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 a University of Illinois. # 
 
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 • ■ . : . \ ' 
 
 
 
I 
 
 THE INDICATOR DIAGRAM. 
 
PKACTICAL GEOMETBICAL TESTS OF INDICATOB DIAGKAMS. 
 By N. P. Burgh, M.E. 
 
 Frontispiece. 
 
 See page 80. 
 
PRAC’ 
 
 Frontispiece . 
 
 lee page 80 , 
 
THE 
 
 INDICATOR DIAGRAM 
 
 PRACTICALLY 
 
 BY 
 
 N. P. BURG 
 
 AIem. Inst. Mech. Eng. & A.I.C.E. 
 
 LONDON: 
 
 E. & F. N. SPON, 48, CHARING CROSS. 
 NEW YORK : 446, BROOME ST REE T. 
 
 1875. 
 
LONDON 
 
 PRINTED BY W. CLOWES AND SONS, STAMFORD STREET 
 AND CHARING CROSS. 
 
w \ c 
 
 / 
 
 P R E FAC E. 
 
 This work was actually commenced in the latter 
 end of the year 1867, when I had occasion to 
 professionally test some indicator diagrams. The 
 means I adopted were to consider, first, the pro- 
 
 secondly, their geometrical delineation. Having 
 proceeded thus far, I then concluded that as the 
 length of the motion for the indicator barrel was 
 virtually that of the stroke of the piston, the 
 scale of the geometrical test that I employed 
 must be subject to that circumstance. I accord- 
 ingly made a drawing of the cylinder ports, slide- 
 valve, link motion, eccentrics and rods, a portion 
 ol the piston, length of the connecting rod. and 
 
 <p 
 
 e> 
 
 CL- 
 
 < 
 
 portions of the details that regulated the admis- 
 sion, expansion, and exhaustion of the steam, and 
 
VI 
 
 PREFACE. 
 
 crank circle at the same scale that the stroke of 
 the piston in inches was equal to the length of 
 the indicator diagram. I acquired thus a correct 
 knowledge of the positions of all the details that 
 regulated the steam at the points of admission, 
 cut-off, expansion, exhaustion, compression, and 
 lead, in relation to the positions of the piston and 
 crank pin at the same scale as the diagram ; and 
 by laying it on the crank-pin’s circle I saw at 
 once how it was formed in relation to time and 
 speed, and the cause of the defects, if any existed ; 
 indeed, being the only method of gaining that 
 information truthfully, which is illustrated by the 
 plate as the frontispiece. 
 
 After I had well succeeded with my test, I 
 looked around me to see if any one else had 
 published a similar process, but could not find 
 any record, or even a hint on the subject. I 
 therefore thought it worth while to put the 
 matter in print for public use, intending at that 
 time to make a small work only on that special 
 branch. On conversing, however, with a few of 
 my professional friends on the affair, they urged 
 
PREFACE. 
 
 Vll 
 
 me not to condense the matter thus, but to make 
 a really practical work on the entire subject, as it 
 was much needed, at the same time offering me 
 all the assistance necessary for the purpose : and 
 when I mention the names of Messrs. Penn, 
 Maudslay, Watt, Rennie, and Napier, I feel no 
 hesitation in stating that no author but myself 
 has been so honoured with their contributions, 
 not only in this case, but in others when I have 
 solicited information from them. I am therefore 
 enabled to put forth the most reliable informa- 
 tion from those firms on the indicator diagram 
 in ten chapters, in the following order. 
 
 Chapter I. contains the description and use of 
 the indicator, illustrating, at a working scale, 
 Messrs. Maudslays’ and Mr. Richards’ Indicators. 
 
 Chapter II. is under the heading, “How to 
 take an indicator diagram correctly which treats 
 of the action of the steam in the cylinder ; the 
 definition of the diagram ; correct indicator gear 
 for horizontal, vertical, and oscillating engines, 
 and indicating notes. 
 
 Chapter III. deals with the proof of atmo- 
 
Vlll 
 
 PREFACE. 
 
 spheric pressure and particulars of steam pres- 
 sures, and includes rules and tables bearing on 
 the subject, with practical examples and illus- 
 trations. 
 
 Chapter IV. is a complete description and 
 illustration of the theoretical geometry of the 
 indicator diagram in a more practical manner 
 than hitherto published. 
 
 Chapter V. is the practical geometry of the 
 indicator diagram, which fully explains the 
 frontispiece plate and other figures in connection 
 with it. 
 
 Chapter VI. commences the illustrations of 
 indicator diagrams and gear constructed by the 
 firms I have mentioned, and others whose names 
 are noted under the figures : this chapter contains 
 twenty-one diagrams from ordinary modern screw 
 engines of all classes ; three from compound 
 engines ; three of steam-launch engines ; and two 
 illustrations of indicator gear for return acting 
 engines. 
 
 Chapter VII. is devoted to diagrams taken 
 from the most modern paddle-engines, and con- 
 
PREFACE. 
 
 IX 
 
 tains eighteen illustrations of them ; also the 
 most improved indicator gear by Messrs. Penn 
 and Napier, for oscillating engines. 
 
 Chapter VIII. treats of land-engine indicator 
 diagrams, showing eleven examples taken from 
 various classes, including locomotive engines. 
 
 Chapter IX. fully explains and illustrates air 
 and water pump diagrams. 
 
 Chapter X. closes this work, with the explana- 
 tion of the indicated horse-power in connection 
 with the diagram. 
 
 The whole of this is expressed in one hundred 
 and sixty-four pages, and illustrated by one 
 hundred engravings ; so that the entire matter 
 has been fully explained, but not more so than 
 requisite. 
 
 N. P. BURGH. 
 
 78 , Waterloo Bridge , London , 
 
 January 1 , 1869 , 
 
CHAPTER I. 
 
 Page 
 
 1 
 
 THE DESCRIPTION AND USE OF THE INDICATOR . 
 
 CHAPTER II. 
 
 HOW TO TAKE AN INDICATOR DIAGRAM CORRECTLY . .11 
 
 CHAPTER III. 
 
 THE PROOF OF ATMOSPHERIC PRESSURE, AND PARTICULARS OF 
 
 STEAM PRESSURES . . . . „ . .28 
 
 CHAPTER IY. 
 
 THE THEORETICAL GEOMETRY OF THE INDICATOR DIAGRAM . 46 
 
 CHAPTER Y. 
 
 THE PRACTICAL GEOMETRY OF THE INDICATOR DIAGRAM . 74 
 
 CHAPTER YI. 
 
 MODERN INDICATOR DIAGRAMS, CONTRIBUTED BY THE MOST 
 EMINENT ENGINEERS IN ENGLAND AND SCOTLAND, TO 
 SHOW THEIR LATEST AND BEST PRACTICE . 
 
 91 
 
Xll 
 
 CONTENTS. 
 
 CHAPTER VII. 
 
 Pagti 
 
 INDICATOR DIAGRAMS TAKEN FROM THE MOST IMPROVED 
 
 MODERN PADDLE WHEEL ENGINES . . . .117 
 
 / 
 
 CHAPTER VIII. 
 
 EXAMPLES OF INDICATOR DIAGRAMS TAKEN FROM LAND 
 
 ENGINES 134 
 
 CHAPTER IX. 
 
 EXAMPLES OF INDICATOR DIAGRAMS, TAKEN FROM AIR AND 
 
 WATER PUMPS 142 
 
 CHAPTER X. 
 
 THE FORMULAS REQUISITE TO DEFINE THE DUTY OF AN 
 
 ENGINE FROM THE INDICATOR DIAGRAM . . • 148 
 
THE INDICATOR DIAGRAM 
 
 PRACTICALLY CONSIDERED. 
 
 CHAPTER I. 
 
 THE DESCRIPTION AND USE OF THE INDICATOR. 
 
 A very large proportion of the young members 
 of the engineering profession look" at an indicator 
 diagram as a mysterious production ; and even 
 supposing that they comprehend how it is formed, 
 they do not understand the causes for the various 
 forms of figures. There is, therefore undoubtedly, 
 room for a practical work on the subject which 
 shall deal with the matter just as a learner 
 requires "• leading him on step by step with- 
 out slipping, and impressing on his mind 
 all the realities of the case ; for directly an 
 author skips over any portion of his subject, 
 with the phrase appended, “ this can be readily 
 understood,” it is generally assumed that he does 
 
 A B 
 
2 
 
 THE INDICATOR DIAGRAM. 
 
 not know it himself, and shuffles out of the 
 argument with bad grace. The best course of 
 instruction for the young engineer then is, that 
 the truth of each minute portion of the subject 
 before him be laid bare, so that he can com- 
 prehend it. When he understands thus far, 
 obviously his knowledge will enable him to put 
 the same into practice boldly : for by being 
 acquainted with the ground- work of the subject, 
 he is master also to a great extent of the result 
 of his labours. 
 
 First let us consider with what we have to deal 
 — it is the steam cylinder of an engine, with its 
 piston in motion, and our aim is to explain what 
 the steam is doing, or how the piston is impelled 
 from the commencement to the termination of its 
 stroke. The next question is, how can we effect 
 this? Simply, by an instrument termed an 
 “indicator,” which is a cylinder fitted with a 
 piston, surmounted by a spring to keep the 
 piston always down to its work, when in contact 
 with the steam. The piston-rod is in connection 
 with a pencil, or marker, which indicates the 
 motion of the piston up or down. The length of 
 the stroke of the engine piston, of course, exceeds 
 that of the indicator diagram in practice, while 
 the principles of both are the same. The paper 
 
USE OP THE INDICATOR. 
 
 3 
 
 on which the diagram is traced can he laid flat if 
 preferred during the operation, but generally it is 
 wound around a barrel, -which receives its motion — 
 nearly rotary — from the piston-rod of the engine. 
 There is, however, a certain discrepancy in the 
 present mode of indicating which has been 
 overlooked; it is this — the indicator piston is 
 always exposed to the atmospheric pressure, 
 while the engine piston is often closed from it. 
 
 This is the fault with all steel spring indicators 
 of the present day, which not only permit the 
 atmosphere to act on the indicating piston, but 
 also require a spring to ensure that the piston 
 follows the decrease of the pressure of the 
 steam. A perfect indicator, for example, is that 
 which is arranged so that its piston and the 
 engine piston are operated on equally by the 
 same volume of steam, proportionately to their 
 areas. The indicator piston should be weighted 
 in proportion to the inertia the engine piston 
 has to overcome, so that the resistance in each 
 case shall be alike relatively. 
 
 A good form of direct-acting indicator is shown 
 by Fig. 1, as constructed and used by Messrs. 
 Maudslay, Sons, and Field, the author being 
 indebted to Joshua Field, Esq., for the drawing. 
 Its combinations and arrangement are as follow : 
 
4 
 
 THE INDICATOR DIAGRAM. 
 
 C is the steam cylinder open at the top T. The 
 piston P is fitted steam-tight, and transmits its 
 motion oy a tube R, the top of which is guided 
 
 Fig. 1 
 
 by side rods S. The tube R contains a spring, 
 which is prolonged, as shown, to the cross-piece 
 c at the extremities of the side rods S. The 
 marker or pointer p is fixed to an arm g, pro- 
 
USE QF THE INDICATOR. 
 
 O 
 
 jecting from tlie guide at the top of the tube E, 
 so that the piston P and pointer p move simul- 
 taneously. The motion barrel M, on which the 
 paper is wound and held by the vertical spring 
 h , is also fitted internally with a watch-like 
 main-spring W, to ensure that the barrel will 
 always tend to resume its original position when 
 in action. The barrel is mounted on a rod, which 
 is supported at the side of the base of the cy- 
 linder C, below which is the main pulley D, and 
 the guide pulley Gf, the position of the latter being 
 fixed as required by the set screw s. The steam 
 is admitted and shut off by the plug-cock S, and 
 the clearance of the condensed steam is effected 
 through the little opening m. The screw a a at 
 the extremity makes the connecting-joint either 
 with the engine cylinder cover direct or with 
 the branch pipe, as required. 
 
 Another kind of indicator is constructed by 
 Messrs. Elliott Brothers, London, and illustrated 
 by Eig. 2. Its principal object is to reduce the 
 motion of the piston as much as possible, which 
 is attained by the ordinary parallel motion shown 
 in the side elevation, where the pencil or marker 
 is depicted in the centre of the connecting bar. 
 This arrangement is evidently entirely foreign 
 to the original indicator, with which the height 
 
6 
 
 THE INDICATOR DIAGRAM. 
 
 O 
 
 S3 
 
 of the diagram taken, and the stroke of the in- 
 dicator piston, were alike in dimensions, where, 
 as in the present example, the pencil travels 
 about 3‘5 times of the motion of the piston. This 
 
USE OF THE INDICATOR. 7 . 
 
 difference in the two motions magnifies the action 
 of the piston so much, that the pencil indicates the 
 least convulsive movement of the piston, as well 
 its direct action up and down, caused by the 
 steam and the spring. The makers’ description 
 of their indicator is this : — 
 
 “ The indicators are made of a uniform size, the 
 area of the cylinder is one-half of a square inch, 
 its diameter being *7979 of an inch. The piston 
 is not fitted quite steam-tight, but is permitted 
 to leak a little ; this renders its action more 
 nearly frictionless, and does not at all affect the 
 pressure on either side of it. The motion of the 
 piston is §§ of an inch, and the motion of the 
 pencil, or extreme height of the diagram, is 
 3-J- inches. The paper cylinder is 2 inches in 
 diameter, and the length of the diagram may he 
 51 inches if this extent of motion is given to the 
 cord. The diagram is drawn hy a pointed brass 
 wire on metallic paper. This is a great improve- 
 ment over the pencil ; the point lasts a long time, 
 cannot be broken off, and is readily sharpened, 
 and the diagram is indelible. The steam-passage 
 has two or three times the area usually given to 
 it. The stem of the indicator is conical, and fits 
 in a corresponding seat in the stop-cock, where it 
 is held by a peculiar coupling, which is a circular 
 
8 
 
 THE INDICATOR DIAGRAM. 
 
 nut with two screws of unequal pitches. This 
 arrangement permits the indicator to he turned 
 round, so as to stand in any desired position, 
 when, the coupling being turned forward, the 
 difference in the pitches of the screws draws the 
 cone firmly into its seat ; and when the coupling 
 is turned backward, the cone is by the same 
 means started from its seat. The leading pul- 
 leys may be turned by some pressure, to give any 
 desired direction to the cord, and will remain 
 where they are set. By these means the indi- 
 cator can be readily attached in almost any situ- 
 ation. 
 
 “ The Springs . — In order to adapt this indicator 
 for use on engines of every class, springs are 
 made for it to nine different scales, as follows : — 
 
 No. 1, +in, 
 
 . motion, shows 1 lb. pressure] 
 
 j— 15 to -f 10 
 
 
 on 
 
 the sq. in. 
 
 Indicates from . J 
 
 ?? 
 
 9 1 
 
 T2 
 
 ?? 
 
 5) 
 
 55 
 
 —15 „ + 22-5 
 
 55 
 
 T6 
 
 j» 
 
 55 
 
 55 
 
 —15 „ -j- 35 
 
 55 
 
 a l 
 ** 2f 
 
 ?> 
 
 55 
 
 55 
 
 —16 „ -f 60 
 
 55 
 
 K l 
 
 2 4 
 
 55 55 
 
 55 
 
 Atmosphere to -j- 75 
 
 55 
 
 8 1 
 
 HIT 
 
 55 55 
 
 55 
 
 55 
 
 55 “f-100 
 
 5) 
 
 7 - 1 - 
 
 'j 40 
 
 55 55 
 
 55 
 
 55 
 
 55 +125 
 
 55 
 
 8 - 1 - 
 °5 4 8 
 
 55 55 
 
 55 
 
 55 
 
 „ +150 
 
 55 
 
 () 1 
 5 IT 
 
 55 55 
 
 55 
 
 55 
 
 55 +175 
 
 “All the scales, except No. 2, are multiples 
 
USE OF THE INDICATOR. 
 
 9 
 
 of 8, and the common rule will measure all the 
 diagrams, if the proper scale is not at hand. It 
 will be observed that the five higher scales do 
 not indicate the vacuum. These are so made 
 for the following reasons : the far greater num- 
 ber of engines which work steam at high pres- 
 sures do not condense, and moreover, at these 
 pressures, the scale of the indication necessarily 
 becomes small, while it is always highly desirable 
 to show the vacuum on a large scale. Spring 
 No. 1 may be employed to indicate the vacuum, 
 in engines which work steam at high pressures 
 and with condensation. It can be readily sub- 
 stituted in the indicator, and the diagram which 
 it will give will be on a satisfactory scale. It 
 is provided with a stop, which prevents it from 
 being compressed too much, so that a high 
 pressure of steam will not injure it. Moreover 
 the vacuum being omitted from the scales which 
 go above 60 lbs., the entire range of the pencil 
 is available for the pressures above the atmo- 
 sphere, which are therefore shown on a somewhat 
 larger scale. The springs indicating pressures 
 above 60 lbs. will be made, however, to indicate 
 the vacuum also, when so ordered.” 
 
 The next consideration is the scale of the 
 diagram, for if the pressure of the steam is 
 
10 
 
 THE INDICATOR DIAGRAM. 
 
 increased in one example to that of another, and 
 the heights of the diagrams are alike, obviously the 
 scale of each cannot be the same. For example, 
 if 2 1 inches equals the height of the diagram, or 
 of the upward motion of the indicator pencil from 
 the atmospheric line, and the scale is equal to 
 y^th of an inch per pound of steam on the square 
 inch, then 2'5 x 16 = 40 lbs. on the square inch ; 
 but if the scale is ^th, then 2 - 5x20 = 501bs. 
 We learn from this that the piston of the indi- 
 cator, if unaltered in its area, must be loaded 
 relatively to the pressure of the steam, and 
 the scale of the diagram must correspond also. 
 
 It will be noticed that, for their indicator, the 
 Messrs. Elliott adopt nine different springs, each 
 to correspond with certain pressures and scales, 
 the stroke of the piston being alike in all cases. 
 The result, then, is nearly the same as would be 
 attained by proportioning the area and load on 
 the piston to the pressure of the steam in the 
 engine cylinder. 
 
 A really perfect indicator can be made, how- 
 ever, by arranging the detail so that the steam 
 takes the place of the steel spring or load over 
 the piston ; by which arrangement the load can 
 be increased or decreased to exactitude. 
 
11 
 
 CHAPTER II. 
 
 HOW TO TAKE AN INDICATOR DIAGRAM 
 CORRECTLY. 
 
 The first matter for notice is the arrange- 
 ment of the gear, and the position of the instru- 
 ment. It must be remembered that it is the 
 action of the steam inside the engine cylinder 
 we wish to portray : consequently the motion 
 for the indicating paper or card, must be derived 
 from the engine piston rod, as it is the action of 
 the steam on that piston we wish to learn. 
 Starting then with this rule without exception, 
 we must next note the correct position of the 
 indicator on the engine cylinder before alluding 
 to anything else. The indicator should be se- 
 cured to the end of the cylinder, never on the 
 side : for this reason, the steam that is impelling 
 the piston is also rushing along with it, and 
 when exhaustion ensues, the volume has a retro- 
 grade motion, but still in a line with the 
 cylinder’s length. The illustration Fig. 3 will 
 assist to understand this matter : the motion and 
 pressure of the steam on the piston and cover 
 
12 
 
 THE INDICATOR DIAGRAM. 
 
 are shown by the large straight arrows. The 
 opening A is the situation for the indicator 
 nozzle to be fitted into to take a correct indication 
 of the action of the steam within the cylinder ; 
 
 Fig. 3. 
 
 An Illustration of the action of Steam when propelling the Piston, and 
 showing also the correct position for the Indicator. 
 
 the smaller straight arrows, at angles, show that 
 the steam alters its line of motion but very 
 slightly to pass through the opening A, because 
 that opening is in a line with the motion of the 
 
A CORRECT INDICATOR DIAGRAM. 13 
 
 steam in the cylinder. Notice next the opening 
 B, and the form of the arrows there, which 
 indicate that the steam has actually to stop and 
 turn at right angles to pass through that aperture, 
 so that the actual pressure or motion of the 
 steam in the cylinder can never be known from 
 the branch volume issuing at right angles to the 
 cylinder’s length. 
 
 The position of the indicator beyond the nozzle 
 must be close to it to ensure a truthful indica- 
 tion of the steam in the engine cylinder. If a 
 branch pipe is requisite, let it be as straight 
 as possible, to form a direct communication. 
 When the indicator is secured at right angles 
 with the nozzle pipe, of course a bend branch is 
 requisite ; let this be always a curve whose 
 radius is from four to six inches — never a right 
 angle bend. 
 
 Having supposed the indicator to be fixed, 
 and in connection with the cylinder, our next 
 determination is the best mode to give motion 
 to the paper or card. We have already stated 
 that the original movement must be from the 
 engine piston rod, and there only remains now 
 to explain how to reduce that travel to suit 
 the indicator or card barrel. Now this barrel 
 must not of course make an entire revolution. 
 
14 
 
 THE INDICATOR DIAGRAM. 
 
 for the obvious reason that, if it did, the dia- 
 gram taken would be connected at its end ex- 
 tremities; the final motion therefore depends 
 on the diameter of the pulley, at the base of the 
 barrel. The general length for this movement 
 is about 4 to 5 inches, the circumference of the 
 pulleys being of corresponding dimensions, plus 
 the space required between the ends of the dia- 
 gram described. The motion from the engine 
 piston-rod is reduced in length by levers of such 
 proportions as required for that purpose ; for 
 example, if the stroke of the engine is 30 inches, 
 and the length of the diagram is to be 5 inches, 
 then the lengths of the levers are as 1 is to 6, or 
 if only one lever is used, then the indicator’s 
 motion must be taken from a point on the lever 
 sufficiently below its fixed end to obtain the 
 reduced travel required. The mechanical con- 
 nection of the lever and the indicator barrel is 
 usually a cord of the kind known as “ whip- 
 cord,” its normal elasticity being expended, by 
 sufficiently stretching it, before its application 
 for the purpose required. 
 
 Supposing now that all is ready, the diagram 
 is taken in this manner, — the communication 
 pipe between the engine cylinder and the indi- 
 cator is blown through by opening the plug-hole, 
 
A CORRECT INDICATOR DIAGRAM. 
 
 15 
 
 after which it is closed. Next, the cord is con- 
 nected to the motion-barrel, the paper of course 
 being in its place : the pointer is made to form 
 the atmospheric line : this motion, without the 
 steam, being permitted for a few times, the plug 
 is again opened, and the diagram described by 
 the pointer as illustrated by- Fig. 4. The 
 
 At the left hand the pointer commenced from 
 the atmospheric line A ; it rose instantly to the 
 highest point, and as quickly fell, and performed 
 the undulation to 27*. It described from thence 
 the uneven line to 23*, when the steam was cut 
 
16 
 
 THE INDICATOR DIAGRAM. 
 
 off. Expansion now commenced, and as a decrease 
 in the pressure of the steam in the cylinder ensued, 
 the pointer gradually fell from from 23‘ to 14 - , 
 when the uneven line was traced to 9*4. Expan- 
 sion now ceased, and as at the same instant ex- 
 haustion commenced, the pointer gradually fell to 
 the “atmospheric line” before the end of the stroke, 
 describing below it the undulated line until the 
 completion. On turning the corner — the return 
 action here commenced — the pointer marked its 
 duty by an uneven line until reaching 9'8. Here 
 compression commenced, and continued until 
 the steam was readmitted into the cylinder 
 termed the “lead,” which produced the round 
 corner at the right hand. The pointer next 
 ascended and joined the line it commenced. 
 
