Need help with leaking nipples

Discussion in 'Irrigation / Sprinkler Forum' started by mears, Sep 29, 2008.

  1. mears

    mears New Member

    Messages:
    2
    I am having a devil of a time attempting to seal threaded PVC fittings on my sprinkler system valves and manifolds. My valves have threaded female fittings as do the T’s in my manifold. The two are connected together using 1†and ¾†nipples (depending on the size of the valve). I am using ½†PTFE tape around both ends of the nipples. I am wrapping three to four full turns around each end, stretching the tape fairly tight. Now that everything is attached, the several of my valves are (very) slowly dripping at one end of the coupler when I open the water line. I used a pair of Channellock pliers to tighten them to the point where I was worried they might crack/snap. This worked for a couple of them, but I still have slow dripping at a few joints.

    Any ideas why the fittings are dripping? Should I add more layers of PTFE or not stretch it? I did try adding 5 or so layers, but I wasn’t able to fully tighten the nipple.
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    You have probably damaged the threads.

    Proper procedure is 2 wraps max of tape, tighten by hand, then 1/2 turn to one turn by wrench. That's it'
  3. mears

    mears New Member

    Messages:
    2
    Is that two turns with the tape stretched? I've seen very inconsistent recommendations on the number of layers to use. For example, this guide http://www.greenhousekits.com/resources/D5024-ACF-Sprinkler-Ins.pdf recommend 4-6 layers of PTFE. I chose 3 since it seemed to be right in the middle of everything I've read.
  4. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    The advice has to be tailored to the specific valves in question. Some of the most reliable of lawn sprinkler valves are manufactured to be deliberately 'out of spec' and with teflon tape alone, can require numerous wraps to make a leak-free connection. Use less, and the male threads (especially with some slip x MPT adapters) can bottom out in the end of the valve.
  5. 99k

    99k Radon Contractor and Water Treatment

    Messages:
    460
    Location:
    Fairfield Co.,Connecticut
    I have found 6 turns of tape is too much and I cannot start the threads. I use a small amount of tthread dope first, two turns of tape, and finished with thread dope ... not problems. DON'T OVERTORQUED the connection because the female will split (and usually at a later time).
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,255
    Location:
    Cave Creek, Arizona
    thread

    IF you add pipe dope it MUST be suitable for PVC threads. One study of a major installation with multiple thread failures found that almost all of them were due to excessive layers of tape which stressed the fittings during the process of tightening them. I do not know what your definition of "stretching" the tape is, but usually you just keep a little tension on it so the tape conforms to the peaks and valleys of the thread.
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Tape should not really be stretched, just snug. Most of the white tape today is a very thin mil guage. But with plastic fittings, the problem is that too much build up of tape on the threads stresses the fittings. On female fittings you can actually crack it, and on both male and female, the threads are distorted and thus leaks develop. These problems do not really happen on metal, although in theory you can also overtighten a metal fitting. It is just way easier to overtighten a plastic fitting because the material is so soft, and plastic on plastic, especially with tefon tape, is somewhat self lubricating, so you can easily continue to tighten past the breaking point.

    The procedure I mentioned before is from the PPFA ( Plastic Pipe and Fittings Association.)
  8. dcd

    dcd New Member

    Messages:
    3
    Hahahaha

    I had to laugh when I saw the title of this thread :D
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