THE FORCING PUMP. 



275 



A 



Fig. 76 



Vessel is a discharge pipe KF, which passes air-tight nearly 

 to the bottom. When water is forced into the air vessel 

 through the valve V by the de- 

 scent of the piston, it rises 

 above the lower end of this 

 pipe. The mass of air which 

 the vessel contains is compressed 

 into a smaller volume; its elas- 

 tic force, pressing on the sur- 

 face of the water at K, with a 

 varying but continuous press- 

 ure, forces it up the pipe ; and 

 if the size of the vessel be suit- 

 able to that of the pump, and to 

 the rate of working it, the com- 

 pressed air will continue to ex- 

 pand, forcing water up the pipe during the ascent of the 

 piston, and will not have lost its force before a new com- 

 pression is applied to it, carrying with it a new supply of 

 water, and thus a continuous, although varying, flow will 

 be maintained. A few strokes of the piston will generally 

 be sufficient to raise water in the pipe KF, to any height 

 consistent with the strength of the instrument and the 

 power at command. 



COR. Let h = the height of the water barometer; dur- 

 ing the ascent of the piston the valve B is open and V is 

 closed ; the pressure upon the upper surface of the piston = 

 gpk ; the pressure upon the lower surface = gp (h MC), 

 the water surface in the pump being at M ; therefore, call- 

 ing A the area of the piston, the tension of the rod when 

 the piston is ascending = gpA-M.0. 



That is, the tension of the rod is equal to the weight 

 of a column of water whose base is the area of the 

 piston, and whose height is the height of the water in 

 the barrel above the level of the well. 



