Siemens Actuator SQN72.2A4A20

The Siemens actuator SQN72.2A4A20 is intended for positioning air dampers and mixing valves in burner and boiler systems. It has a synchronous motor and is rated for 230 V at 50–60 Hz. Torque is 1.5 Nm, running time for 90° is 4 s, and the maximum angular adjustment is 160° (scale range 0...130). Power consumption is 6 W, protection class is IP54, and safety class is 2. It is maintenance-free; the mounting position is optional and fixing is done via through-holes. Housing length is 117 mm, and the unit has two auxiliary switches.

Actuators of this kind are selected by their required torque, running time for 90°, control signal type (such as three-point, 0–10 V or on/off), maximum angle of rotation, and the number of auxiliary switches. The mounting interface must be checked as well: shaft diameter and coupling pattern have to match the damper or valve stem. During installation, the front of the gear train is the mounting surface and the actuator is fixed with screws through the provided holes. If a potentiometer is required for position feedback, choose a version prepared for it; the potentiometer is ordered separately.

Typical failures of actuators of this class are stripped gears in the drive train, failed end switches that prevent proper travel limits, and a seized valve stem on a mixing valve after long inactivity. The visible symptom is that the damper or valve stops at an incorrect position or does not reach the required angle, which can disturb combustion air supply or water flow. When this occurs, check that the drive shaft turns freely, that the auxiliary and end switches change state at the correct points, and that the valve stem is not stuck before ordering a replacement.