Which component prevents sudden loss of pressurization if the source is lost?

The delivery air duct check valve plays a critical role in maintaining cabin pressurization by preventing sudden loss of pressure if the primary source of air supply is compromised. In the operating environment of an aircraft, pressurization is crucial for passenger and crew safety, comfort, and overall operational effectiveness.

The check valve allows airflow into the cabin but restricts air from escaping back through the duct when there's a sudden decrease in pressure or when the air supply is lost. This design helps ensure that any remaining pressurization within the cabin is preserved, thereby providing a buffer against potential depressurization incidents.

In contrast, while other components have important functions in the cabin atmosphere control system, they do not specifically address the prevention of sudden loss of pressurization. For instance, the mixing valve is responsible for blending different air sources for temperature regulation, the negative pressure relief valve manages external pressure differences, and the expansion valve controls the flow and regulation of refrigerant in cooling systems. However, none of these directly mitigate the risk of cabin depressurization as effectively as the delivery air duct check valve does.