What is the primary role of spring brakes in air brake systems?

The primary role of spring brakes in air brake systems is to provide both parking and emergency braking. Spring brakes are a type of brake that relies on a spring mechanism to apply the brakes when the air pressure in the system drops below a certain point. This design is crucial for safety, as it ensures that the vehicle can be stopped and held in place even in the event of a failure in the air brake system.

When the air pressure is released, the spring brakes automatically engage, providing a reliable method to prevent the vehicle from rolling when parked or to bring it to a stop in case of an emergency. This feature enhances the overall safety of vehicles equipped with air brake systems, especially in combination vehicles, where the weight and momentum can be substantial.

Other roles such as assisting with acceleration, serving as the primary brake system, or controlling trailer sway are not applicable to spring brakes specifically. Acceleration is typically managed by the vehicle's engine, and primary braking is handled by the service brakes, which are different from spring brakes. Additionally, trailer sway is generally controlled through other means such as electronic stability control or proper load distribution, rather than through the function of spring brakes.