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Capt Morgan
21-06-2016, 08:20 PM
I was wondering what PO2 people base the diluent MOD on ?
I'm asking from a cylinder depth marking point of view.

dwhitlow
21-06-2016, 08:29 PM
interesting question with 2 answers. However, I never mark the MOD on my diluent I merely mark the contents.

If I did the MOD would be based on 1.6 as that reflects the suitability of the gas for OC use, which might the case if you bailed out.

However, suitability for diluent is somewhat different and higher than 1.2 might give you challenge to flush down the loop ppo2.

Barrygoss
21-06-2016, 08:37 PM
I was wondering what PO2 people base the diluent MOD on ?
I'm asking from a cylinder depth marking point of view.

Dil cylinder is for my use only. Contents are marked, but as I'll not be switching to it at some point in the dive, no point in marking the MOD, as it's good for the dive.

B

Capt Morgan
21-06-2016, 08:42 PM
Likewise Dave I never mark my cylinders with MOD but I was wondering what others based it on.
I always have my BOV connected to my deep BO tank so I know what I base it on.
When the CNS clock might be an issue I would run my unit at 1.2 so I like to have a po2 of around
1 - 1.1 bar but when CNS isn't an issue I run a sp of 1.3 and would be happy enough with an MOD
based on 1.2
It's not a game changer but I would just like to know what others think.

Capt Morgan
21-06-2016, 08:44 PM
Dil cylinder is for my use only. Contents are marked, but as I'll not be switching to it at some point in the dive, no point in marking the MOD, as it's good for the dive.

B

But what are you basing the fact that it is good for the dive on ?
Do you see the MOD as dynamic ?

JPTaylor
21-06-2016, 08:49 PM
I base MOD for diluent on a ppO2 of 1.1. But also consider EADD (equivalent air density depth) I like this to be max. 40m, breathing dense gas increases risk of a CO2 hit.

So I only use 10/50 to about 75m.

Barrygoss
21-06-2016, 08:52 PM
But what are you basing the fact that it is good for the dive on ?
Do you see the MOD as dynamic ?

Dil is the 3 or 5 mounted to the unit, usually 15/55, and marked as such, hence it'll be good to use throughout the dive (or I'll use a different dil, I'm currently looking at 10/60 for a dive)
But I think you're thinking of deep bail, that's normally the same as dil for me, and again it's not marked as its plumbed into the unit using a QC6, should someone else need it at depth, it's a matter of disconnecting the QC6 and passing over the whole cylinder, takes about 10 seconds.
I don't see the need to mark a MOD on a cylinder that is good for the max depth of the dive I'm doing?

B

JPTaylor
21-06-2016, 09:04 PM
I don't see the need to mark a MOD on a cylinder that is good for the max depth of the dive I'm doing?

B

It's for when your pulling a cylinder out of your dive store to prep your unit...

Capt Morgan
21-06-2016, 09:06 PM
Dil is the 3 or 5 mounted to the unit, usually 15/55, and marked as such, hence it'll be good to use throughout the dive (or I'll use a different dil, I'm currently looking at 10/60 for a dive)
But I think you're thinking of deep bail, that's normally the same as dil for me, and again it's not marked as its plumbed into the unit using a QC6, should someone else need it at depth, it's a matter of disconnecting the QC6 and passing over the whole cylinder, takes about 10 seconds.
I don't see the need to mark a MOD on a cylinder that is good for the max depth of the dive I'm doing?

B

No I'm interested what people think about Dil MOD ;)

Barrygoss
21-06-2016, 09:14 PM
It's for when your pulling a cylinder out of your dive store to prep your unit...

I only dive 15/55 as dil. That's the only trimix in my garage (so far, as its good to 90)
Dil cylinders have 15/55 in them.
This weekends 45m max dives were on 15/55, so I did a bit more deco.

Having cylinders of dil in the garage with different MOD's is a mistake waiting to happen. (Me being risk adverse)

And with only 3 gasses in my garage I have managed to fill my O2 with dil once already in 7 years of mix diving. (As I couldn't get the unit to read 0.9 before the dive, I bailed the dive)

B

Vanny
21-06-2016, 09:40 PM
It's late and I'm working , but 15/55 good to 90? Is that metres ?? OC or CC Surely that's too rich ?

dwhitlow
21-06-2016, 09:45 PM
It's late and I'm working , but 15/55 good to 90? Is that metres ?? OC or CC Surely that's too rich ?
yep, too rich for 90

Vanny
21-06-2016, 09:51 PM
Must be a typo or he's on the sauce.

