Regulator breaths hard while surfacing

[srcalDiver]

I recently purchased an Aqua-Lung Legend LX ACD regulator. When I am surfacing in the vertical position I notice that the breathing becomes noticeably more difficult with I look up and point the 2nd state regulator toward the surface. Is this a result of the 2nd stage diaphragm being at a lower pressure than the mouthpiece because it is slightly closer to the surface in that orientation?

 

[Couv]

First off....Welcome to Scuba Board,

To answer your question; yes, in part, but the increase in breathing resistance is more due to the distance between your lungs and the mouthpiece. See this thread for a few relative post.

http://www.scubaboard.com/forums/regulators/205714-regulator-breathes-good-all-directions-2.html



c

 

[spectrum]

It's actually the water pressure differnetial between your diaphragm (or averaged depth of your lungs more or less) and your regulator's diaphragm. The cracking rseistance and WOB of your particular regulator also factor in there. The different depths is the driver however.

If you bob vertically with a snorkel the resistance of having your chest that deep while breathing from 1 ATM is very noticable if you pay attention.

Pete

 

[mempilot]

A couple of things.

1. The IP may not be set properly, or after break-in, it needs to be readjusted. It should be at a minimum of @ 125psi with a maximum of @ 150 psi. That regulator works great at about 140 psi.

2. The second stage cracking pressure should be set while the manual adjustment knob is a half turn from all the way out so that the regulator will just barely freeflow when the 1st stage IP is set properly. At the surface, you would dive the 2nd stage with the knob turned in between all the way and out as far as you need to get the WOB where you like it. All the way out and it will freeflow if you purge it, but will stop if you put a finger in front of it.

I would take the reg to your shop and have them check this. I've seen regulators come new where they are not dialed in anywhere near where they should be. This is most often noticeable when purchased online from discounters that don't pre-tune them for you. Also, after about 25 dives or so, everything wears in and they can be retuned to perform better at that point.

As for looking up or being in a heads up position, that regulator should show no noticeable difference in ease of breathing. Go get it tuned and dive safe!

Eric

 

[DA Aquamaster]

It is caused by case geometry fault issues and has to do with the relative positions of the center of the diaphragm and the upper edgfe of the exhaust valve.

In a face down positon, the cenmter of the diaphragm is lower in the water column than the upper edge of the exhaust valve. The result is that air dribbles out the exhaust until the pressure inside the case is equal to the pressure at the exhaust valve. this means the diaphragm is already pressing in (up) on the lever so very little inhalation effort is needed to start air flow. In fact with an adjustabel reg, you may find you need to crank the knob in a turn or two to stop a slight freeflow between breaths.

The opposite occurs when you are looking up. The center of the diaphragm is higher in the water column than the upper edge of the exhast valve and the pressure inside the case is higher than on the outside of the diaphragm. So when you inhale you have to overcome this extra pressure before you even begin to move the lever to inititiate air flow.

This is of course why you bought an adjustable reg in the first place - a turn or two outward will ease the spring pressure and return inhalation effort to normal.

Most regs with a conventional case design dsiplay this trait and if you turn it to various orinentations and pay attention to the relative depths of the diaphragm and exhaust valve, it begins to become apparent what is occurring.

It has nothing to do with the relative position of your lungs and it has nothing to do with the IP of your first stage.

 

[Luis H]

The short answer is: yes.

Couv and Pete already explained how the actual WOB is affected by the water column pressure differential.

If you look at the link that Couv included you will see that IMO another important pressure difference is the water column distance from the regulator diaphragm to the vertical location of the inner ear. Our pressure sensors are in the inner ear so that is where we would perceive any pressure difference.

On the other hand the actual work is done by the muscles surrounding the lungs so that is where the actual WOB will be happening. But, my observation of the measuring equipment used to test WOB the pressure tap is just outside the mouthpiece.



Now there is certain college professor (who seems to have become a very good regulator technician) who may drop in at any minute to debate this subject again.

 

[Luis H]

It is caused by case geometry fault issues and has to do with the relative positions of the center of the diaphragm and the upper edgfe of the exhaust valve.


It has nothing to do with the relative position of your lungs and it has nothing to do with the IP of your first stage.

Well here, for a change, I can’t totally agree with you in some of the details.

Obviously we agree that it is related to the pressure difference, but my observation is that the effect is the same on a Poseidon Cyklon as in any other regulator geometry.

