Atmospheric air contains essentially 78% nitrogen and 21% oxygen. Ordinary dry compressed air is filtered and passed through a technically advanced bundle of hollow membrane fibers where nitrogen is separated from the feed air by selective permeation. Water vapor and oxygen rapidly permeate safely to the atmosphere, while the nitrogen gas is discharged under pressure into the distribution system. Pressure, flow rate and membrane size/quantity are the main variables that affect nitrogen production. Nitrogen purity (oxygen content) is controlled by throttling the outlet from the membrane bundle(s). At a given pressure and membrane size, increasing the nitrogen flow allows more oxygen to remain in the gas stream, lowering nitrogen purity. Conversely, decreasing nitrogen flow increases purity. For a particular purity, higher air pressure to the membrane gives a higher nitrogen flow rate. Purity ranges of less than 90% to 99.9% are possible. By combining multiple membrane bundles, an infinite number of flow/purity ranges are available to satisfy practically any application that requires nitrogen gas.