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D R I V E R S H A N D B O O K
About Air Brakes
Blue Bird air brake system uses compressed air pressure to operate drum or disc 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.
A motor driven air compressor maintains normal operating pressure 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 moisture, 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. During normal operation, the compressor cycles
on and off based on operating pressure. As this occurs, the air dryer occasionally expels a blast of air (chuff) which can be heard by the
driver. This is a normal “backflush” behavior of the air dryer.
Summary of Contents for Vision 2021
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