Exam Question
Describe with a sketch a pneumatic relay and show how feedback can be achieved when such a relay is used in conjunction with a flapper mechanism.
Class 2 (2nd Engineer)
MEKG
📅 Oct 2020
Reference Answer
The pneumatic relay operates on the principle of a nozzle-flapper arrangement. Air supply pressure acts on a diaphragm located below a spring. A rod and plug, connected to the diaphragm, control the flow of output air through a nozzle. A flapper is positioned near the nozzle.
Operation:
An input signal (which can be a change in pressure or displacement of the flapper) affects the flapper's position.
Flapper movement changes the distance between the flapper and the nozzle. A decrease in distance (flapper closer to the nozzle) restricts the output airflow. Conversely, an increase in distance increases output airflow. This is the direct action of the relay.
Operation:
An input signal (which can be a change in pressure or displacement of the flapper) affects the flapper's position.
Flapper movement changes the distance between the flapper and the nozzle. A decrease in distance (flapper closer to the nozzle) restricts the output airflow. Conversely, an increase in distance increases output airflow. This is the direct action of the relay.
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