[Robert MacCurdy] at MIT wants to change how people think about hydraulics. Using fluid can be very useful in systems like robots, but it is often the case that the tubing that carries hydraulic fluid is not an integrated part of the overall design. [MacCurdy] and his colleagues have modified a 3D printer to allow it directly include hydraulic components as it prints.
The idea is simple. The team started with a printer that uses a liquid ink that is UV cured to produce solid layers. The printer has the ability to use multiple liquids, and [MacCurdy] uses hydraulic fluid (that does not UV cure) as one of the print materials. Just as you can use a 3D printer to build structures within other structures, printing the hydraulics allows for complex closed systems that use the UV-cured resin as mechanical parts that can transfer pressure to and from the hydraulic system.
The group has printed several structures including a gear pump. The pump uses a pair of cogs in a tube that move fluid that is trapped between the teeth. This pumps the fluid in one direction. The gears mesh tightly to prevent flow in the reverse direction. If you have access to a UV resin printer like this, you might be interested in the source paper, so you could try to duplicate their results.
Hydraulics show up in many places in the non-3D printed world. Examples include power steering and even amusement parks. With the MIT technique, designers have a new tool to use when 3D printing moving systems.