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Potato Gun

(This page is still in progress- I'll be cleaning up the writing, improving the diagram, and adding some photos soon. I believe the content is largely complete though ... so enjoy but forgive any typos, etc.)

This is another project that abounds on the internet; in as many different styles as there is opinions ... So, because I have an opinion too, I'll add my style to the mix.

Safety

Those who have had good luck with one of the multitude of designs out there are probably wondering why I decided to re-invent the wheel. Very simply, I found the usual design to have an unnacceptable safety margin (IMHO, of course).

Seeing these devices all over the place working just fine, I decided to ignore the commonly known warning against using PVC pipe for compressed air. I've always wondered why that would matter anyway .. most compressors operate well under the pressure rating of the pipe; so it seemed odd that it would matter between air and water.

As you may have guessed by now, yes, I did find out the hard way. After carefully building a unit and testing it in a contained area; I went to actually use it the next day. I do not know what caused the joint to let go .. but let go it did. There is now a 6 inch by 2 inch dent in the side of my house, and another in the carport roof. From a 2 1/2" PVC CAP fitting, the largest piece we ever found was about 1/2" long and a 1/4" wide; and only a couple of those. It quite literally disintegrated.

Considering the damage done to metal siding and roofing, I am quite afraid to think what it would have done to my flesh had it chosen a different direction.

I still do not know the difference between water and air pressure; but I now would guess it has to do with momentum and pressure decline rate. When a fault develops, water will not get moving as quickly due to its weight. In addition, if a pipe is full of water, it only takes a very small amount of venting to bring the pressure down. Air, on the other hand, can expand and therefor hold a high pressure much longer - sending shards of plasting flying everywhere. This is just my theory ... I'm no expert.

That was my last experiment with compressed air and PVC pipe.

A New Design

Still, the usefullness of a potato gun for ham radio operators in inescapable. But, I wasn't taking another chance with PVC. I decided my version would have to have cold, hard steel for the compressed air ... but what could be used for such a tank?

Galvanized pipe readily came to mind, but the cost of it for a large enough tank was rather steep. Finally, I got my mind wrapped around the idea of a design that didn't need a tank that large; and so my design had begun.

This one won't throw potatoes around, nor tennis balls, as is commonly used. I made a much smaller barrel diameter; thus reducing the need for a large air tank. A galvanized-pipe tank is now much more reasonable on the budget.

Interestingly enough, this new design actually presents a couple of nice features over the more common tennis ball launchers. First, its much less bulky. Easier to work with, easier to carry to field day, etc. Second, by looking along the pipe, you can actually achieve a rather accurate aim. Finally, it doesn't take as much air to operate; which is a big advantage on field day if you are using hand pumps!

In the next section, I'll show you the particulars.

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