Leaking copper unions for compressed air.

[PoorOwner]

The copper unions I bought from Lowe's doesn't doesn't hold air 150psi no matter how much I tighten them.

Do you guys recommend putting rectorseal or some other sealer. I don't really care if it is semi permanent. I already took them apart once to move so probably they don't work as well now. But a couple of ends at the reel and the compressor are already soldered on there so it is not easy to replace.

If I seal the threads does that also seal off air that escape past the mating service.

 

[rlitman]

Is it leaking from the NPT taper threads or the mating seal in the middle?

 

[Dr Stan]

Is it leaking from the NPT taper threads or the mating seal in the middle?

Put some soap & water solution in a spray bottle to help isolate the leak.

 

[PoorOwner]

Both side are soldered. The thread is not NPT. Just draw the surface together. I have heard of people tape or seal the threads though. Helps lubricate and prevent leaks?

 

[akdiesel]

I always use pipe dope on my sealing surface areas.

 

[padroo]

Unions make a metallic seal, take it apart and inspect the mating surfaces, something is wrong. You could lubricate the union threads and it might tighten up a little more.
Is there any stress on either pipe?

 

[Norcal]

Both side are soldered. The thread is not NPT. Just draw the surface together. I have heard of people tape or seal the threads though. Helps lubricate and prevent leaks?

If it leaks at the mating surfaces of the union, no amount of thread sealant on the threads will help as the battle is already lost, try some pipe dope on the mating surfaces of the union to help seal them.

 

[PoorOwner]

mating surfaces doesn't look great, although I didn't ding them up, there was some corrosion and I had to polish up a bit. I am also not using the same male and female, maybe using a new piece on one side.

 

[ddawg16]

mating surfaces doesn't look great, although I didn't ding them up, there was some corrosion and I had to polish up a bit. I am also not using the same male and female, maybe using a new piece on one side.

As in not a matched set? That would most defiantly cause a potential problem.

I have a couple of unions in mine with no issues....but then again, I got mine from HD (like that really matters)

Something to try....If you have some really wide Teflon tape, as in wide enough to cover the mating surface....stretch a piece over the mating surface and then crank down. Next option would be pipe dope.

 

[matt_i]

What I would try is anti-seize compound, preferably copper-based, although the nickel-based silver stuff will work too. The anti-seize reduces friction in the threadform, allowing more clampload for the same torque (vs dry). And the clampload is what you need to deform the metal surface slightly to get a good seal.

You can always heat the pipe and knock those off and get a new set to try. My only recommendation is to buy them at McMaster Carr. They will be slightly more expensive than the box store but I've never bought a junky fitting from them yet.

 

[RAYJAY]

I always use pipe dope on my sealing surface areas.

=1 on this Teflon base pipe dope / also if the fitting are not square to each other that will cause them to leak

 

[Mr onetwo]

Try this stuff...I used it in industrial settings for years on stubborn metel to metal leaks or weeps.https://www.summitracing.com/search/product-line/loctite-518-anaerobic-gasket-maker Modern day unions are really thin and cheap....I hate them!You used to get nice heavy cast bronze ones from Mueller or Nibco that sealed very well, but no more.

 

[gungatim]

I would cut them off and put on a new matched set. keep them connected when you sweat them on so they are perfectly aligned. I seriously doubt sealant will help, especially if they are not a matched set. when I was re-doing my still to make the thumper removable, I learned the hard way not to mix and match. the tapers on the mating surfaces are NOT the same between mfgr's and generations. I no longer save pieces of unions to re-use for that very reason.

the only other thing to try is to remove them, chuck them in a lathe or drill and put some valve grinding compound on them, spin one while holding the other in place without the nuts. you may get them to hone together and mate properly, but for the work, I would just bite the bullet and replace them altogether...

 

[TTTTTT]

I have 4 on my system for the filter/dryer and regulator. all soldered as well. No leaks. Are they perfectly aligned when tightened?

 

[The Cobbler]

they are no longer matched set, that's your problem like others have said.

 

[The Tool Tyrant]

they are no longer matched set, that's your problem like others have said.

^^ I concur. The panel has spoken, change them out to a matched set.

 

[PoorOwner]

Sorry. They are all the same unions. Just that I took them off one house and put it back at another. Like the drop or ball valve drain is completely modular but the pipe routes are different

So they were not coupled to their original opposite side.

 

[PoorOwner]

Try this stuff...I used it in industrial settings for years on stubborn metel to metal leaks or weeps.https://www.summitracing.com/search/product-line/loctite-518-anaerobic-gasket-maker Modern day unions are really thin and cheap....I hate them!You used to get nice heavy cast bronze ones from Mueller or Nibco that sealed very well, but no more.

