Sand filters operate on the basis of “depth” filtration where dirt is driven down through the sand bed and trapped within the spaces between the sand particles. Clean water is then filtered through the underdrain lateral system and returned back to the pool.
Initially, a clean sand bed removes larger particles, and then, as the bed starts to load up with dirt, the filter removes finer particles. The filter’s pressure gauge is utilized to measure the amount of pressure build-up caused by the dirt load within the filter. The sand can be cleaned by “backwashing” which involves reversing water flow through the filter through the “waste” line.
