Leaking unions

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by nate379, Jan 9, 2013.

  1. nate379

    nate379
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    Anyone have a solution for leaking di-electric unions?

    I've replaced the washers a couple times and they don't last. If it was just ONE union I'd figure maybe it's out of spec or something, but pretty much all of them do it.
     

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  2. huffdawg

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    Clean them up good then put some thread sealer on. Everyone of mine leaked till I put on a thin coating of thread sealer
     
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  3. huffdawg

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    Sorry I missed the dielectric part. I have. Some that leak on my Dhw tank when the temp is low.
     
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  4. Bob Rohr

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    get rid of them and use a copper to male or female adapter :)
     
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  5. Fred61

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    Free abrasive machining AKA "Lapping". Remove fittings > clamp one side in vise > apply silicone carbide slurry mixed with oil > mate surfaces and rotate clockwise then counter clockwise 'till your sick of it.
     
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  6. nate379

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    I'm going to have to read up on exactly the benefits of a di-electric union vs just metal to copper connection. I think it's worse since the boiler has a temp swing of ~150* between when it's on or off.

     
  7. BoilerMan

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    I have asked about the benifits of dielectric unions to my supplier and plumbing friends. They all say the same thing "don't use 'em 'cause they'll leak" It's been my expierence and observation, and I do look at these things, that in a closed loop system they are totally un-necessary. There are many old direct transitions from iron/steel to copper with no leaks or problems. That have been that way for several decades. This said fill water quality may have something to do with it.

    On open systems however, I only will use male copper adapters threaded into iron or steel. Never female threaded over iron/steel. Again water chemistry has alot to do with this type of connection. Never use galvinized for a transition to copper though, you will have trouble and in short order.

    Chemistry says, as well as the engineers, there will be galvanic corrosion and pitting in a direct transition of disimmilar metals in the presence of an electrolte. This has not been my oopservance in plumbing systems here in the north, and if you think about it, you are going to have a leak with dielectric unions, with direct connections you may not at all, I'm going with the chance that I may not at all. Tape and dope has never led me astray.

    These are my own personal observations, and findings in my area, take it as you may.

    TS
     
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  8. Bob Rohr

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    What temperatures are you running. You need to order the high temperature gaskets for use above 180°F. We have switched to a silicone rubber gasket for our solar fittings where temperatures can exceed 300°F under stagnation conditions.
     
  9. Fred61

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    Oh, dielectric unions! Sorry!! Yea, don't use them. I'm taking my chances with disimilars in contact with each other.
     
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  10. maple1

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    Me too.
     
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  11. heaterman

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    The only place we use Dielectrics is in fresh water situations as you would have on a domestic hot water heater. Never on a heating boiler or piping connected to it.

    They will all leak eventually. Period.

    Best to get rid of them.
     
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  12. nate379

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    The main one that is leaking right now is the main output of the boiler which is a 1.25" line. Cold start boiler so it might be at room temp 50-60ish all the way up to around 200* all depending on outdoor temp (have an outdoor reset)

    This is all on my natural gas boiler, but doesn't really matter how it's fired in this case.
     
  13. Bob Rohr

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    Water heaters see a wide temperature swing also, they should be able to work from 32° to the rated 180°F.

    The only plus of a dielectric union is you can easily remove the tank or boiler. Other that that they are more headaches that value.

    Usually a plumber takes a tube cutter or hacksaw and cuts the tube anyways. It's's rare to find a replacement water heater that fits up to the old piping.
     

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