Abstract: A passive dual modulating regulator that responds to a pressure differential between a hydrogen-side and an oxygen-side of one or more proton-exchange membrane (PEM) cells is provided. The passive dual modulating regulator includes a flexible diaphragm that is clamped along its periphery between hemispherical chambers. A bi-directional valve assembly extends through the flexible diaphragm and includes opposing valve plugs for selectively closing the output ports of the respective hemispherical chambers. Large or sustained pressure imbalances between the hydrogen-side and the oxygen-side of a hydrogen generation system are avoided without active control inputs of any kind, and consequently a rupture of the PEM is entirely avoided.