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VuGHAN-PENDR
M.lHsnMECH E< MAM S.l.shT
of tbe
'Qlnivereiti? of Mfsconefn
V
-2.-^- ■■
X-
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zrbe "Mestminster" Series
THE RAILWAY LOCOMOTIVE
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THE RAILWAY
LOCOMOTIVE
WHAT IT IS AND WHY
IT IS WHAT IT IS
BY
VAUGHAN PENDRED, M.Inst.Mech.E. M.I. & S.Inst.
LONDON
ARCHIBALD CONSTABLE & CO. LTD.
lo ORANGE STREET LEICESTER SQUARE W.C.
1908
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tCbc Mestminstcr ©erics.
Uniform. Bx. Cr. 8vo. Fully Illustrated. Price 6«. net per volume.
India^Rubber and its Manufacture, with Chapters on
Qutta-Porcha and Balata. By H. L. Terry, F.I.C, Assoc. Inst.M.M.
Liquid and Gaseous FueiSy and the Part they play in
Modern Poinrer Production. By Professor Vivian B. Lewes, F.I.C,
F.C.S., Prof, of Chemistry, Royal Naval College, Greenwich.
Eiectric Power and Traction. By F. H. Davibs, A.M.I.E.E.
Coal. By James Tonge, M.I.M.E., F.G.S.,etc. (Lecturer on Mining
at Victoria University, Manchester.)
Town Qas for Ll^^htin^ and Heatinflr. By W. H. Y.
Webber, C.E.
iron and Steel. By J. H. Stansbie, B.Sc (Lond.), F.I.C.
Eiectro-iVietailurs^. By J. B. C. Kershaw, F.I.C.
Precious Stones. With a Chapter on ArtiflciBil Stones.
By W. GooDCHiLD, M.B., B.Ch.
The Book; Its History and Development. By Cyril
Davenport, V.D., F.S.A.
Natural Sources of Power. By Robert S. Ball, B.Sc,
a.m.i.c.e.
Radio-Teie^raphy. By C. C F. Monckton, M.I.E.E.
Patents. Trade iViarks and Designs. By Kenneth R.
Swan, B.A. (Oxon.), of the Inner Temple, Barrister-at-Law.
QIass. By Walter Rosenhain, Superintendent of the Department
of Metallurgy in the National Physical Laboratory, late Scientific Adviser in the
Glass Works of Messrs. Chance Bros. & Co.
IN PREPARATION.
Electric Lamps. By Maurice Solomon, A.C.G. I., A.M.I.E.E.
The iVianufacture of Paper. By R. W: Sindall, F.C.S.
Wood Pulp and its Applications. By C. F. Cross, £. J.
Bevan and R. W. Sindall.
Steam En^^ines. By J. T. Rossiter, M.I.E.E., A.M.I.M.E.
Qold and Precious IVietais. By Thomas K. Rose, D.Sc, of
the Royal Mint.
PhotOS^raphy. By Alfred Watkins, President of the Photographic
Convention, 1907.
Commercial Paints and PalntinsT- By A. S. Jennings,
Hon. Consulting Examiner, City and Guilds of London Institute.
Brewins^ and Distillins^. By James Grant. F.C.S.
Leather. By H. Garner Bennett.
Pumps and Pumpins^ IViachinery. By James W. Rossiter,
A.M.LM.E.
Workshop Practice. By Professor G. F. Charnock, A.M.I.C.E.,
M.LM.E.
Ornamental Window QIass Work. By A. L. Duthie.
Textiles, and their IVianufacture. By Aldred Barker, M.Sc
Timber. By J. R. Baterden, A.M.I.C.E.
Published by ARCHIBALD CONSTABLE 8 Co. Ltd.
10 ORANQE STREET W.C.
And for Sale at all Booksellers. Detailed Prospectus on application.
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149219
JAN d 1911
.P57
CONTENTS
SECTION I
THE LOCOMOTIVE ENGINE AS A VEHICLE
CHAP. PAGE
I. FRAMES 1
II. BOGIES 15
III. THE ACTION OE THE BOGIE 27
IV. CENTRE OF GRAVITY 33
V. WHEELS 40
VI. WHEEL AND RAIL 54
VII. ADHESION 58
VIII. PROPULSION 66
IX. COUNTER-BALANCING .73
SECTION II
THE LOCOMOTIVE AS A STEAM GENERATOR
X. THE BOILER 84
XI. THE CONSTRUCTION OF THE BOILER 91
Xn. STAY BOLTS 97
XIII. THE FIRE-BOX 102
XIV. THE DESIGN OF BOILERS 114
XV. COMBUSTION 121
XVI. FUEL 127
XVII. THE FRONT END 136
XVIII. THE BLAST PIPE 144
XIX. STEAM 152
XX. WATER 158
XXI. PRIMLC^G 162
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vi CONTENTS
CHAP. PAGE
XXII. THE QUALITY OF STEAM 169
XXIII. SUPERHEATING 171
XXrV. BOILER FITTINGS 180
XXV. THE INJECTOR 187
SECTION III
THE LOCOMOTIVE AS A STEAM ENGINE
XXVI. CYLINDERS AND VALVES 198
XXVII. FRICTION 209
XXVIII. VALVE GEAR 213
XXIX. EXPANSION 217
XXX. THE STEPHENSON LINK MOTION 223
XXXI. walschaert's and joy's gears 230
XXXII. SLIDE VALVES 236
XXXIII. COMPOUNDING 239
XXXIV. PISTON VALVES 246
XXXV. THE INDICATOR 250
XXXVI. TENDERS 263
XXXVII. TANK ENGINES 271
XXXVIII. LUBRICATION 282
XXXIX. BRAKES 285
XL. THE RUNNING SHED 288
XLI. THE WORK OF THE LOCOMOTIVE 294
STANDARD WORKS ON THE LOCOMOTIVE ENGINE 305
INDEX 307
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LIST OF ILLUSTRATIONS
>10. PAGE
1. STEPHENSON'S INSIDE AXLE BOX 5
2. STEPHENSON'S STANDARD LOCOMOTIVE, 1838 .... 7
3 — 16. THE DEVELOPMENT OF THE BAR FRAME .... 9
17. AXLE BOX 11
18. COMPENSATING LEVER 12
19. BI8SELL BOGIE 15
20 — 21. GREAT NORTHERN SWING LINK BOGIE 16
22. FLANGING PRESS 18
23. OPEN END BOGIE 19
24. CLOSED END BOGIE 19
25. STANDARD BOGIE, GREAT EASTERN RAILWAY .... 20
26. STANDARD BOGIE, GREAT EASTERN RAILWAY .... 21
27. DETAILS BOGIE, GREAT EASTERN RAILWAY 21
28. SWING LINK BOGIE, GREAT WESTERN RAILWAY .... 22
29. TRAVERSING LEADING AXLE, LANCASHIRE AND YORKSHIRE
RAILWAY 24
30. MR. BALDRY'S RULE FOR FINDING THE CENTRE FKUM WHICH TO
strike the curve of a radial axle box .... 25
31. centrifugal effort 34
32. tire- rolling mill 41
33. tire sections, lancashire and yorkshire railway . . 46
34. standard tire and rail, great eastern railway . . 47
35. adams' elastic wheel 54
36. centrifugal couples 75
37. rigg's diagram 77
38. wire test for hammer blow 81
39. sectional diagram of boiler 85
40. radial stress 91
41 — 44. exploded boiler 100
45. girder stay 102
46. BELPAIRE BOILER, **STAR" CLASS, GREAT WESTERN RAILWAY . 104
47. FIRE HOLE 107
48. expansion slide 114
49. drummond's water tube fire-box 118
50. smoke-box, LONDON AND SOUTH WESTERN RAILWAY . . . 140
51. SMOKE- BOX, SOUTH EASTERN AND CHATHAM RAILWAY . . 141
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viii LIST OF ILLUSTRATIONS.
FIG. PAGE
52. SMOKE-BOX, SOUTH EASTERN AND CHATHAM RAILWAY . . 142
53. STANDARD FRONT END 149
54 — 55. BALDWIN SMOKE-BOX 150
56. HEAT PEG 153
57. THE PEABODY CALORIMETER 166
58—60. THE SCHMIDT SUPERHEATER 175
61. AMERICAN THROTTLE VALVE 180
62. THROTTLE VALVE DETAILS . 181
63. SAFETY VALVE 183
64. ramsbottom's safety valve 184
65. SECTION OF injector 191
66. SELF- STARTING INJECTOR 194
67. SLIDE VALVE 200
68. CYLINDER WEAR 202
69. ACTION OF CONNECTING ROD 204
70. JOY^S VALVE GEAR 205
71. CROSS-HEAD, GREAT EASTERN RAILWAY 207
72. GAB GEAR 214
73. STEPHENSON'S LINK MOTION 216
74. EXPANSION CURVE 218
75. ANGULAR ADVANCE 223
76 — 78. wainwright's reversing gear 226 — 228
79. walschaert's gear 232
80. joy's gear • . . . . 233
81. smith's piston valve 248
82. THOMPSON indicator WITH OPEN SPRING 251
83. INDICATOR DIAGRAMS 255
84. PICK-UP APPARATUS, LONDON AND NORTH IVTISTERN RAILWAY . 2G5
85. FEED WATER-HEATER, LONDON AND SOUTH-WESTERN RAILWAY. 269
COLLISION AT BIN A, GREAT INDIAN PENINSULA RAILWAY . .272
86 — 87. FINDING THE CENTRE OF GRAVITY OF A TANK ENGINE 274 — 275
88—89. DERAILMENTS 278 — 279
90. RAMSBOTTOM GRAVITY LUBRICATOR 283
91—93. TRACTOMETER DIAGRAMS 298, 299
94. IVATT'S SPEED DIAGRAM 301
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INTRODUCTION
The literature of the railway locomotive engine is already so
copious that I think some explanation of how this book came to
be written is desirable.
It forms one of a series of volumes, the idea of publishing
which originated with Messrs. Archibald Constable & Co. In
the present day specialisation is universal, and in no profession
does it prevail more than in that of engineering. This will not
appear remarkable when we recognise the enormous range of
subjects with which the engineer has to deal.
The ** Westminster " series is intended in a sense to bridge
over the gaps left by specialisation. Thus the marine engineer
may have but a very slight knowledge of electrical engineering,
and the civil engineer may be comparatively ignorant concerning
the locomotives which run on the railways which he makes. But
engineers should have — the younger members of the profession in
particular need to have — a great deal of information in common,
and all perfectly understand technical language.
Speaking then of my own work, I may say that I hope engineers
in any branch of the profession who may read this book will find
in it information which they did not possess before. The
books which have hitherto been written about the locomotive
engine are all either strictly specialised or very '* popular." None
of them go far into the life of the locomotive engine. The
technical treatise deals with the locomotive almost altogether as
a machine. Its parts are described, but the reasons why they
assume particular shapes, and why one shape is better or worse
than another are not dwelt upon, and nothing is said about the
daily life of the engine. To use a metaphor, the locomotive is
handled by its authors anatomically, not physiologically.
I have in this volume attempted, I hope with some success, to
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X INTRODUCTIOISI
break new ground. Of the history of the locomotive I have
written next to nothing. I have endeavoured to describe the
modern locomotive, using the words in the generic sense, and to
explain why it is what it is.
That I have left much unsaid that might have been said
with advantage is a very evident proposition. My excuse lies in
the dimensions of this book, and the fact that it is not intended
to be in any sense or way a complete treatise on railway
locomotives. My purpose has been to make the locomotive
intelligible ; to show what it means ; the mechanical and the
physical phenomena on which it depends for its action, and the
objects carefully kept in view by those who design, construct, and
employ it as one of the most useful servants of mankind. I do
not think this has been done before with anything like the same
simplicity of intention.
There are very wide differences in externals, but in essentials
all locomotives without exception, are the same. They are
survivals of the fittest. The conditions of working are compara-
tively inflexible ; and the more closely any type of locomotive
conforms to these conditions the greater are the chances of its
success. Yet the influence of nationality and climate have
made themselves felt ; and various designs may be regarded as
indigenous to particular countries. The British locomotive is,
above all others, simple, strong, and carefully finished. It is
intended to last as long as possible. The American locomotive
is the incarnate spirit of opportunism. It is intended to meet
the wants of the moment ; a long life for it is neither desired nor
sought. It is held that before an engine can wear out it will be
superseded by something bigger, and more suitable to new re-
quirements and conditions. In Europe complication is favoured
rather than disliked. The workmanship is as a rule admirable ;
but simplicity is the last thing studied. In all cases the national
character appears to stamp itself on machinery of every kind.
I have treated the modern locomotive from three points of
view, namely, as a vehicle, as a steam generator, and as a steam
engine. A certain amount of overlapping is unavoidable, but it
will not confuse the issues.
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INTEODUCTION xi
I am deeply indebted to old friends and acquaintances for
valuable assistance. I have only had to ask for drawings and
information to obtain them. Among others, I must mention
Mr. J. A. Aspinall, General Manager, Lancashire and Yorkshire
Railway ; Mr. G. Churchward, Great Western ; Mr. Dugald
Drummond, London and South Western ; Mr. J. Holden, Great
Eastern ; Mr. G. Hughes, Lancashire and Yorkshire ; Mr. Ivatt,
Great Northern; Mr. Wainwright, S. E. and C. Railway;
Mr. G. Whale, London and North Western ; and Mr. Theodore
N. Ely, Chief of Motor Power, Pennsylvania Eailroad.
I have not attempted to quote all the books, British and foreign,
and papers read before such bodies as the Institution of Civil
Engineers, or Institution of Mechanical Engineers, which have
helped me ; but I have given at the end of this volume a short list
of the names of works which can be studied with advantage by
those who wish to know more about the locomotive engine.
Finally, I may say that in writing I have carefully kept in
view the needs of the student. I have endeavoured to make the
study of the locomotive attractive. Unfortunately, it lends
itself in many ways to mathematical treatment ; and, the
mathematics of the locomotive are very far from being a good
introduction to its study. It may be added that in practice they
play but a secondary part ; and this principally because they do
not always fit in with existing conditions. Anyone who has the
chance of standing on the running board of an express engine
moving at fifty or sixty miles an hour, and watching the
behaviour of the valve gear, will understand just what I mean.
I have endeavoured, as I have said, to tell my readers what
the modern locomotive is and why it is what it is. For this
purpose, I have only required a comparatively small number of
diagrams, and I have not illustrated any types of locomotive.
Photographs will be found of these by the hundred in other
volumes, where they serve a good purpose no doubt. They
would be superfluities in this book.
Vaughan Pendred.
Streatham,
1908.
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THE
EAILWAY LOCOMOTIVE
SECTION I
THE LOCOMOTIVE ENGINE AS A VEHICLE ^
CHAPTEE I
FRAMES
No characteristic of the locomotive possesses so much import-
ance for the travelling public as its performance as a vehicle.
By far the larger proportion of the serious, or even terrible,
accidents which occur in the present day on railways in this
country are derailments.^ The train runs off the track, and is
more or less smashed up according as the speed is high or
moderate. It is certain that in nearly all cases it is the loco-
motive that first leaves the line ; carriages are occasionally derailed,
^ The locomotive was first dealt with as a vehicle by the late D. K. Clark,
in '* Eailway Machinery," published in 1855.
2 Among the more recent may be mentioned the derailment of a Great
Western express near Loughor, South Wales, on October 3rd, 1904, 5 killed
and about 50 injured ; on December 23rd in the same year a Great Central
train was derailed at Aylesbury, 4 killed and 4 injured; January 19th,
1905, Midland train derailed near Cudworth, 8 killed and 20 injured ;
September 1st, 1905, train derailed at Witham Junction on the Great
Eastern, 11 killed and 40 injured; July 1st, 1906, American boat train
wrecked at Salisbury, South Western Eailway engine upset on a curve,
28 killed and 12 injured; and October 15th, 1907, London and North
Western train derailed on a curve at Shrewsbury, 18 killed and many injured.
R.L: B
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2 THE EAILWAY LOCOMOTIVE
but the fact that each is tied by the draw-bar to the coach next in
front and next behind it tends powerfully to prevent the escape
of the wheels from the rails. Indeed, there are well-known
instances in which a pair or more of wheels have left the track,
run for a while on the sleepers, and then been pulled back to the
rails and continued running very little the worse. No one has
ever heard of an engine getting off the road and on again
automatically. Furthermore, if an engine runs badly, it may
break rails and injure the road in various ways, as will be
explained further on. A bad road is an unsafe road, and so,
although the engine's defects may not be those w^hich induce
derailments directly, they may be exceedingly mischievous in
other respects.
The locomotive is subjected to two classes of disturbance,
the one external to it, the other internal. The object of the
designer is to combat or get rid of both, and as we proceed it
will become evident that the task is by no means easy to
perform.
Ifc must be steadily kept in mind that the locomotive and the
permanent way are but two parts of the same machine. The
rails bear precisely the same relation to the engine that the V
grooves of a planing machine do to the sliding table. Good
planing cannot be done unless the grooves and slides are in order ;
and smooth, safe travelling is impossible unless the engine and
the road are both in excellent condition, and in as nearly as may
be perfect mechanical adjustment. If the road is bad, uneven,
and weak, the disturbing effects may be so great as to mask
defects in the engine. On the other hand, the road may be so
excellent that the inherent defects of the engine may be forced
into prominence, the internal factors of disturbance then masking
such defects in the track as may still exist.
Let us deal with the external disturbing forces first.
If the track was dead straight and absolutely smooth, level
and rigid ; if the wheels were quite cj^lindrical and carefully
balanced, then a vehicle might be run at any speed without the
least danger. No force would solicit it to jump off the rails or
overturn. These conditions represent the maximum limit of
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FRAMES 3
safety. Just in so much as these conditions remain unfulfilled
will the probability of derailment or upsetting be augmented.
In practice the maximum limit can never be attained. The rails
are never wholly smooth, level, and unyielding, and any vehicle
intended to run on them with safety must be provided with
expedients by which the effect of the imperfections in the track
on the stability of the machine will be minimised. The
influence of imperfections may be divided into two sections, one
vertical, the other horizontal. Thus the rails not being dead
level, the wheels have to run up and down so many steel waves
more or less long and seldom coincident on both rails. To reduce
the jumping motion springs are placed between the axle boxes
and the body of the vehicle. To neutralise the effect of horizontal
imperfections a certain amount of lateral flexibility is imparted
to the vehicle. Curves may be regarded as horizontal defects in
the permanent way ; and to help the locomotive to deal with the
centrifugal effort the outer rail is raised above the level of the
inside rail by an amount fixed by the radius of the curve and the
speed at which it is traversed. These are general principles ;
we may now proceed to consider them in more detail.
Every locomotive consists of a framework or chassis supported
by springs on wheels. The framework carries in its turn a
boiler, and an engine with two, three, or four horizontal or
nearly horizontal cylinders, two being the usual number. The
framing may be regarded as the link between all the various
parts of the whole locomotive. There are two types of framing,
namely, the plate frame and the bar frame. The latter is very
little used in this country ; the former very little used in the
United States. In certain cases it is not easy to say to which
type the framing belongs ; but these are very exceptional.
The plate frame is a rectangular steel structure, composed
mainly of two plates extending from the leading to the trailing
end of the engine. Their depth and thickness vary in different
designs ; but it may be taken generallyHhat the plates are 1 inch
to 1^ inch thick, and 18 inches to 2 feet deep. They are secured
to each other by cross plates and angle steels. These main
frames are usually supplemented by secondary frame plates much
b2
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4 THE EAILWAT LOCOMOTIVE
lighter and narrower, on top of which rests a flat steel plate,
known as the ** running board," along which the driver can walk,
and so oil and inspect his engine while it is running. Little or
nothing of the main frame can be seen in many engines, because
it is concealed by the wheels, splashers, running board, &c.
It is of the utmost importance to the good and safe running of
the engine that the framework shall always remain quite rigid;
that the angles between the longitudinal and the cross plates
shall be true right angles ; and that, in a word, no twisting in
any plane shall take place. If the track were a dead level there
would be no risk of twisting ; but it is not level, and one corner
of the engine may be raised by a wheel on a ridge, while another
is lowered because the nearest wheel is in a hollow. Changes in
the amount and direction of the stress occur every moment. The
stresses are far too complicated to permit of mathematical treat-
ment. The designer never attempts to calculate their amounts.
He adapts the proportions, and method of riveting or bolting,
which have been found by experience to be the best. Any con-
siderable change in design involves something of an experiment.
Risks are got over, however, by the simple expedient of making
things very strong.
Frames may be either " inside " or " outside." In the first
case the journals of the axles are inside the wheels. In the latter
case they are outside the wheels. The distance between the
bosses or hubs of the wheels cannot for a line of 4 feet 8 J inches
gauge be more than 4 feet 5J inches, and with inside cranks
this reduces the length of the bearing or journal within narrow
limits. If the journals are placed outside, then the bearing can,
of course, be made as long within reasonable limits as may be
desired ; the load per square inch is reduced, and a substantial
advantage gained. But the cross breaking stress on the crank
axle is augmented; and besides, with coupled engines, cranks
fitted on the ends of the axles become necessary, and the design
of the engine ceases to be compact. With inside frames no
crank arms are used, the pins being secured in radial prolonga-
tions of the wheel bosses.
So long as engines remained small, and particularly with
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FEAMES 5
single engines, either the outside bearing or a combination of
the outside and inside bearings remained in favour. The com-
bination was in a way a compromise. Two short journals were
used, one inside, the other outside the wheel, which was then so
far supported that even if the axle broke anywhere but in a
journal the wheel could still carry its load, and the engine would
not be derailed. The advent of the big coupled engine, however.
Pig. 1. — Stephenson inside axle box.
gave the coup de grace to outside bearings, and they are very
seldom seen now except on old locomotives. But from the first
there was trouble. The crank axles of those days were not very
trustworthy forgings, and as far back as 1838 we find Eobert
Stephenson putting in no fewer than four inside frames, which
were thus described by Mr. W. N. Marshall many years ago.
This description and the illustrations. Fig. 1, are worth pro-
ducing, because the inside frame to sustain the crank shaft
against the thrust and pull of the connecting-rod is still used.
The axle box also shows the system of wedges for tightening the
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6 THE EATLWAY LOCOMOTIVE
bearings on the shaft, and also in the horn-plates. All driving
axle boxes are fitted with wedges to take up wear 'between the
axle boxes and the faces of the horn-plates, but only a single
wedge is used, as the small longitudinal displacement cannot
affect the running of the engine.
" Four wrought iron frames A A, 3J inches deep and f inch
thick, are fixed between the smoke-box and the fire-box to
afford additional strength to the engine by securing firmly the
back plate of the smoke-box in which the cylinders are fixed, and
which has to bear the whole strain of the working of the engine.
These inside frames have also bearings in them for the cranked
axle, and hold it steadily against the action of the connecting
rods, by which it is strained alternately in opposite directions.
They are attached to the smoke-box by means of T-shaped pieces
of iron, which are riveted on to the inner and side plates, and
are bolted to the ends of the frame. The two middle frames are
made to approach each other, and are welded together at the
back end, so that there are only three bearings on the cranked
axle. The inside bearings shown in Fig. 1 are formed by
thickening the frame plate A to 2^ inches at B. It is made into
two inclined limbs C C, and between which are placed the two
bearings G G, by which the axle is embraced. These are tightened
and adjusted by means of wedges E E, taken up by screws and
nuts P P. The lower ends of C C are united by a tube D placed
between them, and a bolt and nut passed through it.''
The plate frame possesses a good deal of lateral elasticity
through a small range, and this is of use. In the early days of
locomotive engines, Messrs. Sharp, Roberts & Co., Atlas Works,
Manchester, built hundreds of engines the side frames of which
were ash planks about 3 inches thick, secured between two iron
flitch plates. For the comparatively small locomotives of the
period these frames were most excellent. Fig. 2 is an elevation
of a standard type of engine constructed by Robert Stephenson
& Co. It was closely followed in design by Sharp, Roberts & Co.
The illustration is given here because the general features
of the design were copied for many years, and the arrange-
ment of the springs is used to this day. A few engines are
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FRAMES 7
still running with them ; indeed, at one period the ash side
frame was in extensive use. In the present day, however, only
the plate and the bar frame are used. This last was introduced
by Mr. Bury, of the firm of Bury, Curtis & Kennedy, about
the year 1833. As its name denotes, it is built up of a number
of rectangular bars, either welded together or secured to each
other with rivets, dovetails, and, in most cases, bolts. These
Fig. 2. — Stephenson standard locomotive, 1838.
last are turned dead true, and are made tight driving fits for the
holes into which they are put. In the early days the United
States possessed no rolling-mills which could make plates fit for
side frames. The average smith possessed skill enough to build
up frames from bars forged under a water-driven tilt hammer.
So the bar frame found favour, and although the United States
can supply steel plates of any required dimensions now, the bar
frame is still retained. It is a very good frame, and possesses
some advantages over the plate frame, but it is expensive to
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8 THE EAILWAY LOCOMOTIVE
make and very costly to repair. The plate frame is so simple
that its essentials and its qualifications for the work it has to do
can be understood in a moment. This is far from being the case
with the bar frame, and an account of some of the modifications
which it has undergone is introduced here because its history
sets forth almost directly the nature of the stresses to which the
framing of a locomotive, no matter how constructed, is exposed,
and the way in which development proceeds. For the drawings
the author is indebted to the pages of the Railroad Gazette. In the
United States the bar frame has always been made in two pieces
as shown in Fig. 3, the front end carrying the cylinders and the
back piece the horn blocks for the axle bearings. Bury almost
invariably forged his frames in one piece, which he could easily
do because the engines were small, and it must not be forgotten
that when the plate frame first came into being it was made of
iron in three lengths with two welds. The modern frame is a
continuous plate of steel. The great trouble has always been with
the joints. In Fig. 3, which explains this, is shown the arrange-
ment used in the earlier days — say 1845. The key was supposed
to save the vertical bolts some shear. While the cylinders were
small this plan answered fairly well ; with larger cylinders the
bolts stretched and the nuts worked loose. Then came Fig. 4,
with the principal bolts a hard driving fit, and in double shear.
Double keys were used, but they twisted, and did not then help
the bolts. This was followed by Fig. 5. Still the longitudinal
alternating stresses were too much for the joint. Then came
Figs. 6 and 7, all still depending on bolts.
In some designs the frames had double bars — they are called
" rails " in the States — as seen in Figs. 8, 9, 10, 11, and 12. In
these it is clear that bolting had been carried as far as possible,
and for the more modern big engines a somewhat different
method of construction has been adopted, as shown in Figs. 13
and 14. Here the two front bars or ** rails " have been united
in a single deep slab, to which the cylinders are bolted. The
first frames made in this way had the fastening to the main
frame made as in Fig. 13, but they have to some extent been
superseded by the plan shown in Fig. 14.
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^ 1 ■ | --l^
P Jl-" p p ■!''■ }IO H ^ »4--i
Fig. 4. TJ^ pJ — I
^
, ff? ««-*nMWfu» V — m «k
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Fig. 5.
Fiq.7. 4fe=Si
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Flg.9. L^:^ - Figje.
(^IGS. 3— 16.T-The development of the bar frame.
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10 THE RAILWAY LOCOMOTIVE
Seeing how unsatisfactory in certain respects the built-up bar
frame has been, at least for large locomotives, it is not surprising
that attempts have been made to do away with it. The United
States locomotive designer is obstinately determined not to have
the plate frame, and he has turned his attention to the produc-
tion of cast steel frames in whole or in part. One is illustrated
in Fig. 15. The back ends of the frame being spared the worst
of the longitudinal stresses are very much what they always
were. One is illustrated in Fig. 16. It must be understood that
the engravings given here do not represent every kind of bar
frame in use. It lends itself to wide diversities of treatment, and
is much favoured on several European railways.
The plate frames are secured to each other by cross plates,
usually four in number — that is to say, one at the trailing end,
another just in front of the fire-box, the leading head stock
carrying the front buffer beam, and a very heavy, strong frame-
work supporting the bogie. There is besides the ** spectacle
plate " or " motion plate," which is a steel casting supporting
the outer ends of the piston-rod guides, and the valve motion.
The cylinders are in the present day usually cast in one piece,
and being bolted between the frames, stiffen them still further.
As has been said, the stresses to which the framing is exposed
are very great. Thus, in large engines, that due to the steam
effect on the pistons may reach as much as fifty tons. Then
there is not only the weight of the boiler and the water in it, but
the various stresses set up by the arrested momentum of the
boiler when the engine lurches or rolls.
For the bar frame it is claimed that it is on the whole lighter
than the plate frame, and that various parts may be more
conveniently secured to it, while it gives unexampled facilities
for access to the mechanism. But it has been found essential
to stiffen it by plates bolted to the frame and to the boiler, a
practice which has been almost given up in this country, as
grooving is very likely to take place where the stiffening plate is
riveted to the boiler shell. This grooving is the result of minute
bendings backward and forward of the boiler plate just where the
frame plate is riveted to it.
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FEAMES
11
The frame has to be fitted with wheels and springs. The
axles revolve in boxes, either made entirely of gun metal or of
pressed steel lined with brass or gun metal. The practice of
making axle boxes of cast iron has long since been given up.
At one time they were forged under a steam hammer ; but about
1872 the late Mr. John Haswell, locomotive superintendent of
the Austrian State Eailways, invented and constructed a very
powerful hydraulic forging press in which axle boxes, cross heads,
and such like were pressed out of white hot steel billets, at the
rate of about half a minute for each. An axle box is shown
diagrammatical ly in Fig. 17.
To the plate frames are bolted steel castings or forgings
called horn plates, in which
the axle boxes can move up
and down through a range
in Great Britain usually of
about 2 inches, in France,
often of nearly twice as much,
the springs being longer and
more flexible than in Great
Britain. When plate springs
are used, they either rest
directly or through the medium of struts on the tops of the axle
boxes as shown in Fig. 2. In some cases, however, the springs
are placed under the axle boxes and secured to them by links, as
in Fig. 17. Here A is the axle, B brass, C axle box, F the
spring, the ends of which are supposed to rest on rubbing plates
under the frame. The spring is coupled to the axle box by the
links E and the pin D. An example of the overhead spring is
given in Fig. 2. Coiled springs are favoured, because they save
space. They are invariably worked in compression.
In the United States almost always, in this country frequently,
the ends of springs are coupled to each other by what are known
as balance beams or compensating levers. An example is shown
in Fig. 18, which illustrates a portion of an American bar
frame locomotive. A is a compensating lever; at C is seen
the end of another lever. In this way stresses are eased, and
Pig. 17.— Axle-box.
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12
THE EAILWAY LOCOMOTIVE
the engine runs more smoothly. For let it be supposed that
each spring works by itself, and has no connection with its
fellow; then it is easily understood that when a wheel is passing
over the summit of a wave in the rail, a large part of the load
will be taken off a neighbouring wheel in a hollow, and a corre-
sponding stress will be thrown on the whole frame, &c. If,
however, the ends of the springs are coupled by a balance beam,
then a portion of the extra load on the first spring will be trans-
ferred to the second, and the engine will run with more flexibility.
The risk of breaking springs or axle boxes is besides much
Fig. 18. — Compensating lever.
reduced. Many engineers in this country hold, however, that on
a first-class road balance beams are quite unnecessary ; and, by
imparting too much resilience to the engine as a vehicle, tend to
promote rolling and pitching, and even to make it unsafe at high
speeds. When, however, an engine encounters a steep incline
which does not "melt into the level" as it ought to do, the
leading springs may have so much extra load thrown on them
that they will break. Again, in running off the incline on to the
level again an extra load may be thrown on the driving wheel
springs. The evil has in some cases been so pronounced that
the road has been improved by modulatina the incline at the
instance of the locomotive superintendent.
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FBAMES 13
So far only vertical stresses have been considered, and the
vehicle has been supposed to traverse only a dead straight road.
We have now to regard it from another aspect. Eailways abound
in curves, and these have to be traversed at various speeds,
sometimes very high.
The smallest locomotives, such as are used by contractors on
civil engineering works, alone have four wheels and no more.
Until a comparatively recent period all but exceptional engines
were carried on six wheels. The practice then arose of carrying
the leading ends on a four-wheeled bogie, and this gave eight
wheels. A further increase in length brought in a fifth pair
under the footplate. An addition in size gave six coupled
driving wheels instead of four. The practice has recently grown
up of indicating the number of wheels thus: 2 — 4—2, which
means 2 leading, 4 driving, and 2 trailing wheels. Again,
4 — 2 — 2 means a 4-wheeled bogie, 2 driving wheels and 2
trailing wheels, and so on. In goods engines as many as twelve
coupled wheels are used, for the most part in the United States,
where at certain seasons of the year trains carrying as much as
2,500 to 3,000 tons of grain are hauled at speeds of ten or twelve
miles an hour from eastern corn lands to western seaports.
The so-called wheel base of a locomotive is the distance from
the centre of the leading to the centre of the trailing axle ; the
wheels are all firmly secured on the axles by forcing them on by
hydraulic pressure, so that they must turn together. The end-
wise play of the axles in their bearings, and of the boxes in the
horn plates, is but a fraction of an inch. When the engine
stands on a curve, in order that all the wheels may fit it the frame
ought to bend to the same radius as the curve. This is im-
possible, yet it would also be a mechanical impossibility for a
rigid vehicle with six wheels to get round a rigid curve if the
flanges of the wheels fitted the rails closely. The difficulty is
overcome in various ways. In the first place the rails are always
about half an inch wider apart than the distance between the
flanges. This distance is increased to about an inch on sharp
curves. Secondly, one or more pairs of wheels about the mid-
length of the engine are sometimes made ** blind," that is to say.
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14 THE EAILWAY LOCOMOTIYE
they are without flanges. Thirdly, one or more of the axles are
provided with boxes which can slide right or left in the horn
plates, a couple of inches each way. They are kept normally
central by strong coiled springs ; and lastly, there is the bogie.
Any reader interested is advised to set out a curve on a
drawing-board and set out a vehicle on it. He will see that no
matter how many wheels the vehicle has, it will do its best to
arrange itself as a chord to the arc. Now a four- wheeled vehicle
can always do this without trouble, and the axles will approxi-
mate in position to radii of the curve. In this country it may
be taken that the minimum radius of curves traversed at any
but the very slowest speed is about 6 chains, or say 400 feet.
Let our four-wheeled vehicle be a bogie with a wheel base of
6 feet; it will be seen that to all intents and purposes both
axles are radii to the curve, with an approximation to the truth
so close that the difference must be measured by small fractions
of an inch. Such a curve, therefore, could be traversed by the
bogie almost as easily as if the track were straight. If now we
take an engine with four wheels coupled near one end, and
support the other end on a bogie, all the axles will virtually
radiate to the centre of the curve. But a horizontal centre line
drawn through either a pair of coupled wheels or a pair of bogie
wheels will be a tangent to the curve, as the engine frames
extend for several feet in advance of the leading pair of driving
wheels, and, being a tangent to the curve, it follows that a central
line prolonged along this tangent cannot fall on the centre of the
bogie, but at some place outside it. Thus to get the best results
the whole bogie must be able to move inwards, or, what comes
to the same thing, the engine frame must be permitted to retain
its tangential position while rounding the curve.
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CHAPTER II
BOGIES
At first sight the hogie appears to be a very simple thing whose
action can readily be understood. In point of fact, however,
this is not the case, and the bogie plays so important a part in
the present day that both the theory of it and practice with it
Fig. 19. — Bissell bogie.
deserve very careful consideration. It originated in the United
States. It is claimed for it that it was an English invention,
because small four-wheeled coal mine trucks were called "bogies."
But in the United States what we term '' bogies" always were
and are still called ** trucks." The first railways made in
America were very bad indeed, much worse than English rail-
ways, and the four-wheeled locomotives were continually running
off the road, particularly on curves. It was decided then to copy
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16
THE EAILWAY LOCOMOTIVE
I
s
I
&
2
the ordinary horse-drawn
vehicle and fit locomotives
with a species of fore
carriage. For convenience
this was made at first with
four wheels, while the
engine proper had but two.
No traversing gear was
required, because the lead-
ing end of the engine could
follow the bogie round the
curve. After a time it was
found that coupled wheels
were necessary. Traversing
then became essential, and
Mr. Bissell, an American
engineer, invented the
** Bissell truck," which had
two wheels while the loco-
motive had four. His was
a very clever device much
used at one time in the
United States, and still
enjoying favour there. The
accompanying diagram. Fig.
19, will tell the reader
almost at a glance what it
is. It is a plan of an im-
proved ** pony " used on the
Great Northern Eailway.
As first used the pony had,
as stated above, but one
pair of wheels. Afterwards
four wheels were employed
and it ceased to be a pony.
In this country it was fitted
to all the locomotives
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BOGIES 17
designed by the late Sir John Fowler for the Metropolitan
Railway. We have only to substitute a bogie with four
wheels for the single pair in Fig. 19, and the description will
apply. A frame A enclosed the axle; to the back end of the
frame was bolted a heavy flat bar triangle or tail D; through
the eye on the end of this passed a bolt C ; and round this
bolt as a pivot the truck could describe an arc, swaying to the
right and left. It was essential, however, that it should always
tend to keep in the centre line of the engine. To ensure this,
the axle casing was fitted at the forward end with flat trans-
verse plates provided with inclined planes. The cross beam
under the engine was fitted with similar planes B which rested
on those first named.^ Whenever the bogie moved to the right
or the left it had to lift the leading end of the engine, which,
tending to slide down the inclined planes, always returned the
truck to its normal position as soon as the locomotive, having
passed over the curve, entered the straight again. In the United
States a somewhat different arrangement is in use. The leading
end of the engine is hung by links from the bogie, which
virtually shorten, as the engine moves to left or right, in a way
quite obvious. The modern bogie is only a modification of the
original. Figs. 20 and 21 show a bogie on the Great Northern
Eailway fitted with swing links.
A A are the cylinders, S the valve chest. The cylinders, and
with them the leading end of the engine, rest on a heavy casting D
circular in plan to allow the bogie to turn round the pin P. This
iron casting rests in turn on one of steel M. This casting has
no power of traversing — it may be regarded as part and parcel
of the engine. B B shows one of two cross beams. The
entire weight of the leading end of the engine is supported
by four links L L, and will always tend to return to the
position shown, just as a pendulum seeks its lowest position.
Traversing is obtained very simply in this way. A saucer-shaped
steel plate is pinned on the bottom of the upper casting, and a
1 In the Great Northern pony, the spring pedestals rest directly on the tops
of the axle boxes E. The circles show the enlarged ends of the pedestals
made of brass to reduce friction.
R.L.
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18
THE RAILWAY LOCOMOTI\^
B
similar plate is laid under it in M. This permits the bogie to
rock. One corner may rise while another falls, in a way that
will be explained further on.
It is desirable that the reader should clearly understand what
a complete bogie is like, which it is not easy to do from sectional
drawings. To this end Figs. 23 and 24 are given. The bogie
frame is usually a built-up structure like an engine frame. If,
however, it could be produced with a less number of riveted
and bolted joints a substantial advantage would be gained. The
Leeds Forge Company, Limited, has for years turned out great
quantities of flanged furnaces, &c., the
flanging being done by an hydraulic
press in a way whiph will be understood
from the annexed diagram (Fig. 22).
Here A is the plate to be bent, let
us suppose, to the shape of the lid of
a pill box. C is the hollow top of a
hydraulic press of which D is the ram.
B is a fixed circular block, just as much
smaller all round than C as the plate is
thick. The fiat circular plate is heated
to a dull red heat and placed as shov/n.
Then the ram is pumped up, and the plate is forced into C, curling
up all round the edges without crumpling or buckling. Of course
a trough could be made in the same way by using a long mould
and several hydraulic rams. The system is in use all over the
world ; but certain firms make a speciality of pressed work. The
Leeds Forge Company includes bogies of all kinds. Figs. 23 and
24 illustrate two standard wagon bogies made of pressed steel.
Fig. 23 is an open-ended bogie ; the sides are united by the
cross beams near the middle. On the top of these is bolted a
casting with a circular boss. A similar boss is bolted under the
wagon body, which rests on it, a pin being dropped through
-i^etJ^TOl;l^d which the bogie swivels. As there is a bogie at each
end of tlt^ wagon no traversing motion is required. On each
side frameWe seen bearing blocks on which a part of the weight
is carried. Vhe axle boxes and the coiled springs in compression
3
Pig. 22. — Flanging press.
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BOGIES
19
Fig. 23.— Open end bogie.
Fig. 24. — Closed end bogie.
which transmit the load to them and the horn plates are all very
clearly shown. Fig. 24 is a wagon bogie with closed ends and
leaf instead of coiled springs. It is not fitted with brakes ; the
open-ended bogie, Fig. 23, is. The hinged hanger gear for them
can be seen bolted to the cross beams. An enormous number of
c2
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20
THE RAILWAY LOCOMOTIVE
pressed steel bogies is in use; the Leeds Forge Company alone has
made 15,000 of them.
Figs. 25, 26, and 27 illustrate a standard engine bogie designed
by Mr. James Holden, locomotive superintendent of the Great
Eastern Kailway. Traverse is controlled, not by metallic springs.
Fig. 25.— Standard bogie, Great Eastern Eailway.
but by indiarubber discs, which Mr. Holden prefers because
they deaden the shock when an engine takes a curve. Engines
fitted in this way ride very easily. Sliding takes place on the
surface B. There is a cushion of indiarubber, C, between A and
the sliding portion above the top of the surface B. The amount
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BOGIES
21
Fig. 26. — Standard bogie, Great Eastern Eailway.
of traverse is IJ inches. The slide is controlled by the six india-
rubber pads shown in the sections. The casting A is bolted
Fig. 27. — Details bogie, Great Eastern Eailway.
to the main frame, A^ being one of the bolts used for this
purpose.
On the Great Western Eailway Mr. Churchward uses a bogie
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22
THE EAILWAT LOCOMOTIVE
which is a modification of Mr. Ivatt's on the Great Northern.
Swing links are employed to give traverse. Fig. 28 illustrates
this bogie as fitted to Mr. Churchward's latest design, the four-
cylinder simple engines of the Star class working the heavy
long-run West of England express. A strong casting A, closely,
resembling an old Greek seat or stool, with four curved legs, of
which two are shown by B B, is bolted to the front end of the
engine and drops down between the bogie frames. Four links C
unite A with the bogie. So far we have the ordinary swing link.
The difference lies in the use of double suspension pins D D,
Fig. 28. — Swing link bogie, Great Western Eailway.
one in each of the elongated holes. On the straight the engine
is carried on both pins. When a curve is taken the lower end
of C is swung on a curve to the right or left. The link then
leaves one pin and is carried only by the other. The condition
is then one of unstable equilibrium, and the front end of the
engine being raised it tends to fall and restore the link to a
bearing on both pins D D. The Great Western bogie is fitted
with the vacuum brake, the mechanism for which crowds all the
available space, and this arrangement is found more convenient
than the two inclined links of the Great Northern. The pins
D D run fore and aft between two cross beams uniting the two
side frames of the bogie.
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BOGIES 23
Three typical bogies have now been illustrated. Those used
on other railways only differ from these in details, as, for example,
the use of coiled or leaf traverse springs instead of indiarubber
pads.
Eeference must be made here to a very noteworthy express
locomotive designed by the late Patrick Stirling while locomotive
superintendent of the Great Northern Eailway, about 1872, which
represented an exception. A number of engines built to this
design carried on the express trafl&c of the line for several years
with the utmost success, until, indeed, they were overcome by
the increasing weight of the trains which they were called upon
to haul. They had " single " driving wheels — that is, only one
pair — 8 feet 1 inch in diameter, with new tires, and outside
cylinders 18 inches diameter by 28 inches stroke — at the time
probably the largest locomotive cylinders in the world, certainly
the largest in Great Britain. A pair of trailing wheels 4 feet
1 inch in diameter was placed under the footplate. The leading
end of the engine was carried on a four-wheeled bogie, with
wheels 3 feet 11 inches in diameter and 6 feet 6 inches between
the axles. This bogie was altogether remarkable and excellent.
It had no traversing arrangement ; no springs to restore it to the
normal ; no complications of any kind, and yet it did, up to a
certain point, all that the most complex bogie can do. It
swivelled on a pin like other bogies, but this pin was not put in
the centre of its length, but 6 inches nearer to the hind than the
front axle. If the pin had been placed in the centre of the length
of the bogie then the leading wheels could not follow the curve,
because the leading end of the engine would pull the whole bogie
outward. As, however, the pin was placed far back, then the
centre point in the length of the bogie could move inwards, which
is precisely what the traversing gear already described is intended
to permit, and the moment the curve had been traversed the
bogie would automatically set itself normal to the road. For
very sharp curves the amount of traverse which can be had in
this way is, however, not sufficient, but on the Great Northern
these engines ran with a minimum of resistance. D. K. Clark,
writing of them, says : " The bogie leads better in having the
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24
THE EAILWAY LOCOMOTIVE
Fig. 29. — Traversing leading axle, Lancashire and Yorkshire Railway.
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BOGIES
25
leading wheels better in advance than if the pivot were equi-
distant between the axles. Not only do the leading wheels turn
to the curve with greater facility, but the hind bogie wheels make
less transversal movement towards the outer rail, and in so much
the guiding of the engine is eased."
The place of the bogie is in some cases taken by the traversing
axle box, which has assumed several forms. One of the best was
that invented by the late W. Bridges Adams, and successfully
used on many railways, among others the London, Chatham and
6'
Fig. 30. — Mr. Baldry's rule for finding the centre from which
to stiike the curve of a radial axle box.
Dover, and the Metropolitan extension. Fig. 29 illustrates a
traversing leading axle as used now on the Lancashire and York-
shire Eailway. The axle C is enclosed in a curved casing or
inverted trough A, which carries at each end the axle box. The
spring strut is shown by D. Its lower end drops into a brass
foot or pedestal which rests on the flat top of the axle box, which
moves under it as the engine takes a curve. A is in the same
way enclosed in a trough B, which is part of the cross framing of
the engine under the smoke box. Suitable guiding faces are
provided on and in the two troughs ; consequently the leading
wheels can move freely right and left in a curve the length of the
radius of which is that of the curve of B. To regulate and
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26 THE EAILWAT LOCOMOTIYE
control the amount of the traverse, and to supply the necessary
effort required, as just explained, to get the engine round a curve,
a species of box E is fitted on the lower part of B, so as to clear
the axle. In this is placed a coiled spring. Through the spring is
passed a bolt G, the ends of which are secured, as shown, to cross
heads H H bolted, as shown, to A. Cast iron blocks are placed
at each end of the coiled spring, and on these it bears. Brass
ferrules F F are interposed at each end, between the cast iron
block and the cross head. The spring is put in with some initial
compression. If now the axle traverses, the ferrule at one end
will be pushed in with the cast iron block away from I, and the
coiled spring will be compressed. Of course the same thing
occurs in reverse order if the curve is reversed. This arrange-
ment is typical of many others — in all the principle is the same,
the difference is in details. The rule for finding the centre from
which the curve of the axle casing is struck is given by Mr.
Baldry ; x is the length of the radius wanted. The diagram.
Fig. 30, explains itself.
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CHAPTER III
THE ACTION OF THE BOGIE
Leaving now the construction of the bogie, let us consider what
it does, how it behaves on the road, its merits and demerits.
In theory the bogie facilitates the movement of an engine
round a curve. The entire weight of the leading end of the
engine is distributed over four wheels instead of two, and the
bogie's action is to consolidate the track by sending the sleepers
down to their bearings on the ballast in advance of the driving
wheels. All this is meritorious to a very high degree ; and it
has been plainly stated that the bogie greatly reduces the
chance of derailment, and indeed enables curves to be traversed
which without its aid would be quite inadmissible. So long as
speeds are moderate all these propositions may be accepted as
true.
It is, however, a fact worth notice that in former years derail-
ments seldom occurred with serious results. The cause of them
was almost invariably obvious. A rail was broken or the ballast
was defective, or points were wrongly set. The worst accidents
were collisions. In the present day the worst accidents are due
to derailment, and in notable instances no satisfactory explanation
has been forthcoming to account for the engine leaving the rails.
There are large numbers of locomotives still running which have
not bogies ; they appear to be exempt from mysterious derail-
ment.^ Under the circumstances it is not unfair to say that the
^ It is right to say here that many engineers maintain that there are no
such things as mysterious derailments, and that in far the greater number
of cases when an engine leaves the rails the fault lies in the permanent way
and not in the engine. The whole subject is dealt with statistically further
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28 THE EAILWAT LOCOMOTIVE
excellence of the bogie is open to question. We shall see
presently, when we come to consider the internal disturbing forces
of a locomotive, how these affect the bogie. For the moment we
must confine our attention to the external forces. We have seen
that these are of two kinds, vertical and horizontal. Of course
it is obvious that various combinations of both can take place.
The first is due to the absence of uniform level in the rails.
However carefully the platelayer may attend to packing up the
sleepers, the road always sinks under the tread of an engine, and
rises again when it has passed ; the amount of sinking is a
variable quantity. Again, the rails spring between the sleepers
under the tread of the engine. The rail tables are not dead true.
The result of all this is that, as has already been said, the loco-
motive continually moves on a road full of waves of varying
altitudes and lengths. It is true that they are very small waves.
It is none the less certain that they make themselves felt — how
much felt the traveller in a luxurious carriage little knows. A
full appreciation of the good and bad qualities of the permanent
way of any railway can only be got by standing on the footplate
of a locomotive for a couple of hours while it runs at various
speeds.
In by far the larger number of locomotives the entire weight
of the leading end of the engine, say sixteen tons, is carried on a
bolster crossing the bogie frame, in such a way that it acts at
the centre of the bogie frame only. Each of the four corners of
the bogie will represent four tons, and that — less the weight of
the wheels and springs — is the weight pressing down each axle
box on the journal. This load is transmitted outwards from the
fore and aft centre line of the locomotive. There is nothing
whatever, so far, to prevent any one corner of the bogie from
rising or falling. If the right-hand leading wheel goes down half
an inch, the centre of the leading end of the engine bearing on
the bogie bolster would fall half as much, and so on. The
behaviour of a four-wheeled bogie on the road is very interesting.
As fitted to passenger coaches nothing is easier than to watch it
when two suburban trains run side by side. As a rule a leafed
spring is fitted over each axle box. It will be seen, however, that
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THE ACTION OF THE BOGIE 29
these springs never bend. The bogie is continually on the jump
as a whole, wheels and all, but it plays about the centre pivot.
The axle-box springs are of no use; and, indeed, some bogies are
made without them, elasticity being obtained by the springs
between the cross bolsters of the carriage frame and the bogie near
the centre. It has never been disputed tbat the ease with which
all the four wheels take the same load and transmit it to the rail is
an excellent thing. Bogies relieve the stress on the permanent
way, and for that reason are in favour with the civil engineering
staflf of railways ; but it will not do to forget that this very
freedom of motion may be a direct source of danger. It will not
do to leave the leading end of the engine to wander from side to
side. The bogie itself, too, is liable to '* get across the road."
Its wheel base is short, and unless special precautions are taken
it may " wobble " — there is no better word — as it runs, and the
wobbling may throw the flanges of the wheels to the right and
left alternately with such violence that the wheel may escape
from the rails. Many engineers, therefore, insist that the wheel
base of a four-wheeled bogie shall be made at least half as long
again as the gauge is wide. In this country and in the United
' States 6 feet is a very usual wheel base, but on the Continent,
and notably in Austria, a wheel base of as much as 9 feet is
favoured.
It is right at this point to bring a fact into prominence which
is frequently overlooked — it is that all the principal parts of a
locomotive possess a great deal of mass ; in popular phrase, they
are very heavy. Mass is the complement of momentum, and
the stresses set up in starting and stopping motion are corre-
spondingly severe. Thus, if from any cause, such as crossing
points, &c., the leading or trailing end of a bogie is violently
flung right or left, although the distance traversed may not
exceed three-quarters of an inch, yet there will be quite momen-
tum enough to cause a jerk and a recoil, and it may easily happen
that a very free and easy bogie may give a very unsteady, lurch-
ing engine at high speed.
Hitherto we have been considering the behaviour of a bogie on
a straight line. We have now to consider the behaviour of the
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30 THE EAILWAY LOCOMOTIVE
bogie on a curve, a thing of the utmost interest in its relation to
the rest of the locomotive. The modern bogie is always, as we
have seen, permitted to traverse under the engine. If the bogie
is quite free to traverse across the engine it is clear that it can
do nothing to guide the engine round a curve. That duty would
then devolve on the driving wheels, or at all events on the wheels
next behind the bogie. But the bogie is never quite free. It is
always returned to the central position by inclined planes, swing
links, or springs shown in the illustrations. A compromise is,
in short, effected between perfect freedom of traverse and
absolute restraint of lateral motion ; and the result is that the
bogie guides the leading end of the engine round curves. To do
this requires an effort, the amount of which varies as the square
of the speed and the radius of curvature. In popular language,
the bogie has to overcome the centrifugal force acting on the
engine. Inasmuch as a good deal of confusion of thought
exists about all this, even among very well informed persons, it
is necessary here to go into some explanatory details.
It is an axiom of dynamics that a body moving freely in space
under the action of a single force will describe a straight line.
If it is to describe a curve of any order another force or forces
must also act upon it. An engine traversing a curve does not
want to fly outward, but to move straight on. It is not that the
engine would leave the line, but that the line leaves the engine.
The effort of the engine is to pursue a straight course which is
always a tangent to the curve; there is no effort at radial
departure made by the engine.^
The bogie then must keep on sluing the leading end of the
engine round the curve, while the trailing end is similarly worked
on by the other wheels. To calculate the centrifugal effort of
every portion of a locomotive on a curve would be a tedious and
a profitless task. In practice the whole "mass" of the engine
^ It is for this reason that a locomotive running at speed is never derailed
radially. It runs off the line obliquely, and in many instaiices a derailed
engine has continued its course for several yards along the sleepers quite
close to the rails. This is just what might be supposed to happen if by any
agency the rails were suddenly pulled away to one side from beneath the
wheels.
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THE ACTION OF THE BOGIE 31
is supposed to be concentrated at the centre of gravity, and the
centrifugal stress can be determined by a very simple calculation,
W V^
C = ^^ T) . Here C is the centrifugal effort which must be over-
come to make the engine follow the curve, W is the weight of the
engine, V^ its velocity in feet per second, E the radius in feet
of the curve. In other words, the effort required to keep the
engine moving round the curve is equal to its weight multiplied
by the square of the velocity and divided by 32*2 times the radius
of the circle of which the curve forms a part.
Let us suppose that the curve has a radius of 600 feet, and
that the engine is running at thirty miles an hour, or 44feefc per
second, and its weight is fifty tons. Then the effort required to
keep it on the rails and prevent it from flying off at a tangenfc
will be approximately five tons. If the speed were sixty miles
an hour then the necessary centripetal effort would be twenty
tons, and so on. Now the effort must be distributed among the
wheels, and only those whose flanges can get access to the rails
can take it up. It may easily happen that the distribution is not
uniform. Thus, if an engine is fitted with six wheels and a four-
wheeled bogie, both the bogie-wheel flanges resting against the
inner side of the outer rail will act. So will the first and last
wheel of the six wheels, but the middle-wheel flange cannot touch
the outer rail unless one or both of the other two are fitted with
a traversing arrangement or its equivalent, such as a blind tire.
It will be seen that while "blinding" tires gives freedom of
motion round a curve it also augments the stress on the flanged
wheels.
Although it simplifies calculations to refer the whole effort to
the centre of gravity of a locomotive, really the stresses are
distributed about it in a very complicated way impossible to
follow as a whole. Thus, for example, we have to keep in mind
that the complete engine has not only to get round the curve,
but that it is also continually rotating round its own longitudinal
centre of gravity. Very complicated mathematics are involved,
and the result after all is fortunately not needed. The general
rule to be observed is that as many wheels as possible shall act
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32 THE EAILWAY LOCOMOTIVE
on the outside rail to resist the tangential effort of the engine to
leave the line. It is, however, often assumed that if the leading
wheels radiate to the curve, the engine will follow just as a
motor car does when steered to right or left ; but the analogy is
far from perfect, because first, in the motor car, there is only one
pair of wheels to follow the lead, and the differential gear permits
the outer wheel to move just as much faster than the inner wheel
as corresponds to the extra distance which it has to pass over ;
but besides this, the motor car is subjected to centrifugal effort
just as the locomotive is, and the effort may suffice to skid the
car across the road, producing side slip which is the analogue of
derailment.
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CHAPTER IV
CENTRE OF GRAVITY
So far, although the subject has been treated as though the
whole effort has been concentrated on the centre of gravity of the
engine, nothing has been said concerning the position of that
centre. For anything to the contrary it might be at the rail
level, and the outward thrust of five tons named above might be
supposed to be exerted directly on the inside of the rail. In
point of fact the conditions lack this simplicity. The vertical
centre of gravity is somewhere between 4 feet and 5 feet above
the rails, according to the design of the engine. The centrifugal
effort consequently tends not only to make the engine leave the
rails, but to upset it. Overturning will take place, if at all, on the
outer rail as a pivot, and complete upsetting cannot occur until
a vertical line drawn through the centre of gravity falls outside
the rail. Regard the triangle C E F, Fig. 31, as a solid block
standing on a table. Then C represents the base, on the width
of which, as compared with the height, the stability of the triangle
depends.
