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Mistral DH Reg (~1959) and modern tanks

Discussion in 'Vintage Equipment Diving' started by CT-Rich, Apr 21, 2020.

  1. Scuba Lawyer

    Scuba Lawyer Manta Ray

    # of Dives: 5,000 - ∞
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    Actually, not really different at all. If you can work on a SH Conshelf (VII, XIV whatever) (i.e a diaphragm reg) you can rebuild a DAAM (especially if you are adding a Cyclone or Phoenix 1st stage and an HPR 2nd stage). Plenty of folks available here and on VDH's Board to give advice and assistance. My 2psi
     
    JamesBon92007 and Sam Miller III like this.
  2. JamesBon92007

    JamesBon92007 Great White

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    Yes, I'm thinking about adding the Cyclone and the HPR and, if I find one, a silicone diaphragm (and probably a silicone mouthpiece). Right now I'm wondering how difficult it is just to change the LP seat. The diagram I have is not very detailed in that section. Based upon my single-hose regs, I think the LP seat is not sealing very well and that might make an immediate improvement. Also, there is no duckbill in my reg. I also did not see a duckbill on the diagram, but all the instrucitons I've read talk about the duckbill types and the duckbill eliminator etc. Are there some without a duckbill? The air only seems to flow one way through the hoses but it has the valves on the mouthpiece for that.

    Edit: I think I found it. It must be part 29, the "Exhaling Valve." The picture is not very clear.
     
    John C. Ratliff likes this.
  3. John C. Ratliff

    John C. Ratliff Instructor, Scuba

    # of Dives: I'm a Fish!
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    A couple of things. First, at 300-500 psi tank pressure, adjust the first stage until it just leaks, then back it off a quarter turn. That should make I think breath much better.

    That duckbill exhalation valve is needed to keep water from entering the hose when inverted. You can get it at Vintage Scuba Supply, or get a Duckbill Eliminator at VDH. If you get a duckbill, be sure to order the longer one. You want the openings to be below the center is the diaphragm so that when the IP is adjusted finely there won't be a slight leak through the second stage due to the difference in water pressure being greater than the cracking effort. You can place the duckbill into the bottom box with a pencil (eraser end) and ensure that it lays right on the diaphragm with the end parallel to the diaphragm. Then fold the extra back over the outside of the exhaust horn, and replace the hose. By the way, if you took it into the pool without a duckbill, and it leaked air when in an upright position, this is probably the reason.

    The hoses should be adjusted so that, with the regulator face down on a flat surface, the mouthpiece points straight back at the regulator. That way, when in the water there is no twist that can cause jaw fatigue.

    Now, about the LP sear holder, if it is not leaking when you set it up, leave it alone. Hyour problem is probably something else. To remove that nut on the top that holds the washer and demand lever, you'll need a good needle ose pliers to grasp the shaft. The round shaft is in a round hole, so without the pliers you cannot turn the nut independent of the shaft. In the old days, the U.S. Navy simply cut the top of the seat holder off, and replaced the whole thing (the Navy procedure was to glue the nut down so it could not move, necessitating it being cut off). But, like I said, if it ain't leaking, don't "fix it."

    SeaRat
     
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  4. JamesBon92007

    JamesBon92007 Great White

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    The instructions I found for adjusting the LP seat said to do what you said, then wait, then check it again, cycle it a few times, check it again, turn of the air, check it again.... It seemed like it wasn't going to stop leaking and it finally did. I think I have it set about right now, but I'll check it again in a little while.

    I was very surprised to find no duckbill when I opened the can.
     
  5. Scuba Lawyer

    Scuba Lawyer Manta Ray

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    Invest in an IP gauge. IMHO they are invaluable. Also, personally, I ALWAYS replace the HP and LP seats in any two-stage vintage DH I'm rebuilding, along with a substituting a silicone 2nd stage diaphragm for the old ones and replacing all o-rings and gaskets. VDH sells kits. Some folks don't do that and they get along just fine. I have an aversion to keeping 60 year old soft parts in my life support equipment so that's just me. :)
     
  6. James79

    James79 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 50 - 99
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    Regarding the lp seat holder, you can remove the lever screws without removing the lever first if you are careful. That will let you get the lever off, then remove the second stage as an assembly. Once that is done, you can use a wrench to hold the seat holder at the seat end, and a wrench on the nut... Tighten the nut first, as it is probably staked... Then work it gently off some, back on, off a little more etc. til it comes off. Presto, dis assembled second stage. Carefully pick out the seat, and replace same as a Conshelf poppet. I used the same seats I punched for the Conshelfs.
    Bear in mind, I am new to this... But most of this was gleaned from VDH.
    Respectfully
    James
     
  7. GJC

    GJC Solo Diver

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    No duckbill? When was the last time it was serviced? It may be worth doing a full servicing. Internal parts are pretty much Conshelf parts, so it shouldn't be hard for you to get comfortable with a DAAM.

    When you get it apart, the second stage parts are the same as in a Conshelf second stage. It jus has a bigger diaphragm and lever.

    Exhalation effort should be much better when you get a duckbill in it (or duckbill eliminator).

    Cyclone makes your DAAM (unbalanced first stage) into a Royal Aquamaster (balanced first stage) and gets you an brand new first stage except for the diaphragm and external spring.

    If you get an HPR, I think you need to get the silicone diaphragm at the same time because it won't work with the old diaphragm. The old diaphragm has 2 feet that engage the old lever and I don't think you can get things lined up right unless you replace both.

    The band clamp is a must get item.
     
    scrane likes this.
  8. halocline

    halocline Solo Diver

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    When I was working on my DA aquamaster years ago I found it frustrating because I couldn't get stable IP on it no matter what I tried, and I'm used to working on regulators. Turned out the seat was simply not that stable with regards to lock up, and I found that to be true for several seats. Moral of the story is, get a phoenix, you will not regret it. The RAM seats are much much better performing than the old unbalanced seats.

    I guess the cyclone 1st stage is after my time, so I just looked on vdh to learn about it and did not find anything. I'd be interested in info on them.
     
  9. Scuba Lawyer

    Scuba Lawyer Manta Ray

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    Store | Vintage Double Hose
     
  10. James79

    James79 ScubaBoard Supporter ScubaBoard Supporter

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    Here's the Cyclone;
    Store | Vintage Double Hose
    Respectfully
    James
     

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