Selection principles and applicable scenarios for butterfly valves

Thread Content

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 even 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. Selecting the sealing pair based on medium properties: 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/base solutions and strong oxidizers), metal-sealed butterfly valves should be selected. Priority should be given to using wear- and corrosion-resistant hard alloy sealing surfaces such as Stellite alloy 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 and 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 components 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 only fully open or fully closed operation is needed, centerline butterfly valves are suitable; they are low-cost and 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 backside of the butterfly plate, causing distortion in the flow characteristics; moreover, the rubber seal pair is prone to fatigue failure due to repeated compression. 4. Consider ease of installation and maintenance. Wafer-type butterfly valves are compact, lightweight, and take up little space; however, their flanges at both ends must be loosened during disassembly. They are suitable for applications where maintenance is required infrequently. 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 permitted, 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 usually 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 substances 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.