What are Air Brakes and How do they Work

Now a mainstay of heavy-duty road vehicles, air brakes can stop mighty loads quickly and safely!

Air brakes were originally designed to stop trains, however today – due to reduction in their component size and cost – they are equipped to many heavy-duty road vehicles too.

Air brakes work differently to those on standard road vehicles, creating a system where the brakes are always on when in a neutral state. As such, rather than using compressed air to activate a vehicle’s brakes, it is used instead to deactivate them. This is a design feature very much aimed to maximize safety, as if the air brake system fails (ie the system depressurises), then the vehicle will automatically stop rather than suddenly have no brakes at all.

A compressed air brake array is divided into a supply system and control system. The former draws air into a compressor from the surrounding environment, filters it for impurities, stores it in a reservoir and then distributes it to the control system. The latter consists of a brake circuit and trailer brake circuit, which themselves are split into front and rearwheel circuits. These individual circuits receive air from the supply system’s reservoir.

As such, the brakes of heavy-duty road vehicles are essentially engaged on a permanent basis, requiring the driver to disengage them to accelerate – ie the brake circuits’ release valves are opened, dropping the contained air pressure and releasing the physical brake components (ie the callipers and brake pads) from the wheels, leaving the vehicle free to move.

Air Brake parts

Drive – The air compressor is driven off the truck’s engine either by crankshaft pulley via a belt or directly off its timing bare.

Distribution – Filtered air is stored in a reservoir from which it is distributed via a four-way protection valve into the front/rear brake circuits.

Filter – Compressed air is drawn in and then routed through a cooling coil and air dryer to remove moisture and any impurities in the oil.