I agree with Luis, the new Mistral lacks a proper design to achieve an effective venturi action, much like the Trieste, you can get a low cracking force but the performance still is mediocre.
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new aqua-lung mistral
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I am not sure how bad the venturi in the Trieste is. It is hard to tell because I have found that it has an overshadowing flaw. The diaphragm shape is like a structural dome. You can set the diaphragm in an empty can (no lever or mechanism behind it) and start adding weight on the diaphragm until it moves and it takes relatively a lot weight to move it. I can’t remember the exact numbers (I have it on my notes), but it was not good. It didn’t mater if it was a very soft diaphragm. It just has a bad geometry.
I have some ideas for my Trieste, but again it is in the list of things to do.
Many regulators can be adjusted to very low cracking suction and are very stable. The limiting factor is often the exhaust location to avoid a free flow. A regulator with a cracking effort of less than 0.5 inWC is going to free flow in some position even with the exhaust right in the middle of the diaphragm. When you get vertical just the width of the exhaust (even with a perfectly position duckbill) will be close to 1/2 inch from the center.
For that reason there is no point on get the cracking effort any less than about 0.6 inWC. Then it is the design of the venturi that makes the difference.
When I inhale on a good regulator you will normally see the suction effort dropping after the initial cracking effort. Like I said it often goes into positive flow if adjusted carefully.
I have fine tuned the new Mistral to very low cracking and (in my experience) even if I suck very suddenly I can not initiate any venturi flow. The meter never dips below the initial cracking effort. Note: different flow rates and flow build up will affect venturi effects.
It is kind of like an old Broxton (Navy Type DA, etc.). They can also be adjusted with very low cracking effort, but they have no venturi effect.
I have some ideas for my Trieste, but again it is in the list of things to do.
Many regulators can be adjusted to very low cracking suction and are very stable. The limiting factor is often the exhaust location to avoid a free flow. A regulator with a cracking effort of less than 0.5 inWC is going to free flow in some position even with the exhaust right in the middle of the diaphragm. When you get vertical just the width of the exhaust (even with a perfectly position duckbill) will be close to 1/2 inch from the center.
For that reason there is no point on get the cracking effort any less than about 0.6 inWC. Then it is the design of the venturi that makes the difference.
When I inhale on a good regulator you will normally see the suction effort dropping after the initial cracking effort. Like I said it often goes into positive flow if adjusted carefully.
I have fine tuned the new Mistral to very low cracking and (in my experience) even if I suck very suddenly I can not initiate any venturi flow. The meter never dips below the initial cracking effort. Note: different flow rates and flow build up will affect venturi effects.
It is kind of like an old Broxton (Navy Type DA, etc.). They can also be adjusted with very low cracking effort, but they have no venturi effect.
Double Diver
Contributor
Luis your absolutely right! The new Mistral is a horrendous design (and I use the term design loosely) the guys at Aqualung did not pay any attention to the Flo pattern. The biggest problem is the propensity to fill the air box first, therefore creating a positive presser against the diaphragm. Not not go in to detail here but I have been working on a modified second that creates plenty of venturi effect. The main problem is tuning the effect, so the next step is to modify the unit to allow for a variable bypass and give the diaphragm a little lift, not a lot.
sharkinabus
Registered
The new Mistral has always felt like an unfinished prototype to me.
Second stage bolted onto a Titan, connected to the Titan first stage by an improvised hose arrangement. Re-breather hoses too wide in diameter for comfort and an over bulky mouthpiece.
A good idea but unfinished and wasn't refined enough to go into production.
I have had mine adjusted to improve the cracking resistence but my DAAM and PRAM still breath better.
The Phoenix as others have noted is the ticket if you want to use all the current accouterments while enjoying a double hose regulator. About mine.
Pete
Pete
Luis is right about these two defects in the design of the Trieste. I have a Trieste II, and bought it new. But I was unhappy when it did not breath as well as my USD Mistral at low tank pressure. I actually measured the suction pressure of the regulator, using a home-made water manometer, and it was something around five inches of water--horrible. The diaphragm contributed about 2-3 inches of water inhalation resistance.
