Prism Scrubber

**Steve** · 11th October 2005, 06:10

Following on from the Meg scrubber thread I would like to explore an issue that I have heard bits and pieces about over the years but have never seen any data to back up claims. I don’t mean this in a confrontational way but rather a does anyone really know for sure way.

As we know the gas flow in the Prism scrubber flows radially from the inside to the outside. A few Prism guys have told me that this is the optimum way for a radial scrubber to operate. Is this the case for all radial scrubbers or just the Prism scrubber? Is it even the case for the Prism scrubber or is it a myth?

As we hear (often :-P), the Prism has had a lot of independent testing and there is a wealth of documentation out there on this CCR. Has the scrubber been tested in both directions by the one tester and what were the results?

JonnyB · 11th October 2005, 06:15

A radia scrubber will either go from in to out or out to in, i do not know the flow of the prism, and i do not know if you could use it any way(meaning in, out/out, in). The Cis-Lunar scrubber has a scrubber which the air passes from the outside towards the inside of the scrubber, and the Cis scrubber fits the Meg, but the prism will be fitting the Meg two, so i am not sure if that means that the prism is also an out/in type or that a radial scrubber can use either ways deending on the gasflow of the specific rebreather.
Stefan... any info on the scrubber on the prism please?

kind regards
Jonny

***schford*** · 11th October 2005, 10:52

See example I gave in Meg thread but In to Out flow will always give increased run times compared to Out to In, but at the expense of being able to cope with a partial flood.

There is no right or wrong answer to this just different design views - eg do you think there is say more chance of you getting lost in a wreck and needing x% more capability of your scrubber or do you think there is more chance of you flooding your scrubber.....

Though now you come to mention it I have never seen hard test data....that will be interesting....

Stuart

LukeN · 11th October 2005, 15:40

One thing with the prism scrubber is with the in to out the gas flow it will slow as it passes through not quiken, don't know how this affects the picture?
Also the sorb temp increases in a outward direction with the reaction, don't know if it would radiate inward?
On that one if the temp will increase inward like the Cis scrubber would the increase on gas flow drop the loop temp?

lof · 12th October 2005, 02:48

I would think that out-in flow in radial scrubber would be more effective. The reaction will be kept at a higher temperature when travelling from outside in, since there will be no cooling by the can wall. Also, the condensation should be reduced, since the hot gas is not hitting the large surface of the colder can as it is during in-out flow.

Yann A. · 12th October 2005, 03:35

Quote: (Originally Posted by lof)

I would think that out-in flow in radial scrubber would be more effective. The reaction will be kept at a higher temperature when travelling from outside in, since there will be no cooling by the can wall. Also, the condensation should be reduced, since the hot gas is not hitting the large surface of the colder can as it is during in-out flow.

Hi,

I was in the same impression. And also in an out-in direction, more contact with larger area of scrubbing material for gas richer in CO2.

Rgds,

Yann.

Underwaterbear · 12th October 2005, 04:36

Hi guys,

I have been searching for a thread I contributed to on diveoz explaining the relative merits of radial v axial and particularly in->out and vice versa. I can't find it so I'll try to summarize here.

In -> Out is preffered for the following reasons:

1. As exhaust gas hits the centre of the scrubber and moves out it is slowing down and it encounters greater and greater surface area of absorbent. This means dwell time is longer, breakthrough is more gradual, and channelling is less likely than if the flow was reversed(out ->in).

2. Because the scubber temp > exhaust gas temp, moisture is absorbed by gas as it travels through the scrubber. When this gas hits the relatively cooler scrubber wall it condenses and runs down into a moisture trap (if the unit has one - and it should when using this scrubber design). If you have out->in the moisture will condense on the next bit of cool pipework or hardware and then if not trapped could run back into the scrubber or condense on sensors etc. So in->out makes for an easy and convenient moisture trap.

