Arizona Air Brakes CDL Practice Test

What happens to the spring brakes when air pressure is released?

1. They remain engaged until manually released

2. They are held back by spring pressure

3. They are automatically applied

4. They get locked in place

The correct answer is: They are automatically applied

When air pressure is released, the spring brakes are designed to be automatically applied. This is a fundamental safety mechanism in air brake systems. The system uses air pressure to hold the brakes off. When there is a loss of air pressure—due to a leak or if the driver releases the air pressure intentionally—the springs in the brake system engage and apply the brakes. This ensures that the vehicle does not roll away and remains stationary even when the driver is not managing the brake system actively. The other choices reflect misunderstandings of how spring brakes operate. Spring brakes are not meant to remain engaged until manually released, nor are they held back by spring pressure under normal operating conditions. Instead, they rely on air pressure to remain disengaged. Furthermore, while the brakes do get "locked" in the sense that they will not release without sufficient air pressure, they are automatically applied as a safety response to ensure the vehicle is secure when air pressure falls below a certain threshold.