What is the function of a fuel return line?

The function of a fuel return line is to return excess fuel from the engine back to the tank. This system is essential for maintaining optimal fuel pressure within the engine and preventing vapor lock. When fuel is injected into the engine, any excess that is not consumed is directed back to the fuel tank through the return line. This helps in keeping the fuel at an appropriate temperature and pressure, ensuring efficient engine performance.

By recycling the unused fuel, the return line also contributes to the overall efficiency of the fuel system, as it minimizes waste and helps keep the tank from becoming pressurized due to fuel expansion. Understanding this function is critical for maintaining aircraft fuel systems and ensuring they operate correctly.