Pneumatic control valve selection factors


Pneumatic control valves are used for control valves wi […]

Pneumatic control valves are used for control valves with operating temperatures above 450°F (232°C) and temperature conditions must be considered when designing and selecting. Standard materials for regulator (control valve) construction may not be suitable under high temperature conditions such as boiler feedwater systems and superheated bypass systems. For example, plastics, elastomers, and standard gaskets often prove to be unsuitable and should be replaced with more durable materials. Metal-to-metal seat materials should always be used, semi-metallic or elastic laminated graphite filler materials are often used, and gaskets wrapped around stainless steel and elastic graphite are indispensable.

Pneumatic Control Valves For applications above 1000°F (538°C), the valve body is usually cast from chrome-molybdenum steel. ASTM A217 grade WC9 material is available at 1100°F (593°C). For high temperatures up to 1500°F (816°C), the usual materials are ASTM A351 grade CF8M, 316 stainless steel. For temperatures between 1000 °F (538 °C) and 1500 °F (816 °C), the carbon content must be controlled to the upper end of the range of 0.04 to 0.08%. 9%Cr-1%Mo-V materials, such as ASTM A217 grade C12a forgings and ASTM A182 grade F91 forgings are suitable for high temperatures up to 1200°F (650°C). The extended bonnet helps prevent the stuffing box components from being subjected to extremely high temperatures. Typical internals include Cobalt No. 6 alloy, 316 with hard alloy No. 6 and 422 SST with nitriding.