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Requirements for the metal sealing butterfly valve valve in low temperature

Release date:2015-05-05    The number of clicks:

With the rapid development of economy and technology change rapidly, high-tech and people's demand for valves, the valve industry faces enormous challenges and opportunities. Especially the butterfly valve used in low temperature medium, in addition to meet the general performance of the valve is under the condition of normal temperature, it is more important at low temperature valve sealing reliability, flexibility and movement of low temperature and some other special requirements of the valve.

The butterfly valve has the advantages of compact structure, small size, light weight (with the same pressure, the same diameter of the valve can be reduced by 40% compared to 50%) fluid resistance small, open and close rapidly and a series of advantages, so it has been widely used.

But in some of China's low-temperature devices, such as natural liquefaction equipment, air separation equipment and pressure swing adsorption equipment used in the chemical industry has more than 80% valve or valve or gate valve, butterfly valve using a small number. The main reason is the low temperature metal sealed butterfly valve sealing performance under adverse conditions, and other irrational structure caused by leakage and leakage within the media phenomenon, serious effects of low temperature and normal operation of security equipment, can not meet the requirements of low temperature equipment.

According to the continuous development of China's low-temperature devices, the requirements for increasing low temperature valve, so the metal sealing butterfly valve for structural improvement, development of pure metal high three eccentric butterfly valve sealing performance of the valve, whether the medium is high or low temperatures can meet their needs.

Is combined with its structural features, only for a brief low-temperature performance.

A, butterfly valve for low temperature sealing performance requirements:

Low temperature valve leak because there are two cases, one leakage leakage is two.

1) leakage within the valve

The main reason is sealing at low temperature due to deformation.

When the medium temperature dropped to the material phase change caused by volume changes, so that the original sealing surface of high precision grinding produces warpage caused by low-temperature sealing side. We have conducted experiments on DN250 cryogenic valves, medium for liquid nitrogen (-196 C) butterfly plate material is 1Cr18Ni9Ti (without cold treatment) found that the sealing surface of the warping deformation is about 0.12mm, which is the main cause of inner leakage.

The newly developed valve cone from the flat seal to seal. Is an oblique elliptical cone seat sealing surface, and is embedded in the circular elastic disc sealing rings sealing. Seal ring groove in the disc radial float. When the valve is closed, the first elastic sealing ring and sealing contact surface of the short axis of the ellipse, with the stem of the rotating seal ring gradually pushed inward, forcing the elastic ring again and the long axis oblique cone surface contact, resulting in elastic sealing oval ring and all contact with the sealing surface. It relies on elastic sealing ring deformation and to achieve.

So when the body or disc in the low temperature deformation, the seal ring will be flexible to absorb the compensation, will not produce the phenomenon of leakage and card dead. When the valve opens the network immediately disappear when the elastic deformation, in the process of opening and closing relatively little friction, so the service life is long.

2) the leakage of the valve.

One is the use of valves and pipe flange connection, the connection pad, connecting bolts, and connections between the materials at low temperatures have not synchronized contraction and relaxation lead to leakage. So we put the body in connection with the pipeline replaced by a flange welded structure, a low temperature to avoid leakage.

The second is the stem and the packing at the leakage. Most of the filler valve with F4, because of its good performance from the sliding, low coefficient of friction (the friction coefficient of steel f=0.05 ~ 0.1), but also has a unique chemical stability, so it has been widely used.

But F4 also has some shortcomings, a cold flow tendency to large; two is the linear expansion coefficient, resulting shrinkage at low temperatures lead to leakage, resulting in a large number of frozen stem Department, to open the valve failure. Since the seal structure is reduced by using F4 expansion coefficient characteristics used for this developed by low-temperature valve, through the gap to the left to reach room temperature, low temperature can be the purpose of sealing.