I always use 4 way valves with my air cylinder props. The air compressor goes into teh solenoid valve, then one two of the ports go to the cylinder. One port pushes the cylinder rod out and the other pushes it back in. But it really depends on what you are trying to accomplish. If the prop is heavy enough, use a cheaper 3 way solenoid valve and let the force of gravity reset the cylinder.

What effect are you trying to accomplish?