Water pressure comes out of the faucets normal than drops to what seems 1/2 the flow. I put a pressure test on the outside faucet and when I turn it on, it jumps between 60-70. After that it slowly drops down to 30-35. We just changed the pressure reducing valve. The faucet is the first water connection from the main line about 10 ft. Any suggestions?

  • 1
    Welcome. You should revise to tell us about your water source and why you needed a reducing valve, plus the type and age of your plumbing. There's not much information up there.
    – isherwood
    Aug 18, 2020 at 13:08
  • I am on city water. I had a break in the line just after the meter and a plumber fixed. Had no water when done so he replaced the PRV. Since than, water starts good but in a couple seconds drops to about 1/2 the flow.
    – Jeff
    Aug 19, 2020 at 11:55

2 Answers 2


A suggestion to keep a pressure reducing valve from causing low flow is how I see this as a question.

The problem sounds like your valve is rated for a lower flow rate than you want. An example of this you could install a 1/4” valve with no flow you measure 60-70 psi just as you do now. Opening the valve relives the pressure on the system and once any tanks like your water heater and the plumbing are equalized you have the flow at the maximum rate the valve can supply.

With a 1/4” orifice the valve is restricting the flow thus the pressure drops I have seen this with city water systems where the owner just grabbed a 1” PRV and did not realize it had 1/4” orifices and their sprinklers would not work on the low flow. I replaced the valve with a PRV rated at 20 gallons a minute (the city max delivery rate) and the problem was solved.

So your valve internal orifices are two small in my case I actually had to get an 1-1/4 PRV to get the 20 GPM valve it was a bit more expensive but they never saw the drastic drop in water pressure after that and they used 60 psi as that was the max recommendation on some of the components in their system they said it worked better than it used to probably because the original valve had smaller orifices than the valve I used therefore more restrictions.


Just to start off. Flow and pressure are 2 different things. TONS of water flow can be quickly lost in 10 feet of line if there are lots of bends and connections. The most direct route with as few as bends as possible has the least friction loss which results in more flow. Pex crimp connections also cause more friction loss than copper or Sharkbite push connections because PEX crimp connections slide inside the pex pipe instead of outside the pipe.

Is the main line 3/4” or is it 1/2” ? I suspect you have 1/2” with a bunch of connections.

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