Check that the mating nuts are actually seated fully into their pockets. If they are not fully seated, the M12 screws will seem too short.
Conventional PAPR’s like 3M’s don’t operate in the same way as a Bunny PAPR. They use MUCH higher flow rates and are essentially unsealed. They rely on high volume, continuous flow out the bottoms of their hoods to do their isolation. Typically that is 150 L/min or more to get enough flow out of the unsealed hood to be an effective barrier against contaminated air getting in from the lower end of the hood. Think of them as an open ended cup into which one is continually pump a LOT of clean air through the top to keep anything from getting in from below.
A Bunny Science PAPR is a low flow, sealed system. The seal isn’t perfect, but very nearly so. Only a small amount of positive pressure is needed to reinforce the seal. The sealed arrangement enables function at much lower air flow rates in the 20 to 30 L/min range. That lower rate remains within range of anesthesia filter, needs less fan power, less battery power. Output ports provide controlled, one way expiratory path unlike conventional PAPR’s.
Filters I have not been sourcing independent of the hospital. Not as easy to obtain if you are not a medical facility.
Search against “anesthesia HMEF”
You will find things like…
Look for anesthesia bacterial/VIRAL filters. Ideally find one with <1 cm H20 resistance at 30L, but up to 2 cm H20 at 30L can work. Be sure it is a viral filter, not just bacterial. Also, it has to be a filter, not just plain HME (heat moisture exchanger). We’re actually not interested in the HME function, but really just the filtering. You may run across some anesthesia ventilator filters that are not HME’s like
O2 supplied configuration was deprecated due to risks of high FiO2 and fire. I removed the oxygen tubing clips from current STLs. If one were still needed to run in O2 configuration, an oxygen tube could be taped to the Halo loop. Oxygen fed configuration has considerable risk and I would only use if there was no alternative or actual intent is to deliver more than 97% oxygen. Failure of O2 source must also be guarded against if used on a patient. If they fell asleep and the O2 source failed, they would likely die.
I do not recommend the O2 configuration for most uses.
The only 5 volt fans at Digikey that are in the desired range for static pressure and CFM flow are a pair of Delta fans, BFB0505HHA-CF00 and BFB0505HHA-C. Unfortunately, neither are in stock and they have a minimum factory order of 672. Thereafter, the 5 volt fans drop way down to the 140 pas static range. That might work with a pair of filters in parallel, but for a single filter, it would be tough getting enough flow.
AA’s have long been the highest energy density of the alkaline batteries. LSD NIMH’s like the Eneloops are my current favorite AA format cell.
Suitable fans appear to be falling into the 190 to 250 pascal static pressure / 3 to 10 CFM range. Can’t really tell from the specs how a particular fan will work until after putting them after the load of an actual viral filter. I must have nearly 10 different fans in my test collection.
Takes time to evaluate each for CO2 clearance using gas monitoring.
It may be possible to find a 5 volt blower fan of correct static pressure and CFM. I have not actively looked for one.
Balancing the fan power, filter, and output ports is important. That was the first problem to solve. Took hours with gas monitoring and prolonged wear to establish a good balance. Big push was to get this out initially with a working configuration.
Different fan size mounting options are doable. Have already circled around to improve comfort with the flex fit iteration. Making the fan mount more generalizable is reasonable so long as users balance the flows.
Shaft preparation including the diameter issue is already in Step 18
Shafts may arrive with a diameter that is slightly too large to pass through bearings. Chuck the shaft on a drill and use an abrasive paper to reduce the shaft size while the drill spins.
Thanks for dealing with the links getting shifted on Amazon
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