CDL weak-area practice

CDL Compressor and Governor Drill

Your score review found missed questions about the compressor, governor, reservoirs, cut-in, cut-out, or air supply behavior.

Study the weak area

What to understand before you answer.

Compressor and governor questions test whether you understand how the system builds and controls air pressure before braking happens.

01

The compressor builds air pressure; the governor controls when it cuts in and cuts out.

02

Storage tanks hold compressed air for braking and system operation.

03

Do not confuse air-supply behavior with the act of applying the brakes.

04

Pressure readings matter because they show whether the system can operate safely.

Before the questions

How to improve this score.

Review the air brake system parts before answering.
Identify whether each question is about building air, storing air, or using air.
Review any missed cut-in or cut-out explanation.
Retake the air brakes set when these system basics are clearer.

Common traps to watch for

Confusing compressor cut-in/cut-out behavior with brake application.

When this pattern appears in a missed answer, review the explanation before trying another set.

Thinking tank draining is unrelated to brake safety.

When this pattern appears in a missed answer, review the explanation before trying another set.

Confusing air supply control with brake application.

When this pattern appears in a missed answer, review the explanation before trying another set.

Assuming higher pressure is always better.

When this pattern appears in a missed answer, review the explanation before trying another set.

Waiting for the system to improve during the trip.

When this pattern appears in a missed answer, review the explanation before trying another set.

Practice questions

CDL Compressor and Governor Drill Quiz

Answered 0 / 13

Question 1

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

To pump air into the storage tanks. To cool the brake drums. To apply the parking brake. To supply hydraulic fluid to the calipers.

Question 2

What does the air compressor governor control?

When the compressor will pump air into the storage tanks. The temperature of the brake drums. When the spring brakes will engage. The speed of the engine.

Question 3

At what pressure does the air compressor governor typically 'cut out' (stop pumping air)?

Around 60 psi. Around 90 psi. Around 125 to 130 psi. Around 150 psi.

Question 4

What is the purpose of alcohol evaporators in some air brake systems?

To increase the pressure in the storage tanks. To reduce the risk of ice freezing in the air brake valves in cold weather. To clean the brake shoes. To make the brakes apply faster.

Question 5

Why is it important to drain air storage tanks daily?

To check for rust inside the tank. To remove water and compressor oil that can freeze or damage the valves. To release excess air pressure overnight. To cool the compressor down.

Question 6

If your vehicle does not have automatic drain valves, how often should you manually drain moisture from the air tanks?

Once a week. At the end of each day of driving. Only when the low pressure warning comes on. Every 500 miles.

Question 7

What is the function of the supply pressure gauge?

It tells you how much pressure is in the air tanks. It shows how much pressure you are applying to the brakes. It shows the temperature of the air compressor. It indicates the pressure of the engine oil.

Question 8

Why should air tanks be drained?

To remove moisture and oil that can damage the system or freeze. To lower normal operating pressure before every trip. To make spring brakes release faster. To increase brake lag.

Question 9

What does the air compressor governor control?

When the compressor pumps air into the tanks and when it stops. How much fuel the engine uses. The brightness of the ABS light. The distance between the brake shoes and drums.

Question 10

If the compressor cut-out pressure is much higher than normal, why is that a concern?

The system may be overpressurizing and should be checked. It proves the brakes can stop faster. It means the parking brake is released. It means no leakage test is needed.

Question 11

What is the safest interpretation of slow air pressure buildup during a pre-trip check?

The system may not recover pressure fast enough and should be inspected before driving. The compressor is saving fuel. The brakes are fully adjusted. The parking brake is stronger than normal.

Question 12

During an air brake inspection, why should you wait for normal air pressure before moving?

The brake system needs adequate air pressure to operate safely. Low pressure makes the vehicle accelerate faster. Normal pressure is needed only for the horn. The system works better with empty tanks.

Question 13

What does slow air pressure buildup during a pre-trip check usually indicate?

A possible air system problem that should be corrected before driving. The brakes are stronger than normal. The vehicle is ready to descend a mountain. The parking brakes are no longer needed.

Study before retesting

Review before you try again.

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