Driver Training - Air Brakes Study Questions

Question 1

1. When should a low air pressure warning come on?

Answer 1

Will come on when pressure in the tanks fall below 60 psi

• Required on all vehicles with air brakes
• Or one half the compressor governor cutout pressure on older vehicles
• A “wig wag” is a mechanical arm that drops into view when the system pressure drops below 60 psi

Large buses
- Common for low pressure warning devices to signal at 80 to 85 psi

(5-4)

Question 2

2. When should the air compressor governor cut-in?

Answer 2

When the tank pressure falls to the cut-out level, around 100 psi
- The governor allows the compressor to start pumping again after “cut-in”

“Cut-out” pressure: about 125 psi

(5-1)

Question 3

3. When should the air compressor governor cut-out?

Answer 3

When the air tank pressure rises to the cut-out level, around 125 psi
- The governor stops the compressor from pumping air after reaching the “cut-out” position

“Cut-in” pressure: about 100 psi

(5-1)

Question 4

4. When testing air brakes, during fanning of brakes, when should the parking brake valve “pop out” or “close”?

Answer 4

?

5-7?

Question 5

5. What is the air loss rate for a single vehicle?

Answer 5

Start with a fully charged system
For Single Vehicles:
- Loss rate should be less than two (2) psi in one minute

Apply 90 or more psi with the brake pedal
- After initial pressure drop, if the air pressure falls more than three (3) psi in one min, the air loss rate is too much

For Combination Vehicles:

• Should be less than three (3) psi in one minute
• After application of 90+ psi, air pressure falling more than four (4) psi in one min, air loss rate is too much

(5-7)

Question 6

6. What are the maximum leakage rates (with brake pedal depressed) for a single vehicle?

Answer 6

Apply 90 or more psi with the brake pedal
- After initial pressure drop, if the air pressure falls more than three (3) psi in one min, the air loss rate is too much

(5-7)

Question 7

7. With dual air systems the air pressure should build?

Answer 7

Before driving a vehicle with a dual air system, allow time for the air compressor to build up to a minimum of 100 psi in both the primary and secondary systems.

(5-6)

Question 8

8. What is brake lag?

Answer 8

Time required for air to flow through the lines to the brakes

(5-9)

Question 9

9. What does the application pressure gauge show you?

Answer 9

Shows how much air pressure is being applied to the brakes

5-4

Question 10

10. What does the supply pressure gauge show you?

Answer 10

Shows how much pressure is in the air tanks

5-4

Question 11

11. What does the service brake system do?

Answer 11

Applies and releases the brakes when you use the brake pedal during normal driving

(5-1)

Question 12

12. What does the emergency brake do?

Answer 12

Uses parts of the service and parking brake systems to stop the vehicle in the event of a brake system failure

(5-1)

Question 13

13. What should you do if your low pressure signal comes on?

Answer 13

Stop and safely park your vehicle as soon as possible

5-10

Question 14

14. How much can a slack adjuster move?

Answer 14

Should not be able to move more than about one inch
where the push rod attaches to it

(5-6)

Question 15

15. Why must air tanks be drained?

Answer 15

Drain the tanks completely to remove any water and oil that has collected in the bottom of the tank

(5-2)

Question 16

17. What are spring brakes?

Answer 16

Spring brakes mechanically hold the emergency brakes and parking brakes of trucks, tractors, and buses

• Springs are held back by air pressure
• When pressure is removed, the springs put on the brakes

(5-5)

Question 17

18. What should you do if your low air pressure signal comes on when you are driving a vehicle with dual air tanks?

Answer 17

Stop and safely park your vehicle as soon as possible

5-10

Question 18

19. Can brakes fade or fail from excessive heat caused by using them too much?

Answer 18

Yes

5-9, 5-10

Question 19

20. When testing the air brakes, when must the low pressure warning signal come on?

Answer 19

Before pressure drops to less than 60 psi

5-7

Question 20

20. When testing the air brakes, when must the low pressure warning signal come on?

Answer 20

Before pressure drops to less than 60 psi in the air tank (or tank with the lowest air pressure, in dual air systems)

(5-7)

Question 21

22. All vehicles with air brakes must have what signal?

Answer 21

Low Air Pressure Warning

5-4

Question 22

23. When is it ok to leave your truck unattended without applying the parking brakes and chocking the wheels?

Answer 22

Never

5-11

Question 23

24. A slack adjusters free play needs to be adjusted if it is more than about how many inches when you pull hard on it?

Answer 23

More than about one inch where the push rod attaches to it

5-6