Rebreather World - View Single Post - MCCR in-depth

***jradomski*** · 24th April 2006, 12:10

Quote: (Originally Posted by solocavediver)

Thanks for a really great article.

One small point, you wrote how flow would stop at 130m deep in your CMF valve if you had a 1st stage valve delivering intermediate pressure of 14 bar. Now that is absolutely true if the 1st stage valve is an "unbalanced" valve. But if it is a "balanced" valve - which many are - it will deliver an IP of 14 bar more than ambient, at any reasonable depth. Or some unreasonable depths - I suspect that a decent "balanced piston" valve would go on pumping gas at the same relative pressure right down to the spine-chilling depths where external pressure was 14 bar less than in the tanks. (i.e. 1850 meters if your tank is pumped to 200 bar). For me this is all hypothetical - my personal max depth is about 55m and I have not yet felt what people tell me, that the 2nd stage of a open circuit rig becomes harder to breathe at such depths if the 1st stage reg. is unbalanced. But if you want to feed a CMF valve at serious depth, get hold of a balanced piston reg. IN THEORY - as I say I've never tried it nor am likely to for a good while to come.

Cheers,

Charles.

Balanced or unbalanced first stage has nothing to do with it.. You can use EITHER with a CMF system. That function is to compensate for changing cylinder supply pressures ( a cmf will function more smoothly with a Balanced design).. What matters in a CMF system is depth compensation or not... This keeps the IP relative to ambient pressure.

Fixed orifice works best with a non depth COMPENSATED 1st stage
Needle valves work well with either, but is usually used with a depth compensated 1st stage.

24th April 2006, 12:10	#6 (permalink)
*jradomski* Moderator Current Rebreather/s: Inspiration Classic Sport Kiss Optima rEvo Other CCR Home Build Other Rebreather/s: Inspiration Vision Evolution Megalodon Classic Kiss rEvo Other CCR Home Build Join Date: Mar 2005 Location: "Da" Bronx Posts: 2,997	Re: MCCR in-depth Quote: (Originally Posted by solocavediver) Thanks for a really great article. One small point, you wrote how flow would stop at 130m deep in your CMF valve if you had a 1st stage valve delivering intermediate pressure of 14 bar. Now that is absolutely true if the 1st stage valve is an "unbalanced" valve. But if it is a "balanced" valve - which many are - it will deliver an IP of 14 bar more than ambient, at any reasonable depth. Or some unreasonable depths - I suspect that a decent "balanced piston" valve would go on pumping gas at the same relative pressure right down to the spine-chilling depths where external pressure was 14 bar less than in the tanks. (i.e. 1850 meters if your tank is pumped to 200 bar). For me this is all hypothetical - my personal max depth is about 55m and I have not yet felt what people tell me, that the 2nd stage of a open circuit rig becomes harder to breathe at such depths if the 1st stage reg. is unbalanced. But if you want to feed a CMF valve at serious depth, get hold of a balanced piston reg. IN THEORY - as I say I've never tried it nor am likely to for a good while to come. Cheers, Charles. Balanced or unbalanced first stage has nothing to do with it.. You can use EITHER with a CMF system. That function is to compensate for changing cylinder supply pressures ( a cmf will function more smoothly with a Balanced design).. What matters in a CMF system is depth compensation or not... This keeps the IP relative to ambient pressure. Fixed orifice works best with a non depth COMPENSATED 1st stage Needle valves work well with either, but is usually used with a depth compensated 1st stage. __________________ Joe Radomski CCR Trimix Instructor Trainer ANDI Instructor Trainer Director #10 All posts are personal opinions and DO NOT reflect any affiliated agency unless specifically stated.
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