# Rebreather construction project #1



## WhackUmStackUm

Since there seems to be some interest amoung Forum members, I started this thread to record the progress of the design and construction of my low budget rebreather project.

:nuke:I'm not recommending that anyout build one of these.:nuke: I just thought some folks might be interested in following my progress.


Initial design goals:
This will be a *b*ail-*o*ut re*b*reather (or BOB). During deep dives I will carry it as a backup incase my main rebreather fails completely.
This rebreather will be used to support diving on deep reefs in open water. It may not be suitable for cave diving and other overhead environments.
It must be reasonably light-weight and low volume.
It must be inexpensive relative to commercial rebreathers. Target cost is $500 to $1,000, not including the dive computer.
O2 will be added manually on the first version, but version two will add O2 automatically.
Diluent gas will be added manually. Although this is easy to add on, I doubt I will need automatic dil addition since I will be ascending in a bail-out situation.
It must support diving to 400'.
It should be flexible enough to support different amounts of anticipated deco time (30-90+ minutes).
I will use off-the-shelf parts whenever possible.
Keep it simple by including only options that I will use. For example, I allways use the same PPO2 set points, so there is no need for me to be able to adjust them.
Since I will be switching from one rebreather to another in a bail-out situation, I plan to use an independent dive computer to track my deco obligation.
Displays need to be both BIG and simple.
No, I am not allowing others to take life insurance policies out on me. 
Since no one in their right mind would build a rebreather from scratch, I decided to call this project "Whack BOB."

Cheers,
Whack 'um


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## WhackUmStackUm

Silent said:


> Since you probably won't be shooting fish, or will you....


No spearfishing initially. However, there is a BIG warsaw grouper out there with my name on it.



Silent said:


> ...at 100 meters or more have you considered a chest mounted scrubber with a manual needle valve for O2 injection. A couple of 9 cf bottles of dil and o2 on your back should be more than enough to get back to the surface. With a little creative plumbing, between the little tanks and your standard tanks you would probably not have to abort a dive. A couple of sensors built into the inhale side of the scrubber to keep things compact.


Yes, I am considering the same type of setup.



Silent said:


> Would a single counter lung be enough at that depth for dwell time? A scrubber shaped like my dolphin scrubber with its oval shape would probably work.


The counter lung configuration is something I will have to experiment with.



Silent said:


> Will your _(3D)_ printer make clear objects?


I am not sure. I have been building parts out of black and yellow ABS plastic filament. The way the plastic is melted and laid down in layers, I doubt a part would end up clear, even if you started with clear filament.


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## coolbluestreak

I'm following....
What are you looking to use for a computor, make model?


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## WhackUmStackUm

I will add to this list as needed during the project. 

Please note these are quick and dirty definitions. If you would like the complete definitions, including special cases, feel free to Google the terms.


*Rebreather-related terms:*

*Open circuit*: The term used to describe a normal scuba setup. You breathe air in from a tank and out into the water.
*Closed circuit*: A breathing system which allows you to breathe the same gas over and over again.
*Semi-closed circuit*: A breathing system which allows you to breathe most of the gas over and over, but some gas is exhausted into the water.
*Rebreather bailout* or *bailout*: A completely redundant scuba system which allows a rebreather diver to fulfill his deco obligation and return to the surface should the rebreather fail in a catastrophic way.
*PPO2*: Partial pressure of oxygen. There is a range of PPO2 levels, in your breathing gas, in which your body will function normally. PPO2 is equal to the % of O2 of your mix (fraction of O2 or FO2) times the numbers of atmospheres of pressure the gas is under when it enters your lungs. So the PPO2 of 30% (0.30) nitrox at the surface would be 0.30 (FO2) x 1 (ATM) = 0.30 (PPO2). At a depth of 33 feet (one more atmosphere) the PPO2 of the same mix would be 0.30 (FO2) x 2 (ATM) = 0.60 (PPO2).


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## WhackUmStackUm

coolbluestreak said:


> I'm following....
> What are you looking to use for a computor, make model?


My current plan is to go with a Liquivision X1. I need a trimix computer which supports constant PPO2 diving. My friends that have one, love it.


