The Hayward ProSeries™ 21" Side Mount Sand Filter utilizes a precision engineered umbrella-fold self-cleaning lateral system to provide efficient flow and evenly distributed water for totally balanced backwashing and long lasting performance. An integral top diffuser ensures even distribution of water over the sand media bed while a 2" internal piping provides superior hydraulic performance. Its flanged inspection and access cover provides convenient access to the top of the filter. The patented service-ease design with unique folding ball joint provides easy access to the lateral assembly.