Air Brake Practice Test

The device that plays a crucial role in maintaining pressure in the air brake system when it detects low pressure levels is the low pressure warning light. This light serves as an alert to the driver that the air pressure in the system has dropped below a certain threshold, indicating a potential problem that could affect brake functionality.

When the warning light activates, it signals the operator to take immediate action, such as checking the air pressure and inspecting for potential leaks or malfunctions. Thus, the low pressure warning light is essential for ensuring the driver is aware of the system's status and can respond accordingly to maintain safe braking performance.

Other options discuss devices related to pressure management or adjustments, but they do not perform the critical function of warning the driver about low pressure specifically. The pressure relief valve, for example, is designed to prevent over-pressurization, while the regulator valve helps maintain consistent pressure levels. The brake adjustment gauge is used for checking and adjusting the brake's mechanical components, but it does not play a direct role in monitoring air pressure levels.