DAF 95XF. Manual - part 413

4

XE ENGINE FUEL SYSTEM

General

95

XF series

2-8

2.3

DESCRIPTION OF COMPONENTS

Hand pump with fuel coarse filter
A hand pump with fuel coarse filter is installed in
the fuel system.
When the fuel is drawn in by the fuel lift pump, it
flows to the suction side of the fuel lift pump via
the non-return valve (2) and through the fuel
coarse filter (1).

A hand pump (3) is installed to bleed the fuel
system.
To operate the hand pump, it must first be
released.
During the upstroke the volume above the piston
of the hand pump is reduced.
As a result, the non-return valve (2) is closed
and the fuel flows to the piston bottom along the
piston seal.

During the downward stroke the volume below
the piston of the hand pump is reduced.
The fuel is then forced to the fuel fine filter via
the fuel lift pump.
At the same time, fuel is drawn in at the piston
top via the non-return valve (2).
The hand pump must be re-tightened after it has
been used.

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4

95

XF series

General

XE ENGINE FUEL SYSTEM

2-9

Fuel lift pump
The fuel lift pump (1) is installed at the rear of
the pump housing and is driven by the camshaft
in the pump housing.
The fuel lift pump is designed as a gear pump.

There is a pressure-relief space (2) at the
bottom of the fuel lift pump.
This pressure-relief space prevents fuel from
penetrating the lubricating-oil system in the
event of leaks at sealing ring A and it prevents
lubricating oil from penetrating the fuel system in
the event of leaks at sealing ring B.
It also enables a visual inspection for any leaks.

A pressure-relief valve (3) has been installed in
the fuel lift pump to protect the low-pressure
area of the fuel system from too high a fuel lift
pump pressure due to the flow resistance being
too high.

Note:
When the fuel lift pump pressure is too high, the
fuel filter element may be damaged and/or leaks
may occur along the seals.

A non-return valve (4) has been installed in the
fuel lift pump to bleed the fuel system.
This non-return valve is opened when the hand
pump with the fuel coarse filter is operated.
As a result, a direct connection between the
supply and discharge sides of the fuel lift pump
is created.

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4

XE ENGINE FUEL SYSTEM

General

95

XF series

2-10

Pump unit
The valve (6) with back plate (8) and the pump
piston (14) are located at the top of the pump
unit.
These parts are lubricated by the fuel.
The roller (18) with rocker roller (16) and
spring (15) with spring retainer (17) are located
at the bottom of the pump unit.
These parts are lubricated by the engine
lubrication system.
The lower sealing ring of the pump unit
separates the fuel system from the engine
lubrication system.

A delivery valve (5) has been installed at the top
of the pump unit.
The delivery valve serves to prevent the
low-pressure area from being disturbed by the
pressure peaks from the injection line.

Using a magnetic valve (9) consisting of a
solenoid and valve (6) with back plate (8), the
injection timing and quantity of injected fuel are
controlled by the electronic control unit.

When the magnetic valve (9) is not activated,
the valve (6) is pressed against the valve
stop (4) by valve spring force.
This creates a very small opening between the
high-pressure area above the pump piston (14)
and the low-pressure area of the return bore (2).

The fuel flows to the fuel return bore (2) via the
fuel supply bore (11) and the fuel filter (10). As a
result, the high-pressure area above the pump
piston (14) is also completely filled with fuel.

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95

XF series

General

XE ENGINE FUEL SYSTEM

2-11

When the magnetic valve (9) is activated by the
electronic unit, the back plate (8) with valve (6)
will be attracted by the solenoid under the
influence of the magnetic field.
Valve (6) closes the connection between the
high-pressure and low-pressure areas, enabling
pressure to be built up above the pump
piston (14).
As a result, injection takes place.

Due to the high pressure in the high-pressure
area the valve (6) is not re-opened against the
magnetic force, because there is a state of
balance in the groove of valve (6).
This is because the areas to the left and right in
the groove of valve (6) are the same.

The time when valve (6) is closed depends on
the injection timing calculated by the electronic
unit.
The closure time of valve (6) and, consequently,
the quantity of injected fuel, is also calculated by
the electronic unit.

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