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## TONER

Brian
what are the major benefits of a rebreather over scuba how much training do you need is it as safe as scuba with proper training and how much for a good set-up thanks


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## WhackUmStackUm

TONER said:


> Brian
> what are the major benefits of a rebreather over scuba?


Good question! 

Here are what I consider to be the benefits and drawbacks of diving a rebreather:


*Cons:*
Rebreather gear is expensive to buy and maintain relative to recreational open circuit systems. However, technical diving open circuit gear is expensive as well. Rebreather prices are coming down, but they are still costly.
Pre-dive checks and equipment cleaning are more time consuming.
Certification training can be expensive, depending on where you get it, and how far you have to travel.
A rebreather capable of deep diving (500'+) can be more hassle than it is worth when diving shallow spots of 60' or less.
As with any technical diving, staying down longer presents new challenges such as becoming chilled, muscle fatigue, chaffing because you are swimming longer, and wrinkling up like a prune!
*Pros:*
You can stay in the water much longer given the same volume of gas. A fresh setup on my rebreather is good for about 4 hours in the water, independent of depth. My rebreather uses two 15 cu ft tanks, one with O2 and one with air or trimix. When I go diving I like to spend as much time as I can in the water!
A closed circuit rebreather is almost silent. The wildlife experience is completely different. Animals treat you more like a fish, than an intruder.
I get about 20% more no-deco bottom time over nitrox. However, I almost always have deco to do. Why not stay longer? I have plenty of gas!
Because we carry many redundant systems, I feel that I have more options if/when there is an equipment failure. Honestly, this has more to do with a tech diving mindset than the rebreather. Open circuit tech divers also carry redundant systems.
Like open circuit technical diving, rebreather diving is not for everyone. For me the pros outweigh the cons. Diving is my main hobby these days, and I dive a lot.



TONER said:


> How much training do you need?


Like any scuba certification, the requirements depend on the agency. IANTD requires classroom time, a test, about 500 minutes in the pool, and about 8 hours of rebreather diving in order to get an open water card (130' max). Most of the other agencies have either added recently, or will be adding soon, recreational rebreather certification classes.



TONER said:


> Is it as safe as scuba with proper training?


Personally I would not switch to a rebreather if I was going stick to no-deco diving at recreational depths (< 130'). So let me rephrase the question as, "_Is closed circuit technical diving as safe as open circuit techincal diving?_"

Indeed, I feel _*safer*_ on closed circuit than open circuit. Why? Because there is little risk of running out of air.

Think about it. How would your diving experience change if you were carrying 4 hours of air?



TONER said:


> How much for a good set-up thanks


Retail prices vary depending on the bells and whistles you choose. Prices are also coming down steadily. Today most new closed circuit rebreathers cost between $5,000 and $10,000. You can sometimes find good deals on used gear on the Internet. I sold one that needed some TLC for less-than $2,000 this year. It was given to me in exchange for some work I did.


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## Silent but Deadly

I'll jump in on this. Yes a rebreather is a lot of maintenence. But, I can dive all day for about 10.00 a day, NOT a dive. I generally spend about 2 hours and some change diving a day, limited to the other guys out of air and tired of waiting on me. I have what I call a true recreational rebreather. Its completely self contained. I have 19cf of dedicated bailout and 19cf of dil, with a 13cf tank of O2 underneath the other tanks in a stand. I strap it on like a bc, turn on my O2 and go diving. I can be ready faster than the other guys usually. The downside is the manufacturers depth limit is 165' and I'm not trimix certified so most of my diving is relatively shallow. (compared to whackum) When you are pushing black snapper away instead of chasing them, you know something has changed for the better.


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## Orion45

TONER said:


> Brian
> what are the major benefits of a rebreather over scuba how much training do you need is it as safe as scuba with proper training and how much for a good set-up thanks


Are you thinking about switching to a rebreather?


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## TONER

i dont know enough about them i have always heard they were dangerous but before i moved down here i thought scuba diving was crazy Brians posts has sparked some intrest


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## Evensplit

Hollis is here this week doing an instructor certification class for the Prism2 rb. We've had lots of rb's come through the shop over the years, but this is the first full blown class we've had here. The future instructors must complete 100 hours on the unit before they get their instructopr credentials. 

The best question I've heard so far was "what if you puke in the loop?" The look on everyone's face was priceless. "Well, it's kinda like shi**ing in your drysuit."


