Weight of air?

[NAM001]

8# per hundred cu ft air

nitrox is so close it is the same

helium I think is about 2# per hundred


and no some of the specs don't seem to follow the 8 per hundred.

Its possible that some groups specs are weight empty no valve and the full is with a valve.

 

[Divin'Papaw]

Always entertaining to see threads spring back to life ... almost 9 years after the last post in the thread!!

 

[Leadking]

I had an instructor friend tell me that the weight shift in an aluminum tank was greater than a steel tank. I told him the weight shift is equal in both tanks. He didn't believe me.

 

[emoreira]

I found this table somewhere in Internet. The table is in spanish. however, the information is pretty clear.

 

[Gill]

Always entertaining to see threads spring back to life ... almost 9 years after the last post in the thread!!

They know how to use the search function. Yeah, that's it.

 

[duckbill]

I had an instructor friend tell me that the weight shift in an aluminum tank was greater than a steel tank. I told him the weight shift is equal in both tanks. He didn't believe me.

You're both correct......or incorrect.....depending.

He is right in that an aluminum 80 has more of a weight swing from full to empty than a steel 72 does.

You are right if you are simply referring to an equal swing caused by equal amounts of air being emptied.

It was probably just a disagreement based on a misunderstanding of the eachother's rationale.

 

[dberry]

This is a very odd, confused thread, IMO. In any case, if you're talking about equal amounts of air leaving two tanks, the change in weight will be exactly the same (ca. 8# per 100 cf as normally calculated.) That would be comparing an Al 100 to a steel 100, etc. Now the PERCENTAGE change in weight of the tank would be greater for the lighter (Alum) tank, but the "swing" due to the air in pounds would be identical.

Now, something that some folks fixate on is that an Alum 80 tank changes from negative to positive buoyancy when dropping from 3000 to 500 psi, but a steel tank stays negative (although less negative at 500psi). In other words, an empty Al 80 tank will float, but an empty steel tank will sink. But in terms of the buoyancy of the diver + rig + tank, the change in weight from using 2500 psi of air is the same, so if you're properly weighted (slightly negative with 500 psi), what's the big deal?

You need less lead with a (heavier steel) tank, but otherwise, why does the change from neg to pos buoyancy of the alum TANK make any difference at all? All I can think is the trim changes, since the empty Al tank becomes a "float" on your back, but the lead is on your belt / pockets. All the more reason to put some weight in cam band pockets, I guess...)

Anything wrong with my thinking?

 

[duckbill]

Anything wrong with my thinking?

Nope.....with one caveat........

Now the PERCENTAGE change in weight of the tank would be greater for the lighter (Alum) tank, but the "swing" due to the air in pounds would be identical.

This is true if using underwater measurements of "weight". On dry land, the opposite would be true. (Not to add to any confusion :headscratch This is because in most cases equivalent capacity aluminum cylinders are actually heavier than their steel counterparts. :idea:

 

[dberry]

Wow, and I thought my steel 119s were heavy on land!