Characteristics of Mistral Regulator

[rstofer]

I am looking at the repair manual for the Mistral single stage regulator and have realized that I know nothing about single stage regulators. One has to admire the simplicity but what about other characteristics such as how well it breathes, what to do about the lack of IP for BC/octo, things like that.

Was the Mistral a pricing thing or did it fill another need? How does it compare to the RAM or AM?

Just looking for information.

Thanks!
Richard

 

[Nemrod]

The Mistral is superb. They work best with LP tanks and really start to breath smooth as silk below about 1800 psi.

You don't use an octopus with a double hose, especially a single stage. To get an spg you have to use a banjo and a long yoke from vdh that will soon be out. Or convert another yoke like I did. Vintage divers don't use a BC, octopus or even an spg.

The Mistral is not quiet like a dual stage reg, the powerful venturi jet makes a swoooooosh, swooooshh, sound as you inhale, really cool.

A good Mistral breaths great, do not use on 3,000 psi tanks (it will work but will be stiff and will wear the seat). On a steel 72 filled to 2250 psi by the time you hit bottom and level out you will be in the sweet spot. Doing a swimming descent as vintage divers do you will be head down and the head down position provides easier breathing. Once the tank is below about 1800 psi the Mistral comes into it's own and will get easier and easier to breath as the tank pressure gets lower through the dive.

I have been well beyond 130 feet on my old Mistral. Mistral is very, very, very good.

N

 

[DA Aquamaster]

The Mistral is my favorite strictly vintage diving reg.

As nemrod points out, there are no octo options with one as there is with a DA Aquamasster where the hookah port can be used to add a low pressure accesory (or an adapter and a splitter to add up to 3 of them). The DA can also be converted to a PRAM with the Phoenix nozzle while the DW Mistral cannot.

Consequently if you need LP accesories like an octo or low pressure inflator you either need a different double hose reg or you need to bring along a pony bottle or another reg on a Sherwood Selpac manifold or perhpas an H valve.

Many horse collar BC's work well with oral inflators only and if properly weighted you use it very little anyway so there is no real need for an inflator hose. A pony makes a decent bailout option if you don't trust the reg or if you need an octo.

In the past, divers used a J-valve with either a 300 or 500 psi reserve. As you got down to the specified reserve, the reg got hard to breathe and you just pulled the lever to activate the reserve and ascended with no spg used at all. You got good at estimating air consumption at various depths and in general with US navy tables you would not get bent on a single steel 72 if you stayed above 100', so the reserve always allowed enough gas for a normal (for then) 60 fpm ascent to the surface. So it worked, but it had its limitations and it was not unknown for the reserve to get snagged and pulled early in the dive, leaving you with no reserve.

Another SPG option was provided by both J and K valves that incorporated a 3/8" high pressure port on the valve. On most of them the port is closed when the valve is closed so you could swap 1 spg between tanks. You can still find them on e-bay along with vintage SPG's with the older 3/8" thread HP hose, or you can get a 7/16" to 3/8" adapter and use a modern hose and or spg. These valves show up on e-bay all the time.

The Mistral is an upstream design so it gets easier to breathe as the tank pressure falls. As nemrod indicates, you get a swoooosh sound when you breath off on, particularly in the right (intake) hose, so it is not quiet - especially if you do not wear a hood.

I would not say the Mistral breathes better or worse than a RAM, just different. The cracking effort needed to intitiate the flow is higher on the Mistral, but the venturi effect makes it almost effortless once the flow is established. In contrast with a RAM or PRAM, the cracking effort is lower but fairly constant in terms of maintaining the air flow.

On both of them the position of the cans and orientation of the diver have a large impact on how easily the reg breaths.

 

[John C. Ratliff]

Richard,

I had my Mistral in the water this morning (pool), and always enjoy it. To maintain it you need a circlip pliers to remove the sintered filter, seat and spring. There is also a pin that extends through the body.

The boxes can be separated using a vice grip and screw driver to remove the clips. With the vice grips, grip the clip, pull them down just a bit, get the screw driver blade behind it, and pry it off with the combined effort of the screw driver and the vice grips. Once out, use the vice grips to flatten the clips a bit to make it much easier to get off (the open end only). Then remove the bottom box (the one with the name place) and the diaphragm.

Examine the diaphragm for holes, cracking, etc. Usually, it will be fine, but could use some conditioning with silicone grease. Coat it, let it sit for a day or two, then remove all the excess.

