What is Water Hammer and How to Prevent It

prevent water hammer

Water hammer and its effects

What is water hammer? If you’ve ever heard a loud bang when your washing machine stops its filling cycle or a thumping when you turn off a faucet, you’ve heard a water hammer noise. Water hammer is a shock wave inside your pipes that results from water turning off suddenly, and the result is shaking pipes and banging noises.

Water hammer isn’t just annoying. It can cause damage to pipes, joints, connections, and fittings. If it continues for too long, you could experience water leaks or costly repairs.


The causes of water hammer

What causes water hammer? Water has flowing momentum similar to other liquids. When the flow changes, shock waves spread through the pipes. Flow changes can occur from valve operation, the starting and stopping of pumps, and directional changes caused by pipe fittings. When there are sudden changes in flow, surge pressure builds up in the water system. When you turn off a tap quickly or if you have a fast-acting solenoid valve, water will stop moving through the pipes and send a shockwave through the water. 

Check these five areas for causes of water hammer:

  • Inadequately secured pipework — New pipework is more likely to cause water hammer. Make sure your pipework is clipped, secured, and supported using appropriately sized pipe clips.
  • Ball and float valves — Ball and float valves can cause an inflow of water when the valve float is constantly opening and closing. The shock waves vibrate through the pipework causing the water hammer effect. This usually occurs when the ball and float valves are worn or have low-pressure valve nozzles when there’s a high-pressure water system.
  • Solenoid valves — Electronically operated valves can stop water flow instantaneously, which sends shock waves through the pipes and cause water hammer. Attaching a flexible water hose to your water system can absorb any shock in the pipework and prevent excess pressure from building up.
  • Worn stop valves — Water hammer can occur if the stop valves have loose gland packing or worn washer jumpers. Make sure to tighten the gland packing and replace any loose jumpers to prevent shock waves from traveling through the pipework.
  • Trapped air — Using air-relief valves that are placed at high points of the piping system will prevent air from accumulating in the system. When the terrain is relatively flat, these valves should also be placed near the middle and downstream end of the line where the pump discharges. Make sure to fill empty pipelines as slowly as possible, so entrapped air can escape.


How to prevent water hammer

There are several methods of water hammer prevention. High water pressure is the general cause of water hammer, so the first step is to check the water pressure levels in your home. If the pressure exceeds 80 psi, it may be best to install a pressure regulator on the water mainline.

Besides excessive water pressure at the main valve, water hammer can also be caused by water or debris in air chambers. If the plumbing in your home is older you may not have any air chambers installed.

If a single appliance seems to be causing your water hammer, you can install a water hammer arrestor. Arrestors will absorb the water jolt that comes from water valves closing suddenly which should stop the hammer noise from bothering you.

Lastly, it’s always important to make sure your pipes are mounted securely and fixed in place. Not properly secured pipes shake freely when water runs through them providing an ideal setting for water hammer.


Keep your home’s plumbing worry-free

If water hammer is bothering you, the first step is to call a plumbing professional. Waiting too long may lead to water leaks or expensive repairs. To make sure your home’s plumbing system is inspected each year, consider signing up for a Lee Company Home Maintenance Plan. As a member, you’ll receive annual plumbing inspections to make sure everything water-related in your home is working properly. And if you suspect water hammer is a concern, ask one of our technicians to get an answer you can trust.