickly,
and are sensitive to slight changes of pressure or condition of
the fire. The arrangement of a water-tube boiler is such as to
form a flexible construction, any member being free to expand
without unduly expanding any . other member. This very
important feature tends to prolong the life of the boiler.
There is considerable difference in the amount of soot col-
lected in a fire-tube and on a water tube. Soot accumulates
within a fire-tube, and it may become filled, while the water
tube holds the soot only on the top surface. Water-tube boil-
ers are of sectional construction, and hence may be transported
and erected more readily than other types.
33. Babcock and Wilcox Boilers. The Babcock and Wil-
cox boiler is built in two classes, namely, the longitudinal -
drum type and the cross-drum type. These types are made
with vertical or inclined tube headers, which are formed in
pressed steel or are iron castings, depending on the working
607
6J/I
i
Kf ?& e* M>
30
TYPES OF STEAM BOILERS
pressure for which the boiler is constructed. The longitudinal
drum is standard, although, where head room is a factor, the
cross-drum type is built to meet the requirements.
In Fig. 17 are illustrated the details of construction of the
longitudinal-drum Babcock and Wilcox boiler. It consists of
one or more horizontal drums a, dependent on the size of the
FIG. 17
boiler and its capacity, usually made of three cylindrical courses
riveted together with single-riveted seams. These particular
seams are called girth seams, or circumferential seams. The
riveted joints running lengthwise of the drum are called longi-
tudinal seams. They are made by butting the longitudinal
edges of the drum sections together and covering the joints-
with outside and inside plates, which are riveted together with
the shell plate. Joints made in this way are called butt joints.
The heads b close the ends of the drum.
TYPES OF STEAM BOILERS
31
34. The drum heads are pressed to the form shown in
Fig. 18, with a manhole opening a. The flange of the man-
hole acts as a stiffening ring and provides additional strength
to the plate around the opening. The
stiffening ring is faced off to form a
seat for the manhole cover-plate. Flat
raised seats are also pressed in the head
at b for the water column and at c for
the feed water connection. Cross-tube
boxes c, Fig. 17, are riveted to the drum
of the boiler. These tube boxes are
pressed to the form shown in Fig. 19
and shaped so as to fit snugly to the
curvature of the drum. Tube holes are
bored in the bottom face of the box, for
the attachment of the tubes d, Fig. 17,
that connect the tube headers e and the
drum a, thus providing the means for cir- " FlG " 18
culation of steam and water in the front and rear tube headers.
The tube headers e are curved along the sides, being so shaped
that adjoining header
sections fit snugly to-
gether and permit a
staggered arrangement
of the water tubes.
The sectional view,
Fig. 20, shows the out-
line of the header sec-
tion, with tube holes
and handholes. The
latter are placed di-
rectly opposite the
tube holes and are of
sufficient size to per-
mit cleaning and re-
newal of the tubes. A section is shown of the handhole plate a
and the crab 6. The nut c is used in bringing the handhole
plate a to its seat so as to form a steam-tight joint.
FIG. 19
32
TYPES OF STEAM BOILERS
35. The mud-drum g } Fig. 17, to which the header e is
connected, is a steel box .7J inches square, and of sufficient
length to connect the tube-header sections. It collects mud
and sediment that settle at the bottom of the vessel. The sedi-
ment is removed through handhole openings in the drum or is
blown out through the blow-off connection /z. The pressure
gauge and the water column i are connected to the drum a. A
safety valve / is attached to the drum and another safety valve k
is connected to the main steam pipe / that leads from the super-
heater m.
The superheater is constructed of pipe coils and headers
through which the steam from the steam space of the drum a
is circulated. The superheater is set directly in the furnace,
and is subjected to the hot gases.
If at any time no steam should be
drawn from the boiler, the super-
heater would become overheated.
The safety valve k is provided to
prevent this condition. It is set at
a pressure slightly below that of
FlG - ^ the safety valve j, and when the
pressure rises it will open and permit some steam to flow
through the superheater.
36. Feedwater is introduced through the front dram
head b, Fig. 17, and is carried back to the rear of the drum.
It flows downwards in the rear header *, then through the
tubes / to the front header e, and upwards through this header
to the drum a. The water that is not transformed into steam .
again follows the circulation. The steam that is liberated in
the drum a is stored in the steam space and is drawn off either
through a dry pipe or through the superheater m.
^ The method of supporting the longitudinal-drum boiler shown
is to suspend the rear and front ends from steel I beams n
which rest on columns, thus forming a structural frame support
independent of the brickwork in the setting. This method
allows for expansion and contraction without affecting the boiler
or setting. This type of boiler, in common with most boilers
TYPES OF STEAM BOILERS 33
of the water-tube type, requires a brick setting to form the fur-
nace and combustion chambers. The boiler furnace is built in
the setting at the front of the boiler under the tubes. At the
bottom of the furnace, extending up to the tubes, is built a
bridge wall o, which forms a support for the grates p. The
bridge wall prevents the gases and flame from traveling directly
back to the rear of the boiler. By means of the walls r, built
in between the tubes, and commonly called baffles, or baffle walls,
the products of combustion are compelled to travel in a zigzag
path around the tubes to the smoke outlet s f thus increasing con-
siderably the gas travel in the boiler furnace.
37. Boilers of the cross-drum type are constructed simi-
larly to the longitudinal-drum type. The main difference is in
the arrangement of the upper drum, which is placed above and
across the rear header. Horizontal circulating tubes are used
to connect the drum and the front header to provide .means for
the circulation of water and steam. Vertical tubes connect the
drum and the rear tube header.
38. Heine Water-Tube Boiler. A boiler differing in many
respects from that shown in Fig. 17 is the Heine boiler, illus-
trated in Fig. 21. It consists of a large main drum a, above and
parallel to the nests of tubes b. Both drum and tubes are
inclined to the horizontal at an angle that brings the water level
to about one-third the height of the drum in front and to about
two-thirds the height in the rear. The ends of the tubes are
expanded into the large wrought-iron water legs c. These legs
are flanged and riveted to the shell, which is cut out for about
one-fourth of its circumference to receive them, the opening
being from 60 to 90 per cent, of the cross-sectional area of the
tubes. The drum heads form segments of a sphere, and there-
fore do not need bracing. The water legs form the natural sup-
port of the boiler, the front water leg being placed on a pair of
cast-iron columns d that form part of the boiler front, while the
rear water legs rest on rollers, shown at e } that can move on a
cast-iron plate embedded in the rear wall. These rollers allow
the boiler to expand freely when heated.
34
TYPES OF STEAM BOILERS
39. The Heine boiler is enclosed by a brickwork setting
in the usual manner. The bridge wall f, Fig. 21, made largely
of firebrick, is hollow, and has openings in the rear to allow
air to pass into the chamber g and mix with the furnace gases.
In the rear wall is the arched opening h, which is closed by a
door and further protected by a thin wall of firebrick. When
it is necessary to enter the chamber g t the .wall at h may be
removed and afterwards replaced. The feedwater is brought
FIG. 21
in through the feedpipe i, which passes through the top of the
drum. As the water enters, it flows into the mud-drum ;,
which is suspended in the main drum below the water-line and
is thus completely submerged in the hottest water in the boiler.
This high temperature is useful in causing the impurities con-
tained in the feedwater to settle in the mud-drum ;, from
which they may be blown out through the blow-off pipe k. The
water passes back out of the open end of the mud-drum and
circulates in the same direction as in the boiler shown in Fig. 17.
40
TYPES OF STEAM
35
B?*^^C^>x^
36
TYPES OF STEAM BOILERS
tubes. In front of each tube a handhole t is placed to give
access to the interior of the tube. When a group, or battery,
of several boilers is used, additional steam drams are placed
parallel to the drums a.
41. Edge Moor Water-Tube Boiler. The Edge Moor
water-tube boiler, shown in Fig. 22, is also made up of tubes,
tube headers, and drums. The distance feature in its con-
struction is the tube header a, which is carried above the
FIG. 23
drums b, thus providing additional steam and water space.
The section, Fig. 23, shows the tube-header details and how
the drum is arranged and stayed to the header connection. A
flange a is turned on the header plate b, into which the drum c
is set and riveted. To reinforce the outer sheet d around the
manhole opening e, the stays / are installed. All flat plates of
the headers are stayed with screw staybolts g t which are
screwed into the inner and outer sheets and riveted over.
Opposite each tube is placed an elliptical handhole, The hand-
... a^.^josK,..
I- js*93SoQbOs\
,: !| 33*39oQoOoV
:;;'? v^-ii.- 1 -^lii.S'> ". j ^iipj?.^ ^ <^ C .3 3 o ci 1 !
38 TYPES OF STEAM BOILERS
hole plates are removable through their own openings ; and
through these openings the tubes are cleaned or repaired.
Fig. 22 shows the relative arrangement of the tube headers a,
drums b, tubes c, baffles d, and bridge wall e, and a section of
the boiler setting / with the front structural supports g. The
grates and other details are not shown. The grate sections
would be placed in front of the bridge wall, under the high
end of the boiler. The fuel gases travel in the direction of the
arrows, upwards around the front tube section, downwards
about the middle tube section, and upwards around the rear
tube section to the smoke breeching h.
42. The Edge Moor boiler is supported by columns or
suspended from overhead beams. Column supports for the
headers are shown in Fig. 24 (a) and (&). View (a) shows
an H column used for supporting the front of a battery of
boilers. It is placed between the headers and bolted to angle
clips a that are fastened to the headers. Angles b are riveted
to the web of the H column. A foundation plate c is embedded
in the concrete floor that forms a base for the column. The
saddle support, view (6), is placed at the rear of the boilers,
under the back headers. The suspension method of supporting
the boilers is illustrated in view (c). Either H or I beams a
form the column supports, and channels b form the cross-beams.
The channels are bolted together at each end by bolts c, and
spacers or sleeves are placed between the backs of the channels,
through which the bolts pass. The spacers keep the channels
apart and in alinement A special steel sleeve d rests on the
channels. A hanger bolt e passes through the sleeves d and f f
and an adjusting nut g facilitates adjusting the boiler so that the
headers hang plumb with the supports.
VERTICAL WATER-TUBE BOILERS
43. Bigelow-Hornsby Water-Tube Boiler. The differ-
ence between the Bigelow-Hornsby boiler and those already
described is in the tube arrangement and the shape of the tube
headers. A typical installation, represented in Fig. 25, is com-
TYPES OF STEAM BOILERS
39
posed of a steam and water drum a, connected to the tube head-
ers b by circulating pipes c. The headers b are cylindrical and
the upper head d of each header is flanged and riveted to the
shell. A standard manhole opening, 11 inches by 15 inches, is
flanged in each head. The bottom heads in the lower tube head-
FIG. 25
ers are made in the same way, and standard manholes permit
access to the drums to inspect, clean, and repair the tubes or
header plate. The manholes eliminate the use of handhole
plates. Tube plates e are shaped by a hydraulic press and dies
to form suitable seats for the tubes. Each nest of tube headers
IT
40 TYPES OF STEAM BOILERS
is connected to the adjoining set by circulating tubes /,, giving
the required means for circulation of steam and water. A nest
of 21 tubes directly connects the upper and lower tube headers.
Feedwater enters the top rear header through the connec-
tion g, passes down the rear tubes, and is then, carried by the cir-
culation up the tubes in the front tube units. It thus passes
through the rear tube units, which are in contact with the cooler
gases of combustion, before entering the forward units where
the heating surfaces are directly in contact with the fire and
hottest gases. Baffle plates h are placed between the tubes to
jj change the gas travel.
l ] 44. The lower drum headers, Fig. 25, collect the mud and
i , other sediment that settles when the water is heated to a high
temperature. Bottom blow-off connections i are installed in
the lowest part of the drum heads for the purpose of blowing
out mud and sediment. Beneath the main drum a is shown a
superheater / made of pipe bent to a U shape, with the legs con-
necting headers k. To protect the wrought pipes or tubes from
the corroding effect of the gases, cast-iron cover-plates /, called
grids, are fixed around the superheating tubes. Steam is drawn
from the drum a, passes down the pipe w, and circulates through
the U tubes of the superheater to the main steam piping n f which
is connected to the superheater by the pipe o.
Owing to the length of the drum and tube-header units, the
setting must have high headroom. The tube-header units are
suspended from structural members installed outside the boiler
setting. Suitable clean-out and inspection doors p are provided
for the convenient removal of refuse that collects back of the
bridge wall q, and for the inspection of the boiler sections,
which must be made periodically. The furnace in this installa-
tion is constructed for firing the fuel with a mechanical device r,
called a stoker. The coal hopper is shown at j and the propel-
ling machinery at t. The grates of the stoker are inclined.
45. Stirling Water-Tube Boiler. A well-known type of
bent-tube stationary boiler is the Stirling water-tube boiler,
shown in Fig. 26. It consists of a lower drum a connected with
three upper drums b by three sets of nearly vertical tubes c.
TYPES OF STEAM BOILERS
41
The upper drums are connected by the curved tubes d. The
curved forms of the different sets of tubes allow the different
parts of the boiler to expand and contract freely without strain.
The boiler is enclosed in a brickwork setting, which is provided
with various openings e, so that the interior may be inspected or
repaired. The boiler is suspended from a framework of
wrought-iron girders, not shown. The bridge wall / is faced
>: \:' ; *' : -" :: :^ : '^
FIG, 26 ' '"'"
with firebrick, and is built in contact with the lower drum a
and the front nest of tubes. A firebrick arch g is built above
the furnace, and this, in connection with the brick baffles h,
directs the course of the heated gases, causing them to pass up
and down between the tubes. The arch g becomes heated to a
white heat, promoting combustion, and heating the incoming air
when the furnace doors are opened, thus protecting the boiler
from being chilled when the fires are being cleaned or stoked.
46. The feedwater enters the rear upper drum through the
pipe i, Fig. 26, passes into the trough /, and descends through the
TYPES OF STEAM BOILERS
FIG. 27
rear nest of tubes to the drum a,
which acts as a mud-drum and
collects the sediment from the
water. From the drum a the
water passes upwards through
the two forward sets of tubes
and is vaporized as it rises, the
steam passing from the front
drum to the middle drum through
the upper set of curved tubes d,
while the unvaporized water cir-
culates between the front and
middle drums through the lowest
set of curved tubes d f and thus
the heated water does not again
mingle with the comparatively
cold water in the drum a. The
steam collects in the upper
drums b. A blow-off pipe k
permits the removal of the sedi-
ment. The steam pipe and the
safety valve / are attached to
the middle drum. The chimney
connection m-is located behind the
rear upper drum. The water col-
umn n, with its fittings, is- placed
in communication with the front
upper drum. Each drum is pro-
vided with a large manhole o.
47. Hazelton Water-Tube
Boiler. The Hazelton boiler,
sometimes called the porcupine
boiler, because of the rather pe-
culiar arrangement of the water
tubes, is shown in Fig. 27, It
consists of a vertical shell a, to
which a large number of radial
TYPES OF STEAM BOILERS 43
tubes b are attached, having their inner ends expanded in the tube
holes in the shell and their outer ends closed. The grates c sur-
round the cylinder near the bottom. The inner ends of the grate
bars rest on a ring d supported by brackets riveted to the shell,
and the outer ends rest on a plate on the brickwork enclosing the
ash-pit. The boiler rests on a circular cast-iron base c placed
on a masonry foundation. The boiler and furnace are enclosed
in brickwork that supports the chimney. The brickwork is
built up square to the height of the lower tubes and circular
above that point. The furnace brickwork is encased in sheets
of steel riveted to angle irons at the corners and reinforced by
angle and T bars riveted to the casing. An air space is provided
between the brick lining and the casing to decrease the radiation.
48. The top of the furnace wall, Fig. 27, supports a cir-
cular steel plate /, on which is built the brick setting above the
furnace. The circular brick setting is enclosed in sections of
sheet steel bolted together. The firebrick lining of the furnace
is built so as to slope inwards at the top and deflect the flame
against the standpipe of the boiler. The lower end of the stand-
pipe below the grates forms a settling chamber, or mud-drum.
It is fitted with a blow-off pipe g and a manhole h opposite one
of the ash-pit doors. The blow-off pipe enters the mud-drum
below the grate and terminates in a cone-shaped nozzle i. The
feed-pipe / enters the shell below the grate and extends verti-
cally nearly to the water-line k I in the boiler. It then passes
downwards and delivers the water through a spraying nozzle m
at the level of the grate.
49. The steam outlet is through a heavy nipple , Fig. 27,
screwed through the center of the top head of the steam drum,
A T on the outer end of the nipple provides openings for the
steam pipe o and a pipe p leading to the safety valve q, but this
arrangement is not to be recommended ; for, when the safety
valve blows, the rush of steam to the outlet may cause water
to be drawn along with the steam to the engine or turbine, and
may result in a wrecked cylinder or stripped turbine blades. It
is good practice to keep the steam outlet and the safety-valve
outlet separate and as far apart as possible, A handhole r is
44 TYPES OF STEAM BOILERS
located on the end of the pipe below the safety valve, which it
uncovered to afford ventilation to the interior of the boiler wher
It is necessary for a man to enter it. The nipple n terminates
at its lower end in a flange s, to which is bolted a blank flange t
at a distance of several inches. This blank flange closes the top
of a short length of large pipe u suspended from it.
50. A diaphragm plate v, Fig. 27, is attached to the lower
end of the pipe u and the shell of the boiler and closes the
annular space between them. From the central pipe u a large
number of small pipes w radiate horizontally and extend into the
boiler tubes nearly to their outer ends. The steam flows from
the central pipe through the small pipes into the boiler tubes,
and thence backwards into the top of the steam drum, whence
it passes out between the two flanges ^ and t. A drip pipe x is
suspended from the diaphragm and extends a short distance
below the water level in the boiler. Two firing doors y are
located at one side of the furnace, and several doors are con-
veniently located in the brick setting, so that an examination can
be made of the exterior of the boiler shell and tubes.
51. Wickes Water-Tube Boiler. Another form of ver-
tical water-tube boiler, known as the Wickes boiler, is shown in
Fig. 28. It consists of two cylindrical drums a and b joined
together by a number of long straight tubes r. The tubes are
separated by a baffle plate d of firebrick, passing through the
center of the tube nest, thus dividing the tubes into two banks.
The boiler drums are of the same diameter, but differ in height
and in the arrangement of the convex heads e. The upper, or
steam, drum a is closed at the bottom with a tube-sheet f. The
drum 6, which 'is the water drum and mud-drum, is much shorter
than the steam drum, and its top is closed by a tube-sheet g. At
the bottom of the mud-drum, a blow-off pipe connection is made
at h for the removal of mud and sediment. The arrangement of
the manholes i in both the upper and lower drums permits enter-
ing the boiler at its highest and lowest points for inspection, for
repairing of the tubes, and for cleaning purposes, as required in
the removal of scale from the drums and boiler tubes.
TYPES OF STEAM BOILERS
45
The feedwater enters the steam drum a through a pipe /
located at the back of the boiler, farthest from the furnace, and
flows directly down through the rear tubes, called downcomcrs,
to the water drum. The circulation is continued up the risers,
or tubes, in front of the baffle wall d. A baffle plate is arranged
FIG. 28
on a level with the water-line in the steam drum a, directly over
the risers. By it the water that rises with the circulation is
deflected to the section above the downcomers,' and thus par-
ticles of water are prevented from escaping with the steam that
passes out the main steam outlet k.
46 TYPES OF STEAM BOILERS
/'
'/ 52. The brick setting- around the boiler in Fig. 28 is inde-
pendent of the boiler installation. By this arrangement, the
J boiler is free to expand and contract without affecting the walls
i , of the setting. The brick wall is surrounded by a steel jacket m,
i and non-conducting material n, such as asbestos or magnesia, is
]' placed between the jacket m and the brick wall. The boiler is
I supported by brackets o that are riveted to the mud-drum and
f< that rest on a foundation placed under the boiler. Incorporated
ntf with the setting are the furnace and grates p, so arranged out-
,?' side of the boiler that the heat and flames have a long travel
')| around the boiler tubes. The flow of the heated gases is pro-
I duc ed by the draft of the chimney q. They flow around the
p; first bank of tubes in front of the baffle d, over the baffle, clown
I 1 about the downcomer tubes, through the breeching r, and to the
f stack - A double swinging damper j is installed in the breeching
$ between the stack and the boiler setting, to control the draft or
I flw of gases. A clean-out door t is placed back of the stack,
m the setting, so that entrance is made for cleaning, inspection'
and repairs to the stack connection. Boiler accessories, such as
the water column u, with the gauge glass v and the gauge-
cocks w, are attached to the steam drum a by the piping x. The
upper pipe x is in communication with the steam space above the
highest water-line and the lower is attached below the water level.
53. Cahall Boiler.-The Cahall boiler, shown in Fie 29
consists of a cylindrical mud-drum a and steam drum * which
are connected by nearly vertical tubes c that form a tube nest
havmg an open space in the center in the form of an inverted
The f ur SPa ? "? fnStaIled dfleCtin S P lates * or baffles,
i he furnace e Is placed to one side of the boiler, and the eases
o combust^ surround the tubes, being deflected by the'b -
fles d to a sweep nearly at right angles to the tubes They
fSarT ^f h ' T tral ^ in th StCam drum -
smokestack. The steam becomes slightly superheated in this
c S 1 ' th T h , C ming ^ C ntact ^ th the -f ce ofth
central passage, wbch is kept at a fairly high temperature by he
TSSS The , steam drum and mud - drum - c
an external circulating pipe / that enters the steam drum
FIG. 29
48 ' TYPES OF STEAM BOILERS
some distance below the water-line. The feedwater enters the
mud-drum and, becoming highly heated, rises through the ver-
tical tubes to the steam drum, where the steam bubbles are
liberated.
Some of the water in the lower part of the steam drum flows
continually into the circulating pipe, and since this pipe is not
exposed to the heat of the fire, the density of the water in it is
much greater than the density of the water in the vertical boiler
tubes. In consequence, the water is continually flowing clown-
wards and a rapid circulation is -promoted. The blow-off pipe g
is connected to the bottom of the mud-drum, and the blow-off
valve h is arranged on the outside of the boiler setting. The
water column i f the gauge-cocks /, and the water glass are
attached to the drum b for determining the water level. A
whistle k is incorporated with the water column, its purpose?
being to give an alarm when the water level falls too low in
the boiler.
MARINE BOILERS
CLASSIFICATION
54. Steam boilers for marine service are made in a great
variety of forms, but there are at least four well-defined types,
as follows: Scotch, locomotive, tubular, and water-tube boil-
ers. Each branch of marine service demands a boiler adapted
particularly to its requirements. For example, the Scotch
boiler is used in freighters and large, slow-moving passenger
steamships ; the locomotive and tubular types are used in small
vessels ; and the water-tube types are mainly used in high-speed
passenger, freight, and war vessels.
FIRE-TUBE MARINE BOILERS
55. Scotch Boilers. The Scotch boiler is distinctively a
marine boiler. It is of the fire-tube type and is internally fired,
the number of internal furnaces varying from one to four,
TYPES OF STEAM BOILERS 49
according to the size of the boiler ; but three is a very usual
number. The diameter of the furnace ranges from 24 to 48
inches. Boilers under 9 feet in diameter have one furnace ;
those from 9 to 13| feet in diameter have two; those from
13-J to 15 feet in diameter have three; and those beyond 15 feet
in diameter have four. Large furnaces are preferable as they
permit a greater inclination of the grates, thus assisting in the
efficient combustion of the fuel and producing better economy.
The thickness of the shell plates of the largest Scotch boilers
is 1J inches.
The simplest Scotch boiler is of the single-ended type, hav-
ing furnaces and tubes at one end only, and fired at only one
end. This type of boiler is made in sizes up to 18 feet in
diameter and 12 feet in length. In the early form, the furnaces
opened into one common combustion chamber, which made it
difficult to operate the boiler economically. In the present type,
each furnace and its combustion chamber are independent of
the other furnaces and their combustion chambers, with water
surrounding each section.
56. Single-Ended Scotch Boiler. An end view of a sin-
gle-ended Scotch boiler is shown in Fig. 30 and a longitudinal
section in Fig. 31. The boiler consists of a cylindrical shell a,
which is made in one or two sections, depending on the length
of the boiler. The furnaces b are corrugated and of the horse-
collar type, taking this name from the shape of the collar, or
flange connection, by which the furnace is riveted to the rear
tube plate c. Circular collars or flanges may be used, but the
advantage of the horse-collar type is that the furnace can be
removed through the circular opening in the front end in case
repairs are required. Each corrugated furnace opens into a
combustion chamber d, and the adjoining combustion chambers
are stayed together by screw stays e. A nest of fire-tubes /
extends from the front tube plate to the rear tube plate and the
tube ends are expanded in the tube holes and then beaded over.
The tubes ' g, of heavier metal, called stay tubes, are threaded
and screwed into the tube plates, thus forming stays that support
the tube plates.
(O) CO
OOOOOOOOOOO
oooooooooooo
oooooooooooo
oooooooooooo
ooooooooooooo
ooooooooooooo
ooooooooooooo
ooooooooooooo
ooooooooooooo
ooooooooooooo
ooooooooooooo
ooo ._ oooo
ooo
FIG. 30
FIG. 31
I LT459- 5
52
TYPES OF STEAM BOILERS
57. Owing to the size of
the boiler heads j they are
usually made in two or three
sections and riveted to-
gether. The flat sections of
the rear and front heads are
supported by large end-to-
end stays h, Figs. 30 and 31,
which are fitted with inside
and outside nuts and wash-
ers. The sides of the outer
combustion chambers are
stayed to the shell plate, and
the rear plates of these
chambers to the back head i.
The crown sheets / are sup-
ported by steel girder stays,
or crown bars, k. The man-
holes / give access to the
boiler for inspection and
cleaning the various boiler
parts. Furnace details, such
as the grate bars m and dead
plates n, are placed within
the corrugated flues b. It is
necessary to make the grates
long in order to provide the
necessary grate area. A
cast-iron plate o supports the
rear ends of the grate bars
and also carries the sectional
bridge wall p, which is
made up of a series of cast-
iron sections set side by side
across the furnace. Slots be-
tween adjacent sections ad-
mit air from, the ash-pit into
the current of gases passing
TYPES OF STEAM BOILERS S3
over the top of the bridge wall and thus improve the combustion.
Below the grates is the ash-pit q. The gases arising from the
combustion of the coal pass into the combustion chamber rf,
where they are more thoroughly mixed with air and consumed.
They then pass through the tubes to the breeching r. The mate-
rial used in the heads is flange steel of ductile quality, and the
tubes are made of the best charcoal iron or of seamless drawn
steel tubes, both of which under good operating conditions give
equally satisfactory results.
58. The Scotch boiler is supported by saddle plates s,
Fig. 30, details of their construction being shown in Fig. 32.
The lug a is of heavy steel, bent to shape and riveted to the shell ,
of the boiler. Each lug has a calking strip b, made of J-inch
plate, between it and the shell. Girders c are fastened to the
framing of the ship, and to these the lugs a are bolted, provision
being made at one end for freedom of movement to accommo-
date expansion and contraction. To promote economical opera-
tion, the bottom of the boiler is covered with lagging, made of
asbestos or magnesia, that prevents cooling by the circulation of
air along the bottom.
59. The diagrammatic views given in Fig. 33 (a) and (6)
show the direction of circulation of the water in the Scotch
boiler. The water directly above the tops of the furnaces a
becomes heated and rises among the tubes b as well as between
the nests of tubes. The cooler water above descends to take
the place of the water that rises, and it travels along the shell,
outside the outer nests of tubes, as well as between the rising
streams between the tube nests. The directions of these various
currents are indicated by the arrows.
At the bottom of the boiler, below the furnaces, as at c, the
movement of the water is very sluggish, because the water in
that space is not in contact with effective heating surface ; also,
there is some conflict between the rising and descending cur-
rents, to retard the circulation. As such inequality of tempera-
ture in different parts of a boiler sets up stresses in the plates
and seams, devices for creating circulation of the water are
sometimes used. One method is -to place a steam nozzle in the
= g.ooqpoo,goooooc5oo
I -jui...?ftu :::
TYPES OF STEAM BOILERS
55
water space near the bottom, and to use the escaping jet to
induce a rapid circulation of the water, thus keeping all parts
of the boiler at approximately the same temperature. The
incoming feedwater also tends to set up a circulation of water
in the boiler.
60. Double-Ended Scotch Boiler. The double-ended
Scotch boiler has furnaces at each end, and resembles two sin-
gle-ended boilers placed back to back. It is lighter, cheaper,
and occupies less space than two single-ended boilers. In
double-ended Scotch boilers the furnace flues at each end com-
FIG. 34
muhicate with a centrally located combustion chamber, from
which the products of combustion pass through fire-tubes, as
in Fig. 34, leading to two smoke flues, one on each end. Some-
times the boiler is so arranged that each opposite pair of fur-
nace flues opens into a common combustion chamber, as shown
in Fig. 35. In such a case, each combustion chamber will have
two nests of tubes, one nest connecting it with one head, the
other nest with the other head. The gases from two opposite
furnaces mix together in the common combustion chamber,
and then pass through the two nests of tubes, one-half to cue
smoke flue, the other half to the other.
56
TYPES OF STEAM BOILERS
61. On account of the high steam pressures used in mod-
ern marine engines, the marine boiler must be carefully designed
for strength. It is likewise necessary to reduce its weight and
size to the lowest possible limits. The following data relating
FIG. 35
to the boilers of a naval vessel will give an idea of the principal
dimensions of a Scotch marine boiler made of Siemens-Mar-
tin steel.
Diameter of shell ................................ 15 ft. 2 in,
Length of shell ............... ..................... 9 ft. 5 [ llt
Working pressure ........................... 135 Ib. per sq. in.
Thickness of shell plates ....................... '. . ..... IB j n ,
Thickness of heads ..................................... * j, j n
Number of furnace flues ................................ 4
Diameter of furnace flues ......... , ............... 3 ft. \ j llu
Thickness of furnace flues ..... ..... .............. ; i. ' m
ll| j^
Diameter of stayrods
Diameter of staybolts
Number of tubes
Diameter of tubes.
49Q
21 in
"
Length of tubes ............ . ....... .../..". '.",*." '.".'. "5" ft n
Heating surface ...... . ............................ 2,500 sq. ft
Weight without water .......................... about 40 tons
For the sake of safety, the Scotch type of boiler must be
made extremely heavy and bulky when high steam pressures
TYPES OF STEAM BOILERS 57
are used, and much attention is being paid to devising a type
of boiler that, while retaining the good features of the Scotch
type, will be lighter, smaller, and cheaper for the same power.
62. Advantages of Scotch Boiler. The Scotch boiler is
durable under rough usage, and is easy to operate and repair.
The tubes are straight and standard in size, making it possible
to obtain new tubes in almost any seaport. Leaky tubes can
be plugged without reducing pressure on the boiler. As the
tubes are straight, they are accessible for cleaning and repairing
without removing boiler connections. The number of pounds
of water evaporated per pound of fuel burned has proved
satisfactory. It is internally fired and therefore eliminates
the air leakage that arises in built-up settings. The disad-
vantages of this type are: excessive weight, poor circulation in
the body of water below the effective heating surfaces; loss of
time in starting boilers for operation ; and time required to
blow off and cool the boiler down for repairs.
GUNBOAT
63. Locomotive Type for Marine Purposes. In some gun-
boats and other small naval vessels, there is not sufficient room
under the decks for the large Scotch boilers, and the type of
boiler shown in Fig. 36, resembling the locomotive boiler, is
frequently used. It is a plain cylindrical boiler with two rec-
tangular fireboxes a (only one of which is shown), each con-
nected by a nest of fire-tubes b to the rear boiler head. The
furnaces are large, so as to leave sufficient space for combustion
over the fires. Handholes c and d are located in the front head ;
and on top of the shell, near the rear end, is a manhole c that
affords ready access to the interior of the boiler for inspection,
cleaning, or repairs.
64. Tubular Type. A modification of the Scotch boiler,
made for the purpose of providing a boiler of small diameter
that can be placed where headroom is very limited, is the gun-
boat boiler shown in Fig. 37. The peculiarity of this boiler is
that the tubes, instead of being placed above and around the
1J
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58
TYPES OF STEAM BOILERS
59
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furnace flues, are placed in
in the rear and in line with
them. By this arrangement
of the parts, the boiler is
greatly reduced in diameter,
but its length is doubled.
The reduced diameter en-
ables the shell to be made of
thinner plates. This boiler
consists of a cylindrical
shell a with flat heads h.
T ti e corrugated furnace
flues c are similar to those
used in the ordinary Scotch
boiler, and, as usual, con-
tain the grates.
65. The combustion
chamber d, Fig. 37, is made
twice the depth of the com-
bustion chamber of a Scotch
boiler of the same capacity,
to compensate for its re-
duced height. The tubes e
extend from the rear wall
of the combustion chamber
to the rear head of the
boiler. The uptake or
smokebox (not shown in the
illustration) leading to the
smokestack is attached to
the rear head of the boiler.
The combustion chamber is
provided with the vertical
tapering tubes /. These
connect the upper and lower
parts of the water space,
promote circulation, add
60 TYPES OF STEAM BOILERS
considerably to the heating surface, and assist in staying and
strengthening the flat top of the combustion chamber. They
are made tapering to enable the flange at the lower or smaller
end of the tube to be passed through the opening in the top
sheet of the combustion chamber while the boiler is under con-
struction. The tapering form, with the large end uppermost,
also facilitates the release and discharge of, the steam that is
generated within the tubes, which are called Galloway tubes.
66. The heads of the boiler in Fig. 37 are braced by the
tubes e, the furnace flues c, the longitudinal braces g, and the
diagonal braces, or palm stays, h. The palm stays are made of
round bar iron or steel forged with flat ends. In some cases,
they have palms i at the ends, which are riveted to the shell
and the head of the boiler ; in other cases, they have a palm at
one end only and are threaded at the other end. When they are
made m this way, the palm end is riveted to the shell of the
boiler and the threaded end passes through the head, with a nut
on each side of the plate, as shown at /. The flat top of the
combustion chamber is braced by the sling stays k. The sides
and bottom of the combustion chamber are secured to the shell
of the boiler by the staybolts /. The Clyde, or dry-back, boiler
described in a preceding article is another boiler of the tubular
type employed on small vessels.
WATER-TUBE MARINE BOILERS
67. Types of Water-Tube Marine Boilers. The water-
tube boilers in marine service resemble the water-tube boilers
already described and possess the same advantages and dis-
advantages. Boilers of this type are classified as small-tube
and large-tube; horizontal, vertical, and inclined; and as hav-
ing straight tubes or bent tubes. The general custom is to des-
ignate marine water-tube boilers as either large-tube boilers or
express boilers. Large-tube boilers, considered suitable for big
ships, have tubes If inches or larger in diameter. Practically
all boilers of this type have straight tubes. Express boilers
are made of small tubes,, from 1 to If inches in diameter
TYPES OF STEAM BOILERS 61
These are closely spaced so as to obtain a high ratio of steam
production to weight of boiler., which is necessary in small ves-
sels of high speed, such as destroyers and torpedo boats. The
tubes in this type may be straight or curved.
68. Features of Large-Tube and Small-Tube Boilers.
Each of these types has its advantages and disadvantages, and
it is a question as to which is the better. Large tubes require
fewer joints for a given amount of heating surface,, and they
may be made thicker without decreasing materially their inter-
nal diameter. They contain a larger body of water than small
tubes and so are not so liable to have all the water in them sud-
denly converted into steam under extreme forcing conditions,
and thus leave the tubes exposed to overheating, as might occur
in small tubes. Small-tube boilers generate steam more rap-
idly, and in case a tube is ruptured, less damage is likely to
result than if a large tube should burst. Should it be necessary
to plug a small tube, less heating surface will be made inef-
fective than in the case of the large tube.
69. Tube Arrangements. Tubes in water-tube boilers are
placed at all possible angles, from horizontal to vertical posi-
tions. The efficiency of the boiler and the ease of repairing
and cleaning the tubes depend on the arrangement of the tubes.
Horizontal tubes are liable to produce foaming, as the steam
and water are delivered spasmodically, or in spurts, from both
ends of the tubes when the boiler is forced. This condition
may leave the tubes unprotected for a time and lead to over-
heating of the tubes. Scale and soot gather very readily on
horizontal tubes, more so than on those that are vertical or are
inclined at a considerable angle. Water does not circulate as
freely through horizontal tubes as through inclined or vertical
tubes, as the tendency of the heated water, and steam to rise
is resisted by the horizontal position and the small area of the
tubes. As a result, the water and steam flow spasmodically.
Boilers having straight tubes properly arranged possess the
advantage of being easily cleaned. Scaling tools can be passed
through the tubes to remove the scale. Straight tubes can also
be removed and replaced more readily than bent tubes. In
62 TYPES OF STEAM BOILERS
some bent-tube boilers it is necessary to remove sound tubes
in order to replace a tube in one of the inner rows. Bent
tubes permit a design that makes a lighter and more compact
boiler than straight-tube types ; hence, they are used for express
boilers. Moreover, bent tubes are less liable than straight tubes
to injury from expansion and contraction due to the severe
operating conditions to which boilers of this type are subjected.
70. Belleville Water-Tube Boiler. One form of large-
tube boiler, known as the Belleville boiler, is shown in Fig. 38.
It consists of a number of nearly horizontal tiers of water
tubes a, screwed or expanded at each end into return bends b,
making a series of zigzag inclined tubes, beginning at the top
of the furnace door and ending at the steam drum c f which is
located above the tubes. There is a handhole in each of the
front bends or connecting boxes b. The mud-drum d stands
vertically, and is located in front of the boiler and below the
lowest tubes. The top of the mud-drum is connected to the
bottom of the steam drum by a vertical pipe e. From the side
of the mud-drum, a rectangular feedpipe / extends across the
front of the boiler, joining each vertical tier of water tubes a.
The mud-drum blow-off is at the center of the lower head.
71. The Belleville boiler is enclosed in a steel casing, as
shown in Fig. 38. The fire-box is arranged below the tubes
and runs their full length; the grate bars g slope downwards
toward the rear. The products of combustion pass upwards
between the tubes, thence about a superheater, and out near
the top of the casing, as indicated by the arrows. Baffle
plates I of steel or tile are fitted in the nest of tubes to deflect
the hot gases, in order that the entire surface of the tubes may
receive the benefit of the heat. The feedwater enters at one
end of the steam drum and flows into a shallow pan h, then
downwards through the external circulating pipe e to the'mud-
drum, and into the rectangular feedpipe /; thence it continues
through the steam coils to the steam drum. The outlets of
the water tubes in the steam drum are several inches above
the bottom of the drum, so that the steam will not mingle
with the comparatively cool water in the drum.
64 TYPES OF STEAM BOILERS
72. The water passes into the mud-drum of the Belleville
boiler through a non-return valve, and then to the bottom and
up around a vertical baffle plate. The bottom of the dram
forms a settling chamber, into which much of the sediment is
deposited. The non-return valve keeps the water circulating
in the same direction through the water tubes even when the
ship is rolling. It also regulates the direction of flow when
steam is being raised. The casing of the boiler is made of
steel plates riveted together. Angle irons are used at the joints
for stiffeners. The upper part of the casing is lined with mag-
nesia and asbestos, and the "lower part next to the lire with
firebrick.
This kind of boiler has very little water capacity, and hence
it is usually fitted with an automatic feeclwater regulator. In
operation, it requires very close attention. There is "a strong
upward flow of steam and hot water as they pass from the
tubes into the steam drum. The pan h, Fig. 38, and its curved
cover / serve as a deflector over the openings of the tubes to pre-
vent the water from being carried out through the steam nozzle k
on the top of the drum.
73. Babcock and Wilcox Marine Boiler. The Babcook
and Wilcox boiler of the mixed-tube type, built for either coal
or oil burning, is one that meets the requirements of the British
Admiralty, and is largely used in the United States in a variety
of vessels. The dry weight of this boiler is much less than that
of the Scotch boiler, averaging less than 20 pounds per square
foot of heating -surf ace as compared with 40 to 50 pounds per
square foot for the Scotch boiler. The weight of water within
the boiler ranges from 3 to 5 pounds per square foot of heating
surface as compared with 17 to 20 in the Scotch type ; hence,
the space occupied by the Babcock and Wilcox marine boiler is
considerably less than that occupied by the Scotch boiler of
equal power.
, The general features of construction, shown in Fig. 39 (a)
and (6), are similar to those of the land boiler. The cross-
drum a is placed at the front and is connected to the tube head-
ers b by circulating tubes c. Each section of the front header b
66 TYPES OF STEAM BOILERS
is connected to the mud-drum d, by a short nipple c. At each
end of the steam and water drum a is a manhole /. Directly
over the furnace, in oil-burning- boilers, the lower tubes g are
inclined at an angle of 18 with the horizontal, while those above
are inclined 15 with the horizontal. This difference in inclina-
tion leaves a space at the front of the boiler for the brick or
tile baffle plate h.
74. As the tubes of the boiler in Fig. 39 are straight and
accessible from each end, they are easily inspected and repaired.
Handhole plates i are placed in the outside sheet of each tube
header and opposite the tube openings. The circulation in the
boiler is rapid and the steam produced is remarkably dry. Feed-
water enters the drum a, descends through the front header,
passes into the tubes, flows up through the -back tube header,
and through the horizontal tubes c into the steam and water
drum a, striking the baffle plate /. The downcomers k also
assist in promoting the circulation. These pipes connect the
drum a and the mud-drum d. Mud and sediment are blown off
through a blow-off valve and piping attached to the mucl-clrum.
Handhole plates are fitted to each end of the mud-drum for
cleaning and inspection purposes. The boiler furnace is
encased in firebrick I and backed with a steel casing m, rein-
forced with angle irons . The back tube header b is usually
not covered, as boilers are usually set back to back, with a cas-
ing common to both, thus economizing room. Separate stack
connections are made by installing uptakes leading from each
boiler to the stack. Baffles o cause the gases to flow three times
at right angles to the tubes. The boiler fittings, such as the
steam gauge, water column, etc., are not shown. The devices p
are oil-burning apparatus.
75. Babcock and Wilcox Box-Type Marine Boiler. The
distinctive feature in the construction of the Babcock and Wil-
cox box-type marine boiler, shown in Fig. 40 (a) and (6), is
the arrangement of the steel headers a and 6. They take the
place of drums usually fitted in what is known as the A type of
marine boiler, and are either of straight box form or of corru-
gated form: They run crosswise, as shown at a, or longitu-
67
I L T 459-^6
68 TYPES OF STEAM BOILERS
dinally, as shown at b. Each header opposite a bank of tubes
is so fitted with handhole plates c that examination, cleaning,
and repair of the tubes may be made without interfering with
other tubes. The view (a) is a conventional view of the boiler.
The sectional drawing to the right of the vertical center line
illustrates the interior arrangement of the combustion chamber
and its side walls d and grates e. The tubes / are straight,
except the end sections that join to the drum g, which are curved
in order to have the tubes enter the drum at right angles to the
contour of the shell. The view to the left of the center line
indicates the details of the boiler covering, showing the steel
casing h, fire-door i, and ash-pit door /. A lengthwise sectional
elevation of the boiler is shown in view (6). Baffling of the
gases is obtained by the use of baffle plates that are placed
between the tubes and parallel to them.
76. Babcock and Wilcox Drum-Type Boiler. In the Bab-
cock and Wilcox cross-drum water-tube boiler, shown in
Fig. 41 (a) and (b), the arrangement of the water drum a
and steam drum b is such that the boiler is fired from the
water-drum side. This type is an efficient design and can be
operated with oil or coal as fuel. The water drum a is made
in two sections ; the lower section is semicircular and the upper
part is made of heavier metal and is bent to a larger radius
except at the corners, where the joint is made. This shape of
the upper section permits a better arrangement and a larger
number of tubes c in the boiler than would be possible if the
section were made semicircular. At each end of the drums
a and b is fitted an elliptical manhole plate d. The tubes c are
bent at both ends, so that they will fit properly into the drum
shells and have a good seat in the boiler plate. The bent sec-
tions have the advantage of yielding uniformly with the stresses
set up by expansion and contraction. The gases are directed by
baffles e, which are set perpendicular to the tubes, this arrange-
ment causing the gases to make three passes around the tubes
before they reach the smoke breeching f, which is brought for-
wards over the water drum a. The boiler setting g is arranged
for oil burning, the oil burners being located at suitable open-
TYPES OF STEAM BOILERS 71
ings in the boiler front, shown at h. The outer casing of the
boiler is composed of an inner and an outer steel jacket, as
shown at i, between which non-conducting material / is placed,
such as asbestos, magnesia, and other mineral substances.
Doors k are placed in the boiler casing in line with the tubes
for boiler inspection and cleaning purposes. The duct / at
the back of the boiler is for the purpose of admitting additional
air to the furnace as needed for the combustion of fuel oil.
77. Thornycroft Water-Tube Boiler. In Fig. 42 is shown
the Daring type of Thornycroft boiler, a small boiler much used
on boats of very high speed. It consists of a large horizontal
steam drum a at the top, connected by a series of bent tubes b
to a small central drum c located at the bottom, between the fur-
naces. There are also two smaller drums d, at the outside edges
of the grates. These side drums are connected by rows of bent
tubes e to the steam drum a, and by nearly horizontal pipe / to
the lower central drum. There is a grate on each side of the
central drum, and the products of combustion pass upwards
between the tubes to the flue g at the front of the boiler. Inside
the casing and near the front of the boiler are several large
downcomers h, h', joining the steam drum a to the lower water
drum c. The feedwater enters the steam drum and descends
through the vertical downcomer h to the lower drum, a portion
passing to the small side drums d, thence up through the bent
tubes b and e, where the mingled steam and water is delivered
against a baffle plate i inside the upper drum.
The boiler setting is made of sheet-steel casing, lined with
non-conducting material. Numerous doors are provided in the
casing for cleaning and repairing the boiler. This type of boiler
has been very highly developed and has proved very successful
in torpedo-boat and , torpedo-boat-destroyer ' service. Like all
water-tube boilers, it holds very little water and is sensitive to
slight changes in the condition of the fire.
78. Thornycroft-Schulz Water-Tube Boiler. The Thorny-
croft-Schulz boiler, shown in Fig. 43, is a modification of the
Daring boiler. It is superior to the latter in that it is more effi-
cient in fuel consumption and evaporation. The main steam and
72 TYPES OF STEAM BOILERS
water drum a is connected to three lower drums. The bent
tubes b connect the two outer drums c with the drum a, and the
tubes are numerous, thus giving a large effective heating surface.
The central drum d is connected to the drum a by bent tubes r
and straight tubes / that form downcomers. Large clowncom-
ers g also connect the drums a and c, and assist very much in
promoting rapid water and steam circulation. All of the tubes e
and the downcomers / and ,g discharge into the steam drum
below the water level, but only a few of the tubes b do this. As
shown in view (a), most of the tubes b discharge directly into
the steam space of the drum a. The tubes are formed to a large
curvature and are therefore less liable to be damaged by expan-
sion and contraction. The gases travel from the furnace in
FIG. 43
the direction of the arrow and finally pass o\it through the
breeching h. Baffle plates are installed between the tubes to
cause the gases to travel as shown.
79. Modified Thornycroft Boiler With Superheater. The
distinctive feature of the modified Thornycroft boiler shown in
Fig. 44 is the tube arrangement. View (a), to the left of the
vertical center line, shows the interior of the boiler. The
arrangement of the boiler front, superheater, and smoke breech-
ing is illustrated to the right of the vertical center line. A rear
view of the boiler is given in (6). The boiler is composed of
an upper drum a and lower drums b, connected by the circulat-
ing tubes c. These tubes are straight, to the point where they
ysrcrew^
74 TYPES OF STEAM BOILERS
join the lower drums b, at which point they are curved so as to
fit properly into the holes in the drum. The outer rows of
tubes c' are bent to a. larger curvature and are used to baffle the
gases as well as to increase the boiler heating surface. All of
the tubes c and <f discharge into the water space of the upper
drum.
80. The superheater drums d, Fig. 44, are placed outside
of the boiler front, parallel with the boiler tubes. The sec-
tional view, taken on the line x x, illustrates thfe U formation of
the superheater coils or tubes e, and shows how the ends are set
into the drum d of the superheater. The coils e are set directly
on each tube bank, and are so connected to the steam drum d
that the steam is drawn from the drum and circulated through
the superheater coils. As the coils are directly in the path of
the hot gases, the temperature of the steam is greatly increased.
To convey the steam from the drum and superheater, suitable
piping and pipe flanges must be installed. In view (c) bent
pipes / are shown connecting the steam space of the drum a
and the flanges g of the superheaters ; also, bent pipes h connect
the main steam piping i with the steam outlets / of the super-
heaters. This arrangement of the superheater coils and pipe
connections with large bends makes the installation flexible, so
that the pipes and bends give readily with the expansion and
contraction stresses arising in the operation of the boiler. The
superheater outlet into the main steam pipe is fitted with a
safety valve. View (a) shows a sectional view of the super-
heater tubes with the drum removed, and the full front view to
the right of the center line indicates the position of the super-
heater drum, with the pipe flanges / and g riveted thereto.
81. For the purpose of cleaning- the steam ancl water
drums, manholes .4, Fig. 44, are provided in the heads of the
drums. These openings also give access to the boiler for inspec-
tion and repairs. The furnace is built for burning fuel oil and
is lined with firebrick I Oil-burning equipment, such as the
oil piping and the burner nozzles m, is arranged at the front of
the boiler. The boiler casing n is made of two thicknesses of
sheet steel, with asbestos or some other non-conductor between
TYPES OF STEAM BOILERS
75
Angle-iron stiffeners o give additional strength and stiffness to
the casing. The smoke breeching p is placed at the rear of the
boiler. Suitable clean-out doors q are provided in the casing
for cleaning and inspection of the boiler parts.
82. Yarrow Water-Tube Boiler. Another form of small-
tube boiler, known as the Yarrow boiler, used in torpedo-boat
service, is shown in Fig. 45. It consists of a large steam drum a,
FIG. 45
with two smaller semicylindrical drums b below it and joined to
it by inclined tubes c. The arrangement forms a triangle, with
the grate d for the base. The lower drums have removable
covers e for cleaning. The feedwater enters the steam drum
below the water-line and descends through the inclined tubes
most remote from the fire into the lower drum, deposits sedi-
ment, and rises through the tubes nearest the fire. The products
76 TYPES OF STEAM BOILERS
of combustion pass between the tubes to the smokestack f at the
rear of the boiler. The boiler casing g is of iron and steel lined
with non-conducting material. There is also an external cas-
ing h so arranged that before entering the furnace the air for
supporting combustion enters the opening i and flows between
the casings g and h. This aids materially in keeping down the
temperature of the boiler room by preventing the radiation of
heat.
83. Yarrow Water-Tube Boiler With Superheater. A
recent development of the Yarrow boiler adopted by the Brit-
ish Admiralty, is illustrated in the sectional view (a) and the
side view (&), Fig. 46. It is installed with a superheater, and
except for the lower drum construction, which is cylindrical in
form, and the tube arrangement, it resembles the type just
described. It is used for small speedy war vessels and large
battleships and cruisers. The water, or generating, tubes a are
straight, except the bottom row nearest the lire, which are bent.
The tubes connect the water drums 6 and c to the steam and
water drum d. As the water drums b and r are circular, the
upper plate section e must be made heavier so that the tubes will
have sufficient bearing area to insure steam-tight connections,
and also to give the required strength to the tube-plate sections!
The superheater drums / and g are also cylindrical and run
parallel with the water drums b and c. The superheater tubes h
are bent to a shape and their ends are expanded into the super-
heater drums. To do this work to the best advantage, handhole
plates i are installed opposite the superheater-tube openings, and
through them the tubes are expanded. A downcomer / connects
the drum / of the superheater with the steam pipe k inside the
steam space of the boiler. Steam is drawn through the pipe k
and the downcomer and circulates through the drum / and the
tube sections of the superheater to the drum g t which is con-
nected with the main steam stop-valve /. An auxiliary steam
pipe m is also arranged in the steam space of the steam drum
to which is also fitted an auxiliary steam stop-valve n The
auxiliary steam feed piping and valve are used in case it is
necessary to cut out the superheater for repairs.
TYPES OF STEAM BOILERS 77
#4. Feeclwater enters the steam drum d, Fig. 46, through
a perforated pipe o, or an auxiliary feed-pipe p. The arrange-
ment of this piping is shown in the sectional view (a), and
in view (&) is shown how far the perforated pipes extend into
the drum. Feed check-valves are arranged in the feed piping
as shown at q to prevent the f eedwater from returning from the
boiler into the feed piping. A gauge glass is placed at r and a
scum blow-off valve at ,9 with internal piping t. The scum blow-
off is used to remove oil and other matter that collects on the
surface of the water. At the bottom of the water drums is a
blow-off valve u, connected to suitable piping, for the removal of
mud and other sediment that collect in the water drums. Double
safety valves v are connected to a flange riveted to the steam
drum. One of the valves is set to blow at a slightly higher pres-
sure than the other, so that, in case the first valve should not
blow off and relieve the rising pressure within the boiler, the
auxiliary valve will then blow and prevent an excess of steam
pressure. Attached to the water drums and steam drum are
zinc slabs arranged in trays w and supported by hangers that
are riveted to the drums. The zinc offsets corrosion due to the
galvanic action that arises in the boiler. The corroding elements
attack the zinc plates instead of the boiler plates. Air and drain
valves x are attached to the superheater drums, to relieve them
of air or water of condensation that collects when the boiler is
not in operation. In starting the boiler to meet sudden emer-
gencies, these valves are opened, which allows the air and water
to escape, and the steam circulates more freely in the superheat-
ing tubes.