At one period in the history of the locomotive it was held to
be good to keep the centre of gravity low, because upsetting was
feared ; but it has long been recognised that while the chances
of an engine overturning are very few, a rise in the centre
of gravity confers substantial advances, which may now be
considered.
In the diagram, Fig. 31, let the arrow A indicate the centri-
fugal effort supposed to be concentrated at the rail level. Let
this effort be represented by screw jacks, A and D, laid on their
sides, one for each wheel, tending to force it off the rail. The
resistance to derailment will then be measured by the stress with
B.L. D
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34
THE RAILWAY LOCOMOTIVE
which the wheel presses down on the rails due to gravity^ and
it will be resisted by the chairs and keys supporting the outer
rail, B.
Next let the screw jacks, as represented by the arrow D, act
at a level 4 feet 6 inches above the rail ; we then have, instead of
a single stress, two. The first as before horizontal, and the
second exerted along the inclined line E. It is easy to see that,
by the ordinary laws of the composition and resolution of forces,
the whole derailing effort is concentrated along the line E. The
Fig. 31.— Centrifugal efPort.
result is that the load on the outside wheel is much increased,
that on the inside wheel much diminished. The effort to burst
the track is reduced, and the resistance to derailment augmented.
But it must not be forgotten that while the chances of derailment
are minimised the risk of overturning is increased. Mr. John
Audley Aspinall, while chief mechanical engineer of the Lanca-
shire and Yorkshire Eailway, of which line he has been general
manager for some years, in the course of a report on the
^ In the sense that the greater the weight, the greater the effort required
to force the flange over the rail.
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CENTEE OF GRAVITY 35
type of locomotive most suitable for high speed, presented
to the International Railway Conference some ten years ago,
wrote : " The oscillations of an engine with a high centre of
gravity will be longer than those of a low engine. It will
also ride easier, owing to the elasticity of the springs being
brought more into play. This is also conducive to the
reduction of side shocks and the stresses in the wheels and
axles are minimised. It must not, however, be overlooked that
the higher centre of gravity, when passing round a curve, causes
the load on the inner rail to be diminished, and as the front
end of the engine is liable at any time to be thrown violently
to the inside it will have a tendency to leave the road if the
super-elevation of the outer rail is excessive. The effect produced
by raising the centre of gravity will be readily understood if the
reader will compare No. 1 and No. 2 and the relation which C
bears to E in each."
Other things being equal, the lower the centre of gravity
the greater the chance of derailment due to centrifugal effort,
and the less the chance of overturning, and vice versa. Now in
practice curves traversed on main lines at high speeds have
radii so great that the chance of overturning is very small,
and a high centre of gravity gives an engine which runs easily
and does not stress the road sideways. The reason is that
the vertical component of the centrifugal effort tends as shown
to compress the outer and relax the inner springs. In other
words, if the derailing effort were concentrated at the rail level,
there would be no resilient resistance offered to it; but the
elevation of the locus of effort bringing the springs into play eases
the movement round the curve. For the mere purpose of
explanation or calculation it is assumed that every portion of
the engine traverses a true curve in a determinate circular path.
In practice, however, this is very far from being the truth. A
locomotive always gets round a curve in a series of jerks, so to
speak. It is as though the permanent way represented a
polygonal instead of a circular path. Why this should be,
and the influence of small matters of detail in design and
construction, must now be explained. To do this it is necessary
d2
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36 THE EAILWAY LOCOMOTIVE
to consider the effect of an expedient universally adopted to
add to the safety and improve the running of railway vehicles
round curves. The outer rail is raised above the level of the
inside rail, the amount of super-elevation is given by the
formula E = W ..^^ -p . Here E is the super-elevation in inches,
W the gauge in feet, V the velocity in miles per hour, and E
the radius of the curve in feet. For moderate curves plate-
layers work to a rule which is sufl&ciently exact for ordinary
railway practice. They stretch a 66 feet tape as a chord of the
curve, and then measure the distance between the tape and
the rail at 33 feet ; that distance is the super-elevation. The
purpose served is precisely that with which a cyclist turning
a corner or racing round a circular track inclines inwards.
Eacing tracks are indeed very steeply inclined when the turns
are sharp. Unfortunately the super-elevation that is suitable
for one speed must be too great for a lower speed, and too
little for a higher speed, and that not only as the speed, but
as the square of the speeds. In practice the super-elevation
is ** jimmered" — that is to say, a compromise is arrived at, the
tendency being to make the super-elevation too great. So far
nothing has been said about wheels. They will be more fully con-
sidered presently. For the moment it is enough to say that when
tires are new they are slightly conical. The inclination is usually
one in twenty. The object is to keep the flanges away from the
road as much as possible. Let us suppose that the difference in
the inner and outer diameter of a 6-foot wheel is 0*4 inch, then
the circumference will be a little over 1 inch greater inside,
next the flange, than outside, and the difference between the
two circumferences will be about 2 inches. The outside wheel
on the curve therefore has a longer distance to traverse per
revolution than the inside wheel, and this of course tends to
compensate for the trouble due to the wheels being rigidly
secured to the axles, but in practice we find that, thanks to the
super-elevation and the coning, the wheels continually slip
across the rail tops, moving outwards and then inwards. In
a word the whole traverse of a curve is always effected, as stated
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CENTRE OF GRAVITY 37
above, in a series of jerks, the violence of which depends on the
condition of the road, of the tires, of the axle boxes and springs,
and of the good or bad qualities of the design. In some cases
the engine " rides " like a coach, the slipping being almost
imperceptible, in others the action is very disagreeable and
injurious to the track.
One more adverse influence has to be explained, that is
to say lurching or rolling. It can best be illustrated by a
practical test. If the reader will stand on a railway platform
and watch an engine coming towards him at speed he will
see at once what takes place. Indeed, if the road be not in
perfect order and the engine well designed, he may now and
then feel a little surprise that derailment does not take place.
But the essential condition of safety is that the wheels should not
lift oflf the rails. The rolling and jerking and pitching all take
place, be it remembered, above the wheels. These last are always
practically, at least in so far as all but the drivers are concerned,
in contact with the rails. The movements of the engine above
them are at once controlled by the springs and due to them,
and therefore the ** springing " of an engine is a very nice
question of design, as on it a great deal depends. Diversities of
opinion exist as to the amount of resilience permissible. The
maximum range of motion allowed in an axle box in this country
is, as has already been stated, about 2 inches ; abroad it is almost
always 3 inches, not infrequently 4 inches. But balance beams
or compensating levers profoundly afifect the range.
So far we have confined our attention to the engine only, but
the engine when at work is either coupled to a tender or a train.
In the former case, two buffer heads, actuated by a powerful
cross spring or two helical springs under the tender, rest
against the transverse hindermost plate of the engine framing.
The tie bar between the engine and tender is secured by a pin
dropped into eyes in a casting under the footplate provided for
them. The result is that the engine and tender resist lateral
bending effort, and so the stress when passing round a curve
is increased. The same thing happens when a tank engine is
tightly coupled to a train.
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38 THE RAILWAY LOCOMOTIVE
A review of all the conditions shows that a locomotive engine
and tender are specially contrived to run straight on straight
roads ; and that although devices are provided to permit the
lateral flexure required to traverse a curve, yet that all these are,
regarded from one point of view, of a nature to favour derailment,
and that so powerfully that a mistake might easily render it
impossible for a locomotive to traverse curves of even great radii
without risk. Thus, for example, a long six-wheeled engine tight
to gauge could not get round if the controlling springs of a
traversing axle were too stiff and unyielding. It may be added
that the conditions are so variable and complicated that minute
calculation is set at defiance, and the lateral resistance put in is
settled by the results of experience, and it is never made greater
than will just suffice to meet the conditions.
Before leaving this section of our subject it is worth while
briefly recalling to the reader's notice a few important facts. In
the first place, as has been already set forth in Chapter I., if a rail-
way were absolutely level and smooth, and the wheels truly
cylindrical, springs and bogies would not be needed. At the
most, indeed, india-rubber blocks interposed between the axle
boxes and frames to deaden vibration could satisfy all the
vehicular conditions. Secondly, the railway of reality is curved.
It is not level and it is not smooth. The task of the designers
and builders of locomotives is not only to produce a machine
which can pull a train, but to reduce to the lowest possible point
the effects of the external disturbing agencies due to the imper-
fections in the road. It is not enough in getting out a design to
put in sufficient boiler power, an excellent engine, and so on.
The locomotive as a machine which has to traverse an imperfect
road at a very high speed is a much more important considera-
tion. It will not do to say of a given engine that it is more
economical of fuel than any other on a given line, if it is feared
that it will ran off the track if driven at more than 50 miles an
hour. This, it may be added, is in no way a fancy picture ;
many engines of the kind have been built. Take, as an example,
the Great Liverpool, a very powerful engine designed by the late
Mr. Thomas Crampton many years ago. The engine could not
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CENTRE OF GRAVITY 39
be used because it broke the rails. In the present day, a wide
difference exists among locomotives doing the same work at the
same speeds, some being much lighter on the permanent way than
others. It has been said of a big engine that " she never got
through a week without breaking a rail." Too much stiffness,
too much flexibility, bad springing, bad distribution of weight,
and various other factors which will be dealt with when we come
to consider the internal disturbing forces of a locomotive
contribute to the unhappy result.
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CHAPTER V
WHEELS
Obviously, the wheels of a vehicle are an important part of it.
It is time now to speak in some detail of those of a locomotive.
In the earlier history of locomotives they were made of cast iron,
round which a wrought iron tire was shrunk on ; the tires were
rolled in straight bars, cut off in lengths, scarfed at the ends,
bent into rings and welded. They frequently broke at the weld.
It is said that in the early days of the London and Birmingham
Eailway a driver of an up train at night, when passing Tring, felt
the engine jump, but nothing more happened except that she ran
roughly the rest of the trip to London. On going round with
his lamp at Chalk Farm he found that one of the driving-wheel
tires had come off. The journey was completed on the wheel
centre. The tire was found in the ditch next day near Tring.
Very dreadful accidents have resulted from broken tires.
Many years have elapsed since a method of producing tires of
solid steel without a weld was invented, and tires so made are
invariably used now. A suitable steel billet or ingot is forged
into the shape of a cheese under a heavy steam hammer.
Through the centre of this steel cheese a succession of punches,
larger and larger, are driven until the cheese has become a very
thick ring. This is heated and placed on the beak of a special
anvil, and forged out until it is perhaps half the finished
diameter, and is then put on to the central vertical roller of a
very powerful machine.
There are various tire-rolling machines in use. It will suflSce
to illustrate one of the latest type, which is made by Messrs.
P. E. Jackson & Company, Limited, Salford, Manchester. In
the space at disposal it is impossible to illustrate the details of a
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WHEELS
41
illlH
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42 TflE fiAlLWAY LOCOMOTIVE
very large and complex machine ; only the outline is given on
page 41, Fig. 32. It is 20 feet 6 inches long on the floor line,
and about 15 feet high from the base. The tire, whatever its
diameter, is laid on a horizontal circular table A. The tire is
first roughed out between the two rolls to the section marked B ;
then the table is raised and the tire is passed through the
grooves C, and again through the grooves D, and so finished.
Described more in detail, these mills roll tires up to 9 feet
diameter. The tires are rolled on a horizontal table, the rolls
being vertical, and having two to four grooves for roughing and
finishing the tire at one operation. The table carrying the tire
is adjustable vertically to suit the rolls. This adjustment is
quickly made through a hydraulic cylinder and suitable gearing.
The table is fitted with rolls for carrying the tires, and with a
movable carriage moved back by the tire as it enlarges, and
carrying a top roll, assisting to keep the tire true ; also with side
rolls working on slides. A very sensitive gauging apparatus is
provided for indicating the size of tire, the pointer and index
being on the front side of the main frame. The levers and
handles are also on the same side and placed as most convenient
for use. In some cases the main or large roll is cast complete
and the grooves turned in it, the roll then being changed for
different sections, or, as is now more general, the centre of the
roll is a forged steel shaft, and loose rolls for the various sections
are put on it. These loose rolls are readily changed for the
various sections. The smaller roll working inside the tire is
quickly raised and lowered by a hydraulic cylinder. The large
roll moves in and out a distance of 21 inches, allowing for the
changing of the loose rolls and the greatest thicknesses of tire
blooms. The roll is carried by bearings at top and bottom on
strong slides worked by screws in the main frame. The slides
have a slow speed for the rolling pressure and a quick speed for
bringing the rolls up to the work and for reversing. The roll is
turned by a large bevel wheel at the foot, driven by a steel bevel
pinion on the shaft running under the main frame to the driving
wheels at the engine.
The mill consists of a cast iron main frame, fitted with strong
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WHEELS 43
slides and screws for moving the main roll shaft in and out, the
slides forming the bearings for the roll. The main frame carries
the bearings for the small roll, and is provided with a bracket
and hydraulic cylinder for lowering and raising this roll in and
out of the tires. The frame also carries a double cylinder engine,
8-inch cylinders with quick spur gear and slow worm gear for
working the slides (carrying the roll shaft) in and out. The roll
shafts are of steel, the shaft for the large or main roll, i.e., the
roll working on the outside of the tire, being 13 inches in
diameter at the bottom bearing, and it can be made up to
11 inches diameter of top bearing. The shaft for the smaller
roll, i,e., the roll working on the inside of the tire, can be made
up to 11 inches diameter in the top bearing. The large roll
shaft is also supported on a cast iron sliding footstep and stand,
and is provided with a steel bevel wheel about 6 feet diameter
and steel pinion about 2 feet 9 inches diameter, 5-inch pitch,
14 inches wide.
The positive screw motion for forcing the rolls together during
the rolling ensures an even thickness and full section and true
rolling of the tire, which is said to be lacking in mills with only
a hydraulic forcing motion. The hydraulic motion is found to be
more or less yielding, and to give unequal thicknesses and hollow
places on the surface of the tire. About 100 wagon tires can be
made per day.
As far back as 1835, John Day invented and patented a method
of making railway wheel centres which was universally adopted
and remained in use until a comparatively recent period. He
welded up, in wrought iron, f-shaped pieces, each of which formed
a portion of the circular rim, one spoke and a part of the hub or
boss. The whole was gradually welded up by highly skilled
wheel-smiths. The hub being first completed, the ends of the
portions of the felloes — the heads of the T's — did not abut
against each other, filling pieces called "gluts" being welded
between them. Very great care was required to secure sound
welds and a good finish, the forgings undergoing little dressing-
up after they left the smith's shop. The hubs were bored to fit
the axle, and turned up to a true circle. The tire was subsequently
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44 THE RAILWAY LOCOMOTIYE
shrunk on. The wheels were forced on to the axle by hydraulic
pressure and put in a tire lathe, by which they were made truly
cylindrical. Very beautiful workmanship distinguished rhost of
these wheels. About the year 1860, M. Arbel, a French iron-
master, greatly simplified the whole process. The separate parts
were stamped out in dies and then grouped. The whole was
raised to a welding heat. A white-hot cylindrical plate of iron
was put under and another over the inner ends of the spokes,
and the whole placed under an exceedingly powerful hydraulic
press and welded up at one blow, so to speak. Large driving
wheels required two heats to finish them. In 1862, in London,
Herr Krupp, of Essen, exhibited cast steel disc driving-wheels.
That is to say, the place of the spokes was taken by a disc, not
flat, but slightly curved in and out to give elasticity. They were
marvellous castings for the period, or indeed for any period.
What they cost, who can tell ? It was claimed for them that they
did not raise as much dust as spoke wheels. They were tried in
Germany, but nothing came of them.
For many years the wrought iron wheel has been given up.
It was very expensive to make and so full of centres of danger in
the numerous welds that it was easily superseded by cast steel
as soon as the steel founders had overcome the difficulties which
attend the production of all steel castings. These difficulties are
largely the result of the very high temperature at which steel
melts. One consequence is that the metal when poured attacks
the surface of the mould, melting the sand, and so not only
injuring the surface of the finished casting, but developing gases
which are occluded in the steel, producing blow holes and honey-
combing. The history of steel founding is for many years a
history of failure. By degrees troubles have been overcome, and
steel castings can now be had with as much certainty of sound-
ness as those of cast iron. To the late Mr. Francis Webb,
locomotive superintendent of the London and North Western
Eailway, the world is indebted for an exceedingly beautiful
method of casting steel wheels. The moulds are mounted
horizontally on whirling tables, and as the metal is poured in at
the centre, the moulds revolve, and by centrifugal efifort the metal
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WHEELS 45
is forced outward into the minutest cranny of the mould, and
sound castings result. For locomotives and tenders the use
of cast steel centres is now all but universal. Some very
ingenious machinery has also been introduced for cutting felloes
and spokes to shape, or, more strictly speaking, taking off the
rough surface of the casting, and so imparting that finish of
which British engineers are proud.
In all cases the wheels are fitted with separate tires. These
are usually 3 inches thick in the tread, before they wear. They
are put in the lathe and turned up from time to time as they
wear until they are reduced to about one half their original
thickness, when they are sent to the scrap heap and replaced by
new tires. The wheel centre never wears out, and breakages are
very rare. It is a matter of the last importance that the tires
shall be firmly secured on the wheels. The shrinking on is a
very simple matter. The tire is bored out a small fraction of an
inch too small in diameter to go on the wheel centre cold. The
usual allowance for shrinkage is as follows : for 4 feet internal
diameter, "042 inch ; for 5 feet, "049 inch ; 6 feet, '058 inch,
which are the thicknesses of wires, Nos. 19, 18, and 17, Birmingham
wire gauge. The centre is laid flat on a large circular cast iron
slab similar to that which may be seen outside village smithies,
and used for putting tires on wooden cart wheels. Close by is a
reverberatory furnace, in which tires are heated while resting on
a sand bed to little more than the temperature of boiling water.
A couple of labourers take out a tire with the aid of a small
crane, and brushing away dirt they drop it down on the wheel
centre. If it is a shade tight the blow of a heavy wooden pounder
sends it home. As it cools it contracts, and seizes the wheel
centre. In some cases the tire is heated by a ring of gas jets,
urged by a moderate blast. This is cleaner and much less likely
to set up oxidation of the surfaces than in the furnace. For
some sections of tire, as will be understood further on, the process
is reversed. The tire is laid on the plate and the cold wheel
centre is dropped into it. Much care is taken that the boring
of the tire and the turning of the wheel centre shall be so
managed that the tire shall not be stressed when in place to
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46
THE RAILWAY LOCOMOTIVE
much more than about one-third of its elastic limit. The
difference in diameters is expressed, as stated above, in terms of
a fraction of an inch per foot in diameter of the wheel. The
fraction varies with the nature of the steel used, and indeed with
Fig. 33. — Tire sections, Lancashire and Yorkshire Railway.
the views of the wheel maker. Usually the amount of contrac-
tion allow^ed for is the result of practical experience rather than
of theoretical estimation. It would not be safe to rely on
friction to hold a tire on, and particularly a driving-wheel tire.
The most obvious way of securing the wheel centre and the tire
is to rivet them together, and this was the method used almost
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WHEELS
47
universally for several years. The holes in the tire were made
larger outside than in, and taper rivets with counter-sunk heads
were used so that the tire could be trued up several times, the
tapered rivet of course retaining a good hold. But the tires
often broke through the holes, riveting was given up as
dangerous, and numerous very ingenious devices were invented
and patented for securing
tires without boring holes
in them. Some of these
are illustrated in the
drawings of wheel sec-
tions on pp. 46, 47, and
52. The illustrations
given in Fig. 33 are
sections of standard
engine, carriage, and
wagon tires on the Lanca-
shire and Yorkshire Eail-
way. The thin flange is
used on middle wheels to
give more clearance on
curves for reasons already
fully explained. The
engine tire is secured by
about a dozen screwed set
bolts and an outer lip, the
object of which is to pre-
vent the wheel from being
forced outward through
the tire, as in rounding curves,
BetweenTires
Fig. 34.
-Standard tire and rail, Great
Eastern Eailway.
The wagon tire is given because
it illustrates a very popular method of securing tires. Here the
wheel centre is dropped into the tire, which has an outer lip just
like the engine tire. Then a ring A is put in — there is sufficient
clearance between it and C. This is then forced home by
the ring B, which is of soft steel. One end is put in place
first and driven home. The rest is then gradually forced into
place, and then C is beaten down on it all round with swages
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48
THE RAILWAY LOCOMOTIVE
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WHEELS
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50
THE RAILWAY LOCOMOTIVE
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WHEELS
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52
THPJ RAILWAY LOCOMOTIVE
f Thrck Hsnges
£. Thin flanges
and sledge hammers. An exceedingly firm job is made in
this way.
Fig. 34 is a section of a standard Great Eastern Eailway tire.
A ring A is dropped in here as in the wagon tire, Fig. 33, but it
is secured in its place by counter-sunk rivets, B. When a tire has
to be removed the rivet head at one end
is drilled off, and it can then be driven
out. If the tire were broken in half a
dozen places it could not leave the wheel.
The thinning of the flange for the
central pair of wheels in a six-coupled
engine is shown by the dotted lines.
The standard section of the Great
Eastern main line rail is also given.
The slight inward " cant " always used
j\^. K i" order that the coned tire may get a
£I^ L >. -^:A . .: . -\^ .. | .^^ fair bearing all over the rail table is to
|_^| , ^^ y~ be noticed.
The difference between wheel-tire sec-
tions on various railways is not very
great, and recently a standard section
has been proposed by the Engineering
Standard Committee. The accom-
panying table, for which the author
is indebted to Mr. George Hughes,
mechanical engineer-in-chief of the
Lancashire and Yorkshire Railway,
explains itself. It will be seen that it
includes not only locomotive tires, but
those of coal and goods wagons. The
figures which it contains have never been
made public before. They give minute information as to the
dimensions adopted on thirty-two, that is to say all, the principal
railways in the United Kingdom. The three sections given on
this page accompany the tables.
^ Returning now to the construction of wheels, it may be said
that the practice of securing tires by steel screwed pins passing
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WHEELS 53
through the felloes and som e way into the tire has become quite
usual. It is very simple and cheap. The screwed studs are a
tight fit and seldom or never work loose. When a tire has to
be renewed they are easily screwed out. The tire is heated by
a ring of gas jets until it is sufficiently expanded, when it is lifted
off. It will be enough to add here that probably as many as
fifty different practicable methods of securing tires on railway
wheels have been patented, if not tried, on various railways at
home and abroad.
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CHAPTEE VI
WHEEL AND RAIL
Thirty or forty years ago, while rails were still made of
wrought iron, the weights of locomotives gradually increased.
The load on driving wheels at last reached as much as nine
tons bn each. The result was that rails began to give
way. They split along the top, and their ends " were beaten
into besoms." Numerous devices were schemed to get over the
difiSculty. We need only now
1
m
&J^m^.
\^k-^x^^
V^
Fig. 35. — Adams* elastic wheel.
concern ourselves with one.
It was agreed that if a rail-
way wheel was itself elastic
the rail would be spared much
hardship. A modern driving
wheel weighs with the tire
complete from three-quarters
of a ton to one-and-a-quarter
tons, according to the dia-
meter. This is dead weight
and not, like that of the engine, spring-carried. In the United
States a Mr. Griggs mounted his tires on hardwood wedges
driven between the felloe and the tire, with the immediate
result that he greatly' prolonged the life of his tires. In this
country Mr. Bridges Adams, the inventor of the traversing
axle box already referred to, invented and patented about 1858,
and, what is more to the purpose, fitted engines and waggons
with, the wheel shown in Fig. 35. It is stated that he got excel-
lent results. A steel ring or rings was interposed between the
tire and the centre. The ring was supposed to give way slightly
under the Iread of the wheel. The system got a fair trial on
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WHEEL AND EAIL 55
several lines, with the result that the lives of the iron tires then
used were more than doubled. All devices of this kind were,
however, rendered unnecessary by the universal adoption of
steel rails, which will not split, and steel tires. It is worth
notice that these last were looked on with much doubt at first
by locomotive superintendents, as it was held that a hard steel
tire could not get a good grip of a hard steel rail. There was
some truth in the argument, but not much. The mention of
it leads directly, however, to a very important question which
is best considered here, although it has only indirectly to do
with the locomotive considered as a vehicle — a very expressive
word first applied by a French engineer, Count Pambour,
namely " adhesion."
It is not necessary to do more than call attention to the fact
that a locomotive depends for its motion along the rails on the
same causes as those which determine the movement of a
bicycle or a motor car. The engine tries to turn the driving
wheel round. This it cannot do unless the wheel moves for-
ward, because of the friction between its rim and the road. Now
if we confine our attention to a driving wheel and a rail we
shall find much that repays consideration. The surface of the
tire is very hard — so hard that it can scarcely be cut by a file,
and turning a tire up is a tedious process, and can only be
carried out by special tools. The surface of the rail although
softer is also hard. The hard and rigid tire rests on a hard
and rigid rail — what is the contact surface between them?
Absolute hardness and stififness would entail a line contact
across the rail table, because a geometrical circle can touch a
straight line or double tangent only at a geometrical point.
In practice, of course, some give and take occurs. The tire
flattens and the rail bends a little, and so contact becomes more
than a line. As far back as 1845, Mr. Samuelson carried out
some experiments on the Eastern Counties Eailway — now the
Great Eastern — to ascertain the area of contact. He used gold
leaf slips pushed under a driving-wheel in front and behind, and
measured the distance between them. The weight on the rail
was, however, only about three tons. In 1865 the author made
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56 THE RAILWAY LOCOMOTIVE
some experiments on the same railway, by Mr. Sinclair's per-
mission, with the same object, and with several locomotives
having driving wheels 5 feet to 6 feet 6 inches in diameter, and
carrying loads of five to five-and-a-half tons on steel tires in fair
order. A part of the rail being well cleaned, the engine was
brought over the spot and two slips of thin stiff paper, or in
some cases thin sheet iron only y^^ of an inch thick, were
placed on the rail, one in advance and the other in the rear of
the vertical line descending from the axle through the locus of
contact of the wheel and the rail. These slips were then brought
together as closely as the wheel would permit. That is to say,
they were wedged between the tire and the rail until the distance
between these was so small that the slips could go no further.
It is obvious that so long as the tire is removed from the rail by
the smallest conceivable fraction of an inch no contact exists.
It is also clear that the curve of the tire near the point of
contact and the rail very nearly approximate to parallel lines.
That is to say, the curve of the tire and the rail table includes
so small an angle that we are justified in making a considerable
deduction from the length of contact surface as determined by
these experiments. A mean of six experiments gave f inch.
The length of surface of true contact was, however, not more
than half this, or say ^ inch. The breadth of surface of contact
measured by the bright ribbon worn on the rail table would be
about IJ inches, and the whole area of contact say a fraction
over one square inch. In this case, however, the rail was of
iron, and did not weigh more than about 68 lbs. to the yard ;
the rails of the present day weigh from 90 lbs. to 105 lbs. per
yard, and the whole road is incomparably more rigid than any-
thing existing in 1865. There is every reason to think that, at
all events with fairly new tires and new rails, the surface of
contact may not exceed half a square inch. Now the total load
on the rail, including the weight of the complete wheel, with its
axle, axle box, and spring, will be anything between eight and
nine tons. Consequently the stress between wheel and mil will
be at the rate of at least 8 by 2, or sixteen tons per square inch,
and may reach very much more, as well as much less, when the
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WHEEL AND BAIL 57
engine, running at high speed, is also rolling on its springs.
There is besides another and very important factor exerting its
influence on the relations between wheel and rail which will be
understood when the internal disturbing forces are dealt with.
How, it may be asked, can a rail table escape being crushed by
a load so heavy as sixteen tons to the square inch, which is close
to or above the elastic limit of many rail steels ? The tire is so
hard that it may escape. The only explanation is that the
portion of steel which carries the load is supported by the metal
all round. It is, so to speak, in the same position as would be
a steel peg driven into a hole in the rail. It cannot spread or
move in any direction, and therefore the rail table is not torn to
pieces all at once, but is slowly disintegrated.
It has been necessary to consider this point at considerable
length because two factors of great importance are involved. In
the first place, the weight that may be placed on any one pair
of wheels is limited by two considerations. The first is what
will the rails stand ? the second is what will the bridges stand ?
Both these are affected by the performance of the locomotive
as a vehicle.
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CHAPTER VII
ADHESION
The author has written to little purpose if he has not made it
clear that the pressure of a wheel on a rail continually varies.
Now the better the design of the engine the less will this varia-
tion be. Thus, the use of balance beams will assuredly distribute
weight, rendering the whole machine more flexible vertically.
But it may be taken as proved- that, in this country at all events,
a load of twenty tons must never be exceeded on two wheels, and
that in good practice eighteen tons is considered the maximum.
It will be seen presently that if the load could be doubled, or
even increased by 50 per cent., important advantages would be
gained. As for bridges they could be strengthened, but it would
be impossible to make tires or rails that could endure the addi-
tional stress. The rail tables would give out for the reasons
stated above, and the tires, however hard, would be very short-
lived.
In practice it is the rule to put the greatest possible weight
on the driving wheels, because this weight determines the eflS-
ciency of the locomotive as a hauling machine. The conditions
prevailing between wheel and rail are quite outside those of
ordinary friction, in that the loads carried are excessive. It has
become the custom, therefore, to speak of locomotive ** adhesion,"
the word being used in a sense quite different from that given
to it in dictionaries ; what is its co-efficient we shall see further
on. It must be kept steadily in mind that if the phenomena
of locomotive adhesion had no existence engines with smooth
driving wheels would possess no power of locomotion. Adhesion
is as necessary as steam in the cylinder or coal in the fire-box.
It lies at the root of every calculation and enters into every
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ADHESION 59
formula intended to determine the tractive power of a locomotive.
Again, after a certain point has been reached, raising pressures
or increasing the size of cylinders or boilers — the augmentation,
in short, of every element that represents energy — will not confer
the least practical advantage. On the foothold, so to speak, of
an engine depends its hauling power. Adhesion means foot-
hold, no more and no less. What its relations are to ordinary
friction has been the subject of many discussions; that it is
akin to statical friction is clear, because the tire is always at rest
however fast the train is running with regard to the rail, unless
the wheel slips. It would, however, be mere waste of time to
try to draw a parallel between the two. Eailway authorities
have long since made up their minds and settled on a co-efficient"
for adhesion which has proved to be of sufficiently general
application, and so nearly accurate that the design of any
locomotive can so far be based on it with satisfactory results.
In this country the co-efficient is one-sixth. This means that,
unless the force tending to make the wheel revolve measured at
the point of contact with the rail is greater than one-sixth of the
vertical stress between wheel and rail, the wheel will not slip.
Thus, if the load is nine tons, then the turning moment must
exceed 1*5 tons, or the wheel will not slip. In the United States
it is usual to take the co-efficient at one-fifth or a little more.
Climate exercises a very important influence on adhesion. The
co-efficient is highest when the rails are quite clean, dry, and
moderately warm. Under a tropical sun the co-efficient is a
little reduced. When a rail is thoroughly wet and washed clean
the adhesion does not suffer much. In fog or damp weather,
particularly if the rail is dirty, as it is sure to be near cities
because of smoke, adhesion almost vanishes. The wheel spins
round on the rail without moving the engine. Various devices
have been schemed for augmenting adhesion, one of which — the
coupling of driving wheels — must be considered here, because
the use of coupled wheels affects the performance of the loco-
motive as a vehicle, and modifies its design very considerably.
As we have seen, by degrees the outside bearing was given up,
and in the present day the inside bearing alone is almost always
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60 THE RAILWAY LOCOMOTIVE
used in Great Britain for passenger engines. Exceptions may,
however, be found in other countries. Statistics carefully col-
lected by the late William Adams on the North London Railway
showed that steel crank axles with inside bearings would run
about 120,000 miles without failure, while those with outside
bearings had a life of only about 60,000 miles.^ With the much
larger cylinders and heavier pressures of the present day the
disparity in endurance would no doubt be much greater.
In pursuit of greater adhesion, two, three, or more pairs of
wheels are coupled so that they must all revolve together. The
coupling might be effected by cogged wheels or by chains, but a
far more simple and elegant device is used. In each driving
wheel a crank pin is fitted, and a rod extends from crank pin to
crank pin. The pins at opposite sides of the engine are set at
90 degrees apart, so that if all the pins at one side are in a
horizontal line, and so on the dead centre, all those at the other
side are fully ** alive." The result is that, as we have said, any
number of wheels may be coupled. The adhesion of the loco-
motive is, therefore, proportionately augmented; for let it be
supposed that an engine has four driving wheels 6 feet in
diameter, each pressing on the rail with a weight of eight tons —
no coupling rods are on — then the weight for adhesion is 16 tons,
1 1 fi
and the co-efficient of adhesion being - , we have — =2*66 tons.
o D
If now we put on coupling rods, we get the adhesion due to the
second pair of wheels, which is also 2*66 tons, and the total
adhesion is now 5*32 tons, and so on. It must not be supposed,
however, that this advantage can be secured without paying for
it. It is well known that the resistance of the locomotive regarded
as a vehicle — or, as it is sometimes, though not with strict
accuracy, called, the rolling resistance— is augmented by coupling
rods. Various estimates of the resistance have been made. The
late Patrick Stirling, of the Great Northern Railway, often
asserted that coupling rods always meant an extra fuel consump-
tion of something over one pound of coal per mile, or say
5 per cent.
* These mileages do not apply to modern practice with steel crank axles.
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ADHESION 61
When two axles only have to be coupled, the inequalities of
the road — either end of the rod can rise or fall — have no effect.
If three are coupled it is essential that a joint shall be put in
the coupling rod to permit the axle centres to rise and fall above
and below this horizontal line. The trailing end of each section
of the coupling rod is extended past the crank pin, and an eye
is forged in it, between the jaws of which the leading end of the
following section of the coupling rod is secured by a pin put
through the eye. This secures flexibility in a vertical plane.
The crank pins are got up dead true by grinding, and the bear-
ings are in the present day brass bushes lined with white metal,
and forced and pinned into eyes at each end of the side rod.
Adjustable coupling rod ends have long since been given up in
this country. When they get too slack the bushes can be driven
out and replaced by new bushes. The side rods are invariably
made in the present day each of a single steel forging. Formerly
they were made in three pieces of the best forged scrap iron,
that is to say, there were the two heads, one for each end, and a
middle length. There were thus two welds in each rod, and
breakages constantly occurred at the welds. Then an improve-
ment was effected by making each head in one piece with half
the length of the rod, and this saved one weld. But this is all
now ancient history. The stresses which a side rod has to
withstand are severe. A very moderate knowledge of geometry
will suflSce to show that every portion of a side rod describes as
regards the engine a circular path, and is consequently submitted
to centrifugal effort. There are besides tensile and compression
stresses. There is as a result some form of rod which will give
the maximum strength with the minimum of material. What
this form is has been ascertained by mathematicians. Their
investigations would be out of place here ; but the reader who
cares for further information may be referred to the Engineer for
January 16 and 23, February 20, and March 6, 1903, where he
will find the whole subject elaborately treated at great length in
a series of papers by Mr. Parr.
Some designers use fish-bellied rods, but the favourite rod, at
all events for fast work, is a straight parallel bar, with a channel
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62 THE EAILWAY LOCOMOTIVE
cut in each side of it in a milling machine, so that it is in cross
section a double-flanged girder in miniature ; such rods are
very handsome and very good.
Although mathematics would be out of place in this book, it is
very easy to convey an idea of the amount of the stresses which
a side rod has to endure. In a four-coupled engine, assuming
that the adhesion is the same for all wheels, then if, as is very
usual, the distance from the centre of the coupling rod pins from
the wheel centre is the same as that of the crank pin centre from
the centre of the axle, then the stress on the coupling rod will
be equal to one half the total effort of the steam on the piston,
the other half being intercepted by the driving wheel just in front.
An 18-inch piston has an area of 254*5 square inches, and
if the pressure is 150 lbs., then the total eflfort on the piston
= 38175 lbs. or seventeen tons; one half of this is 8*5 tons. Now
the stresses are both push and pull, push when the crank pins
are below the centre, pull when they are above them. The latter
is easily dealt with. A bar in tension with a sectional area of
3 square inches would be ample. But the push or thrust is quite
another matter, for the bar must be stiff enough to act as a strut
and withstand the tendency to bending. But the centrifugal stress
is much more serious. Let us take the case of a four-coupled
engine with 6-feet driving wheels, running at a little over sixty
miles an hour. The crank length for the coupling rods is
12 inches. The circle described by the coupling rod pins and
therefore by every portion of the rod is 2 feet in diameter, or
one- third that of the driving wheel. Now the velocity of the
6-foot driving wheel rim is 88 feet per second, as regards the
engine, with which fact alone we have to do. The coupling
rod rotates at one-third of the speed, or say 30 feet per second.
The centrifugal effort per pound weight of rod is by the rule
already stated a fraction under 28 lbs. If the rod weighs 250 lbs.,
then the tendency to fly away from the crank pins would be a
little over three tons, and twice in each revolution the rod will
be in the condition of a girder, say 8 feet long, and carrying a
distributed load of three tons. This transverse stress tends of
course to break the rod. It will be readily understood that it is
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ADHESION 63
of all things desirable that the rod should be made as light and
as stiff as may be.
It has been stated above that the addition of coupling rods
augments the resistance of the locomotive as a vehicle. The
reason remains to be explained. The side rod compels all the
coupled wheels to revolve at the same speed ; but they would
not if left free all make the same number of revolutions in
running from, say, Euston to Birmingham, unless for one thing
their circumferences were identical ; but this they cannot be, for
two reasons : in the first place, however accurately they have
been turned to the same diameter to begin with, they will wear
unequally. But, in the second place, it must be remembered
that the tires are conical, not cylindrical, and that some of the
flanges are pressed against the outer and some against the inner
rail in rounding a curve ; slipping must therefore take place, not
only as between the outer and inner wheel, but as between one
pair of wheels and another. This slipping is due to the coupling
rods. But beyond all this, the coupling of wheels causes resist-
ance in a way not easily explained, perhaps because the modus
operandi is not very clearly understood. In the old sea-going
days when ships sailed, and pursued and were pursued, it was
well known that to get the maximum speed the utmost possible
flexibility was needed in the hull and rigging ; and we read of
chased schooners and luggers whose crews unwedged the masts,
and even sawed deck beams through to let the hull **work.''
Now in something the same way, the more flexible and less rigid
the locomotive as a vehicle is, the less will be its resistance.
Coupling rods are more or less inimical to this flexibility. They
deprive the wheels of their individuality. The go-as-you-please
element is eliminated. To realise what this means it is necessary
to travel first on the foot-plate of an engine with only a single pair
of driving wheels and then on that of a six-coupled engine. Much
can be, and is, done, of course, to render coupling as unobjection-
able as possible, but it is always regarded as a necessary evil — a
something to be got rid of, if only it were possible.
It has been said above that various expedients to get rid of
coupling rods have been proposed and tried. Two only need be
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64 THE RA.ILWAY LOCOMOTIVE
mentioned here. The first consisted in putting sharp sand on
the rail in front of the driving wheel. Unless rails are very
** greasy '' this will usually bring up the co-efiQcient of adhesion
to at least one-seventh, probably to one-fifth. The sand is some-
times merely dropped on the rail through a pipe in front of the
driving wheel. To this plan there are various objections ; one is
that sand is wasted. Instead of lying on the rail where it is
wanted it falls oflf. Another is that suddenly, just when wheels
are revolving at a high speed on a very slippery rail, one will be
pulled up by sand and the other will not. The result is a very
heavy stress on the crank axle, which has not infrequently been
twisted across. Again the sand is apt to fall on to the oiled
plates on which the tongues of crossing switches work, and cause
so much friction that the signalman cannot move them. In the
present day, therefore, it is usual to fit a small steam jet at each
side of the engine which blows a fine jet of sand right into the
place under the wheel where it is wanted.
Even in the present day there are many single driving wheeled
engines at work, and they have always given so much satisfac-
tion, they are so easy on the road, and economical in fuel, that
their use has been abandoned with the utmost regret. It is worth
while to digress here to say a few words about in many respects
the most beautiful locomotives ever built. These were the single
driver, outside cylinder engines, to which reference has already
been made, designed by the late Mr. Patrick Stirling, while he
was locomotive superintendent of the Great Northern Railway.
This engine weighed only 39 tons, distributed as follows :
Leading bogie wheels
Trailing
Driving wheels
Trailing „
Total .... 39 tons.
As to the performance of these engines, which conducted
express traffic for many years between King's Cross, Leeds, and
York, it will suffice to say that trains of from 16 to 20 coaches
7 tons.
8
9>
16
>>
8
»
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ADHESION 65
represented normal loads. As many as 28 coaches have been
taken and schedule time kept. These weighed 10 or 12 tons
each, or say one-half the weight of a modern coach. From King's
Cross to Potter's Bar, 13 miles, the work is all uphill — the
sharpest curve 15 chains radius. The tractive effort of the
engine would probably reach at slow speeds about 9,000 lbs.
The load under the driving wheels would be 35,840 lbs., so
that the co-efficient of adhesion must have reached about 0*25,
which could only have been got on a dry road and with
sand. Many engineers, however, believe that the co-efficient
is better under a large than it is under a small wheel. Some
years ago Mr. Ivatt greatly improved these engines by adding
domes to them. These permitted the water to be carried at a
higher level in the boiler, a matter of much importance in
climbing long hills, because the feed can be cut off and the heat
stored in the water used in the cylinders. When the hill was
surmounted the boiler could, of course, be filled up again
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CHAPTER VIII
PROPULSION
We have now, it is believed, considered all the external
disturbing forces of a locomotive engine, the principle of their
action and of the methods adopted in combating them. Any
reader with a mathematical turn of mind will not fail to perceive
that all the questions involved admit of mathematical treatment,
but everything of the kind would be out of place in a book such
as this which is intended to explain in general terms why the
locomotive engine is what it is. Thus the reason why the front
or leading end of an engine is carried on a four-wheeled bogie
instead of on two wheels has been set forth, but no attempt has
been made to treat the questions raised as geometrical problems
to be solved algebraically.
At the outset it was stated, it will be remembered, that the
locomotive regarded as a vehicle was subjected when running to
two classes of disturbing forces — the first external to it, such for
example, as the imperfections of the road on which it moves ; the
second, internal. The first it has in common with all railway
carriages, vans, wagons, &c., and indeed all vehicles traversing
streets or highways. The internal disturbing forces are quite
different in character, of great importance, and not so easily
dealt with as the external forces.
At this point it becomes necessary to explain precisely how
a locomotive is propelled — a matter concerning which entirely
erroneous ideas are generally held. Thus the accepted explana-
tion is that the driving wheel pushing back against the rail, the
crank-axle bearings push forward continuously against the engine
frames, the amount of the push rising and falling with the
position of the crank and the pressure on the piston, but always
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PROPULSION 67
being forward in the direction in which the train is moving.
The author believes that he was the first, many years ago, to
publish a statement of the true facts in the Mechanic's
Magazine.
The author may be permitted to quote here from a paper on
" The Adhesion of Locomotive Engines,*' which he read before
the Society of Engineers in 1865. The facts have been in no
wise altered by the lapse of time : —
** For the purpose of illustration, we will assume the case of a
locomotive engine with a single pair of drivers 6 feet in diameter ;
the cylinders, outside, a minute fraction less than 16 inches in
diameter ; the pistons having a stroke of 2 feet, and an area of
precisely 200 square inches. For the present, let it be further
assumed that one cylinder only is in action, the other being
uncoupled, and the pressure throughout the stroke taken at
50 lbs. per square inch above the atmosphere, back pressure, &c.
Suppose now that this engine is at rest on the rails in such a
position that the crank stands up vertically, the crank pin being
directly above the centre of the axle, and the piston approximately
at half stroke. If now we turn on steam behind the piston, we
shall find that it is urged forward with a force equal to 10,000 lbs.
The crank pin will also be urged in the same direction with a
similar force, less the small amount of loss due to the obliquity
of the connecting rod, which loss we may totally disregard in
the present investigation. The wheel we shall assume to have
so much adhesion that no slipping takes place ; we may then
regard that spoke directly in the vertical line below the crank
axle as constituting with the crank a lever of the second order,
in which the load to be moved (the engine) is placed between the
power (applied to the crank pin), and the fulcrum (the rail) : the
axle journal will then be thrust against the forward brass with a
force greater than that due to the strain on the piston by an
amount exactly equivalent to the proportion existing between the
distances intervening between the crank pin and the rail, and the
axle centre and the same point. The engine would, therefore,
tend to advance with a force equal to 13,333*33 lbs., and were
there nothing to be deducted these figures would represent the
f2
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68 THE RAILWAY LOCOMOTIVE
gross tractive force of the machine while the crank remains
vertical. But from this total we must subtract the retarding
force operating on the hinder lid of the cylinder, amounting, of
course, to a stress precisely equal to that on the piston, or
10,000 lbs., and we find that the gross effective force of traction
is reduced to 3,333 lbs., the force at the rail, or that to be resisted
by adhesion being precisely the same. The hauling power of
the machine, therefore, is only due to the lever action proper to
the wheel and crank, and so far it is certain that the advance of
the machine is a consequence of the pressure of the crank axle
on the forward brasses."
" But the crank is above the axle only during one half-revolution,
and during the other half the state of affairs changes materially.
Suppose all things arranged as before, the crank, however, being
directly below the wheel centre instead of above it, steam being
admitted in front of the piston. This last tends to move back-
wards in the cylinder, or in a direction contrary to that in which
we wish the engine to move. This pressure is communicated
directly to the crank pin, and were the wheel free it would
revolve — but the wheel is not free. It now acts the part of a
lever of the third order, the power (the force on the crank) being
applied between the load to be moved (the engine) and the
fulcrum (the rail). The crank shaft is, therefore, thrust, not
against the forward brass, but against that which is behind, with
a force proportional to the distance intervening between it and
the rail and the crank pin and the rail. A little calculation will
show at a glance that the stress on the pin being 10,000 lbs., the
retarding thrust on the axle brass will be one-third less, or
6,666 lbs., while the force to be resisted by adhesion will still be
3,333 lbs. Under these conditions the machine would retrograde
were it not for the force exerted by the pressure of the steam
reacting from the piston on the forward lid of the cylinder,
amounting to 10,000 lbs., from which, deducting 6,667 lbs., we
have 3,333 lbs., as before, for the tractive force of the machine
at that moment."
** From the foregoing it is clear that a locomotive is propelled
during the forward stroke by the pressure on the axle brasses and
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PEOPULSION 69
retarded by that on the hinder cyUnder lid ; while during the
back stroke, the propulsion of the machine is due to the pressure
on the forward lid of the cylinder, the strain on the axle brasses
directly opposing its advance. Bo far we have only considered
the case of an engine with a single cylinder, nor is it necessary
that we should enter at any length into the phenomena presented
in ordinary practice. It will be seen that the introduction of
the second cylinder and piston acting at riglit angles to the first
complicates the relations of the stresses to which the machinery
is exposed without materially altering their character. Thus the
engine is alternately forced forward on its path by a cylinder lid
located at one corner and a shaft bearing placed in the mid length
of the framing. If the thrust on the axle boxes were steadily
exerted in the direction in which the engine proceeds, crank
axle, brasses, and guides would give little trouble ; as it is they
require constant attention."
To make what takes place still clearer, let us imagine the crank
pin on the dead centre. At the end of one stroke the brass will
be thrust back when steam enters the cylinder, and the front
cylinder cover will be thrust forward, the two efforts being equal
and opposite. When the piston is at the other end of the stroke
the conditions and efforts will be the same, but in the reverse direc-
tion. All the circumstances are analogous to those of rowing.
The rower exerts forward effort on the rowlock, and a backward
efifoit against the stretcher. The propelling force is the difference
between the stress on the rowlock and that on the stretcher.
Summing up, we find that the crank axle brass is pushed and
pulled at every revolution backwards and forwards. If longi-
tudinal slackness existed, the axle boxes would knock in the horn
plates, and to prevent this a driving-wheel axle box is always
fitted with a wedge for taking up w^ear. See Fig. 1.
If we trace out the motion of the piston it will be readily
perceived that in space it is continuously moving faster and
slower than the engine. This subject has been dwelt upon
because unless the relations between the piston, cylinder covers,
driving wheels, and rails are fully understood much that follows
will ba incomprehensible.
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70 THE EAILWAY LOCOMOTIVE
Now, so far the engine has been dealt with as though there
was only one cylinder and piston ; but there are two, and their
lines of action are on different vertical planes, and the motions
are not simultaneous, but rhythmical. The cranks are at an angle
of 90° with each other. The result is that as the engine advances
along the rails it is propelled, as has been just stated, first by a
cylinder cover at one side, then by an axle box at the other side,
then by two axle boxes, then by two cylinder covers, then by a
cylinder cover at the other side. The tendency is to set up
a sinuous motion in the engine. The magnitude of this lateral
movement depends on the distance of the cylinder from the
longitudinal centre of the frame ; and the earlier outside cylinder
six- wheeled single-driver locomotives ** wiggled " along the road
to such an extent that some of them were termed ** boxers " by
the drivers, and to this day an engine is said ** to box" when
the leading end beats backwards and forwards. In some engines,
indeed, a peculiar action takes place when the train is running
on a straight piece of track. A rhythmical motion takes place,
and the engine begins to " wander," swaying slowly from side to
side across the road in a very alarming fashion. The moment a
curve is reached wandering ceases, and it can always be stopped
by shutting the regulator for a moment and so throwing the
engine "out of step."
We have then, in the position of the cylinders and the mode of
action of the piston and crank, one internal source of disturbance.
We have so far neglected the effect of the angular action of
the connecting rods. The engine tends to revolve round the
crank axle with precisely the same energy as the crank axle
tends to revolve under the boiler. When the engine is running
forward the cross head is pressed against the upper guide bar,
and tends to lift the leading end of the engine by an amount
which varies from nothing at the end of the stroke to a maximum
when the piston has made a certain advance ; what this point
will be depends on the pressure in the cylinder. Let the length
of the connecting rod be 7 feet, and that of the crank one foot,
then by the composition and resolution of forces it can be shown
that at a point near the middle of the stroke one-seventh of the
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PEOPULSION 71
whole pressure on the piston will be exerted in lifting or attempting
to lift the leading end of the engine. An equal effort will tend to
force the crank down on the rail ; thus, let the piston be 18 inches
in diameter and 24 inches in stroke, and the connecting rod
7 feet long, if the net pressure in the cylinder at a point a little
in advance of half stroke is 50 lbs. on the square inch, the thrust
or pull of the piston rod will be about 9 tons, and the upward effort
9
on the slide bars will be — = 1*287 tons nearly, but the lifting
effort varies in amount continuously, and so we have introduced
what many writers regard as a distinct factor of disturbance. It
is worth while to consider whether it is or is not, because there
is a principle involved. Let us take the case of an engine carried
on six wheels, without a bogie. The load on each leading wheel
is six tons, the weight of each wheel is, say, half a ton, including
its spring, axle box, and half the axle; the total load is then
13 tons under the leading wheels.
Now it will be seen that any lifting effort exerted above the
axle box can be resisted only by, in this case, six tons, the wheel,
axle boxes, axle and springs, regarded as so much dead weight,
remaining unaffected. There is then at each side of the engine
six tons holding down the guide bar. The upward lift on the
guide bar exerted by the cross head represents only, as we have
seen, less than IJ of a ton, and would have no effect whatever as
a disturbing force were it not for the fact that the external
disturbing forces come into play and prepare the way, so to
speak, for this particular factor. We have already referred to
the " rolling '' of an engine. Experiments made some years ago
in France have shown that an engine may roll so much that the
whole of the load is taken off the leading springs and axle box at
one side first and then the other, and the wheels kept the track
only because of their own weight. It appears again that when
an engine is running round a curve the centrifugal effort may
take a very large percentage of weight off the inside wheel. In
that case, again, the slide-bar thrust might be very much felt,
tending to exaggerate rolling, and so promoting unsteadiness.
When a bogie is used the conditions are somewhat different —
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72 THE EAILWAY LOCOMOTIVE
rolling has little or no effect on the bogie-wheel loads. Indeed,
one of the advantages of the bogie is that it is exempt from the
influence of internal disturbing forces up to a certain point,
which will be considered presently. On the whole, then, although
it is right to include cross-head thrust as an internal disturbing
factor, care must be taken not to exaggerate an importance
which is under any circumstances small.^
^ On the London and South Western Eailway certain locomotives were
many years ago built by Mr. Beattie. They were six-wheeled four-coupled
outside cylinder engines ; aU the wheels had inside bearings. They rolled eo
much that outside bearings were put on the leading axles, and the springs
were fitted under the lower guide bars, as there was nowhere else to put
them. The expedient was quite successful.
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CHAPTER IX
COUNTER-BALANCING
We have now to consider a much more important source of
disturbance than any named yet.
When a body of any shape revolves, it tends to turn round its
centre of gravity. Rankine has put this fact so admirably that
the author cannot do better than quote from the treatise ** On the
Steam Engine and other Prime Movers," page 27, second edition,
1861 : " The whole centrifugal force of a body of any figure, or
of a system of connected bodies, rotating about an axis is the
same in amount and direction as if the whole mass were con-
centrated at the centre of gravity of the system. When the axis
of rotation traverses the centre of gravity of the body or system,
the amount of the centrifugal force is nothing, that is to say,
the rotating body does not tend to pull its axis as a whole out of
place. The centrifugal forces exerted by the various rotating
pieces of a machine against the bearings of their axles are to be
taken into account in determining the lateral pressures which
cause friction, and the strength of the axles and framework. As
these centrifugal forces cause increased friction and stress, and
sometimes also by reason of their continual change of direc-
tions produce detrimental or dangerous vibration, it is desirable
to reduce them to the smallest possible amount ; and for that
purpose, unless there is some special reason to the contrary, the
axis of rotation of every piece which rotates rapidly ought to
traverse the centre of gravity, that the resultant centrifugal force
may be nothing. It is not, however, sufficient to annul the
efifect of centrifugal force that there should be no tendency to
shift the axis as a whole ; there should also be no tendency to
turn it into a new angular position. To show, by the simplest
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74 THE EAILWAY LOCOMOTIVE
possible example, that the latter tendency may exist without
the former, let the axis of rotation of the system, shown in
Fig. 36, be the centre line of an axle revolving in brasses at
E and F. At B and D let two arms project perpendicularly
to that axle in opposite directions in the same plane, carrying
at their extremities two heavy bodies H and C. Let the weight
of the arms be insensible as compared with the weights of
those bodies ; and let the weight of the bodies be inversely as
their distances from the axis ; that is, let H H B = C C D, let
H C be a straight line joining the centres of gravity of H and C
and cutting the axis in G; then G is the common centre of
gravity of H and C, and being in the axis the resulting centri-
fugal force is nothing. In other words, let a be the angular
velocity of the rotation, then the centrifugal force exerted
2 XT TT T>
on the axis by H = '- ; the centrifugal force exerted
c? C C~D
on the axis by C = *- , and these forces are equal in
magnitude and opposite in direction, so that there is no ten-
dency to remove the point G in any direction. There is,
however, a tendency to turn the axis about the point G, being
the product of the common magnitude of the couple of centri-
fugal forces above stated into their leverage ; that is the
perpendicular distance B D, between their lines of action. That
product is called the ' moment of the centrifugal couple ' ; and
is represented by Q . B i), Q being the common magnitude of the
equal and opposite centrifugal forces. That couple causes a
couple of equal and opposite pressures of the journals of the axle
against their bearings at E and F, in the directions represented
by the arrows; and of the magnitude given by the formula
BD
Q . . These pressures continually change their directions
E F
as the bodies A and C revolve ; and they are resisted by the
strength and rigidity of the bearings and frame. It is desirable
when practicable to reduce them to nothing, and for that
purpose the points B, G and D should coincide, in which case
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COUNTEE-BALANCING 75
the centre line of the axle E P is said to be a permanent
axis."
The meaning of this passage should be fully mastered by the
student ; what follows is based on it.
In the locomotive engine we have a crank axle, and it is quite
clear that that axle is out of balance ; or if we take a pair of
driving wheels mounted on a straight axle, these alone will be
out of balance because of the crank pins.
Let us picture to ourselves a crank shaft caused to revolve in
a lathe between the centres, and it will be seen at once that the
conditions resemble those laid down by Eankine, and that not
only will the axle tend to revolve round a centre of gravity, but
about two centres, one proper
to each crank; the conse- j^^r-^--^ r^
quence is that a peculiar i^'^^^r^ ^-^-j^^J
" wobbling " motion would
take place unless the bearings
held it steady, and that then
the bearings would have
thrusts and pulls to withstand
which would vary in magni- ^^^' 36.— Centrifugal couples,
tude as the square of the number of revolutions made per minute.
At first sight it seems to be enough to balance the crank, say by
back- weights, as is done in marine engines, and indeed in some
locomotives, but this will not sufl&ce. The forces to be balanced
are much greater than that due to the weight of the crank.
