NPSH is not just a technical parameter. It’s a safety margin — a line between optimal performance and catastrophic failure.
There are two terms associated with NPSH (net positive suction head)
NPSH – A (Net positive suction head-available): The actual pressure head at the pump’s suction, based on the system.
NPSH – R (Net positive suction head-required): The minimum pressure head the pump needs to avoid cavitation, specified by the manufacturer.
NPSH – A < NPSH – R → Cavitation will occur.
NPSH – A > NPSH – R → Pump will run perfectly without cavitation
Cavitation is the bubbles form and collapse violently inside the pump, damaging impellers, reducing performance, and eventually causing pump failure.
As a fluid’s velocity increases, its pressure drops — assuming elevation stays constant.
Now from the Continuity Equation “a narrower pipe means higher velocity”.
High velocity = Low pressure
If pressure falls below the liquid’s vapor pressure, the liquid starts boiling — even at ambient temperature.
