Myth busting - Scrubbers

depth

depth

Member
Hi

I am just curious as I would like to learn more about my life support system.

I just talked to a buddy of mine, he just finished his MOD 3 course. Their instructor told them that packing a scrubber very tightly causes two issues:

1. The scrubber will be less effective as the pellets are now touching one another more, leaving less surface to scrub the CO2.

But is this a myth? If you are packing the sorb hard, it will leave room for extra granulates, meaning the canister will contain more scrubber material. Will the one thing not out-weigh the other?

2. Packing the scrubber will increase WOB.

Is this a myth? I am not looking for "it feels like there is more WOB" answers, did anyone actually test this to see if there is any measurable difference? I think that WOB will increase, but I could be wrong...

Give me your thoughts...

/Christian
 
Both sound reasonable to me.

If you pack too hard you can crush some of the granules and make a powder which clogs up the gas paths, not to mention getting carried around the loop into your mouth!

Obviously pack density directly effects WOB- it introduces many restrictions and bends, how much it effects the overall score I don't know- not sure I remember reading anyone having tested an overpacked scrubber though? Paul from rEvo is rather inventive with his testing and might be the best man to ask :-)

There are plenty of guidelines in training and online how to pack correctly- why would anyone try to ram more in? the few extra grams will make no endurance difference!
 
Both are common concepts widely taught.

Like anything, were just trying to avoid extremes. Trouble is, people take everything too literally and then via chinese whispers it can get out of control.

Originally the old inspo classic divers were told to pack properly to avoid channeling and sorb falling out. This ended up being taught as 'pack tightly to avoid channeling' and was interpreted by some to mean ' pack tightly to get more sorb in and extend your scrubber' which started to affect work of breathing. So any gains were negated by a higher co2 production.

I had a woman in my shop put gardening gloves on and literally bang her meg canister on the table repeatedly:)

Now we have a video that we shop evo / inspo students that aims to set this straight. It shows a simple quick tapping technique and off you go. Now Im starting to see some loosely packed scrubbers!! You cant seem to win.

Anyway, it depends on the unit. Radials need to be packed fairly well it seems as does the sentinel axial. rEvo's are a piece of cake and dont need much tapping.

I think its true to say that overpacking can crush the granules and reduce the surface area available for the gas to come into contact with and also create more dust. It will also be harder to for your lungs to move the gas through creating more 'static lung load' but equally you dont want your sorb so loose that it moves around or can settle.

You need to take into account bumpy boat rides / car journeys off road and work out if its going to settle.
 
If it rattles its too loose. If you've crushed sorb and made dust its too tight.

The happy middle is usually reached by fill 1/3, tap and repeat until full.

(people really need a video for this?)
 
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I don't know the scientific answer to the OP's question. I do know that when I manually pack my sorb (8# radial basket - HH) that it works fine for 10-11 hours (haven't pushed it past that). I also know that when I use the vibration table I built for packing my sorb I can usually get the manually packed sorb to compact about 1 inch more than it was, so I add more sorb - and vibrate - to make up the difference. (FYI: I put the spring-loaded top on the manually packed basket before I do the vibration. Once I remove the spring-loaded top the sorb level has compacted about 1 inch from where it was.) The mechanically packed sorb also works fine for 10-11 hours.

Personally, I don't notice any difference in the WOB. I notice more dust with the vibration - probably from being vibrated out of the basked - but don't see any evidence of sorb "crushing" when the sorb is emptied. There may be some, but it's not obvious to my eye.

FWIW, I don't believe I over do either the manual or mechanical packing. The mechanical packing does produce a denser compaction, IMO

Note: Most times I dump my sorb after 8- 9 hours.
 
depth said:
Hi

I am just curious as I would like to learn more about my life support system.

I just talked to a buddy of mine, he just finished his MOD 3 course. Their instructor told them that packing a scrubber very tightly causes two issues:

1. The scrubber will be less effective as the pellets are now touching one another more, leaving less surface to scrub the CO2.

But is this a myth? If you are packing the sorb hard, it will leave room for extra granulates, meaning the canister will contain more scrubber material. Will the one thing not out-weigh the other?

2. Packing the scrubber will increase WOB.

Is this a myth? I am not looking for "it feels like there is more WOB" answers, did anyone actually test this to see if there is any measurable difference? I think that WOB will increase, but I could be wrong...

