The device has a piston-cylinder unit (1). The cylinder chamber (3) has a valve (V) between the piston (2) and the pressure medium connection (8). The opening pressure of the valve is above its closing pressure. The valve may be formed by two plate springs (9), located above each other in the cylinder chamber. The upper plate spring faces the medium connection, and can be movably fastened to the other spring, which has a medium passage. Thus it may be closed sealed by the moveable plate spring, and may be locked in closed position.
