I builded 4 motorized pneumatic LEGO valve switches. All switches do have a different type of motor. I used a small PF LEGO motor, a regular NXT motor, a old (legacy) RCX Mindstorms motor and a micromotor. And I used NXT Mindstorms to control the switches. These 4 actuated pneumatic switches are based on the same principle: A regular LEGO pneumatic switch is controlled by a motor a touch sensor. The motor can move the pneumatic switch into three positions: Left, Center and Right. NXT doesn't know the position of the pneumatic switch, but in the center there is a touch sensor (electric switch) which will determine when the pneumatic switch is in the center position.
Of cource the software is very important. After starting the demo program it will seek for the center position of the pneumatic switch. The motor will run forward and backward until it reach the touch sensor. But reaching the touch sensor is not the exact center: That's because the touch sensor is reached before the switch is in the exact center. Therefore the software will move on the motor, pass the center, until the touch sensor is released. And then it can calculated the exact center position and it will move to the calculated center position of the pneumatic switch.
The demo programs I made are written in NXT-G. After calculating the center position, the switch will switch between the center, the right position (left outlet of the pneumatic switch is open), the left position (right outlet is open) and return to the center again. Before every step in the program NXT will display a status message in the display and then wait 3 seconds before it demonstrate the next step. So in real use the switches can of cource act must faster!
The third motorized pneumatic valve switch I build is based on a regular NXT motor (partno: 53787). The construction is partly similar to the previous pneumatic switch, but with a NXT motor it is more easy to write software to control the switch. Of cource this design is bigger, but is is also faster. Ones the center of the switch is determined, the taco meter within the NXT motor will tell the software exact where it moves to! Again a technic gear 24 tooth clutch prevents that the motor to run to fair.
The last motorized pneumatic valve switch is powered by a technic LEGO mini motor 9v (partno: 43362) (old style legacy RCX Mindstorms). An advantage in comparing to the switch with the NXT motor is it's size: It is rather compact! The switch can move smooth and fast and the construction is nice.
Watch my video with this pneumatic switch in action: