Which component opens to pull air in if an internal vacuum occurs?

The component that opens to pull in air if an internal vacuum occurs is the sniffle valve. This device is designed to allow atmospheric air to enter a system when the pressure inside falls below a certain level, effectively equalizing pressure.

In systems where maintaining proper ventilation is critical, such as fuel systems or hydraulic systems, a sniffle valve prevents the formation of a vacuum by permitting outside air to flow in when negative pressure is detected. This operation is essential because it protects against potential damage that could arise from a vacuum condition, ensuring the system can function efficiently without the risk of collapsing or creating issues with fluid movement.

Other components, while they serve important roles in different contexts, do not perform this specific function of allowing air to enter under vacuum conditions. Float check valves, check valves, and flapper valves typically operate to prevent backflow or control flow direction, rather than responding to changes in internal pressure by admitting air.