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In modern industrial automation and control systems, the control valve is an essential part, so that the normal operation of the control valve to the relationship between the quality and security of production of industrial products and, therefore, the plant instrumentation workers, must master the basic electric control valve and a method of repair and maintenance of the pneumatic valve (21).
Regulating valve into the electric control valve and pneumatic control valve, a few occasions as well as hydraulic control valve. Regulating valve repair in general, there are two: First, preventive maintenance, mainly referring to in order to ensure reliable operation of the control valve, and preventive maintenance measures when the fault does not appear to be taken, including regulating valve installed in the field using a series taken preventive measures. Second, the failure of the repair, overhaul work that regulate a series of valves in case of failure can not be carried out to meet the operational requirements, generally done in the workshop, special circumstances may also be repaired directly on the pipeline.
Preventive Maintenance: Preventive maintenance is the regulator valve failure before planned maintenance, can be understood as routine maintenance, usually include the following work.
1.1 to eliminate stress; pipeline due to improper installation will produce a variety of combinations or force, such as thermal stress generated by high temperature medium, when loaded by the stress caused by uneven tightening force, artificially caused some pong hit to its pipeline valve stress. These stresses are easily generated on the control valve and pipeline valve performance impact of severe affect regulating valve system itself, leading to deformation of the valve stem and guide can not be aligned with the center of the seat; valve for split control valve body, may cause body flange disengaged; stress may also cause seat leakage, etc. Therefore, any time should guarantee to avoid or eliminate stress, the stress away from the valve guide place.
1.2 check support cases; best position is to install valve stem direction of travel at the top of the actuator body in a vertical plane. If the valve must be in a position to make the stem horizontal movement or direction of movement of the valve stem has a certain inclination with the horizontal installation, the implementing agencies should support them, so that all parts are regulating valve in a natural state. If you do not support the erection of additional support or could cause improper valve stem and seat of different heart, easily lead to poor change or even the filler valve leakage and other faults fixed and support measures must also be checked on a regular basis, usually 2 ~ 3 months check again.
1.3 Clear or foreign matter into trouble stop valve should always check whether the connection pipe rust, welding slag, dirt, etc., should be promptly removed after the discovery. If the control valve and the pipeline to the accumulation of foreign matter, will have to consider regulating valve upstream side Easy to install filtering devices. In the process medium hard debris easily penetrate the occasion, be sure to install a permanent filter. Because when the valve is closed, a small piece of rust or welding slag abrasive enough to damage the sealing surface is very good, besides the dirt Ye regulating valve plug and seat caused by wear and tear, affecting its normal operation.
1.4 regularly check gas supply and power; gas source is one of the key energy-driven control valve. Driven valve membrane chamber, though not consume air, but if the air supply system contains water, oil and other impurities, then make valve positioners, relay and other accessories clogging and malfunction. Therefore must be regularly checked the gas source and the power to ensure gas supply clean, dry, power and reliability.
1.5 Regular maintenance and refueling; fillers and oiling need to re-adjust after short-term use. Multiple occasions to dust around the stem with plastic wrap or a rubber sleeve to protect the stuffing box and a guide part, the presence of corrosive gas or liquid droplets occasion to adopt special measures of protection, usually with anti-corrosion wrap bag valve, but Note that not affect its operation. In the fire resistance requirements of the occasion, you can use a special fire-resistant coatings, sets fire bags and other methods, fire bags of material containing multilayer ceramic or glass fibers.
1.6 Transportation and storage; after adjusting valve assembly and paint as required actuator handwheel, positioning and other accessory equipment, in order to prevent foreign material from entering the control valve, control valve connected to be stuffed full of air interface connection method mounted on a blue shield, pay attention to the various connecting parts, such as valve positioners intake manifold, state execution interface. Any outstanding fragile accessories such as oiling and potentiometer gauges, the joints should be removed, and the control valve packaged separately and together transport. Regulating valve application-specific bracket to prevent loosening, to the overall vertical position or horizontal position. If long-distance transport, it is best to use a solid wooden shipping. When keeping control valve, not to adjust the valve support in sensitive areas, such as valve positioners, valve stem, etc.. Transportation and storage environmental conditions should meet the product specification requirements. Storage area is best not to carry out other operations, when unavoidable, care must be taken not to touch the valve. Also avoid places affected by sand, dust, rain and other harsh conditions, if no suitable place, in front of the storage control valve must be installed in moisture-proof bag or placed in a container.
