kevorkian cmf rebreather

rhelsley

Hello fellow homebuilders!

Awhile back I introduced myself in "introductions" & mentioned my homebuilt rebreather nicknamed "kevorkian". Here's a video clip of a recent dive with kevorkian. Dangling clumsily from my harness is my video light canister--not part of the Rebreather.

Kevorkian is a scratch-built, fully manual cmf closed circuit rebreather. I was inspired by the simplicity of Gordon Smith's KISS rebreathers, but they weren't quite simple enough for me.

Gone with the ADV, BOV & other trinkets. On with large volume cylinders (suitable volume for bailout for no-deco dives), bypassable screened orifice (no lack of o2 due to blocked filter), bottom-mounted-water-purgeable-counterlung, & streamlined profile.

Soon I'll post a detailed breakdown of kevorkian. Stay tuned.

regards,

russell helsley

Attached Files

kevorkian.wmv (963.6 KB, 112 views)

babar

Nice, but if it's got an orifice, it can't be fully manual?

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Babar
Evolution Plus
Sport kiss

rhelsley

OK, you got me on that one. Fully manual, that is, aside from the orifice.

russell

jmurba

Hi Russel,
impressive work !!
you says the lung is bottom mounted, is this lung location increases the work of breathing ?
regards
jean mi

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when will I be able to think about something else then spending hours underwater, when will I be normal ?

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rhelsley

Yes, the WOB changes as your body position changes. However, I attached about 3 pounds worth of lead "medallions" to the outside of the counterlung which helps to counteract the upward hydrostatic pressure. The medallions provide weight, but still allow the CL to fully collapse.

In the normal swimming position the CL is at the same level as the lungs, so WOB is minimal.

In my original design I worked up (on paper) a counterweighted mechanical contraption where the weighted CL bottom would ride on bearings along rails in the outer wall of the CL housing. In a head-up position the weight would draw down the CL, counteracting the upward hydrostatic water pressure. In a normal swimming position the weight would have no effect. In a head-down position the weight would help push the air in the CL down to the divers lungs, theoretically offering the same WOB characteristics regardless of attitude, and keeping the CL protected and diver profile streamlined.

During my early water trials though, with a simple bag counterlung WOB was surprising acceptable (to me), the addition of the lead medallions seemed to be an improvement as well. Being as it was I scrapped plans for the mechanical weight system.

I'm sure OTS CL's would offer less WOB in all positions, but the CL protection, clean profile & streamlining is a worthy tradeoff for me. Kevorkian is very sleek--I don't have to breathe as hard to keep up with some of my "christmas-tree" adorned buddies. :-)

The only times I find it uncomfortable is if I stay in a vertical position for an extended period, and not so much of the increased effort to exhale, but the chipmunk cheeks gets tiring. It's not a big problem for me though as 98% of my time is spent in the swimming position, even on deco. Also the deeper you are, the lesser the effect of your attitude.

The other uncomfortable position is breathing on the unit while swimming on my back on the surface. Again, easily remedied by swimming face-down or breathing off-loop if face-up.


russell helsley