CCR Trimix question

[boogeywoogey]

I hope you can help with an explanation...

How does a trimix CCR work with the added complications of the additional gas as opposed to an air CCR? Is it down to computer software or what extra hardware, if any, is needed to cope with the extra gas? Can any CCR deal with both situations? I would love to know more if anyone can help.

Thanks.

boogey

 

[wedivebc]

Most dive plan programs such as v-planner and GAP etc can handle fixed set point CCR decompression with helium based gasses. With diluent the ratio of helium to nitrogen remains the same, only the %O2 changes in relation to the other gasses.
My computer HS Explorer will also calculate CCR deco using trimix. The VR3 and I'm sure some others can do the same.

 

[silent running]

I hope you can help with an explanation...

How does a trimix CCR work with the added complications of the additional gas as opposed to an air CCR? Is it down to computer software or what extra hardware, if any, is needed to cope with the extra gas? Can any CCR deal with both situations? I would love to know more if anyone can help.

Thanks.

boogey

Hello boogey, if I understand your ? properly, then the answer is that there isn't anything extra necessary to dive with trimix in a CCR. Remember that a CCR has 2 cylinders, O2 and diluent. The dil is used to make up the remaininng volume needed to keep your lungs full, the O2 is mixed in to maintain a constant PPO2. You can put whatever gas mix you want in the dil cylinder, provided it's appropriate for your max depth and training. To my knowledge, all CCRs can be used with He. You would need a computer that has a constant PO2 capability or constant PO2 trimix tables and a timer/depth gage. It's pretty simple... -Andy

 

[boogeywoogey]

Silent,

Thanks. I asked because, I keep hearing the term "CCR trimix rebreather" and, not being rebreather conversant, i wondered if there were different types?

If I understand your rsponse correctly, it makes no difference....any rebreather will work with any mix, the computer is the key???

kinetic

 

[caveseeker7]

If I understand your rsponse correctly, it makes no difference....any rebreather will work with any mix, the computer is the key???

Kinetic, rebreathers fall into semi-closed and closed circuit categories. Some of the former, like the Dräger Dolphin, use pre-mixed gas (from a single tank) which is supposed to be nitrox (32% - 60% on that model). SCRs like the Halcyon RB80 that are designed for deep dives are set up to use any gas you would on open circuit, and use a switch block to add into the loop. That includes trimix and heliox as needed.

In a CCRs, as Silent pointed out, O2 is added based on the diver's consumption of it. Diluent is added to keep the loop gas breathable and compensate for ambient pressure. They either use air, trimix or heliox depending on the depth of the dive, just as you would use on OC.

Some CCR models have integrated deco computers, those either have He capability standard or optional. In regards to the automatic O2 addition (setpoint control) the diluent makes no difference as it is added through different valves.