Idea for mitigating solenoid-failure: open...

Padowan

I was reading a thread on here about the Open Revolution and the discussion that was going around regarding whether to have one or two solenoids, or a stepper controlled needle valve, and I had a cunning (I think) idea.

Consider this - using YBOD as example:
O2 comes from depth un-compensated first stage, to KISS valve. Output hose from KISS valve goes to solenoid.

Under normal circumstances (within KISS principle depth limits) the KISS valve will feed O2 into and pressurise the hose that connects the valve to the solenoid to the point where the hose pressude balances the first-stage pressure - when the solenoid fires, this slug of gas feeds into the unit. Solenoid closes, process starts again.

If the solenoid ever fails open, instead of getting a huge flow of O2 into the loop like it would normally, once the slug has passed, the unit will just feed O2 like a normal KISS. Solenoid failure closed, can be managed using the manual injector as usual (for extra redundancy and depth potential, the manual buttin could be fed from an independant compensated first stage).

I guess this is basically just an elaboration of the idea used on the Boris and Mk15.x where tiny bore pipe is used to reduce the rate of O2 addition into the loop.

Thoughts, comments?

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JonnyB

This idea sounds awsome, just need to find a way to overload the flow for deeper dives....

/jonny

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decoweenie

Use the SS accumulator idea from the MK-15 unit instead of a hose to store O2 after the KISS valve...

JonnyB

So to use this, which parts and where to i get them from?

/Jonny

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A quote from Crazyduck - In remembering our own Rob Davies.
"Outbound flight 777 heavy you are cleared for flight
Due west into that warm red Texas sunset
You have angels on your wings and divers memories on your six."

Rest In Peace

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Padowan

That won't help, as the KISS valve will only be able to get the pressure of that accumulator up to that of the IP of the first stage so the KISS principle limits still apply.

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undrh2o

I was thinking about this the other day too - but I came up with a different idea. It doesn't solve the stuck off problem - but you can manually add O2 for that, but it should solve the stuck on. Why not two solenoids one after the other? If one sticks open the other is there to stop the flow.

Of course to fix the stuck off problem two gas paths with redundant solenoids (4 total) could be used. Feedback to the controller that no gas is flowing could give an alarm too in a stuck off situation.

My appologies if this has been done.

decoweenie

And... ?

I was going for the large volume readily available once the injector opens up. If the volume isn't enough, very little will flow despite the long injection cycle (i.e. up to around 15 secs on the Insp).

Genesis

There is a trade-off here.

If you restrict flow you solve the problem of a too-rapid add but increase the risk of a hypoxic event during a rapid ascent as the solenoid will not be able to keep up.

Also, there is a power consumption issue. Solenoid valves consume huge amounts of power compared to the rest of the electronics. Stepper motor driven valves do not except when moving, of course, but there are patent issues with that, as well as potential practical issues as well.

There are ways around all of this but as with all design choices you have to be aware of the compromises you are making, why you're making them, and the side effects.

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koputai

And that is why the Mk15 O2 system is so good.
It is essentially as described above, but uses a depth compensated 1st stage. The IP goes via an orifice to an accumulator (like your hose idea) and the accumulator builds up to the IP pressure over a period of time. When the solenoid fires, it dumps the contents of the accumulator into the loop. Because the accumulator is at a given pressure over ambient, the O2 added per solenoid fire is always the same surface amount of O2. ie half a litre at 1Ata regardless of depth.
Now, if the solenoid fails open, the IP can flow straight to the loop, but it goes via the same orifice, which limits the flow to around 5 litres per minute. That may sound like a lot when comparing it to metabolic need, but adding to the total loop at this rate gives the diver plenty of time to realise there's a problem. This is enough for most ascents, but I suppose in a very rapid ascent there could be an issue, but then again, it's a lot les of an issue than on a kiss style system.

Cheers,
Jason.

SINUS

Try this >>> http://www.swagelok.com/shopping/pro...t=SS-4CS-TW-50

Cheers

Wei lan

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