Just to confirm GeeTwo and IndySam,
Attached is a photo of our 2014 Robot, where we used two pneumatic cylinders to shoot the ball.
This shot is a little blury due to the camera DOF at the solenoids, but if you look closely and follow the tubing, you will see that the output of the solenoid, there is about a 1" of tube ported directly to the cylinder. The opposite end of the cylinder was left open to atmosphere.
On the input end of the solenoid, you will see about a 6" piece of tubing, to the bottom of a storage tank. This was a dedicated low "working" pressure storage tank for the solenoid and cylinder. With his set up we were able to shoot just with pneumatics, and also be able to shoot back to back shots, needed for out two ball autonomous.
https://youtu.be/IOU_eZ6CrqI