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Thread: Dielectric unions and water heaters

  1. #16
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    We are seeing the nipples supplied by the heater manufacturers fail before the heater. Take a look at these nipples they are not sch 40 steel nipples.

    John

  2. #17
    Master Plumber Redwood's Avatar
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    Here the water conditions are good enough that the dielectric nipples are sufficient.

    However in some areas the water conditions are poor enough that the dielectric nipples are not enough.

  3. #18
    Moderator & Master Plumber hj's Avatar
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    Default nipples

    Dielectric nipples have a plastic liner that is supposed to provide the break between the parts of the tank and the pipe in contact WITH the water. WATER is the electrolyte which powers electrolysis, not the mere fact that two materials are contacting each other. You could screw a steel pipe into a copper fitting and set it on your workbench, then come back 100 years later and they would be the exaCTLY same, except dirtier.

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    DIY Member SemiHandyRon's Avatar
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    Quote Originally Posted by Redwood View Post
    However in some areas the water conditions are poor enough that the dielectric nipples are not enough.
    What would be in the water for it to be considered "poor" in the sense used here?

  5. #20
    General Contractor dx's Avatar
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    Quote Originally Posted by hj View Post
    Dielectric nipples have a plastic liner that is supposed to provide the break between the parts of the tank and the pipe in contact WITH the water.
    Better look again. The Bradford heater I just bought has steel nipples. No liner on the nipples, just the heat trap retainers.I don't know if the nipples are separated from the rest of the tank and it doesn't matter.

    The nipples are steel and they sit in water. If I connect copper fittings to them, there WILL be galvanic cells and the nipples WILL corrode.

    Edit: Still curious, how did you decide how long of a brass nipple is "sufficient separation"?
    Last edited by dx; 12-23-2009 at 09:33 PM.

  6. #21
    Forum Admin, Expert Plumber Terry's Avatar
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    Edit: Still curious, how did you decide how long of a brass nipple is "sufficient separation"?
    The City of Bellevue prefers 6" brass nipples too.

  7. #22
    Plumber Cass's Avatar
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    Here the only insulated nipples that I see fail are the ones that some plumber attatched a copper FIP adap. to and then soldered tubing to it causing it to melt the plastic lining of the nipple...personaly I solder pipe to the adapter first then install it on the nipple...I have no dialetric problems when doing it that way...

  8. #23
    Master Plumber master plumber mark's Avatar
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    Talking why not use flex connectors????

    Quote Originally Posted by dx View Post
    Better look again. The Bradford heater I just bought has steel nipples. No liner on the nipples, just the heat trap retainers.I don't know if the nipples are separated from the rest of the tank and it doesn't matter.

    The nipples are steel and they sit in water. If I connect copper fittings to them, there WILL be galvanic cells and the nipples WILL corrode.

    Edit: Still curious, how did you decide how long of a brass nipple is "sufficient separation"?
    I know that this is falling on deaf ears, but
    why not use BLACK SS Brass craft flexible water heater connectors??

    female to female ...

    connecting to the dialectric nippels
    on the top of the heater and then onto the copper male adaptors soldered
    to the copper pipe about 18 inches away???

    .isnt that about 10 times better than
    just shitty old dialectric unions??





  9. #24
    General Contractor dx's Avatar
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    Mark, funny you should mention those.

    My plumber ended up using a version of those, only better. He used ss flex hoses with a threaded brass female at the heater end

    BUT

    they have brass sharkbites at the other end so you can go to copper directly. No adapters, no soldering.

  10. #25
    Master Plumber master plumber mark's Avatar
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    Talking those are sweet but expensive

    Quote Originally Posted by dx View Post
    Mark, funny you should mention those.

    My plumber ended up using a version of those, only better. He used ss flex hoses with a threaded brass female at the heater end

    BUT

    they have brass sharkbites at the other end so you can go to copper directly. No adapters, no soldering.
    the ones you are talking about are real nice but they cost about
    19 bucks each... and dont seem too flexible to me


    the black ones are about 10 each and you can almost tie them in a knot .... and no future call backs for any leaks in the handful of copper fittings going to the heater...

    no stress on the pipes if the heater begins to sag or their is movement in the foundation of the home...

    we have probably gone through about 1000 of them

    I carry 24 inch, 18 inch and 12 inch with me and they
    probably save me a good hour on the install


    some people like to see straight pipes going intothe heater
    but these definitely work much better for the union effect



  11. #26
    DIY Junior Member Couch-Tuber's Avatar
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    Quote Originally Posted by dx View Post
    My plumber ended up using a version of those, only better. He used ss flex hoses with a threaded brass female at the heater end

    BUT

    they have brass sharkbites at the other end so you can go to copper directly. No adapters, no soldering.
    I thought this thread was about dielectric unions and ways to isolate any current, dissimilar metals? If you use flex tube which has stainless steel jacket, you still have a conductor running the length and depend on that little plastic T flange inside the brass nut. That is about 1/32" separation wihch could form rust in bad water and create contact.

    I saw the Brasscraft black pipe Mark mentions but shy'd away as I'm afraid of plastic thinking copper is stronger. But they're website says it is made from as polymer tube with polymer braid. Like PEX perhaps? THey don't say cross linked polymer. But still, no conductivity the length of the tube. Sounds like what I was looking for (see my other thread on dielectric unions).
    Ask the experienced rather than the learned (old arabic proverb)

  12. #27
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    Quote Originally Posted by hj View Post
    Dielectric nipples have a plastic liner that is supposed to provide the break between the parts of the tank and the pipe in contact WITH the water. WATER is the electrolyte which powers electrolysis, not the mere fact that two materials are contacting each other. You could screw a steel pipe into a copper fitting and set it on your workbench, then come back 100 years later and they would be the exaCTLY same, except dirtier.
    So when tightening down a fitting to the top of the dielectric nipple, is it important that the fitting compress down on the plastic that extends above the top of the nipple so that it acts as a seal to keep water from contacting the threads of the nipple and fitting (where the dissimilar metals would be making contact)? Does that protruding plastic act as any long-term seal to keep water away from the threads? Or does a proper amount of Teflon tape on the threads act as the separation?

    Also, is there a greater deal of insurance in attaching a brass fitting to the nipple than a copper one? I've read in this thread about using flexible pipes to come off of the nipples to further reduce problems but this particular instance involves a solar hot water heater where I need to use copper for the solar loop and I'm having to tie in a mixing valve between the cold in and hot out between tank and house, plus an thermal expansion tank on the cold side. It seems like it would be impractical to do this in other than copper. I don't want the weak link of the system to be the connection to the tank (in this case, four ports: solar in, solar out, cold in, hot out) so I want to do it in whatever way is deemed best by those of you who have had years of experience in observing system failure at this point (although it sounds like the dielectric nipples have only been out a few years).

    Thanks.

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