The pool water passes through a filter, and tiny dirt is captured and filtered by the sand bed. The filtered clean water is returned to the pool through the control switch at the bottom of the filter and then through the pipeline. This whole set of procedures is continuous and automatic, and provides a complete cycle process for the pool sand filter and pipeline system.FENLIN is a manufacturer specializing in the production of pool sand filter with 17 years of experience. We are committed to providing you with the best products and services at wholesale prices and factory prices.