[Ill.u.s.tration: FIG. 21.--Smeaton"s Newcomen Engine.]
A "jack-head" pump, _N_, is driven by a small beam deriving its motion from the plug-rod at _g_, raises the water required for condensing the steam, and keeps the cistern, _O_, supplied. This "jack-head cistern" is sufficiently elevated to give the water entering the cylinder the velocity requisite to secure prompt condensation. A waste-pipe carries away any surplus water. The injection-water is led from the cistern by the pipe, _P P_, which is two or three inches in diameter, and the flow of water is regulated by the injection-c.o.c.k, _r_. The cap at the end, _d_, is pierced with several holes, and the stream thus divided rises in jets when admitted, and, striking the lower side of the piston, the spray thus produced very rapidly condenses the steam, and produces a vacuum beneath the piston. The valve, _e_, on the upper end of the injection-pipe, is a check-valve, to prevent leakage into the engine when the latter is not in operation. The little pipe, _f_, supplies water to the upper side of the piston, and, keeping it flooded, prevents the entrance of air when the packing is not perfectly tight.
The "working-plug," or plug-rod, _Q_, is a piece of timber slit vertically, and carrying pins which engage the handles of the valves, opening and closing them at the proper times. The steam-c.o.c.k, or regulator, has a handle, _h_, by which it is moved. The iron rod, _i i_, or spanner, gives motion to the handle, _h_.
The vibrating lever, _k l_, called the _Y_, or the "tumbling-bob,"
moves on the pins, _m n_, and is worked by the levers, _o p_, which in turn are moved by the plug-tree. When _o_ is depressed, the loaded end, _k_, is given the position seen in the sketch, and the leg _l_ of the _Y_ strikes the spanner, _i i_, and, opening the steam-valve, the piston at once rises as steam enters the cylinder, until another pin on the plug-rod raises the piece, _P_, and closes the regulator again.
The lever, _q r_, connects with the injection-c.o.c.k, and is moved, when, as the piston rises, the end, _q_, is struck by a pin on the plug-rod, and the c.o.c.k is opened and a vacuum produced. The c.o.c.k is closed on the descent of the plug-tree with the piston. An eduction-pipe, _R_, fitted with a clock, conveys away the water in the cylinder at the end of each down-stroke; the water thus removed is collected in the hot-well, _S_, and is used as feed-water for the boiler, to which it is conveyed by the pipe _T_. At each down-stroke, while the water pa.s.ses out through _R_, the air which may have collected in the cylinder is driven out through the "snifting-valve,"
_s_. The steam-cylinder is supported on strong beams, _t t_; it has around its upper edge a guard, _v_, of lead, which prevents the overflow of the water on the top of the piston. The excess of this water flows away to the hot-well through the pipe _W_.
Catch-pins, _x_, are provided, to prevent the beam descending too far should the engine make too long a stroke; two wooden springs, _y y_, receive the blow. The great beam is carried on sectors, _z z_, to diminish losses by friction.
The boilers of Newcomen"s earlier engines were made of copper where in contact with the products of combustion, and their upper parts were of lead. Subsequently, sheet-iron was subst.i.tuted. The steam-s.p.a.ce in the boiler was made of 8 or 10 times the capacity of the cylinder of the engine. Even in Smeaton"s time, a chimney-damper was not used, and the supply of steam was consequently very variable. In the earlier engines, the cylinder was placed on the boiler; afterward, they were placed separately, and supported on a foundation of masonry. The injection or "jack-head" cistern was placed from 12 to 30 feet above the engine, the velocity due the greater alt.i.tude being found to give the most perfect distribution of the water and the promptest condensation.
[Ill.u.s.tration: FIG. 22.--Boiler of Newcomen"s Engine, 1768.]
Smeaton covered the lower side of his steam-pistons with wooden plank about 2-1/4 inches thick, in order that it should absorb and waste less heat than when the iron was directly exposed to the steam. Mr.
Beighton was the first to use the water of condensation for feeding the boiler, taking it directly from the eduction-pipe, or the "hot-well." Where only a sufficient amount of pure water could be obtained for feeding the boiler, and the injection-water was "hard,"
Mr. Smeaton applied a heater, immersed in the hot-well, through which the feed pa.s.sed, absorbing heat from the water of condensation _en route_ to the boiler. Farey first proposed the use of the "coil-heater"--a pipe, or "worm," which, forming a part of the feed-pipe, was set in the hot-well.
