The use of fire for forging metals, heating water, making bread and the like was known at a very early day in history (Gen. iv. 22; xviii. 6), but we have no knowledge as to the time when this serviceable element was discovered. "Probably it was one of man's very earliest acquisitions, being the agent he has most constantly employed in the preparation of his food. Flints have been found that have been subjected to the fire for the purpose of breaking them into small and angular pieces, and the charcoal and ashes of ancient hearths have been exhumed in deposits which competent geologists place as remote in time as the Interglacial period." Implements of bronze have come down to us from prehistoric times, and these also give evidence of the very early use of fire. But its employment for converting water into steam for practical purposes is of comparatively recent date.
The first recorded instrument for illustrating the power of steam was that described by Hero of Alexandria
in his Pneumatic a
about 120 B. C, though there is nothing in the text to indicate that it was his invention.
It was named the " Aeolipile
" (Fig. 1), and consisted of a boiler partly filled with water and placed over a fire. Over the boiler there was pivoted on two bent tubes a spherical vessel ("steam-turbine") which was supplied with steam through one of the pivots from the boiler below. Projecting from the sphere in a direction perpendicular to the axis of rotation were two bent pipes, through which the steam escaping into the air exerted a force in a contrary direction, after the manner of Barker's mill, thus causing the sphere to revolve. It is not known that the Aeolipile was ever more than an amusing toy, though some have supposed that it was applied by the Greek priests for producing motion of apparatus in their temples.
Further trace of the force of steam is lost in history until the time of Justinian (A. D. 554), when it was employed by Anthemius, architect to the emperor, to frighten his neighbor Zeno, by connecting tubes to the cauldrons of water and extending them up into the building, so that when the steam ascended the house was shaken by the escape of the imprisoned air. Alberti, the Florentine architect, notices (A. D. 1412) the prodigious expansion by heat of water shut up in the cavities of some stones, "which blows up the whole kiln with a force altogether irresistible."
If the statement of Spanish writers that Blanco de Garay, A. D. 1543, applied steam to the propulsion of a ship at Barcelona, is apocryphal, as the majority of writers on the subject believe it to be, there was made from the time of Hero to the seventeenth century no practical application of the power of steam worthy of special illustration. Here and there are found evidences of a knowledge of its force in its employment for trivial purposes, such as blowing organs and turning spits, but it devolved on a later period to demonstrate its power in its application to the performance of important and useful work.
John Mathesius (A. D. 1567) hinted the construction of a machine in which "the volcanic force of a little confined vapor might be made to perform the work of horses or water." The "Pneumatics of Hero" were in A. D. 1587 translated into the Italian, which drew attention to the "ingenious toys," as they have been called, in which "air" was applied with great skill to produce motion. Sir Hugh Plat describes (A. D. 1594) the construction of "a rounde ball of copper or latten that will blowe the fire very stronglie by the attenuation of water into aire."
Porta’ s Steam-engine
Porta’s Steam Apparatus
In 1601, Giovanni Battista della Porta, in a treatise on pneumatics, described an apparatus for raising a column of water by the pressure of steam. Figure 2, from Porta's book, shows the furnace surmounted by a boiler, above which is a tank nearly filled with water. As the steam from the boiler enters the tank near the top, the water is driven out through the curved pipe.
Previous to 1605 steam was employed in artillery instead of gunpowder. Rivaul in 1608 announced the invention in the form of a problem, "How a cannon might be fired with pure water."
De Cans's Steam-fountain
Salomon de Caus (1611) was employed by the prince of Wales to decorate his gardens at Richmond in Surrey. He clearly understood the action of the "air" in "Hero's fountain," and improved the machine by the insertion of valves to prevent the return of the water which had been elevated, though he did not observe that it was the expansion and condensation of the vapor in the air that mainly produced the effects in the Egyptian machine and in his own. Had De Caus made a coal fire under his improved fountain, he would have had a good steam-engine. In 1615 he suggested forcing water by a steam-fountain from a vessel by the expansion of steam within the same.
De Caus’s Steam Apparatus
In Figure 3, taken from a drawing probably made by De Caus's own hand, (A) is a spherical boiler containing water, (B) is the cock at the extremity of the pipe which takes water from the bottom of the vessel boiler at (C), and (D) is the cock through which the boiler is filled. The elastic force of the steam formed in the boiler by the application of fire drives the water out through the vertical pipe.
David Ramsey and Thomas Wildgosse patented in 1618 a compendious form of engine to plough ground without horses or oxen, to raise water from any low place to high places for well-watering cities, towns, and gentlemen's houses, and to make boats run upon the water as swift in calms and more safe in storms than boats full-sailed in great winds. In 1630, Ramsey took out another patent of nine claims, the second of which reads, "To raise water from lowe pittes by fire;" and this is considered the earliest notice of an engine for raising water by fire in England.
Branca’s Steam Apparatus
In 1629, Giovanni Branca published at Rome an account of an engine, shaped like a water-wheel, which was driven by steam issuing in a jet from a boiler and impinging on the vanes of the wheel (Fig. 4).
Worcester’s Steam Engine
Tradition relates that the marquis of Worcester had the first glimpse of his steam-engine when he was a prisoner in the Tower of London in 1655. The marquis wrote (about 1659) his celebrated manuscript entitled "A centurie of the names and scantlings of such inventions as att present I can call to mynde to have tryed and perfected." The sixty-eighth scantling of this manuscript announces the great invention, which has popularized and preserved the fame of this wonderful inventor in the public mind. He calls it "An admirable and most forcible way to drive up water by fire," etc. Worcester's ninety-ninth scantling can be explained only by the use of a piston in a cylinder with water under it. In 1663, Worcester, in his Century of Inventions
, describes an engine no drawings of which are extant, but which his biographer, Dircks, has suggested was like the sketch shown in Figure 5. Two vessels (A, A) are connected by a steam-pipe B, B) with the boiler (C), which is placed behind them. (D) is the furnace. A vertical water-pipe (E) is connected with the cold-water vessels (A, A), by the pipes (F, F), which reach nearly to the bottom. Water is supplied by the pipes (G, G), containing valves (a, a), and dipping into the well (H). Steam being admitted from the boiler to each vessel (A, A) alternately, is there condensed, and the vacuum formed permits the pressure of the atmosphere to force the water from the well through the pipes (G, G). While one is being filled, the steam is forcing the water from the other up the discharge-pipe (E). As soon as one is emptied the steam is shut off and turned into the other, and the condensed steam remaining in the vessel permits it to fill again. Worcester's apparatus was not an engine in the proper sense, but a water-raising machine. One of Worcester's engines of about two horsepower was in use at Vauxhall in 1656, but the hopes of its inventor were not realized, as it never became a commercial success.
Mr. Boyle, while experimenting with Aeolipiles in 1678, observes, "The elastical power of the steam seems manifestly due to the heat that expands and agitates the aqueous particles whereof the steam consists;" and he considered that these were alone condensable, while air was not— the explanation of a fact which may be said to have laid the foundation of the condensing steam-engine. Abbé Hautefeuille
in 1682 introduced alcohol into a cylinder and evaporated and condensed it tour-d-tour
, without allowing it to escape or be lost in the processes. In 1682, "Sir Samuel Morland
announces his principles of the new force of fire. Water being evaporated, these vapors immediately acquire a greater space, and, too forcible to be always imprisoned, will burst a piece of cannon. But, being governed according to the rules of statics and reduced to science, weight, and measure, they will then peaceably carry their burden, and thus become of great service to mankind."
found, in 1690, that "a small quantity of water converted into steam by heat had an elastic force like that of air, but when exposed to cold was again resolved into water, so that no trace of its elastic force remained." He constructed a machine wherein water, by means of no very intense heat, produced that perfect vacuum which he could not obtain by firing off gunpowder. Papin further says, "Immense power may be accumulated by the enlargement of the piston that can be employed to draw water or ore from mines or propel ships against the wind."
In 1695, Papin still further developed the power of steam by improvements in the method of making it . The flame and air were made to descend through the fuel, completing the combustion. The smoke was conducted through the boiler in a zigzag-immersed flue, and, still further to hasten the evaporation, he used his rotary fan to blow the fire.
The aeolipile was applied to new uses at Pekin in 1694. Two experiments were made with it before the emperor Caus Hi. In the middle of a wagon about two feet long was placed a brazen vessel full of live coals, and upon them an Aeolipile, the wind of which came through a little pipe upon a sort of wheel made like the sails of a windmill; this wheel turned another, and by that means set the wagon in motion for hours together. This wagon was furnished with mechanical devices by which it could be turned around in any given circle. The same contrivance was likewise fixed to a little ship with four wheels. The Aeolipile was hidden in the middle of the ship, and the wind from two small pipes filled the sails and made it wheel about a long while.
Savery s Steam-engine
Savery’s Steam Engine
The first successful experiment with the steam-engine, or "fire-engine," as it was then called, was by Thomas Savery
, who in 1698 obtained a patent the title of which reads, "A grant to Thomas Savery, Gentl., of the sole exercise of a new invention by him invented, for raising of water, and occasioning motion to all sorts of millworks, by the impellant force of fire, which will be of great use for draining mines, serving towns with water, and for working of all sorts of mills when they have not the benefit of water nor constant winds." This machine, which was applied to raising water from the deep mines of Great Britain, was an adaptation of Worcester's "fire-engine." It required for what we know as a "horse-power" (that is, the equivalent of 33,000 pounds lifted one foot high in a minute, or 550 pounds lifted one foot high in a second) the combustion of thirty pounds of coal. Savery's device possessed neither cylinder, piston, crank, nor fly-wheel—in fact, no moving parts. The model of his machine (Fig. 6), a description of which he presented to the Royal Society, consisted of a furnace (A) heating a boiler (B), which was connected by pipes (C, C) with two copper receivers (D, D). From the bottoms of these receivers were led branch-pipes (F, F) turned upward, which were united to form a "forcing-pipe" (G); from the top of each receiver was led a pipe turned downward, and these two pipes united formed a supply-pipe which extended to the bottom of the well from which the water was to be drawn. Steam being generated in the boiler (B), and the cock (C) being opened, the receiver (D) is filled with steam. Closing the cock condenses the steam in the receiver, in which a vacuum is created, and the pressure of the atmosphere forces the water up through the supply-pipe from the well into the receiver. Opening again the cock (C), the check-valve in the suction-pipe at closes; the steam drives the water out through the forcing-pipe (G), the clack-valve (E) on that pipe opening before it. The valve (C) is again closed, the steam again condenses, and the operation is repeated. While one of the two receivers is discharging the other is filling, and thus the steam is drawn from the boiler with tolerable regularity, and the expulsion of water takes place with similar uniformity, the two systems of receivers and pipes being worked alternately by the single boiler. A modification of this employed surface-condensation to hasten the work. John Theophilus Désaguliers
, in 1718, substituted jet- for surface-condensation. Blakely, in 1766, interposed a cushion of oil between the water in the reservoirs and the steam which drove it out.
Savery's engine, which was subsequently much improved, was extensively employed in pumping out mines, and was occasionally used in raising water to supply houses in towns and for driving mill-wheels. Though it was entirely displaced by Newcomen's engine, its inventor must be awarded the credit of having first practically employed the steam-boiler, without which Newcomen and Cawley could not have set their more advantageously acting machine in motion. The piston moving in a cylinder was proposed by Huygens in 1680.
Papin’s Steam Engine
, a humble French physicist, endeavored in 1688 to improve Huygens' apparatus, but having unsuccessfully tried gunpowder, he proposed in 1690, while professor at Marburg, the substitution of steam for producing a vacuum under the piston. Papin's engine (Fig. 7) was constructed practically on the same principle as Huygens'. Instead of gunpowder a small quantity of water was introduced into the cylinder through an opening in the piston, and the opening was then closed by means of the rod (M). A fire being started beneath the cylinder, whose bottom was of very thin metal, steam was rapidly generated, and by its elastic force overcame the weight of the piston (B) and the pressure of the atmosphere, and drove the piston to the top of the cylinder, where a latch (E), engaging a notch in the piston-rod, and kept in contact with the latter by a spring, held it up. On removing the fire, there followed a condensation of the steam, by which a vacuum was produced below the piston, and, upon disengaging the latch, the piston, being forced down by atmospheric pressure, raised the weight attached to the rope (L) passing over the pulleys (T, T). The cylinder had a diameter of two and a half inches. Papin's was the earliest cylinder-and-piston steam engine, but he was not successful in perfecting his apparatus, though he devised various transmitting mechanisms for the motion of the piston, especially for propelling a vessel.
