Mistral all pressure wonky

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Discussion of diving methods and equipment available prior to the development of BCDs beyond the horse collar. This forum is dedicated to the pre-1970 diving.
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ScubaLawyer
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Mistral all pressure wonky

Sun Oct 23, 2016 6:53 pm

Ok, looked at the manuals and past forum discussions. I used Bryan's Mistral tool to set the lever height at the Sweet Spot. At that setting the regulator automatically bleeds air beginning at 500 psi but breathes fine at 2000 psi. Lowering the lever height a tiny bit stops the low pressure free flow, but at 2000 psi the pin isn't being depressed far enough and the air is delivered in honking fits and starts. If I raise the lever a tad I'm back to a free flowing reg beginning at 400 to 500 psi and getting adequate for delivery at higher pressures. I must have tried 30 micro adjustments and placed the reg back and forth on adjacent tanks (one at 400 psi and a one at 1500+ psi.) No happy spot found, although I could achieve hi/low balance as long as the top can wasn't in place and tightened down with a band clamp. I should mention it is all new internals. Ok you regulator jockeys, what stupid thing am I doing wrong? Mark

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Goodlifedivers
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Re: Mistral all pressure wonky

Sun Oct 23, 2016 10:27 pm

If it makes you feel better I was having the same issue with mine, I erred on the side of not free-flowing. My other single stage regs breathe great all the way through including a FX with mistral guts and a spiro mistral (which I can't get the lever to the height of the adjustment tool).


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SurfLung
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Re: Mistral all pressure wonky

Mon Oct 24, 2016 9:18 am

- I wonder if you are dealing with a problem created by somebody who modified or damaged something before you acquired this regulator?
- For instance, I think all Mistrals push the pin far enough even if the lever isn't adjusted to maximum height. I'm wondering if your pin might be shortened or if the leverage might be screwed up by levers that are bent or shortened?
- Have you got another Mistral that's working properly so that you can maybe compare the parts?
SurfLung
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ScubaLawyer
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Re: Mistral all pressure wonky

Mon Oct 24, 2016 9:36 am

Hi Eben, I don't have a spare Mistral. I do have a Voit Polaris V22 that I believe has the same pin length and levers. From eyeballing everything I don't see any difference. The one thing I did not replace in the Mistral was the pin. Guess I could try that. But, again, I don't see anything wrong with it. Still looking for answers. Thanks. Mark.

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Bryan
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Re: Mistral all pressure wonky

Mon Oct 24, 2016 11:49 am

Once you get water pressure against the diaphragm the fluttering/honking will go away. Greg did a write up on this sometime back but I cannot locate the info right away. I'll see if I can get him to refresh the subject.
Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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captain
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Re: Mistral all pressure wonky

Mon Oct 24, 2016 9:54 pm

What Roger and Greg said. Water seems to act as a buffer to eliminate or reduce honking. Also light breathing seems to produce more honking than bigger breaths.
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ScubaLawyer
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Re: Mistral all pressure wonky

Tue Oct 25, 2016 12:14 am

Thanks for all the good info. I'll adjust for low pressure and see if water pressure on the diaphragm takes care of the upper pressure ranges. Although it's sort of like telling an astronaut not to worry about the funny noise his life-support equipment is making on Earth because it'll work just fine in space. :D I'll report my findings. Mark

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8dust
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Re: Mistral all pressure wonky

Tue Oct 25, 2016 12:33 pm

Hey Mark,

I have the same experience on both my Mistral and Polaris, although my Polaris seems a little worse about it. I have both now set a little on the low side to not FF at low pressure as at the tail end of a dive I'm generally not looking to burn through my reserve any quicker than I have to... Interestingly, I haven't noticed the issue with my JetAir, but I don't dive it near as often. I just write it off as the cost of 3 moving parts and 1 o-ring, remembering something maybe in Roberts' book, about this being a sport for those with "well developed lungs." :)

If I'm smart and thinking enough, which I'm generally not, I save my beautiful yellow-hose Mistral for the "pretty fish dives" or at least my second dive of the day when I've had a chance to see the lay of the land (water), conditions, and get comfortable. This was precisely my mistake on my first dive at SHF/SS this past March. New location, totally unknown conditions with unexpectedly heavy current (spring flow), wearing more rubber & lead than usual, excited to see friends, anxious to "show off" for boats & camera with Big Yellow... and I realized about 5 min. in I wasn't quite as "well developed" as I could have been in the lung department and could have used a bigger squirt of air... Swapped to RAM for 1st dive and everything beautiful, back to Mistral for later dives, everything still mostly beautiful.

Moral of the story: single-stage'res, not a great choice when multiple unknowns & variables at play, but wonderfully simple & dependable for those dives when you're just puttering around.