85. The furnace of the boiler in Fig. 46 is constructed for
burning fuel oil, and is lined with a special grade of firebrick
that withstands very high temperatures. The baffle plates y
cause the flame and products of combustion to circulate freely
about the generating tubes and superheater before reaching the
uptake or breeching z. The division plate </ separates the
uptake into two parts and prevents the formation of eddies or
back currents due to the meeting at this point of the gases from
each side of the boiler. The funnel V is directly attached to the
78 TYPES OF STEAM BOILERS
breeching, and where there are a number of boilers set in a bat-
tery, the breeching is made so that it receives the gases from
all the boilers in the battery. This breeching connects directly
with the stack. Fuel-oil burners c f are installed at the front of
the boiler. Attached to the water drums are boiler supports d* \
shaped to fit the contour or outline of the drum shell and made
with flat bases for bolting down. The boiler is covered with a
steel jacket composed of two steel plates, with asbestos between,
and stiffened by angle irons. The exposed parts of the drums
are covered with non-conducting material, commonly called lag-
ging. The bottom of the furnace is composed of firebrick laid
on steel plates e f , called a pan. A layer of asbestos is placed
between this plate and the bottom steel plate /'.
86. Normand Water-Tube Boiler. The Normand boiler,
shown in Fig. 47 (a) and (6), is considered one of the most
efficient small-tube boilers. It is largely used in small war ves-
sels of the speedy type by France and to some extent by the
United States. The dry, or empty, weight of the boiler, as
fitted for oil burning, with steam and water accessories, but not
including the uptake and stack connections, is approximately 1 1
pounds per square foot of heating surface. The weight of
water under steaming conditions is about 2 pounds per square
foot of heating surface. The boiler is of the A type, having a
main steam and water drum a and water drums 6 connected by
generating tubes c and a downcomer e. These tubes are small
in diameter and bent so as to form an arch-shaped nest of tubes
above the furnace. To the drum a is riveted a steam dome d.
Ihe steam m passing to the steam dome strikes the baffle plate e
which aids in preventing the very moist steam from entering
sTh
stays / The feedwater enters the drum a through the valve
connections g and piping /.
87. A scum blow-off pan h, Fig. 47, is located at the ri
80
TYPES OF STEAM BOILERS 81
readily determined. A manhole opening / is formed in the shell
of the drum a and is so shaped that the flanged section around
the manhole opening adds strength to and supports the shell
plate of the drum. Manholes are also installed in the water
drums b. The furnace is lined with firebrick m and the boiler
tubes are baffled at n so that the gases pass entirely around the
tubes and drum before entering the uptake o. Oil-burning
apparatus p is arranged conveniently at the front of the boiler
furnace. Clean-out doors r are installed in the boiler front for
the removal of soot. The casing .$ is made of two steel plates,
between which asbestos or other non-conducting material is
placed. Angle-iron stiff eners t are used to give the necessary
strength to the casing.
88. White-Forster Water-Tube Boiler. The White-For~
ster boiler, shown in Fig. 48 (a) and (6), is also of the small-
tube type. The generating tubes, or water tubes, a are all 1 inch
in diameter, outside, and have a thickness of .104 inch. The
downcomers b are 4 J inches in diameter, outside, and have a
thickness of .212 inch. The generating tubes a are bent and
connect the steam and water drum c with the water drums d.
The forward drum heads are fitted with manholes e, thus giving
access to the drums for cleaning and repairs, The tubes are
curved alike, as shown in the side view (&), and their arrange-
ment and curvature are such that any tube or number of tubes
can be readily removed through the manhole opening e in the
steam drum c without affecting adjoining tubes. The tube holes
in the drum c are larger than those in the drums d, to facilitate
the work of installing tubes. As the tubes are curved when
viewed from either the side or the front, stresses are not likely
to affect the tubes by reason of expansion or contraction. The
boiler furnace and casing are similar to those previously
described, but there is no baffling of the gases. The boiler
shown is arranged for oil burning. This type of boiler produces
rapid evaporation of water without forcing the fires.
82 TYPES OF STEAM BOILERS
LOCOMOTIVE BOILERS
89. Classes of Locomotive Boilers. The locomotive type
of boiler is used to the exclusion of all other types in railroad
work. It is made in three general forms, known as the straight-
top boiler, the extended wagon-top boiler, and the conical boiler.
Any one of these forms may have either a Belpaire firebox or
a wide firebox.
90. Straight-Top Boiler With Wide Firebox. In Fiff. 49
is shown the straight-top locomotive boiler with wide firebox.
The general construction is similar to the other types of loco-
motive boilers. The shell courses a are of uniform diameter,
and as the courses are straight instead of tapering, the boiler is
designated as a straight-top boiler. The firebox is known as
the wide firebox on account of its shape, being shallow and
extending beyond the driving wheels of the locomotive at the
sides. A boiler of this shape, designed for burning anthracite,
is known as the Woolen firebox. In some of the designs the
roof sheet b slopes toward the back head c instead of being
straight, as illustrated. The bottom of the shell course adjoin-
ing the firebox is also made tapering in some designs, to furnish
more water space around the tubes: and the forward end of the
firebox. The back head c, throat sheet d, and door sheet c are
flanged so as to fit the firebox side sheets properly, The door
ring / is riveted to the flanges of the door openings in the back
head and door sheet. The crown sheet g slopes toward the door
sheet, to which it is riveted. Crown stays support the roof and
crown sheet against internal pressure and the stays h support
the flat surfaces of the side sheets and the heads of the firebox,
TTQ had is als su PP rt ed V diagonal stays *,
Fig. 49 which are attached to T-iron braces / that are riveted to
the back head. A number of washout holes * are arranged in
convenient places in the outer sheets of the firebox for the pur-
pose of cleaning the crown sheet and removing mud and other
'
e k of the mu
at the back-head and throat-sheet ends are used to attach
TYPES OF STEAM BOILERS
83
the ash-pan installed below the
fire-box. A ring m at the front
of the smokebox permits the
attaching of the smokebox
front. Gusset plates n are riv-
eted to the bottom of the shell
courses and used for bolting the
boiler to the engine frame. The
shell-plate opening o for the
dome is reinforced by a steel-
plate ring p f called a dome
stiffening rwg, which ring adds
strength to the plate around the
dome opening,
92. Extended Wagon-Top
Boiler With Belpaire Firebox.
The extended wagon-top boiler
with a Belpaire firebox is shown
in Fig. SO. The barrel section
of the shell is made up of three
sections a, b, and c t called
courses, riveted together by cir-
cumferential seams d. The
course a, next to the firebox, is
cylindrical and is called the
dome course. The course b is
the taper course, as it is tapered
so as to join the cylindrical
courses a and c, which are not
of the same diameter. The
course c is commonly called the
first course, and to the front of
it is riveted the smokebox e.
Id the earlier designs, the taper
course b extended to the firebox,
and from this arrangement it
was known as a wagon-top
I L T 4597
84 TYPES OF STEAM BOILERS
boiler, its name being taken from the shape of the tapering top
section of the course b. The dome in the wagon-top type was
placed on the top of the firebox and required sj>eeial staving.
The use of the cylindrical shell' a next to the firebox, and the
setting of the taper course forward, permitted the dome to be
installed on the cylindrical shell, in front of the firebox. To
distinguish this arrangement of shell courses from the earlier
, wagon-top boilers, the type illustrated is called the extended
wagon-top boiler.
93. The firebox shown in Fig. SO is known as the Bdpaire
. firebox. The top sheet f, called the roof sheet, and the crown
sheet f are made flat, or with a slight curvature. The cor-
ners g of the crown sheet are bent to a slight radius, and suffi-
cient material is allowed to form a lap joint, connecting the
inside firebox side sheets h and the crown sheet. The roof-
sheet corners g / are rolled to a larger ' radius and with depend-
ing sides that butt against the outer side sheets h'. By the use
of cover-plates i and , commonly called welt straps or butt
straps, the joint is riveted, forming a butt joint. The inner and
outer sheets of the firebox ran practically parallel and their flat
surfaces are supported by straight stays /. Transverse stays or
cross-stays /' support the flat surfaces between the roof -sheet
corners and the outer side sheets.
94. The door end of the inside firebox, Fig. SO, is closed
with a flanged head k, called. a door sheet, that has a flanged
opening turned near the center of the head for the door connec-
tion. The outside head V, called the back head, is riveted to the
outside side sheets. It is also flanged for the door opening so
that when the two flanged heads are relatively arranged and riv-
eted to the firebox, the flanges of the back head and the door
sheet overlap to form a riveted connection called the door ring
The flat surface of the back head above the plane of the crown
sheet is braced by T irons /. A flanged sheet m } called the throat
sheet, connects the outside sheets of the firebox to the bottom
of the shell a. The throat sheet is made in different shapes,
depentog on the form of the firebox. Usually it is flanged so
that it fits around approximately one-half of the shell For the
I L T 4592173
- r iWflJJJgf
!!
<&;/; : . / -Kr^->/->8-\ c
i i
I
TYPES OF. STEAM BOILERS 85
installation of the tubes n and flues n f , a firebox tube-sheet o
and a front tube-sheet o f are drilled for the required number and
diameter of tubes and stays. The tubes and flues extend from
the firebox tube-sheet to the front tube-sheet. The tubes are
2 or 2;j inches in diameter and the flues from 5| to 5^ inches in
diameter. The superheater tubes are placed inside the flues
and extend from the smokebox to the firebox tube-sheet. The
flat section of the firebox tube-sheet o is supported by stays p
called belly t or throat, stays and the segment of the front tube-
sheet (/ above the tubes is supported by gusset stays or diagonal
braces q.
915. In the firebox, Fig. 50, bent tubes r, called arch tubes,
extend from the firebox tube-sheet to the back head. The ends
of the tubes terminate in the water space so that water will
circulate freely in the tubes. The tubes form a support for a
firebrick arch s that causes the fuel gases to mix with the air
more thoroughly, thus inducing a more complete combustion of
the gases before they strike the tubes. It also prevents cold-
air blasts, which enter through the fire-door during the period
of firing, from striking directly into the boiler tubes, and thus
reduces the stresses that otherwise would arise from the con-
traction of the boiler plates. The bottom of the firebox is closed
with a wrought-iron ring t, called the mud-ring.
90. The gases of combustion pass directly from the fur-
nace, Fig. 50, through the tubes and flues to the smokebox e f and
out of the stack opening u. In locomotives, a strong draft is
produced by allowing the exhaust steam from the engine to dis-
charge through the smokestack. The exhaust nozzle is placed
below the stack entering through the opening v. The escaping
steam from the nozzle carries with it the air and gases in the
smokebox, drawing the gases from the furnace and thus increas-
ing the draft in the furnace and tubes.
97. Conical Boiler With Jacobs-Shupert Firebox. The
conical boiler, Fig, 51, is of similar construction to those already
described. It is made up of a cylindrical course a, of uniform
diameter, attached next to the firebox. A taper course b having
a uniform taper is employed to connect the shell course a with
86 TYPES OF STEAM BOILERS
the first shell course c. From this arrangement of the shell
courses, the term conical boiler has been given to designate the
boiler.
The Jacobs-Shupert firebox shown in the illustration is a
patented sectional firebox having the inner and outer sides and
top made up of a series of bent channel shapes d with depending
flanges. Between the channels and riveted thereto are stay
sheets e. By the use of this construction, no additional staving
of the side sheets is required. To permit circulation of the
steam and water between the channels, openings / are cut in
the stay sheets e. The door sheet g, back head h, tube-sheet **,
and throat sheet ; are flanged so as to fit the upright flanges of
the channels, to which they are riveted, as shown. The bottom
edges of these sheets are straight and are riveted to the mud-
ring k. The back head and door sheet are stayed together with
the screw stays /, and the upper section of the back head, which
is a flat plate, is supported by the diagonal stays in. The stay
plates e are cut out so as to allow the diagonal stays to extend
from the roof of the firebox to the back head. Sling stays n
are used to stay the sections of the channel plate, left weakened
by the removal of the solid plate sections of the sheets. Wash-
out plugs o are installed above the mud-ring and in the outside
channel sections in line with the crown sheet of the inside fire-
box plates.
98. The tubes of locomotive boilers range from 6 to 22
feet in length, and may be made of steel or iron. The tubes of
stationary boilers of this type are usually 3 to 3| inches in diam-
eter. The tubes of stationary locomotive boilers are not spaced
as closely as in locomotive boilers of the railroad type With
the smaller diameter and larger number of tubes, steam is gen-
erated more rapidly than in the stationary types, small tubes
proving more efficient in breaking up the fuel gases and in con-
ducting the heat more effectively to the large body of water in
the boiler.
BOILER MOUNTINGS
SAFETY DEVICES
SAFETY VALVES
FOBMS OF SAFETY VALVES
1. Purpose of Safety Valve. A safety valve is attached to
a boiler to prevent the steam pressure from rising above a
certain safe limit. If steam is generated faster than it is
used, it will accumulate in the boiler, causing increased pres-
sure; and if the increase of pressure beyond a safe limit is not
prevented, a rupture of the boiler or an explosion may result.
It is the work of the safety valve to allow the excess of steam to
escape, thus automatically reducing the pressure. To do this,
the valve or valves must be of such size as to permit steam to
escape at least as rapidly as it is formed in the boiler. Other-
wise, the steam pressure will continue to rise, even though the
safety valve is open, and will result in stresses that may lead
to a rupture of some part of the boiler or to an explosion.
2. Classes of Safety Valves. A safety valve consists of a
valve disk held down on its seat by pressure applied in one of
several ways and acted on underneath by the pressure of the
steam in the boiler to which the safety valve is attached. As
long as the downward pressure exceeds the upward pressure,
the valve remains closed; but when the upward pressure
becomes greater than the downward pressure, the disk is forced
up off its seat, and some of the accumulated steam escapes,
COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTO MK8BRVBO
BOILER MOUNTINGS
thereby lowering the pressure in the boiler. When the pres-
sure is lowered to such an extent that the upward pressure on
the disk no longer exceeds the downward pressure, the valve
closes. There are three ways of applying pressure to the disk
to hold it to its seat: (a) By a dead- weight; (b) by a weight
acting on a lever, and (c) by the action of a spring. According
to these methods of applying the downward pressure, safety
valves are divided into three classes, known as dead-weight
safety valves, lever safety valves, and spring-loaded, or pop, safety
valves, respectively. The dead-weight type is used only on
boilers that carry low pressures, such as heating boilers. It
consists of a valve attached to a vertical 'stem on which are
placed a number of disk-shaped weights, the valve being held
to its seat by the dead- weight of the disks. On vessels that
carry high steam pressures, the lever and the pop types are
used.
3. Lever Safety Valve. A form of lever safety valve is
shown, partly in section, in Fig. 1. It consists of an iron
body a with a heavy flange b by which it is connected to the
boiler, and a flange c to
which is connected the
pipe through which
the steam escapes. In
the body of the valve
is fastened the beveled
seat d, on which rests
the beveled disk e. The
disk is connected to
a stem / that passes
through the cover g and
is formed into a yoke h
at its upper end. The
lever i (which is broken away at the middle, so that its full
length is not shown in the illustration) passes through the yoke h
and is fulcrumed at one end on the pin /, held in a bracket that
forms part of the cover g. On the other end of the lever is hung
a weight k, consisting of a cast-iron ball, which may be moved
FIG. 1
BOILER MOUNTINGS 3
along the lever. The weight of the ball puts a downward
pressure on the stem / and tends to hold the valve disk e to
its seat. Steam from the boiler enters the space below the
valve and tends to force the disk upwards, off its seat. By
shifting the ball k, any desired pressure may be put on the
stem /and the disk e, and thus the valve may be set to open
when the steam pressure reaches a certain point.
4. Safety valves of the lever and dead-weight types are
not looked upon with favor by engineers. There is always
danger that the stem of the valve may stick in its guide and
thus increase the pressure at which the valve will open; the
weight on the lever may be shifted accidentally and thus
change the blow-off pressure; or ignorant boiler attendants
may add weights so as to obtain a higher working pressure in
the boiler, regardless of the ability of the boiler to withstand
the increase4 pressure.
The use of lever safety valves or dead-weight safety valves is
not permitted under the rules of the American Society of
Mechanical Engineers, commonly referred to as the A. S. M. E.
Boiler Code.
5. Pop Safety Valves. Lever and dead-weight safety
valves have been superseded by pop safety valves. In the
pop safety valve, the pressure by which the valve disk is held
to its seat is obtained by a helical spring made of steel. The
valve disk is made of metal that will not corrode, so as to avoid
the danger of having the disk stick to its seat when in service.
The disk and its seat may be flat, or both may be beveled at
an angle of 45. Pop valves of different types are made for
use on stationary, marine, and locomotive boilers; also, valves
for use with superheated steam differ from those for use with
saturated steam. Valves for superheated steam have larger
springs and in order that they may not be affected by the
higher temperature, the springs are not incased in the body of
the valve. Such valves may also be used to advantage with
high-pressure saturated steam.
6. Pop Safety Valves for Stationary Boilers. The pop
safety valve shown in section in Fig. 2 is intended for use on
BOILER MOUNTINGS
a stationary boiler generating saturated steam. The valve a
is held to its seat 6 by the helical spring c, which is made
of crucible steel. A stem d fits into a socket in the valve a
and carries a collar e against which the pressure of the spring
is exerted, A similar collar / bears on the upper end of the
spring. The spring is completely enclosed by the casing g,
which is part of the
casting that forms the
cover of the safety
valve. The upper col-
lar / is adjustable and
may be forced down by
turning down the screw
h, this operation putting
greater compression on
the spring, forcing the
valve more^firmly to its
seat, and thus raising
the pressure at which
the safety valve will
open. Backing out the
screw k, so as to allow
the collar / to rise, de-
creases the compression
on the spring and
makes the valve open
at a lower pressure. After the adjustment has been made,
the^locknut i is tightened so as to hold the screw h in a fixed
position. The screw h is a sleeve that forms a guide for the
upper end of the stem d.
7. A cap /, Fig. 2, is fixed permanently over the upper
ends of the valve stem and the adjusting screw by having a
lip forced into a groove k around the upper end of the valve
cover. In the side of the cap is a slot just wide enough to
admit the forked end of the lever /, which is pivoted on a pin m.
The forked end fits around the stem d beneath the collar n
which is screwed to the upper end of the stem. By depressing
FIG. 2
BOILER MOUNTINGS 5
the outer end of the lever /, the stem d is raised, the pressure
of the spring is removed from the valve, and the steam pres-
sure beneath will then open the valve. This forms a method
of testing the safety valve to see whether it is in working
order. The pin m is drilled to receive the bow of a padlock o.
No adjustment of the screw h can be made until the lever /
is removed, which is done by taking out the pin m. The
pressure at which the valve will blow off is fixed at the factory,
and the valve is locked. No adjustment of the blow-off
pressure can be made thereafter, except by the boiler inspector
and under his supervision.
8. The upper part of the valve a, Fig. 2, is made with
a sleeve that fits around the lower end of the casing g, thus
forming a closed chamber for the protection of the spring.
An annular space p is formed in the valve face, just outside the
seat, and inside the lip q. When the steam pressure beneath
is just on the point of raising the valve, the first steam to escape
past the seat collects in this annular space. The area of
valve surface exposed to steam pressure is thus increased,
and the valve is lifted suddenly, or with a pop. It is from
this sudden opening of the valve that the pop safety valve
derives its name. The valve and its seat are shown beveled
to an angle of 45. Sometimes the seat is ball-ground; that
is, it is ground with a curved face that is part of a spherical
surface. The valve is then ground to the same curvature.
The advantage of this construction is that the valve and the
seat will always have a perfect bearing, even if the valve gets
slightly out of alinement.
9. The extent of the reduction of pressure, or the dif-
ference between the pressure at which a safety valve opens
, and the pressure at which it closes, is called the blow-down.
With the valve shown in Pig. 2, the amount of blow-down may
be regulated by the adjusting ring r. This ring is threaded
and is screwed over the seat ring, and its outer edge is notched
all around. If the plug 5 is removed, a rod may be inserted,
engaging with the notches, and the ring may be turned. If
the ring r is turned up, the amount of blow-down will be
6
BOILER MOUNTINGS
increased; that is, the drop of pressure between the opening
and the closing of the valve will be made greater. If the ring
is turned down, the blow-down will be decreased. A properly
adjusted pop safety valve opens sharply and closes promptly,
preventing undue loss of steam.
10. A pop safety valve for use on a stationary boiler that
generates superheated steam is shown in Fig. 3. Its internal
construction is almost exactly like that of the type just
described; but the shape of
the body is different, and the
spring is not enclosed, so that
it will not be affected by the
high temperature met with in
connection with superheated
steam. The valve is locked,
so as to prevent unauthorized
changing of the blow-off pres-
sure; also, it is sealed with a
brass tag a, on which is
stamped the number of pounds
of steam that can escape
through the valve in an hour,
known as the steam-relieving
capacity of the valve. A
safety valve should always be
attached to a superheater,
and set to blow at a pressure slightly below that at which
the safety valve on the boiler will blow. Then, if the engines
or turbines are shut down, or the amount of steam used is
suddenly decreased, . the resultant rise .of pressure will cause
the safety valve on the superheater to open, and steam will
escape by way of the superheater, thus preventing the over-
heating or burning of the superheater tubes.
11. Safety Valves for Marine Boilers. Safety valves for
marine boilers are similar to the pop valves used on stationary
boilers and are made with "either enclosed or exposed springs,
according to the service demanded. They may be mounted
BOILER MOUNTINGS 7
separately on the boiler or in pairs on Y fittings; or, two or
more valves may be incorporated in one valve body, in
which case the safety valve is known as a duplex, triplex, or
multiplex valve.
If two or more valves are connected separately to the
boiler or the steam drum, an opening must be cut for each
valve, . To avoid this when two valves are to be installed,
the arrangement shown in Fig. 4 may be used. One opening is
FIG. 4
cut in the shell and over it is riveted the nozzle a. To this
nozzle is bolted the branch fitting b that carries the safety
valves c and d. Pipes e and/ lead from the valves to the main
exhaust, and these pipes must be supported in such a way as
to put no stress on the valves. To prevent accumulation of
condensation on top of the valves, drain pipes g are supplied.
A duplex valve for use with superheated steam is shown in
Fig. 5. The two valves a and b are installed on one body c.
1 2. Locomotive-Boiler Safety Valves. Locomotive boilers
are subjected to a service entirely different from that of
BOILER MOUNTINGS
FIG. 5
stationary and marine boilers, for they must produce steam
very rapidly so as to take care of variable loads. As a
result, the locomotive safety valve will frequently be in
almost continual action. The feed-
water in some localities is very poor,
and may therefore cause scale to
accumulate around the working parts,
thus necessitating frequent cleaning of
the safety valve. On account of the
hard usage to which the valve is sub-
jected, it must be designed to with-
stand the frequent blow-off action and
must be of a form that readily permits
repairs and cleaning operations.
A locomotive-boiler safety valve
with encased spring is illustrated in
Fig. 6 (a) and (6). In construction
it is similar to the types of safety
valves already described, except that
the blow-off is at the top instead of at the side. The
valve base a, case b, adjusting ring c, spring washers d and #,
compression screw /, and check-nut g are made of bronze;
and the spring h and the spindle i are made of steel. View-
(V) shows the arrangement of the steam discharge outlets /,
which makes it possible for the steam to rise vertically, thus
preventing spreading of the escaping steam, which would
cloud cab windows and handicap the men operating the loco-
motive. Locomotive safety valves may also be fitted with
mufflers to reduce the noise made by the steam while blowing
off. The muffler is made of bronze, in the form of a shell,
and is mounted over the body of the safety valve. To allow
the escape of the steam, numerous openings are drilled in the
muffler.
13. Use and Care of Safety Valves. The safety valve
must be connected directly to the boiler, steam drum, or
superheater, so that there is no possible chance of cutting off
communication between the boiler and the valve, The cross-
BOILER MOUNTINGS
sectional area of the safety-valve nozzles or saddles and the
close nipples (short sections of threaded pipe) that are used
with valves having screwed flanges should not be less than that
of the valve inlet. No valve of any kind should be placed
between the a safety valve and the boiler. A new boiler should
be blown down and cleaned before the safety valve is used,
FIG. 6
otherwise, boiler-plate chips that might be left in the boiler,
and other refuse, such as red lead, waste, etc., may get into the
valve seat and injure it. During the hydrostatic test of the
boiler, the safety valve should be gagged, instead of having the
compression of the spring increased to hold the valve shut.
This may be done by the use of a clamp that pulls the spring
down, thus forcing the valve to hold its seat. A far better
plan is to remove the valve and plug the safety-valve opening
during the test.
14. Safety- Valve Rules and Regulations. Safety valves
on government marine boilers must meet the requirements
fixed by the rules and regulations of the United States Board of
10 BOILER MOUNTINGS
Supervising Inspectors. Safety valves used in stationary
power plants in the United States must be made and installed
in accordance with the rules of the state in which the boilers
are operated. The rules of the American Society of Mechanical
Engineers have been adopted by most of the states ; therefore,
the following data relating to the capacity, installation, and
adjustment of the safety valve are taken from the A. S. M. E.
Boiler Code.
SAFETY VALVE REQUIREMENTS
Each boiler having more than either 500 square feet of water-heating
surface, or in which the generating capacity exceeds 2,000 pounds per
hour, shall have two or more safety valves. (The method of computing
the relieving capacity of the safety valves according to the A. S. M. E.
requirements is given in Art. 19.)
The safety-valve capacity for each boiler shall be such that the safety
valve or valves will discharge all the steam that can be generated by the
boiler without allowing the pressure to rise more than 6 per cent, above the
maximum allowable working pressure, or more than 6 per cent, above
the highest pressure to which any valve is set.
One or more safety valves on every boiler shall be set at or below the
maximum allowable working pressure. The remaining valves may be set
within a range of 3 per cent, above the maximum allowable working pressure,
but the range of setting of all of the valves on a boiler shall not exceed 10
per cent, of the highest pressure to which any valve is set.
All safety valves shall be so constructed that no shocks detrimental to
the valve or to the boiler are produced and so that no failure of any part
can obstruct the free and full discharge of steam from the valve. Safety
valves may be of the direct spring-loaded pop type, with seat and bearing
surface of the disk inclined at any angle between 45 and 90, inclusive, to
the center line of the spindle. The maximum rated capacity of a safety
valve. shall be determined at a pressure of 3 per cent, in excess of that at
which the valve is set to blow and with a blow-down of not more than
4 per cent, of the set pressure, the blow-down to be in no case less than
2 pounds.
Safety valves may be used which give any opening up to the full dis-
charge capacity of the area of the opening of the inlet of the valve, provided
the movement of the valve is such as not to induce lifting of the water
in the boiler.
Dead- weight and weighted-lever safety valves shall not be used.
Each safety valve inch in size and larger shall be plainly marked by tjie
manufacturer. The marking may be stamped or cast on the casing, or
stamped or cast on a plate or plates securely fastened to the casing, and
shall contain the following markings:
BOILER MOUNTINGS 11
(a) The name or identifying trade mark of the manufacturer.
(b) The pipe size of valve inlet.
(c) The steam pressure at which it "is to blow.
(d) Blow-down, or difference between the opening and closing pres-
sures.
(e) The weight of steam discharged in pounds per hour at a pressure
3 per cent, higher than that for which the valve is set to blow.
(/) A. S. M. E. Standard.
The minimum aggregate relieving capacity of all the safety valves on a
boiler shall be determined on the basis of 6 pounds of steam per hour per
square foot of boiler heating surface for water-tube boilers. For all other
types of power boilers, the minimum allowable relieving capacity shall be
determined on the basis of 5 pounds of steam per hour per square foot of
boiler heating surface for boilers with maximum allowable working pressure
above 100 pounds, and on the. basis of 3 pounds of steam per hour per
square foot of boiler heating surface for boilers with maximum allowable
working pressures at or below 100 pounds per square inch.
The heating surface shall be computed for that side of the boiler surface
exposed to the products of combustion, exclusive of the superheating sur-
face. In computing the heating surface for this purpose, only the tubes,
fireboxes, shells, tube-sheets, and the projected area of the headers need be
considered. The minimum number and size of safety valves required shall
be determined on the basis of the aggregate relieving capacity and the
relieving capacity marked on the valves by the manufacturer.
If the safety-valve capacity cannot be computed, or if it is desirable to
prove the computations, it may be checked in any one of the three follow-
ing ways, and if found insufficient, additional capacity shall be provided:
(a) By making an accumulation test ; that is, by shutting off all other
steam discharge outlets from the boiler and forcing the fires to the maximum.
The safety-valve equipment shall be sufficient to prevent an excess pressure
beyond that specified in the second paragraph of these requirements.
(b) By measuring the maximum amount of fuel that can be burned and
computing the corresponding evaporative capacity on the basis of the
heating value of the fuel.
(c) By determining the maximum evaporative capacity by measuring
the feedwater. The sum of the safety-valve capacities marked on the
valves shall be equal to or greater than the maximum evaporative capacity
of the boiler.
When two or more safety valves are used on a boiler, they may be
mounted 'either separately or as twin valves made by placing individual
valves on Y bases, or duplex, triplex, or multiplex valves having two or
more valves in the same body casing. The valves shall be made of equal
sizes, if possible, and in any event if not of the same size, the smaller of the
two valves shall have a relieving capacity of at least 50 per cent, of that
of the larger valve.
12 BOILER MOUNTINGS
The safety valve or valves shall be connected to the boiler independent
of any other steam connection, and attached as close as possible to the
boiler, without any unnecessary intervening pipe or fitting. Every safety
valve shall be connected so as to stand in an upright position, with spindle
vertical, when possible.
The opening or connection between the boiler and the safety valve
shall have at least the area of the valve inlet. No valve of any descrip-
tion shall be placed between the required safety valve or valves and the
boiler, nor on the discharge pipe between the safety valve and the atmos-
phere. When a discharge pipe is used, the cross-sectional area shall not
be less than the full area of the valve outlet or of the total of the areas of
the valve outlets discharging thereinto, and shall be as short and straight
as possible and so arranged as to avoid undue stresses on the valve or
valves.
All safety-valve discharges shall be so located or piped as to be carried
clear from running boards or platforms. Ample provision for gravity
drain shall be made in the discharge pipe, at or near each safety valve, and
where water of condensation may collect. Each valve shall have an open
gravity drain through the casing below the level of the valve seat. For
iron- and steel-bodied valves exceeding 2 inches in size, the drain holes
shall be tapped.
If a muffler is used on a safety valve it shall have sufficient outlet area
to prevent back pressure from interfering with the proper operation and
discharge capacity of the valve. The muffler plates or other devices shall
be so constructed as to avoid any possibility of restriction of the steam
passages due to deposit.
When a boiler is fitted with two or more safety valves on one connection,
this connection to the boiler shall have a cross-sectional area not less than
the combined areas of inlet connections of all of the safety valves with which
it connects.
Safety valves shall operate without chattering and shall be set and adjusted
as follows: To close after blowing down not more than 4 per cent, of the
.set pressure but not less than 2 pounds in any case. For spring-loaded
pop valves operating on pressures up to and including 300 pounds per
square inch the blow-down shall not be less than 2 per cent, of the set
pressure. To insure guaranteed capacity and satisfactory operation, the
blow-down as marked upon the valve shall not be reduced.
To insure the valve being free, each safety valve on boilers with maxi-
mum allowable working pressures up to and including 200 pounds per square
inch, shall have a substantial lifting device by which the valve disk may be
positively lifted from its seat at least J^ inch when there is no pressure
on the boiler. For boilers with working pressures above 200 pounds per
square inch, the safety-valve lifting device need not provide for lifting the
valve disk ^ inch except at such times as there is at least 75 per cent,
of the full working pressure on the boiler.
BOILER MOUNTINGS 13
The seats and disks of safety valves shall be of suitable material to
resist corrosion. The seat of a safety valve shall be fastened to the body of
the valve in such a way that there is no possibility of the seat lifting.
Springs used in safety valves shall not show a permanent set exceeding
yg- inch ten minutes after being released from a cold compression test
closing the spring solid. The spring shall be so constructed that the valve
can lift from its seat at least xV ^ e diameter of the seat before the coils are
closed or before there is other interference.
The spring in a safety valve shall not be used for any pressure more than
10 per cent, above or below that for which it was designed.
A safety valve over 3-inch size, used for pressures greater than 15
pounds per square inch gauge shall have a flanged inlet connection. The
dimensions of flanges subjected to boiler pressures not exceeding 250
pounds per square inch shall conform to the American Extra-Heavy
Standard, except that the face of the safety-valve flange and the nozzle to
which it is attached may be flat and without the raised face,
Every superheater shall have one or more safety valves near the outlet.
The discharge capacity of the safety valve or valves on an attached super-
heater may be included in determining the number and size of the safety
valves for the boiler, provided there are no intervening valves between the
superheater safety valve and the boiler, and provided the discharge capacity
of the safety valve or valves on the boiler, as distinct from the superheater,
is at least 75 per cent, of the aggregate valve capacity required.
Every safety valve used on a superheater, discharging superheated steam ,
shall have a steel body with a flanged inlet connection, and shall have the
seat and disk of nickel composition or equivalent material, and the spring
fully exposed outside of the valve casing so that it shall be protected from
contact with the escaping steam.
Every boiler shall have proper outlet connections for the required
safety valve or valves, independent of any other outside steam connection,
the area of the opening to be at least equal to the aggregate areas of inlet
connections of all of the safety valves to be attached thereto. An internal
collecting pipe, splash plate, or pan may be used, provided the total area for
inlet of steam thereto is not less than twice the aggregate areas of the inlet
connections of the attached safety valves. The holes in such collecting
pipes shall be at least J inch in diameter and the least dimension in any
other form of opening for inlet of steam shall be i inch.
SAFETY-VALVE CALCULATIONS
1 5. Lever Safety- Valve Calculations. No safety valve can
open without a slight increase of pressure above that for which
it is set; since, in order to lift the valve, the pressure on
the under side of the valve, which may be called the internal,
I L T 4598
14 BOILER MOUNTINGS
or upward, force, must exceed the external, or downward, force
on the valve plus the friction of the mechanism of the valve.
If the internal and the external forces on the valve are equal,
the valve will be balanced, and an increase of the internal force
will cause it to open. A safety valve will not close until the
pressure has been reduced somewhat below the pressure at
which the valve opened.
The point at which a safety valve will blow off depends
on the external force on the valve. To be balanced, or in
equilibrium, the external load exerting a downward pressure on
the valve must be equal to the internal force exerting an upward
pressure on the under face of the valve. Evidently, the upward
pressure is equal to the area of the valve multiplied by the
pressure per unit of area.
16. Spring-loaded safety valves are always adjusted by
comparison with an accurate steam gauge, and this practice
is now generally employed when setting the lever safety valve.
If it were possible to measure all the parts of the lever safety
valve accurately, it might be finally adjusted in accordance with
calculations based on such measurements. However, a slight
inaccuracy of measurement of one or more of the parts may
produce a considerable error, even though the figuring is
correctly done. Because of this, calculations regarding the
position of the weight on the lever of a lever safety valve are in
practice considered as giving only an approximate, or trial,
position of the weight on the lever.
FIG. 7
17. Referring to Fig. 7, the distance from the fulcrum
F to the end A of the lever is the over-all length of the lever;
this is used only for finding the distance c of the center of
gravity G of the lever from the fulcrum F. When the lever is
straight and of the same width and thickness throughout, the
BOILER MOUNTINGS 15
distance c is one-half the over-all length of the lever ; for any
other case the distance c is determined in practice by balanc-
ing the lever over a knife edge. The distance % from the
fulcrum to the point of attachment B of the weight P is
often called the length of the lever, but on account of the liability
of confusing this term with the end-to-end length of the lever,
it is not used here. The distance d is the distance between
the fulcrum F and the center line of the valve stem C of the
valve V.
Let A = area of valve, in square inches ;
d = distance from center line of valve to fulcrum, in
inches ;
# = distance of weight from fulcrum, in inches;
p = steam pressure, in pounds per square inch;
P = weight of load or weight on lever, in pounds;
F weight of valve and stem, in pounds;
w = weight of lever, in pounds;
c = distance from fulcrum to center of gravity of lever,
in inches.
To find the pressure for which a lever safety valve is set,
use the formula
Px + wc +Vd
Ad
To find the weight necessary on a safety-valve lever, use
the formula
p _pAd-(wc+Vd) (2)
X
To find at what distance from the fulcrum the weight must
be put, use the formula
EXAMPLE 1. At what pressure will a safety valve having a diameter of
4 inches blow off, when the weight of the valve and stem is 10 pounds; of
the lever, 20 pounds; and of the ball, 120 pounds?' The total length of the
lever, which is straight and of uniform section, is 44 inches; the weight is
40 inches from the fulcrum, and the distance from the center line of the
valve to the fulcrum is 4 inches.
16 BOILER MOUNTINGS
SOLUTION. The area of the valve is ^4=4 2 X-7854. As the lever is
straight, the distance c from the fulcrum to the center of gravity is taken
as one-half its length, or ^-. Apply formula 1 , and
120X40+20X^+10X4 .
- 4 2 X .7854X4 - * ^ SQ " m " Y *
EXAMPLE 2. -With a safety valve having the dimensions given in
example 1, what weight is necessary to have the valve about to blow off at
a steam pressure of 100 pounds per square inch?
SOLUTION. Apply formula 2, and
EXAMPLE 3. A safety valve has an area of 11 square inches; the dis-
tance from the center line of the valve to the fulcrum is 3 inches; the steam
pressure, 40 pounds per square inch; the weight weighs 50 pounds; the lever
is straight and parallel, 32 inches long, and weighs 15 pounds; the valve
and stem weigh 6 pounds. How far from the fulcrum must the weight be
placed?
SOLUTION. Apply formula 3, and
T HX40X3-~(15Xy+6X3)
k= -- - - = 21. 24m. Ans.
ou
A candidate for American marine engineer's license should
thoroughly familiarize himself with the calculations pertain-
ing to a lever safety valve, as a candidate for a marine engineer's
license must be rejected by the examining inspectors if he
fails to solve safety-valve problems similar to those given in
the preceding examples.
18. Spring Safety-Valve Calculations. The question
often arises as to the pressure for which a safety-valve steel
spring is intended. When made with 13 complete turns, the
standard prescribed, the question can be answered by an
application of the rule of the Board of Trade, Great Britain,
governing this problem.
Rule. To find the steam pressure for which a spring is
intended, cube the diameter, in inches, of the wire, if round, or
the side of square, if square, and multiply by 8,000 for round
wire and 11,000 for square wire. Divide the product by the
product of the diameter of the spring, in inches, measured from
center to center of the wire, and the area of the safety valve.
BOILER MOUNTINGS 17
Stated as a formula,
in which P = steam pressure, in pounds per square inch ;
d = diameter, or side of square, of wire, in inches;
c = 8,000 for round wire and 1 1,000 for square wire ;
D = diameter of spring from center to center of wire ;
A = area of safety valve, in square inches.
EXAMPLE. For what pressure is a spring made of square wire measur-
ing J inch and 3 inches in diameter intended, if the valve has an area of
6 square inches?
SOLUTION. Apply the formula, and
.53X11,000 .
p _ - = yg 4 jfo p er SQ m Ans.
3X6 F 4
Spring-loaded safety valves are finally adjusted under
pressure by comparison with an accurate steam gauge, the
tension of the spring being increased or diminished until the
valve opens at the desired pressure. The rule given will show
the approximate pressure for which the spring can be used.
19. Methods of Checking Safety- Valve Capacity. The
discharge capacity of a safety valve must be sufficient at
least to take care of the maximum boiler evaporation. Accord-
ing to the A. S. M. E. Boiler Code, the safety-valve capacity
may be determined by measuring the maximum amount of
fuel that can be burned and substituting the value in the
formula
1,100
in which W= weight of steam generated per hour, in pounds;
C"= total weight (or volume) of fuel burned per hour
at time of maximum forcing, in pounds (or
cubic feet) ;
.ff = heat of combustion of the fuel, in B. t. u. per
pound (or cubic foot).
In the formula, the term .75 represents an average boiler
efficiency and the term 1,100 represents the average number of
18
BOILER MOUNTINGS
heat units required to convert a pound of feedwater into
steam. The value of C is found by making a test to determine
TABLE I
HEATING VALUES OF VARIOUS FUELS
(A. S. M. E. Boiler Code)
Fuel
Heating Value
B. t. u.
per Pound
B. t. u.
per Cubic Foot
Semi-bituminous coal
14,500
13,700
12,500
13,500
7,700
6,200
6,400
7,500
10,000
20,000
20,700
18,500
960
100
150
290
Anthracite
Screenings
Coke
Wood, hard or soft, kiln-dried
Wood, hard or soft, air-dried
Wood shavings
Peat, air-dried, 25 per cent, moisture.
Lignite
Kerosene
Petroleum, crude oil, Pennsylvania
Petroleum, crude oil, Texas
Natural gas
Blast-furnace gas
Producer gas
Water gas, uncarbureted
the greatest amount of fuel that can be burned per hour, and
the heating value H of the fuel may be found from Table I.
20. After the value of W, the weight of steam generated
per hour, has been found by the formula of the preceding
article, the size of safety valve required may be determined
by use of Table II. The table gives the discharge capacities of
safety valves from | inch to 8 inches in diameter at pressures
ranging from 15 to 250 pounds per square inch, gauge.
EXAMPLE l.The amount of fuel burned under a boiler during the
period of maximum forcing is 1,140 pounds of semi-bituminous coal per
hour. If the boiler pressure, as shown by the steam gauge, is 125 pounds per
square inch, find the size of safety valve required.
3
o
PQ
OD |
tf !
p
o
tf
H
o
fe
O
QD
P
o
<M IO
CO* >O" 00*
rH Oi *O O *O rH
a^ oo^ co^ oo^ c^ !>_
C4" CO** CO* 00*" rH* CO**
rH rH
CCJ^OOOCOCNIOCOCO
rH rH rH
COCOCOOJN-COOOOtOCO
COTHUSOOWW5OJ_C^COO'
PH
H COi>COO5OrHCQCO_TjH_JU^S_
O
W
CO(MOO5COCDOCOOOOCO
r-T r-T CM" co~ co" "st^ ui" co* i>" oo" oa*
6
P.
tS
*o
I
3' .. , . . ,
" cf
OO^I(MO5b-
rHHOCT3C<JCO
rH CM CO TH CO l>
CO CO CO CO IQ rH C^| rH
3 H t u l a-reng
wdspunoj
<
20 BOILER MOUNTINGS
SOLUTION. Apply the formula of Art. 19. From Table I, H= 14,500
B. t. tu; and C= 1,140 Ib. Then,
On referring to Table II, it is discovered that, at a pressure of 125 Ib.
per sq. in., the largest size of valve, 6 in. in diameter, has a discharge capacity
of 13,711 Ib. per hr., but, two valves should be used on a boiler. A 4-in.
valve will discharge 6,128 Ib. per hr. at 125 Ib. per sq. in., and two such
valves will discharge 12,256 Ib. per hr., which is slightly more than the value
of W. Hence, two 4-in. valves will be used. Ans.
EXAMPLE 2. A boiler carrying 250 pounds pressure burns 1,000 pounds of
Pennsylvania crude oil per hour when forced to its maximum. What size of
safety valve is required?
SOLUTION. Apply the formula of Art. 1 9 . From Table I, H = 20,700
B. t. u. for Pennsylvania crude oil; and C= 1,000 Ib. Then,
Trr .75X1,000X20,700
- 1100 =14 >1H Ib. per hr.
Table II shows that two 3 j-in. valves will furnish the necessary capacity.
Ans.
FUSIBLE PLUGS
21. Purpose of Fusible Plugs. A fusible plug is a
device that is screwed into the crown sheet, tube-sheet, or
water leg of a boiler to protect the boiler in case of low water.
It consists of a brass or bronze shell cored out and filled with
pure tin, which has a melting point a trifle higher than the
temperature of the water in the boiler. As long as the plug is
covered with water, it transmits the heat to the water rapidly.
When the crown sheet or other boiler surface into which it is
screwed is exposed directly to the heat without being covered
with water, the fusible part of the plug melts quickly, and
steam and water are blown through the cored opening of the
plug, thus giving warning of low water. The reliability of the
plug depends on the melting or fusing temperature of the tin
filling at the time it should operate. The presence of relatively
small amounts of impurities in the filling may cause a change in
its composition and possibly render it useless. Correct
methods of manufacture and the use of the best grade of filling
material are the means of insuring reliable plugs.
BOILER MOUNTINGS
21
XnetUle Type
(a)
22. Inside and Outside Fusible Plugs. The inside type
of fusible plug, shown in Fig. 8 (a) , is screwed into the
boiler plate from the water side. The hexagonal head of the
plug in (a) makes a strong construction and enables the plug
to be screwed into
place. The outside
type, shown in (b)
and (V), is screwed
into the boiler
plate from the out-
side. Plug's are
made in standard
sizes from f inch
to If inches; they
are also made with
oversize and extra
oversize threads, to
take care of carelessly tapped holes and holes that have been
retapped.
A form of plug especially adapted to internally fired boilers
of the locomotive type is shown in Fig. 9. The plug a is
screwed into, the crown sheet 6, and the fusible cap c is laid on
top of it and kept in place by the nut d. A
very thin copper cup e is placed over the top
of the cap c to protect it from any chemical
action of the water. The top of the cap
extends from 1J to 2 inches above the crown
sheet, so that when it melts on account of
low water, there will still be enough water
left to protect the sheet from being over-
heated, or burned, as it is often termed.
23. Rules for Use of Fusible Plugs. Although the
advisability of using fusible plugs in boilers subjected to con-
tinuous overloads is questioned, the requirements of the
American Society of Mechanical Engineers with regard to
fusible plugs are as follows: Fusible plugs, if used, shall be
filled with tin with a melting point between 400 and 500 F.
FIG. 9
22 BOILER MOUNTINGS
and shall be renewed once each year. The least diameter of
fusible metal shall be not less than f inch, except for maximum
allowable working pressures of over 175 pounds per square inch,
or when it is necessary to place a fusible plug in a tube, in
which case the least diameter of the fusible metal shall be not
less than f inch.
The use of fusible plugs is not advisable in boilers that are
to be operated at working pressures exceeding 225 pounds per
square inch. If a fusible plug is inserted in a tube, the tube
wall must be not less than .22 inch thick, or thick enough to
give four threads.
24. Location of Fusible Plugs. In horizontal return-
tubular boilers, the plug is usually placed in the back head,
not less than 2 inches above the top row of tubes, measuring
from the top of the tube to the center of the plug. In
firebox boilers of the locomotive type, the plug is screwed into
the highest point of the crown sheet. In Scotch boilers, the
plug is screwed into the top plate of the combustion chamber.
In vertical fire-tube boilers, the plug is screwed into one of the
outside tubes, and arranged so that it is at least one-third the
length of the tube above the lower tube-sheet. In water-tube
boilers of the Heine type, it is screwed into the shell of the
steam drum, not less than 6 inches above the bottom of the
drum. In general, the plug should be so located that it will
be in the path of the hot gases and arranged so that it is at the
highest point of the boiler, where low water would first become
evident.
WATER-LEVEL INDICATORS
25. High- and Low- Water Alarms. It is important to
maintain proper water level in a boiler, so as to safeguard life
and valuable equipment, as well as to insure economy in the
burning of fuel Low water may mean burned-out tubes, or
crown sheets, which might lead to boiler explosions. An
excessively high water level may cause priming, and flood the
steam line leading to the pumps, engines, or turbines, so that
damage will result to this equipment.
BOILER MOUNTINGS
23
26. A device is often attached to the boiler to give an
audible warning, usually by blowing a whistle, of a shortage or
a surplus of water. Devices that indicate a shortage of water
are called low-water
alarms; those that in-
dicate either a surplus
or a shortage of water
are called high- and low-
water alarms.
In low-water alarms,
the whistle may be
sounded by the melting
of a fusible plug, which,
through the falling of
the water level in a
separate chamber out-
side of the boiler, is
brought in contact with
the steam. Fusible-
plug, alarms are cheap
and easily applied ; they
are rather unreliable,
however, because they
are liable to become
incrusted with scale.
The usual form of
low-water alarm em-
ploys a float operating a
valve leading to a steam
whistle, the float being
buoyed up by the water.
It is like the high- and
low-water alarm. Fia 10
27. One form of high- and low-water alarm is illustrated
in Fig. 10. It consists of a hollow air-tight float a, suspended
from a lever b. Within the body of the water column are guides
that prevent the float from binding or sticking. When the
24
BOILER MOUNTINGS
water falls in the column to a low level, the weight of the float a,
acting through the vertical stem c, pulls the lever b down and
thus opens the valve d, allowing steam to pass and sound the
whistle e. When the water level rises sufficiently the float
rises until the stop / engages the lever 6, pushing it up. As
this lever is double-acting, it operates the valve d by either an
upward or a downward motion. The stop/ is adjustable and
can be set in any desired position on the rod c. The proper
action of the signal can be tested by opening the drain valve
attached at g, which will drain the water and allow the float
to fall and sound the whistle. Gauge-cocks h and a gauge glass
i are connected to the body of the water column, as shown.
The device is connected at / with the steam space of the boiler
and at k with the water space.
28. Gauge-Cocks. A gauge-cock is a simple cock or valve
attached either directly to the boiler, or, preferably, to a
water column, for the purpose of testing the level of the water
in the boiler. Three gauge-
cocks are generally em-
ployed. The lowest is
placed, at the lowest level
that the water may safely
attain, and the uppermost
at the highest desirable
level. The third cock is
placed midway between the other two. On opening a. cock
above the water level, steam will issue forth, and on opening
one below the water level, water will appear. Hence, the
level may be easily located by opening the cocks in succession.
29. The gauge-cock most commonly used is of the com-
pression type. Such a cock, with a wooden hand wheel, is
shown in Fig. 11. It consists of a brass body a having a
threaded shank for attaching it to the boiler or water column.
The seat within the body is closed by the end of the threaded
valve stem b. The steam or water issues from the nozzle c
when the cock is opened. Compression gauge-cocks can be
obtained with a lever handle in the form of a crank. Such
FIG. 11
BOILER MOUNTINGS
25
cocks can be operated from a distance by means of a rod. In
some designs the valve is held to its seat by a strong spring,
which automatically closes the valve the moment the hand
releases it.
30. A weighted gauge-cock, known to the trade as a
Register pattern cock, is shown in Fig. 12. It consists of
a body a having a threaded shank for attaching it to the boiler
or the water column. The weight b is pivoted
at c to the body, and when down presses a strip d
of soft-rubber packing against the face of the
opening at e. The cock is opened by lining
the weight slightly, and the issuing si cam or
water is deflected downwards by the curved
end wall of the slot. In order to
show the construction clearly, the
weight is shown raised to the full
limit. The strip of soft-rubber
packing is simply pushed through
two opposite slots. It must be re-
newed frequently, as it rots under FIG. 12
the high temperature to which it is subjected in service.
31. Glass Water Gauges. The gauge glass is a glass tube
whose lower end communicates with the water space of the
boiler and whose upper end is in communication with the steam
space; hence, the level of the water in the gauge glass should be
the same as in the boiler. Fig. 13 shows a common method of
connecting a gauge glass a. The lower fitting b opens into
the water space, and the upper fitting c into the steam space
of the boiler. A drip cock d is placed at the lower end of the
glass for the purpose of draining it. Two brass rods e tend to
protect the gauge glass against accidental breakage. The
fittings may be screwed directly into the boiler. The gauge
should be so located that the water will show in the middle of
the gauge glass when at its proper level in the boiler. Both
fittings have cocks / by means of which communication with
the boiler can be shut off and the escape of steam and water
prevented in case the gauge glass breaks.
26
BOILER MOUNTINGS
32. Automatic Safety Water Gauges. To prevent loss of
steam and water, and to obviate the danger of scalding the
workman who tries to close the valves, it is desirable to
have water gauges that will automatically shut off communica-
tion with the boiler whenever the gauge glass breaks. There
FIG. 13
are many designs of such valves on the market. Fig. 14 (a)
is a typical automatic pattern with hand-control valves a.
A ball b is placed within the shank of each fitting, and is pre-
vented from falling out by a brass pin c. Should the gauge
BOILER MOUNTINGS
27
glass break, the outward rush of steam and water will carry
the balls forward and thus close the openings leading to the
gauge glass. The balls close the gauge-glass openings suffi-
ciently to permit the hand valves a to be closed without danger
of scalding the boiler attendant. The shut-off valve at the
top of the gauge-glass fitting may be offset, as shown in the
<*)
FIG. 15
plan view (6), so as to enable the glass to be inserted or removed
easily. A plug a is screwed into the fitting b directly over the
gauge glass. When this plug is removed and the packing nuts
on the glass have been loosened, the glass may be pushed
straight up through the top fitting.
To avoid entirely the danger of scalding the hands, the
lever type of safety water gauge, with automatic ball control,
28
BOILER MOUNTINGS
as shown in Fig. 15 (a) and (b), may be used. The balls are
arranged as shown at a in the cross-sectional view (a) and work
on the same principle as in Fig. 14, in case of glass breakage.
The levers b, Fig. 15, are operated by chains c and the valves
are closed and opened by pulling the chains.
33. Water Column. A common form of water column is
shown in Fig. 16. It consists of a hexagonal cast-iron stand-
pipe a tapped at the top and the
bottom for pipe connections to the
boiler. Tapped bosses are provided,
which receive the threaded shanks
of the gauge-glass fittings b and the
gauge-cocks c. Each maker has his
own style of standpipe, the differ-
ent makes varying chiefly in the
ornamentation. The steam gauge
is frequently mounted on top of the
water column.
