Am i missing something--question for caveseeker7 and other RB gurus

[teksimple]

I almost bought the Prism. But didn't because:

1. Could not change the setpoint underwater. I could change the set point manually, I suppose, but then the flashing lights would probably irritate me. Then what would be the point of electronics? This was a show stopper.
2. I prefer rear mounted CL's, even at the expense of WOB.
3. I dive deep. Maybe for liability reasons the depth of the Prism was limited. But I know of another rebreather that has been proven at extreme depth.
4. No guaranteed delivery date from Steam Machines.

The Cis-lunar is very expensive to maintain because of it's complexity.
The Ouroboros is not out yet.
The Megalodon seems awesome, but I did not want to wait for delivery with the radial scrubber that I wanted, plus no training available in Hawaii.
KISS didn't have a big enough scrubber.

So I bought Pete's personal Mk 15.5, and paid out the nose for it (supposedly there are only 10 original Mk 15.5s in the world). Paid thousands more to have the unit restored to a clean diving condition and then thousands more to have Hammerhead electronics installed. I am fairly confident I have among the most expensive rebreathers in the world. Obviously, price was not extremely critical for me.

I also want to put Suunto transducers on the regulators so that I can monitor diluent and O2 pressure with my hoseless D9 computer. By having absolutely no rubber hoses on the unit, it reduces the risk of a gas loss.

Now after having dived the toy that I just purchased, there are some not insignificant issues. Moving 75 pounds of mass around is some work. Add that to the 40cf bailout I carry, and my ability to maintain position in a current is significantly hampered. I definitely appreciate my graphite free diving fins.

If I had my choice of dream rebreather, it would probably be the Ouroboros with larger scrubber, and Inconel spheres from my Mk 15.5 if I could modify it. Would also try to have DIN valves instead of the O-ring'd oxygen post valves that are currently on the Inconel spheres.

OR, rip the electronics out of a Prism, replace it or modify it so I can change the setpoint mid-dive, trick it out for deeper depth, and then I might be able to get used to over the shoulder C.L.

 

[caveseeker7]

Hi Joe,

let me guess, you figured that since CO2 on a Prism isn't gonna give me a headache you will ... :bluthinki

Quite frankly, I don't know enough about absorbants and scrubbers to really go mano a mano on the subject.

Nor could I find any data regarding the maximum absorbing capacity of diving grade absorbants from the manufacturers. And I use plural here because the Prism was tested and rated with Sodasorb.

But a few thoughts on the subject:
You qoute Lugo data, how did they test that (140 l/kg)?
Temperature, ambient pressure, humidity, what was the protocol?

Why does the amount of CO2 in the loop influence the speed with which the gas moves through the loop? If you mean the difference in density (which I don't know in the first place) between a 1.6 lpm and a 1.35 lpm CO2 injection, you really think it leads to such a veocity difference?
I'm asking because from what I gather the velocity of the gas flow through the loop for most part leads to the dwell time ... with single and double counterlungs making some difference. So the RMV (40 lpm in the published Navy tests) should make the difference, not the percentage of injected CO2 when it comes to dwell time.

What's "scalling"?

Add-ited:
I consider the NAVY's testing data, both what has been posted on SMI's website and what they are allowed to share in person, as solid data. As solid and complete as it gets, no other manufacturer has bothered or dared to publish it.

Furthermore, I consider the NAVY's 1.35 lpm CO2 addition rate as quite reasonable. I for can not sustain it for 5 hours, not even on multiple dives. So it seems more "reality based" than the CE's 1.6 lpm or UT's 1.8 lpm CO2 rates.
I rather doubt anyone can sustain either for long ... has anyone ever overbreathed their CCR to an extend that O2 addition couldn't keep up?

Especially the KISS users, if you set your O2 cmf rate to somewhere around 1 lpm (which translates into less than 1 lpm CO2)?
Are you guys jacking the flow rate up the wahzoo or just duck tape the manual add button down? Because from the conversations I had that manual add button isn't used all that often during the dive, right?

