PUMPS
Every steamship carries several varieties of pump. First, there are the large pumps, generally of a simple type, for emptying the bilge or any compartment of the ship which may have sprung a leak. "All hands to the pumps!" is now seldom heard on a steamer, for the opening of a steam-cock sets machinery in motion which will successfully fight any but a very severe breach. It is needless to say that these pumps form a very important part of a ship's equipment, without which many a fine vessel would have sunk which has struggled to land.
The pumps for the condensers form another class. These are centrifugal force pumps; their duty is to circulate cold sea-water round the nests of tubes through which steam flows after passing through the cylinders. It is thus converted once more into water, ready for use again in the boiler. Every atom of the water is evaporated, condensed, and pumped back into the boiler once in a period ranging from fifteen minutes to an hour, according to the type of boiler and the size of the supply tanks.
Some condensers have the cooling water passed through the tubes, and the steam circulated round these in an air-tight chamber. In any case, the condenser should be so designed as to offer a large amount of cold surface to the hot vapour. A breakdown of the condenser pumps is a serious mishap, since steam would then be wasted, which represents so much fresh water—hard to replace in the open sea. It would be comparable to the disarrangement of the circulating pump on a motor-car, though the effects are different.
We must not forget the feed-pumps for the boilers. On their efficient action depends the safety of the ship and her passengers. Water must be maintained at a certain level in the boiler, so that all tube and other surfaces in direct contact with the furnace gases may be covered. The disastrous explosions we sometimes hear of are often caused by the failure of a pump, the burning of a tube or plate, and the inevitable collapse of the same. The firms of Weir and Worthington are among the best-known makers of the special high-pressure pumps used for throwing large quantities of water into the boilers of mercantile and war vessels.