2l6 



GENERAL SCIENCE 



lifted out of the pump. The air pressure on the water in 

 the well is what forces the water up through the first 

 valve of the pump, but it will do this only when the air 

 pressure in the pump is reduced by the upward move- 

 ment of the piston. The piston must always be placed 

 less than 34 feet from the surface of the water in a well. 



Lift pumps are used in wells that are not very deep 

 and in places where it is not desired to pump the water 

 very far. The quantity of water thrown depends upon 

 the size of the pump and the speed at which the piston 

 moves up and down. The piston is usually placed down 

 in the well far enough to prevent freezing. 



147. The Force Pump. The top of a common lift 

 pump is not water-tight, and so water cannot be raised 

 any higher than the pump, even if 

 a hose is placed on the pump spout. 

 If the top were made water-tight, 

 water could be forced through a 

 hose attached to the spout, and the 

 pump would then be a force pump. 

 Force pumps are usually made so 

 that the downward stroke of the 

 piston forces the water out. This is 

 done by placing the second valve in 

 the side of the cylinder rather than 

 in the piston. In the illustration, 

 the valve V closes when the piston 

 goes up, and the valve D opens to permit water to flow 

 in from the well. When the piston descends the valve 

 D is closed by the pressure of the water on it, and the 

 valve V is forced open and the water flows out through 

 the delivery pipe. The weight of the water in the 

 delivery pipe closes the valve V when the piston 







FORCE PUMP 



