Annoying, Slow leak from Compression Nut on new Sink Supply valve

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by pickleparade, Jun 23, 2011.

  1. pickleparade

    pickleparade New Member

    Jun 23, 2011
    Sierra Madre, CA
    Doing a kitchen remodel I wanted to replace the hot and cold supply valves to the sink.
    We have 1/2" copper pipes and they are clean and shiny. I put in the new hot water valve and it is working just fine. But the cold water valve continues to leak.. ever so slowly.. about a 1/2 cup of water over night. It is the compression kind, with the little brass seat and the large compression nut which is suppose to expand it as you screw it onto the valve. i have tried multiple seats, tried putting back the old valve, tried different compression nuts, and still, this annoying little leak. The package for the new supply valve says, in bold letters, NOT TO USE ANY TEFLON TAPE. So i am not. But the leak is mostly coming from the back side of the compression nut, not the side with the threads. I am going crazy trying to fix this. Anybody have any ideas??
  2. Starglow

    Starglow New Member

    Jun 14, 2011
    North Carolina
    Was the supply pipe end bent, dented, crooked, out of round? Is the pipe clean with no solder on it? Any and all of those things can cause a leak. Make sure you seat the pipe fully inside the valve and it doesn't pull out as you tighten the nut. If all else fails, then you might have to resort to just using a soldered valve. I'm no plumber, but personally I'm not a big fan of those new compression shutoff valves, but it seems like the big box home stores are moving away from stocking the traditional soldered on brass connections to some degree.
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    All it may require is another 1/8-turn or so on the compression nut. When tightening, it doesn't hurt to put a drop of lubricant on the threads, but by no means is this required. it makes turning the nut easier without sticking - sometimes, the threads aren't the best quality and are rough. A pro probably wouldn't take the time to do this, but then they do this every day and have developed the 'feel' as to what's tight enough. Also, ensure that you are using two wrenches: one to hold the valve and the other on the nut.

    If the pipe is scored or bent, it makes it hard to get a good seal. But, if you were able to get the compression ring on, it can't be too bad.
  5. bsperr

    bsperr Member

    Apr 23, 2008
    Athens, GA
    If the pipe isn't the problem, then maybe the ferrule is deformed. Maybe try replacing that and reinstalling the valve.
  6. plumber2011

    plumber2011 Expert Plumber

    Jun 4, 2011
    Licensed master plumber and owner of small residen
    Boston, Massachusetts
    Hi PP,

    I would recommend that you cut the pipe and the old ferrule about an inch in back of the old ferrule and nut and install an entirely new compression nut and ferrule (purchase separately) to the new shutoff (can just purchase a new nut and ferrule).

    When you slide the new ferrule on (nut goes first) be sure to use the pipe reamer on the tubing cutter to ream out the inside of the pipe to full size, which also aids in locking the ferrule into place, and then install the compression shutoff as the instructions tell you, too. Do NOT overtighten compression fittings...not needed!

    Good luck!

    Attached Files:

  7. DonL

    DonL Jack of all trades Master of one

    Mar 30, 2011
    Rocket Scientist
    Houston, TX
    I think Jim is correct,

    Just tighten the fitting a little more, and if it still leaks, then redo it.

  8. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona
    HOW you removed the old nut and ferrule may give us a clue as to why the new one does not seal. Did you cut it off with a hacksaw, or use a "puller" to remove it?
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