PRV Causing water hammer?

[Ivan Blackford]

Hi All,

I've started to experience fairly extreme water hammer when the toilet is flushed, or sometimes when the shower is used. This doesn't happen every time, but when it does, it's violent. Here are a few details/things I tried:

-Nearly all of the plumbing system is pex, with some lengths of copper at the water main, water softener, water heater
-The toilet closest (in terms of developed pipe length) most often causes the water hammer issue. The toilets furthest away almost never do it.
-The water hammer is when the toilet is filling, NOT when the toilet stops filling.
-I installed water hammer arrestors at each toilet, and no change
-I removed and cleaned the PRV, using a decalcifier (CLR) on it. It wasn't visibly blocked up or dirty.
-When I reinstalled the PRV, the water hammer persisted....I then adjusted the water pressure down, and kept testing with the toilet. I was eventually able to find a pressure that wouldn't hammer...but I still suspect I haven't solved anything, and the problem will return sometime.

Questions:
-Can a PRV suddenly fail in this way, and cause this kind of water hammer? If so, what is the mechanism by which it fails? Does the rubber in the regulator get stiff and no longer respond to the demands of the system, and hence start "hiccuping"?
-Can there be resonance at play in the system whereby sometimes a valve opening triggers resonance? If so, are there guides on how to engineer the plumbing system to counteract this? My gut instinct says that putting deadlegs in the system may help with this, if it's resonance.

Any help would be greatly appreciated!

Thanks, Ivan

 

[Reach4]

PRVs can make noise, that you might call machine gunning. Technically it is not called water hammer because water hammer is a single bang when you shut water off.

I don't know what would cause the oscillation. Put your hand on the PRV, and there is a good chance you will feel the oscillation.

Some have screens, and you could try cleaning that.

You could also try adjusting the pressure up or down to see if that lets you not have to rebuild or replace the PRV now.

 

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[Ivan Blackford]

I can feel the oscillations through the PRV....the whole plumbing system oscillates, haha.

I cleaned the screens, and as I mentioned, I tried adjusting the pressure...adjusting down (to an unknown pressure...I didn't have a pressure gauge with me) eventually resulted in a setting seems to have alleviated the problem, but I'm not sure for how long?

 

[GReynolds929]

If the toilet shut off is a multi turn valve make sure it's open all the way.

 

[Jeff H Young]

im not sure how long either but your a happy camper now. probebly the regulator is shot Time to buy a guage

 

[John Gayewski]

Betting the toilet has a multi turn stop and it either needs opened all of the way or changed to a ball valve type of stop.

You need to check the pressure to know anything about the prv.

 

[Jeff H Young]

oh yea good call the rubber washer in the angle stop can flutter some how i suppose debris might cause it but if you run other water without issue good chance itll be the stop. certain fluidmasters have a flow restrictor too and ones with a flow restrictor tend to stop that. . but angle stop and or regulator nothing wrong with checking