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NPSH calculator: centrifugal pump power, NPSH and affinity laws
NPSH available and its margin over NPSH required, hydraulic and shaft power, and affinity laws for a speed change on a centrifugal pump. Free, no sign-up.
- Instant result
- Formula and standards shown
- On desktop and phone
Result
4.079kWHydraulic power Ph
- Shaft power
- 5.827kW
- Caution : Newtonian liquid assumed; for slurry or viscous liquid, use the manufacturer's curve.
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Pump figures filed with the cavitation work order
Here, the calculator is free and the result is gone when you close the page. In Reglova, it is attached to the work order on the right machine: you find it again at the next breakdown, and on audit day.
The CMMS software comparison, our gaps included- Attached to the work order with its inputs: the server recalculates it, it stays verifiable.
- On the technician's phone, even without a network.
- In the machine's history, for the next breakdown.
- The asset's nameplate data pre-fills the calculation.
When to calculate NPSH available
01
Check that a replacement motor is large enough for a pump.
02
Track down the cause of cavitation: suction level, water temperature, losses.
03
Estimate the energy savings of a speed reduction on the drive.
Good to know
Keep at least 0.5 m between NPSH available and NPSH required. The calculations assume a Newtonian liquid: for a slurry or a viscous liquid, follow the manufacturer's curve.
NPSH formula, pump power and affinity laws
Three calculations: the hydraulic power Ph = ρ·g·Q·H and the shaft power from the efficiency; the NPSH available at the suction and its margin over the manufacturer's NPSH required; and the affinity laws, which give flow, head and power when the speed changes, for example on a variable speed drive.
Formula · Reference documents
Ph = ρ·g·Q·H ; Pa = Ph/η ; NPSHa = (p − pv)/(ρ·g) + z − losses ; Q2/Q1 = n2/n1, H2/H1 = (n2/n1)², P2/P1 = (n2/n1)³
Fluid mechanics ; KSB, centrifugal pump design (0.5 m margin) ; IAPWS (pv)
Inputs and accepted ranges
| Input | Unit | Accepted range | Example |
|---|---|---|---|
| Calculation | 3 options | Power | |
| Flowif Calculation: Power, Speed change | m³/h | 0.001 to 100,000 | 50 m³/h |
| Head Hif Calculation: Power, Speed change | m | 0.01 to 5,000 | 30 m |
| Liquid densityif Calculation: Power, NPSH available | kg/m³ | 500 to 2,000 | 998.2 kg/m³ |
| Pump efficiency ηif Calculation: Power | 0.01 to 1 | 0.7 | |
| Water temperatureif Calculation: NPSH available | °C | 0 to 100 | |
| Pressure on the liquid surfaceif Calculation: NPSH available | bar | 0.01 to 50 | |
| Liquid level z (+ flooded, - suction lift)if Calculation: NPSH available | m | -15 to 100 | |
| Suction lossesif Calculation: NPSH available | m | 0 to 50 | |
| NPSH required (manufacturer)if Calculation: NPSH available | m | 0 to 50 | Optional |
| Current shaft powerif Calculation: Speed change | kW | 0.001 to 100,000 | |
| Current speedif Calculation: Speed change | rpm | 1 to 100,000 | |
| New speedif Calculation: Speed change | rpm | 1 to 100,000 |
Calculated results
- Hydraulic power PhkW
- Shaft powerkW
- NPSH availablem
- NPSH marginm
- New flowm³/h
- New headm
- New powerkW
- Vapour pressurePa
What the calculator flags
- NPSH margin below 0.5 m: risk of cavitation.
- Newtonian liquid assumed; for slurry or viscous liquid, use the manufacturer's curve.
Pump breakdowns and their causes kept per pump
- Breakdowns reported by QR code
- Work orders on the phone, even without a network
- Mandatory inspections reminded by email
- Audit file as a PDF, in one click
Free during the beta, no credit card