The APU bleed valve controls airflow to the aircraft bleed-air system and protects the APU from what condition?

The APU bleed valve plays a crucial role in maintaining optimal operating conditions for the Auxiliary Power Unit (APU). It primarily serves to manage the airflow from the APU to the aircraft's bleed-air system, ensuring that the pressure and temperature remain within safe limits.

In this context, the correct answer highlights the protection against overtemperature condition. The APU generates heat during operation, and if excessive airflow is not controlled, it can lead to higher temperatures that may damage the APU components. By regulating the airflow, the bleed valve effectively prevents the APU from reaching temperatures that could compromise its integrity and operational efficiency.

The other options, while they refer to important operational parameters, do not specifically relate to the primary function of the APU bleed valve in protecting against temperature-related issues. Hence, focusing on overtemperature is essential for understanding how the APU bleed valve safeguards the unit during operation.