Question The tractor protection valve: Answers Ensures that oil adequately lubricates the engine. Protects the tractor from exceeding a set speed. Keeps air in the truck braking system if the trailer develops a leak. Explanation 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. Take a FREE Practice Test Now This questions appears in the following tests: Rhode Island Double , Alaska Combination , Arizona Combination , Iowa Combination , Kentucky Combination , Missouri Combination , Vermont Combination , Virginia Combination ,