 The motion in this case was taken from the 
 engine piston-rod, and reduced by a lever, the 
 latter being connected to the indicator by a cord 
 of the usual kind. 
 
 The class of engine alluded to is a direct- 
 acting single piston-rod horizontal engine of the 
 usual arrangement for screw propulsion ; but as 
 there are other classes of engines both on land and 
 water, we must not omit to describe the mode of 
 taking an indicator diagram from each type. 
 
 As the directions given about the position of 
 
CORRECT INDICATOR GEAR. 
 
 17 
 
 the indicator are in connection with its move- 
 ments, we shall now follow on to a few hints as 
 to the most correct method to obtain a true 
 motion for the card-barrel. For steam-engines, 
 whether over-head or side-lever, the cord can be 
 attached either sufficiently near the centre of the 
 gudgeon or to a relatively suitable point on the 
 radius-bar, of course taking precaution in each 
 case to allow no back-lash, slack-string, or non- 
 coincident motion for the barrel with the engine 
 piston-rod. The indicator is secured to the end 
 of the cylinder ; and a motion-pulley, situated at 
 a suitable distance, guides the cord from the 
 engine-motion to the pulley of the card-barrel ; 
 levers, therefore, are not required. 
 
 Now for horizontal, vertical, inclined, or an- 
 gular, direct, or return-acting engines, the case 
 is widely different ; for with these the original 
 motion for the barrel must be taken from the piston- 
 rod, because there is no other direct sliding 
 point of any detail coincident with its motion. 
 There are, of course, various methods of arriving 
 at this means ; one is as illustrated by Fig. 5. 
 In this example the indicator, I, is secured to the 
 front of the cylinder ; the piston-rod, R, is at half- 
 stroke. The first lever, L, is secured to the 
 head, T, of the piston-rod, and therefore moves 
 
 c 
 
18 
 
 THE INDICATOR DIAGRAM. 
 
 always in a vertical position, with a horizontal 
 motion of the same stToke as the engine piston. 
 The length of this lever is proportioned to the 
 position of the motion-pulley of the indicator ; it 
 is looped also at the lower end, to permit suffi- 
 cient vibration for the pin of the second lever, L 1 , 
 
 rig. 5. 
 
 Direct-acting Lever Indicator Gear. 
 
 which being hung on a pin secured to a bracket 
 or any other fixture, acts as a pendulum. The 
 final motion, therefore, is derived from a point on 
 the second lever, the chord of the arc described 
 being equal to the length of diagram taken. 
 
 A second arrangement for this purpose is illus- 
 trated by Fig. 6 ; in this instance one lever, L, 
 
CORRECT INDICATOR GEAR. 
 
 19 
 
 only is used, and the motion end is looped and 
 attached to the head, T, of the piston-rod, R, 
 being in direct connection with the lever end 
 supported on a fixed pin, L 1 . 
 
 The indicator, I, is situated as before, but the 
 
 Fig. 6. 
 
 motion pulley is at right angles ; a second pulley, 
 P, below is introduced to guide the cord to the 
 motion point on the lever, L. 
 
 In direct opposition to the last method, as far 
 as the position of the lever is concerned, the 
 
20 
 
 TEE INDICATOR DIAGRAM. 
 
 arrangement illustrated by Fig. 7 is often used : 
 here the indicator is in the same position again, 
 but the lever and pulley are reversely situated. 
 The lever, L, is hung on a pin, L 1 , supported by a 
 bracket or anything equally applicable : it is 
 looped as before, but attached to the pin on the 
 
 Fig. 7. 
 
 Pulley and Lever Indicator Gear, Over Motion. 
 
 head, T, of the piston-rod, R. The barrel of the 
 indicator, I, derives its motion from the correct 
 point on the lever, L, being connected by a cord 
 passing quarter round the pulley, P, and then 
 continued to the pulley on the barrel. 
 
 These three arrangements for the gear are, as 
 already stated, correct for any class of direct or 
 
CORRECT INDICATOR GEAR. 
 
 21 
 
 return-action engine. The main-motion pin for 
 the latter type being fixed on the piston-rod instead 
 of on the head. We may add, that for high speeds 
 the arrangement shown by Fig. 5 in page 18 is 
 the best, because the second pulley, P, in Fig. 6, 
 is dispensed with, its introduction being really a 
 break in the direct connection for the cord. 
 
 When the performances of oscillating engines 
 require to be indicated, the pulleys must be 
 introduced; but as the speed of these engines is 
 never high, comparatively, there is no objection 
 to their use. The best arrangement we know of 
 for this purpose is shown by Fig. 8, which 
 illustrates the half-end elevation of an oscillating 
 cylinder with its piston-rod, and head, T, at 
 full down stroke and the cylinder vertical. The 
 cylinder is fitted with two small steam branch 
 pipes, B B, with bends, b b, at each end, connected 
 to the ends ; centrally of the length is a two-way 
 cock, C, with a branch, at right angles to which is 
 connected the indicator, I. The motion for the 
 pulley, P, is attained by the cord being attached 
 to the head, T, and led down to the pulley, P‘, 
 which is supported by a bracket secured to the 
 flange of the stuffing-box ; following from this, at 
 right angles, the cord is secured at a point on the 
 periphery of the largest pulley, P 2 , which has 
 
Fig. 8 
 
 22 
 
 THE INDICATOR DIAGRAM. 
 
 on its shaft another pulley, P 3 , being supported 
 by a bracket secured to the cylinder. From the 
 
 Arrangement of Indicator Gear for Oscillating Engines, Vertical position. By Messrs. James Watt and Co. 
 
CORRECT INDICATOR GEAR. 
 
 23 
 
 pulley, P 3 , a second cord is attached to the 
 barrel-pulley, P, so that a certain connection 
 between P and T is obtained. 
 
 Of course the radii of all the pulleys must he 
 in strict ratio ; for example, if the motion of the 
 pulley, P, is five inches lineally, and that for the 
 piston-rod head, T, fifty inches; then the radius 
 of the larger pulley, P 2 , must be five times more 
 than that of P, P \ and P 3 , supposing each of 
 them to be alike ; hut if there is any difference 
 in their radii, then the radius of P 2 must be in 
 due proportion. To explain that the gear is in- 
 dependent of any vibratory action of the cylinder, 
 as far as the pulley, P, is affected, the drawing, 
 Fig. 9, is introduced on the next page, which 
 shows the piston-rod, R, at half-stroke, and the 
 cylinder gear and indicator at the relative angle. 
 
 The hack-lash of the cord is prevented by the 
 pulley, P 2 , being fitted with a circular spring, 
 which contracts bv the ascent of the head, T, and 
 unwinds when it descends ; this pulley is there- 
 fore loose on its bearing, and P 3 is fixed to it. 
 
 Very little consideration is therefore necessary 
 to understand that, as far as the motion for the 
 indicator is concerned, it must he coincident with 
 the engine piston rigidly so, without slip or faulty 
 return action, the cause of slip being the result of 
 
Arrangement of Indicator Gear for Oscillating Engines, Extreme Angular position. By Messrs. James Watt and Co. 
 
INDICATING NOTES. 
 
 25 
 
 the speed of the piston exceeding that of the indi- 
 cator, and the faulty return action the jerking of 
 the piston-barrel. 
 
 As we shall dilate on the errors and their causes 
 in indicator diagrams further on, we will here 
 point out the list of notes an engineer should 
 make when indicating various engines : — 
 
 Notes to be made when indicating Marine Engines. 
 
 Name of ship. 
 
 Name and locality of trial. 
 
 Time and date of ditto. 
 
 Type of engines. 
 
 Nominal horse-power collectively. 
 
 Number of cylinders. 
 
 Fore or aft, or port or starboard cylinder indi- 
 cating. 
 
 End of cylinder (top or bottom, back or front). 
 
 Effective area of piston in square inches. 
 
 Scale of the diagram. 
 
 Length of stroke of piston in feet. 
 
 Length of crank connecting-rod. 
 
 Number of strokes of piston per minute. 
 
 Type of slide valve, the dimensions of the 
 steam-ports, and the travel and outside lap of 
 valve, and width of opening for supply of steam. 
 
 Class of link motion. 
 
26 
 
 THE INDICATOR DIAGRAM. 
 
 Grade of expansion cut off, if in gear. 
 
 Pressure of steam indicated by the gauges in 
 the engine and boiler rooms. 
 
 Exhaustion indicated by the vacuum gauge. 
 
 Amount of injection-water passage opened. 
 
 Feed water, off or on. 
 
 Temperature of the engine and stoking-rooms. 
 
 State of fires in the boilers. 
 
 Height of water in ditto. 
 
 Priming, if any symptoms. 
 
 State of the working bearings of the engine, 
 and shafting from the forward main bearing to 
 the stern tube stuffing-box. 
 
 General appearance of the duty of the engine. 
 
 Type of screw-propeller or paddle-wheels, and 
 proportions. 
 
 Speed of the ship in knots per hour; her di- 
 mensions, draught, tonnage, and displacement. 
 
 State of the water and tide. 
 
 For Land , Stationary , and Portable Engines. 
 
 For land-engines, the portion of the above 
 notes that refer to them must be used, with this 
 addition, for locomotive engines. 
 
 The diameter of the driving-wheels. 
 
 Weights of the engine and train. 
 
 The incline of the line of rails, if any. 
 
INDICATING NOTES. 
 
 27 
 
 The radii of the curves of ditto. 
 
 In the case of combined, or high and low 
 pressure steam-engines, the length of the stroke 
 of each piston must be recorded, together with 
 the pressures of the steam in each, if gauges are 
 attached. 
 
 There are, of course, with all kinds of engines, 
 other incidents that are exceptional, which the 
 engineer who understands his profession will 
 not fail to notice, but, as they are casual, need 
 no comment here. 
 
28 
 
 THE INDICATOR DIAGRAM. 
 
 CHAPTER III. 
 
 THE PROOF OF ATMOSPHERIC PRESSURE, AND 
 PARTICULARS OF STEAM PRESSURES. 
 
 The two preceding chapters may be considered 
 as preliminary to the present one ; for the mere 
 fact of understanding the mechanical arrangement 
 of an indicator, and the mode of using that instru- 
 ment properly, do not constitute the entire require- 
 ments bearing on the subject. What is excep- 
 tional is a correct knowledge of the principles on 
 which the indicator diagram is founded, for by 
 an acquaintance with them the real utility of the 
 instrument becomes apparent. 
 
 To begin, then, we must first notice the nature 
 and real cause and effect of atmospheric pressure, 
 the exhaustion of which, in relation to the con- 
 densing-engine is termed “ vacuum.” The utility 
 of this natural phenomenon was experimented on 
 as far hack as 1643, by Torricelli, a pupil of the 
 renowned astronomer and philosopher Galileo, in 
 the following manner : — A glass tube, about a yard 
 in length, and of a quarter-inch diameter inside, 
 
PROOF OF ATMOSPHERIC PRESSURE. 29 
 
 was sealed at one end, and quite filled with mercury. 
 The open end being stopped either by the thumb 
 or other efficient means, ready to be removed at 
 pleasure, the tube was then inverted, and the 
 lower end inserted in a trough of mercury ; the 
 tube still remaining vertical, and the thumb 
 being removed, or the immersed end opened, the 
 mercury sank six inches from the sealed end, 
 which showed thirty inches of mercury in the tube 
 from the level of that in the trough. The mass 
 m the tube was therefore held by the atmosphere, 
 or the pressure of the latter on the mercury in the 
 trough prevented that in the tube descending 
 below the six inches alluded to. Now if the top 
 end of the tube had been opened, the mercury in 
 it would have sunk into the trough ; because the 
 pressure of the atmosphere would have been in 
 equilibrium on the inside and outside of the 
 tube, and thus the mercury would fall, owing to 
 gravity. 
 
 The application of this experiment for prac- 
 tical purposes was thus carried out. A tube, 
 one square inch in area, filled as before, and in- 
 verted likewise in a trough of suitable dimen- 
 sions, retained the mercury thirty inches high, 
 under the same circumstances. Then, as 2 cubic 
 inches of mercury equals about 1 lb. avoirdupois 
 
30 
 
 THE INDICATOR DIAGRAM. 
 
 weight, and there are 30 cubic inches resisting 
 the atmosphere, the matter is resolved into a 
 simple calculation, thus : — W = weight of the 
 mercury, in the tube, C = cubic inches of 
 mercury to equal 1 lb., and x = full pressure of 
 the atmosphere in pounds avoirdupois per square 
 
 inch ; therefore, x = 
 
 W 
 
 c 
 
 30 
 
 ’ 2 = 1 lb. 
 
 1 5 lbs. on 
 
 the square inch, which is termed a perfect vacuum ; 
 but 14‘9 lbs. is the utmost yet attained actually. 
 
 From the above conclusion emanate the well- 
 known symbols, Y 26, or Y 28, &c., which, in 
 reality, mean that, relatively, a vacuum was ob- 
 tained equal to 13 or 14 lbs. on the square inch, 
 being the pressure relieved or absorbed by the 
 air-pump in practice. 
 
 Another mode of learning the actual pressure of 
 the atmosphere has been often tried, as illustrated 
 by Fig. 10. The vessel V was filled with mercury, 
 M, the vessel being surmounted by a frame //, 
 which supported two glass tubes T and T', per- 
 forated at the top. These tubes are fitted with 
 pistons P P', and rods r r, for the purpose of de- 
 monstrating the utility of the apparatus. On 
 raising the piston P to the height h in the tube 
 T, the mercury immediately ascended after it for 
 30 inches, as shown ; the level of the mercury in 
 
PROOF OF ATMOSPHERIC PRESSURE, 
 
 31 
 
 the vessel sank to L ; while the pressure of the 
 atmosphere not only caused this, but also held or 
 forced the piston P f down to that level of the 
 mercury in the vessel. Now when P', in the 
 
 Fig. 10. 
 
 Practical Method for Testing the Atmospheric Pressure. 
 
 tube T', was raised to b', the level of the mercury in 
 the vessel fell to L'or Y: for as the piston ascended 
 it caused a vacuum behind it, and the mercury in 
 the vessel was forced by the atmospheric pressure 
 up into the tube till reaching 30 inches from the 
 
32 
 
 THE INDICATOR DIAGRAM. 
 
 level 1 / ; while the mercury in the tube T of course 
 sank to the same level b', as that in the tube T\ 
 We again learn from this, as in the preceding 
 experiments, that there can be no other agency 
 for causing the mercury to rise in the tubes than 
 the natural pressure of the atmosphere ; for as 
 the pistons were raised, they drove the air in the 
 tube above them out at the apertures at the top, 
 and as there was no air in the tube below, the 
 pressure of the atmosphere acted only on the 
 outside of the tube and on the mercury, which 
 resulted in the latter being forced up as shown. 
 
 We have now sufficiently explained how it is 
 certain that there is an atmospheric pressure, 
 which in round numbers is about 14 • 5 lbs. on the 
 square inch, or 29 inches of mercury in general 
 practice, when a nearly perfect vacuum is 
 attained ; for undoubtedly the state of the atmo- 
 sphere in an engine-room is not clear ; conse- 
 quently the natural pressure is proportionately 
 reduced, in accordance. 
 
 Our next step in instruction is the explanation 
 of the nature of steam ; for, as we stated before, 
 if the young engineer or student wishes to he 
 practically acquainted with any subject properly, 
 he must know the principles first. 
 
 It matters not for the present purpose about 
 
PARTICULARS OF STEAM. 
 
 33 
 
 the chemical properties of steam, but rather its 
 “ nature ” and proportions in particular, which 
 are given by the following table : — 
 
 Table of Saturated Steam at different Pressures. 
 
 Actual 
 pressure of 
 the Steam 
 exclusive of 
 the 
 
 Atmospheric 
 
 Pressure. 
 
 Tempera- 
 ture in 
 degrees of 
 Faht. 
 
 Elastic force 
 in inches of 
 Mercury. 
 
 Cubic inches 
 of Water to 
 produce 
 1 cubic foot 
 of Steam. 
 
 Volume of 
 Steam 
 produced 
 from one of 
 Water. 
 
 Weight of 
 one cubic 
 foot of 
 Steam in lbs. 
 
 lbs. 
 
 1 
 
 216-3 
 
 32*64 
 
 1*099 
 
 1572 
 
 *0397 
 
 2 
 
 219*5 
 
 34*68 
 
 1*162 
 
 1487 
 
 *0419 
 
 3 
 
 222*5 
 
 36*72 
 
 1*226 
 
 1410 
 
 *0442 
 
 4 
 
 225-4 
 
 38-76 
 
 1*287 
 
 1342 
 
 *0465 
 
 6 
 
 228*0 
 
 40*80 
 
 1*350 
 
 1280 
 
 *0487 
 
 6 
 
 230*6 
 
 42*84 
 
 1*411 
 
 1224 
 
 *0510 
 
 7 
 
 233*1 
 
 44*88 
 
 1*474 
 
 1172 
 
 •0532 
 
 8 
 
 235*5 
 
 46*92 
 
 1*536 
 
 1125 
 
 *0576 
 
 9 
 
 237-9 
 
 48*96 
 
 1*597 
 
 1082 
 
 *0598 
 
 10 
 
 240*2 
 
 ‘ 51*00 
 
 1*658 
 
 1042 
 
 *0620 
 
 11 
 
 242*3 
 
 53*04 
 
 1*719 
 
 1005 
 
 *0642 
 
 12 
 
 244*4 
 
 55*08 
 
 1*779 
 
 971 
 
 *0664 
 
 13 
 
 246*4 
 
 57*12 
 
 1*840 
 
 939 
 
 •0686 
 
 14 
 
 248*4 
 
 57-16 
 
 1*910 
 
 909 
 
 •0707 
 
 15 
 
 250*4 
 
 61*20 
 
 1*959 
 
 881 
 
 •0729 
 
 16 
 
 252*2 
 
 63*24 
 
 2*021 
 
 885 
 
 •0751 
 
 17 
 
 254 " 1 
 
 65*28 
 
 2*079 
 
 830 
 
 •0772 
 
 18 
 
 255*9 
 
 67*32 
 
 2*138 
 
 807 
 
 •0794 
 
 19 
 
 257*6 
 
 69*36 
 
 2*198 
 
 785 
 
 *0815 
 
 20 
 
 259*3 
 
 71*40 
 
 2*258 
 
 765 
 
 *0837 
 
 21 
 
 260*9 
 
 73*44 
 
 2*316 
 
 745 
 
 •0858 
 
 22 
 
 262*6 
 
 75-48 
 
 2*376 
 
 727 
 
 •0879 
 
 23 
 
 264*2 
 
 77*52 
 
 2-433 
 
 709 
 
 •0900 
 
 24 
 
 265*8 
 
 79*56 
 
 2-493 
 
 693 
 
 •0921 
 
 D 
 
34 
 
 THE INDICATOR DIAGRAM 
 
 Actual 
 pressure of 
 the Steam 
 exclusive of 
 the 
 
 Atmospheric 
 
 Pressure. 
 
 Tempera- 
 ture in 
 degrees of 
 Faht. 
 
 i 
 
 1 
 
 Elastic force 
 in inches of 
 Mercury. 
 
 Cubic inches 
 of Water to 
 produce 
 1 cubic foot 
 of Steam. 
 
 Volume of 
 Steam 
 produced 
 from one of 
 Water. 
 
 Weight of 
 one cubic 
 foot of 
 Steam in lbs. 
 
 lbs. 
 
 25 
 
 i 
 
 267-3 
 
 81-60 
 
 2-552 
 
 677 
 
 •0942 
 
 26 
 
 268-7 
 
 83-64 
 
 2-610 
 
 661 
 
 •0963 
 
 27 
 
 270-2 
 
 85-68 
 
 2-670 
 
 647 
 
 •0983 
 
 28 
 
 271-6 
 
 87*72 
 
 2-725 
 
 634 
 
 •1004 
 
 29 
 
 273-0 
 
 89-76 
 
 2-787 
 
 621 
 
 •1025 
 
 30 
 
 274-4 
 
 91-80 
 
 2-842 
 
 608 
 
 •1046 
 
 31 
 
 275-8 
 
 93*84 
 
 2-899 
 
 595 
 
 •1067 
 
 32 
 
 277-1 
 
 95-88 
 
 2-958 
 
 584 
 
 •1087 
 
 33 
 
 278-4 
 
 97*92 
 
 3-015 
 
 573 
 
 •1108 
 
 34 
 
 279-7 
 
 99-96 
 
 3-074 
 
 562 
 
 •1129 
 
 35 
 
 281-0 
 
 102-00 
 
 3-130 
 
 552 
 
 •1141 
 
 36 
 
 282-3 
 
 104-04 
 
 3 188 
 
 542 
 
 •1150 
 
 37 
 
 283-6 
 
 106-08 
 
 3-248 
 
 532 
 
 •1170 
 
 38 
 
 284-7 
 
 108-12 
 
 3-304 
 
 523 
 
 •1192 
 
 39 
 
 285-9 
 
 110-10 
 
 3-361 
 
 514 
 
 •1212 
 
 40 
 
 287-1 
 
 112-20 
 
 3-415 
 
 506 
 
 •1232 
 
 41 
 
 288-2 
 
 114-24 
 
 3-465 
 
 498 
 
 •1252 
 
 42 
 
 289-3 
 
 116-28 
 
 3-526 
 
 490 
 
 •1272 
 
 43 
 
 ' 290-4 
 
 118-32 
 
 3 585 
 
 482 
 
 •1292 
 
 44 
 
 291-6 
 
 120-36 
 
 3-645 
 
 474 
 
 •1314 
 
 45 
 
 292-7 
 
 122-40 
 
 3-700 
 
 467 
 
 •1336 
 
 46 
 
 293-8 
 
 124-44 
 
 3-756 
 
 460 
 
 •1356 
 
 47 
 
 294-8 
 
 126-48 
 
 3-814 
 
 453 
 
 •1376 
 
 48 
 
 295-9 
 
 128-52 
 
 3-865 
 
 447 
 
 •1396 
 
 49 
 
 296-9 
 
 130-56 
 
 3-927 
 
 440 
 
 •1416 
 
 50 
 
 298-0 
 
 132-60 
 
 3-981 
 
 434 
 
 •1436 
 
 51 
 
 299-0 
 
 134-64 
 
 4-037 
 
 428 
 
 •1456 
 
 52 
 
 300-0 
 
 136-68 
 
 4-094 
 
 422 
 
 •1477 
 
 53 
 
 300-9 
 
 138-72 
 
 4-143 
 
 407 
 
 •1497 
 
 54 
 
 301-9 
 
 140-76 
 
 4-204 
 
 411 
 
 •1516 
 
 55 
 
 302-9 
 
 142-80 
 
 4-256 
 
 406 
 
 •1535 
 
 56 
 
 303-9 
 
 1 144-84 
 
 4-309 
 
 401 
 
 •1555 
 
PARTICULARS OP STEAM, 
 
 35 
 
 Actual 
 pressure of 
 the Steam 
 exclusive of 
 the 
 
 Atmospheric 
 
 Pressure. 
 
 Tempera- 
 ture in 
 degrees of 
 Faht. 
 
 Elastic force 
 in inches of 
 Mercury. 
 
