A butterfly valve is a kind of quarter-turn valve.
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 flat circular plate is positioned in the center of the pipe. The
plate has a rod through it connected to an actuator on the outside of the valve.
Rotating the actuator turns the plate either parallel or perpendicular to the
flow. Unlike a ball valve, the plate is always present within the flow,
therefore a pressure drop is always induced in the flow regardless of valve
position.
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 process 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.
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