I have an air cannon, which launches a ping pong ball. The setup for this includes the reservoir, solenoid and barrel. I have to find a function for the range of the launcher. I am currently stuck at working out the downstream pressure for the solenoid. At the moment I have the mass flow rate through the solenoid and the gauge pressure for the reservoir. I was wondering if there was a way of using these values to calculate the downstream pressure acting on the ball? Any help would be greatly appreciated.