Composite-action butterfly valve

A composite-action butterfly valve to be disposed in a fluid transport line to regulate a flow of a fluid, comprising a valve element to be moved relative to a valve seat to regulate the flow of a fluid through the fluid transport line;

• wherein the valve element (4) is supported on a valve element operating shaft (7) through two support means having different functions including a fixed-length support means (5) and a variable-length support means (6), which are connected to a back surface of the valve element, opposite a front surface thereof facing a valve seat (3),
• the fixed-length support means (5) comprises an arm (5a) of a fixed length pivotally connected to the valve element (4) and mounted for turning on the valve element operating shaft (7), and
• the variable-length support means (6) of a variable length comprises an elastic member (6a) acting to reduce a distance between opposite ends of the variable-length support means (6), a transmission mechanism for converting a torque on the valve element operating shaft (7) into an operating force to increase the distance between the opposite ends of the variable-length support means (6), and a stopper (6f) for limiting a range of variation of the distance between the opposite ends of the variable-length support means (6);
• an external torque being applied to the valve element operating shaft (7) to operate the valve element (4).