704 



HYDRAULICS AND ITS APPLICATIONS 



3-463 



(3) 



From expression (2) it appears that as h d is increased from zero 

 (keeping h 8 constant) the efficiency .will increase until some point 

 is reached at which the (velocity of flow) 2 increases more rapidly 

 than does h d . This gives the value of h d for maximum efficiency. 

 In practice it is found that the ratio h s -f- h d then lies between 

 1-5 and 2'5, the larger values of the ratio being used with low values 

 of h d . 



The following table gives the results of tests on a plant of the 

 type illustrated in Fig. 340 c, carried out by Professor Josse at 

 Charlottenburg : 



