Siemens Actuator SQN30.121A3500

The Siemens Actuator SQN30.121A3500 is a rotary positioning device for air dampers and mixing valves in burner and boiler systems. Its type designation is 23542. It converts a control signal from a burner control or separate controller into rotary motion to modulate airflow or water flow according to heat demand.

Parts of this type are selected by required torque, running time, control signal format (three-point, 0–10 V, or on/off), shaft or coupling pattern, angle of rotation, and the presence of auxiliary switches. Before ordering, compare the mechanical interface and electrical specifications of the existing installation. The actuator mounts on the air damper or mixing valve; the motor may be a separate spare part, while the actuator itself is the rotating element that connects to the valve stem. Verify that the output shaft or coupling matches the valve connection.

Common failure modes include a stripped gear train, a failed end switch, or a seized valve stem after prolonged standstill. These faults can prevent the actuator from turning the damper or valve to the commanded position.