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Thread: Fitting education

  1. #1

    Default Fitting education

    Hi all,
    It seems that every time I use a threaded fitting (pvc or cpvc) I have problems with leakage. The fittings seep around the threads. This occurs when threading pvc to pvc or cpvc to cpvc also when threading to galvanized. What is the proper way to make these connections to prevent this?

    When transitioning from pvc to black poly what is the best way to do this? There is a steel transition fitting and a pvc transition fitting. I am trying to get away from fittings that corrode inside and restrict flow. If I use the pvc transition in a suction line and use "hose clamps" to secure it to the poly is there a problem with air tight seal?

    My whole house is now cpvc. My well supply line is black poly. I want to replace the lines between the well supply line and the pump with pvc. Currently it is galvanized and I am sure it has closed up and reduced flow. That is why I want to do this.

    Your help is greatly appreciated.

  2. #2
    Master Plumber Redwood's Avatar
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    For CPVC use transition fittings like these...


  3. #3
    Plumber jimbo's Avatar
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    The usual cause of a leak on plastic threads is OVER tightening.

  4. #4

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    Is it advisable to use any thread compound or teflon tape on the pvc threaded joints.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Tapered pipe fittings MUST have something to seal them - you can use either/both teflon tape or pipe dope. Unions, hoses, flared fittings should not have anything added to the threads, but may have a gasket/washer that makes the seal.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6

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    Thanks all.
    Since overtightening creates leaks, is there a recommended way to sense the correct amount of tightness? What is the rule of thumb for tightening these fittings?

  7. #7
    Plumber jimbo's Avatar
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    Quote Originally Posted by Rufus View Post
    Thanks all.
    Since overtightening creates leaks, is there a recommended way to sense the correct amount of tightness? What is the rule of thumb for tightening these fittings?
    Well, as we used to say when people asked us where we went and what we did on submarines....." I could tell you, but then I would have to shoot you!!"

    Seriously, this is to some extent on of those things which is learned by trial and error...lots of both!

    For plastic to plastic, the PPFA recommends fully hand tight, then 1/2 to 1 full turn by wrench. This is considerably less than is done on metal to metal, and is due to the softness of the plastic.

  8. #8
    Radon Contractor and Water Treatment 99k's Avatar
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    My experience has been that the combination of both dope and tape is much more forgiving than trying to apply the exact amount of torque. One thing you can do is choke up on the wrench so that you are not using the handle and lost the mechanical advantage and hence more difficult to overtorque ... basically the jaw is in your hand

  9. #9
    Moderator & Master Plumber hj's Avatar
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    IF you remember the first rule of plastics, namely NEVER install a female adapter on a metal thread, then it is difficult to tighten them TOO much. I screw them together as far as possible. Hand tight and 1 or 2 additional turns MAY result in a leakproof joint, but only if the threads were perfectly matched, and that is not always the case with plastics, as you will discover the first time a male thread decides to cross thread because it is not a perfect fit to the female thread.

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