Pneumatic Diversity Vent
The Aperture Science Pnuematic Diversity Vents were testing elements that were to appear in test chambers throughout the game, but were cut from the finished product, instead only making a few cameos. Valve has not released any statement on whether or not the vents will make an appearance in later DLC.
Function
The vents would suck up any object placed below them. This could be utilized to dispatch turrets or to remove some panels on the wall. At one point in the trailer for the vents, a player is required to create and loop and continuously send several turrets through the vents.
It is unknown how else the player would have interacted with the vents in order to get somewhere more quickly, or to transport Weighted Storage Cubes or other such objects across the map.
Appearances
Portal 2
While not appearing as a testing element in Portal 2, it can be seen several times.