Poor air delivery or Weak Diaphragm?

[James79]

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)

The majority of "don't mix and match" is marketing (vendors wanting to upsell the whole package).... As @lowwall stated, all the second stage cares about the 1st stage is that it provides air at an intermediate pressure (IP) within the range it can be adjusted to. Most modern regs have significant overlap in their IP ranges (main exception I know off hand is Poseidon at 165 psi). Where the issue can come in is aftermarket parts within a second stage having unsuspected consequences.... Like you found with the "minor" inside diameter change of the mouthpiece having a major effect on venturi.
Short version: most 1sts and 2nds can be mixed at will with no ill effects.
One last thought on that. A balanced first stage provides a stable IP throughout the supply pressure range. A balanced second stage is relatively unaffected by IP variations. There are some other minor effects involved, but that's the main point. Which means a balanced first with balanced or unbalanced second will perform the same right down until the tank is at or below IP. An unbalanced first with a balanced second will behave about the same. An unbalanced first with an unbalanced second will breath a tiny bit harder as the tank pressure drops.

Respectfully,

James

 

[lowwall]

The majority of "don't mix and match" is marketing (vendors wanting to upsell the whole package).... As @lowwall stated, all the second stage cares about the 1st stage is that it provides air at an intermediate pressure (IP) within the range it can be adjusted to. Most modern regs have significant overlap in their IP ranges (main exception I know off hand is Poseidon at 165 psi). Where the issue can come in is aftermarket parts within a second stage having unsuspected consequences.... Like you found with the "minor" inside diameter change of the mouthpiece having a major effect on venturi.
Short version: most 1sts and 2nds can be mixed at will with no ill effects.
One last thought on that. A balanced first stage provides a stable IP throughout the supply pressure range. A balanced second stage is relatively unaffected by IP variations. There are some other minor effects involved, but that's the main point. Which means a balanced first with balanced or unbalanced second will perform the same right down until the tank is at or below IP. An unbalanced first with a balanced second will behave about the same. An unbalanced first with an unbalanced second will breath a tiny bit harder as the tank pressure drops.

Respectfully,

James

This is all good info. I'll just add that Mares is the other big brand to use a higher IP, although not as high as Poseidon. The center of most manufacturers spec for IP is 9 bar/130 psi, Mares is 10bar/145psi. Mares is also an example of a brand that uses balanced first stages (except for their rental spec piston first stage) and unbalanced seconds. They work well together because the firsts are engineered specifically to provide a very stable IP so the unbalanced seconds have consistent performance.

It's very easy to adjust the IP of a Mares first stage and I would not hesitate to use one that is adjusted to 9 bar with other seconds, but I would be a little wary about doing the reverse and using Mares seconds with a first from another brand unless I could see how stably it could provide 10 bar by looking at an IP gauge at various tank pressures and flow rates.

Which reminds me. An IP gauge is a very good thing to have as it can tell you quite a bit about the health of your first stage. They are cheap to buy and easy to use, you just pop them on to the end of the hose you normally use to inflate the BC.

The next bit is copied from the Intermediate Pressure check section of @Couv's invaluable Regulator Inspection and Checklist post.

Find out what the IP range should be for your regulator (most are ~ 135 +/- 10 psi.) Connect the regulator to a tank and pressurize the system. Connect the IP gauge to the LP inflator hose, and lightly press the purge a few times to "cycle" the regulator. The IP should dip whenever air is flowing and immediately return to the acceptable range and remain steady. Leave the regulator pressurized with the IP gauge connected for several minutes to check for slow IP creep. If the IP tends to climb, that indicates a problem with the first stage and must be corrected.

 

[duke dive medicine]

The other consideration with increased work of breathing is hypercapnia (CO2 buildup). With extremely restricted inspiratory flow there is also a risk of negative pressure pulmonary edema, though the discomfort you described would probably force you to abort before that happened.

Best regards,
DDM

 

[landshark_IPA]

The other consideration with increased work of breathing is hypercapnia (CO2 buildup). With extremely restricted inspiratory flow there is also a risk of negative pressure pulmonary edema, though the discomfort you described would probably force you to abort before that happened.

Best regards,
DDM

I am aware of hypercapnia being the result of short breathing (got an education on it once when my father was in the hospital for shortness of breath due to it and the respiratory nurse gave us the run down after getting him to take slow deep breaths).
That was actually my very first thought of the cause which is why I stopped the decent and hung out at the surface.

The "lack of air" feeling was immediate with the reg, it wasn't after a few breaths, but from the very first. Lowwall was spot on about the restricted gas egress causing the airflow to not fully open. I was literally lacking air.

Here's a side pic of the offending mouthpiece (blue) and the Scuba Pro 620Ti's mouthpiece (which doesn't reduce orifice size either). Notice how the mold actually restricts in dimension after the regulator mounting pipe. What's worse is that the material thickens at that point on the inside to give it strength but I guess more pleasing aesthetics? Biggest waste of $50 in my life!

