Cdl Practice Questions 5 - Air Brakes

Front 1

In a vehicle equipped with an air brake system, what should happen when air pressure drops below 60 psi

Back 1

A warning signal you can see must come on before the air pressure in the tanks falls below 60 psi (or one-half the compressor governor cutout pressure on older vehicles).

Before air pressure drops below 60 psi, the low air warning signal will activate. When the warning activates, you need to quickly find a safe place to pull your vehicle to the side of the road. If you wait too long, the emergency brakes will activate once your air pressure reaches 45 psi and you may not be able to clear the roadway.

Front 2

Why do air tanks need to be manually drained?

Back 2

Air Tank Drains - Compressed air usually has some water and compressor oil in it, which is bad for the air brake system.

For example, the water can freeze in cold weather and cause brake failure. The water and oil tend to collect in the bottom of the air tank. Be sure to drain the air tanks completely. Each air tank is equipped with a drain valve in the bottom. There are two types of drain valves:

1. Manually operated by turning a quarter turn or by pulling a cable. You must drain the tanks yourself at the end of each day of driving.

2. Automatic, in which the water and oil are automatically expelled. They may be equipped for manual draining as well.

The automatic types are available with electric heating devices. These help prevent freeze-up of the automatic drain in cold weather.

Front 3

What does the Air Compressor Governor do?

Back 3

The governor controls when the air compressor will pump air into the air storage tanks.

When air tank pressure rises to the "cut-out" level (around 125 pounds per square inch, or "psi"), the governor stops the compressor from pumping air. When the tank pressure falls to the "cut-in" pressure (around 100 psi), the governor allows the compressor to start pumping again.

Front 4

Which of the following is true about the Air Compressor?

Back 4

The air compressor pumps air into the air storage tanks (reservoirs). The air compressor is connected to the engine through gears or a V-belt.

The compressor may be air cooled or may be cooled by the engine cooling system. It may have its own oil supply or be lubricated by engine oil. If the compressor has its own oil supply, check the oil level before driving.

Front 5

Which of the following statements about the Air Compressor is false?

Back 5

The air compressor pumps air into the air storage tanks (reservoirs). The air compressor is connected to the engine through gears or a V-belt.

The compressor may be air cooled or may be cooled by the engine cooling system. It may have its own oil supply or be lubricated by engine oil.

If the compressor has its own oil supply, check the oil level before driving.

Front 6

What happens when the brake drums exceed their designed temperature?

Back 6

Too much heat can make the brakes stop working.

As the brake drums heat up, they become less and less effective. This is a process known as "brake fade" which is a very popular term in the trucking industry.

After a while, they will become totally useless. Brake Fade is the #1 cause of brake failure on steep downgrades.

Front 7

Spring brakes should activate when air pressure drops to:

Back 7

The spring brakes will come on when the air pressure drops into the 20 to 45 psi range

Front 8

What is the proper braking technique on long or steep downgrades?

Back 8

Proper Braking Technique - Remember, the use of brakes on a long and/or steep downgrade is only a supplement to the braking effect of the engine. Once the vehicle is in the proper low gear, the following is the proper braking technique:

1. Apply the brakes just hard enough to feel a definite slowdown.

2. When your speed has been reduced to approximately 5 mph below your "safe" speed, release the brakes. (This brake application should last about 3 seconds.)

3. When your speed has increased to your "safe" speed, repeat steps 1 and 2.

Front 9

What is the service brake?

Back 9

Air brake systems combine three braking systems: service, parking and emergency brake systems.

1. The service brake system applies and releases the brakes when you use the brake pedal during normal driving.
2. The parking brake system applies and releases the parking brakes when you use the parking brake control.
3. The emergency brake system uses parts of the service and parking brake systems to stop the vehicle in the event of a brake system failure.

Front 10

The following statements accurately describe Wedge Brakes, except:

Back 10

Wedge brakes: In these types of brakes, the brake chamber push rod pushes a wedge directly between the ends of two brake shoes. This shoves them apart and against the inside of the brake drum. Wedge brakes may have a single brake chamber or two brake chambers, pushing wedges in at both ends of the brake shoes. Wedge-type brakes may be self-adjusting or may require manual adjustment.

Front 11

How do you properly use Anti-Lock Brakes?

Back 11

For normal or emergency stopping using anti-lock brakes, the driver's foot remains on the brake pedal in which the anti-lock module then acts as a foot pumping the air brake system.

On the air-brake system the driver must pump or use stab braking in an emergency. If the anti-lock brake system fails or malfunctions, the driver must resort to stopping the vehicle by using the normal air-brake method.

If an emergency arises, the driver should use the controlled or stab braking method. The anti-lock brake system should be serviced as soon as possible.