Presair utilizes diaphragm switches to monitor rising water levels and prompt a sump pump to action. These switches sense pressure against the diaphragm to accurately read how much water is present in a system. As the water level rises in a sump basin, the pressure pushing against the diaphragm builds within the switch. Therefore, the switch is preset to actuate at a specific water level. When the specified water level is reached, it will generate a precise pressure in the basin. The diaphragm is calibrated to complete a circuit at that exact moment and initiate the pump.