A pressure-increasing unit comprising: a first receiving means for receiving a pipeline conveying pressurized gas from a main source, at least one first pipeline connected to the first receiving means and configured to further transfer the pressurized gas to applications utilizing pressurized gas from the main source, and a second receiving means for receiving a second pipeline conveying reduced-pressure gas returning from the gas-utilizing applications, the pressure-increasing unit further comprising at least one pressure intensifier, the pressure intensifier being arranged to receive the reduced-pressure gas; said second receiving means being connected to the at least one pressure intensifier, the pressure-increasing unit further comprising a substitution means arranged to connect the pressure intensifier with the first receiving means for receiving pressurized gas from the main source, and configured to transfer re-pressurized gas back to the gas-utilizing applications via the first pipeline, the pressure-increasing unit being characterized in that the pressure intensifier is arranged to re-pressurize the reduced-pressure gas by utilizing energy contained in the gas flow returning from the gas-utilizing applications, and wherein the substitution means is disposed between the pipeline and the first pipeline such, that when the pressure of the re-pressurized gas received from the pressure intensifier is higher than the pressure of the pressurized gas coming from the main source via the pipeline, the substitution means is arranged to cut off a flow of the pressurized gas coming from the main source via the pipeline and the re-pressurized gas moves through the substitution means to the gas-utilizing applications via the first pipeline, and wherein the pressure increasing unit is separable from the main source. a first receiving means for receiving a pipeline conveying pressurized gas from a main source, at least one first pipeline connected to the first receiving means and configured to further transfer the pressurized gas to applications utilizing pressurized gas from the main source, and a second receiving means for receiving a second pipeline conveying reduced-pressure gas returning from the gas-utilizing applications, the pressure-increasing unit further comprising at least one pressure intensifier, the pressure intensifier being arranged to receive the reduced-pressure gas; said second receiving means being connected to the at least one pressure intensifier, the pressure-increasing unit further comprising a substitution means arranged to connect the pressure intensifier with the first receiving means for receiving pressurized gas from the main source, and configured to transfer re-pressurized gas back to the gas-utilizing applications via the first pipeline, the pressure-increasing unit being characterized in that the pressure intensifier is arranged to re-pressurize the reduced-pressure gas by utilizing energy contained in the gas flow returning from the gas-utilizing applications, and wherein the substitution means is disposed between the pipeline and the first pipeline such, that when the pressure of the re-pressurized gas received from the pressure intensifier is higher than the pressure of the pressurized gas coming from the main source via the pipeline, the substitution means is arranged to cut off a flow of the pressurized gas coming from the main source via the pipeline and the re-pressurized gas moves through the substitution means to the gas-utilizing applications via the first pipeline, and wherein the pressure increasing unit is separable from the main source.