My dil Max's out at 1. Don't mind a bit less. Wouldn't put MOD on , it's hidden in a plastic box.

Barrygoss
21-06-2016, 09:53 PM
yep, too rich for 90

And that depends on what you want a dil flush to do.
15/55 is has a mod of 97m so at 90 would flush to 1.5. A nice round figure for cell verification.
I dive MCCR, as does Morgan, I'm not looking to drive the PO2 down fast because the solenoid has tried to kill me. I'm looking to verify cells that may be a bit "funny"

I won't have had an O2 spike that might be up in the 2.0's and need the emergency crash that the low O2 dil has. Just another thing to consider.

B

dwhitlow
21-06-2016, 10:06 PM
And that depends on what you want a dil flush to do.

:OMG: I don't want to dil flush as that uses dil! I might need that!


15/55 is has a mod of 97m so at 90 would flush to 1.5. A nice round figure for cell verification.
I dive MCCR, as does Morgan, I'm not looking to drive the PO2 down fast because the solenoid has tried to kill me. I'm looking to verify cells that may be a bit "funny"

different units different priorities


I won't have had an O2 spike that might be up in the 2.0's and need the emergency crash that the low O2 dil has. Just another thing to consider.

scooting down the shotline has interesting consequences, whatever you are diving, but is so civilised :)

Vanny
21-06-2016, 10:06 PM
An honest question. MCCR or not , your happy with a dil upto 1.6 at any depth? The Depths your talking does the cns clock not become an issue ?

Barrygoss
21-06-2016, 10:13 PM
An honest question. MCCR or not , your happy with a dil upto 1.6 at any depth? The Depths your talking does the cns clock not become an issue ?

Having run MCCR for 7 or so years now, yes. MCCR really lets you see the effect of a squirt of O2 into the loop. You can see it hit 1.8 on the first breath, then it takes at least 3 or 4 loops to settle back to 1.2/3/4 or whatever you want to run on that dive.
I've never worried about the cns clock, have you looked at what a chamber ride does to it?

B

Vanny
21-06-2016, 10:17 PM
Interesting

Ta

MikeF
21-06-2016, 10:55 PM
And that depends on what you want a dil flush to do.
15/55 is has a mod of 97m so at 90 would flush to 1.5. A nice round figure for cell verification.
I dive MCCR, as does Morgan, I'm not looking to drive the PO2 down fast because the solenoid has tried to kill me. I'm looking to verify cells that may be a bit "funny"

I won't have had an O2 spike that might be up in the 2.0's and need the emergency crash that the low O2 dil has. Just another thing to consider.

B

interesting. I max out 15/55 at 70m 1.2bar ppO2 as I may want to flush down and even that seems a bit hot. for me more than 75m is firmly in 10/70 territory.

PeterL
22-06-2016, 06:56 AM
Ah Morgan ya arm chair diver..... You need to get out more laddo....

I don't mark MOD on DIL, who could see it after all, but I do get a bit bum squeaky when my PPO2 exceeds my set point.

PeterL
22-06-2016, 06:59 AM
I base MOD for diluent on a ppO2 of 1.1. But also consider EADD (equivalent air density depth) I like this to be max. 40m, breathing dense gas increases risk of a CO2 hit.

So I only use 10/50 to about 75m.

Erm... from an air density perspective you want to be staying circa <30M. The work of breathing above that can bite you badly under sustained exercise (>4 minutes) and 40 is definitely off the cliff territory based on Quinitec research.

jturner
22-06-2016, 07:09 AM
I was wondering what PO2 people base the diluent MOD on ?
I'm asking from a cylinder depth marking point of view.

1.4 for me. Pure habit really. Usually the dil will have been chosen to be 1.0 at max depth I'd be going to but that's not it's max operating depth.

JPTaylor
22-06-2016, 07:16 AM
Erm... from an air density perspective you want to be staying circa <30M. The work of breathing above that can bite you badly under sustained exercise (>4 minutes) and 40 is definitely off the cliff territory based on Quinitec research.

An EADD of 30m means you shouldn't use 10/50 past 54m, try telling dives that, 10/50 is seen as a go anywhere gas!

My limit of 72m/75m is seen as shallow! I've seen it used to 96m without any problems...

nickb
22-06-2016, 07:49 AM
An EADD of 30m means you shouldn't use 10/50 past 54m, try telling dives that, 10/50 is seen as a go anywhere gas!

