Balanced VS Over-Balanced Regulators

[DA Aquamaster]

So it's not true that the second stage is so well balanced that the IP won't affect the way the second stage behaves. It does, and the fact that the second stage won't vent when the dial is turned down really isn't relevant to whether it does or not when it is adjusted fully open.
The effect would be subtle, but these days differences in breathing effort in high performance regulators are subtle, so that's all it takes, if it indeed works.

Please bear in mind I'm not arguing for Apeks or their overbalanced design. And I agree that it is a problem that the second stage can be dialed down such that it won't vent within reasonable IP. I just don't agree that we can dismiss the overbalancing as complete BS due to those particular arguments.

Lower is not neccesarily better when considering inhalation effort. Below minimum levels, the lighter inhaltion effort is not useable and if that same unusuable level also creates a safety issue than you are creating a solution to a non problem that in turn results in a major problem.

Due to issues with case gemoetry fault in second stages using a conventional case layout, you cannot readily use an inhalation effort much below about .8" of water as the differing ambient pressure effects between the center of the diaphragm and the top of the exhaust valve when you are in a face down position or in a normal swimming position will result in air leaking from the case lowering the pressure enough nside the case to depress the lever enough to open the valve slightly and create a slight freeflow between inhalations.

Balanced poppets are readily capable of producing inhalation efforts in the .5" of water range already so any additonal reduction inhalation effort due to over balancing the first stage and by neccesity not designing in adequate downstream bias in the second stage would result in an "improvement" in halation effort that you can't even use.

 

[John_B]

Can someone explain why would you turn the cracking adjustment all the way down on the backup to begin with? Why not limit any potential second stage freeflows with the venturi switch instead of the cracking adjustment?

On a semi-related question, do the EU market XTX second stages still have the same cracking adjustment limiter that the ATX/TX seconds used to have?

John

 

[Luis H]

I know, one of the local divers here blew his stops due to this exact issue and went to the chamber. He then sold all his Apeks and got Scubapros.
But this was on the left post of his doubles setup, with one second stage that was turned down all the way.
Another of the local divers did an experiment with Apeks second stages after the above incident, varying the adjustment dial and IP.
With the cracking effort dial in the open position, the second stage vented fine.

So it's not true that the second stage is so well balanced that the IP won't affect the way the second stage behaves. It does, and the fact that the second stage won't vent when the dial is turned down really isn't relevant to whether it does or not when it is adjusted fully open.
The effect would be subtle, but these days differences in breathing effort in high performance regulators are subtle, so that's all it takes, if it indeed works.

Please bear in mind I'm not arguing for Apeks or their overbalanced design. And I agree that it is a problem that the second stage can be dialed down such that it won't vent within reasonable IP. I just don't agree that we can dismiss the overbalancing as complete BS due to those particular arguments.

Of course, I use Atomics and also sold my two Apeks a couple years ago to get more Atomics, so I guess I don't care too much. Uhh.. except I guess that I have a number of buddies using Apeks.

The malfunction I am referring to on my friends regulator was over a year ago, but I am fairly positive that I checked it with the adjustment knob all the way out. I didn’t have an IP gauge with me at the time, but I tried what I could to isolate the problem.

He ended up borrowing one of my spare regulators (I always carry a couple of spares for situations like this). I gave him a choice between an almost mint condition Scubapro MK-5 or a double hose regulator. He jumped on the opportunity of trying a double hose. I didn’t mention until later that he was using my prototype experimental Phoenix regulator. There was no risk, but it sounded cool after the fact.


You are correct in that I should have been more precise in the following statement:
“I am aware of at least one brand that the second stage is so well balanced that an increase in IP will not affect its performance”
I should have used adjectives like: barely, or unnoticeably, insignificant, etc., etc.

The point is that the second stage is design to not take full advantage of the over pressure feature.

The sealed first stage is IMO a good thing. My wife’s regulator uses a sealed Aqua Lung Titan first stage (with a Scubapro D400 second stage).


