PVC unions and constant pressure?

Discussion in 'Homeowner Assistance Forum' started by Geoff A, Jul 16, 2008.

  1. Geoff A

    Geoff A LawnSite Member
    Messages: 3

    Is it advisable to use PVC unions under constant pressure? I have an assembly of shutoff valve -> filter -> RPZ. Everything can be serviced without breaking any connections, so I saw no need to use unions and risk a leak. Well, the threaded connections are leaking ever so slightly, and I have to cut the PVC mainline every time I want to tighten them. As you can imagine, this is a major PITA. So I'm thinking of adding a union or 2 so I can tighten leaks as they develop, without breaking out the pipe cutters and cement. Any suggestions?

    The pressure is 85 PSI, by the way.

  2. greendoctor

    greendoctor LawnSite Fanatic
    Messages: 9,975

    It is very advisable to use unions. Your situation explains why. PVC is not very forgiving of being overtightened. Crank down on it like you do galvanized pipe thinking it won't leak because it is so tight and fitting will crack. It is preferable to have unions so the fitting can be adjusted. I am not an irrigator, but I frequently fix their work.
  3. steve45

    steve45 LawnSite Bronze Member
    Messages: 1,325

    I've used unions for years on my pool plumbing. Max presure is only about 30 PSI.

    One thing I do is put some lubricant on both the O-ring and the threads. I use Jack's lube from Leslie's Pool Supply.
  4. Geoff A

    Geoff A LawnSite Member
    Messages: 3

    Hmm, that pressure worries me. I mean, I've seen prefab manifolds used in pressures over 100 PSI with no leaks, and they use o-ring seals, right? So unions should stand up to the pressure, correct?
  5. steve45

    steve45 LawnSite Bronze Member
    Messages: 1,325

    Should work, as long as you use the appropriate grade of pipe for the pressure. Make good joints, i.e. clean, primed, and adequate glue with twisting motion during assembly.

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