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There are two general types of valve maintenance: First, preventive maintenance, mainly refers to the preventive maintenance measures taken to ensure the reliable operation of the Regulating Valve, and in the absence of failure, including the use of the regulating valve in the field installation and use A series of preventive measures; Second, faulty maintenance, that is, a series of maintenance work performed when the regulating valve fails to meet the operating requirements in the event of a fault, and is generally completed in the production workshop. Under special circumstances, it may also be performed directly on the pipeline. service.
1 Preventive maintenance
Preventive maintenance is planned maintenance prior to failure of the regulating valve. It can be understood as routine maintenance and usually includes the following tasks.
1.1 Eliminate stress
Improper combination or improper installation of pipelines can cause various stresses, such as thermal stress caused by high-temperature medium, stress caused by unbalanced fastening force during installation, and stress caused by man-made collisions to control valves and pipelines. These stresses act on the regulating valve and its pipeline, and it is easy to affect the performance of the regulating valve. When it is serious, it will affect the regulating system itself, causing the valve stem and the guide element to deform and cannot align with the valve seat center; for the split valve The body's regulating valve may cause the valve body flange to disengage; stress may also cause the valve seat to leak. Therefore, at all times, it must be ensured that stress is avoided or eliminated and the stress is directed away from the regulating valve.
1.2 check the support situation
The best position for installing the regulating valve is to make the stem stroke direction and the actuator above the valve body in a vertical plane. If the regulating valve must be installed in a position where the valve stem moves horizontally, or if the moving direction of the valve stem has a certain inclination with the horizontal plane, the actuator should be supported so that all parts of the regulating valve are in a natural state. If no additional support is provided or the support is incorrectly installed, misalignment between the valve stem and the valve seat may be caused, which can easily lead to differential or leakage of the filler. Even if the regulating valve has fixing and supporting measures, it must be checked regularly, usually 2 to 3 months.
1.3 Remove or prevent foreign matter from entering
Always check whether there is any rust, welding slag, dirt, etc. inside the connecting pipe of the regulating valve, and remove it immediately after discovery. If foreign matter is likely to accumulate in the regulating valve and pipe, consider installing a simple filter device on the upstream side of the regulating valve. Whenever it is easy to infiltrate hard materials in the process media, a permanent filter must be installed. Because the regulating valve is closed, a small piece of rust or welding slag is enough to damage the well-sealed valve seat sealing surface, and these contaminants will also cause wear on the regulator valve spool and valve seat, which will affect its normal operation.
1.4 Regularly check the air supply and power supply
Gas source is one of the key energy sources to drive the regulating valve. Although the air chamber of the pneumatic control valve does not consume air, if the air source system contains impurities such as moisture, oil, etc., the accessories such as the valve positioner and the relay may become clogged and fail. Therefore, the gas source and power supply must be checked regularly to ensure that the gas source is clean and dry and the power supply is reliable.
1.5 regular maintenance and refueling
Fillers and oilers need to be readjusted after a short period of use. For dusty occasions, use plastic sleeves or rubber sleeves around the valve stem to protect the stuffing box and guides. Special protective measures should be used in the presence of corrosive gas or liquid droplets. Generally, the anti-corrosion bag is used to wrap the regulating valve. Note that it cannot affect its operation. In the case where fire resistance is required, special fireproof coatings, fireproof bags, etc. may be used. The material of the fireproof bag contains multilayer ceramic fibers or glass fibers.
1.6 Transportation and Storage
After assembling and painting the valve, and fitting the actuator, hand wheel, positioner and other accessories as required, in order to prevent foreign substances from entering the regulating valve, all air interfaces connecting the regulating valve shall be plugged, and the connecting flange shall be equipped with a protective cover. , Pay attention to the status of each connection, such as the valve positioner intake manifold and actuator interface. Any protruding attachments that are easily damaged, such as pressure gauges for lubricators and potentiometers, should be removed from the fittings, packaged separately from the regulating valve and transported together. The control valve is fixed with special brackets to prevent loosening and to ensure the overall vertical or horizontal position. If transported long distances, it is best to use a solid wooden box shipment.
When storing the regulator valve, do not support the regulator valve at sensitive locations, such as valve positioners, valve stems, etc. The environmental conditions for transportation and storage should meet the requirements of the product specification. It is best not to perform other operations in the storage area. When it is unavoidable, care must be taken not to touch the regulator. Sites should also be protected from the harsh conditions of sand, dust, rain, etc. If there is no suitable place, the regulator must be placed in a moisture-proof bag or placed in a similar container before storage.
1.7 Safe Operation Check
For the control valves and related accessories used in explosive hazardous locations, check their safe operation, such as whether the sealing cap is tightened, the operation status of the safety barrier, power supply, etc., to ensure that the regulating valve and related accessories can operate safely.
2Faulty maintenance
When the regulating valve cannot operate or does not meet the operating requirements, it means that there is a fault and the fault must be repaired. In the case of failure to determine the cause of the fault, generally follow the steps described below.
2.1 Cleaning
After removing the defective regulator from the pipeline, the first step in maintenance is to thoroughly clean the regulator. The regulating valve is easily contaminated by the process fluid. If the process medium is corrosive, explosive, or radioactive, it will harm the human body. The components soaked in the process media must be cleaned by special methods.
Gate valve structure: gate valve is the use of the gate and seat to control the opening and closing of the valve. Gate valve mainly has a valve body, valve seat, gate, valve stem, valve cover, stuffing box, packing gland, stem nut, hand wheel and other components. Depending on the change of the relative position between the gate and the valve seat, the channel size can be changed and the channel can be cut off. In order to make the gate valve close tightly, the mating surface of the gate plate and the valve seat are ground.
Maintenance valve control method
Maintenance valve control method