Check and a butterfly valve combination valve. Also the supplier of back flow preventor valve.
have just seen once a check/butterfly combination valve built by Mokveld.
This combination has the bad disadvantage, that you can not replace the check valve without draining and depressurizing the system.
You also have a very special item in your system instead of two "standard" itmes.
Try to contact a check valve manufacturer like Noreva and see if they can offer a butterfly together with their check valve as a package.

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