MCCR in-depth

paulraymaekers

hello, to make things better clear, I never talk about compensated, non-compensated, balanced etc...

I always use the term: APR absolute pressure regulator: this device always gives you a constant ABSOLUTE pressure, whatever depth you go, whatever pressure in your tank!

and you can change a normal regulator into an APR by shielding off the back-side of the membrane, so that waterpressure does not push on that membrane, increasing pressure as you go down. (mostly done by mounting a cap over the regulator)

and Padowan: you can bye an APR: the dolphin SCR first stage is an APR

regards
paul

__________________
www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

gibbogeo

It is a common mistake, don't worry.

The correct sentence is ""as long as inlet pressure is about 2X that of the outlet pressure the mass flow remains proportional to the inlet pressure"

If the inlet pressure double, the flow will double. If the inlet pressure is fixed, untile the outlet pressure is less than 1/2 of the inlet pressure, the flow will not vary in a significant way.

Check the first page of this document:

http://www.okcc.com/PDF/Choked.pdf

solocavediver

Aha!

>The correct sentence is ""as long as inlet pressure is about 2X that of the outlet >pressure the mass flow remains proportional to the inlet pressure"

>If the inlet pressure double, the flow will double. If the inlet pressure is fixed, untile the >outlet pressure is less than 1/2 of the inlet pressure, the flow will not vary in a significant >way.

Thanks Mr. Gibbigeo, now at last I understand why it's done that way. Glad I posted!

Cheers,

Charles.

paulraymaekers

and more correct:

as long as inlet pressure is at least about 2X that of the outlet pressure

regards
paul

__________________
www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

zèècalcoene

Hello all,

So if I understand correct..

If I want to dive to -60m (trimix ofcoarse) with my mCCR Dolphin fitted with a Swagelock needle valve and a constant flow set (on the surface) to 1 l/m,
then I would need an IP of 14 bar !

Am I right ??

Thanks for any reply

Ivan

__________________
mCCR Dolphin Diver

jaap

No, you could manange using a lower IP. You would need around 14 bar to get around 1l/min (unusuallay high flow!?) at 60m. But you could also manage just fine to that depth with a lower IP of say 9-10 bar. Only the flow would gradually be reduced as you go deeper so that you would have to bypass O2 a bit more often.

With an IP of 14 bar you could theoretically get O2 from the unit down to almost 130m by bypassing, having no constant flow.

dozer

a little late in seeing this thread but i am reading into this as i am planning to add a second bottle to my drager of a rich mix through the "pool" jet thus switching to this at deco depth and turning off supply should significantly reduce the deco (with monitoring of course) hopefully bringing the deco more closer to my inspiration, so firstly if someone can tell me do i need to cap my ds4 or will it be ok compensating due to the shallow deco depths (10m and shallower)?

and now to add my 2pence to the above thread.....


to my understanding and correct me if i am wrong the cmf works by certain criteria being met... you need at least 2 times input pressure to output, hence 14 bar more than adequately meets this, once the criteria of pressure is met then the operation is down to molecular size and weight not solely pressure (where i think a little confussion is being created), the o2 molecules are forced through a narrow space, thus allowing a certain amount of molecules to flow through in a given time (ie 1 min) as long as the force (pressure) remains above the x2 threshold the same amount of molecules flow into the loop irrespective of depth, so when we talk about a litre per minute flow we should really refer to it as molecules per minute flow, therefore realistically as the name cmf suggests it is "mass" that flows and mass refers to molecular weight and size not volume.

side tracking i know but... this is why on the dolphins you are supposed to use the correct mix for the correct jet, as the orrifice is set to the molecular sizes of the supply gas molecules therefore if you supply say 40% through a 50% jet the flow will not be as the guide states (7.3 litres per minute) it will actually vary slightly from this as the orrifice is designed to let 50% through which has a 50 50 split of molecules 14 and 16 *10^26 kg, where if you pass 40% through it you have 40% one size (16 *10^26) and 60% the other, hence you will not get the correct flow theroetically.

getting back on point this made me wonder and im hoping one of you can confirm or deny (with explaination).....if we have a fixed supply of 14 bar and we dive to 60m plus we suddenly violate the 2x rule??(14 bar supply and 7+ bar ambient) obviously this is only a slight variation but if we venture to the 100m mark there is significant reduction in the ratio affecting the force of the molecules

thus i am finding it a little difficult to stomach when people say at the sudden magic 130m the operation will not work.

in my opinion the mass flow will (assuming 14 bar fixed) will degrade from the 60m (7 bar) due to the violation of the 2x rule, and addition will become more and more apparent from that point on.. and at the 130m (14 bar) the hose will equalise with the loop pressure and if you go deeper the hose will theoretically become the lower pressure, and then the hose pressure will increase in a paracitic way through the cmf from the loop???

sorry about the lengthly post!!! an answer to the second would be nice but a plain answer 2 the ds4 question will suffice!!!

regards


sib