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Thread: Water pressure high? Need PRV.

  1. #1
    DIY Junior Member larrymcg's Avatar
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    Question Water pressure high? Need PRV.

    I just had a serious bout with our sewer line (maybe fixed now) but the people who did the work also did an inspection of our plumbing. They measured our water pressure at 90psi and got really agitated about that being way too high and that I needed to install a PRV, immediately! A previous reading taken a year or so ago showed 80psi. I know it varies over time so I'm thinking of getting a gauge with the extra hand that records the max.

    The house has all copper pipes installed around 1994 (probably not relevant).

    The plumber gave a pretty big quote to install a PRV in the 1" line inside the garage just after the water line enters the garage. There is a gate valve on the line just outside the garage but it is from 1994 and *almost* turns the water off. Rather than trying to fix or replace it, I thought we would just install a PRV and shutoff inside the garage in the 1" copper pipe.

    Now I'm seeing info on this forum that 90psi isn't really that bad. And if a PRV is installed, an expansion tank is also needed because the PRV has some kind of back flow prevention device in it. The plumber did not mention an expansion tank.

    Have I got this kind of right? (My experience with plumbing is that if I touch it it will leak! That is, I'm totally inexperienced).

    --Larry

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Code requires limiting in-home water pressure to no more than 80psi, and most people are fine with about 60 or even less. Yes, if you install a PRV, unless you want your WH to start releasing water after a large hot water use, you need an expansion tank. The only reason that wouldn't happen is if you have a leak somewhere to let the expanded water escape.

    High pressure is not particularly good for the supply hoses, and the seals in valves.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades Gary Swart's Avatar
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    While you are in this process, get rid of that old valve. It won't improve with age, and will probably leak sooner or later. Ditto Jim's comments.

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    DIY Junior Member larrymcg's Avatar
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    I have a recirculating pump to keep hot water available through the house (water heater at one end of house, two bathrooms at the other end).
    Does a recirculating pump add appreciably to the water pressure in the house?

    --Larry

  5. #5
    Moderator & Master Plumber hj's Avatar
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    It is merely a "transfer" device. It has absolutely no effect on the house pressure
    Licensed residential and commercial plumber

  6. #6
    DIY Junior Member larrymcg's Avatar
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    Quote Originally Posted by jadnashua View Post
    Yes, if you install a PRV, unless you want your WH to start releasing water after a large hot water use, you need an expansion tank. The only reason that wouldn't happen is if you have a leak somewhere to let the expanded water escape.
    I'm seeing PRVs which claim to have a standard bypass feature which permits the flow of water back through the valve into the main when pressures, due to thermal expansion on the outlet side of the valve, exceed the pressure in the main supply.

    Wouldn't that remove the need for an expansion tank?

    --Larry (and thanks to all for the responses!)
    Last edited by larrymcg; 02-16-2013 at 01:48 PM. Reason: minor correction

  7. #7

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    Quote Originally Posted by larrymcg View Post
    I'm seeing PRVs which claim to have a standard bypass feature which permits the flow of water back through the valve into the main when pressures, due to thermal expansion on the outlet side of the valve, exceed the pressure in the main supply.

    Wouldn't that remove the need for an expansion tank?

    --Larry (and thanks to all for the responses!)
    Most codes require the expansion tank or some form of thermal expansion control. Yes the bypass would work to relieve the pressure.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    Let's say your city water pressure is 100#. No expansion tank. WH running, pressure reaches 100# (which is over what's supposed to be in the house!), only then when it gets ABOVE what's coming into the house can water push back into the main. So, no, you need an expansion tank to prevent problems and keep the pressure at a safe, steady pressure within the house. A bypass in the PRV is not in compliance with keeping the pressure below the maximum of 80# specified by code.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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