Poor air delivery or Weak Diaphragm?

[landshark_IPA]

This thread is inspired by a recent find of mine related to "lung trainers". I did search the forums on this topic, but the threads and responses didn't quite hit on what I'm looking for. Please read the following details that setup the scenario and the reasoning behind my inquiry. I did see the numerous responses about how you "can't train your lungs". I get it, but the purpose of the trainers (at least for my scenario) isn't to train the lungs, but to strengthen the diaphragm to easily draw in air through a narrow opening (this will make more sense further down).

My primary Regulator is an Apex XTX50 setup pretty much at factory default (this summer marks it's one-year anniversary) with the fine breather dialed all the way out (easiest breathing) and I LOVE it. My secondary is a Scuba Pro 620Ti, also one-year old and factory setup, and it doesn't breathe quite as nicely (easy) as the XTX50; even dialed all the way out. Yes, I know my shop can tune these for me, that's not the point yet.

Over the past week, I changed out my mouthpiece from the factory Apex one to a moldable one by Jax. The very first dive I felt like I couldn't get enough air at the surface and aborted our decent. I thought it was nerves as it was a deep dive certification far out in the blue, but I was unable to get a satisfactory breath even after relaxing. I switched to my secondary and was instantly content with air flow. While calm and collected at our target depth, I switched regs again to test again if it was pre-dive jitters, however I instantly felt starved of air and soon switched back to my secondary. The only equipment change was the mouth pieces, so I compared the two on the surface (I kept the factory piece in my Save-A-Dive bag). That's when I noticed the orifice area of the JAX mouthpiece was some 50-75% smaller than the factory Apex one. I reinstalled the Apex mouthpiece and finished the dive weekend happy as a clam on my primary XTX50.

I've heard too many good things about the Jax moldable mouthpiece to blame the orifice size, so it must be something with me and my breathing. So here's the question... Should I take my regulators to the shop to be retuned with the new mouthpieces or is the issue with my breathing/fitness level? (I suspect I know the answer)
Would a "Lung Trainer" that uses air-flow restrictions be exactly what I need to breath happily with the Jax mouthpiece after some diaphragm strengthening, or could this be the results of poor fitness?

I have a computer job, so while I'm not heavy set, I'm not terribly active either, so I recognize how poor cardio MAY play into the situation. Though, it doesn't escape me that using the "trainer" to get comfortable with an air-flow restriction may be exactly what I need to replicate the restricted flow of the mouthpiece orifice. Or perhaps the solution requires implementing both solutions (weekly cardio plus the "trainer"). Input from those with experience or more knowledge regarding airflow would be helpful and appreciated.

I find it hard to believe that the proper route would be to have the shop tune the reg to deliver more air. I was already suspicious of my breathing habits by having both regs fine tuner dialed all the way out at surface.

Thank you in advance for reading this through.

 

[lexvil]

Stick with the factory mouthpiece, you’ve solved the problem now believe the result. No adjustment will increase the flow through the small hole.

 

[tursiops]

There are other moldable mouthpieces.
Forget the "lung trainer." That is solving the wrong problem, if in fact it is solving any problem at all.

 

[Akimbo]

Should I take my regulators to the shop to be retuned with the new mouthpieces or is the issue with my breathing/fitness level?

Check the most important part first. See a pulmonologist to make sure your respiratory system is functioning to spec.

 

[johndiver999]

I am surprised that the mouthpiece is really restricting flow rate to a noticeable degree. I suspect that it is mental and uncomfortableness with the different style.

 

[lowwall]

I wonder if the new mouthpiece is disrupting the venturi flow that second stages rely on to decrease breathing effort. Once airflow starts it should flow literally effortlessly until you start your exhale.

 

[landshark_IPA]

Good Advice all.
"If it ain't broke, don't fix it": stick with the factory one that works fine.

"Look at other moldable options to see if there are vendors with airway diameters more aligned with the factory's dimension"

"If you're questioning your breathing, then get checked by an expert. Doctors can run tests with various machines to confirm if it is a diaphragm strength issue, poor oxygen to blood transmission, or neither (which would be equipment after all)": I'm only 45 and in average health, but I'm thinking this is likely the surest approach rather than wasteful guessing.

