Circulating pump outlet butterfly valve operation common fault analysis Sha A power plant 200MW and 300MW generating sets of circulating pump outlet regulating valve are used heavy hammer hydraulic control check butterfly valve, which can be linked with the circulating pump control, the butterfly valve can be pre-open after 15 ° Circulating pump. Hydraulic drive system opens automatically when the packing pressure, so that the hammer does not fall. Even if there is a slight oil leakage in the hydraulic system, the hammer will drop more than 15 °. The electronic control system can also charge the oil pump motor to keep the oil pressure. When the circulating pump is turned off, the butterfly valve is closed, the two phases of fast-closing and slow-closing are closed, the effect is to prevent the impact of water hammer pressure rising in the pipeline when the valve is closed, and buffer protection pipeline to prevent the circulating pump from reversing. Because of this type of butterfly valve can play a check and cut-off function, can effectively prevent the water hammer, and a valve linkage, safe and reliable, and many other advantages, since put into operation, water, thermal power plants, public drainage, chemical metallurgy The industry has been widely used. In recent years, a series of forms and structures have been gradually developed, including anti-seawater type, mud-resistant sand type, locked type, non-weight type, disc three-dimensional eccentric structure and the like. However, the basic control methods are used electro-hydraulic control, the hydraulic system is characterized by simple, reliable, easy maintenance. 2 working principle 2.1 to KD741X-6V-type butterfly valve, for example, the hydraulic principle 2.2 hydraulic principle brief 2.2.1 open the valve to start the pump motor, pump running, hydraulic oil through the filter, pump, speed control valve, check valve and high pressure hose Into the swing cylinder, pushing the piston in the size of the piston that did not pass the valve excess hydraulic oil flow back through the overflow valve tank. Cylinder piston connected with the connector so that the weight lifting, and at the same time bring the valve shaft to rotate the disc, to achieve open. Adjustable speed control valve can be a predetermined opening speed. During this movement, the manual valve is open, the solenoid valve is off, and the bypass manual valve is off. 2.2.2 close the valve solenoid valve is energized, the solenoid valve is opened, under the action of the hammer, the pressure oil in the cylinder by the fast, slow off the angle of the regulating valve, close the control valve, slow closing valve and high pressure hose, normally open Manual valve and solenoid valve into the fuel tank, the use of the potential energy of the hammer to close the valve to achieve closed valve. Close the valve in the process of fast closing, slow closing time and fast, slow off the angle of the cylinder by the fast-closing control valve, slow closing valve and the valve speed control valve to adjust the angle. 2.2.3 After the full automatic protection To ensure long-term work cylinder, the pressure is not lower than the required oil pressure so that the hammer will not drop due to low oil pressure, so the hydraulic system in parallel with a spring oil reservoir Energy device. Under normal circumstances, the accumulator pressure of oil pressure rating, when the system trace leakage, the accumulator can make up the system. When the hydraulic system leaks to cause the butterfly valve to close, when the butterfly plate closes to 75 °, the electric control system automatically turns on the power to restart the pump to open the butterfly plate to 90 °. When the system has a serious leak, the oil pump can not maintain the output of the butterfly valve open, the butterfly plate closed to 15 °, then stop circulating pump power. Avoid damaging pumps and piping. 3 to use some of the common problems of discussion Bypass (unloading) valve and manual valve The two valve shape and structure is the same. When the butterfly valve is operating normally, the unloading valve should be in the normally closed state and the manual valve in front of the solenoid valve should be in the normally open state. If you mistakenly put the solenoid valve manual valve closed, when the butterfly valve to be closed, the hydraulic oil can not unloading solenoid valve, and the butterfly valve will not automatically shut down. Special needs to be pointed out that the solenoid valve is a positive type and reaction type of two types, is the role of the solenoid valve is open in the case of the butterfly valve, the solenoid valve is often energized, when the solenoid valve power failure, the butterfly valve closed. Reaction type solenoid valve is the butterfly valve is open, the solenoid valve is not energized, when the solenoid valve is energized, the butterfly valve is closed. The latter is more suitable for power plant, because the power plant has a stable control power supply, solenoid valve can be guaranteed to open at any time, but also to avoid the power failure caused by the butterfly valve off the linkage pump. 4 maintenance defects in the common approach and explore Butterfly valve repair hydraulic system common defect is leakage, including internal and external oil spills. Leakage caused mainly due to damage to the sealing parts, in recent years due to the replacement of oil and rubber sealing materials, and to strengthen the regular maintenance of minor repairs, the operation of leakage was basically eliminated. The main reason for the internal leakage is that the sealing ports (wire seals) of the hydraulic control valves are scratched. The scratches caused by the sealing ports are mainly caused by the impurities in the system, which are accumulated on the