Cut-off valve to choose the knowledge and skills

by:AIRWOLF     2020-05-22
In applications demanding high levels of regulator is proposed to cut off the request, so cut off function is the use function of regulator is one of the most important and inherent quality indicator ( To cut off the level and standard of dividing see related information) 。 In the field use, often can appear the regulator to cut off the bad, such as large leakage fault. Except for intercepting, allow the pressure difference is too small and to be open to causes such as leakage increase, mostly due to the defects of structure and the improper selection of regulator. A, selection of structural type double sealed class regulator ( Such as two-seater valve, double sealing sleeve valve, etc. ) One of the major drawbacks is leaking. But until the 1980 s, due to the relatively popular sleeve valve, however, many manufacturers are up and down in the sleeve valve has a lot of work to improve the structure. To reduce the leakage, make it become very complicated structure. So it brought many disadvantages: parts, poor reliability and spare parts, maintenance, cutting effect is not ideal, and so on. In fact, it is design thinking into the erroneous zone, rather than the body & other; Heart & throughout; In such a complex changes, it is better done by external adjustment. Therefore, we should choose single seal class regulator. In this way, seal, reliability problems, maintenance and spare parts problems are solved one by one. At this point, solve the contradiction of valve into the focus of the media the problem of unbalanced force increase, solve it only with a strong piston actuator, enlarging the valve stem. Such apparently by external solution is much easier than through internal complex improvement, this is not so much to problems, as it's a matter of thinking. Into the ninety s, people began to look for structure more simple, more reliable shut-off valve seal. At this moment, found quarter-turn valves than straight trip valve ( Single seat valve, sleeve valve, gate valve) Has more advantages, so the triple eccentric cut butterfly valve, fully functional cut-off valve, hard seal cutting ball valve. Second, the choice of sealing surface ( 1) Face to face seal: common plunger valve core, its sealing surface is small cone 60 ℃, the seat is also a small cone 60 ℃, the width of the small cone used in 0. 5 mm ~ 2 mm, between two cone to seal it is necessary to ensure good contact. But, in fact, it is always under the influence of processing error ( Such as concentricity, roundness, gradient, etc. ) , the sealing effect is not ideal. This kind of valve leakage rate is usually 10-4, precision grinding can reach 10-6, can achieve a good seal. ( 2) Spherical seal: using the spherical rotation of valve core and the fixed seat small cone and tangent, for line contact between them, it's better than the face to face of sealing effect. Shenyang company launched a fully functional ultra light valve, the spherical sealing butterfly valve is to use this approach to make, such as the leakage rate can reach 10-6 ~ 10-8, high-performance triple eccentric butterfly valve can be as high as 8, 10 - and even zero leakage.
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