DAF CF65 Series Service Manual page 74

CE ENGINE FUEL SYSTEM
Description of components
During the downward stroke, the fuel is supplied
by the fuel lift pump via the suction valve (9) (see
illustration on left). During the delivery stroke
(illustration on right), the suction valve closes
under the load of the spring (8) and the fuel
pressure that has built up. The fuel leaves the
pump element via the delivery valve (10). The
compressed fuel from the three pump elements is
2 collected in the pump housing and leaves the
pump via a joint high-pressure connection.
Leaking fuel from the pump elements is
discharged via the return connection.
The fuel lift pump has over-capacity in relation to
the high-pressure pump. If there is only limited
fuel off-take on the rail, the fuel pump control
solenoid valve will be virtually closed. The over-
supplied fuel will cause an increase in pressure at
the inlet of the fuel pump control solenoid valve.
The pressure is limited by the circulation valve
(7). If the valve is open, the excess supplied fuel
will be returned to the suction side of the fuel lift
pump. A small amount of fuel is diverted via a
restriction to the shaft and the eccentric of the
high-pressure pump for lubrication.
When bleeding with the primer pump, any air
bubbles will be carried along by the fuel through
the low-pressure circuit. Fuel is forced inwards at
the connection (5). The fuel pump control
solenoid valve is opened fully without being
energised, so that the fuel can pass. The pump
elements create a high resistance to the fuel, so
that the fuel will escape via the lubricating
restriction in the pump. In this way the fuel, along
with any air bubbles, is discharged to the return
pipe.
3-2
9
8
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