Ultrasonically sealed inside the thermo-plastic housing, the Mayfair Automatic Bilge float switch #26012 activates your bilge pump with an audible "click". As water exceeds acceptable levels, the pump is turned on by a rolling steel ball that changes pressure on the micro switch. Rapid on-off cycling is prevented by a built-in differential of 1-5/8-in and by an exclusive anti-spike feature.