water pressure drop?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by djwehr, Mar 11, 2012.

  1. djwehr

    djwehr New Member

    Messages:
    7
    Location:
    Washington
    I recently replaced my PRV and it is set at 70 psi. when we open a faucet, etc the pressure drops to 40 psi is this normal or could something be wrong? prior to the old prv going bad we never noticed any drop in pressure while showering. Upon taking the old prv apart i notice a large portion of one of the rubber o-rings was missing. could this be blocking flow in our meter? not sure what to do any suggestions?
  2. kreemoweet

    kreemoweet Member

    Messages:
    377
    Location:
    Seattle. WA
    How about a little more info as to: how did you set the PRV to 70 psi? How and where are you measuring the 40 psi?
    Pressure in an open pipe (faucet open) will always go from zero at the opening to some higher value at the source.
    The greater the flow, the lower the pressure readings will be.
  3. Runs with bison

    Runs with bison Member

    Messages:
    897
    Location:
    Midwest
    It's not normal, but is a sign of a failing PRV. With my old PRV even tiny flows would drop the pressure 15-20 psi. I'm talking about setting the flow so low that water was just barely coming out of the faucet in a stream vs. a nearly continuous set of drips. If you see high DP at very low flows then it isn't a system DP problem, but something specific to the new PRV/install.

    What was the failure mode of the old PRV? Was it letting through full line pressure all the time?

    If you have your PRV model number, you can actually look up the performance curve and determine what the DP should be for the flowrate being drawn. It should be low for normal shower flowrates (unless you are running multiple 2.5 gpm shower heads.)
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