Axial/Radial scrubber question

Posidion

Aloha, this being my first post, I have no idea if this is a good place to ask questions, but I would really like to know what the performance differences are between axial and radial scrubbers. Also concerning scrubbers, is more better (a 5lbs canister vs. an 8lbs canister) for deeper or longer dives?

Lake_Tahoe_Diver

We had a thread on this a while back, you can check the archives for the long debate we had on this. Mostly the radials have a better WOB, but can be a problem if you did not pack them correctly due to channeling.

I love the WOB of the Prism (radial scrubber) compared to the Kiss Sport (bi-axial scrubber), but then again you really can not compare the two since they are for two differnet purposes.

After you checked the archives out come back and ask some more question we may be able to give you a more exact answer.

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OceanOpportunity

Just being devil's advocate here...but aren't they both designed to scrub CO2. period.? I can see how limitations of performance might dictate what each is used for, but a scrubber is a scrubber is a scrubber.

In response to the original post...the scrubber duration questions is not even close to black and white. It is possible to have an axial out perform a radial, and vice versa. Variables include flow velocity, depth (gas density/#'s of molecules CO2), temperature, resistance/dwell time through the bed, etc. Now, pound for pound, yes, a larger scrubber would be better for deeper diving given the reduction in duration with depth. A 3-5 pound scrubber, generally speaking, is more than adequate for 90% of the diving done out there, and this tends to be the range for most comemrcially available units.

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Lake_Tahoe_Diver

[quote=OceanOpportunity;179124]Just being devil's advocate here...but aren't they both designed to scrub CO2. period.? I can see how limitations of performance might dictate what each is used for, but a scrubber is a scrubber is a scrubber.
quote]


Ok maybe I should have been clearer when I was refering to which rebreather breathed easier. An made note that there are other facters that made the difference beside the scrubber alone. Thanks for keeping me on my toes...

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silent running

Hello P, as LTD said above, this has been covered in other threads, so do a search and read on...

As for basic differences, radial scrubbers typically have shorter distances that the gas must travel through the scrubber-grain boundary-which in turn gives a lower work of breathing than a similar weight axial. Also, owing to the radial geometry, an in-out flowing radial will allow for a longer dwell time as the gas slows down as it flows out from the center and the cross sectional area increases. Axials usually have more scrubber housing wall surface area than a radial, which can increase the possibility of channeling insufficiently scrubbed gas due to the larger amount of sorb that is next to the hard surface. But, radials are, as mentioned above, harder to pack than axials.

There are exceptions to this, and a good book to pick up is Mastering Rebreathers by Jeff Boznic. It has a chapter on the various scrubber designs which explains their basic function and the relative advantages and disadvantages of each type.

Also as mentioned above, the efficiency of a scrubber depends on many factors, any of which can affect the others-thermal insulation and canister material, size, flow direction, moisture collection, size of granuals, placement and number of counter lungs, to name some. A good scrubber is designed to work in a particular system and will not necessarily work as well in a different unit.

And yes, a bigger scrubber will usually give longer duration, but if a scrubber is too big, it will increase the work of breathing which is not desireable for any dive and especially not a long, deep one. -Andy