With the rapid development of industrial technology, for the valve industry, made more stringent requirements, especially for low-temperature media used in the butterfly, in addition to possess to meet the general performance of the valve and, more importantly, in low temperature under the valve seal reliability, flexibility of movement as well as a number of other low-temperature valve special requirements.
As we all know, Valve has a compact structure, small size, light weight (with the same pressure, the valve diameter compared to the same reduce the 40% ~ 50%), fluid resistance is small, open and close rapidly and a series of advantages. However, some of China's low-temperature devices such as days of burning liquid equipment, air separation equipment, and pressure swing adsorption equipment, valves used in chemical industry has more than 80% cut-off valve or gate valve, using a small number of butterfly valves. Analyze the main reason is too metal sealing butterfly valve at low temperature sealing performance under adverse conditions, as well as other irrational structure caused by internal leakage and dielectric leakage, serious implications of these low-temperature equipment, safety and normal operation can not meet the cryogenic equipment.
According to China's continuous development of low-temperature devices, the requirements for low-temperature valve and increasing the development of market economy to adapt to the needs of the metal sealing butterfly valve structural improvements, developed a three eccentric high-sealing properties of pure metal butterfly valve (Figure 1, has been declared national patent), whether the medium is high or low temperatures can meet their needs. Is combined with its structural characteristics, only the low-temperature performance, make a brief introduction.
1, for low-temperature disc valve sealing performance requirements
Produce low-temperature valve, there are two main reasons for the leakage of the situation, one internal leakage; second is leakage.
1) generated within the valve seal leakage mainly due to the Deputy at low temperatures caused a state of deformation. When the medium temperature dropped to produce the material phase change caused by volume change, so that the original seal with high precision surface grinding produces warpage caused by low-temperature seal bad. We have proposed to DN250 valves for low-temperature test medium is liquid nitrogen (-196 ℃) butterfly plate material 1Cr18Ni9Ti (not subject to low temperature treatment) found that the sealing surface warpage amounted to about 0.12mm, which is the main reason resulting in leakage .
The newly developed valve seals replaced by a flat cone seal. Is an oblique elliptical cone seat sealing surface, and embedded board is mounted on butterfly seal ring composed of circular elastic seal pair. Seal ring in radial floating butterfly board tank. When the valve is closed, flexible sealing ring first and the sealing surface of the short axis of contact ellipse, with the stem of the rotating seal ring gradually pushed inward, forcing elastic ring again and the long axis oblique cone surface contact, eventually leading to elastic sealing ring with an oval all contact with sealing surface. It relies on elastic sealing ring deformation and to achieve. So when the butterfly valve or plate deformation at low temperatures, when the seal ring will be flexible to absorb the compensation, will not produce the phenomenon of leakage and choked to death. When the valve opens, the elastic deformation disappear, in the process of basically not open and close relative friction, so long service life.
2) The leakage of the valve: one is the use of valves and pipe flange connections, because connections litter, connecting bolts, and connectors under the material at low temperatures are not synchronized between the contraction and relaxation lead to a leak generated. So we put body in connection with the pipeline replaced by a flange welded structure, avoiding the low-temperature leakage. The second is the stem and packing at the leakage. In general the majority of the valve filler with F4, because of its good performance from the sliding friction coefficient (for steel friction coefficient f = 0.05 ~ 0.1), but also has a unique chemical stability, so widely used. But the F4 is also inadequate, first cold flow tendency to large; second is linear expansion coefficient, at low temperatures lead to leakage resulting shrinkage, resulting in a large number of frozen stem Department to open the valve malfunction. To this end developed by low-temperature valve seal structure of a self-shrinkage expansion coefficient, namely the use of the characteristics of F4, through the gap to the left to reach room temperature, low temperature can be sealed purpose.
2, valve body, stem bushing design requirements
1) The low-temperature structure and shape of the shell valves. The correct choice of material or failure of the normal valve has an extremely reliable and important work. The structural characteristics of butterfly valves and globe valve, gate valve, compared not only to avoid a result of irregular shape, uneven shell thickness, at low temperatures resulting from shrinkage, thermal stress caused by the deformation, and because small butterfly , body shape is basically about is called, and thus heat capacity is small; to the consumption of cooling capacity is also small; shape of the rules would facilitate the valve cold measures. If the new model developed DD363H valve disc valves ensure reliable at low temperatures, the use of cryogenic valves in full accordance with the particularity of the design and manufacture, such as: shell material selection of a cubic lattice of 1Cr18Ni9Ti austenitic stainless steel.
2) The stem bushing choice: according to the user to reflect, and some low-temperature valve in the running among the rotating parts of the valve occurred viscous, occlusal phenomena have occurred, mainly due to: matching material selection reasonable, I stay in the cold gap is too small, and processing precision reasons. In the development of low-temperature valve, and take a series of measures to prevent the above phenomenon. For example: we stem the upper and lower bushing selected with friction coefficient and self-lubricating properties of SF-1-type composite bearings, so that can be applied to some of the special needs of low-temperature valve.
Metal Sealed Butterfly Valve has the features of an ordinary valves do not possess. In particular, flow resistance is small, sealed, reliable, open and close rapidly, and long service life. The company developed three eccentric butterfly valve sealing ability of metal sealing ring from the elastic deformation to achieve sealing, thus eliminating the need with medium force, it can be done with a two-way seal. According to some characteristics of butterfly valves will be more people paying attention to. Butterfly in the future there will be more applied to the low-temperature devices. ball valve Trunnion Mounted Ball Valve Floating Ball Valve Top Entry Ball Valve ball valve V Type Ball Valve
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