STATIONÄRE ENGINES.
219
calculated to work with a pressure in the boiler of 40 lbs. per squareinch. The piston is 17 inches in diameter, the stroke being 3 feet,and the number of revolutions of the crank about thirty-five. Thepump is double-acting, consisting of bücket and plunger; the dia-meter of the barrel is i8 x 9 -g- inches, that of the plunger 13^5 inches,with a stroke of 3 feet. The bücket packing consists of rings ofgutta percha about 1 inch square insection, let into grooves cut in thebücket; two holes, *4 inch in diame-ter, are bored in the top, communicat-ing with the grooves, the water pres-sure being always constant pressesout the rings of gutta percha, mak-ing them perfectly water-tight. Thevalves are of the ordinary ilap kind;a large air vessel is fitted to thepump, 3 feet 6 inches in diameterand 14 feet 6 inches high. The mo-tion for driving the pump consists ofa pinion on the engine shaft and spur wheel on the pump shaft,the gearing being in the proportion of 3 to 1. The fly wheel onthe engine shaft is 11 feet in diameter, and weighs 5 tons 12 cwts.;a balance is placed on the spur wheel to counterpoise the weight ofthe pump ram. The boilers are 26 feet long and 6 feet 6 inches indiameter, with a single flue 3 feet 3 inches in diameter; the firegrate is arranged underneath, with return side flues; thickness ofplates in body of boiler, inch; of end plates, yi inch. Thechimney stalk is 84 feet high, 7 feet 6 inches square at the level ofthe ground, and 3 feet 6 inches square at the coping. The boileris fed with a small plunger pump, worked off the end of the pistoncrosshead, the water being previously heated in a tank by theexhaust steam. The engine and pump cost ^950. The risingmain, 9 inches in diameter, has turned and bored joints exceptwhere lead and yarn ones were required for sharp bends; and alsofour air and fourscouring plug valves with a clack valve immediatelyabove the air vessel and another half-way up the track. A brauchpipe leads into the lower Service cistern, fitted with a self-actingball valve, 6 inches in diameter. The pipes cost when laid aboutI2j. per lineal yard. The actual work done by the engine can bedetermined by means of a cast-iron measuring box placed at the