PUMP VALVES 



591 



the body of the bucket is transferred to its upper side to be pumped to 

 the surface on the succeeding stroke. A double-acting pump of this 

 type is also on the market. 



ART. 160. PUMP VALVES. 



The valve area should be so designed as to allow of a mean velocity not 

 exceeding 4 feet per second. For low pressures these valves usually 

 consist of rubber or composition discs (Figs. 274, 275, 280 a and b), 



FIG. 280. Types of Pump Valve. 



working against a perforated grid, and are either spring loaded or 

 automatically return to their seats in virtue of their own elasticity, 

 together with the pressure of water above them. For moderate speeds 

 and pressures these are very satisfactory. 



At high pressures, however, the discs quickly become indented, and 

 some form of metallic valve becomes essential. Fig. 280 c shows a 

 double-beat valve of this type. These valves may be spring loaded, or 

 may return to their seats by their own weight, and so long as the speed is 

 moderate are satisfactory. 



