Most Redundant OC SCUBA?

[victorzamora]

lowviz, this is the only time John Ratliff mentioned why he needed this setup.

I dive in a river, in high current where regulator performance is crucial. The setup allows twice the air available at the second stage as other configurations. This is done with a regulator that I bought new in the 1980s. But the A.I.R. I would be hard to beat without this configuration by any of the newer regulators today. My point is that this is a redundant system, with the limitation of the O-ring/LP hose failure that has been pointed out. Yes, it is complex, and yes, probably unnecessary for most diving. My whole point was that it was a possibility that may not have been considered by any of you before, and it worked and worked well.

As I said before, modern regs should be able to provide PLENTY of air....even at depth. At 27ft (as he claimed), any reg should be able to provide enough air. If he's exerting himself enough to NEED more than that amount, then there's a lot of danger there regardless of tank config. If he's within easy CESA depth, and that's your main backup plan.....then why worry about redundancy at all?

I agree, this is an interesting concept that I hadn't considered before. That doesn't make it better. Not all change is progress.

 

[Akimbo]

IDK, here is all I "know" about it:

"Perhaps the best-kept secret of WWII was the use of oxygen-enriched air re-breathers by the British commandos defending Gibraltar…”

reference:
Eanx History

That could never have happened. Nobody in WWII could dive mixes on a CCR, wish they could have. Rebreathers were for stealth access to shore and floating targets, not combat-diver to combat-diver assault. Think about it, how are you going to drag someone down on a rebreather? All they have to do is inflate their counterlung and drop their weightbelt and you are both on the surface where his buddies can just shoot your butt.

Oh wait, it is on the Internet so it must be true!!!

 

[John C. Ratliff]

This may clear up some of the advantages of the configuration of the A.I.R. I with independent doubles, using a separate regulator for each side. By the way, I have looked again at the interstage pressures, and found out some interesting things. First, my pressure gauge is old, and starts at 10 psig. So I should have removed 10 psig from the previous readings before "publishing" it here. If you'll look below, I have done some comparisons of different configurations, and have the photos below. I have traded the second regulator from the Dacor Olympic to the AMF MR-12, as its profile is better. I also have removed extraneous hoses, and so this is not a dive configuration, only a test configuration (I need a LP inflator, an octopus, and my computer on this system rather than straight HP pressure gauges). Finally, I turned one cylinder around so that they both faced the diver.

I have a full steel 72, at 2100 psig, and the two 52 cubic foot steel cylinders at 600 and 500 psig respectively. So I'm getting an interesting combination of different configurations and cylinder pressures. Here are the results:

Steel 72, 2100 psig with Scubapro as a single hose regulator

IP: 135 psig
Interstage Drop, hard inhalation: 110 psig
Interstage Drop, easy inhalation: 118 psig

Steel 52, 600 psig with Scubapro as a single hose regulator

IP: 125 psig
Interstage Drop, hard inhalation: 105 psig
Interstage Drop, easy inhalation: 115 psig

Steel 52 ID, 500 and 600 psig with Scubapro and MR-12

IP: 125 psig
Interstage Drop, hard inhalation: 110 psig
Interstage Drop, easy inhalation: 115 psig

Steel 72, 2100 psig with Scubapro as a two hose regulator (2 LP lines off 1st stage)

IP: 135 psig
Interstage Drop, hard inhalation: 110 psig
Interstage Drop, easy inhalation: 120 psig

Steel 52, 600 psig with Scubapro as a two hose regulator (2 LP lines off 1st stage)

IP: 125 psig
Interstage Drop, hard inhalation: 105 psig
Interstage Drop, easy inhalation: 115 psig

Steel 72, 2100 psig & Steel 53 at 600 psig, with Scubapro and MR-12
IP: 135 psig
Interstage Drop, hard inhalation: 115 psig
Interstage Drop, easy inhalation: 120 psig

What is interesting about this is that the interstage pressure varied with the cylinder pressure, even though this was a flow-thruogh balanced piston design and a balanced diaphragm design. What's happening here?

Looking at the data, however crude, it seems that there is an advantage to the two regulator feeding the one second stage, and therefore Scubapro's proclamation in their technical manual is upheld, but only for two first stages feeding the A.I.R. I. The data for single hose verses double hose off the same first stage shows no advantage.

I do not have the ability to look at this in the water, or look at flow rates themselves. But with two first stages there is an advantage to the diver in interstage pressure drop.

I have also recently been given by my LDS a second A.I.R. I, which I have disassembled. You can look at the difference in design, as this is one of the first balanced second stages manufactured in the USA (1979).

SeaRat

 

[lowviz]

...//... this is an interesting concept that I hadn't considered before. ...//...

Front-to-finish, this defines my interest.

I think that you, like most, consider change to be something that must always be better to allow for progress. Change that uncovers hidden weaknesses is also progress.

---------- Post added September 25th, 2013 at 10:16 PM ----------

...//...Oh wait, it is on the Internet so it must be true!!!

I agree that it is a stretch, one of those persistent irritations that I can't put to rest. I'd love to find something solid to prove/disprove. Does England have a "freedom of information" equivalent?

 

[Akimbo]

This might give you a better appreciation for the state of the art in WWII:

…
I have read that the need for lower oxygen levels for divers and combat swimmers wasn’t discovered until WWII. Initial limits were determined in animal and dry human chamber tests. That research was driven more by the needs of caisson workers than divers. Several combat swimmers blacked out within the “established limits” before anyone thought to actually test divers underwater (chamber “wet pot&#8221. Those studies set the limit in the UK for pure oxygen in the water at 33'/10 Meters (1940s). It was 25'/7.6 M in the USN by the 1960s.

