Device for automatically clearing water tank through forward and reverse rotating of fan

The invention discloses a device for automatically clearing a water tank through forward and reverse rotating of a fan. When fan blades need to rotate reversely to clear impurities adsorbed on the water tank, an electromagnetic controller controls a carbon brush combination to be energized, an electromagnetic coil is energized through a wire to generate magnetic force, thus a whole composed of a reverse-rotating outer cone, the fan blades and a forward-rotating outer cone is attracted to move leftwards, a shifting rod drives an axial sliding bearing and sliding blocks in the fan blades to moveleftwards to abut against a reverse-rotating body friction ring to rotate; after the adsorbed impurities are completely cleared, the electromagnetic coil is deenergized, the whole composed of the reverse-rotating outer cone, the fan blades and the forward-rotating outer cone moves rightwards under axial thrust of wind force and the acting force of spring to be closely combined with the a forward-rotating friction ring to