Hi ! 

I am trying to setup a diagram where I have three level sensors in a tank that will output +5V (over 4.2V) when they are reached and if the level falls below "half full" (or minimum level) it should fill up the tank until reached "maximum". But it should not fill upp the tank when the max falls below the threshold value which happens in the diagram below.

Any ideas how I can set this up ?

Hello, try this