Definition
A pressure carburetor that meters fuel using the difference between two air pressures sensed at the throttle body — impact (ram) air pressure and venturi (low) pressure — to operate a fuel-metering valve. The pressure difference acts on a diaphragm or servo unit that regulates fuel flow in proportion to airflow through the engine, delivering fuel under positive pressure rather than relying on suction at the venturi.
Plain English
A type of carburetor that uses the difference between incoming air pressure and the pressure inside the venturi to push fuel into the engine in the right amount. Instead of fuel being sucked in by low pressure, it is pushed in under pressure by a small valve that responds to how much air the engine is taking in.
Context Anchor
Seen in aircraft engine, fuel-system, and maintenance discussions, especially when comparing float carburetors with pressure-type fuel-metering systems.
Derivation
The word 'servo' comes from the Latin 'servus,' meaning 'servant.' In engineering, a servo is a device that uses a small input signal to control a much larger output. Here, the small pressure difference between ram air and venturi air 'serves' as the control signal that regulates the much larger flow of fuel into the engine.
Why Pilots Care
Correct fuel metering across power settings and altitudes prevents engine damage from overly lean or rich mixtures.
Intuition Check
Do not read “servo-type” as meaning the carburetor is driven by a small electric hobby servo. Here, “servo” means the carburetor uses air-pressure signals to control fuel flow automatically.
Example Sentence 1
The aircraft's servo-type carburetor delivered fuel reliably even during steep climbs, where a float-type unit might have starved the engine.
Example Sentence 2
During the preflight, the mechanic verified that the servo-type carburetor responded smoothly to throttle changes.