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Scrubber material use calculations...help

Discussion in 'Rebreather Diving' started by Instructor_Tom, Mar 13, 2014.

  1. Instructor_Tom

    Instructor_Tom DIR Practitioner

    # of Dives: 200 - 499
    Location: UpState SC
    351
    93
    So i'm about 43 minutes short of getting my pilots license on the PRISM 2 and i was wondering if there was a tool or app to help calculate scrubber life.

    I know the PRISM 2 is rated for 240min in 40degree water to 60fsw. But i will probably never want to get in the water if its 40degrees and i will always be deeper that 60fsw. so how do i calculate the scrubber life and make sure i stay within a safe margin.

    Im really liking the bottom time last dive 111min, 189 for the day; but i don't want to push it on the scrubber material.

    Any input would be appreciated.

    Thanks

    T.


    Sent from my iPad using Tapatalk HD
     
  2. tstormdiver

    tstormdiver Instructor, Scuba

    # of Dives: 2,500 - 4,999
    Location: Kentucky
    6,189
    1,137
    Why not just stay with the recommended rating? Yes, it is geared toward the worst case scenario,... but if you do not want to "push it" then just stay within the known duration, where it is gernerally known to be effective.
     
    Capt Jim Wyatt likes this.
  3. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Florida
    4,160
    3,317
    I think he's trying to figure out what that is for his type of diving. Obviously he has the limits for 40 degree water and 60', but what is that in real world diving. Say 100' in 70 degree water.
     
  4. Cave Diver

    Cave Diver Divemaster

    17,866
    2,523
    I would have assumed this would have been covered during your class. A quick search turned up the following info:

    So it sounds like 4 hours is probably the "safe" answer.

    I'm not familiar with the Prism, but from a quick glance, it sounds like you pack the scrubber yourself, not use cartridges. When I first started doing CCR we dumped the scrubber after hitting about 70% of the recommended duration. If the dive was deeper/colder than normal, that was bumped back some. Dumping the scrubber right after the dive gives a good indication of how much of it has been used by the "clumping factor." If it's still dry and loose then it's not taking part in the primary reaction. Making note of your depth/duration/temp and the amount of clumping gives an idea how much scrubber is being used.

    Something else to keep in mind is that different people produce CO2 in different amounts, so two divers on the same dive may have different scrubber usage. Color change scrubber can also be useful in helping you determine how much reaction is occurring, but again it needs to be checked immediately post dive for accurate readings.

    For me, its one of those things I'd rather have the practical experience than to rely on the theoretical projection of an app.
     
    w ripley likes this.
  5. Superlyte27

    Superlyte27 Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Florida
    4,160
    3,317
    I recently got a rEvo with RMS. It was interesting to see what kind of scrubber times the RMS gave. So, for gits and shiggles, I used the color indicating sorb. After 4.5 hours in 72 degree water at 100', the RMS indicated 90 minutes left on the top scrubber. At the end of the dive, I dump the top scrubber to see that approximately 80% of the sorb was bright blue/purple. The second canister (bottom canister) was completely white, indicating that the sorb had not been used very much at all. This is very cool to me.

    CD is right that on a given dive, two people will produce CO2 quite differently from each other. I will also state that the same person doing the exact same dive any two given dives can/will sometimes produce CO2 differently. We simply don't breathe the same way every day ever dive. Dive conservatively.
     
    Nuribromanski likes this.
  6. rigdiver

    rigdiver Course Director

    # of Dives: I'm a Fish!
    Location: Republic of Texas
    910
    58
    What, no temp stick in the PRISM;-)
    Pound of sorb = about an hour of dive time. 5.5 lb stack per the manuf = 3 hours. Now, add a temp stick and your good for 5 to 7 hours. I asked Peter Readey about the safety factor and the reply was: "I won't tell you."
    Inspo and Meg pilot;
    Bill YMMV
     
  7. Dsix36

    Dsix36 Solo Diver

    1,541
    1,179
    If this kills you, it is your own fault for listening to my BS. I know nothing about the Prism and have absolutely no business trying to instruct or teach others about this stuff. If you try to push a scrubber, make damn sure to have plenty of BO gas and know how and when to use it.

    5.5 lb = 3 hr per the previous post for a Prism

    rEvo scrubber:
    Scrubber temperature versus usage ...
    if water temp > 4C then change 1 canister after 2 hours or both after 3 hours
    if water temp > 15C then change 1 canister after 3 hours or both after 4.5 hours
    Now 4C = 39F and 15C = 59F

    Using this logic, I deduct that going to 60 degree water will increase your scrubber time to 4.5 hours and still leave a safety factor.

    I will probably get flamed for this post, since so many people are afraid of the rebreather police.
     
  8. Cave Diver

    Cave Diver Divemaster

    17,866
    2,523
    ^^^^ This, if nothing else. ^^^^
     

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