What produces the braking action in a spring-loaded brake cylinder?

You answered correctly. In a spring-loaded brake cylinder, the braking force is created by the power of the spring. When the system is activated, the spring pushes the brake components to apply the brakes. Compressed air is used to release the brake, not to apply it. This is a safety feature, ensuring that if air pressure is lost, the spring will automatically engage the brakes. Understanding this helps you identify how safety brakes work, especially in vehicles like trucks and buses with air brake systems.