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Thread: Override depth limitation with CMF.

  1. #1
    Tinkerer madvic is an unknown quantity at this point madvic's Avatar
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    Override depth limitation with CMF.

    This is a theoretical post; only just to check with you if the idea is feasible:
    I propose to have a dual O2 injection with the same Reg in order to bypass the depth limitation of the CMF.

    Description of the system: the system work as a CMF like, we have a capped reg, and we use a needle valve( 2 ) adjusted to have a FIXED flow ( 3 ) (CMF like).

    The cap has a modification; A valve that isolate the reg chamber to 1 atm (Isolator) ( 1 ). This valve allows the “decapping” of the reg connecting the chamber to ambient pressure.

    When you dive without trespassing the limit the rig behaves like a CMF rig. When you approach to the limit depth the flow begin to change same way as the CMF (the differential pressure in both points that flank the fixed needle valve decrease, changing the nature of the flow.)

    At this point you have a pre-set position of the needle valve ( 4 ). You change the to this pre-set that “will constrict the flow” and you open the isolator in order to increase the IP of the O2 reg. For example you open it at 80 meters, so you will add 9 Atm to the reg chamber, at this point the O2 reg increase the IP +9. ( we take a moment to fine tune the needle valve position according to the ppO2 readings)

    Lets say that the O2 reg has a pre fixed IP of 8atm. 8+9 17atm. Minus the ambient pressure 9atm: you will have again 8atm of differential pressure between the O2 line and ambient. “So it’s like a fresh start for the reg”. DANGER: in this point you need prior to open the isolator to change the needle valve position to a “restricted” established flow. (Maybe a dial with the needle valve screw will be needed). After equalizing pressures with the ambient you CLOSE again the isolator keeping this internal pressure. And you continue to descent.

    After “grabbing the car keys in the bottom”, when you begin the ascent, you cross the 80 meters again, but no need to change the dials. At this point the ambient pressure will decrease, increasing the differential pressure of the O2 line. (But internally the O2 amount is steady). In the example when you reach 30 meters you will have a differential of: fixed IP:8atm + 8atm of the “equalization point”, when you opened the isolator , minus 4 atm (ambient pressure) so: 8+8-4:
    12Atm (this pressure is not a big deal to O2 line).

    The problem arises when you are ready to surface; at this point the ambient pressure is low compared to the 8+8 atm. So maybe another equalization step is needed at shallow depths ( 5 ). (at 20 meters you open FIRST the isolator and after you change the needle valve to another preset point).

    With this system you dive same way as if you had a CMF. And you avoid the constant play with the needle valve and non caped reg.

    So please may we discuss this idea? Any impressions or comments in order to say that it will be a perfect suicide machine.?
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    RBW Member yorkie_chris is an unknown quantity at this point yorkie_chris's Avatar
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    Re: Override depth limitation with CMF.

    Too much messing about for me.

    What about:
    http://www.rebreatherworld.com/showthread.php?t=12844

  3. #3
    Tinkerer madvic is an unknown quantity at this point madvic's Avatar
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    Red face Re: Override depth limitation with CMF.

    The Idea is quite easy;

    When you perform normal dives (not deep ones) the rig will behave like a CMF. No need to touch the needle valve, nor the insulator. Exactly the same as if you had the CMF.

    When you go for a deep dive, the same configuration allows you to descend, by only; “changing the pre-set in the needle and opening and closing the insulator valve” after that the rig will add oxygen as if it where ruled by a CMF but in “deep mode” (you increase the reg IP, you fix this IP, you change the pre-set flow)

    And always you could let open the whole dive the insulator valve and dive “needle style way”.

    In fact it’s a system that has many advantages, it fuses the easiness of the CMF diving and overrides the limit depth. Also It give you redundancy: “ dive CMF style or Needle style”.

    And its very cheap and KISS thinking; no need of “arcane variable constant differential flow controller valves” that has several moving parts, diaphragms,… And for sure it will cost one of my kidneys… (I admit that my rig is the product of scavenging a lot through internet and home depots, but its cheap).

    And for the calibration, you only need to connect the insulator valve to a IP from another reg, add one flow meter, and adjust the pre-sets on the needle valve, (as many as you want…).

