Footbrake Valve, Component Description
Footbrake Valve, Component Description
Footbrake Valve, Component Description
00 29/12/2020
Chassis ID Path
5631/Description, Design and function//Footbrake valve, component description
Model Identity
139584907
5 Air exhaust
Description
Copyright to this documentation belongs to the Volvo Group. No reproduction, copying, change, amendment or other similar disposal is entitled without prior written consent by
the Volvo Group
The information contained herein is current at the time of its original distribution, but is subject to change. The reader is advised that printed copies are uncontrolled.
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IMPACT 4.04.00 29/12/2020
The purpose of the footbrake valve/modulator is to control the service brakes. It is located at the front
of the cab and is connected to the footbrake pedal. The footbrake valve consists of a two-circuit
pneumatic valve where the circuits are independent of each other.
Note
WARNING
It is not permissible to either open or repair the footbrake valve.
Pneumatic part
The pneumatic part consists of a two-circuit pneumatic valve where the circuits are independent of
each other. The two circuits have separate inputs (port 11 and port 12) and outputs (port 21 and port
22).
The output from port 21 supplies:
● The front brake circuit
Compressed air is always available at the circuit inputs (port 11 and port 12). When the driver
presses the brake pedal, compressed air is supplied to both circuits separately. The pressure applied
at the brakes is proportional to the brake pedal stroke.
On an unloaded truck in EBS (Electronically controlled Brake System) back-up mode, the pressure in
the rear circuit starts lower than in the front circuit to avoid over braking on the rear axle. The
pressure difference decreases with higher pressure and at full pressure they are equal.
In working mode, the brake pressure from the modulators is controlled by the electric signal and in
back-up mode it is controlled by the pneumatic signals. In order to avoid excessive brake pressure in
back-up mode, the APM (Air Production Modulator) limits the system pressure.
Electronic part
Copyright to this documentation belongs to the Volvo Group. No reproduction, copying, change, amendment or other similar disposal is entitled without prior written consent by
the Volvo Group
The information contained herein is current at the time of its original distribution, but is subject to change. The reader is advised that printed copies are uncontrolled.
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IMPACT 4.04.00 29/12/2020
The brake demand sensor is an electronic unit which monitors the driver’s request for speed
reduction through the stroke of the footbrake pedal. The brake demand sensor is electrically
connected to the EBS. The wake-up switch is normally open, but closes at the start of braking. This is
used to activate the EBS if the ignition is switched off, in case electrical braking should be required in
that situation.
The sensor sends information to the EBS regarding how hard the brake pedal is pressed and the
speed of the motion. The information is processed in the EBS to provide the brake pressure needed
for the towing and the towed vehicles. If the electrical control fails, the pneumatic circuit takes over
(back-up). When the driver presses the footbrake pedal, a push rod activates the brake demand
sensor; the inductive sensors send signals to the EBS, which calculates the requested speed
reduction. The signal sent from the EBS is proportional to the brake pedal stroke.
Copyright to this documentation belongs to the Volvo Group. No reproduction, copying, change, amendment or other similar disposal is entitled without prior written consent by
the Volvo Group
The information contained herein is current at the time of its original distribution, but is subject to change. The reader is advised that printed copies are uncontrolled.
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IMPACT 4.04.00 29/12/2020
11 Air inlet
12 Air inlet
21 Air outlet
22 Air outlet
3 Air exhaust
Related information
For more information on the electrical architecture, refer to:
Wiring diagram
➠ Vehicle electronics overview, system description
Related function
➠ Service braking, system description
Related systems
➠ Air supply, system description
➠ Service braking, system description
Related components
➠ Air valve, component description
➠ APM, component description
➠ Compressor, component description
➠ Modulators, component description
RCIOM, component description ➠ RCIOM, component description
➠ Relay valve, component description
➠ Trailer brake control valve, component description
Copyright to this documentation belongs to the Volvo Group. No reproduction, copying, change, amendment or other similar disposal is entitled without prior written consent by
the Volvo Group
The information contained herein is current at the time of its original distribution, but is subject to change. The reader is advised that printed copies are uncontrolled.
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IMPACT 4.04.00 29/12/2020
Copyright to this documentation belongs to the Volvo Group. No reproduction, copying, change, amendment or other similar disposal is entitled without prior written consent by
the Volvo Group
The information contained herein is current at the time of its original distribution, but is subject to change. The reader is advised that printed copies are uncontrolled.
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