Dielectric union for aluminum water heater to brass connector?

Discussion in 'OnBoard Electronics & Controls' started by sdowney717, Nov 5, 2012.

  1. sdowney717
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    sdowney717 Senior Member

    Got me thinking. A few years ago I pulled out the AC water heater for inspection etc...
    I noticed the aluminum threads going into water tank were corroded where the brass connector for the pipe fits. I then bought a large long magnesium anode rod and used that in place of the plastic drain valve.

    Now I was wondering if it should have an insulated union between these 2 differing metals.

    Any ideas?
     
  2. michael pierzga
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    michael pierzga Senior Member

    Aluminium and steel are friends. Aluminum and brass are enemies. When in doubt use steel with aluminium.
     
  3. sdowney717
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    sdowney717 Senior Member

    Steel will rust.
    A short piece of PEX or perhaps a plastic fitting for the water tank. Join 3/4 plastic fitting to 1/2 copper pipe idea.

    Connection is currently done with 1/2 bendable copper pipe and a brass compression sleeve mated to a brass fitting.
     
  4. gonzo
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    gonzo Senior Member

    Nowadays plumbing is usually all plastic, so the problem doesn't exist. A plastic fitting between copper and aluminum will help but not totally eliminate the problem.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Installing a simple PVC male to female adapter will solve this issue easily.
     
  6. sdowney717
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    sdowney717 Senior Member

    Just what I was thinking.
    Water heater is 3/4 thread female

    My brass coupler uses 1/2 copper compression sleeve on one side and 3/4 male on the other which screws into the water heater.

    Is there a PVC fitting 3/4 male by 3/4 female thread?
    If not then what fitting to get to use with the compression sleeve 1/2 copper pipe?
     
  7. PAR
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    PAR Yacht Designer/Builder

    [​IMG]

    Commonly called a riser or extender fitting. Schedule 80 would be my choice (usually gray). Conversely, you could use a reducing fitting or a slip union with a male adapter. There's a bunch of ways to skin this cat. Pick one with no moving parts to be safe.
     
  8. SamSam
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    SamSam Senior Member

    The PVC adapter is best, but would plumbers tape work at all?
     
  9. PAR
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    PAR Yacht Designer/Builder

    Technically, you're not supposed to tape a male to female PVC fitting, because it'll tend to split the female, but I've experienced leaks on high pressure joints without dope or tape. The biggest issue I've found with amateurs is they over tighten PVC joints. I made this mistake a lot, until I learned. Hand tighten the joint, then another turn or two is all you need. Yep, it'll feel like it's not tight enough, but the plastic has deformed in the tapered thread (pipe threads) and it'll seal. Most recommend a sealant in a threaded joint, not tape.
     
  10. SamSam
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    SamSam Senior Member

    What I was wondering is if plumbers teflon tape alone would insulate between the aluminum and brass/copper connections.?
     
  11. PAR
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    PAR Yacht Designer/Builder

    No, it will not. The tape lubricates and seals, but thread to thread contact still occurs. The tape fills tiny imperfections in the threads and helps them slip past each other as they're tightened. Simply put, they'll still carry a "bond" and retain continuity.
     
  12. sdowney717
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    sdowney717 Senior Member

    Nice idea that fitting.

    If you ever have trouble with weeping threads use some automotive silicon Permatex gasket maker to seal them. I tried all sorts of pipe dope and teflon tape on a weeping expansion valve which never sealed. Part of the problem was where I wanted the output to be oriented. So cleaned it all off and used the gasket maker and it stayed dry.
     
  13. sdowney717
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    sdowney717 Senior Member

  14. PAR
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    PAR Yacht Designer/Builder

    Yes, all the major big box stores carry this fitting. I have two on my PVC shelf, here. You can also use a female to slip in adapter, a short length of pipe and a slip in to male adapter, which can solve some installation issues, as you're gluing instead of trying to tighten.
     

  15. sdowney717
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    sdowney717 Senior Member

    Yes, I found it at Lowes for 70 cents each.:p
    thanks Par for the idea on that fitting.
     
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