This Standard Practice covers dimension@ design@ testing and marking requirements for butterfly valves Further reference should be made to the MSS Standard Practice for high pressure@ offset@ butterflyvalves@ when published This standard practice covers two types of butterfly valves: Type I -Valves for tight shut of (tested per subsection 11.2.1). Type II - Valves permitting seat leakage (see subsection 11.2.2). This Standard Practice covers flangeless (wafer type)@ single flanged (lug type)@ flanged end and grooved end valves in sizes 11/2 thru 72 with pressure rating up to and including ANSI Class 150