Low temperatureValveThere are many types and types of, now take the low temperature stop valve as an example, the common failures can be divided into three types:
The first type: the failure occurring on the top of the valve. The valve top (valve head) of this kind of valve is connected with the valve stem by movement, so that when the valve is closed, the two sealing surfaces can be "corrected automatically ". After long-term use, sometimes the lock nut is loosened due to the damage of anti-back gasket, and finally the top of the valve falls off when opening the valve. At this time, the valve will lose its function of closing. Sometimes the damage of the lock nut is caused by the improper material and the replacement of cold and fragile metal. Another common fault is that the valve top is not closed strictly, that is, the valve leaks. The common reason is that the sealing surface of the valve top and the valve seat is crushed by hard objects (such as hard objects such as silica gel, metal scraps, welding slag and so on), forming dents. In this case, in order to close the valve tightly, we often use a lot of strength, which makes the pressing injury worse instead. Sometimes the center line of the valve stem of the valve is not perpendicular to the sealing surface (valve surface) of the valve seat, or the top and valve surface of the valve are worn out due to long-term use, which will cause leakage of the valve.
The second type: the failure on the stem. The common fault is that the screw buckle on the valve stem and the screw sleeve is worn out, which makes the valve unable to close. Generally, the screw buckle of the valve stem is not easy to be worn out, while the negative thread on the screw sleeve (brass) is easy to be damaged. Most of the reasons are that the valve is too hard when it is opened, or it is hard to screw after it is opened or closed, which makes the screw Button bite. Sometimes the screws are completely "bitten", and the valve can only be opened, but not closed. To close the valve, the valve rod can only be topped inward with temporary external bolts, waiting for repair before repair. To prevent this kind of failure, the most important thing is not to use too much force when opening or closing the valve, and not to open or close hard when opening or closing.
The third category: the fault occurs at each connection. Those that belong to this kind of failure include cold freezing of valve filler, leakage of valve seat and pipe connection flange, leakage of tin thread at both ends of valve screw sleeve, etc. The valve stem stuffing is generally in the stuffing groove where the valve stem is close to the wall of the cold box. When the stuffing is uneven or tight, or the valve stem is not straight or round, the low temperature liquid or gas will leak out along the gap of the stuffing. Due to the outside transmission of cold energy, the moisture in the air will freeze on the stuffing, which will freeze the valve stem. In this case, the valve can only be opened and closed by using steam or hot water to heat the stuffing. However, after the valve is switched on and off, the accumulated water in the stuffing will freeze again. Because the valve switch is laborious, it often results in the fracture of the valve stem, the fracture of the hand wheel and so on. Therefore, after the maintenance of the valve, the stuffing should be packed evenly and tightly, and the pressing nut should be tightened. During the overall leak test of the air separation unit, the leakage of the valve stem stuffing should also be checked, and this problem should be solved before the cold start. The common causes of flange leakage are that the sealing surface is not smooth and smooth, the pipeline compensation is insufficient, the bolts are not evenly tightened, the bolt material is improper, etc. The two ends of the outer screw sleeve of the valve stem are connected by tin-filled threads, which will easily cause cracks and leaks after long-term use. When testing pressure and leak test, if this kind of leak is found, it is better to draw out the valve stem to fill tin and tighten it again, and it is better to use silver welding.
Low temperature valve inAir separation equipmentDuring the normal operation, it is a equipment that should be maintained frequently. We should have high standards and strict requirements, carefully maintain and use it well.
