Pump NPSH and Cavitation — online
NPSH available for four cases side by side — tank or suction-gauge route, altitude, hot liquid, low level — against the vendor NPSH3 curve with margins, suction specific speed and vortex submergence.
Yellow cells are inputs; orange cells are choices; blue cells choose the unit. Select or hover over an input to see its help in the box below the toolbar. The sheet is the same as the Excel tool (USD 29) — the Guide, method and references are in the Excel file.
What this pump npsh and cavitation calculator does
Check the suction before the pump tells you with noise. NPSH available for four cases side by side — tank or suction-gauge route, altitude, hot liquid, low level — against the vendor NPSH3 curve with margins, suction specific speed and vortex submergence.
- Four cases at once. Rated, maximum flow, hot liquid and low level — or any four of your own.
- Two routes. From the suction vessel (open tank at altitude, closed vessel, boiling liquid) or from a suction gauge reading.
- Vendor NPSH3 curve. Fitted and scaled to your speed; recommended margins by service from the Pump Handbook; ANSI/HI 9.6.1 named as the authority.
- Liquids done properly. Vapour pressure from the built-in liquid list, bubble point for mixtures, or your own values; flashing and boiling checks.
- Extra checks. Suction specific speed, suction velocity and vortex submergence.
- Print-ready report. Case table, findings and the NPSHa / NPSHR chart.
What you enter
- Source vessel
- Suction line loss
- Liquid data
- Liquid
- Concentration (% by mass)
- Watson characterisation factor K
- Kinematic viscosity at 40 °C
- Kinematic viscosity at 100 °C
- Mixture composition in
- Mixture
- Flow
- Liquid temperature at the suction
- Vessel (surface) pressure
- Liquid level above the pump centreline
What you get
- Liquid density
- Vapour pressure (absolute)
- Vessel surface pressure (absolute)
- Pressure head above vapour pressure
- Static head (liquid level)
- Suction line velocity
- Margin NPSHa − NPSHR
- Ratio NPSHa / NPSHR
- Recommended NPSHa
- Verdict
- Submergence needed against vortexing
- Liquid height above the vessel outlet
- Suction specific speed Nss at BEP (US: rpm, gpm per eye, ft)
- Atmospheric pressure at the site
How it was checked
Reproduces the free web NPSH calculator (7.80 m) and an independent Python model; suction-gauge route checked by hand (8.76 m).
Related
- Free quick calculator — a simpler free version for a fast estimate.
- Calculation guide — the equations behind this tool, with a worked example.
- Pump NPSH and Cavitation Excel tool — USD 29, keep the workbook and its Guide.
- All 40 online tools
Questions
Is the pump npsh and cavitation calculator free?
You can enter and check all your data free. The full results, findings and printable sheet are unlocked with a 3-run pack (USD 9), a monthly subscription to all 40 online tools (USD 15) or a yearly one (USD 99).
Are the results the same as the Excel tool?
Yes. The online tool runs the formulas of the Pump NPSH and Cavitation Excel workbook, checked cell by cell against the Excel file.
Which units can I use?
SI, US customary and British units — choose the unit next to each input.