Nitrox Membrane Systems

What is nitrox?

In diving terminology; any mixture of nitrogen and oxygen, where these two gases represent the major constituents of the gas mix, is termed nitrox. Note that mixes which contain more than trace levels of other gases in addition to nitrogen and oxygen are not nitrox. Air is considered a nitrox mix. Nitrox mixes which are hyperoxyc (contain more than 21% oxygen) are variously known as; enriched air, enriched air nitrox (EAN or EANx)

Who Uses Nitrox?

Nitrox is used extensively within the Recreational, Technical and Commercial Diving Industries. It is also receiving widespread adoption amongst Fire and Rescue Service professionals and has been used for many years by elite military and Naval units.

NITROX, is no longer breaking news, it has been used for more than 4 decades by technical and commercial divers in order to extend their bottom time and to reduce the content of Nitrogen gas in favor of a higher percentage of Oxygen. Divers undoubtedly can enjoy several benefits by using nitrox instead of normal air. The most significant benefit is the increased level of safety for divers, less nitrogen means less bubbles and decreased exposure to DCS. However the expenses and skill level required for Nitrox production has made Nitrox sometime difficult to find, limited to only a few specialized facilities. The recent introduction of de-nitrogenating air membranes, has changed all this. The production and processing of nitrox and tri-mix has now become safe, practical and easy. Training agencies are now seriously considering promoting Nitrox as the gas of choice for leisure scuba diving. Diving is now a intensely competitive industry and any technology which can offer the dive shop manager or owner a competitive advantage can only be an asset, the membrane allows the filling of Nitrox tanks at the same rate as the filling of standard air tanks, no more expensive O2 cylinders, no need for any booster pumps or the worry that your dive shop will go up with a bang with an inadvertent blending mistake. With our Nitrox production membrane systems Coltri-Sub Asia Pacific offer an affordable and reliable way to produce Nitrox as cheaply and as fast as your HP compressor can deliver air.

Seize this opportunity! Be at the forefront of dive technology and ahead of your competition.

Nitrox Filling utilizing a Membrane production system. Membrane Systems have dramatically changed the concept of diving with Nitrox. The System produces any blend of N202 (nitrox) from 21% through 40% oxygen by de-nitrogenating (removing nitrogen) instead of enriching standard air with high-pressure oxygen. The de-Nitrogenated air is produced by the Low pressure membrane system which in turn feeds a High Pressure compressor, pumping Nitrox directly into a scuba cylinder.

Operator's Benefits


Much safer to operate eliminating all the HAZARDS related to handling 100 % OXYGEN Complete "Turnkey" operation- Preset' mix( 21-40%) Simply adjust input pressure to get the desired o2% Percentage of mix is readable on real time the LCD Oxygen anlyser.Only 1-hour operator training required operator DOES NOT require Gas Blender Certification 2 Hour average installation


Does not require O2 cleaning of tanks and/or equipment
No practical need to have dedicated Oxygen clean Nitrox equipment as the filling procedure never involves O2 mixtures above 40 % virtually eliminating possibility of Oxygen induced explosion-Decreased liability deterioration and lower Live aboard vessel or building- insurance premium. No broker will insure a dive boat and /or building knowing that a 100 % O2 is blended aboard the vessel with a partial pressure blending panel, as well no insurance company will reimburse an occurrence if ascertained that hazardous gas was blended on board. High filling performance: as fast as the HP compressor No need for consumables, with the membrane system there is no need to use oxygen cylinders, which needs frequent refilling. In Asia O2 tanks are often filled at anywhere from 120 - 250 Bar, but the last 50 bar of the oxygen tank is inaccessible without an expensive booster pump (approx 7,000U$). Also note that the oxygen used in Asia is often not medical grade and usually utilized for welding. Cost Effective: High volume output means no waiting for fills Easy maintenance (1 inexpensive filter change each quarter) Operates on Grade E Air .No hidden costs


Mix accurate to one tenth of 1%.

No need for time consuming and complicate blending calculation.

Membranes do not have mechanical wear or chemical deterioration, if correctly utilized membrane components have over 20 years life span.

