Valve device is a component of engine valve mechanism, which plays a very important role in engine operation. The operation of a fuel engine consists of four working processes: intake, compression, work and exhaust. To make the engine run continuously, it is necessary to make these four working processes cycle again and again, and the sequence of regular cycle work. Two of the working processes, the intake and exhaust processes, rely on the engine's valve mechanism to accurately deliver the combustible mixture (gasoline engines) or fresh air (diesel engines) in accordance with the working sequence of each cylinder, as well as the exhaust gas after combustion. The other two working processes, compression and work process, must be isolated from the cylinder combustion chamber and the external inlet and exhaust channels, do not let the gas leakage to ensure the normal operation of the engine. The part responsible for the above work is the valve in the valve mechanism. It is like the human respiratory organ, breathing in and out, without it.