How does a piston gets 'sucked' back?

[Tsukiten]

Okays, I've recently started on making a piston-valve gun, but there's something bothering me... What makes the piston gets 'sucked' back so that it opens?

According to from what I know, a piston-valve opens by letting the air out of some small chamber so the piston gets sucked back, opening a way for the air from the big chamber to rush out. Am I right?
If so, it just makes no sence to me... That little chamber behind the piston is under pressure, and you let the air out which equalizes the pressure inside and outside the gun, but makes no vaccuum to suck the piston back...could someone plz explain?!

And I got the first part wrong, explain it anyway Thanks

[Fnord]

If you haven't already read it:

http://www.spudfiles.com/spud_wiki/inde ... ston_valve

[iPaintball]

It doesn't actually get sucked back, it gets pushed back. Here's a great explanation.

[Tsukiten]

AHHHHHHH I see now First I thought in T-piston valves the piston actually COVERS the hole to the chamber, making it impossible to push it backwards... Heh thanks y'all

But a pocket-sized bb semi will be still a loooong way to go...though

But another thing: to equalize the pressure in the main chamber and the pilot thing there needs to be a hole right? No tire valves or anything to prevent the air from the main chamber leaking to the pilot chamber? Thanks

[Hawkeye]

Of course. The piston is either an imperfect fit or there is a small hole or groove in the side of the piston to let the air past it when filling.