DA Mistral Project

[Chez7222]

Very interesting an in-depth input based on several scenarios, controlled or otherwise John & Luis. What I deal with in my line of work is practicality and ease of use. Also durability and longevity as in, I'm willing to sacrifice some performance for a part which tends to be more rugged than another. I agree with Nemrod on this but obviously I don't have as many dives with this type of equipment. Bottom line up front, what would you rather have in your can?

 

[simonbeans]

Both types of duckbills have +s and -s. The original rubber ones worked well, but they had a limited longevity. The new silicone ones are almost indestructible. However, that being said they are very thin and sometimes if you could possibly inhale very sharply it can become inverted. I never had it happen, but I know others who have had it occur. The DBE was a three person development and does eliminate some other issues with the duckbill. With it, the exhaust hose goes on and off the horn as easily as on the intake side. Some of the early ones had a minor issue with the mushroom valves popping out. However, I believe that problem is fixed. In order to use the DBE, it must be installed in the can. Again, not a major issue, but it does take a bit of care and following directions. Once installed, the DBE can be rather difficult to remove, if you would want to. All this being said, I think both work fine in breathing, the DBE might be a bit more convenient in the long run.
Again, you need to decide your reason for diving a double hose, i.e., historically correct or as I prefer, historically reproduction correct. (Using modern reproduction parts that are made visually identical to the original but possibly with different materials, aka silicone vs. rubber). Or do you want to be diving a modern double hose with modern updated parts, DBE, HPR, Phoenix, etc.;
a discussion that rears it head occasionally on this forum but is banded on others.

 

[John C. Ratliff]

Simonbeans, thanks for the input. Since I have no experience with the Duckbill Eliminator, I cannot say about how it works. I do like Nemrod's ideas about it though.

You brought up an interesting idea though about the silicone duckbill inverting; I think that could only happen if there were no non-return valves in the mouthpiece on the exhaust side. For those who are purists, the original Mistral from La Spiro in France came with the "Professional Mouthpiece." This was a metal mouthpiece you will see in the Cousteau movies (World Without Sun, for instance). They did not have any non-return valves in the mouthpiece in the Professional Mouthpiece. This allowed unobstructed breathing, as the mushroom valves in the mouthpiece do somewhat impede air movement (this is better now with silicone non-returns). My Overpressure Breathing regulator (the original USD single stage regulator with a hose-within-a-hose venturi concept) has no non-returns in its metal mouthiness, and is a joy to use.

Enjoy,

SeaRat

 

[simonbeans]

It would make better sense if the inversion came with a mouthpiece without non-return valves. However I know of 3 people who had a duckbill inversion with mouthpieces having non-return valves. I could think of a couple of reasons why, but without good scientific method techniques, I would rather let the speculation come from those who know more about fluid dynamics than I.

 

[Nemrod]

I have had several inverted duckbills, both the silicone type and a NOS duckbill. I use cage valves. I do not recall anything special happening, perhaps the hose got tugged a little, beats me.

Changing subject a little, the four double hose regulators that I dive frequently all have the DBVE, three have the HPR and two have the Phoenix conversion. I have band clamps on all of them. I love my Mistral with the DBEV, Superflex diaphragm, all silicone parts and band clamp. Breaths very nicely and requires virtually no maintenance, just a rinse out.

N

 

[Luis H]

Lewis,

My "data" was from the NEDU--their tests. I was trying to see why their tests came out the way that they did. If my demonstrations are misleading, then why do they correspond to the graphs in the NEDU tests of these regulators?

The answer to this question has several parts to it and it is complex. I also don’t have the time (and this is not the place) for me to teach a hydrodynamics course. I am probably not a very good teacher either. Hydrodynamic courses are normally semester-long courses… not something you get on a message board in the internet.

So I will only address one obvious issue with your demonstration. As you mentioned, you knew what results you expected to see.
The issue is related to lack of scientific methodology.

In the two pictures below you can see that you made adjustment to get the results that you expected to see. You might have thought that you were being impartial and probably didn’t even notice all the adjustments you made.

If you look at the two demonstrations below, you can immediately see that the elevation was adjusted to give the water particles more momentum in the picture on the right (2nd picture). You were probably not even been aware that you were making that adjustment.

You can also see that the stream on the right (2nd picture) is getting narrower toward the bottom (before impacting the horn). The stream gets narrower because the water particles are speeding up (accelerating) the further they drop.

It is also noticeable that the stream on the right is already more turbulent, due to the water velocity, and that the shape of the flow half-way down continues to change. I can’t see how much higher is the faucet, since it is not in the picture.

From the diameter of the streams and the turbulence, it also looks like the flow in the picture on the right (2nd picture) is higher than that in the picture on the left (1st picture). Again, you probably thought both faucets were open about the same amount, but didn’t realize that faucets are not linear. A small change can make a huge difference. You probably adjusted the faucet by eyeballing what it looked right.

Here are two photos of my evaluations:

SeaRat

You were probably not even aware that you made all those (seemingly minor) adjustments to match you expected results, but it is not uncommon to make this kind of error if you are not following strict scientific methodology.

