Hi everyone, thanks in advance for your help. First some background. We got a new bathroom countertop and new faucet too. Our pipes are 1/2” CPVC. The old stop valves under the sink were looking corroded, so I decided to replace them with new quarter turn valves.

For future proofing, I didn’t want to have to cut CPVC pipe down to the floor each time I replace, so I installed a CPVC to metal threaded adapter. Then I installed a threaded stop valve. At first I used Teflon tape. They leaked right at the threaded joint. Then I reinstalled used Blue Monster Pipe Thread Sealant. Now they leak les but still leak.

The only place they are leaking is as the threaded 1/2” connection between the two parts I bought. Links below.

So what am I doing wrong? Is it part comparability? Missing something? Different pipe sealant?

Thank you for your advice!
-J

CPVC to threaded adapter LINK: [www.acehardware.com]

Stop valve LINK: [www.lowes.com]

A homeowner who is really appreciative of your help!

you're OK. you just need to get them tighter.
take them apart again, use 4 wraps of blue monster tape and smear a little pipe dope on top.
use two wrenches. one as a hold back and one to tighten.
P/S. if i were doing that i would have taped and gunked that adapter, tightened it into the valve really well and then glued it together.

Thanks for the reply. I did get them super tight with two wrenches. One on each part. I did not use both pipe dope and tape. Just pipe dope. Should I really use both together?

A homeowner who is really appreciative of your help!

It may be that you OVERtightened and stretched the female threads.

First: use 5 wraps of TPFE tape and reinstall

if still leaking

Second: get a roll of YELLOW TPFE (rated for gas, it is thicker) and use 5 wraps and new stops

tighten NO MORE than 4 turns and see if it leaks


no=good to go

yes=two more turns



if STILL leaking

time for a pro

Thanks bernabeu. I’ll give it another shot!

bernabeu, one follow up question. Everything I’ve read says pipe door seals better than thread tape. But you’re suggesting I go back to the thread tape. Do you think the tape gives me a better shot at getting it water tight?

Thanks again!
-J

Installer's preference dope vs. tape.

When I use dope I use permatex #12 pipe joint compound - very very messy black goo.

The pipe tape 'generally' sold at a big box store is very very thin UNLESS you are purchasing the yellow gas rated variety (which is often not stocked).


As for tapered pipe threads: They should NEVER be 'made up' all the way since the ending threads are imperfect and will stretch (like a wedge) the female fitting OFF OF the threads.

A 'perfect' male 1/2" NPT is 3/4" long and requires 1/2" make-up - 7 total turns IF the male has 10-11 visible threads, if the male is 'short' one must 'cheat' on the make-up to avoid the wedging effect.

The (female) fitting has 7 threads - all fittings 1/8" through 2" have 7 threads - go ahead, y'all, count.



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Sooo...When tightening the valve onto the threads, I still have a couple threads visible, so I'm not going to end of that. However, it is possible that the male threads are reaching the end of the female threaded opening.

My local place carries the yellow tape, so I might just start with that this time around. Taking these things apart and putting them back together (while turning off the water to the whole house) is getting sort of old.

Thanks again...
-J

[th.bing.com]

You want full engagement into the female threads but NOT beyond then as you are then stretching the fitting open.


If it HAS been stretched it can not be UNstretched but must be replaced.



Edited 1 times.

Hi, just wanted to say thanks to everyone for the advice. I ended up using five wraps of blue monster tape combined with a little bit of blue monster thread sealant, and 4 to 5 complete turns no leaks after several days.

Thanks again!
– J



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