Produces from 21% to 40% oxygen with continuous production

A conversion Kit is available to allow the system to produce Trimix.

The HP compressor part of the system can be used to fill air or nitrox tanks with no adjustments.

Portable The unit can be moved around from boat to dive shop wherever Nitrox is required.

Function of The Permeable Membrane System

Function of The Permeable Membrane System

Low-pressure air (100psi-300psi) is fed to the hollow membrane fibers. All the oxygen molecules pass through the hollow fiber walls but only some of the nitrogen molecules move through resulting in up to 40% nitrox

The Coltri/Nuvair Nitrox Membrane System uses a Semi-Permeable Membrane to produce oxygen-rich air (Nitrox). A portion of the nitrogen in air is separated out, producing a Nitrox mixture containing between 24 and 40% oxygen (O2). The input pressure to the Membrane System determines the %O2 produced. The Nitrox is then delivered to a High Pressure (HP) Compressor to fill Scuba Cylinders or Storage Tanks or to a Low Pressure (LP) Compressor for delivery to surface-supply divers. This Compressor is described as the "Nitrox Compressor", but is also used for air. The Membrane System requires a source of clean, pressurized, and heated air for separation. The two most common sources are HP Air Storage Tanks (HP Supply Option) or an LP Compressor (LP Supply Option). The air must be properly filtered to CGA Grade D or E air quality prior to entering the Membrane System so it will not damage or plug the Membrane fibers. Specifications for Grade D and E air are provided in the Appendix. Maximum allowable supply pressures are 5000 P.S.I. for HP Supply and 250 P.S.I. for LP Supply. An Input Pressure Regulator reduces these pressures to acceptable levels for the Membrane. The air is then heated to a temperature that provides stability over a wide range of ambient conditions and is optimal for membrane permeation. The heated air then enters the Membrane, which is made up of thousands of miniature hollow fibers running axially through a cylindrical housing. 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 an 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 establishes the %O2 of the permeate and is factory set via a fixed orifice to contain approximately 44% O2 under all operating conditions.

The permeate is a concentrated mixture that must be diluted with additional air prior to delivery to the Nitrox 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 %O2, is obtained by adjusting the Input Pressure Regulator. As pressure is increased, permeate flow increases, air flow decreases, and a higher %O2 Nitrox is produced. As pressure is decreased, permeate flow decreases, air flow increases, and a lower %O2 Nitrox is produced. This relationship between permeate flow and air flow exists because the total of these two flow rates will always equal the intake flow rate demanded by the Nitrox Compressor. The resulting Nitrox mixture is analyzed for %O2 before delivery to the Nitrox Compressor and again at the point of Nitrox delivery.

The production benefits are just as significant especially the safety of the staff responsible for producing enhanced breathing gasses.

Existing oxygen mixing and blending setups employ high oxygen concentrations that require oxygen clean (free of contamination) equipment. Our denitrogenated air never exceeds 40% oxygen and does not require O2 cleaning. It eliminates the traditional procedures designed to reduce the risk of explosion and fire. Furthermore, concerns such as additional insurance costs; hazard potential and voided warranties for equipment exposed to pure oxygen are eliminated.

Why Choose our Membrane?

The Coltri/Nuvair (Patent Pending) De-nitrogenating membrane can operate at temperatures 15 degrees C and above supplied by a low pressure compressor and no heater, but the Permea membrane is most efficient at about 40 degrees C. And our integrated heater provides temperature stability, which means that there will be very little temperature fluctuation resulting in a stable O2% flux level during the course of the day. Reheating the air also accomplishes what is known as air conditioning. During the manufacture of the nitrox the air is heated by compression. (Within an LP type system) It is then cooled in an air after cooler and volume tank which changes the dew point of the compressed air. The cooled air drops moisture in the volume tank which is then filtered for moisture, particles and oil vapor. After filtration heating the air (before passage through the membrane) raises the dew point, therefore remaining moisture will not come out of the air as it travels through the membrane resulting in longer membrane life and a more stable flux level.


