Can a first stage "overpower" a cheaper octo?

[tc]

Hmmm ... You OBVIOUSLY need THIS stuff!!!

Ow......OW.......OW!

Why is my head starting to hurt when I get near this thread?

 

[snowmaker]

I almost bought an Apeks ATX200 until I heard about this issue, initially from the LDS and from Apex. I emailed Apeks to confirm the statement. I heard at around 100 ft, the non "over balanced" octo would start to free flow as the IP pressure increased. In the end, I did not buy the reg. I did not like the concept and thought it would have problems over time.

I doubt Apeks is lying about this. (Is it possible I drank the kool-aid?) If they were, I suspect there would be more comments on the web on this topic. I am not willing to buy the reg, use my old octo and see what happens. However, it would be great if someone on SB ran into this issue and shared the experience. Apeks/Aqualung makes some good regs. I doubt they are lying about this.

There is another option, don't buy an "over balanced" regulator. There are plenty of great regs that match their performance.

Tom

I have an Apeks 200 and have dived passed 100' with both Scubapro and Mares regs hooked to it with no problem. Guess I am one of the lucky one to have made it back.

 

[ChrisA]

I'm looking at upgrading to the Aqualung Lexend lx. When I was at my LDS the sales guy told me I would also need to spend $240 on the legend octo because my Mares Brigade was not good enough and would be overpowered by the legend 1st stage, causing a constant freeflow. Anyone heard of this before or is the lds just trying to take me for an extra 240?

He is almost right but for the wrong reasons. Different regs have different intermediate pressures (IP) if the first stage puts out 160psi and the second stage wants 140psi you are setting up for free flow. Mostly this can be adjusted and made to work. But you really are best off getting a first and second stage that can use the same IP setting. Most are close I think the LX is like my Apex and uses more pressure at depth (reverse balanced?) so yu do want an octo that can handle it. That said I think most can.

 

[DA Aquamaster]

Interesting... I'm familiar with the market-speak of an 'over-balanced' 1st, but never gave it much thought since I don't presently dive one. What exactly does it mean in terms of IP psi/fsw? Or is it a more likely a curve? Has anyone actually seen a measurement or spec of IP delta @ depth for an 'over-balanced' reg?

Why create a design with this characteristic? It doesn't affect balanced 2nds and it could affect unbalanced 2nds.

In my opinon it is pretty much marketing BS.

The effect, if any, would be linear as it would be created by having the pad or diaphragm that controls ambient pressure be slightly oversized relative to the internal area so that the intermediate pressure would rise farther and farther above ambient pressure as depth increased.

If this really occurred, all "overbalanced" regs would eventually begin to freeflow at depth due to excess intermediate pressure - unless the second stage were not designed with a downstream bias, which would mean there was now no safety mechanism to vent excess IP in the event of a leaking high pressure seat. This would ultimately result in failure of a hose (catastrphic air loss) or the low pressure inflator (uncommanded and uncontrolled inflation of the BC) at depth. Both are firmly in the "really bad things to happen on a dive" category.

Plus, if the IP increases at depth the reg becomes hard to tune since you would be tuning for the higher IP at depth which in essence means it will breathe like a rock in shallow water or at a minimum require more diver adjustment using the inhalation resistance knob at depth.

In practice I don't see the effect as I have tuned "overbalanced" regs and never had a customer come back complaining that it freeflows at depth, so the effect if any is small. Plus I have seen many with non balanced and non adjustable octos that again should be freeflowing at depth if the effect is significant.

The purpose of overbalancing is to offset the decrease in gas flow occurring at depth where the air passing through the first stage is now much denser and according to some marketing folks much more viscous. The problem with that reasoning is that it is pretty much BS, it is denser, but it flows just fine and any benefit in flow rate from increasing the IP a few more psi is totally insignificant. And personally, I would question the wisdom on using any reg at depth where the flow rate would noticeably improve by increasing the IP slightly. If it is that close to being inadequate, it does not belong on a deep dive. In practice, I have yet to encounter a high perfromance reg that does not have more than enough flow rate for supporting two divers at depth and in all cases the second stage is the limiting factor anyway as none of them flow more than 65-70 SCFM and a good first stage will deliver 150 SCFM with the highest performance first stage available delivering 300 SCFM.

So there is absolutely no need for overbalancing and if it exists it's only contribution to the diving world is as a marketing gimic to sell regs to divers ho are being misled and to generate discussion on on-line forums.

 

[PhilEllis]

He is almost right but for the wrong reasons. Different regs have different intermediate pressures (IP) if the first stage puts out 160psi and the second stage wants 140psi you are setting up for free flow. Mostly this can be adjusted and made to work. But you really are best off getting a first and second stage that can use the same IP setting. Most are close I think the LX is like my Apex and uses more pressure at depth (reverse balanced?) so yu do want an octo that can handle it. That said I think most can.

