CHAPTER 15 



PUMPS AND FORCED DRAFT BLOWERS 



This chapter deals with shipboard pumps and 

 with the forced draft blowers used aboard many 

 surface ships to supply combustion air to the 

 propulsion boilers. In general, we are concerned 

 here with the driven end of the units rather than 

 with the driving end; the auxiliary steam turbines 

 used to drive many pumps and blowers are dis- 

 cussed in chapter 16 of this text, and the electric 

 motors used to drive others are discussed 

 in chapter 20. 



PUMPS 



As we saw in chapter 8, the pump is one of 

 the five basic elements in any thermodynamic 

 cycle. The function of the pump is to move the 

 working substance from the low pressure side 

 of the system to the high pressure side. In the 

 conventional steam turbine propulsion plant, 

 "the pump" of the thermodynamic cycle is ac- 

 tually three pumps— the condensate pump, the 

 feed booster pump, and the main feed pump. 



In addition to these three pumps which are a 

 part of the basic thermodynamic cycle, there are, 

 of course, a large number of pumps used for 

 other purposes aboard ship. Pumps supply sea 

 water to the firemains, circulate cooling water 

 for condensers and coolers, empty the bilges, 

 transfer fuel oil, discharge fuel oil to the 

 burners, supply lubricating oil to main and auxil- 

 iary machinery, supply sea water to the distilling 

 plant, pump the distillate into storage tanks, sup- 

 ply liquid under pressure for use in hydraulically 

 operated equipment, and provide a variety of 

 other vital services. 



Pumps are used to move any substance which 

 flows or which can be made to flow. Most com- 

 monly, pumps are used to move water, oil, and 

 other liquids. However, air, steam, and other 

 gases are also fluid and can be moved with 

 pumps, as can such substances as molten metal, 

 sludge, and mud. 



A pump is essentially a device which utilizes 

 an external source of power to apply a force to a 

 fluid in order to move the fluid from one place 

 to another. A pump develops no energy of its own; 

 it merely transforms energy from the external 

 source (steam turbine, electric motor, etc.) into 

 mechanical kinetic energy, which is manifested 

 by the motion of the fluid. This kinetic energy is 

 then utilized to do work— for example, to raise 

 a liquid from one level to another, as when water 

 is raised from a well; to transport a liquid 

 through a pipe, as when oil is carried through an 

 oil pipeline; to move a liquid against some 

 resistance, as when water is pumped to a boiler 

 under pressure; or to force a liquid through a 

 hydraulic system, against various resistances, 

 for the purpose of doing work at some point. 



Principles and Definitions 



Before considering specific designs of ship- 

 board pumps, it may be helpful to examine 

 briefly certain basic concepts and to define some 

 of the terms commonly used in connection with 

 pumps. 



FORCE - PRESSURE - AREA RELATION- 

 SHIPS.— When we strike the end of a bar, the main 

 force of the blow is carried straight through to 

 the other end. This happens because the bar is 

 rigid. The direction of the blow almost entirely 

 determines the direction of the transmitted 

 force. The more rigid the bar, the less force is 

 lost inside the bar or transmitted outward 

 at right angles to the direction of the blow. 



When weapplypressureto theendof a column 

 of confined liquid, however, the pressure is 

 transmitted not only straight through to the other 

 end but also equally and undiminished in every 

 direction. Figure 15-1 illustrates thedifference 

 between pressure applied to a rigid bar and pres- 

 sure applied to a column of contained liquid. 



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