What happens to feedback bellows pressure when the flapper of a basic pneumatic transmitter moves toward the nozzle?

When the flapper of a basic pneumatic transmitter moves toward the nozzle, the feedback bellows pressure increases. This occurs because the flapper's movement reduces the area through which the air can escape from the nozzle. As the flapper approaches the nozzle, it creates a restriction that leads to an increase in the air pressure in the feedback bellows. The design of the transmitter relies on the relationship between the flapper position and the resulting pressure changes to ensure accurate measurement and control.

In a pneumatic system, the flapper acts as a control element that modulates the flow of air based on the variable being measured. When the flapper moves closer to the nozzle, it restricts airflow, which results in increased pressure within the bellows. This pressure change can then be used to indicate a higher level of the measured variable, effectively translating the mechanical movement into a measurable pneumatic signal that can be processed by control systems.

Understanding this mechanism is crucial for interpreting how pneumatic transmitters function in various applications, particularly in monitoring and controlling processes in power engineering.