Just a quick update on this post, and a BIG thank you to both of the responders! I finally got some pumping.
So I changed a couple of things: As was suggested, I replaced the input and output chambers with silicon tubing. As Harold suggested, I ditched the HSBB and replaced it with a Tesla Valve. I also put hot glue over the edges of the piezo disc to improve the seal and safety.
Even with a Tesla valve with only one baffle, there is some decent flow rate (relatively speaking). The noise is also greatly reduced with a triangle wave instead of the previous square wave. There’s about 30 mm head pressure developed.
Please see the Cad Model of the new valve and a video of the pump working.
Once again, thanks so much for the suggestions from both of you, I would’ve still been scratching my head if I hadn’t come here :D.
Uploading: IMG_20201010_153505.jpg…
Video: https://streamable.com/4hi56k