Open source rebreathers - an alternative approach

Skipbreather

There well may be other gas flow related reasons, but big attraction for me- after years of diving various single CL rigs- is having a water trap barrier between your exhale hose and your CL. Properly done w/ OPV at bottom of exhale CL it makes center section/ can/ scrubber/ highly resistant to all but catastrophic floods, and the purging of the occasional lapse of DSV discipline a no-brainer.

Ken

Crazyduck

If dealing with metal cable- please take something to cut it. Your knife will do you any good. I have run across it in lakes when they have put in temporary booms (gives me the willies)


Also, if the trees are fallen and laying- no problem. However, trees still standing in submerged orchards are a totally different problem. Some canopies cannot be vertically swam through and makes an overhead environment. Plus, trees are pretty weird if you are narc’d.


Lift bags help to move things and if something falls on you.
Sometimes LED or wide beam lights help in really bad vis verses pinpoint lights.
Bring extra gas and listen to that listen voice in the back of your head.


Good luck, Andrew

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Howdy Senor- What’s Happening!
Rob Davie April 2005-

Presently in a state of transition from Open Circuit to Closed Circuit.

"You will not be punished for your anger; you will be punished by it." - Buddha.

montyg

OK, maybe you are further down the line than what I am, but I have run the idea past some people around here and they think it can work. I guess the proof is in the pudding....

One thing is for sure, though: I'd rather dive OC than a kludged together rebreather ;-)

I agree with the KISS principle, and at the moment I don't see that I'd have to deviate from it. Let's hope I am not wrong!

Now it's just to find some time to sit down with the CAD guy and figure how this baby must get put together. The solid models of all the components are done (like sensors, P-Ports, cable glands, ect)

rgds
monty

Simon A

Well it's late at night, here's my initial ramble on the subject. Please feel free to ridicule/pick holes in it.

With regards to the KISS principle, I would sugest that initialy it's probably not worth actualy designing our own scrubber, however it must be available without fuss and at a known price with commonly available connections.
Much as it pains me to say this, the only scrubber that I think meets these criteria is the extendair scrubber for the dolphin. Also it gets rid of the largest (most expensive machine required) machined piece.

Also I'd agree with making all the holes for connecting stuff 3/8 UNF 24tpi, this is a standard size for scuba low pressure hoses, and is also a standard size for cable glands (I believe this is the size that the Kiss PPO2 monitors and the sheerwater stuff uses, can anyone here confirm/deny?). This also makes holes easy and cheap to plug, if you need to go bigger then go to either the 1/2inch UNF that Apeks use or the same thread as the HP port on a 1st stage (sorry don't know the thread specs off the top of my head).

Thats all for now. Undoubtedly I'll type out some more badly written, and badly thought out garbage in the future.
Simon A

Genesis

IMHO you need to have room in the head for electronics.

I define that as enough space for:

1. 4 x R22BUDs or equivalent (O2 sensors); 3 for a voting-logic controller, and one for an external computer (e.g. VR3)

2. Room for a solenoid, if one is to be used.

3. Room for a big enough "cube" for signal conditioning and/or solenoid drive and/or simple wiring connections for the above.

This immediately gets rid of the mCCR and SCR "premade" scrubber configurations, as they don't have any room in the head for such things. Making up "whatever" to make that work without this support is not impossible, but it radically increases the trouble factor. Unused space is not a major problem, but not having the room is.

The ExtendAIR cartridges LOOK at first blush to be attractive. I am actually moving AWAY from them due to some challenges with mounting and anti-channeling issues. There are half-baked solutions to this but they still require work and a loose-pack scrubber requires almost as much work AND you get the advantage of cost efficiency that disappears with the ExtendAIR in actual use.

The ExtendAIR folks make a "service kit" that comes with two cones (one for each end of the cartridge) and a handful of O-rings; Tech Blue has them for a reasonable price. With the right size pipe this is very close to all you need for a working scrubber, BUT you end up with an axial design (coaxial is hard to do well unless you want to figure out an "inner tube" - not impossible, but quite a bit of work to deal with the sealing issues as the inbound gas flow must go AROUND the cartridge.) This is ok for a cross-shoulder scrubber, but not so good for a vertical one. The tricky parts then become making the spacers and seals so the cones are in the proper place and gas doesn't leak around them and down the side of the scrubber without going through the bed. Not terribly hard to accomplish.

I don't think that a scrubber can with a coaxial feed that takes loose pack is hard to put together. I've got both options on the table and am starting to work on the latter beginning this week; we'll see how it turns out. I do agree with standardizing gas connections on the Scuba inflator connector, as that's in wide use and makes hoses easy to source. Remember too that cable glands are not high-pressure devices in this environment, since the scrubber is at ambient pressure - they have to be leakproof, but only to 1 ATA or thereabouts (well before you get that differential your lungs have either been blown up or sucked into the can!) The need to have a 10, 20 or 30 ATA rating does not exist at the scrubber connections.

Making the actual lid is pretty simple. Two pieces of 1/2" sheet HDPE will do it - you can rough-cut them to fit (one inside, the other outside) and use an O-ring ala-scooter seal and Nielsen Sessions latches. For a 1-1/4" pipe thread breathing hose connection you need a 27mm drill, then use a NPT tap and you're done. Simple. A quick pass with the solid modelling shows that there's plenty of room for the sensors around the periphery plus a solenoid, and you can leave an inch of space or so at the top for any electronics. Cable glands are simple as well; the ones used for light cannisters are inexpensive and easily obtained, making them a standard part - again, drill and tap for it.

The bottom lid is the same as the top but with no penetrations, unless you want a bottom water dump (e.g. pull dump off a BCD), in which case you drill a hole and put one in.

I'll take some pics as its coming together....

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

Genesis

Here's an image of what I'm talking about... this requires nothing more than a handfull of drills and a tap to mount the stand-offs for the scrim (which holds the sensors - the small holes are the M16x1 threaded holes for the sensors (4), the larger ones are just flow holes for the gas to flow through.)

You also need a back lid which is the same as the front (two pieces of HDPE sheet fastened together) but this one has no holes in it. For the interior of the cannister itself - the actual scrubber media holding part - you use the same scrim design but with many more holes drilled on a closer pattern, and SS perf sheet, with a spring arrangement on the top to keep pressure on it and prevent channeling...

Actual photos as I get it built.... None of this should require machine shop parts - a drill press perhaps, but the rest is definitely hand and handheld power tool (e.g. scroll saw to cut out the sheet itself) capable.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

montyg

I agree 100%. Anybody got a solid model of a solenoid and maxuimum dimensions of an electronics package - ie, how much space should we allow?

How would you feel about a plenum which can be inserted for eCCR or mCCR or left out (for SCR) which can accomodate 3 sensors and/or solenoid and/or electronics?

How about a single female p-port connector in the head which will be sufficient for SCR, and provide an attachment point for the 4th cell of a VR3 or HSE in a CCR config?

I agree with Karl (Genesis)

Extendair cartridges is not even an option for me. You just don't get them here and if we did, the cartridges would cost an arm and a leg.

The scrubber has been the easiest and cheapest part of the excersize so far, at US$15 for the HDPE tube and US$20 to get the inside cleaned up on a mill so that it's perfectly round and so that an o-ring can seal.

Yes please!

rgds
monty