First, the valve moving parts have jamming phenomenon. This may be due to improper assembly, dirt and impurities mixed or parts corrosion; poor surface finish of the piston chamber, surface damage, there are defects such as groove marks caused by defects. So that the friction between the moving parts and fixed parts fm increases, the other conditions remain unchanged f1 <f2 + f3 + fm So the main security door refused to move. For example, a major security door reflex movement occurred during the overheating main safety gate run-in test before the overhaul of furnace No. 3 in 2001. Inspection disintegration inspection found that the piston chamber has a lot of rust and impurities, the piston can not move in the piston chamber, resulting in the main security door refused to move. Maintenance of the piston, expansion ring and the piston chamber was rust treatment, the piston chamber groove marks and other defects were ground, the piston chamber before assembly evenly coated with lead powder inside the wall, and in strict accordance with the order of the valve assembly. In the boiler hydrostatic test, the pulse tube to be washed, and then the main safety valve and the impulse safety valve connection, after overhauling the furnace again when the safety valve running test is all normal. Second, the main security door piston chamber leak large. When the valve piston chamber a large amount of air leakage, the formula (1) in a force acting on the piston f1 is too small, other conditions remain unchanged f1 <f2 + f3 + fm Therefore, the main safety door refused to move. Piston chamber caused by a large amount of air leakage and the valve itself is not air tightness and piston ring does not meet the size requirements or excessive wear and tear of the piston ring seal does not meet the requirements. For example, 3 ~ 9 furnace main valve safety valve ring quality requirements of the piston ring should be smooth edges and corners, the free state of the opening gap is not greater than 14, the opening gap after assembly △ = 1 ~ 1.25, piston and piston chamber clearance B = 0.12 ~ 0.18, the gap between the piston ring and the piston chamber is S = 0.08 ~ 0.12, the piston ring is in good contact with the piston chamber, and the light transmission should not exceed 1/6 of the circumference. The requirements of the piston chamber is that the groove depth of the piston chamber shall not exceed 0.08 ~ 0.1mm, the ovality of not more than 0.1mm, the conicity of not more than 0.1mm, should be smooth and no scratches, but disintegration inspection found that each furnace The main safety gate piston ring, piston and piston chamber does not meet the requirements of maintenance procedures, the current general piston ring and piston chamber gap are S ≥ 0.20, and the piston chamber surface defects more serious, seriously affecting the piston chamber of the steam Density, resulting in excessive leakage of piston chamber steam. The way to eliminate this kind of defect is to deal with the inner surface of the piston chamber, replace the qualified piston and piston ring, and close the small throttle opening in the throttling safety device system with throttle valve to increase the inlet into the piston chamber of the main safety gate Steam volume may also be increased by increasing the stroke of the relief valve to increase the amount of intake air entering the piston chamber of the main safety gate, as conditions permitting, to facilitate actuation of the main relief valve. Third, the main safety valve and impulse safety valve mismatch, impulse safety valve steam flow is too small. Impulse safety valve nominal diameter is too small, resulting in the main relief valve into the piston chamber of the steam is insufficient to promote downward movement of the piston force f1 is not enough, that f1 <f2 + f3 + fm cause the main safety valve spool does not move. This phenomenon occurs mostly in the main safety valve impulse relief valve has a replacement, due to poor consideration caused. For example, in 2002 overhaul of furnace 5, the two heavy hammer type safety relief valve replaced by two Harbin valve factory production A49H-P54100VDg20 pulse safety valve, the safety valve and A42H-P54100VDg125 type spring main safety match, It will be used with the Soviet-made Dg150 × 90 × 250-type old main safety valve, the main safety valve and the A29H-P54100VDg125 spring-type main safety valve than the nominal diameter not only larger and less air tightness, at 5 No. Furnace safety valve is set to be saturated, running test caused by the main safety valve refused to move. Later, we disassembled the impulse safety valve and expanded the gap between the guide sleeve and the valve plug to increase its flow area, and ran the test once more successfully. So impulse safety valve and the main valve matching properly, the smaller nominal diameter will cause the main valve to refuse to move. 2.4, after the impulse safety valve recoil after the main safety valve delay back seat too long? The main reason for this failure occurs in the following two aspects: On the one hand, the main relief valve piston chamber leakage size, although the impulse safety However, the pressure of the steam in the pipeline and the piston chamber is still high, and the force of pushing down the piston is still very large, so the main safety valve is sluggish due to the recoil. This kind of failure occurs in A42Y-P5413 .7 VDg100 type safety valve, because this type of safety valve piston chamber Gland is good. 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. Another reason is that the main safety valve friction between the moving parts and fixed parts can also cause the main safety valve back seat slowly, to solve this problem is the main safety valve moving parts and fixed parts with the gap Console standard range. ? 2.5, the safety valve seat back pressure is low? Safety valve seat back pressure is low 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. On the one hand, the pressure before the relief valve due to the main relief valve medium displacement is not enough and continue to rise, so the pulse tube steam along the steam drum or gas header continue to flow to the impulse safety valve to maintain impulse safety valve action. On the other hand, due to this type of impulse safety valve medium flow through the gap between the valve core and the guide sleeve flows to the main safety valve piston chamber, medium out of the sealing surface of the impulse safety valve to form a dynamic pressure zone around it, The valve lift, so to achieve the momentum of the relief valve to continue emissions, the greater the steam emissions, the spool part of the kinetic energy pressure zone pressure greater role in the upward thrust on the spool greater impulse safety valve, the less Easy to back to seat, then eliminate this failure is to throttle the small, so that flow out of the flow of the relief valve to reduce the flow of media, reducing pressure in the kinetic energy area, so that the impulse safety valve back seat. 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. 2.6, safety valve frequency jump Frequency jump 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 up high, back seat pressure is high, the container less excess media emissions, safety valve has been back to the seat, and when the improper adjustment of the operator, the pressure in the container 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 throttling 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. 2.7, 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, resulting in Serious equipment problems, chatter occurs mainly in 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 of the method should be selected valve The rated displacement is as close as possible to the required discharge of the equipment. On the other hand is due to the inlet pipe diameter is too small, smaller than the inlet diameter of the valve, or inlet pipe resistance is too large, the elimination of the valve is installed, the inlet pipe diameter not less than the inlet diameter of the valve or reduce the import pipe resistance. Excessive discharge pipe resistance, resulting in excessive discharge when the North pressure is also a factor that causes the valve flutter can be reduced by reducing the resistance of the discharge pipe to be resolved. ?? 3, concluding remarks on the boiler safety valve common causes of failure were analyzed and put forward specific solutions, although the power station boiler safety valve is composed of the main and auxiliary valves, and the use of mechanical and thermal control Double protection, some failures are not easy to occur, but only fully grasp the safety valve common causes of failure and elimination methods, handle it in case of failure can be handy, to ensure the safe operation of equipment is of great significance. ?