Thinking gauges for a minute......

quickean

Rule of thirds doesn't work doesn't work so well when you don't know when you've used a third.
Accident waiting to happen.

diverklondike

I am a very analytical person and would rather always know where I stand when it comes to gas.

The other consideration is that I usually do more than one dive in a given day and it's a pain to look at button gauges etc...

Dive Safe....

Mark

Genesis

Explain why you believe so.

Running out of O2 is not a death sentence on a CCR - you're not out of something to breathe, assuming you have diluent and offboard bailout. If your bailout has a QC on it you can plug it into the inhale lung and go SCR for a LOOONG time on even something as small as a 40. You already have to carry enough bailout to cover a catastrophic loop failure; if you've got that then you've got anywhere from three to six times as much time in SCR mode on the same gas supply. Where's the emergency in this scenario?

This contrasts with OC where zero really is zero! I wouldn't dive backgas on OC to thirds without a SPG because when the OC tanks are gone they really are gone and so are my options. Even so, I only look at the gauge every 5 minutes or sometimes less often - I already know what should be there before I look at it.

Which is more likely - that I have a failure of the extra two O-rings, hose or moving parts in the SPG, or that if I look at a button gauge SPG before I go in the water I will run out of O2?

And IF I run out of O2, that's not going to lead to my demise. I've still got plenty of breathable gas.

Also, routing on the DS4s on the K1 place the SPG inboard between the tank and the body of the wing; if I bash it hard enough to break it I'm likely to shear off the OPV as well, and doing either would require quite the event.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
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dantheman

The "rule of thirds" for gas volumes is next to useless for CCRs . . .

Mind you, for small O2 supplies, maybe not. And for large scrubber durations, maybe not.
But for "average" 3l O2 bottles and 3hr scrubbers, it's not a useful rule. Even of thumb.

It's a great rule for OC, but I question its utility in CC diving.

--dan

decoweenie

What about the gas volume is marginal to get both of you out of the cave if everyone to remain calm, or even have to skip-breath a bit, to conserve the gas instead of getting all excited and huffing like crazy ?

By knowing that it is critical to conserve gas and try not to do any unnessary wastage manuever, it will help instead just exiting blindly in an emergency situation.

Running out of O2 on a CCR isn't (and shouldn't be) a life-threatening event. However, by knowing that it is going to happen (i.e. via the SPG), the diver anticipates it, prepares multiple contigency back-up options to be ready and executes them with no stress.

By comparison, some divers might be stressed with alarms going off without knowing exactly where the problem source is. Depending on the experience level, there will be a delay in reaction which could add to the chance of something worse to happen.

And depending on the unit, there might not be any alarm. Couple that with a busy diver will gravitate the situation.

At the end of the day, people dive without gauges know the risk and have worked out plans to overcome the issue. This has been discussed extensively on the other thread.

Since you will not be taking any training course diving your home-built unit, it might be wise to dive with as much information as possible as many things COULD go wrong until you work out all of the bugs. We all think we could handle anything thrown at us, but some people react differently in the real world.

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dantheman

I don't think you need either gauge.
Every failure mode relating to an empty bottle, will get reflected in your pO2, or in the course of normal ops.
This is true, but also minimalist thinking.

I have SPGs on both tanks.
I think having them is helpful.
--dan

Joe

I am not going to argue or debate the merits or lack thereof of what I do. I am simply going to state it and my logic. If anyone disagrees please don't get upset. If you have a calm, lucid counterpoint, I am happy to listen. I just don't want this to turn into a big argument. I am NOT trying to sell the idea. It is simply what I do and why I do it.

I have button gauges on both my O2 and my dil. I always dive with FULL (boosted) bottles so there is no question that I have enough gas.

That said, I also always dive with adequate OC bailout which can also be plugged into the loop. I maintain my bailout skills and am confident in my ability to plug into the loop. I always dive with a buddy who can look at my gauges if necessary, plus, his presence doubles my bailout options, and, I can plug into his onboard gasses if need be. I "fly" my unit manually and I dive minimum loop volume.

So, for me, running out of gas is not a big traumatic event. When you fly manually you can sense low tank pressure by the sound and intensity of the gas flow through the valve. If you suspect you might be running low you can plug your bailout into the loop so when button "A" fails you press button "B". Or, lets say worst case, it catches you by surprise. On min loop volume it is not a crisis because the diminished volume warns you that you need to add O2 but you still have a few breaths before it becomes even close to critical, so, worst case, you continue to breathe slightly short breaths until you plug your bail out in and turn the dive.

