(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Turbines"

This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project 
to make the world's books discoverable online. 

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject 
to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books 
are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover. 

Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the 
publisher to a library and finally to you. 

Usage guidelines 

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the 
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to 
prevent abuse by commercial parties, including placing technical restrictions on automated querying. 

We also ask that you: 

+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for 
personal, non-commercial purposes. 

+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine 
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the 
use of public domain materials for these purposes and may be able to help. 

+ Maintain attribution The Google "watermark" you see on each file is essential for informing people about this project and helping them find 
additional materials through Google Book Search. Please do not remove it. 

+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just 
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other 
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of 
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner 
anywhere in the world. Copyright infringement liability can be quite severe. 

About Google Book Search 

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers 
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web 



at |http : //books . google . com/ 






^ ^( '■■ 



\ ^ 



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 



gg 

O O 

» o 

^ H 
P< EH 
Eh Eh 

g s 

HH PJ 

o < 
. o 



o 



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: 

» o 

> u 

^ 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 











■■ 


W4TMM eOMSUMPnOM M 
^m LH.t>.Xr¥AMIOUS s 






7 


























i 




















\ 


. 


tB 












« 


OiAMONo' 






> 




« 












t6 




V 




























1" 
































^-ffll 


\ 




V 




























\ 




\ 


















7 


?. 






K 




\ 


i 


V 
















J 


{/ 






> 




\ 


N, 


\ 












T 


A 


f 


r 






k^ 






V 


n; 


\ 












'-i 










§^ 










^ 


t- 





J> 


^ 












o 












\ 


^ 


















t 














\ 


^ 


.A 














K 
















\ 


V 














md 










— 1 








^ 


s, 


^ 




A 






if 






















A 




-* 


A 




S8 
































1/ 

































































10/118 



1^ tS 1$ /7 19 t$ SO & 
SP£ED IN KNOT'S 



gg 29 J>4 



FIG. 61. TURBINES AND RECIPROCATING ENGINES. THE FIRST 
COMPARISON. (BY PERMISSION OF " ENGINEERING.") 

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. 

i66 




Q 

i 

o 
S 



OQ 

n 
» 



2 



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 
crews 
ipeeds 
bines, 
' than 
about 
B it is 
., and 
ih the 
option 
lerate 

thout 
it the 
orow 
bine ; 
must 
pond- 
tes it 
irs, sa 
and, 
large 



much 
ne of 
^and 
ich of 
tons, 
•r the 
r the 
aieter 
•cum- 
igh a 
er, sa- 



172 

numbe 
whichi 
regard 
the pr- 
of the 
to sec I 
trefoil 
The 
display 
Carart- 
recipr« 
carry i 
are of 

to iYxi 

press t 
that * 
Acor3C3 
very ^ 
of t\xe 
turbii 
by a^U 

Caroti 
speed 

23,O0 
2019 
CarO'f 
with 
20-6 
ciea^.* 
AS 
in tb 
requi 



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 




m :cc;cc>:ccccccccccc i 



MOVING filVlE^, 
SfATJONAfW BL/OtS 



cccccccccccccccccccc 



}m^mmmmm>i^ 



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 




£3 

u 

n 
o 



g 

» 

Eh 

o ^ 

^ 6 

, o 

a S 



(4 

S 

O 
P^ 

O 

o 

X 
E-b 



S 

m 

S3 
O 



C5 



210 STEAM TURBINES 

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 




K 
■ E- 

CO 

??; 

o 






M 

O 

» 

c 



'A 

o 



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 



PS 






o 

o 

> 
o 






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. 




h 



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 

"^^^^AAAAAAAAAAAAA/^yVWWVWWVWV 

tteyoL urious srAitaf fmopeLLCH. 

<^ V— V — u — tr— V — V — V — V — V — w — 
TIME ft eCOKO. 

_yi — n — ft — ft ft ft A. A A ft A 

mtVOLUTIONS FORT FROFeULfR 
HOmiZONTAL l^iamATIOHS. 

FIG. 79. VIBRATIONS OF HULL OF SS. **CAR0NIA" (QUADRUPLE 
ENGINES). 

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 



YtttnCAl VtMltATiaiS . 






itevoiOTtONS ponTPttoniLeR 

HOmZOItTAL Vi§MTmS_ 



TmffiB 

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.