air-lock

verb (used with object)

1. to place in or confine to an air lock: to air-lock divers before they descend.

noun

1. Civil Engineering. an airtight chamber permitting passage to or from a space, as in a caisson, in which the air is kept under pressure.
2. the impedance in the functioning of a pump or a system of piping caused by the presence of an air bubble; vapor lock.