What is an acceptable pressure drop when a faucet is opened, if the PRV is functioning correctly and all the pipes are sized right? I have a 1.25” supply transitioning to a 1” and then splitting into two 3/4” lines for the hose bibs The pressure gauge at the hose bib reads 65 psi with no water running. When I open a hose bib next to the one being monitored, the pressure drops to 40 psi. I see drops of 20-24 psi, even when if I were to open a faucet in the home instead.

Thanks for any pointers.


1 Answer 1


Well it depends on the system most pressure reducing valves or regulators are there to prevent problems on the customer side , 60-80 psi is normal and most faucets can Handel this pressure. I have seen 120 psi city pressure , without a pressure reducing valve or regulator there will be problems or earlier failures. Is it time to replace OR repair your regulator It sounds like a repair could take care of your problems for less than a replacement

  • Thanks for your comments. In my case, I was curious as to what would cause such a large pressure drop when a faucet is opened, irrespective of which one it is (even one on the hose bib right after the PRV). The pressure gauges I have report a steady 68-70 static psi (no water flow). The city supply pressure is well over a 100psi. Can a defective PRV lead to a large pressure drop when just one faucet is open while still maintaining a steady regulation with no water flow. BTW, my PRV sits on a 1.25” supply
    – Sam
    Commented Jul 30, 2020 at 15:06
  • 1
    If rust or scale get in the valve orifices that can limit the flow. The regulator can still be doing its job of holding the pressure constant. So yes obstructions that limit the flow can be the issue
    – Ed Beal
    Commented Jul 30, 2020 at 15:25
  • Thanks again. I appreciate your taking the time and effort to reply. I’ll look into replacing the PRV.
    – Sam
    Commented Jul 31, 2020 at 7:08
  • 1
    How did this work out? My reaction on reading this is that one would expect a large pressure drop under high flow and this could be absolutely normal. What is the size of the water meter? In Dallas the customer can select the size of the water meter for service from 5/8", 3/4", . . . Commented Aug 26, 2020 at 10:25
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    @jim Stewart a properly sized regulator will have very little affect on the flow. If you have a 1” main the most common size I have seen and 90 plus psi Supply with 3/4” plumbing there should be less than 3 psi drop if properly sized for the load. Most people just get a valve that fits the pipe and that is not the way to size the PRV.
    – Ed Beal
    Commented Aug 26, 2020 at 13:51

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