The tractor protection valve:

Question

A tractor protection valve keeps air in a tractor or truck air brake system should the trailer break away or develop a bad leak. The valve will close automatically if the pressure drops to an unsafe level.

Accepted Answer

Keeps air in the truck braking system if the trailer develops a leak.

Answer

Ensures that oil adequately lubricates the engine.

Answer

Protects the tractor from exceeding a set speed.