Examine the duckbill valve; it may need to be replaced. You can get new ones from Vintage Scuba Supply or Vintage Double Hose. These original valves don't last too long; there are new ones of both neoprene and silicone (which lasts much longer).

Remove the two levers, and the pin. There is a small O-ring in the housing which probably should be greased. Put some silicone grease on the pin, then put it down the hole to grease this O-ring.

Reassemble the seat and spring under the sintered filter, and use a pencil with the eraser side, or a flat pencil, to push down the spring and get the circlip into position to re-install with the circlip pliers. You'll need to take the thumb screw out of the yolk to do this.

To set the Mistral for optimum performance, there is a nut over a round thumb wheel just to the side of the platform for the levers. Loosen the nut, and move the thumb wheel to lift or lower the platform just enough to allow the levers to be about 1/4 inch over the top box's opening. Secure the nut, and put the two boxes together, pushing against them very tight (with the diaphragm in place, of course). Put the regulator onto a tank and see whether it leaks. If yes, then you'll need to readjust the levers lower. You want the levers as high as possible without causing a leak. Basically, the platform height adjusts the levers up and down. This is the only thing needed to adjust this regulator. Manuals will tell you to have the lever height at the level of the top box, but I have found that there is better performance with this regulator if the levers are as high as possible without causing a leak.

Now, put the top and bottom boxes together, with the horns oriented symmetrically (look at the label on the bottom box, and put the top box horn in the same relative position as the bottom box. Place the clips onto the box, with the open end down, top (closed end) into the grove of the mating surface. Open your vice grips fairly wide, and clamp these clips down as you go, initially not tight. Two go between the horns, and five below. I always put one just below the horns, then the bottom one, and finally one between the other two on each side. Once they are in place, close your vice grips a quarter turn or so, and re-tighten each one (you'll find that they are pretty loose initially). Do this until they are very tight on the box.

This is a wonderful regulator to play around with, as there simply is not much you can do when you work carefully to hurt it.

John

 

[BSea]

When I was looking for my 1st double hose, I didn't consider a Mistral because of all the factors you mentioned. After getting a DA without a serial number, I went looking for a matching Mistral with no serial number. After getting one & refurbishing it, I went on a few dives with it. It has quickly become my double hose of choice for recreational diving. I can't add anything to what the others have said other than you won't regret buying one. But you better hurry, it seems they are growing in popularity based on the prices lately on E-Bay.

 

[Slonda828]

The thing to admire about the mistral is its simplicity in my opinion. Cousteau's team used it because it was bulletproof, and if they needed to take it apart, you can fix it with a leatherman if you really have to. It only has ONE O-ring! The only adjustment you can really make is to the lever height. I think I would've called this reg "Soldier proof" when I was still in the service. It is the literary equivalent of a good haiku. It is basic and appears limited at first, but that is the beauty of it when you study it, and you could end up discussing it for hours. I think it may be my favorite regulator ever.

I don't worry about using an octo with it because I feel very safe when I use it. It breathes great, sounds amazing, and if using one doesn't make you a vintage diver, in my opinion, nothing else will.

Besides....YELLOW hoses!

 

[pescador775]

The box clips can be removed expeditiously with a medium size end cutter. Just grab the clip and rotate or pull with the cutter. Before reinstalling the clips look at them closely. The back of the clip should not be rounded. If a rounded clip is found place it on an anvil and tap with a small hammer. Place the clip on the can and squeeze with pliers.

 

[DA Aquamaster]

I second the end cutter suggestion. I use a fairly small set to just grip the box clip from the side and then just pull it off with a rolling motion. No damage to the clip and no risk of slipping with a screw driver or pliers.

 

[rstofer]

Thanks all for the terrific information.

I went ahead and bought the Mistral from VDH. Now I'll have 3 of the DH regs. These things multiply fast!

I finally got my DA in the pool Saturday. It worked ok but I am looking forward to getting it upgraded with the Phoenix nozzle when it comes in. The RAM hasn't arrived yet but I am expecting it today.

I don't think it matters but does anyone know why my DA whistles? This reg has the stealth capabilities of a battle tank. I suspect this will all go away when I have it rebuilt and upgraded so it's not a big deal, one way or another.

Again, thanks!

Richard

 

[DA Aquamaster]

A whistle often means something is vibratring/resonating as it moves and that is often due to inadequate lubrication. In a Da that woudl possibly be in the seat carrier where the o-ring bears on the stem of the seat.

A honking sound on the other hand is more often a lower frequency vibration caused by a diaphragm or duckbill issue.