Solve a water hammer upstream?

[Girafdaniels]

My upstairs shower has an annoying water hammer issue when turning the water on/off “upstream” of the shower. For example, when water is turned on/off for the faucet (or toilet) in the same bathroom, the shower will “knock” right at the valve. I’ve been able to ensure that the valve itself (and supply lines) are secured, and also confirmed that there are not any air chambers installed, so I think that isolates the issue.

I could access the shower valve area itself on the backside by opening up the drywall, but right now I have open access to the supply lines in the basement. Can I add a mechanical arrestor (or something) to those supply lines to avoid working directly at the shower valve? All the accessible supplies are recently installed Pex, while the upstairs shower supplies are copper.

Thanks in advance for the good advice!

 

[Fitter30]

Water hammer arrestors or air chambers have to be installed at the device.

 

[Sponsor]

 

[Bannerman]

Check the supply pressure. Perhaps there may be a pressure regulator valve between the municipal supply and your home that requires repair or adjustment.

With a pressure-balancing shower control, the valve requires sufficient pressure at both the hot and cold inlets so as to regulate the pressure and temperature to the showerhead.

If the incoming supply pressure is too low, the valve may not regulate properly which can cause the control to chatter when attempting to compensate, which you may be interpreting as water hammer. If the incoming pressure is only marginal, flushing a toilet or operating another faucet may be reducing the pressure sufficiently to cause the shower control to chatter.

 

[Jadnashua]

The issue is, the water column in the pipe is moving. When you shut a valve, it wants to keep moving, and the kinetic energy will try to move the pipe. The hammer arrester is like an air bag. In the car, it doesn't help if the bag is behind you...you need something in front of you to soften the blow while trying to slow down, just like the water column.

The higher your water pressure, the faster the water can flow, which means more energy to try to absorb, so the first thing is to see what water pressure you have, and regulate it down if it's high.

 

[Girafdaniels]

Thanks for all the advice. The pressure was high when we moved in, so we had a regulator installed then. So, looks like I need to get to the back side of that valve and add the arrestors. The explanation of the air bags makes good sense.

Thanks again!

 

[Reach4]

My upstairs shower has an annoying water hammer issue when turning the water on/off “upstream” of the shower. For example, when water is turned on/off for the faucet (or toilet) in the same bathroom, the shower will “knock” right at the valve. I’ve been able to ensure that the valve itself (and supply lines) are secured, and also confirmed that there are not any air chambers installed, so I think that isolates the issue.

When you turn the lavatory faucet hot ON, fast or slow, do you get the knock?
When you slowly turn the lavatory faucet cold ON, do you get the knock?
When you slowly turn the tub faucet hot ON, do you get the knock?
When you slowly turn the tub faucet cold ON, do you get the knock?

Thanks for all the advice. The pressure was high when we moved in, so we had a regulator installed then. So, looks like I need to get to the back side of that valve and add the arrestors.

I don't see that will help the knock when you flush the toilet or turn on the lavatory.

Get a pressure gauge, and measure the pressure at a laundry tap or the drain for the water heater.

 

[WorthFlorida]

Don't open the walls just yet. Not everything is a water hammer, most are not but everyone has a different interpretation of what it is. This sounds exactly the same issue I had years ago. Please read this post.

https://terrylove.com/forums/index.php?threads/water-hammer-recently-in-shower.82769/#post-596947

 

[Jadnashua]

FWIW, a PRV doesn't last forever...yours could be shot, so checking the pressure is called for. As I said, the higher the pressure, the faster the water will flow, and that creates more kinetic energy that must be absorbed when you try to stop it later. You can minimize the effects when running the pipe by trying to ensure you don't have right-angle turns up against something that the pipe can bang into and to use adequate clamps/supports to keep movement in check. That's really hard to fix once things are all closed in, if that's what's causing your noises.