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Unread 12-09-2006, 02:10 PM   #1
surfcaster
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On board air system

Has anyone installed this yet? I can not figure out where to mount the compressor or tank. Then I considered eliminating the compressor and just go with a mounted tank, I can fill it from my garage air compressor everytime I go off road, but I can not figure out where to mount it. Every place I look is to small. I want to go with a 2 gal tank.

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Unread 12-09-2006, 02:18 PM   #2
CNY
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You can't fill a tire from just a compressed air tank. Even if you had a 10 gallon tank, pressurized to 150 psi, you would not have enough volume to air up four tires after a day of offroading.

I'll bet you couldn't do two tires.

You would need something like a SCUBA tank (3000 psi), to do tires with compressed air.

Your viable options are:

- Belt driven compressor
- 12 volt compressor
- 110 VAC compressor and an inverter (poor choice, I used to run this).
{any of the above, you can add a tank to}

- CO2
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Unread 12-09-2006, 06:00 PM   #3
surfcaster
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I am only airing down to about 20 to 22 psi. It's a beach vehicle, I used a 5 gal tank for my explorer, it worked great. It held 150 psi. So if I need 12 pounds per tire @ 4 tires, all I am using is 48 pounds. A tank is more than sufficient for my needs.
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Unread 12-09-2006, 06:09 PM   #4
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Quote:
Originally Posted by surfcaster
I am only airing down to about 20 to 22 psi. It's a beach vehicle, I used a 5 gal tank for my explorer, it worked great. It held 150 psi. So if I need 12 pounds per tire @ 4 tires, all I am using is 48 pounds. A tank is more than sufficient for my needs.
It doesn't quite work that way... by that math, at 150psi you could air up 4 tires from 0-30psi and have air left over

It may work to go from 22-30psi on smallish tires, but the larger your tires are, the larger your tank would need to be.
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Unread 12-09-2006, 09:47 PM   #5
CNY
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Yeah, the math on that would only work out if the volume of your tires was only 5 gallons (or would it be 1 1/4 gallons?).

I don't know how the math works for psi vs. volume. For example, does an air tank with 100psi have twice as much air in it as a tank with 50psi?
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Unread 12-10-2006, 07:13 AM   #6
surfcaster
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The math should work on equalizing pressure, if a tank has 100 psi and another tank has 0 psi, when filling the second tank from the first tank, the air would transfer to the second tank until it is equal in both tanks. 50 pounds of air in both of the tanks. It's the amount of pressure in the tank, not the size of the tank. Now, with that said, are there any math wiz's here that knows what the correct answer is?
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Unread 12-10-2006, 07:33 AM   #7
CNY
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Quote:
Originally Posted by surfcaster
......if a tank has 100 psi and another tank has 0 psi, when filling the second tank from the first tank, the air would transfer to the second tank until it is equal in both tanks.

50 pounds of air in both of the tanks. It's the amount of pressure in the tank, not the size of the tank......
That's definitely wrong.

You're right that the two tanks will equalize, but the volume of the tank comes into play.

For example, 10 gallon tank at 100 psi, equalized to a 1 gallon tank that starts at 0 psi, the two will equalize, but probably at 90psi, not at 50 psi.

Our 0 psi tank is theoretical, since you'd have to seal it in a vacuum. Realistically, your "empty" tank has whatever the ambient air pressure is.

Somebody step in and tell us the volume of a 32" tire on 16" rims (that's what a JK has, yes?)
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Unread 12-10-2006, 08:09 AM   #8
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Quote:
Originally Posted by TeamCNY
Somebody step in and tell us the volume of a 32" tire on 16" rims (that's what a JK has, yes?)
Volume vs. Pressure. Any one with thoughts???

My JK has 18" rims. This is starting to give me a headache!
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Unread 12-10-2006, 08:58 AM   #9
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Quote:
Originally Posted by surfcaster
.... This is starting to give me a headache!
Me too.

Here are my VERY rough numbers:

Volume of one tire = the volume ot the space of the tire, minus the volume of the rim.

