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RES: [PSUBS-MAILIST] Ambient pressure design considerations

Shawn,
 
I'm afraid you're taking the wrong track.
 
"...every breath you expel in the SportSub is also expelled ..." This is not so. First off, you must analyse the whole breathing cycle and not only part of it.
 
Think about this: "...the only real difference...is that you have on the order of ... of air as a buffer". It's a huge difference. The buffer is the single most important thing in a rebreather, that's what makes rebreathing possible !
 
If you plot a scuba air flow graph it will be full of "steep mountains and deep valleys". Do the same for a rebreather and you'll find out a very different behavior: the curve is much flatter because the buffer AVERAGES the air flow. Deppending on the buffer's volume the curve will closely approximate a flat line. If you are familiar with electronics a good analogy is a power suplly filtering capacitor.
 
Another point you might want to give more thought: What's rebreathing all about ? Why RE-breath ?
 
Try locking yourself in a air tigh box for a while. What happens ? (just kidding, do not do that without adult assistence ;-)
 
Hope it helps
 
Jorge L.
-----Mensagem original-----
De: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]Em nome de NeophyteSG@aol.com
Enviada em: sábado, 15 de novembro de 2003 07:02
Para: personal_submersibles@psubs.org
Assunto: Re: [PSUBS-MAILIST] Ambient pressure design considerations

In a message dated 11/14/03 10:02:00 PM Pacific Standard Time, ronleonard@shaw.ca writes:
Of sorts....  It is an air environment. There is a big cockpit full of air (30 cu ft), you add more air to that, and as you do, other air bleeds off because you maintain 30 cu ft. Therefore, you are partially rebreathing some of your air. It's not like a scuba reg where you exhale and the air is gone.
Ron,
 
I hate to disagree, but I do.  I understand your comment about partially rebreathing some of the air, which in fact you do.  However, the only real difference between SCUBA and the SportSub is that you have on the order of 30 cubic feet of air as a buffer.  Bottom line is that, barring depth/compression differences, every breath you expel in the SportSub is also expelled from beneath the SportSub's canopy ... gone ... just the same as SCUBA.
 
Warm Regards
Shawn