This is my air tank, it is 2.5 Gallons, I can pressurize it to 200# with my Viair 12 volt pump. You can run air tools, air tires up, air bags, and of course supply air horns, train horns and stutter horns.
You can get these tanks at Train horn web sites, or ebay.
http://tinyurl.com/yjzzq9u