When you pull out the trailer air supply control, what is being tested?

When you pull out the trailer air supply control, you are effectively testing the emergency brakes of the trailer. This control is designed to supply air to the trailer's braking system and ensure that the emergency brakes are functioning properly. When the control is pulled, it allows air pressure to fill the trailer's air tanks, which in turn releases the brakes if they were previously engaged.

The emergency brakes are a crucial safety feature in commercial vehicles, especially since they are designed to activate automatically if there is a disruption in the air supply between the tractor and the trailer. Understanding this function helps drivers confirm that the emergency systems are operational before departing. This test is vital for maintaining safety on the road, particularly when transporting heavy loads, where effective braking is essential.