Hi,
I have seen 2 systems to control submersible sump pumps.

The float system, uses either a small float on a guide wire and goes up and
down vertically or a bulb that just floats up on an arc.

The diaphragm system, which, I think, senses pressure.

Any advantage to either. I am leaning toward the diaphragm since it has less
moving parts to get stuck.