If you are a SCUBA enthusiast, as well as possibly a hacker/maker/tinker, you’ll definitely want to take a look at what biketool has posted on Thingiverse. Using items that you could find anywhere for the most part, as well as some that are easily 3D printed, biketool has created a scuba regulator that could possibly one day actually be a feasible (and certified, he hopes) design for people. While right now the OpenSCAD design is available at Thingiverse for anyone to 3D print and then test, he recommends that it only be considered a science demo—not for people or animals. You can test it using other methods, however, and see what you think. Read more at 3DPrint.com: https://3dprint.com/147220/scuba-3d-printed-regulator/