| 摘要 |
An actuator ( 16 ) for a rotor valve ( 10 ). The actuator includes a rack ( 86 ) for driving a pinion gear ( 87 ) of the valve. The rack is moved between first and second positions by the action of a first piston ( 88 ). Movement of the first piston and rack is selectively restricted in one direction by the movement of a moveable stop ( 104 ) from a withdrawn position to an extended position, thereby defining a third position of the rack. The moveable stop may be driven by a second piston ( 102 ). The first and second pistons may be powered by a common compressed air supply ( 122 ). The cross-sectional area of the first piston may be at least 1.4 times the cross-sectional area of the second piston to ensure that the force exerted by the first piston is not sufficient to displace the moveable stop from the extended position when the second piston is open to the compressed air supply. |
