I've got a few extra propane tanks. The kind used in small bbq grills. Anyway, I've already emptied, cleaned, and welded on brackets to mount it, but I'd like to know how much pressure is ok? I was going to use it as an air tank in my truck's toolbox for my train horn and maybe for inflating tires. Already have the compressor. My guess is it's about 5 gals. Is 120psi too much?

 

I would not. They are not ment for high pressure. Do not go over the pressure as listed on the tank.

 

Im not sure I would want to add compressed air in a propane rich environment
Too many safer methods of air tanks (like some schedule 40 A53 pipe and pipe caps)
I know free is hard to beat, but so is blowing a 5 gallon tank of compressed air.

 

If I'm not mistaken propane tanks are rated well over 120 psi.
Consider a full tank sitting in the sun, I'm sure the pressure goes sky high.
I wouldn't have any problem at all using them, the smell might take a long time to come out but the gas will be long gone.

 

the new tanks have pressure relief valves buit in (hence the reason you only get one good bbq out of a tank)

EDIT:
http://wolfstone.halloweenhost.com/H...neAirTank.html
Admins feel free to delete if the content is questionable, I quite honestly didn't look..

 

I'd pressureize it several times and then turn it upside down to vent it. Propane is heavier than air so this should get it out of the tank. The mercaptins will haunt you for quite some time however. You might try flushing it out with some light oil or diesel.

As long as you get all of the gas and fumes out of it it shouldn't be a problem. People have been using freon tanks for a long time and I'm sure propane tanks are built to higher standards.

Edwin

 

Thanks for the link. I guess 100-120 psi is nothing for these tanks. I love free stuff...

 

My dad has had a few of those around for years, they work great for that purpose. Make sure you put a shut off valve on top, they always seem to leak down after a while. 120 is about the most I've put in one, might just be the most the compressor can put out.

 

Propane has a vapor pressure of 172 psi at 100*F. I believe the tanks are rated to 250 psi. If the tank has an opd valve, it is restricted as to the amount of gas volume it will pass. Older non opd tanks work better for air.

 

There is no more valve. Removed totally. Will weld in new bungs for threaded fittings.

 

We use an old propane tank for a portable air tank, it holds 120 psi for a joke.

 

I have one on my service rig... they are great and you can hide them pretty good.
OG

 

Propane that is in a regular 5 gallon BBQ bottle is stored at around 200- 250 PSI at ambient temperature and they hydro test them around 2 times the service pressure if I remember correctly since the wall thickness is so thin. You should have no safety problems using air.
However allot of people do use old empty R-22 bottles for air tanks and there is no problems but I believe the traces of the R-22 react with the oxygen and are corrosive and weaken the tank lining.
But that is just what I have been told.
And I have used them for years with NO problems.
Jim

 

An interesting tidbit - propane has almost identicle physical properties as r22. If it weren't for flamability, it would make an excellent refridgerent.

 

Some people have used it as a refrigerant.