[apples000]

I believe that the air from the tanks/compressor connects to port 1 on the festo valve, and that the one you have it connected to is the exhaust. Also, it is designed to let pressure out of either port 4 or port 2. If you want to use the valve as a single valve (to fire a t-shirt) you should plug 4 and use 2 as your output. Also, this valve probably isn't the best for a t-shirt cannon, as it will let the air out slowly.