3/4" Copper UNION - Use Teflon Tape or Pipe Dope?

[chuck b]

3/4" Copper UNION - Use Teflon Tape or Pipe Dope (after sweating the two ends)? Or do you just tighten the nuts. Thanks!

[dlarrivee]

Are the threads tapered?

[Hackney plumbing]

I use a little pipe dope on the threads.

[kreemoweet]

The threads on a union play no part whatever in the sealing function, they are there solely to enable the sealing surfaces
to be pulled tightly together. No dope, no tape, no nuttin'.

[jimbo]

Although nothing is required on ANY part of a union joint, I like a little non-setting paste like Great White, both on the threads and very lightly on the mating surfaces, just as a lube and protector. It works for me! Many will suggest a little coating of light oil.

[Hackney plumbing]

The threads on a union play no part whatever in the sealing function, they are there solely to enable the sealing surfaces
to be pulled tightly together. No dope, no tape, no nuttin'.

Pipe dope on the threads would be used as just a lubricant. Not to seal anything.

[hj]

Pipe dope on the two mating faces will compensate for any minor irregularities. On the threads it helps them tighten easier. Putting it on the surfaces BEFORE soldering, makes them "dirty" so the solder does not adhere to the brass, which helps in a vertical installation.