Dielectric union vs brass adapters

[chander]

I have been seeing brass male propress adapters connected to black unions lately. Is this an acceptable practice now? I was always taught to use a dielectric union in this application. This piping is used for boiler hot water.

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[Turtleman]

i will bite , obviously no black pipe being used for the water. I have only seen dielectric unions on the water side.

and as far as the gas line i believe you can use dissimilar metals.

[Spitz]

Not necessary in a closed loop

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[chander]

Not necessary in a closed loop

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Dielectric unions are not necessary on a closed loop system? All of the commercial sites that I am on use them.
Is this something specified by engineers or required by code?

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[ammoniadog]

Lots of different opinions on this. I believe dialectic breaks between copper and steel ARE needed in a closed boiler/chiller system. I have been taught that if using brass fittings between the copper and steel to accomplish this, the brass should be at least 4" long.

I don't like dielectric unions because they tend to be a weak link that will end up leaking. The brass propress adapter screwed into a black union might not provide a long enough break between the steel and the copper, but it's better than screwing copper right into the steel, and it's probably better than using a dielectric union that has a high possibility of leaking.

If I were doing it, I would use the black union with a short brass nipple, going to a brass coupling, going to the brass propress male adapter.

Or I might do the black union with the brass nipple going to a brass propress female adapter, but I try to avoid female adapters if I can help it because they seem to leak often too. The brass propress female adapters are better than normal copper female adapters though. I avoid copper female adapters at all costs whenever possible.

Another solution would be to incorporate a brass ball valve as the dielectric break. For example, a black threaded union going to a short black nipple going to a threaded brass ball valve with a brass or copper male adapter screwed into it. I think that would be alright too.

[chander]

Lots of different opinions on this. I believe dialectic breaks between copper and steel ARE needed in a closed boiler/chiller system. I have been taught that if using brass fittings between the copper and steel to accomplish this, the brass should be at least 4" long.

I don't like dielectric unions because they tend to be a weak link that will end up leaking. The brass propress adapter screwed into a black union might not provide a long enough break between the steel and the copper, but it's better than screwing copper right into the steel, and it's probably better than using a dielectric union that has a high possibility of leaking.

If I were doing it, I would use the black union with a short brass nipple, going to a brass coupling, going to the brass propress male adapter.

Or I might do the black union with the brass nipple going to a brass propress female adapter, but I try to avoid female adapters if I can help it because they seem to leak often too. The brass propress female adapters are better than normal copper female adapters though. I avoid copper female adapters at all costs whenever possible.

Another solution would be to incorporate a brass ball valve as the dielectric break. For example, a black threaded union going to a short black nipple going to a threaded brass ball valve with a brass or copper male adapter screwed into it. I think that would be alright too.

Thanks for your info.

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[superscifi12]

I was taught to use dielectric nipples with a brass threaded union in heating water situations.

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[Calgaryhvac]

Most all threaded fittings are taped and doped. It’s not designed to be a gasket but still allows some measure of separation from corrosion.

[ammoniadog]

Most all threaded fittings are taped and doped. It’s not designed to be a gasket but still allows some measure of separation from corrosion.

Nice try, but not good enough. I do subscribe to your theory a little bit by using anti-sieze instead of teflon tape or pipe dope when installing probe-type low water cut-outs in boilers. My theory is that the anti-sieze is electrically conductive, which in my mind is what you would want with these types of probes.

When you screw a copper male adapter into a steel fitting (or worse yet a copper female adapter onto a steel pipe), the tape/dope won't do much to prevent the electrolysis from happening if the conditions are right.

[bc5272]

This is a huge topic of conversation in our company. Here is my take I have 32 years in the business and am still as dumb today as on day one. Please give any feedback be it good or bad. A brass ball valve IMO breaks electrolysis. In a closed-loop system that is chemically treated and air is out of the system I do not see much of a problem. I do however see more issues with the rubber gaskets on dielectric unions leaking as well as a dielectric nipple, the plastic inner causes leaks. You tighten the nipple into one side of the fitting I have seen the plastic inner be pushed a bit out on the other end. When you go to tighten the other end the plastic bottoms out before you actually get the fitting tight causing a leak. Also on a system such as a water source heat pump loop, I never see this issue. I retrofit 60-year-old courthouses that have no dielectric anywhere and no issue whatsoever. In chilled water systems, I see a lot of issues but more from condensation. Please any input or if anyone knows of an engineer or someone that could convince me or my shop other wise jump in . Have a great day all.

[Calgaryhvac]

Most things on a heating system conduct electricity. There’s “best practice” and reality. The reality is that by the time electrolysis has taken its toll on a heating system due to dissimilar metals being joined together, you’ll be due to replace it anyway.

I agree with what you’re saying completely. That being said, if it leaks, it’s a job; it will most likely leak long after any questions pertaining to quality of installation are long gone.

Additionally, most systems that are large in Canada are built from black iron (or some ferrous metals). Every valve is brass or copper or some composite. Most all our products are from the USA. Is there really any way around electrolysis? And why is a 4” nipple going to help prevent electrolysis ? Just curious as I’ve never heard that before. Thanks