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Post by seakrakken on Jan 4, 2005 23:44:56 GMT -8
I think you've hit the nail on the head Searat! I should have thought of it myself. If the Tygone tube folds at a sharp bend and collapses then that would readily explain the resistance I experienced.
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Post by nemrod on Jan 8, 2005 12:05:00 GMT -8
I did not actually use Tygon but instead used a blue urethane fuel line often seen on ultralights and small aircraft. The line is the same diameter as the Tygon mentioned but is much less prone to kinking but is still very flexible. This is a kink proof tubing! Therefore I am certain that my tube was not kinked and the poor breathing resulted from the loss of or reduced venturi effect. Nemrod
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Post by seakrakken on Jan 8, 2005 13:49:42 GMT -8
I have since removed the tubing from my MIstral and tried again. The results were to me surprising. The venturi effect makes all the diiference. I had thought that the friction of the intake hose would be more of a problem. Instead it seems to have no impact. That venturi nozzle makes all the difference. It is possible that if the valve body had no other ports other than the one of the venturi jet that it could make the tubing a beneficial change but, I think back pressure in the tubing may have been a contributing factor to what I experienced.
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Post by nemrod on Jan 8, 2005 17:47:54 GMT -8
Seakraken, yes, sad to say but the tube idea just does not work so good, darn! The venturi effect is very important for the Mistral to operate correctly and breath easily apparently. Had you not used your Mistral without the tube "rig" in place? How do you think it compares before and after? To me the Mistral breaths really well without the tube and with it your jello analogy fit very well. Nemrod
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Post by SeaRat on Jan 8, 2005 19:31:06 GMT -8
Okay guys, we really need a bit of a Mistral Tutorial here. The "tube within a tube" principal really does work, but has it's own problems. As I said, I have a DX Overpressure Aqua-Lung, circa 1955-1956. Here is what Fred Roberts wrote about it in Basic Scuba: I have replaced the outer hoses with SCBA hoses, which a several inches longer than even the regular hoses available today. I have also replaced the inner hose with a different one which will not collapse, but is also impervious to corrosion (which the original was not). These changes have allowed me to drop my twin tank unit lower on my back, and this gives me extreme ease of breathing, and further removes the bubbles from interferrence with my macro photography. So I really like the unit. Recently, I developed a small hole in the mouthpiece, and that was very problematical as it allowed a mist of air to be injected directly down my throat. But I have replaced the mouthpiece, and it's now functioning mormally again. But, to further the tutorial on the Mistral venturi, let me give more information on its development from Fred Roberts in his book: Mr. Roberts also has a section on what a venturi actually is in another section of the book, which I don't have time to type in right now. Notice in the text above he states that the Mistral orifice overcomes the DW orifice's problems, and "approaches" the performance of the DX. The DX hose within a hose concept still out-performed the Mistral, but with the above-mentioned problems. I hope this provides some of the reasoning behind the Mistral orifice, and will allow the discussion to proceed with the knowledge-base the Fred Roberts provides us. John
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Post by nemrod on Jan 8, 2005 19:52:21 GMT -8
SeaRat, I am very mechanical but realize that I probably am missing something here, what I am missing is the part I don't know--lol. Anyway, additionally, is there a diagram that shows the innards of the over pressure unit you have compared to the Mistral? Perhaps I and SeaKraken were incorrectly installing the inner hose? and you have a different suggestion? I am not arguing, really, I just want to understand fully. Thank you for the excellent and informative posts that you always make!! Nemrod
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Post by SeaRat on Jan 8, 2005 21:46:16 GMT -8
Nemrod,
I had Linda put a diagram of the DX Overpressure unit into the last post, so refresh and look at it again. The diagram came from page 161 of Rick and Barbara Carrier's book, DIVE: The Complete Book of Skin Diving, Wilfred Funk, Inc., 153 East 24th St., N.Y., 1957. This was, in fact, the first venturi-assisted two hose regulator that US Divers came out with, as it came out before the DA Aquamaster when the DA Aqualung regulator was king.
I also put two photos of me taken with my Nikonos II (another antique) last summer on the Clackamas River by one of the lifeguards there. The two photos show me wearing the DX Overpressure regulator on my twin 42s with the Sherwood manifold and a backup Sherwood Blizzard regulator. Note the length of the hoses that I've put on the DX Overpressure regulator. The regulator can easily handle this length hose because of the inner hose; other regulators would have a falloff of performance with the longer hoses due to hose resistance.
