CDL Air Brake Air Brake Compressor and Governor 2 — Questions and Answers
Question 1: At what pressure does the safety relief valve typically open to protect the air brake system?
- 100–110 psi
- 125–135 psi
- 150 psi or more (Correct answer)
- 75–85 psi
Correct answer: 150 psi or more
The safety relief valve opens at 150 psi or more to prevent dangerous over-pressurization if the governor fails.
Question 2: What should you do if the safety relief valve is frequently releasing air during operation?
- Continue driving — this is normal operation
- Increase driving speed to consume more air
- Have the governor and compressor inspected immediately (Correct answer)
- Add oil to the compressor reservoir
Correct answer: Have the governor and compressor inspected immediately
Frequent safety valve releases indicate a governor malfunction and require immediate inspection by a qualified mechanic.
Question 3: What must you do before manually draining the air tanks?
- Let the engine warm up for 10 minutes
- Bring the vehicle to a complete stop and apply the parking brake (Correct answer)
- Drive for at least 15 minutes to build full pressure
- Turn off the air dryer
Correct answer: Bring the vehicle to a complete stop and apply the parking brake
You must bring the vehicle to a complete stop and apply the parking brake before draining air tanks to ensure safety.
Question 4: Water that accumulates in air tanks can be drained manually using what device?
- The governor control
- The drain cock or petcock (Correct answer)
- The air dryer filter
- The pressure relief valve
Correct answer: The drain cock or petcock
A drain cock or petcock at the bottom of each air tank allows manual draining of water that accumulates from compressed air.
Question 5: How often should air tanks be manually drained in cold weather compared to warm weather?
- Less frequently — cold air contains less moisture
- At the same frequency year-round
- More frequently, ideally daily, to prevent moisture from freezing (Correct answer)
- Only when the low-pressure warning activates
Correct answer: More frequently, ideally daily, to prevent moisture from freezing
In cold weather, tanks should be drained more frequently (ideally daily) to prevent accumulated moisture from freezing and blocking air lines.
Question 6: What is the first thing that happens in the air brake system when you press the brake pedal?
- The spring brakes release
- Air flows from the tanks through the brake valve to the brake chambers (Correct answer)
- The compressor starts pumping additional air
- The governor raises the cut-out pressure
Correct answer: Air flows from the tanks through the brake valve to the brake chambers
Pressing the brake pedal opens the brake valve, allowing compressed air to flow from the storage tanks to the brake chambers to apply the brakes.
CDL Air Brake Air Brake Compressor and Governor 2
At what pressure does the safety relief valve typically open to protect the air brake system?