A piston rod with a piston is installed with freedom of axial movement in a damping medium-filled cylinder, where, as a function of the stroke position of the piston, a bypass connects the two working spaces separated from each other by the piston. The piston has at least one through-channel for at least one flow direction, which channel is at least partially covered on the outlet side by at least one valve disk, so that a first pressure-actuated surface to which pressure can be applied in the opening direction is present on the valve disk. In addition to the first pressure-actuated surface, the valve disk has a second pressure-actuated surface, which is separated from the first when the valve disk is closed and which can be actuated via the bypass, in which case the effects of the two pressure-actuated surfaces are additive. The second pressure-actuated surface of the valve disk, in addition to the first pressure-actuated surface of the valve disk, is designed with its throttle point in the area of the second pressure-actuated surface at least during a certain phase of the travel of the valve disk.