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Old 17-01-2012, 09:53   #61
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Re: Rebreathers for Beginners ?

These are good points, however the no decompression limits are much longer than on air open circuit because the O2 is optimized at every depth instead of a single depth.
The biggest advantage I see for a 100 ft dive is the extended bottom time. Granted, 80 cubic ft of Ean36 gives you almost same bottom time, but total dive time will be about an hour before you run out of gass. The rebreather with 13 cubic ft tanks give you 3 hours dive time in total silence. Its amazing how quite it is underwater with out the bubbles.
A software upgrade will allow you to switch to normoxic trimix when you are ready. Then you get a max depth of 190 feet and still get three hours of dive time.
One thing I don't like...... I like to invert and descend as fast as possible. On open circuit we can get to 225 feet in a minute and a half. This is a really (really) bad idea on closed circuit.
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Old 01-02-2012, 12:11   #62
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Re: Rebreathers for Beginners ?

I completed the checkout dives for the discovery unit this weekend.
After 3 90 minute dives we had a zero no fly time and we came out of the water with less disolved nitrogen than we went in with. I used 14 cubic feet of O2 for all three dives combined. I think I have moved over to the dark side.....
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Old 01-02-2012, 13:48   #63
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Re: Rebreathers for Beginners ?

Awesome! You now belong to the select few whom compressed air physics do not apply.
Unshackled! Congrats.
How is the dissolved nitrogen ascertained at the end? Can Co2 also be measured?

As an aside, physiologist once told me that I got "tingles in my face" because I had blown to much Co2 out of my blood by over breathing on extertion. I could never confirm this.
My spiro was one of the highest he had ever measured.
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Old 01-02-2012, 14:14   #64
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Re: Rebreathers for Beginners ?

Quote:
Originally Posted by lateral View Post
Awesome! You now belong to the select few whom compressed air physics do not apply.
Unshackled! Congrats.
How is the dissolved nitrogen ascertained at the end? Can Co2 also be measured?

As an aside, physiologist once told me that I got "tingles in my face" because I had blown to much Co2 out of my blood by over breathing on extertion. I could never confirm this.
My spiro was one of the highest he had ever measured.
If breathing a high He, low N2 mixture you could come out with lower body nitrogen than when the dive started but I too am interested in how that was documented.

Never heard that about low CO2 tingles before. I have gotten narced as hell from CO2 buildup on exertion at depth before. Very fast onset, like 5-10 seconds.
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Old 01-02-2012, 14:18   #65
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Re: Rebreathers for Beginners ?

And I'm pressure testing the keel fuel tank this weekend...I love it when a plan comes together.
Life is good. Maybe this "life on the water" thing will actually happen soon.
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Old 01-02-2012, 14:36   #66
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Re: Rebreathers for Beginners ?

" I have gotten narced as hell from CO2 buildup on exertion at depth before. Very fast onset, like 5-10 seconds."

I don't follow.
On compressed air, or a rebreather? If compressed air, you must have been skip breathing, or N was the toxic gas. How did you know it wasn't N?
How did you recover? N is incrementally subtle.
Co2 I am not aware of apart
from theoretical, hyperventilation , panic , disorientation.

Bearing in mind, it was a long time ago I did this stuff.
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Old 01-02-2012, 14:53   #67
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Re: Rebreathers for Beginners ?

The instructor in our class was diving a Sentinal. It displays a no fly time and it was zero. The part about the nitrogen being less than when we started was deduced because we spent 90 minutes at 40 feet on a 1.2 PpO2. Open circuit on air would be a Ppo2 of 0.46. Just for fun I wore my open circuit wrist computer during the dives and it had an 18 hour no fly count down.
Air has a PpN2 of about .79 on the surface. During the dive we were breathing a PpN2 of .46 (at that depth) so for 90 minutes we were breathing an O2 rich mix as compared to the surface.
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Old 01-02-2012, 15:03   #68
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Re: Rebreathers for Beginners ?

As to the C02. I took the Co2 scrubber out of my unit and breathed it (not in the water). It took about 25 breaths to get a head ache from hell and got really loopy despite breathing 40% O2 the entire time. It took about 15 minutes to go away after I quit.
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Old 01-02-2012, 15:20   #69
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Re: Rebreathers for Beginners ?

Yes the Co2 can be measured on the sentinal, not the descovery, however it is very unrelaible. So much so you have the option of turning off the sensor during the dive if you think its not reading correctly. The sentinal has thermisters in the scrubber. The scrubber heats up as it absorbs Co2. Warm scrubbers are working scrubbers......sometimes....
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Old 29-02-2012, 16:49   #70
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Re: Rebreathers for Beginners ?

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Wow, 5 grand ! I used a rebreather back in the 60's, simple canvas bag with a cannister of co2 absorbing crystals and a small oxygen cylinder on top, when you had difficulty breathing you opened the valve for more oxygen, probably didnt cost $50, how things change !!