And while we're on the subject, and my goal here is not to praise the Prism and slam the Buddy, can you explain the similar scrubber ratings of SportKiss and Ourobors? That one I just don't get.

The SportKiss has a 5 lbs scrubber, the cannister isn't really insulated ... .
The Ouroboros has a 6 lbs scrubber, the radial cannister is insulated, the very large diameter hoses should reduce gas velocity and increase dwell time ...
What am I missing?

Always wonder (ing)
Stefan

 

[hoopa]

Wow-- what great responces-- first off i just want to say thanks to all that responded-- i didnt respond to anyones cause i just wanted to let you guys write what you write without a bias from anything i might have said... But i have been reading.... Also i just want to make sure that i was understood when i asked if the guy who makes the Prism was a Ahole-- it was a retorical question-- like " is the reason these arent as popular as they should be-- is why?-- is the guy a jerk?" -- i never personally thoguht anything like that-- it was just a question so i do hope it didnt come accross as a statement-- i have seen his pics around and he looks like a great guy-- But i still dont understand why these things arnt all over the place..

A few questions left over from what i have read--

First off-- why wouldnt i go with a eccr over a manual ccr-- it would seem to me that having it controled by electronics would just make the whole experience that much more transparent while diving and if things go wrong i have the option to go to manual and get my butt home alive.

Second of all--- Is the idea of putting something together like padiscubapro was talking about and take all the best parts and have them put into one rig-- Bigger scrubber-- hh electonics-- back lungs-- ect(not so say these are the best-- just refering to what he was saying-- it did make sence to jsut get the best and make a rig with all the best stuff)

3rd of all---Yes i agree with those that have said to get the rig that best suits your diving but to me i look at it like this== why have a rb that has only 2 hours of dive time when i can have one that has 5-with vitually no penalty to have the extra time(no more weight or loss of performance)-- i dont have to use all 5 hours but its nice to know its there if i need it-- sort of like a having a car with very little horsepower and one with alot== i would rather have alot and not need to use it then have one with very little and then have to get out of the way of a truck and not be able to do it cause of not enough power.

4.-- Is there anything on the horizen that i(we that are looking) should think about waiting for?--

5. Has anyone personally seen or know of any of the specs on the Optima by diverite?-- Looks like a nice new rig but just wonder about the specs.

6. is changing the set point in the middle of a dive something that is done often?-- (of course a newbie to Rb's here so havnt done the classes yet). It would seem to me that it would only be done in case of something going wrong-- and if that was the case cant i just go to manual and then get my butt back to the top?

caveseeker7-- I got your PM and will get in touch-- i do appreciate your offer..

 

[caveseeker7]

Hoopa,

glad you're enjoying the show. Joe and I by the way get along just fine ... unless we discuss my choice in rebreathers. eace:

... it was a retorical question ...

And one that Shas read.
If you ever get a Prism make sure the battery isn't hooked up to the crotch strap. :linkz:

Second of all--- Is the idea of putting something together like padiscubapro was talking about and take all the best parts and have them put into one rig

It's come full circle ... :lol: ... with the arrival of his new scrubber he'll have two rigs, a Closed Circuit Radomski and the original starting point. Which means he's finally got an Inspiration to teach on again.

why have a rb that has only 2 hours of dive time when i can have one that has 5-with vitually no penalty to have the extra time

I asked myself the same question and couldn't find a good answer.
Especially when you consider our local boat diving. Out of L.A. usually 3 dives/day, from Ventura mostly 4 dives/day, each with 45' to 60' window. With the Prism that means you can do them all and have a good safety margin without having to change absorbant on the boat.

5. Has anyone personally seen or know of any of the specs on the Optima by diverite?

Specs haven't been released for the Optima afaik, but they're out for the HH and the ExtendAir cartridge, so you can make a pretty decent estimate in regards to scrubber duration and electronic capabilities. For size, weight and such you'll have to wait.

