Turning 4th cell OFF in a 2pin VR£ - impossible??!

Padowan · 28th June 2006, 07:30

Quote: (Originally Posted by Barrie Law)

Mark,
I am not disputing you are metabolising the oxygen and that it will be replaced by the solenoid depending on your metabolism, the ADV would not normally kick in when the diluent is correct for the depth ie 1.3 PPO2.
The remainder of the Partial Pressure is the inert gas in the diluent eg Nitrogen or Helium the only variable is the loop volume that is to say, if you inject diluent to over pressure and then breath it down the PPO2 can be dropped but not in a significant way.

If you breath down the loop on the surface with the oxygen switched off you will notice the loop deflating and the ADV kicking in or if no diluent is added the counter lungs will collapse further until the loop becomes hypoxic.

This is because the loop has a PPn2 of .79% (air Dil) and when you remove some or all of the Oxygen you still have a PPn2 of .79% but you have reduced the loop size not increased the PPn2 to 100%, think of someone putting a plastic bag over their head it will shrink as they metabolise the oxygen and they suffocate.

Regards

I've got to disagree with your last paragraph on this one Barrie.

In a CCR when your body metabolises the O2, and the scrubber removes the CO2 that is created, then as the PPO2 drops, the PPN2 increases.

Each time the ADV would inject in the instance of "breathing down the PPO2" it's replacing metabolised O2 volume with diluent volume, so the net effect is an increase in N2% and therefore PPN2.
If you start with 10L of air (7.9L N2, 2.1L O2 = PPN2 0.79bar), metabolise 1L of O2 and replace it with 1L of air you end up with 8.69L N2 and 1.31L O2 = PPN2 0.869bar.

mortenkjerulff · 28th June 2006, 07:32

Quote: (Originally Posted by Barrie Law)

Hi John,
The connectors on the Vr3 will not be effected by Salt water and the caps are Dust protectors only, you would have to clean the connectors regularly with white vinegar to prevent corrosion building up.

Regards

Hi all.

I have tried on some ocassions to run a lower setpoint than the diluent on my mccr Dolphin by turning off the oxygen feed. No problem.

Also I have ruined my VR3 link cable because saltwater has travelled through the connector (due to a bad o-ring) and into the cable, which is now rusting away. Hence I will not recomend disconnecting the cable under water.

Best regards
Morten

Mark Chase · 28th June 2006, 09:06

Quote: (Originally Posted by Barrie Law)

Hi Mark,
You are assuming you can breath down the PPO2 of your Diluent to a point below your unit setpoint ie 1.3 (air at 100mtrs = 2.31 PO2) this is not correct.
The PPO2 of the diluent gas can be altered very slightly by reducing the loop volume but it is fractional, the ADV will kick in and restore the PPO2.
If you isolate the ADV and use the manual diluent injection you will find the counter lungs bottoming out before you see a significant drop in the PPO2.

In short you cannot breath down the PPO2 of a diluent gas.

Regards

God forbid you should not dive minimum loop during the final phase of the decent, then this shouldent be an issue.

I was taught that diving a CCR on air the END was significantly higher than on oc. This is because OC you will always have 21% 02 and 79% nitrogen but with a CCR diving 1.3 as soon as you drop past 52m your diving an ever decreasing level of 02 and an ever increasing level of Nitrogen.

ATB

Mark Chase

johnv · 28th June 2006, 15:13

Quote: (Originally Posted by Barrie Law)

Hi John,
The connectors on the Vr3 will not be effected by Salt water and the caps are Dust protectors only, you would have to clean the connectors regularly with white vinegar to prevent corrosion building up.

chuckle, that may be what the manual says, you are welcome to your opinion, but if this is how you treat your 4th cell I'd suggest considering a fifth ;-)

John

Barrie Law · 28th June 2006, 16:43

Ok so let's go through this and see what I think is happening:

With the example Mark used of Air to 100 mtrs this gives us 11 bar total pressure.
2.31 is the PPO2
8.69 is the PPN2
11 Bar is the total Pressure of gas in the loop and also the Ambient Pressure at 100mtrs.

Running the loop at 1.3 gives this result.
8.69 is the PPN2
1.3 is the PPO2
9.99 is the total loop Pressure assuming you can breath down the oxygen.
11 Bar is still the Ambient Pressure at 100mtrs

11 Bar Ambient - 9.99 Loop = 1.01?

1.01 Bar is the drop in loop volume thus far and the 8.69 PPN2 would also be rapidly dropping as our body absorbs the inert gas.

Now look at the other figures mentioned:
"However you work the maths I can say for sure I did a 65m dive on 1.3 set point on air which should have given me 1.55 loads of flashing lights and the ocasional buzzer. That just didnt hapen i just sat on a 1.3 set point."

