Hi Everyone -

Would love some help with solving water hammer. House built in 1987 with copper pipes. Moved here in 2000. At some point, long ago, water hammer developed. We installed a hot water recirculator years ago that alleviated the issue as well as provided instant warm water. Well, that device has broken and while we might replace it, we felt we should get to the bottom of the hammer before we try to sell the house (soon, we hope) and a home inspection leads to an expensive repair needed immediately.

The pipes do a fading echoing bang (3 or 4 times, about a second in between each bang) when the water at all faucets is shut off (toilets, sinks, sprinklers, dishwasher, clothes washer - everything). When the water comes on, we hear one "bang," more a of a knock really (that we can hear over the water running).

Several times, we've done the routine of turning the water off at the main, draining the pipes, flushing the toilets, turning the water back on and shutting faucets from bottom up when water runs steadily. This solves the problem but only for a very short time, last time less than an hour. We've installed water hammer arrestors at the dishwasher and the washing machine but the banging has returned. Every toilet has had its insides replaced with Korky Quiet Fills. Still have the banging.

Professional plumber says he can install an inline arrestor at the main for under $220 and says it has about a 75% chance of fixing our problem. But I am skeptical. Because the hot water recirculator stopped the hammer as long as it constantly recirculated water through the pipes, I suspect we have a water pressure issue. Can anyone offer guidance?

Thanks!

 

What is your incoming water pressure? If the recirculator fixed the problem, why not fix the recirculator. The water hammer suppressors work good for the most part, but you have a built in fix with the recirculator.

 

The water pressure is 65 PSI at the front outdoor faucet and 66 PSI at the rear outdoor faucet. We can reinstall the hot water circulator. However, a home inspector might turn it off, hear the banging and inquire. We thought it might be useful to get to the root of the problem.

 

Your pressure is fine. To get to the root of the problem, you would need to dig into the walls and fasten pipes to the structure. Installing arrestors will depend on what exposed piping you have.

 

Do you have a pressure reducing valve (PRV) in the main piping supplying the home? A failing PRV, or an incorrectly installed one, can induce hammering noises in the system.

If you do have a PRV what is the pipe size of the unit and what are the pipe sizes ahead and after it? How long are the straight sections of pipe ahead and after the PRV?

Are there any shut-off valves that are not fully open?

 

Hubby isn't entirely sure but he doesn't think we have a PRV. If we do not have one, would adding one be of any benefit?

We'll check to make sure all shut-off valves are fully open.

 

If it is truly water hammer causing the noise, it is the result of a fast closing valve. In the home, there are snap action solenoid valves that control the water to the Dishwasher, Washing machine, Ice maker, and maybe others.

Water has mass, and when water is flowing in a pipe it has inertia. The bigger the pipe or the faster the water flow, the higher the inertia.
Since water in not compressible, the moment the solenoid valve snaps shut, the piping must absorb all of the inertia (energy) of the flowing water.
This causes the piping to move, clang, etc. and sometimes break...this is water hammer.
A column of water flowing inside a pipe that is suddenly stopped will move something.
Law of Physics "For every action, there is a equal and opposite reaction".

A "Inline Arrestor" or "surge arrestor" as I call them is simply a rubber bladder full of air that is enclosed inside a steel chamber. This arrester uses the air as a cushion to absorb some, if not all of the energy of the flowing column of water. As the water valve snaps shut, the water flow is forced into the arrestor chamber (to the outside of the rubber bladder), and and compresses the air bladder.
It effectively acts as a cushion to slow the water flow to a stop.
This absorbs the energy of the moving column of water, and makes it a lot easier on the plumbing.

I would install a whole house "Surge arrestor" in the main incoming water line. It can't hurt, and will most likely help the problem greatly.

Hope this helps

 

If your water pressure is in the 65+/- range without a PRV then adding one will not help. Ace gave a detailed explanation of true water hammer and I concur with his analysis.

Shut off valves with loose internal parts CAN vibrate at certain flow rates and introduce the staccato noise many people call water hammer. Cheap "gate" (style) valves are probably the worst for this as there is nothing that can be done to them other than replacement. If it is the main shut off for the entire house it will often require a plumber or the water utility to shut off the water at the meter or street in order to change the valve. Globe type valves might be able to have the disc (washer) changed but that still entails having the water shut off prior to the valve. The best type of shut off valve to use is a ball type valve.


Sometimes you can listen near the individual valves and hear the disc vibrating. If you post a picture of your main water shut off one of us can tell you what style of valve you have and how difficult it will be to change.

 

Your answer makes a good bit of sense. We plan to have a plumber install a whole house arrestor. Do you, by any chance, have a theory about why the hammer went away when the hot water recirculator was running?

 

Theory? Not really. It might have had something to do with the water being constantly in motion with the recirculating pump running.