Fred
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ScubaLawyer
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Re: Mistral all pressure wonky

Tue Oct 25, 2016 5:05 pm

Hey Fred, great to hear from you. That's interesting about the Polaris. Mine breathes great at 2400 psi and below with no honking at any pressure and no free flow at low pressure. Must have it zeroed in. Now I'm afraid to tinker with it. Anyway, I agree with your assessment. Love my single stagers but I have to be in the right conditions and mindset for them. Looking forward to another epic rubber knife fight with you at SS again next year. Mark

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Bronze06
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Re: Mistral all pressure wonky

Tue Nov 15, 2016 10:14 am

Pool dive it with the lever adjusted for optimum delivery at 2400-3000 psi. Adjust the lever so you can get both cans and the band on it without air hissing. Stick the whole thing tank and all under water. (bathtub). If it is sealing up at the high end of the psi scale and not sealing at 300-500 check the following:

HP seat spring (new or old) if old replace.
HP seat (New or old) look for scrib lines to show if it is sealing relatively centered and uniform. If original replace.

HP orifice ( check orifice for tiny blemishes or verdigris areas.) Use a magnifying glass it really helps.
What I do is exactly what the trouble shooting portion in the manual tells you to do when you have the problem you have been having (though I read it much later). For our puposes take a new, unused number two pencil and ensure that you place it down into the body, eraser end first, it so as to completely cover the orifice lip ensuring not to let the aluminium retaining band on the pencil rub up against the lip of the orifice. Once centered, using even pressure (firm but not maniacal) gently rotate the pencil clockwise three complete turns then reverse for two turns. Inspect the orifice. US Divers had a rod shaped light abrasive rubber eraser for just this operation. If there is still a hint of verdigris or uneven surface at the rim of the orifice, repeat the above procedure as necessary, replacing the pencil about every TWO iterations. Don't be afraid to swap out one pencil for another new one during this. You will see a nice ring of black on the eraser when the pencil is withdrawn. This is a very easy way to evenly "rub out" any irregularities on the lip, the outside of the orifice as well as the inside of the orifice thus giving you an even reshaped (or as I think of it) "sharpened" orifice. With the even pressure you splay the eraser head to the outside as well as condense/remove material on the lip and the eraser head also penetrates the inside of the orifice for an even across the board re-surfacing.
This has worked for me on every Stream Air, Jet Air and Mistral I have ever re-built. (12 to date)
I say this because since you said you had problems at low pressure initially, I am thinking micro lip issues such as an uneven lip surface due to errosion (vedigris or uneven wear) over time. Even if you had a new spring and seat, the lower pressure might not be enough to seal a micro lesion in the orifice lip. Thus the US Divers use of an elongated abrasive solid rubber "stick" to evenly reduce and reshape the orifice lip. I use a number two pencil and get the same results. I stopped four regs from the very same issue you had by following the above.
I don't believe in leaks and the Mistral shouldn't leak at high or low pressure. Hope this technique helps.

PS;
When checking for air delivery dry, cover the exhaust holes on the can with you hands or a cloth. It should stop most of the honking and as stated earlier in this post the clattering and honking should disappear when submerged. It's just that there is no water pressure on the face of the actuator diaphragm to counter balance the sudden inhalation effort which will cause the diaphragm to vibrate or honk.
"Where'd ya get that ol' thang, don't cha' know them thare things ill kill ya!"

Live From the Red Sea,

Russ

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ScubaLawyer
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Re: Mistral all pressure wonky

Tue Nov 15, 2016 10:33 am

Thanks for the info Russ! I ended up adjusting the lever height slightly lower than what the lever height tool said was optimal and it now works great at all pressures, no leaks or honking. Go figure. Next time I have it apart I'll refer to your post and have a look-see at the issues you address. Mark.

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captain
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Re: Mistral all pressure wonky

Tue Nov 15, 2016 10:52 am

Kind of why I have never been a "by the book" guy. Although alike every device has small differences inherent in manufacturing process. Correcting for these differences in some cases requires going outside the book.
Captain

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Bronze06
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Re: Mistral all pressure wonky

Tue Nov 15, 2016 12:25 pm

captain wrote:Kind of why I have never been a "by the book" guy. Although alike every device has small differences inherent in manufacturing process. Correcting for these differences in some cases requires going outside the book.

Hey Captain.

I was outside the book for 3 years. I only read the trouble shooting for HP orifice in the manual about 3 months ago. I guess it's the military, anything that isn't shiny gets a scrub, LOL. It just made sense like a bad radio contact needs a good rubbing with an eraser to get the oxides off. :D
"Where'd ya get that ol' thang, don't cha' know them thare things ill kill ya!"

Live From the Red Sea,

Russ

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