Butterfly valves are used in both heavy and light uses. Butterfly valves are flow regulating, pivoted disc valves. The circular disc or plate, having the same radial dimensions as the pipe is pivoted exactly in the centre of the pipe, perpendicular to the direction of the flow.
Butterfly valves belong to a family of valves known as "quarter turn valves" because of this type valve fully close or open with only a quarter of a turn.
The disc if the butterfly valve is mounted perpenticular to the flow stream, The disc turns to open/block the flow stream when the actuator turns, Though the valve gives an unrestricted flow of fluid, it induces a pressure drop in the flow as the disc is always present within the flow.
When the valve is closed the disc turns so that the disc block the flow, When the valve is open, the disc turns quarter turn, so that to allow unrestricted flow. The valve may also open incrementally to regulate flow.
The discs in butterfly valves can have different shapes. Different shape discs can improve throttling characteristics and provide a tight shut-off
Different position of dics is shown below.
There are three popular types of butterfly valve based on the actuators used:
Manual gear reducer: Manually operated by hand wheel
Electric motor: Electrical motor enables the roatation, widely used type in automation.
Hydraulic cyclinder: Hydraulic system enable the roation of the actuator.
Low pressure drop
Small and light weight