What Are Class A And Class B Butterfly Valves?

Class A Butterfly Valves and Class B butterfly valves are classified according to API 609. The main differences are sealing performance, structure design and application scenarios. Class A valves require high sealing performance.
This classification standard can help you quickly match the requirements of different operating conditions to avoid leakage or damage due to poor selection.
1.Core Difference Comparison (Air Pollution Index 609 standard)
Comparison Dimensions: A Butterfly Valve (Class A Butterfly Valve (B)
Sealing Level: Bidirectional sealing with very low leakage or leakage rate (meets strict test requirements for API 598)
One-way sealing, can achieve a certain degree of leakage control
Structural design: Typically adopt metal seals or high-performance elastomeric seals, valve body and disc processing precision. Most of the relatively simple structures are Mostly elastomeric seals (e.g. EPDM.
Applicable Pressure: Medium and high pressure applications (e.g., grades 150 to 600)
Low pressure applications (mostly 150 and below)
Typical applications: applications requiring high sealing requirements, such as petrochemicals, natural gas transportation, high temperature, high pressure fluid control, etc.
Suitable for water treatment, heating, ventilation, air conditioning, low pressure water supply and drainage, etc.
2.Additional Notes
Standard Applicability: API 609 is the global standard for butterfly valve design and testing. Class A/B applies only to butterfly valves specified in these standards. Other criteria (e.g. GB/T 12238) can be classified differently.
Key choices: Prioritize operational pressure levels and sealing requirements, rather than simply relying on A/B labels. Type A butterfly valve, for example, may be suitable for low-pressure applications requiring zero leakage.
To provide a more accurate selection guide, would you like me to create a comparison chart for A/B butterfly valves under different operating conditions? Can directly input actual pressure, media, temperature and other parameters, quickly match the appropriate model.