API 609 pdf download.Butterfly Valves: Double Flanged, Lug- and Wafer-Type 1 Scope 1.1 This standard covers design, materials, face-to-face dimensions; pressure-temperature ratings; and examination, inspection, and test requirements for gray iron, ductile iron, bronze, steel, nickel-base alloy, or special alloy butterfly valves that provide tight shutoff in the closed position and are suitable for flow regulation. Two categories of butterfly...