It is a very common issue in college labs, and it is human nature to try to match the expected results. One of the first things we learned in labs was how to follow scientific methods and how to do error analysis.

If you don’t know the fundamental difference and characteristics between open flow and pipe flow, it is not likely that you can truly judge what “minor” adjustments you are making, and how they are affecting your results.

You can’t do any kind of error analysis if you were not even aware that open flow can not be described or analyzed using Bernoulli’s equation (the equation set up that describes pipe/ hose flow). As I mentioned, open flow requires impulse-momentum equations. They are very different.


BTW, the pictures are great. The water droplets are very clear and I like how the action is frozen. The picture quality shows a lot of great details.

Lewis, you are saying this is not a valid "test." Perhaps not, but it let me understand the difference in flow between the exhaust designs I wanted to better understand; yes they are old, vintage even, but that's what I'm interested in.

You still seem to be questioning that open flow and closed flow are two very different types of flow.

When I post an opinion, I try to make it very clear that it is an opinion and of course it is always subject to debate. The differences between open flow and pipe flow are easily verifiable facts, not an opinion.

I don’t post as often as I used to because I don’t have the time (or energy). I can’t rely on my memory for details so I normally research the facts to make sure they directly apply to the subject. I make a lot of effort to avoid mistakes (but I am sure that I have made plenty).

There is a lot more to this subject and fluid dynamics, but I has already consumed too much time...


BTW, my name is Luis not Lewis.

 

[John C. Ratliff]

Luis,

First, the name...my apologies We have a very dear friend named Lewis, and my fingers probably went to that as I typed. I am usually pretty sensitive to names, so I feel pretty badly about that.

Concerning science, without presenting any numbers I don't see how it could be interpreted as a "science project." That was not its intent. Your criticisms are right if, but only if, I was trying to say something from the demonstration other than the obvious differences that could be visually seen.

The science comes from the NEDU's different graphs of breathing resistance; I did not do that science, but it is publicly available.

Concerning the height and the amount of water flowed, I got those results not by "trying" to manipulate anything, but simply by putting the different cans under approximately the same flow. Nothing measured...this was a demonstration, not science, but whenever we try to describe something like resistance of show flow graphs, many find that hard to understand.

I have done some science in my time, but in the field of industrial hygiene. My MSPH degree is in Industrial Hygiene, and my Capstone Project was on occupational noise exposures. I have made presentations concerning noise, which requires a lot of information on noise. So I am pretty familiar with the scientific method. Noise instruments need calibration, for instance, and you need to have a "chain of custody" for any sampling for chemical hazards in order to have varied results.

But I am also a diver, who is interested in vintage diving equipment. I do not own a flow bench, and so sought a means of demonstrating the differences is flow that these photos show. These were "tests" in that I tested the various equipment that I own to see how they perform. They were not "studies" and so do not even approach the criterion for publishable results. But they do demonstrate how water flows through the system. Was this science? No! Was it meant to be science? No! Was it a demonstration people could see and understand--maybe.

Let me give several examples of demonstrations.

--In teaching about double hose regulators, we can show clearing the mouthpiece by raising it above (higher than) the regulator to initiate free flow. Do we measure the number of inches above center line to initiate free flow? No! But it is an effective demonstration.

--In my work, I had workers who routinely worked with liquid chemical hazards--sulfuric acid, hydrochloric acid, hydrofluoric acid, and others like ammonia. These workers, when I first arrived, wore chemical protective clothing, a face shield and safety glasses. I had tried unsuccessfully to get them to wear chemical-protective goggles. They would not do it, as the goggles fogged. So I set up a demonstration where I wore safety glasses and a face shield, and had one worker splash me with a cup of water over the face shield. I got water into my eyes. It was effective in saying that their then-current practices needed to be upgraded. Splash goggles would not do it, so we went to powered air purifying respirators with chemical protective hoods (PAPR). It paid off when one worker was sprayed with 49% HF onto his PAPR-protected face. Was it a scientific demonstration? No! Did we quantify the amount of water splashed on my face? No! Did we match the viscosity of the water with the viscosity of sulfuric acid or phosphoric acid (79%)? No! Did we demonstrate that our then-current PPE was inadequate? Yes!

--I worked a lot with occupational noise. I also taught about hearing protection, and how to fit foam ear plugs. I showed how to roll them to get a good fit, how to place them into the ear canal, and the amount of protection they provided using a Noise Reduction Rating, along with an OSHA-required derating system for real world conditions. Was that science? No! Did we present numbers? Sort of--the NRR is a number, but may or may not be valid depending upon the fit of the plug. A year later, we had a 3M come out with a fit-testing machine for ear plugs, which actually took individuals, had them place the plug into their ear canal, and then measured the noise inside verses outside the ear. Was this science? Yes, it was applied science. Did it improve the fit of our hearing protection devices? Yes, dramatically.

So there is a place for science, but ScubaBoard is not a science venue. It is a discussion board, and the two should not be mistaken.

