Looking for an approval standard for copper butterfly valves.
can't help with the approval standard.
However, I am interested in knowing the application that you are using a copper butterfly valve, instead of say, stainless.
Perhaps you mean bronze butterfly vavles, and the standard may be AWWA.  If so, do an internet search for AWWA butterfly valves and you will find many manufacturer's catalogs from which you can find the rest of what you are looking for.

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