physics-why upside down breathing is hard

[boomx5]

Part numbers appreciated.

Thanks!

Mares Part# 1184006

 

[cmalinowski]

Here is a partial answer to your question: It is a diagram of the effects of diver position on breathing. It shows both single hose regulators and the older vintage double hose regulators. The basic physics has to do with the regulators position relative to the center of volume of the lungs and the variance in water pressure. -Ryan

http://vintagescuba.proboards2.com/index.cgi?board=instruction&action=display&thread=1071253464

Hmmm... very interesting. I never really noticed the vertical, heads-up being difficult to breath in and easy to exhale. I'll have to pay attention next time. Maybe that's why that first suck of air after the giant stride seems a bit more difficult. I just thought it was the "shock" of hitting the water.

 

[cmalinowski]

<stupid grin> And this is what I use to relieve dry mouth. <big stupid grin>
So if you see me doing a headstand now you'll know why.
<and now I know why it works>

I do the headstand to look behind me. It seems easier than twisting my body around... and I just kind of like doing it. Helps me practice bouyancy as well. Being on my back (facing the surface) is the biggest test of my bouyancy control... and I am definitely in need of practice. But that darned water into my mouth is a PITA.

 

[cmalinowski]

When you are heads up vertical in the water your lungs are much lower with respect to the regulator than when you are supine horizontal (on your back.) But it is easier to breath vertical than supine so the position of the regulator in relation to your lungs isn't the answer.

However the position of the diaphram in the second stage with regard to the water column does seem to make a difference. When your second stage is facing up the air inside it is exerting an upward force on the diaphram offsetting some of the downward force of the water column... making it breath harder.

Try this sometime: get vertical and with out changing the position of your regulator vs your lungs tip your head forward reg facing down and breathe... then tip your head backward reg facing up and breathe. Can you tell any difference? Why?

My zeagle/apeks T50Ds all give me a shot of water when I turn over on my back or go head down. I suspect it is the way the second stage traps some water at the bottom of the case when in the normal position and that is what I get when I invert.

Thanks for the info. Glad to know it's not just my reg that spits water at me. I'll have to check out that Mares change before purchasing a new reg... although, a new reg is tempting.

 

[Uncle Pug]

Here is another way to demonstration that second stage diaphram orientation is what makes the difference in breathing resistance:

Connect your regulators to a tank and turn the tank on. Place the second stage mouth piece up in a tub of water and see how *deep* you can get it before it free flows.

Now turn it over, mouth piece down, and repeat the above. Was there a difference?

Conclusion?

 

[jonnythan]

Conclusion is that pressure delta between the diaphragm and second stage valve is what matters.

 

[Uncle Pug]

Correct.

The pressure delta between the second stage diaphram and the diver's lungs is of no consequence... unless the diver has an unusually long neck.

The pictogram from 1962 in the link above is misleading.

 

[pennypue]

Correct.

The pressure delta between the second stage diaphram and the diver's lungs is of no consequence... unless the diver has an unusually long neck.

The pictogram from 1962 in the link above is misleading.

So really only giraffes, llamas and camels should be concerned?
:laughing:

 

[boomx5]

So really only giraffes, llamas and camels should be concerned?
:laughing:

Don't forget to add "Kate Moss" to your list.

 

[DA Aquamaster]

1. How come when I roll onto my back or go head-down my breathing becomes harder? I am sure that there is some physics lesson hear that I need to understand.

UP describes the effect well from a practical stanpoint. In technical terms the effect is called "case geometry fault".

In a normal swiming position with a conventional second stage case design, the center of the diaphragm is approx 3/4" lower than in the water column than the exhaust valve. ) So the average pressure on the diaphragm is slightly higher than on the exhaust valve. When you exhale, air continues to to exit the exhaust valve until the pressure in case is equal to the water pressure at the top of the exhaust valve (well...not exactly equal as it requires some effort to lift the valve off the seat, but close enough for our purposes). So there after the exhaled air is done exiting the second stage, there will already be some pressure from the diaphragm on the lever assisting the next inhalation cycle.

This effect is maximized when the diver is facing straight down as in this position it creates the maximum vertical difference between the center of the diaphragm and the top of the exhaust valve. Second stage cracking efforts on non adjustable second stages sneed to be set fairly high (around 1.2 to 1.4 inches of water) to prevent a slight freeflow in this position.

At the other extreme, when you are facing straight up the diaphragm is at a maximum height above the exhaust valve and the pressure inside the case is slightly higher than the water outside the dipahragm. So the diver not only gets no free assist from the water pressure but actually has to overcome a bit more water pressure. The result is that most second stages breathe harder when you are inverted.

2. Are there regs where breathing is pretty much the same no matter what position you are in? I read the latest scuba diving mag article and review of regs. They have a category about breathing in different positions.

Some regulator designs have used an exhaust valve coaxially mounted in the center of the diaphragm. This was used most successfully on the Scubapro D300,D350 and D400 series second stages The design meant that at no time would there ever be a difference of more than .5 inches between the top of the exhaust valve and the center of the diaphragm. This meant that there was virtually no change in inhalation effort in different attitudes and it also allowed the inhaltion effort to be very stable at very low cracking efforts. (around.5 to .6" of water rather than 1.2 to 1.4 inches of water). Scubapro also angled the diaphragm in the case so that the worst case positions occurred in attitudes the diver was normally never in. The result was a very natural breathing regulator that could deliver minimum inhaltion effort without any diver adjustment feature.

Of course, all good things must come to an end and given that it was a little harder to tune a D300/350/400 than the average reg and soem techs had problems with this, after over 20 years of production SP stopped trying to train better techs and instead discontinued the design in 2003. Bad move. The X650 technically replaced it and while it looks a little like a D400 with the angled diaphragm, it does not share the coaxial exhaust valve design and in no way performs as well as a D400

The Dacor Quantum second stage also used a coaxial exhaust valve design, and it worked well when the second stage poppet could be made to perform. I have found that the performance abilities of individual Quantum regulators varies greatly. Some are outstanding and can take advantage of the design and others are real dogs that cannot.

3. When I turn on my back, I end up with a little water in my mouth (< 1/8 oz I'm guessing) which makes breathing all the more difficult. Is this normal? Do all regs have some water seapage?

When you are inverted, water that slips past the exhaust valve will pool in the "top" of the second stage where it easily enters the mouthpiece on the next inhalation. In a normal position, this water would otherwise collect at the bottom of the second stage and exit back out the exhaust valve on the next inhalation.