670 



HYDRAULICS AND ITS APPLICATIONS 



cause a deflection of the lines of flow in the direction of rotation before 

 the wheel is reached. This has the effect of increasing the value of the 

 inlet angle /3 for entry without shock at any given speed of rotation, 

 though experimental results are too scanty to allow of the magnitude of 

 this effect being calculated. 



The assumption that all particles of water on leaving the impeller have 

 the same velocity i' 3 and are moving in paths making an angle y with 

 the tangent to the periphery, or that ic 3 = u 3 / 3 cot y for all particles, 

 is also incorrect as appears from the results of experiment. A measure 

 of the error involved may be obtained by comparing the actual and 

 theoretical manometric efficiencies, for if from the energy expended in 

 driving a pump, that necessary to overcome disc and mechanical friction 

 be deducted, the remainder should equal ?/ 3 w a H- g foot Ibs. per Ib. of 

 water. If the ratio of the measured manometric head H m to this 

 quantity be termed the experimental manometric efficiency, the ratio 

 of the theoretical and experimental manometric efficiencies will be a 

 measure of the ratio of the true iv 3 to that given by the foregoing formula. 



The following results from tests of a pump by Mr. Parsons l have been 

 chosen to illustrate this point. The details of the pump are as follow : 

 ?- 3 = 9'25 inches; r 2 = 4*625 inches; 1% = 1 3 = 5*75 inches; y 15; 

 (3 = 40 ; 8 vanes, assumed f inch thick for purposes of calculation. 



Mean ... -M: 



In these experiments the mean power necessary to overcome the 

 friction of the pump bearings and driving belt and the disc friction of th< 

 pump was found to be T37 H.P., and this value has been used in deducing 

 the values in column 5. 



Again experiments on an experimental pump, r 3 == 4*41 inches ; r 2 = 

 2-188 inches; 1 2 = l> 3 = 1125 inches; y 90; ft = 18 50', at the 



" Proc. Inst. C. E.," Vol. 53, p. 271. 



