Low and High Pressure Side

LOW PRESSURE SIDE
The fuel supplied by the low pressure pump flows through the fuel feed to the throttle valve. Any air entrained by the fuel is directed through the restrictor to the return flow. The throttle valve opens against the force of the spring at a pressure of approx. 6 PSI (0.4 bar) and the fuel is able to flow along a ring line to the individual pistons. The eccentric shaft with its eccentric plate moves the pistons up and down against the piston spring of the three pump elements. The leak fuel from the pistons flows along the return flow to the fuel tank. The fuel flowing out of the throttle valve, also flows off along the return flow.

HIGH PRESSURE SIDE
A. Filling the piston: The piston is moved down as a result of the piston spring. The fuel supplied by the fuel delivery pump flows along the ring passage, the valve disk and the valve spring into the cylinder. The ball valve prevents the fuel from being able to flow back from the high pressure passage.
B. Producing high pressure: The piston is moved up by the rising eccentric shaft and the fuel is thus compressed. The valve disk shuts off the delivery volume to the fuel feed. Once the fuel pressure in the cylinder rises beyond the pressure which exists in the high pressure circuit, the ball valve opens and the fuel is pumped into the high pressure circuit.
C. Fuel Temperature Regulation: The ECM can Interrupt the fuel high pressure delivery of one of the pump elements in the particle load range in order to reduce the power required for driving the high pressure pump so as to reduce the fuel temperature. The pump element is switched off if the fuel temperature is excessively high (above 278°, 120 bar).