Newcomen’s Steam Engine
It was reserved for the Englishmen Thomas Newcomen
and his assistant Cawley to make a practical application of Papin's plan of using steam, which was effected in 1705 by connecting with a steam-boiler a cylinder containing a piston. It was a steam-engine, but employed the pressure of the atmosphere to move the piston and to do the work, and hence was called an "atmospheric steam-engine," which proved to be well adapted for working the main rods of pumps in mines, and, later on, for driving revolving shafts. Figure 8 represents a Newcomen machine in its higher form of development. Immediately upon the dome-shaped boiler, half sunk in a brick furnace, is seen the cylinder with its movable piston. A chain fastened to the piston is placed over a segment attached to a wooden double-armed lever or "beam." This beam at its centre swung upon a pivot, and was united with a connecting-rod, a crank, and a revolving shaft provided with a fly-wheel; and suspended to it were two rods properly secured by chains to two segments. The cylinder, being entirely open on top, allowed the atmospheric pressure to act upon the piston and to set it in motion, together with the described mechanism, when a vacuum was formed in the lower space by the condensation of the steam admitted into it. It is, therefore, worthy of notice that the actual motive-power was not steam, but atmospheric pressure left free to act by the condensation of steam. The use of the chain referred to, did not even allow of the direct action of the steam. This machine took twenty pounds of coal per horse-power per hour.
In the first machines the condensation of the steam was effected by simply throwing cold water in a shower over the outside of the cylinder. In an improved form of construction it was effected by injecting into the cylinder a jet of water taken from a reservoir, shown on top of the Figure, and kept constantly filled by the machine itself. This improvement was suggested by an accident: "As they were at first working, they were surprised to see the engine go several strokes, and very quick together, when, after a search, they found a hole in the piston, which let the cold water in, condensing the steam in the inside of the cylinder." The alternate admission and exclusion of steam, originally effected by a workman opening and closing a cock with his hand, were here effected by a mechanism connected with a vertical rod, seen in the illustration in front. The valve-gear was first made to work thus automatically in 1713 by a boy, Humphrey Potter, who caused the beam itself to open and close the valves by means of suitable catches and strings; but in 1718, Henry Beighton substituted for the latter a plug-rod, which worked the valves by means of tappets. Smeaton improved this type, in 1774, by oakum cylinder-packing, and by raising the water used for condensation by a pump worked from the main beam; he also covered the lower side of the piston with wooden plank, to reduce unnecessary and untimely cylinder-condensation.
After Newcomen's engine had been in use more than fifty years, and had been much improved in its mechanical details, it was entirely superseded by the condensing steam-engine invented by James Watt
, a mathematical-instrument maker at the University of Glasgow, who in 1763, having put a model Newcomen engine in order, and having been struck with its enormous consumption of steam, began a series of improvements which finally rendered the steam-engine universally applicable. Watt's improvements consisted in lagging the boiler, pipes, and cylinder with non-conductors, in condensing in a separate vessel, and in making the engine double-acting by closing the cylinder at the top and passing the piston-rod through a steam-tight stuffing-box. In 1774 he produced a beam-engine in which the steam passed above the piston and depressed it, raising the weight of the pump-rods, the lower end of the cylinder being in communication with a separate condenser; then a valve was opened, allowing the steam which was above the piston to flow beneath the piston, which was raised by the weight of the pump-rod. He introduced the "air-pump" to relieve the condenser of air and of an excess of water, and used oil and tallow for lubricating the piston instead of water, which caused excessive cylinder-condensation. In 1781 (in order to avoid the payment of royalty upon the crank, which was patented) he employed the sun-and-planet
movement, to produce a rotary from a reciprocating motion, and added a fly-wheel and a shaft, so that it could drive machinery. In 1782 he patented the use of the expansion of steam—the application of steam on each side of the piston alternately, the opposite side being in communication with the condenser—the double or coupled engine, and the use of a rack upon the piston-rod, working upon a sector on the beam, to give perfect straight-line motion to the rod. For guiding the piston-rod in a straight line Watt also provided the so-called "parallel motion."
Watt’s Fly-Ball Governor
In 1784 he added the poppet-valve, the centrifugal ball-governor acting on a throttle-valve (Fig. 5), and the steam-jacket. He also invented the indicator by which the occurrences in the cylinder might be made known and regulated; and patented a locomotive steam-engine.
Watt’s Steam Condenser
Watt's most important improvement on Newcomen's machine was the addition of the condenser in 1765. Fig. 9 illustrates such an apparatus. Instead of effecting the condensation in the cylinder itself, there was placed under it an hermetically-closed iron box into which the steam from the cylinder was introduced and condensed by an injected spray of cold water. But as the injected water as well as the condensed steam would in a short time entirely fill the box, a pump (seen on the right in the cut) was connected with it, by means of which the water and also the air contained in it could be constantly sucked up and removed. This pump is therefore called the "air-pump."
Murray’s D-Slide Valve Distribution
By adding the three-port slide-valve, invent in 1799 by Murray, and intended to replace the distributing-cock originally used and the valves later on substituted for it, we have the modernized form of the principal part of the machine—namely, the cylinder with its immediate mechanisms—shown in Figures 11 and 12, in which the fresh in-flowing steam is indicated by the whitish color in the engraving. It will be seen that the steam is conducted from the boiler, by means of the steam-pipe (D), first into the steam-chest (C, E), and passes thence in Figures 11 and 12, the piston (K) by means of the steam-passages (d, e) and (e,d) in the direction of the arrows. Hence in. Figure 12 the piston is forced down, in Figure 11 upward, being, however operative only if the steam already used and standing above or below the piston can pass into the condenser. For the latter purpose again serve passages (g,f) and (e, d), further the exhaust-pipe (O), and finally, as also for the alternate admission of the steam, the three-port valve (A, B). This valve is given the positions required for the distribution of the steam, which are indicated in Figures 11 and 12, by the machine itself, by means of a mechanism connected with the valve-rod (F). The other parts are the piston-rod (G) and the stuffing-box (S), while the aperture seen in the centre of the bottom is closed by a cock through which the water collected in the cylinder is from time to time discharged.
Watt Type of Beam Engine
Figure 4, which represents a modern Watt's engine of the most perfected type, exhibits only a portion of the parallelogram connecting the piston-rod with the oscillating beam. This Figure also shows the solid frame consisting of six columns, an iron foundation, and an architrave-like upper support, in which Watt enclosed his perfected machine, thereby considerably increasing its solidity.
Watt Type of Beam Engine (Cut-Away Cross-Section)
The jacket in which Watt enclosed the cylinder to prevent the cooling off of the steam therein is more plainly recognized in Figure 6, which represents in section the steam-cylinder with jacket (K) and the air-pump with the condenser (J) concentrically arranged around it. (A, B) is the frame carrying the engine, and (C, D, E, F, G) a mechanism replacing Watt's parallelogram. Beighton used for feeding the boiler the heated water of condensation, when it was soft; but when it was hard, he heated the feedwater by a coil passing through the condensing-water. The first inventions by Watt were based less upon the properties of steam than upon the phenomena of heat, because by the peculiar construction of the condenser and of the steam-jacket, as well as by the closure of the upper portion of the cylinder against the entrance of cold air, he prevented the losses which, in an economical respect, made Newcomen's machine practically useless for many purposes. He also later on planted the germ of an improvement, which occupies the foremost rank as regards the advantageous application of the steam-power, by the utilization of the expansive action of steam. This action commences when the supply of steam is shut off and the steam in the cylinder is left to itself before the piston has arrived at the end of its stroke. Though the steam from the boiler is shut off, the piston continues to be pushed forward by the steam through the expansive force which constantly becomes weaker. Thus, for instance, a given quantity of mechanical effect is produced by the gradual expansion of the steam to double its normal volume, and consequently to half the normal tension that would otherwise be produced by double the quantity of steam. For the purpose of ascertaining the exact amount of this gain of effect it is necessary to determine the specific relation existing between the tension and the volume of this shut-off expanding steam, a problem of physical science on which much ingenuity has been expended since Watt's time.
Watt’s Steam Indicator as Improved by Richard(Cut-Away Cross-Section)
To ascertain empirically the complex result of all these and other component activities on a machine, Watt devised and used an instrument called an "indicator," which, as improved by Richard, is shown in its modernized form in Figure 10. This instrument when connected with the inner space of the steam-cylinder indicates graphically, by a closed curve upon a strip of paper, the varying steam-pressures succeeding one another during the duration of a stroke. This is effected by means of a piston, which on the one hand is connected by a spring with the indicating mechanism, and on the other hand is subjected to and actuated by the same varying steam-pressure in the cylinder as is the large piston.
Recorder & Water Meter
From the diagram traced by this instrument the effect of the steam during a stroke can be calculated, a counter (Fig. 1) connected with a rotating portion of the machine indicating the number of strokes made in a given time, and a water-meter (Fig. 2) measuring the quantity of steam conducted into the cylinder during the time. These observations form the elements for the calculation of the degree of effect or utility of the steam-engine, and from them also the capacity in horsepower and the consumption of steam per indicated horse-power are calculated.
Another apparatus, the dynamometer, is used to indicate the effective or actual amount of power given out by the engine. The dynamometer is fastened upon the shaft of the fly-wheel, and its indication of the effective result in horse-powers, when subtracted from the indicated horse-power calculated from the indicator curves, shows the amount of mechanical force consumed in moving the mechanism of the engine by friction and inertia. In this manner it has been determined that modern machines carefully constructed according to Watt's system produce six times as much effect with a given quantity of coal as Newcomen's.
The development of the steam-engine to its completed form, as shown in Figure 4, was not, however, Watt's work alone. As already mentioned, the three-port slide-valve, described in Figures 11 and 12, was invented by Murray, while the crank mechanism and the flywheel originated with other English inventors and mechanics. It was but natural that Watt and his co-workers should only gradually and cautiously, step by step, have developed the actual steam-engine from the atmospheric motor of Newcomen. The pressure they employed was never much above that of the atmosphere, and they even attempted to have passed an act of Parliament forbidding the use of high pressure for reason that it endangered the lives of the public.
The idea that steam of high pressure possessed more advantageous properties than steam of low pressure gradually gained ground, and led to experiments with a pressure of from 150 to 300 pounds to the square inch. But the increased danger, the more rapid wear of machines, and especially the considerable loss of steam by leakage, rendered these experiments so unsuccessful that in practice there was only a gradual progress up to 45, 60, and 90 pounds, and it is only in later practice that we find pressures of 100 pounds and upward in ordinary use Though with these higher tensions the condenser can be dispensed with, it nevertheless considerably increases the efficiency in cases where the expansive effect is to be turned to the best account, and as these cases occur more frequently the gain is considerable. Hence the endeavors to use a higher degree of expansion go hand in hand with the efforts to use higher tensions, so that at the present time the utmost is accomplished in this respect.
Hornblower’s Compound Steam-engine
Hornblower’s Compound Non-Condensing Engine
In 1781, Jonathan Hornblower
, a contemporary of Watt, patented a "compound" or double cylinder engine (Fig. 3) whose cylinders (A, B), which were of unequal sizes, were placed side by side, while the piston-rods (C, D) of both were attached to the end of a beam overhead. Steam is led to the cylinder (B) through the pipe (G, Y). The cocks (a, b, c, and d), which are adjustable so as to let the steam into and from the cylinders, are moved by the plug-rod (IV), which actuates handles not shown in the illustration. (K) is the exhaust-pipe leading to the condenser. The cocks (c, a) being opened and (b, d) being closed, the steam passes from the boiler into the upper part of the cylinder (B), communication at the same time being opened between the lower part of (B) and the upper part of (A). Before starting the engine the steam is shut off from the cylinder, which, by reason of the great weight of the pump-rod (X), causes the pistons to rise to the tops of their respective cylinders. The engine being freed of air by opening all the valves and permitting the steam to drive through the cylinders and out of the condenser through the "snifting-valve" (O), the valves (b, d) are closed and the cock in the exhaust-pipe is opened. The steam beneath the piston of the cylinder (A) is immediately condensed, and the pressure on the upper side of the piston causes it to descend, carrying the end of the beam with it, and thus raising the opposite end of the beam and its attachments. At the same time the steam from the lower end of the high-pressure cylinder (B) is let into the upper end of the large cylinder (A) by the pipe (Y), and the completion of the downward stroke finds a cylinder-full of steam transferred from one to the other, with a corresponding increase of volume and decrease of pressure. When the pistons have reached the bottoms of their respective cylinders, the valves at the top of the small cylinder (B) and at the bottom of the large cylinder (A) are closed and the valves (c, d) are opened. Steam from the boiler now enters beneath the piston of the small cylinder, the steam in the larger cylinder is exhausted into the condenser, and the steam already in the small cylinder passes over into the large cylinder as the piston rises. Thus at each stroke a small cylinder-full of steam is taken from the boiler, and the same weight occupying the volume of the larger cylinder is exhausted into the condenser.
