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CDL > Air brakes > Flashcards

Air brakes Flashcards

1
Q

Air brakes are three different braking systems

A

Service brakes
Parking brake
Emergency brake

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2
Q

Service system brake

A

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

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3
Q

Parking brake

A

Applies and releases the parking brakes when you use the parking brake control

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4
Q

Emergency brake

A

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

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5
Q

Air Compressor

A

Pumps air into the air storage tanks(reservoirs)

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6
Q

Air Compressor Governor

A

Controls when air compressor will pump air into the air storage tanks. When air tank pressure rises above 125psi the governor stops the compressor from pumping air. When reaches 100psi the governor allows the compressor to start pumping again.

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7
Q

Air Storage Tanks

A

Used to hold compressed air. The tanks will hold enough air to allow brakes to be used several times, even if the compressor stops working.

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8
Q

Air Tank Drains

A

Compressed air usually has some water and compressor oil in it, which is bad for the brake system. The water can freeze in cold weather and cause brake failure. The water and oil collect at the bottom of the tank. Be sure to drain the air tanks completely end of each day unless automatic.

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9
Q

Alcohol Evaporator

A

Some air brake systems have an alcohol evaporator in the air system. This helps reduce the risk of ice in air brake valves and other parts during cold weather. Ice can make the brakes stop working. Check alcohol container and fill up as necessary, every day during cold weather. Daily air tank drainage is still needed to get rid of water and oil unless has automatic drain valves.

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10
Q

Safety Valve

A

Installed in the first tank the air compressor pumps air into. Protects the tank and system from too much pressure. Valve is usually set to open at 150psi. If it releases air something is wrong.

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11
Q

Brake Pedal

A

You out brakes by pushing brake pedal.(also called a foot valve or treadle valve). Pushing harder applies more air pressure. Letting up reduces air pressure and releases brakes. Releasing brakes lets some compressed air out of the system so the air pressure in tanks is reduced. The air compressor makes that air back up. Pressing and releasing unnecessarily can let out too much air faster than compressor can replace. If pressure gets too low the brakes won’t work.

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12
Q

Foundation Brakes

A

Found at each wheel with the most common type being the s-cam drum brake.

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13
Q

Brake drums, shoes, and linings

A

Drums are located on each end of the vehicles axles. The wheels are bolted to the drums. To stop, the brake shoes and linings are pushed against the inside of the drum. This causes friction, which slows the vehicle(and creates heat). The heat a drum can take without damage depends on how hard and long the brakes are used. Too much heat can make the brakes stop working.

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14
Q

S-Cam Brakes

A

When you push the brake pedal air is let into each brake chamber. This pushes rod out moving the slacker adjuster, twisting the brake camshaft. This turns the s-cam which forces the brake shoes away from one another and presses them against the inside of the brake drum. When release brake pedal the s-cam rotates back and the spring pulls the brake shoes away from drum, letting the wheels roll freely again.

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15
Q

Wedge and Disc Brakes

A

Less common than a-cam brakes. Disc brakes are air operated but instead of the s-cam a “power screw” is used .

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16
Q

Supply Pressure Gauges

A

All vehicles with air brakes have a pressure gauge connected to the air tank. If dual air brake system there will be one for each half of the system. These gauges tell you how much pressure is in the air tanks.

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17
Q

Application Pressure Guage

A

Shows how much air pressure you are applying to the brakes. This gauge is not on all vehicles.

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18
Q

Low Air Pressure Warning

A

Required on vehicles with air brakes. Warning signal comes on before the air pressure in tank falls below 60psi. Usually a red light or a buzzer might come on too. Another warning is the “wig wag” mechanical arm that drops in view when the pressure drops below 60psi and cannot be raised in place until above 60psi.

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19
Q

Stop Light Switch

A

Drivers must be warned when you put brakes on. The air brake system does this with an electronic switch that works by air pressure. It turns on the brake lights when you put on the air brakes.

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20
Q

Stop Light Switch

A

Drivers must be warned when you put brakes on. The air brake system does this with an electronic switch that works by air pressure. It turns on the brake lights when you put on the air brakes.

