Double-tube vibration damper

DETAILED DESCRIPTION What is claimed is: 1.
A double-tube vibration damper particularly for use in a combination shock absorber spring unit comprising a cylinder member having an axis and two ends defining a cavity therein; a bottom valve unit adjacent a first end of said cylinder member; a piston rod guide unit adjacent a second end of said cylinder member; a piston rod member extending through said piston rod guide unit; a piston unit connected to said piston rod member within said cavity, said piston unit dividing said cavity into a first working chamber adjacent said first end and a second working chamber adjacent said second end, said piston unit further comprising a piston valve unit interconnecting said first and second working chambers; a container surrounding said cylinder and defining a compensation chamber in the annular space between said cylinder and said container, said compensation chamber being connected to said first working chamber through said bottom valve unit; a body of liquid in said cavity; a body of liquid and a body of gas within said compensation chamber; a by-pass passage interconnecting said cavity and said compensation chamber; a by-pass valve unit controlling the cross-sectional area of said by-pass passage, said by-pass valve unit comprising an actuating device; said actuating device comprising a pressure element, said pressure element defining a pressure element chamber, said pressure element chamber having at least one wall movable in response to the pressure difference between the pressure element chamber and the surrounding atmosphere, the effective cross-sectional area of said by-pass passage being responsive to the position of said movable wall, said pressure element being housed within said compensation chamber, said pressure element chamber being hermetically closed with respect to said compensation chamber, a pressure source connected to said double-tube vibration damper controlling the pressure difference between the pressure element chamber and the surrounding atmosphere