copper airline union leaks

[mikeyr]

I am building out my airline setup in the garage and because my garage is really 2 garages (2 440sq. ft. garages separated by a half wall), I ended up wanting to be able to remove a section and put some unions in so I could easily remove or modify sections in the future. I used a total of 4 unions. 2 of them are fine, one has a tiny leak that i can live with, but one is leaking pretty bad, going to have to replace it.

So...
1. Can I UN-sweat a copper pipe connection, clean the daylights out of it and re-sweat a new fitting ? or do I need to cut that fitting out and put in a new short section ?
2. On a copper pipe union, do you put anything on the threads when assembling ? I did not, I tried on the leaky one to put on some teflon tape but because of its location way up near the 9ft. ceiling, I ended up messing up the teflon tape and got frustrated. Are you supposed to put any goop or tape on the threads ?

 

[Northislander]

nothing on the threads required but i will put pipe dope on the sealing face of a pesky unions.

 

[sberry]

I put a little sauce on the threads to make them slippery. When they are dry they stop turning but don't really tighten even if they don't seize. I often polish union faces with some purple scotchbrite. It takes little dings off.

 

[rlitman]

Yeah, copper unions can be more fussy than other types of unions. I prefer to keep the threads dry, as dope attracts dirt, but a little bit of clean dope during the install can lubricate the threads a little, and that can help.

Yes, you can unsweat copper connections. It takes a LITTLE more heat than it did to sweat it in the first place. I'll apply a small amount of flux, and then carefully remove it with pliers to hold the hot part. Then, WHILE IT IS STILL HOT, carefully use a dry paper towel to wipe any access solder off. Any blobs of solder that cool in place will make the fitting not fit back together. I'll then drop the parts in a bucket of water, and finally after drying, brush or sand any spots that aren't nicely tinned before re-assembling liberally fluxed.

 

[Oldbear]

I'd use "pipe dope" before teflon tape (application specific) for air, water and such. Assembly as normal and then let it cure before putting the pressure to it (one of the few times I follow directions). We've been know to use both for a field fix - just to make sure it will finish out a project before coming back to the shop.

I think prep before sweating fittings is paramount. I hate redoing fittings when I know I should have put 2 minutes more time into prep first.

 

[Boomer343]

For the union that is the worst leave it tight and in place then heat one of the joints to a soft melt of the solder and watch for it to move slightly. Have a wet cloth handy and cool the joint. See if the leak stopped or got better. If better then put some pipe dope on the mating surface and the threads. If all that fails then pull the joint and replace.

 

[Git]

I have used my dremel tool with one of the sanding bits does a good job cleaning up the solder.

Also, when I installed my mini split - I found out about this 'nylog' gasket/thread sealant that people recommended to use, especially on the mating surface of the flares which is similar to your copper union.

It was only $8 and since I had it already, the last time I worked on an union I used it. Not sure if it helped any, but no leaks
https://www.amazon.com/gp/product/B008HOSQQQ/?tag=atomicindus08-20

Also - I came across these Apollo ball valves that I thought were pretty cool, because you could actually take them apart, like a union. They list for around $40, but I found one in Amazon Warehouse and bought it. (they still have one for $15)
https://www.amazon.com/gp/product/B0062RZP6O/?tag=atomicindus08-20

 

[kbs2244]

Remember that most unions are made to meet water pressure specifications.
40 to 80 lbs. psi

So, you are out of specification on both pressure and fluidity.

Sberry's idea has a lot of merit if you cannot find an air system union.

 

[mikeyr]

I had no idea they are designed for such low water pressure but it makes sense. I tried putting some pipe dope on the threads and they sure went good and tight really easily, but it still leaked even though with the dope I felt I got it much tighter. I took it apart and tried cleaning up a few spots but still leaked. I broke down and redid the joint, kind of a pain since I had piped up against the wall and I could only move it about 6 inches from the drywall, but I removed the union and re-sweated a new one in its place. Really happy that worked or i would have had to cut and redo the section.
Thanks for the help.

