constant jack-hammering when hot water runs -- sometimes

[scooterhanson]

Once a day, every few days, when the hot tap is turned on in the bath (doesn't happen with shower, sinks, dishwasher, etc.. I think it needs a higher flow to trigger), there is a loud and worrying jack-hammering around the pressure reducer valve.

I have a pressure gauge installed inline just after the valve & meter, and the pressure oscillates quickly by about 20psi.

When the water is turned off for a second and then back on, it's fine.

It's not a constant problem and might only happen once in a week, so it's hard to say what other factors are at play.

The only thing that had changed prior to the start of this was that I installed a new expansion tank, but since I have the pressure gauge inline at the inlet I am pretty confident that the exp tank pressure matches the street pressure.

It's not an issue with a loose pipe. Since it's such a dramatic pulse, it's hard to pinpoint exactly where it is but if I had to guess I would point a finger at the pressure reducer valve.

Any thoughts? Could this be a faulty PR valve?
Thanks!

 

[garry26]

I'm not a plumber or even a handyman so I can offer no insight. However,....

This has happened to me as well. It's an old old apartment building and the owner is a borderline slumlord. You describe it as a jack-hammering sound. I describe it like someone took a hammer to the pipes and hit them repeatedly. One hot water pipe outside the wall (again, old building) shakes violently when this happens.

Every time this happens, you will hear the landlord screwing around in the basement with a couple of undocumented day laborers. The pipe shaking and hammering will continue for a few days and then stop. It happens every 5-7 months.

 

[thedrainguy]

Bahaha.. Undocumented day laborers... To funny!


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[jigs-n-fixtures]

Try putting a restriction on the feed to the expansion tank. This will make it into a surge suppressor. Adding or changing the tank has changed the system harmonics.

I'm thinking that the prv and new tank are bouncing off each other. The the sudden high flow is causing the pressure to drop on the discharge side of the prv. The pressure wave is then coming back up and slamming the prv closed, dropping the pressure and starting the cycle again.


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[scooterhanson]

Try putting a restriction on the feed to the expansion tank.

What exactly should I be looking for as a restriction? Is there a fitting that would do this?

Thanks

 

[tim666]

If this is a 2 handled faucet, shut the water off and remove the hot side cartridge, replace if possible or tighten the washer down. A loose washer in the cartridge will vibrate as the water passes by creating water hammer by quickly opening and closing



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