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Safety valve of the common fault
Safety valve is a very important protection valve, widely used in various pressure vessels and piping systems, when the pressure in the pressure system exceeds the specified value, it can automatically open, the excess media to the atmosphere Go, 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 can automatically shut down. Safety valve work is directly related to the reliability of equipment and personal safety, it must be given attention. First, the valve leakage Under the normal working pressure of the device, the valve flap and valve seat sealing surface occurred more than the allowable degree of leakage, leakage of the safety valve will not only lead to 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. Second, the valve body surface leakage refers to the junction between the upper and lower valve leakage phenomenon, 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 a combination of surface The sealing surface is not good. Second, the valve body with the tooth surface seal does not meet the standards. Third, the flatness of the valve body with poor or hard padded impurities caused by seal failure. Third, the impulse safety valve does not move after the main safety valve action This phenomenon is often referred to as the main safety valve refused to move. Main safety valve refuse to move on the operation of the boiler hazards is very large, is a major hidden danger to equipment, seriously affecting the safe operation of equipment, once the pressure in the operation of the media and pipeline pressure exceeds the rated value, the Lord Safety valve does not move, so that equipment over-pressure operation can easily cause equipment damage and major accidents. Fourth, the impulse safety valve seat back after the main safety valve delay back seat too long This failure occurs mainly in the following two aspects: On the one hand, the main relief valve piston chamber leak steam size, although the impulse safety valve back Seat, but there is still pressure in the pipeline and the steam in the piston chamber is still high, pushing the piston downward force is still large, resulting in slow back seat main safety valve. The way to eliminate this kind of failure is mainly solved by opening the large throttle opening and increasing the throttle aperture. The large opening of the throttle valve and the increase of the throttle aperture allow the steam remaining in the pulse tube to be drained rapidly , Thereby reducing the pressure inside the piston, so that the downward thrust on the piston quickly reduce the thrust in the steam turbine steam accumulator up thrust and the main safety valve spring pull up rapidly under its own back seat. On the other hand, the main safety valve is the friction between the moving parts and fixed parts can also cause the main relief valve seat back slowly, to solve this problem is the main safety valve moving parts and fixed parts with the gap Control within the standard range. Fifth, the safety valve seat back pressure is low Relief valve back seat low pressure on the boiler's economic operation has a great harm, back seat pressure is too low will cause a large number of media time-out emissions, resulting in unnecessary energy loss. This failure occurred in 200MW units used in the A49H-type spring pulse safety valve, the analysis of the reasons are mainly caused by the following factors: First, spring pulse relief valve on the steam discharge, this form of impulse After the safety valve is opened, the medium is continuously discharged to promote the action of the main safety valve. The second factor that causes the low seat back pressure is that the fitting clearance between the valve core and the guide sleeve is not suitable and the gap between the valve seat and the guide sleeve is too small. After the impulse safety valve opens, a high dynamic pressure zone is throttled instantaneously in this position. Spool elevation, delayed back seat time, when the container down to a lower pressure in the kinetic energy area decreases, impulse valve back seat. Way to eliminate this failure is to carefully check the size of each part of the valve plug and the guide sleeve, with the gap is too small, reducing the diameter of the valve disc sealing surface straight valve cap or increase the radial clearance between the valve disc and the guide sleeve , To increase the flow area of ​​the site, so that steam will not flow too much over the throttling, leaving the local pressure rise to form a high kinetic energy pressure zone. Another reason for the low seat back pressure is the friction of various moving parts, some parts have jam, the solution is to carefully check the various moving parts, maintenance standards in strict accordance with the maintenance of the various components, the components of the gap to adjust to Standard range, eliminating the possibility of jam. Sixth, the safety valve frequency hopping refers to the safety valve back seat, to be slightly elevated pressure, the safety valve will open again and again several times, this phenomenon is called the safety valve "frequency hopping." Safety valve mechanical requirements Safety valve in the entire process reaches the required opening height, not allowed to appear jam, tremor and frequency hopping phenomenon. Occurrence of frequent jumps on the safety valve seal is extremely unfavorable, can easily lead to the sealing surface of the leak. Analysis of the main reasons for the safety valve seat back pressure is too high, the back seat pressure is high, the container less excess media emissions, the safety valve has been back to the seat, and when the operator improper adjustment, the container pressure will be very fast Rise, it also caused the safety valve action, like this situation can be opened by opening a large throttle method to be eliminated. When the throttle valve is opened, the steam source leading to the main safety valve piston chamber is reduced, the force pushing the piston downward is smaller, and the main safety valve is less likely to operate, thereby avoiding the continuous starting of the main safety valve. Seven, safety valve flutter Safety valve in the discharge process of jitter phenomenon, called the safety valve flutter, flutter phenomenon can easily lead to metal fatigue, the safety valve to reduce the mechanical properties, causing serious Equipped with hidden dangers, the main reasons for the occurrence of quite the following aspects: On the one hand the improper use of the valve, the use of the valve discharge capacity is too large (relative to the amount of emissions must be), the elimination method is to make the selection valve rated Displacement as close to the equipment as necessary emissions. On the other hand is due to the inlet pipe diameter is too small, smaller than the inlet diameter of the valve, or import pipe resistance is too large, the elimination of the method is installed in the valve, the import pipe diameter is not small dry valve inlet diameter or reduce the import pipe Resistance. Excessive discharge pipe resistance, resulting in excessive back pressure discharge is also a factor that causes the valve flutter can be reduced by reducing the resistance of the discharge pipe to be resolved. At present, power station boiler safety valve is composed of main and auxiliary valves, and adopts double protection of mechanical and thermal control. Some faults are not easy to occur. However, it is easy to handle the common failure causes and elimination methods of safety valves, To ensure the safe operation of equipment is of great significance.