We have the piston rod and cross head moving in a straight
line, and the connecting rod, each portion of which describes a
path varying from a straight line to a circle, according to its
position in the length of the rod. Now the piston rod, &c.,
have momentum and inertia. It is not necessary to go here
into the mathematics of the problem in detail.^ It is enough
to say that Mr. Arthur Eigg, in his treatise on the steam engine,
^ Those readers who raay wish to see the problem treated mathematically
cannot do better than consult a paper, '* The Counter Balancing of Locomotive
Engines," by Edmund Lewis Hill, read and discussed at a meeting of students
of the Institution of Civil Engineers, January 30, 1891.
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76 THE RAILWAY LOCOMOTIVE
showed, it is believed for the first time, that the influence of the
reciprocating masses of a steam engine may all be dealt with as
though the weights were concentrated at the centre of the crank
pin. Their effect is to cause the crank axle to try to revolve round
a centre which is not identical with its mechanical centre ; and
taking four positions only for illustration, to make the crank
axle bearing push forward, accelerating the engine ; push back-
ward, retarding the engine; push downward, augmenting the
apparent weight on the rail ; and push upward, reducing the
load on the rail.
It must be steadily kept in mind that we have two disturbing
forces to deal with, first the weight of the crank cheeks, pins,
and eccentrics. This can be dealt with by putting balance
weights on the wheel bosses or inside the rims ; and inasmuch
as these weights would be symmetrically outside the cranks, and
the cranks would be symmetrically inside them, the common
centre of gravity would fall about the middle of the length of
the crank axle, and there would be no centrifugal couple pro-
duced, and the axle would revolve harmoniously in its bearings.
Balancing of this kind is very old. Among the first engines
built by Bury, Curtis and Kennedy, the wheels were made of
cast iron with wrought iron tubular spokes ; the bosses had
balance weights cast on them. The second disturbing force is
the momentum and inertia of the piston, cross head, piston
rod, and connecting rod. The effect of these factors on any
high-speed engine is well known. Their effect on a locomotive
is usually made the subject of rather abstruse mathematical
investigation. For instance, Makinson, on " The Internal Dis-
turbing Forces in a Locomotive," a paper which was read
before the Institution of Civil Engineers, which will be found in
vol. ccii. of the Transactions, page 106, may be cited, or Mr.
Hill's paper, already quoted. Happily the whole problem
admits of being stated in general terms with quite sufficient
accuracy for ordinary purposes. Although the parts move in
straight lines and ovals they can be treated, as has just been
said, as if they revolved round the centre of the crank axle ;
thus in the accompanying diagram. Fig. 37, we have a crank
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COUNTER-BALANCING
77
axle A, a crank B, and a crank pin C. Now the effort of a
piston, connecting rod, &c., may be regarded as the same as
that which would be produced if a symmetrical ring D, equal to
the reciprocating portions in mass, that is to say, in weight,
surrounded the crank pin. This simplifies the matter enor-
mously. Thus, let us suppose that the total weight of the
reciprocating parts is 500 lbs., that the engine has 6-feet driving
wheels, and runs at sixty miles an hour. Then the speed of the
crank which is one foot long, as regards the engine is 29*3 feet
per second, and by the rules already given the centrifugal
effort or " force," as Eankine calls it,
will be, in round numbers, nearly six
tons. When the crank is horizon-
tally forward the axle is forced
against the axle box, urging the
engine onward ; and when the crank
is horizontally pointing backwards,
then the engine is retarded by a
similar amount. To understand what
really takes place, let us consider the
piston at the termination of the
forward stroke. It has to be made
to move backward at once with a
velocity accelerated from nothing to ^^^- ^^--^^g'^ diagram,
about 1,000 feet per minute, and the crank has to drag the piston
away from the end of the cylinder. In the same way, when
acceleration ceases about mid-stroke, the piston, &c., pushes on
the crank which has to retard it and bring it to rest. The amount
of push and pull will be modified by the pressure of the steam
in the cylinder in a way sufficiently obvious.
It will be seen now that after all allowances have been made
we have very serious disturbing forces to deal with. The general
result of the combination is to make the engine move by jumps
instead of going steadily forward, and inasmuch as the influence
of want of balance is not symmetrical, because the cranks are not
opposite each other, but at angles of 90 degrees, the whole effect
on the engine is to set up a violent fore and aft oscillating
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78 THE RAILWAY LOCOMOTIVE
movement, which is not only objectionable and even dangerous, but
inimical to speed. Although much was done in a rule of thumb
way before D. K. Clark took the subject up, it may be safely said
that he was the first to introduce the systematic use of balance
weights in the driving wheels of locomotives, and this he did
after many experiments, putting, in 1856, balance weights into
the driving wheels of the Canute on the London and South
Western Eailway. The engine had already had the dead weights
balanced by 85 lbs. bolted inside the rims of the driving wheels.
Mr. Clark added 186 lbs. for each wheel. ** The engine runs so
much more steadily and freely with the new balance weights as
to take the engine men by surprise. On the first, day after the
alteration, the stations were considerably overshot by the engine,
although steam was shut off and the brakes applied at the usual
distance from the stations. The saving in fuel by the improving
of the counterweights of the engine was estimated at 20 per
cent.''
It must be kept carefully in mind that balance weights ^ are
used for two purposes — in the first place, to deal with dead
weights ; in the second place, to deal with the forces due to the
reciprocation of the moving parts. Now it so happens that the
useful action of these latter compensating weights is limited to a
portion of each revolution, while centrifugal force is constant all
through each revolution. The consequence is that the weights
put in to deal with reciprocating masses are superfluous for large
portions of each revolution, and they are not only superfluous,
but mischievous. What we want in anj' case is not their
centrifugal energy, but their momentum, which is quite a
different thing.
Thus their centrifugal effort when they are at the top of the
wheel tends to lift the wheel off the rail, and again when it is at
^ The words " balance weights " are misleading. We have the small
weights necessary to balance the rotating masses, and properly so called ;
but the remaining and much larger weights are not intended to ** balance "
anything ; they are really compensating weights intended to neutralise the
effect of momentum and inertia in the reciprocating masses on the rest of
the engine ; thus when a piston is flying backward the compensating weight
is flying forwards.
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COUNTER-BALANCING 79
the bottom it tends to force the wheel down on the rail : the
result of the first is to tend to cause slipping ; the result of the
second is what is known as ** hammer blow," very destructive
to the rail. To reduce the mischief as much as possible in
practice the custom is to balance all revolving weights and only
three-fourths of the reciprocating weights with inside cylinder
engines. With outside cylinder engines the balancing is a little
more complete, the moving parts being generally lighter. The
result is that the inertia and momentum of the reciprocating
parts are not quite compensated, but, on the other hand, the
mischief done by centrifugal effort is reduced ; and indeed com-
plete compensation is not necessary, because compression at the
beginning of each stroke tends to bring the piston quietly to
rest, and lead — that is, the admission of steam before the crank
reaches the dead point — helps the piston away from the end of
the cylinder. While on the whole compensation is quite satis-
factory, it must not be forgotten that it is bought at a price ;
centrifugal force comes in as a factor which would be gladly
spared, and has indeed been eliminated in a way which will be
explained further on.
The balance weights usually take the form of the new moon.
The reason why will be explained when the locomotive as a
steam engine is considered.
In former practice the cast iron balance weights were placed
between the spokes just under the rim and secured by two flat
wrought iron segmental plates riveted through the cast iron,
one outside, the other inside. In modern engines they form part
of the steel wheel centre, being cast with it. Sometimes they
are hollow and lead is poured into them so that precisely the
proper weight can be provided. For reasons which cannot be
explained here, in some cases the centre of gravity of the weight
is not diametrically opposite to the cranks ; in others it is
divided. Thus the cranks are balanced by '' back weights " as
in marine engines, which are in effect prolongations of the crank
cheek backwards. Again, the coupling rods have to be taken
into account. Obviously they balance some of the weight.
But their presence introduces further complications. Several
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80 THE RAILWAY LOCOMOTIVE
designers divide the balance and compensating weights among
all the driving wheels, contending that in this way hammer
blow is minimised. But generally only the weight of half the
side rod and the crank pin is balanced in a coupled wheel.
Although compensation and balance weights are always pro-
vided, and rightly so, as if they described circular paths, it must
be remembered that they only do this as regards the engine.
Their true path in space is a cycloid, and this as regards the
rail has, it is held by some engineers, an effect on the relations
between wheel and rail. Thus they point out that the effect of
hammer blow does not take place immediately under the balance
weight, but before it has reached the rail. Experiments show
that the place of what may be termed impact varies with the
speed and other conditions, so that it is by no means easy to say
what is really the best angle with the cranks at which to fix the
weights. Mathematical investigations have not given results
which necessarily coincide with those obtained in practice.
There is in consequence no such thing as absolute uniformity ;
and balancing and compensating are carried out very much in
the way that experience has shown to give the smoothest running
engine without much regard to theory.
In the United States the effect of hammer blow has
received far more consideration than in this country. Kails are
not made with the same care as in Great Britain, and a sharp
controversy has gone on between the locomotive superintendents
and the rail makers, the latter asserting that it is hammer
blow that splits and breaks the rails.
In order to supply some information on the subject a number
of experiments were carried out on the testing plant of the
Pennsylvania Eailway at the St. Louis Exhibition. It will be
remembered perhaps that this testing plant consisted essentially
of a set of wheels, the distances between which could be
adjusted, and fitted with very powerful dynamometer brakes. The
engine to be tested was run into the shed, and its wheels were
supported on the brake wheels which revolved when the driving
wheels turned. The locomotive was prevented from running off
the brake wheels by its draw bar, which was secured to a
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COUNTER-BALANCING
81
tractometer, the other end of which was secured to a strong
anchorage. This plant was in the main a reproduction of that
designed by Professor Goss for the Purdue University. A very
similar plant has now been in use for nearly two years at the
Great Western Eailway Works, Swindon.
In order to settle what the effect of the balance weights might
be. Professor Goss, by whom the experiments were carried out,
adopted the ingenious expedient illustrated in the accompanying
Fig. 38. — ^Wire test for hammer blow.
engraving, Pig. 38. Annealed steel wires '06 inch in diameter
were passed between the driving and the brake wheels, and
subsequently measured with a micrometer calliper at intervals of
5 inches. Guide pipes f inch in diameter were used to lead the
wires to the point of contact between the wheels. Before being
used the wires were carefully straightened, cut to lengths 3 feet
greater than the circumference of the driving wheel, and rubbed
bright with emery cloth. Behind the points of contact of the
driving and supporting wheels were galvanised iron cones placed
B.L. G
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82 THE RAILWAY LOCOMOTIVE
to throw the wires away from the machinery after passing the
wheels. A small groove was cut across the driving-wheel tire in
the same plane and. on the same side of the wheel as the outside
crank pin. This gave a reference mark on the wires so that the
wheel positions could be determined. It would be impossible to
go into a consideration of the results obtained at any length. The
conclusions of the most interest reached by Professor Goss are that
wheels balanced according to the usual rules, which require all
revolving parts, and from 40 to 80 per cent, of all reciprocating
parts, to be balanced — this latter portion being equally dis-
tributed among the wheels coupled — are not likely to jump the
track through the influence of the weight. Where a wheel is
lifted through the action of its balance weight its rise is com-
paratively slow and its descent rapid. The maximum lift occurs
after the counterbalance has passed its highest point. The
rocking of the engine on its springs may assist or oppose the
action of the counterbalance in lifting the wheel. It therefore
constitutes a serious obstacle in the way of any study of the
precise movements of the wheel. The contact of the moving
wheel with the rail is not continuous even for those portions of
the revolution where the pressure is greatest, but is a rapid
succession of impacts. There is reason, however, to believe
that the lifting does not affect the wheel as a whole, but is the
result of vibration, which in its turn is a consequence of the
elasticity of the metals concerned, namely, the surface of the
tire and the rail.
These experiments go to show that the received theory that a
driving wheel rolls quietly on a rail with an insistent pressure
varying rhythmically throughout each revolution is not quite
consistent with the facts, the phenomena of the relations of
wheel and rail being complex instead of simple.
The reader has, it is believed, been now placed in possession of
the principal facts concerning the locomotive as a vehicle. He
has seen something of the forces to which it is subjected, and
of the methods adopted in dealing with them. But it must
be carefully kept in mind, particularly by the student, that
the mathematical inwardness of the subject remains for his
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COUNTER-BALANCING 83
consideration, and that even the observed facts have not been
completely set forth. Thus, for example, the influence of elasticity
in the roads on the locomotive has not been considered, and yet
elasticity is a thing that has to be carefully provided in permanent
way. For reasons already stated, and indeed restated, a com-
plete consideration of the locomotive as a vehicle would be out of
place in this volume.
g2
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SECTION II
THE LOCOMOTIYE AS A STEAM GENERATOR.
CHAPTER X
THE BOILER
It is probable that as many as fifty different types of loco-
motives are at work to-day on the railways of the world. If
we except a small number of motor railway coaches, which
have vertical boilers, all have boilers presenting the same
general features. We have at one end a box with a round
or flat top, at the other end another box with a chimney set
on top of it, and the two boxes are connected by a cylindrical
barrel. It will be seen at once that the form and arrangement
lend themselves admirably to being carried on wheels. We
have only to look at a locomotive and try to adapt a vertical
or rectangular boiler to the engine framing and wheels to
arrive at the obvious conclusion that it is not possible to improve
on the general design. In fact, the external characteristics
of the locomotive may be said to have been fixed for us- by
conditions which cannot be altered ; and that is the reason why,
notwithstanding the many attempts whick have been made to
modify the external characteristics of the locomotive, they remain
in the main what they were to begin with.
As this book is not historical, it will be enough to say that
from the day when George Stephenson ran the Rocket at the
Rainhill competition on October 6, 1829, to this moment, the
locomotive boiler has remained unaltered in principle, and this
notwithstanding the fact that various modifications have been
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THE BOILER
85
proposed and tried. The locomotive engine boiler will therefore
be dealt with as it is and not as it might be.
We have, as has been said above, at one end a rectangular
box with a flat or circular top. Inside the box is placed another
made of copper, or of steel plates, with a space between the two
boxes which is filled with water. The first, or external fire-box,
is riveted to a cylindrical ** shell " or '* barrel." To the other
end of the shell is secured the smoke-box; the internal fire-
box is united to the smoke-box by a great number of tubes
about 2 inches in diameter. The boiler is filled with water
to such a height as will drown the fire-box and the tubes. A
Fig. 39. — Sectional diagram of boiler.
grate is fixed in the bottom of the fire-box, and a fire being
lighted on it, the smoke and gas pass from the fire through
the small tubes and into the smoke-box, and thence up the
chimney. The heat is communicated to the water through the
walls and roof of the fire-box, and the metal of the tubes. What
is left goes to waste up the chimney. The accompanying
diagram, Fig. 39, shows a locomotive boiler in section. Here A
is the internal fire-box. B B are two of the flue tubes and C the
smoke-box, D the chimney, E a door giving access to C. A
brick arch is shown at P and a deflector at G to beat down
the air entering through the fire door on to the burning coal.
H is the grate, I the foundation ring, K bridge stays, sometimes
reinforced by sling stays P P, L is the fire door, M screwed stays.
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86 THE RAILWAY LOCOMOTIVE
Before considering in detail the construction of a boiler, it
will be necessary to say something of what goes on inside it,
because it is this that settles the interior characteristics of the
boiler, just as the fact that a locomotive engine is a comparatively
long narrow vehicle has settled its external appearance.
The first thing to be done is to burn coal ; the second to absorb
the heat given off during the process, and use it to make steam.
What is subsequently done with the steam will be discussed when
we come to deal with the locomotive as a steam engine. It has
been dealt with as a vehicle. It is now to be dealt with as a
means of turning water into steam.
It is a curious truth that in this extremely scientific age next to
nothing is known concerning the conversion of any liquid into a
vapour or gas. The whole literature of the subject is represented
by two or three pages of Ganot's " Physics." The question is
much too large to handle adequately here, but it cannot well be
passed over when we bear in mind that the durability of a boiler,
its safety from explosion, and the good and bad qualities of the
steam, are all matters of the utmost importance, presenting
problems which depend for their solution on a knowledge of how
steam is made to the best advantage and what it really is.
The received theory is that steam while in the saturated state,
that is, with no free heat, is nothing more than water with its
molecules driven asunder by heat. When steam is superheated,
it becomes a gas like air, that is all. As an apt expression of the
received concept of the formation of vapours — steam and gas —
nothing can be better than the following extract from an article
by Mons. L. Houllevigue in the Revue de Paris, of April 1,
1903, translated by Chief Engineer B. F. Isherwood, United
States Navy, for the Journal of the Franklin Institute.
" Physicists saw matter formed of molecules or aggregated
molecules isolated from each other and pursuing each other in
incessant movement like the particles of dust vibrating in the
sunbeam, and from this eddying mass they saw escaping waves,
that propagated themselves in space by means of an infinitely
rare medium, which was to the lightest of known bodies, hydrogen,
what the density of hydrogen was to the density of the heaviest
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THE BOILER 87
metals. Gases, especially, appeared as microscopic projectiles
darting in every direction and continually boEdbarding, without
loss of force, the sides of the vessel that contained them, only to
rebound again and recommence their eternal movement. The
heat contained in the gases took from similar impacts a more
precise significance; it showed the present energy of all these
moving corpuscles. If the gas be cooled, the velocity of the pro-
jectiles diminishes, their trajectories flatten, then all the corpuscles
collapse, but still retain eddying movements ; this is liquefaction.
Then, in measure as more and more energy is taken out of them,
the vibrating molecules make less and less extended movements,
and the liquid contracts in cooling. Very soon the increasing
nearness of the molecules to each other enables them to make
among themselves new interactions, their relative positions
become nearly invariable, and the liquid solidifies; but the
resulting solid is still animated with life-like shiverings ; it could
still be cooled down to the point at which its molecules would
repose, inert, one upon the other ; and then the matter would
be dead,"
Here we have the whole process of the conversion of, say, ice
into superheated steam stated in inverse order.
Man produces more steam than any other manufactured article.
It is quite impossible to ascertain with certainty what weight of
coal is burned annually in making steam for the factories, mines,
railways and ships of Great Britain. There is, however, reason
to believe that not short of 60,000,000 of tons. Allowing that
each ton of coal will make seven tons of steam, we have then an
annual output of no less than 420,000,000 of tons of steam for
this country alone, or forty-two times the weight of iron we
make. All this is manufactured by the aid of costly apparatus,
and with a certain amount of risk of life, limb and property.
Allowing 35 cubic feet to the ton, the water converted into
steam, as stated above, would amount to 14,700,000,000 cubic feet,
which would fill a lake 100 feet deep and over 2J miles long
and 2 miles wide. The quantities are stupendous, yet, as has just
been said, next to nothing is known of the nature of the material,
steam. The author is quite prepared to find this statement
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88 THE RAILWAY LOCOMOTIVE
treated with incredulity. It will be said that everything is
known, that the literature of the subject is profound and
practically complete. These statements, however, it will be
found on examination, apply not to steam, but to the apparatus
by which it is made, namely, boilers and furnaces ; and to that by
which it is used, namely, engines. If nothing had ever been
written about iron but treatises on the blast furnace, the con-
verter, the mill and the cupola, no one would say that the
literature of iron and steel was complete. Let us draw an
analogy between the blast furnace and the steam boiler. Into
the first we put coke and ore and limestone and air, and out of it
we get pig-iron and gas. Every step of the process by which the
iron and gas are obtained has been made the subject of careful
inquiry. Into a boiler we put water and we take out steam.
But of the inwardness of the process practically nothing is known.
Things are taken for granted, and when phenomena present
themselves out of the common we are told either that they have
no real existence, that they are quite usual, or that it is not worth
while to pursue an inquiry. A great deal has been written about
the conductivity of boiler plates, to name one thing, but no one
cares to inquire how or why the heat is passed into the water, or
what it does when it gets in.
The accepted explanation advanced by scientific men has been
given above. Somewhat different views have recently been
advanced by physicists in the first flight of scientific research ;
but these do not admit of beipg briefly stated, and their extended
consideration would be out of place in this book.
Descending from the more or less transcendental region of pure
thermodynamics to practice, let us consider how the heat gene-
rated by the combustion of fuel and imparted to the water is
distributed. In other words, to crystallise our ideas the facts
must be stated quantitatively. This has never been done in more
detail or more lucidly than by Benjamin Isherwood in his
splendid " Eesearches in Steam Engineering." For convenience
of reference his table has been reproduced on the next page. It
will be seen that he has used the old thermal unit 772 instead of
the modern unit 774, but the difference is of no importance, and
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THE BOILEE
89
some uncertainty even now exists as to the precise foot-pound
value of the heat required to raise one pound of water 1° F.
Incidentally it may be pointed out that minute and precise as
Isherwood's statement is, it gives no clue, and pretends to give no
clue, to the way in which water is converted into steam. At first
Distribution of heat in the conversion of
1 lb. of water at 32° F. into steam at
212° F.
H
Thermal
units.
D
Dynamical
Equivalents.
Per cent, of
total Heat.
D -f- 772.
H X 772.
Total heat of steam of 212° from
water at 32°
1,146-600
885,175-200
100000
S
a
■4^
'Increasing the temperature of
the water from 32° to 212°
and lessening the cohesion
of the water between 32°
and 212°
18.0-898
139,653,359
15-776
&
Increasing the volume of water
between 32° X 212° . .
0-0018
1-4406
0-0002
1
CD
'^Destroying the cohesion of the
water (i.e., converting it into
steam from the boiling point)
893,666
689,910,025
77-940
.9 ■
i
to
Increasing the volume of the
water from that which it had
as water at 212° to that which
it had as steam at 212°
72-0341
55,610,374
6-2820
1.146-600
885,175-200
100-000
sight it may appear that if we really understood all about it, the
fact would have no practical value, but this is not the case.
There are peculiarities in the performance of different locomotives
which await explanation. Thpre are explosions, such as that at
St. Lazare, in Paris,' that remain wrapped in mystery ; and it
^ On the 4th of July, 1904, at 11 a.m., the boiler of engine No. 626, at the
time standing in a cutting outside St. Lazare Terminus of the "Western
Bailway of France, exploded with extraordinary violence. It was literally
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90 THE EAILWAY LOCOMOTIVE
seems to be by no means impossible that if we possessed more
knowledge, improvements of real value might be introduced in
our methods of making steam. As the reader proceeds, it is
hoped that the relation between what has just been read and the
facts of the everyday life of the locomotive engine may become
more apparent than they are for the moment.
blown to bits, the fragments, some of them very small, being projected to
great distances, falling in the neighbouring streets. No one was killed,
though a few people were hurt by falling glass and flying gravel. The
damage to propeiiy was estimated at £80,000. At first it was believed that
Anarchists had put a bomb in the fire-box, as there was no one on the foot-
plate at the time. The theory was untenable, and three special independent
mquiries were carried out. Each reached a different conclusion. To this
day the explosion remains unexplained. The interested reader will do well
to consult the ** Bulletin dela Societe d'Encouragement " for July 31st, 1905,
where he will find complete details and illustrations.
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ATv.
CHAPTEE XI
THE CONSTRUCTION OF THE BOILER
We may now proceed to consider in detail the construction of
the locomotive boiler. No better boilers are made than those
produced in Great Britain and Ireland. The railway companies
take care that the material and workmanship of the boilers
made in their own shops shall be the best possible ; and the
splendid reputation possessed by our loco-
motive engine building firms all over the world
is sufficient testimony as to what they can do.
We have to do, in the first place, with the ;<
stresses to which a boiler is exposed. The \]
simplest case is that presented by the barrel
or cylindrical shell. In calculating the stress,
the curved area of the plates is to be treated
as though it was flat, as shown in the accom- I^'io- 40.— Eadial
panying diagram, Fig. 40, wherein the dotted
line shows the shell as it is and the two full lines the areas
giving the stress. Let us suppose that the shell is 48 inches in
diameter and that it is divided up into rings each one inch long.
Then the area we require is 48 square inches, and the effort of
the pressure, 100 lbs. per square inch, tending to separate the
halves of the boiler, is 4,800 lbs. on each inch of its length.
Now the effort may be supposed to be concentrated at the point C
in each section, and is, of course, resisted by two thicknesses of
the shell, one above, D, the other below, E. Let the plates be
half an inch thick ; then the sectional area to carry the pressure
will be one inch, and the stress per square inch of section of the
shell plates will be 4,800 lbs., or a little over two tons. The total
bursting stress in a large modern boiler, with a barrel 14 feet
E
).-
stress.
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92 THE BAILWAY LOCOMOTIVE
long and 5 feet in diameter, carrying 220 lbs., is in round numbers
900 tons. If the plates are half-inch thick, then the stress will
be 13,200 lbs., or approximately 6 tons per square inch of
sectional area.
The facts have been stated in this elementary way, because
many persons, students especially, find some difficulty in under-
standing how radial pressures act, and are disposed to think that
the whole surface should be taken into consideration.^
The formulae for calculating bursting pressures are, of course,
very simple. They will be found in most treatises on steam
boilers and various text-books.
Let d = the diameter of the boiler in inches ; t = the thick-
ness of the plate in inches ; s = the ultimate strength of the
metal in tons per square inch ; and p the pressure in pounds per
square inch.
Then d p in the total pressure on a 1-inch length of both sides
together ; 2 Hs the sectional area of both sides ; and 2, t s x
2,240 = dp.
Then V - h^9ll . t - -^^ and s ~ ^^
±nen p -^ ^ , t - ^^^^^^ ^, and s _ ^^^^^ ^.
It must not be forgotten, however, that a boiler shell is not
made up of solid plates, but of rings riveted together, and as no
riveted joint, no matter how made, can be as strong as the
solid plate, a deduction must be made. That is to say, the
tensile strength of the solid plate must be multiplied by the
fraction co-efficient proper to the system of riveting employed.
Thus, the joint may be single or double riveted, or it may have
a single butt strap, or two butt straps, one inside, the other out.
In the diagram. Fig. 39, at a single butt strap is shown.
In a general way it may be taken that the strength of a single
riveted joint is 56 per cent, of that of the solid plate, while a
double riveted joint has a co-efficient of about 78 per cent. ; but
there are various qualifications depending on the way in which
1 Some years ago an inventor, reasoning in this way, took out a patent for
a corrugated piston, the expanded surface of which would be much greater
than that of a plane piston. The advantage to be gained he explained with
some care.
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THE CONSTEUCTION OF THE BOILER 93
the rivet holes are made. The Board of Trade rules for marine
boilers go most elaborately into the question. The following
formulae are quoted from the rules as laid down in Trail's ** Hand-
book for the Guidance of Engineers, Surveyors and Draughtsmen,"
written in 1888. Certain modifications have been made since,
which, however, do not affect the formulae. If the plates and the
rivets and the workmanship comply with the stipulations laid
down, then the percentage of strength of any joint or other par-
ticulars of the joint may be found by the following formula : —
p = pitch of rivets in inches.
d = diameter of rivets in inches.
A = area of one rivet in square inches.
n = number of rivets in one piston (greatest pitch).
fo = percentage of plate left between rivets of greatest pitch.
% = percentage of rivet section as compared with solid
plate.
% = percentage of combined plate and rivet section when
the number of rivets in the second row is twice that
in the outer row.
c = 1 for lap or single butt-strap joint.
c^ = 1-75 for double butt-strap joint.
T = Thickness of plate in inches.
Then to find the percentage strength of any given joint : —
i5»f* = % a)
100 X 23 X A X n X c _ ^. ^
28 X i> X T " /° ^' ^"^^
Fortunately the Board of Trade has nothing to do with locomo-
tive boilers. If they were made in conformity with the formula
given above they would be very much heavier than they
are. A very large factor of safety is provided mainly because of
the corrosion which takes place at sea, and not on land. The
locomotive boiler again does not work for weeks at a time without
examination. The boiler is under constant supervision, and the
most watchful care is exerted to secure immunity from explosion.
The result is that scantling can be reduced without risk in a way
that would not be admissible at sea. But the Board of Trade
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94 THE RAILWAY LOCOMOTIVE
rules have been given here because they are of general value as
guides to those engaged in the designs of any boilers, locomotive,
marine or stationary, which have riveted joints.
The boiler barrel is made up of two or three rings according to
its length. The plates are cut to the proper length, and their
edges are planed. They are then bent between three rolls until
the ends of each plate meet, and they are secured together by
two butt straps, one inside, the other out, double riveted. In
some cases the rings are secured end to end by narrow hoops
and a double row of rivets for each hoop. The whole inside of the
barrel is then flush from end to end. In other cases the rings
are telescopic ; that is to say, each is pushed about 3 inches into
the one behind it, the largest ring being next the fire-box.
This is a good plan, because it increases the water space next the
fire-box. There are two or three methods of securing the barrel
to the fire-box, but a minute description of these would be out of
place here.
So far no one has yet had the courage to risk welding
longitudinal seams. Flues for stationary and marine boilers are
now almost always welded. But the stress being external tends
not to open, but to close their seams. The circumferential seams
are exposed to precisely one half the stress, the longitudinal
strength of a tube with closed ends being to the circumferential
strength as two to one. To make this quite clear, let us suppose a
tube 8 inches in diameter, the sectional area of which is 50 square
inches ; the pressure inside is 100 lbs. on the square inch. Then
we have 100 x 50 = 5,000 lbs. tending to pull the tube asunder
endways. The circumference of the tube is (omitting fractions)
25 inches. The thickness of the plate is 0'5 inches. Then the
25
sectional area of metal resisting the stress is -^ = 12*5 square
inches. The bursting stress for length = 1 inch = 800 lbs., and
the area of metal to sustain it is one inch. But the longitudinal
effort is 5,000 and ^.^ = 400, or just one half the bursting
stress.
We come next to the flat surfaces of the inside and outside
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THE CONSTRUCTION OF THE BOILER 95
fire-boxes, and the staying of these constitutes the most important
structural problem that has to be solved by the locomotive super-
intendent. No part of the complete machine gives so much
trouble or causes so much anxiety as the boiler, and it is not too
much to say that 90 per cent, of this is due to the fire-box. The
nature of these troubles will be considered in some detail before
any attempt is made to explain the special means taken to elude
or otherwise get over them. Take, for instance, an internal fire-
box which is 6 feet long, 5 feet deep, and 3*25 feet wide. The
area of the flat crown of this box is, in inches, 72 by 39 = 2,808.^
Let the pressure be 200 lbs., then 2,808 by 200 = 561,600 lbs., or
250 tons. Each side has an area of 72 by 60 = 4,320 square
inches and 4,320 by 200 = 864,000 lbs., or more than 385 tons.
How many persons realise as they stand beside a locomotive
that stresses so enormous represent the effort of the steam to
escape ? 900 tons to rip the shell open ; 385 tons to force out the
flat side of the fire box ; 250 tons to drive the fire-box down on the
rails, and blow the rest of the boiler through the station roof.
Is it wonderful that the boiler of a locomotive should claim and
get from day to day more attention than any other part of the
machine ?
We have now to consider how these enormous stresses are
carried. In the barrel they only put the metal in tension, and
being quite simple they can be dealt with easily enough. It
suffices to provide a sufficient section of metal and adequate
riveting. It is far different with the flat surfaces. There is so
far as the vertical portions of the fire-box are concerned, only
one method of support available, namely, tieing the plates to
each other by stay bolts, and tieing the front plate of the fire-
box to the plate at the leading or smoke-box end of the barrel.
There are two methods in use for supporting the top or crown
of the fire-box : first, screwed stays attach it to the top of
the outside fire-box ; secondly, girders are placed on the top of
the inside box, to which it is secured by screwed bolts. Both
these systems are illustrated.
* This is virtual area, being that of the rectangle formed by the foundation
ring. The top of the fire-box is almost always wider than this.
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96 THE EATLWAY LOCOMOTIVE
Numerous experiments have been made to ascertain the pres-
sures that flat plates of iron, steel and copper will sustain when
supported by screwed stays. The results, however, of practice —
in other words, those obtained in the regular performance of their
work by locomotives — have resulted in the almost universal
spacing of stay bolts 4 inches apart, centre to centre, the
bolts being i inch diameter. Now these bolts are an endless
source of trouble, expense and even danger. They are short,
the distance between the two plates stayed varying from
2J inches as a minimum to 4 inches as a maximum. The inside
fire-box being of copper, which has a co-efficient of expansion of
•1722, while the outer box is of steel with a co-efficient of '1145,
and the inner box being besides always hotter than the outer
when the fire is alight, it follows that the inside box rises inside
the outer box, it may be by as much as 0*25 inch. This
cannot take place without bending the stay bolts, or the plates
in which they are set ; and inasmuch as this tendency does not
take place once for all, but goes on continuously as the tempera-
ture of the furnace varies, in time the stays become " fatigued "
and break. The only ways of ascertaining whether they are
broken or not is by sounding the heads with a hammer — by no
means a certain test — or by finding a bulge in the plate. In
some cases a hole about one-eighth of an inch in diameter is
drilled down the centre from the outside of each stay, but not
quite through. If the bolt breaks, water will escape violently
through this hole. The breakage of a large number of stays at
once has caused some frightful catastrophes, the engine often
turning a somersault. Inventors have not been idle, and various
patents have been taken out for imparting flexibility to the bolts.
These as a rule contemplate a reduction in the sectional area of
the bolfe. One inventor cuts four slots longitudinally in the bolt.
These are made with a small circular saw, and the slots are
deeper in the middle than at either end. The ordinary practice
is, however, to make the stays on the same principle as a Palliser
armour-plate bolt, a principle involving so much and of such
wide application that it claims some explanation here.
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CHAPTEE XII
STAY BOLTS
In the early days of armour plating the targets consisted of
beams to which the plates were fixed by bolts about 3 inches in
diameter. The heads were tapered and counter-sunk into the
plate. The screwed ends and the nuts, under which large
washers were placed, were inside the ship's side, so to speak.
When a projectile struck the plate a number of the nuts always
flew off, the bolts breaking through the threads ; and to say
nothing of the mischief they were quite capable of doing among
a crew, it was only necessary to hit a plate two or three times,
and it would fall off altogether. Various attempts were made to
get over this radical difl&culty. Elastic washers were put under
the nuts with indifferent results. Then Captain Palliser, an
artillery ofl&cer, solved the problem by reducing the diameter of
the bolts somewhere about the middle. A reduction in section, no
matter how effected, had the same result. Thus boring holes down
the centre of the bolts had the same effect as turning them down
outside. This is the reason why the crank shafts and crank pins
of marine engines are hollow. But this is not all. The effect of
cutting a screw thread on a bolt is about the same as if it were
nicked all round. Thus an armour plate bolt being screwed,
would in effect be nicked, and would break generally just where
the last thread of the screw joined the solid. Captain Palliser
turned his bolts down in such a way that the screwed part was
always ** proud " of the rest of the bolt. Thus if the thread of a
3-inch bolt was one-fourth of an inch deep, then the body
was turned down until it was something less than 2J inches in
diameter. In most cases the fire-box stay bolts of locomotives
are made in this way, but it is doubtful if an adequate return has
B.L. H
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98 THE RAILWAY LOCOMOTIVE
been obtained. The Palliser principle works to admiration in
dealing with sudden stresses or shocks, but it does not appear to
be equally efficacious when a bar under steady stress is bent
frequently through very small angles. At all events, stay bolts
are still prone to break ; and it is held by many engineers that
the best chance of success lies in providing a wide water space,
which gives a long bolt, and making the bolts thicker. As much
as IJ inch over the threads has been adopted with success.
When a stay is renewed it is almost always necessary to enlarge
and retap the holes, and then stays of 1 J inch over the threads
are put in. In the United States no stay bolts less than | inch
diameter are used in locomotive fire-boxes, and then only for 150 lbs.
pressures. Both in the United States, in this country and on
the Continent various materials have been tried. In America
the preference is given to treble-refined iron, but then copper
boxes are almost unknown in the United States, mild steel taking
the place of the more expensive metal. In this country, although
steel is used to a limited extent, it has not met with general
favour, and the stay bolts are almost always of copper. Various
bronzes have been tried, and for the lower rows of bolts bronze
is still being used to some extent. Lately recourse has been had
again to Bowling or Lowmoor Iron. The strength of a fire-box
is largely dependent on the riveted heads of the stay bolts, and
these are very liable to be worn away by the friction of the fuel
against the sides of the box.
It is worth notice that although theoretically the bending
stresses are the same at each end of the bolt, yet that ife is usually
at the inside of the outside plate that fracture occurs.
The pulling stresses on the bolts are very moderate. Each
has to support an area of 4 by 4 = 16 square inches. With a
pressure of 200 lbs., this gives 3,200 lbs. as the tension. If the
bolt has been turned down to '601 inches area and we take the
ultimate strength of copper at 16 tons or 35,840 lbs. per square
inch, then 35,840 X '601 = 21,600 lbs. as the breaking strength
21 600
of each bolt, and * = 6*4 which is the factor of safety when
the boiler is new. Apparently this is enough, but as it is
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STAY BOLTS 99
unquestionable that deterioration begins from the first day, few
engineers regard it as sufficient, and for these higher pressures
larger diameters or closer spacing is always adopted. Stays as
much as 1 J inches diameter spaced 8 J inches centre to centre, have
been used.
How long a stay bolt will last is a vexed question. According
to some authorities, long before fracture is likely to take place,
the rivet heads will have been worn off and the stay begin to
leak. A great deal of this difference of opinion seems to be due
to varieties in the quality of the coal used on different lines,
methods of firing, and, above all, the characteristics of the metal
of which the stay is made. An explosion which occurred on the
Hull and Barnsley Eailway last September is so instructive and
bears so directly on what has just been said, that particulars of
it may well find a place here. The three engravings. Figs. 41, 42,
43, show the construction of the fire-box and the effect of the
explosion. The crown was supported by sling stays G G for
about two-thirds of its length. Thence onward by three trans-
verse bridge stays, E, the ends of which rested on angle irons
riveted to the inside of the outer fire-box ; the water spaces
do not appear to have been more than 2 J inches wide. The fire-
box seems to have always given trouble, no matter for surprise
when the great depth of the thin sheets of water at the sides of
the box are considered. Fig. 44 is very instructive, showing as
it does how the inside ends of the stays disappeared. The
riveted heads first went, then leakage took place and caulking
began, and the unfortunate stays had their ends beaten down in
the plate until they lost their hold, and this took place in less
than two years. The engine (a goods tank) was standing in a
siding when, about 3 a.m., it exploded ; the driver who was on the
footplate was killed, the fireman who had gone to a signal box a
little way off was not hurt. The Board of Trade report states
that " The explosion was caused by the failure of a group of
stays, about 30 in number, situated near the bottom of the left-
hand side of the fire-box in the 2nd, 3rd, 4th, and 5th rows,
counting from the bottom, the attachment of which to the copper
plate had become most defective. The clenched heads of these
h2
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100
THE EAILWAY LOCOMOTIVE
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STAY BOLTO 101
stays were completely wasted away, and this part of the fire-box
side was in consequence dependent for support on the screwed
parts of the stays in the stay holes, but owing to the repeated
hammering and caulking of the ends to make them steam tight
the threads had been seriously damaged and the stays had become
too short, the ends being below the fire surface of the plate. In
this condition they were unable to support the plate, and the
latter was forced over the ends in the form of a bulge. Once the
bulge started the surrounding part of the plate appears to have
slipped easily and rapidly over the adjacent stays, many of which
also were without proper heads, the scalding steam and water
escaping through the stay holes into the fire-box and thence to
the atmosphere. When the bulge had extended the full length
of the side of the fire-box to the back plate and tube plate, these
crumpled in and the bulged side appears to have begun to tear
away at the two upper corners simultaneously, and after com-
pletely tearing along the top, it was driven downwards, hinging
along a line level with the top edge of the upper row of rivets
attaching the bottom part of the side to the foundation ring, and
it appears to have held on at this part until the plate itself had
bent through an angle exceeding 180 degrees from its original
position. The plate was then blown to the left-hand side of the
boiler, its flight in that direction being due to the bottom edge
remaining attached to the foundation ring until the last. The
failure of the side stays described above occurred with extreme
rapidity, the whole operation lasting probably less than a
second."
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CHAPTEE XIII
THE FIRE-BOX
Slingbolt
Fire
We have now to consider more in detail how the crown sheet
or top of the fire-box is supported. In the older type of engines
the outer shell is always semicircular. The metal is in tension,
and no staying is required. Two methods of supporting the
inside box have been mentioned. The first, and by far the most
common, consists in bridging the top with girders, and slinging,
so to speak, the crown sheet from these girders. Formerly the
girders were always made each of two
wrought iron flitch plates, riveted to-
gether with distance pieces between.
The sling bolts came up between them,
and the nuts were carried on large
washer plates spanning both bars. In
the present day cast steel bars are used.
These have nipples on them which are
bored and tapped, and into these the sling bolts are screwed as at
N N, Fig. 39. The ends of these girders, no matter how they are
made, are extended downwards and very carefully bedded on the
fire-box in a way which will be best understood from the sketch,
Fig. 45. In most cases — invariably in this country — the girders
run fore and aft instead of transversely. Seeing that the shorter
a beam is the stronger it is for a given section, this appears to
be a mistake. The long girder has not been retained without a
reason however. The internal fire-box is always built up of a
single sheet of copper — which may be as much as 8 feet wide by
18 or 20 feet long— a front plate known as the tube sheet, and a
third known as the back plate. The system is rendered necessary
by the fact that the tube sheet is nearly twice as thick as any of
Fig. 45.— Girder stay.
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THE FIKE-BOX 103
the other plates. The back plate and tube plate are flanged
inwards all round, and the plate forming the sides and crown is
riveted over these flanges in the way shown in Fig. 45. On the
flanges rest the toes of the girders, which transmit their load
down the vertical plates, which are stiffened by the stays and
the tubes, so that they cannot buckle. Ultimately in this way
the stress is transmitted to the foundation ring. If the girders
ran across they would find no adequate bearing for their toes ;
but besides this, as holes fitted with screw plugs are provided in
the upper part of the outside back plate, clearing rods can be
passed between the girders to remove deposit from the crown of
the fire-box in a way that would be impossible with the trans-
verse girder. It is also thought that the circulation in the boiler
is better with longitudinal girders. The strength of these girders
is generally calculated by the formula for a beam of uniform
section, supported at each end and carrying a distributed load.
Let w = the load in pounds,
b = breadth of beam in inches,
d = depth of beam in inches,
I = length of beam in inches,
c = a constant, usually 16,000,
Then ^^'QQ^ X/' X ^ = safe load.
Of course when the girder consists of two flitch plates, b will
equal the sum of their thickness.
The reader will probably have noticed that many of the
locomotives of the Great Western and Great Central Railways
have boilers with large rectangular structures over the fire-box.
The illustration Fig. 46 of one of Mr. Churchward's boilers
(p. 104) shows this very clearly. The side plates of the outer fire-
box, instead of forming a semicircle as just described, are carried
up and united by a flat at the top, in so far representing in shape
the inside fire-box. This design was the invention of Mons.
Belpaire, a Belgian engineer, and it possesses several advan-
tages. It gives a large steam spac§, and it entirely dispenses
with the heavy bridge girders. The method of staying is the
first referred to on p. 95. The crown of the inside fire-box
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THE EAILWAY LOCOMOTIVE
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THE FIEE-BOX 105
is supported by screwed stays just as the sides are, only the stays
are much longer. The flat sides of the outer box are supported
by transverse stay bolts. Some modifications in the size and
arrangement of the stays have been introduced by different
makers, but with these we need not concern ourselves.
Attention has been directed to the prejudicial action of expan-
sion and contraction. It is the usual practice, as already stated,
to tie the bridge stays each by two slings, P P (Fig. 89), to the
semicircular crown of the fire-box. However tightly these may
be screwed up when cold, as soon as the box is heated, by rising
it leaves the slings slack, and they can then give no real support.
The idea is, however, that they prevent the gradual crumpling
down of the front and back plates under the toes of the girders,
and that in any case they will help to prevent the blowing down
of the crown plate should the side stays give way and permit
the fire-box plates to buckle in. It does not appear, however,
that there is any recorded instance of this. When a crown
collapses the girders or the slings break. Unless care is taken
in fitting the slings they may do much harm. It is right to
state here, however, that many engineers hold that the rising of
the inner box only takes place when steam is being got up, and
that when the boiler is fully heated the slings to the roof are
again tight. But the fact remains that the co-efficient of the expan-
sion of copper being much greater than that of steel, the crown
of the inner box must be higher up in the boiler when it is hot
than when it is cold. To this it is replied that the outer crown
rises a little by expansion while the roof girders spring or deflect
downwards a little under the load, and so the slings come into
use. Whatever force may be allowed to these arguments as
mere expressions of well considered opinion, the fact seems to
remain that girder sling stays prevent the gradual crushing down
of the tube plate, which in process of time makes the holes oval
and renders it almost impossible to keep the tubes tight. No
doubt the parts under stress fight it out among themselves and
adjust their differences. We may take as proved that the all but
universal employment of these girder slings is not the result of
fashion or prejudice ; they are of use or they would not be fitted.
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106 THE EATLWAY LOCOMOTIVE
A very simple boiler has been made by slightly curving the top
of the inside box and staying it directly to the curved top of the
outer box, some of the stays, of course, radiating, as in Pig. 41.
But the stays then prevent the inner box from rising when
expanding, and a heavy stress is put on the foundation ring,
tending to buckle the plates at the root of the fire-box. At first
sight, the Belpaire arrangement would be open to the same
objection, but it is not, because the plates are flat and pliable,
and stresses are taken just as they should be taken. Two
objections have been urged against the Belpaire design ; one is
that it is very ugly, which we may pass over ; the other is more
serious. It is, that the external fire-box interferes with the
driver's view. On the continent the objection does not apply,
because a footplate at least a foot wider than that which the
loading gauge permits in this country is admissible.
The reader is referred to detailed descriptions of the locomotive
for information about the various methods in use for supporting
such plates as the back plate above the inside fire-box, and the
smoke- box tube plate above the tubes. It is enough to say here
that longitudinal steel bars running from end to end of the
boiler in the steam space are often used.
Mention has been made of the foundation ring, sometimes
called **the bottom rail,'* by which the space between the inside
and outside fire-box is filled up at the bottom. It has already
been shown in section. Fig. 39. It is in the present day
almost invariably a rectangular steel casting softened by anneal-
ing. When it has been roughly fitted it is ground all over to
remove scale and impart a true surface. It is put in place and
holes are then drilled through it and the inside and outside
boxes, and rivets subsequently put through these secure the
boxes to each other; afterwards the seams are caulked on the
outside. Foundation rings, if well made and fitted and properly
riveted, give little trouble.
A firing hole is provided in both the inside and outside fire
box. The space round this must be filled up. At one time,
a ring precisely similar to the foundation ring, but much
smaller, was used in the same way, see Fig. 39. For some
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THE FIEE-BOX
107
reason, not quite clear, the inner seam between the copper and
the ring was very liable to leak. One improvement consisted
in dishing the copper plate, so that only a thin ring was
required. This checked leaking, but the copper was found liable
to groove or crack in the dished part, and the method shown
in the accompanying sketch, Fig. 47, invented by the late Mr.
Webb, of the London and North Western Eailway, finds much
favour. The inside fire-box is bent outwards all round in the
form of a truncated cone. The back plate of the outside box is
dibhed in like .manner to fit it. The inside fire-box without the
foundation ring, can be dropped in as far for-
ward as it will go, and is then pushed back
until the inner cone slips into the outer one.
A special tool for drilling the plates in place .
for the rivets is used.
Some diversity of opinion exists as to the
quality of the copper in a fire-box. Many nrabox
engineers specify for **pure" copper. This
appears to be a mistake, for pure copper is
very soft and will not withstand the attrition
of the burning coals. The consequence is that
the lower parts of the boxes are worn thin, and
have to be renewed. It is a much safer prac-
tice to specify for " best " copper, which is by ^i^- 4'^-
no means the purest. The specification in use on the London
and South Western Eailway is given here.
** The copper is to be of the very best quality manufactured,
and to be of the exact dimensions, both as regards form and
thickness, as given on the drawings or list supplied.
" The copper plates are to be properly annealed, and a piece
taken from each plate must stand the following tests, viz. : —
" The ultimate tensile strain to be not less than fifteen tons
per square inch, with an elongation of not less than 40 per cent,
in 2 inches.
** A piece 6 inches long is also to be bent double when cold
without showing signs of fracture at the heel of the bend.
"A duplicate test piece to be sent to Nine Elms to be tested.
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108 THE EAILWAY LOCOMOTIVE
** Any question arising must be referred to the Chief Mecha-
nical Engineer, whose opinion and decision are to be taken as
final and binding."
The grate H, Fig. 39, which in this country is always made
of thin wrought iron or steel bars, wedge shaped in cross
section, is carried on bearers, resting on studs screwed into
the copper box. A great many patents have been taken out for
improvements in grates, and some of very ingenious construc-
tion are in use in other countries. They are usually of the
** rocking*' type, and are intended to break up slag, and keep
the air spaces clear. They are not used in this country, because
the coal is good and clean.
Great diversity of practice exists as regards fire doors. No
two railways use the same kind of door. It has to be so small
that the amount of air passed through the fire hole can be
regulated, and it must be under the control of the driver with
one hand, as he opens it for every shovelful of coal put in by
the fireman, closing it again immediately. A long chapter
might be written on fire doors alone, the quality of the coal and
the method of firing mainly determining its construction.
In the early years locomotive furnaces had no ash pans.
The dropping of red-hot cinders on the road was found to be
objectionable, and a plain " scoop *' of sheet iron was placed
under the box. This caught the cinders ; but it did more, its
open mouth caught the air, which rushed up through the fire-
bars and greatly promoted combustion, too much so indeed.
Then a flap was fitted in front, controlled by a rod from the
foot-plate, and the fireman found himself provided with a very
efficient means of regulating the draught. When the engine was
standing, by closing the damper he could save fuel and prevent
waste of steam. But further experience showed that the ash pan
might be made to play a more important part. The combustion
of the fuel is effected partly by air admitted through the grate
bars and partly by air admitted through the fire hole. The latter
is regulated by the fire door, the former by the ash pan damper.
Long since the ash pan became a somewhat elaborate con-
trivance. In the United States the dampers are sometimes worked
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THE FIEE-BOX 109
by steam cylinders. The following description of the ash pans
designed for use on the London, Brighton and South Coast Rail-
way is taken from a paper which was read before the Institution
of Civil Engineers by Mr. Stroudley. Speaking of the Gladstone
class of express engines with four coupled drivers and a pair of
trailing carrying wheels under the foot-plate, he said : ** Care
has been taken to provide these engines with means for eflfecting
perfect combustion of the fuel, and to prevent the emission of
sparks. To do thig, they have been fitted with an air-tight ash-
pan, which has an angle across the opening for the damper at
the back. Water is allowed to escape into this to quench the
ashes, and so keep the firebars cool and in good order. A
deflector-plate is placed across, above the opening for the
damper, pointing inwards, and this throws the cinders which
fall near the opening towards the centre of the ash-pan. The
opening itself is covered to within 4J inches of the top, with a
perforated plate mounted on hinges ; this allows the air to pass
into the ash-pan, and prevents large cinders from falling out.
A damper, having a handle convenient to the driver, is arranged
to shut practically air-tight, giving him the means of adjusting
the amount of air. These contrivances, combined with the
comparatively extensive grate and heating- surface, and with
large blast nozzle, entirely prevent the emission of sparks. The
ashes carried forward into the smoke-box would pass through a
sieve having J-inch mesh ; the average quantity being, for the
heavy passenger or goods engines, about 2J cubic feet per
100 miles run.''
All the air for the grate is admitted at the back, not the front,
of the ash pan.
The flue tubes, B B, Fig. 39, which run through the boiler
barrel, are usually 2 inches in diameter and 8 to 11 feet long in
this country. In the enormous boilers which have come into
vogue in the United States they are 14 to 20 feet long and as
much as 3 inches in diameter.
In British practice, they are usually spaced f of an inch
apart. In some boilers, tubes have been used only 1 J inches in
diameter inside, spaced but f inches apart. This is bad practice,
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no THE RAILWAY LOCOMOTIVE
because evaporative efficiency depends, as will be shown when
the actual working of a boiler is dealt with, on much besides
heating surface. The late Mr. W. Adams, many years ago,
when locomotive superintendent of tho North London Eailway,
startled the world by introducing 1-iiich water spaces — a wholly
unorthodox innovation — with 2-inch tubes. Instead of losing in
power his boilers steamed much better than before, and the
tubes did not leak.
Flue tubes are made of copper, brass, mild steel, or mild steel
with a length of about one foot of copper brazed on to them.
The holes in the smoke-box tube plate are always bored from
^ inch to J inch larger than those in the fire-box tube plate.
The leading end of the tube for a length of 2 or 3 inches is
swelled out to fit the larger hole ; the purpose of this is to facili-
tate the taking out of a tube, which always has a little scale on
it. This will pass through the larger hole.
As an example of modern practice a Lancashire and Yorkshire
Eailway tube specification is given here : —
" Copper tubes must be solid drawn and seamless, perfectly
sound and well finished ; free from surface defects, and also
capable of withstanding expanding and bending, without show-
ing the least sign of splitting, or cold shortness. The ends must
b3 left * hard,' or * half hard,' throughout, because, if the ends
are annealed, the junction of the hard and soft metal becomes
a plane of weakness, and the tube invariably collapses there.
The thickness must be 10 I. W. G. = 0-133 inches, for 12 inches
from the fire-box end, and then taper from 10-12 I. W. G. in
a length of 18 inches. The remainder parallel 12 1. W. G. thick;
to be swelled ^ at the smoke-box end to facilitate withdrawal.
The weight per lineal foot is as follows : —
" Diameter Outside.
If in. .
.. 1-98 lbs.
If ,, .
.. 2-15 „
A maximum of 10 per cent.
IJ „ .
.. 2-31 „
above each, and 5 per cent.
2 „
.. 2-47 „
under will be allowed.
2i „ .
.. 2-63 „
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THE FIEE-BOX 111
" They must be free from dirt inside and out, each tube must be
branded, and capable of sustaining an internal pressure of
800 lbs. per square inch and an external pressure of 250 lbs.
per square inch."
As to the popularity of various materials, the author is indebted
to the North British Locomotive Co., Hyde Park Works, Glasgow,
for the following facts. Of the last 834 locomotives built by
the Company, 566 had brass tubes, 61 had copper tubes,
89 had steel tubes, 118 had iron tubes. On the Great Western
Eailway mild steel tubes have been used exclusively for some
years. In the United States steel or iron tubes are always used.
The quality of the tubes and the way in which they are fixed
in the plates is of very great importance. The leakage of tubes
is a matter of almost daily occurrence, and when it is at all
considerable it is very mischievous.
For many years the tubes were always fixed in the same way.
They were put in place, and then a smooth tapered ** drift " was
hammered into them. The metal was in this way expanded and
the joint between the tube and the plate made good. To maintain
tightness, a ring called a ferrule, about 2 inches long and one-
eighth of an inch thick, made of wrought iron or steel, and
slightly tapered, was then driven into the tube. The smoke-box
end was not considered to need ferrules, because it was of iron,
not copper. If a tube leaked afterwards the ferrule was driven
in a little further. Sometimes the tubs plate was cracked in this
way ; more often a tube was split. It was no uncommon thing
to see an engine running with a dozen tubes plugged at each
end with hard wood plugs, which were carried as part of the
tool-box outfit. The *' expander,'' invented by Mr. Dudgeon,
wrought a great improvement. The expander is a small circular
frame in which are put a number of little hardened steel rolls.
These can be forced apart by a tapered steel drift. The tool is
provided with a heavy cross handle, by which it can be caused
to revolve. It is placed in the end of the tube, the drift driven
in by a tap with a light hammer, and the whole turned round
by the cross handle. The little rollers then revolve inside the
tube and literally roll out the metal, expanding the tube in a way
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112 THE RAILWAY LOCOMOTIVE
quite different from the action of the plain drift, and hardly ever
splitting a tube. Tube-fitting in this way has become a very
simple and straightforward job, requiring little skill, while
drifting in the old way was a work demanding much practice
and skill if the result was to be satisfactory.
If instead of plain rollers grooved rollers are used, then the
tube ends can be swelled out on both sides of the plate. A
beading tool on the same principle turns over the end of the
tube and so prevents it from being pulled through the plate.
Ferrules are still almost always used at the fire-box end, not to
keep the tube tight, but to save the ends from destruction by the
attrition of the minute hard cinders which are drawn through
by the powerful draught.
Tube leakage is a disease from which the locomotive boiler is
very likely to suffer. It is due t6 expansion and contraction.
The tube expands, and if neither the fire-box nor the smoke-box
plates will give way, the tubes slip in the holes. They are
also liable to expand diametrically to such an extent that they
dilate the holes in the copper tube plate beyond the elastic limit
of the metal. The result is that when they cool they are slack
enough in the holes to leak. Various methods of dealing with
longitudinal expansion have been tried. One used by the late
Mr. W. Stroudley on the London and Brighton Railway consists
in cambering the tubes a little more than one diameter. Tlius
an 11 foot tube, 2 inches in diameter, would be uniformly curved
by about 2J inches. When the tube expanded the camber
increased for reasons sufficiently obvious. In other cases the
smoke-box tube plate has had flexibility imparted to it by making
it with a corrugated ring all round. The best and simplest plan,
however, consists in making the front plate so large that a good
margin exists all round between the tubes and the rivets by
which it is attached to the shell.