  4. #4
    Dark, cold and wet. DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ is a glorious beacon of light DwayneJ's Avatar
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    Re: Override depth limitation with CMF.

    tecme sell a replacement spring for the apeks ds4 which provides tuning and operation from 12-20 bar IP... Combined with an appropriately sized orifice, this is a pretty simple and elegant solution.

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    Re: Override depth limitation with CMF.

    Very cool. Have you seen any adverse wear or other issues using it?

    Quote Originally Posted by DwayneJ  View Original Post
    tecme sell a replacement spring for the apeks ds4 which provides tuning and operation from 12-20 bar IP... Combined with an appropriately sized orifice, this is a pretty simple and elegant solution.

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    Tinkerer madvic is an unknown quantity at this point madvic's Avatar
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    Re: Override depth limitation with CMF.

    Quote Originally Posted by DwayneJ  View Original Post
    tecme sell a replacement spring for the apeks ds4 which provides tuning and operation from 12-20 bar IP... Combined with an appropriately sized orifice, this is a pretty simple and elegant solution.
    Its a good Idea!

    But I see minor drawbacks:
    1-// you need to have a very good Piping work, this high IP I guess eliminates the possibility to use push-in fittings (max pressure is about 20 bar (not sure).
    (the push-in fittings are so neat and cheap that is marvelous to work with and you could reconfigure your rig in minutes)

    2-// If you have one leak, at this high IP I guess that you will have a problem. (tank empty faster) and if the leak is in your circuit... then you have a real problem.

    3-// the MAV must stand this High IP, and it will be a little gruesome to fine tune your manual O2 addition.
    Last edited by madvic; 19th September 2013 at 17:16.

  7. #7
    RBW Member michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn's Avatar
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    Re: Override depth limitation with CMF.

    Quote Originally Posted by madvic  View Original Post
    Its a good Idea!

    But I see minor drawbacks:
    1-// you need to have a very good Piping work, this high IP I guess eliminates the possibility to use push-in fittings (max pressure is about 20 bar (not sure).
    (the push-in fittings are so neat and cheap that is marvelous to work with and you could reconfigure your rig in minutes)

    2-// If you have one leak, at this high IP I guess that you will have a problem. (tank empty faster) and if the leak is in your circuit... then you have a real problem.

    3-// the MAV must stand this High IP, and it will be a little gruesome to fine tune your manual O2 addition.
    no way id want to put 12-20bar o2 in my medium pressure circuit just to increase CMF depth limit, short term solution , long term strain on components
    mike

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    Tinkerer madvic is an unknown quantity at this point madvic's Avatar
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    Talking Re: Override depth limitation with CMF.

    Exactly Mike
    totally agree with you.

  9. #9
    RBW Member michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn is a jewel in the rough michael hearn's Avatar
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    Re: Override depth limitation with CMF.

    Quote Originally Posted by madvic  View Original Post
    Exactly Mike
    totally agree with you.
    i solved this problem in another way , i incorporated a minature 1st stage valve into my unit , no wider than a 2 euro coin , it has an output of 8 bar non compenating and it feeds the orifice only . the tank 1st stage is a standard compensating valve.when diving normally ,and when this valve reaches its maximum depth and shuts down the dive can continue on solenoid and or manual inject. no bumping up IPs,no extra stress on components . an inline shutoff allows allows disabling of the valve at anytime should there be a problem or you simpely dont need it .
    mike

  10. #10
    Roland Somodi rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver is a glorious beacon of light rolanddiver's Avatar
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    Re: Override depth limitation with CMF.

    I thought about doing the same thing, but never got to make the mini first stage. Only have it on paper(CAD). Since I dive mainly in caves redundancy is way too important for me. I put a 2l 200Bar lightweight small draeger O2 tank mounted on the right side behind my light canister just like the argon drysuit bottle on the left side. It feeds the orifice using a modified scubapro MK2 first stage. Everything else(solenoid, MAV) are supplied from the 3l tank thru a scubapro MK17 on the side of the rebreather. In this case, I have enough O2 supply for the orifice for 285minutes. No depth limitation, I have at least two O2 supply tanks all times, and should the dive last longer(never did) I can just manually add more frequently and have the solenoid as a safety parachute. I didn't mean to hijack the thread, just shared my idea.Also have a swagelok needle valve, and hopefully one day I can give it a try.
    Very Respectfully

    Roland Somodi

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