Air Brakes – Practice Test Questions Flashcards by Jay Liu

Why must air tanks be drained?

To release oil and water buildup

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What is a supply pressure gauge used for?

To check tank pressure

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All vehicles with air brakes must have a low pressure warning signal. True or False?

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What are spring brakes?

Emergency/parking brake

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Front wheel brakes are good under all conditions. True or False?

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What is a dual air brake system?

2 systems which use a single set of brake controls

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What are the slack(a. 松弛的) adjusters?

Adjusts the slack in the brakes

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How can you test the low pressure warning signal?

Apply parking brake and pump the brake pedal again and again

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

Release parking brake and press the brake pedal again and again

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What are the maximum leakage rates?

More than 3 psi in one minute

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

The use of brakes is only a supplement to the braking effect of the engine

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What factor can cause brakes to fade or fail？

Excessive use of service brakes

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The use of brakes on a long steep downgrade is only a supplement to the braking effect of the engine. True or False?

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If you are away from your vehicle for only a short time, you don’t need to use the parking brake. True or False?

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How often should you drain air tanks?

At the end of each working day

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How do you use the stab braking technique during emergency braking?

Brake hard with the pedal until the wheels lock, then let off until the wheels start rolling again

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When using brakes on a long steep downgrade, which of these is True?

Use the engine braking effect, then when the vehicle reaches the safe speed, apply brakes until speed is reduced to about 5 mph below safe speed.

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Why should you NOT fan the brakes on and off during long downgrades?

Does not allow brakes to cool

PS: Fanning reduces air pressure and serves no useful purpose on dry pavement, and fanning on a long downhill grade may reduce air pressure below the minimum pressure needed for proper brake operation. … If brakes should fail on a level road, you should downshift and use engine braking to slow the vehicle.

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If you must make a quick emergency stop, you should:

Stay in a straight line and maintain control.

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A straight truck or bus air brake system cannot leak more than_______psi per minute with engine off and brakes released.

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A combination vehicle air brake system cannot leak more than ______psi per minute with engine off and brakes released.

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During normal operations, what are the parking and emergency brakes usually held back by?

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When do you use the parking brake in air brake equipped vehicles?

Every time you park the vehicle

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If your truck has dual control valves, you can use pressure from a separate tank to

Release emergency brakes to move short distances

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If the air system develops a leak, what will keep the air in the tanks?

The one-way check valve

Which of these is normal to find in the air brake system?

Air

What turns on the electrical stop light switch in an air brake system?

Air pressure

If the vehicle is equipped with an alcohol evaporator, what should you do everyday during winter weather?

Check and fill the alcohol level

If a failure occurs in the service brake system, what system do you need to stop the vehicle?

Emergency brake system

What determines how effective the spring emergency brakes or the parking brakes work?

Depends on the adjustment of the service brakes

What does the brake pedal do?

Controls the air pressure to operate the brakes

What does the air compressor governor control?

When the compressor will pump air into the storage tanks

On heavy commercial vehicles, what is the most common type of foundation brake?

S-cam drum

In manual slack adjusters, how do you check the _free play(空转)_?

Park on level ground, chock wheels, release parking brake and pull slack adjusters

What must air brake equipped vehicles have?

An air pressure gauge to show pressure available for braking

The warning device comes on when the air pressure in the service air tank falls below

60 psi

**Air loss in a single vehicle (not comb. vehicle) should not be more** **than** _\_\_\_\_\_\__**with engine off and brakes** **on**.

3 psi in one minute

Three systems are found in modern air brake systems, Service brakes, Parking brakes and:

Emergency brakes

When using parking or emergency brakes, what type of pressure is being used?

Spring pressure

Which brake system applies and releases the brakes when the driver uses the brake pedal?

Service brake system

What does the air supply pressure gauge show?

How much pressure is available in the air tanks

What does an alcohol evaporator do?

Gets rid of alcohol that condenses in the air tanks

What is the purpose of the engine retarders?

Helps slow the vehicle and reduce brake wear

Which of these statements is True about brakes?

The heavier the vehicle or the faster the vehicle is going, the more heat the brakes have to absorb to stop it.

The air loss rate for a straight truck or bus with engine off and brakes applied should not be more than

3 psi in one minute

Oil and water usually collect in compressed air tanks. If you do not have an automatic tank drain, when should you drain the air tanks?

After every working day

Why drain water from the compressed air tanks?

Water can freeze in cold weather and cause brake failure

Air brake equipped vehicles must have

A supply pressure gauge

What can legally hold a parking or emergency brake in position for a truck, truck tractor or bus?

Spring pressure

You should know that your brakes are fading when

You have to push harder on the brake pedal to control your speed on a downgrade

Slack adjusters on s-cam brakes need adjustment if they move more than two inches when the push rod attaches.

With the engine at operating rpm, the air pressure should build from 85 to 100 psi in 45 seconds in a dual air system.

**Air pressure loss in a combination vehicle should not be more than 1 psi per minute while pressure is on the brake** **pedal.**

**At 55 mph on dry pavement, the air brakes lag(n.延迟) distance adds about 32 feet to total stopping** **distance.**

Air brakes cool very slowly.

