Pressure relief valve (safety valve) common failures and causes

1. Valve Leakage Under the normal working pressure of the equipment, the valve flap and valve seat sealing surface occur more than the allowable degree of leakage. The leakage of the relief valve (safety valve) will not only cause the loss of the medium. In addition, the continuous leakage of media will make the hard sealing material is damaged, but the sealing surface of the commonly used pressure relief valve are metal materials on the metal material, although strive to make it smooth and neat, but under medium pressure To be absolutely 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: The first case is: dirt impurities fall on the sealing surface, the sealing surface pad, resulting in a gap between the valve core and the valve seat, so the valve leakage. The way to eliminate this kind of failure is to remove the dirt and impurities falling on the sealing surface. Usually, when the size of the boiler is about to be shut down, the safety door running test should be conducted first. If the leakage is found, the equipment will be disassembled and repaired. If it is run furnace after the blast furnace test found leakage of the security gate, it is estimated that this situation caused by cooling after running can run 20 minutes after rudder once again on the sealing surface erosion. The second case is the sealing surface damage. Seal surface damage caused by the following main reasons: First, poor sealing surface material. 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. The third cause of the safety valve leakage is due to improper assembly or parts size is not appropriate. 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. The valve body surface leakage refers to the upper and lower valve body surface leakage at the junction, resulting in leakage of the main reasons for the following aspects: First, the binding surface of the bolt tightness or tight bias, resulting in a combination Surface seal is not good. 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. The second is: the tooth surface of the valve body gasket does not meet the standard. 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 the poor surface or hard impurities caused by gasket failure seal. 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. 3. Impulse safety valve action after the main pressure relief valve (safety valve) does not move This phenomenon is often referred to as the main security door refused to move.