Here's an interesting switch: http://www.fluidswitch.com/pages/fh0708.htm

They also come in SS, but those are pretty expensive. I like this style because you can use 2 switches for hysteresis and not worry about submerging the lower one. They install through the sidewall, so all of the wiring is external.

Might pose a cleaning hassle though.

Sure Igor,
It is perfectly possible to do it this way. There is little difference between switching a pump or switching an ASCO valve. It only assumes that you have a gravity flow setup. In fact, I have the parts to do exactly this, but just have not yet put it together.

Seriously? You can use ASCO valves inline with the wort? What if a few grain husks made it through the false bottom. Would the design of the valve not allow the valve to be stuck open? I would have thought that you need the (much more expensive) motorized gate valves - like those on automated pool equipment.


Mylo

You make a good point Mylo. Some grain could get stuck. A larger ASCO valve would certainly help there.
Actually, the best place for the ASCO would be to control the flow of the sparge water.