Turbines

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^ ^( '■■

\ ^

TURBINES

- /f;-'

TURBINES

BY

.^

wrn: STUART garnett

NINTH WRANGLER, AND FIRST-CLASS CAMBRIDGE ENGINEERING
TRIPOS; OF THE INNER TEMPLE, BARRISTER- AT-LAW

SECOND EDITION

LONDON
GEOEGE BELL AND SONS, YOEK HOUSE

PORTUGAL STREET
1908

PREFACE TO THE FIRST EDITION.

IT was my intention, when I first undertook the
task of writing this book, to give a popular
account of the history, construction, and operation
of the turbine, and particularly of the various
steam turbines which are attracting, and very
properly attracting, so much public interest. In
the course of its growth the work has been some-
what modified by my experience of the extra-
ordinary ignorance prevailing among men of some
degree of technical knowledge, and even among
competent engineers, of the very nature of this, one
of the simplest and most beautiful among modern
machines, the heir of all the ages of engineering
experience and development.

It is undoubtedly very much to the credit of the
technical institutions of this country, that the
engineers who leave their doors after a three years'
course should be masters of that most complicated
mechanism the reciprocating steam engine, but I
cannot but think it a pity that these students

i^^-^ioi

vi PEEFACE

should spend long hours in drawing valve diagrams
' and studying the advantages of steam jacketing,
to the exclusion of any notice of a simpler prime
mover which bids fair in course of time completely
to displace the reciprocating engine from the
market. 1 have endeavoured,' therefore, while
bearing in mind the paramount necessity of pro-
ducing a book intelligible and, I trust, interesting,
to the amateur, to call attention to those points
and problems which deserve the more particular
notice of the student.

With this object, I have, in the fourth and sixth
chapters of Part I, awarded to questions of blade
design, and to other details of like importance in
the construction of steam turbines and of water
turbines, a rather more intimate consideration than
some readers may consider necessary. The pages
are in the reader's hand to turn when he will.

For the rest, it has been my object to trace the
development of the science of turbines, as it
appears to have grown in the minds of the in-
ventors responsible for its material manifestations ;
and I am confident that the reader who has studied
the problems solved and the difficulties overcome
by the pioneers of the ^vater turbine, will approach
the subject of the more modern and more interest-
ing steam turbine with a full appreciation of the
scientific principles underlying its action.

PEEFACE • vii

I desire to express my thanks to the Hon.
C. A. Parsons, C.B., F.R.S., and to other engineers
whose machines are described in these pages, for
their very kind and valuable assistance. The
courtesy of the Librarian of the Royal Society
and of his staff has enabled me to offer a brief
review of the history of the water turbine, and my
thanks are due to him and to many others who
have taken an active interest in the work.

W. H. S. G.

3, Temple Gardens,

Temple, E.G.
Aprily 1906.

PREFACE TO THE SECOND EDITION.

SINCE these pages were first laid before the
public two important events in the history
of the steam turbine have taken place. The first is
the steam trials of H.M.S. " Dreadnought/' the
second the development of the gas turbine by
MM. Armengaud and Lemale somewhat on the
linlr which I foreshadowed in Chapter XII of
this book, and in other writings.

The records of the trials are, however, at present
so imperfect, and the advances made by the gas

viii PEEFACE

turbine so small, that it has seemed well to confine
the alterations in the present edition to a few ne-
cessary corrections and explanations, leaving the
more substantial additions to a later day.

W. H. S. G.

7, Fig Tree Coubt,

Temple, E.G.

CONTENTS.

PAET I.
WATEE TUEBINES.

CHAPTER PAGE

I. Some Eably Engines 3

n. The Evolution op the Water Turbine . . 10

III. Three Pioneers 20

IV. A Theoretical Discussion op Turbines . . 34
V. Modern Impulse Turbines 48

VI. On Eeaction Turbines 65

Vn. Some Inward Flow Turbines 79

VIII. Erection and Control 96

PAET II.
STEAM TUEBINES.

CHAPTER PAGE

I. The Steam Engine 109

II. The History op the Steam Turbine . . . 116

III. The Parsons Steam Turbine 122

rV. The Parsons Turbine applied to Electric

Generation 130

V. The Marine Steam Turbine 147

VI. The Turbine in the Merchant Service . . 166

VII. The De Laval Turbine 178

ix

X CONTENTS

CHAPTER PAGE

VIII. The Curtis and other Impulse Turbines 195

IX. Turbo-Blowers and Eotary Pumps . . 211
X. The Governing and Operation of the Steam

Turbine 221

XI. The Future op the Steam Turbine . . . 232
XII. On the Trend of Modern Scientific Inven-
tion 243

APPENDICES.

APPENDIX P4GE

I. Some Mathematical Principles 253

II. On Fluid Motion 262

III. On the Behaviour op Gas 269

IV. On the Gyroscopic Effect of Turbines . . 274

Index 279

LIST OF ILLUSTRATIONS.

PIQ. PAGE

1. Undershot Watee- wheel 5

2. Overshot Water-wheel 7

3. The Eoloptle {circa 150 B.C.) 8

4. PoNCELET Wheel (1826) 11

5. Garonne Turbine {circa 1730) 13

6. Barker's Mill (1730) 16

7. Path op Water in Barker's Mill 16

8. Burdin's Turbine (1824) 18

9 & 10. Fourneyron's Turbine (1827) 23

11. JoNVAL Turbine (1837) 27

12 & 13. Howd's Turbine (1838) 31

14. Diagram op Guiding Curve 40

15. True and Apparent Flow op Water in Pblton

Bucket 44

16. Low Speed Pelton Wheel under Construction 47

17. High Speed Impulse Wheels 50

18. Pelton Wheel Running 51

19. Pelton Wheel 53

20. Pelton Nozzle and Needle, showing cleanness

OP Jet 55

21. " Victor " Girard Bunner 58

22 & 23. 1,600 H.P. Girard Turbine at Gurtnellen 60

xi

xii LIST OF ILLUSTRATIONS

FIG. PAGE

24. Vortex Turbine, cover removed 70

25. ** Victor " Francis Eotor for High Falls . . 73

26. Francis Turbine for Low Falls 75

27. Runner of Jonval Turbine, 40 H.P. under head

2 feet 81

28. Vortex Turbine, cover replaced 83

29. " Victor " mixed Flow Rotor 90

30. Distributor for Cylinder Gate Turbine ... 92

31. Double Turbine Set 95

32. Vortex Turbine Driving a Mill 98

33. 10,000 H.P. Francis Turbine installed at

Niagara 100

34. Pelton Wheel G-overnor 104

35. Pumping Engine (] 710) 110

36. Harthan's Turbine (1858) 117

37. Perrigault's Turbine (1865) 118

38. Pbrrigault's Turbine (1865) 119

39. An Early Parsons Turbine of 10 H.P 123

40. 75 Kw. Parsons Steam Turbine with Electric

Governor 126

41. 3,500 KW. Turbo-Generator at Carville . . . 131

42. Rotor of Modern Steam Turbine 134

43. Sectional Diagram of 1,000 kw. Turbo-Gener-

ator 136

44. Blading of Parsons Turbine 137

45. Steam Velocities 139

46. Parsons Vacuum Augmentor 143

47. S.Y. " TuRBiNiA " steaming at 34 Knots . . . 148

48. Machinery AND Propellers of S.Y. "Turbinia" 150

49. Cavitation, 4,000 R.P.M 151

50. H.M.S. " Amethyst " 160

LIST OF ILLUSTRATIONS xiii

FIG. PAGE

51. TUBBINES AND EeCIPROCATINO EnGINES. ThE

first comparison 162

52. Diagram op proposed Turbine arrangement of

H.M.S. " Dreadnought " 164

53. The Turbine Steamer " King Edward "... 167

54. Sectional Diagram of Marine Low-pressure

AND Astern Turbine 168

55. S.Y. " Emerald." The first Turbine Vessel to

CROSS THE Atlantic 1 70

56. Low Pressure and Reversing Turbines op

Allan Liner " Victoria, " partially bladed

at page 172

57. Transatlantic Vessels of the Past and

Present 176

58. The De Laval Wheel 179

59. De Laval Nozzle and Blades 182

60. Wheel of large De Laval Turbine, Blades

enlarged 184

61. Wheel of small De Laval Turbine showing

Flexible Shaft 186

62. 150 Kw. De Laval Turbo-Generator .... 189

63. Rotor of Riedler-Stumpf Turbine 192

64*. Sections op Riedler-Stumpf Rotor and Nozzle 193

65. 250 KW. A.E.G. Turbine 196

66. Solid Steel Rotor Wheel of Curtis Turbine,

Blades partially cut 198

67. Diagram op Blades and Nozzles in 2-stage

Curtis Turbine 199

68. Rotor of 4-stage Curtis Turbine 200

69. Inside of 4-stage Curtis Turbine Cylinder

SHOWING FIXED BlADE RoWS 201

xiv LIST OF ILLUSTRATIONS

FIG. PAGE

70. Low Pressube DiAPHRAaM OF Curtis Turbine

SHOWING Nozzles 202

71. 1,100 Kw. Curtis Turbine and Condenser. . . 204

72. Blading of Zoelly Turbine 207

73. Zoelly Turbine with cover of Low Pressure

Cylinder removed 209

74. High Speed Centrifugal Pump 213

75. Centrifugal Blower connected to 15 H.P. De

Laval Turbine 215

76. Parsons Turbo-Blower directly connected

WITH Parsons Steam Turbine 219

11, Relay Governor for Zoelly Turbine .... 225

78. Turbine Eoom of SS. " Londonderry '* . . . 239

79. Vibrations of Hull of SS . " Caronia " (quad-

ruple Engines) 240

80. Vibrations of Hull of SS. " Carmania " (Tub-

bines) 241

81. Diagram of Velocities 253

82. Diagram of Vortex Surface 266

-83. Diagram of Angular Momentum 275

^

PAKT I
WATER TURBINES

CHAPTER I.
SOME EAELY ENGINES.

THE primary object of science in general, and of
mechanical science in particular, is the application
of the forces of nature to the service of man. The more
intelligent and the more idle of mankind have alike sought
means of lightening the daily task by the service of some
animate or inanimate agent. So in 1713 a boy left in
charge of a pumping engine lightened his duties by the
invention of the self-acting steam valve, and made poss-
ible the modern steam engine; and so no doubt men
have been continually seeking a key to the stores of energy
which Nature has provided.

Energy exists in a great variety of forms, chemical as -
in coal, electrical as in a thunder-cloud, mechanical as in
a lake raised above sea-level, or in a flowing river; and in
the last form its presence is fairly obvious to the casual
observer. It would not require any great intellectual
effort in a savage, who daily saw trees carried along on
the surface of a river, to conceive the idea of utilizing
the same agent for the transport of his own roof-tree
when he wished to build him a house; and so it is prob-
able that, far back in the prehistoric ages, the rivers of
Asia performed, in the service of man, the work that
the Ottawa and the Oregon do to-day. But it was not for
transport only that power was required in early day^:

3

4 WATEE TUEBINES

the ancient Egyptians and the savages who preceded them
ground their corn in a hand-mill, as many peoples do at
present, and for relief in this, and in many other direc-
tions,! .a stationary supply of natural power was emi-
nently desirable. The obvious source of power was the
river, and the problem was to derive from its rectilinear
motion a form of motion mechanically useful, which yet
should not remove the machine in which it existed away
from the spot at which power was required : a motion, that
is to say, of rotation. The solution of this problem was
the water-wheel, ^^escribed by Vitruvius in a book written
in the fourth century B.C. ) This is probably the oldest of
the power-giving engines invented by man; and indeed '
the first machine of his ancestors appeals so strongly to
the modern boy that there are. probably few children to
whom a stream is available who have not at some time
made a rudimentary model for themselves. Not that the
early water-wheel was itself-^nything but rudimentary,
consisting as it did of a heavy wheel with wooden paddles
or floats, set in the circumference and standing out
radially all round: the inner end of the axle turning in
a bearing built into the wall of the mill or house where
the power was required, and the other end carried on a
post or pier standing in the stream.

Such a machine did very well in early days, but, as
population and competition increased, more work was
required of the mill, and the miller began to notice its
defects, especially the very obvious one that a great part
of the water flowed past without touching the wheel at all.
To rftmpdy thi|^^ fl, ^prp . or weir. was put across the rive r,
alid the greater part of the water was led down a mill-
race and through a narrow channel where it could not
well pass the wheel without acting on its floats. Now it
is evident that at every point in the race or channel the

J

SOME EAELY ENGINES 6

same amoant of water must go past in one minute (for
all that comes in at one end travels along and leaves at
the other), and it follows that where the channel is nar-
rowest the water must flow fastest, so that at the mill
itself the speed must be very great; and for this to be the
case there must be a considerable difference in the water
level before and behind the mill ; in other words the level
of water in the head race must be considerably above
that in the tail race, and the water, therefore, passes the

FIG. 1. UNDERSHOT WATER-WHEEL.

mill on a slope. /As the modifications were carried furthei^^
the machine reached the form (shown in the figure) in
which it was used by the Eomans, and in which it is used
still in a great many parts of England, j

It must not, however, be supposed that these were the
only lines along which development took place in early
days. jL ong before the und ershot water-wheel had reached
the stage which we have jusrdeBciibyd,'anumber of other
sources of natural power had been tapped. Wind was
used both for transport and for power supply. Early

6 WATEE TURBINES

windmills consisted, indeed, simply of a number, usually
four, of masts, with flat sails set obliquely on them,
stepped, like spokes, in a hub, so as to balance one an-
other and to revolve, instead of moving to and fro as they
would do in a vessel reaching./ Such mills were used in
/ this country, and in Holland, stjon after the days of Wil-
liam the Conqueror, and were the only ones known until
Biram, in the year 1842, suggested the idea of curving
the sails, and introduced the many-bladed windmill which ^ ,
has since, particularly in America, developed enormously^V
It is worth noting that the action of a windmill depends
on the pressure of the moving fluid on a plane inclined
to its direction of motion, that is, on the principle of the
screw; so that when the time came for the screw pro-
peller and the other uses of screws of which we shall
have occasion to speak, an example was at hand in the ]
windmill to illustrate this method of conversion of recti- J
linear into rotary motion. /

Another early ^ engine, the overshot water-wheel, has
for its object the utilization of potential energy stored in
high-level lakes and in water at the top of a fall. In this
machine the weight of the water is used, the vanes of
the wheel being set against the drum and between two
annular plates or shrouds. These vanes are so curved as
to form, with the shrouds and drum, buckets capable of
holding water. The water runs down a short sloping
culvert or spout, from which it shoots across the top of

^ The invention of the overshot water-wheel was a great event
in educated Borne, and the subject of an ode by Antiparos the
Greek, the Kipling of the period (60 B.C.) :

** Sleep, ye maids of the mill . . .
Your burdens Jove has laid on the nymphs.
Lightly they trip it over the wheels,
Turning the trembling shafts."

SOME EAELY ENGINES 7

the wheel, and after striking the vanes with a slight im-
pulse, partially fills the buckets and carries them down,
till, near the bottom of the wheel, it is poured out into
the tail race. The overshot wheel has this advantage over
the other, that the water is poured out from the moving
buckets in a direction opposite to that of their motion,

FIG. 2. OVERSHOT WATER-WHEEL.

and is consequently left almost at rest. Unlike the water
which drives an undershot wheel, it gives almost the whole
of its motion to the machine. The overshot wheel is a
highly eflScient engine when applied to falls having a
small flow of water, and not less than twelve, nor more
than forty, feet in height. For higher falls it has been
proposed, notably by Fussel in 1803, to arrange buckets
on a chain (as in a dredger) passing round wheels at the

8 WATER TURBINES

top and bottom of the fall, or to arrange a number of
oyershot wheels in series one above another, so that water
faUing from the bottom of one wheel enters the backet at
the top of the next. None of these arrangements, how-
ever, have been found commercially satisfactory, and
they have all now given place to the high-speed water
turbine. ^-^

One more application of natural power deserves men-
tion in this place, though the tracing of its further de-
velopment must be postponed to a later stage of our work.
Hero of Alexandria, in his "Pneu-
matica," written in the second cen-
tury B.C., described the first recorded
utilization of steam to produce mo-
tion. The machine of which he wrote
consisted of a sphere in which steam
was generated over a lamp. The
sphere was mounted in bearings, and
free to rotate. From it the steam
escaped by means of two narrow tubes
set opposite to one another in a

FIG. 3. THE BOLOPYLS ,. , - , , v i. ^ i.u

leirea 150 B.C ) diameter of the sphere ; each of these
tubes was bent over at the end and
narrowed into a fine jet, through which the steam was
expelled in a direction at right angles to the axis of
rotation; these two jets faced in opposite directions, and
the action between the steam and the pipe, which forced
the steam out of the jet, forced the jet itself backwards,
so that the sphere rotated with considerable velocity.
This machine was not, however, applied to any prac-
tical use until the year 1784, when it was revived, or
perhaps re-discovered, by De Eempelen, who took put a
patent for it in that year. Another use of a jet of steam
was made in the year 1629 by Giovanni Branca, who

SOME EARLY ENGINES 9

drove a small mill-wheel by the impact on its vanes of
steam issuing direct from a boiler.

Between the days of this machine and that of De
Kempelen self-acting steam valves were introduced, and
great progress was made with the reciprocating steam
•engine, so that attention was to a certain extent diverted
from the simple rotary engine, and in fact, for forty years
after De Kempelen's time, very little progress was made
with rotary machines for either steam or water power;
but it is worth noting that these two machines, invented
by Hero in the second century b.c, and Branca in the
seventeenth century a.d., exemplify, though very im-
perfectly, the two principles of action and re-action on
which is based the whole theory and practice of turbine
.engineering.

CHAPTER II.
THE EVOLUTION OF THE WATEE TURBINE.

IT will be evident from a consideration of the principles
enunciated in Appendix I, that the old undershot
water-wheel was open to serious criticism on the ground
of inefficiency, and, as more and more was required of
machinery, it became necessary to bring about some im-
provement in the design of these wheels. The gravest
defect of the undershot wheel was, that, while, owing to
the narrowing of the channel necessary to bring all the
water passing to bear on the wheel, the speed of the
water in that part of the channel was considerable, yet
the speed of the wheel itself was small. If rapidly
moving water had to strike a slowly moving float, there
was a great loss of energy by impact; if, on the other
hand, the wheel were arranged to work at a high speed,
then the water, being discharged at the speed of the
wheel itself, carried oflf with it the greater part of the
energy which should have been supplied to the machine.
To obviate these disadvantages it was required to de>
sign a wheel in which there should be little if any impact
between the water and the floats, but in which, neverthe-
less, the water should be left by the wheel almost without
motion. It was pointed out that water, on leaving the
curved buckets of the overshot water-wheel, remained
almost at rest, so that it may not unreasonably be sup-

lO

EVOLUTION OF THE WATER TURBINE 11

posed that floats similar in shape to the buckets of the
overshot wheel would be an improvement on the flat
boards formerly in use on the undershot wheel; and in fact
General Poncelet, in the year 1826, suggested improve-
ments in the undershot wheel, consisting of a channel
so narrowed and shaped as to fit the wheel very closely
for some distance, and of floats of a shape rather like

FIG. 4. PONCELET WHEEL (1826).

that of the overshot buckets. The wheel was situated as
before at the lower end of a sloping channel, and the
form of the machine was .that shown in the accom-
panying figure.

The curved floats of the Poncelet wheel had another
advantage besides that already set forth, namely, that
the water approached the floats tangentially, and wasted
no power in impact; it ran smoothly up the blades press-

12 WATEE TUEBINES

ing on the curved surface, and ran back still so pressing,
leaving the wheel at last entirely without motion. Thus
the Poncelet wheel was a highly eflScient engine, differing
only from the true turbine in that the fluid approached
and left the blades by the same edge, and this machine
is still in common use where a low speed is wanted and
the available head of water is small.

It was Carnot who first enunciated, in 1787, the two ]
propositions illustrated by the Poncelet wheel, that effi- ^
ciency could only be obtained by a water engine if the
fluid entered it without impact and left it without energy.
Poncelet, in a paper published in 1826, claims very pro-
perly that his wheel satisfies the requirements of Carnot.

In a paper published by M. Burdin two years later, the ^
same virtues are claimed for an engine of quite a different
type. This is the first wheel described by the name turbine,
and belongs to a different class from the early turbines
already described. To understand its origin and develop-
ment we must go back for a moment to see what was
being done in this country a hundred years before.

The precise significance, in engineering practice, of
the term "turbine," an adaptation of the Latin turbo
(which means a top) made 'by M. Burdin for the purpose
of distinguishing his invention, has never, apparently,
been defined. The practice of eighty years, for Burdin's
first machine was constructed in 1824, has, however, so
far fixed the meaning of the term that it is now fairly
easy to predicate of any particular machine whether or
no it will fall into the class of turbines, and the following
generic description of this engine will perhaps serve to
discriminate between the machines which deserve to be
classed as turbines and those which do not : —

** A turbine is a rotary engine in which power is de-
rived from the pressure of a fluid on the sides of channels

)

EVOLUTION OF THE WATER TUEBINE 13

in the rotating part, which channels the fluid traverses
in one direction only, approaching the rotor with velocity
in the direction of rotation, and leaving it wholly or
partly deprived of that velocity."

' If this definition of a turbine be accepted, then the first
recorded turbine is probably that described in M. Belidor's
" Architecture Hydraulique " as being in common usage
on the Garonne at the date of the book, 1737. The ac-

FIG. 5. GARONNE TURBINE {circa 1730).

companying figure (Fig. 5) is taken from that work, and
fairly indicates the nature of the machine. Sloping blades
run round a cone from base to vertex, the cone being
mounted on a shaft and set in a conical pit, which should
fit the outer edges of the blades as closely as possible;
water is introduced to the machine by a sloping channel
in such a manner as to strike the blades at right angles ;
and after sinking to the bottom of the pit (acting on the
blades all the time), it finally escapes by a channel.
The action of the machine can be easily followed.

14 WATEE TUEBINES

Suppose the water to enter the pit with velocity, V, due
to a fall, H, then for efficiency the angular velocity of
the cone should be V/E, where E is the radius of the
cone at the top. The water then enters the pit without
impact, and forms part of a vortex in which every particle
of water has the same angular velocity about the axis,
namely, the angular velocity of the conical wheel. Now
as the water, under the action of its weight, sinks lower
in the pit and approaches more nearly the axis of the
wheel, so its velocity and angular momentum are con-
tinually diminished ; and when it reaches the bottom it
has actually very little motion, and is finally, if the ma-
.chine is well designed, completely deprived of angular
momentum and almost of its velocity.

This machine is, therefore, if properly made, a turbine
of no mean merit; the early forms were, however, as
may be seen from the figure, of a very crude type, for the
constructors were largely ignorant of the advantages of
their own machines. Indeed, so distinguished an en-
gineer as Belidor himself dismisses them with the curt
notice that many curious wheels of the form shown may
be seen in operation on the Garonne, and that their speed
is considerable; he then goes on to speak of the installa-
tion of le Basacle as worthy of deep consideration.

In this mill, wheels of the form of ventilating fans
were set in the bottom of the head race channel, and
through them the water escaped into the tail race.
M. Belidor very prudently declines to enter into a mathe-
matical discussion of these wheels, but states that, for
the best results, the fans or blades should be set at an
angle of thirty-five degrees with the horizon. We shall
80 far follow M. Belidor as to pass over the theory of
these wheels, simply remarking that they are not true
turbines, as the water enters them without velocity in

r

EVOLUTION OF THE WATER TURBINE 15

the direction of motion; but they belong to the large
class of reaction wheels — wheels, that is to say, which
depend for their motive force on the reaction of fluid,
which enters without velocity in the direction of rotation,
but leaves with large angular momentum in the opposite
sense. At a very high speed they have a fair efficiency.

Of such reaction wheels perhaps the most typical, and,
with the exception of Hero's engine, described in Chap. I
of this book, probably the first, was Barker's mill, in-
vented by Dr. Robert Barker about the year 1780. This
machine was an application to water of Hero's engine,
and consisted of a long horizontal barrel, called the trunk,
mounted on a vertical axis, and pierced by two orifices at
opposite ends of the trunk, opening in opposite directions.
Into this trunk water was led from the head through a
sleeve joint in the hollow axis which supported it; and
this water, escaping through the orifices at the ends of
the trunk, caused it by its reaction to rotate in the manner
of a tourbillon. A shaft ascending from the middle point
of the trunk was mortised into the upper mill-stone.

It will be evident that this machine satisfies the
first of the requirements enunciated by Poncelet, for the
water enters it without impact and is gradually acceler-
ated, each particle moving from the centre along a path
somewhat similar to that sketched out in figure 7, till
at A it attains the velocity of the end of the trunk.
During this time the pressure of the water is, thanks to
centrifugal action, being continually increased, and when
it comes to A at the end of the trunk, the pressure on
one side of the stream being suddenly removed, it receives
a very rapid acceleration in a direction opposed to that
of its previous motion, and is ejected from the orifice
into the air just above the tail race of the mill.

This machine is, of course, very far from satisfying the

FIG. 6. barker's mill (1730).

1

FIG. 7. PATH OF WATER IN BARKER'S MILL.

EVOLUTION OP THE WATER TURBINE 17

second of Poncelet's requirements, for it is of the very-
essence of its action that the water should leave it with
considerable velocity. The efficiency will only be high if
the speed of the rotor is high in comparison with that of
the escaping water ; this implies a low head and a high
speed of rotation. Since, however, the head, H, is to be
small, a large output requires a large flow of water,
and therefore the section of the trunk must be large. ^
The mass of the trunk, together with that of the water
in it, is therefore very great, and, as this mass is to be
driven at a high speed, much power will necessarily be
wasted on pivotal friction. A limit is thus set to the
speed at which it is wise to drive th e machine, and in
practice a peripheral speed of v2GHis found to give the
best result.

The theoretical efficiency of Barker's mill under the
best conditions of working is 0*82§, and owing to the
mechanical difficulties of which we have spoken, this
efficiency has never been even approached in practice; in
fact, in spite of comparatively recent improvements in
construction, and in the shape of the arms, in conse-
quence of which their section and weight can be much
diminished, Barker's mill, as a source of power, is now
obsolete. It has, however, furnished some ingenious toys,
an example of which is the neat little lawn sprinkler,
with which most of our readers are probably familiar.

Now, if the reader will examine the path (sketched in
Fig. 7) followed by the fluid in the trunk of the simple
mill, he will observe that the whole forward thrust on
the mill is exerted at A, where the stream bends sharply,
and that in flowing outwards it continually receives an-
gular motion from the machine, and consequently exerts
on it a backward pressure. If, instead, this angular mo-
tion were communicated to the water before it entered

18

WATEE TUEBINE8

the rotor, a great increase in efficiency would result; and
this is precisely the improvement effected by M. Burdin
in his machine of 1824. He also secured that the water
should leave without velocity.

The rotating part of this machine consisted of a tank,
from which the water was discharged, as from Barker's
mill, in a direction opposed to that of rotation. The
water entered the tank just within the circumference,

r

•^u^

FIG. 8. burdin's turbine (1824).

from horizontal nozzles, with considerable velocity in the
direction of rotation. The nozzles were set in the bottom
of the head race.

If the head of water above the nozzles be H, then the
ve locity with which the water enters the tank must be
V2GH, and in order that all impact should be avoided
at the entrance, the velocity of the tank at the circum-
ference should be the same, so that, if the radius of the
tank be E, its angular velocity should, for high efficiency,

EVOLUTION OP THE WATEE TURBINE 19

be ^2GH/E. To satisfy the second condition of efficiency
the water must leave the tank without velocity, and there-
fore its velocity of discharge through the nozzle should
be equal, as it is in any case opposite, to the velocity of
the nozzle itself. In order to acquire this velocity, ^^2GH,
relative to the orifice, the water must he discharged under
a head H, so that the depth of water in the tank should,
for satisfactory working, be H.

The theoretical efficiency of this machine is perfect,
so that, if there were no mechanical losses, the output
would be the whole work done by the fall. The mechan-
ical losses are, however, great. The depth of the rotating
tank must be one half of the height of the fall, and its
weight is therefore very great in comparison with the
power developed. The only method of regulation is by a
sluice gate, and whether the power or the speed of the
machine is altered, a great loss of efficiency is the result.

In spite of its disadvantages, Burdin's turbine is worthy
of study as representing the first conscious effort to pro-
duce an engine the importance of which the public are,
even now, only beginning to realize.

Scientific men had, however, appreciated the possi-
bilities of such an engine to some extent, even before the
appearance of this turbine. In 1823, the Societe d'En-
couragement de Paris had ofifered a prize of 6,000 francs
to the inventor of a water-wheel similar to those described
by Belidor, which should be of real commercial utility.
For eleven years no inventor worthy of the honour made
his appearance, and then, in 1884, the prize was awarded
to M. Fourneyron, who produced a machine incomparably
superior to any then existing. The design of this turbine
has scarcely required modification to meet the exacting
requirements of the present day.

CHAPTER 111.
THREE PIONEERS.

THE obvious defects of the Burdin turbine arose
from the fact that it was necessary to have, in the
rotor itself, a considerable d^erence of level between the
point where the water entered without either pressure
or velocity, and the point at which it was to acquire a
velocity of discharge, relative to the machine, equal to
that of the machine itself, and at which a considerable
pressure was therefore necessary.

This velocity of discharge the fluid must have for
efl&cient working, whether it be steam, water, or gas; and
this velocity it can acquire (if it has not had a velocity
relative to the rotor during the whole of its passage
through it) in two ways only, namely, by the action of
gravity, or else by the pressure of the fluid behind. For
the first action to take place, the rotor must be large
enough to give gravity an opportunity of doing the-
necessary amount of work on the fluid during its pas-
sage. Generally the rotor will have to be, as in Burdin's
machine, half as high as the fall. For the second action,,
namely, acceleration by fluid pressure, the rotor need
not be large, but, since the pressure drops continually as
the speed increases, the water must enter the wheel at
considerable pressure.

On the other hand the water may have at all times-

20

THREE PIONEERS 21

during its passage through the wheel the necessary
velocity relative to the wheel, and in that case neither
of these actions is necessary.

The problem, then, which the Societe d'Encourage-
ment set in 1823 to the engineers of the day, resolved
itself into that of doing away with the necessity for the
great height of Burdin's rotor, and this, as we have just
seen, involves the admission of fluid to the wheel, either
at a considerable pressure or else with a velocity relative
to the wheel equal to that of the wheel itself at the point
of admission (App. II). It may be thought that so great
a velocity or pressure at admission is not necessary if
the fluid is to leave the wheel at a point near to the axis,
where the velocity is small; but this impression would
be erroneous, for considerable pressure or velocity will
be required to overcome the centrifugal action of the
rotating water within the wheel, and in fact it will be
found, when we come to enter more fully into the theory
of water turbines, that the necessity for admission at
high velocity or else under pressure remains entirely
unaffected by the relative positions of the points of ad-
mission and discharge (App. II).

FOURNBYRON, 1827.

Having regard to the fact that Poncelet published in
1826 a description of the undershot water-wheel which
goes by his name, we ought perhaps to give him some
credit for the form of the first satisfactory solution of
this problem. The turbine which Fourneyron constructed
in 1827, and described in a paper presented to the Society
in 1834, has, in the form of its blades at least, a distinct
resemblance to the Poncelet wheel. This machine is
shown in elevation and plan in Figs. 9 and 10.

The external diameter of the wheel was 6 feet, and

22 WATEE TUEBINES

the internal diameter 4 feet 2^ inches. The blades were
circular, and perpendicular to the rim at their inner ends,
resembling very much those of the Poncelet wheel. At
the outer ends they made an angle of 16° with the cir-
cumference. The whole wheel was formed of a single
casting.
^ As may be seen in Fig. 9, the wheel surrounds the
bottom of a fixed pipe or well, from which water enters
. the moving channels. The direction of the water at
' entrance into the wheel is determined by guide blades of
/ the spiral form shown in Fig. 10. These guides are in-
clined at an angle of 45° to the rim of the wheel, so that
they bisect the angle between the rim and the moving
blades.

Fourneyron found that the machine worked almost
equally well above and below the tail water, but the best
result was obtained when it was set above the surface
and under a head of 4 feet. The turbine then gave a
torque of 561 pound-feet at 50 revolutions per minute.
This amounts to a rate of working of 2,940 foot-pounds
per second or 5*35 H.P. The flow of water was then 845
pounds per second, and the work done by the fall was
therefore 3,880 foot-pounds per second. This shows an
efficiency in the machine of 87%, an efficiency still un-
surpassed.

Poncelet investigated the theory of this wheel in 1838,
and maintained that the highest efficiency should result
from a speed of the inner rim equal to \^0'6 of the
free velocity due to the fall. If he is right, the speed of
the wheel in the circumstances above set forth should be
56\ revolutions per minute.

An investigation of the theory of this simple turbine
will conduce to an understanding of the more complicated
engines, and may be very briefly conducted.

FIG. 9,

FIG. 10. FOURNEYRON'S TURBINE (1827).

24 WATEE TURBINES

The velocity of the water as it emerges from the guiding
channels is that due to the head of 4 feet, a velocity of
16 feet per second. This is made up (App. I) of a velocity
of 11"3 feet per second along the rim and 11*3 feet per
second along the radius; that is to say, along the moving
blade. Now, if there is to be no impact, the blade must
have the same velocity of 11"3 along the rim. According
to our theory, then, the speed of the inner rim should be i
4j\ the free velocity due to the fall, and the speed of the
wheel will then be 51^ revolutions per minute, very nearly
the speed found experimentally by Fourneyron.

Now the velocity of the water along the blade at the
inner end is 11*3 feet per second, the velocity of the
wheel at the same point, so that if the water were dis-
charged from the wheel at the inner rim in a direction
opposite to that of the wheel's motion, it would be at rest
after discharge. As the water flows outwards, centrifugal
force increases its speed, but the speed of the wheel in-
creases at the same time; and it is shown in App. II
(Vortex Motion) that these increases are equal. It is clear,
then, that if the water were discharged from the outer
rim of the wheel in a direction opposite to that of the
wheel's motion, the velocity of the water after discharge
would be nil. This state of things is very nearly realized,
and the turbine therefore satisfies the two requirements
of Carnot, when running at the correct speed.

The necessity of clearing the discharged water away
from the wheel makes it impossible to satisfy completely
these requirements, and the water is discharged, as stated
above, at an angle of 16° with the rim. The path of the
water in this turbine is very like that in Barker's mill,
with the difference that the fixed channels — an essential
feature of a turbine — shape the earlier part of the curve.

Fourneyron soon went on to the construction of larger

THEEE PIONEERS 25

machines, which were, for the most part, built up of
wrought iron, and not cast like the early one. The
third of these was built in 1833, and was designed to
give 20 H.P, under a fall of 1*8 metres or about 4 feet
4 inches. The machine actually developed 50 H.P. and
was the most powerful hydraulic engine of its day. It
was found that it could be run with only slight varia-
tion of efficiency under any heads between 7 inches and
8 feet.

In all these larger turbines Fourneyron adopted the
precise design of the original wheel, with the modification
that the crown of blades was narrowed, in proportion
to the diameter of the wheel, for the purpose of keeping
the weight within reasonable limits. Though the angles
of the blades and guides were not varied, none of these
later engines met with the same success as did that re-
sulting from the first attempt.

For working at low loads it was necessary to regulate
the machines, and this was done in the later ones by a
very economical method; the height of the orifices in the
fixed drum, by which the water escaped into the wheel,
was altered by a sluice worked from above by a worm-
wheel. This sluice was so curved that it did not narrow
the channel suddenly, but allowed a smooth flow of
-water.

The gravest defect of the turbine, and that which to a
certain extent unfitted it, and unfits others made on the
same principle to-day, for many engineering purposes,
was the exceeding want of stability of its motion when
running under a heavy load. Under these circumstances
the speed of the wheel would be somewhat, and might be
considerably, below the theoretically best. When this
was the case not only was the efficiency lowered, but
the fact that water entered the wheel with impact caused

26 WATEE TURBINES

a back pressure outside the orifices of the fixed drum, and
thus reduced the speed of the water entering the wheel,
and consequently the total flow of water. Now if the load
on the turbine were reduced for an instant, the speed
of the wheel would increase, causing a corresponding in-
crease in the centrifugal action and diminution in the
impact, which would both tend to diminish the back
pressure and so to increaae the flow, and which might
even increase it out of proportion to the increase of
speed, so that the torque exerted by the wheel would
actually increase and the acceleration of the wheel would
continue for some time. The result of this peculiarity of
the turbine would be a ludicrous exaggeration of the
phenomenon known in the case of steam engines as
hunting; and, for electric and other work in which
steady speed is required, this vice to a great extent puts
the Fourneyron turbine out of court.

It has been remarked that the efficiency of Fourneyron's
experimental machine, under the best conditions, was
87%> a result which was equalled by some elaborate
machines constructed on similar lines in 1837 to give
190 horse-power, but which does not appear to have
been surpassed by any outward flow turbine. This is in
part due to the fact that in the larger wheels the crown
was narrower and the blades more numerous, so that
some strangulation of the flow took place in the wheel,
causing a certain amount of pressure at the point of
admission and completely upsetting the theory on which
the whet'l was originally designed.

This trouble was remedied by Girard in a modified
form of the Fourneyron turbine> of which we shall speak
hereafter. The Girard turbine is free from the vice of
instability and has almost entirely displaced the original
form fivm m^Hiern practice.

THREE PIONEERS

27

JONVAL, 1837.

Another of the varieties of turbine in modern use owes
its origin to Jonval of Miihlhausen, who, in 1887, designed
and constructed a machine in which the blades and
guides were set round cylindrical drums, so that the water
in its passage through the wheel remained always at the
same distance from the axis. Such turbines are known
in this country as axial or parallel flow machines, and
on the continent as Jonval turbines.

FIG. 11. JONVAL TURBINE (1837).

The machine consists essentially of two wheels, of
which one is a reversed copy, or reflection, of the other.
The inner part of each wheel is solid and bounded by a
cylindrical rim. Between it and a concentric exterior rim
of the same width are fixed blades, dividing the space
between the rims into channels. These blades, shown in
the accompanying figure are vertical at the top, and
are bent so as to make an angle of about thirty de-
grees with the horizontal at the bottom, differing in the

28 WATER TURBINES

two wheels only in this respect, that they are bent in
opposite directions. The upper wheel is fixed, so that
water entering it vertically from the pit, of which it forms
the bottom, is deflected on to the blades of the moving
wheel. This is situate immediately below the other, co-
axial with it, and fitting with as little clearance as pos-
sible.

The whole flow through each of the wheels of the
Jonval turbine is the same, and the section of the channel
at any point in the moving wheel is the same as the section
at the corresponding point in the fixed wheel; so that, if
the channels are always full, which it is clear that they
must be, the velocity of the water relative to the wheel
at any point in the lower wheel is equal to the velocity of
the water at the corresponding point in the upper wheel.
The velocity of the water relative to the wheel at the
point of discharge is^ therefore, equal to its absolute
velocity at the point of admission; but, in order that
admission should take place without impact, the hori-
zontal velocity at admission must be equal to the velocity
of the wheel, and the horizontal velocity relative to the
wheel at discharge must accordingly also be equal, and
in this case opposite, to the velocity of the wheel. The
water, therefore, leaves the wheel without horizontal
motion, but with considerable vertical velocity.

We will reserve for another place the discussion of the
theoretically best velocity for the wheel, but we may say
here that the most satisfactory results have been ob-
tained, with speeds of the outer circumference equal to
from 3/5 to 2/8 of the free velocity due to the fall.

In modern practice there is a great variety in the forms
of the blades used in axial flow turbines, as in those of
every other type, but, in the machines which most nearly
resemble the early one of Jonval, the principal change is

THEEE PIONEERS 29

a slight increase in the curvature of the guides, by reason
of which their discharge ends are more nearly horizontal
than those of the moving blades; the consequence of this
is that the water leaves the wheel with a diminished
vertical velocity but with a slight velocity in the direction
of motion.

Jonval's turbines were usually set above the level of
the tail race, and they discharged into a suction pipe*
By this means an excellent clearance of the discharged
water was secured, while the benefit of the whole avail-
able head was obtained.

The output of Jonval's turbine in its original form was
regulated by a sluice in the supply pipe, which diminished
the flow of water through the machine. Since, however,
the sluice had the further effect of diminishing the elSect-
ive head, this system caused a serious loss of power on
light loads, and has long been abandoned in favour of
more efficient methods.

The solution offered by Jonval to the problem set out
at the beginning of this chapter differs from that of
Fourneyron primarily in this, that the water is not en-
tirely dependent for its velocity of discharge on the
velocity with which it enters the wheel, but rather on the
pressure with which it enters, and which accelerates it
gradually as the passage through the wheel narrows. The
solution of the problem which we have still to consider
presents this difference from that of Fourneyron in a still
more marked degree.

HowD, 1838.
A third class of turbines are driven in the manner
claimed in the specification of the United States Patent
granted to S. B. Howd in 1838. This specification de-
scribes a turbine designed for low falls, and whose con-

80 WATER TURBINES

struction is of the simplest. The wheel, cast in one piece,
resembles that of the Fourneyron turbine in general
construction, but the blades, being designed for inward
flow, are concave to the circumference, and their curva-
ture is comparatively small, the angles which they make
with the inner and outer rims of the crown being about
80° and 75° respectively. The upper face of this wheel
is a solid disk, and the lower a ring, so that the water,
leaving the blades at the end near the axis, can escape
downwards, through the hole in the lower face, and so
into the tail race. This wheel fits closely inside a case
formed by two annular plates in the same planes with
the faces of the wheel. Between these plates are straight
guides meeting the wheel at an angle of 20°. From the
outside of the case a cylinder rises to the surface of the
water. The output of the machine is regulated by a sluice
gate sliding on the outside of this cylinder, and operated
by a lever to cover wholly or partiaUy the channels be-
tween the fixed guides. The accompanying illustration
is taken from Howd's patent specification (Fig. 18).