 Cubic inches 
 of Water to 
 produce 
 1 cubic foot 
 of Steam. 
 
 Volume of 
 Steam 
 produced 
 from one of 
 Water. 
 
 Weight of 
 one cubic 
 foot of 
 Steam in lbs. 
 
 lbs. 
 
 57 
 
 304-8 
 
 146-88 
 
 4-363 
 
 396 
 
 *1574 
 
 58 
 
 305*7 
 
 148-92 
 
 4-419 
 
 391 
 
 *1595 
 
 59 
 
 306*6 
 
 150*96 
 
 4-476 
 
 386 
 
 *1616 
 
 60 
 
 307*5 
 
 153*00 
 
 4-535 
 
 381 
 
 •1636 
 
 61 
 
 308-4 
 
 155-04 
 
 4-583 
 
 377 
 
 •1656 
 
 62 
 
 309*3 
 
 157-08 
 
 4-645 
 
 372 
 
 *1675 
 
 63 
 
 310-2 
 
 159*12 
 
 4-695 
 
 368 
 
 •1696 
 
 64 
 
 311*1 
 
 L61-16 
 
 4-747 
 
 364 
 
 *1716 
 
 65 
 
 312-0 
 
 163*29 
 
 4-812 
 
 359 
 
 *1736 
 
 66 
 
 312*8 
 
 165*24 
 
 4-867 
 
 355 
 
 •1756 
 
 67 
 
 313*6 
 
 167*28 
 
 4-923 
 
 351 
 
 •1776 
 
 68 
 
 314*5 
 
 169*32 
 
 4-965 
 
 348 
 
 •1795 
 
 69 
 
 315*3 
 
 171*36 
 
 5-023 
 
 344 
 
 •1814 
 
 70 
 
 316*1 
 
 173 '40 
 
 5-082 
 
 340 
 
 *1833 
 
 71 
 
 316*9 
 
 175*47 
 
 5-127 
 
 337 
 
 *1852 
 
 72 
 
 317*8 
 
 177*48 
 
 5-189 
 
 333 
 
 *1871 
 
 73 
 
 318*6 
 
 179*52 
 
 5-236 
 
 330 
 
 *1891 
 
 74 
 
 319*4 
 
 181*56 
 
 5-300 
 
 326 
 
 •1910 
 
 75 
 
 320*2 
 
 183*60 
 
 5-349 
 
 323 . 
 
 •1929 
 
 76 
 
 321*0 
 
 185*64 
 
 5-400 
 
 320 
 
 •1950 
 
 77 
 
 321*7 
 
 187*68 
 
 5-451 
 
 317 
 
 •1970 
 
 78 
 
 322*5 
 
 189*72 
 
 5-520 
 
 313 
 
 •1990 
 
 79 
 
 323*3 
 
 191*76 
 
 5-574 
 
 310 
 
 •2010 
 
 80 
 
 324*1 
 
 193*80 
 
 5-628 
 
 307 
 
 •2030 
 
 81 
 
 324*8 
 
 195*84 
 
 5-665 
 
 305 
 
 •2050 
 
 82 
 
 325*6 
 
 197*88 
 
 5-721 
 
 302 
 
 •2070 
 
 83 
 
 326*3 
 
 199*92 
 
 5-779 
 
 299 
 
 *2089 
 
 84 
 
 327*1 
 
 201*96 
 
 5-837 
 
 296 
 
 •2108 
 
 85 
 
 327*8 
 
 204*00 
 
 5-897 
 
 293 
 
 •2127 
 
 90 
 
 331*3 
 
 214*20 
 
 6-150 
 
 281 
 
 •2218 
 
 95 
 
 334*6 
 
 224*40 
 
 6-424 
 
 269 
 
 •2317 
 
 100 
 
 338*0 
 
 234*60 
 
 6-672 
 
 259 
 
 •2406 
 
36 
 
 THE INDICATOR DIAGRAM. 
 
 The use of the above table for practical pur- 
 poses is this : — Suppose the capacity of a cy- 
 linder is 80 cubic feet, and the steam is cut off 
 from it when the piston has made ^-tli of the 
 
 complete stroke, then 
 
 = 20 cubic feet of space, 
 
 which is the amount of steam contained in the 
 cylinder during one stroke of the piston. We 
 will imagine that the full pressure of the steam 
 is 60 lbs. on the square inch, and next, that we 
 require to know the amount of water which the 
 steam in question represents ; looking at the 
 table, we see that one cubic foot of steam at 
 60 lbs. pressure is produced from 4535 cubic 
 inches of water, then 20 x 4' 535 = 90’7 cubic 
 inches of water, in the form of steam, used in 
 the cylinder for each stroke of the piston. 
 
 Next we must notice the elasticity of the 
 steam, and its temperature corresponding with 
 the pressure. Conclude, as an example, that the 
 steam is 40 lbs. on the square inch, we shall see 
 in the table that its temperature is 287T 0 . Sup- 
 pose the 40 lbs. to be the pressure in the boiler, 
 and that it loses 5 lbs. on the square inch when 
 reaching the cylinder, what will the loss of heat 
 be? Here let 40 — 5 = 35 ; then 35 lbs. pres- 
 sure, according to the table, = 281°, which shows 
 
LAW OF EXPANSION OF STEAM. 
 
 37 
 
 that 287’ 1° — 281 = 6T° loss of heat, or what is 
 lost by radiation. 
 
 Imagine next that the steam, at 35 lbs. pres- 
 sure, entering the cylinder, is cut off at ^-tli of 
 the stroke of the piston, and is exhausted at fths 
 of the stroke, what will be the reduction of the 
 pressure at the point of exhaustion ? The area 
 of the cylinder is assumed as 20 feet, the stroke 
 of the piston 4 feet ; then 20 x 1 = 20 cubic 
 feet, being the amount of steam in the cylinder 
 when the supply terminated ; the exhaustion 
 occurring when the piston has reached 3 feet. 
 Now, as the theoretical law which governs 
 the rate of the expansion of steam is, that in- 
 versely as the cubical contents of the space in 
 the cylinder for expansion increases, so will the 
 pressure of the steam in it be reduced, supposing 
 the supply to be cut off. This is founded on the 
 law discovered by Boyle and Mariotte, who 
 proved “ that the volume of a given quantity 
 of steam is inversely as the pressure it bears 
 for example, if steam, at 60 lbs. on the square 
 inch, occupying 20 cubic feet, is expanded 
 into 40 cubic feet, the pressure will be re- 
 duced to one-half, or 30 lbs. ; which converts 
 the following formula introduced by the author 
 in his paper read at the Hall of the London 
 
38 
 
 THE INDICATOR DIAGRAM. 
 
 Society of Arts, to the members, December 18th, 
 1867 
 
 “ To the cubical contents for the supply, add 
 the cubical contents for expansion; divide the 
 total sum by the cubical contents for supply ; the 
 initial pressure of the steam, divided by the 
 quotient, equals the pressure of the steam when 
 expansion terminates. Now, let A = cubical 
 contents for supply ; B = cubical contents for 
 expansion ; C = initial pressure of the steam ; and 
 x = the pressure when expansion terminates; then, 
 by the above formula, the symbols are thus ar- 
 
 ranged, x = C 
 
 which, if put into 
 
 the figures alluded to in the question, are thus — 
 A = 201 qf- 
 
 B = 40 1 20 + 40, then — = 3, and = 11-666 
 C = 35J 20 3 
 
 for the pressure of the steam when expansion is 
 concluded.” 
 
 It will, therefore, be understood that A = the 
 area of the cylinder, x the length of the stroke 
 of the piston during the supply of the steam, 
 and that B = the length from the end of A, that 
 the piston travels till exhaustion ensues, x by 
 the same area, and that C is the maximum pres- 
 sure of the steam in the cylinder. 
 
EXPANSION OF STEAM. 
 
 39 
 
 Now, on referring again to the table, we shall 
 find the relation that the volumes of the steam bear 
 to each other under the two pressures named ; at 
 35 lbs. the volume is 552, and at 11 lbs. the 
 volume is 1005, and at 12 lbs. it is 971, so that the 
 
 mean = 1005 + 971 ,988; therefore, 11-666 lbs. 
 
 2 
 
 pressure corresponds with a volume of about 996 ; 
 996 
 
 then = l - 80, which proves that the steam is 
 
 552 
 
 reduced in rarefication in the proportion of as 
 1 is to l - 80, or that the saturation of the steam is 
 1'80 times more apparent at 11666 lbs. pressure 
 than at 35 lbs. on the square inch, while the 
 temperatures are 243'4° and 281° respectively, 
 showing a reduction of 37‘6° of heat, radiation 
 excepted. 
 
 Leaving the table for the present, we now 
 direct attention to the mean pressure of the steam 
 in the cylinder from the point of admission and 
 exhaustion. The mode of arriving at this con- 
 clusion approximately is to divide the length of 
 the stroke of the piston during expansion into a 
 certain number of parts, and by the preceding 
 formula produce the sums of the pressures at 
 those points ; add the whole together, and by 
 dividing the result by the numbers of the divi- 
 sions, the mean pressure can be known ; but 
 
40 
 
 THE INDICATOR DIAGRAM. 
 
 this mode is rather approximate for the pur- 
 pose of learning the actual mean pressure. An- 
 other method is to introduce hyperbolic loga- 
 rithms into the formula, because the curve of 
 expansion is said to be hyperbolic, which we 
 have explained in the next chapter, and also 
 shown the geometrical means of producing it. 
 
 Hyperbolical Rule to produce the Sum 
 of the Mean Force or Pressure of the Steam 
 in lbs. per Square Inch for one Stroke of 
 the Piston. — 
 
 Divide the length of the stroke in inches by 
 the distance in inches the piston moves from the 
 commencement of its stroke to the point of cut- 
 ting off the steam, and divide the maximum 
 pressure by the quotient ; then add 1 to the 
 hyperbolic logarithm of the first quotient, which 
 is the number of times the steam has expanded, 
 and multiply the sum by the second quotient, 
 which is the number of lbs. to which the steam 
 is expanded, and the product is the final result. 
 Example : — 
 
 Maximum pressure of steam . . 50 lbs. 
 
 Length of stroke of piston. . . 40 inches. 
 
 Length of stroke to cut off . . 10 inches. 
 
 Then 40 in. -f- 10 = 4, the first quotient, and 
 50 lbs. — 4 = 1 2*5, the second quotient; then 
 
RULES FOR THE MEAN PRESSURE OF STEAM. 41 
 
 hyp. -log. of 4 = 1 • 386 + 1 = 2 '386, and 
 2 '386 x 12' 5 = 29'825 lbs. mean pressure. 
 
 Table of Hyperbolic Logarithms. 
 
 No. 
 
 Hyperbolic 
 
 Logarithm. 
 
 No. 
 
 Hyperbolic 
 
 Logarithm. 
 
 No. 
 
 Hyperbolic 
 
 Logarithm. 
 
 No. 
 
 Hyperbolic 
 
 Logarithim. 
 
 i 
 
 •0000 
 
 B| 
 
 1-32175 
 
 64 
 
 1-87180 
 
 11 
 
 2-39790 
 
 li 
 
 •22314 
 
 4 
 
 1-38629 
 
 6f 
 
 1-90954 
 
 12 
 
 2-48491 
 
 H 
 
 •40546 
 
 4J 
 
 1-44691 
 
 7 
 
 1-94591 
 
 13 
 
 2-56495 
 
 If 
 
 •55961 
 
 4i 
 
 1-50507 
 
 n 
 
 1-98100 
 
 14 
 
 2-63906 
 
 2 
 
 •69315 
 
 4f 
 
 1-55814 
 
 n 
 
 2-01490 
 
 15 
 
 2-70805 
 
 2'i 
 
 •*81093 
 
 5 
 
 1-60944 
 
 7f 
 
 2-04769 
 
 16 
 
 2-77259 
 
 2j 
 
 •91629 
 
 
 1-65822 
 
 8 
 
 2-07944 
 
 17 
 
 2-83321 
 
 21 
 
 1-01160 
 
 5* 
 
 1-70474 
 
 84 
 
 2-14006 
 
 18 
 
 2-89037 
 
 3 
 
 1-09861 
 
 
 1-74919 
 
 9 
 
 2-19722 
 
 19 
 
 2-94444 
 
 H 
 
 1-17865 
 
 6 
 
 1-79176 
 
 94 
 
 2-25129! 
 
 20 
 
 2-99573 
 
 
 1-25276 
 
 1 ^4 
 
 1-83258 
 
 10 
 
 2-30259 
 
 21 
 
 3-04452 
 
 There is, of course, no allowance made for the loss 
 of heat or reduction of the pressure in either of 
 the preceding or the following rules. 
 
 Professor Rankine’s Rules for the Mean 
 Pressure. — These formulae are to obtain the ratio 
 in which the mean absolute pressure will be less 
 than the initial absolute pressure, being nearly 
 exact for dry saturated steam. 
 
 /)N Pm 17 -16 r- A- 
 
 r 
 
42 
 
 THE INDICATOR DIAGRAM. 
 
 For moderately moist steam — 
 
 /o\ P m _ 1 + hyp-dog. r 
 
 W * PI r 
 
 Where r = rate of expansion ; where — PI 
 = initial absolute pressure, and P m — mean 
 absolute pressure.* 
 
 The Professor has also a geometrical method, 
 as shown by Fig. 11, and described as follows. — 
 Draw a straight line CAB, in which make 
 A B = 4 A C. Draw A D perpendicular to 
 CAB; and about C describe the circular arc B D 
 cutting A D in D. 
 
 Professor Rankine’s Diagram of the Expansion of Steam. 
 
 D E 
 
 Then in D A take E, so that ■ — shall represent 
 
 D A 
 
 the effective cut-off (and consequently =— the rate 
 
 D E 
 
 * The quantity r — is known by taking the reciprocal cf 
 
 r, and extracting the square root of it four times 
 
RULES FOR THE MEAN PRESSURE OF STEAM. 43 
 
 of expansion). At E draw E F parallel to A B. 
 E F 
 
 Then . -will be the required ratio of mean to 
 A B 
 
 initial absolute pressure, nearly. 
 
 Simpson’s Rule for the Mean Pressure. — 
 To the sum of the extreme pressure per square 
 inch, add four times the sum of the even pres- 
 sures, and twice the sum of the odd pressures ; 
 then this sum, multiplied by one-third of the 
 distance between the consecutive points at which 
 the pressures are taken, will give the work done 
 expansively per square inch of the area of the 
 piston in one stroke. 
 
 Ordinary Rule for the Mean Pressure. — 
 To the pressure of the steam at the point of cut- 
 off add the mean of the divisional pressures 
 during expansion ; the sum divided by the 
 numbers of the different pressures equals the 
 mean pressure of the steam. 
 
 Example, — 
 
 
 Maximum pressure of steam . . 
 
 . 60 lbs. 
 
 Length of stroke of piston during 
 
 
 supply 
 
 . 12 in. 
 
 Length of stroke of piston during 
 
 
 expansion 
 
 . 12 in. 
 
44 
 
 THE INDICATOR DIAGRAM. 
 
 Supply. Expansion. 
 
 Motion of piston 12 in. 3 3 3 3 
 
 Ratios of position 0 If 1 \ If 2 
 
 Initial pressures 
 
 of steam 60 48 40 34 - 28 30 
 
 Mean of divisional 
 
 pressures 54 44 37-14 32-14 
 
 Mean of initial 
 
 pressures 4245 
 
 The meaning of this table is this : — when the 
 piston travelled 12 inches, the steam was 60 lbs. 
 on the square inch ; on its moving 3 inches more, 
 which was If of the amount of the stroke for sup- 
 ply, the pressure was reduced to 48 lbs. from the 
 
 formula = 48. 
 
 1-25 
 
 The piston then moved 
 
 3 inches more, this position being If of the length 
 
 60 
 
 for supply, and again the formula — = 40 ; an- 
 
 I.D 
 
 other 3 inches advance, and If of the supply 
 stroke was made, and the pressure was then 
 
 known from -^2= = 34'28 ; and, lastly, the 12 
 
 inches were completed, and the ratio was twice ■ 
 
 n a 
 
 then— = 30 being the pressure of the steam at 
 
 the point of exhaustion. Next comes the appli- 
 cation of the rule, 60 + 48 + 40 + 34-28-1-30= ~ 
 212-28, then 212-28 — 5 = 42*45, which proves 
 
RULES FOR THE MEAN PRESSURE OF STEAM. 45 
 
 that the mean of initial pressures at the five points 
 from the beginning of the stroke to the point of 
 exhaustion equals 42 - 45 lbs. The mean divi- 
 sional pressures are given more for comparison 
 than use in the formulae. 
 
46 
 
 THE INDICATOR DIAGRAM. 
 
 CHAPTER IV. 
 
 THE THEORETICAL GEOMETRY OF THE INDICATOR 
 DIAGRAM. 
 
 It will be remembered that in Chapter I. we 
 explained the arrangement of the indicator and 
 its use. Chapter II. we devoted to the mecha- 
 nical questions of the gear, and in the preceding 
 chapter to this we dwelt on the matters of atmo- 
 spheric and steam pressures in connection with the 
 steam-engine ; we have not therefore yet touched 
 on the theory of the form of the diagram, which 
 subject is in its proper place as this chapter. 
 
 It has been proved for some years past that 
 the true curve the indicator pencil should trace 
 on the card, when the steam is expanding in the 
 cylinder, is hyperbolical ; and as the remainder 
 of the pencilled figure is a portion of a parallel- 
 ogram, the curve is the only geometrical question 
 of any note in it. As a proof of this, we intro- 
 duce Fig. 12. 
 
 The explanation of this is, that when the 
 pencil was stationary, the atmospheric line was 
 described straight, because there was no steam 
 
THEORETICAL INDICATOR DIAGRAM. 47 
 
 Fig. 12. 
 
 A practical Definition of the Theoretical Form of an Indicator Diagram. 
 
 pressure to start the indicator piston ; but when 
 the steam acted on it, the pencil rose vertically for 
 the length or height of A . At this point, it must 
 be remembered, the motion for the indicator barrel 
 commenced, and therefore, as the pencil was held 
 still by the steam acting on the piston during 
 the supply, again a straight horizontal line, for 
 the length of B, was traced ; here the steam was 
 cut off from the cylinder, and the expansion com- 
 menced, which of course gradually reduced the 
 pressure; and as the card-barrel was still turn- 
 ing, the pencil described a curve as it descended, 
 until reaching the atmospheric line. Here the 
 card-barrel stopped, and the pencil continued to 
 fall continuously at right angles to the steam line 
 B, until the vertical line D was traced, which indi- 
 cated the amount of vacuum attained in the 
 cylinder ; the pencil then became stationary, for 
 the atmospheric pressure forced the indicating 
 
48 
 
 THE INDICATOR DIAGRAM. 
 
 piston down and kept it in that position while the 
 vacuum lasted, as firmly as the steam held it up 
 while the steam pressure remained, so that the 
 pencil is always still when the full pressures are 
 on, either under or over the piston. When the 
 pencil stopped at the lower end of the line D 
 the barrel began to turn, but in the opposite 
 direction, and thus the line E was traced, at the 
 end of which the barrel again stopped, and when 
 the steam entered the cylinder the pencil in- 
 stantly rose, and completed the diagram by form- 
 ing the line F. 
 
 The motions for the pencil are therefore thus 
 arranged : A, F, and D are instantaneous vertical 
 movements ; C is a gradual descent ; while B 
 and E have no motion. 
 
 It is also evident that A is admission, B 
 supply, C expansion, and often a portion of it — 
 before joining the atmospheric line — is exhaustion 
 also. D sudden exhaustion, E continuous steady 
 exhaustion, and F re-admission. Then, by know- 
 ing this, we can learn also that, while there is 
 admission A, the pencil moves, as indicated by 
 the arrow, and stops at the top end ; the 
 supply B is fixed, or a stationary position for the 
 marker, therefore there is no arrow ; C, the ex- 
 pansion, is shown by the arrows as being pro- 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 49 
 
 duced by the pencil gradually descending : D, 
 the sudden exhaustion, is where the pencil stopped 
 at the end of C, and fell at once in the direction 
 of the arrow, to the line E ; it then became 
 stationary, therefore the arrow is omitted again , 
 after this E, continuous exhaustion, was traced ; 
 when F, re-admission, shows by the arrow that the 
 pencil rose vertically, as it did at A. This proves 
 also that the lines B and E are portions of a 
 circle ; D, F, and A, vertical straight lines ; and 
 C, a hyperbolical curve. 
 
 The theory of the indicator diagram is thus 
 proved to be the simple fact that 'pressure under 
 the indicating piston causes the pencil to rise ; whether 
 that pressure is steam, water, or air, it matters 
 not, as the force is the main agent ; and that 
 immediately the decrease of pressure occurs, the 
 pencil descends. So that if the young engineer 
 will note this in his memory, he will save him- 
 self, and others he is professionally connected 
 with, a vast amount of trouble. 
 
 Our next step is the explanation of the hyper- 
 bolical curve of expansion, which Watt agreed to 
 be correct at the time he invented the indicator ; 
 his theory is described by Mr. J. Scott Bussell, 
 M.A., Engineer, in his work on the Steam 
 Engine, as far back as 1841. 
 
 E 
 
50 
 
 THE INDICATOR DIAGRAM. 
 
 “Let ABCD (Fig. 13) represent a section of 
 the cylinder of a steam-engine, and EF the sur- 
 face of its piston. Let us suppose that the steam 
 was admitted while EF was in contact with AB, 
 
 Fig. 13. 
 
 Watt’s Method of Illustrating the Expansion of Steam. 
 
 and that as soon as it had pressed it down to the 
 situation EF, the steam-cock is shut. The steam 
 will continue to press it down, and, as the 
 steam expands, its pressure diminishes. We may 
 express its pressure (exerted all the while the 
 piston moves from the situation AB to the situa- 
 tion EF) by the line EF. If we suppose the 
 elasticity of the steam proportional to its density, 
 as is nearly the case with air, we may express 
 the pressure on the piston in any other position 
 such as IvL or DC, by L l and D c, the ordinates 
 of a rectangular hyperbola E Ic, of which AE AB 
 are the asymptotes, and A the centre. The 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 51 
 
 accumulated pressure during the motion of the 
 piston from E F to DC will he expressed by the 
 area EFcDF, and the pressure during the whole 
 motion by the area ABFcDA 
 
 “ Now it is well known that the area EFcDF is 
 equal to ABFE multiplied by the hyperbolic 
 AD AD 
 
 logarithm of —— = L — — , and the whole area 
 AE AE 
 
 ABEcDB is = ABFE x (l + L—\ 
 
 V AE/ 
 
 “Thus let the diameter of the piston be 24 
 inches, and the pressure of the atmosphere on 
 a square inch be 14 lbs. ; the pressure on the 
 piston is 6333 lbs. Let the whole stroke be 
 6 feet, and let the steam be stopped when the 
 piston has descended 18 inches, or 1*5 feet. The 
 
 hyperbolic logarithm of is F3862943. There- 
 fore the accumulated pressure ABEcDB is = 
 6333 x 2-3862943 = 15112 lbs. 
 
 “ As few professional engineers are possessed of 
 a table of hyperbolic logarithms, while tables of 
 common logarithms are, or should be, in the 
 hands of every person who is much engaged in 
 mechanical calculations, let the following method 
 be practised : — Take the common logarithm 
 
52 
 
 THE INDICATOR DIAGRAM. 
 
 of — - and multiply it by 2 ’30 2 6, the product is 
 AE 
 
 AD 
 
 the hyperbolic logarithm of — -. 
 
