Why Is Face Up Breathing Easier? - Scuba Tech Tips: S17E13
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- čas přidán 12. 06. 2024
- Breathing with todays regulators is almost effortless so why is upside down breathing still easier? Alec explains why divers find breathing on their back is easier than face down.
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Appreciate the physics behind this. However, for mine, the reverse is true. When I look up and on my back, it is harder to breathe. Beuchat V90.
Hi to all who have commented on this seeming discrepancy. While your suggestion about the air wanting to push up sounds logical, the various pressures affecting the regulator overcome this. Realize that the water pressure is pushing down on the 2nd stage diaphragm too.
The reason that you may experience a reverse sensation is simply - you are using modern, very sophisticated regulators. The phenomena I discussed was a very regular concern on older regs, VERY noticeable on 2 hose regs. New regulators have all but overcome the problem except in the very simplest, basic, unbalanced regs. You actually do get some benefit from buying a more expensive regulator!
Someone questioned whether the Intermediate Pressure changed. It does. On the surface it is usually close to 150 psi but, the design of a regulator accounts for the water pressure as a diver descends. The IP increases in direct proportion to the water pressure. That is, at 33', assuming the water pressure is 15psi, that will be added to the base IP of 150 so the the actual pressure at 33' will be 165psi. However, that is moot to this discussion other than the following:
the regulator provides an IP equal to the base pressure (say 150psi) PLUS the surrounding (ambient) water pressure. This is all measured at the 1st stage. So, when the 1st stage is lower (deeper?) than your lungs & 2nd stage, the pressure on the 1st is greater so the IP is greater than that required. Air flows more freely into your lungs. When the 1st is higher (not as deep) than the 2nd, the IP will be slightly less. You have to work a bit harder to get air out.
With a 2 hose reg where both the 1st & 2nd are one unit, this effect is exacerbated. Turning from face down to face up with a 2 hose reg, raises the unit the better part of 2' - a big change in water pressure & subsequently a big change in the IP.
I hope this helps .
Alec
thank you. much appreciate your content that relates to my question months ago
Happy to help!
A
My understanding is that the first stage will always supply the second stage with the same pressure, regardless of depth. It maintains this pressure as the tank pressure decreases.
When face down, the second stage sees a higher pressure than your lungs and flows more easily as its 'deeper'
In my experience, face up is harder to breathe.
Regardless, great video and it'll certainly open up a discussion 👍
Apparently is has.
A
Hello Alec! Back in the water after a tough 2023. Turks and Caicos first dive, now off Rockport and Gloucester, MA. Feels great to be back!
Sounds like a good start to this year so keep on diving.
A
Very good explanations! Simple, but makes sense! The physics involved are amazing!
Keep em comin!
Thanks, will do!
A
Also balanced and unbalanced and up stream, down stream first stage. It is so interesting and crucial to understand how diving equipment works and the physiological impact on the body. Great topic.
Planning more on this topic soon.
A
Hi Alec I recall in one of your earlier vintage tips you talked about a complete barrel roll L to R or R to L was the way to completely purge water from a two hose reg, A forgotten skill for sure . Take care Owen m
I remember that video and doing rolls to clear my one piece double hose. Thankfully the Hope-Page one-way mouthpieces came along!
A
I always wondered about that
Now you know.
A
I've watched this a few times and the one piece of information that i feel is missing is the funtion of the second stage of the regulator in modern single hose setups.
In the middle of the video it mentions that the first stage provides you with gas at 150psi plus ambiant pressure, but you don't notice because of ambiant pressure on you and your lungs. This is not so. It provides gas at 150psi plus ambiant pressure to the second stage, not your lungs.
The second stage then provides gas to your mouth and lungs AT the ambiant pressure of the water at the depth of the second stage regulator (in this example 12.99psi freshwater 13.35psi salt water at 30ft (14.7psi at 33ft or 10m).
So if you are in proper trim (face down or up) your second stage regulator is at the same depth as you lungs and delivering air AT the same ambiant pressure exerted on your lungs and everything feels normal (13.35psi). Breath in breath out.
Salt water psi per foot is 0.445 (fresh 4.33psi/ft). If you are face down with regulator deeper in the water column than your lungs it will deliver air at a higher pressure than the ambiant pressure surrounding your lungs and inhaling air is easier.... BUT exhaling is sligtly harder.
Conversely if your second stage is at a shallower depth than your lungs (face up or body positioned vertically in the water) it delivers air at a pressure that is lower that the ambiant pressure on your lungs (0.445psi/ft of depth difference between the 2nd stage reg and the bottom of your lungs), making it harder to inhale, BUT easier to exhale.
This demonstrates why neutral level trim in the water is beneficial becaue both inhaling and exhaling are all at the same pressure as the ambiant pressure on your lungs.
Face down or head down tilt will make it easier to inhale, bht more difficult to exhale.
Face up or head up trim (sitting upright or vertical in the water) will be harder to inhale but easier to exhale.
This all applies to systems where the second stage is in your mouth, rather than behinde your head.
Thanks for the detailed explanation. For anyone else reading this helpful tip, please correct the fresh water psi/ft, not 4.33. Well said.
A
it nis more noticable on a double hose regulator.
to me, this topic should be teached on the basic scuba training.
To me, it is a safety concern as we know that panic is one of the best diver killer
very good point
excellent teacher.
I did like teaching way back then, never with todays kids and problems.
A
Alec , base on my experience , it is not match to your comment , when I turn my body and face up , it is more harder to breath not easy , my reg is Apeks xtx200
Hi to all who have commented on this seeming discrepancy. While your suggestion about the air wanting to push up sounds logical, the various pressures affecting the regulator overcome this. Realize that the water pressure is pushing down on the 2nd stage diaphragm too.
