I found this propane tank in the woods near my house that I want to use with an air compressor, but I don't know what threads it has. 1/2" pipe sort of threads in but is too small.

 

Most compressed gas bottles (oxygen, acetylene, nitrogen, etc.) have a CGA number stamped on them. I think that propane bottles do to, although I'm not sure. It is a specialized part that might be difficult to find unless you have access to a Parker or Swagelok catalog, but if you do you can get an adapter that will take you to pipe threads.

 

Propane is a flammable gas, so the threads on the valve are going to be reversed. If you don't feel like changing the valve, you could probably get away with getting a fitting and some brass tubing, brazing it together and put a regular thread fitting on the other side.

Another thing to take into consideration is the relief valve that'll blow off if you have too much pressure in the tank. I don't remember what pressure it is since I haven't worked on tanks in 10 years.

Hope this helps.

 

i work at a gas station and regularly dispense propane. the cylinder will not work. it has an relief valve inside and will open once pressure gets beyond a certain point.
I get a kick out of people who get propane and go to put it in there trunk, then think they can let it sit for 4 hours while they go shopping. pressure gets too high, overfill valve opens, next thing you know you got a bomb... open the trunk up with a cigarette and you're toast.

anyways,

 

Yea, but would the relief valve open under only 145 psi which is what I would be using it for?

 

Old BBQ grills aren't too hard to find at the curb on trash day, tanks and all. Why not take the coupling off of one, and plumb it to your compressor? I think all small non-commercial propane tanks use the same pipe thread, whatever the heck it is.