What Is Water Hammer in a Pipe?

Water hammer can occur when the flow of water through a pipe stops suddenly.

Water moves through pipes with a certain amount of momentum, called kinetic energy. When a valve closes to stop the water's flow, the water crashes into the valve. When this happens, the water's energy is sent back through the pipe and into the plumbing system. This event, called water hammer, is accompanied by a banging noise that sounds like someone is hitting the pipes with a hammer.

Pipe Damage

The pressure caused by water hammer weakens pipes and can eventually cause them to leak or burst.

Sound

Since the sound travels so well through water pipes, the source of the sound may not be the source of the problem.

Velocity

The faster water flows through a pipe, the greater the chances are of water hammer occurring when the flow is stopped. High water pressure and flow volume can also increase the likelihood.

No Spontaneity

Water hammer does not occur naturally or spontaneously. A valve closing or other event in the plumbing system is always the cause.

Flowing Water

Noises heard in water pipes when water is flowing is not water hammer. Water hammer only occurs when water is turned off.

Progress

Many newer plumbing systems have water hammer arresters built in. A water hammer arrester is an air cushion that allows room for the energy created to dissipate when the water flow is stopped.

References

• IrrigationTutorials.com: Water Hammer and Air in Pipes
• Jim's Home Repair Stuff: Plumbing Noises