I've finished my observatory filtered-air positive pressure system. I need this to prevent the fine New Mexican dust from entering through the Dome’s opening between the dome and support structure, and also the cracks along the shutter. I have a dusty dirt country road upwind of the dome, and cars kick up the dust which then blows all over the dome, and enters it.
The system uses two 12-volt marine ventilation fans, that move 540 CFM of clean air from outside. The filter is an aluminum electrostatic washable filter, although I will be replacing that with a paper HEPA filter later. The intake is eight inches in diameter and the output are each four inches (x2). I power it off two 12volt Marine deep-cycle 100 AH batteries that are charged by two solar panels. I am going to get a timer, and turn it off between midnight and 5am, when I am not using the dome. If I am using it, I turn them off as soon as I open the shutter.
The first video shows the system in operation. It’s quite loud but fortunately I don’t do much work in the dome itself, so it’s not a huge issue right now. Plus at night when I am using it and the dome is open, I turn off the air system.
The second video shows testing. It works great! What would be cool is to build a RPi controller to have the system slow down when there is no wind, and then speed back up when the wind speed increases.
Here's the pump being built. I have since added a weather seal and lid. Four hand-knob bolts secure the lid tightly.
Here's the installation video, showing the system running: https://youtu.be/CYYdD8mqo2s
Here's a short video showing testing done with an open flame: https://youtu.be/KzZqeMaPiC8