1 Introduction
Sha A power plant 200MW and 300MW generating sets of circulating pump outlet valves are heavy hammer hydraulic control check butterfly valve, which can be linked with the circulating pump control, butterfly valve pre-open after 15 ° can start the 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
2.2 hydraulic principle outlined
2.2.1 Open the valve
Start the pump motor, pump operation, hydraulic oil through the filter, pump, speed control valve, check valve and high pressure hose into the swing cylinder, the size of the piston in the cylinder to move, not through the governor valve excess hydraulic oil through the relief valve Back to the 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 is controlled by the angle control valve of fast and slow closing, the valve of quick closing, the valve of slow closing and the hose of high pressure, the normally open manual valve and solenoid valve Into the fuel tank, the use of the potential energy of the hammer to drive closed butterfly 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 manual switch valve
Turn off the manual valve before the solenoid valve and swing the hand pump to open the butterfly valve slowly. The bypass (manual) valve is opened, the oil in the cylinder flows through the bypass valve back to the tank, so that the disc is closed under the action of the potential energy of the hammer.
2.2.4 after the full open pressure
In order to ensure the long-term working of the hydraulic cylinder, the pressure is not lower than the required hydraulic pressure so that the hydraulic hammer does not drop due to the low hydraulic pressure. Therefore, a spring-type accumulator is connected in parallel with the hydraulic system hydraulic circuit. 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 use of some common questions to explore
Bypass (unloading) valve and manual valve The two valves in the 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 discussion
Butterfly valve hydraulic system repair 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.
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 reasons 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.
5 concluding remarks
Only familiar with every detail of the equipment, timely and thorough maintenance and rigorous testing, in order to ensure the safety and reliability of equipment operation, improve the health of equipment.
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