This standard establishes minimum requirements for rubber-seated butterfly valves, 3 in. (75 mm) through 72 in. (1,800 mm) in diameter, with various body and end types, for freshwater having a pH range from 6-12 and a temperature range from 33º-125ºF (0.6º-52ºC). This standard covers rubber-seated butterfly valves suitable for a maximum steady-state fluid working pressure of 250 psig (1,723 kPa, a maximum steady-state differential pressure of 250 psi (1,723 kPa), and a maximum full open velocity of 16 ft/sec (4.9 m/sec). Valves described in this standard are provided in four body types and in classes as follows: Wafer valves, Class 150B, in sizes 3-20 in. (75-500 mm); short-body and long-body flanged valves, Class 25A, class 25B, class 75A, class 75B, class 150A, and class 150B, in sizes 3-72 in. (75-1,800 mm), and class 250B in sizes 30-48 in. (75-1,200 mm); and, mechanical-joint-end valves, Class 150B and class 250B, in sizes 3- 24 in. (75-600 mm), and class 25A, class 25B, class 75A, class 75B, class 150A, class 150B, and class 250B, in sizes 30-48 in. (750-1,200 mm). In each case, the numeric designation represents the pressure rating (the maximum steady-state fluid working pressure, in pounds per square inch gauge) and also the maximum steady-state differential pressure, in pounds per square inch, for which the valve is designed. The designations A and B define the flow-rate capabilities with the valve in the fully open position. A valves are rated for a maximum velocity of 8 ft/sec (2.4 m/sec), and B valves are rated for a maximum velocity of 16 ft/sec (4.9 m/sec) in the piping section upstream of the valve. The major revisions made to the standard in this edition include the following: revised material references to use Unified Numbering System (UNS) designations; added ductile iron as an acceptable material for actuator worm gears in buried service; allowed the use of the valves from the proof-of-design tests to be rebuilt and used as production valves; and, added advisory text on valve and adjacent pipe installation in Appendix A.