Two-way fuse for a fluid line

An axial flow passageway includes a bulbous chamber (8) that is circular in cross section and has a smoothly curved sidewall that blends into the fluid line in which the fuse (2) is installed. The cross-sectional diameters of the chamber (8) increase from a predetermined diameter at the inlet and outlet ends to a maximum diameter at an intermediate portion of the chamber (8). A circular plug (12) is concentric with the axis of the flow passageway and has a maximum diameter equal to said predetermined diameter. The plug (12) moves in the axial direction between an intermediate equilibrium position and first and second closed positions in which the plug's periphery seats against the sidewall of the chamber (8). In the equilibrium position, there is an annular flow passageway between said periphery and said sidewall. A spring (22) biases the plug (12) in its equilibrium position. Preferably, the plug (12) is free to move toward its second closed position, and the spring (22) is preloaded to oppose movement of the plug (12) from its equilibrium position toward its first closed position. Bleed holes (16) may be provided in the plug (12).