HELP sealing copper pipe unions...

[David Rose]

I've spent the past 5 days putting together all my rigid copper pipe for my shop air. Whew! There are over 300 solder joints.

Only two (found so far) soldered leaks and they were biggies and easy to find and repair. I've found three screw connector leaks that teflon tape will not seal, but they are to aluminum (drier and regulators) and steel (blast cabinet). I will try pipe dope instead of tape tomorrow. Without the unions, I could not be redoing these easily.

But... All 8 of my unions leak seriously! The faces all look good and clean on the easily accessed ones... I have tried polishing the faces, and the seating ring appears to go all the way around. I have read that you can over tighten them. I've tried putting everything I "have" on them with 14" wrenches after trying lower pressure to tighten them. Other statements are "tighten them with 2 foot cheaters". I think I could break them that way! I have not tried pipe dope or tape on the faces, which some say "can" work.

The big compressor is here, but not wired yet, so I am charging (for leak testing) with my small one. It will drop from 100 psi to 0 in an hour or so.

Any ideas?

Thanks,

David

[Dave Richards]

The unions are compression fittings? I chase leaks on compression fittings frequently at work although I'm sure they are much smaller fittings than you're using. I always start with just a firm tightening but I don't wrench hard. Then I pressurize the line and squirt a bit of soapy water on the joint. Then I tighten it until the bubbles quit coming out. Sometimes I find that no matter how tight I go, it won't seal. I pitch the cone and try again with a new one. I haven't found a better way. Most of the time this is for those portable liquid O2 tanks which are a pain because it seems to make the aluminum parts brittle. fortunately the cones are brass and they don't seem to mind the cold.

[Rob Russell]

David,

Our plumber told me that he wouldn't use teflon tape on any threaded pneumatic connection, in case any threads of the material broke off and lodged in the air tool. He always uses pipe dope.

Rob

[Kyle Kraft]

Loctite PST pipe dope in the "toothpaste" style tube. Won't foul your system and will seal up most anything. Try a thin film on the faces of your unions and then tighten. I have never had to use cheaters on copper unions to get them to seal.

No I don't work for Loctite either

[Mike Cutler]

David.

Is this an NPT to NPT fitting? or is it a compression fitting?

If it is NPT. Take it apart, clean it and apply some thread sealant to it. The Loctite PST 580 is OK, but I would go with the Loctite hydraulic thread sealant. I don't use PST anymore at work. I use Grafoil Tape, but I don't think it is available to the public. Another good product for low pressure applications is TFE Free, by Cajon.

If they are compression fittings. replace them, all parts. Overtightening compression fittings causes a deformation of the ferrule and the seating surface. If they are brass 3/4 of a turn past fingertight should seal them. Then do what Dave suggested and leak check the fittings before tighteneing.Unfortunately the compression nut and ferrule is harder than the copper pipe. You may have to replace the section of copper pipe also. Sorry.

[Kent Fitzgerald]

I recently replaced the water pressure regulator in our home, and the union that came with the new reg had an O-ring between the mating faces. I've never seen this before, but it seems to work quite well - the input is at about 100 PSI, and it's tight. You might be able to do the same.

[Cliff Rohrabacher]

I put dope on my unions when they won't obey.

[Lee Schierer]

I did a long study of piping leaks on equipment we used to build at a company I used to work for. What we found was that teflon tape isn't a sealant. It si a thread lubricant which may work, but more often than not does not. We found the most successful sealant was Loctite pipe sealant. It worked 99% of the time, even if the fitting was adjsuted after the initial assembly. We reduced our leaks per machine from 3 per machine to less than 1 leak in 50 machines just by eliminating teflon tape and switching to Loctite pipe sealant.

Teflon tape leaves shreds in the threads and can clog pneumatic equipment like valves and regulators.

We also found that certain brands of fittings weren't worth the cheap price. We stayed with the name brand fittings (Swagelock and Parker) and although we paid more, we had far fewer problems.

[Al Willits]

I'd make sure the unions are rated for the pressure your dealing with, then I'd try the soap thing and start to tighten till it either quit leaking or felt they were gonna/did break, tight to each of us is not the same, the 3/4" unions I used on the black pipe required the use of a 18" and 24" pipe wrench to quit leaking at 180 psi.
Most of them unions will take a lot more torquing than you think...unless your name is Arnold..

If they won't stop leaking, toss em and try another manufactures union.

I have used Retorseal pipe dope on a few unions to seal them, not to fond of it though, they should seal with out a compound on them....famous last words...

Al

[David Rose]

Dave: The unions are 1" soldered copper. That makes replacing more of a pain, but still doable. These things are relatively expensive at about $14 a pop. And yes, some of them came from the Borg. Others came from a plumbing supply, but I didn't notice the brand.