3. Packing is less critical in radial c.f. axial since any settlement of sorb will occur in a smallre cross sectional area of the gas path. Imagine the liquid level in a 90% full coke can as you tip it on its side. Now imagine that simulates loosely packed sorb, an axial scrubber would allow a channel whereas the radial scrubber does not. (sorry not really an in vs out factor) I just like the analogy.

4. Following on from that point radial scrubbers are more tolerant of water since only a fraction of the cross sectional gas path is flooded by modest amounts of water.

Hope that helps, I'd be interested to hear other arguments.

Cheers
UWB

Crazyduck · 12th October 2005, 04:42

The Prism-

The heating aspect is considerably easier to warm a smaller area and then allow the heating and chemical reaction to expand or radiate outward. This will allow the process to move through the bed uniformly and provide an expansion process. The greatest temperature change is then when the warm gas hits the walls and then excess moisture is allowed to collect at the bottom of the bucket. Please note the scrubber is elevated and the foams does an excellent job of containing excess moisture. I personally prefer this method because it falls into my views of gas expansion, slowing the velocity of the gas and removing moisture before hitting the oxygen sensors.

Is it flood tolerant? I had my mouthpeice pop out during training in 5ft of water and no problems when I snatched it back from the pool; and plugged it into my hole. Ask Luke he was proabably laughing his butt off at me.

The Meg-

In comparison you have the gas entering into a much larger area were the walls are metal. Metal is an excellent heat sink and you are dealing with a much larger area. The gas is not going to fill the space as fast and you are then relying on the gas to be pulled through the bed. After moving through the bed and enjoying the chemical reaction it will move up the tube and then pass directly in front of the sensors without any of the excess moisture being allowed to be wicked away. While I agree that the surface area is larger it does not provide any benefit in my humble opinion. Plus, the chemical reaction if working its way inward and not providing any benefit to the metal walls that going to need to be maintaining the temperature as much as possible.

I pulled a Prism scrubber after a dive and you could feel the heat radiating out from the scrubber- it was an amazing thing. I held it thinking this was the perfect heating pad for my girlfriend

hehehe.

Guys, this is not any kind of personal attack- just my newbie thought process and what I have seen with my very limited exposure.

Going to bed now to be some ones heating pad-

Night Andrew

Bear · 12th October 2005, 04:47

Quote: (Originally Posted by Underwaterbear)

I have been searching for a thread I contributed to on diveoz explaining the relative merits of radial v axial and particularly in->out and vice versa. I can't find it so I'll try to summarize here.

Sorry. It seems your post on Dive-Oz was caught up in an argument regarding access to forums and the intellectual ownership of forum posts.

Due to the number of threads/posts involved and quotes/sub-quotes in the subsequent discussions, it became easier to remove whole threads from the forums.

The decision by the Admins/Moderators of Dive-Oz wasn't an easy one to make and lots of good information was lost.
Cheers

**Steve** · 12th October 2005, 05:21

Hi UWB,

A few of your reasons jump out at me and I would like it if you would expand on them. This is a tricky comparison to make due to the inconsistencies of not only the scrubbers but the rebreathers themselves.

As exhaust gas hits the centre of the scrubber and moves out it is slowing down and it encounters greater and greater surface area of absorbent. This means dwell time is longer, breakthrough is more gradual, and channelling is less likely than if the flow was reversed(out ->in).

I can’t wrap my head around this at all Andrew. I might be having a bad day but dwell time is more than likely going to be longer if the dirty gas is sitting around in the comparatively larger space surrounding the scrubber and being in contact with the larger volume of sorb in the outside of a radial scrubber?

Could you expand on your channelling point please? As I see it channelling is a by product of packing and has nothing to do with direction of gas flow. Either the channel is there or it isn’t?????

2. Because the scubber temp > exhaust gas temp, moisture is absorbed by gas as it travels through the scrubber. When this gas hits the relatively cooler scrubber wall it condenses and runs down into a moisture trap (if the unit has one - and it should when using this scrubber design). If you have out->in the moisture will condense on the next bit of cool pipework or hardware and then if not trapped could run back into the scrubber or condense on sensors etc. So in->out makes for an easy and convenient moisture trap.