"It's all in your head": Is exactly why I repeated the test at depth when relaxed as well as on the surface. I'm not tossing out "something I'm not used to" explanation, but I'm fairly sure it's not anxiety or other false perception of air flow performance.

"surprised that small of a change in diameter would be noticeable": This is why I picked the physics forums. flow rate of water or air is the pressure x diameter. If you decrease the diameter (which the mouthpiece does), then you have to increase pressure to equal the same flow, else you have to "pull" harder on the inhale. These means that the regulator would need to be re-tuned to accommodate the change in diameter (possible since I made change an element defined in the factory tuning). Or, I'm too used to being force fed air like a little baby at mealtime.
If the new piece of kit is in fact reducing flow (and it's not just my perception), then increasing pressure (measure at the mouthpiece and not at the reg valve) would restore flow to factory specifications with no cost on air consumption.

My takeaway from your valuable input is to get the shop tech's assessment on whether the two pieces make any difference at all on the airflow. AND get my respiratory system check by a doctor just to be certain everything is working aye okay up there. The results of both steps combined will give me the proper answer/solution. I'll follow-up with the results incase this information on how "changing your bits can have a bigger impact than you think" can help anyone else.

 

[lowwall]

"surprised that small of a change in diameter would be noticeable": This is why I picked the physics forums. flow rate of water or air is the pressure x diameter. If you decrease the diameter (which the mouthpiece does), then you have to increase pressure to equal the same flow, else you have to "pull" harder on the inhale. These means that the regulator would need to be re-tuned to accommodate the change in diameter (possible since I made change an element defined in the factory tuning). Or, I'm too used to being force fed air like a little baby at mealtime.
If the new piece of kit is in fact reducing flow (and it's not just my perception), then increasing pressure (measure at the mouthpiece and not at the reg valve) would restore flow to factory specifications with no cost on air consumption.

You want physics

Your contention is true if you were dealing with continuous flow through a straight pipe of infinite diameter. It's also a reasonable approximation if dealing with a continuous flow device like a CPAP. But flow rate in a demand valve device like a second stage is a very different beast. Especially a modern second stage that utilizes a venturi assist to decrease breathing effort.

The valve in a second stage is opened by your initial inhalation decreasing the pressure inside the case body. This causes the diaphragm at the front of the case to move towards you, which pushes a lever that opens the valve. Once the valve opens, the internal geometry of the case is designed to use the venturi effect to keep a low pressure area next to the diaphragm and thus keep the valve open with little if any sucking effort on the part of the diver.

This is why regs can freeflow if you drop them into the water diaphragm first. The difference in pressure between the diaphragm and the mouthpiece is enough to open the valve and the venturi keeps it going. You can stop the freeflow by restricting the airflow leaving the case. This disrupts the flow that causes the low pressure area, the diaphragm moves forward and the valve closes.

I suspect this is exactly what is happening in your situation. Gas is flowing into the case body faster than it can flow out which collapses the low pressure area and thus the venturi assist, leaving all the work of keeping the valve open to your sucking ability. If this is the case, then nothing you can do to the second stage will solve the problem. Second stage adjustments are limited to adjusting the pressure difference necessary to open the valve either through manipulating the lever height or the spring preload on the valve.

You can go to the first stage to adjust the pressure of the gas incoming to the second stage. This is called the Intermediate Pressure or IP. If my guess is correct then your proposed solution of increasing the IP will have the opposite effect of what you intend. Yes, some more gas will be able to enter your mouth, but this will be offset by the lack of venturi assist and the additional sucking effort required to counteract the higher pressure gas pushing outward on the diaphragm.

Counterintuitively, decreasing the IP might work if it decreases the backpressure in the case and allows smooth enough flow for the venturi to reform and drag the diaphragm inward. I say might because there is a lower limit somewhere on the mass of gas that has to flow for a low pressure area to form that is strong enough to provide an assist.

If decreasing the IP doesn't solve it, then I'd start looking for a different mouthpiece that has a larger inlet. Or maybe you can remove some material from the inside of the Jax.

 

[landshark_IPA]

You want physics

Your contention is true if you were dealing with continuous flow through a straight pipe of infinite diameter. It's also a reasonable approximation if dealing with a continuous flow device like a CPAP. But flow rate in a demand valve device like a second stage is a very different beast. Especially a modern second stage that utilizes a venturi assist to decrease breathing effort.

