Valve quality measurement has the following indicators: seal reliability, motion response ability, strength, stiffness and life, the valve as a whole unit of the thermal equipment system to consider the basic unit, there are fluid-solid coupling vibration and vibration control requirements. To ensure these indicators, we must first solve the following major issues. 1 control (to determine the reliability of valve action) The main steam valve and reheat valve control system failure is one of the five major turbine accidents, mainly in the valve opening and design does not match, including the transmission failure, advanced travel, hysteresis, these Affect the strength and vibration of the valve. Valve opening control directly affects the working conditions of the steam turbine, so highly valued, has become one of the core issues of the study. In recent years, in the study of the reliability of the valve, the smart valve is the main direction of research, intelligent valves have to judge the working conditions, and real-time self-adjusting function. The key component in the smart valve is the digital positioner. The microprocessor of the digital positioner accurately positions the actuator of the valve and monitors and records the relevant data of the valve. 2 intensity (should meet the life expectancy, rigid requirements) frequent start of the unit on the strength of the valve and the valve life is particularly prominent, especially with the governor valve speed governing the focus of previous studies on the control valve, and now look Strength problems can not be ignored. Carolann Giovando, associate editor of power engineering magazine, wrote an article stressing that researchers should not focus all their attention on control issues and should pay attention to the study of valve strength, life expectancy and tightness because they are the most basic conditions of. (1) Due to frequent start-up of the unit, the original main steam valve may not meet the new operating requirements. Because the general main steam valve is designed according to the basic load, the design process only static pressure, temperature, creep assessment of its strength, there is no problem of low cycle fatigue life. Now conditions change, the original design does not necessarily meet the requirements. Therefore, it is necessary to consider the design of low cycle fatigue life design, the design conditions and operating conditions consistent in order to achieve the purpose of extending the life expectancy. (2) Due to the inaccuracy of the actuator stroke control, the valve core will have an impact load on the valve seat. There have been power plants have cracked the valve seat, cracked block was rushed into the steam turbine, resulting in a sharp decline in steam turbine output, serious damage to the rotor failure. In addition, for high pressure valves, there are cavitation phenomenon, the valve body of the original casting defects, valve body cracks and life prediction and other issues are worthy of further study. 3 Vibration valve opening changes, the poor dynamic performance of the implementing agencies and the existence of the body leakage is the cause of the vibration, the vibration damage to the valve itself is very small, but a great impact on the entire unit, the performance of low-frequency oscillation. Low-frequency oscillation unit is divided into two types: one is the oil film oscillation, which is the unit in the run-up or no-load operation, produced by the support bearing oil film; the other is the steam oscillation, which is more complex than the oil film oscillation, Vibration under the action of exciting force, often occurs after the unit is loaded. Valve opening changes and leakage is an important reason for steam oscillation. Data show that the United States and Germany have occurred vapor vibration damage accident, our country has also occurred 50 mw and 200 mw turbine damage, due to the lack of real-time data records, so the cause of the malfunction can not be determined, but doubts and two Low-frequency oscillation related. From this it can be seen that it is very important to eliminate and reduce the vibration of the steam, which depends on the systematic study on the variation of valve opening and on the exciting force generated by the leakage. Through the reasonable design of the valve opening and closing stroke, you can reduce the risk of steam oscillation. 4 Leakage (internal leakage and external leakage) (1) Leakage is not only the cause of vibration, and leakage can cause pollution, internal leakage can also cause energy loss. Solve the leakage problem, to a certain extent, to avoid system vibration, but also can extend the life of the equipment and improve efficiency. (2) The life of the high-pressure valve of the supercritical unit is sometimes very short, it is necessary to change the packing several times. The study of new packing or the design of new and effective sealing forms is necessary to prolong the life of such high-pressure valves and to improve the operational reliability. - At present, the level of complete sets of valves continue to improve, only a good solution to the above problems in order to ensure the overall performance of the valve and better overall quality.
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