1, Preface ?? 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 surplus The medium is vented to the atmosphere to ensure the safe operation of pressure vessels and piping systems and to prevent accidents and to shut down automatically when the system pressure drops back to or slightly below the operating pressure. Safety valve work is directly related to the reliability of equipment and personal safety, it must be given attention. 2, safety valve common cause of failure analysis and solutions ?? 2.1, safety valve leakage valve? In the normal working pressure of the device, valve and valve seat sealing surface occurred more than allowable degree of leakage, not only the leakage of safety valve Will cause media loss. 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. 2.2, safety valve leakage at the junction of the valve body? 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 tightness or tight bias, Resulting in poor sealing surface. 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. Second, the safety valve body with tooth-shaped gasket seal 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 flatness of the valve is too poor 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. 2.3, Impulse safety valve does not move after the main safety valve action This phenomenon is often referred to as the main security door refused to move. The main security door refuse to move to the boiler in danger is very large, is a major hidden dangers of equipment, seriously affecting the safe operation of equipment, and pressure in the pipeline when the medium pressure exceeds the rated value, the main safety gate No action, so that equipment over-pressure operation can easily cause equipment damage and major accidents. Before analyzing the reason why the main safety valve refuses to move, first analyze the action principle of the main safety valve. As shown in Figure 1, when the pressure in the pressure vessel rises to the full pressure of the impulse relief valve, the impulse safety valve is actuated. The medium flows from the container through the pipe to the main relief valve piston chamber. There will be a slight expansion in the piston chamber Step-down, if at this time the pressure inside the piston chamber P1, piston throttle area Shs, at this time on the piston f1: f1 = P1 × Shs ........................ (1)? If this time The pressure of the medium in the pressure-bearing vessel is P2 and the area of ​​the valve spool is Sfx, then an upward force f2 of the medium on the valve spool at this moment is: f2 = P2 × Shx? ............ .. (2) Valve piston diameter larger than the spool, so equation (1) and (2) Shs> Sfx? P1 ≈ P2 If the spring through the valve stem upward pull force is set to f3 and the moving parts and fixed parts Between the friction (mainly the piston and piston chamber friction) is set to fm, the main safety gate action preconditions: only the role of force on the piston f1 slightly larger than the force acting on the spool upwards f2 and spring through the valve stem upward pull force f3 and moving parts and fixed Frictional force between the member (mainly the friction between the piston and the piston chamber) FM sum, that is: f1> f2 + f3 + fm to start the main security gate. Through practice, the main safety valve safety valve refused to move mainly with the following factors: safety valve 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. Search Keyword: More Valve Technical Articles
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