Mk5 possible devil spring?

[L13]

I am considering sport diver depths to 165 feet and conventional open circuit scuba gear.

The statements you were arguing against were talking about deep air (both the Navy's evaluations, and Scubapro's design decisions).

That is not exactly correct. The volume does not change with depth. Density of course does but your lungs hold the same volume at 5 atmospheres as they do at the surface.

True, my (and the Navy's) calculations assumed that.

The demand flow through the regulator remains the same, the density increases, but the lpm is the same as at the surface.

That is not true. The volume of gas that a regulator can flow changes with molecular density. Look up Reynolds number. A regulator that flows ~2,000 LPM STP of gas at 1 ATA does not flow ~20,000 LPM STP of gas at 10 ATA.

Peak inspiration flow is an interesting point as a diver's SAC or RMV is an average over time but at the moment of peak inspiration the flow could be instantaneously much higher. And there is enough volume in the system to compensate at sport diving depths. You guys diving at 10 atm on open circuit, at that point I want to be in a submersible (a good one) or on a CCR.

So, no, I am not considering esoteric possibilities at great depths.

But the Navy and ScubaPro's designers were. The 5th port came about because of that, not routing concerns.

 

[Nemrod]

I did not drag the Navy into this, another poster did. I disregarded the Navy document as dated, inconclusive and did not agree that it substantiated any difference between top or side of turret ports due to the incompleteness of the test, small number of test samples and lack of basic scientific method.

Without going too deep into the quagmire and getting into mass flow and Reynolds numbers we can look at the diver as a constant volume machine, nothing the Navy did then or now changes that. Now, the density and therefore the mass flow must increase and as we get deeper and deeper the effects of that increase in density become important. But at sport diving depths and where this particular argument began, the end port vs a side port on a Mark 5, you are not going to see any difference as a sport diver. You will see more difference due to 26 inches standard hose vs a 72 inches hose. And that has been hashed out over and over as has this subject multiple times.

I like your point though about instantaneous respiratory influx. Good point to consider on. Thanks for that. When we average things, well, we lose the highs and the lows, such is an average of anything. And in doing so that is incomplete data as you pointed out.

 

[John C. Ratliff]

Nemrod,

I was not challenging your basic assumption that the diver won't feel the difference under sport diving circumstances. You can see that the two R/M/V tested for normal ops (22.5 and 40 R/M/V) in the graphs below are almost identical. It is only when the work requirements get really bad that you would see this difference.

Now, lot me say that I have investigated one diving fatality that involved a Scubapro 109 regulator. This was decades ago, at the request I believe of the local authorities. It was a situation where the diver was overweighted, had been digging clams out of the bottom, and had passed away I think of a heart attack. If my memory serves me, the guy was obese too. His regulator was in awful shape, and had been adjusted completely in (hardest breathing) using the adjustment knob. He had a sack full of gaper clams, which were quite heavy, and was trying at attain the surface without a BCD. So workload was extreme. He was not deep (probably 40-50 feet at the deepest), but was also fighting a current because of the tides. I say this to indicate that even sport divers can have very high demands and workloads.

I used these charts from a second study of the Pilot regulator that the Navy EDU conducted, and then linked a paper that explained the Navy EDU study methods and why they did things.

Now, the one statement about volume staying the same at depth, while correct, is a bit deceiving concerning regulator performance. Density does make a huge difference in how much air a regulator can output, and comparing surface output with a theoretical output at depth by saying it is the same workload is not really true. It's like the difference between putting water through a facet and using syrup through the same opening; both are liquids and both flow the same volume, but the flow rate will differ. The same principal holds for air on the surface and at depth (not my depth of 23 feet, but sport diving's limit at 130 feet).

I just found an interesting paper on this subject, which I don't have access to right now but my wife might. I'm going to try getting the entire paper. But you can see the abstract here:

THEORETICAL AND EXPERIMENTAL STUDY OF TURBULENT GAS FLOW THROUGH A PNEUMATIC MECHANISM - ProQuest

Explore millions of resources from scholarly journals, books, newspapers, videos and more, on the ProQuest Platform.

www.proquest.com

I also found the original study of the Scubapro Pilot regulator:

https://apps.dtic.mil/sti/pdfs/ADA048033.pdf

SeaRat

 

[Nemrod]

Mr. John, the volume does exactly remain the same at depth. What varies is density of the gas and therefore the mass flow changes in relationship with the density of the gas.

The turret in a Mark V or a Mark 25 acts as a plenum, the direction of the ports out of the turret is somewhat unidirectional.

