In a sensor project I'm involved with, we have a requirement to bypass the airflow from one sensor while it does some further measurements. To do this, I implemented a flap driven by a standard servo which rotates the flap through approximately 90 degrees, opening one port and closing another.
I'd like to try and improve this with a better, less leaky, mechanism. The first thing I've thought of is a cylinder rotating within another:
The green outer cylinder contains three ports to which the inlet pipe and two outlet pipes (~20mm dia) are connected. The inner cylinder (~30mm dia) rotates to select one or other of the outlet pipes - thus it has either a really elongated inlet port or four ports. I figure I can place the servo in the centre - this dictates the inner cylinder diameter.
Is there an existing off-the-shelf product that would do this for me or will I have to try and 3-D print it (or find two waste pipes that will fit appropriately)?
Is this a reasonably way to do airflow selection or will it turn out to be even more leaky than the airflap (which wasn't particularly well done as it happens - it can be improved)?
Edit: As an addition in the OP rather than as an answer/comment: This is another way of doing this. Once you know "pneumatic" is the term you can add terms like "servo valve" to google image search and get all sorts of neat ideas (including little lego valves!):