My numbers assume rectangular cross-sections, and a non-flexible tire

Volume of a cylinder = pi r^2 \ h r = radius of circular face, h = distance between faces

Volume of rim = 2,797 cubic inches (18inch rim, 11" cross section)
Volume of tire (including rim) = 8,842 Cubic inches
Volume of tire, minus rim = 6,044 cubic inches

6,044 inches = 3.49 cubic feet = 26 gallons of air volume.

You air these down 10 psi below what you want to air up to. In our example 30 psi, aired down to 20 psi.

Using a 10 gallon tank, at 150 psi, our working range is 120 psi (we can't go below 30psi in the tank, because we can only equalize pressure).



Our tire has 2.6 times the volume of the tank, so if we take our 20 psi tire, and equalize it to the tank, we can fill one tire to 47 psi.

We can equalize two tires to 27 psi. Having started at 20 psi in the tires, and 150 psi in a 10 gallon tank.

So, you would need more than a 20 gallon tank, to air up 4 tires.

Using a 2 gallon tank, at 150 psi, you will be able to air up one tire, from 20 psi, to 27-29 psi.
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Unread 12-10-2006, 09:01 AM   #10
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How's this, for an answer....


Add 10 psi to your spare tire, for every tire you need to air up. Spare starts at 30psi, ad 40 psi. Now you can air up your tires from your spare! Hahahahahaha

Watch out, as the spare gets warm, the pressure increases in the sun.... BOOM!




- - - - - - For those who are reading this, I'm kidding. Don't do this. - - - - - -
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Unread 12-10-2006, 09:09 AM   #11
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Back to the question at hand, my thoughts are if you do a muffler up grade and relocate the muffler that should leave plenty of room to mount both units up under there.
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Unread 12-10-2006, 09:19 AM   #12
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Quote:
Originally Posted by TeamCNY
How's this, for an answer....


Add 10 psi to your spare tire, for every tire you need to air up. Spare starts at 30psi, ad 40 psi. Now you can air up your tires from your spare! Hahahahahaha

Watch out, as the spare gets warm, the pressure increases in the sun.... BOOM!




- - - - - - For those who are reading this, I'm kidding. Don't do this. - - - - - -

Believe it or not, I thought about that too!!!!
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Unread 12-10-2006, 09:28 AM   #13
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Quote:
Originally Posted by RedRocRubi
Back to the question at hand, my thoughts are if you do a muffler up grade and relocate the muffler that should leave plenty of room to mount both units up under there.
I was thinking the same thing, but 2 things came to mind...

1- Alot of extra $$ and work for nothing because I have a portable compressor

2- If the compressor is mounted under the vehicle, when I go through the sand and water wont this ruin the compressor?

I orginally wanted the on board system because there is less room in the jeep, than my Explorer, to carry things, so I figured I could leave the portable compressor in the garage. I thought I could mount the compressor somewhere under the hood and the tank elsewhere, but it's so damn cramped!
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Unread 12-10-2006, 10:24 AM   #14
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Again, for just a tiny bit of storage space, and 50 bucks, you can get a 12 volt compressor that will do the job for you.

Actually puts out decent volume, for the size and price:

http://www.jeepforum.com/forum/showt...37#post1718537

http://www.jeepforum.com/forum/f27/checker-auto-12v-tire-inflator-133377/
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Unread 12-10-2006, 01:05 PM   #15
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Quote:
Originally Posted by TeamCNY
Again, for just a tiny bit of storage space, and 50 bucks, you can get a 12 volt compressor that will do the job for you.

]
I have a portable, but I wanted to be able to leave it at home. I found one on ebay thats a complete unit;http://cgi.ebay.com/ebaymotors/ws/eB...7952869&rd=1,1.

If anyone ever makes a front hitch reciever for the JK, I can mount it directly to the rod rack that I have; http://www.quadratec.com/products/92038_10.htm with the hitch post. I'll use a quick connect for the electrical, strait to the battery with an inline fuse. Do you think this unit would be suitable for my needs?
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