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Thread: thread sealing... pipe or dope?

  1. #1
    DIY Senior Member Hube's Avatar
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    Default thread sealing... pipe or dope?

    After making the connection to my house water filter, I noticed a very small leak where the 3/4" threaded plastic(mip) adaptor fitting goes into the filters' housing.
    I unscrewed it, and removed the old teflon tape and applied new tape, wrapped tightly about 3 times around the threads and re-installed it.
    Again it still has a very small leak(drip). I have turned this fitting in as tight as I dare to go so as to not damage the housing of the filter.
    Should I try installing it again with more teflon wrapping, or is there a better thread sealant than teflon.?
    Perhaps "pipe dope" is the answer.
    what would you pros suggest?
    Thanks for any reply.

  2. #2
    DIY scratch-pad engineer leejosepho's Avatar
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    I am no pro, but I believe pipe dope and plumber's putty should not be used on plastic. Take a close look at the threads on both parts, and maybe you will see some imperfection that could be tearing your tape on the way in. Or, maybe a different part would work better. With all of the various manufacturers around the world making fittings and so on, it is just not possible to believe all fittings are made to exact and precise tapers and tolerances.

  3. #3

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    They do make a teflon-based pipe dope, which is suited for plastic. I'd try wrapping it a little more with teflon tape first to see if that solves the problem.

  4. #4
    In the Trades kordts's Avatar
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    I use tape and dope. I seldom have leaks. Most dopes are safe for plastic. The labels on the cans tell you what they are combatible with.

  5. #5

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    Quote Originally Posted by kordts
    I use tape and dope.
    My experience is that you have to use one or the other, but not both. The tape seems to slide all over the place if you put it on with pipe dope. What's your technique?

  6. #6
    In the Trades kordts's Avatar
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    I buy the cheap tape on ****. I wrap 3 or 4 times then use the dope. The reason I do this is because almost all the fittings are made overseas. Now Taiwan or India means an upgrade over the chinese junk.

  7. #7
    General Contractor Carpenter toolaholic's Avatar
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    With both you can back off a gas fitting 90 degrees with no leak!!!!

  8. #8
    DIY Member Hardt's Avatar
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    Default bad housing?

    This may not be your problem but in my case, I've had similar problems and the causes were hairline cracks in the plastic housing. The blue/green plastic housing I thought was deteriorating because of UV rays from the sun so I made a wood cover for it but the problem persisted. After replacing the filter housing 3 times, and still getting the cracks, I gave up and now use a faucet filter. Good luck...

  9. #9
    DIY Senior Member Hube's Avatar
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    Thanks for all the advice guys.As far as I can see there is no hairline crack in the housing,just a very, very small leak at the adaptor thread, so I am going to purchase a small tube of the pipe dope (plumbing shop) that has liquid teflon in it. It is supposed to be safe for plastics too. Im going to wait a week or so before doing this fix,because who knows, it may just "seal" itself.
    Thanks again. Hube

  10. #10

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    I have been having the same problem. I recently had to replace a valve comming from my sprinklers vacuum breaker. All my solder joints are good as gold. The problems I have is the drain spigot in the basement leaks and also where I attached the new pipe to the PVC leaks as well.

    I have redone this project twice already. I have never had a problem with leaky threaded joints until now. Where the copper pipe meets the sprinkler line. I have a plastic coupler. Male threads on on end. The male threads into the copper fitting. The other end of the coupler has barbs that are pushed into the plastic sprinkler line and secured with hose clamps. The leak I have is where the plastic fitting threads into the copper. I have replaced this part twice and am affraid to over tighten it for obvious reasons. Same goes for the drain spigot in the basement. I inspected all the threads and made sure they were clean, wrapped them very well with tape. Thread them together and snug it up and I should be good to go. or so I thought. :-(

    Any clue as to why the threaded joints are leaking. Im at my wits end here. Wraping threads with tape and screwing them in is basic plumbing.

    Any ideas would be greatly appreciated.

    Thanks in advance!
    Last edited by de3rox; 05-07-2007 at 03:19 PM.

  11. #11

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    Have you tried adding teflon pipe dope over the teflon tape as mentioned above?

  12. #12
    DIY Senior Member OldPete's Avatar
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    I use teflon tape _ONLY_ -- Each time I have used "dope" I feel like a dope because I end up with nothing but problems.

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