Leupold’s Steam Engine
The high-pressure steam-engine—that is, an engine which is rendered effective without the assistance of atmospheric pressure—was first proposed by the prolific German technical writer Jacob Leupold
in 1724, in his Theatrum Machinarum
, from which our illustration (Fig. 1) is reproduced. It consists of two single-acting cylinders (r, s) which receive steam alternately from the same steam-pipe through a "fourway" cock (z), and exhaust into the atmosphere. The pistons (c, d) are thus alternately raised and depressed, which action raises and lowers the pump-rods (k,l) by means of the levers (i,i) to which they are attached. The alternate action of the steam-pistons is secured by turning the cock (x) first into the position shown in the Figure, and then, at the completion of the stroke, into a reverse position, by which change the steam from the boiler (a) is led into the cylinder( s), and the steam in (r) is discharged into the air. Leupold acknowledges his indebtedness to Papin for the suggestion of the peculiar valve employed.
Bull, in 1798, produced the Cornish single-acting pumping-engine without working-beam, the weight of the engine piston and pump plunger being carried by a weighted balance-beam. Oliver Evans introduced the non-condensing high-pressure stationary engine which was the forerunner of most of our modern engines. Cugnot, Stephenson, and others applied the steam-engine to railroads; Stephens, Fitch, Evans, and Fulton, to steamboats.
In 1779, Oliver Evans
, an ingenious American mechanic, devised the first permanently successful non-condensing engine in which the power was derived exclusively from the tension of high pressure steam. In 1772, when but seventeen years of age, he turned his attention to the discovery of "some means of propelling land-carriages without animal power." Observing the power of steam exerted on a wad rammed down over a small quantity of water in a gun-barrel, from which, through the heating of the barrel in a blacksmith's forge, the wad was expelled accompanied with a loud report, he fancied he had discovered a new source of power. Meeting about this time with a description of a Newcomen engine, he was surprised to find that the elastic force of confined steam was not there utilized, while the piston was moved by atmospheric pressure. This he believed to be an erroneous application of the force of steam, and he conceived the idea of a high-pressure engine using steam at a pressure of about 120 pounds per square inch, which he proposed to apply to the propulsion of carriages.
Evans' "Columbian" Engine
Evans’ Columbian Steam Engine
In 1800 or 1801, Evans began the construction of a steam-carriage to be driven by a non-condensing steam engine, but, changing his plans, he built a beam-engine having a cylinder 6 inches in diameter and 18 inches stroke, with which he successfully drove a plaster-mill. This "Columbian" engine (Fig. 2), as it was called, had a beam supported at one end by a rocking column. The connecting-rod was attached to the other end and drove a crank below; the piston-rod was connected directly to the beam at a point nearer the connecting-rod, and the feed-pump piston-rod was also directly connected at a point nearer the beam-fulcrum. The beam and piston-rod constituted a sort of parallel motion. In 1804, Evans produced the steam-dredge "Oruktor Amphibolis
," which had a five-horse-power engine similar to the "Columbian." About the same time one of his engines, which was built for a steamboat on the Lower Mississippi, was put to work in driving a saw-mill.
Cartwright's engine of 1798 took steam above the piston, the rod of which extended upward to a cross-head driving cranks above, and downward to an air-pump piston which had the same stroke as that of the steam-cylinder. The bottom of the steam-cylinder was in communication with the condenser, the steam-piston having in it a valve, which was opened automatically when the full stroke had been made. The air-pump removed the excess of air from the condenser, which was composed of two concentric cylinders within and around which the water of condensation flowed, while the exhaust steam passed into the annular space.
In 1802, Richard Trevithick of England patented a model steam-engine carriage in which high-pressure steam was employed and the condenser was dispensed with.
During the first half of the nineteenth century progress in steam engineering was very largely in the direction of the application of the steam-engine to the propulsion of road-carriages, locomotives, and vessels; there were but few striking innovations, each inventor and builder striving to perfect construction rather than to start out in a new field of original design. Those desirous of tracing in somewhat greater detail than is here given the growth of the steam-engine during the period mentioned, will find it in the sections devoted more particularly to the locomobile, the locomotive, and the marine steam-engine. The "Oruktor Amphibolis
" of Evans (1804), Trevithick's steam-carriage (1802), the steam-carriages of Griffiths, of Gurney (1827), and of Hancock (1831) show a development as interesting as it was important. The locomotives of Trevithick (1804), Hedley (1812), the Stephensons, Horatio Allen, Peter Cooper (1829), Baldwin (1831), and Jervis (1832) marked a gradual growth rather than startling flights of invention.
Corliss introduced the straight girder frame for stationary engines; he also introduced the plug-valve, and made the detent cut-off, as applied thereto and operated by the centrifugal governor, a mechanical and commercial success. Hartnell brought out the shaft governor controlling the eccentric throw, and J. W. Thompson made it practicable and successful in connection with a balanced valve. John E. Sweet has carried the "straight-line" system of construction to a satisfactory conclusion; and to Charles T. Porter more than to any other man do we owe the success of the modern high-speed automatic cut-off stationary engine. Ball has made a good start in the line of governing by load rather than by speed, and Westinghouse has made high-speed single-acting engines, both throttling and automatic cut-off, compound and non-compound, practicable in a high degree; while, among others, Wootten, Stevens, and Strong in the United States, Mallet in France, and Worsdell and Webb in England, have done much to lift the locomotive out of ruts of design.
Having considered the steam-engine from an historical standpoint, with reference both to its design and construction, we shall now consider it from a more strictly technical standpoint. We shall minutely define and scientifically describe it, and shall then give those details which
would be out of place in a chronological narrative of its development and growth.
A steam-engine is a machine by which the pressure of steam, due to its temperature, may be utilized in mechanical work. The term steam-engine is usually restricted to a motor in which a shaft is rotated directly or indirectly by the pressure of steam upon an alternating or a rotating piston fitting steam-tight, with as little friction as possible, in a cylindrical (or approximately cylindrical) case. A steam engine may be employed to drive a line of shafting, to run one or more machines connected to its main shaft, to actuate a pump or a blower having its piston attached to its piston-rod, to propel a boat in which it is placed, or to move a vehicle on which it is mounted.
Steam-engines maybe classified into horizontal, vertical, and inclined, according to the position in which the cross-head guides to the piston-rods are placed. But this classification, being merely structural, has theoretically little or no value. The oscillating engine has no cross-head, and consequently has no guides.
According to their use, engines may also be designated as stationary, semi-portable, portable, locomotive, locomobile (traction), marine, hoisting, or pumping engines, and steam fire-engines.
Engines whose pistons travel lengthwise in the cylinders, and which have a reciprocating motion, are called "rotative" or reciprocating engines, rotative being an arbitrary term practically meaning the same thing as "rotary," which term is applied to those engines wherein, the piston (often called the "follower") rotates in the cylinder about its axis and about the axis of the cylinder.
Engines may be further distinguished as "single-acting" if the steam works only on one side of their pistons, and "double-acting" if the steam is admitted first on one side and then on the other. They may be “single" or "duplex" respectively; single if there is but one cylinder works upon the shaft, and duplex if there are two cylinders which have exactly the same function. They may be " compound " if the exhaust from one or more of the cylinders enters one or more other cylinders, and "non-compound" if the exhaust discharges into the open air or into a condenser If the exhaust is condensed by contact with a jet of cold water or metallic surfaces cooled by a current of water, they are "condensing engines, in contradistinction to those in which the exhaust is not condensed and which are known as "non-condensing" engines. They may have "fixed" or "variable" cut-off. If variable, they may be variable only by hand or "automatic," which variation may be effected by changes in the load or in the steam-pressure, or as this change must be made by hand. If adjustable, they may be variable while the engines are running or only when they are stopped. If automatic, they may be so by reason of the point of cut-off being changed, or by merely choking off the steam supply so as to lessen it in case of decreased load or initial pressure. They may or may not have a beam. The cylinders may be fixed or oscillating.
When the piston consists, instead of a piston-rod acting upon a connecting-rod or directly upon a plunger or piston, of a "trunk" or hollow cylinder in which vibrates the connecting-rod attached directly to the piston, the construction is known as a "trunk" engine. If the trunk passes through a stuffing-box so that steam may be used upon the full area of the piston upon one side and upon a smaller area upon the other, it is a "half-trunk" engine. When the diameter of the cylinder equals the stroke of the piston, it is known as a "square" engine.
When the connecting-rod of a horizontal reciprocating-engine on the out-stroke passes under the line of the main shaft, the engine is said to be "under-running;" if it passes over the line of the main shaft on the out-stroke, it is "over-running." (A locomotive is under-running when moving ahead, and over-running when moving backward, because the cylinders are arranged with the piston-rod and cross-head behind them.) In an over-running horizontal engine, the top of the fly-wheel, when there is one, runs from the cylinder; in an under-running engine it runs toward the cylinder.
That end of the cylinder which is next the cross-head is called the "inner" end of any engine, the "front" end of any horizontal stationary engine, and the "crank" end if there be a crank. The end farthest from the cross-head is the "out" end in any engine, and the "back" end in any but a locomotive. The heads of a vertical engine having a crank may be designated either as the "crank" and the "out" end, or as the "upper" and the "lower" end.
Definitions of Parts
Of the various parts of the steam-engine it may be well to name its principal pieces and functions in a running form. The steam from the boiler passes into and through the supply-pipe
, in which there is placed a stop-valve
and in which there should also be a back stop valve
. In an engine which throttles the steam or cuts off its supply in the pipe there is a throttling-valve
worked by a governor
. From the supply-pipe the steam passes in many engines into the steam-ches
, in which there is placed a valve
, generally in these cases a slide-valve
, which may or may not be balanced for the purpose of making it work with a maximum of pressure and friction upon its seat. In some slide-valve engines there is a separate cut-off valv
e working upon the back of the main valve
or upon a partition in the steam-chest. Many engines have no steam-chest
proper, and many have no slide-valve
, its place being taken by a
, which is a slide-valve bent to a curve around an axis at right angles to its motion, instead of being flat upon its working side.
, which is equivalent to a slide-valve wrapped around an axis parallel to its direction of motion.
, which is practically a rock-valve having control of only one port and only one function instead of two ports and two functions.
(4) by a poppet-valve
, which is a disc or a pair of discs fixed upon a stem, having motion parallel to that stem, and opening or closing a circular aperture for the passage of steam.
