I did this project last year when hurricane Irene hit our area in late August of 2011. I live in an area where even heavy rain would cause flooding in the basements. The sump pumps work hard to keep us dry most of the time. I learned my lesson during hurricane Floyd in the late 90s that sometime a pump simply cannot keep up with the incoming water if the ground is totally saturated. So, I thought what if I installed two sump pumps they will be able to pump the water faster. Keep in mind a pump's success depends on availability of electricity of course, to run it and the float switch which turns the pump on when needed. The float should be free of any obstruction in the pit. With that said, I could not house two pumps side by side. So, I came up with this idea of pumps stacked on top of each other. My design below basically has two pumps. The bottom one is a 1/2 hp submersible pump and the top one is a pedestal type. There was no specific reason to choose the top one as a pedestal type. I think the reason might have been the availability of that pump in the hardware store at that time. I also like the idea that the bottom pump will do all the heavy lifting. In case of breakdown or when the water level is rising fast, the second pump will kick in. Since the second pump is sitting higher, it will kick in only when the pit is 60-80% full.