Give me your thoughts...

/Christian
Click to expand...



I pack my sorb as tight as possable. IE I keep slapping the sides till I can no longer get free movement on the center nut.

9 years, 1000+ hours, four diferent scrubber designs and no C02 hits to mention dispite diving to double the recomended scrubber duration and down to 116m.

ATB

Mark
 
depth said:
1. The scrubber will be less effective as the pellets are now touching one another more, leaving less surface to scrub the CO2.
Click to expand...

Define less effective.

WOB
Maximum CO2 absorbing potential
Turbulence in gas flows inside channels in sorb (depth of reaction front)
Dust
...

All a compromise, same as every other part of the design.
 
Mark Chase said:
I pack my sorb as tight as possable. IE I keep slapping the sides till I can no longer get free movement on the center nut.

9 years, 1000+ hours, four diferent scrubber designs and no C02 hits to mention dispite diving to double the recomended scrubber duration and down to 116m.

ATB

Mark
Click to expand...

I love these anecdotes so here is the counter.

I soft pack as per the AP video and have done since Big Mike taught me in the car park at Plymouth 11 years ago. 1000+ hours, only axial scrubbers and no CO2 hits down to 130m.

Molecular say their material is self packing, you can read about its shape on their web site. I don't know if anyone tested endurance or WOB but both points are internet folklore which sound plausable to me.

Cheers
Matt.
 
depth said:
Their instructor told them that packing a scrubber very tightly causes two issues:

1. The scrubber will be less effective as the pellets are now touching one another more, leaving less surface to scrub the CO2.

But is this a myth? If you are packing the sorb hard, it will leave room for extra granulates, meaning the canister will contain more scrubber material. Will the one thing not out-weigh the other?

2. Packing the scrubber will increase WOB.

Is this a myth? I am not looking for "it feels like there is more WOB" answers, did anyone actually test this to see if there is any measurable difference? I think that WOB will increase, but I could be wrong...

Give me your thoughts...

/Christian
Click to expand...

Because there is documented evidence for these effects, you have to go with the premise that this is simply BS. Nothing more, nothing less. If you think about it, it is simplistic thinking, and not an effective way to teach.

It's yet another example of instructors trying to make their divers 'safer' by feeding them bollocks, instead of just giving them some simple, easy to understand facts. The flip side is that these people being certified to dive on CCR are NOT in fact, capable of safely diving a rebreather.

To think that you are some sort of good example of an educator by making up evidence and presenting them as facts just goes to show how appalling the state of dive instruction really is. This lack of educational integrity (not to mention personal honesty) would get a genuine educator sacked. The instructor cited here needs to be 're-educated' or simply struck off.

Sorry if you don't like this, but it's not rocket science. Fill the scrubber in thirds, tap gently to settle the sorb. Your aim is not loose and rattling, not jammed in, but a nice compact bed of sorb. If you can't teach this, then don't try to!

cheers

Andy
 
Andy Del said:
Because there is documented evidence for these effects, you have to go with the premise that this is simply BS. Nothing more, nothing less. If you think about it, it is simplistic thinking, and not an effective way to teach.

It's yet another example of instructors trying to make their divers 'safer' by feeding them bollocks, instead of just giving them some simple, easy to understand facts. The flip side is that these people being certified to dive on CCR are NOT in fact, capable of safely diving a rebreather.

To think that you are some sort of good example of an educator by making up evidence and presenting them as facts just goes to show how appalling the state of dive instruction really is. This lack of educational integrity (not to mention personal honesty) would get a genuine educator sacked. The instructor cited here needs to be 're-educated' or simply struck off.

Sorry if you don't like this, but it's not rocket science. Fill the scrubber in thirds, tap gently to settle the sorb. Your aim is not loose and rattling, not jammed in, but a nice compact bed of sorb. If you can't teach this, then don't try to!

cheers

Andy
Click to expand...

Whoa, steady on! Thats a bit harsh.

'overpacking' and 'underpacking' are subjective terms and as I said, its unit specific. For example, the AP training is fill the scrubber up, then tap. Not thirds. Not thirds on the sentinel either.