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21
Q

Front Brake Limiting Valve

A

Older vehicles before 1975 have this. It is marked “normal “ and “slippery” used to prevent front wheels from skidding on slippery surfaces when place on “slippery” setting. Newer vehicles have automatic front wheel limiting valves to reduce air to front brakes

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22
Q

Spring Brakes

A

All trucks and tractors must be equipped with emergency and parking brakes. Must be held by mechanical force because air pressure will leak away. Spring brakes are usually used to meet this need. Spring brakes will come fully on when air pressure drops to a range of 20-45 psi. Do not wait for light and buzzer to come on, bring vehicle to safe stop right away.

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23
Q

Parking Brake Controls

A

In newer vehicles with air brakes you put on parking brake using a diamond shaped yellow push-pull control knob. Pull to put in and push to release them. Caution: never push the brake pedal down when spring brakes are on. This could damage the brakes. Most systems are designed for this to not happen but not all are. Develop habit of not pushing brake pedal down when the spring brakes are on.

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24
Q

Antilock Braking System (ABS)

A

Trucks built after 1997-1998 are required to have this. This is a computerized system that keeps your wheels from locking up during hard braking. Vehicles with ABS have yellow malfunction lamp to tell you if something isn’t working. If malfunction it does not decrease or increase your normal braking capability.

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25
Q

Why must air tanks be drained?

A

To remove oil and water

26
Q

What is a supply pressure gauge used for?

A

Shows how much air pressure is in the air tanks.

27
Q

All vehicles with air brakes must have a low pressure warning signal t/f

A

True

28
Q

What are spring brakes?

A

Mechanic force that holds emergency and parking brakes.

29
Q

Front wheel brakes are good under all conditions T/F

A

True

30
Q

How do you know if your vehicle is equipped with antilock brakes?

A

Yellow malfunction lamps on instrument panel, trailers on left side(front or rear corner), and wires coming from back of brakes on towed units that are older.

31
Q

Dual Air Brake

A

Most heavy duty vehicles have dual air brake systems for safety. Two separate systems with one set of brake controls. Each with its own air tanks, hoses, lines, etc. one usually operates the regular brakes on the rear axle or axles and other operates the regular brakes on the front axle. Before driving a vehicle with dual air brakes allow time for air compressor to build up to a minimum of 100psi in both systems. The warning light and buzzer should come on before pressure drops below 60psi. Stop right away and safely park.

32
Q

Inspecting air brake system

A

1- check slack adjusters on a-cam brakes. Park on level ground and chock wheels. Turn off parking brakes and with gloves pull hard on each slack adjuster. If it moves more than 1 inch it probably needs adjustment. If too much slack can be hard to stop. This is the most common problem found in roadside inspections.

33
Q

Check brake drums, liners, and hoses

A

Must not have cracks in drums or discs longer than one half the width of the friction area. Mechanical parts must be in place, not broken or missing. Air hoses make sure not cut, worn or rubbing. No less than 1/4 inch thickness brake drums.

34
Q

Final air brake check

A

Test low pressure warning signal. Shut engine when have enough air pressure, turn electrical power on and step on and off the brake pedal to reduce air tank pressure. Low pressure warning signal must come on before the pressure drops to less than 60psi. If signal doesn’t work you could lose air pressure and not even know it.

35
Q

Final air brake check

A

Check that spring brakes come on automatically- step on and off the brake pedal to reduce tank pressure. The tractor protection valve and parking brake should close (pop out) when the air pressure falls to manufacturer’s specifications. This will cause brakes to come on.

36
Q

Final air brake check

A

Check rate of pressure buildup- when engine is at operating rpms, the pressure should build from 85 to 100psi within 45 seconds in dual air systems. If air pressure does not build up fast enough your pressure may drop too low during driving requiring emergency stop don’t drive until fixed.

37
Q

Final air brake check

A

Test air leakage rate- when fully charged (125psi) turn off engine and release parking brake. Time pressure drop should be bless than 2 psi in one minute for single vehicles and 3psi in 1 minute for combo vehicles. Check for air leaks and fix before driving you could lose your brakes.

38
Q

Final air brake check

A

Check air compressor governor cut in and cut out pressures- pumping by the air should start at about 100psi and stop about 125psi. Run engine and idle fast. The air governor shouldn’t out the air compressor at specified pressure . With engine idling step on and off brake to reduce air tank pressure. Compressor should begin to rise. A governor that does not work properly may not keep enough air pressure for safe driving.