I thought you were joking until I found this....Cant go past 20 feet, but it is a rebreather.



INSTRUCTIONS FOR THE USE OF THE DESCO MODEL “A” LUNG

Catalogue No. 59114

DRESSING: The diver slips the neck strap over his head so that the lung will hang on his chest very much like an apron. A slide is provided for the desired adjustment of the height of the lung on the chest. Further adjustment will seldom be necessary. Important - It is recommended that at no time should this strap be tightened so that it cannot readily be slipped over the head in an emergency, thus, the lung should be put on and taken off without adjustment of this slide.
The waist strap is next fitted around the diver’s waist. This should be secure enough to hold the lung firmly against the chest. This strap is adjusted by means of the quick release buckle.
Note that the relative position of the breathing bag to your own lungs is important for maximum ease in breathing. This will vary somewhat in different positions that you may assume in the water. In an erect position, you will find that raising or lowering the position of the bag on your body will make exhalation easier or harder, respectively, and inhalation harder or easier, respectively. Be sure not to raise it so high that you cannot easily slip the strap over your neck. In horizontal or normal swimming position the above e positioning of the bag obviously will make little difference .

SURFACE SWIMMING: If the shut-off valve is closed at the mouthpiece no air can escape from the lung nor can water enter. The swimmer may thus let the entire mouthpiece fall into the water, if he so chooses, or he can carry it in his mouth with the shut-off valve closed and breathe through his nose with the mask slipped up on his forehead. Note: Whether the shut-off valve is open or closed, the breathing bag is always connected to the exhaust valve, so that excess gas accidentally admitted into the lung will be automatically released.
A DESCO or other make swimming mask is worn with the lung. This mask should be of the popular type which cover eyes and nose but not the mouth, since a mouthpiece is worn with the “A” Lung.
Caution is suggested against many inexpensive masks sold widely the stores. Many of these are poorly designed and are made of an inferior grade of rubber with the result that a satisfactory seal cannot –be accomplished. A leaking mask can be dangerous to the novice, since vision will be seriously effected and the diver may get water in his nose, either of which could result in confusion and alarm, which could result in serious consequences in deep water.
The diver should learn how to “blow his mask” before diving with it and should practice until he can do it easily. This is the art of blowing the water out of the mask when completely submerged. Since he may accidentally bump or hit his mask when diving or suffer leakage from a poor fit or other causes, it is important that he know how to clear it.
In practice, flood your mask as you stand in shallow water. Move your head into an erect position or in a side-swimming position so that the glass of the mask is vertical. Break the seal of the mask from your face at the lowest possible point with your finger. With the mask thus open to the external water, exhale through your nose into the mask. A partial breath of air will now push the water level down until it reaches the opening, and then air will blow out. Remove your finger and your mask will be clearer, completely washed, and ready for continuation of your dive.
Goggles are not ordinarily recommend for diving since there is no provision for equalizing pressure in them, and in most types they give differential axes of vision for each eye.



-1-A-

PREPARING TO DIVE: Before entering the water, carefully check and inspect the entire apparatus., be certain that the oxygen cylinder is sufficiently full and that you have a fresh sufficiently filled cartridge of Baralyme with ample margin of safety for the dive that you plan to make.
Void all air from the breathing bag and your lungs, This may be done before entering the water by pressing against the bag with the hands and then sucking the last portion out with the lungs. If in the water up to your neck, merely open the exhaust valve or the shut-off valve ( with the mouthpiece out of your mouth) and the water pressure will automatically force it out.
Unless you are preparing for an immediate deep dive with full understanding of the special instructions do not take a deep breath before putting the mouthpiece in your mouth. This inhaled air is approximately 79% nitrogen and only 21% oxygen. Nitrogen cannot support life and its presence in the breathing bag may be very dangerous. It may mislead you to think that you have vital oxygen since it will distend the bag and your lungs. After you burn up the small amount of oxygen with it, it may result in a dangerously low oxygen content air.
Rather, exhale before placing the mouthpiece in your mouth and empty your own lungs of air. With the breathing bag also collapsed, now admit fresh oxygen. You will thus be assured that you will have pure undiluted oxygen.
If your mouthpiece is in the water as you prepare to dive spill or shake the fraction of a teaspoon of water out of the mouthpiece tube. Place the rubber mouthpiece in the mouth, biting on the rubber tabs and placing the rubber flange between the 1ips and the teeth. If you have not yet voided the system of air, do so now by opening the exhaust valve and exhaling thus clearing your lungs. The water pressure will now void the breathing bag of air. Now admit fresh, pure oxygen and start breathing.
Breathe for a few seconds before starting down just to make certain that everything is in operating order.
There are two valves on the cylinder. The large cylinder valve, the shaft of which is coincident with the centerline of the cylinder, is used only for filling the cylinder. The small “needle valve” which connects to the breathing bag is the only one with which you will be concerned in actual diving. This controls the feed of oxygen into the apparatus.
The diver has his choice of methods of admitting oxygen, intermittent or constant flow. In the former method he admits gas at the start of his dive until his breathing bag is properly distended (as explained later) and then turns it on or off at intervals as he consumes the oxygen or as the increasing pressure requires distension of the bag. In the latter method he cracks his needle valve until he has attained what he estimates is the proper flow (about a quart a minute). He will soon learn correctness of his assumption, for if he has not opened it far enough he will soon find that his bag is collapsing on the end of a deep inhalation. If he has opened it too far he will find that his bag is completely inflated and that he cannot quite complete the end of an exhalation. He must then exhaust a little into the water with a resultant waste of oxygen.
Probably the best system is a combination of the two – crack your valve to admit a constant flow a little less than you need. Then, at infrequent intervals, as you need it, admit a little more. This will obviate any chance of wastage.

