638 



HYDBAULICS AND ITS APPLICATIONS 



will thus require balancing for end thrust or not, just as does the open 

 vaned pump. The possibilities in this direction are somewhat greater 

 than with the latter type. 



It is very suitable for heads between 30 and 80 feet, but must, for high 

 efficiency under high heads, be fitted with guide vanes outside the impeller 

 ring. As thus constructed, efficiencies up to about 80 per cent, may be 

 obtained. Free circulation of water behind the impeller and into the 

 suction space is usually prevented by the introduction of a brass packing 

 ring at P (Fig. 306). 



Where the working head exceeds about 100 feet, the single impeller 



r 



730 



FIG. 307. Worthington Single Impeller High Lift Pump. 



pump as usually constructed falls off rapidly in efficiency owing to tne 

 necessary high speed of rotation and the consequent excessive frictional 

 and eddy losses. It may be compounded, and so made suitable for such 

 work by mounting a number of impellers in series in separate chambers 

 and on the same shaft, each taking the discharge from its predecessor 

 and raising it through a fraction of the whole head depending on the 

 number of impellers used. For this to be done with fair efficiency, it is 

 essential that as far as possible the kinetic energy of discharge from each 

 wheel be converted into pressure energy before entering the next chamber, 

 and this renders the use of efficient volute chambers or of guide or diffu 

 vanes on the discharge side essential. 



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