What component supplies the force to keep air brakes released?

The component that supplies the force to keep air brakes released is the coil springs. In an air brake system, when the brakes are released, the energy stored in the coil springs is utilized to maintain the brake in an unengaged position. This is essential because it ensures that the brakes are not applied when the train is in motion or when it's not required to be stopped.

Once the brake system is activated, compressed air is used to apply the brakes, but to keep them released, the coil springs provide the necessary force to counteract the air pressure. This mechanical action is critical in preventing unintentional braking, which could occur if the air supply were to fail or be lost.

Other components mentioned, such as pneumatic actuators and electric motors, serve different purposes within the braking system. Pneumatic actuators are primarily responsible for applying the brakes when needed, while electric motors are not directly involved in the release mechanism of air brakes. Hydraulic fluid pertains to hydraulic brake systems, which are different from air brake systems found on trains. Thus, the role of coil springs as the mechanism that keeps air brakes released is foundational to the operation and safety of train braking systems.