678 HYDRAULICS AND ITS APPLICATIONS 



thickness of vanes has been decided upon the above value of 6 3 must be 

 increased in the ratio 



2 T ?* 3 

 2 TT r 3 n t a cosec 60' 



Thus, taking eighteen vanes, each having a thickness at the tips of J inch, 

 this ratio becomes 



2 TT X 12-75 80-1 _ 



18 74 9 " 



and the true breadth 1 3 = T275 X T07 = 1'865 inches. 



49*9 

 Again o> = -- - = 47'0 radians per second. 



.-. N = -z - = 449 revolutions per minute. 



L TT 



49'9 



Assuming r 3 = 2'5 r a , this makes 2 = ~^r^ = 19*95 f.s., while if the 



' 



vanes be broadened out towards the centre so as to keep the velocity of 



flow 



5012. 



/ 



The manometric efficiency, 



J 



flow down to say 10 feet per second, this makes tan /8 = = - ~ = 



1/2 -*' ^" 



/3 = 26 37' 



(us -./scoty)' 

 is equal to 



_ 1,610 1,610 _ 



49-9. (49-9 - 7-09 X '5774) 2,282 



Probably mechanical and hydraulic frictional resistances will combine to 

 reduce this efficiency to about '65. 



Taking this value, the work done on the pump shaft per second 



62-4 Q H' 



= -- ? 



'DO 



_ P _ 62^ x_B_xJO _ 



" 550 X '65~ 550 X '65 

 The speed at which the pump begins to lift is given by 



uf -i/ 2 2 - 2 g H = 3,220 



or o> 2 (r a a - r a a ) = 3,220 



3,220 



offl - -425* = 



= 58-5 



= 60 X68-6 = 55 



