SPRAY IRRIGATION. 



29 



rise in the suction pipe and fi.ll 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 C 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 



Fig. 



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. 