The experiment your friend did is very significant, but I am sure you are aware that is only one data point. Unless he tested several, 3 or more, it is not statistically significant.

That would be like me assuming that all Apeks are failure prone because out of my four friends that own Apeks three have had major failures within a year of owning them. Three out of four is a statistical anomaly, but the sample is not large enough to draw a definitive conclusion. I will admit that I am not impressed; in 36 years of diving and servicing regulators I have never seen such a coincidence with any other brand.

I don’t own an Apeks and don’t see any reason for ever owning one. So it doesn’t matter much to me either, I just find the different technologies and mechanisms interesting.

I actually own some new regulators, but only dive 30 year old classic regulators. I have yet to find any significant improvements in regulator design in the past 30 years.

As an engineer I am always interested in new technologies. But, I am not always impressed with some of the modern trends. Many seem driven by marketing and of course cost cutting. Cost cutting is important and a worthy cause in moderation.
I am particularly not impressed with some of the material selection, both synthetics and metal alloys being used now a day.

 

[Randy43068]

I know this is an old thread, however, a good one.

Forgive my ignorance, here, but considering the design of a power inflator I find it very hard to believe that the power inflator would be forced open with a very high IP.

When you say "turned down all the way" you're saying the knob was turned fully clockwise which would cause the second stage poppet to require more pressure to open?

My wing inflation is from the right post as is my primary regulator. I would think most other doubles are set up in similar fashion. Given that, how could the wing inflator be over-powered into inflate mode?

I know, one of the local divers here blew his stops due to this exact issue and went to the chamber. He then sold all his Apeks and got Scubapros.
But this was on the left post of his doubles setup, with one second stage that was turned down all the way.
Another of the local divers did an experiment with Apeks second stages after the above incident, varying the adjustment dial and IP.
With the cracking effort dial in the open position, the second stage vented fine.

So it's not true that the second stage is so well balanced that the IP won't affect the way the second stage behaves. It does, and the fact that the second stage won't vent when the dial is turned down really isn't relevant to whether it does or not when it is adjusted fully open.
The effect would be subtle, but these days differences in breathing effort in high performance regulators are subtle, so that's all it takes, if it indeed works.

Please bear in mind I'm not arguing for Apeks or their overbalanced design. And I agree that it is a problem that the second stage can be dialed down such that it won't vent within reasonable IP. I just don't agree that we can dismiss the overbalancing as complete BS due to those particular arguments.

Of course, I use Atomics and also sold my two Apeks a couple years ago to get more Atomics, so I guess I don't care too much. Uhh.. except I guess that I have a number of buddies using Apeks.

 

[knowone]

People started out routing their hoses how they wanted then argued about it.
Short inflator hose from the left post was common for streamlining.
Also you sourced whatever wing you could get, that came with many types of inflator, slapped it all together and went.
And if high pressure air gets in, then it has to get out if it's not where it's supposed to be.

 

[aquaregia]

Why are inflators, unlike UW tools, based on an downstream design?

 

[LeadTurn_SD]

I know this is an old thread, however, a good one.

Forgive my ignorance, here, but considering the design of a power inflator I find it very hard to believe that the power inflator would be forced open with a very high IP.

When you say "turned down all the way" you're saying the knob was turned fully clockwise which would cause the second stage poppet to require more pressure to open?

My wing inflation is from the right post as is my primary regulator. I would think most other doubles are set up in similar fashion. Given that, how could the wing inflator be over-powered into inflate mode?

My recollection (which could easily be flawed) was that not only did the problem occur with wing inflators, but with drysuit inflators too.

The thread I'm recalling indicated that Apeks was very aware of the problem, and it resulted in a modification of the 2nd stage poppet and/or balance chamber to ensure that there was some additional "downstream" protection (i.e., the 2nd stage was made less balanced, so it would freeflow if the IP spiked too high)...

Again, this is all from "something I read somewhere", and the person writing it is well-respected and in a position to "know", so I expect it to be reliable.... but maybe not

Best wishes.