Final answer:
A dual air brake system consists of two independent air brake systems controlling the front and rear brakes, providing a fail-safe for large vehicles like buses and trucks.
Step-by-step explanation:
A dual air brake system is commonly found in larger vehicles, such as buses and trucks, specifically those requiring a commercial driver's license (CDL) to operate. This system consists of two separate air brake systems which control the front and back brakes independently. The purpose of the dual system is to provide a fail-safe in case one of the systems fails, ensuring that the vehicle can still be brought to a stop safely.
In simpler hydraulic brake systems, as discussed in Figure 14.18 regarding Pascal's principle, when the brake pedal is engaged, force is transmitted through a hydraulic fluid to apply pressure on the wheel cylinders. This pressure then causes the brakes to engage. Some more complex systems, particularly in larger vehicles, may have a motorized pump to assist in generating the necessary pressure in the braking system, which are referred to as power brakes. However, in a dual air brake system, air pressure is used instead of hydraulic fluid, and there are two independent systems for added safety.