Loud water knocking from pressure reducing valve

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Sohcrates, Nov 10, 2021.

  1. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Retired Systems engineer for defense industry.
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    New England
    Does the house pressure change when you change the PRV adjustments? If it say rose from 40psi to 55 as you adjusted, but didn't go further, it may be okay...but if it was at 55 when you started, and didn't change, then either the supply is at 55, or the prv is bad. Sometimes, it nice to have a pressure gauge, or a port where you can check it, both before and after the PRV.
     
  2. Jeff H Young

    Jeff H Young In the Trades

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    Definitely good to have a spot that's not on the regulator to check, he might have 55 psi coming in or it could be more impossible to know the pressure based on provided info.
     
  3. Sohcrates

    Sohcrates New Member

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    So I still get the occasional knocking. I just tried adjusting the PRV down (instead of up) and it doesn't really change anything. Still hovering around 50-55psi. That alone seems to tell me that it may indeed be a bad PRV at this point.

    Does anyone know if it matters what "type" of PRV I replace it with? I currently have a Watts setup but there seem to be many alternatives out there.
     
  4. Jeff H Young

    Jeff H Young In the Trades

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    I dont think it matters as long as it can supply needed volume. I use watts brand and zurn/wilkins. i guess you never determined the water pressure or if you need a regulator?
     
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  5. Bannerman

    Bannerman Well-Known Member

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    When reducing the pressure setting on a PRV, a downstream faucet will need to be open slightly so as to relieve the initial higher pressure after the PRV. When there is no water being drained downstream, the pressure after the PRV will not usually change regardless of how much the pressure is being lowered.
     
  6. Bannerman

    Bannerman Well-Known Member

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    To assist to determine the source of the sound, use a long screwdriver equipped with a hard handle (not rubber covered). Use the screwdriver as a makeshift stethoscope by holding the tip firmly against the suspected source of the sound (PRV, water meter, water heater TPRV or other device). Place your ear against the handle to attempt to determine where the sound will be sharpest and most intense.

    If the water pressure from the city is less than 80 psi, a PRV should not be needed, but perhaps your home is located nearby to a pumping station which may cause the mains pressure in your area to exceed 80 psi whenever that pump is operating.
     
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  7. Jeff H Young

    Jeff H Young In the Trades

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    Tried telling him to check pressure if you don't know what's incoming you can't know if regulator is needed or doing anything
     
  8. Sohcrates

    Sohcrates New Member

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    I am planning to replace the PRV and before I do that I have an adapter to check the water pressure from the city I will install. Planning to do this before the holidays. Will also check with the "stethoscope" to verify where sound is coming from.
     
    Jeff H Young likes this.
  9. Reach4

    Reach4 Well-Known Member

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    Location:
    IL
    I would ask the water department if they expect that you need a PRV. Also consider talking to a neighbor or two if they have any knowledge of the local conditions.

    But yes, a way to measure pressure before the PRV is good. I would not like to have a PRV if the pressure from the street is only 55 or 60.
     
  10. Jeff H Young

    Jeff H Young In the Trades

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    We have no idea what the max pressure to the house is only that where and when he checks it, it as least 55 but whether it rises in off times low demand who knows ? We can only repeat these obvious things to the OP and hope he gets it.
     
  11. Bannerman

    Bannerman Well-Known Member

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    Location:
    Ontario, Canada
    The 200 psi gauge example linked to below, includes a 'maximum pressure' pointer which will indicate the maximum pressure sustained since the pointer was last reset manually. The garden hose adaptor fitting maybe removed so as to thread the guage to an alternate fitting before the PRV.

    https://www.amazon.com/Watts-0950200-Water-Pressure-Gauge/dp/B000YMU8JC/ref=sr_1_6?crid=140LRMJ21UPVI&keywords=water+pressure+gauge+with+max+pointer&qid=1638376435&sprefix=Water+pressure+gauge+with+,aps,341&sr=8-6&th=1
     
    Last edited: Dec 1, 2021 at 8:42 AM
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