Calculating capacity of an air tank

[Clown Boy]

I am going cross eyed.

I need to know how far my 9l, 200PSI air tank will go toward filling my 31"x11.5" tyres before I am running directly off the compressor.

I figure if I work out how many tyres it will fill from empty, I can double that for how many it will fill from 20PSI.

Help!?

[Clown Boy]

If you guys agree with the maths, then I do not think it will suit.

And it is an 11L tank by the way.

11L @ 200PSI = 11 x 14bar = 154L

My tyre volume is as follows:
Full wheel = 31"^2 x pi x 11.5" = 34,701 cu in = 568 litres
Rim only = 15"^2 x pi x 11.5" = 8124 cu in = 133 litres

So the tyre volume = 435.6 litres.

the volume of air that gets this volume of tyre to 40PSI is
435.6 x 2.8bar = 1219.68L
the volume of air that gets this volume of tyre from 20PSI to 40PSI is
435.6 x 1.4bar = 609.84L

So my air tank would do quarter of the job of pumping up 1 tyre from 20PSI to 40PSI.

Is all of this correct?

[STIKA]

Remeber that equalising pressure will still have to remain in the air tank + the air stored in the hose

[Clown Boy]

I only need an approximate.

This tank will be fed by my existing aircon pump (obviously without air con anymore.

Does anyone have any idea of what rate these pumps work at?

[Clown Boy]

Hey guys. I was way off. The following comes from OVerlander where I was totally proven wrong by a guy called Smooth Cruiser.

Clown Boy wrote:
Definitely not impressive.

IS you guys agree with the maths, then I do not think it will suit.

11L @ 200PSI = 11 x 14bar = 154L


Firstly 200psi is actually 13.6 bar so 150L.

Clown Boy wrote:
My tyre volume is as follows:
Full wheel = 31"^2 x pi x 11.5" = 34,701 cu in = 568 litres
Rim only = 15"^2 x pi x 11.5" = 8124 cu in = 133 litres



Full tyre Diameter = 31 inches = 0.787m. Radius = 0.394m
Width = 11.5 inches = 0.292m
Volume = pi x r squared x width= 3.14 x 0.394 x 0.394 x 0.292 = 0.142 m^3 = 142L

Rim only by a similar method = 0.033m^3 = 33L

Clown Boy wrote:
So the tyre volume = 435.6 litres.


Tyre volume = 142 - 33 = 109L

Clown Boy wrote:
the volume of air that gets this volume of tyre to 40PSI is
435.6 x 2.8bar = 1219.68L


109L x 2.72 bar = 296L

Clown Boy wrote:
the volume of air that gets this volume of tyre from 20PSI to 40PSI is
435.6 x 1.4bar = 609.84L


109L x 1.36 bar = 148L

Clown Boy wrote:
So my air tank would do quarter of the job of pumping up 1 tyre from 20PSI to 40PSI.



So the tank contains 150L. The tyre needs 148L. Sounds good. Except the tank will still be at 40psi at the end which is 11L x 2.72 bar = 30L so the air available is only 120L. Hence it won't quite do one tyre.


Clown Boy wrote:
Is all of this correct?

No Laughing - but now it is!!

[just cruizin']

You're squaring the diameter of the tyre and rim rather then the radius for a start so divide all your volumes by 4.

[STIKA]

divide you volume by 5

if you want to inflate a trye to 30psi you will still need to have 30psi remaining in your tank

[Clown Boy]

So 31" is the diameter of my tyres? Oops.

[big bundy]

So 31" is the diameter of my tyres? Oops.

stay at overlander

[Clown Boy]

If you read the post above where I show smooth cruiser's correction of my maths - he already halved te 31" (after converting to metric.

So the Overlander guys beat you to proving me wrong.

Does this make me an outcast?

[of4x4]

I only need an approximate.

This tank will be fed by my existing aircon pump (obviously without air con anymore.

Does anyone have any idea of what rate these pumps work at?

Endless Air systems use "Air Conditioner Compressor Technology" and are are claimed to be 200psi at upto 8 cu ft/min. Claims to fill a 31" tyre from flat to 30psi in 55seconds. No mention of a tank.
http://www.4wdworld.com.au/products/end ... /index.htm

I do not know if Endless make any adjustments to the compressor rate, or if this is typical of a standard aircon compressor.

BTW Here's my 2 cents worth to add to your capacity formula: the measurements you've used are the outer dimensions of the tyre. Therefore the volume of air required will be slightly less. ( a 31" diameter A/T tyre will probably have more than 1" of tread across the diameter when new) Taking this and the sidewall thickness into account, you're probably looking more like 95 litres volume at standard atmosphere.

[ISUZUROVER]

Converted Air-con compressors are very fast. My York at about 1500 engine rpm takes about 30s per 33" tyre to go from 10-40psi. I do have two small air tanks, but they don't do much - I have set mine to cut out at 120psi (they get too hot if you go up to 200. The air tanks at 120psi are only enough to take one tyre from 0-20psi.

Sanden (barrel shaped) compressors are a bit lower in CFM for the same engine revs but not much.

I once put up a 20mx2m timber fence with a huge nail gun running from my york, and never once ran out of air.

[Mad Cruiser]

Outcast

[PJ.zook]

I think my head just exploded

[Clown Boy]

Converted Air-con compressors are very fast. My York at about 1500 engine rpm takes about 30s per 33" tyre to go from 10-40psi. I do have two small air tanks, but they don't do much - I have set mine to cut out at 120psi (they get too hot if you go up to 200. The air tanks at 120psi are only enough to take one tyre from 0-20psi.

Sanden (barrel shaped) compressors are a bit lower in CFM for the same engine revs but not much.

I once put up a 20mx2m timber fence with a huge nail gun running from my york, and never once ran out of air.

I am starting to get excited. This is going to be cool.

[Witchdoctor]

A CO2 system will give you exactly what you need (over 200psi)& you can retain you AC

Dave

[Clown Boy]

I don't use the AC. I would keep it if I did.

It has needed to be regassed for about 2 years but I am a systems consultant so I work in air con, my house has air con and I take the train to work in air con - I actually like sweating and getting outdoorsy when going fourby.

Damn, I sound like a naturalist

Besides, the CO2 kits sounded limiting as they have a certain amount of air and no more. And this is going to be cheaper.