Hovercraft fill air chambers as they hover over sea or land.
A plenum is essentially a type of ventilation or air transfer system. These air-filled chambers can be found in vehicles and machines, or in the floors and ceilings of a room. The term chamber normally refers to a space with positive air pressure, where the air pressure inside the space is greater than that outside the chamber. Therefore, a plenum chamber can be represented as the opposite of a vacuum chamber, which is characterized by a negative air pressure or an internal pressure less than the surrounding air pressure. Positive pressure inside a chamber creates natural forces that push air out and then replace it with fresh air from outside the chamber.
In homes and businesses, a plenum is an alternative to traditional duct-based ventilation systems. Instead of relying on two separate ducts to supply and return air, plenum systems use only one set of supply ducts. As these ducts pump fresh air into the room, stale air naturally exits through exhaust vents in the ceiling. This air enters the entire space above the ceiling, where it is forced through a single air outlet and directed outside. This system helps reduce the cost of ventilation equipment and related ductwork, and also reduces maintenance.
When used in engines and other machines, the plenum acts as an exhaust chamber to help cool the engine or motor. A positive pressure chamber is located between the air intake assembly and the engine valves. Fresh air remains in the chamber until the valves open, allowing air to enter the engine. This allows each valve to open and receive fresh air as needed, resulting in better performance and a longer lasting engine.
While the hovercraft may seem like a complex space-age device, it actually relies on a simple plenum to help it hover above the ground. The boat is elevated off the ground, with a solid platform or siding around the perimeter acting as a base of support. This platform also forms a plenum chamber between the bottom of the hovercraft and the ground. When a series of fans at the top of the ship blow air into the plenum chamber, the pressure in this chamber increases, causing the ship to lift off the ground.
Plenum chambers have also been used in a variety of other applications. They are found in many large organs, where they help create that characteristic sound associated with the organ. A plenum chamber below the floor or above the ceiling in a room can act as a sound barrier, making this type of design suitable for recording studios. These chambers are also found at the base of ovens and certain types of ovens, where they act as cooling chambers.