CDL Practice Test: Video 4 Answers (25 Questions)

Question 1

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.

Question 2

At what air pressure must the low air pressure warning signal come on?

Accepted Answer

60 psi

Answer

Federal regulations mandate that the low air pressure warning signal must activate when the air pressure in the service air tanks falls below 60 psi (or half the governor cut-out pressure on older vehicles). This warning alerts the driver to a critical loss of air pressure, indicating a potential problem with the air brake system that requires immediate attention.

Question 3

What is the alcohol evaporator's primary purpose?

Accepted Answer

Put alcohol into the air system

Answer

An alcohol evaporator, found in some older air brake systems, is designed to inject alcohol vapor into the air lines. This alcohol helps prevent moisture in the air system from freezing during cold weather, which could otherwise cause brake components to malfunction and lead to brake failure.

Question 4

What is the typical air pressure of a fully charged air brake system?

Accepted Answer

125 psi

Answer

125 psi. A fully charged air system typically has 125 psi of air pressure.

Question 5

Which of the following devices can be used as the low air pressure warning signal?

Accepted Answer

Any of the above

Answer

Federal regulations require commercial vehicles with air brakes to have a low air pressure warning signal to alert the driver when system pressure drops below 60 psi. This critical warning can be provided by various means, including an audible buzzer, a visual red warning light, or a mechanical arm known as a 'wig-wag.' All these devices serve the same essential safety function.