The accompanying table may be taken as representing average
practice of the best kind. Some makers turn out rather heavier,
others rather lighter boilers with almost the same amount of
heating surface. It must not be forgotten that pressures over
180 lbs. remain the exception and not the rule. Pressures of
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THE FIRE-BOX 113
200 lbs. and upwards entail difficulties in manufacture and
maintenance. The boilers are heavier and require more staying,
and they wear out sooner in the fire-box. Altogether it remains
a disputed question whether an increase of pressure above 180 lbs.
is justified commercially.
Weight of LocoMOTnrE Boilers.
The weights given are of complete boilers with fire-bars, but without any
mountings.
Working Pressure 160 lbs. per sq. inch.
Heating surface 976 sq. ft. . . 1,592 sq. ft. . . 1,956 sq. ft
tons cwt. tons cwt. tons cwt.
Weight of boiler and fire-bars .. 10 10 12 10 .. 15 5
Working Pressure 170 — 180 lbs. per sq. inch.
Heating surface 1077 sq. ft. . . 1,349 sq. ft. . . 1,931 sq. ft.
tons cwt. tons cwt. tons cwt.
Weight of boiler and fire-bars .. 10 10 13 .. 17
R.L.
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CHAPTEE XIV
THE DESIGN OF BOILERS
The smoke-box appears to be a very innocent addition to the
boiler ; not a thing about which much controversy can exist, yet
it may be doubted if any other portion of the locomotive has been
made the subject of keener disputes, or more varying practice.
For a full explanation of the reason why, the reader must wait
until a consideration of the locomotive at work comes up. For
the moment it must suffice to point out that it is of extreme
importance that sparks should not be ejected up
the chimney which might set fire to crops at
the roadside in dry weather ; while on the con-
struction of the box, and on what is inside it,
depends in considerable measure the economy
or the reverse of the boiler.
Usually the front tube plate and the front
plate of all are rectangular below, and they
rest on the cylinder castings when these are
inside; or they are united by a flat horizontal plate. The bottom
of the box is always filled in with fire bricks, set in fire clay,
on which the hot cinders and ashes which come through the
flue tubes are deposited. The boiler is invariably secured in
the side frames at the smoke-box end. This is done in various
ways, but it is always done. The fire-box is fitted with two
angle steels riveted to it. The heads of the stay bolts in the
wake of the side plates are countersunk to form a flush surface,
or holes are drilled in the angle so as to fit over the stay bolt-
heads, and the fire-box outer shell fits closely between the frames,
to which are also riveted two angle steels on which those of the
boiler rest, as shown in the sketch. Fig. 48. A few bolts passing
Side Frame
Fig. 48.
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THE DESIGN OF BOILEES 115
through oval holes and a slack fit are sometimes put through the
angle irons, or a species of clip is put over both. As the boiler
expands and contracts the angle steels on the fire-box slide
backwards and forwards on those on the frames and straining is
thus avoided.
To large numbers of boilers domes are fitted. These are short
cylinders of steel, with tops bolted to them, sometimes made of
cast iron, sometimes dished out of steel plates. The domes have
large curved flanges at the bottom, by which they are riveted to
the barrel. As a large hole is cut out in the barrel, a strengthening
ring is fitted inside and the rivets pass . through the three
thicknesses of plate.
In some cases the dome is made large, and is regarded as an
important factor in providing steam space. The steam, too, was
always taken off by an internal steam pipe which opened higher
up, above the general water level in the dome. The modern big
engine boiler is so high that there is no room for a high dome,
and that which is used plays rather the part of a convenient
casing for the regulator valve than an addition to the steam
space.
In the designs of boilers considerable differences exist. So
long, however, as they are of moderate size, that is to say, with
a heating surface of 1,200 to 1,400 square feet, and grates with
18 square feet or so of surface, they are all very much alike.
The standard modern English locomotive is of the 4 — 4 type,
that is to say, it has a four-wheeled bogie in front, and four
coupled driving wheels; the cylinders are 18 or 18J inches
diameter, the stroke 26 inches, and the working pressure 160 lbs.
The driving wheels are 6 feet, or 6 feet 6 inches in diameter ;
the side coupling rods about 8 feet long. Between these there is
no diflSculty in getting in a fire-box 6 feet long. Mr. Drummond,
chief mechanical engineer of the London and South Western
Eailway, has not hesitated to use side rods ten feet long, and
they have been quite successful.
The shape of the internal box is modified by various considera-
tions which have greater or less weight with different designers.
The normal outer box for engines of the 4 — 4 type cannot have a
i2
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116 THE EAILWAY LOCOMOTIVE
greater width at the bottom where the grate rests than 4 feet
1 inch, the gauge being 4 feet 8J inches. If from this we deduct
the thickness of four plates, the inside and outside fire-box, two at
each side — say, 2J inches, we have left, allowing a 3 J inch water
space at each side, 3 feet 2J inches for the width of the grate ;
with a 2J inch water space it may be 3 feet 3 J inches wide. By
reducing clearance, a little here and a little there, the absolute
width of the box may be slightly increased so as to give a grate
3 feet 4 inches wide with a 2J inch water space. The idea is, of
course, to get the largest grate area possible, but it will be shown
further on that an increase or decrease of two or three inches in
the width of a grate is of no importance, while an extra inch
given to the water space may be of the utmost value. There is,
indeed, excellent reason to believe that when pressures of 200 lbs.
or over are used, the water spaces should in no case be less than
4 inches wide. It has been shown already that the longer the
stay bolts are the better, because they are more flexible. But it
is imperative that the circulation of water should be thoroughly
efficient to prevent the plates from becoming over-heated.
Copper, there is every reason to believe, deteriorates in quality
when. exposed for long periods to severe stresses when heated.
The metal is always hotter than the water in the boiler ; the
temperature proper to 240 lbs., absolute — 225 lbs. safety valve
pressure — is 397° P. That of the inner face of the plate is
perhaps twice this, and may be much more unless fairly
** solid " water in rapid movement is in the water space.
So far the fire-box has been spoken of as though it was in all
respects rectangular with the exception of the bending at the
corners. This view is, however, incorrect, if we except very
small locomotives. It has been pointed out that the width of the
lower portion, of the external fire-box cannot much exceed 4 feet,
while that of the internal box can only be about 3 feet 3 inches.
If now the inner box were carried up straight it would be
impossible to get in a sufficient number of flue tubes ; accordingly,
the inner box is wider at the top than the bottom, and in this
way a barrel even 5 feet in diameter can have all the tubes it will
accommodate, say 300, put in.
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THE DESIGN OF BOILEES 117
But this is not all. The enormous engines now in use are
fitted with grates as much as 9 feet long. These must be placed
over the axle of the last pair of wheels and with this object the
grate is made in two portions, one horizontal, next the fire door,
and the other steeply inclined. The fire-boxes inside and out
are cut to fit. This is very clearly seen in the photograph of a
Great Western boiler on page 104. In certain cases the front
portion only of the box is curved, the width required to accom-
modate the tubes being obtained by ** pocketing out '' the side
sheets. The advantage is that more water space is left in the
** legs " at each side. It is essential in some respects that when
a boiler is large the fire-box should be deep. Now for reasons
that will be explained, sunken or deep boxes do not make steam
as freely as shallow boxes. To improve the deep box, Mr. Dugald
Drummond, Chief Mechanical Engineer of the London and South
Western Eailway, some years ago puttransversiB water tubes into
the fire-box, an experiment which answered so well that a
large number of the most powerful express engines on the line
have been fitted. A cross section of a fire-box is given on page
118, Fig. 49. The tubes A A are of very mild steel set on a slight
incline, and are " rolled " into the inner box side plates just as
though they were flae tubes. Access is got to them by doors at
each side. These doors are carried on hinges for convenience,
but the hinges have nothing to do in the way of securing them.
The doors are made with faced joints, which are bolted to steel,
faced, rectangular castings B B bolted in their turn to the outside
of the fire-box shell. Through a certain number of tubes are
passed stay bars C C so that the outer shell is properly braced.
It can be proved that if a tube containing water is put on a slight
incline, say one inch to the foot or even less, provided it is not
more than twenty-four diameters long, it cannot be over-heated,
the circulation within being very ample. The endurance of the
Drummond tubes seems to be almost phenomenal. Their average
life is eight years and two months and their average mileage is
306,992. After 200,000 miles they are clean inside and as good
as new, and this although they are exposed to the highest
temperature in the fire-box, which nearly approaches that of a
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118
THE EAILWAY LOCOMOTIVE
steel melting furnace. In the section it will be seen that bridge
girders are not used. The crown of the fire-box is slung to the
CROSS SECTION OF FIREBOX
FiG« 49. — Drummond's water tube fire-box.
outer roof plate. But it will also be seen that the slings being
in couples and fitted with nuts resting on cross pieces, the
internal fire-box is quite free to rise when the fire is first lighted,
simply lifting the nuts off the cross bars. With the advent of
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THE DESIGN OF BOILERS 119
pressure the nuts come down again to their bearings. In this
way the principal objection to the sling stay is removed.
One other type of fire-box has to be described. In this country
the best coal in the world is available for locomotives, and we
have as yet built but a few boilers which can compete in dimen-
sions with those of some freight engines in the United States.
So long as the fire-box is placed between the frames, the maximum
grate area cannot well exceed 28 square feet. This means a
grate nearly 9 feet long, which is not easily fired. In Belgium
much of the locomotive fuel is ** dead slack.'* It is little more
than coarse dust, and being moistened it is not much unlike
black mud. This is burned by being spread out thinly on
enormous grates — as much as 70 square feet in a few cases — 50
square feet is quite common. Engines may be much wider in
Belgium than in Great Britain, because Belgian platforms either
do not exist at all or are very low. The fire-box does not go
between the frames but rests on top of them. A width of as
much as 9 feet being given to the external fire-box, grates 6 feet
wide and 9 feet long become possible. There are two fire doors
because the grate could not be kept covered from one. In this
country a few locomotives of the ** Atlantic " or 4 — 4 — 2 type
have been built in which the external fire-boxes are about 6 feet
wide. The grates stand over the trailing wheels, which are of
comparatively small diameter. The details of construction do
not demand any special description. They are in all respects
similar to those already dealt with.
Incidentally, it may be mentioned that various attempts have
been made to get rid of the flat-sided firebox. Thus circular
corrugated furnaces similar to those in a marine boiler have
been tried on various railways with but moderate success. It
is very improbable that the normal box will be displaced by
innovations.
It is assumed that the reader has now formed an adequate
conception of not only what the locomotive engine boiler is, but
why it is what it is. We have next to consider what it does, the
nature of the work it performs, and how it does it. It is worth
while, however, to repeat that there is no other type of steam
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)20 THE RAILWAY LOCOMOTIYE
generator so suitable for being carried about the country at a
high speed on a wheeled vehicle. Into none others could so
much heating surface be put of just that kind best fitted to absorb
the energy of a furnace working at a temperature not attained
in any other boilers, save those of torpedo boats, and giving oflf
huge volumes of intensely hot gas. It is not so much that the
locomotive boiler is excellent, as because it is the only practic-
able boiler that it enjoys universal favour. It is in nowise too
much to say that it is to the locomotive boiler we owe the success
of the railway systems of the world.
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CHAPTER XV
COMBUSTION
It is advisable here for the sake of completeness to put before
the reader a few general facts concerning combustion. They
ought to be known, although they are little considered in the
everyday life of a railway.
The burning of coal means the chemical combination of
oxygen, carbon and hydrogen, with the evolution of heat,
carbonic oxide, and water in the form of steam. With the various
other combinations of carbon, hydrogen, and oxygen, which take
place we need not here concern ourselves. They have interest,
of course, for the chemist, but not for the locomotive superinten-
dent, the engine driver or fireman.
In most text-books it is taught that the whole of the energy
comes from the coal, in which it has been stored up by the sun's
rays acting on trees and plants millions of years ago, but no
attempt is made to say how energy exists in the inert black
substance. That remains one of the insoluble mysteries of
nature. It may, however, not be out of place to advance here
the theory that the energy does not reside in the coal, but in
the gas with which it combines. Thus the molecular energy —
that is to say, the energy due to the motion of its molecules — is
much greater in oxygen than it is in carbonic acid gas. But
this gas is the result of the combination of oxygen with
the carbon. The difference appears as heat. If we turn to
hydrogen, we find that probably of all known substances it pos-
sesses the highest molecular dynamic energy. Accordingly, when
it combines with oxygen, water is formed which has little or no
molecular energy, and the result is the liberation of the largest
quantity of heat that can be obtained by direct combustion.
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122
THE BAILWAY LOCOMOTIVE
Leaving, however, the region of theory and turning to that
of fact, the following figures, which show the heat of combustion
with oxygen of one pound each of the substances named, in
British thermal units are given, and also what is perhaps more
to the point, in pounds of water evaporated from and at
212° F. The required weight of oxygen is also given. The figures
are the result of a series of experiments carried out by MM. Favre
and Silbermann some sixty years ago. Certain corrections have
been made since, but they are unimportant refinements.
Combustible.
Pounds of
Oxygen.
Pounds of
Air.
Total
B.T.U.
Evaporation.
Hydrogen gas
Carbon imperfectly
burned to CO
Carbon completely
burned to CO2
8
U
2J
36
6
12
62,032
4,400
14,500
64-2 lbs.
4-55 „
15 „
Rankine deduced from these figures the following formulae
for general application : —
Let C H and be the fractions of one pound of the compound
which consists respectively of carbon, hydrogen and oxygen, the
remainder being nitrogen, ash, and other impurities. Let h be
the total heat of combustion of one pound of the compound in
B.T.U. Then
h = 14,500 I C + 4-28 (H - 1)1 (1)
Let E denote the theoretical evaporative power of one pound
of the compound in pounds of water evaporated from and at
212° F. Then
The facts of interest, as concerned with locomotive perform-
ance, are mainly that combustion should be so carried on that
no CO shall be made. This end can be attained in theory with
ordinary coal by admitting a minimum of 12 lbs. of air per
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COMBUSTION 123
pound of coal. In practice, however, no complete union of all
the oxygen can be obtained ; and the minimum quantity of
air requisite is about 18 lbs. per pound of coal. At 62° this
would occupy a volume of about 235 cubic feet ; then if a loco-
motive is running at 60 miles an hour and burning 80 lbs.
of coal per mile, the volume of air admitted to the fuel
will not be less than, in round numbers, 7,000 cubic feet.
But at 2,000° F. a pound of air occupies 62 cubic feet,
instead of 13 cubic feet, and so the volume which has to be
withdrawn from the fire-box through the tubes is not less
than 88,480 cubic feet per mile and per minute. Inasmuch,
however, as the gas is rapidly cooled in its passage through
the tubes, it contracts in them, and thus, although 33,480
cubic feet enter at the fire-box end of the tubes, probably not
more than 16,000 or 17,000 are delivered into the smoke-box.
It must be carefully borne in mind that these figures are
simply approximations. They are based on the weight of air
used and do not include the volume of CO, for example, which
replaces an equivalent volume of air. They are given here only
in order that some idea may be formed of the quantities which
must be dealt with in the ordinary working of a locomotive
engine. Thus we see that while some 83,000 cubic feet have to
get into the tubes, only about 17,000 have to get up the chimney.
In order that this end may be attained means must be provided
for exhausting the smoke-box, so that the external pressure of
the atmosphere under the grate bars and at the fire door may be
greater than that at the top of the chimney. This result is
secured by turning the exhaust steam from the cylinders up the
chimney. It was the employment of the exhaust in this way
that enabled the " Eocket " to beat all its competitors at the Kain-
hill trials ; and a very keen discussion at one time took place as
to who invented a device which has proved of crucial importance
to the railway system. Indeed, it is in no way second in value
to the tubular boiler, which without the blast pipe would be
useless. It is true that forced draught by means of a fan might
have been adopted; but it could not compare in general
eflficiency and activity with the blast pipe. What the blast pipe
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124 THE BATLWAY LOOOMOTIYE
is, and how it works, will be considered when we come to the
smoke-box. The two original claimants for its invention were
Davie Giddies, a friend of Trevithick, and George Stephenson.
The honour of inventing it is also claimed for Trevithick him-
self, in the " Life of Kichard Trevithick,'' written by his grand-
son, Francis Trevithick, published in 1872 by Messrs. Spon,
will be found, on p. 154 of Vol. I., a letter which refers to a
locomotive for common roads, which was built to Trevithick's
designs in 1802. A passage in this letter has been construed to
mean that the exhaust steam was used to produce a draught ;
but as it stands the passage is quite unintelligible. On p. 125,
however, of this volume is a description of the famous Camborne
engine, the first locomotive that ever conveyed passengers, and
we are told that " The exhausted steam having done its work in
the cylinder at a pressure of 60 lbs. to the inch, passed into the
chimney as a steam blast causing an intensely hot fire, and in
its passage it heated the feed water."
There is reason to believe, however, that it was in no sense
any one's invention. The obvious way to get rid of the exhaust
is to turn it up the chimney. Thus, leaving Trevithick out, it
is known that this had already been done in Hackworth's engine
of the '* Puffing Billy '' type. Its action in promoting combustion
in the ** Eocket '' seems to have been a discovery rather than the
result of a direct act of invention. It is of interest to add that
it is fairly certain that the knowledge that a steam jet would
entrain air and so induce a draught was possessed by the old
Greeks and Egyptians. More to the point, however, is the fact
that in 1594 Sir Hugh Piatt published an enquiry and a
description of " a round ball of copper or of latten (brass) that
blowes the fyre verie stronglie by the attenuation of water into
ayre." The ball or balls were to be " hung in the chimney
directly over the fyre to cure smoky chimneys, for being so hung
the blast arising from them carries the loitering smoke along
with it."
For many years after railways began to play an important
part in the world's work locomotives were fired with coke. Most
of the railway companies manufactured their own coke. Fifty
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COMBUSTION 125
years ago coke ovens still existed near New Cross, the property
of the South Eastern Kail way Company. It was just the fuel
for the locomotive boiler. The tubes kept clean, there was no
smoke and no soot. It was believed that flame could not pass
through a tube only 1^ inches or 2 inches in diameter, and coke
made little flame. Engines on the best lines were spotlessly
clean. Drivers and firemen wore white clothes in summer.
When the steam was shut oflf the supply of air diminished and
much carbonic oxide was evolved. This escaping up the chimney
at a high temperature caught fire the moment it reached the
outer air. At night engines arriving at say, Eugby, came in
with a long trail of lambent blue flame from their funnels. The
sight was pretty, but not comforting to those whose luggage was
stowed, as was then the custom, on the roofs of the carriages.
Coke was an expensive fuel, and about the year 1860 a deter-
mined effort was made to substitute coal for it. Patents were
taken out by the dozen, and large sums of money were expended
by the railway companies with very indifferent success. They
could not burn bituminous coal without sending torrents of
smoke into the air, and the engines did not make steam. The
trouble was, however, at last got over by very simple means.
Across the fire-box was thrown a fire brick arch supported at the
ends on studs screwed into the copper plates, as shown at F
in Fig. 89. The forward face of this arch came below the ends
of the tubes. The rear side was pitched rather above the level
of the top of the fire door. Into the fire hole was fitted a sheet
iron scoop deflector, G, Fig. 39. When the train was running,
the fire door was left partly open, and the ash-pan dampers were
more or less closed. The products of combustion could no longer
rush straight into the tubes. They had to curl backward to get
to the upper side of the bridge. Now the bridge very quickly
became white hot, and kept up the temperature of the gases;
but these encountered a rush of air, which the scoop beat down
on them and the surface of the blazing coal below. The result
was that the space above the brick arch became full of a brilliant
white flame, and no smoke worth mentioning came out of the
chimney.
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126 THE BAILWAY LOCOMOTIVE
With various modifications, principally in the construction of
the fire door and of the bridge, as for example the use of toggled
instead of plain wedge-shaped bricks, this is the system
invariably adopted on all railways everywhere to-day where coal
is burned with a minimum of smoke. The arrangement is
represented diagrammatically in Fig. 89.
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CHAPTEK XVI
FUEL
It would be mere waste of space to reproduce here any of the
elaborate tables which have been prepared from time to time
setting forth the constituents of coal. The railway companies
purchasing coal by the 100,000 tons at a time do not much
concern themselves with analysis unless coal from a new seam
should be brought to their notice. The locomotive super-
intendents purchase particular coals or leave them alone as the
result of experience ; and the selection is based on quite other
considerations than a chemical analysis, which might be quite
misleading. Nevertheless, on all the great Railways coal testing is
continually carried on in the laboratories as a check on the results
of practice, and to make it as certain as the analytical chemist
can that the companies get full value for their money. Various
characteristics of the coal have to be kept in mind, and as a good
deal of misconception appears to exist, it is worth while here to
state the facts as they are.
Coal is only a means to an end. That end is the production
of steam. The price paid by the railway company for its steam
depends largely, but of course not altogether, on the performance
of the coal. Let us suppose that a given coal costs ten shillings
a ton, and that it is so good that each ton of it will make ten
tons of steam.
A different coal is to be had, however, which will make only
eight tons of steam per ton. This coal it will be said is inferior
to the first. So it is in one sense, but it may be selected notwith-
standing by the railway company because it costs only seven
shillings a ton. With the expensive coal seven shillings will
only supply seven tons of steam. The second-rate coal will give
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128 THE BAILWAY LOCOMOTIVE
eight tons for the same money. Here then we have one factor
in the work of selecting coal.
But not only has the cost of steam to be considered, but the
rate at which it is made. Thus a coal in other ways desirable
on the score of price, might be quite unfit for express work, when
the power of the engine is taxed to the utmost and steam must
be made as quickly as possible. The cheaper coal might, however,
answer very well for goods and slow passenger trains. The dear
coal might be a necessity for one class of traflSc, and cheap coal
quite suitable to another.
In the present day, moreover, there is a factor so important
that it in a way overshadows all others. The coal burned on
long continuous runs, such as are now fairly common on most
lines, must be free from any impurity which will cause clinkering.
Lime is a great offender in this respect. Again, a trace of iron
will cause the formation of " birds' nests " — rings of clinkers like
india rubber umbrella rings — round the ends of the tubes in the
fire-box, which obstruct the draught. At sea and on land, fires
can always be cleaned, but no cleaning can take place with a
running locomotive. If clinkers form on the fire bars they may
indeed be broken up, but the steaming power of the boiler will
be seriously affected. Time cannot be kept with a ** dirty fire."
The coal used on these long runs is known by experience to be
good. Nothing that can be done in the laboratory can give the
same certainty of the attainment of a desirable result.
Another quality essential to a good locomotive coal is its
keeping power. Large quantities are of necessity stored by the
railway companies. The coal parts continuously with its more
volatile constituents. No coal a year old is as good as coal
fresh from the mine. Some of the Welsh steam coals, in other
respects the best coal in the world, deteriorate rapidly by
** weathering." Some of the bituminous coals will keep for
years with little loss. It is practically impossible to gather from
chemical analysis whether a coal will keep well or not ; experience
is the only certain guide. Yet another factor is the mechanical
structure of the coal. Thus, some coals, otherwise excellent, are
exceedingly friable. They fall into dust the moment they enter
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FUEL 129
the furnace, and go through the bars or up the chimney. They
are besides bad to handle, being brittle and producing a large
quantity of slack and dust when put in or taken out of wagons
or tenders. Others again swell up in the fire, and check the
passage of air.
It will be seen that while the selection of a coal is simplified
so long as it is obtained from certain seams whose quality is
well known and whose reputation is kept up, it is by no means
easy when new supplies are offered in the half-yearly competition
for railway coal contracts.
We now come into a region of pure empiricism, namely, the
process of burning the coal whatever may be its quality. We
have seen how much air is needed, in theory — what the actual
quantity used is no one knows, because it cannot be measured.
The firing of a locomotive is skilled work. To get the best
results is an art not to be acquired in a few months, and never
acquired at all by some men ; and the reason is that there are
factors in operation which are quite inexplicable on any known
theory, and which can only be utilised or combated by men
who thoroughly comprehend what they are doing.
It is to be understood that we are speaking now of express
locomotives hauling heavy passenger trains at high speeds. As
a rule, the boilers of these engines are worked very nearly to
their utmost capacity. It is, therefore, inevitable that the fire
shall be kept in the best possible condition for steam-making.
What is that condition ? It is not unlikely that it is different
for every engine. But leaving this on one side, only a general
answer can be given. It is a matter of common knowledge with
all those who have to do with the generation of high temperatures
by the direct firing of coal, that it is possible to attain certain
conditions which result in maximum efficiency ; and that these
conditions can be quite easily upset by trifling changes apparently
quite inadequate to the results they bring about.
Applying this to a locomotive, we find that everything is going
well ; she is keeping time ; the pressure gauge is steady, and the
water at the proper level ; suddenly the steam begins to fall. To
all intents and purposes, the fire is apparently as it was. The
K.L. K
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130 THE RAILWAY LOCOMOTIVE
mischief may have been wrought by putting a couple of shovelfuls
of coal too far forward under the bridge. Why this should be so
harmful no one knows. The mere levelling of the surface of
the fire may have an important effect. One day an engine will
steam well, another day all the efforts of the most skilful fireman
" will not get her out of the sulks." The locomotive sets science
at defiance. Just as the best powers of a horse or a yacht are
only put forth in obedience to the will of someone who knows
just what to do and how to do it, so does the locomotive depend
for its efl&ciency on the driver and fireman — a fact either not
known at all to the general public, or but faintly appreciated.
Inasmuch as the hauling power and speed of a locomotive
engine depend on the quantity of steam that can be made in a
given time, a primary consideration is the rate at which coal can
be burned. If, for example, one engine can burn 80 lbs. a minute,
and another engine 60 lbs. it is clear that, other things being
equal, the latter engine is twice as powerful as the former. Now
the quantity that can be burned in a given time depends on the
amount of air that can be supplied to the furnace. So far no one
knows how quickly coal will combine with oxygen. When the coal
is in the condition of dust it will burn so fast that it explodes.
Awful catastrophes have taken place in coal mines because of
the chance ignition of the dust which filled the air in the workings.^
The weight of air which enters the fire-box depends on the resis-
tance to its entrance and the force available to overcome that
resistance. This force is supplied by the establishment of a
partial vacuum in the smoke-box. Other things being equal, the
larger the grate the less the resistance to the passage of air.
The products of combustion have to get into the tubes and rush
through them. The combined area of opening through the tubes
at the fire-box end is called the ** calorimeter " of the boiler. It
must not be confounded with an instrument, also called a calori-
meter, by which the wetness of steam is measured and about
which more will be said presently. Let us suppose that a given
boiler has 200 flue tubes, each 2 inches in diameter inside. The
cross sectional area of each is 3'14 inches and 3*14 X 200 = 628
^ Dusty mines are carefully watered in the present day as a safeguard.
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FUEL 131
square inches. This is much less than the area through the
grate bars ; very much less than the area of fire hole combined
with that of the grate opening. It would be wrong, however,
to suppose that it is too small. So far is this from being the case
that it is only with the greatest difficulty that an equal distribu-
tion of the products of combustion among the tubes can be
secured. They invariably follow the line of least resistance.
It may be taken that in general they will select the highest
tubes and will avoid those at the sides, but as will be shown
presently, there are exceptions.
Draught is measured in inches of water. The horizontal
prolongation of one leg of a U-shaped glass tube passes through
the side of the smoke-box. When the engine is running, the
exhaust establishes, as we have seen, a partial vacuum in the
smoke-box. The water falls in one leg of the vacuum gauge and
rises in the other. The difference in level is measured in inches
and fractions of an inch. Under ordinary working conditions it
varies between about one inch and seven inches. In 1893,
Mr. J. A. Aspinall read a paper before the Institution of
Mechanical Engineers recording draught experiments which he
had carried out. These go to show, as was to be expected, that the
air pressures vary all through the locomotive boiler. From 5 up
to as much as 18 inches of vacuum have been measured in the
chimney ; 3 to 7 inches in the smoke-box ; and 1 to 3 inches just
over the brick arch. With a vacuum of 3 inches in the smoke-box,
60 lbs. of coal per square foot of grate per hour were burned. There
seems to be reason to suppose that the rate of combustion varies
directly in any given engine as the square root of the air
gauge height. Mr. Paul holds that applying this rule to Mr.
Aspinairs results, a vacuum of 3 inches in the fire-box would
enable 60 X VF = 105 lbs. per square foot per hour to be
burned.
The weight of the coal burned is always expressed in terms of
square feet of total grate area and hours. Thus, let us suppose
that an engine with 17 square feet of grate is running at 30 miles
an hour, and burning 30 lbs. of coal per mile. As a mile is
traversed in two minutes, the consumption is 15 lbs. per minute
k2
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132 THE EAILWAY LOCOMOTIVE
900
and 900 lbs. per hour. Then ^ = 53 lbs. nearly. The con-
sumption is 53 lbs. per square foot of grate per hour.
Nominally coal can be burned at nearly three times this rate
by the aid of fans ; but a considerable quantity then goes out of
the chimney in the shape of cinders and large sparks. If we
look into a locomotive boiler furnace through blue glass to save
our eyes from the blinding glare, it will be seen that the surface
of the fire is covered with dancing incandescent fountains of fine
coal carried up by the force of the inrush of air through the fire-
bars. If the draught is strong enough cinders may be seen snatched
up and thrown over the bridge to enter the tubes. One hundred
pounds of coal appears to be the maximum that can be burned
without much waste per square foot per hour. These high rates
of combustion are accompanied by extremely high temperatures.
It is quite possible that as much as 3,000° F. may be reached
in the heart of the fire with good coal, and 2,500° F. anywhere
in the fire-box. When cast-iron fire bars were used, it was not
at all an uncommon event to melt half a dozen down, and bring
a run to an abrupt conclusion. The risk is diminished in the
present day by using wrought iron or steel fire-bars, which are
very infusible. Excellent fire bricks are required for the arch,
which is severely tried, not only by the extreme heat but by
the jolting of the engine. One way of expressing the power of a
boiler is in terms of pounds of water evaporated per hour per
square foot of grate surface ; thus, if the 53 lbs. of coal spoken
of above made 370 lbs. of steam, then it would be said that the
boiler was capable of evaporating 370 lbs. of water per hour per
square foot of grate.
The next factor is the heating surface, that is to say, all the
inside of the fire-box and of the tubes. If there are 60 square
feet of heating surface to one of grate, then the evaporation
370
would be -7^ = 6*16 lbs. of water per square foot of heating
surface. These figures are given simply for the sake of illustra-
tion. What the real figures may be will be set forth presently.
Afci the hot products of combustion pass through the tubes
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FUEL 133
they are cooled down. Entering the tubes at, say, 2,000° F.
they leave them at, say, 700° F. The greater the difference in
temperature between the gas and the water in the boiler the
more rapid will be the loss of heat by the gas. It follows, there-
fore, that the heating surface of the tubes is more effective near
the fire-box than it is near the smoke-box. It has been said, with
a fair approximation to the truth, that one-half of all the steam
made in a locomotive boiler is produced by the fire-box and the
first three inches of the tubes.
To ascertain facts, the engineers of the Chemin de fer du Nord
carried out a series of experiments which have long been regarded
as classical. These experiments have been recorded by MM.
M. C. Couche and Paul Havrez in 1875 and 1876. The boiler of
a small locomotive was divided by thin plate iron partitions
into four sections. The first plate next the fire-box was only
3J inches from the tube plates. The fire-box was 3 feet square,
with 9 square feet of grate and a heating surface of 60*28 square
feet ; the tubes were 125 in number, 12 feet 4 inches long, and
about If inches diameter. The boiler barrel was divided into four
sections, each 3 feet and a fraction long. Each section could be
tried separately under steam of the ordinary working pressure.
The draught was got by steam from another boiler. The
conditions of the trial could be varied by plugging the tubes.
The total heating surface with the tubes all open was 792*43 square
feat ; with one-half plugged, 424 square feet.
The result of this series of trials showed that from two-fifths to
one-half of the whole quantity of water was evaporated in the
fire-box section, which was about one-tenth of the whole surface.
The table on page 134 gives some of the principal results, the
fuel being (1) coke and (2) briquettes.
These figures are very instructive. They show that the
efficiency of the tubes depends very much on the weight of hot
gas passing through them, and on the nature of the fuel burned.
It will be seen that in all cases the briquettes gave the best
results ; and this particularly when the consumption was least.
The explanation of this is worth stating, because the fact is not
without its influence on locomotive boiler design.
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134
THE EAILWAY LOCOMOTIVE
It has been incidentally mentioned above that at one time it
was believed that flame would not pass through a small tube.
In treatises on smoke prevention one still finds an analogy
established between the safety lamp and a locomotive boiler.
The safety lamp may become filled with gas flame, the gas — fire
damp — passing through the gauze ; but the flame will not explode
the mixture in the mine because flame cannot pass through
Weight of fuel biinied
per foot of grate per
hour.
Quantity (
Ist section.
)f water evaporated per hour per 60 degrees to steam at
60 lbs. pressure.
2nd section. [ 3rd section.
4th section.
5th section.
Coke:
48-5 lbs.
85-7 ,,
Briquettes :
53 lbs.
109 „
lbs.
20
23-6
23-5
38-9
lbs.
5-6
10-6
5-4
14
lbs.
2-9
6'H
2-5
6-8
lbs.
1-28
3-44
1-33
4-32
lbs.
•72
2-47
•83
2-81
Briquettes :
With Half the Tubes Plugged.
43 lbs.
94-3 „
lbs.
26-5
44-7
lbs.
9
21
lbs. i lbs.
4 2-1
10-6 6-34
lbs.
1-31
4-76
small orifices and so cannot get out of the lamp. This is, how-
ever, only one of those half-truths whose propagation has done
so much harm in the world. It is only true of the lamp if it is
shielded from a strong current of air ; otherwise the flame will
be forced through the gauze with perfectly appalling results.
Whether flame will or will not pass through the flue tubes of a
locomotive depends in like manner altogether on the draught and
on the diameter of the tubes. A moderate vacuum in the smoke-
box will pull flame for as much as 6 feet through a 2J-inch tube.
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FUEL 135
In a locomotive worked to its maximum power there is little
doubt that flame may extend a long way even in a 2-inch tube.
If it did not then it would be mere waste of material to use, as
is done abroad, tubes as much as 14 to 20 feet long with bitumi-
nous coal. The tubes in M. Couche's boiler were 12 feet
4 inches long. It will be seen that the last 3 feet or so added so
little to the total result that it might have been suppressed, at all
events with coke as a fuel, with apparently small loss. The
reduced cost of the boiler and its diminished weight would
probably have gone far in the way of compensation. It will
be noticed that the briquettes were under all conditions better
than the coke. Now there were no special smoke prevention
appliances, and briquettes usually make much smoke. The
probability is that the tubes were filled for a portion of their
length with red-hot flame. The flame from a coke fire (if any)
is blue, and of the Bunsen burner character. But the Bunsen
flame gives out little or no radiant heat. The late Sir William
Anderson years ago called attention to the circumstance that
smoke prevention appliances to steam boilers, while often success-
ful in one way, failed in another. A dull smoky flame filling
flues radiates heat with great power, which clear flame does not ;
and the result was that while the economy of a boiler might
perhaps be increased, its steam-making power was diminished.
In the United States, tubes as much as 3 inches in diameter and
of great length are used in the mammoth engines of which so
much is heard. It is fairly certain that only the presence of
flame in them renders the great length of them economical.
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CHAPTER XVII
THE FRONT END
We have now to consider the results obtained in everyday
practice, and this cannot belter be done than by reference to
direct experiment.
Perhaps the most complete experiments of the kind ever
carried out were those made by Professor Goss, of Purdue
University, U.S.A., with an engine known as *' Schenectady
No. 1," a second engine known as " Schenectady No. 2," and at
the St. Louis Exhibition.
With ** Schenectady No. 1 '' — a fairly typical American loco-
motive — as much as 181 lbs. of Indiana block coal were burned
per square foot of grate surface per hour ; 1,037 lbs. of water
were evaporated per square foot of grate, and 14*98 lbs. per
square foot of heating surface per hour, representing 518 i.h.p.
Taking a normal rate of combustion, namely, 64 lbs. per foot of
grate, the evaporation was 507 lbs. and 7*20 lbs. The latter is
the more important figure, because the power of a locomotive is
very usually estimated by its heating surface. A normal
English locojnotive with 1,500 square feet of heating surface
may be counted upon to convert 7 X 1,500 = 10,500 lbs., or
1,050 gallons of water into steam per hour. If the engine uses
30 lbs. of steam per effective horse-power per hour, that is to
say, at the rails, then we have 850 h.p. available for haulage,
including, of course, the engine and tender. This is, however,
far from representing thfe maximum effort of which such an
engine would be capable. The coal used by Professor Goss was
soft and of indifferent quality. Judged by the conditions laid
down above, the best result obtained was only 7*67 lbs. of steam
per pound of coal, and that was in only one experiment. The
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THE FEONT END 137
average was under 6 lbs. With English or Welsh coal, 8 lbs. might
be reckoned upon, which could give one-third more steam, other
things remaining equal, and about 465 horse-power.
At the Louisiana Exhibition, the De Glehn compound engine,
very similar to ** La France," put to work on the Great Western
Railway, evaporated 8*83 lbs. of water per square foot of heating
surface, the temperature of the feed being taken as 212° F.,
and the boiler was rated as 680 horse-power, and the total
heating surface 2,656 square feet, if the inside of the tubes is
taken, and 1,646 square feet if the outside. The difference is
due to the fact that the boiler is fitted with Serve tubes, so
called after the inventor, which have eight longitudinal ribs
inside them.
We now come to the consideration of the leading end of the
boiler — that section of it on which the chimney stands. It is an
obvious cylindrical continuation of the barrel of the boiler, and
is known as the smoke-box. Until recently it was short — just
long enough to accommodate the flange by which the chimney is
bolted to it ; but of late what is known as " the extended smoke-
box" has been introduced from the United States. It reaches
out far in front of the chimney. The back plate of the smoke-
box is, as has already been stated, the front tube plate. In the
front of the smoke-box is a large circular door made with great
care and accurately fitted, so that when closed and bolted no air
may leak in. The bolts are moved by a central handle which in
turn can be locked by a second handle on the same spindle. The
door is required to give access to the tubes so that they may be
swept or *' run." The tool used is a long rod with an eye at the
end through which some oakum or a strip of canvas is threaded.
Ashes which collect in the smoke-box are removed from time to
time through this door.
The smoke-box is included in what has come to be known as
" the front end." It plays a part not less important than the
fire-box in the daily life of the locomotive ; and, as has already
been stated, its construction and action have from an early period
in railway history been made the subject of keen controversy
and many inventions. The functions of the smoke-box cannot,
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138 THE RAH^TV^AY LOCOMOTIVE
perhaps, be better described than in the following extract from
Professor Goss's recent book on ** Locomotive Performance,"
detailing the results of experiments carried out since September,
1891, at Purdue University, Lafayette, Indiana, U.S.A. "The
term * front end ' refers to all that portion of a locomotive
boiler which is beyond the front tube plate. It includes the
extended shell of the boiler which forms the smoke-box, and in
general all mechanism which is therein contained, such as steam
and exhaust pipes, netting, diaphragm, and draught pipes. It
also includes the stack [chimney]. The front end as thus defined
is to be regarded as an apparatus for doing work, receiving
energy from a source of power and delivering a portion thereof
in the form of a specific result. The source of power is the exhaust
steam from the cylinders, and the useful work accomplished is
represented by the volumes of furnace gases which are delivered
against the difference of pressure existing between the smoke-
box and the atmosphere. That the power of the jet may be
sufficient, it is necessary that the engines of the locomotive
shall exhaust against back pressure. The presence of the back
pressure tends to lower the cylinder performance, and it is for
this reason that designers of front ends have sought to secure
the required draught action in return for the least possible back
pressure. In other words, the effort has been to increase the
ratio of draught to back pressure, which ratio has been defined
as the efficiency of the front end. The office of the front end is
to draw atmospheric air into the ash pan, thence through the
grate and fire ; to draw the furnace gases through the tubes
of the boiler ; thence under the diaphragm and into the front
end ; and to force them out into the atmosphere. In order that
this movement may take place a pressure less than that of the
atmosphere is maintained in the smoke-box, so that when the
locomotive is working there is a constant flow from the atmo-
sphere along the course named and back to the atmosphere
again. The difference in pressure between the atmosphere and
the smoke-box is spoken of as the draught, and under normal
conditions of running is represented by from 4 inches to 10
inches of water." As a result of a multitude of experiments
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THE FEONT END
139
carried out with the locomotive '* Schenectady No. 1," Professor
Goss gives the following table : —
Percentage of Total Draught Eequired.
Miles per hour.
To draw air into
fire-box.
To draw gases through
tubes.
To draw gases under
diaphragm.
20
30
40
22-6
30-1
30-4
41 -1
33-6
32-0
36-3
36-3
37-6
All this is excellent as far as it goes, but it does not go far
enough. It is not throughout of general application, and to
practice in this country much does not apply at all.
The diaphragm is a baffle plate introduced to beat
down the cinders and sparks and prevent their flight up the
chimney. Diaphragms find no place in English locomotives.
Again, as has already been explained, a large percentage of all
the air required comes in through the open fire door, which
offers little resistance. The major part of the work done by the
exhaust in an English locomotive is expended in overcoming the
friction of the tubes, and the netting or other devices used to
prevent the ejection of sparks and cinders, and in the lifting and
propulsion of the products of combustion up to the top of the
chimney. The products of combustion and the air taken together
will represent, say 20 lbs. per pound of coal burned. Let this be
40 lbs. per mile, and the speed a mile a minute, then we shall have
800 lbs. If the engine is indicating 500 horse-power, and using
25 lbs. of steam per horse-power per hour, we shall have 208 lbs.
of steam to add, that is to say, about 1,000 lbs. of air and
steam to be lifted per minute and blown out of the chimney top
at a high velocity. Again, Professor Goss worked with an
engine standing in a shed, and consequently took no account of
the effect which may be produced by the rush of air through the
front of the ash pan, which may easily amount to several inches
of water. At sixty miles an hour, or 88 feet per second, the
pressure of the air on a flat surface is about 17 lbs. per square
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140
THE RAttWAY LOCOMOTIVE
foot, or about 3 inches water pressure per square inch. This is
the force of a full gale.
The designers of smoke-boxes in this country are trammelled
by legal restrictions which either do not exist at all in the
United States, or only in a lesser degree. "^ It will not be far
Fig. 50.— Smoke-box, London and South Western Railway.
from the truth to say that the first consideration with the
designer here is that the locomotive shall not be likely to set fire
to fields of standing corn, stacks, hay-ricks or woods past which
it runs ; the second is, that the production of black smoke may
be avoided; the third, that the back pressure in the cylinders
may be as small as possible, and the fourth, that the distribution
of heat among the tubes shall be quite equal.
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THE FRONT END
141
Fig. 51. — Smoke-box, South Eastern and Chatham Railway.
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THE EAILWAY LOCOMOTIVE
rr,_.J • Lj]i
Fig. 52. — Smoke-box, South Eastern and Chatham Eailway.
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, THE FRONT END US
As to the first point, it has usually been found sufl&cient to
place a flat grating in the smoke-box above the level of the tubes.
Against the bars of the grating cinders strike, and are either
broken so small that they can do no harm if they pass through,
or else fall to the bottom of the box. A second device is the
invention of Mr. D. Drummond, of the London and South
Western Railway, which is illustrated on p. 140, and may be
thus described, Fig. 50. In the smoke-box are placed two plates
.of thin steel A A. Between these plates are fixed others B B,
closely perforated ; C C are the two main steam pipes, E E is an
ejection pipe for the vacuum brake. The hot gases fill the smoke-
box, and only escape by passing through the perforations in B B
from the sides of the smoke-box. Not only is this a most eflScient
spark arrester, but it is found that the effect of the blast on the
fire is made more uniform, with a resulting economy not only in
coal but in fire-boxes. Some are now running on the South
Western Railway which have been in use for about nine years, in
very heavy traflSc. Figs. 51 and 52 illustrate Stone's spark
arrester, which has been adopted by Mr. Harry Wainwright,
Chief Mechanical Engineer of the South Eastern and Chatham
Railway, for all his fast passenger engines. The conditions on
these lines are very exacting because the coal used is at once dear
and not very good, much of it running small and given to making
sparks. The drawing requires little or no explanation. A
double cone is fitted to the base of the chimney up the centre
of which, carried on the ring T, the exhaust passes. The cone
is made of a frame of ten bars, each IJ inch wide by J inch
thick. In the edges are notches, round the cone in these notches
is wound a continuous steel wire J inch thick. The notches are
spaced wider and wider apart, counting from the bottom. Round
the blast pipe is a brass ring as shown, in which slots are cut,
these carry the suction action of the blast well down in the smoke-
box. In order to give access to the tubes the whole lower cone
may be turned round to the right or left on a pivot P by taking
out a single pin A. This spark arrester works very well.
Mr. Wainwright is perfectly satisfied with it after an experience
extending over several years.
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CHAPTEE XVIII
THE BLAST PIPE
It has already been pointed out that the products of com-
bustion will take the most direct course they can find to the
outer air. They will follow the line of least resistance. The
object of the designer is therefore to make all lines of resistance
alike, and this seems to be very fairly done by the diaphragm
plate. Indeed, Professor Goss tells us that a most elaborate set
of experiments failed to detect any differences in vacuum in the
space between it and the tube sheet. When the diaphragm is
omitted, as in this country, there is good reason to believe that
the central and topmost tubes pass more gas than the outer and
lower tubes. It does not appear, however, that this seriously
militates against the efl&ciency of a boiler.
The method of operation of the blast pipe has already been
explained in general terms. A complete examination of the
problem which it presents would be out of place in this book ;
but much that is at once interesting and ought to be known by
those who wish to understand the locomotive remains to be said.
The steam which has done its work in the cylinders is discharged
up the chimney, in some cases through one pipe, in others
through two pipes. In any case the pipes are two more in name
than in reality. The blast pipe proper rests on a box which
is a portion of the cylinders and to which it is bolted. It is
usually somewhat oval in cross section at the bottom, and tapers
slightly to the top where the *' nozzle" is bolted on. This is
always bored out truly cylindrical, and is made as large in
diameter as possible, that is to say, between 4 inches and
5J inches. A greater diameter than 5 inches is exceptional.
The larger the diameter the better, because the back pressure in
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THE BLAST PIPE 145
the cylinders, which is so much waste, depends for its amount
more on the diameter of the blast nozzle than on any other
factor. The smaller the nozzle, the greater is the velocity with
which the exhaust steam issues, and the more powerful is its
action in establishing a minus pressure in the smoke-box.
Therefore, when an engine is found to steam badly, in the last
resort a nozzle of less diameter than that in use is put on.
This augments the back pressure and decreases the power of the
engine ; but the increase in the quantity of coal that can be
burned in a given time more than compensates for this loss.
So that an engine which will not keep time with a 4J inch blast
noz2jle may very well do so with a 44 nozzle. This is one
of the many facts which show how sensitive a machine the
locomotive is. There are, however, other factors besides diameter
to be considered. It is essential that the nozzle shall stand
absolutely under the centre of the chimney, so that a vertical
line may be drawn through the centres of both. Care must also
be taken that the blast is not projected against one side of the
chimney more than the other. In some cases, particularly with
outside cylinders, the blast from one cylinder hits one side, and
from the other cylinder the other side of the chimney, although
there is only a single nozzle. This means loss of efl&ciency, and
to avoid it a partition usually extends some way up the vertical
portion of the blast pipe. Again, the height of the nozzle in
relation to the tubes is of much importance. If it is low it will
usually be found that the lower tubes have the better draught.
If it is high, then the upper tubes. Then the relation of the
blast nozzle to the base of the chimney has to be considered.
Sometimes raising the nozzle improves the draught, sometimes
lowering it has that effect. Then the form of the pipe has an
effect. Various blast pipes have been tried, such as Adams'
Vortex pipe, a concentric pipe with the exhaust from one cylinder
passing through the inner ring and the exhaust from the other
cylinder through the outer ring and so on. It may be said
that on the whole the advantage derived from these inventions
has been too small to enable them to supersede the plain pipe to
any extent. But advantage has been derived from supplements,
B.L. L
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146 THE EAILWAY LOCOMOTIVE
SO to speak, to the blast pipe. Thus, in smoke-boxes of large
diameter, *' petticoat '' pipes are sometimes fitted with advantage.
These are intended to diffuse the *' pull '' of the exhaust and
equalise the draught among the tubes.
In all cases a " blower '' is fitted, which usually takes the form
of a ring round the top of the exhaust pipe, which is perforated
with a number of small holes. Through these, by opening a
cock in the cab, steam can be blown up the chimney to create a
draught when the engine is standing. The blower is used when
getting up steam ; in stations to prevent smoke ; and is always
turned on just before steam is shut off to prevent flames coming
out through the fire door, by which the men on the footplate
would be burned. Indeed, men have been killed in this way.
Until a recent period, the chimney was always a pipe of some
length, as much, for example, as 5 feet, and it was wholly outside
the smoke-box. But of late years huge engines have been built
with boilers of great diameter, and the limits of height in tunnels
and under bridges have reduced the apparent length of the
chimney until it has been defined as ** a frill round a hole in the
top of the smoke-box " ; in such cases the chimney extends down
some distance into the smoke-box.
A curious fact is that on the continent of Europe no such
uniformity of blast-pipe practice exists as in this country.
There are, perhaps, fifty different kinds of pipe and arrange-
ments of the smoke-box in use, and while it is claimed for each
that it is the best possible, all seem to answer their purpose
equally well. Thus, on the Austro-Hungarian State railways,
the blast nozzle stands just inside the base of the chimney, a
semi-circular grating just above the tubes acting as a spark
arrester. On the Eastern Eailway of France, the chimney is
flared at the base, the blast pipe is level with the top of the
smoke-box, and is rectangular instead of circular. The " nozzle "
is fitted with two flaps or doors which can be brought together or
separated by a rod from the footplate, so that the draught can
be adjusted to the demand for steam. An express engine on the
Paris, Lyons and Mediterranean line has been fitted with a nearly
similar adjustable nozzle, wliile inside the chimney is placed a
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THE BLAST PIPE 147
long second tube up which the steam blower is turned. On the
Belgian State railways rectangular chimneys are still in use.
The list might readily be extended, if it were necessary, which it
is not.
It is impossible to look at locomotives with understanding and
not perceive that the chimneys vary remarkably in form and
dimensions. The old rule was that the chimney should be the
same diameter as the cylinder, and as long as possible. Thus,
an engine with 16-inch cylinders had a chimney 16 inches in
diameter. Not that there was any real connection between these
proportions. The tendency in the present day is to keep down
diameter. Thus, while an engine with 1,100 square feet of
heating surface may have a 17-inch chimney, one with 2,200
feet will have a chimney no larger, possibly indeed smaller. It
might indeed be argued from modern practice that no relation
existed between boiler power and the dimensions of the chimney.
There can, however, be no doubt that some forms and sizes of
chimney are better than others, but apparently the difference is
not great. Professor Goss carried out at Purdue University the
most elaborate set of experiments intended to give data for
standardising dimensions ever undertaken. The experiments
were got up at the instance of the American Engineer,
published in New York ; and a very strong committee of repre-
sentative railway engineers carried them out with the aid of
Professor Goss on a locomotive known as " Schenectady No. 2,"
a more powerful engine than " Schenectady No. 1." It would be
beyond the scope of this book to give more than the result of the
inquiry as decided by the committee. This may be stated in
six equations.
When the exhaust nozzle is on the centre line of the boiler
d = -246 + (00123 H) D. (1)
Here d is the diameter of the chimney in inches, H its height
in inches, and D the diameter of the front end, that is to say
the smoke box, in inches.
Tapered stacks were tried. It was assumed that they would
act somewhat like a *' diverging nozzle," and prove more eflScient
than straight tubes. The experiments enabled the important
l2
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148 THE RAH.WAY LOCOMOTIVE
conclusion to be drawn that a tapered stack of 13J inches
diameter gives maximum results for all heights between the
limits of 26J and 56J inches. The diameter of the tapered stack
does not need to be varied with change in height. Hence, we
may write for all locomotives and all heights of stack where the
exhaust nozzle is on the centre line of the boiler
d = -25 D. (2)
Here d is the least diameter of the tapered stack and D the
diameter of the front end of the boiler.
It must be kept in mind that the foregoing equations only
apply when the nozzle is on the centre line of the smoke-box. In
this country it is almost invariably higher, that is, nearer the root
of the chimney. Nor is practice in the United States, much less
in Europe, invariable as to the position of the exhaust nozzle.
Therefore, the committee carried out further experiments with
varying heights of nozzle, from the results of which Professor
Goss prepared the following general equations : —
For straight stacks :
When the exhaust nozzle is below the centre line of the
boiler
d = (-246 + -00123 H) D + '19h. (3)
When the exhaust nozzle is above the centre line of the
boiler
d = (-246 + -00123 H) D - 19^. (4)
For tapered stacks :
When the nozzle is below the centre of the boiler
d = '25 1) + 'L6h. (5)
When the nozzle is above the centre line of the boiler
d = -25 D - 'l&h. (6)
Here d is for (3) (4) the diameter of the stack in inches. For (5)
(6) it is the diameter of the *' choke " or smaller part : H is the
height in inches which should be the greatest possible ; D is the
diameter of the smoke-box in inches, and h the distance between
the centre line of the boiler and the top of the exhaust pipe.
These particulars by no means cover the whole ground traversed
by the committee, but they are quite sufficient for the
purpose of this volume. The inquiry appears to supply the
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THE BLAST PIPE
149
latest available information. As has already been pointed out,
so much variation in practice occurs that it is doubtful that it
has been altered to any considerable extent. As a result of the
investigations, Professor Goss suggests a standard front end,
the general arrangement of which and the chimney are
given in Fig. 53. Here T is the front tube plate and K a
diaphragm, the object of which is to beat down the cinders
and sparks issuing from the ends of the tubes ; W is the blast
nozzle. The diaphragm finds no place in English locomotives.
In America it appears in various forms, sometimes as a thin plate
of iron, at others as a stout wire netting. It is invariably so made
that it can easily be removed in order
that the tubes may be swept. It may
be taken as proved that the diaphragm
checks the draught about as much as
the fuel on the grate, but it appears to
be a very efficient spark arrester.
Professor Goss gives the following
rules as applicable to the standard front
end: —
Make H and h as great as possible.
„ d = -21 D + -le/t.
„ ft = 2 d 02 -5 D.
„ P = -32 D.
„ p = -22 D.
Figs. 54 and 55 are longitudinal and cross sections of the front
end of a 4 — 4 — 2 Baldwin compound ** Atlantic "of great size shown
at the St. Louis Exhibition. The grate surface is 49*5 square
feet, the external heating surface of the tubes is 3016 square feet,
that of the fire-box 190 square feet, and the boiler pressure is
220 lbs. There are 273 tubes 2i inches diameter and 18 feet 9
inches long. The chimney for this enormous boiler is only 15|
inches diameter at the smallest part, which is just f inch larger
than the high pressure cylinder. There are four cylinders, two
15 inches and two 25 inches diameter, with a stroke of 26
inches. By the old rules the chimney would have been 25 inches
diameter.
Pig. 53. — Standard front
end.
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THE RAILWAY LOCOMOTIVE
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THE BLAST PIPE 151
The diaphragm next the tube plate is of thin iron plate, the
remainder of it of stout wire netting as shown in Fig. 55. The
gases have to go to the front of the smoke-box before they can
reach the chimney.
A few words remain to be said as to the theory of the blast
pipe. It has already been explained that the friction of the
exhaust steam drags the products of combustion with it, and that,
furthermore, they find their way into it and mingle with it. This
they do because the jet not only exerts no lateral pressure, having
no tendency to expand in the ordinary sense of the term, but
because its pressure is actually less than that of the vacuum in
the smoke-box, in the same way and for the same cause that the
pressure of a fan-blast is always least at the point in the wind-
trunk nearest the fan case.
But there is reason to believe that another factor also plays a
part, which has been overlooked. If left to itself, the external
atmosphere would rush down the chimney into the smoke-box to
fill up the vacuum. Now just at the extreme top of the chimney
the blast acts to push the air away. Its influence extends indeed
for some distance above the stack to form a second vacuum outside
the smoke-box, into which the gases, of course, rush. Experiments
carried out by Mr. Aspinall go to show that at the very top of the
stack a negative pressure equal to as much as 10 inches of water
may exist.
The reader has now had placed before him in a succinct form
sufficient information to enable him to form a fairly complete
idea of the way in which coal is burned in a locomotive. He will
have seen that simple things as the putting of coal through a
fire hole and the issue of heated gases, steam, and, perhaps,
smoke from the engine chimney may appear to be, they are
really only the initial and terminal stages of a series of complex
processes on the complete working out of which depend the
success of the locomotive engine. While the general reader may
rest content with what he has learned in this connection, it is
hoped that the student will only find that his appetite for further
information has been stimulated.
