Do I dope unions?

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Joey D

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Do I add pipe dope to the pipe nipple going into the unions on both sides? Do I dope the threads of the union.. first time using this fitting. Thanks
 
I put a very thin layer on the threads of both.

And once assembled, if there is a leak from the union, I put a super thin layer of teflon dope in there also.
But they usually don’t leak.

Some people will probably say never to add any dope inside the union, but hey.

Putting some valve grease on the big threads of the union fitting helps it to tighten extra tight.
And helps to get it apart more easily someday.
 
The threaded portions for the nipples or pipe get taped or doped. Put a little dope on the thread of the union itself. You should not need to put anything on the union. Typically one side is brass and will deform slightly to achieve a good seal. Adding pipe dope in actual union can prevent the smooth deformation of the brass and prevent a seal.
 
Pipe nipples always require sealant (teflon or dope).
Nothing within a union requires anything extra, but a tiny dash of dope on the threads of a union to create an anti-seize film couldn't hurt.
The sealing on a union is on its faces and they come apart readily w/o sealant.
Unions are not allowed on gas
 
I think most all jurisdictions allow unions on black gas pipe, in exposed locations.
At least right at the appliance itself.
I have seen them by water heaters and furnaces.
 
We have a lot of 2lb systems that are all copper tube and flare fittings.

All joints are made in exposed locations. Attics, crawlspace, etc
 
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I've cut out leaking couplings in the main line and put a union in its spot so the whole line didn't have
to be tore out.
 

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