Pre-Trip Inspection and Air Brake Tests
Pre-Trip Inspection and Air Brake Tests
This domain tests the ordered checks that prove an air-brake system can build, hold and release pressure, and that emergency braking will work. The exam expects a safe sequence: secure the vehicle, drain moisture, build pressure, test warning and leaks, then inspect foundation brakes.
Core rules
- Chock wheels and use safe PPE. Drain all reservoirs, including the wet tank, and watch for excessive water or oil.
- Start the engine and build pressure. Note governor cut-out and cut-in. The compressor should build pressure within the manufacturer's time; a slow build can indicate a weak compressor, leak or restricted intake.
- With the engine off and system charged, check the low-pressure warning. It must activate before pressure falls below about 60 psi.
- Perform static and applied leak tests. Common limits are no more than 3 psi/min for a single vehicle and 4 psi/min for a combination with the service brake applied; always use the current Saskatchewan test standard and vehicle specification.
- Test spring brakes: with wheels chocked and pressure built, release the parking brake; as pressure is drained, spring brakes should apply in the typical 20–45 psi range.
- Inspect pushrod stroke, slack adjusters, linings, drums/discs, hoses and chamber condition.
Worked example
After draining tanks, pressure builds from 85 to 100 psi in 40 seconds and cuts out at 122 psi. Engine off, brakes released, the gauge drops 5 psi in the first 30 seconds, then holds at 118 psi for the next minute. Reasoning: the initial drop is normal stabilization; the steady reading shows no continuing leak. The build time and cut-out are acceptable if they match the vehicle specification. Record the values.
Traps
Do not test leaks with the engine running. Do not accept a warning that sounds only below 20 psi. Do not skip the applied leak test. Do not confuse pushrod stroke with slack-adjuster free play. Do not release spring brakes before chocking wheels.