My limit of 72m/75m is seen as shallow! I've seen it used to 96m without any problems...I see people driving with a mobile phone attached to their ears or without a seat belt......without any problems.

10/50 is a shit gas and using it is an admission that the user hasn't really thought anything through.

Past 70m I'm aiming to use 12/60 or 10/70

nickb
22-06-2016, 07:53 AM
And that depends on what you want a dil flush to do.
15/55 is has a mod of 97m so at 90 would flush to 1.5. A nice round figure for cell verification.
I dive MCCR, as does Morgan, I'm not looking to drive the PO2 down fast because the solenoid has tried to kill me. I'm looking to verify cells that may be a bit "funny"

I won't have had an O2 spike that might be up in the 2.0's and need the emergency crash that the low O2 dil has. Just another thing to consider.

BWTF!! Is this a wind-up Baz?

Is cell validation the only reason you might want to flush?

PeterL
22-06-2016, 07:54 AM
You took words from my mouth Mr B, there is no good use for heliar when one starts caring about anything other than PPO2.

JPTaylor
22-06-2016, 08:07 AM
You took words from my mouth Mr B, there is no good use for heliar when one starts caring about anything other than PPO2.

Disagree... there are other heliair gases other than 10/50! I use 8/62 & 6/72 on deeper dives. 15/29 is a gas I like on shallow dives.

Pointless adding small quantity of O2 to small dil cylinders, let the unit add the oxygen, it'll do a better job of it.

Maybe different if you fill off premixed J's

PeterL
22-06-2016, 08:12 AM
Maybe different if you fill off premixed J's

That's the way I spend my winters, there is no joy trying to blend in 3L's......

Mark Chase
22-06-2016, 08:27 AM
MOD marking for Dill cylinders in sotrage isnt such a daft idea

It would be easy to be planning an 80 and see a tin of 15/55 and mistakenly think that will do for tomorow.

1.35 on the bottom at 80 would be useless if you had an 02 spike and needed to flush it down. Your need to do a triple loop flush just to get close to 1.35????

I made the mistake of diving hoter mixes on MCCR in the past and it taught me a valuble lesson of stay below 1.1pp02 on dill and where possable stay below 1.0

END I stay above 25m especialy on deeper dives. This takes care of the whole gas viscosity issue.


So for me a DILL MOD sticker would be 1.1PP02 max depth so 15/55 would be MOD 60m


10/50? sure why not

If you have issues with home fills and are decanting from a J of helium and getting air tops from the LDS its a great idea.

I dont because i dont have too. I have banked gas, a compressor and a booster but if I lived in a flat in London then 10/50 would seem like a very good idea as its cheep simple and quick.

I dont agree with the whole hypoxic gas thing.

I dive hypoxic gas regularly and so my procedures are based on that and dont change even when diveing non hypoxic mix.Yes i fill with non hypoxic gas when i can as a safety enhancement, but again i stress, thats because i can easily do so so to not do so would be lazy.

Only issue with 10/50 is the ultimate depth limitation on the 50% HE trying to keep to a low END. Id not want 10/50 past 70m

Barrygoss
22-06-2016, 08:42 AM
WTF!! Is this a wind-up Baz?

Is cell validation the only reason you might want to flush?

what other failure modes would require a flush on a MCCR? (I'd agree with you on ECCR and choose different gases based on the risk of the solenoid dumping O2 into the unit)
CO2 - off the unit, forget flushing
Blocked O2 orifice - you need O2, run the unit on manual add - this, I think, is the highest risk at depth.
CMF valve lets go - off the unit as it'll be too much O2 to flush down anyway (I run 16 bar on the O2 side so that will be coming in quick)
cell validation - flush
Spike the O2 on a fast descent - Slow the descent, DIL flush and turn the O2 CMF off, wait.

Maybe it's about risk perception, people try to cut deco to the bone, but won't let PPO2 go above 1.3.

I try to do more deco than needed, but I'm not worried if I see a 1.5 on the display as it comes down soon enough on MCCR (again this might just be a MCCR habit)

B

Capt Morgan
22-06-2016, 09:25 AM
Ah Morgan ya arm chair diver..... You need to get out more laddo....

I don't mark MOD on DIL, who could see it after all, but I do get a bit bum squeaky when my PPO2 exceeds my set point.

