CDL Air Brakes Section 5 Review Practice Test.
What makes air brakes work? - CORRECT ANSWER Compressed air.
What are the three braking systems? - CORRECT ANSWER Service brake, parking brake, emergency brake
What does the service brake do? - CORRECT ANSWER Applies and releases the brakes ...
What makes air brakes work? - CORRECT ANSWER Compressed air.
What are the three braking systems? - CORRECT ANSWER Service brake, parking brake, emergency
brake
What does the service brake do? - CORRECT ANSWER Applies and releases the brakes when you use the
brake pedal during normal driving.
What does the parking brake do? - CORRECT ANSWER Applies and releases the parking brake when you
use the parking brake control
What does the emergency brake do? - CORRECT ANSWER Uses parts of the service and parking brake
system to stop the vehicle in event of a brake system failure.
What does the air compressor do? - CORRECT ANSWER Pumps air into the air storage tank reservoirs.
Connected to the engine through gears or a belt. May be cooled by air or engine cooling system. May
have its own oil supply or use engine oil.
What does the air compressor governor do? - CORRECT ANSWER Controls when the air compressor will
pump air into the air storage tanks. When it rises to "cut-out" of 125psi it stops the compressor. When it
falls to "cut-in" at 100psi it allows it start again.
What do the air storage tanks do? - CORRECT ANSWER Used to hold compressed air.
What are the air tank drains? - CORRECT ANSWER Used to drain water and oil. Can be manaul or
automatic.
, What does the alcohol evaporator do? - CORRECT ANSWER Puts alcohol into the air system to reduce
the risk of ice in air brake valves. Check the container and fill up every day. Daily tank drainage is still
necessary.
What does the safety valve do? - CORRECT ANSWER Installed in the first tank and protects the tank and
rest of system from too much pressure. Set to open at 150psi.
What does the brake pedal do? - CORRECT ANSWER Pushing harder applies more air pressure. Letting up
releases air pressure and releases the brakes. This lets some compressed air out of the tanks. This must
be made up by the air compressor. Pressing and holding unnecessarily can let air out faster than it can
be replaced.
What are foundation brakes? - CORRECT ANSWER Used at each wheel. Most common type is teh s-cam
drum brake.
What do brake drums, shoes, and linings go? - CORRECT ANSWER Drums are located on each end of the
axles. The wheels are bolted to the drums. The braking mechanism is inside the drum. To stop, the brake
shoes and linings are pushed against the inside of the drum. This causes heat which can be a problem.
What are s-cam brakes? - CORRECT ANSWER When braking air pressure pushes the rod out, moving the
slack adjuster, and twisting the brake cam shaft. This turns the s-cam which forces the brake shoes away
from one another and against the drum.
What are wedge brakes? - CORRECT ANSWER The brake chamber push rod pushes a wedge directly
between the ends of two brake shoes to force them against the drum. May have one or two chambers.
What are disc brakes? - CORRECT ANSWER Instead of an s-cam a power screw is used.
What do supply pressure gauges do? - CORRECT ANSWER Tell how much air pressure is in the tanks. If a
dual system there will be one for each half of the system.
What does the application pressure gauge do? - CORRECT ANSWER How much air pressure you are
applying to the brakes. Increasing application pressure to hold the same speed means the brakes are
fading.
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