See also:

• STEAM
• STEAM (0. Eng. steam, vapour, smoke, cf. Du. steam; the origin is unknown)

His labours stand in natural sequence to those of See also:

• THOMAS
• THOMAS (c. 1654-1720)
• THOMAS (d. 110o)
• THOMAS, ARTHUR GORING (1850-1892)
• THOMAS, CHARLES LOUIS AMBROISE (1811-1896)
• THOMAS, GEORGE (c. 1756-1802)
• THOMAS, GEORGE HENRY (1816-187o)
• THOMAS, ISAIAH (1749-1831)
• THOMAS, PIERRE (1634-1698)
• THOMAS, SIDNEY GILCHRIST (1850-1885)
• THOMAS, ST
• THOMAS, THEODORE (1835-1905)
• THOMAS, WILLIAM (d. 1554)

1)1 is interesting as the prototype of a class of engines which long afterwards became practically important. A hollow See also:

• ALTAR (Lat. altare, from alias, high; some ancient etymological guesses are recorded by St Isidore of Seville in Etymologiae xv. 4)

4. Another See also:

• LINE

The steam engine first became commercially successful in the hands of Thomas Savery,2 who, in 1698, obtained a patent for a water-raising engine, shown in fig. 2. Steam is admitted to one of the See also:

• OVAL (Lat. ovum, egg)

Papin's was the earliest See also:

• CYLINDER (Gr. KvAwSpos, from KvXivaety, to roll)

Pressures as high as 8 or to atmospheres were employed—and that, too, without a safety-valve—but Savery found it no easy See also:

• MATTER

4. Steam admitted from the boiler to the cylinder allowed the piston to be raised by a heavy counterpoise on the other See also:

• SIDE
• SIDE (mod. Eski Adalia)

After the steam had done its work in the displacement-chamber it was allowed to See also:

• ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

This device was simplified in 1718 by See also:

• HENRY
• HENRY (1129-1195)
• HENRY (c. 1108-1139)
• HENRY (c. 1174–1216)
• HENRY (Fr. Henri; Span. Enrique; Ger. Heinrich; Mid. H. Ger. Heinrich and Heimrich; O.H.G. Haimi- or Heimirih, i.e. " prince, or chief of the house," from O.H.G. heim, the Eng. home, and rih, Goth. reiks; compare Lat. rex " king "—" rich," therefore " mig
• HENRY, EDWARD LAMSON (1841– )
• HENRY, JAMES (1798-1876)
• HENRY, JOSEPH (1797-1878)
• HENRY, MATTHEW (1662-1714)
• HENRY, PATRICK (1736–1799)
• HENRY, PRINCE OF BATTENBERG (1858-1896)
• HENRY, ROBERT (1718-1790)
• HENRY, VICTOR (1850– )
• HENRY, WILLIAM (1795-1836)

To preserve the vacuum in his See also:

• CONDENSER

In cases where cold water cannot be had in plenty, the engines may be wrought by this force of steam only, by discharging the steam into the air after it has done its See also:

• OFFICE (from Lat. officium, " duty," " service," a shortened form of opifacium, from facere, " to do," and either the stem of opes, " wealth," " aid," or opus, " work ")

At the end of the down-stroke a and c are shut and b is opened. This puts the two sides in equilibrium and allows the piston to be pulled up by the pump-rod P, which is heavy enough to serve as a counterpoise. C is the condenser, and A the air-pump, which discharges into the hot well H, whence the supply of the feed-pump F is drawn. 13. In a second patent (1781) Watt describes the " See also:

• SUN
• SUN (0. Eng. sonne, Ger. sonne. Fr. soleil, Lat. sol, Gr. ijXior, from which comes helio- in various English compounds)

The engine was still single-acting; the connecting-rod was attached to the far end of the beam, and that carried a counterpoise which served to raise the piston when steam was admitted below it. 14. In 1782 Watt patented two further improvements of the first importance, both of which he had invented some years other before. One was the use of double action, that is Inventions to say, the application of steam and vacuum to "watt. each side of the piston alternately. The other (invented as early as 1769) was the use of steam expansively, in other words the plan (now used in all engines that aim at See also:

