Safety of radial vs axial scrubber

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GO..

New Member
After thinking for a long time, I have decided that I should go over to dive ccr.
I am very cautious by nature, and now it just before I'm about to order a unit.

I wonder:
I currently live in northern Norway, and the water temperature is usual between 4 and 12 degrees Celsius.

Is axial scrubber safer than radial scrubber?

- Gerhard
 
Once correctly packed there is no difference in "safety".

Packing Radials is "generally" more time consuming than packing axials.

Other than this there are no real generalities, each particular design is different.


Dave

.
 
Dave Sutton said:
Once correctly packed there is no difference in "safety".

Packing Radials is "generally" more time consuming than packing axials.

Other than this there are no real generalities, each particular design is different.
Click to expand...
The differences are especially in thermal protection.

http://johnclarkeonline.com/wp-content/uploads/2011/10/Picture12.png
http://www.ccrexplorers.com/showthread.php?t=13338

Radial absorber for the correct direction of the gas flow, provides excellent thermal protection for the soda lime (Interspiro (Sweden) has long been used radial absorber.). Axial requires special heat protection.

greet rc
 
Nice topic and thread.

Personally, I think WOB is equally important to knowing your pPO2.

WOB is critical to O2 uptake and CO2 elimination, hence it is equally important to pPO2 management.

The Radial has a much lower WOB vs. an Axial scrubber, and I don't dive Axial scrubbers.

From a WOB perspective, the Axial is less "safe" (having a higher WOB) than the Radial, and there is no logical basis for diving an Axial scrubber, when the Radial is as or more effective than the Axial scrubber at removing CO2, and offers a much lower WOB.

Furthermore, Sofnolime swells and clumps after initial use, and during initial use, and it may even increase/exacerbate further the WOB of an Axial scrubber.

Last, the Radial scrubber makes it easier to remove almost entirely any absorbent dust, reducing clumping, improving WOB, and reducing the risk of dangerous absorbent dust reaching the airways.

I see not one reason to dive an Axial scrubber, and would not dive one, based on risk management assessment on one vs. the other.

Axial scrubbers are cheaper to produce, but then less safe, so thank-you, but no thank-you (I'd rather pay more and dive safer)... and equally I will not purchase and/or dive a rebreather whose WOB has not been independently tested and published.

Any evidence that a Radial is less safe than an Axial I'd love to hear about (to take in consideration in my risk assessment).
 
GO.. said:
After thinking for a long time, I have decided that I should go over to dive ccr.
I am very cautious by nature, and now it just before I'm about to order a unit.

I wonder:
I currently live in northern Norway, and the water temperature is usual between 4 and 12 degrees Celsius.

Is axial scrubber safer than radial scrubber?

- Gerhard
Click to expand...

I've seen some very dangerous smal volume radials.

In general, low volume scrubbers, axials are safer, because when gas travel path becomes very short, the risk of tunneling because of uneven desity inside the scrubber is higher: so for low volume scrubber I recommend axial

High volume scrubbers: there radial becomes more interesting because when going from low to high volume, with axials usually the WOB increases, where as for radials the WOB decreases.

For your application, temp between 4 and 12, but not especially long duration dives (because to cold anyway), a normal axial will just do fine.

For cold water diving the most important thing is: only use good sorb that is recommended by the manufacturer, and stick to the recommended durations, and you will be fine (anyway related to scrubber)

paul
 
paulraymaekers said:
I've seen some very dangerous smal volume radials.

In general, low volume scrubbers, axials are safer, because when gas travel path becomes very short, the risk of tunneling because of uneven desity inside the scrubber is higher: so for low volume scrubber I recommend axial

High volume scrubbers: there radial becomes more interesting because when going from low to high volume, with axials usually the WOB increases, where as for radials the WOB decreases.

For your application, temp between 4 and 12, but not especially long duration dives (because to cold anyway), a normal axial will just do fine.

For cold water diving the most important thing is: only use good sorb that is recommended by the manufacturer, and stick to the recommended durations, and you will be fine (anyway related to scrubber)

paul
Click to expand...

Numbers?

What is meant by "low volume" in numbers?"

What is meant by "high volume" in numbers?"

What is a "normal axial?"

What is "good sorb" in numbers?

Talking about a scrubber WOB as if it was a color or shade of color is not enough, when WOB is quantifiable and measurable.

In relative terms, Radial is safer than Axial in WOB (WOB is lower, and to be specific, for the Meg Radial the duration is higher than any Axial, based on available published numbers).

I am only looking at existing scrubbers for existing rebreathers where some numbers are actually available - none of which can be said are poorly designed Axial or Radial scrubbers as far as I know (maybe Duration should be added to my comparative WOB Spreadsheet and it will).

Let us talk numbers and compare risk/benefit in measurable terms (not generic affirmations or generalizations).
 
From what i have seen and read, Radials are much more particular about how you pack them.

I am sure a well packed radial is better than a well packed Axial but a badly packed one is considerably more likely to happen than a badly packed Axial.


