Featuring a non-mercury design, the pump operates with simple air pressure. As water rises in the bilge, the rising water compresses the air in the tube attached to the switch. This increased air pressure activates the switch which controls your pump. There are no moving internal parts, all wiring is out of the water, and there are no submerged electrical connections at all. Offering complete reliability and outstanding performance, the Rule ECO-Switch offers a viable alternative to traditional float switches. For pumps drawing up to 20 amps.