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Most heavy-duty vehicles use dual air brake systems for . A dual air brake system has separate air brake systems, which use a single set of brake controls. Each system has its own tanks, hoses, lines, etc. One system typically operates the regular brakes on the rear axle or axles. The other system operates the regular brakes on the axle (and possibly one rear axle). Both systems supply to the trailer (if there is one). The first system is called the “” system. The other is called the “” system. (See Figure 5.4.)
Before driving a vehicle with a dual air system, allow for the air compressor to build up a minimum of psi pressure in both the primary and secondary systems. Watch the primary and secondary air pressure (or needles, if the system has two needles in one gauge). Pay attention to the air pressure warning light and buzzer. The warning light and buzzer should shut off when air pressure in both systems to a value set by the manufacturer. This value must be than psi.
The warning light and buzzer should come on before the air pressure drops psi in either system. If this happens while driving, you should right away and safely the vehicle. If one air system is very low on pressure, either the front or the rear brakes will not be operating fully. This means it will take you to stop. Bring the vehicle to a safe stop and have the air brakes system fixed.
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