FS ES 

26 BULLETIN 495, 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 or 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 cylinders they contain, while each group can be subdivided 
| is into single-acting or 
double-acting pumps, 
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 
evlinders should be 
double-acting. Three 
evylinders should be 
single-acting. 
A typical one-cylin- 
der or stmplex pump 
is shown in figure 16, 
with its principal 
parts numbered and 
named. These pumps 
are adapted for spray 
Fic. 16.—Typical simplex, double-acting displacement gystems requiring up 
pump. i, Air chamber; 2, discharge opening; 3, tight z 
and loose pulleys; 4, vaive chamber; 5, cylinder; to 114 gallons per 
6, gear; 7, connecting rod; 8, suction opening; 9, base; minute, and will work 
Reape eee against a total head of 
175 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 


