Regulator Geeks: Scubapro Mk19EVO - teardown & discussion

[Angelo Farina]

@Nemrod, WOB is measured with a fixed sinusoidal ventilation cycle, same volume and same rate for all regs.
Humans are not fixed machines. My claim is that, when breathing from a 109, I modify my breathing cycle, resulting in much slower exhalation and lower breathing rate. As the energy wasted over the cycle is the integral over time of pressure multiplied by volume rate, with the modified breathing cycle I waste less energy per minute than breathing with a modern reg, which, yes, provides me much more air (unneeded), in a shorter and faster breathing cycle (which is much less efficient, due to the "death volume" which simply goes up and down not reaching the alveoli).
When the volume rate reduces, the overpressure required for winning the exhaust restriction diminishes strongly, as it is roughly proportional to the square of the flow rate.
You are dealing with physics, is am talking about physiology...
People (particularly engineers, as me) tend to give more weight to measurement results made with accurate instruments than to what your body is telling you. I did learn the error in this approach in a completely different field (acoustics, that is my main job).
When technological devices interact with human beings, a purely physical approach is quite reductive in evaluating what happens in our body (and in our brains, which is strictly interconnected with our body).

 

[Mariner11]

Sorry I missed the talk due to family issues thanks for putting up the video

 

[datth]

Thank you Rob for the very educational teardown! So much knowledge and wisdom!

Quick question on the piston vs diaphragm debate, if you don't mind. An often touted/repeated pro of piston reg (with the Mk25 in particular) is its ability to tolerate flooding as a stage/deco reg on the occasions where it's depressurized underwater. While this is true, it seems that the end result is the same that you gotta service your 1st stage afterwards anyways. It seems like a rather moot point just like the flow rate debate.

What's your opinion on this, @rsingler ? Thanks!

 

[lexvil]

Finally finished, very informative but I’ll be sticking with my 17evo’s. Rob convinced me through his evangelism to give up on the self destructing mk25 for diving in california grit and he followed that up with convincing me on the center balance seconds.

thank you Rob.

 

[Nemrod]

@Nemrod, WOB is measured with a fixed sinusoidal ventilation cycle, same volume and same rate for all regs.
Humans are not fixed machines. My claim is that, when breathing from a 109, I modify my breathing cycle, resulting in much slower exhalation and lower breathing rate. As the energy wasted over the cycle is the integral over time of pressure multiplied by volume rate, with the modified breathing cycle I waste less energy------

.
People (particularly engineers, as me) tend to give more weight to measurement results made with accurate instruments than to what your body is telling you. I did learn the error in this approach in a completely different field (acoustics, that is my main job).

It is both measurable and in use noticeable to me and results often in a headache from CO2 retention. If you can modify your breathing cycle as you state then you can apply the same techniques to a regulator with better/lower (measurably) exhaust effort. Any sort of engineering terminology you can pull from your hat will not change the fact that a larger exhaust valve (G250/G260/Legend etc.) will, through a complete cycle, regardless of what breathing techniques you use, have a lower WOB. If you are able to get along with the lesser performance and restrictive exhaust of the 109/156 and similar vintage second stages, then be happy, I am not telling you to toss them away. I enjoy my 109s also but I use them for cake dives. The last of the line CE 156 BA second stages did have a full size exhaust valve crammed into the existing manifold and used as far as I know the same tee. I have only seen a few in the wild and I agree those are a grail regulator, the small valve versions, well, they are pretty.

James

 

[Bald Wookie]

Watched the whole vid - thanks @rsingler

Would you be able to put a comparison shot of the mk25 and the mk19 with the yoke/din connections lined up? I often run into issues with rental tanks where some have a short valve, and using the 5th port for a 7ft hose the reg is on a weird angle and/or the other hoses get weirdly angled with the tank.
I'm curious how much less the 5th port sits below yoke/din.

Thanks!

 

[Angelo Farina]

It is both measurable and in use noticeable to me and results often in a headache from CO2 retention. If you can modify your breathing cycle as you state then you can apply the same techniques to a regulator with better/lower (measurably) exhaust effort. Any sort of engineering terminology you can pull from your hat will not change the fact that a larger exhaust valve (G250/G260/Legend etc.) will, through a complete cycle, regardless of what breathing techniques you use, have a lower WOB. If you are able to get along with the lesser performance and restrictive exhaust of the 109/156 and similar vintage second stages, then be happy, I am not telling you to toss them away. I enjoy my 109s also but I use them for cake dives. The last of the line CE 156 BA second stages did have a full size exhaust valve crammed into the existing manifold and used as far as I know the same tee. I have only seen a few in the wild and I agree those are a grail regulator, the small valve versions, well, they are pretty.

James

You did not get the point. Yes, a modern reg wil require less WOB for the same volume of air breathed than an old one.
And in case of need, a modern reg can provide much larger air flow.
But, for a given reg, the WOB is proportional to the SQUARE of the air volume vented per minute.
Using old regs, many people, as me, tend instictively to switch to a much slower ventilation cycle, so the air usage reduces significantly. In particular, the exhalation becomes much slower and profound. This way you also reduce the WOB.
In theory one should control his breathing in the same way when using a modern reg. However, this is not our instict: a modern reg has almost no resistance, so you tend instictively to breath "normally", a very shallow and fast cycle. Which wastes a lot of air and in the end requires more WOB (due to the larger air flow) and risk of CO2 accjmulation (due to fast, short exhalation).
Very few divers have enough self control for breathing in a controlled way. Under stress, or distracted by other tasks, breathing goes on under control of istinct and automatic reflexes.
A reg with some additional resistence on exalation makes the proper way of breathing to kick in spontaneously.
At least for me, and some other old-style divers who were primed using CC rebreathers for months, during their first diving course.

 

[datth]

Thank you Rob for the very educational teardown! So much knowledge and wisdom!

Quick question on the piston vs diaphragm debate, if you don't mind. An often touted/repeated pro of piston reg (with the Mk25 in particular) is its ability to tolerate flooding as a stage/deco reg on the occasions where it's depressurized underwater. While this is true, it seems that the end result is the same that you gotta service your 1st stage afterwards anyways. It seems like a rather moot point just like the flow rate debate.

What's your opinion on this, @rsingler ? Thanks!

I guess I found the answer from Rob himself earlier. Thanks!

 

[rsingler]

I guess I found the answer from Rob himself earlier. Thanks!

Aw, too bad. I was halfway through building a set of diagrams that show exactly why a diaphragm locks up after flooding. Unfortunately, it slipped off my radar and I forgot about it.

The short answer is that it has to do with how a diaphragm balances, as opposed to a piston.

 

[datth]

Aw, too bad. I was halfway through building a set of diagrams that show exactly why a diaphragm locks up after flooding. Unfortunately, it slipped off my radar and I forgot about it.

The short answer is that it has to do with how a diaphragm balances, as opposed to a piston.

Would love to see those diagrams whenever you finish them anyways. I'm sure we would all learn a lot.

All my regs are Apeks XTX's with FSR/DS4/DST, save my argon MK2. Do they lock up when flooded like other diaphragm regs?

I used to own 2x MK25Evo/S600's, but sold them away recently because I just couldn't deal with the unsealed chamber and finicky post-dive maintenance.