The valve in a second stage is opened by your initial inhalation decreasing the pressure inside the case body. This causes the diaphragm at the front of the case to move towards you, which pushes a lever that opens the valve. Once the valve opens, the internal geometry of the case is designed to use the venturi effect to keep a low pressure area next to the diaphragm and thus keep the valve open with little if any sucking effort on the part of the diver.

This is why regs can freeflow if you drop them into the water diaphragm first. The difference in pressure between the diaphragm and the mouthpiece is enough to open the valve and the venturi keeps it going. You can stop the freeflow by restricting the airflow leaving the case. This disrupts the flow that causes the low pressure area, the diaphragm moves forward and the valve closes.

I suspect this is exactly what is happening in your situation. Gas is flowing into the case body faster than it can flow out which collapses the low pressure area and thus the venturi assist, leaving all the work of keeping the valve open to your sucking ability. If this is the case, then nothing you can do to the second stage will solve the problem. Second stage adjustments are limited to adjusting the pressure difference necessary to open the valve either through manipulating the lever height or the spring preload on the valve.

You can go to the first stage to adjust the pressure of the gas incoming to the second stage. This is called the Intermediate Pressure or IP. If my guess is correct then your proposed solution of increasing the IP will have the opposite effect of what you intend. Yes, some more gas will be able to enter your mouth, but this will be offset by the lack of venturi assist and the additional sucking effort required to counteract the higher pressure gas pushing outward on the diaphragm.

Counterintuitively, decreasing the IP might work if it decreases the backpressure in the case and allows smooth enough flow for the venturi to reform and drag the diaphragm inward. I say might because there is a lower limit somewhere on the mass of gas that has to flow for a low pressure area to form that is strong enough to provide an assist.

If decreasing the IP doesn't solve it, then I'd start looking for a different mouthpiece that has a larger inlet. Or maybe you can remove some material from the inside of the Jax.

What an amazing response and detail on how the whole flow system works vs simple piping dynamics!
I thoroughly enjoyed learning this! It also makes me more confident that that simple piece change could cause the issue and reinforces the previous suggestion by @lexvil of sticking with the original factory piece. Now I understand the depth behind your first statement about the new piece disrupting the venturi flow.

Given this new understanding of how changing something so seemingly benign can have such a cascade effect I may just order a spare one or two from Apex and not fiddle with it any further. Though, since I can't return the now molded piece, no harm in removing some material to get the two in similar dimensions. I can't break what I'm not using right?

I wish this explanation had been given when I've been told to not mix second stage vendors. I now see how the two are so interdependent on being tuned to one another. I must have just got lucky that my XTX50 and 620ti both play nice with the Apex DST 1st stage (perhaps the 620Ti is suffering a little not being mated with a Scuba Pro MK 25, but I hadn't noticed). I'm not one to typically listen when told to do or not to do something if I'm not given the why behind the recommendation.

Thank you for sharing this!

 

[lowwall]

What an amazing response and detail on how the whole flow system works vs simple piping dynamics!
I thoroughly enjoyed learning this! It also makes me more confident that that simple piece change could cause the issue and reinforces the previous suggestion by @lexvil of sticking with the original factory piece. Now I understand the depth behind your first statement about the new piece disrupting the venturi flow.

Given this new understanding of how changing something so seemingly benign can have such a cascade effect I may just order a spare one or two from Apex and not fiddle with it any further. Though, since I can't return the now molded piece, no harm in removing some material to get the two in similar dimensions. I can't break what I'm not using right?

I wish this explanation had been given when I've been told to not mix second stage vendors. I now see how the two are so interdependent on being tuned to one another. I must have just got lucky that my XTX50 and 620ti both play nice with the Apex DST 1st stage (perhaps the 620Ti is suffering a little not being mated with a Scuba Pro MK 25, but I hadn't noticed). I'm not one to typically listen when told to do or not to do something if I'm not given the why behind the recommendation.

Thank you for sharing this!

Happy to help.

FWIW, most combinations of first and second stages work fine together. Neither knows what is of the other end of the hose, so everything will work as long as the first stage is putting out gas at an IP that is within spec for the second (and octo).