In certain States, it is not allow-
able to place valves in the piping
between the water column and the
boiler, because of the danger that
such valves may be closed and thus
cause incorrect indication of the
water level, with the possibility of
serious consequences. Yet it is
convenient to have shut-off valves,
to avoid the necessity of closing
down the boiler in case of accident to the water column. If
such valves are installed, the fireman should make sure that
they are fully open when the boiler is in operation. The pipe
connections to the water column should not be less than
1J inches in diameter.
34. Water-Column Connections. The connection to the
boiler should be made with a T on the top, as at e, Fig. 16, and
a cross/ on the bottom, with the unused openings plugged with
brass plugs g. If the connections are made in this manner,
FIG. 16
BOILER MOUNTINGS
29
they can be cleaned with a rod when the plugs are unscrewed.
A drain pipe d with a valve in it, and leading to the ash-pit,
should always be provided for the standpipe, and should be
frequently used for blowing out sediment collecting in the
standpipe. For low-pressure boilers no valves need be
placed in the pipes leading to the steam
and water spaces of the boiler; for high-
pressure boilers, however, valves should
always be provided. These valves are
used in blowing out the standpipe and
connections. Closing the valve in the
upper pipe and opening the valve in
the drain pipe blows out the lower pipe;
closing the valve in the lower pipe and
opening the valve in the drain pipe blows
out the upper pipe and the standpipe.
35. An arrangement of water col-
umn, gauge glass, gauge-cocks, and steam
gauge recommended by the Hartford
Boiler Insurance Company is shown in
Fig. 17. The round cast-iron column a
has an inside diameter of about 4 inches.
The upper end communicates ^yith the
steam space of the boiler by means of
the pipe connection b, and the lower end
with the water space through the pipe
connection c. A drip pipe d is used for
removing the water from the column
occasionally in order to prevent it from
becoming clogged. The gauge glass e
communicates with the column through
the connections / and g. The gauge-cocks h, i, and / are
attached to the water column ; a siphon k protects the steam
gauge /.
36. Installation of Gauge Glasses, Gauge-Cocks, and
Water Columns. The Boiler Code of the American Society
of Mechanical Engineers specifies the following requirements
I L T 4599
FIG. 17
30 BOILER MOUNTINGS
for the installation of gauge glasses, gauge-cocks, and water
columns :
Each boiler shall have at least one water-gauge glass, the lowest visible
part of which shall be not less than 2 inches above the lowest permissible
water level. The lowest permissible water level for various classes of
boilers shall be the location for the fusible plug.
Automatic shut-off valves on water gauges, if permitted to be used, shall
conform to the following requirements:
(a) Check- valves in upper and lower fittings must be of the solid non-
ferrous ball type to avoid corrosion and the necessity for guides.
(b) Ball check- valves in upper and lower fittings must open by gravity,
and the lower check- valve must rise vertically to its seat.
(c) The check balls must not be smaller than J inch in diameter, and
the diameter of the circle of contact with the seat must not be greater than
two-thirds of the diameter of the check ball. The space around each ball
must not be less than f inch, and the travel movement from the normal
resting place to the seat must not be less than J inch.
(d) The ball seat in the upper fitting must be a flat seat with either
a square or a hexagonal opening, or otherwise arranged so that the steam
passage can never be completely closed by this valve.
(0) The shut-off valve in the upper fitting must have a projection
which holds the ball at least J inch away from its seat when the shut-off
valve is closed.
(f) The balls must be accessible for inspection. Means must be pro-
vided for removal and inspection of the lower ball check- valve, while the
boiler is under steam pressure.
; I When shut-offs are used on the connections to a water column, they shall
be either outside-screw and yoke-ty'pe gate valves or stop-cocks with levers
permanently fastened thereto arid marked in line with their passage, and
such valves or cocks shall be locked or sealed open.
Each boiler shall have three or more gauge-cocks, located within the
range of the visible length of the water glass, except when such boiler has
two water glasses with independent connections to the boiler and located
on the same horizontal line and not less than 2 feet apart.
No outlet connections, except for damper regulator, feed- water regulator,
drains, or steam gauges, shall be placed on the pipes connecting a water
column to a boiler.
PRESSURE GAUGES
37. Steam Gauge. The steam gauge, the face a of which
is shown in Fig. 18 indicates the pressure of the steam contained
in the boiler. The most common form is the Bourdon pressure
gauge, the distinguishing feature of which is a bent elliptical
BOILER MOUNTINGS
31
tube that tends to straighten out under an internal pressure.
Bourdon pressure gauges are made in various ways by different
manufacturers; a very common design is shown in Fig. 19.
It consists of a two-branched bent tube a, of elliptical cross-
section, that is filled with water and connected at b with a pipe
leading to the boiler. The two ends c are closed and are
are attached to a link d, which is, in turn, connected with a
quadrant e ; this quadrant gears with a pinion / on the axis of
the index or pointer g.
FIG. 18
38. When the water contained in the elliptical tube a,
Fig. 19, is subjected to pressure, the tube tends to take a
circular form, and, as a whole, straightens out, throwing out
the free ends to a distance proportional to the pressure. The
movement of the free ends is transmitted to the pointer by the
link, quadrant, and pinion, and the pressure is thus recorded
on a graduated dial in front. The illustration shows the
gauge with the dial removed in order to display the mechanism.
This type is especially adapted for stationary, marine, and
portable boilers subjected to a .great deal of vibration.
32
BOILER MOUNTINGS
FIG. 19
The single-tube steam gauge, shown in Fig. 20, consists of
a tube a, the free
end of which is con-
nected to a lever b
attached to a
toothed sector c that
moves a small pinion
on the pointer shaft
d. Lost motion is
prevented by the
action of a small
hair-spring e, which
is also used in steam
gauges of the double-
tube type.
Pressure gauges
for indicating steam
pressure are gradu-
ated to show the
pressure above that of the atmosphere, in pounds per square
inch, wherever the English system of weights and measures
is used.
39. Steam-Gauge
Siphons. A steam gauge
must be connected to the
boiler in such a manner
that it will not be injured
by heat nor indicate the
pressure incorrectly. To
prevent injury from the
heat of the steam, a siphon
may be used to connect the
steam gauge to the steam
space of the boiler. The
siphon may be arranged as
shown in Fig. 21 (a) and (&),
or as in Fig. 22. Within a short time after the steam gauge is
FIG. 20
BOILER MOUNTINGS
33
put into use, the siphon becomes filled with water formed by the
condensation of steam. The water protects the tube of the
gauge from injury that would result if the hot steam had free
circulation in the tube. Temperatures above 150 F. may
affect the elasticity of the tube and thus impair the accuracy
of the gauge. The steam-gauge pipe should not be connected
to the main steam, pipe leading from the boiler, nor should it be
located near the outlet of that pipe, as this may cause the
gauge to indicate a lower pressure than really exists in the
boiler. The gauge should be connected to the siphon as
FIG. 21
FIG. 22
indicated in the illustrations so that the water which accumu-
lates in the siphon does not act to increase the pressure.
The siphons shown in Fig. 21 cannot be drained without
disconnecting them from the boiler. To overcome this dis-
advantage, a petcock, as shown at a, Figs. 21 (a) and 22,
may be placed at the lowest point of the siphon. The petcock
should not be opened while the steam gauge is in service, as
then the water seal would be lost and the tube would be
damaged by the steam.
40. Testing Steam Gauges. A steam gauge will lose its
accuracy after it has been in use for some time, owing to the
34 BOILER MOUNTINGS
fact that the tube loses its elasticity and takes a permanent
set. In this case the gauge will indicate a pressure higher than
the actual pressure in the boiler. This can usually be dis-
covered by the failure of the pointer to return to the zero
mark when there is no pressure in the boiler. If the pressure
apparently indicated when there is no pressure is subtracted
from the pressure indicated when the boiler is under steam,
the correct pressure will be given approximately. However,
when a gauge shows a wrong pressure, a new one should be
immediately substituted and the old one discarded or sent to
the maker for repair.
When inspecting boilers, the inspectors of boiler-insurance
companies or municipal boiler inspectors usually test all steam -
gauges in the plant by comparison with an accurate test gauge.
The gauge to be tested and the test gauge are both attached
to a vessel in which the pressure is raised by means of a small
force pump, and the readings of the two gauges at different
pressures are compared.
41. The safety valve can be checked by means of the
steam gauge when the latter is known to be accurate. Con-
versely, when the safety valve is known to be set correctly,
the steam gauge can be checked for the blow-off pressure by
watching its indication when the valve just blows off. If a
steam gauge shows an error of more than 5 pounds, it will be
condemned by most boiler inspectors. The steam gauge should
be taken off periodically and the connecting pipe cleared by
blowing steam through it. When the gauge is off, care should
be taken to see that the hole in the nipple is perfectly clear.
Good practice demands that a steam gauge should be
attached to each boiler, when more than one boiler is used.
In some regions, however, it is not uncommon to see one steam
gauge do duty for a whole battery of boilers. Such an arrange-
ment has nothing but cheapness to recommend it and is
severely condemned by engineers and insurance companies.
42. When the boiler supplies steam to a steam engine,
it sometimes happens that, when the engine is running, the
pointer of the steam gauge vibrates so much that the pressure
BOILER MOUNTINGS 35
cannot be read. This can be prevented by partly closing the
petcock shown below the gauges in Figs. 21 and 22. The
greatest care must be taken, however, to prevent entire
closing of the cock. The pointer of a steam gauge will stick
occasionally; hence, experienced engineers always jar the
gauge a little, in order to dislodge anything that may be pre-
venting movement of the pointer, before they accept its
indication as correct.
43. The spring tube of a steam gauge is liable to corrode
when certain kinds of water are used. Under no circumstances
should an attempt be made to fix a corroded tube by solder-
ing up the hole or holes; instead, the gauge should be sent to
the maker to have a new tube fitted and adjusted. When a
gauge has been taken off, it should not be replaced without
making sure that the passage through the cock on the steam-
gauge pipe is clear when the cock is in the open position.
Care should also be taken to see that the gauge is free to operate
after it has been replaced. It has happened that, when the
piping was being put up, the gasket placed between the two
parts of the union was so large that in tightening the nut it was
squeezed out so as to stop the hole in the pipe completely, thus
preventing the gauge from showing the pressure.
44. Rules for Installation and Use of Steam Gauges. The
rules given by the A. S. M, E. Boiler Code for the installation
of steam gauges are as follows :
Each boiler shall have a steam gauge connected to the steam space or
to the water column or its steam connection. The steam gauge shall be
connected to a siphon or equivalent device of sufficient capacity to keep
the gauge tube filled with water and so arranged that the gauge cannot be
shut off from the boiler except by a cock placed near the gauge and provided
with a tee or lever handle arranged to be parallel to the pipe in which it is
located when the cock is open. Connections to gauges shall be of copper,
brass, or bronze composition.
Where the use of a long pipe becomes necessary, an exception may be
made to the rule that the gauge must be arranged so that it cannot be shut
off except by a cock placed near the gauge, and a shut-off valve or cock
arranged so that it can be locked or sealed open may be used near the
boiler. Such a pipe shall be of ample size and arranged so that it may be
cleared by blowing out.
36 BOILER MOUNTINGS
The dial of the steam gauge shall be graduated to approximately double
the pressure at which the boiler will operate, but in no case to less than
1J times the maximum allowable working pressure on the boiler.
Each boiler shall be provided with a J-inch pipe size valved connection
for the exclusive purpose of attaching a test gauge when the boiler is in
service, so that the accuracy of the boiler steam gauge can be ascertained.
SUPERHEATERS
45. Purpose of Superheating. Steam in contact with
the water in a boiler has the same temperature as the water and
is known as saturated steam. Additional water may be taken
up by the steam through priming of the boiler or from the
movement of the boiler, as in marine, portable, and locomotive
boilers. Moisture also arises from condensation of the steam.
Large heat losses result from the use of wet steam for power
purposes, and there are other disadvantages in the effect of
such steam on turbines, engines, etc. In turbines, water in the
rapidly moving steam erodes, or wears away, the blades, and
increases the amount of steam used. The same conditions
arise in reciprocating engines, and there is a possibility of
damaging the cylinder heads and the stuffingboxes around
piston rods and valve stems.
46. The demand for greater economy in the performance
of steam engines has led to the development of the super-
heater, by means of which the steam may be superheated to a
moderate degree so that it will contain more heat and therefore
do more work than would the same weight of saturated steam,
and thus insure increased engine economy. In order to super-
heat the steam, it must pass from the boiler into a separate
compartment and have more heat applied to it. This may be
done with a separate furnace or by using a coil of pipe within
the boiler setting itself ; or, the superheater may be arranged
in the smokebox of a locomotive boiler, or in the uptake leading
to the stack in other boiler installations.
47. Wrought-Iron Superheater.-One form of superheater
as arranged m connection with a water-tube boiler, is shown
in Pig. 23 (a) and (6). It consists of a number of bent wrought-
BOILER MOUNTINGS
37
iron tubes a with their ends expanded into headers 6, &',
and is located in the tipper part of the combustion chamber of
- V \ .
". ^. : . .. .
&# : &&}^^ 'o V-r^v 1 -;: ^^ :- ^
................
FIG. 23
the boiler. The upper header & is connected with the dry pipe d
by two vertical pipes c, c f , while the lower header b f is con-
38
BOILER MOUNTINGS
nected by means of two pipes e, e* ', to the steam outlet / on
top of the boiler. The steam is drawn from the dry pipe
through the pipes c, c' to the upper header 6, thence through
the superheater tubes a to the lower header b', and up the
external pipes e, e', to the steam outlet /. The lower header b'
is connected to the water space of the boiler by means of the
pipes g and h, fitted with valves i and / for the purpose of filling
the superheater with water when not in use, as is the case when
getting up steam or when the engine is not running. To put
FIG. 24
the superheater into service, the water is drained from it by
means of the three-way valve i. Not all superheaters have
provision made for flooding while steam is being raised. In
many cases a valve on the superheater is opened, allowing air
and steam to escape from the superheater until full pressure
on the boiler is reached, when the valve is closed and the super-
heater is cut into service.
^48. Foster Superheater. The Poster superheater, two
views of which are shown in Fig. 24 (a) and (6), consists of a
BOILER MOUNTINGS
39
series of straight seamless steel tubes, over which are slipped a
large number of cast-iron rings a; these cover the tubes with
cast-iron fins that absorb the heat and conduct it to the tubes.
At the same time, the cast-iron rings prevent the tubes from
burning out and protect them from the corrosive action of the
furnace gases. The steel tubes are expanded into the headers
b and c and at the other end are joined by
the tube fittings d. Steam enters the
header b at e, flows through the upper
bank of tubes, down through the fittings d,
back through the lower bank of tubes into
the header c, and out at /. Handholes g
are provided in the headers b and c and
in the fittings d opposite the tubes. A
cross-section through one of the handhole
plugs is shown in Fig. 25. The plug a is
tapered and is in one piece with the stud b.
A copper gasket c is inserted between the
plug and the tapered seat, the yoke d is set
over the stud, and the plug is drawn to its seat by the nut e.
The form of superheater shown in Fig. 24 is so arranged in the
boiler setting that the headers b and c and the fittings d are
accessible from the outside of the boiler, thus making it easy
to remove the handhole plugs for cleaning, inspecting, or
repairing the superheater.
FIG. 25
FIG. 26
49. Elesco Superheater. A form of superheater for
stationary boilers is shown in Fig. 26. It consists of a large
number of cold-drawn seamless steel tubes a attached to two
headers b and c. The tubes are bent, as shown, so as to provide
40
BOILER MOUNTINGS
a large amount of surface to be exposed to the hot gases, and
at the same time to take care of the expansion and contraction.
Saturated steam from the boiler enters the header 6, which is
closed at the end d, and flows through the banks of piping a,
wherein it is superheated. It then passes out of the tubes a
into the header c, which lies behind the header 6, and which is
also closed at one end. The flange e on the header b forms a
connection for the installation of the safety valve.
FIG. 27
50. The ends of the tubes are connected to the headers by
metal-to-metal joints, as shown in the sectional view, Fig. 27.
The end a of each tube is formed by a special forging process
and is then ground to an angle of 45 to fit the conical seat in
the header, as shown at 6. Between each pair of tubes is a
stud c that passes through the wall of the header into a rein-
forcing strip d. A two-armed clamp e is slipped over the stud
and its ends bear against the collars/ on the tubes. When the
clamp is forced against the collars by screwing up the nuts g
on the stud, the ends of the tubes are held tightly in the conical
seats in the header. This construction enables the tubes to be
removed or replaced with little labor or loss of time
BOILER DETAILS
(PART 1)
FIRE-TUBE AND WATER-TUBE BOILER
DETAILS
RIVETED JOINTS
RIVETS AND RIVETING
1. Forms of Rivets. The plates that form steam boilers
are fastened together by rivets. A rivet is a piece of soft iron
or steel rod with a head formed at one end. The cylindrical
part of the rivet is called the shank; it is inserted into a hole
drilled or punched through the plates to be joined, and its end
is then hammered or pressed to form a second head, the plates
'being gripped and held firmly between the heads. The most
common forms of rivet heads are shown in Fig. 1, and the
dimensions are given in terms of the diameter d of the shank.
From these dimensions it is easy to calculate the proportions
of a rivet head of any type for any diameter of rivet shank.
For example, suppose that the dimensions of the head shown
in (a) are required for a rivet whose shank is f inch in diam-
eter. As rf = t inch, the height of the head is .75 d=.75X.7S
= .5625 inch, or j\ inch, and the diameter of the head is
1.75 d=l.75x.7S=*l'& inches.
2. The proportions of rivets shown in Fig. 1 are in
accordance with the A. S. M. E. Boiler Code, but a variation
of 10 per cent, is permissible; that is, any dimension may be
COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. AL.L. RIGHTS RESERVED
2 BOILER DETAILS, PART 1
as much as one-tenth larger or smaller than that Indicated. In
boiler, plate, and tank work, various forms of rivets are used,
and their names are derived from the shapes of their heads.
Of the several forms shown in the illustration, those in (/;),
Straight- Base
Buifon Head
' (a)
Cone Head
Pan Head
(c)
Mead
!S3r* ******
(9) (h) (i)
FIG. 1
(0, 00, (0, and (0) are most commonly used in boiler
construction. The cone-head rivet is slightly tapered under
the head, the depth a of the tapered part being ^ inch for
rivets from J inch to 1 inch in diameter and & inch for rivets
greater than 1 inch in diameter. The outer edge of the rivet
BOILER DETAILS, PART 1 3
hole is correspondingly beveled, or chamfered, when this form
of rivet is used, as shown in Fig. 2 (a), thus removing the
sharp corner around the hole and making a good seat for the
rivet head. Frequently this form of rivet is driven, or headed,
by the use of tools that form button heads on both ends,
instead of on one end only, as shown in (b) ; it has proved to
be a very good form to obtain steam-tight joints.
IJ. The double-radius button-head rivet, shown in Fig. 1
(V), and known also as the conoid-head rivet, is another very
good form. In fact, it is generally believed to be superior to
the button-head type, as it is easily made tight in the plate
and remains so. The countersunk rivet, shown in (g), is
used in riveted joints when it is undesirable to have rivet heads
project above the surface,
where they might interfere
with the placing of plates or
other parts in their correct
positions. T h e flat-head
rivet, shown in (ft), is also
used for some connections
of the same kind, but is
more extensively employed in lighter sheet-metal work, such
as breedings, stacks, and boiler casings. The rivet holes in
plates are 'made from $$ to -jfe inch larger in diameter than the
rivet shank, so that the rivet may be inserted readily.
4, Methods of Riveting. The act of joining pieces of
metal by means of rivets is known as riveting; and it consists
of passing a rivet through holes in the metal and then form-
ing a second head. That part of the shank from which a sec-
ond head is formed is usually known as the neck of the rivet.
The rivet head may be formed entirely by hammering with a
light hammer, in which case the process is called hand riveting.
If the head is formed by striking a die with a heavy ham-
mer, the process is called snap riveting, which is a modification
of hand riveting; the die, which is called a set, or snap, is a
piece of hardened steel hollowed out to the desired form of
head. If the head is formed by striking comparatively light,
BOILER DETAILS, PART 1
but very rapid blows, with an air hammer, or pneumatic ham-
mer, the process is called pneumatic riveting. If the head Is
formed by squeezing, or upsetting, the metal of the neck under
high pressure in a machine, the process is called machine
riveting; and if the machine is operated by hydraulic pres-
sure, the process is called hydraulic riveting, or bull riveting.
5* For boiler work in general, machine riveting' has
important advantages over hand riveting, and it is now
employed wherever possible. The advantages are as follows:
(a) A tighter joint can be made for the reason that the plates
that are being riveted can be held together with greater force
while the second rivet head is being formed, (b) The holes
in the plates can be filled better, because the shank is made to
spread out by the pressure applied to upset the rivet and to
form the head, (c) It is faster and cheaper, if many rivets
are to be driven.
FORMS OF RIVETED JOINTS
6. Terms Used in Riveted Work. If a joint is formed
by having the edges of two plates overlapped and joined by
one or more rows of rivets, it is called a lap joint. If the
plates are placed edge to edge and the junction or seam is cov-
ered with a narrow strip of boiler plate, called a strap, on
either one or both sides of the plate, and the- whole is riveted
together, the joint is called
a butt joint. The strap is
also known as a cover-plate,
a welt, or a butt strap. The
terms seam and joint mean
the same when applied to
riveted connections. Riveted
joints are also classified, according to the number of rows
of rivets in the seam, as single-riveted, double-riveted, triple-
meted, and quadruple-riveted joints, and from the arrange-
ment of the rivets in the joint as staggered-weted and chain-
rrveted joints. A single-riveted lap joint is shown in Fig. 3
The distance between rivet centers, measured in the direction
FIG. 3
BOILER DETAILS, PART 1
5
of the length of the seam, is the pitch of the rivets, and the lap
is the distance / from the center of the rivet hole to the edge
of the plate.
7. Double- and Triple-Riveted Lap Joints. Two differ-
ent forms of double-riveted lap joint are shown in Fig. 4, that
Q Q Q
FIG. 4
in (a) being chain-riveted and that in (b) staggered-riveted.
In a joint having chain riveting, the rivets in one row are
directly opposite those in the next row; but, if staggered rivet-
ing is used, the rivets in one row are opposite the centers of
the spaces between the rivets in the adjacent row. A joint
with staggered riveting is often referred to as a zigzag-riveted
joint. The diagonal distance a from the center of one rivet
to the center of the next rivet in the adjacent row is called the
diagonal pitch. The distance b between the center lines of
adjacent rows of rivets is the back pitch; it is measured at
right angles to the direction of the seam.
Q Q Q Q Q
Q Q Q Q Q
Q Q Q Q Q
Q Q Q Q Q
<
Q' Q Q Q
<
[Q Q Q Q Q
<
^
FIG. 5
Two types of triple-riveted lap joint are shown in Fig. 5,
that in (a) having chain riveting and that in (6) staggered
riveting. Quadruple-riveted lap joints have four rows of
rivets and either chain or staggered riveting may be used.
I L T 459-10
BOILER DETAILS, PART 1
Triple-riveted and quadruple-riveted lap joints are now seldom
used in boiler work. Formerly such joints were used for
longitudinal seams, but owing to the offset produced by over-
lapping the plate, difficulty arose in obtaining a true cylindrical
shell. Another objection to such seams is that when the shell
is under pressure, a bending action arises in the joint, which
produces crystallized metal between the rivets. A correctly
designed butt joint is superior to the lap joint in regard to
strength and by its use the shell can be rolled to a true cylin-
drical form.
8. Single-Riveted Single-Strap Butt Joint. A single-
riveted butt joint with a' single cover-plate a is illustrated in
Fig. 6 (a) and (J). The ends of the boiler shell b are butted
against each other, and in order to have the edges straight and
parallel with each other they are machined on a plate planer.
It will be seen that the joint has two rows of rivets c and yet
is called a single-riveted butt
joint. This follows from the
fact that the separation of
one plate from the other is
, opposed by only one row of
rivets. Thus, if the plate is
stronger than the rivets, the
plates b can be separated only
by shearing off the rivets,
The pull on the joint, as
shown by the arrows in (a),
tends to break or tear the
FlG ' 6 butt strap along the line d d f
to crush or shear the metal in front of the rivets, as indicated by
the dotted lines e, and to shear the rivets as shown at / in (6)
Rivets driven through the plate and the butt strap and acted
on by the pressure are in single shear, as the resistance of the
rivet to shearing action is that of the sectional area of each
rivet. Butt joints with single butt straps may be double-
riveted, triple-riveted, etc., and the rivet arrangement may be
chain or staggered.
BOILER DETAILS, PART 1 7
9. Double-Strap Butt Joints. The butt joint in Fig 7
(.) con.si.sts of plates that butt together at b and are joined
by the use of two butt straps c and d. The outer strap c is
narrower than the inner strap d. It will be noticed in the sec-
tional view (ft) that the outer strap is riveted to the plates and
the inner butt strap by two rows of rivets, and that the inner
Q
PIG. 7
strap Is riveted to the plates by four rows of rivets, two rows
being on each side.
Butt joints may also be triple-riveted, as shown in Fig. 8 (#),
or quadruple-riveted as in (b), with the rivets arranged accord-
ing to the staggered or the chain method. The chief advan-
tage of the double-strap butt joint having the outer strap
narrower than the inner strap is that it may be designed to
give a stronger form of joint than any other. The rivets are
8
BOILER DETAILS, PART 1
usually staggered. The pitch of the rivets in the outer rows,
which are in single shear, is double the pitch of the rivets
in the inner rows.
10. Butt Joints With Straps of Equal Widths. A triple-
riveted double-strap butt joint with chain riveting is shown in
c
Q C
Q Q Q Q Q
Q Q Q Q Q Q
Q Q Q
Q
Q Q Q Q Q Q Q
Q Q Q Q Q Q (
Q Q Q Q Q Q Q
Q Q Q Q Q Q Q
Q Q Q Q Q Q (
> Q Q Q Q Q Q
Fig. 9 (a) and the same type of joint with staggered riveting
in (&). The inner and the outer butt straps are of the same
width. On each side of the center line of the seam, indicated
by the dotted line, there are three rows of rivets. The rivets
BOILER DETAILS, PART 1 9
in the outer and the inner rows of these three have twice the
pitch of the rivets in the center row.
Another form of double-strap butt joint, known as the saw-
tooth joint, is shown in Fig. 10 (a) and (&). It is quadruple-
riveted, and the outer strap a is cut to the outline indicated,
Q Q Q
Q
c
c
"c
(a)
Q Q Q
0000000000
Q Q Q C
Q Q Q
QQQQQQQQQQ
Q Q Q Q C
FIG. 9
the joint taking its name from the shape of this strap. The
overall width of the strap a is the same as that of the inner
strap b. This form of joint is more expensive to make than
an ordinary double-strap butt joint and is seldom used in boiler
practice, except for the shells of Scotch boilers ; but it enables
better calking to be done along the edges of the outer cover-
10 BOILER DETAILS, PART 1
plate. By calking, is meant the forcing of the edge of the plate
or rivet into close contact with the plate, so as to produce a
steam-tight joint. It should be observed that the rivets in a
double-strap butt joint are in double shear ; that: is, it is neces-
sary to shear each one along two sections to tear the joint
apart by shearing off the rivets.
ARRANGEMENTS OF BIVETED JOINTS
11. Location of Longitudinal Seams in Shell Boilers.
Owing to the high furnace temperatures, the eroding- action
of the fuel gases, and the number of overlaps in the plates, it
is customary to locate the longitudinal seams of shell boilers
as far as possible from the fire. Shell boilers of the horizontal
return-tubular type usually have two or more sections, or
courses, with only one longitudinal seam to the course- The
longitudinal seams are so arranged that they break joints, or
alternate, as shown at a and of, Fig. 11 ; that is, the longitudinal
seams in adjacent courses are not in one line, but one seam
is to the right and the other to the left of the center. Each
BOILER DETAILS, PART 1
11
seam is midway between the top and the side of the boiler.
This arrangement of the seams permits the dome b to be
installed, if one is required, and also the brackets c, without
interfering with the joint construction.
FIG.
12. Location of Longitudinal Joints in Internally Fired
Furnaces. In plain cylindrical furnace flues of internally
fired boilers the longitudinal joint, as shown in Fig. 12, is gen-
erally located just below the grate, either to the right, as in the
illustration, or to the left. The distance s is made as large as
possible in order that the seam will not interfere with cleaning
out the ashes.
FIG. 12
12 BOILER DETAILS, PART 1
In a vertical tubular boiler, the longitudinal (vertical) seam,
if the boiler has only one course, may be located wherever Con-
venient, provided it is clear of the .fire-door opening. If the
boiler has two or more courses, the longitudinal seams should
break, or alternate.
13. Connecting Longitu-
dinal Lap Joints at Girth
Seam. If plates lap together
at the girth seams in boilers
having longitudinal lap joints,
the inner end a, Fig. 13, of
the plate must be hammered
out thin or scarfed, as it is
commonly called, at the cor-
ner b. The outer end c of the
plate is bent circular so as
to fit the scarfed corner of a.
If the lap joint is double
zigzag-riveted, as shown, it is customary to make the pitch of
all the rivets in the outer row uniform; in the inner row, 'the
distance d from the rivet in the girth seam to the first rivet of
the longitudinal seam will then be equal to 1J times the pitch,
14. Connecting Single-Strap Butt Joint and Girth Seam.
In the case of butt
joints having single
cover-plates, the junc-
tion of the longitudi-
nal seam and the girth
seam is made as shown
in Fig. 14. The larger
shell course a overlaps
the smaller course b,
thus forming the girth
seam c. The butt ^ G - ^
strap d extends to the outer overlapping edge of the larger
course a and the rivets e of the girth seam pass through the
shell plates a and b and the s f rap d. In staggered riveting,
BOILER DETAILS, PART 1 13
the rivets in the butt joint adjoining the girth seam are usually
pitched as explained in the preceding article.
15.^ In single-riveted longitudinal lap joints and butt
joints it frequently is necessary, in order that the rivet die used
on the inner head of
the rivet may clear the
inner edge a, Fig. IS,
of the girth seam, to
in a k e the pitch b
greater than the pitch
of the rivets in the
longitudinal seam. The
inner end of the plate c
is scarfed at the junc-
t i o n of the two
courses, and the outer end of the plate d is bent to fit properly
over the plate c and make a tight joint.
FIG.
16. Longitudinal Seam at Smokebox of Locomotive
Boiler. In boilers of the locomotive type, having double-
strap butt joints, the joints at the smokebox end may be
arranged as shown in Fig. 16. The end course a extends
beyond the tube-sheet b so that the smokebox course c can be
riveted to it. The tube-sheet b
is flanged outwards so that it
can be riveted to the shell
courses a and c. From this
arrangement of the tube-sheet,
or head b, it is said to be
backed in. The outer butt
strap d at the smokebox end
is flush with the outer edge of
the flange of the head b, and
the inner strap e is scarfed at the end to fit the curvature of
the flange. The rivets in the girth seam at the smokebox end
pass through the shell a, the flange of the head b, and the butt
strap d.
FIG. 15
14
BOILER DETAILS, PART 1
The connection of the girth seam / and the longitudinal seam
is made by extending the inner butt strap e to the edge of the
course a. The external strap d is either made straight and
butted against the plate g or else it is scarfed and placed under
the larger course g. In the former case, sufficient space must
io
i| Q \
I 1 "?'
ij ojj
1
j
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! OOQOOOOG
( ll
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ip
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-ft
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a
Fio. 16
be allowed between the shell and the butt strap for calking the
seam. To prevent leakage at the junction of the butt joint
and the smokebox, a stop-rivet h is used. It is usually a plug
f or | inch in diameter, threaded and screwed tightly into the
sheet a, after which both ends are formed into heads and then
calked.
17. Connecting Double-Strap Butt Joint and Girth Seam.
In a horizontal return-tubular boiler having three courses as
m Fig. 17 (a) and (b), the middle course a is slightly smaller
in diameter and fits inside the two end courses b and c The
outer butt strap d of the longitudinal seam of the small course
is scarfed at both ends and placed under the plate of the larger
i 'n
ol
in
!g-
" x
9i
r^J
/ ip
/ P-
o o o o
o o o o
o o o o
o o o o
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ol!
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k?
'QT 1
o o o o
o o o o
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ol c
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t:
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FIG. 17
1 d
"if
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/
/ " ^- ^
j s o
1
1
j
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yl o o o o o o
jo
o
1
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/ \ O O O O O !
^
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I
1
/ OJ
Lt,
ro
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(a)
16
BOILER DETAILS, PART 1
courses b and c as shown at e in the sectional view (&). The
inner butt strap / is not scarfed and extends the full length of
the middle course a.
The arrangement of the girth seam and the longitudinal
seams in the end courses is illustrated in Fig. 18 (a), and (&).
The outer butt strap a is made equal to the length of the end
course b. The inner butt-strap c is usually scarfed at both
ends, as indicated at d. At one end it is passed over the flange
of the tube-sheet and at the other end over the middle course c
if
,k
1 9-
(^QO'Q o o o o ci"' 1 *(-\*Q
Jjo
OOQOQOOOQOOOOOOOO Oi[~3^,
ooooooooooooooooo o
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a
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FlC-. 19
at the girth seam /. In the return-tubular boiler, the heads or
tube-sheets usually have their flanges placed inside the boiler ;
but there are types having the shell forming the smokebox as
shown in Fig. 16, and in such a case the head at the smokebox
end is backed in.
18. Seam Connections of Shells of Locomotive Boilers
An approved arrangement of the circumferential and longi-
tudinal seams of the first, second, and third courses of a loco-
motive boiler is shown in Fig. 19. The circumferential seams
are double-riveted and the longitudinal seams have double butt
BOILER DETAILS, PART 1
17
o
Q Q Q Q Q|Qi! O
straps, with the inner strap wider than the outer one, alternate
rivets being" omitted in the outer row. It is the usual practice
to make the first course a, to which the front tube-sheet is
riveted, the smallest; the second course b fits outside of the
course a, and the third course c fits outside of the course b.
The outer butt strap
d of the longitudinal
joint of the second
course b is of full
thickness at the girth
seam between the
courses a and b f but
is scarfed sufficiently
at the seam between
the courses b and c to
go under the first row
of rivets, as shown at
<*. The plate of the
course c is bent up-
wards slightly to give
room for the scarfed
end of the strap d.
The inner butt strap /
is of full thickness at
the girth seam be-
tween the courses b
and c and extends far
enough to take both
rows of rivets. At the
girth seam between
the courses a and &,
the butt strap is
scarf eel, as shown at g,
and lies on top of the first course, the plate a being bent down-
wards slightly to accommodate the scarfed end of the strap /.
The distance h from the girth-seam rivets to the first rivet in
the outer row of the longitudinal seam should be the same
at both ends.
- To !|
i "
o
! * j|
jjo j! o
o
o o
o o *o iio l! o o
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o
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FIG. 20
18
BOILER DETAILS, PART 1
19. Arrangement of Smokebox Joints. In the locomo-
motive type of boiler, which always has a smokebox, and in
the horizontal return-tubular boiler, which may have one, the
smokebox may be a separate course, or the first course may be
extended, serving for both the smokebox and the first course.
The first mentioned construction is customary for large boilers,
and the second one for small boilers. In boilers having double-
riveted longitudinal lap joints and the first course and smoke-
box made of one sheet, there is no need of double-riveting the
longitudinal joint of the smokebox, as it is not subject to pres-
sure. The usual method of arranging the seams is shown in
Fig. 20 (a). In this illustration, part of the first course is
shown at a; the smokebox end of the sheet, at b; and the front
flue sheet, or round head, which is backed in, at c. Because
the smokebox is single-riveted while 1 the shell sheet is double-
riveted, the shell sheet is cut away as shown. The inside of
the shell plate is scarfed at d in order that a tight joint can be
made between it and the head c.
20. In a boiler having the first course and the smokebox
made of one sheet and a longitudinal double-riveted double-
strap butt joint, it is the usual practice to scarf the inner butt
strap a, Fig. 20 (i), and insert the scarfed end between the
flanged head b and the shell sheet c. The outer butt strap d
is made long enough to reach to the end of the smokebox and is
single-riveted, as shown. A stop-rivet e is placed at the edge
of the flange of the front head.
FIG. 21
21. Methods of Making Angular Connections. There are
various ways of making angular connections in structural and
boiler work. Some of the methods are illustrated in Fig. 21.
For structural work, such as tanks, breechings, and bases for
BOILER DETAILS, PART 1
19
boilers, the plates can be readily joined by riveting them to an
angle iron, as shown in (a). For boiler work, in which the
ends of the shells are closed in, it is the usual practice to use
flanged heads, as shown in (b) and (c). The head in (&) is
turned with the flange in-
wards and in (c) it faces
outwards.
Two ways of connecting
an internal furnace to a
tube-sheet are s h own in
Fig. 22 (a) and (6). To
make the connection shown
in (a), the tube-sheet a
must have a flange b turned
imuards. The furnace c is
then brought flush with the FlG - 22
outer surface of the tube-sheet and riveted to the flange. The
connection shown in (6) is made by turning the flange a out-
wards and riveting it to the furnace b, which is set flush with
the outer edge of the flange. This method requires a longer
shell &, but it permits the riveting to be done 'on the outside.
ARBANGEMENT OF FIREBOX JOINTS
22. Fire-Door and Mud-Ring Connections. A method
of forming the fire-door hole for the furnace of a vertical
boiler is shown in Fig. 23, the same method being also used
to some extent with the smaller types of locomotive boilers
used for stationary purposes. The door ring a is usually a
steel casting or a wrought-iron ring placed between the shell
plate and the furnace plate, and riveted with a single row of
rivets. An objection to placing the door ring in this way is
that it is so rigid that it prevents free expansion of the furnace
plate, which causes leaks within a short time along the calking
edge b and at the inner rivet heads c. The bottom of the
water space may be closed by forming an ogee flange d on the
furnace sheet and then riveting it to the shell. This construc-
tion, however, is not adopted when the furnace plate is rela-
20
BOILER DETAILS, PART 1
tively thin or the water space at the bottom very large, because
the thickness of the sheet will be reduced considerably by the
operation of flanging.
23. In locomotive-type boilers, the fire-door hole is usually
constructed as shown in Fig. 24. The door sheet a of the fur-
nace is flanged outwards and the back head b is flanged inwards,
FIG. 23
I
Q Q\
Q Q
fflffl
Q Q
*'<
Q Q
/m
I
il
Q Q
!J_
o
Q Q
Q
Q Q
}
Q
Q
Q Q
< T~
a
9f
Q Q
I
S
Q Q
<
mi
Q Q
<
Q Q
<,
^777;
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Fro. 24
the two flanges being united by a row of rivets c. The bottom
of the water leg must not be closed by flanging the furnace
sheets, as this would prevent the holding on and driving of
the rivets c. It is closed by placing a mud-ring d between the
furnace sheets and the outer plates and securing the ring to
the sheets with rivets. The mud-ring is usually made of
wrought iron, although cast-steel rings are extensively used
BOILER DETAILS, PART I
21
24. Experience has shown that in fire-door holes con-
structed as shown in Fig. 24 the inner sheet will sooner or
later crack from the calking edge to the rivet holes c, and also
in the curved part of the flange. The inner, or furnace, sheet a
is highly heated when the boiler is in
use, but owing to the rigidity of the
flange and the joint at the fire-door
hole, aided by the adjoining staybolts,
the flanged part of the fire-door of the
furnace sheet cannot expand as freely
as the other parts of the sheet, and
stresses are thus set up in this part.
Every time the fire-door is opened the
stresses are intensified by the inrush
of cold air that cools the joint and
causes contraction. The repeated
bending of the 'material under these
stresses will ultimately cause rupture
at one or more places. A collection
of sediment on top of the fire-door ^10.25
hole leads to overheating and increases the danger of cracking
the plates.
25. To lessen the danger of cracking at the fire-door
holes, the construction illustrated in Fig. 25 has been devised.
The end sheet of the furnace is flanged to an ogee curve hav-
ing radii as shown at
a; for this reason, the
furnace sheet is ren-
dered rather flexible
at the fire-door hole.
A good-sized washout
hole b placed directly
over the fire-door per-
Fic - 26 mits the ready re-
moval of foreign matter that collects around the top of the
door flanges at c. In Fig. 26 (a) to (V) are shown several
other forms of construction for door-hole openings.
I L T 45911
22
BOILER DETAILS, PART 1
26. Connecting Sheets to! Mud-Rings. In large locomo-
tive-type boilers the bottom of the water leg is dosed by a
wrought-iron or steel mud-ring. In modern practice, the ring-
is made of sufficient depth to project about | inch below the
lower edge a, Fig. 27, of the furnace and water-leg sheets, thus
permitting the edges to be calked from the sides. If the nnui-
ring does not project below the lower edges of the sheets Jeaky
calking edges are calked with great difficulty, especially if the
boiler is standing on a frame or foundation. To prevent the
mud-ring from cracking at the corners, it is good practice to
provide a boss b at each corner. The extra metal in the boss
will counteract the weakening effect of the holes drilled for
the corner bolts, which are bolts used to fasten the sheets to
/rv0-p > " ~"~ ~ ~' ta r -^
'""Q
i
0!
O
i
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O
O|
O
o ! O O
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O
\Jo Q|0 Q0 00 CLJL3
r-r
]
FIG, 27
the mud-ring at the corners. Mud-rings for boilers carrying
medium pressures are generally single-riveted; for high-pres-
sure boilers, double zigzag riveting is considered good practice.
27. When studs are to be screwed into mud-rings for
attaching an ash-pan or for a similar purpose, the studs must
be so located as to clear the rivets. In a single-riveted mud-
ring, the studs should be placed midway between rivets ; in a
double-riveted mud-ring, they should be placed directly beneath
a rivet of the upper row, as shown at c, Fig, 27.
28. In modern practice, mud-rings are machined both inside
and outside, thus eliminating the expensive and difficult work
required to make the sheets fit metal to metal over an unfinished
or rough mud-ring. The corners of mud-rings should be
shaped as illustrated in the plan view, Fig. 28 (a). This con-
BOILER DETAILS, PART 1
23
struction makes the flange of the furnace sheet a and the out-
side firebox sheet b lie flat. The furnace side sheet c and the
boiler head d are scarfed to go under the sheets a and b. If
the corners of the mud-ring are shaped as shown in (6), the
FIG. 28
flanged furnace sheet a will have to be bent inwards to go over
the scarfing of the furnace side sheet c, and the outer firebox
sheet b will have to be bent outwards to go over the scarf-
ing of the boiler head d. Such construction is not only
expensive and unsightly, but it also requires three lengths of
rivets at the joints, whereas only
two lengths of rivets will be re-
quired if the corner is laid out
as shown in (a),
29, The outside sheets of
firebox boilers are fastened to
the corners of the mud-rings by
threaded corner bolts, the num-
ber and arrangement at each cor-
ner depending on the radius of
the corner and whether the sheets
are single-riveted or double-riv-
eted to the mud-ring. A usual
arrangement of corner bolts is shown in Fig. 29, in which the
boiler head is shown at a, the outer firebox sheet at 6, the flanged
furnace sheet at c, and the furnace side sheet at d. The sheets a
and c are first laid against the mud-ring, after which the holes,
FIG. 29
24
BOILER DETAILS, PART 1
for the corner bolts e are drilled through the sheets a and c into
the mud-ring. The holes are then tapped, and enlarged or
countersunk in the plates a and c, so that the heads of the cor-
ner bolts will be similar to oval countersunk rivet heads.
Instead of using corner bolts with oval heads, some mechanics
thread a rod and screw it into the mud-ring. This rod is then
cut off, sufficient material being left to form a head, and the
projecting ends are riveted over, thus filling the countersunk
holes in the plates a and c. The edges, of the bolt heads are
always calked down to the sheet. In the illustration* corner
bolts are used at the corner, but very often rivets are used
at this point.
30. In Fig. 30 (a) is illustrated a longitudinal section and
in (6) a cross-section of a firebox corner, showing the con-
FIG. 30
nection between the side sheet a, the crown sheet 6, and the
tube-sheet c. If the tube-sheet is flanged to a very small
radius in the corner, it is very difficult to drive a rivet prop-
erly midway between the rivets d and in (&), that is, directly
in the corner. The usual practice is to drill and tap a hole at
this point, generally using a tap f inch in diameter and hav-
ing twelve threads per inch. A plug / is then screwed tightly
into the tapped hole and its ends are riveted over and calked,
31. Fire-Cracks in Joints. It has been found by experi-
ence that in firebox boilers the furnace side of the furnace
sheets is liable to crack at the joints from the rivet holes out-
wards toward the edge of the plate, such cracks being termed
fire-cracks. The lap joints are kept relatively cool on the
BOILER DETAILS, PART 1
25
water side, but the fire side of the lap, especially with thick
plates, becomes so hot as to set up stresses that ultimately
result in cracks. To reduce the liability that fire-cracks will
occur, it is the practice to bevel the furnace side of the lap
from a, Fig. 31, to the edge b,
countersink the rivet holes, and
drive oval countersunk rivets c. The
thinning of the material assists the
water on the water side in keeping
the furnace side of the lap cool, and
does not reduce the strength of the
joint, as the pressure tending to
rupture the joint acts in the direc-
tion of the arrow.
32. In an externally fired boiler
of the horizontal return-tubular or
flue type, part of the girth seam is
exposed to the flames and fire-cracks may occur on the fire side
of the seam. As the internal pressure, indicated by the arrows
in Fig. 32 (a) and (6) tends to pull the lap apart and to crush or
shear out the metal between the rivet holes and the edge of the
plate, the lap should not be beveled as shown in Fig. 31, because
this would materially weaken the joint. A common construction
at the girth seams is shown in Fig. 32 (a), the rivet having an
oval head on the fire side. If, however, the rivet is made with
a countersunk head on the fire side, as shown in (&), there
FIG. 32
will be less material at the joint without greatly weakening the
plate; consequently, the water will tend to maintain a more
nearly uniform temperature at the lap, thereby reducing the
liability of the occurrence of fire-cracks.
26
BOILER DETAILS, PART 1
HEADS OF BOILERS AND DRUMS
PLAT HEADS
33. The tube-sheets of locomotive, vertical, flue, and
horizontal return-tubular boilers are flat circular plates with
flanges at the outer edges, by which they are riveted to the
shells of the boilers. As a general rule, the tube-sheet, or
head, is Inserted in the manner shown in Fig. 21 (ft) ; that is,
the edge of the flange is inside the shell and the convex part
.Km. 33
of the flange faces outwards. However, it is not uncommon
for the head to be backed in, as in (c), in which case the flat
part of the head lies well within the outer end of the shell As
flat surfaces are not self-supporting when subjected to pres-
sure, the flat heads of boilers are braced by diagonal stays
above the tubes and by through stays, from head to head,
below the tubes and on each side of the manhole
BOILER DETAILS, PART 1
27
34. It is customary to make the head of a boiler of a
single piece of plate; but if the boiler is of great diameter, the
head must be built up of two or three sections riveted together.
For example, Fig. 33 (a) and (/;) shows the back head of a
marine boiler of the Scotch type, which is of such diameter
that itj is made of three plates that are flanged separately, as
at a, and then riveted together. After the flanging has been
clone, the sections are fitted together and the positions of the
rivet holes b are marked. A few rivet holes are drilled and
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FIG. 34
bolts are inserted' to hold the sections together in their correct
relative positions, after which the remaining holes are drilled.
If the flanges of adjoining sections are lapped, as at c, the
outer flange is scarfed and the inner one set in a trifle, as
shown. In some cases, however, the flanges are welded
together, as at d.
The front head of a Scotch boiler having three openings a
for the furnace connection is shown in Fig. 34. The openings
are cut in the lower sheet and the flange required for riveting
28
BOILER DETAILS, PART 1
the furnaces to the head is turned in as shown at b in the
sectional view. The tube holes c are drilled in the section d
and the manholes e and handhole openings / are cut in the
lower plate. The manhole openings may be flanged in, in the
same manner as the furnace openings, or they may be rein-
forced by riveting wrought-iron or steel rings to the head, as
shown at g.
BUMPED HEADS
35. Heads that are bent to the convex and concave forms
shown in the sectional views, Fig. 35 (a) and (ft), are called
bumped heads, or dished heads. They are used in plain cylin-
drical boilers, steam drums, mud-drums, oil tanks, air reser-
voirs, etc. The head in (a) is convex outwards and is therefore
a convex head, whereas the head in (6) is concave outwards
and is a concave head. A dished head backed in, as shown
in (ft), is used only in cases where there is in the shell no open-
ing large enough to
permit the driving of
the rivets.
Dished heads with
the pressure on the con-
vex side of the head,
as in (ft), are not so
strong to resist pres-
sure as heads having
the pressure on the con-
cave side, as in (a).
The A. S. M, E. Boiler
Code provides that a
bumped head having the pressure against the convex face, as
in (ft), shall be allowed a maximum working pressure of only
60 per cent, of that for a bumped head of the same dimensions
but having the pressure against the concave face, as in (a).
The depth a of the dished part of the head depends on the
inside diameter ft of the shell to which the head is riveted.
The curve of the dished head has a radius c equal to the inside
diameter ft of the shell. The corner radius d is not less than
FIG. 35
BOILER DETAILS, PART 1
29
1J inches nor more than 4 inches. A bumped head arranged
as in (a) is self-supporting for certain working pressures,
since the head is a section or segment of a sphere and is already
curved to the shape it would naturally assume under pressure.
FIG, 36
36. The strongest form of dished head is the hemispherical
head, Fig. 36 (a), which is used in some types of cylindrical
boilers built in England, The form of head illustrated in
Fig. 36 (&) is used in tank work; the objections to it are that
there is difficulty in shaping it and in maintaining tight rivets
at its joint with the shell. Bumped heads may have manhole
openings flanged inwards or outwards, as shown in Fig. 37
(a) and (6), respectively. These flanged openings are known
as plain flanged manholes. In the
flanging process, the metal is
stretched along the face a of the
flange, and this condition is more
pronounced in light-plate than in FlG - 38
heavy-plate flanging. To compensate for the reduction in plate
thickness and to give greater stiffness and strength to the
flange a, a steel band or ring b may be shrunk on the flange
and secured to it by studs c, as shown in Fig. 38.
30 BOILER DETAILS, PART 1
DOMES AND DRUMS
STEAM DOMES
37. Domes on Stationary Boilers. In small fire-tube
boilers of the locomotive, horizontal return-tubular, and Hue
types, domes of the form shown in Fig. 39 are very often
attached at the top of the boiler shell. A dome is placed on a
boiler for the purpose of increasing the steam space and also
for the purpose of obtaining drier steam, the supposition being
that the steam will be drier on account of its being farther
removed from the water. The dome shell a in (a) is flanged
and riveted to the boiler shell b. A flanged head c closes the
dome at the top. To support the flat surface of the head,
either of the methods of bracing shown in (a) and (/>) may
be employed. In (a) the stays d are threaded and screwed
into the boiler plate b, the dome liner e, and the head r, and the
ends are then headed over. The method of bracing shown
in (fc) consists of using diagonal braces a having at each end
a palm or foot b parallel to the surface to which it is riveted.
38. Communication between the steam space and the
dome may be provided by cutting a number of small holes f,
Fig. 39 (a), through the shell- plate below the dome; or, a
single opening may be cut in the boiler shell, as in (b). In
either case the total cross-sectional area of the opening or
openings should be greater than the area of the steam outlet.
The openings in the shell reduce its strength, and to compen-
sate for its weakened condition the practice is to rivet a rein-
forcing ring, or liner, around the dome connection as at e
in (a). The rivets g that hold the dome to the shell pass
through both the liner and the shell. Drain holes h are also
provided in the boiler shell near the lowest point of the junc-
tion of the base of the dome and the boiler shell. Water that
collects from the condensation of steam flows back through
these holes into the boiler.
.An approximate rule for determining the size and height of
a steam dome is to make its diameter equal to one-half the
A
r
( *
JOt,
<\ >
31
32
BOILER DETAILS, PART 1
JL
/
i O O O OOC
diameter of the boiler, and its height equal to nine-sixteenths
of the diameter of the boiler.
39. Locomotive Boiler Domes. The domes of locomo-
tive boilers are usually made of heavier plate than those of
stationary boilers. The principal types of locomotive domes
are shown in Figs. 40 and 41. The three-piece dome shown
in Fig. 40, which is quite common, is made with a heavy collar
or base a, from f to 1 inch in thickness, having two flanges of
about the same length. One of these flanges is riveted to the
boiler shell and the other to the dome shell b. The shell b is
made of lighter plate
than the dome base
and is closed at the
top by a flanged flat
head c. Domes are also
formed in one piece,
as illustrated in Fig.
41. This method of
construction produces
the strongest type of
dome and offsets the
need of several riveted
joints. Such domes
are p r e s s e d out of
heavy plate, from f to
1 inch thick. It will
be noticed in (a) that the dome has a slight taper, being 29
inches in diameter at the top and 30 inches at the base. Owing
to the heavy plate thickness the right-angle flanges are made
with a large radius a of 4* inches, and a raclius b of 3 inches
is used for the larger flange angle, as shown in (&).
