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Often ignored and the poor relation to the Oxygen side of the life support equation, it's also the most abused and of course there is no monitor or warnings
Packing the Scrubber Correctly (with Pictures)
How does the Scrubber work during a dive (Gordon Henderson is abducted by aliens to explain how)
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1. Only use Sofnolime 797
2. Maximum scrubber time 180 minutes
3. Be shallower than 50m at all times after 100 minutes use
4. Be shallower than 20m at all times after 140 minutes use
5. If in doubt, tip it out
6. Always re-grease and check the fitting of the scrubber O ring and spacer
7. If you don't follow 1 - 6 fine, but don't moan if you get injured or die!
(thanks to Stephen Bird for this very clear explanation)
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It is very important that this is done correctly. Its seems that a lot of folks don't do this right and are getting CO2 bypass during dives. It is very important that you put the right quantity of Sofnolime into the canister and that you pack it well enough but not to well. There are a few techniques to do this But I shall detail the one taught to me by Dave Thompson which has stood me in good stead. I've not had a Hypercapnia issue on any of my dives
I also have cut circles of synthetic chamois, which I leave at the bottom of my scrubber under the spring base to absorb moisture here rather than let it go up into the scrubber. I purposely leave the down tube of the scrubber un-insulated so condensation takes place there
1) Check Sofnolime is in date and has been correctly stored
2) Inspect the 2 Thinsulate end pads to check for wear, holes etc. They're not expensive so replace them each season if you have any doubts. Make sure they are dry (I swapped mine at the beginning of this season so they look really clean in the pictures
3) Inspect the canister outer and inner, check for contamination, scratches, wear. Especially check for the Inner canisters rim detaching from the body
4) Turn the inner body upside down and place a Thinsulate end pad down into the canister with the flaps pointing up. make sure it is sat evenly and no spaces are showing (I use the bathroom sink here. The bottom handle of the canister goes down the plug hole, its stable and if I miss and spill any Sofno, I can just wash it away afterwards)
5) Pour Sofnolime into the canister until it is JUST short of the top. You want a gap which is just enough to get the top pad and the black plastic Spider to locate inside. Level the Sofnolime off
6) Place the top Sofnolime pad onto the top of the scrubber with the tags stuck out over the sides
7) Place the Black Plastic Spider onto the Thinsulate pad and make sure it is located inside the scrubber all the way round
8) Add the thumb screw and screw it down finger tight. Check the spider is inside the canister
9) Place Canister on your chest and Slap it once with a cupped hand, rotate 180 degrees and Slap again. Tighten thumbscrew to finger tight again
10) Repeat step 9
(Have you any idea how hard it is
to slap canister with one hand and take photo with other, thank god for beer
guts!!!!)
Make sure the spider is inside the canister and the Thinsulate pad is tidy all the way round
11) Check the packing density by pressing your finger into the far end of the Sofnolime, it should depress and stay dented when finger is removed. If its hard to push, you have over compressed and if soft, under compressed. It is best to have tested this on someone else's correctly packed scrubber
12) Place Inner canister into outer with the springs going to the base. Make sure the canister is free to go up and down on its springs
13) Lube the Inner O ring (o2 compatible grease) and place it around the scrubber top. Make sure it is even and fully in place
14) Clean the Spacer ring and place this on top of the O ring. Check to make sure the spacer projects above the lip of the scrubber outer
15) Check all components fitted so far are free to move up and down
16) Place the electronics head on the unit, making sure that it contacts the Spacer Ring. Put on the 4 silver screws a couple of turns. make sure the head can go up and down on its bolts and that it is always fully in contact with the Scrubber stack and that it is being pushed up under spring tension. Screw the 4 silver screws down evenly
(OK so this is my Hammerhead,
but you can clearly see how the electronics head contacts the spacer ring and
presses the whole lot down onto the springs. pinching the Sealing O rings)
17) Shake scrubber vertically to ensure no free play and that The inner canister is tensioned against the head, O ring and spacer
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A lot of people cant seem to get their head around how the scrubber works while diving and how depth, breathing rate etc effects it. Gordon Henderson came up with the best explanation yet for the non techie
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<FX: TwilightZone music...>
Here on Zorg, we abducted some humans to test your resistance to CO2 and the efficiency of our patented CO2 grabbing demon chamber.
