THEORY AND PRACTICE OF ENGINEERING.
1250
Boor II.
sun-wheel, the latter and the fly-wheel, upon whose axle and shaft it is fixed, are made torevolve in the desired direction, and give motion to the mill-work.
As the piston descends, the plug-tree Z also descends, and a clamp or slider q. fixedupon the slide of the plug-tree, presses upon the handle I, of the upper shaft or axis,Y, and shuts the valves G and E; and by the same operation, hv disengaging itself,permits a weight suspended to the arm of the lower \ shaft to turn the shaft uponits axis, and thereby to open the valves K and II. The moment previous to openingthese valves, the piston reaches the lowest part of its stroke, and the cylinder abovethe piston is filled with steam ; but as soon as II is opened, that steam rushes by theeduction-pipe J into the condenser, and the cylinder above the piston becomes exhausted ;the steam from the boiler, entering by I and K, acts upon the lower side of the piston, andforces it to return to the top of the cylinder; when the cylinder is very near the uppertermination of its stroke, another slider a raises the handle, and in so doing disengagesthe catch, which permits the upper Y shaft to revolve upon its own axis, and open thevalves G and L, and the downward stroke recommences, as has been related.
"When the piston descends, the buckets, It, S, of the air-pump and hot-water-pump Talso descend ; the water which is contained in these pumps passes through the valves oftheir buckets, and is drawn up and discharged by them through the trough t, by the nextdescending stroke of the piston : part of the water is raised up by the pump Y, for thesupply of the boiler, and the rest runs to waste. Engines of this kind, as described byMr. Watt, were emploved in producing rotary motions, but they were also used to workpumps by a reciprocating motion : for this purpose half of the pump-rods were sus-pended by means of a sloping rod from the working beam near the cylinder, and the otherhalf were suspended directly from the outer end of that beam, so that the ascending motionof the piston pulls up one-half of these rods, and works the pumps to which they belong,while the descending motion of the pistons pulls up the other half of the rods, and workstheir pumps: such an engine was employed at Wheel Maid Mine in Cornwall ; it hada cylinder of 63 inches in diameter, and 9 feet stroke; but the stroke in the pumps, whichwere 18 inches in diameter, was only 7 feet.
Mr. Watt gave the following account of the actual performance of one of his engines,working in the Cornish mines: — “ One bushel of good Newcastle or Swansea coal in thereciprocating engine, working more or less expansively, was found to raise 2*1,000,000 to32,000,000 pounds of water one foot high. In engines upon the rotative double construc-tion, one having a cylinder of 3IJ inches in diameter, and making seventeen strokes and ahalf of 7 feet long per minute, called forty-horse power, consumed about four bushels ofNewcastle coal per hour, or four cwt. of Wednesbury coal. A rotative double engine witha cylinder of 23J inches in diameter, making twenty-one and a half strokes of 5 feet longper minute, was called twenty-horse power ; and an engine with a cylinder of 1 inchesdiameter, making twenty-five strokes of 5 feet long per minute, was called ten-horsepower ; and the consumption of coals was nearly proportionate to that of the forty-horsepower : a bushel of Newcastle coals, which is the quantity a ten-horse engine consumesper hour, grinds and dresses about ten bushels of wheat.
Hornblower's Engine with two Cylinders, though it does not essentially differ from the onealready described, displays much ingenuity: the chief parts are two cylinders. A, B, thelargest of which is A ; a piston moves in each, having their rods, C and D, movingthrough collars at E and F: these cylinders are supplied with steam by means of thesquare pipe G, which has a flanch to connect it with the rest of the steam-pipe ; this squarepart branches off to both cylinders; c and d are two cocks, worked by the plug W bymeans of handles and tumblers: on the foreside of the cylinders is another communicatingpipe, whose section is square or rectangular, having also two cocks, a, b : the pipe ^, imme-diately under the cock b , establishes a communication between the upper and lower partsof the small cylinder, B, by opening the cock b: there is a similar pipe on the other sideof the cylinder, A, immediately under the cock d when the cocks c and a are open, andthe cocks b and d are shut, the steam from the boiler has free admission into the upperpart of A, but the upper parts of each cylinder have no communication with theirlower parts: from the bottom of the great cylinder proceeds the eduction pipe K,having a valve at its opening into the cylinder, which bends downwards, and is connectedwith the conical condenser, L. The condenser is fixed on a hollow box, M, on whichstand the pumps N and O for extracting the air and water, which last runs along thetrough T into the cistern U, from which it is raised by the pump V for recruiting theboiler, being already nearly at a temperature of 212°; immediately under the condenseris a spigot valve, at S, over which is a small jet pipe, reaching to the bend of the eductionpipe.
The cistern of cold water, R, contains the whole of the condensing apparatus; a smallpipe 1* comes from the side of the condenser, and terminates at the bottom of the tioughT, and is there covered with a valve Q, which is kept tight by the water that is alwaysrunning over it; the pump-rods X cause the outer end of the beam to preponderate, so