This story starts on wikipedia, where I discovered the Tesla valve, a one way valve for fluids with no moving parts. I was so impressed that I designed a part in OpenSCAD and uploaded it to Thingiverse, here. Unfortunatly, it didn’t work very well. I tried three different designs, all of which only kind of worked. So, I went back to the drawing board and kept designing.
But before I tell you about the designs, let me point out why this is important. Fluidics is the art of using fluids to do computation and control in the same way that electrical computers compute, but using a fluid instead. The Tesla valve is an example of what a Fluidicist, just made that up, would call a fluidic diode. You can also make the fluidic equivalent of transistor(fluidic amplifier), capacitor, resistors, inductors and more. Home 3d printers print in plastics which limits what they can do. In particular, they can’t print an electric stepper motor, one of the main components of an extrusion based 3d printer. BUT extrusion 3d printers are awesome at printing solid parts like gears and pipes and such. With such elements, fluid stepper motors can be made along with fairly complex logic to control and drive it. In a way, fluidics could be a killer application of 3d printers because complicated ducts can be printed at no extra cost. In essence, you could print out complicated fluidic microchips at home. I should also point out that I’m not suggesting some untested crack pot wild scheme. Fluidics is a very well developed technology with a history that dates back to the 1950s and with applications that range from aerospace to biology. For the more technical reader, I’ve collected some useful links at the bottom of the page.
Now back to the story. So the Tesla valve wasn’t working as well as I wanted it to. I thought I’d do away with the “no mechanical parts” paradigm and include a flap that closes if air goes in one direction and opens when air goes in the other. This worked much better but still only reduced the air flow, by what felt like 30% or so, I’m guessing here. If the material was softer, I’m using PLA, I’m sure this would work much better. You can download and print it here.
But then through my reading and on Thingiverse, I found out about the fluidic vortex diode. Sounds cool, huh? It works the same way that draining a bath tub works. Huh? When you drain a bath tub, the water has some angular moment and creates a whirl pool as it goes toward the drain. This whirl pool limits the speed at which water can drain. But going the opposite way, pumping from the drain, there is no whirl pool and so less resistance. A fluidic diode works like this, only the angular momentum is maximized by pumping the fluid in perpendicular to the sink and by putting the whole contraption in a closed cavity.
I made two designs. The first one you can download here. It also only kind of worked. So I went to the drawing board and did some math. It turns out that a spiraling fluid with no friction experiences a pseudo-potential barrier that varies inversely with the radius squared, meaning that if you double the radius of the vortex diode, it should take four times as much energy to overcome that centrifugal barrier. So I designed a vortex diode with over twice the radius, which you can find here. It also didn’t quite work as well as expected. So now I’m calling out to the community, YOU, can you help me find a better fluidic diode?
Links and further reading: