As the tank fills up, the float lifts up and as it reaches the top level, the top switch is triggered. This signal is processed by the logic control unit and according to the program it puts the pump off. Eventually as the liquid from the tank is utilized in the plant, the level goes down , taking the float down with it. The low level switch is actuated, which is again connected to the logic control and it triggers the pump on. This way a cyclic operation of the pump is achieved.