A valve actuator (10) has a damping circuitry including a capacitive damping circuit (37), which is activated in the event of generator operation of the stepper motor (18). The damping circuitry, together with the motor winding (26), forms a resonance assembly LCR, which has the effect of stabilising and regulating rotational speed. The rotational speed of the stepper motor (18), running in generator operation, is held constant within limits, specifically without the control intervention of control circuitry. Therefore, the damping circuitry can operate even in the currentless state of the control system and is reliable regardless of external current supply. Fast closing is achieved, and excessively long post-running of the motor (18) is reliably prevented.