39
Q

Final air brake check

A

Test parking brake- stop vehicle put parking brake on and gently pull against it in a low gear to test that parking brake will hold

40
Q

Final air brake check

A

Test service brakes- wait for normal air pressure release parking brake and move vehicle slowly 5mph. Apply brakes firmly and note any pulling to one side, unusual feel or delayed stopping action.

41
Q

What is a dual air brake system?

A

Has two separate air brake systems with one single set of brake controls.

42
Q

What are slacker adjusters?

A

Controls the play for push rod on brakes

43
Q

How can you check for slack adjusters?

A

Park in level ground, chock wheels and turn off parking brakes. Use gloves and pull hard on each one. If moves more than 1 inch it needs adjustment

44
Q

How can you test the low pressure warning light?

A

Shut engine when enough air pressure , turn on electrical power and step on and off brake pedal to reduce air tank pressure. Light must come on before pressure drops less than 60psi

45
Q

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

A

Pump brakes until psi is 20-45

46
Q

What are the maximum leakage rates?

A

3psi per 1 minute single and 4psi in 1 minute combo

47
Q

Normal stops

A

Push brake pedal down. Control the pressure so the vehicle comes to a smooth safe stop. If have a manual transmission don’t push the clutch in until the engine rpm is down close to idle. When stopped select a starting gear.

48
Q

Braking with antilock brakes

A

Without ABS you will still have normal brake functions. Drove and brake as you always have. If your ABS malfunctions you will still have regular brakes. Get system serviced soon.

49
Q

Emergency stops

A

You should brake in a way that will keep your vehicle in a straight line and allow you to turn if necessary. Controlled braking- apply brakes hard without locking wheels, keep steering wheel movements small. If wheels lock release brakes and reapply as soon as can. Stab braking- apply brakes all way, release when wheels lock up, as soon as wheels start rolling apply brakes fully again.

50
Q

Stopping distance

A

With air brakes there is an added delay (brake lag) this is the time required for the brakes to work after pushed. Takes little more time in air brakes for air to flow through the lines to the brakes. Four factors- perception distance+reaction distance+brake lag distance+ braking distance=total stopping distance. Air brake lag distance at 55mph adds about 32 feet or total stopping distance of 450 feet.

51
Q

Brake fading or failure

A

Braking creates heat but brakes are designed to take a lot of heat. Brakes can fade or fail from excessive heat. Excessive use and poor adjustment can lead to brake fade

52
Q

Proper braking technique

A

The use of brakes on long and/or steep downgrade is only a supplement to the braking technique. Once vehicle is in proper braking technique:
1-apply brakes just hard enough to feel definite slowdown
2- when speed reduced to around 5mph release the brakes
3- when speed has increased to your “safe” speed repeat steps 1 and 2.

Example- if your safe speed is 40mph you would not apply brakes until reach 40mph. Apply brakes hard enough to gradually reduce speed to 35mph and then release brakes. Repeat as often as necessary until reach end of downgrade.

53
Q

Low Air Pressure

A

If light comes on stop and safely park. There might be an air leak in the system. Spring brakes will come on when pressure drops to 20-45 psi. A heavily loaded vehicle will take long distances to stop and light load vehicles on slippery roads may skid out of control when spring brakes come on. It is safer to stop while enough air in tanks to use foot brakes.

54
Q

Parking brakes

A

Any time park use them except if brakes are very hot or if brakes are very wet in freezing temperatures. Use wheel chocks to hold vehicle and let hot brakes cool before using parking brake. If brakes are wet use the brakes lightly while driving in a longer to heat and dry them. Drain tanks at end of each working day to remove oil and water if don’t have automatic air tank drains.

55
Q

Why should you be in the proper gear before starting down a hill?

A

You may not be able to downshift after starting downhill.

56
Q

What factors can cause brakes to fade or fail?

A

Overheat and out of adjustment

57
Q

The use of brakes on a long, steep downgrade is only a supplement to the braking effect of the engine T/F

A

True

58
Q

If you are away from your vehicle only a short time, you do not need to use the parking brake? T/F

A

False

59
Q

How often should you drain air tanks?

A

End of every working day

60
Q

How do you brake when you drive a tractor trailer combination with ABS?

A

Normally

61
Q

You still have normal brake functions if your ABS is not working T/F

A

True

CDL (1 decks)

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