Fleck 9100 water softener control valve dual tank replacement head Fleck 9100 Twin Tank Replacement Control Valve Automatically switches between dual tanks 9100 valve to fit on twin tank softener, heavy duty construction for long life, 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