The Vital Apparatus Vent.
The Aperture Science Vital Apparatus Vent is the final part of a system that distributes Weighted Storage Cubes into the Enrichment Center Test Chambers.
Description[]
Located on ceilings, they are connected to the Pipe Network which uses varying air pressure to move Weighted Storage Cubes through the facility. It automatically delivers a new cube each time Chell destroys one. In Test Chamber 16, a damaged vent is randomly opening and closing, allowing a large pile of cubes to build up below it. It was probably intentionally sabotaged by Doug Rattmann, explaining the presence of a radio, a set of tools and a coffee mug, as well as a black hand-print on the wall. The Pneumatic Diversity Vent, used to transport any object, is a more complex variant.