Anyone up to “no good” with design ideas?

PeteS

I used to work for a company that moulded Delrin. IIRC, when heated to injection temperature for tooooo long, it can rapidly decompose into gasses. That is, explode, taking the injection moulding machine with it.

But when it's cold, it's as tough as old boots.

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Pete S.

http://www.steggle.co.nz

Every silver lining has a cloud

onetime

Excellent! Now that's the kind of stuff I love to see. Interesting design, coming at things from a slightly different angle. Now, split up your scrubbers, put them on either side (from just under the armpit to the waist) add bottles on either side so they're completely independent, breathing hoses for each, and you're in the ballpark of what I'm looking to do.

Can you provide some details on your unit? Scrubber details, duration, etc?

--Paul

AD_ward9

I was very interested when the first pictures your rebreather were posted, but then it said the scrubbers were in series. Protos 1, 2 and 3 of the twin scrubber demonstrator we developed use serial scrubbers, but we changed so proto 4 has the scrubbers in parallel. The reason for the change was the breathing resistance results under the EN14143 tests were really borderline with the series scrubbers at depth when there is water in the system. We did try drains between the two scrubbers into the exhale bag (very nice little connectors), but still not wonderful. With parallel scrubbers we found it allowed the user to change from one scrubber, two scrubbers one Rebreather, to RB + independent bail out RB just by swapping over two port fittings (choosing a U, a blank or a hose to plug in). Your scrubber is a lot shorter than ours, so perhaps the CE issue did not press you so firmly.

There is something else in the wings: The non-sports market is taking up twin scrubbers big time in new designs. These are all parallel scrubbers and US led. The non-sports market can take an age to release products, so people will just need to watch that space - most Rebreather manufacturers and CCR technology companies know about this already.

Returning to the sports/techi market use of twin scrubbers became much more interesting when we found a way to package 5 inch diameter scrubbers in the same profile as 4 inch scrubbers, and a change to the hoses and breathing bags, so the user can decide whether to use it as one Rebreather or two. Instead of the hoses coming over the shoulder, they come in parallel across the chest from breathing bag on left and right (over shoulder dual bag containing two bags of different length). Again a difference to proto III which had breathing bags in the same position as the Dolphin.

On your timescale, turning around a set of rebreather mechanics takes us about 4 to 5 months, including 3-D flow simulation etc for the scrubbers and other non-standard bits. Anyone who wants a Rebreather in this time can get it. When done, add on CE approval which takes between 1 month and 9 months depending on the design. The timescales for most of our work is the electronics and tooling. Electronics takes a lot time in design validation and verification, and the cleverer the electronics, the more time to validate it.

Our technology content is high because clients are either commercial users (requiring safety for liaibility reasons), or who want to sell to the average diver who someone described on this thread as a "burger flipper", with billion hour MTBCF. Your market is more specialist. We are technology providers in various industries rather than manufacturers, so time to market is usually an issue decided by clients rather than us.

Can you post details of how your twin serial scrubbers can work as a single Rebreather or as a RB plus bail out RB? I did not see the additional hose fittings on your picture. I would be interesting to see how you have done that. I note your scrubber is very shallow also: why is that? A final question: the scrubbers are very short: what is the load each one takes?

I like the way you have the axis vertical when the diver is prone, when you use a granular scrubber. This should carry less risk of tunnelling when the diver is prone, than the usual in-line or horizontal config for axial scrubbers.
Cheers,
Alex

caveseeker7

Here is another dual inline cannister design, this one shown at DEMA last year by O2 Technologies on their Tiger CCR prototype. The U-shaped counterlung connects the two cannisters, wrapping around them. The cannister can take either the pre-filled inserts (lying next to) or refillable cannisters.