Yup. This is a plus of in>out in my eyes as well. Having said that, this is a little gem of the Meg with moisture pads either side of the scrubber. Whilst not perfect it is a good compromise.

3. Packing is less critical in radial c.f. axial since any settlement of sorb will occur in a smallre cross sectional area of the gas path. Imagine the liquid level in a 90% full coke can as you tip it on its side. Now imagine that simulates loosely packed sorb, an axial scrubber would allow a channel whereas the radial scrubber does not. (sorry not really an in vs out factor) I just like the analogy.

I won’t buy into this one at all mate. Packing a radial is much more critical on a radial than an axial due to the much shorter gas path.

4. Following on from that point radial scrubbers are more tolerant of water since only a fraction of the cross sectional gas path is flooded by modest amounts of water.

This one is very dependant on the breather design and your statement rings true to either type in the right CCR.

11th October 2005, 06:10	#1 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,117	Prism Scrubber Following on from the Meg scrubber thread I would like to explore an issue that I have heard bits and pieces about over the years but have never seen any data to back up claims. I don’t mean this in a confrontational way but rather a does anyone really know for sure way. As we know the gas flow in the Prism scrubber flows radially from the inside to the outside. A few Prism guys have told me that this is the optimum way for a radial scrubber to operate. Is this the case for all radial scrubbers or just the Prism scrubber? Is it even the case for the Prism scrubber or is it a myth? As we hear (often :-P), the Prism has had a lot of independent testing and there is a wealth of documentation out there on this CCR. Has the scrubber been tested in both directions by the one tester and what were the results? __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
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11th October 2005, 06:15	#2 (permalink)
JonnyB Johnny The Hatch Current Rebreather/s: MK 15.X Titan Other CCR Other SCR Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Megalodon Sport Kiss Classic Kiss Other CCR Other SCR Home Build Join Date: Jan 2005 Location: Sweden (Stockholm)/Cyprus(Ayia Napa) Posts: 971	A radia scrubber will either go from in to out or out to in, i do not know the flow of the prism, and i do not know if you could use it any way(meaning in, out/out, in). The Cis-Lunar scrubber has a scrubber which the air passes from the outside towards the inside of the scrubber, and the Cis scrubber fits the Meg, but the prism will be fitting the Meg two, so i am not sure if that means that the prism is also an out/in type or that a radial scrubber can use either ways deending on the gasflow of the specific rebreather. Stefan... any info on the scrubber on the prism please? kind regards Jonny
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11th October 2005, 10:52	#3 (permalink)
*schford* Despotic Overlord Current Rebreather/s: Megalodon Sport Kiss Other Rebreather/s: Join Date: Jan 2005 Location: London, UK Posts: 3,564	See example I gave in Meg thread but In to Out flow will always give increased run times compared to Out to In, but at the expense of being able to cope with a partial flood. There is no right or wrong answer to this just different design views - eg do you think there is say more chance of you getting lost in a wreck and needing x% more capability of your scrubber or do you think there is more chance of you flooding your scrubber..... Though now you come to mention it I have never seen hard test data....that will be interesting.... Stuart
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11th October 2005, 15:40	#4 (permalink)
LukeN New Member Current Rebreather/s: Optima Other Rebreather/s: Not Bought Yet Prism Topaz Join Date: Jun 2005 Location: Australia,West Aus Posts: 84	One thing with the prism scrubber is with the in to out the gas flow it will slow as it passes through not quiken, don't know how this affects the picture? Also the sorb temp increases in a outward direction with the reaction, don't know if it would radiate inward? On that one if the temp will increase inward like the Cis scrubber would the increase on gas flow drop the loop temp? __________________ Luke Nelson www.imagedive.com.au
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12th October 2005, 02:48	#5 (permalink)