So I started experimenting with it. And I sent it to a Vancouver BC dive shop that specialized in refitting the Trieste at the time (1980s). Between the two of us, we created quite a nice breathing machine, on par with the newest double hoses (Phoenix Royal Aquamaster and Mossback Mk III). What did we do? Here's a summary:
--Made a home-made diaphragm with flexible rubberized fabric and Shoe-Goo. Cut out the fabric, and glue the stainless disk on its middle area. Then spread silicone grease on both the top and bottom can sealing edge (which is held in a vertical position with books or other support), so the Shoe-goo won't adhere. Spread Shoe-Goo onto the top box, then carefully place the diaphragm onto the can with the glue. Spread more Shoe-goo on the top of the diaphragm, then place the bottom box on top of the diaphragm, again being careful not to smear the glue. Let the whole thing sit for a few days for the glue to set completely, then separate the two cans and take the diaphragm off. Clean off all the silicone grease from all surfaces, and trim off the excess material (I left about an inch all the way around initially). What I ended up with was a diaphragm which has zero resistance to inhalation pressure.
--The Vancouver BC dive shop took the Trieste II and modified the nozzle. They blocked off one of the two large holes emptying into the second stage housing (the one pointed backward away from the inhalation tube). They then slightly enlarged one of the small side holes to provide just a bit more backflow into the case. With this modification and the new diaphragm, the venturi is tremendous--slightly too good, actually, as there is a bit of blow-by into the exhaust hose.
--Because of this blow-by with the improved Trieste II venturi, I took an old Healthways mouthpiece, and took out the deflection disk that was used in the final Healthways Gold Label Scuba single stage regulator. I mounted this disk, again with Shoe-goo, into the curved AMF Voit mouthpiece (same as the USD curved mouthpiece, but with the "AMF" on the front). I did this on an older AMF Voit mouthpiece made of neoprene; the newer silicone mouthpieces may not allow glue to adhere. If any glue which is solvent-based, as is Shoe-goo, is used, it must be allowed at least a week to completely dry and off-gas. Otherwise, you may be inhaling a solvent during a dive--not a good thing (same with the diaphragm).
This rounded out the modifications. But there is one other characteristic of the Trieste nozzle, and that is that the set screw with the Allen wrench head is slightly off, and can allow the nozzle to not be aimed straight down the hose. I carefully made sure that the nozzle was aimed straight down the hose, and it is now a really wonderful regulator. Mine cracks at less than a half inch of water inhalation pressure, and goes down from that during the inhalation cycle.
There is one other characteristic of the Trieste, and that is with the smaller diaphragm area, the duckbill is always lower than the center of the diaphragm, so it can be adjusted very, very finely (below 0.5 inches of water) for inhalation effort without the leaking Luis described.
On the larger sized regulators, this can be overcome by ensuring you have an uncut duckbill, and keeping the length such that the duckbill extends to below the center line of the diaphragm. But not too many people work on these USD-based regulators in that manner.
I have described what I did with my regulator. Realize that these are life-support systems, and should not be modified unless you are ready to take complete and unconditional responsibility for what happens as a result of experimenting. For instance, I don't dive this regulator without its mate, an MR-12 second stage octopus. It is good that I did, as this regulator is the only regulator that I've ever had which completely stopped breathing (inhalation wise) in a dive. It happened as I was ending a dive at about 35 feet at Edmonds Underwater Park in Washington state. I simply switched to the MR-12, and continued the dive (the first stage was not affected). What had happened is that the Healthways disk had become dislodged. Healthways mouthpieces had a groove that they fit into--the USD curved mouthpiece does not, and I had not built up enough glue to keep it in place. The loose disk, which is round, plastic with holes around the periphery, unfortunately went to the right side of the mouthpiece, and lodged against the silicone non-return, completely blocking any attempt to inhale through the regulator. So if you decide to do any modification to any regulator, be prepared to bail out with a different system.
