Fleck 9100 SXT Digital valve for water softener control valve dual tank replacement head Fleck 9100 SXT Twin Tank Replacement Control Valve Automatically switches between dual tanks 9100 Digital SXT valve to fit on twin tank softener, quality tested construction, 5 year warranty 5 cycles water softener replacement valve, easy to use, dependable Continuous soft water, soft water regeneration, soft water refill Most efficient valve, immediate regeneration as needed