Are Atomics worth the cash?

[rsingler]

If that's in reference to my post, read it again because I didn't say ALL positions.

It's a pleasure to respond to someone who writes exactly what they mean. Thanks for clarifying, and now I won't disagree with you regarding your comment about the special virtue of the Atomic when "looking up inverted" as a photographer.

For those who are just watching the play-by-play here, this is the single most fascinating thing about 2nd stages (to me, at least). It's why I like my D-400. It's why I like my Poseidon pneumatic. It's why I'm in awe of Atomic (and Aqua-Lung, and Scubapro) getting great performance out of a fundamentally flawed design. Here I will give complete and unadulterated credit to Mr. Peter Wolfinger, whose (doubtless copyrighted) pictures I comment from so shamelessly.
The chapter in Regulator Savvy on Case Geometry Fault is a light bulb moment of awakening for many of us. When you dive your Atomic and glance down at the bottom at some starfish:
...you must have your cracking effort set to over 1" water to keep your reg from freeflowing slightly, as the pressure of the sea water in which you dive wants to push in on your diaphragm, and initiate an unwanted breath. A pneumatic reg like the Poseidon has coaxial inhalation and exhaust valves, and there is less than 1/2" of height difference between the center of the diaphragm and the highest point on the exhaust valve in ANY position of diving. Add in the diminutive effort required to tilt the little servo valve and you now know why Jetstream divers get a little fanatic about their praise of their gear.
Well, it's the same for the Pilot, Air1 and D-series crowd: In a normal diving position, there's ZERO difference between the inhalation valve center and the highest point on the diaphragm. And when looking straight down (the worst case for the standard regulator geometry), there's about 0.25" difference in height between the two valves. That allows some pretty low cracking efforts. And the flow characteristics of the regulator with its variable Venturi adjustment are similarly impressive (even slightly better than the G-250 and one Atomic that I've tested):

So I love all three! But I'll give diversteve a pass on this one. When looking up inverted (if I understand his comment correctly), his minimum cracking effort COULD be as little as 0.5" if he swam that way all the time.
But then, he'd freeflow slightly most of the rest of the time.
What I'm hearing him say is that with Atomic's standard case design (and its associated case geometry fault), adjusted to a max capability of (say) 0.8" cracking effort, when he's working hard upside down, the reg gives him a gentle freeflow that makes breathing effortless in that position.

All this just reinforces my basic belief that we need to buy the quality we can afford, and maintain it to it's best capability. And if we select special tuning (like 0.7" in a T1), we'll get some special side effects (like a gentle bubbling when looking straight down). It's all good! But when we argue here on SB (unlike diversteve and me) it's probably good to have some facts to back up your assertions.

The OP's thread was, "Are Atomics worth the cash?" Damned right they are! Just maybe not for some of the reasons cited. Seat-saver valves are a perfect example. It was mentioned as a negative, when it is actually a technological addition designed to address a specific problem, which it does very well! Okay, so you have some special considerations when you soak your regs afterward. I'll take that any day, when the benefit is that all I need to do is adjust cracking effort from time to time over a decade, instead of changing a seat every 1-3 years. Elan's got more money than I have, if she'd be willing to let a T1 sit on a stage bottle (if only it didn't have that darned seat-saver valve!). But I'm just picking on her by way of example. Some people like the new tech, some don't. It's all part of the law of unintended consequences.

Would I spend an extra $150 just to have an Aqualung ACD? Nah! I'll save it for my double-hose restoration, and pay a little attention when I disconnect my regs. If I had a bone to pick, it would be with technology that just makes scuba diving more foolproof.

Because that just allows more fools to dive.

 

[rsingler]

BTW, I'll bet that my curve of the Atomic T1 performance is conservative. With it's depth compensating venturi, as the air gets thicker at depth, I'm guessing the venturi effect is more pronounced and inspiratory effort drops even lower. Just can't demonstrate that at Surface Air Pressure with a flow bench.

I'll bet Luis H. can add some perspective here on the relative equivalence of 12 SCFM at the surface with 3 SCFM at 99 ft/4 ATM.

 

[Luis H]

Hi rsongler,

Nice write ups. I agree with most of what you have posted… with one exception.
I don’t agree with this statement: “To me, it's the huge flows of piston regs over some diaphragms (Poseidon excluded).”
I have not seen any actual work of breathing data that shows that the huge flow makes any noticeable difference in performance… especially with a good balanced second stage, a D400 couldn’t care less what first stage it was attached to. I am sure the Atomic second stage performs just fine if it is attached to a Conshelf or its flow through piston first stage.

