The hydraulic oil is used as the working medium in the hydraulic transmission system, the transfer of energy, the control of the transfer box, and the lubrication, corrosion, rust prevention and cooling of the components in the hydraulic system. The seals in the hydraulic system prevent leakage of fluid from the joint surface, maintain pressure, and maintain energy transmission or conversion. At present, most of the sealing materials used at home and abroad are polymer elastomers, and plastics and metals are also used in some special conditions. However, no matter which material it belongs to, it should have the following properties:
1., it has certain mechanical and physical properties, such as tensile strength, elongation strength and elongation.
2., it has a certain degree of elasticity and hardness, and has small compression permanent deformation.
3., it is not easy to produce swelling, decomposition and hardening with the working medium.
4. wear resistance, have a certain resistance to tear performance;
5. has the characteristics of aging resistance to high temperature and low temperature.

However, no sealing material includes all the above properties. It is necessary to choose suitable sealing materials according to the working environment, such as temperature, pressure, medium and movement mode, and meet certain requirements by formulating the matching formula of the material. Or use two or more materials in the form of coincidence or combination to give full play to their strengths and achieve more comprehensive results.