A valve actuator apparatus is provided, which further comprises a linkage mechanism, which can convert rotational force into translational force. This linkage mechanism also imparts a much greater degree of mechanical advantage than typical rack-and-pinion linkages allowing either for greater closing force on the valve or for the use of smaller drive motors to actuate the valve. Furthermore, this linkage mechanism can lock the valve closed, with full seating force, even when no torque is provided by a drive motor.