 AE 
 
 “The accumulated pressure while the piston 
 moves from AB to EF is 6333 x 1 , or simply 
 6333 lbs. Therefore the steam while it ex- 
 pands into the 'whole cylinder adds a pressure 
 of 8781 lbs. 
 
 “ Suppose that the steam had got free admis- 
 sion during the whole descent of the piston, the 
 accumulated pressure would have been 6333 x 4, 
 or 25332 lbs.” 
 
 Now accepting this hypothesis as correct, 
 which it is in the main, but subject of course to 
 various deviations of importance, to which we 
 shall refer as we proceed, we next direct attention 
 to a practical demonstration of the relation that 
 the indicator diagram bears to the engine 
 cylinder. 
 
 The present general practice to define this has 
 been to make a section of the cylinder, and draw 
 an outline of the diagram within its limits. 
 Now nothing possible can be more faulty than 
 this method, because the diagram in practice is 
 never formed to scale, so that its height equals 
 the diameter of the cylinder, and its length equal 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 53 
 
 to the stroke of the piston. It becomes then 
 important to remove this erratical mode, and 
 introduce a correct one. But before we illustrate 
 this we will dwell a little on the matter, as a 
 discussion. 
 
 First. What is the meaning of the height of 
 the indicator diagram ? It is the extent that the 
 pencil moves up or down according to the pres- 
 sure on the piston, which movement above the 
 atmospheric line depicts steam pressure, and 
 below it natural pressure or atmospheric. 
 
 Second. What is the definition of its length ? 
 Of course a direct answer to this is — the limit of 
 the motion given by the card-barrel ; but this is 
 not all ; it involves also that, inasmuch as the 
 movement of the barrel is proportionate to the 
 stroke of the piston, the length of the diagram re- 
 presents that stroke. Then if the length of the 
 movement of the barrel has nothing to do with 
 the pressure in the cylinder, which it has not, 
 to suppose that the height and length of the 
 diagram, taken at the same scale, represents the 
 cylinder in its correct proportion is fallacious in 
 the extreme. 
 
 Third. Then what is the correct way of repre- 
 senting the connection of these matters ? It is 
 to know that, as the horizontal length of the 
 
54 
 
 THE INDICATOR DIAGRAM. 
 
 diagram above the atmospheric line indicates the 
 greatest lineal equal pressure in the cylinder, it 
 must bear a definite relation to the pressure of 
 the steam only, and not therefore to the diameter 
 of the cylinder at all ; simply because the pencil 
 is held by the pressure, and that the force would 
 be the same in a large as in a small cylinder, if 
 it were supplied from the boiler proportionally, 
 which of course it always is ; hence this axiom — 
 the indicator diagram, in practice, represents the 
 action of the steam in the cylinder ; its properties 
 are that the height above the atmospheric line 
 represents the greatest pressure, without relation 
 to the diameter of the cylinder ; but its length is 
 a direct proportion to the stroke of the piston, 
 ancl that the scale for the height bears no refer- 
 ence to that for the length. 
 
 If, however, it is preferred to arrange the theo- 
 retical diagram within the cylinder proportion- 
 ately to it, the method is as illustrated by Fig. 14. 
 
 Here S equals the stroke of the piston, the 
 cubical contents of the steam passage, and 
 piston clearance, and D the diameter of the 
 cylinder, at a scale of £ inch = 1 foot ; s is 
 the length of supply-steam line, the steam being 
 cut off at one-third of the stroke ; HC is the 
 hyperbolical curve of expansion, and AL the 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 55 
 
 atmospheric line. The production of HC is of 
 course the only purpose in question, and it is 
 thus obtained : — The spaces 0 to T, 1 to 2, and 
 2 to 3 are each equal to s. The total pres- 
 sure of D is 60 lbs. on the square inch ; the 
 
 Fig. 14. 
 
 D 
 
 Theoretical Indicator Diagram within a Cylinder, the Diameter = 1), and 
 the Length = S. 
 
 height of the first ordinate is equal to D ; 
 60 
 
 the second equals -^-p = 40 in., because it is 1|- 
 of 0 to 1 from 0 ; then, as 2 is 2 of 1 to 0 from 
 
 0, its height is 
 
 60 
 
 2 
 
 30 in. ; next, 2| equals 
 
 2 ^- = 24 in., and 3 is 20 in. drawn from — =20, 
 
 which, of course, is the lowest pressure; then, 
 where the horizontal lines and 4 inter- 
 
 sect with the ordinates 1^, 2, and 3, are the 
 
56 
 
 THE INDICATOR DIAGRAM. 
 
 points through which the line HC is drawn to 
 join the top of the ordinate 1. 
 
 It is obvious that the principle of this method 
 is founded on the law of Mariotte, which is, “ that 
 the volume of a given quantity of steam is in- 
 versely as the pressure it bears,” as we expressed 
 in page 37. Similarly, therefore, in all cases, 
 if D is divided by the relative position of any 
 ordinate to the length of s, the quotient equals 
 the height of that ordinate ; then the height of 
 [1 = D], [H = Dx2t 3], [2 = D -r- 2], 
 [2^ = D x 2 -T- 5], and [3 = D 3] ; therefore, 
 irrespective of any pressure being taken into con- 
 sideration, the line HC can he drawn correctly. 
 But suppose the pressure is considered, it will be 
 expressed thus : — 
 
 Positions of the Ratios. 
 
 piston in relation 112 2 3 
 to its stroke. . . 1 g ^5 3 3^5 3* or s t r °ke. 
 
 Pressure of the 
 
 steam in lbs. per 
 
 square inch at Pressures . 
 
 these points . . 60 60 40 30 24 20, exhaustion. 
 
 Or it may be expressed in this manner, — 
 
 Pressures . 
 
 Pressure of steam ... 60 60 40 30 24 20 lbs. 
 
 Lengths of the ordinates Patios. 
 
 in proportion to the dia- 2 12 1 
 
 meter (D) of the piston. 1 1 - - - 
 
 O 2 D o 
 
THEORETICAL INDICATOR DIAGRAM. 57 
 
 As a matter of comparison, we next introduce 
 Fig. 15. This illustrates that the proportions 
 
 Fig. 15. 
 
 Theoretical Indicator Diagram within a Cylinder, the Diameter = D, and 
 the Length = S. 
 
 of D and S are as before ; but the length of 5 is 
 much less, or ^ of S ; then, as 5 in Fig. 14 was 
 ^ of S, and the main ordinates 1, 2, and 3 were 
 repetitions of position, so are the ordinates 1, 2, 
 3, 4, and 5 equidistant as 0 to 1 in Fig. 15. 
 Here, also, as the positions of the ordinates are 
 whole numbers, so their heights are even frac- 
 tions of D, in this manner : — 
 
 Positions of the ordinates 
 or piston, as numbered 
 Proportions of their posi- 
 tions to S, or stroke of 
 the piston 
 
 Pressures of the steam 
 in lbs 
 
 Numbers . 
 
 0 1 2 3 4 5, end. 
 
 0 1 
 
 Ratios . 
 
 1 1 1 
 
 2 3 4 
 
 Pressures. 
 60 60 30 20 15 
 
 lexhaus- 
 ’ ) tion. 
 
58 
 
 THE INDICATOR DIAGRAM, 
 
 This defines that the exhaustion of the steam 
 ensues at a pressure of only 12 lbs. on the square 
 inch, by cutting off at -J- of S the stroke of the 
 piston; whereas in Fig. 14 the lowest pressure 
 was nearly double at the same point, or 20 lbs. 
 
 To further elucidate this matter, we illustrate 
 another diagram by Fig. 16. Here the diameter 
 
 Fig. 16. 
 
 Theoretical Indicator Diagram within a Cylinder, the Length = S, and 
 the Diameter — D, 
 
 Fig. 17. 
 
 Theoretical Indicator Diagram within a Cylinder, Length = S, and Diameter = D. 
 
THEORETICAL INDICATOR DIAGRAM 
 
 59 
 
 D is 60, but the stroke S is 72 instead of 36, as 
 in Figs. 14 and 15. The length of 5 being again 
 jr of S, all the ordinates in length and position 
 are precisely as before, with the same ratios and 
 pressures. As a comparison, Fig. 17 is intro- 
 duced, where s is ^ of S, and D 60, while S is 
 72, their ordinates and their ratios being figured 
 as in Fig 15. The table in page 57 applies in 
 this case also. 
 
 There not being much difference in the lengths, 
 and none with the diameter D in the two last ex- 
 amples, we next illustrate one with a greater 
 contrast by Fig. 18. 
 
 Fig. 18. 
 
 Theoretical Indicator Diagram within a Cylinder, the Length = S, and the 
 Diameter = D. 
 
 Here D is 60, and S is 108, or three times of 
 s, as in Fig. 14 ; but as the cut-off, however, is 
 of the same ratio, the ordinates and pressures 
 are similar also. 
 
60 
 
 THE INDICATOR DIAGRAM. 
 
 Next, Fig. 19 depicts a contrast with Fig. 15 ; 
 here, too, the length of s is the same in pro- 
 portion to S as in the second example, and all 
 the other matters here are as there. 
 
 Fig. 19. 
 
 Theoretical Indicator Diagram within a Cylinder, the Length = S, and the 
 Diameter = D, 
 
 The main purpose for the theoretical diagram 
 has now been fully illustrated ; which, as we have 
 stated before, is, “ a definition of the curve of 
 expansion for example, if the curves in Figs. 
 
 14 and 18 are compared, a difference is apparent, 
 although the pressures indicated are alike. Next 
 compare Figs. 15 and 19, and a similar relation 
 occurs with Figs. 14 and 16, also with Figs 
 
 15 and 17. 
 
 It must be understood that the lengths of the 
 diagrams depicted as S, or termed as equal to the 
 stroke of the piston, include also the clearance 
 and the cubical contents of the steam passage 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 61 
 
 from the end of the cylinder to the slide-valve 
 facing, and that unless this is added to the stroke, 
 the theoretical diagram will be indefinite. 
 
 As the comparisons of indicator diagrams are 
 not only interesting, but also instructive, we 
 illustrate a series in one parallelogram by Fig. 20. 
 
 Fig. 20. 
 
 Comparative Theoretical Indicator Diagram illustrating Several Points of 
 Cut-off. 
 
 These are all formed on the Mariotte law, and the 
 vertical and horizontal dotted lines illustrate the 
 points of intersections through which each curve 
 is traced. The pressures at the end of the 
 diagram are known from the formula = 
 initial pressure 
 grade of expansion ’ 
 
 for example, the first curve is commenced 
 at gw of the total length ; and as the height 
 is 36, the pressure at the other extremity 
 
62 
 
 THE INDICATOR DIAGRAM. 
 
 = = 1 '8 lbs. on the square inch at the ter- 
 
 mination of expansion ; then, as the point is 
 twice the distance of from the beginning, the 
 pressure of the steam at the other end is twice of 
 that below it, or 3' 6 lbs ; and as ^ curve is in the 
 same ratio, dr double of yy, the pressure above 
 it is doubled also, or 7*2, and so on by the 
 same formula the other pressures are obtained ; 
 indeed, the formation of the curves depends 
 entirely on the proportion of the length of the 
 supply line to the entire length of the diagram, 
 as we have already stated. 
 
 Our next consideration is, what is the best 
 proportion for an indicator diagram ? for we have 
 condemned the method of considering the dia- 
 meter of the cylinder as any function of the 
 matter, because, as we have already explained, 
 the height of the diagram represents the pressure 
 only, and not any other limit. The next way to 
 arrive at the solution of this question is to reason 
 about the facts on which it bears. 
 
 First, the forward stroke of the piston is theo- 
 retically supply steam and its expansion ; and 
 the backward stroke, exhaustion and compression 
 on the same side of the piston. This, then, is 
 what the indicator diagram shows above and 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 63 
 
 below the atmospheric line ; but if the engine is 
 non-condensing, of course these features are indi- 
 cated above that line, as shown by Fig. 20, where 
 the lowest pressure is 1’8 lbs. and the base line 
 zero. 
 
 Secondly, the speed and travel of the pencil is 
 due to the pressure of the steam and motion of 
 the barrel. Then, if the pressure shifts or holds 
 the pencil, the longer the act of tracing or mark- 
 ing occurs the more time is given for the opera- 
 tion. We are not forgetting here, either that the 
 speed of the paper will be greater with a large 
 than a small barrel, but remembering that with 
 the greater size there must be a longer travel for 
 the pencil or marker, and thus the undulations 
 of the indicator piston will be more truthfully 
 illustrated than with a lesser travel. The matter 
 indeed is really very simple if its aspect is pro- 
 perly viewed ; for, after all, it is but a pencil 
 either shifting up and down or still on the paper, 
 and the more lineal travel given for the 'pencil the 
 better will its motion be illustrated. For example, 
 if the indicating piston is jerky in its movement, 
 we require the cause of it ; then, if the pencil’s 
 travel is short, the indication is reduced to the 
 lowest ebb, instead of being fully and properly 
 depicted, as it would be if the travel were longer. 
 
64 
 
 THE INDICATOR DIAGRAM. 
 
 The length of the diagram should therefore 
 bear some proportion to the velocity of the piston 
 in its strokes per minute ; but this ratio cannot 
 be constant, because the speed of the piston in 
 feet is in proportion to the length of its stroke 
 and the velocity, while the length of the diagram 
 does not take the speed in feet into consideration. 
 We have therefore arranged this matter for 
 future practice as follows, which will doubtless 
 be recognized as an improvement : — ■ 
 
 No. of strokes of the 
 
 piston per minute ' 100 200 300 400 500 600. 
 
 Lengths of the indicator 
 
 diagrams in inches .5 6 7 8 9 10. 
 
 Diameters of the paper- 
 
 barrels in inches . 2 \ 2 T 9 F 2-| 3 T 3 g- 3 T 9 g- 3^f. 
 
 Professor Rankine's Explanation of Theoretical 
 Steam Indicator Diagrams. 
 
 In Fig. 21 let A F Gf B H K represent the in- 
 dicator diagram of any steam-engine, F being the 
 point of admission, Gr that of cut-off, B the point 
 of release, H the end of the forward stroke, and 
 K the point where cushioning (if any) begins. 
 
 Let the horizontal line through C be the zero 
 line of absolute pressures, so that heights above 
 that line represent absolute pressures of the 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 65 
 
 steam ; B C, for example, being the absolute 
 pressure at the instant of release. 
 
 Fig. 2i, 
 
 P C 
 
 Theoretical Indicator Diagram by Professor Rankin e. 
 
 Through B draw B A parallel to the zero line ; 
 and, if necessary, set back the point A, so as to 
 allow for clearance, in order that the length A B 
 may represent the whole volume of steam con- 
 tained in the cylinder and ports at the instant of 
 release. From A let fall the perpendicular A 0 
 upon the zero line. Then horizontal distances 
 on the diagram from the vertical line 0 A F re- 
 present volumes occupied by the steam in the 
 cylinder. 
 
 In expressing the pressures and volumes of the 
 steam such units ought to be adopted that the 
 
 F 
 
66 
 
 THE INDICATOR DIAGRAM. 
 
 product of a pressure and volume may be a 
 certain number of units of work — say, foot- 
 pounds. For easmple, if volumes are expressed 
 in cubic feet, pressures should be expressed in 
 pounds on the square foot ; being 144 times the 
 corresponding pressures in pounds on the square 
 inch. If pressures are expressed in pounds on 
 the square inch, volumes should be expressed in 
 prisms one foot long by one inch square ; the 
 volume of such a prism being of a cubic foot. 
 
 In the Fig. 21, Gr 1 represents an expansion 
 curve for steam gas in a non-conducting cylinder ; 
 the absolute pressure varying inversely as the 
 thirteenth power of the tenth root of the volume, 
 or nearly so. 
 
 G 2 represents an expansion curve for saturated 
 steam, dry on its admission , in a non-conducting 
 cylinder ; the absolute pressure varying inversely 
 as the tenth power of the ninth root of the 
 volume, or nearly so. 
 
 Neither of the preceding cases can be perfectly 
 realized in practice ; and, therefore, they only 
 represent limits which practical results may ap- 
 proach but not attain. 
 
 G 3 represents an expansion curve for saturated 
 steam , dry on its admission and during its expan- 
 sion, being prevented from partially liquefying 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 67 
 
 by means of a supply of heat through the cylinder. 
 The absolute pressure varies inversely as the 
 seventeenth power of the sixteenth root of the 
 volume, or nearly so. 
 
 This is, probably, the best result actually 
 attainable in practice with steam that is not 
 superheated. 
 
 G4 represents a common hyperbola, the pres- 
 sure varying inversely as the volume simply. 
 To produce such a curve the steam must contain 
 a little liquid water on admission, or immediately 
 afterwards, and that water must be evaporated 
 during the expansion by heat drawn from the 
 cylinder. This is the form of diagram on which 
 calculations are most commonly based, and differs 
 but little from the preceding. 
 
 G 5 represents an expansion curve, in which 
 the pressure varies inversely as the fifteenth 
 power of the sixteenth root of the volume ; being 
 assumed as an example of the effect of the pre- 
 sence of a still greater quantity of liquid water 
 during the admission, which is evaporated during 
 the expansion. 
 
 Then if we calculate in a series of particular 
 cases by the exact formulae of thermodynamics, 
 a quantity which may be called the heat of release, 
 consisting of the total heat, sensible and latent, 
 
68 
 
 THE INDICATOR DIAGRAM. 
 
 of the volume of steam A B at the absolute 
 pressure C B, together with the quantity of heat 
 which that, steam would carry off from the 
 cylinder and valve ports, supposing it to expand 
 down to the back pressure without liquefaction, 
 that quantity is found to be given approximately 
 to the accuracy of about 1 per cent, by the 
 following rule : — 
 
 Rule for the Heat of Release. 
 
 Multiply the product of the absolute pressure 
 and volume of the steam at the point of release 
 by 16 for a condensing engine, or by 15 for a 
 non-condensing engine. The result will he the 
 mechanical equivalent of the heat of release 
 nearly. 
 
 (This may, if desired, be reduced to ordinary 
 thermal units by dividing by Joule’s equivalent, 
 viz., for foot-pounds and Fahrenheit’s scale, 772 ; 
 for foot-pounds and the centigrade scale, 1390; 
 kilogrammes and the centigrade scale, 424.) 
 
 To represent the preceding rule graphically, in 
 Fig. 21, produce AB to D, making AD = 16 AB 
 for a condensing engine, or 15 A B for a non- 
 condensing engine ; complete the rectangle 
 A D E 0 ; then, inasmuch as the area of the 
 rectangle A B C 0 represents the product of the 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 69 
 
 absolute pressure BC and volume AB of the 
 steam at release, the area of the rectangle ADEO 
 (=16 or 15 AB BC) represents the heat of 
 release in units of work. 
 
 The area ABHK of that part of the steam 
 diagram which lies below the pressure of release 
 represents a portion of heat saved out of the heat 
 of release by conversion into mechanical work ; 
 and the area A F G B of that part of the steam 
 diagram which lies above the pressure of release 
 represents an additional expenditure of heat, all 
 of which is converted into work. Hence the 
 following rules : — 
 
 Rules for the Expenditure and Disposal 
 of the Heat (in Units of Work). 
 
 Whole heat expended on the steam = area 
 ADEO + area AFGB. 
 
 Heat converted into mechanical work = area 
 AFGrBHK = area AFGB + area ABHK. 
 
 Heat rejected with the exhaust steam = area 
 ADEO — area ABHK. 
 
 Rule for the Efficiency of the Steam. 
 
 Efficiency of the steam = 
 
 area AFGB H K 
 
 area A D E 0 + area AFGB" 
 
70 
 
 THE INDICATOR DIAGRAM. 
 
 Rules as to Calculation of Theoretical 
 Steam Diagrams. 
 
 Supposing the absolute pressure of admission 
 given, the absolute pressure of release is easily 
 calculated for the common hyperbola G4, by 
 dividing the absolute pressure of admission by 
 the ratio of expansion. When the expansion 
 curve deviates but little from a common hyper- 
 bola (as G2, G3, and G5), it is often more con- 
 venient to take as a first approximation the 
 pressure of release as calculated for a common 
 hyperbola, and then to subtract (for such curves 
 as G2, or G3) or add (for such curves as G5) a 
 correction computed as follows : — Multiply to- 
 gether the approximate pressure of release, the 
 hyperbolic logarithm of the ratio of expansion, 
 and the fraction by which the index of the power 
 of the density to which the pressure is propor- 
 tional exceeds or falls short of unity. For G2 
 the index exceeds unity by ^ ; for G3, by T y ; 
 for G5, it falls short of unity by T (j. 
 
 When the pressure of release is known by ob- 
 servation on an actual diagram, to calculate the 
 index of a curve of the hyperbolic class which 
 approximates to the actual expansion curve ; from 
 the difference of the logarithms of the pressures 
 of admission and release subtract the difference 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 71 
 
 of the logarithms of the volumes of admission 
 and release ; the remainder will be the index 
 required. 
 
 Should the only table of logarithms at hand be 
 one containing hyperbolic logarithms of rates of 
 expansion, the same question may be approxi- 
 mately solved as follows : — Divide the absolute 
 pressure of admission by the ratio of expansion ; 
 then, with the quotient as a divisor, divide the 
 actual absolute pressure of release, and take the 
 difference between the new quotient and 1. 
 Divide that difference by the hyperbolic logarithm 
 of the ratio of expansion : the quotient will be 
 the fraction by which the required index exceeds 
 or falls short of 1, according as the pressure 
 diminishes faster or slower than the density. 
 For example, suppose absolute pressure of admis- 
 sion = 40, ratio of expansion 5, actual absolute 
 pressure of release 8-848. Then 40 5 = 8 ; 
 
 ^^ = 1406; hyp. log. 5 = 1-609 ; °' IQ6 = — , 
 8 n s 1-609 16’ 
 
 which is to be subtracted from 1, because the 
 pressure falls slower than the density ; finally, 
 1 — y-g- = yf, index required. 
 
 The area A F G B, above the pressure of re- 
 lease, when the expansion curve is the common 
 hyperbola G4, can he found either by the well- 
 
72 
 
 THE INDICATOR DIAGRAM. 
 
 known formula, absolute pressure of admission x 
 volume of admission x hyperbolic logarithm of 
 the ratio of expansion, or by drawing the curve 
 accurately to scale (which is very easy) and 
 measuring the area by ordinates or by the plani- 
 meter. 
 
 The corresponding area for other expansion 
 curves is found by formulae which are given in a 
 previous note. But when the expansion curve 
 deviates but little from a common hyperbola, it is 
 often more convenient to take as a first approxi- 
 mation the area A F G B as for a common hyper- 
 bola ; then to calculate a correction as follows : — 
 take the difference between unity, and half the 
 hyperbolic logarithm of the ratio of expansion ; 
 multiply that difference by the fraction by which 
 the index of the power of the density to which 
 the pressure is proportional differs from unity, 
 and by the approximate area ; and then to apply 
 that correction as follows : — 
 
 
 Hyp. Log. of Expansion. 
 
 
 Less than 2. 
 
 Greater than 2. 
 
 For such curves as G2, G3, . 
 
 acid. 
 
 subtract. 
 
 „ „ G5, .... 
 
 subtract. 
 
 add. 
 
