How to install a union properly?

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    • #276841
      Avatar photoCraig Helber

        How does one go about install/re-install a galvanized union correctly? Can I re-use a old union and expect a perfect air-tight seal? Do I use Teflon tape or pipe dope on the threads that connect the two halves together? I’m having a real problem getting a perfect ‘vacuum seal’ around three 1-1/4″ unions I’ve installed on a well. I’m using two 18″ pipe wrenches with 3-foot extensions and am tightening a much as I possibly can but still have a small vacuum leak. I’m using about two feet of Teflon tape per union. The unions are perfectly in line and I can start threading them by hand. What am I doing wrong?

      • #294862
        Avatar photoRobert Stephen Morton

          Are they brass seated unions or are they flat seated unions?
          If they are flat seated unions – have you made up a grommet?

        • #294863
          Avatar photonicktheplumber

            Unions can leak from two places: 1) the connections to the pipe (threaded or sweated), and; 2) the mating surfaces of the union itself (these surfaces are either machined directly mated metal surfaces or surfaces or surfaces mated through a gasket of some sort, usually rubber or plastic).

            In unions with a seal formed by metal to metal matched surfaces, the surfaces must be exactly matching, clean, and undamaged…or there will be a leak. You can try to reassemble such unions after they have been taken apart, but if they do not hold with reasonable efforts to tighten them down, you need to replace the union.

            Disassembled gasketed unions should have the gasket replaced.

            Leaks at the pipe connections to threaded unions are minimized by a judicious use of pipe dope and teflon pipe tape. or in sweated unions by careful attention to soldering technique.

            Some plumbers swear by the use of pipe dope or tape on the threaded union nut itself, on the theory that any leak from the mating surfaces can be stopped by extra sealant at the union nut. This may prevent some leaks, but in my opinion the purpose of the union nut is to hold the union mating surfaces together, not to serve as a primary seal to leaks from the mating surfaces. The practice of doping or taping the nut threads cannot be condemned outright, but it does, in my opinion, betray a “Hail Mary” approach to plumbing, since your main efforts should be to assure a good pipe connection to the union and a solid leakproof connection at the union mating surfaces.


          • #294864
            Avatar photoPhil_H

              Unions can be disassembled and reassembled. I usually do not waste too much time trying to get a union to seal; I would rather replace it with a new one. I am assuming that you are having problems with a metal union with ground faces.

              I put a little pipe dope or other lubricant on the union nut so that it can be tightened smoothly and more easily. I am not shy about tightening the bejesus out of the nut; the worst thing that can happen is that the nut distorts and then you may have to replace the union anyway. I have been known to put pipe dope on the ground faces of the union when I have had problems with them sealing (Shh don’t tell anybody, I do not want the purist-plumbing-police to come after me).

              Use teflon tape or pipe dope on the pipe threads like any other pipe fitting. My experience is that cheep unions waste too much time. I hate imported fittings. At 1-1/4″, I might consider companion flanges rather than unions. Vacuum leaks are a PITA. Are you sure you know where it is leaking?


            • #294865
              Avatar photoSelgas

                Shhhhhhhhhhhhhh – try puting some graphite grease on both the face and the blade of the unions – just a smear it usually all it takes to take up a small imperfection.

                Whot said that??????????? nope not a Plumber awwwwww heck No it couldn’t be could it lol.

                Selgas Services Ltd
                Craftsman Gasfitters, Plumbers, Electrical Service Technicians

              • #294866
                Avatar photomonomer

                  Thanks for all the responses you guys.

                  I got more information about unions on this bulletin board than on the well driller’s forum and all the ‘do-it-yourself’ plumbing books I could browse through at Schuler’s bookstore. You guys are great!

                  This is what I ended up doing… I bought 3 new unions (brass seated) at Home Depot (they were made in China, sigh). I disassembled all the plumbing between the (3) wells and the pump, cleaned up all the nipples, tees, and couplings. Reinstalled all the plumbing including the new unions using a slow setting pipe dope and yes, I even put a very thin coating on the union nut’s threads (not to stop leaks but rather as a ‘lock tight’ measure so that the union nut won’t vibrate loose over time… remember there’s a pump motor running at other end). Snugged everything down using two 18″ pipe wrenches (no ‘cheater bars’ this time) and IT ALL WORKS!!!!! No vacuum leaks after shutting down for more than 24 hours!!!

                  So again, thanks to everyone that replied… I couldn’t have done it without all that good info you provided.

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