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Plastic tube fittings

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  • Plastic tube fittings

    I used plastic tubing and fittings to pipe an under sink drinking water filter in my home. The fittings look like regular compression fittings except they have a trumpet-shaped tube liner to insert into the end of the tube before tightening. There is a small shoulder inside the fitting that the belled end of the insert bears on. The nut has a ferrule-compression piece inside of it which is grips the plastic tube when it is tightened.

    I have 62 PSI water pressure and the fittings held tight for four years but then one of them blew out. Fortunately we were at home and shut the water off quickly.

    When installing I tightened the nuts as much as I dared without stripping the threads and the end of the tube that pulled out looked as though it had been gripped. After the event I had to use two wrenches to back off the nut. I clamped the fitting into my bench vise and tightened it almost to destruction but still the tube was not any more deformed than it had been,

    I don't understand what happened to it. Has anyone had a similar experience with this type fitting? Does plastic "creep" over time which would allow the pressure to blow it free? My wife suggested that maybe the vibration of the garbage disposal unit in the sink drain hastened the failure?

    Any thoughts? Ronny

  • #2
    Re: Plastic tube fittings

    I have seen so much of this over the years and it did not matter if a homeowner did it or a plumber. That's why if it's a hot and cold water dispenser or an ice maker line, I always upgrade to brass fittings and 1/4" soft copper.


    • #3
      Re: Plastic tube fittings

      It is not likely that the disposer vibrated it loose.
      Do you store lot of things under the sink?

      It could be enough pushing an pulling to stretch the plastic.

      More likely it got tangled on something and pull on pretty hard.

      Unless you have sunlight under the sink the plastic should last.


      • #4
        Re: Plastic tube fittings

        what i see is
        the plastic got old and broke
        use copper or braided flex lines
        plastic is like a ticking bomb, to me, in a home .
        you saw what it does if you have any more change it out


        • #5
          Re: Plastic tube fittings

          Hello and thank you all for your thoughts. I had never used plastic before except for DWV, but it's difficult to work under a sink at this point in my life so I gave in. But! you can bet that I will replace it with copper tube when I re-do it. I had coiled the plastic and strapped it carefully behind the filter out of harms way so I am positive it did not pull out but was blown out by the water pressure. Thanks again. Pinebarren


          • #6
            Re: Plastic tube fittings

            I would rather use copper for strength and reliability over plastic tubing. However, if your drinking water filter system is Reverse Osmosis then plastic must be used or you will get an onion flavor from the copper tubing from the R.O. water attacking it. When using plastic tubing, I trust "push-fit fittings more than compression type whenever possible.