API 594 pdf download.Check Valves: Flanged, Lug, Wafer and Butt-welding 1 General 1.1 SCOPE This standard covers design, material, face-to-face dimen- sions, pressure-temperature ratings, and examination, inspec- tion, and test requirements for two types of check valves. 1.1.1 Type ‘A’ check valves are short face-to-face as defined in Tables 2A and 2B and can be: wafer, lug, or double flanged;...