Offboard connection setup - Thoughts please?

womble

For a while now I have been thinking about plumbing in a system which will allow me to:

1) use a redundant o2 source
2) isolate the solenoid
3) allow access to onboard and offboard diluents through the ADV
4) allow access to onboard and offboard gasses throught the BOV

Currently I have been using a gas switch block (from M&J) just to select which gas goes to the BOV - onboard or offboard with good results. Yes, it does make breathing through a 2nd stage with high flow rates harder, but only slightly so. So low flow rates, like that on a Rebreather on the loop should be no problem.

Encouraged by this, I have drawn up a schematic diagram of how things would work. I know it looks rather untidy, but with careful hose routing I think it should be fairly neat.

The M&J switch blocks are pivotal to this design, as they allow isolation of one or both sources of gas plumbed into them.

On the diagram, should you have a catastrophic BOOM on the O2 side, you would turn off the O2 cylinder, check handsets/gauges, dil flush etc etc to manage the immediate problem, then open the redundant O2 cylinder, flip the GSB and away you go. You have access to redundant O2 through the solenoid.

If the failure is further upstream, e.g within the GSB or stuck open/closed solenoid, the redundant O2 can be unplugged from the GSB and either sources of O2 can be used to fly the unit manually through the manual add valve and standard LP inflators on both O2 sources.

Similarly on the dil side, you can put both your onboard and offboard dils through the ADV, giving a very quick way of flushing the loop. Also, you know that whatever you have in the loop is what will pass through the BOV, so no need to switch gasses on your VR3, just switch to OC - only 2 switch presses.

Catastrophic loss of onboard dil, turn off the cylinder, check handsets / gauges etc etc. Just flip the GSB to offboard and open the cylinder valve.

Failure of the GSB, unplug the offboard and just add manually through the manual add valve using the standard LP inflator on the offboard / deep bailout. This would also mean loss of use of the BOV, but you have standard 2nd stages on the offboard, so this would mean a standard OC bailout.

Leaking ADV? you can still isolate the ADV as normal, but you can also isolate from the GSB as well.

I think that is everything. I am aware this would open up a load more potential failure points, but the degree of flexibility this would offer I think outweighs this.

I am very keen to hear your thoughts, feel free to criticise as I may have missed something glaringly obvious!

Thanks for reading this!!

Attached Images

offboard schematic001.pdf (281.6 KB, 125 views)

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Fun Under Pressure

Hi Womble,

to many hoses for me. I use for deeper dive´s (more than 20 meters) a 7 L Ali o2 tank. With an inflator hose at the 1st stage. So i can plump in the manual Inflator at the CL. When the solonid stuck i close the inboard valve and use the outboard ali stage. I use 2-3 80´s Ali stage tank´s with various gases too. All stage tank´s have 1st stages with inflator hose, so i can close the inboard dil stage and plumb in the manual dil inflator any gas i need. I connect a shearwater on my classic inspiration so when the electronics failt, the oxygen 1st stage failt and the dil bottle is empty i can fly the unit maually and use the gas from o2 and dil stages(I think this is the maximum worst case). All stage tank´s have 2nd stage reg´s so i use when the scrubber is flooded. So i use only the hoses i need on my Rebreather. When you can manage all your hoses it´s ok. But for me it is to much.

That´s the problem when you are not a DIR Guy, you must think about it by YOUR SELF.

Cheers Markku

womble

Thanks for youer input Markku, yes, i agree, there does seem to be a lot of hoses, but in actual fact there is only one more hose on each side to the standard setup. My issue is more with the number of joins / reliability of Y blocks, 90 degree swivels, switch blocks, etc. I was wondering if anyone has tried this sort of setup and what their experiences were.

Please keep the comments coming in!!

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Simon A

Womble,
It seems like you are adding a load of extra joints and making it over complicated.
You say you are using a BOV and offboard O2/Dil?
If so, I would consider something along the lines of:-
Onboard O2 plumbed into solenoid
Offboard O2 plumbed into O2 manual add.
Onboard Dil plumbed into ADV
Offboard Dil (bailout) plumbed into BOV

That gives you access to all your gases, the onboard O2 cylinder valve can be used to isolate the solenoid, the onboard Dil cylinder valve can be used to isolate the ADV and you have access to your bailout through the BOV without any restrictions that could give higher WOB at depth (high WOB is bad when trying to recover from a CO2 hit)

HTH
Simon A

Ivon

Hey Pete,
This is the same set up as I use but without the BOV, just into the CL, it works for me.

Hope your good, you down at Chepstow next weekend?

Ivon.

Brad_Horn

Womble,

Curious as to why you specifically want to:
"1) use a redundant o2 source
2) isolate the solenoid
3) allow access to onboard and offboard diluents through the ADV
4) allow access to onboard and offboard gasses throught the BOV"

What is your failure analysis for needing redundant O2 physically bolted to the rig, wouldn't an O2 stage suffice with whip for manual inflator?

Could you add a standard 2nd stage shutoff close to your 1st stage for the solenoid feed lp hose, allowing open/close solenoid option, without disconnecting any hoses. Similar to what I understand the boris has for dil/o2 cutoff.

Do you need the ADV to have dual feed, wouldn't it be less complex to just alternate to manual inflation if the ADV or its feed fail?

Use of a gas switch block allows access to on/off-board gas, but how do you confirm what gas you are breathing under stress? In particular I am thinking of when a hypoxic dil is in the onboard gas you have to go emergency oc through the bov on the surface and lights out... or alternatively, you accidentally leave the gas block switched to a hot mix from a stage through decent, need a couple of sanity breaths due to high workload on the bottom and ox-tox....


Just my 2 cents

regards
brad

womble

simon, this is what I have at the moment, and it is pretty foolproof. If I dont go for the setup mentioned this is what i'll do. No halfway house. The downside to this is
1) you cannot isolate the solenoid and still use onboard O2 to fly manually
2) Only one gas is available thro the BOV (unless you use QDs - which I dont on my BOV)

Hello mate, I'm gonna be there sat or sunday, maybe also monday/tue/weds as I had a trip to st abbs blown out and nothing better to do!! send me a pm if you want to meet up.

Brad,

I dont use 100%O2 as a bailout, as it can only be used at 6m. if you run some plans on V planner you will find that you will need Sh*tloads of deep bailout to get you to 6m, and it will give you a longer in water time than 50ish % which is what I use. Just what I have been thought and what works for me. Hence the small redundant O2 bottle.

RE: your other 2 points, dual ADV feed would be nice, but not essential, and yes, task loading could lead to accidents. . . . Dilemma

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