A system for controlling a gas fuel flow in a fuel delivery system includes an on-demand pressure regulator. The pressure regulator includes an internal diaphragm configured to provide the gas fuel flow from an outlet port of the pressure regulator within a desired pressure range and a cut-off valve selectively blocking the gas fuel flow through the pressure regulator.

A pressure regulating chamber and an atmospheric pressure chamber are divided with a diaphragm, a pressure regulating lever connected to the diaphragm through a diaphragm pin is included in the pressure regulating chamber, and a valve element provided in a tip end side of the pressure regulating lever regulates a fuel in the pressure regulating chamber to have a predetermined pressure near an atmospheric pressure and sends the fuel while opening or closing a fuel introduction port, as the pressure regulating lever swings following displacement of the diaphragm. Connection on the pressure regulating lever side or connection on the diaphragm side, of the diaphragm pin, is separable within a predetermined range in the atmospheric pressure chamber direction. The diaphragm pin is separated to cancel the connection between the diaphragm and the pressure regulating lever when at least the pressure regulating chamber has a positive pressure of a predetermined level or more.

Example embodiments relate to a gas-pressure regulator having an inlet, an outlet, a housing, a diaphragm, a control element, a control chamber and a discharge chamber. The inlet and the outlet each open onto the control chamber, wherein the diaphragm partially delimits the control chamber. The diaphragm and the control element are movable relative to each other, wherein a passage between the control chamber and the discharge chamber is open in a relative discharge arrangement of the diaphragm and the control element. An adjustable biasing element impedes a relative movement between the diaphragm and the control element.