• ECONOMY

His boilers were fed, as Newcomen's had been, through an open pipe which rose high enough to let the See also:

• COLUMN (Lat. columna)

Both Evans and Trevithick pressure applied their engines to propel carriages on roads, Steam. and both used for boiler a cylindrical vessel with a cylindrical flue inside—the construction now known as the Cornish boiler. In partnership with See also:

• WILLIAM
• WILLIAM (1143-1214)
• WILLIAM (1227-1256)
• WILLIAM (1J33-1584)
• WILLIAM (A.S. Wilhelm, O. Norse Vilhidlmr; O. H. Ger. Willahelm, Willahalm, M. H. Ger. Willehelm, Willehalm, Mod.Ger. Wilhelm; Du. Willem; O. Fr. Villalme, Mod. Fr. Guillaume; from " will," Goth. vilja, and " helm," Goth. hilms, Old Norse hidlmr, meaning
• WILLIAM (c. 1130-C. 1190)
• WILLIAM, 13TH

In Hornblower's engine the two cylinders were placed side by side, and both pistons worked on the same end of a beam overhead. This was an instance of the use of steam expansively, and as such was earlier than the patent, though not earlier than the invention, of expansive working by Watt. Hornblower was crushed by the Birmingham See also:

• FIRM

Woolf introduced the compound engine somewhat widely about 1814 as a pumping engine in the mines of Cornwall. But here it met a .strong competitor in the. high- Cornish Engine. Pressure single-cylinder engine hnder en See also:

• INE

For many years monthly reports were published of the " duty " of these engines, the " duty " being the number of foot-pounds of work done per See also:

• BUSHEL (from the O. Fr. boissiel, cf. med. Lat. bustellus, busellus, a little box)

Steam of higher pressure than had formerly been used, after doing work in the new cylinder, passed into the old or low-pressure cylinder, where it was. further expandea. Many engines whose power was proving insufficient for the extended machinery they had to drive were " MNaughted " in this way, and after conversion were found not only to yield more power but to show a marked economy of fuel. The compound form was selected by William See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

In and in 1872 Sir F. J. See also:

• BRAMWELL, GEORGE WILLIAM WILSHERE BRAMWELL, BARON (1808-1892)

Some particulars of the dimensions reached in modern practice will be given later. Several of the vessels engaged 'in the Transatlantic passenger service, and also a few armoured cruisers, have engines in which the twin sets together have an indicated horse-power exceeding 30,000. But even these figures are eclipsed in See also:

• SHIPS

A. Parsons that we owe not only the main idea of the modern steam turbine, but also the working out of many novel mechanical details which have been essential to success, as well as the adaptation of the turbine to marine propulsion. 24. In the steam turbine, as in the water turbine (for which see See also:

• HYDRAULICS (Gr. iS&,p, water, and ai,Xos, a pipe)

Parsons attacked the problem at an earlier date, in an entirely different way in the invention of his " compound " turbine. By dividing the whole expansion of the steam into a great number of successive and separate steps he limited the velocity acquired at each step to such an extent as to make it comparatively easy to See also:

• EXTRACT (from Lat. extrahere, to draw out)

Ten years later Henry See also:

• BELL
• BELL, ALEXANDER MELVILLE (1819—1905)
• BELL, ANDREW (1753—1832)
• BELL, GEORGE JOSEPH (1770-1843)
• BELL, HENRY (1767-1830)
• BELL, HENRY GLASSFORD (1803-1874)
• BELL, JACOB (1810-1859)
• BELL, JOHN (1691-178o)
• BELL, JOHN (1763-1820)
• BELL, JOHN (1797-1869)
• BELL, ROBERT (1800-1867)
• BELL, SIR CHARLES (1774—1842)

The first application to marine propulsion was in the " Turbinia," in 1897. The success of this little experimental vessel of See also:

