Have you done the maintenance work of the regulating valve?

The control valve should be maintained and maintained after normal operation. As a part of the automation control system, the control valve should be maintained at the same time as the automation instrument and other equipment.

The maintenance of the regulating valve is similar to the maintenance of general instruments, and can be divided into passive maintenance, preventive maintenance and predictive maintenance. Passive maintenance is a maintenance method that is performed only when the regulating valve and other equipment fails. Maintenance is only due to equipment failures, which often results in shutdowns during the production process, and even equipment damage or casualties in severe cases. Passive maintenance is maintenance that is not desired in the production process, and preventive maintenance is a maintenance method that is based on past operating experience and time-based maintenance. For example, the commonly used regular maintenance is preventive maintenance, which makes corresponding maintenance schedules according to the operating conditions of different equipment, and performs maintenance before the equipment fails. Since the maintenance is carried out before the failure occurs, the probability of the occurrence of the failure can be greatly reduced. However, this maintenance method does not analyze the actual situation of the currently used control valve, and often disassemble and inspect the control valve that can be used for a certain period of time, which wastes time and resources. Predictive maintenance starts from the data analysis of the currently used regulating valve, and predicts the status of the regulating valve, so that the regulating valve can be utilized to the maximum.

1. The daily maintenance work content of the regulating valve

The daily maintenance work of the control valve is divided into two parts: patrol inspection and regular maintenance. The patrol inspection work is as follows.

1. Learn about the operation of the regulating valve from the process operator on duty.

2. Check the supply energy of the regulating valve and related accessories (air source, hydraulic oil or power source)

3. Check the operation of the hydraulic oil system.

4. Check whether the static and dynamic sealing points of the regulating valve are leaking.

5. Check whether the connecting pipelines and joints of the regulating valve are loose or corroded.

6. Check the regulating valve for abnormal sound and large vibration, and check the supply situation.

7. Check whether the action of the regulating valve is flexible and whether it changes in time when the control signal changes

8. Listen to the valve core and valve seat for abnormal vibration or noise.

9. If problems are found, contact and deal with them in time.

10. Make a record of the touring inspection and file it.

The contents of regular maintenance work are as follows:

1. Regularly clean the outside of the regulating valve.

2. Regularly adjust the regulating valve stuffing box and other sealing parts. If necessary, replace the sealing parts to maintain the tightness of the static and dynamic sealing points.

3. Regularly add lubricating oil to the parts that need to be lubricated.

4. Drain and clean the air source or hydraulic filter system regularly.

5. Regularly check the connection and corrosion of each connection point, and replace the connection if necessary.

Second, the regular calibration of the regulating valve

Units that have not yet carried out predictive maintenance of regulating valves should conduct regular calibrations on regulating valves. Periodic calibration work is preventive maintenance work.

According to different production processes, the regular calibration of the regulating valve should have different calibration cycles. The data provided by the manufacturer can be combined to determine the period of regular calibration of each regulating valve. Usually it can be carried out at the same time as the overhaul is carried out during the production process. When some regulating valves are used in high pressure, high pressure drop or strong corrosive occasions, the inspection cycle should be shortened.

The content of the inspection is mainly the static performance test of the regulating valve. Corresponding test items can be added when necessary, such as the test of the flow characteristic of the regulating valve. Periodic calibration requires related test equipment and instruments, as well as replacement parts. Therefore, the manufacturer can usually be entrusted to complete it.

Three, the maintenance of the regulating valve

Regulating valve maintenance is divided into emergency maintenance, regular maintenance and predictive maintenance. Emergency maintenance is the maintenance when the regulating valve fails and cannot meet the requirements of the process operation. Regular maintenance usually includes routine maintenance and maintenance that is carried out at the same time as process shutdown overhaul. Predictive maintenance is based on the analysis results of predictive maintenance, targeted maintenance of the relevant control valve components. Emergency maintenance is the maintenance after the failure of the regulating valve, and regular maintenance and predictive maintenance are the maintenance before the failure of the regulating valve. Usually, the routine maintenance of the regulating valve is carried out by the instrument maintenance personnel, and the regular maintenance carried out at the same time as the overhaul is carried out by the manufacturing technicians.

