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53 Cards in this Set
- Front
- Back
Air brakes are really made up of three different braking systems, what are they?
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service brake, parking brake, emergency brake
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What is the service brake?
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The service brake system applies and releases the
brakes when you use the brake pedal during normal driving. |
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What is the parking brake?
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The parking brake system applies and releases the
parking brakes when you use the parking brake control. |
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What is the emergency brake?
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The emergency brake system uses parts of the service
and parking brake systems to stop the vehicle in the event of a brake system failure. |
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There are many parts to an air brake system. What is the air compressor?
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The air compressor pumps air into the air storage tanks
reservoirs. The air compressor is connected to the engine through gears or a belt. |
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Can the air compresssor have its own oil supply?
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It may have
its own oil supply, or be lubricated by engine oil. If the compressor has its own oil supply, check the oil level before driving. |
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There are many parts to an air brake system. What is the Air Compressor Governor?
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The governor controls when the air compressor will pump
air into the air storage tanks. |
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When air tank pressure (Air Compressor Governor) rises to the “cut-out” level of what psi?
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Around 125 pounds.
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When air tank pressure (Air Compressor Governor) rises to the “cut-in” level of what psi?
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Around100 psi.
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What is Air Storage Tanks?
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Air storage tanks are used to hold compressed air. The
number and size of air tanks varies among vehicles. |
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Will air storage tanks allow the breaks to stop several times.
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Tanks will hold enough air to allow the brakes to be used
several times even if the compressor stops working. |
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What does the Air Tank Drains do?
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Releases water and oil that tend to collect in the bottom
of the air tank 9this should be done daily). |
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What is the Alcohol Evaporator?
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Some air brake systems have an alcohol evaporator to put
alcohol into the air system. This helps to reduce the risk of ice in air brake valves and other parts during cold weather. |
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How often should the alcohol container be filled or changed?
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Check the alcohol container and fill up as necessary, every
day during cold weather. |
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What is a Safety Valve?
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The safety valve protects the tank and
the rest of the system from too much pressure. The valve is usually set to open at 150 psi. |
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Is the safety relief valve installed in the first tank the air compressor
pumps air to. True or False |
True
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If the safety valve release air (set to open at 150 psi)....
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something is wrong
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Pushing the break pedal harder applies ________ air pressure.
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more
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Letting up on
the brake pedal __________the air pressure and releases the brakes. |
reduces
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What are Foundation Brakes?
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Foundation brakes are used at each wheel. The most common
type is the s-cam drum brake |
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What are the parts of the Foundation Brakes
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Brake Drums, Shoes, and Linings,S-cam Brakes, Wedge Brakes, Disc Brakes
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What is S-cam break?
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The s-cam forces the brake
shoes away from one another and presses them against the inside of the brake drum.When you release the brake pedal, the s-cam rotates back and a spring pulls the brake shoes away from the drum, letting the wheels roll freely again. |
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What is a Wedge Brake?
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the brake chamber push
rod pushes a wedge directly between the ends of two brake shoes. |
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What is a Disc Brake?
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In air-operated disc brakes, air pressure acts
on a brake chamber and slack adjuster, like s-cam brakes. |
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What is a Supply Pressure Gauge?
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All air-braked vehicles have a pressure gauge connected to
the air tank. These gauges tell you how much pressure is in the air tanks |
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What is a Application Pressure Gauge?
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This gauge shows how much air pressure you are applying
to the brakes. This gauge is not on all vehicles. |
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What is a low air pressure signal? When does it come on?
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A low air pressure warning signal is required on vehicles
with air brakes. A warning signal you can see must come on before the air pressure in the tanks falls below 60 psi. |
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When does the low pressure air warning come on on a large bus?
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On large buses it is common for the low pressure warning
devices to signal at 80-85 psi. |
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Should Drivers behind you be warned when you put your
brakes on. |
The switch turns on the
brake lights when you put on the air brakes. |
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What are spring breaks?