SURFACING: As your head rises above the surface close off the mouthpiece. When this is closed, you may drop the mouthpiece in the water, if you choose. If you do not close the valve, there is the possibility of water running through the mouthpiece down into the lung and also the undesirable loss of oxygen in your bag. Since the lung will ordinarily still be in the water, the pressure of that water will instantly expel all of the gas in the bag unless the valve is closed. With the shut-off closed, please note again that the manual or automatic relief valve is still operative.

-2-A-






To remove the canister from the bag, disconnect the breathing hose by turning the breathing hose "coupling'' nut. Next remove the canister "seating nut" immediately below it. The supplied wrench fits both of these. With this off the "annular" sealing plate may be lifted off. The canister may now be easily removed from the breathing bag. With the canister removed from the breathing bag, the locking bar is turned a fraction of a turn to the left and lifted out. This will allow the cartridge to be easily removed. A new cartridge may be inserted and the canister put back into the breathing bag.
Always be sure that the large open end of the cartridge is inserted last into the canister and that the end with the small hole is inserted first. This s will readily be remembered by noting that the small hole in the metal end of the cartridge corresponds to the small inlet of the canister where the breathing tube is connected. The large open screened end of the cartridge corresponds to the large open end, or locking bar end, of the canister. It will be noted that the metal ring on the cartridge is intended to seat against the, gasket on the top end of the canister, such that air must go through the cartridge. rather than around it. It will be noted that on the large, or lower and of the canister a pressure "perforated plate" is applied to insure the diver that the pellets will be under pressure at all times. This will avoid any possibility of looseness among The pellets and possible channeling, such that the air won't go over rather than through the chemicals, Although the cartridge will work if put in backwards, it will be noted that the gasket seat, will not be as satisfactory and the spring will not apply pressure directly to the pellets.
Do not use the lung unless the canister is fully filled with Baralyme and there is full tension on the spring connected to the locking bar end.
Be sure to remove pecking seals from the cartridge before inserting for use.

The DESCO A-Lung

Also known as the Adventurer, and the Sportster Lung. This unit was designed in the early 1950's. It was a simpler, more compact design than the B-Lung. The unit evolved during its short run. Early units had a canvas breather bag, while later units had a vinyl bag. The A-Lungs were only produced for a few years in the mid-50's.
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Old 03-03-2012, 12:15   #71
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Re: Rebreathers for Beginners ?

I am a fairly experienced technical diver, and a trained RB (KISS) diver.

For me one of the advantages were the extraordinary duration potential of RB dives, up to 5 hours. I personally went to three or four hours. Another advantage for deep and/or long duration dives was the optimal O2 levels for deco. Of course there is the mere pennies in helium used in the diluent on even the longest dives. However, for me the great practical advantage for the RB was the ability to interact far more closely with sea life than you could ever dream with open circuit. When you're not making a thundering plume of exhaust bubbles every couple seconds, the fishies and such simply pay you no mind. I have had nearly magical dives completely surrounded by fish or turtles(!) that were simply unconcerned with my presence.

This to me is the advantage.

The disadvantages are twofold. While I relished the complexities of planning and executing higher level technical dives, I came to be frustrated by the level of diligence required in cleaning, maintaining and prepping the machine. In the back of your mind is always the knowledge that if you had made even one seemingly minor error or oversight in assembling and testing the machine, this could be your last dive. The second disadvantage, and this goes back to three years ago, people are still dying at far too high a statistical frequency for this to be an acceptable practice for me. I came to understand that my kids needed their dad much more than I needed a thrill.

I gave up rebreathers, and shortly after technical diving as well. I am now quite satisfied to do a few nice mellow dives on vacation.

I am furthermore of the considered opinion that these machines are still simply not foolproof enough for the general diving public. Murphy is the cruelest force in the universe.
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Old 19-10-2012, 06:15   #72
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Re: Rebreathers for Beginners ?

I forgot about this thread.....a couple of months ago I took a cruise on the Argo out to Cocos island. Its about 300 miles off the Pacific coast of Costa Rica. I got 18 hours on the rebreather. It worked out great. What a fun trip.
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