Question What must be on an air tank in an air-braked vehicle? Answers A check valve A lock A trap door An oxidizer Explanation All air tanks on air-braked vehicles must have one-way check valves located between the air compressor and the first reservoir. This prevents air from flowing out in the event of a leak. Take a FREE Practice Test Now This questions appears in the following tests: Utah Knowledge Test Class A , District Of Columbia Double , Wyoming Double , Nebraska Air Brakes , New Hampshire Air Brakes ,