Pneumatic Potato Cannon
Or just a general air-powered projectile launcher
I built the potato cannon many years ago, probably sometime before 2013. It's made of PVC rated for up to 280 psi, though we never even go close to that. I think the max we've used is 80, but 40 is plenty to send a potato flying. It worked well for several years.
Then, disaster struck. I believe I had loaded the barrel up with water to see what would happen. I was all set to fire by pulling the big wooden lever. What I had failed to account for is that a barrel's volume of water is a helluvalot more mass than a mere potato. So when I pulled the trigger, not only did the water hurl out spectcularly in front of me, but the cannon itself was launched backwards, out of by grasp, and onto the driveway where it crashed and broke in half.
Needless to say, I was dissappointed. Unfortunately, I didn't have parts to replace the now broken U-turn in the pipe, so the parts of the cannon went into the back of the garage, to be repaired another day.
As happens all too often, that day did not come for several years, until finally (in 2018) my friend and I just went to the hardware store and got the parts, for flop's sake. Thankfully, the cannon is now back in one piece, and it works fine. This version is what you see in the picture above, though it doesn't look very different from the original. There are a few improvements, though. Namely, the firing lever is a bit longer and it's attached to the valve slightly more sensibly.