Maintenance of the hottest regulating valve

2022-08-08
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Talking about the maintenance of regulating valve

talking about the maintenance of regulating valve

there are generally two kinds of maintenance of regulating valve: one is preventive maintenance, which mainly refers to the preventive maintenance measures taken when there is no fault in order to ensure the reliable operation of regulating valve, including a series of preventive measures taken when the regulating valve is installed and used on site; The second is fault maintenance, that is, a series of maintenance work carried out when the regulating valve fails to meet the operating requirements and stops automatically under fault conditions. Generally, it is completed in the production workshop, and under special circumstances, it may also be repaired directly on the pipeline

1 preventive maintenance

preventive maintenance is the planned maintenance before the failure of the regulating valve, which can be understood as routine maintenance, and usually includes the following tasks

1.1 stress relief

pipelines will produce various stresses due to improper combination or installation, such as the thermal stress caused by high-temperature media, the stress caused by uneven tightening force during installation, and the stress caused by some man-made collisions to the control valve and its pipelines. These stresses act on the regulating valve and its pipelines, which can easily affect the performance of the regulating valve. In serious cases, they will affect the regulating system itself, resulting in the deformation of the valve stem and guide parts, which cannot be aligned with the valve seat; For the control valve of the split valve body, it may cause the separation of the valve body flange; Stress may also cause seat leakage, etc. Therefore, it is necessary to avoid or eliminate stress at any time and guide the stress away from the regulating valve

1.2 check the support condition

the best position for installing the regulating valve is to make the travel direction of the valve stem in a vertical plane with the actuator above the valve body. If the regulating valve must be installed at the position where the valve rod moves horizontally, or the moving direction of the valve rod has a certain inclination with the horizontal plane, the actuator should be supported to make all parts of the regulating valve in a natural state. If no support is added or the support is improperly added, it may cause the non concentricity between the regulating valve stem and the valve seat, which is easy to lead to differential or packing leakage and other faults. Even if the regulating valve is fixed and supported, it must be checked regularly, usually once every 2 ~ 3 months

1.3 remove or prevent foreign matters from entering

regularly check whether there is rust, welding slag, dirt, etc. in the connecting pipe of the regulating valve, and remove it in time after discovery. If foreign matters are easy to accumulate in the regulating valve and pipeline, it is necessary to consider installing a simple filter device on the upstream side of the regulating valve. Where hard sundries are easy to penetrate into the process medium, permanent filtering devices must be installed. Because when the regulating valve is closed, a small piece of rust or welding slag is enough to damage the well ground sealing surface of the valve seat, and these dirt will also cause wear to the regulating valve core and valve seat, affecting its normal operation

1.4 regularly check the air source and power supply

the air source is one of the key energy sources to drive the regulating valve. Although the membrane chamber of the pneumatic control valve does not consume air, if the air source system contains impurities such as water and oil, the valve positioner, relay and other accessories will be blocked and malfunctioned. Therefore, the air source and power supply must be checked regularly to ensure that the air source is clean, dry and reliable

1.5 regular maintenance and refueling

packing and oiler need to be readjusted after short-term use. For dusty occasions, protect the stuffing box and guide parts with plastic or rubber sleeves around the valve stem. For occasions with corrosive gas or liquid droplets, special protective measures should be taken. Generally, the regulating valve is wrapped with anti-corrosion bags, but attention should be paid not to affect its operation. In the occasions with fire resistance requirements, special fire-resistant coatings and fire-proof bags can be used. The materials of fire-proof bags contain multi-layer ceramic fibers or glass fibers

1.6 transportation and storage

after the control valve is assembled and painted, and the actuator, handwheel, positioner and other accessories are installed as required, in order to prevent foreign substances from entering the control valve, all air interfaces connecting the control valve should be blocked, and the connecting flange should be equipped with a protective cover. Pay attention to the status of each connecting part, such as the inlet pipe of the valve positioner and the interface of the actuator. Any protruding accessories that are easy to be damaged, such as the pressure gauge of the oiler and potentiometer, should be removed from the connector, packaged separately from the regulating valve and transported together. The regulating valve shall be fixed with a special support to prevent loosening, and the overall vertical or horizontal position shall be ensured. If it is transported over a long distance, it is best to use strong wooden cases indicated by BASF's relevant personnel

when storing the regulating valve, do not support the regulating valve on sensitive parts, such as valve positioner, valve stem, etc. The environmental conditions for transportation and storage shall meet the requirements of the product specification. It is better not to carry out other operations in the storage area. When it is unavoidable, you must be careful not to touch the regulating valve. The place should also avoid being affected by harsh conditions such as wind, sand, dust, rain, etc. if there is no suitable place, the regulating valve must be installed in a moisture-proof bag or in a similar container before storage

