New Spiral cover system which aids the operations of opening and closing.The air purge is built inot the cover which can be feeicient to release the air from the filter.The distance between the upper part of the sand layber and the diffuse head("Free board") has been increased to ensure greater distribution of water in the filtration phase and avoid sand feing spilt into he drain during backwash.The specially designed hole in the sand filter can make the sand exchanging prociess more convenient and efficient. in the filtering process ,the filtering effect of water can be observed through the perspective hole which is designed in the sand filter.