How to compare 3000psi air tanks to 4500psi tanks?

[AirGunEric]

I am attempting to source large 4500psi carbon fibre tanks- but have no knowledge of how to compare a, say 88cuft 3000psi tank to a carbon fibre unit which is measured in Litres or cubic inches.

Any know how to calculate such a comparison?

[Gippeto]

88 cuft is sort of misleading....it's 88 scuft....which is 88cuft @60F and 14.7psi.

Multiply 88cuft by 14.7psi....then divide by the service pressure (4500psi, 3000psi, etc). You now have cuft volume. Use an online converter at this point.

http://www.onlineconversion.com/volume.htm

[rsterne]

I usually go the other way.... converting the paintball type tanks that are rated in CI to what they hold in "standard" air.... then you have a direct comparison with the SCUBA and SCBA tanks which are rated in CF.... To convert, take the CI, multiply by the service pressure (in bar) and divide by 1728....

EG> 48 CI @ 3000 psi.... 3000 / 14.5 = 207 bar.... 48 x 207 = 9936 CI.... 9936 / 1728 = 5.75 CF....
>>> 90 CI @ 4500 psi.... 4500 / 14.5 = 310 bar.... 90 x 310 = 27900 CI.... 27900 / 1728 = 16.1 CF....

HTHs....

Bob

[Dukemeister]

88 cu ft air is tank rating at room temp and atmospheric pressure (14.7 psi); ignoring temperature since it will have negligible effect, the volume of air at 3000 psi can be calculated from Boyle's Law: P1V1=P2V2, so V2=P1V1/P2
Let V1 = 88 cuft P1 = 14.7psi, P2 = 3000 psi, your tank will have an internal volume of V2 = 0.43 cuft. The same tank pressurized at 4500psi will have 50% more air in it... so it`ll have 132 cu ft at atmospheric pressure.
But I speak from a purely academic standpoint, and there is no substitute for experience...
Use the formula anyhow, it works.

[AirGunEric]

OK- so let me complicate this (Boyle's Law- you b@stard! I thought I left that behind 30 years ago in school...)

by these calculations, an 88cuft 3000psi tank has .43 cubic feet of air, then we have a 550cu in CF tank at 4500psi, or what works out to be .46 cubic feet of air. How might one figure out how much air must be removed for that CF tank to reach 3000psi? 50%?

The whole point to this of course is to calculate how many fills an "average" airgun reservoir of what- maybe (.00625 cubic feet at 3000psi on a 1" diameter reservoir that is 15" long)? can get before a 550cu in CF tank falls below 207bar (3000psi)- the idea being that people need to fill 300bar airguns, not 200bar airguns...

Applying these formulae without developing an aneurism, this .00625cuft reservoir should be approximately 37 fills to drop the 550cu in tank from 4500psi to 3000psi?

[rsterne]

Most airguns are filled to ~200 bar, not 300.... The exceptions are things like the Ranger which are filled to 4000-4500 psi (275-310 bar).... The easiest way is to use a fill calculator.... Lloyd Sikes' is one of the better ones....

http://calc.sikes.us/

The other calculator linked from that page is an Efficiency Calculator....

You have an air tank that is 550 CI of internal volume?.... At 4500 psi, it contains (4500/14.5) x (550/1728) = 310 x 0.32 = 99 CF.... At 3000 psi, it contains 2/3rd of that, or 66 CF.... Plunking the 4500 psi version (99CF) into the fill calculator, and filling (as an example) a Marauder (which happens to have the same air capacity as a 13 CI / 3000 psi tank) of 215 cc.... starting from 2000 psi and filling to 3000 psi you would get about 63 fills....

Using your example of a reservoir 1" inside diam. by 15" long = 11.8 CI = 193 cc.... From 1500 to 3000 psi, you would get about 47 fills.... From empty, twice that ~93 fills....

Bob

[DocGadget]

I was also going to suggest Lloyd calculator, they're easy to use yet precise and accurate.

So when are those tanks coming Eric? Those 88cu/ft 4500 psi tanks are nice but at 700/800 $$ the 4500psi 90cu/in carbon fiber tanks they sell for painballers are inexpensive but have 850psi regulated valve.

[AirGunEric]

I am beginning to get the idea the 'large' CF tank market is quite small in respect to tank maufacturers. Got some pricing from one of the apparent larger players- and without a valve on the tank- the price was higher than I can get the same tank w/valve setup for airgun use already. Don't ask anything technical- i.e. what the threading is on their "generic" valve either- product knowledge is apparently not a requirement for sales people in that market. I guess when the majority of your customers are one form of "government" or another- you can play it lazy.

On the small tanks, the regulator pressure can be adjusted (ask Bob, I don't think he's seen a regulator he left alone ).

[DocGadget]

Firefighters and divers must be buying a lot more tanks than airgunners. Those small paintballers 90cu/in tanks can be found for around 200$ yet would provide 12.5 full fills.
The same size tank sold by Benjamin and available from Pyramyd Air but with a different valve yet sell for double the price! http://www.pyramydair.com/s/a/Benjam...isconnect/4203
Can that valve and "Benjamin" sticker really be worth 200$?

[AirGunEric]

Here's a kick in the pants for you- Crosman won't ship these tanks to Canada anyways- seems their 'lawyers' must have gotten involved again, and not having alot of knowledge of Canada decided that they should get a TC or CSA label on the tanks, which would be time consuming and expensive, so they won't do it (I believe US approved DOT stickers are valid for pressure vessels in Canada, so this may all be BS)...