CDL Air Brakes Practice Test 4

Question 1

Which device allows you to remove oil and water from the air brake systems?

Accepted Answer

Air tank drain

Answer

Compressed air naturally contains moisture, and over time, oil from the compressor can also enter the system. These contaminants collect in the bottom of the air tanks. Air tank drains, located at the bottom of each tank, allow drivers to manually or automatically remove this accumulated water and oil, preventing corrosion, freezing, and damage to other air brake components.

Question 2

What does it mean when the safety valve opens and releases air?

Accepted Answer

A and C

Answer

The safety valve is designed to protect the air brake system from excessive pressure, typically opening and releasing air if the pressure in the tanks exceeds 150 psi. If this valve frequently opens, it indicates a malfunction in the air compressor governor, which should be controlling the pressure within the normal range. Therefore, both excessive pressure and a system malfunction are indicated, requiring immediate inspection by a mechanic.

Question 3

What should the air pressure loss be in a single vehicle with a fully charged air system?

Accepted Answer

Less than 2 psi per minute

Answer

During a static air brake test, a single vehicle with a fully charged air system should not lose more than 2 psi in one minute after the initial pressure drop from applying the brakes. This low rate of pressure loss indicates that the air brake system is relatively free of leaks. Exceeding this limit suggests a problem that needs to be addressed for safe vehicle operation.

Question 4

In a combination vehicle, what should the air pressure loss be with a fully charged air system?

Accepted Answer

Less than 3 psi per minute

Answer

For a combination vehicle (tractor-trailer), the acceptable air pressure loss during a static air brake test is slightly higher than for a single vehicle due to the increased complexity and number of air lines. With a fully charged system and the brakes applied, the pressure loss should not exceed 3 psi per minute. A greater loss indicates potential leaks in the system, which must be repaired for safe operation.

Question 5

Where is compressed air stored?

Accepted Answer

Main reservoirs

Answer

Compressed air, generated by the air compressor, is stored in large metal tanks called main reservoirs or air tanks. These tanks hold a reserve of compressed air, which is then supplied to the brake chambers and other air-operated accessories. Having these reservoirs ensures a constant supply of air pressure for braking, even if the compressor is not actively pumping.

CDL Practice Test

CDL Practice Test

CDL Air Brakes Practice Test 4