Don't breathe tanks to zero?

[Slamfire]

Not to sidetrack this into a technical diving discussion, but I don't know anybody that dives like that [draining a stage] and I don't think it's a sound plan

I do it all the time. On big dives where my big doubles are not enough for bottom gas by themselves I'll breathe down the stage until it starts getting difficult to breathe out of it (around IP ~130psi). I will also do this for repetitive dives where doubles will not give me decent bottom times for 2 dives.

Once the stage is empty and floating you just move it out of the way into a leash clipped on to your left hip D-ring. This way it does not interfere at all with arms or legs -- it's much more comfortable that carrying it under your arm.

There is also the added advantage that it makes blending after the dive easier. Your helium and O2 supply cylinders don't have to have much pressure to blend in an Al80 of 21/35 when you start with 130 psi of 18/45. The same cannot be said of trying to blend in on top of double LP108s with 1000 psi of 18/45. By using stages you can drain down the helium supply cylinder even lower without having to pay for a booster or venting out helium.

Yep. I originally intended to make that difference clear in my remarks, but I forgot to include it. My real point for this discussion is that as a result of doing those kinds of dives, I have taken many tanks down to a very low pressure (above ambient) and never had a drop enter them as a result.

I breathe down my bottom mix stages until it starts getting difficult to breathe out of them. There is no point in struggling to bring it lower than that. I haven't ever had a problem with humidity in them either.

Eventually you reach the point that there is not enough pressure in the fill tank to put enough in the scuba tank. For that reason, as the fill tank pressure drops, you generally want the tanks you are filling to start empty so you can get the right amount of O2 in them....It is usually for the reasons described above that people want you staring with empty tanks.

I call shops beforehand to ask them how much pressure they have in their supply cylinders. If they don't have enough, I call the next one in line.

Fill Express (GoDive Florida)... They are a huge shop that does tons of business, including air fills, nitrox fills, and trimix fills. They have a huge bank of EANx 32, a huge back of EANx 36, and a huge bank of EANx 40.

The last time I dove out of Pompano they were also banking 21/35. The first time I paid them for a gas fill I was expecting a larger gas bill because I didn't know they charged only for the volumes of gas you put in. I was very pleasantly surprised with their operation.

HOWEVER, the only question I got wrong on the exam was something along the lines of "customer brings in a cylinder that you did not fill with a known blend of trimix, and asks for this, how do you fill?" and the options included adding topping off with appropriate gases (which I would do after analyzing and confirming) and emptying and starting over using more gas (which was the correct answer)

I'm still scratching my head on that one...

There would be serious problems if a dive shop attendant tried to vent out my precious helium into the atmosphere. My doubles come out of dives with reserves for contingencies. For some dives, the amount of reserve gas in the doubles is considerable.

What do your regulators do as your tank approaches empty?

I mostly use Mk10s and G250 Graphites for consistent and predictable performance. I do have a Hog 2nd stage that has performed adequately with Mk10s. If a dive requires more cylinders than the amount of Mk10s I have, I'll put in a Sherwood Brut piston with dry ambient chamber in the O2 bottle. It has also performed adequately. That is all I'm using these days. I am bidding on a couple of Mk10's on Ebay to alleviate the deficit. So stay out of ebay Mk10s for now. I don't want to get into bidding wars .

 

[chrpai]

Yes I took the class. Not sure what it is blended with. Assume a mix with much lower o2 levels than what you have at the end since it is starting 100% o2. When I picked up the tanks I watched them hook them to the gauge and test them and saw the percent 02. I don't have my own gauge if that is what you mean.

Your class should have covered all of this. It doesn't get topped off with nitrogen, it gets topped off with modified grade E air aka oxygen compatible air. The point is the air has to be really filtered well to remove hydrocarbons that could build up inside the tank to the point of reacting with the oxygen and going BOOM.