The breathing performance is mostly driven by the second stage… the only thing the first stage does is keep a reasonably constant IP and a Conshelf does that just fine.

BTW, I used to be very much a flow through piston fanatic back in the 70’s… it is just too bad they don’t make that regulator anymore.



I didn't want to derail this thread, but I think the OP question has been answered, so I will share my opinion about first stages.

First, flow through pistons are great… they are relatively simple (specially the Mk-5) and they have super high flow rate. But, the only practical outcome of the high flow rate is a quick IP recovery during the breathing cycle. That in theory could be noticed if you have an unbalanced second stage… with a balanced, doesn't make much difference.



Now why I like balanced diaphragm (in particular the Conshelf and all its twins)? Primary reason: reliability. It also helps that in is the same first stage (and uses all the same parts) as my 1965 Royal Aqua Master double hose. Using the same parts in all my regulators helps reduce parts inventory.

The Conshelf is the longest production first stage ever. All modern Aqua Lung regulators still use the basically the same internal design as the first Conshelf and the Royal Aqua Master.

In recent years I have purchased over a dozen vintage Conshelf. At least half of them have never been service (they had the original seat from the 60’s or 70’s) and they worked just fine. Many Conshelf first stages can easily go for 40 years without service and work just fine. Is this surprising? Not to me.

My observation is that all industrial pressure reducing regulators are of diaphragm design. Also my observation is that they never get serviced. In the very rare occasion when they fail, they normally just get replaced. Note: my observation does not include all types of industrial application. My related experience is limited to power plants, some petrochemical, marine (Navy and commercial) and a few other.

Many industrial regulators operate in environments that are much harsher than a scuba regulator, both in corrosive environments and temperature extremes.

Also the consequences of a malfunction in an industrial regulator could be much more severe than in a scuba regulator. A failure in an industrial regulator could result in an explosion or a fire or many other disruptions that could easily escalate into a major accident, involving the lives of many. Regulators that are used in a critical application can be very specialized, but everyone I have seen is of diaphragm design.


So how often do I plan on servicing my Conshelfs, Royal Aqua Master, Phoenix RAM, and now the Argonauts? Only when they need it. That could easily be tomorrow if I flood one by accident or maybe in a few decades if the first stage is not abused. At this moment I have a few hundred dives in one of my Phoenix RAM (in several years) and the first stage has not needed any service. When I upgraded the second stage with the HPR, I didn't touch the first stage.



About the flow rate scaling, I think you are in the ball-park, but I will explain more later. This is not just a straight Reynolds number scaling situation.

 

[rsingler]

Awww, Luis! Isn't there a sealed piston guy left in the house?

 

[Luis H]

Awww, Luis! Isn't there a sealed piston guy left in the house?

"Sealed piston"? Are you referring about Sherwood?

 

[Couv]

Hi rsongler,

Nice write ups. I agree with most of what you have posted… with one exception.......

Luis, Luis, Luis.

Only one exception? I was praying RSingler was going to get his wish that you would show up; but for a different reason. You've skipped right over our favorite (one of mine anyway) subject of case geometry. In the past I've tried (and failed) to address some of the faulty conclusions some of my esteemed brethren have come up with re case geometry. I'll have to dig out "the gospel according to Wolfinger" to see if I can figure out why there is such a divergence in beliefs. I suspect it has more to do with how we define what CGF really is. I was/am hoping Luis was/is going to tackle the subject but until then I ask my friends to perform this (thought) experiment. Remove the exhaust valve and tape over the port so that no exhaust valve exist. What effect does this have on CGF?

Cheers,

Couv

P.s. I'm still a piston fan, with or without sealing.

 

[halocline]

Remove the exhaust valve and tape over the port so that no exhaust valve exist. What effect does this have on CGF?

It means you could tune the reg to open at the absolute minimum cracking pressure that is possible for that particular reg, and not worry about it flowing due to differences in depth between the diaphragm and the exhaust valve.

Unfortunately it also means that you could not exhale, except (I guess) through your nose.

Oh, on another subject, I have an extra of Herman's MK5 tools. Any idea why?

 

[Luis H]

Hi Couv,

Controversy… I know there have been some debates in the past, but it really is not that difficult.

In 1943 Cousteau dove a regulator that Emile Gagnan set up for him with the exhaust by the mouthpiece, but the demand valve with its diaphragm was mounted on the tank (on his back). The regulator free flowed whenever the exhaust was higher than the diaphragm. This is the effect of the water column pressure differential.

