Auto Shut Off - Auto Bailout Auto Flush

iain-hsm

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iain-hsm

For clarity this was an actual dive, the C02 was produced by the diver during an open water dive and logged by a C02 detector in the breathing loop (inhale side hose) The C02 data in turn was used by the wrist controller to automatically flush the bag.

What the print out shows is the first 70 minute period of a dive showing C02 against temperature. The points of interest are:
1. The log recorded a massive rise in C02 of 1 kPa in the bag during the first heavy work period 20 minutes into the dive

2. Four further heavy spikes were recorded at 40, 50, 55 and 60 minutes with a peak of 1.2 Kpa into the dive again during a heavy work period.

3. The main point to be made is that the bag spiked with the work load ( a known fact)

4. In the event that no C02 detector (and no solenoid diluent flush controller) had been fitted then no flushing would have been performed during this dive and we would have been looking at a possible different outcome.

5. Now consider the temperature graph this shows a non event, nothing.

iain-hsm

As for automatic flush under this extreme dive the controller has no option but to override (flush) I fear PPC02 over 1Kpa. In the event of no over ride the high level of C02 would have continued as would the heavy work load until the diver packed up. Of course a warning is given first, if the diver does nothing then the controller will.

Please understand that these are (to a point) subjective manned tests, for legal reasons I have been KITA now not to disclose what who where and how for fear of legal reprisals. However the make and model aside the results should speak for themselves. It’s simply interesting and informative.

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abowie

Your idea of automatic electronic diluent flush in response to hypercapnic inspired gas is interesting but from you graph I'm not sure that it is that effective in it's current form.

While flushing the loop does clear however many ml of CO2 go out the OPV with the flush, the loop PCO2 rapidly climbs again. This fits with both the continued loading of the loop with CO2 by the diver and also the presumed "recovery time" for want of a better term required by the sorb to get back to it's maximal function.

A fit diver exercising heavily might be able to sustain a VO2(max) of perhaps 3l/min for a period of time. This could produce as much as 2.5l of CO2 per minute. For some time after this exercise ceases CO2 production and excretion will continue at these high levels and probably doesn't return to baseline for 15 minutes or more. To produce sustained reduction in PiCO2 it seems you'd need to flush the loop more or less continuously.

__________________
Andrew Bowie

Rebreather-friendly Buddy

iain-hsm

A unique feature of the controller I had not disclosed.

The reason for the original post was the importance of the graph not the wiring. But the controller does two things and the graph shows this up. Firstly it controls over the max/min dead band settings like all other commercially available CCR controllers, however with a few additions. What you have highlighted is the second part of the program logic control board in that it also analyses the information for trends.

This part of the controllers programming is called trend setting. Any changes in depth, pressure, time PP02 PPC02 goes back to the trend program, this re plays the information and within certain parameters will anticipate your next move so to speak. It’s a bit like voting logic but by adding depth and time it knows your decompression penalty, by adding depth and depth change it know the difference between decent or accent while normal diving and it can differentiate between this and final accent and decompression obligations.

By adding gas percentage analysis with gas contents of oxygen and C02 in the bag together with the diluent gas bottle Air or He02 pressure it knows if it can flush or if it cannot and say with low bottle pressure it will warn you to bail out. To this also is added a program called SAD (Safe accent depth)

Also the program has a Return to Surface (RTS) logic. So if the program thinks you have been too deep too long, or the tread program thinks your loosing any of the onboard gas say due to a leak or half full cylinders. If the C02 increase is due to a poor pack or a half pack. If the scrubber is only half full or you have used vets grade absorbent. All these poor declining “trends” will vote you off the dive so to speak.

Back to the graph. The sharp increase in C02 shows very heavy work, the sharp drop in C02 show an automatic bag flush. This is an attempt of the controller to reduce the high level of C02, it warns the diver of high C02 then if nothing is done will override and flush.

What you have also highlighted here is that the bag even after flushing appears to rapidly increase in C02 again to a point almost the same as before highlighting the question. Was the flush adequate? Was the position of the 0xygen and C02 detector important (inlet hose, shoulder mount) giving a reading of bag contents but not the whole loop content? Or did the diver continue working?

Look at 45 minutes into the dive, rapid decrease in oxygen followed with rapid increase in C02. This is the classic symptoms of work, everything kicks in oxygen, flush. The trend program also got to work at this point increasing the frequency of control.

The important thing to remember is that this is a subjective manned trial graph with snot spit and plenty of water in the loop using a typical divers rebreather in dive shop service.
This all has bearing on the results. A controlled machine dive in a test rig with a brand new rebreather would have been a much prettier graph.

However as we all still await anyone sending in a graph on the temp stick parameters and performance this is the best I can do for the moment. Iain Middlebrook. HSM Engineering Technology Ltd.