• LOO (formerly called " Lanterloo," Fr. lanturlu, the refrain of a popular 17th-century song)

Enough has been said to show that the invention of the steam turbine is the most important step in steam See also:

• ENGINEERING

See also:

• JOULE, JAMES PRESCOTT (1818–1889)

When steam enters the cylinder it finds the metal chilled by the previous exhaust, and a portion of it is at once condensed. This has the effect of increasing, often very largely, the volume of boiler steam required per stroke. As expansion goes on the water that was condensed during admission begins to be re-evaporated from the sides of the cylinder, and this action is often prolonged into the exhaust. It is now recognized that any theory which fails to take account of these exchanges of heat between the steam and its metal envelope fails also to yield even comparatively correct results in calculating the relative efficiency of various steam pressures or various ranges of expansion. But the exchanges of heat are so complex that there seems little prospect of submitting them to any comprehensive theoretical treatment, and See also:

• INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

As it enters the water it will produce the following effects in three stages r. The temperature of the water rises until a certain temperature t is reached, at which steam begins to be formed. The value of t depends on the particular pressure p which the piston exerts. Until the temperature t is reached there is nothing but water below the piston. 2. Steam is formed, more heat being taken in. The piston (which is supposed to exert a constant pressure) rises. No further increase of temperature occurs during this stage, which continues until all the water is converted into steam. During this stage the steam which is formed is said to be saturated. The volume which the piston encloses at the end of this stage-the volume, namely, of 1 lb of saturated steam at pressure p (and temperature t)-will be denoted by v in cubic feet. 3. If after all the water is converted into steam more heat be allowed to enter, the volume will increase and the temperature will rise.

The steam is then said to be superheated. The difference between saturated and superheated steam may be expressed by saying that if water (at the temperature of the steam) be mixed with steam some of the water will be evaporated if the steam is superheated, but none if the steam is saturated. Any vapour in contact with its liquid and in thermal equilibrium is necessarily saturated. When saturated its properties differ considerably, as a rule, from those of a perfect See also:

• GAS

29. Relation of Volume and Temperature.-The same table shows the volume v in cubic feet occupied by lb of saturated steam at each temperature. This is based on the investigations of H. L. Callendar who has shown (see THERMODYNAMICS and See also:

• VAPORIZATION

Supply of Heat in Formation of Steam under Constant Pressure.-We have next to consider the supply of heat in the imaginary experiment of § 27. During the first stage, until the temperature rises from its initial value to to t, the temperature at which steam begins to form under the given pressure, heat is required only to warm the water. Since the specific heat of water is nearly constant, the amount of heat taken in during the first stage is approximately 1-to thermal See also:

• UNITS, DIMENSIONS OF
• UNITS, PHYSICAL

See also Ewing's Steam Engine (3rd ed., 1910). See also:

• TEMPERA (the Italian term), or DISTEMPER

The heat of formation of I lb of steam, when formed under constant pressure from water at any temperature to, is H-ho, where ho corresponds to to. It has been pointed out by Moilier that for the purpose of calculations in technical thermodynamics it is convenient to add to the heat of formation the quantity pw/J, which represents the thermal equivalent of the work spent in introducing the water under the piston, against the constant pressure p, before the operation of heating imagined in § 27 begins, w being the volume of the water. We thus obtain a quantity which in its numerical values differs only very slightly from H, namely I=H+pw/J• We shall call this the total heat of saturated steam. Values of I are stated in the table. Since the volume of i lb of water is only Properties of Saturated Steam. 0016 cub. ft. the term pw/J is numerically insignificant except at the highest pressures. Similarly, in reckoning the total heat of water Ia we add pw/J to h, and this quantity is also given in the table. The latent heat L is to be found from the table by subtracting I,s, the total heat of water, from the total heat of steam. We shall use the centigrade scale of temperature throughout this article, and accordingly the total heats are expressed in terms of a unit involving the centigrade degree, namely, the quantity of heat required to raise the temperature of unit mass of water through I° C. at 15° C. With this unit of heat the mechanical equivalent is 1400 foot-pounds when the unit of mass is the lb, and is 427 ilogram-metres when the unit of mass is the kilogramme. 32. Internal Energy.-Of the heat of steam the part pv/J is spent in doing external work.

