Fuel Pump: Description and Operation

PURPOSE
Provides pressurized fuel to the fuel injectors.

CONSTRUCTION
The pump is a turbine type hydraulic unit directly coupled to a permanent magnet motor. Fuel is used as a lubricant and coolant for the motor.
A check valve is incorporated in the fuel outlet and a pressure limiter valve is located on the pressure side of the fuel pump housing with a return passage to the fuel inlet side.

OPERATION
When the rotor disc rotates, the rollers are pressed outwards by centrifugal force and act as a circulating seal. A pumping action is created by the circulating rollers which draw in fuel at the inlet port and force the fuel through the outlet port into the fuel system.
When the pump is shut off, the check valve in the fuel outlet will close, therefore prohibiting the fuel from returning to the fuel tank via the fuel pump. The check valve will therefore maintain a pressure in the fuel lines called the "rest pressure".
The maximum fuel pump pressure (not fuel system pressure) is dependent on the calibration of the pressure limiter. If the fuel pump pressure exceeds a preset limit (for example a clogged fuel filter), the pressure limiter will open a by-pass to the fuel inlet side of the pump.