[Scott358]

In the end, you'll need to calculate the force you need, then the question can be answered, but as some data, consider the following....

If you use a single 2" dia pneumatic cylinder with a working pressure of 60psi (which is the working limit within FIRST), it will exert 188lbs of force in extension, and 170lbs of force retracting. If you use 90psi (which is more typical in industrial applications), the force increases by 50% (since the force equals the pressure x piston area).

Hope that helps.