Think you'll find it is a Reverse Buckling Disc. Io ensure it is assemble correctly, the disc is held between the holders by the 'Side Strap' which should indicate the direction of flow. This is so done as to ensure proper installation in the direction of flow. See attached. Most discs now being self rupturing are installed the over way.
Per ISO-4126, only the term Safety Valve is used regardless of application or design.
Thank you for the replies,
Here is a drawing showing the side strap and assembly screws. I believe this is the same as the generic drawing Obturator provided in that the side strap is to hold the disc between the holders and that this strap and screws are not wetted parts correct?