The steam is admitted by the valves that open and control the ports, which are the mouths of the steam-passages
(also called steam-ways
) into the cylinder
, where it acts upon the piston
. The ports and passages which admit the steam are called induction-ports
and passages, the term eduction
being applied to those used only to discharge steam which has been in the cylinder. The steam which has been used in the cylinder is termed waste
t steam, and is discharged through the exhaust-port
either into the open air, or into another cylinder, or into a condenser
, where it is condensed into hot water by the action of cold circulating-water
, constantly renewed by the circulating-pump
or by a head from a tank, reservoir, or other source of pressure and flow. (In a locomotive the exhaust goes through a blast-pipe
, whose end is called the exhaust-nozzle
.) The ends of the cylinder
are called heads
, in one of which there is a stuffing-box
through which passes the piston-rod
. The lubricator
discharges into the steam-cylinder, or into the steam-chest, or into the steam-pipe near the steam-chest, its object being to lubricate the valves and piston. At each end of the cylinder there may be an automatic escape-valve
or blow-off cock
(also called cylinder-cock
) for the discharge of water which may collect in the cylinder. The cylinder is usually covered with a lagging
, purposely a poor conductor of heat. Sometimes its walls are double, and the space between, through which there is a circulation of live steam, or exhaust steam, or hot air, is called the jacket
. Where there is a condenser the excess of air, which would otherwise mar the vacuum, is removed by the air-pump at the same time that the water of condensation is taken away, the reservoir which contains this water being called the hot well
. Through the blow-through valves
live steam is forced through pipes, chest, and cylinder (escaping by the snifting-valve
) before the engine is started. The pressure in the condenser is measured by the vacuum-gauge
. The piston-rod
is usually attached to a cross-head
generally working in or upon guides
, which give a straight-line motion to the piston-rod and to the piston. The cross-head may, however, be given a true straight-line motion by radius-rods
. In those engines in which the cylinders oscillate they swing upon trunnions
. The reciprocations of the piston are communicated to the crank
by a connecting-rod
in most other than beam-engines; sometimes a beam is interposed before the acting-rod. On the crank-shaft there is a fly-whee
l which by its momentum equalizes the motion and tends to keep the engine steady, although the load and the pressure of the steam may vary. The valves are worked by the valve-gear
or valve mechanism
Action of Steam
For a complete understanding of the operation of the modern engine it will be necessary to explain some of the more ordinary terms used to express details of the steam action. The entrance of the steam into the cylinder is usually given the name of admission
, although engineers distinguish between the almost instantaneous admission which takes place (or should take place) before the piston has made any part of its stroke and that fuller admission which continues after the piston has commenced its stroke, and while it is in communication with the steam in the chest. When communication is closed between the cylinder and the steam-chest, "cut-off" is said to have taken place; and from that point the next period is called "expansion." The point at which the exhaust-valve is opened and the expanding steam is allowed to enter the exhaust-passage (whether to go into another cylinder, into a condenser, or into the air) is called release
, the operation which follows being exhaust
. Just as admission may take place a trifle before the piston gets to the beginning of its stroke, so the exhaust may be released a trifle before stroke-end, the terms pre-admission
being used. The closing of the exhaust-valve, so as to confine what is left of the exhaust steam in the cylinder between the advancing piston and the cylinder-head, is called exhaust-closure
, the result being "cushion" or "compression;" and this exhaust-closure is generally made to take place earlier in high-speed engines than in those which run slower, the compressed steam acting as a cushion to absorb the momentum of the reciprocating parts and to prevent jarring and racking of the engine. Cushioning also has the effect of heating the compressed steam and the walls of the cylinder and passages in communication with such compressed steam, this being of advantage in preventing the chilling of the new "live" steam which is admitted when "admission" takes place.
Cylinder and Piston
The most essential points of a reciprocating engine are the cylinder and the piston, with the distributing-valves. In a rotary engine the cylinder is replaced either by a cylinder having a rotating piston or by a case containing two gear-wheels meshing together. A reciprocating engine is usually built with one or more distributing-valves, and these are most frequently put in a steam-chest, but many high grade engines have no steam-chest, and it is possible to construct reciprocating engines which use the piston-head as the distributing-valve. The piston may be said to consist of the "head" (that circular portion which fits in the cylinder) and the "rod;" and the head generally consists of a "spider" attached to the rod and a "follower" plate attached to the spider. There are often packing-rings which serve to make a steam tight joint between the piston-head and the cylinder-bore, and these rings may be steam-packed—that is, driven out by the action of the steam-pressure (communication being permitted by orifices contrived for that purpose)—or they may be spring-packed, in which case they are held out by the pressure of springs (generally German silver or similar metal, as steel loses its temper under the high temperature of most steam-cylinders) between them and the rim of the spider. The piston-rod may be screwed into the head, or passed through and riveted, or passed through and kept by a nut from being pulled out, or passed through and keyed in; or combinations of these methods may be employed.
In a horizontal engine the steam-chest (where there is one) may be above, on the side, or below the cylinder, and in a vertical or an inclined engine may occupy the same relative positions. A chest placed below the cylinder of a horizontal engine has the advantage of permitting the steam which may be condensed in the cylinder, or the water which may be carried over into it, to be drained out through the exhaust-passages without accumulating in sufficient quantity to cause damage to the cylinder-heads or the piston. Where the steam-chest is upon the side, this advantage is possessed only in part, and when above, not at all.
As to the valves themselves, which effect the steam distribution, a detailed study of which is necessary to a thorough understanding of steam-engine design, construction, and operation, they may be (1) flat slides; (2) cylindrical slides, each of these having a movement lengthwise of the cylinder; (3) cylindrical oscillating (or "rock") valves, having a motion about an axis at right angles to that of the engine-cylinder, but controlling the ports in the same way as the slide; (4) plugs which oscillate about an axis at right angles to that of the engine-cylinder, but each controlling but one port; or (5) poppets (sometimes written "puppets," and also called "beat-valves"), which are circular discs that open close circular ports by rising and falling.
Murray’s D-Slide Valve
The operation of the ordinary D
-valve in steam distribution and its effect upon the piston position are exhibited in Figures 11 and 12, where Fig. 12 shows the piston at about the centre of the down stroke, with the slide-valve admitting live steam from the chest above the piston, and opening communication between the lower end-port (g) of the cylinder and the exhaust-passage (o). The valve is moving upward or in the direction opposite to that of the piston. A little later, when the piston has gone lower, the upper edge of the valve will begin to cut off steam from entering the port (d), and during the up-stroke the lower end-port will begin to close by the advancing inner edge of the valve. Fig 11 shows the piston at about the middle of its up-stroke, the valve moving downward. The live steam is here entering the lower passage (g) through the end-port (f) while the upper passage (e) is in communication with the exhaust by the upper end-port (e), the arch (d) of the valve, and the exhaust port and passage (d).
Oscillating or Rock-valve
The so-called "oscillating" or "rock-valve," controlling two end-ports and an exhaust-port, is a development of the flat slide, but the objection to this form is that it wears to arc of shorter radius, while its seat wears to one of a larger radius, so its tightness cannot be maintained.
A modification of the flat slide is the piston-valve, a cylinder moving lengthwise of the engine, and so ported as to act, as regards distribution, exactly like a flat slide, its advantage being that it pressed to its seat by the steam in the chest, as in the case of the flat slide although many consider that this advantage is offset by the difficult keeping it tight.
The three-port slide, commonly called the "D
-valve," and its equivalents the rock- and the piston-valve, have the merit of extreme simplicity, but their steam distribution, which will be explained farther on, is defective. An improvement gives the exhaust a separate valve or valves, with time of opening or closing not dependent upon load or point of cutoff, while the admission and cut-off are effected by another and a separate valve or valves.
Double Seat Poppet Valve
The flat slide, the piston-valve, and the oscillating valve never escape from the control of the driving-mechanism; the poppet is usually closed by its own weight or by a spring; and of the "plug" type, those used for admission only are generally opened by positive means and closed by a spring or a weight, while those employed for exhaust alone or for both admission and exhaust are never released from the driving-mechanism. Figure 1 shows a double-seat poppet-valve.
The slide-valve may be wholly or partially "balanced"—that is, relieved from the pressure of the steam in the chest—by a plate or ring playing against the lid of the chest, and thus lessening the area upon which unbalanced pressure may be exerted. Most stationary and all locomotive engines employ the slide. The oscillating or "rock" type is used on a few stationary, the "plug" on high-grade automatic cut-off stationary, and the "poppet" principally on the better class of marine engines, although some recent stationary engines, like many of the old beam engines, employ poppets. The piston type is used very largely on direct acting steam-pumps, and is slowly coming into favor for small marine engines. There may be in double-acting engines but two cylinder-ports, one for each end, each acting alternately for admission and exhaust; or there may be two for admission and two for exhaust. Where there are four ports, those for the exhaust may be controlled by the same kind of valves as those for admission, or by a different kind.
Meyer's Variable Cut-off Slide-valve
Meyer’s Variable Cut-Off Slide Valve
Figure 2 shows a variable cut-off valve-motion (Meyer's); the upper valve is moved by an eccentric-rod, but it is placed directly upon the back of a three-port slide-valve, also operated by an eccentric-rod. The time at which live steam is cut off by the upper valve (earlier or later according as the load on the engine is light or heavy) is varied by moving the two parts of the upper valve farther apart or closer together by a right- and a left-hand screw operated by hand as may be desired by the engineer. A throttling governor might be used with this movement to make the engine automatic under varying loads and pressures; but the Meyer valve is usually employed where there are no sudden changes either in load or in pressure.
Farcot’s Slide Valve Motion
Figure 3 shows the successive stages of distribution by the Farcot slide-valve motion, in which a riding cut-off valve is actuated through a cam (f) by the governor. At (I) the live steam has been cut off by the main valve from the left-hand end-port (d1
), while the right-hand end-port (d) is also closed by the same valve as an exhaust port. The position of the cut-off valve is therefore immaterial. In (II) the right-hand end-port (d) of the seat and the end-port of the main valve are open to live steam, and the left-hand end-port (d1
) of the seat is partly open for exhaust. In (III), although the passages (b) and (d) are in communication, the right-hand end-port is closed to live steam by the action of the end (c) of the cut-off plate worked by the cam (f). The left-hand end-port (d1
) is exhausting. In (IV) the valve has commenced to move to the right, but while the left-hand end-port (d1
) is still in exhaust communication with the exhaust passage (o) through the valve-arch (a), the right-hand passages (b) and (d) are still closed by (c) to live steam. In (V) the end (c1
)l of the cut-off plate has uncovered the left-hand end-passage (b1
) so that live steam can enter it, but the main valve has not yet opened the left-hand end-port (d1
) to live steam, although it has closed the right-hand end-port (d). This is an automatic cut-off system.
George Distributing Valve
The George distributing system (Fig. 3) has a plate consisting of two parts placed one above the other, and arranged between a three-port slide-valve and an expansion-valve which is moved by a special eccentric-rod. This double plate divides the steam-chest, as in Figure 4, into two portions communicating by ports which can be closed by the upper valve. The time of cut-off (consequently the degree of expansion) can be changed by displacing the two central portions of the upper part of the plate by a rack and a cogwheel, the cog-wheel being movable by a rod passing through the steam-chest cover. The main valve, which serves solely for admission and exhaust, works steam-tight both upon the main valve-seat and against the lower side of the partition. As shown, this becomes an automatic cut-off system when the eccentric operating the upper valve has its position on the shaft changed angularly, or the amount of its throw varied, by a governor.
Figure 4 shows the Gonzenbach valve. The ordinary three-ported slide (A) gets its reciprocating motion on the valveseat (B) through an eccentric-rod which puts first one and then the other of the end-ports in communication with the steam in the steam-chest, while the third port is placed in communication with the exhaust opening through which the steam passes into the air or into a condenser. The upper valve (E), which is in a separate steam-chest (C) and is also moved by an eccentric-rod, permits "live" steam from the boiler to go through the orifice (D), but as soon as (D) is closed the steam is worked by expansion only. If the upper valve has constant travel, this type will require a throttling governor to make it automatic under varying loads and pressures, but if the eccentric throw or its position on the shaft is varied by the governor, the whole becomes an automatic cut-off system.
Sulzer Poppet Valve and Gear
In the Collmann poppet-valve system there are independent exhaust-valves placed below, one for each end, and the so-called "steam-valves" which control the admission are placed on top, one at each end, being opened by eccentrics at regular intervals and closed at variable times by a trip-motion controlled by the governor. Figure 11 gives the details of the Sulzer poppet-valve motion. The exhaustvalves below and the admission-valves above are all poppets, and are opened at fixed times by eccentric-rods. Each exhaust-valve has a fixed time of closure, but the admission by each steam-valve is cut off by a spring at periods determined by the position of the governor, tendency to increase of speed in the engine causing earlier cut-off. In the Nolet valve system the exhausts are below, by means of a slide-valve at each end, with fixed periods of opening and closing; admission is at the side by poppets (one at each end) which have a fixed time of opening, but which are dropped by the influence of a weight at variable times determined by the position of a centrifugal governor.
Oscillating Engine Valves
Figures 6 to 9 show details of the valve-motion of oscillating engines.
Meyer Throttling Valve with Governor
Figure 10 represents the Meyer throttling-valve motion, which controls the passage into the steam-chest by a conical valve, whose times of opening and closing are controlled by a stem bearing a yoke operated by a revolving double cam, which is raised and lowered, according to the position of the governor, earlier or later in the stroke.
