Blue Bird Coachworks 450 LXi, Owner'S Manual

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450 LXi Owner Manual 4-13 Air Pressure System
Rev. “C”
~ 4-13-1 ~
4-13 Air Pressure System
4-13.1 Description and Operation
An engine-driven compressor supplies the air pressure system on your coach. It provides pneumatic power for brakes,
suspension, and numerous accessories. This complex, but effi cient system is not intended to be totally leak free. After
overnight parking, you may notice a signifi cant loss of pressure on the air pressure front/rear gauge, or in systems connected
to auxiliary air. This condition is normal, and in fact, our air leakage tolerance is tighter than most manufacturers within the
heavy-duty equipment industry. Once the engine is running, the engine-driven compressor will quickly build up the system to
the correct pressure.
4-13.1.1 Air Brakes
Your coach is equipped with dual service air brake systems for front and rear, with integral fail/safe operation; and manual/
automatic rear spring (parking) brakes. The service brakes are completely independent systems, each including a reservoir
and separate distribution lines and valves. The reservoirs are pressurized from a single compressor. Both service brake
systems are brought into operation each time the brake treadle is depressed to slow or stop the coach. Reservoir pressure
for each service brake system is monitored by a respective pressure gauge on the front panel; system failure(s) are indicated
by low-pressure readings, illumination of the Low Air failure lamp and sounding of a buzzer.
4-13.1.2 Operation
When the coach is parked, and the engine is off, the rear spring brake will normally be set by operating the parking brake.
The spring brakes cannot be fully released until the air pressure is above 65 psi. These brakes are in the released position
when the control is pushed in. In the event that there is a loss of air pressure, the spring brakes will set automatically at the
brake-applied position, and will not release until the air reserve has again built up to required value. Consequently, there will
be a normal delay, after the coach is fi rst started, while the compressor builds up pressure before the brakes can be released
and the coach driven. When the brake treadle is depressed to slow or stop the coach, reservoir air is applied simultaneously
to both front and rear service brakes to effect the braking action. The spring brakes are held in a released position by the air
pressure supplied from the associated reservoir tank.
4-13.1.3 Brake Failures
To compensate for normal lining wear, each brake system is individually self-adjusting.
Fail/safe features provide protection against brake system failures. If the front brakes fail, operating the brake treadle still
activates the rear service brakes to provide stopping capability.
If a failure occurs in the rear, the front service brakes and rear spring brakes provide braking action.
In the unlikely event of a failure where both service-braking systems are disabled, the rear spring brakes will apply
automatically and bring the vehicle to a stop. As a safety factory, the coach should not be driven until any type of brake failure
is corrected.
4-13.1.4 Anti-Lock Brakes
In addition to the above, a four-channel anti-lock brake system for the steer and drive axles are installed. In the event one
of the wheels begins to lock up under severe braking conditions, the anti-lock system will detect this situation and gradually
remove air pressure from the brake chamber until the wheel begins to turn. This will help assure smooth braking action and
minimize wheel lockup.
4-13.1.5 Air Suspension System
Air suspension bags cushion the front and rear axles. Ride height is automatically maintained by height control valves.
Dumping these air bags when the vehicle is parked allows the rubber bumpers to come together and eliminate vehicle
springiness. A switch, located on the lower left side of the LOWER DASH PANEL, controls dumping and fi lling of air bags. The
SUSP. DUMP switch controls the front and rear suspension.
CAUTION!!
Do not attempt to drive the coach until system pressure is above 90 psi.
NOTE: With the front brake system service reservoir fully charged, enough air pressure is available
to provide for four full releases of the rear spring brakes. This will allow the coach to be brought to a safe
position until repairs can be made.