Nitrox Production Methods
A Comparison of Three Methods
There are three popular methods of producing Enriched Air Nitrox. These are: 1) partial-pressure filling, the method Dive Sports uses, 2) de-nitrogenated air production, and 3) atmospheric oxygen-air pre-blending. Each of these three methods have advantages and disadvantages. The following paragraphs describe each of these methods.
Partial-Pressure Filling is the process of placing a predetermined amount of oxygen in the customer's cylinder, then topping that oxygen with normal compressed air. It is known as partial-pressure filling because the proportion of oxygen and nitrogen needed for a certain mixture is calculated based upon the final pressure you want each gas to exert. The pressure of each of these individual gases is known as it's partial pressure of the entire mix. Partial pressure mixing is the only one of the three methods that requires the introduction of pure oxygen into the target cylinder. Partial pressure mixing is the most common method employed by scuba stores in the United States. Some operations use partial-pressure mixing to produce banked pre-mixed Nitrox, but removal of all of the Nitrox from the bank requires a special pump known as a Haskel pump to effectively fill cylinders from pre-mixed banks. Note: This type of mix is often known as EANx, with the "x" representing the target oxygen percentage in the final mix.
De-Nitrogenated Air Production is the process of subjecting pressurized atmospheric air to a number of screens or filters which remove some portion of the larger nitrogen molecules from the air, leaving a higher concentration of the smaller oxygen molecules in the output air. This results in a mixture that now contains more oxygen molecules, by proportion, than normal atmospheric air and therefore a higher oxygen content. While this is the best system for high volume production of Nitrox, it is quite equipment intensive and as a result, quite expensive. However, because of the absence of pure oxygen anywhere in the production process, it offers production safety advantages over other methods. The production of mixes higher than 36%-40% Nitrox with this method is extremely difficult. Note: This type of mix is often known as DNAx, with the "x" representing the final oxygen content in the mix.
Atmospheric Oxygen-Air Pre-Blending is very similar to partial-pressure filling, in that pure oxygen and air are mixed to produce the final mixture. However, with this method, the pure oxygen and the air are mixed at atmospheric pressure in a mixing vessel, known as a blending stick. That mixed air is then fed into the compressor air intake and compressed to high pressure for filling into the cylinder or a bulk storage bank. Unlike using partial pressure mixing to pre-mix in a storage bank, this method allows for simpler "topping" of the pre-mix banks. Note: Also known as EANx.
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