How to motorize a LEGO Pneumatic valve?
I tried many designs I found


A quick Google search resulted in the following designs. Have you tried them all?

Sariel's Autovalve:

Philo's pneumatic valve:



Sariel's Servo Valve:

Tamas Juhasz's small autovalve with compressor:

Technic-Dragon's Compact Pneumatic Autovalve:



Bonus entries, not using exclusively PF motors, but could be adapted to:

Conchas' Micromotor valve:



Pneumatically controlled valve from the B model of 8868-1: Air Tech Claw Rig