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CHAPTEK XIX
STEAM
We have now seen what goes on at the fire-side of the heating
surface. We have next to consider what takes place at the water
side. Before going further, it will be well to give a short state-
ment of the pressures and temperatures, &c., most commonly met
with in locomotives. The reader will, perhaps, scarcely need to
be told that the temperature at which water boils bears, so long
as the water is pure, an unalterable relation to the pressure. In
the accompanying table fractions have as far as possible been
Propekties of Saturated Steam.
Boiler
Pressure.
Tempera-
ture.
Degrees
Fah.
lbs.
150
366°
160
371°
170
375°
180
380°
188
382°
195
386°
205
390°
215
394°
225
398°
Total Heat
from Water at
32°.
Latent
Heat.
1193°
856°
1194°
853°
1196°
849°
1197°
847°
1198°
845°
1199°
842°
1200°
839°
1202°
836°
1203°
834°
1
Weight of one
Cubic Foot.
lbs.
•3695
•3899
•4117
•4327
•4431
•4634
•4842
•5052
•5248
Volume 1 lb.
of steam.
Cubic Feet,
2-71
2-56
2-43
2^31
2-26
2-16
2^06
1-98
1-90
Cubic Feet
of Steam to
One of Water.
169
159
151
144
141
135
129
123
119
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STEAM 153
omitted, and the nearest round numbers used. The figures refer
to what is known as dry saturated steam, that is to say, to steam
free from water carried in the form of spray or priming. The
pressures given are those which are read on steam pressure
gauges, and are not the absolute pressures, which are 14'73 lbs.
higher.
The heat produced by the combustion of the coal in the fire-
box has to be transferred to the water in the boiler, and to do
this it must pass through the metal of the plates and tubes.
Precisely how the transmission takes place is not known. In
effect, the side of the plate next the fire is made hotter than the
side of the plate next the water, and heat goes
through ; the water side of the plate being in
turn hotter than the water, the transmission con-
tinues. This is all apparently very simple, but
the process is really complex.
It is assumed that the plate resists the trans-
mission of heat through its substance, and that
the fact that one material is a better conductor
of heat than another is due to variation in the
amount of the resistance. Hence, we find it
argued that copper plates being much better * ' •
conductors of heat than iron or steel, they are preferred by astute
railway engineers to steel or iron plates. There is, however, no
basis of truth in this theory. Steel fire-boxes are almost always
used in the United States. They have been tried in this country.
Careful experiments, and indeed long- continued practical trials,
show that copper possesses no advantage whatever over iron or
steel. It is used because it is much more durable than any other
material ; and when a copper fire-box is worn out it can be sold
as old metal at from 50/. to 701, a ton, according to the state of
the market, while an old steel fire-box will hardly pay the cost of
breaking it up.
The efficiency of a fire-box plate does not in practice depend on
its conducting powers at all. It does depend on its receiving and
emitting powers. It has been shown by Peclet and others that
a square inch of copper in a fire-box can " conduct " about twelve
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154 THE EAILWAY LOCOMOTIVE
times as much as it can absorb or emit. Thus, let A in Fig. 56
be the side of a fire-box, in which is fixed a pin 6J inches long
and 1 inch in diameter. A length B of 3 inches of the pin
is in the furnace and a similar length C in the water, and it is a
little over 1^ inch in diameter. Its cross-sectional area at D is
therefore 1 square inch. The surface which it offers to the fire
is 11'6 inches, and that to the water the same. Now, it is
impossible to melt the 3 inches of pin in the fire, simply
because all the heat that the 11*6 inches of surface can absorb
can be conducted through the square inch section of pin in the
plate, and the water will take up the heat, provided the pin is
clean, and so the pin is kept cool.
A knowledge of this fact led Mr. Charles Wye Williams, a very
eminent engineer in the early portion of the last century, to put
**heat pegs" in the furnace plates of boilers. He thus very
largely augmented their power ; but the invention was ' doomed
to failure because it was impossible to keep the pegs clean and
free from deposit on the water side, and so plates and pegs were
involved in one common ruin.
We may rest content, then, that the transmission of heat has
in practice nothing to do with the conducting powers of the plate,
while it has everything to do with its emissive and absorbing
powers. Now these depend on two factors. The first is the way
in which the heat is applied to the plate ; the second is the com-
pleteness, or the reverse, of the contact of the water with the
plate.
It may be stated without fear of contradiction that the best
results will be got when the flame or hot air impinge directly on
the plate to be heated, that is to say, the flow of the products of
combustion ought to be at right angles to the surface. The
impingement of the flame leads, furthermore, to a breaking up
and mixing of columns or bodies of hot gas. The parallel flow
of hot air or even flame along a surface to be heated is not so
effective. This is no doubt one reason why a tube plate does so
much work, the products of combustion strike it directly when
rushing to the tubes.
All this holds good to a still greater extent as regards wa.ter,
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STEAM 155
Water is to all intents and purposes a non-conductor of heat.
Any quantity of it can only be heated throughout by convection,
that is to say, only the film in immediate contact with a hot plate
is heated. Fortunately, water expands, and the hotter water
being lighter than the cold rises, and is replaced by cold water,
which is in its turn heated. This process is termed convection.
It may be taken as certain, that unless every drop of water in a
boiler comes into contact either with the heating surface or with
steam, it will remain cold. Water, it is well known, cannot be
raised in temperature from above downwards. In marine boilers
the heat is always supplied at a height of at least 3 feet above
the bottom of the boiler. The result is that steam may be up
and the engines at work for an hour or two while the water at
the bottom of the boiler is quite cold. This stresses the boiler
plates severely, as the plates in the steam space are expanded by
the heat, while the bottom plates are not. The rolling and
pitching of the ship at sea sets the water in motion, and so
equalises temperature. But it is the custom nowadays to use
what is known as a " hydrokineter," which is simply a jet nozzle
near the bottom of the boiler. A pipe from the steam space
leads down to this, and as soon as steam is up to ten or twelve
pounds pressure it is sent through the jet into the cold water,
where it condenses and heats up the stagnant water, putting it
in motion at the same time. In large vessels, as steam is always
up in some one boiler to supply electric light, &c., steam of full
pressure is taken from this and blown into the bottoms of the
other boilers as -soon as the fires are lighted. In the locomotive
it is true that there is no stagnant water ; none the less does the
incapacity of water to conduct heat play a very important part,
as will be understood in a moment.
Eeference has been made to Mr. Charles Wye Williams, who,
it may be added incidentally, was one of the first to make Atlantic
steam n0,vigation a success. He was a most competent authority
on boiler furnaces and the prevention of smoke. In the year
1860 he published a very curious book, in which he set forth the
theory that water can never be heated at all. The application of
heat at once transforms it into steam, and this steam is diffused
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156 THE EAILWAY LOCOMOTIVE
through the main body of the water, just as carbonic acid gas is
in a bottle of " soda water." A thermometer put into the water
is heated by the steam in it. It may be said of this theory that
it is very difficult to disprove it — a difficulty augmented by the
circumstance, already pointed out in a preceding chapter, that no
one knows anything with any completeness of knowledge as to
how water is converted into steam, or the true difference between
dry saturated steam and water.
It will be seen from what has been said that a steam boiler
cannot be worked without circulation. Thus we find that the
claims of various inventors of boilers always include a statement
that the " circulation is excellent," or ** the best possible,'' or
" violent." In point of fact, circulation is really a curse instead of
a blessing, but it cannot be done without. In the locomotive
boiler good circulation is essential not only to success, but to
safety. The heating surface must be kept wet, that is to say, the
water must be in direct contact with it at all times. If the
crown sheet of the fire-box of a locomotive, with a heavy fire on,
became dry, about thirty seconds would suffice to make it red hot,
when it would be so weakened that it would collapse, with the
most disastrous results.
Now, so long as the boiler is kept sufficiently full there will be
two or three inches of water over the crown sheet, and as there is
free access to it from the boiler barrel, and the steam generated
can rise straight from it, we seldom hear, if the water is good, of
the failure of this plate. But the case is entirely different with
the ** water legs," that is, the space round the bottom of the fire-
box, and with the tube sheet. It has already been explained that
at the sides of the fire-box the space filled with water is some-
times only 2 J inches wide, seldom more than 3J inches. This is
the portion of the fire-box in direct contact with the burning
fuel. The ebullition in these narrow water spaces must be very
violent, the access of water to them not easy. They are in
point of fact full of a mixture of steam and water in the condition
of foam rather than of solid water. The plates are no doubt in
a constant condition of over-heat, and it is not surprising that
cracking and buckling and deformation of the plates between the
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STEAM 157
stay bolts should be rife. Water legs should never be less than
4 inches wide. The attempt to make the grate a little wider by-
narrowing the water legs is a mistake.
As to what really takes place in the water-legs, some direct
information exists. In the course of a paper on *' Large Loco-
motive Boilers," read by Mr. G. T. Churchward, Chief Mecha-
nical Engineer of the Great Western Eailway, he said that,
** with modern high pressures, the rate of evaporation is so much
increased that the provision for circulation which was sufficient
for the lower pressures formerly used, is doubtless insufficient."
The general theory is, that cold water being put into the barrel
near the front end, sinks to the bottom under the tubes, and
flows back, entering the " water-legs," and passing rou,nd the
back of the fire-box where it rises and flows over the top of the
box forward. Mr. Churchward's experiments showed that in the
main this view was accurate, but a little alteration in the firing
has the effect of changing the direction of the currents and even
of reversing them. This is a fact of much greater importance
than appears at first sight. It is one explanation of the extra-
ordinary way in which a small mistake in firing may cause loss
of pressure in a hard-pushed boiler.
The tubes are spaced at distances varying between f inch and
f inch, according to the views of the designers. When it is
considered that the temperature at the tube plate is probably
the highest in the fire-box, it is easy to understand that here
again we have a place in which it is impossible for "solid"
water to exist. It is in this way that the constant liability of
tubes to leak can be explained. It may, then, be accepted as
a deplorable fact that until we get to a point a couple of feet
forward in the barrel, nothing but a mixture of steam and
water is available to keep the plates from being overheated.
The condition has to be accepted ; but it is responsible for rapid
wear and tear, which add largely to the cost of maintaining
locomotives in good order.
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CHAPTER XX
WATER
So far all water has been spoken of as though it was invari-
ably equally good and suitable for a locomotive boiler. But not
only is this not the case, but water which will answer very well
with pressures of 150 lbs. may be quite unfit for boilers carrying
200 lbs. It is almost impossible to command a supply of pure
soft water all over a great railway system. Nearly all the water
available is more or less ** hard/' that is to say, it carries salts
of lime, or magnesia, or both in solution. Now unfortunately
these salts are more soluble in cold than in hot water, and the
result of raising the temperature is to cause the deposit of the
lime on the heating surfaces. The boiler of the locomotive
becomes " furred " like the inside of the domestic tea-kettle.
The lime is not only an exceedingly bad conductor of heat, but
there is reason to believe that its emissive powers are also
low, and a very moderate thickness of it accumulated on a fire-
box plate will secure the overheating and more or less rapid
destruction of that plate. It is held by some persons that if
the circulation is rapid, deposit will not have time to attach
itself to the metal. This is, but only in a very small way, true.
It holds good of water-tube boilers — provided the tubes are short
in proportion to the diameter, and the water is not heavily
charged with lime ; but there is no circulation round a locomotive
fire-box powerful enough to save the situation. The true way
out of the difl&culty lies in getting rid of the lime before it enters
the boiler. On a few railways, however, much good has been
done by change of water. Thus, when locomotives are worked
for some time in a district where the water is bad, they are then
sent to another district where the water is soft and good. In
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WATER 159
two or three days the deposit will be loosened by the soft water
and can be washed out as mud. Locomotive boilers are always
washed out at intervals of two or three days, or a week, or even
more, according to the quality of the water, as will be explained
when the daily life of an engine is dealt with.
A long account of the chemistry of water-softening would be
quite out of place here. It will be enough to say that lime is
kept in solution in the water by the presence of free carbonic
acid, CO2. If now more lime is added, the acid is neutralised
and the whole of the lime, namely that originally in the water
and that added, are thrown down together in settling tanks.
Various systems are employed.
The general principle of neutralising free carbonic acid must
be modified in various ways to suit special conditions. What
will do very well for the treatment of the water supply of a large
town, where space for filtering tanks and plenty of time are
available, will not suit railways. Lime must be supplemented,
usually with caustic soda or soda ash, and the water must be
heated to secure rapidity of action. The system devised by
Messrs. Archbutt and Deeley, and used on the Midland Eail-
way, may be taken as typical. The process is completed in
about three hours, so that only comparatively small settling
tanks are required. The water is sent in by an injector and
mixed with a solution of slacked lime and soda ash which have
been boiled together. Air is blown by another injector through
a series of perforated pipes at the bottom of the tanks which
effects a thorough mixture, not only of the reagents, but of the
mud left in the tank with the fresh water. This mud seems to
cling to the new deposit and carry it down to the bottom of
the tanks as soon as the blowing in of air ceases. The softened
water is drawn off from the surface by a floating delivery pipe,
and has subsequently a small quantity of carbonic acid from a
coke fire blown into it, to prevent any trifling percentage of
lime which may remain in the water from settling in the feed-
pipes or injector nozzles of the engines. From time to time
the sludge which accumulates in the tanks is cleared out.
In some cases where the water is fairly good much benefit is
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160 THE RAn.WAY LOCOMOTIVE
derived from putting a few pounds of caustic soda into the
tender tank every day. Quite a small quantity suflSces to
render the deposit in the boiler soft, so that it can be readily
washed out.
Assuming that the water is suflSciently purified, we have next
to consider what is the best way of putting it into the boiler.
This does not refer to the pump or injector by which the feed
water is forced in — apparatus which will be dealt with further
on — but to the locality of its introduction. The following state-
ment, made by Mr. James Stirling at a meeting of the Insti-
tution of Mechanical Engineers, in the course of the discussion
on Mr. Churchward's paper on ** Large Locomotive Boilers,"
read in February, 1906, covers most of this ground and is
highly suggestive : —
" With regard to feed- water, he believed he had fed water into
locomotive boilers in almost every way possible to think of. He
had delivered it through the smoke-box tube plate, sending it
straight back to the fire-box under, the impression, as was
natural, that the ebullition being most violent at the top of the
fire-box and in the immediate neighbourhood of the tube plate,
that the current of water must necessarily flow to the smoke-box
end and come back to the fire-box under the tubes ; the results
were very satisfactory as to steaming. The next thing was to
deliver the water over the top of the fire-box in front of the
tube plate, but that only created fouling of the tubes where they
could not be got at in washing out. He then fed the water in at
either side of the fire-box, with the result that all the stays began
to leak forthwith. The next and the last thing was to feed the
water in the old-fashioned place, namely, in the side of the first
plate from the smoke-box of the boiler, and he there had a
command of the fouling, and could get the hose-nozzle at it on
washing-out days and clear it away ; in that way he managed to
keep his boilers fairly clean. Those dealing with locomotive
boilers knew that the moment the water reached the heat it
immediately precipitated any lime or deleterious matter that
might be in it."
If cold water is sent into a boiler it <?an do much harm by
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WATER 161
setting up local contractions, and so causing leakage. That is
the explanation of the fact stated above, that when the feed was
put in at the sides of the fire-box the stay bolts leaked. An
attempt is often made to raise the temperature before the water
enters the boiler, both to save the plates and to economise fuel.
As far back as 1850 a pipe was carried from the boiler to the
bottom of the tender tank ; when steam began to blow oflf at the
safety valve, a cock in this pipe was opened and the steam
blown into the tank, thus raising the temperature of the feed
water and avoiding waste. Subsequently Mr. Stroudley turned
a portion of the exhaust steam into the tender. Mr. Drummond
has a special apparatus for this purpose, the description of which
must be postponed until tenders are dealt with.
The injector, which will be described presently, always raises
the temperature of the feed. Sometimes the feed pipe is carried
along inside the boiler for several feet, the temperature of the
feed water inside rising within it. The true solution of the
difficulty, however, lies in sending the feed water into the steam
space as spray. It can then exert no chilling effect, and much
if not all the lime will be deposited as a fine powder which can
be washed out. Experiments made in this direction have been
quite successful. There is, however, what may be termed a
popular delusion that if cold spray were turned into the steam
space it would at once condense all the steam. This is quite a
mistake. A small quantity of steam would undoubtedly lose its
heat, but the boiler would at once replace the steam condensed,
and the net effect on the quantity of steam available for the
engines in any unit of time will be the same, whether the cold
water goes into hot water or into the steam space. An equally
grave error is based on an erroneous theory of the injector, accord-
ing to which the injector cannot send water into steam. It will
be shown further on that the injector will work equally well no
matter into what the water is forced. Mr. Churchward has been
carrying out experiments on the Great Western Railway on the
introduction of feed water into the steam space; certain con-
structive difficulties have been encountered, but nothing affecting
the soundness of the principle.
R.L. M
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CHAPTER XXI
PRIMING
Nothing has been said so far about the quality of the steam.
To the general public no doubt all steam is the same. But the
engineer understands that the quality of steam has a wide range.
Good steam is almost entirely free from water and dirt, and can
only be had from clean water, heated in a clean boiler. Bad
steam is wet — ** priming " goes on in the boiler. The water in
the boiler is dirty, and so is that in the steam — doubly or trebly
dirty. The steam may carry with it j&ne mud, fine sand, now
and then hard lime, which has a disastrous effect on the engines.
But even when the water is clean, if a boiler is hard pressed
priming may take place, and to such an extent that the trains
cannot keep time. The causes of priming ^re very imperfectly
understood. A small quantity of oil or grease in the feed w^ater
will make the water *' foam," and priming will go on until the
grease has been got rid of. On the other hand, in the old days
before surface condensers were used, and marine boilers were fed
with sea water, syringes were carried which could be screwed on
to small clack-valve boxes near the water level, and melted
tallow was forced into the boiler which was giving trouble, and
almost always stopped the priming.
Although a clean boiler will not prime, the water always lifts
in a locomotive boiler while the throttle valve is open. It is for
this reason that while a locomotive is running, the glass water
gauges are almost always full to the top. When steam is shut
off ebullition ceases at once for the time, and the water falls a
couple of inches. The steam space in a locomotive is restricted,
and two different systems are used to get dry steam. According
to the first, the entrance to the pipe which supplies the cylinders
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PKIMING 163
is placed as far above the level of the water as possible in a dome
on the top of the boiler. According to the second system, the
steam pipe runs the whole length of the barrel of the boiler,
quite close to the top, and in the top of the steam pipe are
drilled small holes, or else a number of transverse cuts are sawn
in it, through which the steam has to enter, the rear end of the
pipe being stopped up by a plug screwed in. In this way the
steam being drawn not from one spot, but from, so to speak, the
whole steam space, the lifting of the water is diminished, and
the steam kept dry. The perforated pipe has, however, gone
out of use, not so much because it was inefficient as because
the regulator or throttle-valve box has to be placed in the
smoke-box, where it is not wanted, and is indeed very much in
the way.
It may be asked. How is it known that a boiler is priming ?
When the priming is profuse there can be no doubt about it,
because hot water is blown through the cylinders out of the
chimney. But there are all degrees of priming, from a fraction
of 1 per cent, up, and a good deal of ingenuity has been
expended in devising means of measuring the amount of pure
water in any stated volume of steam. It cannot, however, be
said that the results are quite satisfactory. In point of fact, the
precise estimation of water, or degree of wetness of steam, is
very far from easy, because a great many chances of error have
to be guarded against. Three different methods have been tried.
The first and simplest consists in putting a good deal of salt into
the boiler, and then condensing a known weight of steam drawn
from the main steam pipe. If the boiler primes it must prime
salt water. The water resulting from the condensation of the
steam is evaporated in a shallow pan, and the salt left at the
bottom is weighed. A simple calculation too obvious to need
stating then gives the percentage of water in the steam. The
fundamental objection is that the presence of the salt may itself
set up priming, and is besides bad for the boiler. A refinement
of the process consists in using very little salt and adding to the
condensed steam in a test tube a solution of nitrate of silver,
which if salt be present gives a curdy or flocculent deposit. The
m2
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164 THE BAILWAY LOCOMOTIVE
system has been used to a limited extent with water-tube, but
never with locomotive boilers.
The second system seems to have been first used some thirty
years ago by Mr. Barrus, an American engineer. The principle
involved is very simple. The total heat in a pound of steam is
much greater than the total heat in a pound of water of the same
temperature. If now we turn any known weight of steam into
cold water the temperature of the water will be raised, and the
drier the steam the greater will be the rise in temperature. Thus
the total heat in one pound of steam at an absolute pressure of
165 lbs. — boiler pressure 150 lbs. — is 1192*9 from water at 32^
F. and the total heat in water of the same temperature is 366^.
Now if we condensed one pound of steam to water at 32^, 1192*9
British thermal units would be given up. If we cool down one
pound of water through the same range of temperature, 366
thermal units will be given up, and any mixture of the water and
the steam will give up less than the one and more than the
other. So if we mix one pound of steam with one pound of water
the total available heat will be 1192*9+366=1529 units, whereas
if the two pounds of fluid drawn from the boiler had been pure
dry steam there would have been 2,386 units available. All
we have to do then, is to ascertain how much less than 1,193 units
is given up by each pound of steam drawn from the boiler, and
a very simple calculation will give the percentage of water
present.
In practice a small wooden cask is placed near the boiler on
the platform of a weighing machine ; in the cask is a known
weight of water. The temperature is taken by a thermometer.
Communicating with the boiler or the main steam pipe is a
tube fitted with a stop cock. To the end of this tube is
attached a piece of india-rubber piping. All being ready, and
weights being placed in the scale to overbalance the cask and
its contents by a certain amount, steam is blown through the
pipe to warm it up and clear it of condensed steam. The end
of the india-rubber pipe is then plunged into the water in the
cask and steam is allowed to flow until enough of it, say 5 lbs.
or 10 lbs. or 20 lbs., has been condensed to turn the scale. The
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PRIMING 165
steam cock is then closed. The rise in emperature and the
increase in weight are carefully noted, and a simple calculation
gives the percentage of priming. An improved form of apparatus
was devised by Mr. Barrus, but the chances of error are so great
that it is impossible to regard the results as certainly correct
within 3 per cent.
The Bcirrus system has been entirely superseded by the
throttling calorimeter invented by Mr. Peabody, also an American
engineer, which with care will give very accurate results. It
depends for its action on entirely different phenomena.
If the reader will turn to the table of the properties of steam
given on page 152, he will see that as the pressure and
temperature rise, so does the total heat, only very much more
slowly. Let us take, as before, our pound of pure dry steam at
165 lbs. Its total heat we have seen is 1,193° F. Let now this
steam fall in pressure, without doing any work, to that of the
atmosphere = 14*7 lbs. Its temperature will then be 212° F.,
and its total heat 1,146° F., and we have 1193° - 1146° F. The
difference is 47°. What becomes of this ? Eankine was the' first
to show that if the steam contained no free water the 47° F.
would superheat it. We may further deduce that if ifc did
contain water then that water would be all converted into steam
unless there was too much of it. If the reader has followed so
far he will have no difficulty now in seeing that it is only
necessary to take the temperature of the steam before and after
the fall in pressure to ascertain the percentage of water present.
As the specific heat of steam, that is to say, the quantity of heat
required to raise it one degree Fahrenheit in temperature, is to
that of water as *48 to 1, the 47° available would raise the
temperature of one pound of steam by nearly twice as much.^
The calorimeter in its most improved form is illustrated by
Fig. 57.
The steam is allowed to expand without doing any work by
1 The true value of the specific heat of steam cannot be regarcJed as settled ;
inquiry is still proceeding. There is reason to believe that it varies with
the pressure. The figure given is, however, quite accurate enough for the
present purpose.
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166
THE RATT.WAY LOCOMOTIYE
passing through a small orifice in a thin plate at I. The main
steam pipe is shown at G, and the collecting pipe atF. It enters
the steam pipe as shown, and much discussion has taken place
as to the hest way to admit the steam into F. With this we
need not concern ourselves. A is a so-called drip box, which is
intended to remove some of the priming water if it is plentiful.
This is collected and measured, its height in the drip box being
Fig. 57. — The Peabody calorimeter.
shown by the glass water gauge C. The discharge cock is shown
at D. The steam passes from the top of the drip box by E P
into K, into which is screwed the thermometer M. The thin
plate is shown by E. J and S are flanges between which E is
bolted. The expanded steam passes through into L and thence
into the atmosphere. N is a thermometer similar to M. The
difference between the reading of the two thermometers expresses
the quality of the steam, in other words the percentage of water
in it. It is not necessary to give here a general equation. In
practice, nothing in the way of an elaborate calculation is
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PRIMING 167
necessary. Mr. Barrus gives in Vol. XI. of the Transactions of
the American Society of Mechanical Engineers the following
instructions for using this instrument : —
" In order to compute the amount of moisture from the loss of
temperature shown by the heat gauge, the number of degrees of
cooling of the lower thermometer (N) is divided by a certain
co-ef&cient, representing the number of degrees of cooling due to
1 per cent, of moisture. This co-ef&cient depends upon the
specific heat of superheated steam, which, according to Eegnault's
experiments, is 0*48. In other words, the heat represented by
1° of superheating is 0*48 of a thermal unit. This quantity
cannot be applied exactly to the form of instrument under con-
sideration. The quantity to be used varies somewhat according
to the degree of moisture. For an instrument working under a
temperature of 314° F., by the upper thermometer, and with a
cooling by the lower thermometer from 268° to 241°, the
quantity was found to be about 0*42. When the cooling, however,
was from 266° to 225°, the quantity to be used was found to be
about 0*51. The experiments have not as yet covered a sufficient
range to determine the exact law which can be applied to every
case, but it seems probable that the specific heat is more or less
constant until the temperature by the lower thermometer
approaches the point of saturation for the low pressure steam,
while beyond this point the specific heat rapidly increases. For
the present, it is assumed that the quantity 0*42 is the proper
one to apply whenever the temperature by the lower thermometer
is above 235°, and that in cases where the temperature is below
235°, the quantity to be used is an increasing one, reaching
perhaps to 0*55 when the temperature drops to 220°.
" One per cent, of moisture now represents the quantity of heat
determined by multiplying the latent heat of one pound of steam,
having a pressure corresponding to the indication of ther-
mometer M, by 0*01, and this product is to be divided by
0*42 (provided the lower temperature is not below 233°) in
order to express it in terms of degrees of superheat. For
example: when thermometer M shows 312°, the latent heat
is 894 thermal units, and 1 per cent, of this is 8*94 ; dividing
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168
THE EAILWAY LOCOMOTIVE
by 0*42, the number of degrees of superheat corresponding to
1 per cent, of moisture is found to be 21*3. For several
other temperatures, which cover the ordinary range that would
commonly be used, the necessary co-efficient is given in the
following table: —
Temperature by Ther-
moiiieter M.
Co-efBcient.
Temperature by Ther-
mometer M.
Co-efficient.
270
220
320
211
280
21-8
330
21-0
290
21-7
340
20-8
300
21'o
350
206
310
21-3
360
20'o
Certain corrections have to be made for radiation from the
calorimeter itself, and curiously enough it has been found that
when the steam is very wet so much water remains in the drip
box that the steam going into the instrument proper is actually
drier than is steam which does not deposit any sensible quantity
in thedrip box."
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CHAPTER XXII
THE QUALITY OF STEAM
We may now turn to the results obtained in practice from the
modern locomotive boiler as ascertained by the calorimeter. In
this country nothing has been done in this way. Indeed, the
only information on this point which covers a sufiBciently wide
range of locomotives has been supplied by tests carried out at
the St. Louis Exhibition of 1904, to which reference has already
been made in these pages. The importance of the figures will
be better appreciated when we come to deal with superheating
and its effects on the economical efficiency of locomotives.
It is very constantly assumed that locomotive engine boilers
do not supply dry steam. That is to say, it is asserted that it
never contains less than 5 per cent, of water. The St. Louis
experiments do not bear out this proposition. In all eight engines
were tested ; of these four were passenger and four were goods
engines. The following table gives the results of tests made
with the Peabody throttling calorimeter just described: —
Loco. Number.
Maximum.
Minimum.
Goods.
1499
•9903
•9877
734
•9871
•9837
929
•9846
•9445
585
•9845
•9828
Passenger.
628
•9986
•9936
2512
•9859
•9812
3000
•9835
•9499
585
•9823
•9626
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170 THE KAILWAY LOCOMOTIVE
The decimals express the percentage of steam in ten thousand
parts of the mixture of steam and water supplied by the boiler.
The maximum percentage of water, it will be seen, is about 5*5,
the minimum a shade over 1 per cent. It must not be forgotten
that these results were obtained from very dissimilar boilers
working under dissimilar conditions, and, therefore, may be
taken as thoroughly representative. But it must also be kept
in mind that the boilers were very clean, and were supplied with
water of excellent quality.
A complete explanation of the causes of priming has not yet
been framed ; why, for example, dirty water should prime and
clean water will not is not known.^ The theory of the matter
is that surface tension has something to do with it;. This means
that the bubbles of steam have a comparatively tough envelope
of water, which rises through the main body. When the bubble
bursts this water is scattered in all directions, and remains
suspended in the steam. Again, when water is boiling in an
open vessel it will be seen that a multitude of little fountains of
spray rise from the surface and fall back again. The water in
these may be readily entrained and carried away by the steam
if there is a strong current moving in any particular direction,
as, for example, to the opening of the regulator.
^ Water- tube boilers supplied with pure clean rain water will prime, and
with distilled water will not. Locomotive type boilers supplied to H.M.S.
Poh/pherntis primed so much on board that they had to be taken out. They
were worked with water from surface condensers. They were subsequently
put up on land and used for driving dockyard machinery with similar water,
and gave no trouble whatever. Abundant examples of the capriciousness
of boilers could be supplied.
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CHAPTEK XXIII
SUPERHEATING
A CONSIDERATION of how far, and in what way, the economical
and absolute efficiency of a locomotive are affected by the quality
of the steam must be postponed until we come to deal with the
engines. It is open, perhaps, to question whether superheaters
are part of the boiler or part of the engine. The author holds
it to be most convenient to adopt the first view, and to regard all
that affects the quality of the steam as delivered to the engine as
part of the generating apparatus.
Before describing superheaters it is necessary to explain what
they are intended to do.
It will be understood from what has gone before that saturated
steam is an unstable fluid. It is not easy, indeed, to realise how
unstable. It is always on the point of reverting to its original
condition of water. Now, when any percentage of a given weight
of steam liquefies it surrenders all its latent heat, and if only the
heat could be utilised, then liquefaction might do very little
harm. It can be shov/n, however, that such utilisation does
not take place in practical work; and it becomes expedient,
therefore, to impart stability to the steam. If we reduce the
temperature of dry saturated steam by withdrawing heat some
of it will condense. If, however, the steam possesses a sensible
temperature greater than that due to its pressure, then no con-
densation can take place until such a time as the whole of this
additional temperature has been withdrawn. Thus, let us suppose
the case of one pound of steam, with an absolute pressure of
165 lbs. per square inch. Its temperature is 366° F., the total
quantity of heat in it is 1,193°, its volume is 2*71 cubic feet.
If now we withdraw nominally one-tenth of the total heat, then
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172 THE EAILWAY LOCOMOTIVE
one-tenth of the steam will be reduced to the condition of water,
and so on. But O'l means 119*^, omitting fractions. If, however,
we had added to the steam beforehand the equivalent (depending
for its amount on the specific heat) of 119^, then the withdrawal
of one-tenth might take place — there would be a reduction in
temperature, but no condensation. This is the principle on which
the value of superheating depends.
The figures given above must be regarded only as illustrative,
for the conditions of superheating are much more complex than
may appear at first sight. Thus, one of the immediate effects
of superheating is to increase the volume of the body of steam
superheated^; it has been shown by Fairbairn that the volume
augments much more rapidly at first than it does sub-
sequently. One explanation of this fact is that the water
suspended in the steam is evaporated first and that the steam
so produced goes to add to the volume, and that once that has
been effected, expansion takes place purely as if the steam were
a gas. Again, as has been already pointed out above, consider-
able uncertainty exists as to what the precise specific heat of
steam gas is. Probably it is about '48°, or rather less than one-
half that of water. The specific heat of dry saturated steam is
•305°, that is, the quantity by which the total heat of saturated
steam is increased for each one degree of added temperature.
The expression '305 is used in a compound sense, taking account
as it does of the changes both of volume and pressure which
take place in the generation of saturated steam. Regnault's
experiments gave the specific heat of steam-gas — that is to say,
of steam out of contact with water in any shape — as "475 under
constant pressure, or upwards of one-half more than that of
saturated steam. Recent researches, however, seem to prove
^ A shai-p difference of opinion exists among engineers as to whetlier the
increase of volume has or has not any economic value. On one side it is
maintained that such a reduction of temperature always takes place in the
engine that the increase of volume disappears ; on the other, an eminent
authority, Dr. v. Oarbe, of the Prussian State Railways, and- the apostle of
the Schmidt system, maintains that superheating, or, as he calls them, ** hot
steam, locomotives," must have larger cylinders than saturated steam loco-
motives in order to utilise this augmented volume.
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SUPERHEATING 173
that the more correct co-efficient is '48. To complete this state-
ment, Eankine lays it down that the total heat required to
convert a given substance from a state of great density at a
given temperature, To, to the perfectly gaseous state at a given
temperature, Ti — tlie operation being completed under any
constant pressure — is given by the equation
h = a + c^ (Ti - To),
where a is a constant and c^ is the specific heat of the
substance in the perfectly gaseous state under constant pres-
sure. Thus, to convert one pound of water at 32° into steam-
gas at 212° requires -1092 + -475 X 180 = 1,177 units of
heat, being more than the quantity required to make saturated
1 177
steam in the ratio ^-Vttt = 1*028. Here a = 1,092 and c^ =
1,146
•475.
The principal utility of these equations lies in showing how
much heat must be added to steam to convert it into a compara-
tively stable gas. In so far as regards the locomotive, however,
their value is in the main academical ; because, in the first
place, heat which would otherwise be wasted is supposed to be
utilised, and because, in the second place, the results obtained
in practice do not bear any traceable relation to the figures
given. The conditions are far too complex to permit such rela-
tions to be established. In a word, superheating has hitherto
been carried out by rule of thumb, derived from rough experi-
ments. The general result is that no matter how the super-
heating is effected, the hotter the steam the better in so far as
economy of fuel is affected. As to its effects on rubbing surfaces
in the engine, that is another story to be told further on.
Although various methods of superheating have been devised
and even patented, there is only one in use. The steam flowing
from the boiler to the engine is made to pass through pipes in
which its temperature is raised. Now it so happens that while
wet steam will absorb heat rapidly, dry steam will not. Indeed,
it is by no means easy to superheat steam beyond some 30 or
40 degrees. To make the superheating apparatus worth having,
however, the temperature of the steam should be raised at least
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174 THE EAILWAY LOCOMOTIVE
200 degrees, so that 150 lbs. boiler steam must have a tempera-
ture of 366^ + 200° = 566° F. But Scbmidt wants much
more than this ; he likes 650 to 700 degrees. Where on a loco-
motive engine can space be found for the required pipes ? Here
the inventor comes in. Four or five different systems have been
tried. Of these only one appears to have come as yet into any-
thing like regular use, namely, the Schmidt. Several others
are still in the experimental stage — the Notkin, American,
Cockerill, Cole & Vaughan, and Horsey may be mentioned.
It will suffice if we confine our attention to the system. first
named, because so far it is the only one in regular use. It was
introduced by M. Schmidt on the Prussian. State Railways as far
back as 189B. Originally the place of a number of the lower
flue tubes was taken by one large tube about a foot in diameter.
In the smoke-box were fitted at the sides inverted (j'^^^es.
These were cut off from the smoke-box by partition plates. The
steam was taken in at one end of the u-tul>68 ^^^d delivered to
the engine from the other end, superheated by the hot gas
passing through the large tube, and rising at each side to the
top of the smoke-box and thence up the chimney. The arrange-
ment was not very successful, and has been superseded by one
quite diflerent.
This cannot be better described than in tlie words of Herr
Eobert Garbe, Chief Mechanical Engineer of the Prussian State
Railways, who has recently dealt with the whole subject in a
series of articles contributed to the Engiiieer, It will be seen
from Figs. 58, 59 and 60 that the ordinary small tubes in the
upper part of the barrel of the boiler are replaced by two or three
rows of larger size. In the figures there are three rows of eight
tubes of 4-88 in. internal and 5*23 in. external diameter. Within
each of these are four smaller tubes spaced at equal distances,
connected together at their fire-box ends by cast steel return
bends to form a single continuous passage, so that the steam
passes four times along the length of the superheater tubes.
Near the fire-box the outer tubes are contracted to 4*48 in. to
allow of a freer movement of the water near the tube plates, into
which they are expanded in a special way. The ends of each
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SUPERHEATING
175
Fig. 60.
The Schmidt superheater.
group of superheater elements on the smoke-box side are
expanded into flanges, which are connected to the steam col-
lecting box by screwed joints arranged either horizontally or
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176 THE BAILWAY LOCOMOTIVE
vertically, the joint being made tight by copper asbestos packings.
The former arrangement involving a semicircular return bend
for the superheater tubes, has the disadvantage of requiring an
extra long smoke-box, but as it causes a better utilisation of
the heat it is retained on the Prussian lines up to the present.
The cast iron superheated steam collector. Fig. 60, which is
made of the same metal as the cylinders, is so divided and
connected with the boiler and the valve chest that the steam
from the former must pass through the whole of the superheater
system before reaching the engine cylinders. The fire gases
being divided between the lower normally arranged boiler tubes
and the larger upper tubes containing the superheaters, give up
their heat partly to the surrounding boiler water and partly to
the steam circulating in the superheater. The regulation of the
flow of the gases through the superheater is effected by a
system of dampers, which are kept open by steam pressure as long
as the regulator valve is open, but are closed when the latter is
shut either by a spring or a counterweight. When the engine
is standing or running without steam the flame is entirely
diverted from the superheater tubes, which would otherwise
become red hot. The position of the dampers can also be varied
while the engine is under steam by a hand wheel and rod on
the footplate, so that the superheating may be regulated inde-
pendently of the automatic arrangement. The latter, placed
outside the smoke-box on the left-hand or fireman's side, is a
small steam cylmder whose piston is connected by levers with
the damper flaps. There is a pipe connection between the valve
of the small piston and the valve chest, so that when the regu-
lator is open and steam is admitted to the cylinders the piston
travels forward, opening the dampers, which are closed by the
counterpoise as soon as the pressure is taken off by the closing
of the regulator.
The removal of soot and ashes from the large smoke tubes
may be most readily effected by steam or compressed air either
from the fire-box or the smoke-box, but preferably from the
former. As a rule, air at ten atmospheres is the best clean-
ing agent both for these and the ordinary boiler tubes. If
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SUPERHEATING 1*77
steam is used the cleaninjg should be done while the boiler is
still hot.
The Notkin superheater is very similar in all respects, except
that instead of using very elongated U -tubes the inventor employs
two concentric tubes, placed in special fire tubes 3 inches in
diameter. The outer concentric tube is secured to one half of a
steam chest and the inner tube to the other half. The steam
passes down the annular space between the two tubes from one
half and returns up the centre tube to the other half of the
steam chest, whence it goes on to the cylinders.
The Pielock superheater, so called after the inventor, has been
fitted to locomotives on the Eoyal Prussian Kail ways, and been
tried in the United States. It consists of a steel chamber placed
in the barrel of the boiler far enough forward to prevent the tubes
being overheated. Into the ends of the box the boiler tubes are
made tight by rolling them, the expander being placed at the
end of a long steel staff which passes down the tubes. It is not
necessary that much care should be taken to make the joint
tight, as the pressure is nearly the same inside the superheater
and outside. It is only required that the water shall be kept
out. The box is divided inside by diaphragm plates parallel to
the tubes in order that circulation may be secured inside it. The
steam is collected at the top of the dome, passes down into the
superheater, and then rises again to the regulator valve box and
thence to the engine. The total heating surface taken inside the
tubes in a normal locomotive is 1,753 square feet, the total
heating surface of the superheater inside is 283*79 square feet or
•16 of the whole tube surface. At the St. Louis Exhibition, the
quality of the steam, before it entered the superheater at all,
was excellent, the moisture never exceeding one half per cent.
The lowest superheat was 161° F. and the highest 192° F.
Curiously enough, the amount of superheat did not seem
to be much affected by different rates of combustion or
evaporation. The explanation is that when more steam was
passed through the superheater the fire was hotter and, of
course, the gas in the tubes. As the steam pipe from the super-
heater passed through the boiler the temperature of the steam
R.L. N
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178 THE RAILWAY LOCOMOTIVE
was reduced. It is clear, therefore, that there was loss of heat
before the steam reached the engines. The Pielock superheater
is fairly efficient, but it is argued about it that on the whole as
much in the way of evaporation is lost as the superheater can
gain. The more cogent argument against it is said to be the
fact that the flue tubes are liable to rapid corrosion inside the
superheater.
It was not to be supposed that such an innovation as super-
heating would be accepted without question, and very keen
discussions have taken place concerning not only the respective
merits of various systems, but the theoretical and actual value
of superheating. When superheating was first proposed in
locomotives it was maintained that the heat which was wasted
up the chimney could be utilised and in this way superheating
could be had for nothing. It was very soon stated, however, that
a smoke-box temperature of at the most 700 degrees could not
raise the temperature of the steam to anything like the necessary
amount.^ Therefore, as has been shown, in the preliminary
Schmidt heaters, a large proportion of the gases was conveyed
through a flue tube of considerable diameter to the smoke-box.
This did not answer, and now nearly all locomotive superheaters
save the Pielock differ from each other only in details. Into
enlarged flues are put small pipes, one end of each pipe receiving
steam from the boiler, the other end delivering steam to the engine.
No waste heat is utilised. The steaming power of the boiler is
diminished because the heating surface of large flue tubes is less
than that of the more numerous small tubes which could be put
into the same space. As, however, the economic efficiency of a
boiler is, other things being equal, measured by the smoke-box
temperature, and this does not appear to be augmented by the
presence of a superheater, it may be taken for granted that
the only loss incurred will be in the ability of the boiler to make
steam. This means that an engine with a superheater would
1 It is however claimed that the Baldwin smoke-box superheater raises
the temperature as much as is really necessary with the waste gas only.
The claims made are so conflicting as regards the temperature which repre-
sents all-round maximum economy that the author reserves all expressions
of oninion on the point.
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SUPERHEATING 179
not be able to draw trains as heavy or as fast as it would be
without the superheater, although the cost of coal per ton per
mile might remain unaltered. On the other hand superheated
steam being more efficient than ordinary steam, the balance is
restored, the power of the engine is increased, and an economy
of fuel effected. How much, remains a bone of contention among
railway engineers, the dispute being strengthened by the lack of
uniformity in results obtained on different railways. In this
country, very little has been done, because it is maintained that
the large addition to the first cost of the locomotive, and the
heavy expenditure on the upkeep of an apparatus so liable to
wear and tear and corrosion cannot fail to neutralise much of the
economical advantage that it may be able to bestow. So far the
experience obtained on Continental lines has not been regarded
as convincing. The size of the smoke-box, too, is increased, as is
the weight on the leading bogie. The kind of work done in this
country is different in many respects from that performed by
Continental locomotives. Our coal is very much better, and on
the whole, cheaper ; and lastly, we have the somewhat sentimental
objections held by British engineers to anything savouring of
complications, which are for the most part favoured rather than
condemned in Europe.
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CHAPTER XXIV
BOILER FITTINGS
Wk come now to the several adjuncts or appurtenances with
which the boiler is fitted. Although these always serve the same
purpose they vary widely in design and the details of their con-
struction. None of them, perhaps, is so obvious to the railway
Fig. 61. — American throttle valve.
traveller as the regulator, a handle on the back plate of the fire-
box, which seems to possess a magic power of calling the enormous
machine into life. It derives its name from its function, which
is to open or shut a valve inside the boiler, which controls and
regulates the supply of steam to the cyhnders. When the boiler
is fitted with a dome of any kind, this valve is always placed
within it. When there is no dome the valve is placed, as a rule,
in the smoke-box. If not, then just inside the front tube plate.
The valves are of two kinds. They are either double-beat
valves, or sliding valves. The first type is almost invariably
used in the United States. Figs. 61 and 62 give the general
arrangement and a section to an enlarged scale of an American
regulator valve. It will be seen that the valve is of the double-
beat equilibrium type. It is entirely surrounded by steam,
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BOILER FITTINGS
181
which tends to force the upper valve down on its seat and lift
the lower valve oflf it. A bell-crank lever A is arranged in such
a way that by pulling on the lower extremity E the valve is raised
from its seat, and steam is admitted to the cylinders. A rod E
extends from the bell-crank lever to the back plate of the fire-box,
where it traverses a staffing box, and is jointed to a transverse
lever which is moved by the engineman
pushing it in to shut oflf steam ; pulling
it out turns steam on.
The "dry pipe," that is, the steam
pipe inside the boiler, is shown at F ;
the whole valve box is supported inside
the dome on the angle-iron ring B,
Fig. 62, by a flange D, Fig. 61. At B
is a conical ground joint fitting a seat in
a flattened portion of F. The surfaces
are drawn together steam tight by the
bolt C. The fulcrum of the bell crank
is at G.
The valves are not perfectly balanced,
because in the first place it is desirable
that there should be a tendency to keep
the valve closed, and in the second, the
lower valve has to be passed through
the seating of the upper valve to get it
into place. In the valve illustrated, the
upper valve is 6 inches diameter and
the lower valve 5f inches. The area of the upper valve is 28*27
square inches, that of the bottom valve 22*7 square inches. With
a boiler pressure of 200 lbs. the top valve is held down with a
force of about 5,654 lbs., or over 2-5 tons. The lower valve,
however, tends to lift oflf its seat with a force of 4,540 lbs. The
diflference is 1,114 lbs., and at first sight it would appear that the
engine driver would have to pull very hard indeed to get the
valve oflf its seat. But this is not so. In the first place he has
considerable leverage to help him and the moment the valve is
opened a hair's breadth the valve is in equilibrium. In the
Fig. 62.— Throttle valve.
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182 THE BAIL WAY LOCOMOTIVE
second place, the rod, where it passes through the stufl&ng box
before referred to, is more than an inch diameter. If it has a
square inch of sectional area then the steam pressure inside the
boiler will tend to push the rod out, so assisting the driver with
an effort of 200 lbs. By making the rod still larger we can go
on restoring, so to speak, equilibrium. But it must be kept in
mind that the resistance to opening the valve only exists so long
as it is shut ; as soon as it is opened at all the pressure inside and
outside the valve box becomes nearly the same. The thrust on
the rod is then unbalanced, and the valve as soon as opened a
little would be forcibly lifted as far as it would go. To prevent
this the lever on the back of the fire-box works in an arc, known
in the United States as a " gate '' ; this is provided with notches
into which drops a detent working on the edge of the regulator
lever. In this way, the valve may be set open much or little.
Sometimes the lever is fitted with a fly nut, by which it may be
secured in any position.
In some cases the bell crank is so set that the regulator handle
has a very greatly augmented leverage at first, so that the
valve can be opened by a small effort just enough to admit
steam to the engine and so establish equilibrium.
In this country the double -beat valve is little used, the sliding
valve being preferred. The main steam pipe is fitted with an
elbow rising into the dome. The mouth of the pipe is stopped
by a vertical plate, in which are two or more rectangular holes or
ports; on this plate slides another with similar holes. When
the holes coincide, steam is admitted to the cylinders. The plate
can be moved up and down in either of two ways. According to
the first, a bell crank and rod are fitted precisely as just described.
The horizontal limb of the bell crank then moves the sliding
plate up and down. More usually a " winch " handle is used,
and an arm on the long spindle is jointed just under the dome to
the valve. A partial revolution of the regulator handle then
suffices to put on or shut off steam in a way with which every
one who has seen a locomotive started is familiar. In all this
there is little room for variety. One improvement may be
mentioned in the valve. It consists in placing a subsidiary
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BOILER FITTINGS 183
sliding plate on the back of the principal valve, which plate has
a small hole in it. When steam is shut off, there is, of course, a
heavy pressure on the back of the sliding valve which makes it
hard to open the regulator. Now the first effect of moving the
regulator handle is to act on the subsidiary valve, which offers
little resistance. This admits steam at once to the main steam
pipe between the cylinders and the regulator. This equalises
the pressure on both sides of the larger plate, which can then
move quite freely. On the London and South Western Eailway,
Mr. Drummond has entirely done away with the stuflftng box.
A collar on the regulator spindle has a face ground to fit the
inner end of the brass casting through which the spindle passes.
The pressure of the steam thrusts «^
the collar against the casting, ^=
making a steam-tight joint.
Safety valves are important,
although good firemen seldom
give them much work to do. —
They do not require minute ' ^^'
description. The first safety valves were always loaded directly by
a lever of the second order. They were, as they are still, conical
brass or gunmetal valves resting on seats of the same metal. They
constituted ornamental features, being carried on fluted columns,
standing a couple of feet above the top of the boiler. The load-
ing was always effected by a spring balance as shown in Fig. 68,
and the area of the valve, the length of the lever, and the
graduation of the spring balance index were so adjusted to each
other that the figures on the index plate B showed the pressure
when the valve blew off. Now, the index hand was carried by a
stout stud, and it was quite possible by turning the adjusting
nut by which the pressure at which the valve lifted was regulated,
to set the stud hard against the top of the slot in which it moved.
Then the valve could not lift at all. Engine drivers with irains
a little too heavy were in the habit of so setting safety valves fast
in order to get more pressure. Even when an explosion did not
follow, the boilers were strained and the tubes caused to leak.
Ferrules, as at A in dotted lines, were then fitted on the screws
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184
THE RAILWAY LOCOMOTIVE
of the spring balances, so that they could no longer have the
indexes set up against the tops of the slots. Then the engine-
men loaded the lever direct with anything, such as a couple of
links of wagon chain. To meet this, Mr. Ramsbottom, when
Locomotive Superintendent of the London and North Western
Eailway many years ago. invented a most ingenious valve,
which is largely used now, and was used to the almost total
exclusion of all other valves up to a recent period. It is illus-
trated in Fig. 64. Two valves of precisely the same size are
placed side by side on top of short pillars ; between them is a
stout coiled spring, one end of which is hooked into an eye
between the two pillars, and the other into a hole in the middle
of a lever. Projections or horns
on the lever bear on the centres
of the two conical valves. It
will be understood in a moment
that the one spring loads both
the valves, and must be twice as
strong as if it loaded only one.
A diameter of a little over three
^^^^^^ inches, with an area of ten
■^^^- ^^' inches, is a very common size
for a safety valve. It the pressure is 150 lbs. then each valve
must be held down under a force of 150 X 10 = 1,500 lbs. or for
the two valves, 3,000 lbs., and the spring must be strong enough
to apply this pressure. The end of the lever is prolonged into
the cab, and the driver can always be certain that a valve is not
sticking, because by pulling down the end of the lever he takes
all the load oflf the valve furthest from him, and by lifting it up
all the load oflf the valve next to him.
At first sight it would appear that this valve could not be over-
loaded, as the load was settled for good in the workshops by
adjusting the lengths of the horns on the lever. But, even so,
the enginemen were not beaten. They overloaded the valves
by putting shot into the excavation in the tops of the valves.
When there was no steam in the boiler, by pulling down the lever
they lifted the horn on the outer valve and the shot ran in under
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BOILER FITTINGS 185
it. The same process produced a like result with the other valve.
The effect was the same as lengtheninjj; the horns ; the tension
of the spring was increased, and in this way 10 lbs. or 20 lbs.
were added to the pressure. All loose shot was carefully removed,
and until the valves came to be specially examined the fraud
was never detected. Mr. Webb, Mr. Ramsbottom's successor,
then fitted the valves with a casing so constructed that shot
could not be put into the valves, and he offered a reward of i*5
to any man who could overload the valves ; the money was
never claimed.
Within the last few years it has been deemed desirable to fit
more than two safety valves to the very large boilers now in use,
and something more compact than the Ramsbottom valve
became desirable. Therefore, we now find three or even four
valves loaded direct, each by a coiled spring, and grouped in one
casing. No easing gear is needed, because the valves are
constantly under observation, and it is almost impossible that
they should all stick. On some lines ** Pop " valves have been
tried. They are so called, because instead of rising gradually as
the pressure increases after they have begun to blow off, they lift
suddenly with a " pop '' and blow off hard for a minute or so until
they have reduced the pressure about 3 lbs., then they shut
suddenly until the pressure again rises, and so on. This inter-
mittent action is very noisy and objectionable in railway stations.
It alarms passengers, and does no good, so pop valves have never
found much favour with locomotive superintendents. The pop
action is got by so shaping the valve and valve seat thai the area
on which the steam can act is augmented by the rising of the
valve.
It is essential that the precise level at which the water stands
in the boiler should be known. In old times — and indeed, to this
day in America — three ** pet " cocks, or " try " cocks, were screwed
into the back of the fire-box about 3 inches above each other. If
when the lower one was opened steam came out, then tlie water
was too low. If when the top one was tried water came out, it
was too high ; when it was just right, steam came out of the
top cock, water and steam out of the middle cock, and water alone
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18G THE RAILWAY LOCOMOTIVE
out of the lower cock. The indications thus supplied were not
easy to read, because the hot water flashed into steam at once.
The whole system was dirty and ineflficient, and has long since
been superseded by the glass water gauge, which is too familiar
to require illustrations. The tube is made of a very special hard
glass with a minimum of alkali in it, which will not dissolve
under the high pressure to which it is exposed. Soft glass in high
pressure steam will become cloudy and corroded in a few hours.
The glass tube is passed through a stuffing box at each end, in
which it is packed by india-rubber rings, which permit free move-
ment. Any attempt to confine the tube is certain to result in
breakage. It is usually about half-an-inch bore. Since very
high pressures have been introduced, it is usual to box the gauge
up in a shield made of pieces of thick plate glass, because a
broken gauge tube is apt to fly and wound the driver or fireman.
In some cases gauges are fitted with ball valves at the top and
bottom, which remain at rest in little pockets unless the glass
gives way. Then the violent rush of steam above and water
below lifts the balls, and blowing them on to seats, the steam and
water are automatically shut ofi^. When the driver shuts the
stop cocks the automatic valves fall away again to their normal
position.
We have now got the boiler complete, with all the appur-
tenances which concern the outflow of steam from it except the
whistle, which does not require description ; and we have, lastly,
to consider the means by which water is put into it.
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CHAPTEB XXV
THE INJECTOU
A LOCOMOTIVE will evaporate, according to its size and its load,
from three to seven tons of water per hour, and as this has to be
forced into the boiler with certainty and regularity just as it is
wanted, it will be seen that the efficiency of the feeding apparatus
is of the last importance. For many years the water was invari-
ably pumped in. Two horizontal plunger force pumps were fixed
inside the frames, one at each side, the plungers being moved by
the cross heads on the piston rods. Now and then short-stroke
pumps, worked off the crank shaft by eccentrics, were used. The
steam locomotives on the Metropolitan and District Railways were
thus fed. No recently built engines, however, are fitted with feed
pumps save under special circumstances, and it is unnecessary to
say more about them than that they presented no particular features
of any kind calling for description. The system was inconvenient
because no water could be put into the boiler while the engine
was standing. It was not at all unusual to have to uncouple a
locomotive from its train, and run it up and down the line for
half a mile, both pumps going for all they were worth, until the
boiler was replenished, and then couple it up again to its train.
A simpler plan was to jam the brakes hard on the tender wheels,
then to oil the rails and the rims of the driving wheels, which of
course were not coupled, and then to turn on steam and let the
driving wheels revolve, both pumps being at work. When the
boiler was satisfied the brakes were taken off, and a couple of
shovelsful of sand on the rails enabled the engine to move ahead.
Later, engines were often fitted with small donkey feed pumps.
Locomotive boilers in the present day are always fed by injec-
tors. The injector is an instrument so remarkable and so
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188 THE RAILWAY LOCOMOTIVE
paradoxical in its action that it cannot be dismissed in a few
words. It has been made the subject of much mathematical
investigation, to which it lends itself so badly that no satisfactory
theory has been established which will account for all the
phenomena which it presents. Enough is however known to
enable an entirely adequate explanation of its action to be given.
A comparatively small quantity of steam supplied by the boiler
is passed through the injector and picks up cold water from the
tender, heats it, and forces it into the boiler. The paradox is
that steam of, say, 150 lbs. pressure should come out of the boiler,
and then find its way in again, carrying the feed water with it,
against the same 150 lbs. pressure. Here we apparently eat our
cake and still have it. It is not remarkable that on its first intro-
duction engineers refused to believe in it. Articles indeed were
written to prove that all the laws of the conservation of energy
would have to be remodelled if the injector really worted, and
much more to the same efifect. The injector works, however,
and no one now thinks that it upsets any law. On the contrary,
it is a beautiful embodiment of laws lying at the root of all
thermodynamical facts.
How the injector came into existence is not accurately known.
It originated with M. Henri Gififard, a French engineer, in
1858. So far as available information goes it was a discovery,
not an invention. He brought it over to this country, and
Messrs. Sharp, Stewart & Company, very eminent locomotive
engine builders of Manchester, acquired the sole rights, and for
many years constantly effected improvements. The expiration
of the original patents threw the injector open to the world.