I am very aware of the case fault geometry and is effects (or limitations) due to the distance from the exhaust to the center of the mechanical pressure sensor (the diaphragm), but there are a number of regulators (the Cyklon, the very old Calypso, etc.) that have exhaust that are concentric to the diaphragm and they still suffer from the same vertical column of water pressure differential effects.

The most interesting experiment is put your double hose regulator on a small tank in front of you. With your eyes closed move it up and down and you will be able to tell when the center of the diaphragm moves above or below the level of your ears.

This kinds of backs my theory about human perception on WOB, but I still say that the actual work happens at the lungs, but we have less sensation since the pressure differential is not that big and our lung muscles are not that sensitive to pressure differentials.

 

[mempilot]

...it has nothing to do with the IP of your first stage.

You're right. Too low IP will breath just fine at the end of a dive when the tank pressure is low and the diver is heads up vertical. Whatever, mate.

 

[DA Aquamaster]

Well here, for a change, I can’t totally agree with you in some of the details.

Obviously we agree that it is related to the pressure difference, but my observation is that the effect is the same on a Poseidon Cyklon as in any other regulator geometry.

I am very aware of the case fault geometry and is effects (or limitations) due to the distance from the exhaust to the center of the mechanical pressure sensor (the diaphragm), but there are a number of regulators (the Cyklon, the very old Calypso, etc.) that have exhaust that are concentric to the diaphragm and they still suffer from the same vertical column of water pressure differential effects.

The most interesting experiment is put your double hose regulator on a small tank in front of you. With your eyes closed move it up and down and you will be able to tell when the center of the diaphragm moves above or below the level of your ears.

This kinds of backs my theory about human perception on WOB, but I still say that the actual work happens at the lungs, but we have less sensation since the pressure differential is not that big and our lung muscles are not that sensitive to pressure differentials.

I'd argue that in the experiment above, the difference is due to the change in distance from the mouthpiece to the center of the diaphragm in the can at your chest. If you connect the two so that the vertical difference cannot change as you tilt your head back and forth to change the relationship of mouth to ears, I doubt you would perceive any difference in WOB.

I know one of the things I liked with the D400 was that with the concentric diaphragm you could not produce more than .5" of difference bewteen the best and worst case scenarios with a commensurately small increase in WOB.

Or looking at it another way, I feel a lot more effect in second stage position with a G250 than with a D400 even when both produce the same WOB in the same positition. That lends support to the argument that it has much more to do with the second stage position than with relationship of ears and mouth.

With a double hose reg, the relationship of exhaust valve, and diaphragm is not the same as it is with a single hose reg but more importantly the mouthpiece is widely separated from the second stage diaphragm and difference between the diaphragm and the mouthpiece causes a large change in effort with the reg practically force feeding you as you look up or roll on your back and having a much greater WOB when you are head down with the mouthpiece well below the diaphragm.

 

[Luis H]

Or looking at it another way, I feel a lot more effect in second stage position with a G250 than with a D400 even when both produce the same WOB in the same positition. That lends support to the argument that it has much more to do with the second stage position than with relationship of ears and mouth.

I think that is also due to the distance from the center of the diaphragm on a D400 (versus a G250 or metal adjustable) to the center of the inner ear. Put either regulator in you mouth and look at yourself in a mirror wile you are looking up, forward or down (hopefully your neighbors are not watching).

The distances are small, especially in the D400, so it is hard for a human to accurately perceive the pressure differences. We need some volunteers that wouldn’t mind having some pressure probes taped into the ears, lungs etc.

Actually, I have been trying to get some of the WOB data that has been collected for re-breathers, since I think that it kinds of supports my theory also. I talked to some re-breather guys (and actually tried an Inspiration re-breather about a week ago). I hope to find the source of the data that I have seen and follow with more discussions about counter lung location and WOB.




A neat experiment for anyone with a single hose regulator:
Attach an extra octopus to your first stage. For that octopus replace the mouthpiece with a short (not more than 6” to 8”) section of flexible hose. Now you can try breathing out of the regulator in many different positions without moving your head. You can also experiment by moving the regulator up and down relative to your head.

The reason for the short hose is to prevent any large differential pressures that could be harmful. Less that 8 inWC should not hurt anyone that is involved in diving.

I haven’t actually tried this, but I have tried the equivalent with a double hose regulator on a pony bottle. I think this summer I got try this. Actually I will use one of my LP splitters and I try to use a D400, a metal balanced adjustable, and a Poseidon Cyklon, to test them side by side. It sound like something fun to do.