SeaRat
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Double Diver
Contributor
I must disagree with your statement that the Phoenix "is the ticket". The Phoenix was the ticket, but I do believe that the MK3 has surpassed it, in that it is a complete and well thought out unit. And when it comes to DIN it wins hands down. Now please don't get me wrong the Phoenix is a very good upgrade. While I have not had the opportunity to dive one all who have sing its praises. And it has brought all of us to a better place in double hose diving, but it is an add on not a complete replacement like the MK3 which functions and feels like a modern regulator.
I really do not understand this statement. I have no diving experience with the MK-3 but many many hours with modern regs and the Phoenix. I do however understand how both work and have studied the design of both (as much as I can get hold of)....as well as that of the DH regs they modify. The MK3 and the Phoenix both function in exactly the same and they both accomplish the same ends; they provide a modern HP seat and orifice (the exact same ones) and add HP and LP ports to the DH reg, just in a slightly different way. Both in their own way are complete replacements, the MK3 replaces the entire first and second stage assembly of the regulator as opposed to the Phoenix replacing the entire first stage. Both designs have their advantages. The MK3 may be a little better suited for DIN use but adds a good bit more weight to the entire reg, a down side for the traveling diver. The MK3 eliminates the gasket between the first and second stages but at the cost of hose alignment. The second stage of both use the same USD design and parts so there is no difference in the operation of the second stages. Since they are both using the same IP, HP components and second stage components there is going to be no difference in the final result. A double hose reg will never "feel like a modern regulator" which I assume means a single hose reg of modern design; physics simply will not allow that. The MK3 is a well designed and thought out piece of gear but in the end with it on your back and the mouthpiece in your mouth, the diver will never know the difference in the 2. Both have greatly improved the old DH design for use in today’s world and both have their strong points but to say one is superior to the other is misleading in my opinion.
Double Diver
Contributor
The "statement" to which you refer I assume is mine (Double Diver) not Spectroms. Although he does make a fairly strong endorsement of the Phoenix and I quote "The Phoenix as others have noted is the ticket if you want to use all the current accouterments while enjoying a double hose regulator" Now he does credit others for their positive opinions (no doubt posted on SB) of the Phoenix conversion and once again I agree, the Phoenix is a very good upgrade. But as in many of the forms on SB individuals opinions on products and services are freely given and many times specifically sought out by others looking to make a better informed decision. Now if done in a polite and professional manner as was the case here I don't understand your concern about voicing one's validated opinion. I do however understand the dynamics in this instance are some what different given the fact that the products in question are not manufactured by a corporate conglomerate but at a Cottage level by members of this very small community. As is the entrepreneurial way, another mouse trap has been invented and there is now a strong competitor on the field, it was inevitable. Personally I hope it will lead to the design and manufacture of a completely new double hose reg. So we members of SB will continue to voice are opinions, and hopefully they will be well informed ones, posted in a civil manner and supportive of any one who is willing to take an idea to the next level.
If I sounded rude, I am sorry, that was not my intent.
My point is they are pretty much the same thing. While the designers used a different approaches, they both accomplished the same result- adding HP & LP ports and upgrading the first stage with modern parts and yoke. Considering they both use the same internal parts and the same second stage design, there can not be an appreciable performance difference in them as far as the end user is concerned. Each has it’s advantages and disadvantages, all of which are minor, functionally there is little difference between them. Both are welcome additions to the DH diving community and I thank both designers for their work but neither of them…..or the new Mistral for that matter.. will function or feel like a modern regulator. Speaking for myself, if they did I would not see any reason to dive either one of them, I like to differences in the way a DH dives. Unless I am with a class, I rarely dive a single hose reg these days.
My point is they are pretty much the same thing. While the designers used a different approaches, they both accomplished the same result- adding HP & LP ports and upgrading the first stage with modern parts and yoke. Considering they both use the same internal parts and the same second stage design, there can not be an appreciable performance difference in them as far as the end user is concerned. Each has it’s advantages and disadvantages, all of which are minor, functionally there is little difference between them. Both are welcome additions to the DH diving community and I thank both designers for their work but neither of them…..or the new Mistral for that matter.. will function or feel like a modern regulator. Speaking for myself, if they did I would not see any reason to dive either one of them, I like to differences in the way a DH dives. Unless I am with a class, I rarely dive a single hose reg these days.
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