Air-over-hydraulic brake systems operate using a combination of compressed air and hydraulic pressure, and the release of the air and hydraulic pressure engages the master cylinder. It then applies pressure to the valves, and the brake fluid is released. The brakes then exert friction on the tires, which stops them.Know More
Air-over-hydraulic brake systems contain an air-over-hydraulic power cylinder. This cylinder has both an air cylinder and a hydraulic cylinder inside, which work in tandem with each other. The air and hydraulic cylinders each contain a piston and common rod. The air cylinder's piston is a larger diameter than the hydraulic cylinder's piston. This results in greater hydraulic pressure being released during normal breaking. When the brake pedal is pressed, the valves are opened by the master cylinder, releasing the atmospheric pressure that builds up when the valves are closed. During hard braking, the master cylinder causes greater valve movement. This results in the valve releasing more air into the air-over-hydraulic power cylinder, allowing for faster braking.
Most modern vehicles have two-circuit brake systems, which are operated by the master cylinder. Each circuit controls two wheels. This increases safety because if one circuit fails, drivers can still brake as long as the other circuit remains operational.Learn more about Brakes
Drum brakes work by pressing brake shoes against the inside of a drum-shaped cylinder attached to the wheel of the vehicle. The friction produced by this contact slows the wheel, slowing down the vehicle. Drum brakes are most common on older vehicles. On newer vehicles, they are often attached to only the rear wheels, and more-efficient disc brakes slow the front wheels.Full Answer >
A disc brake uses a set of calipers to press braking pads against a disc attached to the wheel. The friction from this contact slows the wheel and, by extension, slows the vehicle. Most cars have disc brakes attached to the front wheels and older drum brakes on the rear, while some have disc brakes on all four wheels for maximum control.Full Answer >
Hydro-boost brakes work by applying hydraulic pressure from the power steering system to assist in braking. When the brakes are applied, hydraulic fluid flows from the power steering pump to increase braking effort, while fluid also flows from the hydro-boost system to the steering gear to assist in power steering.Full Answer >
Truck drivers and other professionals who are interested in procuring a commercial driver's license (CDL) can take air brakes practice tests at websites like Trucking Truth and the Crist CDL Training Center. Both online tests are free to use and score.Full Answer >