A butterfly valve is a quarter-turn valve used to regulate flow. A metal disc in the body of the valve is positioned perpendicular to the flow in the closed position, and rotated one quarter of a turn to be parallel to the flow in the fully opened position. Intermediate rotations allow regulation of liquid flow. They are often used in agricultural and water or wastewater treatment applications and are one of the most common and well-known valve types.

Butterfly valves are similar to ball valves but have several advantages. They are small and, when actuated pneumatically, open and close very quickly. The disc is lighter than a ball, and the valve requires less structural support than a ball valve of comparable diameter. Butterfly valves are very precise, which makes them advantageous in industrial applications. They are quite reliable and require very little maintenance.

One disadvantage of butterfly valves is that some portion of the disc is always presented to the flow, even when fully opened. The use of a butterfly valve therefore always results in a pressure switch across the valve, regardless of the setting.

Butterfly valves can be configured to operate manually, electronically or pneumatically. Pneumatic valves operate most rapidly. Electronic valves require a signal to the gearbox to open or close, while pneumatic valves can be either single or double actuated. A single-actuated valve is typically set up to require a signal to open with a failsafe, meaning that when power is lost the valve springs back to a fully closed position. Double-actuated pneumatic valves are not spring loaded and require a signal both to open and to close.

Automated pneumatic butterfly valves are both reliable and durable. Reduced wear improves the valve life cycle, which reduces operating costs otherwise lost in working hours to maintain the valves.