Prism II?

silent running

Hi Charlie, I have no problem getting the bucket off by myself. The key is to use plenty of silicone grease and tapping the bottom of the bucket to break the seal before taking it off.

Are talking about the scrubber canister itself? I've not seen one crack yet. Mine is pretty flexible, and doesn't seem likely to crack.

I agree, but given that you can still use the Prism without the solenoid or the even the electronics, losing the solenoid is just an inconvenience.

They already have.

Yes, it might be nice, but it would also add weight to a unit which is one of the lightest ones out there and travels very well.

I think Hollis mentioned the harness will be a modular system that will adapt to different back plates. I Personally think that the Stovall plate I have is by far the best option as it's smaller, allows for a standard harness plate and allows you to see the scrubber seals all the way around, as opposed to the stock SMI plastic plate. I only wish it was made of ally, as then it would be even lighter for carry on travel. -Andy

chunter

Ok...then I guess nothing needs changing.

The KISS brackets weigh about as much as a velcro strap. The canister does crack...I've seen a few. Any rig can be dived without a solenoid (except for the CIS-Lunar Mk 6), but that doesn't mean they should be a perminent part of the unit. My feeling is that solenoids should probably be replaced annually.

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"Foolish consistency is the hobgoblin of little minds." - Emerson

"Hobgoblin is a cool word."
- Charlie

Chris

Well all I can say is I really hope you guys change the materials for head and scubber construction. After the nightmares we have had with breaks and cracks, fingers crossed you can get it right.

Oh and whatever you do don't move the computer you use to upload the units software, it corrupts it

Cheers
Chriso

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silent running

No, I can think of things I would change, lots of significant mods have been done to Prisms.

I haven't seen them up close in a while, do you know what they are made of? I don't particularly love web straps, but they don't weigh anything-at least when dry-and they are bone simple, no pins to lose or bend, unlike some bracket systems.

OK, I wasn't suggesting they are impervious to it, just haven't seen it, you have. I hope Hollis will figure out why those canisters cracked and use something a bit stronger or at least more flexible without making the
structure too heavy or bulky.

No, I believe all APD Vision CCRs can't be dived without the solenoid passing the pre-dive CPU check. The unit will lock out the diver from PO2 monitoring if it detects a solenoid fault. I don't know if other integrated deco units also test the solenoid and will go into alarm and lock out when it won't pass, but they may have to, from a liability standpoint, which may be why APD do this. My main point was that the Prism-like the MKs-can be dived safely with no solenoid, no electronics, no alarms, no lock-outs.

Yes, I think the solenoid should be easy to replace and said so to Hollis. The Prism solenoid is supposedly replaceable in the field, but I don't exactly know how it's done.

sunnyboy

I posted this on the SB thread, but since we're discussing the Prism II here as well, I thought I'd post my resonse to the Hollis post here as well...

Although I have only been diving a Prism for a year now, I love my unit and have some very definite comments on your post regarding the new Prism 2 and the direction you should pursue.

First and foremost, you should consider the rig a TECHNICAL rebreather and not bother with all the recreational BCD stuff. As soon as I got my Prism home, the BCD was completely removed and the DSS "Prism 6 bolt to 2 bolt adapter plate" was installed as well as their "Counterlung yoke adapter". This allowed me to ditch the BCD in favor of a stock backplate and wing (I use the Agir 38lb which is perfect for the Prism).

This puzzles me. While much in the OC world can be of value to the rebreather diver, I would not necessarily seek out just OC advice.
Please don't go this route. The counterlungs are NOT shoulder straps, and trying to make them do double duty is a less than optimal approach, IMO. My shoulder straps are provided by the stock backplate (single webbing design). The counterlungs attach at the top to the yoke adapter, and at the bottom I use the stock Prism web between the fastex on the bottom of the CL and have the harness waistband pass through. Since that opening is rather large, I have rubber innertube loops to reduce the opening thru which the waistband passes. Works great.

