The Force Pump
Pumps and their Value to Man
In the common pump, water cannot not be raised higher than the spout. In many cases it is desirable to force water considerably above the pump itself, as, for instance, in the fire hose; under such circumstances a type of pump is employed which has received the name of force pump
. This differs but little from the ordinary lift pump, as a reference to Figure will show. Here both valves are placed in the cylinder, and the piston is solid, but the principle is the same as in the lifting pump.
An upward motion of the plunger allows water to enter the cylinder, and the downward motion of the plunger drives water through E
. (Is this true for the lift pump as well?) Since only the downward motion of the plunger forces water through E
, the discharge is intermittent and is therefore not practical for commercial purposes. In order to convert this intermittent discharge into a steady stream, an air chamber is installed near the discharge tube, as in Figure. The water forced into the air chamber by the downward-moving piston compresses the air and increases its pressure. The pressure of the confined air reacts against the water and tends to drive it out of the chamber. Hence, even when the plunger is moving upward, water is forced through the pipe because of the pressure of the compressed air. In this way a continuous flow is secured.
The height to which the water can be forced in the pipe depends upon the size and construction of the pump and upon the force with which the plunger can be moved. The larger the stream desired and the greater the height to be reached, the stronger the force needed and the more powerful the construction necessary.
The force pump gets its name from the fact that the moving piston drives or forces the water through the discharge tube.
FIG. - Force pump.
FIG. - The air chamber A insures a continuous flow of water.