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CDL Practice Test: Combination Vehicles

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CDL Practice Test: Combination Vehicles

Combination Vehicles Questions

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Good Luck!

The trailer air supply control valve will pop out, thus closing the tractor protection valve, in what air pressure range?
  • 20 to 45 psi
  • 100 to 125 psi
  • 50 to 70 psi
  • 0 to 20 psi
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The trailer air supply control on newer vehicles is a red 8-sided knob used to control the tractor protection valve. Push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes. The valve will pop out, thus closing the tractor protection valve, when the air pressure drops into the range 20 to 45 psi. Tractor protection valve controls or "emergency" valves on older vehicles may not operate automatically. There may be a lever rather than a knob. The "normal" position is used for pulling a trailer. The "emergency" position is used to shut the air off and put on the trailer emergency brakes.

Next
What does the Trailer Air Supply Control do?
  • Activates the air compressor located on the trailer
  • Supplies the tractor with air from the trailer
  • Controls the parking brake on the tractor
  • Supplies the trailer with air from the tractor
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The trailer air supply control on newer vehicles is a red 8-sided knob used to control the tractor protection valve. Push it in to supply the trailer with air, and pull it out to shut the air off and put on the trailer emergency brakes. The valve will pop out, thus closing the tractor protection valve, when the air pressure drops into the range 20 to 45 psi. Tractor protection valve controls or "emergency" valves on older vehicles may not operate automatically. There may be a lever rather than a knob. The "normal" position is used for pulling a trailer. The "emergency" position is used to shut the air off and put on the trailer emergency brakes.

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Next
What is the usual color for the Service Line?
  • Blue
  • Green
  • Orange
  • Red
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

Emergency lines are often coded with the color red (red hose, red couplers or other parts) to keep from getting them mixed up with the blue service line.

TruckingTruth's Advice:

While not an actual regulation, the normal color scheme is usually as follows:

  • Emergency Line: Red
  • Service Line: Blue
  • Electrical Line: Green

Again, these are not actual regulations so colors may vary from truck to truck, but these colors have become the industry norm.

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Next
Which of the following statements about the Emergency Air Line is false?
  • When the line loses air pressure, it causes the tractor protection valve to close
  • It supplies air to the trailer air tanks
  • It carries air controlled by the foot brake or trailer hand brake
  • It controls the emergency brakes on combination vehicles
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The emergency line (also called the supply line) has two purposes:

  • (1) To supply air to the trailer air tanks
  • (2) to control the emergency brakes on combination vehicles.

Loss of air pressure in the emergency line causes the trailer emergency brakes to come on. The pressure loss could be caused by a trailer breaking loose, thus tearing apart the emergency air hose. Or it could be caused by a hose, metal tubing or other part that breaks, letting the air out. When the emergency line loses pressure, it also causes the tractor protection valve to close (the air supply knob will pop out).

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Next
Which statement about inspecting a combination vehicle is false?
  • Be sure the landing gear is fully raised, no missing parts, not bent or otherwise damaged
  • Make sure the fifth wheel locking jaws are around the head of the kingpin and not the shank of the kingpin
  • If you have a sliding fifth wheel, you must make sure the fifth wheel is securely locked in place
  • Check the the air lines and electrical line to be certain they are properly secured and connected
This is a question from page 54 - click here to look up the answer

Quote From Page 78 Of The Illinois CDL Manual:

Inspecting a Combination Vehicle

  • Locking jaws around the shank, not the head of kingpin.
  • Landing gear is fully raised, no missing parts, not bent or otherwise damaged.
  • Air lines properly connected to glad hands, no air leaks, properly secured with enough slack for turns.
  • All sliding fifth wheel locking pins present and locked in place
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Next
Which device inside the cab of a truck controls the Tractor Protection Valve
  • The yellow "parking brake" control valve
  • The brake pedal
  • The red "trailer air supply" control valve
  • The trailer hand valve
This is a question from page 49 - click here to look up the answer

Quote From Page 73 Of The Illinois CDL Manual:

The tractor protection valve keeps air in the tractor or truck should the trailer break away or develop a bad leak. The tractor protection valve is controlled by the "trailer air supply" control valve in the cab. The control valve allows you to open and shut the tractor protection valve. The tractor protection valve will close automatically if air pressure is low (in the range of 20 to 45 psi). When the tractor protection valve closes, it stops any air from going out of the tractor. It also lets the air out of the trailer emergency line. This causes the trailer emergency brakes to come on.

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Next
When you turn suddenly while pulling doubles, which trailer is most likely to turn over?
  • The front trailer
  • The rear trailer
  • Both trailers are equally as likely to turn over
  • The tractor is more likely to turn over than either trailer
This is a question from page 48 - click here to look up the answer

Quote From Page 70 Of The Illinois CDL Manual:

Trucks with trailers have a dangerous "crack-the-whip" effect. When you make a quick lane change, the crack-the-whip effect can turn the trailer over. There are many accidents where only the trailer has overturned.

"Rearward amplification" causes the crack-the-whip effect. The rear trailer is twice as likely to turn over as the tractor. You can roll the last trailer of triples 3.5 times as easily as a 5-axle tractor-semi.

TruckingTruth's Advice:

When pulling more than 1 trailer, the rear-most trailer is always at a higher risk of overturning than the front trailer.

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Next
Which of the following can help reduce the chance of a truck rollover?
  • At night, drive slow enough to see obstacles with your headlights before it is \ too late to change lanes or stop gently
  • Look far enough down the road to avoid being surprised and having to make a sudden lane change
  • All of these can help reduce the chance of a truck rollover
  • Slow down to a safe speed before going into a turn
This is a question from page 48 - click here to look up the answer

Quote From Page 70 Of The Illinois CDL Manual:

Steer gently and smoothly when pulling trailers. If you make a sudden movement with your steering wheel, you could tip over. Follow far enough behind other vehicles (at least 1 second for each 10 feet of your vehicle length, plus another second if going over 40 mph). Look far enough down the road to avoid being surprised and having

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