The selection of right type of pump will require planar magnetic headphones of systems head and pump characteristics curves . The normal procedure is to first determine the system head curves and the desired discharge. The characteristic curves or tables giving the performance of various models of pumps are used to select the right type of pump, which will operate efficiently at or near the desired discharge and the systems total dynamic head.
System head curve
The system head curve gives the relationship between the discharge and the total head in pumping system. The contribution of various parameters to the total head such as well drawdown, frictional head and operating head usually increases with discharge.
To determine discharge drawdown relationship for particular well, a pumping test should be done by adopting proper procedure. When the pump is used to lift water for operating a pressurized irrigation system, the operating pressure is to be worked out using standard procedure and should be included in the total head.
Discharge capacity of pumps :
The data on the safe discharge rate of the well ( or other source of water ) and the discharge rate required for the crops to be irrigated with a particular cropping pattern are estimated, if necessary cropping pattern can be adjusted according to safe yield of well in different season. Thus, pumps capacity should be designed considering two factors : 1) Safe yield of well and 2) Water requirement of selected cropping pattern in peak periods. If there is no constraint on the availability of water , the pump capacity may be determined on the basis of the water requirement of the crops to be grown : otherwise pumping plant is to be designed to match safe yield of well. The safe yields of wells can be determined by conducting a pumping test.