Air Dil at 65 mtrs gives 7.5 Bar total pressure.
1.58 PPO2
5.92 PPN2
7.5 Bar is the total pressure of gas in the loop and also the Ambient Pressure at 65 mtrs

Running the loop at 1.3 gives this result.
5.92 PPN2
1.3 PPO2
7.22 is the total loop pressure.

7.5 Bar Ambient - 7.22 Loop = 0.28?
The 0.28 Bar is the drop in loop volume and again the PPN2 would also be dropping as our body absorbs the inert gas.

The 0.28 represents only a 3% drop in the Oxygen and as you said it was not a problem doing the dive with those margins but Boyle I'm afraid still wins in that the combined Partial Pressure of all the gasses present has to equal the Ambient Pressure with the loop volume being the only variable.

Regards

Barrie Law · 28th June 2006, 16:53

Quote: (Originally Posted by johnv)

chuckle, that may be what the manual says, you are welcome to your opinion, but if this is how you treat your 4th cell I'd suggest considering a fifth ;-)

John

John,
I do keep my Vr3 4th cell lead connected, the point I was trying to make is the lead end and the Vr3 I/O connector are both sealed units and the caps are to prevent dust, crap etc from entering the connectors.
Corrosion will be a problem if the connectors are not cleaned regularly when exposed to salt water but no damage will be caused to the Vr3 if the cap or cable is removed intentionally or not underwater.

Regards

bgpartri · 28th June 2006, 17:04

Although it is a REALLY BAD practise, it is pretty easy to dive your dil deeper than its PPO2 and maintain a lower setpoint.

If you are at 11 bar and you have a PPO2 of 1.3, then there is 9.7 bar of N2 in the loop.

As you slowly descend, you consume O2. As you consume O2, more dil is added to make up the volume. As you consume even more O2, even more dill is added.

Since you are consuming the O2 and keeping the N2, when you stop descending , your loop will stabilize. The solenoid will maintain your PPO2. No more dil will be added as long as you don't descend any more.

But at this point you have no way to flush the loop to lower the PPO2, because flushing will increase the PPO2. So if you forget and clear your mask a really nasty chain of events begins.

Let me say again, this is a REALLY BAD practise.

jknights · 6th July 2006, 20:23

Quote: (Originally Posted by Mdemon)

Hmmm... I could, but it would be better the other way round. Plug it in when I need it... However, I don't know if this will work, whether it might damage things, whether the sea water will affect the connection or the reading...

Or ramp up the conservatism, but I'm already on 20%. I wouldn't be getting out until next week...

Do they have this problem with the Explorer?

I believe that plugging in or unplugging is not recommended when underwater.

Stupid question - But have you calibrated your 4th cell properly ?.
What I would suggest is that it is possible to have a custom cable made with a switch in it. Ideally a reed switch but there are othere ways of skinning the cat.

Mdemon · 6th July 2006, 21:37

Quote: (Originally Posted by jknights)

I believe that plugging in or unplugging is not recommended when underwater.

Stupid question - But have you calibrated your 4th cell properly ?.
What I would suggest is that it is possible to have a custom cable made with a switch in it. Ideally a reed switch but there are othere ways of skinning the cat.

Have calibrated to the Nth degree. As it happens, I now have a cell I am happy with that pretty much matches the Inspo cells. This has now gone into the second loop, and since the ADV is pumping just dil, the PO2 isn't an issue deco-wise.

The reed switch idea sounds like an idea for the future though...

