Water Hammer while the water is running

[RSpeth]

History, I had high water pressure. So high that when the water heater was heating it would begin to leak.
I tried to adjust the PRV in my home but couldn't reduce the pressure. It was over 30 years old.
So I purchased a new PRV. Cut out the old one and put in the new one.
The new PRV has the pressure set at 45psi.
The problem is that when the pressure in the house gets down to about 30psi I get this hammer until the pressure gets back up to about 40psi. I have a guage that I am watching.
You can here the PRV opening and closing. The pipes start to vibrate.
Anyway I have taken it back 3 times and tried new ones assuming that maybe I got a bad one.
I have adjusted it up to 60psi but I still get the hammer again only when water is running and the presssure gets down to about 30 psi.
Does anyone have any ideas on what else may make my PRV start to open and close when the pressure is low.
Its kind of strange because most of the time when you flush the downstairs toilet it won't happen until you open the faucet to wash you hands then the hammer start at about 2 times a second but it won't go away until the toilet stops running even if you closet he faucet.
Any help would be appreciated.
Thanks,
Ron

 

[Terry]

If you have water hammer while the toilet is running, first try opening the valve all the way. A loose rubber washer in the shutoff can flutter.
You may also look into the fill valve. Sometimes the problem is there.

 

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[RSpeth]

Sorry to maybe lead you down the wrong path. This appears to be a pressure thing. I can cause it by opening only hot water faucets in the house. When the pressure gets below 30psi then the hammer starts.

 

[Reach4]

It seems odd that you are getting only 30 PSI when you have a PRV.Maybe there has been a change in the city water system, and you could get rid of the PRV?

 

[hj]

That is often a sign that the PRV is installed backwards.

 

[FullySprinklered]

Dude. Water hammer is a noise that sounds like Boom. Shakes the house. Pressure issue noises sound more like a love-sick whale moaning. You may be assuming too much in your diagnosis, and not be quite up to speed on what the symptoms are called, and what's causing them. I can drink two tall-boys and pee 35 pounds of pressure. I think HJ might be on to something with the backward PRV install idea.

 

[RSpeth]

OK. The arrow that shows the direction of flow is in the correct direction. And OK maybe it is not called water hammer but it is the same problem sort of. The PRV shuts and backs up the water and then opens and lets the water go it sounds like chug chug chug about two maybe three chugs per second and it does shake the pipes and the house and no its not Boom but it is qute loud it is not just a moaning. I replaced the PRV because the pressure in the house was so high so I assume that the city water is at about 110 psi which is what I had before I changed the PRV.

 

[FullySprinklered]

I've also heard a PRV making a light tapping noise, but only once. A thirty pound drop when you turn on a fixture sounds like a lot. Fifteen pounds would be closer to normal hereabouts. Crank it up to 70 and see if that gets you above the chug line. Terry's probably right. Something is fluttering somewhere.

 

[hj]

I have never seen a "good" PRV drop more than psi under FULL flow. And, it is 'linear", meaning it drops continually until it reaches that level, it does NOT operate at one pressure and then suddenly drop to the lower point.

 

[RSpeth]

Well, I'm pretty upset with it. It is the sharkbite PRV from Home Depot. I turned it up to 70 PSI. It still makes noise but it is much harder to make it happen and I haven't had time to figure out at what pressure it makes the noise now or watch to see how low the pressure gets when the water is running. If it is only supposed to affect the high end not the low end maybe I have a problem with the water from the city. I thought I might go pick up a watts PRV and see if it does it also. If it fixes the problem chalk it up to lessons learned.

 

[RSpeth]

I didn't put in a different brand PRV because the one I purchased didn't have the same threads as the sharkbite. Anyway I turned it up some more then my water heater started leaking again. So I started looking into that closer and decided to test my expansion tank. Anyway the expansion tank had failed so I purchased a new expansion tank and put it in. Now the pressure gauge that I have been watching is staying down at about 75 psi and that banging is basically non existent. In fact I haven't heard it since changing the tank. The expansion tank that I had was pretty new but I guess because of the high pressure from the old bad PRV it had failed. On reason that I hadn't checked it sooner is because it w.as so new. The new one came pre-charged at 40 psi. I left it at 40 psi and it is working. So this problem appears to have been the expansion tank all along.

 

[Reach4]

Glad it is fixed. If you leave your PRV at 75, it would be best to add air to bring the precharge in the pressure tank to 75. Precharge air pressure is measured with no water pressure.