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Old 10-10-2016, 06:43 AM   #1
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Very slow leak from brass fittings


Installing a new shower control using mostly PEX, which is working great. Only problem I am having is that the two brass supply connections have a VERY slow leak - like it takes an hour for a drop to form. I've assembled and disassembled both joints twice now and rewrapped (in the correct direction) with telflon tape. The leak is definitely at the brass joint - not the PEX. I can see the drop form at the same spot on each fitting (see photos).

I've never had a problem with threaded connections at sinks and toilets (or never notices a drop or two), but I want to be ultra-careful with the shower as I'll be walling up the shower with expensive tile.

Any tips for fixing this type of leak? Is there any merit to putting pipe compound over the teflon tape? I hate to keep dismantling these joints. The space is cramped (reason I went with PEX), but replacing PEX is tedious since you need to destroy the pipe to disassemble the fitting.

Thanks for any help.
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Old 10-10-2016, 07:26 AM   #2
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Re: Very slow leak from brass fittings


If I understand the picture in your other thread, you are screwing a NPT into a BSPP fitting and that ain't gonna work well as you've discovered.
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Old 10-10-2016, 07:36 AM   #3
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Re: Very slow leak from brass fittings


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Originally Posted by SeniorSitizen View Post
If I understand the picture in your other thread, you are screwing a NPT into a BSPP fitting and that ain't gonna work well as you've discovered.
That's not correct. The PEX barb to NPT Male (where the drip is) is threaded to a Female NPT x Male G adpater which is threaded to the G Female supply inlet. The G seals work great. So it's NPT to NPT and G to G.
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Old 10-10-2016, 07:56 AM   #4
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Re: Very slow leak from brass fittings


G thread female according to the package. Which thread is on the pex fitting?
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Old 10-10-2016, 08:09 AM   #5
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Re: Very slow leak from brass fittings


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G thread female according to the package. Which thread is on the pex fitting?
NPT, but you're crossing threads (no pun). The photo from the other thread shows a mislabeled fitting, which spawned the question over naming them, and the reason I ordered the wrong adapters (x7) and needed to reorder -- all of which has nothing to do with this thread but just to lay any type of G to NPT conflict to rest, I inspected all 14 adapters with digital calipers and sorted and then re-confirmed which were NPT and which were BSPP.

The order of mating is this:

- PEX supply to
- PEX barb - Male NPT to
- Female NPT - Male G to
- Sealing washer to
- Female G valve
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Old 10-10-2016, 08:57 AM   #6
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Re: Very slow leak from brass fittings


I stand corrected. The mis-labeling I missed.

thanks

Last edited by SeniorSitizen; 10-10-2016 at 09:02 AM.
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Old 10-10-2016, 09:27 AM   #7
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Re: Very slow leak from brass fittings


IMO- never screw metal fittings without pipe dope use Blue Monster tape if you can find it
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Old 10-10-2016, 10:50 AM   #8
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Re: Very slow leak from brass fittings


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IMO- never screw metal fittings without pipe dope use Blue Monster tape if you can find it
I had read something about brass fittings needing a day or so to "settle in", so the tension equilibrates across the threads. Honestly, the dripping has slowed from about 1 drop per hour when first assembled. Under constant pressure and a day later, it is taking about 3 hours for one drop to form.

Still, rather than just hoping it'll be OK, I've resolved myself to pulling it apart again. Do you think there's any benefit (or detriment) to using dope over teflon tape or should I just do away with tape and just use dope?
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Old 10-10-2016, 11:08 AM   #9
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Re: Very slow leak from brass fittings


I dope first- then tape on top. My theory is that the dope embeds into the male threads and will stay there even if the tape rolls out while screwing together.
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Old 10-10-2016, 06:11 PM   #10
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Re: Very slow leak from brass fittings


Ayuh,.... I use paste, 'n rarely tape,....
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Old 10-10-2016, 06:37 PM   #11
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Re: Very slow leak from brass fittings


The few times I have used tape and still had a small leak, I use both; tape on the male fitting, and dope on the female. Never had a leak after doing this.
good luck!!
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Old 10-10-2016, 10:09 PM   #12
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Re: Very slow leak from brass fittings


Couple of PEX tips you evidently need too: 1. Your crimp rings are too far from the end of the pex. Next time install them about 1/8" from end. 2. You never need to destroy the PEX when unscrewing from a threaded fitting. Just unscrew it. The fitting spins in the PEX.
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Old 10-11-2016, 05:30 AM   #13
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Re: Very slow leak from brass fittings


I've had leaky fittings in a couple of water heaters and had to conclude that the factory part was defective. I let the water leak for a week, though, it sealed itself. The shower fittings, however, may see more movement and I would replace the fitting or the valve. I am not a plumber but I think the fitting must be leak free from the start, not wait for the metal to settle. Cold-hot cycles would give it more movement anyway.
These days, I dry fit the fittings all the way and feel for any binding, etc. The leaks happened both times when I thought the tightening was less than smooth.
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Old 10-11-2016, 05:51 AM   #14
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Re: Very slow leak from brass fittings


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Originally Posted by SHR Plumber View Post
Couple of PEX tips you evidently need too: 1. Your crimp rings are too far from the end of the pex. Next time install them about 1/8" from end. 2. You never need to destroy the PEX when unscrewing from a threaded fitting. Just unscrew it. The fitting spins in the PEX.
Thanks for the tips. I was using the attached photo from PEXUniverse as reference. Caption reads "Position the PEX crimp ring 1/4”-1/8” from the end of the tubing. This way the crimp ring will be right above the PEX fitting’s barbs."

I just double checked my fittings - all are within or at 1/4" from the end of the PEX, but I'll aim for closer next time.

As far as needing to destroy the PEX to remove a fitting, yes, in my case I do because the diverter valve is huge and takes up most of the space between two studs (the supply elbows are up against the studs on either side). Definitely could not have gotten everything in there if the PEX couldn't rotate.
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Old 10-11-2016, 06:01 AM   #15
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Re: Very slow leak from brass fittings


I think I have this resolved now. I replaced the supply connections, using dope over tape this time and have been leak free. Just checked it again (overnight) and there's not a drop. I'm still a few days from sealing up the wall and will keep an eye on it.

I did try the tape over dope, but didn't like that approach. Maybe I had too much dope under the tape, but the tape seemed lumpy and I was concerned it might shift as the threads squished out the dope. Anyhow, the dope over tape seems to have done the trick. Thanks, everyone!
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