As early as 1743, the metal used for the cylinders was cast-iron. The earlier engines had been fitted with bra.s.s cylinders. Desaguliers recommended the iron cylinders, as being smoother, thinner, and as having less capacity for heat than those of bra.s.s.
In a very few years after the invention of Newcomen"s engine it had been introduced into nearly all large mines in Great Britain; and many new mines, which could not have been worked at all previously, were opened, when it was found that the new machine could be relied upon to raise the large quant.i.ties of water to be handled. The first engine in Scotland was erected in 1720 at Elphinstone, in Stirlingshire. One was put up in Hungary in 1723.
The first mine-engine, erected in 1712 at Griff, was 22 inches in diameter, and the second and third engines were of similar size. That erected at Ansthorpe was 23 inches in diameter of cylinder, and it was a long time before much larger engines were constructed. Smeaton and others finally made them as large as 6 feet in diameter.
In calculating the lifting-power of his engines, Newcomen"s method was "to square the diameter of the cylinder in inches, and, cutting off the last figure, he called it "long hundredweights;" then writing a cipher on the right hand, he called the number on that side "odd pounds;" this he reckoned tolerably exact at a mean, or rather when the barometer was above 30 inches, and the air heavy." In allowing for frictional and other losses, he deducted from one-fourth to one-third.
Desaguliers found the rule quite exact. The usual mean pressure resisting the motion of the piston averaged, in the best engines, about 8 pounds per square inch of its area. The speed of the piston was from 150 to 175 feet per minute. The temperature of the hot-well was from 145 to 175 Fahr.
Smeaton made a number of test-trials of Newcomen engines to determine their "duty"--i. e., to ascertain the expenditure of fuel required to raise a definite quant.i.ty of water to a stated height. He found an engine 10 inches in diameter of cylinder, and of 3 feet stroke, could do work equal to raising 2,919,017 pounds of water one foot high, with a bushel of coals weighing 84 pounds.
One of Smeaton"s larger engines, erected at Long Benton, was 52 inches in diameter of cylinder and of 7 feet stroke of piston, and made 12 strokes per minute. Its load was equal to 7-1/2 pounds per square inch of piston-area, and its effective capacity about 40 horse-power. Its duty was 9-1/2 millions of pounds raised one foot high per bushel of coals. Its boiler evaporated 7.88 pounds of water per pound of fuel consumed. It had 35 square feet of grate-surface and 142 square feet of heating-surface beneath the boilers, and 317 square feet in the flues--a total of 459 square feet. The moving parts of this engine weighed 8-1/2 tons.
Smeaton erected one of these engines at the Chasewater mine, in Cornwall, in 1775, which was of very considerable size. It was 6 feet in diameter of steam-cylinder, and had a maximum stroke of piston of 9-1/2 feet. It usually worked 9 feet. The pumps were in three lifts of about 100 feet each, and were 16-3/4 inches in diameter. Nine strokes were made per minute. This engine replaced two others, of 64 and of 62 inches diameter of cylinder respectively, and both of 6 feet stroke.
One engine at the lower lift supplied the second, which was set above it. The lower one had pumps 18-1/2 inches in diameter, and raised the water 144 feet; the upper engine raised the water 156 feet, by pumps 17-1/2 inches in diameter. The later engine replacing them exerted 76-1/2 horse-power. There were three boilers, each 15 feet in diameter, and having each 23 square feet of grate-surface. The chimney was 22 feet high. The great beam, or "lever," of this engine was built up of 20 beams of fir in two sets, placed side by side, and ten deep, strongly bolted together. It was over 6 feet deep at the middle and 5 feet at the ends, and was 2 feet thick. The "main centres," or journals, on which it vibrated were 8-1/2 inches in diameter and 8-1/2 inches long. The cylinder weighed 6-1/2 tons, and was paid for at the rate of 28 shillings per hundredweight.
By the end of the eighteenth century, therefore, the engine of Newcomen, perfected by the ingenuity of Potter and of Beighton, and by the systematic study and experimental research of Smeaton, had become a well-established form of steam-engine, and its application to raising water had become general. The coal-mines of Coventry and of Newcastle had adopted this method of drainage; and the tin and the copper mines of Cornwall had been deepened, using, for drainage, engines of the largest size.
Some engines had been set up in and about London, the scene of Worcester"s struggles and disappointments, where they were used to supply water to large houses. Others were in use in other large cities of England, where water-works had been erected.
