Need for Dielectic Unions?

[DenaliChuck]

I've just heard that you don't need a dielectic union between copper and cast iron. Is this true?

Thx!

 

[DWW68]

This is true. Copper to galv., different story.

 

[DenaliChuck]

Thanks DWW68

Also, copper to black pipe wants a dielectric union if I understand correctly?

 

[in hot water]

if it is a closed loop system, skip the dielectric unions on cast to copper or steel to copper.

Open loop systems see fresh O2 and as a result corrosion from electroylsis is possible.

Really no reason to use galvanized pipe in a closed lop system, so you shouldn't have a copper to galv issue.

In open loop plumbing you need a means to disconnect dis-similar metals. Ii prefer dielectric nipples, copper flex with the proper ends, even a brass nipple. Dielectric unions are a bit of a headache for plumbers.

JMO

hr

 

[Jackpine Savage]

This is true. Copper to galv., different story.

I can personally attest to this one. I helped my BIL the plumber put in some underground water piping in a barnyard. The place had a high water table and the hole kept collapsing. Somehow in our haste to get things put together we ended up with a galvanized nipple in between two brass fittings (I guess it wasn't copper, per say). Two years later we were again back down in the hole replacing it.

 

[pybyr]

copper and zinc (galvanized pipe) make a heck of battery- just stick a scrap of each in a cut open lemon, which supplies the acidity, and you can light a penlight lightbulb with it.

galvanic action

Look up Luigi Galvani on Google...

the ions of the metals give themselves up in the corrosive solution, yielding a flow of electric current.

the ions quite literally get off on this, but you won't like the results... it results in dissolution of the competing metals into the corrosive solution

iron is way less active than zinc, so is copper, especially in an electrolyte depleted environment, which is what a hydronic system with proper pH and air vents should quickly become