We took a human and connected a hose to them. The hose supplies gas and has one-way valves. The exit of the hose goes into a box. Inside this box are 1000s of little demons. These demons adore CO2. They will grab a passing molecule of CO2 and hang onto it for the rest of their lives. They can only hold one each. After the CO2 demon box there is another box with different demons inside - these count the number of O2 molecules you have used and replaces them.
We observed that humans when in a steady state consume the same amount of O2 per breath, regardless of the pressure we subjected them to. When given 100 molecules of our gas, they would use 4 molecules of our oxygen and turn this into 3 molecules of CO2 and 1 molecule of water vapour.
So in the test, with 100 molecules of gas in the loop. The human push/pulled this through the box with the CO2 demons in it. Every breath, 3 lucky demons grab a CO2 molecule each and are happy for the rest of their lives. We repeated this for many of your earth hours, pushing 100 molecules of gas through the CO2 box at a nice steady rate - the happy demon front line progressed linearly through the CO2 demon box until eventually they are all happy. At that point, the loop gas has some CO2 in it and we observed that the humans started to show signs of unease, panic and general ill-feeling. They eventually died a rather uncomfortable death.
To continue our experiments, we abducted more humans and carried on, this time we subjected them to a pressure of 2 bar. This is the same as being under 10 metres of your water. There is now 200 molecules of gas in the loop, but the human still only uses 4 molecules of O2 and turnes these into 3 molecules of CO2 and 1 water vapour. Each breathe pushes 200 molecules through the CO2 demon chamber, so the demons have to work faster to grab the CO2 molecules and die happy. Sometimes a front-line demon misses, but the 2nd line catches it OK. This carries on and eventually all the demons are happy, then as above, the human dies painfully and horribly from CO2 poisoning.
We needed to do more experiments, so we continued with our abduction programme. Now we're testing to 90m. There are now 1000 molecules of gas in the loop, but as observed before, then humans still only take 4 molecules of O2 out and metabolises these into 3 of CO2 and one of water with each breath, However, the poor CO2 demons now have 1000 molecules of gas going through their chamber like a hurricane, and in those 1000 molecules there are still only 3 molecules of CO2! It's now very hard for the demons to catch a CO2 molecule and hang on to it! The front-line demons have a real hard time catching the CO2 molecules and a lot more pass further down the line to be caught by the latter ones. Eventually, the front-line demons are full, but still the latter ones need to work to catch the CO2 and there will come a stage where there aren't enough latter ones who can catch the CO2 fast enough, so some will get through. Eventually so many will get through that the human starts to notice it and dies horribly as before - even when there are still some unhappy and empty CO2 demons left.
Continuing our experiments with more abducted humans, we test again at 90m, but then we decide to ascend the human to some depth where the number of molecules in the loop is much less, so each breath the CO2 demons have more of a chance to catch the CO2 molecules left.
Eventually, after 100's of trials, killing a great many humans every time, (And you should have seen our abduction budget! Off the scale!) we have come up with some rules for keeping humans alive and maximising the happiness of the CO2 demons. Our rules are many, long and complex but to simplify them for you humans we have reduced them to 3 simple rules..
Rule 1: You have 3 hours maximum.
Rule 2: For subsequent dives deeper than 20m: You must leave the bottom when the _total time_ breathed through the system reaches 140 minutes.
Rule 3: For subsequent dives deeper than 50m: You must leave the bottom when the _total time_ breathed from the system reaches 100 minutes.
<FX: We return to our normal program>
I'm glad the Inspiration was machine tested at DERA. Glad I wasn't the human being killed every time. I wonder what other rebreathers would show given the same tests? I wonder why others don't bother with these tests, and instead resport to cycling in the garage with a unit on their backs. It's fairly obvious from reading above that things happen differently at depth. The deeper you go, the wider the reaction front becomes and eventually you'll run out of scrubber before the reaction front reaches the end.
On my first hit, I was on my 2nd 60m dive with the same scrubber. First had been 60m for 30 minutes and about 60 minutes of deco. Second was 60m for 30 minutes... Thats 20 minutes at depth too many. (3rd rule) Combine that with an increase in breathing rate and workload and bingo, I got a hit. You can not do 2 x 30 minute, 60m dives on the same scrubber without violating the rules.
Enjoy,
Gordon
(Many thanks to Gordon for allowing me to use this)
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