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Thread: threaded joint on pvc pipe leaks

  1. #1
    DIY Junior Member rickard681's Avatar
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    Default threaded joint on pvc pipe leaks

    The threaded pvc joint on my pool filter leaks with tape or paste. I have a 1 1/2" pvc threaded elbow into the pool filter (also of 'plastic' case) that leaks whether I use tape ot paste. I have tried replacing the elbow with new pipe and tried threading the pipe into the female filter until all threads were in .. all to no avail. The joint leaks about 1 drop per second when the filter is in the filter housing. With no filter in the housing .. no leak because of no pressure. With the filter in the housing the joint is under approximately #25 psig and then leaks. The filter housing is OK. (the old housing was OK too but I replaced it thinking the housing female threads were the problem = $650 wasted). Is there a flexible paste or rubber sealant that can be used instead of pipe dope that doesn’t completely harden yet holds a little pressure when used instead of the paste?
    Any help would be greatly appreciated. This is th second swimming season I am about to lose to this problem.

  2. #2
    Plumber jimbo's Avatar
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    Clearly you have screwed that pipe in WAY too far. Probably damaged the male threads and possibly cracked the female housing.

    Pipe dope and/or tape make plastic pipe too slippery. You should thread together hand tight...then at most another 1/2 turn.

    Tape is actually not preferred at all on plastic, because it adds thickness, which increases the pressure on the parts.

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    DIY Junior Member rickard681's Avatar
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    First I tried screwing in the elbow and tightening about ¾ turn after hand tight. It leaked. Then I tried tape. It leaked. Then I tried paste. It leaked. Then I replaced the male elbow and did it all over again (tape then paste). It leaked each time. Finally, I tried tape and then paste and putting more threads into the filter housing. That slowed the leak to about 1 drop per second.
    The filter housing is of a very hard plastic compound and is undamaged.
    Any other suggestions other than ‘ you have screwed the pipe in WAY to far’?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Female plastic threaded fittings are a disaster waiting to happen especially when you add vibrations and potential UV exposure to them. You're better off using only pipe dope that is compatible with plastic piping (not all are), but the better choice would be a metal female threaded fitting which won't distort or crack. The tape makes a smooth connection even smoother, letting you thread it in further than desired. Since the pipe fittings are tapered, it's like hammering in a wedge - bad things can happen. Pipe dope alone, while it can also make things slippery, at least conforms to the threads better with less pressure.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member rickard681's Avatar
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    Unfortunately the female threads are in the filter body itself. There is no way to alter all the piping to fit other than the fittings I am using. (filter, heater Lectranator and heater bypass are all on the same pump outlet line .. in series to the pool. Not a lot of choices. I used a digital caliper set to check the roudness of the female inlet in the filter. It is out of round by .32 mm. Although it doesn't sound like much, it is enough to require running the male elbow in far enough that the tapered threads compensate (almost) for the out of round. There in lies the problem. I think I will have to go with RTV in both the felmal & male threads and on the inside of the inlet & on the flange of the female elbow in hopes that it will cure (in about 7 days) to a hardness able to support approximately #25 psig pressure through the 'out of round' fitting.
    Any other idea?
    PS I only use pipe dope correct for PVC.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    If there is any portion of the female thread "sticking out", remove the pipe from it, place a hose clamp around the female thread and tighten it as much as possible. Then put tape on the thread and screw it in tightly.
    Licensed residential and commercial plumber

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    DIY Junior Member rickard681's Avatar
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    Unfortunately, no. The femal threads are all in the body of the filter. Thicker and deeper than the threads on the male elbow. The male PVC elbow threads into the body of the filter approximately 3/4 of the way. Great idea though.
    I would hate to use something permanent on the filter body - female connection that would harden (like epoxy) because when the pump starts it really jambs (vibrates , shocks) the inlet pipe. Anything I use will have to remail pliable yet plug the leak. I think I will have one shot at getting it right or I am out another $650 or so.

