psi vs. fps [TANKS]

[Christopher Clark <cjkkclark-at-comcast.net>]

Is there an easy way to calculate how much velocity one would get by  
knowing the psi?  I imagine the size of the chamber where the air is  
being stored before sent down the barrel influences the psi.  In the  
case of those solenoids Gary recommended for the rocket system  
(http://www.surpluscenter.com/item.asp?UID=2006062119193174&item=20 
-1138&catname=air) will I still get 200-300 fps with the 150 psi  
rating?  (Right now I am thinking the air can be stored in the  
accumulator at a high psi and so long as all the solenoids open  
simultaneously the air will be equally distributed and I don't have to  
worry about bursting a solenoid?)
Thanks,
Chris C.