API 609 Standard specifies requirements for the design, materials, manufacturing, testing, and inspection of butterfly valves (quarter- turn, resilient-seated) with:
Center-guided or double- offset designs.
Lug-type or Wafer- type body configurations.
Nominal pressure classes 150 and 300 (ASME B16.34).
Sizes NPS 3 to 48 (DN 80 to 1200).
It covers valves for flanged or butt-welding end connections used in general petroleum, chemical, gas, water, and air services. Key requirements include:
Bidirectional sealing capability.
Fire-safe design requirements (optional but common).
Specific pressure-temperature ratings.
Rigorous production testing (shell, seat leakage).
Marking and documentation standards.
