US Patent 7325569 Butterfly valve with integral split flapper relief valve

A valve is provided that includes a valve housing, a valve element, and a flapper. The valve housing has a passage. The valve element is rotationally mounted in the passage and moveable between an open position and a closed position. Additionally, the valve element has a flow channel extending therethrough. The flapper is coupled to the valve element and moveable between a closed position, to thereby substantially seal the flow channel, and an open position, to thereby unseal the flow channel, the flapper configured to move to the open position when a differential pressure across the flapper reaches a predetermined value.