# 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

## Formula

$$H = \frac { a \Delta v } { g }$$

Where:

$$H$$ = 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:

$$a = \frac { H g } { \Delta v }$$

$$\Delta v = \frac { H g } { a }$$

$$g = \frac { a \Delta v } { H }$$