Rule 20SA Bilge Pump800GPH Electronic Sensing Bilge Pump - 12V In the next generation sensing bilge pumps, the 800GPH 12V 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 inch and 3/8 inch. Great idea when power conservation is needed and as an added benefit, no float switch is needed! All that plus the added benefits of our standard bilge pump:Check valve included with hidden air vent to prevent airlockingTrue electromagnetic suppression EMCA built-in thermal cell that protects the pump and the vessel when things get too hot These are the smallest automatic pumps available on the market! Features:Completely automatic with manual override - No Float Switch Needed!Submersible and Ignition ProtectedHigh efficiency, low amp motorStainless-steel shaftIncludes backflow preventer