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> I can't comment on the Cis-Lunar rebreathers, and (unfortunately) I don't 
> have a CCR-1000 to tinker with so what follows is deduced from the manual.  
> Gas addition is, as you say, through a solenoid valve.  However before the 
> solenoid valve there is an accumlator.  This accumulator is fed by a flow
> restrictor.  Input preasure to the flow restrictor is 120-140 psi and the 
> restrictor limits the flow to 4 liter/minute.  All this is specked out
> in the manual.  Now I'm guessing that the flow restrictor is a cmfv.  
> Given it's specification this seems quite likely.  There are some good 
> engineering reasons for making this a cmfv.

On the Cis-Lunar, and I asusmed on other fully-closed systems, this "flow 
restrictor" is simply a first-stage regulator (or analgy thereof).


> The maximum flow required
> is probably around 3 liter/minute O2 at 1 ATA.  This should cover most
> metabolic needs.  The CCR-1000 goes a bit farther and has a max flow 
> rate of 4 liter/minute.  However as one descends the actual flow needed 
> is reduced, at 2 ATA you only need 1.5 liter/minute etc.  A cmfv fills this
> need nicely.  Now the question might be why restrict the flow at all.  I'm
> guessing the reason is that 1. the solenoid is open for some finite
> period and one wants to control the amount of gas added during each opening.
> Otherwise some large slug of gas might enter the system.  The second reason 
> is solenoid failure.  If the solenoid fails open it would be nice if the
> flow was slow enough that the diver had some reasonable chance to react 
> before breathing in 10 ATA of O2.  

Hmmmm....Rod, any comments about the biomarine?  In any case, the 
difference is that a rebreather that uses a cmfv to control the flow of 
O2 into the loop is prone to failure if the cmfv clogs.  On fully-closed 
systems with electric solenoid valves, they would only be there (as far 
as I can see) as a safety measure in the event the solenoid valve is stuck 
open (allows more time for the user to react before PO2 climbs).  
However, if it clogs, then the solenoid supply would dwindle, and the 
sound of the click would be clearly different than it is when the 
solenoid is passing O2 through the valve, so the user would know to go to 
manual control.
 
> I'd be interested to know if anyone can confirm or deny the existence of 
> a cmfv in the CCR-1000 or any other electronic rebreather.  The problem 
> with a cmfv of course is the potential to become plugged.  If it did, one 
> might hear the solenoids clicking happily away and not adding any gas to 
> the system what so ever.

I'd be interested in knowing about other rebreather designs as well. From 
my experience, there is a substantial audible difference between a 
solenoid injecting O2 and a solenoid that is "dry clicking".  You would 
notice this difference even if you were very distracted.

Aloha,
Rich

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