Unbalance SCR regs

[deepblueh2o]

Hey, we're back! I had to print it all out just to keep my place.
For both Superman and Swisstrav-The 2 ways to use a balanced first stage with a rebreather (there may be more) that I know of, are a balanced piston, which gives no adjustment control over the pressure, requiring you to use different orifices depending on your requirements. The second is a balanced diaphram. You control the pressure setting and usually use one orifice. BOTH types MUST be sealed against outside pressure. They become 1 atmosphere regulators, always supplying the same pressure to the orifice. As far as changing out orifices goes, the Dolphin comes with 3 and Dreager sells others, your already doing it.
Metabolism- using the Dolphin as an example- just because the jet has 50% on it does not mean you can only use 50% nitrox. Using oxygen gauges to read your use rate of oxygen on a given jet of a given % oxygen, you can then change gas mixes based on your #' s for deeper depths. Take a mix, hook up to a jet, relax at the surface, and read your O2 gauge. That reading plugs into the nitrox depth formula because it gives you your starting O2 level. No, it is not safe, it's a rebreather.
I am presently running something that started as a Ray, is sandwiched between a backplate and a tank plate, with a KISS style O2 system. Things are hanging from it everywhere. I never met something I didn't at least want to try.
I think the lowest mix I used on the semi system was 35% on the 60% jet. Specialty dive. COULD NOT BE USED AT SURFACE.
I sort of, like, hold the O2 gauge in my hand during a dive. That's why it's there.
I have been to Cozumel, Cabo San Lucus, Bahamas, Coco Island, Similan Isl.(Thailand), Bimini, PNG, Honduras, Socorro Isl., and all over the Seattle to Canada area.
Did I get them all?, I tried.

 

[swisstrav]

@deepblueh2o

the way i understand it, you have changed your ray to ccr. using o2 and diluent-gas.

have a nice day
swisstrav

 

[swisstrav]

@ superman thats what you are. thanks for the addr. in bonaire.

if it works out, will be there with my 2 boys during easter vacation. (12+15 need to do their advanced.

nice day swisstrav

 

[Batman]

Hi Guys,
Here is my question:

Assume a "60%" Drager orifice with 220 PSI above ambient in the hose that supplies it, at the surface.

Now assume the same orifice 100 (or 200 or 300 or 400) feet deep with 220 PSI above ambient.

Would not the flow (in terms of mass) be the same?????????????????????????

Thus, would not a 1st stage that compensates imtermediate pressure to maintain a constant PSI above ambient pressure be desireable?????????????????????

Thanks for the free education. I do not have time to get a degree in physics right now.

 

[pipedope]

Hi Guys,
Here is my question:

Assume a "60%" Drager orifice with 220 PSI above ambient in the hose that supplies it, at the surface.

Now assume the same orifice 100 (or 200 or 300 or 400) feet deep with 220 PSI above ambient.

Would not the flow (in terms of mass) be the same?????????????????????????

NO!

The sonic orifice doesn't work that way.

The orifice size and the UPSTREAM pressure determine the flow until the downstream pressure gets higher than the critical pressure which is about half of the upstream pressure.

With a compensated reg the orifice flows more mass as you go deeper because of the increasing absolute pressure at the input.

 

[Batman]

OK, so in that case, if you are on a SCR Drager modified to hold 120 cubic feet of supply gas and want to go to 300 feet for 30 minutes and do not care about a high flow rate for this short duration (because you use a low oxygen content trimix), THEN could you use a compensated reg???????

(This really hits on what I hope to do some day when I understand all this stuff)

Thanks

 

[fins wake]

OK, so in that case, if you are on a SCR Drager modified to hold 120 cubic feet of supply gas and want to go to 300 feet for 30 minutes and do not care about a high flow rate for this short duration (because you use a low oxygen content trimix), THEN could you use a compensated reg???????

The compensated reg doesn't even come into play. First of all, 30 min BT at 300 feet is not a short duration, you'd be on around a 5-hour runtime in any case, and the bailout required on its own would be demanding. (Unless you mean a planned bounce dive to 300 feet, with an overall runtime of 30 min? That would still present problems, albeit somewhat less.)

Second, a low flow flow rate and low O2 content might not give you hyperoxia problems at depth, but it would give you serious hypoxia problems in the shallows, requiring e.g. use of OC gas in the shallows in RB80 fashion.

Most serious RB divers would do a dive as outlined on a CCR (with proper bailout or alpinist, as it were). Most CCR divers diving KISS would not use a depth-compensated reg. (I know some do, but I don't consider them KISS.)

There's an awful lot of talk on this board right now about CMF (active SCR)Drägers used at great depth, and it really isn't the ultimate tool for that purpose. Could it be that irrational fear of the CCR makes people choose an SCR which is more dangerous when used outside its remit?

 

[swisstrav]

a scr is not the tool to do deep dives. if you realy want to do those 300ft go oc or ccr. whatever you choose, this is serious diving. needs a lot of planing ahead.

swisstrav

 

[padiscubapro]

OK, so in that case, if you are on a SCR Drager modified to hold 120 cubic feet of supply gas and want to go to 300 feet for 30 minutes and do not care about a high flow rate for this short duration (because you use a low oxygen content trimix), THEN could you use a compensated reg???????

(This really hits on what I hope to do some day when I understand all this stuff)

Thanks

A 300 for 30 is a dive I'll do with my trimix ccr students, this is a LONG dive. depending on the decompression model (and conservatism) used, runtimes are between 3 and 4+ hours., If you were to do this on either Open circuit or an SCR the run times would be MUCH longer. The pre dive planning is critical, especially bailout gases and emergency support. Blow as little 60 minutes of deco on helium and the odds are not good, even with prompt hyperbaric treatment.

If you are not careful with PO2 levels OTOX, will come and bite you in the a*s. AT a PO2 of 1.4, you have 153 minutes, for 1.5 you only have a 120 minutes exposure (45 at 1.6), to make the mix acceptable for some reasonable range you will have to run a PO2 even higher than 1.4 at the working depth, by 165 the PO2 will be much lower than you want, so you'll need another mix.. with a CMF unit you really nead multiple gases. I don't feel like working out the numbers but to do it in an acceptable fashion you probably need at least 3 different gases, 4 would be better, plus oxygen for the last stops

 

[Batman]

I appreciate the general info. But I am familiar with the requirements of diving up to 400 FSW on OC. I dive in a place that helium is quite expensive, but oxygen is not as bad. I do not mind carrying lots of bail out bottles.

But I want to modify a Draeger to go to 300 with bottom time of 30 mins with a compensated reg to simply repalce doubles of trimix. Everything else (including bail out) would be separate.

When I call this a short dive, I mean that it is well within the scrubber limit, and with 120 cubic feet of gas for just the RB, I could accomidate a huge flow rate for 30 mins. My question is specifically about the workability of this with a compensated reg. (Is not the halcon passive assist SCR being used for long 300 FSW dives?)

Again, could a compensated 1st stage make it feasible for a Drager (with lots of supply gas) to dive trimix at 300 for 30????????????????????
I do not see any post thus far saying this is impossible.

I am also interested in arguments the CCR would be safer. What I have described above seems pretty safe to me.
I have in mind using an integrated VR3.