CHAPTER XXVII. TRIPLE-EXPANSION SCREW-ENGINES AND BOILERS OF THE U. S. S. PHILADELPHIA, DESIGNED AND BUILT BY THE WM. CRAMP & SONS SHIP AND ENGINE BUILD ING CO., PHILADELPHIA. GENERAL DESCRIPTION. THE engines have, each, a high, intermediate and low-pressure cylinder, of 38, 56, and 86 inches diameter, respectively, and a piston-stroke of 40 inches. The engines are placed in separate water-tight compartments, and are duplicates, the low-pressure cylinder being forward in the forward, and aft in the after compartment; the forward engine turning the port-propeller. The main steam-valves are of the piston type; there is one for the high-pressure, two for the intermediate, and two for each low-pressure cylinder, worked by radial valve-gear and arranged for a minimum cut-off of 0.4 of the stroke of the high pressure, and 0.5 in the intermediate and low-pressure cylinders. Each piston has one piston-rod secured to a cross-head, which runs on guides, supported by the engine bed-frame. Each crank-shaft is built-up, made of steel, in one piece, with cranks at equal angles and with the necessary coupling discs forged on. The castings containing the crank-shaft bearings are cast in five pieces for each engine. They are bolted to engine keelsons, and stayed to cylinders by steel tie-rods and the engine bedframes. Each main engine has two air and two bilgepumps, all vertical and single-acting, driven by an independent compound engine. Also one centrifugal circulating pump arranged with bilge as well as sea-injection. Air-pumps deliver into one feed-tank of boiler-iron. The tank has a capacity of about 500 gallons, and is partitioned and fitted as a filter. The shells of condensers are cylindrical and made of brass. They are fitted with brass tubes 5% inch diameter outside, and have a total cooling surface of about 13,500 square feet measured on the outside of the tubes. The tubes are placed fore-and-aft, the water circulating through them and thence overboard through outboarddelivery valves. Suitable baffling and supporting plates are arranged in each condenser to assist in the circulation of steam and to support the tubes. There are two vertical duplex pumps fitted in each fire-room of ample capacity for feeding the boilers. One set in each fire-room is fitted to draw from feed-water tank and bottom of forward condenser and discharge through boiler check-valves. The second set in each fire-room is fitted to draw water from tank, sea, bilge, and boilers, and discharges into fire-main, through boiler-checks, and overboard. The pump in forward fire-room likewise discharges through distiller. A horizontal pump is placed in each engineroom, and fitted to draw water from the sea and bilge, and to discharge into fire-main and through outboard-delivery. The water-cylinders and chests of all pumps are of composition. The distilling apparatus consists of one distiller capable of furnishing 3,000 gallons of potable water in twenty-four hours. The circulating water for the distiller is supplied by the auxiliary pump in forward fire-room. The propellers are three-bladed, right and left-handed, respectively, of about 14 feet 6 inches diameter, and are made of manganese bronze. There are four double-ended horizontal return tubular boilers, containing an aggregate grate surface of 624 square feet, arranged fore and aft, in two water-tight compartments, with four athwartship fire-rooms. Each boiler is 14 feet in diameter and about 20 feet long. The smoke-pipe is fixed, and its top is about 60 feet above the grates. Fire-rooms are arranged to work under airpressure when required, and are fitted, each, with two blowers, capable of supplying continuously, with ease, sufficient air for the required horse-power. DETAILED DESCRIPTION. Cylinder Casings. — The cylinder casings, which include the steam and exhaust ports and passages, inboard heads, and valve-chests, are of cast-iron. They are fitted with cylinder linings of hard cast-iron. The cylinder casings have extensions cast on them with flanges 134 inches thick for securing them to engine bed-frames. The cylinder casings and covers are covered with non-conducting material, and neatly lagged with black walnut. Receivers.-The receivers consist of the spaces between high-pressure and intermediate, and intermediate and low-pressure piston-valves and their connecting pipes. There is a 31⁄2-inch copper pipe, with compoposition stop-valve, connecting main steam-pipe to each receiver space; and a composition safetyvalve, with nickel seat of 234 inches diameter, on each receiver, the intermediate pressure weighted to 80 pounds per square inch above the atmosphere, and the low-pressure to 30 pounds. Cylinder linings.-The linings are of cast-iron as hard as tools can work, with central ring or rest. They are 1% inches thick, and are accurately fitted and secured to the casings. They are smoothly and accurately bored to diameters of 38, 56, and 86 inches respectively, and for a piston-stroke of 40 inches. Cylinder linings are jacketed. Cylinder Heads and Covers.-The cylinderheads are cast solid with cylinder casings and amply stiffened by ribs. They have suitablé openings for the stuffing-boxes. The cylinder covers are made of cast-steel and well-ribbed. Each low-pressure cover has a man-hole cast in, which is faced to receive the man-hole plate. The cylinder covers are faced true on the inside. They have faced flanges, and are secured to cylinder casings by wrought-iron bolts with finished nuts. Bolts are spaced not over 6 inches apart. Holding-down Bolts.—All holding-down bolts for securing the engines in the ship are fitted with locked nuts. Man-holes and plates.-The man-holes in lowpressure cylinder covers are 20 inches in diameter. The plates are turned to loosely fit the holes, faced on the inner surface to fit the facingstrip on cover or head, and finished on the outside. Valve-Chests and Covers.-The valve-chests |