If you have the owners manual for your Vulcan, it should give you the sizes in there. I have a Vulcan Tactic in .25 cal which is basically the Vulcan 2 with an extended stock on it and a cheek rest. My manual says that the air tube and regulator O-rings for the Vulcan 2 are:
4- 25.2x3 90 Duro
1- 9x2 90 Duro
3- 17x1.5 70 Duro
2- 3.5x1.5 90 Duro
1- 3.5x1.5 70 Duro
In looking over this parts list it appears to me that these o-ring sizes are for a 30 cal Vulcan because it lists the breech o-ring as being a 7.5x2 70 Duro. Now … whether the 30 cal is the same in the .22 and .25 cals inside the air tube and regulator, I am not sure. But if you are going to open up the air tank and start replacing O-rings, you might as well replace all of them.
It might be a good idea to call or e-mail Tony at Talon Tunes and ask him if these sizes are correct
www.talontunes.com
Hope this helps