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Post by nemrod on Dec 5, 2004 22:40:37 GMT -8
Hello, I am new here and had a quick question. I scanned back through previous messages and did not find the answer but maybe I missed it. Hope you don't mind asking it. OK, what are the adjustments on a Mistral pressures and most importantly--what is the maximum tank pressure a Mistral (USD) should be exposed to? I assume they are fine with tank pressures to 2250? Would this be correct? Thanks in advance. Nemrod
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Post by Mistral on Dec 6, 2004 4:40:16 GMT -8
There are members here who are a lot more knowledgeable who will probably give a more complete answer and can do a far better job of answering the adjustment question (I am only aware of one adjustment on the Mistral - it is a very simple design.)
My understanding is that the Mistral was designed for use up to 2250 psi but 3000 psi will potentially cause damage due to the seat design. I am a little hazy about how it would do with modern 2400-2640 psi steel tanks, but I currently own over 18 serviceable steel 72's so it has never been an issue for me.
Even with the pressure limitation, the Mistral is still a great regulator and I think my Mistral breathes better than either of my DA Aquamasters.
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Post by John Ratliff on Dec 6, 2004 8:50:34 GMT -8
I routinely use my Mistral on 2250 psi tanks, but I destroyed a seat on one at 3000 psi. Luckily, I have extras. I would say that they probably are safe to 2475 psi (10% overfill on new steel tanks of the period), but somewhere between that and 3000 there is a definate limit. I would not go above 2475 psi on mine.
Concerning breathing easier than a DA Aquamaster, I'd say that a Mistral at tank pressures below ~1000 psig would fit that category. But if a DA Aquamaste is set up properly, and tuned to the max enterstage pressure at 500 psi, it would outperform the Mistral. The problem is getting there, and keeping it there. The Mistral is much, much easier to maintain.
SeaRat
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Post by nemrod on Dec 6, 2004 9:33:40 GMT -8
Thanks for the answers. That is the way I remembered it but wanted to make sure. The Mistral sounds like a great and simple regulator, maybe not the best performer but nonetheless very good. I have two serviceable steel 72s. What modern tanks would be equivilent to them when operated at 2200 psi? and with similar bouyancy characteristics? The equipemnt made back in the vintage era is just so much more cooler than the junk they make now. Looking through a 1968 USD catalog, neat twin tanks and maonifolds and double hoses and look in their catalog today and it is just plastic junk and no tanks. N
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Post by Mistral on Dec 6, 2004 14:54:45 GMT -8
The Faber 75.8 is about as close as you will get to a steel 72 with a current production tank. It is an inch or so taller and has a 2400 psi service pressure (2640 with the "+" rating) but holds the same 65 cu ft at 2250 psi as a steel 72.
The good news is that a Faber 75.8 will hold 69 cu ft at 2400 psi and offer about the same capacity at its service rating of 2400 psi as a steel 72 would at its "+" rating of 2475.
The bad news is that they are much more expensive. You could buy several steel 72's for the price of a single Faber 75.8. In this area, a galvanized steel 72, in good condition with current hydro, VIP and J valve will sell for around $50-$60. A Faber 78.8 would cost you about $250.
Faber also makes a 71.4 but it is a 3000 psi tank that is about 5 inches shorter and much more negatively bouyant than a steel 72 (-11 lbs when full) so it is comparable in capacity only.
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Post by SeaRat on Dec 6, 2004 19:38:07 GMT -8
From a buoyancy standpoint, a standard 72 is about as good as it gets, being almost neutral in fresh water when empty.
John
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Post by nemrod on Dec 7, 2004 0:05:27 GMT -8
Yes, Searat, I know you are correct. I just wondered on the off hand that someone might be having luck with something newer. So much of the bizzare weighting that occurs with modern era divers is a result of tanks that go from negative to positive during a dive. The old 72s started out negative a bit but were so close to neutral at the end that they had little effect on your bouyancy. I would like to see someone make a modern set of low pressure 38s or so in a twin configuration! Nemrod
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Post by Mistral on Dec 7, 2004 5:17:54 GMT -8
Be careful what you ask for.
OMS makes a 46 cu ft steel tank (at 2640 psi) that is neutral when empty and they also sell the bands and manifold needed to double them up. Doubled, they will weigh around 36 lbs. when empty.
The manifold however is not real ammenable to a double hose reg though as it has a post over each tank in current technical fasion rather than in the center. But the tank threads are standard 3/4 14 NPSM so with a custom set of bands with the proper spacing, a more traditional 3/4" center post manifold or something like the old Sherwood selpac could be used.
Another single tank option may be OMS's 85 cu ft 2640 psi steel tank. It has about the same dimensions as an aluminum 80, but is 6.7 lbs negative when full and neutral when empty.
But again, both these tank set ups will cost about the same as a half dozen steel 72's. 72's are so under rated and under appreciated by modern divers that they are available for a fraction of what they are really worth.
