Fuel Prefilter - Mercedes-Benz OM 471 Introduction Into Service Manual

System components
The fuel filter module (1) consists of the following components:
Fuel prefilter (2) through which large dirt particles are
f
removed from the fuel.
f Water separator (3) with water collector through which the
water in the fuel is separated.
f Fuel filter (4) through which small dirt particles are removed
from the fuel.
f The fuel collection chamber (5) via which the fuel is collected
from all fuel return lines and led into either the fuel prefilter
(2) via a bypass or directly into the fuel tank.
Function

Fuel prefilter

2 Fuel prefilter
16 Fuel inlet
17 Filter element
18 Elastomer ball
19 Wastegate
20 Fuel outlet
D Not cleaned fuel
E Precleaned fuel
Not cleaned fuel (D) passes over the fuel inlet (16) into the fuel
prefilter (2).
The suctioned up fuel presses the elastomer ball (18) off its seat
and flows through the filter insert (17) from inside to out. The
larger dirt particles remain in the filter insert (17) and the
precleaned fuel (E) flows via the fuel outlet (20) to the fuel pump.
The elastomer ball (18) has the task of preventing the intake duct
from running dry with the fuel prefilter (2) open.
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The hand>operated delivery pump (6) with the aid of which
f
the fuel system can be vented, for example after replacing a
fuel filter insert.
f The filling valve (7) with the aid of which the fuel system can
also be vented, for example after replacing a fuel filter
insert.
f Shutoff valves (9) which prevent fuel escaping when
disassembling the fuel lines between the fuel tank and the
fuel filter module (1).
If the fuel prefilter (2) is fouled and the fuel flow rate is blocked in
the process then the fuel is suctioned over the wastegate (19).
When removing the filter insert clipped on the cover (17) a drain
bore to the fuel collector (5) is released so the fuel can flow out of
the fuel prefilter housing.
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