Question What is a tractor protection valve? Answers A valve to keep air in the brake system should there be a bad leak A valve that prevents a truck from being stolen A valve that prevents the driver from driving too fast 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: Oklahoma Tank , Alaska Combination , Maryland Combination , Mississippi Combination , Virginia Combination ,