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Butterfly valves are rotary valves wherein a disc-shaped closure element rotates approximately ninety degrees to open or close a flow passage. The original butterfly valve is a rudimentary, non-sealing pipeline damper. This valve remains an essential member of the family of butterfly valves.
The advent of elastomers has accelerated the development of butterfly valves with a tight shut-off in which the elastomer functions as the sealing element between the disc's rim and the valve body. Originally, these valves were used for water.
As more chemically-resistant elastomers became available, the adoption of butterfly valves in the process industries expanded. These elastomers must not only be corrosion-resistant, but also abrasion-resistant, dimensionally stable, and resiliency-retentive, i.e., they must not solidify. In the absence of any of these characteristics, the elastomer may be inappropriate. Manufacturers of valves can provide guidance regarding the selection and limitations of elastomers for a given application.