Pressure relief valve just above main shut-off

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by mikew, May 31, 2006.

  1. mikew

    mikew New Member

    Messages:
    3
    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. 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..
    1 person likes this.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
    New England
    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.
    1 person likes this.
  4. plumber1

    plumber1 Plumber

    Messages:
    1,423
    Location:
    Florida
    relief valve

    "leaky pressure relief valve soldered just above it "

    Wouldn't think that it is soldered.
  5. Terry

    Terry Administrator Staff Member

    Messages:
    15,314
    Location:
    Bothell, Washington
    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. mikew

    mikew New Member

    Messages:
    3
    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. mikew

    mikew New Member

    Messages:
    3
    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. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,060
    Location:
    Cave Creek, Arizona
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,273
    Location:
    New England
    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).
  10. perrycat

    perrycat New Member

    Messages:
    39
    .....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. perrycat

    perrycat New Member

    Messages:
    39
    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 :D
  12. brianj

    brianj Member

    Messages:
    35
    Location:
    Maryland
    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 :D
  13. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    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. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

    Messages:
    1,328
    Location:
    Columbus, OH
    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. perrycat

    perrycat New Member

    Messages:
    39
  16. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,387
    Location:
    Yakima WA
    There seems to be confusion in this thread. A PRV is a Pressure Regulator which is installed in the main water supply line where it enters the house. It is used when the water supply has excess pressure. A TP is a temperature/pressure safety valve an is install on top of the water heater. Some heater maybe in the side, but they function to release excess pressure that can build up in the water heater due to over heating. They are two separate animals. A pressure regulator installed as described creates a "closed system". When the water heater kicks on and heats the water, the heated water expands and has to go somewhere. In an open system, the expansion can go right back into the city water main with no problem. In a closed system, the PRV prevents the expansion from passing in to the main. The result is that the TP valve on the water heater will trip and relieve the excess pressure. The solution is to install an expansion tank between the water heater and the PRV. Now I read the post that says that the new WATTS PRV have somehow eliminated this problem, but I know nothing of that at this time.
  17. vaplumber

    vaplumber Guest

    Lol! I have learned something now which you regular guys may want to keep in mind with me! Us older guys in this area call a pressure relief valve a prv valve, and a regulator valve a prg! I will try to keep this in mind when posting!
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