BUTTERFLY VALVE METHOD AND APPARATUS EMPLOYING VARIABLY POSITIONABLE PIVOT SHAFT

摘要

A butterfly valve method and apparatus (10) employing a variably positionable pivot shaft (30). The apparatus (10) comprises a duct (16), a valve plate (12), and a pivot shaft (30). Near closed rotational positions of the valve plate (12), the plate is pivotally supported by a support shaft (18) which is movably secured to the duct (16). Over a substantial range of open rotational positions, the valve plate (12) is pivotally supported by the pivot shaft (30), which is translationally movable relative to the valve plate (12) so that fluid-dynamic torque exerted on the plate can be altered. The method comprises the steps of rotationally moving the valve plate (12) away from the closed position whereby fluid-dynamic torque is increased, and translationally moving the pivot shaft (30) relative to the valve plate whereby the torque is then decreased.