Which component prevents air from entering a siphonic roof drain system?

The component that prevents air from entering a siphonic roof drain system is an air baffle at the inlet. In siphonic drainage systems, maintaining a continuous, negative pressure is essential for efficient operation. The air baffle is designed to provide a barrier that restricts airflow into the system, thus ensuring that the water can flow freely through the drainpipes without allowing air to disrupt the siphonic action.

By effectively sealing the inlet, the air baffle ensures that the pressure differential required for siphoning is maintained. This is crucial since the siphonic action relies on the right balance of pressure to transport water away from the roof efficiently. If air were allowed to enter through the inlet, it could break the siphon, leading to improper drainage and potential water accumulation on the roof. This specific function highlights the importance of the air baffle in maintaining the integrity and performance of siphonic drainage systems.