Mercedes-Benz OM 471 Introduction Into Service Manual page 102

The remaining fuel is led away via the 2>stage valve (19). The first
stage of the 2>stage valve (19) opens at around 2 bar and provides
the lubrication of the camshaft plain bearings in the fuel system
high pressure pump (5).
The second stage opens at around 4.5 bar and regulates the
system pressure in the thrust side fuel feed (B) to a range between
4.5 and 6.5 bar by leading excess fuel from the 2>stage valve (35)
to the fuel collection chamber (13) via the fuel return line.
If the maximum rail pressure is exceeded, the pressure limiting
valve (20) opens and the excess fuel is led from the pressure
limiting valve (38) to the fuel collection chamber (13) via the fuel
return line.
The fuel that is required for hydraulic pressure boosting is
collected in a bore in the cylinder head and led to the fuel cooler
(10) via the fuel return line of the pressure booster (36), from
where it is delivered to the fuel pump (3).
The fuel cooler (10) serves to cool down the fuel, which is at a
temperature of about
120 ∞C.
Component description for fuel
temperature sensor
Diesel fuel metering device, component
description
Fuel filter module pressure sensor,
component description
Component description for quantity
control valve
Pressure limiting valve, component
description
Component description for fuel pump
Component description for fuel cooler
Component description for fuel filter
module
Nozzle unit for DPF regeneration,
component description
i Introduction of engine OM 471 and exhaust aftertreatment > 09/2011 >
– This printout will not be recorded by the update service. Status: 09 / 2011 –
The excess fuel from the nozzle needle valves is also gathered in a
bore in the cylinder head and led into the fuel collection chamber
(13) via the fuel return for the nozzle needle valves (37) and the
check valve (12).
The check valve (12) in the fuel return of the nozzle needle valves
(37) has the task of achieving the required back pressure of about
2 bar while the engine is running and therefore ensuring that the
fuel injectors work perfectly.
Part of the returned fuel is taken from the fuel collection chamber
(13) and led back into the fuel low pressure circuit via the fuel
return bypass (42) just upstream of the fuel prefilter (7).
The fuel quantity is determined by the throttle (11) and the check
valve (12) in the fuel return bypass (42), which reduces the suction
load on the fuel pump (3). The remaining fuel from the fuel
collection chamber (13) is led back to the fuel tank (1).
The shutoff valve in the fuel return line (16) prevents fuel from
escaping when the fuel line between the fuel tank (1) and the fuel
filter module (2) is disconnected.
B602
B625, B626, Y628, Y629
B638
Y642
Functions
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