|Automated butterfly control valve.|
A butterfly valve is used for stopping or controlling flow of liquids or materials through pipes. The "butterfly" refers to the round, flat disk that allows for flow through the valve. Butterfly valves are a member of the "quarter-turn" valve family, meaning fully open to fully closed in 90 degrees rotation. They are opened and closed via a lever, manual gear operator, pneumatic actuator, or electric actuator. Butterfly valves can be used for on-off service and some varieties are used as control valves. Butterfly valves are generally less expensive than other high flow valves, lighter in weight, and take up less piping length. Since the disk is always in the flow path, butterfly valves always have a pressure drop across the valve.
There are two primary types of butterfly classifications:
- So called "rubber lined" butterfly valves (resilient seated) which are best suited for lower pressure, lower temperature, general purpose applications.
- High Performance Butterfly Valves (HPBV) which are designed to ANSI pressure classifications and are suited for more robust industrial applications.
|Rubber lined butterfly valve.|
High performance butterfly valves have precision machined teflon, or metal seats, and are slightly offset as to lessen the amount of seat-to-disk interference. The disc still is pushed against he seat, but in a much more controlled and measured manner. Seat wear is still an issue, but not like rubber lined valves. Seating and unseating torque effects are much less as well.
|Triple offset butterfly.|
Butterfly valves come in three body styles:
- Wafer body, whereby the valve is "sandwiched" and held in place between two pipe flanges and are suitable for lower pressure applications.
- Lug style bodies that have threaded "lugs" cast in to the body of the valve and bolts are used to secure the valve for end of line service or keeping the valve in place when the piping is disassembled.
- ASME flanged butterfly valves where the valve body is in-between two ASME flanges.