The control valve has the characteristics of simple structure and reliable action. However, because it is in direct contact with the process medium, its performance directly affects the system quality and environmental pollution. Therefore, the control valve must be maintained and overhauled regularly, especially on bad and important occasions.  Key inspection parts: 1). The inner wall of the valve body. For the control valve used in the occasion of high-pressure difference and corrosive medium, the inner wall of the valve body and the diaphragm of the diaphragm valve is often impacted and corroded by the medium, and the pressure resistance and corrosion resistance must be checked.  2). During the use of control valve seat , due to the infiltration of the medium, the inner surface of the thread used to fix the valve seat is easy to be corroded, which makes the valve seat lose. Attention shall be paid during the inspection. For valves operating under high-pressure differences, check whether the sealing surface of the valve seat is damaged.  3). The valve core is a movable part during the regulation work, which is most seriously scoured and corroded by the medium. During maintenance, carefully check whether all parts of the valve core are corroded and worn, especially under the condition of high-pressure difference, the wear of the valve core is more serious (due to cavitation), which should be paid attention to. Replace the valve core when it is seriously damaged. In addition, pay attention to whether the valve stem has similar phenomena, or the connection with the valve core is loose.  4). Diaphragm "O" rings and other gaskets. Check whether the diaphragm and "O" gasket in the control valve is aging and cracked.  5). The sealing packing shall pay attention to whether the PTFE packing and sealing lubricating grease are aging and whether the mating surface is damaged. It shall be replaced if necessary.