In the hydraulic system and its system, the sealing device is used to prevent the leakage of the working medium and the intrusion of external dust and foreign matter. The element that acts as a seal is the seal. External leakage will cause waste of working medium, pollute the machine and the environment, and even cause mechanical operation failure and equipment personal accidents. Internal leakage will cause the volumetric efficiency of the hydraulic system to drop sharply, failing to reach the required working pressure, or even unable to work. The tiny dust particles intruding into the system can cause or exacerbate the wear of the friction pair of the hydraulic components, and further lead to leakage.

Therefore, seals and sealing devices are an important part of hydraulic equipment. The reliability and service life of its work is an important indicator to measure the quality of the hydraulic system. Except for gap seals, seals are used to control the gap between two adjacent coupling surfaces below the minimum gap through which the liquid to be sealed can pass. In the contact seal, there are two types of self-sealing compression seals and self-sealing self-tightening seals (ie lip seals).