Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS 



Figure 15-28.— Main feed pump. 



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Propeller pumps must be located below or 

 only slightly above the surface of the liquid to be 

 pumped, since they cannot operate with a high 

 suction lift. 



MIXED- FLOW PUMPS. -A mixed-flow pump 

 is one in which the pumping action occurs partly 

 by centrifugal force and partly by propeller ac- 

 tion. Pumps of this type can be used to handle 

 very viscous liquids or liquids that contain dirt; 

 they are better than either centrifugal pumps or 

 propeller pumps for these services. 



JET PUMPS.— Devices which utilize the rapid 

 flow of a fluid to entrain another fluid and thereby 

 move it from one place to another are called jet 

 pumps. Jet pumps are sometimes not considered 

 to be pumps because they have no moving parts. 

 However, in view of our previous definition of a 



pump as a device which utilizes an external 

 source of power to apply force to a fluid in order 

 to move the fluid from one place to another, it 

 will be apparent that a jet pump is indeed a pump. 



Jet pumps are generally considered in two 

 classes: ejectors, which use a jet of steam to 

 entrain air, water, or other fluid; and eductors, 

 which use a flow of water to entrain and thereby 

 pump water. The basic principles of operation of 

 these two devices are identical. 



A simple jet pumpof the ejector type is shown 

 in figure 15-29. In this pump, steam under pres- 

 sure enters chamber C through pipe A^ which is 

 fitted with a nozzle, B. As the steam flows 

 through the nozzle, the velocity of the steam is 

 increased. The fluid in the chamber at point F, 

 in front of the nozzle, is driven out of the pump 

 through the discharge line, ^ by the force of the 

 steam jet. The size of the discharge line 



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