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I replaced the supply valve on my bathroom sink with this ¼-turn angle valve.

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Both valves (hot and cold) are leaking about 1 drop every few seconds at the valve's input. I got them hand tight, then added about 2 full turns with a wrench. Should I tighten them more, or are they leaking because of over-tightening?

Before installing the valve, I shined the copper pipe with scotch brite, and I put 3 wraps of PTFE tape on the male threads. I am reusing the nut and ferrule that was there.

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    Valves can leak at three places. Where it attaches to the supply, where it attaches to the outflow, and at the stem of the valve. First step is to identify where. If it does not leak when the valve is closed, then it is not the first. Tape some papertowel around two of the three may help figure that out. – user14016 Jul 16 '13 at 0:25
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Compression fittings do not use tape, so that's one mistake to fix. Tape seals a leak in threads, but a compression fitting is sealed at the ferrule, not at the threads. Leaks are frequently caused by over tightening, so this is certainly a possibility in your situation. Here are my suggestions:

  • Replace the nut and ferrule. The ferrule gets deformed when compressed, so a new ferrule won't have the deformations from the previous valve.

  • Hand tighten the assembly, though I typically use a wrench and guess where I could likely get it by hand without destroying my fingers. Add another half turn by wrench.

  • Test for leaks, and if found, add another quarter to half a turn until the leak stops. By doing this in iterations, you minimize the risk of over tightening. You can always tighten it more if you under tightened it, but once you over tighten, you have to get a new ferrule.

  • the thing that scares me about not going tight at the beginning is the possibility of the valve blowing off when I turn on the main. I am doing this right now and after tightening the nut, the angle valve was able to spin on the pipe -- if it does that, won't it blow off? Anyhow, I tightened it more and now it leaks. :( – Dave May 23 '18 at 4:35
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PTFE ("Teflon") tape is not likely useful on the valve's male inlet threads. I've only ever used it in place of pipe joint compound on male pipe threads, which of course are tapered threads. I believe the male threads on your valve's inlet are simple SAE. There is a particular technique to wrap PTFE, which if not used can increase friction. And that technique includes having the final wrap stretch over the end of the nipple. Anyway, the leak could be from PTFE being caught between the ring and its seat. Or there could be a mismatch between the geometry of the old ring and the new seat.

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I suspected that the tape made it so that the nut didn’t tighten down enough to compress the Ferrule all the way. I would first try removing all the tape and then re-tightening the nut and then checking to see if you still have a leak. Then if you still have a leak you would need to replace the ferrules.

For replacing the Ferrule , Usually once the Ferrule is compressed onto the pipe it requires cutting off the end of the pipe with a ferrule. If you could pull the ferrule off at the pipe then it wasn’t compressod properly.

The nut should be fine only the ferrule should need to be replaced. In my experience Ferrules need much tighter compression than what hand tightening would supply. Used two wrenches, one on the Valve to keep it from spinning and one to tighten the nut that compresses the ferrule to the copper pipe. Tightening The nut i’m to the valve pulls the valve towards the nut with the feral in the middle thereby compressing the ferrule to the copper and squeezing the valve and the nut together on the Ferrule, which makes it a watertight seal if done properly.

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