[Haichuan Chemical Valve Management] Series Posts -- Selection Principles and Application Scenarios of Butterfly Valves

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Proper management of valves is the foundation for stable operation. Everyone is welcome to engage in discussions and share insights on this series of posts: 【HaiChuan Chemical Valve Management】 series of posts: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=5719309 ---------------------------------------------------------------- Disclaimer: The content contained in this article is intended solely for technical exchange and reference purposes only; it does not constitute any form of professional engineering advice, design basis, or operational guidance. -----------------------------------------------------------------------------------As a type of valve that is compact in structure and easy to operate for shut-off or regulation purposes, the butterfly valve is widely used in various industrial piping systems thanks to its advantages such as small size, light weight, and low flow resistance. However, if not selected properly, it can lead to medium leakage and seal failure; in severe cases, it may also affect the safe and stable operation of the process system. The following are the selection principles and applicable scenarios for butterfly valves, provided for reference only. I. Selection Principles 1. Select the sealing pair based on the properties of the medium. For non-corrosive or mildly corrosive clean media such as water, air, and ordinary mineral oil, soft-sealing butterfly valves lined with rubber (such as nitrile rubber NBR for temperatures up to 90°C, or ethylene propylene diene monomer rubber EPDM for temperatures up to 120°C) or polytetrafluoroethylene (PTFE for temperatures up to 230°C, and up to 260°C for short periods of time) can be used; these options offer excellent sealing performance at a moderate cost. For high-temperature steam (≥250°C), hot oil, or highly corrosive chemical media (such as acid and alkali solutions, strong oxidizers), metal-sealed butterfly valves should be used. Priority should be given to using wear- and corrosion-resistant hard alloy sealing surfaces such as Stellite alloys and Hastelloy. It should be noted that cast steel (WCB) valve bodies can withstand temperatures up to 425°C. Valve bodies made of alloy steel (such as WC6, WC9, CF8C), combined with metal seals, can handle temperatures up to 600°C; however, for temperatures above 600°C, nickel-based alloys such as Inconel along with special graphite seals are required. For media containing solid particles and fibers, such as sewage, pulp, and slurry, eccentric-style butterfly valves (double-ecentric or triple-ecentric) should be preferred to prevent particles from getting stuck or scratching the sealing surfaces; wear-resistant sealing pairs should also be used in conjunction with them. 2. Select the valve body material based on pressure and temperature: For normal temperature and low pressure (≤1.6 MPa, ≤80°C), gray cast iron (HT200) or ductile iron (QT450-10) is suitable for water supply and drainage systems as well as low-pressure air pipelines. Medium temperature and medium pressure (≤4.0 MPa, ≤250°C): Cast steel (WCB) or stainless steel (304/316L); it is necessary to verify the compatibility of the lining material (PTFE, rubber-lined) with the medium. For high-pressure conditions (>4.0 MPa) with a diameter of ≥DN150, it is recommended to use double-eccentric or triple-eccentric butterfly valves. Note: When the diameter is > DN400 and the pressure is > 4.0 MPa, the sealing reliability of butterfly valves is lower than that of gate valves or ball valves, and a comprehensive evaluation is required. For frequent opening and closing, a double-eccentric/triple-eccentric design should be preferred, as it results in less wear of the sealing surfaces and a lower torque required for operation. 3. Select the structural type based on flow control requirements. When full opening or full closing is sufficient, a centerline butterfly valve is suitable – it has a low cost and is easy to install. When flow regulation is required, double-eccentric or triple-eccentric butterfly valves should be used, as their flow characteristics are approximately equal percentage type and they offer high regulation accuracy. If a regulation accuracy of ≤±5% is required, butterfly valves should not be used; instead, control valves or ball valves should be employed. Due to its high sealing specific pressure, centerline butterfly valves are generally not recommended for regulation. At opening angles of 30° to 70°, a vortex region forms on the back side of the butterfly valve, causing distortion in the flow characteristics; moreover, the repeated compression of the rubber sealing pair leads to fatigue and failure. 4. Consider ease of installation and maintenance: Wafer butterfly valves are compact, lightweight, and require little space, but they need to have their flanges at both ends loosened for disassembly, making them suitable for applications with low maintenance frequency. Flanged butterfly valves are easy to disassemble and assemble, making them suitable for workstations that require frequent inspection and maintenance; they represent the most widely used type in industrial settings. Welded butterfly valves are used only in high-pressure applications or in situations where leaks are not permissible, and they are difficult to replace once installed. It should be noted that welded butterfly valves are rarely used in extreme operating conditions such as those in power plants; instead, welded gate valves or globe valves are more commonly employed. II. Applicable Areas 1. In the water supply, drainage, and water treatment industries, medium-line soft-sealed butterfly valves are the preferred choice; they are used in the inlet and outlet pipelines of water treatment plants and sewage treatment plants, as well as in aeration, sludge discharge, and circulating water systems. 2. HVAC systems: Butterfly valves are used in the main cooling water and chilled water pipelines of central air conditioning and heating systems; they are typically equipped with handles, worm gears, or electric actuators. 3. In the chemical and pharmaceutical industries, corrosion-resistant butterfly valves lined with PTFE or PFA are preferred for use with media such as acid and alkali solutions and organic solvents; these valves require a smooth inner surface, no areas where fluid can accumulate, and ease of cleaning. 4. Food and beverage industry: Sanitary-grade polished stainless steel butterfly valves with clamp-type quick connections are used to meet the requirements for CIP and SIP cleaning and sterilization. 5. In the metallurgy and power industries, triple-eccentric metal-sealed butterfly valves are the preferred choice for use in circulating water systems, desulfurization and denitrification pipelines, as well as high-temperature flue gas systems (it is necessary to confirm the temperature resistance rating of the valve body material). 6. Ship and ocean engineering: Use special butterfly valves that are resistant to salt spray corrosion and vibration; the preferred materials are bronze or seawater-resistant stainless steel (such as 2205 duplex steel). The selection of butterfly valves is not fixed; it is necessary to properly consider the actual operating conditions such as the properties of the medium, operating pressure, design temperature, and the suitability of the sealing mechanism. Additionally, practical factors like installation space and maintenance frequency must be taken into account to avoid any issues.