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Thread: Conshelf Supreme first stage?

 

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    Conshelf Supreme first stage?

    On impulse, and for no good reason other than a hyperactive sense of nostalgia I just paid (probably too much) for a Conshelf Supreme in what appears to be very good condition.
    I haven't received it yet but looking at the pictures I see the yoke is stamped 4000 PSI service, was this typical of the Supreme model?

    Also, does anyone know how the Conshelf first stage compares with more current diaphragm designs- in terms of the much vaunted flow rate and IP drop during inhalation.
    I know that they are very reliable and the service kit is the same as current Aqualung units but maybe there are differences in case design that would affect first stage performance?

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    Have posted some pics to help, is this the unit ?CONSHELF 30 SUPREME.JPGCONSHELF SUPREME 30 OCTO 2ND..jpg

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    I have tried to post some pics but not sure it worked? The first stage is a typical Conshelf shape and the second stage exhaust tee looks different on yours- but it could just be the angle!

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    Quote Originally Posted by reefrat View Post
    I haven't received it yet but looking at the pictures I see the yoke is stamped 4000 PSI service, was this typical of the Supreme model?
    SE models were 4000 psi regs. One reason to consider the SEs over the venerable XIV, but I'll bet the XIV's 3000 psi yoke works just fine with a 3442 tank, assuming it was yoke and not DIN. I use an SE2 with my old PST 100's (3500 psi).

    Quote Originally Posted by reefrat View Post
    Also, does anyone know how the Conshelf first stage compares with more current diaphragm designs- in terms of the much vaunted flow rate and IP drop during inhalation.
    IMHO, no diaphragm compares to a Poseidon diaphragm for flow. Take the orifices apart, and you'll see what I mean. But I'm open to others' different experience. Get a used 2960 off EBay and see what I mean. Even the old Poseidon unbalanced diaphragm 300's (Model 2305) down-tuned to 130 psi Intermediate Pressure (at near-empty tank) do better than the Conshelf with a balanced second stage. But military units have used both Poseidon and Conshelf.
    Last edited by rsingler; August 16th, 2013 at 02:22 PM.

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    The Supreme is the enviro sealed version of the 1st stage.....can be 14 through to 30.
    The older USD ones use an oil cap and the newer AquaLung ones use the Apeks type dry seal.

    For me the two least desirable Conshelf 1st stages are the SE and the Flying Saucer (30, PRO or Royal). Not because of any inferiority in their performance but simply due them having all their LP ports sized 1/2" (SE2 and 3 just have the one 1/2" port).
    The 21 and 22 are my Conshelf of choice as they have 4 3/8" LP ports and are smaller and lighter than the ones with 1/2" ports.

    All Conshelfs will have a similar performance to the 1st generation Titan and Mares MR12.

    Most manufacturers have switched to a T shaped design for their diaphragm regs. I suspect this allows for a better air flow and gives more room to provide 2 HP ports.
    Luis H likes this.

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    Luis H's Avatar
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    I have several Conshelf yokes that were stamped 4000 psi and many with the 3000 psi. They are exactly the same yoke. There are no dimensions or material change between the two. It is just a change in the times… yokes were considered acceptable for higher pressures at one time (Cousteau used 5000 psi yoke tanks for a while).



    Quote Originally Posted by rsingler View Post

    IMHO, no diaphragm compares to a Poseidon diaphragm for flow. Take the orifices apart, and you'll see what I mean. But I'm open to others' different experience. Get a used 2960 off EBay and see what I mean. Even the old Poseidon unbalanced diaphragm 300's (Model 2305) down-tuned to 130 psi Intermediate Pressure (at near-empty tank) do better than the Conshelf with a balanced second stage. But military units have used both Poseidon and Conshelf.
    That is a very interesting observation and I agree that the Poseidon Cyklon 300 has a large first stage orifice. This does rebound the IP very quickly during the breathing cycle. The trade off is that having a large orifice in an unbalanced first stage, causes a larger IP change as a function of tank pressure change. The reason most non-balanced regulators have a small orifice is to try to limit the intermediate pressure swing as a function of tank pressure change. The larger the orifice in a non-balanced first stage, the more it is affected by tank pressure.

    It has been over two decades since I service a Cyklon 300 first stage, but I do recall that the IP does change a lot with the change in tank pressure (back then I didn’t actually wrote down this type of data).

    I have several Poseidon Cyklon second stage (I have retired their first stage) and I have paired them up with Conshelf first stages. It is easy to adjust the Conshelf to the higher pressure and I like the consistent performance of a constant IP (independent of tank pressure). It makes it a lot easier to fine tune this regulator combination.

    I have serviced a lot of Poseidon regulators (in the early 70’s in my first job at Divers Service Center in PR) and I spent a lot of time fine tuning does regulator. We did have a work bench with a regulator to supply any tank pressure I dial in, but it still was more time consuming than other regulators.

    My favorite (single hose) regulator back then was the Poseidon, due to its performance (followed by the Scubapro Mk-5).

