1 Pressure control valve
2 Return bore
3 Feed bore – high-pressure chamber
4 Leak-off fuel – fuel injectors
5 Fuel return to fuel tank
6 High pressure channel to fuel rail
7 Fuel feed to the transfer pump
The low pressure fuel return has the following functions:
โข Cools and lubricates the high-pressure pump by the internal return flow of the fuel, at low pressure, to the fuel tank,
โข recirculates the leak-off fuel from the fuel injectors to the fuel tank.
When accelerating, fuel is delivered, unrestricted, to the high-pressure chamber. In addition, a proportion of the fuel is used to cool and lubricate the pump and flows through a calibrated return bore and then through the venturi back to the fuel tank.
The venturi in the fuel return works by the principle of a suction jet pump and produces a slight partial vacuum in the leak-off pipes, allowing the leaking oil to drain off optimally.
1 Pressure control valve
2 Fuel injector fuel return bore
3 Feed bore – high-pressure chamber
4 Leak-off fuel – fuel injectors
5 Fuel return to fuel tank
6 Fuel feed to the transfer pump
When decelerating, the feed to the high-pressure chamber is closed by the fuel metering valve. As a result, the pressure in the feed bore rises.
When a specific maximum pressure has been reached, the pressure control valve, which is connected with the transfer pump via a bore, opens.
The some of the excess fuel flows back to the intake side of the transfer pump and via the venturi in the fuel return back to the fuel tank.