I've just got a chest infection so It looks like I could be missing my weekend in Malin
so could defiantly be on the arm chair :(
I only used the term cylinder marking to try and tie it down, I don't know anyone who
marks CCR Dil with depth ;)

PeterL
22-06-2016, 09:37 AM
I've just got a chest infection so It looks like I could be missing my weekend in Malin
so could defiantly be on the arm chair :(
I only used the term cylinder marking to try and tie it down, I don't know anyone who
marks CCR Dil with depth ;)

You could try cleaning the lungs for your unit for a change...... :)

nickb
22-06-2016, 09:38 AM
Spike the O2 on a fast descent - Slow the descent, DIL flush and turn the O2 CMF off, wait.Youre gonna have to slow that descent down quite a bit to breathe down a PO2 of 1.5 at your target depth.

If you wanna spend half your dive crawling down the shot, fill your boots. I wanna see the wreck

Capt Morgan
22-06-2016, 10:15 AM
You could try cleaning the lungs for your unit for a change...... :)

The bloody things were just disinfected before my last dive. I'm only the latest in the household to have got it :(

dwhitlow
22-06-2016, 10:15 AM
Youre gonna have to slow that descent down quite a bit to breathe down a PO2 of 1.5 at your target depth.

If you wanna spend half your dive crawling down the shot, fill your boots. I wanna see the wreck

I know it isn't the case for those leaky valve folk but I found having the setpoint change deeper worked and even scootering down the shotline it didn't spike much above 1.0 and had switched before I hit bottom. It also avoided that silly moment of trying to flush down from 1.7 using an inappropriate dil to the sound of the beeping Inspo.

Bubblesless
22-06-2016, 01:48 PM
An EADD of 30m means you shouldn't use 10/50 past 54m,
..

At 54m on a 1.3 setpoint the gas in the loop would be 20% O2 44.44% He & 35.55% N2. This would give an END of 18.8 m which is perfectly acceptable. I always aim to keep the END below 30m and use helium mixes to provide this at all depths to 120m. The O2 content of the dil I keep to below 1.1 PPO2 at target depth so I can flush down an O2 spike.

I have had no problems with gas density by using this approach and have many hundreds of hours under my belt

Brillo
22-06-2016, 01:58 PM
At 54m on a 1.3 setpoint the gas in the loop would be 20% O2 44.44% He & 35.55% N2. This would give an END of 18.8 m which is perfectly acceptable. I always aim to keep the END below 30m and use helium mixes to provide this at all depths to 120m. The O2 content of the dil I keep to below 1.1 PPO2 at target depth so I can flush down an O2 spike.

I have had no problems with gas density by using this approach and have many hundreds of hours under my belt

As a non-rebreather diver can you explain how this works to me please? I'm not trying to learn CCR on the web, just curious.

IainC
22-06-2016, 02:28 PM
I mark the MOD on all my cylinders including CCR Dil and O2 based on what it would be as an OC gas, which according to my training is 1.4 for bottom / travel gases and (up to) 1.6 for deco gasses.

Even if (as usual) I am using a lower 'working' PO2 for the dive, that's what it gets, just for consistency and for bail out / buddy 'can i breathe this now?' reference.

nickb
22-06-2016, 03:44 PM
As a non-rebreather diver can you explain how this works to me please? I'm not trying to learn CCR on the web, just curious.The CCR will add oxygen into the loop to maintain a setpoint of 1.3. At 54m that will be 20.3125% O2 in the loop. Call that 20%, therefore there will be 80% of He and N2, which remain in the same ratio as before (5:4)

So 80 * 5/9 = 44.44 He and 80 * 4/9 = 35.55 N2

Brillo
22-06-2016, 03:50 PM
The CCR will add oxygen into the loop to maintain a setpoint of 1.3. At 54m that will be 20.3125% O2 in the loop. Call that 20%, therefore there will be 80% of He and N2, which remain in the same ratio as before (5:4)

So 80 * 5/9 = 44.44 He and 80 * 4/9 = 35.55 N2

Got it, thanks.

nickb
22-06-2016, 03:59 PM
At 54m on a 1.3 setpoint the gas in the loop would be 20% O2 44.44% He & 35.55% N2. This would give an END of 18.8 m which is perfectly acceptable. JP was referring to the air density though not the END. The EAD at that depth is more like 26m so approaching the 30m limit he referred to.

