| Diameter of Steam Cylinders. | Diameter of Water Plungers. | Length of Stroke. | Gallons delivered per minute at ordinary speed. | Diameter of Plunger required in any single cylinder pump to do the same work at same speed. | ||
|---|---|---|---|---|---|---|
| 6 | 71⁄2 | 6 | 285 | 101⁄4 | ||
| 6 | 81⁄2 | 6 | 375 | 12 | ||
| Diameter of Steam Cylinders. | Diameter of Water Plungers. | Length of Stroke. | Sizes of Pipes for Short Lengths To be increased as length increases. | |||
| Steam Pipe. | Exhaust Pipe. | Suction Pipe. | Delivery Pipe. | |||
| 6 | 71⁄2 | 6 | 1 in. | 11⁄2 in. | 5 in. | 4 in. |
| 6 | 81⁄2 | 6 | 1 „ | 11⁄2 „ | 6 „ | 5 „ |
The purposes for which pumps are used on shipboard, aside from the air and circulating pumps for condensers, are:
(1.) Feeding the boiler.
(2.) Emptying the tanks and pumping out bilge.
(3.) Supplying water for washing down decks, extinguishing fires, filling evaporators and sanitary service.
A special pump for each separate purpose is not always supplied, but one pump may have the necessary pipe connections to serve alternately various duties.
Feeding the boilers is so important an operation that a supplemental special pump is always required. To make absolutely sure of an ample supply of feed water one of the other pumps is made strong enough to serve the same purpose, or sometimes an injector is fitted as an auxiliary feeding mechanism.
A bilge pump has special fittings, for the reason that it handles very dirty water, undesirable to be transmitted through any other pipe system. In small ships, however, one pump, the so-called “donkey,” often serves for nearly all other purposes, including auxiliary boiler feeding.
A special form of pump in use on Western river steamers is the so-called “doctor,” an independent pump with a walking beam, by which one steam cylinder drives a system of pumps for feed, fire and bilge pumping purposes (Fig. [450]).