Air Brakes

Question 1

Why must air tanks be drained?

Answer 1

because water and compressor oil will start to build up and can cause brake failure

Question 2

What is a supply pressure gauge used for?

Answer 2

used to measure how much pressure is in the air tanks

Question 3

What are air storage tanks used for?

Answer 3

air storage tanks are used to hold compressed air. The tanks hold enough air to allow brakes to be used several times even after the compressor stops working

Question 4

all vehicles with air brakes must have a low air pressure warning signal?

Answer 4

TRUE

Question 5

Front wheel brakes are good under all conditions?

Answer 5

TRUE

Question 6

what are spring brakes?

Answer 6

an alternate power source for emergency and parking brakes that will activate when air pressure is gone

Question 7

how do you know your vehicle is equipped with antilock brakes?

Answer 7

THE VEHICLE WILL HAVE A YELLOW ABS MALFUNCTION LAMP

Question 8

purpose of air government control?

Answer 8

controls when the air compressor will pump air into the air storage tanks

Question 9

what is cut-out and cut-in pressure levels and how does it work?

Answer 9

cut out level is around 125 psi. Air compressor governor will stop the compressor from pumping air.

Cut in level is around 100 psi and the air compressor governor will allow the compressor to start pumping again

Question 10

Purpose of alcohol evaporator?

Answer 10

helps to reduce the risk of ice in air brake valves and other parts during cold weather

Question 11

what two types of air drains?

Answer 11

manual and automatic

Question 12

what is the purpose of a safety relief valve

Answer 12

purpose is to protect air tank and rest of system from too much pressure. Valve is usually set to open at 150 psi

Question 13

what is a dual air brake system?

Answer 13

SYSTEM HAS TWO SEPARATE AIR BRAKE SYSTEMS, WHICH USE A SINGLE SET OF BRAKE CONTROLS. ONE SYSTEM OPERATES THE REGULAR BRAKES ON THE REAR AXLE OR AXLES WHILE THE OTHER OPERATES ON THE FRONT AXLE. Both systems supply air to trailer (if there is one)

Question 14

what are slack adjusters?

Answer 14

Slack adjusters are mechanical links between the brake-chamber push rod and the camshaft on cam type brakes.

Question 15

how can you check slack adjusters?

Answer 15

release parking brake so you can move them and pull them

Question 16

how can you test low pressure warning signal?

Answer 16

turn engine off when you have enough air pressure. Turn electrical power on and press on and off the brake pedal. The low air pressure warning signal should come on around 60 psi

Question 17

what is application pressure gauge (not on all trucks)

Answer 17

a gauge that measures how much air pressure you are applying to the brakes.

Question 18

how can you check that the spring brakes come on automatically?

Answer 18

lower air pressure by stepping on and off brake pedal. The tractor protection valve and parking brake valve should close (pop out) when air pressure falls to 20-45 psi

Question 19

what are the maximum leak rates?

Answer 19

4 pounds in one minute with combination vehicle

3 pounds in one minute with single vehicle

Question 20

what does the braking power of spring brakes depend on?

Answer 20

the adjustment of the brakes

Question 21

what are service brakes?

Answer 21

the foot pedal that you use to apply brakes while traveling up and down the road

Question 22

how does s-cam brakes work

Answer 22

when the brake is applied, air pressure pushes slack adjuster which turns the s-cam and forces brake shoes to press against the inside of the brake drum

Question 23

purpose of front brake limiting valve? (used for vehicles made before 1975)

Answer 23

limiting valve cuts the “normal” air pressure to the front brakes by half effectively reducing braking power of front brakes

Question 24

when engine is at operating rpms what psi range and how long should it take for the pressure to build?

Answer 24

pressure should build from 85-100 psi within 45 seconds in dual air systems

Question 25

how to test parking brake?

Answer 25

stop vehicle, put parking brake on, and gently pull against it in a low gear to test if the parking brake will hold

Question 26

how to test service brakes?

Answer 26

wait for normal air pressure, release parking brake, move vehicle forward about 5 mph and apply brakes firmly.

Question 27

what is controlled braking?

Answer 27

when you apply your brakes as hard as you can without locking the wheels. Keep steering movements small while doing this manuever

Question 28

what is stab braking?

Answer 28

apply brakes all the way and release brakes when wheels lock. Apply brakes again when wheels start ROLLING

Question 29

what is brake lag

Answer 29

time required for the brakes to work after the brake pedal is pushed

Question 30

what is air brake distance formula?

Answer 30

PERCEPTION DISTANCE+ REACTION DISTANCE+BRAKE LAG DISTANCE+ BRAKING DISTANCE= TOTAL STOPPING DISTANCE

Question 31

what should you do when brakes get wet?

Answer 31

use brakes lightly while driving in low gear to heat and dry them

Question 32

when should you not use parking brakes?

Answer 32

if brakes are very hot from coming down a steep grade or if the brakes are very wet during freezing temps.