Continuous Gas Blender
History of the "Nitrox Stik"
Continuous Gas Blender
Dr. Morgan Wells, the former Director of the National Oceanographic and Atmospheric
Administration (NOAA), developed a process for mixing oxygen enriched air which he called a
continuous blending system. His patented invention originated as a coil of pool hose attached to
the intake of an oil free compressor. Into the opening of this hose he injected pure oxygen. The
idea was that the oxygen and air, being drawn into the compressor, would mix in the coils before
being compressed. The mixture was then measured on the downstream side of the compressor
for oxygen content. With a little trial and error he was able to gauge the oxygen input to get the
desired fraction of oxygen in the final mix.
Wells recognized that the compressor had to be oil free because the oxygen/air mixture was not
always homogenous. It was possible that streams of pure/unmixed oxygen could enter the
compressor, and when combined with the elevated temperature and the pressure in the final
stages of compression, the condensed hydrocarbons in an oil-lubricated compressor could
potentially be a combustion risk.
If more coils were added to increase the turbulence, resulting in a more complete mix, the
additional restriction (Delta P) to the compressor intake could cause damage to the compressor.
This limited Well’s system to an oil free compressor. But even with these limitations Dr. Wells'
invention was the only practical alternative to partial pressure blending for many years. That is,
until the early to mid nineties.
Ross Cowell, a Canadian maritime engineer, technical diver, and a fan of Dr. Well’s, came up
with a simple but effective method of blending nitrox without restricting the flow to the intake of
the compressor. Utilizing a mixer that blends gases at least ten times more thoroughly than the
mixing coils on the NOAA continuous mixer, he was able to produce a completely homogenous
mix of nitrox, in less than 2 milliseconds. He called his invention the "LlewocSIS". That's
"Cowell" spelled backwards, with the acronym for "Scientific Injection System".
The market, however, had other ideas. As children often acquire nicknames more appropriate
than their given names, so it happened with the LlewocSIS. Because of its appearance, people
just simply called it the "Nitrox Stick". To add a little flair we called it the "Nitrox Stik". Again
the market had different ideas and usually refers to it as the "Stik".
A "Stik" is sized according to the compressor it is to be used on/with, and the sizing takes into
consideration two main design requirements: Reynolds numbers and Delta P's.
A Reynolds number is an engineering term that is used to describe how thoroughly mixed
something is. A Reynolds number of 2000 or higher denotes something that is thoroughly (or
homogeneously) mixed.
The "Stik" has Reynolds numbers ranging from 5,000 to 60,000, depending on the size of "Stik",
and the flow of air being drawn through it.
The Delta P for the "Stik" ranges from .00 to .33 of one PSI, and refers to the additional
resistance that the "Stik" adds to the intake of the compressor. In other words, the workload of
the compressor is not noticeably increased when a "Stik" is added.
After eighteen months of field testing, an independent engineering study was commissioned and
patent applications followed. The unit now holds both US Patent and Canadian patents.
With the "Stik" being dependable, consistent, and accurate, diving operations find that they can
get into producing Nitrox at a fraction of the cost of any other system.
At the November 2000 “Nitrox Symposium” held at Duke University and sponsored by Divers
Alert Network (DAN), one of the most notable items, unanimously agreed upon, was that
40% oxygen content can be used in diving equipment,
up towithout modification.*
As most shops follow this forty percent guideline, they restrict the maximum fraction of oxygen
to 40%, and use oil-lubricated compressors.
For those facilities that choose to operate using the 21% guidelines, the use of an oxygen
serviced, oil free compressor would be indicated. Interestingly, almost one hundred percent of
the Nitrox Stik blenders are attached to oil lubricated compressors.
Mixing accurate Nitrox with the “Stik” is simply a matter of turning on the compressor,
calibrating/setting the oxygen analyzer to 21% as it analyzes the intake air, and then adding
oxygen until the desired mix is indicated on the analyzer. It is so simple to use that the phrase
"Dial-a Mix" has been used to describe its operation. What goes into the compressor intake is
what comes out. Simple.
The Gas Blending Technician is always aware of the O2 concentrations entering the compressor
because the oxygen analyzer measures the oxygen content before the gas mix is introduced into a
compressor’s intake.
The "Stik" itself is capable of mixing very high fractions of oxygen, therefore a locking micro
metering valve is placed inline to limit the oxygen content to 40%.
A medical oxygen regulator, specifically designed and manufactured for oxygen use, is used to
control the flow of oxygen through the unit. The oxygen regulator is the only part of the system
that is exposed to high-pressure oxygen concentrations above 40%, and as such, is oxygen
serviced.
The rest of the system uses much safer low pressure oxygen until it is mixed with air to become
Nitrox, eliminating the need for oxygen servicing the rest of the system, and making this a very
user friendly way of blending nitrox.
When Dr. Morgan Wells looked over the Nitrox Stik, which is the evolution of something he
started many years ago, he said, "It makes an old diver happy to see a simple philosophy in use".
One of the biggest problems facing the diving industry today is the expense of setting up a safe,
effective, and accurate Nitrox fill station in diving operations.
The Nitrox Stik solves these problems.
