This SAE Aerospace Information Report (AIR) presents historical information and background data related to hydrant valves and couplers used in worldwide ground refueling of commercial aircraft (hereafter generically referred to as hydrant devices). Military hydrant devices are not included since their mission requirements demand approaches that may differ.The purpose of this document is to provide definitions, background and educational information for use by design engineers, users of the systems and other interested parties who are involved with hydrant devices and associated equipment.