GEM recreational rebreather

[Thalassamania]

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

 

[Dive-aholic]

What were you using for diluent?

The GEM is a Gas Extender. You plumb into a cylinder filled with the gas you need. At shallow depths (read less then 4 ata), you will have a 3-5% drop in O2 percentage in the inhalation side of the loop. Get deeper and the difference is much less. At 150', ~ 5.5 ata, your ratio drops enough to be almost insignificant. It will be insignificant enough that you will not detect a difference in your ppO2 readout unless you can get a readout to 1/100th. Yesterday's dive I used 21/35 and was getting 1.1 ppO2 readout, the same I would be getting had I been on OC. However, at 50' I was getting a .4 ppO2, which would be .5 if I were on OC.

Is there a ADD port / manifold on the Gem? Have some guys already hot-rodded the thing?

X

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.

 

[Thalassamania]

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?

 

[divejay]

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.

My dive this morning on Grand Cayman from shore on the GEM, 32% nitrox @ 3,000 psi, standard 80 cu.ft. tank: 45 minutes at 130' then 45 minutes at 60' then 62 minutes of deco on a awesome shallow reef at 15' and still had 1400 psi left in my tank.

 

[Thalassamania]

What was your FiO2 at 15 fsw using EAN-32?

 

[Mr.X]

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.

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.

X

 

[Dive-aholic]

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?

I'm not familiar with specs on the Dolphin, but I can tell you there isn't a 25% drop with the GEM, ever. 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. 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. Keep in mind that while KISS markets this rebreather as a recreational rebreather, that was not how it was initially designed.

What was your FiO2 at 15 fsw using EAN-32?

It should be about .4.

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.

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.

 

[Kim Smith]

Hi Everyone,

Kim here from KISS Rebreathers.

I was just chatting with Jay from Dive Tech today, and he mentioned that there were a few questions about GEM. So far i think Jay and also Rob Neto have answered the questions well.

Regarding shipping of units, our production is going well. For those that are still waiting, it is probably as we are still setting up instructors in various areas. Knowing that it would take time to get this done, is one of the reasons i offered a discount when we released GEM last year. I will email those on my list separately to touch base.

With regards to GEM and deep diving, so far we only have a recreational course. But we are actively working on the next level of training, and hope to have that available soon.

Yes, GEM as it stands right now, is designed for the recreational market. but yes, it did come from deep cave diving. We tweaked the unit to make it more appropriate for recreational diving; but in essence very little has changed.

Deep diving on the GEM involves gas switches and carrying various gases, as well as a true understanding of what happens when you dive a low nitrox mixture in a semi closed rebeather. this is why a training program is important. When this level of training is complete, we will have an annoucment.

If anyone has others questions for me, please let me know.

all the best,

Kim Mikusch
Kiss Rebreathers and Boosters

 

[Thalassamania]

I'm not familiar with specs on the Dolphin, but I can tell you there isn't a 25% drop with the GEM, ever.

What is the drop? Do you have actual measurements of it on your unit?

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.

So you are doing purges and gas switches? Do you have instrumentation built in?

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.

With helium that makes sense, with EAN, it does not.

Keep in mind that while KISS markets this rebreather as a recreational rebreather, that was not how it was initially designed.

Using a rebreather in a manner it was not designed for is something I would be unlikely to do.

It should be about .4.

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?

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.

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.