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Leaking Plumber's Union

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DumOleBob

04-08-2001 13:29:22




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I'm not asking for myself you understand. It's for a "friend"...

He just put in a black iron air line from his compressor. A plumber's union leaks air from it's center - seemingly no matter how tight it is! He has pulled till he thought he/it would pop, but it still leaks air. Is there supposed to be something between the two mating surfaces? Do unions just not hold air? Maybe some unions are just funky? I know they're regularly used in plumbing water lines so they must hold - it must be my friends installation? Anything he could use in place of a union? Ideas appreciated! Thanks!

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Steve

08-24-2002 20:34:23




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 Re: Leaking Plumber's Union in reply to DumOleBob, 04-08-2001 13:29:22  
try using pipe dope(pipe thread sealer) on that union (use on threads and mating surfaces) this does not act as a seal but will lubricate so that you can tighten the union completely and will also minimize scratching and scaring of mating surfaces ,reducing the chances of leaks. this is a trick known to most plumbers.



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Ken McWilliams

04-10-2001 03:39:14




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 Re: Leaking Plumber's Union in reply to DumOleBob, 04-08-2001 13:29:22  
DumbOleBob,

RTV will fix about anything. Smear some on the mating faces and on the threads. Allow the RTV to get little stiff before tightening and give it time to set up before use.

If it's an air line apply the RTV toward the outer part of the sealing area to minimize the amount of squeeze into the air line.

The RTV will stay there until you need to take it apart.

KRM



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Joe Evans

04-08-2001 20:07:10




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 Re: Leaking Plumber's Union in reply to DumOleBob, 04-08-2001 13:29:22  
Everyone has covered the possiblities; I'll summarize. Typical unions are made as sold as "GJ" or ground joint. The sealing surfaces are indeed ground for a supposed perfect seal. Once in a while you'll fine one that the QC folks missed or again, maybe the two ground mates are no longer married and an interloping half of a union found its way into your assembly. Also could be that you used a thread x thread dielectric union that would require a sealing ring or washer. Is it gone if this is the case? Just for laughs: there is a brand of forged steel unions called Catawissa that are machined so well that you can mix halves and still get a seal.

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ron

02-18-2003 16:47:19




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 Re: Re: Leaking Plumber's Union in reply to Joe Evans, 04-08-2001 20:07:10  
why don't steel to copper gas lines use dielectric unions?



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Dean

04-08-2001 16:01:05




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 Re: Leaking Plumber's Union in reply to DumOleBob, 04-08-2001 13:29:22  
Your "friend" reminds me of a guy who told me that he cut a piece of pipe 3 times and it was still too short!

Seriously, 99% of the time over-tightening will destroy the mating surface and the union will never seal. Buy a new one.



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rhudson

04-08-2001 15:56:20




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 Re: Leaking Plumber's Union in reply to DumOleBob, 04-08-2001 13:29:22  
Olebob, A few months ago i went to a pipe fitting seminar. the instructor told us that unions are fitted at the factory as a pair. not to dissasemble and random reassemble them. that leaks could occur if this happens. i had never been told this before. could this be?



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Al English

04-08-2001 15:41:54




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 Re: Leaking Plumber's Union in reply to DumOleBob, 04-08-2001 13:29:22  
Hi Bob, Not being a plumber, I'm sure someone here will be able to tell you more than what I can say. There are two kinds of unions. One is a "ground union" which has ground mating surfaces intended to seal metal to metal. The other kind is not ground, and requires a sealing ring. Is it possible you have an un-ground union and are missing the sealing ring? I once had a ground union that had no visible imperfections in the sealing surfaces but it wouldn't seal. So, that's another possibility. The guys who put the air system in my business were plumbers by trade. They insisted on using ground unions, so I assume that's the right thing to do. Good luck...Al English

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Alvin

04-08-2001 15:13:43




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 Re: Leaking Plumber's Union in reply to DumOleBob, 04-08-2001 13:29:22  
I would go and buy another one, put it in. very possible he got one that doesn't mate up,probably made on a friday afternoon. You also have to use pipe dope on threads, other wise air will leak.



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bob

04-08-2001 17:37:37




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 Re: Re: Leaking Plumber's Union in reply to Alvin, 04-08-2001 15:13:43  
both answers are correct overtighting and mismated only other thing i,v got plumbing at Menards chinese and have had it leak due to p;oorly cut threads buy anew one and bury old one



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