What is the purpose of placing the electric fuel pump inside the fuel tank?

The purpose of placing the electric fuel pump inside the fuel tank is to pump combustion gasoline from the fuel tank into the fuel line and maintain a certain pressure to supply the fuel injector and cold start valve. Its function is to transport fuel from the fuel tank to the engine in the fuel supply system of gasoline or diesel engines.

Electric fuel pumps are divided into roller type, turbine type, rotor type, and side channel type according to their structure. According to the installation location, they can be divided into built-in type and external type.

The principle of the fuel pump structure:

Vane pump (turbine pump) characteristics: small pulsation in oil pressure, smooth operation, low noise, no need for pulsation dampers in the fuel supply system, easy miniaturization, but lower delivery efficiency. Positive displacement pumps (roller type, rotor type, sliding vane type) characteristics: high oil pressure, but due to discontinuous operation, oil pressure pulsation is large, so a pulsation damper is also required at the outlet of the fuel pump.

The turbine-type electric fuel pump mainly consists of a motor, turbine pump, check valve, and safety valve. When the fuel pump is energized, the motor drives the turbine pump blades to rotate. Due to centrifugal force, the blades in the small grooves around the impeller press against the pump housing, carrying fuel from the inlet chamber to the outlet chamber.

As the fuel in the inlet chamber continuously increases, a certain vacuum is formed, sucking fuel from the inlet. Meanwhile, the fuel in the outlet chamber continuously increases, raising the fuel pressure. When it reaches a certain value, the outlet valve opens to output fuel. The outlet valve prevents fuel from flowing back into the tank when the fuel pump is not working, maintaining a certain pressure in the fuel line for easy next startup.

From an engineering perspective, the in-tank fuel pump leverages liquid immersion for reliability. Petrol’s thermal conductivity cools the motor, while submersion reduces wear by preventing dry running. The design also simplifies packaging—no extra space is needed under the bonnet. It’s a trade-off: accessing the pump for repairs requires tank removal, but the benefits in durability and efficiency outweigh maintenance drawbacks.