Pre-Trip Inspection of the Air Brake System
What the exam tests
This domain covers the visual and physical inspection you perform before driving. The exam expects a logical walk-around, correct drain procedure, and recognition of unsafe air-brake conditions.
Walk-around checks
Chock the wheels and use safe PPE. Check the compressor belt for condition and tension, the air dryer, hoses and lines for cracks or rubbing, brake chambers, slack adjusters, drums, linings, and mounting hardware. Pull hard on each slack adjuster; it should not move more than about 1 inch. Inspect the warning light and buzzer, gauges, and spring-brake condition.
Draining tanks
Open reservoir drain cocks and drain until the air is clear. Water or milky fluid means contamination; oil means compressor carryover. Drain daily, and do not simply add air and drive.
Air buildup check
Start the engine, run at fast idle, and build pressure from 85 to 100 psi within 45 seconds. Slow buildup points to a leak, a weak compressor, a slipping belt, or a governor problem.
Worked example
During draining, the first tank releases milky fluid. You drain until it runs clear, then note the condition and report it. The correct reasoning is that water in the system can freeze or corrode valves; clearing it is necessary, but the source still needs attention.
Traps that cost marks
Do not skip chocking or drain checks. Do not judge the system only by the dash gauge. Do not ignore a slack adjuster that moves too far or a chamber with a cracked housing. A quick visual glance is not a complete pre-trip inspection.