I have the 75 cu ft air cylinder that I use to fill my rifles with. I am thinking about getting the 12 cu ft tank for portability. Does anyone know if I can use my 75 cu ft tank to fill the 12 cu ft tank..??
Simple answer is NO. Pressure will just equalize in both tanks. Example: I had 4300psi in my guppy and 3900psi in my tiger shark. Hooked together and opened valves. Now I have about 4000psi in both tanks. You could make a fitting that quick connects to your fill line to place a check valve in front of the small tank, but not sure it would be worth the effort as you will only be able to top off the small tank a few times from the big tank I would assume.
If you do get a small tank, they are awesome. I have carried mine in my pack when hunting and often take it and just leave it in the truck just in case. Light, small, and easy to pack or throw in your vehicle. After buying one, I consider a small tank a must have for pcp hunting an will never go without one!!