Abstract: A rotary actuator for a valve includes a cam mechanism for transmitting opening force to a movable valve member to move the valve member off a valve seat, against the bias of a closing spring. The cam mechanism does not transmit spring force to the valve member when the valve member is being moved to the closed position or is in the closed position. Also, the parts of the cam mechanism have a large surface area of contact when the valve is in the open position, to minimize unit loading of the cam surfaces. The movable cam is movable axially relative to the actuator handle. The movable valve member is blocked from rotation relative to the valve body. The cam mechanism does not transmit spring force to the movable valve member when the valve member is in the closed position.