Which valve is responsible for switching between ram vent air and blower air?

The flapper valve is crucial for switching between ram vent air and blower air in an aircraft's environmental control system. This type of valve operates based on pressure differences, allowing it to toggle between two sources of air. When ram air is available and sufficient for the desired cabin pressure or temperature, the flapper valve diverts airflow from the ram vent. Conversely, when the ram air is insufficient or not available, the valve redirects the air from the blower to maintain the necessary conditions inside the aircraft.

This functionality is essential for ensuring that the cabin remains pressurized and comfortable for passengers and crew, especially at high altitudes where external air pressure is significantly lower. The flapper valve's design allows it to provide reliable operation under varying flight conditions, making it a critical component in the aircraft's air distribution system.