646 



HYDRAULICS AND ITS APPLICATIONS 



outlet from the collecting chamber of the pump, the connecting pipe 

 having a gradual divergence. By this means a partial conversion of 

 kinetic into pressure energy is obtained in this connecting pipe. 



With heads exceeding about 100 feet, a non-return valve should be 

 fitted on the delivery side, while when delivering into a rising main of 

 great length an air vessel should be fitted on the same side of the pump 

 to avoid shock on starting and stopping. 



This is specially advisable with a belt-driven pump, where the vibration 



of the belting may produce variations of 

 considerable magnitude in the angular 

 velocity of the shaft under normal work- 

 ing conditions. In a belt-driven quad- 

 ruple high-lift pump under the author's 

 observation, making 1,400 revolutions 

 per minute and discharging through 

 600 feet of 4-inch piping, against a 

 total head of 143 feet, the pressure in 

 the last collecting chamber varied from 

 122 to 164 feet. One successful com- 

 bination of non-return valve and air 

 vessel is illustrated in Fig. 318. 



Self -charging Device. Since a centri- 

 fugal pump will not begin to lift unless 

 first charged with water, if fixed above 

 supply water level provision must be 

 made for priming or flooding the pump 

 casing from an auxiliary pressure 

 supply or for withdrawing the air by 

 means of an ejector or auxiliary air 

 pump. 



FIG. 318. Delivery Valve with Air Vessel 

 for High-Lift Centrifugal Pump. 



ART. 175. GENERAL THEORY OF CENTRIFUGAL PUMP. 



In the following discussion of the theoretical considerations govern- 

 ing the design of the centrifugal pump, the symbols used are the 

 same and have the same meaning as in the case of the turbine 

 (p. 532). 



Thus the suffix (1) refers to the water just before entering the impeller. 



(2) refers to the water just after entering the impeller. 



(3) refers to the water discharging from the impeller. 



