[Mike o.]

A big question would first be what is the application of which you are using the pistons for? Also, how big are they? You can use branch connectors and using tubing to put them into a parallel system. I would be cautious though, because there is the possibility of running into a problem of pistons not firing at the same rate or pistons having the same amount of pushing force as it would if just connected to an individual solenoid. There are many things that you need to take into account and sometimes do a little math and physics.

Bottom line, just look at the application that you are using it for, test it out (prototyping over and over again never hurts, and its always fun), and think it through. Hope this helps.