An assembly provides a proportioned gas flow and includes a device that provides a pressurized flow of said gas, a release unit that releases the proportioned gas flow, and a chamber having an inlet fluidically connected to the device and an outlet fluidically connected to the release unit. The assembly further includes an admission valve inserted between the inlet of the chamber and the device, a metering valve inserted between the outlet of the chamber and the release unit, and a computer programmed to control the admission valve and the metering valve to provide a proportioned gas flow to the release unit. The assembly further comprises a calibrated orifice inserted between the outlet of the chamber and the release unit.