His calculations assumed 10/50 in the loop.

nickb
22-06-2016, 04:01 PM
I have a spreadsheet somewhere that will give the loop contents and EAD/END at 5m increments for any given diluent and setpoint. I'll see if I can find it.

JPTaylor
22-06-2016, 06:02 PM
JP was referring to the air density though not the END. The EAD at that depth is more like 26m so approaching the 30m limit he referred to.

His calculations assumed 10/50 in the loop.

As nickb said I was talking about EADD rather than END.

I have a spreadsheet that estimates the effective loop mix based on diluent and set point. From that you can estimate END & EADD.

Personally I'm OK with 10/50 to 72/75m. It was PeterL that mentioned an EADD max. of 30m that implies a max. Of 54m limit.

Bubblesless
22-06-2016, 06:17 PM
As nickb said I was talking about EADD rather than END.

I have a spreadsheet that estimates the effective loop mix based on diluent and set point. From that you can estimate END & EADD.

Personally I'm OK with 10/50 to 72/75m. It was PeterL that mentioned an EADD max. of 30m that implies a max. Of 54m limit.

I realise that. I was just pointing out that 10/50 is used a lot and like you I'm ok to dive it to 75m. I've never had a problem with gas density at those depths. If people are really worried about gas density then heliox would be the best way to go.

EngelenD
23-06-2016, 07:46 AM
Don't mark my dill. Only contents . I do like my dil to be 1.0 at Mod of the dive accept 1.1 but don't want to exceed 1.2
I think 1.2 is already high if you would have a high po2 you need to get down.



Sent by my rEvo scrubber using a shearwater Nerd

Capt Morgan
23-06-2016, 10:46 AM
It's interesting to see what different people think and the reasons for the thinking.
I like to keep my Dil to a max of 1.1. I find that not only is it good for cell verification
but it is also quite good at allowing me to make a relatively fast descent onto the wreck
while avoiding any big o2 spikes.
Also interesting that we seem to have a few different trains of thought and not one set
in stone.

Baron015
23-06-2016, 11:22 AM
It's interesting to see what different people think and the reasons for the thinking.
I like to keep my Dil to a max of 1.1. I find that not only is it good for cell verification
but it is also quite good at allowing me to make a relatively fast descent onto the wreck
while avoiding any big o2 spikes.
Also interesting that we seem to have a few different trains of thought and not one set
in stone.

I found that scootering down the vertical shot line to the Viknor let me generate a pretty big O2 spike even using 10/66. :)


Sent from my iPhone using Tapatalk

Capt Morgan
23-06-2016, 11:27 AM
I found that scootering down the vertical shot line to the Viknor let me generate a pretty big O2 spike even using 10/66. :)


Sent from my iPhone using Tapatalk

LOL, one of the advantages of MCCR :) and not having a scooter :(

JPTaylor
23-06-2016, 12:07 PM
Also interesting that we seem to have a few different trains of thought and not one set
in stone.

Isn't that the key difference between OC and CCR!?

germie
27-06-2016, 10:32 AM
I base MOD for diluent on a ppO2 of 1.1. But also consider EADD (equivalent air density depth) I like this to be max. 40m, breathing dense gas increases risk of a CO2 hit.

So I only use 10/50 to about 75m.

But if you go to 130m or more, the eadd will be an issue, or you want to dive without nitrogen? I use on 70+ dives most times the poormansmix: 6/72
The eadd on 135m will be around 48m. I have used that. 1 time I had almost a CO2 problem at 130m. And another time a little bit hpns. So deep diving is always tricky. If the END is ok, then the eadd is not, or you are unlucky to get hpns. Always be aware of these things if you do such deep dives.

MadUKDiver
28-06-2016, 11:49 AM
But if you go to 130m or more, the eadd will be an issue, or you want to dive without nitrogen? I use on 70+ dives most times the poormansmix: 6/72
The eadd on 135m will be around 48m. I have used that. 1 time I had almost a CO2 problem at 130m. And another time a little bit hpns. So deep diving is always tricky. If the END is ok, then the eadd is not, or you are unlucky to get hpns. Always be aware of these things if you do such deep dives.

Thanks for sharing this, very thought provoking.

Gas density of DIL 6/72 @ 130msw set point PPO2 1.1 bar (7.9/70.6 in the CCR loop) is 6.8g/l. This is significantly beyond Gavin Anthony's suggested max limit (6.3) and may explain the near CO2 problems your experienced. You need 6/83 to stay within the recommended limit (5.2).

