A Fuel intake
B Fuel delivery
C Fuel feed from fuel metering valve
D Fuel delivery to high pressure ring line
1 Inlet valve
2 Outlet valve
3 Piston
4 Drive shaft
5 Eccentric
The three pump plungers are actuated by the rotary movement of the high pressure pump drive shaft and the eccentric on the shaft. When the fuel metering valve opens the inlet to the high pressure chambers, the pressurized fuel from the transfer pump is fed to the inlet valves at the high pressure chambers. If the transfer pressure exceeds the internal pressure of the high pressure chamber (pump plunger in TDC position), the inlet valve opens. Fuel is now forced into the high-pressure chamber, which moves the pump plunger downwards (intake stroke).