CENTKIFUGAL PUMPS 679 



Thus the speed necessary to institute pumping is considerably higher 

 than that necessary for working once delivery has commenced. This 

 assumes that until flow takes place the whirlpool chamber has no effect 

 in converting kinetic into pressure energy. Actually, however, owing to 

 viscosity, the actual speed for lifting to commence is somewhat less than 

 that indicated above. 



(3) Compound high-lift pump, fitted with guide vanes and vortex 

 chambers having a pressure conversion efficiency of 75 per cent., to 

 deliver 5 cubic feet per second under 300 feet head. Assuming a lift of 

 50 feet in each of six chambers ; y = 60, / 3 = J V 2 g H' ; and considering 

 each chamber as a separate pump, we have, as in example (2),/ 8 = 7'09 f.s. 



Then, taking b 3 = ~, we get, as before, 6 3 = 1-275 inches, or, allowing 



for the same vanes, b 3 = 1*365 inches, while r a = 1*06 feet. We now 

 have the factor k of equation (20) (p. 664) equal to '75, and this equation 

 becomes : 



75 (MS - 4-09) 2 + uf - 66'95 + 37'6 = 8,220. 



.-. u<? - 3-51 u 3 1,850 = 0. 



v u 3 = 44-76 f.s. 



This makes % = M16 V g H'. 



60 u 3 60 X 44-76 

 Also N = g - = -g - Qg = 403 revolutions per minute, while 



since tan a = - & - 7 = -~r - 77v7 = '1744, this gives a 

 ^3 ./a cot y 44*76 4*09 



guide vane angle a = 9 54'. 



Assuming u 3 / 3 cot y or w 9 to have '95 times its theoretical value, 

 p. 671, this makes tan a = "1834 and a = 10 24'. 



n TJ r 



In this case the manometric efficiency -, " ^ -- r 



cot 



1,610 1,610 _ 



~ 44-76 X 40-67 " 1,822 ~ 



Frictional losses would probably reduce this to about -80, so that the H.P. 

 would be equal to 



62-4 X Q X n H' _ 62'4 X 5 X 300 _ 

 550 X -80 550 X '80 



EXAMPLES. 



(1) A centrifugal pump is 4 feet in diameter and makes 200 revolutions 

 per minute, delivering 64*8 cubic feet of sea water per second, against a 



