Megalodon over Ouroboros

silent running

What else is there to say, how about something other than BS? If I've gotten something wrong in relaying a bunch of facts and figures, it hardly qualifies as BS. But I do appreciate your putting up the figures.

And by the way, I did not start this discussion on scrubber duration, Steve did. SMI have way more data up on their site than any other current manufacturer. They have the Navy muzzling them, what's everybody else's excuse?

silent running

OK, I know this is still off topic but I think there's more info worth mentioning...and the original topic wasn't so great to begin with anyway...


In the NEDU document up on SMI's website, on the fist page it states that they were looking for a replacement for the MK16 and had certain criteria that had to be met. After the first round of testing, the Prism met or exceeded all these criteria. So by definition, I don't think that the USN would have moved it on to the next stage of testing if the Prism scrubber performed less well than the MK16. And as such, comparisons btw the 2 units are of interest, inevitable and difficult, due to many things, especially the changing test protocols. It is my understanding that the MK test protocols mentioned in SteveL's post are from 1980 and have been revised several times. The latest protocols under which the Prism was tested for the replacement UBA are from 1994.

Evaluating the 2 units with 2 different protocols is difficult but here's one set of facts and figures available from the 1980 MK16 public domain test and the 2001 first public domain NEDU testing of the smaller first generation, smaller Prism scrubber. And keep in mind that there are more tests of the .5lb larger Prism scrubber which are not in the public domain.

MK16 8.4lb actual or gross(?) anular scrubber: CO2 .9-2.0 lts per minute 23-50 rmv cycled back and forth 30ft @70F to 1.% sev CO2 =332 minutes

Prism 6lb gross wt. radial scrubber: 1.35 lts per minute continuous CO2 inject at 40 rmv 60ft @40F to 1.% sev CO2 =283 minutes

Difficult to compare, but given that the Prism test was done at a continuous injection rate of CO2, not cycled, at 40 rmv, deeper and 30F colder, one could see it being at least equal in duration to the MK16's excellent scrubber. I certainly believe Mike when he says that he knows people who routinely push the MK scrubbers past 10 hrs, just like when I hear that people have pushed the Prism scrubber to 11hrs. I have gotten a consitant 10 hrs out of mine and would have never even tried it without some good data.


Over the years of talking with people in the Rebreather business, it has become clear to me that many aspects of RB design are not well understood and scrubbers may be the most difficult to understand of all. It's not surprising to me that the USN have revised their test protocol several times. And when people complain about the lack of standards for consumer unit scrubber performance, they should remember that if the USN keep moving the goal post, it is an evolving science. So it's not really so surprising to me that recreational RB manufacturers have not formalized theirs-it's not easy to do.

When I first started reading about the rebreathers in The Simple Guide to Rebreathers, the MKs seemed like dinosaurs, big, old, out-dated. But over time thanks to people on this forum, Pete and Sharon Readey and others, I have come to appreciate all the serious thought that has gone into them. But the fact that they have been tested so rigorously by that most demanding of agencies-the USN-probably has as much to do with their great reputation among serious divers as anything else. And the only other ECCR to be tested as extensively by the USN is the Prism.

If I were rich enough, needed a top notch BMCL and didn't care about paying excess baggage for all my dive trips, it would be a very tough call btw MK15X and Boris...

PS. I reserve the right to be corrected by any of you. -Andy

Drmike

Woooh there thats a bit of a jump. The prism scrubber may well have passed their scrubber requirements but it may be abLe to do that but still not last as long as the MK16 scrubber - it depends on what their requierements are yes?


Ok honest question - can a prism do this - at 300fsw temp =70F time to reach 1%SEV = 310 minutes?



Anyway If the PRISM is better why didnt they buy any and why do the navy still use their old MK16s??

(honest question)

I asked them USN and was told "because they havent tested a rebreather yet that is overall better (for their needs) than the MK16"

Having owned and dived many CCRs I agree. Boris is too complicated, Prism with OTS CL and dodgy po2 meters. The USN requirements dont also have to be the same as ours - yes?

I dont think scrubber design is rocket science.

__________________
Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you

silent running

No Mike, scrubber design is not rocket science, certainly not as exact anyway, which is part of the issue.

And no, USN and our requirements are not exactly the same, but are certainly relevent. Could the Prism scrubber have passed the basic specs and still not lasted as long as the MK16? Maybe, but why wouldn't this have been mentioned in the first round of testing documentation? Why wait to point out a short coming in one of 3 main requirements? Why go any further and spend more money if the scrubber was not as capable as the MK16? And BTW, the current Prism 2dry PO2 meters are double movement and potted, an improvement over the old MK single movement 1ata housing models. I believe the ones you had on your 1600 were the older, single movement potted ones, yes?

The USN has purchased a number of Prisms, tested them comprehensively and they progressed further than any other CCR in the aquisition process. And the units were "off the rack" standard consumer grade units, as opposed to a defense contractor trying to work towords a specification on a bid as their objective. Why they haven't moved further, I don't know. The report posted on SMI's site states that the MK16 and LAR5 don't meet the criteria for the ASDS program due to size, depth requirement and operational reliability, a tall order by anyone's standards. Several recomendations were made to modify the stock unit to better meet the USN requirements, not sure if they were implemented. AFAIK, the bid is still open.

As for the 300ft @70F 1.0% sev =310 minutes, yes I could believe that the larger 6lb scrubber could handle this based on what I've heard from SMI and my experience getting 10 hrs in similarly warm water, limited though it is. As was said before, there is another set of tests for the larger scrubber which are restricted, not sure if they offer a more direct comparision. And remember that those MK figures are from older protocols. How do they compare in detail to the current protocols? I don't know...

Drmike

ok your right the Prism is a better rebreather than the MK16.

So I guess you dont want to swap then?

Shame I have a MK15.5 you could have had - LOL!

BTW I had both old and new analogs 2ndrys the later being from SMI - I trusted neither. I now have a MK16 digital - I suspect there is a reason they dropped the analogs after the MK15


BTW USN tested my system (non diving)...they didnt buy any ...and THAT is the ONLY thing that matters

__________________
Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you