Rule 39 ECO-Switch, Bilge Pump Control Switch, No Internal Moving Parts, No Submerged Electrical Connections An ecologically sound automatic bilge pump control switch, non-mercury design, the pump operates with simple air pressure As water rises in the bilge, air rises in the air tube that is attached to the switch, this air pressure activates the switch that controls the pump Offering complete reliability and outstanding performance, the Rule ECO-Switch offers a viable alternative to traditional float switches