The pack flow control valve automatically closes for all but which of the following?

The pack flow control valve is a critical component in managing cabin air flow and ensuring passenger comfort on the A320. It automatically closes in various situations to maintain safety and system integrity.

During engine start, the pack flow control valve closes to prevent excessive bleed air from the engines while they are starting. Similarly, in the event of a pack overheat scenario, the valve closes to limit airflow from a malfunctioning pack, protecting the system from further damage and ensuring safe operation. When a fire switch is released (meaning the fire protection system is activated), the valve also shuts to isolate the affected engine and prevent smoke or fire from entering the cabin.

However, when it comes to high air pressure, the pack flow control valve does not automatically close. While high pressure can arise in the bleed air system, it is managed differently, and the system is designed to operate efficiently under high pressure conditions without the need for the valve to close. This allows for continued airflow and pressure stability in normal flight operations.

Thus, recognizing that the pack flow control valve is designed to respond to specific safety-critical scenarios, understanding that it does not close due to high air pressure helps clarify its operational parameters.