A compressed gas regulator cap assembly for a pressure vessel, said compressed gas regulator cap assembly comprising: a cap body; a high pressure cavity at least partially defined by the cap body, wherein the high pressure cavity is configured to receive pressurized gas from a compressed gas reservoir; a low pressure cavity at least partially defined by the cap body, wherein the low pressure cavity is connected to the high pressure cavity via a high pressure gas passageway, wherein the low pressure cavity defines a low pressure gas passageway that penetrates the cap body and allows regulated gas to enter into the pressure vessel when such a vessel is attached to the cap assembly; a piston seat positioned on a high pressure cavity side of the high pressure gas passageway; a piston at least partially positioned in the high pressure cavity, the piston configured to regulate introduction of the pressurized gas into the high pressure gas passageway, the piston biased in a first direction by a high pressure spring to engage the piston seat; an ambient pressure cavity at least partially defined by the cap body; a spring hat; characterized in that the compressed gas regulator cap assembly comprises: a translating diaphragm positioned between the ambient pressure cavity and the low pressure cavity, the translating diaphragm being configured to translate within the cap body, wherein the translating diaphragm includes a piston translation portion configured to translate the piston relative to the piston seat and a spring surface defining a boundary of the ambient pressure cavity; a drive screw that defines a first portion of a threaded connection; in that said spring hat that includes a second portion of the threaded connection; and in that the compressed gas regulator cap assembly further comprises a main spring positioned between the spring surface of the translating diaphragm and the spring hat to bias the translating diaphragm in a second direction opposite to the first direction, wherein rotation of the drive screw translates the spring hat to affect compression of the main spring against the translating diaphragm. a cap body; a high pressure cavity at least partially defined by the cap body, wherein the high pressure cavity is configured to receive pressurized gas from a compressed gas reservoir; a low pressure cavity at least partially defined by the cap body, wherein the low pressure cavity is connected to the high pressure cavity via a high pressure gas passageway, wherein the low pressure cavity defines a low pressure gas passageway that penetrates the cap body and allows regulated gas to enter into the pressure vessel when such a vessel is attached to the cap assembly; a piston seat positioned on a high pressure cavity side of the high pressure gas passageway; a piston at least partially positioned in the high pressure cavity, the piston configured to regulate introduction of the pressurized gas into the high pressure gas passageway, the piston biased in a first direction by a high pressure spring to engage the piston seat; an ambient pressure cavity at least partially defined by the cap body; a spring hat; characterized in that the compressed gas regulator cap assembly comprises: a translating diaphragm positioned between the ambient pressure cavity and the low pressure cavity, the translating diaphragm being configured to translate within the cap body, wherein the translating diaphragm includes a piston translation portion configured to translate the piston relative to the piston seat and a spring surface defining a boundary of the ambient pressure cavity; a drive screw that defines a first portion of a threaded connection; in that said spring hat that includes a second portion of the threaded connection; and in that the compressed gas regulator cap assembly further comprises a main spring positioned between the spring surface of the translating diaphragm and the spring hat to bias the translating diaphragm in a second direction opposite to the first direction, wherein rotation of the drive screw translates the spring hat to affect compression of the main spring against the translating diaphragm. a translating diaphragm positioned between the ambient pressure cavity and the low pressure cavity, the translating diaphragm being configured to translate within the cap body, wherein the translating diaphragm includes a piston translation portion configured to translate the piston relative to the piston seat and a spring surface defining a boundary of the ambient pressure cavity; a drive screw that defines a first portion of a threaded connection; in that said spring hat that includes a second portion of the threaded connection; and in that the compressed gas regulator cap assembly further comprises a main spring positioned between the spring surface of the translating diaphragm and the spring hat to bias the translating diaphragm in a second direction opposite to the first direction, wherein rotation of the drive screw translates the spring hat to affect compression of the main spring against the translating diaphragm.