Some engines had also been erected to drive mills indirectly by raising water to turn water-wheels. This is said by Farey to have been first practised in 1752, at a mill near Bristol, and became common during the next quarter of a century. Many engines had been built in England and sent across the channel, to be applied to the drainage of mines on the Continent. Belidor[32] stated that the manufacture of these "fire-engines" was exclusively confined to England; and this remained true many years after his time. When used for the drainage of mines, the engine usually worked the ordinary lift or bucket pump; when employed for water-supply to cities, the force or plunger pump was often employed, the engine being placed below the level of the reservoir. Dr. Rees states that this engine was in common use among the collieries of England as early as 1725.
[32] "Architecture Hydraulique," 1734.
The Edmonstone colliery was licensed, in 1725, to erect an engine, not to exceed 28 inches diameter of cylinder and 9 feet stroke of piston, paying a royalty of 80 per annum for eight years. This engine was built in Scotland, by workmen sent from England, and cost about 1,200. Its "great cost" is attributed to an extensive use of bra.s.s.
The workmen were paid their expenses and 15_s._ per week as wages. The builders were John and Abraham Potter, of Durham. An engine built in 1775, having a steam-cylinder 48 inches in diameter and of 7 feet stroke, cost about 2,000.
Smeaton found 57 engines at work near Newcastle in 1767, ranging in size from 28 to 75 inches in diameter of cylinder, and of, collectively, about 1,200 horse-power. Fifteen of these engines gave an average of 98 square inches of piston to the horse-power, and the average duty was 5,590,000 pounds raised 1 foot high by 1 bushel (84 pounds) of coal. The highest duty noted was 7.44 millions; the lowest was 3.22 millions. The most efficient engine had a steam-cylinder 42 inches in diameter; the load was equivalent to 9-1/4 pounds per square inch of piston-area, and the horse-power developed was calculated to be 16.7.
Price, writing in 1778, says, in the Appendix to his "Mineralogia Cornubiensis:" "Mr. Newcomen"s invention of the fire-engine enabled us to sink our mines to twice the depth we could formerly do by any other machinery. Since this invention was completed, most other attempts at its improvement have been very unsuccessful; but the vast consumption of fuel in these engines is an immense drawback on the profit of our mines, for every fire-engine of magnitude consumes 3,000 worth of coals per annum. This heavy tax amounts almost to a prohibition."
Smeaton was given the description, in 1773, of a _stone_ boiler, which was used with one of these engines at a copper mine at Camborne, in Cornwall. It contained three copper flues 22 inches in diameter. The gases were pa.s.sed through these flues successively, finally pa.s.sing off to the chimney. This boiler was cemented with hydraulic mortar. It was 20 feet long, 9 feet wide, and 8-1/2 feet deep. It was heated by the waste heat from the roasting-furnaces. This was one of the earliest flue-boilers ever made.
In 1780, Smeaton had a list of 18 large engines working in Cornwall.
The larger number of them were built by Jonathan Hornblower and John Nancarron. At this time, the largest and best-known pumping-engine for water-works was at York Buildings, in Villiers Street, Strand, London.
It had been in operation since 1752, and was erected beside one of Savery"s engines, built in 1710. It had a steam-cylinder 45 inches in diameter, and a stroke of piston of 8 feet, making 7-1/2 strokes per minute, and developing 35-1/2 horse-power. Its boiler was dome-shaped, of copper, and contained a large central fire-box and a spiral flue leading outward to the chimney. Another somewhat larger machine was built and placed beside this engine, some time previous to 1775. Its cylinder was 49 inches in diameter, and its stroke 9 feet. It raised water 102 feet. This engine was altered and improved by Smeaton in 1777, and continued in use until 1813.
Smeaton, as early as 1765, designed a _portable_ engine,[33] in which he supported the machinery on a wooden frame mounted on short legs and strongly put together, so that the whole machine could be transported and set at work wherever convenient.
[33] Smeaton"s "Reports," vol. i., p. 223.
[Ill.u.s.tration: FIG. 23.--Smeaton"s Portable-Engine Boiler, 1765.]
