CENTKIFUGAL PUMPS 677 



breadth at inlet be increased to 4*5 inches so as to reduce the velocity of 

 flow at this point, this makes : 



fi =/, X g X 2-35 = ^L** = n . 20 { s _ 



Since / 2 = ?/ 2 tan /?, we have : 



fa 11-20 ' 11'20 X 2-25 

 tan/ * = ;7 2 = 1U^ = -31-5"" 8 ' 



2-25 



)3 = 38 39' 



giving the inlet angle for the vanes. 



(2) A pump 50 feet working head is fitted with a whirlpool chamber 

 whose radius is twice that of the impeller, and whose efficiency is 50 per 

 cent. The pump is to deliver 5 cubic feet per second. Determine its 

 leading dimensions its speed of rotation its hydraulic efficiency, and 

 the probable H.P. necessary to drive it. 



To begin with, we will assume that since the whirlpool chamber is 

 fairly efficient and the head high, the value of y may be taken as fairly 

 high say 60 so as to keep down the speed and friction losses. Also 

 assume / 3 = J *J 2 g H'. 



o.rvo 



Then/3 = -g- V 50 = 7'09 f.s. 



Now substituting *5 for c and '5 for K in equation (18), (p. 663), we 

 get 



.5 ( Ws _ 7-09 cot 60) 2 X | + 3 2 - 50-2 cosec 2 60 + 25'1 x 



= 100 g = 3,220 

 /. uf 2-232 1/3 - 2,378 = 0, 



or tt s = 49-9 feet per second. 



Since VT^ = 40'1, this makes u 3 = 1'245 V g H'. 

 Next taking fc 3 = ^ we have ^3 = 2^ r 3 & 3 = -, 



n 



and since Q = A 3 f 3 = ^- X 7'09, 



o 



we have r 8 2 = = 1-122. 



.'. r 3 = 1'06 feet = 12} inches, 

 /. 6 3 = 1-275 inches. 



This neglects the effect of the vane thickness. Since the vanes reduce 

 the effective discharge area by 1 3 n t 3 cosec y, when the number and 



