Pump NPSH Available
Atmospheric, vapor, static, and friction heads to NPSHa with cavitation flag.
Example
You enter
- Water temperature (°F) 60
- Source elevation vs pump (ft, + above) 5
- Suction friction loss (ft) 2
- NPSH required (ft, optional) 8
You get
- Atmospheric head 33.90 ft
- Vapor pressure head 0.59 ft
- H friction (ft) 2
- NPSH available 36.31 ft
Checked against published worked examples from: Hydraulic Institute / centrifugal-pump cavitation practice; Joe Evans (Pumps & Systems Pump Ed 101), via R.C. Worst & Co.; Pumps & Systems (Jim Elsey, Summit Pump); and 1 more.
Details, formula, and sources
Formula or tableNPSHa = H_atm + H_static_source − H_friction − H_vapor (all in ft of 60 F water). H_atm from elevation-lapse; H_vapor from a public engineering psi-by-temperature table converted via 2.31 ft/psi.
Source and editionHydraulic Institute by name; ASHRAE Fundamentals water-property tables.
Free accessHI standards licensed; vapor-pressure data free at NIST.
What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
API field nameswater_temp_F, source_elevation_relative_ft, friction_loss_ft, npsh_required_ft, H_atm_ft, H_vapor_ft, H_friction_ft, NPSHa_ft
- Vapor-pressure table ASHRAE Fundamentals; converted via 2.31 ft H2O / psiASHRAE Fundamentals
- Elevation lapse P_atm = 14.696 × (1 − 6.876e-6 × elev_ft)^5.2561ICAO Standard Atmosphere