Tank buoyancy numbers

[gfaith]

Check out the LP80 on the website you posted guruboy.. Interesting??

Looks like you had bad numbers to start with according to the chart Luis attached.

 

[gfaith]

I was crunching some numbers and trying to figure out the buoyancy of a Luxfer AL80 tank when empty.

It listed as +4.4 lbs when empty here
Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan
Saltwater .. I'm thinking

But comes out to +3.4lbs if you do the math, such as here
Scuba tank size and buoyancy calculator
Freshwater.. Here

Not sure where the discrepancy is coming from.

Note - I am trying to figure out buoyancy of tank alone without valves or air.

Thanks for the link it is very interesting.

 

[guruboy]

Which numbers are you taking about? The "specs" I quoted or the value I calculated?

 

[gfaith]

The "specs". Your calculation look real close to mine and the chart Luis attached. I never would have thought LP72 and LP80's are positive when empty. Thanks again for the Link..

 

[tech3324]

I never would have thought LP72 and LP80's are positive when empty.

Looking at the LP80 here Scuba tank size and buoyancy calculator the empty weight is shown as 26.5 lbs, that's too low. My LP80 (Coyne) is more like 34 lbs IIRC. Plugging in 34 makes the buoyancy look more realistic and always negative.

 

[gfaith]

If the LP72 empty weight was 28 lbs instead of 26 lbs in the first post, the calculator seems to work.

 

[Kharon]

Personally I like to fill my steel 72s to about 2650 which gives me about 76.25 cu/ft and the whole thing (including the weight belt) ends up weighing several pounds less and you get nearly the same amount of air as the aluminum 80.

The steel LP's are 72 CF with the 10% + rating. Their non-plus fill pressure is 2400. With the plus they fill to 2640 and that's 72 CF. You are not getting 76.25 CF at 2650. You are getting just a tiny hair over 72 CF.

 

[2airishuman]

The steel LP's are 72 CF with the 10% + rating. Their non-plus fill pressure is 2400. With the plus they fill to 2640 and that's 72 CF. You are not getting 76.25 CF at 2650. You are getting just a tiny hair over 72 CF.

Unlike most other LPs, 72s are rated 3AA2250 and have an authorized fill pressure of 2475 with the 10% + rating. They approach the rated capacity of AL80s when the LP72 is filled to around 2700 PSI.

 

[Luis H]

The "specs". Your calculation look real close to mine and the chart Luis attached. I never would have thought LP72 and LP80's are positive when empty. Thanks again for the Link..

The traditional steel 72 (3AA 2250) had a reputation for being neutral (with a regulator) when empty. That made them an ideal cylinder when we used to dive without a BC or any other surface flotation device.

In the days before BC, if you ever got into trouble at the end of a dive, you just ditched your weights and any thermal protection (wetsuit) you might be wearing would keep you afloat.

The AL80 was not a bad cylinder for the same reason when diving without a BC.

You may notice in my table that the empty steel 72 buoyancy varies a bit from one cylinder to the next. I should mention that they all have the same Sherwood valve, but no regulator.

 

[JamesBon92007]

The steel LP's are 72 CF with the 10% + rating. Their non-plus fill pressure is 2400. With the plus they fill to 2640 and that's 72 CF. You are not getting 76.25 CF at 2650. You are getting just a tiny hair over 72 CF.

Perhaps there are/were other steel 72s that had that rated pressure but all of mine clearly have "2250 stamped on them. Add 10% and that gives you 2475."