28th June 2006, 07:30	#21 (permalink)
Padowan Proper Boffin Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Feb 2005 Location: Kent, UK. Posts: 517	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Quote: (Originally Posted by Barrie Law) Mark, I am not disputing you are metabolising the oxygen and that it will be replaced by the solenoid depending on your metabolism, the ADV would not normally kick in when the diluent is correct for the depth ie 1.3 PPO2. The remainder of the Partial Pressure is the inert gas in the diluent eg Nitrogen or Helium the only variable is the loop volume that is to say, if you inject diluent to over pressure and then breath it down the PPO2 can be dropped but not in a significant way. If you breath down the loop on the surface with the oxygen switched off you will notice the loop deflating and the ADV kicking in or if no diluent is added the counter lungs will collapse further until the loop becomes hypoxic. This is because the loop has a PPn2 of .79% (air Dil) and when you remove some or all of the Oxygen you still have a PPn2 of .79% but you have reduced the loop size not increased the PPn2 to 100%, think of someone putting a plastic bag over their head it will shrink as they metabolise the oxygen and they suffocate. Regards I've got to disagree with your last paragraph on this one Barrie. In a CCR when your body metabolises the O2, and the scrubber removes the CO2 that is created, then as the PPO2 drops, the PPN2 increases. Each time the ADV would inject in the instance of "breathing down the PPO2" it's replacing metabolised O2 volume with diluent volume, so the net effect is an increase in N2% and therefore PPN2. If you start with 10L of air (7.9L N2, 2.1L O2 = PPN2 0.79bar), metabolise 1L of O2 and replace it with 1L of air you end up with 8.69L N2 and 1.31L O2 = PPN2 0.869bar. __________________ Padowan The future's bright, the future's Yellow .....for now padowan.net - Latest Video: Scapa Flow Rebreather Diving
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28th June 2006, 07:32	#22 (permalink)
mortenkjerulff Customise Me! Current Rebreather/s: Megalodon Other Rebreather/s: Not Bought Yet Join Date: Mar 2005 Location: Denmark Posts: 135	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Quote: (Originally Posted by Barrie Law) Hi John, The connectors on the Vr3 will not be effected by Salt water and the caps are Dust protectors only, you would have to clean the connectors regularly with white vinegar to prevent corrosion building up. Regards Hi all. I have tried on some ocassions to run a lower setpoint than the diluent on my mccr Dolphin by turning off the oxygen feed. No problem. Also I have ruined my VR3 link cable because saltwater has travelled through the connector (due to a bad o-ring) and into the cable, which is now rusting away. Hence I will not recomend disconnecting the cable under water. Best regards Morten
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28th June 2006, 09:06	#23 (permalink)
Mark Chase I go down for ages Current Rebreather/s: Classic Kiss Other Rebreather/s: Inspiration Classic Join Date: Jan 2005 Location: Kent Posts: 2,539	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Quote: (Originally Posted by Barrie Law) Hi Mark, You are assuming you can breath down the PPO2 of your Diluent to a point below your unit setpoint ie 1.3 (air at 100mtrs = 2.31 PO2) this is not correct. The PPO2 of the diluent gas can be altered very slightly by reducing the loop volume but it is fractional, the ADV will kick in and restore the PPO2. If you isolate the ADV and use the manual diluent injection you will find the counter lungs bottoming out before you see a significant drop in the PPO2. In short you cannot breath down the PPO2 of a diluent gas. Regards God forbid you should not dive minimum loop during the final phase of the decent, then this shouldent be an issue. I was taught that diving a CCR on air the END was significantly higher than on oc. This is because OC you will always have 21% 02 and 79% nitrogen but with a CCR diving 1.3 as soon as you drop past 52m your diving an ever decreasing level of 02 and an ever increasing level of Nitrogen. ATB Mark Chase __________________ Is it supposed to make that noise ? I took my unit to the dive shop and demanded they bolt on every thing that would fit. Join my elite diving teem and get a Tshirt "Doing It Chasey"Hammerhead Eccr Advanced Diving System
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28th June 2006, 15:13	#24 (permalink)
johnv Custom Title Allowed! Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Dec 2005 Location: UK Posts: 132	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Quote: (Originally Posted by Barrie Law) Hi John, The connectors on the Vr3 will not be effected by Salt water and the caps are Dust protectors only, you would have to clean the connectors regularly with white vinegar to prevent corrosion building up. chuckle, that may be what the manual says, you are welcome to your opinion, but if this is how you treat your 4th cell I'd suggest considering a fifth ;-) John
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28th June 2006, 16:43	#25 (permalink)
