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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

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.

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PFTE 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 PFTE, 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 PFTE 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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