Pump NPSH (Net Positive Suction Head) Calculator & Cavitation Check

Pump NPSH (Net Positive Suction Head) Calculator & Cavitation Check | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Math & Numbers
Input types: number, select
Output type: json
Sample coverage: 4
API ready: Yes

Overview

Calculate a pump’s available Net Positive Suction Head (NPSH_a) from absolute surface pressure, vapor pressure, static head, friction loss, liquid density, and gravity, then compare it with the pump’s required NPSH (NPSH_r) to assess cavitation risk.

When to use

Check whether a pump has enough suction head for a selected operating condition.
Compare calculated NPSH_a with NPSH_r from a pump curve.
Evaluate how suction lift, vapor pressure, or friction loss affects cavitation margin.

How it works

1Enter absolute surface pressure and absolute vapor pressure, selecting Pa, kPa, bar, atm, or psi.
2Provide static head, where a positive value represents flooded suction and a negative value represents suction lift.
3Enter suction-line friction loss, liquid density, gravity, and optionally the pump’s required NPSH.
4The calculator returns NPSH_a, margin, ratio, and a classification of safe, marginal, or cavitation likely when NPSH_r is provided.

Use cases

Pump selection and preliminary hydraulic design for centrifugal pump systems.
Suction-piping checks for flooded tanks and suction-lift arrangements.
Troubleshooting cavitation risk by testing pressure, temperature-related vapor pressure, elevation, and friction-loss changes.

Examples

1. Open tank with flooded suction

Pump engineer

Background

A water pump draws from an open tank with the liquid surface 2 m above the pump centerline.

Problem

Verify that the available NPSH exceeds the pump’s required NPSH.

How to use

Enter surface pressure as 1 atm, vapor pressure as 2.34 kPa, static head as 2 m, friction loss as 0.5 m, density as 1000 kg/m³, gravity as 9.81 m/s², and NPSH_r as 3 m.

Pressure units: atm and kPa; head units: m; density unit: kg/m³.

Outcome

NPSH_a is approximately 11.5902 m, with an 8.5902 m margin and a safe classification.

2. Pump with suction lift

Fluid systems designer

Background

A pump draws water from a source located 3 m below the pump, and the suction line has 0.8 m of friction loss.

Problem

Check whether the suction-lift arrangement provides sufficient NPSH for the pump.

How to use

Enter surface pressure as 1 atm, vapor pressure as 2.34 kPa, static head as -3 m, friction loss as 0.8 m, density as 1000 kg/m³, gravity as 9.81 m/s², and NPSH_r as 2.5 m.

FAQ

What is the NPSH_a formula?

NPSH_a = (p_surface_abs - p_vapor) / (ρ·g) + H_static - h_friction.

Should surface and vapor pressure be absolute?

Yes. Both surface pressure and vapor pressure must be entered as absolute pressures.

How do I enter suction lift?

Enter static head as a negative value when the liquid level is below the pump centerline.

What does the margin represent?

Margin is NPSH_a - NPSH_r. A positive margin means available NPSH exceeds the required value.

What happens if NPSH_r is zero?

The calculator reports NPSH_a only and skips the cavitation comparison.

Pressure units: atm and kPa; head units: m; density unit: kg/m³.

Run this tool

Examples that match this tool

Continue with connected tools and hubs

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Open tank with flooded suction

2. Pump with suction lift

FAQ

Web Image Processing Python Samples

Android Image Processing Java Samples

Android Image Processing Kotlin Samples

macOS Image Processing Objective-C Samples

Density Calculator (ρ = m/V)

Minimum Spanning Tree (Kruskal / Prim)

AHU Coil Capacity Calculator (Cooling / Heating)

Bulk Density & Porosity Calculator