1 Selection Principles
1.1 Selection of Sealing Pair Based on Medium Characteristics
For non-corrosive or weakly corrosive clean media such as water, air and general mineral oil, soft-sealed butterfly valves with rubber lining (e.g., NBR ≤90℃, EPDM ≤120℃) or PTFE (≤230℃, short-term ≤260℃) can be adopted, featuring excellent sealing performance and moderate cost.
For high-temperature steam (≥250℃), hot oil or highly corrosive chemical media (e.g., acid-base solutions, strong oxidants), metal-sealed butterfly valves shall be selected. Stellite alloy, Hastelloy and other wear-resistant and corrosion-resistant hard alloy sealing surfaces are preferred. Note: Cast steel (WCB) valve body is temperature resistant up to 425℃; alloy steel (e.g., WC6, WC9, CF8C) valve body matched with metal seal can meet working conditions up to 600℃, while Inconel and other nickel-based alloys combined with special graphite seals are required above 600℃.
For media containing solid particles and fibers (e.g., sewage, pulp, ore slurry), eccentric structure (double-eccentric or triple-eccentric) butterfly valves are preferred to avoid particle jamming or scratching of sealing surfaces, with wear-resistant sealing pairs matched.
1.2 Selection of Valve Body Material Based on Pressure and Temperature
Normal temperature and low pressure (≤1.6MPa, ≤80℃): Gray cast iron (HT200) or ductile iron (QT450-10), applicable to water supply/drainage and low-pressure air pipelines.
Medium temperature and medium pressure (≤4.0MPa, ≤250℃): Cast steel (WCB) or stainless steel (304/316L), and compatibility of lining materials (PTFE, rubber lining) with media shall be confirmed.
High pressure (>4.0MPa) with nominal diameter ≥DN150: Double-eccentric or triple-eccentric butterfly valves are recommended. Note: When nominal diameter >DN400 and pressure >4.0MPa, the sealing reliability of butterfly valves is lower than that of gate valves or ball valves, and comprehensive evaluation shall be made.
Double-eccentric / triple-eccentric structures are preferred for frequent on-off services, with small sealing surface wear and low operating torque.
1.3 Selection of Structure Based on Flow Control Requirements
On-off service only: Concentric butterfly valves are sufficient, with low cost and easy installation.
Flow regulation required: Double-eccentric or triple-eccentric butterfly valves are selected, whose flow characteristic is approximately equal percentage with high regulation accuracy. Butterfly valves shall not be used if regulation accuracy ≤±5% is required; control valves or ball valves shall be used instead.
Concentric butterfly valves are generally not recommended for regulation due to high specific sealing pressure. Eddy current zone occurs at the back of the disc at 30°~70° opening, resulting in distorted flow characteristics and fatigue failure of rubber sealing pairs under repeated compression.
1.4 Consideration of Installation and Maintenance Convenience
Wafer-type butterfly valves: Compact structure, light weight and small space occupation, but both flanges need to be loosened for disassembly; suitable for occasions with low maintenance frequency.
Flanged butterfly valves: Easy to assemble and disassemble, suitable for stations requiring frequent overhaul and maintenance, the most widely used form in industrial sites.
Butt-welded butterfly valves: Only used for special high-pressure or zero-leakage occasions, difficult to replace once installed. Note: Welded butterfly valves are rarely used in extreme conditions such as power plant main steam; welded gate valves or globe valves are mostly adopted.
2 Applicable Occasions
2.1 Water Supply & Drainage and Water Treatment Industry
Concentric soft-sealed butterfly valves are the mainstream, used in inlet/outlet pipelines, aeration, sludge discharge and circulating water systems of waterworks and sewage treatment plants.
2.2 HVAC Systems
Butterfly valves are used in cooling water and chilled water main pipes of central air conditioning and heating systems, usually matched with lever, worm gear or electric actuators.
2.3 Chemical and Pharmaceutical Industries
PTFE or PFA lined anti-corrosion butterfly valves are preferred for media such as acid-base solutions and organic solvents, requiring smooth inner wall, no retention zone and easy cleaning.
2.4 Food and Beverage Industry
Sanitary stainless steel polished butterfly valves with clamp quick connections are selected to meet CIP and SIP cleaning and sterilization requirements.
2.5 Metallurgical and Power Industries
Triple-eccentric metal-sealed butterfly valves are the first choice for circulating water, desulfurization and denitrification pipelines and high-temperature flue gas systems (temperature resistance grade of valve body material shall be confirmed).
2.6 Shipbuilding and Offshore Engineering
Special butterfly valves resistant to salt spray corrosion and vibration are selected, with bronze or seawater-resistant stainless steel (e.g., 2205 duplex stainless steel) as preferred materials.
The selection of butterfly valves is not fixed; it shall be based on actual working conditions such as medium characteristics, operating pressure, design temperature, matching of sealing structures, combined with actual conditions such as installation space and maintenance frequency to avoid inappropriate selection.