CDL Combination Vehicles TestInspecting Combination VehiclesMedium
During an en route inspection, a driver notices that the trailer's air tanks are not draining water when the drain valves are opened. What is the most likely cause and concern?
- AThe drain valves are clogged or frozen, preventing water removal.
- BThe air compressor is not building enough pressure to force out water.
- CThe air dryer is malfunctioning, allowing moisture to enter the tanks.
- DThe trailer's braking system has a significant air leak.
Show answer & explanationAnswer & explanation
Correct answer: A. The drain valves are clogged or frozen, preventing water removal.
Air tanks accumulate moisture, which must be drained regularly to prevent corrosion and freezing. If no water drains, the most probable cause is that the drain valves themselves are clogged with debris or frozen in cold weather, preventing the trapped water from escaping. This can lead to serious brake system issues if the water freezes or corrodes components.
Why the other options are wrong
- B. Air pressure is usually sufficient to drain water; lack of drainage points to a valve obstruction, not insufficient pressure.
- C. While a malfunctioning air dryer allows moisture, the immediate problem described is the inability to drain, suggesting a valve issue.
- D. An air leak would cause pressure loss, but wouldn't directly prevent water from draining if the valve was functional.
Air Tank Draining
The process of opening air tank drain valves to remove accumulated moisture and contaminants, preventing corrosion and freezing within the air brake system.
- Moisture accumulates naturally in air tanks.
- Failure to drain can lead to corrosion or frozen brakes.
- Drain valves must be checked regularly for proper function.
Memory trick: Drain the tanks, or the ice will prank!