Page 323 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

reverse actuator (apply pressure to close open/fail open)

Spring Actuator
When control pressure applied to the actuator is used to open the valve and energy on the spring return used to
close the valve safely, it is called a direct acting actuator. The valve closes as a fail safe action in case of direct
acting actuator control signal failure. When control pressure applied to the actuator is used to close the valve and
energy in the spring return used to open the valve safely, it is called a reverse actuator. Reverse actuator control
signal failure results in the valve opening as a fail safe action.
However, lock to lock position can be achieved by installing an air lock relay so that when the control signal fails,
the pressure applied to the actuator must be constant to hold/lock the valve in the same position.
Double acting actuator
In double acting actuator, there are two signal ports in such a way that controlled pressure on one port is used to
open the valve and controlled pressure on the other port is used to move the valve to close. . Most double acting
actuators fail to lock type. However, fail open and fail close conditions can also be achieved by using control valve
accessories such as valve positioners and solenoid valves etc.
Pneumatic actuator applications
There is a wide field of applications of pneumatic actuators in process plants and industries. Now a days such
actuators are integrated with electronic devices using solenoid valves, positioners, I/P converters etc. to take
commands in electrical form directly from the digital controller by manipulating the signal output. Some of their
areas of application are as follows-
Chemical plants and refineries ,
Water treatment plants ,
Manufacturing industries ,

Food handling industries,
Electronic Industry ,
Automotive industries ,
Agriculture applications ,

Construction, Coal Mining Equipment , etc.

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CITS : E & H - Electronics Mechanic - Lesson 188 - 198