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Humor Section: Building Electrically Controlled Pneumatic Valves
This was a seriously expensive few months. I decided (like so many others) that I wanted remote controlled pneumatics. At my part time job we used 12V/24V solenoid-operated pneumatics a lot, so first I tried those. They work really well, pneumatically. But they take 12V/1A when passing air through, and they're big. About 2x3x1", most of them.
So I tried building my own valves. That's easy enough - drill a hole in a lump of steel, lathe down a second bit to slide inside the hole, and cut some grooves. Then cut more grooves for some small O- rings to stop the leaks. Use a hammer to push the valve backwards and forwards (not quite, but it was pretty stiff).
Buy some brass pipe as used in model steam engines. Get a guy with said model steam engine to let me use his jewelers lathe to make the inside bit again, this time more precisely. Use oil as a sealant this time. These ones worked great. Then I magnetised the steel core, and used a big coil (actually a 240/12V transformer core) to move it backwards and forwards. This also worked. So I wound a coil to fit the valve properly and run off about 9V. This worked at 25V/5A, most of the time. It smelled, um, bad.
I ordered some rare earth magnets from a mail order place in Colorado, at $US60 each. They were the right size, and supposed to be able to be machined if you were careful. Luckily I got 20 of them, because it took a while to discover what careful meant. I suggest anyone else pay a professional to do this. I did, eventually. I have no real idea what she did, but it worked. Down to 15V.
To get the resistance I needed, I ended up with enamelled silver wire, the thinnest I could find. I used about $US300 worth of it in the end. Pretty sad for about 1/4 ounce of silver, really. Winding these was very very hard, and I used the coil winding machine at school for this. It still broke the wire most times. I got there in the end, winding the coil straight onto the brass pipe.
There's a wee picture here that shows a quick cross section of the valves. At the top you have the outside view - a big pipe with three little ones sticking out of it, and 4 coils wrapped round it. They're actually 6 coils, in parallel electrically to get the resistance down. Note the three left hand ones have opposite polarity to the right hand ones, and the core has a N end and a S end, whatever that's officially called. The inside bit is shown below in the two positions - centred, left (right is a mirror of left). Centred allows no flow, left takes air from the center inlet to the left hand outlet, while letting air from the right outlet escape. This thing is actually round, and the notch is a groove right round it.The open ends I sealed up, with tiny weak springs in them to hold the core centred when there was no power.