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## WhackUmStackUm

I broke the larger design tasks down into the following subsystems:
PPO2 measurement and display
CO2 scrubber
O2 addition
Diluent addition
Breathing loop (i.e mouthpiece, hoses, counter lungs and water management)
Physical layout


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## Silent but Deadly

Do you have a starting design that we can pick apart, make suggestions (or copy)? I think I would start with arranging everything since you are filling space you don't really have to spare. And then work on every component to make it the best design possible.


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## WhackUmStackUm

Evensplit said:


> Hollis is here this week doing an instructor certification class for the Prism2 rb. We've had lots of rb's come through the shop over the years, but this is the first full blown class we've had here. The future instructors must complete 100 hours on the unit before they get their instructopr credentials.
> 
> The best question I've heard so far was "what if you puke in the loop?" The look on everyone's face was priceless. "Well, it's kinda like shi**ing in your drysuit."


lol - I wish I had been there to see their reaction. However, it is not difficult to deal with, in practice.


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## Orion45

WhackUmStackUm said:


> However, it is not difficult to deal with, in practice.


Which one...the puking or the shi**ing?


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## WhackUmStackUm

Orion45 said:


> Which one...the puking or the shi**ing?


Yes!


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## TONER

OK another dumb question 
how long can you dive (rebreather) at 160' (depth at tenaco house) with minimal deco time? i am assuming you generaly have a deco stop?


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## mike6043

Have you looked at using msr bags for counter lungs?


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## WhackUmStackUm

TONER said:


> OK another dumb question
> how long can you dive (rebreather) at 160' (depth at tenaco house) with minimal deco time? i am assuming you generaly have a deco stop?


There are a number of variables. The PPO2 level you are diving, the amount and mix of the bailout gas you are carrying, the amount of helium in your diluent bottle, and a few other variables factor in. The higher the oxygen level (PPO2), within safe limits, the slower you will accumulate deco time. More helium generally adds to your deco time. The amount and type of your bailout gas(es) limit how much deco time you can do should the rebreather fail completely. 

Here are some scenarios:

If you were diving my rebreather with my gradient settings (ignore this for now) and...
if you dive to 160' and...
you do not want to do any deco and...
you keep your PPO2 at 1.3, and...
you are using 21% oxygen and 20% helium in your diluent, then...
your maximum bottom time would be around 8 minutes.

This is not enough time to do much, so let’s plan on doing some deco.

If you want to only carry one 40 cu ft bailout bottle (with 1/3 reserve) and...
you keep your PPO2 at 1.3, and...
everything else is the same, then
your maximum bottom time would be a little over 16 minutes and with a bailout mix of 26/8 (02%/He%).

Better...but still too short for me.

If you were willing to carry both a 30 cu ft and a 40 cu ft bailout bottle, then...
your maximum bottom time would be a little over 26 minutes, with bail-out mixes of 26/8 trimix and 63% nitrox. In this case you would do 22 minutes of deco.

My dives typically run from 60 to 90 minutes, with 20-40 minutes of deco.


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## TONER

why do you keep your PPO2 so low (1.3) ? if i'm understanding the term right i set my computer to allow a 1.6 higher O2 means less nitrogen?
by the way those last numbers were very informative to me to help guage your alloable time thanks


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## SaltAddict

If I had 60-90 minutes of bottom time, I would need about 30 lift bags and a very attentive chase boat captain


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## WhackUmStackUm

TONER said:


> why do you keep your PPO2 so low (1.3) ? if i'm understanding the term right i set my computer to allow a 1.6 higher O2 means less nitrogen?
> by the way those last numbers were very informative to me to help guage your alloable time thanks


Your body can only take high partial pressures of O2 for so long before you run into problems. At a PPO2 of 1.6 you can dive for about 45 minutes. Lower PPO2 levels allow you to dive longer before oxygen toxicity become a threat.


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## WhackUmStackUm

Silent said:


> Do you have a starting design that we can pick apart, make suggestions (or copy)? I think I would start with arranging everything since you are filling space you don't really have to spare. And then work on every component to make it the best design possible.


Right now I am mulling over the size and types bottles to carry and the amount of scrubber material I will need. The size and weight of these items will have a great affect on the potential layouts of the components. 


