The main function of rear shock absorbers is to absorb vibration energy and accelerate the attenuation of frame and body vibration. When the wheel jumps, the shock absorber is compressed, and the piston moves down relative to the cylinder, so the volume of the lower chamber of the working cylinder is reduced, the oil pressure is increased, and the oil flows into the upper chamber of the working cylinder through the flow valve. When the wheel falls, the shock absorber is stretched, and the piston moves up relative to the cylinder, so the oil pressure in the upper chamber of the working cylinder increases, the circulation valve is closed, and the oil pushes the extension valve into the lower chamber.