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Thread: Clear Tubing For T&P Relief Valve?

  1. #1
    DIY Senior Member molo's Avatar
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    Default Clear Tubing For T&P Relief Valve?

    Hello,
    Would it be a good idea to run clear tubing from the T&P relief valve on a hot water tank? This would allow for observation of a leak.

    Thanks,
    Bill
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

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    Forum Admin, Expert Plumber Terry's Avatar
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    The code requires piping rated for high temperatures.
    If the tubing collapses and plugs, it could be dangerous. For example, CPVC can be used, but not PVC.
    Normally we run those in copper.

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    Moderator & Master Plumber hj's Avatar
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    quote; For example, CPVC can be used,

    Here, they interpret the code requirement for a "full size drain from the relief valve to the outlet", to mean the i.d. MUST be 3/4" which precludes ALL plastics, (other than PVC which cannot handle the temperature so it is also excluded), and corrugated copper flex lines. It has to be steel or copper. And since it MUST terminate ABOVE the drain there is no problem with seeing a leak.
    Licensed residential and commercial plumber

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    DIY Senior Member bluebinky's Avatar
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    I can see the need for this if, for example, the drain terminated outside behind a hedge or somewhere you might not ever notice a small leak.

    Obviously clear plastic is out.

    What about something like a sight glass similar to what you'd find on the fuel system of an an old-fashoned engine?

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    In the Trades Gary Swart's Avatar
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    It has to be full flow. That means 3/4" inside diameter. The simplest and cheapest thing to use is 3/4" galvanized. This may be the only place galvanized still has a place. Since is it rarely has water in it, it will never rust or corrode in a significant amount and it fits the requirements. Sure, nothing at all wrong with copper, but it is overkill as far as cost is concerned. I can't visualize a leak in a T/P drain in the first place, and even if there was, it couldn't amount to more than a slight bit of moisture. This line is (a) rarely used, (b) is only for a very short period of time when it is used, (c) is never under pressure, so how can there be much water escape from it.

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    DIY Senior Member bluebinky's Avatar
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    Agreed, that done properly, the drain itself would not leak. However, a TPV can start leaking, and unless the you notice water coming out of the end of the drain (or hear it) you'd never know.

    Once possible scenario for a leaking TPV is if you have a pressure regulator and your expansion tank goes flat...


    On a side note, when I bought my place in Texas, the TP drain was done in coper, and terminated in the septic tank!

  7. #7
    In the Trades Gary Swart's Avatar
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    Yes, the T/P valve itself can leak, but that has no bearing on the type of pipe leading from it. The pipe is what I was referred to, not the valve.

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    DIY Senior Member molo's Avatar
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    The question was raised when I discovered a very slow leak from the T&P relief valve after draining the tank for cleaning and then refilling it. The tank was also moved to a different location and the tube cut so that the end was temporarily above the floor level. I would not have noticed this if the tube was going directly to a drain or into a crawl space.
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

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    Moderator & Master Plumber hj's Avatar
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    quote; The tank was also moved to a different location and the tube cut so that the end was temporarily above the floor level. I would not have noticed this if the tube was going directly to a drain

    It was SUPPOSED to be above the floor level, by code. If it was into the drain it was done improperly. It should also terminate where the end of the pipe is visible, not into a crawl space.
    Licensed residential and commercial plumber

  10. #10
    DIY Senior Member molo's Avatar
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    Quote Originally Posted by hj View Post
    quote; The tank was also moved to a different location and the tube cut so that the end was temporarily above the floor level. I would not have noticed this if the tube was going directly to a drain

    It was SUPPOSED to be above the floor level, by code. If it was into the drain it was done improperly. It should also terminate where the end of the pipe is visible, not into a crawl space.
    Does code allow water tanks allowed to be installed in bathrooms? If so an exposed T&P tube could harm someone if it went off.
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

  11. #11

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    Quote Originally Posted by molo View Post
    Does code allow water tanks allowed to be installed in bathrooms? If so an exposed T&P tube could harm someone if it went off.
    My code says terminate "OUTSIDE" 6" to 18" above the ground, I go 6". End of pipe can't be threaded. Add an expansion tank following directions. No weeping

  12. #12
    DIY Senior Member bluebinky's Avatar
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    IMHO terminating outside is better, as a drains can be overwhelmed when a TPV opens. However, that's not always easy/possible, like when the water heater is in a basement.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A T&P rarely initially fails in a full open mode...usually, there's some advanced warning there's a problem and the thing weeps some. You're more likely to notice that inside, rather than outside behind a shrub. Plus, if it weeps slowly, it's cold outside, and the run is long, it could freeze up and then you'd have a MUCH bigger problem. Now, if you lived in SCAL, where it never freezes (or very rarely), freezing isn't a big consideration, but for much of the country, it is a factor.
    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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    DIY Senior Member molo's Avatar
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    Does code require the T&P outlet to be visible for observation if installed in living space? Can it be behind a panel?
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

  15. #15

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    Quote Originally Posted by molo View Post
    does code require the t&p outlet to be visible for observation if installed in living space? Can it be behind a panel?
    " you seem intent on flooding your house,i give up ! "

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