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NPSH Calculator (NPSHa / NPSHr)
Enter your suction-side data — NPSHa, margin and cavitation verdict update instantly.
Formula
NPSHa = Pa + Hs − Hv − hf
Water Vapor Pressure Head Hv
| Water temp (°C) | Pv (bar abs) | Hv (m) |
|---|---|---|
| 0 | 0.0061 | 0.06 |
| 20 | 0.0234 | 0.24 |
| 40 | 0.0738 | 0.75 |
| 60 | 0.199 | 2.03 |
| 80 | 0.474 | 4.83 |
| 100 | 1.013 | 10.33 |
Guidelines
Keep NPSHa − NPSHr ≥ 0.5 m minimum (1 m for hot water or hydrocarbons). Suction velocities of 1–2 m/s keep hf low.
FAQ
What is NPSH?
Net Positive Suction Head — the absolute suction head above vapor pressure available at the pump inlet. If NPSHa < NPSHr the liquid flashes and the pump cavitates.
What are typical symptoms of cavitation?
Gravel-like noise, vibration, and falling flow/head. Long-term it erodes the impeller.
How do I fix low NPSHa?
Lower the pump, shorten suction piping, enlarge the suction line, reduce elbows, or lower fluid temperature (to cut vapor pressure).