A butterfly valve is a type of flow control device, typically used to regulate a fluid flowing through a section of pipe. The valve is similar in operation to a ball valve. A plate or disc is positioned in the center of the [pipe (material)|[pipe]]. The disc has a rod through it connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow; therefore a pressure drop is always induced in the flow, regardless of valve position. Large butterfly valve used on a hydroelectric power station water inlet pipe in japan a butterfly valve is from a family of valves called quarter-turn valves. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid. The valve may also be opened incrementally to regulate flow.There are different kinds of butterfly valves, each adapted for different pressures and different usage. The resilient butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high performance butterfly valve, used in slightly higher-pressure systems, features a slight offset in the way the disc is positioned, which increases the valve's sealing ability and decreases its tendency to wear. The valve best suited for high-pressure systems is the tricentric butterfly valve, which makes use of a metal seat, and is therefore able to withstand a greater amount of pressure.
Types- 1. Resilient butterfly valve, having a flexible rubber seat. Working pressure 232 psi 2. High performance butterfly valve, usually double eccentric in design. Working pressure up to 725 psi 3. Tricentric butterfly valve, usually with metal seat design. Working pressure up to 1450 psi. Butterfly valve for controlling fluid flow in conduits, and including a butterfly co acting with a seating bore in a casing having a peripherally mounted, solid sealing ring for engagement with a seating bore, wherein the sealing ring is mounted on the butterfly for radial movement to conform to the seating bore when the valve is closed.
