Is there such a thing as cavitation in positive displacement pumps?
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For example, with screw pumps and things like that, can cavitation occur?
Yes, whenever there is insufficient liquid supply at the pump inlet, resulting in inadequate suction, cavitation at the pump inlet will occur. It’s just that positive displacement pumps can transport a mixture of gas and liquid, and they can operate normally as long as there is no particularly severe cavitation ； And when a centrifugal pump suffers from cavitation, it loses all its effectiveness.
Positive displacement pumps can also suffer from cavitation, but the manifestations and effects of this phenomenon are different. In centrifugal pumps, cavitation represents a serious fault: the pump experiences severe vibration and the impeller is severely damaged. In positive displacement pumps, cavitation mainly manifests as insufficient suction; therefore, for such pumps, there is no requirement of an NPSH margin of 1 meter – it is sufficient as long as the value of A is greater than that of R
Yes, for positive-displacement rotor pumps, the calculation method for the net positive suction head available, NPSHa, is the same as that for vane pumps. For positive-displacement reciprocating pumps, the net positive suction head available NPSHa value should also take into account the head loss due to acceleration