41. Why must air tanks be drained?
Detailed Explanation
The correct answer is "To drain moisture and oil out of tank.". This is based on federal CDL regulations and safety standards.
Correct Answer: To drain moisture and oil out of tank.
Why This Matters on the CDL Test
This question belongs in your brake safety review. Pay close attention to pressure limits, inspection steps, stopping distance, and warning signs because brake-system mistakes are a common reason CDL applicants miss endorsement questions.
How to Remember It
Say the rule in your own words, then explain why the wrong answers are unsafe or incomplete. That habit makes similar Air Brakes questions easier when the exam changes the wording.
Answer Review
Choose "To drain moisture and oil out of tank." because this answer matches the safe CDL action for brake system safety. On the knowledge test, the safest answer is usually the one that protects space, control, visibility, legal compliance, or inspection accuracy before the vehicle is put at risk.
Why the other answers are weaker
- To drain all the air out of the tank."To drain all the air out of the tank." does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
- To tell you how much air is in the air tanks."To tell you how much air is in the air tanks." does not best answer this brake system safety question. When you see a similar option on the CDL permit test, compare it against the exact safety rule and choose the answer that prevents the most immediate risk.
Test-Day Checklist
- Read the question once for the topic, then read it again for the exact CDL action being tested in Air Brakes.
- Eliminate answers that sound convenient but skip an inspection, warning sign, or safety step.
- Say the correct rule out loud before moving on so you can recognize it when the exam changes the wording.
Study the Full Topic
Review what the air pressure gauge tells you, how low-pressure warnings work, and why air tank checks matter.
Air Brake Pressure Gauge CDL GuideReady to practice for real?
Take our free, full-length Air Brakes practice test. Simulates the actual DMV exam with timed questions.
Start Practice TestRelated Questions
1. Oil and water usually collect in compressed air tanks. If you do not have an automatic tank drain, when should you drain the air tanks?
10. The safety valve is set to automatically reduce pressure at:
100. Your bus or truck has a dual air brake system. If a low air pressure warning comes on for only one system, what should you do?
101. It is not safe to drive a vehicle that has brake drums (or discs) with cracks or that are thinner than the manufacturer's specifications, generally this will be — an inch.
102. Emergency controlled braking is when you:
Keep Studying Air Brakes
Question pages help you review one rule at a time. To build test-day speed, move back into the full Air Brakes practice test and answer a mixed set without looking at the explanation first.
State CDL Practice Paths
After you understand this answer, use a state practice path to connect the federal CDL rule with the DMV test pages drivers search for most.