Commercial Driving Air Brakes

Question 1

What is the purpose of the air compressor in an air brake system?

Accepted Answer

To pump air into storage tanks to provide the energy for braking

Answer

The air compressor pumps air into storage tanks, building the air pressure that is used as the force to apply the brakes when the driver presses the brake pedal.

Question 2

At what PSI should the low air pressure warning activate?

Accepted Answer

60 PSI

Answer

The low air pressure warning signal must activate before air pressure drops below 60 PSI, alerting the driver that the air brake system is losing pressure.

Question 3

What happens when the air pressure drops too low in the brake system?

Accepted Answer

The spring brakes automatically apply, bringing the vehicle to a stop

Answer

Spring brakes are held off by air pressure during normal operation. When pressure drops below about 20-45 PSI, the springs apply the brakes automatically as a safety measure.

Question 4

What is the purpose of the air brake system's governor?

Accepted Answer

To control the air compressor by starting it when pressure drops and stopping it when pressure reaches the maximum

Answer

The governor controls the air compressor, engaging it when tank pressure drops to about 100 PSI and disengaging it when pressure reaches about 125 PSI.

Question 5

What is 'brake lag' in air brake systems?

Accepted Answer

The delay between pressing the brake pedal and the brakes actually applying, typically about 0.5 seconds

Answer

Air brake lag is the time it takes for air to travel through the lines to the brake chambers after the pedal is pressed. This adds to stopping distance compared to hydraulic brakes.

Commercial Driving Practice Test

Commercial Driving Practice Test

Commercial Driving Air Brakes