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What were you using for diluent?
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What were you using for diluent?
Mr.X:Is there a ADD port / manifold on the Gem? Have some guys already hot-rodded the thing?
X
Since I started diving the GEM since May, I have now upgrade my unit with the Shearwater computer. This computer makes my GEM complete. I would still recommend first time buyer watching their budget to buy the basic GEM package and upgrading down the road when you get the bucks.
There is a ADD on the right T piece. You can manually activate it but don't have to. The only time I manually add gas is when I switch to my deco gas and want to purge the loop and get the deco gas flowing faster to stay on my deco schedule. There have been modifications made to some units, most to the prototypes that have been out for several years. Keep in mind that while the GEM is being marketed as a recreational PSCR, it was developed for use in a deep cave.
OK, I'll bite. How is the GEM different as compared to the Drager Dolphin (the only SCCR that I've used for more than a "demo")?
My memory is that with the Dolphin there was significant FiO2 drop (not 3 to 5 percent, but 5 to 25 percent) so that you needed to use a diluent mix that was rather oxygen rich, or risk hypoxia at shallow depths. So the SCCR was not of much use below 90 to 100 feet. My memory is also that I was told not to use any helium, though I have to admit that I did not pay a whole lot of attention to the whys and wherefores since there's little reason to pay for helium for a dive that's gonna be less than 100 feet as a result of the PPO2.
The write up on the GEM that I saw said:
This is a light weight, simple, safe, fun way to extend the duration of your cylinder. If you usually finish your cylinder before everyone else, attach a GEM to your cylinder and you will solve the problem. No more twin 15 litre cylinders required.
The GEM is a simple rebreather that allows you to dump 1/3 of every breathe and recycle 2/3s. You will use a 36% to 40% Nitrox mix, so get the longer no-deco benefits of Nitrox as well. The GEM has a safe diving range down to 30m, your recreational dive limit.
So something's not jibing, can you tell me what?
What was your FiO2 at 15 fsw using EAN-32?
Mr.X:Thanks for the info. Curious - what does 'deep cave' have to do with this recreational unit? I can imagine limited use as a altered bailout breather for epic dives, but beyond that it is simply a SCR. Something that's been around in various iterations for decades. Since I have caved with CCR - I like the idea of using bailout caches, team mentality and breathers built for purpose like the CIS Lunar, Megalodon with Cis Lunar canister, or the RB 80.
What is the drop? Do you have actual measurements of it on your unit?I'm not familiar with specs on the Dolphin, but I can tell you there isn't a 25% drop with the GEM, ever.
So you are doing purges and gas switches? Do you have instrumentation built in?I just did a dive to 280' this weekend on my GEM and it performed flawlessly. I used a 50% travel gas at 50' for about 24 minutes to get to the pit, then switched to 14/50 for the deep portion of the dive.
With helium that makes sense, with EAN, it does not.WOB was better at depth. That's probably due to the helium, but I've noticed even with nitrox, WOB is slightly better at depth.
Using a rebreather in a manner it was not designed for is something I would be unlikely to do.Keep in mind that while KISS markets this rebreather as a recreational rebreather, that was not how it was initially designed.
Anyone who can knows Dalton's Law of Partial Pressures can calculate what it SHOULD be, the question, however is not on of "should" but rather on of "is." What IS your FiO2 at 15 fsw using EAN-32? Do you have a way to measure it on board?It should be about .4.
Here's the problem as I understand it: an SCCR that is designed for deep use will tend to have problems shallow because of the FiO2 drop. An SCCR that is designed for EAN, is, by definition, designed for shallow use and should not work well deep because of the ppO2. Perhaps your solution of shifting gasses is a reasonable solution to the problem, I don't know, it is not my area of expertise, but it flies in the face of what I have been lead to believe about rebreather design.Read above. The first prototype was made for use in a deep cave. In fact, the deep cave I had mine in yesterday. The nice thing about the GEM is it simple. While you still have to be concerned about CO2, as long as your breathing effort remains constant, that will not be an issue. Other than that, there is nothing left to do with the GEM. It is that simple. I have made it so I can do gas switches with mine, but that's a matter of changing what cylinder I'm plumbed into not by injecting O2 or diluent into it. Again, even though KISS is marketing the GEM as a recreational unit, it was not conceived that way.