






SPRAY IRRIGATION. 29 
rise in the suction pipe and fill the pump. The hand pump must be 
a vacuum pump when placed above suction lift of the. water level 
(see Table 5). In this case an air-tight check valve is placed in the 
discharge pipe just above the centrifugal pump to prevent air enter- 
ing through the discharge pipe. The smaller centrifugal pumps can 
be purchased with a “hand primer” built into the suction and are 
adapted to low suction lifts. Figures 5 and 6 show centrifugal pumps 
submerged in water, so that the case is always full and needs no 
priming. Figure 2 illustrates how the pump can be primed from a 
barrel or any elevated source. In this case it is necessary to have a 
check valve or foot valve in the suction pipe below the water level 
to prevent the priming water from running out through the suction 

Wie. 19.—Typical two-stage split-case centrifugal pump. 1, Top half of split case, 
raised ; 2, impellers; 3, packing; 4, suction; 5, discharge; 6, base. 
pipe. A check valve is preferable to a foot valve because of the ease 
in entering and less resistance to the water. When the pump is 
started the priming barrel will be refilled if the valve is left open 
for a short time. 
THE DESIGNING OF SPRAY IRRIGATION SYSTEMS. 
Every ‘spray irrigation system can be divided into three parts, 
which must be considered in their proper relation to each other in 
the design of a plant. First, the distribution-pipe system, which ap- 
plies the water directly to the crops through some type of nozzle; 
_ second, the main feed pipe, which conveys the water from the source 
_to the distributaries; third, the pumping equipment, which lifts the 
water and develops the pressure, unless the water and pressure are 
obtained from a gravity or municipal supply. 


