Part 6 (1/2)
[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 Stirlings.h.i.+re. 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 s.h.i.+llings 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.