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I just replaced the 90° cutoff valve because the old washer perished and the valve was shut off very hard. The cutoff was threaded onto a copper adapter which is sweated onto 1/2" rigid copper pipe. I put the new valve on with ~4 wraps of teflon tape, and it had a slight leak. So I removed the new cutoff, gave it 9 wraps of tape, tightened the valve back on, but there is still a slight leak at the threaded joint, maybe a drop every 20 minutes.

I would just replace the sweated fitting, but as the picture shows it's very tight to the wall -- I think I'd have to make a fairly large hole around the area and maybe still run some fire risk.

I'm looking for a creative solution, possibly with continuing to use the stripped fitting.... Would it be possible to bed the threads in epoxy and reconnect the cutoff? Would that use liquid or gel consistency, or a putty type? Is there a way to solder a tube into the adapter or over it? Or do I have to lump it and tear into the wall?

Thanks for suggestions enter image description here

edit, added: wondering if I could sweat threads to threads if I put a FIPS copper adapter or brass coupling onto the male adapter sticking out of the wall. Would that work, in a pressure holding sort of way? The adapter threads seem to be the part that's leaking, and soldering will not depend just on the threads.

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    Check your angle-stop valve carefully for cracks. These cheap-ass valves these days are prone to cracking if even slightly over tightened, and it's hard to see the hairline crack. – Jimmy Fix-it Aug 23 '17 at 2:17
  • Some are chrome plated plastic.+ – Ed Beal Aug 23 '17 at 4:51
  • The one in the picture looks like black plastic to me. – Michael Karas Aug 23 '17 at 7:49
  • This valve is chromed metal, trick of light makes it look plastic. – Old Uncle Ho Aug 23 '17 at 11:09
  • Teflon tape is convenient, but perhaps overrated. I have had stubborn leaks in threaded connections that Teflon tape refused to seal, but pipe dope did the trick. – mickeyf Aug 23 '17 at 12:00
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1-2 wraps of teflon tape, then use pipe dope. You can't go wrong. Too many wraps of teflon only distort threads.

Same theory as your idea of epoxy, but more 'plumbery'.

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Next thing to try is unscrew the valve, remove the Teflon tape and use a good quality pipe dope. Put some dope on the female threads as well as the male. This might fix the leak, but even if it still seeps a little, the seep may gradually seal over a week.

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It's hard to tell from the photo, but you should have 1 1/2 to 2 threads showing once the joint is properly tightened. If you have more, the joint is not tight enough and will likely leak. If you have less, the joint is too tight and you may damage the female threaded fitting.

You didn't mention how tight you tightened the valve, so it's hard to say if you tightened it enough, or too much. If you really cranked it down, you might have damaged the valve, the threaded fitting, or both.

If the valve isn't tight enough, try tightening it a bit before trying anything else. If you see the proper number of threads, you'll have to look for another problem.

As others have mentioned, you only need a couple wraps of tape dope. As I've said many times in the past, dope is there to reduce friction, not to seal the threads. More dope, doesn't mean more better.

Remove the valve, and closely inspect the threads on the copper fitting. Copper is a soft metal, and the threads are likely slightly deformed, This deformation either occurred when the old fitting was originally installed, or when you installed the new valve. If the threads are damaged, you'll likely have to replace the fitting.

If the threads of the fitting in the wall don't look too bad, you might still be able to get the joint to seal. I'd probably start with a new valve, a couple wraps of tape dope, and tightening the valve down enough. If you still have a drip, try giving the valve another 1/8th of a turn.

  • Thanks for the specifics, more detail than I knew. I did try the 1/8 turn routine, and started with less tape -- I always assumed it would help seal the threads at least a little. The copper threads did look worn, the front most ones looked a bit stripped, but the fitting was able to thread onto the copper adapter. I would have started by replacing it, but it is a much bigger job. Trying to avoid opening up the wall, I'm looking for a solution - maybe soldering to the male MIP cu fitting and attaching to that? – Old Uncle Ho Aug 23 '17 at 18:20
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I would remove the valve and replace it with a new valve since the valve you have may have become distorted due to too much teflon tape and over-tightening. And as others have said the valve could also be cracked or have a hair-line split. I would use RTV silicone caulking to seal the threads (costs about $5.00), Install the new valve, tighten and let sit overnight. One word of caution; apply the silicone or any pipe dope only to "male" threads. Never dope "female" threads. I would not try to resolder fittings in a wall unless you have the fire company standing by. If you feel you need to replace soldered joints call for professional help.

  • "Never dope "female" threads." Please don't make a statement like this without any explanation. Indicate why you think this is a bad idea. – mickeyf Aug 23 '17 at 11:58
  • I had always heard not to dope the female threads, but in a recent replacement of outside faucets I had to put dope on the female threads as well as the male in order to reduce seeping to negligible. My thinking is that one does not traditionally dope the female threads because this will cause the dope to pile up inside the pipe and so get into the water whereas if only the male threads are doped then the excess goes out. I can only assume that today's threads are not as well made and need dope to be pushed by water pressure from the doped female threads into the sealing joint. – Jim Stewart Aug 23 '17 at 12:07
  • So who did the down vote? obviously you have little experience working on piping of all sizes and types with screwed up threads. Anyway, the main reason for not doping the female threads is that the dope could get onto the seat and cause the valve to leak. I am not going to toot my own horn, I will just consider the source. As far as my answer it is the best i have seen so far and it does work. – d.george Aug 23 '17 at 14:19
  • I did not downvote, ugh. What type of dope are we all recommending, that containing Teflon? (I've heard that it's best not to mix Teflon tape and conventional products.) I have also not seen Teflon pipe compound at the box store, but going there this PM to get another replacement valve to try so I'll see if they have that product. – Old Uncle Ho Aug 23 '17 at 18:25
  • Just regular RTV silicone clear or white – d.george Aug 23 '17 at 18:30

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