1) 　Daily inspection and maintenance of control valves include the following:

1. Eliminate stress. Various stresses caused by improper installation or combination. For example, the high temperature medium generates thermal stress, and the installation is tight. The imbalance of solid force causes stress and so on. The imbalance of stress acts on the regulating valve, deforming the regulating valve stem and guide, and not being able to align with the valve seat correctly, causing leakage and increased deterioration. Therefore, maintenance work to eliminate stress should be carried out in daily maintenance.

2. Remove rust and dirt. Frequently check whether there is rust, welding slag, dirt, etc. in the connecting pipe of the regulating valve, and remove it in time after discovery. Because these dirt will cause the abrasion of the valve core and valve seat of the regulating valve, and affect the normal operation of the regulating valve. Generally, filter devices such as filters can be installed in front of the regulating valve and cleaned regularly.

3. Check the control valve support. The control valve support makes the parts of the control valve in a position that is not affected by gravity and the like. If the support is improper, the valve stem and the valve seat of the regulating valve will not be centered, which will increase the deterioration and reduce the sealing performance. Therefore, it is necessary to check whether the support of the regulating valve is proper.

4. Remove the dirt that supplies energy such as air source and hydraulic oil. Air source and hydraulic source are the energy source for the operation of the regulating valve. Impurities contained in the instrument compressed air and hydraulic oil can block the orifice and pipes, causing malfunctions. Therefore, it is very important to check the air source and hydraulic oil regularly, and to drain the filter device regularly.

5. Inspection of gear transmission. The gear transmissions of the hand-wheel mechanism, electric actuator and hydraulic actuator should be checked regularly and lubricants should be added to prevent seizure. Check whether the brake and limit device are flexible and easy to use.

6. Stuffing box inspection. The wear and compression force of the packing should be checked, and the stuffing box should be replaced regularly to ensure that the packing can seal while reducing the impact of its friction. Lubricating oil should not be added to the stuffing box without oil lubrication.

7. Check for safe operation. Regulating valves and related accessories used in explosive hazardous locations should be checked for their safe operation, such as whether the sealing cover is tightened, the operation of the safety barrier, and the power supply, etc., to ensure that the regulating valve and related accessories can operate safely.

8. Transport and storage. During transportation and storage, the regulating valve should be fixed with a special bracket to prevent loosening; the relevant accessories installed on the regulating valve, such as valve positioner, handwheel mechanism, etc. should be firm, and the feedback lever connected with the regulating valve should be prevented from being subjected to external force Damage; each connection interface should be covered with plastic film to prevent the intrusion of foreign objects; the connection port of the regulating valve can be sealed with matching flanges and blind plates, or adhesive paper can be used to seal to prevent foreign objects from intruding. A firm wooden box should be installed during transportation, and the impact of harsh transportation environmental conditions such as wind, sand, rain, and dust should be taken. The environmental conditions for transportation and storage shall meet the requirements of the product specification.

2) The main contents of daily maintenance of control valves and accessories are as follows:

1. Replacement of diaphragm of pneumatic actuator. The diaphragm of the pneumatic film actuator is stretched during operation, so it is easy to fatigue and damage. The rubber diaphragm of the same specification should be used for replacement, and the diaphragm should be evenly stressed during tightening to prevent leakage and crushing of the diaphragm.

2. Grinding. Leakage occurs between the valve core and the valve seat after a certain period of operation, and internal leakage will also occur between the piston and the cylinder body of the cylinder. At this time, grinding should be carried out. Hand-grinding, mechanical grinding, coating treatment and inserting methods can be carried out. The emery grain size used for grinding should be suitable, and the grinding force should be uniform and suitable. After grinding, it should be polished to meet the required finish and precision requirements, and to meet the centering requirements of the valve core and the valve seat. After the final assembly, a tightness test is required.

3. Replace the stuffing box. When replacing the stuffing box, the same type of stuffing box should be used. When replacing the stuffing box, carefully hook out the packing and remove the packing correctly to prevent damage to the valve stem. The installation of the new stuffing box should be in accordance with the requirements of the instructions. The incision should be misaligned to prevent the thread of the valve stem from scratching the packing. The packing pressure should be uniform and appropriate to prevent stress and increase friction.

4. Replacement of transmission parts. If part of the transmission parts in the regulating valve and accessories are worn out, parts can be replaced and repaired. After replacement and repair, the transmission should be flexible and the transmission gap should be as small as possible.

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