247SimpleTests
CDL · Using Air Brakes

Why should you drain the air tanks (reservoirs) regularly?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

To remove water and oil/sludge that accumulate and can damage the system or freeze in cold weather

  1. A To remove water and oil/sludge that accumulate and can damage the system or freeze in cold weather
  2. B To add more air
  3. C To make the truck lighter
  4. D It is unnecessary

Why this is the answer

Air tanks must be DRAINED regularly to remove WATER and oil/sludge that accumulate (the compressor pumps in air that contains moisture, which condenses in the tanks). CDL air brakes. Accumulated water can: reduce braking effectiveness, damage the system, and FREEZE in cold weather (causing brake failure). Many systems have automatic moisture ejectors, but manual draining (via drain valves) may still be needed. ALCOHOL EVAPORATORS and air dryers also help remove moisture. Knowing to drain the tanks to remove water/oil (preventing freezing and damage) is commonly tested air brake maintenance.
Source: FMCSA CDL Manual — Air Brakes, Draining Tanks

Practice more questions

This question is from our CDL Practice Tests practice test. Take the full practice test to test your knowledge across all Using Air Brakes and other topics.

Take the Air Brakes practice test →

About this topic: Using Air Brakes

Air brakes feel different from hydraulic brakes — there is brake lag, and pumping defeats ABS. Hot brakes fade on long downgrades; engine braking saves them. This is one of 12 Air Brakes questions on using air brakes, each with a full explanation on a single study page.

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

Related questions

Using Air Brakes

What is the proper way to apply the air brakes during normal driving?

 Using Air Brakes

On a long downgrade, what gear should you select?

 Using Air Brakes

What is the proper procedure if your brakes start to fail on a downgrade?

 Using Air Brakes

Why is it a bad idea to drive a vehicle with anti-lock brakes (ABS) as if it does not have ABS?

State-specific guides

Need information for your state? Our state guides cover local requirements, fees, and what to expect on exam day.

California Texas Florida New York Pennsylvania Illinois Ohio Georgia

Recommended study materials

Study guide

CDL Study Guide (Trivium)

Complete prep for all CDL written tests: general knowledge, air brakes, combination vehicles, hazmat, and all endorsements. Includes full-length practice tests.

Check Price → Study guide

CDL Practice Tests & Flashcards (Accepted Inc.)

600+ practice questions covering every FMCSA knowledge area, plus 400 flashcards for endorsement prep.

Check Price → Study guide

Master the CDL Truck Driver's License (Arco)

Arco's classic CDL prep with in-depth FMCSA manual coverage, endorsement chapters, and scored practice exams.

Check Price →

As an Amazon Associate, CJ Affiliate, and AWIN publisher we earn from qualifying purchases. Links above are affiliate links. Full disclosure →