The valves may be operated (1) by a beam, (2) by one or more eccentrics or cranks on the main shaft, (3) from the connecting-rod, (4) by the piston-rod or the cross-head, (5) through a shaft driven by gears from the main shaft, (6) by toes on a rock-shaft worked by a beam, or (7) by cams giving a positive motion. The eccentric-rod may be attached directly to the valve-stem or to a crank-arm fastened thereto, or to a rocker-arm connected therewith, or it may drive through a so-called "link," which may be connected to the valve-stem or to a rocker-arm. The eccentric is practically a crank-pin so enlarged as to embrace the shaft. In all motions where a rotating shaft drives a reciprocating member, it acts exactly as does the crank, while dispensing with the necessity of cutting or bending the shaft, and permitting of its eccentricity being increased or diminished and its position on the shaft being varied by rotation; but it is not available for driving a rotating shaft from a reciprocating part.
Where there is an oscillating link it may have a fixed centre of oscillation and a sliding block, by varying the position of which the amount of travel of the valve may be altered; or the same effect may be produced by varying the point of suspension of the link. The link may be either curved or straight, and if straight its convexity may be turned either toward or from the eccentric. Usually the amount of variation of the motion of the link or of the block is sufficient to give the valve movements, varying from a maximum in the direction which will drive the engine forward to a maximum in the direction which will run it backward, there being an intermediate point at which the motion of the eccentric produces no motion in the valve. Most eccentric-and-link engines are thus reversible, this being essential in locomotive and marine practice and for hoisting-engines. Reversal may also be accomplished (1) by throwing the eccentric around on the main shaft, so that it shall follow, instead of preceding, the crank, or (2) by sliding it across the shaft to reach the same position and to produce the same result.
The peculiar advantage of the eccentric-and-link valve-gear is not only its reversibility while the engine is running, but also its affording a wider range of valve travel and consequently of expansion ratio. The block may either slide in a parallel slot in the link or embrace it and slide over it, the different constructions producing, other things being equal, the same valve-motion. In nearly all reciprocating engines the valve-movement is effected by means of an eccentric or its equivalent upon the driving shaft This introduces irregularities of motion, which increase with the comparative shortness of the eccentric-rod, and are of the same class as those caused by the angularity of the connecting-rod. There is, moreover, considerable friction between the eccentric-sheave and its encircling strap.
An excellent class of valve-motion, and one which has already been largely introduced in marine engines and has made a good record in locomotive work, is that in which the valves are moved by lever-connections with the connecting-rod. Of this class the Joy valve-motion appears to be the best known and to have the best record.
The walking-beam was a great convenience in working the valves and the air-pump, as well as in making connections with the water-pumping machinery which constituted the only loads that were at first applied to steam-engines, and it was also a great convenience in paddle-wheel steamboats, where the high position of the shaft above the water-level demanded that the engines should sit low; but the necessity of having the shaft below the water-level, as in propeller engines, led in most cases to its abandonment, although it is still employed in certain classes of marine work (ferryboats, etc.), and, notwithstanding the large amount of room which it takes up, it is still used on large stationary engines in Europe. But the air-pump and feed-pump are worked by eccentrics quite as well as they formerly were by the beam, and now, in many cases, the air-pump is operated by an independent motor.
It is now thoroughly understood that, as discovered by Watt, steam does the most possible work (other things being equal) when it leaves the engine at the lowest pressure—that is, when the terminal pressure is least compared with the initial; it is therefore desirable to "cut-off" after the piston has been started, so that its expansion from a high tension to a low one shall impel the piston, the release of the expanding steam being effected at the end of the stroke, or slightly before it in order to permit a free exhaust.
The point at which cut-off is effected may be varied in two ways: by the hand of the engineer or by the governor of the engine. The first is practicable for marine and locomotive but not for stationary engines. Cutting off the steam has the double advantage of working it (in most cases) more economically and of proportioning the force exerted and the steam expended to the load. The fly-wheel of course aids greatly to a regular motion, but, leaving out of consideration the question of economy of steam-consumption, it would be an absurdity to keep on storing power until there was more than the fly-wheel could absorb, or to let amount thus stored run down to near that point at which there would not be enough left to supply the demand for power. Besides this, the fly-wheel can take care only of temporary and short-lived irregularities. Variations of load may be provided for by choking off the steam-supply either by hand, as in marine and locomotive engines, or by a governor, as in those which are stationary or so-called "portable." But this choking or throttling, while an efficient means of taking care of load variations, uses the steam very wastefully (without proper expansion) under heavy loads, when there is the most steam needed and used.
The Drop Cut-off
The Drop Cut-off (also known as the Sickels cut-off, and claimed by both Sickels and Hogg) was introduced about 1841. It consisted of a set of steam-valves, each raised by a catch which could be thrown out at the proper moment by a wedge so adjusted that it would drop the valve at any desired point in the earlier half-stroke. Later, this was improved by the addition of a "wiper" having a motion at right angles to that of the valve and its catch, by giving to this wiper a motion in the direction coincident with the piston. This enabled the cut-off to be effected at any point in the stroke. For stationary engines this detaching was made automatic, depending upon the action and position of the governor. The action of the governor to determine the cut-off had been made in 1834 by Allen, who had a cut-off valve separate from the main valve. In 1849, Corliss attached the governor to a drop cut-off, and in 1855, Greene produced an engine which had the advantages of plain slide-valves at all ports, a range of cutoff from zero to full stroke, and automatic action of the governor to effect cut-off. In Wright's engine the governor operates cams which hold the valves open a longer or a shorter time, according to the speed, cutting off the steam earlier when the speed tends to grow too high, and vice versa.
Watt’s Fly-Ball Governor
The automatic device used to control either the throttle or the point of cut-off is called a "governor." Its most common form, the centrifugal fly-ball type (Fig. 5), was invented by Watt.
Farcot Centrifugal Governor
Farcot’s centrifugal governor
In the Farcot centrifugal governor, shown in Figure 15, there are connected with the extended shaft of a conical pendulum (driven by a horizontal shaft seen below) two friction plates. Between these there is a pair of conical wheels which engage with the upper or the lower of these friction plates according to the increase or decrease in the engine speed, moving the conical wheels to the left or to the right as the case may be. The conical wheel of the upper horizontal shaft gearing into these conical wheels is, together with the shaft, moved to the left or to the right, and moves by a screw in one or the other direction the spindle of the expansion-valve. When the conical pendulum is in its normal position by reason of the engine speed and its own being normal, neither of the friction plates is disengaged.
Allen’s Governor Cross-Section
Figures 12 and 13 show the Allen governor, in which there is a paddle-wheel in a corrugated cylinder filled with oil (Fig. 13). Increase of engine speed tends to turn the cylinder faster about the wheel, and by means of a segment gear this motion is made to move the cut-off to an earlier point.
Hartnell’s "Buckeye" Governor
There are very many successful engines in which there is a centrifugal governor upon the main shaft; a variation in the rotation speed, due to change of load or of initial pressure, causes the weights to approach or recede from the centre, and the levers to which they are attached to vary the angle which the eccentric makes with the crank, or its amount of eccentricity, thus varying the point of cut-off, and in many of these engines other functions, such as the times of steam admission and exhaust opening, and the point at which the exhaust is closed. Of this "Hartnell" type the "Buckeye" is the best known (Fig. 16).
Ball’s Regulator Governor
There are regulators by which the amount of throttling or the earliness of cut-off is controlled in proportion to the load and not to the speed, as in the Ball engine, the governor of which is shown in Figure 14.
Kenyon's Rotary Engine
Rotary engines while having the advantage of being able to run with great speed and with little jar, cannot very well work steam expansively. The difficulty of keeping them tight is due to the fact that friction is proportionate to the speed of the wearing surfaces, and the exterior of a revolving circle must of necessity travel faster than portions nearer the centre. Hence it is almost impossible to keep the ends of such rotating cylindrical pistons or "followers" packed. The extreme simplicity of such engines, and the convenience with which they may be used for "direct-driving" high-speed machinery, such as circular saws, would make them very popular if they were not so wasteful of steam and so difficult to pack. Figures 5 and 6 show Kenyon's rotary engine, in which the steam is admitted and permitted to exhaust by a slide-valve. As shown in Figure 6, it is exhausting from the left-hand side and taking steam at the right; the direction of motion being contrary to that of the hands of a watch.
Runkel's Rotary Engine
In Figure 1 is shown Runkel's rotary engine, in which a rotating piston or follower is made to turn a crank, thus combining all the disadvantages of both the reciprocating and the rotary type.
Turner's Rotary Engine
Borries' Rotary Engine
Hall's Rotary Engine
Cox's Rotary Engine
Figure 2 shows Turner's; Figure 3, Cox's; Figure 7, Hall's; and Figure 2, Borries' rotary engines.
Marine Engines are for the most part vertical, and are generally are known as "inverted"—that is, the cross-head is below the cylinder unless there is a beam. Marine service necessitates high economy of steam, hence compounding and condensing are carried to the utmost possible grade of perfection. The modern ocean steamer requires from 5000 to 20,000 indicated horse-power to propel her 5000 to 15,000 tons' burden at speeds which, while increasing almost with each successive high-grade vessel, now reach the average rate of 20 knots or 23 1/10 statute miles per hour between Queenstown and Sandy Hook.
The oscillating type of steam-engine was suggested by Trevithick, and is the best for ordinary paddle-wheel vessels, as it is light and compact and has the fewest working parts. It will work with the cylinder in any position from horizontal to vertical, although best in the latter position. It does not, however, admit of very early cut-off, and the trunnion is apt to leak.
Westland's Oscillating Engine
In Westland's oscillating engine, shown in Figure 5, while the crank rotates the cylinder oscillates on trunnions. There are on top of the cylinder four valves, worked by a rock-shaft placed in the centre of the cylinder's length and having tappets which catch in bell-cranks moving the valves.
Mackintosh 's Oscillating Engine
Figure 1 represents the Mackintosh type. The steam is admitted through the trunnions or pivots upon which the cylinder oscillates. In this type the fly-wheel shaft is below and the cylinder oscillates above it.
Hicks’ Oscillating Engine
Fevre's Oscillating Engine
Root’s Oscillating Engine
In Figure 4 (the Hicks) the fly-wheel is above; and in Figure 3 (Fevre's) the oscillating axes are on the bottom instead of at the centre of the cylinder. Figure 4 shows the Root oscillator.
Penn’s Trunk Engine
Penn’s Marine Trunk Engine
In the trunk type of steam-engine (Fig. 1) there is no piston-rod, the connecting-rod being hinged to a pin in the centre of the piston, which is surrounded by a cylindrical case or "trunk" concentric with the cylinder and continued out at its other end, so that there are the same effective piston-areas back and front. This is the lightest and most compact of all marine screw-engines; but the friction of the stuffing-boxes for the trunks is excessive, and the bearings of the pin in the piston are liable to become heated, and are then difficult to cool, besides which the side-cylinder wear is very great, particularly in running astern.
Beam-engines are those in which the shaft receives its rotary motion through the intermediation of a lever either above or at the side of the cylinders. Ordinarily the expression "beam-engine" refers to one in which the "walking-beam" or "working-beam" is above, the other types being generally spoken of as "side-lever" engines. Beam-engines are now but little used, except for marine purposes, although at one time they were the only type, and later on the most common one, for stationary engines; in fact, the beam was used in early locomotives.
When used aboard ship, a beam-engine requires a higher deck than is given to it in other countries than the United States.
The American Beam-engine
The American Beam-engine for river-steamers was first designed in 1822 by Robert L. Stevens. Its great advantage is its flexibility, permitting long vessels to spring without crippling the engine. It works smoothly, and is economical and compact.
The Mississippi River steamboat constitutes a type of marine construction deserving special mention; but its peculiarities are so dependent upon the construction of the hull which it drives that its consideration will be deferred for the Volume on Marine Architecture. The North River and Long Island Sound steamboats are in themselves a special variety to be found in no other country and in no other section of the United States.
The Side-lever Engine
“Grasshopper” Side Lever Steam Engine
Side Lever Steam Engine
The Side-lever Engine is of two kinds: (1) that in which the fulcrum is between the connecting-rod and the side-rods from the piston-rod crossheads, as in Figure 3; and (2) that in which the fulcrum is at one end, as in Figure 2. The first is the true side-lever type, the second being often called the "grasshopper" engine. This type is especially adapted for marine purposes by reason of its simplicity, cheapness, capability of giving a long stroke in a shallow ship, comparative freedom from racking, and absence of a dead point even where there is but a single cylinder. It will run when in a state of repair under conditions, which would disable any other type.
