I'm installing a shut off valve under my sink. It will be attached to a threaded pvc fitting. My question is this, I used 3 turns of teflon tape as I was instructed to by the man at the hardware store and I tightened it by hand and then 1/4 turn with a wrench. Is this correct because it keeps wanting to leak? It's one of those metal shut off valves that the knob turns 1/4 turn to shut it off. Should I try to turn it to tighten it more or just take it apart and try again? Of course I installed 2(one on the hot side and one on the cold side), and the other one isn't leaking...go figure!

1/4 turn is not very much. Make sure you are using a backup wrench on the plastic. These connections are a problem. You may want to use teflon pipe dope on top of the tape. While three turns is usually correct sometimes we have to use more to beef a plastic male fitting up in order to seal.

I think Lonny is right about maybe just needing more turns but if this doesn't work, then you should also make sure the rubber washer didn't come out of the female end. This happened to me a few weeks ago. Thought I was going insane until I found it.

I was afraid to tighten it too much because the hardware store guy said not to. So if 1/4 turn isn't enough, how do I tell if it's tightened enough without messing up the threads.

I don't recall rubber washers but there could have been but it doesn't seem like it.

I got out my package and this is what I have:
Made by: Mueller industries inc
Called: BESTOP
Ball Valve Water Supply Stops
Straight Stop
1/2" FIP X 3.8" O.D. Comp.

That was supposed to be 3/8"

Learning the different tensions for plumbing connections took me almost three years to learn and I'm still learning. The most important issue is that the strength goes to the connection and not to the pipe. Back up.
A broad statement of iron pipe size tightness is that of the 9 threads, three of them go on hand tight, tighten for 3 more threads and leave 3 exposed. However this is broad and not a specific guideline and plastic to metal varies because plastic is not as exact.
Mueller is a good valve. I have not seen a threaded shut off that usings an o ring to seal instead of the tapered pipe threads. But they evidently are out there.

So what you're saying is that how tight to tighten isn't an "exact science" ay? Hahaha! Looks like it's just "practice practice practice!" Thanks you very much for your help!

I'd believe that it would take time to learn out to tighten fittings properly. I've done it enough times and always have trepidation about it.

My two cents: In my limited experience, there is a right way and a wrong way to wrap the teflon tape. Maybe this sounds intuitive (it wasn't to me)...but it should be wrapped in the direction of the threads (as if it's getting tightened on as well). OK, thi is assuming I'm doing it properly...correct me if I'm wrong Lonny!

I'd guess the reason for this is that it all tightens together, not bunches up inside into a big mess. I've definitely had to remove fittings and put on new teflon tape before, and have had good experience doing so.

Regards,
-k2 in CO

Moderator, Miscellaneous Forum

http://www.bobvila.com/BBS/Miscellaneous

Good point from k2. Applying tape does have a technique.