You guys can believe the top turret port provides a substantial and noticeable increase in flow to the diver over the turret side ports if you want. It can only deliver what the diver demands. As I said, even elite athletes top out around 8 cfm, your stressed diver with a bag of clams is not likely to exceed that amount. That is why he had a heart attack. People have a heart attack shoveling snow. An aquantence of mine had a heart attack on his bicycle in a race and crashed. Fortunately he is going to be okay and has a new heart stint or something like that. Has nothing to do with which first stage port the diver is breathing from. Anecdotal examples just do little for me as proof of anything.

Oh well. Yes, if you get a copy of that please share it. In any case, I am sort of tiring of this thread, but I would like to read that paper please. Thanks. Love you Mr. John .

 

[MARK74]

At the request of Mr. Ratliff, who has done it privately, I delete my two JOKES from the post, I consider it censorship and I delete it for not creating controversy. They have contaminated a post that I opened about the damn mk5 spring talking about the navy experiments and the flow rates of the ******* fifth port, THEN OPEN ANOTHER SEPARATE AND DON'T CONTAMINATE MINE. I am deeply disappointed with the hypocritical, arrogant and puritanical attitude of some of you. I WILL NOT INTERVENE IN THIS FORUM AGAIN DIVE MORE AND TYPE LESS MARK74 ACTIVE SATURATION OVERALL

 

[L13]

@Nemrod, two things can be (and are) true:

• The reason the 5th port exists on the SP Mk5 is that SP and the Navy determined that in extreme conditions it was necessary to provide required flow.
• In normal recreational diving, you can't tell the difference. The main value to a recreational diver of the 5th port is the routing advantage.

 

[axxel57]

Mr. John, the volume does exactly remain the same at depth. What varies is density of the gas and therefore the mass flow changes in relationship with the density of the gas.

The turret in a Mark V or a Mark 25 acts as a plenum, the direction of the ports out of the turret is somewhat unidirectional.

You guys can believe the top turret port provides a substantial and noticeable increase in flow to the diver over the turret side ports if you want. It can only deliver what the diver demands. As I said, even elite athletes top out around 8 cfm, your stressed diver with a bag of clams is not likely to exceed that amount. That is why he had a heart attack. People have a heart attack shoveling snow. An aquantence of mine had a heart attack on his bicycle in a race and crashed. Fortunately he is going to be okay and has a new heart stint or something like that. Has nothing to do with which first stage port the diver is breathing from. Anecdotal examples just do little for me as proof of anything.

Oh well. Yes, if you get a copy of that please share it. In any case, I am sort of tiring of this thread, but I would like to read that paper please. Thanks. Love you Mr. John .

SP designer at least believed that the fifth port on the MK5 with its Venturi provides a significant higher flow than the other four LP Ports.........

 

[axxel57]

On November 1, 2013 I downloaded several images of the U.S. Navy EDU's study of the Mark 5/AIR-1 combination, using both the 4-port and 5-port (with the LP hose to the AIR-1 second stage on the top port) regulators. Unfortunately, I did not download the entire NEDU report, as I thought I'd be able to access it through the Rubicon Research Repository website (no longer on-line). Note the difference in work of breathing and pressure drop between the two regulators at very high respiratory rates and deep depths.

SeaRat

If you still don't have the study, pm me, I could send it to you.

 

[Angelo Farina]

At the request of Mr. Ratliff, who has done it privately, I delete my two JOKES from the post, I consider it censorship and I delete it for not creating controversy. They have contaminated a post that I opened about the damn mk5 spring talking about the navy experiments and the flow rates of the ******* fifth port, THEN OPEN ANOTHER SEPARATE AND DON'T CONTAMINATE MINE. I am deeply disappointed with the hypocritical, arrogant and puritanical attitude of some of you. I WILL NOT INTERVENE IN THIS FORUM AGAIN DIVE MORE AND TYPE LESS MARK74 ACTIVE SATURATION OVERALL

Mark, these "off topic" deviations are actually quite typical of Scubaboard, and make it a very nice forum!
Do not get upset if certain comments are apparently harsh, I ensure you that, although they can appear a sort of personal attack, instead they were given in good faith.
Generally speaking, posts are not necessarily tailored to the OP.
Many peolle post mostly for providing info to the general audience, not to the OP.
And even when you start a thread with a very specific technical question, you should expect that the thread can grow out of control and wandering on completely different topics.
All that said, I warmly suggest and hope that you reconsider your decision to leave.
We all learned from your posts and you look to be a valuable resource for the forum.
You just need to accept that Scubaboard is not regulated and "neutral" as other forums. And this is in reality its beauty!

 

[Nemrod]

Well, I suppose Mark74 has a point except that I think his questions were fully answered, early on. Maybe we should have taken another thread. Esoteric arguments like these can certainly remain civil and this one has, I think, and entertaining and educational.

Perhaps a mod could split the thread please? How can get a mod to do that? Would it be too much work to do that?