Originally Posted by aamcle
If I recirculate through a grain bed, in at the top, out at the bottom, through the pump and back in at the top a simple closed loop.
If the flow through the bed was too slow then the pump would suck all the wort from under the grain be and could be damaged....
If that is happening then air has to be is getting in somewhere, as it should be impossible to do otherwise.
I do the same thing as you and it' impossible to suck wort from under the MLT false bottom without new wort being introduced from above the false bottom.
So the only two possibilities should be: Constant flow, or stopped flow (pump is off, or false bottom is clogged).
So before looking for a solution that involves liquid sensors as a bandaid solution, I'd fix the problem at the source.
Or maybe i'm not understanding your setup?