There is also the field of non-moving parts fluidic devices[0] which did find some industrial applications and might even be in use today. Unfortunately, becaus

There is also the field of non-moving parts fluidic devices[0] which did find some industrial applications and might even be in use today. Unfortunately, because they have no moving parts there's not much to see when they are in operation. They are interesting though because they can be made to operate at kilohertz frequencies, can be made quite reliable(no moving parts), and can operate in conditions electric circuits cannot. Because operation is dependent on shape and not material properties, fluidic devices can operate in harsh conditions like inside nuclear reactors, in molten steel, or in intense electromagnetic fields. Because they had no moving parts they are fairly insensitive to high accelerations and shocks, which is useful for things like missile guidance systems[2] and tank gun stabilization systems[3]. One very interesting demonstrated use of fluidics was an aircraft autopilot built with very little moving parts[1]. They found their biggest use in industrial control systems for some period to control things like factory equipment. [0]http://miriam-english.org/files/fluidics/FluidControlDevices.html http://miriam-english.org/files/fluidics/FluidControlDevices... [1]https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19730002533.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/197300... [2]https://apps.dtic.mil/dtic/tr/fulltext/u2/a204334.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/a204334.pdf [3]https://archive.org/details/DTIC_ADA038394 https://archive.org/details/DTIC_ADA038394