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Item Part Number Description A - High-pressure fuel to fuel rail B - Fuel return C - Fuel supply 1 - High-pressure chamber outlet valve 2 - High-pressure chamber inlet valve 3 - Pump plunger 4 - VCV return spring 5 - VCV 6 - Admission pressure control valve (pump internal pressure) 7 - Transfer pump 8 - Fuel inlet 9 - Fuel filter 10 - Eccentric cam ring 11 - Eccentric cam 12 - Drive shaft 13 - Fuel tank 14 - Fuel overflow valve The transfer pump draws fuel out of the fuel tank through the fuel inlet (8). The pump internal pressure is adjusted through the admission-pressure control valve (6), ensuring that sufficient lubrication and cooling are always provided for the high-pressure pump components. The excess fuel is transferred to the inlet side of the transfer pump (7) through the admission-pressure control valve, with a portion of the fuel being transferred to the VCV (5) from the transfer pump. The fuel quantity delivered to the high-pressure chambers is determined by the opening cross-section of the VCV. The small restriction bore in the fuel overflow valve (14) provides for automatic bleeding of the high-pressure pump. The entire low-pressure system is designed to allow a defined quantity of fuel to flow back into the fuel tank through the overflow pressure regulator tube, which assists cooling of the high-pressure pump. A total of 2 high-pressure chambers (1 and 2), each with a pump plunger (3), are used for high-pressure generation. The drive for the pump plungers is through an eccentric cam (11), which is in turn driven by the drive shaft (12). The high-pressure pump permanently generates the high system pressure for the fuel rail. Principle of High-Pressure Generation |