Dripping thermal expansion relief value

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by psyq, Oct 22, 2013.

  1. MACPLUMB 777

    MACPLUMB 777 TROJAN WORLDWIDE SALES RP

    Messages:
    679
    Location:
    Houston, Texas, United States
    you are all missing the point !
    This is the correct answer that is a ball valve to shut the water off and a combination thermal expansion relief valve that opens at 80 psi
    to relief excess water pressure and yes it is doing exactly what it is designed for ! ! And it also wastes water !
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    No, I don't think we all are missing the point...this was already discussed. But, the better solution is an expansion tank - and maybe a PRV, if the supply pressure is also high, then the thing, if you left it there, should never open except if the other things fail.
  3. Jerome2877

    Jerome2877 In the Trades

    Messages:
    397
    Location:
    BC
    :) Thanks Gary but I think your the one that needs things cleared up. Like I said the valve is designed for thermal expansion relief and instead of a bladder tank it just drains off to accomplish this. While I agree that an expansion tank is a better solution, the valve (like Macplumb agreed) is doing its job!
  4. Jerome2877

    Jerome2877 In the Trades

    Messages:
    397
    Location:
    BC
    Nope, the point your missing is the fact that thermal expansion accommodation was provided and the leaking valve you say starts to leak with age is designed to leak and is doing its job.
  5. Reach4

    Reach4 Active Member

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    1,932
    Location:
    IL
    You seem to have missed the "even if the pressure isn't too high" bit.
  6. Jerome2877

    Jerome2877 In the Trades

    Messages:
    397
    Location:
    BC

    No, he was stating that the leaking valve was "an indication that the house pressure was too high OR there was no accommodation for expansion". I am saying that in fact that valve is the "accommodation for expansion"

    The valve like anything mechanical could fail and start to leak when its not supposed to but I don't see where I am missing anything here?
  7. Gary Swart

    Gary Swart In the Trades

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    In my opinion, you had Rube Goldberg do the plumbing.
  8. DonL

    DonL Jack of all trades

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    3,817
    Location:
    Houston, TX
    Most of the safety valves I have played with are not made for Cyclic operation. Some do not even auto-reset.

    You can build a old school expansion / hammer Protector - Tester with a dead ended piece of pipe.


    A Expansion tank is the best solution, If the problem is do to heating water.
    Last edited: Oct 24, 2013
  9. psyq

    psyq New Member

    Messages:
    8
    Location:
    Vancouver, BC
    Home Depot was actual sold out on all their pressure gauges. I'll see if I can find one today somewhere else.

    I did consider a DIY gauge from assorted fittings... but, nah
  10. Jerome2877

    Jerome2877 In the Trades

    Messages:
    397
    Location:
    BC
    You find this valve that complex? lol
  11. Terry

    Terry Administrator Staff Member

    Messages:
    14,801
    Location:
    Bothell, Washington
    Ballvalve loved those pressure releasing valves that needed drains.
    He didn't like the expansion tanks. I would rather install an expansion tank, and not worry about where to drain the "pop off" water.

    But if the vavle is releasing too often, I would look at house pressure first. It may be too high.
  12. wjcandee

    wjcandee Wise One

    Messages:
    1,771
    Location:
    New York, NY
    Like this (and other photos and videos out there show that this is no joke): [video=youtube;bVf6naulS1s]http://www.youtube.com/watch?v=bVf6naulS1s[/video]
  13. psyq

    psyq New Member

    Messages:
    8
    Location:
    Vancouver, BC
    Got the reading. Holding steady at 70psi
  14. Wrenched

    Wrenched In the Trades

    Messages:
    5
    Location:
    Vancouver, BC
    To meet code in Vancouver, auxillary thermal expansion relief valves have to dump at 80psi or less. The tag on the valve will tell you what the factory set point is.

    When a residential tank is heating from cold a valve can dump as much as a cup of water, but usually it's less than that.

    A steady drip or stream when the tank is not heating can be a sign of valve failure -if- the system pressure is below relief point.

    Typically plumbers here will set house pressure at 60psi - a system pressure above that means either someone cranked the PRV, or the PRV isn't regulating properly.
  15. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Most descriptions of the PRV's I've had mentioned a bypass feature that was designed to allow excess downstream pressure to bleed back through the device. Since expansion tanks are de rigueur in a system with a PRV, does that mean that the bypass feature of PRV isn't really being counted on to accomplish anything?
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    The bypass, if it exists, can only open if the house pressure exceeds the incoming pressure. The goal is to keep the house pressure fairly constant, which is typically the reason a PRV is installed in the first place. That entails an expansion tank unless you want to deal with dumping water periodically along with the periodic rise in pressure.

    One poster here recently said his incoming water pressure was peaking at something like 190. At that pressure, before the PRV would ever open the bypass, the WH's T&P would have relieved the pressure or something else would have leaked or busted.

    Certainly, a pressure relief valve can keep the pressure from maxing out, but if anything, I think the preference is to keep it steadier, and not have to deal with periodic dumping of water. With a PRV and no expansion tank, it is not uncommon at all to have a weeping T&P valve.
  17. psyq

    psyq New Member

    Messages:
    8
    Location:
    Vancouver, BC
    The thermal expansion relief valve is made by Apollo and has a rating of 80psi. Since my pressure is WAY below that I should probably look at either replacing that valve, or buying an expansion tank. Thanks everyone, huge help!
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,824
    Location:
    New England
    A closed system can easily get high enough to cause the T&P valve to open (at 150psi) unless there's some other path to relieve the pressure from thermal expansion. Fluids like water do not compress to any significant amount like a gas does...expansion correlates directly with raising the pressure in a closed, primarily rigid system. The expansion tank, containing air, provides an easy place for that water to be accommodated. To keep from dripping through that valve, install an expansion tank. You can keep that valve or take it out if you want...if you did keep it, it would act as a secondary backup. Some people like the redundancy, but it is not required. Without it or an expansion tank, your T&P valve would be weeping each time the WH ran after you shut the hot water tap off. How much would depend on the aquastat setting and how much and at what temperature the incoming cold water was. Say you were to raise 1 gallon of water from 12C to 60C, you'd have about 1.32oz or almost 40ml of expansion http://www.engineeringtoolbox.com/volumetric-temperature-expansion-d_315.html Dealing with that is typically a nuisance, especially when an expansion tank takes care of it nicely with no leaks.
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