In place of the beam, a large pulley was used, over which a chain was carried, connecting the piston with the pump-rod, and the motion was similar to that given by the discarded beam. The wheel was supported on A-frames, resembling somewhat the "gallows-frames" still used with the beam-engines of American river-boats. The sills carrying the two A"s supported the cylinder. The injection-cistern was supported above the great pulley-wheel. The valve-gearing and the injection-pump were worked by a smaller wheel, mounted on the same axis with the larger one. The boiler was placed apart from the engine, with which it was connected by a steam-pipe, in which was placed the "regulator," or throttle-valve. The boiler (Fig. 23) "was shaped like a large tea-kettle," and contained a fire-box, _B_, or internal furnace, of which the sides were made of cast-iron. The fire-door, _C_, was placed on one side and opposite the flue, _D_, through which the products of combustion were led to the chimney, _E_; a short, large pipe, _F_, leading downward from the furnace to the outside of the boiler, was the ash-pit. The sh.e.l.l of the boiler, _A_, was made of iron plate one-quarter of an inch thick. The steam-cylinder of the engine was 18 inches in diameter, the stroke of piston 6 feet, the great wheel 6-1/2 feet in diameter, and the A-frames 9 feet high. The boiler was made 6 feet, the furnace 34 inches, and the grate 18 inches in diameter. The piston was intended to make 10 strokes per minute, and the engine to develop 4-1/8 horse-power.
In 1773, Smeaton prepared plans for a pumping-engine to be set up at Cronstadt, the port of St. Petersburg, to empty the great dry dock constructed by Peter the Great and Catherine, his successor. This great dock was begun in 1719. It was large enough to dock ten of the ships of that time, and had previously been imperfectly drained by two great windmills 100 feet high. So imperfectly did they do their work, that a _year_ was required to empty the dock, and it could therefore only be used once in each summer. The engine was built at the Carron Iron Works, in England. It had a cylinder 66 inches in diameter, and a stroke of piston of 8-1/2 feet. The lift varied from 33 feet when the dock was full to 53 feet when it was cleared of water. The load on the engine averaged about 8-1/3 pounds per square inch of piston-area.
There were three boilers, each 10 feet in diameter, and 16 feet 4 inches high to the apex of its hemispherical dome. They contained internal fire-boxes with grates of 20 feet area, and were surrounded by flues helically traversing the masonry setting. The engine was started in 1777, and worked very successfully.
The lowlands of Holland were, before the time of Smeaton, drained by means of windmills. The uncertainty and inefficiency of this method precluded its application to anything like the extent to which steam-power has since been utilized. In 1440, there were 150 inland lakes, or "_meers_," in that country, of which nearly 100, having an extent of over 200,000 acres, have since been drained. The "Haarlemmer Meer" alone covers nearly 50,000 acres, and forms the basin of a drainage-area of between 200,000 and 300,000 acres, receiving a rainfall of 54,000,000 tons, which must be raised 16 feet in discharging it. The beds of these lakes are from 10 to 20 feet lower than the water-level in the adjacent ca.n.a.ls. In 1840, 12,000 windmills were still employed in this work. In the following year, William II., at the suggestion of a commission, decreed that only steam-engines should be employed to do this immense work. Up to this time the average consumption of fuel for the pumping-engines in use is said to have been 20 pounds per hour per horse-power.
The first engine used was erected in 1777 and 1778, on the Newcomen plan, to a.s.sist the 34 windmills employed to drain a lake near Rotterdam. This lake covered 7,000 acres, and its bed was 12 feet below the surface of the river Meuse, which pa.s.ses it, and empties into the sea in the immediate neighborhood. The iron parts of the engine were built in England, and the machine was put together in Holland. The steam-cylinder was 52 inches in diameter, and the stroke of piston 9 feet. The boiler was 18 feet in diameter, and contained a double flue. The main beam was 27 feet long. The pumps were 6 in number, 3 cylindrical and 3 having a square cross-section; 3 were of 6 feet and 3 of 2-1/2 feet stroke. Two pumps only were worked at high-tide, and the others were added one at a time, as the tide fell, until, at low-tide, all 6 were at work.
The size of this engine, and the magnitude of its work, seem insignificant when compared with the machinery installed 60 years later to drain the Haarlemmer Meer, and with the work done by the last. These engines are 12 feet in diameter of cylinder and 10 feet stroke of piston, and work--they are 3 in number--the one 11 pumps of 63 inches diameter and 10 feet stroke, the others 8 pumps of 73 inches diameter and of the same length of stroke. The modern engines do a "duty" of 75,000,000 to 87,000,000 with 94 pounds of coal, consuming 2-1/4 pounds of coal per hour and per horse-power.
