Alabama Air Brakes Class B CDL Test 2

In an air brake system, the air compressor governor controls when the air compressor pumps air into the air storage tanks.

Before driving a vehicle with a dual air brake system, you should wait for the air compressor to build up at least 100 psi in both the primary and secondary systems.

It is important to know the maximum air loss rate that is safe for your specific vehicle. A single vehicle with air brakes should have a leakage rate no higher than 3 psi in a minute during an applied leakage test.

The air that enters air storage tanks in an air brake system usually contains a certain amount of water and compressor oil. Because accumulations of these materials can damage the braking system, tanks are equipped with drains to allow their removal.

After the brake pedal is pushed down in a vehicle with air brakes, it takes a half-second or more for air to flow through the lines and make the brakes work. This contrasts with hydraulic brakes used in cars and light and medium trucks, which instantly begin working when the pedal is pushed.

Most heavy-duty vehicles use dual air brake systems, in which there are two separate braking systems operated by a single set of controls. Each system operates the brakes on different axles.

In a vehicle with air brakes, never push the brake pedal down when the spring brakes are activated. The combined force of the springs and the pressure of the air brakes could damage the brakes.

An air compressor governor will stop the compressor from pumping air once the air tanks are at an air pressure level of 125 psi. This air pressure level is referred to as the “cut-out” level.

Air brakes consists of three separate braking systems: the service brake system, the parking brake system, and the emergency brake system. The service brake system applies and releases the brakes when you use the brake pedal while driving normally.

When driving a vehicle with air brakes, if the low air pressure warning light comes on, it is important for you to stop and safely park your vehicle as soon as possible. There may be a leak in the system. Controlled braking will remain possible only as long as there is enough air left in the tanks.

In an air brake system, a low air pressure warning signal must come on if air pressure in the tanks falls below 60 psi. This warning signal may come in the form of a light, a buzzer, or a wig wag.

Compressed air in an air brake system usually contains a certain amount of water and compressor oil. The water and oil can damage the brakes if left to accumulate in the system. Manually operated air tank drains must be opened daily to remove this build-up.

The function of an Anti-Lock Braking System (ABS) is to prevent the vehicle’s wheels from locking up from hard brake application.

Drum brakes are attached to the wheels and located on the axles of a vehicle. The braking mechanisms that cause the vehicle to stop can be found inside of a drum brake.

Truck tractors with air brakes built on or after March 1, 1997 must be equipped with Anti-Lock Braking Systems (ABS).

Before beginning a trip, it is important to check the brake drums during your walk-around inspection. It is unsafe to drive if any brake drum has a crack more than one half of the width of the friction area.

While driving downhill, you should hold down the brake pedal until your vehicle reaches a speed 5 mph below your safe speed, then release the brake pedal. Repeat this process.