 

[engineer2]

Tip for sweating unions: tighten the halves together before sweating the connections. Go easy on the solder or you might sweat the union faces too. Pressure table:

 

[4 FN 27]

1. Can I UN-sweat a copper pipe connection, clean the daylights out of it and re-sweat a new fitting ? or do I need to cut that fitting out and put in a new short section ?

Yes you can...I agree with rlit and sberry below...lightly lube the threads (after sweating).

I turn Union Faces on my Lathe dusting them off with Scotchbrite. You can also do this on a bench by laying the Scotchbrite on the Bench and turning the Union with your hand with even pressure. It doesn't take much.

But prior to that I would try to re-sweat the fitting without removing it from the Copper Tube. Warm it up, add a little flux to the leaking area and re-sweat that area. I have fixed quite a few leaks like this over the years.

2. On a copper pipe union, do you put anything on the threads when assembling ? I did not, I tried on the leaky one to put on some teflon tape but because of its location way up near the 9ft. ceiling, I ended up messing up the teflon tape and got frustrated. Are you supposed to put any goop or tape on the threads ?

The type of Unions I have used do not require Tape or Sealant on the Threads. The seal is created by the 2 surfaces of the Union coming together flat. The threads are there to make that happen. This is where a little light oil or antiseeze can help in the tightening process.

Make sure there are no burrs on the threads that can break off during the assembly process and get caught on the mating surfaces causing a small gap creating a sealing issue.

I put a little sauce on the threads to make them slippery. When they are dry they stop turning but don't really tighten even if they don't seize. I often polish union faces with some purple scotchbrite. It takes little dings off.

Yeah, copper unions can be more fussy than other types of unions. I prefer to keep the threads dry, as dope attracts dirt, but a little bit of clean dope during the install can lubricate the threads a little, and that can help.

Yes, you can unsweat copper connections. It takes a LITTLE more heat than it did to sweat it in the first place. I'll apply a small amount of flux, and then carefully remove it with pliers to hold the hot part. Then, WHILE IT IS STILL HOT, carefully use a dry paper towel to wipe any access solder off. Any blobs of solder that cool in place will make the fitting not fit back together. I'll then drop the parts in a bucket of water, and finally after drying, brush or sand any spots that aren't nicely tinned before re-assembling liberally fluxed.

 

[Lelandwelds]

I have only used the steel unions. I have always just soldered and spliced copper without and never even priced copper unions. How weird is that?

I use so many of the steel ones that co workers teased me.

 

[PoorOwner]

I am doing the same thing and I am using whatever I am putting for NPT threads in this case rectorseal number 5. it's just tiny gaps amongst the 2 mating surface.. that the air can pass through, a coating of dope or rectorseal should make it 100% leak free.

I am trying to pull a valve off and reuse it though, does anyone know if I may heat it up too much when desoldering it? I am going to keep heating and keep twisting with pilers so I know as soon as it frees

 

[Mr onetwo]

Remember that most unions are made to meet water pressure specifications.
40 to 80 lbs. psi

So, you are out of specification on both pressure and fluidity.

Sberry's idea has a lot of merit if you cannot find an air system union.

WTF? totally false information. 3/4" union is rated at 505 PSI @ 200 F with 95/5 solder...that should cover any air system spec.I find that modern day unions tend to distort and leak from over tightening.Wipe a bit of dope on the faces, tighten hand plus 1/2 turn, pressurize and further tighten if you have a small leak.Too much of a good thing can cause problems...always leave yourself a little room to tighten further.

 

[Lelandwelds]

WTF? totally false information. 3/4" union is rated at 505 PSI @ 200 F with 95/5 solder...that should cover any air system spec.I find that modern day unions tend to distort and leak from over tightening.Wipe a bit of dope on the faces, tighten hand plus 1/2 turn, pressurize and further tighten if you have a small leak.Too much of a good thing can cause problems...always leave yourself a little room to tighten further.

I remember packaging listed pressure WOG (figured water,oil,gas because it sure wasn't cleaned for oxygen )