A flexible fuel bladder assembly for an aircraft, comprising: a flexible fuel bladder disposed at an airframe and having an opening to allow a flow of fuel into and/or out of the fuel bladder; a gravity fill breakaway valve operably connected to the fuel bladder at the opening to control a flow of fuel therethrough, the gravity fill breakaway valve being affixed to the fuel bladder via a cup connected to the fuel bladder, with the cup being affixed to a bladder wall and to a first fuselage surface at the opening via one or more fasteners, or other attachment means, the gravity fill breakaway valve including a valve body; and a reaction collar, affixed to a second fuselage surface opposite the first fuselage surface at the opening,and the reaction collar being non-contacting or loose with respect to, and interactive with, the breakaway valve such that movement of the breakaway valve relative to the reaction collar results in breakage of the valve body of the breakaway valve and closure of the breakaway valve to prevent flow of fuel therethrough, wherein the valve body includes a reaction flange extending radially outwardly from the valve body, having a flange outer diameter greater than a collar outer diameter of the collar end and located axially beyond a collar end such that the collar end is located axially between the reaction flange and the cup, wherein the valve body extends from the cup, through the fuel fill opening, through the reaction collar and further into a fuel passage fill line located within a fuel vapor barrier hose, and the reaction collar and the reaction flange are configured and aligned such that when the fuel bladder moves relative to the fuselage, the valve body moves with the bladder, such that the reaction flange impacts the collar end, and results in breakage of the valve body, the breakage of the valve body resulting in closure of the gravity fill breakaway valve, preventing fuel leakage from the bladder via the fuel fill opening. a flexible fuel bladder disposed at an airframe and having an opening to allow a flow of fuel into and/or out of the fuel bladder; a gravity fill breakaway valve operably connected to the fuel bladder at the opening to control a flow of fuel therethrough, the gravity fill breakaway valve being affixed to the fuel bladder via a cup connected to the fuel bladder, with the cup being affixed to a bladder wall and to a first fuselage surface at the opening via one or more fasteners, or other attachment means, the gravity fill breakaway valve including a valve body; and a reaction collar, affixed to a second fuselage surface opposite the first fuselage surface at the opening,and the reaction collar being non-contacting or loose with respect to, and interactive with, the breakaway valve such that movement of the breakaway valve relative to the reaction collar results in breakage of the valve body of the breakaway valve and closure of the breakaway valve to prevent flow of fuel therethrough, wherein the valve body includes a reaction flange extending radially outwardly from the valve body, having a flange outer diameter greater than a collar outer diameter of the collar end and located axially beyond a collar end such that the collar end is located axially between the reaction flange and the cup, wherein the valve body extends from the cup, through the fuel fill opening, through the reaction collar and further into a fuel passage fill line located within a fuel vapor barrier hose, and the reaction collar and the reaction flange are configured and aligned such that when the fuel bladder moves relative to the fuselage, the valve body moves with the bladder, such that the reaction flange impacts the collar end, and results in breakage of the valve body, the breakage of the valve body resulting in closure of the gravity fill breakaway valve, preventing fuel leakage from the bladder via the fuel fill opening.