Airing up Offroad

Let me preface this by admitting I am a total newb. Please forgive anything stupid I might say.
Anyway, I have been off-roading several times in friend's vehicles and noticed that most of them have a compressor for airing up their tires (currently have a taco on order). Now I'm an engineer working for a Scuba diving company and I came across a cool little accessory. Essentially what I can do with this is attach it to a quick disconnect hose which is attached to a pressure reducing regulator mounted on a Scuba tank. Now I have a couple of high pressure steel tanks (3500 PSI 80 cu ft.) and regulators that step down that pressure to 145 PSI.

My question to you guys is it safe to air up tires with a 145 PSI air source. Of course I would stop way before coming anywhere near that, but I don't know if the tires would air up too fast. I can reduce this pressure up to a certain point if need be as well. Can you think of any other drawbacks? Is it not wise to carry a compressed air cylinder in a truck?

I don't know, I thought it was a cool idea. Just wanted to run it by the experts.

By the way, I can also attach 4 of these to a regulator and given enough hands, air up all tires at once.

 

Setups similar to what you're describing is actually a pretty common solution used by a lot of people. They usually use compressed CO2 though because it's easier to get, and the tanks are smaller. As long as you regulate the pressure down to a reasonable level (100-150psi) that's just fine for filling tires.

 

145 psi is fine. We run 125 psi for plant air pressure and I would not worry about 145psi at all.

 

I've aired up using my nitrogen tank set just below 300lbs on my 42's and 48's. Makes it quick to get to a streetable pressure.

 

This company Powertank has been making CO2 kits for close to 20 years.

 

stay away from scuba. 145 line pressure to the tire is fine, but you will run a scuba tank empty very quickly. we run CO2 because it condenses to a liquid under that much pressure, allowing you to carry a far greater volume when expanded to atmospheric pressure (or more realistically, the 35-40 lbs you run in a tire.

 

That's interesting. Do you know what the volume of CO2 expands to at ambient pressure? Also what pressure is it compressed to in the tank?

 

How long do these co2 tanks last filling up tires? Also what price to get the co2 refilled?

 

You can find all the stuff you need including prices at a local weld shop or search airgas. My dad uses CO2 for old tractor tires and it works great at low expense. Never use the tank laying down. You can pump liquid into a tire and thats real bad.

 

I now use a 10 lb co2 tank to air up.

I used to use a 20 lb n2 tank and it would fill all 4 tires (35" tires, 15 psi increase) about 10 times.
N2 is stored in the cylinder as a gas at 1600 psi, similar to a scuba tank.

Co2 has a big advantage because it's stored as a liquid in the cylinder at around 1200 psi. Co2 has a liquid to gas expansion ratio of 450 : 1.
So as you drain the cylinder the liquid turns to a gas (if the cylinder is mounted upright). Due to the expansion a 10 lb co2 cylinder will fill 4 tires (increase pressure of 35" tire by 15 psi) about 40+ times.

I get my co2 tank and my n2 tank filled at a beverage supply store http://tavernservice.com (fill tanks for bars/restaurants and home brewers). They are cheaper than a welding supply store. And they fill my own aluminum cylinders on site while I wait. Most welding supply stores want to swap out your cylinder with a already filled steel cylinder filled at a offsite facility.

It costs me about $18 for a full fill. Same price for co2 & n2. But co2 I fill once a year, n2 I fill 4-5 times a year.

The some benefits of n2 is that it's an inert gas. It will not cause any corrosion and its used inside shock absorbers. So you can use it to fill tires and charge shocks. It will not expand due to heat like air and co2. N2 is used in race car tires and aircraft tires because the pressure will remain the same regardless of temperature.

All that being said, if you already have scuba tanks and can get them filled for free or cheap, then go with that. Nothing wrong with filling with compressed air.

 

Thanks for the info. Very informative.