The shock absorber is widely used in automotive suspension system, and can play a role in reducing vibration during compression and stretching travel. Therefore, it is also called bi-directional shock absorber.

Components include: piston rod, cylinder, piston, expansion valve, cylinder, compression valve, compensation valve, flow valve, guide seat, dust cover, oil seal.

When the wheel of the car moves close to the body and the shock absorber is compressed, the piston in the shock absorber moves downward. The volume of the lower chamber of the piston decreases, the oil pressure increases, and the oil flows through the flow valve to the upper chamber (upper chamber) of the piston. The upper chamber is occupied by the piston rod, so the increased volume of the upper chamber is less than the reduced volume of the lower chamber. A part of the oil then pushes the compression valve open and flows back to the storage cylinder. The oil savings of these valves form the damping force of the suspension in compressive motion. The shock absorber is pulled away from the wheel and the piston of the shock absorber moves upward. The oil pressure in the upper chamber of the piston rises, the flow valve closes, and the oil in the upper chamber pushes the expansion valve into the lower chamber. Because of the existence of piston rod, the oil flowing from the upper chamber is not enough to fill the increased volume of the lower chamber, which mainly causes a vacuum in the lower chamber. At this time, the oil in the storage cylinder pushes the compensation valve to flow into the lower chamber to supplement. Because of the throttling effect of these valves, the suspension acts as a damper in stretching motion.

Because the spring stiffness and pre-tightening force of the expansion valve are larger than that of the compression valve, under the same pressure, the total cross-sectional area of the expansion valve and the corresponding normal-pass gap and passage is smaller than that of the compression valve and the corresponding normal-pass gap passage. This makes the damping force produced by the extension stroke of the shock absorber larger than that produced by the compression stroke, and meets the requirement of rapid shock absorption.