The remainder has gone to increase the stock of internal energy which the substance possesses. In dealing with the heat required to produce steam we adopted the state of water at o°C. as an arbitrary starting-point from which to reckon the reception of heat. In the same way it is convenient This See also:

• FORMULA
• FORMULA (Lat. diminutive of forma, shape, pattern, &c., especially used of rules of judicial procedure)

33. Wet Steam.—In calculations which relate to the action of steam in engines we have often to deal, not with dry saturated steam, but with wet steam, or steam which either carries in suspension, or is otherwise mixed with, a greater or less proportion of water. In any such mixture, assuming it to be in equilibrium, the steam and water have the same temperature, and the steam is saturated. The dryness of wet steam is measured by the proportion q of dry steam in each See also:

• POUND
• POUND (2)—(a)

Superheatt'in°C. 80° 120° 160° I800 200° 100° 0.49 150° 0.49 0'51 200° 0.49 0.51 0.54 0.57 25o° 0.48 0.50 0.53 0.56 0.59 300° 0.48 0.50 0.52 0.54 0.57 35o° 0.48 0.49 0.51 0.5,3 0.56 4000 0.48 0.49 0.51 0.52 0-55 450° 0.48 0.49 0.51 0.52 0.54 35. Isothermal Expansion of Steam.—The expansion of volume which occurs during the conversion of water into steam under constant pressure is isothermal. From what has been already said it is obvious that steam, or any other saturated vapour, can be expanded or compressed isothermally only when wet, and that evaporation (in the one case) or condensation (in the other) must accompany the process. Isothermal lines for a working substance which consists of a liquid and its vapour are straight lines of See also:

• UNIFORM

(Ql-Q2)IQl = (Ti ` T2)/T1 and W, the work done, is QW(TI-Try)/ri. In the ideal engine imagined by Carnot the action is of this simple See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

This part of the operation is shown by the line ab in fig. 9. 2. Remove A and apply B. Allow the expansion to continue adiabatically (bc) with falling pressure, until the temperature falls to ,T{,2. The pressure will then be C2, namely, the pressure given in the table corresponding to T2. 3. Remove B, apply C, and compress. Steam is condensed by rejecting heat to C. The action is isothermal, and the pressure remains p2. Let this be continued until a certain point d is reached, after which adiabatic compression will complete the cycle. 4.

Remove C and apply B. Continue the compression, which is now adiabatic. If the point d has been rightly chosen, this will complete the cycle by restoring the working fluid to the state of water at temperature Ti. The " indicator See also:

• DIAGRAM

In engines of ordinary construction the pressure is rarely so much as 250 lb per sq. in. It must not be supposed that the efficiency (ri—See also:

• R2(rt-s2)

,At the end of the expansion See also:

• RELEASE (O.Fr. reles, variant of relais, from relaisser, to release, let go, Lat. relaxare)

Accordingly, we may investigate as follows the ideal performance of an engine following the Rankine cycle. Let SQ represent that portion of the whole heat which is taken in at any temperature T. Then the greatest amount of work obtainable from that portion of heat is SQ(r-T2)/T, and the whole amount of work ideally obtainable in the complete process is found by calculating,XSQ(r-r2)/T where the summation includes all the heat that is taken in. In a steam engine using saturated steam the principal See also:

• ITEM (a Latin adverb meaning " also," " likewise ")

This expression applies whether the steam is initially superheated or not. I2 will in general be the total heat of a wet mixture, and to calculate it we must know the condition as to wetness which results from the expansion. This is most easily found, especially when there has been initial superheat, by making use of the entropy-temperature diagram to be presently described, or by other graphic methods, for an account of which the reader should refer to the See also:

