A control device (10′) comprises a control unit (10′) with a control element for controlling a fluid flow and being rotatable about a first axis (13) between an open position and a closed position, and a separate motor-driven actuator unit (24), which is mechanically coupled to said control unit (10′) to rotate said control element about said first axis (13) in a controllable fashion, whereby said actuator unit (24) comprises a driving part (25) with a driving element (31) being rotatable about a second axis (26), to be mechanically coupled to said control element in a coupling position to rotate said control element about said first axis (13), and a control part (28) for driving said driving element (31) in a controllable fashion. Said driving element (31) is removably coupled to said control unit (10′) by means of a spur gearing (Hirth serration) (22, 29).