VALVE ACTUATORS
Process Controls
VALVE ACTUATORS
Remote operation of a valve is easily managed by one of the four types of
actuators.
EO 1.7
DESCRIBE the operation of the following types of
actuators:
a.
Pneumatic
b.
Hydraulic
c.
Solenoid
d.
Electric motor
Actuators
Figure 35 Pneumatic Actuator: Air-to-Close/Spring-to-Open
By themselves, valves cannot
control a process. Manual valves
require an operator to position
them to control a process variable.
Valves that must be operated
remotely and automatically require
special devices to move them.
These devices are called actuators.
Actuators may be pneumatic,
hydraulic, or electric solenoids or
motors.
Pneumatic Actuators
A simplified diagram of a
pneumatic actuator is shown in
Figure 35.
It operates by a
combination of force created by air
and spring force.
The actuator
positions a control valve by
transmitting its motion through the
stem.
A rubber diaphragm separates the
actuator housing into two air
chambers.
The upper chamber
receives supply air through an
opening in the top of the housing.
IC-07
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