Now, concerning what you guys are doing compared to what the DX Overpressure regulator does, let me explain a few things (some of them I've talked about above). First, the DX regulator had a hose within a hose all the way to the mouthpiece, where it dumped air aimed directly down the diver's throat.
Your modification of the Mistral does not do that, and stops short of the mouthpiece, possibly compromising the venturi effect. The Mistral orifice is designed to produce exactly the right venturi for the hose/mouthpiece system. By modifying it, and still using the Mistral orifice, you may have defeated the system. The Mistral orifice has two holes drilled in the side of the venturi, and they aren't small holes. They let a significant amout of air out of the orifice. If you did not in some way cover those holes, then the venturi may be over-compensated for by air coming from those holes. The DX regulator had a fitting, actually, to which the inner hose was attached, without holes drilled in it.
The Mistral venturi nozzle has a decreased hole designed in the end of the nozzle which accelerates the air going down the intake hose. It also helps push air out the two compensating holes. If you did anything to cause more air than normal to come out of those holes, you could have compromised the venturi effect, or negated it altogether.
The DW regulator differed from both the Mistral and the DX in that the venturi nozzle was a screw-in nut with a simple hole in it. This is why it was so violent in its venturi effect, and why it had to be aimed to one side of the intake hose instead of directly down it. This regulator was also named the Stream-Air and the Jet-Air regulator.
To make it a Mistral, you needed to not only change the venturi nozzle, but then take the pin out holding the top box in place and redrill it so that the nozzle was aimed directly down the intake hose.
My reconstruction of the DX Overpressure regulator concept would be to take the Mistral's orifice, block the two side outputs, and take a hose within a hose concept directly into the mouthpiece. One wagon wheel would have to be drilled out, and the tubing goes all the way to the far side of the mouthpiece (being held into place by glue on the far wagon wheel). An oval hole would then need to be cut into the side of the tube, and aimed directly down the mouthpiece into the diver's mouth. Glue would need to be placed in the far end of the tubing to prevent water accumulation and subsequent misting. The glue would need to be both non-toxic, and also allowed to dry and cure for several days.
I hope this discussion helps in the understanding of the Mistral venturi system, and how the tube within a tube concept led to it.
John
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Post by seakrakken on Jan 8, 2005 22:41:03 GMT -8
Great input Searat. This is why I love this forum! I've just got'ta get that book by Fred Roberts! I'm the kind of person that just never wants to leave well enough alone. I love to tinker with things and try to "improve on it" ;D When I tried that Tygone tubing experiment I had pushed the tubing all the way up against the valve housing thus covering up the side holes on the venturi jet. It is possible that the tubing may have kinked somehow while I tried it but I don't think so. It is as you illustrated so well more likely that I had defeated the venturi action by terminating the tubing just short of the wagon wheel. Like the Coyote of Loony Tunes fame I'll keep on trying different things until that magical day when I get it right ;D
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Post by SeaRat on Jan 9, 2005 0:19:52 GMT -8
!!!!!DANGER[/U]!!!!!
At work, where I work in the safety field, we have what we call "Alert Messages" whenever there is a problem that could affect a person's safety. I have just thought of one here, and so will state it below:
DO NOT, UNDER ANY CIRCUMSTANCES, PUT A VENTURI TUBE INTO YOUR MOUTH WITH NO WAY FOR THE AIR TO ESCAPE. TO DO SO COULD OVERPRESSURIZE YOUR LUNGS, AND LEAD TO AN AIR EMBOLISM! THIS COULD BE LIFE-THREATENING.[/I]
The DX Overpressure breathing regulator had a venturi tube which went into the mouthpiece, and pointed the air at the diver's mouth. However, it ended inside the mouthpiece, where any excess air would vent out the exhaust hose.
There have been reports of children putting a tube connected to the regulator of a helium cylinder into their mouth and cracking the valve in order to inhale helium, and speak with a very funny voice because of the lighter gas. Some of those children embolized, and died!
Do not ever put any pressure tubing directly into your mouth and breath off it! The results could be fatal.
John
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Post by nemrod on Jan 9, 2005 0:43:59 GMT -8
I can second the part about put pressureized air into the lungs. I inflated mine pretty good once long ago and it hurt like heck--I did not die-lol---but I don't suck air out of a tank no more either! Cool Nikons, I once had a Nikonos III, I stupidly sold it and bought a video camera and housing. I wish I had the old Nikonos! Thanks for the diagram as well. I think that given the good performance of my Mistral I should just leave it alone for the time being. I am sure it is breathing a sigh of relief. Nemrod
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Post by SeaRat on Jan 9, 2005 16:11:52 GMT -8
Nemrod and Seakkraken, and any others trying to modify the Mistral to the DX Overpressure concept--Don't.
