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I live in a three-storey townhouse and have measured with a pressure gauge on an outside faucet, at the laundry machine cold water feed and on the hot water's hose-compatible drain a pressure of around 105-110 PSI. For additional context, there is a pressure reducing valve installed just after the incoming main that looks to have been put in when the house was built. When I open a faucet or flush a toilet, the pressure appears to drop to mid-20 to mid-30s PSI. Is this normal?

The reason I started looking into this is because the pressure drop is super noticeable when taking a shower and, at least until recently, I had never noticed issues when a toilet was flushed or even a dishwasher or laundry run when I was in the shower.

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  • You just had a pressure reducing valve installed? Was the 110PSI measurement after the pressure reducer or before?
    – JPhi1618
    Commented Jan 7, 2020 at 21:25
  • I updated the question to be more clear. All measurements were taken from points after the PRV, as far as I can tell. The PRV was always part of the home's setup.
    – Robert Eggers
    Commented Jan 7, 2020 at 22:20
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    110 psi is insane for a house. Literally I would be using Sched 80 steel pipe for my water pipes, like you use on compressor lines. Are you low in a hilly area? Having to serve customers 150' above you would be a sensible reason for that much pressure.
    – Harper - Reinstate Monica
    Commented Jan 8, 2020 at 0:38
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    Most valves I have installed have a recommendation of 60 psi with a 80 psi max and do not exceed 90 unless rated. Not hard to understand there is a problem.
    – Ed Beal
    Commented Jan 8, 2020 at 2:37

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It sounds like your pressure reducing valve (regulator) is not working properly. Normally the max pressure is 80 psi or less, there are several possibilities since this was not a problem in the past we will go to debris plugging the orifices. I have found that rust / scale has prevented the valve from fully closing thus you see full pressure at all times static, once there is flow the valve opens but the orifices are partly blocked so the flow is limited and the pressure falls.

Hopefully you have a shutoff valve prior to the valve / regulator turn the pressure off bleed the water pressure off and back the adjustment. now disassemble you will see several small channels and the debris are probably obvious, I put a rag over the body and turn the water on for a second to flush other small bits of crud. I clean the diaphragm and reassemble (if you can find a rebuild kit these are a good idea incase the diaphragm gets damaged) the last kit I bought was mid 20$ some are less depending on size and type. Make sure to get a potable kit since this is a source of drinking, bathing and dish washing water.

Once reassembled or possibly replaced turn the water on and increase the pressure setting to the 60-80 range (this is normal fro many homes) now when you turn on a faucet the pressure should stay at or close to your pressure setting.

The one thing I did not talk about was a ruptured diaphragm but these normally have full flow because the water bypasses the valve section through the rupture.

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