A sand filter tank is made of metal, concrete or fiberglass and contains a thick bed of special-grade sand. While filtering, dirty water from the pool comes in through the filter’s inlet pipe, which leads to the water distribution head inside the tank. While gravity pulls the water down through the sand, tiny sand particles catch dirt and debris. At the bottom of the tank, the filtered water flows through the pick-up unit and out the outlet pipe.
If the water flow is slowed by dirt and debris, pressure gauges at the filter inlet and outlet give the pool owner an idea of the blockage level inside. If the inlet pipe has more pressure than the outlet pipe, there is collected debris in the sand. You will then need to backwash the filter.
The coarseness of sand traps debris particles and over time, the sand will become smooth and round. This sand should be changed every five (5) to seven (7) years. Contact a pool professional to change the sand or you can choose to do it yourself.