Siemens Actuator SQN70.424B20

The Siemens SQN70.424B20 is an actuator designed for automatic control of air dampers in gas and liquid fuel burners. It operates on a 230 V supply at 50 Hz, with a power consumption of 6 W. The actuator provides a torque of 2.5 Nm and a rotation angle of 130°, with a runtime of 12 seconds. It features a reversible synchronous motor, protection class IP40, and weighs 400 g. The cam calibration can be performed without removing the actuator, and it includes end and auxiliary switches as well as built-in position indication. This model is the current replacement for the discontinued SQN70.424A20.

When selecting an actuator of this type, ensure that the supply voltage, frequency, torque, runtime, and rotation angle match the requirements of the damper or valve. The mounting pattern and shaft coupling must be compatible with the existing equipment. Check the control signal type (e.g., three-position, analog, or on/off) to ensure compatibility with the burner control system. For mixing valves, verify that the actuator's drive pattern matches the valve stem.

Common failure modes for actuators of this kind include stripped plastic gears, worn or stuck end switches, and seized valve stems if left inactive for long periods. Symptoms may include the damper not moving or moving erratically, burner lockouts, or unusual noises. Routine inspection during annual service can help detect these issues before they cause a lockout.