Unbalance SCR regs

[pipedope]

to use a compensated reg on your primary O2 source is to go manual addition ONLY.
NO bleed orifice at all.

Get LOTS more training.
If you don't understand how this works before you dive you will die, it is not a question of IF, only WHEN.

Why choose a kludge on a poor choice of gear when there are good choices of gear for this kind of dive.

KISS, MEG, Inspiration, MK15, and many others are far better for this kind of dive.

 

[padiscubapro]

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.

The big problem with using a compensated reg is trying to figure out what your PO2 is going to be, as soon as the change in pressure differental is no longer 2x the outlet pressure the nozzle is no longer in the sonic range, the flow rates on the drager were designed for a much higher IP.. you would need bigger nozzles to get the same flow rate at a lower IP... standard regs only operate at about a max of 150psi (older poseidons do 170+), plus you also have to figure out the actual flow rate of the various gases you are using.. the standard flow guages will give wrong values for mixes with helium in it..

Passive addition SCRs work differently they are more acceptable for deeper diving..
The best tool by far is a CCR, very little gas needed and the highest decompression efficiency.. in the long run it pays for itself.. The amount of trimix dives I do yearly pays for the unit each year...

and its not the amount of bailout bottles you need its the amount of gas switches you must do.. 1 gas is not going to cover it, if you run very high flow rates you can probably cut it down to two plus oxygen, but you will incur additional penalties.. this dive you really have to treat as, 1 travel mix, 1 midrange gas, 1 bottom gas,1st deco gas then oxygen.. If the runtimes are shorter you could probably skiip the 1st deco gas, and cover it on oxygen..

In this type of dive the difficulty and danger level is higher than an OC dive even if everything is going as planned, if you go to a CCR the dive for an experienced ccr diver is much safer than either oc or scr, the danger point being not having enough bailo out gas IF the unit fails..
.

 

[Batman]

A. I like kludging a lot.
C. I already own a Drager.
B. No one has explained WHY this would be a poor choice of gear. But, obviously, I am open to suggestions.

Cheers

 

[swisstrav]

using a compensated regulator does not help in any way. it worsens the situation. once again due to increasing intermediate pressure you get also a higher gas flow. thus a higher ppo2.

rebuild your drager to ccr with a kiss-valve or go for any other ccr on the market. do lots of training and then start to calculate this dive.

even if helium is expensive there is no way arround it. as a diluent you will need trimmix or heliox.

 

[caveseeker7]

A. I like kludging a lot.

Unless you really understand what you're doing, kludging, no matter how much you like it, is not a good idea. Fins Wake makes a good point: It's not a matter of 'if', but 'when'.

B. No one has explained WHY this would be a poor choice of gear.

Actually, Padiscubapro just did. Operating principles of a cmf SCR being one reason, deco disadvantages another.

C. I already own a Drager.

Do you just own the Dräger, or are you trained and certified to dive it?
The reason I'm asking is that you don't quite seem to understand the MO of cmf addition. Throwing an active addition and passive addition SCR into the same basket also shows a lack of knowledge.

But, since you're open to suggestion:
a. Get training on the unit you have, or re-read the manuals.
Visit http://www.tmishop.com/ and read the 'How it all works' section.
Read 'Mastering Reabreathers' by Bozanic and understand it.
b. Stay within the range of abilities of both your training/experience and your equipment.
c. Heed the advice of people who have the knowledge and experience with deep and long dives on rebreathers (especially Padiscubapro).
d. If you even remotely consider to turn your Dolphin into a CCR understand what you are doing, both in theory and actual changes, and get CCR training.

 

[Batman]

using a compensated regulator does not help in any way. it worsens the situation. once again due to increasing intermediate pressure you get also a higher gas flow. thus a higher ppo2.

Please allow me to be more specific with my question:
Assume: -Dive plan: 300 feet for 30 minutes, plus deco
-all appropriate deco to be done on OC stage bottles
-Drager dolphon used for depths from 200 to 300 FSW
-Drager with 32% orifice (it rips)
-Compensated 1st stage starting at 180 PSI at surface
-120 cubic feet of 12/60/28 mix feeding the SCR
-408 Sofnolime (less resistance than 812)
-VR3 computer with integrated O2 sensor

Thus no matter how darn fast the gas flows, it would be physically impossible to get over 1.2 PO2 (the main objection I have heard so far).
Also, with I ripping flow, I would think it would be hard to get below .3 PO2 since you are only using the thing below 200 FSW.

