need to modify

jepuskar

I notice alot of posts about people modifying their rebreathers.

Is it because of the type of diving you do on your kit...several minutes of deco and you feel you need something extra that your original kit doesnt provide...say a 4th or 5th cell holder?

I have an electronics background and know how to work some tools, but I am having a very difficult time picturing myself modifying a rebreather. Some people do this daily as a hobby or to make a buck....but unless the manufacturer designs and tests the modification then I wouldnt really feel touching it in a manner against the manufacturer's guidelines.

Let me explain why I am posting this. Like a few of you know I am a seeker...and as a seeker I am feeling out the whole rebreather thing and right now I am very interested in the Evolution. However, I do like the Prisms analog secondary driven directly from the current output of of the O2 cells.

It leaves my wondering why APD doesn't have a 4th cell holder customary and just have an extra port on the scrubber lid for users to interface too. Install the 4th O2 sensor and interface to the scrubber lid. I'm sure 3rd parties would jump on this. APD could give the standard and typical legal disclaimer and anyone wishing to use the extra port could...and if not, then you dont use it. Or APD could offer a device to use this extra port, yet still make it compatible with 3rd party products.

It seems like APD or another other manufacturer would benefit from this kind of flexibility...even if it means that the end-user may choose another monitoring system for that extra port. If it makes the overall system more attractive they win.

I am not very business savy or rebreather savy...so tell me where the issues arise with my thinking.

Jason

silent running

Jason, the Boris does come with space for a 4th sensor, and I don't know why APD don't do the same. It could be that by providing one after many years of not having one, they'd open themselves up to a liability claim if someone from the past felt that the lack of it previously was resposible for an injury or death. That might be why they are slow to fix some of the other problems with their units.

As for the need for a 4th cell, you might have noticed from other posts, that I'm not a fan of any extra cables, seals, or sensors. ECCRs are complicated enough as it is and if your unit can hold SP well, then what difference does it make whether your comp has input from 1 sensor? Your breather is basing it's calculation about what the loop PO2 is on 3, methinks it's going to be more accurate. And since most ECCRs seem to run hot in varing degrees, the stand alone comp set to the same SP will actually give you a safety hedge.

Mark Chase thinks 4th cells are important for SCR emergency, I think a stand alone comp set OC to the average gas fraction of the SCR loop will get you home just as well, without all the extra potential leaking seals/cables/consumables/calibrations. Either you will have enough gas to get you home on your 3 or 4/1 ratio, or you won't.

All that being said, the 4th cell does make some sense for units that can't display PO2 without power, but now you're talking about spending another grand plus on top of your 10 grand unit for a VR3, cable, cell holder, cell...
Is it really a good idea to add more complexity to something that's already complex? And what is the root cause of all this extra trouble one has to go to?

jepuskar

Hey Andy,

I understand your point, but why all the modification then?

From my current observations so far of the rebreather world....some people are either are fanatics about safety or are followers.

As your last sentence mentioned....why add something to something already complex?

I respect several members whom I know from other boards as well...but some of their disaster scenarios are very far fetched. I think any rebreather is susceptible to some sort of failure no matter the precautions taken. Any backup, no matter how warm and fuzzy you think it is could be feeding you false data..given the right...err wrong circumstance, you're screwed.

At one point do you say I accept that risk and it is what it is?

J

silent running

Part of it is people going the extra mile because they believe it will make the unit more safe. Some people mod their units just because it increases their comfort, which itself can be a safety enhancing thing to do as a comfortable diver will make better decisions in a crisis.

Me, I most comfortable with simplicity, so anything I don't really need, I will try to avoid. It has taken me some time to wrap my mind around the BOV issue as most Prism users feel comfortable enough with the scrubber performance and placement of the ADV right next to the inhale hose that they don't think it's necessary. While I mostly agree-except in the case of low flow at extreme depth-I want to get rid of the Air2 and I don't like having all my dil coming through one crude little shrader valve. That's why I'm leaning towords getting one, in addition to the benefits of quick BO. But that will be the biggest mod I'll do as I consider the BP sidemount thing to be a normal mod for deep diving BO capability.

All that said, the rig you think will need the least amount of mods, is probably the best candidate and a good indication that the design is a good one...

caveseeker7

The only two units equiped to hold a 4th cell from the manufacturer are the Ouroboros and the O2ptima. One of the Ouroboros owners just posted that Kevin doesn't like the idea of using his $$$ VR3 ith a 4th cell in the unit, why eludes me. The O2ptima has the HH which already had a 4th cell space in the replacement head for the Inspiration.

