Rebreather World - View Single Post - Why does depth matter for scrubber lifetime

Abbo · 28th October 2007, 03:12

Quote: (Originally Posted by Shawn)

So then if I understood correctly that break through is the largest determining factor when determining the scrubber life using calcium hydroxide then would (on deep dives) lythium hydroxide be a better alternative? (sorry about the spelling)

And if alot of this problem is negated by the use of radial scrubbers, how come Rebreather's don't come with a radial scrubber instead of the axial scrubber?

Sounds like somebody has just been watching the movie 'The Cave'! Lithium hydroxide absorbs more CO2 per unit volume than calcium hydroxide does, and it has lower density too. It is used in submarines and a tub of it became a major factor in the lives of the Apollo 13 crew. Its higher efficiency would make it very attractive for scrubbers in rebreathers, and mountaineers would absolutely love it too, if it were not for the fact that it is exceedingly caustic. A caustic cocktail from normal sorb is life threatening, but one from lithium hydroxide would be far, far worse. If a rebreather could be designed where there were no risk of that caustic cocktail, then lithium hydroxide, though expensive, would become attractive. In addition to having almost double the absorbent capability, the reaction is highly exothermic, which would be a positive on cold water dives.

Radial scrubbers are highly efficient right up until they're not. They are better on work of breathing and are more efficient. However, when breakthrough occurs, the amount of CO2 getting through rises far more suddenly with a radial.

28th October 2007, 03:12	#18 (permalink)
Abbo Nicholas Smith Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Aug 2006 Location: Tokyo Posts: 460	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Shawn) So then if I understood correctly that break through is the largest determining factor when determining the scrubber life using calcium hydroxide then would (on deep dives) lythium hydroxide be a better alternative? (sorry about the spelling) And if alot of this problem is negated by the use of radial scrubbers, how come Rebreather's don't come with a radial scrubber instead of the axial scrubber? Sounds like somebody has just been watching the movie 'The Cave'! Lithium hydroxide absorbs more CO2 per unit volume than calcium hydroxide does, and it has lower density too. It is used in submarines and a tub of it became a major factor in the lives of the Apollo 13 crew. Its higher efficiency would make it very attractive for scrubbers in rebreathers, and mountaineers would absolutely love it too, if it were not for the fact that it is exceedingly caustic. A caustic cocktail from normal sorb is life threatening, but one from lithium hydroxide would be far, far worse. If a rebreather could be designed where there were no risk of that caustic cocktail, then lithium hydroxide, though expensive, would become attractive. In addition to having almost double the absorbent capability, the reaction is highly exothermic, which would be a positive on cold water dives. Radial scrubbers are highly efficient right up until they're not. They are better on work of breathing and are more efficient. However, when breakthrough occurs, the amount of CO2 getting through rises far more suddenly with a radial.
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