Sand cylinder generally placed a certain size of quartz sand, in a certain range of quartz sand size specifications are different, in the sand tank, quartz sand from top to bottom, from small to large according to this arrangement, normal filtration, water is from the upper layer of the sand into, from the lower layer out. When water flows through the filter layer from the upper layer, the tiny empty eye formed by the solid suspended material in the water enters the upper filter material is intercepted by the adsorption and mechanical blocking action by the surface layer of the filter material, and at the same time, the overlapping and bridge effect between these trapped suspended suspended materials, as if forming a film on the surface of the filter layer, continue to filter the suspended material in the water. This is called film filtration of the surface layer of the filter material.
This filtering effect not only has the surface of the filter layer, but also has this retention effect when water enters the intermediate filter layer, which is different from the filter ingestion of the surface layer.
In addition, because the sand particles are tightly arranged with each other, the suspended particles in the water flow through those curved holes in the sand layer, there will be more opportunities and time and filter surface collision and contact, so that the suspended matter in the sand layer of the particle surface and flocculation stolicing each other and contact coagulation process. In summary, the filtration of the sand cylinder is through thin film filtration, permeation filtration and contact filtration process, so that water is further purified.