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Thread: Copper Pipe Sweating Question

  1. #1
    DIY Junior Member crosby1's Avatar
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    Default Copper Pipe Sweating Question

    i'm getting ready to install a shower rough-in valve and all associated plumbing connections.

    i need to attach a few elbows to the valve before installing it.

    question: if i sweat the elbows to the valve and then come back to sweat the pipe to the elbows, how do i prevent the 1st solder joint from breaking down and coming apart when i reheat the connections?

    thanks.

  2. #2
    Plumber Cass's Avatar
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    If you can solder some pipe to the 90s at the same time and cut it back to the right length later that will take care of the problem.

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    DIY Junior Member crosby1's Avatar
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    thanks cass,

    so really, all fittings have to be sweated both sides at the same time?

    no way to do one side of a fitting then come back to do the other without screwing up the first one?

    one more (stupid) question: when sweating a vertical fitting (like a straight connector), how does the solder go "up" into the bottom part of the connector? is it just capillary action?

    thanks again.

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    DIY Senior Member seaneys's Avatar
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    Quote Originally Posted by Cass View Post
    If you can solder some pipe to the 90s at the same time and cut it back to the right length later that will take care of the problem.
    Could you also use wet towels in a pinch? I'm curious..

    Thanks,
    Steve

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    Master Plumber Redwood's Avatar
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    Not really... I'd do both at the same time.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You really should do both sides of an elbow at the same time. If other connections are close, then a damp rag should keep the ones you've done intact. If you dry fit everything, then solder, it can work out well.
    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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    Jack of all trades frenchie's Avatar
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    Quote Originally Posted by crosby1 View Post
    when sweating a vertical fitting (like a straight connector), how does the solder go "up" into the bottom part of the connector? is it just capillary action?
    Yeah, pretty much. Solder's drawn in by the flux.

    I've never heard of anyone successfully soldering one side of an elbow, then the other.

    Sweat on a short length of pipe, then use straight couplings to connect to the roughed-in pipes.
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    I&C Engineer (mostly WWTP) Lakee911's Avatar
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    Really? I've sweated a lot of one side of connections on the bench and then brought it in the field and soldered in the other half. Elbows and 45s included.
    Then again, I don't just hang the whole contraption from the elbow while I heat is. Is that the issue?

  9. #9
    Master Plumber Redwood's Avatar
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    Any movement of the original joint could yield a cold solder joint.

  10. #10
    Jack of all trades frenchie's Avatar
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    Quote Originally Posted by Lakee911 View Post
    Really? I've sweated a lot of one side of connections on the bench and then brought it in the field and soldered in the other half. Elbows and 45s included.
    Then again, I don't just hang the whole contraption from the elbow while I heat is. Is that the issue?
    Okay, I've never heard of anyone doing it... until now!
    Master Plumber Mark:

    there is nothing better than the
    manly smell of WD 40 in the air
    while banging away on brass with a chisel and hammer...

    it smells like......victory......

    do not hit your thumb...
    __________________
    Just so everyone's clear: I'm the POODLE in the picture ("french", get it?) The hot woman is my wife.

  11. #11

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    Quote Originally Posted by frenchie View Post
    Yeah, pretty much. Solder's drawn in by the flux.

    I've never heard of anyone successfully soldering one side of an elbow, then the other.

    .

    No?

    I do it all the time,

    If you know how to work with solder and flux it can be done easily , But if you are a beginner I would advise to listen to the others

  12. #12
    Master Plumber Redwood's Avatar
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    I always do one then the other... A couple of seconds apart!

    I'd like to do them both at once but its just to hard to apply the solder to 2 joints at once... Sorry I'm not that good!

  13. #13
    DIY Member shag_fu's Avatar
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    When I solder 2 side of an elbow at dif time I always reclean and flux the unsoldered connection. Ive had no problems. I run into that situation alot with male/fem adapters. Put the first piece into the adapter, dope and tape, screw into whatever, wet towel on the joint and solder away.

  14. #14
    Plumber krow's Avatar
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    Quote Originally Posted by frenchie View Post
    I've never heard of anyone successfully soldering one side of an elbow, then the other. .
    Its more common than most people think. You may have a scenario where the one side of the 90 is right at the egde of the drywall or combustable area where you do not want to put direct flame. I find it reassuring that the joint has solder around it and you can visually see it as apposed to guessing.

    I don't recommend that inexperienced folks try this, you may end up cursing a blue streak.

  15. #15
    Jack of all trades frenchie's Avatar
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    Well, I be...

    ...learn something new every day!

    I'd have thought for sure the old joint would let go when you re-heated the fitting.
    Master Plumber Mark:

    there is nothing better than the
    manly smell of WD 40 in the air
    while banging away on brass with a chisel and hammer...

    it smells like......victory......

    do not hit your thumb...
    __________________
    Just so everyone's clear: I'm the POODLE in the picture ("french", get it?) The hot woman is my wife.

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