portable trimix

[Peter Bomberg]

Ok here is a question I am sure has been asked before (but I cant find the answer), I am looking for a trimix setup on a sailing Cat, so weight and electrical current use are important to me, but I can not figure out should I go with a couple of K cylinders of 100% O2 and one of He or look at a 100% O2 generation system (they are pricey and big and suck a lot of power).

Most of the diving would be on a rebreather but some OC and in most of the cases it would be many shorter (1hr) dives and most likely 130ft range, however I do like the option of deeper or longer if we are in an area where there is something special.

The issue is we will be 1-3 months between populated areas so getting a refill may be hard, we will have a 40% O2 capable system for the OC shallow dives was my thinking in addition to the tech rig, please give me your thoughts.

Peter

 

[wedivebc]

Small compressor, jetsam baby booster and a couple of 80s filled with helium and another couple with O2 and you should be good for a month of RB diving.
Heliair is basically helium topped off with air. Not great for OC diving but ideal for quick and easy RB mixes. For every 5% of helium you add your O2 drops by 1%. real easy to calculate mixes on the fly.

Ok here is a question I am sure has been asked before (but I cant find the answer), I am looking for a trimix setup on a sailing Cat, so weight and electrical current use are important to me, but I can not figure out should I go with a couple of K cylinders of 100% O2 and one of He or look at a 100% O2 generation system (they are pricey and big and suck a lot of power).

Most of the diving would be on a rebreather but some OC and in most of the cases it would be many shorter (1hr) dives and most likely 130ft range, however I do like the option of deeper or longer if we are in an area where there is something special.

The issue is we will be 1-3 months between populated areas so getting a refill may be hard, we will have a 40% O2 capable system for the OC shallow dives was my thinking in addition to the tech rig, please give me your thoughts.

Peter

 

[CraigAClark]

The small size PSA units that I have worked with (275 cu ft/day) will produce a maximum of 93%, +/_ 3% purity. OGSI has a unit that they call an OEM 15. You would have to provide the other components required. You can get the OG 15 which has all the components required to deliver the above purity at atmospheric pressure. This could be coupled with a Rix Micro-Boost compressor to pump up to 2250 psi. The Micro-Boost alone is around $5K though. In order to get 99.9% purity you first have to make the 93% and then put it through a second PSA to bring the purity to the higher level. The smallest system would be weight and size prohibitive, not to mention the price.

Depending on where your ports of call are located, you will run into the problem of getting the O2 and helium bottles refilled. There is no standardization of bottle valves or fill attachments through out the world. Our CGA-540 (O2) valves and connections will cause you a problem as close as Mexico. Europe, S.E. Asia and Australia all have different combinations. You will probably run into problems in the Caribbean as well.

If you do not already have a compressor for air, you will run into generator requirements. To start a 2hp motor (smallest require for a H.P. compressor), you would need a minimum of a 6KW generator to start it straight up. Most small machines are offered with 3hp motors as standard, which would require an 8KW generator to start it straight up. Most all other electrical draws would have to be shut off when the compressor is started, i.e. AC units etc. Many folks with sail boats that have small diesels allow themselves to be talked into installing a compressor in the engine compartment which will be run off the engine. Bad Plan! The heat inside that compartment at minimum will require purification filters to be replaced more often and maintenance intervals will be drastically shortened. From experience, I would not recommend operating a compressor above a 90F maximum ambient temperature and Bauer has an absolute max of 125F, I believe. These small machines are not recommended for use with storage and you are looking at 22 minute plus fill times for a single 80.

Most continuous duty compressors start out in the 5hp range, which would require a 20KW to start it straight up. Three phase power isn't an option in these compressor ranges because most three phase generators start at 25KW. Frequency drives are an option to reduce the start up load and they will generally allow start up with smaller generators.

Craig

 

[Peter Bomberg]

Thanks Craig, you have hit the issue square on (refills are problematic and super pricey but then I still will have to carry He so maybe I don't bother with 100% O2 and just fill both, but this means a lot of OC diving on 40% until I find a source!

Sadly I will have to wait a while anyways as I just lost my job and it will set me back a while before I can head out!

Peter

 

[veriqster]

if you have the time and are mechanically inclined look into the Kidde / Noah-Howden units. Sometimes you can get a rezonably priced one. Those are designed to run in an environment that would drive crazy any of designers of other compressors, like mounted in engine compartment of a tank roling through a desert, ...
You could power it of your auxiliary, if you have one, and just plumb the intake so it gets fresh air; add the piping to watercool the output and you should have a pretty nice setup.
that's if you have the time and skills to do it, otherwise I would go straight rebreather and forget about compressors in general.
P.S. James at sheldensportinggoods used to have some but best of my knowledge ran out of them, however, he is one of the experts on these "military items" and usually more than willing to help, be that advice, parts or anything else.

 

[Scuba Duck]

If your compressor was small enough (2.2 cfm range), you could use a PSA system (10 LPM O2 at 93% purity) to make the oxygen you need on demand to continuous gas blend 32% nitrox. You wouldn't need storage (cylinders) for the oxygen. You would need enough electrical power to run the PSA system.

You would stilll need storage bottles for the Helium.