Don't breathe tanks to zero?

[Jon_R]

Me thinks that's a lazy gas blender. He doesn't want to take the time to analyze the starting FO2 and starting pressure and do the math of how much O2 to add. He just wants to start at zero every time and follow the same math each fill.

Maybe. There shop so how ever they want to do it. Nitrox fills are 7 bucks so does not matter much to me how they want to it. I was told they start empty fill with 100% o2 then add nitrogen to get to the number. When you pick up tank they show you on their meter and write it on tape.


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[chrpai]

Maybe. There shop so how ever they want to do it. Nitrox fills are 7 bucks so does not matter much to me how they want to it. I was told they start empty fill with 100% o2 then add nitrogen to get to the number. When you pick up tank they show you on their meter and write it on tape.

Topped with nitrogen? Kind of, not really though.

Curious, have you taken a nitrox class? It's called enriched air for a reason. Also I don't trust other people to analyze my gas for me. I'm breathing it, not them.

 

[nimoh]

Maybe. There shop so how ever they want to do it. Nitrox fills are 7 bucks so does not matter much to me how they want to it. I was told they start empty fill with 100% o2 then add nitrogen to get to the number. When you pick up tank they show you on their meter and write it on tape.


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If they are charging a flat rate for a nitrox fill, then I agree -- their shop, their rules. They are only costing themselves money since it takes less time to analyze a tank and calculate the fill than it does to empty the tank (and it's quieter too).

If they are charging for nitrox by volume, then I would have a problem with them draining my tank first.

The bottom line is one way is not safer than the other way since you will be analyzing the tank after the fill anyway.

 

[Abdullah]

Me thinks that's a lazy gas blender. He doesn't want to take the time to analyze the starting FO2 and starting pressure and do the math of how much O2 to add. He just wants to start at zero every time and follow the same math each fill.

Probably not so much a lazy guy as a practical guy in business to make money. Oxygen is cheap for one. Time is money and PP blending takes plenty of time without doing a custom blend on every tank.

And, unless the shop has a Haskel pump, the O2 delivery pressure is limited to whatever pressure remains in the oxygen supply tank. So PP blending on top of 500 psi or more of residual gas pressure limits the amount of oxygen the supply tank can donate to your tank (more hassles for the blender).

 

[The Chairman]

Topped with nitrogen? Kind of, not really though.

Curious, have you taken a nitrox class? It's called enriched air for a reason. Also I don't trust other people to analyze my gas for me. I'm breathing it, not them.

Dude, lighten up. He saw the O2 meter, so he did the analysis. No need to box everyone's ears who happens to disagree with you.

As for using banked over partial pressure mix, I agree. In fact, I avoid PP NitrOx whenever I can. Banked, continuous blend or membrane are my three preferred methods of getting NitrOx.

 

[chrpai]

They are doing PP blending either way. Problem is they charge $12 per nitrox fill and talk about how it's a complicated time consuming "process" with 24 hours notice. Bottom line is hardly anyone bothers diving it around here because it's not worth the money or hassle.

Banking would help with both of these problems.

 

[nimoh]

In all fairness, the DSAT Gas Blender manual and course teaches when you're blending helium mixes, if you didn't fill it, you start over with an empty cylinder.

It reads: "As a blender, if you did not personally mix the gases for the previous dive, you have no way of knowing what combination of gases are in the remaining mix without an oxygen analyzer and a helium analyzer. In this case, you must always start with an empty cylinder." -- DSAT Gas Blender Manual, p. 45.

As I neither dive nor mix helium blends, I've never done this. But as far as Nitrox goes, I never drain unless I need to bleed down to hit a specific mix.

I both dive trimix and fill it, and I would never do either without an analyzer.

As for draining the tank, bleeding out $100 worth of helium for no reason is just plain ludicrous. Perhaps the course material was written before analyzers were generally available.

 

[Abdullah]

I both dive trimix and fill it, and I would never do either without an analyzer.

As for draining the tank, bleeding out $100 worth of helium for no reason is just plain ludicrous. Perhaps the course material was written before analyzers were generally available.

The manual is telling the blender in that paragraph that he needs to know the residual mixture - analyze the residual gas, or start with an empty cylinder. Anyone blending trimix will have both oxygen and helium analyzers, so testing the residual mix is standard procedure.

 

[chrpai]

In all fairness, the DSAT Gas Blender manual and course teaches when you're blending helium mixes, if you didn't fill it, you start over with an empty cylinder.

It reads: "As a blender, if you did not personally mix the gases for the previous dive, you have no way of knowing what combination of gases are in the remaining mix without an oxygen analyzer and a helium analyzer. In this case, you must always start with an empty cylinder." -- DSAT Gas Blender Manual, p. 45.

As I neither dive nor mix helium blends, I've never done this. But as far as Nitrox goes, I never drain unless I need to bleed down to hit a specific mix.

Why not also bold the "In this case" part? It doesn't say you must start with an empty cylinder every single time like you wrote, it says you must if you don't have the equipment to establish O2 and He2. (Maybe this made sense when He cost a lot less and analyzers cost more?)

Personally I can't agree with how it's written at all. "If you did not personally mix"? What use is that? That almost sounds like "I mixed it so I know it's right. I didn't mix it so it must be wrong." Analzyze the contents and go from there. Head scratch....

The only thing I can think of is He +/1 X% isn't a big deal so you might avoid spending money on the analyzier and therefore be relying on "I did it". Seems stupid to me. Just buy the right gear.

 

[Tortuga68]

If they are charging for nitrox by volume, then I would have a problem with them draining my tank first

Do people actually do that?