Valve Standard Reference
API 609
AmericanButterfly Valves: Double-Flanged, Lug- and Wafer-Type
API 609 is the dimensional and performance standard for butterfly valves in petroleum and natural gas service.
Overview — API 609
API 609 is the dimensional and performance standard for butterfly valves in petroleum and natural gas service. It covers double-flanged (wafer), lug, and tapped-lug body designs in concentric (resilient seat), double-eccentric (high-performance), and triple-eccentric (metal seat) configurations. API 609 aligns butterfly valve design with ASME pressure classes and defines testing requirements for seat tightness.
Scope
Covers butterfly valves from NPS 2" to 200" in pressure classes 150 to 600. Three categories: Category A (concentric resilient seat, general service), Category B (offset seat, high-performance / fire-safe), and Category C (triple-offset, metal-seat, high-pressure / high-temperature).
Applicable Valve Types
Butterfly Valves — concentric (resilient seat)
Butterfly Valves — double-eccentric (high-performance)
Butterfly Valves — triple-offset (metal seat)
Applicable Pressure Classes
Key Requirements — API 609
Category A: concentric design, resilient seats (EPDM, NBR, PTFE), maximum ASME Class 150
Category B: offset disc, fire-safe per API 607, Class 150–600
Category C: triple-offset, metal-to-metal seat, Class 150–600, −29°C to +600°C
Face-to-face dimensions per API 609 Table 1 (or ASME B16.10 for flanged)
Shaft sealing — stem blowout prevention design mandatory
Maximum operating torque at full differential pressure
Testing Requirements — API 609
Shell test: 1.5× rated pressure
Seat leakage test: 1.1× rated pressure, Class A or D per API 598
Torque measurement at rated differential pressure
Fire test per API 607 if fire-safe designation
Documentation Required for API 609 Compliance
API 609 design conformance on data sheet
Hydrostatic test certificate
API 607 fire test certificate (for fire-safe valves)
Material certificates (EN 10204 3.1)
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