SpudFiles

I made a tennis ball cannon using a 3” sprinkler valve. It fires a ball at ~150 yards at just 30 PSI. The valve is manufactured by Dorot, repackaged by Galcon, and sold by Drip Depot. The stated flow rate is 390 gallons/minute which is 10x the flow rate of an average 1” sprinkler valve. The valve is currently available from Drip Depot for $200, I bought it on sale for $160. The valve is actuated by a 1” ball valve.

The barrel is 2.5” thin wall PVC from drip depot. It has an inner diameter that better fits tennis balls compared to regular 2.5” PVC.

Initial Requirements
I wanted to build a cannon that I could use to play fetch with my dogs. I needed it to be portable so I could bring it to the park or beach in a backpack. I also needed it to be filled up by a bike pump and not an air compressor. Consequently, I wanted to prioritize efficiency since I would be pumping it up by hand. Performance wise, I wanted the flexibility to use it inside my apartment to plunk balls 15 feet while also shooting a ball at least twice as far as I can throw. Finally, I didn’t want to have to pressurize anything over 60 PSI for general safety.

Previous Design
My initial version of this was using a piston valve inside a 3” tee. Unfortunately I wasn’t able to get the piston to seal against the barrel. I’m guessing it’s because I was using a bike pump and couldn’t build enough pressure behind the piston; air was leaking between the piston. I guess I could have used a spring to apply some initial pressure on the piston, but I was quite frankly sick of making pistons after my first two failed to seal.

Sprinkler Valve Troubleshooting
After my issues with the piston valve, I did some low pressure testing with the sprinkler valve. I was worried because water would flow between the inlet and the outlet and thought I would have the same issues as before because the valve had a minimum pressure rating of 5 PSI.

I attached a schrader valve opposite of the ball valve pilot so I could build pressure on top of the diaphragm to seal the the inlet from the outlet. I planned on filling the air tank by having air leak through the equalization hole. This sort of worked, but I had to wait a bit for air to equalize before pumping again.

That took longer than I preferred so I attached another schrader valve to the air tank assuming I would have to pressurize the top of the diaphragm first and then pressurize the air tank. That ended up not being necessary and enough air leaks from the air tank through the equalization hole and above the diaphragm to keep everything sealed.

Safety Considerations
In the name of efficiency, I considered replacing the pilot ball valve with a 1” sprinkler valve/blow gun. I decided against this because I wanted the trigger to be something I couldn’t accidentally actuate since I would be using this around my dogs.

Ball Notes
I use the ChuckIt Ultra balls. They’re the same diameter as regular tennis balls, but slightly heavier. I also tested an orange dot tennis ball (tennis ball with 50% compression). Those had slightly less range than the ChuckIts. The dogs prefer the ChuckIts because they hold up to chewing better.

Cannon Efficiency
According the ChatGPT, this has a 40% efficiency. Intuitively this seems higher than it should be. ChatGPT assumes that 139 joules is required to launch the ball 150 yards (assuming drag) and there’s 432 joules stored in the air tank at 30 PSI. The air tank is around 18” of 3” PVC. Distance was estimated using Google Maps distance calculator.

https://youtube.com/shorts/RjqNVUkrzNQ? ... yRXFGC3mCx


(Not 150 yards, just a better video of how it’s used)

Well done, good to see "traditional" pneumatics are still being made and put to good use!

Unfortunately I wasn’t able to get the piston to seal against the barrel. I’m guessing it’s because I was using a bike pump and couldn’t build enough pressure behind the piston; air was leaking between the piston.

Were you filling from the pilot chamber or the main chamber?

Thank you! I’ve always found pneumatics to be the more elegant option in comparison to combustion cannons. This may be due to my background with spring and pneumatic nerf guns.


I was filling from the pilot area. My first piston may have had too big of a notch cut in front of the o-ring to act as a check valve. My second piston failed low pressure testing although I wonder now if it would have worked given that sprinkler valve also failed low pressure testing, but works in real world use.

Either way, I had concerns that my piston was fundamentally regardless of the seal. It was fairly heavy since I used 2” Schedule 80 CPVC to slide inside of 3” pipe. I also wasn’t sure if there would be enough of a difference in diameters between the piston and 2.5” barrel.

Without machine tools it's definitely more challenging to get a piston to work so going for the sprinkler valve was probably the best option.

Nice catch!
and nice launcher, neat to see people still building in 2024.