Regulator Geeks 3: Reg Performance at Max Safe Gas Density
- Thread starter rsingler
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
OP
Excellent question. Complicated answer.
1) Requirements
You're right, if you're vacation diving in calm conditions under 80 feet, you can get by with almost anything. If you can't feel much resistance on the surface when you take a breath, and the gear is well maintained, any difference won't be very apparent during your vacation until you happen to try your buddy's ZZZ-brand "super regulator." When you take your tried and true to Key Largo on an iffy day, you may come back thinking, "I wonder if I need a new reg?"
2) Design
There are only so many ways to skin a cat, if we're talking about modern molded-case standard barrel design balanced seconds. So if you've got a mainstream manufacturer, you can be assured that the flow characteristics are probably not weird. That said, something is clearly going on with the C350 & C370 that seems unusual, at least at high gas density and high flow (two slightly unusual conditions for a medium-experience diver). But even there, a little tweak of the Pre-Dive lever fixed it. And as tuned by most shops to 1.4" cracking effort, that obvious "clatter" on heavy breathing in current would only be noticed at max gas density.
Bottom line? Pick any reg!
That said, there are current regs from reputable manufacturers that I wouldn't touch with a ten foot pole. That's where, if you're about to spend $2k on yourself and your wife for new gear, you need to find someone you trust, who is NOT selling that brand.
2) Cracking effort
With ANY attention to detail, even a novice diver can feel the difference between a hot reg and a stiff one. But for a novice, that's only if they're compared side by side. I have sampled many divers' regs when they're showing off their new toy, only to walk away thinking, "How can they possibly think that's a well-tuned reg??!!"
One doesn't know what one doesn't know. They could have easily felt the difference, had they done a cracking effort comparison, but they didn't know what cracking effort even meant. If it breathed okay, and their shop gave it to them, it must be good, right?
So this is one way to judge your shop. Ask what min spec is for your reg. Ask them to tune it to min spec (knowing you may need to return it in three months once the seat takes a set, and it starts to leak). If they balk, that's a warning sign. If they don't know what you're asking, walk away.
3) Edge of the envelope
So you have a fair bit of experience and plan to hire a guide to dive the Spiegel Grove, but have discovered how erratic the current is off the coast. You have good gear and have done a test in your sink with a borrowed tank and know that it's cracking around 1 1/4 inches.
Without doing a Wolfinger A.I.R. graph, the best way to not find yourself with either stiff breathing or runaway freeflow is to be "middle of the road". Don't "hot tune" it for that first dive.
Maybe skip that first "edge of the envelope dive" if the current is up.
Once you go, try a little heavy breathing down on the wreck or at depth and see how it feels.
Once you have that experience under your belt, you can hot tune your primary and try again. If it "clatters" like one of mine, just switch to an octo for the rest of the dive.
And at that point, come back to ScubaBoard and all your regulator geek friends will help you get it sorted!
My new C370 arrived last week with a cracking effort of 1.9" !!!
My Mk19EVO arrived last year with a barely tight DIN bolt and a bulging environmental seal.
There's more.
Scubapro makes great gear, but their recent QC sucks.
OP
I only wish I had. With an ANSTI machine to directly compare surface flow tests to ANSTI loops, plus maybe an in-water test at a bit more air density than I had the courage to try, we could come up with one.
Here's what I think we know:
A little positive pressure is probably a good thing. Those ANSTI loops that show a crossover into positive territory are helping you breathe, especially at high workload and high gas density.
In-water testing revealed that a hot-tuned reg from a reputable manufacturer had such a degree of positive flow that it interfered with easy breathing.
Wolfinger A.I.R. testing of that reg showed a curve that seemed to cross over early into positive pressure (freeflow).
There is a suggestion that a device from the company that sells ANSTI machines correlates EN250 conditions with 35 SCFM for at least one point on the inhalation side of an ANSTI loop.