lof RebreatherWorld Sponsor Current Rebreather/s: Megalodon Prism Topaz Sport Kiss Classic Kiss MK 15.X Other CCR RB80 / Clone Other SCR Home Build Other Rebreather/s: Other CCR RB80 / Clone Other SCR Home Build Join Date: Jun 2005 Location: USA Posts: 482	I would think that out-in flow in radial scrubber would be more effective. The reaction will be kept at a higher temperature when travelling from outside in, since there will be no cooling by the can wall. Also, the condensation should be reduced, since the hot gas is not hitting the large surface of the colder can as it is during in-out flow. __________________ Jakub Golem Gear ShopKeeper www.golemgear.com
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12th October 2005, 03:35	#6 (permalink)
Yann A. New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Feb 2005 Location: Indonesia Posts: 49	Quote: (Originally Posted by lof) I would think that out-in flow in radial scrubber would be more effective. The reaction will be kept at a higher temperature when travelling from outside in, since there will be no cooling by the can wall. Also, the condensation should be reduced, since the hot gas is not hitting the large surface of the colder can as it is during in-out flow. Hi, I was in the same impression. And also in an out-in direction, more contact with larger area of scrubbing material for gas richer in CO2. Rgds, Yann.
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12th October 2005, 04:36	#7 (permalink)
Underwaterbear A Prismer in Megland Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: May 2005 Location: Seattle, WA Posts: 192	Hi guys, I have been searching for a thread I contributed to on diveoz explaining the relative merits of radial v axial and particularly in->out and vice versa. I can't find it so I'll try to summarize here. In -> Out is preffered for the following reasons: 1. As exhaust gas hits the centre of the scrubber and moves out it is slowing down and it encounters greater and greater surface area of absorbent. This means dwell time is longer, breakthrough is more gradual, and channelling is less likely than if the flow was reversed(out ->in). 2. Because the scubber temp > exhaust gas temp, moisture is absorbed by gas as it travels through the scrubber. When this gas hits the relatively cooler scrubber wall it condenses and runs down into a moisture trap (if the unit has one - and it should when using this scrubber design). If you have out->in the moisture will condense on the next bit of cool pipework or hardware and then if not trapped could run back into the scrubber or condense on sensors etc. So in->out makes for an easy and convenient moisture trap. 3. Packing is less critical in radial c.f. axial since any settlement of sorb will occur in a smallre cross sectional area of the gas path. Imagine the liquid level in a 90% full coke can as you tip it on its side. Now imagine that simulates loosely packed sorb, an axial scrubber would allow a channel whereas the radial scrubber does not. (sorry not really an in vs out factor) I just like the analogy. 4. Following on from that point radial scrubbers are more tolerant of water since only a fraction of the cross sectional gas path is flooded by modest amounts of water. Hope that helps, I'd be interested to hear other arguments. Cheers UWB
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12th October 2005, 04:42	#8 (permalink)
Crazyduck Underwater Mechanic Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Mar 2005 Location: TEXAS, Dallas/ Ft.Worth Posts: 711	another perspective The Prism- The heating aspect is considerably easier to warm a smaller area and then allow the heating and chemical reaction to expand or radiate outward. This will allow the process to move through the bed uniformly and provide an expansion process. The greatest temperature change is then when the warm gas hits the walls and then excess moisture is allowed to collect at the bottom of the bucket. Please note the scrubber is elevated and the foams does an excellent job of containing excess moisture. I personally prefer this method because it falls into my views of gas expansion, slowing the velocity of the gas and removing moisture before hitting the oxygen sensors. Is it flood tolerant? I had my mouthpeice pop out during training in 5ft of water and no problems when I snatched it back from the pool; and plugged it into my hole. Ask Luke he was proabably laughing his butt off at me. The Meg- In comparison you have the gas entering into a much larger area were the walls are metal. Metal is an excellent heat sink and you are dealing with a much larger area. The gas is not going to fill the space as fast and you are then relying on the gas to be pulled through the bed. After moving through the bed and enjoying the chemical reaction it will move up the tube and then pass directly in front of the sensors without any of the excess moisture being allowed to be wicked away. While I agree that the surface area is larger it does not provide any benefit in my humble opinion. Plus, the chemical reaction if working its way inward and not providing any benefit to the metal walls that going to need to be maintaining the temperature as much as possible. I pulled a Prism scrubber after a dive and you could feel the heat radiating out from the scrubber- it was an amazing thing. I held it thinking this was the perfect heating pad for my girlfriend hehehe. Guys, this is not any kind of personal attack- just my newbie thought process and what I have seen with my very limited exposure. Going to bed now to be some ones heating pad- Night Andrew