6. is changing the set point in the middle of a dive something that is done often?

Well, if you just paid three grand for your Hammerhead you better be changing it every other minute.
Just kidding. :1poke:
Some people like to be able to adjust them during long deco dives, especially raise during deco to accelerate it. For that of course you'll need an accurate controller (like the Hammerhead), you don't want to set it to let's say 1.6 ata pO2 and have it go past 1.8 ata pO2 ... .
On the Prism you can raise them manually as Kent pointed out, which also means you pay attention to your gauge. Some divers don't like to be bothered with that during the rigors and task loading of hours of deco.
The HDD display, by the way, can either be turned away or the electronics shut off if the LEDs bother you. It's not like you need them to fly the rig safely.

 

[Shas]

first a few points to clarify, testing at a higher flow rate will not only eat up chemical faster but it will also skew the results shorter because there will be a point were some co2 is being removed not just all of it (the dwell/contact time) is different, the higher rate will change the overal "scalling" slightly ...

Depends on what the RMV is, whether it's a pulsed test or continuous flow, whether there is a recovery period etc.
Suffice to say we published data that lets the consumer know what test method was used and what figures were attained. No other CCR manufacturer has published theirs so there is nothing to accurately compare the data.

as to how much co2 it can absorb - the prisms and inspirations were both tested using the same chemical (although now a different manufacture is recommended with the prism).. its manufacture rating is only 140 liters per kg, this means BY MANUFACTURER (chemical) ratings the prism if 100% effective it could remove 381 (individual batches could yield a higher adsorbtion rate (and frequently do, but we should respect guaranteed minimums), and the inspiration would be 350.. therefore the prism threoretically could do 4hrs at 1.6lpm, and the inspiration 3.6 hours @ 1.6, actual testing on machines has shown at worse case slightly above 3.25 hours, other runs closer to theoritical.. which is about a 90% efficiency (worse case) at 1.6lpm.. at a slower flow rate the efficiency should go up since there will be a longer contact time with the chemical, and in the design of an axial scrubber, the chemical gets exhaused in a linear fashion, so the flow rate near the break throug point is critical....

The Inspiration has a shorter dwell time than the radial prism canister and with an axial you get veins or fingers of CO2 running up the canister wall which is indicated by a slow increase in CO2 before major break through. When we ran an axial on the first Prisms we started to see CO2 earlier than expected, a smart knock on the canister would stop the CO2 creep until it found another path up the side.

The only data I have seen is for medical grade absorbent (4-8 grade) it is publicly available and gives approximate figures of 15 liters CO2 for 100grams. So based on 4-8 grade medical this would be 1kg for 150 liters or for 6 Lb load 409. Liters. Close to your number but we are talking 4-8 NOT 8-12 or 6- 12, and not high performance diving grade - NOT the same animal.

There have been tests on both canister types under the same conditions, we have published ours on the web site for 255 mins to 0.5 CO2. I belive the Insp is around 200mins for the same test. I think this is acurrate because the old Prim axials were around the same.

The Sodasorb 6-12 is a little different to the old 6-12 in that the new grade of Sodasorb is harder @ 90 on a scale of 100 and because it is a smaller mesh size you can pack more into our radial scrubber which has resulted in even longer duration.

As you know Joe there are many factors governing duration. A pound in one rig is not the same as a pound in another. I have read as much as I can on calculating canister performance, the best book I found is Life Support System Design. This sums up the problems pretty well.

With the advent of the new CAD programs you can buy after market programs for fluid dynamics. We use a CFD program called EFD Lab which has helped a great deal to improve design but only independant manned and unmanned testing will get you the most accurate results.

As for numbers there is a very good reason why we moved to TN and it wasn't just to play the guitar

Pete

a biased manufacturer, not as biased as a user.

