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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.
The butterfly valve has a body, a resilient seat, a
butterfly disk, a stem, packing, a notched
positioning plate, and an actuator. The resilient
seat is under compression when it is mounted in the
valve body, thus making a seal around the periphery
of the disk and both upper and lower points where
the stem passes through the seat. Packing is
provided to form a positive seal around the stem for
added protection in case the seal formed by the seat
should become damaged. To close or open a butterfly
valve, the actuator is turned only one quarter turn
to rotate the disk from 0° to 90°. Actuators used on
butterfly valves vary based on the application and
size of the valve. A simple handle oriented in the
same direction of the metal disc (to indicate valve
position) is common. Some larger butterfly valves
may have a handwheel that operates through a gearing
arrangement to operate the valve. This method is
used especially where space limitation prevents use
of a long handle. Acuators may also be air driven or
electrically operated when used as part of an
automated control system.
Butterfly valves are relatively easy to maintain.
The resilient seat is held in place by mechanical
means, and neither bonding nor cementing is
necessary, Because the seat is replaceable, the
valve seat does not require lapping, grinding, or
machine work.
Butterfly valves are valves with a circular body and
a rotary motion disk closure member which is
pivotally supported by its stem. A Butterfly valve
can come in various styles including eccentric and
high-performance valves. These are normally a type
of valve that uses a flat plate to control the flow
of water. As well as this, Butterfly valves are used
on fire apparatus and typically are used on larger
lines, such as front and rear suctions and tank to
pump lines. A Butterfly valve is also a type of flow
control device, used to make a fluid start or stop
flowing through a section of pipe. The valve is
similar in operation to a ball valve. Rotating the
handle turns the plate either parallel or
perpendicular to the flow of water, shutting off the
flow. It is a very well known and well used design.
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