Day #5 - TFX vs D400 at max safe gas density
Today we dove Devil's Throat to 136 ft. Picked up 8 minutes of deco because we all hung around at 136' making sure everybody came out. That gave me plenty of time to breathe hard on both regs.
As you'll recall from
@Dr Simon Mitchell 's presentation, 6.5 g/l is the inflection point after which CO2 retention became a real issue for exercising rebreather divers. Granted, OC might have less risk in this regard, but the point is, 136' on Air is already over 6.5 g/l.
Head down position
First, while descending through the throat, there are two passages where you are literally vertical head down. Both regs were
absolutely dry in this position. Keep in mind the regulator position when head-down vertical. Since you are looking in the direction of travel, the reg is held with the top cover at ~225° and the diaphragm/exhaust valve is vertical. While this doubtlessly admits a few drops of water as the exhaust valve flutters during exhalation, the water collects in the head and is expelled as you roll horizontal.
The only time I've had a wet TFX or D400 is looking
past vertical head down (like looking back between your legs) which puts the exhaust valve high and the mouthpiece low. I'll test that again tomorrow against a stiffer TFX tuning.
Inhalation
Inhalation was a delight from both regs. With the low diaphragm both valves are preloaded by ambient pressure and are ready to open, held back by positive pressure in the case (because the diaphragm is lower measured from your throat than the cracking effort). Thus, all you have to do to breathe is inhale and the air flows. (To prove to yourself that the valve is always ready to open in the standard diving position, just take your mouth off the mouthpiece - it freeflows like crazy as soon as that positive pressure maintained by your mouth seal is removed.)
Exhalation
Exhalation was the whole reason for this repeat test against the D400.
I am unclear on what your expectation is for a D400 with a TFX diaphragm. Do you think that combo will be an overall nicer reg than either of the two alone? Or is this just your nostalgia prompting you to stick with the D400, but improve it?
As you know,
@James79 is interested in creating a diaphragm retainer with a larger top circle and lower collar, to potentially facilitate Exhalation WOB by using the TFX diaphragm instead.
The D400 suffers from increased exhalation work of breathing because of three factors:
- a small exhalation valve
- a circuitous exhalation pathway, and
- small cover holes for exhalation without wings that might "chimney" the bubbles.
In my test on the Spiegel Grove at 120' that was the data set behind Regulator Geeks #3 a year ago, I noted the difference in exhalation effort between it and standard barrel regs (and the D420). I was concerned that a diver might be at risk for a CO2 hit during exercise at max gas density. But I was gas and deco constrained to a very short test (just three quick heavy hyperventilation cycles) because I was comparing so many regs.
Today, we hit and held at 136' with air (6.6 g/l). I didn't feel stupid, though I'm sure I was. In any case, I was collected enough to compare the two regs as we waited for the rest of the group to emerge from the Throat.
To my pleasant surprise, although I could feel a clear difference between the TFX and the D400, holding position in current was not stressful on my old favorite: the D-series. I had no doubt that I could increase my effort if needed, and maintain it without feeling short of breath or working too hard. I'm no longer concerned about a CO2 hit with the D400, though the TFX was WAY easier.
So that means that IF we can come up with a diaphragm retainer that has a lower collar and accomodates a larger exhaust valve, and design a new cover that's easier to remove and has larger, directed exhaust ports, we will have a reg that has better exhalation WOB, and there will be a potential source of diaphragms for this aging reg. I'm down to my last five, and my last two from a SB friend who recently got them from Germany for me, were beyond expensive. Any way you look at it, the D400 remains a fantastic reg, albeit with huge service challenges.
But the TFX is better. And is easy to service. And has a sharp knife edge. And is titanium.
I've deliberately beat up this reg. I've not used a case, and have tried to ignore it when it falls on the deck or the ground on my 60" hose at day's end during packing up. I just jumble it up with my gear during tank changes and transport. I'll include a picture at week's end, to show how it's held up. I can't speak to scratches on the plastic, as it's hard to tell when it's wet. But the soft purge cover has really performed well, and I have no indication that it's at all fragile. It's VERY lightweight.
I'm out of regulators to try, but it has beaten every one I brought. It's only slightly better than my G250 and T3, moderately better than the Mares XR/HR and C370, and (to my surprise) definitely better than the XStream.
Stiff tuning test for wet breathing in the 210° position next (and last).