Unfortunately, no figures are now obtainable as to the
performance of this machine; its efficiency was certainly
much lower than that of Fourneyron's turbine, but it
had the advantage of extreme simplicity, cheapness, and
compactness, which, in a country like America (where, at
that time at least, water power was much more plentiful
than capital) was of more importance than economy, and
secured for it great popularity. All the preparation re-
quired for this machine was the construction of a conduit
to lead the water off from a hole in the bottom of the
head race; the turbine set down on top of the hole could
be run, regulated, and stopped without further trouble.

In view of the advantages which it possessed, it is not
surprising [that in 1849, when J. B. Francis, of Lowell,

FIG. 12.

FIG. 13. HOWD'S TURBINE (1838).

82 WATER TUBBINE8

Mass.y took this turbine in hand with a view to its more
scientific construction and improvement, there were
already a very large number of the machines in opera-
tion in the United States.

Francis conducted experiments on a very considerable
scale in connection with turbines, sluices, and other
hydrauUc machinery, of which investigations an excellent
account will be found in his book, '' Lowell Hydraulic
Experiments." One of the wheels, the subject of these
studies, was designed by him in 1849, and is really an
improved form of Howd's machine, the straight guides
having given place to curves, and the angle of the blades
being considerably altered. The diameter of this wheel,
which was capable of giving 230 H.P. under a fall of
19 feet, was 11*338 feet, and the height of the wheel at
the exterior circumference was 1 foot, whUe at the inner
end of the blades it was 1*23 foot, or 23 per cent, greater;
a feature of the design which suggests that Francis him-
self did not fully realize that, to obtain a satisfactory
result, the speed of the water relative to the wheel should
increase during its passage through the wheel, and that
the water should enter under pressure. Instead of per-
mitting this to take place the designer would appear to
have been at some pains to secure that the channel should
not narrow to any great extent, so that the water entered
only under slight pressure, and was not greatly accelerated
in its passage. Now as the direction of the stream at
entry does not nearly bisect the angle between the blade
and the direction of its motion, as it does in the case of
Fourneyron's turbine, this involves the condition that
the water must either enter with impact or else leave
with velocity, according to the speed at which the wheel
is run.

Francis found that the best result was obtained from

THREE PIONEEES 88

the wheel when the speed under a fall of 18*878 feet was
0*6719 revolution per second, the speed of the curcum-
ference being then 0*672 of the free velocity due to the
fall. It is pretty evident that under these circumstances
there is considerable impact at admission, a fact which
Francis himself observed and was somewhat at a loss to
I explain, seeing as he did that it involved some defect in
the design of the turbine. Francis was also surprised to
find that under these most favourable conditions the
efficiency of the wheel was only 0*797, but in view of our
observations as to the design, we are more inclined to
wonder that so good a result was obtained.

Turbines made on this plan have from the time of
Howd been the most popular in America, though for a
long time European practice favoured the Jonval type;
and it appears that at present, for low falls at least,
turbines with external admission are ousting, even from
the Continent, machines of every other design.

CHAPTER IV.
A THEORETICAL DISCUSSION OF TURBINES.

WE have already seen that a turbine will act in a
satisfactory way only if the fluid enters the wheel
either under pressure or else with a velocity relative to
the wheel, and this is true alike of water and of steam
turbines, and it must be true of every other form of
turbine which the future may bring forth. The exact
relation between the pressure and velocity with which
the fluid enters the wheel must be the first subject of our
investigation.

The conditions to be satisfied are twofold, and were
laid down in the year 1787. They are that the fluid
must enter the wheel without impact and must leave it
without velocity.

The first condition is comparatively unimportant where
steam is concerned, on account of its elasticity, for there
can be no true shock on an elastic body (App. I). The
second condition, however, applies equally to every work-
ing fluid.

With hydraulic engines, the first condition is of
supreme importance. It implies that, if the water enter
the wheel with velocity relative thereto, that velocity
must be along the blades; if it were not so, there would
be impact on the blades.

The pressure of the water at the point of discharge is.
the pressure outside the wheel; it may be atmospheric^

34

A THEOEETICAL DISCUSSION 35

but in many modern machines it is below the atmo-
spheric pressure. For our present purpose we shall speak
of it as zero pressure. It will then be understood that a
pressure of ten pounds means a pressure of ten pounds
above that at the point of discharge.

Now the second condition implies that the velocity of
the fluid, relative to the wheel, at the point of discharge,
shall be equal to the velocity of the wheel at that point
(and in the opposite direction). The outer surface of the
wheel moves more quickly than the inner surface, but, if
water is discharged from the outer surface, its motion is
accelerated by centrifugal force as it flows through the
wheel; if it flows inwards, the motion is correspond-
ingly retarded, so that it is immaterial (as is more fully
explained in App. II), to our consideration of the second
condition from what part of the surface discharge actually
takes place. We shall assume, then, that the fluid is dis-
charged, as in a Jonval turbine, at the same distance from
the axis as that at which it enters the wheel.

If, then, the velocity of the wheel at the points of
admission and of discharge be V, the velocity of the fluid
relative to the wheel at the point of discharge must also
be V. Now, if the fluid enter the wheel without pressure,
as is the case in the turbine of Fourneyron, and in very
many steam turbines, the velocity of the fluid relative to
the wheel at the point of admission must be V, the
velocity of the wheel at the point of admission.

Suppose, however, that the fluid enters the wheel
under pressure. It is shown in App. II that a stream of
water may move with a velocity varying from point to
point, according to the section of the channel in which it
flows, and that the pressure of the water varies also, the
law connecting pressure and velocity being
P+iMV' = A Constant

86 WATER TURBINES

(P being the pressure per square foot in absolute units,
and M the mass of a cubic foot of water). The same law
holds good for small expansions of steam.

Now, if we consider the stream of water in one of the
wheel channels, the constant of this stream must be equal
to the value of IMV at the point where P is nothing, that
is, at the point of discharge. If then the water were to
enter the wheel without velocity relative to the wheel (a
state of things impossible to realize), the pressure per
square foot at the point of admission should be ^MV*, V
being the velocity of the wheel at the point of discharge,
and also at the point of admission.

Considering what takes place in the two turbines dis-
cussed, we can see that the difference between the
pressure-velocity changes taking place between the guide
blades in the two cases is really this, that, in the first, all
the pressure of the water is converted into motion between
the fixed guides, before it enters the wheel; while, in
the second case, of the same total pressure enough only
is converted to give the water the velocity of the wheel
and none relative thereto. The commonest case, how-
ever, is intermediate between these two; and, what is
there necessary is that the constant of the motion at
admission should be the same as in the two previous
cases; that is to say, if the water enter with a velocity TJ
along blades moving with velocity V, the pressure of
the water should be IMV*— ^^MU"^; the pressure neces-
sary if the water were to enter without velocity, less the
pressure necessary to produce the velocity which the
water actually has.

According to the system of admission, turbines are
divided into two classes. Those of the first class, in
which the water enters the wheel without pressure, are
known in England as impulse turbines, and on the

X

A THEORETICAL DISCUSSION 87

Continent, for the most part, as turbines of free devia-
tion. An example of this class of machine is Foorneyron's
turbine running at the theoretically best, or any higher
velocity. The second class of machines consists of those
in which the water enters the wheel under pressure, either
with or without velocity relative to the wheel; these
machines are known in England as reaction turbines,
and are well exemplified by Thomson's case wheel, and
by Fourneyron's turbine, when running at less than the
normal speed. It may serve to fix the distinction between
these two classes of machines, to suggest that they consist,
as to the first class, of developments of Poncelet's water-
wheel, and, as to the second, of developments of Barker's
mill, though neither of the two patriarchal engines is
itself a turbine proper.

There is another system of classification of these
machines; classification, namely, according to the ar-
rangement of the blades. Provided the fluid enters the
wheel with velocity in the direction of rotation and
leaves it wholly or partially deprived of that velocity,
there is no restriction on the path which it may follow
within the machine, and in fact a great many different
arrangements of the blading are used. For the most part
however the blades are set either in the plane of rotation,
forming a radial flow turbine, which is an outward or
inward flow (Francis) machine according to the path of
of the water, (of these, Fourneyron's and Howd's turbines
are the earliest examples); or else on a cylindrical sur-
face, forming the parallel flow turbine, of which Jonval's
is the archetype, and in which the acting fluid maintains
an invariable distance from the axis.

Besides these, there are machines of the type generally
described as "conical flow," exemplified by the early
turbines of the Garonne, described in a former chapter^

88 WATER TURBINES

and by the less strictly conical variety of the same
machine, patented, together with his case-wheel, by
James Thomson in 1850. There is also a great variety
of turbines, not very clearly distinguishable from the
" conical flow " group, in which the water enters by the
internal or external surface and leaves by the bottom, or
enters by the top and leaves by the circumference, or
follows some other devious path. A large number of these
are made nowadays, and are classed together as '^ mixed
flow" turbines, among which the "conical flow" machines
are often grouped. These varieties are, however, only
matters of form, and, although no doubt some forms give
rather better results than others, there is no difference of
principle involved, and this classification is consequently
of much less importance than the one which we have
previously mentioned, and to which we shall now return.

Firstly, then, let us consider the machines of the
*' impulse" type. In these the water is at atmospheric
pressure during the whole of its course through the
wheel, and therefore will not, generally, press on both
sides of the channel through which it flows. For this
reason it is not necessary that the channel should always
be full, or that it should be designed to fit the stream
which passes through it ; all that is necessary is that
there should always be room in the channel for the
water to pass, while pressing only on the blade by which
the machine is driven.

In the parallel flow impulse turbine, the speed of the
water relatively to the wheel is the same at admission
and at discharge, and throughout the motion, so that the
section of the stream does not alter at all in the course
of its passage through the wheel. In designing a parallel
flow impulse turbine, it is, therefore, necessary to secure
that the section of the channels is not reduced, at any

A THEOEETICAL DISCUSSION 39

point, below the section of the stream at the point of
admission; an increase in section on the other hand does
not affect the machine in any way. In radial flow impulse
turbines, the speed of the fluid will, owing to the influence
of centrifugal action, alter between admission and dis-
charge, increasing in the case of outward flow, diminish-
ing in the case of inward flow; and so, while the section
of the channels may in an outward flow turbine be, as in
the Fourneyron wheel, contracted towards the point of
discharge — a result naturally following from the form of
the blades — the section in an inward flow turbine, must
be expanded towards the centre, and this to such an
extent as to render the design of an inward flow impulse
turbine almost impossible; and, in fact, we are not aware
that any such have ever been constructed.

The modification of the section of the channels can be
achieved after the form of the blades has been fixed
(though not quite so efficiently as by properly forming the
blades) by the arrangement of the upper and lower sur-
faces of the channels, and is therefore a secondary con-
sideration. The first problem — given the type of machine
to be constructed, the available fall and flow, and the
speed and power required of the machine — is to settle the
forms and inclinations of the guide curves and blades,
which are to determine the path of the water, and to
communicate its driving power to the turbine wheel.

Suppose, then, that AB represents the velocity of the
wheel at the point at which the water is admitted, and
AC the direction of the blade at this point. The water
must at admission, as we know (p. 35), possess the velocity
represented by AB, together with an equal velocity along
the blade, that is, in the direction AC, so that if we com-
plete the parallelogram ABDC, the line AD will repre-
sent, in magnitude and direction, the whole velocity

40 WATEE TUEBINES

which the water ought to possess at admission, in order
to give the best result (App. I). This direction bisects
the angle BAG; and it is the direction of the guide blades
that determines the direction of the stream; we may,
therefore, take it as one of the first principles of design
of an impulse turbine that the inclination of the guide
curve to the rim should be one half of that of the blade.
It may be slightly less without loss of efficiency.

The direction of the guiding curves, therefore, depends
on that of the blades at the point of admission, or, as
we shall call it, the beginning of the blades; and this,
as will appear hereafter, depends to a large extent on

C p

-^Motion of Wheel
FIG. 14.

local considerations. Of the proper directions for the
ends of the blades, however, there can be no doubt; it is
required of them so to direct the efflux of water that it
leaves the wheel as far as possible without motion, and
their directions should, therefore, be as nearly opposed to
that of the wheel's motion as is compatible with a proper
clearance of the discharged fluid. For an outward flow
turbine Fourneyron found an angle of 15° sufficient; this
is large enough for a parallel flow machine, but in an
inward flow wheel it should be rather larger. The same
considerations control the discharge of reaction turbines,
so that these remarks may be applied to them with equal
force.

The beginning angle of the blade has now to be deter-
mined, and this depends principally on the speed at

A THEOEETICAL DISCUSSION 41

which the machine is to run. In Fig. 14, AD represents
the velocity of the water at admission, i.e., the velocity
due to the fall, and AB represents, on the same scale,
the velocity of the wheel at the point of admission ; and
it is quite clear that the relation between AB and AD
depends on the size of the angle BAG; if, for instance,
BAG were very small, AB would be little more than half
AD. It is, in fact, clear enough that, if the beginning of
the blade is almost — it may even be quite — parallel to
the direction of the wheel's motion, then the water must
have double the velocity of the wheel; and as the angle
BAG increases, so also does the ratio of AB to AD. When
the angle is a right angle we have the case of Fourney-
ron*8 turbine, and the velocity of the wheel is ^|^(or
0-707) of the velocity due to the fall. If the angle be-
tween the convex side of the blade and the wheel be
increased above 90°, the velocity of the wheel is still
further increased ; thus, when this angle is 120°, and the
blade, the guide, and the circumference of the wheel are
all equally inclined to each other, the velocity of the
wheel is equal to the velocity due to the fall ; and if the
angle were large, that is to say, if the concave surface of
the blade were to make a small angle with the reversed
direction of motion, the velocity of the wheel for high
efficiency would be much greater than the free velocity
due to the fall.

For the purpose of driving dynamos, for which turbines
are nowlargely used, a high speed (500 to 1,500 revolutions)
is required, and if the available fall be small it may be
very desirable to produce a relatively high blade speed;
but an impulse turbine is a very unsuitable one for the
purpose, and for this reason: — In order that the dis-
charged water may clear the wheel, the ends of the blades
must be inclined at 15° or so to the direction of motion,

42 WATEE TUEBINES

and, if the beginnings of the blades be inclined at only a
small angle, the blades will be nearly straight. Now an
impulse turbine derives its motion from the change in
the direction of flow of the fluid as it passes along the
blades, and, if the blades are nearly straight, then the
change cannot be a prolonged and steady one, but must
take place, to a great extent, when the water first meets
the blades ; the turbine is then driven by impact, which
is fatal to eflSciency.

Impulse turbines, then, are unsuited for the develop-
ment of high speed motion from low falls, a function
which must be left to machines of the other type. For
running, on the other hand, at low speeds under a high
fall, the impulse turbine cannot be surpassed.

The forms of impulse turbine in most general use are
the outward flow Girard turbine and the parallel flow
Pelton wheel. The latter is commonly used for the very
highest falls. Descriptions and illustrations of both
these machines, as made by some leading firms, will
be found in the next chapter.

The directions of the blades at their beginnings and
ends being determined, we have to settle the curve they
are to follow between the two limits, as well as their
number. These are matters in which experience is a far
better guide than mathematical reasoning. Bearing in
mind, then, that the water must exert a steady pressure
on every part of the blade, and, to do this, must flow in
a smooth curve, the designer of hydraulic machinery,
like the designer of ships, must to a great extent rely on
experience, and on the look and feel of the curves. We
shall, therefore, confine ourselves at this place to a few
general remarks, referring the reader for further detail
to the drawings of modern machinery set out in the
later chapters.

A THEOEETICAL DISCUSSION 43

In dealing with this part of our problem, it will be well
to consider not only the path of the fluid relative to the
wheel, but also its actual path in space, and we may
begin by sketching either the one or the other; when one
is drawn the other is also determined. Suppose, for in-
stance, that we draw out the path to be followed by the
fluid in space. We know that the total velocity at any
point is made up of the velocity which the water has in
common with the wheel, and an equal velocity along the
blade; and it follows that the direction of motion in.
space at any point bisects the angle between the direction
of motion of the wheel and the direction of the blade at
that point. We can, therefore, from the direction of flow
in space, construct the direction of the blade at any point,
and to plot the blade is then a very simple piece of
geometry. It will, however, be found advisable to draw,
first, the proposed shape of blade, and to test this by
plotting the curve in space followed by the fluid during
its passage through the wheel.

If we bear in mind the fact that the fluid meets the
blade not only at the beginning, but also at all points
within some small distance of the beginning, depending
on the breadth of the jet, we can see that, to avoid impact,
the blade should be almost straight for a small distance
at the beginning; and, in order that the water may be
discharged without eddies, the blade should be straight,
or nearly so, for a small distance at the end. In design-
ing a blade for a Pelton wheel whose velocity is to be
half of the free velocity due to the fall, we should adopt
a form something like that shown in the accompanying
figure (Fig. 15).

Having now determined the form of blade to be adopted,
we proceed to find the path described by the fluid in the
following way. The velocity of the water along the blade

FIG. 15. TRUE AND APPARENT FLOW OF WATER IN PELTON BUCKET,

A THEOEETICAL DISCUSSION 45

is uniform, and so is the velocity of the blade itself;
accordingly, if we choose any particular point on the blade
in its present position, then the fluid which meets the
blade at the knife will have reached this point on the
blade when the point has moved from its present posi-
tion through a distance equal to that travelled by the
fluid along the blade. So we find a point on the path
through space of the particle of water which met the
blade at the knife. If then we take a number of points
— preferably at equal distances along the blade — we can
in this way construct the position of a number of points
on the path of the particle of water, and so draw the curve
which it follows, precisely as we have drawn the curve
in the accompanying figure. This, then, is the curve
described by one side of the stream past the blade —
that side, namely, which touches the blade itself; to
draw the curve described by the other side of the stream
we must first draw the curve on the wheel which is the
margin of the stream through the wheel. Now the
velocity of flow relative to the wheel being uniform, the
width of the stream in the wheel is uniform, and its
bounding curve may be sketched in. Having this curve
we construct the other from it exactly as before.

A study of these curves of flow of the liquid in a turbine
will explain in a very clear and graphic manner the
nature of the action which takes place. For instance, the
curvature of the stream in space shows that some force
is acting on it to change its direction, and that conse-
quently it must be pressing on the blade of the wheel.
The increasing width of the stream shows that its velocity
in space (though not relative to the wheel) is continually
diminishing, and that it is therefore doing work on the
wheel.

But we have not yet finished with the problems of

46 WATEE TURBINES

design before us. We have to consider the proper number
of the blades and the number of fixed guides or nozzles
to be used in the machine. We have already remarked
that impulse turbines are used chiefly in connection with
high falls, and when only a moderate speed is required ;
and, the fall being high, only a small flow of water will
be necessary to give considerable power. Now it is not
possible to design a turbine in which the blades shall
move with less than half the free velocity due to the fall,
and in which the efl&ciency shall still be high; and the free
velocity may be very large indeed. In the case of a 200
feet fall, for instance — and such a head is not unusual —
the velocity is 120 feet per second, so that the blades
must move with a speed of not less than 60 feet per
second. If at the same time it is necessary, as for the
direct driving of certain machinery, that the speed of
the shaft should be moderate, it will be necessary to use
a wheel of great diameter.

If the whole circumference of a wheel of such diameter
were to be surrounded with nozzles, the flow of water
would be immense — unless the nozzles were mere sprays,
unsuitable for engineering purposes — and this in a case
where only a small flow is required. But in a turbine of
free deviation it is not necessary that the channels of
the wheel should always be full, or should even have any
water at all in them throughout the motion, and it will
therefore be sufi&cient to place only one or two nozzles
at the circumference of the wheel, which shall bring each
blade into action once or twice in the course of its revo-
lution. This is, in fact, the practice adopted in connection
with the Pelton wheel and with the Girard turbine, in
each of which only one or two nozzles are used.

J

CHAPTER V.
MODEEN IMPULSE TUEBINES.

AN examination of the statistics published by any of
the large firms will show that by far the larger part
of their output at the present day consists of the wheels
which we have classed as reaction turbines. While, how-
ever, the number of reaction turbines in use increases by
leaps and bounds, the number of impulse turbines is also
advancing steadily; for the two different types are no
longer in competition, and it is now very generally recog-
nized that, while the reaction machine can most advan-
tageously replace the old water-wheel, the impulse wheel
is the proper machine for very high falls, where the flow
of water is often insufficient to fill the channels of a re-
action turbine of such size as to give the required slow-
ness of motion.

There are only two impulse turbines in common use
at the present day — the Girard turbine and the tangential
wheel, well known in this country in the form of the
Pelton wheel — and of these we will now speak.

Tangential Wheels

We have discussed the Poncelet wheel of 1825, the first

wheel in which shock at admission was avoidied by causing

the water to enter in a direction tangential to the floats,

and we have pointed out the objection to classing this

48

MODERN IMPULSE TURBINES 49

wheel among turbines, that the water approaches and
leaves the blades by the same end. This anomaly makes
it necessary that the height of the floats should be at
least a quarter of that of the fall; otherwise, when the
wheel runs at the proper speed, the water will rise to the
tops of the floats, and waste its energy in impact on the
drum.

The Poncelet wheel therefore laboured under the dis-
advantage of being suitable only for very low falls; a
disadvantage which was not overcome till 1856, when
Cheetham produced a wheel in which the blades were
modified in form, so that the water, instead of rushing
straight up to the drum of the wheel, was diverted to the
sides, and there thrown off in a direction nearly opposed
to that of its entrance, so as to be practically deprived
of motion.

In this wheel of Oheetham's, then, the blades were
become very like buckets, and, as the water was received
in the middle of these, and the stream there divided, it
may be said that each of these buckets consisted really
of two turbine blades joined at the admission ends, so
that the tangential wheel was in fact a double turbine.
This general construction of a tangential wheel has been
adhered to ever since its first appearance, but the manner
of setting the wheel is now very much altered. It is
usually mounted on a horizontal shaft, directly con-
nected to the dynamo or other machine to be driven; the
required speed is obtained by giving a suitable diameter
to the wheel. Below this the stream is concentrated in a
single horizontal jet discharged from a nozzle, the line
of the jet being, as the name of the machine suggests,
tangential to the circle of the wheel.

As the turbine turns, bucket after bucket drops into the
stream, moves along in it, subject all the time to impulse

E

50

WATER TURBINES

of the water, until it is gradually eclipsed by the next
bucket, which pares away the jet. In a few cases, where
it is desired to obtain considerable power from a small

FIG. 17. HIGH SPEED IMPULSE WHEELS.
(ESCHER WYSS AND CO., ZURICH.)

wheel, as when a high speed of rotation is required, two
jets are used, but better results are generally obtained
by keying two single jet wheels on the same shaft.
An enormous variety of impulse wheels is turned out

MODERN IMPULSE TURBINES 51

by the different manufacturing firms, ranging from the
21 foot wheel, illustrated in Fig. 16, running at 36 R.P.M!,
and developing 200 H.P. under a fall of 96 feet, to the
9 ft. 10 in. wheel, recently constructed by the Pelton Water
Wheel Co. of San Francisco for a fall of 865 feet, which
develops 5,000 H.P. at a speed of 225 revolutions (Fig.
19). Some of the many forms of wheel manufactured are
illustrated in Fig. 17 ; it will be noticed that they differ
chiefly in the shapes of the buckets, which are formed of
two spherical or cylindrical cups. These are the results

FIG. 18. PELTON WHEEL RUNNING. v
(PELTON WATER WHEEL CO., U.S.A.)

of many costly experiments, as well as of a good deal of
somewhat unprofitable theorizing, to which we, for our
part, would be loth to add, but it may be interesting to
take some slight notice of the points to be considered.

A bucket is required which will enter the jet without
unduly breaking it or deflecting it from the bucket be-
yond — will receive every particle of the water with the
least possible shock — distribute it over the surface of the
metal so as to reduce the wear, always very considerable,

52 WATEK TURBINES

to a minimum — and will finally discharge it as nearly as
possible without motion.

In order that the latter function may be performed,
and at the same time a satisfactory clearance obtained,
it is desirable that the buckets should be set at some
distance apart, and that the water should be discharged
from a great part of the rim at once. The buckets must,
however, be set closely together if the cylindrical form
without a base is used, as in some of the wheels in
Fig. 17, since, if the water continues to act on one of these
buckets after it is past the perpendicular, some of it is
bound to escape from the bottom, and that with con-
siderable velocity. The spherical or ellipsoidal form of
cup is open to the objection that the whole stream is
concentrated at the vertex in every position of the bucket
while in action, and this part is therefore liable to rapid
erosion.

The cylindrical form with a sloping base, generally
known as the Pelton bucket, which is very well shown in
Fig. 19, would appear to be fairly free from objection,
and the high efl&ciency of 82|^ per cent, has been obtained
with wheels of the Pelton type. It is claimed that, if
losses behind the nozzles are neglected the true eflBiciency
of the turbine is 86^ per cent. Messrs. Escher Wyss &
Co. of Zurich have obtained 81'5 per cent, efficiency with
baseless cylindrical buckets, in a 300 H.P. wheel, working
at half load under a head of 508 feet.

In all these wheels, however well designed they may
be, there is bound to be considerable erosion of the
buckets, and when this is once started the stream Knes
of the water are affected, with the result that a perceptible
decrease in efficiency is experienced; and the erosion,
once started, generally proceeds with increasing speed.
For this reason it is advisable, and, in the larger machines

FIG. 19. PELTON WHEEL.

54 WATEE TURBINES

at any rate, usual, to cast the buckets separately from
the wheel, and to fix them with bolts so that they may
be renewed after a few years' service.

Important as is the construction of the wheel itself,
the design of the accessories and the conditions of run-
ning contribute equally to the efficiency of the machine.
In the first place, the diameter of the stream at the point
of entrance should never be more than 1/5 of the whole
width of the bucket; if the stream is wide enough to
make any approach to filling the bucket, it is not able to
follow properly the curves of the blades, and eddies are
set up; that part of the stream, too, which does not meet
the knife, or central line of the bucket, wastes a great
part of its energy in impact on the surfaces, round which
it should glide smoothly. The losses due to excessive
water supply are in fact so marked that nearly all the
tangential water-wheels on the market will give a higher
efficiency when running at half load than under the full
load for which they are professedly designed — a fact to
be borne in mind in setting up a power plant for a high
fall.

Another source of loss in every turbine installation is
the resistance to the flow in the pipe which conducts the
water to the machine; and this may cause a serious
diminution in the effective head behind the nozzle.
Every such diminution of the effective head is to be
avoided with the most anxious care; the rather that, of
all the possible ways in which power may be waste-
fully expended, this is the one which gives least return
of any kind.

This is a point of great importance in connection with
the regulation of the machine. When the full power of
the plant is not required, it is obviously necessary to
reduce the flow of water, and this must be done in such

MODEEN IMPULSE TURBINES 55

a way as not to diminish the effective head. To shut off
the water above the turbine by a sluice gate, as is un-
fortunately a very common ijractice, is to use a system
of regulation infinitely worse than that of controlling a
steam engine by the throttle, a course which no modern
engineer would willingly adopt.

FIG. 20. NOZZLE AND NEEDLE, SHOWING CLEANNESS OF JET.
(PELTON WATER WHEEL CO. )

So far as it affects impulse turbines, the problem of
control can be easily and satisfactorily solved by narrow-
ing the nozzle, a proceeding which reduces the section
of the stream without affecting its velocity (unless slightly
to increase it if the resistance in the supply pipe is high).
This is achieved in most tangential wheels by means of
a needle forced into the nozzle, either by a screw turned
by hand, or, as shown in Fig. 34, by some automatic

56 WATEE TUEBINES

governing device. When it is required to reduce the
power more rapidly than can be done by checking the
flow, without danger of bursting the supply pipe, it is
usual to deflect the nozzle so that the jet misses the
buckets. The means adopted with impulse turbines of
the Girard class is rather different, and will be described
later.

We have now discussed pretty fully, omitting the
more strictly technical matters of lubrication, scantling,
and so on, the large and interesting class of turbines
known as tangential wheels. Wheels of this type have
been made for all powers up to 5,000 H.P., and for
heads varying from 50 to 2,200 feet. We must turn
our attention for a time to the other class of impulse
turbines, known by the name of their inventor, Louis
Dominique Girard.

Girard Turbines.

IN discussing the original turbine of Fourneyron, we
made, and the inventor's experiments appeared to
confirm, the assumption that the water entered the
wheel moving freely under atmospheric pressure. In the
later and larger machines, although manufactured on
the same general plan, the narrowness of the crown in
which the blades were set, and the increased number of
the blades, made this assumption no longer tenable, as
the constriction of the channels in the rotor caused con-
siderable pressure at the point of admission. At the
same time it would appear that these turbines were still
designed as if they belonged to the impulse class, that is
to say, with the guides bisecting the angle between the
blades and the direction of motion, with the natural

MODERN IMPULSE TURBINES 57

consequence that none of these later wheels, in spite of
the increased experience of the designer, showed so high
an efl&ciency as the first which he constructed.

Nor is the diminished efl&ciency the only objection to
running an outward flow, or Fourneyron, turbine as one
of the " reaction " class, for, as we have already pointed
out, the wheel is, under these circumstances, highly un-
stable in its motion and subject to the vice of hunting, a
slight increase in the speed tending to diminish the
pressure at admission, and so to increase the flow of
water and the power, and to accelerate the wheel still
further.

These defects may all be remedied by the cure applied
by Girard in 1856, that of maintaining a constant section
of the channels in the wheel by increasing the height of
the crown towards the circumference; this secures what
the inventor terms free deviation of the liquid within the
wheel; and since it is not now requisite to maintain any
pressure at the point of admission, it is no longer neces-
sary that admission should take place all round the
wheel; the number of fixed channels within the wheel is,
therefore, greatly reduced, and in the modern machines
it is usual to restrict the flow to one, or, at any rate, to
a very small number of nozzles.

This partial admission makes it possible to run a
wheel of considerable diameter with only a small flow of
water, and a moderate speed of rotation is thereby
secured, even when, as under a large head, the speed of
the blades must be great. The Girard turbine is, there-
fore, well suited for developing the power of a high fall,
when the flow of water is too large for a small tangential
wheel, and the speed of rotation required makes a large
tangential wheel unsuitable.

So it came about that this machine, which, at its in-

58

WATER TURBINES

ception, found outward flow turbines almost displaced
from the European market by those of the more recent

FIG. 21. ** VICTOR " GIRARD RUNNER.
(STILLWELL-BIERCE AND SMITH-VAILE CO., DAYTON, OHIO.)

Jonval type, established, within a very few years, a
recognized position as the proper wheel for use in con-
nection with falls of 40 feet and upwards. It is true that
of late years the Pelton wheel has largely displaced the

MODERN IMPULSE TUEBINES 59

Girard for low powers, on account both of its extreme
simplicity and of its suitability for the use of a very
small stream of water; the high efficiency of the Girard
turbine has, however, maintained its position for the
development of large powers under heads too great for
the Francis turbine.

In the detail of these, as of all other turbines, there
is considerable difference between the European and
American practices. According to the first system the
rotor is usually built up of forged steel parts, while,
according to the second, it is more often cast as a whole,
the surface exposed to the action of the water being
finished by grinding (Fig. 21).

The wheel here described (Figs. 22 and 23) is a tur-
bine of 1,600 H.P., installed by Messrs. Piccard, Pictet
et Cie., of Geneva, under a head of 590 metres (about
1,935 feet), at Gurtnellen, in Switzerland. The internal
diameter of the rotor is 6 feet 6 inches, and its speed
500 revolutions per minute, so that the velocity of the
blades at the point of admission is about 170 feet per
second. At this speed, of course, there might be some
danger of the crown, which is cast (Fig. 22), bursting,
and so the makers have recourse to the following con-
struction. The hub of the wheel is cast and keyed on to
the shaft, and the crown is joined to this hub by a web
of forged steel. Outside the crown, rings (B) of steel
are shrunk on to the wheel, effectively strengthening
the crown against the forces which might otherwise
injure it. Should the crown, in the course of time, be-
come worn away to any serious extent, it can be removed
and replaced, without any change in the other parts of
the wheel.

The essential feature of the Girard turbine is the form
of this crown, which does not vary much. The shape

2

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MODEEN IMPULSE TURBINES 61

of the blades can be clearly seen in Fig. 22, which
shows also the constriction in breadth of the wheel-
passages inevitable in all outward flow turbines. Fig. 23
shows the increasing width of the blade (0), peculiar to
the Girard turbine, which compensates this constriction
by increasing the depth of the passages, thereby in-
suring free deviation of the water within the wheel.

As is proper in impulse turbines, regulation is effected
by altering the width of the nozzles through which
water is admitted to the wheel. These nozzles (DD), lined
with phosphor bronze in order to resist the wear of the
water, and the corrosive effect of the gases liberated
when the pressure is relieved, are very well seen in
Fig. 22. They are bolted directly to the two pipes
forming the end of the pipe, and are furnished with
cylindrical gates (E) by means of which the open-
ings can be reduced from their full width of 6 centi-
metres to anything that may be desired. These gates
are so designed that they do not, in closing, alter the
direction of the stream, but only its width, so that it
continues at all times to enter the wheel at an angle
of about 45° with the direction of its motion, that is, in
a direction bisecting the angle between the blade and
the rim.

It follows that for perfect eflBciency the velocity of the
stream should be \/2 (1*4) of the speed of the wheel
at the point of admission, which is about 170 feet per
second. The theoretically best speed then for the water
at admission is just over 240 feet per second.

The height of the fall being 590 metres or 1,935 feet,
the free velocity due to the fall would be nearly 360 feet
per second, but since the water has to flow down a long
pipe of 40 centimetres diameter to enter the machine,
the friction in this pipe reduces the speed at the nozzles

62 WATER TURBINES

to a much smaller figure. This actual speed we are not
in a position to estimate with any great accuracy, never-
theless we are able to trace very approximately the
various losses of energy in the machine.

Thus a glance at Fig. 22 will show that the blades
are inclined at 80 degrees to the rim of the wheel at the
discharge end, and we can easily estimate the speed of
the rim as about 188 feet per second. It follows that the
least velocity in space with which the water can possibly
leave the wheel is 94 feet per second, when its velocity
relative to the wheel is 168 feet per second, and the
energy then carried off by the water (which flows at
the rate of 60 gallons a second) is iMV^ or 2,650,000
foot-poundals, that is to say, 87,500 foot-pounds per
second, and probably the energy of the discharged water
is more than this. But the whole work done by the fall
is 1,161,000 foot-pounds per second, and the useful work
developed by the turbine is 1,600 H.P. (French), or
868,000 foot-pounds per second. This leaves 205,500
foot-pounds per second wasted in friction in the pipe
and injector nozzles, impact at admission and friction
in the wheel channels. But we must remember that all
the energy represented by the motion of the water at
discharge is not carried away. It will be noticed that
the wheel runs in an air-tight case, and the motion of
the water at discharge is converted into pressure by a
diverging pipe as it emerges into the tail race, while the
wheel runs in a partial vacuum.

Friction in the wheel channels is not a very large
item in any impulse turbine, and it would appear on
every ground that the greater part of the above loss is
due to impact at admission, as the velocity of the water
at admission is probably about 330 feet per second. The
losses may be assigned to the following causes:

MODERN IMPULSE TURBINES 68

9%
7%

Friction in pipe and nozzles .
Impact at admission
Friction in wheel passages
Journal friction and air friction
Energy of discharge

Output 75%

100%

It is not very easy to see how much of the energy
wasted before discharge is consumed in friction in the
supply pipe and how much in impact on the wheel, but
the supposition that the greater part of the loss is due to
impact is confirmed by the behaviour of the machine at
low loads, for as the gate is closed the efficiency is found
to drop fairly rapidly. The action is as follows. As the
flow is diminished, the speed of the water in the pipe
diminishes and the effective pressure at the nozzles in-
creases. The velocity of the water is, therefore, increased
and the loss due to impact increases with it. There is
also a small increase in the amount of energy carried off
by the water. Now, since the whole loss of energy on a
gallon of water passing through the turbine increases
when causes operate which tend to diminish the loss in
the pipe, while increasing that due to impact, it is fair
to assume that the loss due to impact is at all times in
excess of that due to friction.

It is clear that a great part of the loss due to shock
might be done away by increasing the speed of rotation
of the wheel to 700 K.P.M., but if this were done the
amount of energy carried off by the water would in-
evitably be doubled.

64 WATEE TURBINES

The loss due to the speed with which the water is dis-
charged can only be reduced by diminishing the in-
clination of the blade to the rim at the discharge end of
the passage, but this modification, too, is attended with a
certain amount of inconvenience, owing to the constric-
tion in the width of the wheel channels, and the diflSculty
of securing an adequate clearance. At the same time, if
we bear in mind the extraordinarily high efficiency
obtained by Fourneyron with his original wheel, in which
this inclination was much smaller than in most of the
modern Girard turbines, it seems likely that some im-
provement might still be effected in the design of these
latter, which are in all their details so far superior to the
original machine.

* .

CHAPTER VI.
ON EE ACTION TURBINES.

FOR the purpose of utilizing the power of high falls,
and that more particularly in the cases where it is
required to produce a slow motion of rotation, as for the
direct driving of mill and factory machinery, impulse
turbines, such as we have described, are the most satis-
factory and eflScient machines that have yet been con-
structed. Direct driving from water power is, however,
becoming very uncommon in modern factories and works,
where any large amount of power is used. The great
superiority of electrical over mechanical methods of
transmitting power, the small preparation and trouble
involved in the installation of electric motors, and the
considerable advantage in efficiency and cheapness of
building and running possessed by larger over smaller
prime movers, have made it more usual in modern
practice to generate in one central station or power
house the whole power required for the running of a
large factory, and to distribute this power by electrical
means to the various points at which it is consumed. This
tendency to centralize the generation of power is very
aptly illustrated, and the possible future developments
of the policy are revealed in a striking manner, by the
bills which have recently been brought before Parliament
for the supply of power on a gigantic scale, and in which
steam turbines play so prominent a part.

66 WATER TURBINES

In consequence of this, now almost universal, practice,
it is for the driving of dynamos that turbines are now
most largely required; and, for the supply of power within
a moderate distance of the source, a continuous current
installation, of, say, 150 volts, is at once the simplest and
the most economical. It is obviously desirable that the
engine or turbine from which the power is derived should,
when possible, be directly connected to the dynamo, and
the objection of irregular speed, to which many engines,
and particularly gas engines, are in this connection open,
does not apply to turbines at all. The best speed, for a
turbine which is to drive a dynamo, is, therefore, the
speed at which the dynamo is intended to run, and con-
tinuous current machines are now built for speeds rang-
ing from a minimum of 400 R.P.M., for direct coupling to
steam engines, up to 4000, or even more, revolutions, for
machines designed to be driven directly by Parsons and
by some other high speed steam turbines. It may,
however, be fairly assumed that speeds ranging from
1,000 to 1,500 revolutions per minute are the most con-
venient at which to drive moderate-sized dynamos of the
class under consideration. For the generation of power
on a large scale, polyphase multipolar dynamos much
more slowly driven are generally used.

We may take it, then, that the smaller water turbines
are desired to run at speeds of 1,000 R.P.M., or even
more, while the larger machines should be designed for
speeds diminishing as the size of the wheel increases.
Further, in the great majority of cases in which water is
used for the supply of power, the available fall is not a
very large one; a river with considerable flow and moderate
fall is a source of energy far more frequently met with
than a high fall, and that even in the mountainous dis-
tricts where turbines are most commonly used.

EEACTION TURBINES 67

Now we have seen that impulse turbines are not at all
suited for the purpose of developing high speeds of rota-
tion from low falls, and it is clear that a very large wheel
will be necessary if a large flow is to be used on the
free deviation system ; so that, for the purpose of driving
dynamos, except under a very high fall, a reaction turbine
is the most suitable.

In designing a turbine for such a purpose the following
points have to be considered : (1) the diameter must be
small enough to give the required speed of rotation: (2)
the speed must be regular and capable of rapid automatic
adjustment to variations of the load put upon the machine:
(3) the wheel- and guide-passages must provide for a
large flow of water, and must be capable of such modifica-
tion as to diminish the flow considerably without seriously
impairing the efficiency of the machine.

The first condition necessitates complete admission,
that is to say, it requires that all the passages should be
full throughout the motion, a condition inconsistent with
the use of an impulse turbine. The second condition puts
an outward flow reaction turbine out of court, for the
reasons given in connection with Fourneyron's wheel,
and in fact it suggests the superiority of the pure inward
flow type of wheel, generally known as the Francis turbine,
over machines of every other design. It must be admitted
however that wheels of the mixed flow type, now very
popular on the Continent, gain to some extent in com-
pactness, and consequently in speed of rotation, what
they lose in efficiency and regularity of running.

We shall probably be very near the truth in saying
that the output of reaction turbines is now practically
confined to two types : (1) the pure inward flow, or Francis
machine, in which the water leaves the wheel passages
almost radially, near the centre, and then, changing its

68 WATEE TUEBINES

coarse, is discharged from one or both faces of the wheel
according to the amount of flow and the conditions to be
fulfilled, and (2) the mixed flow turbine, known by various
names, in which the water is admitted at the circumfer-
ence, but leaves by one or other face of the wheel, in a
direction parallel to the axis, after passing through a
twisted channel, formed by blades of the type illustrated
in Fig. 29. The first of these machines is now preferred
for large installations, but for small powers the mixed
flow turbine is extremely popular, and seems to be be-
coming more so.

The elements which go to make up a good machine
are (1) proper materials and workmanship, particularly
in the bearings, (2) suitably shaped wheel channels,
admitting and discharging the water at the most satis-
factory points, (3) properly designed fixed distributing
blades, (4) an efficient system of governing. These being
given, the turbine has only to be run under proper con-
ditions to give high efficiency and uniform speed.

To go into the details of material and construction
would be to venture too far into the realm of technical-
ities for the present work, and we will only remark that
there are two different systems of construction very
commonly adopted: the American, according to which
the whole rotor is cast in one piece and keyed to a steel
shaft, the faces of the blades being ground afterwards ;
and the European, according to which the rotor is built
up of forged steel plates bolted together.

