Gas flow lag/restrictions when using BOV under heavy OC conditions

J

jwd

New Member
Hi guys,

With all these suggestions for fancy plumbing of on/off board gasses into their rebreathers, has anyone tested the actual performance under arduous OC bailout conditions? I'm wondering what effect all the numerous turns and restrictions inherent in Swagelok and Omniswivel fittings have on actual gas flow.

Not a problem for low flow applications (ie when the rebreather is working) but when you're using the BOV you're essentially putting high flow OC gas requirements through a restricted gas path.

I was doing some experimentation last night using different configurations of onboard/offboard BOV connections using commonly available high flow Swagelok and Omniswivel fittings.I wanted to check the flow rate of gas going through all this new plumbing to test whether it would deliver enough gas during emergency bailout situations requiring high flow (eg deep CO2 hit).

I connected an I.P gauge to the BCD hose (also driven off the DIL first stage) to see the IP drop on large inhalations.

Doing some big inhales (trying to replicate the heaviest type of breathing I might require), there was a significant IP drop when breathing gas delivered through all the rebreather plumbing vs breathing directly from a 2nd stage connected to the bailout tank.

1. Breathing from the BOV was a drop from 140PSI (no flow) to 100PSI (at the end of a big inhale)
2. Breathing a standard 2nd stage (ie 1st stage - hose - 2nd stage) was a drop from 140PSI (no flow) to 130PSI (at the end of a big inhale).

The configurations I was trying were similar to what I've commonly seen so wondering has anyone else noticed this?

Is this something you live with because of the convenience of having a single mouthpiece or do you look at the BOV as a "transition" reg before you switch to a real second stage without all the plumbing attached?

I should note that this wasn't a 2nd stage issue as I got the same result when disconnecting the BOV and using a 2nd stage on the BOV hose (ie it is related to the amount of piping the gas has to pass through before I breathe it).

Thanks
 
jwd said:
I connected an I.P gauge to the BCD hose (also driven off the DIL first stage) to see the IP drop on large inhalations.
Click to expand...

Intresting and important subject.

Can you specify all parts between 1st stage and the bov/2nd stage please.
Have you tried another 1st stage?
Even if it delivers proper IP at rest, it may (?) be an ungenerous giver...
Regards
Sven Becker
 
jwd said:
Hi guys,

With all these suggestions for fancy plumbing of on/off board gasses into their rebreathers, has anyone tested the actual performance under arduous OC bailout conditions? I'm wondering what effect all the numerous turns and restrictions inherent in Swagelok and Omniswivel fittings have on actual gas flow.

Not a problem for low flow applications (ie when the rebreather is working) but when you're using the BOV you're essentially putting high flow OC gas requirements through a restricted gas path.

I was doing some experimentation last night using different configurations of onboard/offboard BOV connections using commonly available high flow Swagelok and Omniswivel fittings.I wanted to check the flow rate of gas going through all this new plumbing to test whether it would deliver enough gas during emergency bailout situations requiring high flow (eg deep CO2 hit).

I connected an I.P gauge to the BCD hose (also driven off the DIL first stage) to see the IP drop on large inhalations.

Doing some big inhales (trying to replicate the heaviest type of breathing I might require), there was a significant IP drop when breathing gas delivered through all the rebreather plumbing vs breathing directly from a 2nd stage connected to the bailout tank.

1. Breathing from the BOV was a drop from 140PSI (no flow) to 100PSI (at the end of a big inhale)
2. Breathing a standard 2nd stage (ie 1st stage - hose - 2nd stage) was a drop from 140PSI (no flow) to 130PSI (at the end of a big inhale).

The configurations I was trying were similar to what I've commonly seen so wondering has anyone else noticed this?

Is this something you live with because of the convenience of having a single mouthpiece or do you look at the BOV as a "transition" reg before you switch to a real second stage without all the plumbing attached?

I should note that this wasn't a 2nd stage issue as I got the same result when disconnecting the BOV and using a 2nd stage on the BOV hose (ie it is related to the amount of piping the gas has to pass through before I breathe it).

Thanks
Click to expand...

