From: mayne@pipe.cs.fsu.edu (William Mayne)
Subject: Re: Rebreathing system
Reply-To: mayne@cs.fsu.edu
Organization: Florida State University Computer Science Department
Date: Wed, 27 Jan 93 15:10:12 GMT

In article <YfNVz4600WB24JOydd@andrew.cmu.edu> "Rudolph R. Zung" <ru+@CMU.EDU> writes:
>
>In a recent issue of Outside magazine, they did this article about a guy
>who wanted to do some diving in the world's deepest cave system. His
>problem was that all existing scuba technology did not allow him enough
>downtime in the water. So, he scrounged up a few million dollars, did lots
>of reading, designed and built a complete closed, rebreathing system...

That would be Dr. Bill Stone (Ph.D. in engineering). I was at the test
site last spring, acting as a safety diver for someone training in use
of the rebreather, when the guy from Outside magazine showed up.

>Because this was potentially BIG money yet to be patented, the article
>writer had sign a confidentiality form indicating that he would not write
>about the technical aspects of the system.
>
>My question: has there been any more information? Does anyone have any idea
>how a system such as thus might work?

Everyone allowed on the site had to sign that agreement. But some details
have been published, presumably with the approval of Dr. Stone and
his company, which is called Cislunar. Chapter 20 of "Mixed Gas Diving"
(Watersport Books, 1992 and 1993) by Gilliam and Mount goes into this
and some other rebreathers, but concentrating mostly on the Cislunar
MK-2. The chapter is written by Richard Nordstrom. Photographs and
diagrams are included. If you just want to know about this, and not
try to build one (which would be foolish for the average Ph.D. engineer
off the street to attempt :-)) this chapter would tell you most of what
you would want to know. My impression is that the MK-2 rebreather is not
as close to being marketed as the article says. Otherwise it is accurate.
Hopefully I am wrong and they will hit the market this year.

There was also a much less detailed article on it by Wes Skiles in
Rodale's Scuba Diving magazine several months ago. It concentrated
mostly on describing the experience of using a rebreather in a cave.

Rebreathers are of great interest to the mixed gas diving community.
Because the price of helium is so high and so much gear is needed
anyway rebreathers, even at several thousand dollars apiece, become
cost effective. I may have to take out a second mortgage on my house
to buy one someday.
 
>This guy does have a several working models; it's probably well beyond beta
>testing. The pictures of it look pretty high-techy. The inventor said that
>the whole thing has redundant designs in it for safety and is driven by
>several computers. From what I remember, the system takes a diver's
>exhalation, remove the CO2, and recycles the rest back into the system
>again. I think he calculated his system to be able to support dives
>measured in the teens of hours (13, or 16).

That is basically it. The onboard electronics control adding oxygen
to make up the oxygen used by the diver and maintain a safe partial
pressure. It also has a small bottle of helium (or other diluent gas
- air can be used for shallow dives) to make up changes in volume
due to depth. Decompression is also computed by the controlling
computer.

Bill Mayne
Newsgroups: rec.scuba