The hang valve should be used for what purpose?

The hang valve is primarily used to test the trailer brakes. When conducting a brake check, engaging the hang valve allows the driver to apply air pressure specifically to the trailer brakes without also affecting the tractor's brakes. This is crucial for determining whether the trailer brakes are functioning correctly and to confirm that they will operate safely while driving. Testing the trailer brakes in this manner ensures that they respond promptly and effectively, which is essential for safe operation of combination vehicles.

Using the hang valve helps verify that the brakes on the trailer are in good working condition before hitting the road. If a driver were to skip this test, they could potentially overlook a malfunctioning braking system, which could lead to dangerous driving conditions.