1. An isolated chamber on vessels with their own air supply
(including submarines and space craft), which has two airtight doors.
One connects with the body of the vessel, and the other with outside.
The inside of the vessel is at atmospheric pressure. The only way for a person to leave
the vessel is through the
air lock. The chamber is pressurised (or filled with air) to atmospheric pressure. The person
enters through the inner door, dons a space suit (or diving suit). The inner door is closed and
the air is let out of the chamber; the person then exits via the outer door.
2. A piece of equipment used in home wine making that allows ventilation without
contamination.
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The air lock is placed in a bung in the top of the demijohn containing fermenting wine.
A small quantity of water is poured into the section which connects the two chambers.
Excess CO2 from fermentation forces the water into the right hand chamber,
until the water level is high enough for a bubble to pass through, returning the water
to its original state. This is accompanied by a characteristic "bloop" sound.
3. An air bubble in the fuel intake to a diesel engine. Air locks are a problem to the
engine, as they result in a loss of power, compression, and potentially damage to the engine.
Modern diesel engines are self bleeding, hence air bubbles do not succeed in reaching the
intake valves.
4. Drawing an analogy from 1. an air lock is also the name given to an anteroom with a pair
of security doors which cannot be open at the same time. These are used in military establishments
and some banks. A similar arrangement is used with gates in safari parks to allow vehicles to
pass through without the animals escaping. | 
