•  Fuel is sucked into the inside of the pump cylinders by the rotating motion of the drive shaft, and is supplied under pressure to the common rail and also to the high pressure system.

•  During acceleration fuel is passed unrestricted from the transfer pump through the supply channel to the supply pump.

•  A proportion of the fuel passes through a calibrated return bore, past the fuel temperature sensor and back to the tank, thus serving to cool and lubricate the pump.

•  In over-run, the fuel metering valve closes the supply channel from the transfer pump to the supply pump. This causes the pressure in the supply channel to increase.

•  When a given pressure is reached, a pressure control valve opens, which is connected by a bore to the transfer pump.

•  The excess fuel partly flows back to the suction side of the transfer pump, partly back into the tank.