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Old 24th February 2007, 14:27   #1 (permalink)
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DIY rebreather under construction

I have been sketching this current DIY-model in my thoughts and on paper for a few years. Now after Mikko (Ekke) joined the project in January it have got forward much faster. The rebreather have been almost completely modelled with a CAD program (DSS Catia). In the pictures green means O2.
First parts have been machined. Our goal is to get the Rebreather into pool testing in the next two months.

Desing goals are low profile (about the same as twin 12l), back mounted counterlungs, simple and robust design. Tanks will be 3l steel 232bar. The scrubber size will be about the same as Inspiration (OD 144mm & length 170mm for the lime).

O2 feed will be handled with a leaky valve or a solenoid or both (solenoid as a parachute). The PO2 display will be the PO2 controller display or a 3xPO2 display aka KISS. HUD will be a separete unit sharing the three cells and blinking smithers code. The PO2 setpoint controller is designed by Tommi (TSA).

The backplate is almost like a standard model. It will have two bends less for lower profile. MAV's will be attached to the backplate strap above the shoulder D-rings. SPG's will be attached to the straps beside backup lamps. More detailed hose routing is still under work.

The pool version will have Ray hoses and DSV. Cooper or RE Darling hoses are in mind for the final version. BOV would be nice but is not at top priority at this stage.

I have got 2mm neoprene with smooth surface for the counterlungs. It's easy to sew and seal the seams with Aquasure. We are looking for cordura laminated PU for the final version. It's quite hard to find.

Exhale counterlung (red in pictures) got a Apeks OPV at the bottom. Water drains from the scrubber and exhale counterlung into the bottom of exhale counterlung and may be expelled though the OPV. Counterlungs are directly connected to the scrubber. The connectors are made by George Fischer.

We will not use an ADV in the first model. It may be used in the final version or left as an option. Let see how much it is needed. I have dived the ADV shut off with my Inspiration. It's no problem pushing the DIL button during descent at the same time you ad more gas to drysuit or wing. Less taskload is better for some situations though.

I wrote this story in such a early stage so we could get comments and new views for the design. All comments and suggestions are welcome. We would also need a name for the project.

Pictures of the Rebreather:
DIY Rebreather
The big yellow tanks are for size comparison (12l 200bar).

First machined parts. The virtual CAD model is turning into reality.

Setpoint controller under construction.

-Pasi

Last edited by plazma; 24th February 2007 at 16:10..
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Old 24th February 2007, 14:40   #2 (permalink)
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Re: DIY rebreather under construction

Must say that it is a very different orientation of the in/outlet hoses on the scrubber that I have not seen before. Do you have a CAD drawing showing the entire unit (just for curiousity) ?

Best wishes with your project, BTW. And hope you still have time left to build my little video board... ;)
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Old 24th February 2007, 14:42   #3 (permalink)
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Re: DIY rebreather under construction

Quote: (Originally Posted by decoweenie) View Original Post
Must say that it is a very different orientation of the in/outlet hoses on the scrubber that I have not seen before. Do you have a CAD drawing showing the entire unit (just for curiousity) ?
There are CAD-pictures of the entire unit in the first link..

-Mikko
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Old 24th February 2007, 14:47   #4 (permalink)
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Re: DIY rebreather under construction

Quote: (Originally Posted by Ekke) View Original Post
There are CAD-pictures of the entire unit in the first link...
Missed it the first time. Thanks...

OK, I see what you guys are doing now...
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Old 24th February 2007, 16:23   #5 (permalink)
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Re: DIY rebreather under construction

Hello.

What materials are you using for the scrubber canister, and are they sealed by o-rings or glue?

Also, the clear lid is a nice touch. I think I might borrow that idea for my large scrubber design

Cheers.
-Marek
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Old 24th February 2007, 16:40   #6 (permalink)
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Re: DIY rebreather under construction

Quote: (Originally Posted by marekm) View Original Post
Hello.

What materials are you using for the scrubber canister, and are they sealed by o-rings or glue?

Also, the clear lid is a nice touch. I think I might borrow that idea for my large scrubber design

Cheers.
-Marek
The scrubber parts are made of PVC-U (made by George Fischer). It's glued together with Tangit.

The top lid is sealed with an O-ring. The proto will have a clear PC lid. Final version will have some different material. Maybe PVC-U. Other DIY builders have reported PC may deteriorate with lime dust and humidity.

-Pasi

Last edited by plazma; 26th February 2007 at 16:32..
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Old 24th February 2007, 17:17   #7 (permalink)
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Re: DIY rebreather under construction

Quote: (Originally Posted by marekm) View Original Post
Hello.

What materials are you using for the scrubber canister, and are they sealed by o-rings or glue?

Also, the clear lid is a nice touch. I think I might borrow that idea for my large scrubber design

Cheers.
-Marek
I will put some better pictures from the connectors in next week when(/if) they are ready. "Thread parts" is glued to scrubber and "counterlung connectors" are sealed with o-rings to them.

PC lid has protecting film on it, so it looks little scrappy and seems to have lot of scratches. It isn't ready yet and will go to workshop with me, so I haven't removed it yet..

-Mikko
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Old 24th February 2007, 17:31   #8 (permalink)
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Re: DIY rebreather under construction

As far as clear plastics are concerned, polycarbonate (PC) is a much better material structuraly than polyacrlylic (PA). However, as I mentioned in another thread PC is not stable in caustic solutions (over many years that is). Still, you should probably use PC for the lid. What you may consider doing is coating the inside of the PC lid with a clear glue on plastic (like what is used on book covers to protect them or on tinted car windows). This will place a thin layer of clear high pH stable plastic between the lid and the scrubber lime.

As for naming your rebreather, how about following the sort of standard homebuild naming system of using the first letter of your name followed by the model number. So for my rebreather it would be M for Marek and 1 for the first rebreather I have built, hence the M1 rebreather. Others homebuilds using this include the G1 and K1 rebreathers.

Anywya, good luck with the build, and keep us posted.
-Marek
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Old 24th February 2007, 18:38   #9 (permalink)
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Re: DIY rebreather under construction

Nice job real interesting - look forward to seeing your progress!
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Old 24th February 2007, 20:04   #10 (permalink)
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Re: DIY rebreather under construction

Quote: (Originally Posted by marekm) View Original Post
As far as clear plastics are concerned, polycarbonate (PC) is a much better material structuraly than polyacrlylic (PA). However, as I mentioned in another thread PC is not stable in caustic solutions (over many years that is). Still, you should probably use PC for the lid. What you may consider doing is coating the inside of the PC lid with a clear glue on plastic (like what is used on book covers to protect them or on tinted car windows). This will place a thin layer of clear high pH stable plastic between the lid and the scrubber lime.
I think polyacrylic is PMMA (Polymethyl methacrylate), not PA (Polyamide) which sucks water and is pretty useless in underwater use.

Anyway..

The main components of soda lime are :

* Calcium hydroxide - Ca(OH)2 (about 75%)
* Water - H2O (about 20%)
* Sodium hydroxide - NaOH (about 3%)
* Potassium hydroxide - KOH (about 1%)

(source: Reference.com/Encyclopedia/Soda lime)

PMMA is OK with NaOH, PC isn't. With Calcium hydroxide thing are vice versa so neither isn't the best option but PC seems to be better. Not sure about KOH but I don't think it's a problem. However that coating could help.. Will keep it in my mind, thanks.

Last edited by Ekke; 24th February 2007 at 20:06..
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