Abstract: In an oscillation damper with bypass between an annular working chamber and a compensating chamber, a shut-off valve is provided in the bypass. The shut-off valve is on the one hand exposed to the pressure in the annular working chamber and on the other hand to the pressure in a control chamber which is constructed directly adjacently to a valve shut-off element of the shut-off valve and is supplied by a throttle section with the pressure in the annular working chamber. The control chamber is constructed with a control chamber outlet. This control chamber outlet is opened or closed selectively by a cross section dimensioning module.

Abstract: In the case of a vibration damper with a by-pass (32, 32a) between an annular working chamber and a compensating chamber (28), there is in the by-pass (32, 32a) a shut-off valve assembly (36) with a valve shut-off element (42) and a valve seat (40b). The valve shut-off element (42) is for its part subject to the pressure (p.sub.1) in a first section (32) of the by-pass and on the other to the pressure (p.sub.2) in a control chamber (48). The cross-section of a control chamber outlet (46c) can be controlled by an outlet cross-section dimensioning device (52). The shut-off valve assembly (36) is so constructed that at maximum control chamber outlet cross-section the valve shut-off element (42) begins to be lifted off the valve seat (40b) when the throughflow rate through the control chamber outlet (46c) amounts to at least 0.2 times the total throughflow rate through the shut-off valve assembly (36) which becomes adjusted to a damper velocity of 1 m/sec.

Abstract: A vibration damper has a variable damping effect. The variation of the damping effect is obtained by a control valve. This control valve is subject to the pressure force of a damping liquid on the one hand and to a pressure force of a electrorheological liquid on the other hand. The pressure force of the electrorheological liquid is responsive to the viscosity of this electrorheological liquid. The viscosity of this electrorheological liquid is responsive to variation of a high voltage electrical field applied to the electrorheological liquid within a flow path. The pressure force obtained by the pressure of the damping liquid acts in a first direction onto a valve body of the control valve. The pressure force resulting from the pressure of the electrorheological liquid acts in a second direction onto the valve body. The direction of both pressure forces are invariable irrespective of the direction of movement of the piston rod with respect to the cylinder.