I personally don't agree that you are "better off" getting one octopus over another. Almost ALL regulators on the market currently specify an intermediate pressure of between 135 PSI and 145 PSI. All second stages on the market are designed to operate well anywhere in this range, and most can be adjusted to operate perfectly to pressure up to 30 PSI above and below this range.

The "overbalanced" feature of such regulators may well result in a very slightly elevated pressure/depth curve. My experience is that this additional increase is less than 6 or 7 PSI at depths up to 160 feet. This is hardly enough to cause a problem with most second stages I am familiar with. It CERTAINLY will not cause a problem with a balanced second stage.

I would not accuse anyone of simply providing complete market buzz by claiming a benefit from a feature that is not there. Unfortunately, they come VERY close to this with the claim of "overbalancing" to acheive "improved performance" at depth with these regulators. The addition of a few additional pounds of pressure would not be noticed by even the most attentive of divers.

My Opinion: I think the aging and resulting changes in physical properties (slightly hardening with age) of the external environmental diaphragm over time would have more impact on pressure changes at depth than would any "designed" attempt to provide a slightly larger surface area on that diaphragm to acheive an increase in the IP curve at depth. A GIGANTIC difference in the size of those two diaphragms might cause a noticable change, but the two diaphragms in questions are almost the exact same size. Oh well.

Phil Ellis

 

[innocent bystander]

I almost bought an Apeks ATX200 until I heard about this issue, initially from the LDS and from Apex. I emailed Apeks to confirm the statement. I heard at around 100 ft, the non "over balanced" octo would start to free flow as the IP pressure increased. In the end, I did not buy the reg. I did not like the concept and thought it would have problems over time.

I am currently using a Legend LX 1st and 2nd stages with a 20year old Conshelf occy have taken it to a max depth of 40m with no problem.

 

[Sam G]

I know this is old but I'm wondering if anyone has learned anything in the last two years. I bought an Oceanic FDX-10/Delta4 ('overbalanced'), and got an Aqualung Titan Octo (unbalanced) cheap from a friend. I was totally unaware of this issue until leafing through the Titan manual and it says it's not to be used with an overbalanced 1st stage.

The octo has a venturi adjustment that I could conceivably turn down if there was some leaking....

Thanks if there is anyone with some more experience in the matter.
-Sam

 

[Sam G]

In my continued research I found this old post. Clearly the FDX-10 1st stage is compatible with the Alpha 8 octo, which is unbalanced. I think this is much ado about nothing (but please, please correct me if I'm wrong).

Quote:
__________
With this hot deal you receive a free Oceanic Alpha 8 Octo with the purchase of an Oceanic Delta 4 Regulator. Completely configured and ready to dive.

Here's how it works.... Put the Delta 4 regulator in your cart, proceed to checkout and put in discount code sbdelta4 , an Oceanic Alpha 8 will be automatically be added to your cart free of charge.

Don't forget that all orders shipped to the USA receive free shipping. Offer Expires: 11/18/09

Delta 4 Regulator:


The Oceanic Delta 4 is one hot new regulator ready to take on all challengers with improved performance, new features, improved styling, and the new FDX-10 First Stage featuring DVT ( Dry Valve Technology). Even with the best laid dive plans, there are times you encounter conditions beyond your control. That's why you can count on Oceanic's Delta 4.

• Diver adjustable inhalation effort
• Patented Dynamic Adjustment automatically maintains inhalation effort throughout the dive
• Adjustable Venturi Switch (A.V.S.) for simple Dive/Pre-Dive Adjustment
• Paired with the new FDX-10 Over-Balanced Diaphragm First Stage featuring Oceanic's DVT (Dry Valve Technology)

Oceanic Alpha 8 Octo


The Oceanic Alaph 8 Octo gives the same rugged design as its primary counterpart Large high visibility purge button is easily identified in an emergency. High visibility yellow hose making it easy for the out of air diver to locate that next breath.

• Lower Profile Second Stage
• Easy to Maintain
• Great Price to Performance Ratio
/quote

 

[halocline]

You can try it, but I don't think you'll have much of a problem. The whole idea of "overbalancing" which BTW is a BS name, it should be "over-depth-compensating", is pretty idiotic to begin with. I am certain that substantial increases in IP over increases in ambient would cause all kinds of problems with inflators, some 2nd stages, etc. The truly dumb thing about this is that balanced 2nds simply take the increase in IP and use it to increase cracking resistance, so the whole concept is a wash. Sure, there's theoretically increased flow at higher IP, but since the 2nd stage is always the limiting factor in flow anyway, there's essentially nothing to be gained. Oh, except another opportunity for a sales rep to push it, I guess.

Just tune your octo a little stiffer, or tune it to a slightly higher IP, whatever you think the 1st stage might be putting out at maximum depth, and then dive with it.

 

[herman]

Hi Sam, you might find this thread interesting, http://www.scubaboard.com/forums/ge...ons/318255-mixing-matching-2.html#post4960088

And, the venturi adjustment has no effect on slight freeflows but it will be of some assistance in stopping violent freeflows which are different than slight, gental freeflows.