A butterfly valve (BTFLV) is a quarter turn valve (90° or less) with a circular disk as its closing element. The standard design has the valve stem running through the disk, giving a symmetrical appearance. Other designs offset the stem. Advantages include less wear and tear on the disk and seats, and tighter shut-off capabilities. When space is limited, sometimes larger valves may use a hand wheel with a gear arrangement. Butterfly valves are rather easy to maintain. These valves are used for gases, liquids, slurries, powders, and vacuum.
There are two butterfly valve categories:
Category A: Manufacturer’s rated cold working pressure (CWP) butterfly valves, usually with a concentric disc and seat configuration. Sizes covered are NPS 2 to NPS 48 for valves having ASME Class 125 or Class 150 flange bolting patterns.
Category B: Pressure-temperature rated butterfly valves that have an offset seat and either an eccentric or a concentric disc configuration. These valves may have a seat rating less than the body rating. Sizes covered are NPS 3 to NPS 24 for Classes 150, 300, and 600.
High Performance Butterfly Valves (HPBV) must meet certain criteria. For a butterfly valve to be determined as high performance it must:
Provide bubble tight shutoff for the entire range of its rated ANSI differential pressure across the valve.
Be bidirectional in nature
Typically, HPBV will be of a double or triple offset design.
When using valves in a service that may provide fuel to a fire, it is important to ensure that they are “fire tight.” Typically the seat in a soft seated fire tight valve contains a metal strip that will provide additional sealing should the seat be burnt or melted away. Fire tight valves can be found on fuel gas applications, VRU systems and in other flammable systems.
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