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BULLETIN 4!>5, U. S. DEPARTMENT OF AGRICULTURE. 



lift depends greatly upon the speed of the impeller, which usually 

 makes it desirable to adopt a two-stage pump when the lift exceeds 

 100 to 150 feet, which can be run at practically one-half the speed 

 of a single stage. Figure 10 shows a typical two-stage turbine pump 

 with a split shell which allows easy access to the impeller and bear- 

 ings. The volute type usually is cheaper in first cost than the turbine, 

 but the latter is more efficient. 



Centrifugal pumps can be used for spray irrigation to lift w T ater 

 from surface supplies (fig. 2), shallow wells (fig. 4), or deep wells 

 (fig. G). The pumps are built with horizontal shafts, as shown 

 in figures 18 and 19, and with vertical shafts, as shown in figures 5 

 and 6. Centrifugal pumps may be driven by belt connection to the 

 power or, where electric power is available, the motor can be con- 

 nected direct, as shoAvn in figure 18. 



Fig. 18. — Single-stage centrifugal pump direct connected to electric motor, showing 

 an open-type impeller. 1, Discharge ; 2, suction ; 3, pump volute or case ; 4, 

 stuffing box ; 5, coupling ; 6, electric motor ; 7, base ; 8, impeller. 



The chief advantages of centrifugal pumps compared with dis- 

 placement for spray irrigation are their low first cost for the same 

 capacity, their simplicity, and the few wearing parts. A centrifugal 

 pump also fits itself readily to pressure changes of a spray system 

 without the use of a by-pass or relief valve. One spray line or all 

 may be shut off to suit the needs of the farmer while the pumping 

 plant is running, without ill effects to the machinery. 



Centrifugal pumps must have a free suction intake and usually 

 should not be attached directly to well casings, but should have a 

 separate suction pipe extending into the water well below suction lift. 

 All centrifugal pumps must be full of water before they will draw 

 through the suction. All air should be excluded from the suction 

 pipe and pump case before starting. A common method is to pump 

 the air out with an ordinary hand pump, which causes the water to 



