Thinking gauges for a minute......

Genesis

Ok guys, here's one for you to ponder....

Why do you have an oxygen pressure gauge on a hose on a CCR?

I can see the point to a diluent gauge that's accessible during the dive, because you might do mask clears, diluent flushes, etc.

But why an O2 gauge you can read? Your metabolic consumption is a relatively known figure, right? You don't go in without enough, right? So..... why?

See, here's why I'm asking. The hose contains quite a bit of gas, and is where the problems with fethering a stuck solenoid come from. Use a button gauge, you can still read it before you dive, but in the water, you can't see it. HOWEVER, you lose all that gas space at tank pressure, which means that feathering a valve becomes a very viable option.

All the rigs I see have gauges for each tank "front and center" - but is it really all that useful? More to the point - is it necessary?

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lizardland

I don't.

I know (roughly) how much O2 I need, I've gauged the tank before I get in the water and if there is anything that is causing a major loss of oxygen then I'm pretty sure I'll know about it. I can generally hear O2 flowing to the KISS valve so I know there is a gas there.

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Barrie Law

Good point, worth considering.

Regards

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Sutty

Can see what you mean, and it adds failure points. However a small leak which starts after your initial bubble check could go unnoticed (especially if close to an o/c diver). On the other hand the leak is quite likely to be from the hose/guage!
The other thing is that if using one cylinder of O2 for several dives I feel more comfortable knowing I still have enough left
Doing drills I haven't felt the volume of the hose caused a big problem. I suppose narrower bore hoses or a pressure transducer on the 1st stage and a remote readout would be possibilities if it is a problem.

Neil

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koputai

I don't have one on the O2 side of the Mk15, and am seriously considering ditching the dil one as well.

Jason.

Genesis

Interesting viewpoints....

A button gauge on the K1 would be visible when not diving the unit, but not while underwater, obviously. I think I may do that for the O2 side, and use a traditional SPG on the diluent - at least for a while. After I get comfortable with the unit I may ditch the Diluent one as well - since I'll be carrying bailout gas in a sling bottle with a plug in whip, if I have a "no gas" problem with the diluent side I can always jack it into the unit anyway via the manual add, and even go open-loop (so long as I don't have a flooded unit, in which case the old-fashioned OC reg will come out.)

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"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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quickean

Who taught your guys' CCR classes?

Skipbreather

To each his own, of course, but I'd much rather know what is available for both O2 and dil. Yes, metabolic is indered predictable, buy mother nature ain't. Hard swim against an unanticipated current? Is enough O2 left for deco? Are you doing O2 flushes @ 20 ft. Great, but did you get somewhat too aggressive w/ the flush and blow away some of the gas needed for deco? You get the idea.

Simply put, if all goes to plan a gauge is redundant. As the generals say, though, no battle plan survives beyond first contact with the enemy.

Best,
Ken

Steve

Keeping both provides you with valuable information in understanding where a fault has occured. If you don't plan to stay on the loop, ever, of there is a boom then remove both. Otherwise have a look at this thread as this very issue wan kicked around

http://www.rebreatherworld.com/megal...highlight=boom

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Genesis

I hear that argument but let's think about this one a bit.

If the dive doesn't go according to plan then either you have enough gas to complete out closed loop or you don't.

If you don't, seeing the needle go to zero on the O2 pressure doesn't add anything except stress. You're still screwed and going to have to go SCR off your bailout gas at best anyway.

This is kinda like the argument I've gotten into over cave diving when you donate gas. There's a "dogma" that says you show the donee your SPG so he knows how much gas you have, and you look at it too.

Why? Either you have enough to get out, or you don't. If you don't you're dead. If its marginal knowing 20 minutes ahead of time that you may be dead is likely to make it happen!

I've had a "boom" in an overhead on OC. I got the situation under control and started exiting. I was solo, so it was "all me buddy." I didn't look at the gauge. Either I had enough gas to get clear and to where I could breathe my deco bottle safely, or I did not. If I did not knowing ahead of time wasn't going to suddenly make more gas appear in the can!

I can see the argument on the diluent bottle since there's a whole host of things that can screw you there, and some are "normal" (e.g. your mask gets knocked off, etc). But on the oxygen bottle I'm less convinced, and there IS a downside to the gauge and its hose - its a significant reservoir of gas which can get dumped through a stuck-open add (either solenoid or manual), and too much O2 in the loop is bad.

I'm trying to weigh the ying and the yang here. Its not hard to run the SPG hose up and over the shoulder, but I'm not sure its a good idea for the O2 gauge for that reason.....

PS: Logic wins over dogma (e.g. what someone told you.) They should be able to defend their position, and if you learned something in a class so should you!

__________________
"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