- By restricting the pump throughput, the head is artificially raised to a level above the normal discharge system resistance at that particular throughput.
- Throughput is reduced to a level equal to, or below, the natural flow of liquid to the pump so that cavitation does not occur, i.e. the flow of liquid to the tank suction strum is closely matched to the pump throughput.
The performance of a centrifugal pump declines if gas is entrained in the liquid being pumped.
Manual matching of pump input and output is difficult, and without external aid suction cannot be regained once the strum has been uncovered and air allowed to enter the suction piping. It is for this reason that separate positive displacement pump stripping systems are usually installed. Centrifugal pumps can be made self-priming if air or gas is removed from the liquid being pumped before it enters the pump suction.
The discharge valve on the pump performs as important function during this process by matching the discharge rate of the pump to the natural flow of liquid to the pump suction.
The sequence of events is:
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