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BULLETIN 4!l"), U. S. DEPARTMENT OF AGRICULTURE. 



Displacement pumps are those which force water by means of a 

 piston or plunger traveling backward and forward in a close- fitting 

 cylinder. Centrifugal pumps are those which force water by means 

 of an impeller <>r fanned wheel revolving at a high speed in a close- 

 fitting shell or case. 



DISPLACEMENT PUMPS. 



Displacement pumps are divided into groups according to the num- 

 ber of cjdinders they contain, while each group can be subdivided 



into single-acting or 

 double-acting pumps r 

 depending on whether 

 the water is forced 

 during the forward 

 stroke only or during 

 both the backward and 

 forward strokes of the 

 piston. For spray ir- 

 rigation one and two 

 cylinders should be 

 double-acting. Three 

 cylinders should be 

 single-acting. 



A typical one-cylin- 

 der or simplex pump 

 is shown in figure 16, 

 with its principal 

 parts numbered and 

 named. These pumps 

 are adapted for spray 

 systems requiring up 

 to 114 gallons per 

 minute, and will work 

 against a total head of 

 IT.", feet. This type of pump is adapted to small plants where the 

 water can be obtained within suction lift, and may be installed on the 

 surface or in a pit, and driven by belt or gear connection to power. 

 Single-cylinder double-acting pumps are adapted also to deep-well 

 pumping where the cylinder is suspended in the well and operated 

 from the surface by a power working head, of which figure 17 is a 

 typical design for small plants. 



Duplex or two-cylinder pumps usually are constructed with two 

 cylinders lying horizontally on a common base, which also holds a 

 power working head. The duplex pumps are adapted to large plants 



Fin. !<;. — Typical simplex, double-acting displacement 

 pump. 1, Air chamber; 2, discharge opening; 3, tight 

 and loose pulleys; 4, valve chamber; 5, cylinder; 

 6, gear ; 7, connecting rod ; 8, suction opening ; 9, base ; 

 10, packing gland. 



