Air tank volume question

[Trouble]

I have both smittybilt compressors small one and the big one in my shop right now so i did a little test.

tire: 35x12.50r15

small one from 15-30psi 2min 5 seconds. 0psi-30 psi: 4 min 58 sec
big one from 15-30psi 1 min 20 seconds. 0psi-30 psi:3min 15 sec

I also tested two of their deflators i had in stock. One is my personal one that has been modified and one is new out of box, along with an older currie ( like 20 years old)

stock 30psi-10psi: 42 seconds
modified 30psi-10psi: 33 seconds
currie 30psi -10psi: 40 seconds

 

[denverd1]

The compressor and deflator shootout.

All good info, I suppose. Maybe need a new thread for it tho

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[Greenz]

This may be more appropriately posted in the Tools and Garages forum, but I figured it would get more views here. The moderators can always move it if so inclined.

I’m thinking of getting an air tank, not to mount up as part of an onboard air system, but just to bring along on the trail or leave at camp to fill tires faster than my portable compressor. Space is an issue, so I’m looking to go small. My question, specifically, is this: will a 2.5 gallon tank rated to 150 psi hold enough air to fill four 35x12.5x15 tires from 10 psi to 32 psi? I’m no math or physics whiz, and I haven’t been able to find the answer on line. If anybody has some practical experience or knowledge that can shed light on the question, please post up. Thanks.

No it wont.


I installed a 3 gallon tank coupled to ARB twin compressor 150psi. Bottom line is 3 gallons is practically nothing for filling tires. The only advantage of having a tank for filling tires is the compressor is partially recovering the tank between filling tires where as without a tank the compressor reaches 150 psi and shuts off before you can screw the valve cap back on. The tank will help some but the savings is just a few seconds per tire. Not really worth it.


If you are planning other uses like air tools, forget it. To blow out a filter, clean debris from a work area, fill inflatables, train horns, (lol) the tank will be useful.

 

[devildog0]

I would of course have a regulator on it.... so you're saying there's not significantly more volume of air in a tank with that kind of pressure?

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No. Because CO2 is stored as a liquid and converts into a gas as you use it. This is why the tank needs to be mostly upright when being used.

800psi of atmospheric air is still just a gas.

A 20 lb CO2 tank has 20ish lbs of liquid CO2 in it. As you use the gas off the top the liquid CO2 converts to gasseous form and cylinder pressure stays around 800-1000 psi. Once your tank pressure needle starts coming down from that point you no longer have liquid in there and just gaseous CO2.

This is why CO2 tanks are so useful for onboard air, for a given tank size you get far more energy than something stored in the same size bottle as a gas.

FWIW we can use our 45 min SCOTT SCBA bottles to "power" our lift bags for emergency rescues. These bottles when full are at 4500psi. They dont last very long using them like that.

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[denverd1]

Great

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[Greenspan]

Previous Poster said a 35" tire has 3.47 ft^3 which is about 98L

A 2.5 gal tank is almost 9.5L so

9.5L * 150psi = X * 98L * 20psi

Where X is the number of tires you can fill from 10psi to 30psi (20psi)

X= 0.72 tires

So a 2.5gal tank would not work, you would need at least 16gal at 150psi


For the 10lb tank filled up with 800psi of air:

https://www.mathesongas.com/industrialgas/pdfs/Industrial-Cylinder-Dimensions.pdf

Looks like a 10lb tank has 7.8L so

7.8L * 800psi = X * 98L * 20psi

X = 3.18

So you should be able to fill up three 35" tires from 10psi to 30psi using a 800psi 10lb tank of just air.


For the 10lb liquid CO2 tank, 10lb of CO2 = 103mol. Using PV=nRT (800psi * V = 103 * R * 60). V = 44L, so since its a liquid the small tank is equivalent to a 44L tank.

44L * 800psi = X * 98L * 20psi

X = 17.9 tires with the liquid CO2 at 800psi

*These are all spitball approximations