Net Positive Suction Head Available — computes NPSHA and compares against NPSHR for cavitation risk assessment. Enter inlet pressure directly, or describe the installation geometry and let the calculator derive it.
Turbomachinery · CavitationAbsolute pressure at the pump inlet flange
At operating temperature — use water presets above
From inlet pressure (direct):
From installation geometry:
Cavitation criterion and safety margin:
| Margin (NPSH_A − NPSH_R) | NPSH_A / NPSH_R | Status |
|---|---|---|
| < 0 m | < 1.0 | Cavitating — immediate damage risk |
| 0 to 0.5 m | ≈ 1.0 | High risk — increase margin urgently |
| 0.5 to 1.0 m | 1.05–1.1 | Marginal — monitor closely |
| > 1.0 m | > 1.1 | Safe — recommended operating zone |
Water vapor pressure at key temperatures:
| T [°C] | Pv [kPa] | ρ [kg/m³] | Pv head [m] |
|---|---|---|---|
| 20 | 2.34 | 998 | 0.24 |
| 40 | 7.38 | 992 | 0.76 |
| 60 | 19.9 | 983 | 2.07 |
| 80 | 47.4 | 972 | 4.97 |
| 100 | 101.3 | 958 | 10.8 |
Cavitation occurs when local pressure drops below Pv, forming vapor bubbles that implode as pressure recovers — causing noise, vibration, impeller pitting, and head loss. Always design for NPSHA > NPSHR with an adequate safety margin, especially for hot liquids where Pv is high.