The Steeple Engine
The Steeple Engine of Trevithick has the piston operating directly upon the crank; it is compact, light, and cheap, and has fewer working parts than the side-lever type, but requires a deep ship and needs two piston-rods, between which the shaft is placed. This engine, so modified as to lie horizontally, is well adapted for war-ships, in which the machinery must be low down in the hull. This modification is often known as the "return-connecting-rod" type.
The Return-connecting-rod Engine
The Return-connecting-rod Engine, in very general use for marine purposes, has the connecting-rod on the side of the crank-shaft opposite to the cylinder, and there are two piston-rods, one above and the other below the crank. This allows of very long stroke, but limits the diameter of the piston, makes packing the stuffing-boxes difficult, and allows of but very short eccentric-rods, unless they are placed on the same side as the connecting-rod.
In the theoretically perfect steam-engine the steam should be discharged at a pressure corresponding to absolute zero and at the temperature of the external air. The nearest approach to these points that can be obtained, consistent with other desirable features, the better. A device, which would so condense the steam as to remove all pressure from the exhaust side of the piston would be very advantageous. The earliest attempt in this line effected this condensation in the cylinder itself by a jet of cold water, the unbalanced atmospheric pressure alone being the motive power. The use of the working cylinder as a condensing vessel having the disadvantage of cooling the entering steam before it had done any work, the employment of a separate condenser, due to Watt, has been found necessary; but the methods of effecting condensation in a separate vessel are various. A jet from a plain tube or from a "rose" may be employed; or the steam-exhaust may be made to circulate against surfaces cooled by currents of cold water; and such surfaces may be either flat metal partitions or tubes containing the cooling liquid.
Figure 7 shows in section and in perspective an improved surface-condenser combined with an independent air-pump and a circulating-pump. The exhaust steam entering from the engine at A is scattered to the perforated plate (O); it expands in the upper part of the case, then passes among the tubes, and leaves the case at (B), going thence to the air-pump. The cooling water entering the circulating-pump passes into the compartment (F), thence into the small tubes, which it traverses, then returns through the annular spaces between the wall and the large tubes, and empties into the compartment (G). Thence it passes into the compartment (H) by the passage-way (E). It next circulates through the upper section of the condenser in the same way, and finally passes out through (D). This type of condenser differs essentially from others in that it employs concentric tubes, and that each tube is free to expand and contract without requiring any ferules or special joints. It has extraordinary capacity and is very readily cleaned. Tests with a small experimental apparatus show 101.8 pounds of steam condensed per hour per square foot of condensing surface with vacuum, and 204.2 pounds without. In the first case the injection-water temperature was 56½° Fahr., discharge 98°, hot well 138°, and average vacuum by the gauge 24½ inches. In the second the injection was 78½°, discharge 139°, and hot well 201°.
The old jet-condenser has been transformed into what is now known as the siphon-condenser (Fig. 4), in which no pump is necessary; the vacuum produced by the condensation of the steam by a jet being sufficient to raise the water in a continuous current when the action of the apparatus is established.
It should be distinctly understood that a condensing engine may be either compound or non-compound, single or duplex, and that the air pump and circulating-pump of the condenser may be so arranged that they may be either driven by the main engine itself or operated as separate pieces of mechanism. It is well to have the condenser so attached that it may be thrown out if it be desired to inspect, clean, or repair it, or if it be found that the engine is under loaded.
Watt Type of Beam Engine
Watt Type of Beam Engine (Vertical Section)
Hornblower’s Compound Non-Condensing Engine
Woolf’s Double Cylinder Beam Engine
Rowan’s Twin Triple Compound Steam Engine
Examples of non-compound condensing engines are given in Figures 4 and 6; of compound condensing in Figures 3 and 4; and of triple-expansion condensing in Figure 4.
There being in a very early cut-off and in an excessive amount of expansion in one cylinder certain disadvantages—for example, the chilling of the internal surfaces of the cylinder and passages by the low temperature of a low-pressure exhaust, and the great range of pressures upon the piston and crank-pin during a single stroke—these disadvantages are lessened by what is known as "compounding;" that is, running one or more engines with the exhaust from another engine, thus requiring only a moderate degree of expansion in the first cylinder, and running the second cylinder by expansion only, both engines being connected with the same crank-shaft, or, in the case of those direct-acting pumping-engines which have no crank, with the same pump-plunger. There may be between the high- and the low-pressure cylinder either direct communication by steam-passages or a receiver or intermediate vessel, which permits the low-pressure piston or pistons to act upon the crankshaft at right angles to the high-pressure cylinder.
Wolff Compound Engine
In the Wolff or receiver compound engine the cranks are at right angles, so that they pass through dead-points at different times. The steam from the small or high-pressure cylinder passes into the receiver before going into the large or low-pressure cylinder; the pressures being thus equalized, although there is some loss caused by condensation of steam in the receiver. The condenser, with air-pump and feed-pump moved by a rock-shaft, is on the front. (It should be noted in this connection that the Wolff compound engine has a receiver; the Woof compound has none.)
Collmann’s Receiver Compound Steam Engine
In Figure 4 is represented Woolf's compound beam-engine. Figure 3 shows a Collmann compound engine in which the cranks are at right angles. Figure 4 shows a compound engine on Woolf's plan, but there are one high-pressure cylinder and two low-pressure cylinders, which have equal functions.
In the Woolf or receiver-less compound engine the small or high-pressure and the large or low-pressure cylinder stand side by side under the same end of the beam, their pistons moving in the same direction at the same time; the exhaust passing from either end of the small to the opposite end of the large cylinder. McNaught's improvement has the cylinders at opposite ends of the beam, the pistons moving different ways, and the steam passing from either end of the small cylinder to the nearest end of the large one. Elder's compound engine has the large and the small cylinder side by side in close contact, inclined at 45°; pistons moving oppositely and driving cranks projecting in opposite directions from the shaft; a similar pair of cylinders acting on the same pair of cranks and inclined the opposite way at the same angle.
Craddock's compound type has the cylinders side by side, their pistons driving cranks nearly opposite and moving for the greater part of the course in the same direction; the stroke of the small piston being made a little in advance of that of the large one, to prevent stopping on the dead points.
Concentric cylinders were employed by Rowan, the steam being admitted into a small cylinder and expansion continued in the larger one which surrounded it; the outer piston being ring-shaped, and having two rods fastened to the same cross-head as that of the inner one.
In the end-to-end double-cylinder type the steam commences its action in one end of a small cylinder, and completes it in the opposite end of a large one, the piston being attached to one rod. The space between the two pistons communicates with the condenser and is at all times a partial vacuum. In Garrett's double-piston engine the steam commences its action in one end of the cylinder and finishes its expansion in the opposite end, the former end having its capacity diminished by a plunger of large diameter passing through a stuffing-box and having one end fixed to the piston.
In Elder's treble-cylinder compound the piston of the small cylinder drives one crank, and those of the two lateral large or low-pressure cylinders work a pair of cranks pointing in a direction opposite to the middle one. Rowan's treble-cylinder engine has the rods of the small piston and of the two large lateral pistons attached to one cross-head.
Triple and Quadruple Expansion
Compounding is also accomplished in three or even four cylinders or sets of cylinders working successively. Where there are three grades of expansion the system is said to be triple
(or treble) expansion, irrespective of the number of cylinders employed. The cylinders may be placed in the same vertical axis or may be arranged side by side. Where there are more they may be arranged in pairs, in threes, or in fours, respectively side by side.
The cylinders of triple-expansion engines may be either three, four, five, or six in number. One arrangement is for the "intermediate" to be under the high-pressure and alongside the low-pressure cylinder; another, for the low-pressure cylinder to be under the high-pressure cylinder and beside the "intermediate;" or all three may be in line. There may be two cylinders for high pressure, one over the "intermediate" and the other over the low-pressure cylinder, or there may be two low-pressure cylinders beside each other, one with the high-pressure cylinder over it and the other with the "intermediate." There may be two high-pressure cylinders, each over a low-pressure cylinder, which latter have the "intermediate" between them, or there may be three low-pressure cylinders, side by side, having one high-pressure cylinder and two "intermediate" above them. Avery convenient, although in some respects complicated, arrangement is that by which the steam may be worked through all three cylinders of a triple-compound engine with successive expansions; or two of the cylinders may be worked high pressure and one low pressure; or two cylinders may be worked at the same degree of expansion at low pressure and the other at high pressure; or all three may be worked high pressure; or any one or any two may be thrown out altogether. Triple-expansion engines have proved more economical than the ordinary compound, the fuel consumption being about twenty five per cent less. This is very largely due to the higher steam-pressure. Their wear and tear is rather less when three cranks are employed than where there are but two, as in the ordinary compound.
1800 H. P. Triple-Expansion Marine Steam Engine
Figures 4 and 5 illustrate a set of triple-expansion marine engines of eighteen hundred horse-power (indicated), constructed by E. Cravero & Co., of Genoa, Italy. To economize space the three valves are placed behind the cylinders, and are worked by levers from ordinary link motions. The cylinders are perfectly free among themselves, to the end that they may expand and contract without restraint.
The following are the principal dimensions, which are given because such engines are not very common, and their proportions are not familiar even to professional engineers:
Diameter of high-pressure cylinder . . . 26 in.
""intermediate " ... 42.5"
""low-pressure " . . . 70"
Stroke of pistons 43.2"
Revolutions per minute 70
Piston speed 504 ft.
Proportions of cylinders: high : intermediate 1 : 2.67
Proportions of cylinders: intermediate: low 1 : 2.70
Proportions of cylinders: high : low . . 1 : 7.2
Order of cranks: high, low, intermediate.
Indicated horse power: high 602
""intermediate . . 612
"" low 627
"" total 1841
Diameter of steel crank-shaft 12.6 in.
""propeller-shaft . . . 11.4"
Number of tubes 888
Diameter of tubes 87 in.
Useful length 14 ft. 5 in.
Total cooling surface 2906 ft.
Total cooling surface per indicated horse power 1.56 sq. ft.
Diameter 24.8 in.
Stroke 27.5 in.
Proportion between volume of pump and volume of low-pressure cylinder 1:9
Circulating pump (single-acting):
Diameter 15.75 in.
Volume swept per horse-power and per hour 6.2 cub. ft.
Inverted-cylinder Triple-expansion Marine Engine
Triple-Expansion Marine Steam Engine (Plan of Cylinders)
Triple-Expansion Marine Steam Engine
Figures 1 and 2 show a very recent example of a triple-expansion engine constructed for the screw steamer “Ivy.'' The engines are of the ordinary inverted-cylinder marine type, with three cranks, and are designed for an initial working pressure of 160 pounds per square inch in the high-pressure cylinder. The high-pressure, intermediate, and low-pressure cylinders are respectively 16½, 26, and 44 inches in diameter, and their common stroke is 36 inches. The high-pressure cylinder has a piston-valve, and the others have ordinary slides. The valve-gear consists of double eccentrics and double-bar link-motion. The cranks are of forged iron 8½ inches in diameter in the body, and their pins are inches in diameter and 9 inches long. The piston-rods are 4 inches in diameter; the connecting-rods are 6 feet long and 4 inches in minimum diameter. The condenser is of the "surface" type and has 800 square feet of cooling surface.
The Four-cylinder Triple-expansion Engine
Four Cylinder Triple-Expansion Steam Engine
The Four-cylinder Triple-expansion Engine shown on Plate 88 has the cylinders disposed in pairs, tandem fashion, the two next the crank-shaft being the high-pressure and the intermediate cylinders respectively, while the two rear cylinders are low-pressure and are of unequal diameter. It is in this inequality of diameter that one of the peculiarities of the engine consists. By this arrangement there are obtained two engines, either of which could be worked as an independent tandem-compound engine in case of accident, or which could be worked coupled as tandem compounds (there being then two high- and two low-pressure cylinders), in case of circumstances necessitating a reduction of boiler-pressure below that suitable for the triple-expansion system of working. The engine is thus available for working in three different ways, the necessary changes being made by the arrangement of pipes and valves connecting the cylinders. The arrangement is also one, which could be advantageously adopted for converting a tandem-compound engine into the triple-expansion system.
In the engine illustrated the diameters of the cylinders are as follows: high-pressure, 11.02 inches; intermediate, 15.75 inches; and low-pressures, 20.08 inches and 35.43 inches. The stroke is 35.43 inches. The engine, running at seventy revolutions per minute with steam at an initial pres" sure of one hundred and fifty pounds per square inch absolute, cut-off at from 40 to 50 per cent, in the first cylinder, will indicate three hundred horse-power.
