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This post was last edited by shiwendong on 2017-1-18 at 22:03. Common faults and causes of pressure relief valves (safety valves) (purely personal opinions). Fellow sailors, please feel free to add more information to share and learn together. 1. Valve leakage: At the normal operating pressure of the equipment, leakage occurs at the sealing surface between the valve disc and the valve seat in an amount that exceeds the allowable limit. Leakage in pressure relief valves (safety valves) not only results in a loss of fluid. Furthermore, continuous leakage of the medium can also damage the hard sealing materials. However, the sealing surfaces of common pressure relief valves are made of metal against metal; although efforts are made to keep them smooth and flat, it is very difficult to ensure complete leaklessness when the medium is under pressure. Therefore, for safety valves whose working medium is steam, at the specified pressure value, if no leakage can be seen with the naked eye or heard at the outlet, the sealing performance is considered satisfactory. Generally, there are mainly three reasons for valve leakage. The first reason is that dirt and impurities settle on the sealing surface, covering it and creating a gap between the valve stem and the valve seat, which leads to leakage. The method to eliminate this fault is to remove the dirt and impurities that have accumulated on the sealing surface. Generally, when the boiler is prepared for major or minor repairs, a safety valve test is carried out first; if leakage is detected, the boiler is shut down for detailed inspection and repair. If leakage is found in the safety valve during a test conducted after the boiler has been started up, it is likely that this is the cause of the problem. In such cases, the valve can be tested again after cooling for 20 minutes, thereby flushing the sealing surface. The second scenario is damage to the sealing surface. The main reasons for damage to the sealing surface are as follows: first, the material of the sealing surface is of poor quality. At present, the sealing surfaces of valve spools fabricated by surfacing with YST103 general-purpose steel electrodes yield good results. Secondly, the quality of maintenance is poor; the grinding of valve cores and seats does not meet the required quality standards. To resolve this issue, the sealing surfaces are repaired by grinding or by grinding after turning, depending on the extent of the damage. The third cause of safety valve leakage is improper assembly or inappropriate dimensions of the related parts. During assembly, the valve core and seat may not be fully aligned, there may be light penetration at the joint surface, or the sealing surfaces of the valve core and seat may be too wide, which hinders proper sealing. The solution is to check the size and uniformity of the clearances around the valve spool, to ensure that the hole at the top of the valve spool is aligned properly with the sealing surface; it is also necessary to check that there are no gaps in any part that could cause the valve spool to lift ； Reduce the width of the sealing surface appropriately as required by the drawings to achieve effective sealing. 2. Leakage at the valve body joint refers to the leakage that occurs at the junction between the upper and lower valve bodies. The main reasons for this type of leakage are as follows: First, the bolt tension at the joint is insufficient or uneven, resulting in poor sealing at that junction. The solution is to adjust the bolt tension; when tightening the bolts, it is necessary to do so in a diagonal manner. It is best to measure the gaps at various points while tightening, and keep tightening until the bolts can no longer be tightened any further, ensuring that the gaps across the joint surfaces are uniform. Second: the toothed gasket at the valve body joint surface does not meet the standards. For example, minor radial grooves on the toothed gasket, poor parallelism, or defects such as overly sharp or steep teeth can all lead to seal failure. This causes leakage at the joint surface of the valve body. During maintenance, ensure the quality of spare parts; using standard-compliant toothed gaskets can prevent this phenomenon from occurring. Third: The flatness of the joint surface of the valve body is too poor, or it is blocked by hard impurities, resulting in failed sealing. For leaks at the valve body joint surfaces caused by poor flatness of these surfaces, the solution is to disassemble the valve and re-grind the joint surfaces until they meet the quality standards. In cases where seal failure is caused by impurities blocking the area, thorough cleaning of the mating surfaces should be carried out during valve assembly to prevent impurities from getting there. The phenomenon in which the main pressure relief valve (safety valve) does not activate after the impulse safety valve operates is commonly referred to as the failure of the main safety gate to function.