Wikipedia has a short reference to it:
Oxygen toxicity - Wikipedia, the free encyclopedia...

This is consistent with Robert H. Davis’ book Deep Diving and Submarine Operations. Nobody was going to wrestle like Mike Nelson in the head-to-foot drysuits that the Brit divers had to use.

Some desk-bound bureaucrat under the streets of London might have proposed the idea and got it stamped Top Secret, but nobody at the Admiralty’s Experimental Diving Unit or the commandos themselves would have taken it seriously. It would be fascinating to follow the linage of this one.

 

[John C. Ratliff]

IDK, here is all I "know" about it:

"Perhaps the best-kept secret of WWII was the use of oxygen-enriched air re-breathers by the British commandos defending Gibraltar. Those attacking the British stronghold were using 100% O₂ re-breathers. The deeper maximum operating depth of the British mixes (45-60% O₂) was a distinctive underwater combat advantage since opposing divers (using 100 % O₂) would be at “convulsive depths” while the British divers was still within their operating parameters. A major component of the British strategy was to simply take the opponent down until convulsions overwhelmed the enemy diver. This secret was so well kept, that much of this was not even revealed to the US Navy until the 1950’s."

reference:
Eanx History

I did some searching on the Rubicon Foundation Research Repository, and found only one real reference to the history of rebreathers:
A HISTORY OF
CLOSED CIRCUIT OXYGEN
UNDERWATER BREATHING APPARATUS,
by ,
Dan Quiok
Project 1/70
http://dspace.rubicon-foundation.or...56789/4960/RANSUM_Project_1-70.PDF?sequence=1

There is only one reference to mixed gas, and that was at the very end of this document:

...The next logical stepin design to be investigated is a closed circuit mixed gas
breathing apparatus, with some form of electronic oxygen
sensor which would allow the exact amount of oxygen to be
introduced into the circuit for any given depth, thereby
keeping the oxygen concentration in the breathing bag at a
safe level at all times. This type of set is in development
at the present time in the United States.

SeaRat

 

[DaleC]

From what I've read about WWII, divers rarely, if ever, encountered each other UW. They were used mainly for salvage/ship repair, sabotage (planting mines), counter sabotage (finding and removing mines), LZ recon and piloting manned torpedoes.

Frogmen: First Battles by W. Schofield, P.J. Carisella. 1989 Branden Publishing (Italian)
The Final Dive: The Life and Death of Buster Crabb By D. Hale. 2007 Sutton Publishing (British)
Underwater Warriors by P. Kemp. 1999 Brockhampton Press (British, Italian, Japanese, German)
The Naked Warriors by F.D. Fane, D. Moore. 1956 US Naval Institute (US)

 

[lowviz]

From what I've read about WWII, divers rarely, if ever, encountered each other UW. ...//...

That is what I always thought. I would expect exciting stories being told and re-told (from both sides) about such encounters if they ever happened.

 

[halocline]

John, I'm pretty sure that the way you're measuring IP drop is not entirely reliable for dynamic IP drop. I have a strong suspicion that as air is moving in the hoses, it causes a venturi effect that influences the action of the needle in hobbyist level IP gauges. The way you have yours set up seems better in this regard than using one at the end of the LP inflator hose, at least if I'm seeing what I think I am in your photos, but I would still not trust the accuracy of measuring dynamic IP drop without better test equipment.

I realize that by using two tanks, you're essentially doubling the volume of IP air available to the 2nd stage at any given instant. This does certainly mean theoretically less IP drop during inhalation, which does translate theoretically into improved 2nd stage performance. But you could easily get the same effect simply by using a MK25 on a long hose. And since, as I'm sure you understand, the center balanced valve on the air1 is somewhat less biased for downstream force than conventional 2nd stages, the air1 reacts less to changes in IP. In other words, drop in IP also means drop in the upstream force against the balancing spool. You might be able to 'see' better performance on a graph, but I guarantee that you would not be able to tell any difference in actual diving between your set up and simply using a higher performing 1st stage with a long hose set at the same IP. I suggest you try borrowing a MK25 or MK20 with the composite piston (that piston has a VERY strong flow rate) and try your measurements again, but mostly just try it on a dive. Chart measurements in scuba regulators don't tell the whole story.

But the real objection I have to your post is calling this 'perhaps the most advanced..." and titling the thread "most redundant..." It's neither of those things; in fact it's really the opposite of redundant, unless there's something I'm not seeing correctly. If you had simply said "here's an interesting experiment based on an old SP technical bulletin" or something like that, you'd get no objection from me anyhow.

One last point, you could likely improve the performance of your air1 by changing the poppet to one of the metal stem versions. I don't know why it is, but when I bought a bag of those and started using them on my converted pilots and D300s, they noticeably improved, primarily in cracking effort stability.

 

[victorzamora]

halocline, I believe we're seeing eye-to-eye on a lot of this.


lowviz: I hate to use definitions again, because I HATED that entire section of this thread. However, I'm at least not cherry-picking a definiton. Most of the definitions on this page allude to (or specify) improvement as part of progress. So, yes, I believe that change has to be for the better to allow for progress. Changes must occur to determine if it's getting better (progressing)....but this is NOT a case of progression.

Progress | Define Progress at Dictionary.com