Excessive brake use from speed can cause too much heat to build up in the air brakes.

**If the low pressure alarm comes on you should stop and park your vehicle as soon as possible.**

**It is suggested that you drain your air tanks at the end of each week to remove dirt and oil**.

**When spring brakes come on, lightly loaded vehicles will build air pressure** **quickly**.

**The s-cam drum is the most common type of foundation** **brake.**

The supply pressure gauge tells you how long before the s-cam turns.

F PS: Supply pressure gauges are connected to the air tanks and indicate the pressure in each tank. The application pressure gauge displays how much pressure is being applied to the brakes.

**Drum brakes are the only type of brake in which brake fade** **occurs.**

On a heavy vehicle, the emergency brake is usually held in place by spring pressure because air pressure can leak away.

Some vehicles have a separate air tank which can be used to release the spring brakes.

The two systems of a dual air brake system is the primary and secondary.

The spring brakes come on when the air pressure drops too much.

When the brakes are very hot you should not use the parking brake.

The total stopping distance travelling at 55 mph under normal conditions is about 100 feet.

F ## Footnote PS:With all of these factors included, an air brake-equipped vehicle traveling at a speed of 55 mph under ideal driving conditions will need approximately 450 feet to come to a complete stop.

Modern air brake systems use three braking systems - service, parking and emergency.

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

The alcohol evaporator condenses the air in the brake system.

The first tank the air compressor pumps air to is installed with a safety relief valve to protect the tank and the rest of the system from too much air pressure.

While testing the service brakes, if your vehicle pulls to one side, there may be a problem with the service brakes.

When going down a long or steep downgrade, the braking effects of the engine should be supplemented by the use of the brakes.

**You should maintain steady pressure on the brakes and hold the steering wheel firmly when the wheels lock** **up.**

The air compressor governor controls:

when the compressor will pump air into the storage tanks

Modern air brake systems combine three different systems. They are the service brake, the parking brake and the:

emergency brakes

If the air compressor develops a leak, what keeps the air in the tank?

the one way check valve

**Vehicles with air brakes must** **have:**

an air pressure gauge, to show the pressure available for braking

A straight truck or bus air brake system cannot leak more thanper minute with the engine off and the brakes released.

2psi

During normal driving, parking and emergency brakes are usually held back by:

air pressure

To check the free play in the manual slack adjusters, you need to:

park on level ground, chock the wheels and release the parking brake

The effectiveness of the spring brakes:

depends on the adjustments of the service brakes

Which of the following makes total stopping distance longer for air brakes than hydraulic?

brake lag

The first thing to do when a low pressure warning comes on is:

stop and safely park as soon as possible

Air braking takes more time than hydraulic braking because air brakes

need to have air flow through the lines to work

Experts do not recommend fanning (on-again off-again braking) for long downhill runs because:

the short time off the brakes does not allow the brakes to cool.

Oil and water that collects in air tanks can make brakes fail. If you do not have automatic tank drains, when should you drain the air tanks?

every day

the driver must be able to see a warning that is given when air pressure in the service air tanks falls below:

60 psi

An air brake system safety relief valve opens at about:

150 psi

When some air brakes in the system are doing more work than others:

1. those brakes will develop more heat. 2. vehicle handling will be effected. 3. all the above.

Your safety relief valve has opened several times. This means _\_\_\_\_\__.

the system needs immediate attention.

At what air pressure should the low air warning alarm come on?

must come on by 60 psi.

With the brakes released on a single vehicle, what is the allowable air loss?

2 psi

**To test the air compressor on a dual air brake vehicle, run the engine at a fast idle** **to charge the air system. Your gauges should** **show** **your\_\_\_\_\_\_****.**

your pressure builds from 85 to 100 psi within 45 seconds

Spring brakes are applied by _\_\_\_\_\_\__?

a means other than air, electrical or hydraulic

Most large vehicles with air brakes have spring brakes which _\_\_\_\_\__.

are part of both the parking and emergency brakes.

What color is the parking control knob on the dash of the vehicle?

Yellow

What would cause all of the air brake systems on a vehicle to have poor braking power?

brakes being out of adjustment.

If a low air pressure warning comes on what should you do?

pull off the road as soon as it is safe to do so.

"Cut – in" pressure is normally set to\_\_\_\_\_\_psi.

100

How often should you drain your air tanks?

Daily

Which of the following is not an air brake subsystem?

Spring brake system

What is a "Wig Wag"?

A mechanical arm that signals low air pressure.

"Cut – out" pressure is normally set to\_\_\_\_psi

125

Front brake limiting valves are found on:

Older vehicles made before 1975.

To reduce the risk of ice, some air systems incorporate:

An alcohol evaporator

At 55 MHP brake lag ( on-air brake vehicles) can add an additional _\_\_\_\_\__feet to your overall stopping distance.

32ft

When testing service brakes you should look for:

1. Pulling to either side. 2. Delayed stopping action. 3. All the above.

In newer vehicles, parking brakes are applied using:

A yellow diamond shaped push-pull knob