Excalibur Water Systems’ Duplex Alternating Water Softeners utilize two standard control valves integrated with one fully ported motorized alternating valve (MAV) to allow one unit to be in regeneration or stand-by at a time while the other unit is in service. This system provides a continuous supply of soft water with the control valves indicating which unit is online and in stand-by operation. Its internal non-corrosive single piston & patented 1-piece compressible seal/ spacer stack assembly allow it to be hydraulically balanced. The MAV has a sight glass that allows you to view the position of the valve to know which softener is online and which is always on stand-by.