In proportioning the cylinders of the engine it has been deemed of less importance to attain equality of power in the two halves of the engine than to secure as small a variation as possible from what is known as "the mean turning moment," it being of special importance for mill purposes to obtain the steadiest possible driving.
Only the high-pressure and intermediate cylinders are steam-jacketed. The front and rear cylinders of each pair are connected by three bolts passing through cast-iron distance-pieces. This arrangement makes a firm connection, and at the same time affords facilities for the examination of the stuffing-boxes, etc. The steam and exhaust-valves are of the Corliss type. The exhaust-valves are nearest to the ends of each cylinder, and are so placed that they drain the latter. The steam-valves are driven from one side and the exhaust-valves from the other side of each engine, this simplifying the disposition of the parts and rendering them more accessible. The steam-valves on the high-pressure cylinder are fitted with a trip cut-off gear controlled by the governor, which member actuates a rod carrying cams with serrated faces, the point of the stroke at which the detent is released depending upon those parts of these cams that act upon the releasing rods. Each rod operating the detent gear has a hardened steel chisel-shaped point, which comes into contact with the cam as the valve is opened by the action of the eccentric, the further movement due to the eccentric, after the detaching rod has been stopped by the cam, causing the rod to actuate the detent, and, by releasing the valve from the pull of the eccentric, to leave it free to be closed by the action of a spring. This gear has the advantage of throwing exceedingly little work on the governor, the contact of the points of the releasing-rods with the cams being merely momentary. The bed-plate is made with a long foot under the crank-shaft bearing, this foot being extended toward the guides to prevent twisting of the bed under the action of the connecting-rod on the cross-head. There are two vertical air-pumps, which are driven from the cross-heads through bell-crank levers.
Twin Triple-compound Engine
Rowan’s Twin Triple Compound Steam Engine
Figure 4 shows a twin triple-compound engine arranged to drive the screw of a vessel. Of the six cylinders, each has its separate supply of steam, but all work upon the same shaft. The large cylindrical vessel seen in front is a surface condenser— that is, one in which the steam is condensed by contact with metal surfaces cooled on the outer side by a current of water, and not, as in Watt's condenser, by the direct action of a jet of water.
Quadruple-expansion Engines may have from four to eight cylinders. The most common arrangements are—(1) where the high-pressure is above the low-pressure cylinder, the first intermediate beside the high-pressure cylinder, and the second under this and beside the low-pressure; (2) where the high-pressure is above one low-pressure cylinder, with two "first intermediates" beside it, and a "second intermediate" below one of the first intermediates and between the two low.
Quadruple Disconnective Non-condensing Land-engine
Disconnective Non-Condensing Steam Engine
A good example of a quadruple engine is shown on Plate 89. While this style is intended for stationary purposes, it embodies many features of marine engines, as, for instance, double web-cranks instead of the usual overhung single cranks, and connecting-rods with T-ends for the crank-pin bushes, The cylinders are unjacketed and are covered with non-conducting material and lagged with polished teak; they are 12 inches, 16 inches, 22 inches, and 28 inches in diameter respectively, all having a piston stroke of 36 inches. Each pair is bolted to a bed-plate of box section, with planed seats for the cylinders and pedestals. These latter are four in number, strongly bolted to the bed-plates and adjustable by wedges. They are fitted with heavy gun-metal bushes, each cast in four pieces, rendered easily adjustable by two wedge-bolts. The crank-shaft is 10 inches in diameter at the inside journals and yyi inches in diameter at the outside journals; it is constructed on the "built" principle, and is fitted with two sets of double web-cranks placed at right angles to each other. The heavy fly-wheel, 16 feet in diameter, is built in eight segments bolted together; the rim has fifteen grooves suitable for ropes 5% inches in circumference. The valve-gear is of the usual slide-valve pattern for all the cylinders except the high-pressure one, which is fitted with Proell's automatic expansion-gear and governor. The exhaust from both ends of the cylinder is controlled by a single piston-valve worked by an eccentric and rod off the crank-shaft. The feed-pump is worked off the low-pressure piston-rod cross-head.
Tandem Compound Condensing Steam Engine
The exhaust from the low-pressure cylinder or cylinders of a compound engine in which there are only two successive expansions (or from the last cylinder or cylinders, where there are three or four successive expansions) may be either discharged into the atmosphere (in which case the engine is said to be "compound non-condensing") or conveyed to a condenser, in which case the entire system is said to be "compound condensing." Figure 1 shows a tandem-compound condensing engine, both pistons acting on the same rod, and there being no receiver and but one crank.
The Corliss Engine
The Corliss Engine has the original cock used to effect steam distribution developed into an oscillating plug, and»the hand-power or simple cords employed to open and close it have been replaced by a beautiful automatic system, by which the governor permits a weight or an air-spring suddenly to close the valve when the time for cut-off (as determined by the governor itself) has arrived in each stroke. The use of four valves reduces to a minimum the waste clearance-space between the valves and the counterbore. The valves are given partial rotation by rods from a wrist-plate oscillated by an eccentric and giving sudden opening and prompt closing, while practically holding the valve still between opening and closing times. When it is time to cut off, the admission-valve is sharply detached from the driving mechanism. The detaching mechanism is directly connected with the governor, which has not to do the actual work of valve-moving. When either admission-valve is detached from the driving mechanism, it is closed by a spring, a weight, or a vacuum-pot The oscillations of the governor are controlled by a dash-pot.
Tandem-compound Corliss Engine
Tandem Compound Corliss Steam Engine
Figure 4 is a good type of the Corliss engine arranged as a " tandem-compound "—that is, with the high- and low-pressure cylinders in the same axial line. In the example given, instead of the admission- and the exhaust-valves of each cylinder being worked from a common "wrist-plate" or disc, as is usual in the Corliss construction, there is in each cylinder one crank-disc to work the two admission-valves and one to work the two exhaust-valves. The two admission-valve discs are connected by a "parallel-rod", as are the two exhaust-valve discs. Each of the four admission-valve cranks is in communication with the regulating device, and also with the vertical rods extending from the dash-pot pistons and with its admission-valve wrist-plate, so that when the governor and its attached regulator-rods disengage the valve-cranks from the control of the wrist-plate rods, the valve is suddenly closed by the action of the dash-pot rod. The wrist-plates of the high-pressure cylinder (the one nearest the crank) are actuated by eccentric-rods from eccentrics on the main shaft, and in turn, by the parallel-rods shown, give motion to the wrist-plates on the low-pressure cylinder.
A lengthwise central vertical section of a horizontal Corliss engine is shown in Figure 1. Both admission-valves are closed, as is also the left-hand exhaust-valve, the right-hand exhaust-valve being open. Figure 2 shows the "tangent crab-claw" which hangs to the shaded piece shown in the cut, and which is attached to the valve-crank until the action of the governor depresses the entire claw- or thumb-and-finger-like member and allows the vacuum dash-pot piston, which has been drawn up by the crab-claw as the latter opened the admission-valve, to fall suddenly, thus closing the valve and cutting off steam quickly and sharply. The vacuum dash-pot is shown, with a part of its rod, in Figure 3.
The Centennial Exhibition Corliss Engines
Centennial Exhibition Corliss Steam Engine
The Centennial Exhibition Corliss Engines were such a marked departure from the usual type of construction of their builders, and by reason of their position were so prominent and familiar, that we have selected them for our Frontispiece.
These engines have a double-acting vertical beam, constructed upon the Corliss pattern. The frame is A-shaped, the beam-centre being at the vertex, with the cylinders and main shaft at the base angles; the various parts of the frame are in the hollow or box form, and the corners are flattened, producing a section almost octagonal. The cylinders are 40 inches in diameter, 10 feet stroke, and are rated at fifteen hundred horse-power collectively, with a capacity up to twenty-five hundred, the lesser power calling for about twenty-seven and a half pounds mean effective pressure per square inch. The single shaft to which they are connected carried at the Centennial Exhibition a gear-wheel 30 feet in diameter, 24 inches face, having two hundred and sixteen teeth, cut with a pitch of 5.183 inches. It has been stated that this is the largest cut iron gear ever made; it weighs fifty-six tons, and, at thirty-six turns per minute, its periphery travels at the rate of about thirty-eight miles per hour. The crank-shaft carrying this wheel is 19 inches in diameter and 12 feet long. The cranks are of iron gun-metal, and weigh three tons each. The beams are 9 feet wide in the centre, 27 feet long, and each weighs about eleven tons. The connecting-rods, 25 feet long, are manufactured out of "scrap" iron, requiring in their construction ten thousand worn horse-shoes. The piston-rods are steel, 6¼ inches in diameter, with a speed of 720 feet per minute. The gearing by which motion was imparted to the shafting at the Exhibition was in covered ways under the floor. The great gear-wheel drove a pinion 10 feet in diameter, and parallel to its axis was a Hue of shafting diminishing from 9 to 8, 7, and 6 inches, the pinion gear weighing seventeen thousand pounds.
Diameter of cylinders, 3 1/3 feet; stroke, 10 feet; diameter of piston-rod (steel), 6¼ inches; speed, thirty-six revolutions per minute, corresponding to a piston-speed of 720 feet per minute; length of beams, 27 feet; depth of beams at centres, 9 feet; weight of each beam, eleven tons; length of fly-wheel shaft, 12 feet; diameter of fly-wheel shaft, 1 foot 7 inches; diameter of fly-wheel shaft in bearings, 1½ feet; length of flywheel shaft in bearings, 2¼ feet; diameter of fly-wheel, 30 feet; width of fly-wheel across the face, 2 feet; number of teeth on fly-wheel, two hundred and sixteen; and weight of fly-wheel, fifty-six tons.
The main line of underground shafting was 252 feet long, running north and south. The first line of shafting, by means of four trios of mitre-bevels, transmitted power to eight 6-inch shafts at right angles, leading in different directions to walled pits under heavy standard frames which carried the driven pulleys on the ends of the shafting overhead. Each of the lines of shafting was capable of transmitting a power of one hundred and eighty horses at its normal speed, and was 658 feet long, reaching from the transept to the east and west ends of the building. The larger portion of these lines ran at the rate of one hundred and twenty revolutions per minute, but the one specially devoted to wood-working machinery made as many as two hundred and forty per minute. The total weight of the main gearing, shafting, mitre-gearing, and pulleys to which these engines were attached was 365,855 pounds; the weight of the engines, underground shafting, and boilers was 1,552,180 pounds.
The boiler-house connected with these engines was located 36 feet from the Machinery Hall, and contained twenty upright boilers, each having nominal power of seventy horses. The main steam-pipe, which was located under the floor, was of wrought iron, 320 feet long and 18 inches in diameter. These unparalleled engines were intended to operate a length of shafting estimated (main and subsidiary lines together) at 10,400 feet and to answer the purpose of exhibition required by the larger portion of machines occupying a floor-space of about thirteen acres, of which machines more than eight thousand were in position on the opening day of the exhibition.
The Wheelock Engine
The Wheelock Steam Engine
The Wheelock Engine as originally constructed (Fig. 2), has but two ports, one at each end to each cylinder. Upon each of the valve-seats corresponding to these ports there is an oscillating valve, which admits steam at one fixed point and exhausts it at another. Back of or below each of these main valves is another oscillating valve, which causes cut-off by a detent motion regulated by the governor: the lighter the load, the earlier the cut-off. There is about this an elegant simplicity of design, which leaves but little to be demanded.
The Greene Engine
The Greene Steam Engine
The Greene engine (Fig. 1) has four flat valves. Those for the exhaust have their own eccentric-rods; those for admission have each a sliding bar which has motion parallel to the centre line of the cylinder and coincident with that of the piston. This bar has two tappets adjustable vertically, so as to engage rock-shaft arms on the ends of rock-shafts attached to the valve-links inside the steam-chest. Springs hold these tappets to their work and in contact with a "gauge-bar," which is adjusted to various heights by the action of the governor.
