Have connected a galvanized 3/4" water pipe to a copper fitting inside a wall and wondered how important is it that these are separated by a brass type fitting or union? OK to use a union inside an outside wall?

Thanks,
Flickit

Hey Flickit,

If you recall from high school chemistry, two dissimilar (different) metals, when placed in an acidic solution, will create a battery. And one metal will usually erode away as the chemical reaction progresses. The other metal may have a buildup of new material, which may be a chemical combination of the eroded metal and the acid. Since virtually all domestic water is slightly acidic or slightly basic, this electro-galvanic action can occur in any metal plumbing system.

When copper and steel pipes are connected together directly, the "battery" has a path for electrical current to flow. (This current is tiny, and the voltage is not a safety hazard.)

If the current cannot flow, because there is no electrical connection (interrupted by the plastic insulators) then the "battery" never discharges. In theory there will always be a small voltage between the different metals. The metals do not erode.
In answer to your question it's acceptable to use a union inside a outside wall. Hope this answers your question, Tom

Thanks, Tom!

I mostly remember sodium and potassium from chemistry and how explosive they are when exposed to water in the school's bathroom! ;)

Flickit

Thanks, Tom!

I mostly remember sodium and potassium from chemistry and how explosive they are when exposed to water in the school's bathroom! ;)

Flickit
Ahhh! The old "cherry bomb" in the toilet trick. Are you saying that you blew up a toilet when you were in school?? Shame on you! We did the same thing in high school in the girls bathroom with a cherry bomb. Made quite a splash! Cheers, Tom

Ahhh! The old "cherry bomb" in the toilet trick. Are you saying that you blew up a toilet when you were in school??? Shame on you! We did the same thing in high school in the girls bathroom with a cherry bomb. Made quite a splash!! Cheers, Tom


Yes, we did and enjoyed it but the stuff is really dangerous. BTW... we used the men's room. After all, we weren't vandals or hooligans... just experimenters.