Siemens Actuator SQN90.570A2793

This Siemens actuator, model SQN90.570A2793, catalogue article 3012885, positions air dampers and mixing valves in burner and boiler systems. It converts a control signal into rotary motion to adjust the flow of combustion air or the blending of heating circuit water. The actuator is delivered as a separate component and can be used with three-way or four-way valves.

Parts of this type are selected by matching torque, running time, control signal type (three-point, 0-10 V, or on/off), shaft or coupling pattern, angle of rotation, and the presence of integral auxiliary switches. Before replacing an actuator, inspect the shaft interface and verify that the control signal from the burner control corresponds to the actuator input. When used with a valve, the motor may be replaced independently of the valve body.

Typical failures of this kind include stripped gear trains, failed end switches, and seized valve stems after prolonged standstill. These failures can prevent the actuator from positioning the damper or valve correctly, leading to incorrect combustion air supply or water temperature. Check that the actuator rotates freely and that all auxiliary switches operate correctly.