40. In boilers of the locomotive type it is usually neces-
sary to have a large opening in the dome head to permit the
erection of the steam pipe and the throttle valve. Such an
opening is circular in form and covered with a pressed-steel
cap rf, Fig. 40, which is fastened to the dome head by studs
and nuts e. The upper surface of the dome head and the
FIG. 40
BOILER DETAILS, PART 1
33
bottom face of the cap d are faced or machined so that when
the cap is bolted clown on the copper gasket / a steam-tight
joint will be obtained. The dome cap may be made in several
ways. Sometimes it is straight, as shown, and sometimes it
is dished, as indicated In Fig. 41. The latter form adds
strength to the cap. To reinforce the -opening in the shell, a
steel reinforcing ring is riveted to the shell and the dome, as' in
FIG. 41
Fig 1 . 40, with a double outer row of rivets g and a single inner
row of rivets h. Drip holes, as at c, Fig. 41 (&), are provided
to drain away water that collects at the base of the dome. To
attach the safety valve and the whistle to the dome, threaded
flanges like the one shown at d are riveted to the side of the
dome shell.
41. The Boiler Code of the A. S. M. E. requires that the
longitudinal joint of a dome 24 inches or more in diameter
shall be of butt and double-strap construction irrespective of,
pressure. When the maximum allowable pressure exceeds 100
pounds per square inch, the flange of a dome 24 inches or over
in diameter shall be double-riveted to the shell. For domes
less than 24 inches in diameter the longitudinal seam may be
34
BOILER DETAILS, PART 1
of the lap-joint type, and the flange may be single-riveted to
the boiler, provided that a factor of safety of not less than 3
is used in determining the allowable working pressure on the
dome.
The corner radius of the flange, measured on the inside of
the plate, shall equal at least twice the thickness of the plate,
for plates 1 inch thick or less, and at least three times the plate
thickness! for plates over 1 inch in thickness.
The dome may be located on the barrel or over the firebox
on traction, portable, and stationary boilers of the locomotive
type, up to and including a shell diameter of 48 inches. For
larger boiler diameters, the dome shall be located on the shell
of the boiler.
42. Dry Pipe. The use of steam domes is giving way to
the practice of installing larger boilers with the required steam
space and placing inside a fitting known as a dry pipe. It is
usually made as shown in Fig. 42. The central, section a is a
tee into which are screwed the pipes / and c and the nipple (L
The pipes b and c are slotted along the top, or else holes are
drilled through them,
as shown, The com-
bined area of these
openings should be
larger than the cross-
sectional area of the
steam outlet c. It is
u s u ally one - third
greater than the area
of the steam outlet.
The ends of the dry
pipe are closed with caps / and at the bottom of the pipe a drip
hole is drilled to allow water to drain out. The dry pipe
should be connected at the highest point in the steam space of
the boiler, and in such a manner that the steam can enter it
through the perforations at the top. It is supported at the
ends by iron straps g riveted to the drum h<
FIG. 42
BOILER DETAILS, PART 1 35
STEAM DRUM
43. Purpose and Arrangement of Steam Drums. The
steam drum is a cylindrical vessel often attached at the top
of a fire-tube boiler to increase the steam space, thus serving
as a substitute for the steam dome. One form of steam drum
attached to a fire-tube boiler is shown in Fig. 43. The drum
is composed of two shell courses a, closed by two dished
heads &, and is attached to the top of the shell c by two flanged
steel nozzles d. There is some objection to this construction
on account of unequal expansion and contraction stresses that
arise in the boiler shell and drum, which may cause the nozzle
seams to leak. To overcome this condition, one nozzle is
sometimes used. To provide an entrance to the steam drum
for cleaning, inspection, and repairs, a manhole e is placed in
one of the dished heads. The steam outlet is connected at the
top of the drum, as shown at /, and the safety valve is attached
at g. The feeclwater enters through the pipe at the bottom
of the drum, passes down through the front nozzle and deposits
much of its sludge in the pan beneath the nozzle.
44* A steam drum is not generally used on a single
boiler, but it is often used if a number of boilers are set in a
battery, the steam drum being connected directly to the top
of each boiler. It is then placed transversely, and is usually
connected to the boilers by long curved pipes, to allow for the
expansion and contraction of the header. In most designs of
water-tube boilers steam drums are used; however, they are
partly filled with water. If each boiler in a battery has an
independent furnace, there should be a stop-valve between each
boiler and the steam drum, to allow each boiler to be cut out
of service; if the battery of boilers has one furnace common
to all, no stop-valve should ever be placed in the nozzle or pipe
between each boiler and the drum. A single steam drum,
when it is applied to a battery of boilers, is often called a
header. If a header is applied to a battery of boilers that has
a furnace common to all the boilers, one safety valve is suffi-
cient for the entire battery; but if a header is connected with
a battery of boilers, each of which has its own furnace and
36
BOILER DETAILS, PART 1
37
stop- valve, an independent safety valve, attached directly to
the shell, should be placed on each boiler of the battery.
45. Size and Strength of Steam Drums. When a steam
drum is used for a single boiler, its diameter may be made
equal to one-half the diameter of the boiler, and its length
equal to the diameter of the boiler. When one steam drum is
common to several boilers, its diameter is usually made equal
to half the diameter of one of the boilers, and its length equal
to the horizontal outside-to-outside measurement over the sev-
eral boiler shells.
The strength of steam drums may be determined by the
rules governing the strength of boiler shells. They require
just as rigid inspection as the boiler itself.
MUD-DRUMS AND BLOW-OFFS
46. Mud-Drums. Cylindrical mud-drums made of steel
in the same manner as the steam drum in' Fig. 43 are some-
times used with station-
ary boilers of the fire-
tube type. In such
cases the drum is at-
tached to the bottom of
the boiler to provide a
suitable place for the
collection of mud and
sediment held in sus-
pension in the feed-
water. The feedwater
is sometimes introduced
into the drum, from
which it passes into the
boiler. In shell boilers
the mud-drum is lo-
cated at the end far-
thest from the furnace,
as shown in Fig. 44. The drum a rests on a standard b
and, is connected to the boiler shell by flanged nozzles c. A
I L T 459-12
FIG. 44
38
BOILER DETAILS, PART !
manhole d is provided in the end of the drum for clean-*
ing and repairs, and blow-off piping" e is. connected at the
bottom of the drum for blowing out the mud and other sedi-
ment A protecting wall of brick may be built in front; of
the drum when it is placed inside the boiler setting, so that
it may not be directly exposed to the fire temperature.
The difficulty arising in the use of such drums is that the
mud deposited tends to become baked and hard, and unless
the drum is frequently cleaned, there is danger of its becom-
ing entirely clogged.. In some types of water-tube boilers one
or more cylindrical drums form water-drums and mud-drums,
serving primarily to distribute the feedwater to the tubes and
incidentally to collect mud and other feedwater sediment.
FIG. 45
47. Surface Blow-Off.-The surface blow-off a, Fig. 45
is a sheet-metal funnel or scoop so arranged that its outlet is
submerged at the lowest water level and its upper edge at the
highest water level. It should be placed at about one-third
of the length of the boiler from the rear head It is installed
for the purpose of removing the scum and other impurities
that rise to the surface of the water. When the valve h is
opened, the steam pressure forces the scum and some water to
flow out through the blow-off piping c which is usually con-
nected to a blow-off tank. If the scum is not removed it will
prove detrimental to the operation of the boiler, for it will
BOILER DETAILS, PART 1
39
* prevent the steam bubbles from escaping freely, and some of
the scum may be carried off with the steam into the power-
plant auxiliaries, affecting their operation. Sometimes, the
funnel a is fitted with floats and the pipe d is swiveled, so that
the funnel will follow the rise and fall of the water level in
the boiler.
48. Blow-Off Tank. A blow-off tank is a cylindrical
vessel made of boiler plate, as shown in Fig. 46, the shell a being
riveted to dished heads b. The top head contains a manhole c
to provide entrance into
the tank for cleaning.
A vent pipe d is pro-
vided at the top so as
to prevent the accumu-
lation of excessive pres-
sure in the vessel. The
blow-off pipe leading
from the boiler is con-
nected at e and the
water is drained out
through the pipes / and
g. The purpose of the
blow-off tank is to en-
trap the hot water
blown off from the
boiler, so that it will
cool before being dis-
charged into the sewer.
FIG. 46
By this arrangement the danger of
damaging the sewer by hot water is avoided. The blow-off
tank is provided with a siphon breaker h to prevent a siphon-
ing action through the pipe g, as it is desired to keep the tank
filled with water to the level of the overflow pipe i.
40 BOILER DETAILS, PART 1
OPENINGS IN BOILERS
STEAM, WATER, AND WASHOUT OPENINGS
49. Classes of Openings, In all types of boilers, a num-
ber of holes, or openings, must be cut through the boiler shells,
heads, domes, or drums for the outlet of steam, for the inlet
and outlet of water, and for the purposes of cleaning, inspect-
ing, and repairing. It is customary to designate each opening
in accordance with the purpose it serves ; thus, the hole through
which the f eedwater is admitted is the f eedwater hole ; the hole
into which a gauge cock is screwed is the gauge-cock hole. An
opening cut into a boiler for the purpose of washing out for-
eign matter and incidentally permitting inspection is an inspec-
tion hole, a washout hole, or a handhole, the last term being
preferably used when the hole is large enough to admit the
hand. When a hole is large enough to permit the passage of
a man's body it is a manhole. One or more manholes should
be placed in each boiler that is large enough to permit this,
one manhole being placed in the front head and another in the
boiler shell. Sometimes a manhole is placed in the rear head
instead of in the boiler shell.
50. Washout Holes and Plugs. In locomotive-type
boilers, washout holes are placed in convenient places in the
water legs below and above the tubes, for washing out mud
and other sediment that collects in the boiler. These open-
ings are threaded and plugged. Round brass plugs for closing
washout holes are called washout plugs. They generally have
twelve threads per inch, cut on a taper of f inch per foot.
Two types of washout plugs are used, differing only in the
manner of receiving the wrench for screwing* them in or out.
The form shown in Fig. 47 (a) is a male plug, and is the one
most generally used; the form shown in (6) is a female plug,
and is used only where the projecting square shank of the
male plug is not permissible. The body of the female plug is
recessed to receive the wrench by which it is screwed into
place.
BOILER DETAILS, PART 1
41
51. Washout plugs are generally screwed directly into
the sheet, as shown in Fig. 47 (a), but when placed in a part
of the sheet curved to a very small radius, the sheet is flanged
out and the plug is screwed into the flange, as shown in (&).
The flanging of the sheet for a
washout plug is necessary in such
a case in order to provide a suffi-
cient number of perfect threads
for holding the plug and making
<*)
J t
(*) FIG. 47
it tight. The length c of the threaded part of the plug, as
shown in (a), should be sufficient to give, when the plug has
been screwed home, at least two threads inside and three or
four threads outside the sheet into which it is screwed.
52. Handhole Openings and Coyer-
Plates. Handhole openings may be
made circular in form, but they are
generally elliptical. The common sizes
are 3 in. by 5 in., 4 in. by 6 in., 5 in. by
7 in., 6 in. by 8 in., and 6 in. by 10 in.
They are made to fit either flat or bent
plates. For stationary boilers two gen-
eral types of handholes are used, one of
which is shown in Fig. 48. It consists
of a' cast-iron or steel cover-plate a and
a yoke, or crab, b of steel or cast iron.
The bolt c passes through the cover-
plate, which has a countersunk head
riveted over at the end d. To pro-
duce a steam-tight joint > a gasket e is
placed between the boiler plate and the cover-plate; then, by
tightening the nut /, the cover-plate is brought to bear against
the gasket and plate. The gasket should be made of heat-
FIG. 48
42
BOILER DETAILS, PART 1
resisting and waterproof material when used for steam con-
nections. Various compositions of rubber and asbestos are
employed for this purpose. Before being placed in position
the gasket should be coated on both sides with graphite in
FIG. 49
order to prevent it from sticking to the metal when the
cover is removed. It may then be used a number of times.
The different parts of an elliptical pressed-steel handhole
cover-plate are shown in Fig. 49. The plate a is formed under
hydraulic pressure and the two curved transverse ribs provide
(a)
FIG. 50
a socket b into which is slipped the head of the bolt c. The
yoke d is also of pressed steel, and the combination of plate and
yoke gives a stronger and lighter form of handhole cover
arrangement than the cast-iron or steel type.
BOILER DETAILS, PART 1
43
53. Handholes for water-tube boilers are made either
circular or elliptical. When the circular form is used, it is
necessary to have a number of large elliptical handholes through
which the covers for the adjoining circular handholes can be
installed and removed. In Fig. 50 is illustrated the type of
handhole equipment used in the Edge Moor water-tube boiler.
The outer plate a opposite the point where each tube b
enters the inner tube-sheet is pressed to form a raised elliptical
seat c, as shown in the rear view of the plate a, given in (b).
The edges of these seats are machined to provide smooth faces
against which the handhole plates d can be drawn to produce
steam-tight joints. A gasket e is placed between the plate and
the handhole cover. The yoke / and the plate d are drop f org-
ings and the plate is formed with a boss g that is threaded to
receive the stud h.
54. In some makes of water-tube boilers, a special form
of metal-to-metal handhole construction is used. It is known
as the Key handhole, and is shown in Fig. 51. The handhole
cover a is a plug or cap with tapering sides that match the
taper of the opening cut in the boiler plate b. The plug is
inserted from the inside, opposite the end of the tube c f and
FIG. SI
is pulled into place from the outside by a special tool made for
the purpose. The boiler pressure against the head of the plug
forces it to its seat. Because of its shape the plug is stronger
than the ordinary handhole cover. It eliminates the necessity
of a yoke, bolt, and nut, and also avoids the use of a gasket,
which very often blows out and causes trouble. As the head
44
BOILER DETAILS, PART 1
of the plug is circular, it cannot be put in from the outside
through the circular opening that it closes. Instead, master
handholes, as shown in Fig. 52, are provided in the bottom of
the headers, through which the tapered plug is inserted and
FIG. 52
then placed in the circular opening. When a handhole open-
ing exceeds 6 inches in any dimension, the metal around the
opening must be reinforced by a steel ring or liner.
MANHOLES
55. In general, the construction of a manhole and its
cover does not differ materially from that of a handhole and
its cover, except that the former is larger, being 10 in. by 14 in.,
11 in. by 15 in., or 12 in. by 16 in. The usual size is 11 inches
by 15 inches. A manhole should be cut in a boiler shell with
the long diameter, or long axis, parallel to the girth seam,
FIG. S3
because the stress per inch of girth seam is only half as great
as the stress per inch of longitudinal seam. As the shell is
materially weakened by cutting such a large hole, it is neces-
sary to reinforce the plate around the manhole opening. The
general practice in reinforcing manholes in shell boilers is to
BOILER DETAILS, PART 1
45
rivet a reinforcing plate or a flanged ring a, Fig. 53, on the
inside of the shell plate. The cover-plate b is held in position
by two crabs c and the bolts d and nuts e, A gasket / is
employed to obtain a
steam-tight joint. The
formation of the
saddle or reinforcing
ring is illustrated in
Fig. 54 ; the plan view
indicates the shape of
the elliptical openings,
and the width of the
flange b, and the sec-
tions show the form
of the flanges b and d.
The flange b is turned
to fit the curvature of
the shell, and the flange d is straight across the face e to fur-
nish a seat for the cover.
56. In the perspective, Fig. 55, is shown an assembly of
a manhole plate, reinforcing ring, and crab made of pressed
steel. It will be noticed that only one crab is employed, thus
making a light form of
manhole cover installation.
When a manhole is placed
in a head, the sheet is usu-
ally flanged inwards, the
flange serving to stiffen the
metal around the opening.
A flat manhole cover and
other details for attaching
the cover-plate in position
are made like those already
described. The manhole plates may be made of wrought steel
or steel castings; cast iron is not suitable for pressure vessels.
The least width of bearing surface for a manhole gasket is
\ inch and the gasket should not be over \ inch thick.
FIG. 55
46
BOILER DETAILS, PART 1
WATER AND STEAM-PIPE OPENINGS
57. Reinforcement of Pipe Openings. If water pipes or
steam pipes that enter the head, shell, dome, etc., of a boiler
are rather small and the plate is relatively thick, they may be
screwed directly into the plate; but if such pipes are compara-
tively large, the plate must be reinforced where the pipes enter.
The manner in which plates are reinforced at pipe openings
depends somewhat on the size of the pipe and the thickness
of the* plate, and, in case a boiler fitting is attached, on the
character of the fitting. The respective boiler rules specify
how the pipe openings and other fitting connections should be
reinforced. The A. S. M. E. Boiler Code contains the follow-
ing requirements as to pipe connections to boilers: "If the
thickness of the material in the boiler is not sufficient to give
the required number of threads in accordance with Table I,
the opening shall be reinforced by a pressed-steel, cast-steel,
or bronze-composition flange, or plate, so as to provide the
thickness of plate for the required number of threads."
TABLE I
MINIMUM NUMBER OF PIPE THREADS FOR BOIM3R
CONNECTIONS
Size of Pipe
Connection
Inches
Number
of Threads
per Inch
Minimum Number
of Threads
Required
in Opening
Minimum Thick-
ness of Material
Required
Inches
1 and li
Hi
4
.348
Hand 2
Hi
5
.435
2| to 4
8
7
.875
4|to6
8
8
1.000
7 and 8
8
10
1.250
9 and 10
8
12
1.500
12
8
13
1.625
58. Reinforcing Small Pipe Openings. Small openings
that are to be tapped for pipes not exceeding 1J inches nomi-
nal diameter usually have the holes reinforced with a triangular
liner a, Fig. 56, which is riveted to the inside of the shell plate
BOILER DETAILS, PART 1
47
as shown. The sectional view is taken on the line A A of the
front view.
In horizontal tubular boilers having the blow-off attached to
the bottom of the rear course, the hole is reinforced by an otit-
FIG. 56
FIG. 57
side circular liner a, Fig. 57, attached to the boiler sheet by
several rivets; flanges of the form shown in Fig. 58 are also
used extensively, being riveted to the shell and calked. Con-
nections for feedwater piping are made in this manner. This
form of flange permits the
pipe to be screwed in from
each side and in addition re-
inforces the metal around
the opening. The minimum
size of pipe and fittings for
blow-off piping is 1 inch,
FIG. 58
FIG. 59
and the maximum size is not over 2\ inches in diameter. Brass
or steel bushings a, Fig. 59, are used for attaching feedwater
piping up to and including pipes 1^. inches in size. The bush-
ing is threaded on the outside at b so as to enter the threaded
48
BOILER DETAILS, PART 1
opening in the plate c. The internal thread d permits turning
the feed-pipes e and / into position. In tubular boilers, bush-
ings of this kind are used extensively, being secured to the
front head of the boiler and calked to prevent any possibility
of leakage.
FIG. 60
59. Boiler Nozzles. For openings 2\ inches in diameter
and larger it is necessary to use flanged fittings called nobles.
Such fittings are made of steel or iron castings of the form
shown in Fig. 60 (a}, or -of pressed steel of the form shown
). The latter construction is the stronger and is best
in
BOILER DETAILS, PART 1 49
suited for boiler-fitting connections. If cast steel or iron
nozzles are used, the requirements governing their use and
manufacture must be complied with. The A. S. M. E. Boiler
Code does not permit the use of cast-iron fittings for pressure
parts over 2 inches in diameter, for pressures above 160 pounds
per square inch. For fittings of this kind up to and including
160 pounds per square inch, the nozzles must conform to the
American Manufacturers' standard, except that in the case of
nozzles for safety valves the face of the safety valve and nozzle
may be made flat. In some cases the flange faces are made
with a raised face that is machined to provide a straight bearing
surface between the connecting fittings. Some authorities pro-
hibit the use of cast iron for this purpose, owing to its low
tensile strength and its liability to be in a weakened condition
due to a porous formation of the metal in molding.
60. Pressed-steel nozzles, also referred to as saddle
flanges, are made of the shapes shown in Fig. 60 (6) and (c).
In either form the nozzle is pressed from steel plate to form
the face a for the seat of the connecting fitting and the base b
to conform to the shape of the boiler shell c. This form of
construction produces a very strong fitting. The saddle shown
in (c) is reinforced with a liner d of the same plate thickness,
which is usually welded at four points to the saddle. To hold
the pipe flange e, studs / are screwed into the plate d and the
metal of the saddle. Both types of nozzles are beveled so that
they can be calked. In the case of a cast nozzle, as in (a),
a copper or steel strip a is placed between the nozzle and the
plate for calking purposes.
BOILER DETAILS
(PART 2) .
STAYING
TYPES OF STAYS AND BRACES
PURPOSE AND CLASSIFICATION
1. Introduction. The terms stay and brace are applied ,o
boiler details designed to support plates not strong enough in
themselves to resist safely the steam pressure that the boiler
is intended to carry. A stay or brace may be in tension or in
compression, depending on the method of installation. Cylin-
drical shells, hemispherical heads, and spherical shapes subjected
to internal pressure are self-supporting, as the pressure tends to
maintain the curved forms; therefore, boiler plates of such
forms and of sufficient thickness need no staying. Curved
sections that cannot be made thick enough to sustain the steam
pressure must be stayed.
Internal or external pressure acting on a flat plate tends to
distort the metal to a spherical form ; hence, a flat plate is not
self-supporting, as it cannot be made sufficiently thick to prevent
undue deformation. It is advantageous to use light boiler plate
and stay it to withstand safely the given pressure.
2. Classification of Stays. Stays used for bracing steam
boilers may be divided into three general classes ; namely, direct
stays, diagonal stays, and girder stays.
A direct stay is one in which the load due to the steam pres-
sure is applied directly in line with the axis of the stay. In
COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED
2 BOILER DETAILS, PART 2
case the stay braces a flat surface, it will make an angle of 90
degrees with that surface; and if it is applied to a curved sur-
face, it will be normal to it at the point of application. By
normal is meant that the stay is at right angles to a straight line
tangent to the surface at the point of application. A diagonal
stay is a stay that is not placed at right angles to the surface it
supports. A girder stay is a stay in the form of a girder, and
is subjected to bending stresses produced by the load.
TYPES OF DIRECT STAYS
3. Solid Screw Staybolt. A common form of solid screw
staybolt, which is used for bracing in the small water spaces of
locomotive-type and vertical boilers, is shown in Fig. 1. The
staybolt, which is threaded for its entire length, is screwed into
place, after which the ends are 'riveted over. The thread
employed for screw '
stays is the United
States standard, or 12
threads per inch.
FIG. i "* ^>trew Staybolt
With Telltale Hole.
An improved form of screw staybolt used extensively for stay-
ing flat plates and internal fireboxes of vertical fire-tube boilers
is shown in Fig. 2 (a). Only the ends are threaded, leaving
the body of the stay smooth, as a smooth surface is not attacked
so readily as a threaded surface by the corrosive elements of the
leedwater. A hole a f called a telltale hole, is drilled into one
or both ends of the staybolt, this hole having a diameter of
from & inch to inch and a depth of from 1 inch to If inches.
When such a staybolt breaks, which, in locomotive-type boilers,
occurs near the outside sheet, water or steam escaping through
the crack and the hole a, as shown in 0), gives warning of
the break. Many engineers prefer to have the telltale hole
extended through the entire length of the staybolt, as shown in
Fig. 3. A staybolt with a hole extending from end to end is
called a hollow staybolt.
BOILER DETAILS, PART 2 3
5. Screw Staybolts With Nuts. In the Scotch type of
marine boilers, the sides and back of the combustion chambers
are generally braced with screw staybolts, fitted with nuts, as
shown in Fig. 4. The staybolt a is screwed into the plates b
and has, on the out-
side of the plates,
nuts forming heads.
One of the nuts is
shown enlarged at the
left of the illustra-
T, 1 KSS ^ } FIG. 3
tion. It has a recess c
in its face, which, before the nut is applied to the stay, is filled
with stiff red-lead putty mixed with iron filings; this mix-
FIG. 4
ture aids in making a tight joint. If nuts are applied to stay-
bolts used in stationary and locomotive work, they are put
I L T 45913
4 BOILER DETAILS, PART 2
on without any mixture or preparation; but in marine work,
it is the usual practice to calk the sheets around the body of the
bolt before applying the nuts.
6. Through Stays. A long stay passing through the
boiler from head to head is called a through stay, a stayrod, or
FIG. 5
an end-to-end stay. A common construction of one end of a
stayrod is shown in Fig. 5. \ The end of the stay rod a is'
enlarged and threaded, and passes through a hole in the plate b,
the hole being slightly larger than the threaded end of the stay-
FIG. 6
FIG. 7
rod. A large washer c is placed on the outside of the plate b
and riveted to it, thus strengthening the head. A small washer d
is usually placed on the inside. Nuts e lock the stayrod to the
plate. Instead of using a large washer for each stayrod, a stiff-
ening plate, often called a doubling plate, is used. This plate
BOILER DETAILS, PART 2
covers the whole area of that part of the head braced by the
stayrods and is riveted to either the inside or the outside of
the head.
7. Washers are not always used under the nuts of the
stayrod ; when they are not used, the nuts bear directly against
the plate, as shown in Fig. 6. The nuts a are recessed like
those in Fig. 4, and the recesses are filled with the mixture
described, or are packed with asbestos rope packing, so as to
make a steam-tight joint against both sides of the boiler head b,
Fig. 6.
8. Occasionally, the construction shown in Fig. 7 is
adopted. The stayrod a is supplied with two washers b and two
nuts c, which are not recessed. A steam-tight joint is made by
filling the space between the head d and
the hole of the washers and the threads of
the Stayrod with asbestos rope packing.
Sometimes, as shown in Fig. 8, the stay-
rod a is screwed into the head b and locked
by a nut c placed on the outside of the head.
9. Through stays are also made in
other ways. In Fig. 9 (a) is shown a stay
having one end a threaded and screwed
into the tube-sheet b. At the other end c,
the stay is formed with an eye. To fasten
the eye end of the rod in place, angles d are riveted to the
boiler head and the rod is then slipped between the angles
and held in place by the bolt e. Another method of connect-
ing the ends of stayrocls to boiler heads is shown in (&).. The
end of the stayrod a is formed with a fork b to receive the
forged leg connection c. Each leg c has a flat foot d that can
be riveted to the tube-sheet. The combined sectional area of
the two legs should exceed the cross-sectional area of the stay-
rod a. Forged connections of this type are used very often to
support the tube-sheets of Scotch boilers.
10. Flexible Staybolts. Rigid staybolts screwed into the
furnace sheet and the outside sheet of a boiler are subjected not
6 BOILER DETAILS, PART 2
only to tension but also to bending as the result of repeated
expansion and contraction of the boiler plate. To overcome the
breakage caused by this bending, flexible staybolts have been
designed. There are two principal forms of the screw type, as
shown in Fig. 10 (a) and (&). The standard screw type shown
in (a) is used extensively in the water legs of locomotive boil-
ers. The inner end a of the staybolt is threaded and screwed
into the firebox sheet b. The head c of the outer end is partly
FIG. 9
spherical and fits a spherical seat in the sleeve d, which Is
screwed into the outside sheet e. The sleeve d is enlarged on
the inside at / to permit the stay a to move freely in accommo-
dating itself to the movement of the firebox sheets. A cap nut g
is screwed over the sleeve to make a steam-tight joint. After
the stay has been screwed in place, the threaded end is headed,
as shown, and during the riveting process a bar with a spherical
recess is held against the opposite end. '
BOILER DETAILS, PART 2
The flush type of flexible staybolt, shown in (&), is used in
places where the projecting head, like that shown in (a), would
interfere with setting other connecting parts. The construction
of the bolt a shown in
(&) is the same as the
one shown in (a), ex-
cept that it is shorter.
The sleeve b, view (&),
is screwed into the
outer sheet c Until it is
flush with the outer sur-
face. The plug d is
screwed into the sleeve
to produce a steam-
tight connection.
11. Stay-Tubes.
Many authorities re-
quire the flue sheets
of large high-pressure boilers, to be braced so that very little
stress will come on the boiler tubes, which are expanded in place.
In such a case, flue sheets are braced by using stay-tubes, which
are tubes that act as end-to-end stays. Two methods of secur-
ing such stays to the tube-sheets are shown in Fig. 11 (a) and
FIG. 10
(a)
FIG. 11
(6). The ends of the tubes in both types are threaded and
screwed into the tube-sheets. When the end is flared, as shown
in (a), it should project beyond the tube-sheet J inch. Stay-
8 BOILER DETAILS, PART 2
tubes when threaded must not be less than -^ inch thick, meas-
ured at the bottom of the thread. The body of the tube is
made about | inch smaller than at the threaded end, so that
after the threaded end has been screwed through the first sheet,
the tube can be easily shifted to install it in the second sheet,
and then both ends can be screwed into the tube-sheets at the
same time. In the construction shown in (&), a nut is screwed
over the end of the tube, to bear against the tube-sheet. Nuts
on stay-tubes are not advised where such tubes are used in
staying the heads of tubular boilers, because the heat will burn
the nuts away.
DIAGONAL STAYS
13. Radial Stays. In locomotive boilers, the shape of the
firebox and the outside furnace sheet is often such that it is
FIG. 12
convenient to brace the entire firebox with screw stays, arranged
as shown in Fig. 12 (a). It will be noticed that various groups
BOILER DETAILS, PART 2 9
of stays, in the curved surfaces radiate from common centers,
as a, b, and d. It is customary to apply the term radial stays
to the stays that radiate from the center d and brace the crown
sheet e. A locomotive boiler having radial stays for the crown
sheet is a radial-type locomotive boiler. All staybolts of loco-
motive boilers are generally made with enlarged threaded ends
and are screwed into the sheets. The radial stays are some-
times simply riveted over -at both ends, as shown in (a), but it
is also common to make the radial stays with a hexagonal head
at the firebox end, as shown in (b). Staybolts supporting a
crown sheet and having a head or a nut on the firebox end are
FIG. 13
often called crown bolts. The diameter of the body / of the
stay should be made slightly less than the diameter at the root
of the thread.
13. A standard crown stay of the dimensions now used
for some locomotive boilers is shown in Fig. 13. The reduc-
tion of diameter of the stay between the threaded ends, effected
by upsetting the ends for the smaller sizes and machining those
of greater lengths, relieves to a certain extent the bending action
due to the expansion and contraction of the sheets. This con-
struction assists also in reducing the breakage of the stays, a?
the smoothness and flexibility of the stay lessen the accumulation
of scale around it. The taper head a assists in assuring a
steam-tight joint and a greater thread area to resist the pres-
sure. Each end has twelve threads per inch and is upset so-
that a head J inch in depth is obtained, as shown at &. The
square head c is used for turning the stay into place, after
which it is burned off with a gas torch.
10
BOILER DETAILS, PART 2
14. The firebox ends of some crown stays are formed as
shown in Fig. 14. The stay shown in (a) is an ordinary screw
(e)
stay screwed into the crown sheet a. When set in place the
nut b is screwed tight against the crown sheet, and the end of
FIG. 15
the bolt is then riveted over as at c to retain the nut b in place.
The crown bolt shown in (J) has a solid hexagonal head
BOILER DETAILS, PART 2 11
forged on it and is screwed into the crown sheet. In order to
make a steam-tight joint, a soft steel or copper washer d is
usually placed under the head. In (c) is illustrated a button-
headed crown bolt, which is provided with a square head e in
addition to the button head. The square head is for the pur-
pose of screwing the bolt tightly into the crown sheet c, after
which it is removed. This may be done by nicking the groove /
with a sharp chisel and then twisting off the head ; or, the head
may be burned off with a gas torch, the latter method being pre-
ferred. When crown bolts with nuts are used, as shown in (a),
it is the practice of some boilermakers to calk the crown sheet
to the bolts, on the fire side, before applying the nuts.
15. Flexible Radial Crown Stays. In Fig. 15 are shown
some of the different forms of flexible stays used for supporting
the roof sheet a and crown sheet b.
The sleeve c, spherical head d and cap e
are similar to those in Fig. 10. The
radial stays are headed over at the
crown sheet, as shown at f, Fig. 15,
the smaller head / being preferred to
the button head g, as the larger body
of metal of the button head burns
away under the direct action of the
heat from the fire. The square shank h FlG * 16
of the button head is removed after the stay is in position. A
roof liner i is attached to the roof sheet and the additional plate
thickness provides a greater bearing area for the screw threads
of the sleeves.
The sleeve arid cap shown in Fig. 16 are now being used
extensively and are preferred by most engineers in place of the
screw sleeves shown in Fig. 15. The cap a, Fig. 16, is welded
to the roof sheet b by a light bead c and is closed by a cap d
that is screwed down on a gasket in the recess e. The sleeve
can be readily attached to a roof sheet of any curvature.
16. Gusset Stays. A gusset stay, as shown in Fig. 17,
consists of a steel plate a secured to the boiler head b and the
shell c by angles d ; or, tee irons may be used instead of angles.
12
BOILER DETAILS, PART 2
This form of stay is used in bracing boiler heads of internally
fired boilers, but the rigidity of the stay is objectionable as it
FIG. 17
localizes the stresses on the connecting boiler plates. With the
construction shown, the rivets in the ends of the gusset are in
double shear; but if a tee iron is used instead of the pair of
angles, the rivets at the connection with the gusset will be in
single shear. When tees or
angles are used
diagonal braces
they should be
oooooooooooo
oooooooooooo
oooooooooooo
oooooooooo
oooooooo .
FIG. 18
tubular boiler must be stayed.
to connect
to heads,
placed as
shown in Fig. 18, in lines
radiating from the center of
the head.
17. Diagonal Stays.
That part of a tube-sheet that
does not receive support from
tubes :as, for example, the
segment of a flat head above
the upper row of tubes in a
A common form of stay used
for this purpose is the diagonal stay. It may consist of a rod
welded at the ends to flat pads that are riveted to the head and
BOILER DETAILS, PART 2
13
the shell ; or, it may be made from a solid strip of boiler plate
formed to the desired shape under hydraulic pressure. The lat-
Jt
ter type is considered more reliable than the welded type. A form
of welded brace is shown in Fig. 19 (a) . The wrought-iron rod a
is welded at one end to the flat pad, or palm, b by which the stay
is connected to the shell plate, and at the other end to a pad c
that is riveted to the tube-sheet segment or boiler head. This
form is frequently called the palm stay. Another form of
welded stay is shown in (&). The end a is enlarged and
threaded and passes through a still larger hole in the boiler
head. Wedge-shaped washers fit against opposite sides of the
plate and are set up tightly by means of the nuts. The palm
end b is riveted to the shell. This form of stay is not used
extensively because of
the difficulty of main-
taining a steam-tight
connection at the end a.
18. The weldless
forms of diagonal
braces shown in Fig.
20 (a) and (&) are an
improvement over the welded types previously described. The
brace shown in (a) is the McGregor weldless brace. It is
14 BOILER DETAILS, PART 2
made in one operation by heating a piece of sheet steel,
splitting one end to form the crowfoot, and bending the other
to the desired angle, all under heavy pressure. Because of
the manner in which the branches at the end are split and
bent outwards, this type of brace is frequently termed a
crowfoot brace. Another form of diagonal stay, known as
the Huston crowfoot brace, is shown in (6). The body of the
brace is doubled, thus enabling the foot to be made solid, with-
out splitting-. The palm end is formed to a channel shape, pro-
ducing a strong brace.
GIRDER STAYS
19. Girder Stays in Scotch Boilers. The tops of the com-
bustion chambers of Scotch boilers are usually supported by
girder stays, also called crown bars. In Fig. 21 is shown how
FIG. 21
girder stays are arranged over the top of a combustion chamber.
Each girder consists of two steel plates a of the same shape and
thickness, set side by side and held at a fixed distance from
each other by thimbles b through which pass rivets that hold
the plates a together. This built-up girder is placed on top of
the combustion chamber, with its ends c resting on the upper
BOILER DETAILS, PART 2
15
ends of the heads d and e of the combustion chamber. Bolts f,
threaded at both ends and fitted with nuts, are inserted through
holes in the crown sheet g that is to be supported. These bolts
fit between the plates a and at their upper ends pass through
clips h having lugs that fit over the plates a and help to prevent
their spreading. The nuts on the
bolts are tightened, and thus the
pressure of the steam on top of the
plate g is transmitted by the bolts
to the girder, and by it to the
plates d and e, which carry the en-
tire load. Girders of this type are
spaced at uniform intervals across
the top of the combustion chamber.
20. A different form of girder
stay is shown in Fig. 22. The gir-
der itself is composed of two- plates
held apart by spools, or distance
pieces, and the bolts that support
the crown sheet fit between the gir-
der plates as in the type just de-
scribed. But the load is not carried
by the combustion-chamber heads.
Instead, stays a are attached at the
ends of the girder, between its
plates, and the upper ends of these
stays are connected to* angle irons b
riveted to the inside of the top sheet
of the boiler. Thus, the load due
to the downward pressure on top of
the crown sheet is carried by the
outer shell, from which the girders are suspended by the stays a.
As the plates c and d are thus relieved of the load, they need
not be so heavy as when a girder of the form shown in Fig. 21
is used. The bottom of the combustion chamber, Fig. 22, is
braced by angle irons e riveted to the bottom plate /. Alter-
nate angle braces are connected to angles g riveted to the boiler
a
..& 6-
J
a
1-
Dj \\ @ \\ j! j @ (.0,
j!i ij j
\
fl , , < i i c
4- + 4- 4- 4- -
(,, _i_ j_ .1 ,.i
4 4- 4- 4- 4
44-4-4-4
4, 4 1 4. _j_
4- 4- 4- 4/ 4/
+ + + 4. 4.
_l_ i 1 1 i
h
. i
y?
4- 4/ 4- 4- -f
4- 4- .4- 4- 4- -
+ 4-4-4-4-
+ + + + .+ .
4-4-4-4-4-
r ]][jjjjl _
i i ilil
!!
! lli! -
JJJLJ !l 1 II 1 ll llUnN
^TTTXl
IfcMf^lfirJ^
BWI
FIG. 22
16
BOILER DETAILS, PART 2 17
shell. In some constructions, screw stays are employed for
staying the bottom sheets. The sides of the combustion cham-
ber are stayed by screw stays h that may be riveted over at
the ends; or, they may be riveted over on the ends inside the
combustion chamber and have nuts on the outside.
21. Locomotive-Boiler Crown Bars. In some types of
locomotive boilers the crown sheets and side sheets are so
arranged and shaped that there are no projecting sections, as in
Fig. 21, on which to set the ends of the girder stays. An exam-
ple of this kind is shown in Fig. 23 (a) and (&). The usual
practice in staying such a firebox is to install radial stays a, or
crown bolts, and at the forward end two crown bars b, bent to
the curvature of the crown sheet c. Usually the crown bars
are made of structural forms, such as tee irons. The crown
bar b is attached to the crown sheet by means of crown bolts d
that pass through the flanges of the crown bar and through
spools e inserted between the crown sheet and the crown bar.
The roof bar / is a tee iron bent to conform to the curvature
of the roof sheet g to which it is riveted. Flat steel-plate stays h
called sling stays, connect the roof bar / and the crown bar b.
The brace pins i are threaded and are inserted into holes in the
stays and tees. The nuts / that hold the pins i in place are
prevented from turning off by cotter pins through the ends of
the brace pins. The hole in the lower end of each sling stay is
made oblong for the following reason: As the radial screw
stays a are rigidly fixed and as the crown sheet is rigidly sup-
ported by the flange of the tube-sheet, the unequal expansion
and contraction of the crown sheet causes a bending action on
the stays. To overcome this condition it is customary to use a
sling stay having an oblong hole, as this allows the outer plates
of the firebox to contract without placing any great bending
load on the sling stays.
MIS CELL, ANJSOtTS BRACES
22. Throat Braces. In boilers of the locomotive type the
firebox tube-sheet must be braced below the tubes. In some
constructions this can be done satisfactorily by ordinary screw
FIG. 24
BOILER DETAILS, PART 2 19
staybolts; but where the arrangement of the firebox sheets is
such that the tube-sheet extends beyond the throat sheet, special
forms of stays are used to stay the tube-sheet to the boiler shell.
The stays employed for this purpose are called throat braces, or
heel braces. Several types of throat braces are shown in Fig.
24. The brace a shown in (a) is made with a palm b that is
riveted to the boiler shell, and the other end is formed into a
fork c that is attached to a crowfoot d by means of the brace pine.
The crowfoot d is fastened to the tube-sheet /by two stays g
that pass through distance pieces h. The end of the staybolt
passing through the crowfoot is made usually with a hexagon
head L
23. The throat brace shown in Fig. 24 (6) is a steel drop
forging bent at a to clear the rivet seam between the boiler shell
and the throat sheet. The end of the stay that is riveted to the
shell is flat and the other is upset to form a projecting end or
boss b. The boss is drilled and tapped to receive the staybolt c,
which is screwed into the tube-sheet d and riveted over. The
throat sheet e is made somewhat thicker than the sheet d. In
order that the brace need not have too large an offset, which
would introduce transverse stresses and affect its staying quali-
ties, it is customary to use countersunk rivets / in the throat
seam under the brace.
A modification of the brace in (6) is shown in (c). In this
type the brace a is made with a crowfoot b that is riveted to the
tube sheet c by rivets d passing through distance pieces. The
distance pieces allow a larger water space between the tube-
sheet and the crowfoot. The rivet holes in the tube-sheet are
usually countersunk so that only a. small amount of the rivet
head projects into the firebox.
In the stay installation shown in (d), a threaded stay is
employed. It produces a strong support and one that is readily
applied. The lug a is a drop forging of steel and the projecting
end b is drilled and threaded to receive the stay c. The stay is
screwed into the tube-sheet and headed. Owing to its length
the stay gives with the expansion and contraction of the firebox,
which is a desirable feature.
I L T 45914
20
BOILER DETAILS, PART 2
34. Steel Angle Stays. For the upper segments of tube
heads of boiler shells not exceeding 36 inches in diameter, and
when the boilers are designed to carry a working pressure not
greater than 100 pounds per square inch, the method of bracing
shown in Fig. 25 may be employed. The steel angles are
placed back to back so that their short legs a can be riveted to
Q
oooooooo
oooooooo
oooooo
o /^ o
FIG. 25
the boiler head b. The projecting legs c of the angles are also
riveted together. The spacing of the rivets in the legs c should
not be over 8 inches and the spacing of the rivets attaching the
angles to the boiler head should not be over 4 inches. The bot-
tom of the lower angle should be not less than 2 inches above
the top row of tubes d. Rivets of the same diameter as are used
in the boiler shell should be used for this method of bracing.
BOILER DETAILS, PART 2 21
TUBES, FLUES, AND FURNACES
BOILER TUBES AND FLUES
BOILER TUBES
25. Purpose of Boiler Tubes. The principal purpose of
boiler tubes is to increase the heating surface of the boiler and
thereby increase its steaming capacity. The tubes also divide
the water and heated gases into small bodies, which assists in the
transmission of the heat from the fire to the water. When
the tubes are expanded in the boiler heads, or tube-sheets, they
act as stays to support the flat plates.
26. Manufacture of Boiler Tubes. Boiler tubes may be
made of iron, steel, brass, copper, or monel metal. Steel tubes
may be either lap-welded or seamless. In making lap-welded
tubes, strips of metal, or skelps, are prepared with scarfed
edges, so that, when these edges are overlapped to form the
welded seam, there will be no undue thickness of metal. The
skelp is heated, and while hot is- bent to a circular form through
a die, after which it is reheated to a welding temperature. In
the welding operation it is passed through or between rolls
grooved to give it the desired tubular form. A mandrel inside
the tube forms the anvil on which the overlapping scarfed edges
are pressed firmly together to form the weld. After welding,
the tubes are annealed to remove the internal stresses set up by
heating, and working the metal during the welding process.
Lap-welded charcoal-iron tubes are made in the same way by
using charcoal-iron skelp.
27. Seamless tubes of steel and charcoal iron are used
extensively in locomotive boilers, as both kinds withstand to
good advantage the severe service arising in the operation of
22
BOILER DETAILS, PART 2
locomotives. Seamless steel tubing is produced from a round
steel billet that is placed in a furnace and heated to a white
heat. The billet is then pushed by special machinery and at
the same time pierced by a pointed mandrel, which produces
a 'rough tube several times as long as the original billet. The
next process consists in rolling the rough tube over a mandrel,
whereby the thickness of the tube wall and the diameter are
TABLE I
DIMENSIONS AND WEIGHTS OF BOILER TUBES
Outside
Diameter
Inches
Thickness of Wall
Theoretical
Weight
per Foot
Pounds
Length of Tube in Feet
per Square Foot of
External
Surface
Internal
Surface
Inch
B. W. G.
1
.095
13
.918
3.820
4.715
li
.095
13
1.171
3.056
3.604
14
.095
13
1.425
2.546
2.916
11
.095
13
1.679
2.182
2.448
2
.095
13
1.932
1.909
2.110
2i
.095
13
2.186
1.697
1.854
24
.109
12
2.783
1.527
1.673
21
.109
12
3.074
1.388
1.508
3
.109
12
3.365
1.273
1.373
3i
.120
11
4.011
1.175
1.269
34
.120
11
4.331
1.091
1.171
3f
.120
11
4.652
1.018
1.088
4
.134
10
5.532
.954
1.023
44
.134
10
6.248
.848
.902
5
.148
9
7.669
.763
.812
reduced and the rough tube is converted into a longer and
smoother tube. The tubing is then passed through a burnishing
machine to give it a smooth burnished surface, after which
it is sized through finishing rolls that produce the required out-
side diameter. Tubes manufactured in this manner are known
as hot-rolled seamless tubes. Cold-drawn seamless tubes are
BOILER DETAILS, PART 2
23
made in a similar manner, except that the metal is not reheated
while being worked. Such tubes are annealed to insure ductil-
ity of the metal, so that they can be easily expanded, flared, and
beaded without splitting the ends.
Brass and copper tubes for boilers are seamless ; such tubing,
however, is not used to any great extent in the United States
and Canada. European countries use it in preference to steel
and iron tubing, on account of the resistance of such metals to
the corrosive effects of the feedwater.
28. Sizes and Gauges of Boiler Tubes. The sizes of
tubes are designated by their outside diameters to distinguish
them from pipes, which are de-
signated by their normal inside
diameters. Tubes more than 6
inches in diameter are usually,
called fluefs. The thickness of
tubes is generally expressed by
giving the number of the corre-
sponding notch of the Birming-
ham wire gauge, generally abbre-
FIG. 26
viated to B. W. G. Table I gives ^
the standard thickness of lap-
welded and seamless-drawn boiler
tubes, both by the wire gauge and
in decimals of an inch, together
with the minimum weight per
foot of length and the length per
square foot of surface. Boiler
tubes in all sizes can be obtained one gauge number thicker than
given in the table, for use in boilers carrying a very high work-
ing pressure. In estimating the effective heating surface of
boiler tubes or flues, the surface in contact with the products
of combustion is considered, whether internal, as in the case of
fire-tubes, or external, as in the case of water-tubes.
29. Upset Tubes. Tubes known as upset tubes are pro-
duced by upsetting the tube ends, thus increasing the thickness
of the wall at those points. Such tubes are used for stay-tubes,
I
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BOILER DETAILS, PART 2
25
which may be threaded at the ends and screwed into the tube-
sheets ; or, nuts may be placed on the threaded ends, on the out-
side and also inside of the tube-
sheet. Upset tubes may also be
used in place of ordinary boiler
tubes. There are two general forms
of upset tubes, which are shown in
Fig. 26 (a) and (6). The type
shown in (a) is the plain upset
tube and that in (&) is the upset
and swelled-end form. In either
case the usual length of the upset a Fia 27
is 2| inches. There is a limit to the thickness to which the
tube ends can be properly upset. Above this maximum it is
difficult to upset the ends to a greater thickness. Table II
gives the sizes of tubes and thicknesses of tube walls, with the
corresponding outside diameters of the upset ends as ordinarily
used.
30. Installation of
Boiler Tubes. T h e
method of securing the
fire-tubes in the heads
of tubular boilers is
shown in Fig. 27. The
tube a is from ^ to -f^
inch smaller in diam-
eter than the tube
holes in the tube-
sheets b and c. This
is essential so that the
tubes can be readily
put in place. Each
tube end should pro-
ject J inch beyond the
tube-sheet. When the
tubes are in place,
they are expanded by means of a tube expander, or tube roller.
The projecting ends are then peened over, or flared, as shown
FIG. 28
26 BOILER DETAILS, PART 2
at the end d, which may be done by using the ball end of the
boilermaker's hammer, or with a flaring tool, which is taper-
ing in form and operated by an air hammer. After the ends
are flared, they are beaded, as shown at e, by the use of a
beading tool, or boot tool, which is made as shown in Fig. 28
(a) for hand beading. For beading done by the use of an air
hammer, a tool of the same shape is used, having at the end
a circular shank, as shown in (&), which is inserted in the
driving end of the air hammer. The beading tool should be
held in about the position indicated so that the bead is brought
down over the edge of the plate ; otherwise, the bead may be
forced away from the tube-sheet, resulting in
leaky tubes.
31. In the installation of tubes in Scotch
boilers, the tube a, Fig. 27, is inserted from the
front head of the boiler. The ends of the tubes in
the combustion chamber are set to project i inch
beyond the combustion-chamber tube-sheet, and
at the front end from J to f inch outside the
\A m front head. Both ends are expanded and those
:ij FIG. 29 j n ^ com b us tion-chamber end are flared and
:i;Sj beaded; but at the front end the tubes are usually expanded
:-. ; ! and flared. Stay-tubes having upset and threaded ends are
:;] extensively used in staying the heads of Scotch boilers.
"\ Locomotive boiler tubes are installed in a similar manner
; except that a copper liner, or ferrule, is usually placed between
'; the tube-sheet in the firebox and the tubes. Such liners take
i; up the inequalities in the metal of the tube and plate, thus
:/< insuring a tighter connection. The ferrules are usually about
-fa inch thick and are set to extend about fa inch inside the hole
from the tube-sheet, as shown in Fig. 29. It is also the prac-
tice to weld the bead of the tubes to the firebox tube-sheet to
insure steam-tightness. Water tubes in water-tube boilers are
expanded and flared.
BOILER DETAILS, PART 2
27
BOILER FLUES
32. The purpose of boiler flues is identical with that of
boiler tubes. In sizes from 6 inches to 16 inches, external
diameter, they can be obtained lap-welded and of sufficient
length. The larger sizes of flues are often made, however,
with longitudinal lap joints or butt joints, and are constructed
of short sections riveted together. The standard sizes of lap-
TABLE III
PROPERTIES OF LAP-WELDED FLUES
Outside
Diameter
of Flue
Inches
Thickness of Flue
Theoretical
Weight
per Foot
Pounds
Length of Flue, in Feet,
per Square Foot of
Inch
B. W. G.
External
Surface
Internal
Surface
6
.165
8
10.282
.636
.673
7
.165
8
12.044 ,
.545
-572
8
.165
8
13.807
.477
.498
9
.180
7
16.955
.424
.442
10
.203
6
21.240
.381
.398
11
.220
5
25.329
.347
.361
12
.229
28.788
.318
.330
13
.238
4
32.439
.293
.304
14
.248
36.424
.272
.282
15
.259
3
40.775
.254
.263
16
.270
45.359
.238
.247
welded boiler flues, minimum weight per foot of length, and
length of flue per square foot of surface, together with "their
thickness by wire-gauge number and in decimals of an inch, are
given in Table III.
The standard thicknesses of boiler flues having an external
diameter of 12, 14, and 16 inches, do not correspond to B. W. G.
numbers, and hence are given only in decimals of an inch.
28
BOILER DETAILS, PART 2
FURNACE FLUES AND COMBUSTION CHAMBER!
CYLINDRICAL FURNACE
33. Plain Furnace Flue. The simplest form of furnac
flue is a plain cylinder of wrought-iron or steel plate, which ma]
have a riveted longitudinal seam or may be welded. If condi
tions were such as to call for a comparatively large furnace flu*
and a high pressure, a plain furnace flue would have to be sc
thick as to interfere seriously with the transfer of heat fron
the fire to the water. To overcome this defect, plain furnact
flues are stiffened by means of strengthening rings, which an
attached to the outside, where they are in contact with the
water in the boiler.
34. Furnace Flues With Strengthening Rings. To
strengthen the plain type of furnace flue, stiffening rings of
FIG. 30
FIG. 31
angle iron or tee iron are attached to the outside. A common
construction is shown in Fig. 30. The strengthening ring a is
made of angle iron and encircles the flue, from which it is
separated by a spool b placed around each rivet c. The spools
hold the ring away from the flue and thus provide for a free
circulation of water between them. The circulation of water
next to the flue protects it from injury by the fire. A short
furnace flue of a given diameter and thickness is much stronger
than a long one of the same diameter and thickness ; therefore,
furnace flues are often made in sections united in such a man-
ner as to secure great strength with comparatively thin material.
Flues thus constructed are called built-up furnace flues, and also
sectional furnace flues.
BOILER DETAILS, PART 2
29
35. A simple method of constructing a built-up furnace
flue, but one that is little used, is illustrated in Fig. 31. A
welded T-iron ring a has its legs b and c riveted to the plain
cylindrical sections d and e of the furnace flue. Although this
construction is an improvement over that shown in Fig. 30, there
are better forms in use for joining the sections, as, for instance,
the Adamson ring joint shown in Fig. 32. When this type of
ring joint is used, the ends a and b of the sections are flanged
FIG. 32 FIG- 33
and riveted together with a welded and finished ring c between
them. The flanging provides stiffness to resist the external
pressure, and the rounded corners of the flange allow for a
little expansion and contraction. In Fig. 33 is shown a method
of building a cylindrical furnace. The sections a and b are
joined by a U-shaped ring c, called a bowling ring. This ring
stiffens the plain cylindrical sections and at the same time, owing
to its curvature allows for longitudinal expansion and con-
traction.