1.7 inspection of safe operation

check the safe operation of the regulating valve and relevant accessories used in explosive dangerous places, such as whether the sealing cover is tightened, the operation of safety barriers, power supply, etc., to ensure that the regulating valve and relevant accessories can operate safely

2 fault maintenance

when the regulating valve cannot be operated or cannot meet the operating requirements, it indicates that there is a fault and fault maintenance must be carried out. When the cause of the fault is uncertain, the following steps can be generally followed

2.1 cleaning

after the faulty regulating valve is removed from the pipeline, the first step of maintenance is to thoroughly clean the regulating valve. The regulating valve is easy to be polluted by the process fluid. If the process medium is corrosive, explosive and radioactive, it will be harmful to human body. Special methods must be used to clean the parts soaked by the process medium

cleaning methods vary with the properties of process media. Generally, it is only necessary to purge with water or steam. For some pollution, such as alkaline medium, pickling method should be used, and for heavy metal pollution, special treatment should be carried out at high temperature and for a long time. Avoid repeated pollution during cleaning and conduct it in a safe place. All cleaning tools such as containers, heating equipment, steam hoses, washing equipment, etc. should be prepared in advance

2.2 disassemble the regulating valve

when disassembling the regulating valve, it is necessary to mark the connection position of the actuator corresponding to the valve body, separate the actuator from the upper bonnet, and separate the upper bonnet from the valve body. After disassembling the upper bonnet and stuffing box components, the valve core, valve rod and other components can be removed from the valve body. All disassembled parts and components must be carefully inspected in order to determine the parts that need to be repaired and replaced

generally, after the disassembly of the regulating valve, the following parts should be paid attention to during the inspection: 1) the inner wall of the valve body. Check the pressure resistance and corrosion resistance; 2) Valve seat. Due to the infiltration of media, the threaded surface used to fix the valve seat is easy to be corroded, which makes the valve seat loose. For high-pressure occasions, it is also necessary to check the corrosion or damage of the sealing surface of the valve seat. Of course, in some structures, the valve seat and the valve body are not connected by threads, but are compressed by gaskets. However, no matter which method is adopted, the sealing parts of the valve seat and the valve body must be inspected emphatically, which is the core of the sustainable development of the enterprise; 3) Valve element. Carefully check whether all parts of the valve core are corroded or worn, especially under the condition of high pressure difference, the valve core is worn more seriously. In addition, the valve rod should also be checked for similar conditions, and whether the connection with the valve core is loose; 4) Packing and gasket. Check whether the sealing packing and gasket are aging, cracked, etc., and whether the mating surface is intact

2.3 disassembling the actuator

after disassembling the actuator, carefully check the support, diaphragm, spring, push rod and threaded connector, among which the support is a stress-bearing member and cannot have cracks; The diaphragm is a key component and cannot be damaged or aged; The spring shall not have cracks. For multi spring actuators, as long as one spring is damaged, the performance of the whole actuator will be seriously affected. No matter what kind of parts are corroded or rusted, it is best to replace them with new ones

2.4 reassembly

reassemble after all parts and components are repaired. In the process of reassembly, pay attention to the selection of appropriate gaskets and bolt connectors, accurately align and tighten evenly to prevent flange leakage. The torque load of bolt or stud bolt is related to its size, and it is not allowed to tighten it too tightly. The type, quantity and installation method of packing have a direct impact on the sealing performance, and should not be taken lightly during assembly

after reassembling the actuator, apply appropriate lubricant to all friction parts, including valve stem and guide parts, actuator push rod and guide parts, bearings, transmission parts, adjusting nuts, etc

2.5 test

after reassembly, the control valve must be tested, such as basic performance test, air tightness test, leakage test, etc. after passing the test, it can be sent to the site for installation

3 conclusion

fault maintenance, also known as passive maintenance, is a maintenance method that is carried out only when the regulating valve fails. Maintenance is carried out only when the equipment fails, which often leads to the shutdown of the production process, and even equipment damage or casualties in serious cases. Failure maintenance is not expected to happen in the production process. Preventive maintenance is a kind of preventive maintenance method for the regulating valve on time in the process of installation and use, according to the past operating experience, when the regulating valve has not failed. Its purpose is to prevent the trouble before it happens. People usually formulate corresponding fault prevention measures according to the different operating conditions of the regulating valve. Because the maintenance is carried out before the failure occurs, the probability of failure can be greatly reduced

in the practical application of the regulating valve, preventive maintenance and fault maintenance are usually combined. The former is the main and the latter is the auxiliary, so as to maximize the effective service life of the regulating valve. Only in this way can the utilization efficiency of the regulating valve be improved, the system failure rate be reduced, and it has a practical positive significance for the improvement of the production efficiency and economic benefits of the process and the reduction of energy consumption, It can effectively improve the regulation quality of the system, so as to ensure the long-term, safe and efficient operation of the production device

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