The changeable filter is developed to be used as semi-permanent filter. The original water is filtrated by compressing the filter with the porosity and the permeabiliy having shrinkage and elasticity using a cylinder and is back flushed after the decompression of the cylinder. in particular, the efficiency of the filter can be maximized because the back flush is done with the variable filter being relaxed by reciprocating the cylinder.

Applications - It can be used for the pre-filtration process in all areassuch as wastewater treatment, water purification processing, heavy water treatment, sewage treatment, and removing the floating materials from the artificial lakes and fisheries.