Chapter 15. -PUMPS AND FORCED DRAFT BLOWERS 



147.105 



Figure 15-2. — Pressure in liquid is not affected by the shape of the vessel. 



When the pump is installed below this level, 

 as shown in figure 15-4, a certain amount 

 of energy in the form of gravity head will already 

 be available when the liquid enters the pump. In 

 other words, there is a static pressure head , A, 

 on the suction side of the pump. This head is part 

 of the total input head necessary to produce the 

 output head, F, that is required to raise the 

 liquid to the top, T, of the discharge reservoir. 



FORCE 1= 

 20 LBS- 



FORCE 2 = 

 200 LBS 



li 



PISTON 1 

 2 SO. IN. 



PISTON 2 

 20 SO. IN 



10 LBS. PER SO. INCH 



FttW?" 



rttf f t:: 



\LLLLLL1 



4.7 

 Figure 15-3. — Relationship of force, pressure, 

 and area in a simple hydraulic system. 



The action of the pump produces the total head 

 differential . B, which can be broken down into 

 friction loss , C , and net static discharge 

 head , D. Since D_ is the vertical distance from 

 the surface of the supply liquid to the surface of 

 the liquid in the discharge reservoir, it is clear 

 that our previous definition of head would apply 

 only to ID. E, the total static discharge head, is 

 the vertical distance from the center of the pump 

 to the surface of the liquid in the discharge res- 

 ervoir; thus, ^ is equal to D plus A. 



As may be seen in figure 15-4, atmospheric 

 pressure is acting upon the free surface of the 

 supply liquid and upon the free surface of the 

 liquid in the discharge reservoir. Since atmos- 

 pheric pressure is exerted equally on both sides 

 of the pump, in this system, the two heads created 

 by atmospheric pressure cancel out. 



Now consider the case of a pump that is in- 

 stalled a vertical distance^ above the free sur- 

 face^of the supply liquid (fig. 15-5). In this case, 

 energy must be supplied merely to get the liquid 

 into the pump ( static suction lift . A). In addition, 

 energy must be supplied to produce the static 

 discharge head , E, if the liquid is to be raised 

 to the top of the discharge reservoir, T. B, the 

 total head differential produced by pump action, 

 is here the total energy input. It is divided into 

 A on the suction side— the head required to raise 



393 



