Compressed air powers many of the most vital functions in rolling stock of all lengths and capacities.

The components of a train that rely on compressed air include the brakes, doors, and suspension system. Without compressed air, a train would be unable to halt when needed, open and close its doors properly, or offer smooth rides for passengers and cargo. Each of these functions can slow and ultimately fail if impurities enter the compressed air that is used to power the doors, brakes, and other components.