Which Swagelock did you use? Usually QC6 should have the best flow and are recomended.
QC4 are less efficient. The AP system is good up to 40m if I remember correctly.
 
I have tried and owned both shrimp and ibov and they both breath terribly compared to a normal second stage - and thats with them plumbed straight to a hose. So much so, that I think I am going from neutral on the BOV/DSV debate to proDSV ...
 
jwd said:
With all these suggestions for fancy plumbing of on/off board gasses into their rebreathers, has anyone tested the actual performance under arduous OC bailout conditions? I'm wondering what effect all the numerous turns and restrictions inherent in Swagelok and Omniswivel fittings have on actual gas flow.

Not a problem for low flow applications (ie when the rebreather is working) but when you're using the BOV you're essentially putting high flow OC gas requirements through a restricted gas path.
Click to expand...
Great topic. Have a look at:
Right angle adapter testing https://www.facebook.com/pg/Atelier...b=album&album_id=413320019421416&__tn__=-UC-R
Flow stop https://www.facebook.com/254464535306966/photos/a.286157995470953/633560454064037/?type=3&theater

Bobjr said:
I have tried and owned both shrimp and ibov and they both breath terribly compared to a normal second stage - and thats with them plumbed straight to a hose. So much so, that I think I am going from neutral on the BOV/DSV debate to proDSV ...
Click to expand...
Try an actual low WOB BOV that has testing published for its WOB in both OC and CC modes...
OC http://www.deeplife.co.uk/or_files/DV_DL_ALVBOV_Breathing_Params_A3_100318.pdf
CC https://www.opensafety.eu/datasheets/ALVBOV_40m_75lpm_air_081014.pdf
 
Brad_Horn said:
Great topic. Have a look at:
Right angle adapter testing https://www.facebook.com/pg/Atelier...b=album&album_id=413320019421416&__tn__=-UC-R
Flow stop https://www.facebook.com/254464535306966/photos/a.286157995470953/633560454064037/?type=3&theater


Try an actual low WOB BOV that has testing published for its WOB in both OC and CC modes...
OC http://www.deeplife.co.uk/or_files/DV_DL_ALVBOV_Breathing_Params_A3_100318.pdf
CC https://www.opensafety.eu/datasheets/ALVBOV_40m_75lpm_air_081014.pdf
Click to expand...

Hello Alex

I think its important to say that your rebreather is still an imaginary rebreather despite your best efforts to wow us with PDFs - if you want to send me your BOV for real world testing (rather than the likely imaginary test results you post here) please let me know here!

Graham
 
Bobjr said:
I think its important to say that your rebreather is still an imaginary rebreather despite your best efforts to wow us with PDFs - if you want to send me your BOV for real world testing (rather than the likely imaginary test results you post here) please let me know here!
Click to expand...
Graham, The interesting thing about the Apocalypse Type IV rebreather and even the ALVBOV separately, is that when you rightly claim the lowest WOB for a mixed-gas rebreather. Do you not think that other manufacturers wouldn't acquire a copy to test themselves to try and knock you down a peg or two! A decade later and there is still crickets.... Noting that at 1.44J/L at 40m on Air at 75lpm for the whole Apoc it is comparable to the WOB of your Shrimp BOV in CC mode!

Though some have incorporated features of the Apoc in their units which is good to see. And yes OSEL has had some very interesting feedback on the Apoc as a whole and ALVBOV from those rebreather manufacturers capable of testing rebreather breathing performance. If you want the kit to do this yourself OSEL will happily sell it to you http://www.opensafety.co.uk/files/Datasheet_iBreatheMkIV_1906.pdf

You can order as many ALVBOVs as you want for whatever form of testing you want to conduct from https://www.opensafety.eu/product_info.php?products_id=58
Couple of images of the ALVBOV in use on different rebreathers and as a result automatically lowering their WOB https://www.facebook.com/pg/OpenSafetyEquipment/photos/?tab=album&album_id=151310394898469

Same for the rebreather https://www.facebook.com/pg/OpenSafetyEquipment/photos/?tab=album&album_id=224248967604611
Sorry to disappoint you.
 
No current images or apparent user base ?

