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(dielectric) unions VS brass fittings

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  • (dielectric) unions VS brass fittings

    i don't know if this has been discussed before but i figure it was worth asking.

    do any of you guys use dielectric unions?

    this is why i'm asking, because i don't know if i'm right on with my thinking or am i standing at the flow-edge.

    years ago when i worked for the gooberment the powers that be insisted that we install all staff housing HWT with 3/4" female threaded X 3/4" copper dielectric unions.

    i understand the idea of electrolysis, but we all know that there is bare steel. so the thinking that they prevent corrosion at the take-offs doesn't wash with me. especially with the amount of leaking i see at the joint between the union and tank nipple (take-off).

    i believe the other idea was that when the HWT finally started leaking (7-10 years service up here), one could simply undo the unions and bang bang, HWT is changed right? wrong, at least from what i've observed.

    well, 7-10 years later, i'm changing the same HWT i installed. and i didn't re-use a single one of the dielectric unions. i ended up cutting above and installing new fittings but this time using brass FIP's.

    it's kinda weird to see my old work. but even though it was my work, i still didn't feel comfortable re-using old fittings.

    i have noticed that brass fittings work very well when in direct contact with steel (galv) pipe and fittings.

    any thoughts on this?

    Vince

    i also think that it's just a way to sell expensive, useless fittings to the HO, BO

  • #2
    Re: (dielectric) unions VS brass fittings

    Well, well, well...I want to know the answer to this question too. We all know dissimilar metals will set up a site for corrosion (in this case copper and iron or Brass and iron). This is true (and is how the sacraficial anode inside the tank works)...but how long will it take for the corrosion to have an effect? Too many factors to say for sure. All I know is by practise and what I have come to see. I had a 32 year old Rheem hot water tank connected with 1/2" copper sweat to brass 3/4" female threads...no corrosion at the threads...but after 32 years the tank started to leak from the bottom (heat stress for sure). When I installed a new tank (Home Depot $188 4 years ago) I thought should I use dielectric unions? I did not....When my cousin had a tank installed I asked if the plumber installed dielectric unions? He said no and asked if he should have..I said ..."well, you're supposed to, but I didn't". He bought them for 10 bucks each and made me put them in on his tank...shoulda kept my mouth shut...LOL I do NOT see dielectric unions in most houses I look at...so what is the concensus? Dielcetric unions yes or no?

    Comment


    • #3
      Re: (dielectric) unions VS brass fittings

      I don't like them. Kind of a weak link in the chain. The lined nipples installed from the factory (or available separately) are said by 50% of the people and some manufacturers to be considered a dielectric break even though they are galvanized on the exterior. The state I'm in does not consider them to be a dielectric break at all. Just a galvanized connection.

      The quick answer is I like a brass coupling as the start off. Lasts longer with less chance of problems than a dielectric union or flex connects in my experience.

      But the way water heaters are getting thinner on metal & glass lining, probably any connection will last longer than the heater. Then the connection is just going to be changed anyway.

      J.C.
      Last edited by BobsPlumbing; 12-21-2008, 08:38 PM.

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      • #4
        Re: (dielectric) unions VS brass fittings

        Dielectrics are pure junk.. the rubber gaskets go bad and old heaters that have the unions are so corroded they have to be cut off (useless) I never install those factory nipples with those ridiculous heat traps either ( more like heat raps) I use brass nipples with a brass ground joint union

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        • #5
          Re: (dielectric) unions VS brass fittings

          di electric unions and brass fittings r the same thing they are both di electrics and prevent electrolosis... i prefer the unions and always use them when going from steel pipe to copper. water heaters now usually come with dielectric nipples that r galv. on outside a plastic coated on inside, in which you can come right off width and fip adpt.

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          • #6
            Re: (dielectric) unions VS brass fittings

            Dielectric unions and brass fittings are NOT the same thing. Dielectric unions electrically separate the piping from the hot water tank using a plastic sleeve and rubber gasket. Brass fittings will not do this. Brass fitting basically electrically bond the pipe to the steel hot water tank which you don't want to do.

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            • #7
              Re: (dielectric) unions VS brass fittings

              I like to use s.s. nipples out of the heater into a ground joint union. The kind that is n.p.t. X sweat.

