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Voyager IV Nitrox System
Nuvair www.nuvair.com
Page
9
5.0 Theory of Operation
The Voyager IV Nitrox System is a turnkey package that produces oxygen-rich air (Nitrox) and then
compresses it with a High Pressure (HP) Compressor to fill Scuba Tanks or storage cylinders. The
package is designed to be fully automatic, with a quieted enclosure for noise reduction and protection
from moving parts while it is running. Although it is described as the “Nitrox Compressor”, it can also
be used to pump air.
The Nitrox System allows for efficient and cost effective Nitrox production using electric power,
without the hazards or expense of blending with stored high pressure oxygen (O
2
). Instead, the
system uses a Semi-Permeable Membrane to produce Nitrox from air. A portion of the nitrogen in air
is separated out, leaving an oxygen rich Nitrox mixture.
The Voyager IV uses a Rotary Screw LP Compressor, Air/Oil Aftercooler, Refrigerated Air Dryer, and
Filtration to provide the Membrane System with a source of clean, pressurized feed air for separation.
The air is filtered to CGA Grade D or better air quality prior to entering the Membrane System so it will
not damage or plug the Membrane fibers. Specifications for Grade D air are provided in the
Appendix.
The Voyager IV’s Membrane System is rated for a maximum feed air pressure of 300 psi (21 bar) and
has been configured to work well with the 175 psi (12 bar) maximum pressure delivered by the LP
Compressor. A Back Pressure Regulator is used to adjust the amount of air the screw compressor
produces to meet the appropriate levels for various %O
2
Nitrox production. The air is then heated to
a temperature that provides stability over a wide range of ambient conditions, is optimal for
Membrane permeation, and prevents moisture condensation.
The heated air enters the Membrane, which is made up of thousands of miniature hollow fibers. The
walls of these fibers are semi-permeable and designed for different gases to move through them (or
permeate) at different speeds. The resulting gas mixture is known as the “permeate”. As air flows
through the hollow fibers, both oxygen and nitrogen permeate through the fiber walls. The oxygen
permeates faster than the nitrogen, which produces permeate with oxygen content greater than air.
The gas that reaches the end of the hollow fibers without permeating is almost entirely nitrogen and is
discharged. The flow rate of this discharge is set by the factory via a fixed orifice, which controls the
permeate to contain a constant 44% O
2
under normal operating conditions.
The permeate is a concentrated mixture that must be diluted with additional air prior to entering the
HP Compressor. It exits the Membrane at ambient to slightly negative pressure and travels into the
Mixing Tube, where it mixes homogeneously with filtered outside air. The amount of dilution, and
thus final %O
2
, is obtained by adjusting the amount of air produced by the compressor and supplied
to the membrane, with the Back Pressure Regulator. As air flow to the membrane is increased,
permeate flow increases and a higher %O
2
Nitrox is produced. As air flow to the membrane is
decreased, permeate flow decreases, compressor intake air increases, and a lower %O
2
Nitrox is
produced.
This relationship between permeate flow and intake air flow exists because the total of these two flow
rates will always equal the intake flow rate demanded by the HP Compressor. The resulting Nitrox
mixture is analyzed for %O
2
before entering the HP Compressor for approximate content and again
when pumping Nitrox for precise content. The HP Compressor pumps the Nitrox to a maximum
pressure of 3600 psi (250 bar) to fill Scuba Tanks or storage cylinders.
A unique feature of Nuvair Nitrox Systems is that the feed air pressure that correlates to a specific
Nitrox %O
2
is repeatable. For example, if your HP Compressor pumps 36% O
2
when the feed air
pressure is at 125 P.S.I. (9 bar), then adjusting the Back Pressure Regulator to 125 psi (9 bar) during
the next use will produce the same mixture.