192 



PUMPS AND THEIR VALUE TO MAN 



forth depends upon the speed with which the piston is moved. 

 A strong man giving quick strokes can produce a large flow; 

 a child, on the other hand, is able to produce only a thin 

 stream. Whoever pumps must exert sufficient force to lift 

 the water from the surface of the well to the spout exit. For 

 this reason the pump has received the name of lifting primp. 

 184. The Force Pump. In the common pump, water can- 

 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 

 =JL=j| hose ; under such circumstances a type of 



pump is employed which has received the 

 name of force pu mp. This differs but little 

 from the ordinary lift pump, as a reference 

 to Figure 134 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 down- 

 ward 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 135. 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 



FIG. 134. Force 

 pump. 



