Engineering Wonders of the World
Volume I

THE PROPELLING MACHINERY OF A SHIP. 35 same operation is repeated. After the steam has performed its work in the first intermedi- ate cylinder, it passes vid the second interme- diate valve chest, x, to the second intermediate cylinder, c, and thence vid the low-pressure valve chest, y, to the low-pressure cylinder, b. From the low-pressure cylinder, b, the steam is exhausted down the eduction pipe, s, into the condenser, t, where, by being brought into contact with a The number of tubes through which Condenser. ... cold sea-water is circulating, the steam is condensed. A powerful air- pump, controlled by the levers marked u, draws the air and water from the condenser, thus creating a vacuum, so that the exhaust steam entering the condenser lias not to overcome the atmospheric pressure. The air drawn from the condenser is permitted to escape, and the water is passed into the hot well, whence the feed pumps force it back to th© boilers, to be used again for the purpose of generating steam. For reversing the engine when the ship is required to go astern, a small steam engine is fitted at the back of the main engine, and the large wheel, marked v, is Reversing connected with this reversing Engine, etc. engine f00thed wheel w can be connected up with another small steam- engine for turning the main engine while in harbour, when that operation is necessary for overhauling, etc. The engines of modern paddle-wheel steamers are usually of the (1) “ beam engine type, (2) the “ oscillating,” or (3) the “ diagonal or in- clined direct-acting type. The Paddle beam engine was the first ap- Engines. plied to marine work, since at the time when the steamship was in its infancy this particular form of steam engine had alone proved successful for land work. In the beam engine the piston-rod crosshead is coupled to one end of a beam above—rocking on a central support—by means of links, and the motion of the opposite end of the beam is transmitted to the crank by a long connecting-rod. The beam engine, it is interesting to note, is still used extensively in American river steamers, with but little departure from the design adopted in the very earliest marine engines, except that the parts formerly made of wood are now of steel. The oscillating engine is light and compact, Fig. 9.—ENGINES OF THE ISLE OF MAN STEAM PACKET COMPANY’S PADDLE STEAMER “ EM- PRESS QUEEN,” 10,500 H.P. CYLINDERS 7 FEET STROKE BY 68, 68 AND 92 INCHES BORE. (By courtesy of the Fairfield, Shipbuilding and Engineering Company, Limited.} and specially suited for working at low steam pressures, the most successful engines of this type using a pressure not ex- ceeding 30 lbs. per square inch. Oscillating t -n J • +i Engines. In the oscillating engine the connecting-rod is dispensed with altogether, the upper end of the piston-rod being fitted with an ordinary connecting-rod to enable it to work directly on the crank. The cylinder is usually placed vertically under the crank- shaft, and is carried on two trunnions near the middle of its length, so that it may rock or oscillate to and fro freely, and thus permit the piston and piston-rod to follow the movement of the crank. This principle reduces the distance between the cylinder and