This hack began as my youngest son's fifth grade science project. We still loft an occasional balloon since it is so much fun. As the range safety officer, I try to keep all shots vertical and all payloads water filled. Air pressure was chosen as the propellant so that shots would be consistent and maximum pressure in the system would always be known. The heart of the system is the 2” ball valve which is able to release the air quickly and give the best push to the payload. A low pressure (20 psi) turned out to work best with water balloons, and the expensive (10 cent) balloons hold together best. We compared different pressures and different barrels for launch height.
As can be seen in the photo, the components are (from bottom to top) : 5 gallon propane tank, steel collar, copper tube, brass ball valve, copper fitting, PVC barrel (2” SCH40). The difficult welding was done by my mentor Dave, the easier joints done by my son and I. We tested the work at 80 psi, and hypothesized that it was very safe to 100 psi since the components are all rated greater than 250 psi minimum working pressure. The results were better than we could have hoped. With a 10 foot 2” diameter barrel and 20 psi charge, the tough little water balloons (with a styrofoam cup as sabot) got about 9-10 seconds of air time. We timed the up and down segments of dozens of launches to get a good average, and then calculated the height and muzzle velocity at an average of 470 feet and 270 mph respectively. An examination of frames in a video confirmed that the muzzle velocity was about that fast. With a pressure of 30 psi, most balloons are destroyed on emerging from the barrel. My suspicion is that a snooker ball at 100 psi would travel to the next county, but I will not test that conjecture.
