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As @nickbutcher said - dil flushing becomes more efficient.
Operations is another reason. Suppose you dove with 15/55 to 75m; dil PPO was 1.27 on the bottom and your high set point was 1.3.
You still some of that gas left, but your next dive is 60m. What do you do? Well, if you don't have extra CCR tanks, you probably want to use 15/55 again. However, now your bottom dil PPO2 is 1.05.
Haven't seen "my" way of doing this in posts. Autoset 0.7->1.3 10 meters before target dept. Diluent 1.0-1.1 at target depth. Autoset kicks in solenoid just before reaching bottom and get you nicely to target p02. Usually good buoyancy at target depth. Autoset 2nd computer to switch at dept to high set point. JJ as rebreather.
OK so your saying that you want to have a dil with a lower PPO2 than your SP so that you can have more effective dil flushes, fair statement it has a strong argument but your saying that diving a 15/55 at 60m gives you a dil PPO2 of 1.05 and your complaining about this? Wouldn't a 15/55 be a nice 60m mix?
If not in the exact scenario you descried above what 1 mix would you propose to use for those 2 dives? I would have no issue diving a 15/55 at 75m and then at 60m for the next dive. I have no issues diving a 1.0 SP, but also for that scenario I would just dive 1.2 SP and just switch to high SP on the fly at about 50m I have never had issue with my solenoid screwing up my buoyancy when I switch over.
Majority of my diving is sub 100m and after 120m I always like to dive a 1.0 SP for sub 180m I might even consider 0.9 SP. But I do this for two reason and yes one of them is to make dil flushes more effective and to have more buffer if my PPO2 spikes at depth (its amazing how little O2 it takes to make your PPo2 spike at those depths) the other reason is I calibrate at 1.0 so I want to dive as close to this as possible. Also on a side note when you start getting super deep HPNS is of concern and I am trying to keep as much nitrogen in the mix as possible while still having a half decent END and gas density.
Normaly I switch from 0.7 to 1.3 during descent at about 20m. I had a discussion: Dil 21/35, 20m, switch to 1.3, stay for 1 min, then very fast descent to 60m. A lot of dil is added, which brings the mix close to 21/35. But you still have the mix which was in the loop at 20m, this is a hotter mix. And during fast descent you consumed very little O2, so your mix at 60m might be to hot, pO2 for ex. 1.8.
I wonder if this is a problem in reality. I think the amount of dil you add during descent is much more then what you have inside the loop at 20m so I expect pO2 not to be very high. PO2 of 21/35 at 60m is 1.47. A bit higher because of the gas you had at 20, a bit lower because of consumption. These "a bit" are not precise at all, can they be calculated?
Or even more simpel: is this a problem in real life?
This thread is so off the original point that I don't know how to start replying to your post.
Why not just match your dil with your bottom SP.
You arrive at depth and your PO2 will be really close to your SP. Flip over to high SP and have a nice dive
Keep it simple.
As @nickbutcher said - dil flushing becomes more efficient.
Operations is another reason. Suppose you dove with 15/55 to 75m; dil PPO was 1.27 on the bottom and your high set point was 1.3.
You still some of that gas left, but your next dive is 60m. What do you do? Well, if you don't have extra CCR tanks, you probably want to use 15/55 again. However, now your bottom dil PPO2 is 1.05.
It was just an example of the case where the in the first dive your PPO2 at the bottom is close to the set point. However, on the subsequent dive the delta between PPO2 and the set point was going to be greater, i.e., the letting the solenoid fill the gap automatically could lead to buoyancy issues. There was nothing wrong with gas choices.You then made a very valid point but also you kind of contradicted your self. If there was a second 60m dive what I would do is dive the 15/55 why is having a PP02 of 1.05 a problem? This actually makes dil flushes more efficient as you suggested.
Speaking of the thread... did you not cover various techniques for dealing with this stuff in your coursework?
Not trying to be a prick - simply askingSpeaking the thread and getting off topic. I don't think questioning my CCR course work/knowledge of a CCR is relevant, but yeah I have taken a CCR course or two...
lol that’s like asking AJ or Beckner etc if they have any cave experienceNot trying to be a prick - simply asking