Check valves

A check valve comprising:

• a valve housing defining a pair of valve openings;
• a pair of flappers pivotably mounted for rotation relative to the housing between an open position in which they permit fluid flow through the respective valve openings and a closed position in which they prevent fluid flow through the valve openings;
• and
• a stop element arranged such that the flappers will contact the stop element in their open positions;
• wherein:
• each flapper comprises a primary flapper element pivotally mounted to a hinge pin extending across the valve, and a secondary flapper element;
• the primary flapper element further comprises at least one flapper opening formed therethrough;
• and
• the secondary flapper element is pivotally mounted such that it may rotate relative to the primary flapper element for opening and closing the at least one flapper opening in the primary flapper element;
• wherein:
• the stop element, each primary flapper element and each secondary flapper element are configured such that when each flapper is in the open position and in contact with the stop element, both the primary and secondary flapper elements contact the stop element and a clearance is provided between the primary flapper element and the secondary flapper element of each flapper.