Re: 15mm compression couplings/isolators

The "roughness" which is left by cleaning the pipe with steel wool is effectively obliterated by plastic deformation of the tube and the olive at each end of the olive. This seals the leak path "under" the olive, while the leak path over it is sealed by the two conical contacts between the nut and the fitting with the olive. Only one of the two "under" path seals needs to be good, but the conical seal between the olive and the fitting has to be good, otherwise there is a potential leak path via the threads. (Although this can be sealed with boss white, etc).

I certainly don't believe that the thread has any role in sealing - therefore PTFE is not needed. Cleanliness ir important.

Absolutely. But a deep longitudinal scratch running under the olive can cause problems. The sort of scratch you might get when running a length of pipe in over masonry, etc. Which is why I prefer end feed solder fittings, where possible.

Personally, I almost always put PTFE on the threads, but this is because of the low friction, and it means you get more axial force for a given torque. It is the axial force which provides the sealing loads. While I generally try to avoid getting any tape on the sealing faces this is more for neatness than any practical benefit.

newshound wrote in news:8fCdnQ snipped-for-privacy@brightview.co.uk:

I use a drop of oil for the same reason.Only on the threads.

The Wiki IIRC suggests that the function of PTFE tape is to reduce friction on the threads so that it's easier to get the torque required, which could be high for a difficult joint (pipe warped but not easily replaceable, etc. etc.).

I wonder if petroleum jelly a.k.a. vaseline might be easier to apply and longer lasting (if that should matter).

snipped-for-privacy@Freeola.net.invalid (Windmill) wrote in news: snipped-for-privacy@way.freeola.net:

Probably. I always like to think that I have tightened them just enough. Then I can always tighten them a bit more if needed. Some people over- tigten them.