Schneider Electric (Barber Colman) MK-4451 11 sq. in Dual Range Damper Actuator (3-6 and 9-12 psig)

Proportional pneumatic actuator with 11 sq. in. (71 cm2) effective area used to control damper and air valves in heating, ventilating and air conditioning systems.

The type of positioning, proportional or two-position, is determined by the controller, such as a thermostat or relay. Actuators are positioned by air pressure acting upon a diaphragm and piston. Opposing the force on the top of the piston is a spring. The piston force overcomes the spring force, as the air pressure increases, extending the actuator shaft if the pressure lessens, the spring force retracts the shaft.