2i8 GENERAL SCIENCE 



dome is determined by the size of the pump. The 

 distance that water can be thrown depends upon the 

 force applied to the piston. 



Force pumps are often used in wells, and especially 

 when a windmill is used as power for pumping. City 

 fire engines which force water to the tops of high build- 

 ings use the force pump with a very large air dome. 

 City water companies use high pressure force pumps 

 to pump water into standpipes and hilltop reservoirs. 

 Force pumps are also used for spraying fruit trees and 

 other vegetation. 



148. The Centrifugal Pump is a very modern type of 

 pump without a piston or valve in the pump chamber. 



It consists of a wheel 

 enclosed in a strong 

 metal case. The wheel 

 is made to rotate very 

 rapidly, and curved, 

 spoke-like parts throw 

 the water to the outer 

 >UMP part of the wheel and 



case, and it is thus forced through the pipe or tube 

 which leads from the case. As the wheel rotates rapidly 

 a partial vacuum is produced in the case, and the air 

 pressure on the water in the river or other source of 

 supply forces the water through a tube to the center of 

 the rotating wheel. The wheel forces it to the outer cir- 

 cumference of the case and out through the delivery tube. 

 The quantity of water delivered by such a pump is 

 dependent upon the size and speed of the wheel. The 

 centrifugal pump is not a high-pressure pump, and it is 

 used only where it is not necessary to raise the water 

 many feet and where a large quantity of water is desired. 