Emile figure it out on their drive back to Paris and solve it by routing the exhaust back in front of the pressure sensing diaphragm (and the demand valve). BTW, this was what the original patent was all about, the exhaust hose and duckbill in front of the diaphragm.

This issue was solved 70 years ago.

The case fault geometry is just the distance between the exhaust and the center of the diaphragm. That distance limits how light you can set the cracking effort to avoid a small free flow. That is it… it is that simple.

It just happens that we measure the cracking effort in inches of water column (inWC) and that the “case fault geometry” can be measured in inches. That makes it convenient.


I have set many double hose regulators to 0.5 to 0.6 inWC. The exhaust is in front of the diaphragm, but the radius of the exhaust valve is 0.5 inches. It is not uncommon that I have to detune a Phoenix RAM with the new HPR (and the new super flexible diaphragms) so that the cracking effort is higher than 0.5 inWC. In the early design I was consistently getting reliable cracking efforts in the 0.2 to 0.3 inWC, but I had to detune it to avoid free flow in the water due to the exhaust valve diameter. In some position the top of the exhaust will be 0.5 inches higher than the diaphragm.

The same occurs with the D400 or the old, 1960’s, US Divers Calypso regulator. The old Calypso could never be adjusted to that low of a cracking effort, but it did have the exhaust in the middle of the diaphragm.


BTW, if you tape the exhaust closed you just got rid of the exhaust. The only difference is that in that situation you can now set your cracking effort lower… to 0.1 inWC (or slightly less) and get no free flow in any position, but you would have to exhale out your nose.


You can also take the exhaust hose of a double hose and move it up or down anywhere you to. It is not going to affect the inhalation effort. Only if you raise it above the diaphragm (a bit higher than the cracking effort) it will cause a free flow. But you can lower it all you want to or pinch shut the exhaust hose and it makes absolutely no difference to inhalation mechanism. The exhalation will get harder, but it will not affect inhalation.

Does this answer your question?


Once you get that Phoenix RAM put together, you will see that it will all be much clearer… You will also set aside some of those piston first stages…

---------- Post added September 1st, 2013 at 10:55 PM ----------

Well, halocline said the same thing I did... in a lot less words. And he bit me by one minute. But at least I added some historical information...

 

[rsingler]

Uh, oh, couv! Wolfinger had a nice, simple analogy to help explain required cracking effort So what if it wasn't the exact distance from the diaphragm to the top of the exhaust valve?
Now things are going to get complicated, very fast.

Game on!

---------- Post added September 1st, 2013 at 09:15 PM ----------

Oh, on another subject, I have an extra of Herman's MK5 tools. Any idea why?

You got my order.

 

[rsingler]

I'll have to dig out "the gospel according to Wolfinger" to see if I can figure out why there is such a divergence in beliefs. I suspect it has more to do with how we define what CGF really is. Remove the exhaust valve and tape over the port so that no exhaust valve exist. What effect does this have on CGF?

Cheers,

Couv

P.s. I'm still a piston fan, with or without sealing.

You guys were a little unfair to couv, who with his experience doesn't really need the explanation you gave. His question was legitimate. And I'd answer it this way:
It's less a question of cracking effort, than "what force does it take, pressing the valve lever down against the diaphragm, to keep the reg from freeflowing?" It's not a question of how much you have to suck to trigger the valve, as much as it is how much upward force on the diaphragm you have to counteract due to the presence of the exhaust valve and a column of air underwater. Everybody's already given the answer to couv's question: no exhaust valve = no CGF, and minimal "cracking effort."

But this is how I visualize the exhaust valve that may be sitting higher in the water column than the diaphragm. That "case geometry fault", which is less with a coaxial exhaust valve, is what determines how hard you need to press down on the diaphragm to keep the valve from triggering. Picture a cylinder with a free-floating piston and a hole in the top:

In these pics, just substitute the inhalation diaphragm for the piston, the exhaust valve for the hole and CGF becomes apparent. You need to add in 1" of valve lever "resistance" (cracking effort), to hold down the red diaphragm against water pressure coming from 1" lower depth than the zero-resistance exhaust valve. When you rotate the regulator 90 degrees, the problem goes away. When you rotate 180 degrees exhalation gets harder, and the reg may breathe wet.

I realize that I've likely confused the issue by using a frictionless PISTON to demonstrate a second stage issue revolving around a DIAPHRAGM, but that's just too damned bad!

Cheers, to my (probably only) piston buddy in a diaphragm-congested world. Alas.