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Water Pressure Spike

We recently install a new PRV and checked it with a gauge by placing it after the PRV. The gauge is reading 58 psi with a spike of 120. Do we need to be worried about the spike? The 58 psi is without any water running.

Re: Water Pressure Spike

When do you see this 120# spike?

Is it perhaps a little while after running some hot water? (As in.....after you've used enough hot water to cause the water heater to kick in.)

Re: Water Pressure Spike

You should not get any kind of spike with a properly installed PRV. That is what is does. Pressure Reducing Valve. 58 psi is ok. But, 120 psi is crazy. Also, the guage should be installed in the line, so as you turn up or down the PRV you can see what pressure you are getting (have the water running through). Process of elimination. Good luck.

Re: Water Pressure Spike

Pressure spikes of 120 psi are not at all uncommon after installing a PRV...........*if* a PRV was installed which does not have a high pressure bypass to relieve back into the city water line....or if the city has a check valve on their side that prohibits backfeeding.

When hot water is used, it is replaced with cold water.....and eventually the WH kicks in. The cold water in the WH tank is then heated.....and expands. If that expanding water does not have an escape route (all water usage has ceased and relief back into the city supply is prohibited)..... the line pressure increases. This is what expansion tanks are for.

If the increased pressure from heating the water gets high enough ....it will/should theoretically relieve itself (to some degree) from the T&P valve on the WH..............*if* the T&P is working properly. I'd recommend installing an expansion tank instead.

Re: Water Pressure Spike

Hi.  I saw this kind of behavior on my system.  We're on a community well, and I don't have a PRV.  I decided to test the pressure because my wife wants me to install a reverse osmosis filter faucet in the kitchen, and I didn't know what my pressure was.  Normal static pressure is 55 - 60 psi.  IFirst night I left a pressure guage connected, I saw spikes from 90 to 120 psi.  I suspected water hammer, because we have a 30-foot run of 3/4" pipe.  To test this theory, I ran the bathtub full blast and shut it off quickly -- it created a spike of 170 psi.  I am going to try installing water hammer arrestors at the ends of both cold and hot water runs, and see if that improves things.  I was thinking maybe this is what you are seeing, too?  Good luck.

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