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Problem with 3/4 copper unions


 
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Steve-Maine
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PostPosted: Fri Nov 30, 2012 1:55 am    Post subject: Problem with 3/4 copper unions Reply to specific post Reply with quote

I have been running a 3/4" copper air line in my shop. I can"t seem to get the 3/4" copper unions to stop leaking. They are leaking around threads not solder joints.I bought Nico brand at HD made in USA. Would teflon tape and paste help?? Thanks for any help..
 
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Ken Macfarlane
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PostPosted: Fri Nov 30, 2012 4:57 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

The threads on a union don't hold in the pressure, they just draw the mating surfaces together. Don't put paste or tape on them. You can lube the threads to make it easier to tighten.

Open up the union, see if there are burrs on the bell or boot (right terms? the convex and concave mating surfaces). They also can't have misalignment. You need to crank them down tight for air service.

In my old shop I replaced them with straight couplers. No leaks after that, could leave the compressor valve open.
 
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showcrop
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PostPosted: Fri Nov 30, 2012 5:08 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote


I would have a problem with a union seating once in a great while. I always had silicone grease in my box so I would smear a dab on one side of the mating surface, which enabled it to seat a little better, and almost always stopped the leak.
 
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circus
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PostPosted: Fri Nov 30, 2012 7:06 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

"Would teflon tape and paste help??" Yes
 
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Mike (WA)
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PostPosted: Fri Nov 30, 2012 8:15 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

You don't really need unions with sweated copper- just "unsolder" a joint if you need to take it apart.
 
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Brian G. NY
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PostPosted: Fri Nov 30, 2012 8:43 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

Ken is correct.......I have noticed that the China made plumbing "fittings" just don"t "fit" like the old USA fittings.
 
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glennster
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PostPosted: Fri Nov 30, 2012 10:00 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

if you are going to use the airlines for spray painting, i would not use silicone. it will cause fish eyes in the paint.
 
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Steve-Maine
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PostPosted: Fri Nov 30, 2012 11:06 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

To Mike,
I should have used connectors in the beginning. Everyone of the unions leaked. I'm now in process of cutting them out. Thanks
Steve
 
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showcrop
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PostPosted: Fri Nov 30, 2012 3:45 pm    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

Mike (WA) wrote:
(quoted from post at 09:15:00 11/30/12) You don't really need unions with sweated copper- just "unsolder" a joint if you need to take it apart.


Ever work with copper?
 
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Dean Olson
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PostPosted: Sat Dec 01, 2012 6:23 am    Post subject: Re: Problem with 3/4 copper unions Reply to specific post Reply with quote

I was taught to use pipe dope on mating surfaces and threads of unions as an apprentice plumber 30 years ago. We tested all systems with air before turning water or gas on. I remember very few leaks and never a problem with unions other than not getting them tight enough. Nico or did you mean Nibco. Nibco is the preferred brand of copper fittings.
 
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