So you watch them hook up a gauge and saw the percentage of O2? IMO that's not good enough. How do you you they followed the correct procedures for the device? How do you know it was properly calibrated in the first place? While nitrox is mostly thoery, math and dive planning, the critical performance skill is knowing how to analyze a tank so you know for an absolute fact what you are breathing. Otherwise it's a trust me dive.

YOU can use their device but the operative word is YOU.

 

[flots am]

Mine breathe wonderfully them simply stop.

I amost wish there was a little warning in there; that it would get more difficult around 300-400PSI.

flots.

 

[Slamfire]

Mine breathe wonderfully them simply stop.

I amost wish there was a little warning in there; that it would get more difficult around 300-400PSI.

flots.

With mine you can keep on breathing after it reaches IP but it keeps getting increasingly difficult. They don't just stop. You can get some WOB assistance by pressing the purge button on inhalation, but again, there is no point in bothering to do that when you have a plentiful gas supply on your back. It's good to know that if push comes to shove, you can still squeeze out some breathes out of that cylinder.

Testing your reg at its limit isn't same as planning to dive it to its limit, by that I mean at empty tank. What happen to your buddy if he need air? If you plan your dive to empty your tank, what are you going to do?

Buddy will have to go for the long hose if he happened initially grab the reg from my mouth just as I was approaching an empty tank. Contingency reserves are in the back tanks. Bottom gas stages are for sucking them dry.

 

[eelnoraa]

I disagree with this sentiment.

Which part? The take it to viz part or the nothing will happen to the tank part?

 

[The Chairman]

Which part? The take it to viz part or the nothing will happen to the tank part?

There's no need to take it in for a vis if you breathe it dry.

 

[Jon_R]

Your class should have covered all of this. It doesn't get topped off with nitrogen, it gets topped off with modified grade E air aka oxygen compatible air. The point is the air has to be really filtered well to remove hydrocarbons that could build up inside the tank to the point of reacting with the oxygen and going BOOM.

So you watch them hook up a gauge and saw the percentage of O2? IMO that's not good enough. How do you you they followed the correct procedures for the device? How do you know it was properly calibrated in the first place? While nitrox is mostly thoery, math and dive planning, the critical performance skill is knowing how to analyze a tank so you know for an absolute fact what you are breathing. Otherwise it's a trust me dive.

YOU can use their device but the operative word is YOU.

Probably was covered in class and I forgot what exactly the mixer does. The class taught in the shop had us use their equipment and test a tank. The guy at the shop that I watched did the same thing I would have done on the same equipment. I just stood next to him while he did it.

Just using the tanks in the pool for now helping my girlfriend get through OP. i will get them refilled for the upcoming 60 feet drift dive. Probably check them myself for that. Hope she gets through class and can do the dive. I will be on the boat either way.


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[beanojones]

What do your regulators do as your tank approaches empty?

I have a couple of overbalanced first stages that actually breathe much easier on the last breath before they shut off mid breath.

 

[chrpai]

I just stood next to him while he did it.

Just using the tanks in the pool for now helping my girlfriend get through OP. i will get them refilled for the upcoming 60 feet drift dive. Probably check them myself for that. Hope she gets through class and can do the dive. I will be on the boat either way.

Letting someone else analyze your mix just breeds complacency IMO. Was the gas free or something? Fairly pointless to use nitrox in a pool and 60' is really marginal for any value at all.

 

[Abdullah]

Letting someone else analyze your mix just breeds complacency IMO. Was the gas free or something? Fairly pointless to use nitrox in a pool and 60' is really marginal for any value at all.

Agree with the first part, disagree with the second. You get the same benefit from EANx regardless of depth - less nitrogen loading. Saying EANx is a waste in shallower dives is a cost based value judgment more than a physiology based rationale.

Unless you are doing multiple repetitive dives and are concerned with oxygen loading for toxicity, there isn't a disadvantage to less nitrogen loading resulting from using EANx. Unless I'm diving deeper than 40m, I always dive EANx.