In the next generation sensing bilge pumps, the 1100 GPH S-Series pump works on the principle of impeller resistance. The pump will turn on every 2-1/2 minutes for about one second to sense for water. If water is present, the pump will sense resistance and continue to run until all water is removed. After that, it will resume checking for water every 2-1/2 minutes. Water is kept in check between 1/8" and 3/8". Improved design and performance means that our new 1100 GPH pump will produce this flow at just 12 volts rather than 13.6 volts as previously required, more typical of on board voltage supply. Our next generation of Rule pumps include check valves and to do this we've created a hidden air vent to prevent air locking. Under each strainer tab there is a small hole that vents any air trapped in the pump housing preventing airlocks. We have true electromagnetic suppression (EMC) and have a built-in thermal cell that protects the pump and the vessel when things get too hot. These are the smallest automatic pumps on the market.