It would be the height of presumption to pronounce on
the relative merits of two systems, both adopted by lead-
ing engineers, and both giving eminently satisfactory
results. The first has the advantage of reducing the
initial cost of the turbine, whereas the second reduces
the danger of flaws in the metal. Perhaps a composite

REACTION TURBINES 69

rotor, such as that of the Girard turbine shown in Fig.
22 has as far as possible the merits of both construc-
tions.

For the sake of reducing wear, it is desirable that the
wheel should be so formed that the water exerts upon
it only a simple torque. A thrust along the axis is
particularly to be avoided, and the hydraulic parts of
the turbine should therefore be made as symmetrical as
possible.

We now come to the design of the channels in the
wheel, which, unlike those of impulse turbines, must be
always full of water in order that the pressure at the
admission end may be maintained. The pressure at the
discharge end of the channels must be the pressure in
the wheel case; and the diminution of pressure of the
water, in passing through the wheel, may be due to
either of two causes (neglecting for the moment the not
inconsiderable friction of the wheel passages) : ^(1) that
the pressure is being spent in increasing the speed of
flow through the wheel, or (2) that the water is mov-
ing through the wheel against some force acting on it,
as when it flows inwards in spite of its own centrifugal
tendency. This state of affairs is realised in the case
wheel patented by James Thomson in 1850 (Fig. 24),
the only water turbine type really native to this country.

For the most part, in inward and mixed flow turbines,
both of these causes are brought into play to diminish
the pressure of the working fluid; and the blades, which
are much shorter than those of the case wheel, are so
bent as to diminish the section of the channels while dis-
charging the water in a direction opposite (or nearly so)
to that of the wheel's motion.

The section of the channels can be very largely adjusted
by the forms given to the two faces of the wheel, inde-

70

WATEE TURBINES

pendently of the forms of the wheel blades, so that the
designer has a very free hand in shaping the blades
themselves, being restricted only by the necessity of in-

FIG. 24. VORTEX TURBINE, COVER REMOVED.
(GILBERT GILKES AND CO. )

suring that the water shall flow in a smooth curve in
space, thus giving up its energy to the rotor with a certain
uniform continuity essential the efficient working of the
machine.

EEACTION TURBINES 71

Coming now to the subject of the shape and inclina-
tion to be given to the fixed blades, we have one or two
points to consider.

In discussing the subject of impulse turbines, we
reached the conclusion that the direction of the dis-
tributor blades at the point of admission should bisect
the angle between the direction of the wheel blades and
the direction of their motion. If, however, the water is to
be admitted under pressure, and without velocity along
the blades, the direction of the distributor blades at
admission must obviously be the direction of the wheel's
motion, which is to be the only motion possessed by the
water, as it leaves the guides. This is indeed very nearly
the state of affairs in the case wheel of Fig. 24, but in the
majority of reaction turbines this state of things is not
even approximately realized, as the water is admitted at
a lower pressure than in the case wheel, and with a very
considerable velocity along the blades.

A reaction turbine, so called, may, therefore, be any-
thing from a machine of the almost pure reaction type
to a machine approaching very nearly to the impulse
class. A reaction turbine proper is not in fact a me-
chanical possibility, for water obviously cannot enter
the wheel without any velocity along the blades. The
less the velocity of the stream along the blades, the less
the flow in the machine, and when this velocity is quite
abolished, the turbine, though a machine of perfect
efficiency, is not working, for the simple reason that there
is no water going through.

This harsh fact is the more to be lamented that we
shall find numerous reasons for holding the pure reaction
inward flow turbine to be the most desirable of all forms
which the machine can take. But the approximation of
the turbine to this form is very strictly limited by the

72 WATER TURBINES

necessity of passing a reasonable amount of water through
a wheel of moderate size.

We may take it, then, that in reaction turbines the
guides are inclined to the rim at some angle less than
half the inclination of the wheel blades (which would be
the proper angle for the guides of an impulse turbine)
an angle which is greatest when the velocity at admission
is considerable, and the pressure at admission low.

What this pressure shall be is one of the first questions
which the designer has to answer, for it depends very
largely on the constriction of the wheel passages; if these
are narrow at the discharge end, the pressure at admis-
sion must be high, and till the desired pressure is known
the shape of the blades cannot be determined.

In the theoretically pure — ^and purely theoretical — re-
action turbine, the water, being admitted without velo-
city relative to the wheel, must move at admission with
exactly the velocity of the wheel itself, and must be sub-
ject to a pressure sufficient to produce the same velocity
in the course of its passage through the wheel; it must
therefore be subject to a pressure of half the head above
the turbine, while moving with a velocity due to the
other half, and this velocity must also be that of the
wheel. In this case, therefore, the velocity of the rim
must always be that due to half the head, that is, it must
be 7/10 of the velocity due to the head, and this entirely
without regard to the shape or direction of the wheel
blades, or to the form of the wheel.

On the other hand, in impulse turbines, the speed
varies very greatly with the slope of the blades, from
half the speed due to the head, when the direction of the
blade at admission is in line with the direction of motion,
as in the Pelton wheel, to a speed far greater than that
due to the head, which is obtained in some Francis

EE ACTION TURBINES

73

turbines with nearly flat blades, in which the water is
admitted under very moderate pressure.

If then we have a turbine with blades shaped like those

FIG. 25. " VICTOR " FRANCIS ROTOR FOR HIGH FALLS.

in Fig. 25, the guide blades, whatever the pressure at
admission, will never make any but a small angle with
the rim. The pressure at admission will depend almost
entirely on the section of the wheel channels at the dis-

74 WATEE TURBINES

charge end; if these openings are increased, the speed of
the wheel will be diminished, while the torque and flow
will be increased, the turbine tending to the impulse type;
while a diminution in the section of the wheel passages
will cause the speed to increase (the water still entering
without shock, and leaving without velocity) and the flow
and torque to diminish.

With blades at right angles to the rim of the wheel, as
in the case wheel, the turbine will run at exactly the
same speed, either as an impulse turbine, or as a pure
reaction turbine, that is to say, at a rim speed of ^^i or
7/10 of the velocity due to the fall. We can, therefore,
in such a turbine, set the guide blades at any angle less
than 45° to the rim, without affecting either the speed
or the efficiency of the turbine; but the forms of the
wheel channels must be such as to give a pressure at
admission corresponding to the inclination of the guide
blades.

The most common form of reaction turbine, however,
has blades shaped like those in Fig. 26; and in these
machines the guides may occupy any position interme-
diate between FG and HG. The effect, however, of turn-
ing the guides from FG to HG is in this case the opposite
of what it was in the case illustrated above; for now,
when the machine tends to the impulse type, the speed
of running is very greatly increased, as well as the flow,
while the torque, increasing at first, attains a maximum
when the position of the guides is about HG, and would
drop to a very small figure if the guide could be turned
further. It is usual, therefore, to design inward flow
reaction turbines with the guides inclined to the rim at
some such angle as is made by KG, so that the water
enters with considerable velocity, and at the same time
under high pressure.

REACTION TURBINES

75

Having got the elements of the design, we can now cast
the rotor and distributor in accordance therewith, and
we have a turbine possessing, under the conditions for
which it is designed, all the attributes that make for

FIG. 26.

FRANCIS TURBINE FOR LOW FALLS.
(PICCARD, PICTET ET CIE. )

eflSciency. But he would be a poor engineer who should
design a machine to run only under one set of conditions.
It may be that the turbine is to run almost continually
at full load, so that it is not necessary that its efficiency
at low loads should be high; and in such cases it will be

76 WATER TDEBINES

sufficient to regulate it mth a sluice gate in the penstock,
or more advantageously in the manner of Howd's turbine,
with a gate sliding on the distributor itself. Such a gate
adds very little to the cost of the turbine, and, if the water
supply is ample, it will suit the consumer very well to
keep down first cost at the expense of efficient regulation.

This method of regulation is very far from first-class
practice. In generating electric power, turbines run at
ever varying loads, often very far below full load, and, if
it is worth while to put in a good machine at all, it is
worth while to put in one that will be a good machine all
the time; that will give at half, or even at a lower load,
an efficiency almost as high as under the best conditions.

In impulse turbines the only regulation necessary can
be effected perfectly well by means of the injector nozzles,
but the regulation of reaction turbines presents a more
complicated problem, and one that has never been com-
pletely solved. For the first condition to be satisfied is
that the speed of the turbine should be constant, and to
avoid the carrying off of a wasteful amount of energy at
discharge, this involves the condition that the velocity of
discharge should also be constant; but the quantity of
water in the channels is to be reduced for low loads, so
that the velocity of discharge cannot be constant unless
the section of the wheel passages at the discharge end can
be reduced. No system of control can therefore be per-
fect which does not operate to some extent on the rotor
blades; and no practical regulator operating on the wheel
blades has ever been produced.

But, while waiting for the invention of a perfect regu-
lator which shall control at once the wheel blades and
those of the distributor, engineers have not been idle in
the matter, and many excellent systems of control are
now in use.

REACTION TURBINES 77

The best systems are so contrived that the wheel
passages remain fall throughout the motion; and in order
that they may do so, no part of the orifices by which the
water leaves the distributor may be blocked. Now, in
order to keep the same aggregate width of orifices, while
narrowing the channels in the distributor, it is neces-
sary to alter the inclination of the guide blades; and
this is commonly done. It is only at the end of the
blades that any modification is necessary, and some
makers prefer to obtain this, as in the Ficcard Pictet
turbine illustrated (Fig. 26), by swivelling the end of the
guide blade while the beginning is fixed ; others, as in the
case wheel (Fig. 24), by turning the whole blade.

Whichever of these methods is adopted, the turning is
usually effected by connecting each blade to a common
frame, by a short link, so that a turn given to the frame,
either by hand or by the governor, widens or closes every
channel in the distributor at the same moment.

When the flow is reduced by turning the guides in this
manner, the direction of flow of the water at admission
is changed, and the velocity along the blades greatly
reduced, while the velocity at discharge is altered in a
much less degree. The consequence of this is that the
pressure at admission rises, so that the total velocity at
admission drops, and the machine becomes a more purely
reaction turbine. It is a happy consequence of these
changes that the velocity of the water in the direction of
motion of the wheel is not greatly, though it must be to
some extent, increased; so that, while a certain amount
of shock at admission is unavoidable, it is kept within
very moderate limits.

A reduction of output, then, even if obtained by the
most satisfactory method yet known, is attended by an
increased loss of energy carried off by the water, and an

78 WATER TURBINES

increased shock at admission » and the problem of control
must remain to a certain extent unsolved, until some
mechanician is able to devise a governor capable of act-
ing at the same time on the stationary blades of the
distributor and on the rapidly moving blades of the
wheel.

CHAPTER VII.
SOME INWAED FLOW TUEBINES.

THEEE are, as we have stated before, three classes
of reaction turbines in common use at the present
day, and of these at once the earliest, and in many ways
the simplest, is the parallel flow, or Jonval turbine.

The design of these turbines has been very considerably
modified since they originated in the simple form shown
in Fig. 11; but the essential features of the old machine
are still unaltered. Perhaps the most important modern
improvement is the greater compactness obtained by
using, when the flow is large, a number of concentric
rings of fixed and movable channels, by which means the
quantity of water with which the wheel can deal is greatly
increased without increasing the diameter.

By multiplying the turbine in this way another ad-
vantage is obtained. In early days the Jonval turbine
was regulated by a sluice valve, but when this process
was condemned as ineflScient the most popular system
was that of closing a number of the fixed channels by
sliding gates, a system attended with rather better re-
sults. Even so, however, the machine suffered under the
disadvantage that the pressure in the wheel channels
at admission could not be maintained, as these channels
were emptied in passing the closed gates, and so when
they were filled again it was with considerable shock.

79

80 WATER TURBINES

With the multiple turbines, however, it is possible to
cut out a whole ring of channels without in any way
affecting the operation of those which remain in use, and
consequently the output of the machine can be reduced
with little, if any, decrease in efficiency.

Now each ring of channels in the turbine is moving
faster than the ring inside it, and slower than the one
outside, while the water pressure acting on each ring is
the same, so that if all the blades are to do their duty
faithfully they must not be all of the same shape; in
fact, while the blades in the inner ring are very much
curved so that the direction of the water is reversed as it
flows past them, as in a Felton wheel, the blades in the
outer ring will be very much flatter and will be set very
obliquely to the axis as in a screw propeller. So also the
forms of the fixed, or distributor, blades will be very
different in the inner and outer ring, being designed to
inject the water, in the first case, in a direction only
slightly inclined to the direction of motion, while at the
outside of the wheel the water is to enter more in the
direction of the axis and to press on the flatter blades as
they move rapidly past.

' The variation in the set of the moving blades can be
seen in the accompanying figure, which represents the
rotor of a Jonval turbine of inoderate power for use in
connection with a large flow and small head. The bottom
of the head race consists to all intents atid purposes of a
large sieve, which imparts a screw motion to the water
as it passes through, and this motion is given up to the
fan-like runner which confronts the stream at the end of
its passage through the distributing channels. So in the
modern Jonval turbines we have got back nearly to the
old fan set in the bottom of the head race, which Belidor
described in 1737; but with this difference, that the water

SOME INWARD FLOW TURBINES

81

is given a screw motion before it meets the runner, and
so is able to issue therefrom without the whirl which was
at the same time essential to the working of the Basacle
reaction wheel and fatal to its efficiency. The Jonval

FIG. 27. RUNNER OF JONVAL TURBINE, 40 H.P. UNDER HEAD 2 FEET
(ESCHER WYSS AND CO.).

wheel can, theoretically at any rate, like all other tur-
bines, develop power with perfect efficiency.

The Jonval turbine, however, has now for some time
ceded the premier position among reaction turbines to
those with external admission only, and in the discussion

82 WATEE TURBINES

of modern machines it is to these, the inward and mixed
flow turbines, that we must devote the greater part of
our attention.

We have already mentioned Howd's turbine (Fig. 14),
which had in earlier days a great reputation among
New England farmers and others, who desired to make
use of unlimited water in a convenient, but not neces-
sarily efi&cient, manner. Howd's turbine was indeed,
thanks to its cheapness and simplicity, well known to
power users of that class for many years before it was
taken up and scientifically treated by Francis in the
Lowell experiments. Francis, reviewing his work in 1849,
mentions some of the advantages of the inward flow
machine, but remarks that a great increase in efficiency
must be made before it can compare with the Fourneyron
turbine in economy of working.

This increase was effected by James Thomson's in-
vention of 1850 (Fig. 24) — an invention which first put
the inward flow turbine into the field of scientific en-
gineering — and was effected in great part by increasing
the length of the blades, and introducing adjustable
guides. By these means the inventor claimed to secure,,
and unquestionably did, in fact, secure, an increased
efficiency at full load, a more economical system of con-
trol, and an almost perfect regularity of motion.

Fig. 24 represents a case wheel as made by Gilbert
Gilkes and Co., of Kendal, who have developed the native
British turbine with a great deal of success. One side of
the case is removed, and one half of the wheel cover, so
that it is possible to follow the path of the water, from its
entrance into the case at the top, between the movable
guide blades, and into the wheel. From this the water
is discharged near the hub, and then pours out of the
case in an axial direction, by the pipes shown in Fig. 28^

SOME INWARD FLOW TURBINES

88

The larger turbines are built symmetrically, and the water
leaves by two pipes in opposite directions, but in many
of the smaller machines the water is discharged only
from the lower end of the axis, which is then set vertically,
80 that the weight of the wheel to some extent compen-
sates the upward pressure of the water.

FIG. 28. VORTEX TURBINE, COVER REPLACED.

The spiral guide blades are four or six in number, ac-
cording to the size of the wheel, forged of steel, pivoted
on pins near to their ends, and adjusted by the connect-
ing rods and cranks, which can be seen in Pig. 24 keyed
on to the long shafts projecting from the front of the case.
These shafts are connected, as shown in Fig. 28, so that

84 WATEE TURBINES

every adjustment takes effect equally on all the guides.
The blades of the wheel are also forged, with lugs on their
edges, which are riveted through the crown plates, so that
the blades are not susceptible of any adjustment.

When the turbine is working normally under full load
the speed of the rim is that due to half the head, namely,
^^GH feet per second, and the water enters the wheel
with this velocity, at a pressure of half the head.
This pressure is spent to a certain extent in developing
the required velocity of discharge (the velocity of the
inner rim of the wheel), but to a much greater extent in
overcoming the outward pressure of the great weight oif
rotating water in the wheel; a pressure proportional, as
we have seen, to the square of the speed of rotation. The
turbine is driven like the old turbines of the Garonne by
a forced vortex in which the blades are placed, but with
this difference, that in the old turbine the wheel was in
the vortex, while, in the new one, the vortex is in the
wheel; in the old turbine, too, as in Burdin's turbine,
the action of gravity on the water took place while it
was in contact with the blades, necessitating a rotor of
enormous size, whereas in the modern wheel gravity does
its work in the supply pipe.

Now, if by fluctuation of the load on the turbine the
speed is momentarily increased, the pressure at the cir-
cumference increases as the square of the speed, and, as
it increases, the velocity of the water at admission drops,
with the twofold effect, that the flow is diminished, and
that there is a shock on the backs of the blades as they
meet the water, so that the original speed of the wheel
is very quickly restored. If, on the other hand, an in-
creased load reduces the speed of the wheel for an instant,
the flow IS immediately increased, and this greater volume
of water enters the wheel with a shock due not only to

SOME INWARD FLOW TURBINES 85

its own increased velocity, but also to the diminished
speed of the blades themselves; and this shock, objection-
able as it may be from the point of view of the seeker
after efficiency, causes a large torque, and so ensures the
stability of the motion.

Even without attention, then, the case wheel may be
trusted to maintain a fairly uniform speed, and may for
this reason be run without a governor, a saving both in
first cost and in the expense of upkeep; but if the turbine
is to run at low load for any length of time, the con-
scientious engineer will not tolerate either the slightly
increased speed, or the loss by impact, involved in the
automatic regulation.

For this reason the guides are hinged, and may be
adjusted by turning a hand wheel so that their outer
ends are shut down on to the wheel, narrowing the
channels of the distributor, and reducing the flow; and
this regulation can be effected with far less loss of effi-
ciency than in any of the turbines of the more impulsive
type, for two reasons. Firstly, because a slight altera-
tion of the direction of the blades is sufficient to close
the channels as required, so that the velocity of the water
relative to the wheel at admission is unaffected; and
secondly, because, though the velocity of discharge must
of necessity be somewhat diminished, the said velocity is
always so small that this is not a serious matter. For
these two reasons, regulation by the guide blades does
not perceptibly affect the pressure, or (consequently) the
velocity, at admission, so that the water still enters with-
out shock, and leaves with very little motion.

We have dilated at some length on the merits and
beauties of the vortex turbine, as the modern case-wheel
is called, and probably there is no machine calculated to
rouse so much artistic enthusiasm in the breast of an

86 WATEE TURBINES

engineer; but, like all things earthly, it has its limit-
ations; and its most serious limitation is this: that the
slow speed at which the water enters the wheel requires
a very large wheel to allow sufficient flow for the de-
velopment of much power, particularly from a low fall;
and the length of the blades, which is an essential feature
of the design, implies a heavy wheel, containing while in
motion a great weight of water. But a more serious in-
convenience results from the size of the wheel. The
speed of the rim is in every case the free velocity due to
half the head, so that the speed of the rim under a head
of 50 feet would be 40 feet per second, and the speed of
rotation of a wheel of 2 feet diameter, capable of de-
veloping 50 H.P., with a flow of about 4,000 gallons a
minute, would be not more than 382 revolutions per
minute — too slow a speed for running a dynamo.

Now, as a wheel of some size is an absolute necessity,
the speed of rotation of a vortex turbine under a given
fall is very strictly limited, while the weight of the rotor
restricts less rigidly the greatest power that is by any
means obtainable from this type of machine. For very
large powers and for very low falls we have recourse to
turbines of the Francis and mixed flow classes; but for
such purposes as lighting and power supply for a country
house or farm, under a head of 50 to 200 feet, the vortex
turbine is probably the best, as it is certainly the simplest,
machine that has ever been produced.

Many of the features of the vortex wheel will be found
in all external admission turbines, as, for instance, the
movable guides by means of which the flow is regulated
in all the larger and more elaborate machines, but the
features which render the case wheel unsuitable for very
high powers or very low falls have in some of the other
machines been abolished. Thus it is usual in a Francis

SOME INWAED FLOW TUEBINES 87

turbine to find the gaides inclined (as in Fig. 26) at a
considerable angle to the rim of the wheel, so that the
flow is large even through a small runner. To facilitate
a still larger flow, the blades are made very wide; but,
of course, this means that it is no longer possible to
maintain a large channel at discharge by giving a conical
form to the crown plates, and so it is not possible to
carry the blades very far towards the centre, where they
would approach each other too closely. Short blades
are therefore used, so that there is not a great deal of
water in the wheel when in motion, and the bearings are
therefore subject to less strain than in Thomson's wheel.
On the other hand there is not the same mass of water
to exert centrifugal force, in order to regulate the speed,
and steadiness of motion is to some extent sacrificed.

The problem of control also becomes more difficult
than before, as, in order to narrow the distributor pass-
ages, it is necessary to alter the inclination of the guide
blades, thereby causing a certain amount of shock at
admission. The losses due to this cause are, however,
small.

The general construction of the Francis runner is not
at all unlike that of the Girard. The crown (Fig. 25) is
cylindrical in form, and so like the crown of the Girard
wheel, shown in Fig. 21, that one might almost be taken
for the other at first sight. The wheels, too, are built up
in very much the same way; the crown being connected
to the hub by a conical or curved web, which forms one
face of the wheel, and serves to deflect the water as it
issues from the channels, so that it leaves the machine
axially. The pressure of the water on this web exerts
considerable thrust along the shaft of the turbine, but
this is now balanced by the way in which the turbine
is set.

88 WATEE TURBINES

We have claimed for Francis turbines that they are
able to deal with a very large flow of water in a very
small wheel, as water is admitted with considerable ve-
locity relative to the rotor; but the real difficulty of
dealing with large quantities lies not in the admission,
but in the discharge. The water, if discharged near the
shaft, leaves with but little velocity, and wherever dis-
charged, it must leave at a small angle with the surface,
so that it is necessary that the surface from which dis-
charge takes place should be of considerable extent.

It is found in the Francis turbine that the internal
surface of the cylindrical crown is inadequate for the
discharge; as the water flows inwards its motion is to be
retarded, and it is necessary that some should escape
from the channels to make this possible. For this reason
the crown is built with only one face, so that some of the
water can escape from the bottom of the blades while
the rest flows inwards; but the energy of the former is
not wasted, for, though its path in the wheel is very
short, it is also very crooked, and the water leaves in
a direction opposed to that of the wheel's motion,
practically without velocity. These are the reasons for
the form of the Francis runner shown in Fig. 25, and for
high falls it would be hard to beat.

The Francis turbine, in fact, is decidedly the best for
large installations, and it holds the market at present.
The 10,000 H.P. Francis turbine erected • by Escher
Wyss & Go. at Niagara, is probably the most powerful
hydraulic engine ever constructed.

For other conditions other types of runner are neces-
sary. The wheel shown in Fig. 25 has a rim speed of
little more than half the free velocity due to the fall, and
would therefore be very suitable for driving a dynamo
under a head of 60 to 200 feet; the wheel in Fig. 26 on

SOME INWAED FLOW TUEBINES 89

the other hand, is designed to run under a head of less
than 60 feet, and has a peripheral velocity about twice
that due to the fall, so that it, too, is well suited for
electrical work, its normal speed being 490 E.P.M.

Mixed Flow Turbines.

The elements of design which have rendered the com-
pact inward flow turbine capable of developing such .
enormous power, are present in a still higher degree in
the remaining wheel that we have to consider.

The conditions that confront the manufacturer of tur-
bines for use in this country are the absence of high
falls, combined generally with copious water supply, and
the necessity in many cases of running at speeds sufl5-
cient for electric generation.

High efficiency is no longer the suminum bommi. What
is wanted is a turbine that will run steadily, utilize a
large flow, and that with a moderate peripheral speed,
and high speed of rotation.

The first condition is to a large extent secured by
using external admission only; the second requires that
the action should be very different from that in the "pure
reaction " type of machine. Now if the blades are made
as flat as is consistent with the absence of shock at
admission, and inclined at a moderate angle, say 35°, to
the rim, it is possible to secure a peripheral speed of about
twice the free velocity due to the fall, or about 26^ feet
per second on a 6 foot fall; and, given that fall, this is
about the highest speed attainable. Now if we wish to
couple directly to a dynamo, we want a speed of rotation
of about 500 E.P.M., so that we must have a wheel of

90

WATEE TUEBINES

ODly 1 foot diameter, while, reckoning on 70 per cent,
efficiency, the flow must be 13 gallons per second per
horse-power.

The water enters, as we have said, at a considerable
angle with the surface of *he wheel, and, if we make the

FIG. 29. " victor" mixed flow rotor.

barrel of some length, there need be no difficulty about
letting enough into the wheel for quite a large power,
but since it must leave at a small inclination to the
surface of the rotor, the discharge may present some
difficulty; at any rate, the surface of discharge must be
much larger than the surface of admission, and yet the
water has to attain the discharge end of the channel by

SOME INWAED FLOW TUEBINES 91

flowing in a smooth curve, and, so far as possible, by
inward flow towards the shaft.

How this result has been attained is very strikingly
illustrated by the mixed flow rotor shown in Fig. 29. A
very large development of the sidelong discharge of the
Francis turbine has taken place, and the water now leaves
not only inwards and axially, but even outwards, almost
from the surface by which it entered. The greater part
of the water in mixed flow turbines leaves axially; it is
important to keep the a^mount of water discharged out-
wards within very moderate limits, lest the effect of
centrifugal force on that water should cause the machine
to experience the disadvantage of unstable running
common to all outward flow reaction turbines.

In a mixed flow turbine, such as we have described, all
the water enters the rotor at the same pressure and
velocity, but the pressure of that part of the water which
is discharged from the inner edges of the blades is used
up in overcoming its centrifugal tendency, while that of
the water discharged from the outward facing edges goes
to accelerate the flow. It follows that if we examine the
motion of the water as it is discharged from the long
edge of one of the blades, we find it everywhere of the
same pressure, but moving at a higher and higher speed
as we follow the edge away from the centre of the wheel,
and, as the speed of discharge gets higher, the aperture
between the blades gets narrower.

It might be possible to investigate very fully all the
different sources of loss in connection with this machine
and to criticize it with more or less justice on the sub-
ject of its efficiency; the fact is that this turbine was
never designed to satisfy a theoretical standard of per-
formance, but to meet a very real need for a turbine that
should be capable of developing considerable power at

92

WATEK TUEBINES

high speed under a fall of a few feet, and so well has
it met this need, that there are tarbines on the market at
the present day, which, with a rotor of 9 inches diameter,
will develope 2 H.P. under a 6 feet fall, at speeds of

FIG. aO. DISTRIBUTOR FOR CYLINDER GATE TURBINE.
(PICCARD PICTET ET CIE.)

from 300 to 400 E.P.M. ; and that with an efficiency of
something like 75%.

The efficiency of these turbines may, then, be very
high. This is the machine used above all others by
the average miller, and there are probably more of them
in use in the world at the present day than of all

SOME INWARD FLOW TUEBINES 93

the other turbines put together, though it may well be
that the aggregate power of the Francis machines would
exceed theirs. This wide use among small power con-
sumers, who have often a great flow of water at their
disposal, renders initial cheapness a more important
attribute than economy of regulation, and, for the sake
of cheapness, this regulation is generally effected by a
gate sliding on the outside or inside of the distributing
cylinder. The latter type of gate has the advantage that
the water cannot spread out in the distributor and lose
speed after passing the gate; on the other hand, the
inner gate changes the direction of the stream entering
the rotor as it is shut down.

When gates of either of these types are used, the
stream will naturally spread on entering the rotor, so
that it is not easy to keep up the pressure at admission,
and the chief loss of efficiency arises from this source.
The reader may remember that this difficulty was over-
come in the case of the Jonval turbine by the use of a
number of concentric rings of channels in the rotor, of
which one or more could be cut out of action by the
gate; a similar system has been employed with some
success both in inward and mixed flow turbines, the
different rings of admission ports being situated one
above the other up the barrel of the rotor; but in the
mixed flow wheel, owing partly to difficulties of manu-
facture, and partly to the desirability of allowing the
water to adjust its own curves of motion (particularly
at full load) by passing from one channel into the next,
the different rings are not entirely divided, each full-load
channel being fitted with partitions which do not entirely
fill it. Similar partitions are often fitted in the rotors of
turbines not so controlled (Fig. 31).

When an internal gate has exactly reached one

94 WATEE TUEBINES

of the partitions, the sections in use are full, and the
turbine will run almost as efficiently as at full load, but
such high efficiency cannot be expected when one of the
sections is partly gated, and so using water at lower
pressure than do the other sections. ^"^

The cylinder gate is not very far behind the more
complicated regulators in efficiency, and it is much
cheaper to construct, so that it both is, and will probably
continue to be, the most popular among the small users
for whom mixed flow turbines are principally designed.

: o
5 Q
g <

CHAPTER VIII.
EEECTION AND CONTEOL,

THE problem of erection, which is so complicated in
the case of the reciprocating steam or oil engine,
and which has given rise in this connection to endless
litigation, is vastly simplified in the case of water and
steam turbines by the absence of the vibration which
requires heavy foundations and massy bedplates for all
machines with reciprocating parts.

In the early days of the art it was much debated
whether a turbine ought to be set above or below the tail
water. If the first arrangement were adopted, a part of
the head above the wheel was necessarily sacrificed; and
if the second, difficulties as to clearance and back press-
ure were inevitable. It has now become the custom to
set reaction turbines, in a manner introduced by Jonval,
at the head of a short suction pipe leading down into the
tail race; this ensures that water leaving the wheel will
flow down the pipe and out of the way as quickly as pos-
sible, and at the same time secures that the difference of
pressure between the admission and discharge ends of
the machine shall be the full difference due to the head.

But this is not the only advantage obtained by the use
of a suction tube, for it is an occasional, and might
with advantage be a very common, practice to form this
tube of a small section near the turbine, giving it a flare

96

EEECTION AND CONTROL 97

as it enters the water. The water leaves the turbine, how-
ever well designed, with a certain speed, and so enters
the tube, but as the section of the tube increases, the
motion of the water is retarded, and its pressure con-
sequently increased. Thus the diflference in pressure be-
tween the two ends of the pipe is more than that caused
by its length, and the kinetic energy of the discharged
water is not entirely wasted.

Further, the suction along the shaft, exerted on the
rotor by the water in the tube, balances the pressure of
the water on the conical face, and so does away with
thrust on the bearings. To secure that all such thrust is
accurately neutralized, it is now a common practice to
mount reaction turbines in pairs on the same axis (Fig.
81).

The ^smaller machines, particularly those for use in
connection with the low falls available on the Thames and
other English rivers, are supplied by the manufacturers
in a compact form, requiring nothing but a resting place,
a supply of water to the outside of the case, and a channel
to conduct the discharged fluid from the base of the
turbine. These wheels are now almost invariably mounted
at the top of suction tubes, and only just below the surface',
of the head water, and the operation of mounting is some-
what as follows.

A floor is constructed over the tail race, and on a level
with the bottom of the head water ; this floor may be
carried by brickwork arches, steel joists, or wooden beams,
according to the weight of machinery to be erected.
Water is admitted to the floor by a large sluice, which is
closed when it is necessary to get at the turbines for
repairs, and it is carried down into the tail race by pipes
of an inverted funnel shape, which it enters by holes in
the floor. To erect a turbine all that is necessary is to

H

1

raiBRineooio^^^

EEECTION AND CONTBOL 99

seat it on the floor above the mouth of the suction pipe,
just as the vortex turbine is seen placed in the illustration
(Fig. 82); even the bolts used for its better securing
are not a necessity.

The larger machines, however, are treated with the
respect which they deserve, and are not infrequently
built into great flumes of masonry at enormous expense.
In other cases the water is conducted down iron pipes
to the turbine, and these supply pipes are in turn
surrounded by a well of brickwork giving access to the
machine. It must be borne in mind that as one of the
principal uses of turbines is for direct coupling to
dynamos, which naturally are situated in a power house
directly above the turbine itself, the latter must be under-
ground, and, therefore, when high falls are to be used, the
construction of elaborate wheelpits, such as those shown
in the illustration of Messrs. Escher Wyss and Co.'s in-
stallation at Niagara, is one of the features of the under-
taking. For the development of power under very high
falls it is common to use machines with horizontal axes,
like the Girard turbines at Gurtnellen, and the power
house is then situate at the base of the fall, the penstock
being in the open; or, if machines with vertical axes are
used for very high falls, they are surrounded by a steel
case, into which the water enters at the side, while the
shaft pierces the top of the case.

The solution of all these problems of erection depends,
perhaps even more than does the design of the turbine
itself, on the local conditions; thus, though flumes of
brickwork may suffice to carry the water to a turbine set
under a low fall, a steel pipe is necessary to withstand
the pressure of a high head. Now, to withstand a given
pressure it is necessary that the thickness of a pipe
should be proportional to its diameter, so that the

mMm»^^» i ^xii ^ ^n , ^ ' ^ -

FIG. 33. 10,000 H.P. FRANCIS TURBINE INSTALLED AT NIAGARA.
(ESCHER WYSS AND CO.)

ERECTION AND CONTEOL 101

amount of metal in it varies as the square of the
diameter, and the cost of a large pipe is therefore an
important consideration. So is the loss of head by fric-
tion in the pipe, and as this loss is proportional to its
length, and inversely proportional to fifth power of
its diameter, it is important that the consideration of
first cost should not lead us to economize unduly in the
section.

We can, however, save both in first cost and in economy
by making the pipe as short as possible, and, for a given
head, this object is of course to be obtained by making it
as nearly vertical as may be.

" The only two rules, then, that can be confidently given
for the installation of every turbine are: — that it should
be situate directly above the tail race at a height of
not more than 25 feet, that the lower part of the pipe
should be vertical, and that, at any rate where very large
and heavy rotors are used, the power house should be
situate at a short distance directly above the machine, so
that the dynamo armatures may be keyed or pressed on
to the shafts of the turbines.

♦ ♦ * ♦ »

The operation of the turbines is generally controlled
from the power house, when they are used for driving
dynamos, or, in mills, from the floor immediately above
that on which the turbines are situate. If it is required
to run the wheel at low load, it is always possible to effect
by hand the necessary regulation of the sluice, guide
blades, or nozzle, by which the flow is regulated; but the
construction of even the largest turbines is so simple, and
their running so smooth, that it is an unnecessary expense
and trouble to have a man always on the spot to look after
them, and it is therefore very desirable to render them
self-governing.

102 WATEE TURBINES

Two properties are required of a governor: — ^that it
should act with the greatest promptitude in the case of
any serious divergence from the normal speed, and that
it should be sensitive and powerful enough to keep
the speed appreciably constant.

Now, whether it is a steam engine, a water turbine, or
any other form of prime mover that we are controlling,
it is not easy to combine these two properties in one
governor. A governor which is to adjust the gate or blades
with extreme accuracy must move it slowly into position,
and this is inconsistent with prompt action. A governor,
too, which is to satisfy the first condition must act directly
on the gate; but if it is to do this, serious difficulties will
be found in the way of constructing it, so that it may
control a heavy gate or the numerous bearings of adjust-
able guide blades, when the variation of speed is so
small as 1 in 300.

Nearly, if not quite, all mechanical governors act on
the centrifugal principle; that is to say, the controlling
force is derived from the tendency of two weights, carried
on a spindle in gear with the rotor, to fly outwards. When
the wheel is running at normal speed, this outward ten-
dency is exactly balanced by springs, which may be ad-
justed by hand to any required speed. If the speed of
the machine be at all increased, the weights move out,
stretching the springs. But, obviously, the force which
these weights exert is proportional to the variation of
speed, so that they are rather ineffective when this varia-
tion is slight; also, this governor can only act power-
fully if the radius of motion of the balls is rather a large
one; and then they have a tendency to hunt, or sway out
and in, which would make the motion very unsteady, if
they were not so controlled as to act only under strong
provocation in the form of a variation of speed.

EEECTION AND CONTEOL 108

For these reasons it is now usual to fit the larger
machines with two governors, of which one acts promptly,
generally on the gate, while the other acts slowly on the
nozzle or guides, with great delicacy and power.

Of this governor prompt action is not required, so that
it may go to work by a roundabout way; but it must act
with extreme delicacy, and with great power, however
slight the variation from the normal speed. In con-
structing a governor of this sort we do not, therefore,
have recourse to the actual centrifugal action of the
weights for the power required to move the gate or
blades, but we make this force unlock the door by which
a far more powerful agent comes into play.

There are a number of mechanical devices by means of
which this is effected. In one, very commonly used on
steam engines, the governor operates by throwing into
gear cog-wheels through which the regulating valves
are driven from the shaft of the engine. A device more
commonly found in turbines connects the governor
directly to a small slide valve, through which the steam
or water is admitted from the boiler or head to a small
piston; and by means of this the admission valve is
operated.

The distinguishing feature of both these mechanisms
is the fact that the heavy work necessary to regulate the
flow is performed directly by the working fluid, so that
the governor has a duty requiring very little mechanical
force, and it can therefore be constructed in such a
fashion as to act with extreme delicacy; also its action is
very powerful, even when the variation from the normal
speed is slight.

Pig. 34 shows a governor of this last type as
applied to a Pelton wheel. The flow in these wheels is
regulated by the extrusion of a needle through the con-

(4
c

iz; ^

^ 1:

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^ Hi

525 3

O

EEECTION AND CONTROL 105

verging nozzle, so that speed, direction and line of action
of the stream are unaltered — this causes the very high
efficiency of these wheels at low load — and the needle is
operated either by hand or by a piston on the same shaft.
The figure shows the piston C sliding in a small cylinder
to which water is admitted, on either side of the piston,
by the motion of the slide valve E, controlled directly by
the governor.

This gives a delicate and efficient control, but by no
means a rapid one, so the nozzles are also set on a ball
and socket joint, which allows them to be deflected, in
the case of a sudden rise of speed, and the water is then
thrown clear of the bucket. Of course this involves a
waste of energy, but, in emergency, efficiency must at
times be sacrificed.

One more point requires mention. It does not often
fall to the lot of an engineer to erect plants in England
under a high head, but when such a head is used, he
must bear in mind that while the turbine is running
there is a flow of water throughout the entire length of
the supply pipe, and when the admission is reduced or shut
down, the whole moving mass of water is checked, so that
a shock like that in a hydraulic ram acts on the base
of the pipe, and in a less degree on its whole length.
The flow must therefore be checked very slowly; and yet
the action on the wheel must at times be very quickly
stopped. We have to check the action therefore, either,
as is done in the Pelton wheel, by diverting the stream,
and allowing it to run to waste; or, in a rather more
economical fashion, by the introduction of a sort of
buffer, which takes the form of a reservoir of compressed
air in permanent connection with the base of the pipe.
Into this the water rushes, when suddenly debarred
from the turbine, and it continues to fill this reservoir.

106 WATEK TUEBINES

against a rising air pressure, until the motion of the
column of water behind has slowed down. Then the air
begins to recover, and forces the water out of the reservoir
again, either through the turbine or back to the head,
so that none of the energy is finally lost to the machine.
If this device is used, the only danger is that the steady
increase of pressure in the reservoir may be too much
for it, or for the supply pipe, before the flow is checked,
and it is therefore necessary to provide a reservoir of
volume proportional to the section of the pipe and to
the square of the speed of flow in it at full load. Of
course, in some of the machines which we have de-
scribed, such a reservoir would be extremely difficult to
construct, and the compressed air inside, under a head
of 800 or 900 feet of water, would be a fruitful source of
danger, so that in such cases we must either combine
with it the deflecting nozzle, or else rest satisfied with a
slow cut off for the turbine.

Such are, in brief, the solved and unsolved problems
presented by the installation of water turbines, a branch
of engineering enterprise not yet fully worked out, and a
science not yet perfected, offering at once the simplest of
all prime movers to the user of natural power, and at the
same time affording some of the prettiest of problems to
the expert engineer.

PAKT II

STEAM TURBINES

CHAPTER I.
THE STEAM ENGINE.

WHEN Humphrey Potter, in 1713, devised auto-
matic steam valves for use in connection with a
pumping engine, the engineers of his time were prompt to
recognize the truth that this step was the first and most
difficult one in a great advance in the arts of civilization;
but they failed to perceive the further truth, which indeed
we have only begun to discern at the present day, that
this was not a step in the direction of the true and
natural development of the steam engine, but, on the
contrary, one which was to postpone that development
for a hundred years, while the minds of men wandered
in the paths that the inventor had laid open.

Hero of Syracuse and Giovanni Branca had used the
pressure of steam escaping from a boiler to drive a wheel,
and, familiar as we are with the high pressure boilers in
use at the present day, it seems almost incredible that
the engineers of the eighteenth century were in the habit
of using steam to operate a piston not by pressure at all,
but by suction. Yet this was in fact the case.

At the time to which we refer, steam was not used to
produce rotation. The crank, an essential part of the
rotary-reciprocating mechanisms which are common
to-day in so many forms, was not yet invented. The
purpose for which steam was used was that of pumping,

109

110

STEAM TUEBINES

and the reciprocating pump, a very old mechanism, re-
quired a reciprocating motion to drive it, and naturally
suggested the steam cylinder and piston, which was well
adapted for the purpose. If we notice what was at this
time the desired object, it becomes clearer to us why the
reciprocating engine, ill-adapted as it is for the production
of rotary motion, was the first, and for a long time the
only successful, steam engine. In these early pumping

FIG. 35. PUMPING ENGINE (1710).

engines, steam was admitted to the bottom of the cylinder
at atmospheric pressure. The weight of the pump rod
drew the piston up, and the steam was then condensed,
forming a partial vacuum below the piston, which was
thus forced downwards by the pressure of the air above
it. As a matter of fact, atmospheric pressure at admission
was not the invariable rule, and before the time of Watt
it became customary to use a double acting engine with
a higher pressure.

