CDL Combination Vehicles Practice Test 2 — Questions and Answers
Question 1: The trailer protection valve is designed to close automatically if the air pressure reaches the range of
- 0 - 9 psi
- 10 - 19 psi
- 20 - 45 psi (Correct answer)
- 46 - 60 psi
Correct answer: 20 - 45 psi
The trailer protection valve is designed to automatically close and seal off the tractor's air supply to the trailer if the air pressure drops too low. This typically occurs when the air pressure falls into the range of 20-45 psi. This mechanism prevents a trailer air leak from completely depleting the tractor's air brake system.
Question 2: You should always test the trailer brakes before driving by
- Using the hand valve
- Pulling the air supply control
- Using the foot brake
- Options 1st & 2nd (Correct answer)
Correct answer: Options 1st & 2nd
Before driving, you should always test the trailer brakes using both the hand valve and by pulling the air supply control. The hand valve allows you to apply only the trailer brakes to check their function. Pulling the air supply control (which applies the trailer's emergency brakes) and then pushing it in while listening for air flow also confirms proper connection and function.
Question 3: If you are parking a trailer without spring brakes, which of the following should you use?
- Wheel chocks (Correct answer)
- Parking brake
- Emergency brake
- Trailer hand brakes
Correct answer: Wheel chocks
For trailers without spring brakes, wheel chocks are absolutely necessary when parking. Spring brakes automatically apply when air pressure is lost, but trailers without them rely solely on air pressure to hold the brakes. Without spring brakes, the trailer could roll away if the air pressure leaks down, making chocks vital for safety.
Question 4: The coupling device used to connect the service and emergency air lines from the truck to the trailer is known as?
- Trailer air supply control
- Relay valve
- Glad hands (Correct answer)
- Cut-out cocks
Correct answer: Glad hands
Glad hands are the coupling devices used to connect the service and emergency air lines from the tractor to the trailer. They are designed to create an airtight seal, allowing air pressure to flow between the two vehicles for proper brake operation. Their distinctive 'handshake' shape gives them their name.
Question 5: Which of the following is a valve used at the back of a trailer that allows the closing of the air lines when another trailer is not being towed?
- Drain valve
- Cut-out cocks (Correct answer)
- Dummy coupler
- Tractor protection valve
Correct answer: Cut-out cocks
Cut-out cocks are valves located at the back of a trailer, specifically designed to close off the air lines when another trailer is not being towed. This prevents air from escaping from the open lines, maintaining proper air pressure in the brake system of the single trailer. They are essential for proper air system management in multi-trailer operations.
Question 6: Which of the following devices should you use to prevent water and dirt from getting into the coupler and air lines when they are not in use?
- Dead end or dummy couplers (Correct answer)
- Shut-off valves
- Relay valves
- Tractor protection valve
Correct answer: Dead end or dummy couplers
Dead end or dummy couplers are essential devices used to protect the glad hands and air lines when they are not connected to a trailer. They prevent dirt, moisture, and other debris from entering the air brake system, which could cause damage or malfunction. Keeping the air lines clean is crucial for reliable brake performance.
Question 7: How are the air lines color coded to keep them from getting mixed up?
- Emergency line is BLUE. Service line is RED.
- Emergency line is RED. Service line is WHITE.
- Emergency line is GREEN. Service line is BLUE.
- Emergency line is RED. Service line is BLUE. (Correct answer)
Correct answer: Emergency line is RED. Service line is BLUE.
To prevent confusion and ensure correct connection, air lines are color-coded. The emergency line is always RED, and the service line is always BLUE. This standardized coloring helps drivers quickly identify and properly connect the lines, which is critical for the safe operation of the trailer's air brakes.
Question 8: You could experience steering problems because of friction between the tractor and trailer if you do not lubricate which of the following?
- Relay valves
- Glad hands
- Fifth wheel plate (Correct answer)
- Dead end couplers
Correct answer: Fifth wheel plate
The fifth wheel plate is the large, flat surface on the tractor that supports the trailer's kingpin. Proper lubrication of this plate is crucial to reduce friction between the tractor and trailer during turns and maneuvers. Without adequate lubrication, excessive friction can lead to steering problems, binding, and potential damage to the coupling system.
Question 9: If you are lowering the landing gear of a loaded trailer, you should
- Lift the trailer off of the fifth wheel
- Lower the landing gear until it makes firm contact with the ground
- Turn the crank in low gear a few extra turns after firm contact with the ground (Correct answer)
- Turn the crank in high gear a few extra turns after firm contact with the ground
Correct answer: Turn the crank in low gear a few extra turns after firm contact with the ground
When lowering the landing gear of a loaded trailer, it's important to turn the crank in low gear a few extra turns after it makes firm contact with the ground. This ensures that the landing gear is securely seated and provides stable support for the trailer. Using low gear provides more leverage and control for this critical step.
CDL Combination Vehicles Practice Test 2
The trailer protection valve is designed to close automatically if the air pressure reaches the range of