AD_ward9

I cannot speak about Iain´s auto dil flush, but I can speak about mine.

The picture I posted of my Rebreather has auto loop shutoff, auto bail out and auto flush, all without affecting bouyancy (much). I can disclose this openly as we have patents granted on it and are looking for manufacturers for whom we can customise it to their needs and licence it.


If you look closely at the picture I posted of my Rebreather, it has a "thing" on the hose as it comes out of the scrubber cannister. A blow up using 3D CAD is below.

The device is an auto-shut off valve, so when the breathing loop is not able to sustain life or is beyond set limits, it shuts.

The valve incorporates a second stage regulator downstream of the shut-off valve, which is preferably balanced (see the four cams in the 3D CAD picture) so it does not free-flow.

This means the shut off shuts the breathing loop and one has just the bits to worry about that go from the valve to the diver´s mouthpiece (the outlet mushroom valve stops gas coming down the other way). The valve is a combined auto-shutoff and also an auto-bail out valve. These functions act independently.

In the case where the mouthpiece has an exhale valve, then the diver breaths gas from the combined auto-shut off and auto-bail out valve show, then when he exhales he sees bubbles. Otherwise, when he exhales, the gas is vented by the overpressure relief valve that is always fitted to the
breathing loop of breathing bag.

The mouthpiece is preferably with an adjustable exhale valve built in, shown below. The diver can either wind that down, or cover it with his hands, then when he breaths out, the gas goes around the loop into the breathing bag,
where the overpressure blows the relief mushroom valve. The result is auto flush.

The toggle on the left by the way is the manual override. The buttons one the valve are on both sides and allow the diver to press both and flush manually.

This one invention can provide three functions:
Auto shut-off
Auto bail-out
Auto flush.

It does not cause significant bouyancy issues. It removes very many points of failure from the life critical loop in a rebreather, removing the scrubber, most hoses, breathing bags, connectors etc.

The mouthpiece picture does not show the HUD or annunciation that goes with it.

We did extensive 3D gas flow modelling of the design, to ensure equipment using it still could get the CE mark. This particular picture shows one version during development being checked for pressure drop and backpressure at 6 bar.

I notice there is even an icon for auto flush on this site:

Cheers,
Alex

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caveseeker7

Hope I didn't miss anything in the original thread, sorry it took so long.
Good subject, I think, let the discussion begin.

__________________
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.'!"

UWSojourner

Is this CO2 detector the scubber temp version? Or something else?

Drmike

That I like.

Simple, and has the benefit that even if the diver is unable to bail the unit will effectively bail for him.


Bouyancy will only be increased by lung volume. Nice, simple - I like it.

pchanning

Hi there,

Could you please expand on the above as, it would appear, that fresh gas injected at the mouthpiece gets it directly where it needs to go. Considering the need to bail to a different circuit is because the loop has become either unpalatable or down-right dangerous is covered by the design and considering the fact that it is automated is excellent, particularly in the light of some of the Co2 experiences shared lately in other threads. Well done for that. But this is only one set of issues. What of a compromised (flooded loop), what sense is there in incorporating the same circuit as a supply path in the case of an emergency..??



At least with a OC/CC DSV all of the above can happen and the diver is physically removed from the problem/ problem circuit and on the gas of choice. No reg swap involved as one can be directly routed to a stage (if required) rather than the in-board which is likely to be inadaquate. Can it be any simpler than this..??



The chances of severing both the loop and the LP reg hose going to the 2nd stage is slim and promotes better odds for survival. One doesn’t really have redundancy if a failure point to the primary circuit jeopardises the emergency secondary. It seems that it is only a small portion of the loop in your design and that could be armoured, perhaps with stainless steel… and a “Max Power” sticker of course.



An upstream (of the mouth) ADV definitely empowers the diver if he/she can remember to breathe out of their nose in the first instance of any ‘uncertainty’ as to the contents of the breathing loop and perhaps should be taught as the first part of a skill toward a full manual dil flush (but thats another story best left to the Instructors here at Rebreather World to decide).
Here however the diver has access to inboard (via ADV) and offboard gas (via OC/CC DSV) both of which are separate and afford true redundancy.


One last point to consider is the fact that a buddy rescuing a stricken diver with an OC/CC DSV is empowered by the visual simplicity of the device. But the diver better protect their airway as otherwise it won’t IMHO be much of a rescue.



I know, I know its n’th degree and all that, by why else do we buy/ harp-on about all this stuff if not to improve our chance of survival. I'd welcome any thoughts.



I don’t want to seem overly critical and as a designer, I value the ingenuity. Keep up the good work. I’m looking forward to one of these “super-breathers” in 4 years or so.



cheers

paul channing