The Coltri/Nuvair (Pat. Pend.) Membrane is very efficient and also very durable (30 years+) compared to other membranes on the market. We offer a 50,000 Hour/30 Year limited warranty on our membranes The increased durability comes from the patented process that allows permeation, and has a special coating on the outside of the plastic tubes in the membrane unlike other manufacturers which choose to place the coating inside the plastic tubes. This outside coating means the fibers will not be damaged as easily with hydrocarbons and oil vapor.

Output Ratios

The efficiency of the membrane means a relatively low input output ratio, meaning lower usage and operating levels and consequently lower production cost. The nitrox output can be guaranteed up to 40 % ++ No other membrane currently on the market can match these results

Below is a production ratio chart compared with a rival membrane system

Function of The Permeable Membrane System

NRC Membrane ratios are taken from NRC's own published figures *40 % figure are not published but an estimate based on extrapolating 32/36% production figure

Effects of the Uncontrolled Permeation found in other membranes in the marketplace

Also on the market is the Parker (Aquilo) membrane. This is capable of producing a high output volume at normal ambient temperatures but unfortunately also allows a high level of nitrogen to permeate with the O2. As temperatures increase this unwanted nitrogen permeation also increases, not desirable in tropical diving settings. This means O2 is also flowing out the N2 exhaust port and N2 is also flowing out of the N2O2 output port. The high flow rates also tend to concentrate CO and CO2. CO and CO2 are known as fast gases. (The faster the gas the more likely it will permeate out the N2O2 output side of the membrane. The slower the gas the more likely it will permeate out the N2 exhaust side of the membrane.) CO and CO2 are faster gases that O2, this means they will permeate faster than O2 and tend to concentrate on the N2O2 output side.

If we take the Coltri Sub/Nuvair system and say that there is a level of 200 p.p.m. CO2 in the ambient air and if (worst case scenario) all of this CO2 concentrated through permeation when making a 40% O2 mix , The p.p.m. in the final mix would be:

200 x 2.4 = 480 p.p.m.(where 2.4 litres is volume of air required on the input side for a 40% mix)

This still falls within the specifications for Grade E breathing air anywhere in the world.

If on the other hand we take a rival membrane that requires around 5 litres on the input side the concentration could be:

200 x 5 = 1000 p.p.m. (where 5 litres is volume of air required on the input side for a 40% mix)

CO2 levels over 1000 PPM are not acceptable anywhere in the world for breathing air.

The same concentrating effect would also occur with CO portions in the mix.


Function of The Permeable Membrane System

The above system diagram shows configuration using either the MCH6 Explorer Nitrox or the MCH14 Standard Nitrox. Both of these compressors have the Nitrox membrane and filtration mounted within the compressor frame, see specifications following.


The schematics show Coltri Sub compressors being used as the high pressure unit. Clients however may opt to use their existing compressor instead: In this case Units are available featuring the membrane system and LP regulator port mounted on a universal skid frame which can be fitted with the clients own compressor. It should be noted though, that it is important that the output of the membrane system is sufficient to satisfy the intake requirements of the compressor. The HP compressor should be operated only if in good mechanical condition and using the recommended high performance synthetic lubricant recommended by Coltri Sub Anderol Airteck 755. In is recommended that any existing machine undergoes a thorough service and oil change before use.


Function of The Permeable Membrane System

The above system diagram shows configuration that can be achieved using either the LP 250 Compressor or the LP Silent Rotary compressor range to feed a separate high pressure tank filling system. Both of the LP compressors types have the membrane and filtration combined within the unit frame. The Rotary is designed for around a rotary unit for more economical output at lower sound levels and also to supply higher volume systems (upto 720 Lt/min)

Matching a Rotary LP Nitrox compressor with you current HP compressor

The tables below give examples of some standard compressor matches with Coltri Sub Rotary LP units.

Function of The Permeable Membrane System


Function of The Permeable Membrane System

It is also possible to utilize the membrane for Trimix production as can be seen in the diagram above. The Coltri gas production system is very flexible and the Trimix adapter can be installed with the initial system or as an addition later on.