Water Hammer

Written by Jerry Ratzlaff. Posted in Fluid Mechanics

Water hammer occurs when a valve is suddenly opened or closed. This can creates a repeating pressure wave of the liquid in the pipe that could cause a rupture to the pipe or even damage equipment. As a liquid is traveling through the pipe at a high pressure and the valve is suddenly closed, the flow and pressure come to a sudden stop dropping both to 0. When the valve is closed slower the pressure has a chance to equal out. The resulting sound created is like a hammer, hence water hammer.

Most people are familiar with water hammer in the home when a faucet is shut off or the toilet is flushed, that's the banging or rattling sound you hear in the pipes.

  • Abbreviated as WH


\(H = \frac { a   \Delta v } { g }   \)


\(H\) = hammer (surge fluid)

\(a\) = pressure wave velocity (acceleration)

\( \Delta v\) = velocity differential

\(g\) = acceleration of gravity

\(P\) = maximum surge pressure

\(y\) = unit weight of fluid

Solve for:

\(a = \frac { H   g } { \Delta v }   \)

\( \Delta v = \frac { H   g } { a }   \)

\(g = \frac { a \Delta v } { H } \)