AirHog 88cf Tank Capacity Question
Wondering if someone can explain something to me. Just got my CF tank the other day (bought the one advertised as 88cf) and brought it down to get filled. Had lots of big eyes looking at it but was talking with the owner and he asked it’s capacity. I told him that it’s a 88cf tank and his reply was “no way”.
We spent some time looking through the internet and trying to figure out where they got that capacity but could not figure it out.
The tank has 146.2 cc listed on the label and has a fill pressure of 4500 PSI. Does anyone know how this equates to 88 CF?
Thanks in advance,
Glenn
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The tank has 146.2 cc listed on the label and has a fill pressure of 4500 PSI. Does anyone know how this equates to 88 CF?
Thanks in advance,
Glenn
For an 88 cu ft bottle, this means at 4500 psi the tank contains 88 cu ft of air. Tanks come in a variety of combinations of volumes and fill pressures but the cubic foot (cu ft) volume is the measure of how much air a tank holds at the stated pressure.
The 146.2 cc refers to expansion volume during hydro testing and not to the internal volume of the cylinder itself. Found the following good description of hydro testing.
for cylinder volume, determine the actual internal volume of the cylinder, and multiply by 315 (bar) which is (4500psi).
of course if the guys at the fill place are used to 3kpsi tanks the 4500 accounts for 50% more air in any given volume.
As pressure is applied to “inflate” the cylinder, the cylinder expands and forces water out of the test jacket and up into the Expansion Bowl or burette. After the thirty second test time has elapsed, the Expansion Bowl or burette is then read to determine the Total Expansion (in cubic centimeters) of the cylinder under test pressure. The test pressure is released and the cylinder “deflates”. As the cylinder shrinks to it’s approximate original size, water is allowed to drain back into the test jacket from the burette or Expansion Bowl. In most cases, the cylinder will not return to it’s original size, having been slightly stretched by the pressurization process.
This stretching is called the Permanent Expansion. The difference between the “Total Expansion” and the “Permanent Expansion” is called the Elastic Expansion. The Percent Expansion of the cylinder is determined by the following formula:
Percent Expansion = (Permanent Expansion / Total Expansion) X 100
When the Percent Expansion exceeds the predetermined limits for the cylinder being tested, the cylinder must be condemned and removed from service. A high percent expansion value is an indication that the cylinder metal has lost it’s elasticity, or that there has been excessive thinning of the cylinder wall and that the cylinder is no longer safe for use.
All test records must be saved and maintained for the duration of the requalification Plus (+) stamped cylinders may be filled to an additional 10 percent beyond the rating which is stamped on the cylinder shoulder. Star (*) stamping makes the cylinder eligible for an extended ten year re-test interval. The Water Jacket Method of testing compressed gas cylinders is the only hydrostatic test method that qualifies cylinders for filling to 10% over service pressure.
The procedures and requirements for plus stamping and star stamping are found in 49 CFR 173.302(c) for plus stamping, and 173.34(e)(16) for the star. REE values for common cylinders can be found in Compressed Gas Association Pamphlet C-5, “Cylinder Service Life, Seamless High Pressure Cylinders”. This pamphlet is available from Galiso, or from the Compressed Gas Association at the address indicated above.
top ~ Water Jacket Method ~ Direct Expansion ~ Proof Pressure Method ~ Ultrasonic Testing Method ~
Abe
I think I’ve got it. 146 cc is very close to 88 cubic *inches* (not feet). I suspect what we have here is a HPA tank intended for paintball like this:
A clue would be the small size (smaller than a football) and the male QD for filling.
Doug Owen
How big is it physically? An 88 should be about ten inches in diameter and close to two feel long. It’s the largest of the tanks Fire Fighters use (called ‘one hour’ based on it’s capacity measured in time, the other common sizes being 45 minute and 30 minute). So if it’s not ‘a backpack full’ I doubt it’s an 88.
88 cubic feet of air is what’s inside when it gets let out at ‘room pressure’. Inside the tank is about 300 times smaller than that. About one third cubic foot, 8500 cc.
Is the shop used to filling to 4500 psi? They probably have a good feel for thses things.
Doug Owen
Glenn,
Here’s the math, etc. (you know me). I may be in error, but I’m confident with what I did. First of all, like the guy said, “No way!”
146.2 cc, from the lable, equates to 0.01 cubic feet (ft^3, the best I can do quickly on this keyboard). This is the tank capacity at 1 atmosphere.
4500 psi, the fill pressure, = 306 atmospheres appx.
To get the tank fill capacity, multiply the tank cap. at 1 atm. by the number of atm’s. of pressure. 0.01 X 306= 3.06 ft^3.
Checking AirHog’s CF 88 Ft^3 tank, it has a displacement of 550 in^3 NOT CC, which yields appx. 98 ft^3, not bad since the displacement is the OUTSIDE volume, not the capacity.
Someone does not know whereof they speak. This tank does NOY (IMHO) have anywhere NEAR an 88 ft^3 capacity. I could not get the numbers to yield 88 anything. If someone can, please show me how.
Abe
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Found this forum that explained it http://www.pyramydair.com/blog/2007/10/how-air-pressure-relates-to-filling.html
Thanks for your help guys