What should be paid attention to maintenance of control valve
Control valves are divided into electric control valves and pneumatic control valves, and hydraulic control valves are also available in a few occasions. There are generally two types of control valve maintenance: one is faulty maintenance, that is, a series of maintenance work performed when the control valve fails to meet the operating requirements in the case of failure, which is usually completed in the production workshop, and may also be on the pipeline under special circumstances. Repair directly. The second is preventive maintenance. We are talking about faulty repairs
1. Faulty maintenance: When the control valve cannot be operated or cannot meet the operating requirements, it means that there is a fault, and faulty maintenance must be carried out. If the cause of the failure is uncertain, the following steps can generally be used.
2. Cleaning: After removing the faulty regulating valve from the pipeline, the first step of maintenance is to thoroughly clean the regulating valve. The regulating valve is easily contaminated by the process fluid. If the process medium is corrosive, explosive, or radioactive, it will be harmful to the human body. A special method must be used to clean the parts that have been soaked in the process. The cleaning method varies with the nature of the process media. Under normal circumstances, it is enough to blow with water or steam. For some pollution, such as alkaline medium, pickling method is used, and for heavy metal pollution, special treatment is required under high temperature and long time. Avoid repeated contamination when cleaning, and it must be done in a safe place. All cleaning tool containers, heating equipment, steam hoses, washing equipment, etc. must be prepared in advance.
3. Disassemble the regulating valve; when disassembling the regulating valve, mark the connection position of the actuator corresponding to the valve body, separate the actuator from the upper bonnet, separate the upper bonnet cover from the valve body, and disassemble the upper bonnet and stuffing box After the parts are assembled, the valve disc, stem and other parts can be removed from the valve body. All disassembled parts and components must be carefully inspected in order to determine the need for repair and replacement of parts. Generally, after disassembling the regulating valve, pay attention to the following parts during inspection: 1) The inner wall of the valve body. Check its pressure resistance and corrosion resistance; 2) Valve seat. Due to the infiltration of the medium, the threaded surface for fixing the valve seat is susceptible to corrosion and the valve seat is loosened. For high-pressure occasions, the sealing surface of the valve seat should also be checked for corrosion or damage. Of course, in some structures now, the valve seat and the valve body are not Use threaded connection, but the sealing part must be checked; 3) Spool. It is necessary to carefully check whether each part of the valve disc is corroded or worn, especially in the case of high pressure difference, the valve disc wear is more serious, and the valve stem should also be checked for similar conditions and whether it is loosely connected with the valve core, etc.; 4) Sealing Packing and gasket. Check whether the packing and gasket are aging, cracked, etc., and whether the mating surface is intact.
4. Disassemble the actuator; after disassembling the actuator, carefully check the bracket, diaphragm, spring, push rod and threaded connections, etc. The bracket is a stressed member and must not have cracks; the diaphragm is a key component and cannot be damaged or aging ; The spring must not have cracks. For multi-spring actuators, as long as one of the springs is damaged, the performance of the entire actuator will be seriously affected. No matter what kind of parts are corroded or rusted, it is best to replace new parts.
5. Make sure that it is centered and tightened evenly to prevent flange leakage. The torsion load of the bolt or stud bolt is related to its size, and it is not allowed to over tighten it. The type, quantity and installation method of the packing directly affect the sealing performance, so the assembly should not be taken lightly. After reassembling the actuator, appropriate lubricants should be applied to the friction parts, including valve stems and guides, actuator push rods and guides, bearings, transmission parts, adjusting nuts, etc.
6. Test: After reassembly, the control valve must be tested, such as basic performance test, air tightness test, leakage test, etc. adjustments, the failure maintenance of the control valve can be sent to the scene after the test is qualified. Install.
