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What is the difference between NPSH, NPSHa and NPSHr?


Could our members please explain what is the difference between NPSH, NPSHa and NPSHr? Your information will help when end users when looking.
NPSH = Nett Positive Suction Head - This is the head that is on the suction side of the pump. Every pump has a requirement that the manufacturer will specify this on its datasheets. It is different for every pump and system.
NPSHA = Available - This is what is actually available on the system. This must always be greater than that required by the pump to prevent cavitation.
NPSHR = Required - This is specified by the pump manufacturer once they have the duty details.


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