How to understand net positive suction head
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How to understand the net positive suction head? What does it mean when the net positive suction head is negative?
Effective net positive suction head: the head that remains, after the medium reaches the pump inlet via the inlet pipeline from the tank, and is higher than the vaporization pressure of the medium. The net positive suction head must be independent of the suction pipe; it represents the pressure loss that occurs before the fluid gains kinetic energy once it enters the pump, and it is a performance parameter of the centrifugal pump itself. Both of these two values should be positive.
A negative value indicates that this pump has a strong resistance to air entrainment and certain exhaust capacity, such as self-priming pumps
NPSH does not have negative values; it is an absolute pressure. Additionally, if you look at the English term for cavitation margin, Net Positive Suction Head, it can also be translated as “net positive suction head”. I personally think it is more accurate than translating it as cavitation margin.