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Coltri LP713

Coltri Nitrox.gif
Coltri Nitrox back.gif
All maintenance logs are current and available for inspection

Asking $10,000 but owner will consider reasonable offers

Membranes are ideal in operations where the owner does not want to deal with obtaining and handling pure oxygen. The industry considers O2 concentrations below 40% as much safer than higher concentrations.

The initial expense of a Nitrox generator will be paid back over time with the savings from purchasing pure oxygen. 

Note: This is a used item, it is sold as is. There is no warranty.


Please note: The information contained here is provided by the seller. We provide advertising for air systems for our customers on a commission basis. We try to work with the sellers to insure complete and accurate information about the items for sale. It is not possible for Bob Ledbetter Sales or the Tropical Sales Reps to verify the information contained within, we cannot guarantee or warrant the accuracy of this information nor warrant the condition of the vessel, compressor or equipment. We are not responsible for any special, incidental or consequential damages suffered by any party resulting from errors and / or omissions. A buyer should instruct his agents, or his surveyors, to investigate such details as the buyer desires validated. This item is offered subject to prior sale, price change, or withdrawal without notice. Hours are as of the date of the original listing and are a representation of what the listing broker is told by the owner and/or actual reading of the hour meters. The broker cannot guarantee the true hours. It is the responsibility of the purchaser and/or his agent to verify hours, warranties implied or otherwise and major overhauls as well as all other representations noted on the listing brochure.

The LP 713 Nitrox GeneratorTM system is a system that produces oxygen-rich air (nitrox) ready for delivery to a High Pressure (H.P.) compressor to fill scuba tanks or storage cylinders. The package is designed to be fully automatic with an operator overseeing the production to maintain proper Nitrox mixtures not to exceed 40% oxygen. 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 (O2). 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 which is delivered into the intake of a separate high pressure compressor.

The LP 713 Nitrox Generator TM uses a rotary screw L.P. compressor, air / oil aftercooler, 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. 


The LP 713 Nitrox GeneratorTM membrane system is rated for a maximum feed air pressure of 300 P.S.I. (21 bar) and has been configured to work well with the 175 P.S.I (12 bar) maximum pressure delivered by the L.P. compressor. A back-pressure regulator is used to adjust the amount of air the screw compressor produces to meet the appropriate levels for various O2% 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 permeate is a concentrated mixture that is diluted with air prior to entering the H.P. 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 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 O2% nitrox is produced. As air flow to the membrane is decreased, permeate flow decreases, compressor intake air increases, and a lower O2% 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 H.P. compressor. The resulting nitrox mixture is analyzed for O2% before entering the H.P. compressor for approximate content and again when pumping nitrox for precise content. The H.P. compressor pumps the nitrox to a maximum pressure of 3600 P.S.I. (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 O2% is repeatable. For example, if your H.P. compressor pumps 36% O2 when the feed air pressure is at 125 P.S.I. (9 bar), then adjusting the back pressure regulator to 125 P.S.I. (9 bar) during the next use will produce the same mixture.

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