Simple Question I should know the answer to! Plumbing...

[James "Cubby" Culbertson]

Hiya All, Well today I spent the day trying to get a couple of shut off valve leaks to stop. These were feeding a couple of sinks in the bathroom. I bought new valves that had compression fittings and all seemed well except I couldn't get them to not leak. I had to put a nipple on the valve to connect to the copper supply line as they didn't have the exact type setup. I'm beginning to think I got NPT nipples and that was my problem. Anyway, I finally went to a decent plumbing supply store and got the correct valves. On leaving, I happened to mention to the guy that I was using teflon tape on the threads. He said not to and just crank the thing down as tight as I could. I've always just used teflon tape on just about any plumbing work and never really thought about it. So my question is: Just when do you use teflon tape? ie. Compression fittings, NPT, Flared fittings etc....

Incidentally, the damn valve leaked without tape yet didn't leak when I put tape on it. So now I'm not even sure the guy at the store was right.

Just curious. Cheers, cc

[Speedy Jim]

Threads (NPT) - Tape

Compression (ferrule) - No Tape Flare - No Tape

4 legs good - 2 legs baaaad

Jim

[toller]

Tape isn't needed on compression or flare, but why would it hurt? Some believe it reduces friction and helps you tighten the joint up properly.

[stretch]

Always use some type of lubricant on any mechanical connection. I have seen plumbers tighten flare and compression fittings so tight they split trying to stop a small leak. I prefer pipe dope, but tape will work as will grease or oil on compression fittings. On refrigeration flare fittings all manufacturers will tell you to use refrigeration oil, bit pipe dope will work on plumbing flares as well. On threads use your choice of dope or tape. On ground joint unions use dope on the faces. Never assemble a mechanical joint dry, the chance for a leak is much higher.

If I had a nickel for every plumber who assembled a compression or flare joint dry in front of me and told me that it was the first leak he ever had, I would be rich!

Stretch

[Ken]

I think the basic principle to follow is that when the threads form the watertight seal, then use teflon tape (e.g. NPT fitting). If the threads are just there to hold a fastener and something else forms the watertight seal, then no tape is necessary (e.g. compression fitting with a ferrule).

Ken

[Doug Miller]

You're missing the other purpose of using tape or dope: ease of disassembly.

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

[scott_z500]

I'll add your story to my long list of reasons why I won't use compression fittings.

[James "Cubby" Culbertson]

Thanks folks for the inputs. I did in fact assemble these dry so perhaps that was my problem. The tape seems to have cured the leaks but nevertheless, I worry about them long term. I appreciate the inputs and it does make sense that when the threads are making the seal, use the tape. Otherwise, don't. Not sure why it wouldn't hurt to use the tape in all cases but anyway. Thanks for the insight! Cheers, cc

[Stormin Mormon]

NPT: Teflon on the male threads, and then Rectorseal #5 over the teflon.

Compression: Spray generously with WD-40 or Zoom Spout turbine oil.

Flare: Oil generously with WD, or zoom spout.

Unions: Oil generously on the loose nut, and the mating surface. Do the teflon and rectorseal on the pipe thread.