1.7 safe operation checks; explosive dangerous places for use in regulating valves and related accessories shall be checked for safe operation, for example, closures are tightened, operation of the barrier, power supply, etc., to ensure that the control valve and related attachments can safe operation.
2 Fault maintenance: When adjusting valve inoperable or can not meet operational requirements, it shows there is defective and must be fault repair. In the cause of the failure can not be sure of the situation, according to the following general steps.
2.1 Cleaning; after the faulty valve removed from the pipeline, the first step in the maintenance work is carried out on the control valve thoroughly cleaned. Valve is easily contaminated by the process fluid, if the process media is corrosive, explosive, radioactive, the harm to the human body, special methods must be used to process parts made soaked clean. With the process of cleaning methods different media vary. Under normal circumstances, as long as water or steam blowing can be, for certain pollutants, such as alkaline medium to use pickling method, the heavy metal pollution will have special treatment at a high temperature for a long time. To avoid duplication of contamination when cleaning should be in a safe place. All cleaning tools containers, heating equipment, steam hoses, washing equipment, etc. should be prepared in advance.
2.2 Removing the valve; connected to indicate the position of the valve actuator corresponding to the demolition control valve, the actuator and the valve cover apart, put the lid on the valve cover and valve body apart, open the bonnet and stuffing parts after the spool can be removed from the body, stem and other parts. Must be carefully examined all the disassembled parts and components to determine need for repair and replacement parts. After adjusting valve is usually in the demolition, the inspection should focus attention to the following areas: 1) body wall. Check its pressure resistance, corrosion; 2) seat. Due to infiltration of the media, the threaded surface of the fixed seat with a loose seat leaving susceptible to corrosion, high-pressure situations, you should also check erosion or destruction seat sealing surface, of course, now some structure which, valve seat and valve are not threaded connection, but with the sealing parts must focus on examination; 3) spool. To carefully check whether all parts spool corrosion or wear, especially in the high differential pressure valve wear more serious cases, the stem should also check whether there is another similar situation, and is connected with the valve loosening; 4) Seal packing and gaskets. Check packing and gasket is aging, cracking and other damage, the mating surface is intact.
2.3 Removing the implementing agency; after disassembling the actuator bracket to double-check, diaphragm, spring, push rod and threaded connections, etc., where the stent is force component, there can crack; diaphragm is a key element, not damaged or aging; spring can not have cracks, multi-spring actuator, as long as one of them spring is damaged, the entire performance of the implementing agencies will be seriously affected. Regardless of the parts, once they are corrosion or rust, is best replaced with new parts.
2.4 reassembled; in all parts and components are repaired later, to re-assemble. In the reassembly process, pay attention to appropriate gasket and bolt connections, accurate alignment, evenly tighten the flange to prevent leakage. Bolt or stud torque load and its size related, are not allowed overtighten. Type of packing, quantity and installation methods directly affect the sealing performance, the assembly can not be taken lightly. After reassembling the actuator, but also suitable lubricant is applied to the friction parts, these parts including stem and guide, the actuator rod with guides, bearings, transmission parts, adjusting nuts.
2.5 Test; After reassembly, the control valve must be tested, such as testing, air tightness testing basic performance, leakage testing, etc., can be sent to the scene after the installation tested.
3, the conclusion; fault maintenance, also known as passive maintenance, repair method is to adjust a valve failure when performed, due to equipment failure before repair, often resulting in the production process of stopping, or even serious damage to equipment or personnel casualties and so on. Failure of maintenance is the production process does not want to happen. Preventive maintenance is based on past operating experience in the installation and use, in the case of the control valve is not faulty, a preventive maintenance schedule for regulating valve method, its purpose is to take preventive measures, people usually develop according to different operating conditions regulating valve corresponding fault precautions did not happen because of a failure to carry out maintenance, can greatly reduce the probability of failure. In actual application control valve, preventive maintenance and fault maintenance is usually combined use of previously dominated the latter supplemented by maximizing the effective life of the control valve, and only in this way can improve the utilization efficiency of the control valve, reducing system failure rate, process technology and production efficiency and improve the quality of the energy system of economic adjustment, thereby ensuring long-term production facilities, safe and efficient operation.
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