Pump Selection Criteria on type of Duty : Process duty or Transfer duty?
Pump selection criteria lay substantial emphasis on the type of duty the pumps will be subjected to in the field. Depending on whether the required operation is for process or for transfer, the pump may selection may vary.
1) Process duty:
In this case, the pump is expected to deliver the desired constant flow against a constant head i.e. the duty point of the pump does not vary substantially with time. In this scenario it is important to select the pump where the duty point is as close as possible to the BEP.
In case of transfer duty, the pump is expected to merely transfer a certain amount of liquid from place A to B against a constant (or sometimes varying) head. In this case, the operation point of the pump shifts with time. The pump selected must be stable within the expected variation of the duty point and the selection must incorporate a margin to the left and right of the BEP.