Off board gas

[mrmints]

What's the best way of getting off board gas into a Classic?

Via the BOV? Via the manifold? A 2nd. MAV?

Interested in how you do it and how you'd do it in an ideal world?

[Capt Morgan]

On my unit I run the off board deep gas to the BOV.
I have a second MAV fitted to the dil and into the left
side of the head, it takes a direct feed fitting so I can
plug in off board O2 if needed.
I don't use it during regular diving as the ADV is just so
easy to use.

[Dave1w]

I bought a rEvo 3 Gas MAV, with orifice, and you can add an off board gas to the bottom, which works well.
I also sometimes have an AP GCS quick (ish) disconnect or an omniswivel on a hose into the dil reg, so you can plug your bailout into you unit and have access for BOV or dil, whatever. Only good for normoxic stuff with no switching.


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[JPTaylor]

deleted

[jturner]

What's the best way of getting off board gas into a Classic?

Via the BOV? Via the manifold? A 2nd. MAV?

Interested in how you do it and how you'd do it in an ideal world?

Assuming you want off-board to the loop, then for me (though mine's a APD Vision but it shouldn't make any difference) it would be to disconnect the MAV feed and connect the stage cylinder's LPI hose to it instead. This applies to the O2 or dil side in my case. Assuming you want off-board to the BOV, I use the APD GCS hoses with the female on the stage and the male straight from the BOV.

FWIW, I can't see the point in a second MAV - it's another potential thing to leak and why would you need to add two different gases at the same time? With only one connected (and from two clearly different sources), there's no mistaking what you are adding. Can't see the point of connecting to the manifold either, as then you need to mess about with closing valves, flow-stops or fiddling with IPs to stop one cylinder attempting to fill the other, plus for me, a reason to be using off-board gas is that the on-board side has sprung a big leak (perhaps due to a burst hose for example) and by connecting the off-board through the manifold, you'll just drain that too through the same leak.

[notdeadyet]

Why dont you just plug it into the mav on the lung when needed?

I've messed about with offboard connections on various units and always end back at the start. If you dont need to add extra failure points then dont.

With a back mounted lung, I just use my bov to blow offboard gas into the loop if needed.

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[JPTaylor]

deleted

[Capt Morgan]

I think you guys have missed that this is in the KISS section :D

[JPTaylor]

deleted

[notdeadyet]

I assume you descend, when you can't get a lung full of gas, flip BOV to OC, get lung full of gas, flip BOV to CC, exhale lung full of gas into loop......
Yep. I've tried various alternatives but a CEJN connector on the BOV is nice and simple for adding gas.

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[notdeadyet]

I think you guys have missed that this is in the KISS section :D
Stick with the bov method then.

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[ebt]

If after #69, I'd route it in via the 2nd O2 port on a separate whip....

[mrmints]

I was considering two options...

1) BOV with an OmniSwivel style QD

or

2) Gollum Gear (or similar) MAV, with omniswivel QDplumbed into the head.

Or maybe both, but it seems most peoples preference is the BOV.

Is it not quite fiddly to swap hoses on the BOV?

Has anyone had a go (either as a test or for real) sucking down bailout through the BOV with a QD?

[Capt Morgan]

I just connect my BOV to off-board via a QC6 I also have a second stage strapped to the tank.
I don't like the idea of connecting it through the manifold like some people do as you then have
a common failure point and run into problems if you have to share your off-board with another
diver.
I run a long hose from the BOV along the exhale hose, behind my head, down through the case
and out the bottom left. QC6 on end of long hose connects into off-board via a short hose.

I hope this photo helps show what I'm trying to describe

http://i63.tinypic.com/w81e9s.jpg

[MikeF]

I was considering two options...

1) BOV with an OmniSwivel style QD

or

2) Gollum Gear (or similar) MAV, with omniswivel QDplumbed into the head.

Or maybe both, but it seems most peoples preference is the BOV.

Is it not quite fiddly to swap hoses on the BOV?

Has anyone had a go (either as a test or for real) sucking down bailout through the BOV with a QD?

yes. though the performance of the BOV is OK or a complete disaster depends on QD design (primarily flow coefficient, Cv), gas composition, BOV design and depth (gas density). It's notoriously hard to get manufacturers to stick their necks out and publish standard test results for side by side comparisons though I'm sure Brad will be along shortly to explain why you should buy the ALBOV.

[notdeadyet]

CEJN hoses are a piece of piss to swap. If you plan on doing it underwater I'd rather blow seawater into the BOV than into the MAV and its plumbing.

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[mrmints]

yes. though the performance of the BOV is OK or a complete disaster depends on QD design (primarily flow coefficient, Cv), gas composition, BOV design and depth (gas density). It's notoriously hard to get manufacturers to stick their necks out and publish standard test results for side by side comparisons though I'm sure Brad will be along shortly to explain why you should buy the ALBOV.

I'm afraid I've already bought the Hollis Explorer BOV...

[Capt Morgan]

yes. though the performance of the BOV is OK or a complete disaster depends on QD design (primarily flow coefficient, Cv), gas composition, BOV design and depth (gas density). It's notoriously hard to get manufacturers to stick their necks out and publish standard test results for side by side comparisons though I'm sure Brad will be along shortly to explain why you should buy the ALBOV.