I am not interested in comments on logistical problems of managing stage bottles. I am not interested in comments on decompression requirements. I am not interested in comments on how to bail while in the 200 to 300 feet range on the RB. And finally I understant that CCR is specifically designed for this type of dive (maybe I need to go find a Kluger's board.)

I am interested in comments on what might initiate a bail out in the 200 to 300 foot part of this dive while on the modifed Drager.

Feel free to throw in barbs, because I know I am pressing the issue. But if this would work, it would save me money.

Cheers

Batman

 

[Batman]

I sent the following private message to Caveseeker, then figured it would post it here:

I am Dophin certifed. I understand the basic principles. I am not out to kill myself. I take diving in baby steps. I enjoy OC mix diving to 400 FSW. I am trying to evalute if I can incorporate my new Dophin into dives more than 130 FSW (the manual's stated limit) I am trying to get a handle on the more advanced principles of RB's.

I could use performance curves for Drager sonic orifices that show flow rates for changing input and output pressures. Do you know where to find such data?

Don't let me worry you too much. I consider myself to be pretty safety conscious. Smoking out objections to my shcemes on this board is just a quick easy first step in what will be either a long road, or another scuba day dream that gets shelved as unworkable

Cheers

 

[Batman]

But, with all that niceness behind, I do want anyone to give me their best shot at what is wrong with my "Call me hard headed" post above.

Hit me with you best shot, but stick to the 200 to 300 FSW part of the dive.

Cheers!

 

[padiscubapro]

using a compensated regulator does not help in any way. it worsens the situation. once again due to increasing intermediate pressure you get also a higher gas flow. thus a higher ppo2.

Please allow me to be more specific with my question:
Assume: -Dive plan: 300 feet for 30 minutes, plus deco
-all appropriate deco to be done on OC stage bottles
-Drager dolphon used for depths from 200 to 300 FSW
-Drager with 32% orifice (it rips)
-Compensated 1st stage starting at 180 PSI at surface
-120 cubic feet of 12/60/28 mix feeding the SCR
-408 Sofnolime (less resistance than 812)
-VR3 computer with integrated O2 sensor

Thus no matter how darn fast the gas flows, it would be physically impossible to get over 1.2 PO2 (the main objection I have heard so far).
Also, with I ripping flow, I would think it would be hard to get below .3 PO2 since you are only using the thing below 200 FSW.

I am not interested in comments on logistical problems of managing stage bottles. I am not interested in comments on decompression requirements. I am not interested in comments on how to bail while in the 200 to 300 feet range on the RB. And finally I understant that CCR is specifically designed for this type of dive (maybe I need to go find a Kluger's board.)

I am interested in comments on what might initiate a bail out in the 200 to 300 foot part of this dive while on the modifed Drager.

Feel free to throw in barbs, because I know I am pressing the issue. But if this would work, it would save me money.

Cheers

Batman

The one BIG issue with a Dolphin whether it be one used as an SCR or modified to a CCR using a KISS orifice..

The loop is not very flood tolerant.. Sh*t happens, a LITTLE water in the loop (not uncommon) your off it.. there is very poor water trapping or evacuation abilities.. IF you switch to a micropore disposable cartridge (and larger scrubber) you have a bit more leeway with a partially flooded canister.
On a RB designed for deep use, water traps are an intergral part of the design.. On an Inpsiration you can Isolate several liters of water before it becomes a problem.. On a CIS you can totall flood the loop and recover... The Prism and Megladon can also isolate/dump water... but agian these are all CCRs.

If you are running the flow wide open, with practice your other tanks could be fed into the loop, but starting/ending OC is safer.


Also the IP of a drager is 450psi it will work in the sonic range at 300fsw, the no compensated regs on a kiss first of all act like restricted orifices not sonic and they are based on standard 1st stages with the pressure port blocked, thats why they stop at around 300 fsw - when set at 135psi (150 psia) the pressure at 300 psw is about 148 psia

 

[fins wake]

I am not interested in comments on logistical problems of managing stage bottles. I am not interested in comments on decompression requirements. I am not interested in comments on how to bail while in the 200 to 300 feet range on the RB.

Fair enough. You just want to use the cmf Dolphin as a mere bottom gas extender. That's very limited use and there are all those issues you don't want to talk about. But okay.

And finally I understant that CCR is specifically designed for this type of dive

Yeah, that's probably one of the reasons everyone is suggesting this route.

But if this would work, it would save me money.

Warning flags going up all round on this one. Besides, it's probably not true. You probably only will save some money, and then only compared to OC.

But it's a free world.