breathing upside down
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Mambo Dave
Contributor
SmileMon:
I'm not sure it's that much of an issue, SmileMon. Divers have got by for years with older style regs that were more difficult to breathe upside-down. Unless goofing around, or doing momentary glances at the surface, I find it rarely comes into play in my diving.
The most amount of time I have spent upside-down was scraping the hull of a friend's boat, and in that case, at that shallow depth, I didn't experience the tougher upside-down breathing that my reg has at, say, 30 feet depths. In fact I completely forgot about that characteristic of my regulator as I zoned-out and just scraped away. Meditative and Zen-like, actually, but I digress...
My regulator is regularly used by local tech divers for dives past 200 and 300 feet, and it performs well for those ship explorers. It's worked well for me in the adventures I've had, too, so I can't really complain about it breathing a little less well in a situation most I've dove with are rarely in. If all regulators were easy to breath while facing the surface, would we see a lot more divers swimming while facing up during dives? I doubt it. The general position, from what I've seen, is horizontal and facing down, and I believe it still would be even if all regs performed well while facing up.
-- Peace
:water: MD
The issue is due to what is called case geometry fault. Spin your reg around and note the relationship between the cneter of the diaphragm, the exhaust valve and the mouth piece.
The pressure acting on the second stage is essentially the water pressure at the center of the diaphragm. If the mouth piece is lower, there is less pressure inside the reg than there is at the upside down (and consequently lower) mouth piece where you are inhaling. This means your lungs have to create the extra inch or so of water pressure to get gas flowing through the reg.
The other factor here is exhaust valve position. If the presure in the secnd stage is higher than the water pressure outside the exhaust valve, air will leak out until the pressure equalizes. So the upside down exhaust valve also plays a part in lowering the pressure inside the second stage to a pressure lower than what is at the upside down (and consequently lower in the water column) mouthpiece.
Also, in order to prevent a free flow in an unusual attitude, it is often neccesary for the second stage to be detuned to the point where the decrease in pressure between the center of the diaphragm and the upper edge of the exhaust valve is not enough to depress the lever and start a light freeflow.
So referring back to the example of the ATX 50 not breathing any differently upside down or upright, it's probably more accurate to say it breathes equally badly in any position as it is tuned heavily enough that it does not make much noticeable difference what position you are in.
In most cases, a finely tuned high performace reg will have a more noticeable increase in inhalation effort in unusual attitudes than an inexpensive and heavier breathing regulator.
The double hose diagram provided above is really not relavent other than to highlight the advantage of the single hose reg - locating the diapragm very close to the mouthpiece to minimize the effect of differences in the water column.
The pressure acting on the second stage is essentially the water pressure at the center of the diaphragm. If the mouth piece is lower, there is less pressure inside the reg than there is at the upside down (and consequently lower) mouth piece where you are inhaling. This means your lungs have to create the extra inch or so of water pressure to get gas flowing through the reg.
The other factor here is exhaust valve position. If the presure in the secnd stage is higher than the water pressure outside the exhaust valve, air will leak out until the pressure equalizes. So the upside down exhaust valve also plays a part in lowering the pressure inside the second stage to a pressure lower than what is at the upside down (and consequently lower in the water column) mouthpiece.
Also, in order to prevent a free flow in an unusual attitude, it is often neccesary for the second stage to be detuned to the point where the decrease in pressure between the center of the diaphragm and the upper edge of the exhaust valve is not enough to depress the lever and start a light freeflow.
So referring back to the example of the ATX 50 not breathing any differently upside down or upright, it's probably more accurate to say it breathes equally badly in any position as it is tuned heavily enough that it does not make much noticeable difference what position you are in.
In most cases, a finely tuned high performace reg will have a more noticeable increase in inhalation effort in unusual attitudes than an inexpensive and heavier breathing regulator.
The double hose diagram provided above is really not relavent other than to highlight the advantage of the single hose reg - locating the diapragm very close to the mouthpiece to minimize the effect of differences in the water column.
Hank49
Contributor
deeper thoughts:
I have a B1 on an SPMK20 (and on an MK25) and when I fin to descend fast, it free flows when adjusted as "loose" as it can go. They are really sensitive.
Oh what heresy! To have my old Aquamaster still....
DA Aquamaster:
The diagram just happens to show both types of regulators. The right hand column shows a single hose regulator in four simplified positions. My intention was to show the single hose, the double hose just happen to be there.
The diagram does happen to show some breathing advantages and disadvantages of a single hose regulator. I havent kept up with the most recent research, but I recall studies (both Navy and commercial diving comp.) that determine that exhalation resistance was more critical to over all fatigue (during heavy work) than inhalation resistance. That is just one example of the tradeoffs. I believe that is the reason why WOB includes the full cycle.
Your last statement doesnt take into account the potential (depending on diver position) water column between your mouth piece and your lungs. This is often ignored (it is often not even noticed by many divers), but it is there. Back in the 80,s I worked with one of the engineers that were involved in the studies behind the Zero Differential Pressure Suit intended for commercial diving and military use. They were trying to borrow some technology from an Air Force g suit and it intended to keep a diver at a single pressure a few inches of water deeper than the lowest physical point of the diver (therefore eliminating the differential pressure caused by the water column around a diver). The concept has merits, but the benefits did not justify the complications.
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