Luis (I got it right this time), if you have actual science to provide to this discussion, I would like to see it. If you have measurements of duckbills verses a mushroom valve, please present it. If not, please accept that there is a difference in trying to educate with a demonstration verses trying to apply science and engineering to the problem (this is sometimes hard for engineers--I have worked with many). In taking those photos, I was holding the camera in one hand and the bottom box in the other. It was never meant to be a scientifically-valid study, but rather a demonstration of what I had found.

You have helped me to see some of the problems with this demonstration, and I have asked my son about this too. He has his Masters Degree in Mechanical Engineering, and his thesis was on fluid dynamics. He explained some of the meaning behind the Reynolds Number and said that the main problem with my demonstration was that the velocities would be much different. He also mentioned that a duckbill would have virtually no resistance to flow, whereas the mushroom valve would have some as the valve would need to be lifted in order for flow to occur. But with the Duckbill Eliminator, I have looked at it and it appears that there would be very little resistance, as there is no direction change in the air flow. That was not the case for the Healthways mushroom valve I tested.

These kinds of discussions results in learning, and I have learned from this. My hope is that you can learn the difference between an educational demonstration and an engineering scientific study. This was not a "marketing" gimmick, as I am not a sales person, and have nothing to sell here.

SeaRat

---------- Post added February 24th, 2013 at 01:50 PM ----------

I have had several inverted duckbills, both the silicone type and a NOS duckbill. I use cage valves. I do not recall anything special happening, perhaps the hose got tugged a little, beats me.

Changing subject a little, the four double hose regulators that I dive frequently all have the DBVE, three have the HPR and two have the Phoenix conversion. I have band clamps on all of them. I love my Mistral with the DBEV, Superflex diaphragm, all silicone parts and band clamp. Breaths very nicely and requires virtually no maintenance, just a rinse out.

N

Nemrod,

I have been thinking about the inverted duckbill, and I think that with a thin duckbill, it would be possible with hose flexing to provide enough negative pressure to invert the duckbill. I like longer hoses, but many hoses are just barely long enough to reach the mouthpiece (depending upon regulator placement). If during an inhalation the diver turned his/her head to the right, and stretched the left exhalation hose, I think enough negative pressure could be imposed in the hose by the increased length to cause the inversion. However, I personally have not experienced such a duckbill inversion.

SeaRat

 

[Luis H]

Oh John,

I can’t believe I am getting dragged into this again.

Demonstrations are great… if they are relevant. You had your co-worker throw water at you to simulate a liquid (that is a very relevant demonstration). You would not have asked him to blow air in your face or throw a foam ball (nerf ball) on your face. Why, because it would not have been a relevant demonstration (if you use air or a nerf ball).

For your demonstration there was obviously no need to try to precisely match the density or viscosity of the fluid (since it is a demonstration). But you would have also objected if one of your co-workers would have proposed to use honey or thick molasses. Not because it would have been a mess, but because it would have been a miss-leading demonstration. It would not have provided a relevant dispersion pattern.

If you intended for this to be only a demonstration, why would you have come up with general conclusions like this? No need to answer.

my tests indicate that no mushroom valve will equal a duckbill.
SeaRat

I seriously doubt that your son would have given you a universal statement like this without qualifying very specifically what designs this statement applies to:

He also mentioned that a duckbill would have virtually no resistance to flow, whereas the mushroom valve would have some as the valve would need to be lifted in order for flow to occur.

This would only be correct when comparing some very specific designs. As you said the NEDU had some test results for some very specific designs. That statement those not apply to other designs and it is far from being universally correct.


As I mentioned before, there is a reason why rebreathers use mushroom valves. They are the lowest flow resistance valves that can be designed for this application. A duckbill with the same characteristics (for sealing, etc.) would have a much higher flow resistance.

Before you ask again, I can not share any data. The data is not classified, but I do not have any, I did not ask for any data, any of it is for official use only.

You can try asking any of the rebreathers companies, but I am sure they are not going to share either. I am sure you know that data in the wrong hands can be very dangerous.


In any case this horse has been beaten to death enough.



My “criticism” (as you called it) was intended to be constructive; I apologize if it ever sounded otherwise. I just hope some of it has been helpful.

 

[John C. Ratliff]

Actually, I also consider it constructive criticism. I'll let you have the last say on this.

Concerning asking for data, I read that there had been tests on the Duckbill Eliminator which showed it would "...improve your exhaust flow." I was giving you the opportunity to share that data, not knowing that you did not have it. It appears that there is no data other than that of the NEDU, some of which is now half a century old. My apologies...

John

 

[Luis H]

I thought you were asking for the modern NEDU data. As I mentioned, the data is not classified, but it is not for public release.

There is no data showing that the DBE can improve the exhaust flow. The exhaust resistance/ impedance is so low (for duckbills or modern mushroom valves), that taking improved flow measurements is not very realistic.

The data I have taken shows exhaust flows so low (for duckbills or mushroom valves) that it is hard to measure. Yes, I increase the flow rate to try to match the Reynolds number found at depth (in order to measure relevant flow impedance).

My instruments only measure to 0.1 inWC. Since it is an analog needle gauge, I can estimate 0.05 inWC, but anything less than that is very imprecise… but at that point, why do I care.

At some point we may get better data from the Dive Lab in Panama City.