WATER OR LIQUID PUMPS 



217 



ascends, so there is only an intermittent flow of water 

 from the spout or hose attached to such a force pump. 



In order to avoid this intermittent dis- 

 charge and have a steady stream, an air 

 dome or chamber must be attached to the 

 delivery tube, as shown in the illustration. 

 The downward movement of the piston 

 forces water through the delivery tube and 

 also into the air dome, because air can be 

 easily compressed. (If air is compressed 

 to one-third its original volume, it exerts a 

 pressure three times as great as before.) 



FORCE PUMP 

 WITH AIR DOME 



So when the piston again ascends, the 



valve V closes, but the compressed air in the air dome 



AIR DOMES or HIGH PRESSURE PUMPS 



From photograph of those used for pumping the water to wash the 

 sand of the niters of the Pittsburgh city water. 



forces the water out of the delivery tube and keeps the 

 stream of water flowing until the next downward stroke 

 of the piston, when the dome is again filled. In this 

 way a continuous flow is obtained. The size of the air 



