[tommyp]

jl, for gravity feed and R/O feeds they are mechanical. They are usually Kent valves that mechanically shuts off the feed as the float raises.

For the floats that control a Power Head which pumps water up to the tank. It is a electrical switch. When the water lever drops the switch turns on the ph pumping water up to the tank. It is a lot smaller than the kent. Alot of people use them in nanos or if they dont have a sump or if they just want a cool way to top off.

Tom