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.