Overpressure and Mistral difference?

[Robohips77]

Any thoughts on this. I read the HDS info about a venturi hose? going down the inhalation hose. any diagrams or pics of this?. Realize the removable horn but what else. Rest looks like a Mistral. Thanks for your time.

[Bryan]

The overpressure breathing regulator had a green tube that ran from the outlet in the can to the mouthpiece on the regulator. It was an overachiever at flowing air and sometimes forced too much air into the mouth of the diver. The original setup with the hose running inside the outer hose into the rare mouthpiece is very hard to come by and I’ve only seen a few examples of the complete original design. Most were converted to the Stream Air venturi nozzle or better yet to the Mistral venturi nozzle. Nice looking regulator with a bright chrome front can and dull or brushed chrome bottom can. Besides the nozzle variants it’s the same as any Stream Air or Mistral inside. The Mistral being one of Gagnans finest works…. This is JMO and not to be taken as fact….I’ve been wrong before!

[Robohips77]

this one must have been converted or later in the production run as it is a serial number in the 34,000's. It i has the Mistral guts to it including the nozzle. My other Mistral is a great breather especially after that silicone diaphragm I won at SDIV. I think this OP will turn out and be very divable. I am going to have to order a few parts but even on the initial try after probably 45 -50 years of no use it still worked very well. Only one dead spider and one dead bee came out. I need to compare the venturi nozzle on this one to my other mistral but I am pretty sure they are the same. Looking at the HDS Number 42 winter 2005 I am on the hunt for a different type of mouthpiece. But if I can't find one, a straight black one will have to do. thanks for the info.

[Greg Barlow]

The overpressure unit had excessive venturi effect, and on a deep inhalation the reg could start rapidly free-flowing.

The DW Stream Air had the venturi nozzle angled slightly off center so that some turbulence occured. Using the nozzle pointed straight down the horn would also lead to excessive venturi action.

The Mistral used secondary vents on the nozzle to cushion the venturi effect of the primary vent. If you convert a DX to a nozzle, then use the Mistral version. If you choose to use the Stream Air nozzle, then you will need to slightly rotate the valve body so that the air flow is not directly down the center of the horn. It is much simpler to just use the Mistral nozzle.

Bryan and I have the same high opinion of the Mistral. I believe that it is the best design ever when used with tank pressures under 2,300psi. The design is mechanically simple, and extremely robust. Just compare the number of parts to a DA, or RAM.

Greg

[Robohips77]

Well Now I know the need to take pictures of all the insides of my regs. Attention to detail. tthis nozzle only has one orifice in it. I will compare to the Mistral and Jet Airs tht I have. Thanks again Greg.

[Greg Barlow]

If the nozzle looks like a cone, then it is the Stream Air version. The Mistral has very obvious vents on the stepped area.

Greg

[Robohips77]

this definately a Mistral nozzle. It does have the vents on the stepped area. there are three holes/orifices in all. I love this forum. Great info and thanks. Old dog keeps learning new tricks.

[Greg Barlow]

this definately a Mistral nozzle. It does have the vents on the stepped area. there are three holes/orifices in all. I love this forum. Great info and thanks. Old dog keeps learning new tricks.

That would be the Mistral...Just don't use tank pressures in excess of 2,400 or so. The HP seat is subject to damage from the excessive pressure.

Greg

[Robohips77]

I always us these on my lp tanks.
Will Bryans repro seats take the pressure. I never thought of those as I am putting in one of the new ones. Although I do have some new old stock.

[Greg Barlow]

I always us these on my lp tanks.
Will Bryans repro seats take the pressure. I never thought of those as I am putting in one of the new ones. Although I do have some new old stock.

Bryan's underwent some serious R&D, and did withstand some pretty high pressures. However, since the incoming pressure is working to force the seat closed, it makes little sense to use high pressures. A well tuned Mistral at 1,500 psi (and below) rivals any other DH reg I have used. In fact, when using a Mistral at around 700psi or so, the WOB is almost effortless.

Greg

[Bryan]

According to Ryan, Cousteau used the Spiro Mistrals at 5k without modifications.....Last year at Portage I spoke with Sam Lecocq on this exact subject and in his opinon 3000psi wont hurt the HP seat but it could wear more quickly. As of right now there is very little need to worry about running out of new HP seats. I made quite a few......I used mine on alu 80's in Hawaii and on my mini doubles all the time but IMO the ideal range for any version of the Mistral setup is 2250 and below....

[capn_tucker]

This is more great info. I've been using my Voit Polaris on tanks w/10% overfill (2475 psi), and had been wondering if that would eventually cause problems..