SpudFiles

Sounds like what you have found is a water storage tank. It has a balloon or a bag if you will inside of it. The water goes inside of the bag and therefore never touches the metal. I'm not sure of the pressure rating but water pressure is hardly over 80lbs. Would work great as an air storage tank in any case.

Ah thank you Taterhead so when im pumping it up to 100+psi tommarow i take it the bag inside will "pop" lol it probly will glad you told me that or i prolly would have wet my pants tommarow haha.