Progressive Equalization

[BobbyT22]

Hello Everyone. I recently read about a technique for use with manifolded doubles with an isolation valve called "Progressive Equalization". Briefly, it involves diving manifolded doubles with the isolator closed, giving you in essence independent doubles. During the dive you breathe from one tank only, and leave the other alone for redundancy. When you reach a pre-determined level on the designated tank (say every 1000 psi), you open the isolator to equalize the tanks, then close it again. I think this technique might have applications for solo diving. I did a cursory search of this forum and did not find any threads describing this technique as an alternative to either independent doubles or a dedicated pony. Does anyone here use this technique for solo diving? It seems to me that it could be a useful way to get the benefit of independent back mounted doubles, using tank equalization instead of reg switches to maintain trim. Thoughts?

 

[Akimbo]

I have been using progressive equalization since learning the technique from ex-British Navy divers around 1974. We didn’t have isolation manifolds then but did have doubles with individual cylinder valves that manifolded together to support a single regulator. A lot of doubles in Scandinavia and northern Europe were like that, as well as doubles in the US with an inexpensive adapter manifold. I preferred the adapters to the standard US doubles manifold which used metal to metal seats instead of O-rings in those days.

My most recent sets of valve-down doubles were built because complying with the SDI solo card requires a redundant gas source. Of course modern doubles with an isolation manifold and two regulators meets the criteria. I got the solo card to let charter boat skippers off the liability hook. Probably about 80% of my recreational dives have been same-ocean-buddy or nobody-on-the-beach solos most of my life.

To be honest, I am more comfortable with them. I would be perfectly happy to dive solo with a single regulator but progressive equalization makes it pretty darn difficult to get distracted and run low on gas.



Progressive equalization is discussed in these posts:

Nigel's twinset rig

http://www.scubaboard.com/forums/ad...y-bailout-strategies-recreational-diving.html

http://www.scubaboard.com/forums/tanks-valves-bands/393392-double-valve-single-tank.html

http://www.scubaboard.com/forums/vintage-equipment-diving/397498-baby-doubles.html

http://www.scubaboard.com/forums/tanks-valves-bands/399622-isolation-manifold-question.html

http://www.scubaboard.com/forums/tanks-valves-bands/394714-custom-manifolds.html

http://www.scubaboard.com/forums/ad...-cant-reliably-reach-doubles-valves-help.html

http://www.scubaboard.com/forums/ba...cuba-tanks-set-up-like-firefighters-scba.html

 

[BobbyT22]

Akimbo, thanks for your quick and indepth response, although my thread-search skills obviously need some work! It is good to know someone with your experience uses this technique.

 

[Akimbo]

Akimbo, thanks for your quick and indepth response, although my thread-search skills obviously need some work!...

Here is the search trick I learned from HowardE, scroll down to Post #12

http://www.scubaboard.com/forums/basic-scuba-discussions/404059-points-failure.html

BTW, this thread is also useful to help you analyze failure potential.

I must use this trick several times a day on different sites.

 

[Akimbo]

… It is good to know someone with your experience uses this technique.

Very flattering, but I didn't invent it and it isn't exactly rocket science. It isn't much different than using independent doubles except you have more way-points to trigger events. This thread is a good discussion of http://www.scubaboard.com/forums/ad...y-bailout-strategies-recreational-diving.html

Thread #30 starts comparing and debating the trade-offs between pony, independent doubles, conventional isolation manifold use, and beyond. Every system has advantages and drawbacks; nothing is free. For solo, I personally find the "hard reserve" aspect attractive. However, a leaking valve or sloppy operation can blow the advantage. Ultimately, I recommend avoiding solo deeper than you can perform a free ascent.

 

[BobbyT22]

WOW. Thanks for all the links. There is a ton of info there and it will take me awhile to get through it all. Great discussions though, and exactly what I was looking for. Also thanks for the heads up on the google trick.

The baby doubles thread is particularly germane to my latest exploits as I am assembling a pair of LP45 doubles myself. No particular reason other than they look really, really fun. I can't wait to try them out, they look about perfect for poking around my local quarry when I can steal a day for myself to dive alone. I'll probably stick with my current HP120 and slung pony for any ocean dives I do, but cruising around with some little doubles looks like it would be a blast.

Rob

 

[japan-diver]

I can not see any advantage to doing this with a set of manifolded doubles. It does not eliminate any failure points there are as many negatives as positives for this scenario. If you already have the isolation manifold why bother with this procedure? If you have independent doubles then keeping them within 500 psi is a good idea but why add the hassle of doing this if you already have a method in place to keep them equal the whole dive??

 

[BobbyT22]

In my mind, the difference is not having to reach back and close the isolator if there is a failure. It is already closed, and only opened a few times during the dive intentionally. You are not reducing the number of failure points, rather eliminating the need to act if a failure does occur. Your backup is already isolated, so you just switch to it and ascend slowly.

Given that situation, I would think that some would say it is better to do independent doubles and just switch regs. The rationale being that it really isn't any harder to switch a reg than open a valve, you save the failure points of the isolator (but gain an addtional spg) and I guess they have a point. But I don't have any experience with this technique, hence my originial question. I am just getting through the threads mentioned by Akimbo, and the one about failure points really addresses just this point better then I could ever could.

 

[Doppler]

Sidemount diving... the solo diver's friend?

The technique (and variations of) outlined above was developed for a specific application. Although it can be adapted for recreational (sport and technical diving) it is probably unnecessarily convoluted for the majority of divers since it requires multiple actions and the insertion of waypoints into a dive's normal flow. If one is diving with a set of twin with a manifold, slightly modified gas management rules will help maintain life support within acceptable parameters for a solo diver. In addition, diving this configuration requires action from the diving ONLY in the event of a gas hemorrhage. I dived with a standard North Florida Cave Rig (doubles, manifold, etc.) for about 20 years. It was necessary for me to shut my isolator two, perhaps three times during that period: approximately 2,000 dives. You can dive however you wish, but do think about risk management. Which "action chain" do you believe is more likely to break. One that requires action several times per dive or one that MAY require the same action once in several hundred dives?

The failure points here are not equipment-based but something that needs to be planned out of diving as much as possible... human error.

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

 

[Akimbo]

The advantage of keeping the isolation valve shut is simple. If failure on the HP side of the first stage occurs (valve-cylinder O-ring, regulator O-rings, or blow out plug) when you are at or near your minimum reserve gas limit, all the gas lost in the time it takes to close the isolation valve is lost. If it occurs when the isolation valve is closed then you are in the same position as if wearing independent doubles. The added advantage you can't breathe all your gas done down due to distraction of oversight.

I have always preferred valve-down as do commercial and rebreather divers, firefighters, and miners. Even Cousteau's rigs were valve down for their reserve cylinders. Valve-up is what is silly if you really think through the ergonomics. Unfortunately, there aren't any really great protectors on the market at the moment.

I will be out of town for about a week so will continue the conversation then.