Nerf Pocket Vortex cannon: Questions from a new builder

[STHORNE]

I'm looking to build a cannon to fire Nerf Pocket Vortex footballs. The targets will be people, so obviously it has to be reasonably weak.

You might want to re-phrase that lol.
sounds like a neat project though

[socoj2]

Use Chamber Seal.
And a really light piston

[Thom]

Thank you, socoj2!

By "really light", I assume you mean the weight of the poppet? I guess I'll fiddle around with it.

[socoj2]

yeah GGDT ask you for a Piston weight. since the QEV only has a diaphragm and weight is negligible. use something light.

[psycix]

I believe there were some standard values for things like QEV's and sprinklers. Either by giving the right values as piston valves or as entering it simply as a "generic valve"

[Thom]

Hmm. At 60 psi, GGDT is telling me that using a 3/4" QEV (The biggest I see on McMaster) would basically cut the power in half. Whereas a 2" barrel-seal piston valve with "default" params should get 306 ft/s, a .75" QEV with 7.84 Cv and .1g piston mass maxes out at about 180. I don't really need the extra power, but I'd much rather just downsize it and save myself some pumping. Is this drop expected? I guess I did cut the valve size in less than half. I don't have an intuitive sense of these things yet.

EDIT: Could I seal a piston valve with the bike pump if I used a very small hole in the piston?