PRINCIPLES OF NAVAL ENGINEERING 



REVOLVING IMPELLER 



STATIONARY OIFFUSER VANES 



23.19 

 Figure 15-26.— Volute turbine pump. 



vanes and the volute reduce the velocity of the 

 liquid, there is in this type of pump an almost 



complete conversion of kinetic energy to poten- 

 tial energy. 



Centrifugal pumps may be classified in sev- 

 eral ways. For example, they may be either 

 single-stage or multistage, a single-stage pump 

 has only one impeller; a multistage pump has two 

 or more impellershousedtogether in one casing. 

 In a multistage pump, as a rule, each impeller 

 acts separately, discharging to the suction of the 

 next-stage impeller. Centrifugal pumps are also 

 classified as horizontal or vertical, depending 

 upon the position of the pump shaft. 



The impellers used in centrifugal pumps may 

 be classified as single suction or double-suc- 

 tion. The single-suction impeller allows liquid to 

 enter the eye of the impeller from one direction 

 only; the double- suction type allows liquid to 

 enter the eye from two directions. Single- suction 

 and double- suction arrangements are shown in 

 figure 15-27. The double- suction arrangement 

 has the advantage of balancing end thrust in one 

 direction by end thrust in the other. 



Some of the more important centrifugal 

 pumps used on naval ships are the main feed 

 pump, the feed booster pump, the main and auxil- 

 iary condensate pumps, fire pumps, freshwater 

 pumps, and gasoline pumps. 



A typical main feed pump is shown in figure 

 15-28. This is a horizontal, high speed, turbine- 

 driven pump. Main feed pumps on most surface 

 ships operate at a dischargepressurethat is 100 

 to 1 50 psig above the maximum steam drum pres- 



23.25 

 Figure 15-27. —Single-suction and double- 

 suction arrangements in centrifugal pumps. 



sure of the boiler. On ships having 1200-psig 

 boilers, the discharge pressure of the main feed 

 pumps is approximately 200 to 300 psig above the 

 steam drum pressure. A main feed pump must 

 operate at varying speeds to maintain a constant 

 discharge pressure under all conditions of load. 

 A constant-pressure pump governor" is used to 

 regulate the admission of steam to the turbine 

 and thus control the discharge pressure of the 

 pump. 



PROPELLER PUMPS.— Propeller pumps are 

 used on some ships for pumping water. Although 

 they are often classified as centrifugal pumps, 

 this classification is incorrect because propeller 

 pumps do not actually utilize centrifugal force for 

 their operation. 



A propeller pump consists essentially of a 

 propeller fitted into a narrow, tube-like casing. 

 The propeller pumps the liquid by pushing it in 

 a direction parallel to the pump shaft. 



Constant-pressure pump governors are discussed in 

 chapter 16 of this text. 



410 



