Experimental Powered Air Purifying Respirator (PAPR)

This is an experimental Powered Air Purifying Respirator. The build is complicated. The idea with this design is to allow for some customization depending on the motor, electronics, and filters available. My test implementation uses an a 775 DC motor I had from a hand drill, a PWM motor speed controller I bought on Amazon some time ago, and filters from my Eufy 11+ robotic vacuum.

I printed at 0.30 mm. Tolerances are tight and some deburring may be necessary.

The blower wheel is held to the 5mm motor shaft in part with a small hose clamp. I used 3/4" #6 sheet metal screws to assemble most of the unit except the two corners near the hose where I used 1/2" #6. Motor plate mounts with 5mm flat head screws. The 775 mount uses 5mm bolts for friction and allows you to adjust the blower wheel in the fan box. The filter cover is held on using 5mm screws in heat set inserts placed in 6mm holes. I used a counter sink post print to add a slight bevel to aid in setting. I used M5x10mm long x 7mm wide Hilitchi inserts from Amazon but shorter would have been better as I did not leave enough bottom clearance for the over-melt at 10mm. I found adding a small amount of food safe silicone grease to be helpful with the hose adapter.

I've mad two versions of the blower wheel. The original is pictured and isheavier with thicker blades. The light version is not pictured but was printed and so far seems to work well. I suggest balancing the blower wheel.

The 32mm hose adapter pictured next to the box fits 1 1/4" ID pool discharge hose I got from Ace Hardware. I also made a 34mm pinch adapter that fits hose from my local vacuum supply. The main problem with this is that the collar interferes with the screw mounting point.

The motor box's battery compartment has an area where you can slide perfboard. You could consider splitting the battery plate in two to have a fixed and removable portion. I envisioned an on-off switch on the switch plate.

To avoid motor slippage, I strongly recommend slow motor ramp up using PWM or other methods.

This was a large print and I had problems at several phases so I went through quite a bit of filament. As a result, I have not printed final versions of all parts. Changes from the version in my photos are...

• Motor box: added strap mounts and fillets on corners
• Fan box: added heat set screw
• Motor cover - heat set insert for battery plate changed to 6mm from 8mm
• Battery plate - not yet printed
• Switch plate - not yet printed

Things to consider:

• Silicon or glue between motor box, fan box, filter box.
• Thermal control - I've not run the unit very long so I don't know if heat will build up in the motor box. Perforations in the motor cover if heat becomes a problem but this would allow increased leak around the motor with possible unfiltered air contamination. It might be possible to have internal perforations to circulate air from the blower output instead.
  -Gasket between motor mount and fan box
• Vibration dampening: Slight widening of 775 motor hole and placement of rubber dampener around motor.
  -Engineered Blower wheel: I just eyeballed something that looked reasonable and it seems to work ok.
  -PAPR hood - the next project
• Eufy 11s filter box - I didn't realize there was a difference in size between the 11s and 11+ (what I own) so now I have a bunch of 11s filters so I might make another filter box for them.

Disclaimer - I've done my best to consider a real word use for this device. I cannot tell you that it would be effective at filtering in any situation. The consequences of its use are strictly the yours.

Note: Photos show one filter. Videos were taken with both filters in place.

YouTube water test: https://youtu.be/g4K87gPUxf4
YouTube assembled: https://youtu.be/8Wv7aYr8OZ8