SGI SGI Air Brakes Endorsement 2 — Questions and Answers
Question 1: What is the correct method for descending a long steep grade with air brakes?
- Select a low gear before descending and use steady light brake applications (Correct answer)
- Use brakes continuously and hold them on
- Turn off the engine to use compression braking only
- Apply brakes hard at intervals to cool them
Correct answer: Select a low gear before descending and use steady light brake applications
Selecting a low gear before the grade and using light, intermittent brake applications prevents heat build-up and brake fade.
Question 2: What does the governor in an air brake system do?
- Maintains air pressure between the cut-in and cut-out range (Correct answer)
- Applies the spring brakes automatically
- Releases pressure from the system
- Monitors wheel speed
Correct answer: Maintains air pressure between the cut-in and cut-out range
The governor controls the air compressor, turning it on at the cut-in pressure (around 100 psi) and off at the cut-out pressure (around 120–130 psi).
Question 3: What is the purpose of the tractor protection valve?
- To protect the tractor air supply if the trailer develops a severe leak (Correct answer)
- To increase air pressure to the trailer
- To apply trailer brakes independently
- To release the fifth wheel
Correct answer: To protect the tractor air supply if the trailer develops a severe leak
The tractor protection valve closes automatically if the trailer's air line ruptures, preserving enough air in the tractor for safe braking.
Question 4: In a combination vehicle, what do the red and blue glad hand couplings connect?
- Red is the emergency (supply) line; blue is the service (control) line (Correct answer)
- Red is service; blue is emergency
- Red is left brakes; blue is right brakes
- Red is trailer power; blue is brake signal
Correct answer: Red is the emergency (supply) line; blue is the service (control) line
The red glad hand connects the emergency (supply) line and the blue connects the service (control) line between the tractor and trailer.
Question 5: What does a driver do first when testing parking brakes before a trip?
- Apply the parking brake and attempt to move the vehicle forward slowly (Correct answer)
- Release all brakes and check for movement
- Drain the reservoirs
- Check the air pressure gauge only
Correct answer: Apply the parking brake and attempt to move the vehicle forward slowly
Testing the parking brake by applying it and gently moving the vehicle confirms that it holds the vehicle securely.
Question 6: What is the maximum air pressure drop allowed in one minute during a static leakage test for a combination vehicle?
- 8 psi (Correct answer)
- 4 psi
- 12 psi
- 2 psi
Correct answer: 8 psi
For a combination vehicle (tractor-trailer), the static leakage test allows a maximum drop of 8 psi per minute with brakes applied.
SGI SGI Air Brakes Endorsement 2
What is the correct method for descending a long steep grade with air brakes?