Build a Compressed Air Water Balloon Cannon
Water balloons are often not very useful in a neighborhood water fight because they have terrible range, challenging to transport, are prone to exploding prematurely, and woefully easy for an adversary to evade. The obvious solution is to increase the power, the accuracy, and the range ... basically creating water field artillery.
For decades, the go-to solution was a catapult using surgical tubes and a fabric basket to propel the water balloon. But these required a three person crew minimum in order to operate them. Furthermore, the team tends not to be consistent in holding positions for predictable long range accuracy. Even worse, as the surgical tubes age and dry-rot, they will eventually snap under stress and really hurt the water balloon crew from the whiplash. This can all be alleviated with some quick parts from a local hardware store to basically build a little water balloon mortar system.
The parts list is relatively simple:
- (2) 2 inch PVC end caps
- (1) 2 foot length of 2 inch PVC pipe
- (1) 1 foot length of 3 inch PVC pipe
- (1) 2 inch PVC pipe ball valve
- (1) 2 inch PVC T connector
- (1) 3 inch to 2 inch PVC reducer
- PVC cement
- (1) Schrader valve insert
The first step is to cut one of the 2" PVC pipes down into three pieces. These pieces, in conjunction with the t-adapter, the end caps, and the ball valve will become the pressure chamber. While it is not necessary to build it into a "T" shape, that shape will make it easier to use the water balloon cannon as a shoulder launched system later.
Measure 6" in, from both ends of the pipe, and make a line around the circumference to guide your cutting. This should render the tube into (2) 6" pieces and (1) 12" piece. It's easy to keep the lines straight by using a T-Square and making various dots around the circumference and just connecting them with a Sharpie. The PVC pipe can be cut easily with a jigsaw though some have been known to use a miter saw for speed.
One more 3" long piece of 2" PVC pipe is necessary for attaching the water balloon barrel in front of the ball valve. This 3" piece can either be cut from the existing 12" piece from above, or from an additional PVC pipe. This one only needs to be 3" so that it can slide into the ball valve fitting and the reducer fitting. Do not make it much longer than 3" otherwise the compressed air will be reduced during the launch.
Before connecting the pieces, the schrader valve insert must be installed into the pipe. There are many optional locations, but roughly 1/3 down the 12" pipe works well. Use a 1/2" hole cutter or drill bit and smooth out the PVC edges. Then squeeze the schrader valve through the pipe. It will be tight but the rubber will create an airtight seal.
Now connect the PVC components together using the PVC cement. Using the cement brush (usually part of the bottle), quickly coat the contacting male and female ends of the pipe. They will slip together easily and rapidly set into place. Because it sets fast, make sure you have aligned the pieces prior to connecting if you care about the positioning of the valves, etc. After assembly, allow the parts roughly 24 hours to fully cure to maximize the pipe's ability to maintain a seal against the air pressure.
It's not necessary to cement the non-pressure side where the PVC barrel attaches to the ball valve. This will allow swapping 3" or 4" barrels to accommodate different sizes of water balloons in the future. Furthermore, it will allow experimenting with different barrel lengths to determine what improves accuracy while keeping barrel friction on the balloon to a minimum. It's possible to utilize PVC reducers for this attachment or a rubberized reducer with hose clamps.
Once assembled, it is easy to fire the cannon. First, close the ball valve. Second, either use an air compressor or a bicycle pump to compress the chamber. Utilize different pressures for different shot ranges - but do not exceed the pressure capacity of your chosen PVC. Third, pour a little water down the barrel to fill the reducer. This water "baffle" absorbs the initial burst of air pressure and shoves the balloon down the barrel without tearing it apart. The reducer also serves to prevent the water balloon from settling down against the ball valve itself. Lastly, aim at your dry adversary and release the ball valve.