I just looked at some of my older Mistral innards, and the orifice extends almost to the top box opening for the inhalation tube. It is also not centered on it, but very low to the opening. This means that any tubing you put on the Mistral orifice will kink going over the opening to the inhalation hose. On the DX, the tubing connector only extends half that distance, allowing the tubing to smoothly go into the inhalation hose. The Mistral orifice won't allow that, so I would not recommend using it in this manner.
Nemrod, your Mistral can breath easier now;D.
John
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Post by nemrod on Jan 12, 2005 11:14:39 GMT -8
This is a probably dumb question but what is the correct lever height for the Mistral. When I took my Mistral apart for rebuild the lever height was slightly proud to the case. In other words, a straight edge layed across the box showed the lever approx 1/32 proud. This Mistral has never been taken apart therefore I believe this setting was factory. Is this the correct setting for the lever assembly or if not what do you go by? Thanks. Nemrod
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Post by Bryan on Jan 12, 2005 12:26:11 GMT -8
The factory setting is level with the box. After the diaphragm gets some wear on it and stretches a bit you may have to raise the lever height a little to compensate for that. If there is too much space between the diaphragm and the lever you will have to pull harder to get the lever to depress and start the flow of air thus increasing your breathing resistance. Water pressure will take care of a lot of this but the regulator will breathe easier if there is no gap or a very slight one between the lever and the diaphragm to begin with.
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Post by SeaRat on Jan 23, 2005 16:14:31 GMT -8
I have a publication called Science Diving International, edited by N. C. Flemming. It is the "Proceedings of the 3rd Symposium of the Scientific Committee of Confederation Mondiale des Activities Subaquatiques, 8th-9th October, 1973." In it there is a paper titled "An Attempt to Link Objective and Subjective Performance of Sport Divers' Regulators," by R.J. Nyman and J. G. Van Der Walt, a study sponsored by the South African Under-water Union, P.O. Box 201, Rondesbosch, Cape Province, Republic of South Africa.
I bring this up because some have asked why double hose regulators have not been tested for flow. They have, in the above study. This pertains directly to the above discussion on the use of the Mistral under varying tank pressures. Here is a quote under one of the figures:
The curve for the 190 Bar (2756 psi) evaluaton shows a begining suction pressure at 0 flow at -10 cm of water, at 100 liters/minute going up to about -15 cm of water, and at 200 liters/minute going up over -20 cm of water.
The curve for the 140 Bar (~2016 psi) starts at -4.5 cm of water at zero flow, approximately -7 cm of water at 100 liters/minute flow, and -12 cm of water at 200 liters/minute of flow.
The curve for 90 Bar and 40 Bar were nearly identical, starting at about -2 cm of water at zero flow, going up to -4.5 cm of water at 100 liters/minute, and about -9 cm of water at 200 liters per minute.
The maximum flow that they showed in the graph was about 390 liters/minute. The suction pressure to get about 350 liters per minute for the 190 Bar (2756 psi) pressure was huge, at over -30 cm of water suction effort. The lower pressures fared better, at between -23 cm and -27 cm of suction effort to get a flow of about 390 liters per minute (140, 90, and 40 Bar).
As a contrast, they also tested a number of Nemrod Snark III regulators, which ranged from -2.2-3.8 cm cracking pressure at zero liters/minute to -8.3 to -17.4 cm of water suction effort at 380 liters/minute flow (again tested at 40, 90, 140, and 190 Bar). The two-stage design of the Snark III helped a lot to decrease the suction effort over the single-stage, upstream valve design of the Mistral.
To me, this says that while we probably can get away with putting a Mistral on a 3000 psi tank, we ought not do it because of the design problems inherent (Cousteau's use aside) in doing so. I'll keep my 1800 psi tanks for my Mistral and DX Overpressure Breathing regulators, and use my two-stage regulators (DA Aquamaster, Snark III, Trieste II and Hydro-Twin) on the 3000 psi systems.
John
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Post by seakrakken on Jan 24, 2005 0:46:13 GMT -8
Can't argue with the numbers! Thanks for the research SeaRat. Where do you find stuff like that?
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