 

[hoopa]

lol ok i give again== i reworded my question on the first page-- lol

it was a bad attempt at bad humor with a real question mixed in--- we have all known places that made a great product but the owner was a bit of a jerk and made you not want to use their products-- so i was just throwing that into the option for the reason why these things arnt all over the place-- my bad-- ill go to the corner now and give myself a time out(but will be dreaming of the day i get my new Rb--lol)

After reading these posts i still dont see a technical Reason that any of those other Rb's outshine the prism. Price-- yes i can see that might be a reason for someone-- Front Cl's-- ok yes that too-- but for proformence-- no.... The units seem light-- tough-- super long lasting scrubber--- eccr (transparent) with manual as a back up-- batter power out of the loop-- all this seems good to me....

But im still reading and enjoying each persons point of view--

 

[padiscubapro]

Nor could I find any data regarding the maximum absorbing capacity of diving grade absorbants from the manufacturers. And I use plural here because the Prism was tested and rated with Sodasorb.

I knew they retested it afterwards buut from what Shas told me they originally tested with sofnilime.

But a few thoughts on the subject:
You qoute Lugo data, how did they test that (140 l/kg)?
Temperature, ambient pressure, humidity, what was the protocol?

from what I was originally told when I asked the question myself to oc lugo it was by chemical makeup.. which would set the minimums..

Why does the amount of CO2 in the loop influence the speed with which the gas moves through the loop? If you mean the difference in density (which I don't know in the first place) between a 1.6 lpm and a 1.35 lpm CO2 injection, you really think it leads to such a veocity difference?
I'm asking because from what I gather the velocity of the gas flow through the loop for most part leads to the dwell time ... with single and double counterlungs making some difference. So the RMV (40 lpm in the published Navy tests) should make the difference, not the percentage of injected CO2 when it comes to dwell time.

My last answer probably wasnt the clearest (a little incomplete), but the injection rate has a few implications.. depending on the protocol when the co2 rate injection rate increases, the rate at which gas is moved through the loop is also increased..

the second we all know more co2 means shorter chemical life, but when the bed is near the end of life (especially in an axial), the ammount of co2 it has to pull oot has big implications. think of it this way - these are pretend numbers.. say it took 1 inch of scrubber to pull the rate of 1,6lpm of co2 out of the loop but youe scrubber is exhausted to the point you only have 3/4 of an inc if good media, this may be able to pull sat 1.2 lpm of co2, there will be a slight rise if you are a bit above this point, but unless you are deep you wount break the faulure threshold for some time, the loop contents will also vary base on changes of workload.. but if you pumped 1.6 through it it would faill very quickly at this point.. thats why I said you cant directly scale two different rates to each other based on testing... testing with a low flow rate and scalling up in real kife would fail before this point, and etesting at a higher rate but scaling down would result in testing a somewhat longer duration..

Add-ited:
I consider the NAVY's testing data, both what has been posted on SMI's website and what they are allowed to share in person, as solid data. As solid and complete as it gets, no other manufacturer has bothered or dared to publish it.

Furthermore, I consider the NAVY's 1.35 lpm CO2 addition rate as quite reasonable. I for can not sustain it for 5 hours, not even on multiple dives. So it seems more "reality based" than the CE's 1.6 lpm or UT's 1.8 lpm CO2 rates.
I rather doubt anyone can sustain either for long ... has anyone ever overbreathed their CCR to an extend that O2 addition couldn't keep up?

I never doubted the validity of test but I also believe if any number come above the rating of the chemical company you still have to use them as the maximums, because in reality they know that what they are stating is the MINIMUM they have to meet..

And while we're on the subject, and my goal here is not to praise the Prism and slam the Buddy, can you explain the similar scrubber ratings of SportKiss and Ourobors? That one I just don't get.

