Michigan CDL - Air Brakes Practice Exam

What device indicates the pressure in the air tanks of a vehicle with air brakes?

1. Air pressure regulator

2. Supply pressure gauge

3. Brake warning light

4. Pressure relief valve

The correct answer is: Supply pressure gauge

The device that indicates the pressure in the air tanks of a vehicle with air brakes is the supply pressure gauge. This gauge plays a critical role in monitoring the air pressure within the system, ensuring that it remains at an optimal level for safe and effective brake operation. When drivers check the supply pressure gauge, they can assess whether the air tanks have adequate pressure to engage the brakes properly. Insufficient air pressure can lead to brake failure or reduced braking effectiveness, making it vital for the gauge to provide accurate readings during vehicle operation. This allows the driver to take necessary action if the pressure drops below a safe threshold. The air pressure regulator, while related to managing air pressure, does not directly indicate pressure levels. Instead, it functions to maintain consistent pressure within the system. The brake warning light is designed to alert the driver to critical issues with the braking system, but it does not provide specific pressure measurements. Lastly, the pressure relief valve is a safety feature that prevents excessive pressure buildup in the air tanks but does not indicate the current pressure level. Thus, the supply pressure gauge is clearly the device responsible for showing how much air pressure is available in the air tanks.