238

MODERN STEAM PRACTICE.

compact. In one of the cylinder covers or ends there is a bear-ing supporting the spindle on which the wheel is fixed, in theother cylinder cover there are a gland and stuffing box throughwhich the shaft for the revolving wheel passes. The suction pipemay, if desired, be run any moderate length horizontally, and thepump may be placed from 15 to 20 feet vertically above the waterto be raised; in most cases it is advisable to have a foot-valve atthe bottom of the suction pipe, so as to retain the water in thepump when Standing still. The delivery pipes, as seen in Fig. 149,are fitted with self-acting flap valves, to prevent any water flowingback on to the land when the pump is not working. The pumps arefitted to discharge 30,000 gallons per minute, 12 feet high; the pipesare 42 inches in diameter; the engines are of the horizontal condens-ing type; diameter of cylinders 21 inches, length of stroke 21 inches.

The action of the pump is as follows:—The pump and pipesbeing filled with water, which the foot valve at the bottom of thesuction pipe retains, the wheels or discs are coupled to the engine,and the latter being started at a high velocity, a centrifugal motionis given to the wheel, and to the water contained in the disc, whichis driven out into the case or receiver of the pump. The partialvacuum thus formed in the disc is filled by the water forced up thesuction pipe by the pressure of the atmosphere; the water enteringthe disc receives centrifugal motion in the same way, and thus acontinuous stream is received into and discharged from the pump.To prevent the water from rotating in the case, and to give it adirection upwards to the discharge pipe, a stop or plate is placed atthe base of that pipe, reaching to the joint between the piston andthe case. The joints between the suction pipes and disc are so madethat sand, mud, or gritty matter cannot lodge near them, by whichmeans the wear is so reduced as to become almost imperceptible.

The following may be enumerated as the principal advantagesof the centrifugal pump:—(1.) It can be erected easily and quickly.(2.) It works with an easy rotary motion, without valves, eccentrics,or other contrivances, which consume power in friction. (3.) It willdischarge a quantity of water greater in proportion to the poweremployed than any other pump—75 per cent. being taken as anaverage. (4.) It is economical in use, and of very great durability—an important point in all machinery. (5.) It discharges a con-tinuous and steady stream without air vessels. (6.) It is littleaffected by sand, mud, grit, or other foreign matter in the water,