There's no stopping average Joe buying an ALBoV and connecting half the swagelock catalog to it though is there which is what this thread is about....

How about using your fancy machines and showing the reduction in performance through some common connectors ?
 
jwd said:
Is this something you live with because of the convenience of having a single mouthpiece or do you look at the BOV as a "transition" reg before you switch to a real second stage without all the plumbing attached?
Click to expand...

Has anyone ever advocated that a BOV is the only OC source / only 2nd stage?
Tearing the mouthpiece is potentially fairly bad - holding a conventional 2nd stage in your mouth by the port is doable in a pinch but a BOV with loop attached needs a mouthpiece. Ditto if you get enough caustic material in it.

I have never seen anyone say you didn't need a proper 2nd stage on the BO. I use a conventional 2nd stage with a stuff long hose on my deep BO - which is connected to my BOV by a QC6. No flow stops on either.
 
Sven Becker said:
Intresting and important subject.

Can you specify all parts between 1st stage and the bov/2nd stage please.
Have you tried another 1st stage?
Even if it delivers proper IP at rest, it may (?) be an ungenerous giver...
Regards
Sven Becker
Click to expand...

Sven.

Rough chain of components below. Tank to BOV

Offboard cylinder
- Apeks DS4 1st stage (set to 140PSI)
-LP Hose
-QC6 connector (M&F)
-LP hose
-omniswivel switchblock
-Right angle adaptor
-LP Hose
-Omniswivel 4 way manifold (inflator hose with the IP gauge is also connected to the manifold)
-BOV Hose
-Golem Shrimp BOV (or any other 2nd stage)

I see a lot of comments below about a low WOB BOV. I was getting the same results when I disconnected the BOV and used a Scubapro G250 2nd stage on the hose (first thing I checked), so the issue appears to be plumbing vs 2nd stage related.

General breathing feels fine but its the high flow stuff where I see the IP drop and makes me wonder if this will be an issue at depth.
 
Bobjr said:
I have tried and owned both shrimp and ibov and they both breath terribly compared to a normal second stage - and thats with them plumbed straight to a hose. So much so, that I think I am going from neutral on the BOV/DSV debate to proDSV ...
Click to expand...

Bobjr, I disconnected the BOV and connected a Scubapro 2nd stage to the BOV hose to see if this was the problem. No change
 
rjack said:
Has anyone ever advocated that a BOV is the only OC source / only 2nd stage?
Tearing the mouthpiece is potentially fairly bad - holding a conventional 2nd stage in your mouth by the port is doable in a pinch but a BOV with loop attached needs a mouthpiece. Ditto if you get enough caustic material in it.

I have never seen anyone say you didn't need a proper 2nd stage on the BO. I use a conventional 2nd stage with a stuff long hose on my deep BO - which is connected to my BOV by a QC6. No flow stops on either.
Click to expand...

rjack.

I have dedicated second stages on both bailout tanks but have also connected the deep bailout via QC6 to the main system so I can access this gas in the first instance via the BOV (then switch over later if needed)
 
Brad_Horn said:
Great topic. Have a look at:
Right angle adapter testing https://www.facebook.com/pg/Atelier...b=album&album_id=413320019421416&__tn__=-UC-R
Flow stop https://www.facebook.com/254464535306966/photos/a.286157995470953/633560454064037/?type=3&theater
Click to expand...

So basically the results say that with one right angle elbow there was a big drop in flow (flow stop was worse) but it was considered still perfectly breathable. Most of the fancy configurations I've seen lately have at least 4-5 restrictions so maybe it just all adds up.

Any reports from people who have tested these configurations on actual deep OC bailouts on OC?
 
Last edited:
jwd said:
Is this something you live with because of the convenience of having a single mouthpiece or do you look at the BOV as a "transition" reg before you switch to a real second stage without all the plumbing attached?
Click to expand...
Why accept anything less than the performance of a "real second stage" on your BOV in the first place?

DeepUnderground said:
There's no stopping average Joe buying an ALBoV and connecting half the swagelock catalog to it though is there which is what this thread is about....
Click to expand...
Your quite right, which was why the above French study was linked to by OSEL to highlight to their users that it's slightly pointless having the best WOB BOV on the market if you don't supply it with sufficient gas supply.

