Two questions on Insp/Evolution

jepuskar

Hi,

1) When diving with the Vision electronics and when you power the handset down...does it continue to calculate your O2 exposure and your nitrogren loading so when you power up the handset it again it has an updated NDL and O2 times?

2) When doing a diluent flush I notice you can do it with and without the DSV open. When its closed the diluent is forced (backwards if you will) down through the scrubber and then up the downpipe to be vented out of the inhale CL? With the DSV open and you on the loop the same thing happens, but some gas makes its way into your lungs on inhale?

Thanks in advanced.

Jason

PeteS

Go on then, I'll bite....

It can't calculate your O2 and N2 powered down, because it's powered down. It can come up with new data when you power up though.

I'm sorry, the TLA has me . Diver Support Vessel perhaps?
And the vent (OPV = overpressure valve) is on the exhale counterlung. So now I'm really .

And the gas cannot go backwards from the scrubber to the inhale counterlung, the mushroom valves in the mouthpiece should stop that.

This is probably a valid question, so would you like to rephrase it?

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Pete S.

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jepuskar

Hi Pete,

I realize once its powered down you cant see anything, but once powered up then it has the new values..meaning you can see where you are at regarding exposure levels etc?

Yes..sorry about that.. I meant the exhaust on the exhale CL.

When pushing the DIL button on the inhale CL, with the DSV closed..the gas gets pushed back through the scrubber and exhausted from the OPV located on the exhale CL? Assuming the OPV is in the dive position and you are pulling the cord at the same time.

Jason

PCDiver

Hi Jason,

1) you can see the exposure limits (OTU, ..) via the menu.
2) With the DSV closed, the loop is still a full circle. The closing the DSV only blocks the moutpiece, it does not split the the loop, like with a BOV. I'm not 100% sure of the flow direction. Gas normally goes the way of the least resistance. Therefore I assume it will go straight in the exhale CL. Although nothing prevents it going through the scrubber as well.

hth,

Peter

colinicky

Jason
Yes you will see your new NDL's calculated .

The DSV (Demand Supply Valve) has one way valves in it which stop backward travel of gas BUT due to the manual dil button being on the inhale lung the dil gas can travel from inhale lung through the DSV to the exhale lung which has the Over Pressure Valve on . It could take the "reverse" route through the scrubber but wil take the path of least resistance which due to the sofnalime is not the scrubber .
Hope that makes sense !

__________________
Colin

I trust my rebreather completely ,
I just don't trust the user

onwards & downwards

cramerdn

However from the manual...

"higher risk dive profiles include but are not limited to yo-yo (up, down, up, down) profiles, multiple dives in one day, multiple days diving. Understanding the problems associated with these profiles is not fully understood even by the latest generationof decompression experts but are beleived to place the diver at a higher risk of DCS. The Evolution's decompression calculator makes no adjustment for these profiles."

So it keeps track during the dive but apparantly not from dive to dive.

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Tino de Rijk

Yes it does calculate correctly (otherwise you would not be able to make repetitive dives with a Vision.....).
It works really simple: The vision has a real-time clock (normal time & date) that always keeps running (like your wristwatch, sort of). So if you switch off Vision, and then later switch it on again, it will see how many hours passed since switch off, and re-calculate tissue values based on the last stored tissue loading values (which were at switch off).
So the only thing it wouldn't catch is if you climbed a mountain in between and came back (which is not good practice anyway for a diver.....).
This works the same in e.g. a VR3 to my knowledge. Reason is it would otherwise consume too much battery power if it would stay full on all the time (which could be many days) while not being "cleared" yet for N2 tissue loading.

As to the DSV or ADV & flushing: keep in mind that you will typically only do this with an (almost) empty loop, so the OPV will not come into action anyway (your mouthpiece would probably have been blown out of your mouth before that....). So gas could travel direction of exhale C/L, but as explained by someone else, will choose path of least resistance, so will typically sort of stick in the area of the inhale C/L. It wouldn't be a problem if part of it travelled to the exhale C/L. What it would do there is dilute the gasses there - and that is what a diluent is all about......

bottom line:
- vision works without problem with repetitive diving;
- dil add is no problem and will not activate DSV or ADV or whatever device, assume normal minimum loop volume values as in normal in (E)CCR's (but not in SCR'S!).

Ciao,

Tino.

jepuskar

Ok,

This makes sense. Thanks everyone.

The reason I asked the 2nd question was that on the c-19 video I noticed they did a DIL flush while on OC (DSV closed). Because of the mushroom valves and seeing them vent from the exhale CL while doing the DIL flush..there seems to be only one way for the gas to travel.

Jason

Tino de Rijk

That is in fact a proper operation they show on the DVD. If you suspect a high PO2, you should first go OC to breath a "safe" gas (as in known low(er) PO2) before attempting to correct the fault.
of course you close the mouthpiece before going OC. If you now flush the loop (and watch handset for hopefully falling PO2; if PO2 does not fall, suspect solenoid stuck open), the gas you inject (and do not partly metabolise as you are not on the loop) has to go somewhere. So in this particular case you have to open the OPV manually for the gas to get out.
Not doing it would not dilute the gas enough, and would also cause an ascent as the loop volume increases too much (causing negative trim: being too light, as the C/L's now effectively act as a BCD).

This procedure though has nothing to do with "normal" manual dil addition, where you typically inject a bit of dil during descent to refill your compressed (due to descent) low volume loop. The OPV plays no role there. and with an ADV fitted you wouldn't need to do it manually.

The other time you might/must use it is when you run the unit in SCR mode, i.e. breath a few times and then flush the loop (while you are still on the loop. Same reason: "dirty" gas ( in this case: consumed low-PO2 gas) has to go somewhere other than in the diver during refill/refresh of the loop, so you open the OPV manually.

End of free lecture...

ciao,

Tino.

dave t

Interesting point, It could be argued that with the standard AP mouthpiece the flush gas could go out of the inhale lung, through the mouthpeice and into the exhale lung without flushing the scrubber. With a bov style mouthpeice that actually shuts the loop at the mouthpeice (rather than just shuts the diver out) the gas is forced backward going through the scrubber and into the exhale lung making a better flush if you are off the loop.....maybe

Dave