CORRUGATED FURNACES
36. Manufacture of Corrugated Furnaces. There are sev-
eral types of corrugated furnaces, commonly called suspension
furnaces, that differ only in the shapes of their corrugations and
their ends. The corrugations are produced in plain cylinders
having welded longitudinal joints. Preparatory to being cor-
rugated the cylinders are heated uniformly. They are then
passed through rolls and the corrugations are formed under
hydraulic pressure. When the forming process is complete, the
shells are again heated to anneal them and relieve the stresses
due to expansion and contraction of the metal. The corruga-
tions strengthen the furnace, increase the heating surface, and
30
BOILER DETAILS, PART 2
permit the furnace to expand and contract longitudinally, or in
the direction of its length. Furnaces of this kind are made
M-
i&-*-.
from 28 to 60 inches in diameter, inside, and with a plate thick-
ness of from $ to f inch.
37. Morison Corrugated Furnaces. In Fig. 34 (a) is
illustrated the Morison suspension furnace. The curved sec-
tions a, called the corrugations, have a pitch b of 8 inches from
center to center, the depth c of the corrugations being 1| inches.
BOILER DETAILS, PART 2
31
This type of furnace is made with different forms of plain ends,
to suit the requirements of design of the combustion chamber
and furnace connections of Scotch boilers. The furnace is con-
structed with an inside end d and an outside end e. The-end d
would fit inside and the end e outside the flange connections of
the boiler heads. There are two other forms of plain ends, one
form of which has two ends of the inside type and the other
form has two ends of the outside type. In view (fr) is shown a
furnace with two inside plain ends a, one of which is riveted to
FIG. 35
the outer head b f which has the flange c turned out for installing
the furnace. The head d of the combustion chamber e is also
turned out, as shown at /. It will be seen from the construction
that, in order to replace the furnace, it is necessary to remove
the front head, as such a furnace cannot be taken out through
the circular flanged opening in the front head. To overcome
this condition, furnaces of a special type have been designed, so
as to make the work of removal easy.
38. There are in general use two types of removable fur-
naces, which are of the forms shown in Fig. 35 (a) and (6).
32
BOILER DETAILS, PART 2
The one shown in (a) has one plain inside end a, and the oppo-
site end is cut away and flanged at b. The flanged portion
extends only a short distance around the top of- the furnace.
The bottom section c is of the same shape as the end a. The
other form, shown in (ft), is known as the horse-collar type, on
account of the shape of the oval end a, which in profile has the
shape of a horse collar. The flange b is set flush against the side
of the combustion-chamber head and riveted to it. The oppo-
site end c is made of a plain circular form.
In replacing a furnace of the horse-collar type it is inserted
into the front end of the boiler and raised off center, so as to
give it a slant, thus allowing the upper flange a to slide inside
the circular flange of the front head. After the furnace has
been raised sufficiently so that the lower edge clears the bottom
FIG. 36
flange of the head, it is swung so as to bring it central with the
furnace opening. From this position it can be slid back against
the tube-sheet of the combustion chamber.
39. Purves Ribbed Furnace. A Purves ribbed furnace
flue is shown in Fig. 36. The height of the ribs is If inches
and the distance from center to center of ribs is 9 inches. The
thickness of the flue must not be less than -f$ inch, and the
length of the plain part of the ends not more than 9 inches.
This form of flue is a modification of the built-up bowling-ring
principle of construction.
There are other corrugated furnaces having similar construc-
tion, such as the following: the Leeds corrugated furnace,
which has the corrugations pitched 8 inches between centers and
not less than 2J inches deep ; the Fox corrugated furnace, hav-
BOILER DETAILS, PART 2 33 '
ing corrugations pitched 8 inches between centers and not less
than 1^ inches deep; and the Brown corrugated furnace, having
corrugations 9 inches from center to center and not less than
If inches deep. The plate thickness of the Leeds, Morison,
Fox, and Brown furnaces should be not less than T % inch ; for
the Purves furnace and other furnaces having corrugations not
over 18 inches from center to center, the plate thickness should
not be less than $ inch.
COMBUSTION CHAMBERS
40. Purpose of Combustion Chamber. The combustion
chamber of a steam boiler is an enclosed space that provides a
place for the unconsumed gases to be mixed thoroughly with
air, which promotes their complete combustion. In some cases,
a small quantity of air is admitted into the chamber from the
ash-pit through small openings in the bridge wall or in the
diaphragm below the bridge wall. In other cases, the air is
admitted through small perforations in the furnace door.
Sometimes, the excess of air that passes through the grates is
depended on to produce the complete combustion of the gases
in the combustion chamber ; or, small openings may be made in
the sides of the combustion chamber through which the air
may enter.
41. In all cases, provision should be made to regulate the
quantity of air admitted to the combustion chamber, because, to
consume the gases completely, more air is required under some
conditions than under others. If bituminous coals are used, a
large quantity of air will be required, while with anthracite much
less air will be needed. The lowest temperature at which igni-
tion of the gases can take place is about 1,800 F. It is, there-
fore, evident that if the gases are cooled below the point of igni-
tion by too much air, or by coming in contact with heating sur-
faces before combustion is completed, they will be carried to
the smokestack unconsumed. It follows that the furnace must
be of sufficient height to provide a space in which the great vol-
ume of gas can burn before being cooled, or else there must
34
BOILER DETAILS, PART 2
be, adjacent to the furnace, a combustion chamber in which the
gases can burn.
42. Forms of Combustion Chambers. Internally firec
boilers have built-in combustion chambers. The combustior
chamber is constructed of steel plates which are riveted and
stayed to withstand safely the steam pressure carried by the
boiler. The design of the internal combustion chamber depends
on the form of the boiler. Usually it is made circular at the
bottom to conform to the curvature of the boiler shell. The
upper plates are either straight or arched and are braced by
suitable forms of stays.
BOILER DETAILS, PART 2
35
Externally fired boilers usually have brick settings that con-
tain the furnaces and combustion chambers. Their design
depends on the type and size of boiler. Fire-tube boilers have
combustion chambers of different forms from those of water-
tube boilers.
43. Combustion Chambers of Scotch Boilers. The
arrangement of the combustion chambers of a Scotch boiler
depends on whether the boiler is single-ended or double-ended.
Fig. 37 (a) and (b) shows a longitudinal and a transverse sec-
tion of a four- furnace single-ended Scotch boiler and illustrates
the details of arrangement of the combus-
tion chambers a. Each of the chambers
communicates with the front head of the
boiler through a separate corrugated fur-
nace flue. This construction is considered
preferable to that in which a single com-
bustion chamber is common to all the fur-
naces, although the latter is the cheaper to
construct. The front sheet of the com-
bustion chamber, which is also the tube-
sheet, is shown at b, and the rear sheet
at c ; d is the furnace flue. The tube-sheet
and the rear sheet are flanged inwards, as
shown at e, and the side sheets / and the
crown sheet are riveted to the flanges. A
circular opening is cut in the lower part
of the tube-sheet to receive the rear end of the furnace flue, the
two being firmly riveted togther, as shown at g.
44. Combustion chambers of Scotch boilers are secured to
the shell and the rear head of the boiler and to each other by
staybolts, as shown at h, Fig. 37. The bridge wall i, which is
constructed of firebrick, is built on the cast-iron bearing bar /.
The brickwork extends across the floor of the combustion
chamber and up the rear sjieet of this chamber for some dis-
tance above the top of the furnace flue, as shown at k and /,
to protect the metal at those points from the intense heat of
'the flame, which otherwise would impinge directly against it.
I L T 45915
L
FIG. 38
I
I
36 BOILER DETAILS, PART 2
Combustion chambers are sometimes constructed with round
or arched backs, as shown at a, Fig. 38. The purpose of this
is to facilitate -the flow of the gases of combustion into the
tubes, the curved top of the combustion chamber acting as a
deflector for the gases. A sheet of this form does not require
such extensive bracing as does a flat crown sheet.
PIPES AND PIPE FITTINGS
PIPES
PIPE MATERIALS
WROUGHT PIPE
1* Wrought-Iron and Mild-Steel Pipe. Boiler-room pip-
ing is generally made of wrought iron or of mild steel, that is,
soft steel. For most piping mild steel is suitable and with-
stands higher working pressures than genuine wrought-iron
pipe, and on account of its lower cost it is generally employed.
Genuine wrought-iron pipe is more durable and withstands
the corrosive elements; therefore, for pipes placed in the
ground, boiler blow-off connections, pipe drains and drips,
etc., wrought-iron pipe is preferable. The term' wrought pipe
is applied in the trade to both wought-iron and steel pipe and
it is the trade custom to supply mild-steel pipe unless genuine
wrought-iron pipe is specified.
2. Commercial Grades of Wrought Pipe. Wrought pipe,
which includes both wrought iron and steel, is classified accord-
ing to weight as standard, extra heavy, double extra heavy, and
large 0, D. The first three classes are designated by nominal
diameter, which ranges from inch up. The dimensions and
weight of various sizes of standard wrought pipe are given in
Table I. It should be observed that the actual inside diameter,
in pipes under the 1-inch size, is considerably greater than the
nominal diameter. Standard pipe is usually sold in lengths
COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED
PIPES AND PIPE FITTINGS 3
of from 18 to 20 feet. Hydrostatic tests are made at the mill
to detect defects in the welds or other parts of the pipe. Each
manufacturer has his own schedule of tests, but the average is
somewhat like the following : Standard butt-welded wrought
pipe in sizes from inch to 3 inches is tested to from 700 to
1,000 pounds per square inch; standard lap-welded pipe, in
sizes from 1| to 12 inches, to from 500 to 1,000 pounds. The
test pressures on extra-heavy and double extra-heavy wrought
pipe range from 1,000 to 3,000 pounds. Cold-drawn seamless
steel tubing can be obtained in standard and extra-heavy
grades in sizes from inch to 4 inches in diameter.
3. Extra-heavy pipe has the same external dimensions as
standard pipe, but the wall of the pipe is made heavier, which
reduces the internal diameter. The internal diameter should
be taken into account when pipe of this kind is required.
Extra-heavy pipe is shipped without threaded ends and coup-
lings, unless they are specified. It is used for high steam pres-
sures, for feedwater piping, and for heavy pressures in hydraulic
work. Table II gives the respective dimensions and weight
of the pipe.
Double extra-heavy pipe has a thicker wall than extra-
heavy pipe, but its internal diameter is less. Its external
diameter is the same as that of standard wrought pipe. It is
used for very high pressures and for structural purposes.
Double extra-heavy pipe is always shipped without threads
and couplings, unless specified in the order. Table III gives
the dimensions and weight of the pipe.
Large 0. D. pipes are designated by their external diameter,
which ranges from 15 inches up to and including 30 inches.
Large 0. D. pipes have a wall thickness ranging from J to f
inch.
4. Cast-iron fife, owing to its low tensile strength, is
seldom used in high-pressure work; however, it is employed in
low-pressure heating systems for main steam pipes, in places
where acids are employed, and where pipes are laid in the
ground and left unprotected. Cast-steel fipe is used for super-
heater headers and where high temperatures exist, but owing
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6 PIPES AND PIPE FITTINGS
to its high cost and difficulty of manufacture without blow-
holes and other hidden defects, it is not extensively employed
for piping purposes. Brass and copper pipes are more expen-
sive than mild-steel and wrought-iron pipe, but they with-
FlG. 1
stand the corrosive action of hot water better than wrought-
iron and steel pipe. Owing to their high cost, low tensile
strength, and weakness at high temperatures, these materials
are not used for piping in high-pressure work to any great
extent. They are used for pipe coils in water tanks and in
steam tanks or condensers and for boiler connections where
there is great liability of corrosion, such as between f eed-purnps
and boilers. When brass feedwater piping is used, the diameter
need not be so large as when extra-heavy steel pipe is used,
because there will be no scaling or corrosion to obstruct the
flow of water.
5. Galvanized Pipe. The galvanized pipe used in the
smaller sizes is regular wrought-iron or steel pipe coated inside
and outside with zinc. It has the same dimensions as are
given in Table I. Galvanized pipe is used for water mains,
for underground piping, and where corrosion may occur, as
its coating of zinc prevents rapid oxidization or rusting of the
PIPES AND PIPE FITTINGS 7
metal. Sometimes it is desirable to know whether a galvanized
pipe is made of wrought iron or steel. This may be determined
by subjecting a piece of the pipe to the hammer test. On
TABLE IY
STANDARD SPIRAL-JOINTED PRESSURE PIPE, DOUBLE
GALVANIZED
Dimensions and Weight
Inside
Diameter
Inches
Approximate
Weight
per Foot
Pounds
Thickness
B. W.
Gauge
Number
Diameter
of Flanges
Inches
Approximate
Bursting
Pressure
Pounds
3
2i
20
6
1,500
4
3
20
7
1,125
5
4
20
8
900
6
5
18
9
1,000
7
6
18
10
860
8
7
18
11
750
9
8
- 18
13
665
10
11
16
14
750
11
12
16
15
680
12
14
16
16
625
13
15
16
17
575
14
20
14
18
670
15
22
14
19
625
16
24
14
21i
585
18
29
14
23i
520
20
34
14
25|
470
22
40
, 12
28i
595
24
50
12
30
540
26
58
12
34J
505
28
72
10
36
605
30
79
10
38f
560
32
85
10
41
525
36
94
10
45|
469
40
106
10
50
420
hammering the test piece, if the coating of zinc flakes ^ and
falls off, the pipe is steel, whereas, if the pipe is of wrought iron,
the zinc coating adheres to the surface and shows little effect
of the blows. By continuing the test until the pipe is flattened
8 PIPES AND PIPE FITTINGS
out, the fracture of the metal will show, in the case of wrought-
iron pipe, a ragged and fibrous structure, having a dull gray
color. In the case of steel the fracture will appear even in
texture, having a bright and crystalline appearance; but it
develops a dull appearance when exposed to the atmosphere.
It will be noted, in threading wrought-iron pipe, that the
chips are fibrous and easily break or crumble; but with steel
the chip is smooth, tending to curl up and form spirals that .
are hard and wiry.
6. Spiral Jointed Pipe. In the manufacture of spiral
pipe, strips of steel plate are rolled into a cylindrical pipe as
shown in Figs. 1 and 2. The seam may be riveted, as in Fig. 1,
or lap-welded; or, a lock seam like that shown in section in
Fig. 2 (a) may be used. The latter is rolled into a continuous
interlocking seam as shown in (6). The ends of the pipe are
fitted at the factory with cast-iron or steel flanges, which are
either welded or riveted to the pipe. Bolt holes are drilled in
the flanges so that the pipe sections can be bolted together.
The pipes are covered inside and outside with either a zinc
coating or an asphaltum paint to protect them from corrosion.
They range from 3 to 40 inches in diameter and are cut in
lengths up to and including 20 feet. The spiral arrangement
of the seam produces a stiff and very strong structure, so that
thinner metal can be used than is possible with ordinary
riveted or welded pipe. The safe working pressure of spiral
pipe is considered to be one-third of the bursting pressure.
Spiral pipe is suitable for exhaust steam pipes, water piping,
smokestacks, and compressed-air piping. Table IV gives
data on the plate thickness and weight of pipe per foot of length,
size of flanges, and bursting pressure for spiral pipe.
PIPE FITTINGS
7. Materials for Fittings. The materials used in the
manufacture of pipe fittings are cast iron, cast steel, malleable
iron, wrought iron, and brass. Cast iron is used for pipe
connections and boiler fittings on pipes for saturated steam,
for boiler feedwater piping/and for low-pressure heating work!
PIPES AND PIPE FITTINGS
9
FIG. 3
Cas5t steel and wrought-iron fittings are employed on high-
pressure piping and on pipes for superheated steam, as well
as on high-pressure feed lines and blow-off connections. Brass
flanges and piping are used
very little, and then only in
the form of screwed con-
nections.
8. Pipe Couplings. Pipe
couplings are short sleeves
threaded on the inside and
are used to connect lengths of pipe. They may be obtained
for standard, extra-heavy, and double extra-heavy piping. A
common form of wrought coupling is shown in Fig. 3 (a). It
is threaded at each end with a right-hand pipe thread.
Standard pipe is furnished in lengths threaded at one end and
fitted with couplings at the other end. If two pipes of differ-
ent diameters are to be connected, a reducing coupling, as
shown in (6), may be used. Its ends are threaded to receive
the two sizes of pipe.
9. Pipe Unions. Pipe unions are used for making the
final connections in lines or systems of piping. They are of
two classes, namely, nut unions and flange unions, the latter
being commonly called pipe flanges. One type of nut union
is shown in Fig. 4. The part a, made
of brass, is screwed on the end of one
pipe, and the part c t carrying the nut b
loose on it, is screwed on the end of the
adjoining section. The ends of the
parts a and c are then brought together
and the nut b is screwed on to the
part a, making a tight metal-to-metal
joint at d. The faces at the joint d may
be ground spherical or may be beveled. No gasket is required
to produce a water-tight or steam-tight joint. Nut unions
are made for pipes from | inch to 4 inches in diameter. For
medium pressures, unions are used on pipes up to 2 inches in
diameter, and flange unions for larger sizes of pipe.
FIG. 4
10
PIPES AND PIPE FITTINGS
10. The pipe union shown in Fig. 5 represents a type that
is used in high-pressure steam and hydraulic work for pipes up
to 3 inches in diameter. It is made of forged steel throughout
and has a V-shaped ground joint, as shown at a. When the
parts b and c are drawn together by the union ring d, the pro-
jecting V enters the groove in the part 6, forming a steam-
tight metal-to-metal joint along the surfaces a and e. The
slot/ in the V-shaped tongue is to take care of the slight changes
due to expansion and contraction caused by variations of
temperature in high-pressure work.
11. Flange Unions. Lengths of pipe may be joined in a
continuous line by the use of flange unions such as are shown
in Fig. 6. The flanges a and b are circular metal rings threaded
FIG. 5
FIG. 6
on the inside so that they may be screwed on the ends of the
pipes that are to be joined. The flanges are then brought
together, face to face, a gasket c is placed between them, the
bolts d are inserted in holes drilled through the flanges, and the
nuts are drawn up. The faces of the flanges are machined
and the pipe sections are lined up so that the faces of the
flanges are parallel. Compression of the gasket between the
flat faces then produces a water-tight or steam-tight joint.
Flange unions are made of brass in standard sizes from | inch
to 6 inches for steam pressures up to 125 pounds per square
inch, and extra-heavy flanges are made for pressures up to
250 pounds per square inch. Cast-iron and malleable-iron
flange unions may be obtained for pressures up to 250 pounds
and for pipe sizes from f inch upwards. For very high
PIPES AND PIPE FITTINGS
11
pressures, flange unions are made of steel. All types of flange
unions are sold in pairs.
12. Pipe Flanges. For joining pipes that are to be
subjected to medium and high working pressures, pipe flanges
of the type usually called companion flanges are extensively
used. The cost of these flanges is greater than that of unions
(a)
FIG. 7
for the same work, and some styles of flanges require special
machinery for, attaching them to the sections of pipe. How-
ever, the additional cost is warranted by their freedom from
leaks, their reliability, and the advantages they possess
in case alterations and repairs must be made on lines on which
they are used.
A majority of the manufacturers of flanged fittings and
valves have agreed on standard dimensions for the thickness
12 PIPES AND PIPE FITTINGS
and diameter of the flanges, the diameter of bolts and holes,
the number and size of bolts, and the diameter of -the bolt
circles; unless specially ordered otherwise, flanges are generally
made according to this standard. This standard was recom-
mended for adoption by a joint committee of the American
Society of Mechanical Engineers and the Master Steam Fitters'
Association; it is known as the Manufacturers' Standard.
13. Types of Pipe Flanges. Several types of companion
flanges are shown in Fig. 7. The screwed flange in (a) is the
least expensive style, and is satisfactory for low and medium
pressures. The flange is screwed on until the end of the pipe
projects through it. Then the end is cut off flush with the
face and both are faced so that the surface is square with the
center line of the pipe. Sometimes the face of the flange has
a number of shallow concentric grooves cut in it, allowing a
soft gasket to be used between adjacent flanges without danger
of its being blown out. In (6) are shown male and female
flanges. The male flange a has a shoulder that fits into a
corresponding recess in the female flange 6, a gasket c being
inserted in the recess to make a tight joint. A tongue-and-
groove type is shown in (<;), the tongue a on the flange b
fitting into the groove c in the flange d, in the bottom of which
a gasket is placed. The flanges in (d) have raised faces, between
which the gasket is held, and recesses are provided at a to
enable the pipe joints to be calked.
The disadvantages of the types shown in (b) and (c) are
that great care must be taken in manufacture to insure aline-
ment of faces, tongues, and grooves, to prevent subsequent
trouble through leaky joints; and if a break occurs in the
gasket, the ends of the pipe must be sprung apart to allow a new
gasket to be inserted.
Table V shows the dimensions of standard flanges and flange
bolts and Table VI gives similar data for extra-heavy flanges.
Flanges are designed with an unusually large factor of safety, to
cover possible defects in the metal or imperfections in casting.
In all cases, it is important that the castings shall be absolutely
sound and free from flaws, blowholes, and shrinkage cracks.
PIPES AND PIPE FITTINGS
13
14. Gaskets for Flanges. Packing rings, or gaskets, for
steam-pipe flanges and flange unions may be made of various
materials. In low-pressure heating systems, composition
TABLE V
DIMENSIONS OF STANDARD THREADED PIPE FLANGES
(For Pressures up to 125 Pounds per Square Inch Manufacturers' Standard)
Pipe
Size
Inches
Pipe Flanges
Bolts
Outside
Diameter
Inches
Thickness
of Flange
Inches
Diameter of
Bolt Circle
Inches
Number
of Bolts
Required
Diameter
of Bolt
Inches
Length of
Bolt
Inches
1
4
A
3
4
A
H
It
4|
1
31
4
A
ii
1|
5
&
3|
4
i
H
2
6
f
4}
4
!
2
2|
7
H
5}
4
1
2i
3
7|
1
6
4
f
2i
3}
8}
H
7
4
I
2i
4
9
if
7}
8
f
2}
4}
9i
tt
7|
8
*
2J
5
10
tt
8}
8
f
2J
6
11
i
9}
8
*
3
7
12|
1*
10f
8
I
3
8
13}
i
HI
8
f
3t
9
15
i*
13i
12
*
3t
10
16
i*
14i
12
f
31
12
19
i*
17
12
f
3i
14
21
if
18i
12
1
4
15
22J
if
20
16
l
4
16
23J
i*
211
16
1
4
18
25
i*
22i
16
it
4}
20
27J
itt
25
20
U
4J
22
29J
itt
27|
20
it
5
24
32
if
29}
20
it
Si
NOTE, Flanges, flange fittings, valves, etc. have the bolt holes drilled in multiples
of four, so that fittings may be made to face in any quarter and holes straddle the center
line. All bolt holes are drilled J inch larger than the diameter of bolts.
packing rings of asbestos, rubber, etc., are used. For high-
pressure steam lines, a corrugated copper gasket like that
shown at a, Fig. 8, is reliable, as it can be drawn up tight with-
out danger of compressing the material into the pipe and it
14
PIPES AND PIPE FITTINGS
will effectively resist a very high temperature. For hydraulic
pipe flanges, reinforced rubber packing and composition pack-
ing to resist very high water pressures are used.
TABLE VI
DIMENSIONS OF EXTRA-HEAVY THREADED FIPK FLANOES
(For Pressures up to 250 Pounds per Square Inch Manufacturers' Standard)
Pipe
Size
Inches
Pipe Flanges
Bolts
Outside
Diameter
Inches
Thickness
of Flange
Inches
Depth
of Thread
Inches
Numbc
Re-
quired
Dia-
meter
Inches
Length
Inches
Diameter of
Bolt Circle
Inches
1
4*
H
1
4
j
2
3*
li
5
f
U
4
$
2*
3|
li
6
if
li
4
3
2*
4*
2
6*
f
if
4
f
2*
5
2
7*
i
1A
4
f
3
5}
3
Si
li
1&
8
1
3*
3*
9
1*
If
8
3*
7*
4
10
if
If
8
f
3*
7}
44
10*
1*
Iff
8
i
3*
8*
5
11
if
li
8
3!
9*
6
12*
1*
2
12
j
3J
lOf
7
14
li
2A-
12
*
4
11 f
8
15
if
2&
12
1
4*
13
9
16*
if
2J
12
i
4}
14
10
17*
if
2f
16
i
5
15*
12
14
15
23
24J .
2
2!
2rV
1
16
20
20
H
it
H
5*
5*
5|
17f
20*
21*
16
18
20
22
24
28
30>f
33
36
2i
21
2i
2f
2f
21
sf
20
24
24
24
24
li
If
li
H
6
6*
7
7*
22|
24|
27
29J
32
15. Types of Pipe Joints The joints in pipe lines
subjected to low pressures may be made with unions like those
shown in Figs. 4 to 6; and the screwed flange joint shown in
.big. 7 (a) is suitable for pipes carrying saturated steam at or
PIPES AND PIPE FITTINGS
15
below 125 pounds pressure, for boiler-feed lines carrying not
more than 150 pounds pressure, for boiler blow-off piping, and
FIG. 8
FIG. 9
for low-pressure heating systems. In joints of the foregoing
types, however, the threading of the pipe reduces its strength
in the joint, and so other
types of joints are used for
piping that is to be subjected
to high working pressures.
The welded joint shown in
Fig. 9 is used on high-pressure
work and on pipe lines convey-
ing superheated steam. The
flange a is welded directly to
the pipe b, so that the two
form one piece, the welding
being done usually by the
electric arc. The strength of
the weld depends on the care
with which it is made, but the
welded flange has been found
stronger than the screwed
flange. After the weld is com-
pleted, the face of the flange
is machined, so as to make it flat and square with the center
line of the pipe. A gasket is inserted between adjacent flanges .
I L T 45916
16
PIPES AND PIPE FITTINGS
16. The type of flange shown in Fig. 10 is excellent for
high-pressure piping. As indicated in the sectional view (a),
the flange a is shrunk on the end of the pipe b. In doing this,
the flange is heated so as to cause it to expand, and while hot
it is driven over the end of the pipe. When it cools, it shrinks
and grips the pipe firmly. The inner edge c of the flange is
rounded off and the end of the pipe is then peened over by
striking it lightly with a hammer, thus giving the flange
additional grip on the pipe. Sometimes the security of the
fastening is further increased by riveting the pipe to the flange
in the manner indicated at d. A part of a flange is shown in
perspective in (6). The bolt holes a are formed in bosses b,
and the spaces between the bosses enable the rivet holes c
to be drilled and the rivets inserted
and headed.
17. The Van Stone joint, shown
in Fig. 11, is made by upsetting and
flanging the heated end of the pipe a
over the flange b. The face of the
flange of the pipe is faced smooth
and to a uniform thickness, so as to
produce a tight joint and perfect
alinement. The edges of the flange
are also finished. The flanges b are
loose on the pipes, being a trifle larger in diameter than the
outside diameter of the pipes, and serve as rings that bear on
the flanges of the pipes. A gasket c is inserted before the
flanges are bolted together. When this joint is properly made,
it is strong and has no superior for durability. For high
pressures, on steam and water lines, forged steel flanges should
be employed. Table VII gives the principal dimensions of
Van Stone flange connections.
18. A special type of flanged connection is shown in Pig. 12.
The flange a has a shallow groove b on the inner surface, into
which the pipe c is expanded by rolling under pressure. A
recess is cut in the face of the flange a, and the end of the pipe
is turned out and forced down into this recess, as at d, after
FIG. 11
PIPES AND PIPE FITTINGS
17
which it is machined, so that the face of the pipe is flush
with the face of the flange a. A copper gasket e is inserted
TABLE VII
DIMENSIONS OF VAN STONE JOINTS
Pipe
Size
Inches
Diameter
of Flange
Inches
Flange
Thickness
Inches
Diameter of
Bolt Circle
Inches
Diameter
of Bolt
Inches
Number
of Bolts
Required
Length
' of Bolts
Inches
4
10
li
7J
1
8
3!
41
101
1*
8i
\
8
4
5
11
U
i
1
8
4
6'
121
1ft
10|
j
12
4i
7
14
H
m
i
12
4i
8
15
if
13
7
5
12
4!
9
16i
if
14
1
12
5i
10
17|
if
15i
1
16
5i
12
201
2
17|
U
16
i
14
23
2J
20i
14
20
6
15
24|
2&
21i
It
20
61
16
25i
2i
22
li
20
6i
and the bolts are drawn up. This form of construction has
been found satisfactory for high-pressure lines carrying either
steam or water, and for superheated steam as well. Tests
have shown that it will withstand
pressures as high as 1,250 pounds
per square inch.
19- Expansion and Contraction
of Pipes. Piping is put up at ordi-
nary temperatures; but when steam
is turned on, the temperature of the
piping is increased considerably, par-
ticularly if superheated steam is being
used. Increases or decreases of tem-
perature may occur while the piping
is in service. As a change of tem-
perature causes metal to expand or
contract, a line of steam piping must be so installed that
expansion and contraction will not set up stresses that may
FIG. 12
18
PIPES AND PIPE FITTINGS
bend or break the pipe or its fittings. The linear expansion
or contraction of a line of piping may be found by the formula
m = C 1 1
in which m = amount of linear expansion or contraction, in
inches ;
C= coefficient of linear expansion;
Z= length of piping, in inches, before the change of
temperature occurs;
t = change of temperature, in degrees Fahrenheit.
The value of C for wrought-iron or steel pipe is ,00000599;
for cast-iron pipe it is .00000617; and for cast-steel pipe it is
.00000636.
EXAMPLE. A steel pipe line 250 feet long is put up at a temperature of
60 F. When it is finished, superheated steam at a maximum temperature
of 370 F. is turned on. Find the linear expansion.
SOLUTION. Apply the formula just given. The pipe is of steel and so
C=. 00000599; / = 250X12 = 3,000 in.; and 2 = 370 -60 = 310. Substi-
tute these values, and m=*. 00000599X3,000X310 = 5.57 in., or 5^ in.,
nearly. Ans.
20. Expansion Joints. The example of the preceding
article shows that the change of length of a straight pipe
FIG. 13
line, under change of temperature, may amount to several
inches. One way of preventing damage to the pipe and fittings
PIPES AND PIPE FITTINGS
19
is to use an expansion joint, or slip joint. One type of
expansion joint, shown in Fig. 13, is a slip joint that is inserted
at some convenient point in the line. The flange a is bolted
to the flange b of the main piping, and between them is held
the flange of a short sleeve c.
This sleeve fits inside the pipe
d, which in turn is bolted to an
adjoining section of the main
steam pipe. A stuffingbox e
is formed around the sleeve,
the packing being held in
place by the gland /, which
can be drawn up by tighten-
ing the nuts g. Guides h are
firmly bolted to the large
flange of the section d, and
the outer ends of these guides
fit against the flanges a and b.
If expansion occurs in the
main piping, the sleeve c slips
farther into the section d, the
stuffingbox e preventing leak-
age of steam. If the pip-
ing cools and contracts, the
sleeve c moves out of the sec-
tion d an amount equal to
the change of length. The
sleeve c is held firmly to the
flange b of the main pipe and
moves with it. The long
studs i prevent the joint from pulling apart completely, and
are used simply as a safety device.
21. The expansion joint shown in Fig. 13 is intended to be
inserted directly in a straight run of piping, the sleeve c moving
lengthwise to accommodate the change of length. The type
shown in Fig. 14 (a) is a swivel expansion joint, the section a
being held in such a way that it can turn, or swivel, inside the
(by
FIG. 14
20
PIPES AND PIPE FITTINGS
section b. A stuffingbox c maintains a steam-tight joint
between the two. The method of installing this joint is shown
in (6). The sections a and b of the main steam piping are
not in a straight line, but are offset. They are connected
by elbows to the swivel ex-
pansion joints c and d, these
being joined by the pipe e and
connecting elbows. Thus,
any change of length of the
pipes a and b simply causes
swiveling of the expansion
joints and prevents stresses
from being set up in the
piping.
A flexible joint is shown in
Fig. 15. The section a and
the section b into which it
fits are made spherical, and a
FlG - 1S stuffingbox is provided to
form a tight joint between them. The packing c is compressed
by turning the setscrews d. The section a can move in any
direction sidewise. This type of joint is made in standard
and extra-heavy styles to carry pressures up to 250 pounds
per square inch.
i
22. Damage through change of length of straight piping
may be provided against by inserting a section of corrugated
piping, such a section being called a corrugated expansion
joint. A joint of this kind is illustrated in Fig. 16, the
material of which it is
made usually being cop-
per. The elasticity of
the section, due to the
corrugations, allows it
to be compressed or drawn out to some extent, and so it takes
up expansion or contraction of the pipe line in which it is
inserted. The corrugations are rolled into the sheet from
which the pipe is made. The form shown is used principally
FIG. 16
DooHe-Offset Expansion Vffe/jJ
FIG. 17
21
22
PIPES AND PIPE FITTINGS
on exhaust-steam lines. Another form, in which iron or steel
rings are used to reinforce the corrugated section and yet not
interfere with its axial lengthening and .shortening, is used in
high-pressure work.
23. Pipe Bends. An excellent way of allowing for
expansion and contraction of pipe lines is to use -pipe bends,
as shown in Fig. 17. The forms of bends illustrated are used
extensively on long pipe lines as well as on steam-engine
connections and other piping subjected to considerable vibra-
tion. Wrought-pipe bends are made while the material
is red hot. The radius r of .the bend must be large, so as to
give the proper spring to the bend and to reduce as much as
possible the friction of the steam in flowing through it.
FIG. 18
The larger the radius, the more fully these objects are attained.
Generally, the radius should not be less than six times the
diameter of the pipe. The bends are connected to other
pipes by extra-heavy flanges of cast steel, forged steel, or
malleable iron, these being fastened to the bends by one
or other of the methods previously illustrated. A short
section a of each bend, near the flange, is left straight, so
that the flange will stand square with the axis of the adjoining
section of pipe. In large bends, as, for example, the double-
offset expansion U bend, the fitting is made in three sections,
flanges being used at b to connect them.
Pipe bends made of copper pipe may have shorter radii,
as copper is more ductile than steel and yields more readily to
the bending operation without undue buckling. Small sizes
PIPES AND PIPE FITTINGS
23
of bends are made from seamless drawn tubing, which comes
in standard lengths of 12 feet. Copper bends may be fitted
with either composition or brass flanges, riveted and brazed on,
as shown in Fig. IS (a) ; or they may have loose steel flanges,
the ends of the pipe being flanged as shown in (6).
24. Pipe Coverings. To reduce the loss of heat by radia-
tion and convection, steam pipes are covered with lagging
FIG. 19
made of some material that is a poor conductor of heat, such
as magnesia, asbestos, slag wool, or kieselguhr, the last being
a natural earth containing minute fossil shells. Sometimes,the
covering material is made in the form of a cement, mixed with
lime, animal hair, or vegetable fiber, and applied in a plastic
form. As a rule, however, it is manufactured in short molded
24
PIPES AND PIPE FITTINGS
sections of different sizes to fit pipes of different diameters.
The sections are split lengthwise, so that they may be placed
over the pipe, and are held together by a canvas jacket that
may be painted or tarred to resist the weather. Polished and
lacquered brass bands are also used to hold the sections in
place on the pipe. Charcoal, slacked lime, and sawdust are
inexpensive materials that may be placed around pipes laid in
trenches.
25. Pipe Supports. Great care must be exercised in
hanging and supporting steam piping so as to take care of
FIG. 20
*
the movement of the pipes due to expansion and contraction,
to keep the pipe sections in proper alinement, and to provide
for a rise or fall in the steam line so- that the water formed by
the condensation of steam will not flow back toward the
boiler, in opposition to the direction of flow of the steam.
The style of support will vary according to the piping arrange-
ment. Pipe supports in general are standardized and may be
classified as hangers, standards, and brackets. Hangers,
shown in Fig. 19, carry the pipe overhead and are attached
to rafters or other structural members in the frame of the
PIPES AND PIPE FITTINGS
25
building. The hangers shown in (a) and (6) are adjustable
within the limits of the length of the turnbuckles a. By this
arrangement, short pipe lines can be raised or lowered to give
a slight pitch to the piping. Rollers b are attached at the
bottom of the brackets in (6) and (c) to allow the piping a
lengthwise movement when expansion or contraction occurs.
26. Standards, as shown in Fig. 20 (a) and (6), are fixed
to the floor and support the pipe saddles a, which are made
Fie. 21
V-shaped, as shown in (a), or are curved to fit the pipe, as
in (6). The V-shaped support has the advantage that it can
hold pipes of different sizes, whereas the curved support is
suitable for practically only one size. The saddles can be raised
or lowered by turning the pipe b up or down in the fitting c,
which is threaded to receive the pipe. Standards are also
made with rollers for supporting piping of great length.
Brackets are pipe supports that are attached to side walls
and columns, as shown in Fig. 21 (a) and (6) . Mounted on the
26
PIPES AND PIPE FITTINGS
bracket a is a frame b that carries a roller c. For long piping
of large diameter, the bracket shown in (b) is equipped with an
upper roller d, which assists in maintaining proper alinement of
the piping. To take care of the expansion of the pipe, and
-
SMe-Quttef Elbow
FIG. 22
at the same time hold the roller in position, springs e are
installed at the bottom of the support rods for the upper roller.
27. Flanged Fittings. American standard flanged fittings
for the several classes of pipe are of the forms shown in Fig. 22.
For standard pipe the face of the flange is plain, but the
extra-heavy flange has a shoulder tV inch
high, as shown in section in Fig. 23. These
fittings are employed in making bolted
pipe connections, where it is necessary to
ran the piping in different directions. The
dimensions of the different flanges for
pressures up to 125 pounds per square inch are given in
Table VIII. The reference letters in Fig. 22 indicate the
respective dimensions and correspond with those given in
the table. Similar data for extra-heavy flanged fittings,
TABLE VHI
AMERICAN STANDARD FLANGE FITTINGS
(For Working Pressures up to 125 Pounds per Sqziare Inch)
Size
of
Pipe
Inches
Dimensions of Pitting, in Inches
Size
of
Pipe
Inches
Dimensions of Fitting, in Inches
A
B
C
D
E
F
A \ B
c
D
E
F
1
Si-
5
If
71
5|
If
8
9
14
54
22
17}
44
It
Si
5}
2
8
6}
if
9
10
15J
6
24
19}
44
14
4
6
21
9
7
2
10
11
16}
6}
254
204
5
2
41
61
24
101
8
2}
12
12
19
7}
30
244
51
2J
5
7
3
12
9|
2}
14
14
21}
7|
33
27
6
3
51
7|
3
13
10
3
15
14}
22f
8
344
284
6
31
6
81
* 3 *
14}
111
3
16
15
24
8
364
30
64
4
61
9
4
15
12
3
18
16}
26}
8}
39
32
7
41
7
04
4
151
12|
3
20
18
29
9}
43
35
8
5
74
10J
41
17
131
34
22
20
31}
10
46
37J
84
6
8
111
5
18
14}
3}
24
22
34
11
49J
40J
9
7
81
12|
51
20}
16}
4
TABLE IX
AMERICAN EXTRA-HEAVY FLANGE FITTINGS
(For Working Pressures from 125 to MO Pounds -per Square Inch}
Size
Dimensions of Pitting, in Inches
Size
Dimensions of Fitting, in Inches
of
Pipe
Inches
of
Pipe
Inches
A
B
C
D
F
A
B
c
D
E
F
1
4
5
2
84
64
2
8
10
14
6
254
204
5
11
41
54
24
94
7J
2J
9
104
15i
64
274
224
5
11
44
6
2f
11
84
24
10
114
164
7
294
24
5}
2
5
6*
3
H4
9
24
12
13
19
8
334
274
6
2|
54
7
34
13
104
24
14
15
214
84
374
31
64
3
6
7f
3*
14
11
3
15
154
22|
9
394
33
64
34
64
*}
4
154
124
3
16
164
24
94
42
344
74
4
7
9
44
164
134
3
18
18
264
10
454
374
8
44
74
9^
44
18
144
34
20
194
29
104
49
404
84
5
8
101
5
18*
15
34
22
204
314
11
53
434
94
6
84
114
54
214
174
4
24
224
34
12
574
474
10
7
9
12|
6
234
19
44
(
27
28
PIPES AND PIPE FITTINGS
carrying pressures from 125 to 250 pounds per square inch,
are given in Table IX. The diameters of the flange and of the
bolt circle, the thickness of the flange, and the number of
bolt holes, for both standard and extra-heavy flanged fittings,
are the same as for the corresponding sizes of companion
flanges, and are given in Tables V and VI. Where it is neces-
sary to run two pipes of different sizes from the same flanged
fitting, a reducing tee, cross, or lateral is employed. The usual
forms of these fittings are illustrated in Pig. 24. Flanged
fittings may be made of cast iron, cast steel, or malleable iron.
28. Standard screwed fittings, such as tees, elbows, and
laterals, are made for the smaller sizes of piping, and can be
obtained in many different forms, threaded with right-hand
FIG. 24
threads. The size of a tee is designated by first stating the
size of the run and then the size of the branch. The run is
the line of pipe that enters and leaves the tee in the same
straight line, " Thus, the tee in Fig. 25 (a) has a 2-inch run
and a lf-inch branch, and would be called a 2"X1|" tee.
If all the outlets of the tee had been for 2-inch pipe, it would
have been termed a straight 2"X2" tee, or simply a straight
2-inch tee. The tee shown in (6) connects pipes of three
different diameters and is called a reducing tee. "It is designated
as a 1J"X11"X1" reducing tee, the numbers being given in
the order of their size, the largest first.
29. A lateral, or Y, having a branch at an angle of 45,
is shown in Fig. 25 (c). The method of designating the size of
a lateral is the same as for a tee; thus, the lateral shown would
PIPES AND PIPE FITTINGS
29
be called a 4"X3"X3" Y. The term Y branch is often used
to designate this form of fitting. Laterals may be obtained
in either standard or reducing-type sizes.
'Pipe
The fittings shown in (d) and (e) are right-angle el&ows,
or 90 elbows, commonly termed ells; but elbows with the
faces of the flanges at 22J, 45, or 60 may also be obtained.
The style of elbow in (d) may be had with either right-hand
30
PIPES AND PIPE FITTINGS
or left-hand threads; or, the ends may be threaded in opposite
directions. Reducing ells, of the type shown in (e), and, in
fact, all other reducing fittings, have right-hand threads only.
YALVES AND COCKS
30. Globe Valves. Valves are used to control the flow of
water and steam in boiler piping. The bodies may be made
of brass or iron, but the valve disks and seats are of composition
FIG. 26
FIG, 27
metal. The working pressure and the kind of service deter-
mine the weight, size, and design of valve to be used. A sec-
tional view of a globe valve such as is used on steam piping is
shown in Fig. 26. The body a and^the partition in which the
seat 5 is formed are cast in one piece. The seat b is ground
to a bevel to match the bevel of the valve disk c, which is
fastened to the lower end of a threaded stem d carrying a
hand wheel e. The threaded stern fits in a nut/, in the upper
PIPES AND PIPE FITTINGS
31
end of which a stuffingbox is formed to prevent leakage of steam
past the stem. The packing in the stuffingbox is compressed
by screwing down the nut g. Turning the handwheel opens or
closes the valve by raising the disk or forcing it down against
its seat. The nut/, or yoke of the valve, is held to the body a
by a nut h.
31. The globe valve shown in section in Fig. 27 has a
brass body and a flat seat; but the valve disk a is a copper
ring having two faces. Thus, if one face becomes worn or
marred, so that the valve leaks, the disk may be turned over,
bringing the other face into use.
Metals softer than copper have
been used for valve disks of this
kind, but they have not proved so
satisfactory. The use of the globe
valve as a throttling device for
regulating the flow of steam to a
pump forms a severe service, be-
cause of the erosion of the seat and
the valve disk. To overcome this
trouble, a so-called throttling nut
has been developed, which prolongs
the life of the valve disk and seat.
Valves of the types shown in Figs. 26
and 27 are made for pressures up
to 250 pounds per square inch.
A globe valve with an iron body is shown in Fig. 28. A
brass seat a is screwed into the partition in the valve body
and the valve disk b is made of brass, or of steel faced with
brass. The threaded part of the stem c fits in a nut in the
yoke d, the latter being flanged and bolted to the valve body.
The small stem e slides in a guide in the spider / and serves
to hold the disk central on its seat.
32. Angle Valve. An angle valve having an iron body is
shown in Fig. 29. The outlet a and the inlet b are at right
angles, and the valve is used to connect pipes that meet at a
right angle; hence, the valve is known as an angle valve.
I L T 45917
FIG. 28
32
PIPES AND. PIPE FITTINGS
The seat c is placed directly in the inlet opening, and as there
are fewer changes of direction of the fluid passing through the
valve, it offers less resistance to flow than does the globe valve
shown in Fig. 26. Because the valve stem is long, a guide is
provided in the form of a spindle d held in the spider e. The
valve disk f is faced with brass. This valve is intended for
large pipes that carry pressures of from 125 to 250 pounds per
square inch.
33. Gate Valves.- Gate valves are made either as single-
gate valves, which receive pressure on one side only, or as
FIG. 29
FIG. 30
double-gate valves, which may receive pressure on either side.
Some forms of double-gate valves close the opening of the valve
with a solid wedge; others close with a box wedge, and others
with sectional gates having either parallel or wedge-shaped
seats.
Gate valves are advantageous where little resistance to
the flow of the liquid is desired, as they leave an unobstructed
PIPES AND PIPE FITTINGS
33
passage when fully open. Therefore, they are largely used on
water and exhaust-steam connections. When throttled that
is, only partly opened, they are hard to regulate and they often
chatter. When they are used for steam, the seats should be
made of bronze, which withstands high temperatures success-
fully. In all gate valves, the disks rise into the upper part of
the body and bonnet to allow a straight passage for the liquid.
34. The valve shown in Fig. 30 is a double-gate valve
with a tapering disk a machined flat on the sides and guided
FIG. 31
FIG. 32
by a slot b in each side of the disk, fitting over a guide c at
each side of the valve body. The disk seats against soft
metallic rings d, firmly embedded at each side of the opening
and faced off to the same taper as the disk. The valve shown
is an iron-body flanged gate valve. The lower end of the
stem is threaded, and the disk travels on this thread, the
stem being prevented from risiqg by the collar e.
35. For valves of 6 inches and upwards, on steam lines, it
is desirable to use the outside-sctew yoke type, with stationary
wheel and rising spindle, as shown in Fig. 31. The advantages
34 PIPES AND PIPE FITTINGS
of this type are that the extension of the stem shows the position
of the gate, and that the screw can always be properly lubri-
cated and does not come in contact with the steam.
By-passes are desirable on or around all live-steam valves
of 6 inches and upwards. Fig. 32 shows a gate valve provided
with a small by-pass valve a. By first opening the small valve,
the pressures on the two sides of the disk are equalized, thus
making the valve easy to open.
Gate valves should be installed in a vertical position, so that
the regulating spindle is upright and the hand wheel on top.
The valve should
never be placed so
that the hand wheel
is on the bottom, be-
cause, when the gate
is partly opened, a
pocket is formed and
the steam and water
have a tendency to follow along
the spindle and drip.
36. Automatic Stop- Valve..
An automatic stop-valve, often
called a non-return .valve, should
be placed in the pipe leading
from each boiler to the main
_ _ steam pipe, when two or more
r IG. 33 1*1 1*1
boilers ar6 connected in a bat-
tery. If one of the boilers becomes sluggish in generating
steam, its stop-valve will close automatically and will remain
closed until the pressure in the sluggish boiler has been built
up to that existing in the main, when the valve will open.
Such a valve is a protection against accidents. If one of a
battery of boilers has a blown-out tube, or any other mishap
that suddenly lowers the pressure, the stop-valve closes and
prevents the steam from backing into the damaged boiler
from the main pipe. If a boiler is undergoing repairs, the
presence of such a valve on its steam line is a safeguard
PIPES AND PIPE FITTINGS
35
against admission, of steam while workmen are engaged on
the boiler. The stop-valve shown in Fig. 33 is built for
pressures up to 250 pounds per square inch. It is connected
with the inlet a faced toward the boiler, so that the boiler
pressure acts under the valve b and raises it until the
ports in the surrounding sleeve are uncovered. The steam
then passes through these ports and out of the valve into
the steam line. The space above the valve is subjected
to the pressure in the steam line because of the small opening
through the side of the sleeve just beneath the valve cover.
If the pressure in the boiler becomes less than that in the
steam line, the pressure in the upper end of the sleeve, above
the valve, will force the valve to its seat, and thus prevent
FIG. 34
FIG. 35
steam from flowing back into the boiler from the line. When
it is necessary to close the valve by hand, to cut out the
boiler, or to test the automatic action of the valve, the
spindle c is screwed down until the valve is forced into its
closed position. In addition to the automatic stop-valve, a
gate valve should be installed in the steam piping between the
boiler and the main steam pipe. Ample drains must be pro-
vided for such valves, if water can accumulate in them.
37. Check- Valves. Check-valves are valves that permit
fluids to pass through them in one direction only; they are
designed so as to close automatically whenever the flow of the
fluid is reversed. They are made in different forms, as vertical,
horizontal, and angle check-valves.
36
PIPES AND PIPE FITTINGS
38. The check-valve shown in Fig. 34, known as a swing
check-valve, may be used in either a horizontal or a vertical
pipe. The valve disk a is attached to an arm b hinged at c.
The disk and arm are so connected as to permit a slight move-
ment of the disk so that it will close on the seat d properly.
The lug e on the arm strikes the screw/ when the disk is swung
open, thus preventing
it from swinging too
far. The screw cap g
covers the opening
that gives access to
the valve for inspec-
tion. The direction
of flow of the fluid is
indicated by the ar-
rows. This type of
check-valve probably
offers less resistance
to the passage of a
fluid than any other
form.
39. In Fig. 35 is
shown a globe check-
valve, the form most
commonly used. The
disk a is provided
with wings b on the
bottom and a guide c
on the top to keep the
valve from tilting sidewise. Special forms of these types of
valves are made to take the place of elbows in pipes. In such
cases, they are known as angle check-valves.
40. Blow-Off Valves and Cocks. The blow-off pipe is
connected to the bottom of the boiler or mud-drum, or at the
lowest part of the water space. Its purpose is to drain the
boiler, as well as to remove scale, mud, and other sediment
that collect at the bottom of the boiler. The blow-off con-
FIG. 36
PIPES AND PIPE FITTINGS
37
nections for a return-tubular boiler are shown in Fig. 36.
The blow-off pipe a is carried straight down through the
combustion chamber and then out through the setting, being
fitted with a Y blow-off valve b and an angle blow-off valve c.
With this arrangement, the pipe a should be protected from the
hot gases by cast-iron sectional sleeves clamped around it;
or, a firebrick pier of V section
should be built in front of the
pipe, the angle of the V point-
ing forwards and the pipe a
being inside the angle formed
by the wing walls. As blow-
off valves are repeatedly
opened and closed, they are
subject to rapid wear, or cut-
ting, by the escaping water,
dirt, and scale. This cut-
ting is noticeable particularly
when the steam pressures are
high, for then the escaping
current has a high velocity
through the valves. Blow-off
pipes extending through com-
bustion chambers should be
of genuine wrought iron and
extra heavy.
4 1. Owing to the frequent
use of the blow-off valve and
the danger of its working
parts becoming damaged, the
necessity of additional pro-
tection is apparent. On all new boiler installations, the
A. S. M. E. Boiler Code prescribes the rule that where the
steam working pressure is above 125 pounds per square inch,
the blow-off from any pipe line shall have two valves, or a
valve and a cock, of extra-heavy pattern, arranged in^the
piping. The minimum size of pipe shall not be less than 1 inch
FIG. 37
38
PIPES AND PIPE FITTINGS
in diameter and the maximum not over 2| inches in diameter.
No reducing fittings are permitted in the line, as the piping
must run full size its entire length. A blow-off valve or cock
must be absolutely tight to prevent leakage, and should also
be capable of being opened and closed easily. It must also be
constructed of materials that will withstand the severe service
to which it is subjected. Ordinary steam globe valves are
not suitable for connections of this kind.
42. A very good form of angle blow-off valve is shown in
Fig. 37. The body a and yoke b are made of iron, and the work-
ing parts, such as the valve stem c, the valve disk d, the valve
seat e, and the bushings /, are
made of bronze. In the valve
disk d are seating sur-
faces g made of an alloy
that, being softer than
the valve seat, will yield
to any irregularities and
make a tight connec-
tion. At the back of the valve
is a dean-out plug h, which is
removable, permitting the inser-
tion of a rod into the valve for
clearing away sediment, scale,
etc. that may accumulate in the
inlet i. All angle valves should
be connected so that the inlet or
side opening i is toward the boiler and thus have the pressure
on top of the valve disk. This arrangement protects the valve
disk and the valve seat from the direct impact of the steam
and sediment. The valve should be opened wide when the
boiler is blown down, so as to reduce as much as possible the
wear on the seat and disk.
The Y blow-off valve, Fig. 38, is sometimes placed in the
run of piping between the boiler and the angle blow-off valve,
as shown at b, Fig. 36. The valve shown in Fig. 38 is of
special design, and constructed of a hard, non-corroding
FIG. 38
PIPES AND PIPE FITTINGS
39
material. It should be installed so that the pressure is
exerted on top of the valve disk.
