Checking The Pressure Control Valve On The High-Pressure Rail - Bosch EPS 708 Repair Instructions

en 82 | EPS 708 | Trouble-shooting
9.2 Checking the pressure control valve
on the high-pressure rail
The task of the pressure control valves is to generate
and maintain the pressure required in the high-pressure
rail. All three pressure control valves are fitted in the
high-pressure rail and are connected in parallel.
Mode of operation:
Inside one pressure control valve is an armature which
is depressed by a spring. The armature presses a ball
into a sealing seat, thus sealing off the high-pressure
end from the low-pressure end. The spring force may
also be assisted by a solenoid acting on the armature.
If the pressure control valves are not actuated, i.e. the
solenoid remains de-energized, the force of the high
pressure in the rail acts in opposition to the spring
force, with the result that the pressure control valves
remain open to a greater or lesser extent depending on
the pump delivery rate. If the pressure in the rail is to
be increased, the magnetic force must be built up in
addition to the spring force. The pressure control valves
are actuated (energized) and thus closed until equilib-
rium is established between the force of the high pres-
sure on one side and the magnetic and spring force on
the other. They then remain in open position and keep
the pressure in the rail at a constant level.
Electrical check:
1. Detach the connecting cable from the pressure
control valve.
2. Connect a digital multimeter to the two blade termi-
nals of the pressure control valve and measure the
internal resistance.
i
Do not check the internal resistance when the
pressure control valve is warm. Allow the pressure
control valve to cool to room temperature.
Internal resistance 4.2 ohms
Tolerance ± 1 ohm
In the event of a fault:
Replace the pressure control valve.
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Hydraulic check:
The following three fault situations may occur:
R
Somewhat increased rail pressure with non-ener-
gized pressure control valves during the
pump test.
R
The test pressure required during measurement
cannot be attained although the high-pressure pump
is intact.
R
Calibrating oil emerges from the pressure control
valve during the test.
Fault situation 1
Somewhat increased rail pressure with non-energized
rail pressure control valves during the pump test.
Cause:
Clogged pressure control valves
Remedy:
1. Remove the pressure control valve
(see section 6.37).
2. Clean the fine strainer (1). To do so, immerse the
pressure control valve in the ultrasonic bath until
the entire strainer is completely covered by the fluid
in the bath.
1
458797-16_2
Fig. 150: Pressure control valve with strainer
!
Note the tightening torque when installing the pres-
sure control valve.
!
Always use a new sealing cone when fitting a pressu-
re control valve in the high-pressure rail.
3. Screw the pressure control valve back into the high-
pressure rail and tighten.
Robert Bosch GmbH