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12th October 2005, 04:47	#9 (permalink)
Bear Smelling Dairy Air Current Rebreather/s: Other CCR Dolphin Home Build Not Bought Yet Other Rebreather/s: Other CCR Dolphin Home Build Not Bought Yet Join Date: Apr 2005 Location: Melbourne, Australia Posts: 101	Quote: (Originally Posted by Underwaterbear) I have been searching for a thread I contributed to on diveoz explaining the relative merits of radial v axial and particularly in->out and vice versa. I can't find it so I'll try to summarize here. Sorry. It seems your post on Dive-Oz was caught up in an argument regarding access to forums and the intellectual ownership of forum posts. Due to the number of threads/posts involved and quotes/sub-quotes in the subsequent discussions, it became easier to remove whole threads from the forums. The decision by the Admins/Moderators of Dive-Oz wasn't an easy one to make and lots of good information was lost. Cheers __________________ http://www.victech.org VICTECH.ORG: A web resource for Technical Divers in Victoria
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12th October 2005, 05:21	#10 (permalink)
Steve Ladies bring a plate Current Rebreather/s: Megalodon Home Build Other Rebreather/s: Not Bought Yet Inspiration Classic Sport Kiss Classic Kiss MK 15.X Home Build Join Date: Feb 2005 Location: Perth - Australia Posts: 1,117	Hi UWB, A few of your reasons jump out at me and I would like it if you would expand on them. This is a tricky comparison to make due to the inconsistencies of not only the scrubbers but the rebreathers themselves. As exhaust gas hits the centre of the scrubber and moves out it is slowing down and it encounters greater and greater surface area of absorbent. This means dwell time is longer, breakthrough is more gradual, and channelling is less likely than if the flow was reversed(out ->in). I can’t wrap my head around this at all Andrew. I might be having a bad day but dwell time is more than likely going to be longer if the dirty gas is sitting around in the comparatively larger space surrounding the scrubber and being in contact with the larger volume of sorb in the outside of a radial scrubber? Could you expand on your channelling point please? As I see it channelling is a by product of packing and has nothing to do with direction of gas flow. Either the channel is there or it isn’t????? 2. Because the scubber temp > exhaust gas temp, moisture is absorbed by gas as it travels through the scrubber. When this gas hits the relatively cooler scrubber wall it condenses and runs down into a moisture trap (if the unit has one - and it should when using this scrubber design). If you have out->in the moisture will condense on the next bit of cool pipework or hardware and then if not trapped could run back into the scrubber or condense on sensors etc. So in->out makes for an easy and convenient moisture trap. Yup. This is a plus of in>out in my eyes as well. Having said that, this is a little gem of the Meg with moisture pads either side of the scrubber. Whilst not perfect it is a good compromise. 3. Packing is less critical in radial c.f. axial since any settlement of sorb will occur in a smallre cross sectional area of the gas path. Imagine the liquid level in a 90% full coke can as you tip it on its side. Now imagine that simulates loosely packed sorb, an axial scrubber would allow a channel whereas the radial scrubber does not. (sorry not really an in vs out factor) I just like the analogy. I won’t buy into this one at all mate. Packing a radial is much more critical on a radial than an axial due to the much shorter gas path. 4. Following on from that point radial scrubbers are more tolerant of water since only a fraction of the cross sectional gas path is flooded by modest amounts of water. This one is very dependant on the breather design and your statement rings true to either type in the right CCR. __________________ WARNING: I contain occasional coarse language, extreme sexual references, nudity, and adult themes, which may offend some people - Usually churchy types.
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