A Butterfly valve is an on-off valve or a shut-off valve. Butterfly valves are quarter turn valves with a straight through flow configuration. For large sizes butterfly valves offer savings in weight,space and cost over other types of valves. They are usually low maintenance valves as there are minimal number of moving parts and no pockets to trap fluids.
Butterfly valves are especially well-suited for the handling of large flows of liquids or gases at relatively low pressures and for handling of slurries or liquids with large amount of suspended solids.
Construction
Butterfly valves are available in following body patterns
- Wafer type that fit between flanges
- Lug wafer type with drilled or tapped holes
- Conventional flanged ends for bolting to pipe flanges
Butterfly valves are not generally used for end of line applications. Where required for end of line applications such as drain points, lug wafer type with drilled holes can be used.
Butterfly valves should be postioned in lines such that the disk does not interfere with adjacent valves, fittings or connected pipework. This aspect becomes critical where butterfly valves are used with lined piping such as teflon lined piping or frp dual laminate piping.
High performance butterfly valves are used in critical applications. High performance butterfly valves have stems mounted eccentrically on disk which makes them suitable for tight shut-off.
Butterfly valves are generally suitable for bi-directional sealing but some designs have a preferred direction of flow. Butterfly valves create higher pressure drop than a full bore ball or gate valve and are not suitable for lines requiring pigging.
Industry Codes and Standards
- API 609 - Butterfly Valves: Double Flanged, Lug and Wafer Type
- BS 5155 - Specification for butterfly valves
- MSS SP 67 - Butterfly Valves
Operators for Butterfly Valves
Most operators use the following guidelines to select the type of operators for Butterfly valves
| Operator | Size | Rating |
|---|---|---|
| Handwheel | 8-inch and below | Class 150 and 300 |
| Handwheel | 4-inch and below | Class 600 and 900 |
| Handwheel | 3-inch and below | Class 1500 and 2500 |
| Gear Operator | 10-inch and above | Class 150 and 300 |
| Gear Operator | 6-inch and above | Class 600 and 900 |
| Gear Operator | 4-inch and above | Class 1500 and 2500 |