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1) Particle impurities fall on the sealing surface and the sealing surface is cushioned, resulting in a gap between the valve plug and the valve seat, so that the valve leaks and forms an indentation on the sealing surface. The way to eliminate this failure is to grind the indentation that has fallen onto the sealing surface. Generally, when the equipment is to be repaired and repaired, the medium of the equipment piping will fluctuate into the valve due to the fluctuation of the system pressure and the temperature change. When the safety valve is calibrated, if the test pressure medium such as clean water, nitrogen, compressed air, etc. contains too much impurities, it will also directly affect the sealing effect of the sealing surface.
2) The dirt pits, corrosive media, and pits generated between the sealing surfaces will accumulate between the sealing surfaces, resulting in tight seals between the valve discs and the valve seats; the safety valve of the steam boiler will be used once. After take-off, there will be a layer of scale between the valve core and the valve seat when it falls back. Over time, it will generate iron oxide. After a long period of use, the safety valve that has not taken off will leave some impurities on the sealing surface and generate dirt rust and generate. Corrosion, which reduces the sealing performance of the safety valve, needs to be repaired once a year.
3) The sealing surface is damaged. The main causes of damage to the sealing surface are as follows: 1 The material of the sealing surface is poor. For example: 1 # fast boiler main safety valve due to many years of maintenance, the main safety valve spool and valve seat sealing surface welding layer has generally been grinding off, so that the hardness of the sealing surface is also greatly reduced, resulting in reduced sealing performance, eliminate this The best way is to turn the original sealing surface, resurfacing the alloy layer, and then processing it according to the original size to increase the surface hardness of the sealing surface. Pay attention to ensure the quality of processing in the processing process, such as cracks in the sealing surface, trachoma and other defects must be re-processing after turning. The newly processed valve seat must meet the requirements of the drawings. At present, the valve sealing surface of the YST103 general-purpose steel welding electrode is relatively effective. 2 The scratches caused by the erosion and wear of the medium cause the seal between the valve disc and the valve seat not to be tight, and the more the safety valve is opened, the more erosion and wear will occur between the sealing surfaces; in addition, if the pressure of the safety valve return seat is too small, The valve flap can only return to the seat when the pressure is reduced, the discharge time increases, the sealing surface is eroded by high-speed media, and the wear is increased. 3 The quality of the inspection is poor, and the finish of the valve seat is not up to the quality standard. Grinding of the valve core and valve seat of the safety valve is an important task for the maintenance of the safety valve. For defects such as scratches and crushes on the sealing surface, the depth is less than 0.05 mm, which is generally eliminated by grinding. When grinding the valve, the grinding of the sealing surface of the valve body is more difficult than the grinding of the valve core, and the key to the grinding of the sealing surface of the valve body is that the grinding head is smooth. The method to eliminate this kind of failure is to repair the sealing surface by grinding or grinding after turning according to the degree of damage. At the same time, there can be no tilting or uneven wear during grinding.
4) The material is not suitable due to improper assembly or related parts. During the assembly process, the valve seat of the valve core is not completely aligned or light-transmitting at the joint surface, or the valve seat sealing surface is too wide to seal. Elimination method is to check the size and the uniformity of the clearance around the valve plug to ensure the concentricity of the top hole of the valve plug and the sealing surface. It is not allowed to check the clearance of each part to lift the valve core; according to the requirements of drawings, the width of the sealing surface should be properly reduced to achieve effective sealing. Suitable materials must be selected for the sealing material.
5) There is an error in the safety valve check. In regular calibration, the opening pressure is not strictly adjusted according to the specified value, and only whether the exhaust pressure can be used as a good or bad standard. If the adjusted opening pressure is close to the normal working pressure of the boiler pressure vessel, it may cause the tightness of the sealing surface to be too small. When the valve takes over too long to generate vibration or pressure fluctuations, it easily leaks; in addition, when the cold state When the calibration is different from the actual operating conditions, there are indeed some errors in the adjustment of the opening pressure. Safety valve
Safety valve leakage what reason
Under the normal working pressure of the equipment, leaks exceeding the permissible level cannot occur at the sealing surfaces of the valve flap and the valve seat. The leakage of the safety valve will not only cause loss of the medium, but also the continuous leakage of the medium will cause the hard sealing material to be damaged. . However, the commonly used safety valve sealing surfaces are made of metal materials and metal materials. Although they are designed to be smooth and smooth, it is very difficult to achieve absolutely no leakage under medium pressure. Therefore, for a safety valve where the working medium is steam, the seal performance is considered to be acceptable if the leak is not heard at the outlet end under the specified pressure value.