Regulator Geeks 2: Scubapro's Balanced Regs
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The VR does have VAD.
I have not noticed anything different when I stop inhaling or during the exhale. They do feel different on the inhale. I haven't used their new balanced adjustable models, but IMO their traditional downstream second stages like your VR take a very small, but noticeable, greater effort to crack than a balanced type. Then once cracked the gas basically rushes in to the point where I can't really sip or draw out the inhale. OTOH, I have never felt like I'm not getting enough air no matter how hard I'm working. Depth is also immaterial, although I've only gone to 40m so again as expected.
I have not used them, but this appears to be similar to the gas delivery with the upstream Poseidon second stages like the Jetstream or Xstream. But maybe not as pronounced? Mares' regs do have a normal purge, unlike the blast purge on these Poseidons which apparently require a special technique to avoid getting residual water forced into your airway.
So, a VERY rough/approxmative calculation for Air@15℃, assuming that NDEU peak flow of 3.7 l/s, and a hose ⌀1cm (I know I am off here, probably clser to o.5) get the Re# in the range of 500~600; wich is laminar (didn't ecxpect that); I also neglected pressure drop across the hose and tempreture changes...
Now upcoming venturi phenomena in the SS will for sure bump that number up (pressure goes down, velocity goes up)
Now here is the xhart for 𝜁, another magic unitless number that represents friction losses in pipes, plotted against Re#
I know it’s almost unreadable (it’s a tiny handbook)
But that dotted vertical is at 2.5k Re; we are (guess work) playin in that range between the straight line and that exponential decay solid line (top one)
EDIT: ignore the partial /discontinous lines; these are variations if we wanna do iterrative numerical analysis and consider significant pressure losses (not drops); but maybe.. IDK, some one at JFD (Ansti ppl) can tell us
I would assume based on that that the equivalence between surface and depth further stabilizes since the ratio of Abs IP:Ambient starts to plateau (we’re not trying to think of 300m+ dives right?)
Ok, I’ll get back to cleaning that g250 now
OP
@Mobulai , I am trying to wrap my head around all that you and @Michelle Louise have contributed in these recent posts. This will take some time. Please continue your analysis as you have time! This is fantastic.
Two comments:
It has just come to my attention that Pete Wolfinger, the author of Regulator Savvy, passed away in the last two weeks. It think we should acknowledge here the huge debt we all owe this former Scubapro employee for his contributions in helping shop technicians (and us DIY'ers) understand the inner workings of scuba regulators. His book is indeed the shop tech's Bible. And his testing equipment and the A.I.R. graph is at the heart of everything we play with as Reg Geeks.
Returning to topic, @lowwall makes a great point about the contribution of the Mares VAD with its short and unconvoluted flow path to the great gas delivery of the Mares regs! To continue our friendly rivalry, I am obligated to counter that the other reg design with a short and direct flow path from valve to mouthpiece is of course the center-balanced valve (Pilot, Air 1, D-series & TFX).
This brings me back to @Mobulai's list of factors above as we try to unpack the way any given reg "feels", especially after we "hot tune" it and take it to depth.
On the one hand we have turbulence, which may be a function of weird maths in addition to reg design. Here, @lowwall 's comment about the Mares VAD is particularly relevant, as it may be beneficial to supply gas to the diver as directly as possible. As @Michelle Louise and @Mobulai have outlined, there can be Venturi pressure effects that are seen in multiple local areas, as the gas flow path and various restrictions constrict and accelerate local flow. Think of the God-awful (and yet ubiqitous) barrel design second stage valve, for example. Local Venturi pressure changes are secondary to flow issues that affect gas delivery. And here, Mares may be superior.
But on the other hand we have valve opening. This is (I think) the only place where the Venturi-induced drop in local pressure is of direct significance to the diver. When the Venturi induced pressure drop is inside the case, diaphragm displacement is assisted, thus further dropping the lever and opening the valve. The farther that local pressure drop is from the diaphragm, the more pronounced it will have to be to help "suck in" the diaphragm, given the elasticity of breathing gas. For a classic barrel design, I think the relevant flow acceleration and pressure drop is at the opening in the barrel that points at the mouthpiece, rather than at the valve. For a servo design like the Poseidon, the negative pressure area that helps pull in the diaphragm is less easily discerned. For Mares, that point is probably where the VAD tube joins the mouthtube.
This is all relevant because if we are searching for the optimal second stage for gas delivery in extreme circumstances (a high effort emergency at depth), anything that decreases our work of breathing (in this case, ongoing effort required to keep the valve open during inhalation) will improve our gas delivery over time by lessening fatigue.
Of course in recent decades, manufacturer attention has been directed at the exhalation side of the ANSTI loop, since (until the return of the TFX) there was little left to improve on the inhalation side. But for Reg Geeks, we "get what we get" with case and exhalation valve design, so the only things we can play with are cracking effort and the Venturi vane.
If we're trying to use Pete Wolfinger's AIR graph to compare and tweak our regs, we're looking only at the inhalation side of the loop. But since (for competitive reasons) the folks that have ANSTI machines won't compare regs under real world emergency conditions (e.g., something much less than 62.5 RMV @ 165 feet @ 4°C), Pete's rotameter and AIR graph are all we've got.
