FAA Aviation Mechanic Powerplant (AMP)Reciprocating EnginesEasy
What type of pump is most commonly used as the primary pressure oil pump in a reciprocating aircraft engine lubrication system?
- ADiaphragm pump
- BCentrifugal pump
- CPositive-displacement gear-type pump
- DVane-type variable-delivery pump
Show answer & explanationAnswer & explanation
Correct answer: C. Positive-displacement gear-type pump
Reciprocating engine lubrication systems almost universally use a positive-displacement gear-type pump (two meshing gears) driven by the engine to move a consistent volume of oil regardless of discharge pressure, with excess pressure relieved by a relief valve.
Why the other options are wrong
- A. Diaphragm pumps are typically used for fuel systems (engine-driven fuel pumps), not oil.
- B. Centrifugal pumps produce pressure proportional to speed and are not positive-displacement; unsuitable for oil systems needing consistent flow at low RPM.
- D. Vane-type pumps are less common in reciprocating engine oil systems; gear pumps dominate.
Oil Pressure Pump (Gear-Type)
A positive-displacement pump using two meshing gears to move oil at a rate proportional to engine speed, supplying pressurized oil to the lubrication system.
- Positive displacement delivers consistent volume per revolution
- Paired with a pressure relief valve to prevent excess pressure
- Driven directly by the engine accessory section
Memory trick: 'Gears grab oil and shove it through'