THEORETICAL INDICATOR DIAGRAM. 
 
 73 
 
 If the hyperbolic logarithm is 2, no correction is 
 needed. 
 
 For example, suppose absolute pressure of ad- 
 mission, 40 ; volume of admission, 25 ; ratio of 
 expansion, 5 ; index, ; then because hyp. log. 
 5 = T609, we have as a first approximation to 
 the area AFGB, 40 x 25 x 1*609 = 1609. Then 
 
 to compute the correction we have 1 — ^ = 
 
 0*1955 ; and 0*1955 x ^ x 1609 = 20, correc- 
 tion required ; and this is to be subtracted ; 
 therefore 1609 — 20 =1589, corrected area. (By 
 the more exact process the area is 1587, the dif- 
 ference being practically inconsiderable.) 
 
 The area of the part of the diagram ABHK 
 that lies below the pressure of release is in every 
 case the product of the volume at release, A B, 
 and the excess of the absolute pressure at release, 
 B C, above the absolute hack-pressure, H C. — 
 Appeared in the Engineer, Vol. 21. 
 
74 
 
 THE INDICATOR DIAGRAM. 
 
 CHAPTER y. 
 
 THE PRACTICAL GEOMETRY OF THE INDICATOR 
 DIAGRAM. 
 
 Having in the preceding chapters described the 
 arrangement of the indicator, how to use it 
 properly, and the facts to be learnt from that 
 operation, we now enter on the test of the 
 veracity of an indicator diagram ; for it is obvious 
 that that figure can be subjected to various 
 methods of production : it may be so imperfectly 
 taken that it does not indicate the action of the 
 steam or imperfection of the valve and gear, 
 while, on the other hand, it may be cooked or 
 shaped to suit the mind of the operator, or please 
 the eye of the critic, so much so that it is made 
 too perfect, or, what nature has failed in, art has 
 supplied.. To guard against all this, then, we must 
 resort to a practical geometrical test, which can- 
 not fail to show the truth, let it be what it may. 
 
 As we shall make use of the technical terms 
 “ lead, full-steam, and cut-off,” in our description 
 of the present matter, we will commence with 
 an explanation of their meaning. 
 
 Lead is the position of the slide-valve to allow 
 
GEOMETRY OF THE INDICATOR DIAGRAM. 75 
 
 a certain amount of steam to enter the cylinder 
 before the piston completes its stroke, so that the 
 motion of the valve is said to be in advance of 
 that of the piston on the return stroke of the 
 latter. 
 
 Full-Steam is the position of the valve when 
 it is at its full stroke, and the piston continuing 
 its motion in the same direction as before that. 
 
 Cut-off is the position of the valve when it 
 has returned and closed the supply-port or open- 
 ing, and the piston is advancing as before, but the 
 valve moving in an opposite direction. 
 
 We know, therefore, that the slide-valve regu- 
 lates the flow of the steam into and from the 
 cylinder, and consequently the proportions of 
 the valve, ports, and laps must determine the form 
 of the indicator diagram at certain points. 
 
 We must next consider the mechanical action 
 of the valve, which is this : — When the piston of 
 an engine steam-cylinder is at its full stroke, the 
 slide-valve has a lead ; or its position is so that the 
 supply-port in the cylinder is opened for a given 
 width, and the steam, therefore, is admitted be- 
 fore the piston has completed its stroke. The use 
 of the lead is to provide for what is termed the 
 concussive action of the piston, and act as a 
 spring, and, therefore, when a slide-valve has no 
 
76 
 
 THE INDICATOR DIAGRAM. 
 
 lead on the piston, the tremor in the cylinder 
 ends betrays the fact ; so far is this certain that 
 even, with considerable clearance, with a quick- 
 speed engine the covers rise and fall perceptibly 
 at the centre. Next, then, presume the valve to 
 have opened the supply-port for full steam, it is 
 now at the end of its stroke, but returns and 
 closes the supply-port while the piston is still 
 moving in the same direction as before. The steam 
 is here cut off from the cylinder, and the steam 
 in the boiler is allowed to accumulate for a time 
 — this is the advantage of an early cut-off: time 
 is allowed for evaporation in the boiler, and a 
 saving of steam results by using the smallest 
 quantity possible during each stroke of the piston, 
 and producing sufficient power from expansion. 
 Suppose now, for example, an engine has a 3 ft. 
 stroke of piston, and the valve cuts off when the 
 piston reaches nine inches, or one-fourth, the 
 cylinder is filled to one-fourth of its capacity, or 
 an amount of steam to that extent is taken from 
 the boiler at each first quarter- stroke of the 
 piston. Again, presume the same stroke of 
 piston and diameter of cylinder, but the cut-off 
 to be one-half, or eighteen inches from the end 
 of the stroke, double the capacity of cylinder is 
 open to the boiler — but only about one-half of the 
 
GEOMETRY OF THE INDICATOR DIAGRAM. 77 
 
 time allowed more than before for the steam to 
 escape from the boiler, although nearly double 
 the amount of the steam is admitted at each 
 first half-stroke of the piston with this latter 
 grade than with the former. 
 
 So much for the supply ; now for expansion. 
 When the steam is in the cylinder, and the valve 
 has closed the port, the steam is expanding, 
 simply because the piston is advancing, and 
 therefore more space is allotted for the steam. 
 Now as the cut-off is determined by the outer 
 edge of the valve, so is the time of expansion by 
 the inner edge, or on the exhaust side ; so that 
 it is absolute that the amount of expansion is due 
 to the time that the valve is traversing over the 
 port, and keeping it closed ; therefore the outside 
 lap, or breadth of valve cover, not only settles 
 the cut-off, but also the amount of expansion. 
 
 The exhaustion next occurs when the valve has 
 opened the port with its inner edge, and continues 
 until the inner edge of the valve returns and 
 closes the port at that end of the cylinder. 
 
 Lastly, we have compression, so termed because 
 if there is any steam or air in the cylinder it 
 cannot escape, neither will the vacuum be im- 
 paired — perfection of the valve surface to be 
 accepted — and the piston is driving all before it ; 
 
78 
 
 THE INDICATOR DIAGRAM. 
 
 besides, the valve has closed the port until the 
 “ lead ” occurs, when the release is met by the 
 volume of the steam from the boilers. Evidently, 
 therefore, if the steam is governed by the valve, 
 and the indicator is open to the cylinder, the 
 action of the valve must determine the various 
 points of cut-off, release, and compression on the 
 diagram. But the lengths of the eccentric and 
 main connecting-rods will settle the exact posi- 
 tions of the valve and piston at the various parts 
 of their travel. 
 
 Dispensing now with these preliminary obser- 
 vations, we will proceed direct to the geometrical 
 questions and diagrams. 
 
 Fig. 22 is a diagram, full size, from the 
 cylinder of a pair of marine engines by an 
 eminent firm in London, to whom we are in- 
 debted for the proportions and illustrations here 
 given in relation to this subject. It will be seen 
 that the diagram is partially enclosed within a 
 circle, and this circle is the path of the crank- 
 pin. The diagram is divided into four divisions 
 determined by the action of the slide valve — 
 supply, expansion, exhaustion, and compression. 
 Now the length of the diagram must in all cases 
 represent the stroke of the piston, simply owing 
 to the fact that the figure traced is due to the 
 
GEOMETRY OF THE INDICATOR DIAGRAM. 79 
 
 pressure of the steam and motion of the indicator 
 card-barrel, and its motion is derived from the 
 steam cylinder piston-rod if possible. Obviously, 
 therefore, the length of the indicator’s figure 
 
 and the piston’s stroke are virtually the same ; 
 therefore, by dividing the length of the diagram 
 into parts equal to the stroke of the piston 
 in inches, and constructing from that scale a 
 drawing of the slide valve, piston’s depth, cylinder, 
 
80 
 
 THE INDICATOR DIAGRAM. 
 
 ports, length of eccentric, and main connecting- 
 rods, a relative proportion of the various positions 
 of the whole of these details in connection with 
 this matter is produced. 
 
 The next question is, how the diagram, Fig. 22, 
 was proportionately and truthfully divided into 
 the four parts as shown, and the angles of the 
 crank determined ? In order to fully demon- 
 strate the answer to this, we have illustrated the 
 entire matter at a large scale on the folding plate, 
 entitled, “ Geometrical Tests of Indicator Dia- 
 grams.” 
 
 Fig. 2 in the plate is an illustration of the 
 cylinder ports, slide valve, position of the crank, 
 the piston at full stroke, and the angle of the 
 eccentric proper to the lead required. 
 
 Here let it he noticed that as the eccentric’s 
 angle is due to the present position of the crank, 
 it is virtually connected to the crank by a chord 
 of the arc of the eccentric circle, and that there 
 can he no alteration in the length of this chord 
 afterwards ; and that in this case the angle of the 
 crank is determined from the angle of the eccen- 
 tric, and the position of the latter from the slide 
 valve. 
 
 The diagram Fig. 3, outside the crank path, is 
 the same as Fig. 22, in page 79, but reduced by 
 
GEOMETRY OF THE INDICATOR DIAGRAM. 81 
 
 the scale common to the whole of these details. 
 The atmospheric line is below the centre line of the 
 circle or intersects at the angle, L, the crank would 
 be at when the valve commenced the lead. Now 
 assume that the motion has been given to the 
 indicator and the atmospheric line described, the 
 steam admitted to the cylinder — common to the 
 lead — drives the indicator piston from the at- 
 mospheric line to A, which in the present case is 
 the greatest pressure. 
 
 Fig. 4 now demands attention. Here it is 
 seen that the crank has risen in the direction of 
 the arrow, and the piston has advanced in a 
 relative distance, while the slide-valve has closed 
 the steam-port, and has a retrograde motion to 
 that in Fig. 2. Notice also that the space tilled 
 in in the diagram Fig. 5 is the same distance 
 the crank-pin has travelled on the plane line ; 
 the dotted curve line in each case shows the 
 relative position of the piston. When the crank 
 arrived at B, the steam was cut off by the slide- 
 valve and expansion commenced, and the non- 
 escape from the cylinder was continued until the 
 valve and crank were in the positions, as shown 
 by Fig. 6. 
 
 Turning again to Fig 2, it will he apparent, on 
 comparing it with Fig. 6, what distance the 
 
 G 
 
82 
 
 THE INDICATOR DIAGRAM. 
 
 piston has travelled before the steam is dispensed 
 with or exhaustion commences, also the portion 
 of the circle described by the crank-pin during the 
 same time. 
 
 Fig. 7 represents the amount of pressure in 
 the cylinder at the moment the exhaustion occurs ; 
 it explains, also, the decrease of pressure from 
 the point of cut-off to the release. The relative 
 diagram areas of supply and expansion are mani- 
 fest, and the length on the atmospheric line 
 agrees with the plane travel of the crank-pin. 
 Now the time allowed for exhaustion is due to 
 the travel of the slide-valve , less the inside laps , 
 and while the valve is performing this the piston 
 also completes its stroke and has a return 
 motion. The Fig. 8 will assist now. Here 
 the valve has just closed the supply-ports, 
 terminated exhaustion, and the crank-pin has 
 travelled from C in Fig. 6 to D in Fig. 8, where 
 the relative positions of the pistons are also 
 shown. 
 
 Fig. 9 shows the amount of vacuum attained, 
 and that when the crank left 0 in Fig. 7 the 
 pressure in the cylinder gradually fell to that ot 
 the atmosphere before the stroke of the piston 
 was complete, as shown by the pencil’s trace 
 intersecting with the atmospheric line. On 
 
GEOMETRY OP THE INDICATOR DIAGRAM. 83 
 
 reaching this point the pencil descended. When 
 the piston completed its stroke, simultaneously 
 the indicator drum, or barrel, stopped, and 
 moved again in the contrary direction with the 
 piston. The steam was nearly, if not finally, 
 exhausted just after the round corner was formed 
 by the pencil, and the vacuum attained was faith- 
 fully recorded, as shown by the line nearly 
 parallel with the atmospheric line. Exhaustion 
 was continued, for the supply-port was open to 
 the condenser, until the piston reached the 
 position depicted in Fig. 8, when the valve closed 
 the port and compression commenced. The mo- 
 tions of the piston and valve being in reverse 
 directions, as indicated by the arrows, no steam 
 or vacuum affected the travel of the piston until 
 the crank reached L in Fig. 11. 
 
 Then the steam rushed into the cylinder, 
 simultaneouslv into the indicator, when the 
 piston of the latter instantly rose, and the pencil 
 ascended to the atmospheric line, which completed 
 the indicator diagram. It will be noticed, how- 
 ever, in the diagram, Fig. 9, that the rounding 
 of the corner must have been formed before the 
 steam, admitted by the lead of the valve, could 
 nave caused it, as shown by the angle of the 
 crank at L in Fig. 11. This was due to com- 
 
84 
 
 THE INDICATOR DIAGRAM. 
 
 pression, or, perhaps, leakage of the valve before 
 the port was opened. 
 
 We may mention here, in passing, that as the 
 lead of the valve governs the grade of expansion, 
 so that if the lead were increased, the grade of ex- 
 pansion would be reduced. 
 
 The diagram, Fig. 9, just explained was taken 
 from the back end of the cylinder, and as all 
 cylinders should be indicated at both ends, the 
 diagram, Fig. 11, was taken also. Fig. 10 
 shows the position cf the crank, slide-valve, and 
 piston exactly opposite to that in Fig. 2. Fig. 12 
 depicts the positions of the valve, piston, and 
 crank at the point of cut-off, or reverse to Fig. 4. 
 Here must be noticed the relative position of the 
 pistons, also that although the leads for the valve 
 are alike, the points of cut-off are not the same. 
 
 It may be added, as a guide for young 
 engineers, that if equal lead is preserved at each 
 end of the cylinder, unequal expansion results, 
 and vice versa, so that if expansion is equal, 
 uneven outside lap and lead must ensue to obtain 
 the same when the connecting and eccentric rods 
 are on the same side of the crank shaft. 
 
 Alluding next to Fig. 14, the relative positions 
 for the termination of exhaustion are illustrated 
 analogous with Fig. 6, common to the opposite 
 
GEOMETRY OF THE INDICATOR DIAGRAM. 85 
 
 end of the cylinder. Observe the different posi- 
 tions — due to the obliquity of the connecting- 
 rod — of the pistons in each case from the vertical 
 centre lines of the cylinders. The length of the 
 expansion sections in Figs. 7 and 15 will also be 
 found to be unequal in consequence of the action 
 resulting from the length of the connecting-rod. 
 Fig. 16 shows the valve cutting off the com- 
 munication from the condenser, or the commence- 
 ment of compression, but the position of the 
 piston in this case, and in Fig. 8, are strikingly 
 at variance, owing to the relative angles of the 
 cranks being on opposite sides of the 'centres 
 of the crank circles. The length of the compres- 
 sion section on the diagram, Fig. 17, is much 
 shorter also than in Fig. 9. 
 
 The evidence certain from the preceding 
 remarks is that the diagrams under notice bear a 
 strict relation to the angles of the crank at the 
 points of supply, expansion, exhaustion, and com- 
 pression. There are, however, other matters to 
 be considered, to which we now direct attention, 
 which are, that indicator diagrams are of two 
 classes, independent of high and low pressure 
 steam, or condensing and non-condensing engines 
 — viz., crank diagrams and piston diagrams. 
 
 Our next proceeding is therefore to define the 
 
86 
 
 THE INDICATOR DIAGRAM. 
 
 difference in the two figures, and their separate 
 relations to the crank and the piston. If we 
 notice the illustrations in the plate again, in 
 reference to this, we shall see that all the indicator 
 diagrams are divided by perpendicular lines pro- 
 jected from the intersections of the angles of the 
 crank with its path or circle, which divisions of 
 course refer specially to the angles of the crank 
 at the points of cut-off, expansion, exhaustion, 
 and compression. Now this mode of subdivision 
 does not define the positions of the piston in rela- 
 tion to those for the crank unless they are set out 
 as illustrated ; so that when this is not done the 
 formation of the diagram in relation to the speed 
 of the crank-pin is only shown. 
 
 To render a comparison obvious, the illustra- 
 tion Fig. 23 is introduced, which being full size, 
 shows at once the proportions of the divisions 
 of the diagram, taken from the front end of the 
 cylinder, as shown in the plate ; the intersection 
 of the vertical lines with the circle depict the 
 positions of the crank-pin during the four stages 
 of the formation of the figure ; the dotted curves 
 starting from those points and ending at the at- 
 mospheric line, are formed with the length of the 
 connecting rod as the radius, and show thereby 
 the lineal advance of the crank-pin over that of 
 
Fig. 23. 
 
 Indicator Diagram taken from the Cylinder shown in the Plate. Full size. 
 Fig. 24. 
 
88 
 
 THE INDICATOR DIAGRAM. 
 
 the piston, which is equal to the versed sines of 
 the dotted arcs. The separate relation of this 
 diagram to the piston is shown by Fig. 24, where 
 the divisions contrast with those in Fig. 23. 
 In the present case the vertical lines are tangents 
 to each arc, instead of chords as in the other 
 instance. The letters refer to the stages of con- 
 struction ; thus S is supply steam ; and the 
 length of S in Fig. 23 is longer than that in 
 Fig. 24 ; E is expansion, and its length is 
 shorter in Fig. 23 than in Fig. 24. Exhaustion 
 is next indicated by E 2 , the difference in the 
 lengths in both figures is apparent also ; lastly, 
 C, which is compression, is shorter in Fig. 24 
 than in Fig. 23. 
 
 As the diagrams in the plate are taken at each 
 end of the cylinder, we illustrate by Fig. 25 the 
 diagram full size, taken at the back end, which 
 shows also the contrast between the crank 
 positions in it and in Fig. 23. The difference in 
 the piston diagrams is shown by Fig. 26, which 
 is that, in this Fig. the supply S is larger than in 
 Fig. 24, and also compression C, while exhaus- 
 tion E 2 is about one-fourth shorter above. 
 
 The object attained by this geometrical test is 
 now apparent, it being that as the actual length 
 of the stroke of the piston is virtually that of the 
 
Fie. 25. 
 
90 
 
 THE INDICATOR DIAGRAM. 
 
 diagram, or vice versa , and the paths of the crank- 
 pin and piston are subdivided virtually also, by 
 the action of the slide-valve we can arrive at a 
 correct conclusion, of not only the proportion of 
 these divisions, but also the time occupied to 
 produce each portion of the diagram com- 
 paratively ; in fact we can see obviously what the 
 steam has been actually performing during the 
 given strokes of the piston, and as the steam is 
 governed by the valve and its gear, we learn also 
 their action. Indeed this geometrical test is the 
 only method that can be adopted to detect 
 fictitious indicator diagrams and the imperfect 
 mechanism of the steam-engine. 
 
91 
 
 CHAPTER VI. 
 
 MODERN INDICATOR DIAGRAMS, CONTRIBUTED BY 
 THE MOST EMINENT ENGINEERS IN ENGLAND 
 AND SCOTLAND, TO SHOW THEIR LATEST AND 
 BEST PRACTICE. 
 
 Fig. 27. 
 
 S S 
 
 Inverted Direct-acting Screw-engines. 
 
 Messrs. Maudslay’s indicator diagrams, showing a high working grade of 
 cut-off, with almost equal lead, and equal expansion. Original scale T h in. 
 = 1 lb. Half size. 
 
 Screw-engines. — The pair ol diagrams shown 
 by Fig. 27 have been very lately taken from 
 both ends of one of the cylinders of a pair of 
 horizontal return-acting engines of 120 h.p., 
 fitted by Messrs. Maudslay into the steamship 
 “Rostoff.” The slide-valves are the most modern 
 three-ported type, and the link motion of the 
 usual kind of their late practice. It will be seen 
 that the supply-lines S S are nearly equal in 
 
92 
 
 THE INDICATOR DIAGRAM. 
 
 length and form ; also that the curve lines ex- 
 tending to E E depict that the expansion is per- 
 fect, and the points of exhaustion alike ; indeed 
 the figures in toto are pairs, in the literal meaning 
 of the word. Although the grade of expansion 
 is high, it is the working power for the engines 
 to drive the ship at eight knots per hour. 
 
 As a contrast to the preceding example, Messrs. 
 Maudslay have given the figures shown by Fig. 
 28. At C C there was a little concussive action of 
 
 Fig. 28. 
 
 c c 
 
 INDICATED HORSE POWER 6 8S7 
 
 Return-acting Screw-engines. 
 
 Messrs. Maudslay’s indicator diagrams, showing unequal cut-off, nearly equal 
 expansion, and equal lead. Original scale, ^ in. = 1 lb. Half size. 
 
 the marker, which occurs generally from cylinders 
 whose diameters exceed their lengths. It is pro- 
 duced chiefly by the least priming of the water 
 
TAKEN FROM SCREW-ENGINES. 
 
 93 
 
 in the boiler, or partial condensation of the steam 
 in the cylinder, which compound of steam and 
 water entering the indicator piston causes an ex- 
 cessive undulation, doubtless being the result of 
 the water striking the piston before the steam acts 
 under it, and the response given by the spring 
 above. The engines these figures were taken 
 from are 1350 h.p., and are fitted into H.M.S 
 “ Agincourt.” The indicated horse-power is 
 6687 collectively. 
 
 Leaving the London practice pro tem., we 
 direct next to the diagrams shown by Fig. 29, 
 
 Messrs. Napier’s indicator diagrams, showing unequal cut-off, but equ&l expan- 
 sion and lead, from aft engine. Original scale T * 0 in. = 1 lb. Half size. 
 
 being the practice of Messrs. R. Napier and Sons, 
 of Glasgow. The forms of both figures are nearly 
 
94 
 
 THE INDICATOR DIAGRAM. 
 
 alike proportionately ; the lengths of the supply 
 lines at S S are unequal, but the actual, limit for 
 supply is beyond the straight parts, and a little 
 below on the curve lines ; the cause for the round- 
 ing from the straight lines S S to the dotted 
 curves below, is that the steam pressure was 
 reduced in the cylinder, either from partial con- 
 densation or contraction of the supply opening. 
 The cause of the undulations of the curves above 
 and below the atmospheric line is either from the 
 shaking of the instrument or oscillation of the 
 steam in the cylinder produced by unsteady ex- 
 pansion and exhaustion ; the lead-corners L L at 
 each end are equal, and show a steady re-admis- 
 sion for the steam. 
 
 These diagrams were taken from the aft engine ; 
 we therefore next turn to those taken from the 
 forward engine, depicted by Fig. 30. The supply 
 lines S S are curved, instead of straight, as they 
 should be, owing to the supply of the steam 
 being insufficient to maintain an equal pressure 
 or force in the cylinder during the admission ; or 
 similarly as the result of partial expansion and 
 supply at the same time. The expansion and 
 exhaustion lines above and below the atmospheric 
 line are undulated as those before, and equal 
 lead, L L, also is demonstrated again now. 
 
TAKEN FROM SCREW-ENGINES. 
 
 95 
 
 Fig. 30. 
 
 Return-acting Screw-engines. 
 
 Messrs. Napier’s indicator diagrams, showing curved supply lines, undulated 
 expansion lines, but equal lead ; from forward engine. Original scale 
 ^ in. = 1. lb. Half size. 
 
 The preceding four diagrams are taken at full 
 power ; and therefore we know exactly the dif- 
 ference in the mean pressures on the piston 
 on each side — for example, the left-hand diagram 
 in Fig. 29 is 19'3 lbs . ; but that in Fig. 30 is 
 21T lbs. ; the right-hand diagram in the former 
 figure is 21*8 lbs, but in the latter it is 21 '4 
 lbs. on the square inch. 
 