Now the invention of the automatic steam valve made

THE STEAM ENGINE 111

all the difference to this engine, and it was already popu-
lar when Watt took it in hand; for it was the one kind
of heat engine that would really go by itself. Watt's im-
provements raised the reciprocating engine almost to its
present day level. He observed, and he applied in his
inventions, the following principles: (1) that the pressure
to which the steam could be raised by heating was just
as important as (indeed, more so than) the vacuum which
could be produced by cooling it; (2) that the energy of
the steam required careful husbanding; and (8) that the
steam engine might be applied to several other purposes
than that of pumping out Cornish tin mines.

The steam that Watt turned into his cylinder was a
valuable product; it cost money to produce, and was
able to do a good deal of work when properly treated.
The inventor did not see any advantage in wasting half
its heat to warm up a metal cylinder, which had been
cooled in condensing the steam during the previous stroke;
he therefore stated, in his celebrated patent specification
of 1769, the principle that the working cylinder should
be maintained, so far as possible, at a uniform tempera-
ture; a principle which it has not been possible to carry
out in any engine in which the work is done by steam
remaining in contact with the containing vessel during
the operation, but to which an approximation is made in
compound, triple and quadruple expansion engines.

Thus an efficient engine was created, and it was soon
applied to produce rotary motion by means of a connect-
ing rod driving a shaft by gear wheels or a crank. From
that time the advance of steam power was rapid, until it
reached what was long thought to be its highest develop-
ment, in the locomotive engine of George Stephenson,
who has been so often called the inventor of the steam
engine. Tempora mutantur. We are already faced by the

1

112 STEAM TUKBINES

possibility that the locomotive steam engine may be
superseded by the electuc motor, but steam power is
almost as essential a factor in engineering enterprises as
heretofore.

So a machine, designed for the purpose of producing a
purely reciprocating motion, came to be the accepted
prime mover for the production of rotation; and for a
century never an engineer dared to devise a steam
engine, but he so clothed it with valves and links and
reciprocating mechanisms as to make of it a kind of
conglomeration of inter-dependent sewing machines.

Fifty years after the time of Watt the water turbine
was first heard of in this country, and it came very quickly
into prominence; but it was still another fifty years be-
fore any successful attempt was made to apply similar
machines to the development of steam power. It is not
to be supposed that no inefiEiectual efforts were made in
this direction: the records of the Patent Office are full of
unsuccessful experiments, but every one of these resulted
in a machine so inefficient, and consequently such a
fearful " steam-eater," that it had to be abandoned. The
fact is, that it is not sufficient to produce a machine con-
forming to the general mechanical laws laid down for
water turbines, in order to possess a satisfactory steam
turbine. That such an engine must obey these laws (with
<;ertain modifications) is true; but it is also true that it
must be designed in accordance with principles depending
on the nature of the working fluid, and to which every
steam engine must more or less conform.

In all heat engines, of which class steam engines form
the most important section, the action is of one general
type: the working fluid is heated, and rises in pressure,
it then expands, doing work in the engine, and at the
same time giving up a portion of its heat until it is dis-

THE STEAM ENGINE 118

charged, carrying off a certain amount of unused energy
to the air or to the condenser. In steam engines, in
particular, the heat derived from the furnace performs
two operations, namely, converting the water into steam,
and raising the steam to a high temperature and pressure.
Now, after the steam has done its work it has fallen in
temperature and pressure, but most of it is still steam,
and is so discharged into the air or into a condenser; and
exhaust into a condenser has this advantage, that, whereas
the steam may in this case leave the cylinder at a tem-
perature of 100° to 120° Fahr., and a pressure of say
2 or 3 inches of mercury, it can only enter the air at a
pressure at least atmospheric, and a temperature above
212^^ Fahr.

Now, considering the case only of the condensing engine,
which is much the more efficient — and practically all
large steam turbines are now provided with condensers —
we see that, of the heat given to the steam in the boiler,
part is employed usefully in the cylinder, and part is
taken on into the condenser and wasted in heating the
condensing water. Of course, the lower the temperature
and pressure at which steam enters the condenser the
less heat will be wasted in this way, and the more
complete will be the expansion in the cylinder. But in
a reciprocating engine the amount of expansion that
can take place in the cylinder is limited by the size of
the cylinder, so that the benefit of a condenser can
never be completely appreciated.

Suppose, however, that we have got a good vacuum in
the condenser, so that discharge takes place from the
cylinder at a pressure of ten inches of mercury and a
temperature of 160° Fahr. Then every pound of steam
going through the engine carries into the condenser a
definite amount — 1,131 units — of heat, and if the feed

I

114 STEAM TUEBINES

water temperature were 70°, the boiler heat wasted in the
condenser would be 600 units per pound. The amount
of heat used in the cylinder depends on the total heat
which the steam brought from the boiler. The greater'
the proportion of heat used to heat wasted, the higher
the efficiency of the engine; and it is therefore important
that each pound of steam should bring the greatest
possible amount of heat from the boiler; in other words,
that the boiler temperature (and consequently pressure)
should be as high as possible; and for this reason the
boiler pressure in a modern steam engine ranges from
150 to 250 pounds per square inch. To secure sufficient
expansion, two, three, or four cylinders of increasing size
are used in succession.

Consider, for a moment, to what head such a pressure
would be equivalent in water turbine practice. The
volume of a pound of boiler steam under a pressure of
200 pounds to the square inch, or 28,800 pounds to the
square foot, is 2*3 cubic feet, so that the pressure is
equivalent to that of a column of the steam 62,000 feet in
height. Now if it is difficult, and we know that it is so,
to design a turbine to run under a head of from two to
three thousand feet, can we blame the inventors who
found difficulty in producing a satisfactory turbine for a
head of 12 miles?

As a matter of fact, it is found that steam from a
boiler under a pressure of 200 pounds per square inch dis-
charges into the atmosphere with a velocity of something
over 3,000 feet per second, and if the steam be super-
heated to the extent of 100"" Fahr. (a treatment which
adds greatly to the economy of the engine) the speed of
discharge is raised to about 3,500 feet per second. If
we take the conditions under which turbines are most
commonly run — with a boiler pressure, that is to say, of

THE STEAM ENGINE 115

150 to 200 pounds, considerable superheat, and a vacuum
of about 27 inches of mercury — the free velocity of dis-
charge from boiler to condenser will be over 4,000 feet per
second. Even saturated steam at atmospheric pressure
would discharge into a perfect vacuum at a speed of
nearly 3,000 feet per second.

Perhaps the most suitable of all the turbines described
in the former part of this work, for use under a head of
great height, is the Pelton wheel; but a Pelton wheel, in
order to develop efl&ciently the power of a jet moving at
4,000 feet per second, would have to rotate with a rim
speed of 2,000 feet per second itself. Unfortunately, the
outside limit of rim speeds with modern materials is
considerably short of this figure, and for a steel wheel,
having most of its weight in the rim, the limit is reached
at about 700 feet per second, though no one would think
of running this speed very close.

This problem, how to use a head so great that no
single wheel can do justice to it, was the one confronting
the would-be designers of steam turbines. A certain
amount of guidance was afforded by Jonval, the inventor
of the parallel flow turbine, who, when using a head of
water too great for the speed which he wished to develop,
had in several cases erected two water turbines, one
below the other, so that the second was run by the water
discharged from the first, at a height of half the head.
Jonval invented the system of compounding, on which
every successful steam turbine, with one solitary and
interesting exception, has been constructed.

CHAPTER II.
THE HISTOEY OF THE STEAM TUEBINE.

WE have already mentioned Hero's reaction wheel,
the earliest known form of steam engine. Of
course, this was a very ineflScient machine, because, while
the wheel turned slowly, the steam escaped with great
velocity, carrying oflf all but a very small part of the
energy which it brought from the boiler. Nevertheless,
this machine was re-invented and patented by De Eem-
pelen in 1784, under the style of " A Reaction Machine
set in motion by Fire, Air, Water, or any other Fluid " ;
with the further explanation that it was primarily in-
tended to be driven by "boiling water or rather the
vapour proceeding therefrom."

Engineers were slow to drop the application of the
reaction principle pure and simple; in fact there is a
patent granted to one Francis Bresson, in 1852, for a
method of driving a train by the reaction of a jet of
steam projected out of the van, and many attempts were
made to improve De Kempelen's wheel by increasing
the number of arms, altering their shape, and so on.
One really valuable suggestion was made by Burstall in
1838, to the. effect that a set of arms curving in the oppo-
site direction should be mounted on the same shaft, for
the purpose of reversing the engine.

The first suggestion, however, that really went to curing

ii6

THE HISTOEY OF THE STEAM TUEBINE 117

the radical defects of the reaction wheel, was that em-
bodied in Hale's patent of 1836, which was, that steam
issuing froin a simple reaction wheel should be diverted
to the use of a second wheel mounted on the same shaft.
The mechanism by which Hale proposed to effect this
diversion was unsatisfactory, as there was no adequate
provision made for destroying the angular momentum
of the steam about the shaft, between the times of its
issuing from the first wheel and enter-
ing the second; however, the principle
of the invention was sound enough.

Prom this time onward the possi-
bilities of the steam turbine began to
be realized, and among the numerous
patents for water turbines which fol-
lowed the success of Fourneyron's
wheel, few can be found that do not
claim the application of the same
machine to steam power. For the most
part these inventions are valueless, so
far, at least, as steam is concerned,
because they neglect the compounding
essential to success; but there are aria. 36. harthan's
few which deserve mention. ^^^^^^^ (^^^^)-

The first in which any satisfactory attempt to com-
pound the turbine is made, is the subject of a patent of
Harthan in 1858. The machine consists of a pair of
wheels with curved blades, through which parallel flow
takes place; and between the two moving wheels are a
set of blades exactly similar but reversed, so that the
direction of the steam is changed between its discharge
from the first wheel and its admission to the second.
The turbine is therefore almost exactly like the modern
De Laval, compounded by the addition of a second

118

STEAM TUEBINES

wheel, but it lacks the peculiar nozzle to which the De
Laval turbine owes its success.

A second ingenious inventor, after passing his steam
through a parallel flow turbine wheel, conducts the ex-
haust by a looped channel into the same wheel again,
and then again, until a number of impulses have been
derived from it, and all its energy is communicated to the

wheel. The obvious defect of this
machine is that, as the steam
expands further and further, its
temperature continually drops,
so that it cools down the blades
through which it passes at its
last admission to the wheel; and
these, in turn, meeting the high
pressure steam from the boiler,
abstract heat from it, to the
great detriment of the efficiency
of the engine. In fact, this tur-
bine defies the general principle
that, where complete expansion
is to take place, high pressure
and low pressure steam must not
come in contact with the same
piece of metal. The different
stages of the expansion ought to
take place in different parts of the machine.

A turbine free from this defect is described in the
same specification (949 of 1865). The rotor of this ma-
chine contains a number of separate blade rows very
similar to those in the earlier compound turbine. In this
machine, however, the steam is conducted from row to
row by channels, and the intention appears to be that
the steam shall expand in these channels, and that the

FIG. 37. perrigault's

TURBINE (1865).

THE HISTORY OF THE STEAM TURBINE 119

pressure should drop, not in one step, as in the earlier
machine, but in a^ number of stages corresponding to the
number of blade rows. The author is not aware that this
turbine was ever constructed; possibly the practical difl&-
culties would have been found insurmountable in the
early days of machine tools; the design of the steam
passages, too, is not correct; but it might have been
fairly successful. Harthan's turbine is practically iden-
tical with the smaller A.E.G. turbines now very popular
in Germany, thanks to the improvement effected by the
divergent nozzle, which is a feature
of all modern machines. A combina-
tion of the two turbines of 1858 and
1865 has produced the American
Curtis turbine, one of the most suc-
cessful yet constructed.

All these turbines are obviously
impulse turbines, but we may now
make use of a second method of clas-
sification of compound turbines, in
addition to that on which we relied
in the earlier part of this work — we
may divide them into those in which the whole velocity
due to the head of steam is developed in the nozzle at
admission to the first wheel, as in Harthan's turbine ;
and those in which the pressure falls in a serie6 of steps,
and the velocity is developed and annihilated alternately.
Turbines of the latter class are known as many stage
turbines. Those of the former are commonly called
single stage machines, but this description is not an
accurate one, inasmuch as, although there is only a
single pressure stage, the steam velocity is generally
destroyed in a series of steps, and the turbine has there-
fore (except in a few cases) a number of velocity stages.

FIG. 38. PERRIGAULT
(1865).

120 STEAM TURBINES

If we have to design a compound steam turbine of the
single stage type (Fig. 35), to use a steam pressure of
200 pounds per square inch, we must recognize that the
velocity developed at the nozzles will be of the order of
4,000 feet per second. Suppose, then, that we pass this
steam through four rows of moving blades of the form
adopted by Harthan, and through three intermediate
rows of fixed blades of the same shape but reversed.
Then the velocity parted with by the steam in passing
through each moving row will be nearly twice that of the
row itself. It will therefore be necessary to run each
blade row at a speed of 500 feet per second, and the
steam will then give up all its energy to the turbine.
The small A.E.G. turbine is designed on these lines.

If, on the other hand, our object is a many stage turbine,
we may still adopt the impulse type of machine, and the
same rotor blades will still serve our purpose. It is re-
quired now that the steam should enter the first blade
row with a velocity of 1,000 feet per second. This means
a drop in pressure from 200 to just over 150 pounds per
square inch in the nozzles. The same speed is required
at admission to the second blade row, and a somewhat
smaller loss of pressure (about 36 pounds) will be involved.
The drop in pressure in the successive stages of passage
through the turbine diminishes continually, so that the
steam reaches atmospheric pressure only after some ten
stages, each developing a velocity of 1,000 feet per second,
and it does not attain a vacuum of 26 inches until the
same velocity has been generated and destroyed another
seven times. This is the action in the Zoelly turbine.

It must not be supposed, however, that the work done
in the latter turbine is any greater than that done in the
former, in spite of the increased number of blade rows,
for, in the many-stage turbine, the work done in each row

THE HISTOEY OF THE STEAM TURBINE 121

is the same as that done in the last row of the single
stage turbine, but, in the first row of the latter, seven
times as much work is done, in the second row, five times,
and in the third row, three times as much as in the last;
the work done in each row being of course proportional
to the change in energy of the steam as it passes through.
In the many-stage turbine, then, every row of blades
is important, and each does its fair share of the work,
whereas in the impulse turbine the first wheel bears the
burden and heat of the steam, and the others could be
abolished with nothing more than a loss of efl&ciency be-
coming less and less serious as the speed of the wheel
is increased; a fact which will be strikingly brought to
our notice in connection with the De Laval turbine.

We have barely outlined the principal conditions affect-
ing the construction of steam turbines, but we have
already entered more fully into the principles govern-
ing their operation than anyone had done before the
Hon. C. A. Parsons produced the first steam turbine of
practical and commercial merit, the first to be classed for
eflSciency and utility with the reciprocating engine, and
the first at this day in popularity, among the creations of
the large and increasing class of distinguished engineers
who have followed in the path which Mr. Parsons found.

It seems proper, then, to give some account of the
Parsons steam turbine, and of its rivals, before we digress
any further into the rather tempting field of theoretical
discussion.

CHAPTER III.
THE PAESONS STEAM TUEBINE.

PAESONS'S turbine was invented in 1884, but its
early form was very different from that of the huge
machines which are turned out at Heaton nowadays,
and as for its efficiency, it was a great day for the
makers when they got the steam consumption down to
36 pounds per horse-power-hour.

This early form is very clearly described in the speci-
fication of the 1884 patent, which shows clearly the new
and essential features of the turbine. And the really
essential feature was this, that the engine was com-
pounded of a number of simple turbines mounted on
the same shaft. In fact, the rotor was at this time built
up of a number of brass disks or wheels; the rim of
each wheel was cut away, leaving a row of flat project-
ing blades oblique to the plane of the wheel, so that a
blast of steam in the direction of the shaft would tend
to turn the wheel, exactly as a windmill is turned by a
blast of air acting on its sails.

But these blades were not subjected to a blast of
steam parallel to the shaft; for outside each wheel was
a brass ring, and the inner surface of each ring was cut
away, leaving a row of inwardly projecting blades. The
solid part of these rings when bolted together formed a
cylinder which completely surrounded the turbine rotor,

122

THE PAESONS STEAM TUEBINE

123

fitting so closely outside the rotor blades as to allow just
suflBcient clearance for turning; while the rows of fixed
blades, projecting inwardly from the cylinder, separated
the moving rows one from another, and allowed the
drum a bare clearance for rotation. These clearances
were so small that steam, in passing from one end of the
turbine cylinder to the other, had to pass through alter-
nate rows of fixed and moving blades. Now the moving

FIG. 39. AN EARLY PARSONS TURBINE OF 10 H.P.

blades and fixed blades were both oblique to the axis, as
if they were parts of screw-worms, but of right and left-
banded screws respectively, so that the blades of alter-
nate rows were nearly at right angles, and the path of
•steam going through the turbine, while the rotor stood
-still, was a zig-zag with very sharp corners. Its general
direction was then parallel to the shaft.

When the machine was running, the path of the steam
"between the rotor blades was affected by the motion of
these blades, so that its general course through the

124 STEAM TUEBINE8

turbine changed; the direction being, on the whole, in a
screw round the shaft, and the sharp corners being con-
siderably flattened.

The first Parsons turbine was constructed in 1884 and
is now very properly placed, as a machine of historical
interest, in the South Kensington Museum. This tur-
bine developed 20 H.P. at a speed of 18,000 revolutions
per minute, and was coupled directly to a small dynamo.
Steam entered the turbine case at the middle and flowed
in either direction to the ends, whence it exhausted at
atmospheric pressure. This design was followed in all
the early machines, so that the turbines were symme-
trical about their middle points, and the blading formed
right and left-handed screws on the two halves of the
rotor. Since the steam expanded in its passage through
the cylinder, it was necessary to provide larger passages
at the ends than at the middle of the machine. With
this object the length of the blades was increased towards
the ends of the turbine, and the diameter of the solid
disks correspondingly diminished, so that the solid part
of the rotor had a barrel shape, and the steam entered
at the greatest diameter.

The first notable public appearance of the steam tur-
bine was at the Boyal Jubilee Exhibition at Newcastle-
upon-Tyne in 1887, when the courts of the exhibition
were entirely lit by turbine power. The smooth running
and compactness of the machines used there received
universal admiration, but unfortunately their daring
novelty, combined with their more serious defect of a
large steam consumption, caused engineers to regard
them rather in the light of mechanical toys.

Efforts were now made to minimise the losses due to
faulty design. It was found that, partly, no doubt, owing
to the inevitable leakage of steam past the blades, which

THE PARSONS STEAM TUEBINE 125

took place pretty equally in large and in small machines,
a much higher efficiency was attained by the larger than
by the less powerful turbines; but a twenty H.P. turbine
constructed on the old plan consisted practically of two
ten-horse turbines abutting at the point of admission of
the steam, an arrangement which secures, it is true,
that the steam shall exert no end- wise pressure on the
rotor, but which assigns to each turbine the efficiency
which might otherwise be attained by one of half the
size. It is clear, then, that by admitting steam at the end,
instead of at the middle of the cylinder, economy can be
materially improved, and size and weight reduced at the
same time.

The disadvantage of a steam flow in one direction
only through the cylinder is that it causes a pressure on
the rotor, tending to displace it towards the exhaust end
of the case and causing friction at the bearings ; and it
is very important that no such displacement should be
permitted, lest the rows of fixed and moving blades
should come into contact, with disastrous results. In
1887, however. Parsons patented a new form of turbine
in which this difficulty was overcome, by the intro-
duction of balancing pistons, and a considerable in-
crease in economy was experienced with the new type of
machine.

Although with the introduction of the condensing tur-
bine, in which the ratio of expansion is much greater
than in the early machine,- an increase in the number of
blade rows has been found necessary, and various other
modifications in matters of detail have been adopted, jet
the form of turbine shown in the patent specification
of 1887 is substantially the same as that of the best
machines in use at the present day.

For reasons unconnected with the science of turbine

h3
X

O

THE PARSONS STEAM TURBINE 127

design, Mr. Parsons found it necessary to abandon for a
short time the construction of parallel flow turbines, and
to adopt the less satisfactory radial type, and the first
condensing and the first marine turbine were both of
this form. Subsequently the manufacture of the more
efficient parallel flow turbines was again taken up.

In 1891, as at present, every steam engine which made
any claim to efficiency was a condensing engine, exhaust-
ing, that is to say, not into the air, at a pressure above
14*7 pounds absolute, but into a vacuum more or less com-
plete. In 1891 Mr. Parsons decided to construct a con-
densing steam turbine, being confident that a consider-
able improvement in economy would result. The first
condensing steam turbine was built in 1892, and was, as
mentioned above, of the radial type. In spite of this
disadvantage, it showed, in a series of tests conducted
by Professor Ewing, of Cambridge University, in 1894,
the fairly economical consumption of 27 pounds of steam
per kw.-hour at a pressure of 100 pounds per square inch,
equivalent to about 16 pounds per indicated horse-power-
hour in a'' reciprocating engine, a result about equivalent
to that which might be expected of a compound engine
of the same size.

These tests took the steam turbine once and for all
out of the category of toys, and the return to the parallel
flow type of turbine, with condensation, resulted in a
further increase of efficiency, which put the steam tur-
bine almost, if not quite, on a level, in the matter of
steam consumption, with the triple expansion engine.
Still further improvements have been made in recent
years, and, while it has not been found possible, up to the
present, to equal the efficiency of the triple expansion
engine in the smaller turbines, a marked improvement
is apparent in the larger machines, and with every in-

128 STEAM TURBINES

crease in the size of the set, the advantage of the steam
turbine over the reciprocating engine becomes more
obvious.

In a test of a 8,500 kw. turbo-alternator at the Gar-
ville power station in February, 1906, in the course of
v^hich the machine was run under a 40% overload for the
space of an hour, the consumption was 15*4 pounds of
steam (at pressure 199 pounds and 160° superheat) per
kw.-hour when running at a load of 4,142 kw., 15'87
pounds at the full overload, and only 16*94 pounds per kw.-
hour at the approximate half load of 1,896 kw. This
test shows the maximum efficiency at 20% overload : The
steam consumption then is 16*4 pounds per kw.-hour,
amounting, if we assume the very high dynamo efficiency
of 96%, to a consumption of 10*6 pounds per B.H.P.-
hour, a result better than any that has been obtained
from a reciprocating engine.

A 4,000 kw. Parsons turbine, built by Messrs. Brown,
Boveri and Co., of Baden, has achieved a steam con-
sumption of only 1474 pounds per kw.-hour, and it
seems reasonable to suppose that with the increasing
size of the units the economy will be still further in-
creased.

But the advantage of the turbine over the reciprocat-
ing engine does not stop here. Having regard to the far
better results achieved by the large turbines than by the
smaller ones, it is fair to assume, and it is vigorously
contended by the designers of the Parsons turbine, that
the steam consumption of a 10,000 kw. machine could be
reduced as low as 13 pounds per kw.-hour. In addition to
this advantage, the small space occupied by the turbine
gives to its user a great advantage in the matter of
capital outlay on buildings and the like, while the cost
even of the smaller turbines is little greater than that of

THE PAESONS STEAM TURBINE 129

a good reciprocating engine of the same size. It has
been found that the large steam turbine has a great
advantage over the reciprocating engine in the matter of
first cost, and Mr. Parsons declared before the Com-
mittee of the House of Lords on the "Administrative
County of London and District Electric Power Bill," his
willingness to undertake the construction of a 10,000 kw.
steam turbine, at five times the cost of a 1,000 kw.
machine, that is to say^ at little more than half the
cost of a first class reciprocating engine of the same
power.

CHAPTER IV.

THE PARSONS TURBINE APPLIED TO ELECTRIC
GENERATION.

SUPPOSE that we approach a steam turbine of 1,000
kw. output, that is to say, of about 1,400 I.H.P.,
running in one of the big electrical power stations where
these turbines are becoming so common and so popular.
We see a large barrel of blue steel, of which one end is
almost hidden in the regulating machinery, while the
other merges into a massive iron casting, forming at
once the end of the cylinder and the bearing of the
turbine shaft. Prom this, bearing we see the shaft emerge
to enter the dynamo. The cylinder is supported at both
ends. The base at the end near the dynamo has the form
of a large ring, together with a rectangular pedestal,
which carries the bearing bushes. At the other end the
support is a long pedestal carrying, not only the cylinder
end and bearings, but also a certain amount of other
gear. On top of the cylinder stands a steel clad steam
chest, containing certain valves. We can recognize easily
the steam pipe entering this chest and the enormous
exhaust pipe disappearing through the bed-plate at the
base of the cylinder near the dynamo.

With the regulation of the turbine we will not concern
ourselves for the moment, but fall to upon the bolts of
the steam chest and the regulating and other surround-

130

\

132 STEAM TUEBINE8

ing machinery, and we can very quickly have the steel
cylinder stripped of all encambrances. At the end of the
turbine, remote from the dynamo, is a long pedestal, and
over the outer end of the pedestal is a small cover, form-
ing with the pedestal itself a kind of box. This is one of
Mr. Parsons's patented devices, and has for its object the
prevention of longitudinal motion of the shaft.

The shaft under this cover is grooved in rings, and
semicircular grooves are turned both in the cover and in
the hollow face of the pedestal, forming together a set of
circular rings, which engage with those on the shaft and
form a thrust block similar to that in a marine engine
room. But the beauty of the device lies in this, that,
unlike the top of a thrust block, the top of this keeper is
susceptible of delicate adjustment by means of screws, so
that wear on the keeper rings may be taken up, and the
position of the rotor very nicely defined.

From the keeper the shaft emerges into view. Here it
carries a stout worm, designed to engage with a worm
wheel which we have already removed, and which should
make one revolution for every thirty or so made by the
turbine shaft. Of this wheel and its appurtenances we
shall speak more anon. The oil pump is driven from
the shaft of this wheel by a connecting rod visible in
the photograph.

Next the shaft disappears under a second and larger
cast iron cover concealing the gun-metal bushes which
carry one half of the weight of the rotor. These bushes
are lined with soft white metal, such as Babitt's metal,
and are supplied with oil under high pressure, so that the
shaft is almost oil borne. The bearing carries the shaft
right up to the wall of the cylinder, which it enters with-
out again becoming visible, but at the junction of the
cylinder and bearing covers we could detect, if the turbine

THE PAESONS TURBINE 133

were running, a faint leakage of steam as from the spout
of a kettle beginning to boil.

The cylinder itself is about 15 feet long, and appears to
be of uniform diameter, but we shall find that the blue
steel cleadings are only attached by small screws to give
a finish to the appearance of the engine, and as it is the
construction that we wish to examine, we shall very
quickly demolish them.

Stripped of its trappings, the turbine cylinder looks
like nothing so much as a large Egyptian sarcophagus.
From the low pressure end, where the cylinder is wide
and rests on the large ring which vents into the exhaust
pipe, or, in the best installations, direct into the con-
denser, it tapers down by a series of steps and then
suddenly flares out again to the original diameter, as if
making provision for the feet of a mummy; but the
inhabitant is something much more lively and vigorous
than the inhabitant of a sarcophagus. At the narrowest
part of the case a small platform is formed to carry the
steam chest, and the port in its face enables us to catch
a glimpse of the rotor. All we can see, however, is a
bright steel barrel, rather larger than the shaft visible
outside, and to get a more complete idea of its construc-
tion we must remove the cover of the turbine case.

The cylinder is made in two halves, divided horizon-
tally. Both parts are flanged and planed up to a true fit,
so as to form a steam-tight joint. The upper half is fitted
with ring bolts, by which it may be slung from a crane
and so removed. When we have raised it we have reached
the heart of the engine and our exploration will be well
rewarded.

The inside of the cylinder is almost entirely filled by
the spindle of the rotor, and the intervening space is filled
with row after row of little blades attached alternately to

134 STEAM TUEBINES

the spindle and to the cylinder case. The cylinder cover,
too, bristles with a little forest of brass.

The body of the rotor is formed by a steel casting or
forging. Its shape may be seen in the figure, from which
it will be gathered that it consists of three or four long
drums, and of an equal number of short drums or disks,
increasing in size from the chamber A (Fig. 43) to which
steam is admitted, to the chamber Eg, which communi-
cates with the exhaust. The long drums increase in

FIG. 42. ROTOR OF MODERN STEAM TURBINE.

size from the chamber A to a chamber which is at the
end of the turbine near to the dynamo and in com-
munication with the exhaust. Each of the disks is of
slightly greater diameter than the corresponding drum,
but of smaller diameter than the section of the case
surrounding that drum.

A certain amount of space filled with blades is left
between the case and the drums, particularly the large
low pressure drum, but the disks on the other hand fit
the case very closely, and, instead of being garnished

THE PARSONS TURBINE 135

with blades, carry circular projecting ridges which
engage with grooves in the case to form a practically
steam-tight rotating joint. Between consecutive disks,
however, there are slight recesses forming chambers,
and the case is slightly recessed at A, to form a high
pressure steam chest.

At each end, also, there is considerable clearance be-
tween the rotor and the ends of the cylinder, so that
chambers of considerable size are formed (Ei, Eg, Fig. 43),
each of which is connected to the condenser, and in each
of which there is, therefore, an almost perfect vacuum.
Lastly, there are small chambers (B^, C^, Dj) formed at
the shoulders of the rotor between consecutive drums,
so that the steam emerging from the blades on one drum
is brought, relatively speaking, to rest before it enters
the guide blades which direct it on to the first row of
blades on the next drum. Each of these chambers is
connected by a small pipe or channel to the correspond-
ing chamber between the disks. These channels are
formed in the cylinders of the smaller turbines, but
external pipes are used with the larger ones.

It appears, then, that when the throttle is shut there
is a vacuum throughout the cylinder, but when the
throttle is opened and steam at high pressure is admitted
to the cavity A, the situation is changed, for the steam
naturally seeks a passage to the chambers in which there
is a vacuum. Now the disks at the one end of the rotor
fit the cylinder closely, so that there is no passage for
the steam in that direction, except in very small quan-
tities, and it must find its way between the long drums
and the cylinder.

This is where the blades are set. Each drum is garnished
with a number of rows of blades, and all the blades on
each drum are of the same size and shape; but they vary

THE PARSONS TURBINE 137

a little in the method of setting from one end of the
drum to the other. The scheme of blading is something
like that shown in the figure. The shaded blades are
those that project inwardly from the case and are
attached thereto, the blades shown in blank project
outwardly from the rotor and run in the direction indi-
cated by the arrows. It is clear that the volume of the
steam increases greatly between the two ends of any
drum, and it follows that its velocity must increase

MovifuBtiofSi/ ^^5-

FIG. 44. BLADING OF PARSONS'S TURBINE.

correspondingly, in order that it may pass the channels.
The blades are so arranged as to get the full benefit of
the different velocities at admission to the various rows,
according to the principles of blade design laid down in
Chapters lY and YI of Part I. At the same time the
width of the steam channels is slightly increased near
the low pressure end.

The similarity of blading of the Parsons steam turbine
and of the Jonval water turbine is apparent, and it will be
clear to the reader that in consequence of the restriction
of each blade passage (whether fixed or moving) at the

188 STEAM TURBINES

discbarge end, this is a true reaction turbine, so tbat the
pressure falls not only in eacb passage tbrougb tbe guide
rings, but also in each passage through the moving blade
rows, a feature which forms the fundamental distinction
between the Parsons turbine and those of Zoelly and
Bateau. Each of the rows in which the pressure falls is
known in the technics of turbine design as a " pressure
stage," and it will perhaps help the reader to picture
correctly the operation of the various turbines which
we shall describe, if we premise that the De Laval
turbine has only 1 pressure stage, the Curtis 3 or 4,
the Zoelly as many pressure stages as moving blade
rows, generally about 10, the Bateau on the same
grounds 15 or 20, and the Parsons and Schultz turbines,
twice as many pressure stages as moving blade rows,
that is to say, from 40 to 400 in all.

The ratios of expansion in the various pressure stages
are not the same. We have already pointed out that the
steam velocities increase towards the low pressure ends
of each drum; and it is clear that, since each of the rotor
drums is larger than the preceding one, the blade speed,
and consequently the steam velocity, increases from
drum to drum. The increase of steam velocity is there-
fore continuous throughout the turbine, and since the
velocity developed in any expansion depends on the ratio
of expansion, it follows that the ratio of expansion in
each pressure stage is continually on the increase. While,
however, we should do wrong to assume the same ratio
of expansion in each blade row, we can make a very
accurate assumption that the total expansion on each
drum is the same. If, then, there are four drums (as will
be the case on a turbine of some size) and if superheated
steam be admitted to the cylinder at a pressure of 180
pounds per square inch abs., the condenser pressure

THE PAESONS TUEBINE

139

being 1| pound abs., then the absolute pressures in
the three intermediate chambers will be 52, 16, and 5
pounds respectively.

Now let us — premising that these figures differ con-
siderably from those adopted in the construction of
modern turbines, and that the resulting design will there-
fore be rather different from that of the large machines,
of which it would obviously be unwise to give details

FIG. 45. STEAM VELOCITIES.

assume a total of 45 moving blade rows, of which 20
shall be set on the high pressure drum, and 12, 8, and 5
on the other three drums. There are then 40 pressure
stages on the first drum, and the mean expansion in each
stage is therefore 3*12, an expansion capable of developing
a steam velocity of nearly 400 feet per second. Now
suppose that one end of the blades is parallel to the axis,
and that the other is inclined at 60° thereto; if the speed
of the steam is 450 feet per second at discharge from the
fixed blades, this is equivalent to a speed of 390 feet per

140 STEAM TUEBINES

second in the direction of the blade's motion, together
with a speed of 225 feet per second along the blade. The
expansion in the moving blade row will raise this last
speed again to 455 feet per second relative to the rotor,
so that steam enters the next fixed row with a velocity
along the blades of 228 feet per second.

If there is to be no impact the blade speed of the first
drum should be 890 feet per second. As a matter of fact,
impact is not very disastrous, owing to the elasticity of
steam, and a blade speed of 250 feet per second will serve
our purpose excellently. If, then, the diameter of the
rotor be 1 foot, the speed will be 4,800 E.P.M.

We have now to find the length of the blades on the
small drum. If the machine is to be capable of a maxi-
mum load of 1,000 kw. it must be capable of passing
80,000 pounds of steam per hour through the blade row
under consideration, and this at a speed of 450 feet per
second. The aggregate width (at the narrowest part) will
be found to be almost exactly 1 foot. The pressure of the
slightly superheated steam at this point is about 110
pounds, so that the volume of 1 pound is nearly
4*5 cubic feet; the quantity of steam to be passed per
second is therefore 87^ cubic feet. This gives for the
height of the blades 87J/450 foot, or 1 inch.

Now if we turn our attention to the last drum, we find
that the mean expansion in each pressure stage is 18^%.
The velocity due to this expansion is slightly over 800 feet
per second. The steam velocities on the last drum are
therefore just over twice those on the first, and the blade
speeds must of course be increased in the same propor-
tion. The diameter of the low pressure drum ought,
therefore, to be 2*06 times that of the high pressure drum,
or 2 feet f inch, and the aggregate width of the steam
passage round this drum will be 2*06 times as great as

THE PAESONS TUBBINE 141

that of the high pressure passages. Now the volume of
the steam is increased in the ratio 82:1, and the velocity
in the ratio 2*06: 1. It appears, then, that the ratio of
increase in the length of the blades should be d2-r (2*06^
or about 7'5:1, so the low pressure blades must be 7 J
inches long.

The reader can apply the same method to calculate
out the elements of design of the other drums. A similar
process will enable him to work out the elements of all
the other turbines now on the market, and each is capable
of simple theoretical treatment, provided the assumptions
made are reconcilable with the laws of thermodynamics,
a condition precedent which too many turbine designers
have been rash enough to neglect.

The blades (both fixed and moving) are mounted on
the rotor or cylinder in circular channels cut in the steel,
according to a patented process. Into these channels the
feet of the blades are inserted, alternately with small
distance pieces, until the circle is nearly completed, when
a good deal of mechanical ingenuity is called into play
in inserting the last blades and wedging the whole firm.
Special tools are used for this purpose, and, when the
whole ring is fitted, the blader goes over the circle once
more to make sure that all blades are evenly spaced and
properly erect. Any faulty blade can be easily extracted
and replaced.

For the better securing of the erection and fixity of
the blades they are further stayed, in all the larger
machines, by connections at their outer ends. In the
small turbines only the long low pressure blades are so
connected.

The fixed blades are exactly the same in size, shape,
and setting, as those in the corresponding moving row,
and, except that they direct the steam in the opposite

142 STEAM TURBINES

sense, their action on it, and that of the steam on them,
is exactly the same as in the moving rows. Qaite apart
from this consideration, however, it is obvious that the
torque exerted by the steam on the rotor and cylinder
must be the same, so that if the cylinder were free to
turn it would revolve in the opposite sense to the rotor,
and at a speed depending on the resistances. It has
been suggested that an application of this fact might be
made to electrical generators, for the purpose of reducing
the centrifugal forces, since it is evident that one rotor
might rotate under these circumstances at half the present
speed, and an application to marine propulsion has also
been discussed. Though the principle is used to a certain
extent in the Seger turbine, the various engineers who
have endeavoured to adapt the Parsons and other power-
ful engines for its use have now abandoned the attempt.
One more part must be noticed before the cylinder
cover is replaced. The shaft emerges from the rotor at
both ends into a chamber in which there is an almost
complete vacuum, and from this chamber it passes into
the open air. These low pressure spaces are directly con-
nected with the condenser, and the importance of keeping
the condenser free from air is well known to every
engineer. Vast quantities of steam enter the condenser
from the cylinder, but these are there condensed so that
the pump has only to deal with a comparatively very
small quantity of water; if air should leak in, since this
cannot be condensed, it has to be pumped out at great
inconvenience, and a high vacuum becomes impossible,
and since turbines are designed to use advantageously a
much higher vacuum than is commonly found in con-
nection with reciprocating engines, very careful provision
against leakage is necessary in their design. It is there-
fore of the utmost importance that no air should enter

- J

THE PARSONS TUEBINE

143

the turbine cylinder at the ends. To guard as far as
possible against leakage a series of rotating pistons is
formed on the shaft at the point where it penetrates tbe
cylinder, end, and these run like the disks on the rotor in
brass sleeve rings fitted to the cylinder itself.

These rings and sleeves form a rotating joint through
which, in any case, there could be very little leakage, but
as it is of the utmost importance that there should be

FIG. 46. PARSONS'S VACUUM AUGMENTOR.

none whatever, steam from the main steam pipe is led
through a narrow tube into the middle ring (K, Fig. 43)
so that it reaches the packing rings at a pressure a little
above the atmosphere. Some of this steam leaks into the
condenser and is so returned into the boiler ; a little may
be seen escaping into the outer air and effectually pre-
venting the leakage of air into the turbine cylinder.

We have already pointed out that it is possible to use a
much higher vacuum in the turbine than in the recipro-

144 STEAM TUEBINES

eating engine, because while the steam is at rest in the
reciprocating engine it is flowing at a high velocity in
the turbine cylinder, and a large specific volume does not
therefore imply a cylinder of corresponding size. To
secure this high vacuum is the function of the vacuum
augmentor (Fig. 46). This is an ejector steam jet by
which the steam remaining after a part has been con-
densed at a very low pressure in the main condenser, is
drawn off and condensed in a second condenser where
the pressure is higher. The water from both condensers
mingles and is returned to the boiler.' By this augmentor
a vacuum of 28 inches of mercury can be secured in the
main condenser, while that in the air pump is only 25 ins.
Admission to the turbine cylinder takes place through
a port in the top of the cylinder cover in the large
machines (in others by a steam pipe), and a steam chest
containing the admission valves is secured by bolts above
the aperture, or seated, in a small turbine, upon the cover.
There are two double beat valves in the chest (Fig. 40):
the first, Yi, is a runaway valve, permanently open unless
the controlling apparatus refuses to work. The second, a
similar valve, Vg, is operated by a piston working in a
chamber above it, and the motion of the piston is in turn
controlled by the slide valve in the steam chest along-
side. The position of this slide valve depends on three
different adjustments. In the first place, the floating lever
&om which the valve is suspended is supported at one,
end, D, by the governor, which may be a mechanical one,
or electrical, as shown in the figure. This governor is
itself susceptible of adjustment to varying speeds. The
fulcrum, E, of the floating lever, is on a second link fixed
at one end, but rising and falling at the other with the
motion of a cam carried by the worm wheel previously re-
ferred to, and rising and falling about twice in each second.

THE PAESONS TURBINE 145

The result of this arrangement is that the slide valve
oscillates continually, but its centre of oscillation is fixed
by the governor. The steam is therefore admitted to the
turbine when running at full speed in a series of periodic
blasts the duration of which the governor determines; but
while starting, or when much overloaded, the blast is
continuous, and the highest efficiency is consequently
often obtained with considerable overload.

In starting the turbine we first raise the runaway
valve and then open the throttle very slightly, so as to
expel the air from the cylinder without spoiling the
vacuum in the condenser. Then the stop cocks leading
the steam to the keeper rings are opened to guard against
any return of the air.

Now comes the critical moment. One man has his
hand on the throttle; a couple more begin to raise the
great sluice gate that shuts off the exhaust. One turn of
the wheel puts the cylinder into communication with the
condenser, and the rotor is now lying in a vacuum.
Slowly the throttle is opened. Now the sluice is raised
with a will to give a free passage to the expanded steam,
and the gauge on the high pressure steam chamber rises
suddenly from 13 pounds below, to 180 pounds above, the
atmospheric pressure. The gauges on the intermediate
chambers rise more slowly as the rotor gathers speed.

