Abstract: A damper comprises a piston rod which is disposed along a central longitudinal axis and extended out of an end of a casing through a guide and seal unit. A piston assembly on the end, inside the casing, of the piston rod divides the interior of the casing into two sectional casing chambers. A pressure-piston member and a traction-piston member of the piston assembly respectively comprise an flexibly deformable valve disk at a distance from their respective front walls. The piston assembly there-between comprises an annular piston which is movable relative to the piston rod along the axis between the valve disks in such a way that, by deformation conferred to the valve disk by the annular piston bearing against one of the valve disks, the valve disk rests on the associated piston member in such a way that a by-pass channel between the sectional casing chamber is at least narrowed.