The hot air pressure regulating valve automatically closes if what condition is met?

The hot air pressure regulating valve is designed to ensure the safety and efficiency of the aircraft's thermal management systems. It automatically closes when specific conditions indicate that maintaining airflow could lead to potential overheating or system failure. In this case, the valve will close if the duct overheats or if at least two trim valves fail.

When the duct overheats, it's a clear indication that the temperature is rising to an unsafe level, which could damage components or create hazardous conditions. The failure of trim valves, particularly in pairs, suggests a significant issue with the airflow regulation, which could further exacerbate the risk of overheating. Therefore, closing the valve in such scenarios is a critical safety measure to protect both the system and the aircraft.

The other conditions listed relate to operational modes that do not directly trigger an automatic closure of the hot air pressure regulating valve under routine circumstances.