For the turbine began to run at the moment when the
throttle was opened. One would hardly know it, so quiet
is the motion, but just at the first moment it is possible
to see the shaft and the rotor of the dynamo beginning
to turn. Before a minute is past they are running so
fast and so smoothly that they seem to be at rest. One
can trace the increase of speed, if there are pressure
gauges on the chambers, as there are when a trial is
being made, for, as the speed increases, and the impac

L

146 STEAM TURBINES

of the steam on the blades diminishes, the pressure in
the first chamber rises slowly to about 88 pounds, while
pressure in the next chamber rises up to a pound or two
above the atmosphere. In the chamber Dj the vacuum re-
mains unaltered until full speed is almost attained, when
it diminishes gradually by about 10 inches of mercury.

Now it is very clear that the steam acting on the
blades and contained in the chambers must exert a con-
siderable endwise pressure on the rotor which would tend
in time to wear out the thrust block, while causing some
frictional resistance to motion. But it will be remembered
that the chambers at the opposite ends of the cylinder
are in communication, so that the pressures above re-
ferred to are exactly balanced by the pressures on the
disks at the other end of the rotor, and consequently
there is absolutely no endwise pressure exerted. In fact,
the bearings of the turbine carry the weight of the rotor
only, and are subject to no other stresses whatever, a
state of perfection which it is impossible to attain in any
other form of prime mover.

The weight of the rotor itself is, as a matter of fact,
carried to a large extent on a layer of high pressure oil
supplied to the bearing, so that the rotor is really float-
ing altogether, but this bearing is entirely outside the
turbine cylinder, and the steam itself never comes into
contact with any sliding parts, any packing or any lubri-
cating oil, an advantage to the boilers which can hardly
be overrated.

CHAPTER V.
THE MAEINE STEAM TURBINE.

MR. PARSONS, in producing the first commercially
successful steam turbine, would have done his
generation no mean service had the usefulness of the
engine been confined to the stationary generation of
power; but to the same inventor belongs the credit of
having been the first to apply the turbine to a purpose
for which its peculiar features render it even more con-
spicuously suitable than for that of electrical generations.

In 1894 the Marine Steam Turbine Co., Ltd*, was
formed, and under its auspices the Turbinia was built at
Wallsend-on-Tyne. The Turbinia was rather a trial to
her owners at first. Low speed turbines had not then
been developed, so that the shaft (she commenced her
career with a single propeller) made 2,000 revolutions
per minute, and it was not practicable to run a propeller
of any size at that speed. The two-bladed propeller of
80 inches diameter which was first fitted got no sufficient
grip of the water, and others were little more satisfactory.
The best result was obtained with three propellers on
the shaft. Their slip was 37 '5 per cent., and the speed
attained was 19| knots.

The original shaft was now replaced by three separate
ones, each driven by a turbine. We are familiar with
the compound turbine as constituted of three or more

147

THE MAEINE STEAM TURBINE 149

separate drums in one cylinder, the steam passing
from drum to drum. Now the Turbinia was driven by a
turbine set consisting of three drums in different cylin-
ders, the high pressure turbine driving the starboard
shaft, the intermediate the shaft to port, and the low
pressure turbine the central shaft. The change in driving
power due to this re-arrangement was enormous, and,
after a little further experiment with propellers, the then
unsurpassed speed of 34 knots was attained over a run
from Spithead to Southampton Water, a distance of about
twelve miles.

The length of the TurUnia is 100 feet, beam 9 feet,
draught 5 feet 6 inches, and with her full crew on board, in
sea-going trim, she displaced 44| tons. The actual pro-
pulsive H.P. at a given speed is very difficult to determine
from direct measurement. It might be done if there were
any vessel capable of towing her at the speed in question;
failing that, the horsepower must be worked out from
tank experiments with models. In this way it has been
estimated that the propulsive H.P. at 31 knots was 905,
and at 32 knots 980. The consumption of feed water at
the lower speed was measured as 27,000 pounds per hour;
at the higher speed it was estimated to be 28,200, or 28*8
pounds per propulsive H.P.-hour. Similar calculations in
the case of high speed vessels driven by reciprocating
engines have led to the conclusion that the proportion
of propulsive power to the power developed in the engine
is between 55 and 60 per cent.; that is to say, the effi-
ciency of a high speed screw is from 0*55 to 0*6. The
most efficient of such reciprocating high speed marine
engines have shown a steam consumption of about
18 pounds per indicated H.P.-hour, or say 30 pounds per
propulsive H.P.-hour, a steam consumption more extra-
vagant than that of the Turbinia.

THE MARINE STEAM TURBINE

161

It has always been one of the chief difficulties of high
speed work at sea to design an efficient screw. Large
slow-moving screws are generally used for trading vessels,
where economy is the only criterion of merit, but the
propellers of small and fast boats, such as torpedo boats,
are necessarily run at higher speeds.

So long as the propeller is large enough to get a good
hold of the water, no diminution of efficiency appears to

FIG. 49. CAVITATION, 4,000 R.P.M.

result from the adoption of a small diameter, and corre-
spondingly high speed; on the contrary, the excellent re-
sults attained by the propellers of the Carmania would
appear to indicate that a gain in efficiency is the natural
result of such a modification; and this gain may perhaps
be attributed in part to the decrease in surface friction
on the propeller. When, however, we adopt a very high
speed of running, a new trouble makes itself felt. It is
inevitable that the water should derive a certain rotation
from the propeller with which it is in contact, and when

152 STEAM TURBINES

the speed of this rotation is considerable, '' centrifugal
force " comes into play, and forms a kind of submarine
whirlpool surrounding the propeller and tail shaft. This
phenomenon is known as cavitation, and results in a
serious diminution of the driving power of the propeller,
combined with an increase in slip. The speed at which
the shaft may be run depends on the pressure of the
water surrounding the cavity (inside which there is a
vacuum relieved only by a negligible steam pressure),
and this in turn depends on the submersion of the screw.
The shafts of the Tiirbinia were inclined to the horizontal
for the purpose, among others, of securing adequate sub-
mersion.

In the turbines finally adopted on the Tm-binia, steam
passed through each cylinder from the fore to the
after end, whence it was led to the fore end of the
next cylinder in the series. Provision was made for the
expansion of the steam in the course of its passage
through each cylinder by increasing the height of the
blcbdes towards the stern, so that the section of the pass-
age was increased while the rotor remained a uniform
drum.

The general effect of the steam on the rotor and shaft
was therefore a turning couple, together with a direct
thrust aft. Had the turbine been devoted to the purpose
of driving a dynamo, it would have been necessary to
balance this thrust by disks on the fore end of the
shaft in the manner described in the last chapter; but
the circumstances are here completely changed, the water
is exerting a forward pressure on the propeller, and so
on the shaft, and it will obviously be desirable, if possible,
to balance this pressure against that of the steam. This
was, in fact, done, so far as careful calculation and
experiment could do it.

J

THE MAEINE STEAM TURBINE 158

The situation was therefore this. Each shaft was car-
ried in a number of gun-metal bushes, the bushes being
themselves mounted in a series of concentric tubes separ-
ated by thin films of oil under pressure, so that a very
slight vibration of the bushes might take place without
being felt in the vessel. These bearings carried the weight
of the shaft, propeller and rotor; but, in addition to the
weight, the shaft was subject to a forward thrust exerted
by the water, and to the opposing thrust of the steam.
The rotor was so designed that these two thrusts prac-
tically balanced one another when running at full speed,
and, at that speed, the shaft ran practically free in the
bearings, unlike the shaft of a vessel fitted with recipro-
cating engines, which grinds continually against the
thrust block, by means of which it transmits the pro-
peller's pressure to the hull. The actual force driving the
hull in a turbine vessel is not a thrust derived from the
shaft directly, but the forward pressure of the steam
against the fore end of the turbine cylinder. So that we
have really got the steam pressing forward on the hull
and backward on the water by means of the shaft, which
acts as a buffer between steam and sea.

It was not possible, of course, to trust entirely to the
balance of steam and water pressure to maintain the
equilibrium of the shaft, particularly in an engine in
which the consequences of an endwise displacement of
the rotor would be so serious as in those of the Turbinia;
each shaft was therefore fitted with a thrust block which,
at starting or stopping the turbines, as well as while
running at slow speeds, had to carry a considerable load.
The ends of the turbine cylinders were fitted with brass
rings projecting into grooves in the rotor and steam
sealed, according to the system in use ashore. The central
or low pressure shaft carried, between the turbine and

154 STEAM TURBINES

the fan for forcing the draught, a small reversing turbine
used for going astern^ since to reverse the propelling
turbines was impossible.

The speed of 2,200 revolutions per minute, for which
the turbines were designed, was considerably lower than
that generally in use at the time in stationary steam
turbines, and it was necessary, in order to secure adequate
blade speed, to adopt a correspondingly larger diameter
of rotor. To maintain a moderate section of steam pass-
age it was necessary to use short blades and many of
them, so that the various parts of a marine steam turbine
have a very different appearance &om those of an elec-
trical turbo-generator. Even so the blade speeds of a
marine steam turbine are not usually so high as those of
the stationary machine, and the stages of expansion are
therefore still further subdivided by the use of a large
number of blade rows. Instead of permitting complete
expansion from boiler to condenser in a single turbine
cylinder two or three such cylinders are used in series,
each containing a separate drum, and driving a separate
shaft, but the whole forming only a single turbine set.

In the Turhinia three drums were used, of which the
high pressure one drove the starboard shaft, the inter-
mediate that to port, and the low pressure the central
one. The slip of the propellers on the two side shafts
was found to be about 26 per cent, and that of the central
one 16 per cent. This difference is no doubt due in part
to the fact that the central propeller was acting on water
following in the wake of the vessel; it may be doubted
whether it is fair to infer that the low pressure turbine
did less than its fair share of the work.

In modern practice, at any rate, it is usual to connect
the two low pressure drums in parallel, and to drive the
central propeller by the high pressure drum. In some

THE MAEINE STEAM TURBINE 155

cases, the central propeller is the largest of the three
and is run at the lowest speed, so that the greatest
duty is put upon the high pressure drum, while high
steam velocities are utilized in the other two.

The Turhinia finally established the utility of the steam
turbine for the propulsion of high speed vessels, and in
the year following her official tests two orders were placed
with the Parsons Marine Steam Turbine Co. for sets of
high speed marine turbines. The one was fitted in the
Cobra, built by Armstrong, Mitchell and Co., and after-
wards purchased by the Admiralty, the other equipped the
torpedo boat destroyer Viper, built by the Turbine Co. to
the Admiralty's own order.

These two ships, Viper and Cobra, were very nearly
alike, both in engines and in general design, and were of
nearly the same dimensions as the 30 knot destroyers
previously constructed, viz., length 210 feet, beam 21
feet, and displacement 370 tons.

The tragic fate of the Cobra is not yet forgotten; she
had passed through a number of trials with credit, and
attained the speed of 34 knots without showing any signs
of strain, and was being taken at an easy cruising speed
from the Tyne to the Thames, when she broke com-
pletely in halves during the night, and was lost with all
her crew.

There can be no doubt that this misfortune was due in
the main to the excessive lightness of the ship's build,
and happily the lesson taught by her sad example has
not been altogether lost. But it is exceedingly unfortu-
nate for the progress of marine turbines and of the British
navy, that the winds and waves should have chosen for
scapegoat the second destroyer to be fitted with the new
engine, giving occasion to amateur mathematicians and
newspaper experts to shake their heads and talk about

156 STEAM TURBINES

the gyroscopic effect of steam turbines as responsible for
the occurrence. We shall hope to show in a later chapter
that this criticism is little more reasonable than that
rhetorically put by the average seafarer, " What could
they expect when they gave her a name like that ? "

The engines of the Viper and Cobra were, as we
have stated, of very similar pattern, and the action
was substantially the same as in the Turbinia. The de-
stroyers, however, had four shafts, driven by two high
pressure turbines on the outer shafts discharging into
two low pressure turbines on the inner ones. On each
shaft were two propellers, the after of the two having a
slightly greater pitch than the forward one.

The system of tandem propellers has now gone out o
vogue. The real reason for its adoption was the high
speed of the shafts. This made it necessary to use pro-
pellers of moderate pitch and diameter, and a number
of these must be employed to get a sufficient grip of
the water. There were then two alternatives, either to
use a large number of shafts and corresponding number
of turbines, which adds to cost and diminishes efficiency
— for small turbines are always comparatively wasteful
— or else to set a number of propellers on every shaft.
The whole problem has now become somewhat academic,
as it has been found practicable to run the turbine rotors
at much slower speeds than were thought possible in the
early days of their application to marine purposes, but
it is now held that, even on the fastest running shafts,
it is better to fit a single propeller of comparatively
large diameter than a number of smaller ones of the
same pitch arranged on the tandem system. This view
would seem to be confirmed by recent experiments on the
Turbinia.

This problem of propeller design is an extremely n-

THE MAEINE STEAM TURBINE 157

teresting one. The simple theory is that each blade of
the propeller is a part of a screw surface, and that as
the shaft turns, this screw traverses the water, exactly
as a joiner's screw traverses a plank. The water, how-
ever, does not oflfer to the propeller the same firm sub-
stance that the wood offers to the screw; the same force
which urges the vessel forward throws the water back. If
the propeller is mounted, as it should be, almost clear
of the disturbance in the water effected by the passage
of the hull, then it cuts into practically still water as it
goes forward, and as it cuts into it, the water is thrown
back. The action is that of a Jonval turbine reversed, so
that the blades might well approximate to the form of
those in the Jonval turbine, or more nearly to the form
of a bird's wing on the down stroke, slightly concave
on the after surface and convex forward. In fact, how-
ever, the blades are usually made of a true screw form.
The propeller presses on the water astern and sucks in
that ahead, creating a backward moving stream. The
propulsive force is proportional to the speed of this
stream, to the speed of the propeller through it, and to
the section of the stream, which is the area of the pro-
peller circle. Thus the propeller is continually driving
tihrough what is practically a head tide of its own
making.

Suppose that the speed of the vessel is 18 knots, and
that the water is streaming past the propeller with a
velocity of 3 knots towards the stern. The average speed
of the water on which the propeller is acting is 8 knots,
and the shaft must, therefore, run as if the ship were
making 21 knots instead of 18, the slip of the propeller
is then 3 knots or 11%, and 14% of the work done by
the engines is wasted from this cause, besides that
wasted by friction of the water on the propeller surface.

158 STEAM TUEBINES

The case against tandem propellers is briefly this.
The second propeller on the shaft, instead of cutting into
smooth water, enters water which has already been in
<iontact with the leading one, and which is, therefore,
moving with a speed of 8 knots in the opposite direc-
tion to that of the motion of the propeller. Caeteris
paribus, the water will pass the blades with a velocity of
6 knots, and the mean slip of the second propeller will
be 6 knots or 26%, the shaft running as if the ship were
making 24 knots. In like manner, if there were a third
propeller on the shaft, it may be taken that its mean
slip would be 9 knots or 33J%. Of course all these pro-
pellers being on the same shaft, their speed of rotation
must be the same, and the different degrees of slip must
be allowed for by giving them different pitches, as was
in fact done in the Viper and Cobra,

In the above discussion we have, for simplicity, treated
rthe action of the screw on the water as if it were a direct
thrust. As a matter of fact, it is nothing of the sort,
though the practical effect of the action is not thereby
altered. The actual motion of the water in leaving the
propeller is a screw motion, as may be very well seen
from the stern of a liner under full steam, particu-
larly if she be a twin screw vessel. This motion is
even more fatal to the eflSciency of a second propeller on
the same shaft than is the direct flow considered in the
Above paragraph.

We have referred to the propeller as a kind of reversed
Jonval turbine. This scarcely represents the state of
affairs accurately, as every true turbine has fixed as well
as moving blades; the screw propeller is really a reversed
reaction wheel of the kind described on page 14, and is
subject to the same limitations of efficiency as the re-
action wheel. The way to render the propeller a true

THE MARINE STEAM TUEBINE 159

tarbine would be to add fixed blades, forming a propeller
of very large pitch, set in the reverse sense to the
moving ones. In this way the screw motion of the water
might be used for propulsion, and it is possible that
where tandem propellers are used, some real benefit
might be derived from setting such fixed blades on the
bearing brackets between consecutive screws. Attempts
to adopt some such device have not, however, met with
any success.

The contract speed of the Viper was 31 knots, and she
was bound to do half speed astern. At her actual trials
she attained a speed of 86'581 knots, the revolutions per
minute being 1,180, and she successfully achieved the
guaranteed 15J knots astern. The reversing was accom-
plished by turbines carried on the low pressure shafts
and permanently coupled to the condenser. These tur-
bines, like the propulsive ones, were steam sealed, after
the fashion of those described in the last chapter, so that,
when the ship was going ahead, the reversing turbines
ran in an almost complete vacuum, and caused very
little waste of energy. They were very small, since the
power spent in reversing at half speed is only about one-
eighth part of that required to drive the vessel at full
speed ahead.

A conspicuous feature of the Viper's engines, as com-
pared with those of the TurUnia, was the reduced speed
of rotation. This was obtained partly by increasing the
diameter of the rotors, and partly by increasing the
number of rows of blades on each. The reversing tur-
bines were of smaller diameter than the propulsive ones,
and their eflSciency was very low as compared with that
of the propulsive machines, which used 2*38 pounds of
coal per I.H.P.-hour at full speed ahead, a very large con-
sumption compared with that of modern turbine vessels.

160

STEAM TUEBINES

The British navy then possessed the fastest vessel
afloat, an advantage which does not appear to have been
properly appreciated at the Admiralty, as the next class
of destroyers ordered consisted of 25-knot boats fitted
with reciprocating engines.

The action of the Admiralty is the less to be lamented,
since it compelled Mr. Parsons to turn his attention to

FIG. 50. H.M.S. ** AMETHYST. =

the adaptation of steam turbines to the needs of the
merchant service, where their merits met with a more
ready recognition.

The Viper was wrecked on the Casquets in a fog during
the naval manoeuvres of 1901, and for some time the
British navy included no turbine propelled vessels. In
1902 the Velox (T.B.D.) of 400 tons was purchased; and

THE MAEINE STEAM TUKBINE 161

in 1904 the Amethyst, built by Armstrong, Whitworth
and Co. for the British Government, was launched, and
was fitted with turbines by the Parsons Marine Steam
Turbine Company.

This vessel is, not only in design, but also in boiler
capacity, an exact counterpart of the other cruisers of
the Topaze class, and so gave the first opportunity of a
precise comparison of the merits of steam turbines and
of reciprocating engines. Each of these vessels is of
length 360 feet, beam 40 feet, and about 8,000 tons dis-
placement. They were designed for a speed of 21 '75
knots.

In the actual trials, which took place in 1904, the
Amethyst attained a speed of 28*6 knots as against 22*1
developed by the Topaze, while the coal consumption of
the turbine vessel was 88^% less than that of the sister
ships. The turbines of the Amethyst were in fact more
economical than the reciprocating engines of the other
vessels at all speeds exceeding 15 knots, while the
smaller weight and bulk of the turbines allowed her a
greater bunker capacity, so that her radius of action in
time of war would be about 50% greater than that of her
rivals.

To appreciate the full significance of these results, it
must be borne in mind that the Amethyst was the largest
vessel at that time fitted with steam turbines, and that
the design of her machinery was, therefore, to a great
extent experimental, whereas the other ships of the class
were propelled by reciprocating engines of a perfection
only to be attained by long experience of similar work.

At the time when the tests of the Amethyst took
place, the success of the marine steam turbine was
already assured, but these results announced it to the
public and to the engineering profession in a far more

M

162

STEAM TUEBINES

striking fashion than ever before, and formed a fitting
climax to twenty years of steady, but not always very
obvious, progress. The Admiralty appreciated the im-
provement to the full, and resolved very properly to adopt

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turbines throughout the navy. Every ship laid down
during the year 1905 is to be fitted with Parsons turbines,
including the Dreadnonghty the first line of battle-
ship to be so propelled, and the revolution in marine
engineering long prophesied by those interested in tur-
bines is accomplished at last.

THE MAEINE STEAM TUEBINE . 163

The Amethyst was the first vessel in which an arrange-
ment now common in turbine propelled warships was
adopted.

In these vessels, although a high speed is necessary
in case of war, the usual cruising speed is, for the sake of
economy, very much lower. Now the only method of regu-
lation possible for a Parson's marine turbine is that of
throttling, which is an exceedingly wasteful method for
two reasons, firstly because it takes away from the
effective head of steam at admission, and secondly be-
cause the quantity of steam being reduced, with no cor-
responding decrease in the section of the wheel channels,
the full steam velocities are not developed in these chan-
nels in the most desirable way.

If, however, the steam could be partially expanded
while doing useful work before admission to the high
pressure turbine, both these objections would lose their
weight. This expansion was effected on the Amethyst by
means of a high pressure and an intermediate cruising
turbine, carried on the two outer shafts, which also
bore the reversing and the low pressure turbines. When
full speed was required, the cruising turbines ran
in vacuo, but for low speeds steam was passed through
the cruising set and then through the main set. The
increased resistance in its path reduced the flow of steam
without throttling, and a very large expansion was se-
cured, as is done in a reciprocating engine when the cut
off is shortened. The turbine escaped the great losses
which arise from the variations of temperature in the
<3ylinders when the reciprocating engine is so regulated.

In the battleship Dread/noiight, which exemplifies the
latest developments in marine turbine work, there are to
be two sets of main turbines, the high pressure drums
jdriving the outer shafts, and the low pressure drums the

A. Main H.P. turbines.

B. Main l.p. turbines.

C. Condenser.

D. Astern H.P. turbines.

E. Astern l.p. turbines.

F. Cruiser H.P. turbines.

G. Main throttles.

H. Astern throttles.

I. Cruising and emergencjr

throttles.
J. Cruising intermediate steam

valves.
K. Emergency intermediate

steam valves.

FIG. 52. DIAGRAM OF PROPOSED TURBINE ARRANGEMENT OF H.M.S^
"DREADNOUGHT."

THE MARINE STEAM TUEBINE 165

inner. Two high pressure cruising turbines are also
carried on the inner shafts, and from these the steam
will pass to the ordinary high pressure turbines for low
speed work. It has been suggested that these cruising
turbines may be used in parallel with the main high
pressure drums for the development of very large power
on emergency. The whole set would not then permit of
expansion nearly so complete as in the normal case, and
this is the more to be regretted that the boiler pressure
is to be very high (250 pounds). The arrangement is
not likely, therefore, to prove entirely satisfactory so far
as economy is concerned, but this must, of course, be
sacrificed in times of emergency.

Another feature of the Dreadnought's machinery which
deserves mention is the fact that she is to carry high and
low pressure astern turbines on the same shafts with the
main high and low pressure drums. She will, therefore,
have ten turbine cylinders in all, forming four complete
turbine sets.

It is estimated that this vessel will be two knots faster
than any battleship previously launched, an advantage
which the battle of the Japan Sea has enabled naval
architects to appreciate at its full value, and which goes
a long way to support the suggestion that the naval
supremacy of the future lies with a turbine propelled
fleet.

n

CHAPTER VI.

THE TUEBINE IN THE MERCHANT SERVICE.

IT seemed in 1901 as if, in spite of the efforts made by
the believers in the steam turbine to secure its adop-
tion for marine purposes, science and enterprise had been
overcome by mere idle prejudice, and the struggle were
all to begin again. The Cobra was lost under the tragic
circumstances previously referred to, and the Admiralty
seemed to look on the turbine with a far from favouring
eye. The Parsons Marine Steam Turbine Company
were at that time the only firm willing to construct
turbines for marine propulsion, and the works of that
company had been for some time almost idle.

At this juncture a firm which has throughout been the
best of friends to the steam turbine, decided to give it
a trial in a branch of marine enterprise different from
that to which its use had been hitherto confined. Messrs.
Wm. Denny and Bros, were among the promoters of
Turbine Steamers Limited of Glasgow, and built for
that company the triple screw passenger steamer. King
Edward, of 562 tons. This vessel was launched in the
year 1901, and was engined by the Parsons Marine
Steam Turbine Company. Triple expansion was aban-
doned in this vessel, and the turbines driving the two
outer shafts were coupled in parallel; an arrangement
which has been more or less faithfully maintained in
the subsequent passenger steamers.

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168

STEAM TUEBINES

In the King Edward, therefore, the installation was
precisely symmetrical. The high pressure turbine drove
the central shaft, carrying, according to figures given in
a paper by Mr. Parsons, a single propeller 57 inches in
diameter, while the two outer shafts carried each a pair
of smaller propellers of 40 inches diameter, and a small
reversing turbine (D, Fig. 54) running in the same
cylinder with the low pressure drum, and discharging
into the same exhaust, E.

We have already pointed out, in connection with the

FIG. 54. SECTIONAL DIAGRAM OF MARINE LOW-PRESSURE AND
ASTERN TURBINE.

design of steam turbines for stationary work, that it is
desirable to have faster moving blades at the low pressure
than at the high pressure end of the cylinder, in order
that the expanded steam may pass through more rapidly
without loss of eflSciency. This condition is secured in
most marine steam turbines by the use of larger drums in
the low pressure than in the high pressure cylinders. The
method adopted on the King Edward was to run the
outer shafts faster than the middle one, but the modern
modifications of design, which have made it possible to
run the machines at the comparatively low speed of 180

TUEBINE IN THE MERCHANT SERVICE 169

E.P.M. adopted on the Carmania, have done away with
the necessity for this curious arrangement.

The King Edioarcl achieved a speed of 20^ knots on
her trial, the speed of the middle shaft being then 505,
and of the outer shafts 755 R.P.M., speeds notably
smaller than those obtained with the turbines pre-
viously constructed.

Up to the time when the King Edivard entered upon
her trial, no opportunity had occurred of comparing the
efficiency of the marine steam turbine with that of the
reciprocating engine, for turbines had only been fitted
to vessels running at a speed unattainable by those pro-
pelled by reciprocating engines. The steam turbine was
peculiarly well fitted for the propulsion of light, fast boats,
as these could be driven by small screws rotating at a
high speed; but in adapting the machines to the require-
ments of heavier and slower vessels, it was essential to
design rotors which should run at a comparatively low
speed with a high efficiency, and grave doubts were
entertained as to the possibility of this modification. It
appeared, however, from the tests of the King Edward
that the turbines developed an even higher power than
could be obtained from the best reciprocating engines
with the same steam consumption.

The next turbine steamer constructed after the King
Edicard was a somewhat larger vessel of very much
the same type, and built by the same firm, the Queen
Alexandra, The success of these two vessels, the economy
of their machinery, and the great increase in comfort
resulting from the smooth running of the turbines, led
the railway companies to take up the new prime mover,
and from that time a very rapid advance was made both
in the number and in the size of vessels fitted with turbine
machinery. Several turbine yachts were launched soon

TUEBINE IN THE MEKCHANT SEEVICE 171

after the Queen Atexandra, and one of these, the Emerald ^
was the first turbine vessel to cross the Atlantic.

The boldest step of all was, however, taken by the
Allan line, in laying down the turbine vessels, Victorian
and Virginian, of 11,200 and 11,400 tons, a tonnage
nearly five times as great as that of any turbine steamer
then building. The turbines in these two ships are
arranged on the usual system, that is to say, with the
high pressure drum driving the middle shaft. The outer
shafts are driven by low pressure drums connected in
parallel, and carry in addition reversing turbines for the
purposes of manoeuvring and of going astern. The
weight of each low pressure turbine is about 70 tons, and
the speed of the shafts 350 E.P.M. The vessels were
designed for speeds of 18 knots, but following the
honourable traditions of turbine steamers succeeded in
attaining 19^.

The last and largest of turbine propelled steamships
will be observed by engineers and ship builders with
greater interest than any previously constructed, and
this not only on account of her gigantic dimensions.

In 1903 Messrs. John Brown and Co., of Clydebank, laid
down the Caronia, gross tonnage 19,500, for the Cunard
line, and early in 1904 they commenced the building of
the twin ship Carmania, identical, in every respect except
the engines, with the Caronia. The latter ship was fitted
with twin screws driven by quadruple expansion recipro-
cating engines at 84 revolutions per minute. The Car-
mania, on the other hand, is propelled by three screws
equal in all respects, and driven by a high pressure and
two low pressure turbines arranged on the usual system.
These turbines made 180 revolutions per minute, a much
greater number than has ever previously been adopted
on a vessel of the same size, but, on the other hand, a

1

172 STEAM TURBINES

number scarcely more than half as great as the least for
which earlier steam turbines had been designed. Having
regard to the high speed of the shafts, the diameter of
the propellers is kept very small as compared with that
of the Caronia's screws. The blades are made very wide
to secure an adequate grip of the water, and a very pretty
trefoil propeller form results.

The Carmania is 672 feet 6 inches long over all, and
displaces, when loaded, 80,918 tons. The hull of the
Caronia is identical, except that the supports of her
reciprocating engines are necessarily heavier than those
carrying the turbines of the sister ship. The boilers also
are of the same shape, but differ inasmuch as those of the
Carmania are designed for a steam pressure of 195 pounds
to the square inch, and those of the Caronia for the
pressure of 210 pounds, a point in favour of the Carmania
that can best be appreciated by a sea-going engineer.
A comparison of these two vessels will therefore afford the
very best test that could be desired of the relative merits
of the perfected reciprocating engine and of the steam
turbine. This comparison has been eagerly anticipated
by all those interested in marine engineering.

The guaranteed speed of each vessel was 19 knots. The
Caronia on her trial, with a clean bottom, attained the
speed of 19*5 knots with an indicated horse-pov^er of
23,000. The Carmania ^ with a very foul bottom, attained
20-19 knots, and by comparison with the tests of the
Caronia the builders of both vessels have estimated that,
with a clean bottom, the Carmania would be capable of
20*6 knots, representing a gain in horse-power and effi-
ciency of about 15 % to the credit of the steam turbine.

As we have already pointed out, the principal difl&culty
in the way of the adaptation of steam turbines to the
requirements of large ships, such as the Carmania^ has

173

all be
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TUEBINE IN THE MEECHANT SEEVICE 173

always been that of producing a turbine which shall be
efl&cient at the very low speed required for driving screws
large enough to propel these enormous hulls. The speeds
of running of the largest stationary steam turbines,
turbines, that is to say, of somewhat lower power than
the Carmania's high pressure drum, are generally about
1,300 revolutions per minute. For marine purposes it is
desired to run at a speed of not more than 180 E.P.M., and
for this purpose it is necessary first of all to diminish the
speed of each blade row, and secondly, by the adoption
of a large diameter for the drum, to secure a moderate
rotary speed in spite of a high peripheral velocity.

In order to secure a low speed for the blades without
sacrifice of eflSciency, it is necessary to arrange that the
speed developed by the steam in passing from row to row
shall be very much less than in the high speed turbine ;
it follows that the drop in pressure from row to row must
be diminished, and the number of blade rows correspond-
ingly increased. The large number of rows makes it
advisable to separate the drums in different cylinders, sa
as to form a compound or triple expansion turbine; and,
to satisfy the second condition, drums of a very large
diameter are used.

The marine steam turbine is consequently a much
larger and heavier engine than a stationary turbine of
the same power, and, although the drums are hollow and
constructed as lightly as possible, the weight of each of
the low pressure turbines of the Carmania is 340 tons,
as against the corresponding weight of 78 tons for the
Victorian. According to figures communicated by the
builders to engineering, Dec. 1st, 1905, the diameter
of each low pressure drum is 11 feet. The large circum-
ference enables a large flow of steam to pass through a
somewhat narrow space between rotor and cylinder, sa

174 STEAM TUEBINES

that the blades are small, and a large number of blades
in each row is therefore necessary. When we consider
also the large number of rows in the whole turbine set,
it becomes abundantly clear that the work of blading a
liner's turbines is no trifle. There are in fact 1,115,000
blades in the Carmania's turbines, and every one of these
is separately fitted by hand.

The outer ends of the blades, throughout the machinery,
are secured by a brass band, arranged with a telescopic
extension to permit of the necessary expansion and con-
traction.

The reversing turbines are carried on the outer shafts
immediately abaft the low pressure turbines, and within
the same casing, so that ahead and astern turbines
exhaust into the same space (Fig. 54). The rotors are
so formed that the steam pressure exactly balances the
thrust or pull on the shaft at full speed ahead or astern.
For manceuvring, steam is admitted to the low pressure
turbines from the boiler, through a reducing valve, while
the high pressure drum rotates idly in a vacuum.

At certain intervals in the casings of all the turbines,
recessed grooves are bored, forming small chambers
which may be connected with a pressure gauge. When
the turbines are running, the pressure should fall steadily
from chamber to chamber, and any accident within the
cylinder will be immediately revealed to the engineer in
charge by these gauges. In the extremely improbable
event of any of the blades coming to grief, travelling
•cranes, fitted in the engine room for this purpose, are
brought into service, and the cylinder cover, and rotor if
necessary, are removed from the injured machine, while
the others continue their duty.

Any faulty blade can be very quickly replaced, and, if
necessary, a whole row, or several rows of blades, can be

TUEBINE IN THE MEECHANT SEEVICE 175

entirely removed without spoiling the action of the engine.
A case is on record in which a Parsons turbine ran for
several days, and ran satisfactorily, when a number of
blade rows had been completely stripped by the unex-
plained presence of a one-inch bolt in the turbine
cylinder.

Owing to the high speed, the absence of complicated
stresses near to the cranks, and the small diameter of
the screws, it has been found possible to use lighter
shafting in the turbine driven Carmania than in the
sister vessel; the hollow turbine rotors are also lighter
than reciprocating machinery, so that there is a very
considerable gain in the weight of the moving parts, and
consequently in the rapidity with which the propellers
can be reversed, stopped, or accelerated. The Carmania
has been successfully manoeuvred in the Clyde, without
the help of the rudder.

There can be little doubt but that the turbines of the
Caiinania are the most carefully planned and successful
yet constructed, but even they must yield in interest to
the remarkable sets which are to propel the Cunard grey-
hounds now building.

The vessel now in course of construction by Swan,
Hunter, and Wigham Eichardson, Ltd. is 760 feet long
between perpendiculars, 88 feet in beam, and will register
about 30,000 tons gross with a displacement of over
40,000 tons. She is to be capable of mounting several
quick-firing guns, and her guaranteed speed of 25 knots
will make her a notable addition to the British reserve
fleet.

The engines will consist of four Parsons turbines driv-
ing four separate shafts for propulsion, and two astern
turbines mounted on the inner shafts. These engines
will be arranged on the twin system, the inner shafts

> 207'x 34W^ 24y/

SAVANNAH 1819. Paddie-steamer (350 tons.) Took 32 days to steam
from Sauannah to New York.

"^ BRITANNIA 1840. Cunard S.a. Co. CharUs Dickens made a oogage
mJ in the Britannia.

. \ \ \ \^\ \

\ Sij/xsaH'x 32}^' 2984 ton, /GREAT BRITAIN 1845.
<• -^ ^ ^ Great Western Steam Navigation Co.

, \ \ ^ i\ ^r\\ \\ \ ,

\ - , . GREAT EASTERN 1858. J

C 67^^82-8 % 482 18,915 grote tons ^

_o n \

685-7^ * 68-3* X 445'

OCEANIC 1899.

White Star Line.

D

I

\ t\ f\ f\&

DEUT8CHLAND 1900.

h9 X 67-3 X 403

\>— EL-^i^

E

(^ 582'x64^X 41-5'

IVERNIA 1900.

Hamburg -American Line.

23% Knots

i Built at the Waltaend Shipyard
for the Cunard s.s. Co.

1

i_D_fL_fl_ILM.

1492

SANTA MARIA NEW CUNARDER 1904-6.

FIG. 57. TRANSATLANTIC VESSELS OF THE PAST AND PRESENT.
Reproduced from "The Mid-Tyne Link," WaUsend-on-TTne. By permission of the Editor.

TUEBINE IN THE MERCHANT SERVICE 177

driven by the low pressure and the outer by the high
pressure drums.

The enormous progress that is being made in this
branch of science at the present day is aptly illustrated
by the accompanying diagram (reprinted from the "Mid
Tyne Link "), showing the increase in the size of trans-
atlantic packets since the time of Columbus. Some
further idea of the colossal nature of the new Cunard
enterprise can be gathered from the facts that the com-
bined I.H.P. of the main engines of the new ship reaches
the hitherto unapproached figure of 70,000, that there
are to be 23 double ended boilers and two single ended,
and that the full boilers and engines will together weigh
over 10,000 tons, and will consume about 1,000 tons of
coal per day. A horse and cart could pass easily down
either exhaust pipe.

CHAPTER VII.
THE DE LAVAL TURBINE.

WE notice a contrast very clearly defined when we
torn from the turbine of Parsons to the second
successful steam turbine of modern times. In 1888, De
Laval, a member of the Swedish House of Represent-
atives, and already well known as an inventor in con-
nection with dairy machinery, first endeavoured to pro-
duce a rotary steam engine for the direct high speed
driving of a churn. In the year 1889 he evolved the
steam turbine known by his name, which has already
achieved great popularity in its native country, and bids
fair to be equally successful in America and France.
The machine has only recently been introduced into this
country, but there is every reason to suppose that its
suitability for the driving of light machinery will meet
with full recognition in the course of time.

This turbine is in every respect the direct antithesis
of that of Parsons. The latter is a somewhat complex
turbine of the reaction class, depending for its efficiency
on the large number of expansions taking place within
the turbine cylinder; the former is an impulse turbine,
exceedingly light and simple in construction, developing
the kinetic energy of the steam by a single expansion,
and that not strictly within the cylinder at all.

The principle of the De Laval turbine is that of the

178

THE DE LAVAL TUEBINE 179

Pelton wheel; the detail of the arrangement is very
different. The rotor itself consists of a single wheel of
forged steel, very thick at the central boss, and tapering
to the rim in the manner indicated in the figure. The

FIG. 68. THE DE LAVAL WHEEL.

diameter of the wheel varies from 4 to 30 inches, according
to the power of the turbine. The blades are not unlike
those of the Parsons turbine in shape, but are consider-
ably more curved, and are set symmetrically, otherwise
than those of Parsons, in the plane of the wheel, both

180 STEAM TURBINES

edges being inclined at an angle of SO"" to 45° to the
direction of motion. These blades are dovetailed into
the rim of the wheel in such a fashion that it is im-
possible to remove them by a direct outward pull, and
the ends of the blades are flanged to form, when fitted
together, a rim round the outside of the steam passages.
Such blades are known to turbine engineers as buckets.
The whole of the rotor is designed for the express pur-
pose of withstanding enormous centrifugal forces, on
account of the very high speeds at which these wheels
are run.

Steam enters the wheel from a nozzle or nozzles in-
clined to the plane of the wheel at an angle of 20"*.
The form of this nozzle (patented in 1889), is the sum
and substance of De Laval's invention.

In order that the action of the turbine may be efficient,
it is essential that the velocity at admission should be
as great as possible. Now, if we were dealing with
water, this condition would be sufficiently ensured by
the mere fact that there is no back pressure, and the
velocity would depend only on the pressure behind
the jet. In dealing with steam, however, we have the
elasticity of the fluid to consider, and some interesting
physical conditions result.

If boiler steam be allowed to escape, either through a
hole in a plate or through such a nozzle as we have
described in connection with the Pelton wheel, it will be
found that, after issuing from the restricting channel,
the steam jet spreads out in every direction, so that it
is not possible to direct it into a blade channel, as mast
be done in a turbine; neither is every part of the stream
moving (as is required) in the same direction. This is
only true in the case where the boiler pressure is more
than double that of the medium into which the jet is

THE DE LAVAL TURBINE 181

discharged, and the reason of the phenomenon is sus-
ceptible of a simple explanation (see App. III).

There is no simple relation connecting steam pressure
with velocity developed, and the complicated formulae that
have been suggested for the purpose will hardly be useful
in our present investigation. We may illustrate the re-
lation by saying that steam of 160 pounds pressure and 50°
superheat will develop a velocity of about 1,450 feet per
second on expansion to a pressure of 85 pounds, when the
ratio of expansion is 1*70 : but will only develop a speed of
4,000 feet on expansion to a 26 inch vacuum, when the
ratio of expansion is 70. Now the section of a channel
necessary to carry a given flow of steam is inversely pro-
portional to the velocity of the jet, and directly propor-
tional to the volume of a given weight of the vapour. If,
then, steam is being blown off from a chamber in which the
pressure is 160 pounds and the superheat 50°, the section
of channel necessary to discharge the steam occupying

1'70
1 cubic foot of the reservoir in one second will be ^ .^^

1,450

square foot (or 0*169 square inch) if the discharge is to

70
take place at a pressure of 85 pounds, but will be j..^7r

4,000

square foot (or 2 J square inches) if the discharge is to

take place at a pressure of 2 pounds absolute. If, on the

other hand, the pressure in the orifice of discharge were

140 pounds, the velocity of discharge would be 660 feet per

second, and the volume would be increased by 10%, so

that the necessary section would be -^^ square foot or

or 0*24 square inch.

In the same way we could find the necessary orifice
of discharge for any pressure within the neck which we
might care to assume, and it would appear at the end

182

STEAM TUKBINES

that the smallest aperture is arrived at with pressure of
about 85 pounds. This, then, is the pressure which steam
would naturally possess in escaping through a simple
orifice from a boiler in which the pressure was 160 pounds.
If we adopted, in a steam turbine working at this press-
ure, the nozzles described earlier in connection with
the Pelton wheel, the steam would pass through these
nozzles at the pressure of 85 pounds, and would then ex-
pand in every direction into the vacuum or atmosphere,
instead of continuing in a straight line as the water
does.

dmi€m:

FIG. 59. DE LAVAL NOZZLE AND BLADES.

To prevent this bushing out of the steam at the mouth
of the nozzle, De Laval — and herein lies his invention
— adds to the simple nozzle an expanding cone (Fig. 59).
Now when the steam expands laterally, after passing
through the neck, it meets the conical surface and is
reflected into the desired direction. All the steam, there-
fore, passes along the funnel, increasing rapidly in volume
and more slowly in velocity.

