What should be paid attention to when selecting a regulating valve
The use characteristics of the regulating valve determine the main use performance and scope of the valve. The use characteristics of the valve include the type of valve, the type of product, the material of the main parts of the valve, and the valve transmission mode. Structural characteristics It determines some structural characteristics of the valve installation, repair, maintenance and other methods. The structural characteristics include the structural length and overall height of the valve, the connection form with the pipeline, the form of the sealing surface and the structural form of the valve stem. It is worth noting that in the formation of certain structures, their use characteristics and structural characteristics are interrelated and cannot be separated.
The adjustment and cut-off control of the regulating valve is already a difficult problem in automated production control. As for the cut-off of high temperature and ultra-high temperature, it is even more difficult. The main manifestation of this problem is the jamming and shut-off caused by high-temperature expansion. Therefore, the high temperature and ultra-high temperature control of the regulating valve has always been the focus of attention. How should we choose the right regulating valve?
1. Regulating valve body and valve trim material selection: used for regulating valves in an environment above 450°C, the usable temperature of general materials is about 500°C. For occasions higher than 500℃, the valve body is usually made of chromium molybdenum steel. For occasions where the temperature reaches about 1000℃, SUS310S stainless steel is usually used, and the carbon content of the material must be controlled between 0.038% and 0.078%. For higher temperatures, it is recommended to use non-metallic heat-resistant lining materials (which can be used in high-temperature situations 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 directly used at 1000°C) High temperature occasions).
2. Temperature resistance of regulating valve packing: standard PTFE packing can only be used in occasions below 200℃. If it needs to be used in medium and high temperature occasions, an elongated valve cover is required to prevent the packing from being exposed to 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 good temperature resistance should be used under high temperature conditions, which can also greatly reduce the height of the elongated valve cover. At the same time, it can also be equipped with a "rotary valve + thick stem" to improve the overall strength of the valve, so as to better solve this problem.
3. Selection of the sealing method of the regulating valve: it is difficult to achieve high cutting performance under high temperature conditions, and many conventional high-performance sealing methods are not advisable (such as PTFE materials, O-rings, elastic metal materials, etc.) ). The soft sealing method of special composite graphite seat can be used within 500℃. Under the condition of 500℃ or higher, only metal-to-metal hard seal can be used (butterfly valve structure is generally used).
4. The choice of the type of regulating valve: the fluid has a certain viscosity and contains more impurities. Choose the type that is not easy to be blocked and has good self-cleaning properties, such as butterfly valves, diaphragm valves, and angle valves; if the fluid medium is toxic and harmful, It is necessary to choose a regulating valve with a bellows seal to ensure a tight five-discharge flow to ensure the safety of the users.
