Quote Originally Posted by kls-ccc View Post
What if you used a larger pipe on the vacuum end, reduced it on the other end to hold the ping pong ball, so you would have more air rushing in?
To much air would get past the ping pong ball, so it wouldn't move fast enough.
The pipe needs to be enough bigger than the ball that a little air will get past it, but not so much bigger that to much of the air goes around it.

Visualize it as blowing a ping pong ball down a pipe with 14.7 psi of air pressure.
The ping pong ball will go much faster down a pipe that has an inner diameter just slightly larger than the ball than it will down a larger pipe.