Good size for a "small" air tank?

[The Adam Blaster]

I would rethink the notion of running air tools with that small compressor. It takes alot of air to run them for more than a brief moment. I have an $800 12v compressor from commercial use that barely will run an impact for 5 lug nuts with a 2.5 gal tank. I recommend a 12v impact gun if you want for tires-may work better for you. Adding even a 1 gal. tank will help you, but the ARB compressor will still be working hard to even keep that full.

Ya, that is the issue I've been faced with...
I actually already own an electric impact gun, I would just need to run it off an inverter I suppose. But the elec. gun is fairly bulky, and not that powerful to be honest.
I think in the long run I would definitely need to get a beefier compressor to run air tools properly.

 

[jeffy]

To be able to run air tools you need a compressor with a lot of Cubic Feet per Minute (CFM). Most air tools have a minimum or average CFM requirement on the specs. Most of your small electric compressors are maybe 2-3 CFM at 0 psi. So by the time it gets to 60 or even 80, it's probably less then 1 CFM. A large tank can help but you'll burn though the air in there quickly and then have to wait a LONG time to recharge the tank. Stuff like impact wrenches uses a lot of CFM. 2-6 CFM at 60-90 psi for your standard 1/2" gun.

To give you an idea here are ARB's compressors specs:

CKSA12 Compact On-Board - 0.88CFM @ 0 psi
CKMA12 High Vol On-Board - 2.65CFM @ 0 psi
CKMA24 High Vol On-Board - 2.65CFM @ 0 psi
CKMP12 High Vol Portable - 2.65CFM @ 0 psi

I believe the only have a 50% duty cycle so you have 30 minutes on and 30 minutes off.

A York compressor will give you around 4CFM @ 90 psi and have a 100% duty cycle.

You would be better off either doing an A/C Compressor conversion or going with CO2 if you really want to run tools.

 

[expedition4x4]

Arb's have a 100psi air pressure switch installed center top of the small tank, I ran tools successfully for short bursts with a warn powerplant and a 3 gallon tank. I also replaced its air shutoff switch with a 150psi one

 

[007]

Besides the air tool factor, does anyone have an idea on how many gallons of air it would take to fill 4 255/85/16's from say 10 psi to 50?

 

[expedition4x4]

Not exactly sure of the measurements of that particular metric equivalent tire but

T = Tire radius (diameter/2), in inches
W = tire section Width, in inches
R = Rim radius (diameter/2), in inches

Then, you have:

r = Radius of tire body in a radial direction = (T-R)/2
w = radius of tire body in the width direction = W/2

The volume of a torus is equal to the length around its center times the cross sectional area, or;

Length = (2 * pi * (R+r))
Area = pi * r * w

So for a 33x12.50R15 tire, you get:

T = 33/2 = 16.5
W = 12.5/2 = 6.25
R = 15/2 = 7.5
r = (16.5 - 7.5)/2 = 4.5
w = 12.5/2 = 6.25

So the volume in cu.in. is:

Length * Area = Volume
(2 * pi * (7.5 + 4.5)) * (pi * 4.5 * 6.25) = 6662 cu.in.


231 cu.in./gallon and 1728cu.in./cu.ft

so then you need to compute one more time

PV = MrT
where:
P = Pressure
V = Volume
M = Mass of the gas
r = Ideal gas constant (air is not an ideal gas, but who cares)
T = Temperature

So how would you apply this in practice? The simplest case is to assume you have a closed system (no leaks) and you have two volumes at different pressures. Then open the valve between them and let the pressure equalize and see what pressure you end up with. Lets put some real-world numbers in here and see what happens.

Assume you had a 20gal tank at 150psi and a 4 - 30gal tires at 10psi and you then hook the tank to the tire (assumes Mass and Temperature remain constant), you'll see something like:

Tank + Tire(s) = Combined
(20*150) + (4*30*10) = newP * (20 + 120)


solve for newP and get

(3000+1200)/140 = 30psi.

So a 20gal tank could air up four 33x12.50 tires from 10 to 30 psi.

Mind you this is not exact but close enough to know you need a compressor to kick in as you would need a 30 gallon tank to fill them up once

 

[007]

pfff.. duh, I could have done that math in my head:sombrero:

 

[expedition4x4]

Short answer to being able to run tools and fill up tires is a york compressor, fab up a mount to drive it off the engine

 

[jeffy]

Would probably be cheaper to go with a CO2 setup then a York/Sanden unless you got a good deal on a compressor and made your own brackets. It's all the little things like fittings, valves, solenoids, and what not's that really jack the price up.

FWIW, I run a Kilby/York setup with a 2.5 gal tank.

 

[bandit455]

1st post, time to stop lurking!

I run oba off of my stock a/c compressor, I only use a 1.5 gallon tank, and run a fairly high pressure switch (145off 115on)

this allows the tank to never dip much below 70-90 when filling tires, and it runs an impact better then my compressor at home!

heres a pic of my setup