You used it on compressed air?. Is it soft set? It needs no air to cure and I am fighting against leaky air. Hmmm

 

[95vette]

Hello, Since you don't have anything to lose try putting a o-ring on the face of the union and see if it will help. Good Luck, Jim

 

[Falcon67]

X2 on the Loctite 518. Use that a LOT on transmission sealing surfaces, servo covers and the like.

 

[myredracer]

I'd say throw away those copper unions and get brass ones. I have a couple of brass ones in my setup and they don't leak. The copper ones I've seen at HD look cheap to me. I buy most of my plumbing stuff at a local wholesaler where it's both cheaper and better quality (they sell to the general public).

 

[rlitman]

Sorry. They are all the same unions. Just that I took them off one house and put it back at another. Like the drop or ball valve drain is completely modular but the pipe routes are different

So they were not coupled to their original opposite side.

No. We don't care if they're the same brand. They need to be matched from the moment they left the production line! Buy two identical unions and swap the ends and you will have problems.

 

[Firebrick43]

Can you rotate one side? If so some valve grinding compound on the face and putting pressure as you turn will lap them to each other.

Also you could de solder, heat to dull cherry and quench. That is unless these are dielectric unions with plastic in them.
This will make the faces dead soft and will seal. This is how you reuse copper sealing washers and head gaskets.

 

[The Cobbler]

just an idea, maybe get some lead or brass sheet and make some gaskets

 

[acmikee]

why not just cut the union out and install 2 no stop couplings and apiece of pipe. done problem solved no leak

 

[Carroll B]

I bought two from Lowe's when I installed my air system. These unions were copper to copper too. I lubricated the junction where the two copper pieces met with a little liquid soap. I was still surprised at how much torque I had to apply to the fitting to get the air leak stopped. Next time I will use brass unions but still lubricate the joint with a little liquid soap.

 

[PoorOwner]

I bought two from Lowe's when I installed my air system. These unions were copper to copper too. I lubricated the junction where the two copper pieces met with a little liquid soap. I was still surprised at how much torque I had to apply to the fitting to get the air leak stopped. Next time I will use brass unions but still lubricate the joint with a little liquid soap.

I am not sure what lubricating the mating surface does? I think I would put oil on the threads and really tighten it with NOT an adjustable wrench, but something longer like a pipe wrench. (one side has a much smaller nut so usually that wrench is much shorter and limit the torque applied) Also didn't want to shear or twist the copper pipe apart!

 

[DieselNut88]

The copper unions from HD I have used for water need to be tightened a LOT to not leak. They don't seem to be great quality. Just torque them down more.

 

[csp]

No. We don't care if they're the same brand. They need to be matched from the moment they left the production line! Buy two identical unions and swap the ends and you will have problems.

^^this^^

They are lapped together in the production line.

As was mentioned already they should also be fastened together when you sweat them to the pipe.

 

[LS6 Tommy]

They're done. Get new ones. Once a union is tightened the two halves deform to fit eachother and they are "mated". Now that the parts were mixed up and tightened they most likely won't mate anymore even if they're switched back. I second going with bronze next time, too. Most sealants don't do anything on union/flare faces or threaded parts other than the NPT threads where they are connected to the piping, but Loctite 567 is specifically designed for it. I have only used it once ad a temp fix, bit it did work. 518 is for flat flanges, but it might work on a union face.

Tommy

 

[Mr onetwo]

You used it on compressed air?. Is it soft set? It needs no air to cure and I am fighting against leaky air. Hmmm

Yes to the compressed air...up to 1500 PSI as I remember.Follow the directions and let it cure properly...it will solve the problem.It's anaerobic....there is no air between the mating surfaces.

 

[2gslse]

I would try an oring or cut a small gasket if you really dont want to replace them

 

[jhelrey]

Rtv!!!

 

[nehog]

I use a *small* amount of Permatex #2 on the faces of the unions. Seems to work well.

 

[Itsahobby]

I am just finishing up my air lines and having the same issue. I was able to really bear down on the unions and get the leak to stop.
All mine are matched and from lowes.
My system is 135 psi.

Sent from my SAMSUNG-SM-G900A using Tapatalk

 

[RECox286]

Look in the odd fastener and parts drawers at Lowes

and see if you can find a teflon (white, plastic-y) washer

that looks like it might fit the inside of the fitting, to act

as a gasket. Forget twisting the fitting until it starts getting

easier, forget permatex, forget fooling with teflon tape,

forget about the fitting and change them for brass ! You

most likely picked the bin that has the cheapest and also

the worst Chinese fittings. Insure that the fittings and valves

you choose are "WOG" (water, oil, gas) certified, sometimes

engraved on the item. Keep your frustration to a minimum...

Uncle Bob