Closed Pneumatic System?

[BlackMesa]

I have a little experience with Ant weight robot pneumatics such as these: http://robotcombat.com/marketplace_ant_pneu.html But Im not quite sure about the problem Im having. What I want to do is have a system where I will push a button and a piston will shoot out to its max length momenterially (sic), and then return to the starting position. The only catch is I dont want to have to refil this with compressed air every time I use it so Im wondering if I can build a contained system where the air is simply recycled, like a hydraulic system except without the fluid. Would I just connec the vent from a 3 way valve back to the tank? Does anyone know if those tanks have two fittings at the top? Would this work or would the pressure diminish after the first shot? Thanks.

[saladtossser]

have 2 valves, one in, one out, have a chamber onboard, use a small onboard compressor to recollect the air from the output valve and into the chamber, the chamber to the input valve, that to the piston

not sure if 3way will work, good luck

[BlackMesa]

Do you know where I can find a really small compressor?