I am having some leaking problems when I instal a galvanized water union

i am having some leaking problems when i instal a galvanized water union

I broke into the trade before copper and plastic in mt area. The reason you are having trouble is that you're treating it like a PVC compression fitting, IF I crank down hard enouth the two faces will join up."
Not so with galvanized unions. The two faces must be perfectly allined. If they don't mate up you'll have a small keak. Try this.
Make sure the two faces are in alignment and coat the two faces with pipe dope.
Now tighten the union back up. Good luck, Tom