Valve stem seal is one of the valve seals on the engine. Valve oil seal is generally made of outer framework and fluororubber by vulcanization. Self tightening spring or steel wire is installed at the diameter mouth to seal the valve guide rod of engine. It is a kind of oil seal.

Because the valve oil seal works in the environment of high temperature and high pressure, it is necessary to use materials with good heat resistance and oil resistance. Oil seal commonly used materials are: nitrile rubber, fluororubber, silicone rubber, acrylate rubber, polyurethane, polytetrafluoroethylene and so on.

When choosing the material of the oil seal, the compatibility of the material to the working medium, the adaptability to the working temperature range and the ability of the lip to follow the rotating shaft at high speed must be considered. Generally, the temperature of the lip edge of the oil seal is 20 ~ 50 ℃ higher than that of the working medium, so the selection of the oil seal material should be paid attention to when selecting the oil seal.

When NBR is used as the material, the working range of oil seal temperature is - 40 ~ 120 ℃; acrylic rubber (ACM) - 30 ~ 180 ℃; fluororubber (FPM) - 25 ~ 300 ℃. The valve oil seal is generally made of fluororubber.

Valve oil seal has two major functions: one is to prevent the leakage of gasoline and air mixture and exhaust gas; the other is to prevent engine oil from entering the combustion chamber.