Siemens Actuator SQN72.4A4A20

This actuator positions air dampers and mixing valves in response to a control signal from a burner or heating controller. The control signal may be three-point, 0-10 V, or on/off. The actuator is supplied as a separate spare part and is replaceable independently of the valve body.

Actuators of this type are selected by matching torque, running time, control signal type, shaft or coupling pattern, angle of rotation, and auxiliary switch configuration to the installation. Before ordering, verify that the mechanical coupling fits the damper or valve shaft, and that the electrical wiring and control signal are compatible with the burner control. During installation, set the correct rotation direction and end stops.

Common failure modes for this type include stripped gear trains, failed end switches, and a seized valve stem after prolonged standstill. These can prevent the actuator from positioning correctly and result in incorrect airflow or flow rate.