Under the counterlung d-rings (again DSS) are a perfect solution. Putting D-rings on the counterlungs will put stress on the counterlungs that is totally unnecessary. Let the harness do it's job, and let the counterlungs do their job - please.
Again, please just let the counterlungs be counterlungs. Let the harness /backplate do it's job.

As for sidemount, once you have a harness/backplate, you can easily add sidemount to it, so there's no need to worry about it in the Prism 2 design (unless you want to do all this tomfoolery about the counterlungs and D-rings and such).
Again - why not just ditch all this nonsense and provide a proper mount point (i.e. two bolts) for a backplate and wing of the owner's choice? You could supply one with the unit (most backplate/harnesses are pretty much the same from various vendors) and a good small (38lb) wing. (Whether you go donut or horseshoe is one of those "mine's better than your's debates anyway).
AGAIN... a stock harness/backplate/wing will provide this without Hollis wasting time reinventing the wheel. This bit of the kit has pretty much been refined by now - just use something classic and proven.
That is good news.
I agree with a prior post - there is no reason the solenoid could not be user replaceable. The Prism currently uses molex connectors for the cells, so something similar could be inside the head for the solenoid.
OK. Don't really care, but these type of options are common in most rebreathers now, so you have to offer them or risk being labeled "dinosaur". I prefer tables, a bottom timer and a brain, but others will have different desires and choices. :-)

Sounds OK. I have not had any problems with the cables or attachments, so I'm not sure this is really a big item, but if it improves routing without introducing a failure point, that's alright. Mind you, I've never had good luck with ANYTHING electronic and a 90 degree connector, but who knows - you might be the one to get that right. ;-)

As long as you don't make major changes to the current radial scrubber or the technologies that keep the scrubber away from the small amounts of moister in the bucket, and still provide the duration, that's good.

Sounds good. Please post some pictures of a unit AFTER you have done the first dive or two on it. I'm looking forward to seeing the new unit.

ONE OTHER THING - it would be nice to offer the unit in two configurations - "ready to go" (that is, with wing, backplate and harness) and "almost ready to go" (no backplate, wing or harness but ready to attach to one of the purchaser's choice).

Cheers,

-S

silent running

Hi sb, considering that Hollis's post was mostly a repsonse to my post on SB rebreather forum, I think he meant "a depth of experience in the CC world" as I had a prior conversation with him where we talked about my Rebreather diving history. -Andy

Hollis

Sonnyboy

Thanks for catching the OC, that should have been CC.

Hollis

gkndivebum

Hi there -

A couple of observations about the PRISM from someone who has 550+ hours on Peter's rig.

I've missed two dives out of hundreds, both due to problems with the secondary. Problem #1 is that
the plastic bolt which holds the selector wheel in place gave up the ghost suddenly (I managed to
find the little ball before it disappeared out the scuppers ).

Problem #2, which I'm on my third go-around with, is that the magnet in the selector wheel
is too big to be potted effectively, resulting in gradual leakage from the epoxy holding it in
place and it rusting out. I've finally found a suitable replacement which is half the size that
SMI uses and I can firmly encase in epoxy. Sigh.

So - my pleas: pot the magnet in the secondary selector wheel better, and PLEASE make the
solenoid field-replaceable; I've got two heads at SMI for repairs due to TSA damage... (long story,
involving a bunch of monkeys )

__________________
Best regards -

gkn
--
Gerard K. Newman - Kona, HI

Mike

I've had my unit for a few years now, and disagree. After doing ~50 hours with a standard backplate plus the counterlungs, including using under counterlung D-Rings, I decided that approach was harder to get into and out of, and conferred no benefits. So I've gone back to using the counterlungs as shoulderstraps, with a simple webbing waist band.

I sidemount bailout (up to 2 steel 12s or ali 80s) and don't need to clip off to the counterlungs at all. So the ease of getting into the unit with just the counterlungs is well worth it to my mind.

