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CDL · General

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

Correct answer

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

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

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