[Kevin Sevcik]

Several comments here. First, the double solenoid valve spec sheet says the maximum operating frequency is 10 Hz on the solenoid valve. So take that into account in your multi-positioning thing.

Second, I just had a brain wave. From Eagle Master's post up there. It's hard to get high pressures on both sides of a FIRST piston and still move it and such. But you could use a piston to hold something in place if it was otherwise actuated. You connect the extend and retract ports of the piston together, except you put a solenoid valve between them. You close the valve when you want the piston to maintain position and the piston acts as an air spring. You open the valve to allow the piston to move freely. This has some interesting characteristics, however. The more you pre-pressurize this closed system, the stiffer the spring. The closer to the end of the stroke, the stiffer the spring becomes. At the middle of the stroke, the spring is reasonably linear over short displacements, but becomes less linear towards the ends of the stroke. The only real problem, I think, is that there would be a net extension force on the piston due to the shaft of the piston.

Similarly, you could make a shock absorber by putting a needle valve between the two ports.

Note, I'm doubting the FIRST legality of this. The pressures could get dangerously high. Especially if the system started at 60 psi.