Set Point switching for CCR's

[poseidan]

Been diving the Draeger Dolphin SCR for two years and thinking of moving up to a CCR. One of the features I've been looking at is the ability to switch set points mid dive. How often do you guys do this, or do you think this feature is not needed. I'm new to this board so any commentary or opinion is welcomed. Thanks

 

[padiscubapro]

Been diving the Draeger Dolphin SCR for two years and thinking of moving up to a CCR. One of the features I've been looking at is the ability to switch set points mid dive. How often do you guys do this, or do you think this feature is not needed. I'm new to this board so any commentary or opinion is welcomed. Thanks

You are going to get several answers..

If you speak to someone who has a RB that Can't switch setpoints mid dive they will say it is not necessary..

Most will tell you you can start with 1 setpoint a fly it manually...

Personally I belive any RB that doesn't allow changing of setpoints on the fly is missing an important feature... Sure I CAN fly the unit manually above my chosen setpoint but there are times where task loading makes this a more difficult issue than having the unit maintain it by itself.

personally on a stock inspiration I sometimes bump it up to a 1.5 during deco (on a Hammerhead I can set it higher)

The way I use setpoint switching the most is to allow me to do multilevel and faster descents without having to use a severely hypoxic mix...

I'll start with a setpoint of about 1.0 and use my descent to keep it reasonably above that.. If you use the same setpoint as you are going to use on the bottom it limits the rate in which you can get to depth (unless you have a highly hypoxic mix) since the controller will inject oxygen to raise the po2.

I dont buy the excuse that you may forget to switch to your higher setpoint and screw your dive plan.. You should be checking your controllers religiously.. Seeing a 0.7 or even a 1.0 tells you you forot something.. A few minutes at a lower setpoint doesn't really alter your deco that much on deeper dives it DOES have an efect of shallow ones.. Run a few profiles for yourself by 60m (200fsw) the change is very small and is within the variations of the different conservatisms of the various deo algs. By 100m its even smaller...

Joe

 

[caveseeker7]

... that has been popping up in different threads over time.

One of the features I've been looking at is the ability to switch set points mid dive. How often do you guys do this, or do you think this feature is not needed. I'm new to this board so any commentary or opinion is welcomed.

Generally, there are two sides to it, those who insist to have it, and those who couldn't care less because they can always manually override the electronics anyway.

The Inspiration and Megalodon allow you to change the setpoint.
The former needs the switch from shallow water setpoint to the chosen setpoint for the dive to be made manually, which also means it can be overlooked and make a serious difference in your deco obligations.
On the Meg I'm not sure, even less so as the electronics are still evolving from what I understand.

In contrast to that is the Prism Topaz, which has a shallow water default setpoint of .7, and pre-dive adjustable dive setpoints of .7, 1.0, 1.2, 1.3 and 1.4. A pressure transducer is inside loop, automatically switching between the two at around 15-18ft. Early prototypes were made with dive adjustable setpoint controls, but with an eye on safety and user friendlyness discarded.
If you want to increase the pO2 during deco for example, you can just manually do so.

So in regards to the selectable setpoint during the dive you have safety vs. convinience (of not maintaining a raised set-point manually).

Some people claim that during a shallow water dive on the way to deeper waters the electronics will constantly switch setpoints and waste O2. And that the automatic switch to the high setpoint means you have to descent so slow that enormous amounts of deco will be accumulated on your way to the bottom.

As there are plenty of Prism divers diving deep it's less of an issue for them as for everyone else.

As with a lot of issues regarding any rebreather.


Add-ited:
LOL, see what I mean?
I started typing before Joe posted. Of course, if everybody would be watching their pO2 readouts as they're supposed to there would be fewer incidents and accidents. Problem is, not everyone does it all the time ... .

 

[gkndivebum]

Here's an interesting story by Howard Hall about what happens when you forget to switch your
setpoint on a deep dive. Many thanks to Howard for sharing this experience, and may we
all learn from it.

"Decompression Hit"