Remote operation of a valve is easily managed by one of the four types of
DESCRIBE the operation of the following types of
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
A simplified diagram of a
pneumatic actuator is shown in
It operates by a
combination of force created by air
and spring force.
positions a control valve by
transmitting its motion through the
A rubber diaphragm separates the
actuator housing into two air
The upper chamber
receives supply air through an
opening in the top of the housing.