Air lock

device that permits passage between regions of differing air pressures, most often used for passage between atmospheric pressure and chambers in which the air is compressed. A typical modern air lock consists of a cylinder of steel plate with airtight doors located at both ends, one opening from the outside into the lock, the other from the lock into the compressed-air chamber, together with valves to admit or to exhaust compressed air. One of the doors must always be closed; before the other is opened, the pressure within the air lock must be equalized with that on the opposite side.(099)