 Asa contrast we have introduced the Figs. 31 
 and 32, to depict the difference in full and half 
 boiler power, and to show also that the supply 
 line depends as much on the quantity as the 
 pressure of the steam, These four figures relate 
 
96 
 
 THE INDICATOR DIAGRAM, 
 
 Fig. 31. 
 
 Return-acting Screw-engines. 
 
 Messrs. Napier’s indicator diagram, showing the result of half boiler power; 
 aft engine. Original scale ^ in. = 1 lb. Half size. 
 
 Fig. 32. 
 
 Return-acting Screw-engines. 
 
 Messrs, Napier’s indicator diagram, showing the result of half boiler power ; 
 forward engine. Original scale A in. = 1 lb. Half size 
 
TAKEN FROM SCREW-ENGINES. 
 
 97 
 
 respectively to those of full power, and the differ- 
 ence in the form and length of- the line S is clearly 
 illustrated, it being remembered that it is the 
 horizontal length of S that depicts the point of 
 cut-off ; the difference in the mean pressures are 
 also easily understood. All of these diagrams, 
 Figs. 29 to 32 inclusive, were taken from the 
 engines fitted by Messrs. Napier in H.M.T.S. 
 “ Malabar,” 700 nominal h.p. collectively. Tlie 
 mean pressure of the steam in the cylinder, full 
 power, was 20*9 lbs. on the square inch ; vacuum 
 27 inches; and the revolutions 70 per minute ; 
 the indicated horse-power being 492 2*3 1. The 
 mean pressure of the steam at half power in the 
 cylinder was 13‘5 lbs. ; vacuum, 27 in. ; number of 
 revolutions, 57 - 66, and the indicated horse- 
 power 2619, each result being collective. 
 
 Direct-acting Screw-engines. 
 
 Messrs. Watt’s indicator diagrams, showing full supply steam, even expansion, 
 with equal exhaustion and lead. Original scale ^ in. = 1 lb. Half size. 
 
 Leaving the Scottish practice for the present, 
 
 H 
 
98 
 
 THE INDICATOR DIAGRAM. 
 
 and returning to the English examples again, we 
 refer now to the* oldest firm — Messrs. James 
 Watt and Co. ; their recent and best practice 
 being depicted by Fig. 33. 
 
 These were taken from the steam-ship “Ipojuca.” 
 The engines are direct acting, the crank-pins 
 making 33 revolutions per minute, with 20 lbs. 
 pressure of steam per square inch in the boiler, 
 and the condenser attaining 23^ lbs. of vacuum. 
 The marker was slightly undulated at U U, but 
 the lines S S are creditably straight, and parallel 
 with the atmospheric line. 
 
 We may here add in passing that as the lines 
 S S are the indications of the stationary posi- 
 tions of the pencil or marker when the indicator 
 piston is held up by the steam pressure, these 
 lines should be always parallel with the atmo- 
 spheric line, because the marker is stationary then 
 also when describing it. 
 
 To show that the least difference in the work- 
 ing of the engine is faithfully indicated by the in- 
 dicator diagram, Fig. 34 is introduced. Here the 
 supply lines S S show that the pressure of the 
 steam gradually decreased after it entered the 
 cylinder, instead of, as in Fig. 33, maintaining it 
 until the cut-off occurred. In this case the steam 
 pressure in the boiler was 22 lbs. ; vacuum 23 - 5 
 
TAKEN FROM SCREW-ENGINES. 
 
 99 
 
 inches in the condenser, and revolutions 3 6 ; the 
 indicated mean total pressure on the piston was 
 19T5 lbs., and in Fig. 33, 19*7 lbs. 
 
 Original scale ^ in. = 1 lb. Half size. 
 
 Another example by this firm is shown by 
 Fig. 35. Here the indicating marker undulated 
 
 Fig. 35. 
 
 U U 
 
 mencement of the supply steam line. Original scale -^in. = 1 lb. Half size. 
 
 at U U, and from thence gradually lowered until 
 the cut-off occurred. These diagrams were taken 
 from one of the cylinders of the engines fitted 
 
100 
 
 THE INDICATOR DIAGRAM. 
 
 into the steam-ship “ Medusa,” twin screws* — the 
 starboard aft cylinder ; steam pressure in the 
 boiler 25 lbs. ; vacuum 24 inches, and revolutions 
 124 ; mean indicated pressure on the piston, 21 ‘5 
 
 Fig. 36. 
 
 Return-acting Screw-engines. 
 
 Messsrs. Rennie’s indicator diagrams, from their best return-acting screw 
 engines, A A being full supply steam, and B B expansion. About half size. 
 
 The diagrams shown by Fig. 36 are from 
 
 * For full particulars of engines, see “Modern Marine 
 Engineering,” also Messrs. Rennie’s. 
 
TAKEN FROM SCREW-ENGINES. 
 
 101 
 
 engines of 350 h.p., collectively, fitted lately by 
 Messrs. Rennie into the Egyptian steam-ships 
 “ Charkieh,” and “ Dakahlieh.” The two pairs 
 of figures show clearly the results of working 
 with full steam at half-stroke and an earlier cut- 
 off by a separate valve. 
 
 As the engines for transport service should be 
 reliable, we illustrate next the indicator diagrams 
 of engines fitted by Messrs. Laird, of Birkenhead, 
 into H.M.T.S. “ Euphrates,” sister ship to the 
 
 Fig. 37. 
 
 Return-acting Screw-engines. 
 
 Messrs. Laird's indicator diagrams, showing almost equal supply and exhaustion 
 lines ; forward engine. Original scale | in. = 1 lb. Half size. 
 
 “ Malabar,” by Fig. 37 ; the first being from 
 the forward cylinder, and the second, Fig. 38, 
 from the aft cylinder. 
 
 The engines are 700 h.p. nominal; horizontal 
 return action ; diameter of cylinder, 94 in. ; stroke 
 
102 
 
 THE INDICATOR DIAGRAM 
 
 Fig. 38. 
 
 Return-acting Screw-engines. 
 
 Messrs. Laird’s indicator diagrams, showing unequal lines of supply and ex- 
 pansion ; aft engine. Original scale J in. = 1 lb. Half size. 
 
 Double-trunk Screw-engines. 
 
 Messrs. Penn’s indicator diagrams, showing equal supply, expansion, and lead, 
 with nearly equal exhaustion. Half size. 
 
TAKEN FROM SCREW-ENGINES. 
 
 103 
 
 of piston, 4 ft. 6 in. ; number of revolutions of 
 crank-pin, 62 - 4 per minute ; pressure of steam 
 in the boiler, 27 lbs.; vacuum in the condenser, 
 2 6 4 5 in. ; and the indicated horse-power, 4981. 
 
 We now turn to a pair of diagrams that are 
 really twin, or nearly duplicate one with the 
 other, as shown by Fig. 39. Here T T are the 
 limits of steam pressure, E E opposite the points 
 of exhaustion, and L L the indications of lead.* 
 As the forms of the lines are explanatory without 
 description, we allude next to Figs. 40 and 41.* 
 These diagrams were taken from one of the 
 cylinders of the three-cylinder arrangement as 
 constructed by Messrs. Maudslay, Sons, and 
 Field. 
 
 The slide-valve used is the three-ported kind, 
 and is worked by crank-and-spur gearing in the 
 place of eccentrics and link motion. The dia- 
 grams show that the time for full supply steam 
 was very short, as the horizontal length of the 
 supply-lines indicate. The actual cut-off was at 
 one fifth of the stroke of the piston ; therefore 
 the openings caused by the valves must have been 
 gradually reduced in width and area before half 
 the time expired for the admission of the steam. 
 
 * For full particulars of engines, see “ Modern Marine 
 Engineering.” 
 

 Return- acting Screw-engines. 
 
 Messrs. Maudslay’s indicator diagrams, showing nearly equal supply, with 
 equal expansion, exhaustion, and lead ; forward engine. 
 
 % 
 
 Messrs. Maudslay’s indicator diagrams, showing nearly equal supply, with 
 equal expansion, exhaustion, and lead ; aft engine. 
 
TAKEN FROM SCREW-ENGINES. 
 
 105 
 
 "VVe may here again remind the young engineer 
 that when the supply-line is inclined or angular 
 a rapid reduction of the pressure of the steam 
 occurs during’ admission ; but when that line 
 is horizontal for the half of its length and ter- 
 minates suddenly with a curve, as in Fig. 29 in 
 page 93, the reduction of the pressure is slower ; 
 but when those lines are fully horizontal, as with 
 Fig. 33, in page 9 7, then the full pressure must 
 have been maintained during the time for admis- 
 sion. 
 
 Our next contributed example is shown by 
 Fig. 42, which defines the result of using the 
 
 Fig. 42. 
 
 2 1 
 B 
 
 A 
 
 Return- acting Screw-engines. 
 
 Messrs. Napier’s indicator diagrams, howing six grades of cut-off, by the link 
 motion and slide-valve. Original scale T b lb. to an inch. Half size. 
 
 slide-valve and the link motion for the purpose 
 of cutting off the steam at 6 points of the stroke, 
 The points are depicted by the figures 1 to 6 
 being directly over them. The positions of the 
 letters A A and B B depict that at A A the full 
 
106 
 
 THE INDICATOR DIAGRAM. 
 
 pressure was the lowest at the sixth grade of cut- 
 off, or at half-stroke, and the highest at B B, the 
 5rst grade, or at T J g- of the stroke. These two 
 limits of the pressure show that the readmission 
 of the steam is always more suddenly effective 
 with an early cut-off than otherwise, and that the 
 lead being sooner causes it. These diagrams were 
 taken by Messrs. Napier from the cylinders of the 
 engines fitted by them in the Turkish frigate 
 “ Osman Ghazy.” The diameter of the cylinders 
 is 92 in. ; stroke of the piston, 4 ft. : with full 
 supply steam at the 6th point of cut-off, the 
 pressure was 21 lbs. ; vacuum, 26 in. ; revolutions 
 49, and the indicated horse-power, 3782. 
 
 Another example of the same class of diagrams 
 is shown by Fig. 43, depicting only four grades 
 
 Fig. 43. 
 
 Direct-acting Screw-engines. 
 
 Messrs. Watt’s indicator diagrams, showing four grades of expansion, with the 
 link motion and slide-valve. Original scale in. = 1 lb. Half size. 
 
TAKEN FROM SCREW-ENGINES. 
 
 107 
 
 of expansion, and the points of cut-off by the 
 figures 1 to 4. The diagrams on the right hand, 
 A, are almost perfect in form, as the supply lines 
 are horizontal, the expansion lines true curves — 
 particularly those of Nos. 1 and 2 — and the ex- 
 haustion lines indications of sudden reduction of 
 the pressures, while the lead-lines are in pro- 
 portion to the degree* of cut-off. The left-hand 
 diagrams, B, are not nearly so perfect, except the 
 diagram a, which is the longest limit for supply, 
 or No. 4, where the supply line is horizontal, 
 whereas all the others are inclined, showing an 
 uneven pressure •, hut we may remark that, as 
 these lines are higher from the atmospheric line 
 than those opposite, the mean pressures of both 
 are nearly equal ; and as it is the mean pressure 
 that we deal with, for practical purposes the dif- 
 ference in the forms of the supply lines is not of 
 any great importance in this instance. 
 
 The diagrams Fig. 44 were taken from the aft 
 cylinder, 104|- in. in diameter, stroke of the 
 piston 4 ft., of the trunk engines, 1000 horse- 
 power nominal, fitted by Messrs. Penn into H.M.S. 
 “ Bellerophon.” The cylinders are jacketed, 
 the steam is superheated, and the surface con- 
 densation used. The diagrams depict, an un- 
 equal supply, and the steam slightly throttled, by 
 
108 
 
 THE INDICATOR DIAGRAM. 
 
 the right-hand figure ; the expansion and exhaus- 
 tion lines are nearly duplicates ; but the lead lines 
 are unequal, the least lead being with the most 
 full supply line. 
 
 Fig. 44. 
 
 Double-trunk Screw-engines. 
 
 Messrs, Penn’s indicator diagrams, showing the result of using the slide-valve 
 and link motion for an early cut-off, termed “expansion by link motion.” 
 Original scale, T J g in. = 1 lb. Half size. 
 
 The next set of diagrams, shown by Figs. 45 
 and 46, were taken by Messrs. Penn from a pair 
 of inverted direct-acting engines, of 120 horse- 
 power nominal collectively ; diameter of each 
 cylinder 44 inches, and the stroke of the piston 
 3 ft. The slide-valve is fitted with a sliding 
 expansion valve on the back, both being worked 
 by link motion. The engines were fitted in the 
 Russian Steam Navigation and Trading Com- 
 pany’s steamship “ Azof.” The diagrams are so 
 
TAKEN FROM SCREW-ENGINES. 
 
 109 
 
 perfect in the expansion lines, with complete ex- 
 haustion, that they need no comment, save that 
 the supply lines of the right-hand figure are not 
 as full as those opposite — due to the grade of cut- 
 off being earlier in the former than the latter. 
 
 Inverted Direct-acting Screw-engines. 
 
 Messrs. Penn’s indicator diagrams, showing perfect expansion and lead lines ; 
 from the aft cylinder. Original scale, in. = 1 lb. Half size. 
 
 Fig. 46. 
 
 We may add that Messrs. Penn’s indicator gear 
 is precisely as what Messrs. Napier use, as illus- 
 trated by Fig. 50 in page 113, excepting the loop 
 
 Fig. 45. 
 
 Inverted Direct-acting Screw-engines. 
 Forward cylinder. 
 
110 
 
 THE INDICATOR DIAGRAM. 
 
 for the vibration of the swing lever, as Messrs. 
 Penn prefer a rod to Connect at one end to the 
 lever, and secured by a pin at the other to either 
 the piston or air-pump rods, and Messrs. Maudslay 
 prefer the same. 
 
 Compound screw-engines. — Messrs Maudslay 
 have lately fitted H.M.S. “ Sirius ” with com- 
 pound marine screw-engines of 350 horse-power 
 collectively. The high-pressure cylinder is 34 in. 
 in diameter, and is situated within the low-pressure 
 cylinder, whose diameter is 7 5 in. ; the stroke of 
 the piston being 2 ft. 9 in. < Pressure of steam 
 in the boilers, 49 lbs. ; number of revolutions of 
 the crank-shaft, 99*56 per minute ; and total 
 indicated horse-power, 2293*68. 
 
 The diagram Fig. 47 is from the high-pressure 
 cylinder, and shows that the steam-supply lines 
 are undulated at the commencement — due to the 
 admission of the steam, or lead, being rather 
 early, as shown by the curves at the lead-corners. 
 The exhaust line is undulated a little also over 
 the atmospheric line ; which is caused by the 
 steam not being entirely out of the cylinder on 
 the return stroke of the piston ; but taking the 
 figures in the aggregate, they pair well, and show 
 a good result. 
 
TAKEN FROM SCREW-ENGINES. 
 
 Ill 
 
 Tlie low-pressure diagrams shown by Fig. 48 
 pair better than those preceding, and indicate a 
 vacuum of 12 lbs. on the square inch, with a 
 
 Fig. 47. 
 
 Compound Horizontal Return-acting Screw-engines. . 
 Messrs. Maudslay’s indicator diagrams, showing equal cut-off, expansion, 
 exhaustion, and lead. High pressure ; aft cylinder. Original scale, ^ in. = 
 1 lb. Half size. 
 
 Compound Horizontal Return-acting Screw-engines. 
 
 Messrs. Maudslay’s indicator diagrams, showing complete expansion. Low 
 pressure ; aft cylinder. Original scale, ^ in. = 1 lb. Half size. 
 
 pressure of steam on entering the cylinder 5'5 
 lbs. on the square inch, which expanded almost 
 theoretically perfect in practice. 
 
 The diagrams shown by Fig. 49 were taken 
 
112 
 
 THE INDICATOR DIAGRAM. 
 
 from the same engines when the ship was at 
 “ moorings,” and illustrate how the high and 
 low-pressure indications “piece ” together at pro- 
 portionate scales. 
 
 Fig. 49. 
 
 Compound Horizontal Return-acting Screw-engines. 
 Messrs. Maudslav’s indicator diagrams “ pieced ” together. High pressure, 
 half size ; low pressure, quarter size in height, and half size in length. 
 
 Messrs. Napier’s indicator gear for re- 
 turn-acting HORIZONTAL DOUBLE PISTON-ROD 
 screw-engines. — The firm has kindly given 
 us a working drawing of this gear, which we 
 illustrate at a working scale by Figs. 51 and 52 
 for the benefit of young engineers and students 
 who have yet to learn that the arrangement of 
 the indicator gear should be as simple as possible. 
 
 The motion lever is the same kind as illus- 
 trated for direct-acting engines in page 18, ex- 
 cepting that in this case the looped lever is above 
 
Fig. 50 
 
 SCREW-ENGINE — INDICATOR GEAR. 1J3 
 
 1 
 
 Side elevation and plan of Messrs. Napier’s indicator gear for return-acting engines. Scale, J in. 
 
114 
 
 THE INDICATOR DIAGRAM. 
 
 the piston-rod instead of below it. The steam 
 pipe is connected to the top side of the cylinder 
 rather than to the ends, and the indicator is 
 situated nearer to one end than the other ; also 
 the cord leading from the first motion pulley is 
 at an angle ; all of which are faults, although 
 perhaps not of great magnitude. 
 
 Fig. 51. 
 
 End elevation of Messrs. Napier’s indicator gear for return-acting screw- 
 engines. Scale 3 in. = 1 ft. 
 
 Steam-launch twin screw^engines. — Messrs. 
 Penn’s diagrams, shown by Fig. 52 , indicate that 
 the cut-off points, C, are midway of the length of 
 the figures, and that the expansion and exhaustion 
 
STEAM-LAUNCH ENGINE-DIAGRAMS. 115 
 
 lines are nearly equal ; but not so the leads ; the 
 difference being that the right-hand diagram 
 shows the least amount of lead possible, and a 
 vertical admission line, A ; but that at the left 
 hand depicts the lead indication larger, and the 
 admission line, B, at an angle for the most part of 
 its height. 
 
 Fig. 52. 
 
 Steam-launch Twin Screw- engines. 
 
 Messrs. Penn’s indicator diagrams, showing full supply steam and equal 
 expansion, but unequal leads. Half size. 
 
 Messrs. Rennie have constructed a great number 
 of steam-launch engines with surface condensers 
 that are arranged with piping and valves so as to 
 convert the engines into high-pressure or con- 
 densing while they are in motion. The diagrams 
 shown by Fig. 53 are examples from the same 
 engine at the period of using the steam as de- 
 scribed. It will be seen that the condensing 
 diagram is the better of the two, as the supply 
 
L 16 
 
 THE INDICATOR DIAGRAM, 
 
 line is more regular than the other ; but the ad- 
 mission lines, A A, are both nearly equal ; while 
 the lead in the left-hand figure is not indicated at 
 all — due of course to the slip of the pencil and 
 paper occurring in reverse directions at the same 
 instant — an evidence also that the person who 
 was taking the figure was careless at that moment. 
 
 Fig. 53. 
 A 
 
 ^ u 
 
 
 / Cvtiden~my 
 
 / Hiyli 
 
 i ' $irom,80 Lis 
 
 f f?teaTrb8lTi* 
 
 I G4o 
 
 I 32*- 
 
 1 39 rsp 
 
 / 3 + 1HB 
 
 | AieMlErta* CIO 
 
 Mi an Fre-s sure 6 h5> 
 
 
 v — -y 
 
 Steam-launch Twin-screw Engines. 
 
 Messrs. Rennie’s indicator diagrams, showing the results of condensing and 
 non-condensing the steam with the same engines. Half size. 
 
117 
 
 CHAPTER VII. 
 
 INDICATOR DIAGRAMS TAKEN PROM THE MOST 
 IMPROVED MODERN PADDLE-WHEEL ENGINES. 
 
 Paddle-wheel engines. — The diagrams shown 
 by Figs. 54 and 55 were taken from the cylinder 
 of the engines constructed by Messrs. J. and G. 
 Rennie, and fitted by them into the P. & 0. Co.’s 
 
 Fig. 54. 
 
 Messrs. Rennie’s indicator diagrams, showing unequal supply, nearly even ex- 
 pansion. and exhaustion, and equal lead ; starboard cylinder. Original scale, 
 ^ in. = lib. Half size. 
 
 steam-ship “ Nyanza,” a vessel of mercantile re- 
 cord and renown. On comparing the figures, we 
 
118 
 
 THE INDICATOR DIAGRAM. 
 
 notice that the top diagrams are very like each 
 other at a glance-like observation ; hut on testing 
 the pressures they show a little difference, which 
 may result from the imperfection of the instru- 
 ment as much as the action of the steam. With 
 both figures the supply of the steam appears to 
 
 Fig. 55. 
 
 Oscillating Paddle -engines. 
 
 Messrs. Rennie's indicator diagrams, showing unequal supply, nearly even ex- 
 pansion and exhaustion, and equal lead ; port cylinder. Original scale, T ! a 
 in. = 1 lb. Half size. 
 
 have been limited sufficiently to allow the de- 
 crease of the pressure in the cylinder from the 
 commencement of the stroke, and therefore the 
 supply lines are inclined as depicted. The lines 
 of expansion are nearly duplicates, and also the 
 exhaustion portion shows an almost equal vacuum 
 direct to the lead-point. The latter indication in 
 
TAKEN FROM PADDLE-ENGINES. 
 
 119 
 
 the bottom figures is nearly alike, while in the 
 top figures a little difference is shown ; that 
 in Fig. 55 is a moderate curve, but in Fig. 54 
 it is an irregular line for some distance, and then 
 terminates with a set-off to join the full steam 
 line. Now the cause for the formation of that 
 set-off' has often been questioned by really veritable 
 authorities. One side attributes it to the action 
 of the steam, and the other to the faulty arrange- 
 ment of the gear. Now if we remember that the 
 formation of any straight horizontal line must 
 result from the paper moving while the pencil is 
 still, we can determine that the cause for the set- 
 off is that the pencil must have momentarily 
 stopped before the lead line joined the admission 
 line ; and also the barrel must have moved 
 quicker at that instant than before. Of course 
 the barrel only stopped then, but its movement 
 must have been sudden at the conclusion. The 
 cause for this evidently lay with the gear and the 
 steam also ; the pencil, it being remembered, is 
 the steam indicant, while the paper represents 
 the gear. Or it might be that the indicator 
 piston stuck fast at the same time that the jerk 
 was given to the barrel. At any rate the error 
 show's that the pencil almost ceased its motion 
 for the time the set-off was described ; and the 
 
120 
 
 THE INDICATOR DIAGRAM. 
 
 cause is either that the steam pressure ceased in 
 the indicator from direct condensation, if the 
 piston did not hitch from friction. The jerk 
 given to the barrel proves that the string must 
 have slackened slightly before and become tight 
 at the conclusion. The slackening would be the 
 result of the lever or pin being loose on its 
 bearing. 
 
 The “ Nyanza’s ” cylinders are 6 ft. 6-/^ in. in 
 diameter, and the pistons have each a stroke of 
 7 ft. The engines are 450 nominal horse-power ; 
 mean pressure in the cylinders, 22‘45 ; number 
 of revolutions per minute, 25 ; indicated horse- 
 power, 2304. 
 
