| 摘要 |
A ball-valve member, which in its valve-closed condition must have circumferentially continuous sealed contact with its seat, is mounted for rotation about an axis which is eccentrically gyrated in the course of limited rotation of an actuating element that is journalled in the valve body. The eccentric throw is selected to be such in relation to the full course of actuating-element rotation that, beginning with a fully-closed condition of the valve, an initial fraction of the course of actuating-element rotation is devoted to achieving the eccentric throw (without rotating the ball), whereby to displace the ball-rotation axis in the axial direction away from seat engagement; the ball surface is thus displaced into axially offset clearance with respect to the seat, before devoting the remaining fraction of actuating-element rotation to the task of rotating the ball to its valve-open position. In the presently preferred form to be described, a rotary lost-motion connection between eccentric displacement and ball rotation makes it possible for a single direction of controlled driving torque to the actuating element to perform the indicated sequence for a valve-opening direction, and the reverse sequence for a closing direction of valve actuation; in the closing direction, all rotation of the valve-member ball is in axially offset relation to the seat, while eccentric displacement to achieve a seated closure occurs only after the ball has been rotated into axially offset register with its seat.
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