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To ensure that the valve can cut off the flow of media well and that no leakage occurs, it is necessary to ensure that the seal of the valve is intact. There are many causes of valve leakage, including unreasonable structural design, defective seal contact surfaces, loosening of fastening parts, and incompatibility between the valve body and the valve cover. All of these problems may result in the valve not sealing. Well, there is a leakage problem. Therefore, the valve sealing technology is an important technology related to the valve performance and quality, and requires systematic and in-depth research.
The classification and structure of the valve is very diverse. It is not easy to divide the valve. It can be divided according to the principle, or it can be divided according to the function. It can also be divided according to the structure, and it can even be combined to divide. No matter what kind of partitioning method, Can not change the use of the valve. Currently, the commonly used classification method in the world is to classify valves into these types, namely, gate valves, ball valves, butterfly valves, globe valves, safety valves, pressure reducing valves, throttle valves, plug valves, and control valves. In these valves, gate valves, ball valves, butterfly valves, and globe valves are classified as shut-off valves. They are mainly used to connect or shut off the flow of medium, and pressure reducing valves, throttle valves, and control valves are the types of control valves. It regulates the flow, temperature, and pressure of the medium flow, while the safety valve is mainly used for overpressure safety protection.
In addition to these classifications, they can be classified according to working pressure. At this time, they can be divided into vacuum valves, low pressure valves, medium pressure valves, high pressure valves, and ultra-high pressure valves; if classified according to the working temperature of the medium, they can be divided. For the high temperature valve, medium temperature valve, room temperature valve, cryogenic valve and cryogenic valve; In addition, if classified according to the material of the valve body, it can be divided into metal valve, non-metallic material valve, metal valve body lining valve.
Although the types of valves are numerous, the basic structure is almost the same, and they can generally be composed of a valve body, a valve core and a valve seat. Here take the most commonly used control valve as an example to analyze the valve's structural composition. In the basic valve body structure of the regulating valve, there may be three types of straight-through, angular and Z-shaped structures; in the basic valve core structure, there are three types of parabolic structure, cage structure and V-shaped groove. In the basic seat structure, there are four types of surfacing valve seats, screw-in seats, welded seats and seated seats. The combination of these different basic structures constitutes a wide variety of valve structures. The basic structure of the valve is shown in Table 1.
Research status of valve sealing technology Although the types of valves are numerous, sealing problems are indispensable and very important. Since the valve was produced, its sealing technology has also undergone great development. So far, valve sealing technology is mainly reflected in two major aspects, namely static seal and dynamic seal. The so-called static seal, usually refers to the seal between the two static surfaces, static seal sealing method is the use of gaskets. The so-called dynamic seal, mainly refers to the valve stem seal, that does not allow the valve media to leak with the stem movement, dynamic seal sealing method is mainly the use of stuffing box. The following is a detailed analysis of these two valve sealing technologies.
Static and static sealing refers to the formation of a seal between two stationary sections. The method of sealing is mainly the use of gaskets. There are many kinds of washers. The frequently used washers include flat washers, O-rings, packing washers, shaped washers, wave washers, and winding washers. These types can be further divided according to the materials used.
1 Flat Washer Flat washer is a flat washer that is attached between two stationary sections. It can be divided into plastic flat washers, flat rubber washers, flat metal washers and flat flat washers, flat washers for each material depending on the materials used. Have their scope of application.
2 O-ring O-ring is a gasket with O-shaped cross-section. Because its cross-sectional shape is O-shaped, it has a certain self-tightening effect, so the sealing effect is better than flat washers.
3-Pack of Gaskets A gasket is a gasket that encloses a material on another material. Such gaskets generally have good elasticity and can enhance the sealing effect.
4 Profile washers Profile washers are those that have irregular shapes, including oval washers, diamond washers, gear washers, dovetail washers, etc. These washers are generally self-tightening and are used mostly in high and medium pressure valves.
5 Wave washers Wave washers are washers with only wavy shapes. These washers are usually made of a combination of metallic and non-metallic materials. They generally have a small pressing force and a good sealing effect.
6 Wrapped Wraps Wrapped washers are gaskets that are formed by tying very thin metal tapes and non-metallic tapes together. These gaskets have good elasticity and tightness.
The materials for the manufacture of gaskets mainly include three major categories, namely metal materials, non-metal materials, and composite materials. In general, metal materials have high strength and high temperature resistance. Commonly used metal materials include copper, aluminum, and steel. There are many types of non-metallic materials, including plastic products, rubber products, asbestos products, hemp products, etc. These non-metallic materials are widely used and are selected according to specific needs. There are many types of composite materials, including laminates, composite panels, etc., which are also selected according to specific needs. Generally, they are used in wave washers and wound gaskets.
Dynamic seal seal refers to the seal that does not allow the media flow in the valve to leak with the movement of the valve rod. This is a seal problem during the relative motion. The seal method is mainly the stuffing box. There are two basic types of stuffing box, namely gland type and compression nut type. The gland type is the most used form at present. Generally, from the form of the gland, it can be divided into a combination type and an integral type. Although each type has a difference, it basically contains a bolt for pressing. Compression nut type is generally used for smaller valves. Because of the small size of this form, the pressing force is limited.
In the stuffing box, because the packing is directly in contact with the valve stem, all require that the packing has good sealability, low friction coefficient, can adapt to the pressure and temperature of the medium, and is resistant to corrosion. Currently used fillers include rubber O-rings, PTFE braided packing, asbestos packing, and plastic molding packing. Each packing has its own conditions and range of adaptability, and it is selected according to specific needs.
The prospect of valve sealing technology With the continuous development of science and technology, the requirements for valves are also getting higher and higher, so the valve sealing technology is also constantly developing, and new sealing materials and technologies are also emerging. Mainly reflected in the following aspects:
1 raw material seal What is raw material? It is the material of the polymer organic compound before it is sintered into the product. The raw material has a soft texture and can produce a monomolecular film effect. The raw meal can be shaped freely when used, and as long as there is pressure, a uniform annular membrane will be formed. This annular membrane plays a sealing role. Raw materials are very convenient to use, can be made into a certain shape, easy to replace, and good sealing effect.
2 Liquid Sealing Liquid sealing is a sealing technique that uses a liquid sealant to seal a valve. It is generally used for static sealing. In the liquid seal, the monomolecular film effect of the liquid sealant is mainly utilized so that it acts like a gasket under proper pressure.
3 Bellows seals Bellows seals are sealing techniques that use bellows to seal valves. They are generally used for dynamic seals. In the bellows seal, the two ends of the bellows are usually fixed together with other parts, so when the valve stem moves, the bellows will expand and contract. As long as the bellows itself is intact, the medium will not leak, so that it can be Seal the valve. This kind of valve sealing technology is mainly applied to the chemical industry and atomic energy industry, and it is aimed at the situation where the packing cannot be sealed.
With the further development of the economy and society, the application requirements of the valve will be higher and higher, and the valve sealing technology will also advance by leaps and bounds. More new materials and new technologies will also be applied, and the research on this aspect will be more and more in-depth. .
Analysis and Prospect of Research Status of Valve Sealing Technology
Valve is a kind of widely used mechanical parts. Its role in modern production and life is more and more significant. No matter whether it is high-end technology or daily ordinary life, it is inseparable from it. It is because of the extensive application of valves that the types of valves are very numerous and the structure is not the same, which also brings certain problems to the maintenance of the valve. Although the types of valves are numerous, the basic role is the same, that is, connecting or cutting off the flow of media. Therefore, the valve sealing problem is very prominent.