Parts

• 4' long of 1.5" PVC pipe for the barrel

• 3' long of 3" PVC pipe for the pressure chamber

• A 3" end cap

• A 3" to 1" reducer

• A 1.5" to 1" reducer

• 2 3" pieces of 1" pipe

• A 1" solenoid valve

• 3 9v batteries

• A momentary switch

• Some wire

• Bike tire fill valve

Assembly

• Glue the 3" end cap onto the 3' of 3" pipe

• Drill a hole in the end cap the size of the fill valve

• Glue the fill valve in the hole you made in step 2

• Glue the 3" to 1" reducer onto the other end of the 3" pipe

• Glue the 1.5" to 1" reducer onto the end of the 1.5" pipe

• Glue one of the pieces of 1" pipe into each reducer

• Wire together as shown below

Firing

      Fill the chamber to about 3/4 of the pressure your PVC is rated for, then load the same way you would load a normal combustion gun.  push the switch to open the valve and shoot out the potato.   When using a momentary switch the circuit will shut of as soon as you release it.