Progressive Equalization

[Stoo]

I occasionally dive with my manifold closed, but generally only in the very early (i.e. friggin' cold) part of the season, when the odds of a freeze-up is amplified. To be honest, I'm not convinced there's a huge advantage as Doppler points out... it's about a 3 second exercise to isolate and only a few more to shut down the post. (I think I do it because I practice isolator shutdowns and the "swoosh" of tanks equalizing tanks is confirmation that everything is working as it should!)

If someone was to do this enthusiastically, and assuming that they are in frigid water as I am in the spring (Great Lakes), I would not let the differential pressure get as high as 1000 psi. I suspect that there is some risk that this could increase the odds of condensation forming in the higher pressure tank as it quickly equalizes. Any condensation at all could cause havoc with regs freezing, as well as drysuit and BC inflators.

The other downside of diving with the isolator closed is the SPG doesn't reflect the actual PSI in the right tank (assuming you are diving the typical configuration). This could be remedied by adding a second SPG to the right tank, but this alone increases potential failure points, and possibly increases a divers tasks to perform.

As a matter of course, I tend to have my isolator only open a small amount so that shut-down could be accomplished in a turn or two.

All of this reminds me it's time to start stretching my shoulders out again...

 

[MichaelMc]

@Akimbo, What about the risk/physics of water intrusion into the empty cylinder? A current thread, BSAC avoids annual VIP, and other threads describe common water intrusions from tanks being run dry.

On land I can breath even my unbalanced regs to empty, or removable with no gas hiss, so presumably I can breath the tank down to ambient.

The risk is different than in breathing down a reg during sidemount valve drills, where only the reg is empty or at ambient.

I like the idea and want to try or use it once I get tiny doubles.
(This old thread seemed the main one on progressive equalization.)

 

[Akimbo]

What about the risk/physics of water intrusion into the empty cylinder? A current thread, BSAC avoids annual VIP, and other threads describe common water intrusions from tanks being run dry.

On land I can breath even my unbalanced regs to empty, or removable with no gas hiss, so presumably I can breath the tank down to ambient.

There is less risk of accidently breathing a set of doubles down to ambient using progressive equalization because you have quite a few warnings that can't be ignored. Problems like distraction, zero visibility (can't read gauges), or gauges/computers that misread the pressure can't cause a diver to run out of gas without several warnings.

 

[MichaelMc]

There is less risk of accidently breathing a set of doubles down to ambient using progressive equalization because you have quite a few warnings that can't be ignored. Problems like distraction, zero visibility (can't read gauges), or gauges/computers that misread the pressure can't cause a diver to run out of gas without several warnings.

Thanks. I'm not arguing against the merits of the system in low/no vis.

If you were to use it in calm clear water, you're suggesting you should not actually breath it down to vapor each time, but rather maybe keep an SPG on that side and watch the pressure to learn to stay away from the low low 100s. I've once breathed an unbalanced reg to 0 on land, but not routinely experienced breathing down low an unbalanced or balanced reg during routine diving.

Would you particularly recommend unbalanced regs with it? I guess I can watch and see once I configure a doubles set.

Edit: and I guess do a land test to see where that right SPG's 0 actually is.

 

[Akimbo]

I have never been able to breath a cylinder down to zero without unmistakable increased breathing resistance. I may get it down to around 30 PSI/2 Bar by sucking really hard and slowly, but I notice increased resistance around 90 PSI/6.2 Bar, even on a balanced piston first stage and servo second stage.

 

[Bob DBF]

It's about making things simple folks... why bother trying to invent a better mousetrap... the ones we have already work just fine.

Since progressive equalization was used before the modern manifolded doubles were invented, if someone didn't invent a better mousetrap, we'd all still be using a single reg in the middle of an old school manifold, or cheater bar.

Whether it is a better plan for a individual and their diving is the discussion. In my case it makes sense for me because I still dive old school doubles and my range of motion isn't as good as it once was.


Bob

 

[MichaelMc]

I’m intrigued for open water tiny doubles solo because of the hard reserve, and a bit of built in OOG practice.

 

[Akimbo]

General Info:
The original Cousteau triples used one cylinder as a hard reserve. As I understand it, the procedure was to leave bottom when opening the valve on the bottom of the reserve cylinder. Of course, all three cylinders equalized.

It is all a question of trying to find the most versatile option using two cylinders. It basically comes down to independent doubles versus doubles with an isolation valve. The safest option is to have a team of well-paid professionals babysitting you every second who pack all the extra gas that you don't have to worry about.

 

[Bob DBF]

The safest option is to have a team of well-paid professionals babysitting you every second who pack all the extra gas that you don't have to worry about.

At that point you might as well go back to surface supplied and make it easier on everyone.


Bob

 

[John C. Ratliff]

General Info:
The original Cousteau triples used one cylinder as a hard reserve. As I understand it, the procedure was to leave bottom when opening the valve on the bottom of the reserve cylinder. Of course, all three cylinders equalized.

It is all a question of trying to find the most versatile option using two cylinders. It basically comes down to independent doubles versus doubles with an isolation valve. The safest option is to have a team of well-paid professionals babysitting you every second who pack all the extra gas that you don't have to worry about.

Have you thought about using independent doubles with two first stages hooked into a single second stage (Scubapro AIR-1, or Pilot)? I put such a rig together a while back, and it works very well. I have enclosed photos of the Cousteau triples as well as my independent doubles. You have to synchronize the two regulators so that they both have the same interstage pressure, and you can either draw the two independent tanks down simultaneously, or in series (but orient the valves differently than I did, as the way depicted would be hard to implement underwater.

SeaRat