Definition
An engine-driven pneumatic pump that supplies pressurized or suction air to operate aircraft instruments and systems without using engine oil for internal lubrication. Instead, the pump relies on self-lubricating carbon vanes that wear gradually as they slide inside the pump housing, eliminating the need for an oil separator in the air supply line.
Plain English
A pump driven by the engine that moves air through the aircraft's vacuum or pressure system. It does not use oil inside, so the air it produces is clean and ready to drive instruments directly.
Context Anchor
Seen in aircraft vacuum or pressure instrument system discussions, maintenance inspections, and troubleshooting of air-driven flight instruments.
Derivation
Called 'dry' because earlier 'wet' pumps used engine oil for sealing and lubrication, which then had to be separated out of the air. A dry pump runs without that oil, so the air leaving it is already dry and clean.
Why Pilots Care
Failure or contamination from an oil-lubricated pump can cause loss of attitude and heading reference in instrument flight.
Grounding Statement
The pump’s job is to keep air moving steadily through the instrument system so the connected equipment has the air source it needs.
Intuition Check
Dry does not mean the pump only handles moisture-free air. Here, dry means the pump is not oil-lubricated inside.
Example Sentence 1
After the dry air pump failed in cruise, the attitude indicator slowly rolled off and the pilot transitioned to the backup electric instruments.
Example Sentence 2
During preflight the pilot confirms the dry air pump is producing adequate suction for the gyro instruments.