Pump NPSH Calculator

Inputs

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Absolute pressure at the suction vessel/free surface or pump suction datum. Atmospheric pressure is about 1.013 bar / 14.7 psi absolute.
bar
Positive when liquid level is above the pump centerline; negative for suction lift.
m
Use vapor pressure at the pumping temperature. Water near 20 C is about 0.023 bar absolute.
bar
Friction and minor losses in the suction line, expressed as head.
m
Density at the operating temperature.
kg/m³
Required NPSH from the pump curve at the design flow rate.
m

Results

Default result
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NPSH available(NPSHa)
10.11m
Pass

Absolute pressure head plus static head, minus vapor pressure head and suction losses.

Also computed

NPSH margin(NPSHa - NPSHr)Pass7.114m

NPSH ratio(NPSHa/NPSHr)Pass3.371

Absolute pressure head(P_abs/(rho g))10.35m

Vapor pressure head(P_v/(rho g))0.2391m

NPSHa pressure equivalent(rho g NPSHa)0.9898bar

Method notes 3 notes
  • NPSHa = P_abs/(rho*g) + static suction head - P_v/(rho*g) - suction line head loss.
  • Compare against NPSHr from the pump curve at the same flow. Many installations need additional margin beyond simply exceeding NPSHr.
  • Final pump selection still needs the full system curve, inlet geometry, acceleration head, strainers, valves, temperature, altitude and manufacturer guidance.

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