And reverse the unit flow ;)

[MikeF]

you've started it now. ;)

[mrmints]

I just connect my BOV to off-board via a QC6 I also have a second stage strapped to the tank.
I don't like the idea of connecting it through the manifold like some people do as you then have
a common failure point and run into problems if you have to share your off-board with another
diver.
I run a long hose from the BOV along the exhale hose, behind my head, down through the case
and out the bottom left. QC6 on end of long hose connects into off-board via a short hose.

I hope this photo helps show what I'm trying to describe

http://i63.tinypic.com/w81e9s.jpg

Yep, I can see what you're doing there.

[jturner]

Is it not quite fiddly to swap hoses on the BOV?

Not really. I use the APD GCS and it is quite stiff but then I usually connect it on the boat and disconnect it only when I'm taking off stages at the end of the dive (or sometimes when I'm on the last few minutes of deco so the stage can dangle on the SMB line).


Has anyone had a go (either as a test or for real) sucking down bailout through the BOV with a QD?

Yep. Simulated full system failure and emergency bailout from ~52m IIRC, using the above GCS setup, so that was immediate bailout, begin ascent and launch DSMB all in the first minute or so. The BOV/GCS system worked fine, with me getting more than enough gas even though I made no effort at all to control my breathing - I was wasting expensive trimix so I was damned if I was going to return the cylinder part full (and all this despite the fact that because my BS EN 3247238473 certification wasn't to 100000 miles depth, I would explode immediately). By ~35m, I'd switched onto the OC reg for the rest of the journey as required by my instructor, though the bubbles in my face were the only annoyance during this exercise.

[MikeF]

What's the best way of getting off board gas into a Classic?

Via the BOV? Via the manifold? A 2nd. MAV?

Interested in how you do it and how you'd do it in an ideal world?

I run the unit from offbaord gas with a APD QC male feeding the manifold and a female QC on the deep bailout. BOV, MAV's, ADV feed from manifold. I don't plug and unplug underwater. The issue you have to watch doing this is that you may have hypoxic Dil attached to the BOV at the surface so you will need an alternative bailout method at the surface, though if you are carrying deep bailout you are probably carrying shallow bailout as well. In addition to shallow bailout I have an air2 on the wing plumbed into the onboard 3L (which I leave on the unit as suit feed air when diving trimix) as I can put my hand on it straight away.

I've bailed straight onto offboard via shrimp BOV and AP GCS from 70m ish on 15/55. not the best breathe in the world but OK and no real effort to breathe normally

I've also bailed out via JJ BOV directly plumbed to 1st stage with air from 25m and thought I was going to die whilst suffering a CO2 hit.

so you really need to add breathing rate to the equation as well.

[Capt Morgan]

I run the unit from offbaord gas with a APD QC male feeding the manifold and a female QC on the deep bailout. BOV, MAV's, ADV feed from manifold. I don't plug and unplug underwater. The issue you have to watch doing this is that you may have hypoxic Dil attached to the BOV at the surface so you will need an alternative bailout method at the surface, though if you are carrying deep bailout you are probably carrying shallow bailout as well. In addition to shallow bailout I have an air2 on the wing plumbed into the onboard 3L (which I leave on the unit as suit feed air when diving trimix) as I can put my hand on it straight away.

I've bailed straight onto offboard via shrimp BOV and AP GCS from 70m ish on 15/55. not the best breathe in the world but OK and no real effort to breathe normally

I've also bailed out via JJ BOV directly plumbed to 1st stage with air from 25m and thought I was going to die whilst suffering a CO2 hit.

so you really need to add breathing rate to the equation as well.

Mike, would it not concern you that you have a few hoses connected to the manifold and if
one was to rupture it knocks out using the off-board through the unit ?

[MikeF]

Mike, would it not concern you that you have a few hoses connected to the manifold and if
one was to rupture it knocks out using the off-board through the unit ?

nope.

if a hose out of the manifold goes boom i can unplug GCS which sits on my lower chest where I can see and release it. at that point the deep bailout is isolated and the unit is still fully functional with the exception of diluent feed to BOV/MAV/ADV. If I want more volume in the loop I can either ascend a little to expand the loop volume or add volume by exhaling into the loop from an OC reg or plug in a secondary feed to the MAV to add dil if I really need to.

if it's the manifold feed hose attached to the deep bailout first stage it's a bit of a bugger and probably dive over and ascend as deep bailout is compromised, but that would be the same if it was connected to the BOV rather than the manifold.

secondly look at the probability of a hose rupture, good condition hoses very rarely blow. I can think of one hose I've had blow and even then it's a surprisingly effective isolation to kink over a burst rubber hose and put a tie wrap or piece of line around it to keep it kinked (I once did 40 minutes with a burst suit feed hose kinked and held in my hand to isolate it as I was breathing from the cylinder it was attached to at the time but wouldn't recommend it as a plan).

sometimes we worry too much about things that have a very low probability of occurring and if there is a workaround in place the probability of multiple failure starts to get into lottery odds.

Typically I try to have three workable options to get me home. failure of one is possible, failure of two is very unlikely, failure of all three options is exceedingly remote. For some failures the backup plan has to be bailout as in the case of a compromised loop due to a split loop hose and some risks we accept as a single point failure as there is no practicable solution, eg what's your backup plan if your drysuit zip fails with a two hour deco to do in cold water? do you wear two suits?

I've had more issues caused by aditional kit added as 'solutions to what ifs' than I have from running kit as simple as possible.

[Capt Morgan]

Yea, pros and cons to everything we do or change.