James "Cubby" Culbertson wrote:
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

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