If you don't need the run time? why use one?

If you do, then just be very careful packing it.

ATB

Mark
 
If i understand right what Paul wrote it makes perfectly sense to me.

On a small container the radial surface to enter the scrubber is smaller than on a same size axial. Therefore WOB on axial better. Also the travel distance for gas through scrubber might be too short for CO2 removal...
As the container gets bigger the radial surface gets larger while the distance to travel through an axial container would get longer. Therefore WOB on radial gets better.

So radial is not better in general but it depends on dimensions and design.
Also to consider what already others stated that radial is harder to pack... I'd go for a standard size axial if you don't need extended scrubber times... Otherwise I would still get a axial and a radial for those few dives I'd really need one...

Cheers

Christian

Sent from my iPad using Tapatalk HD
 
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Mark Chase said:
From what i have seen and read, Radials are much more particular about how you pack them.

I am sure a well packed radial is better than a well packed Axial but a badly packed one is considerably more likely to happen than a badly packed Axial.


If you don't need the run time? why use one?

If you do, then just be very careful packing it.

ATB

Mark
Click to expand...

If you do not need the run-time, you use one because of the lower WOB, hence increased safety.

The additional run-time is a further safety margin and benefit.

Basically, it costs me a little bit more to use a Radial (initial purchase price and a bit more for an absorbent fill each usage cycle), but this is offset by the added safety benefit (lower WOB and longer duration).

If one has the actual figures, WOB and Duration, for an Axial vs. Radial scrubber, then the purchaser can use the information to form an expectation of price and value, and vote with his wallet.

For me, it is a no-brainer, when looking at the cost vs. additional performance benefit of a Meg Radial (the 8 lbs.) vs. any other Axial (including Meg Axial).

Others may reach a different conclusion, but you can only form a view if you are given the numbers (price, WOB, duration).

WOB is as important as "Know your pPO2."

If you do not know the WOB of your unit under a range of conditions, you do not "know your WOB" and cannot make a proper risk assessment about the dive (and purchase of a rebreather).

As to packing risk, both Radial and Axial have the risk of channeling due to poor packing procedure, and the risk of the occasional bad batch of absorbent (due to the production process or storage/transport conditions).

The bottom line is that the available numbers to date (and we need more disclosure of data/numbers and true test conditions) show that available Radial scrubbers are safer than available Axial scrubbers (i.e. Radials have lower WOB and longer duration, and they only cost marginally more).
 
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CFU said:
If i understand right what Paul wrote it makes perfectly sense to me.

On a small container the radial surface to enter the scrubber is smaller than on a same size axial. Therefore WOB on axial better. Also the travel distance for gas through scrubber might be too short for CO2 removal...
As the container gets bigger the radial surface gets larger while the distance to travel through an axial container would get longer. Therefore WOB on radial gets better.

So radial is not better in general but it depends on dimensions and design.
Also to consider what already others stated that radial is harder to pack... I'd go for a standard size axial if you don't need extended scrubber times... Otherwise I would still get a axial and a radial for those few dives I'd really need one...

Cheers

Christian

Sent from my iPad using Tapatalk HD
Click to expand...

Based on actual numbers available for actual scrubbers available to date, Radial is "safer" than Axial (having lower WOB and longer Duration).

I have not seen any number to support the contrary (i.e. "Radial is not safer than Axial"), but I'd love to see some if they exist.

Anybody buying a rebreather should consider ordering a Radial and not an Axial on first purchase (provided the WOB and Duration numbers are clearly provided, otherwise you do not really know the true risk you are actually taking and what you are buying and paying for).
 
CFU said:
If i understand right what Paul wrote it makes perfectly sense to me.

On a small container the radial surface to enter the scrubber is smaller than on a same size axial. Therefore WOB on axial better. Also the travel distance for gas through scrubber might be too short for CO2 removal......Cheers

Christian
Click to expand...

no, no, the WOB on the radial will be better, but due to the very short gas path, there is more risk of local preferential break-trough: this also explains the bigger differences in duration when doing multiple testing on the same small radial scrubber

for example I would never make a short duration 1.5kg radial scrubber with a short gas path to have low WOB; a 1.5kg axial is much better then, and the little higher WOB on the axial is preferred over the higher risk of early non-expected breaktrough
 
paulraymaekers said:
no, no, the WOB on the radial will be better, but due to the very short gas path, there is more risk of local preferential break-trough: this also explains the bigger differences in duration when doing multiple testing on the same small radial scrubber

for example I would never make a short duration 1.5kg radial scrubber with a short gas path to have low WOB; a 1.5kg axial is much better then, and the little higher WOB on the axial is preferred over the higher risk of early non-expected breaktrough
Click to expand...

We are/I am talking about real test data on real scrubbers like the rEVO Radial and the ISC Radial neither of which are small or hold 1.5 kg. of absorbent.

Published data on these two scrubbers show that Radials have superior WOB and Duration over any Axial (that I know of).

If it were to cost say USD 400 more at initial purchase of a rebreather, as a first buy, I'd definitely go for the Radial over the Axial.