For a 30-60 min bailout system, I am considering:

6 cu ft (0.9 L) aluminum O2 bottle
6 cu ft (or less) aluminum diluent bottle
Around 2 lbs of scrubber material
Off-the-shelf, lightweight and small, 1st stage regulators
Miflex hoses
Clear plastic housing for the scrubber and electronics, so I can check for leaks. The final version may be opaque.
It would be nice if I could attach it to my scooter, when needed.


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## Silent but Deadly

What about a couple of small carbon fiber 4500 psi bottles (think paintball) with a very very long fill hose for the O2. I wonder if you could make a U shaped scrubber (or something to fit around other components) using 4-8 sorb for a smaller yet longer tube for the scrubber? 4-8 for easier breathing from a non ideal scrubber shape. There is a homebuilt with the scrubber inside the counter lung using a dry suit zipper to access. This could be in a back pack sort of container, strap it on you or your scooter.


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## WhackUmStackUm

Silent said:


> What about a couple of small carbon fiber 4500 psi bottles (think paintball) with a very very long fill hose for the O2.


I bought some 4500 psi paintball tanks some time ago with this in mind. The challange is finding a balanced 1st stage paintball regulator to step the pressure down to about 150 psi. I have some unbalanced paintball regulators to try out, but I am not sure if they will work at deeper depths or how they will handle saltwater. Another drawback is that the 1.5L (88 ci) bottles that I have are pretty big on the outside and will displace a lot of water. If I use these big guys, I may have to strap on a bunch of lead to make the setup neutrally buoyant.

I came across 2L 4500 psi carbon fiber scuba tanks and bought two with this BOB in mind. They weigh 3-4 lbs each. I have used them with my main rebreather a few times and they work well. Since they float, I do have to strap on extra weight. However, I can use standard scuba 1st stage regulators with these tanks. I think the 88 ci paintball tanks are physically bigger, so they would require even more lead.



Silent said:


> I wonder if you could make a U shaped scrubber (or something to fit around other components)...


Initially I'll start with the tried-and-true axial design, just to see how small a scrubber I can get away with. I picked up some CO2 monitoring gear to support scrubber design and CO2 breakthrough experiments.



Silent said:


> ...using 4-8 sorb for a smaller yet longer tube for the scrubber? 4-8 for easier breathing from a non ideal scrubber shape.


Interesting idea. I may go woth 4-8 in the end, but I have 8-12 sorb on hand. So I will start with that.




Silent said:


> There is a homebuilt with the scrubber inside the counter lung using a dry suit zipper to access. This could be in a back pack sort of container, strap it on you or your scooter.


I saw a prototype of a semi-closed loop BOB in the KISS booth at the DEMA show last year like this. It was very interesting. However, I am worried that any pressure on the BOB (i.e. touching it) would increase the work of breathing (WOB) too much.

I picked up a couple of Camelbak packs at a local Army surplus store to try as counterlungs. I would like to use one counterlung, if I can get away with it. However, two lungs may improve the WOB. 

Yep, I have a plenty of experimenting to do. That's half the fun!


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## mike6043

http://www.frogdiver.com/Frog.pdf

single CL scrubber is in the bag.


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## WhackUmStackUm

mike6043 said:


> http://www.frogdiver.com/Frog.pdf
> 
> single CL scrubber is in the bag.


Thanks. Looks like a cool system, very compact. The counterlung/scrubber setup reminds me a bit of the sport KISS rebreather.


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## WhackUmStackUm

Here are some of my tank options, from left to right:
2L 4500 psi carbon fiber scuba tank
1.5L (88 ci) 4500 psi carbon fiber paintball tank
0.9L (6 cu ft) 3000 psi aluminum scuba tank
My "Fred Flintstone" foot, for scale
Given the water displacement and internal volume of the bottles, I think the aluminum tank may be the best fit for Whack BOB.


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## Silent but Deadly

Yep, the aluminum tanks look like the way to go. How much out of a 6 cf bottle would it take to fill the breather if you were at say 350 ft. I guess all you need is one breath and you would be on your way up. Also, when you test your scrubber, are you going to pressurize it to the depth it will hopefully never be used? Can't wait to see how small you can make it before you make a mercedes out of it with electronics.


