Abstract: A valve assembly for selectively connecting either one of a pair of fuel supply tanks through supply and return lines to and from a combustion engine while isolating the other tank from communication both with the selected active tank and with the engine. The valve includes first and second chambers dedicated respectively to supply and return service. Valving elements in the chambers are operated by a selector shaft shiftable between first and second positions corresponding to the first and second tanks. The valve is advantageously ported in a manner which only requires a single supply line and a single return line to and from the engine.