Stem Sealing of Low Temperature Stainless Steel Globe Valve
At present, the stem seal of low temperature stainless steel globe valve has packing box and bellows, which are on the air separation device produced in batches. The stem of low temperature stainless steel globe valve mostly adopts packing box seal structure. For valves working in toxic, flammable and explosive gas medium, the valve stem can be sealed by corrugated tube. But in high pressure gas larger than or equal to 80 MPa, corrugated tube can not withstand such high external pressure. Packing box sealing can only be used because of its simple manufacture, convenient maintenance and replacement. It is widely used in practical production. However, in order to ensure the density of fillers, the working temperature of fillers should not be lower than - 40 C, which requires that filler box devices working on cryogenic valves should work as close as possible to the ambient temperature. Usually, the filler is considered to be in a positive working state without frosting, but if the filler is not sealed due to the filler itself or its working life, low temperature gas will leak through the filler and freeze the filler box, which will cause further leakage failure of the filler. In many cryogenic valve series used in aerospace field, packing box sealing structure is mostly used for reasons. In order to ensure the temperature of the stem packing box, the method of lengthening the length of the stem is adopted, resulting in larger size of these cryogenic valves.
Low temperature stainless steel globe valves are mostly used in situations where medium does not allow micro leakage and improper packing. In the design of bellows, the life of bellows is the key. The life of bellows is related to its stroke and initial installation state. To ensure the service life of bellows cut-off valves, in the case of a certain stroke, the installation of bellows should ensure that they do not bear additional external forces; in the working state, because bellows bear external pressure, their working state is good, but by the rapid closure of low-temperature valves or air holes may exist in the pipeline may lead to water hammer. Therefore, when calculating the pressure on the bellows, a certain safety factor should be added, and the bellows should be protected from water hammer as far as possible.