And here is the best "inside" view I can get. This is my wife's unformed piece (which we'll be returning) as compared to my beloved Apex Comfo-Bite. The Apex opening is larger, but it's a little hard to see with the comfort bridge in the way. You also get a feel for how much the JAX protrudes into the airway when referencing the above image of how it dips in after clearing the regulator, and that's with the packaging/molding insert still installed.

 

[tursiops]

I am aware of hypercapnia being the result of short breathing (got an education on it once when my father was in the hospital for shortness of breath due to it and the respiratory nurse gave us the run down after getting him to take slow deep breaths).
That was actually my very first thought of the cause which is why I stopped the decent and hung out at the surface.

The "lack of air" feeling was immediate with the reg, it wasn't after a few breaths, but from the very first. Lowwall was spot on about the restricted gas egress causing the airflow to not fully open. I was literally lacking air.

Here's a side pic of the offending mouthpiece (blue) and the Scuba Pro 620Ti's mouthpiece (which doesn't reduce orifice size either). Notice how the mold actually restricts in dimension after the regulator mounting pipe. What's worse is that the material thickens at that point on the inside to give it strength but I guess more pleasing aesthetics? Biggest waste of $50 in my life!
View attachment 733294

And here is the best "inside" view I can get. This is my wife's unformed piece (which we'll be returning) as compared to my beloved Apex Comfo-Bite. The Apex opening is larger, but it's a little hard to see with the comfort bridge in the way. You also get a feel for how much the JAX protrudes into the airway when referencing the above image of how it dips in after clearing the regulator, and that's with the packaging/molding insert still installed.
View attachment 733295

Get a SeaCure.

 

[landshark_IPA]

Get a SeaCure.

Looking at the SeaCure X, I saw this in the description:
"Type also includes an improved one-piece molding and sealing attachment with a bite limiter which eliminates the possibility of over closure during the heat molding process. Over closure reduces air flow during diving"

I also noticed they have 5 sizes and a chart which states Apeks regs use #4. I also found this "SeaCure for Apeks" thread in the forums that talks specifically about Apex regs and SeaCure mouthpieces. Back in 2012, they directly stated it was not a good idea, then in 2013, the thread was updated to announce size 4 for Apeks!! I just purchased a pair from scuba.com, we'll see how things go. I'll update this thread once I've tried them out.

I wonder if my issue with the JAX was an incompatible mouthpiece for my regs (probably), or "over closure". The JAX comes with various support components that must be used during the molding process to prevent such things, so I'm guessing its simply not compatible with the required air flow.

More and more information proving Lowwall's point. Heck, I'll be avoiding any aftermarket components that say "fits most.." and stick with proven compatible elements from now on.

Thank you everyone for your excellent and continued input!

 

[dmaziuk]

...
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?
...

On a related side-note, look up "uddiyana bandha" on youtube -- that is a diaphragm stretch that's a much better exercise for your lung fitness than a flow restrictor.

 

[Pearlman]

I am a new owner of both the XTX50 And the the Scubapro S600. I find the Apeks XTX50 such a wonderful fit and it balances so well on my jaw without a sensation of excessive weight (on land) that I instantly began regretting my Scubapro 2nd stage purchases. So I am surprised you wanted to change the mouthpiece on the Apeks. If I could sell my S600 easily without loss, I would and get another XTX50 in place. I am all admiration for its ergonomics and engineering design and thought process behind it - small things done perfectly are a delight.

 

[landshark_IPA]

I am a new owner of both the XTX50 And the the Scubapro S600. I find the Apeks XTX50 such a wonderful fit and it balances so well on my jaw without a sensation of excessive weight (on land) that I instantly began regretting my Scubapro 2nd stage purchases. So I am surprised you wanted to change the mouthpiece on the Apeks. If I could sell my S600 easily without loss, I would and get another XTX50 in place. I am all admiration for its ergonomics and engineering design and thought process behind it - small things done perfectly are a delight.

Your reply is rather ironic considering where things landed...
There was nothing "wrong" with the Apex Comfo-Bite mouthpiece, other than a little bit of "tug" when I would turn my head with my long-hose primary. I heard great things about the moldable pieces, so I thought I'd give it a try. I regretted both options. You've already read about the JAX... It was a great mold, but not compatible with the XTX50 flow needs. I tried the SeaCure which was a perfect compatible fit to the reg, but a terrible mold, very uncomfortable (rubbed my lower gums), and increased jaw fatigue due to increasing the effort to hold it in place.
After these two attempts, the Apex mouthpiece is back in place with 4 replacements on back order, ETA August.
I only got an Apex and Scuba Pro secondary regulators to ensure that at least one of my units could be serviced should I be traveling abroad. In hindsight, I would have just gone with dual XTX50s. I plan to eventually sell my s620Ti's at a loss when I have the funds to first purchase their replacements.

 

[Pearlman]

Your reply is rather ironic considering where things landed...
There was nothing "wrong" with the Apex Comfo-Bite mouthpiece, other than a little bit of "tug" when I would turn my head with my long-hose primary.

The “tug” is likely due to the hose reaching its limit due to the way you wrapped it behind your neck? Do you use a swivel adapter?