PWC 500 GPH Automatic PumpIn the next generation sensing bilge pumps, the 500 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 500 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 airlocking. Under each strainer tab there is a small hole that vents any air trapped in the pump housing preventing airlocks. Rule has 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.Features:Completely automatic with manual override; no float switch neededSubmersible and ignition protectedHigh efficiency, low amp motorStainless-steel shaftIncludes backflow preventerWARNING: This product can expose you to chemicals including 1,3-Butadiene which is known to the State of California to cause cancer, birth defects or other reproductive harm. For more information go to P65Warnings.ca.gov.