Converting liters to cubic feet

[LI-er]

Can someone please help me with my math. I'm drawing a complete blank here.

Now that we're living in Europe, we've diving 12 and 15 liter tanks.

I'm trying to calculate the equivalent volume of a 12 liter tank in cubic feet so I can compare capacities to an AL 80.

I run the calculation through a unit converter and get this:

1 Liter = .035 cubic feet.

A 12 Liter tank, which is slightly less than an AL80 in volume, calculates/converts to .4 cubic feet.

Conversely, converting an 80 cubic feet tank to liters yields 2265 liters.

What am I missing here?

 

[Scubagermany]

It is the gas volume in non compressed state.

80cft Tank has 11.1l

 

[LI-er]

Thanks, still not understanding why there's the difference between calculated and stated amounts of volume of the two tanks.

 

[scubadada]

See this for ideal and true gas capacities

Calculating SCUBA Cylinder Capacity | Dive Gear Express®

Or why does my Aluminum 80 SCUBA tank only hold 77 cubic feet of air? ©2018-2020 by Mark Derrick, Gas Blending Instructor at Dive Gear Express ...

www.divegearexpress.com

Then convert liters to cu ft with any unit converter

Convert Liter to Cubic Foot

Instant free online tool for liter to cubic foot conversion or vice versa. The liter [L, l] to cubic foot [ft^3] conversion table and conversion steps are also listed. Also, explore tools to convert liter or cubic foot to other volume units or learn more about volume conversions.

www.unitconverters.net

 

[Belzelbub]

Thanks, still not understanding why there's the difference between calculated and stated amounts of volume of the two tanks.

Often the capacity used in US spec tanks are rounded. An AL80 doesn’t really hold 80 cu. ft. at 3000 psi.

Also, have a look at the tank specs spreadsheet @tmassey was kind enough to compile. It’s US spec tanks, but also includes water volume in liters, so you could get a feel for rough comparisons.

Updated SCUBA tank specifications list -- in PDF and spreadsheet

Hello! I have wasted my entire day re-working a SCUBA tank specifications list. I've been working with the Huron Scuba list for *years*, but I'm suspicious of the information: where did it come from? Also, it includes a lot of junk I've never seen in real life, as well as tanks that no one...

scubaboard.com

 

[JuLe]

I run the calculation through a unit converter and get this:

1 Liter = .035 cubic feet.

A 12 Liter tank, which is slightly less than an AL80 in volume, calculates/converts to .4 cubic feet.

Conversely, converting an 80 cubic feet tank to liters yields 2265 liters.

What am I missing here?

You are missing the pressure. 12 liter tank is the volume of the tank w/o pressure. When you fill it to 200 bar the air volume inside is 200x12=2400 liters. If it is a 300 bar bottle, then pressurized it holds 300x12=3600 liters of air at your disposal.
I assume (eventhough someone told me that tobassume makes an ass out of u and me) that AL80 has 80cu ft of air in it when pressurized, so a 12L 200bar is about equal.
Why anyone still uses anything other than the metric system is just baffling to me. And don't get me started on DIN vs Yoke...

 

[LI-er]

The responding posters are not understanding my issue.

This isn't about "exact volumes" or finding a conversion table.

It's about why conversion tables, including the one posted by @scubadada show a 12L tank equals 0.4237760007 cubic feet when obviously a 12L tank holds close to 77 cubic feet.

 

[LI-er]

You are missing the pressure. 12 liter tank is the volume of the tank w/o pressure. When you fill it to 200 bar the air volume inside is 200x12=2400 liters. If it is a 300 bar bottle, then pressurized it holds 300x12=3600 liters of air at your disposal.

Ok, this is helpful. So it's really not about a direct conversion, it's simply what the tank will hold when it's full.

Still rather confusing but more along the lines of making sense.

I think.

 

[JuLe]

Ok, this is helpful. So it's really not about a direct conversion, it's simply what the tank will hold when it's full.

Still rather confusing but more along the lines of making sense.

I think.

Exactly. If you want to know the exact conversion, calculate the amount of air under pressure in liters and then convert THAT into cu ft.

 

[Sascha314]

For some very stupid reason the content of a Aluminium tank in imperial units is expressed as it would be expanded to a standard pressure of 1 bar ~14.5 psi for its rated pressure.
A steel tank volume is expresses in the real volumen that can be filled. The "expanded" volume can be calculated by knowing the exact pressure filled in. In reality that will never ne the same.

Al80 has 11.1 liter capacity for reference.
An usual steel tank filling is 190 to 200 bar, rarely you get 220-230 bar.

So for a 12l @200 Bar you have 12x200 bar*liter = 2400 liter at 1 bat
1 liter is roughly 0.035 cubicfeet. So that would be around 84,76 cubic feet - as expected around the factor 12/11.1 for am 80 cubicfeet aluminim tank.