    Note: I also have a bunch of Scubapro 109 second stages and they are all paired up with Conshelf or Aqua Lung Titan first stages. I find their performance being fantastic, perhaps not as good as a flow through piston, but more than adequate for feeding a couple of second stages at the same time.

    In my case one of the major advantage with the Conshelf is the commonality of parts with my Royal Aqua Master, Phoenix Royal Aqua Master, etc.

    The only job of a first stage is to try and maintain as constant of an IP as possible. The IP will always dip some in all first stages during the breathing cycle. The only advantage of a “higher flow” first stage is that the IP recovery will be a bit quicker and the total drop will be less. I have tested the Conshelf (and its many derivatives) for many decades and I find them all good to excellent performance.

    As I mentioned, the flow through pistons are better, but the Conshelf performance are excellent.

    I can’t remember the actual flow rate numbers published for flow through pistons and diaphragm regulators. What I recall is that the flow through pistons are several times the max flow of a diaphragm, but either are like an order of magnitude (10x) the flow that any second stage can use. Those flow rate test are only comparative tests and only give a relative idea of first stage performance during actual operation.


    Quote Originally Posted by Fishpie View Post
    Most manufacturers have switched to a T shaped design for their diaphragm regs. I suspect this allows for a better air flow and gives more room to provide 2 HP ports.
    I am almost certain that the reason for the change is for ease of maintenance and assembly. I have assembled many Conshelf with a wooden dowel, but it is a lot easier with the special assembly tool (like the one Herman makes). My observation with the “T” geometry is that it doesn’t require any special assemble tools (but I have limited experience with most of the newer first stages).

    I don’t believe that the flow rate is any better with the geometry change, at least nothing significant.
    Luis

    Buceador con escafandra autónoma clásica.

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    Luis,
    Here's a question halocline and I were debating awhile back: even though the flow through a small orifice first stage diaphragm reg is adequate by an order of magnitude, does the drop in dynamic IP affect how well a second stage attached to that reg breathes? In other words, paired in the worst case with a plain downstream second, will a reg that shows a big drop in dynamic IP actually make that reg harder to breathe?
    Subjectively, we couldn't feel it. But there's no doubt that a downstream unbalanced second takes more effort to crack at lower IPs.
    We wrote it off to a bad sampling location, and guessed that we didn't REALLY have that big a drop in dynamic IP, that's why we couldn't feel any difference. But I'm not so sure it wasn't a real dynamic IP drop we were seeing.
    But maybe, since the initial static IP is okay, the unbalanced second cracks normally, and then even a big drop in supply pressure doesn't affect breathing once it's open? I dunno. I'm struggling with this one. We were discussing why some regs (Mk10) seem to show such a big drop in IP on breathing, yet clearly perform as well or better than a Mk5 that doesn't show such a big drop.

    Now we've really hijacked this guy's thread, lol!
    Last edited by rsingler; August 17th, 2013 at 01:16 PM.

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    The simple initial answer is: yes, with a basic downstream demand valve the drop in IP will affect “work of breathing” (to some degree).

    It will not affect the initial cracking suction since the drop in IP only comes into play once flow is initiated.

    With a balanced second stage the drop in IP has very little effect.

    Then even a basic down stream second stage that is well designed, will have a good venturi effect that will often compensate very well, for the extra vacuum required to keep the demand valve open (due to the momentary drop in IP).

    For the most part (within reasonable limits) the design of the second stage plays a much bigger role on the breathing performance of a regulator than the first stage.


    I hope this helps and it is clear.
    Luis

    Buceador con escafandra autónoma clásica.

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    I think I'll throw a few on the flow bench and see if I can't pin this down. Then we can discuss some more. I'll start a new thread when I get some measurements done.
    And I'll put an old Poseidon on the variable tank regulator and get the IP spread compared with one of their balanced models.

    Rob

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    Keep in mind that the IP drop is a transient/ dynamic flow response, just like the venturi flow in the second stage.

    If you have the typical flow bench found in most dive shops, you probably don’t have a breathing cycle simulator. Without a breathing cycle simulator (like the ones used in ANSTI machines or at the Navy Experimental Diving Unit), it is very difficult to get significant data of the dynamic response of a regulator.

    You can develop a pretty good feel of dynamic flow response of a regulator, but without a repeatable simulator, there is no practical way of obtaining significant quantifiable data.


    While visiting the NEDU (Navy Experimental Diving Unit) I got to see several breathing simulators. They were basically large pneumatic piston driven by actuators that could be program to produce a desirable cyclic flow. Normally they test breathing system (rebreathers and open circuit) with a sine wave cyclic flow.

    A very interesting comment from one of the lab technicians was that they have actually programmed a different cyclic wave form to more closely simulate the actual human breathing cycle, but at the end the simple sine wave was close enough for most test, and I am sure it is a lot easier to consistently produce a sine wave to obtain repeatable results.


    Rob
    As a USAF hyperbaric officer, I am guessing that you are far more familiar with human breathing cycle than I am… I just deal with fluid dynamics from an engineering perspective... and when it comes to fluid dynamics, some of the real experts will tell you that accurate prediction can involve some witchcraft and magic.
    Luis

    Buceador con escafandra autónoma clásica.

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