The size of the neck regulates the amount of steam
used, and adjustment is made by a needle as in the
Pelton nozzle. Suppose that the section of the neck is

THE DE LAVAL TUEBINE 18S

0169 square inch. One cubic foot of boiler steam is
discharged per second. In order that the steam may not
diverge on leaving the funnel, it is necessary to prolong
the cone until the steam flowing through it attains the
pressure prevailing in the turbine case. If this is equiva-
lent to a 26 inch vacuum, the final section of the cone
must be 2J square inches, and the velocity of the steam
impinging on the wheel will then be 4,000 feet per
second. We have, therefore, the curious and superficially
improbable truth that steam flowing in a diverging
pipe increases in speed and falls in pressure, in precise
contrast to the action of water under similar circum-
stances (App. II).

The number of nozzles used varies according to the
size of the turbine. On the 300 H.P. machine manufac-
tured by Greenwood and Batley, of Leeds, the largest
standard De Laval turbine on the market, the number
of nozzles used is 12, but the machine is capable of de-
veloping the specified power with only eight of them in
operation.

We have seen that, under ordinary conditions, steam
enters the turbine case at a speed intermediate between
3,500 and 4,000 feet per second, and therefore with a
kinetic energy of 1/12 to 1/8 of a horse-power-hour per
pound of steam. In order to communicate all this energy
to the turbine wheel in a single passage, it would be
necessary to run the wheel with a peripheral velocity of
2,000 feet per second, a speed at present unattainable.
Neither is it possible to use the system of impulse of the
Pelton and similar wheels without modification, as this
would require buckets too heavy for the necessary speed
of running (see page 192). Instead, the nozzles are set
alongside of the wheel, inclined thereto at an angle of 20",
and bevelled off so as to come very close to the blades.

The fact that the steam does not approach the blades

184

STEAM TURBINES

strictly in the direction of motion of the wheel would
necessitate, for perfect efficiency, a blade velocity ex-
ceeding half the nozzle velocity of the steam; but the
highest speed yet attained is considerQ,bly less, namely,
1,380 feet per second, the bucket speed of the 300 H.P.
turbine. The diameter of this wheel is 30 inches, so
that it makes 10,600 revolutions per minute.

Suppose that steam enters the wheel case at the
somewhat excessive speed of 4,000 feet per second. We

FIG. 60. WHEEL OF LARGE DE LAVAL TURBINE, BLADES ENLARGED.
(GREENWOOD AND BATLEY.)

can show geometrically (App. I) that it has a speed
of about 2,800 feet relative to and along the blades ;
and it follows that the steam is discharged with an
absolute velocity of 2,000 feet per second, one half the
speed of admission. The proportion of energy carried oflf
by the steam is then i of the whole, and that com-
municated to the wheel is the remaining f , or 3/32 of a
H.P.-hour per pound of steam. Allowing, therefore.

THE DE LAVAL TUEBINE 185

nothing whatever for resistance of wheel passages or
nozzles, for impact and resistances of bearings or gear-
ing and the like, we may say that the theoretically
perfect De Laval turbine, running under these condi-
tions, should show a steam consumption of 10*66 pounds,
per H.P.-hour. It speaks very highly for the con-
struction of this turbine that there should have been
obtained, throughout a prolonged test of a 300 H.P.
machine, running with eight nozzles at 352 H.P. a steam
consumption of 13*94 pounds per H.P. hour.

The foregoing discussion of the theory of De Laval's
turbine sufficiently indicates that the most notable
feature of the machine, in practice, is its extraordinarily
high speed. The speeds of the types now on the market
vary from 10,000 to 30,000 revolutions per minute, and
every part of the rotor must be designed to stand the
stresses arising from this cause.

Let us consider for a moment the 300 H.P. model.
The weight of one of the buckets is 1/28 of a pound, its
length is 1^ inch, and it is dovetailed into the rim of
the wheel. The mean velocity of the blade is 1,380 feet
per second, more than half the speed of a rifle bullet,

and the stress on the inner end is therefore —- x -

28 li
poundals (see App. I) or ^x^®2Llb. (U foot being

Zo fjZ X 1^

the radius of the path of the blade), which reduces to
1,673 pounds, or nearly 15 cwt. The cross section of
the blade is about *045 of an inch, so that the stress
works out at 16f tons to the square inch.

We have seen that some of the fast-running water
turbines have a steel tyre outside the blades to guard
against their being drawn. It is hardly necessary to point
out that no steel tyre could stand the strain created by a
velocity of 1,410 feet per second, or 960 miles an hour,

186

STEAM TUEBINES

that of the outer ends of these blades. The whole stress
is therefore carried by the dovetail joint, and is added to
the other stresses within the wheel itself. These stresses
increase rapidly as we pass inwards from the rim, and
the thickness of the wheel is increased correspondingly.
The curve formed by a section of a wheel of maximum
lightness and strength, is the solution of a differential
equation, which will afford a pretty problem for the ma-

FIG. 61. WHEEL OF SMALL DE LAVAL TURBINE SHOWING FLEXIBLE
SHAFT. (GREENWOOD AND BATLEY. )

thematical reader. The best assumption to make will be
that the stress is to be 12 tons to the square inch in
every direction in the plane of motion throughout the
structure of the wheel.

It is clear that in a solid wheel the stresses across the
centre will be considerable. If the central part is cored
out to make room for the axle, the hub must be made
very heavy to supply the strength lost from this cause.
It will be noticed that the axle of the 300 H.P. turbine is
fitted without coring the wheel (Fig. 60).

THE DE LAVAL TURBINE 187

The axle itself is one of the most remarkable parts of
the machine, and exemplifies another very pretty ma-
thematical problem. Owing to the high speed, the shaft
has no great torque to bear (it is only 158 pound-feet
in the largest machine, and the five-horse wheel gives
0*875 pound-foot only). A stout shaft is therefore un-
necessary. If, however, a thin shaft be used, it will be
necessary to consider the possible effects of want of
balance on its rectitude.

The strain which we found to exist on the buckets
sufficiently indicates the stresses that might arise from
any want of balance in the rotating parts, and, since an
error of one ounce might cause a rapidly alternating
load of one ton on the bearing, it is clear that some mea-
sures must be taken to prevent the racking of the machine
to pieces. Parsons used a floating bearing for his earlier
turbines : De Laval has adopted a flexible shaft.

The shaft of the 150 H.P. turbine is only one inch in
diameter, and the bearings are set at a distance from the
wheel rather greater than the radius. The shaft is there-
fore an elastic rod loaded at the centre, and if displaced
it will vibrate in the same fashion as the reed of a
trumpet, having a definite period. Now, if there is a
slight want of balance in the turbine wheel, the centre of
gravity being at a small distance. A, from the centre of
the shaft, the shaft will be always pulled towards the
centre of gravity, and if the speed of rotation be slow it
will take a set in that direction, increasing still further
the want of balance. The shaft, being bent in one direc-
tion, has a natural tendency to spring back and bend
in the other ; but the centrifugal force is being continu-
ally reversed as the wheel turns. As the rotation is ac-
celerated, this reversal becomes more frequent until it
coincides in period with the natural vibration of the shaft.

188 STEAM TURBINES

This is the critical speed, and if the wheel make many
revolutions at this speed, the shaft is bound to break. To
avoid this, safety bearings are provided close to the hub.

But the question of interest for us is this. ^'What
happens when the speed of the rotor exceeds the critical
speed? " The answer may be suggested by the familiar
'' cowboy'' trick of spinning a lassoo in the form of a
hoop by means of the rope attached to the circumference.
When the critical speed is exceeded, the wheel turns and
reverses the strain on the axle before that strain has had
any appreciable effect; and, as the speed increases more
and more, the force necessary to deflect the middle point
of the axle through a distance of 1/100 of an inch or so,
becomes practically negligible in comparison with the
other forces in operation. The stiffness of the shaft can
then be neglected, and it begins to fulfil the functions
of the " cowboy's " rope, while the wheel turns about its
own centre of gravity.

This very curious fact can be easily shown mathe-
matically. Suppose that the deflection of the shaft is
D towards the centre of gravity. The radius of the path
of that centre is A+D, and the centrifugal force is
CN^(A+D), while the elastic force on the shaft is B.D,
where B and G are constants and N is the speed. If the
motion is steady these forces must balance, and we have

CN^A+D) = B.D, or D = ^^^, It appears, then, that
D, the deflection, is postive if B— CN' is positive, in-
finite if B — CN*' = (this gives the critical speed, N = \/ - ) ,

B'

and negative if N has a greater value than the critical
one. The greater N becomes, the more nearly D ap-
proaches the value— A, at which the centre of gravity of
the wheel is its centre of rotation. The mathematician

190 STEAM TUEBINES

or the draughtsman will find it at once instructive and
interesting to sketch the curves traced by the vibrating
shaft at different speeds of rotation. They can be me-
chanically shown by rotating a conical pendulum at
various speeds and giving to it an oscillation at the same
time. The ellipse corresponds to the critical speed.

The theory of the De Laval turbine is undoubtedly in-
teresting. In practice it has attained a very fair effi-
ciency, and has the merits of extreme lightness, com-
pactness, and simplicity. The turbine, complete, with
the necessary gearing for connection to machinery run-
ning at ordinary speeds, is far lighter and smaller than
a reciprocating engine of the same power, or even than a
petrol motor. The De Laval turbine is not likely in the
near future to come into competition with other steam
turbines, chiefly because it is most suitable for light
work, and has never been applied to the development
of power in excess of 300 H.P., the power q,t which the
other forms of steam turbine begin to be efficient.

Of all the merits of the De Laval turbine the most
conspicuous is its simplicity, arising from the fact that
it is a single stage impulse machine. The position of the
nozzles renders it impossible for the steam to do other
than go through the wheel passages, and once it has
done so, it is done with for the purpose of the turbine. .
Eegulation is effected by a simple throttle with perfect
efficiency. There is no close fitting anywhere, and no
need for any. The engine requires no skilled attention,
and it is a pity that its merits are not more fully recog-
nized by small power users in this country.

The disadvantage of the turbine is that it is not pos-
sible to use the full power of the steam in a single wheel.
To a certain extent the energy of the steam leaving the
rotor can be used, in a properly constructed condenser,

THE DE LAVAL TUEBINE 191

to save the air pump, but the advantage is a small one.
Suggestions have been made for the compounding of
these turbines, but this can only be done by sacrificing
to some extent the pre-eminent simplicity of the machine.
There are two obvious ways of setting about it. The first
is to expand the steam in two stages, with an intermediate
receiver between the two wheels. This receiver may be
simply the case of the first turbine. Whether a separate
one is provided or no, the first wheel-case will in fact
be full of steam at intermediate pressure, and this will
cause a resistance to the motion of the wheel, which, in
view of the high speed and slight torque of the wheel-
shaft, is bound to produce a very serious loss.

According to -the second system of compounding, the
full expansion takes place in the nozzle, but the steam
discharged from the wheel passages enters fixed passages
or ports, by which it is conducted to other wheels on the
same shaft; but this involves the complete sacrifice of
the simplicity of the old machine, and creates a turbine
of greater efl&ci^ncy, power and complication, to which
we must devote another chapter. But before we turn our
attention to these compound turbines, we must notice
the other simple impulse turbine, in some respects the
most extraordinary steam engine yet produced.

The Eiedler-Stumpf steam turbine, which is consider-
ably used in Germany for small installations, and of which
there is at least one large specimen in existence, the
2,000 kw- turbine at Moabit, is practically a Pelton
wheel. It is necessary, as in the De Laval turbine, to
attain a very high bucket speed, but this is done by
using a large wheel, which runs at the comparatively
moderate speed of 3,000 to 4,000 E.P.M. The diameters
of the wheels vary from 5 to 10 feet.

At the high speed used, great strength and perfect

192

STEAM TUEBINES

balance are necessary in the rotor. These are attained
by forming the wheel of a single piece of very hard nickel
steel. The pockets are cut out of the wheel, and differ

FIG. 63. ROTOR OF RIEDLER-STUMPF TC RHINE.
(ALLGEMEINE ELEKTRICITATS GESELLSCHAFT, BERLIN.)

from Pelton buckets in that they are open only at the
sides, for the purpose of discharging steam. It is possible,
therefore, to collect the exhaust steam and to compound
the turbine by re-using it. This has been done in some

THE EIEDLEE-STUMPF TUEBINE

198

cases, and the steam is returned either to another wheel
on the same shaft, or else to the same wheel, as was done
in the turbine - shown in Fig. 36. These machines are,
however, very seldom compounded.

The nozzle is set in the plane of the rotor, as is the
nozzle of a Pelton wheel, but, of course, a divergent in-
stead of a convergent mouth is used. On account of the
difference in the working fluid it becomes important to

^ CJ,t packets

Sectid^i CD.

-^^ -^> Section AB.

FIG. 64. SECTIONS OF RIEDLER-STUMPF ROTOR AND NOZZLE.

have the nozzle close up to the pockets into which it
discharges. The greatest clearance permissible is a quarter
of an inch. The nozzle is therefore bevelled off like that
of De Laval, and fits closely outside the wheel (Fig. 64).
The flexible shaft is now out of the question — the rotor
is too heavy for its use in the first place, and, in the
second, play is undesirable. The smooth running of the
wheel depends, therefore, entirely on the accuracy of the
turning and the care with which the pockets are cut.

o

194 STEAM TUEBINES

Very fair results, so far as steam consumption is con-
cerned, have been obtained with this turbine, the best
result showing a consumption of 19^ pounds of steam
per kilowatt-hour (equivalent to about 18J pounds per
B.H.P.-hour) obtained with the 2,000 H.P. turbine before
referred to, running at rather less than full load. The
engine shares the peculiarity of all the Pelton wheels^
that the highest efficiency is obtained when the load is
below the normal figure, in contrast to the Parsons, and
to most other steam turbinos, which show their mettle
on an emergency, that is to say, when considerably
overloaded.

CHAPTER VIII.
THE CDRTIS AND OTHER IMPULSE TURBINES.

WITHIN the last few years a large number of new
steam turbines have been produced by various
manufacturers, for the most part in Germany; and these
differ one from another in different degrees, but they
have this feature in common, that nearly every one is of
the compound impulse type. The Schultz turbine, the
only other reaction turbine on the market besides that
of Parsons, differs from the latter so little as not to re-
quire a separate discussion in these pages.

The compound impulse turbines, however, though of
very recent invention, have already considerable reputa-
tion both in Europe and in America, and have achieved
excellent results in trials of reliability and economy. The
last of these machines to have been put forward, that
manufactured by the AUgemeine Elektricitats Gesell-
schaft, of Berlin, appears, curiously enough, to be the
simplest of them all. The smaller of these machines have,
like those of De Laval, only a single pressure stage. The
full velocity of the steam is therefore developed in the
nozzle, but this velocity is used and destroyed, not in
passage through a single moving bucket row, but by a
series of actions on successive buckets, usually three in
number. The small A.E.G. turbine is, therefore, to all
intents and purposes, a modification of the early engine

195

O

S

H

Ed

•J
H
H

OS

d

THE CURTIS TURBINE 197

of Harthan (Fig. 36) with the combination of De Laval's
expanding nozzle.

The turbine is mounted on a horizontal shaft (Fig. 65),
and directly coupled to the generator. The efficiency is
fair, and the speed seems very moderate, when compared
with that of the simple De Laval turbine ; but the A.E.G.
is not much used for the small powers which the latter
engine has developed with so much success.

In large A.E.G. turbines a second pressure stage is
introduced, and the action becomes very similar to that
in the earlier Curtis turbine; the two differ principally
in the manner of erection, the Curtis having a vertical,
and the A.E.G. a horizontal axis. The best recorded test
of the A.E.G. turbine shows a steam consumption of
16*6 pounds per kilowatt-hour, as against a correspond-
ing figure of 15*8 pounds for the Curtis, which appears
therefore to merit the greater attention.

* * * * 4tt

The first patent for the Curtis turbine was taken out
in the year 1895, and, since the machine was put on the
market, some four years later, its merits have gained
wide recognition in America, though it still appears to
be little known in this country. The turbine cylinder,
which has a vertical axis, is divided by horizontal dia-
phragms into a series of chambers, usually three or four
in number, and in each chamber there are one or more
rotating wheels carrying rows of buckets. There are
usually two or three such rows in each chamber, and the
older practice was to cut each set of channels out of a
separate disc of solid steel (Fig. 66), so that there would
be a number of such discs or wheels in each stage
chamber. The speeds of running have, however, now
been reduced, and it is therefore found practicable, and
more advantageous, to cut the channels out of steel seg-

198

STEAM TUEBINE8

ments, and to bolt these segments on to the wheels, so
as to form one or more complete circles of buckets on
each wheel.

Between these moving bucket rows fixed buckets are

FIG. 66. SOLID STEEL ROTOR WHEEL OF CURTIS TURBINE, BLADES
PARTIALLY CUT. (BRITISH THOMSON-HOUSTON CO., LTD.)

attached to the walls of the turbine cylinder. These are
cut, like the moving ones, out of steel segments; but,
since admission to the turbine is by nozzles, and round
only a part of the circumference, it is clearly unnecessary
that the fixed buckets should form a complete circle.
Both fixed and moving buckets are of much the same

THE CUETIS TUEBINE

199

shape as those in a De Laval turbine, and the action in
each stage chamber is, therefore, practically that sug-
gested by Harthan in 1858. Admission to the first cham-
ber is by nozzles set in the top of the turbine cylinder.
These are grouped together, and are of a modified De
Laval shape, permitting a partial expansion of the steam.
Groups of passages of similar shape are cut in the dia-
phragms separating the stage chambers (Fig. 67), and it
is in these passages that the expansions take place. The

3TEAM CHEST

NOZZLE
M0VIN6 BUQLS
STAirONARy JiLAOtS
M0Y1N8 BLAOtS

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FIG. 67.

I I I I I t

DIAGRAM OF BLADES AND NOZZLES IN 2-STAGE CURTIS
TURBINE. (B. T. H. CO.)

full velocity of each expansion is developed in the cor-
responding passage, and the action on the fixed and
moving blades is purely impulsive. It is clear that
groups of nozzles must be set diametrically opposite to
one another, in order that the action on the rotor should
be a pure torque.

We have already pointed out that there may be one
or more wheels in each stage chamber. The group of
wheels forms the rotor, which carries, therefore, a
number of rows of buckets, somewhat unevenly spaced,

200

STEAM TURBINES

as, between some, small gaps are left for the fixed backet
rows, and, between others, larger gaps for the nozzle dia-
phragms. The external diameter of the whole rotor is
uniform (Fig. 68), so that the speeds of all the backets
are the same, and the action in each stage chamber
should, therefore, be identical, in spite of the changed
volume of the steam. The solid discs forming parts of

FIG. 68. ROTOR OF 4-STAGE CURTIS TURBINE. (B. T. H. CO.)

the wheels are largest at the end of each stage-chamber
nearest to the admission nozzles, so that those steam
channels through which the flow takes place more slowly
are deeper than the earlier ones.

From the uniformity of the bucket speed throughout
the turbine, it follows that the steam velocities in each
stage should be the same. The total velocities developed
in each set of nozzles should, therefore, be equal, and

THE CURTIS TURBINE 201

this requires the same ratio of expansion in each nozzle,
the pressure in the steam chest be 160 pounds, and if
there be three stages, then, assuming a reasonable super-
heat, the pressure in the first two stage chambers should
be approximately 40 pounds and 9 pounds respectively,
while that in the last chamber will be the condenser
pressure, say 1^ or 1| pound per square inch absolute.
The nozzles of each stage will then be much shorter than
those in the De Laval turbine, having in fact a divergence
of 40%, and the velocity developed in each nozzle will be
about 2,500 feet per second.

FIG. 69. INSIDE OF 4-STAGE CURTIS TURBINE CYLINDER SHOWING
FIXED BLADE ROWS. (B. T. H. CO.)

The inclination of each nozzle to the plane of the
wheel is about 20°, and if the bucket velocity be 480
feet per second, the velocities of the steam at discharge
from the first and second rows respectively will be
approximately 1,600 and 750 feet per second. Since
the work done on any bucket-row is equal (neglecting
frictional losses) to the difference between the energies of
the steam when entering and when leaving the buckets,
the duties of the two rows in the first stage chamber
will be in the ratio 37 : 20. The mass and velocities of
the steam in the second stage chamber will be exactly
the same as in the first, when running at full load, and

202 STEAM TURBINES

therefore the work done by each wheel in the second
chamber is the same as that done by the corresponding
wheel in the first. The volume of steam in the second
chamber is, however, four times greater than in the first,
and, therefore, the section of steam passage must be in-
creased in the same proportion.

FIG. 70. LOW PRESSURE DIAPHRAGM OF CURTIS TURBINE SHOWING
NOZZLES.

It is clear that, since the admission nozzles extend
only round a part of the rim, some only of the wheel
passages in the first chamber are in operation at a given
moment. The diaphragm nozzles, however, extend round
a larger arc, so that a larger number of the blades in the
second chamber are under steam. The last row of dia-
phragm nozzles extends usually round the greater part of
the circumference (Fig. 70). It is not, therefore, necessary

THE CURTIS TURBINE 203

to increase the length of the buckets in this turbine in
the same proportion as in that of Parsons, although the
ratio of expansion is equally great.

The high steam velocities used in this turbine, and
the great pressure on the blades of the first wheel in
each stage chamber, make it probable that a large pro-
portion of the losses in the turbine cylinder is due to
steam friction on the guides and blades. This will be
greatly increased if any water is present in the steam,
and the advantage of superheating is consequently great.
It appears that the best results as yet obtained from
a 1,500 kw. Curtis turbine show a steam consumption
of 15*8 pounds of steam, at a pressure of 200 pounds
per square inch and 150° superheat, per kw.-hour, as
against a consumption of 15*4 pounds by a 3,500 kw.
Parsons turbine with the same superheat, and 18*5 pounds
with a De Laval, developing 250 kw. under rather less
favourable conditions.

It will be seen that the steam consumption of the
Curtis turbine compares favourably with that of the
best triple expansion engines, but is slightly inferior to
that of a Parsons turbine; it must, however, be re-
membered that the Curtis machine is still in its infancy,
and, thanks to the enthusiasm with which it has been
taken up in its native country, is being rapidly de-
veloped and improved, so that an increased efiiciency
may be expected in the future.

We have pointed out that the chief burden of the work
is borne by the first bucket row in each chamber. The
effect of closing one or more of the admission nozzles on
the distribution of duty is worth noting. The pressure in
the first steam chamber falls to a certain extent, and the
velocity in the diaphragm nozzles drops correspondingly,
while that in the admission nozzles increases. The result

204

STEAM TUEBINES

of this is a slight overloading of the wheel or wheels in
the high pressure stage, the duties of the different rows
becoming more evenly distributed than before. The load

FIG. 71. 1,100 KW. CURTIS TURBINE AND CONDENSER. (B. T. H. CO.)

in the low pressure stages diminishes to a corresponding
extent.

If we overload the turbine by opening more than the
normal number of admission nozzles, the brunt of the
overload will be borne by the low pressure stages. On

THE CUETIS TURBINE 205

the other hand, it will be found that any increase in the
speed of the turbine tends to overload the high pressure
stage and particularly the first bucket row, but a dimi-
nution in speed puts the load on to the final stages and
equalizes the distribution between the different rows.

The Curtis, like the Parsons turbine, is capable of bene-
fiting to the full by a good vacuum, and it is, there-
fore, usual to set the condenser immediately underneath
the turbine, which exhausts through the floor of the
engine room. The machine has hitherto been used almost
exclusively for the driving of dynamos, and has been
made in all sizes from IJ to 5,000 kw. Direct driving
is usual. The field magnets of the dynamo, in the
large polyphase machines (in others the armature) are
keyed to the turbine shaft immediately above the steam
inlet. The fixed armature (or field magnets) rests on the
turbine case.

The weight of the whole rotor of engine and dynamo
is carried by a very simple and most ingenious bearing,
suggestive of the mercury bath used in lighthouses.
This bearing consists of a cast iron shoe on the shaft,
resting on a cast iron step, and surrounded by a ball
race to preserve the centring. The step is made slightly
concave and is fed with high pressure oil, so that the
moving parts float freely on the lubricant. The bearing
is entirely external to the turbine case, and contamina-
tion of the steam is impossible.

The permanence of adjustment secured by this simple
and effective device makes it possible to run the turbine
with very small clearance between the fixed and moving
buckets. It is important that this clearance should be
as small as possible, and the large diameter of the rotat-
ing wheels makes the rigid bearing an essential feature
of the machine. It is perhaps for this reason that the

206 STEAM TUEBINES

Curtis turbine has not yet been successfully applied to
marine propulsion, which requires a horizontal axis of
rotation.

The Curtis turbine, like that of De Laval, operates
very economically with low boiler pressures, which would
be unsatisfactory for a reciprocating engine, and it is
possible that a Curtis turbine of two or three blade rows
might be advantageously used to replace the low pressure
cylinder in a compound or triple expansion engine, or to
develop the energy of the steam exhausted from a re-
ciprocating engine of the simple or compound type. It
must, however, be borne in mind that a good vacuum is
essential for the satisfactory operation of the machine,

particularly if the initial pressure be low.

» * « * «

Intermediate between the Curtis and the Parsons tur-
bines in the nature of their action are the less well
known Zoelly, Bateau, and Schultz turbines. None of
these turbines have as yet equalled the former two
machines in efficiency, while all of them run at speeds
rather higher than that of the Curtis. The Schultz in
fact requires a speed considerably in excess of that of
the smallest of Parsons' turbines for the economical de-
velopment of power.

Of all these machines, that which approaches most
nearly to the Curtis in the nature of its action is the
Zoelly turbine. This is also a pure impulse turbine, but
differs from that of Curtis in the fact that expansion
takes place in each fixed blade row instead of in the
nozzle row only, and the steam leaves each rotating row
almost entirely deprived of velocity. This necessitates
a modification in the form of the fixed guide blades.
While the moving blades in the Zoelly turbine are prac-
tically identical in shape with those of the Curtis, the

THE ZOELLY TUEBINE

207

fixed blades (m, Fig. 72) approach much more nearly in
shape to those of the Parsons turbine, or of the Jonval
water turbine previously discussed.

We have explained in Chapter II that a turbine in

FIG. 72. BLADING OF ZOELLY TURBINE. (ESCHER WYSS AND CO.)

-which the pressure drops in successive stages will need
many more blade rows than one in which the full velocity
is developed by a single expansion, or else must run at
a higher speed. It will, therefore, be readily under-
stood that the Zoelly turbine has need of more stages

208 STEAM TUEBINES

than the Curtis. There are 10 wheels (Fig. 73) in the
Zoelly turbine as originally produced, each of these differ-
ing from the Curtis wheels chiefly in carrying only one
blade row, the blades being inserted in a T-shaped slot,
and not surrounded by a rim, like the Curtis buckets.
The shaft of the Zoelly turbine is horizontal, and the
clearances are rather greater than in the Curtis machine.
The speed of running is also greater. To secure the neces-
sary rigidity, the case is divided into two parts between
which there is a bearing, so that the shaft has three
points of support.

The admission to this turbine takes place all round
the wheel, as in that of Parsons, and not by means of
nozzles. The speeds of running are also approximately
those of the smaller Parsons machines, and considerably
in excess of those favoured by Curtis.

Tests show a steam consumption slightly in excess of
18 pounds per kw.-hour, but there is little doubt that'
the engine, which appears to have many features of ex-
ceptional merit, will be made more efficient after further
experiment. The Zoelly turbine has been fitted to Swiss
lake steamers with some success.

The Bateau turbine differs very slightly from that of
Zoelly. The rotor blades are flatter, and are riveted to
the wheels, and admission is partial, by nozzles, as in
the Curtis. The flatter blades make a greater number of
stages necessary in the Bateau than in the Zoelly tur-
bine, but a lower speed of running is secured. This
turbine has been found very successful when running
under a low steam pressure, and its possibilities as a
utilizer of exhaust steam from reciprocating engines de-
serve the attention of power consumers.

The Schultz turbine differs from that of Parsons in no
important particulars except its shape. The inventor

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abolishes the rotating pistons by which the equilibrium
of the Parsons shaft is secured, and sends the steam
instead in opposite directions along the high and low
pressure cones, which compose its rotor.

Nearly all the Continental turbines have been tried in
the German navy, apparently without much success,
though no results have hitherto been published. It is
rumoured that the Parsons turbine is now about to be
adopted by the Imperial Navy to a very great extent.

Another reaction turbine that deserves mention on
account of the extreme originality of its design is the
Gelpke Kugel. This is a compound radial turbine of the
reaction type. The steam expands in a large number
of stages, flowing alternately outwards and inwards,
and the blade designs of the outward and inward flow
sections of the machine are very similar to those in
the water turbines of Pourneyron and Francis respec-
tively. The speed of the shaft is high, and control is
effected by adjustment of the guides on the system'
common in Francis turbines. This, like many similar
machines, is still somewhat experimental.

CHAPTER IX.
TUKBO-BLOWERS AND ROTAEY PUMPS.

THE mere fact that an engine is driven by the pres-
sure of an expanding gas naturally suggests the
idea that, by a reversal of the process, the engine might
be used for the compression of a fluid. It is probably
fair to assume that the reciprocating engine was first
suggested by the older force pump; indeed, except in the
arrangement of the valves, the two machines are me-
chanically identical, and the effect of compelling such an
engine, fitted with a slide valve, to run in the opposite
direction to that for which the valves are set, would be to
pump air into the boiler.

In the consideration of the engines of which we have
been treating in this work the question naturally arises
as to how far the turbine can be used by reversal as a
force pump or as an air compressor. It is clear that when
a fluid presses on a piston there are equal and opposite
forces exerted between the two parties to the action, and
that which advances does work on that which retires.
The action is therefore perfectly reversible. On the other
hand, when a fluid acts on a blade not by reason of its
static pressure, but because the blade is curved and the
fluid rushes quickly round the concave surface, then the
action depends on the fact that the fluid is streaming
past the blade, and is not reversible.

211

212 STEAM TURBINES

We are therefore in a position to give a general answer
to the question just stated in these terms: —

A reaction turbine may be reversed so as to act as a force
pump or air compressor, but an impulse turbine cannot.

The fact that a reaction turbine is reversible had been
discovered as a matter of engineering practice before it
had occurred to any theorist to question whether it was
so or not. The first centrifugal pump was constructed by
Appold in 1851, and is in all essentials the same engine
as the vortex turbine or case wheel patented by James
Thomson in the previous year. Within the wheel of this
pump there is a forced vortex (App. II), and the nature
of the action has already been fully discussed in connec-
tion with the casewheel (Chap. VI). In this discussion
we pointed out that the flow through the case wheel
would cease if the speed at the circumference were that
due to half the head (or rather greater than that, since
the blades do not reach the centre of the wheel). If now
the guides were reversed and the turbine run at a slightly
greater speed, it would begin to act as a pump.

The speed at which such a pump must be run in order
to raise water to a given head can be easily found. If
the speed of the outer rim of the rotor be V and that of
the inner rim U, then the pressure of the water at the

outer rim is V^— US that due to a head — ^7^—, and the

velocity of this water is V, that due to a head, ~^

The sum of the pressure head and velocity head of the
water at discharge from the wheel make up the total
head, or the height to which it can rise if there be proper
guide blades to utilize the velocity possessed by the water*
The speed necessary to raise water to a height H is there-
fore given by V72G+(V^-U2)/2G = H.

TURBO-BLOWERS AND ROTARY PUMPS 213

Now, if the outer radius be R, and the inner radius R',
and if the speed be N revolutions per minute, then

V = Nx^xR=NxRx 0-105, and U = N x R' x 0-105,

so that we have N^ x 0*011 x (2R2-R*2^ = 2GH.

FIG. 74. HIGH SPEED CENTRIFUGAL PUMP.

It is clear from the above work, and indeed it is pretty
clear without any mathematical analysis, that the speed
of a centrifugal pump must in any case be large. As a
matter of fact the blades of the wheel (Fig. 74) are not
perpendicular to the rim at their outer ends, as are those

214 STEAM TURBINES

of the case wheel, and consequently, when there is a large
flow the water has considerable velocity along the rotor
blades, and its pressure and velocity at the rim of the
wheel are less than they would be if the blades were
radial. It follows that the speed must be more than that
found above, so that very high speed driving is necessary
if the head to be overcome is at all a large one.

In the case of a pump wheel of diameter two feet,
to which water is admitted through an orifice of
6 inches diameter, the maximum head resulting from a
speed of 1,000 revolutions per minute, would clearly be
l,000,000x0-011*x(2-l/16)-r2G, or 330 feet. If the
pump were to act against this head there would, of course,
be no flow at all, so that such a pump would be best
adapted in practice for a head about 20 per cent, less,
that is a head of 264 feet, or 115 pounds per square inch.
This is about the maximum head for which a simple
centrifugal pump will be found suitable. Messrs. Escher
Wyss and Co. have constructed some multiple centrifugal
pumps, with alternate stationary and rotating disks, by
which water is raised to a head of 500 lb. to the square
inch. The economy of these turbo-pumps appears to be
superior to that of most of those of the reciprocating type.

For this driving, turbines are pre-eminently suitable.
The makers of the De Laval turbine, in particular, have
devoted a good deal of attention to the production of
turbine driven pumps for feeding boilers and for other
high pressure work. A centrifugal pump designed for
connection to a De Laval turbine is shown in Fig. 75.
The speed of this machine is about 1,100 revolutions per
minute, a speed at which rope or belt driving is wasteful
and difficult, and direct connection to anything bat a

• 0-011 = (^y^=(0i05)^.

TUEBO-BLOWERS AND EOTAEY PUMPS 215

steam turbine or electric motor almost impossible. It
will be noticed that the wheel in the figure is set in a
volute or spiral case, so that the speed of the water
leaving it is used and the stream deflected into the dis-
charge pipe.

FIG. 75. CENTRIFUGAL BLOWER CONNECTED TO 15 H.P. DE LAVAL
TURBINE.

Similar machines have been in use as centrifugal air
blowers for many years. A great variety of blade forms
is used in these wheels, as impact is not deleterious.
Straight radial blades appear to be as satisfactory as any.
The wheels are set in volute cases, like those of centri-

216 STEAM TURBINES

fugal pumps, and are run at even higher speeds than
they, but even at such speeds as 8,000 or even 4,000
revolutions per minute, high pressures are unattainable
with wheels of this type. Fig. 75 shows such a blower
connected to a De Laval steam turbine.

If the central orifice of the blower be 1 foot in diameter,
and the length of the blades 6 inches, we can work out
the pressure attained as before ; for the compression of
the air is so slight that it does not appreciably affect its
volume. In this case the maximum head with 8,000 re-
volutions is 2,715 feet of air, or 8 feet of water (1-36
lb. per square inch).

For pressures higher than 20 inches of water, it is
advisable to use either a compound blower or else a re-
ciprocating pump or bellows. The reciprocating pump is
always open to the objection that, as the air is at rest in
the cylinder, a very large cylinder or bellows is necessary
to deal with any quantity of air; the more so that a
certain amount of throttling in the admission valves is in-
evitable, so that at the beginning of the stroke the air is
even below atmospheric pressure. For low pressures this
defect puts the reciprocating air pump quite out of court,
and it is advisable to use a high speed centrifugal blower,
or else a fan of the screw propeller type.

We have already pointed out that the screw propeller
is a reversed reaction wheel, and the common blower fan
may also be considered as a reversed reaction wheel of
the parallel flow type. This fan running singly is capable
of acting only against very moderate pressures. It may,
however, readily be compounded by the insertion of fixed
blades between a series of fans. It is clear that the re-
sulting blower is a reversed turbine of the compound re-
action type, with parallel flow; is, in fact, a reversed
Parsons turbine.

TUEBO-BLOWEES AND EOTAEY PUMPS 217

The builders of the Parsons turbine have naturally
devoted attention to the construction of such blowers,
and have attained very satisfactory results. The blower
has an enormous advantage over the reciprocating air
pump or bellows, in the quantity of air with which it is
able to deal. A pair of engines now under construction
at Heaton works for the Con sett Iron Company, are each
capable of dealing with 21,000 cubic feet of air per
minute, and delivering at a pressure of 15 pounds above
that of the atmosphere.

It is clear that such quantities of air cannot be touched
by reciprocating pumps, which seem likely to give place
more and more to turbo-blowers. The limitation of these
latter is the pressure which can be attained by their
means.

We have already pointed out that any reaction turbine
is reversible, so as to form an air compressor, and it
follows that the Parsons turbine of the ordinary type
would operate as a turbine blower. However, it is natural
to suppose that the blades of a turbine blower should
be more oblique to the flow of air than are those of a
steam turbine. The ratio of compression is always small
as compared with that of expansion in the steam turbine,
and it is not, therefore, necessary to shorten the blades
as the high pressure end is approached. The diminished
volume of the air may be allowed for by diminishing the
speed of its flow, as may clearly be done by increasing
the obliquity of the blades.

The air passes through a stage of compression in each
blade row, whether fixed or moving. The total com-
pression is the product of the compressions in every row,
and may be easily estimated.

The greatest difference of pressure that can possibly
exist between the two sides of a moving blade row is that

218 STEAM TURBINES

difference which could give to air, at rest on the high
pressure side, a velocity along the blade greater than that
of the blade itself in the same direction

If the diameter of the drum be 2 feet, and its speed
8,000 revolutions per minute, then the blade speed is
314 feet per second. Now suppose that the blades are in-
clined at an angle of SO" to the direction of their motion
(they must then be only slightly curved) ; the velocity of
each blade in the direction of its own surface is (314 feet
per second x cos 30° or) 258 feet per second. The
maximum difference of pressure between the two sides of
a blade row is, therefore, that capable of generating a
velocity of 258 feet per second, and this corresponds to a
compression of about 5 per cent. It can be seen very
easily that the theorem applies both to fixed and to
moving rows, so that fourteen rows in all, or seven fixed
and seven moving rows, will be necessary to double the
pressure.

It is, of course, required that there should be a flow
against the back pressure, and therefore more than
7 moving rows will in fact be needed, and to compress a
large volume of air to 15 pounds above the atmosphere,
it would be desirable to have ten rows at least.

Provided the pressure against which the machine is
working is less than that pressure for which it was de-
signed, the flow of the air is stable. If, however, when
this stable motion is established, the discharge of air be
checked, the engine may continue to deliver air at a
pressure raised very far above the limit, but the flow is
no longer stable, and the air is apt to cough back through
the blade rows, while the discharge pressure falls sud-
denly.

The Parsons turbo-blower is obviously suited for con-
nection to a Parsons turbine running at the high speed

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220 STEAM TURBINES

for which the blower is adapted, and this combination is
quite unequalled by any other compressing plant deliver-
ing air at pressures of 1 to 30 or even 40 pounds per
square inch. Pressures higher than these involve a mul-
tiplication of blade rows, which is somewhat undesirable,
though a pressure of 75 lb. has been successfully ob-
tained. If there were no alternative but the reciprocating
pump, with the absurdly large cyKnder necessary to
collect air at atmospheric pressure, the blower would
remain the most desirable compressor. It appears, how-
ever, that there is a more satisfactory alternative, con-
sisting of a combination of blower and reciprocating
pump. In such a combination the large low pressure
cylinder of the force pump can be done away with, and
the blower will deliver air to the high pressure cylinder
at a pressure of about 30 pounds per square inch, and
occupying only 40% of its volume at atmospheric pressure.
The continuity of the blast derived from a turbo-
blower, and the high duty which it is possible to obtain
from it on emergency, by a slight increase in the speed
of the driving turbine, make it an engine of no mean
merit in the present, and one likely to become more and
more popular in the future.

CHAPTER X.

THE GOVERNING AND OPERATION OF THE
STEAM TURBINE.

WE may divide steam turbines broadly into two
classes, nozzle turbines and blade turbines, ac-
cording to the formation of the passages through which
admission takes place. These classes are not conter-
minous with those of impulse and reaction turbines. The
Zoelly turbine, for instance, which is purely an impulse
machine, has blade admission, whereas admission to the
Rateau turbine, where there may be some reaction, is by
nozzles.

Whatever the class to which the engine belongs, it is
necessary at times to run it at a power less than that
for which it was designed, and it is a question of con-
siderable importance how this may be done with the least
disturbance of the internal conditions and the smallest
loss of thermodynamic eflSciency. In the early days of
the reciprocating engine, reduction of power or speed
was effected, as now on some few engines, by a throttle
valve in the main steam pipe. Of course this throttling
reduced the pressure of the steam at admission to the
cylinder, and so occasioned a loss of energy by no means
inconsiderable. The introduction of Stephenson's link
was a step in the right direction. By " notching up "
the cut off was accelerated and the period of admission
of steam into the cylinder reduced; notching up, how-

221

222 STEAM TUEBINES

ever, occasioned a dead loss, by throttling the flow into the
cylinder at the period of complete admission. This dis-
advantage was in turn abolished by the introduction of
the Corliss valve with its instantaneous cut off, and a
great increase in the economy of regulation was the
result. When control is effected by this means the cut
off takes place earlier in the stroke while there is little
steam in the cylinder, and a more complete expansion is
obtained.

It might be expected that, allowance being made for
the resistance of the engine itself, this complete expan-
sion would raise the efficiency of the engine at half
load ; but, as a matter of fact, great expansion in a single
cylinder is not an unmixed benefit, for the temperature
of the steam falls with expansion, evaporation takes
place from the cylinder walls, so that these are cooled,
and cooling and condensation of the live steam at the
next admission are the highly undesirable results. It is
for the purpose of avoiding losses from these causes that
modern high pressure engines are designed to permit the
expansion of steam in a succession of cylinders; but even
in a triple expansion engine there is considerable varia-
tion in the temperature of the cylinder walls, and the
losses from this cause are still the most serious item in
the waste heat account, even when running at full load.

Now, in a turbine running at full load, there is no
variation in the pressure or temperature of the steam
which comes in contact with any given blade row, and
consequently the most serious cause of loss is wanting.
For this reason alone it may be fairly anticipated that
the steam turbine will, when its construction has become
the subject of further experience, far surpass the re-
ciprocating engine in efficiency of working.

