The filtering flow decreased and stopped despite several minutes of backwash and rinse. I removed the old sand, cleaned the laterals, added new sand (#20), and put the unit together. I back-washed and rinsed (to get rid of loose sand ) but after a few minutes of filter operation the water flow still slows and stops. The flow is great on "recirculate" (bypassing filter) so the intake and outlet lines are not clogged. Is there possibly something weird with the Hayward Variflow valve? Would it help to set the laterals in pea pebble or to use #12 sand. There is no pressure valve on the unit, so there may be a pressure leak in filter mode.