Abstract: The leakage of the valve of the safety valve of the boiler, the leakage of the valve body and the leakage of the valve body are analyzed. The main safety valve does not move after the safety valve of the impulse has been actuated. The back delay of the main safety valve after the recoil of the impulse safety valve is too long and the back pressure of the safety valve Low frequency hopping and flutter and other common causes of failure, and for the cause of the malfunction proposed solutions. Keywords: Safety valve Impulse safety valve Main safety valve? 1, Foreword ?? Safety valve is a very important protection valve, widely used in various pressure vessels and piping systems, when the pressure in the pressurized system exceeds The specified value, it can automatically open, the excess media to the atmosphere to discharge to ensure the safe operation of pressure vessels and piping systems to prevent accidents, and when the system pressure back to the working pressure or slightly lower than the working pressure When it can automatically shut down. Safety valve work is directly related to the reliability of equipment and personal safety, it must be given attention. 2, the safety valve common cause of the failure analysis and solution ?? 2.1, the valve leakage? Under the normal working pressure of the device, valve and valve seat sealing surface occurred more than allowable degree of leakage, not only will cause leakage of the safety valve Loss of media. In addition, the continuous leakage of media will make the hard sealing material is damaged, but the sealing surface of the commonly used safety valve is a metal material on the metal material, although strive to be smooth and smooth, but in the case of media pressure To the absolute leak is also very difficult. Therefore, the working medium is a steam safety valve, at the specified pressure value, if the naked eye at the exit can not see the leak, it is considered the sealing performance is acceptable. Common causes of valve leakage mainly in the following three cases: a situation is that dirt impurities fall on the sealing surface, the sealing surface padding, resulting in a gap between the valve core and the valve seat, so the valve leakage. The way to eliminate this fault is to remove the dirt and impurities falling on the sealing surface. Generally, when the size of the boiler is about to be shut down, the safety door running test is first performed. If the leak is found to be out of service after the shutdown, if it is Point furnace runner test run leak found security gate, it is estimated that this situation caused by the runner can be cooled after 20 minutes and then ran rudder, the sealing surface erosion. Another case is the sealing surface damage. Seal surface damage caused by the following main reasons: First, poor sealing surface material. For example, in the No. 3 to No. 9 furnace main security door due to years of overhaul, the main safety valve spool and seat sealing surface has generally been studied very low, so that the sealing surface hardness is greatly reduced, resulting in decreased sealing performance, eliminating this Phenomenon is the best way to turn the original sealing surface down, and then re-welding the drawings required processing to improve the sealing surface hardness. Note that in the processing must ensure the quality of processing, such as the sealing surface cracks, trachoma and other defects must be machined back after processing. Newly processed valve seat must meet the drawing requirements. Currently using YST103 common steel welding rod sealing surface sealing effect is better. Second, the poor quality of maintenance, valve seat grinding can not meet the quality standards, the way to eliminate this failure is based on the degree of injury using grinding or turning grinding method to repair the sealing surface. Another cause of leakage of the safety valve is due to improper assembly or inappropriate parts dimensions. In the assembly process, the valve seat is not fully aligned or the surface with light transmission phenomenon, or the valve seat sealing surface is too wide, which is not conducive to sealing. Elimination method is to check the spool around the size and uniformity of the gap to ensure that the valve tip hole and the sealing surface with a positive, check the Ministry of the gap does not allow the lift valve; . 2.2, valve body surface leakage refers to leakage between the upper and lower valve body junction, resulting in leakage of the main reasons for the following aspects: First, the binding surface of the bolt tension is not enough or tight bias, resulting in Poor sealing surface. Elimination method is to adjust the bolt tightness, the tight bolt must be diagonally tight manner, it is best to measure the tightness around the gap, the bolt tight so far, and the junction of the gap around Consistent. Second, the valve body with the tooth surface seal does not meet the standards. For example, the radial seal groove slightly grooved, poor parallelism, tip too sharp or over-the-slope and other defects can cause seal failure. So that the valve body surface leakage. In the maintenance of good spare parts quality, the use of standard toothed gaskets can avoid this phenomenon. Third, the flatness of the valve body with poor or hard padded impurities caused by seal failure. The valve body due to the flatness of the joint surface caused by poor bonding surface leakage, the elimination of the valve is to disintegrate the valve to re-ground the joint until the quality standards. As a result of impurities caused by gasket failure seal in the valve assembly carefully clean the surface to avoid impurities fall into. 2.3, Impulse safety valve does not move after the main safety valve action This phenomenon is often referred to as the main security door refused to move. The main security door refuse to move to the boiler in danger is very large, is a major hidden dangers of equipment, seriously affecting the safe operation of equipment, and pressure in the pipeline when the medium pressure exceeds the rated value, the main safety gate No action, so that equipment over-pressure operation can easily cause equipment damage and major accidents. Before analyzing the reasons why the main security gate refuses to move, first analyze the action principle of the main security gate. As shown in Figure 1, when the pressure in the pressure vessel rises to the full pressure of the relief valve, the impulse safety valve moves. The medium flows from the container through the pipe to the main relief valve piston chamber. There will be a slight expansion in the piston chamber Step-down, if at this time the pressure inside the piston chamber P1, piston throttle area Shs, at this time on the piston f1: f1 = P1 × Shs ........................ (1)? If this time The pressure of the medium in the pressure-bearing vessel is P2 and the area of ​​the valve spool is Sfx, then an upward force f2 of the medium on the valve core at this time is: f2 = P2 × Shx? (2) In general, the piston diameter of the safety valve is larger than the diameter of the valve plug. Therefore, Shs> Sfx? P1≈P2 in the formula (1) and (2) f3 and the friction between the moving part and the fixed part (mainly the friction between the piston and the piston chamber) is set to fm, the main safety gate action preconditions: only the force acting on the piston f1 slightly larger than the role of the valve The force on the core to make it upward f2 and spring through the valve stem up F3 tension member and moving the friction between the fixed parts (mainly the friction between the piston and the piston chamber) FM sum, that is: f1> f2 + f3 + fm to start the main security gate. Through practice, the main security door refused to move mainly with the following three aspects:
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