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## WhackUmStackUm

Silent said:


> Yep, the aluminum tanks look like the way to go. How much out of a 6 cf bottle would it take to fill the breather if you were at say 350 ft. I guess all you need is one breath and you would be on your way up.


It will take about 1/4 of the 6 cu ft tank to fill a 4L loop at 350'.



Silent said:


> Also, when you test your scrubber, are you going to pressurize it to the depth it will hopefully never be used?


I'll have to give it some thought. I would need to make a test rig to add CO2 to the unit while it is in a pressure pot. I will test it in the water either way, at depth.



Silent said:


> Can't wait to see how small you can make it before you make a mercedes out of it with electronics.


Manual operation first, then auto-O2 addition.


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## mike6043

What are you planning to use for a scrubber?


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## WhackUmStackUm

mike6043 said:


> What are you planning to use for a scrubber?


I am planning to build a simple axial scrubber.

I am considering starting with a clear plastic food container with a sealing top. To keep the price down, I would love to be able to pick up something cheap at Walmart. Something like these:

Mainstays 2-Qt Canister
Square Flip-Tite Storage Container

However, I may end up making the container myself:
4" OD x 1/8" Wall Clear Cast Acrylic Tubing
6" Clear Rigid Schedule 40 PVC Pipe

I plan to start with a canister that is about twice as tall as it is wide.

Exhaled air will enter the scrubber through holes in the bottom and exit though a large fitting in the lid. There will be water resistant filters on the top and bottom. I like the filters that I use with my rebreather. They work well and are inexpensive. I will need to come up with a spring assembly which will apply pressure to the scrubber material to keep it packed, avoiding voids. 

For scubber material I will use the same stuff in Whack BOB that I use in my main rebreather, to start with. I will use Sofnolime 8-12 Mesh.


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## mike6043

I thought I read somewhere acrylic leaches into the loop.


After further research this info is wrong many scrubbers are built from acrylic.


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## WhackUmStackUm

mike6043 said:


> I thought I read somewhere acrylic leaches into the loop.


Let me know if you find the source of the info. Looks like a lot of home-builts use acrylic parts.


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## WhackUmStackUm

Most home-built BOBs that I have looked at over the years are WAY TOO BIG. Some of them are larger than my primary rebreather!

I want Whack BOB to be as small as possible, while including reasonable safety margins.


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## mike6043

WhackUmStackUm said:


> Let me know if you find the source of the info. Looks like a lot of home-builts use acrylic parts.


I stand corrected, looks like several RBs have acrylic scrubbers.

http://rebreathers.com.au/parts.html


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## Silent but Deadly

I have a big piece of stainless perforated sheet goods I bought (5$ at a used restaurant supply) to use at either end of my home built scrubber. I tried an aluminum bread pan and the sorb disintegrated it after several dives.You are welcome to enough for what you need. McMaster-Carr is your friend for stainless springs and pieces and parts. Also I o-ringed the PVC I used for the scrubber so I could repack and clean. I also bought heat sealing fabric for my lungs so I could make them the size and shape I needed. Also cheap considering your budget. Iron the sides you want to join for a seam and for added safety I thought I would have it sewn on the outer edge of the heat sealed edge. Something else to think about, do you need hoses for the mouthpiece? Or something fixed since its just backup.


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## WhackUmStackUm

Silent said:


> I have a big piece of stainless perforated sheet goods I bought (5$ at a used restaurant supply) to use at either end of my home built scrubber. I tried an aluminum bread pan and the sorb disintegrated it after several dives.You are welcome to enough for what you need.


Thanks! I may take you up on your offer.



Silent said:


> McMaster-Carr is your friend for stainless springs and pieces and parts.


Check



Silent said:


> Also I o-ringed the PVC I used for the scrubber so I could repack and clean.


I will likely do the same, although PVC is thicker than I would like the walls to be. Does PVC float?




Silent said:


> I also bought heat sealing fabric for my lungs so I could make them the size and shape I needed. Also cheap considering your budget. Iron the sides you want to join for a seam and for added safety I thought I would have it sewn on the outer edge of the heat sealed edge.


Good idea. I may have the same stuff on hand. I bought it to make lift-bags.