The first steam-engine applied to working the blowing-machinery of a blast-furnace was erected at the Carron Iron-Works, in Scotland, near Falkirk, in 1765, and proved very unsatisfactory. Smeaton subsequently, in 1769 or 1770, introduced better machinery into these works and improved the old engine, and this use of the steam-engine soon became usual. This engine did its work indirectly, furnishing water, by pumping, to drive the water-wheels which worked the blowing-cylinders. Its steam-cylinder was 6 feet in diameter, and the pump-cylinder 52 inches. The stroke was 9 feet.
A direct-acting engine, used as a blowing-engine, was not constructed until about 1784, at which time a single-acting blowing-cylinder, or air-pump, was placed at the "out-board" end of the beam, where the pump-rod had been attached. The piston of the air-cylinder was loaded with the weights needed to force it down, expelling the air, and the engine did its work in raising the loaded piston, the air-cylinder filling as the piston rose. A large "acc.u.mulator" was used to equalize the pressure of the expelled air. This consisted of another air-cylinder, having a loaded piston which was left free to rise and fall. At each expulsion of air by the blowing-engine this cylinder was filled, the loaded piston rising to the top. While the piston of the former was returning, and the air-cylinder was taking in its charge of air, the acc.u.mulator would gradually discharge the stored air, the piston slowly falling under its load. This piston was called the "floating piston," or "fly-piston," and its action was, in effect, precisely that of the upper portion of the common blacksmith"s bellows.
Dr. Robison, the author of "Mechanical Philosophy," one of the very few works even now existing deserving such a t.i.tle, describes one of these engines[34] as working in Scotland in 1790. It had a steam-cylinder 40 or 44 inches in diameter, a blowing-cylinder 60 inches in diameter, and the stroke of piston was 6 feet. The air-pressure was 2.77 pounds per square inch as a maximum in the blowing-cylinder; and the floating piston in the regulating-cylinder was loaded with 2.63 pounds per square inch. Making 15 or 18 strokes per minute, this engine delivered about 1,600 cubic feet of air, or 120-1/2 pounds in weight, per minute, and developed 20 horse-power.
[34] "Encyclopaedia Britannica," 1st edition.
At about the same date a change was made in the blowing-cylinder. The air entered at the bottom, as before, but was forced out at the top, the piston being fitted with valves, as in the common lifting-pump, and the engine thus being arranged to do the work of expulsion during the down-stroke of the steam-piston.
Four years later, the regulating-cylinder, or acc.u.mulator, was given up, and the now familiar "water-regulator" was subst.i.tuted for it.
This consists of a tank, usually of sheet-iron, set open-end downward in a large vessel containing water. The lower edge of the inner tank is supported on piers a few inches above the bottom of the large one.
The pipe carrying air from the blowing-engine pa.s.ses above this water-regulator, and a branch-pipe is led down into the inner tank. As the air-pressure varies, the level of the water within the inverted tank changes, rising as pressure falls at the slowing of the motion of the piston, and falling as the pressure rises again while the piston is moving with an accelerated velocity. The regulator, thus receiving surplus air to be delivered when needed, greatly a.s.sists in regulating the pressure. The larger the regulator, the more perfectly uniform the pressure. The water-level outside the inner tank is usually five or six feet higher than within it. This apparatus was found much more satisfactory than the previously-used regulator, and, with its introduction, the establishment of the steam-engine as a blowing-engine for iron-works and at blast-furnaces may be considered as having been fully established.
Thus, by the end of the third quarter of the eighteenth century, the steam-engine had become generally introduced, and had been applied to nearly all of the purposes for which a single-acting engine could be used. The path which had been opened by Worcester had been fairly laid out by Savery and his contemporaries, and the builders of the Newcomen engine, with such improvements as they had been able to effect, had followed it as far as they were able. The real and practical introduction of the steam-engine is as fairly attributable to Smeaton as to any one of the inventors whose names are more generally known in connection with it. As a mechanic, he was unrivaled; as an engineer, he was head and shoulders above any constructor of his time engaged in general practice. There were very few important public works built in Great Britain at that time in relation to which he was not consulted; and he was often visited by foreign engineers, who desired his advice with regard to works in progress on the Continent.
[Ill.u.s.tration]
CHAPTER III.
_THE DEVELOPMENT OF THE MODERN STEAM-ENGINE. JAMES WATT AND HIS CONTEMPORARIES._