Balanced or unbalanced?

[anzac65]

"Overbalanced" as used by aqualung and others to describe their regs as easier breathing at depth has nothing to do with air balancing or otherwise compensating a stage for variance in supply pressure. It's used by those manufacturers to describe a design in which the IP is supposed to increase at depth above and beyond the change in ambient pressure. "Over-depth-compensating" would be a more accurate description, but doesn't have the same marketing ring, does it?

I'm kind of glad you brought it up, because it gives me a chance to rant against another example of BS marketing ploys. The idea is that if the reg has a higher IP at depth, it will deliver more air and be 'easier breathing' at depth. Well, in the first place, as has been discussed in this thread, most higher performance 2nd stages are designed to compensate for changes in IP through diverting downstream air pressure and using a portion of it to provide some upstream counter force. What do you think happens when these balanced 2nd stages see higher IP downstream force from the "overbalanced" 1st stage? They simply provide more upstream counter force.

Then there's the issue of higher IP supposedly providing more flow. The problem here is that any high performance 1st stage already provides WAY more flow than any 2nd stage, or in most cases pair of 2nd stages, can handle under full purge. The MK25, for example, has enough flow potential to theoretically empty an AL80 in under 15 seconds.

I've kind of got lost in all this, but I get the idea that you're implying that marketing people are able to dictate to engineers that they design, at extra expense, features into a product that make actually make it worse. Handbags perhaps, regulators no.

 

[Luis H]

I've kind of got lost in all this, but I get the idea that you're implying that marketing people are able to dictate to engineers that they design, at extra expense, features into a product that make actually make it worse. Handbags perhaps, regulators no.

The so called "overbalanced" is a side effect of a balanced diaphragm first with the addition of a dry environmental chamber. The dry environmental chamber in itself is a very good thing for cold water, contaminated water, and even just plain salt water.

The environmental chamber contains a secondary external flexible diaphragm to allow the sensing of ambient pressure with out allowing water to enter the chamber. The pressure is transmitted by a solid rod from the outer diaphragm to the inner diaphragm since two diaphragms have different stiffness it is very difficult for the effective diaphragm area to match perfectly. Therefore IMO, it is easier for the engineers to just design it with the outer diaphragm just slightly larger effective area than the inner diaphragm. The diaphragms are probably physically the same size, but the inner hp diaphragm is stiffer.

The intermediate pressure increase with depth is proportional to the ration of the effective area of the outer diaphragm divided by the effective area of the inside HP diaphragm.

Notice that I am referring to an effective area. What I am referring by effective area is that the actual diaphragm working area is affected by how stiff the diaphragm is, how it is clamped around the perimeter, etc.


Marketing is just talking advantage of a side effect and trying to capitalize on anything they can. Again the dry chamber in itself is a good thing IMO.

 

[DA Aquamaster]

Given that a second stage has to act as an overpressure relief valve, "overbalancing" as Aqualung/Apeks describes it would have very finite depth limits as at some depth the increased IP will be enough to vent the excess pressure through the second stage. In effect, the second stage would breathe easier as depth increased and keep getting easier right to the point of freeflowing.

Adjustment and tuning of the second stage would also be problematic as you would have to set it for the the maximum anticipated depth and IP and then accept an increased inhalation effort at all shallower depths. Alternatively you would have to rely on a diver adjustable inhalation effort to push back the freeflow point at depth.

In that case it just offers increased workload with no real perfromance gain. As stated above, a high performance first and second stage are already passing enough gas and don't need the minimal increase in flow rate offerred by a slight increase in IP relative to ambient pressure. Air does get more viscous as pressure increases, but it does not really become an issue until you reach depths in excess of 600 ft, and even then enlarging or improving the flow passages is a better solution than further increasing the total presure of the gas to boost flow rate.

Based on all that I doubt if over balancing really occurs in Aualung and Apeks regs, although the reports a year or two ago of unbalanced LP inflators failing and auto inflating at depth on Apeks regs when the HP seat leaks suggests that if such an effect is designed into the first stage that the second stage is no longer engineered to act as an overpressure relief valve - a very alarming condition.

Scubapro also uses the term overbalancing but uses it differently. On the Mk 5, Mk 10 and Mk 15, the piston stem was the same diameter in the middle of the stem, where the high pressure o-ring sealed the high pressure area of the first stage from the ambient chamber, as the diameter of the end of the piston stem where the sealing edge was located. This meant the small but still present area of the sealing edge itself was not actually balanced in relation to the area of the stem passing through the HP o-ring. This resulted in a 4 to 6 psi change in IP as the supply pressure fell from 3300 to 300 psi.

On the Mk 20 and 25, the piston stem has a slightly over sized end of the stem so that the area inside the sealing edge is equal to the area of the stem passing through the HP o-ring. The end result of this "overbalancing" is a truly stable IP that will not change at all with changes in supply pressure.

 

[Tortuga68]

Dry-sealed is indeed a good thing, especially for cold/contaminated water diving

But I'm not sure you're right about overbalanced meaning dry sealed

I don't think that's an accurate description of how a dry-sealed reg works either, but thanks

 

[HenrikBP]

What is the potential IP increase at depth for current Apeks regulators? I realize it is depth dependent, so let's say within recreational diving limits of 130'?

Thanks
Henrik

 

[captain]

Definition of "New and Improved" whatever- cheaper to manufacture, more expensive to buy.

 

[DA Aquamaster]

Actually Luis' definition makes perfect sense. You try to get it as close as possible and then take an engineering side effect of a slight rise in IP with depth and market it as a positive.

 

[Couv]

Dry-sealed is indeed a good thing, especially for cold/contaminated water diving

But I'm not sure you're right about overbalanced meaning dry sealed

I don't think that's an accurate description of how a dry-sealed reg works either, but thanks

I too think that Luis pretty much nailed it with his description, but I have an open mind and would very much like to hear your explanation on overbalancing and dry seal technology.

couv

 

[beanojones]

Just one question about the SR1 for Pescador; I believe that it is a flow through piston very much in the style of the MK25 and Atomic regs, not a floating orifice flow by design like the earlier Sherwoods. Am I incorrect in this? I don't see how Sherwood could be touting this reg as high flow or "technologically advanced" if it were in fact a continuation of the older Sherwood/MK2 flow by design.

Word is that Atomic is making the SR1 for Sherwood.

 

[keyshunter]

What is the potential IP increase at depth for current Apeks regulators? I realize it is depth dependent, so let's say within recreational diving limits of 130'?

Thanks
Henrik

A few years ago, we did an informal experiment along these lines to 155' (the deepest depth we had access to at the time). We used a new ATx 200 on an al 80 with the manual second stage control set to the very edge of freeflow at the surface, and an unbalanced octo which was also set as closely as we could get it to the edge of freeflow at the surface.
Our thinking was that if there was any significant increase in IP at depth, then we should experience some amount of freeflow.
We turned the tank on at about 100' and one of us breathed off of the Atx second intermittantly to the bottom, leaving plenty of time for a free flow to develop. We never had a wayward bubble.

What did we learn from this experiment--ABSOLUTELY NOTHING. But I do have a strong tendency to believe that any meaningful increase of IP at recreational depths is zero. And, I also have a strong tendency to believe that this is yet another example of advertising bull excrement.