What is the maximum allowable leakage at the check valve on the air dryer?

The maximum allowable leakage at the check valve on the air dryer is determined based on the standard for air brake systems. A one-inch soap bubble every second indicates a small amount of leakage that is considered acceptable for maintaining efficient air brake system operation. This level of leakage signifies that while there is some loss of air through the check valve, it does not pose a significant risk to the performance or safety of the braking system.

In contrast, larger amounts of leakage, which might be indicated by the other choices, would raise concerns about the potential for brake system failure or inefficiency due to insufficient air pressure. Maintaining air pressure is crucial for the proper functioning of the braking system, so standards are set to ensure that leakage remains minimal. The one-inch soap bubble every second reflects a tolerable limit that ensures the system remains safe and operational while allowing for normal functioning of the air dryer and its associated components.