Why is it necessary to pump the brakes when checking the parking brake?

Pumping the brakes when checking the parking brake is important because it helps to reduce air pressure in the brake lines. When you pump the brake pedal, it allows for the adjustment of the brake system's air pressure, which can enhance the performance of the brakes. This is particularly significant in vehicles equipped with air brake systems, where maintaining appropriate air pressure is crucial for effective brake operation. By reducing excess air pressure, the capacity and reliability of the parking brake can be better assessed, ensuring that it functions correctly when engaged. Thus, the practice of pumping the brakes contributes to a more accurate evaluation of the parking brake's effectiveness and general safety of the vehicle.