air chamber

air chamber
: a cavity filled with air: as
a. : a cavity containing air to act by its elasticity as a spring for equalizing the flow of a liquid in a pump or other hydraulic machine — see hydraulic ram illustration
b. : one of the chambers in the nautilus or other chambered cephalopods

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1. a chamber containing air, as in a pump, lifeboat, or organic body.
2. Also called air cushion. a compartment of a hydraulic system containing air that by its elasticity equalizes the pressure and flow of liquid within the system.

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air chamber,
any compartment filled with air, especially a trap in a pump or other hydraulic system to prevent excessive pressures when the pump is suddenly stopped or started.

Useful english dictionary. 2012.