Source：Time：2021/10/05Views：325
There are generally two types of control valve maintenance: 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 the control valve, including a series of preventive measures taken when the control valve is installed and used on site; The second is fault maintenance, that is, a series of maintenance work carried out when the control valve can not meet the operation requirements under fault conditions. Generally, it is completed in the production workshop, and it may also be repaired directly on the pipeline under special circumstances.
Preventive maintenance
Preventive maintenance refers to the planned maintenance before the failure of the regulating valve, which can be understood as daily maintenance, usually including the following work.
1. Stress relief
Due to improper combination or installation of pipelines, various stresses will be generated, such as thermal stress caused by high-temperature medium, stress caused by uneven tightening force during installation, stress caused by some man-made collisions to regulating valves and their pipelines, etc. These stresses act on the regulating valve and its pipeline, 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 can not be aligned with the valve seat; For the control valve with split valve body, it may cause the separation of 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.
2. 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 barrier, power supply, etc., to ensure the safe operation of the regulating valve and relevant accessories.
3. Check the support
The best position to install the regulating valve is to make the stroke 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 stem moves horizontally, or when the moving direction of the valve stem 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 the support is not added or 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. Even if the regulating valve is fixed and supported, it must be inspected regularly, usually once every 2 ~ 3 months.
4. remove or prevent foreign matters from entering
Frequently check whether there is rust, welding slag, dirt, etc. in the connecting pipe of the regulating valve, and remove it in time. If foreign matters are easy to accumulate in the regulating valve and pipeline, 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 device must be installed. Because when the regulating valve is closed, a small piece of rust or welding slag is enough to destroy the well ground sealing surface of the valve seat. Moreover, these dirt will also cause wear on the valve core and valve seat of the regulating valve and affect its normal operation.
5. regular maintenance and refueling
The packing and oiler need to be readjusted after short-term use. For dusty occasions, the stuffing box and guide part shall be protected with plastic sleeve or rubber sleeve around the valve stem. For occasions with corrosive gas or liquid droplets, special protective measures shall be taken. Generally, the regulating valve shall be wrapped with anti-corrosion bag, but its operation shall not be affected. Where there are fire resistance requirements, special fire-resistant coatings and fireproof bags can be used. The materials of fireproof bags contain multi-layer ceramic fibers or glass fibers.
6. transportation and storage
After the control valve is assembled, painted and equipped with actuator, hand wheel, positioner and other accessories as required, in order to prevent foreign substances from entering the control valve, all air interfaces connecting the control valve shall be blocked, and the connecting flange shall be equipped with protective cover. Pay attention to the status of each connecting part, such as the inlet pipe of valve positioner and the interface of actuator. Any protruding accessories that are easy to be damaged, such as the pressure gauge of oiler and potentiometer, shall 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 ship it in strong wooden cases.
When storing the regulating valve, do not support the regulating valve at sensitive parts, such as valve positioner, valve stem, etc. The environmental conditions for transportation and storage shall meet the requirements of the product manual. It is better not to carry out other operations in the storage area. When it is unavoidable, care must be taken not to touch the regulating valve. The site shall also avoid being affected by harsh conditions such as wind, sand, dust and rain. If there is no suitable site, the regulating valve must be installed in a moisture-proof bag or in a similar container before storage.
7. regularly check the air source and power supply
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 failed. Therefore, the air source and power supply must be checked regularly to ensure that the air source is clean, dry and reliable.