Common faults of control valves and their solutions

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Whether a control valve operates properly is closely related to its maintenance work. There are various types of failures in control valves, and the occurrence of a particular failure can also have different causes. I. Main faulty components of the actuator Different types of control valves, as well as various parts of them, have certain key components that are prone to failure. 1. Pneumatic and hydraulic actuators ① Diaphragm: For diaphragm-type pneumatic actuators, the diaphragm is the most important component. When the air supply system is working properly but the actuator does not function, it is necessary to check whether the diaphragm is damaged or not properly installed. When there are defects such as sharp corners and burrs on the surface of the metal contact, it can puncture the diaphragm, and the diaphragm must not leak under any circumstances. Additionally, prolonged use of the diaphragm and material aging can also affect its performance. ②In pneumatic and hydraulic actuators, the piston generates the driving force; therefore, damage or wear of the piston is absolutely not allowed. ③Air (liquid) inlet pipe: This is the pathway through which pressure is supplied to the actuator; therefore, it is necessary to regularly check that it is securely connected and there are no leaks. ④Push rod: Check whether the push rod is bent, deformed, or detached. The push rod must be firmly connected to the valve stem, and its position must be adjusted properly, so as to ensure sufficient travel and proper valve closure. ⑤Spring: Check whether the spring is broken. Improper manufacturing, processing, or heat treatment can all cause the spring to break. Some springs may also break under excessive loads. 2. Electric actuator ① Motor: Check whether the motor can rotate, whether it overheats easily, and whether it has sufficient torque and coupling force. ②Check the servo amplifier to see if there is any output and whether it can be adjusted. ③Reduction mechanisms: The reduction mechanisms used by different manufacturers vary. Therefore, it is necessary to check whether its transmission components—shafts, gears, worm gears, etc.—are damaged or have excessive wear. ④Check the cause of failure of the torque controller based on its specific structure. II. Main faulty components of the valve: ① Valve body – It is necessary to regularly check the condition of corrosion and wear on the inner wall of the valve body. Especially for valves used in harsh operating conditions such as those involving corrosive media, high pressure differences, or cavitation, it is essential to ensure their pressure resistance as well as their resistance to corrosion and wear. ②The valve core, as it is the component that regulates and stops the flow of fluid and acts as a movable shut-off element, is most susceptible to erosion, corrosion, and impact from particles. It is also more prone to damage under high pressure differences and in conditions of cavitation. Therefore, it is necessary to check whether its various parts are damaged, worn, or corroded, and to determine whether repair or replacement is required. ③Valve seat: The valve seat interface is crucial for ensuring that the valve closes properly, and it is also subject to significant corrosion and wear. Furthermore, due to the penetration of the medium, the internal threaded surface of the fixed valve seat is often corroded and loosened, so this area requires special inspection. ④Valve stem: Check whether the connection between the valve stem, the valve core, and the push rod is loose, as well as whether there is excessive deformation, cracks, or corrosion. ⑤Filler: Check whether the polytetrafluoroethylene or other fillers are aged, lack oil, or have deteriorated, and whether the fillers are properly compressed. ⑥Gaskets and O-rings: These vulnerable components must not crack or age.