Several firms took up its manufacture, and it is to-day a very
different instrument from what it was originally. The first
locomotive in this country to be fitted with an injector was the
** Problem," an engine with outside cylinders and a single pair of
driving wheels, 7 feet 6 inches in diameter. Sixty of these
engines were built by Mr. Ramsbottom at Crewe for the Northern
(Holyhead and Crewe) section of the London and North Western
Eailway in 1862.
When a jet of steam is permitted to strike against an obstacle
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THE INJECTOE 189
it loses its velocity, and its momentum reappears as pressure.
It is only necessary to hold a board in front of a jet of steam to
prove this.^
Let us suppose that a bullet-proof plate is supported by a
spring at the back, and that a rifle is fired at it. The plate
will be driven back and move forward again every time it is
struck.
Let us now further suppose that instead of a single rifle the
plate is fired at by small machine guns ; the bullets will now
impinge on the plate so rapidly that it will not move forward at
all. The spring will be kept permanently compressed, and we
shall have to all intents and purposes the momenta of the bullets
converted into pressure. Now the molecules of steam, however
small they are, possess momentum, and so, as has been said,
they, acting as so many tiny bullets, produce pressure on any
surface against which they strike.
The force with which each bullet strikes is expressed by the
M V^
equation E = -^ttj where E is the stored-up energy in the bullet,
M its mass and V^ the square of its velocity. The meaning of
this is that if a bullet had a velocity of 1,000 feet per second, and
weighed one-tenth of a pound, then at the moment of striking it
represented energy sufficient to lift 1,537 lbs. a foot high, or
18,444 lbs. one inch high, or 184,440 lbs. one-tenth of an inch,
and so on. The fact with which we have to deal is that energy
augments, not as the velocity, but as the square of the velocity.
Next let us suppose that two bullets of equal weight moving at
the same velocity in opposite directions encounter each other.
It is clear that they would be flattened or shattered. Neither
would give way and retire before the other. If, however, one of
the bullets moved faster than the other, then the slower bullet
would be overcome, and we may then suppose the two bullets
* The accepted theory explaining why gases exert pressure on the inside
of the vessel containing them is that the molecules of which the gas consists
are in extremely rapid motion, continually striking against and rebounding
from the wall, just as a billiard ball rebounds from the cushions. The
number is so enormous that individual impacts cannot be distinguished, and
the average effect is to produce pressure.
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190 THE EAILWAY LOCOMOTIYE
moving together at a less speed than either possessed before,
in the direction of the flight of the bullet with the greatest
velocity.
To put this in another way, let us suppose that a jet of steam
is suddenly turned into a swarm of hailstones. If the steam was
moving at, say, 3,000 feet per second, it is clear that the hail
would continue to move at just the same velocity.^ In the same
way, if the steam were turned into water, the velocity of the water
would be that of the steam, and if the water was turned into
another body of water it is clear once more that it would set up a
violent current in that water.
So far nothing has been said about getting water into the
boiler. Let us suppose, however, that our jet of steam, on its
way to the nozzle through which it flows, comes in contact with
cold water. The result will be that it will be condensed, but, as
has just been shown, it will not thereby cease its onward flight.
It will transfer its momentum to some of the cold water, which
will then join the condensed steam, and by dint of sheer
momentum the two will force their way into the boiler. The
steam will play the part of gunpowder, and the water will act as
a bullet, producing, as we have explained for machine-gun bullets,
a pressure which suffices to overcome the resistance offered by
the water under pressure in the boiler, and so the boiler is
supplied, and water thus propelled will enter a steam space just
as freely as it will a water space. All this is so far sufficiently
simple and obvious ; but the discovery of a principle and the
putting of that principle into practice are two very different
things.
The first injectors made were very uncertain in their action,
very large, and required many adjustments to induce them to
start and to keep them going. These troubles have been got
over in large part by the introduction of what is known as the
diverging nozzle, and in part by the use of very simple and yet
1 This is not strictly correct because of the reduction in volume, but the
inaccuracy is of no consequence here. The reader is referred to any good
text book of physics for the mathematics of the flow of gases and liquids under
varying conditions.
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THE INJECTOE
191
very efficient automatic self-adjusting devices which do what the
fireman had to do at first but very much better. The theory of
the diverging nozzle is set forth with much prominence in most
treatises on hydraulics and all treatises on steam turbines, to
which the reader who desires further information is. referred.
For our present purpose, it is enough to say that it gives a more
powerful and compact jet than can be had without it. The
accompanying engraving, Fig. 65, shows an injector as used on
locomotives thirty years ago, and one quite efficient and able to
work. The steam enters at A and passes through the diverging
Fig. 65. — Section of injector.
cone B. Through C cold water from the tender enters. D is a
cock for regulating the supply. In dealing with draught it has
been shown that the exhaust steam draws the products of com-
bustion with it and sends them up the chimney. Now in just
the same way the steam leaving A draws in water, is condensed,
and drives it forward through the second nozzle, which is con-
tracted because the steam being rapidly condensed the volume
to be passed through E is much diminished. The condensed
steam and feed water leap across the gap F and enter the cone E,
which it will be seen is an expanding nozzle at the end of which
is a check valve G, intended to prevent the return of water from
the boiler when the injector is stopped. E is expanded in order
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192 THE RAILWAY LOCOMOTIYE
that the velocity of the steam may be reduced and its ** energy of
translation " converted into pressure. B and E are united by
two bridges in a way that will be understood from the cross section
of the overflow cock H.
It may be asked, Why not make the two cones B and E con-
tinuous ? The answer is that the injector will not always start.
The water is indeed driven into E, but not with force enough to
get into the boiler. Usually this is because too much water gets
in at C and drowns the instrument. To provide for this, the
overflow cock H is fitted, through which the surplus water
escapes until the supply of water has been exactly adjusted to
the steam. It may be that only the proper quantity of water
goes in, but there is too much or too little steam. When all the
proper adjustments are made, the injector sings, and the only
loss of water is represented by a few drops which escape now and
then at H.
The injector illustrated will not lift cold water, because it cannot
make a sufficient vacuum in C. The difficulty is got over by the
simple expedient of reducing the diameter of the steam nozzle,
so that it is smaller than the discharge cone E. This was
formerly effected by putting a conical spindle into A. Once the
injector was started, the cone was gradually withdrawn to permit
the entrance of sufficient steam.
A defect in all the earlier forms of injectors was that they were
liable to be thrown oflf by jerks, which caused the water to surge
in the tender, or in the feed pipes or boiler. When this happened,
the fireman had to make all the adjustments over again, which
was not an easy task on a jumping footplate. Accordingly
various inventors sought a remedy, and now all injectors on
locomotives are of the self-starting self-adjusting type. The
modern injector is not very much larger than a champagne
maj^num, and requires no attention of any kind. To start it, the
fireman has only two handles to turn, one on the tender which
lets water into the injector, and the other on the back of the
fire-box, which admits steam. Two injectors are always fitted.
It is a usual though not an invariable practice to make one of
these very nearly but not quite sufficient to keep the boiler
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THE INJECTOR
193
supplied. At the beginning of a run it is started, and is not
meddled with while the train is running. The rest of the feed
is put in by the other injector, which is used or disused by the
fireman according to the rate at which evaporation goes on in
the boiler.
It may be asked what effect the temperature of the feed water
has on the instrument. The answer is that unless it is cold
enough to condense the steam, the injector will not work.
The critical temperature for ordinary injectors is about 120° F.
At this temperature the quantity of water injected is about
20 per cent, less than at 50° F. The higher the boiler pressure,
the colder must be the feed water. As to the actual amounts
fed, the makers of injectors guarantee those set forth in the
following table : —
Boiler Pressure.
lbs. of Water delivered
per lb. of Steam.
60 lbs.
90 „
120 „
200 „
19
16
14
10
It is not necessary to describe in detail the construction of a
number of the injectors used on locomotives. There are a great
many by different makers. Sufficient has been said to give the
reader an adequate idea of the theory of this very curious
instrument, a theory, it may be added, which is neither so
complete nor so sound as is desirable. All that the injector
has to do is to overcome the static head of the water or of
the steam which is measured by the pressure on the boiler
side of the check valve. In effect there is a close analogy
between the hydraulic ram and the injector. The necessary
momentum being obtained not from gravity but from the
impulse supplied by the steam.
R.L. o
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194
THE RAILWAY LOCOMOTIVE
Any account of the injector would be incomplete unless it
took account of the recent modifications which have made the
instrument self-starting. One example, an injector made recently
§^cH Pressure Vafvs
.*.. _. Ofhve/^
S^e^m
'f^/7gemt:df*tied
Right Hsna injsctar maae
Fig. 66. — Self-starting injector.
for locomotives by Messrs. Gresham & Craven of Manchester,
is illustrated by Fig. 66.
Let it be remembered that the action of an injector depends
upon the fact that the velocity of a jet of steam discharging into
the combining tube is twenty to twenty-five times that of a jet of
water issuing from a boiler under the same pressure, and that
the enormous reduction of the volume of the steam, during
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THE INJECTOR 195
condensation by the water, concentrates the momentum of the
jet upon the area of the delivery tube, which is but a small
fractional part of the orifice from which it issues, leaving a
large margin of available energy.
This action has been ingeniously likened to a pump with a
continuous piston equal to the area of the steam nozzle forcing
a continuous ram equal to the lesser area of the delivery throat,
the ram in this case being a small bar of " solid " water.^
The cones in the Gresham injector are made in four parts,
viz. : — No. 1, Steam Cone ; No. 2, Lifting Cone ; No. 3, Combining
Cone ; No. 4, Delivery Cone.
An internal steam pipe from the dome of the locomotive
conveys steam to the injector steam valve A, which upon being
opened admits steam to the steam nozzle 1 by the passage B.
The steam issuing from the steam nozzle lifts the base of the
combining cone 3, which is free to slide in its guide, off its
seat, and passes out freely through this opening to the overflow
passage C, and on to the pipe of the injector. In so doing, it
creates a partial vacuum in the water pipe D, and the water
rises to the injector. The water coming in contact with the
steam, travels with it through the lifting cone 2, and gradually
condenses it.
The velocity of the steam being now, as previously explained,
largely transferred to the water, the latter passes from the
lifting cone 2, and through the combining cone 3 (which is now
drawn back on to its face at E, owing to the high vacuum
created in the chamber F by the passage of the jet), and these
two cones, 2 and 3, become one combining cone, i.e., the cone
in which the steam and water combine. After passing through
this combining cone the jet flows out at the overflow space G
and down the passage and overflow pipe C until such time as
it attains sufficient velocity to carry itself past this space and
^ The word "solid" is not out of place. Dr. Le Bon, the great French
physicist, cites the case of a jet of water used to drive a Pelton wheel.
The head is 1,600 feet. The jet is 1 inch in diameter. It is absolutely
impossible for the strongest man to cut through this jet with a sword, but
the sword can be broken in the attempt.
o2
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196 THE RAILWAY LOCOMOTIVE
enter the delivery cone 4. When it reaches this point its
velocity is so great that it is suflSciently powerful to pass by the
passage H, and lift the back pressure valve 1, and so enter the
boiler.
The boilers of locomotives are invariably carefully clothed or
" lagged '* for three reasons. First to prevent the radiation of
heat, secondly for protection from the weather, and lastly for
the sake of appearance. The earliest engines were "rattle-
boarded," the lagging consisted of narrow strips of wood beaded,
and tongued with hoop iron, secured round the boiler with hoops,
very often of brass kept polished. The fire-boxes of Bury's
engines, which were semicircular in plan, were carried up in the
shape of domes to give steam room, and covered with copper.
Hence the name of ** copper nob '* which they obtained in the
north. In France, while the boards were retained, they were
covered with thin sheet iron, and in some cases in passenger
engines with brass sheets, which were kept bright. This was
all very well while coke was the fuel, when coal came in brass
went out. Subsequently felt was interposed between the boards
and the boiler, and the whole covered with Eussia iron. When
pressure rose the system would not answer, the felt was scorched
and the boards caught fire. In the present day the lagging
generally consists of some preparation of asbestos, often put on
in the form of mattresses, and covered outside with sheet-steel
plates. Abroad these plates are often left without paint, their
natural oxide coating serving with the aid of a little oil to
prevent rust. In this country they are always heavily painted
and varnished, each railway having its distinguishing colours.
The cost of painting and varnishing is a heavy item. It has been
stated that Mr. Samuel Johnson saved the Midland Company
several thousand pounds a year by substituting red oxide of iron
for more expensive pigments. This is the reason why Midland
engines are dull red. Mr. Webb used black on the London and
North Western, relieved in the case of passenger trains by
lining. The goods and coal engines he kept all black, and they
were called by the profane ** Webb's flying hearses."
The loss by radiation from an unclothed boiler is considerable
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THE INJECTOR 197
and with efficient lagging not great. Professor Goss gives the
following table : —
Power lost by Radiation. Horse power.
Bare boiler at rest 12
,, ,, running at 28 miles an hour 25
Covered boiler at rest 4*5
,, ,, running at 28 miles an hour ... 9*3
Much depends on the external temperature. The maximum
possible loss for an unlagged boiler seems to be about 10 per
cent., and for a clothed boiler 4 per cent.
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SECTION III
THE LOCOMOTIVE AS A STEAM ENGINE
CHAPTEE XXVI
CYLINDERS AND VALVES
In all that concerns the work done by the engines of a loco-
motive they may be treated precisely as though they were
stationary engines on land. By ** work done" must be under-
stood the development of power. The effect produced on the
locomotive as a vehicle has already been mentioned ; it will
be dealt with again further on. The thermodynamic laws ; the
heat exchanges ; the effects of expansion, compression and wire
drawing, are just the same for the engines of a locomotive that
they are for a stationary or marine engine working without
a condenser. The engines do not know that they are travelling
through space at high velocities, instead of working on fixed
frame plates in a factory. The principal difference, indeed,
between them and stationary engines is that the latter as a
rule can run in only one direction, while the engines of a
locomotive must be capable of turning round equally well in
either direction. In this respect they resemble a marine
engine ; the fact complicates the valve gear, as will be explained
further on.
Locomotives are always propelled by the action of steam
pressing on pistons reciprocating in cylinders, which pistons
cause the revolution of an axle by means of cranks and connect-
ing rods. There are no locomotives in existence propelled by
rotary engines or turbines. Up to a comparatively recent period
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CYLINDERS AND YALVES 199
locomotives were divided into two classes only — inside and
outside cylinder. Subdivisions are now necessary, because
locomotives are made with both in combination. In this country
although outside cylinders are freely used, inside cylinders have
always been preferred. In the United States on the contrary
the outside cylinder has been so favoured that very few inside
cylinder engines have been built.
Although in the present day the construction and mode of
action of a simple steam engine are very generally understood, it
is desirable to say a few words here for the benefit of the non-
technical reader who desires to comprehend thoroughly what the
locomotive engine is.
The simple steam engine consists of a cast iron cylinder,
bored out smooth and truly circular inside, in which moves
backward and forward a cast iron piston in the edge of which
are turned grooves. In these are placed elastic rings of steel
or brass, which press outward against the side of the cylinder
and prevent the passage of steam. The steel rod which is
secured to the piston by a collar and nut, goes through a hole
in the cover at one end of the cylinder. It passes through a
stuflSng box, which is filled with packing, so that no steam can
escape round the rod as it moves backwards and forwards. The
outer end of the piston rod is fitted with a cross head, which
travels in guides to compel the rod to move in a straight line.
To the cross head is jointed one end of the connecting rod, the
other end of which lays hold of the crank pin, and as the piston
moves backwards and forwards the connecting rod alternately
pulls and pushes the crank pin and makes it rotate. When the
piston is at each end of its stroke the crank is on a **dead
point,'' but the revolving momentum of the driving wheel
carries the crank over the dead point, and keeps the engine
going, and besides, there are always at least two engines acting
on cranks at right angles to each other, so that when one is on
the dead point the other is in full activity. In this way, the
driving wheels are made to revolve, and propel the locomotive.
Steam is brought to bear on opposite sides of the pisfon alter-
nately in the following way : — In the cylinder at each end is
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200 THE RAILWAY LOCOMOTIVE
made a port, which by a curved passage communicates with the
valve chest. In this are two ports, one for each end of the
cylinder, and between them a third port which communicates
as directly as possible with the blast pipe already described.
The ports are opened and closed by the slide valve, which is in
effect a shallow box with very thick ends and sides. The cast
iron face in the valve chest in which are the ports is made
quite flat and smooth, and on it rest the ends and sides,
also flat and smooth, of the slide valve. The valve chest is
full of steam which presses the valve down on the port face
or seat. The exhaust port is always open to the slide valve
inside. As that moves backwards and forwards it includes
first one cylinder port and
the exhaust port, and then
the other cylinder port and
the exhaust port. When this
last happens the steam in the
Cyihider "■ cylinder escapes through the
Pjq q*j box- slide valve and exhaust
port up the chimney. At
the same time the slide valve opens the port at the other end
of the cylinder, so that steam rushes in and fills the cylinder,
and so on alternately for both ends, and the piston is moved
backwards and forwards, the driving wheel revolves, and the
exhaust steam escapes up the chimney and causes a draught in
the fire-box.
The accompanying sketch, Fig. 67, will make what has just
been said clear at a glance. A is the slide valve in section,
B the bridle, a rectangular frame on the end of the valve spindle
D dropped loosely over the valve, P P are the steam ports, and
C the exhaust port.
The first locomotive had only two simple cylinders. In the
present day we find engines with two, three, and four cylinders
arranged in different ways. However by far the larger number
of locomotives in this country have two cylinders only, fixed
between the frames. In the United States always, and in other
countries almost always, locomotives have outside cylinders.
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CYLINDERS AND VALVES 201
On the whole, for very good reasons, the inside cylinder is
to be preferred. The favour shown to outside cylinders is
due partly to caprice, in part to certain national conditions.
Thus it is beyond doubt that French engineers, and, indeed,
continental engineers, generally, ** like to see the works.*' They
claim that all the parts of an outside cylinder engine are more
under observation, and can be more readily cleaned and examined,
and kept in repair than those of an inside cylinder locomotive.
In Europe and America " pits '* are unusual. That is to say,
the excavations between the rails over which a locomotive can
stand and in which men can work erect on the machinery.
Again, a cranked axle is not required, and greater length of
bearings can be had. In Europe there are scarcely any
passenger platforms, and engines can be made much wider
than in this country, which means that there is plenty of
space available for outside cylinders. Here cylinders up to
19 inches in diameter have been used outside, but the arrange-
ment is more cramped than it is abroad. It is, of course,
true that the platforms are not necessarily on a level with
the cylinders. But it would not do to let the cylinders over-
hang the platform.
In the United States, the outside cylinder is peculiarly suited
to the bar frame. In the same way the inside cylinder goes
naturally with the plate frame. We shall deal with the inside
cylinder engine first.
We have two flat frame plates, spaced about 4 feet 1 inch apart,
between these must be fixed the cylinders. If these are 18 inches
in diameter they will occupy, allowing 4 inches for the cylinder
walls, 3 feet 4 inches, but ports cannot be worked in a thick-
ness of 1 inch. Allowing 3 inches for each cylinder inside we
have 3 feet 8 inches, which leaves only 5 inches for two slide
valves, if they are placed vertically between the cylinders. This
is cutting things so fine that, although 18 inch cylinders with
the valve chest between them have been used, it may be taken
that 17 inches is the largest diameter which can be adopted.
When greater dimensions are necessary, the valve chests are
placed on the tops of the cylinders, or right underneath them.
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202
THE RAILWAY LOCOMOTIVE
On the Western Eailway of France locomotives were at one
time running with the cylinders inside. The valve chests were
outside and came through rectangular apertures cut in the
plate frames. The whole of the valve gear was outside,
although a crank shaft of the normal kind was used. In the
United States slide-valve chests are invariably on top of the
cylinders, the slide valves being actuated by rocking shafts. In
this country top valve chests are usually so inclined that the
valve spindles point directly to the centre of the diameter of the
crank shaft.
Formerly, the cylinders were always cast separately, each
with its valve chest, and each was made
with a heavy flange on the outside to
take the side frame^ and on the inside
to match the other cylinder. These
flanges were all planed and faced up
I / ) I S" ^^^^ *^^®* ^^^ ^^^^ inside flanges were
placed in apposition, and secured to
each other by a number of IJ inch
bolts turned truly cylindrical, and so
tight a fit in carefully drilled holes in
the flanges that they had to be driven
home with a heavy hammer. The two
cylinders thus became ostensibly one. In the same way the two
outside flanges were bolted one to each side frame. Excellent
as this arrangement is, however, it was found that in practice
the cylinders tended to work loose from each other, and from
the side frames, and in the present day the cylinders are almost
always cast together in one piece. The foundry work is a little
more expensive and there is more risk of making "wasters," but
the result is much more satisfactory.
Cylinders are always cast of a special mixture the precise
nature of which is usually kept as a secret in every foundry.
The object is to get a tough cast iron which will not crack, and
yet will be just as hard as will only permit it to be bored with
some difliculty. Cylinders wear oval, but curiously enough, not
on the bottom, as might be imagined, because it has to carry
Fig. 68.
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CYLINDEES AND VALYES 203
the weight of the piston, but at an angle such as shown by the
dotted line in the accompanying sketch, Fig. 68.
While the front ends of the cylinders are open for their full
diameter in order that the pistons may be put in, the back ends
are made with openings of not more than half the diameter,
which are closed by permanent lids, which are cast in one
with the stufiBng boxes. The opening at the back end is
provided because it facilitates moulding in the foundry, and
through the opening is passed the bar which in the boring
machine carries the cutter head, in the edge of which are the
steel boring tools. The modern boring machine is invariably
double. It has two horizontal boring bars accurately parallel,
and both cylinders are bored at the same time. The boring
bars rotate at such a velocity that the speed of the boring tool
is about 20 to 30 feet per minute, depending on the hardness of
the cylinder. The harder it is the slower the cut. Two cuts
usually suffice, one a roughing cut and the other a smoothing cut.
The front cylinder cover is usually cast convex, and with ribs to
give it strength. It may have to support a load of 20 to 30 tons.
Its flanges are carefully faced and scraped up, as are the flanges
of the cylinder, and a steam-tight joint is secured by screwing
up the nuts, which work on studs screwed into the cylinder
flange, sometimes a little very thin red lead and oil are smeared
on the metal faces, and when the cylinders are old and the lids
have been taken oflf and put on several times, it may be
necessary to interpose a ring of thin brown paper which has
been soaked in boiled linseed oil, in order to make the joint
tight. To reduce clearance the piston is cupped to fit the
convexity of the cylinder cover.
Formerly the stuffing box in the back cover was packed with
hemp soaked in tallow. In the present day, it is almost always
packed with white metal rings. White metal is an alloy of tin,
lead and antimony. A great number of patents have been taken
out for metallic packing. This packing consists of a number of
coned segments which are put into the stuffing box and surround
the rod. As the " gland " is screwed down it will be seen that
the cones act to force the packings against the rod on the one
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204
THE EAILWAY LOCOMOTIVE
hand and the sides of the stuflSng box on the other. In some
cases, a coiled spring is used to press the segments together.
When the lubrication is attended to properly, packing of this
kind gives no trouble and remains quite tight for several
months.
As the connecting rod works at various angles throughout
each revolution, the piston rod must be guided. The accom-
panying sketch, Fig. 69, explains why. When the crank A is
vertically up the connecting rod is pulling, as shown by the
arrow. If the length of the rod be taken as the pull then that
pull is represented by two forces ; the one measured by the
length of the crank tending to pull the crank down in the
direction of the arrow, the other precisely equal in amount
Fio. 69.
at the other end of the connecting rod tending to lift the
cross head and piston rod up. If the pull on the cross head was
25,000 lbs., and the connecting rod five cranks long, then the
pull tending to rotate the crank would be 20,000 lbs., and to
push the crank down 5,000 lbs., and to lift the cross head up
5,000 lbs. In the same way, when the crank was vertically
downwards the connecting rod would now push as denoted by
the arrow, and tend still to force the crank down and the cross
head up with a force of 5,000 lbs. It will be seen that the
guides must withstand very heavy vertical stresses.
There are three systems of guiding cross heads in use.
According to the first form, rectangular steel bars are placed
in pairs, one pair at each side of the piston rod. Two long cast
iron blocks slide between these bars. A pin passes through
both blocks and the cross head between them, and on the pin
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CYLINDERS AND VALVES
205
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206 THE RAILWAY LOCOMOTIVE
works the small end of the connecting rod. The arrangement is
illustrated in Fig. 70, which shows a very excellent engine with
Joy*s valve gear, designed several years ago for the Great Eastern -
Railway by Mr. James Worsdell. AA are the guide bars.
Across the engine, about 8 feet further back than the ends of
the cylinders, a '* motion plate " BB is bolted between the
frames. This is always, in the present day, a steel casting
shaped to be as strong and yet as light as possible. In the
casting are four openings, through two of which the connecting
rods pass, through two the valve-gear rods.
On the face of the motion plate are provided four ** snugs,"
through each of which is a hole. The stuffing box is also
provided with snugs DD, and to these the slide bars are secured
by a bolt and nut at each end. Between the bars and the snugs
are placed copper plates. When the engine is being erected
these plates can be reduced in thickness by filing, so that the
distance between the slide bars can be regulated with the most
minute accuracy. This form of guide, with certain improvements
and modifications, is still very popular for inside cylinder engines
with which alone we are now dealing.
The second arrangement is simply a variant of that just
described ; only two guide bars are used. These, instead of being
at the sides, so to speak, of the piston rod are fixed one over, the
other under it, sufficiently far apart to clear the connecting rod
as it rises and falls. The cross head is grooved on the edges to
fit the slide bars. At one time this arrangement was very much
used for outside cylinder engines, to which it is well adapted.
The third and last system is a modification of a marine engine
guide, the " slipper " guide. It has long been a favourite with
Mr. Drummond, of the London and South Western Bail way, and
Mr. James Holden, Chief Mechanical Engineer of the Great
Eastern Railway, used it almost to the exclusion of all other systems.
Fig. 71 is a longitudinal section of a cylinder with the piston,
cross head and connecting rod as fitted on the Great Eastern
Railway ; it will be seen that only a single heavy bar guide is
employed. This is fixed above the piston rod, and on it slides
the " slipper," really a species of box ; B is the motion plate.
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CYIJNDEES AND VALYES
207
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208 THE RAILWAY LOCOMOTIVE
When the engine runs chimney first the thrust due to the
obliquity of the connecting rod is always, as we have seen,
upwards and is taken by the solid part of the slipper. When
the engine runs backwards the fiat plate bolted on the top takes
the stress. The whole arrangement is cheap, easily fitted up
with great accuracy, and easily lubricated. The rubbing
surfaces are very large, and the results had with it are so
satisfactory that all the engines on the Great Eastern Eailway
are made with it. In the larger engines the piston rod is pro-
longed as shown and passed through a stufiBng box in the
leading cylinder cover. This takes some of the weight off the
bottom of the cylinder. It may be added here that when super-
heated steam is used the rod must be carried through the
front cover and provided with a guide to prevent the piston
cutting the cylinder.
The small end of the connecting rod lays hold of the cross
head pin, which is of steel hardened on the outside. Many years
ago the late Mr. Francis Webb, of the London and North Western
Eailway, seeing that the amount of movement round the pin
made by the bearing on the connecting rod is quite small, did
away with all power of adjustment, and forced into the end of
the connecting rod a solid bush, which fits the pin accurately.
This bush is shown at A in Pig. 71. The wear is extremely
small. When the bush has become too slack on the pin, wearing
oval and beginning to knock, it is forced out of the rod by
hydraulic pressure and replaced by a new bush. Previously,
connecting rods were fitted at both ends alike with brasses which
could be closed up on the pin by a tapered wedge, known as a
cotter, D, Fig. 70. This was far more expensive and liable to
get out of order than the bush, but it is still in use on some lines.
As for the ** big end " of the connecting rod — that which grasps
the crank pin — there are many patterns in use, but the principle
is always the same. We have either the strap with a wedge
cotter, or what is known as the marine big end, so called as it
is almost invariably used in marine engines. Here the two
brasses of the connecting rod are held together by a cap and two
bolts with nuts.
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CHAPTEE XXVII
FRICTION
Before proceeding further it is desirable to call attention to
the question of friction. It is a very interesting fact that some
of the loads carried by journals and brasses in locomotive engines
are far heavier than can be regarded as safe in other machinery.
That heating occurs so rarely is due to accurate workmanship, the
use of white metal, efficient lubrication, and, above all, to the
rush of the engine through the air, which carries off the heat.
The bearings are in one sense too small for their loads, because
the gauge — 4 feet 8J inches between the inner faces of the rails— is
too narrow for the large engines now in use, although it answered
very well on the Stockton and Darlington and Wylam colliery
lines on which the first " Puffing Billy '' ran. The diameter of a
crank shaft and of the various journals on it may be increased,
but its length is fixed by the distance between the inside faces of
the main frame, which is precisely 4 ft. 1 in. The accompanying
table gives the dimensions of a crank shaft suitable for an engine
with 17 inch cylinders, 24 inch stroke, four coupled wheels 6 feet
7 inches in diameter, and 160 lbs. boiler pressure : —
R.T
Crank Axle.
Ft.
ins
Diameter at wheel seat
9
do. at bearings
...
7J
do. at centre
7
Distance between centre of bearings .
3
10
Length of bearing
9
Diameter of crank pin
u
Length of ci-ank pin
r,.
...
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210 THE RAILWAY LOCOMOTIVE
As has been said, with larger engines the diameters will be
greater, and with smaller less. The figures given are, however,
sufficient for our present purpose. The actual effective bearing
surface of a railway axle journal may be taken at '3 of its total
surface. Now, the total surface of a bearing 7^ inches X 9 inches
is 212*4 inches, and three-tenths of this is in round numbers
64 inches. The load on each main bearing may be taken as
7 tons, or 15,680 lbs. and — ^ — = 245 lbs. per square inch,
which is quite a moderate load.
The conditions, however, as regards the crank pins are quite
different. Taking the average cylinder pressure as only, 75 lbs.
we have for a 17 inch cylinder a pull and push on the crank
pins of about 17,000 lbs., and 32*4 as the available bearing area
17 000
in square, inches. Now, "okrr" = 521 lbs. as the load, which
is very heavy. When the engine is starting from a station or
climbing a bank it may very easily reach twice this with a boiler
pressure ol 160 lbs.
It may be said. Why not make the crank pins longer ? The
position of the centre of the length of the crank pins is fixed by
the distance between the centres of the cylinders, therefore the
crank pins must be lengthened symmetrically, if at all. This means
that either the main bearings must be shortened, or the crank
webs reduced in thickness. Now, crank axles almost always break
through the webs when they break at all, and for this reason
when webs are rectangular or oval in shape they are always fitted
with wrought iron or steel safety hoops shrunk on. Various
expedients have, however, been tried to get over the difficulty.
Mr. James Worsdell, when Locomotive Superintendent of the
North Eastern Eailway, made the crank webs circular discs. In
this way we get plenty of metal at the weakest part of the web,
and are enabled to thin it down, and so lengthen the crank
pins. Abroad, a curious arrangement known as the half-crank
has been used. The driving wheels are inside, not outside the
frames, and the crank shaft does not pass through the wheel.
The outer end of the crank pin is secured in the boss of the wheel,
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FRICTION 211
and in this way some additional length is obtained, but it does
not appear that the game is worth the candle.
The crank shaft of a locomotive is very expensive. It is forged
out of solid steel, a roughly round bar with two lumps of metal
on it. These lumps have gaps cut in them, either by slotting
out the metal with a thin tool, or by a cold band saw. The
crank pins and bearings are all subsequently finished in the
lathe. In marine engines, for many years, the built-up crank
shaft has been used with great success. The crank webs are
separate pieces, as well as the crank pins and the plain portion'
of the axle ; all the holes are drilled and the parts turned with
minute accuracy, and the whole axle is then put together under
hydraulic pressure. The result is a cheap crank shaft, thoroughly
sound and good. Mr. D. Drummond has used this type of crank
axle for some years on the London and South Western Eailway.
Built-up cranks are also coming into favour in America.
Pistons are usually *made of tough cast iron, although steel is
not infrequently employed, and in certain cases the piston and its
rod are forged in one piece. The securing of a piston to the rod
presents some difficulties ; practice in the matter varies. As a
rule a tapered hole is bored in a boss in the centre of the piston.
The piston rod is coned at the end to fit the hole, into which it
is drawn very tightly by a nut placed on the screwed end of the
piston rod beyond the taper. Some designers turn a collar on
the rod, as at E, Figs. 70 and 71, against which the piston is
forced. Others only use a set-off at the base of the cone. If the
cone is too tapered the piston may be split. The nut is always
liable to work back ; many engineers maintain that the only way
to secure it with certainty consists in riveting over the end of
the rod. Lock nuts and cotter pins have been tried, but not, it
would seem, with all the success desirable. On some lines the
tapered portion of the rod is screwed into the piston. The piston
packing is always very simple. Many years ago Mr. Eamsbottom
introduced on the London and North Western Eailway three
plain steel rings, each cut through in one place. These rings
are about f inch square, and are slipped each into one of three
similar grooves turned in the circumference of the piston,
p2
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212 THE RAILWAY LOCOMOTIVE
and their own elasticity is sufficient to keep them pressed steam-
tight against the cylinder walls. Eamsbottom rings are still
very and deservedly popular. They had not been long before
the world before a precisely similar arrangement — in all respects
but one — known as Swedish packing, was introduced. The
dijBferenco lay entirely in the breadth of the rings. Two, from
f inch to 1 inch wide and about f inch thick, are used, as shown
in Fig. 71. This packing, or some slight modification of it, is to
be found to-day on nearly every railway in the world. When
the steam is superheated very special arrangements are required.
It may be added, perhaps, that many other packings have been
Invented, patented and tried. But the advantage, if any, which
they have is too small to get them into use.
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CHAPTEE XXVIII
VALVE GEAR
The action of a slide valve, and the way in which steam
is admitted to, and discharged from, a cylinder has already
been explained in a rudimentary way. In practice the valve
gear of the locomotive has been made the subject of much
invention, and of papers and disquisitions in every European
language, which would fill volumes. Simple as the operation
seems to be, yet so much depends on its satisfactory performance
that it has always proved an attractive subject for consideration.
The problems presented, thermodynamical and mechanical,
lend themselves freely, and indeed temptingly, to a mathematical
treatment which would be out of place in this volume. But
much can be said quite apart from mathematics to make it clear
not only what the valve gear of a modern locomotive is, but why
it is what it is.
We have seen that the normal slide is moved ^backwards and
forwards on its seat, placing each side of the piston alternately in
communication with the steam chest in which the slide valve
works, or with the exhaust nozzle.
Among the numerous inventions which have been intended
to cause the movement of the slide valve, only three are in
regular extensive use. These are known as Stephenson's
link motion, Joy's radial gear, and Walschaert's gear. The
first two are extensively used in this country. On the Con-
tinent, Walschaert's gear is the favourite ; in the United States,
Stephenson's.
In the first locomotives working the Liverpool and Manchester
Kailway, that is to say, the real progenitors of the modern rail-
way engine, motion was imparted to each slide valve by two
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214
THE RAILWAY LOCOMOTIVE
excentrics. An excentric is neither more nor less than a crank
with a crank pin of great diameter. The " throw " of an excen-
tric, that is, its virtual crank length, is measured from the true
centre of the excentric disc to the true centre of the crank axle.
As the excentrics could not be put on the crank axle because
of the cranks, if they were each made in one piece, they are
made in two parts, secured together by sunken bolts. Each
excentric rod had at the end what was known as a " gab " or
notch, which dropped on a pin at the end of the valve spindle.
One of the excentrics was set for going ahead, the other for going
backwards, and levers were so arranged that the driver on the
footplate could lift the go-ahead gabs oflf the valve-spindle pins
and drop the go-astern gabs on when he wished to reverse his
engine, and vice versa.
But it was quite cer-
tain that, when the
go-ahead gabs were
lifted off, the valves
would be in such a
position that the go-
astern gabs would not
drop on. A very
The gabs were made with
The distance between the
Fig. 72.
simple expedient got over the difficulty,
long horns as shown in Fig. 72 at B G.
horns being greater than the travel of the slide valve, it mattered
nothing at all what position the slide valve might be in. Ic was
only necessary to push down the excentric rod hard, and the horn
would slide along the spindle pin, and move the valve until the
gab dropped on to it. At the first, two reversing levers were used,
one for moving the go-ahead, and the other the go-astern excentric
rods. Then a bell crank was added, and a single reversing lever P
raised one and dropped the other pair of gabs. The next
important invention consisted in simplifying the whole arrange-
ment by turning the go-astern gab upside down, and coupling
the two rods I J, by two links D D to the bell crank E, which
was moved by a single reversing lever on the footplate by the
rod F. In the sketch, A is the slide-valve spindle, B and G
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VALVE GEAR 215
the horned gabs, C is the crank axle, H H the centres of the
excen tries. A single movement then sufficed to lift one gab out
of gear and to lift the other in.
The reader will see that so long as the gab was retained, the
travel of the slide valve must remain constant. There was no
means of varying the quantity of steam admitted to the cylinders
but the regulator. What this involves will be explained presently.
In the early years of railway history little thought was given
outside a very narrow circle to the expansive use of steam in
locomotive engines. However, even in its improved form, the
gab gear was not quite satisfactory. It was noisy. It wore
out rapidly. If there was any steam in the valve chests the
resistance was so great that the horn would not move the valve,
and when the engine was running fast it was not pleasant gear
to handle.
Various inventors sought improvements, and finally arrived
the link motion. The genesis of this is doubtful, and a keen
controversy exists as to the way in which it came into being.
So far as can be ascertained, a pattern maker named Howe
showed Eobert Stephenson a model of an invention which, to
judge from the drawings existing, would not work. He used
extremely short excen trie rods, and coupled their ends by a
slotted bar or link. Into the slot was put a pin on the end of
the valve spindle, and by moving the link up or down, either
one excentric or the other drove the valve. . But the rods were so
short that the excentrics could not get round. Nevertheless, here
in one way was the rudimentary idea of the link motion. In
1898, Mr. W. P. Marshall read a paper before the Institution of
Civil Engineers on " The Evolution of the Locomotive Engine.'*
Speaking of valve gear, he writes : " In 1841, when I was Locomotive
Superintendent of the North Midland Eailway, I was making trial
of different valve motions for Mr. Eobert Stephenson, and on the
15th December, 1841, Mr. Stephenson came into the locomotive
office, Derby, on the way back from Newcastle, and said, * There
is no occasion to try any further at scheming valve motions, one
of our people has now hit on a plan that beats all the other valve
motions,' and he then explained the slotted link. In 1842 an
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216
THE EAILWAY LOCOMOTIVE
engine with the link motion was delivered by Messrs. Stephenson
& Co. to the Northern Midland Eailway.'* No particulars are
available of this engine, but the probability is that the motion
was very like that now in use.
The entire episode is very curious. It illustrates the way in
which the obvious is some-
times missed. If the reader
will examine Fig. 72 he
will see that if the ends of
the horns were joined to-
gether the links D D might
be dispensed with. Instead
of the gabs being in one
piece with the rods, pin
joints would be needed at K K. If, further, the horns were closed
in as shown by the dotted lines, the link was at once obtained.
To curve it to the radius of the excentric rods would follow as a
matter of course, and the link motion as shown in Fig. 73 would
then be complete. The gear is always identified with Stephenson,
and it seems probable that while he was, so to speak, put on the
track by Howe, he really followed much the line of reasoning just
sketched out, and so produced a valve gear which is immortal
among mechanical devices.
Fig. 73.
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CHAPTEE XXIX
EXPANSION
It is desirable here to interrupt the description of valve gear,
and deal with general principles, because until these are mastered
the reason why valve gears are not all alike will not be apparent.
It is assumed that the majority of readers understand the great
principles of thermodynamics sufficiently well to appreciate the
nature of the advantages gained by working steam expansively.
Nevertheless, in pursuance of the scheme of this book, it is
necessary to offer here a few words of explanation.
Let us suppose that gab gear is in use, and that the cylinder
IS, when the piston reaches the end of its stroke, nearly full of
steam. It will not be of much less pressure than that in the
boiler. Suppose the capacity of the cylinder is two cubic feet,
and the cylinder pressure at the moment the exhaust opens is
75 lbs. per square inch, then two cubic feet of steam of that
pressure is blown into the atmosphere to waste ; yet it is quite
obvious that there is plenty of work still in this steam. Let us
suppose now, further, that the supply of steam to the cylinder is
stopped when the piston has gone half way, the exhaust remain-
ing unchanged. It follows that at the end of the stroke we shall
have one cubic foot of steam at 75 lbs. pressure supplied, which
becomes two cubic feet at the end of the stroke. Its volume is
doubled and its pressure will be half 75 lbs., or 37*5 lbs.. Thus
not only shall we use only half the total quantity of steam used
before, but we shall send that half up the chimney with only one-
half as much available work in it. The loss so far will be reduced
to one-fourth of what it was.
It must, however, not be forgotten that the work done in the
cylinder at each stroke, therefore, at each revolution of the driving
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218
THE RAILWAY LOCOMOTIVE
wheel will be less than before; but not so much less as to
neutralise the economical advantage gained. This will best be
made clear by a numerical example. Let a cylinder be 17 inches
in diameter ; the piston surface 227 square inches ; length of
stroke 24 inches ; capacity of cylinder 227 X 24 = 5,448 cubic
inches ; pressure of steam 150 lbs., working without expansion,
steam being admitted for the whole stroke ; piston speed 600 feet
per minute ; we have then
227 X 150 X 600
= 619 h.p.
33,000
Next let us suppose that steam is cut off at half stroke, all
the other conditions remain-
ing the same. The quantity
of steam used per stroke will
then be 2,724 cubic inches;
the average pressure will
obviously be less than 150
lbs. It will be 150 lbs. up
to half stroke, and it will be
75 lbs. at the end of the
stroke. The average pres-
sure is found by the following
Fig. 74. rule :_
Add 1 to the hyperbolic logarithm of the ratio of expansion.
Multiply the result by the initial pressure, and divide by the ratio
of expansion ; the quotient is the average pressure. The ratio
of expansion is 2, and the hyperbolic logarithm of 2 is '6931.
We have, therefore.
1-6931 X 150
= 103*965 lbs. as the average
pressure, or, in round numbers, 104 lbs., and
227 X 104 X 6 Aoai^r.
3-3:000 =426h.p.,
that is to say, we get about two-thirds the power for one-half
the steam.
For a full explanation of what a hyperbolic logarithm is,
the reader is referred to any treatise on logarithms. A gas
expanding exerts pressure in an inverse ratio to the space it
occupies. The curve of falling pressure is therefore a hyperbola.
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EXPANSION
219
The accompanying diagram, Pig. 74, will, it is hoped, make the
facts clear. Here we have a piston P moving in a cylinder A B C D.
The first portion of the stroke A G C H being made with full
pressure, is denoted by 1 in the formula given above. The second
half of the stroke being done expansively, we have our hyperbolic
curve of falling pressure, shown by the line 2. The logarithm
denotes the proportion which the space E, which represents work
done during expansion, bears to the area of the rectangle A G C H,
which represents the work done during the full pressure part of
the stroke.
In the following table are given a few of the hyperbolic log-
arithms most likely to be wanted in locomotive practice : —
Hyperbolic Logarithms.
Ratio of Expansion.
Hyperbolic Logarithms.
20
0-6931
2-0
0-9163
30
1-0986
35
1-2528
40
1-3863
4-0
1-5041
50
1-6994
00
1-7047
6-0
1-7918
6-5
1-8718
70
1-9459
It must be understood that what has just been said is intended
only to exemplify a principle. The expansive working of steam
is really not simple, but complex. The ratio of expansion is
always less than that given above, because the piston does not
touch the cylinder cover ; and the clearance space, as it is called,
is filled with steam, so that the whole quantity expanding is
greater than is represented by the volume swept out by the
piston at each stroke. Again, steam is always condensed when
it first enters the cylinder, unless it has been superheated ; and
the expansion curve is never a true hyperbola, except by accident.
The reader possessed of a fair knowledge of Thermodynamics
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220 THE KAILWAY LOCOMOTIVE
does not need detailed explanations of what takes place inside a
cylinder. The reader who does not, has had so much explained
as will enable him to comprehend what follows about the action
of the Stephenson link, and nothing more is necessary here.
Let it be supposed that the slide valve is made of such a length
that when in the middle of its stroke it just covers all the ports.
Then it follows that if it is moved either forward or backward it
will admit steam to the front or back end of the cylinder. Under
such conditions there could be no expansive working. The
steam must follow the piston full stroke, because the moment
steam was cut off at one end of the cylinder it would be admitted
at the other.
But let the valve be lengthened, so that it will more than cover
the ports. Under these conditions, as shown in the diagram
Fig. 67, and the sectional drawing Fig. 79, both the valve and
the piston would have to move some distance before the port
opened for the admission of steam. But the valve would also
cut steam oflf before the stroke of the piston was complete. Here
then we have expansion. If now the excentric, instead of being
set at an angle of 90° with the crank, is moved forward, then we
shall have steam admitted at the beginning of the stroke, and cut
oflf before the end. The extra length of valve is called the " lap" ;
the angular advance of the excentric is called the ** lead," and
the lap and lead, it will be readily understood, are two very
important factors in the working of the valves of a locomotive
engine. The lead virtually cancels the lap so far as admission
is concerned, and augments it by an equal amount so far as cut-
off is concerned.
In Great Britain long practice has fixed 1 inch as the amount
of lap which best meets all the working conditions. In a few
cases it is only ^ inch, while in others IJ inch has been tried.
But 999 out of every 1,000 locomotives fitted with slide valves
have a lap of 1 inch.
Now if a slide valve has a lap of 1 inch, when it is at rest in
mid stroke it overhangs the port at each end by 1 inch, and it
must be moved at least 1 inch in either direction before it will
open a port. It will be seen, therefore, that the valve spindle
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EXPANSION • 221
pin must be some way from the centre of the link in either direc-
tion before the engine can take steam. Furthermore, let it be sup-
posed that the arrangement of the valve gear is such that steam
is cut off in one cylinder at something less than three-quarter stroke.
Ifc will then be admitted to the other cylinder while the crank is
near the dead point. Then, with a moderately heavy train, the
engine will not start. In railway phraseology ** she has gone
blind,*' that is to say a port is blinded or stopped by the lap on
the slide valve, and the piston which would pull the crank round .
gets no steam or is so near the dead point that it cannot start
the train. To get the engine to start, it must be reversed in
order to put the valves into a new position. Every railway
traveller has seen the regulator opened and no result follow.
Then he has seen the reversing screw turned, and the whole
train pushed back a yard or so. Then the wheel being again
turned the valves are put in full forward gear and the train goes
on its way. One reason for keeping lap down to an inch is that
the longer the lap the greater is the risk of the engine going
blind.
Lap and lead can be so adjusted to each other that when the
engine is in full gear for running in either direction, the steam
will always be cut off at a fixed point of the stroke. What this
fraction may be varies. Generally speaking it may be taken at
about 75 per cent., but the old gab gear would do as much. The
link when in full gear is only the gab improved mechanically in
constructive detail.
If now, leaving everything else as it was, we shorten the throw
of the valve, it will be seen that the steam port at each end,
although not opened fully, may be opened sufficiently to admit
steam ; but the shorter the stroke of the valve the less time will
the port remain open. In other words, the shorter the stroke of
the valve the earlier in the stroke of the piston will steam be cut
oflf, and the higher will be the ratio of expansion. The stroke
can be shortened by moving the link so that the valve spindle
pin is not at the end of the link, but somewhere nearer the middle
of its length. In this way the Stephenson link possesses the
great merit of giving the driver the power of varying the amount
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222 THE RAILWAY LOCOMOTIVE
of expansion. When climbing a hill, for instance, he puts the
engine in full forward gear to get the maximum pulling effort.
On a level he " links her up,'* and cutting oflf earlier he works
expansively.
It is most important that the student should master com-
pletely the parts played by lap and lead. If these are once
understood there will be little difficulty in following out the
details of any gear however complicated. To this end no
mathematics are needed. The facts may be readily mastered by
cutting a valve in section out of thin cardboard, and moving it
backwards and forwards on a section of the port face. The
diagram Fig. 67 may be utilized for this purpose.
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CHAPTER XXX
THE STEPHENSON LINK MOTION
Up to this point, the link has been spoken of as moving on a
fixed centre coincident with the centre of its own length. No
such condition, however, exists in a locomotive ; on the contrary,
the real movement of the link is very complicated. The geometry
of the link motion has been made the subject of careful study by
mathematicians. The reader will find at the end of the volume
Fig. 75.
a list of authors who may be consulted on this subject with
advantage. Nothing more can be dealt with here than principles.
It will be seen that if the excentrics were placed opposite each
other, a line drawn through their centres also passing through
the centre of the axle, the link might be carried on a fixed pin at
the centre of its length, on which it would rock backwards and
forwards. In that case only one excentric would be required as
in Walschaert's gear. But a line drawn from centre to centre of
the excentrics cannot pass through the centre of the axle because
of the angular advance or lead of each excentric.
The sketch, Fig. 75, will make this clear. Here A is the crank
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224 THE RAILWAY LOCOMOTIVE
axle, B is the crank pin, F is the valve spindle, C is the go-ahead
excentric, D is the go-backwards excentric, E is the centre line of
the slot in the link. If now there were to be no angular advance
of the excentrics, and no lead, they would be so keyed on the
axle that their centres H H would fall on a vertical line uniting
G G. They would consequently be set each at an angle of 90°
with the crank, and the link could rock, as stated above, on the
centre M, and when the reversing lever was in mid gear the slide
valve would have no movement. But the centres of the excentrics
not being opposite to each other, their throws do not neutralise
each other. Let the dotted lines show the position when the
crank has made half a revolution. It will be seen that a vertical
line joining the centre of the excentrics has now been carried as
far behind the centre of the crank axle as it previously was in
front of it, and the whole link, and with it the valve spindle
F, has been shifted through a distance equal to that between
N and M. Consequently there is no position in which the slide
valve can be absolutely at rest while the engine is running. A
curious result, by no means generally known, is that if a loco-
motive is running chimney first and the link is put in mid gear,
the engine will continue to run forward because the valve will
give a little steam to the cylinder at each end of the stroke by
reason of the movement M N. If the engine happens to be
running tender first, then in like manner it will continue to run
backwards. Of course, it must be understood that the loads are
light. A search for an explanation of this phenomenon will
constitute an interesting exercise for the student.^
As no point in the link is at rest when the engine is in motion,
and the link as a whole is moved backwards and forwards as
well as each end, the link must be itself carried by a link,
which may be pivoted at the top, at the bottom, or in the middle,
no matter which, so far as the movement is concerned. This
suspending link, playing like a pendulum, causes the centre of
the main link to rise and fall, through only a small distance it is
true, yet small as it is it affects the travel of the valve. The
^ The author's attention was first called to this fact by the late Sir Frederick
Bramwell.
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THE STEPHENSON LINK MOTION 225
usual practice is to suspend the link by the middle, occasionally
at the lower end, never by the top in the present day. A further
complication is introduced by the angular movement of the
connecting rod. The piston is not in the middle of its stroke
when the crank is vertically up or down by an amount equal to
the versed side of the arc described by the big end of the rod. All
difl&culties have, however, been got over, and a well-designed
Stephenson gear gives a completely harmonious action of the
slide valves, and is in every way but two quite satisfactory. The
lead is not constant in the first place,^ and in the second, when
the engine is working expansively and running fast, the admission
port is never opened fully and is kept open only for a minute
fraction of a second. The result is that steam is wiredrawn, and
it is impossible to get a good pressure in the cylinder, and for
the same reason the exhaust is throttled, and the exhaust port
closed too soon. Various means of getting over the difficulty
have been schemed, but as none of them are in use, save experi-
mentally, no more need be said of them here.
The details of construction are very simple and so familiar
that no further illustrations are necessary. The link is dropped
down for running chimney first, and raised up for running
backwards. A weigh bar runs across under the barrel of the
boiler, and is carried in plain bearings bolted to the main frames.
On the weigh bar are keyed four arms. Two of them, extending
forward, carry each one of the links by a pair of sling bars. The
third, always placed halfway between the frames, extends back-
wards and carries a cheese-shaped block of cast iron, which
exactly balances the weight of the links and half that of the
excentric rods. The fourth arm usually stands up at the side
of the boiler, and to it is joined a long flat bar extending to the
driver's cab. Here in the older locomotives it is coupled to the
reversing lever, which moves in an arched guide, provided with
notches into which drops a detent, which can be lifted out by a
small subsidiary lever just in front of the handle. When the
reversing lever is drawn back the link motion is raised by the
^ The student will do well to master the effect of ** crossed" and " open '*
excentric rods on lead.
B.L.
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220
THE RAILWAY LOCOMOTIVE
weigh bar and the notch in
which the detent is placed
determines the point of
cut-off and, as explained,
the ratio of expansion. Too
much precaution cannot be
used in securing the balance
weight, which is very liable
to work loose and fall off.
A terrible accident occurred
some years ago on the
Great Eastern Eailway.
Two trains were about to
pass each other when the
balance weight of one
engine fell on the line and,
rolling under the other
train, derailed a wheel and
threw the engine off the
rails. In the United States
the balance weight is
seldom used. It is re-
placed by a powerful coiled
spring round the weigh
bar shaft or a flat trans-
verse spring between the
frames. The reversing
lever has been superseded
in all modern locomotives
by a hand-wheel and quick
threaded screw.
In many modern engines
power is employed with
much ingenuity to work
the valve gear. About 15
years ago Mr. Stroudley, Locomotive Superintendent of the
London, Brighton & South Coast Eailway, used the air pressure
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THE STEPHENSON LINK MOTION
227
Slide
Valve
Fig. 77. — ^Wainwright's reversing gear.
of the Westinghouse brake for this purpose. More recently Mr.
Drummond, of the London & South Western Bail way, fitted steam
q2
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228
THE RAILWAY LOCOMOTIVE
reversing gear to his largest engines. Then Mr. H. Wainwright,
Chief Mechanical Engineer, London, Chatham & Dover and South
Steim /^fvc
Sleff Tabm
Fig. 78. — Wainwright's reversing gear.
Eastern Eailway, designed, and has for a long time used, the
arrangement illustrated by Figs. 76, 77, and 78. At the right-
hand side of the boiler barrel is fixed a small vertical bed plate
carrying a steam and a water cylinder shown in section in Fig. 77.
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THE STEPHENSON LINK MOTION 229
The admission of steam to the upper cylinder is controlled by
the small slide valve shown in the section Fig. 77. This is
worked from the footplate by a miniature reversing lever ; a
second lever controls the admission of steam and water.
The lower cylinder is what is known as a ** cataract " — a term
derived from old Cornish engine practice — a leather-packed piston
having water at both sides of it. Water being incompressible,
so long as that in the cataract cylinder is locked up the piston
cannot move. The upper or steam cylinder piston being on the
same rod, it also is fixed. It follows, therefore, that the rod being
linked as shown to the weigh bar, already mentioned, of the
Stephenson valve gear, the gear is efficiently locked in position
by the cataract. If the driver wishes to reverse the engine he
can turn on steam to the steam cylinder above or below the
piston, as he wishes to go backwards or forwards, by altering
the position of the slide valve, to the steam chest of which he has
admitted boiler steam. But the piston cannot rise or fall until
the position of the water-cock is changed and water is permitted
to pass from one side of the cataract piston to the other. A small
indicator moving on a plate in the cab shows the precise per-
centage of the stroke during which steam is admitted. The
details are so clearly given that further description does not
appear to be required. This reversing gear acts with great
steadiness. No labour or risks are incurred by the driver in
handling the engine, and the point of cut-off can be settled with
much greater minuteness than is possible with a lever and a
notched quadrant.
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CHAPTEE XXXI
walschaert's and joy's gears
The principles involved in the construction of Walschaert's
gear are in many respects identical with those of the Stephenson
link, lap and lead playing the same part. Let us suppose that it is
hung on a fixed pivot in the middle and worked by a single
excentric only. The excentric rod being attached to the
link at the lower end, the excentric must be keyed on the crank
axle precisely at right angles to the crank, and the crank will
rock backwards and forwards on its centre pin. If now the
pin at the end of the valve spindle were placed at the upper end
of the link, the engine would go ahead. To reverse it we have
only to drop the pin to the bottom of the link. The length
of the travel of the valve will be determined by the place of the
pin in the link just as it is with the Stephenson link. But
such an arrangement gives no lead. This might be got, how-
ever, by giving the excentric sufl&cient angular advance. But if
this were right for going ahead, it would be absolutely wrong
for running backwards, and therefore quite unfit for a locomotive.
In practice, as the gear is usually fitted to outside cylinders, no
excentric is used. Instead, a small counter crank is carried by
the main crank pin, and this, precisely at right angles to the
main crank and much shorter, is coupled by a plain straight bar
to the reversing link.
