Water Pressure Spikes

[IanD]

I could do with ideas for addressing a water pressure spike problem. About 5 years ago, shortly after buying the house, I discovered the water pressure was ~80 psi, with occasional spikes to ~120; and we lacked a PRV. A plumber installed a PRV, set it at 40psi and installed an expansion tank on the electric water heater, also set to 40 psi. We've been dissatisfied with the low shower pressure for years (it's upstairs) so I finally decided to address it, but checked the water pressure as the first step. Static pressure is 40psi, but we were getting spikes up to 120psi during the evening/night. My first thought was thermal expansion due to a ruptured diaphragm on the expansion tank, but depressing the schrader valve on the tank only let out air. I then tested the pressure in the expansion tank, taking the following steps:

1. Shut off power to the water heater
2. Closed the cold water flow to the water heater
3. Opened a hot water faucet (ran dry very quickly)
4. Let some water out of the water heater to take pressure off the diaphragm in the expansion tank
5. Tested the air pressure in the expansion tank (~36psi)
6. Put the air in the expansion tank back to ~40 psi.

In short, the expansion tank seems fine.

That suggests the PRV is faulty, but we know the mains pressure was 80psi 5 years ago when we set the PRV to 40psi. It doesn't seem reasonable to think that in that time the mains pressure in the neighborhood has coincidentally been dropped to 40 psi, the PRV has failed and the 120 spikes we're getting are coming from the mains. That said, I can think of no other way we could be getting these spikes.

Lastly, my hunch is that it's related to the water heater because the spikes seem to be at night (that's when my wife and daughter drain the heater with showers and baths). Right now I'm trying to cause spikes by running the hot water for a while, shutting it off and watching the pressure gauge on an outside faucet. But, I've only seen small pressure changes.

Any thoughts would be much appreciated because I'm out of ideas.

I should also have said I'm writing from the US.

 

[KULTULZ]

Excerpt from a municipal water supply web page-

Why do pressure fluctuations in the water system exist?

The Ramona Municipal Water District (“District&#8221 has a complex water system that encompasses a 75‐square mile area. District staff is responsible for maintaining a multitude of facilities, including 20 storage tanks, 38 booster pumps, and 2 reservoirs. District facilities are equipped with over 100 control valves that regulate water flow into the general water system.

Pressure fluctuations (or “spikes&#8221 occur on a normal basis in the water system, which can increase and decrease water pressure during normal flows, valve operations, and water usage. Pressure fluctuations can increase dramatically when mechanical equipment fails, or when valves are turned on or off too quickly. Signs of high pressure can include leaky faucets or valve leakage at the toilet.

How does a fluctuation in the water system affect me? Water pressure is measured by “pounds per square inch” or “psi.” The District maintains a minimum psi of 20 at the customer’s meter. A pressure spike in the system can increase(surge) water pressure over 200 psi. Most plumbing cannot sustain this increase in pressure, and will “blow out,” causing flooding to the customer’s home, if a pressure regulator is not in place.

You can also figure that late at night/early morning, with much less use, there are pressure surges in the system(s)

ALSO- [ame=https://www.youtube.com/watch?v=MT1MTEZREQk]-Adjusting the Pre-Charge of a Thermal Expansion Tank-[/ame]

 

[IanD]

Thanks so much for taking the time to give it some thought and reply. The video gives me confidence I checked the expansion tank correctly. It's possible the PRV isn't able to handle the level of the mains surges that occur in our area.

That said, I can't help but feel it's somehow thermal expansion, given the close association between the spikes and heavy hot water usage. Last night I put the gauge on the outside faucet (40 psi), checked it again before shower/bath time, it was still 40 psi, and checked it again within a few minutes of showers/baths finishing (and before any faucets were turned on or toilets flushed or water run in any way), and it was 40 psi, but at some point in between the beginning of shower/bath time and the end, the red needle on the gauge had gone up to 120 psi. I left the gauge on overnight but when I came out this morning again it read 40 psi and there had been no movement of the red needle, that also still read 40psi. This suggests thermal expansion, but the diaphragm in the expansion tank hasn't ruptured, the pressure is set to the right level and the tank is the right size for the water heater (47 gallon heater, 2 gallon expansion tank).....

Thanks again for giving it some thought, any ideas would be appreciated.

 

[KULTULZ]

There is also a video of a PRV install (pressure reducing valve) where the installer uses permanent pressure gauges on the incoming side of the PRV and also the outlet side so as you can instantly compare both the pressure(s).

Install hose bibs on either side also and you can determine and record any pressure fluctuations (water pressure testers with tattle-tell hands) on the supply side. It will also determine either a bad or misadjusted PRV.

Forty pounds sounds a little low. Sixty should be ideal (IMO) (I am not a professional plumber).

If thermal expansion, the WH T&P Valve should spit @ 150PSI and/or 210 DEGREES F (this determined after affirmation of correct constant supply pressure).

Just a thought...

 

[IanD]

Thanks KULTULZ. I've had the point raised that 40 is a bit low from other sources too, and since I want higher pressure anyway and can see no reason it should make the spikes worse I raised it over the weekend. Since then I've had no discernible spikes and can't generate spikes with thermal expansion. Still at a loss as to why I was getting them but so far things look ok (I'll keep checking pressure for a couple of weeks to be sure). Think I'll also install a Watts Governor M80-1 to be on the safe side. Thanks again for taking the time to give me input, it's much appreciated

 

[KULTULZ]

I've had the point raised that 40 is a bit low from other sources too, and since I want higher pressure anyway and can see no reason it should make the spikes worse I raised it over the weekend.

Since then I've had no discernible spikes and can't generate spikes with thermal expansion. Still at a loss as to why I was getting them but so far things look ok (I'll keep checking pressure for a couple of weeks to be sure).

Think I'll also install a Watts Governor M80-1 to be on the safe side. Thanks again for taking the time to give me input, it's much appreciated

I wonder what caused the spikes to stop by just raising the delivery pressure? Maybe someone here can answer that.

Maybe hold off on the ballcock ($$$) as the problem may have cured itself...?

 

[KULTULZ]

I wonder what caused the spikes to stop by just raising the delivery pressure?

Maybe someone here can answer that.

CONJECTURE ON MY PART-

MAYBE there was a partial blockage/malfunction in the PRV and it was broken loose by the pressure adjustment?

 

[Mr_David]

Do you actually see the gauge hold 120 psi in the system or you only seeing the red secondary needle indicating that it high 120 sometime between the last time you looked at it.
Closing a single handle faucet or shower valve like a push off/pull on Moen, can cause a spike in the system making the red needle jump.

Just a thought.