Dielectric unions on Bladder expansion tanks?

Used to hear people recommending a brass fitting between iron and copper to step the galvanic potential into 2 smaller steps than straight iron-to-copper.

Makes sense logically but I don't know if it's helpful to any real-world extent.

I'd like to hear an opinion on this from some of the experienced authorities around here.

There was a thread about this awhile ago. in my experience I have seen no need any closed-loop system to use dielectric unions. However, I like to use copper threaded into iron or steel instead of copper threaded over iron or steel. I have little use for female copper adapters.

TS

I researched this recently for my relocate/replumb to bring storage online. In my pressurized closed system I decided to go with copper into iron where necessary, and use brass between copper and iron wherever iron had to go into copper. This lowered the overall cost of fittings and protects those few female copper fittings I have in the loop.

From all that I read, copper into iron is not an issue except where fresh water is continually entering the system or in open systems.

Copper threaded over iron/steel will stretch with time and leak. Copper threaded into iron/steel will not have any issues in a closed loop system, never seen a leak from galvanic corrosion in a closed loop system threaded this way. Ever.

TS

EDIT: The dielectric unions I've seen used (few) in the field that were spec'd to be there in a heating system were leaking from the plastic washer.

I have seen more issues on the dielectrics then I have ever seen on systems with dissimilar metals. The systems I've seen that possibly had a electrolysis problems, weren't mixed metals.

Hey GG - how big are those tanks?

I am also considering swapping out for a bladder tank - maybe a project for next summer. Been thinking about how to do it since before I got my system on-line, or if I should.

Curious on how they handle the temp rises, & pressures you see with them.

gg, you piped them up exactly how I'd have done it, black reducing coupling with copper threaded into it! Nice looking job, I like your shelving too.

TS