Lead is obtained in the following way. The radius rod, that
is to say, a rod one end of which can be raised or lowered in the
rocking link, is not coupled directly to the valve spindle, but to
a swinging or " floating '' lever. To the upper end of this the
valve spindle is jointed. The lower end of it is coupled to the
cross head by an arm extending downwards. A glance at the
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WALSCHAERrS AND JOTS GEAES 231
engraving on p. 232 will suffice to show that when the piston has
reached the end of the cylinder, the slide valve will have been
pushed forward by the floating lever, and nothing more is
required to get the precise amount of lead wanted than to
proportion properly the lengths of the two arms of the swinging
lever.
Fig. 79 shows this gear as fitted to the high pressure cylinder
of an American compound engine of the celebrated De Glehn
type. The engine has a balanced slide, the pressure being
kept off the top of it by a ring fitted with packing to the inside
of a second ring, the upper edge of which moves steamtight on
the lid of the valve chest. A is the crank axle, B is the counter
crank, forged in one with the crank pin. D is the link, which
rocks on a fulcrum pin which does not pass through the centre,
and so leaves the curved slot in it clear for the traverse of a die
on the end of the radius rod E.
From the cross head descends a fixed arm F, which is united
to the floating lever G by a link. The upper end of G swings
on a pivot J, in an extension I of the valve spindle H.
The leading end of E is pivoted to G, about 3J inches under
J. The floating lever is carried by I, which moves, as shown,
in a long guide. The dotted lines show various positions of
D as the driving wheels revolve. L is a bell-crank lever,
worked from the footplate, which shifts E up and down. It
is clear that, as has been explained, the movement of H will
be a compound of that of F — otherwise the piston — and D. For
let us suppose that C is disconnected, and the link D held fast,
then let the piston make its stroke ; G turning then on the pin
in the end of E as a fulcrum would move the slide valve in an
opposite direction to the motion of the piston. Or let the connecting
rod be taken down, and the piston held fast while the crank
shaft was revolved ; then as D rocked, G would turn on the pin
at its lower end as a centre, and the slide valve would be pushed
backwards and forwards through a slightly greater distance than
the travel of the link.
In the engine shown the stroke of the cross head is
25^^ inches. The diameter of the circle described by the
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232
THE RAILWAY LOCOMOTIVE
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Fig. 80.
WALSCHAEET'S AND JOY'S GEAES 233
counter crank pin is 7| J inches. The long arm of the floating
lever is 29^ inches between centres, and the short arm is
3^^^ inches. The radius rod I is 57^^ inches long between centres.
The geometry of this gear is very elegant ; but on the whole it
is much more simple than that of the Stephenson link, because
the radius link D has no motion but one ; it rocks on a fixed
centre. The action is very satisfactory, and it is not really more
complex than other gears.
For compound locomotives the Walschaert gear is easily applied
to inside cylinders, a single excentric being used for each
cylinder. Thus the low pres-
sure inside cylinders of Fig.
79 are so fitted.
Joy's radial valve gear acts
on a principle quite different
from those just described.
As has been stated, a great
number of radial gears have
been invented and tried — this is the only one which has been
adopted for locomotives to any extent. It was invented by the
late David Joy many years ago. Mr. Joy was one of the pioneers
of the railway system, and his great experience with locomotives
enabled him to avoid mistakes made by other inventors possess-
ing less practical knowledge.
Let us suppose that a link A (Fig. 80), similar in its nature to
either of the two described above, is pivoted at the centre of its
length B, but that it can be moved on this centre by the arm C
and rod D, or held fast so as to stand at different angles.
Further, let the valve spindle E be jointed at one end to a long
bar F, called the radius rod, a pin at the other end of this rod
entering the die G in the link. As the length of the rod is equal
to the radius of the curve to which the slot in the link is struck,
it is clear that if the pin is moved up and down in the link by
the rod H, while the link is held straight up and down, no
motion will be produced in the valve. If, however, the link is
inclined in either direction as shown by the dotted line, then as
the pin moves up and down in the slot, the valve will be moved
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234 THE RAILWAY LOCOMOTIVE
backwards and forwards, and to reverse the engine it is only
necessary to alter the inclination of the link. There is here
no excentric or secondary crank. The motion of the valve is
caused by the sliding up and down in the radial link of the die
at the end of the radius rod which is jointed to the valve
spindle.
But the same conditions hold for the Joy radial link as those
obtaining with the Stephenson or Walschaert link — there is no
lead. The objection is got over, however, in just the same way,
by the aid of a floating lever. The practical application of the
gear is shown in Fig. 70.
The links are heavy steel castings in one with a weigh shaft C
carried in bearings secured to the main frames. In each of
these is a hardened die or rectangular sliding block, curved of
course to fit the link D, and to this block is pivoted the floating
lever E, to the upper end of which is pivoted in turn the valve
spindle connecting rod. To alter the ratio of expansion or to
reverse the engine nothing more is required than to change the
angle at which the radial link stands, and this is done from the
footplate, through the bar G, either with a lever or with a hand-
wheel and screw.
The die is caused to move up and down by coupling it with the
connecting rod. As the movement of this rod would be too
great, a secondary link is introduced, as shown in the illustra-
tion. The angles and movements are shown by the dotted lines.
The geometry of this gear is somewhat complex ; it will be found
in most treatises on valve gear.
Joy's gear is exceedingly good, giving an excellent diagram,
and it possesses the great merit that it permits the use of large
inside cylinders, the valve chests being placed on the tops of the
cylinders instead of between them. When properly made, with
large and well-hardened surfaces in the links and dies, it works
with less friction than the excentrics of Stephenson's gear. It
is very easily kept in order and, furthermore, it has the great
merit that the lead is constant for all positions of the link. With
the Stephenson link the lead varies. We have seen that it
depends for its amount on the angular advance of the excentrics.
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WALSCHAERT'S AND JOY'S GEARS 235
which instead of being set at 90 degrees with the cranks are
usually set about 18 degrees forward. But the advance of the
excentrics is virtually settled not only by their relations to the
cranks but by the position of the excentric rod. It is in effect
the same thing, whether we move the excentric round on the
axle, or the excentric hoop round on the excentric, the lead will
be altered in either case, but the place of the die in the Stephen-
son link cannot be altered without moving the excentric hoop
round on the sheave. Both Joy and Walschaert gears have a
constant lead, that is to say, steam is practically always admitted
when the piston is in the same position near the end of the
cylinder, no matter when the cut-oflf takes place.
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y
CHAPTEE XXXII
SLIDE VALVES
It is hoped that the reader has now formed clear ideas as to
the mode of action of the three types of valve gear which are
employed to the almost total exclusion of all others. It is true
that modifications are in limited use ; but it will be found that
these almost invariably include some form of floating lever to get
lead, while in others a species of combination of the Joy and
Stephenson links is made, the die being caused to slide up and
down in the link, without in any way interfering with the move-
ment of the link when actuated by the reversing lever. The
consideration of the advantages sought to be gained by improve-
ments in valve gear must be postponed until we come to deal
with the performance of locomotives as set forth by indicator
diagrams.
Valve gear must be very substantial, with large and well
hardened rubbing surfaces, because the work to be done is trying.
The frictional resistance of a slide valve does not, it is true,
absorb much power ; but this is due to the circumstance that the
stroke of a valve is short. Whether the stroke is an inch or ten
inches affects the power expended but in no way modifies the
stress to be overcome. A slide valve is forced down on its seat
by the pressure on its back, the area over which this pressure is
exerted being that of the exhaust opening in the valve and
sometimes one and sometimes two ports in the seat according as
one or two are covered by the valve. The whole surface of the
valve is not to be taken, because when metal and metal are
apparently in contact there is always a thin film of steam between
them. A slide valve suitable for an 18-inch cylinder will have a
" bridge " about 6 inches X 17 inches, representing, say, 102
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SLIDE VALVES 237
square inches, to which may be added the area of one port, say
17 inches X IJ inch = 25J, or a total in round numbers of
127 square inches. With steam at 150 lbs. in the valve chest, the
total load carried by the valve, jamming it down on its seat,
would be 19,005 lbs. or over 8 tons. What the co-efficient
of friction is it is not easy to say, because it varies almost from
minute to minute with the lubrication, the dryness or wetness of
the steam, and so on. It probably varies between 1 and 10 per
cent. It is greater with vertical than horizontal valves. The
valve gear may therefore have to overcome a resistance of some-
where about 1,900 lbs. It is in no way remarkable that valve
spindles break and excentric hoops open out and heat, and valves
wear away rapidly. To appreciate what goes on it is necessary
to stand on the running board and watch the mechanism at
work at various speeds when it is a little worn. The inexpe-
rienced observer will begin to ask himself if it is possible the
engine can ever get to its destination.
Slide valves must be left free so that they can find their way
to their seats. To this end they are always made with a rect-
angular projection on their backs, which fits into a frame known
as a " bridle," usually forged with great care from the best scrap
iron. Into one end of this — the bridle is much broader than it is
long — is secured the valve spindle. As a rule the spindle and
the bridle are now made in one piece, but formerly the bridle
was made with a boss into which the valve spindle was screwed.
Occasionally a short length of rod is provided at the other end
of the bridle; this passes through a bush in the front of the
valve chest and acts as a guide for the spindle. There are
various methods of supporting the outer end of the valve spindle ;
sometimes it is keyed into a bar, which has been turned on two
centres. The larger part of this bar passes through a long brass
bush or cylindrical guide in the motion plate. The end of the
guide rod is forked, and the fork embraces the link and the die
in it. A pin is then passed through the two jaws of the fork and
the die block. This is a very simple, cheap, and durable arrange-
ment, and has almost entirely superseded the sling links which
at one time carried the back ends of the valve connecting rods.
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238 THE RAILWAY LOCOMOTIVE
It is an incidental defect in the mechanism that as the link
is always rocking backwards and forwards the push and pull on
the die are only momentarily normal to the valve spindle. The
result is that the link continually tends to slip the die up and
down, and, failing that, to fly up and down on the die when the
gear is at all worn. The detent in the notched arc of the old-
fashioned lever or the nut on the reversing screw in modern
engines chatters continuously when the engine is running. The
indirect action puts a heavy stress on the sling straps of the
link and the guides of the valve spindles. Little of this kind
takes place with the Walschaert or Joy gear.
Various attempts have been made at different times to take
some of the pressure off the backs of the valves, and so reduce
the stress due to friction and prolong the life of the valve. We
need not concern ourselves with more than one or two. The
Eichardson balanced valve is an American invention, a modifica-
tion of which is shown in Fig. 79. Essentially it consists of an
ordinary slide valve, to the back of which is fitted a rectangular
ring, one edge of which is seated in a groove running round the
slide valve, while the other edge works steamtight on the
polished inner face of the valve chest cover. Sometimes a
circular projection on the back of the slide fits a ring, the top of
edge of which bears against the lower. As steam cannot find its
way past the ring, the slide valve is relieved of almost all the
pressure on its back. This valve, however, takes up a great
deal of room and can only be used when the slide valves are
placed directly on top of the cylinders. It constitutes an
excellent combination with Joy's gear.
Another balanced slide valve exhausts directly up through the
back of the valve, which, as in the valve just described, is fitted
with a balancing ring on the back. Within the last few years
piston valves have begun to find favour, but these will be best
dealt with in connection with compound and superheated
engines.
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CHAPTEE XXXIII
COMPOUNDING
Although compound locomotives are not much in favour in
this country they are in use on many European railways, and to
some extent in America. They have formed a subject for dis-
cussion for many years, and it cannot even now be said that
anything like a universally accepted decision has been arrived at.
The reason for this want of unanimity will be understood as the
reader proceeds.
It has been already shown that to secure economy the steam
must be caused to expand so that it can be discharged from the
cylinder at a much lower pressure than that at which it entered
it. This means a reduction in the average pressure, and of
course in the pulling power of the engine. This diflSculty could
be got over by putting in larger cylinders — that is to say, by
augmenting cylinder capacity. Although the average pressure
would be reduced, the pulling power of the cylinder would remain
unchanged. The plan has been tried and failed completely for
reasons which are worth stating because they show some of the
difficulties which beset those who design locomotives.
In the first place, when the engine is starting, full pressure
steam acts on the piston, and if this is large, then all the rest of
the mechanism must also be large. Thus a crank axle big
enough for a 17-inch cylinder will not suffice for a 19-inch
cylinder, and so on. Consequently a heavy and expensive engine
results. In the next place, the utilization of the large cylinder
depends on the engine driver. He must " link up '' his engine
in order that the steam may be cut off early in the stroke and
expanded. In practice it has been found impossible to get the
men to do this. On inclines they give their engines too much
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240 THE RAILWAY LOCOMOTIVE
steam, and the result is that they ** run them out of breath," and
then complain that the boiler will not keep steam. It has been
proposed to get over the difficulty by increasing the lap from one
inch to an inch and three-eighths. Then the drivers could not
help using steam expansively, because do what they would the
cut-off would take place fairly early in the stroke. But this plan
failed because the engines easily went blind. Much delay occurred
at starting, and at the best of times the speed of the train rose
too slowly. To get over the difficulty it has been proposed that
a small hole should be bored into the valve seat at each end.
Through this hole, when the engine was blinded, steam would
get in and start the engine, and when speed was obtained, the
small quantity that would find its way in could have little or no
effect on the ratio of expansion. In the United States the same
object is attained by filing a notch in the valve at each end,
through which steam enough to start the engine could find its
way. Neither of these methods has, however, attained any
popularity. The problem remains unsolved. Steam was not used
to the best possible advantage in the locomotive.
Then it was resolved to try compounding — that is to say,
using the steam first in one cylinder and then, instead of turning
it directly up the chimney, passing it on to another cylinder,
precisely as in marine engines. As this book is intended to be
of use to the non-technical as well as to the technical reader, it
is necessary to explain in as few words as possible what com-
pounding means. For detailed information the reader must
consult any good work on the steam engine. It must, however,
not be forgotten that the conditions and limitations under
which the compound system can alone be applied to the loco-
motive render much that is written concerning' stationary and
marine engines inapplicable. This will be explained more fully
presently.
Let us suppose that we have two cylinders of the same
diameter side by side, each capable of holding two cubic feet of
steam, and that pistons in these drive two cranks set at 180°
from each other. Let the cylinders be vertical, then when one
piston is at the top the other will be at the bottom, and so on
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COMPOUNDING 241
alternately. One of these cylinders is full of steam, with the
piston at the bottom. The steam, instead of escaping into the
atmosphere, is now admitted to the other cylinder and pressing
on the piston forces it down. But the steam equally resists the
rising of the first piston. The effort is balanced and no motion
would be produced, and even if it were no expansion would take
place. The action would be analogous to the pouring of a pint
of water from one pint pot into another.
But let cylinder number two be 50 per cent, larger in
diameter, its length remaining unaltered. Instead of holding
only two cubic feet it will now hold four. Its piston will have
double the area. If. the steam at the end of the stroke exerts
5,000 lbs. on the first piston, it will exert 10,000 lbs. on the
second, and we shall have a net driving force of 5,000 lbs. At
the end of the stroke, when piston number one has risen from
the bottom to the top of its cylinder and piston number two has
descended to the bottom of its cylinder and all the steam has
passed from the first to the second cylinder, we shall have four
cubic feet of steam of, say, 50 lbs. pressure instead of two cubic
feet of 100 lbs. pressure. That is to say, the steam will have
been expanded twice ; the ratio of expansion is 2 to 1. Further-
more, let us suppose that the steam had been cut off at half
stroke in the first cylinder. Then when the piston had com-
pleted its stroke the steam would have been expanded twice in
the first cylinder, that is to say, doubled its volume, and this
steam admitted to the second cylinder would at the end of the
stroke have been expanded four times, because we had only one
cubic foot of it instead of two to begin with, and the capacity of
the second cylinder is four cubic feet.
Here attention must be called to an important fact, namely,
that the total expansion, no matter what the number of cylinders
or ratio of expansion in each cylinder may be, is always the same
as though the expansion had taken place in the low pressure
cylinder only. If, for example, the capacity of the low pressure,
that is the largest, cylinder is ten cubic feet, and only one cubic
foot is admitted to the high pressure cylinder, then the ratio of
expansion will be tenfold. In compound engines the steam
B.L. B
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242 THE RAILWAY LOCOMOTIVE
passes through two cylinders only. In triple and quadruple
expansion engines it passes through three or four cylinders. In
every one of these cylinders the ratio of expansion may differ,
but in the end it all comes to the same thing as though the
expansion took place in the low pressure cylinder only. One
practical result is that horse power is calculated on the basis of
the average pressure which should be attained in the low
pressure cylinder, all the other cylinders being neglected. Of
course it must be understood that this is only a general state-
ment. Not only the total power but the distribution of power
among the cylinders has to be ascertained, as far as possible.
This last should be the same for all. If an engine with two
cylinders indicates 1,000 h.p., then as nearly as may be 500 ought
to be obtained from each cylinder. If three cylinders, then
333 h.p. from each, and so on.
Now the form of engines we have been considering is not
suitable to the locomotive, save under special conditions. Instead
of the cranks being opposite each other they are at right angles,
and consequently when one cylinder exhausts the other is not
ready to accept the steam. The difficulty is got over by work-
ing each cylinder as though the other did not exist. The high
pressure cylinder exhausts into a vessel known as the " inter-
mediate receiver," from which the second or low pressure
cylinder draws its supply.
Lastly, instead of using two cylinders, one twice as big as the
other, we may use three cylinders all the same size, the steam
exhausting from one cylinder into two instead of into one of
double the size ; or, conversely, we may use two small cylinders
exhausting into one large one. All these methods are used in
daily practice. The first compound locomotives put into regular
use were invented by the late Mr. Francis Webb, Chief
Mechanical Engineer of the London & North Western Railway.
They had two small outside cylinders, fitted with Joy's valve
gear, which drove one pair of driving wheels, and one large
inside cylinder which turned another pair of driving wheels.
The two high pressure cylinders supplied the single low pressure
cylinder, which exhausted in the usual way up the chimney.
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COMPOUNDING 243
Mr. Webb was followed by Mr. James Worsdell on the Great
Eastern Eailway first, and then on the North Eastern, who used
two inside cylinders only, one much larger than the other.
No engines are now made anywhere on the Webb system.
Before describing any of the systems of compounding in actual
use it is necessary to explain the limitations and conditions
referred to above, for these it is which determine not so much
what is and is not possible as what is and what is not likely to
be satisfactory.
It will be remembered that the clear space between the main
frames of a locomotive for the 4 feet 8J gauge cannot exceed
4 feet 1} inches. If a double cylinder compound is used it will be
found that the small cylinder cannot be much less in diameter
than it would have been if one of a non-compound pair, because
increased cylinder capacity is essential, and that cannot be had
if the high pressure cylinder is reduced in volume in proportion
to the increase in volume of the low pressure cylinder. Now we
have seen that two 18-inch cylinders represent the most that can
be got between the frames unless the slide valves are put on top
of them or underneath them. But an 18-inch high pressure
cylinder requires a low pressure cylinder about 26 inches in
diameter, and to squeeze this into 4 feet IJ inches, keeping their
axes parallel and in the same plane, is not easy. Again, the
larger pistons weigh more than the smaller pistons, and this
entails trouble with balance weights. In a word, the engine is
not symmetrical. For this and for other reasons connected with
the details of construction, when two compound cylinders only
are used in the present day, they are almost invariably outside
cylinders. Plenty of room is in this way got, not only for the
valve gear, but for the intermediate receiver, which in the loco-
motive takes the form of a large pipe carrying the exhaust steam
from the first to the second cylinder. The pipe is often coiled
round the inside of the smoke-box to get capacity in the form of
length, while the steam passing through it is to some extent
dried by the high temperature in the smoke-box.
In Mr. Webb's engines symmetry was obtained, but the
engines were defective in various ways. The large inside
r2
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244 THE KAILWAY LOCOMOTIVE
cylinder could do nothing until steam reached it from one or
other of the high pressure cylinders. It followed that the starting
of a train depended on one cylinder about 15 inches diameter.
The consequence was that heavy trains got away with diflSculty.
Very often they could not start at all but for the fact that the
rear driving wheels were made to slip on the rails, and so steam
found its way to the large cylinder. At the best of times the
starting effort was very unequal and the train advanced by jerks
under the intermittent action of the single inside cylinder-
Passengers did not like this. For long runs the Webb locomo-
tive was fairly successful ; whether it was or was not economical
remains to this day a disputed question.
The starting of trains by two-cylinder compound engines has
always presented a difficulty, as only one cylinder can get boiler
steam, and if its crank is on or near the dead point the engine
will not move. To get over this difficulty a special valve has to
be added which will admit steam to the low pressure valve chest,
the engine starting non-compound, which valve is closed subse-
quently. But it would not be safe to admit high pressure steam
to act on the large, low pressure piston. The piston rod might
be bent or the crank axle broken, therefore a reducing valve
must be introduced, that is to say, the steam has to lift a valve
loaded by a spring. If the pressure rises too high in the low
pressure valve chest, then there is not sufficient difference in
pressure to overcome the resistance of the spring, and the valve
closes. Usually the maximum pressure permitted in the low
pressure cylinder is about one-third of the boiler pressure, say
60 lbs. where the latter is 150 Ibs.^
If the intercepting valve, as it is called, is worked from the
footplate, then the driver after he has started his train may
forget it, or purposely leave it open, and we have then a bad non-
compound engine. To prevent this Mr. Von Borries, a German
engineer, invented a very ingenious automatic intercepting
* In some recent locomotives the intercepting valve is not used, the
parts are made strong enough to take the full pressure. These engines are
four-cylinder compounds, two high and two low pressure, and the sub-
division renders all the cylinders comparatively small.
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COMPOUNDING 245
valve, which is open while the pressure in the low pressure
valve chest is below a certain fixed limit, and closes of itself
as soon as the engine has fairly started its train. Joining with
Mr. James Worsdell, they patented a combination of the two-
cylinder compound and the automatic intercepting valve, the
result being Worsdell and Von Borries' patent engine, which
with various modifications has been extensively used abroad.
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CHAPTEE XXXIV
PISTON VALVES
The modern big locomotive is about twice as powerful as were
its predecessors. The express engine of ten years ago seldom
had more than 1,200 feet of heating surface. The modern
engine has 1,800 to 2,000 feet in Great Britain, much more in
the United States and on the Continent. Large cylinder capacity
is required to use up the steam produced in the enormous boiler.
Engines have been made with very large outside cylinders, but
recently it has been deemed advisable to use four cylinders
instead of two. Usually these are arranged side by side, two
inside and two outside. In some cases the engines are simple,
in others compound. An immense advantage is gained in that
the reciprocating parts, moving simultaneously in opposite direc-
tions, balance each other, and no balance weights, or next to none,
are put into the wheels. The rails are spared " hammer blow,"
and there is no jumping at high speeds. In the United States
two types are made, one the invention of Mr. Vauclain, and the
other the invention of Mr. Cole, both engineers well known in
the American railway world. The four-cylinder engine has
rapidly grown in favour with the demand for very large powers.
In Europe locomotives both compound and non-compound are in
use. In Great Britain its adoption has been more leisurely,
presumably because the demand for mammoth engines is not very
considerable. It would be out of place to consider here the
various types of construction found on different lines. The
reader is referred for detailed information to the fine work *' La
Locomotive Actuelle," by M. Maurice Demoulin, published in
1906 by Beringer, Paris.
The slide valve has already been dealt with very fully. It is
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PISTON VALVES 247
now time to speak of more recent methods of distribution
rendered necessary by the increase in power and the augmented
pressure peculiar to recent locomotives.^
About thirty years ago boiler pressures seldom exceeded 130 lbs.
They were gradually augmented, however, as trains became
heavier, until 150 lbs. was reached. Then came the compound
engines, and it was very soon found that 150 lbs. was not enough
to get advantage from compounding. M. de Bousquet, Loco-
motive Superintendent of the Chemin de Fer du Nord, adopted
220 lbs., and his example has been freely followed. It is not too
much to say that an unbalanced slide valve cannot be successfully
worked at this pressure even when saturated steam is used. When
the steam is superheated an unbalanced slide valve cannot be
used at all, because it will seize on the seat, and something must
give way. The consequence is that piston valves are used for
distribution. Nominally their construction is exceedingly simple,
really their use is attended with certain objections to overcome
which complications have been introduced. Probably fifty kinds
of piston valves have been invented, and about half as many
are in use. The differences lie in constructive details, for in
principle they are all the same, and it will sufl&ce to illustrate
the first piston valve that attained success in this country. It
was invented by Mr. Smith, of the North Eastern Eailway, some
ten or twelve years ago, and used with much success by Mr. J.
Worsdell when Locomotive Superintendent of that line. Cast
with the cylinder is a valve chest, shown in section in Fig. 81 by
H. At each end of this chest is a cylindrical portion L L. These
cylinders are bored out, and into them are forced by hydraulic
pressure other cylinders or barrels of specially hard cast iron,
bored and turned inside and out. In these barrels are cut ports
M M, as shown in the cross section, which establish communica-
tion between the insides of the valve cylinders through chamber C,
and thence to the cylinder ports P.
In the valve cylinders move the two pistons N N, secured on
1 It is very usual to speak of the valves and valve gear of an engine taken
as a whole as '*the system of steam distribution," or, more shortly, "the
distributing system."
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248
THE RAILWAY LOCOMOTIVE
the valve spindle by a collar and nut. The pistons are provided
with packing rings. Steam is admitted from the boiler to each
end of the valve chest, and the pressure only acts to push the
two pistons together. They are therefore balanced and can be
moved backwards and forwards each in its respective cylinder
without any resistance but that of the friction of the packing
rings and the stuffing box for the valve spindle. Into the central
chamber opens the exhaust pipe, which either carries the steam
Fig. 81.— Smith's piston valve.
to the blast pipe or into the valve chest of the low pressure
cylinder, according as the engine is not or is compound. The
action is precisely that of a slide valve, the lap being obtained
by widening the packing rings as shown.
The objections to the piston valve are, first, that it takes up a
great deal of room ; secondly, the ports must be carefully made
in such a way that a packing ring can get into them. This is
easy enough so long as this ring remains unbroken, but rings
will break, and if a portion sticks in a port, then disaster is sure
to follow. Thirdly, the pressure of the steam acting on the rings
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PISTON VALVES 249
when they are over the ports may cause them to collapse at each
stroke, when serious leakage will occur. Fourthly, when water
accumulates in the cylinders, as, say, when priming takes place,
in a slide valve engine, the valve lifts off its seat when the piston
strikes the water at the end of the stroke and no harm is done ;
but the water cannot escape when a piston valve is used, and a
spring loaded relief valve must be fitted at each end of each
cylinder. Fifthly, when steam is shut off with a slide valve
engine the pistons will act as a pump and draw steam out of
the steam pipe and so make a vacuum, but compression takes
place at each end of the stroke and lifts the valve off its seat,
and air enters and restores the equilibrium. This is the reason
why the slide valve of some engine& may be heard " clattering "
as a locomotive runs with steam off alongside a platform. The
piston valve cannot do this, and the result is that when steam is
shut off the pistons run against the full pressure of the atmo-
sphere and resist the movement of the train. To avoid this, a
special valve has to be used which prevents the setting up of a
vacuum. From all this it will be seen that, excellent and indeed
essential as the piston valve is, its use is, as has been said above,
not unattended with difficulties.
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CHAPTEE XXXV
THE INDICATOR
This treatise would be incomplete if it did not contain a setting
forth of some of the arguments for and against the compound
system, which are urged with as much vehemence to-day as they
were at any other period in the history of the locomotive.
It is necessary here to say something about the Indicator, an
instrument which does for the engineer very much what the
stethoscope does for the physician. For reasons already stated,
much in this book is intended for the use of the non-technical
reader. The following short description comes under this head.
The pressure of the steam continually alters in the cylinder
as the piston moves. In order to ascertain what these changes
of pressure are, the indicator is fitted to each end of the cylinder.
The instrument consists of a very carefully finished cylinder
containing a piston with an area usually of precisely half a
square inch. On the top of this piston is fitted a spring holding
it down. The piston rod is jointed to one arm of a very light
parallel motion. The end of this arm carries a blunt-pointed
German silver pin or style, which can be swung into contact
with a strip of metallic paper rolled round a cylinder. This
cylinder can be caused to rotate through about seven-eighths of
a circle by a cord secured at one end to the paper cylinder, at
the other to a lever connected with the cross head of the engine.
Steam from the cylinder gets access through a stop-cock to the
cylinder of the indicator. The piston of the indicator will rise
and fall with the pressure in the engine cylinder, and the paper
roll will rock backwards and forwards. If now the style be
pressed lightly against the metallic paper on the roller, a diagram
will be drawn which represents all the pressures in the engine
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THE INDICATOR
251
cylinder during one revolution of the crank axle. Not only this,
but it will tell precisely at what part of the stroke each pressure
was exerted, and it enables the performance of the valve gear to
be examined. It tells in a word just what is going on inside the
cylinder. Furthermore, by drawing ordinates across it at equal
Fig. 82. — Tliompson indicator with open spring.
distances and measuring the length of these on a scale with
which the indicator spring has been calibrated, we get the average
pressure throughout a stroke, and thence by a very simple
calculation we arrive at the horse power. Examples of diagrams
will be given presently.
Fig. 82 illustrates a modern indicator of the highest class
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252 THE EAILWAY LOCOMOTIVE
made by Messrs. Schaflfer and Budenberg. When the spring is
heated it is weakened, and therefore is no longer accurate. To
avoid this the spring instead of being put inside the cyUnder is
put outside it. All the details are very clearly shown. The
piston is of steel, ground to fit steamtight and yet to move
without friction. Its range of motion does not exceed half an
inch. There are many other types of indicator equally good,
but the differences are in the main in detail, the objects had in
view being the reduction of weight in the primary parts, con-
venience in handling, diminution of friction, and strength.
There are various treatises on the indicator to which the student
is referred for further information.
Now, the pressure of any given weight of any gas whatever
varies with its volume. If we halve the volume we double the
pressure. If we double the volume we halve the pressure, and
so on. This is known as Marriotte's law, and is written
P V =• a constant. That is to say, the pressure and the volume
of any given weight of gas, say 1 lb., multiplied together,
always come to the same amount. It follows from all this that
when the indicator tells us what the pressure is at any point in
the stroke of the piston, as we know the volume occupied by the
steam, we ought to be able to tell precisely what weight of steam
has been admitted to the cylinder. This holds true of a gas. It
does not hold true of saturated steam, which is not a gas, but, as
the reader will remember, a vapour in a state of unstable
equilibrium. We can, by weighing the quantity of water pumped
into a boiler in any fixed period, as, say, an hour, ascertain pre-
cisely what weight of steam is supplied to the engine. If nothing
happened to this steam, the P V = C law would apply. In
practice, however, this is not the case. The pressure is always
less than it ought to be ; in other words, the indicator does not
account for all the water pumped into the boiler. There are
various sources of loss. Thus the slide valves or the piston may
leak ; or part of the feed water was not evaporated at all, but
came over as priming. But the principal loss is due to conden-
sation, and that condensation is in its turn due to the varying
temperatures inside the cylinder. The inner surface of it is
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THE INDICATOR 253
first heated up to, say, 380° F., which is approximately the tem-
perature of 200 lbs. steam — 185 lbs. safety-valve load — when
the admission port opens. Then it falls gradually as the pressure
falls during expansion, and after the exhaust port has opened the
temperature of the vapour remaining in the cylinder is little
above 212° F. It will be seen, therefore, that the insides of the
cylinder covers and the two piston faces are submitted to a range
of temperature of 380° -212°= 168° F. It would be impossible
to go here into the intricate theory of heat exchanges in the
cylinder walls, as worked out by many English, French, and
Belgian engineers. It is enough to say that " initial condensa-
tion " — that is to say, the condensation of the first steam that
enters the cylinder and parts with its heat to warm up the
cylinder and piston at the commencement of each stroke — has
long been recognised as a source of loss. As much as 80 per
cent, of all the steam supplied to a cylinder may be turned into
water in it and do no work, representing a waste of 30 per cent, of
the coal burned.
Condensation is also caused by radiation from the outside and
conduction. The cylinder is cooled down by the air through
which it passes. Heat is conducted through its walls to the side
frames, and so on. The student of thermodynamics knows also
that liquefaction takes place because part of the heat of the steam
is converted into work. The first and most obvious remedy is to
keep the cylinder hot ; the second is based on a theory which
now claims explanation.
In a general way it may be said that the weight of steam con-
densed in a given time by a given metallic surface varies chiefly
as the difference in temperature. If, for example, 30 per cent,
represented the condensation when the limits of temperature
were 168° F., then 15 per cent, would be liquefied if the limits
were 84° F., and so on. It is on this fact that the whole theory
— which must not be confounded with practice — of the compound
engine is based. It will be readily understood that if the pressure
in a cylinder is not permitted to drop too far the condensation
ought to be reduced. We have seen that the range may be 168°
in a single cylinder, but in a compound engine the range in the
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254 THE EAILWAY LOCOMOTIVE
first cylinder might be only 52°, the pressure falling from
200 lbs. to 100 lbs. ; while in the low pressure or second cylinder
the range would be 106°, answering to 100 lbs. pressure and
atmospheric pressure. The range of temperature in any one
cylinder being lowered in a very obvious way, it is claimed that
condensation is greatly reduced.
It may be safely said that the soundness of this theory has
never been universally accepted. In the first place it is clear
that although the range of temperature in any one cylinder is
diminished, yet that the total weight of metal to be heated and
cooled at each stroke — or, in other words, the condensing surface
in the engine — is much increased. Again, in practice, it is found
that the percentage liquefied is about the same in a compound as
it is in a simple engine. Into the general reasons why the compound
engine is more economical than the simple or non-compound
engine it would be impossible to go here. We are dealing with
locomotives, not with engines in general, and the compound
locomotive will be more economical than the simple engine
almost entirely because the cylinder capacity is augmented,
while the objections already explained to cutting off early in a
single large cylinder are avoided. Thus a compound locomotive
properly designed will not under any circumstances ** go blind."
Furthermore, even at low velocities, the steam is worked expan-
sively of necessity. The driver cannot help himself. Now
locomotives as a rule run slowly only when pulling heavy trains,
and when running slowly, if they are put into full gear forward,
the steam leaves the cylinder at a very high pressure, and with
much work still in it. Any reader who has stood beside a steep
incline and heard a locomotive pulling a train up it will realise
this. The tremendous noise of the exhaust tells its own story ;
a compound engine pulling the same load up the same incline
would be comparatively silent. When, however, the speed is high
the conditions are altered. Automatic expansion then takes
place. The steam cannot follow up the piston fast enough
through the ports. The diagrams given here tell the whole
story.
As it is essential that the arguments should be fully understood
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THE INDICATOR
255
a certain amount of repetition is necessary. What expansion
means has ah-eady been clearly explained in Chapter XXIX.
Those who have read with care what has been said about lap
and lead and the link motion will remember that one dis-
tinctive feature of all valve gears worked by a link or its
equivalent is that by shifting the link we can shorten the
A.RS7'20
steam Chest Pres. 135. Speed ii.
Revs, per min. A7'4-l. Cut on 75%
Gradient I in 264 up. Total l.H,F, 370S3.
Steam C/iest Pres. i30 Speed 30.
Revs, per min 129-3, Cut otf 33 %»
Gradient tin 264 up. Total I.H.R SOI -75
A.B 32-40
Steam Chest Pres. 140. Speed 12 .
Revs. per min. 51-7. Cut oFF 33%
Gradient I in 264 up. Total I.H. P. 262-39
Steam Chest Pres. 135,
Revs, per min. 280-15
Gradient I in 264 down.
Speed 65
CutoFF27%
Total I.H.R 615 79
Fig. 83.
stroke of the valve, and therefore open less and less of
the steam port as the point of cut-off becomes earlier. The
result is wire drawing. The steam has to get in through so small
an opening that it cannot follow up the piston moving at a high
velocity, and the pressure rapidly falls throughout the stroke,
indeed it is found that this takes place even if the valve motion
is kept in full gear as the speed of the train augments. The
result is that, whether the driver likes it or not, the steam will be
expanded automatically. As an example of this, four diagrams
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256 THE RAILWAY LOCOMOTIVE
are given, Fig. 83, taken from an engine working a fast passenger
train. The first was taken just as the train started, in full gear.
The steam was admitted over three-fourths of the stroke; the valve
closed at A ; the exhaust port opened at B ; the curve at C in the
exhaust line was due to the opening of the exhaust in the other
cylinder and a consequent rise in the blast-pipe pressure. In the
second diagram the speed had risen to twelve miles an hour ; the
engine had been linked up and the cut-off took place at one-third
of the stroke. Compare now this diagram with No. 3. The
position of the link has not been changed, but the speed has
risen to thirty miles an hour, and we find pronounced evidence
of wire drawing. The whole diagram is much leaner than
No. 2. The precise point where the steam port closed can no
longer be defined. In No. 4 all this becomes still more strongly
marked. It is true that the link' has been raised a little, but the
speed is now sixty-five miles an hour, and the steam is quite
unable to follow up the piston. It is particularly to be noted
that the terminal pressure has now fallen practically to that of
the atmosphere. There is no more work left in the steam ; it has
to be pushed out by the piston.
Now the pjreat utility of compounding, as far as a locomotive is
concerned, lies in sending no steam up the chimney with available
work in it. No compound engine could do this more effectively
than it is done in No. 4. But going to No. 1 we see that the
steam escaped from the cylinder with a pressure of at least
100 lbs., and this was unavoidable under the conditions. If,
now, a low pressure cylinder had been added, in which this other-
wise wasted steam could have been utilised, a considerable
economy would have resulted. Here we have in a nut-shell the
essence of the whole problem. When the speeds are high
the exhaust pressure must be low; when the speeds are low
the exhaust pressure may be very high, unless the engine is
compound. The slow-speed goods or mineral engine may be
made compound with great advantage, while nothing whatever
might be gained by compounding the fast passenger engine.
The position then is this : When the speeds are low and the
loads are heavy the compound engine has beyond doubt a
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THE INDICATOR 257
possible advantage, much depending, however, on the way in
which the engine is handled. At high speeds the compound
engine is worse than the simple engine. It cannot take any
more work out of the steam, the terminal pressures being about
the same. The back pressure resistance is augmented because
the piston area is greater ; and the engine is heavier, more
expensive to make and to maintain. In this country the com-
pound engine has not achieved much popularity, because the
working conditions are not favourable. Abroad, where the roads
are more trying, the speeds low, and the loads heavier, the system
does excellent service and enjoys favour. But, as has been
already said, it does not appear that the loss by condensation in
the cylinders is sensibly reduced, and it is a suggestive fact that
it is claimed that superheating does more good with compound
than with simple engines, which could not well be the case if
cylinder condensation did not remain an important factor.
Proofs exist in abundance that the economy of the compound
system only becomes apparent when the speeds are so low that
the terminal pressures in the cylinders are high. That is to
say, it is not of use in passenger locomotives. A crucial experi-
ment was carried out some months ago by Mr. Ivatt on the Great
Northern Railway. He communicated the facts last year to the
Institution of Mechanical Engineers. The table on page 258 is
reproduced from the Transactions of the Institution. It is full of
valuable information. It will be understood that three modern
engines of great power were used. No. 1300 is a four-cylinder
compound, No. 292 is a four-cylinder locomotive, which can be
worked either compound or simple, and No. 294 is a two-cylinder
simple engine. They are all of the 4 — 4-^-2 type, with almost
identical boilers, the heating surface being approximately 2,350
square feet, the grate area in each being 31 square feet.
The trials from London to Doncaster were so arranged that
each driver and fireman, of the three sets of men selected, should
run each engine for three weeks with the same group of trains
(mostly express) in regular rotation. By this means it was
intended that each driver should make the same number of trips
with each engine on each train, thereby eliminating the personal
R.L. s
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258
THE RAILWAY LOCOMOTIVE
equation and equalizing all conditions as far as possible. The
drivers and firemen took great interest in the trials, and, as an
Results of Trials.
Engine
No. 1300.
4-cylinder
Compound.
Miles run, engine
,, train .
Speed, average, miles per hour
Weight of train, average, tons
Ton-Miles:—
Total train
Including engine and temler
Per hour ,, ,,
Coal used : —
Per engine-mile
Per train-mile
Per ton-mile .
lbs.
n,286
11,045
49 02
229-98
2,5-10,130
3,8015,030
16,759
44 86
•J5-84
0133
Engine
No. 292.
4-cylinder
Combined.
Engine
No. 294.
2-cylinder
Simple.
11,670
11,415
49-9
23803
2,717,112-5
3,993,812
17,337
11,673
11,415
49-58
234-29
2,674,420
3,949,110
17,030
43-02
43-98
0-126
44-31
! 45-31
0-131
Oil used:—
Per 100 engine-miles
Per 100 ton-miles .
. pints
>>
7-34
0022
7-18
0-021
6-22
0-0184
Costs : —
Coal—
Per engine-mile
Per ton-mile .
pence
• »»
2-4
00071
2-3
00067
2-37
0007
Oil—
Per engine-mile
Per ton-mile .
0-165
000049
0-16
000047
0-14
0-00041
Repairs—
Per engine-mile
Per ton-mile .
. „
0-50
0-0017
0-45
0-0013
0-37
0-001
Total—
Per engine-mile
Per ton-mile .
3-125
0-0092
2-91
0-0085
2-88
0-0085
additional stimulant for them to make each engine show to the
best advantage, prizes were arranged based on the aggregate
performance of the men, and not on that of any engine. The men
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THE INDICATOR 259
ran each of the engines for one week prior to commencing each
three weeks' trial, in order to get thoroughly familiar with
them.
The engines were put into the same condition of repair before
the trials, and were treated in the same way throughout, and
were supplied with the same quality of coal, namely, Yorkshire
from the Barnsley bed. Careful account was taken of coal and
oil used, time lost or made up, state of weather, weight and com-
position of trains, and cost of running repairs. An inspector
rode with each engine during the trials.
All three engines drew all the trains in turn. The fastest was
timed at 51*28 miles an hour, and the other two at 47*16 and
46*11 respectively. The average speed was 48*15 miles an hour.
It will be seen that the combined engine had rather the smallest
coal consumption per train-mile, while for repairs the simple
engine came out best. The most telling fact is, however, that
the total cost per ton-mile of the compound engine was greater
than that of either of the other two.
It has been explained in a preceding page that an intercepting
valve is generally used to reduce the pressure where steam has
to be admitted directly lo the low pressure cylinder of a com-
pound engine, as at starting — to reduce the pressure to a limit
which shall be safe on the large piston. Mr. Ivatt has taken
advantage of the small size of each piston, when four are used,
to dispense with the reducing valve in the combined engine
No. 292. The low pressure inside cylinders have one valve chest
in common, and are 16 inches diameter by 26 inches stroke. The
two high pressure cylinders are outside, 13 inches diameter by
20 inches stroke. A change valve is provided, which, in one
position, allows full boiler pressure steam to enter the low
pressure valve chest as well as the two high pressure valve chests
outside, and at the same time puts the high pressure exhaust in
communication with the blast pipe. The low pressure exhaust
of course always goes up the blast pipe. When the valve is in the
other position (compound) it cuts the live steam off the low
pressure chest and changes the exhaust from the high pressure
cylinders to the low pressure steam chest. When the valve
s2
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260 THE RAILWAY LOCOMOTIVE
stands in the " simple " position the engine works as a four-
cylinder simple, and the driver notches up both reversing gears
accordingly. All the parts are strong enough to stand this, and
that is the way the engine would run when working a coal train
or a slow heavy goods. In working a passenger train — say out
of King's Cross — the engine starts as a four-cylinder simple, and,
if the train is heavy, keeps like that until the speed gets up to, say,
40 miles an hour somewhere about Finsbury Park. Then the
driver shifts the change valve and makes her into a compound,
puts the low pressure reversing lever nearly full over, and does
his notching up with the high pressure reversing lever. The
result is, of course, a very useful all-round engine.
Various systems of superheating have been described.
According to the late Professor J. Macquorn Eankine, if steam
is superheated about 40^ F. it acquires, as has been already
stated, the properties of a gas. In other words, it loses some of
its instability. But much more than thip is required to do any
good, and steam is superheated in locomotives by from 200"^ to
over 400°. Thus steam of 380° acquires a temperature of 580°
to 700°. Unfortunately, it is not possible to secure more than
an approximation to regularity of temperature. Care is taken
as far as possible to make it certain that no condensation will
take place in the cylinders. The steam then behaves as a gas
and the indicator will, in theory at least, account for all the
water put into the boiler.
It does not require much knowledge of machinery to see that
surfaces heated nearly red hot — iron begins to glow in the dark
at about 800° — are liable to work on each other with much
friction. But the pressure holding two surfaces together is an
important factor. It is for this among other reasons that super-
heated steam cannot, as already stated, be worked in engines
with unrelieved or unbalanced slide valves ; piston valves are
essential. Again, no vegetable oil can be used as a lubricant.
It would be carbonised at once, and the statement is true, though
■ to a less extent, of animal oils. W^e are driven, therefore, to the
mineral heavy oils, and these have now been brought to very
great perfection as lubricants for engines using superheated
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THE INDICATOE 261
steam. It is indeed doubtful if very hot steam could have been
used at all without the aid of mineral oil.
An energetic controversy has proceeded for some time among
Continental engineers as to the relative merits of compounding
and superheating. On the one side it is held that the loss by
internal condensation in the compound engine is very small,
and that the great increase in cylinder capacity secured by it is of
immense advantage in that the tractive power of the engine can
be augmented to anything desired within the limits of adhesion,
simply by using the intercepting valve and working non-com-
pound when necessary. The speed will, of course, be slow and
the boiler able to supply the demand. It may be taken that the
total capacity of the cylinders of a compound engine is not less
than one half greater than that of a simple engine. If then the
engine is worked non-compound it can utilize three pairs of driving
wheels, while a similar simple engine could only utilize two pairs.
The argument must be taken for what it is worth. Back pressure
in the high pressure cylinder has to be considered, and the admis-
sion of steam of full boiler pressure to the low pressure cylinder
does not seem to be good practice. The most that need be con-
ceded is that compound locomotives properly handled start trains
very well, and are excellent hill climbers. When four cylinders
are used it is quite easy to carry out compounding, difficulties
which exist with the two-cylinder compound being avoided.
On the other hand advocates of superheating like Herr Garbe,
already quoted, maintain that, the steam being more efficient, a
larger cylinder in proportion to the boiler can be used without
risk of ** running the engine out of breath," and that in this
way great tractive effort is secured, while the economy attained
is greater than anything that can be had from compounding.
Furthermore, superheating is of use at all times and under all
conditions, whether the speed is high or low, whether the engine
is climbing a bank or running on a level, and this in contra-
distinction to the compound system, which is of use only at low
velocities when a "fat" diagram is given by the working con-
ditions. It is worth a passing notice that both parties claim a
saving of about 12 per cent, as compared with ordinary "simple"
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262 THE RAn.WAY LOCOMOTIYE
engines on the same duty. Superheating and compounding
have been tried in the same engine, but no one claims that a
saving of 24 per cent, is effected. Indeed, so far as can be
learned, the duplicate system is very little if at all better than
either of the two alone. An advantage is, however, secured, though
a small one, by placing the intermediate receiver, which is in
point of fact the pipe uniting the high and low pressure cylinders,
in the smoke-box, by which means the steam is dried on its way
to the low pressure cylinder.
It is proper to observe here that the arguments used on both
sides extend far beyond what has been just stated. Thermo-
dynamics have been called in by both parties, and it need scarcely
be added that mathematical disquisitions abound. These possess
an academical interest only. The broad facts are as stated, that
compounding may or may not be productive of a saving in the
consumption of fuel, according to the conditions under which
the engine is w^orking. Superheating will certainly give a saving
in fuel ; but an efficient superheater is a very heavy and very expen-
sive addition to an engine, and its life cannot be long. Let us
suppose that in three years a superheater costing £400 is worn
out. During that time the engine will have run 60,000 miles and
burned 10,000 tons of coal. If we take the saving at 10 per
cent., that means 1,000 tons of coal. With coal at 10s. a ton we
have then on the one side a capital outlay of ^£400 and on the other
a saving of i;500 in coal. Whether superheating should be
used or not is obviously determined by the price of coal as a
principal, though of course not the only, factor. The extra cost
of a compound as compared with a simple engine is so small
that it need not be taken into account, piarticularly when it is
remembered that engines practically never wear out.
Summing up, it may be said that so far all the indications are
that simple engines will continue to be built in by far the greater
number for the more moderate powers, and that compounding
and superheating will both be used according to the proclivities
of locomotive superintendents and the conditions under which
the work of their locomotives is performed.
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CHAPTER XXXVI
TENDERS
The tender requires little description. The framing is usually
in all respects identical with that of the engine. In certain cases,
indeed, the tender- wheels axles and axle boxes are interchange-
able with the small or carrying wheels of the locomotive. The
after part of a tender is a water tank of thin plate steel, which
is strengthened by vertical cross ** wash " plates which do not of
course reach to the bottom. They are intended to prevent the
surging of the water in the tank when the train is in motion.
The first effect of starting would, for example, be to carry all the
water to the back of the tender for the moment, and when
stopping it would all rush forward. In front of the tank is the
coal bunker. Much diversity of design is to be found in tenders.
A long, low tender carried on six wheels may be made very
handsome, but its capacity is limited. It possesses the great
advantage that, should the fireman have to go back along the
top to bring coal forward, his head will not strike a bridge.
Fatal accidents have occurred in this way. As a rule the springs
are in the present day always put outside the frames. At one
time they were often placed inside, or the frames were made
double and the springs put between them. The objection is that
a spring may be broken without the knowledge of the driver, or
any one else, and that to replace a spring, or an axle box, the
whole tender having to be lifted, is by no means easy. The
dimensions of the tender are partially settled by that of the
engine. A normal tender carries 4,000 gallons of water and
about five tons of coal. The water occupies 640 cubic feet and
weighs 17| tons. If the engine uses 40 gallons to the mile, then
4,000 gallons will sufl&ce for 100 miles. Coal varies in density.
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2n4 THE RAILWAY LOCOMOTIVE
On a tender a ton will occupy about 45 cubic feet. Tbe bunker
capacity for five tons will therefore be about 225 cubic feet.
The breadth of a tender is limited, as is that of all rolling
stock on British railways, by the width of tunnels and the posi-
tion of station platforms. The length again is limited in another
way, namely, by the diameter of turntables. The wheel base of
the engine and tender together must not exceed about 50 feet.
It is true that at some important termini the diameter of turn-
tables has been augmented. But, as a rule, when more water
and coal have to be carried than the quantities stated the
tender is made high. Examples of this may be seen in the
very large tenders in use for the express traflSc of the London
and South Western Eailway, which are carried each on two
four-wheeled bogies. In the United States enormous tenders
are required by the monster engines employed in the heavy
freight traflSc. As much as ten tons of coal are carried in some
cases.
It is clear that to haul about the country a forty-ton tender is
not an economical thing to do. Furthermore, we have seen that
a run of 100 miles is the limiting distance that can be got out of
4,000 gallons of water. But runs of considerably over twice this
distance are now common. To accomplish these, the tenders
pick up water as they run. This method of replenishing tenders
was invented by Mr. Eamsbottom in 1857, and first used on the
London and North Western Railway. Various other railways
use the Ramsbottom system, modifications being introduced, but
merely in details. The system has been more fully carried out
on the London and North Western Railway perhaps than on any
other. It has certainly been in use for some years, and attention
may therefore be confined to that line.
A number of narrow troughs have been laid down between the
rails at convenient places along the main lines, which by an auto-
matic arrangement are kept continually filled with water, and
from these water is picked up by the engines as they pass over
by means of a scoop attached to the tender. By this arrange-
ment a train is enabled to run from one end of the line to the
other without a stop, as was done on Sunday, September 8th,
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TENDERS
265
1895, when a train left Euston at 8.45 a.m. and ran right to
Carlisle without a stop.
Another advantage is that a smaller tender can be used than
would otherwise be required, and consequently less dead weight.
The troughs and '* pick-up" were, as has been said, first intro-
duced by Mr. Eamsbottom in 1857, and since then troughs have
Fig. 84.— Pick-up apparatus, London and North Western Railway.
been laid down at thirteen different places on the main lines.
The troughs (which are 18 inches wide by 6 inches deep) are usually
560 yards long, and at each end, for a length of 180 feet, they are
gradually reduced in depth, the bottom of the trough running
out at an inclination of 1 in 360, both ends being open. The
rails also dip down at the same inclination as the troughs, so that
by this arrangement an engine passing over the line will, on
arriving at either of the gradients, be gradually lowered until the
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266 THE RAH^WAY LOCOMOTIVE
mouth of its dip pipe is fairly within the trough, but not in con-
tact with the bottom. On approaching the other end of the
trough, the reverse action takes place, the engine ascends the
gradient and gradually withdraws the dip pipe, if this has not
previously been done by the driver when the tanks are filled.
The pick-up apparatus, fully illustrated by the engraving.
Fig. 84, is fixed to the under side of the tender, and consists of
a dip pipe, the upper end of which is secured to the bottom of
the tank. To its lower end is attached a scoop, pivoted at its
sides to the dip pipe, its mouth being curved forward so as to
meet the water when lowered into the troughs between the rails.
On the end of the pivot on which the scoop turns a lever is
fixed, which is connected by a rod to the engine footplate. The
normal position of the scoop is horizontal, with its mouth clear
of the troughs and ballast, and when it is necessary to pick up
water, on approaching the troughs, the driver, by pulling the rod
mentioned above, turns the scoop so that its mouth is lowered
below the level of the water in the troughs, which it scoops up
and delivers into the tender tank. As soon as there is sufficient
water in the tank, the driver pushes back the rod to its former
position, lifting the mouth of the scoop out of the water. Inside
the tender tank, and immediately above the dip pipe, another
pipe is fixed, which forms a continuation of the dip pipe. The
top of this pipe is continued above the highest water level, and
is then bent or curved downwards so that the water after passing
up the dip pipe is directed into the tank. The principle of the
pick-up consists of taking advantage of the height to which
water rises in a tube when a given velocity is imparted to it in
entering the bottom of the tube, the converse operation being
carried out in this case — the water being stationary and the tube
moving through it. On the London and North Western Eailway
the scoop is raised and lowered by a double- threaded screw on
the tender. On other lines a piston in a cylinder worked by
compressed air from the continuous brake is emploj^ed. Others
use a small steam cylinder.
The work of refilling a tender tank is done at a pace which is
not easy to realise. Taking the length of the trough at 1,680 feet
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TENDERS 267
and the speed of the train 60 miles an hour, or 88 feet per
second, the length of the trough will be travelled in 20 seconds.
In this short time ten or twelve tons of water will be lifted into
the tender. Indeed, unless the fireman is on the alert to raise
the scoop, the whole tender and footplate may be flooded in a
cataract of water. This took place once, and the firing shovel
was washed off the footplate. How steam was kept up with
genuine hand-firing until a station was reached where a shovel
could be got is not recorded. The following list of the sixteen
troughs on the London and North Western Eailway will probably
interest the reader.
List of Water Troughs on the London and North
Western Eailway.
Between Pinner and Bushey.
„ Wolverton and Castle thorpe.
„ Rugby and Brinklow.
„ Tamworth and Lichfield.
,, Whitmore and Madeley.
,, Preston Brook and Moore.
„ Brock and Garstang.
„ Hestbank and Bolton-le-Sands.
„ Low Gill and Tebay.
„ Waverton and Chester.
„ Connah's Quay and Flint.
„ Prestatyn and Rhyl.
„ Llanfairfechan and Aber.
„ Diggle and Marsden.
„ Eccles and Weaste.
„ Halebank and Speke.
It is by no means necessary that the speed of the train should
be 60 miles an hour. Indeed, much better results are got at
lower speeds, the water being less splashed about. The water
will rise to any height, provided the scoop moves at a velocity
somewhat in excess of eight times the square root of the height.
Roughly speaking, the water has to be lifted about 9 feet ; the
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268 THE RAH^WAY LOCOMOTIVE
square root of 9 is 3, and 3 X 8 = 24 feet per second as the
velocity which the water would attain if it fell 9 feet. Now 24 feet
per second is only 16*8 miles an hour ; at 60 miles an hour the
water would be lifted over 120 feet, and is, indeed, projected into
the tanks with almost as much violence as though it fell from
that height. The adoption of the trough system, excellent as it
is, has been very slow. There are drawbacks to it. A very large
number of trains — even fast expresses — do not run more than
100 miles without a stop. The troughs are expensive to lay down,
and the line must be dead level and quite straight where they are
placed. But the strongest objection to them is that in winter
they must be kept clear of ice by platelayers who drag a small
plough along the trough. The under bodies of the coach at the
leading end of the train are splashed. The water freezes and the
vacuum pipes of the brake are coated with ice, become stiff, and
disconnect, stopping the train. On other lines the brake gear is
sometimes held fast by ice and is inoperative. But we seldom
have frosts sufficiently severe to give much trouble, and for long
runs the scoop is of course indispensable.
