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Thread: Black iron pipe question

  1. #1

    Default Black iron pipe question

    On my natural gas connections to my furnace and water heater, There is a tee at the connection, with a short length of pipe that is capped. I have seen this in other houses too. What is the purpose of this extra pipe? Why not just a 90 elbow?

  2. #2
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Which way is the capped pipe pointed? I'll guess... down.

  3. #3

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    Yep..pointed down. Curious what the purpose is considering a direct flexible connection is also legal.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    I'm not a plumber, gas expert, or anything, but there are a few neurons with their hands in the air saying it's for draining accumulated moisture/water out of the line. I suppose you unscrew the cap periodically, let the water out, and replace the cap.

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    In the Trades Gary Swart's Avatar
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    It's call a "drip leg", and it's function is to collect anything that might be in the line and prevent it from reaching the appliance. I don't know of anyone ever opening them, there really shouldn't be anything in them.

  6. #6

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    Thanks! I googled the subject and found that it is required by code in some areas, but in any case is a cheap safety precaution. So I will keep it when I replace my water heater.

    This leads to another question...Can black iron unions be reused, or should they be replaced once they've been opened up?

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    Moderator & Master Plumber hj's Avatar
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    Default unions

    They are malleable steel/iron, not cast iron, and are reusable.

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    DIY Senior Member ToolsRMe's Avatar
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    Quote Originally Posted by Smith333
    Thanks! I googled the subject and found that it is required by code in some areas, but in any case is a cheap safety precaution. So I will keep it when I replace my water heater.

    This leads to another question...Can black iron unions be reused, or should they be replaced once they've been opened up?
    I just went through this exercise with my inspector.

    Yes, it is required where I live and it was a terrific PITA to put it in for my gas range since it needs to be downstream of the "easily accessible "gas shutoff.

    Nonetheless, I feel much better that it's there.

    It turns out that a lot of HVAC guys are using the thin (white) teflon tape on gas pipe. THat stuff flakes off and is very light. Even the typical half-pound pressure of gas in gas pipe is enough to get the teflon stuck in the gas regulator that accompanies most (all? some?) home gas appliances. I'm guessing that good things do not happen when that happens.

    Anyone know the consequences of getting teflon or other debris in a a gas regulator?

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    Plumber jimbo's Avatar
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    White teflon tape is not approved for gas line connections.

    On all threaded pipe fittings, industry standard practice is to NOT put tape OR dope on the first 2 threads, because of the problem you mentioned.

    Obviously, any debris in a gas regulator is going to cause trouble.

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    DIY Senior Member ToolsRMe's Avatar
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    Quote Originally Posted by jimbo
    Obviously, any debris in a gas regulator is going to cause trouble.
    What kind of trouble? What does a gas regulator do?

    Sorry for the novice question.

  11. #11
    Plumber jimbo's Avatar
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    A regulator is a mechanical device with small ports, springs, and seals. Any device like this does not want debris inside. You could have a leak, high pressure, low pressure, etc.

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    DIY Senior Member ToolsRMe's Avatar
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    Quote Originally Posted by jimbo
    A regulator is a mechanical device with small ports, springs, and seals. Any device like this does not want debris inside. You could have a leak, high pressure, low pressure, etc.
    Yes ... but what does a regulator DO?

    Does it make sure that the appliance gets

    a) Gas at the right pressure?

    b) Enough gas to make proper combustion?

    (a) and (b) are related (something like voltage and amperage) but are not the same.

    So I'd still like to know what a gas regulator does.

  13. #13
    Retired Defense Industry Engineer jadnashua's Avatar
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    it limits the pressure to the burner so you don't end up with a blowtorch.
    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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    Moderator & Master Plumber hj's Avatar
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    Default regulator

    If the supply pressure is too high it reduces it to the point that the device is adjusted for. If the pressure is too low, or the pipe is not large enough, it will neither provide the correct pressure or adequate gas to the appliance. Any thing that could get on the seat of the mechanism will prevent it from working properly, because is will allow the gas to leak through even though the regulator is trying to reduce the flow.

  15. #15
    DIY Junior Member Stainedrat's Avatar
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    Quote Originally Posted by ToolsRMe
    Yes ... but what does a regulator DO?

    Does it make sure that the appliance gets

    a) Gas at the right pressure?

    b) Enough gas to make proper combustion?

    (a) and (b) are related (something like voltage and amperage) but are not the same.

    So I'd still like to know what a gas regulator does.

    REGULATOR? hmmm my "guess" is it would regulate the gas.

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