Scuba Tanks Steel 72
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Yes, the concept of significant figures is one that escapes most divers and nearly all advertising people.
But more practically, the average pressure gauge is not all that accurate and the average SPG is even less so and/or may be accurate over only a narrow portion of it's range. A 50-100 psi error in the pressure reading makes the tenths of a cubic ft capacity differences at a given pressure meaningless. Add on top of that the pressure differences in the air-conditioned shop, on a sunny boat deck and actually in the water and you'll have three different pressures and theoretical volumes, but obviously the amount of gas in the tank is the same - but you just don't know what it is with any great degree of precision.
In terms of gas planning rounding down the tank capacity or the tank factor is prudent.
But more practically, the average pressure gauge is not all that accurate and the average SPG is even less so and/or may be accurate over only a narrow portion of it's range. A 50-100 psi error in the pressure reading makes the tenths of a cubic ft capacity differences at a given pressure meaningless. Add on top of that the pressure differences in the air-conditioned shop, on a sunny boat deck and actually in the water and you'll have three different pressures and theoretical volumes, but obviously the amount of gas in the tank is the same - but you just don't know what it is with any great degree of precision.
In terms of gas planning rounding down the tank capacity or the tank factor is prudent.
JamesBon92007
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Well, kind of, but under supervision. I started doing hydro testing in my first job in a dive shop close to 40 years ago. I helped install the hydro machine at Divers Service Center (in Puerto Rico) around 1972.
I am friends with my LDS (here in Maine) and I have helped them by setting up their filling cascade system and their compressor, etc. When they have any technical questions they often call me. They also have their own hydro testing equipment.
I have also done the REE calculations for them (in order to plus stamp steel 72 and other old steel tanks). It obviously benefits me.
At this moment I am not certified to run their hydro machine by myself, but I can operate it under their supervision.
As an engineer I can design and certify the calculations related to hydro testing and even design pressure vessels (which I have done under ASME codes) but at this moment I cant operate the machine solo.
A funny thing is that I have actually helped one of the techs with some of the questions on one of the DOT review classes, but I havent taken them myself.
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JamesBon92007
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What an interesting life you have It's funny how a simple certificate can be such a determining factor. But there has to be some kind of system in place otherwise, well, you know.
That's great that your LDS can do the hydros though. They are getting expensive and I'm going to have to get around the middle man next time. Somehow.
It's funny how a simple certificate can be such a determining factor. But there has to be some kind of system in place otherwise, well, you know.That's great that your LDS can do the hydros though. They are getting expensive and I'm going to have to get around the middle man next time. Somehow.
I agree with the need for a certification for this type of work. Just a few years ago I got my PSI certificate (even do I have been doing visuals for several decades). It is just a bit odd. Actually, I got certified from PSI at the same time that I was helping them with some technical questions.
Yes, it is great having a hydro station at my LDS, but that doesn’t make it any less expensive. Their hydros are not particularly cheap (and I pay full price even do I actually do all the labor), but they are very convenient and I know they are getting done right. I also keep a copy of all the records in my own spread sheet.
Yes, it is great having a hydro station at my LDS, but that doesn’t make it any less expensive. Their hydros are not particularly cheap (and I pay full price even do I actually do all the labor
), but they are very convenient and I know they are getting done right. I also keep a copy of all the records in my own spread sheet.
JamesBon92007
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Something's wrong with that scenario. You do all the work and have to pay full price? Even I don't work THAT cheap. Usually.
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