A combined valve-regulator apparatus, for safely regulating the flow of combustible gases such as oxygen. A compressible o-ring is used to provide controllable sealed seating of the valve and regulator during operation. A system is provided in the valve-regulator apparatus for venting the o-ring seat elements, to minimize undesirable ballooning or extrusion otherwise resulting from dynamic pressures and changing forces due to rapid gas flows through the regulator.