Vacuum Vent Valves
WARNING: This page is about a different car, the 1995 Ford Windstar. However, it is still accessible from the selected car via links, so may be relevant.
Valves control induction of fresh air into system to prevent accumulation of fuel vapors, which could cause decay of vacuum diaphragms. Valve may be vent valve only or combination vent and delay valve. Valves should always be mounted so ports point downward.