Air brakes

Question 1

3 types of braking systems

Answer 1

Service, Parking, & Emergency

Question 2

Air compressor

Answer 2

Pumps air into the storage tanks

Question 3

Governor

Answer 3

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

Question 4

Cut-out level

Answer 4

When air tank pressure rises to around 125 psi, or the cut-out level, the governor stops the compressor from pumping air

Question 5

Cut-in level

Answer 5

When air tank pressure falls to around 100 psi, or the cut-in level, the governor allows the compressor to start pumping air again

Question 6

Safety relief valve

Answer 6

Valve is usually set to open at 150 psi (if valve releases air, something is wrong)

Question 7

Parts of the brake

Answer 7

To stop, the brake shoes and linings are pushed against the inside of the drum. This causes friction, which slows the vehicle

Question 8

S-cam brakes

Answer 8

When the pedal is pushed, air is let into each brake chamber. Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake camshaft (and turning the s-cam). The s-cam forces the brake shoes away from one another and presses them against the inside of the brake drum

Question 9

Supply pressure gauge

Answer 9

Tell you how much pressure is in the tank

Question 10

Application pressure gauge

Answer 10

Shows how much air pressure you are applying to the brakes

Question 11

Low air pressure warning signal

Answer 11

A warning signal that you can see that must come on before the air pressure in the tanks falls below 60 psi (can be a red light, buzzer, or a wig wag)

Question 12

Front brake limiting valve

Answer 12

Valve that cuts the air pressure in the front brakes by half (on vehicles made before 1975)

Question 13

Spring brakes

Answer 13

Powerful springs held back by air pressure

Question 14

Spring brakes on tractor and straight trucks

Answer 14

Will come fully on when air pressure drops to a range of 20 to 40 psi

Question 15

Parking brake

Answer 15

You pull the diamond-shaped, yellow knob to put on the parking brakes and push it in to release them (older vehicles may have a parking brake that is controlled by a lever.)

Question 16

Modulating control valves

Answer 16

A control handle on the dashboard may be used to apply the spring brakes gradually

Question 17

Antilock Braking System (ABS)

Answer 17

A computerized system that keeps your wheels from locking up during hard brake applications. (required on truck tractors built on or after March 1, 1997 and other air brake vehicles built on or after March 1, 1998)

Question 18

Dual Air Brake

Answer 18

Most heavy-duty vehicles use dual air brake
systems for safety. A dual air brake system has
two separate air brake systems, which use a single
set of brake controls. Each system has its own air
tanks, hoses, lines, etc. One system typically
operates the regular brakes on the rear axle or
axles. The other system operates the regular
brakes on the front axle

Question 19

PSI in dual air system

Answer 19

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

Question 20

Warning light (systems with dual air)

Answer 20

The warning light and buzzer should shut off when air pressure in both systems rises to the value set by the manufacturer. (The value must be greater than 60 psi.)

Question 21

Slack adjusters on s-cam brakes

Answer 21

Park on
level ground and chock the wheels to prevent the
vehicle from moving. Release the parking brakes
so you can move the slack adjusters. Use gloves
and pull hard on each slack adjuster that you can
reach. If a slack adjuster moves more than about
one inch where the push rod attaches to it, it
probably needs adjustment.

Question 22

Brake drums

Answer 22

Must not have cracks longer than one half the width of the friction area

Question 23

Air pressure build up

Answer 23

Pressure should build from 85 to 100 psi within 45 seconds in dual air systems/single air systems, typical requirements are pressure buildup from 50 to 90 psi within 3 minutes

Question 24

Controlled braking

Answer 24

You apply the brakes as hard as you can without locking the wheels

Question 25

Stab braking

Answer 25

Apply your brakes all the way, release brakes when wheels lock up, and apply brakes fully again as soon as the wheels start rolling.

Question 26

Brake lag

Answer 26

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

Question 27

Total stopping time for vehicles with air brake systems

Answer 27

Perception Distance + Reaction Distance + Brake Lag Distance + Braking Distance

Question 28

Air brake lag distance

Answer 28

The air brake lag distance at 55mph on dry pavement adds about 32 feet. (Ex. 55mph for an average driver under good traction and brake conditions, the total stopping distance is over 450 feet.)

Question 29

Proper braking technique

Answer 29

Apply the brakes just hard enough to feel a definite slowdown, when your speed has been reduce approximately 5mph below your safe speed, release the brakes, when your speed has increased to your safe speed, repeat steps 1 and 2.