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Butterfly valves are
quick opening valves that consist of a metal circular disc or vane with
its pivot axes at right angles to the direction of flow in the pipe, which
when rotated on a shaft, seals against seats in the valve body. They are
normally used as throttling valves to control flow. Butterfly valves
control the flow of gas or liquid by means of a disk, which turns on a
diametrical axis inside a pipe or by two semicircular plates hinged on a
common spindle, which permits flow in only one direction. These
valves offer a rotary stem movement of 90 degrees or less, in a compact
design. Unlike ball valves, butterfly valves do not have any pockets
in which fluids may become trapped when the valve is closed.
Butterfly valves are available in several body styles and seal types.
The flange type or lug style can be held between flanges of any type.
Wafer valves are installed between two flanges using bolts or nuts and
studs, while lug style valves have metal inserts installed in the valve's
bolt holes and the valve is installed between two flanges using a separate
set of bolts for each flange. If the wafer style is used, avoid
placing it between either slip-on or screwed flange types. Some
wafer body styles will not form a proper seal. The wafer style is
used more commonly and is cheaper than the lug style.
Butterfly valves offer a number of advantages when used for the proper
application. They may be used in a wide variety of chemical
services, they are available with small dimensions allowing for use in
areas where space is limited, and they allow a high coefficient of flow.
Conversely, the design of butterfly valve creates the disadvantage of not
being easy to clean, and therefore should be avoided in situations that
call for sterile, medical or food processing applications.
Additionally, some styles may have difficulty dispensing slurries.
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