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