Personally I like the idea of having a 4th cell that runs the computer, or alternately having the computer run off the setpoint info (i.e. the info the computer uses to maintain the setpoint, a reading that is based on the mV value of all three cells and whatever voting logic is used to make it a single value).

As I dive a Kiss I'm reasonably sure my setpoint isn't kept as close during the entire dive as a good set of electronics would keep it. So using the actual loop composition to determins NDL and deco obligation seems like a good idea.

On an AP unit IMHO it is necessary to add some sort of independent monitoring as there are two interdepend setpoint controllers but no independent way of monitoring the pO2. The lack of said monitoring means you have to modify the unit as far as I'm concerned.

I've heard Inspo owners comparing their units with MK-5p in regards to their multiple SP controllers but what they all seemed to lack is the understanding that that unit not only had multiple SP controllers and batteries (all separate), but also the ROD - Redundant Oxygen Display. Reading the analog signal directly from the sensors and displaying it on a digital display that also had its own independent power source.

__________________
Cheers
Stefan



"Political Correctness is a doctrine, fostered by a delusional, illogical minority,
and rabidly promoted by an unscrupulous mainstream media,
which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.!"

Chris

Pretty simple really "Cause its fun to play with toys"!!

Cheers
Chriso

__________________
Megalodon
Sorb and Sensors whilst in Australia www.divetub.com.au
Diving & Photography @ www.uwphotog.com

silent running

Stefan, thanks for the additional details. I couldn't remember if the HH also had a space for a 4th cell. And I'm not surprised that even a diligent diver like yourself believes that a decent SP cntroller will do a better job holding SP than a MCCR user can. Whether this makes a real difference for deco, I don't know, maybe not in normal diving.

And this is part of why I like the Pelagian for MCCR-2 sensors+ a VR/HE sensor plumbed into a comp, and OTS CLs, needle valve, modular design and-supposedly-a BOV. If only someone had actually bought one... It's a very sensible MCCR design.

IMHO, a sensor/deco comp interface is mandatory on KISS MCCR units. What if you got entangled and had to spend a lot of energy to free yourself for 20 minutes and your PO2 was all over the place? We carry knives/surgical snippers for just such an eventuality, why not an integrated O2 comp sensor? IMHO, it comes with MCCR territory.

nigelh

You have to remeber that lots of us were drawn towards rebreathers because of the geek factor. Once we started to assess them there were real advantages, perhaps not enough to justify the expense but advantages, and again the geek factor found the cash.

Look down the list of what we do for a living. So many of us are tech people. We solve engineering problems day by day so we can't help but assess everything in our lives from a 'how can I make it better' point of view. If we see a problem we look about for a ready-made solution and, if we can't find one, we reach into our mental toolbox and start to construct something that may or may not end up as a physical device.

We have a lot of fun dong it. Our excuse might be safety or convenience, I think the two big addons to my Inspiration are the ADV (predating APDs) and the BOV, but the geek factor is always there.

__________________
nigelh

Depth-junkie

spot on
Carry the correct OC bailout fot the planned dive regardless if its a shallow dive were inboard dil is adaquit or of board tins for deeper dive's, any sign of electronic failure, irrigular PP02 readings, something not seeming right etc bailout OC onto a gaurented known gas. And live to fight another day.

If i had a total handset elec-failure i would not fly my unit of the HUD home, i personley would go for the easy option of a known safe OC gas, if i ran out off that gas (wether due to failure or poor planning) the HUD would at least give me another option of going back to the loop if required (shit or bust situation) but surely OC should be the first action taken in a handset failure situation.

I like my HUD on the vision, but i dont have a 4th cell as i dont see any benifit of it to me (i run a VR3 on my dives but not plummed into the loop), i look at a HUD as something to draw my attention to the handset if i am pre-occupied at a given time I.E high 02 on decent, SP change etc. 4th cell's or HUD's IMHO give you an added safety feature and a plan C option but i would not choose to follow mine as a 1st port of call for an elec failure on the handset, i would be on my way up with an OC reg stuck in my gob if that faild i would then have to revert back to the loop and put my faith in the HUD to do it's job, but as i said that would only be if it's shit or bust. Keep it simple and live to fight another day

ATB
Gareth

jepuskar

I'm one of those techie people, but I just dont look at a rebreather the same way I look at a router. You try something on a router and maybe it brings the network down...you look over your shoulder, undo the changes, and look puzzled as to why the network went down.. Ofcourse I have never ever done such a thing in my career.

Gareth, I think the same way.

I guess there are different levels of geekism.

J