CDL Air Brakes TestAir Brake System PartsEasy
A driver is performing a brake test on a vehicle equipped with dual air brake systems. After fully charging the system, the driver applies the parking brake and then releases the service brake. Which of the following should occur?
- AThe service brakes should remain applied due to residual pressure.
- BThe parking brake should remain engaged, holding the vehicle.
- CThe parking brake should release automatically as the service brake is released.
- DThe low air pressure warning should activate immediately.
Show answer & explanationAnswer & explanation
Correct answer: B. The parking brake should remain engaged, holding the vehicle.
The parking brake, typically spring brakes, is designed to remain engaged when applied, holding the vehicle, regardless of the service brake application or release. It is released by air pressure, not by releasing the foot pedal.
Why the other options are wrong
- A. Releasing the service brake pedal should release the service brakes, not keep them applied.
- C. The parking brake operates independently from the foot pedal after it's been set.
- D. The low air pressure warning would only activate if significant air is lost, not simply by applying and releasing the parking and service brakes.
Parking Brake Function
The parking brake on commercial vehicles uses spring brakes that are held in the 'off' position by air pressure and apply automatically when air pressure is lost or the parking brake control is activated.
- Primarily uses spring brakes.
- Must hold the vehicle on a grade.
- Released by air pressure, applied by spring force.
Memory trick: Springs are strong, air keeps them calm.