I can guarantee this from personal experience - if you pack a sentinel scrubber like an evo scrubber it will settle and you will probably get a CO2 hit.

So whilst you may be extremely derogatory towards instructors, are you yourself not passing on 'BS' or 'Talking bollocks' then when you say fill it in thirds? Why thirds? what benefit does it give you? ;)

I havent done this with units other than the evo, but its easy to test this out yourself. I have 'over packed' an evo scrubber by which I mean the following:

- Fill to nearly the top. tap lightly. Fill to top.
-Tap sides until sorb settles. Fill to top again
- Repeat until you cannot get any more sorb in the scrubber.
-Add the scrim and spider and tighten the nut.
-Go diving

You will notice an increase in WOB. Its immediately noticeable to me. Then, when you empty the scrubber - look at the granules and see how they are crushed and there is a huge increase in the amount of dust.

Rather than voodoo instructor fantasy or simply pure BS or bollocks as you suggest, Id put it under the common sense and 'stands to reason' category. There are lots of other reasons not to overpack or underpack scrubbers too, some of which are unit specific. My advice to the OP is take the advice of your instructor as internet advice, whilst often well intended isnt always applicable to your unit or your environment
 
Andy Del said:
Because there is documented evidence for these effects, you have to go with the premise that this is simply BS. Nothing more, nothing less. If you think about it, it is simplistic thinking, and not an effective way to teach.

It's yet another example of instructors trying to make their divers 'safer' by feeding them bollocks, instead of just giving them some simple, easy to understand facts. The flip side is that these people being certified to dive on CCR are NOT in fact, capable of safely diving a rebreather.

To think that you are some sort of good example of an educator by making up evidence and presenting them as facts just goes to show how appalling the state of dive instruction really is. This lack of educational integrity (not to mention personal honesty) would get a genuine educator sacked. The instructor cited here needs to be 're-educated' or simply struck off.

Sorry if you don't like this, but it's not rocket science. Fill the scrubber in thirds, tap gently to settle the sorb. Your aim is not loose and rattling, not jammed in, but a nice compact bed of sorb. If you can't teach this, then don't try to!

cheers

Andy
Click to expand...

So if you were the instructor and taught them "not to jam it in" and they asked you why? How would you answer?
 
Scrubber packing techniques and protocol are highly dependent on the make of the rebreather and the design of the scrubber. There is no one size fits all when it comes to packing a scrubber. To imply otherwise is a bit dangerous in my opinion.

This is one of the MANY reasons why I cringe when I hear people say that they have no need of doing a crossover class. I can hear it now: "What can I possibly learn that I don't already know by taking a crossover class?"
 
There is probably a big grey area where a scrubber is effectively packed.

It can be underpacked where you pour sorb in, pop the lid on and go diving, probably you will get away with this more times than you don't as the sorb will pack itself to an extent, but it is pushing your luck.

You can overpack and crush the sorb by pouring the sorb in, turning the nut, tap a bit, turn the nut until you feel resistence, tap a bit, turn the nut until you feel resistence, and when tapping no longer allows the nut to turn then get a wrench and turn it some more. Again the scrubber will probably work but the chances of issues through WOB are probably higher.

Anywhere netween these extremes is probably fine, with the sweet spot somewhere in the middle. To pick a point on the line and tell anyone who deviates from that spot that they are doing it wrong is a bit silly to me. Obviously it depends on the scrubber type, I talk from Inspo/JJ experience only.
 
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Interesting topics but no one has answered the OPs question. Are those 2 reasons his instructor gave valid?


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Michael Thornton said:
Interesting topics but no one has answered the OPs question. Are those 2 reasons his instructor gave valid?


Sent from my iPhone using Tapatalk
Click to expand...

To properly answer the question you probably need to run tests or find test results in a published article. Mostly all forums will give is hear-say and opinion.
 
Chris Brown said:
Whoa, steady on! Thats a bit harsh.

see the rest above, guys...
Click to expand...

If I run through your reply, yes, I'm harsh and that's for a reason. I've been teaching since 1982 in various fields, have 2.5 degrees in it and suggest very strongly that inventing reasons for instruction is not a valid pedagogy. I only used the thirds example as this is how ALL my rebreathers' scrubbers are supposed to be filled.

