Siemens Actuator SQN70.624A20

The Siemens actuator SQN70.624A20 is a servo drive intended for automatic control of air dampers, gas valves, and mixing valves in burner and boiler installations. It converts a control signal into rotary motion to regulate combustion air or water flow. This model is fully compatible with Siemens equipment and is used in installation, modernization, and maintenance of gas burner and industrial equipment.

For replacement, choose an actuator of this kind with the same rated torque, running time for full stroke, control-signal type, shaft or coupling pattern, total angle of rotation, and integral auxiliary switches as the original. Mounting dimensions and shaft bore can vary between manufacturers and product generations, so measure the present unit and compare before ordering. Confirm the control-signal type (three-point, 0-10 V, or on/off) from the wiring and burner controller before installation.

Common failure modes include stripped gear trains, failed end switches, and seized valve stems after long standstill, especially on seasonal systems. When one of these fails, the actuator cannot move the damper or valve to the requested position, causing the burner to run with an incorrect air-to-fuel ratio or to lock out. Check by hand that the damper or valve spindle rotates freely; if it is seized, replace the valve body or damper linkage as well.