My only other comments are that it's great the new unit will be properly injected molded from something tougher than cheese, and don't dick around reinventing a digital secondary, just OEM the subsea display. They are a great bit of kit.

Mike

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Hollis

Prism counterlung construction

We have gotten a lot of comments from folks regarding the counterlungs, the Prism’s harness and tech harnesses so I thought a little bit of information about the Prism2 counterlungs would be helpful.

Our first design goal in working with the Prism is to not loose the excellent performance Peter has designed in.

First and foremost we do not want to change the breathing characteristics of the Prism. The Prism did meet the Navy’s criteria and we think that is something to be proud of, Way To Go Peter!

Counterlungs are not just bags hanging in space that you swap gas with as you breathe.

The new method of counterlung evaluation that Dr. Dan Warkander (US Navy NEDU) presented at the DAN tech conference in Raleigh deals with 3 breathing factors that must be evaluated for closed circuit systems. Resistive effort is one; this is the difficulty of pushing or pulling gas in the breathing loop, the difference between a soda straw and a snorkel. Hydrostatic Loading is another; this is the relative difference between the pressure center of the diver’s lungs and the maximum and minimum pressure differentials when the counterlung is fully inflated and fully emptied. The last is Elastance; this refers to the change in shape of the counterlung as its volume changes during a breath.

Each of these 3 elements causes the diver to do work when breathing. You can have a mix of theses 3 kinds of work but at some point the diver will become fatigued just from the work needed to breathe. Lower work of breathing is a design objective.

In a normal swimming position the hydrostatic load of back mounted counterlungs produces negative lung loading, and chest mounted counterlungs produces positive lung loading. The hydrostatic load of over the shoulder counterlungs comes very close to reducing lung loading to zero. Less lung loading is less work to breathe.

Small diameter air passages have higher resistance to flow, or resistive effort. So do elbows, long tubes, flow direction mushroom valves, and thick scrubber beds. Using a sufficiently large diameter throughout the breathing loop, avoiding bends and elbows, using low durometer mushroom valves, and a radial scrubber all reduce resistive effort. Lower resistive effort is less work to breathe.

Elastance is related to hydrostatic load changes during breathing. A large flat counterlung (flat side down) would have lower elastance than a long narrow tube (tube vertical in the water column). Over the shoulder counterlungs seem to be a good shape tradeoff for low elastance. Lower elastance is less work to breathe.

If you look at the Prism counterlungs you will see a few features that are important.

First is that the counterlung is attached to a substrate made of two layers nylon cloth with a stiffener sandwiched between the fabric layers. This assembly is very strong. The Prism doesn’t really use the counterlungs as shoulder straps. When we attach items to the counterlungs we actually attach them to this under layer. This layer also helps keep the Prism counterlungs in an optimal shape.

Next are the 3 side release buckles. These hold the counterlungs down and keep the counterlungs near the diver’s lungs, not floating around or shifting when the diver changes position. This does require the use of thigh straps of a crotch strap to hold the Prism down on the diver.

We have discussed making counterlungs that would adapt to a tech harness by some form of attachment to the shoulder straps. We could slap on some Velcro and be done with it, but that may not do the job well. We need to be certain that once adapted for attachment to a tech harness shoulder straps the counterlungs will continue to work as intended. Remember the counterlung is not just a gas bag floating in space.

Our current time line has Prism2 initial production in late July or early August. This will be a small batch to shake out material issues, assembly requirements, in process testing, and final qualification testing for production units. These units will be used for unmanned testing in our hyperbaric lab and for some open water evaluation dives. Once we are satisfied that the rigs work as intended we will enlarge the user base to include some of the folks who have been advising us all long in this project.

Once we are sure we have reached our design objectives we will begin investigating adapting the design to tech plates and harnesses, while retaining the functionality we have worked to preserve.

We appreciate all the input we have gotten from the boards and from CC divers who have told us of their likes, dislikes, and wants. We think we have a great product in the making. We all want one for ourselves. It is difficult to bring a product of this complexity to market, safely.

Hollis