Rob: I suspected that the teflon might gum up the works. I try to keep it away from the very edge, but I'm sure that a strip here and there gets away. Everyone is recommending the Loc Tite. I bought some Oatey Great White pipe joint compound with teflon last night. Yes, the Borg is about I all have access to after work.

Kyle: another vote for Loc Tite.

Mike: Fittings are neither NPT nor compression. They are soldered to the pipe. Only the smaller stepped down fittings are NPT. The unions are my biggest headache at this point. They are leaking on the faces.

Kent: I don't think my problem is unique at least to some extent. Almost all the unions I found online have o-rings.

Cliff: That will be my next step. Hallelujah! The brass to copper NPT fitting that I just tried is holding (so far) with the Oatey dope.

Lee: Everything you are saying is probably right. Some of it will have to be done obviously. I'm going to remove all the tape. It's amazing how many fine "hairs" are left in the female section. I hope to not have to replace all the unions, though I suspect that they are part of the problem.

Al: I have no idea as to the pressure rating on these unions. I suspect they are designed for water line. But they start bubbling at 10 pounds of air so... I'm not Arnold, so maybe a cheater will help. I'm sure it will "help", just not sure it will seal.

Thanks all.

David

The unions are compression fittings? I chase leaks on compression fittings frequently at work although I'm sure they are much smaller fittings than you're using. I always start with just a firm tightening but I don't wrench hard. Then I pressurize the line and squirt a bit of soapy water on the joint. Then I tighten it until the bubbles quit coming out. Sometimes I find that no matter how tight I go, it won't seal. I pitch the cone and try again with a new one. I haven't found a better way. Most of the time this is for those portable liquid O2 tanks which are a pain because it seems to make the aluminum parts brittle. fortunately the cones are brass and they don't seem to mind the cold.

[David Rose]

The thread sealer had no effect on the union faces, which is what I sort of expected. I cleaned off the sealer and "whomped" down on it with extended handles. One union sealed!! Another one got worse. A third one made a rather loud pop and leaks worse. I tore the second one down where I could get to the heavier face. It had two or three little nicks that did not flatten out when I cranked it down. Obviously, those would leak. I lightly filed an even number of strokes around it and finished it with abrasive pads. It will allllmost seal now. I'm waiting for the air to leak down some before blowing the valves and scaring off customers. Then I'll check the one that popped.

Btw, I am getting there slowly. The small fittings with NPT are now sealing with the dope where the tape failed.
From what Lee said, I suspect that the tape must just reduce friction in hopes that the brass will finally seal. That might explain why my brass to brass NPT threads sealed with tape, but brass to aluminum and brass to steel did not.

David

[David Rose]

The brass to steel leaked again. I took the fitting out of the circuit, put it in the vice and gave something a chance to break. Nothing did. And *that* fitting seems to have sealed. One of the "previously sealed" unions has a slow leak.

When I ran PVC 30 years ago, I considered NO leaks acceptable. Of course, at the time I did not realise that PVC was not PC. Now that I am trying to "conform" to what IS acceptable, I find leaks everywhere. I left a call to my plumber, but he has better things to do than baby sit an amateur copper line fitter. I thought I had better things to do also.

I am now wishing I had given more serious consideration to the "prohibitively expensive" aluminum system. With about $1000 in copper and 70 hours, it is looking like a better solution. I guess I can post to the testimonials in a regretful way... I have no testimonies that the aluminum works, but I would recommend it over copper. Steel has its own problems.

David, who can salvage about 1/100th of his investment in copper...

[Al Willits]

Dave can you just lop them unions off and solder in couplings?
I'm a little confused as to why you wouldn't do that in the first place.
If you ever have to disasemble the copper, just heat it and pull it apart.

I work in HVAC and when ever we use copper on AC lines we solder it to prevent leaks.

Al

["Gary Brewer"]

I worked for ten years doing a side job of managing an apartment complex when I was young. I had to occasionally install commercial water heaters that had 1" copper supply and return pipes. I also thought it was a good idea to install copper unions to facilitate future changes. I now believe that it wasn't worth it and would now install a coupling rather than a union. I also had a problem with leaks in the beginning. What I found was that if the two soldered pieces weren't aligned just right it would leak. There is play in the soldering of the two halves of the copper union. If they are not aligned just right the joint will leak! I fixed this by tightening the threaded ring to the union first then soldering the two joints. This assured a perfect alignment and stopped the leaks. Also if you apply too much solder you can get it on the two surfaces that seal and also cause a leak. There were no o-rings on the ones I used. They were all brass and really are a form of compression sealing. The threaded part just keeps the two halves together. If they do not come together on exactly the same plane then it will leak no matter how much pipe dope you use or teflon tape nor how much you tighten the threaded ring. I could explain it more geometric terms if you I didn't make sense to you. I also agree with the writer who said to remove the unions and put couplings in. But if you want to make the unions work since you've invested the money and time try the above. You you'll have to remove and resolder.

[Terry Hatfield]

Might I suggest............