Selection of Body and Valve Internals Materials
For applications above 450℃, the impact of temperature and pressure conditions on the mechanical strength of the materials must be considered during design and selection. In high-temperature conditions such as boiler feedwater systems and superheated bypass systems, conventional body and valve internals materials are not used (e.g., F4, O-rings, elastic materials, and standard gaskets). Therefore, more durable materials must be selected. Generally, the rated temperature of usable materials is around 500℃. For applications above 538℃, chromium-molybdenum steel is typically used for the body. For rated temperatures reaching around 1035℃, SUS310S stainless steel is usually selected, and the carbon content must be controlled between 0.04% and 0.08%. For even higher temperatures, it is recommended to use non-metallic heat-resistant materials for lining, suitable for high-temperature applications up to 1200℃. Alternatively, special high-temperature resistant, high-strength alloys (such as high-temperature resistant, high-strength alloys for engine combustion chambers, which can be directly used in high-temperature applications up to 1000℃) can be used.
The Influence of Thermal Expansion and Contraction
High-temperature valves differ significantly from normal-temperature valves in structure and internal components, such as guide clearance, gate rotation clearance, and bearing type. Besides design and manufacturing controls, minimizing the impact of thermal expansion and contraction through valve design is preferable. Practice has proven that the baffle type is an excellent high-temperature valve; the clearance between the baffle and the inner cavity of the valve body is 4-6mm, completely resolving the high-temperature jamming problem between the gate and the inner cavity, and achieving a high shut-off performance of 5×10⁻⁴.
Guide Bearing and Gate Positioning Issues
For applications with operating temperatures exceeding 400℃, ordinary positioning and guiding structures are unreliable. In such cases, an external bearing structure should be used to ensure gate positioning and support, thus avoiding the influence of internal high temperatures on the guiding structure. Our company's products provide excellent positioning, support, and protection in this regard, ensuring accurate longitudinal positioning of the gate and preventing jamming caused by gate sagging due to gravity. Meanwhile, because the bracket bears the weight of the gate and valve stem, it reduces the load on the actuator and the external bearings, avoiding the one-sided jamming phenomenon that easily occurs in conventional horizontal installations, allowing for vertical installation.
Packing Temperature Resistance
Standard PTFE is only suitable for applications below 200℃. For medium to high temperature applications, an elongated top cover must be used to prevent the packing from being affected by extremely high temperatures. However, longer and thinner valve stems have poor strength under high temperatures and are prone to bending. Therefore, for high-temperature applications, flexible graphite packing with excellent temperature resistance (up to 600℃) should be used, which can also significantly reduce the height of the elongated top cover. Simultaneously, using a "rotary valve + thick valve stem" approach improves the overall strength of the valve, thus effectively solving this problem.
Sealing Method Selection
Achieving high shut-off performance under high-temperature conditions is difficult, and many conventional high-performance sealing methods are not feasible, such as those using PTFE or elastic metal materials. For temperatures below 500℃, a special composite graphite valve seat seal can be used. Typical products include soft-seal high-temperature "O"-type shut-off and "V"-type shut-off valves. For temperatures above 500℃, our high-temperature baffle type valve can also achieve excellent sealing. Furthermore, the wear-resistant alloy welded onto the sealing surface enhances the valve's sealing reliability and significantly extends its service life.