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Mistral - To Grind, or Not to Grind; that is the question

Discussion in 'Vintage Equipment Diving' started by Scuba Lawyer, Aug 26, 2020.

  1. rhwestfall

    rhwestfall Woof! ScubaBoard Sponsor

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    Is the diameter the same as the replaceable volcano on Bryan's modern Phoenix? Wondering about doing away with that orifice and dropping a replaceable one in on it......

    just brainstorming...
     
  2. herman

    herman Divemaster

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    I may have one Mark......and installing a removable orifice is what I have in mind to try.. The body will have to be machined out and if I remember correctly, the opening of the AK/Phoenix seat is a bit larger than optimal but then again , it would be better than an unusable reg body.
     
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  3. Luis H

    Luis H Instructor, Scuba

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    Nope.

    A balanced valve can afford a much larger orifice since (guess what)... it is balanced. :)

    The orifice in a Mistral may seem like it is just a bit smaller, but keep in mind that the area is a function of the diameter square (or the radius square, same relationship).

    Increasing the area of an un-balanced valve orifice will affect the range of forces required to operate, since the pressure differential will have a much larger effect.

    Due to the larger area, with a full tank is going to perform like crap. It will take a lot more force to open the valve.




    Herman,

    If you would like to converted into a balanced single stage regulator, I have the drawings for that (being there, done that :wink:). I called the the "Unicorn 1" project. I called Unicorn for having a single stage (single horn... catchy name I think), and the number 1 was for the first design using cannibalized, ruined Mistral parts... No life Mistrals or even barely lived Mistral were ever sacrificed for that project.

    BTW, you are familiar with the Unicorn 2 (or Unicorn II). The 2 is also a single stage, but it had HP ports. We need to talk about reviving that project.
     
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  4. Scuba Lawyer

    Scuba Lawyer Manta Ray

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    UPDATE: After further sanding, polishing and certain incantations involving goat-leggings and scotch I achieved a great seal of the HP seat and volcano orifice. Thanks for everyone's suggestions.
     
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  5. couv

    couv Instructor, Scuba

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    Is there enough material to drill it out over sized then drop in a custom made correct size orifice? I'm thinking drill and tap it, then make an orifice out of delrin that matches the original. Easy to say sitting on my ass in comfort not knowing anything about machining.
     
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  6. herman

    herman Divemaster

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    It would be easier to make a new one with the correct size hole rather than to modify a AL/VDH one. Don't think delrin is up to the job but a brass one would not be hard to make.

    Luis, I know the orifice opening is not the correct size and would not perform as well, just thinking a poor performing reg was better than a non-working one using a drop in option but making a new orifice with the correct size hole is the best option.
     
  7. rhwestfall

    rhwestfall Woof! ScubaBoard Sponsor

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    Re: delrin: what is the non-metallic material used in the 109/156/Gxxx orifices?
     
  8. herman

    herman Divemaster

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    Delrin is a plastic material that is used for a lot of applications like gears and bearings. It is a wonderful material to work with as it machines easily and holds tolerances well. It is what I used for the bodies of the custom DH regs I have made. Nylon is commonly used for LP orifices, delrin would work well too, just don't think it's quite up to HP applications.
     
  9. Luis H

    Luis H Instructor, Scuba

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    Even if the material strength is adequate, the high pressure orifice will experience a lot more erosion.
     
  10. Luis H

    Luis H Instructor, Scuba

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    IMO, The difference between "poor performing" and "non-working" can overlap and get blurry very quickly.

    I did not want to call it non-working, because I have learned that some divers can really suck and be happy doing so, as long as they get air. :D I am just partially kidding.

    I have not actually calculated the extra force required (or obviously not tested it), but considering the performance of a Mistral with a full cylinder and the percentage area increase, it doesn't take much to figure out that it is going to suck (literally).

    If you are really interested I can run the numbers/ calculations.

    A while back I ran a lot of calculations and did a lot of testing when I was playing with the balanced single stage (what became the Unicorn).

    I think that I have shared with you some of my pictures when I was testing the force on the levers and the Mistral pin using a digital scale. I mounted the Mistral body and the balanced valve body on a yoke fitting with a flexible HP hose so that I could carefully press the levers or pin against the scale.

    All the data I took produced some nice and interesting graphs.
     

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