I was wanting to make a tower garden with a watering system built in. This meant I would need something to pump water to the top of the tower garden. Because I wanted my garden to be about one meter high, this meant I needed a pump that can provide one meter of head pressure. Centrifugal pumps were out of the question, so I decided to design a positive displacement pump. (A positive displacement pump is one that moves a fixed amount of fluid per cycle meaning they are good for higher pressures).

I picked a screw-type pump (https://en.wikipedia.org/wiki/Screw_pump) because, well, it seemed cool.

After printing out the screws, I knew this was likely to fail. Even when pressed together, the tolerances in 3D FDM meant that you could see light between the screws. After printing out the top, I did a test run of just the top and screws. One meter of head was enough not only to make the water run between the screws, but also to penetrate between layers of the print.

Because of these things, I didn't finish off the pump design (ie no shaft for driving the screws). I think I'll leave this one here. If anyone has any suggestions about how to get a better pump, I'm still keen to try things out.

So, what did I learn:

• 3D printing isn't accurate enough for this type of pump for a fluid with the viscosity of water
• One meter of head pressure requires some sort of post-processing of the print to prevent leaks, or a printer with better print quality than mine.