With the continuous application of new chemical materials and the improvement of lining technology, fluorine-lined (plastic) regulating valves and shut-off valves are favored by manufacturers and users for their safety, reliability and high cost performance, and are highly corrosive process media in petroleum, chemical, pharmaceutical and other industries more and more widely used. However, fluorine (plastic) lined valves are not able to adapt to all corrosive conditions. Like other valves, how to choose and use fluorine (plastic) lined valves is a professional job.
Fluorine-lined (plastic) valve temperature should be lower than the upper limit of about 30%
The temperature used for fluorine (plastic) valves: At present, the commonly used valve lining materials are synthetic rubber (-10-120°C), PTFE (-200-180°C), soluble polytetrafluoroethylene PFA (-196- 260°C), polyperfluoroethylene propylene F46 (-85-150°C). The above is the limit resistance temperature of each material that can be checked publicly. The actual temperature of the medium used varies according to the material and pressure. The long-term use temperature should usually be lower than the upper limit of about 30%, otherwise, the lining of each part of the valve will be easily deformed. Resulting in a large amount of leakage or failure of the valve to switch normally.
Fluorine-lined (plastic) valve is not suitable for high pressure and high pressure difference occasions
Pressure (difference) used by fluorine-lined (plastic) valves: fluorine-lined (plastic) valves are usually not used in high vacuum conditions. Open dovetail grooves, punch holes in the valve plate, etc.) to prevent the fluorine lining and plastic lining layer of the valve cavity from being pulled out (bulging), and the lining layer and the metal layer peeling off, resulting in the valve not being able to switch normally.
Similarly, fluorine-lined (plastic) valves are not suitable for applications with high pressure and high pressure difference. Especially for the fluorine-lined bellows sealed control valve (because most of the bellows are made of PTFE, the bellows will easily rupture when the pressure and pressure difference are too large), most manufacturers' selection samples indicate that the nominal pressure is PN≤2.5MPa , this is for insurance purposes. But sometimes due to the special working conditions, it is also necessary to find a solution.
The medium should not have hard particles, crystals, impurities, etc.
Fluorine-lined (plastic) valve requirements for the medium: the medium used in the fluorine-lined (plastic) valve should not have hard particles, crystallization, impurities, etc., so as to avoid the valve wearing the fluorine-lined plastic layer or bellows during the opening and closing operation. For the medium with hard particles, crystals and impurities, corrosion-resistant precious metal materials can be selected according to the characteristics of the process medium, such as Hastelloy, nickel-based alloy, alloy steel and other hard-sealed valves.
The diameter of the fluorine (plastic) valve should be 30~85%
The fluorine-lined regulating valve is usually made of a fluorine-lined bellows sealing structure, which has the advantages of good corrosion resistance and no leakage. When selecting, the valve diameter should be calculated according to the process parameters, and the normal opening should be within the range of 30~85%. If the valve diameter is too large, it will cause long-term operation with a small opening degree, and the valve adjustment performance will deteriorate. Especially in the case of small opening, not only will the scouring be aggravated, but also the valve core and valve stem will be vibrated by the impact of the medium, and even the valve stem will be broken and the bellows will be deformed.