sealing ports and are left squeezed Traces, damage the seal line, thus affecting the sealing. Internal leakage caused by a variety of symptoms, but the cause of the phenomenon of failure is not just internal leakage, there may be failure of the electronic control circuit, which often need to check with the repair personnel identification. Analysis of the method to determine the point of internal leakage is mainly based on the principle diagram, using one by one analysis of discriminant exclusion method. We summarize the "failure analysis tree diagram" method, the defect phenomenon from easy to difficult to investigate, determine the reason until the last troubleshooting the entire process one by one in the form of a tree diagram can be clearly and easily determine the point of failure. Now lists two common fault analysis. A good way to avoid internal leakage is to clean the tank periodically, filter the pressure oil, and rigorously filter oil during oiling. Avoid using rags with cotton yarn heads during maintenance. All these measures will ensure oil cleanliness. Currently the butterfly valve oil system maintenance cycle is one year, the basic equipment to meet the healthy operation. Swing cylinder size piston plating collapse is found in recent years, another major flaw in maintenance, it is estimated that the use of long-term coating is not strong fatigue off. Coated hard chrome layer off the rough piston wall, will aggravate the wear and tear of the ring, causing serious internal leakage. Treatment is to retreat chrome layer, re-plated hard chrome, re-coating thickness can be between 0.10 ~ 0.15mm. Replating a chrome, repair welding, school center, rough, Jing Kai and other technology. Butterfly valve hydraulic system overhaul can not open the valve defects, most of the reason is due to the governor valve or spill valve stroke caused by misplaced. In fact, the governor valve (regulating oil flow), oil spill valve (regulating system maximum pressure) and other hydraulic control valve in a set no need to adjust again. Hydraulic system leakage has also been a major point of failure. The main characterization is swing cylinder and the control valve leakage oil, a serious leak, the system will not be able to maintain hydraulic pressure to jump pump. By carrying out QC activities and counting the number of butterfly valve failures at the outlet of the circulating pump, the main failure reason that the main failure occurred in the hydraulic system by using Plato's 80 ~ 20% principle was analyzed. The main reason for the leakage analysis with the fishbone diagram was improper selection of the material of the hydraulic system sealing ring, Lack of maintenance of the two factors. In the repair will be easy to aging polyurethane seals replaced with oil resistant nitrile rubber material, and strengthen maintenance, insist on each overhaul of all seals, each minor repair oil change oil and inspection and commissioning. After the PDCA cycle activities, the mechanical failure rate of the outlet butterfly valve of 12 circulating pumps in our factory was reduced from 1.25 times to 0.2 times per year, greatly improving the operational reliability and health level of butterfly valves at the outlet of circulating pumps. Threaded Valves This connection is usually done by machining the inlet and outlet ends of the valve into conical or straight pipe threads that allow it to be connected to a conical pipe nipple or pipe. Since such a connection may present a larger leak channel, these channels can be plugged with sealants, sealing tapes, or fillers. If the material of the valve body is weldable but the coefficient of expansion varies widely or the range of variation in operating temperature is large, the threaded connections must be nectar welded. Threaded valves are mainly nominal pass through the valve below 50mm. If the path size is too large, the connection part of the installation and sealing is very difficult. In order to facilitate the installation and removal of threaded valves, pipe fittings are available in place on the piping system. Nominal diameter of 50mm below the valve can use the pipe joints as a pipe joint, pipe joints thread connecting the two parts together. Flange connection valve flange connection valve, the installation and removal are more convenient. But the valve than the screw connection bulky, the corresponding price is high. So it is suitable for a variety of diameter and pressure pipe connections. However, when the temperature exceeds 350 ° C, the load on the bolts is significantly reduced due to a loosened bolt, gasket, and flange, and leakage to the flanged flange subjected to high stress may occur. Welded Connection Valves This connection is suitable for all pressures and temperatures and is more reliable than flange connections when used under more load conditions. But the welded connection of the valve removal and reinstallation are more difficult, so its use is limited to usually long-term and reliable operation, or conditions of load moment, the temperature is high occasions. Such as thermal power stations, nuclear power projects, ethylene projects on the pipeline. Welded valves with nominal diameters up to 50 mm usually have weld sockets to receive the pipe at the load plane end. As the socket welding and sockets in the formation of gaps between the pipe, which may make the gap by some media corrosion, and pipeline vibration will fatigue joints, so the use of socket welding is subject to certain restrictions. In the larger nominal diameter, the conditions of load carved, the temperature is high, the valve body often used to weld the groove, at the same time, butt welds have the original grid requirements, must use skilled welding workmanship to complete this work.
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