Jiangsu cryogenic valves of high quality manufacturers tell you flywheel gases cryogenic valves on valve sealing requirements
Cryogenic valves in the valve sealing requirements
Along with the rapid development of economy and the rapid development in the industrial technology by leaps, the ever-changing high-tech industry and the various requirements of the valve, the valve industry faces great challenges at the same time also brought a lot of opportunities. Regulator is used in low temperature medium, in particular, in addition to general valve can satisfy the normal temperature condition of performance, more important is in the condition of low temperature regulating valve sealing reliability, flexibility of action and some other special requirements of cryogenic valves.
Regulating valve has a compact structure, small fluid resistance, rapid opening and closing, and a series of advantages, usually made up of actuator and valve body, through the automation operation of actuators driven valve adjustment, play a role to adjust the pipeline medium. Widely used in automation system mainly. Therefore widely used.
But our country in some low temperature device, such as natural liquefaction equipment, air separation equipment and pressure swing adsorption equipment used by the chemical industry more than 80% or globe valve valve or gate valve or butterfly valve, using regulator is few in number. Its main reason is that the regulator's cost is higher, this is can't accept by the customers choose regulator factors in the cryogenic system.
According to China's development of low temperature device, mounting to the requirement of cryogenic valves and so on low temperature regulator for structural improvements, developed a high sealing performance of the pure metal valve, regulator whatever medium is high temperature or low temperature can meet their needs.
Is combining with the characteristics of its structure, only the performance at low temperature were briefly introduced.
A, on the properties of low temperature regulating valve sealing requirements: //www.cgvalves.com
Cryogenic valves there are two main causes of leaks, it is leakage; The second is leakage.
1) the valve leakage
The main reason is that sealing deputy in the condition of low temperature deformation caused by.
When the medium temperature drop to make material phase change caused by volume changes, make originally very high grinding precision sealing surface warping deformations caused by poor sealing at low temperature. We had to stop valve for low temperature test, the medium of liquid nitrogen (196 ��) open-close part material is 1 cr18ni9ti stainless steel material (without low temperature treatment), found the sealing surface warping deformation of 0.2 mm or so, this is the main reason for the cause of leakage.
Of newly developed dampers by the flat sealed taper sealing instead. Seat is a ellipse oblique cone sealing surface, and embedded on the open-close part is of circular elastic sealing ring seal. Sealing ring can be open/close a radial groove floating. When the valve is closed, the elastic sealing ring and short axis of elliptic sealing surface contact first, as the rotation of the valve stem seal ring to push, force the elastic ring and long axis of the oblique cone surface contact again, eventually leading to the elastic sealing ring with elliptic sealing surface contact. Its sealing is depends on the elastic deformation and to achieve.
So when the body or open-close part deformation at low temperatures, will be the elastic sealing ring to absorb compensation, won't produce leaks and jammed phenomenon. When the valve is open when the elastic deformation disappear immediately, and no relative friction in the process of opening and closing, so the service life is long.
2) the valve leakage.
One is the valve and pipe flange connection with the payment, due to the connection pad material, connecting bolts, and fitting materials under low temperature shrinkage are not synchronized between relaxation and lead to leakage. So we put the body and the pipe connection consists of flange connection instead of welding structure, to avoid the leakage in low temperature.
Secondly, stem and packing leakage. Packing of the most commonly used F4, because it from sliding performance is good, small friction coefficient, friction coefficient of steel f = 0.05 ~ 0.1), but also has the unique chemical stability, so widely used.
But the F4 also have shortcomings, one is cold flow tend to be big; Second, linear expansion coefficient is big, produce in the low temperature cold lead to leakage, causing stem from a large number of ice, to make the open valve failure. Therefore developed by low temperature regulator using the seal structure of the advantage of the characteristics of the F4 large expansion coefficient, through to leave gaps to achieve under normal temperature and low temperature can be sealed.
2, valve body, valve stem bushing design requirements
1) cryogenic valves shell structure shape.
Material selection is correct or not for reliable valve normal work has extremely important significance. Regulator of structural features compared with the cut-off valve, gate valve, not only avoid the because of irregular shape, shell wall thickness is not uniform, under the low temperature cold, deformation caused by temperature stress, and because the regulator is small in size, body shape or so basic said yes, and thermal capacity is small; To the cold quantity consumption too small; Shape the rules and convenient for the valve of cooling measures. Such as Shanghai chaoguang valve co., LTD., the low temperature regulator in order to ensure the valve under low temperature and reliable use, completely according to the particularity of cryogenic valve design and manufacturing, such as: shell material selection has a cubic lattice 1 cr18ni9ti austenitic stainless steel, etc.
2) stem bushing.
According to customer reflect, some cryogenic valves in operation, the rotation of the valve parts occur viscous, occlusion phenomenon occurs frequently, the main reason is: the matching material selection is not reasonable, gap is too small to stay cold, and the machining accuracy.
In the development of cryogenic valves, adopted a series of measures to prevent the above phenomenon. Bush under the valve stem, we chose has a small friction coefficient and self-lubricating properties SF - 1 type of composite bearing, it can be applied to cryogenic valves of some special need. Metal sealing type regulator has the characteristics of some common valve is not have. Especially, small flow resistance, reliable sealing, opening and closing fast, long service life, etc.