CDL Air Brakes TestUsing Air BrakesEasy
A driver is parking a commercial vehicle equipped with air brakes on a level surface. After securing the vehicle, what is the correct sequence for applying the parking brake and shutting down the engine?
- AShut off the engine, then engage the parking brake.
- BEngage the parking brake, wait for air pressure to drop, then shut off the engine.
- CEngage the parking brake, then shut off the engine.
- DShut off the engine, then release air pressure from the system before engaging the parking brake.
Show answer & explanationAnswer & explanation
Correct answer: C. Engage the parking brake, then shut off the engine.
The proper procedure is to first engage the parking brake to secure the vehicle, then shut off the engine. This ensures the vehicle is safely immobilized before the air compressor stops operating and air pressure might slowly leak down.
Why the other options are wrong
- A. Shutting off the engine first means the air compressor stops, and if there's a slow leak, pressure could drop before the parking brake is engaged, potentially allowing the vehicle to roll.
- B. Waiting for air pressure to drop is unnecessary and counterproductive; the parking brake uses spring pressure, which is released by air pressure, so engaging it is done while air pressure is present.
- D. Releasing air pressure before engaging the parking brake is incorrect; the parking brake applies when air pressure is released from its control line, so it's engaged by pulling the valve, which dumps the air from that line.
Parking Procedure (Air Brakes)
The correct sequence of actions to safely secure a commercial vehicle with air brakes when parking, typically involving engaging the parking brake before engine shutdown.
- Engage parking brake first.
- Then shut off the engine.
- Ensures vehicle is secured.
- Prevents accidental rolling.
Memory trick: Park first, then power off.