Quote: (Originally Posted by 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.
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.