Definition
A positive-displacement rotary pump that uses an inner toothed rotor turning inside an outer rotor with one additional internal tooth. As the rotors turn together off-center, the spaces between their teeth expand to draw fluid in and contract to push fluid out, producing a steady flow.
Plain English
A pump with two gear-like rotors, one inside the other and slightly off-center. As they turn, the gaps between their teeth open up to suck fluid in on one side and squeeze it out on the other.
Context Anchor
Seen in aircraft maintenance when working with oil systems, hydraulic systems, or other systems that need a steady flow of fluid under pressure.
Derivation
The name is a blend of 'generated rotor.' The outer rotor's shape is mathematically generated from the inner rotor's shape, which is what allows the two to mesh smoothly while turning off-center.
Why Pilots Care
Gerotor pumps are common in engine oil and fuel systems. Knowing how they work helps a technician or pilot understand why a worn pump may show as low oil pressure or weak fuel flow rather than a sudden failure.
Analogy
Think of two fitted, rotating shapes making small moving pockets. Each pocket picks up fluid on one side and carries it to the other side, where the pocket closes and pushes the fluid out.
Intuition Check
A gerotor pump is not just any pump with a spinning part. It moves a measured amount of fluid by trapping and squeezing it, not by simply stirring or throwing the fluid outward.
Example Sentence 1
The engine's oil pump is a gerotor pump driven off the accessory gear.
Example Sentence 2
Gerotor pumps maintain steady pressure in constant-speed propeller governors.