The question before us now is this: — How far is it

GOVERNING AND OPERATION 223

possible to maintain this advantage of the turbine when
running at low load or at low speed?

If we consider first of all a nozzle turbine, such as the
De Laval or the Curtis, the answer is a simple one.
When running at full load the blades are in contact with
the steam during only a portion of their revolution. If
there be an almost complete vacuum in the turbine case,
as in the De Laval turbine, the loss of heat in the buckets
during their idle motion is trifling, and, when they come
next into contact with the steam, a free passage is afforded
for it. In the De Laval turbine, and in the Curtis where
the nozzle expansion is incomplete and where the steam
pressure in the first row of moving buckets is con-
sequently higher than in the wheel case, it is found
advantageous to group the nozzles together so that the
pressure in the wheel passages may be maintained
throughout their period of service.

Except as above mentioned, the action of the steam
escaping from each of the nozzles in all the turbines of
this type is entirely independent, and, therefore; no loss
of efl&ciency will be occasioned by closing one of the
nozzles and leaving the others in operation. This regula-
tion by nozzles is the means adopted in all these ma-
chines. The early patents of Curtia describe a system of
regulation by narrowing the neck of each nozzle, but
this has been abandoned in favour of the obviously better
practice of closing the nozzles successively from one end
of the row. When one of the nozzles is partially closed
there is a slight loss of eflSciency owing to the " wire
drawing," of the steam passing through it, but as the
efficiency of action of all the rest of the steam is not
affected, this may be regarded as negligible.

It has been suggested that some advantage might be
gained by extending the regulation to the nozzles of the

224 STEAM TURBINES

second and third stages in order to avoid undue drop in
pressure in the stage chambers, but we are not aware
that this has been tried in practice.

The regulation of blade turbines is a problem much
more difficult of solution. The elementary and obvious
means is a throttle, but the limitations of that system
have already been explained. It is, however, used in
some turbines, and it has the advantage of maintaining
a continuous flow of steam and a constant temperature in
every part of the engine when running at low load. The
relay valve throttling device used by Escher Wyss and
Company not only on the Zoelly turbine, but, with certain
modifications, on their water turbines also, deserves
mention.

The operative part of this mechanism is a floating
lever attached at one end to the governor, by which it
is raised or lowered; at the other end the fulcrum of
the lever is formed by the end of a rod carrying both
the valve itself and a piston operating in a steam
cylinder. At a point on the lever is attached a spindle
carrying the slide valve, which controls the steam in
the piston box. The immediate effect of raising the
lever is the raising of the slide valve and consequent
depression of the piston and closing of the throttle.
This action is prompt and vigorous. But, as the throttle
closes, the slide valve descends, with the fulcrum of the
lever, and the throttle comes gradually to rest before the
speed has fallen to the normal. Lastly, as the speed
falls and the governor returns to the normal position,
the slide valve is depressed below the normal, and the
throttle is gradually opened again until the position of
equilibrium is reached. The combined power and delicacy
of this governor render it an exceedingly pretty and
valuable mechanism.

8

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226 STEAM TURBINES

The simple throttle valve was not thought sufficiently
economical for the Parsons turbine, and the mechanism
previously described (p. 144) was adopted in consequence.
This governor deserves a somewhat fuller consideration
than has yet been accorded to it. The essential feature
of difference from the Zoelly governor is in the fulcrum
of the floating lever, which in the Parsons turbine has a
periodic oscillation. There is a certain purely mechanical
advantage to the governor in this oscillation, for the
following reasons.

The essential virtues in a governor are that it should
be (1) Prompt, (2) Powerful, and (3) Sensitive. In the
Parsons governor the adjustment of the position of the
throttle takes place two or three times in every second,
so that the action of the governor is exceedingly rapid.
Further, since the moving pressure on the throttle is that
of boiler steam, its power is hardly open to criticism.
But the rare virtue of this particular governor is its ex-
ceeding sensibility.

The use of relay governors (in which the power actuat-
ing the valve is derived not directly from the governor but
from some other source controlled by it) is now common.
Such a governor is that of Zoelly. But the Parsons is a
double relay governor; for the steam moving the throttle
is controlled by the slide valve, and the slide valve i&
moved by the rocking lever, and only the fulcrum of this
lever is adjusted by the governor. It is possible to con-
struct an exceedingly delicate governor on these lines, for
it is not limited by the condition that it must be strong
enough to overcome frictional resistances and set the link
work in motion. The motion is already there, supplied
by the cam, and the governor has no friction to contend
with, but will answer to the slightest deviation from the
desired speed by afifecting the duration of the steam blast-

GO\^RNING AND OPERATION 227

The mechanical perfection of this governor can only be
attained by the nse of intermittent admission, and some
farther consideration is dae to the thermodynamical effect
of this action. Now it most be admitted that, in running
a turbine at half load under this system, we lose to some
extent the advantage of continuous action, which main-
tains the temperature of the high pressure end of the
turbine. We lose this, however, to a very small extent
only, for, although when the throttle is shut steam in the
high pressure stages expands and cools, yet the capacity
of these stages is so small that they are almost imme-
diately emptied of steam, and the cooling of the blades
and consequent condensation of steam (if any such
results) at the next admission, are negligible, when com-
pared with that which takes place even in a high speed
reciprocating engine.

It appears, then, that the Parsons governor is one of
rare merit, and performs its task in a very satisfactory way.
At the same time it must be admitted that this task, the
regulation of a blade tmrbine for variations of load at a
constant speed, is more difficult than that of regulating
a nozzle turbine for the same conditions, and does not
admit of quite so satisfactory a solution.

If on the other hand we consider the case for and
against the nozzle turbine on the issue of regulation for
varying speed, our judgement must be in favour of the
blade type, or rather in favour of the reaction turbine
with blade admission, of which the only examples are the
Parsons turbine and the Schultz turbine as constructed
for stationary use (in the Schultz marine turbine, accord-
ing to Stodola, the action is in the high pressure stages
impulsive). The blade speeds in the impulse turbines do
not appreciably affect the flow of steam, and if such a
turbine be slowed down by overloading, there will be

228 STEAM TURBINES

some increase in torque, but no diminution in the steam
consumption. Our consideration of the De Laval turbine
showed us that, in an impulse turbine (particularly if the
pressure stages be few), the full blade velocity is essential
for eflScient working, and the effect of reducing the speed
is consequently a loss of efficiency more or less serious.

In the Parsons turbine, on the other hand, the blade
speeds are never so great as, on theoretical grounds,
might seem proper; but this is not a matter of so much
importance in a reaction machine, and a still further
reduction of the speed does not seriously impair the
economy of the action. If the speed of a Parsons turbine
be reduced by overloading, the steam consumption is
automatically reduced by the greater resistance inside
the cylinder, and the torque is somewhat increased, the
low pressure rings bearing the increased pressure. A
comparatively small adjustment of the throttle valve or
of the governor will therefore cause a considerable reduc-
tion in speed, and that without any great loss of efficiency,
and this fact has greatly contributed to its success at sea.
It may be noted that a reduction of the speed of a set of
marine turbines will increase the proportion of work done
in the low pressure cylinders, just as the same effect is
produced in a compound engine by shortening the low
pressure cut off.

A suggestion has been made that some advantage
might be taken of this fact in vessels, such as the Cunard
greyhounds, in which the high pressure turbines drive the
outer shafts, by running at half speed with one high and
one low pressure turbine under steam, exhausting from
the high pressure cylinder on one side to the low pressure
on the other. It is contended that the excessive load on
the low pressure drum, which is the nearer to the keelson,
would operate to keep the helm steady, and any deviation

GOVEENING AND OPEEATION 229

from this condition could be compensated by the admis-
sion of boiler steam, through a reducing valve, to the low
pressure cylinder.

It is clear that no sensitive governor is required on the
marine turbine; small variations in the propeller speed
are of no consequence, and throttling is obviously pre-
ferable to gust admission where there are two turbine
cylinders and a considerable volume of steam in the con-
necting pipe. To prevent racing in a seaway, all marine
turbines are fitted with a runaway governor, which
operates powerfully as soon as the speed has increased
beyond a definite limit from five to ten per cent,
higher than the normal full speed. Owing, however, to
the depth of the propellers of turbine vessels below the
surface and to their small diameter they have never yet
been known to race, so that no case of operation of the
governors is at present on record.

« « « « «

A word must be said about the conditions of running
v^hich are desirable in a turbine installation.

We have already pointed out that a very high vacuum
is valuable, and have drawn the inference that the con-
denser should be placed in immediate proximity to the
exhaust. This is usually effected by placing the condenser
beneath the floor of the engine room, so that steam passes
into it almost without the intervention of a pipe. Such
pipe as there is must be very large. A horse and cart
could pass down the exhaust pipes of the Cunarders
under construction, without inconvenience.

Another point to be considered is the desirability of
superheat. It is well known that, when saturated steam
is expanded, some of it is immediately condensed, and if
saturated steam undergoes the large expansion which
takes place in a turbine cylinder the condensation is

1

280 STEAM TUEBINES

bound to be considerable. Now not only is the condensed
steam incapable of further expansion and therefore of
doing work, but it adds seriously to the friction on the
blades, and so delays the flow and tends to wear the
blades away.

By sufficiently superheating the steam after it leaves
the boiler, this condensation can be got rid of, and the
amount of superheat necessary for the purpose depends
on the ratio of expansion. Consider for a moment the
condition of the steam used in the standard tests of
Parsons and Curtis turbines referred to on pages 128 and
208. The steam pressure at admission is about 200
pounds, and the superheat 150° Fahr. The volume of the
steam is then 2*72 cubic feet per pound, and it expands

approximately according to the law, P.V = Constant.
When the pressure has fallen to 1*4 pound absolute (a
vacuum of 27 inches of mercury), the volume will be
about 805 cubic feet per pound, and the temperature
115° Fahr. The steam is then saturated, and any further
expansion will involve a partial condensation.

Now in the tests of the Parsons turbine, the expansion
was carried slightly further, and a steam consumption
of 15*4 pounds per kw.-hour was obtained. In some
German tests of a Parsons turbine, where 225° Fahr. of
superheat were used, with the same pressure, a steam
consumption of 14*9 pounds was obtained.

Turning to the Curtis test, we find a vacuum of 28^
inches employed in the condenser. The pressure in the
last nozzles must have been lower still, for the friction
on the blades in the last chamber would cause a certain
rise in pressure as the steam passed through the blade
rows.

It follows that considerable condensation must have

GOVERNING AND OPEEATION 281

taken place in these nozzles. Now when steam passes
through expanding nozzles the speed of the whole in-
creases until condensation begins; but so soon as any of
the steam is condensed the acceleration of that portion
stops; for the water drops, though infinitesimal, are yet
far more heavy than the molecules of steam, and cannot
be accelerated by the impact of these molecules. The
acceleration of the remaining steam still goes on, and, by
reason of the latent heat of the steam condensed, the
remainder attains a velocity higher than that due to its
mere expansion; so that, when discharge takes place,
there is a certain amount of steam moving with very
high speed, and a straggling tail of infinitesimal water
drops, moving with all manner of smaller velocities, from
about 2,000 feet per second upwards.

It is clear that these water drops will actually exert a
back pressure on the last blade row, as the first two rows
deprive them of their whole velocity, and their deleterious
effect upon the economy of the machine is great. We may
therefore infer that the Curtis turbine stands to gain
even more than the Parsons from increased superheat,
and the De Laval will benefit in almost the same degree.

This suggestion is borne out by the benefit experienced
from moderate superheats in connection with the Curtis
turbine, and there can be little doubt but that, if the
superheat of 226° Fahr. can be applied to the Curtis
turbine without injury to the first blade row, a very high
efficiency will result.

CHAPTER XL
THE FUTURE OP THE STEAM TURBINE.

THE rapidity with which the turbo-generator has
been taken up of late years by the most progressive
and successful engineers lends a certain interest to specu-
lation as to the probable future of the engine. The pre-
sent demand for steam turbines makes it seem likely
at first sight that they will before long entirely displace
the reciprocating engine from all large undertakings.
Whether this belief is justified can only be shown by the
event, but some consideration may be given to the rela-
tive merits of the turbine and the reciprocating engine as
prime movers.

The only steam turbines which have as yet been manu-
factured on any large scale, are those of Parsons and
Curtis, and no large units of any other type have shown
an efficiency comparable with that of these machines.
The largest Parsons turbines built by the inventor are
the 4,000 kw. machines running at the Carville power
station on Tyneside. Larger turbo-generators have, how-
ever, been constructed by Messrs. Brown, Boveri and Co.
of Baden, under licence from Mr. Parsons ; and the tur-
bines now building at the Wallsend Slipway for the new
Cunarder, will develop about 17,600 H.P. in each turbine
cylinder, or 35,000 H.P. in each complete turbine, con-
sisting of the high and low pressure parts. The largest

232

FUTUEE OF THE STEAM TURBINE 283

Curtis turbines at present constructed are the 5,000 kw.
machines running at Chicago. Their steam consumption
is 15*8 pounds per kw.-honr, as against 15'4 pounds, the
lowest consumption obtained with the Carville turbines,
and 14*9 pounds the corresponding figure for the Parsons
turbine of Messrs. Brown, Boveri and Co. In the case of
smaller units the low steam consumption is not quite
maintained by turbines of any type, but the small
machines of De Laval are unsurpassed.

In choosing between the various prime movers avail-
able for stationary work, the engineer must look to their
economy in, among others, the following relations: —

(1.) First cost.

(2.) Cost of station and erecting.

(3.) Wear and upkeep.

(4.) Coal and oil consumption.

(5.) Attention required.

(1.) Now as to the first cost, we have seen that large
turbine units of the Parsons type can be built at consider-
ably lower cost than triple expansion engines of the same
size. There is little io choose between the two when units
of 1,000 to 2,000 kw. are concerned, and in the case of
smaller units the advantage is rather on the side of the
reciprocating engine. When we get below 1,000 kw., too,
another competitor comes into the field, in the form of
the internal combustion engine, using producer gas. This
last seems to be very much more economical than the
steam engine, as may reasonably be expected froifi the
abolition of that most exorbitant middleman, the boiler,
but it is handicapped by the unsuitability of internal
combustion for large engines, and by the deleterious
effects of the high temperature inside the cylinder.
- The cost of the Curtis turbine appears to follow much
the same law. Some of the German engines have been

234 STEAM TURBINES

more cheaply prodnced, but they pay for the saving in
coal.

(2,) When we come to the cost of erectmg, housing,
etc., the advantage is entirely on the side of the turbine.
There is, in the first place, an immense saving of space
by their adoption, and a consequent reduction in the size
and cost of the engine house, attended by the advantage
that the engines are very much more under the eye of
the engineer in charge. The economy of the Curtis tur-
bine from this point of view is even more striking than
that of any other.

But every form of turbine has another conspicuous ad-
vantage in the absence of vibration attending its motion.
A reciprocating engine (and gas engines are the worst
sinners of all in this respect) requires very heavy founda-
tions and massive bedplates, which must be laid down at
considerable expense. The weight of piston, piston-rod,
connecting rod and other reciprocating gear moving to
and fro at the high speeds required for the driving of
dynamos, coupled with the thumping of steam admitted
alternately to the opposite ends of the cylinders, causes
a noise and vibration perceptible, not only in the power
house, but too often throughout the neighbourhood; a
vibration which not infrequently exposes the supply com-
pany to the risk of indictment for nuisance, or to an
action for heavy damages consequent on injury to the
foundations of neighbouring buildings. It will be inter-
esting to see whether the attitude of the courts towards
reciprocating nuisances is at all affected by the possi-
bility of running a big station quietly, where turbines
are installed.

(3.) The Parsons turbine, as we have already pointed
out, has only two bearings under stress, the Curtis tur-
bine has only one, and in each case high pressure lubri-

FUTURE OF THE STEAM TURBINE 285

cation is used, the Curtis rotor being completely oil borne.
The stresses on the bearings, too, are due only to the
weight of the moving parts, and are both smaller and
simpler than those on the bearings of a crank shaft,
^vhile the wear is uniform all round the journals, a con-
dition not obtaining in the reciprocating engine. Lastly.
it may be noted that the turbine contains no high speed
or hot wearing surfaces like the cylinder walls, and
there is no packing or stufi&ng anywhere in the steam
turbine.

On the other hand, the wear on the blades must be
considered. The Curtis turbine has been on the market
for so short a time that it is difficult to speak definitely
of the erosion and corrosion of its buckets. It is main-
tained by the makers that there is very little of either,
and that the life of the blades, when superheated steam
is used, is practically indefinite. At the same the steam
velocities in the Curtis turbine are very much higher
than in the Parsons, and the pressure of the steam on the
buckets is greater, so that it seems reasonable to suppose
that the English machine will be the more durable. We
are not aware that any destruction of the blades has been
experienced on the Parsons turbines that have now been
running in this country for periods of nearly twenty
years.

When we bear in mind the continual trouble that is
experienced with glands and packing rings in the recipro-
cating engine and the great loss of efficiency which re-
sults from wear on the slide valve surfaces, causing
leakage of steam and water, we must concede that the
steam turbine promises to be a very much more durable
and less troublesome machine.

(4.) The steam consumption of the two types of steam
turbine under discussion has already been considered.

236 STEAM TUEBINES

We have seen that the large Parsons turbine units com-
pare very favourably in this respect with the triple ex-
pansion engine, and vastly surpass the best recorded
performances of the compound. It is a further merit of
the turbine that its eflSciency does not diminish with in-
creasing age, and that a high boiler pressure is not essen-
tial to efficiency provided that the vacuum is a good one.
Taking into account the fact that steam turbines are
very, commonly run under a lower boiler pressure than
that adopted for reciprocating engines (a fact particularly
noticeable in the published comparisons of marine en-
gines) the advantage of the steam turbine in point of
coal consumption is generally rather more than appears
from the comparison of feed water or steam per H.P.
hour. And it must also be remembered that the recipro-
cating steam engine is now a highly perfect mechanism,
and has probably touched its limit of efficiency, whereas
every type of steam turbine is still in comparative in-
fancy, and their steam consumption is reduced every year.

It is clear that the greater expansion of the steam
possible in a turbine furnishes it with a greater supply
of energy per pound of steam than is available to the re-
ciprocating engine. It lies with the designer so to modify
the modern turbine forms as to reap the full benefit of
this additional energy. Thus the turbine has possibilities
of efficiency which do not exist for the reciprocating
engine.

Further, the most fruitful source of loss in the old en-
gine, the alternate cooling and heating of the cylinder
walls, is absent in the turbine; and the greater mechan-
ical simplicity of the turbine is immediately apparent.
On every ground, then, we may fairly anticipate that the
turbine will, within the next few years, so completely excel
the reciprocating engine in the economy of its working,

FUTUBE.OF THE STEAM TURBINE 237

that the most conservative engineer must perforce declare
himself a convert to the new prime mover.

High pressure lubrication, with return of the oil, through
a filter, to the pump once more, is now the prevailing
system on engines of every type. A certain proportion of
the oil is lost in each cycle, depending on the number of
bearings supplied and on the speeds and stresses in each
bearing. The bearing speeds in a turbine are rather
greater than in the competing engines; on the other
hand the number of bearings is less. It is a vexed question
whether or no the Parsons turbine consumes less oil than
the reciprocating engine. The examples of the latter cited
in the discussion are of course the best that can be found,
but on the whole the supporters of the turbine seem to
have rather the best of it.^

(5.) Lastly, when we come to compare the attendance
required by the tUrbine with that necessary for the re-
ciprocating engine, the advantage is all on the side of
the former, and this for two reasons. In the first place
the smaller number of parts — the rotor is the only moving
part of any size, or subject to stress of any magnitude —
saves almost all surveillance and lubrication, and makes
it very unlikely that anything should go wrong; and,
secondly, the compactness of the machine, and the small
space occupied by it, makes it easy to keep an eye on
several units at the same time, and to move quickly from
one to the other. It may be added that the introduction
of the steam turbine into a factory considerably diminishes
the risk to operatives of injury by the machinery, as the
impossibility of getting entangled in or crushed by a
steam turbine may readily be conceived.

It appears, then, that in a comparison between the
turbine and the reciprocating engine as a stationary
^ Disoussiou at the Institute of Civil Engineers.

238 STEAM TUEBINES

source of power the old-fashioned engine comes oflf a
very poor second.

If, however, we tnrn our attention to the adaptability
of the two machines for vehicular propulsion, we shall
be compelled to take a different view.

Every steam turbine, if it is to work economically, must
exhaust into a condenser, and a condenser is equally
impossible on a locomotive engine and on a motor car.
In addition to this, the flexible shaft of the De Laval
turbine, and the large wheels and small clearances of the
compound impulse turbines unfit them for running in
bearings subject to violent jolting. The Parsons turbine,
which is more solid in construction, is put out of court by
the large steam consumption of the smaller machines, •
particularly when non-condensing, and by the small
starting torque whic^h they are capable of exerting, for if
steam be blown through the cylinder of a Parsons turbine
with the rotor at rest the resulting torque is not very
much greater than that which would be exerted at full
speed. Thus it is not possible to exert a large torque
when required, by slowing the engine; so that, both for
hill climbing and for starting, the Parsons turbine would
be entirely unsuitable.

When, on the other hand, we consider the problem of
marine propulsion, the advantages of the Parsons turbine
appear unique and of the last importance. Here the sav-
ing of space effected by the turbine is of great value, and
the engine appears to be peculiarly adapted for the
economic use of steam for purposes of propulsion.

There can be no question as to the advantage of an
engine room &ee from links and frames up to the level
of the upper deck, and occupied only by the turbine
cylinders on the floor. The compactness of these contri-
butes greatly to the safety of the engineers and greasers.

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Flti. 78i TURBIKE EOOMOF.SS. 'M.DNnONPKREY," (REFEODUCED FBOM
"ENGINEERING.*')

240 STEAM TUEBINES

and reduces the necessary staff to a certain extent. The
lower boiler pressure also diminishes the discomfort of
the stokehold.

The engine room itself may be smaller when turbines
are employed, and the hull need not be so heavily
strengthened in the region of the bed-plates, on account
of the absence of vibration and the stresses inevitable
where the reciprocating engine is employed.

But perhaps the most important advantage of the tur-
bine in a passenger vessel, is the increased comfort of
passengers, particularly at night and in berths near to

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the engine room, from the absence of the continuous
thumping which makes sleep impossible to the most ex-
perienced traveller during the first night at sea. In the
modern turbine vessels, the smoothness of running is so
marvellous, that the author has been unable to discover,
from the sound or vibration in the cabin of a channel
steamer, whether the engines were running or not at any
particular moment, and even the delicate seismograph
employed on the Carmania during her trial trip scarcely
detected the slight vibrations which appear on the record
(Fig. 80).

A point of the utmost importance in marine architect-
ure is the allowance of a suflBcient metacentric height to

FUTURE OF THE STEAM TURBINE 241

ensure great stability in a short roll. Both for comfort
and safety it is desirable to have a low centre of gravity
of the vessel and engines, since these cannot shift, while
the cargo can. The heavy cylinders of a reciprocating
engine, on a level with the main deck, are, therefore, an
unmitigated evil, and the increase of stability arising
from the use of turbines is among their many advantages.
A gain of even more importance arises in connection
with the use of steam turbines for the propulsion of war-
ships from the fact that the turbine is entirely below the
water-line and so protected from the enemy's shells. In
addition to this, the turbine itself is by no means an easy

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FIG. 80. VIBRATIONS OF HULL OF SS. " CARMANIA " (TURBINES).

machine to injure; nothing but the direct impact of a
shell on the turbine case could do serious damage, and
the. target presented is very small in comparison with the
vital part of a ship propelled by the old method.

In armoured vessels, as is well known, the armour
deck springs from the belt and arches over the engines,
so that, while the deck must be raised to a considerable
height, adding to the weight of the vessel and diminishing
its stability, the connecting rods must also be shortened,
to the detriment of the engine's efficiency. These engines
are, therefore, less fitted than those of other vessels to
contest the pre-eminence of the turbine, and it is fair to
suppose that the trials of the Dreadnought will clearly
establish the magnitude of the gain which is to be ex-

242 STEAM TURBINES

pected from the adoption of the steam turbine in this
branch of the service.

Engineers have recognized that the steam turbine is
the engine of the future, and the increasing output of the
various turbine works affords ample evidence of the fact.
The total power of the Curtis turbines now built, or under
construction, is 800,000 horse, and the same figure has
been reached by the marine steam turbines constructed
under the Parsons patents. The Parsons turbo-generators
now running are even more numerous, and attain a total
horse-power higher still.

CHAPTER XII.

ON THE TEEND OP MODEEN SCIENTIFIC
INVENTION.

THE spirit of the age, whose high priest in days gone
by was Matthew Arnold, has spread his cult of late
years throughout society, and is recognized as having a
somewhat peculiar dominion over the spheres of literature
and art.

The influence of this power in the more sordid realms
of science and engineering is a fact which has hardly yet
been appreciated, but a fact none the less; and this in-
fluence has never been so great as at the present day,
when the gap between the engineer and other members
of the educated public is being bridged, at once by the
university training of the engineer (a development of
the last few years) on the one side, and, on the other, by
the wide public interest in the problems and progress of
engineering science. The department of engineering enter-
prise which touches most frequently and intimately the
general public is that which bears upon traffic and loco-
motion. Partly as a result of this fact, the invention of
the petrol engine and consequent introduction of the
automobile and the motor omnibus has aroused of late
years a greater interest in science than has ever been
experienced since the days of Hudson the railway king.

There can be no doubt that the invention of the steam
turbine has contributed in no small measure to this effect,

243

244 STEAM TUEBINES

but the present change in the form of the steam engine
is a less striking manifestation of the spirit of the age
than is the supersession of the steam engine itself as a
motor for the development of small powers. This change
is particularly obvious in the department of traction.
Here the steam engine has always suffered to a certain
extent from the impossibility of getting a starting torque
very much larger than that which is exercised when the
engine is running at full speed. The petrol and the oil
motor are even less satisfactory in this respect. The diffi-
culty has been overcome so far as road cars are concerned
by tiie now familiar device of changing gears, but this is
applicable only to the lighter vehicles, and is out of the
question for railway engines and the like. For this
reason it appears inevitable that the electric motor will
ultimately displace those of every other form from those
railways on which frequent stops are the prevailing rule.

The growing use of electric power, while diminishing
the employment of small steam engines, increases very
greatly the demand for those of high power for the pur-
pose of driving the electric generators, and it is notable,
as an instance of the far-reaching power of this Zeit-Geist
of which we have been speaking, that it is precisely in
the high power machines that the superiority of the tur-
bine over the reciprocating engine becomes most obvious
and undeniable. On the other hand the internal combus-
tion engine, burning oil, gas, or petrol, which is super-
seding the small steam engine, does not require the exist-
ence of steam power in the background.

An obvious advantage of the internal combustion engine
over that using steam is the decrease in weight and
bulk consequent upon the abolition of the boiler, but it
is an important fact that the proportion of fuel used per
horse-power-hour can be reduced to a much lower figure

THE TEEND OF INVENTION 245

in the oil engine than in one in which steam is the acting
fluid. This is particularly conspicuous in the case of the
Diesel motor, which works without explosion, by the
steady combustion of oil vapour within the cylinder.

Now if the turbine is better than the reciprocating
engine, and the oil engine superior (letting alone the
limitations introduced by heating) to one using steam,
it would appear that an internal combustion turbine
would be the best engine of the four.

It is scarcely necessary to say that innumerable at-
tempts have been made to produce such an engine, but
without success. The archives of the Patent Office are
full of the dreary records of disappointed hopes. In spite,
however, of the despondency of most engineers on this
point, it seems probable that in the course of a few years
some method of dealing with the difficulties presented
will be found. But before we turn our attention to the
practical problem involved, there is one preliminary objec-
tion demanding a certain notice.

It has been urged that the steam turbine rivals in
efficiency the reciprocating engine only by reason of the
greater expansion possible in the turbine cylinder, and
the inference is drawn that, as the exhaust gases of an
internal combustion engine are incapable of condensa-
tion, so an internal combustion turbine would necessarily
be inferior in efficiency to a reciprocating engine of the
same type. It is sometimes forgotten by the supporters
of this view that the internal combustion engine exhausts
at a pressure very much above that of the atmosphere,
and that nothing like complete expansion takes place in
the cylinder. If then a turbine of this type were pro-
duced, it would maintain an advantage of precisely the
same sort as that possessed by the steam turbine, and
would probably show a very high efficiency.

246 STEAM TUEBINES

There are two obvious systems on which an internal
combustion turbine might be worked, corresponding to
those of Diesel and Daimler in reciprocating engine
practice. According to the first, which would seem on
many grounds to be the preferable one, a combustion
chamber would be formed in communication with the
admission port to the turbine cylinder, and into this
chamber air would be compressed. Gas or oil injected to
this chamber would supply the heat required for expan-
sion. On the other system, air, charged, by passing
through a carburetter, with the vapour of petrol or of
some other combustible spirit, would be admitted at high
pressure to a combustion chamber and there exploded by
an action either continuous or intermittent. Non-return
valves would prevent lighting back.

The fundamental objection to both these systems,
which have occurred to many inventors of turbines, is
the high temperature of the gases admitted to the turbine
cylinder, a temperature which is fatal to the edges of the
blades, past which the gas flows with great speed and
considerable friction. It has been found impossible, with
the materials at present available, to construct turbine
blades capable of resisting corrosion for the shortest
times. This problem is, therefore, at present one for the
metallurgist, and it is possible that some of the new
steels now the subject of experiment may provide the
desired solution. At the same time there are a number
of questions of blade-design presented by steam turbines
of every class, and worthy of the attention of the mathe-
matician. It cannot be too strongly urged that the in-
vention of turbines has opened a new territory, and offers
a huge field for scientific investigation.

There can be no doubt but that engineers have shown
of late years some appreciation of this fact, and both

THE TEEND OF INVENTION 247

professional men and amateurs have devoted a consider-
able amount of thought to the subject. The file of patents
bears eloquent testimony to their not always well-directed
application, and the waste of money and time which
takes place annually in the pursuit of patents for in-
ventions, either based on fallacies or unworkable by
reason of difficulties unforeseen by the untrained tech-
nician, is matter for great regret. It is still more un-
fortunate that many inventions of real merit remain
unprofitable and undisclosed on account of the dread
experienced by the inventor (particularly if a man of
small means) of the expense entailed, before a patent
can be obtained and the necessary experiments carried
out for proving the merit of the invention.

It may come not amiss if we devote a few words to
the subject of patents in their practical bearing upon
invention.

In all the more important states of the civilized world
protection is granted to the inventor of new machines
and the like, upon the condition that he file a complete
description of the machine, which shall be available to
the public, for the purpose of enabling other persons to
carry out the invention after the expiry of the patent.
To guard the inventor against the danger of publication
during the experiments which may be necessary, and
to enable him to describe fully the method of carrying
his invention into effect, a period of six months is
allowed before the complete specification need be filed,
during which period provisional protection is granted to
the inventor.

For the further relief and encouragement of inventors,
the principal states have entered into a union for the
protection of industrial property, and an application for
provisional protection made in any country of the union

248 STEAM TURBINES

secures protection in all for the period of six months.
This application must, of course, be accompanied by a
description sufficient to identify the invention, but the
description is not published until the complete specifica-
tion is received.

The cost of obtaining, by the aid of a reputable patent
agent, letters patent or the corresponding protection for
a simple invention in every State of the Union may be
roughly estimated at about jg2(X), though, of course, it
varies very much. It cannot be too strongly urged upon
the inventor that to seek this protection without the assist-
ance of a patent agent is at least as foolish a pro-
ceeding as to go into a court of law without the help
of a solicitor, and it should be remembered that as
much or more technical skill is required for the draft-
ing of a complete specification as for that of a freehold
conveyance.

The cost of obtaining letters patent need not, how-
ever, fall upon the inventor. So soon as provisional pro-
tection has been obtained, he will generally find it ad-
visable to put his invention into the hands of one of the
leading firms manufacturing the class of machine con-
cerned. Such a firm is able to call upon wider experience
in this class of work than can be possessed by any in-
dividual, and has at hand facilities for experiment greater
than are likely to be at his disposal. It is usually worth
while to make such communication in confidence, so as
to avoid publication of the invention, in case misdescrip-
tion in the provisional specification should necessitate
the abandonment of the application and the taking out
of a new patent.

Having regard to the possibility of this event, it is a
commendable course to have the provisional as well as
the complete specification drawn by an agent. It is com-

PATENTS FOB INVENTIONS 249

monly supposed that the ^rawing of a provisional speci-
fication requires no particular skill; and this is very
frequently the case. But it happens lamentably often
that a search in the file of patents, after provisional pro-
tection has been obtained, reveals the fact that the greater
part of the invention has been anticipated'; and the one
element remaining on which a good claim could be
founded, will generally be found to be the one not men-
tioned in the provisional specification, and, therefore,
frequently incapable of being claimed in the complete.

In spite of these dijOSculties, however, the present
patent law works with exceeding fairness both to the
public and to the patentee, and great praise is due to the
just and equitable practice of the Patent Office and of its
present Comptroller, whose policy it has always been to
show the inventor that encouragement which he of all
men best deserves.

It is a fact, more and more appreciated of the public,
that the inventor is its most valuable servant, since his
work contributes not only to his own advancement but
to the growth of industry, the employment of the people,
the advancement of science, and the raising of the standard
of life. The inventor is hailed to-day as the herald of the
millennium — a millennium, it is true, ** of luxury and the
electric button," — but a millennium none the less, and
one which it is the tendency of the present age to esti-
mate at too high, rather than at too low a value — a
millennium not without attractions even to the stoic.

We have hoped, in laying shortly before the reader
some of the problems which are confronting the engineer
of the present day, to contribute in some small degree
to the realization of this ideal, and in that hope we
close these pages until it shall please the public to re-
open them.

APl'ENDICES.

APPENDIX L

SOME MATHEMATICAL PEINCIPLES.

THE principles of mathematics involved in the elementary
branches of engineering may be briefly summed up in
one geometrical and a few mechanical propositions. The
geometrical proposition is this: —

If a body has at the same time two velocities which may be
represented by the lines AB and BC, then the line AC repre-
sents its whole velocity. And this is clear enough. If a man
were to walk in one second between the points A and B on
the deck of a steamer, while the vessel itself moved so as to
carry the point that was

at B into the position C, ^^C

then the man would have
the two velocities repre-
sented by AB and BC, and
would move actually from
A to C in the course of
the second; so that his
total velocity is represented by AC.

Suppose that water flowed down a turbine blade in the direc-
tion AB, while the blade itself moved in the direction BC,
and suppose that these lines are proportional in length to the
corresponding velocities; then the whole velocity of the water
is represented by AC, and it is quite clear that the relative
magnitudes of the three velocities represented by these three
straight lines depend on the angles of the triangle ABC,
that is to say, on the angle at which the fluid is admitted to
the turbine wheel, and on the obliquity of the blades.

Since the velocity represented by AC is made up of the

253

A B

FIG. 81. DIAGRAM OF VELOCITIES.

254 APPENDIX I

velocities AB and .BC, it is clear that, if a body change its
velocity from AB to AC, then the change is the velocity BC,
and, even if only the direction of the velocity is changed, that
is, if AB and AC are of the same length, still there is a change
of velocity which may be represented by BC. Now, if the
body is moving round a curve, the direction of its velocity is
always changing, whether its magnitude is changing or not,
and the body is therefore constantly acquiring a new velocity,
which we cannot represent graphically because the velocity
acquired during any small period is itself small. This con-
stant acquisition of velocity is called acceleration.

When the velocity of a body changes in direction only and
not in magnitude, the acceleration is perpendicular to the
direction of motion at any instant, for if it were in the direc-
tion of motion it would cause the body to move more quickly,
and if it were in the contrary direction it would retard the
body. The amount of the acceleration is, of course, propor-
tional to the velocity, and to the rate of turning ; so that, if a
body is moving in a circle, it has a constant acceleration to-
wards the centre proportional to the product of its speed of
moving and its speed of turning; and this is equivalent to
the square of the speed of moving divided by the radius of
the circle.

Mechanical Principles.

In the course of our discussion we shall use two laws, of
which the one can, by the aid of the geometrical proposition,
already stated and a chain of mathematical reasoning, be
derived from the other. For the sake of brevity we shall state
these, the law of " conservation of energy," and the law of
" conservation of momentum,** as separate principles.

The latter principle may be stated as follows: — **No body
or system of bodies can change its momentum, except under
the influence of externally impressed force; and the rate of
change is proportional to the force applied.**

In this statement, which contains all the three laws of

SOME MATHEMATICAL PRINCIPLES 255

motion enunciated by Sir Isaac Newton, we have introduced
a term requiring some explanation. The momentum of a body
in any given direction, is the quantity of its motion in that
direction, and is the product of its mass by its velocity. The
momentum of a system of bodies is the sum of the momenta
in the given direction, of all the bodies composing the system.
Now the mass of a body does not ordinarily change — and
here we touch on a third principle, that of conservation of
matter — the rate of change of momentum is, therefore, the
mass multiplied by the rate of change of velocity, in other
words by the acceleration of the body.

If, then, a body is subject to acceleration, it must be under
the influence of a force proportional to the acceleration and
to the mass of the body, and for mathematical purposes force
is measured by the " mass acceleration '* which it can produce.
One poundal produces unit acceleration in a mass of one
pound. Thus when a body moves uniformly in a circle it must
be under the influence of a force towards the centre. It is
a matter of common experience that it is necessary to apply
such force by a guide, a string, or some other means, in order
to secure the curvature of the path.

Now if one body be attached to, or press on, another, then
the momentum of each will be changed by the force between
them; but since there is no external force acting on the two
bodies, the momentum of the system is not changed; so that
whatever momentum is lost by one body is gained by the
other. We infer from this that the force exerted by the first
body on the second is equal and opposite to that exerted by
the second on the first. This fact is enunciated by Newton as
the third law of motion, " To every action there is an equal
and opposite re-action."

If then a body moving in a circle is under the influence, as
we know it to be, of a force towards the centre, it follows that
it must exert on something a force away from the centre, and
this phenomenon, which one may experience by swinging a
weight on the end of a string, is that known to engineers by
the term, somewhat unjustly condemned by mathematicians, of
" centrifugal force," which is really the reaction of the body

256 APPENDIX I

against the means of constraint, and not a force acting on the
moving body itself.

So far we have dealt onlj with the motion of small bodies or
points, in discussing the motion of large bodies we must not
forget their possible rotation; but it is necessary at this point
to introduce a new term. The " angular momentum,'* about a
given point, of a small body moving in a straight line is the
product of its momentum by the perpendicular from the point
on its line of motion. This quantity measures the amount of
its '' spin " about the point, and clearly it has no spin about a
point on its line of motion.

When a large body is turning, the various parts of it are
moving in all manner of different directions, with different
speeds, and consequently with different momenta. The angular
momentum of such a body about a point is the sum of the
angular momenta about that point of all the constituent
particles. To change angular momentum we must apply a
turning couple, which consists, as the familiar process of turn-
ing a butterfly nut with finger and thumb indicates, of two
equal and opposite forces acting at a distance apart.

By a little mathematical reasoning based on this fact (and
as the reader can easily pursue the chain of argument for
himself we shall not here enter upon it) we can deduce from
the principle already laid down the further principle of the
" conservation of angular momentum." This principle makes
it clear that, if fluid enters a turbine wheel with angular mo-
mentum in one sense about the shaft, and leaves it with a less
angular momentum, or with one in the opposite direction,
then some turning couple must have been acting on the fluid
in the wheel, and consequently an equal and opposite turning
couple must have been exerted on the rotor by the fluid. The
torque of the engine is, therefore, equal to the rate of change
of angular momentum of the fluid in the wheeL This is the
whole principle of the turbine, whether driven by water, steam,
or any other fluid. ^

^ In the case of a large body rotating about an axis, the velocity of
each particle is equal to the angular velocity of the whole, multiplied
by the distance of that particle from the axis, and the perpendicular

SOME MATHEMATICAL PEINCIPLES 257

The principle of " conservation of energy " is wider than
that laid down in the foregoing pages, and may be briefly
stated as follows:

" The energy of a body or system of bodies remains con-
stant, unless work is done by or on the bodies, when it de-
creases or increases by the amount of the work done."

If we define energy, in what is probably the most satisfac-
tory way, as capacity for doing work, we must furnish some
further definition of the latter term in order to arrive at
an understanding of the principle. Work is generally done
"when a moving body is acted on by a force, and the measure
of the work is the product of the force by the distance moved
through by the body in the direction of the force's action.
Thus if a man lift a weight up by means of a pulley tackle,
the work done by the man is the product of the force exerted
by him and the length of rope passing through his hands.
The work done on the body is the product of the weight of
the body by the distance through which it rises; and, by the
principle under discussion, these two quantities of work would
be equal if there were no friction ; for no energy resides in
the pulley tackle, and that put in by the man is, therefore,
equal to that given out to the load.

from the axis on to the line of motion of the particle is also equal to
the distance of the particle from the axis. The anojular momentum of
each particle is equal to the product of the mass of the particle by its
velocity and by that perpendicular, that is to say, to the product of
the angular velocity of the whole body by the mass of the particle and
by the square of its distance from the axis.

The angular momentum of the whole body is the sum of the angular
momenta of all the particles, and is therefore equal to the product of
the angular velocity by the sum of the products of the mass of each
particle into the square of its distance from the axis. This last sum
can be found by mathematical as well as by graphical methods. It is
independent of the speed of rotation, and is in fact a constant of the
body known as its " moment of inertia." The angular momentum of
a turbine rotor about the axis is therefore the product of the '* moment
of inertia '* by the angular velocity. (The angular velocity is 0*106 of
the revolutions per minute. )

It is an important feature of angular momentum, and one capable
of rigid proof, that it obeys the triangle law of superposition, with
which we opened the discussion in this Appendix.

