precision bellows is what kind?

Precision bellows are cylindrical thin-walled corrugated shells with multiple transverse corrugations. Control valve on the bellows only play-the role of isolation, mainly divided into three types: one is to prevent the medium inside the valve outward diffusion, that is, the medium flowing inside the valve is chemically active or toxic and harmful gases, volatile liquids and precious heavy media. To prevent leakage, pollution of the environment or the loss of resources; there is to prevent external impurities and air into the valve, which is for the valve environment and the purity of the medium requirements. For example, there are many granular substances such as external dust. With the action of the valve, the valve stem will bring these substances into the valve or accumulate in the valve stem packing, which is easy to cause the pollution of the valve medium and the lock of the valve; the last one is to protect the internal parts of the valve and prevent the medium from causing erosion and corrosion to the valve stem.

The precision bellows has two installation positions. One is installed in the valve body. The bellows is made of PTFE. Its upper end is integrated with the fluorine lining of the upper valve cover, and its lower end is connected with the valve core to fix the valve core. It also protects the valve stem from erosion and erosion; the bellows installed outside the valve body are mostly made of metal, one end is fixed on the upper part of the valve stem, and the other end is free. There is also a layer of protective layer around the bellows, which not only protects the bellows, but also ensures that the medium in the valve will not pollute the environment within a certain period of time after the bellows are damaged.

According to the material of the precision bellows, it can be divided into two categories, namely plastic bellows and metal bellows. Plastic corrugated pipe, also known as PTFE corrugated pipe, is made by heating and pressing tubular PTFE and massive PTFE. The manufacturing method of plastic bellows is simple, and in some cases it can replace metal bellows to save costs, with low price and outstanding scalability. However, the application of plastic bellows is limited by three factors. One is the temperature of the environment where the valve is located and the temperature of the medium. If the temperature is too high, it is easy to cause aging and deformation of the bellows, so its long-term use temperature is generally not more than 180C, and there is no specific requirement at low temperature; the second is limited by the pressure in the pipeline (the working pressure of the general plastic bellows is not higher than 12kg). If the pressure is too high, the lining material of the valve will be sucked out from the inner wall of the valve, causing the valve to be blocked; another factor is the chemical nature of the medium. Plastic bellows can be used for strong corrosive media, such as formic acid, hydrochloric acid and chloride. However, when the medium is similar to its molecular formula, similar miscibility will occur and cannot be applied at this time, such as silicon tetrachloride.