Inspecting the Air Brake System (Pre-trip Checks)
The inspection domain tests the order and pass/fail limits of the air-brake pre-trip. Florida expects a driver to drain tanks, build pressure, test the warning and spring brakes, measure leakage, and check foundation brakes. A missed step can hide a defect that only appears under braking.
Tank and compressor checks
- Drain every reservoir and watch for water or oil; close the drains before testing.
- With the engine at normal idle, pressure should build from 85 to 100 psi within 45 seconds.
- The governor should cut out near 125 psi and cut in near 85 psi; the safety valve is near 150 psi.
Warning and spring-brake checks
- Engine off, ignition on, release the parking brake, and fan off pressure.
- The low-pressure warning must come on before pressure drops below 60 psi.
- Continue reducing pressure; spring brakes should apply at about 20-45 psi.
Leakage and brake tests
- Fully charged, engine off, brakes released: loss must not exceed 3 psi per minute for a single vehicle or 2 psi for a combination.
- Brakes applied and held: limit is 4 psi per minute single, 3 psi per minute combination.
- At low speed, apply the service brake and check for stopping and pulling; then test the parking brake.
Worked example
A combination vehicle is charged to 120 psi. With the engine off and brakes released, pressure drops 2 psi in one minute; that passes the 2 psi combination limit. With the brakes applied and held, pressure drops 4 psi in one minute; that fails the 3 psi combination limit. The vehicle should not be dispatched until the leak is found and corrected.
Traps that cost marks
- Running the engine during a leakage test and getting a false pass.
- Using the single-vehicle limit on a combination.
- Letting the compressor cycle while fanning pressure down.
- Skipping reservoir drains because the gauge looks normal.
- Chock wheels before crawling under.