S

258 APPENDIX I

ClaBsif jing energy according to its phenomena and neglect-
ing molecular activities and the like, we may divide the forms
of energy into mechanical energy, on the one hand, and energy
due to molecular arrangement, on the other. We shall further
divide mechanical energy (postponing the consideration of the
energy of gases) into potential and kinetic energy.

Potential energy is that possessed by a body by virtue of its
position or strained condition. The energy stored in coal or
gunpowder in a chemical form, or electrically in a Ley den jar,
may also be classed as potential energy. Kinetic energy is
that possessed by a body by virtue of its motion; and the two
forms are mutually convertible without the intervention of
external forces. An excellent contrast of the two forms of
energy, as used in connection with water power, is furnished
by the hydraulic jack and the Pelton wheel. We may notice
the adaptability of each different form to produce the same
effect, as shown in the propulsive power stored potentially in
a bent bow, an explosive cartridge, compressed air, or a raised
cricket bat; the propulsive power of a moving substance will
not be called in question by any man who has ventured out
top-hatted on a windy day.

Seeing, then, that a moving body has the power of doing
work, let us see how the energy of a body of mass M moving
with velocity V can be measured. Let us suppose that the
body in question does work against a force P in moving
through a distance S. Then the work done is clearly P x S.
Now if V be the velocity of the body after doing the work,
and if T be the time occupied in moving through the distance
S, then the distance is equal to the product of the mean velocity

by the time, that is to say, S = x T. The force, as

we have seen before, is equal to the rate of change of the mo-

V- V

mentum, so that P = — — — x M, and the work done is there-
fore, P X S = ^M(V'* - V'^). The difference between the energies
of a body of mass M moving with velocity V and with the
velocity V is therefore ^M(V^ - V'*) ; and it seems fair to
assume that the energy in the first case is ^MV^. This is, in

SOME MATHEMATICAL PEINCIPLE8 259

fact, the kinetic energy of the body, and represents the amount
of work which it is capable of doing.

If a body is at a height H above the ground, its potential
energy is W x H where W is the weight. Its acceleration, if it
be allowed to fall, adds in every second a velocity of a little
over 32 feet per second. This acceleration, equal to 32*2, is
known as Gr. Since the force of its weight produces an ac-
celeration Q-, therefore W = MGr, and the weight of one pound
is Gr poundals. If it fall through the height H it loses its
potential energy and acquires a velocity which we will call V.
If the time of falling were T, then, since the mean velocity
was ^Y, we have H = ^VT, and since the acceleration was G,
therefore V = Q-T. It follows that the loss of potential energy,
that is to say, MGH, is equal to M x V/T x ^VT, and that is
equal to ^MY^ or the kinetic energy.

This is a simple and very important case of the " conserva-
tion of energy." We can infer from it that we ought to get
exactly the same amount of work out of water in an elevated
reservoir, whether the water drives an overshot wheel by its
simple weight, or whether its potential energy is transmuted
to kinetic, and it drives a Pelton wheel by means of a jet.

The Problem of Efficiency.

It appears from the foregoing that all the work that is put
into a machine must come out again in some form or other.
What then is meant by efficiency, if the machine cannot
destroy the energy supplied? To answer that question we
must consider the fact that energy exists in numerous forms,
and that one of the commonest forms is heat. The energy
supplied to the engine may be transmuted into heat and so
given out in a form useless for practical purposes. The effi-
ciency of an engine is the proportion of the energy supplied
which is given out in the desired form.

The most fruitful causes of transmutation into heat are
friction and shock, and if it be remembered that the 1,800

260 APPENDIX I

British Thermal units necessary to raise 1 gallon of water
from freezing to boiling point are equivalent to '707 HP. -hours
of work (2545 B.T.XJ. = 1 H.P.-hour), it will be seen that a very
little heating means a great loss of energy.

That friction converts energy into heat and so dissipates it
is a fact within the experience of every one, but the deleterious
effects of impact are less obvious. They may, however, be very
simply demonstrated in the following way:

True shock takes place only between inelastic bodies, and,
where there is shock, force is exerted between two bodies
moving at different speeds. Now the rate of doing work is
the product of the force exerted by the speed of motion in the
direction of the force ; and the force exerted by the working
body is equal and opposite to that exerted on the other. Since,
however, the velocity of the working body is necessarily greater
than that of the body acted on, it follows that the first does
more work than the second receives, and the balance is dis-
sipated in the form of heat. It is therefore important that
the action should not be one of shock, but should be a steady
continuous one, even if it lasts for a microscopic time; and
the reader will appreciate that it is this fact that makes the
spring of a cricket bat, or of a golf club, a matter of the last
importance. This, too, is the reason why the interposition of
an elastic column of air (rendering the action smooth and
continuous) has developed the spring gun into the very
effective air rifle.

If it is required that a stream of water shall act on a
turbine blade so as to press it forward, the following difficulty
arises: If the blade moves with the stream, and at the same
speed, no force can be exerted and the machine is consequently
useless. If on the other hand the steam impinges on the blade
we have loss due to shock as explained above. What third
system of action is there?

Consider the case of a jet pressing upon a flat board, and
suppose that the board is moving with one half the speed of
the jet. The jet strikes the board and spreads out with shock
and consequent evolution of heat. Further, the fluid that has
acted on the board continues to move with the same speed as

EFFICIENCY 261

the board itself, so that some energy (one quarter of that
originally possessed by the jet) remains with the water, in-
stead of passing to the machine — altogether a very poor con-
trivance. Now, instead of a flat board let us adopt the bucket
shown in Fig. 15 (page 44). It will be seen that there is now
no shock at the first approach, but, siuce the bucket is curved,
the fluid presses upon its walls as it passes along, and leaves,
as the curve of flow shows, practically without velocity. This
bucket is therefore as efficient as any that can be produced.

Let the reader consider for a moment the nature of the
action in the Pelton buckets, in its bearing on the questions of
shock and of the communication of energy. The reader who
appreciates adequately its merits, as stated in the last para-
graph, possesses the same insight into the problems of
hydraulic machinery as moved M. le General Poncelet and
his contemporaries to the creation of the turbine.

1

APPENDIX II.
ON FLUID MOTION.

THE laws enunciated in Appendix I, apply to every form
of matter, and therefore to the fluids whose action is
chiefly interesting to the student of turbines. When we come
to discuss the properties of fluids in greater detail, we find
that we can no longer apply the same principles to every one,
but must divide the objects of our inquiry into the classes of
liquids and gases. The chief difference between the two is that
a liquid is practically incompressible, whereas a gas is vastly
compressible and perfectly elastic. Neither exerts any great
amount of friction on bodies moving at ordinary speeds, and
the friction of gases is peculiarly small.

All fluids are alike in this respect; that they exert the same
pressure in every direction on a unit of surface placed at a
given point in the fluid. This is termed the pressure of the
fluid at that point. In the case of a liquid (which is heavy)
the pressure depends on the depth below the surface, and is
at every point sufficient to support the column of water above.
At the depth H below the surface, the pressure is therefore
MQ-H where M is the mass of unit volume of the water. Be
it noticed that this is the same expression as that for the
potential energy of unit volume of the water at the surface,
and represents the work that it would do in falling to the
depth H. We may take it that the pressure in a reservoir of
gas (which is light) is the same throughout.

Suppose that there is a small hole at the depth H in a tank
of water. The water will flow out; and we may suppose that
it flows out at a speed V. Then, as it flows, the surface level
falls, and by the principle of " conservation of energy," the

262

FLUID MOTION 263

kinetic energy of the water flowing out must be equal to the
potential energy lost by the water in the tank. The loss of
potential energy is due to the fact that a layer of water of mass
M has disappeared from the top of the tank. The same mass
of water has made its appearance at the level of the orifice,
flowing with velocity V. The loss of potential energy is there-
fore MGrH, and the gain of kinetic energy is ^MV*. These
being equal, we have V = -v/2GH, the velocity which the
water would have acquired in falling from the level of the
surface.

In the case of liquid under pressure there is no energy
actually stored in the high pressure layer, by virtue of its
pressure; the energy which gives force to a jet is really the
possession of the top layer which is not under pressure. In the
case of gas, on the other hand, the energy actually resides in
the gas under pressure, any part of which would expand and
do work even if the rest of the gas in the reservoir did not
exist. But even in the case of liquids, since what actually
happens when a hole is made in the tank is that a layer of
liquid loses its pressure of *MGH and acquires on the other
hand a kinetic energy of iMV*( = MQ-H) per unit volume, it
will be convenient to regard the pressure MG-H as a form
of specific energy residing in the liquid under pressure.

Now, if we consider the behaviour of liquid flowing in a
pipe, it is clear that the sides of the pipe do no work (neglect-
ing friction) on the liquid, and the total energy of the stream
is therefore the same at any point (provided that we regard
pressure, as in the last paragraph, as a form of potential
energy). Now the velocity of the liquid varies, being inversely
proportional to the section of the pipe at each point, and there-
fore the pressure must vary too, and we have pressure +
specific kinetic energy = constant. If then the pipe be
narrowed, the pressure falls for the increase of speed at that
point, and the pressure rises again as the tube expands.^

^ If we investigate closely the action which takes place in the
pipe, we can see that, pressure not being a true form of energy,
there is some force acting on an element of the fluid to change its

264 APPENDIX II

When a cistern is emptied through a pipe, the pressure of
the water at the mouth of the pipe is the pressure of the
atmosphere, and the speed of the water at the pipe mouth
depends only on the drop in pressure between the two ends of
the pipe. If the pipe is narrowed at the middle, so as to have
a bell mouth, then the speed at the middle is greater than that
at the end, and the pressure at the neck is less than atmo-
spheric. The only limitation on the speed and pressure obtain-
able at the narrow neck by constructing a bell mouth is that
the pressure cannot fall below zero. This is the secret of the
bell-mouthed suction tube with which modern turbines are
fitted ; by means of this a perfect vacuum can be obtained at
the point of discharge from the rotor.

The Vortex.

We have pointed out (App. I) that, when a body moves in
a circle, some force must be acting on it, and it follows that,
when a mass of water is spinning in a vortex, some force
towards the centre must be acting on each particle of the

velocity. This force is, of course, the difference of the pressures exerted
by the fluid before and behind.

Let the pipe section at a given point be S, the pressure P, the
specific mass of the liquid M, and let the length of a certain element
be X. Let the prefix d represent the change in a quantity between
positions at the distance X apart.

Then the total pressure across* a section of the pipe at any point is
PS, which we shall call Q, and the mass of the element is MSX. It
is a constant and we may call it K.

The force acting on the element is the difference between the total
pressures on the two ends or - dQ, and the work done on the element
as it moves through a distance X is-XdQ. The kinetic energy is
JKV^ and the change in the kinetic energy consequent on the motion
is iKdV^

By the principle of conservation of energy, this change is equal to
the work done, so that iKdV2= _xdQ, and therefore, integrating,
iKV^= -XQ. + a constant.

Now K=MSX, and Q = PS, so that the last equation is equivalent
to iMSXV2 + PSX = constant, or to iMV2 + P= constant, the fact
which we set out to establish.

THE VORTEX 265

water. This force is in fact supplied by the pressure of the
water in the outer rings of the vortex, and so it is clear that the
further from the centre of the motion the greater the pressure
must be.

Now there are two kinds of vortex : the free vortex, which
it must be confessed is the more interesting, is the whirlpool
formed by sucking rotating water towards the centre of the
motion; it obeys the ordinary law of a stream that pressure
+ kinetic energy is constant, and consequently as the
pressure drops towards the centre the speed of the water is
vastly increased. The speed of the water is in fact inversely
proportional to the radius of the circle in which it moves, and
its angular velocity is, therefore, proportional to the inverse
square of the radius. It follows that each ring rubs on the
ring outside, and the friction so caused tends to check the
motion. This is the vortex that would exist in the well of the
antique turbine, described on page 13, if the rotor were not
there. The insertion of the rotor prevents the increase of
speed as the water approaches the bottom of the funnel, and
transmutes the free vortex into a vortex of the second class.

This, the forced vortex, is that which would exist in a
turbine wheel, if there were no flow of water through the
wheel. The peculiarity of this vortex is that the water moves
as a solid mass, every particle having the same angular
velocity about the axis of the motion. The determination of
the pressure prevailing at any point in this vortex involves a
simple application of the integral calculus, which will be
found in the foot-note.^ The pressure may, however, be de-
termined experimentally.

• Let the mass of unit volume of the liquid be M, the angular velo-
city, to, and the pressure at a distance R from the axis, P.

Consider the equilibrium of a small rectangular block of liquid
bounded by faces of area S perpendicular to the radius and distant R
and R + dR from the axis. The mass of the element is MSdR and the
force acting on it to preserve the circular motion is, therefore, MSdR
X w^R. This force is suiiplied by the difference of tlie pressures on
the opposite faces, these pressures being S x P and S x (P + dP). There-
fore SdP = MSdR X io^ or dP=Mui2RdR.

Integrating P= ^Mw'^R^ + a constant = ^MV^ + a constant, where V

266 APPENDIX II

Suppose that a bowl of water — preferably one fitted with
paddles fixed to the bottom, to ensure the proper rotation of
the water — be spun on a tum-table. There is a forced vortex
in the bowl, and it will be found that the free surface of the
water adopts a parabolic form. If we imagine a horizontal
plain through the bottom of the curved surface, then the
height of any point in the surface above the plane is propor-
tional to the square of its distance from the axis of rotation.
Now the pressure at the point N (Fig. 82) is equal to the
weight of the column of water AN, and is, therefore, propor-
tional to the square of the length ON. The pressure at N is,
therefore proportional to the square of the velocity at N, and
. measurement will show, as may be mathe-
■^ matically demonstrated, that this pressure is,
in fact, that necessary to produce the velocity
of the fluid at N.

It is clear that the points O and N, though
on the same horizontal plane are at very
different depths below the surface. If the
FIG. 82. DiA- speed of rotation is fast, the paraboloidal sur-
GRAM OF voR- face is very deep and narrow, and AN may be
TEX SURFACE. y^j.j large in comparison with ON. For this
reason we get the same effect as in Burdin's turbine with its
huge rotating tank (Fig. 8) by the use of a very tiny high
speed case wheel with closed channels. The substitution of
speed for size is characteristic of modem engineering practice.
A curious and important fact results from this stat^e of
affairs : that water would be discharged from the bowl through
an orifice situated at the point N, with a velocity relative to
the bowl exactly equal to the velocity of the bowl at that
point; so that if the orifice were fronted in a direction oppo-
site to that of the bowl's motion, the discharged water would
remain precisely at rest; and this is true of every point in the
horizontal plane through the point O.

is the velocity at the point in question. The constant depends on the
depth below O.

At any point in the plane of the constant vanishes, since P and R
both vanish at the point O.

THE VORTEX 267

It appears, then, that if water be discharged from a turbine
wheel in a direction opposite to that of the wheel's motion,
the absolute velocity of the water after discharge (and, there-
fore, the energy carried off by the water) is practically in-
dependent of the issue whether the dischai^e takes place
from the outer or inner, upper or lower, surface of the wheel,
or whether the flow is inward, outward, or axial ; it depends
only on the pressure and velocity at the point of admission.

When water flows through the rotor of an impulse turbine,
it is moving freely so that the principles of vortex motion do
not apply. The only force acting on the liquid is the pressure
of the blades, and this is at right angles to the direction of
its motion relative to the wheel. Hence the velocity of its
motion in that direction does not change, and the only change
that can take place in its motion relative to the blades is that
due to a change in the velocity of the blades themselves, not
of the water.

In the parallel flow turbine (the Pelton wheel) the acceler-
ation of the blades is upwards at right angles to the flow of
the water, and the velocity of the water relative to the blades
is therefore constant; its rate of flow along them is the same
at admission and at discharge. But in the outward flow
(Fourneyron or Girard) turbine, every point on each blade
has, like everything moving in a circle, an acceleration towards
the centre. This acceleration is not shared by the water, so
that its velocity relative to the wheel increases as it flows
•outwards — in fact to the same extent * as the velocity of the

* Consider a body sliding outwards along a blade or spoke of a
revolving wheel, e.g., water in a Fourneyron turbine, or a reel of
cotton thrown from a cane in the manner dear to schoolboys.

The angular velocity of the blade is w, and the acceleration of a
point distant R from the centre towards that centre is wR. The body
sliding outwards has an acceleration relative to the spoke at that
point of (oR. So if it start from the rest at the centre, the energy of
its motion relative to the spoke when it reaches the point distant R is
^RdR or ^wR-^, and its velocity relative to the spoke is therefore wR,
the velocity of the spoke itself at that point.

This is precisely the case of water in a Girard turbine, or in that of
Fourneyron when running as an impulse turbine. Water entering

268 APPENDIX II

wheel is increased towards the fast moving outer rim. In the
same way the velocity along the blades of water flowing-
inwards in an impulse turbine is retarded to the same extent
as the speed of the wheel is reduced in approaching the shaft.
It appears, therefore, that the velocity relations in an im-
pulse, as in a reaction turbine, are independent of the question
whether the machine is of the inward, outward, or axial flow
type.

with a velocity along the blade equal to that of the blade itself at the
point of admission, will leave with a velocity along the blade equal to
that of the blade at the point of discharge.

APPENDIX III.
ON THE BEHAVIOUE OF OAS.

IN dealing with steam in a turbine or other engine cylinder
we have to bear in mind that it is not a perfect gas, and
does not obey completely the laws of gases; in particular,
when saturated steam (that is, steam direct from the boiler)
is expanded, a certain proportion of it condenses. We may
say, roughly, that 4% of the steam condenses when the
volume is doubled. Since, however, in all the best turbine
practice superheated steam is used, we shall deal here only
with such steam, and our work will be simplified by the fact
that it behaves almost exactly as a perfect gas.

When gas acts without the communication of any heat
from outside or to the outside, the operation is said to be
adiabatic. The law of adiabatic expansion of gas is P x V*^ =
constant, P and V being the pressure and volume. In the
case of superheated steam n is 17/16 so that the volume
varies almost inversely as the pressure, but not quite to the
same extent.

In discussing the pressure-velocity relations of steam and
gas, we must consider two distinct cases. In the first place,
where there is only small expansion, and a small drop in
pressure, the gas behaves very much as does a liquid. If it
expand from a pressure P to a pressure Q, then the drop in
pressure is P - Q. Now the density of the gas behind is more
or less proportional to P, and therefore the pressure P - Q is
that which would be due to a head of gas proportional to
(P - Q)/P. The square of the velocity developed is, therefore,
proportional to (P - Q)/P, and that is the ratio of expansion.
It follows that the velocity due to a small expansion of gas

269

270 APPENDIX III

is approximately proportional to the square root of the ratio
of expansion and does not vary much with the initial pressure.

In any case the velocity developed by a small expansion
is very large in comparison with the ratio of expansion. Sup-
pose that steam at 160 pounds pressure and 50" Fahr. super-
heat, expands to a pressure of 159 pounds through a nozzle.
The volume of 1 pound of the gas is 3 cubic feet, and the head
corresponding to a pressure of 1 pound per square inch
is therefore 432 feet, so that the velocity developed is 170
feet per second, and the expansion is 0*57%. If, on the
other hand, the steam be expanded to double its volume, the
velocity developed is 1,500 feet per second, and if the expan-
sion be two hundredfold, the velocity is only 4,000 feet. It
is clear, then, that for a short time (during which the steam
behaves very much as a liquid) the velocity increases out of
all proportion to the volume, and (as with a liquid) the
pressure drops where the pipe is narrowed and rises where
the pipe expands again — in the Parsons turbine this is the
type of action that takes place throughout — but when a cer-
tain limit of expansion (a little less than 100%) is passed, the
volume begins to increase more rapidly than the velocity, so
that the section of the pipe must increase as the pressure
falls. Here we can no longer apply the principles of liquid
motion, but must consider more intimately the nature of
gaseous energy.

According to the modern theory, gas consists of a number
of free molecules, each in motion; and the number of mole-
cules to one pound of the fluid is invariable. When gas is
heated the motion of these molecules is increased, and the mean
kinetic energy of each molecule (and, therefore, the energy
of 1 pound of the gas) is proportional to the absolute tem-
perature, absolute zero being -461° Fahr.

Now if the volume of the gas be kept constant, the number
of molecules per cubic foot is invariable; but all the mole-
cules are moving, and, therefore, occasionally hitting the
walls of the containing vessel, and the number which hit a
square foot of wall in one second is proportional to the
velocity of the molecules. But the force of the blow dealt by

THE BEHAVIOUR OF GAS 271

each molecule is proportional to its momentum, i.e., to its
velocity; and the pressure on the wall of the vessel is, there-
fore, proportional to the square of the velocity of the mole-
cules, that is to their kinetic energy, or to the absolute tem-
perature of the gas (Boyle's law).

It is usual to say that gas contained in a vessel under
pressure has potential energy, but as we have just seen it is
probable that its energy is really kinetic; the accepted theory,
at any rate, attributes the energy to the motion of the mole-
cules. Now, if the molecular velocity be V, the energy of a
mass M of the gas is ^MV^, proportional to the absolute tem-
perature, and to the pressure of the gas. Let us endeavour
to discover the ratio of pressure to energy.

Consider a cubic foot of gas contained in a cubical vessel
and let the mass of the gas be M and the molecular velocity
V. Then since all the molecules are moving in different direc-
tions, we may take it that M/3 are moving between each
pair of opposite faces with velocity V.^ Now the molecules
are perfectly elastic and move to and fro with no loss of
speed. Every time that a molecule travels through a distance

^ The relation of pressure to molecular velocity can be worked out
without the help of the somewhat crude assumption made in the text.
We must premise that no momentum in any direction is destroyed by
the impact of perfectly elastic molecules, so that we may neglect in-
termolecular impact without impairing the validity of our work.

Consider the impacts on an element, S, of surface during one second.
The only molecules that can reach the surface within the second are
those within a sphere of radius V. Now consider a ring within this
sphere bounded by spherical surfaces at distances R and R + dR from
the element of containing wall, and by cones making angles A and
A + d A with the normal to the element S.

The volume of this ring is 2nR'^ sinA.dA.dR. The distance of every
point in the ring from the element S is R, and the obliquity of the
element to the path of a molecule coming from any point in the ring
is 90° - A. The solid angle subtended by the element at any such point
is, therefore, ScosA.

Now the molecules within the ring are moving in every direction,
and the proportion of them striking the element S is ScosA/4IlR'^.
The whole mass of molecules from this ring striking the element is

272 AJ>PENDIX III

of 2 feet, it hits the same face once. Each of the M/3 mole-
cules, therefore, hits a given face V/2 times in a second, and
at each blow its velocity is reversed, so that the force of the
impact is 2V times the mass of the molecule. The whole
pressure on the face due to this molecule is, therefore, Y/2
times 2MV, or V* times its mass. Thus the total pressure on
the face is M/3 x V*. The energy of a cubic foot of gas is
|MY*, and, therefore, the pressure on a square foot of the
containing vessel (expressed in poundals) is equal to 2/3 of the
energy of a cubic foot of gas.

The energy of a pound of gas must, therefore, be 3/2 x
144 X 32*2 X (pressure per square inch) x (cubic feet to the
pound).

Having given the pressure of a gas and its density, we are
now in a position to say what is the molecular velocity of the
gas ; and that is, of course, the mean velocity which the gas
will develop on complete expansion.

If, then, gas enclosed in a receiver were discharged from a
properly shaped nozzle, the mean square of its velocity of dis-
charge would be the molecular velocity; but it is quite clear
that, since the pressure in the receiver falls continually as the
gas is discharged, that part which escapes first escapes fastest,
and its velocity will be considerably more than the molecular
velocity of the gas. Now in dealing with boiler steam we have
a continual supply of fresh vapour forming in the boiler, so
that the case is practically that of the first discharge of gas
from the receiver. It is required to find the relation of the
velocity of discharge to the molecular velocity and pressure.

M.sinA.dA.dR.ScosA/2. The change of velocity of each molecule at
impact is 2VcosA, since it strikes the surface obliquely, and the
pressure on the element due to this ring is, therefore,
MVSsinAcos^AdAdR.

To find the whole pressure on the element, we must integrate this
•expression throughout the hemisphere.

The resulting expression is

MVS f^f^ sin Acos^AdRdA, or MV'^Sy^^cos^A d cos A

which reduces to MV^S/S ; so that the pressure on an area S is MV^S/3,
And the pressure on unit area is MV73 as found above.

THE BEHAVIOUR OF GAS 273

In the receiver before mentioned (which we will suppose to
be very large), a cubic foot of gas, in the course of discharge,
turns its own molecular energy into kinetic energy ; but besides
the work done by the molecular energy of the gas escaping,
which is ^MV"^, there is work done by the gas pressing behind.
The pressure per square foot is ^MV*. Now, if there were a
piston 1 foot square between the gas discharged and the gas
behind, that piston would have to advance 1 foot in order to
clear out a cubic foot of gas, and the work done by the gas be-
hind would then be JMV^. The whole kinetic energy of the dis-
charged gas is, therefore, ^MV* + ^MV^ or ^MV* altogether.
If, then, it were discharged into a perfect vacuum, the velocity

of the stream would be V x /t •

This velocity will not be attained by steam escaping through
a simple orifice, because the various molecules which use the
opportunity of escape, rush out in all manner of different
directions. The mean velocity of the stream is therefore only
that due to the pressure behind, orV x /f , and the jet bushes

out so soon as it is clear of the orifice.

To attain the full velocity of flow, it is necessary to catch
the wandering molecules and to direct them in the way they
should go. This is done by means of a divergent cone attached
the nozzle, which reflects each particle of gas more and more
into the line of flow at each impact, so that the pressure falls
and the velocity rises while the gas flows down a pipe of in-
creasing section. We have seen that the effect of such a pipe
on water would be precisely opposite.

The flow of steam when not strongly superheated, and even
when superheated, if the ratio of expansion is very large, is
further complicated by the condensation of a portion of the
vapour. The effect of this is to reheat the steam not condensed,
by the latent heat given off by the water in condensing. The
reheated steam then escapes with a greater velocity than that
arrived at by our calculation, while the water drops travel more
slowly. The consequences of this action are discussed on pages
229-231 in connection with the economy of the steam turbine.

T

APPENDIX IV.
ON THE GYEOSCOPIC EFFECT OF TUEBINES.

BOTH the advocates and opponents of the turbine as an
engine of marine propulsion have recognized that it
introduces a new factor of some importance, whether small or
great, into the stresses of the vessel in a seaway, and it has
been maintained on the one hand that the gyroscopic effect of
the high speed rotor will increase the steadiness of the vessel
in a head sea, and, on the other, that it will add seriously to the
straining of the hull.

The large low speed turbines used for mercantile marine
work at the present day can have no serious effect in either
direction, owing to the very slow pitching of the hulls of large
vessels ; but it may be worth while to devote a little more serious
thought to the state of affairs prevailing in those smaller
vessels where high speeds of running are adopted, as in the
earliest turbine vessels and in the torpedo boat destroyers
now under construction.

The phenomena of gyroscopic action are well known. If a
heavy body be rotating, and an effort be made to turn the axis
of rotation into a different position, the effect of the couple
applied is to turn the axis indeed, but at right angles to the
direction intended, and the effort required is out of all pro-
portion to the effect accomplished. This is familiarly instanced
by the top, the axis of which, thanks to the effort of gravity
to lay it down horizontally, turns itself in a horizontal circle
instead.

So a high speed steam turbine resists the effort of seas, lift-
ing the bow or stern of the ship, to sway the turbine in a

.274

THE GYEOSCOPIC EFFECT OF TURBINES 275

vertical plane, and endeavours to sway itself in a horizontal
plane, thereby introducing stresses in the hull of the vessel.
The magnitude of these stresses is what we have to examine,
and, in order to do so, we must first arrive at some idea of the
nature and cause of the action.

We have pointed out (App. I) that every rotating body has
an angular momentum about its axis proportional to a the
angular velocity, and to I the moment of inertia of the body
about its axis. Now angular momenta, like velocities, can be
compounded according to the triangular law, and therefore if
a turbine be rotating about a horizontal axis AB, with an
angular momentum represented in magnitude by AB, and if
it be required, in order to accommodate the pitching of the
ship, to change its axis of rotation to the position AC, this can
only be done by adding to the original angular momentum an
angular momentum about the
line BC, represented in magni-
tude by that line. If the angle
BAC be 0, a small angle, then
the length of BC will be AB x 0. '^ ^ ^

^, ® , , ^ FIG. 83. DIAGRAM OF ANGULAR

The angular momentum repre- momentum.

sented by AB is lu^, so that re-
presented by BC must be Iw^. If, then, the axis turn through
£Ln angle ^ in the time t, the rate of communication of the
angular momentum round BC the vertical axis, will be Iiv^/t
or lio X (rate of turning of the axis AB), and this is the
horizontal couple that must be applied to the turbine to
secure the vertical turning of its axis.

Turning now to the application of these principles to a
torpedo destroyer, we shall make the following assumptions,
all more or less close to the mark:

(1) That the mass of the rotor is three tons.

(2) That the radius of gyration of the rotor is 18 inches.
(I is then approximately 27/4 foot- ton units.)

(SJ That the maximum pitch of the vessel is 5° from the
horizontal.

(4) That the complete oscillation up and down is performed
in 6 seconds.

276 APPENDIX IV

The direction of the turbine shaft is changing most rapidly
when it is horizontal, and the rate of change is then j^ of a
radian per second.. The couple Iwx (rate of turning of the
shaft) becomes then 27/4 x ^j x w, and the full speed will be
about 720 revolutions, which gives u) = 75*5. The horizontal
couple that must be applied to the turbine is therefore 46*3
foot- second-ton units, or, dividing by g, 1*44 foot ton. If the
bearings of the turbine are 10 feet apart, this amounts to a
load on each bearing of 0-144 ton, or one-tenth of the weight
normally carried by the bearing.

It is clear that the strains set up are not, in any case, very
serious. If the bed-plate is properly put in, so as to distribute
the load over the hull, no serious strains will be caused even
by three turbines all running the same way. If the turbines
run in opposite senses, then their tendency, when the bow of
the ship lifts, is to turn in opposite directions, and so to tear
the bed-plate asunder. Where a set of two or four turbines are
fitted, the whole strain will be borne by the bed-plate, and
none will be communicated to the hull when the whole set are
running (contra when the starboard engines are going ahead,
and the port engines astern).

It seems proper to point out that the rotors of the Cobra's
turbines were much lighter than those here considered and
were of smaller diameter. Now the moment of inertia is pro-
portional both to the mass of the rotor and to the square of
its radius of gyration — roughly then to the fourth power of
its diameter multiplied by its length. This is one of the prin-
cipal reasons why the Parsons turbine, which is distinguished
from all other makes by its smaller diameter (and greater
length) has hitherto been found by far the most suitable for
sea-going ships; and this renders it inconceivable that the
turbines of the Cobra should have been responsible for her
lamentable fate.

INDEX

INDEX.

A.E.G. Turbines, 119, 120, 195-

197.
Acceleration, 254.
Admission:

pressure and velocity at, 35,
36.

direction of flow at, 38-40.

to Parsons Turbine, 144-145.

gust, 145, 226-228.

economy of gust, 227-228.
Amethyst, 161-163.
Astern Turbines, 154, 159, 165,
168.

compound, 165.
Attendance, 101, 237.
Augmentor, vacuum, 143-144.

Balance:

of De Laval wheel, 187.

of steam water pressure on
Turbine shaft, 162-153.
Barker's mill, 15-17.
Basacle, reaction wheels at le, 14,

81.
Battleships, Turbines in, 241-242.

Dreadnought, 163-165.
Belidor, 12.
Blades:

number of, 174.

design, 39-43, 179, 246.

of blowers, 217.

arrangement, 37, 134, 137, 141,
180, 184, 186, 207.

speeds, 140, 184, 204.

Blowers, 215-220.

Branca, 8.

Brown, Bo\ eii and Co., 128, 232.

Burdin, 12, 18-19.

Buckets, definition of, 180.

of tangential wheels, 44, 51-52.

speed of, 184, 204.

strain on, 185.

of Riedler-Stumpf Turbine, 193.

Cannania, 171-175.
Camot, 12..
Caratiia, 171.
Carville, tests at, 128.

Turbine at, 131.
Case wheel, 69-70, 82-86.

pressure and velocity in, 84.

as rotary pump, 212.

centrifugal force, 212, 266.

control of, 83.
Cavitation, 151-152.
Chambers, stage, 135, 139, 197.
Cheetham, 49.
Classification of Turbines, 36-38,

119, 221.
Cobra, 155, 276.
Compounding velocities, 253, 254.

water wheels, 7.

steam Turbines, 115, 117.

water Turbines, 115.
Compressors, 217-220.
Condenser :

place of, 229.

augmentor, 143-144.

279

280

INDEX

Condensing :

Parsons Turbine, 127.

pnmping engine, 110.
Conservation :

of energy, 254, 257-259.

of momentum, 254-255.

of momentum, angular, 256.
Control :

by nozzles, 55, 105, 182, 223.

of water Turbines, 101-105.

by throttling, 224-225.

by gusts, 145, 226-228.

by cylinder gate, 93.

of marine Turbine, 229.
Cost of Parsons Turbine, 129, 233.

of Curtis Turbine, 234.

of erection, 234.
Couple, 256.
Cruisers, economy of Turbines in,

161-162.
Cruising Turbines, 163-164.
Curtis Turbine, 197-206.

economy of, 203.
Cylinder gates, 93.

Turbine, 133.

Daimler, 246.
De Kempelen, 116.
De Laval Turbine, 117-118, 178-
191.

nozzle, 179-182, 272.
Design of Turbines, 34-46, 65-78.

of blades, 38-45, 179, 246.

of Parsons Turbine, 139-141.

of nozzles, 181.
Diesel motor, 245-246.
Discharge :

velocity of, 20, 35, 91.

direction of, 24.

pressure of, 35, 62.

place of, 35, 91.

energy of, 69, 96.
Distributor, multiple, 92.
Dreadnought^ 163-165.
Dynamos, 41, 65-66, 89.

Economy of Turbines, 232-233.
in cruisers, 161-162.
in liners, 172.
I Efficiency, 259-261.

of steam Turbines, 232, 233.
j conditions of, 12, 34.
I of Fourneyron Turbine, 22.
i of Girard Turbine, 62-63.
j of Pelton wheel, 52.
I of Parsons Turbine, 127-128.
\ of Curtis Turbine, 203.

of De Laval Turbine, 185.
I of Zoelly Turbine, 208.
I of Riedler-Stumpf Turbine, 194.
I of A. E.G. Turbine, 197.
I effect of superheat on, 230-231,
1 272-273.

i of marine Turbines, 161-162.
Electric power, 65-66, 89, 244.
Energy:
forms of, 3, 257, 270.
of gas, 270-271.
of steam, 270-272.
conservation of, 254, 256-259.
Emerald, 171.
Eolopyle, 8.
Ewing, Professor, 127.
Expansion :
triple, engines, 127.
triple, Turbines, 148-149.
ratio of, 236.
velocity due to, 1 15.

Tlow of water, 35-36, 262-267.

in Pelton bucket, 44.

of steam, 114-115, 180-182.
Foumeyron's Turbine, 21-26.

theory of, 24.

efficiency of, 22.
Francis, 31-33.
Francis Turbines, 73, 87-89.

steam, 210.
Friction in supply pipe, 61, 101.
I in wheel channels, 61.

INDEX

281

Garonne Turbines, 13, 14.
Gas, behaviour of, 268-273.

thermodynamics of, 269-270..

Turbines, 245-246.

energy of, 3, 270, 271.
Gelpke-Kugel Turbine, 210.
Girard Turbines, 26, 56-64.

construction, 59.

blade form, 61.

efficiency, 62-63.
Governing :

of water Turbines, 102, 104.

of Pelton wheel, 104.

of Parsons Turbine, 144-145,
226-227.

of Zoelly Turbine, 224-225.
Guide blades, direction of, 40.

control by, 76-78, 210.
Gurtnellen, Turbines at, 59-63.
Gyroscopic effect, 156, 274-276.

Harthan, 117.
Head:

of working fluid, 112-114.

and energy of gas, 269-271.
Hero, 8.
Howd, 29-32.
Hunting, 25.

Impact, 12, 259-261.

losses by, 63, 259-261.

in Girard Turbine, 38, 64.
Impulse Turbines, 38-43.

design of blades, etc. , 45.

flow of water in, 41.
Internal combustion engines, 244,

245; turbines, 245, 246.
Inward flow Turbines :

Howd, 29-32.

Francis, 30.

Jonval tube, 96,

Jonval Turbine, 27-29, 79-81.

flow of water in, 28.

multiple, 79-81.

control of, 79-80.

Keeper, 132.

King Edward, 166-169.

Lubrication, 237.

of Parsons Turbine, 132.

of Curtis Turbine, 205.

contamination of steam by,
146, 205.
Lusitania,, 175.

Marine Turbines, 147-177, 208,

210, 238242.
Mechanical principles, 254-261.
Mixed-flow Turbines, 89-92.
Moment of inertia, 257.
Multiple Turbines, 79-81.

Needle, Pelton, m, 105.

De Laval, 182.
Newcastle - upon - Tyne, Royal

Jubilee Exhibition, 124.
Niagara, 100.
Nozzle, deflecting, 56, 105.

Pelton, 55.

De Laval, 118, 180-183, 272-273,

Riedler-Stumpf, 193.

Curtis, 202.

Orifice of discharge, 181.

Packing, steam, 143, 153.

Passenger vessels, 166-177.

Patents, 247-249.

Parallel flow, 27-29.

Parsons governor, 144-145, 226-

227.
Parsons Turbo-blower, 217-220.
Parsons Turbine, 121-177.

speed, 124.

efficiency, 127, 128.

control, 145, 226-228.

blading, primitive, 122.

blading, modern, 137, 141.

dummy pistons, 125.

section, 126, 136.

282

INDEX

Pelton wheel, 43-56.

design of blades, 43-46.

flow of water in, 45.

nozzle, 55.

nozzle deflecting, 56, 105.

control, 55-56, 105.
Perrigault, 118-119.
Pipe, supply, friction in, 63, 101.

strength of, 101, 105.
Potter, 3, 109.
Power plants, 65.
Pressure:

at discharge, 35, 91.

at admission, 35, 84.

stages, 119, 139.

boiler, 138, 165, 172.
Propeller, 147, 156-159.

tandem, 147, 156 ; objection to,

158.

speed of, 147, 151, 159, 171.

form of, 157.

slip, 147.

efficiency, 149.

balancing, 152-153.
Propulsion of vehicles, 238.
Pumps, rotary, 212-214.

reciprocating, 211-216.
Puyallup Pelton wheel, 53.

^ueen Alexandra, 169.

Radial flow, 127.
Rateau Turbine, 208.
Reaction wheels, 8, 14-16, 116.
Reaction Turbines, 65-94.

design of, 67-73.

control of, 74-78.

pressure in, 69.
Regulation. See Control.
Reversing Turbines, 159.
Rotor:

of tangential wheels, 50.

of Pelton wheel, 53.

of Girard Turbine, 58.

of Francis Turbine, 73.

of Jonval Turbine, 81.
of mixed flow Turbine, 90.
of Parsons Turbine, 134.
of Parsons marine Turbine,

Fig. 56, p. 172.
of Curtis Turbine, 200.
of De Laval Turbine, 179, 184-

186.
of Riedler-Stumpf Turbine,

192.

Seger Turbine, 142.
Shaft, propeller, 152, 153.

flexible, 187-190.
Speed of running, 124, 140, 185,
191.

in relation to blade form, 41.

for dynamo driving, 41, 65-66,
89.

of compound steam Turbine,
120.

of marine Turbines, 147, 159.

Schultz Tuibine, 195, 206, 209-
210.
Setting:

of water Turbine, 96-101.

of water Turbines at Niagara,
100. ,

of water Turbine under high
heads, 105.

of steam Turbine, 229.

smooth running, 240-241.
Stage chambers, 135, 139, 197.
Stages, compression, 217-218.
Stages, definition of, 119.

pressure, 139, 197, 204.
Steam:

speed of flow, 114-115, 181.

head, 114.

velocities, 139, 184, 204.

packing, 143, 153.
Steam engine :

primitive, 110.

triple expansion, 127.
Stephenson, 111.

INDEX

288

Stress in De Laval wheel, 186.
Suction tube, 69, 96.
Superheat, 230-231, 272-273.
Supply pipe, friction in, 61, 101.
strength of, 101, 105.

Tangential wheels, 48-56.

conditions of efficiency, 6l.
Temperature of steam, 113.
Thermodynamics, 269-270.

of steam engine, 113-114.
Thomson, 69.
Thrust block, 153.
Topaze, 161.
Torque, 142, 187.
Turbine, definition of, 12.

the first, 13.

classification of, 36-38, 119, 221 .
Turbinia, 147-155.
Turbo-generators, 130-146, 189,
204,209.

blowers, 217-220.
Tube, suction, 62, 96.

Vacuum :

augmentor, 143.

importance of, 142, 229.
Velocity :

of admission, 35-36.

of discharge, 20, 35, 91.

due to given head, 259, 262-263.

of expanding steam, 115.
Velox, 160.

Victor Turbines, 58, 73, 90.
Victorian, 171.
Viper, 155-160.
Virginian, 171.
Vortex, 264-267.

free, 265.

forced, 265-267.
Vortex Turbines :

Garonne, 13, 14.
I Thomson, 69-70.

War vessels, radius of action of,
161.

advantages of Turbines in, 241.
Water:

laws of flow, 35-36, 262-264.
Water-wheel :

overshot, 7.

undershot, 4-5.

Poncelet wheel, 11.

compound, 7.
Watt, 110-111.
Wear, 235.

Weight of marine Turbines, 173.
Windmill, 6.

Zoelly Turbine, 120, 206-210, 224-
225.

UNIV. OF MfCHIOAN,

SEP 19 1912

CHISWICK PRESS: PRINTED BY CHARLES WHITTINGHAM AND CO.
TOOKS COURT, CHANCERY LANE, LONDON.