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.
Best Answer
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.