Valve Standard Reference
API 594
AmericanCheck Valves: Flanged, Lug, Wafer, and Butt-Welding
API 594 is the design and testing standard for flanged, lug, wafer, and butt-welding check valves including swing check, dual plate (double door), and tilting disc check valves.
Overview — API 594
API 594 is the design and testing standard for flanged, lug, wafer, and butt-welding check valves including swing check, dual plate (double door), and tilting disc check valves. It defines face-to-face dimensions, pressure-temperature ratings, material requirements, and testing procedures. API 594 is mandatory for most process plant and refinery check valve procurement.
Scope
Covers swing check valves, dual plate check valves, tilting disc check valves, and lift (piston) check valves in flanged, lug-wafer, wafer, and butt-weld end connections. Size range NPS 2 through NPS 48. Pressure classes 150 through 2500 per ASME B16.34.
Applicable Valve Types
Swing Check Valves
Dual Plate (Double Door) Check Valves
Tilting Disc Check Valves
Lift Check Valves
Applicable Pressure Classes
Key Requirements — API 594
Face-to-face and end-to-end dimensions per API 594 tables (Type A wafer; Type B lug; Type C flanged)
Minimum plate/disc thickness and spring material specification
Body and disc material requirements per ASTM A216 WCB, CF8M, and duplex grades
Anti-blowout hinge pin design for wafer-type valves
Bi-directional pressure capability for Type B lug (dead-end service)
Shell and seat hydrostatic tests per API 598 required before shipment
Testing Requirements — API 594
Shell test: 1.5× rated pressure
Seat leakage test: 1.1× rated pressure per API 598
Low-pressure seat test: 6 bar air
Documentation Required for API 594 Compliance
API 594 compliance certificate
Material Test Reports (MTR)
Pressure test certificate
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