Fuel Pressure Regulation
Fuel Flow: From pressure regulator => suction-jet pump in left tank half and suction-jet pump in right tank half => swirl pot in right tank half.
The suction-jet pumps direct the fuel from the left and right tank halves into the swirl pot. This ensures that the electric fuel pump always has a sufficient supply of fuel available.
The fuel filter incorporates the pressure regulator. The pressure regulator is a spring loaded diaphragm regulator, which limits the pressure in the fuel feed line to 3.5 bar (for M54).
When the pressure rises above 3.5 bar, the pressure regulator opens a discharge port. The excess fuel flows back through the discharge port into the right tank half (swirl pot) and drives the two suction-jet pumps (non-return fuel system). The fuel feed line delivers the fuel at 3.5 bar to the fuel rail.