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    Moderator & Master Plumber hj's Avatar
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    As a last resort, glue the threads together with primer and PVC cement.
    Licensed residential and commercial plumber

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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by rickard681 View Post
    Unfortunately, no. The femal threads are all in the body of the filter. Thicker and deeper than the threads on the male elbow. The male PVC elbow threads into the body of the filter approximately 3/4 of the way. Great idea though.
    I would hate to use something permanent on the filter body - female connection that would harden (like epoxy) because when the pump starts it really jambs (vibrates , shocks) the inlet pipe. Anything I use will have to remail pliable yet plug the leak. I think I will have one shot at getting it right or I am out another $650 or so.
    I had a very similar problem several years ago when I replaced a Hayward cartridge pool filter, also with 1-1/2 inch ports. I was very concerned that any more tightening of the pipe into the filter thread port would cause the female port to split. My filter had both ports molded so that the entire female fitting had more than enough external surface to install a full stainless steel hose clamp around it to reinforce the casting. I did not have more than a drip either, and I went through the same combinations of (teflon) pipe dope and then tape only, then both. When I had the clamp around the fitting, I used just a little teflon pipe dope and was able to get it to not leak. It must have been a bad thread on either the port or the schedule 40 (dark grey) pipe nipple I bought at the hardware store. Its been about 8 years since I installed that filter, and it still does not leak. I would not let a pro pool company get away with this fix, but as a DIYer, I accepted my own ineptness, lol.

    I thing the pressure I saw at that time was only about 15 inches at the filter. Very little pressure, but a poor joint leaks at low pressure too
    I am definitely not a pro plumber, but I am a pro crastinator

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    DIY Junior Member rickard681's Avatar
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    Thanks all for your insight/suggestions. I wrote to Hayward tech support and their answer was to use 2-3 wraps of Teflon tape and cover with silicone sealant. I am going to try that.

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    Plumber jimbo's Avatar
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    That is the worst advice I have ever heard.....but you have a big problem, and if something works I NEVER argue with success!

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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by rickard681 View Post
    Thanks all for your insight/suggestions. I wrote to Hayward tech support and their answer was to use 2-3 wraps of Teflon tape and cover with silicone sealant. I am going to try that.
    Their suggestion makes it more likely that you will split the port open. Make sure you don't tighten it too much. oops! Aw, shucks!
    I am definitely not a pro plumber, but I am a pro crastinator

  13. #13
    DIY Junior Member rickard681's Avatar
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    Thanks, but very little chance of splitting the port open. The female port is in/through the wall of the cartridge filter. In order to 'split', it would have to crack the entire housing... not likely since the PVC elbow is MUCH softer than the filter housing!
    Jimbo - I concur. It may be the worst advice but if it works ... This came from their Techsupport guy. I 'gotta believe he has heard it/seen it before. We'll see. It it still leaks ... I'll come back here for more sage suggestions. It isn't rocket science. It IS a PVC pipe joint problem.

  14. #14
    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by rickard681 View Post
    Thanks, but very little chance of splitting the port open. The female port is in/through the wall of the cartridge filter. In order to 'split', it would have to crack the entire housing... not likely since the PVC elbow is MUCH softer than the filter housing!
    Jimbo - I concur. It may be the worst advice but if it works ... This came from their Techsupport guy. I 'gotta believe he has heard it/seen it before. We'll see. It it still leaks ... I'll come back here for more sage suggestions. It isn't rocket science. It IS a PVC pipe joint problem.
    Rick, my Hayward is a small C200 that I have for my hot tub, and I felt it would split if I went any tighter without that SS clamp around it. I hope you are successful and stop that leak. If you dried it out well and gooped up the threads with silicone alone and hand tightened it and let it cure for 24 hours, I think that would not leak either.
    I am definitely not a pro plumber, but I am a pro crastinator

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Depending on the silicon used, some can take up to a week to cure properly. So, read the tube's instructions carefully before applying pressure or letting it get wet.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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