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NPSH (Net Positive Suction Head) measures the pressure margin at the pump suction — the core parameter for avoiding cavitation.
Two NPSH values
- NPSHa (available): what the system provides, set by installation and piping.
- NPSHr (required): what the pump demands, read from the curve.
Selection rule
Always ensure NPSHa ≥ NPSHr + 0.5 m.What cavitation does
Bubbles collapse at the impeller inlet causing noise, vibration and flow loss — and over time, impeller and casing damage.
How to raise NPSHa
- Lower the pump installation
- Shorten and enlarge the suction line
- Reduce suction bends and valves
- Cooler liquid (lower vapour pressure)
NPSH matters most on wells and high tanks — check before you size.