Attached Images

TigerCCR.jpg (64.1 KB, 39 views)

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Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

paulraymaekers

the breather only works as one breather with 2 scrubbers in series: for very good reasons: each scrubber contains 1.5kg sorb, has vertical axix, in diving position very difficult to force water upwards into the first (exhale) scrubber. reason for 2 small scrubbers: total hight of the breather: 16cm, and that includes the backmounted counterlungs. opening from exhalelung to scrubber: diameter 15cm!!! do not forget that WOB is influenced by diameter of internal tubing, in this design, there is none!

efficiency of the total scrubber increases: due to a mixing-chamber between the 2 scrubbers: suppose due to thermal influence, or tunneling, or wathever reason only 80% of the CO2 is scrubbed, and at the outside (cold side) of the scrubber, the gas passes nearly unscrubberd, this gas is mixed with the scrubbed gas, goes into the second scrubber, that also scrubs 80%: that is fine (CO2 left in system is 0.2 times O.2= only 4% of CO2 at entrence)
with only one scrubber it is 20%

also far better (safer) sorb use: in changing sorb you work this way: when you come at half the time to change the total sorb, you take out the exhale scrubber (most used sorb), put the second (less used) scrubber in exhale position, and put fresh sorb in inhale position,and you continue for another half total time: this way you always trow away the most used sord and replace it by new sorb
we did not yet do CO2 testing, but form experience, we always do 3 hours on one scrubber, and change following the procedure, never had any problem, so I don't now yet where the limit is
(in warm water i once pushed it to 5 hours, and the last 30min with high workload: no symptons at all of CO2 charge)

our normal diving temp is +/- 15° celcius

regards

paul

decoweenie

Damn, and I thought that I pushed my scrubber hard...

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paulraymaekers

...each scrubber contains 1.5kg sorb
...we always do 3 hours on one scrubber (ed: in 15C)
...in warm water i once pushed it to 5 hours

yes, but do not forget that the 1.5kg sorb you trow can be used 100%, there is another 1.5kg behind that takes whatever comes out of the first one!

in 15° water, I would never do 6 hours on 3kg, and then change both scrubbers, that is a completely different approach!


regards
paul

decoweenie

OK, I am a little confused about the original post of "always do 3 hours on one scrubber" ?

Could you clarify...

You had 2 fresh scrubber of 1.5kg and dived for 3 hours in 15C. Do you change the used scrubber alone, change scrubber position and dive another 3 hours in 15C, and repeat the process ?

If so, then 3 hour on 1.5kg as I understood is right. If not, then you use more than 1.5kg for the 3 hour.

If the process as I described is what you do, and you expect the second scrubber to take up some of the scrubbing, then the capacity of "second" scrubber actually is reduced each time you repeat the process.

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paulraymaekers

that is what I do!

the reason is the following: during diving your exercian level is never equal, but over a 3 hour time, the averige is!:
also, the moving front of the used scrubber is not a straight line, but at the entrance the sorb is used max, and near the end the sorb is used partially:

suppose you have 1 scrubber 3kg, after 6hours of diving: the first half could be used for 100%, more to the end, it will be used less, so the active lengt and active amount is very reduced, and you will possibly have a breaktrough if you have a sudden rise in CO2 production: you should already have trown away your scrubber, even if it is only used for 60%

now do the opposite: devide your 3kg scrubber into 10 compartments, and say every 30 minutes you remove the first compartment of sorb at the exhale side, of this part you can be sure it is used 100% (the gas with the highest amout of CO2 first passes there, so easy to take up large quantity of CO2) and you move al 9 other towards the exhale side, and you put a fresh amount at the inhale side: now a les used compartment takes the fully charged gas, and will be saturated after some time... and you continue this way
all the sorb you trow away will each time be saturated and used for 100%, wich means that on the averige in the scrubber with more compartments, you always have more unused sorb than in your single scrubber!

where in a single scrubber your sure you have lot's of fresh sorb right after filling, but not after some time of diving, and because you do not know how much of your sorb is saturated, you trow away everything (mostly you scrubber is not even used half!, but your active lenght of your scrubber is reduced, and breaktrough COULD happen)

with the multi-compartment scrubber, you reduce the unknown factor how far the sorb was used.

ofcourse, 10 compartments is not practical, but 2 already go into that direction!

regards
paul

decoweenie

Paul,

Thanks for the clarification.

Yes, I already understood your original reasoning for splitting the sorb and throw away the first 1/2.

However, I still believe about the diminishing sorb supply if you use more than 3-hour worth of scrubbing on the first portion and use a partial amount of the second portion. By replacing and repositioning the first 1/2, you will diminish the total a little more if the second dive uses the same amount of scrubing. So the diminish will increase on subsequent dives. And so on, so on...

But as you mentioned, you don't do 6 hours on one go, so it is not an issue.

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"...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..."

- Rebreather World PM