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Thread: Leaking copper union

  1. #1
    DIY Junior Member MrsTiki's Avatar
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    Question Leaking copper union

    Vertical installation, we have a tiny leak at the union.

    Should we pull it out and steel wool the surfaces? I don't think Teflon tape would help the threads...the leak isn't there.

    Anything we can do to help these surfaces be happy?

    Thanks in advance.

    Denise

  2. #2
    In the Trades Gary Swart's Avatar
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    About the only reasons a union will leak is it has not aligned internally or if there is a flaw on one of the surfaces. The two ends must be straight with each other when it is tightened. You should be able to tighten it by hand almost completely. A wrench just finishes the job. The actual seal is made by the two union surfaces coming together, so no tape or sealant is used on the threads.

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Put pipe compound, not tape, on the mating surfaces and TIGHTEN it with two, or three, wrenches. You will NEVER get a copper union to "seal" hand tight, or even by "slightly" tightening it.
    Licensed residential and commercial plumber

  4. #4
    DIY Junior Member MrsTiki's Avatar
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    Quote Originally Posted by hj View Post
    Put pipe compound, not tape, on the mating surfaces and TIGHTEN it with two, or three, wrenches. You will NEVER get a copper union to "seal" hand tight, or even by "slightly" tightening it.
    I'll try that. It's pretty darn straight on, but perhaps some pipe compound and re-seating it will do the trick. Fingers are crossed!

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Unless the union is connecting steel pipes, tightening the nut SECURELY will correct any slight misalignment.
    Licensed residential and commercial plumber

  6. #6
    DIY Senior Member Hairyhosebib's Avatar
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    I will try to describe what I do to "SEAT" a union. It is best to have a pipe wrench for this. It is a good idea to lubricate all contact areas of the union with a silicone food grade lube.

    1. Put the union together and get the colar good and snug.

    2. Give the colar a good rap or two with a wrench.

    3. Size the pipe wrench so that it catches the outer edge of the colar and with some kind of back up wrench tighten it till it stops leaking.

    Sizing the wrench so that it catches on the flat surface will cause the colar to become out of round and cause it to seize thus working against yourself. This is a great way to get one apart as well. You will be amazed at how much tighter you wil get it. I have showed this trick to experienced plumbers and they tell me how smart I am. This is a trick I learned from the old timer steam fitters when I worked at Purdue University. I started my plumbing experience there in 1978. Now I work at ASU.

    Greg

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