Thank you again, @Mobulai and @Michelle Louise, for helping us continue to try to correlate A.I.R. with ANSTI!
Two comments:
It has just come to my attention that Pete Wolfinger, the author of Regulator Savvy, passed away in the last two weeks. It think we should acknowledge here the huge debt we all owe this former Scubapro employee for his contributions in helping shop technicians (and us DIY'ers) understand the inner workings of scuba regulators. His book is indeed the shop tech's Bible. And his testing equipment and the A.I.R. graph is at the heart of everything we play with as Reg Geeks.
Returning to topic, @lowwall makes a great point about the contribution of the Mares VAD with its short and unconvoluted flow path to the great gas delivery of the Mares regs! To continue our friendly rivalry, I am obligated to counter that the other reg design with a short and direct flow path from valve to mouthpiece is of course the center-balanced valve (Pilot, Air 1, D-series & TFX).
This brings me back to @Mobulai's list of factors above as we try to unpack the way any given reg "feels", especially after we "hot tune" it and take it to depth.
On the one hand we have turbulence, which may be a function of weird maths in addition to reg design. Here, @lowwall 's comment about the Mares VAD is particularly relevant, as it may be beneficial to supply gas to the diver as directly as possible. As @Michelle Louise and @Mobulai have outlined, there can be Venturi pressure effects that are seen in multiple local areas, as the gas flow path and various restrictions constrict and accelerate local flow. Think of the God-awful (and yet ubiqitous) barrel design second stage valve, for example. Local Venturi pressure changes are secondary to flow issues that affect gas delivery. And here, Mares may be superior.
But on the other hand we have valve opening. This is (I think) the only place where the Venturi-induced drop in local pressure is of direct significance to the diver. When the Venturi induced pressure drop is inside the case, diaphragm displacement is assisted, thus further dropping the lever and opening the valve. The farther that local pressure drop is from the diaphragm, the more pronounced it will have to be to help "suck in" the diaphragm, given the elasticity of breathing gas. For a classic barrel design, I think the relevant flow acceleration and pressure drop is at the opening in the barrel that points at the mouthpiece, rather than at the valve. For a servo design like the Poseidon, the negative pressure area that helps pull in the diaphragm is less easily discerned. For Mares, that point is probably where the VAD tube joins the mouthtube.
This is all relevant because if we are searching for the optimal second stage for gas delivery in extreme circumstances (a high effort emergency at depth), anything that decreases our work of breathing (in this case, ongoing effort required to keep the valve open during inhalation) will improve our gas delivery over time by lessening fatigue.
Of course in recent decades, manufacturer attention has been directed at the exhalation side of the ANSTI loop, since (until the return of the TFX) there was little left to improve on the inhalation side. But for Reg Geeks, we "get what we get" with case and exhalation valve design, so the only things we can play with are cracking effort and the Venturi vane.
If we're trying to use Pete Wolfinger's AIR graph to compare and tweak our regs, we're looking only at the inhalation side of the loop. But since (for competitive reasons) the folks that have ANSTI machines won't compare regs under real world emergency conditions (e.g., something much less than 62.5 RMV @ 165 feet @ 4°C), Pete's rotameter and AIR graph are all we've got.
Thank you again, @Mobulai and @Michelle Louise, for helping us continue to try to correlate A.I.R. with ANSTI!
I am reading and learning from his book currently and the clarity of thought, logical flow and thoroughness in presentation without any clutter, and the application of mind to a speciality practice is indeed rare - One amongst the very few who truly deserve the title of a Guru!
Peter Wolfinger Obutiary
Om Shanti to the departed Atman…
halocline
Contributor
Thank you for reporting Peter Wolfinger’s passing. He was a real giant in regulator development.
I haven’t read much of this thread, but if I understand things, you are talking about 2nd stage performance at increasing depth, is that correct? I’m not sure depth affects 2nd stages very much; they are (as Luis H always has reminded me) constant volume devices, and pressure differential, flow rates, etc do not change with depth. The only thing that does change is the viscosity of the gas, and I believe that has a mostly trivial effect on flow given the flow and depths we are discussing. It does affect Venturi assist, in a positive way.
Of course 2nd stages are always paired with a 1st stage and tank valve, which DO work harder at depth, resulting in likely greater IP drop under demand. This means that for practical purposes, 2nd stages might need to compensate at greater depth for whatever flow shortcomings exist in the 1st stage and tank valve.
I haven’t read much of this thread, but if I understand things, you are talking about 2nd stage performance at increasing depth, is that correct? I’m not sure depth affects 2nd stages very much; they are (as Luis H always has reminded me) constant volume devices, and pressure differential, flow rates, etc do not change with depth. The only thing that does change is the viscosity of the gas, and I believe that has a mostly trivial effect on flow given the flow and depths we are discussing. It does affect Venturi assist, in a positive way.
Of course 2nd stages are always paired with a 1st stage and tank valve, which DO work harder at depth, resulting in likely greater IP drop under demand. This means that for practical purposes, 2nd stages might need to compensate at greater depth for whatever flow shortcomings exist in the 1st stage and tank valve.
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