Co2 tanks in 3.5oz, 7oz and 10oz sizes.
These tanks have not been aired up and the valves likely need a rebuild. If you are looking for hydro testing for a co2 or hpa tank I would recommend http://www.paintballtek.com.
Co2 tanks with a width under 2 inches are typically exempt from hydro testing in the United States.
The sites below state the following on this rule but please consult local fields/airsmiths/shops etc since they will be dealing with the filling and handling of the tanks and may have their own exceptions (some fields refuse to fill co2 tanks older than 5 years).
1. http://www.hydrotester.com/information.htm writes:
"CO2 tanks: 2 inches or less in diameter and less than 2 feet long, do not need to be tested. This is a DOT Rule. These CO2 bottles usually have a 1800 psi limit. Greater than 2 inches in diameter must be tested every 5 years. These bottles are not fiber wrapped. These are considered high pressure. "
2. http://www.brassanchor.com/hydrotest/index.html writes:
"If your cylinder is 2 inches or less in diameter, it is exempt from retesting."
3. http://www.sounddive.com/Hydrotest.htm writes:
"CO2 tanks: 2 inches or less in diameter do not need to be tested. They usually have a 1800 psi limit. Greater than 2 inches in diameter or greater must be tested every 5 years. These bottles are not fiber wrapped. These are considered high pressure too."
And for information on hpa tank co2s and testing please visit the above sites and Ynda's site below: