THE FORCING-PUMP 



295 



pump in having a solid piston without a valve. The 

 air which fills the suction-pipe, and afterwards the 

 water, are removed by means of a tube r r (called the 

 force-pipe), which opens into the barrel above the valve 

 i\ this tube contains the valve v 2 , and both valves, when 

 the piston is worked, act like the two corresponding 



FIG. 196 ( 5 X o real size}. 



'valves in the suction-pump. Thus, when the piston is 

 raised, the air in the suction-pipe expands and opens 

 the valve v l ' when the piston descends, the valve v-^ 

 closes, and the air above it is forced by the pressure of 

 the piston through the valve v 2 into the force-pipe. 

 When all the air is thus removed, that is, when the 

 water rises above the valve v^ then at each upward 