43. A blow-off cock is generally used in connection with
a blow-off valve, serving the same purpose as the Y valve and
being located in the same
position as the Y valve in
Fig. 36. The construction
of the cock is shown in the
sectional view, Fig. 39. It
consists of an extra-heavy
body a and a tapered plug b
that is ground to its seat in
the body to produce a tight
joint. The compensating
spring c is located between
the plug b and the clean-out
cap d, its purpose being to take up the wear and to hold the
plug securely to its seat at all times, thus preventing sediment
and scale from collecting around the
bearing surfaces of the plug and seat.
An opening is formed in the plug
from side to side, and the water
passes straight through it when the
opening is turned parallel with the
run of the piping.
The handle e is for
the purpose of turn-
ing the plug to open
and close the cock.
Blow-off cocks are
made with either
screwed or flange con-
nections.
\VJ
40 44. An asbestos-
packed blow-off cock is shown in Fig. 40. The U-shaped
grooves a are cast in the interior surface of the body, form-
ing a seat for asbestos. The asbestos packing is elastic
40
PIPES AND PIPE FITTINGS
and makes a tight joint, and at the same time allows the
plug 6 to be turned easily. For a top packing a vulcanized
composition ring is used. The form of the asbestos packing
contained in the U grooves is shown in (6). Since the asbestos
is not affected by heat or moisture, this form of cock is durable.
In blowing down a boiler the Y valve or blow-off cock is opened
first, and then the angle blow-off valve. After the boiler is
blown down, the angle valve is closed first, and then the Y
valve or blow-off cock.
45. Pressure-Reducing Valves. When steam is required
at a lower pressure than that at which it is supplied by the
boiler, some form of pressure-
reducing valve must be used.
A reducing valve, designed to
give a uniform low pressure
from a varying higher pres-
sure, is shown in Fig. 41. The
steam flows through the valve
from the inlet a to the out-
let b, as shown by the arrows.
When it is desired to use it as
an angle valve, the outlet may
be made at c. The flow of
the steam is impeded and its
pressure reduced by means of
two disks d and e covering the
FlG ' 41 ports in the interior of the
valve body. These disks are connected by the sleeve / and
are rigidly attached to the valve stem, so that the ports are
opened by the downward movement of the valve stem and
closed by the upward movement. Each disk is guided by four
wings on its upper side, and by the valve stem, which passes
through a hole in the bonnet h.
46. The upper end of the stem, Fig. 41, is connected to
the inner ends of two levers i that have their fulcrums / in
the flange of the bonnet. The levers are pivoted on pin con-
nections k in the ends of a yoke I. The yoke is attached to the
PIPES AND PIPE FITTINGS
41
center of a corrugated circular copper diaphragm m, which is
subjected to the steam pressure beneath and the action
of a spring n on top . The amount of steam flowing through the
port o is regulated by means of a screw q. The resistance of
the spring n is regulated by a nut r. The valve not only reduces
the pressure, but also regulates it automatically; that is,
although the boiler pressure may vary considerably, as long
as it does not fall below the pressure for which the valve is
set, the valve will give a
practically uniform pres-
sure on the discharge, or
low-pressure, side. The
pipe on the low-pressure
side of the valve should
be fitted with a steam
gauge.
STEAM-PIPING
ACCESSORIES
47. Separators. A
steam separator is a de-
vice designed to remove
the entrained water, oil,
dirt, and other impuri-
ties from a current of
steam flowing through a
pipe. When it is in-
tended merely to free
the steam from water, the separator is placed on the main pipe
leading from the boiler to the engine, and as close as possible
to the latter. When grease and dirt are to be removed from
exhaust steam before it is condensed and fed back to the
boiler, the separator is placed in the exhaust pipe leading
from the engine to the condenser.
48. Classes of Steam Separators. Steam separators
may be divided into two general classes: centrifugal separa-
tors and baffle-plate separators. In a centrifugal separator, the
FIG. 42
42
PIPES AND PIPE FITTINGS
steam is given a whirling motion, so that the water held in
suspension in the steam is thrown outwards by centrifugal
force against the walls of the separator. In a baffle-plate
separator the steam comes in contact with plates generally
placed at right angles to the direction of flow of the steam.
The plates abruptly change the direction of the steam current.
Either type of separator causes the particles of water to be
thrown out of the steam current, and on striking the walls of
the separator, the water is led away to a drain. The dry
steam passes through the sepa-
rator to the main piping.
49. Centrifugal Separator.
The centrifugal separator shown
in Pig. 42 is arranged to connect
with horizontal piping. The
steam enters at a, and on strik-
ing the curved baffle b is given
a whirling motion as it enters the
chamber c. The particles of
water are thrown off by
the centrifugal action, run
down the walls of the
separator, and collect in
the chamber d. The steam
current is reversed, flows
FlG 43 over the edge of the pro-
jecting pipe e, and escapes
A gauge glass g is provided to show the amount of water
has collected, and a drain pipe h to remove the water.
at/
that
50. The vertical centrifugal separator shown in Pig. 43
operates like the horizontal type. The flange a is connected*
to the boiler side of the vertical piping. The steam flows down
over the baffle 6, by which it is given a whirling motion. The
whirling of the descending current throws the particles of
moisture outwards against the wall c of the separator, from
which they trickle down and collect in the chamber d. The
steam escapes by way of the passage e to a pipe connected at/.
PIPES AND PIPE FITTINGS
43
The moisture is drained away through the valve g. The gauge
glass h shows the depth of water collected in the chamber d.
51. BafHe-Plate Separator. In the baffle-plate separator
shown in Fig. 44 (a) and (6) the steam enters at a and is
deflected outwards at right angles by the
baffle 6, which is deeply grooved on its
face. The water in the steam is caught
in the grooves c, flows down them to the
bottom and drips into the chamber d of
the separator. The steam flows out
around the sides of the baffle through the
ports e into the chamber /. Here it
strikes the curved wall g of the separator
and is thrown back against the opposite
face of the baffle b, which removes further
moisture. This moisture drips through
the pipe h and so cannot be picked up
again by the steam, which escapes at i.
The water collecting in the chamber d is
drained off at /, the level being indicated
by a gauge glass attached at k.
52. Drip Pockets. Attachments
known as drip pockets are sometimes in-
stalled to collect water, dirt, grease, and
other substances that accumulate in steam
piping. As shown in Fig. 45, a drip pocket
is simply a collecting chamber a con-
nected to a tee b. The chamber is fitted
with a glass gauge c and a drain pipe d.
Drip pockets are made in sizes up to
12 inches in diameter, and the flanges are
made to fit either standard or extra-heavy
fittings.
53. Exhaust Heads. Exhaust heads FlG< *
are separators placed on exhaust-steam piping from non-con-
densing engines or pumps to prevent the water in the escaping
steam from being thrown on the roof or on adjoining build-
44
PIPES AND PIPE FITTINGS
ings. Such devices also serve as mufflers, deadening the sound
of the exhaust. Exhaust heads are made of steel plate or cast
iron, that shown in Fig. 46 being a typical steel exhaust head.
The exhaust steam enters at a and travels in the direction of
the arrow until it strikes the inverted conical surface b and the
walls of the cylinder c. A drip through d around the base of
the cylinder c collects the water that flows down its surface.
FIG. 45
FIG. 46
The steam flows down and out at the bottom of the cylinder c
and rises until it strikes a second inverted cone e, on which it
deposits additional water. This water follows the surface of the
cone and drips into the trough or gutter /. The steam passes
out at g to the atmosphere after flowing over the top edge of the
cylinder c, past the lip h, and up through the cylinder . Drip
pipes installed at the bottoms of the gutters carry the water
to the outlet /, .thus draining the water from the exhaust head.
PIPES AND PIPE FITTINGS
45
STEAM TRAPS
54. Purpose of Steam Trap. If no means were used to
remove the condensation from steam pipes, the water might
be carried into pump or engine cylinders and damage them; or,
it might be picked up by the swiftly moving steam current and
produce water hammer, which might wreck the pipe or the
fittings. The steam trap is a device that removes accumulated
condensation from drip pockets or separators attached to
steam pipes under pres-
sure, without allowing
steam to escape. Its
action is intermittent
and automatic.
55. Classes of
Steam Traps. T here
are two general classes
of steam traps: open,
or discharge, traps; and
return, or closed, traps.
An open trap, or dis-
charge trap, empties
the water of condensa-
tion into a sewer or a
tank. A return trap,
or closed trap, delivers
the condensation to the
boiler from which it
came as steam. Steam
traps are also named according to the means by which they
are operated, being known as bucket traps, float traps, tilting
traps, and expansion traps or thermostatic traps.
56. Bucket Trap. The bucket trap shown in section in
Fig. 47 is an open steam trap. Condensation from the steam
pipe enters at a, flows through the passage b and collects in the
body c of the trap. A bucket d is hinged on a pin e and is
connected by a rod / to a valve g that opens and closes outlet h
FIG. 47
46
PIPES AND PIPE FITTINGS
from the trap. As the condensation collects in the body
of the trap, the empty bucket tends to float and swings
upwards on its pin <?, thus forcing the valve g against its
seat and closing the outlet. The condensation accumulates
and eventually spills over the edge of the bucket and collects
in the bucket, which promptly sinks and opens the valve g
The interior of the trap is subject to the pressure existing
in the steam pipe, and this pressure forces the water inside the
bucket to flow up inside the sleeve i, through the opening h
FIG. 48
and out through the discharge at /. When the bucket is
nearly emptied, its buoyancy causes it to float, andTn rising
it agam closes the valve t and prevents the escape of steam
f^f^r ~+ .
C ections.-An example of the way in
a s earn trap may be connected is shown in Pig. 48 The
^<Z^-?ZZ5
by o pm g the valve/. On the discharge side rf ,h e Sp , s a
PIPES AND PIPE FITTINGS
47
valve g in the pipe h leading to the sewer. A by-pass pipe i,
fitted with a valve /, is installed between the tee k and the
pipe h. If the trap must be repaired or cleaned, the
valves d and g are closed and the valve / is opened sufficiently
to drain off the water as fast as it accumulates in the drip
FIG. 49
pocket ; but under normal operation the valve / is closed and
the valves d and g are open.
58. Tilting Trap. To return water of condensation to the
boiler, a return trap is employed. It must be located at
such a height above the water in the boiler that the hydrostatic
head produced by the elevation of the trap will cause the water
I L T 45918
48 PIPES AND PIPE FITTINGS
of condensation to flow Into the boiler. One form of return
trap, known as a tilting trap, with the necessary piping and
valves to connect it to a boiler, is shown in Fig. 49. It con-
sists of a cast-iron receiver a supported at one end by hollow
trunnions 6 and c on the stationary part of the trap and at the
other end by a link, a lever, and a weight g. In the drainage
of a heating or steam-pipe system, the different return pipes
lead to a tank, as shown at d. The water rises through the
pipe e, and passes through the check-valve / and trunnion c
to the receiver a. The water enters this receiver until its
weight is sufficient to overbalance the counterweight g, when
the receiver a moves downwards until it comes against the
guide h. This downward motion causes the lug i to engage the
upper nuts on the stem of the steam valve /, opening the latter
and thus admitting steam at full boiler pressure on top of the
water. Steam enters from the boiler through the pipe k, trun-
nion 6, and curved pipe /, leading to the highest point in the
receiver. Driven by the steam, the water flows from the
receiver to the boiler by gravity, through the trunnion c, check-
valve m, pipe n, and globe valve o. As soon as the receiver is
emptied, the weight g lifts it to its upper position, which closes
the steam valve / and opens a small air valve p below the
valve /, allowing the steam to exhaust from the receiver, A
cock q is provided on the trunnion b for the purpose of venting
the interior of the receiver by hand, if necessary at any time,
59. When there is 'not sufficient pressure to make the
water in the receiver enter the trap on top of the boiler, another
trap may be placed at the point where water will flow into it.
This trap may then be made to discharge into one placed on
top of the boiler, using steam from the boiler as a motive force.
Return traps can be made to discharge the water into elevated
tanks, the height to which the water may be raised depending
on the available boiler pressure. This height, in feet, allowing
for frictional and other resistances, is given approximately
by multiplying the boiler pressure available by 1.4. Thus, if
the boiler pressure is 60 pounds per square inch, a return trap
can discharge into a tank 60X1.4 = 84 feet above it.
PIPES AND PIPE FITTINGS
49
60. Float Trap. The float trap shown in Fig. 50 depends
for its action on the rising and falling of a float a that controls
the opening and closing of the valve 6, through which the water
is discharged. The valve is connected to the float by a series
of levers c, and the higher the float rises, the wider the valve
FIG. 50
opens and the greater the rate of discharge. Thus, if the
condensation enters the trap at d at a fairly uniform rate, the
discharge will occur at the same rate and the operation will be
continuous. To prevent
the weight of the float
from forcing the valve too
hard against its seat, an
adjustable stem e may be
screwed inwards until it
bears against the bent
arm / on the lever that
moves the valve. A
strainer g prevents the pas-
sage of dirt that would clog the valve.
FIG. 51
Air may be removed
through the vent h and sediment through the cocks i and /.
61. Thermostatic Trap. The thermostatic steam trap
depends for its action on the expansion and contraction of a part
50 PIPES AND PIPE FITTINGS
under the effect of heating and cooling. One form is shown
in Fig. 51. The condensation enters by way of the pipe a,
flows past the valve 6, and collects in the chamber c,- which
contains an air-tight circular vessel d made of thin sheet metal.
The water escapes from the chamber c through the outlet e.
When most of it has escaped, and hot water or steam enters the
chamber c, the heat causes the air in the vessel d to expand, and
the flat sides bulge out, as indicated by the dotted lines. The
valve b is pushed against its seat by this bulging of the vessel d,
and the flow is stopped until the collected water cools and the
vessel d contracts enough to open the valve. With a uniform
rate of condensation, the action of the trap is practically con-
tinuous. A dirt pocket is provided at/, and an adjusting screw
at g to alter the quickness with which the valve is closed. The
thermostatic trap is not likely to freeze or become air-bound.
62. Suggestions for Trap Installations. The size of trap
to be used depends on the volume of water of condensation to
be handled and is not based on the size of the pipe to which it is
attached. There are several rules to be followed in the instal-
lation of a trap : The trap must be located at a low point in
the return piping, so that the water of condensation will flow
to it by gravity. Means must be taken to prevent the trap
and piping from freezing; for, when a trap is blocked with ice, the
valves will not work and the water will back up in the return
piping. By-pass piping should be so installed that, in case the
trap must be cleaned or repaired, the condensation may be
discharged through the by-pass.
DESIGN AND ARRANGEMENT OF PIPING
PRINCIPLES OF DESIGN
63. General Requirements. The installation of a complete
steam plant includes the setting of the boiler or boilers, the
arrangement of the various lines of piping, and the location and
arrangement of the various accessories, such as feedwater
heaters, purifiers, separators, economizers, feed-pumps, and
PIPES AND PIPE FITTINGS 51
injectors. An elaborate plant may be fitted with economizers,
mechanical stokers, coal conveyers and ash conveyers, purifiers,
and other labor-saving and fuel-saving devices. On the other
hand, the plant may consist simply of boilers, chimney, and
feed-pump.
The proper designing of a system of piping requires a careful
analysis of the conditions of service, a thorough knowledge of
the methods of distributing and conveying steam and water,
and of the quality and strength of materials employed. A
system of steam piping for a power plant must be so designed
as to insure reliability of service and economy of construction.
The main lines of piping should be so connected that it will
not be necessary to shut down the entire plant to make minor
repairs. Continuity of operation is absolutely indispensable
to a successful power plant.
64. Drainage. The pipes and fittings must be so pro-
portioned as to permit a free flow of steam or water, * so
that no undue loss will be caused by condensation, radiation,
or friction. The steam piping should be so arranged that
water pockets will be avoided; and where such pockets
are unavoidable, they must be drained to free them from
water. The entrained water can be automatically returned
to the boiler. By-pass pipes, with suitably placed valves,
should be arranged around feedwater heaters, economizers,
pumps, etc. The system must be so designed as to give
perfect freedom for expansion and contraction, without
undue stress on any part of the system, and without open-
ing joints and thus causing leakage. An elaborate duplica-
tion of steam mains and connections is not necessary. The
double, or duplicate, system of piping was introduced to insure
continuous power-plant service, which would not be obtain-
able with single piping. Reliability is insured by careful
design and superior workmanship, combined with the use of
high-class materials and fittings and the judicious placing
of cut-out and by-pass valves,
-65. Drainage. Perfect drainage must be provided in
order that all water of condensation shall be fully separated
52 PIPES AND PIPE FITTINGS
from the steam, and, by suitable traps or return systems,
delivered again to the boiler. Drainage is best effected by
arranging the piping so that all the water of condensation will
flow by gravity toward a point close to the delivery end of the
pipe, and then providing a drip pipe at that point. In the
case of large pipes, a trap may be placed at the end of the drip
pipe for automatic draining; the trap serves to seal the end of
the drip pipe and thus prevents waste of steam.
66. Water Hammer. The presence of water in a steam
pipe is the cause of water hammer, the term used to describe
the condition that causes the hammering noise often heard in
the piping of steam-heating plants. It has been shown
experimentally that the pressure produced by water hammer
may be as great as ten times that which the pipe is expected to
sustain in its regular work. In some cases, water hammer has
caused boiler explosions by bursting a steam pipe and thus
relieving the boiler pressure so suddenly that a large quantity of
water flashed into steam.
67. Condensation and Friction. When steam leaves the
boiler and flows through a pipe to the point where it is to be
used, it loses a part of its original energy. Some of its heat is
lost by radiation, conduction, and convection, and if the steam
is not superheated, this loss of heat results in condensation of
part of the steam. It takes place whether the steam is flowing
or at rest, but it may be reduced to a minimum by using non-
conducting coverings on the pipes.
Because of friction in flowing through pipes and fittings,
the pressure of steam at the outlet, or discharge, end of a sys-
tem of piping is less than at the inlet, or boiler, end. The
loss of pressure due to friction reduces the flow below the
estimated capacity of a straight pipe, and must be taken
into account in the case of a long pipe with numerous bends
and fittings.
Friction is greater through elbows of short radius than
through elbows of long radius, because the change of direction
of flow is more abrupt. It is advantageous, therefore, to
make all bends of large radius. Globe valves offer considerable
PIPES AND PIPE FITTINGS 53
resistance to the passage of high-pressure steam, but the drop
in pressure when passing through a gate valve is practically
np.p'lip'ible.
negligible
ARRANGEMENT OF PIPING
68 . General Requirements. In arranging a piping system
for a steam plant, the aim must be to produce a design that
combines low first cost with durability and serviceableness.
A point that must be considered is the extent to which the
piping must be in duplicate in order to prevent a shut-down
in case of an accident to any section. The ease with which
the piping can be taken down for repairs must also be con-
sidered. In general, flanged sections are more easily taken
down than sections united by screwed joints, at least in the
larger sizes. When screwed joints are used, it is advisable to
introduce a liberal supply of unions, so that a section may be
taken out and replaced without having t.o tear down the whole
piping system. The question of whether to place the piping
overhead or under the flooring is chiefly one of convenience
and appearance. With the piping under the flooring, the
engine room will generally look better, but the piping will not
be as accessible as when overhead.
69. Careful thought is necessary in designing piping
connections to boilers. Connections between a single boiler
and the distributing main are comparatively simple to make;
but when two or more boilers are to be connected to the same
main line of pipe, special and adequate provision must be
made for expansion; otherwise, the stresses on the connections
will cause them to leak. If a long line of pipe is connected
directly to the boiler shell, the expansion due to the entrance
of hot steam will so increase the length of the pipe as to twist
or wrench the joints and cause them to leak.
70. Connecting Main Steam Pipe to Boiler. Several
approved methods of connecting the main steam supply
pipe to the boiler are shown in Figs. 52 and 53. In Fig. 52,
the connections are made by means of bent pipe, while in
Fig. 53 straight pipe is used. In Fig. 52 (a) and (c), a short
54
PIPES AND PIPE FITTINGS
length of pipe rises vertically above the shell of the boiler and
connects with a bent branch pipe joined to the main steam
pipe or header, the bent pipe allowing the header to expand
and contract freely. In (6), connection between the boiler
end and the header is made by using a U bend; and (d) illus-
trates the use of two quarter-turn bends in making the con-
nection. It is generally conceded that, when pipe bends are
thus used, the best position for the valve, when only one is
used, is at the center of the bend ; but some engineers regard
(e)
FIG. 52
it as better practice to use two valves, one being placed near
the main and the other at the boiler. When two valves are
used, it is frequently necessary to tap the body of each valve
for a dnp connection to drain away any water of condensation
that may accumulate in it.
71. In Pig. 53, in which a straight pipe a is used, the
length of the vertical sections should be great enough to give
the spring necessary to allow for expansion without straining
any of the pipe parts and fittings. The branch pipe b is the
PIPES AND PIPE FITTINGS
55
steam main, or header, and c is an angle gate valve. In high-
pressure steam plants, it is customary to insert, in addition,
an automatic stop-valve d in the branch from each boiler to the
steam main. Its object is to prevent, automatically, the
flow of steam from one boiler to any boiler that may be
disabled. The non-return valve illustrated is similar to an
ordinary angle globe valve, except that the valve disk e has
sufficient vertical play on the lower end of the stem / to allow
it to seat, should the pressure in the individual boiler become
FIG. 53
much less than that in the main, even when the valve stem
is in its highest position. The arrangement is such that the
disk may be firmly held to its seat when desired. Gate valves
are not suitable for this kind of emergency work, as they require
considerable time to close, and may be difficult to move when
nearly closed.
72. When several boilers of, say, 200 horsepower and
upwards are used, it will be found very convenient to place
PIPES AND PIPE FITTINGS
57
the steam main or header on or near the floor in the rear of the
boilers; this brings all the large valves in accessible positions.
The steam lines leading to the engines are placed below the
engine-room floor. This system is particularly applicable
where horizontal engines are used.
73. The judicious use of long-radius bends, a convenient
arrangement of valves, accessible location of the live-steam
FIG. 55
header, and steam connections to engines below the engine-
room floor are shown in Figs. 54 to 56. From the cross-con-
nection between the steam drums a of the water-tube boilers
leads a connection 6, starting from an automatic stop- and
check-valve c\ the long-radius bend b is placed horizontally
and connects with a similar benddleading vertically downwards
58
PIPES AND PIPE FITTINGS
to the live-steam header e. This arrangement gives great
elasticity to a system of large piping, and the valves are in
convenient positions for ready manipulation.
74. Only the main steam piping is shown in Figs. 54 to
56, the auxiliary piping for the boiler, feedwater heaters, etc.
being omitted. Fig. 54 is
a plan view, Pig. 55 an
end view, and Pig. 56 a
view showing the arrange-
ment of the main steam
pipes looking toward the
rear of the boilers. The
steam pipes /, running
from the header e to the
high-pressure cylinders of
the steam engines, are
placed under the engine-
room floor, and a connec-
tion to the low-pressure
cylinder is provided at g
so that in case of emer-
gency the low-pressure
cylinder can be run with
high-pressure steam. By
examining the arrange-
ment of valves between
the boilers and engines, it
will be seen that without
duplicate piping it is pos-
sible to cut out any en-
gine or boiler in case of
accident and still run the
plant with the remaining
engines and boilers. The main steam header is divided into
two sections by the large gate valve h, Figs. 54 and 56, so
that one half of the header can be cut off from the other half
by closing the valve.
o
B
PIPES AND PIPE FITTINGS 59
75. Steam Piping for Small Plant. A plan and an eleva-
tion of the steam piping of a small electric-light plant are
shown in Fig. 57. The station contains two 100-horsepower
boilers and one 300-horsepower boiler, all of the water-tube
type, which supply steam to two tandem-compound engines
directly connected to electric generators. The branch
steam pipes a from the three boilers deliver into a horizontal
steam main b placed at the level of the drums, an angle stop-
valve c being placed over each boiler, and each branch connect-
ing to the top of the main with a long-radius bend d. The
supply pipe for each engine is taken from the top of the main,
each supply pipe being provided with an angle stop-valve e
and a throttle valve / being placed close to the engine. A
steam separator g is placed in each supply pipe directly over
the throttle valve. Owing to the method in which the piping
is run from the boilers to the engines, it is quite flexible, so
that there will be little or no stress set up by its expansion or
contraction.
76. The exhaust piping is shown by dotted lines in the
plan view, Fig. 57. The exhaust pipes from the two engines
are placed below the floor and are joined by means of a Y
fitting h connecting with the main exhaust pipe, which conveys
the exhaust steam through a closed feedwater heater i pro-
vided with a by-pass ; to the atmosphere. A separator k,
intended to remove oil from the exhaust steam before it reaches,
the heater, is placed in the main exhaust pipe.
The various pipe lines used for draining the piping, heaters,
and separators, and the piping of the boiler feed-system, the
fire-service pipes, the boiler blow-offs, and similar small piping
found in a steam plant are not shown. The purpose of this
illustration is chiefly to show the arrangement of the main
steam pipes and valves.
SINGLE-PIPE AND DOUBLE-PIPE SYSTEMS
77. Single-Pipe System. The diagrammatic view, Fig.
58, illustrates a general piping arrangement when a single-
pipe system of piping is used to connect the boilers with the
60
PIPES AND PIPE FITTINGS
prime movers, such as turbines or engines, or with pumps.
The single-pipe system has a disadvantage in that a break in
the main steam piping, although the piping is divided by valves,
necessitates the closing down of a part of the plant until repairs
can be made. However, if any of the boilers or prime movers
are disabled, it is possible to place the unit out of commission
for repairs by closing the valves in the piping leading to and
from that unit. An auxiliary feedwater system should be
installed to provide additional means for feeding water to the
boilers in case the main feed supply is temporarily disabled.
The single-pipe system is not suitable for very large power
-Sofa
H
1
Co/j deff set"
^ feet? Water Piajm
50rtr l/tr/yas
FIG. 58
plants, especially such plants as generate electricity for rail-
ways, lighting systems, and other purposes for which continu-
ous service at full-load capacity is required.
78. Double-Pipe System. The double-pipe system, or
duplicate system, consists in connecting each boiler and prime
mover with a double-pipe header and valves. The arrange-
ment of piping and valves for such an installation is shown in
Fig. 59. The cost of installation is greater than the single-
pipe method, but this is offset by the greater reliability, as it
insures continued service in the power plant. The main
objection to the double-pipe system is that the colder pipes in
the steam headers will be affected by the stresses arising from
61
62 PIPES AND PIPE FITTINGS
the expansion of the active steam piping, thus causing condi-
tions that are liable to produce leaky pipe joints. This trouble
may be avoided by using long lines of piping and long-radius
bends that will be sufficiently flexible to reduce the stresses on
the pipe joints. Steam headers made in the form of loops
are better adapted to take care of the expansion and con-
traction stresses. For large power plants, an auxiliary set of
boilers and some prime mover units are included in the power
equipment, thus involving an adequate piping system based
on the principles applied in the double-pipe arrangement.
PIPE CALCULATIONS
STEAM-PIPE SIZES
79. Flow of Steam in Pipes. Steam flows through a pipe
because the pressure is higher at one end than at the other.
The greater the difference of pressure at the ends, the faster
. will be the flow, and the greater will be the weight of steam
delivered in a given time. The greater the velocity of flow
of the steam, the smaller will be the diameter of the pipe for
a given discharge of steam ; thus, it is advantageous to have the
steam travel rapidly, as the cost of pipe is reduced. Besides,
a small pipe has less exposed surface than a large pipe,
and so the heat loss from it will be less. On the other hand,
the friction increases as the diameter of the pipe is reduced,
and it increases as the square of the velocity; that is, if the
velocity of flow of steam is made twice as great, the friction
becomes about four times as great. The effect of this friction
is to reduce the pressure at the discharge end, or to cause what
is commonly called a drop of pressure. The drop of pressure
increases at the same rate as the length of pipe increases, and
is proportional to the weight per cubic foot of the steam, or
the density of the steam. Thus, the problem of finding the
size of steam pipe for a given service involves a compromise
between a reasonable drop of pressure and as small a pipe as
can feasibly be used.
PIPES AND PIPE FITTINGS
63
80. There is a definite relation between the weight of
steam delivered and the drop of pressure, which is given by
the formula
in which W = weight of steam flowing, in pounds per second ;
C = a constant, the value of which depends on the
pipe size;
= drop of pressure, in pounds;
w = weight of steam, per cubic foot;
L = length of pipe, in feet.
The values of C for different pipe sizes are given in Table X.
The foregoing formula may be used to find the diameter of
pipe for a given service by assuming a pipe diameter, finding
the corresponding value of C from Table X, substituting in
the formula, and finding the quantity W of steam discharged.
TABLE X
VAI/CTES OF CONSTANT C
Nominal Size
of Pipe
Inches
Value of C
Nominal Size
of Pipe
Inches
Value of C
1
.75
6
97
1|
2.5
8
195
2
5.1
10
350
2J
8.5
12
550
3
15.5
14
800
4
32.5
16
1,100
5
60
If the value is too small, or too large, another pipe size is
assumed and the calculation is repeated. This is continued
until a size is found that will give the desired capacity under
the prescribed conditions.
EXAMPLE. Find the size of 'pipe 160 feet long required to convey
2 800 pounds of saturated steam per hour, with a drop of pressure of
3 pounds, the pressure of the steam at the entrance to the pipe being
200 pounds per square inch, gauge.
I L T 459 19
64 PIPES AND PIPE FITTINGS
SOLUTION. A discharge of 2,800 Ib. per hr. is equivalent to 2,800
-5- (60X60) = .78 Ib. per sec. This is the required capacity of the pipe.
According to the example, = 2 Ib. and . = 160 ft. The weight of a cubic
foot of saturated steam at 200 Ib., gauge, or 215 Ib., absolute, according
to the Steam Table, is w-AQS Ib. For a trial solution, assume a 2-in.
pipe. The corresponding value of C, from Table X, is 5.1. Substitute
these values in the formula, and
Trr r<l /3x7468 An ,
W5.1+ I =.48 Ib. per sec.
As the pipe must discharge at least .78 Ib. per sec., it is plain that a 2-in.
pipe is too small. So, try a 2^-in. size, for which the value of C is 8.5, and
again substitute in the formula. Then,
This is only slightly greater than the required discharge, and so a 2|-in.
pipe will be satisfactory. Ans.
81. Velocity of Steam in Pipes. The pipe sizes used in
connection with the transmission of saturated steam are such
as to give steam velocities of from 3,500 to 6,000 feet per minute
in the pipes. In the case of superheated steam, velocities of
12,000 feet per minute, or higher, are possible, because the
weight of a cubic foot of superheated steam is less than that
of a cubic foot of saturated steam at the same pressure, In
reality, the velocity of flow is of no particular consequence,
so long as the required capacity can be obtained without
exceeding the allowable drop of pressure. The allowable drop
of pressure may be from 1 to 5 pounds per, 100 feet of length
of pipe.
82* Supply Pipes for Steam Engines. In the case of a
pipe supplying steam to a turbine, the flow of steam is con-
tinuous; but if a reciprocating engine is used, steam flows into
the engine cylinder during only a part of each stroke, so that
the flow in the pipe is intermittent, rather than continuous.
This point should be considered in calculating the size of a pipe
to supply steam to a reciprocating engine. Suppose, for
example, that an engine that cuts off at one-fourth stroke
requires 3,600 pounds of steam per hour. As steam flows
into the cylinder during only one-fourth of each stroke, the
PIPES AND PIPE FITTINGS 65
3,600 pounds flows into the engine in J hour, so that the rate
of flow during the time the steam is in motion is 3,600 -^i
= 14,400 pounds per hour, or 4 pounds per second. Hence, in
calculating the size of pipe for the engine, by the formula of
Art. 80, a capacity of W=4 pounds per second must be
obtained.
When the flow of steam in a steam pipe is continuous, as,
for instance, in the supply pipe used for a turbine or a direct-
acting steam pump, the weight of steam to be used for pur-
poses of calculation is equal to the actual weight of steam used
per second.
83. Sizes of Main Steam Pipes. If a series of boilers
A, B, C, and D are set in a battery and discharge into one main
pipe, or header, the main pipe need not be of the same diameter
throughout. Between boilers A and B it must be large enough
to carry the steam from boiler A ; between boilers B and C it
must be large enough to carry the steam from boilers A and B\
and so on. If all the boilers are of the same capacity, the
calculations of the diameters of the sections is a simple matter.
Suppose that the diameter of the main pipe between boilers
A and B has been found to be d. Then, the diameter between
boilers B and C must be d. \2; between boilers C and D it
must be d \3; and beyond boiler D, where it carries the dis-
charge of all four boilers, it must be d \4=2 d.
84. Friction of Valves and Fittings. An elbow or a
valve in a steam pipe offers resistance to the flow and so
increases the friction. In order that this friction may be
taken into account in calculating the size of pipe required,
it is customary to determine the length of straight pipe that
would have the same frictional resistance as the valve or
fitting. The value of L in the formula of Art. 80 is then
taken as the sum of the actual length of pipe and the lengths
of straight pipe having the same friction as the valves and
fittings. The resistance at a globe valve is usually assumed
to be about the same as that of a length of straight pipe equal
to sixty times the pipe diameter, while the resistance at an
66 PIPES AND PIPE FITTINGS
elbow is assumed to be approximately equal to two-thirds that
of a globe valve. It is assumed that the resistance at the
entrance to a pipe is equal to the resistance offered by a globe
valve.
For example, suppose that a 3-inch pipe 128 feet long con-
tains four elbows and three globe valves. Each globe valve
has a resistance of 60X3 = 180 inches, or 15 feet, of straight
3-inch pipe. Each elbow has a resistance of f X15 = 10 feet
of 3-inch pipe. The resistance at the entrance is that of
15 feet of 3-inch pipe. Then, the equivalent length of pipe
with which to make calculations is L = 128 +15 +(4X10)
+ (3 X 15) = 228 feet.
FLOW OF WATER IN PIPES
85. Finding Size of Pipe. In power plants, piping is used
to convey feedwater to -boilers, cooling water to condensers, hot
water to and from pumps, and so on. The determination of
the size of pipe required to carry a known quantity of water,
if it is to be made accurately, must take into account the
length of the pipe, the number of bends, elbows, and valves,
and the friction due to rubbing against the walls of the pipe at
different velocities of flow. To consider the effect of these
various factors, the calculations become intricate, and beyond
the scope of this Section. However, it is possible to determine
the approximate size of a pipe by simple general formulas.
For example, if the quantity of water to be carried is stated in
cubic feet per minute, the size of pipe may be found approxi-
mately by the formula
'183(2
v ^ '
in which d = internal diameter of pipe, in inches ;
Q = quantity of water, in cubic feet per minute;
^ = average velocity of flow, in feet per minute.
If G denotes the number of gallons per minute, the formula
becomes
PIPES AND PIPE FITTINGS 67
86. Velocity of Flow. The average velocity v of the water
in pipes in power plants ranges from 50 to 400 feet per minute,
depending on the nature of the service. Suction lines to
pumps should have low velocities of flow. Thus, a suction
pipe for hot water should be based on a velocity of from 50
to 100 feet per minute, the lower values in the range being
used for long pipes and pipes containing many bends and
valves; if cold water is carried, the range may be from 100 to
200 feet per minute. In the case of feedpipes, the velocity
may range from 200 to 400 feet per minute. The velocity in
water-supply pipes to condensers may be from 300 to 400 feet
per minute.
EXAMPLE 1.-A boiler requires 30,000 pounds of water per hour. What
size of feedpipe is necessary, if the rate of flow is 360 feet per minute?
SOLUTION. The amount of water required per minute is 30,000-^-60
=500 Ib. As water weighs 62.5 Ib. per cu. ft., this is equivalent to
500-r-62.5=8 cu. ft. per min. Apply formula 1, Art. 85, making
0=8 cu. ft. and ^=360 ft. per min.; then,
/183X8
Therefore, an extra-heavy 2-in. pipe may be used although a 2j-in. pipe
would be better. Ans.
EXAMPLE 2. Find the size of pipe required to convey 264 gallons of
water per minute to a condenser, if the average velocity of flow is 400 feet
per minute.
SOLUTION. Apply formula 2, Art. 85, making G= 264 gal. per min.
and = 400 fc. per min.; then,
/24.4X264
Therefore, a standard 4-in. pipe would be used. Ans.
BOILER FURNACES, SETTINGS,
AND CHIMNEYS
(PART 1)
FURNACES OF STEAM BOILERS
FURNACE DESIGN AND CONSTRUCTION
CONDITIONS AFFECTING FURNACE DESIGN
1. Furnace Volume. To insure economical operation of
a steam boiler, the height, width, and length of the furnace
must be such as to enable the gases to be burned completely
before they are brought in contact with the heating surfaces.
The relative proportions of the furnace therefore depend on
the kind and quality of fuel used and the location of the heating
surfaces. For example, a short, wide furnace having a small
volume is not suitable for burning fuel that contains a large
percentage of volatile matter; a long, narrow furnace is pref-
erable to a short, wide one of the same volume. To prevent
contact of the gases with the boiler surfaces until combustion
is completed, walls and arches are used. These are faced or
lined with refractory brick having great heat-resisting quali-
ties. The linings absorb heat, help to maintain a high uniform
temperature in the furnace, and promote combustion.
2. If the boiler is internally fired, of the locomotive type
or the vertical type, the crown sheet should be as far as possible
above the, grate, so as to give a large furnace volume and
2 BOILER FURNACES, SETTINGS,
prevent the hot gases from striking the crown sheet and being
cooled before combustion is completed. The temperature at
which ignition of the volatile gases can take place is from about
900 to 1,200 P.; therefore, if unconsumed gases are brought
in contact with plates having a temperature of from 350 to
400 R, they will be cooled below the ignition point, and if
they are not subsequently brought to a temperature at which
they will burn, they will pass out to the stack and the heat value
of the fuel they contain will be wasted. This explains why a
high furnace temperature, aided by incandescent walls of
refractory brick, is valuable in promoting combustion and
preventing fuel loss.
3. Furnace Temperature. If the furnace is external to the
boiler, and is bounded by firebrick walls, the furnace tempera-
ture may be as high as 2,500 or 3,000 F. ; but if the furnace
is internal, and surrounded by water-cooled plates, the tem-
perature rarely rises above 2,000^P. A high temperature is
desirable, for the reason already stated; and an additional
reason is that the transfer of heat from the gases to the water
is more rapid with a high than with a low furnace temperature.
To insure complete combustion of the fuel gases, an excess of
air above that theoretically required is always supplied to the
furnace. At ordinary rates of combustion, the excess ranges
from 25 to 50 per dent.; but when the fires are forced, the
excess may be from 100 to 300 per cent. This air enters
the furnace at a temperature of from 50 to 90 F. and escapes
to the chimney at a temperature of from 400 to 600 F. ;
thus, air supplied beyond that needed for combustion reduces
the furnace temperature and causes loss by carrying away heat.
4. Effect of Composition of Coal on Furnace Volume.
Coal having a high percentage of volatile matter, such as
bituminous coal, which burns with a long, Smoky flame, requires
a much larger combustion space than coal of low volatile
content. Hence, the volume of the furnace is governed by the
quantity and nature of the volatile matter in the fuel and the
rate at which the fuel is burned. The Bureau of Mines has
conducted experiments with bituminous coals of three grades
AND CHIMNEYS, PART 1
Pocahontas, Pittsburgh, and Illinois-having, respectively,
13, 35, and 47 per cent, of volatile matter. The results are
given in Table L In the first column is shown the degree of
completeness of combustion attained by stating the percentage
of the heat undeveloped, and in the second and third columns
are shown the varying conditions of excess air and rate of
burning of the coal. In the last three columns is shown how
many cubic feet of combustion space are required for each
grade of coal under the conditions stated in the first three
columns. It is seen at once that the coal with the greatest
percentage of volatile matter requires the largest volume
of furnace.
5. The values in Table I bring out several other interesting
facts. In the case of any one of the grades of coal tested,
the loss due to undeveloped heat is lowered by increasing the
TABLE I
SIZE OF COMBUSTION SPACE FOR BITUMINOUS COALS
Rate of Com-
Combustion Space
Undeveloped
Heat
Per Cent.
bustion
Pounds per
Square Foot
of Grate per
Hour L
Excess Air
Per Cent.
Cubic Feet per Square Foot
of Grate Area
Pocahontas
Coal
Pittsburgh
Coal
Illinois
Coal
5
50
50
2.7
2.9
4.3
3
50
50
3.2
3.7
5.3
2
50
50
3.6
4.4
6.3
1
50
50
4.0
5.6
8.9
.5
50
50
4.8
6.8
11.9
5
25
50
2.0
2.2
3.5
3
25
50
2.3
2.7
4.35
2
25
50
2.7
3.1
5.1
1
25
50
3.4
4.0
6.2
.5
25
50
4.0
5.0
7.1
furnace volume, showing that the combustion became more
nearly complete as the space provided for mixing and burning
the gases was increased. The size of combustion space
4 BOILER FURNACES, SETTINGS,
required "does not vary in direct proportion to the quantity of
volatile matter. For instance, doubling the rate at which the
fuel is burned doubles the amount of volatile matter driven off
from the coal in a given time; but it will be seen from the table
that the combustion space is not doubled. For example, take
Pittsburgh coal with a loss of 3 per cent, in undeveloped heat.
At a rate of firing of 25 pounds of coal per square foot of
grate, the furnace volume is 2.7 cubic feet per square foot
of grate, whereas, at 50 pounds per square foot it is 3.7 cubic
feet, or only about 37 per cent, larger; that is, doubling the
rate of fuel consumption required an increase of only about
37 per cent, in furnace volume.
6. Firebrick Arches and Walls. In locomotive boilers that
burn bituminous coal, arches built over the fuel bed assist in
promoting combustion. The arches are built of firebrick blocks
and are supported by arch tubes. The firebricks become
incandescent and thus tend to maintain a uniform temperature
in the furnace. At the same time, the arch lengthens the
travel of the hot gases and prevents cool air from striking the
tube-sheet and firebox plates. The same principle may be
adapted to other types of boilers. For example, the Scotch
boiler or the Clyde boiler has furnace flues of large diameter
opening into combustion chambers. The combustion chambers
opposite the ends of the flues may profitably have firebrick
linings; for, after the brick becomes heated, any unconsumed
gases leaving the flue will be ignited by the incandescent brick-
work and thus will be prevented from escaping to the stack
unburned. Externally fired boilers have various arrangements
of brickwork and baffles to prevent the escape of unconsumed
furnace gases.
7. Distance Between Boiler and Grate. If the setting of a
water-tube boiler is such that the gases rising vertically from
the fuel on the grates immediately come in contact with the
tubes, they are chilled and the process of combustion is checked
before they have become thoroughly mixed with air. To
prevent this condition, it is advisable to set the boiler so that
the tubes are well above the grates, thus providing a conabus-
AND CHIMNEYS, PART 1 5
tion chamber of considerable volume. The addition of a fire-
brick arch over the fire may also prove advantageous The
percentage of volatile matter contained by the fuel governs
the distance from the grate to the lowest row of tubes. For
burning anthracite, the minimum distance is ordinarily about
40 inches, as the flame is short and there is little volatile
matter. For burning bituminous coal, the distance should be
60 inches or more.
8. In the setting of horizontal return-tubular boilers,
the Hartford Steam Boiler Insurance Company recommends
certain distances from the grates to the boiler shell and from
22 S
48 54 . 60 66 72,
Diameter of' Boileri In Inches
FIG. 1
78
84
the top of the bridge wall to the shell, for different kinds of
fuel. This information has been condensed into the form of a
diagram, as shown in Fig. 1 . The method of using the diagram
is to locate the diameter of the boiler along the base line
and from this point to follow vertically to the diagonal line
corresponding to the fuel used. From the intersection on the
diagonal, proceed horizontally to the left, and the scale at
the left will show the distance between the grates and the
shell; proceed to the right from the same point on the diagonal,
and the right-hand scale will show the distance between the top
of the bridge wall and the shell. The diagonal A is to be used
if the fuel is bituminous coal having more than 35 per cent, of
6 BOILER FURNACES, SETTINGS,
volatile matter, as Illinois coal ; the diagonal B is for bituminous
coal having from 18 to 35 per cent, of volatile matter, as
Pittsburgh coals; and the diagonal C is for semi-anthracite
and anthracite containing less than 18 per cent, of volatile
matter, as Pocahontas and Georges Creek coals.
EXAMPLE. A return-tubular boiler 72 inches in diameter is to be fired
with bituminous coal containing 27 per cent. of volatile matter. Find
(a) the distance from the grates to the shell and (b) the distance from the
bridge wall to the shell.
SOLUTION. (a) As the fuel contains 27 per cent, of volatile matter, the
diagonal B, Fig. 1, must be used. At the bottom of the diagram locate
72 and proceed vertically to the line B. From this point proceed horizontally
to the scale at the left, where 40 inches is indicated. This is then the
height of the boiler shell above the grates. Ans.
(&) From the same point on the diagonal B proceed horizontally to
the scale at the right, where 16 inches is indicated. This is the distance
between the shell and the top of the bridge wall. Ans.
FURNACE AND ASH-PIT DETAILS
9. Furnace Mouth. The fronts of boilers consist of steel
or cast iron, lined with firebrick to prevent their warping and
burning under the action of heat from the furnace. They con-
tain the openings to
the furnace and the
ash - pit. The fire-
door opening should
be flared outwards on
the side toward the
furnace, as shown in
FIG 2 the sectional view,
Fig. 2, so that any
part of the furnace may be reached easily by the firing tools.
The sides and front wall of the furnace are indicated by cross-
section lines. The furnace mouth, or fire-door opening, is
fitted with cast-iron cheek plates a at the sides, and a dead
plate b forms the bottom of the opening and serves as a
support for the front ends of the grate bars c\ also, fresh
fuel is thrown on the dead plate "and allowed to remain until
AND CHIMNEYS, PART 1 7
the volatile matter is driven off, after which it is pushed
back on the grates. A dead plate is shown in Fig. 3. The
offset lip a supports the ends of the grate bars and the flat
FIG. 3
part b forms the floor of the furnace mouth. A heavy rib c
strengthens the plate against warping and cracking.
10. The top of the furnace mouth may be protected by an
arch constructed as shown in Pig. 4. A cast-iron arch plate a
is built into the brickwork of the furnace front and forms a
support for special firebricks b that are dovetailed and held
in dovetails in the under side of the arch plate. These bricks
may readily be removed when burned out, and be replaced by
new ones. Some engineers prefer a water-cooled arch, as
shown in Fig. 5. By this construction, horizontal pipes a
form the top of the furnace mouth. These pipes are connected
to headers b that communicate with the boiler at different
levels through the pipes c and d. The water in the pipes a
becomes heated and a circulation is set up in the pipes, thus
preventing them from being burned out. Firebrick is laid on
top of the pipes to form the top of the arch, and thus a water-
cooled arch is obtained. Mud and sediment may be blown
out of the pipes and headers by opening the valve e.
1 1. Intense heat is generated near the fire-doors, and unless
protective devices are u's'ed it will be necessary, frequently, to
S BOILER FURNACES, SETTINGS,
renew the door linings, arches, side walls, and dead plates.
One method of arranging' water pipes for protection has been
described. Another method of accomplishing the same pur-
pose is shown in Pig. 6 (a) and (6). Two rings a of half-oval
section, as shown at b, are connected by the pipes c and d.
Connection is made with the water space of the boiler by the
pipes e and/, so that the hollow rings are filled with water when
FIG. 5
the boiler is in operation. The rings are set in the boiler front
and form the sides and arched tops of the fire-door openings,
As^the level ghof the top of the grates is above the bottom
inside surface of the ring, a dead plate i is inserted. Blow-off
connections / allow the rings and pipes to be cleaned of sedi-
ment.
12. Bridge Wall. The bridge wall is a low wall built
across from one side wall of the setting to the other, beneath
AND CHIMNEYS, PART 1 9
the boiler shell. It forms the rear wall of the furnace and acts
.as a support for the rear ends of the grate bars. It is usually
built of common brick, but is faced with fire-brick on the side
toward the furnace. At the side facing the rear of the boiler
the wall should be vertical. The top of the bridge wall should
_____ h
FIG. 6
be horizontal; that is, it should not be curved to conform to
the shape of the boiler shell. The bridge wall deflects the
hot gases upwards and brings them in close contact with the
boiler shell; also, because of its becoming highly heated, it
aids in the combustion of the fuel, especially when bituminous
coal is used.
13. Rear Arch. At the back end of the setting of a return-
tubular boiler, above the upper row of tubes, an arch must be
10
BOILER FURNACES, SETTINGS,
built to deflect the hot gases from the combustion space into
the tubes. It must extend from one side wall to the other
and must be so constructed that it will not break under repeated
expansion and contraction. It may be either curved or flat.
An example of flat arch is shown In Fig. 7, Angle-iron
supports a extend from one side'wall to the other and from them
are hung a number of circular iron plates b by bolts c. The slab b
that forms the arch is composed of refractory material that is
prepared in plastic form and pressed into place over and around
the plates b and bolts c, between the side walls and between
the boiler and the rear wall e, after which it is allowed to dry
and harden. By this construction, none of the metal in the
supporting frame is exposed to the direct action of hot gases.
The arch must be above the tubes, so that they are accessible
at the rear for repairs; also, the joints between it and the
walls must be tight, to prevent leakage of air into the setting,
with consequent lowering of temperature of the hot gases.
Asbestos rope may be used to plug up all crevices.
14. Ash-Pits. The space below the grates of an exter-
nally fired boiler forms the ash-pit, which may be walled with
brick or concrete. The size and shape of the ash-pit depend on
the size of the boiler, the type of furnace and grates, and the
AND CHIMNEYS, PART 1
11
quality of the coal burned. The capacity should be such as to
take care of the ashes for a working period of from 16 to 20
hours for hand-fired boilers, and from 12 to 16 hours for
stoker-fir edj boilers,
so that too frequent
cleaning of the ash-
pit may be avoided.
As a cubic foot of
ashes weighs approxi-
mately 40 pounds,
the size of ash-pit
may be determined
by using the follow-
ing rule:
Rule. To find the
volume of ashes per
hour, in cubic feet,
multiply together the
grate area, in square
feet, the number of
pounds of coal burned
per hour per square
foot of grate area, and
the percentage of ash
in the coal, expressed as a decimal, and divide the product by 40-
Expressed as a formula, this rule becomes
AWC
40
V=~
in which V = volume of ashes per hour, in cubic feet;
A = grate area, in square feet;
W = pounds of coal burned per hour per square foot
of grate area;
C percentage of ash in coal, expressed as a decimal.
EXAMPLE A boiler having agrate area of 50 square feet burns24 pounds
of coal per hour per square foot of grate. If the coal contains 22J per cent.
of ash, what ash-pit volume is required for a working period of 18 hours?
I L T 45920
12
AND CHIMNEYS, PART 1 13
SOLUTION. Use the formula, and make A = 50 sq. ft., W= 24 lb., and
=.225; then,
T7 50 X 24 X. 225
i
For 18 hr. of working, the volume required will be 18X6.75 = 121| cu. ft.
Ans.
15. The method of removing the ashes, whether by hand
or by mechanical means, must also be considered in the design
of the ash-pit. The pit should be so arranged that it will be
accessible for cleaning and so that ample room will be given
for the use of the cleaning hoe and the shovel. Examples of
ash-pit arrangement are shown in Fig. 8. That shown in (a)
is a simple form for a hand-fired furnace. If greater volume
is required, it may be obtained by constructing the pit as in
(6). The ashes from furnaces fitted with mechanical stokers
may be removed by hand, but it is common to remove them
by some sort of conveyer. The ash-pit construction shown in
Fig. 9 is of the latter class. The ashes produced by combustion
are pushed off at the rear end of the stoker a and fall on a gate b
that, when opened, allows them to fall into the ash hopper c.
A gate d controlled by the hand wheel e may be opened to
discharge the ashes into the buckets of a conveyer/, by which
they are removed. The passage g is a duct that supplies air
beneath the stoker.
SPECIAL TYPES OF FURNACES
16. Dutch Oven. The Dutch-oven type of furnace, as
illustrated in Fig. 10, consists of a brick chamber that encloses
the furnace on the sides, top, and front. It is not located
beneath the boiler, but is set at the front of the boiler, as shown,
thus removing the burning fuel to a great distance from the
heating surfaces. It is especially valuable for burning light
fuels, such as sawdust, shavings, and other wood refuse, these
usually being fed into hoppers fitted to openings directly above
the grates, in the top of the oven; however, the fuel may be fed
through the fire-door in the front. This type of furnace
provides a large grate area, a combustion chamber of large
volume, and, because of its position relative to the boiler,
14
BOILER FURNACES, SETTINGS,
a longer travel of the hot gases than is the case in the ordinary
boiler setting. The firebrick walls surrounding the furnace
maintain a more nearly uniform temperature and promote
combustion of the gases.
FIG. 10
17. Hawley Down-Draft Furnace. The Hawley down-
draft furnace, an example of which is illustrated in Fig, 11,
is so called because the draft through one of the two sets of
grates used is downwards instead of upwards. The upper
FIG. 11
grate a is a water grate; that is, it consists of pipes expanded
into headers at their ends, the headers being connected to the
water space of the boiler to insure continuous circulation of
water. Fresh fuel is thrown on the grate a through the fire-
AND CHIMNEYS, PART 1 15
door b and air for its combustion is admitted above the grate.
After the volatile matter has been burned away, the partly
burned fuel falls to the lower grates c, where combustion is
completed, the air supply being admitted through the door d
below this grate in the usual way. The distance between the
grates a and c ranges from about 12 inches at the front to 18
inches at the rear. Baffles e are arranged to give the hot gases
a long travel over the heating surfaces of the boiler.
