Definition
Flat rectangular blades made of carbon that slide in and out of slots in the rotor of a dry air vacuum pump. As the rotor spins, the vanes are thrown outward by centrifugal force and seal against the pump housing, trapping and moving air through the pump to create the suction that drives gyroscopic instruments.
Plain English
Small carbon blades inside a vacuum pump that spin around and push air through, creating the suction the gyro instruments need to work.
Context Anchor
Seen in dry air vacuum pump descriptions, especially when discussing how engine-driven vacuum pumps create airflow for flight instruments.
Derivation
Called 'carbon' because the vanes are made from carbon, a self-lubricating material that does not need oil. Called 'vanes' from the same root as a weather vane -- a flat blade that interacts with moving air. The carbon material is what makes a 'dry' pump dry: no oil is needed to lubricate the moving parts.
Why Pilots Care
Carbon vanes wear gradually during operation. When they become too short the pump loses vacuum, causing failure of the attitude indicator and heading indicator.
Analogy
Think of the vanes like small sliding paddles inside a turning wheel. As the wheel turns, the paddles push pockets of air along through the pump.
Intuition Check
Do not picture carbon vanes as outside fins or a weather-vane pointer. In this context, they are internal sliding blades inside the vacuum pump.
Example Sentence 1
The mechanic replaced the vacuum pump after finding that several of the carbon vanes had cracked.
Example Sentence 2
During preflight the pilot noted fine carbon dust around the vacuum pump exhaust, indicating the carbon vanes were nearing the end of their service life.