ASE School Bus Technician Brakes (S4) Complete Practice Test 2025

The low pressure warning device in air brake systems is installed on the primary reservoir system. This device is crucial for monitoring the air pressure within the braking system and ensuring safety during operation. When the air pressure drops below a certain threshold, the low pressure warning device activates, providing a visual or audible alert to the driver.

Installing the warning device on the primary reservoir is important because the primary reservoir typically feeds the service brakes, making it essential to monitor its pressure directly. If the primary reservoir experiences low pressure, the effectiveness of the service brakes can be compromised, which poses a significant safety risk. The early warning allows drivers to take necessary action and address potential issues before they escalate.

In contrast, the secondary reservoir, service brake system, and emergency brake system serve different roles in air brake operation and may not provide immediate warning regarding the overall pressure of the system critical to ensuring the service brakes perform effectively.