Question Air storage tanks: Answers Are not allowed on a vehicle. Hold compressed air for the brakes. Should be drained of excess air after every trip. Explanation In an air brake system, the air storage tanks hold compressed air to be used by the brakes. The number and size of air tanks varies among vehicles. Take a FREE Practice Test Now This questions appears in the following tests: Wisconsin Knowledge Test Class B , Wyoming Knowledge Test Class B , Iowa Air Brakes , Missouri Air Brakes , Rhode Island Air Brakes ,