A pressure regulator assembly has a normal mode and a regulated fast-fill mode and includes a spring cage and a body coupled together. The spring cage and body define an inlet in fluid communication with an outlet as well as an interior between the inlet and the outlet. A diaphragm assembly mounts in the interior for selectively closing a flowpath between the inlet and the outlet. A preload spring in the interior applies force on the diaphragm assembly so that in the normal mode, the flowpath is closed if a downstream pressure is above a first pressure. An actuation assembly includes a lever coupled to the spring cage and a push rod mounted so that in the regulated fast-fill mode, the lever slides so that the push rod further compresses the preload spring to open the flowpath and regulate flow therethrough if the downstream pressure is below a second pressure.