Common Rail Fuel System Operation LP HP Common Rail Limiter Safety Valve 19.6 KPSI Limiting Safety Valve 1350 Bar High Pressure Pump Flow Limiter LT DDEC IV ECM DDEC IV ECM 6.8 Bar Fuel filter Housing 2.0 Bar 1.7 Bar Injectors .1 Bar Fuel Tank H. Pr Line L. Pr Line Fuel filters Pro 40 Fig. 5 The Common Rail Fuel System used on the Series 4000 is a two-stage fuel distribution system. Gear driven fuel pumps maintain constant fuel supply pressure. This pressure is supplied to the common rails then to all injectors. Constant high-pressure is available regardless of crankshaft position or engine speed.
The first stage is the fuel transfer side which brings fuel from the fuel tank, through the filters, and provides low-pressure fuel supply of 65 PSI at idle to 85 PSI at full load to the second stage high pressure system. Additionally, low-pressure fuel is sent to the ECM Cold Plates to protect the ECM's from excessive heat (Refer to page 63). An OEM supplied fuel cooler should be incorporated in the fuel system to assist the cooling function for the ECM’s. Additionally, low-pressure fuel is used for cooling and lubrication in the high-pressure fuel pump.
However, unlike other fuel systems, fuel temperature has no affects on engine power or performance due to the extremely high fuel operating pressure, which prevents the fuel from boiling and vaporizing. The high-pressure system receives the low-pressure fuel at the control regulator and further pressurizes it in the high-pressure pump from (8.3 KPSI at idle to 17.4 KPSI) for non-low flow injectors and (7.25KPSI at idle to 13.1KPSI) for low flow injectors at maximum load conditions to the high-pressure rails. (Refer to page 17). Fuel pressure at Full No-Load averages about 11.4 KPSI.
A 19.6 KPSI safety-relief valve on the A-bank rail protects the fuel system components from damage due to excessive pressure. Page 5