Sealing air leak without removing fittings

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  • newbie2wood
    Established Member
    • Apr 2004
    • 453
    • NJ, USA.

    Sealing air leak without removing fittings

    I just replaced the pressure switch on my air compressor. I have a very small leak at one of the fittings (about 2psi per hour).

    Is there any way to seal the leak by applying a sealant to the fitting without removing it?

    It was a PITA to replace this switch, and I would like to avoid removing it again to get to the fitting. I'm also concerned that if I keep removing and reinstalling the switch, I'm going to crack the plastic housing that is connected to the fitting or cause a more significant leak elsewhere.
    ________
    HotCummers
    Last edited by newbie2wood; 09-15-2011, 06:14 AM.
  • cabinetman
    Gone but not Forgotten RIP
    • Jun 2006
    • 15218
    • So. Florida
    • Delta

    #2
    Originally posted by newbie2wood
    I just replaced the pressure switch on my air compressor. I have a very small leak at one of the fittings (about 2psi per hour).

    Is there any way to seal the leak by applying a sealant to the fitting without removing it?

    It was a PITA to replace this switch, and I would like to avoid removing it again to get to the fitting. I'm also concerned that if I keep removing and reinstalling the switch, I'm going to crack the plastic housing that is connected to the fitting or cause a more significant leak elsewhere.

    I would recommend pumping up the compressor with any lines hooked up and brush on a soapy water solution to all the fittings and see what gives. Then remove those fittings and seal with teflon tape.

    I'm not aware of any sealants that will work from the outside.
    .

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    • newbie2wood
      Established Member
      • Apr 2004
      • 453
      • NJ, USA.

      #3
      I already tried the soap trick, that's how I know that one of the fittings is leaking.

      The problem is that to test for leaks I have to install everything each time and torque every fitting tight. It is a PITA to remove the fittings after they are as tight as can be. I did the soap test three times already and managed to seal most leaks. My hand is raw from trying to remove the fittings and reattaching them together again and again.

      The current leak is very small, and I could live with it but was just wondering if there was a specific product for this problem.

      A solution that I was thinking of was to smear some liquid teflon paste on the exposed thread of the fitting, but I'm no sure if it would seal the leak? Does teflon paste dries?
      ________
      The View Condo
      Last edited by newbie2wood; 09-15-2011, 06:15 AM.

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      • cabinetman
        Gone but not Forgotten RIP
        • Jun 2006
        • 15218
        • So. Florida
        • Delta

        #4
        I doubt anything would work from the outside. Having to crank up the fittings that tight means you don't have enough tape on the threads. If you wrap the threads 3-4 times it will allow a gradual tightening without over tightening.

        Wrap the threads so the loose end of the tape gets run over as it gets threaded. IOW you don't want the edge of the tape to be fed into the connection, you want it to trail.
        .

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        • LCHIEN
          Internet Fact Checker
          • Dec 2002
          • 20914
          • Katy, TX, USA.
          • BT3000 vintage 1999

          #5
          i assume you're talking about tapered NPT type fittings. These should close any gaps when tighted w/o having to crank down/ You may not be uisng enough teflon tape. Its also been past practice to use pipe dope before teflon tape became popular.
          Basically these types of fittings should be so reliable in mating that you don't have to test them afterwards. Something is probably wrong... not enough tape or a defective fitting.

          As for sealing without disassembly, I would think you can suck a sealant into the joint if you can somehow pull and hold a vacuum on the tank... otherwise it would just be on the surface and blow out. The sealant would have to be thin to run in and then have to cure in place... Superglue? varnish? I don't know.
          Loring in Katy, TX USA
          If your only tool is a hammer, you tend to treat all problems as if they were nails.
          BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

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          • Black wallnut
            cycling to health
            • Jan 2003
            • 4715
            • Ellensburg, Wa, USA.
            • BT3k 1999

            #6
            Teflon paste does not harden enough to do what you are asking. Teflon tape is a lubricant not a gap filling sealant. If your threads alone do not seal I recommend a hardening paste sealant such as Rector seal. Or better yet chase the female threads with a tap and try again.
            Donate to my Tour de Cure


            marK in WA and Ryobi Fanatic Association State President ©

            Head servant of the forum

            ©

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            • cabinetman
              Gone but not Forgotten RIP
              • Jun 2006
              • 15218
              • So. Florida
              • Delta

              #7
              Originally posted by Black wallnut
              Teflon tape is a lubricant not a gap filling sealant. If your threads alone do not seal I recommend a hardening paste sealant such as Rector seal.

              So, are you saying do not use teflon tape on threaded airline connections?
              .

              Comment

              • Black wallnut
                cycling to health
                • Jan 2003
                • 4715
                • Ellensburg, Wa, USA.
                • BT3k 1999

                #8
                Originally posted by cabinetman
                So, are you saying do not use teflon tape on threaded airline connections?
                .
                Not at all. I'm saying that if you have a poor match up between the threads teflon tape will not seal it, although it might for a while. I normally use teflon tape for small joints. I've seen tape fail lots of times when used with hydraulic fluid. I've seen tape fail lots of times with black iron, galvanized, poly, as well as stainless steel pipe and fittings. I use tape for the lubrication properties. It is the nature of tapered pipe threads alone that they should be self sealing. Tape allows you to put more torque on fittings as well as helps prevent galling in some materials such as aluminum.

                After saying all this I am not a plumber nor have I ever been, I've not stayed in a Holiday Inn Express lately and have not been on TV. I did for 5 years work in a job where plumbing skills were used nearly every day. Working with NH3 and other products, as well as water in pipes as small as 1/4"NPT to as large as 3" NPT (threaded connections) and even larger with PVC pipe. I think it would be fair to say I've done a bit of plumbing.
                Donate to my Tour de Cure


                marK in WA and Ryobi Fanatic Association State President ©

                Head servant of the forum

                ©

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                • newbie2wood
                  Established Member
                  • Apr 2004
                  • 453
                  • NJ, USA.

                  #9
                  Thanks for the responses.

                  I decided to fix the problem the right way by removing the pressure switch and all the fittings again. Rewrapped teflon tape around the male fittings and assembled the pieces. I got to the last fitting and, my luck, cracked the brass compression nut. I guess I will be going to the BORG tomorrow.
                  ________
                  HEADSHOPS
                  Last edited by newbie2wood; 09-15-2011, 06:15 AM.

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                  • phi1l
                    Senior Member
                    • Oct 2009
                    • 681
                    • Madison, WI

                    #10
                    It sounds like you are tightening a lot more than you should have to, especially if you are breaking compression fitting nuts. Compression fittings should only be tightened so tight. Something like only 1/2 to 3/4 turn after being finger tight. (& just to be clear, you do not use Teflon tape or pipe dope on compression fittings). Most old plumbers I know still prefer pipe dope for sealing pipe threads. I have no preference though. after hand tightening pipe threads usually only 2-3 more turns are required to seal the joint.

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