The ONLY plausible way I can see someone running out of gas (other than Darwinian inattention) is if they have some unexpected event such as a massive leak or free flow of some sort, in which case, the gauge will not do any good.

What everyone likes to ignore here is that you have OC bailout which is typically 2 to 4 times or more the volume of the onboard dil and you have OC deco gases also in far greater volume than the onboard O2, both of which can be plugged into the loop, and, that low or OOG problems on CCR are not an immediate crisis like they are on OC.

For me, the 2 extra gauges and hoses are unnecessary clutter and failure points. Button gauges have 2 failure points. The oring and the gauge itself. SPG's have 5 - the gauge, the 2 spindle orings, the hose oring and the hose itself.

Now, it also has a lot to do with your personality and your willingness to maintain skills. If bailing out is even slightly a concern to you, if you are of the ilk that will become worried about not knowing *exactly* what you have, if you are the type that will become very upset if a tank runs dry on you, and, if you are not able to take comfort in the fact that you have 2 to 4 times the volume of gas you really need, DON'T EVEN CONSIDER THIS OPTION. You need to be comfortable with what you are doing.

Joe

Could not agree with you more Phi. What you THINK you will do and what you ACTUALLY do when you are 2 breaths and 30 seconds away from the Grim Reaper are often times very different. Until you have walked in those shoes you do not know.

And to Karl, I might also add that while you may know the technical workings of your unit and you may know the mechanics of diving it superbly, it would serve you well to take training from someone who can pass on experience that others before us probably learned the hard way.

I was able to dive my unit in about 20 minutes. The rest was just practise. I took training not because I needed someone to teach me how to dive. I took it because I reaped the benefit of the (often fatal) experiences of others and had an experienced person validate what I was doing.

Sermon over.....lol. Just give it some thought....

Genesis

The counterpoint to the "get all the infomation you can (e.g. dive with traditional gauges)" is that information that serves no purpose just clouds the mind.

The K1's controller will alert almost immediately (two injection attempt windows worth of time max) if it attempts to raise the PO2 via injection and the PO2 doesn't come up. That's the suspenders to the belt (your notice of the "click but no whoosh".) At MLV as noted you get tertiary warning too. If I ignore the whoosh and beeper I guess I deserve what I get eh?

Unless BOTH tanks are empty even if you find you can't pull a "full" breath you can inject some diluent to resolve that immediate "gotcha", and if they are, I can plug in outboard to the DIL add and hit the button.

As I'm sure you're aware there is no such thing as a class for a homebuild; the agencies have intentionally designed it this way by making all classes unit-specific. I have no intention of cacking myself on the box and am not one of those folks who's gonna strap it on, sort his buoyancy and head for the 300' deep wreck......

I understand the point you're making Joe, but one should not assume whether another has had "Come to Jesus" experiences before (nor in what context and how many), and thus has a fairly decent handle on how they react to them....

In any event I thank you for your perspective - it seems to mesh pretty much with what I have been thinking. I can see some value in a gauge on the diluent bottle, at least initially.

(BTW the K1 has no ADV either - by design - I'm aware of the trade-offs in that choice as well.)

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

lizardland

When I was diving OC I never put gauges on my deco bottles (unless they were also being used for penetration) for the reasons listed by others -- mainly, what good is it doing you? I guess I've just continued that through to CC. I have a gauge on my dil side but if I was diving only in open water then like Jason I probably wouldn't bother. I find it quite useful for cave diving as a "go home time" indicator -- I turn either at a pre-determined time (or distance) or 1/3's of dil if I hit that sooner. 1/3's of O2 is irrelevant to me, 1/3 of a full O2 bottle exceeds my scrubber's rated life. If I reach 1/3's of O2 on a dive where everything is going OK then I have bigger problems than gas supply, my low boredom threshold being one of them.

Kevin Gurr, circa 1995. 3hrs of lectures, 15min on a Cis-Lunar in a pool, hand over £100, IANTD Rebreather Diver cert came through the post 3 weeks later. Glad I'm not doing it now, all those drills, classroom work, reading, lectures, diving... I couldn't be bothered with all that

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