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Spring brakes are usually used to meet these
needs. When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes. |
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When doe the tractor and straight truck spring brakes will come fully on
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When air pressure drops to a range of 20 to 45 psi (typically
20 to 30 psi). |
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When the low air pressure warning light and
buzzer first come on the driver should? |
bring the vehicle to a safe stop right
away, while you can still control the brakes |
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The braking power of spring brakes depends on the brakes
being in adjustment. True or False |
True. If the brakes are not adjusted properly,
neither the regular brakes nor the emergency/parking brakes will work right. |
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What is the Parking Brake Control?
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Put on the parking
brakes using a diamond-shaped, yellow, push-pull control knob. |
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Never push the brake pedal down when the spring
brakes are on. true or false |
True. If you do, the brakes could be damaged by
the combined forces of the springs and the air pressure. Many brake systems are designed so this will not happen. |
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What is a Modulating Control Valve.
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A control
handle on the dash board that may be used to apply the spring brakes gradually. This is called a modulating valve. It is spring loaded so you |
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Dual Parking Control Valves.
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Some vehicles, such as
buses, have a separate air tank which can be used to release the spring brakes. |
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What is a DUAL AIR BRAKE.
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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. |
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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. True or False |
True
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The warning
light and buzzer should shut off when air pressure in both systems rises to a value set by the manufacturer. |
This value must be greater than 60 psi.
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The warning light and buzzer should come on before the air
pressure drops below 60 psi in either system. |
If this happens
while driving, you should stop right away and safely park the vehicle. |
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INSPECTING AIR BRAKE SYSTEMS During Step 2 Engine Compartment Checks
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During Step 2 Engine Compartment Checks
Check Air Compressor Drive Belt (if compressor is belt driven). If the air compressor is belt-driven, check the condition and tightness of the belt. The belt should be in good condition. |
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During Step 7 Final Air Brake Check Test Air Leakage Rate fro single vehicle.
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turn off the engine, release the service
brake, and time the air pressure drop.two psi in one minute for single vehicles typically 125 psi |
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During Step 7 Final Air Brake Check Test Air Leakage Rate fro combination vehicle.
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turn off the engine, release the service
brake, and time the air pressure drop. less than three psi in one minute for combination vehicles. typically 125 psi |
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When testing the air brake after timing the psi loss rate apply apply 90 psi or more with the brake pedal. After the initial
pressure drop, if the air pressure falls more than three psi in one minute for single vehicles more than four psi for combination vehicles, the air loss rate is too much. True or False |
True. Check
for air leaks and fix before driving the vehicle. Otherwise, you could lose your brakes while driving. |
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Test Low Pressure Warning Signal.
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Shut the engine off
when you have enough air pressure so that the low pressure warning signal is not on. Turn the electrical power on and step on and off the brake pedal to reduce air tank pressure.The low air pressure warning signal must come on before the pressure drops to less than 60 |
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Check That the Spring Brakes Come on Automatically
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Chock the wheels, release the parking brakes when you
have enough air pressure to do it, and shut the engine off. Step on and off the brake pedal to reduce the air tank pressure. The “parking brake” knob should pop out when the air pressure falls to the manufacturer’s specification (usually in a range between 20-40 psi). This causes the spring brakes to come on. |
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Check Rate of Air Pressure Buildup.
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When the engine is
at operating rpm, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. |
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Check Air Compressor Governor Cut-in and Cut-out
Pressures |
Pumping by the air compressor should start at
about 100 psi and stop at about 125 psi |
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Test Parking Brake
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Stop the vehicle, put the parking brake
on, and gently pull against it in a low gear to test that the parking brake will hold. |
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Test Service Brakes.
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Wait for normal air pressure, release
the parking brake, move the vehicle forward slowly (about five mph), and apply the brakes firmly using the brake pedal. |
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total stopping distance for vehicles with air
brake systems is made up of four different factors. |
Perception Distance
+ Reaction Distance + Brake Lag Distance + Effective Braking Distance = Total Stopping Distance |
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The air brake lag distance at 55 mph on dry pavement adds--------------fett
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32
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