Scuba tank size and buoyancy calculator

[henrik242]

I scratch my head every time I try to convert between imperial and metric tank sizes, but figure it out in 10 or 20 minutes.

In order to save my hair and time I created a calculator that converts between these values. In addition it shows the buoyancy of the tank when full/empty, adjusted for steel/aluminum tank and fresh/salt water.

It doesn't look very fancy since I've made it compact enough to use on a smart phone.

Here goes: Scuba tank size and buoyancy calculator

All feedback is very welcome! I've probably made an error in there somewhere, or misconfigured or left out a common predefined tank. Or maybe you weird americans use other ways of measuring tanks that I haven't thought of?

(EDIT: By the way, it's made with inline javascript, so you can save the page to your phone and use it without network coverage)

 

[j2s]

HEY !!!!.....Who you calling a WEIRD American !!??.....You guys still driving on the wrong side of the road ;O ????!!!!!...We have more roads and more cars, that's why it's the RIGHT side......SO THERE ;D !!!!

 

[pjhansman]

"weird americans" is redundant

However.....living in a partially metric country, I do like your calculator.

 

[henrik242]

HEY !!!!.....Who you calling a WEIRD American !!??.....You guys still driving on the wrong side of the road ;O ????!!!!!...We have more roads and more cars, that's why it's the RIGHT side......SO THERE ;D !!!!

Hehe. Norway has never had left-side driving, so no weirdness here

 

[Hatul]

I scratch my head every time I try to convert between imperial and metric tank sizes, but figure it out in 10 or 20 minutes.

In order to save my hair and time I created a calculator that converts between these values. In addition it shows the buoyancy of the tank when full/empty, adjusted for steel/aluminum tank and fresh/salt water.

It doesn't look very fancy since I've made it compact enough to use on a smart phone.

Here goes: Scuba tank size and buoyancy calculator

All feedback is very welcome! I've probably made an error in there somewhere, or misconfigured or left out a common predefined tank. Or maybe you weird americans use other ways of measuring tanks that I haven't thought of?

(EDIT: By the way, it's made with inline javascript, so you can save the page to your phone and use it without network coverage)

Something is way off in your calculator. I use a table and the key buoyancy is the empty in sea water with valve. For XS Scuba HP tanks (lbs):

tank table calculator
80 -3.0 -6.5
100 -2.5 -1.5

 

[j2s]

Hehe. Norway has never had left-side driving, so no weirdness here

No cars in Norway ??????.....

 

[Hatul]

Here's where I got the table numbers from:

XS Scuba Worthington Steel Cylinder Specifications

They don't match the calculator, at least not the empty buoyancy for the 80 and 100 tanks.

 

[henrik242]

Something is way off in your calculator. I use a table and the key buoyancy is the empty in sea water with valve. For XS Scuba HP tanks (lbs):

tank table calculator
80 -3.0 -6.5
100 -2.5 -1.5

The XS Scuba HP tank values are slightly different from the "default" HP80 tank (80 cuft, 3442 psi, 32.6lbs) in the calculator.

Regardless, here's the calculation for a XSScuba X7-80 tank (81 cuft, 3442 psi, 27.7lbs). It still differs from XSScuba's own buoyancy values, I guess it's because I don't account for valves and manifolds (which would add about 2 lbs to the tank weight):

1 atmosphere is 14.6959 psi. The internal volume of the tank is 81 cuft / 3442 psi x 14.6959 = 0.3458 cuft
Steel has a density of 490 lbs/cuft. The steel has a volume of 27.7 / 490 = 0.0565 cuft, so the total volume is 0.3458 + 0.0565 = 0.4024 cuft
The density of salt water is 64 lbs/cuft, giving 0.4024 x 64 = 25.7536 lbs
Air has a density of 0.07647 lbs/cuft. The air in a full tank weighs 0.07647 x 81 cuft = 6.1940 lbs

An empty tank has a buoyancy of 25.7536 lbs - 27.7 lbs = -1.94 lbs (XSScuba table: -3 lbs)
A full tank has a buoyancy of 25.7536 lbs - 27.7 lbs - 6.1940 lbs = -8.14 lbs (XSScuba table: -9 lbs)


Since I don't really know anything about how an HP80 is defined, would you say that the XSScuba X7-80 is a standard HP80 tank? (Considering it holds 81 cuft instead of 80 etc)

---------- Post added April 19th, 2012 at 09:53 AM ----------

By the way, there's something fishy with XSScuba's tables.

The metric table says that the X7-80 weighs 13.1 kg, which is 28.9 lbs. The imperial table says that it weighs 27.7lbs, which is 12.6 kgs. If I download the table as PDF, it says that the X7-80 weighs 29.9lbs, which is 13.6 kgs. (I've sent them an email about it)

 

[Lemna]

Hi Henrik,

here is another calculator, with a list of common tanks in several countries: UK Scuba - Cylinder Buoyancy Calculation

 

[henrik242]

here is another calculator, with a list of common tanks in several countries: UK Scuba - Cylinder Buoyancy Calculation

Thanks, I've looked at those. But the "mystery" about if there's a standard AL80/HP80/HP100/HP120 still remains for me, since almost all of the tanks in the UK Scuba list are measured in litres.

It's so much easier here, at least for my head: We commonly have 10, 12 and 15 litre tanks, and they are 200, 232 or 300 bar. If I want to know the tank capacity, I just multiply litre with bar: 12 litres x 200 bar = 2400 litres of air.

I got an answer from XS Scuba, by the way: «Thank you for the feedback on the tank specs. We will take a look and make any corrections needed.». Yay!