But there appears two elements to the equation. Both industry can of worms..... as NO QCs to date have any documented EN250 testing when fitted to BOVs to pick at least a known low level standard as a starting point. Though NORSOK done at 100m might be more applicable for initial comparison use as EN250 only goes to 50m and 3J/L is stupidly high for this need!

1) AFAIK there is NO known openly published studies comparing offboard B/O gas solutions, other than that of a direct good quality short LP hose, that offers a known safe means to get OC bailout gas required in extremis with any certainty that it will actually supply enough gas to work...
- best case industry solution ATM is GUE'esque large onboard manifolded BO cylinders with no unnecessary connectors/adapters/flowstops but see 2) as they have no idea how high their WOB under extremis during bailout actually is....
2) Safest option is to bailout onto an actual high performance integrated first stage on a BOV as both Poseidon and OSEL offer that doesn't expose your airway to water, however one has to note that they are quirkily the only rebreather manufacturers to bother doing so.
Importance of 2) and the relevance to the thread is even if you are getting sufficient gas via a high performance B/O hose solution. If under the extremis high-workload ie.75+lpm if your BOV solution has a WOB through the roof, even the perfect B/O hose solution doesn't help.....
So you need both 1) & 2) to be provided to get the end result the OP wants... 2) isn't rocket science as Diver magazine has been comparing 2nd stage WOB on even the cheapest OC regs since the 90's with very good reason.

If any BOV manufacturer isn't providing you the OC and CC WOB of their BOV, it's obviously a very cheap and untested BOV!

DeepUnderground said:
How about using your fancy machines and showing the reduction in performance through some common connectors ?
Click to expand...
We have! This is one of the reasons why OSEL had custom machined our own lockable QC fittings https://www.facebook.com/pg/OpenSafetyEquipment/photos/?tab=album&album_id=2589302997765851 due to an identified need for a functionally safe bailout gas supply connectivity on our deeper MCM units. And yes these have been in field service for quite some time.
This comparison testing .pdf will be published in due course but will be unavoidably controversial based on current evidence and will likely be released in conjunction with a recreational version of OSELs CE certified functionally safe offboard MCM bailout solution. As it is pointless confirming the problem without offering a solution.
 
Brad_Horn said:
Graham, The interesting thing about the Apocalypse Type IV rebreather and even the ALVBOV separately, is that when you rightly claim the lowest WOB for a mixed-gas rebreather. Do you not think that other manufacturers wouldn't acquire a copy to test themselves to try and knock you down a peg or two! A decade later and there is still crickets.... Noting that at 1.44J/L at 40m on Air at 75lpm for the whole Apoc it is comparable to the WOB of your Shrimp BOV in CC mode!

Though some have incorporated features of the Apoc in their units which is good to see. And yes OSEL has had some very interesting feedback on the Apoc as a whole and ALVBOV from those rebreather manufacturers capable of testing rebreather breathing performance. If you want the kit to do this yourself OSEL will happily sell it to you http://www.opensafety.co.uk/files/Datasheet_iBreatheMkIV_1906.pdf

You can order as many ALVBOVs as you want for whatever form of testing you want to conduct from https://www.opensafety.eu/product_info.php?products_id=58
Couple of images of the ALVBOV in use on different rebreathers and as a result automatically lowering their WOB https://www.facebook.com/pg/OpenSafetyEquipment/photos/?tab=album&album_id=151310394898469

Same for the rebreather https://www.facebook.com/pg/OpenSafetyEquipment/photos/?tab=album&album_id=224248967604611
Sorry to disappoint you.
Click to expand...

38 photos spanning 2011-2019 ... that is an active community right there. There must be as many as 1 or 2 units out there in the wild - way to go! APOC and the AD snake oil sales company continues on at full speed! If anybody is reading this thread and actually is considering what Brad AKA Alex is saying be very careful a few crafted PDFs and smoke screens should not be confused with a real rebreather that you should spend your money on!
 
View attachment 10379
jwd said:
Sven.

