High temperature and ultra-high temperature control has always been the focus of domestic and foreign manufacturers and design institutes. The main reason is that high-temperature regulation and control are difficult problems in automatic control, and it is more difficult to cut off high temperature and ultra-high temperature. The main manifestation of this problem is the jamming and cut-off problems caused by high-temperature expansion.
(1) Selection of materials for valve body and trim
For regulating valves used in environments above 450°C, the maximum temperature that can be used for general materials is about 500°C. For occasions higher than 538°C, the valve body is usually made of chromium molybdenum steel. For occasions where the maximum temperature is about 1035℃, SUS310S stainless steel is usually used, and the carbon content of the material must be controlled between 0.04% and 0.08%. For higher temperatures, it is recommended to use non-metallic heat-resistant lining materials (which can be used in high-temperature applications at 1200°C) or special high-temperature-resistant and high-strength alloys (such as high-temperature and high-strength alloys for engine combustion chambers, which can be used directly at 1000°C). High temperature occasions).
(2) The temperature resistance of the filler
Standard PTFE packing can only be used in occasions below 200°C. If it is used in medium and high temperature occasions, an elongated valve cover must be used to prevent the packing from being affected by extremely high temperatures. However, longer and thinner stems have poor strength under high temperature conditions and are prone to bending. Therefore, flexible graphite packing with excellent temperature resistance (up to 600°C) should be used under high temperature conditions, and the height of the elongated valve cover can also be greatly reduced. At the same time, it is equipped with a "rotary valve thick stem" method to improve the overall strength of the valve, so as to better solve this problem.
(3) Choice of sealing method
It is very difficult to cut under high temperature conditions, and many conventional high-performance sealing methods are not advisable (such as O-rings, PTFE materials, elastic metal materials, etc.). Within 500℃, the soft sealing method of special composite graphite seat can be used. When adjusted under the condition of 500℃ or higher, the difficulty of high-temperature control valve can only adopt the metal-to-metal hard seal method (generally adopt the butterfly valve structure).