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 raw water, potable water, wastewater, and reclaimed water having a pH range from 6–12 and a temperature range from 33° 125°F (0.6°–52°C). This standard covers rubber-seated butterfly valves suitable for a maximum steady-state fluid working pressure of up to 250 psig (1,723 kPa), a maximum steady-state differential pressure of up to 250 psi (1,723 kPa), and a maximum full open fluid velocity of up to 16 ft/sec (4.9 m/sec) based on nominal valve size.

1.1.1 Body types, classes, and sizes. Valves described in this standard are provided in four body types and in classes as follows: 
1.1.1.1 Wafer valves. Class 150B, in sizes 3–20 in. (75–500 mm). 
1.1.1.2 Short-body and long-body flanged valves. Class 25A, Class 25B, Class 75A, Class 75B, Class 150A, and Class 150B and Class 250B, in sizes 3 in.–72 in. (75 mm–1,800 mm). 
1.1.1.3 Mechanical-joint-end valves. Class 150B and Class 250B, in sizes 3 in.–24 in. (75 mm 600 mm), and Class 25A, Class 25B, Class 75A, Class 75B, Class 150A, Class 150B, and Class 250B, in sizes 30 in.–48 in. (750 mm–1,200 mm). 
1.1.2 Definition of classification. 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. 
1.1.2.1 A and B designations. The designations A and B define the flow-rate capabilities with the valve in the fully open position. Valves designated A 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. 
This standard can be referenced in purchase documents for rubber-seated butterfly valves that are described by the scope as defined above.