Alabama CDL General Practice Test

In an air-brake system, what factor ensures the spring brakes remain retracted during normal operation?

Hydraulic pressure Air pressure Oil temperature Tire pressure

Correct Answer:

Air pressure

Explanation:

Spring brakes are spring-applied, air-released. The air pressure in the brake chambers counteracts the force of the release springs, keeping them retracted and the brakes released during normal operation. If air pressure drops, the springs push out to apply the brakes. Hydraulic pressure, oil temperature, or tire pressure don’t control this release mechanism.

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