Safer, for a little higher price.
 
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U Choose

GO.. said:
After thinking for a long time, I have decided that I should go over to dive ccr.
I am very cautious by nature, and now it just before I'm about to order a unit.

I wonder:
I currently live in northern Norway, and the water temperature is usual between 4 and 12 degrees Celsius.

Is axial scrubber safer than radial scrubber?

- Gerhard
Click to expand...

Gerhard
Like you im a new member to this forum ive been diving ccr for 2 yrs approx and certainly dont consider myself qualified to give any educated advise on your question.
What i would say is read through a good chunk of other threads and get a feel for who's advise you would be comfortable investing your hard earned cash on.
My personal view is that there are probably few people on this forum with the experiance with as many differant units as Dave Sutton and his responses seem to be balanced and unbiast and written to allow understanding and teaching .
You will also find many others offering excellent advise U choose who you listen to.


Neil
 
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Casperlad said:
My personal view is that there are probably few people on this forum with the experiance with as many differant units as Dave Sutton and his responses seem to be balanced and unbiast and written to allow understanding and teaching .
Click to expand...

Try as well my friend you see to my right in my avatar picture (far end of the bench).

He is "probably few people... with the experiance with as many differant units as Dave Sutton..."

He is dead.

Experience alone does not cut it (sadly).

We need to build as much safety margin as practicable, and Radial over Axial is an easy way to do it (and not too expensive).
 
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gianaameri said:
We need to build as much safety margin as practicable, and Radial over Axial is an easy way to do it (and not too expensive).
Click to expand...

I'm far from an expert. Quite the opposite actually.

WOB is not derived from the scrubber alone, so why focus that much in the axial vs. radial instead of overall WOB?

The variables in WOB in rebreathers would be the manually packed scrubber and CL adjustment. You can exclude both variables. Pre-packed axials might be better than a manually packed radials, at least in that you know the figures. The same with non-adjustable backmounted CL's inside the frame/box.

If WOB and safety margin really means that much for you, why not stick with OC? At 0.4-0.5 Joules/liter no rebreather will match it.
 
gianaameri said:
We need to build as much safety margin as practicable, and Radial over Axial is an easy way to do it (and not too expensive).
Click to expand...

Security absorber is in very different places, design and diagnostics. The project is a hedge against a possible puncture channel, split into layers with breaks (Faser), crisis (Aqua Lung, Draeger) or split into sections (rEvo). The second method is a diagnosis of his actions during the operation. Here temperature during operation is a method of giving information in advance, this method is still in the early stages of development. Even measuring ruler (Martin Parker) is a small amount of information.

rc greet
 
Oldefors said:
I'm far from an expert. Quite the opposite actually.

WOB is not derived from the scrubber alone, so why focus that much in the axial vs. radial instead of overall WOB?

The variables in WOB in rebreathers would be the manually packed scrubber and CL adjustment. You can exclude both variables. Pre-packed axials might be better than a manually packed radials, at least in that you know the figures. The same with non-adjustable backmounted CL's inside the frame/box.

If WOB and safety margin really means that much for you, why not stick with OC? At 0.4-0.5 Joules/liter no rebreather will match it.
Click to expand...

I am not an expert either, but I understand numbers, and I have seen a lot of marketing fluff (I can see it coming a mile away).

The numbers released for actual scrubbers available to date show that the Radial design is superior to Axial design because it produces in the unit overall and under the same test conditions:

a. lower WOB
b. longer duration

This is fact based on numbers (not an unsubstantiated opinion).

Of course there are other element in a rebreather which affect WOB, but here in this thread we are looking specifically at scrubber design (i.e. "Safety of Radial vs Axial Scrubber"), and all evidence (numbers) point that adopting a Radial scrubber reduces WOB and increases scrubber duration in the same rebreather unit under the same tested conditions.

So, why not use a Radial instead of an Axial?

For some people the additional cost of the initial purchase of a Radial Scrubber and the additional cost of packing it (usually Radial designs take more absorbent material) may be a deterrent, but for me it is acceptable.

The WOB numbers allow me to make a decision about the risk acceptable to me when engaging in an activity like rebreather diving and in forming the price I would accept to buy a rebreather for, and which unit I would purchase over another (and which unit I would not dive at all even if it were given to me for free).

Of course there are other considerations as well, but they are outside the scope of the thread.
 
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gianaameri said:
He is "probably few people... with the experiance with as many differant units as Dave Sutton..."
Click to expand...
Diving experience has nothing to do the construction and design of closed circuits, interesting structures do not doing saturated divers or experiance divers.
:cuckoo:
Check out the pages of the European Patent Office.

greet rc
 
[
Experience alone does not cut it (sadly). Totally agree

All we have is Experiance,Trainiing and a big part of confidence in the kit we use .Initial Confidence in our kit comes in many forms wether its ,homebuild and knowing every nut and bolt,advise from industry respected individuals,or dare i say CE marked kit .

Neil
 
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