Geo7
Contributor
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Well, thanks to my good friends at Marin Diving Center (shameless plug!) with their donation of unlimited gas and exclusive use of the pool, I was able to spend hours with the Atomic Aquatics TFX second stage, and then compare it side-by-side with many of my fave's. I of course ran the TFX alongside its center balanced historical sisters, the D400 and the D420. Recall that the TFX shares a design heritage with the D400, by way of Dave Toth, formerly of Scubapro and now a big part of Atomic. The D420 was Scubapro's resurrection of the center-balanced valve, covered ad nauseum here: D420! How about that?
I also compared with some regs also reviewed recently here:
My side-by-side's with the TFX included the Deep6 Signature, the venerable G250, the successor G260, the newer small case marvel - the C370, and of course, the Atomic Aquatics T2x.D420! How about that?
A lot of divers on the board are hardware fanatics, wanting to extract the last ounce of performance from their equipment. A newer diver would be better to concentrate on ease of use, ease and cost of maintenance, and reliability. Have you read this thread in its entirety? I get the impression...scubaboard.com
For testing, I had a 12-foot deep dive shop pool, so I'm limited to thin gas evaluations. None of the high-density comparisons that we did in Key Largo as part of Regulator Geeks III. Nonetheless, I compared:
- leisurely standard position noodling along
- max effort swims with heavy breathing in the standard position
- vertical position performance
- performance on my back
- incidence of wet breathing when inverted head down (or in the case of the TFX and D400, "inverted plus" to about 210 degrees from the vertical, which places the exhaust leaflets up and horizontal.
Just like ScubaLab and their annual entries in Scuba Diving magazine, this evaluation is a personal comparison wholly apart from the flow and work numbers in an ANSTI loop. I'll stick the TFX on my flowmeter for the next Regulator Geeks discussion night. Yesterday was just one guy's opinion and should be taken with a grain of salt. You all probably know by now of my personal bias towards center-balanced valves, so observer bias is a clear and present danger.
Just as with the Spiegel Grove dive at 120 feet, ALL the regs did fine! They're all solid, well known models, so why wouldn't they do well? If that's all you need not to drop $2,200 on a TFX, just walk away. There are none of them I wouldn't take on a deep dive, and maybe only one I would be concerned with on a tech dive in heavy current (sadly, my heretofore favorite D400). But for recreational diving, they're all solid.
What does matter? TUNING!!!!!
You can make any generic reg do pretty well if it's tuned to the low end of specification cracking effort and the components are corrosion-free and recently lubed. If not, let the horror stories begin...
Therefore, ALL of the regs were "hot-tuned" to the low end of mfr specification cracking effort (abbreviated in the tables as C.E.).
Here's your starting data:
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The TFX is absolutely exquisite when noodling along in the standard diving position!! Even accounting for observer bias, it was the star.
Flow was smooth.
Flow acceleration with a big breath was smooth.
Those multiple outlets and directed exhaust flow worked! Normal exhalation was indistinguishable from an Atomic, and even better than my G250 and G260. Surprisingly, my fave from the recent Cayman Brac trial, the C370, had a little rougher feel to it, and a side-by-side test gave slightly differing results from the day to day switches on my last trip.
Still, they're all great regs. But the TFX was smooth!
Negatives? Almost none.
The D420, I've finally conceded, really does need a higher cracking effort than its center-balanced valve would suggest, because of that aft facing exhaust valve. And while light exhalation favored that regulator over ALL the others, light inhalation with a 1.2" cracking effort, even offset by the diaphragm's low position in the water wasn't quite as good as all the other regs. Picky stuff.
But I did learn something right away...
Tuning a TFX to 0.7" makes it SO twitchy. It would freeflow at the drop of a hat out of my mouth. Turning the Venturi vane to Min didn't help. Standard technique for shutting off freeflow (inverting the reg mouthpiece down, and then slowly turning it upright as it fills with water) didn't work. I had to slowly turn the reg on its side and allow case gas to leak out the exhaust valve and tee, and fill with water with the mouthpiece horizontal. It would start flowing in any other position. That was clearly untenable for standard diving, where leaving it in the standard secondary position might trigger the valve as you swam.
So for the third set of tests, I retuned the TFX to 1.1". That's still below where the factory set it (at 1.3"), and I don't know what spec cracking effort limits are, but that change made it behave much better, with almost no discernable effect (see below).
What else did I learn?
There were ZERO mask bubbles with this reg, with the G260 and (almost) with the Atomic T2x with an added M1 wide exhaust tee. In the standard diving position, looking 30 degrees down or lower, it was delightful. In contrast, the D420, with its narrow case shape, was quite bubbly (though this would not be noticeable with almost any forward motion), and the large case standard shapes (G250, Signature) were slightly worse. Interestingly, the curved exhaust tee's touted by Scubapro for their reduction in exhalation WOB, shared by the C370, G420 and S620Ti (not tested) all had modest or worse bubbles in front of the mask when stationary. As you'll learn below, ALL regs get much worse as soon as you look up from a 30-degree down position.
When one moves from standard diving position to a vertical hover looking straight ahead, case geometry changes things slightly.
The posterior exhaust valve of the standard barrel regs and the D420 now moves lower in the water column. The exhaust tee of all regs moves right below your chin. The diaphragm position changes, also subtly influencing breathing effort:
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Now, with a high cracking effort and a diaphragm that has moved up from its lowermost position, the D420 performance begins to fall apart. While exhalation remains good, high flow inhalation is palpably worse than the others. Meanwhile, even with an increased cracking effort between trial sets, the TFX remained as good as any reg at both light and heavy inhalation.
But oh! The bubbles! As you might guess, EVERY reg sucked when vertical in the water column. No surprise there.
See next post...
Thanks so much for this incredibly thorough review! So many points of consideration and excellent presentation. There will be no need for us to read a magazine review...
I was confident these two reg engineers know their stuff and took care of the exhaust effort. I was hoping it can be hot tuned to 0.7 and not be too twitchy, since many dive their D400s that way. I guess it goes to show that the airflow and venturi is impressive (I think indicated by your high scores for heavy inhalation/breathing), and that's important too. Performance in any orientation, quiet performance, and good bubble dispersion on top of that. Amazing! One additional use case scenario for spending time looking up is teaching and watching students from below.
I also appreciate that you indicate that a bargain G250 gives plenty of performance, and people should take note of that and not get carried away. But I sure want a TFX second stage when they offer one.
Probably lots of us will contribute to fund your review trip! But as posted above, an option for PP friends with no loss would be good.