Silent said:


> Something else to think about, do you need hoses for the mouthpiece? Or something fixed since its just backup.


Using a a fixed breathing tube/hose had not occurred to me as a potential option. Interesting idea. I am currently planning to use hoses. Any recommendations for sources?


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## mike6043

WhackUmStackUm said:


> I am currently planning to use hoses. Any recommendations for sources?


Bc hoses would work, or maybe a vintage diving mouthpiece and hose. The vintage mouthpiece would be made to accept mushroom valves.


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## Silent but Deadly

How brave are you? Still considering your budget, the flea market is full of vacuum cleaner hoses. Diameter big enough for decent WOB, but flexible enough to use. Tear resistance?????? Although when was the last time you tore a hose on a vacuum? I made one way valves out of very thin clear plastic (like boat curtains) and they worked OK. The WOB was off the charts. Not flexible enough.


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## WhackUmStackUm

Just a quick update...

I have not forgotten about this project. I realized that I need build a pressurized O2 sensor tester first. I now have most of the parts on hand to build v1.0. I'll post a thread on that project in the near future. 

I hope to return to the *B*ail*o*ut Re*b*reather (BOB) project soon.


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## mike6043

Silent said:


> I have a big piece of stainless perforated sheet goods I bought (5$ at a used restaurant supply) to use at either end of my home built scrubber. I tried an aluminum bread pan and the sorb disintegrated it after several dives.You are welcome to enough for what you need. McMaster-Carr is your friend for stainless springs and pieces and parts. Also I o-ringed the PVC I used for the scrubber so I could repack and clean. I also bought heat sealing fabric for my lungs so I could make them the size and shape I needed. Also cheap considering your budget. Iron the sides you want to join for a seam and for added safety I thought I would have it sewn on the outer edge of the heat sealed edge. Something else to think about, do you need hoses for the mouthpiece? Or something fixed since its just backup.


I'm saving the clear plastic bags that come out of those wine boxes, they are tough and the perfect size.


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## WhackUmStackUm

mike6043 said:


> I'm saving the clear plastic bags that come out of those wine boxes, they are tough and the perfect size.


Hmmm, guess I have not seen those.


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## mike6043

http://www.google.com/imgres?start=...&tbnw=180&ndsp=65&ved=1t:429,r:40,s:200,i:124





Here is what i'm talking about.


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## mike6043

bag holds 3 liters


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## WhackUmStackUm

mike6043 said:


> http://www.google.com/imgres?start=...&tbnw=180&ndsp=65&ved=1t:429,r:40,s:200,i:124
> 
> Here is what i'm talking about.


Ok. Cool.

Are you planning to use those for rebreather counter lungs?


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## mike6043

That was the plan. I've got a few other ideas though. I haven't moved past the design phase yet. I'm saving for a couple sensors, a display, and a o2 whip. But yes I was going to use them as counterlungs. if I could find a suitable housing.


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## mike6043

Silent said:


> I have a big piece of stainless perforated sheet goods I bought (5$ at a used restaurant supply) to use at either end of my home built scrubber. I tried an aluminum bread pan and the sorb disintegrated it after several dives.You are welcome to enough for what you need. McMaster-Carr is your friend for stainless springs and pieces and parts. Also I o-ringed the PVC I used for the scrubber so I could repack and clean. I also bought heat sealing fabric for my lungs so I could make them the size and shape I needed. Also cheap considering your budget. Iron the sides you want to join for a seam and for added safety I thought I would have it sewn on the outer edge of the heat sealed edge. Something else to think about, do you need hoses for the mouthpiece? Or something fixed since its just backup.


Still have any perforated stainless you wouldn't mind parting with?


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## WhackUmStackUm

mike6043 said:


> Still have any perforated stainless you wouldn't mind parting with?


Gary gave the SS to me. I'm willing to share though. Send me a PM and we can discuss it.


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## mike6043

WhackUmStackUm said:


> Gary gave the SS to me. I'm willing to share though. Send me a PM and we can discuss it.


PM sent


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## Silent but Deadly

How much do you need, I still have some....somewhere.


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## mike6043

I'm going for a 4" PVC scrubber canister so ~4" circles.


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## sniper

A forum member on here years ago built a home built rebreather. Went by the name 'Genisis' haven seen him post much since.


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