Abstract: The invention relates to an actuator for actuating a valve installed in a hydraulic or compressed air system, comprising a coil support which can be displaced by means of air space induction in a magnetically conducting housing on a magnetic cylinder composed of a permanent magnet and a cylinder pole disk. The invention is characterised in that the dimensions of the permanent magnet (16) and the pole disk (17) correspond to each other in such a way that the diameter of the front surface of the permanent magnet (16) is at least the same size as the circumferential surface of a neighbouring pole disk (17) and that the width of the coil (23) associated with the pole disk (17) exceeds the width of the pole disk (17) by the lift amplitude of the coil support (19).