Putting all that together with a hypothetical Wolfinger graph that goes way beyond the limits in his book makes me propose this hypothetical "best curve". This is COMPLETE SPECULATION on my part. The crossover is deliberate, but modest. It does not wildly increase its negative slope. It finally turns up at the very highest flows in recognition of the likely turbulence that would start in even the most well designed case under the most extreme conditions.
L13
Contributor
OP
To take this one step further, in trying to correlate the flow from a SURFACE test with an ANSTI loop at depth based upon hypothetical Reynolds numbers correlations and "Number of Molecules per minute", I am thinking (hoping?) that one can identify two or three points on an ANSTI loop with a surface test.
Not to beat a dead horse, but this is wholly guesswork.
The problem with high surface flow tests is that a diaphragm with air on both sides begins fluttering like a flag in the wind. And if you try to stabilize one side of the diaphragm by immersing the reg partially in water, you preload the valve and shift the whole reg in the direction of freeflow.
It may be an impossible quest, to try to identify a great new regulator (or a lousy one) with a $250 homemade Wolfinger toy. And looking at an ANSTI loop measured at 2.3 CFM at 4 degrees C and 167 feet is comparing apples to oranges with my diving.
Not to beat a dead horse, but this is wholly guesswork.
I would hesitate to point to values at any particular flow, but yes, "flat" curves are more stable. But I think the left hand side (lower flow side) of an A.I.R. curve does not correlate with deep dive conditions. The stability is nice, but it is what happens at high surface flows that may have a closer correlation with what you feel at depth.
The problem with high surface flow tests is that a diaphragm with air on both sides begins fluttering like a flag in the wind. And if you try to stabilize one side of the diaphragm by immersing the reg partially in water, you preload the valve and shift the whole reg in the direction of freeflow.
It may be an impossible quest, to try to identify a great new regulator (or a lousy one) with a $250 homemade Wolfinger toy. And looking at an ANSTI loop measured at 2.3 CFM at 4 degrees C and 167 feet is comparing apples to oranges with my diving.
admikar
Contributor
My experience is nothing compared to @rsingler and what follows is just my personal take.
I think that some exhaust resistance is a very good thing.
It forces the diver to breath "properly".
It keeps your lungs, on a time average, at positive pressure. Having an average positive pressure helps keeping the airways wide open and clean, to expectorate mucus, and does actively contrast oedema.
My previous experence with pure-oxygen CC rebreathers did make me favouring a chest-mounted counterlung. It keeps your lungs constantly in positive pressure, which revelead to be good.
A back-mounted counterlung requires you to "suck" from it, and in the long term this is much more fatiguing, and causes your lungs to become full of blood.
Also consider that your muscles are very effective compressing your lungs, much less effective when sucking air.
Make this test with a long snorkel of the type with corrugated pipe.
You can easily submerge the end of the snorkel at 35 cm underwater and force air bubbling through it.
Now submerge yourself with your lungs 35 cm underwater and try sucking air through the snorkel. Almost impossible.
This explains why the exhaust overpressure during exhalation of a restricted reg valve is not a big concern for me, whilst the depressure required when inspiring is much more a problem, and a good reg with proper Venturi effect is providing instead a modest overpressure also during inspiration.
In conclusion I feel no need to reduce the overpressure due to the small exhaust valve of my SP mod. 109 regs. Instead I try tuning them for minimizing the effort during inspiration, keeping them tuned very "hot", to the point that they tend to slightly freeflow with the knob all out when swimming or facing down (the knob is there for removing the free flow in these conditions).
Thanks, @Angelo Farina. There are a lot of interesting points to think through.
I am possibly more sensitized to C02 than average, both physiologically for myself, and psychologically because of adverse outcomes with others. So CO2 retention is a cause of concern for expiration performance for me - overblown or not.
I am possibly more sensitized to C02 than average, both physiologically for myself, and psychologically because of adverse outcomes with others. So CO2 retention is a cause of concern for expiration performance for me - overblown or not.
Similar threads
