Carbon Fiber Air Tank Liter to Cubic Feet Conversion

[heath]

A friend of mine asked me the other day about carbon fiber air tanks on eBay and how some of this type of HPA tanks that are made here in the USA are measured in cubic feet and not liters. Well I didn’t have a clue what to tell him so I told him I would get back to him when I had the answer. It took a while with Google and the sites that came up and before I knew it bout 4 hours went by and I missed my window to make it to the shooting range. Anyway what I found is that for every liter is 9.5 cubic feet at a 300 Bar fill. Apparently this does not apply to SCUBA tanks that are made of steel or aluminum and the formulas they use to convert them are to say the least confusing as all get out...at least to me anyway which is how I missed out on the shooting range.

According to the information I found listed by Acecare...a carbon fiber tank manufacturer in China this is the amounts they list their tanks to hold at 300 Bar fills.

12 Ltr =115 CF

9.0 Ltr = 86 CF 

6.8 Ltr = 65 CF

3.0 Ltr = 29 CF

2.0 Ltr = 19 CF

1.5 Ltr = 14 CF

1.0 Ltr = 9.5 CF

500cc = 4.25 CF

I hope someone finds this information helpful. The Cubic Feet values are rounded to the nearest whole number for the most part and are accurate on the larger tank sizes within a half of cubic foot. Again these values and conversion do not apply to dive tanks because they are filled to a lower pressure and cannot be filled to the extreme 300 Bar pressures a carbon tank can hold. Another thing that was posted by Acecare was breathing time for liters and they were as simply as 3 Ltr = 30 minutes, 6.8 Ltr =60 minutes, 9 Ltr = 90 minutes, 12 Ltr = 120 minutes.........so basically for every Liter of air compressed to 300 Bar you get 10 minutes worth of breathing time. I don’t see how this is relevant in the air gunning world but simply posted this just Incase that question for whatever reason would arise. Hope you find this helpful. Nothing this simple is posted anywhere else on any Google search I tried. You need a PHD or something and a bottle of headache pills to figure out the formulas that in the end still don’t apply to a 300 Bar fill. Only fill pressures like 200-232 Bar and aluminum steel dive tanks have a different algorithm altogether. I didn’t figure any of this out. The values I have listed are all posted by the manufacturer. If you fill you tank to this 300 Bar pressure or 4351.13 psi, it is your responsibility to make sure that your tank is made for that pressure and in good shape. You or someone near you could be hurt and you equipment could be damaged. Always make sure your equipment is rated for the pressures you intend to obtain. Safety first. Be careful, 300 Bar is the weight of a car! Of course y’all know someone’s not gonna listen and have to clean out their shorts when a burst disk or a line pops. Thanks again for all the guys that have helped me on the forum. Hope this helps someone as much as y’all have help me.

 

[onegoodtrick]

much appreciated - thank you for taking the time,very handy quick reference - well done

 

[srtmat]

Nice work.

I purchased an Ace Care tank a few months ago. I ran into the same thing. I had no idea finding a simple conversion would be so difficult.

 

[d1lazarus]

Thanks for the list. I have been looking at tanks as well and now have a handy reference.

 

[guod123]

Thank You it's really simple when you lay it out like that.

 

[heath]

You all are more than welcome. Glad I could give something back for all the help you all give me.

 

[mclaub]

Yes, Heath, that list is EXTREMELY helpful, and I saved it to a word document for future reference. 

Has anyone purchased and used one of the $240ish 3L 4500 PSI Chinese made tanks that are so plentiful on eBay? What has been your experience with it.?

 

[barneybusa]

I have been beating my head on the wall trying to figure this out, thank you, and if you see this, Merry Christmas!

 

[steve-l]

The reason it is difficult is that you are comparing apples to oranges. You cannot compare tank volume to capacity without dealing with pressure. So don't do it. Stick with volume only. So, you say you can't do that because the volume is not stated. Get the dimensions and use some arithmetic, it works every time. Further, just because the bottle or tank is rated at 300 bar, doesn't mean you need to use that pressure. I never do. I charge my 12 liter bottles to 230 bar and fill my gun from them. I recharge my 12 liter bottles when they drop below 200 bar. I get many gun fills for that pressure drop and I get between 65 and 75 shots at max power with my 25 Crown with the reg set to 135 bar. My point is simple, the difference between using a 300 bar fill as opposed to using a 230 bar fill is not noticeable to me with a 12 liter bottle, so why stress your equipment? You may note that finding a 12 liter tank rated to 300+ bar is difficult.

 

[Bigragu]

Hatsan lists their 6.8 L as 74 cubic feet, which I always knew as a 45 minute tank. Where does that fall into the Acecare chart?

 

[Rider77]

I’m so confused! I’ve tried all kinds of ways (math) I’ve converted cc to cf liters to gals and many other ways

has any body out there ever counted how many fills they get when filling a Air Venturi Avenger just off reg to the 4350 psi from a 88 to 100 cf tank?

I’ve looked a chart on the Marauder with an 88 cf fill tank at 300 bar 4500 psi, and guess-ta- mated about 7fills any body help??

 

[18.13]

I’m so confused! I’ve tried all kinds of ways (math) I’ve converted cc to cf liters to gals and many other ways

has any body out there ever counted how many fills they get when filling a Air Venturi Avenger just off reg to the 4350 psi from a 88 to 100 cf tank?

I’ve looked a chart on the Marauder with an 88 cf fill tank at 300 bar 4500 psi, and guess-ta- mated about 7fills any body help??

https://www.airgunsofarizona.com/Tanks/FillCalc.html

You might get 1 full fill

 

[18.13]

4.5 ltr= 30 min

6.8 ltr = 45 min

9 ltr = 60 min

 

[TN_Yankee]

 

[Mojoatomic]

I'd like to add to this discussion with the math to calculate volume for yourself instead of relying on 3rd party sources. 


First, we have to understand that Liters are a measure of actual volume. Therefore, a 9L tank will hold 9L of water. Imperial tanks are measured differently... this is expressed in the actual amount of air the tank will hold at working pressure. 


To do this conversion, you need to know the working pressure of the tank

. 
Lets say we have a 9L tank and we want to convert those units to Imperial. To do the conversion, multiply 9L x 28.317. This yields 0.317832 Cubic Feet - but we're only half way to our answer. We need to know the working pressure of the tank. Let's assume this is a fairly standard tank with a 300 bar working pressure, or 4351PSI. 


(4351/14.7) x 0.317832 = 94.07CF


So, looking at the list from the Chinese company, there's a discrepancy...they list 9.0 Ltr = 86CF. Where does this discrepancy come from? 


It's because they are conservatively calling 300Bar 4000PSI. 300Bar is actually 4351PSI. They're conservatively underrating for a safety margin. No issue there. If we follow using their conservative math, we get - 


(4000/14.7) x 0.317832 = 86.4848PSI Just as they claim. 


As an added bonus, if you'd like to know how to convert Bar to PSI, just multiply Bar by 14.504. 


300Bar x 14.504 = 4351.2 PSI


Everyone sufficiently bored?