The SportKiss has a 5 lbs scrubber, the cannister isn't really insulated ... .
The Ouroboros has a 6 lbs scrubber, the radial cannister is insulated, the very large diameter hoses should reduce gas velocity and increase dwell time ...
What am I missing?

we do know what the spec the ourobors will have to meet, the sport kiss ratings have been based on use not machine testing.. my guess is that when its finally tested it will be very close to the theoritical rating of the chemical since you get 2 passes through the chemical..
I wouldnt be surprised if I saw a 3hr rating @1.6 on it (even with less checmical than the buddy)

Also if you are working, insulating the scrubber isn't a big deal.. I have dove rbs with thermal monitoring, in both warm at cold water the temperature of a functioning scrubber is fairly close..
This is especially true once you start getting into helium mixtures.. helium mixtures take much less energy to raise the gas temp than nitrogen based mixtures..

 

[padiscubapro]

As you know Joe there are many factors governing duration. A pound in one rig is not the same as a pound in another. I have read as much as I can on calculating canister performance, the best book I found is Life Support System Design. This sums up the problems pretty well.

With the advent of the new CAD programs you can buy after market programs for fluid dynamics. We use a CFD program called EFD Lab which has helped a great deal to improve design but only independant manned and unmanned testing will get you the most accurate results.

As for numbers there is a very good reason why we moved to TN and it wasn't just to play the guitar

Pete

a biased manufacturer, not as biased as a user.

I agree, there are to many parameters.. In my last reponse I was trying to be as brief as possible but still get people thinking.. The book you qute is definately one of the best around.. Its definately an eye opener on what has been done..

The 140l/kg is the number that molecular products has been using for their 797/(812) grade..

I also agree the new 6-12 by Grace is a big improvement over the earlier stuff.. I am definately a believer, as you know. I do use the stuff and will be ordering another palette from you as the new dive season approaches..

I tried keeping out brands in the discussion unfortuantely the only two CCRs out there that have "tested" run time is the PRISM and Inspiration, but since they use different test parameters we can only make approximate comparisons. I also have no doubt when the Prism undergoes CE testing it will come up with numbers better that the Inspiration with regards to runtimes..

I was also trying to point out that the way the scrubbers are packed have a big impact on runtimes.. I pack a very tight scrubber and I can tell you I get more than 5.5 lbs in my cartridge, so far I haven't had breakthough (although I have tried to do it - within reason).
I know, I average 1.0lpm of oxygen (or less) during a dive, so my Co2 production is .9lpm or less, when I do 5-6 hour dives I am still within the capacity of the scrubber for MY metabolism, but I still plan to use OC near the end of the dive..
Personally I feel its about knowing the risks and managing them.
I can pack the 8-12 a bit tighter than the 6-12 sodasorb, but the price/performance of the sodasorb is hard to beat.

No diver can maintain the levels used in testing for an extended period of time.
for those that are unfamiliar, life support through purely carbohydrate based fuel come in about 1.0l of co2 per liter of oxygen, while someone burning 100% protein comes in somewhere around 0.8 liters of co2 per liter of oxygen, and fat around 0.7.

Thats why .9 liters is the accepted value (US NAVY) base on the average diet. (Buhlmann used 1.0).

 

[caveseeker7]

... for those that are unfamiliar, life support through purely carbohydrate based fuel come in about .8l of co2 per liter of oxygen, while someone burning 100% protein comes in somewhere around 1.2 liters of co2 per liter of oxygen.

Uh ohhh, you got me. :bluthinki
Due to my appetite for Filet Mignon, Tri-Tip and spare ribs the Prism was the only option I had.

 

[MikeR]

Uh ohhh, you got me. :bluthinki
Due to my appetite for Filet Mignon, Tri-Tip and spare ribs the Prism was the only option I had.

If you've done your research and feel the prism is your best choice, go for it. Many of us dive different units, we all think we have the best unit, and we are all right. Confused? Most of us went through the stages you are going through now, we all made what we felt was the best decision in our units. I have had the pleaseure of diving many rebreathers that are currently available(except the prism) most of them are great units and offer great benifits and survivability with the right training. As technology advances, the units are getting closer together in quality. IMHO the most important thing, bieng ten fold more important than what unit you choose, is your training. Get references and get the best instructor you can.....in the end it wont matter what's on your back if your training sux.