just an idea.

[Jaygnar]

I had an idea that I thought might be fun and I thought I would share. Basically choadish little launcher that would fire ping-pong balls.
The body and chamber are a pair of 4 inch pvc reducers with just enough pipe between to join them.
The center pipe is big enough to accommodate a ping-pong ball and acts as the interior chamber walls as well as the barrel.
The valve is a spool type piston.
Here's a childish drawing.
I think you'll get my drift.

Anyway, the idea of it is for indoor low pressure use as an toy. The lack of a barrel gives it short range and ping-pong ammo makes it safe, while the piston valve should give it a fun "POP" sound. Maybe house the whole thing inside a stuffed animal like a frog and have the ball shoot out its mouth?!?!
Christmas gift??
Just spitballing

[Jaygnar]

sorry, I had to resize

[Technician1002]

It looks like a small version of my QDV. It should work. I'll have to find some ping pong balls and see what size pipe is a snug fit. You won't need a ball stop. It could simply roll in and stop against the trigger rod.

If you need to resize, simply use the edit button instead of making a second post. You can edit your own posts to fix things like that.

[Jaygnar]

Thanks for the advice! And also, yes I totally ripped off your QDV with the plan.
Kudos on that design by the way!
Love the linear, self contained design!
I have still got soooooooooo much to learn! I'm just glad that I found this site! So many great thinkers and imaginative designs.(you included)