Northwest Dive Club

Is anyone here using a switchblock or an extra bottle with an lp hose etc. to switch diluents for deco?

Just curious if this is common practice who's doing what/why/etc.

Well, I can tell you that I don't do that- but pretty much every Meg diver has an LP whip on every bailout bottle- in the event of catastrophic gas loss, it's easy to plumb something else in. I do know a few guys who use their rich mix (Nitrox) to flush their loops on deco, at whatever the MOD is for whatever they're carrying. I'm still kind of hazy on why they do it, though. The idea is to purge all the He out of the loop, but......it just doesn't seem necessary to me. On deco, running a 1.3 sp, there isn't enough He in the loop by the time one gets to 40 feet to cause any problem, as far as I can see. I've successfully decompressed from a bunch of deep trimix dives without doing it, at any rate.

I haven't done any software trials. Just thought (conceptually) that you might be able to accelerate your (e.g.) 12/60 offgassing by using your 40% bailout as diluent from say 70ft and up. You'd need a periodic flush to keep the offgassed He out of the loop. But an AL40 would supply alot of flushes. Not much ongassing of N2 from there up to worry about. You could obviously do similar stuff with deeper bailout gases; :hello2: I don't know which one might be optimal vs. which ones just create more of a different inert (N2) to deal with later.

Mostly a thought experiment on my part...

Mel could probably answer this best.

I carry the ability to plug in offboard dil in case of a problem but like Josh said once you get shallow with a high PO2 there's no real need to switch dils. You are flushing the loop as you ascend anyway because you are adding O2 and dumping volume so I don't think offgassed HE is much of a problem.

I know this has been heavily discussed on RBW

Dave

CaptnJack wrote:I haven't done any software trials. Just thought (conceptually) that you might be able to accelerate your (e.g.) 12/60 offgassing by using your 40% bailout as diluent from say 70ft and up. You'd need a periodic flush to keep the offgassed He out of the loop. But an AL40 would supply alot of flushes. Not much ongassing of N2 from there up to worry about. You could obviously do similar stuff with deeper bailout gases; :hello2: I don't know which one might be optimal vs. which ones just create more of a different inert (N2) to deal with later.

Mostly a thought experiment on my part...

I've tried that exact thing as an experiment on a 250 ft dive, just to see what my computer would do. I was using tables anyway, so I began purging my loop and bottomed out till I had little or no gas left. I flushed the system with 40% (at 70 ft = 1.3) and changed the computer to 40% dil. Didn't change but maybe a minute.
On the other hand my buddy did the same thing at around 120 feet and flushed with 34% and it cut about 15 minutes off.
But he was waiting for my ass, so it didn't matter.

richard, you know you want a meg... you pop up on half the ccr threads on the non-tech forums (and even some of the tech forums)... you ask questions like this that were in fact discussed in class... why not just step up to the plate and take a class and learn a bit about them? Personally I learned a lot more, a HUGE amount more, taking the class than i did reading page after page after page of mental masturbation and random pontification on TDS, RW, etc... Some of the discussions are great, don't get me wrong, but you really can't grok them fully unless you are diving the 'breather. Again, this question is a perfect example. If you took the class, you'd know that we can plumb in any of our bailouts (or our buddys bailout) etc... its as easy as switching over to your nitrox for suit inflation when you run out of argon

*where is that poking with stick smiley*

A) I don't see a need for a CCR, OC serves my needs amply. B) I'd rather get a new scooter for that kinda coin. C) or get a new camera. or lastly travel. Lots of higher priorities.

I do find it odd that CCR computers (shearwater and others) are sorta the last bastion of neo-Haldanean deco. VPM has shifted that a little, but not as much as I woulda thought. The comparable OC computers are definitely rare, like the Nitek He etc. at least around here.