Arrangement for a spring suspension system

A device for a spring suspension system, comprising:

• a unit having a first and a second part, said second part including an outer cylinder and an inner cylinder disposed inside said outer cylinder, said outer and inner cylinders defining therebetween a first space filled with incompressible fluid and being connected with a second space in contact with surrounding atmosphere, said first and second space being under atmospheric pressure;
• a main spring disposed on said inner cylinder for compressing said incompressible fluid;
• a piston with an associated piston rod for providing a damping function, working in said incompressible fluid in a third working space defined inside said inner cylinder, said piston being supported in a bearing so dimensioned as to allow leakage of said incompressible fluid from said third working space into said second space under atmospheric pressure upon return strokes of said piston;
• a movable device located in said first space between said inner and outer cylinders with main spring acting on one side, and said incompressible fluid acting on another side of said movable device and against said spring, said movable device including a one-way valve allowing flow of said incompressible fluid from said first space into said third working space at the side below said piston whenever low pressure occurs inside said space.