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              • #8
                Re: (dielectric) unions VS brass fittings

                no you r wrong brass stops electrolosis between dissimilar metals look it up. they r not the same fittings but serve the same purpose

                Comment


                • #9
                  Re: (dielectric) unions VS brass fittings

                  Originally posted by Bogart View Post
                  I like to use s.s. nipples out of the heater into a ground joint union. The kind that is n.p.t. X sweat.
                  Do you have a pic of that nipple? If I am reading this right, the nipple is stainless steel, threaded on one end and able to sweat the other?
                  Anyone can tear a man down, few can build one up.

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                  • #10
                    Re: (dielectric) unions VS brass fittings

                    Originally posted by Chemeng View Post
                    Dielectric unions and brass fittings are NOT the same thing. Dielectric unions electrically separate the piping from the hot water tank using a plastic sleeve and rubber gasket. Brass fittings will not do this. Brass fitting basically electrically bond the pipe to the steel hot water tank which you don't want to do.
                    wouldn't the presence of a liquid complete the curcuit anyways? this is way we ground the domestic water right? i could be wrong though.

                    i came across this today.

                    i don't know if this will help.

                    Vince
                    Attached Files

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                    • #11
                      Re: (dielectric) unions VS brass fittings

                      Originally posted by Chemeng View Post
                      Dielectric unions and brass fittings are NOT the same thing. Dielectric unions electrically separate the piping from the hot water tank using a plastic sleeve and rubber gasket. Brass fittings will not do this. Brass fitting basically electrically bond the pipe to the steel hot water tank which you don't want to do.
                      Dr. House....uummm... exactly what part of my posting is wrong?

                      Comment


                      • #12
                        Re: (dielectric) unions VS brass fittings

                        Originally posted by Vince the Plumber View Post
                        wouldn't the presence of a liquid complete the curcuit anyways? this is way we ground the domestic water right? i could be wrong though.
                        I actually just had that debate with an electrician who grounded a whirlpool motor onto the brass valve body.. which had pex adapters sweat onto it. by debate, I mean I made him change it. while it would work in theory, I wasn't comfortable with it. anyone have any input on that?
                        No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

                        Comment


                        • #13
                          Re: (dielectric) unions VS brass fittings

                          Pure water is a poor conductor of electricity when compared to aluminum, copper, silver, etc....but FAR a poor conductor. Water that has dissolved salts in it, (like tap water, and even more ---> sea water) will have increase conductivity, but still, a VERY poor conductor. I don't want to bore you with the numbers,if yo are interested look it up in a chemistry book.

                          For Vince: This would explain how the introduction of a liquid (tap water) POORLY completes the circuit and results in very slow (probably not noticable in a lifetime) electrolysis in the system. You need dissilimar metals in contact for electrolysis to happen.

                          Comment


                          • #14
                            Re: (dielectric) unions VS brass fittings

                            Originally posted by Chemeng View Post
                            Pure water is a poor conductor of electricity when compared to aluminum, copper, silver, etc....but FAR a poor conductor. Water that has dissolved salts in it, (like tap water, and even more ---> sea water) will have increase conductivity, but still, a VERY poor conductor. I don't want to bore you with the numbers,if yo are interested look it up in a chemistry book.

                            For Vince: This would explain how the introduction of a liquid (tap water) POORLY completes the circuit and results in very slow (probably not noticable in a lifetime) electrolysis in the system. You need dissilimar metals in contact for electrolysis to happen.
                            i understand the electrolysis thing with dissimilar metals.

                            but the domestic water pipe is grounded. the elecrical system is grounded. i still don't understand the need for these unions.

                            maybe they should make brass dielectric unions. i would use those.

                            Vince

                            Comment


                            • #15
                              Re: (dielectric) unions VS brass fittings

                              Looking at a technically correct bonding, would it not require a bonding line between the hot / cold lines bypassing the W/H altogether? The Dielectric unions only keep the metals separated. Water, in a this sense is a conductor but if you have an air bound system, it does not really apply if for some reason the home loses water pressure, the tank siphons and has no water to complete the bond...
                              As to the Brass, it is more amenable to to prevent any further bi-metallic corrosion, hence why you see the failure of more galvy piping connections than you do see with brass.
                              Pat Martinez
                              M5 Plumbing Services LLC

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