When the hydraulic cylinder has a large mass or a large load and a high moving speed (>12 m/s), it has a large momentum due to the large inertia force. In this case, when the piston moves to the end of the cylinder, it will mechanically collide with the end cap, causing great impact and noise. The weight of the cylinder affects the machining accuracy and even causes a destructive accident. Therefore, in a large-sized, high-speed or high-precision hydraulic device, a buffer device is often provided, the purpose of which is to increase the oil return resistance when the piston approaches the terminal, thereby slowing the moving speed of the moving member and avoiding hitting the hydraulic cylinder end cover.