Two Air Pumps are smaller 3D printed versions of much larger air / water pumps I built using PVC pipes and fittings when I was much younger. The design is somewhat similar (although inverse in operation) to the 3D printed single cylinder air engine (https://www.youmagine.com/designs/single-cylinder-air-engine) in that there is a single cylinder, a single piston, and dual openings for air intake. However, instead of having a moving valve plate either leading or lagging the piston by 90 degrees in order to control air flow through the dual pressure and exhaust ports, this design utilizes a much simpler valve, an o-ring on the piston itself, and a single exhaust port, the plunger stem. I have included two versions of the air pump in Two Air Pumps, one short and one tall. The differences between the two (aside from one is shorter and one is taller) is the taller version is capable of moving more air per stroke than the shorter version, and as such requires fewer pumping cycles than the smaller version to move the equivalent amount of air. If you have a taller format printer, I recommend printing the taller version, however, the shorter version easily produces enough air to inflate the "punch balloons" I have used in Four Whistles Version 2 (https://www.youmagine.com/designs/four-whistles-version-2), Balloon Powered Single Cylinder Air Engine Open Chassis (https://www.youmagine.com/designs/balloon-powered-single-cylinder-air-engine-open-chassis-by) and Balloon Powered Single Cylinder Air Engine Toy Train (https://www.youmagine.com/designs/balloon-powered-single-cylinder-air-engine-toy-train). Assembling either air pump is via threaded connections. One of the many items on my Autodesk Fusion360 "things to learn list" was to learn threads, so I incorporated threaded connections in this design for a more secure assembly. The threads printed great with no additional scaling or support material required for a good, air tight fit. In order to complete this model, you will need to purchase an "AS568 #222" o-ring (1 1/2" ID, 1 3/4" OD, 1/8" section), flexible gasket material (I've used thick cardboard, inner tubes, thick rubber gloves and 1.5mm thick shelf liner, I liked the shelf liner the best) and petroleum jelly (for lubrication of the o-ring piston valve). I also used scissors, a single bevel razor blade, a modeling knife, and a needle file set for assembly. https://www.youtube.com/watch?v=TD1SxthqsrA https://www.youtube.com/watch?v=k5DUVAcHrsA And as usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to ask as I do make mistakes in plenty. Designed using Autodesk Fusion 360, sliced using Cura 2.3.1, and printed in PLA on an Ultimaker 2+ Extended and an Ultimaker 3 Extended.