A pressure regulator assembly including a regulator valve, a spring guide, a spring extending between the spring guide and regulator valve for setting operation of the regulator valve, a sleeve coupled to the spring guide, a spring cage coupled to the sleeve, an adjustment stem coupled to the sleeve, a dial assembly coupled to the spring cage, and an adjustment cap coupled to the adjustment stem, wherein when the cap is depressed, interaction between the spring cage, spring guide and sleeve causes the spring guide to selectively rotate between a normal mode and a fast-fill mode. In the normal mode, adjustment of the cap determines an output pressure. In the fast-fill mode, the spring is further compressed by movement of the spring guide to a predetermined setting to provide a predetermined output pressure.