There are two maintenance methods for regulating valves: first, preventive maintenance, which mainly refers to preventive maintenance measures taken when there is no failure in order to ensure the reliable operation of the 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 cannot meet the operation requirements under fault conditions, which is generally completed in the production workshop, under special circumstances, it is also possible to carry out maintenance 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, usually including the following tasks.

1. Stress elimination

Pipeline due to the combination or improper installation will produce a variety of stress, such as the thermal stress generated by high temperature medium, the installation of the tightening force caused by uneven stress, some man-made collision to the control valve and its pipeline caused by stress. These stresses in the control valve and its pipeline, it is easy to have an impact on the performance of the control valve, serious will affect the adjustment system itself, resulting in the valve stem and guide deformation and can not be aligned with the valve seat center; for split valve body of the control valve, may cause the release of the valve flange; stress may also cause valve seat leakage. Therefore, at any time to ensure that avoid or eliminate stress, the stress away from the control valve to guide the place.

2. Check the support condition

The best position to install the regulating valve is to make the stroke direction of the valve stem and the actuator above the valve body in a vertical plane. If the regulating valve must be installed in the position of the horizontal movement of the valve stem, or the direction of movement of the valve stem and the horizontal plane have a certain inclination, the actuator should be supported so that the various components of the regulating valve are in a natural state. If you do not add support or improper support may cause the valve stem and valve seat is not concentric, easy to cause differential change or make packing leakage and other failures. Even if the regulating valve has fixed and supporting measures, it must be checked regularly, generally 2 ~3Check once a month.

3. Remove or prevent foreign matter from entering

Always check whether there is rust, welding slag, dirt, etc. in the connecting pipe of the regulating valve, and remove them in time after discovery. If it is easy to accumulate foreign matter in the regulating valve and piping, consider installing a simple filter device on the upstream side of the regulating valve. In the process of the medium is easy to penetrate the hard debris of the occasion, must install a permanent filter device. Because the control valve is closed, a small piece of rust or welding slag is enough to destroy the well-polished valve seat sealing surface, and these dirt will also cause wear and tear on the valve core and valve seat, affecting its normal operation.

4. Regularly check the air source and power supply

The gas source is one of the key energy to drive the regulating valve. Pneumatic control valve membrane chamber although does not consume air, but if the air source system contains moisture, oil and other impurities, it will make the valve positioner, relay and other accessories blockage and failure. Therefore, the air source and power supply must be checked regularly to ensure that the air source is clean and dry and the power supply is reliable.

5. Regular maintenance and refueling

The filler and oiler need to be readjusted after short-term use. Dusty occasions around the valve stem with a plastic sleeve or rubber sleeve to protect the stuffing box and guide parts, there are corrosive gases or droplets of the occasion to use special protective measures, generally with anti-corrosion bag wrapped regulating valve, but to pay attention to can not affect its operation. In the case of fire resistance requirements, special fire-resistant coatings, fire-resistant bags and other methods can be used. The material of the fire-resistant bags contains multilayer ceramic fibers or glass fibers.

6. Transportation and storage

After the control valve is assembled and painted and installed with accessories such as actuator, handwheel and positioner as required, in order to prevent foreign substances from entering the control valve, all air interfaces connected with the control valve shall be blocked, and protective covers shall be installed on the connecting flange. Attention shall be paid to the state of each connecting part, such as the intake pipe of the valve positioner and the interface of the actuator. Any protruding accessories that are vulnerable, such as oil injectors and potentiometer pressure gauges, should be removed from the connector, packaged separately from the control valve and transported together. The control valve shall be fixed with a special bracket to prevent loosening and ensure the overall vertical or horizontal position. If transported over long distances, it is best to ship in solid wooden cases.

(2) Fault maintenance

When the control valve cannot be operated or cannot meet the operating requirements, it means that there is a fault and maintenance must be carried out. In the case that the cause of the fault is not certain, the following steps can generally be followed.

1. Cleaning

After removing the faulty control valve from the pipeline, the first step in maintenance is to thoroughly clean the control valve. Cleaning methods vary with the nature of the process media. 2. 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 valve cover, separate the upper valve cover from the valve body, and disassemble the upper valve cover and the stuffing box parts. Remove the valve core, valve stem and other components from the valve body. All disassembled parts and components must be carefully examined to determine which parts need to be repaired and replaced.

Usually, after the removal of the regulating valve, the following parts should be paid attention to 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 medium, the threaded surface used to fix the valve seat is easy to be corroded and the valve seat is loose. For high-pressure occasions, the corrosion or damage of the sealing surface of the valve seat should also be checked. Of course, in some structures, the valve seat and the valve body are not connected by threads, but are pressed by sealing gaskets. However, no matter which method is adopted, the sealing parts of the valve seat and the valve body must be inspected. 3) valve core. To carefully check whether each part of the valve core is corroded or worn, especially in the case of high pressure difference, the valve core wear is more serious, in addition to the valve stem to check whether there is a similar situation, and whether the connection with the valve core is loose, etc.; 4) Seal packing and gasket. Check whether the sealing packing and gasket are aged, cracked, etc., and whether the mating surface is in good condition.

3. Disassemble the actuator

After disassembling the actuator, carefully check the bracket, diaphragm, spring, push rod and threaded connector, among which the bracket is a stressed member and cannot have cracks. Diaphragm is a key component and cannot be damaged or aged. The spring cannot have cracks. For multi-spring actuators, as long as one of the springs is damaged, the performance of the whole actuator will be seriously affected. No matter what kind of parts, once corroded or rusted, it is best to replace the new parts.

4. Re-assembly

After all parts and components have been repaired, they should be reassembled. In the process of reassembly, attention should be paid to the selection of appropriate gaskets and bolt connections, accurate alignment, uniform tightening, to prevent flange leakage. The torque load of a bolt or stud is related to its size and must not be overtightened. The type, quantity and installation method of the packing directly affect the sealing performance, and the assembly should not be taken lightly.

After the reassembly of the actuator, but also to the friction parts of the appropriate lubricant, these parts include the stem and guide, the actuator push rod and guide, bearings, transmission parts, adjusting nuts, etc.

5. Testing

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