Airlock

Before opening either door, the air pressure of the airlock—the space between the doors—is equalized with that of the environment beyond the next door to open. This is analogous to a waterway lock: a section of waterway with two watertight gates, in which the water level is varied to match the water level on either side.

A gradual pressure transition minimizes air temperature fluctuations (see Boyle's law), which helps reduce fogging and condensation, decreases stresses on air seals, and allows safe verification of pressure suit and space suit operation.

Where a person who is not in a pressure suit moves between environments of greatly different pressures, an airlock changes the pressure slowly to help with internal air cavity equalization and to prevent decompression sickness. This is critical in scuba diving, and a diver may have to wait in an airlock for some hours, in accordance with decompression tables.

US Navy submarine diving lock out, 2007.

Airlocks are used in

• spacecraft and space stations, to maintain the habitable environment when persons are exiting or entering the craft.
• hyperbaric chambers, to allow entry and exit while maintaining the pressure difference with the surroundings.
• submarines, diving chambers, and underwater habitats to permit divers to exit and enter.
• torpedo tubes and escape trunks in submarines are airlocks.
• cleanrooms, protected environments in which dust, dirt particles, harmful chemicals, and other contaminants are excluded partially by maintaining the room at a higher pressure than the surroundings.
• hazardous environments, such as nuclear reactors and some biochemical laboratories, in which dust, particles, and/or biological agents are prevented from leaking out by maintaining the room at a lower pressure than the surroundings.
• pressurized domes such as the USF Sun Dome where pressure loss would cause collapse of the structure.
• electron microscopes, where the interior is near vacuum so air does not affect the electron path.
• parachute airlocks, where airfoil collapse due to depressurization can result in dangerous loss of altitude.
• fermentation vessels, where a fermentation lock allows fermentation gases to escape while keeping air out, such as in breweries or wine-makers.

• In cold climates, two doors arranged in an airlock configuration are common in building entrances. While not airtight, the double doors minimize the loss of heated air from the building. A similar arrangement is common in hot climates, where it is used to keep interior spaces cool. Revolving doors may be used for the same purpose.
• Some jewelry stores and banks have airlock-like doors to slow the escape of thieves.
• Butterfly farms and aviaries usually have an airlock-like entrance to prevent the exit of inhabitants and entrance of predatory species.
• Planetariums may have "light-locks" to minimize outside light, protecting visitors' sensitive dark adaptation. These pairs of doors also reduce outside sound.[1][2]

• Fermentation lock
• Revolving door
• Sally port
• Suitport

Media related to Airlocks at Wikimedia Commons