Dampers contain a pressure tube, a piston rod with a special piston system and the damping medium oil. The piston rod is submerged in the oil-filled pressure tube with its special seal and guiding system. This actually hermetically seals the inside compartment of the hydraulic damper from the atmosphere.
The damping oil passes through the damping bores in the piston system via the movement of the piston rod. The damping forces thereby depend on the piston speed.
By closing the damping borings on both sides by valve washers, the damping forces are regulated in the direction of extension and compression. The damping force during compression decides the hardness of a shock absorber on retraction. The damping force on extension, on the other hand, regulates the extension speed.