Web Extra: The Air We Breath

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Kadey-Krogen was happy to accommodate our dream of outfitting Equinox with a nitrox dive compressor. Bill Harris, our Kadey-Krogen salesman, contacted a number of compressor companies before we purchased the boat to ensure that such a system could be housed within the space constraints of the 58, and the builder worked with us closely to coordinate the installation after we chose a manufacturer.

A custom system by Coltri Americas of Coral Springs, Florida, our dive compressor features a Nuvair 230 Series Nitrox Membrane System, consisting of a two-stage unit made up of a Champion 7.5hp (model 7RCB) rotary-screw air compressor coupled with a Coltri Sub high-pressure compressor. These components use a semipermeable membrane system to produce oxygen-rich air, commonly called enriched-air nitrox (EANx). Instead of enriching standard air with high-pressure oxygen (which would require bulky and potentially hazardous O2 cylinders), the membranes separate out a portion of the nitrogen found in the clean, pressurized, heated air produced by the Champion low-pressure air compressor. With this simpler and safer method, the nitrogen is discharged, and the resulting high-oxygen permeate is diluted with additional air before entering the high-pressure compressor. The amount of dilution can be finely adjusted to produce a specific percentage of oxygen-up to 40 percent-in the EANx.

Normal air is approximately 78 percent nitrogen and 21 percent oxygen; as mentioned above, a nitrox system increases the amount of oxygen in the mix. The most significant benefit of using nitrox is the increased level of safety for divers. Less nitrogen in the breathing gas means a reduction in nitrogen absorption by the body and a decreased incidence of decompression sickness. Contrary to popular belief, nitrox should not be used for deep dives beyond 100 feet. Use of nitrox can allow longer bottom times at shallower depths, and shorter surface intervals between dives.

In EANx, the "x" indicates the percentage of oxygen in the mixture. For example, we generally use EAN32, which contains 32 percent oxygen. Ron, Ally, and I are experienced divers and are nitrox certified, having taken a specialty course on the risks and diving procedures involved with using nitrox. As a routine safety precaution, we always use a separate oxygen analyzer to verify the oxygen percentage of the final EANx mixture in each tank before diving.

Our compressor is capable of filling four tanks at a time, although we generally fill only two at a time. Kadey-Krogen installed an extra ventilation fan for adequate airflow through the lazarette space, which we use in conjunction with our engine room exhaust fan. We have multiple compressor air whips for filling the scuba tanks: shorter ones for use inside the lazarette and, for convenience, longer ones that reach over the transom so we can fill the tanks when they've already been loaded into the dinghy.

As it turned out, the trouble we encountered with our compressor while in the Bahamas was caused by the solenoid, which had gotten wet and shorted out. Once the solenoid was replaced, the compressor was up and running well. We now take care to keep it covered and dry when we aren't using it.