• PAPER
• PAPER (Fr. papier, from Lat. papyrus)

The same result may be extended to a cycle which includes any non-reversible step, by taking account of the heat generated within the substance by such a step, as if it were heat communicated from outside, in the reckoning of entropy. Thus, for example, if at one stage in the cycle the sub-stance passes through a throttle-valve, which lowers its pressure without letting it do work, the action is equivalent in effect to an adiabatic expansion, together with the communication to the sub-stance, as heat, of the work which is lost in consequence of the irreversible expansion through the throttle-valve taking the place of adiabatic expansion against a piston. If this heat be included in the reckoning ZSQ/T=o for the complete cycle. The entropy-temperature diagram for any complete cyclic process is a closed curve, and the area it encloses, being the excess of the heat received over the heat rejected, measures the work done. The entropy-temperature diagram shares this useful characteristic with the pressure-volume diagram, and in addition it shows directly the heat received and the heat rejected by the areas under the forward and backward limbs of the curve. To draw the entropy-temperature diagram for the ideal steam engine (namely, the engine following the Rankine cycle), we have to reckon first the entropy which water acquires in being heated, and next the entropy Li/ri which is acquired when the conversion into steam has taken place. Reckoning from any standard temperature To, in the heating of the feed-water up to any temperature r, the entropy acquired is _ (T adr 4'w Jr0 T ' and taking a as sensibly constant, See also:

• SIS (anc. Sision or Siskia, later Flaviopolis or Flavias)

The area mabcp is the whole heat taken in, and the area made is the heat rejected. Let a curve cf be drawn to show the values of the entropy of steam for various temperatures of saturation: then if ad be produced to meet the curve in f, the ratio fd/fa represents the fraction of the steam which was condensed during adiabatic expansion. For the point f represents the state of 1 lb of saturated steam, and in the condensation of 1 lb of saturated steam the heat given out would be the area under fa, whereas the heat actually given out in the condensation from d was the area under &I,. Thus the state at d is that of a wet mixture in which da/fa represents the fraction present as steam, and fd/f a the fraction present as water. It obviously follows that by See also:

• DRAWING

43. Entropy-Temperature Diagrams extended to the Case of Super-heated Steam.—In the diagrams which have been sketched, it has r been assumed that the steam is supplied to the engine in a saturated state. To extend the same treatment to the case of super-heated steam, we have to take account of the supplementary supply of heat which the steam receives after the point c is reached, and before expansion be-sins. When superheating is resorted to, as is now often the case in practice, the superheat is given at constant pressure. If K represent as before the mean specific heat of steam at constant pressure, the addition of entropy during the process of superheating from r1 to r' is K(r'—rl). The value of K may be treated as approximately constant, and the addition to the entropy may then be written as K(See also:

• LOG (a word of uncertain etymological origin,possibly onomatopoeic; the New English Dictionary rejects the derivation from Norwegian lag, a fallen tree)

Entropy of Wet Steam.—The entropy of wet steam is readily calculated by considering that the change of entropy in the conversion from water to steam will be qL/r if the steam is wet, q being the dryness. Accordingly the entropy of wet steam at any temperature r is e(loger—logero)+gL/r. Further, since cr for water is practically equal to unity this expression may be written 41= logo-- logero+gL/r. We may apply this expression to trace the development of wetness in steam when it expands adiabatically. In adiabatic expansion = constant. Using the suffix 1 to distinguish the initial state, we therefore have at any stage in the expansion loge- - logero+gL/r = logErl — See also:

• LORE
• LORE, AMBROISE DE (1396-1446)

When the pressure of steam in the cylinder has been so far reduced by expansion that it can only overcome the See also:

• FRICTION (from Lat. fricare, to rub)

C.E. It should be added that these figures are exceptional. A consumpcxxxi. 147), who studied the cyclic See also:

