Hallo,
Check axial = nozzle type, non-slam check valve
300# = ANSI flange class 300 rating
RF = Raised face
STL = usually Stainless Steel, but for me this is not a wise way to stamp it since there is so many SS family. More industrial standard is to write for example 316SS or 304 or 401, etc.
STEL = Stellited sealing area. This I am not so sure. More proper way to say it should be ST6 for Stellite 6, ST21 for Stellite 21, and so forth
S&D = ????
some fabricant may use different abbreviation, in order for end user to keep buying 'like to like' valves from the same manufacturer. When in fact it is quite similar with other products.
Regards,
Danlap