As a considerable saving of fuel may be attained by heating
the feed water, and the steaming power of the boiler is for some
ill- understood reason augmented more than theory denotes, a
pipe is always carried from the boiler to the tender. Through
this steam can be passed into the tender tank when the engine is
standing in a station or terminus, instead of being blown off to
waste through the safety valves. But, as has been sliown, the
temperature at which an injector will feed is comparatively low,
and the heating of the water must not be pushed too far; besides,
steam is not available for heating the water when the engine is
running.
More than twenty years ago Mr. Stroudley carried a part of
the exhaust steam back to the tender, and so raised the tempera-
ture of the feed water. The whole of the steam was thus treated
in the tank engines working the Metropolitan Eailway at a much
earlier date, not to heat the feed, indeed, but prevent the dis-
charge of steam into the tunnel. There are objections to the
putting of exhaust steam direct into the water. It is apt to carry
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TENDERS
269
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270 THE RAILWAY LOCOMOTIVE
grease with it, which is bad for a boiler and may set up priming.
For some time past Mr. Drummond has had in use with great
success the water-heating arrangement shown in Fig. 85. Under
the main tank is a subsidiary tank, through which the water must
pass on its way to the feed pump or injector. In this subsidiary
tank are sixty-four tubea, through which a portion of the exhaust
steam is passed. It is condensed, and the resulting water drains
away to the ground. The feed water is considerably raised in
temperature. The whole arrangement is very simple and inex-
pensive, and gives no trouble ; the temperature of the water is,
however, too high to permit the use of an injector, and a duplex
donkey pump is employed to feed the boiler. The net saving in
coal averages about 13 per cent., but the major advc^ntage is no
doubt found in the fact that the life of the fire-box is prolonged,
and the actual steaming power of the boiler is augmented to a
degree theoretically out of proportion to the rise in temperature
of the feed.
The connection between the tender and the engine has been
made the subject of a good deal of invention. Usually there
is one centre drawbar and two auxiliary bars. They pull on
india-rubber spring cushions fixed in a heavy frame under the
footplate ; the water is led from the tender to the injector through
an india-rubber hose pipe at each side of the engine. The flow
of water is controlled by two simple stop cocks, the handles of
which are placed one at each side on the wings of the coal bunker,
where they are under the fireman's hand.
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CHAPTER XXXVII
TANK ENGINES
Locomotive engines, however much alike in their general
characteristics, are divided into two distinct classes, according
as their supplies of coal and water are or are not carried in a
separate vehicle. That is to say, we have tender engines and
tank engines. The former are used for long distance and the
latter for short distance work. Obviously the quantities of fuel
and water needed on suburban lines are much less than those
needed for long runs. Furthermore, the tank engine being much
shorter than an engine and tender, valuable space is saved, and
as the tank engine runs equally well backwards or forwards no
turntables are needed, and a great saving in time is effected.
There are two varieties of tank engine ; in one the water is
carried in a saddle on top of the boiler, which holds 500 or 600
gallons. Locomotives of this kind are much used for shunting
and yard work. They are usually small, and need not be con-
sidered here. On page 272 is given a photograph of a colli-
sion which took place at Bina, a station on the Great Indian
Peninsula Eailway, at night in February, 1907. A mail train
ran into a shunting train ; both drivers and one fireman were
killed. The photograph is interesting because it shows very
clearly the extraordinary way in which railway vehicles of all
kinds tend to mount over each other in collisions. The saddle
tank of the shunting engine is very clearly seen.
The tank engines of importance are those which carry their
water in rectangular tanks at each side of the boiler, and some-
times a third tank is placed under the footplate and coal bunker.
They are, of course, all united by a tube or tubes. The tanks
generally hold about 1,000 gallons. They are often double, that
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272
THE EAILWAY LOCOMOTIVE
is to say, the inner tank portion is fitted with an ornamental
casing. Engines of this kind are largely used for working
suburban traffic. They have gradually augmented in dimensions
until some of them are exceedingly powerful, handsome engines.
They have small driving wheels, often six-coupled, the great
object in view being rapid acceleration, so that they can get away
with their loads from stations very quickly. They are seldom
Collision at Bina, Great Indian Peninsula Eailway.
required to run faster than thirty miles an hour; It has been
proposed to construct tank engines with large driving wheels and
to supply them with water by scoops in order to save the haulage
of a tender, but the proposal came to nothing.
Tank engines in the present day are more often fitted with
traversing leading or trailing axles than with bogies. At one
period all large tank engines had bogies at either one end or the
other. In the general details of the construction they conform
closely to tender engines, except that, as has been said, they
almost invariably have wheels under 6 feet in diameter.
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TANK ENGINES 273
The question of acceleration mentioned above is one of the
utmost importance in working suburban and metropolitan traffic.
To it is mainly due the substitution of electricity for steam in
cases like the Liverpool and Southport line, where ventilation
had nothing to do with the matter. Time saving in the case
of suburban and metropolitan traffic is of the utmost import-
ance. On the Great Eastern Eailway Mr. Holden appears to
have done all that can be done with steam. Travelling inspectors
took a record of the average time occupied at a platform from
stop to start. Over 30,000 observations were made. The average
obtained was 27*5 seconds. To consider the question in all its
bearings, its influence upon gradients, as determining when it is
and is not economically right to flatten a gradient, and so on,
would be impossible here, and indeed somewhat beyond the scope
of this book. It is worth while, however, to give an accelerating
formula used by railway men in the United States.
The resistance due to acceleration energy of retardation is
equal to 70 (Vi^ — ¥2^ -7- D, in which Vi and V2 represent the
initial and the terminal velocities in miles per hour, and D
equals the distance in feet travelled in accelerating or retarding
the velocity.
The distance travelled in accelerating or retarding speeds
from mile to mile is obtained by transposing the equation for
resistance due to acceleration.
Feet distance travelled = 70 (Vi^ — ¥2^) -fr E, where E equals
the difference per ton between power of engine and resistance of
train, as already explained. Whenever the difiference per ton is
positive, i.e, when the drawbar pull is in excess of train resist-
ance, the distance travelled, obtained by the formula, will
represent distances travelled in acceleration, while, when it is
negative, the distances will be those in retardation of velocity.^
A word of explanation is desirable here to render the curious
experiment illustrated by Figs. 86 and 87 intelligible. In every
body, no matter what its shape is, there is a point called the centre
1 For further information the reader is referred to a paper by Mr.
A. K. ShurtlefP, in the Bulletin of the American Eailway Engineering and
Maintenance of Way Association for November, 1907.
R.L. T
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274
TIIE RAILWAY T.OCOMOTITE
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TANK ENGINES
275
of gravity, such that if the body be suspended from this point it
will remain in equilibrium indifferently in any position ; and if
Fig. 87. — Finding the centre of gravity of a tank engine.
the body be suspended from any other point, then it will be in
equilibrium when the centre of gravity is directly under the
point of suspension, and any vertical line drawn from any other
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276 THE RAILWAY LOCOMOTIVE
point of suspension will pass through the centre of gravity. If,
for example, an irregular figure is cut out in cardboard and freely
suspended from any point, behind a plumb line, then a line can
be drawn along the card with a pencil coincident with the string.
Next let the card be freely suspended from any other point in it
as before, and a second pencil line be drawn upon it coincident
with the string, The second pencil line will intersect the first
pencil line, and the point of intersection is the centre of gravity.
And it matters nothing how often the operation is repeated, the
pencil lines will all intersect in the same place.
As it is not always feasible to hang up heavy bodies to get
their centre of gravity, recourse is had to calculation. The
weights of different parts are taken, and their moments, that is
to say their leverages round an assumed point, are taken, and in
this way the centre of gravity is obtained. The influence of the
position of this point on the behaviour of an engine on the road
has already been fully considered in Section I.
In 1905 Mr. Aspinall made the experiment illustrated. He
suspended one of his large radial tank engines, in working
order, with coal and water, from the traversing crane in one of
the Horwich shops of the Lancashire and Yorkshire Eailway.
Two points of suspension were selected. On the back of the
tank are shown three vertical lines drawn by the aid of a plumb
line. They intersect, it will be seen, and the point of inter-
section gives the vertical height of the centre of gravity above
the rails. Calculations which were previously made gave the
height as 4 feet 10 inches, and the actual experiment gave it as
4 feet 11|^ inches, a very close approximation. The great
height of the modern big boiler engine deceives the eye. Thus
an engine with a boiler standing 8 feet 11 inches above the rails
will have a centre of gravity only 5 feet 6 inches above them.
The ordinary observer is apt to forget that little more than
half the boiler barrel is filled with water, and that the upper half
therefore contributes very little weight to the whole structure.
These large engines run with very much greater smoothness
than is possible with an engine whose centre of gravity is very
low down, for reasons already set forth.
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TANK ENGINES 277
In the first section of this book the subject of deraihnent has
been treated on general principles, and no reference has been
made to the relative safety of the two types of engine, tender and
tank, for it appeared that this question would be best postponed
until the tank engine came up for consideration. This, then,
seems the propei* place to mention a discussion which took
place some years ago between locomotive superintendents and
Board of Trade inspectors. These gentlemen assumed that the
tank engine must be more liable to derailment than a tender
engine. Mr. Aspinall determined to ascertain from statistics
whether this was or was not true, and he had information
collected from the Board of Trade returns. These were in a
sense private, and the author is indebted to Mr. Aspinall for per-
mission to make the facts public here for the first time, in the
shape of the following memorandum : —
Memorandum, re Derailments of Passenger Tank Engines.
The diagram has been prepared for the purpose of illustrating
the reports made by the various Board of Trade inspectors upon
all classes of tank engines and all classes of tender engines which
have been derailed during the twenty years ending December 31,
1904, as stated in the return made to both Houses of Parliament,
entitled ** Eeturn of Cases of Derailment of Engines of Passenger
Trains during the twenty years ending 31st December, 1904,
divided into (1) Tank Engines, and (2) Tender Engines, show-
ing in each case the date, place of accident and railway, and the
class of engine " ; signed by Sir Francis Hopwood, and dated
Board of Trade, May 24, 1905. All the facts and figures are
takes from the above official return.
This diagram. Figs. 88 and 89, is divided into nine parts, which
are numbered 1 to 9.
Diagram No. 1. — This gives small diagrams showing how each
type of tender engine reported upon is arranged so far as wheels
are concerned, and what class of tender was hauled behind the
engine.
Diagram No. 2 gives similar information with regard to the
wheel arrangements of the several types of tank engines.
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278
THE RAILWAY LOCOMOTIVE
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280 THE RAILWAY LOCOMOTIVE
Diagram No. 3 shows by means of a black line that the number
of locomotives which were possessed by the different railway
companies had increased from 15,196 in the year 1885 to 22,443
in 1904 ; and it also shows the number of tender engines which
were derailed in each year by means of a dotted line, and the
number of tank engine derailments by means of a heavy line. For
example, it will be observed from this diagram that there were
two tender engines derailed in 1885 and four tank engines
derailed in 1885, but only two of the latter in 1904. This
diagram does not point to there being any greater tendency for
a tank to become derailed than for a tender engine.
Diagram No. 4 is divided into two parts, and shows by the
height of columns either lined or hatched the number of derail-
ments of tender engines on the left-hand side, and of tank
engines on the right-hand side, and enables the different classes
to be picked out by reference to diagrams 1 and 2, where the
letters ** A," " B,'* " C," etc., are applied to each type of engine.
For instance, with tender engines of class ** C,'' with a leading
bogie, sixteen are shown to have left the road by the column
which stands over the letter **C"; in like manner, with tank
engines twelve are shown to have left the road by the column
over the letter " A.'' Those who are familiar with th6 very large
amount of work done upon English railways by tender engines
of class **C" and tank engines of class " A" will recognise that
it is only reasonable to expect that as these classes of engines are
employed most largely, so the number of derailments will be greater
than in exceptional classes, where only few engines are employed.
The same remarks would apply to tender engines of the ** I "
class and tank engines of ** L " class.
Diagram No. 5 shows that there have been ten cases in which
the tender alone has been derailed.
Diagram No. 6 shows how many tender engines of the classes
** A," *'B," "C," etc., were derailed in each year.
Diagram No. 7 gives details of the number of tank engines
derailed in each year.
Diagram No. 8 shows the total number of derailments during
the twenty years ending December, 1904.
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TANK ENGINES
281
Diagram No, 9 shows the reasons which were given by the
different Board of Trade inspectors as to why, in their opinion,
the different classes of engine left the road. It will be observed
by looking at this diagram that there were as many as sixteen
cases of tender engines and eleven cases of tank engines which
are said to have left the road for reasons connected with defective
permanent way, including cases where points have been held over
by stones ; there is also one case with a tender engine, and one
case with a tank engine, where oscillation is stated to have been
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J *"5 S T A StiSBi ^ J * f t 7 3 9'9Sfl ,
Engine Derailments.
caused by defective permanent way, but there is not a single case
where oscillation is said to have been caused by high speed.
The general effect of these diagrams is to show in the most
conclusive way that derailments upon which the Board of Trade
have considered it necessary to make a report during a period of
twenty years became few in number, and that there is nothing
whatever, when a close examination of the reports is made, to
indicate that there is any greater danger with a tank engine than
wath a tender engine. On several of the largest railways in this
country it has been found that no less than 50 per cent, of their
total locomotive stock are tank engines, and that they run a large
percentage of their high-speed passenger mileage, amounting in
one case to 54 per cent., with engines of this class.
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CHAPTER XXXVIII
LUBRICATION
It goes without saying that all rubbing surfaces in a loco-
motive engine must be well oiled. Various methods of lubrication
are employed. The first and most simple consists in screwing
on to the part to be lubricated a brass oil cup. Through the
bottom of the cup descends a small brass tube, which rises nearly
to the lid. Two or three strands of worsted, such as coarse
stockings are made of, are put down the brass pipe like a wick.
A bit of thin copper wire is twisted in with them and hooked
over at the top end so as to prevent the wick falling down. It
acts as a syphon, and delivers the oil from the box drop by drop
until it is all gone. Sharp Brothers & Co., of the Atlas
Works, Manchester, introduced nearly sixty years ago a very
elegant system of lubrication. A long brass box was screwed at
each side to the boiler near the smoke-box. From the bottom of
the box six or eight small copper pipes were led to the slide bars,
valve gear, &c. The pipes passed up through the bottom of the
box and each was ** trimmed " with a wick in the way just
described. The box would hold a quart or more of oil. A stop
cock Nvas fitted to each leading pipe under the box, by which the
quantity of oil distributed to each bearing was regulated. When
a trip was over, or the engine had some time to stand, the fire-
man went out round the engine on the running board and closed
all the cocks, thus effecting a great saving in oil. A precisely
similar arrangement is used in torpedo boats and indeed on
very many high-speed engines.
These methods are not applicable to what may be termed
internal lubrication, as, for example, the working faces of slide
valves. To the late Mr. Ramsbottom the world is indebted for
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LDBEICATION
283
the first automatic arrangement for oiling valve chests. Fig. 90
shows the lubricator in diagram section. It consists of a strong
brass vessel A, which can be screwed to the outside of the smoke-
box B. A pipe C from the valve chest, fitted with a three-way
stop cock, comes up through the bottom and reaches nearly to
the top of the lubricator. E is a small brass funnel provided
with a steamtight screwed plug. Nothing can be simpler. To
use it the three-way cock is turned one quarter round, until the
passage G is vertical. The contents of A will then be dis-
charged at H. The plug at E is then removed, and the cock D
turned until all the passages are blinded. The
lubricator is then filled with oil up to such a
point that it will just not run down the inner
pipe. The filling plug is then replaced and
the cock D is restored to the position shown
in the diagram. As soon as steam is turned
into the valve chest, it will also pass through
the lubricating pipe into the lubricator, filling
the small empty space I. It will there con-
dense, and the heavy water sinking down
through the hght oil will displace the oil,
which floats on it and overflows down through
the steam cock and pipe G and so into the
valve chest. The process is gradual, and by
degrees all the oil is displaced, and the lubri-
cator filled with water. Then the steam cock is shut off and the
drain cock opened. The water is run out, and the lubricator
refilled with oil.
Ingenious and effective as this device is, it is very defective in
certain ways. The rate of discharge from it depends largely on
that at which steam condenses, and as there is no means of
knowing when the oil is gone, without blowing the water
out of it, it sometimes happens that all the oil disappears
a great deal too soon. If the steam cock is partly closed to
prevent this, then the oil may not go quickly enough to the
rubbing surface. In modern engines, particularly those running
long distances, oil is supplied by what are called sight feed
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284 THE RAILWAY LOCOMOTIVE
lubricators, which are fixed in the cab under the driver's eye.
Short lengths of glass tube are full of water, up through which
the drops of oil may be seen rising. There are, perhaps, fifty
sight feed lubricators in the market, but they all depend for
their action on either of two general principles. Either the oil
is supplied under pressure by a small pump, or else the oil moves
by displacement, as in the Eamsbottom lubricator just described.
Small copper pipes lead the oil to the places where it is wanted.
An exception is supplied by big ends and crank pins, which are
always lubricated by hand. They are fitted with large oil boxes.
The wick is, however, no longer a syphon, but a plug of worsted
loosely coiled into a double copper wire and pushed into the pipe.
In these rapidly moving parts, the oil would be jerked down the
pipe, and the box emptied in a few minutes, if it were not
checked by the worsted plug.
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CHAPTEE XXXIX
BRAKES
All locomotives in the present day are fitted with automatic
brakes. These are rather complex systems of mechanism,
and nothing more can be given here than a general description
of them.
Up to about the year 1875 almost nothing had been done
to improve on the very elementary screw brake on the tender
and in the guards' vans, by which segments of wood were
pressed against the tires to stop the train. These were very in-
efi&cient, and involved the expenditure of much labour on the part
of the fireman and the guards. Besides the risk involved there
was the serious delay incurred. Steam had to be shut off a
couple of miles outside a station, and the train brought gradually
to rest. Traffic involving frequent stops could not be conducted
rapidly, because a train had scarcely got up speed before steam
had to be shut off and the brakes applied. Many inventors
attempted to produce something better than the screw brake,
but the only successful attempt was that of Messrs. Newall and
Fay. They put under the carriages a long shaft fitted with
screws, which applied brake blocks to the wheels, and they
coupled these rods end to end between the vehicles by a very
simple universal joint. The effect was that the guard, instead
of braking four wheels, only could brake a dozen. The invention
was used with some success on the Midland Eailway for several
years.
To George Westinghouse, a young American engineer, is due
the credit of first getting the Board of Trade and the Eailway
Companies to interest themselves in brakes. In 1875 a good
deal of money was spent, and a most important trial of various
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286 THE RAILWAY LOCOMOTIVE
systems took place at Newark, under the presidency of the Duke
of Buckingham. From this trial may be dated the ultimate
adoption of the two systems in use to-day. The first is the
pressure system, invented by Mr. Westinghouse, the second is
the vacuum system, invented by Mr. Smith. The general
principle is the same in both. A pipe extends from one end of
the train to the other. Under the coaches this pipe is of iron,
between them it is of india-rubber ; each coach has its own length
of hose, and these are coupled, when the train is made up, by a
highly ingenious joint.
Under each coach are placed cylinders and pistons, the rods of
which work cast iron brake blocks fitted to all the wheels.
Taking the Westinghouse brake first, the brakes are
nolmally kept away from the wheels by springs. Under each
coach is a small reservoir of air compressed by a pump on the
engine, in a large drum, to a pressure of about 100 lbs. So long
as there is an equal pressure in the train pipe and the reservoirs
the brakes remain off. But each cylinder is fitted with what is
known as the " triple valve." If now the pressure in the train
pipe is reduced, by allowing air to escape from it, the triple valve
moves at once and admits air from tlie small reservoirs to the
brake cylinders. The pressure instantly applies the brake. If
the train were to part in two, or an accident happened, the hose
joint between the coaches would give way, the air would run out of
the train pipe, and the brakes would be applied automatically.
In regular work the driver is provided with a valve on the foot-
plate by opening which he can permit the air to escape gradually
from the train pipe. The triple valve will then move very
slowly, and the pressure with which the brakes are applied can
be regulated with minute accuracy. To take the brakes off, the
train pipe is replenished from the main reservoir, which is in
turn filled up again by the pump.
The vacuum brake is in all but details identical. Only the
air in the train pij^e and reservoirs is exhausted by an
ejector on the engine, which works on the same principle as the
blast pipe.^ A vacuum is maintained on both sides of a piston,
* See page 151.
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BKAKES 287
the rod of which is connected with the brakes. If now air is
admitted to the train pipe, a valve moves and air gets into the
cylinder, and pressing with a force of 15 lbs, on the square inch
at one side, while it is only resisted by a comparatively small
pressure at the other side, the brakes are put on. The action
is controlled from the footplate by a valve as already described.
Both systems have been made the subject of many patents.
In some cases the vacuum is maintained by a pump worked off
a cross head or some other part of the engine. It has been found
impossible to prevent leakage altogether ; at first all engines
were provided with a large and a small ejector. The large one
established the vacuum, and the small one maintained it. After
a time, however, it was found that the small ejector wasted much
steam, and the pump was substituted with quite satisfactory
results.
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CHAPTER XL
THE RUNNING SHED
Under this comprehensive title will be considered what may
without inexactitude l>e termed the hidden life of the locomotive
engine. It is not always drawing trains, it is not always being
repaired or repainted. As a horse spends much of his time in
the stable, so does the locomotive in the running shed, which
has, indeed, not inaptly, been termed a stable ere now.
Originally there was provided a shed, literally a shed and
nothing more, in which the engines stood when not at work, and
in which they were cleaned and had small repairs efifected. For
many years and in the present day, a running shed is a large
and important building, often provided with tools, and in which all
but very heavy repairs can be effected. Turntables are arranged
and many lines of rail with pits between to enable men to work
conveniently under the locomotives.
There are various methods of laying out a running shed, which,
by the way, is called a " round house '* in the United States.
Thus the general plan may be circular with a turntable in the
middle, from which radiate lines of rail like the spokes of a wheel.
When an engine comes in it is run on to the turntable, which is
rotated until its rails coincide with a ** spoke " on which there is
room. The engine is then run off the turntable on to the spoke.
The arrangement is very convenient, but has the serious draw-
back that if anything fouls the turntable all the locomotives in
the shed are imprisoned for the time being — an accident by no
means unknown, and commonly brought about by moving an
engine when the rails on the table are not in line with those of
the spoke. Then the leading wheels of the engine drop into the
turntable pit. A much safer system consists in providing a
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THE RUNNING SHED 289
number of bays and shunting an engine into any bay by means
of points. More space is required, but the gain fully compensates
for the extra cost incurred.
The running sheds are placed in localities as convenient as
can be got near large towns. They vary in the amount of
accommodation they supply from holding half a dozen to a
hundred engines.
On the care and skill with which the duties of the running-
shed foremen and the hands under them are carried out depends
in very large measure the satisfactory and economical working
of the trafi&c of a railway. To mention only one point, the
durability of a boiler is settled in the main by the way in
which it is cleaned. If that is badly done, the boiler will steam
badly, use more coal than it ought, and fail to keep time.
Let us take the case of an express engine, which has finished
its work for the day. It is unhooked from its train, and taken
to the running shed. The duty of the driver before handing
it over to the " engine turner," a man whose position resembles
til at of an ostler, is to examine the engine carefully and book all
the defects he discovers. The turner then moves the engine to
the coaling stage, the fireman locks up his tool chest and chalks
on one of the boxes how much coal he requires for his next trip.
The engine is, save under most exceptional circumstances, to be
brought to the end of its journey with little or no fire on the
grate. After the tender has received the stated number of tons
of coal, the engine is moved to another part of the yard, and the
smoke-box is cleaned out. As has already been explained, the
box is floored with fire-bricks laid in fire-clay, and on this will be
found collected ash and cinders which have been carried through
the flues. A spray from a hydrant is used to keep down dust, and
the box is cleared out by a lad with a shovel and broom. The
engine, which has still steam in it, is then moved once more to
stand over a pit, where two *' fire droppers," one on the footplate
and the other under the engine, take charge. Then some fire
bars are lifted out, and through the space thus left, ash, cinders
and clinkers are dropped into the ash pan by the man on the
footplate, while his mate below rakes them out into the pit where
R.L. u
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290 THE RAn.WAY LOCOMOTrV^E
they are sprayed by a hose pipe. In this operation, simple as it
seems to be, we have another illustration of the importance of
doing things in the right way. It seems quite obvious that it
would be far better to make the grate invariably — as is done
sometimes — with a hinged portion at the front end to which the
bars always slope, rather than adopt the clumsy system of
pulling two or three or more bars out. But the drop grate
system has the great defect that if it is used while the boiler is
still hot, and a rush of cold air into the fire-box takes place,
contraction occurs and the tubes leak. Indeed, in some running
sheds, fire dropping is not permitted while a boiler is hot, and
the grate has to be cleaned through the fire door; but the
operation lasts about half an hour, and the time is not always
available. The tubes are then " run *' — that is, swept out. A
long rod about f inch diameter with an eye at the end is used.
Through the eye is threaded a strip of canvas or old ** waste.'*
The smoke-box door is opened and a man standing on the front
running board pushes the rod through one tube after another.
In this way the tubes are swept. The operation lasts from forty
minutes to an hour, according to the number of tubes. A steam
jet at the end of a hose has been tried with great success, much
time being saved.
The cleaners then take the engine in hand. It is rubbed
down with sponge cloths and ** cleaning oil," that is, petroleum.
The cleaners are boys or lads. Cleaning is the first step on the
way to be an engine driver.
Bound the ends of the tubes next the fire-box rings of coke
deposit (due to the presence of minute percentages of iron in the
coal) form and encroach on the size of the orifice. A boy goes
into the fire-box with a stiff broom and knocks off the ** corks," as
they are called — they are termed " birds* nests ** at sea ; they very
closely resemble india-rubber umbrella rings. He then sweeps the
ashes off the top of the brick arch, and replaces the fire-bars. The
engine is then ready to have steam got up again. The ** lighter-up"
puts coal into the box, spreading it carefully all round the sides.
Conveniently situated is a brick furnace of considerable size.
On the top of this sand is dried which is subsequently put into
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THE KUNNING SHED 291
the sand boxes on the engine and used for increasing adhesion, as
already explained. On the Great Western Bail way an improved
furnace is used. The wet sand is put into a chamber with a
grated bottom over the horizontal flue leading to the chimney,
and as the sand dries it falls automatically through the hot gas
and flame. About five times as much sand can be dried in a
given time in this way as by the ordinary furnace.
From this furnace some shovelfuls of burning coal are carried
and put into the fire-box, and so lighting up is effected. As the
fires are not to be hurried, which would be bad for the boilers,
it requires about three hours to get up steam ; and the fire is
usually lighted about four hours before the time at which the
train starts. While in the shed the fireman takes in water and
fills the sand boxes. The driver goes over the whole engine with
minute care, examining every split pin, nut and bolt, knowing,
as he does, that his own life and the safety of the train depend
upon his vigilance.
It has been assumed that the engine requires neither washing
out nor repairs. But washing out must take place every five or
six days. To this end, the engine is allowed to cool down, then
the plugs at the lower corners of the fire-box are unscrewed, and
the water is allowed to run out. All the other wash-out plugs
are removed, and the boiler is then cleaned out by the use of
a jet, by preference of hot water, the nozzle being put into one
plug hole after another. While one man uses the hose, another
works with a rod to scoop out and loosen all the deposit he can get
at. The boiler is then examined, preferably by a boilermaker.
If he pronounces it clean the plugs are oiled with some heavy
oil and screwed in again. The boiler is filled up with fresh water
by a hose through one of the upper plug holes. Washing out is
a very important operation. A book is kept in which are
entered under separate heads, date, station, number of engine,
name of washer, by whom examined, and remarks as to dirt.
When tubes leak, neglect in washing out is always assumed as a
probable cause.
While in the running sheds that careful inspection takes place
which renders the explosion of a locomotive boiler an event of
u2
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292 THE BAILWAY LOCOMOTIVE
the rarest occurrence. Practice varies, but it is not far from the
truth to say that more than a month seldom elapses without an
examination of a very thorough character being made by a boiler-
smith. As a rule there is little trouble with the shells ; grooving
and corrosion are rare, and are detected when the lagging is
taken off and tubes drawn for a thorough repair, which will not
be needed as a rule for three or four years. But the fire-box is
a continual source of anxiety. The wear and tear have been
much increased by the rise in pressure. Boxes which give little
or no trouble with 150 lbs. steam require the utmost vigilance
to make them endure 200 or 220 lbs. pressure. The higher the
pressure the denser becomes the deposit and the more firmly
does it cling to the plates. A fairly soft water is essential to
the well-being of the modern locomotive. The most common
defects in a copper internal fire-box are cracks. The examiner
has a special book in which he records in a species of shorthand
all the defects which he finds. A great deal of information is
got into a small space by a system of hieroglyphics. As an
example of the progress of events in the life of a locomotive
boiler, the following statement is given : —
" Nothing of note occurred to the box during that year, but on
January 13, 1904, the stay heads were slightly reduced. Fifteen
new stays were put in on January 27, 1904. The stays were
reported reduced on April 19, and on May 12 a crack had
developed in the right-hand flange of the tube plate; also, the
top flange of the back plate had dropped down near the second
crown bars. On August 28 the tubes were dirty, and the
casing plates were corroded near the foundation ring. On
August 30, 1904, eighty-four new tubes were put in to replace
those taken out to facilitate the removal of dirt, and this time
also the sides were found to be slightly bulged. Twelve more
stays were put in on April 11, 1905, and on September 12
another crack had developed in the tube plate, this time in the
left-hand flange, and the sides which had been previously reported
as ** slightly bulged *' were reported as ** bulged.'* On October 17,
the tubes were again reported dirty, and after the engine had
been kept running as long as it consistently could be in this
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THE EUNNING SHED 293
condition, it was sent to the factory for general repairs on
January 31, 1906." .
The preceding quotation is taken from a paper read before
the Swindon Engineering Society by Mr. Henry Simpson, of the
Great Western Eailway.
It must, of course, be understood that running-shed work is
not carried on in the same way on all railways. No more can be
done than give the general arrangements and methods adopted.
Thus, for example, on some lines it is the practice to coal the
engines after they have been cleaned and left the running shed,
but in effect practice is the same everywhere.
A locomotive is not cleaned after every trip as described above.
Slag is taken off the grate by the fireman, and the tubes are run
and the smoke-box cleaned out, but steam is not let down below
80 or 100 lbs. pressure, and a fresh supply of coal is, if needed,
put on the tender.
The day's work of an engine is very often worked out as though
it had been running steadily from the time steam was got up
until it returned to the shed. The mileage varies with the
railway, the time of the year, and traffic conditions. At one
time on the London and Brighton line it was four miles an hour
for goods and about eight miles an hour for passenger engines.
A goods engine, for example, will be under steam and out on the
road for say, fourteen hours. Of that time, five hours will be
spent standing still. Two or three hours will be used up at
different stations shunting, the whole distance traversed being
quite small. The rest of the time the engine will spend in
hauling heavy trains at, say, twenty miles an hour.
The average annual mileage of engines in this country is about
20,000. Of course to this there are numerous exceptions, the
mileage being much greater. Individual engines sometimes
make enormous mileages. In the United States it is very much
higher, but as a result the total life of the engine and the number
of miles run is less. The American locomotive is treated very
much on the principle followed by Legree with his slaves, ** use
up and buy more."
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CHAPTEE XLI
THE WORK OF THE LOCOMOTIVE
We have now to consider the work of a locomotive — the duty
which a machine so ingenious, so complex, and so carefully and
cautiously developed has to perform.
In one sense this admits of being very easily stated. The
business in life of the locomotive is to pull. Its value from the
railway companies' point of view is estimated in terms of this
central fact — a fact which must be carefully kept in mind. All
the various devices for securing power and economy have, after
all, no other ultimate object than the securing, other things
being equal, of the greatest possible tractive efifort for the smallest
outlay of money. At first sight it might appear that speed is an
important element in our calculations. It will, however, be seen
presently that speed itself depends on tractive efifort. Once more,
other things being equal, the engine which can pull hardest will
run fastest. Now the drawbar pull will always be precisely
equal to the reaction of the wheels at the points where they rest
on the rails, less the amount required to overcome the rolling or
road resistance of the engine and tender. Deducting this last
we have the net pull on the hook at the back of the tender left
for drawing the train.
The precise way in which the engine is propelled has already
been fully explained on page 66, but this has nothing whatever
to do with the action of the wheel on the rail as a fulcrum. The
wheel continually tries to push the rail backwards, and failing in
this it rolls forward, and with it the engine and train. We have
then, before we can arrive at any just estimate of the hauling
power of a locomotive, to ascertain what this power may be. It
is always calculated by a formula for which the world is indebted
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THE WORK OF THE LOCOMOTIVE 295
to the Chevalier F. M. G. De Pambour, a young French
engineer, who carried out a remarkable series of experiments on
the Liverpool and Manchester Eailway. The results took the
form of a treatise published first in France in 1835. Sub-
sequently an excellent translation was published in English, in
Philadelphia in 1836.
The formula is very simple : —
Let D be the diameter of the driving wheel in inches.
„ d „ diameter of the cylinder in inches.
„ L „ length of stroke.
„ P „ average effective pressure in the cylinder in
pounds per square inch.
Then ^c = T, the tractive effort.
Only one cylinder is to be taken ; usually P is taken as unity.
The result of the calculation is the tractive effort with a cylinder
pressure of one pound, which can be regarded as the coefficient
for the engine. Thus, let T = tractive power.
D = 60; d = 20.
L = 24 and P = 1.
400 V 9,4-
Then T = ^^J^ = 160 lbs. This is the tractive effort at
the points where the driving wheels touch the rails for every
pound of average effective pressure in the cylinders. It is
divided up among the wheels ; if there are two driving wheels,
then it is 80 lbs. each ; if four, 40 lbs. each, and so on.
For compound locomotives, the formula becomes
_ 1-6 P r^ L
D (2 + ly
where T = tractive power, d = diameter of low pressure
cylinder, L = length of stroke, r the ratio of the cylinder volumes,
and D = the diameter of the driving wheels. Normally, a deduc-
tion of 20 per cent, is made in all cases to cover the resistance
of the engine and tender, that is to say, the rolling or road
resistance.
As the formula puzzles the student in some cases, because
only one cylinder is taken although there are two, the following
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296 THE EAILWAY LOCOMOTIVE
passage is reproduced from Pambour's book, which explains how
he obtained it.
** If we find that the steam by causing a known effective
pressure per square inch can make the engine advance, the area
of the two pistons in square inches being known, it is easy to
calculate the total force applied by the steam on those two
pistons. That force being sufficient to make the engine advance
— that is to say, to conquer its resistance — it gives, of course,
the value of that resistance.^ It must only be observed according
to the principle known in Mechanics by the name of ** The
Principle of Virtual Velocities," that the pressure exercised on
the part of an engine being transmitted to another part of the
same engine retains the same intensity only in case the two
parts have the same velocity. If not, the force of pressure is
reduced in an inverse ratio to the velocity of the points of
application. This principle appears in an evident manner, and
a priori in simple machines like the lever, the roll, the pulley,
and an inspection alone is sufficient to demonstrate that, if a
force can by the aid of the machine raise a weight four times
as great as itself, it is only by travelling in the same space of
time four times as far as the weight which it raises. In the case
before us the velocity of the piston is to that of the engine as
twice the stroke is to the circumference of the wheel, the piston
giving two strokes while the wheel turns once round. A force
applied on the piston produces therefore in regard to the progress
of the engine an efifect reduced in the same proportion, that is to
say, as twice the stroke is to the circumference of the wheel.
** Let d be the diameter of the piston, and tt the ratio of the
circumference to the diameter, ^ tt d^ will be the area of one of
the two pistons, and P being the efifectual pressure of the steam per
square inch, then ^ tt d^T? will be the efifective pressure upon the
two pistons. If, moreover, I expresses the length of the stroke,
1 It is worth notice that this appears to be the first recognition of the
fact that there is no such thing as an unbalanced force. Previously, and for
many years subsequently, it was always taken for granted that unless a
force exceeded the resistance there could be no motion; that the resistance
of a train was always less than the pull of the engine, the resistance to a
piston less than the pressure on it.
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THE WOItK OF THE LOCOMOTIVE 297
and D the diameter of the wheel, the efifective force of transfer
resulting to the engine in consequence of that transfer will be
4 ^ ^ P X ^15 ^^ -D~'
which, according to what we have said, gives the measure of the
resistance of the engine."
It must be understood that the word ** resistance " refers here
to the rolling and not to the frictional resistance of the locomotive.
In other words, the equation gives the tractive efifort.
A little thought will sufi&ce to show that there must be some
definite speed which, multiplied by the drawbar pull, will give
maximum efi&ciency. The pull steadily falls off as the speed
increases, because the average effective pressure diminishes,
partly because of wire drawing and partly because the boiler
ca"hnot make enough steam. What this speed will be depends
on various conditions. It is known as the critical speed, and is
in all cases comparatively low. It is impossible to go fully into
the question here. But something must be said in the way of
explanation. Professor Goss's investigations go to show that it
is always about 200 revolutions per minute, no matter what the
size of the driving wheel {vide page 301}.
The question of train resistance has been made the subject of
most elaborate and costly investigation, and even yet it cannot
be said that conclusive results have been obtained. Nothing
more can be done here than give three formulae. The first has
been obtained by Mr, Deeley, on the Midland Eailway :
K = 3-25 + ^^.
The second is by M. Laboriette, a French engineer :
These do not apply to speeds below twenty miles an hour, when
the resistance of tlie axle is higher than at quick speeds. The
following formula of general application to all speeds has been
prepared by Mr. Wolff:
V + 12\
^ - » VV+T/ "•" 300-
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298 THE BAILWAY LOCOMOTIVE
Owing to the great weight and enormous momentum of a
locomotive, it might be supposed that its drawbar pull would be
perfectly steady, but it is not. It will be remembered that not
all the reciprocating motion can be counterpoised, and there are
besides the internal disturbing forces due to the varying crank
moments and piston pressures. On the testing plant at the
St. Louis Exhibition, to which reference has already been made,
the locomotives pulled on a tractometer, which, being fitted with
a recording pencil, gave a diagram of the pull.
Three tractometer diagrams have been selected from a con-
siderable number, and are here given; they are from " Locomotive
AOOO . ,
MJ\AAAArtA/UUVAMA/\AMAaAAAAAAAAAAAA/^A^^^
Draw dor Puf/-^ ^^^^
Datum Line^
T^^t J/J
Doihpotz in Safety '5arz Thrott/ed
Speedy 66,g6 Miltt fur Hour,
Fig. 91.
Tests and Exhibits." Fig. 91 is from a De Glehn compound
four-cylinder engine very similar in all respects to La France,
which attracted much attention when first put to work some
three years ago on the Great Western Eailway. The amount of
the pull in pounds is shown at the right-hand end of the diagram,
which it will be understood is a portion of a continuous trace made
on a strip of paper moving under a pencil. The form of the
trace is somewhat modified by the action of two dash pots
placed at the anchorage. The levelling effect of four cylinders
is manifested. The difference in pulls does not much exceed
about 300 lbs.
The diagram, Fig. 92, is one from a very heavy ** simple '* freight
engine, with eight wheels coupled 53 inch diameter, two cylinders
21 inches X 30 inches. It will be seen that at fifteen miles an
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THE WORK OF THE LOCOMOTIVE 299
hour the maxim pull reached about 22,000 lbs., the difference
in pulls being as much as 1,500 lbs. The third diagram is from
29000-2
MUUUUUjyUUMUyiJMItMI U II^ W^
Drakfbar Pufh
JSOOO-
moo-
dooo-
Datum Ime-^
Te^t aoa
No Da5hpot^ //? Safety Bans
Speedy I4jgg Miles per Hour
Fig. 92.
the same engine at a little under thirty miles an hour ; the
average pull has fallen to 10,000 lbs., but the difference between
the highest and the lowest is now about 2,100 lbs. The causes
Dratrhar Pu/f ^ '. ^
DratrSar Pu/f
5000-
Datum L/ne
^
^
No Doi/ipot^ in <dafetj/ Bam
Speedy 2g,87 Milei per If our.
Fig. 93.
of the vibration have already been explained. It will be under-
stood that each '* saw tooth " stands for one complete revolution
of the driving wheels. The total motion of the draw bar did not
exceed 0-04 inch, so that a locomotive exerting a drawbar pull
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300 TflE RAILWAY LOCOMOTlVfi
equal to the full capacity of the dynamometer^ did not move
forward on the supporting wheels more than this amount. The
motion was increased 200 times at the recording pen, or for each
one hundredth of an inch that the locomotive moved forward
the recording pen moved through a space of two inches, the
total movement being 8 inches for the 0*04 inch movement.
It might be supposed that when the engine is drawing a train
its own momentum would extinguish the vibration, but in point
of fact it does not, and the trace taken in a tractometer van is
very similar in character to that obtained in the test house.
The actual performance of locomotives is very varied. A
complete record of all that has been noteworthy in this country
and in France has been supplied periodically for several years
past to the Engineer by the late Mr. Charles Rous Marten, which
record will be found most interesting reading.
Much is heard now and then about trains making up lost time,
and drivers are censured by the public for incurring risks ; but
as a matter of fact, it is extremely difficult, particularly with fast
trains, to make up lost time. Mr. Ivatt several years ago
prepared a very useful diagram, Fig. 94, which sets this truth in
a very clear light.
As an example, if a train running at sixty-five miles per hour
has lost a minute, it has to run fifteen miles at seventy miles
per hour in order to make up that minute, showing prominently
what a great length of line must be run over in order to make
up even so small an amount of time as one minute.
The diameters of the driving wheels of all but the smallest
locomotives, such as those used by contractors and in engineering
and iron works, vary between 4 feet and 8 feet. Goods engines
have driving wheels as a rule not often less than 4 feet 6 inches
or more than 5 feet 6 inches. Passenger engine driving wheels
are in the present day 5 feet 6 inches to 7 feet 9 inches diameter.
No engines are now being made with 8-feet wheels, but a few
are still running. Very early in the history of railways it came
to be understood that large diameters and speed went together,
* This is the recognised term, but as it may cause confusion the author
prefers to use the word ** tractometer,'* about which no mistake can arise.
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THE WOKK OF THE LOCOMOTIVE
301
1 VATTa
SpBgnPiAgRAH
MtwuTBf fwMit"
to 171 IS 1M IS
Mii^MwHoum
but about the precise reason why no one was troubled. Indeed,
it was not till some ten years ago, when Professor Goss, of
Purdue University, U.S.A., undertook his investigations, that
the facts were reduced to a sound numerical basis.
The steaming power of the boiler is the final measure of that
of the whole machine. It may be taken as proved that a
locomotive boiler may be depended upon to evaporate 12 lbs. of
water per square foot of heating surface per hour. Thus a
boiler with 1,300 square feet
will make 15,600 lbs. of
steam per hour.
Now the dimensions of
cylinders are fixed by con-
ditions which have been fully
explained in preceding pages.
It will be seen at once that
whether the full power of
the boiler is or is not to
be utilised depends on how
many times each cylinder
can be filled and emptied
in a minute. Suppose that
our cylinders are too small,
then let us run the engine
faster. But the speed of the
train is fixed by trafl&c managers. Let us meet this objection
by reducing the diameter of the driving wheels. But this will
not do for reasons already explained. Wire drawing steps
in, the consumption of steam per stroke falls ofif, and so does
the mean effective cylinder pressure. If the horse power of the
boiler is a constant, then T S will also be a constant. Here T
is the tractive effort and S the speed in miles per hour. That
is to say, the tractive effort will fall off as the speed augments,
and a curve plotted for various speeds and tractive efforts is a
hyperbola. The tractive effort depends on the mean pressure
in the cylinder, and that may be so much reduced by wire
drawing that an engine with small wheels may be quite unable
Fig. 94.
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302 THE EATLWAY LOCOMOTIVE
to ase up all the steam the boiler can make, and so actually
exert less pull than an engine with larger wheels. If the reader
will follow this reasoning out he will find that for normal loco-
motives about 200 revolutions per minute, or 800 strokes for the
two cylinders, may be regarded as the limiting condition for
the exertion of maximum drawbar pull. In other words, T S then
represents the maximum power which the engine can exert. If this
is so, then if 30 miles an hour corresponds with 200 revolutions
per minute, 60 miles an hour will demand driving wheels of
twice the diameter. One eminent builder of locomotives in the
United States holds that driving wheels should have one inch
diameter for every mile an hour of maximum speed. But this
gives a 5-feet wheel for 60 miles an hour, which is much too
small.
To make this reasoning clearer, the following experiment is
quoted from Professor Goss's book ** Locomotive Performance."
" A particular engine, with a nominal cut-off at 35 per cent, of
the stroke, when making 188 revolutions per minute, had a
mean effective cylinder pressure of 42*4 lbs. and the tractive
effort T = 4,639 lbs. But to run this engine at 55 miles an
hour and 296 revolutions per minute the mean pressure, the
nominal cut-off remaining unaltered, fell to 27*4 lbs. and the
tractive effort to 2,997 lbs. The wheels were 5 feet 3 inches in
diameter. If they had been increased to 8 feet 3 inches the
speed would have been 55 miles an hour, the revolutions 188,
and T = 2,943 lbs., the loss in tractive effort due to this
increase in the size of the driving wheels being almost entirely
compensated by the maintenance of a high mean cylinder
pressure."
It must not be forgotten, however, that the engine with the
big drivers would start very badly as compared with that with
the small wheels.
Enough has been said to show that the determination of the
diameter of driving wheels to give the best results is a very
delicate point. The facts go far to explain why it is that small
differences in the diameters of driving wheels may produce results
apparently out of all proportion to the differences.
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THE WORK OF THE LOCOMOTIVE 303
There is apparently no limit to what might be said about the
railway locomotive. The book to which these words form the
conclusion deals with many subjects, each and every one of
which might well receive fuller treatment. The locomotive
grows with the growth of nations ; it has been a principal agent
in the extension of civilisation. To it is due the modern great
city and the spread of commerce. No other machine is so
ostensible ; it is always before the public. No other is more
flexible or ready to render service under most varying condi-
tions, probably none other does so much useful work. It is the
only machine that appears to be alive. It is almost impossible
indeed to watch one start its train or thunder through a station
and escape the sensation that we have a sentient being in
evidence. It has been said that electricity will supersede it.
Possibly, but the time is not near. Whenever and wherever, the
locomotive engine will still remain immortal. Its history may
indeed be forgotten or overlooked by future generations. But
among those who admire and love mechanism and the mechanical
arts will always be found a few who will keep its memory green,
and that of the men to whose genius, talents, and indomitable
energy the world is indebted for the most wonderful machine
ever devised.
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STANDAED WORKS ON THE LOCO-
MOTIVE ENGINE
A Practical Treatise on Railroads and Internal Communications in General.
By Nicholas Wood. London: Longman. 1832.
A Practical Treatise on Locomotive Engines upon Railways. By the
Chevalier F. M. G. De Pambour. Philadelphia: Carey & Hart. 1836.
The Machinery of Railways. By D. K. Clark. 1855.
On Heat and its relation to Water and Steam. By Charles Wye Williams.
Longman. 1860.
The Internal Disturbing Forces of the Locomotive. By J. Makinson.
Trans. Inst. C. E. 1862.
Locomotive Engineering and the Mechanism of Railways. By Zerah
Colbum, completed by W. H. Maw and D. K Clark. Glasgow : William
Collins. 1864.
Experimental Researches in Steam Engineering, Vol. II. By Benjamin
Isherwood. Philadelphia : Franklin Institute. 1865.
Treatise on the Locomotive Engine. By G. D. Dempsey. Weale's Series.
London : Crosby Lockwood & Co. 1879.
The Construction of Locomotive Engines. By W. Stroudley. Trans.
Inst. C. E. 1885.
Counterbalancing Locomotives. By Edmund Lewin Hill. Trans. Inst.
C. E. 1891.
The Construction of the Modem Locomotive. By George Hughes.
London : E. & F. N. Spon. 1894.
Valves and Valve Gearing. A practical text-book, by Charles Hirst.
London : Charles Griffin & Co. 1897.
The Evolution of the Locomotive Engine. By W. P. Marshall. Trans.
Inst. C. E. 1898.
The Steam Engine Indicator. By Cecil H. Peabody. New York : John
Wiley & Sons. 1900.
Locomotive Operation. A Technical and Practical Analysis. By G. R.
Henderson, M. A. S.M.E. Chicago; The nailnunf Aijc. 1904.
R.L, X
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306 APPENDIX
The Pennsylvania Railroad System at the Louisiana Purchase Exhibition.
Locomotive Tests and Exhibits, St. Louis, Missouri, 1904. Philadelphia:
The Pennsylvania pailroad Co. 1905.
La Locomotive Actuelle. Etude Gen^rale sur les Types E^cents des Loco-
motives k Grande Puissance. Par Maurice Demoulin, Ing^nieur de la
Traction, Chemin de fer de TOuest. Paris : Beranger. 1906.
Die Dampflokomotiven der Gegenwart. Ein Handbuch fiir Lokomotiv-
bauer. Eisenbahnbetriebsbeamto und Studierende des Maschinenbaufachs.
Von Robert Garbe, Geheimen Baurat, Mitgliod der KgL Eifeenbahndirektion,
Berlin. 1907.
Locomotive Performance. The Result of a Series of Researches conducted
by the Engineering Laboratorj% Purdue University, U.S.A. By W. F. M.
Goss, M.S. New York : John Wiley & Sons. 1907.
Bulletin of the International Railway Congress. English edition, pub-
lished monthly. London : King & Sons.
The Locomotive Catechism. By Robert Grimshaw. New York: Norman
W. Henley & Co. London : E. & F. N. Spon. 1893.
Train Resistance. By J. A. F. Aspinall. Trans. Inst. C. E. 1901.
History of the Furness Railway. By W. F. Pettigrew. Trans. Inst. Mech.
Eng. 1901.
Recent Locomotive Practice in France. By Edouard Sauvage. Trans.
Inst. Mech. Eng. 1900.
Experiments on the Draught produced in different parts of a locomotive
boiler when running. By J. A. F. Aspinall. Trans. Inst. Mech. Eng. 1893.
Superheaters applied to Locomotives on the Belgian State Railways. By
M. J. B. Flamme. Inst. Mech. C. E. 1905.
Large Locomotive Boilers. By George Churchward. Trans. Inst. Mech.
Eng. 1906.
Ten Years of Locomotive Progress. By George Montagu. London : Alston
Rivers. 1907.
Modern Locomotive Practice. A treatise on the design, construction and
working of Steam Locomotives. By C. E. Wolff, B.Sc. Manchester : Scientific
Publishing Co. 1907.
Lectures delivered to the Enginemen and Firemen of the Lpndon and
South Western Railway Co. on the Management of their Engines. By D.
Drummond, C.E., Chief Mechanical Engineer. London : Waterlow & Sons,
Ltd. 1907.
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INDEX
Acceleration, 273
Action of the bogie, 27
Adams' elastic wheel, 54
„ vortex pipe, 145
Adhesion, 55, 58
Adjustable blast nozzle, 146
Ashpans, 108
Automatic expansion, 255
„ lubricator, 283
Axle journals, 4
„ box, 5
B.
Back pressure, 138
Balance valves, 238
„ weights, 79
Baldry's rule, 25
Baldwin smoke-box, 150
Bar frames, 7
Barrus calorimeter, 164
Belgian locomotives, 119
Belpaire fire-box, 103
Birds' nests, 128
Bissell bogie, 15
Blast pipe, 143
Board of Trade rules, 93
Bogie springs, 29
Bogies, 15
Boiler fittings, 180
Boilers, 85
Boring cylinders, 203
Brakes, 285
Bridles, 237
Buffers, 37
Built-up crank axles, 211
Bushed small ends, 208
C,
Cataract, 229
Centrifugal force, 30
Chimney, 146, 147
Circulation, 156
Cleaning engines, 289
Clinkering, 128
Coal, 127
Co-efficient of adhesion, 59
Coke, 124'
Collision at Bina, 271
Combustion, 120
Compensating levers, 11
, weights, 78
Compounding, 239
Connecting rod, 204
Constant lead, 235
Contact area, 56
Cost of superheaters, 262
Counterbalancing, 73
Coupled wheels, 60
Couche and Havrez's experiments,
133
Crank axles, 209
„ pin friction, 210
Crossed and open rods, 225
Curves, 13
Cylinders, 202
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308
INDEX
D.
Db Pambour's formula, 295
Derailments, 1, 27
„ of tank engines, 277, 281
Design of boilers, 114
Development of bar frame, 9
Diaphragm, 189
Distribution of heat, 88, 89
Disturbing forces, 2
Diverging nozzle, 191
Domes, 115
Draught, 131
Drawbar pull, 298
Drummond's feed- water heater, 269
„ water tubes, 117, 118
E.
Elastic roads, 83
Engine mileage, 293
Exhaust steam, 123
Expansion, 217
„ of copper. 105
Explosions, 89
Fay's brake, 285
Finding centre of gravity, 274
Fire boxes, 95, 102
„ holes, 107
Firebrick arch, 124
Firing locomotives, 129
Flanged steel bogies, 19
Flanging press, 18
Floating lever, 230
Flue tubes, 109, 110
Foundation ring, 106
Four-cylinder engines, 246
Frames, 1
Friction, 209
Front end, 136
Fuel, 127
G.
Gab gear, 214
Girder slings, 105, 107
Glass water gauge, 186
Going blind, 221
Grate bars, 108
Gravity, centre of, 34
Great Eastern Railway bogie, 20
Great Liverpool, 38
Great Northern pony, 16
bogie, 17
Great Western Railway bogie, 21
Guide bars, 204
H.
Hammer blow, 79
Heat pegs, 154
Heating feed water, 161, 265
Horn plates, 11
Howe's valve gear, 215
Hull and Barnsley Railway, 99
Hydrokineter, 155
Hyperbolic logs, 219
I.
Indicators, 251
Initial condensation, 253
Injectors, 187
Intercepting valves, 244
Intermediate receiver, 242
Internal disturbing forces, 66
Ivatt's experiments, 257
,, speed diagram, 301
J.
Joy's radial gear, 213, 233
K.
Krupp's disc wheels, 44
L.
La France, 137
Lagging, 196
Lap, 220
Lead, 220
Length of flame, 135
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INDEX
309
Lifting action of cross head, 71
Lighting up, 291
Long grates, 117
Longitudinal seams, 94
Loss by radiation, 177
Lubrication, 282
Lurching, 37
M.
Marriotte's law, 252
Mass, 29
Maximum drawbar pull, 302
Mineral oils, 260
N.
NoTKiN superheater, 177
Nozzle, 143
P.
Falliser bolts, 96
Peabody calorimeter, 165, 166
Pet cocks, 185
Petticoat pipes, 146
Pick-up scoops, 264
Pielock superheater, 177
Pistons, 212
Piston valves, 246
Plate frames, 3
Pop valves, 185
Priming, 162
Propulsion, 66
. Purdue University, 81
Quality of steam, 169
R.
Ramsbottom safety valves, 184
Range of temperature, 254
Rankine's formula, 74
Rate of combustion, 130
„ evaporation, 132
R.L.
Ratio of expansion, 241
Reciprocating masses, 76
Reversing lever, 225
Rolling, 71
Running shed, 288
Safety valves, 183
Banding rails, 64
Schenectady No. 1, 136
Schmidt^s superheater, 174, 175
Screwed stays, 95
Self-starting injectors, 194
Shrinkage, 45
Side rods, 61, 62
Sight feed lubricators, 284
Simple steam engine, 199
Shde valves, 236
Slipper guide, 206, 207
Smith's piston valves, 247
Smoke-box, 137
L. & S. W. R., 140
S. E. & C. R., 141, 142
Springs, 11
Standard front end, 149
Staybolts, 97
Steam, 86, 152
Steam gas, 260
Stephenson's frames, 6
„ link motion, 213, 223
Stirling's express engine, 23
Stresses in boilers, 91
Stuffing box, 203
Super-elevation, 36
Superheating, 171
Tank engines, 271
Temperatures, 132
Tenders, 263
Testing plant, 80
The locomotive as a steam engine,
198
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310
INDEX
The locomotive as a steam generator,
84
,, ,, as a vehicle, 1
Theory of the blast pipe, 151
„ „ injector, 189
Throttle valves, 180, 181
Tire dimensions, 48, 49, 60, 51
,, rolUng mill, 41
,, sections, 46, 47, 52
Tires, 40
Train resistance, 297
Transmission of heat, 153
Traversing axle, 24
Treatment of water, 159
Tube expanders. 111
„ leakage, 112
Vacuum brake, 286
Valve gear, 213
W.
Wain weight's reversing gear, 226,
227, 228
Walschaert's gear, 213, 230
Wandering, 70
Washing out boilers, 291
Wasting of stays, 101
Water, 159
Water legs, 157
„ spaces, 116
Water-tube boilers, 170
Wear of cylinders, 202
Webb's whirling table, 44
Weights of boilers, 113
Westinghouse brake, 285
Wheel base, 18
Wheel and rail, 54
Wheels, 40
Wire drawing, 255
Work of injectors, 193
„ . the locomotive, 294
Wrought iron wheels, 43
BRADBURY, AONEW, & CO. LD., PRINTERS, LONDON AND TONBRIDOE.
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