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Pneumatic Actuator
An air operated mechanical device used to open and close
or modulate a valve. The actuator, which is mounted to the
valve by a bracket and coupled to the stem, is designed to
convert air pressure into mechanical force sufficient to
operate the valve.
Double-Acting Pneumatic Actuator
Any pneumatic actuator which uses air to drive the
actuator output shaft in both the open and close direction.
The air supply is piped to one side of a piston-drive or a
diaphragm while the air contained on the opposing side is
exhausted.
Spring-Return Pneumatic Actuator
Any pneumatic actuator which contains a single coil
spring or group of coil springs to oppose the movement of a
piston or diaphragm. As air moves the piston or diaphragm
the spring is compressed. When the air supply is
discontinued and exhausted, the spring extends and drives
the piston or diaphragm in the opposite direction. This type
of actuator is normally used for applications where it is
necessary for the valve to move to the open or close
position upon loss of air supply, whether by design or by
system failure.
Fail-Open - Spring return pneumatic actuator is
applied to the valve such that the spring will drive the
valve to the open position upon loss of air (may be termed
air-to-close)
Fail-Closed - Spring return pneumatic actuator is
applied to the valve such that the spring will drive the
valve to the close position upon loss of air (may be termed
air-to-open)
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