• VARIATIONS
• VARIATIONS, CALCULUS
• VARIATIONS, CALCULUS OF

In those In the alternate condensation and re-evaporation of steam in the cases the steam was superheated only about 30° to 45° C. above the cylinder more heat is given to the metal by each pound of steam that temperature of saturation, but in more recent practice much greater is condensed than is taken from the metal by each pound of steam amounts of superheat have been successfully applied. See also:

• PROFESSOR (the Latin noun formed from the verb profiteri, to declare publicly, to acknowledge, profess)

But it is important to See also:

• NOTICE

By using hori- by the highly superheated steam; and when this is done, the steam zontal cylinders with admission valves on the top and exhaust may properly receive a still higher degree of initial superheat. valves below, the further advantage of drainage through the exhaust Accordingly, though the initial temperature of the steam may b.e valves is secured. Water which is present at release has then the 4000 C. or more, this is reduced to about 320° by transfer to steam in See also:

• CHANCE (through the O. Fr. cheance, from the Late Lat. cadentia, things happening, from cadere, to fall out, happen; cf. " case ")

The indicator, which was invented by found to lie between 12 and 13 lb per horse-power-hour. Some of Watt, and improved by See also:

• RICHARDS, ALFRED BATE (182o-1876)
• RICHARDS, HENRY BRINLEY (1819-1865)
• RICHARDS, WILLIAM TROST (1833-1905)

One of. these modified forms of Richards's indicator (the See also:

• CROSBY, HOWARD (1826–1891)

The first condition is also invalidated to some extent by the friction of the indicator piston, of the joints in the linkage, and of the pencil on the paper. The piston must slide very freely; nothing of the nature of packing is permissible, and any steam that leaks past it must have a free exit through the cover. The pencil pressure must not exceed the minimum which is necessary for clear marking. Another source of disturbance is the inertia of the moving parts, which tends to set them into oscillation whenever the indicator piston suffers a comparatively sudden displacement. These oscillations, superposed upon the legitimate motions of the piston, give a wavy outline to parts of the diagram, especially when the speed is great. When they appear on the diagram a continuous curve should be drawn midway between the crests and hollows of the undulations. To keep them within reasonable See also:

• COMPASS (Fr. corn pas, ultimately from Lat. cum, with, and passus, step)

Let Ai be the area of the piston on one side and See also:

• A2(z)

Another useful curve is drawn by plotting the steam used per horse-power-hour in relation to the horse-power. 53. Determination of the "Missing Quantity."—When the amount of steam passing through the engine is known, the indicator diagram enables the degree of wetness of the steam to be estimated at various stages in the expansion from cut-off to release, provided there is no direct passage from steam-chest to exhaust, such as has been referred to above in connexion with Messrs Callendar and Nicolson's researches. For this purpose we must first calculate the quantity of the working substance present in the cylinder. It is made up of two parts, namely, the amount supplied per stroke, plus the amount retained by being shut up in the clearance space. If we assume, as may generally be done without serious error, that at the beginning of compression the steam present. in the cylinder is dry, it is an easy matter to deduce from the diagram, knowing the pressure and the volume, how much steam is. shut up in the clearance. Adding that to the supply per stroke, we get the whole quantity that is present from cut-off to release. The volume which this would occupy at each pressure, if saturated, is found from the steam table, The volume actually occupied at each pressure is found from the diagram, and by comparing the two it is easy to infer how much of the substance exists as water and how much as steam. The ratio of the two volumes measures with sufficient accuracy the dryness of the steam. Any direct leakage from the steam side to the. exhaust side of the valve will invalidate this calculation, which proceeds, bra the basis that all the steam' passing through the engine passes through the cylinder. 54. Compound Engines.—In the original form of compound engine, invented by Hornblower and revived by Woolf, steam passed directly from the first to the second cylinder; the exhaust from the first and admission to the second went on together throughout the whole of the back stroke.