The “Buckeye” Engine
The Hartnett Buckeye Governor
The Buckeye Steam Engine (Cylinder Section)
The Buckeye Steam Engine
The Buckeye steam engine is one of the most successful of those which have the cut-off automatically regulated by a centrifugal governor placed on the main shaft and controlling the position of the eccentric. There are three sub-types of construction, the latest of which is shown in Figure 3. Figure 2 is a horizontal section through the valves and cylinder corresponding to any one of the three sub-types, and Figure 16 illustrates the governor employed in all. The live steam enters at (A) (Fig. 2), whence it passes through passages (a, a') and the open pistons (d, d) into the interior of the box slide-valve (B, B, as shown by the arrows. From this box-valve it is admitted to the cylinder through ports (b, b) in its face as these ports are alternately brought to coincide with the cylinder ports. The cut-off valve, which consists of two light plates (C, C) connected by rods (C'), works on seats inside of the main valve, as shown, and alternately covers the ports leading to the cylinder. The cut-off valve-stem (g) works through the hollow stem (G) of the main valve. The exhaust takes place at the end of the valve (as shown by arrows on the right) into the valve-chest; thence into the exhaust-pipe (F) below. In the valve-seats (at e, e) are shallow recesses equal in area to the cylinder-ports, and called "relief chambers," their use being necessary at certain positions of the valve to counteract the excess of pressure tending to force the valve to its seat. In this engine the steam is within, instead of around, the slide-valve, as in most slide-valve engines, and the tendency of the steam in the ports by( )b and in the cylinder is to force the valve from its seat, this being counteracted by the pressure of the entering steam in proportion to the area of the pistons or equilibrium rings (Dd, Dd), which are proportioned to hold the valve to its seat at the moment of admission (see the lefthand end of the valve in Fig. 2), when the tendency to leave the seat is greatest. At other times this pressure would be too great, hence live steam is admitted to the relief chambers (e, e) through the holes (f, f), in the valve-face just after it is exhausted from the cylinders (as shown at the right-hand ends of the valve in Figure 3), and in turn is thence exhausted, as shown at the left, just after the exhaust closure.
In the governor shown in Figure 16, two levers (a, a) are pivoted to the arms of the containing case at one of their ends (as at b), while the movable ends are connected by links (B, B) to ears or flanges on the sleeve of the loose eccentric C, so that their outward movement in obedience to centrifugal force (as indicated by dotted lines) advances the eccentric in the direction of revolution. Springs (F, F) oppose the centrifugal tendency, the tension being adjusted by a screw at (c).
The Straight-line Steam Engine (Top View)
The two special features in the frame of the "straight-line" engine are (1) its support on three self-adjusting points to free it from torsion, and (2) diverging straight arms in the frame, connecting the cylinder and the main bearings, as shown in Figure 4. All boundary-lines are straight, ending in curves; all cross-sections of stationary parts rectangular, with rounded corners; and all moving arms and levers double convex, wide and thin, with the longest axis in the direction of the greatest strain. The frame is cast in one piece with the cylinder, steam-chest, cylinder-jacket, and brackets for rock-shaft and other parts. The valve controls the steam-distribution very much like a common D
-valve, but has a variable travel controlled by the governor.
The Straight-line Steam Engine (Cylinder & Valve Section)
As will be seen in Figure 6, the valve is a thin rectangular plate having through it five openings, working within an opening formed by the valve-seat and a pressure-plate and two distance-pieces. By recesses in the pressure-plate and the small openings through the valve there are opened double ports for the steam-admission and exhaust.
The Straight-line Steam Engine (Cross-Section of Cylinder)
A vertical section through cylinder and valve is shown in Figure 7. The piston-rod is made fast in the cross-head and the cross-head pin (or wrist-pin) is made fast to the connecting-rod, turning in two bearings in the cross-head. The eccentric is cast upon a swinging plate, which is pivoted to the boss of the fly-wheel. It is shifted by the governor, and change of its position changes its eccentricity or throw, the travel of the valve, and the point of cut-off. The crank-shaft and wheels, shown in vertical section in Figure 31 are very original. The crank-pin is oiled while the engine is in motion by means of an eccentric chamber on the outside of one of the balance" wheels and of holes drilled through the crank-pin. The waste oil thrown the inner end of one of the main bearings also finds its way to the crank-pin. The waste oil thrown from the cranks is caught in a recess in the inner surface of each wheel-rim. The main journal-boxes are split eccentric sleeves lined with Babbitt metal.
The Straight-line Steam Engine (Governor & Valve Motion)
The governor, shown in Figure 5 is a single ball linked to the eccentric and a spring, and so located and weighted as to counterbalance the eccentric. Increase of engine speed moves the eccentric nearer the shaft, thus shortening both its throw and the valve-travel.
The Porter-Allen Engine
The Porter-Allen Steam Engine
The Porter-Allen Steam Engine (Fig. 1), which claims to be the first and most perfect type of the high-speed steam-engine, is distinguished for originality of design and for its special adaptation to high-speed running, for attaining which every detail of construction and every movement are made satisfactorily subservient. The central feature of the valve-motion is a link actuated by a single eccentric by which separate and independent movements are given to the steam-admission and exhaust-valves. The eccentric is part of the main shaft and has its centre coincident with the crank itself, so that both arrive at their dead points simultaneously.
The valves are all flat frictionless slides, working under plates which protect them from steam-pressure and permit at once four lines of opening, each the whole length of the port. Two valves for steam admission and two for exhaust are provided, each with the shortest practicable steam-way and least waste room. A highly sensitive and unique governor controls the point of cut-off by moving the block in the link: The movement of the exhaust-valves is constant. Mr. Allen invented the valve-gear, and in 1863 Mr. Porter designed the governor, and also the bed, from which all similar beds have been modeled.
The Ideal Steam Engine
The " ideal" single-cylinder double-acting engine (Fig. 8) is characterized by the valve (a hollow double piston, having steam on each end and on all sides) being driven by direct connection from a "shaft-governor" bolted to the fly-wheel and provided with a dash-pot; by the crank playing in a case containing a considerable quantity of oil, in which the crank discs dip, and which is so thrown by the crank-motion that it lubricates slides, cross-head pin, piston-rod, and all other parts requiring lubrication; by "pop-out cups," which burst if a dangerous quantity of water gets in the cylinder; by the cylindrical guides bored at the same time as the cylinder; by a very heavy frame and bed-plate; and by an "overhung" cylinder of the Porter type (known in England as the "Tangye"). The governor gives an open port at the beginning of stroke, and cuts off from zero to three-fourths stroke. There are no oil-cups on this engine, the system of lubrication providing for continuous circulation of oil through all bearings. About once a week the oil is drawn out of the case, filtered, and used over again.
The Westinghouse Engine
The Westinghouse Steam Engine
The Westinghouse Steam Engine (Vertical Section)
The Westinghouse Engine has among its essential features—many of which are peculiar to it—single-acting inverted cylinders, having no piston-rods, but the piston driving the crank-shaft through a connecting-rod pivoted to the piston-head. The valves are cylindrical pistons. The crank case constitutes a receptacle for oil, in which the crank dashes at each revolution, thereby effecting lubrication of the crank-pin, main-bearing, and wrist-pin. This type exists in three varieties, of which the most recent and important is the compound engine shown in longitudinal vertical section in Figure 6, a perspective being given in Figure 5.
The Westinghouse Steam Engine (Vertical Section of Cylinder & Valves)
The functions of the working portions may be readily studied in Figures 1 to 4; Figure 1 showing the position of the valve and piston at the moment when the steam is being admitted into the high-pressure cylinder; Figure 2, when the steam in the high-pressure cylinder has been cut off; Figure 3, when the high-pressure cylinder is exhausting and the low-pressure cylinder is getting the exhaust therefrom; and Figure 4, when the exhaust of the high-pressure cylinder (which is the supply for the low-pressure cylinder) has been cut off so as to cause cushion or compression, this leaving the low-pressure cylinder to work on expansion alone until stroke-end. Steam is admitted at s and finally exhausted at (E); the space (C) between the valve-heads forms a clearance volume, which is constantly in communication with the high-pressure cylinder through the annular port (P). Steam is admitted to and cut off from the high-pressure cylinder by the valve-edge (a, a); this being the only function performed by that end of the valve. The valve does not cut off on the port (P) to the cylinder, but upon another port (M) , communicating only with the steam-pipe. Since the valve never reaches the port (P), the latter is always uncovered, and the clearance volume (C) is therefore always in communication with, and a part of, the high-pressure cylinder during both the upward and the downward stroke of the piston. This clearance space bears the same relative proportion to the high-pressure cylinder that the latter does to the low-pressure cylinder. The remaining functions of the valve motion are all performed by the short end of the valve, of which the inner edge b, b effects release and compression in the high-pressure cylinder coincidentally with the admission and secondary expansion in the low-pressure cylinder; the outer edge (c, c) effecting the release and compression in the low-pressure cylinder.
Miscellaneous Reciprocating Engines
Small Cylinder Steam Engine
Medium Cylinder Steam Engine
Large Cylinder Steam Engine
Twin Cylinder Steam Engine
The principal types of reciprocating engines having been illustrated and described, it now remains in this class only to give a few more examples of various types of construction, both ordinary and unusual. Figure 3 represents a German engine of large, and Figure 1 one of small, capacity. In these the cylinder and guides and one of the fly-wheel pillow-blocks are fastened to an iron bed-plate, which is bolted to a stone foundation. In Figure 2, a medium engine, the pillow-block is passed in one piece with the iron bed-plate, no mason-work foundation being used. Figure 4 shows a double-cylinder twin engine.
In Figure 4 we have an inclined double-cylinder engine. Figure 3 shows an engine attached to the boiler, thus saving the expense and room of a separate frame. Figure 6 shows a curious type of engine (Sulzer's), in which the fly-wheel is not on the crank-shaft, but is driven by a pinion upon that shaft; of course at a slower rate of speed than that of the engine. Figure 5 shows a three-cylinder engine in which there are three single-acting cylinders, with their axes 1200 apart, driving a common shaft. Such machines, having no dead-point, start easily, and are used for direct-driving high-speed machines, such as saws, dynamos, etc.
Steam Engine & Boiler in Railway Car
German Semi-Portable Steam Engine
German Locomobile with Removable Tubes
Figure 1 shows a steam-engine and boiler contained in a railway-car for convenience in doing construction-work along the line of the road. Figures 3 and 4 show forms of German "locomobiles" or traction engines. Figure 2 illustrates a German semi-portable engine, with locomotive fire-box.
Geared Engines are those in which the screw or other rotating part driven by the engine is given, by means of gear, greater rotation speed than the engine. They were in use for marine work long after engines were known which could have been run at even a greater speed than the screw might have been run at had the latter been made large enough. The term is usually restricted to marine engines.
Hoisting Engine with Boiler
For hoisting purposes there are generally used small double-acting reciprocating engines, geared to a drum upon which a rope or chain is wound and unwound (Fig. 2). These engines must be quickly reversible, and as such machines are most often used in exposed situations, they need be of extreme simplicity. Usually they are attached to, as in the Figure, or are in close connection with, a portable boiler.
Sector Cylinders are very rarely seen. The ordinary cylinder is replaced by a cylindrical sector in which a rectangular piston oscillates, as on a hinge, on a rock-shaft which drives the crank.
The Disc Engine
Section of the Disc Engine
The Disc Engine (Fig. 1) has, instead of a regular cylinder, a spherical zone having for its ends a pair of cones the apices of which coincide with the centre of the sphere. The piston is a flat circular disc, which fits the interior of the spherical zone around its edge, and has in it a radial slit which fits a partition fixed in the cylinder and shaped like the cylinder sector. The disc is fixed to a ball, from which projects (perpendicular to the plane of the disc) a rod, which acts as a crank-pin, its end fitting into a hole in the end of the crank. The disc and partition divide the cylinder into four spaces, two of which enlarge as the others contract, steam being let into the two former, and discharged from the two latter, by ports near the partition.
The Tendency of Modern Steam-engine Practice
is toward higher and higher piston speed and rotation speed, as well as higher pressure and earlier cut-off. This tendency is by reason of the fact that the more rapidly the steam is used, the less it is wasted by condensation from radiation; the higher the pressure, the earlier the cut-off, and the greater the amount of work done with a given weight of steam; and the higher the rotation speed, the less counter-shafting, pulleys, etc. are needed to drive the machinery, the greater part of which is high speed. Of course the cost of small engines is less than that of large ones to do the same work. We must not, however, lose sight of the fact that in any steam-engine the fluid must enter the cylinder at as high a pressure as possible and leave it at as low a pressure, this reduction of pressure being by expansion, not by condensation in the cylinder; and that there must be no waste of heat by conduction and radiation. Within certain limitations, the engine which expands steam at from one hundred to twenty pounds pressure is doing more work than that which expands it only at from one hundred to fifty pounds.
- The Iconographic Encyclopædia Vol 6, Applied Mechanics by Robert Grimshaw, 1890 pages 238-275