Ok, tear it apart (New Home Build Design)

canetoad

Lure Angler; I agree with you about the path of least resistance. Wheather worn back or chest mounted; the main CL should be topmost in most orientations. And given that the 2 side CLs combined wont (or shouldn't) be able to contain a full exhalation; the largest percentage of gas should route to the main CL. I'm hoping anyway.

Teoman; Thank you. Now that I have a little more time to devote to this, hopefully I'll be able to perform an in-water test soon. Maybe the very bottom of the scrubber under the "U" may not get much flow but I think directly in & around the "U" the lime will get used more than most other areas. I did buy indicating Sorb & I'll definately follow your suggestion & check it. I haven't needed to seal the lungs yet, but I am hoping I can get away with a mechanical seal by clamping the ends of the CLs between 2 pieces of flat bar stock bolted togather. I'll definately let you know how it goes.

Thanks,
PM

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PM

teomannaskali

I have tried sealing then with clamps. It didnt really work as I desired. So I turned to welding poly urethane.

Teoman

Please try it on the couch before you go diving.

canetoad

Teoman, it will definitely undergo thorough couch trials before it gets anywhere near the water. I may be totally wrong but I don't think sealing the CLs will be that difficult. I figure that if I can't achieve a reliable mechanical seal solely by clamping and bolting, I will add tire patch adhesive (Monkey Grip, etc.) which I have always had excellent results with.
Thanks,
PM

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PM

teomannaskali

If this was your first rebreather why did you go with something so fantastic ?

I have been bulding for a very long time now. And I definitely think that you should first build something that works and then move on from there.

Your design got me thinking.... I can not think at the moment how your design could be beneficial as a pendulum rebreather on the center section the bottom part is not used and the top part is double used. But this may just be my lack of creativity...

What I thought was you could have the cls positioned in such a manner that with you breath one lung squeezes the other so that it pushes some of the gas back thorugh the scurbber. Or you could installa check valved bypass between the inhale and exhale scrubber so that when you exhale you squeeze some of the gas from the inhale cl to the exhale cl... Dont know if these will work but... One must try..
One thing is for shure is that they will only work with a certain breathing pattern. For example deep and fast breaths or slow and steady breaths. For other cases the scrubber has to be bigger which defeats the purpose.

I will try to make a picture...

Teoman

ChristianM

Hi,

I guess that the cell readings will be wrong at the end of the scrubber life. The should be at the inhale cl (left end of the scrubber).

Cheers!
Christian

Mdemon

Great effort! It must have taken so much work!

What is the benefit of this design? Is it to use both sides of the scrubber as per a normal pendulum? Is the efficiency increase enough to justify the design effort?

Just a thought, but what would happen if you got rid of your current DSV and fitted a single hose DSV where the central counterlung is? Then you'd have two pendulums for the price of one? You could even clamp a side (CL) before diving then switch the clamp over when you wanted a "new" scrubber - instant Bail Out Breather! LOL!

It would need to be chest-mounted, with the CL's pointing up instead of down (think Horse Collar). Then, if you put the OPV/ADV in the blanked-off centre section, you'd have an instant bailout valve (BOV) effect just by clamping the CLs against the scrubber ends with your hands - causing the ADV to fire on each inhalation. You'd need a good 2nd stage reg...

Ooops! Got a bit carried away there...

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"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

canetoad

Teoman; I was originally going to use a more basic design. But, while @ the rebreather store (Lowes) I ran across my current ready made scrubber housing. I gave it a second glance & thought of it's potential advantages. Of course, the fact that it was dirt cheap on clearance, had nothing to do with it. I'm not sure I'm following your line of thought though. Perhaps you could provide your picture when you get the chance.

Christian; I'm not sure that the cell readings taken in the main CL when the scrubber is becoming exhausted would be significantly inaccurate. Would cell output be affected to any large extent unless CO2 levels were way off the scale?

Mdemon; ...Thanks. Not a lot of work, but that was the whole point: to construct a Home Build with readily Available Materials. As mentioned in Teoman's reply above; this started out as something different but I saw the potential benefits of the scrubber shape & decided to make it work. Keep in mind that is an interim design. As noted earlier I have a more optimized scrubber shape in mind. And this unit is intended to be part of a modular & redundant system. More on that later, likely much later. The goal right now is basic proof of concept.
I did consider the "2 pendulums for the price of one" option, but I have always been somewhat wary of the dead airspace issues of single hose designs. Plus; I always prefer a water trap in front of the scrubber. Your instant BOB & BOV ideas actually aren't bad. Especially the instant BOB. Properly developed, could be effective.

Thanks,
PM

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PM

AD_ward9

Your comment brought back a recent memory, and I would underscore the caution on using plumbing bits.

OK, lets forget about offgasing and all that stuff: just say Canetoad's goal is to survive crossing the road, then a small number of dives.

A little while back, one of our staff got fed up of getting bumped to the back of the queue for chamber time, due his project being a bit "blue sky", so he made himself a low pressure chamber out of plumbing bits which he managed to select very cleverly so the bits followed the profile of the circuit board he was testing so he used the barest minimum of gas. He found it kept on leaking. As soon as he fixed one leak, he had another one somewhere else. Then I picked it up and it had leaks everywhere

Turns out that even slight negative pressures in plumbing parts are not too good: the joints all leak. Then of course, when he put positive pressure on, the joints came apart a bit because unlike the same pipework in his bathroom, rebreather sections are not fixed to the wall.

He put some glue in those joints, but when it was set hard that just made matters worse.

Finally, he went into the lab and welded it all together (hot air gun).

Still would not go diving on it, but for the 40milli bar pressures on the bench he was trying to use, it was good enough, and it stood up to 1 bar in a hydraulic test (so 300mbar working!).

Alex

canetoad

AD_ward9; I have read many of the previous posts about offgassing & do have some concerns. I know a number of others have used PVC with varying degrees of success but I doubt I'll use this unit long term in any case. Actually; there should be no PVC to PVC gluing involved; only rubber to rubber & only if the mechanical seal I have in mind fails.

Thanks,
PM

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PM

teomannaskali

Its not the glue it is the PVC itself that is offgassing.


Teoman