I have designed this simple water valve for water flowers as my wife asked. It is not completely sealed. If you want to modify it to seal completely you can modify the f3d file that I attached. The silicon tube's outer diameter is 10 mm now. You can simply make the roller wheel larger to seal the tube better.
  This design is not my original idea. I just remember that when I was ill, the pretty nurse drips me physiological saline and nutrient solution to keep my health. It really helps me out. They use a similar valve to control the solution flow rate. I just make it 3d printable ish. Hope it will give you some help.

https://youtu.be/dJzZ7R5qhSo