In the context of brake testing, what does "pumping down the service brake" involve?

Pumping down the service brake involves gradually decreasing the air pressure in the brake system. This process is a critical part of ensuring that the braking system is functioning properly. When a driver pumps the brake pedal, it allows the driver to assess how the brakes respond and whether there is sufficient air pressure for the brakes to engage effectively.

During this process, if the air pressure decreases excessively or does not return to the appropriate levels, it may indicate a potential issue in the braking system, such as leaks or insufficient air supply. Therefore, understanding how to properly manage air pressure through this method is essential for safe vehicle operation and ensuring that the service brakes are reliable.