Airlock

For other uses, see Airlock (disambiguation)}}}.

An airlock is a device which permits the passage of objects, people, and the like, between a pressure vessel and its surrounding space while minimizing the change of pressure—and loss of air—in the vessel. The lock consists of two airtight doors in series which do not open simultaneously.

Before opening either door, the air pressure of the airlock (volume between the doors) is equalized be the same as the environment behind the next door to open. 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. In situations where an unprotected human is moving from one pressure to another—such as a scuba diver—the slow pressure change helps with internal air cavity equalization, and is critical in preventing decompression sickness.

Airlocks are used in

submarines to permit frogman or other divers to exit and enter underwater. Torpedo tubes also act as a form of airlock.
spaceships, particularly in science fiction.
hazardous environments, such as nuclear reactors and some biochemical laboratories.

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. Revolving doors may be used for the same purpose.

The same principle is employed in the waterway locks used on canals.

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