Rough chain of components below. Tank to BOV

Offboard cylinder
- Apeks DS4 1st stage (set to 140PSI)
-LP Hose
-QC6 connector (M&F)
-LP hose
-omniswivel switchblock <<<<<<<<< try and connect a suit hose + IP gauge here/Sven<<<<<<<<<<<<<
-Right angle adaptor
-LP Hose
-Omniswivel 4 way manifold (inflator hose with the IP gauge is also connected to the manifold)
-BOV Hose
-Golem Shrimp BOV (or any other 2nd stage)

I see a lot of comments below about a low WOB BOV. I was getting the same results when I disconnected the BOV and used a Scubapro G250 2nd stage on the hose (first thing I checked), so the issue appears to be plumbing vs 2nd stage related.

General breathing feels fine but its the high flow stuff where I see the IP drop and makes me wonder if this will be an issue at depth.
Click to expand...

Hello jwd.
Your values seem to be a little worse than mine. I may have a weaker breathing apparatus.
Suggestion:
omniswivel switchblock <<<<<<<<< try and connect a suit hose + IP gauge here/Sven<<<<<<<<<<<<<


I fully agree that the BOV specs are irrelevant.
The BOV hose and the BOV are downstream of the IP gauge and cannot disturb the measuring.
In fact - if you replace the BOV with a really lousy 2nd stage, you probably restrict your inhale speed and get better IP value!
So the Shrimp is fairly good since you get the same value versus a 2nd stage.....

I have made some tests similar to your test. Using bar instead of PSI - sorry.

Measuring IP on DS4 with APEKS 2nd stage: 10bar - 0.8 bar = 9.2 bar (must be normal variation)
Measuring IP on DS4 with APEKS 2nd stage and a Fat flowstop: 10bar - 1 bar = 9 bar

APEKS 1st stages shall be adjusted to 9-10bar according to their Home page FAQ list
Conclusion: Heavy usage imply an IP variation between 8-10 bar.

Since 1000+ hours I run my rebreather with 4 sidemounted tanks, Oxygen and EAN50 on the right side connected with QC6 to an Omniswivel mainfold, and normally AIR and 15/52 on the left side.
See pic for the dil side.

The EAN50, AIR and Trimix tanks has check valves to inhibit water intrusion in the 1st stages.
Added after 200 hours when 2 1st stages had to be served before 1 year. No problems since then.
The minimal water intrusion each time a QC6 is connected is thrown up in the manifold.During the dive, the water is pouring down into the QC6 male and is stopped by the check valve.
It is thrown out when the residual pressure is released by pressing the tip of the QC6 male.
So the check valve is mandatory but is bad for the IP. I believe the opening pressure is 0,2 bar

I have made 3 measurements with the IP gauge connected to my spare suit hose connected to the dil manifold.

Fat flowstop, check valve, QC6 male: 10bar - 2bar = 8bar (picture)
Fat flowstop, QC6 male: 10bar - 1.7bar = 8.3bar
QC6 male: 10bar - 1.2bar = 8.8bar


shutoff checkvalve QC6.jpg
 
I really can't understand why you would need so many ways to get gas into the loop. JJ O2 MAV works pretty much as pefectly as you could ever want - put an inflator hose on your off board O2 and you're good to go. If you really want you could put inflators on deep gas also but in reality a quick bailout breath can be puffed into the loop and that will give you as much DIL as you'd ever need without all those connections.

For the BOV I understand why you might think you need to have a way to change gas particularly with very hypoxic DIL. But in reality you guys need to have done more OC deep trimix to understand how to dive those kinds of DIL - don't switch to BOV in shallow water (just like you can't switch to back gas in shallow water OC with hypoxic back gas). Its a trivial problem overcome by being aware in shallow water and not little DIL into loop above 6m.

Save yourself a bunch of money on swagelok etc and worrying about flow rates: just plumb your deepest gas into the BOV and have a way of adding O2 (like the inflator nipple on the JJ MAV). More complexity and options at stressful times increases the likelyhood of a dangerous choice or no choice (usually the worst option of all).

All that being said there is a certain geeky appeal to all those connectors and switchblocks - which I totally get (I fulfil that by going crazy with mixing equipment :) )
 
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