Bosch-Common Rail System – Zero delivery valve
1 From high-pressure chamber annular channel
2 Zero delivery valve
3 Calibrated bore (ø = 0.4 mm)
4 To transfer pump
The zero delivery valve is located between the annular channel that is connected to the inlet valves of the high-pressure chambers and the fuel metering valve.
Even in the fully closed state, the fuel metering valve is not completely sealed. In other words, a small amount of leakage in the annular channel continues to pass to the high pressure chambers due to the transfer pump pressure. As a result, the inlet valves are opened and an undesirable pressure increase may occur in the high pressure system.
To prevent this, the zero delivery valve features a calibrated bore. In this way, excess fuel is fed back to the intake side of the transfer pump.