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Thread: Pressure relief valve just above main shut-off

  1. #1

    Default Pressure relief valve just above main shut-off

    I'd like to replace my main shut-off valve, but there is a leaky pressure relief valve soldered just above it -- do I need to replace that as well? What is the purpose of the pressure relief valve? Is it for draining the house? I can drain the house easily using a hose bib connected just above the relief valve. Where can I find local plumbing codes? Web/city hall?

    The relief valve is just like the one with my water heater. The label says: "Glauber Model RL-P, ANS Z21.22 Valve, 150psi, for max heater input 200,000 btu/hour thermal exp." My house is 30 years old and it looks like the original plumbing. Other houses in my mid-70s neighborhood have the same set-up.

    Thanks a ton!
    Mike

  2. #2
    Master Plumber master plumber mark's Avatar
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    Talking pressure relief

    If you have a fairley newer water heater that has its own pressure relief
    valve screwed into the side of the tank,
    its probably jsut an old one that was left in the
    line from an earlier or original water heater in the house...

    you are probably fine to jsut cut it all out and re-do the
    stop..

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    A pressure relief valve basically makes the house plumbing a closed system - this means that once water gets into the system, it can't back out through the pipes back out into the street. It also limits the supplied water pressure when you open a valve. This is fine, but water expands and contracts with heat and cold. So, when you use hot water out of the heater, replacing it with denser cold water, when that gets heated up again, it expands and there is no place for it to go. The pressure relief valve opens to bring the water pressure back down to where it should be.

    To account for the expanding/contracting of the water, and to keep the maximum pressure down, you may need to add or replace (if it is already there) an expansion tank. This has an air bladder in it so that when the water is heated and expands, there is someplace for it to go.

    If you have one, it probably isn't working anymore. this usually means that the rubber bladder in it is shot. Check if you have one, and if not, then install one. Fairly easy to do. that will probably stop the leaking from the pressure relief valve, but it could be shot as well depending on its age and use.
    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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    Plumber plumber1's Avatar
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    Default relief valve

    "leaky pressure relief valve soldered just above it "

    Wouldn't think that it is soldered.

  5. #5
    Forum Admin, Expert Plumber Terry's Avatar
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    Default

    Mikew,
    You don't mention what city you are in, but I would guess Bellevue Washington.

    The Bellevue plumbing inspector at that time required a pressure relief on the incoming cold water.

    If you have a T&P on the water heater, then you can leave out the one near the shutoff.

    If you don't have a T&P on the water heater, you will can replace the leaking T&P with a new one.

    Do check the water heater, many of those homes didn't have one on the water heater.
    The city is now quietly correcting that.

  6. #6

    Default More info re: Pressure relief valve just above main shut-off

    Thanks for the quick replies! I was hoping for an answer like Master Plumber Mark's. Just in case, here's a little more info...

    jadnashua: My electric water heater and it's pressure relief valve are much newer (1991) than the house and the original plumbing (1976). I'm pretty confident the newer heater/valve are working fine. The old main shut-off and relief valve are both faulty. I replaced a hose bib a few months ago and both went south. The main shut-off valve didn't close all the way so I had shut the water off at the street. I used the relief valve to drain the house and that's when it started leaking -- now it won't close all the way. I assume they both hadn't been exercised in years.

    plumber1: Correct... the relief valve is threaded to a fitting that is soldered to a "T" which is soldered right above the main shut-off valve. I'd prefer to replace the whole works with just a new shut-off valve.

    Does that info help?

    Regarding plumbing codes, I live in Redmond, WA. The city uses the 2003 Uniform Plumbing Code and Plumbing Standards and I can't find them on the web anywhere without paying $60. Anybody know where I can download them?

    Thanks again.

  7. #7

    Default Thanks -- I got the answer.

    It looks like Terry's post came in while I was typing my "more info" post. I feel confident now I can just leave out the relief valve. Thanks again!

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default relief valve

    Just to correct a previous answer, a relief valve does not create a closed system, but if you do have a closed system the relief valve is there to relieve any excess pressure build up.

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    Whoops, I saw PRV in there, and substituted relief valve...

    Note, though, that if you DO have a PRV, you need an expansion tank...regardless of where your T&P valve is (best on the WH).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  10. #10

    Default

    .....on top of the heater? like in the top part of a tee on the cold side?......If so, I don't think it's a releif valve you're seeing, but a vacuum breaker, and they're required in some places to prevent back flow.
    Perrycat

  11. #11

    Default

    My bad, I heard Pressure relief valve, and I thought water heater, on re reading you said water....MAIN....sorry. But some mains have to have a double check valve, I just still don't see the point of a relief valve on a water main. A check valve yeah, but not a relief valve.
    Perrycat...feeling really dumb

  12. #12
    DIY Member brianj's Avatar
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    Would you guys recommend putting in a check valve and expansion tank? My current setup doesn't have it. I have a pressure relief on the tankless WH though.

    The water meter is inside the house, so would it act like a check valve? I don't think they'd let them spin backwards

  13. #13
    In the Trades Bob NH's Avatar
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    Default

    The water meter will spin backwards and will not act like a check valve.

    Don't put in a Pressure REDUCING Valve if you don't need it. If you don't have it, you probably don't need it. If you put one in, the losses through the un-needed valve will further reduce the pressure in your house. If you do put one in, then you would need to add an expansion tank designed for potable water.

    You can just put a plug in the fitting where you remove the Temp/Pressure valve. Or you can put a boiler drain in that fitting to drain the system if you ever need to do so. Or you can put a reducer in that fitting and add a pressure gauge.

  14. #14
    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Default

    Quote Originally Posted by brianj
    The water meter is inside the house, so would it act like a check valve? I don't think they'd let them spin backwards
    They do. When I drain my house via the stop and waste valve before the meter, it runs backwards. One could hook up a small pump between the waste valve and the sink and pump the meter backwards...just like taking miles off the car

    Jason

  15. #15

    Default

    [QUOTE=brianj]Would you guys recommend putting in a check valve and expansion tank?
    ------------------------
    at the risk of sticking my foot in my mouth again, about check valves, I think you're missing the purpose, check valves aren't for YOUR safety....at least not directly, but for the city's safety. In case your house somehow gets contaminated. And an expansion tank wouldn't even be needed, if there weren't check valves. The water would just get hotter, and expand and as it expanded, push it'self back towards the meter, and past it. The check valves are just that the water authority doesn't want your water back after you've "touched" it so to speak.
    Now, I really might be wrong here, but if you don't have a check valve now, and you're not doing anything building wise that you have to bring it up to present day code, you don't need one. You're "grand fathered" in so to speak. I think the code reads that existing work is considered accepted.

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