Abstract: The invention relates to a device for displacing and locking movable switch parts (1), comprising a hydraulic piston, which is formed by a rod (6) and cooperates, via coupling or locking members (8), with an axially displaceable sleeve (5) intended to receive the radially displaceable coupling or locking members (8), The displaceable sleeve (5) is coupled with the movable switch parts (1) and an externally arranged tube (4), at least partly overlapping the sleeve (5) and the rod (6). A hydraulic duct (11) is connected to the externally arranged tube (4), on a front face of the sleeve (5), facing away from the coupling site for the movable switch parts (1).