JPTaylor
28-06-2016, 03:10 PM
Deleted

simon mitchell
24-08-2016, 08:29 AM
Erm... from an air density perspective you want to be staying circa <30M. The work of breathing above that can bite you badly under sustained exercise (>4 minutes) and 40 is definitely off the cliff territory based on Quinitec research.

Hello Peter,

That research (presented at Eurotek by Gavin Anthony 2 years ago) has just been published (at last). I have put a link so you can obtain it in another thread here:

https://www.thediveforum.com/showthread.php?21234-Evidence-based-guidelines-for-gas-density-planning&p=333639&viewfull=1#post333639

Simon M

Capt Morgan
24-08-2016, 08:44 AM
Hello Peter,

That research (presented at Eurotek by Gavin Anthony 2 years ago) has just been published (at last). I have put a link so you can obtain it in another thread here:

https://www.thediveforum.com/showthread.php?21234-Evidence-based-guidelines-for-gas-density-planning&p=333639&viewfull=1#post333639

Simon M

Hi Simon, have you any idea why the gas density calculations don't
take into account the setpoint being used ?

PeterL
25-08-2016, 06:53 AM
Hello Peter,

That research (presented at Eurotek by Gavin Anthony 2 years ago) has just been published (at last). I have put a link so you can obtain it in another thread here:

https://www.thediveforum.com/showthread.php?21234-Evidence-based-guidelines-for-gas-density-planning&p=333639&viewfull=1#post333639

Simon M

Cheers Simon, that was an eye opener for a bleary Sunday morning, good to see it in circulation.
Currently sitting in Queenstown until the weekend as Zoe got me here without an AKL stop over...

nigel hewitt
25-08-2016, 07:02 AM
Hi Simon, have you any idea why the gas density calculations don't
take into account the setpoint being used ?
Wouldn't that be because the density depends on the mix in the loop so you work that out first.
You could make a formula to do it all but it's easier to do it in two steps.

Mark Chase
25-08-2016, 08:30 AM
I have just skimmed it but id have thaught just sticking to a MOD of 25m would avoid gas viscosity issues and the need fro the calculation


In terms of that calculation, whats the math fo us non scientific types?

If we are working at say 1.3pp02 at max depth do we just reverse that to gas percentage 0.16 to start the calculation?

SO if we are plannig 0.10 max PP02 at 70m do we start with a 02 percentage of say 0.14 and go with that reguardless of the fact we are diveing 10/50?

ATB

Mark

cathal
25-08-2016, 10:33 AM
Likewise a non maths type here a clarification on taking into account the set point would be appreciated. 😄

Capt Morgan
25-08-2016, 11:15 AM
Likewise a non maths type here a clarification on taking into account the set point would be appreciated. 😄

Not a great maths type myself but this is how I work it out.

Dil 18/50
Setpoint 1.3
Depth 40m
Ambient pressure 5bar


Dil is 18/50 balance being 32% nitrogen
Daltons law states that the oxygen content is 1.3 / 5 = 26%

Now 26% O2 + 32% Nitrogen + 50% Helium = 108% ?
So what changes, as we know the O2 is 26% we have to normalise the other two gases.

The remaining gas is still at a ratio of 50 parts helium to 32 parts nitrogen.
So with 74% inert gas (100-26) we can work out the inert gasses.

Helium
(74 x 50) / (50+32)
3700 / 82 = 45%

Nitrogen
(74 x 32) / (50+32)
2368 / 82 = 29%

So now in the bag we have
26% O2
45% Helium
29% Nitrogen

Then use the gas density calculations on the result.



Hope this helps.

Paulo
25-08-2016, 11:19 AM
Not a great maths type myself but this is how I work it out.

Dil 18/50
Setpoint 1.3
Depth 40m
Ambient pressure 5bar


Dil is 18/50 balance being 32% nitrogen
Daltons law states that the oxygen content is 1.3 / 5 = 26%

Now 26% O2 + 32% Nitrogen + 50% Helium = 108% ?
So what changes, as we know the O2 is 26% we have to normalise the other two gases.

The remaining gas is still at a ratio of 50 parts helium to 32 parts nitrogen.
So with 74% inert gas (100-26) we can work out the inert gasses.

Helium
(74 x 50) / (50+32)
3700 / 82 = 45%

Nitrogen
(74 x 32) / (50+32)
2368 / 82 = 29%

So now in the bag we have
26% O2
45% Helium
29% Nitrogen

Then use the gas density calculations on the result.



