Maintenance method of electric control valve

The maintenance of electric control valve includes emergency maintenance, regular maintenance and predictive maintenance. Emergency maintenance refers to the maintenance when the electric control valve fails to meet the process operation requirements. Regular maintenance usually includes routine maintenance and maintenance carried out at the same time as process shutdown and overhaul. Predictive maintenance refers to the targeted maintenance of relevant electric control valve components based on the analysis results of predictive maintenance. Emergency maintenance refers to the maintenance after the failure of the electric control valve, while regular maintenance and predictive maintenance refer to the maintenance before the failure of the electric control valve.

（1） The daily inspection and maintenance of the electric control valve includes the following contents:

1. Stress relief. Various stresses due to improper installation or combination. For example, the high temperature medium produces thermal stress, which is caused by tight installation and unbalanced solid force. The unbalanced stress acts on the electric control valve, which causes the deformation of the valve rod and guide part of the electric control valve, and causes the leakage and increase of the variation due to the incorrect alignment with the valve seat. Therefore, stress relief maintenance should be carried out in daily maintenance.

2. Remove rust and dirt. Regularly check whether there is rust, welding slag, dirt, etc. in the connecting pipe of the electric control valve, and timely remove them if found. Because these dirt will cause the wear of the valve core and valve seat of the electric control valve and affect the normal operation of the electric control valve. Generally, the filter screen and other filtering devices can be installed in front of the electric control valve and cleaned regularly.

3. Check the electric control valve support. The support of the electric control valve makes all parts of the control valve in a position that is not affected by gravity. Improper support will cause the valve rod and valve seat of the electric control valve to be out of alignment, increase the variation and reduce the sealing performance. Therefore, check whether the electric control valve support is suitable.

4. Remove the dirt of air source, hydraulic oil and other energy supply. Air source and hydraulic source are the energy sources for the operation of electric control valve. Impurities contained in compressed air and hydraulic oil for instruments will block the orifice and pipeline, causing failure. Therefore, it is very important to check the air source and hydraulic oil regularly and drain the filter regularly.

5. Inspection of gear transmission device. Gear transmission devices of hand wheel mechanism, electric actuator and hydraulic actuator shall be inspected regularly, and lubricant shall be added to prevent seizure. Check whether the brake and limit device is flexible and easy to use.

（2） The main contents of daily maintenance of electric control valve and accessories are as follows:

1. Replacement of diaphragm of pneumatic actuator. The diaphragm of pneumatic diaphragm actuator is subject to expansion and contraction during operation, so it is easy to fatigue damage. The rubber diaphragm of the same specification shall be used during replacement. When tightening, the diaphragm shall be evenly stressed to prevent leakage and damage to the diaphragm.

2. Grinding. Leakage occurs between the valve core and valve seat after a certain period of operation, and internal leakage also occurs between the piston of the cylinder and the cylinder block. At this time, grinding should be carried out. Manual grinding, mechanical grinding, coating treatment and sleeve inlaying can be carried out. The grit size for grinding should be appropriate, and the grinding force should be uniform and appropriate. After grinding, it shall be polished to meet the required finish and accuracy requirements, and meet the centering requirements of valve core and valve seat, etc. The electric control valve shall be subject to sealing test after final assembly.

3. Replace the stuffing box.. When replacing the stuffing box, the same type of stuffing box should be used. When replacing, the packing should be carefully pulled out, and the packing should be removed correctly to prevent damage to the valve rod. The installation of the new stuffing box should be in accordance with the requirements of the manual. The notch should be staggered to prevent the thread of the valve rod from scratching the packing. The compression force of the packing should be uniform and appropriate to prevent stress and increased friction.

4. Replacement of transmission parts. If the transmission parts of the electric control valve and accessories are partially worn, they can be replaced and repaired. After replacement and repair, ensure that the transmission is flexible and the transmission clearance is as small as possible.

5. Cleaning of pneumatic amplifier. When the throttle hole of the pneumatic amplifier is blocked due to the dirt in the compressed air for instrument, the throttle hole should be cleaned, and the appropriate steel wire can be used for dredging and cleaning. During reassembly, the amplifier diaphragm should be evenly stressed to prevent blocking or leakage. The amplifier gain can be adjusted by adjusting the clamping force of the steel ball to prevent resonance.

6. Inspection of stuffing box. The wear and compression force of the packing should be checked, and the packing box should be replaced regularly to ensure that the packing can be sealed while reducing its friction. Do not add lubricating oil to the stuffing box without oil lubrication.

7. Inspection of safe operation. For the electric control valve and relevant accessories used in explosive dangerous places, check their safe operation, such as whether the sealing cover is tightened, the operation of the safety barrier, and the power supply, to ensure that the electric control valve and relevant accessories can operate safely.

8. Transportation and storage. The electric control valve shall be fixed with special support during transportation and storage to prevent loosening; Relevant accessories installed on the electric control valve, such as valve positioner, hand wheel mechanism, etc., shall be firm, and the feedback rod and other components connected to the electric control valve shall be protected from external force damage; All connecting interfaces shall be sealed with plastic film to prevent foreign objects from entering; The connecting port of the electric control valve can be sealed with matching flange and blind plate, or with adhesive paper to prevent foreign objects from entering. During transportation, solid wooden cases shall be added, and measures shall be taken to prevent the impact of adverse transportation environmental conditions such as wind, sand, rain and dust. The environmental conditions for transportation and storage shall meet the requirements of the product manual.