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SAE AIR4782 Revision A, August 1, 2008
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Hydrant Valve and Coupler Historical Background
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AIA/NAS Aerospace Standards
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.

Field of Application

Soon after World War II, the military techniques for underwing refueling of turbine-engined aircraft were adopted for use on commercial aircraft. Advantages include significantly improved safety, convenience and rapidity of refueling.

Refueling systems for commercial aircraft evolved to comprise five basic elements, as follows:

Hydrant systems (or supply systems)

Hydrant couplers (hydrant system to servicer systems)

Servicer system (hydrant to aircraft)

Aircraft couplings (service systems to aircraft fuel systems)

Aircraft fuel systems

Element (d), the aircraft couplings, are now true worldwide standards, having been adopted for military and commercial aircraft of all countries, and controlled by international standard documents.

This document applies to the hydrant valve portions element (a), the entire element (b) and applicable portions of element (c). Some references to other elements are included, where pertinent.