PANDA PEEP valve

UPDATE2:

cover_gen2 has now more space between flatspring and outlet area to prevent blocking of valve if thick rubber is used.

UPDATE1:

We just released Gen2. No Hardware needed and very easy and accurate to adjust. Just make sure to test print a small section of the cover and the base to check that the thread matches. Scale only the cover in X,Y direction should the thread be too narrow. 101% in X,Y for the cover did the trick for our printer. Use a square piece of rubber that fits into the hole. It doesn’t have to be attached, it stays there.Don’t cover the whole hole. A piece from a bike innertube works just fine.

Additionally I uploaded a Step-File of the base_gen2. You can build on this if you want to have a different adapter diameter or different sealing types.

Team PANDA [Zurich, Switzerland]:

We propose a new 3D printed spring loaded and adjustable PEEP valve. It attaches straight to the 30 mm standard Ambu Bag connector.

This might be interesting for medical personnel should the standard PEEP valves run out (Spain) and the water bubblers aren’t an option.

Secondly for teams that are trying to build ventilator prototypes and do not have a PEEP valve at hand.

WARNING:

We have tested it on our PANDA ventilator test bed but we can’t compare it to a medical PEEP valve since we don’t have one. Someone that has a medical PEEP valve should print ours and compare/benchmark it against the medical one. Please post relevant findings in the comments.

TESTS:

We were able to adjust the PEEP pressure in the necessary range of 5 – 20 cmH2O. While leaking slightly in the lower pressure range, it kept the levels astonishingly accurate.

CONSTRUCTION:

We use a 3D printed triple-helix flat spring that applies force to the sealing disc. Pretensioning (and thus the PEEP cut-off pressure) is adjusted with a M3 bolt and nut. While the setup kind of works without a rubber seal, we found that when you attach a piece of rubber (from thick rubber gloves etc.) it works best. Use Locktite or superglue to secure the lower two M3 nuts that secure the rubber seal. Without the rubber the disc tends to stick to the seal surface if moisture is present and this leads to an excessive initial release pressure. Also, clean the sealing surfaces from any hair spray residue which gets sticky if wet.

PRINTING:

The tolerances of the pieces must match each other and these are different for most 3D printers. If it doesn’t fit, scale it in Cura in X,Y-direction only, in small increments and write down your adjustments for further printing. And note the orientation of printing on Thingiverse.

So for the first print start with the base to make sure it connects well to the standard 30 mm Ambu Bag connector.

Then print the cover and make sure it snaps nicely on to the base.

Then print the spring and make sure it fits into the cover. If its too strong or too weak, scale it in Z direction and comment about your optimal thickness.

The disc will fit anyway, so no need to adjust this.

MATERIAL:

We used PLA with a 0.4 mm nozzle for all parts and it works fine. But the spring should be printed with ABS to keep loss of tension at a minimum. The pretension will still have to be adjusted from time to time. Again, experimental data highly appreciated.

IMPROVEMENT:

I thought about using a 3D printed thread for the adjustment, but it would need to be fine enough to allow for a decent amount of accuracy. And this leads to tolerance problems during mass production.

IMPERIAL BOLTS:

Right now it’s meant for M3 metrical hardware. If a similar imperial nut won’t fit, heat it with a lighter and press it in. Should this be an issue I can upload an imperial version.

https://youtu.be/lfqMNqKA_II