[GeeTwo]

We have a 3/4" brass solenoid on our air cannon quite similar to the one posted by SamM. We'd probably go 1" if we were buying today. We can launch a t-shirt over our stands and press box with 60 psi. Our launch tube has an inside diameter of 2-1/2".

Folding shirts: for large and XL shirts in our 2-1/2" pipe, we lay a shirt out flat, then fold the left third of the thorax over on to the center third, then the right third over the center third, leaving the right sleeve extended on the left.
We then roll the shirt up from the bottom hem, until it is just above the bottom seam of the sleeve. We then flip the sleeve around the cylinder rather like rolling a pair of socks to create a "T-shirt burrito" that we can launch. Smaller shirts need to be folded into fourths; larger shirts only in half. Your breakpoints may vary with your pipe diameter.

Let me reiterate the points about using parts rated for water but not air. Water is essentially in-compressible, which means that not that much work is required to increase water pressure to 60 psi. Compressing air to 60 psi means reducing its volume to less than 20% of its ambient volume, which is a whole lot of work (aka energy). If an air filled tank/tube ruptures, there is a lot more energy for the shrapnel. Do NOT use anything not rated for air pressure, especially the valve, or upstream of the valve. There's just way too much ugly potential there.