Manual Air Vent Valve

vent valve
A normally closed check valve located in a cell which allows the controlled escape of gases when the internal pressure exceeds its rated value.
A valve used for lifting atmospheric air or other gas into a vacuum system. Also called a BTA or back-to-air valve.
A valve that may be manually opened to allow air or fluid or a combination of both to be exhausted into a lower pressure chamber or to the atmosphere.

manual
(of a machine or device) Worked by hand, not automatically or electronically
manual of arms: (military) a prescribed drill in handling a rifle
Using or working with the hands
Of or done with the hands
of or relating to the hands; "manual dexterity"
a small handbook

air
The invisible gaseous substance surrounding the earth, a mixture mainly of oxygen and nitrogen
This substance regarded as necessary for breathing
The free or unconfined space above the surface of the earth
a mixture of gases (especially oxygen) required for breathing; the stuff that the wind consists of; "air pollution"; "a smell of chemicals in the air"; "open a window and let in some air"; "I need some fresh air"
be broadcast; "This show will air Saturdays at 2 P.M."
air out: expose to fresh air; "aerate your old sneakers"