Water pressure drops, then returns to normal (pressure regulating valve issue?)

[GS_Texas]

For two weeks now, our house water pressure oddly drops briefly, then returns to normal. This started after returning from a trip (about a month of no use). Video (https://tinyurl.com/y9oybl5c)

We have city water. About 1 year ago, we called a plumber to adjust our low water pressure; the plumber adjusted the pressure regulating valve (it’s in the ground located right after mains shut off - no basement). I think we got around 60psi after the plumber and was happy.

These days, my water pressure gauge reads 60, 70, or 80 psi (checked at two exterior faucets). You could see the same drop off and return to normal in those faucets too. Video (https://tinyurl.com/y88g6q4f)

I called our city water authority (travis county, Texas), they checked and said we should have 50psi at our mains and that we are lucky to have 60psi or more.

My question is: Does this sound like a pressure regulating/reducing valve issue?

Thanks, G.S.

 

[Reach4]

If the city thinks it never supplies over 80 PSI, it could be that you would be better off removing or gutting the PRV.

Note that your thermal expansion tank should normally be empty when you are trickling water from any faucet. Knock on the tank to see if it sounds empty. If it sounds not empty, you could set the precharge air higher. If it cannot maintain that pressure, replace the tank. The precharge is always set with the water pressure at zero.

 

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[GS_Texas]

If the city thinks it never supplies over 80 PSI, it could be that you would be better off removing or gutting the PRV.

Note that your thermal expansion tank should normally be empty when you are trickling water from any faucet. Knock on the tank to see if it sounds empty. If it sounds not empty, you could set the precharge air higher. If it cannot maintain that pressure, replace the tank. The precharge is always set with the water pressure at zero.

Hi Reach4, I may not have a thermal expansion tank. I don't see it anywhere near my water heater.

 

[Reach4]

Hi Reach4, I may not have a thermal expansion tank. I don't see it anywhere near my water heater.

The symptom of not having a good thermal expansion tank when you need one is a rising pressure after using a lot of hot water, followed by a period of not using any water.

In the past, water meters did not have check (one-way) valves. There were no PRVs. But as those things get introduced, there is a need to handle the water expansion that occurs as water gets heated.

 

[GS_Texas]

So, your potential explanation, if I understand correctly, is that the water heater may have built up pressure and that pressure is pushing back on the inlet side, but the PRV is a one-way valve that doesn't permit "pressure relief" back towards city water supply. Thus, even though we are supplied with about 50psi by the city, I'm measuring 60 to 80psi in my garden faucets; that additional pressure is potentially due to the water heater? Could I shut off the supply to the water heater to troubleshoot this theory?

 

[Reach4]

Thus, even though we are supplied with about 50psi by the city, I'm measuring 60 to 80psi in my garden faucets; that additional pressure is potentially due to the water heater? Could I shut off the supply to the water heater to troubleshoot this theory?

I think so. That means you won't have hot water available during the test. Turning the WH to vacation or off mode would be another test. If the WH doesn't heat during your test, you get no thermal expansion if the indoors temperature does not rise.

You could also watch the pressure following a shower. Make sure there is no water being used while you look for the pressure rise. This includes even the ice maker. So don't use the water dispenser or ice dispenser during the test.

Another less useful test would be to dribble water from a faucet. That would allow thermal expansion water to not build pressure. However that is not a perfect test. If we imagine 100 psi before the PRV and a slightly leaky PRV, then dribbling water would overcome any PRV leakage.

What this would not explain is how the pressure would drop and then rise up while still using water. I am thinking that watching the pressure again while thinking of the possible causes may clarify things.

 

[GS_Texas]

I will test the house water supply (& pressure) with the water heater inlet valve turned off and let you know what I find; indeed, hot water would temporarily be unavailable. Later, I'll repeat, as needed, this test right after a hot shower (with all other water usage on hold).

Pressure drop & rise: If water is being used already, e.g., when commode reservoir is filling, there's no water pressure drop when using other faucets around the house.

 

[GS_Texas]

Problem still there. I just shut off the water heater inlet and made sure the valve was indeed shut by turning on a hot water faucet until the water slows to a dribble and stopped. Then, I turned on the regular cold water and the pressure drop is still there, perhaps a little more pronounced than before (but it returns to normal pressure fairly quickly).

Perhaps I could adjust the PRV pressure slightly to see whether that's the source of the issue. Could the pressure regulation be faulty (e.g., a sticky spring mechanism)? This is pure speculation from an amateur.

 

[Reach4]

Problem still there. I just shut off the water heater inlet and made sure the valve was indeed shut by turning on a hot water faucet until the water slows to a dribble and stopped. Then, I turned on the regular cold water and the pressure drop is still there, perhaps a little more pronounced than before (but it returns to normal pressure fairly quickly).

Perhaps I could adjust the PRV pressure slightly to see whether that's the source of the issue. Could the pressure regulation be faulty (e.g., a sticky spring mechanism)? This is pure speculation from an amateur.

Yes, the PRV could have a sticking mechanism.

I would dribble some water from a faucet. Watch the water pressure. Turn the pressure on the regulator higher. If the pressure gauge goes over 90, then the city is wrong about the water main pressure. If the pressure levels out at some lower level, this probably corresponds to the water main pressure.

 

[GS_Texas]

Thanks for the advice. I'll test this, probably tomorrow morning, and let you know what I find

 

[GS_Texas]

I located the pressure reducing valve (photo attached), but I have not been able to turn the adjustment screw (flat head). I was able to loosen the nut with some WD-40 (though I don't think it was in the lock position when I started). The adjustment screw felt very tight either way and has not budged yet. Perhaps I need a tool with a long handle (I think I've seen it before). Any thoughts on the tool?

 

[Reach4]

The adjustment screw felt very tight either way and has not budged yet. Perhaps I need a tool with a long handle (I think I've seen it before). Any thoughts on the tool?

Big long hollow ground screwdriver, or a drag link socket would be best.

Do not use a blade that is not big enough, and don't use a blade that somebody has sharpened.

 

[GS_Texas]

Thanks, Reach4. I can get a drag link socket. I'll give that a try.