This engine is chiefly designed for dispensing with the multiplying wheels, or chains and drums, hitherto employed, between the engine crank and the shaft of the screw propeller, in order to produce a suitable speed in the latter.

The annexed figure represents a transverse vertical section of the engines; they are ranged side by side in a line coincident with the line of the propeller shaft, and immediately over the engine shaft, which is concentric with the propeller shaft, and is connected thereto by a coupling, which admits of the shafts being readily disconnected, when the vessel is required to be propelled by the sails alone. In order to obtain the requisite speed, the engines are constructed to work with a very short stroke, and a new kind of slide valve is employed, which facilitates the rapid exhaustion of the cylinder. At a a is the cylinder, supported on the upper part of the condenser b, and on a projecting flange on the air-pump c; d is the engine shaft; and e one of the engine cranks keyed thereon, to which the force of the piston is transmitted from the cross-headfof the piston rod, by the connecting rod g. The slide valve is composed of a hollow segmental plate h, working in the cylindrical steam case k; the space above the slide plate being occupied by the steam, and the cavity on the under side of the plate communicating with the condenser by the passage m.

The valve works on its axis with a vibratory motion, and thus brings each side of the piston into communication alternately with the steam and the condenser.

Maudslay And Field s Direct Action Screw Propeller 557

The foot of the air-pump is inserted in a flat prolongation of the condenser; and the foot valve n is situated in the bottom of the pump. The delivery valves o and p in the bucket and pump cover are composed of annular plates, which rise and fall vertically between guides, and admit of the escape of the air and water, both at the periphery, and at the central aperture of the annular plate. The upper portion q of the air-pump forms the hotwell, from which the supply for the boilers is drawn by the feed pumps; and the surplus passes off by the waste water-pipe, which is connected to the aperture r. The air-pump is worked from the parallel motion in the following manner: s is the parallel bar,.

which is connected at the end t to the cross-headf; and at the point v to the radius rod w, the centre of motion of which is at x. The parallel bar is extended beyond its centre of motion to y, from which the cross-head of the air-pump is suspended by links, or a connecting rod z. The feed and bilge-pumps are connected to the cross-head of the air-pump.