Hope this helps.

Where does the other 5% He disappear to?

JPTaylor
25-08-2016, 11:24 AM
Where does the other 5% He disappear to?

It's diluted... only 18% oxygen in diluent, at 1.3 setpoint unit brings oxygen % up to 26%, resulting in inert gases been reduced in proportion. Nitrogen is also reduced.

Dilution is more if you say use heliair like 10/50...

Paulo
25-08-2016, 11:32 AM
It's diluted... only 18% oxygen in diluent, at 1.3 setpoint unit brings oxygen % up to 26%, resulting in inert gases been reduced in proportion. Nitrogen is also reduced.

Dilution is more if you say use heliair like 10/50...

That makes sense. Thanks

Capt Morgan
25-08-2016, 11:38 AM
Where does the other 5% He disappear to?

It and the nitrogen is off set by the increase of O2.

cathal
25-08-2016, 06:34 PM
Thanks for the explanation Morgan. See you in Youghal!

Capt Morgan
25-08-2016, 06:38 PM
Thanks for the explanation Morgan. See you in Youghal!

Counting the days ;)

simon mitchell
29-08-2016, 09:20 AM
Hello,

The question about calculations in rebreathers has been answered. You need to calculate the composition of the loop gas first, then apply the method described in the paper.

Thanks to all the commentators.

Simon M

cathal
29-08-2016, 10:09 AM
Hi Simon
Again many thanks for the release of the notes on the Gas Density issue. As maths is not my first language is there anyway the calculations for the gas density could be avoided when planning each individual dive by assigning a nominal END for the He% e.g. a He% that gives you a END of 20M for every dive?

Regards

Cathal

JPTaylor
29-08-2016, 06:59 PM
Hi Simon
Again many thanks for the release of the notes on the Gas Density issue. As maths is not my first language is there anyway the calculations for the gas density could be avoided when planning each individual dive by assigning a nominal END for the He% e.g. a He% that gives you a END of 20M for every dive?

Regards

Cathal

Multideco shows EADD in both OC & CCR mode for diluent.... simples!

timmoranuk
12-10-2016, 05:39 PM
My dils have a PO2 of no more than 1.00 at max planned depth. I have three standard dils; 20/35 (40 metre), 15/55 (65 metre) and 10/70 (90 metre). The stand-alone Petrel displays the expected dil PO2 but even my enfeebled brain can calulate this on the basis of 20%, 15% or 10% O2...

Capt Morgan
12-10-2016, 06:20 PM
My dils have a PO2 of no more than 1.00 at max planned depth. I have three standard dils; 20/35 (40 metre), 15/55 (65 metre) and 10/70 (90 metre). The stand-alone Petrel displays the expected dil PO2 but even my enfeebled brain can calulate this on the basis of 20%, 15% or 10% O2...

Yea Tim the feature on the Petrel is very handy. I like to keep my dil po2 at about 1.00 at depth so it's easy to see the difference with a good flush.
What I was really wondering was, if people mark their dill mod what do they base it on?

PeterL
12-10-2016, 06:23 PM
Yea Tim the feature on the Petrel is very handy. I like to keep my dil po2 at about 1.00 at depth so it's easy to see the difference with a good flush.
What I was really wondering was, if people mark their dill mod what do they base it on?

They don't darling, do keep up :)


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Capt Morgan
12-10-2016, 06:27 PM
They don't darling, do keep up :)


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But I'm slow, you've met me so should know that :)

PeterL
12-10-2016, 06:29 PM
But I'm slow, you've met me so should know that :)

Trust me, we're all familiar with carrying your intellectual might.... 😉


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Capt Morgan
12-10-2016, 06:34 PM
Trust me, we're all familiar with carrying your intellectual might.... 😉


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Such a heavy burden :D

PeterL
12-10-2016, 06:39 PM
Such a heavy burden :D

It's ok, you're our brother from a nudder mudder......


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OlegG
09-08-2019, 08:31 AM
I have a spreadsheet somewhere that will give the loop contents and EAD/END at 5m increments for any given diluent and setpoint. I'll see if I can find it.
please take a look here: https://blender-toolkit.t-provider.de then follow in menu: CR Diluent END/MOD


http://wetnotes.t-provider.de/ccr/diluentmod.png

OlegG
09-08-2019, 08:37 AM
and to see gas density please set in settings "Show details" - verbose