Barrie Law RebreatherWorld Sponsor Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Jun 2005 Location: Ireland Posts: 726	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Ok so let's go through this and see what I think is happening: With the example Mark used of Air to 100 mtrs this gives us 11 bar total pressure. 2.31 is the PPO2 8.69 is the PPN2 11 Bar is the total Pressure of gas in the loop and also the Ambient Pressure at 100mtrs. Running the loop at 1.3 gives this result. 8.69 is the PPN2 1.3 is the PPO2 9.99 is the total loop Pressure assuming you can breath down the oxygen. 11 Bar is still the Ambient Pressure at 100mtrs 11 Bar Ambient - 9.99 Loop = 1.01? 1.01 Bar is the drop in loop volume thus far and the 8.69 PPN2 would also be rapidly dropping as our body absorbs the inert gas. Now look at the other figures mentioned: "However you work the maths I can say for sure I did a 65m dive on 1.3 set point on air which should have given me 1.55 loads of flashing lights and the ocasional buzzer. That just didnt hapen i just sat on a 1.3 set point." Air Dil at 65 mtrs gives 7.5 Bar total pressure. 1.58 PPO2 5.92 PPN2 7.5 Bar is the total pressure of gas in the loop and also the Ambient Pressure at 65 mtrs Running the loop at 1.3 gives this result. 5.92 PPN2 1.3 PPO2 7.22 is the total loop pressure. 7.5 Bar Ambient - 7.22 Loop = 0.28? The 0.28 Bar is the drop in loop volume and again the PPN2 would also be dropping as our body absorbs the inert gas. The 0.28 represents only a 3% drop in the Oxygen and as you said it was not a problem doing the dive with those margins but Boyle I'm afraid still wins in that the combined Partial Pressure of all the gasses present has to equal the Ambient Pressure with the loop volume being the only variable. Regards __________________ Barrie Law Rebreather World Store Supplying the Rebreather World Tel:US +19548403892 Fax:US+19543333792 Tel:EU+442071930496 Fax:EU+442077606344 Mobile+353876880628 Skype:barrielaw Email: barrie@rebreatherworldstore.com
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28th June 2006, 16:53	#26 (permalink)
Barrie Law RebreatherWorld Sponsor Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Jun 2005 Location: Ireland Posts: 726	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Quote: (Originally Posted by johnv) chuckle, that may be what the manual says, you are welcome to your opinion, but if this is how you treat your 4th cell I'd suggest considering a fifth ;-) John John, I do keep my Vr3 4th cell lead connected, the point I was trying to make is the lead end and the Vr3 I/O connector are both sealed units and the caps are to prevent dust, crap etc from entering the connectors. Corrosion will be a problem if the connectors are not cleaned regularly when exposed to salt water but no damage will be caused to the Vr3 if the cap or cable is removed intentionally or not underwater. Regards __________________ Barrie Law Rebreather World Store Supplying the Rebreather World Tel:US +19548403892 Fax:US+19543333792 Tel:EU+442071930496 Fax:EU+442077606344 Mobile+353876880628 Skype:barrielaw Email: barrie@rebreatherworldstore.com
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28th June 2006, 17:04	#27 (permalink)
bgpartri Rebreather Zealot Current Rebreather/s: Megalodon Other Rebreather/s: Inspiration Classic Sport Kiss Classic Kiss Titan Join Date: Apr 2005 Location: Vancouver, Canada Posts: 393	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Although it is a REALLY BAD practise, it is pretty easy to dive your dil deeper than its PPO2 and maintain a lower setpoint. If you are at 11 bar and you have a PPO2 of 1.3, then there is 9.7 bar of N2 in the loop. As you slowly descend, you consume O2. As you consume O2, more dil is added to make up the volume. As you consume even more O2, even more dill is added. Since you are consuming the O2 and keeping the N2, when you stop descending , your loop will stabilize. The solenoid will maintain your PPO2. No more dil will be added as long as you don't descend any more. But at this point you have no way to flush the loop to lower the PPO2, because flushing will increase the PPO2. So if you forget and clear your mask a really nasty chain of events begins. Let me say again, this is a REALLY BAD practise. __________________ http://www.rebreather.ca Good judgement comes from experience, and experience comes from bad judgement.
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6th July 2006, 20:23	#28 (permalink)
jknights New Member Current Rebreather/s: Inspiration Classic Other CCR Other Rebreather/s: Other CCR Join Date: May 2005 Location: Oliva, Valencia, Spain. Posts: 121	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Quote: (Originally Posted by Mdemon) Hmmm... I could, but it would be better the other way round. Plug it in when I need it... However, I don't know if this will work, whether it might damage things, whether the sea water will affect the connection or the reading... Or ramp up the conservatism, but I'm already on 20%. I wouldn't be getting out until next week... Do they have this problem with the Explorer? I believe that plugging in or unplugging is not recommended when underwater. Stupid question - But have you calibrated your 4th cell properly ?. What I would suggest is that it is possible to have a custom cable made with a switch in it. Ideally a reed switch but there are othere ways of skinning the cat.
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6th July 2006, 21:37	#29 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,903	Re: Turning 4th cell OFF in a 2pin VR£ - impossible??! Quote: (Originally Posted by jknights) I believe that plugging in or unplugging is not recommended when underwater. Stupid question - But have you calibrated your 4th cell properly ?. What I would suggest is that it is possible to have a custom cable made with a switch in it. Ideally a reed switch but there are othere ways of skinning the cat. Have calibrated to the Nth degree. As it happens, I now have a cell I am happy with that pretty much matches the Inspo cells. This has now gone into the second loop, and since the ADV is pumping just dil, the PO2 isn't an issue deco-wise. The reed switch idea sounds like an idea for the future though... __________________ www.southwestmafia.com "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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