Garlock actuators of the GDA type are double action part turn valve actuators for 90° fittings, such as butterfly valves and ball valves. Compressed air is used for actuation in both directions. The force of the air-actuated pistons is transmitted to the shaft using the Scotch Yoke principle. In this method, the force is not transmitted using the gears of pistons and spindle but rather by means of a high quality lever arm system. Unlike in the rack and pinion system, the larger lever arm generates a significantly higher torque in the initial and final phases of the rotation, matching the torque curves of the fittings to be actuated.
