What feature of air brakes helps to prevent overheating during extended braking?

Spring brakes are a crucial feature of air brake systems that contribute significantly to preventing overheating during extended braking. They operate using a combination of compressed air and spring force, which helps to maintain effective braking performance without continuous reliance on air pressure.

When the driver applies the brakes, air from the reservoir is used to compress the spring. In situations where brakes are applied for an extended period, such as when descending long grades, the spring mechanism provides a fail-safe mode. If the air pressure were to drop or fail due to overheating or any other issue, the spring brakes automatically engage, ensuring that the vehicle remains under control and preventing further heat build-up that could result from continued braking.

While the other features listed play important roles in the functionality of air brake systems, they do not directly prevent overheating as effectively as spring brakes. An air cooling system is not an inherent feature of standard air brakes, an automatic adjustment mechanism primarily serves to maintain brake performance through proper adjustment, and an air dryer helps remove moisture from compressed air but does not directly impact brake heating during extended use.