Piston valve trouble

[Mini Khan]

My piston valve makes a seal but it doesn't activate when I open the 1/4" ball valve at the end of my 4" diameter x 9 foot long cannon. I think the problem is the primary chamber before the piston is the only chamber filling up... but why won't it work?

*edited for caps locks by boilingleadbath

[TfAv1228]

General posting guidelines:
When creating any new topic or post, please refrain from the use of ALL CAPS. It's annoying.

[Mini Khan]

ok

[Shrimphead]

I think that it could be that the chamber isn't filling (like you said), but it really just sounds like you need a real pilot valve. A 1/4" ball valve isn't going to vent a 4" chamber fast at all. What you really need is something like a 2" modded sprinkler valve. Even a 1" would work, just not as well.

[boilingleadbath]

It's not possible to only fill the chamber region of a piston valve (barrel or chamber sealing) - the valve would open.

Instead, the pilot valve isn't venting fast enough - the pressure behind the piston doesn't get low enough to "pull" the piston off the barrel. This could be redemied by getting a better-sealing (on the walls of the chamber) piston, or using a larger pilot valve.

[Shrimphead]

I think the problem is the primary chamber before the piston is the only chamber filling up

I think that he's saying that only the pilot is filling.