CHAPTER XVIII 



Centrifugal Pumps Types and Construction Theory Balancing of End Thrust. 



ART. 172. CENTRIFUGAL PUMPS. 



UNDER low heads the efficiency of the reciprocating pump falls off con- 

 siderably, and when in addition very large quantities of water are to be 

 handled its excessive dimensions render it expensive to construct and to 

 instal. When working against a variable head, it also suffers from the 

 disadvantage that its speed cannot be increased to any large extent to 

 enable it to deliver a larger quantity of water as the head is reduced. 



Under such conditions, with heads ranging from about 6 feet to 100 

 feet, the centrifugal pump having a single impeller is on all accounts most 

 suitable, giving as it does a good efficiency up to about 75 per cent, in 

 the modern type of pump along with moderate dimensions, simple con- 

 struction, ease of installation and maintained high efficiency under con- 

 tinuous working conditions. 



In the latter respect its freedom from valves gives it an advantage over 

 the reciprocator, whose valves, glands, and packing rings need to be 

 frequently overhauled if the efficiency is to be maintained, this advantage 

 being still more pronounced where the liquid pumped contains gritty 

 matter in suspension. 



A further advantage is involved in its continuous and even discharge 

 and the consequent freedom from shock in the delivery pipe line. 



The invention, in 1875, by Professor Osborne Reynolds, of the modern 

 form of high lift pump, having an efficiency equal to that of the old ty 

 of low lift pump, opened out a new field of application for the centrifu 

 pump, and of recent years this has been to an increasing extent invadin 

 the province of the reciprocator, its efficiency increasing with impro 

 ments in design, until at the present time heads of upwards of 1,500 f< 

 may be overcome with efficiencies of from 75 to 80 per cent. In a pump 

 designed for such work the water passes through a sequence of impellers 

 mounted in series on the same shaft, the increase in head taking place 

 in stages. 



A further advantage of the centrifugal pump consists in the possibili 