 The condensation is on the surface-condensing 
 principle ; and the diagrams indicate that it has 
 been well carried out. 
 
 The next examples, shown by Figs. 56 and 57, 
 are really beautiful specimens of duplication ; and 
 the firm — Messrs. Napier — deserves praise for 
 their production ; for the two on the right hand 
 are twins, and those on the left are of similar 
 relation ; the irregular expansion lines are also 
 alike, so that what caused them in one case 
 occurred in the others. The cause is that the 
 indicator piston undulated during the expansion 
 of the steam, and the undulation results from 
 
TAKEN FROM PADDLE-ENGINES. 
 
 121 
 
 infinite condensation of the steam. The engines, 
 of 210 nominal horse -power, are fitted in the 
 
 Fig. 56. 
 
 Fig. 57. 
 
 Messrs. Napier’s indicator diagrams, showing full steam, equal supply, expan- 
 sion, exhaustion, and lead ; starboard cylinder. Original scale, T ’g in. = 1 lb. 
 Half size. 
 
122 
 
 THE INDICATOR DIAGRAM. 
 
 steam-ship “ Caroline;” diameter of cylinder, 54 
 in. ; stroke, 6 ft. ; mean pressure in cylinders, 
 27*496 ; number of revolutions per minute, 26i ; 
 indicated horse-power, 1213*69. 
 
 Messrs. Laird’s practice next comes under 
 consideration, illustrated first by Figs. 58 and 59. 
 
 Fig. 58. 
 
 Fig. 59. 
 
 Oscillating Paddle-wheel Engines. 
 
 Messrs. Laird’s indicator diagrams, showing full supply steam, unequal expan- 
 sion, equal exhaustion and lead ; starboard cylinder. Original scale, i in. 
 = 1 lb. Half size. 
 
 These are taken from a pair of cyliiiders 59 in. 
 in diameter ; stroke of piston, 5 ft. 6 in. ; nominal 
 horse-power, 240 ; steam pressure in boilers, 21*5 ; 
 
TAKEN FROM PADDLE-ENGINES. 
 
 123 
 
 vacuum in condensers, 25‘5 in.; revolutions, 24; 
 indicated power of tlie engines, 1231 ; fitted into 
 the steam-ship “ Guar a,” for the Brazilian S.S. Co. 
 
 Leaving these we notice next a pair of diagrams 
 taken from angular oscillating engines by the 
 same makers, depicted by Fig. 60. The supply 
 steam lines are slightly inclined, which may have 
 resulted from two causes ; one being defective 
 
 Fig. 60. 
 
 Angular Oscillating Padlle-wheel Engines. 
 
 Messrs. Laird’s indicator diagrams, showing even supply, expansion, ex- 
 haustion, and lead. Original scale, ^ in. = 1 lb. Half size. 
 
 supply or pressure of steam, and the other the 
 contraction of the steam opening, caused by the 
 valve, or what is often termed “throttling the 
 steam.” The engines are 260 horse-power 
 nominal ; diameter of cylinders, 64 in. ; stroke 
 of the piston, 6 ft'. ; steam pressure in the 
 boilers, 26 lbs. ; vacuum, 24 in. ; number of 
 revolutions per minute, 30 ; indicated horse- 
 power, 2028 collectively. 
 
124 
 
 THE INDICATOR DIAGRAM. 
 
 The diagrams shown by Figs. 61 and 62 are 
 also by Messrs. Laird, but are not as creditable as 
 those preceding. The engines are 100 horse-power 
 
 Fig. 61. 
 
 Inclined Direct-acting Paddle-wheel Engines. 
 
 Messrs. Laird’s indicator diagrams, showing a contracted supply of steam> 
 uneven expansion, nearly equal exhaustion and lead. Original scale, J in. 
 = 1 lb. Half size. 
 
 nominal, fitted into a tug-boat. Diameter of 
 cylinders, 38 in. ; stroke of the piston, 4 ft. 6 in. ; 
 number of revolutions per minute, 39*5; steam, 
 
TAKEN FROM PADDLE-ENGINES. 
 
 125 
 
 29 lbs. ; vacuum 24 in. ; indicated horse-power, 
 673 collectively. 
 
 As a contrast with those preceding, we direct 
 attention to the diagrams shown by Fig. 63, and 
 those shown by Fig. 64, to define the result of 
 
 ZERO LINE 
 
 Vertical Return-acting Paddle-wheel Engines. 
 
 Messrs. Maudslay’s indicator diagrams, showing/w^ supply, unequal expansion 
 and exhaustion, with equal lead ; starboard engine. Original scale, T g in. 
 = 1 lb. Half size. 
 
 Fig. 64. 
 
 Messrs. Maudslay’s indicator diagrams, showing the result of half-boiler power 
 in comparison with Fig. 63 ; starboard engine. Original scale, -jL in. = 1 lb. 
 Half size. 
 
126 
 
 THE INDICATOR DIAGRAM. 
 
 lower pressure and slower speed. The diagrams 
 in Fig. 63 are taken with full boiler power, hut 
 those depicted by Fig. 64 with half boiler power 
 
 Fig. 65. 
 
 Vertical Return- acting Paddle-wheel Engines. 
 
 Messrs. Maudslay’s indicator diagrams, showing the result of the expansion 
 gear used ; starboard engine. Original scale, T l g in. = 1 lb. Half size. 
 
 only ; and as a contrast to both we illustrate a 
 series taken from the same engines with the cam 
 expansion gear on, shown by Fig. 65. The 
 engines are fitted in H.M.S. “Terrible;” hut, 
 although old and costly, shpw clearly that with a 
 long stroke for the piston, time is allowed for the 
 full expenditure of the steam, and that the firm 
 recognized that fact when they designed the 
 engines. We may add that the originals of the 
 above diagrams were taken in March, 1865 ; the 
 mean indicated full boiler-power for six runs was 
 2059*684 ; speed of the ship 105 knots per hour, 
 and the slip of the paddle-fioats 21*7 per cent. 
 
TAKEN FROM PADDLE-ENGINES. 
 
 127 
 
 Messrs. Bennie’s examples now claim attention, 
 as depicted by Figs. 66 and 67. These diagrams 
 
 Fig. 66. 
 
 STEAM 25 
 
 Fig. 67. 
 
 Oscillating Paddle-wheel Engines. 
 
 Messrs. Rennie’s indicator diagrams, showing the result of using the steam 
 expansively ; port cylinder. Original scale, in. = 1 lb. 
 
128 
 
 THE INDICATOR DIAGRAM. 
 
 were taken from the same engines as those were 
 that are illustrated in pages 117, 118, by Figs. 54 
 and 55. In both cases the steam was evidently 
 throttled to some extent ; but what was lost in 
 steam pressure was made up with vacuum, as can 
 be seen from the diagrams Figs. 66 and 67, and that 
 when full steam was admitted the vacuum indi- 
 cation was the least, and vice versa with the third 
 grade of cut-off, and also with the intermediate 
 grades respectively. 
 
 We learn here, again, that the time for the 
 admission of the steam proportionates the time 
 for exhaustion ; and hence with an early cut-off 
 a better vacuum is attainable than with a later 
 limit for the supply. In fact, the whole matter 
 is regulated by the relation that the time bears 
 to the pressure ; indeed, the indicator diagram is 
 only an evidence of time and pressure, and when 
 their relation is understood the facts are as simple 
 as need be. As we have often stated before, the 
 horizontal lines are “ even or full continuous pres- 
 sures,” the vertical lines, “instantaneous pres- 
 sures,” and that all deviations from these are 
 alterations of pressures ; then, as the pressure is 
 to the time, so is the time to the indication. 
 
 Another example of a series of expansion dia- 
 grams is shown by Fig. 68, taken by Messrs. 
 
TAKEN" FROM P ADDLE-ENGINES. 
 
 129 
 
 Maud slay from the cylinder of one of the engines 
 of 800 horse-power fitted by the firm into the 
 steamship “ Oronoco.” The diagrams show very 
 
 Vertical Oscillating Paddle-wheel Engines. 
 
 Messrs. Maudslay’s indicator diagrams, showing six grades of cut-off, and 
 nearly equal lead. Original scale, | in. = 1 lb. Half size. 
 
 clearly the proportion that the supply line bears 
 to the expansion curve, also the relative points of 
 exhaustion and lead. 
 
 The diagrams shown by Fig. 69 were taken 
 from one of the cylinders of a pair of inclined di- 
 
 K 
 
130 
 
 THE INDICATOR DIAGRAM. 
 
 rect-acting engines of 100 horse-power collectively, 
 and fitted by Messrs. Penn in an Egyptian tug- 
 boat. Diameter of cylinder, 38| in. ; stroke of 
 piston, 4 ft. 6 in. The figures show very nearly 
 equally full supply-steam lines, and the remainder 
 almost duplicates. The diagrams illustrated by 
 
 Fig. 70. 
 
 Direct-acting Inclined Paddle-wheel engines. 
 
 Indicator diagrams showing the expansion by the link motion. Original 
 scale, Jg in. = 1 lb. Half size. 
 
 Fig. 70 were taken from the same engines, and 
 indicate the result of using the link motion and 
 slide-valve for the early cut-off of the steam. 
 
 The diagrams that are illustrated by Fig. 71 
 are superior to any we have yet depicted ; for the 
 supply-steam, expansion, exhaustion, and lead lines 
 are perfectly formed, as well as being duplicates ; 
 indeed, so far are they worthy of appreciation that 
 we solicited from Mr. Penn a sketch of the indi- 
 cator he used at the time they were taken, to 
 enable the entire matter to be fully understood — 
 which we illustrate by Fig. 72. 
 
Oscillating Paddle-wheel Engines. 
 
 Perfect indicator diagrams taken from the engines fitted in Mr. Penn’s steam- 
 yacht “ Lara.” Gridiron expansion valves on steam-pipes. Diameter of cylinder, 
 30 in. ; stroke of piston, 2 ft. 9 in. ; nominal horse-power collectively, 50. 
 Original scale, T t in. = 1 lb. Half size. 
 
 Messrs. Penn’s indicator gear for oscillating engines. Scale, § in. = 1 ft. 
 
132 
 
 THE INDICATOR DIAGRAM. 
 
 Messrs. Penn’s indicator gear for oscil- 
 lating engines. — This arrangement shows that 
 the indicator is vertically situated on the top of 
 the steam-pipe, and below the instrument an 
 angular two-way cock forms the connection with 
 the pipe ; we have shown the section of this cock, 
 union joint, and pipe under the cylinder cover. 
 The arrangement of the reducing motion gear is 
 a spring wheel and a series of spur wheels and 
 pinions, contained in a box of suitable form and 
 dimensions : this is found to be more reliable 
 than the large wheel and spring-box. 
 
 Messrs* Napier’s indicator gear for oscil- 
 lating engines. — This “gear,” as shown by 
 Fig. 73, is very like that illustrated in pages 
 22 and 24, excepting that in this case the pipes 
 are attached to the sides of the cylinder, instead 
 of the ends. The indicator also is horizontally 
 situated, and the bracket for supporting the main 
 motion wheel is shorter. The plan and front 
 view of the arrangement is shown too, so that 
 the matter is clear without description. Our 
 reason for illustrating this gear in this portion of 
 the present work is that, as the diagrams shown 
 by Figs. 56 and 57 in page 121 are such excep- 
 tionally good productions, we solicited a drawing 
 of the indicator and gear from the firm to show 
 
Fie. 73. 
 
 PADDLE-ENGINE INDICATOR GEAR. 133 
 
 to our readers the arrangement that produced 
 such good results. 
 
 Messrs. Napier’s indicator gear for oscillating engines. Scale, i ii 
 
134 
 
 THE INDICATOR DIAGRAM. 
 
 CHAPTER VIII. 
 
 EXAMPLES OP INDICATOR DIAGRAMS TAKEN FROM 
 LAND ENGINES. 
 
 Compound beam-engines. — We commence this 
 chapter with an example of diagrams from a 
 compound beam-engine constructed by a well- 
 known firm in London for a seaport water-works. 
 Pig. 74 is the high-pressure diagram, which 
 
 Fig. 74. 
 C 
 
 Compound High and Low Pressure Steam-condensing Beam 
 engine. 
 
 High pressure indicator diagram. Original scale, ^ in. = 1 lb. Half size. 
 
 shows that the point of cut-off, C, is about five- 
 eighths of the stroke of the piston. The portion 
 of the exhaust line at E indicates the full re- 
 lease of the steam from the high-pressure into 
 
TAKEN FROM A BEAM-ENGINE. 
 
 135 
 
 the low-pressure cylinder. The lead-corner L 
 shows the point of readmission. 
 
 The low-pressure diagram is depicted by Fig. 
 75, which shows an almost perfect expansion 
 curve, correct exhaust, and the least amount of 
 lead necessary. 
 
 Compound High and Low Pressure Steam-condensing Beam- 
 engine. 
 
 Low pressure indicator diagram. Original scale, i in. = 1 lb. Half size. 
 
 Fie. 76. 
 
 Compound Beam-engine. 
 
 The high and low pressure indicator diagrams pieced together at the same scale 
 in lbs. High pressure diagram, half size ; low pressure diagram, quarter 
 size in height, and half size in length. 
 
 The diagrams illustrated by Fig. 76 depict 
 
136 
 
 THE INDICATOR DIAGRAM. 
 
 what must be done to faithfully “ piece ” the 
 figures together, and show also that the valves 
 were well arranged to cause such a perfect con- 
 nection ; as the amalgamation of the two diagrams 
 depicts the action of the steam in both of the 
 cylinders as a combination : also the action of the 
 same volume of steam in two cylinders on opposite 
 sides of the relative pistons. The diagrams shown 
 by Fig. 77 are introduced to further show to the 
 
 Fig. 77. 
 
 “ pieced ” together. Original scale, high pressure, ^ in. and low pressure, 
 7(5 in. = 1 lb. Half size. 
 
 uninitiated that the pressure of the steam regu- 
 lates the forms of the diagrams. These were 
 taken from the same engines as those preceding, 
 and depict that the “ piecing ” together at separate 
 scales does not show the actual result. 
 
TAKEN FROM A DIRECT- ACTING ENGINE. 137 
 
 Horizontal condensing direct-acting en- 
 gines. — We have only one example from this 
 class of engine, as depicted by Fig. 78, which 
 
 Fig. 78. 
 
 Diagram taken from the “ Allen ” engine at the French International Exhibi- 
 tion of 1867. Original scale, 1 in. = 24 lbs. Half size. 
 
 shows a high degree of expansion, and an early 
 cut-off to produce it with perfect exhaustion and 
 lead. The undulations of the expansion line 
 result from the slackness of the motion-cord and 
 the jerking of the paper-barrel. 
 
 Locomotive engines. — We cannot commence 
 this section more appropriately than by illus- 
 trating two indicator diagrams taken when the 
 engine started, as shown by Fig. 79. These are 
 creditable examples, as they depict full-supply 
 steam, S, correct expansion, E, good exhaustion 
 with very little back-pressure, ample lead, L, and 
 a vertical admission line, R. A greater length 
 of supply line, S, and a shorter exhaustion line, 
 
138 
 
 THE INDICATOR DIAGRAM. 
 
 E, is shown by Fig. 80, and also the proportionate 
 amount of exhaust line and lead curve, L, with 
 the admission line, It. 
 
 Fig. 79. 
 
 Locomotive Engine L.S.W.R. 
 
 Indicator diagrams from the engine when starting, showing full steam. 
 Original scale, fa in. = 1 lb. Half size. 
 
 Fig. 80. 
 
 Locomotive Engine L.S.W.R. 
 
 Indicator diagram showing the limit of full steam on starting. Original scale, 
 in. = 1 lb. Half size. 
 
TAKEN FROM A LOCOMOTIVE ENGINE. 139 
 
 Fig. 81 is an example of three diagrams taken 
 
 Fig. 81. 
 
 Locomotive Engine L.S.W.R. 
 
 Indicator diagrams showing the proportion of time to velocity. Original scale, 
 in. = 1 lb. Half size. 
 
 when the cranks were revolving 124 times per 
 minute. The proportion of the line S to the 
 line L clearly proves that what is taken from the 
 full supply line is put on to the lead line ; as 
 indeed it must be, because the lead portion of the 
 crank-phi’s circle is opposite to that for supply ; 
 therefore the time for each operation is relative, 
 because the crank-pin moves at the same speed 
 above and below the plane line of motion. 
 
 The diagrams shown by Fig. 82 present a 
 greater contrast, and Fig. 83 the greatest, with 
 the same amount of back-pressure ; which illus- 
 trates again that time regulates the indication as 
 much as the pressure. The diagrams depicted by 
 Fig. 84 illustrate a further explanation of the pro- 
 
140 
 
 THE INDICATOR DIAGRAM. 
 
 portion of time to speed of the piston, proving, 
 too, that the pressure of the steam is more per- 
 fectly indicated with high speeds than the other 
 portions of the matter. 
 
 Fig. 82. 
 
 Indicator diagrams showing a greater indication of the proportion of time to 
 velocity. Original scale, ^ in. = 1 lb. Half size. 
 
 Fig. 83. 
 
 Locomotive Engine L.S.W.R. 
 
 Indicator diagrams showing a high rate of expansion and enlarged lead. 
 Original scale, ^ in. = 1 lb. Half size. 
 
 These diagrams, Figs. 79 to 84 inclusive, just 
 referred to, were kindly contributed by C. F. T. 
 
TAKEN FROM A LOCOMOTIVE ENGINE. 141 
 
 Young, Esq., C.E., and were taken by liim from 
 the cylinders of the locomotive “ Eagle,” on the 
 London and South-Western Eailway, during jour- 
 neys from Waterloo to Southampton and return 
 
 Fig. 84. 
 
 Locomotive Engine L.S.W.R. 
 
 Indicator diagrams showing the result of express speed at the rate of 55 miles 
 per hour. Original scale, -fa in. = 1 lb. Half size. 
 
 — a distance, one way, of 16 L5 miles. The train 
 left London at 11 a.m. and arrived at Southamp- 
 ton at 3 p.m. On leaving Waterloo the number 
 of carriages was 20, and from Southampton, 16, 
 and others were taken on and off at various points 
 of the line, the average load being 13T1. 
 
 The cylinders of the engine are outside, and are 
 16 in. diameter, with a 22-inch stroke of piston ; 
 outside lap of the slide-valve, ■§■ in. ; lead, in. ; 
 working pressure of steam, 120 lbs. on the square 
 inch in the cylinders ; coupled driving wheels 6 ft. 
 in diameter. 
 
142 
 
 THE INDICATOR DIAGRAM. 
 
 CHAPTER IX. 
 
 EXAMPLES OF INDICATOR DIAGRAMS TAKEN FROM 
 AIR AND WATER PUMPS. 
 
 Explanation. — The principles on which the 
 pump indicator diagram is founded are precisely 
 as those from the steam-cylinder, hut the mecha- 
 nical construction is entirely opposite. The cause 
 for this is that the motion for the pencil when 
 illustrating the pressure of the water is rising 
 during the motion of the paper-barrel; whereas 
 with steam it is stationary. Now to render this 
 matter clear to the student, let us imagine a 
 pump with the piston at one end, and the barrel 
 filled with water ; the action of the piston on 
 moving is to compress the water until the dis- 
 charge valves open, when the water will be driven 
 out with a velocity due to that of the piston. 
 We will again assume that the same piston is at 
 the end of its stroke, but the barrel only partially 
 filled with water ; the result will be that on the 
 piston moving for a certain distance there will be 
 no pressure, because the water is being merely 
 pushed, and maintaining its level due to its 
 
TAKEN FROM AIR PUMPS. 
 
 143 
 
 gravity during that time ; but immediately the 
 water fills the space in front of the piston, then 
 the pressure occurs, because the water is lifted 
 above its natural level. 
 
 As a practical illustration of this we introduce 
 the diagram Fig. 85. 
 
 Air and Water Pump Indicator Diagram. 
 
 S = Starting point. 
 s = Vacuum limit. 
 
 S P = Stroke of piston. 
 N = No pressure. 
 
 R = Return stroke. 
 
 D = Compression and commence- 
 ment of discharge. 
 
 D 1 = Full discharge. 
 
 D 2 = Termination of discharge. 
 
 C = Commencement of stroke. 
 
 T = Termination of stroke. 
 
 Original scale, J in. = 1 lb. Half size. 
 
 The pencil described this diagram under the 
 following circumstances. First, the paper vibrated 
 and the atmospheric line was described. The 
 communication from the air pump was then 
 formed by turning the stop-plug ; the pencil 
 then instantly fell for the length of s, because 
 
144 
 
 THE INDICATOR DIAGRAM. 
 
 the piston of the pump formed a suction directly 
 it moved, which caused the atmosphere to force 
 the indicator piston down to the point of resist- 
 ance. The pencil here became stationary, and 
 was kept in that position — by the atmospheric 
 pressure — during the stroke of the pump-piston, 
 S P, or the length from C to T. This piston 
 then returned and shifted the water directly in 
 front of it in the barrel for the length of N, 
 which depicts that during that portion of the 
 stroke there was but little, if any, pressure in the 
 pump. The pencil having traced the parallel 
 line, or nearly so, for the length of 1ST, it rose and 
 formed the remainder of the line R, while the 
 pump-piston moved, until it reached the atmo- 
 spheric line. 
 
 It is perhaps necessary, for further explanation, 
 to state that while the pencil formed the line R 
 the water in the pump — in front of the piston — 
 was constantly maintaining its natural level ; but 
 as there was some air amongst the water, that 
 vapour rose as the liquid was disturbed, and thus 
 caused the pressure as indicated below the atmo- 
 spheric line. 
 
 The compression and discharge of the water 
 here commenced, and thus the load on the piston 
 caused a further pressure under the indicator piston 
 
TAKEN FROM AIR-PUMPS. 
 
 145 
 
 which forced the pencil to rise for the height of 
 D. Here it stopped, and the pressure maintained 
 its level for a moment, which allowed the pencil 
 to form D 1 . The main load on the piston was 
 here overcome because the bulk of the water left 
 was of a lesser quantity than what had been dis- 
 charged ; then, as the pressure decreased so did 
 the pencil descend, and form the line D 2 , and 
 then resume its original position at S. We have 
 introduced the arrows to indicate the motion of 
 the pencil, so that the student can fully under- 
 stand this subject. 
 
 By the next example, shown by Fig. 86, we 
 
 Fig. 86. 
 T 
 
 Double-acting Air-pump ; Horizontal Motion ; Screw-engines. 
 Messrs. Watt’s indicator diagrams, showing sudden discharge and a fair attain- 
 ment of vacuum. Original scale, J in. = 1 lb. Half size. 
 
 illustrate that the pencil started from C ; and 
 as there was no pressure for nearly half the stroke 
 
 L 
 
146 
 
 THE INDICATOR DIAGRAM. 
 
 of the pump, the lines parallel with the atmospheric 
 line were described, and that as the velocity of 
 the piston was 168 strokes per minute, the pencil 
 rose almost vertically to record the limit of the 
 discharge pressure, T, and nearly as quickly fell 
 when the release occurred. The vacuum attained 
 was 26 in., and the pressure of discharge 11^- lbs., 
 being If lb. less than the vacuum. 
 
