Another Mistral question

[time2dive]

Todays dive was with a freshly rebuilt Mistral in great condition. I noticed that at the very beginning of the dive (when the tank pressure was above 2400 psi) it would whistle and the diaphragm would vibrate. After about 5 minutes it stopped, the first stage was still a little clunky for another 5-10 minutes until the pressure was down to about 2200....I'm guessing... no guages.
Is this the regulators way of telling me to keep the fills at 2400 or lower? Towards the end of the dive it was breathing quiet well, I am guessing just above 500 psi, I never had to activate the J valve.

78', 50 minutes. Dolphins, turtles, eagle ray and warm water.... life could be worse.

Tim

[SeaRat]

I'm very envious of your diving, time2dive. Concerning the Mistral, there are a lot of posts, and different threads, here about the pressure to use it at. I feel that 2475 psi (2250 psig at a 10% overfill) was its working pressure limit. I had one Mistral which could not take the 3000 psig, and I destroyed a seat on it. But it was a re-conditioned seat, and that could have influenced how it reacted to the high pressure (reconditioning was to grind the seat down, which in turn grinds down the metal piece that the pin engages, and so could have caused the loss of the seat). The USD repair manual, which Bryan at the other vintage web site, cites the use of 3000 psig to test the seal of the Mistral when it is repaired. I have another Mistral-like reg (the DX Overpressure) that handles 3000 psig well.

Concerning the whistling and vibrating, that is an aspect of the Mistral oriface, and is less noticable while in the water than breathing it out of the water at high tank pressure. It does not affect performance, except that the Mistral breathes harder as the tank pressure increases. The more pressure, the harder it is to open the valve. But it is nice at between 1000 psi and zero, isn't it.

John

[Broxton Carol]

The SEAT is dancing on the cone, or the fingers are set too high. Set it like the book says. They knew what they were doing. Why use this stuff at 3000 psi? Everybody knows what it was designed for. Why stretch the limits? Be safe, and save grief.

[time2dive]

It was set as the book said. Fingers flush with the box top at about 500 psi. The tank pressure was a little high....2600psi at the start of the dive. The regulator did settle down around 2400 psi, no more clunking about 10 minutes into the dive, I'm guessing about 2200 psi.


Tim

[nemrod]

You know, I just don't like using my Mistral above 2200ish. Others may differ but mine also will flutter and vibrate much above that pressure. Ihave only one more seat plus the new one that is in it and the orifice is not really replaceable. You can grind it but I don't much like that. Allowing the seat and orifice to hammer like that is obviously not a good thing for it.

At what pressure an individual Mistral specimen might carry on like that is not the same for each one. Mine really does ok up to around 2,500 but something like a small difference in lever height, spring tension/length, seat quality and condition, diaphram condition might affect this.

James

[Deleted]

I remember reading somewhere in this forum a few months back that the old JC crew dove with modified Mistrals mounted on high pressure tanks.............wonder what type of spring configueration
was used?

[Broxton Carol]

Remember to always set your levers while the reg is mounted TO THE TANK under pressure! This will make the height very. Also remember to NEVER get any silicone lube on or near the seat. It will walk, and chirp and not seal effectively. I have had them "motorcycle" before, but after taking out, and putting back in, in another position, the rat tat tat, STOPS. Got an aquamaster Im rebuilding for a guy now that has that problem. Chucko

[sea.explorer]

Cousteau teams used Spiro Royal Mistrals up to 5000psi. They were unmodified. My source is the former chief diver of the Cousteau team. When I visited the Cousteau warehouse I inspected about 20 used mistral seats. I saw no signs of excessive deformation. I cannot verify for certain that the batch of seats was used with the 5000 psi tanks but it is very likely at least a portion of them were -Ryan

[broxton]

Being that the Royal Mistrals were balanced, the increased pressure shouldn't cause the seat to become more deformed. The main issue would be to have the seating surface made of the proper material to handle the increased pressure. The unbalanced Mistral would cause the seat to deform more under increased pressure. Do you know if the Cousteau team used regular Mistrals at 5000 psi. That would be interesting.

[sea.explorer]

The Spiro Royal Mistrals are unbalanced unlike their USD counterparts. -Ryan