I saw this kit in the latest MakerShed newsletter: http://makezine.com/projects/make-15/compressed-air-rocket/ Had to make one. I used this valve instead, http://www.amazon.com/Orbit-57101-Sprinkler-System-1-Inch/dp/B00004S1V3 which is 1" versus the 3/4" valve in the kit. I figured bigger port means faster rocket (I'm not an engineer though). BTW, this launcher is pretty cool. We got over 100 yards on our first shot! The above rocket lasted two flights. The paper tube crumpled on the second impact, but the plastic survived. Click on the "full size view" of the last picture to see the entire rocket. Next project is to try and incorperate a whistle in the nose cone.The cross sections are .028", so with a 0.4mm extruder, they print nicely with 1 perimeter and no infill. Since these are designed to slide on 1" SCH40 PVC, the inside dia. is about 1.345", but these should be able to be scaled down about 80% to 1.070" dia for 3/4" PVC. (may need to try it and tweak) There should be ~.010 -.015" clearance. To make the rocket, print a nose cone and a fin section. Put both on a section of pipe used as a mandrel. Wrap a piece of paper around the mandrel in between the nose and fin section. Tape up with a couple of layers of clear packing tape.