The invention discloses an automatic
backwashing filter and a working method, which are suitable for filtering impurities in
sewage. The filter comprises a runner switching main valve, a valve plate and a
barrel, the valve plate is arranged on an upper opening of the
barrel, and the main valve is arranged on the valve plate and communicated with the interior of the
barrel through a runner; two flow channels are arranged on the valve plate, one flow channel is a filtering flow channel communicated with the inner space of the filter screen, and the other flow channel is a
backwashing flow channel communicated with the space between the filter screen and the cylinder body; the flow channel switching main valve comprises a valve body, a
sewage draining exit, a water inlet and a water outlet are sequentially formed in the valve body from left to right, and a filtering outlet connected with the filtering flow channel and a
backwashing outlet connected with the backwashing flow channel are sequentially formed in the lower portion of the valve body from left to right; wherein a two-position five-way
reversing valve group capable of automatically switching a normal working mode or a backwashing mode according to the blockage condition of the filter screen is arranged among the drain outlet, the water inlet, the water outlet, the filter outlet and the backwashing outlet. The filter is simple in structure, does not consume energy, and automatically switches backwashing.