Pareto was right...

As it goes, the mechanical design (which I assumed would be a small percentage of my design effort) has become the foremost bottleneck in my quest to automate the spraying of sanitizer. Fortunately, I believe I am on the right track and will hopefully have a fully functional prototype in the coming week. The issue is primarily with the piston, which was originally designed with the thought that at low pressure there would be no overflow or leakage from the cylinder. 

I have since calculated a pressure of approximately 387 Pa and while the pressure is quite low, the imperfect surface of the 3D printed parts leads to leakage. My solution is to make a small groove, sized for a common O-ring, in the tip of the piston. The O-ring will act as a seal to eliminate the need for a perfectly smooth cylinder, the only downside I can see so far is the need for a stronger spring.

The quest for automated spraying continues!

- Jacob