 The undulations made by the pencil on descend- 
 ing above the atmospheric line are produced by air 
 being mixed with the water, and thus there was 
 an unequal pressure at the final discharge. The 
 pencil’s descent to the vacuum line was perpendi- 
 cular for nearly that distance, the curved portion 
 S showing also that the pencil > did not descend 
 as rapidly as the pump’s piston moved, and that 
 the full suction occurred and was maintained 
 when the half-stroke was made. 
 
 The diagrams from vertical pumps next come 
 under consideration, and illustrations of them 
 are given by Fig. 87. The injection-pump dia- 
 gram shows a rapid discharge up to a pressure of 
 23 lbs. from the vacuum line. 
 
 The circulating pump diagram indicates a con- 
 tinuous discharge, and that there was but little 
 clearance for the water to “ wash ” in the barrel 
 before the pressure occurred, as the angular or 
 
TAKEN FROM PUMPS. 
 
 147 
 
 pressure line commences at tlie beginning of tlie 
 diagram, and thus shows that the water began to 
 leave the barrel at about one-third of the stroke 
 of the piston instead of two-thirds, as in the 
 injection-pump. The cause of the discharge 
 limit line being horizontal for such a length 
 is, that the piston had to force the water through 
 the tubes of the condenser, and thus the resist- 
 ance was continuous during that process. 
 
 Fig. 87. 
 
 Double-acting Pumps ; Vertical Motion ; Screw-engines. 
 
 Mr. Spencer’s indicator diagrams, showing the difference in the discharge 
 pressures. Scale, T ! s in. = 1 lb. 
 
 The surface-condenser air-pump diagram in- 
 dicates below the atmospheric line, and shows 
 that the discharge pressure was never above 
 the atmosphere, and that at the return-stroke 
 there was a little pressure in the barrel, as in- 
 dicated by the angular line. 
 
148 
 
 THE INDICATOR DIAGRAM. 
 
 CHAPTER X. 
 
 THE FORMULAE REQUISITE TO DEFINE THE DUTY 
 OF AN ENGINE FROM THE INDICATOR DIAGRAM. 
 
 We have endeavoured to “ drill ” the student in the 
 preceding chapters, and vve now give him our 
 concluding instructions as to the use of his 
 “ attention ” for practical purposes. 
 
 To commence with, we must notice the differ- 
 ence that must occur in indicator diagrams taken 
 from different classes of engines. Now, with 
 engines of slow rotative velocity, the diagram 
 taken will always be more truthful than with a 
 high revolving motion for the crank-shaft and a 
 short stroke for the piston, because there is more 
 time in the former case than in the latter for the 
 steam to expand and exhaust ; and, as a proof 
 of this, it will have been noticed doubtless that 
 the expansion and exhaustion lines in most of the 
 diagrams we have illustrated are the most faulty 
 portions of the whole. 
 
 Of course the real theoretical line for expan- 
 sion should commence from the supply line and 
 terminate at the atmospheric line ; and this can 
 
A PERFECT INDICATOR DIAGRAM. 149 
 
 best occur with engines having a long stroke of 
 piston, an early cut-off, and cam-motion for the 
 working of the equilibrium circular valves that 
 are separately situated at each end of the cylinder. 
 
 When the “ slide”-valve regulates the admis- 
 sion, expansion, and exhaustion of the steam, 
 the perfect indicator diagram will be as illus- 
 trated by Fig. 88, which shows full steam, per- 
 
 Fig. 88. 
 
 A perfect indicator diagram from a cylinder fitted with a slide-valve and di- 
 rect-acting link motion in full gear ; also showing the position of the pistQn 
 and crank-pin at each limit of the progressive construction of the diagram. 
 
 feet expansion, quick exhaustion, and continuous 
 vacuum, with the least amount of lead. 
 
 The position of the crank-pin when the slide- 
 valve is cutting off is at S ; when it is at E the 
 
150 
 
 THE INDICATOR DIAGRAM. 
 
 valve is permitting exhaustion, and that con- 
 tinues until the crank-pin reaches C, usually 
 termed the “ compression ” point ; from here 
 there is supposed to be no admission or escape 
 until the crank-pin reaches L, the lead position, 
 when the readmission occurs. 
 
 The diagram Fig. 89 is introduced as a con- 
 
 Fig. 89. 
 
 An indicator diagram showing an inclined supply-steam line, with full expan- 
 sion, exhaustion, and undulated lead. 
 
 trast to that preceding, which illustrates the 
 imperfections of the gear used for the supply of 
 the steam ; if the pressure in the boiler were con- 
 stant and the gear perfect the dotted lines indicate 
 the formation that should have occurred. 
 
 We will now suppose that the student has 
 taken an indicator diagram, and he desires to 
 prove its utility, and as an illustration for the 
 purpose we introduce the Fig. 90. 
 
 The first process is to divide the length of the 
 figure into ten equal divisions, and then to set off 
 
CALCULATION OP AN INDICATOR DIAGRAM. 151 
 
 half of one space from each extremity and arrange 
 the remainder equidistant. Next, lines are drawn 
 at right angles with the atmospheric line from 
 each intersection or divisional point ; then, with 
 
 Fig. 90. 
 
 The correct method of obtaining the mean pressure of the steam and vacuum 
 as recorded oy an indicator diagram. 
 
 the scale of the diagram, each ordinate is measured 
 and figured above and below the atmospheric 
 line ; the total sum of each set of ordinates is 
 then obtained by simply adding the several 
 lengths together, and the mean is known by 
 dividing the total by the number of the ordi- 
 nates. 
 
 In the example, Fig. 90, the mean pressure of 
 the steam is 15*575 lbs. on the square inch ; and 
 
152 
 
 THE INDICATOR DIAGRAM. 
 
 the vacuum obtained is equal to an atmospheric 
 pressure exhausted of 9 '69 lbs. on the square inch 
 only. Observe, that the vacuum is recorded 
 as “ v. 26,” or 13 lbs. pressure by the gauge, 
 and the steam as 27f lbs. in the boiler; whereas 
 in the cylinder the highest record of full supply 
 is only 24‘2 lbs. This reduction of the steam 
 pressure is due to the friction and radiation ; and 
 the difference in the vacuum pressure is owing to 
 the temperature being higher in the cylinder 
 than in the exhaust steam pipe at the condenser 
 end. 
 
 Our next step is the use of the mean pressure 
 known ; the cylinder is 46 T 9 g- inches in diameter ; 
 the area being known from the square of the 
 diameter x '7854 = 1792'7994 square inches ; 
 then 1792'7994 x 25*265 (the mean pressure 
 of both steam and vacuum) = 43021*2268 lbs. as 
 the total load. 
 
 The length of the stroke of the piston is 1 ft. 
 6 in., and the speed is known by the formula — 
 number of revolutions of the crank-shaft x twice 
 the length of the stroke of the piston. 
 
 Next, 1*5 x 2 = 3 feet, and as the number of 
 revolutions is recorded as B,. 116 per minute, the 
 speed of the piston = 116 x 3 = 348 ; then, 
 348 x 43021*2268 = 14971386*9264 = the total 
 
INDICATED HORSE-POWER. 
 
 153 
 
 power in foot-pounds, because the speed is taken 
 in feet. 
 
 The sura of 33,000 is the constant to equal 
 one horse-power, or the weight in pounds that a 
 horse can lift one foot high per minute. 
 
 Then, if the total power is divided by the 
 
 constant, the quotient equals the indicated 
 
 horse-power ; for example, the total power 
 
 14971386*9624 akq aiyoo „ r 
 
 = 453*6783 horse-power ox the 
 
 ooUUU 
 
 engine under notice ; and as the nominal horse- 
 power is 100, the relation of the indicated power 
 to the nominal is obvious. 
 
 The formula, therefore, for the indicated power 
 of an engine is thus : when 
 
 M x A x [2 x S x R] 
 
 33000 
 
 M = Mean indicated pressure in lbs. per square 
 inch. 
 
 A = effective area of the cylinder in square 
 inches. 
 
 S = Stroke of the piston in feet. 
 
 R =s Number of revolutions per minute. 
 
 Of course with high-pressure engines the mean 
 pressure is obtained from the mean of the depth 
 of the diagram above the atmospheric line. 
 
 As the points on the diagram where the limits 
 
154 
 
 THE INDICATOR DIAGRAM. 
 
 of the duty of the steam occurs are both instruc- 
 tive and interesting, we introduce the Fig. 91, 
 which is a repetition of the diagram. Fig. 90, in 
 page 151, which being figured as this one at the 
 several pressures, it fully depicts their relation. 
 The point S on the circle indicates that when the 
 
 Fig. 91. 
 
 A diagram showing the positions of the crank-pin during certain stages of the 
 construction of the indicator diagram. Fig. 90 m page 151. 
 
 crank-pin reached it, supply steam terminated ; at E 
 the exhaustion of the steam commenced ; at C the 
 steam-ports were closed on that side of the piston, 
 and at L the lead commenced ; therefore No. 1 
 is the chord of supply, No. 2 of expansion, No. 3 
 of exhaustion, and No. 4 of nil or compression ; 
 and the points P P P are the relative positions 
 
THE END. 
 
 155 
 
 of the piston to the crank-pin. This method is 
 precisely as that illustrated by the frontispiece 
 plate, the geometry of which originated from the 
 author, and induced him to write the present 
 work on the Indicator Diagram. 
 
INDEX OF SUBJECTS 
 
 
 
 Page 
 
 Action of steam in the cylinder. 
 
 12, 77 
 
 Air-pump diagrams .... 
 
 . 142 
 
 >> 
 
 action of . 
 
 . 142 
 
 Atmospheric pressure 
 
 . 28 
 
 
 „ test of 
 
 . 30 
 
 Indicating notes .... 
 
 . 25 
 
 Indicator, description and use of . 
 
 1 
 
 
 Maudslay’s 
 
 4 
 
 
 Richards’ .... 
 
 . 6 
 
 99 
 
 springs for 
 
 . 8 
 
 5) 
 
 diagram scale of. 
 
 . 10 
 
 99 
 
 ,', to take correctly 
 
 . 11 
 
 99 
 
 position of 
 
 . 13 
 
 99 
 
 diagram, process of taking . 
 
 . 15 
 
 99 
 
 gear for direct-acting engines 
 
 17, 18, 19, 20, 113, 114 
 
 99 
 
 „ for oscillating engines . 
 
 22, 24, 132, 133 
 
 99 
 
 diagram, theoretical geometry of 
 
 . 46 
 
 99 
 
 „ definition of . 
 
 . 47 
 
 99 
 
 „ formation of. 
 
 . 47 
 
 99 
 
 „ motion of the pencil of the . . .48 
 
 99 
 
 ,, principles of. 
 
 . 49 
 
158 
 
 INDEX OF SUBJECTS, 
 
 
 
 
 
 Page 
 
 Indicator, diagram, 
 
 meaning of height of 
 
 
 . 53 
 
 »> 
 
 „ of length of 
 
 
 . 53 
 
 >> 
 
 correct representation of. 
 
 
 . 53 
 
 jj 
 
 proportions of 
 
 . 
 
 
 55,62 
 
 » j> 
 
 speed and travel of pencil of . 
 
 
 . 63 
 
 ?> 5? 
 
 Rankine’s explanation of. 
 
 
 . 64 
 
 » » 
 
 rules for the calculation of 
 
 
 70, 152 
 
 5? » 
 
 practical geometry of 
 
 
 . 74 
 
 JJ 
 
 practical definition of 
 
 
 . 79 
 
 » J) 
 
 from return-acting screw engines 
 
 
 . 91 
 
 » J> 
 
 from direct-acting engines 
 
 
 . 97 
 
 y> ?> 
 
 with raised link 
 
 • . • 
 
 
 . 105 
 
 5> >> 
 
 from trunk engines 
 
 
 . 108 
 
 5> >5 
 
 from inverted direct-acting engines 
 
 
 . 109 
 
 
 from compound engines . 
 
 
 . Ill 
 
 » » 
 
 
 pieced . 
 
 
 . 112 
 
 J> >5 
 
 
 steam launch engines 
 
 . 114 
 
 » » 
 
 
 paddle engines 
 
 
 . 117 
 
 >J » 
 
 w 
 
 land engines . 
 
 
 . 134 
 
 » » 
 
 
 beam engines. 
 
 
 134, 135 
 
 J> » 
 
 locomotive . 
 
 
 
 . 137 
 
 J> 5> 
 
 formulas 
 
 
 
 . 148 
 
 J) » 
 
 division of . 
 
 
 
 . 151 
 
 Lead, explanation of. 
 
 
 
 . 74 
 
 Logarithms, hyperbolic 
 
 
 
 . 41 
 
 Slide-valve, mechanical action of. 
 
 
 
 . 75 
 
 „ indicator diagram of. 
 
 . 
 
 
 . 149 
 
 Steam, particulars of 
 
 
 
 . 33 
 
 „ expansion of . 
 
 
 
 . 37 
 
 „ radiation of 
 
 • 
 
 
 
 . 36 
 
 „ elasticity of 
 
 . 
 
 
 
 . 36 
 
 „ expansion, rule for . 
 
 
 
 . 38 
 
 „ saturation of. 
 
 
 
 . 39 
 
INDEX ON SUBJECTS. 159 
 
 Steam, expansion, hyperbolical rule for 
 
 „ mean pressure of . . . . . 
 
 „ Kankine’s rule for mean pressure of . 
 
 „ „ diagram of mean pressure of 
 
 „ Simpson’s rule for mean pressure of . 
 
 „ Ordinary rule for mean pressure of . 
 
 „ „ example of mean pressure of 
 
 „ Walt’s method of showing the expansion of 
 „ efficiency of . 
 
 „ lead, description of . 
 
 „ full, description of . 
 
 „ cut-off, description of * . 
 
 Page 
 
 . 40 
 . 40 
 . 41 
 . 42 
 . 43 
 . 43 
 . 44 
 . 50 
 . 69 
 . 74 
 . 75 
 . 75 
 
INDEX OF ILLUSTKATIONS, 
 
 Page 
 
 Action of steam when propelling the piston, showing correct 
 
 position for the indicator . . . . . .12 
 
 Arrangement of indicator gear for oscillating engines, vertical 
 
 position, by Messrs. Watt and Co. . . . .22 
 
 Arrangement of indicator gear for oscillating engine, extreme 
 
 angular position, by Messrs. Watt and Co. . . .24 
 
 Atmospheric pressure, practical method for testing the . .31 
 
 Comparative theoretical indicator diagram, showing several 
 
 points of cut off ....... 61 
 
 Definition of an indicator diagram from actual practice . .15 
 
 Diagram of the expansion of steam by Professor Eankine . 42 
 
 Expansion of steam, diagram of, by Professor Rankine . .42 
 
 Expansion of steam, Watt’s method of illustrating the . . 50 
 
 Indicator, Messrs. Maudslay’s ...... 4 
 
 Indicator, Mr. Richards’ ....... 6 
 
 Indicator, action of the steam when propelling the piston, 
 
 showing correct positions for the . . , . .12 
 
 Indicator diagram, definition of, from actual practice . . 15 
 
 Indicator diagram, definition of the theoretical form of . .47 
 
 ¥ 
 
INDEX OF ILLUSTRATIONS, 
 
 161 
 
 Tage 
 
 Indicator diagrams, theoretical, within a cylinder (six illustra- 
 tions) ...... 55, 57, 58, 59, 60 
 
 Indicator diagrams, comparative, theoretical, and showing several 
 
 points of cnt-ofF. . . . . . . .61 
 
 Indicator diagram, theoretical, by Professor Rankine . .65 
 
 Indicator diagram, practical definition of . . .79 
 
 Indicator diagrams taken from the cylinder shown in the plate. 
 
 Four illustrations, occupying pages . . . 87,89 
 
 Indicator diagrams from oscillating engines (starboard cylinder) 
 
 by Messrs. Rennie . . . . . . .117 
 
 Indicator diagrams from oscillating engines (port cylinder) by 
 
 Messrs. Rennie . . . . . . . .118 
 
 Indicator diagrams from oscillating engines (two illustrations) 
 
 from port and starboard cylinders, by Messrs. Napier . 121 
 Indicator diagrams from oscillating engines (two diagrams from 
 
 port and starboard cylinders), by Messrs. Laird . . 122 
 
 Indicator diagrams from angular oscillating engines, by Messrs. 
 Laird ......... 123 
 
 Indicator diagrams from inclined direct-acting engines (port and 
 
 starboard cylinders), by Messrs. Laird . . . .124 
 
 Indicator diagrams from vertical return-acting paddle-wheel 
 
 engines, by Messrs. Maudslay . . . . .125 
 
 Indicator diagrams from vertical return-acting paddle-wheel 
 
 engines (£ boiler power), by Messrs. Maudslay . .125 
 
 Indicator diagrams from vertical return-acting paddle-wheel 
 
 engines (with expansion gear), by Messrs. Maudslay . 126 
 Indicator diagrams from oscillating paddle-wheel engines (port 
 
 and starboard cylinders), by Messrs. Rennie . . .127 
 
 Indicator diagrams from vertical oscillating engines, by Messrs. 
 
 Maudslay ........ 129 
 
 Indicator diagrams from direct-acting inclined engines, by 
 Messrs. Penn ........ 129 
 
 Indicator diagrams from direct-acting inclined engines (with ex- 
 pansion by link motion) ...... 130 
 
 Indicator diagrams (perfect) from oscillating steam-yacht engines, 
 by Messrs Penn. ....... 131 
 
 Indicator diagrams from direct-acting engines, showing full 
 
 supply of steam, by Messrs. Watt . # . .97 
 
162 
 
 INDEX OF ILLUSTRATIONS. 
 
 Page 
 
 Indicator diagrams from direct-acting engines, showing slight de- 
 flection of supply lines, by Messrs. Watt . . .99 
 
 Indicator diagrams from direct-acting engines, showing vertical 
 
 undulation, by Messrs. Watt . . . . .99 
 
 Indicator diagrams from return-acting engines, by Messrs. Rennie 100 
 Indicator diagrams from return-acting engines, forward engine, 
 
 by Messrs. Laird ....... 101 
 
 Indicator diagrams from return-acting engines, aft engine, by 
 
 Messrs. Laird . . . . . . . 102 
 
 Indicator diagrams from double-trunk engines, by Messrs. Penn 102 
 Indicator diagrams from double-trunk engines, showing the 
 
 result of early cut-off, by Messrs. Penn .... 108 
 
 Indicator diagrams from return-acting engines, forward engine, 
 
 by Messrs. Maudslay .*..... 104 
 
 Indicator diagrams from return-acting engines, aft engine, by 
 
 Messrs. Maudslay ....... 104 
 
 Indicator diagrams from return-acting engines, showing six 
 
 grades of cut-off, by Messrs. Napier .... 105 
 
 Indicator diagrams from direct-acting engines, showing four 
 
 grades of expansion, by Messrs. Watt . . . . 106 
 
 Indicator diagrams from inverted direct-acting engines, aft 
 
 cylinder, bv Messrs. Penn ...... ICQ 
 
 Indicator diagrams from inverted direct-acting engines, forward 
 
 cylinder, by Messrs. Penn ...... 109 
 
 Indicator diagrams from inverted direct-acting screw engines, 
 by Messrs. Maudslay . . . . . . .91 
 
 Indicator diagrams from return-acting engines, indicating 6867 
 
 horse nower, by Messrs. Maudslay . . . .92 
 
 Indicator diagrams from return-acting engines, showing unequal 
 
 cut off, by Messrs. Napier ...... 93 
 
 Indicator diagrams from return-acting engines, showing curved 
 
 supply lines, by Messrs. Napier . . . . .95 
 
 Indicator diagrams from return-acting engines, half-boiler power, 
 
 aft engine, by Messrs. Napier . . . . .96 
 
 Indicator diagrams from return-acting engines, half-boiler power, 
 
 forward engine, by Messrs. Napier . . . .96 
 
 Indicator diagrams from compound horizontal return-acting 
 
 engines, high pressure, by Messrs. Maudslay . . .111 
 
INDEX OF ILLUSTRATIONS. 
 
 163 
 
 Page 
 
 Indicator diagrams from compound horizontal return-acting 
 engines, low pressure, by Messrs. Maudslay . 
 
 Indicator diagrams, “ pieced ” together, from compound horizontal 
 return-acting engines, by Messrs. Maudslay . 
 
 Indicator diagram (high pressure), from a beam engine . 
 Indicator diagram (low pressure), from a beam engine 
 Indicator diagrams (high and low pressure), from a beam engine 
 Indicator diagrams (high and low pressure, wrongly “ pieced ” 
 together), from a beam engine ..... 
 
 Indicator diagram from the “Allen” engine, at the French 
 International Exhibition, 1867 ..... 
 
 Indicator diagrams from a locomotive, 3rd, 5th, and 1st notch, 
 respectively ....... 138, 
 
 Indicator diagrams from a locomotive, 1st notch, 112, 107, 
 105 lbs. pressure, respectively .... 140, 
 
 Indicator diagram from an air and water pump 
 Indicator diagrams from a double-acting air pump, by Messrs, 
 Watt 
 
 Indicator diagrams from double-acting pumps, by Mr. Spencer . 
 Indicator diagram (perfect) direct-acting link motion in full 
 
 gear 
 
 Indicator diagram, showing inclined supply steam line, full ex- 
 pansion and exhaustion, and undulated lead . 
 
 Indicator diagram, correct method of obtaining the mean pressure 
 of the steam and vacuum ...... 
 
 Indicator diagram, position of the crank pin during certain stages 
 of the construction ....... 
 
 Indicator diagrams from steam launch twin-screw engines, by 
 Messrs. Penn ........ 
 
 Indicator diagrams from steam launch twin-screw engines, by 
 Messrs. Rennie ........ 
 
 Indicator gear, direct-acting lever ..... 
 
 Indicator gear, pulley and lever, under motion , # 
 
 Indicator gear, pulley and lever, over motion 
 Indicator gear (side elevation and plan) for return -acting engines, 
 by Messrs. Napier ....... 
 
 Indicator gear (end elevation) for return-acting engines, by 
 Messrs. Napier ........ 
 
 Ill 
 
 112 
 
 134 
 
 135 
 
 135 
 
 136 
 
 137 
 
 139 
 
 141 
 
 143 
 
 145 
 
 147 
 
 149 
 
 150 
 
 151 
 
 154 
 
 115 
 
 116 
 
 18 
 
 19 
 
 20 
 
 113 
 
 114 
 
INDEX OF ILLUSTRATIONS. 
 
 164 
 
 Page 
 
 Indicator gear, arrangement of, for oscillating cylinders, by 
 
 Messrs. Watt and Co. ...... 22 
 
 Indicator gear, arrangement of, for oscillating cylinders, extreme 
 
 angular position, by Messrs. Watt and Co. . . .24 
 
 Indicator gear for oscillating engines, by Messrs. Penn . .131 
 
 Indicator gear for oscillating engines, by Messrs. Napier . .133 
 
 Practical method for testing the atmospheric pressure . . 31 
 
 Practical definition of an indicator diagram . . . .79 
 
 Pulley and lever indicator gear, under motion . . .19 
 
 Pulley and lever indicator gear, over motion. . . .20 
 
 Practical definition of the theoretical form of an indicator diagram 47 
 
 Theoretical indicator diagrams within a cylinder. . Six illustra- 
 tions, occupying pages ... 55, 57, 58, 59, 60 
 
 Theoretical indicator diagram by Professor Eankine . . 65 
 
 Watt’s method of illustrating the expansion of steam . . 50 
 
 LONDON I PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET 
 AND CHARING CROSS.