Arizona Air Brakes CDL Practice Test

Why do air brakes generally take longer to stop than hydraulic brakes?

1. The reaction time is longer for the driver

2. It takes longer for the air to flow through the lines

3. The linings get hotter more quickly

4. None of the above

The correct answer is: It takes longer for the air to flow through the lines

Air brakes generally take longer to stop than hydraulic brakes primarily because it takes time for the compressed air to travel through the brake lines. In air brake systems, the brake pedal's application sends a signal for air to be released from the storage tanks through the lines to the brake chambers. This involves a series of components and the movement of air, which inherently involves a delay compared to hydraulic systems, where fluid is almost instantly transmitted through the lines. Hydraulic brakes utilize incompressible fluid, which allows for quicker engagement and response since there is no significant delay in the medium converting pedal pressure into braking force. The physical properties of air, being compressible, contribute to this difference, making air brakes generally slower in achieving adequate braking force. Understanding this distinction is crucial for drivers to anticipate their stopping distance and manage safety effectively, particularly with vehicles that are equipped with air brake systems, which are common in larger trucks and buses.