The last 24 hours have been quite instructive.
Ordinarily in my adventures, I proceed without doing research. I push the project in the manner I naively think it should go, and only when I get to a point from which I cannot proceed do I seek help. (I've been told I need to seek help anyway, but that is neither here nor there.) This time, as there are explosions involved, I decided to read up on the matter first. Before I proceed any further, let me tell you that the phrase "potato cannon plans" will open up a whole new world to you whether it is typed into the Google search engine or the YouTube search engine. For those of you who are carrying the Y-chromosome let me recommend this link.
I found numerous sources and used the one at this location. It gives a parts list and instructions. In that which follows, I will try to gloss a few things in order to give the reader a firmer understanding of the process.
I did my shopping to fill the parts list at Home Depot on Thursday on my way home from work. On Friday, I discovered I didn't have the size of drill bits I needed. (They're around here SOMEWHERE!) I went to Ace and discovered their selection of PVC accoutrement is better. In any case, I had all of the materials assembled by 3PM Friday afternoon. The one part that had bothered me in the entire process was the igniter. I worried about what it was, how to get it, and how to install it.
I will share the first two parts now and save talking about installation until the appropriate time. I am using a replacement igniter for a gas grill. These only cost about $4. They are by the gas grills in Home Depot. The young man in the store didn't know what I was talking about and sent me over to welding supplies. Catch him gone and look around until you find it yourself like I did. (You don't have to wait long.)
The theory behind the potato cannon is simple. A spark ignites fuel. The heat from the burning fuel causes air to expand. As the combustion takes place in a chamber that is closed in all directions but one, the expanding air is forced out of the chamber in one direction. In the potato cannon, the chamber is made of PVC. It is closed on one end by a clean-out cap. The open end of the chamber goes into a bushing that reduces the pipe diameter. In the case of the instructions I've shown you, it reduces from four inches to one-and-a-half inches. It is then directed into the barrel where the expanding pressure will force out the projective, the eponymous potato.
You can see how the spark is key. If there is no spark, then there is no combustion, no heat, no expanding air. It looked to me as if the igniter should be installed first so that care could be taken that it worked correctly as the addition of subsequent parts would make it harder to get to the igniter. Therefore I ignored the directions and installed it first, making sure that it sparked. It was as I was putting the rest of it together that it occurred to me that this was a safety measure. You see, in order to put the PVC pipe together, you use something called primer which is largely alcohol. This gives off fumes. I noticed this as the work was progressing and the question occurred to me about what might happen if my igniter accidently sparked.
I then told each of my daughters whenever they entered the dining room where I was working on this (Yes, it should have been done outside. It was 105 degrees Fahrenheit.) not to push the button, and they immediately began to tease me by pretending they were going to press the button. Once it was done, I immediately took it outside. This morning I took my walk. When I got back home, Jean was outside watering. I helped her for a few minutes and then I showed her my new toy.
"This is the igniter," I said as I clicked the button. The sound of a click was followed by the sound of a boom.
The spark had ignited the residual fumes from the primer in the combustion chamber.
I've gained in respect for this device. I respected it before but more so now. I will not put a finer point on it lest I should open up pathways that would get young people hurt, but let me say it would be very easy for someone to hurt or kill himself with one of these things if he decided to push boundaries.