18. A view of the water grate used in the Hawley down-
draft furnace is shown in Fig. 12. The pipes a are rather widely
FIG. 12
spaced and the ends of the drums, or headers, b and c are'
provided with handholes so that cleaning may readily be done.
The relative positions of the upper and lower grates, Fig. 11,
are such that the volatile matter driven off from the first fuel
on the upper grate is forced to pass down into the furnace
space above the lower grate. The consequence is that there is
greater likelihood that the combustible gases will -be thoroughly
consumed than if the fuel were fired directly on the lower
grate.
The Hawley furnace is a successful smoke-prevention device
and the makers claim that it will burn low-grade fuels with a
high efficiency. It is not automatic in its action and is there-
fore not so well adapted to the saving of labor in the fireroom nor
foi use with coal-handling machinery as most automatic
stokers; this, however, is not a serious objection in small plants.
16
AND CHIMNEYS, PART 1
17
1 9. Burke Furnace. The details of the Burke furnace and
setting for a corrugated-flue boiler are illustrated in Fig. 13.
The furnace, like the Dutch oven, extends outside the boiler
setting and uses a set of shaking grates a in connection with
fixed or stationary grates b. The stationary grates, which are
at the sides of the furnace, slope toward the rocking grates, and
have such a pitch that the coal will slide down by gravity at
such a rate that it will be coked by the time it reaches the
shaking grates. The coal is fired through the hoppers c at the
sides, and the firing is controlled by hand, which makes this form
of furnace practically a hand-fired stoker. The hot gases
from the furnace pass through the corrugated furnace fiue d
back against the firebrick wall e and the combustion chamber
arch /, through the tubes g and thence to the breeching k.
20. Dorrance Furnace. The Dorrance furnace, shown in
Fig. 14, is another modification of the Dutch oven. The
sloping firebrick arch a is inclined toward the rear of the
furnace and extends into the combustion chamber &, the grates c
18
BOILER FURNACES, SETTINGS,
being parallel with the arch a. Back of the arch a is built a
brick pier d against which the gases strike and are deflected
back upon themselves, thus insuring a more thorough mixing
of the gases and air. The water-tubes e are baffled at / to
give the gases a longer travel. By this form of furnace con-
struction a high furnace temperature is obtained, owing to the
intimate mixing of the gases and air and their combustion
before they strike the cooler boiler surfaces.
21. Wooley Furnace. The Wooley furnace and setting
for a water-tube boiler are illustrated in Fig. 15. The furnace a
is practically a Dutch oven and is so constructed as to
FIG. 15
provide a very large grate area and combustion chamber
A brick wall b is built up solid except at the bottom, where
arched openings c are provided. A view of the wall is shown
m Fig. 16, as it appears from the front of the furnace Fire-
bricks are used for facing the wall 6, and as these bricks with-
stand and maintain high temperatures, the wall promotes
combustion. By placing the gas openings c at the bottom of
AND CHIMNEYS, PART 1
19
the wall, the gases must travel downwards into a second
combustion chamber d, Fig. 15, before striking the tubes e.
Considerable heat is absorbed by the brick walls and floor; but
after they are thoroughly heated they assist in maintaining
efficient combustion. Baffles / are used to increase the gas
travel around the tubes.
STATIONARY GRATES
22. Grate
istics. Grates are gener- FIG< 16
ally made of cast iron,
which is the material best suited to withstand heat and
form a support for the fuel to be burned. Air spaces must
be provided between the bar sections or in the bars for the
admission of air under the bed of fuel Authorities differ as
to the proper "width of air space; in general, it should be made
as great as possible and still prevent the fuel from dropping
through. For the larger sizes of anthracite, such as egg and
nut, and for bituminous and coking fuels, the air space may be
made from f to f inch in width; for pea coal, from f to J inch;
for fine coal, such as buckwheat, rice, culm, and slack, an air
space from & to f inch in width may be used. The air
spaces are distributed uniformly over the grate surface so
as to avoid blowing holes in the fuel bed. The area of the
solid portion of the grate is usually made somewhat greater
than the combined area of the air spaces. Grates are
divided into two
classes: fixed or sta-
tionary grates and
shaking grates.
FIG. 17
23. Common Form of Fixed Grate. The most common
type of fixed grate is made of straight single bars a, Fig. 17,
placed side by side in the furnace. The thickness of the bar
20
BOILER FURNACES, SETTINGS,
FIG. 18
section depends on the width of the grate, on the air space, and
on the number of bar sections in each grate bar. It is the
general practice to make the thickness across the lugs b twice
the thickness of the bar a. The depth of the bar is made about
2 inches at the ends and ranges from 3 to 5 inches at the center.
For long furnaces the
bars are made in sections
3 feet in length, and a
bearer bar is placed in
the center of the furnace
to support the grate
bars. Long grates are
set with a downward
slope toward the bridge
wall of about f inch per foot of length. This position facili-
tates the admission of air at the rear of the grate, and also the
cleaning of the grate.
Grate bars are also made in sections having two or more
bars united in a single casting, as shown in Fig. 18. Bars of
this kind range in width from 3 to 6 inches and are stronger
than the single-bar units. They have the disadvantage,
however, that in case of breakage or warping, it costs more to
replace them than to replace single bars. Another disadvan-
tage is that the bars
must be so thin, in
proportion to their
length, that they will
warp out of shape,
and consequently
break, especially
under forced firing.
FIG. 19
24. The herring-
bone grate bar, shown
in Fig. 19 (a) and (6),
can expand and contract freely, owing to the angular shape
of the cross-bars a, and for this reason it is superseding the
ordinary straight type. Herring-bone bars are made in various
AND CHIMNEYS, PART 1
21
forms and widths of air spaces. The grate bar is made with
straight ends, as in (a), when used for grates in which two
lengths are required. The bar shown in (6) has one straight
end b and the other end c beveled. The end c is set against
the bridge wall and the bevel prevents ashes from crowding
between the grate and the wall; thus the grate bar is free to
expand without danger of damaging the grate or the setting.
25. Sawdust Grate. A form of cast-iron grate bar
especially adapted to burning sawdust is shown in Fig. 20.
. FIG, 20
The bar is semicircular in cross-section and is provided with
circular openings for the introduction of air. As in other types,
lugs are cast on each side of the bar to serve as distance pieces
and maintain air spaces between the bars.
26. Special Forms of Grate Bars. Wrought-iron grate
bars are rolled from a single bar ; they have a head and a web and
are uniform in depth. They are made up in sets and riveted
together, with distance pieces between the bars to form the
required air space. Hollow grate bars through which water
circulates are sometimes
used,
27. Adapting Grate to
Fuel, In general? a grate
bar should be especially
suited for the kind of
fuel to be burned. Thus,
if very fine coal is to be burned, a grate bar like that shown
in Fig. 21, having small air spaces, should be used, since
otherwise a large percentage of the fuel will fall into the ash-
pit. On the other hand, for the large sizes of coal it is advisable
to provide bars having large air spaces, using the largest air
FIG. 21
22
BOILER FURNACES, SETTINGS,
space when caking coals are to be burned. Some varieties of
bituminous coal will cake, that is, fuse together to a consider-
able degree, and the ashes and clinkers formed are of such size
that a large part of them cannot pass through the air spaces
unless these are large; the grate thus becomes clogged, shutting
off the air from the fire, which reduces the rate of combustion
and evaporation.
FIG. 22
28. Installing Stationary Grate Bars. Grate bars must
be installed in such a manner that they can expand freely and
without damage to the boiler setting. The front ends of the
grate bars are supported on the dead plate, and the rear ends
are usually supported by the bridge wall. The space between
the ends of the grate bars and their support will fill up with
cinders and ashes, which will become hard and prevent the bars
from expanding freely if this refuse is not removed frequently.
To overcome this trouble, the grate bars may be supported by
bearer bars, one form of which is shown in Fig. 22. The ends a
of the bearer bars are set into the side walls of the furnace and
the ends of the grate bars rest on the bearer bars; but a better
construction is to set a cast-iron box a, Fig. 23, directly in the
brick side walls and then place the bearer bars b so that the
FIG. 23
ends rest on the bottom of the box a. This allows the grate
bars and the bearer bars free expansion and contraction; also,
the grate bars and bearer bars can be easily replaced when
burnt out or broken.
AND CHIMNEYS, PART 1
23
29. Disadvantages of Stationary Grates. The greatest
objection to stationary grates is that with them the furnace
door must be kept open for a considerable length of time when
the fire is being cleaned, and ashes and clinker must be removed
through the fire-door, causing dust and dirt. Ashes and cinders
will collect on the grate, shut off the air supply to the fuel bed,
and thus affect the combustion and generation of steam; the
fire therefore needs frequent cleaning, which taxes the fireman
severely, owing to the intense heat to which he is exposed.
Also, there is an inrush of cold air into the furnace, which
reduces the furnace temperature and chills the boiler plates,
FIG. 24
thus producing stresses that cause the boiler plates and brick
walls to contract and possibly crack. To overcome these
conditions, grates have been designed that allow the fire to be
cleaned without opening the fire-door for such long periods.
30. Grates for Vertical Boilers. Stationary grates for
vertical boilers are also made in sections, so as to take care of
the expansion and contraction stresses, thus reducing warping
and breakage of grate bars. In Fig. 24 (a) is shown a typxcal
two-section grate, Grates of this type are made circular and
are divided into two, three, or four sections, depending on the
diameter required. For the larger sizes of vertical boilers, the
grate is made as shown in (6), its center a being a round section
24 BOILER FURNACES, SETTINGS,
and the segments b of the herring-bone pattern. The segments
radiate from the round center a, and are supported by a ring
that rests on lugs attached to the boiler shell.
SHAKING GRATES
31. Advantages of Shaking Grates. With stationary
grates, the fires are cleaned by tools inserted through the fire-
door; consequently, during the cleaning period a large amount
of cool air is admitted to the furnace, lowering its temperature
and that of the gases, and causing contraction of the plates
and setting. Shaking grates eliminate these troubles, because
they are so constructed that the fires may be cleaned by moving
levers outside the boiler setting. The grate bars of a shaking
grate are hung on trunnions at the ends and rocked on the
trunnions. The result is that the fuel bed is broken up, and
the ashes beneath the live coal are shaken through into the
ash-pit. Either anthractite or bituminous coal may be burned
on shaking grates, and the cheaper grades may be used to
better advantage on shaking grates than on fixed grates.
The principle of construction of shaking grates of different
makes is the same, but the details may differ.
32. Description of Grates. One form of shaking grate is
shown in Fig. 25. It consists of a number of transverse parallel
bars having trunnions at the ends, by which they are supported
and on which they may be swung. The lower arms of the
grate bars are connected by the bars a and 6. Ordinarily they
stand as shown in the right-hand half of the illustration. When
it is desired merely to shake the fire and thus remove the bottom
layer of ashes, the points c are moved from the level shown to
the lowest position the connections will permit. The points
follow the back of the bar immediately in front of them; thus
no unusual opening is made through which fine fuel may fall
into the ash-pit. The end bar d is curved to fit the frame.
When the ashes have accumulated to a considerable thickness,
or when they have fused together in a mass of clinkers, the
points c are thrown upwards, as shown in the left-hand half of
25
26
BOILER FURNACES, SETTINGS,
the illustration, thus forming a series of deep pockets that are
closed at the bottom by the main rib, or back plate, of the
grate bars. The act of throwing the points upwards breaks
up the fused masses, which drop into the pockets and are dis-
charged when the bars are returned to their normal position.
33. The grate bars in Pig. 25 are operated by means of a
handle fitting the levers shown at e. By means of these levers,
either half of the grate can be shaken independently, making it
possible to clean one half of the fire at a time, without opening
FIG. 26
the fire-door. The two levers can, however, be locked together
and all the grate bars worked back and forth simultaneously.
In Pig. 26 is shown another type in which the grate is divided
into right and left halves, or sections. Either side can be
shaken or dumped independently of the other. The trunnion
bar or bearer bar a that supports the ends of the grates is shown
merely by dotted lines so as to disclose the arrangement of the
grate bars and how they are linked together. The plate b
is the dead plate and it rests on the rib c of the boiler front d
and supports the bearer bar a. A dump plate e is placed at
the rear for removing clinkers that cannot be broken by shaking
the grate bars. The dump plate is operated by a link / that
can be rocked back and forth by the shaker lever at g.
AND CHIMNEYS, PART 1 27
SETTINGS FOR STEAM BOILERS
GENERAL FEATURES
34. Foundations and Walls. A firm foundation is neces-
sary for a boiler setting, because of the weight of the walls and
the boiler structure. The nature of the soil that, supports the
foundation is therefore an important factor to be considered,
as a yielding base will lead to settling and subsequent cracking
of the walls. If soft ground is encountered, piles may be
driven and these then covered with a reinf orced-concrete footing
about 2 feet thick, over the area on which the setting is to be
built!
The side and end walls of the setting should be not less than
12 inches thick and should be lined with refractory firebrick
or cement in those parts exposed to the flames and hot gases
from the furnace. These walls have been built of concrete,
but as a rule they are made of well-burned red brick laid with
a high-grade heat-resisting cement. The ash-pit, bridges,
arches, and combustion-chamber floor are also made of red
brick, those parts subjected to heat being lined with a refrac-
tory cement or firebrick, the latter laid in cement of the same
quality as the brick. The joints in firebrick structures should
be thin.
35. Firebrick. Standard firebrick are 9 inches in length
and are made in various shapes, as shown in Fig. 27. To test
the quality of a firebrick, it should be broken into two parts;
in a low-grade brick the fracture will be fine and uniform,
but in brick of better quality the facture appears flinty
and clean. The temperatures at which firebrick will melt,
or fuse, depends on the quality of the material and ranges
from 2,500 to 3,700 P.; however, the fusing temperature is
not a guide to the fitness of the brick to resist crushing,
I L T 45921
28
BOILER FURNACES, SETTINGS,
erosion, and wear points that must be considered in the case
of brick for furnaces. A cubic foot of firebrick wall requires
seventeen 9-inch straight bricks. If arch bricks, wedge bricks,
No. I Arch
FIG. 27
or other special shapes are used, the quantity required may be
taken as 10 per cent, more than for straight bricks. In laying
common red brick, it is well 'to allow 9 cubic feet of sand and
'3 bushels of lime for laying 1,000 bricks.
AND CHIMNEYS, PART 1
SETTINGS OF RETURN-TUBULAR BOILERS
DETAILS OF BRICKWORK
36. Forms of Wall Construction. Four standard forms of
wall construction for the settings of return-tubular boilers,
recommended by the Hartford Steam Boiler Insurance Com-
pany, are shown in Fig. 28. Each view represents a section
of one side wall taken along a vertical plane crosswise of the
boiler setting, and the dimensions are clearly indicated. The
construction shown in (a) consists of an outer wall 8 inches
(c)
(*>
FIG. 28
thick and an inner wall 16 inches thick separated by a 2-inch
air space a throughout the greater part of their height. The
inner and outer walls are joined at top and bottom, and that
part of the inner face exposed to hot gases is lined with
firebrick 6. The air space hinders the conduction of heat
outwards through the walls and thereby assists in preventing
cracks in the outer wall, through which air would leak into the
furnace and combustion chamber. While the walls are being
built, vent pipes c are set in the brickwork so as to lead
from the air space to the outside. These are plugged after
the setting has dried thoroughly.
30
BOILER FURNACES, SETTINGS,
37. The type of wall shown in Fig. 28 (/>) is solid through-
out and is practically as expensive to build as the one just
FIG. 2P
described. As the heat of the furnace affects the entire wall,
cracks are more likely to develop in the solid wall than in
the wall with an air space. The construction shown in (c)
AND CHIMNEYS, PART 1
31
consists of an outer wall of common red brick and an inner
wall of firebrick separated by a single thickness of insulating
brick a. The insulating bricks are of a special heat-resisting
type and are used to reduce the conduction of heat outwards
through the setting. They are of standard size but are not
so strong as ordinary brick; therefore, metal ties of the form
shown at b are used to bind the inner and outer walls together.
In the case of boilers set in a battery, the division wall between
adjacent boilers may be made as in (c), using firebrick for both
faces, however, and separating them by insulating brick.
38. The boiler wall shown in Fig. 28 (d) is like that in (6)
except that its thickness is considerably less. Also, the entire
outside of the setting is surrounded by a casing a made of steel
plate, and the 2-inch space between the brickwork and the
casing. is filled with some good form of insulating material,
FIG. 30
such as magnesia or asbestos. A setting of this kind is expensive
to build, but it can be made practically air-tight, thereby insur-
ing favorable conditions for economical operation.
32 BOILER FURNACES, SETTINGS,
In all four of the forms shown, it will be observed that the
top of the wall is not built directly against the boiler shell;
instead, a clearance of about 1 inch is left, and this space
is filled with asbestos rope. If the brickwork were built
against the boiler, the expansion and contraction of the shell
would eventually cause cracks to develop in the setting. The
asbestos rope forms a compressible joint and at the same time
prevents inward leakage of air.
39. General Arrangement of Boiler. The general arrange-
ment of a return-tubular boiler and its setting is shown in
Fig. 29 ; (a) is a plan view from above, the walls being shown in
section at the level of the center line of the boiler; (6) is a partial
longitudinal section taken in a vertical plane through the center
line; and Fig. 30 is a combined end view and transverse section.
The boiler is supended from the transverse girders a, which are
supported by the cast-iron columns b outside the walls. The
rear end of the boiler is If inches lower than the front end, so
that sediment will naturally collect at the rear, where it may
be removed through the blow-off pipe c. This pipe is protected
from the direct action of the hot gases by a V-shaped brick
pier d built in front of it. The horizontal part of the pipe,
leading out through the rear wall, is contained in a trench in
the floor and is covered with a steel plate or loose bricks. The
part of the boiler shell not enclosed by brickwork is covered
with a layer of non-conducting material e from 2 to 8 inches
thick, over the surface of which is spread a thin coat of Port-
land cement. A clearance of 1 inch is left between the ends of
the bridge wall and the side walls, to allow for expansion, as
shown at /, and the space is filled with asbestos rope.
SUPPORTS FOR RETURN-TUBULAR BOILERS
40. Columns. Either cast-iron or steel columns may be
used to support the cross-beams from which the boiler is sus-
pended. Four columns are required, and they are set outside
the brickwork and rest on suitable footings. Three boilers
78 inches in diameter may be supported by one set of four
AND CHIMNEYS, PART 1
33
columns. If the columns are of cast iron, they may be of
hollow round or square cross-section; if of steel, an H section
should be used. The ordinary I beam is not suitable, as it is
too weak under compressive loads. In Tables II, III, and
IV, prepared by the Hartford Steam Boiler Insurance Company,
are given the dimensions of cast-iron and steel columns to be
used in supporting one, two, or three boilers of a given size, on
the assumption that four columns are used. The lengths given
for the columns are maximum allowable values and should not
be exceeded.
TABLE II
PROPORTIONS OF ROUND CAST-IRON COLUMNS
1 Boiler | 2 Boilers
3 Boilers
Diameter
of Boiler
Length
of Tubes
Length
of Column
Dimensions of Column, in Inches
Inches
Feet
Ft. In.
Di-
Thick-
Di-
Thick-
Di-
Thick-
ameter
ness
ameter
ness
ameter
ness
54
16
10 6
7
i
7
i
7
1
60
16
11
7
i
7
l
7
1
60
18
11
7
3.
4
7
7
7
1
66
16
12
8
i
8
1
8
ii
66
18
12
8
1
8
1
8
H
72
16
13
9
1
9
1
9
ii
72
18
13
9
J
9
1
9
U
72
20
13
9
I
9
1
9
it
. 78
16
13 6
9
I
9
1
9
it
78
18
13 6
9
1
9
1
9
it
78
20
13 6
9
7
J
9
1
9
it
84
18
14
9
1*
9
It
9
it
84
20
14
10
1
10
1
10
it
41. Cross-Beams. The transverse beams from which the
boiler is suspended, in the case of a setting like that shown in
Figs. 29 and 30, may be arranged as shown in the sectional
view, Fig. 31. Each transverse support consists of two
I beams a placed side by side and held together by bolts b that
pass through distance pieces c. These distance pieces fit the
outline of the beams, and the I beams are thus held at a fixed
distance from each other. Short sections of pipe slipped over
the bolts will serve the same purpose. Across the tops of the
34
BOILER FURNACES, SETTINGS,
TABLE IH
PROPORTIONS OF SQUARE CAST-IRON COLUMNS
1 Boiler
2 Boilers
3 Boilers
Diameter
of Boiler
Length
of Tubes
Length,
of Column
Dimensi
ons of C
Vtlmnn, in Inches
-
Inches
Feet
Ft. In.
Width
Thick-
ness
Width
Thick-
nesH
Width
Thick-
ness
54
16
10 6
6
3
tf
()
7
H'
i)
1
60
16
11
6
5 .
6
7
()
1
60
18
11
6
4
6
i
I
66
16
12
7
2
'7
i
7
1
66
18
12
7
4
7
7
$
7
1
72
16
13
8
4
8
7
8
1
72
18
13
8
4
8
i
8
1
72
20
13
8
4
8
1
8
1
78
16
13 6
8
4
8
1
8
1
78
18
13 6
8
4
8
1
<H
1
78
20
13 6
8
4
H
7
K
8
1
84
18
14
8
l
8
1
8
U
84
20
14
8
i
8
I
8
U
TABLE IV
PROPORTIONS OF H-BEAM COLUMNS
1 Boiler
2 Boilers
3 Boilers
jo &
l*
a'S f
Length
Proportions of Column
9pq y
3*3 w
1V|$
^"3
Ft. In.
Depth
Inches
Weight
Per Foot
Pounds
J)rpth
I'tidics
Wc'iKhl
Per Pout;
Puuiulu
Depth
Ini'lur.
Wei Kht
Per Foot
Pounds
54
16
10 6
5
18.7
5
18.7
6
23.8
60
16
11
5
18.7
6
23.8
8
34.0
60
18
11
5
18.7
6
23.8
8
34.0
66
16
12
5
18.7
8
34,0
8 .
34,0
66
18
12
5
18.7
8
34,0
72
16
13
6
23.8
8
34.0
72
18
13
6
23.8
8
34.0
72
20
13
6
23.8
8
34.0
78
16
13 6
6
23.8
8
34.0
78
18
13 6
6
23.8
8
34.0
78
20
13 6
8
34.0
84
18
14
8
34.0
84
20
14
8
34.0
AND CHIMNEYS, PART 1
35
beams is laid a bearer plate
d through which pass the
ends of the eyebolt hang-
ers e. The loop at the
lower end of the hanger fits
over a pin in the bracket on
the side of the boiler. The
upper ends of the hangers
are threaded and fitted with
nuts/ that rest on the bearer
plate. The upper nuts are
locknuts. In Table V are
given the proportions of I
beams to be used for sup-
porting one, two, or three
boilers. It is understood
that four beams are used,
set in pairs two at the
front end of the boiler and two at the rear. The ends of
pair rest on the tops of the supporting columns.
TABLE V
PROPORTIONS OF CROSS-BEAM SUPPORTS
each
1 Boiler
2 Boilers
3 Boilers
Diameter
of Boiler
Length
of Tubes
Proportions of I Beam
Inches
Feet
Depth
Inches
Weight
Per Foot
Pounds
Depth
Inches
Weight
Per Foot
Pounds
Depth
Inches
Weight
. Per Foot
Pounds
54
.16
6
121
10
30
15
42
60
16
7
15
12
31J
18
55
60
18
7
15
12
35
18
55
66
16
7
15
12
40
18
55
66
18
8
18
15
42
18
60
72
16
8
18
15
42
20
65
72
18
8
18
15
42
20
65
72
20
8
18
18
55
24
80
78
16
8
18
18
55
24
80
78
18
9
21
18
55
24
80
78
20
9
21
18
55
24
80
84
18
9
21
18
55
24
80
84
20
9
21
20
65
24
90
36
BOILER FURNACES, SETTINGS,
SETTINGS OF WATER-TUBE BOILERS
42. Methods of Supporting Boilers. The construction of
the side walls of the settings of water-tube boilers is similar to
that of the walls for return-tubular boilers; but the methods
of supporting water-tube boilers depends altogether on the
type of boiler, size of installation, and local conditions. For
example, the Babcock & Wilcox boiler is suspended from
cross-beams that rest on columns, the suspending rods forming
loops beneath the steam drum at the front and the rear. The
Heine boiler is supported by the front and rear walls of the
setting, the water legs at the front and the rear resting directly
on plates set into the brickwork. The Edge Moor boiler may be
suspended from overhead cross-beams or it may be supported
by short columns riveted to the water legs at the front and the
rear. Similar methods are used with the various other types
of water-tube boilers.
43. Baffles. To direct the flow of hot gases around and
over the tubes of water-tube boilers, it is the practice to build
baffles between or across the tubes. The gases are thus
compelled to make a
longer circuit inside
the setting and give
up a greater percent-
age of their heat.
Baffles are commonly
built of tiles made in
suitable form and size
to fit the particular
type of boiler in which
they are to be used.
Three forms of tiles are illustrated in Fig. 32 (a), (&), and (c),
these being known as B, L, and T tiles, respectively. They
are intended to be used, primarily, in boilers that have hori-
zontal tubes, or tubes nearly horizontal. Another way of
building baffles is to make them of a plastic refractory material
that is put in place while wet. After it has dried and has
become hardened by the heat, it forms a one-piece baffle.
FIG. 32
AND CHIMNEYS, PART 1 37
44. Baffles are arranged in different positions, varying from
horizontal to vertical. The position and condition of the
baffles have much to do with the successful operation of the
boiler. The design of a boiler may be good and the gas area
through the setting may be correct; but if the baffles are
improperly installed, the operation of the boiler will be
faulty. The boiler setting should be such that the gases cir-
culate freely around the tubes, without having any corners
or pockets in which the gases collect and fail to circulate.
Such pockets of dead gas lead to poor circulation of the gases
and redttce the effective heating surface of the boiler.
MECHANICAL STOKERS
DEVELOPMENT AND CLASSIFICATION
45. Development of Mechanical Stoker. The earliest
mechanical stoker is thought to have been invented by Watt,
who obtained a patent in 1785 on a simple device for pushing the
coal, after it had been coked, from the front of the grate back
toward the bridge. Since that time English engineers have
invented a large number of stokers, some of which have been
extensively used and have given satisfactory results when
applied under proper conditions. None of the English designs
have been much used in the United States, but a number of
American designs of mechanical stokers and automatic furnaces,
differing more or less from the earlier English types, have
been developed since 1873, and several have been put into
extensive use.
46. Advantages and Disadvantages of Stokers. Numer-
ous tests have shown that a careful and intelligent fireman
with a properly designed furnace can obtain as good results,
so far as economy in the use of fuel is concerned, as have ever
been obtained with any mechanical stoking device; it is also
certain that hand firing may be so regulated as to produce
practically smokeless combustion. It is well known, however,
that these possible results are not generally attained in every-
38 BOILER FURNACES, SETTINGS,
day work; nor can they be obtained for long periods by hand
firing when the boilers are operated at two or three times their
normal capacity. ' Boiler firing is hard and, in many cases, far
from pleasant work. Most boiler rooms are hot and many are
poorly lighted and ventilated conditions that make it difficult
for any but the best of men to keep up their interest in their
work.
47* With the best automatic stokers the fireman is
relieved from much of the most severe and difficult part of
his work; he is thus more free to devote suitable care and
attention to the operation of the furnace. The coal is fed
to the furnace at a uniform rate and in such a manner that
the gases distilled from it are thoroughly mixed with a proper
supply of air; the gases are then conducted through a part of the
furnace in which there is a high enough temperature to insure
their complete combustion. When the coal supply and air
supply are properly adjusted to suit the working conditions,
the continuous and uniform manner in which the fuel is fed to
the furnace insures a high &nd practically uniform temperature,
which is favorable for the complete combustion of the gases
and relieves the boiler from the stresses produced by the sudden
changes in temperature that occur when cold air enters the
fire-door during hand firing.
48. Economic Considerations. Automatic furnaces are
more expensive, in both first cost and maintenance, than fur-
naces for hand firing, and in small plants they save little or
nothing in the cost of labor; in these cases the question, of
economy in their use depends on the possibility of a saving in
coal and of wear and tear on the boiler. In the matter of coal
they have the advantage of successfully burning cheap grades
of fuel that could not be used with ordinary methods of hand
firing. Automatic furnaces will give better results in the mat-
ter of smoke prevention than can be obtained by hand firing,
unless an unusual degree of care and attention is given to the
management of the fires. In large plants, especially where some
of the modern systems of coal- and ash-handling machinery
are used, automatic furnaces effect a very considerable
AND CHIMNEYS, PART 1 39
saving in labor; this, in addition to their other points of
superiority, makes them more economical than hand firing.
49. Classification of Stokers.~~The principal designs of
mechanical stokers and automatic furnaces may be divided into
three general classes; namely, the overfeed stoker, the under-
feed stoker, and the traveling-grate, or chain-grate, stoker. In
the first the coal is slowly fed by some suitable mechanical
device on a coking plate, where the volatile matter is distilled
off by the heat of the furnace and mixed with a suitable supply
of air. The coke so formed is then fed forwards on to grates,
where it is burned. The mixture of gas and air is burned in
a suitable combustion chamber, usually in as close proximity
as is practicable to the bed of burning coke.
In the second class the coal is forced by some mechanical
device into a chamber under the mass of burning fuel in the
furnace. The volatile matter is here distilled off and mixed with
"a supply of air. The coke formed is pushed upwards by the
fresh coal that is fed into the chamber and burns above the
coking chamber and on suitable grates at the sides, on which it
falls. The mixture of gas and air rises through the bed of burn-
ing coke above the coking chamber and, being highly heated and
thoroughly mixed, burns readily.
The chain-grate, or traveling-grate, stoker consists of an
endless belt composed of grate bars that travel over front and
rear sprockets. Coal is fed from hoppers by gravity and is
ignited under a combustion arch called an ignition arch. As
combustion takes place the burning fuel travels toward the
rear end of the furnace with the grate, which is regulated to
the proper speed for burning the fuel. The ashes are dumped
at the rear end of the grate to an ash-pit or an ash conveyer.
50. Finding Size of Stoker. In order to determine the
size of stoker required for a given boiler, the steam-generating
capacity of the boiler and the kind and quality of fuel to be used
must be known. From these data it will be possible to estimate
the rate of combustion and hence the number of square feet of
grate area required. A stoker can then be selected to give this
required area. As boilers differ in design, there is no fixed
40 BOILER FURNACES., SETTINGS,
relation between the length and width of the furnace. Each
case must be considered as an individual problem. The cus-
tomary method is to supply the stoker manufacturer with all
the data as to type and size of boiler, kind of fuel, nature of
service, maximum rate of steam generation, and so on, and let
him provide a stoker to meet the conditions.
OVERFEED STOKERS
51. General Construction of Overfeed Stoker. The over-
feed stoker usually consists of an inclined grate made up of a
series of bars, part or all of which may be movable. The fuel
is fed on to the inclined grate at the upper end, after passing
over a dead plate on which it is partly coked, or deprived of
its volatile matter, The burning fuel then, moves down the
incline, burning as it descends, its movement being caused by
the inclined position of the grate as well as by a slight rocking
or tilting of some or all of the grate bars, By the time the fuel
has reached the bottom of the incline, it is completely bunted,
and the ashes are dumped into a pit. The hopper from
which fresh fuel is supplied to the stoker may be at the front
or at the side of the furnace, and so the stoker may be of the
front-feed type or of the side-feed type.
52. Roney Stoker. The Roney stoker, shown in Fig. 33,
is an overfeed stoker of the front-feed type. The coal is fed
into the hopper a, at the bottom of which is an inclined pusher
plate b to which a slow reciprocating movement is given by an
eccentric mounted on the shaft 5. At each inward movement
of the pusher plate a quantity of fresh coal is pushed down and
inwards upon the dead plate c, where it is subjected to the heat
of the furnace and has most of its volatile matter driven off.
The pressure of the fresh fuel fed from the hopper causes it to
fall upon the stepped grate bars d, which run crosswise of the
furnace and are supported by end trunnions. By the time the
coal has reached the lower end of the inclined grate, all com-
bustible matter has been burned and only ashes and clinkers
remain, these collecting on the dump plate e. The dump plate
42 BOILER FURNACES,, SETTINGS,
is hinged at its rear edge, next to the bridge wall, and may be
dropped by moving a hand lever that extends to the boiler front.
The ashes are thus dumped into the ash-pit. To prevent fuel
from sliding off the grate and going into the ash-pit when the
dump plate is lowered, a curved guard /, also hinged at
the bridge wall, is raised to the upper dotted position by
moving the handle shown, and is lowered after the dump plate
has been brought back into normal position.
5& As combustible gases are driven off during the coking
of the fuel on the dead plate c, Fig. 33, air for their combustion
may be admitted through hollow tile g. To maintain a high
temperature in the furnace and promote efficient combustion,
a firebrick arch, part of which is shown at h, may be built above
the grate. The lower end of each grate bar d fits into a rocker
bar i to which a reciprocating motion is given by the same
eccentric that drives the pusher plate. The bars d are thus
rocked on their end trunnions, and this rocking assists in
causing the fuel to move down the grate. This stoker is
designed especially for burning all grades of bituminous coal,
but it may be used successfully for burning fine anthracite.
It operates with natural draft and the rate of combustion of
coal varies from 35 pounds per square foot of grate area per
hour in the case of coking fuels to 50 pounds per hour in the
case of free-burning fuels.
54. Wilkinson. Stoker. The Wilkinson stoker is a front-
feed stoker designed more particularly for the burning of fine
anthracite. In Fig. 34 it is shown applied to a horizontal
return-tubular boiler, while in Fig. 35 is shown an enlarged
view of the grate itself. Like parts have been lettered the
same in both illustrations. The grate bars b are cast hollow,
with nearly horizontal openings leading from the interior
through the risers of the steps that form the upper surface;
these openings are shown in the black sectional portion of the
left end of the bar. To each grate bar is given a to-and-fro
motion in a horizontal direction by the rock shaft / and links g,
Fig. 34, the ends of the bars being supported by, and sliding on,
the hollow cast-iron bearing bars d. A pusher i, Fig, 35,
43
1 1 T 46922
44
BOILER FURNACES, SETTINGS,
fastened to the upper end of each grate bar, pushes the coal
from the hopper a through the opening in the furnace front
onto the bars.
55. The motion of the grate bars, Fig. 35, gradually forces
the coal downwards and deposits the ashes and clinkers on the
clinker grates e, from which they are finally pushed into the
ash-pit. Practically all the air for the combustion of the coal
is drawn into the upper ends of the hollow grate bars by the
steam jets c, and forced into the fire from the openings in the
FIG. 33
tops of the bars. In this case, the steam jets, in addition
to furnishing draft, serve an important purpose in keeping the
bars moderately cool, thus preventing both their destruction by
the heat and the sticking of the clinker, which with anthracite
often causes considerable trouble if no special provision is
made to.overcome it. The advantages derived from this use of
the steam jet are considered of sufficient" importance to more
than balance any possible loss of heat, and it is recommended
by the makers that the steam be used, even where sufficient
chimney draft is available to burn the fuel.
AND CHIMNEYS, PART 1
45
5 6. Murphy Automatic Furnace. The Murphy automatic
furnace is. an overfeed stoker of the side-feed type. The
general features of the furnace are shown in the cross-section,
Fig. 36. The coal hoppers a are located above and on each side
of the sloping grates. To facilitate proper operation, the fuel
should be in a finely divided condition, such as that of bitu-
minous slack. The coal is fed atomatically by gravity to the
1 ?:';' * ' . " "
'''^*&:
' :/i'!; : r->
ijv.s.;
FIG. 36
coking plate 6, which is located above an air duct c. The
circulation of air through the duct c prevents the coking plate
from burning away. Pusher blocks d move the coal onto the
coking plate, by the reciprocating motion produced by the
rack and sector gearing e. The speed of this feed mechanism
can be regulated according to the desired rate of combustion.
As the gases from the coking fuel are expelled,they immediately
mix with heated air admitted through openings in the arch
46
BOILER FURNACES, SETTINGS,
plate/ and burn. After the coked fuel has been pushed from the
plate 6, it travels slowly down the sloping grates fe, and during
this movement of the fuel bed,, air is supplied through the grates.
57. The grate bars are arranged alternately in pairs, each
pair consisting of a stationary bar and a movable bar. The
stationary bar, Fig. 37 (a),
is ribbed on both sides with
projections a that break up
the air supply into many
small jets and also prevent
the fine coal from dropping
through into the ash-pit
unburned. Near the bot-
tom of the bar the ribs a
are omitted, as at this point
the fuel has gone through
the coking stage, and a
more liberal amount of air
is needed. The stationary
bars, as shown in Fig. 36,
rest against the air box c at
the top, and at the lower
end are supported by the
bearer rod i. The movable
grate bar, Fig. 37 (6), is a
plain bar having a circular
FIG. 37 opening a that fits over
the pivot b of the stationary
bar in (a). Movement is given to the movable bars, as shown
in Fig. 36, by the rocker-shafts /, which have cams k that engage
with the lower ends of the movable bars. As the rocker-shafts
oscillate, the cams force the lower ends of the movable bars up
and down. This action breaks up the fuel bed sufficiently to
promote combustion and causes the fuel to move down on the
grate.
58. At the bottom of the grates, Fig. 36, is a clinker
breaker I that is oscillated by a link mechanism outside. The
AND CHIMNEYS, PART 1
47
projections on the clinker breaker force the ashes and clinker
against the bottom of the grate and break up the refuse so that
it will fall into the ash-pit m below.
The arch g is in two sections with an air space between them,
the lower arch being made of firebrick and the upper one of
FIG. 38
common brick. Both are carried by the arch plates/ in which
are air openings n leading into the air space of the arch.
As the air circulates through the air space it is heated and
passes through the openings in the arch plate to mix with the
gases from the fuel coking on the plate 6.
48 BOILER FURNACES, SETTINGS,
59. The movable parts of the stoker are driven by an
external mechanism arranged on the front of the furnace, as
shown in Fig. 38. A bar a extends across the front and is
supported by brackets. It is connected by a rod b to a pin on
the worm-gear c, which is rotated by gearing driven by a motor
or a small steam engine; thus, as the gear c rotates, there is
given to the bar a a reciprocating movement in its supporting
brackets. Links and levers d connect the bar a to shafts e,
which are the shafts of the sectors e shown in Fig. 36. The
reciprocating movement of the bar a, Fig. 38, thus causes the
shafts e to oscillate and moves the pusher blocks d, Fig. 36,
thereby feeding the coal to the grates. The bar a, Fig. 38,
is also connected by levers / to the shafts g, which correspond
to the shafts;, Fig. 36, that carry the cams which give movement
to the movable grate bars. Thus the reciprocating motion of
the bar a, Fig. 38, oscillates the shafts /, Fig. 36, and rocks the
alternate bars of the grates. A link h, Fig. 38, connects the
bar a to the clinker-breaker shaft i, shown at /, Fig. 36 ; thus,
the shaft I is oscillated, resulting in the breaking up of the
clinkers. The amount of swing, or oscillation, of the shaft I
is adjustable, so that the movement may be made to suit the
percentage of ash in the fuel. This type of furnace may be
set directly beneath the boiler, but it is usually placed outside
the main setting, like the Dutch oven.
tlTO>ERFEED STOKERS
60. Characteristics of Underfeed Stokers. Underfeed
stokers are arranged at the front end of the boiler, with
the grates in either a horizontal or an inclined position.
The coal is fed from hoppers and is forced into the furnace
by rotating screws or by the intermittent movement of
reciprocating plungers. The principle of operation of the
underfeed stoker is that fresh coal is fed from beneath the fuel
bed. The volatile gases are given off as the coal passes up
through the fire and are subsequently ignited in their passage.
Such a system, if properly managed, brings the fuel gases and
air into direct contact in the incandescent zone of the fuel bed
AND CHIMNEYS, PART 1
49
and thus insures excellent combustion. To burn the fuel
successfully by this method, both forced and induced draft
are needed. A blower system is used to force air under the
grate into the fuel bed and the chimney draft should be
sufficient to carry the product of combustion; if not, an
exhaust fan or a steam jet is used in the chimney to increase the
draft.
FIG. 39
61. Jones Underfeed Stoker. The Jones underfeed stoker
of the plunger type is shown in Fig. 39, (a) being a, longitudinal
section and (6) a cross-sectional view of the furnace and stoker.
The coal is fed into the hopper a and is carried forwards into
the retort, or fuel magazine, b by the action of the ram c
and the pusher blocks d. The ram c is connected to a piston e
50
BOILER FURNACES, SETTINGS,
that moves forwards and backwards in a cylinder under steam
pressure. The form of the retort b and the pusher blocks d
is shown in Fig. 40. Along the top of the retort are hollow
blocks/ that have openings called tuyeres, which permit the air
to flow into the coking fuel bed. The blocks/ are the only parts
of the retort that come in contact with the fire. The cross-
sectional view, Fig. 39 (6), shows the position of the blocks /
and the dead plates g in the furnace. The air introduced
under the dead plate and through the hollow blocks keeps
these parts from burning out for a long period. The forward
and backward movement of the ram c and the pusher blocks d
forces the fresh coal to move upwards in the retort and breaks
FIG. 40
up the fire/automatically slicing the fuel bed at the same time.
Air is introduced under the stoker through a duct h, which can
be opened or closed to the air blast by a blast gate controlled
from the front of the furnace. The illustration shows only one
unit under a boiler; but in large installations several units are
arranged side by side, as in Fig. 41, the reference letters of
which correspond with those of Fig. 39 in the case of cor-
responding parts.
62. Cleaning Jones Stoker. As the movement of the
ram continually forces the fuel back into the furnace, the ash
and clinker are eventually deposited on a balanced dump plate t ,
Fig. 41. By tilting the dump plate, the ash and clinker fall
to the ash-pit below, which in large installations is specially
constructed with an ash-removal system. In the example
AND CHIMNEYS, PART 1
51
shown, the ash-pit / is so shaped that the ashes can be readily
raked into small dump cars k in a tunnel under the boiler-
room floor.
63. American Stoker. The American stoker is of the
underfeed type using a screw for feeding the coal. In Fig. 42
G. 41
are shown sectional views of such a stoker applied to a return-
tubular boiler. Coal is fed into the hopper a, from which it is
drawn by the spiral conveyer b and forced into the magazine d,
in which it is coked. The incoming supply of fresh fuel forces
the coke upwards to the surface and over the sides of the
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AND CHIMNEYS, PART 1 53
magazine on to the grates i, where it is burned. A blower
forces air through a pipe / into the chamber g surrounding the
magazine. From this chamber the air passes upwards through
hollow cast-iron tuyere blocks and out through the tuyeres e.
The gas formed in the magazine, mixed with the jets of air
from the tuyeres, rises through the burning coke above, where
it is subjected to a sufficiently high temperature to insure its
combustion. Nearly all the air for burning the coke Is supplied
through the tuyeres, only a very small portion of the supply
coming through the grate. The ashes and clinkers are grad-
ually forced to the sides of the grate against the side walls of
the furnace, from which they are removed from time to time
through doors in the furnace front similar to the fire-doors of
an ordinary furnace.
64. The construction of the American stoker is such that
the fire must be cleaned and the ashes removed by hand. This
has the disadvantage of a somewhat greater expenditure of
labor than is required with those furnaces that discharge their
ashes into the ash-pit, especially where it is desired to use ash-
handling machinery ; it also subjects the boiler to the deleterious
influences of inrushes of cold air when the cleaning doors are
opened. In this connection it may be stated that it is claimed
by the makers that the fires do not need cleaning of tener than
once in 8 or 10 hours with the poorer grades of coal, and that
once in 12 hours is sufficient with the better grades; it is also a
fact that all furnaces require occasional hand stirring and.clean-
ing in order to secure a thoroughly satisfactory distribution of
the fire on the grates and to prevent the formation of masses of
clinkers that will occasionally stick to the grates, no matter how
carefully the stoker is designed and operated.
CHAIN-GRATE STOKERS
65. Principle of Construction. The chain grate, also
known as the traveling grate, consists of a series of grate bars
or grate-bar sections connected by hinged joints so as to form a
flexible belt. It passes over sprockets or drums set at the
54
BOILER FURNACES, SETTINGS,
front and the rear of the furnace and the top travels from
front to rear. The coal is fed on to the moving grate at the
front and burns as it is carried toward the rear of the furnace,
the ashes being dumped at the rear, where the grate turns down
around the rear drum. This type of grate is extensively used
in burning soft coal containing a large percentage of volatile
matter; but it is also adapted to burn coal of the poorest
grade, such as anthracite culm. Over the front of the grate
is built a firebrick arch, which, when the furnace is in operation,
reflects heat on the fresh fuel fed at the front and causes it to
FIG. 43
ignite. The arrangement thus becomes practically a modifica-
tion of the Dutch oven. The speed at which the grate travels
can be. altered to suit the rate of combustion demanded by the
load on the boiler.
66. Green Chain-Grate Stoker* The stoker shown in
Fig. 43 is designed for burning non-coking coal with natural
draft, and is known as type K. Another form, known as type
L, has an inclined apron below the fuel gate at the front, on
which the fuel is fed before it reaches the grate. This type is
intended for coking coal, and the volatile matter is driven off
AND CHIMNEYS., PART 1 55
while the fuel passes over the apron. The grate a consists of
an endless belt built up of sections jointed together, the whole
being supported by a heavy frame b that also carries the
sprocket wheels c around which the grate passes. The grate
receives its movement from the front sprocket wheel, which
is driven by the gear d. This gear in turn is actuated by a
pawl and ratchet connected to a shaft that is driven by an
engine. The* rate of travel of the grate can be varied. The
frame of the stoker is carried by wheels e that run on the track/,
and thus the whole stoker mechanism may be drawn out in
case repairs or replacements are necessary.
67. Over the front end of the grate, Fig. 43, is a firebrick
ignition arch g, which is so arranged as to protect the back
of the hopper h from the heat of the furnace, and thus prevent
ignition of the coal in the hopper. The arch is supported
by a framework of structural steel. At the front end it is
from 9 to 12 inches above the grate surface and at the rear
it is from 16 to 26 inches above that surface, the distance
being governed by the grade of coal and the percentage of
volatile matter it contains. The bridge wall is supported by
circulating tubes i that are connected with the water space of
the boiler. -The front tube forms a barrier against which the
live coals at the surface of the fuel bed are carried by the
rearward movement of the grate. Burning fuel is thus pre-
vented from being carried over into the ash-pit, but the
refuse is automatically dumped, as shown. The air supply to
the furnace enters through the grate from the ash-pit.
68. Playford Chain Grate. The Playford chain-grate
stoker is made in two forms, known as type A and type B.
Type A corresponds to standard makes of chain-grate stokers
as to size and capacity, but it has its own distinctive features. .
Type B is of heavier construction, being made for large boiler
plants and designed to operate under continuous overload
conditions, if necessary. In Fig. 44 is shown a side sectional
view of the chain grate as applied to a return-tubular boiler.
The stoker consists of a heavy frame e that is provided with
suitable sprocket wheels and rollers on which travels a grate b
AND CHIMNEYS, PART 1
57
made up of sections attached to endless chains. The top of
the grate is driven slowly toward the rear of the furnace, taking
with it coal from the hopper a. The amount of coal fed to the
furnace is regulated by the speed of the grate and by the open-
ing of a gate d, which is water-cooled to prevent the heat of
the fire from igniting the coal in the hopper. The gas is distilled
from the coal in the front of the furnace under the firebrick
arch c and burns as it rises and passes toward the back. The
motion of the grate carries the coke backwards at a rate that
permits the carbon to be compltely burned before the rear end
of the furnace is reached.
69. The ashes and clinkers from the stoker shown in
Fig. 44 are dumped into the ash-pit at the back. A spiral
conveyer g conveys the ashes from the rear of the furnace to a
point near the front or to any convenient point from which they
FIG. 45
can be retno ved. The frame e rests on rollers that run on rails/
and make it possible to withdraw the stoker from the furnace
when repairs are needed. In order to make the removal of
burned-out grates easy and inexpensive, the grates are made in
small sections, as a, Fig. 45, which slide over steel T bars b.
The latter are in turn easily removed from the chain links c
by taking out the pins at the ends.
The amount of power required to run the chain-grate stoker
varies from 1 to 1 J horsepower, depending on the size of the
boiler. Natural draft is used for such installations and under
ordinary operating conditions .15 to .30 inch of draft is suffi-
cient For increased capacity, from .25 to .40 inch of draft
through the firebox or furnace is required. Variable loads are
carried by changing the depth of fire and draft.
58
BOILER FURNACES, SETTINGS,
STOKERS FOR SMALL POWER PLANTS
70. Coal-Throwing Devices. Stoker installations for
small power plants are practically prohibited on account of the
cost and lack of space needed for setting the stoker. There are
devices that not only give good result sin. firing coal, but increase
the capacity and efficiency of hand-fired furnaces and reduce
the labor involved. One such form is the coal -thro wing device
known as the Dayton fuel feeder, shown in Fig. 46. It is
FIG. 46
arranged at the front of the boiler and, as in the larger types of
stokers, a hopper feed is used. Coal is fed, from the hopper a
to a rotating wheel 6, which delivers the coal in small amounts
continuously to all parts of the grate. A pusher c is used to
feed the coal to the wheel b. Whenever coal falls on the dead
plate d it cokes and is subsequently pushed back on the grate
by^hand, the firing tools being inserted through the door e,
which is also used when cleaning the fuel bed. The mechanism
for driving the wheel b and feeding the fuel is operated by
motor or steam engine and is so designed that the feed can be
regulated to the required rate of combustion.
/,,..-;*>*.._ !--
.- "".- ;^v-"^-.-^>... gS
FIG. 47
59
I LT 459 23
60 BOILER FURNACES AND SETTINGS, PART 1
71. Coal fuel feeders of the type shown in Fig. 40 handle
the lowest grades of power-plant coal, which are fired to main-
tain a thin fuel bed. The fuel is usually fired in a moist con-
dition, but wet coal can be fired; in vSuch a case the fuel must be
watched to see that it does not hang in the hopper. Continuous
light feeding of the coal and care in keeping the fire-doors shut
reduce the liability of formation of smoke and insure good con-
ditions for combustion. In case the proper size of fuel is not
available, the fuel can be fired by hand upon the dead plate d,
and after coking it may be pushed back onto the grate.
72. Hand-Fired Stokers. Special forms of hand-fired
stokers and grates are used in small steam-power plants. A
typical form, of such a grate and its general features of opera-
tion are shown in Fig. 47. The grate consists of a number of
grate bars a trunnioned at their ends and arranged to be rocked
by moving the rods b, which are attached to levers at the front
of the boiler. The grate bars are arranged in two sections
that may be rocked independently, thus enabling the coal to
feed toward the dump plate c while it is being burned. The
normal condition of the fuel bed is shown in (a) and the first
cleaning operation is shown in (6), in which the dump plate c is
lowered for the removal of ash and clinker. In (c) the grate
section d is operated after the dump plate c is closed. The
grate sections a are raised and thrown toward the rear, thus
pushing the coked coal back onto the dump plate c. The second
stoking operation is shown in (d), in which the grate section e
is operated, advancing the coked fuel onto the grate section d,
Green coal is then thrown on the grate section e at the forward
end of the grate, as shown at/. A mechanical feed from a hopper
can be installed in conjunction with the hand-operated stoker.
This arrangement saves considerable labor in firing the fuel and
prevents excess air from entering the furnace through the open
fire-doors, as occurs in hand firing. Approximately 10 pounds
of fuel can be burned per square foot of grate per hour for each
.1 inch of draft in the furnace. Combustion rates up to 60
pounds have been obtained, but from 30 to 40 pounds of fuel
per square foot of grate per hour is general practice.
BOILER FURNACES, SETTINGS,
AND CHIMNEYS
(PART 2)
BOILER SETTINGS
SETTINGS FOR BURNING OIL AND POWDERED COAL
OIL-BURNING FURNACES
1. Advantages of Oil Fuel. Oil as fuel for stationary,
marine, and locomotive boilers has come into extensive use
and possesses many advantages over solid fueL The cost of
handling oil fuel is less than the cost of handling solid fuel, and
as no ashes are formed, there is no problem of refuse disposal ;
also, the absence of dust and ashes makes oil-fuel burning far
cleaner than coal burning. It is possible to obtain a more inti-
mate mixture of oil and air than of solid fuel and air, and so
an oil-burning furnace can be operated with a smaller excess of
air than a coal-burning furnace, the result being that there is a
more efficient use of fuel and a higher furnace temperature.
With oil fuel, the steam output of the boiler can be increased
more quickly than is possible with solid fuel, thus making the
boiler more responsive to increases in the load. -
1. The furnace walls and floor must be lined with firebrick
capable of withstanding very high temperatures. There should
be from .9 square foot to 1.2 square feet of firebrick surface
per boiler horsepower to reflect heat and maintain uniform
furnace temperature.
COPYR10HTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS !
2 BOILER FURNACES, SETTINGS,
2. Furnace Requirements) for Oil Burning. A furnace in
which oil fuel is to be burned must be designed with the fol-
lowing requirements in mind:
2. The furnace must be of sufficient volume to insure
thorough mixing of the oil spray and the air, with proper com-
bustion, before the resulting hot gases are permitted to strike
the boiler shell or tubes. A volume of 2 cubic feet per boiler
horsepower has been found to give good results.