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Post by seakrakken on Dec 7, 2004 8:29:26 GMT -8
This is another fine example of why I should have moved to the coast line. Here in the Dallas Texas area 72's are like Hen's teeth. If you go to an RDS and ask for a steel 72 they shriek and hold crosses in your face
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Post by Gomez' echo on Dec 7, 2004 9:40:08 GMT -8
I just love this forum. As the topics come up, there is so much information that appears that brings back memories of the vintage years. I started diving in 1962 when the 71.2 cu ft steel cylinder was the standard. Yes, 38 cu ft tanks were available, but the "72" was like today's Al 80. I currently work at a small dive store that uses the 72 for all of our class work. It is a bit smaller than the Al 80 and saves wear and tear on the compressor. The lower 2250 fill pressure provides more than enough air for the student. If one wants to "relive" or dive with vintage gear, then the use of the 72 is more "correct" than trying to substitue a "modern" cylinder. 72s are available and cheap by today's standards. Most of the backpacs of the early 60's won't fit the larger diameter cylinders. I used a 1962 USD backpac when I started. The adjustment to fasten the pac to the tank did not allow much latitude. I later got a Sportways pac with a cam and the 72 was the cylinder for best fit. So, the use of the 71.2 tank will compliment your AM or 50 fathom or Snark III just perfectly.
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Post by nemrod on Dec 7, 2004 10:19:46 GMT -8
In addition to 38s I also remember 50s. The 38s and 50s were usually teamed up in a doubles rig. The tank sets from USD were available in yellow, black and galvanized finishes with a big round label that had the Aqualung with corrugated hoses. I know that me and my buddy of that time were more in love with a set of black double 38s and thought them more beautiful than any girl in highschool. Yeah, we were retards! Yes, the steel 72 is way underappreciated. When they are hooked up. they only show 2000 psi so modern folks think they are nearly empty and time to surface! I have made numerous strenuous and deep dives with steel 72s. I guess I will have to start lookingt for more of them! N
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Post by Mistral on Dec 7, 2004 14:30:40 GMT -8
My first doubles were 50's. I had a set of Healthways double 50's in the early 80's with the wrap around "H" stickers in really good shape and I also had a set of twin 50's from Sportways. At that time they were just old instead of vintage and I paid about $50 for each set. Eventually when my son started diving at age 12 I broke them up into singles for his use. Then, sadly, I sold them to someone else with a junior sized diver in the family. Of course a few years later I got the vintage bug again and wished I had kept them.
One set was shorter and had a 2015 psi service pressure and the other set were taller but only 1800 psi tanks. I had problems with dive shop monkeys filling trying to fill both to 3000 psi like they would an AL 50.
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Post by John Ratliff on Dec 7, 2004 16:22:34 GMT -8
I have thought about talking to OMS about their 45s with the twin manifold. My idea would be to make a triple tank unit out of them, base upon the "old" 1945's Cousteau idea of their triples. Basically, use their double manifold to make the one side, then get a single 45, invert it, and use double bands to make a triple system out of it. Then, with a HP line, hook the inverted single into the double manifold (would require some work to do).
This would do several things. It would return to the Cousteau design of a full 1/3 as a reserve supply, with its own separate valve below that can be hand-opened when the other two are depleted. With the twin manifold, the right would become the center post, which would be a great place for a double hose regulator. There would be one other post for redundancy too.
This could be done with existing equipment, and one fitting that would hook into the supply valve on the center of the double manifold that OMS provides.
What do you think? Would OMS bite if several of us wanted such a system?
John
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Post by VintageDiverMN on Dec 8, 2004 8:35:51 GMT -8
You guys are on the right track, a Mistral with a steel 72 and J valve is the only way to vintage dive
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Post by Vintage Bob on Dec 11, 2004 12:22:25 GMT -8
Maybe I've been lucky up to this point. I've been diving with Royals since the late 70's and didn't start tinkering with Mistrals or D/A's until a couple of years ago. I have rebuilt/restored six Mistrals to date and regularly use 3000 psi to help break in the refaced seat and polished nozzle, seal. The Aqua Lung repair manual even mentions subjecting the Mistral to 2000-3000 psi on the bench during over haul to check for leaking at the pin. I know with the light weight yoke that it is not recommended to use them on 3000 psi tanks. I'll admit to occasionally using Mistrals on an AL 80 and I haven't had any problem to date with either the yoke or seat. It definately inhales harder at the higher pressure due to the upstream seat. I do have several 72's and recently bought a Faber 95 and feel very confident about using it with any vintage Aqua Lung two hose regulator, at the 2640 psi, 10% over charge pressure. My technique during the over haul, is to set up the levers so that when the case is clamped together, there is a slight leak at 250 psi and below. This allows optimum inhalation performance at the higher tank pressures, where you will be doing your dive. I have found that after a couple of dives, the seat/nozzle usually seals up at 250 or below. I have found in some cases that I can even re-adjust the levers higher after a good break in period without it leaking at low tank pressure. For optimum performance, the Mistral does require finessing and patience. I also am under the opinion, based on my own experiences, that a finely tuned DA or Royal will out perform Mistrals, at least at full or near full tank pressures. The Mistral does shine though when your at half a tank of air or less.
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