Answer :
Final answer:
The trailer supply valve's main purpose is to supply air to the trailer brakes and can activate the emergency brakes during a disconnection or failure.
Explanation:
The main purpose of the trailer supply valve is to supply air to the trailer brakes. When a driver engages this valve, air from the tractor's air system fills the trailer's air tanks and readies the trailer brakes for operation. It is crucial for safely towing a trailer, as it ensures that the brakes are available when needed.
In the event of a disconnection or air supply line failure, this valve can also activate the emergency brakes on the trailer, helping to prevent a runaway situation. The other options, such as supplying air to the tractor brakes, modulating air pressure in the brake chamber, and activating the emergency brakes, are separate functions handled by different components of the truck's air brake system.
