Blue Bird VISION 2011 Driver'S Handbook Manual Download

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r o u t i n e

o p e r a t i o n

About Air Brakes

The optional air brakes system on the Blue Bird

Vision

uses compressed air pressure

to operate drum brakes. The system is divided into two separate circuits; one for rear
brakes (primary) and one for front (secondary). The two circuits have their own air
supplies. However, the system is designed so that if pressure in either circuit drops to
certain levels, the other system can supplement the pressure.

An air compressor mounted on the engine operates whenever the engine is run-

ning and maintains a normal operating pressure range within the storage tanks. The
bus cannot be driven until air pressure is sufficient for normal operation. Therefore, if
the bus has been parked for an extend period, or if the tanks have been drained, as in
normal maintenance procedure to expel built-up moisture, it is normal for additional
time to be required for the air system to fully charge.

As air is compressed, moisture vapor tends to condense inside the storage tanks.

The tanks are equipped with bleeder valves to allow removal of this built-up mois-
ture, and should be used daily, usually when the bus is parked for the night. Some
buses are equipped with an air dryer to assist collection and expulsion of the excess
moisture during operation. The storage tank is mounted under the bus, outboard the
frame rail on the driver’s side, and on buses equipped with an air dryer, the dryer is
mounted inboard of the frame rails just forward of the storage tank. During normal
operation, the compressor cycles between its load mode and unload mode. As this
occurs, the air dryer occasionally expells a blast of air (chuff) which can be heard by
the driver. This is a normal “backflush” behavior of the air dryer.

Parking Brakes (With Air Brakes)

On Blue Bird

Vision

buses equipped with air brakes, the parking brake function is

provided not by the air pressure, but by coil springs incorporated within the rear
wheel brake actuation chambers. When the parking brake valve on the dash is pulled
outward, air pressure is vented from the rear brake actuators, allowing the springs to
engage the rear brakes and locking the rear wheels. When the parking brake valve
is pushed in, it allows the air pressure in the rear brake actuators to overcome the
spring pressure, thereby releasing the rear spring brakes.

Therefore, although the parking brake control is an air valve, it is not air pressure

which applies the parking brake, but the absense of it. The parking brake is applied
by mechanical springs which are released (caged) when the air system pressure is
sufficient for normal brakes operation. Pushing in the parking brake valve to release
the parking brake does not release air pressure, it applies it to cage the spring brakes.
This is why the parking brake button automatically “pops out” if you try to release the
parking brake before sufficient air pressure has built up.

If for any reason the air reserve in both primary and secondary circuits brake

drops below a safe minimum, the spring brakes automatically engage and lock the
rear wheels. If this occurs enroute, the Driver should call for professional service assis-
tance. Provisions are made for a qualified service technician to mechanically release
the spring brakes to allow the bus to be towed for repair.

Pull to apply parking brakes. Push to release.

The parking brake valve does not apply air brakes. It applies
air to release the mechanical spring brakes.

The park brake valve cannot release the spring brakes until
sufficent air is in the system for normal service air brakes
opeartion. If it is pushed in before system pressure is present,
it will automatically “pop out.”