... The trick to making this work is to have a restriction ("small hole") while the pump is pushing the fertilizer out (which keeps the tubing free of more solution), and having open flow when the pump turns off, so the tubing refills readily.
After many hours of thinking I came up with a somewhat redneck, but simple and cheap solenoid valve. I used a piece of latex glove, wrapped around the end of some air tubing with a rubber band. That went into a plastic syringe. As the air pump pumps, some air is diverted to blow up the latex bubble, which blocks the flow through the syringe, therefore restricting the flow and keeping the tubing clean.
I've read this a number of times and I still dont understand exactly what you mean by "which keeps the tubing free of more solution
" or "therefore restricting the flow and keeping the tubing clean
I've played with these airlift dosers myself and by "keep the tubing clean" I assume you mean preventing the retention of solution in the uplift tube so that air can escape as the submerged dose tubing refils?? ...if so... I dont understand why restricting the outflow prevents solution being retained in the narrower uplift tubing. Can you perhaps take another crack at explaining exactly how the solenoid improves the dosing and exactly which bit of tube you are trying to keep "clean"?
.. or have I missed something else?
oh and btw I think those disk based checkvalves sound perfect for this application!