Pneumatic Diversity Vent
The Aperture Science Pneumatic Diversity Vent is the primary component of the tubes in the Portal series. Although the component itself was not present in the first Portal, this component is the only means of supplying pneumatic pressures to push products throughout the Aperture Science computer-aided Enrichment Center, and opposite to the Vital Apparatus Vent.
As the second part of its name suggests, the Pneumatic Diversity Vent's purpose is also to redirect various products to a different location of the Enrichment Center if it were needed there.
The pneumatic pressures providing the suctions in the tubes have existed since Portal, and has remained prevalent throughout Portal 2. The Pneumatic Diversity Vents are the source of the powerful vacuums in tubes, and will therefore suck up any object(s) near it to provide continuous transportation if other Pneumatic Diversity Vent components are nearby. It is never demonstrated just how powerful the suction truly is in Portal 2, however in an early E3 2010 footage when the components were a testing mechanic, these components were originally able to remove various panels from their positions.
These components have transported a wide range of Aperture products such as Cubes (including Weighted Cubes and Edgeless Cubes), Turrets, elevators from a Chamberlock-specific Tube network (straight direction Tubes only), and other such objects to various locations they are needed.
There have been cases where Chell would board a tube to be transported with the help of the pneumatic pressures. In Portal, after Chell had escaped from her testing tracks, she boards a damaged tube, but is unexpectedly pulled back into a Test Chamber by GLaDOS. In Portal 2, she had used it again in a Tube riding scene from the chapter The Escape, in which both Chell and Wheatley had been sucked up through the Transportation Tubes via pneumatic pulls and were rapidly traveling around the facility. Although this was not a part of Wheatley's plans to confront GLaDOS, he realized that the pneumatic pulls have a chance of bringing them to her chamber.
As part of the Peer Review DLC for Portal 2, the Pneumatic Diversity Vents also serves as an entrance to the extra courses found in the Hub.
GLaDOS appears to be the only source of operating the pneumatic pulls in the tubes. Her power over these Vents are demonstrated in Portal 2, near a catwalk scene where the Oracle Turret can be found; unveiling entire tubes to have been completely non-functional after the destruction of GLaDOS.
According to unused skins for the screens, the vents would've been capable of carrying Weighted Companion Cubes, open fire turrets, Hover Turrets and various tables and chairs that are present in observation decks.