Here’s yet another delightful mechanical curiosity from among Nikola Tesla’s 278 known patents. This one is #1,329,559 US, “Valvular Conduit,” issued 1920. You may have to stare at the upper section, for a moment, to figure out what’s going on: Flow from left to right, as illustrated, is against the valve’s bias—the stream is broken up and diverted in circular paths that return to interfere with each other. Flow from right to left, however, is not so impeded.
It includes a brief demonstration of the conduit’s operation in both directions (using a stream of air from the narrator’s mouth), but I for one would love to see a demo using a visible fluid. YouTuber vitglow has posted some animations based on simulated flow in a Tesla valve in both easy and hard directions, but I haven’t found any other moving pictures.
Boston Thingiverse user Brendan Chenelle has posted a 3D model.
The design is amenable to “nano” manufacturing techniques, and has attracted interest among researchers in microfluidics. I am left wondering about fully 3D implementations of the same idea, where the “hard” pathways branch outside the plane and/or are multiply divergent.