SECTION 12: BRAKE AND AIR SYSTEM
8
PA1621 Maintenance Manual All Series | January 2017
2. AIR SYSTEM
The basic air system consists of an air
compressor, reservoirs, valves, filters and
interconnecting lines and hoses. It provides a
means for breaking, operating controls and
accessories and suspension (refer to Section
16, "Suspension", for complete information on
suspension description and maintenance). An
air system schematic diagram is annexed in the
technical publications box provided with the
vehicle for better understanding of the system.
3. BRAKES
This vehicle uses both the service brake and
emergency/parking brake. The service brake air
system is divided into two independent circuits
to isolate front brakes from rear brakes, thus
providing safe braking in the event that one
circuit fails. Front axle brakes operate from the
secondary air system, while brakes on both the
drive axle and tag axle operate from the primary
air system.
NOTE
The tag axle service brake operates only
when the axle is in normal ride position
(loaded and down).
Furthermore, the brake application or release,
which is speed up by pneumatic relay valves (R-
14), will start with the rear axles and will be
followed by the front axle, thus providing uniform
braking on a slippery road. The vehicle is also
equipped with an Anti-Lock Braking System
(ABS), which is detailed later in this section.
The drive is provided with spring-loaded
emergency/parking brakes, which are applied
automatically whenever the control valve supply
pressure drops below 60 psi (413 kPa). The
optional emergency/parking brake overrule
system allows the driver to release spring
brakes, and to move the vehicle to a safe
parking place, such as in the case of a self-
application of these brakes due to a drop in air
pressure.
4. AIR RESERVOIRS
The air coming from the air dryer is first
forwarded to the wet air tank, then to the primary
(for the primary brake system), secondary (for
the secondary brake system), and accessory
(for the pneumatic accessories) air tanks (Figure
1 and Figure 2).
Additional air reservoirs may be installed on the
vehicle: the kneeling air tank, emergency/
parking brake overrule air tank and I-Shift
transmission air tanks.
4.1 MAINTENANCE
Ensure that both the accessories and the wet air
tanks are purged during pre-starting inspection.
In addition, it is good practice to purge these
following the information below.
MAINTENANCE
Air tanks
A recommended purge using the bottom drain
valve should be done at the intervals specified
by the Lubrication And Servicing Schedule in
Section 24: LUBRICATION & SERVICING.
It is important to empty the tanks completely to
ensure that water and moisture are totally
evacuated from the tank.
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