The main function of the valve is to regulate the airflow in the cylinder, including the intake valve and the exhaust valve. Its components include the valve head, valve stem, valve spring, valve guide, etc. The working principle of the valve depends on the elastic force of the valve spring and the movement of the valve stem to control the opening and closing of the valve to ensure the normal operation of the engine. In order to keep the engine in good running condition, the valve needs regular maintenance, including cleaning, lubrication, inspection and adjustment of valve clearance, etc.