Your example is moving to the extreme: getting the maximum amount of sorb into a scrubber then wondering why things are not as good, as in crushed sorb and powder. I'll leave it to others to explain the WOB, but when you consider a Meg scrubber and the tension the spring on the scrubber's lid places on the sorb (as ISC direct), either you have surpassed that deliberately to damage the sorb this way or there's some sort of issue with the scrubber design. (I suspect the former, as Paul's unit design is great) Did you follow the simple rEvo instructions, or do something different?

Common sense says, not to under or over pack a scrubber, of course. Common sense also says to not make up reasoning, and intellectual honesty says to not present your musings as fact either.

Michael Thornton said:
So if you were the instructor and taught them "not to jam it in" and they asked you why? How would you answer?
Click to expand...
I'd tell them 'because you don't want to crush the sorb particles, leave them the way they pour out the container.' I don't need to invent things to reinforce simple information.

Michael Thornton said:
Interesting topics but no one has answered the OPs question. Are those 2 reasons his instructor gave valid?
Click to expand...

How do you discredit someone's imagined 'factual' teaching with opposing facts when there are no facts either way? Think of the old saying, 'Never argue with an idiot, they'll only drag you down to their level and defeat you with logic.'

In my day job there are times I have to coach kids to play their band and orchestra parts correctly. Correctly for whoever is directing the group, which opens up interpretation, opinion, etc. etc. ALL I can do is give them the facts, the commonly acknowledged traditions, accepted styles and warn them of where to be alert as it is a grey area. It normally works, and with the clever kids, they actually appreciate being assisted both with facts they can use, and awareness of what may be a bit tricky. Outside of work I do similar for other groups, including a bunch of doctors a few weeks ago. It's easy as pie to say you're not sure of something, and give them options, or even, if we go back to diving, to say 'I think'. To say otherwise is not honest and, going all the way back - BS.

cheers

Andy
 
Andy Del said:
Because there is documented evidence for these effects, you have to go with the premise that this is simply BS. Nothing more, nothing less. If you think about it, it is simplistic thinking, and not an effective way to teach.

It's yet another example of instructors trying to make their divers 'safer' by feeding them bollocks, instead of just giving them some simple, easy to understand facts. The flip side is that these people being certified to dive on CCR are NOT in fact, capable of safely diving a rebreather.

To think that you are some sort of good example of an educator by making up evidence and presenting them as facts just goes to show how appalling the state of dive instruction really is. This lack of educational integrity (not to mention personal honesty) would get a genuine educator sacked. The instructor cited here needs to be 're-educated' or simply struck off.

Sorry if you don't like this, but it's not rocket science. Fill the scrubber in thirds, tap gently to settle the sorb. Your aim is not loose and rattling, not jammed in, but a nice compact bed of sorb. If you can't teach this, then don't try to!

cheers

Andy
Click to expand...

Hi Andy

I am not an instructor if that is what you are implying, and I have no plans going down that road.

When talking to other CCR divers I often hear them repeat statements by their instructors and I am just trying to filter out the noise.

It could be a bad philosophy, but I suck in all the info I can from Instructors, books, forums and other divers. I then evaluate this info with common sense and the laws of nature, conclude and then apply it in my own diving.

Therefor, all input is welcome.

/Christian
 
Chris Brown said:
Whoa, steady on! Thats a bit harsh.

'overpacking' and 'underpacking' are subjective terms and as I said, its unit specific. For example, the AP training is fill the scrubber up, then tap. Not thirds. Not thirds on the sentinel either.

I can guarantee this from personal experience - if you pack a sentinel scrubber like an evo scrubber it will settle and you will probably get a CO2 hit.

So whilst you may be extremely derogatory towards instructors, are you yourself not passing on 'BS' or 'Talking bollocks' then when you say fill it in thirds? Why thirds? what benefit does it give you? ;)

I havent done this with units other than the evo, but its easy to test this out yourself. I have 'over packed' an evo scrubber by which I mean the following:

- Fill to nearly the top. tap lightly. Fill to top.
-Tap sides until sorb settles. Fill to top again
- Repeat until you cannot get any more sorb in the scrubber.
-Add the scrim and spider and tighten the nut.
-Go diving
Click to expand...

That isn't what the manual says, it says half fill, tap, fill to 6mm. Etc
 
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