THE “BALLAST” PUMP.
This machine is constructed to meet the requirements of steamship builders and is recognized and adopted by marine engineers of this and of other countries as the standard design for this service and for oil tank steamer work.
It will be observed, see Fig. [449], that its proportions are such as to secure the advantages of large pumping capacity with unusual compactness and moderate weight.
This pump is of the packed piston type, and has the valves so arranged that the water pistons are always submerged, thus making it particularly well adapted for long and difficult suction lifts such as are met with in steamers carrying petroleum in bulk, and in steamers having extensive systems of water ballast tanks.
The demands for water ballast service are generally met by the following two sizes, as shown in the table below.
Fig. 449.
Table.
| 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]).
The feed pump should be of simple construction, great strength and ample capacity, to secure great regularity and reliability of service under the severe conditions of high pressure.
The main parts of auxiliary feed pumps are often duplicated. This is a desirable point, as one set of spare parts in piston, rings, valves, etc., is suitable for both pumps.
The main feed pump is, even in the independent type, often placed in the engine room, while the auxiliary pump, or the injector, is in the fire room. The feed pumps draw usually from the hot well, feed heater and feed tanks and discharge through main feed pipe into the boiler.
This “doctor” pump is a substantial piece of mechanism. The bases of columns and pump chamber flanges are accurately planed, the cylinder has spring piston packing and the plain slide valve is made of gun metal.
The hot water pumps, 31⁄2″ diam. × 10″ stroke, have chambers bored and are fitted with a copper and tin composition for valves and scats; the latter are driven into their places and riveted over underneath.
Fig. 450.
Note.—Each valve is reached by removing the bonnet covering it. The joints under caps are made the insertion of sheet lead. The heaters above the frame, as shown, are 22″ × 5′ 0″ long, of hard rolled copper, with a copper worm 18′ 0″ long by 21⁄2″ diameter in each. There is also a baffle plate above the water line in each heater to prevent the exhaust from throwing the water out at the top.