Iveco Stralis AT/AD. Manual — part 257
Figure 47
73915
The duplex control valve generates electric and pneumatic
signals needed to control the brake system.
Under normal circumstances the component works with the
electric circuit only, while the pneumatic circuit is activated
when the electric circuit is out of service.
Figure 48
73914
It takes air from the tanks and distributes it to the braking
elements.
It is self-limited, that is it limits the delivery of air at a set
maximum pressure, the outcome of which is a greater
availability of energy and a constant maximum braking
pressure irrespective of the pressure swings in the tanks.
Vehicles fitted out as trucks have duplex control valves
mounted with the function of correcting the braking force of
the operator elements of the front axle according to the
correction made by the load apportioning valve.
793110
Duplex control valve
(vehicles without EBS)
Duplex control valve with electric transmitter
(vehicles with EBS)
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AIR SYSTEM - BRAKES
Base - January 2003
TROUBLE
POSSIBLE CAUSE
REMEDY
Air leaks from the outlet
hole
Leaks from the outlet pipes due to wear of the
gaskets
Overhaul the device, replacing the worn parts.
Control valve with abnormal
self-limitation
Self-limitation higher or lower than as required Set the device using the specific screw.
Vibration during braking
Spring wear
Overhaul the device, replacing the worn parts.
Air leakage due to piston gaskets in the two
sections
Overhaul the device, replacing the worn parts.
Abnormal operation of the
brake light switch
It fails to close the electric circuit
Replace the switch.
It fails to open the electric circuit
Replace the switch.
Figure 49
The device allows to speed up compressed air release from
combined cylinder section, so cutting down braking time.
793331
Relay valve (vehicles without EBS)
Proportional relay valve for front axle
(vehicles with EBS)
73916
This component modulates the pressure to the cylinders of
the front axle.
It comprises a proportional solenoid valve, a pneumatic relay
and a pressure sensor.
Figure 50
36743
2
1
4
52871
The version for the "Graduated" pipe is equipped with a red
cover and a safety projection (1), while the version for the
"Automatic" pipe is equipped with a yellow cover and a side
safety projection (2). The safety projections are used to avoid
coupling errors.
Figure 51
798510
Coupling heads
AIR SYSTEM - BRAKES
87
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Fault Diagnosis (vehicles without EBS)
TROUBLE
POSSIBLE CAUSE
REMEDY
Air leaks from the outlet
with the control pipe
exhausting
Leakage from the introduction or from the seals. Overhaul the device, replacing any defective parts.
Air leaks from the outlet
with supply in the control
pipe
Leakage from the piston gasket or from the exĆ
haust valve.
Overhaul the device, replacing any defective parts.
Figure 52
Figure 53
73917
Its task is to modulate the pressure to the brake cylinders of
the rear axle.
It has an electronic control unit that controls the rear speed
sensors and the wear of the brake linings of the rear axle.
This electronic control unit communicates over the CAN
network with the E.B.S. control unit.
60934
A = Diagram of rear axle electro-pneumatic modulator (for
4x2 and 6x2 truck versions).
B = Diagram of rear axle electro-pneumatic modulator (for
tractor versions).
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88
AIR SYSTEM - BRAKES
Base - January 2003
Fault Diagnosis
TROUBLE
POSSIBLE CAUSE
REMEDY
Air leaks from the outlet
with the control valve lever
in the brake release position
Piston, outlet valve, seals worn or defective.
Clean thoroughly, check the rubber parts and the seats are
sound.
Air leaks from the outlet
with the control valve lever
in the emergency or parking
braking position
Piston and associated seal defective or deterio-
rated.
Clean thoroughly, check the parts and overhaul the device,
replacing the defective parts.
Air leaks from the cover
of the control valve lever
Plate, gasket, seals worn.
Clean the parts thoroughly, check the surfaces of the
gasket and seals, check the integrity of the rubber parts and
the relevant seats. Overhaul the device, replacing the de-
fective or worn parts, and restore the mating faces if
necessary.
Control valve lever hard
to turn
Interference inside the control valve.
Clean thoroughly and check all the component parts.
Overhaul the device, replacing defective parts. During as-
sembly, grease all the sliding parts in moderation.
If you find any defects or wear such as to jeopardize oper-
ation, replace the complete device.
On vehicles with an ABS/EBL system, this component has the
task of sending the rear axle braking control relay valve the
control pressure from the duplex control valve (normal
working function). With the ASR function active, this
component will send the activation pressure from the ASR
solenoid valve. In addition, it is used on 6x2 vehicles to
transmit the pressure in the air springs, to the added axle
braking control relay valve, according to the load. On vehicles
with the EBS, it has the task of sending the pressure of the
front axle braking relay valves according to the load bearing
on the air springs of the added axle.
73918
35805
73919
33986
Figure 54
This component has the task of ensuring the rear axles brake
even if the EBS is entirely out of service.
ABS-EBS solenoid valve
This component modulates the air pressure in the brake
circuits. When the electronic control unit detects a tendency
for one of the wheels to lock, the valve shuts off the supply
to the brake cylinder, preventing the wheel from locking.
Redundancy valve (for 4x2 and 6x2 trucks)
Dual stop valve
Figure 55
793332
Triple servo control valve
(vehicles without EBS)
22
11
42
41
43
12
Figure 56
Figure 57
The device controlled by the two independent circuits of the
duplex control valve and the spring brake circuit of the tractor
controls trailer braking.
It incorporates a device making it possible to brake the trailer
even in the event of control pipe failure.
AIR SYSTEM - BRAKES
89
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