3. The burner, or atomizing device, must be so located that
the oil spray will not strike the furnace walls or the boiler sur-
faces; for, if it does, there is a probability that oil will drip
from those surfaces when the burner is put into operation, and
enough oil may collect at the bottom of the furnace to cause an
explosion when the furnace walls become heated. The flame
of the burning oil spray should not be localized, but should be
distributed so as not to produce local stresses in or blisters on
any part of the boiler.
3. Furnaces for Oil Burning. A form of setting- for burn-
ing' oil fuel under a water-tube boiler of the Heine type is
shown in Fig. 1 (a) and (6). It will be observed that no bridge
wall or combustion arch is used ; as a result, a furnace of large
volume is obtained. The side walls and floor of the furnace
are lined with high-grade firebrick, to withstand the high tem-
peratures produced by oil burning. This lining, when heated
to incandescence, assists in maintaining and promoting com-
bustion. The bricks a in the floor just in front of the burners
are laid on supports b made of piping and are arranged so as
to leave generous spaces c between them, through which air
enters the furnace. The quantity of air supplied is regulated
by a damper in the uptake and by doors at the front of the
furnace. Baffles d of refractory tile are provided to lengthen
the gas travel over the tubes. The burners e are set in open-
ings / in the front wall of the furnace, and the oil is sprayed
toward the rear of the boiler by either steam or air. This
arrangement gives the burner the name of front-shot burner,
A Stirling boiler arranged for oil burning is shown in Fig. 2
(a) and (b). The sectional view (a) is taken transversely
BOILER FURNACES, SETTINGS,
through the drums of the boiler
to indicate the position of the
baffles a and the oil burners b.
The burners, which are termed
rear-shot burners, are placed at
the back of the furnace, and as
the firing is from the rear to
the front, the gases travel for-
wards and then back under the
front baffle a. W h e n the
burner is so placed it must be
protected from the furnace
heat. For this purpose a
housing c of brick is set
around it. The piping d to
the burner is placed under the
furnace floor <?, The air is
admitted into the furnace
through openings in the floor c,
and air slots / are allowed be-
tween the bricks in front of
the burners h to prevent the
formation of soot, which would
form on the floor and fuse
with the brick.
4. Oil Furnace for Scotch
Boiler. For burning oil in an
internally fired boiler of the
Scotch type, as in Fig. 3, the
burners a are placed at the
front of the corrugated fur-
naces. To protect the mouth
of the furnace against the in-
tense heat, a firebrick lining
is built around the burner set-
ting and back into the furnace
to a distance of about one-half
AND CHIMNEYS, PART 2 7
the furnace length, as indicated at 6. The rear plate c of the
combustion chamber is also protected by a firebrick wall d,
which is called a target wall, or flash wall. This wall forms a
retainer of heat, as it becomes incandescent after the fire has
been in operation for a time. When the oil spray strikes the
wall, it flashes immediately into flame.
FIG. 5
5. Oil Furnace for Locomotive Boiler. The firebox of a
locomotive-type boiler burning oil fuel is also lined with fire-
brick, which is built up along the sides of the firebox to provide
a target wall and an arch. A combustion arch is essential, as
otherwise the gases would pass out directly into the tubes only
partly consumed. The combustion arch promotes a more inti-
mate mixture of the gases and air and maintains a more nearly
uniform furnace temperature. Fig. 4 (a) and .(&) illustrates
a method of constructing the walls a and combustion arch b
for firing oil from the front. In order to obtain sufficient fur-
8
BOILER FURNACES, SETTINGS,
nace volume with some types of firebox boilers, it is necessary
to set the firebrick walls and floor well below the crown sheet.
Doing this may necessitate building part of the brickwork out-
side the firebox, as shown in the illustration. The furnace illus-
trated is arranged for two burners, each of which has its own
combustion arch.
Another form of arrangement is shown in Fig. 5. The lower
part of the firebox is lined with firebrick a, and the arch bricks b
FIG. 6
are supported by the arch tubes c. The burner is located at d f
so that the flames are directed against the target wall e. Air
is admitted through the holes f, as well as through the hopper
door g when it is opened.
6. Adapting Coal-Burning Furnaces for Oil Burning. A
boiler setting intended for the use of coal as fuel may be
adapted to oil burning with little change, and in case of necessity
AND CHIMNEYS, PART 2 9
it may be reconverted to a coal-burning furnace with little delay.
The grate bars usually need not be removed, but firebrick must
be laid on them, with proper openings to admit air beneath the
burners. If a large combustion space must be obtained, the
grates may be taken out and the floor of the ash-pit arranged as
in Fig. 1 or Fig. 2. In the setting shown in Fig. 6, the grates a
are left in place and are covered with, a layer of firebrick b. A
front-shot oil burner c is installed in the front of the furnace
and the flames are projected against the bridge wall d. Baffles
across the tubes cause the hot gases to follow the course indi-
cated f It will be observed that the upper front ends of the
tubes are not in the direct path of the hot gases, which is a
disadvantage. The use of a rear-shot burner would overcome
this and would probably result in a better distribution of heat.
EQUIPMENT FOR BURNING POWDERED COAL
7. Preparation of Powdered Coal. Furnaces used in the
cement industry and in various metallurgical processes have
long been burning powdered coal as fuel with great success;
but the application of such fuel to the firing of steam boilers is
of more recent adoption. To bring the coal to the desired con-
dition, it must be put through a number of processes, involving
crushing, drying and powdering, for which special machinery
is required. A typical system for producing powdered coal is
illustrated in Fig. 7 (a) and (&). The lump coal is dumped
from the railroad cars into a bin a beneath the track, from
which it is lifted by a bucket elevator to the crushing rolls 6,
where it is broken into pieces small enough to dry readily. It
then descends by gravity to the feeder c, which feeds it into
the upper end of the dryer d. The dryer is a long cylinder that
is inclined slightly from the horizontal and is rotated by suitable
gearing It passes through the combustion chamber of a fur-
nace * and so is heated externally. At the same time, the hot
gases from the furnace are led by the pipe /to the" hood g
enclosing the lower end of the dryer, from which they flow
through the dryer and escape to a stack at its upper end. Inside
the dryer are longitudinal shelves, so that, as the dryer rotates,
10
BOILER FURNACES, SETTINGS,
the coal is picked up, carried part way round, and dropped off
the shelves, while at the same time it is acted on by the current
of hot gases passing through the dryer and the heat transmitted
FIG. 7
through the shell of the dryer. As the dryer is inclined, the
coal gradually works down to the lower end, where it is picked
up by an elevator h and carried into a storage bin i.
AND CHIMNEYS., PART 2 11
8. Before the dried coal is discharged into the storage
bin i, Fig. 7, it passes over a magnetic pulley that catches all iron
that may have accidentally found its way into the crushed coal
These pieces of iron, if allowed to remain, would interfere with
the working of the crushing mill, or pulverizer /, into which the
dried coal is fed through the gate k and its connecting pipe.
Here it is ground to a powder of such fineness that at least 95
per cent, of it will pass through a 100-mesh screen, which
means a screen having 10,000 openings to the square inch.
During the pulverizing, coal clttst is formed, which is drawn into
the dust collector /and caught, instead of being allowed to go to
waste. The pulverized coal is delivered to the boilers by suit-
able conveyers and is ready for use without further treatment.
The coal crusher, elevators, dryer, and pulverizer are driven by
electric motors. Coal of any kind can be powdered and
burned, regardless of the ash it contains; but the higher the
fusing point of the ash, the better will be the operating condi-
tions, as an ash with a low melting point is likely to form a
slag on the furnace walls, whereas an ash of high melting point
will be deposited as dust.
9, Burning Pulverized Coal. One form of equipment for
burning pulverized coal, as applied to a Stirling boiler, is shown
in Fig. 8. The powdered coal is contained in the bin a, to
which it is brought from the pulverizers by the screw conveyer b.
The bin is elevated, so that the fuel may be supplied to the
burner by gravity and also to leave ample room around the
boiler setting for making repairs. The powdered coal descends
from the bin into the coal feeder c 9 which is a cylindrical casing
containing a spiral conveyer driven by chain gearing from the
motor d. A slide or gate at the bottom of the bin enables the
fuel supply to be shut off completely, if that becomes neces-
sary. The motor d is of the variable-speed type, so that the
rate "at which the feeder c operates may be adjusted to the
load on the boiler and to the demand for fuel. From the feeder
the powdered coal falls through the pipe e into the burner /,
where it is met by a blast of air supplied through the pipe g
from the blower h and driven into the furnace, where it burns.
12
BOILER FURNACES, SETTINGS,
Additional air for combustion enters through the adjustable
register i f the damper-controlled ducts /, and the shutters in the
ash-pit doors k.
10. Furnace Design for Burning Powdered Coal. The
furnace for burning powdered coal must be of such proportions
that the fuel will be burned before the resulting hot gases touch
FIG. 8
the boiler surfaces. For bituminous coals high in volatile mat-
ter, the volume of the furnace may be satisfactorily taken as
2 to 2J cubic feet for each boiler horsepower. The interior of
the furnace should be made in the form of a cube, if possible,
with the side walls sloping inwards toward the ash-pit, so that
the dust and slag will slide easily into it. Furnaces are some-
times extended in the form of a Dutch oven to provide addi-
AND CHIMNEYS, PART 2 13
tional space for the combustion of the fuel. The firebrick walls
should be made heavy and of high heat-resisting quality, as high
temperatures and gas velocities are developed in burning this
fuel. These conditions in combination with the erosive action
of the dust and slag cause the brick to waste away.
RECLAIMING WASTE HEAT
11. Utilizing Waste Gases From Kilns. In the various
processes involved in the manufacture of iron, steel, and cement,
heat is used, and the hot gases coming from the furnaces and
kilns contain much heat that may be utilized instead of being
allowed to go to waste. The temperature of these so-called
waste gases may be from 1,000 to 1,600 F., and much of their
heat may be reclaimed by passing them through specially
designed boiler settings. In a direct-fired furnace, the tempera-
ture may range from 2,000 to 3,000 F. As a waste-heat
installation has to deal with temperatures only about half as
high as these, the problem of design is quite different, as the
heat transmitted per square foot of boiler heating surface is
much less at the lower temperatures. In early waste-heat
installations, 20 square feet of heating surface was allowed for
each boiler horsepower to be developed, and as a result, both the
boilers and their settings were very large.
(Experience showed that the rate at which heat was trans-
mitted from hot gases to water inside a boiler was increased by
increasing the speed with which the gases swept over the heating
surfaces, and this fact was used as a means of reducing the size
of waste-heat installations.- The waste gases were given higher
velocities in moving over the boiler surfaces, and thus smaller
boilers could be used with no reduction of capacity. At present,
the hot gases in waste-heat installations move at such a rate that
from 2,500 to 4,500 pounds of gases pass through the boiler set-
ting per hour per square foot of area of gas passage. Water-
tube boilers are extensively used The waste gases from cement
kilns carry much dust, and so a boiler with horizontal baffles
should not be used for such gases, as the dust would collect on
them and eventually choke the gas passages.
AND CHIMNEYS, PART 2 IS
1SJ. A typical waste-heat installation is shown in Fig. 9.
The water-tube boiler is set high and the tubes are longer than
in the type of boiler used with a direct-fired furnace. Vertical
baffles give four passes of the hot gases over the tubes. The
waste gases enter at a> follow the course indicated by the arrows,
and escape at b into an. economizer c, where they give up further
heat to the feedwater. A fan d in the passage leading to the
stack v draws the gases through the boiler setting at the desired
speed. The speed of the fan may be varied by driving it from
a steam turbine or a variable-speed motor. As the fan creates
a suction through the economizer and the boiler, there is a partial
vacuum inside the boiler setting, and the danger of air leakage
through the setting and the clean-out doors is thereby increased.
The clean-out doors should be fitted with gaskets to mate them
air-tight.
13. Preheating Air by Flue Gases. One of the large
losses of heat in boiler operation arises through the escape of
flue gases at a high temperature. To recover a part of the heat
thus leaving the boiler, a feedwater economizer may be set in
the path of the flue gases. Still another way of accomplishing the
same end is to utilize the heat of the flue gases to preheat
the air supplied to the furnace. An apparatus constructed ^for
this purpose is shown in Fig. 10, in which (a) is a general view,
partly in section. The middle section a encloses a rotating heat-
ing element b, shown in detail in view (fe), made up of alter-
nate series of flat and corrugated plates bent to cylindrical form,
and driven by chain gearing from the shaft c that carries the
fans d and *. The fan d forces the cool fresh air into the upper
section f, which is fitted with a partition g that deflects the air
downwards through the rotating element b into the lower sec-
tion h The partition * compels the heated air to pass down into
the flue / that leads to the furnace of the toiler. The interior
of the lower section is shown clearly in view (c).
14 The escaping flue gases from the boiler are led to the
prehe'ater, Fig. 10 (a), by the flue *, and discharged into the
lower section A, the fan e acting as an exhauster to keep the gases
in motion. The baffle plate I compels the hot gases to
1 L T 459-24
AND CHIMNEYS, PART 2 17
rise through the left half of the rotating element b, to which
they give up their heat. They then pass into the upper sec-
tion /, are deflected by the partition m } and are forced out to
the chimney by the fan c. Thus, there is a steady flow of
fresh air down one side of the device and a similar flow of
hot flue gases up the other side. The rotating element b
absorbs heat from the flue gases, and, after rotating into the
path of the fresh air, gives up the heat to the fresh air. Thus,
there is a continuous, transfer of heat from the flue gases to
the air supply without mixture of the two currents, the rotating
element b serving to transfer the heat. The effect of preheat-
ing the air supply in this manner is to increase the efficiency of
combustion and at the same time to recover heat that would
otherwise go to waste. The valve n, view (c), admits steam
to the perforated pipe o that acts as a soot blower to clean the
plates of the rotating element.
CHIMNEYS AND DRAFT
HANDLING FLUE GASES
BREECHINGS
15 Forms of Breechings. The breeching forms the con-
nection between the smoke outlet of the boiler and the ; chim-
ney Its shape depends on the type and number of boilers m
. the installation and whether they are stationary or marine. A
common form of breeching for a stationary boiler shown
Fte 11 (a). The base a, which is connected to the smoke
outlet of the boiler, is rectangular in shape, whereas the top b
to which the stack is fastened, is circular, the two being joined
by the tapering body c. If two boilers are to be connectedjo
the same stack, the form of breeching shown m (), known
as a Y breeching, is used. The bases a and & are connected to
the smoke outlets of the boilers and the stack is conncrtriat^
To prevent collision and eddying of the gases flowing from the
18
BOILER FURNACES, SETTINGS,
two branches d and e, it is customary to provide a separating
plate, or baffle, at the throat where the two branches unite.
16. In case a breeching' must serve a battery of boilers,
it is made tapering in form., so that its cross-sectional area
FIG. 11
, increases toward the stack and thus accommodates the greater
quantity of gases. Such a breeching is shown in Fig. 12. The
sides are straight, flat surfaces and the top is arched. The
bottom is flat, and in it are the openings a through which the
gases from the boilers enter the breeching.
AND CHIMNEYS, PART 2
19
17. The form of breeching used on a Scotch boiler is
shown in Fig. 13. It is attached to the front of the boiler and
is of such shape as to cover the ends of the tubes and leave the
space in front of the furnaces unobstructed. Its taper is such
that the area of the passage increases toward the top, where it
joins the uptake. Doors a are provided so that access may
be obtained to the tube-sheet for cleaning and repairing tubes.
Clean-out doors must also be provided at the bottom of the
breeching, to facilitate the removal of dust and soot carried
FIG. 12
through the tubes and deposited in the breeching. Breechings
are made of steel plate about $ inch thick.
18. Breeching Design. Breechings and their connections
to the stack should be so designed as to offer the least possible
resistance to the flow of gases. * Straight connections with
angular bends, as shown in Fig. 14 (a), hinder the gas cur-
rents, as the corners a cause eddies to form, as shown by the
shaded area. To overcome this, the entrance to the smoke
outlet should be rounded, as shown in '(&), by the use of elbows.
A round elbow and breeching will cause less draft loss than a
square or rectangular type with curved top or bottom. The
20
BOILER FURNACES, SETTINGS,
cross-sectional area of the breeching should be made larger
than that of the stack. In general practice the cross-sectional
area is made from 10 to 25 per cent, larger than the cross-sec
FIG. 13
tional area of the stack, depending on the nature of the fuel to
be burned and the amount of flue dust expected. Builders of
chimneys prefer to make the area of the flue opening from 7
to 10 per cent/larger than the cross-sectional area of the stack.
AND CHIMNEYS, PART 2
21
(a)
TYPES OF CHIMNEYS
19, Details of Construction. Chimneys are usually built
of brick, though concrete, iron, and steel are often used for
those of moderate height. Brick chimneys are usually built
with a flue having parallel sides and a taper on the outside of
the chimney of from -^ to J inch per foot of height. The
external diameter at
the base of a brick
chimney should be
made about one-tenth
of its height to insure
stability. The thick-
ness of the outer wall
is usually one brick, or
about 8 or 9 inches,
for the first 25 feet
from the top, increas-
ing one-half bricks for
each additional 25 feet
from the top down-
wards. If the inside
diameter exceeds 5
feet, the top should be
one and one-half
bricks thick ; if less than 3 feet in diameter, it may be one-half
brick in thickness for the first 10 feet from the top.
20. A round chimney gives greater draft area for the.
same amount of material in its structure and exposes less sur-
face to the wind than a square chimney. Large brick stacks
are usually made with an inner core and an outer shell, with
a space between them. The core is free to expand with the
heat without; distorting the shell. Sometimes the shell has iron
rings laid up in the -brickwork every 4 to 5 feet. Large brick
chimneys are usually constructed with a series of internal
pilasters, or vertical ribs, to give rigidity. The top of the
chimney should be protected by a coping of stone or a cast-
22
BOILER FURNACES, SETTINGS,
1_,
W^\^^
H^T- ^28-d -H
FIG. 15
iron plate to prevent the destruction
of the bricks by the weather ; some
ornamental finish is usually added at
the top of the chimney.
SI. Iron or steel stacks are
made of plates varying from \ to \
inch thick. The larger stacks are
made in sections, the plates being
about \ inch thick at the top and in-
creasing to i inch at the bottom ;
they are lined with firebrick about
18 inches thick at the bottom and
4 inches at the top. Some design-
ers prefer to use no lining on ac-
count of the likelihood of corrosion
and the difficulty of inspection, and
also because the inside of lined
stacks cannot be painted.
On account of the great concen-
tration of weight, the foundation
for a chimney should be carefully
designed. Good natural earth will
support from 2,000 to 4,000 pounds
per square foot. The footing be-
neath the chimney should be made
of large area. In compressible soils,
piles should support the footing.
22. Brick Chimney. A brick
chimney 162 feet high is shown in
Fig. IS. The flue is 12 feet 3 inches
in diameter at the base, tapers to 8
feet half way up, and remains of
the same size to the top. The outer
wall a is 17| inches thick for the first
50 feet, 13 inches for 60 feet, and 9
inches thick to the ornamental top b.
The core c is 13| inches thick for 20
AND CHIMNEYS, PART 2 23
feet above the flue openings, 9 inches for the next 70 feet, and
4|- inches for the remainder. There are two flue openings
d and c with a deflecting partition / extending about two-thirds
of their height between them.
23. Reinforced-Concrete Chimney. Reinforced concrete
is especially adapted for constructing chimneys that are to be
located where foundation soils are not good, because its com-
paratively light weight permits the use of lighter and less
expensive foundations than for any other kind of permanent
chimney. Since a reinforced-concrete chimney is used as a
conduit for hot gases, its heat-resisting properties are of para-
mount importance. Engineers have not reached definite
agreement as to the best construction to use within the chim-
ney; some insist upon a lining of firebrick for at least the
lower portion; others use a lining of concrete for the entire
height or for a portion only ; and some use a single shell of
concrete, which in some cases has been left unprotected and
in other cases has been encased in special clay tile.
There are at present in common use two principal designs of
reinforced-concrete chimney, known respectively as the Weber
chimney and the Wiederholdt chimney, both of which are pat-
ented. The Weber chimney is entirely of reinforced concrete,
while the Wiederholdt chimney is of reinforced concrete encased
in tile.
24. The Weber chimney may be either cylindrical, or
tapered, but the cylindrical form is not often built now. The
tapered, or coniform, chimney is constructed as shown in
Fig. 16, in which (a) is an elevation with a portion removed to
show the construction; (6) is a half plan of the footing; (c} a
half section showing the reinforcement of the footing, and (d)
an enlarged section on the line A B of view (a) . The chimney
has an outer shell a reinforced to withstand the force of the
wind; its thickness and reinforcement depend on the locality
and on the height and diameter of the chimney. Within this
shell is a 4-inch shell b, also of reinforced concrete ; this shell
withstands the heat of the gases and extends up far enough
24
BOILER FURNACES, SETTINGS,
for the gases to be somewhat cooled
before coming in contact with the outer
shell. Between the shells is an air
space c that prevents the heat from
penetrating to the outer shell Since
concrete expands under heat this space
also permits the inner shell to expand
as required.
25. At the top of the chimney, Fig.
16, is an ornamental cap d consisting of
a heavy ring of concrete with extra
reinforcement to stiffen the concrete at
the top. Some distance above the
ground is the flue opening* c through
which the gases are admitted to the
chimney. The concrete immediately
surrounding the flue opening is rein-
forced with extra steel rods and thick-
ened by the omission of the air space
at this place, as plainly shown in (d).
Below ground is the footing g, consist-
ing of a tapered block of reinforced
concrete constructed as shown in (5)
and reinforced as indicated in (c).
The wall of the chimney is solid below
grades, as shown at h in views (a)
and (6).
26. The Wieclerholdt chimney,
Fig. 17, differs from the Weber chim-
ney in being built
without molds, the
wall consisting of H-
shapecl tiles of the
shape shown in? Fig.
18. These tiles are
laid up first to form a
- ,, hollow wall into which
FIG. 16
AND CHIMNEYS, PART 2
25
the concrete is poured. The tiles permit of the installation of
the vertical and horizontal rods that are required. The arrange-
ment of steel shown in Fig/ 17 is typical of all reinforced-
concrete chimneys. The main reinforcing rods a extend ver-
tically the entire height of the chimney and at their lower ends
serve to tie the chimney to the footing block b so as to prevent
FIG. 17
the chimney from blowing over, because in the footing the
rods a interlock with the footing rods r, of which there are
four layers. At intervals throughout the height, horizontal
rings d surround the vertical rods ; these horizontal rings con-
sist of lighter rods than the vertical and are often -J-inch round
rods 14 inches apart. In order to permit these rods to pass
through the tiles, the partition a, Fig. 18, is notched, leaving
an open space b for the passage of the rods.
26
BOILER FURNACES, SETTINGS,
27. Steel Chimney. A self-supporting
steel chimney is shown in Fig. 19. It is
225 feet high above the foundation, and the
inside diameter of the shell is 14 feet 8
inches at the top and 17 feet at the top of
the flare at the base, and the inside diameter
of the lining is 13 feet 9 inches. It "is set
on a foundation about 16 feet high, built
of dimension stone laid in Portland-cement
mortar. (Dimension, or cut, stones are
stones that have been cut to dimensions in
advance of laying.) The chimney is com-
posed of a number of rings made of plates
4 feet high by about 6 feet long and | inch
thick for the first 40 feet from the top, in-
creasing in thickness by -^ inch per 40 feet
for 160 feet. The first 25 feet at the bot-
tom is made of -jVinch plates cut to such
shape that when riveted together they form
a bell-shaped section that flares from 17 feet
in diameter at the upper end to 27 feet in
diameter at the foundation-bolt circle at the
base. Vertical anchor bolts hold the chim-
ney to the foundation and prevent it from
blowing over. The chimney has a firebrick
lining ranging in thickness from 18 inches
>
X*
FIG. 18
FIG. 19
AND CHIMNEYS, PART 2
27
at the bottom to 4J inches at the top. Four smoke flues, one
on each side, enter the foundation near the bottom.
28. Guyed Steel Stacks. Stacks made of light sheet iron
are neither so high nor so large in diameter as self-supporting
steel chimneys and consequently do not require heavy founda-
tions. Stability, or resistance to overturning under the effect of
wind pressure,, is obtained by running guy wires from the upper
part of the stack to anchors or suitable fastenings at the ground
level or on adjoining buildings. The stack is usually built of a
series of cylindrical rings riveted together, as shown in Fig.
20 (a), alternate sections a being made of such diameter as to
fit inside the adjacent sections 6. The rivets in the circumfer-
ential seams have a pitch of about 3 inches, and those m the
vertical seams a pitch of 3 to 4 inches. Another form of con-
struction, shown in (6), makes use of sections of the same
diameter, which are butted together and joined by butt straps
riveted on the outside, though they may be put on the inside.
28
BOILER FURNACES, SETTINGS,
Outside straps are preferable, as the inside of the stack then
has a uniform diameter throughout, with nothing to interfere
with the flow of the gases.
29. In the stack construction shown in Fig. 20 (r), the
sections are tapered, the upper end of each being slightly
smaller in diameter than the bottom. The top of each section
then fits into the bottom of the section next above, and the
TABLE I
PLATE THICKNESSES AND RIVET DIAMETERS FOR GUYED STACKS
Diameter
of
Stack
Inches
Thickness
of Plate
Minimum
U. S. Standard
Gauge
Diameter
of Rivet
Inch
Thickness
of Plate
Maximum
Inch
Diameter
of Rivet
Inch
30
10
f
8 (gauge)
1
36
10
I
A
A
40
10
1
4
A or |
48
8
I
i
A or i
54
& in.
' A '
A
iorf
60
T =Vin.
A
A
iorf
two are riveted together. The lap on the outside thus faces
down, and so does not form a ledge on which moisture can
collect.
The plate thicknesses and diameters of rivets for guyed
steel stacks of different diameters are given in Table I. For
each diameter a minimum and a maximum plate thickness are
suggested with corresponding rivet diameters. If durability
and permanence are desired, the thicker plate should be chosen
for a given stack. Through the action of flue gases and
atmospheric moisture, corrosion is very likely to attack the
steel stack unless its surface is protected. It is, therefore,
recommended that the stack be painted frequently with a good
grade of metal paint.
AND CHIMNEYS, PART 2 29
PROPORTIONS OF CHIMNEYS
30. Requirements of Chimney. The height of a chimney
must be such as to produce the proper draft in the furnace,
and the diameter must be such as to enable the chimney to
carry off the gases from the boiler or boilers. The chimney
may have a circular or a square flue, but the circular form is
considered more efficient than a square one of equal area,
because its inside surface offers less resistance to the pas-
sage of the gases, and there is less likelihood that eddies will
be formed. There is much difference of opinion among
engineers as to whether a stack should be narrower toward the
top or increased in size. The usual practice is to taper a
stack toward the top, this being done more on account of the
necessity for increasing its stability than because of the draft.
Some stacks have been built, however, with a larger inside
diameter at the top than at the bottom, the idea being to pro-
vide a greater sectional area for the passage of the gases as
their velocity is decreased.
31* The top of a chimney should extend above nearby
buildings, trees, hills, etc., so that air-currents sweeping over
such adjacent elevations will not be deflected downwards on
top of the chimney and interfere with the draft it produces.
The minimum height of a chimney depends on the kind of
fuel burned in the boiler. Fine anthracite requires a strong
draft and, therefore, a high chimney; bituminous coal requires
a chimney of medium height ; oil fuel requires less draft than
coal, and, therefore, a shorter chimney; and wood requires
the least height. Of course, the rate of combustion, the form
of the gas passages in the boiler, the length and shape of the
breechings, and the number of boilers also have a bearing on
the height of the chimney. Because of the expense of con-
struction, it is not economical to build chimneys more than
about 200 feet high. Except in cases where the surrounding
conditions require a chimney of unusual height, it is better to
build two or more chimneys, and to make each of them shorter
than a single chimney would need to be.
30 BOILER FURNACES, SETTINGS,
32. Height of Chimney. The relation between the
height of the chimney and the pressure of the draft, in inches
of water, is given by the following rule :
Rule. To find the draft pressure of a chimney in inches of
water, divide 7.6 by the absolute Fahrenheit temperature- of the
outside air and divide 7.9 by the absolute Fahrenheit tempera-
ture of the chimney gases; subtract the latter quotient from
the former and multiply the difference by the height of the
chimney, in feet.
Expressed as a formula, the rule becomes
* a
in which p = draft pressure, in inches of water;
H = height of chimney, in feet;
T a and T c = absolute temperature of the outside air and of
the chimney gases, respectively.
EXAMPLE. What draft pressure will be produced by a chimney
120 feet high, the temperature of the chimney gases being 600 P.,
and of the external air 60 R?
SOLUTION. By the formula,
33. To find the height of chimney to give a specified
draft pressure, the following rale may be used :
Rule. To find the height of a chimney, in feet, divide 7,6
by the absolute Fahrenheit temperature of the outside air, and
divide 7.9 by the absolute Fahrenheit temperature of the chim-
ney gases; subtract the latter quotient from the former, and
divide the required draft, in inches of water, by the difference
of the quotient's.
Expressed as a formula, this rule becomes
rr P
fl&J
IT T
\ J- a -i c
EXAMPLE. Required, the height of the chimney to produce a draft of
14 inches of water, the temperature of the gases and of the external
air being, respectively, 550 and 62.
AND CHIMNEYS, PART 2 31
SOLUTION. By the formula,
1 125
Ans -
522 1,010
34. Area of Chimney. The height of the chimney being
decided on, its cross-sectional area must be designed to carry
off readily the products of combustion. The following rules
for finding the dimensions of chimneys are in common use :
Rule I. To find the effective area of a chimney, in square
feet, multiply the horsepower of the boiler or boilers by .3
and divide the result by the square root of the height of the
chimney, in feet.
Rule II. To find the effective area of a chimney, in square
feet, subtract .6 times the square root of the actual area from
the actual area, in square feet.
Rule III. To find the horsepower of boilers a chimney will
serve, extract the square root of the height of the chimney in
feet and multiply it by 3.33 times the effective area in square feet.
Rule IV. To find the side of a square chimney, in inches,
multiply the square root of the effective area, in square feet,
by 12, and add 4 to the product
Rule V. To find the diameter of a round chimney, in inches,
midtiply the square root of the effective area, in square feet,
by 13.54, and add 4 to the product.
These rules may also be expressed in the form of formulas.
Let H= height of chimney, in feet;
P = horsepower of boiler or boilers ;
A= actual area of chimney, in square feet;
E = effective area of chimney, in square feet ;
$= side of square chimney, in inches ;
d= diameter of round chimney, in inches.
Then, = =A-.6VA (1)
P=3.33 J EV# (2)
S=12V+4 (3)
d=13.54VE+4 (4)
Table II has been computed from these formulas.
I L T 459 25
32 BOILER FURNACES, SETTINGS,
EXAMPLE 1. What should be the diameter of a chimney 100 feet
high that furnishes draft for a 600-horsepower boiler?
SOLUTION. By formula 1,
.3P .3X600
E= 1S Vioo ~ 18
Now using formula 4,
d= 13.54 ^18+4*61.44 in. Ans.
EXAMPLE 2. For what horsepower of boilers will a chimney 64
inches square and 125 feet high furnish draft?
SOLUTION. By simply referring to Table II, the horsepower is found
to be 934. Ans.
35. Maximum Combustion Rate. The maximum rates
of combustion attainable under natural draft are given by the
following formulas, which have been deduced from the experi-
ments of Isherwood:
Let F= weight, in pounds, of coal per hour per square foot
of grate area;
H= height, in feet, of chimney or stack.
Then, for anthracite burned under the most favorable con-
ditions,
F=2VH-1 (1)
and under ordinary conditions,
F = 1.5Vff-l (2)
For best semianthracite and bituminous coals,
F = 2.25VH (3)
and for less valuable soft coals,
F = 3Vl (4)
The maximum weight of combustion is thus fixed by the
height of the chimney; the minimum rate may be anything
less.
The foregoing formulas may also be expressed in the form
of a rule, as follows :
Rule. To find the maximum weight of cool that can be
burned per square foot of grate area per hour, with natural
draft: Subtract 1 from tmce the square root of the chimney
height, in feet, for anthracite burned under the most favorable
conditions; subtract 1 from 1.5 times the square root of the
AND CHIMNEYS, PART 2 33
chimney height for anthracite burned under ordinary condi-
tions; multiply the square root of the chimney height by 225
for semi-anthracite and bituminous coals; and multiply the
square root of the chimney height by 3 for less valuable soft
coals.
EXAMPLE. Under ordinary conditions, what is the maximum rate
of combustion of anthracite coal if the chimney is 120 feet high?
SOLUTION. By formula 2,
, H=1.5 Vl20- 1 = 15.4 Ib. per sq. ft. per hr. Ans.
36. It will be observed that in Table II the capacity of
the stack is given in horsepower. In calculating this table it
was considered that 5 pounds of coal was burned to develop
1 horsepower, this being a high figure with the present econom-
ical systems of power generation. Allowance has also been
made, in this table, for the friction of the gases against the side
walls of the stack, it being considered that a 2-inch layer of
dead air exists between the stack lining and the gases ; that is,
the air and gases for a thickness of 2 inches next the walls of
the stack are assumed to have no movement, or circulation.
EXAMPLES FOR PRACTICE
1. What should be the height of a chimney to give a draft pressure
of inch of water, the temperature of the air being 60 F. and of the
gases 440 R? Ans. 107 ft.
2. A chimney is 135 feet high and 5 feet square inside; calculate
the horsepower for which it will furnish draft. Ans. 851 hp.
3. What is the maximum rate of combustion of best bituminous
coal in a marine boiler with chimney stack 100 feet high? Ans. 22.5 Ib.
4. Calculate the side of a square chimney 150 ' feet high that fur-
nishes draft for boilers of 1,000 horsepower. Ans. 63.4 in.
5. What draft pressure will a chimney 80 feet high furnish, the
temperatures of the air and gases being, respectively, -60 and 600 R?
Ans. .57 in.
6. Under the most favorable conditions, what height of chimney
will allow a maximum rate of combustion of anthracite coal of
23 pounds per square foot of grate per, hour? Ans. 144 ft.
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AND CHIMNEYS, PART 2 35
DRAFT
METHODS OF PRODUCING DRAFT
37. Natural Draft The hot gases that escape into the
chimney from the boiler may have a temperature of from 250
to 650 R, whereas the air outside usually has a temperature
below 90 F. Thus, the gases inside the chimney are lighter
than the air outside; that is, they weigh considerably less per
cubic foot. As a result, they rise in the chimney and the heav-
ier outside air flows in to take their place. If the boiler set-
ting and the connections are in good condition, the outside air
can enter only through the furnace ; thus a continuous current
is set up, fresh air flowing through the fuel bed into the fur-
nace and the gaseous products of combustion passing over the
heating surface and out through the chimney to the air. This
movement of air and gases is called draft, and when it is pro-
duced only by the relative lightness of the gases inside the
chimney and the air outside, without the aid of any appliances,
it is known as natural draft.
38. Draft is caused by a difference of pressure. Suppose
that hot gases at a temperature of 500 F. flow into a chim-
ney 150 feet high. A column of such gases 150 feet high and
1 square foot in cross-section weighs approximately 6| pounds.
A column of air of the same height and cross-section, at a
temperature of 60 F., weighs about 11J pounds. The differ-
ence of weight is 5 pounds ; hence, the pressure at the base of
the chimney is greater outside than inside by about 5 -pounds
to the square foot of area of cross-section. Flow of gases or
liquids always takes place from the point of higher pressure to
the point of lower pressure, and it is this difference of pressure
of 5 pounds per square foot that causes the outside air to flow
into the furnace and thence by way of the boiler passages^ to
the chimney. The difference of pressure inside and outside
the chimney, at its base, is called the draft pressure.
39. Measurement of Draft Pressure. The intensity of
the draft, or the draft pressure, is usually only a small fraction
36
BOILER FURNACES, SETTINGS,
of a pound to the square inch; therefore,, draft pressures are
not expressed in pounds per square inch, but in inches of
water. In other words, the draft pressure is measured by the
height of a column of water that will produce a pressure equal
to the draft pressure. A column of water 34 feet high and
1 square inch in cross-section weighs 14.7 pounds; that is, the
pressure at the foot of such a column is equal to atmospheric
pressure. As 34 feet is equivalent to 408 inches, a column of
water 1 inch high has a pressure at its base of 14.7 -^-408 = .036
pound per square inch. Thus, if a draft pressure is said to be
1J inches of water, the difference of pressure is 1JX.036=.045
pound per square inch. The U gauge, shown in
Fig. 21, may be used to measure draft pressure.
As will be seen, it is a glass tube bent to the shape
of the letter U. The left leg communicates with
the chimney, and the right leg at the top is open
to the outside air. The air outside the chimney
being* heavier, it presses on the surface of the
water in the right leg and forces some of it up
the left leg. The difference in the two water
levels h and g in the legs represents the intensity
of the draft and is expressed in inches of water.
40. Mechanical Draft. Under certain con-
ditions it may be out of the question to use natural
draft. For example, certain kinds of fuel require
very high draft pressure in order to force the
necessary amount of air through the fire. The cost of a
chimney of sufficient height to supply the required draft
may be so great as to make it impracticable to use natural
draft. Again, there may not be sufficient room to build a
chimney of the desired capacity. In such cases, the draft may
be produced by appliances, such as fans, blowers, or steam jets.
Draft produced by these means is called mechanical draft to
distinguish it from natural draft. It may be either forced
draft or induced draft. With "fdrcecl draft, the air is forced
into the ash-pit under pressure; with induced draft, a partial
vacuum is formed at the chimney, and the air and gases are
FIG. 21
AND CHIMNEYS, PART 2 37
drawn through the furnace and boiler passages instead of
being forced through.
41. Advantages and Disadvantages of Mechanical Draft.
Forced draft has certain advantages for a .number of installa-
tions and conditions. It produces sufficient air pressure to
force air through very thick fuel beds, and is, therefore, of
great advantage in burning fuel with underfeed stokers and
where hollow grates are used. When anthracite screenings
are burned, the tendency of the fuel is to cake and form
clinker on the grate; but from the intensity of forced draft,
this tendency is overcome. The disadvantage of forced-draft
systems is that when the air is forced into the boiler setting
under high pressure, some of it escapes through the fire-doors
and ash-pit doors, and through other openings in the furnace
walls. The fire and ash-pit cannot be cleaned when the blast
is on, for the reason that soot, smoke, and ash dust would be
blown out into the boiler room.
42. Induced draft tends at all times to draw the air into
the furnace and stack and thus affords a means of ventilating *
the boiler room. The firing and cleaning operation may be
carried on without the objections of smoke and dust. By this
system a uniform condition of the fuel bed can be obtained.
It is efficient where an economizer is used, as it makes up the
draft loss in the stack due to the reduction of flue-gas tem-
perature that occurs when the gases give up their heat to
the water in the economizer. When head room is limited and the
breeching is large, it is sometimes difficult to install the
induced-draft system. However, since it utilizes the space
above the boilers, it is out of the way and makes it possible to
use ground floor space that would be taken up if forced draft
were used. The steam consumption of a blower system pro-
ducing either induced or forced draft varies from 2 to 5 per
cent, of the steaming capacity of the plant.
38
BOILER FURNACES, SETTINGS,
EQUIPMENT FOR MECHANICAL DRAFT
43. Fans and Steam Jets. For forcing air under pres-
sure into the ash-pit, either a fan or a steam jet may be used.
Steam jets are not favored to any great extent and their
use in modern boiler plants is limited. With some fuels, live
steam is introduced under the grate to prevent the forming of
large clinkers. The steam in passing through the fuel bed is
broken up into its two elements, hydrogen and oxygen, and
the heat taken from the fuel bed to produce this dissociation
cools the lower bed of fuel sufficiently to prevent large clinker
formation. It also tends to prevent the grates from over-
heating. A steam jet has a lower first cost than a fan blower,
but the latter is preferable, as it produces better results in the
combustion of fuels.
44. A common construction of fans is shown in Fig 1 . 22
(a) and (&). The shell or housing a is made of steel plate,
(a)
FIG. 22
Fro. 23
with a substantial base b of cast iron or wrought iron. An
outlet c is placed at the desired point of the circumference,
whence the air is discharged into the duct leading to the ash-
pit. In the fan shown there is one inlet, which surrounds the
fan shaft on the side opposite the pulley d through which the
fan is driven. The fan shaft is supported in two bearings and
carries the fan wheel within the casing. The usual construc-
tion of the fan wheel is shown in Fig. 23. Arms a made of
T iron are fastened to the hub b and carry at their ends the
blades c. These blades are tied together by the side plates d.
AND CHIMNEYS, PART 2
39
45. Typical Forced-Draft Installations. One of the
usual methods of installing a forced-draft system for two or
more horizontal return-tubular boilers is shown in Fig. 24.
The equipment consists essentially of a fan a and an engine b.
The fan may be located above the boilers, in which case the
FIG. 24
air is conveyed to the ash-pit by sheet-metal ducts. Ordinarily
the fan is set on the floor and discharges into underground
concrete air ducts c. The air ducts may enter the ash-pit
directly under the bridge wall or from the side or rear of the
setting, as conditions permit. Where a number of boilers are
set in a battery and are connected to a common stack d by a
breeching e, it is customary to install an induced-draft fan in
the breeching near the stack or else to use a short stack to
furnish draft to overcome the friction of the gases in passing
from the furnace.
46. Ash-Pit Fixtures for Forced-Draft Installations.
The air discharged by the fan may be introduced into the ash-
pit through an opening in the bridge wall, and the draft through
it may be regulated by a damper as shown in Fig. 25 (a).
This arrangement is recommended for a new boiler plant.
When forced draft is applied to an old plant, the air may be
introduced in front through an opening in the bottom of the
ash-pit, as shown in*(&). When the damper is closed, the
40
BOILER FURNACES, SETTINGS,
ashes may readily be raked over it. The clamper, when opened,
serves to distribute the air thoroughly in the ash-pit.
Concrete air ducts are the most durable, but when low first
cost is essential, galvanized iron ducts may be used; in such a
case it is customary to have the main supply overhead and a
branch pipe extending down to each boiler.
47. Horsepower Required for Producing Forced Draft
The horsepower necessary to furnish forced draft may be cal-
culated by the following rule:
AND CHIMNEYS, PART 2 41
Rule. To find the horsepower required to furnish forced
draft, divide the product of the draft pressure, in pounds per
square foot, the weight of fuel burned per minute on the grate,
in pounds, and the volume of air, in cubic feet per pound of
fuel, by the product of 33,000 times the efficiency of the draft
apparatus, expressed as a decimal.
Expressed as a formula, the rule becomes
__
33,000 y
in which P= horsepower required;
p= pressure of draft, in pounds per square foot;
W~ total weight of fuel, in pounds, burned on grate
per minute ;
F= volume of air, in cubic feet per pound of fuel;
y= efficiency of draft apparatus.
EXAMPLE. What horsepower is required to supply air at a pressure
of 21 inches of water to a total grate area of 120 square feet burning
20 pounds of coal per square foot per hour and requiring 220 cubic
feet of air per pound of coal? Assume the efficiency to be 60 per cent.
SOLUTION. By the formula,
pWV 2^X5.2X1^X120X220
= = - 33,OOOX.60 -
48. Turbine Blower. The turbine blower forms an effi-
cient and a satisfactory means of forcing air into the furnace
through the fuel bed from the ash-pit. As shown in Fig. 26
(a) and (&), it consists of a bladed fan a, shaped like a ship's
propeller, connected to a shaft b on which is fixed the rotor of
a turbine inside the casing c. The rotor, or turbine wheel, is
driven by steam that enters through the pipe d, the exhaust
escaping through the pipe e. The blower is installed in the
wall / of the boiler setting, which may be the side, front, or
back wall. The rapid rotation of the fan a by the steam tur-
bine draws air into the blower and forces it into the boiler
setting beneath the fuel bed. The exhaust steam from the
blower may be conducted to a f eedwater heater or to a heating
system; or, a part or all of it may be allowed to pass up
through the grates with the air, to prevent clinkering when
42
BOILER FURNACES, SETTINGS,
coal with a fusible ash is used. The number of blowers
required depends on the number of boilers, the rate of com-
bustion of fuel, and the capacity of the blower.
49. Induced-Draft Apparatus. A typical induced-draft
installation for a battery of three boilers is shown in Fig-. 27,
It consists of a single exhaust fan a driven by a steam engine b
directly connected to the fan shaft. For such installations a
FIG. 26
short stack c is directly connected to the fan outlet d. A by-
pass pipe e connecting 1 with the breeching / and fitted with a
damper g should always be installed, so as to permit operation
with stack draft when starting* the fires, when the plant is
operating under a light load, or when repairs are required to
the fan or the engine. By using induced draft with hand-
fired furnaces an increase of boiler capacity up to 200 per
cent, of rating may be obtained; and an increase of capacity
up to 400 per cent, of rating can be obtained by using forced
draft in combination with induced draft. The intensity of
draft may be regulated either by hand or by some form of
automatic control.
DRAFT CONTROL
50. Balanced Draft. A system of combined forced draft
and induced draft has been worked out, in which the fuel feed,
the air supply, and the stack draft are all automatically con-
43
44
BOILER FURNACES, SETTINGS,
trolled by an interlocking regulation, so that the combustion
conditions are always suited to the condition of the fire. The
arrangement of the various regulating devices used in this
system is shown in Fig. 28. A fan a driven by a 'steam tur-
FIG. 28
bine supplies air under pressure beneath the grates b and thus
enables the air to overcome the resistance due to the thickness
of the fuel bed. The minimum speed of the turbine driving
the fan is fixed by the amount of opening! of the valve c in the
AND CHIMNEYS, PART 2 45
steam-supply pipe. In addition, there is a by-pass containing
a valve d connected by a chain e to the piston of the regulator f f
which has a diaphragm subjected to the pressure of the steam
in the steam main g. 'Any change of steam pressure causes
movement of the regulator piston and thus moves the valve d,
admitting either more or less steam to the turbine and thus
altering the fan speed, and consequently the quantity of air
supplied beneath the grates.
51. At the side of the boiler setting, Fig. 28, is a fur-
nace pressure regulator. Inside the casing h is a pivoted blade
or leaf that swings in a chamber communicating by a tube with
the furnace. If the pressure in the furnace changes even
slightly, this blade is swung on its pivot. Connected to the
blade by levers is a pilot valve that controls the flow of water
under pressure to the upper or lower end of the cylinder i.
This cylinder contains a piston to which the chains / and k.
are attached. The chain / leads to the damper / and the
chain k to a cam m on the valve n that controls the steam
supply to the stoker engine o. Thus, the damper position and
the rate of feed of the fuel are both automatically altered in
case the pressure in the furnace changes.
Suppose that the steam pressure drops slightly. The regu-
lator / opens the valve d slightly and the fan speeds up, increas-
ing the air supply. The combustion becomes more rapid, pro-
ducing more gases in the furnace, and the draft over the fire
tends to decrease. This causes the blade in the regulator h
to move and so the piston in the cylinder i is moved, opening
the damper enough to restore the draft above the fire. At
the same time the cam m is moved, opening the valve n, speed-
ing up the stoker engine, and consequently the rate of fuel feed.
52. Automatic Damper Regulators. In steam power
plants, the aim is to promote economic combustion of the fuel
and to maintain uniform steam pressure. For this purpose
automatic damper regulators are used, which depend for their
operation on a change in the steam pressure. The Spencer
hydraulic damper regulator, shown in Fig. 29, illustrates one
means of regulating the draft. The chamber b contains a
46
BOILER FURNACES, SETTINGS
flexible diaphragm dividing the chamber into two parts. The
under part is filled with water subjected to the boiler pressure
through the steam pipe d. The diaphragm tends to move
upwards under the influence of the steam pressure, but its
upward motion is resisted by the downward force exerted by
the weighted lever c. The weights are so adjusted that the
lever will occupy a position midway between its two extreme
FIG. 29
positions when the steam pressure in the boiler is exactly at
the point at which it is to be carried. A secondary lever / is
hinged at f to the free end of the lever c. The secondary lever
is fulcrumed at m, and at g the valve stem of the operating-
valve is attached to it. This valve works inside a piston that
is closely fitted to the stationary cylinder h, the valve serving
to admit water under pressure to either side of the piston. The
piston rod passes through both heads of the cylinder h ; at its
lower extremity it is connected to the lever i pivoted at V,
AND CHIMNEYS, PART 2
47
which, through the medium of the connecting-rod /, transmits
any motion of the piston to the damper k.
53. Let the steam pressure rise
above that for which the damper is
set. Then the diaphragm and the
free end of the lever c, Fig. 29, move
upwards. The lever f, being con-
nected at f, swings upwards around
m as a fulcrum ; this raises the valve
inside of the cylinder h and thus ad-
mits water under pressure from the
pipe a to the bottom of the piston in
the cylinder h. At the same time,
the valve places the upper side of the
cylinder in communication with a
water-escape pipe. In consequence
thereof, the piston ascends and pulls
the lever i Upwards, which in turn
rotates the damper k, closing it still
farther. As the piston ascends, the
fulcrum m is moved upwards and
the lever /swings around f as a
fulcrum, causing the valve in the
piston to move downwards in rela-
tion to the piston, closing the water-
supply port and holding the piston
in its new position. When the
steam pressure falls below normal,
the levers c and / descend, and as
the lever / swings around m, the
valve also descends, placing the up-
per side of the piston in communica-
tion with the water supply and
the under side in communication with the water-escape pipe.
Then the piston descends and the damper opens. But the
lever / now swings around f , and thus causes the valve to ascend
in relation to the piston, which is then brought to rest.
I L T 459-26
FIG. 30
48
BOILER FURNACES, SETTINGS,
54. The cylinder h, Fig. 29, is shown in section in Fig. 30.
The piston is made water-tight by the cup leather packing
rings r. The water under pressure enters through the supply
pipe a and surrounds the piston, entering through a small port
into the central valve chamber and then surrounding the cen-
tral part of the piston valve if. When the valve moves upwards
FIG. 31
it uncovers the ports tf and e ; the water under pressure flows
through the port e f into the lower part of the cylinder ; at the
same time the water in the upper parts flow through the port e
into the hollow piston rods s and out at /. The resultant motion
of the piston then returns the valve to the central position shown.
If the valve descends, it admits the water into the port e and
allows the water in the lower half of the cylinder to escape
through the port ef into the passage s f 9 which, through a by-pass
port not shown, communicates with the passage s. The descent
of the piston again returns the valve to its central position.
55. Hand-Operated Draft Regulator. In Fig. 31 is
shown a breeching with hand-operated dampers, as used in
some power plants. The damper consists of a plate a, which
may be placed in either the uptakes or in the stack b. The
plate is fastened to the damper rod, and is opened or closed by
AND CHIMNEYS, PART 2
49
chains attached to the lever c. The damper reduces the draft
area and thus the volume of gases escaping into the chimney,
and so retards the flow of air through the fire into the fur-
nace. This reduction in the air supply reduces the intensity
of the fire and the generation of steam. Dampers are also
fitted in ash-pits so as to regulate the amount of air admitted
under the grates.
OTHER DRAFT-PRODUCING DEVICES
56. Steam Jets. In hand-fired furnaces steam jets are
often used to mix the fuel gases and the air. A larger amount
of air is required in a furnace at the time of firing the fuel than
during the distillation of the volatile matter in the fuel bed.
Several automatic devices for introducing steam and air into
the furnace have been patented, and one of them is shown in
fa)
FIG. 32
Fig. 32 (0) and (ft). It consists of a steam pipe a, fitted with
a valve b, through which steam is admitted from the boiler to a
number of steam jets c arranged in a horizontal row across the
front of the furnace, so that the steam flows into the furnace
at an angle to the fuel bed. The valve b is connected to a
50
BOILER FURNACES, SETTINGS,
lever d that is fastened to the piston rod e of a piston that fits
inside the dash-pot /. The lever d is connected by a crank to
the shaft g, which in turn is connected to the fire-door by a
rod h and a crank. The fireman in opening the fire-door
causes the shaft g to turn, which in turn operates the lever d
and thus opens the valve b, allowing steam to enter through
FIG. 33
the jets c. The air door i is also opened at the same time by
the turning of the shaft g, which carries a dog / that presses
against the lever k. Steam and air are "admitted for some time
after the fire-door is closed; but during this period the dash-
pot piston automatically descends, gradually moving the lever d f
turning the shaft g, and thus closing the valve b and the air
door i. The advantage of this device is that the gases and the
air are intimately mixed during the period in which the vola-
tile matter is being driven off from the fresh fuel, thus pre-
venting smoke and saving fuel.
in
57. Argand Blower. The Argand blower, shown
Fig. 33, is a device for producing a supply of air under pres-
sure in the ash-pit and is operated by steam jets. It consists
of a long air tube flared at both ends and inserted through the
front wall of the setting, so that the inner end b ist beneath the
f orwarii end of the grates c. At the outer end is a hollow
AND CHIMNEYS, PART 2
51
ring d perforated with numerous holes on the side toward the
ash-pit and supplied with steam through the pipe e and the
valve /. When steam is admitted to the ring d, it escapes
through the perforations in many small jets, as shown, drawing
air in at the outer end, and carrying it along into the ash-pit.
58. Induced Draft by Steam Jet. Increased draft in the
furnace and boiler passages may be obtained by inserting a
steam- jet blower at the base of the stack, as shown in Fig. 34.
The blower consists of a nozzle a held in place in the center of
FIG, 34
the stack by the piping b through which steam is supplied. The
steam enters an annular passage c in the base of the blower,
from which it escapes through the orifices d into the nozzle,
drawing gases through the nozzle .and discharging them at the
top and thus producing a strong upward current in the stack.
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