This arrangement is possible only when the high and low pressure pistons begin and end their strokes together, as in engines of the " tandem type, whose high and low pressure cylinders are in one line, with one piston-rod common to both pistons. Engines in which the high and low pressure cylinders are placed side by side, and See also:

• ACT (Lat. actus, actum)

Compound Diagrams.—Wherever a receiver is used, care should be taken that there should not be a wasteful amount of unresisted expansion into it; in other words, the pressure in the receiver should be not greatly less than that in the high-pressure cylinder at the moment of release. If the receiver pressure is less there will be what is termed " drop " in the steam pressure between the high-pressure cylinder and the receiver, which will show itself in an indicator diagram by a sudden fall at the end of the high-pressure expansion. This " drop " is, from the thermodynamic point of view, irreversible, and therefore wasteful. It can be avoided by selecting a proper point of cut-off in the low-pressure cylinder. When there is no " drop the expansion that occurs in a compound engine has precisely the same effect in doing work as the same amount of expansion in a simple engine would have, provided the See also:

• LAW
• LAW (0. Eng. lagu, M. Eng. lawe; from an old Teutonic root lag, " lie," what lies fixed or evenly; cf. Lat. lex, Fr. loi)
• LAW, JOHN (1671—1729)
• LAW, WILLIAM (1686-1761)

The exhaust line CD shows a falling pressure in consequence of the increase of volume which the steam is then undergoing through the advance of the low-pressure piston. EFGH is the diagram of the low-pressure cylinder drawn alongside of the other for convenience in the construction which follows. It has no point of cut-off; its admission line is the continuous curve of expansion EF, which is the same as the high-pressure exhaust line CD, but drawn to a different scale of volumes. At any point K, the actual volume of the steam is Kt. + MN. By drawing OP equal to KL + MN, so that OP represents the whole volume, and repeating the same construction ,, at other points of the diagram, we may set out the curve QPR, the upper part of which is identical with BC, and so complete a single diagram which exhibits the equivalent expan- See also:

• SION [Ger. Sitten]

57. See also:

• ADJUSTMENT (from late Lat. ad juxtare, derived from juxta, near, but early confounded with a supposed derivation from justus, right)

Another point in favour of the compound engine is that, although the whole ratio of expansion is great, there need not be a very early cut-off in either cylinder; hence the common slide-valve, which is unsuited to give an early cut-off, may be used in place of a more complex arrangement. The mechanical advantage of the compound engine has long been recognized, and had much to do with its See also:

• ADOPTION (Lat. adoptio, for adoptalio, from adoptare, to choose for oneself)

is credited to See also:

• MURDOCK, WILLIAM (1754-1839)

61. See also:

• LAP

The relation of these, however, to the piston's motion is still undefined. If the eccentric were set in advance of the crank by an angle equal to ACa, the opening of the valve would be coincident with the beginning of the piston's stroke. It is, however, desirable, in See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

22 and 23 separately; the single diagram (fig. 24) contains the solution of the steam distribution with a slide-valve whose laps, travel and angular advance are known, the same circle serving, on two scales, to show the motion of the crank and of the eccentric. Zeuner's Diagram.—The graphic construction most usually employed in slide-valve investigations is the ingenious diagram published by Dr G. Zeuner in the Civilingenieur in 1856.1 On the Line AB (fig. 25), which represents the travel of the valve, let a pair of circles (called valve-circles) be drawn, each with diameter equal to the half travel. A radius vector CP, drawn in the direction of the eccentric at any instant, is cut by one of the circles at Q, so that CQ re-presents the corresponding displacement of the valve from its middle position. That this is so will be seen by drawing PM (as in fig. 19) and joining QB, when it is obvious that CQ=CM, which is the displacement of the valve. The line AB with the circle on it may now be turned back through an angle of 90°+0 (0 being the angular advance), so that the valve-circles take the position shown to a larger scale in fig. 26. This makes the direction of CQ (the eccentric) coincide on the paper with the simultaneous direction of 1 Zeuner, Treatise on Valve Gears, trans. by M. See also:

• MULLER, FERDINAND VON, BARON (1825–1896)
• MULLER, FRIEDRICH (1749-1825)
• MULLER, GEORGE (1805-1898)
• MULLER, JOHANNES PETER (18o1-1858)
• MULLER, JOHANNES VON (1752-1809)
• MULLER, JULIUS (18oi-1878)
• MULLER, KARL OTFRIED (1797-1840)
• MULLER, LUCIAN (1836-1898)
• MULLER, WILHELM (1794-1827)
• MULLER, WILLIAM JAMES (1812-1845)

.—s with Lap. sh.f silos the crank, and hence to find the displacement of the valve at any at rest, and then re-engaging the gear. The eccentric sheave, position of the crank we have only to draw CQ in fig. 26 parallel to the crank, when CQ represents the displacement of the valve to the scale on which the diameter of each valve circle represents the half-travel of the valve. CQ0 is the valve displacement at the beginning of the stroke shown by the arrow. Draw circular arcs ab and cd with C as centre and with radii equal to the outside lap o and the inside lap i respectively. Ca is the position of the crank at which pre-admission occurs. The lead is aoQo. The greatest steam opening is a1B. the direction Cb. Cc is the position of the crank at release, and Cd marks the end of the exhaust. 63.

In this diagram radii drawn from C mark the angular positions of the crank, and their intercepts by the valve circles determine the corresponding displacement of the valve. It remains to find the corresponding displacement of the piston. For this Zeuner employs a supplementary graphic construction, shown in fig. 27. Here ab or a'b represents the connecting rod, and be or b'c the crank. With centre c and radius ac a circle ap is drawn, and with centre b and radius ab another circle aq. Then for any position of the crank, as cb', the intercept pq between the circles is easily seen to be equal to aa', and is therefore the distance by which the piston has moved from its extreme position at the beginning of the stroke. In practice this diagram is combined with that of fig. 26, by drawing both about the same centre and using different scales for valve and piston travel. A radius vector drawn from the centre parallel to the crank in any position then shows the valve's displacement from the valve's middle position by the intercept CQ of fig. 26, and the piston's displacement from the beginning of the piston's motion by the intercept pq of fig. 27.

64. In the figures which have been sketched the events refer to the front end of the cylinder, that is, the end nearest to the crank (see fig. 23). To determine the events of steam distribution at the back end, the lap circles shown by dotted lines in fig. 26 must also be drawn, Ca' being the outside lap for the back end, and Cc' the inside lap. These laps are not necessarily equal to those at the other end of the valve. From the diagrams it will be seen that, especially with a short connecting-rod, the cut-off and release occur earlier and the compression later at the front than at the back end if the laps are equal, and a more symmetrical steam distribution can be produced by making the inside lap greater and the outside lap less on the side which leads to the front end of the cylinder. On the other hand, an unsymmetrical distribution may be desirable, as in a vertical engine, where the weight of the piston assists the steam during the down-stroke and resists it during the up-stroke, and this may be secured by a suitable inequality in the laps. 65. By varying the ratio of the laps o and i to the travel of the valve, we produce effects on the steam distribution which are readily traced by means of the diagram. Reduction of travel (which is equivalent to increase of both o and i) gives later pre-admission, earlier cut-off, later release and earlier compression; the ratios of expansion and of compression are both increased. Increase of angular advance accelerates all the events and causes a slight increase in the ratio of expansion.

66. In designing a slide-valve the breadth of the steam ports in the direction of the valve's motion- is determined with reference to the volume of the exhaust steam to be discharged in a given time, the area of the ports being generally such that the mean velocity of the steam during discharge is less than too ft. per second. The travel is made great enough to keep the cylinder port fully open during the greater part of the exhaust; for this purpose it is 22 or 3 times the breadth of the steam port. To facilitate the exit of steam the inside lap is always small, and is often wanting or even negative. During admission the steam port is rarely quite uncovered, especially if the outside lap is large and the travel moderate. Large travel has the advantage of giving freer See also:

• INGRESS (Lat. ingresses, going in)

To set the engine in gear to run in the opposite direction (b) it is only necessary to shift the eccentric into the position crank.