The reason that you may experience a reverse sensation is simply - you are using modern, very sophisticated regulators. The phenomena I discussed was a very regular concern on older regs, VERY noticeable on 2 hose regs. New regulators have all but overcome the problem except in the very simplest, basic, unbalanced regs. You actually do get some benefit from buying a more expensive regulator!
Someone questioned whether the Intermediate Pressure changed. It does. On the surface it is usually close to 150 psi but, the design of a regulator accounts for the water pressure as a diver descends. The IP increases in direct proportion to the water pressure. That is, at 33', assuming the water pressure is 15psi, that will be added to the base IP of 150 so the the actual pressure at 33' will be 165psi. However, that is moot to this discussion other than the following:
the regulator provides an IP equal to the base pressure (say 150psi) PLUS the surrounding (ambient) water pressure. This is all measured at the 1st stage. So, when the 1st stage is lower (deeper?) than your lungs & 2nd stage, the pressure on the 1st is greater so the IP is greater than that required. Air flows more freely into your lungs. When the 1st is higher (not as deep) than the 2nd, the IP will be slightly less. You have to work a bit harder to get air out.
With a 2 hose reg where both the 1st & 2nd are one unit, this effect is exacerbated. Turning from face down to face up with a 2 hose reg, raises the unit the better part of 2' - a big change in water pressure & subsequently a big change in the IP.
I hope this helps .
Alec
Hello Alec , love this channel . I have been wondering about this , but my experience is , like with the others , is the opposite, I find it harder to breathe on my back , facing the surface . My theory is , when on our back facing the surface , the air inside the 2nd stage wants to go up , so will end up pushing the 2nd stage diaphragm outwards , making it more difficult to “suck” the diaphragm in , hence making it a little more difficult to breathe . Just my thoughts .
Hi to all who have commented on this seeming discrepancy. While your suggestion about the air wanting to push up sounds logical, the various pressures affecting the regulator overcome this. Realize that the water pressure is pushing down on the 2nd stage diaphragm too.
The reason that you may experience a reverse sensation is simply - you are using modern, very sophisticated regulators. The phenomena I discussed was a very regular concern on older regs, VERY noticeable on 2 hose regs. New regulators have all but overcome the problem except in the very simplest, basic, unbalanced regs. You actually do get some benefit from buying a more expensive regulator!
Someone questioned whether the Intermediate Pressure changed. It does. On the surface it is usually close to 150 psi but, the design of a regulator accounts for the water pressure as a diver descends. The IP increases in direct proportion to the water pressure. That is, at 33', assuming the water pressure is 15psi, that will be added to the base IP of 150 so the the actual pressure at 33' will be 165psi. However, that is moot to this discussion other than the following:
the regulator provides an IP equal to the base pressure (say 150psi) PLUS the surrounding (ambient) water pressure. This is all measured at the 1st stage. So, when the 1st stage is lower (deeper?) than your lungs & 2nd stage, the pressure on the 1st is greater so the IP is greater than that required. Air flows more freely into your lungs. When the 1st is higher (not as deep) than the 2nd, the IP will be slightly less. You have to work a bit harder to get air out.
With a 2 hose reg where both the 1st & 2nd are one unit, this effect is exacerbated. Turning from face down to face up with a 2 hose reg, raises the unit the better part of 2' - a big change in water pressure & subsequently a big change in the IP.
I hope this helps .
Alec
Hi Alec.
Question - when IP pressure goes up with depth, why 2nd stage don't start to free flow ?
It's because there is a 'cracking pressure' on the second stage valve. That's how much you have to suck to get air to flow. It's not very much so just breathing in normally, lowering the pressure in your mouth, is enough to overcome it without even thinking about it. The change in pressure between the first and second stage when you're on your back is less than 1/2 a psi and if the cracking pressure is more than that you won't have a problem. On the other hand, if your reg is set up on a real hair trigger you might indeed get a free flow.
Remember it's the 1st stage that generally free flows, not the 2nd. The 2nd stage only opens when you inhale to open the valve that holds the air from the 1st stage. As you descend, the IP remains the same, say 140 psi + depth pressure of say 33' or another 14.7 psi (total now 154.7 psi). Modern Low Pressure hoses are rated to 500 psi generally with a burst pressure of 2,000 psi so you see there is LOTS of pressure the 2nd stage hose can take to normal recreational dive limit of 133' (base IP is 140 psi + (14.7 x 5=73.5), total IP at 133' is 213.5 or 42.7% of rated pressure. Hope this helps
A
Hello Alec. Is there a manufacturer still making the Twin Hose regulator setup?
YES ... he did a video showing one of them
@@diverdave4056 The Woman who Inspired me to get Certified uses a Twin Hose. But hers is Vintage Mistral??
The truly modern double hose reg, the Kraken, has not resumed production since the passing of Bryan P. who designed and made them. You may get a vintage reg safe for diving but first watch my videos on which regs are safe for diving and which are display only.
A
Hi Alec. On the contrary, i find it easier to breathe while facing down and harder while facing up. I do understand the science behind, and your explanation makes perfect sense. I just don't know why it's the complete opposite for me! Any idea why? I use the Apeks XTX200 regulator with XTX40 octopus.
The key factor is the distance from your lungs to 2nd stage. If you're perfectly flat that may be 6" to 8" (20" for Kevin). The pressure difference is very slight or maybe your reg is tuned slightly harder so you don't notice the difference.
A
I have the same regs and its the same for me, happy diving