# Engine Fuel Pumps

> Pumps used in piston engine fuel systems, including engine-driven and auxiliary electric pumps.

- **Subject:** 021 — Airframe, Systems, Electrics, Powerplant
- **Section:** 021-10 — Piston Engines
- **Topic code:** 021-10-03
- **Last reviewed:** 2026-03-24
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/airframe-systems-electrics-powerplant/piston-engines/engine-fuel-pumps/

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## Auxiliary Pumps

*   **Type**: Usually **electrical** (not engine-driven).
*   **Function**:
    *   **Backup**: Parallel to the main engine-driven pump.
    *   **Vapour Lock Prevention**: Pressurize fuel lines to suppress vapor formation.
    *   **Priming**: Used for engine starting.
*   **Operation**:
    *   **Normal**: Switched ON for takeoff and landing. Switched OFF in cruise.
    *   **Abnormal**: Switched ON if main pump fails or vapour lock is suspected.

### Fuel Injection System Pumps

*   **Principle**: Delivers fuel under pressure directly to the cylinders (injector assembly) rather than relying on a venturi (carburetor).
*   **Engine-Driven Pump**:
    *   Supplies fuel at **positive pressure** to the injector assembly.
    *   Pressure is often determined by engine speed.
    *   Excess pressure is returned via a relief valve.
*   **Advantages**: Uniform delivery, better icing protection, quicker throttle response.

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