Pressure Measurement · Glossary

What is Water Hammer?

pressure surgePressure Measurement

Water hammer is the pressure surge created when a moving liquid is suddenly stopped, for example by fast valve closure.

Water Hammer Explained

When a valve closes quickly the liquid column stops and its momentum turns into a pressure wave travelling at the speed of sound in the pipe. Surges can be many times the operating pressure.

Water hammer damages gauges, transmitters and pipe supports. It is prevented with slower valve closure, surge vessels, air chambers and check valves with suitable dynamics.

Water Hammer Formula

Δp = ρ × a × Δv

ρ	density (kg/m³)
a	pressure wave speed (m/s), about 1000 to 1400 for water in steel pipe
Δv	velocity change (m/s)

Example: Water stopped from 2 m/s with a = 1200 m/s: Δp = 1000 × 1200 × 2 = 2.4 MPa, or 24 bar.

Calculators for Water Hammer

CalculatorWater Hammer CalculatorFree online calculator with formula and worked example.CalculatorActuator Stroke Time CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Water Hammer?

Water hammer is the pressure surge created when a moving liquid is suddenly stopped, for example by fast valve closure.

What is fast closure?

Closing in less than the wave round trip time 2L ÷ a. Then the full Joukowsky surge occurs.

Can a snubber stop water hammer?

It protects the instrument from the spike but does nothing for the pipe; fix the cause.

Learn more on the blog

Pressure transmitter installation tips

A practical guide on instrumentationblog.in with more detail on water hammer and how it is applied on real plants.

Read Full Article

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