Be it known that I, Nikola Tesla, a citizen of the United States, residing at New York, in the country and State of New York, have invented certain new and useful Improvements in Valvular Conduits of which the following is a full, clear and exact description.

Above is the first sentence of a little known patent filed by Nikola Tesla in 1916 for a device that has since been referred to as a Tesla valve. I figured as I’ve spent the last 2 weeks working on adapting this design, the very least I could do is make sure to acknowledge the original inventor.

As I mentioned in my post a few weeks ago, my current project (VADR) is to develop a breath sensor that will work in tandem with other breath collection technologies. When I started on the project, I had envisaged simply sticking a sensor to the inside of a breathing tube using some kind of high-tech ‘tape’.

However, as I researched the chemistry and developed the design of the sensor systems, I realised that I would need to have the sensor encased in some kind of static chamber that would hold the breath sample for a number of seconds.

My first ideas to create a kind of trap seemed, clunky.

So I moved on, to thinking about creating something that would not trap the breath, but simply impede it enough to get a stable reading.

After a few half-hearted attempts, I quickly realised that I was woefully under-qualified to design a new flow system and anything I made was going to require many, many iterations. So I did what any scientist does and tried Google, searching for a ‘valve with no moving parts’. Which gave me a hit from a scientist’s second favourite website, Wikipedia – on something called a Tesla Valve.

A Tesla valve uses what is now known as the Conda effect – which is the tendency of a flow to follow the nearest wall. Each of the looping offshoots divides the flow and also creates back pressure on the remaining flow.

The overall effect this creates is that any fluid or gas passing in the ‘wrong’ direction will require greater pressure than in the ‘right’ direction.

This kind of flow control is perfect for my application. I need the flow to pass into a chamber over my sensor and then out of the device and carry on down the breath sampling tube. When the person stops blowing, their breath would be preferentially retained in the chamber.

The valve only works in one direction, so I have not stopped all air movement from the chamber, but as I only need to retain a sample of the breath for a matter of 10-20s this should be more than sufficient to get stable results.

Using the dimensions from Tesla’s patent, I very carefully translated his drawings to a drawing package via a process called ‘tracing’. I then scaled up the 2D drawing to have a tube size which would match a breathing tube. Then (as I showed in my live stream video) I translated this 2D drawing to a 3D structure that was suitable for 3D printing.

You can also get a better idea of the 3D-ness of it from this little funky animation I made yesterday. The video below also includes an animation of the flow within the system.

Through the miracle of 3D printing, I’ve had this design made already and I did some quick testing – and it does work. The pressure difference isn’t quite as much as I’d like it to be. There is a difference between blowing into the two paths but it’s very small. But I’ve done some reading and I’m sure that v0.2 will be much improved!

As project VADR is funded by the Research Councils (public money) I feel quite strongly about openness – so if anyone wants to play with this themselves, they can download the STL file HERE. Like everything else in project VADR I’ll keep you updated as I change and improve the design.