SECTION 16: SUSPENSION
22
DOB 2490-2789 | X3-45 Commuter PA1605 Maintenance Manual (Section 16 revised April 2019)
8.2 EMERGENCY FILL VALVES
The vehicle is equipped with two air system fill
valves to supplement the air system when air
pressure is low and engine cannot be operated.
The rear valve
is located in engine
compartment and accessible from engine R.H.
side door (Figure 23).
FIGURE 23: REAR VALVE LOCATION
12211_1
CAUTION
No other point should be used to supply air
system. The maximum allowable air pressure
is 125 psi (860 kPa).
The front valve is located in the front service
compartment close to accessory air filter (Figure
24).
FIGURE 24: FRONT SERVICE COMPARTMENT
These two air valves are fitted with the same
valve stems as standard tires, and can be filled
by any standard external air supply line.
The rear valve will supply air for all systems
(brakes, suspension and accessories) while the
front valve will supply air for accessories only.
CAUTION
Air filled through these two points will pass
through the standard air filtering system
provided by Prevost. Do not fill air through any
other points.
9. FRONT KNEELING SYSTEM
The kneeling system is used to lower the front of
vehicle. This allows passengers to board the
vehicle with greater ease. The kneeling action is
achieved by exhausting air from the front air
springs (bellows). This system bypasses the
height control valve to provide a fast up and
down movement of the front suspension. Only
four seconds are required to lower vehicle from
normal level to the lowered position, and
approximately the same time to raise the vehicle
back to normal level. The quick response is
achieved by an auxiliary air tank installed beside
the secondary air reservoir (for exact position,
refer to Section 12,
“Brake and Air System”).
This tank provides sufficient air supply to the
kneeling system for some successive
operations.
The system is provided with two safety features;
first, a speed switch will enable the kneeling
system to work only at less than 5 mph (8 km/h).
Secondly, the parking brake is automatically
applied, and a limit switch will keep it applied as
long as the vehicle has not returned to a certain
height where the driver will be able to manually
remove the parking brake.
9.1 PRINCIPLE OF OPERATION
Refer to the air system schematic diagram.
DOWN (FRONT KNEELING):
Both the bellows control and bellows exhaust
solenoid valves are energized, so the air control
valves release air from front air springs. The
height control valve is bypassed to ensure no air
is forwarded to air springs while lowering the
front suspension.
9.2 MAINTENANCE
Since the kneeling action is issued from both the
air system and electrical system, refer to
Section: 12,
“Brake and Air System”
and Section
06,
“Electrical System”.
For diagnosis and understanding of the system,
refer to wiring diagrams, and to the appropriate
air system schematic
.
