Proposed new gas routing: opinions please....

Padowan

After reading Marks great write up on his Golem BOV installation and the really nice installation of a Whitey shut off, I was thinking about some possible changes to the routing I have within my YBOD for the Dil, offboard, O2 and BOV.

Here is the current setup:

Key points:
The BOV is supplied totally indepentantly from my offboard via a GCS.
The ADV has a shut off.

Here's a proposed new configuration:

Key points:
There is now a Whitey valve in-line with a direct feed from the O2 first stage to the solenoid - this would allow me to isolate the solenoid and retain manual O2 operation.
The GCS now feeds into a T-piece fitted into the spare end port in the manifold.
Both the Diluent and Offboard feeds go through one-way valves to prevent tanks equalising (see bottom paragraph for how I *think* this will work).
BOV fits into the new top-port of the T-Piece.

Here's how I imagine running the system:
Offboard connected but turned off, all diluent items fed from inboard cylinder, including BOV.
If there's a problem, I can switch the BOV and have access to dil for a short period of time, if I want longer, I can open the offboard, and then effectively have 10L of OC gas accessible through the BOV (assuming a 7L is carried).
By turning off the onboard, I can run all diluent sources fed from just the offboard tanks.

My questions:
This puts the manifold as a single point of failure over my existing config - how much of a risk is this in reality (considering I will still have an OC reg on the offboard, and can disconnect the GCS to make it independant again) are there any known manifold failures?
With the one way valves in the 2 dil feeds, I guess that gas will come from the tank with the highest IP to start with, once this stops delivering gas (tank empties and IP drops) I should then get gas from the lower IP first stage - if I set the offboard IP to be lower, I will automatically get a gas switch from my lean dil, to a slightly richer offboard bailout mix, whilst still maintaining all functions (wing, ADV, manual injection and BOV)?

Any comments? Am I overlooking anything obvious?!

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Digger

Won;t the gas pressure in the bailout end up in the dil tank, and vice versa? Won't the gas mixes do the same? EDIT just read bit about one way valves. Won't that be complicated? And expensive?

A lot of my dives I carry different bailout to dil, and I know at the end of a weekend I can be running low on dil, but then the rebreather is for rebreathing, so it doesn't worry me too much.

Personally I'd have the valve between the line on the right and the manifold, so I could open it if I had to, but would normally be closed. That way you can use it to drive the functions of the unit if you want to, but only if you want to.

Are you planning on running the unit from offboard then? Does this mean the dil will be on but the line closed? Just thinking out loud. And remembering my eggs in one basket situation, which is kind of the other way round, but I still try and avoid it if at all possible. One major failure and all that. It's not just the manifold bar but all those hoses and fittings which could fail, and if they have capacity to do you in from one failure I'd be avoiding it.

My 2c, and I now see a grandmother sucking eggs

Digs.

PCDiver

Hi Padowan,

nice drawings.

I'm using the GCS as well but I'm still working on some improvements. I like the ability to disconnect the solenoid and will implement that as well.

one-way valves - I don't think you need them. I believe your first stages will act as one-way valves but I'm not 100 percent sure. Can somebody else confirm this?

manifold - the manifold and all hoses to and from the manifold are single point of failure. If you rupture one of those you'll could loose a lot. Go through the entire setup and think what would happen if you loose a hose/o-ring or manifold.

automatic selection of diluent based on IP - that is too tricky. The IP of a first stage could change underwater (creep) and you don't know which tank you are using. Why don't you keep one tank open at a time? Especially if you are running different mixes. When you have problem with the loop and you have to bailout, you have time enough to switch to BOV, turn on the off-board and close the on-board.

Disconnecting the GCS underwater is not easy when they are pressurized. What you could do is take a deep breath from the regulator and disconnect at the same time. That should lower the pressure on the GCS with a couple of bars. Or close the tank completely, purge, disconnect and open the valve again.

Ben Field

APD reccomend a shutoff valve upstream of the GCS to make connecting/disconnecting easier...

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Beware Fridge Suck

Mdemon

Wouldn't a GCS on the dil first stage give you the same functionality but with less plumbing?

Not sure how useful isolating the solenoid is. If it sticks on, isn't the drill involving the cylinder valve good enough?

I think your current config is simple and elegant as it is. I don't think you'll gain much from the whitey idea. Sorry mate!

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Padowan

I agree with the comments on the unnecessary complication of the "auto IP gas switching" function, I guess that was really more of a "is this what will happen?" rather than a "I want it to do this". I agree with you PCDiver that turning on the offboard if I need it (either for BOV or use on inboard functions) is certainly an easier option.

If I can be religious about not having both valves open at once, then the one way valves are unnecessary, but I like the idea of them being in there just in case - so in that case, I'm interested in what would happen. If the first stages would not allow backflow, then I guess they are unnecessary. Some more information on this would be good if anyones tried it out before.

I don't find the GCS hard to disconnect, but re-connecting it is a b!tch?!

Isn't that the tank valve?!

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Padowan

Yes the drill on the tank valve works, but I think that being able to isolate the solenoid is an improvement. The Boris has this function for sure, and the meg has a soleniod connector thats disconnectable in-water, so there must be some good to be had by this....

Also I reckon that having access to the inboard dil would help my bailout volume a bit. I must admit I AM a believer in the "Rebreather for Rebreathing" philosophy - but I'd be mighty pissed off if I had a problem and ran out of bailout knowing that I was carrying 3L of perfectly good gas I had no way of accessing.

For me it's all about options, but also being able to select/deselect options as the situation arises - more of a modular approach I guess.

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PCDiver

That would help but it would also lower the maximum flow through the hose. The GCS without flowstop is rated deeper than the GCS with flow stop. But when a critical failure occurs with manifold or hoses, you could use the flowstop to quickly isolate the off-board and then switch to the off-board regulator. That would prevent major gass loss. Another "design decission" I guess.

PCDiver

There is a lot to say for this new config.
Bailout scenario - You switch to the BOV. And when you're onboard is used or you have to switch to a richer gass, you just open the off-board. Nothing else needs to be done. You can still manage everything connected to the manifold (wing, dry-suit) as usual. No other actions required.

Mdemon

Hmmm... My car has a cup holder, but I never use it...

I totally agree on being able to breathe all gases. Open loop won't work if the loop floods so you need something for sure. I think a GCS on the first stage will give you a last ditch source should you need it, and no brain overhead - "have I left my valves on?". Cheaper too, and won't compromise the manifold.

Modular approach gets my vote too...

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