VII.4 Actuators
The introduction on actuators has been provided in Module IV. Few types of such actuators will be discussed in the following subsections.
VII.4.1 Pneumatic Valve
Pneumatic valves are air-operated valves that are used for regulating fluid flow through a pipeline (Fig VII.9). Varying air pressure (3 to 15 psig) is used as an actuating signal for the pneumatic valves. Usually control signal is generated and transmitted in electrical form (4 to 20 mA) from the controller. Hence, a current to pressure converter (I/P) converts an analog signal (4-20 mA) to a proportional linear pneumatic output (3-15 psig). Its purpose is to translate the analog output from a controller into a precise, repeatable pressure value to control pneumatic actuators/operators, pneumatic valves, dampers, vanes, etc .
|
|
Fig. VII.9: Pneumatics Valves |
|
(a) Fail Open 
(b) Fail Closed