JOHNSON PUMP Spx Flow 12V Bilge Pump Magnetic Switch

The SPX Johnson Pump Electro-Magnetic Bilge Pump Switch employs a magnetically activated (reed) switch that is controlled by a magnet located on top of a float. The float (1) rises with rising bilge water. Air in the float housing (2) is forced out through a vent hole (3) at the top of the float housing. The float reached the top of the housing when the bilge water is 50mm deep. The float magnet activates the reed switch, switching on the bilge pump. At the same time an air valve (5) is shut, closing off the vent hole. This creates a vacuum above the float, causing it to stay in position at the top of the chamber as the level of the bilge water falls. When the bilge water has dropped down to 20mm, air enters through an opening (6) at the bottom of the float housing, releasing the vacuum in the housing. The float drops down and the power to the pump is switched off.